BIAXIALLY ORIENTED BARRIER HEAT SHRINKABLE PACKAGING FILM COEXTRUDED FROM MULTIPLE LAYERS, PACKAGING

专利摘要:
multi-layer pvdc heat shrinkable barrier films. The present invention relates to multi-layer heat shrinkable barrier films and flexible containers made therefrom, such as bags, pouches and the like, useful for packaging articles, particularly food items. these films are characterized by particular shrinkage properties, which provide tight packages that reduce the drip loss of the product contained in them. furthermore, the bags obtained from such films are endowed with very good optical properties and high resistance to abuse.
公开号:BR112016015680B1
申请号:R112016015680-3
申请日:2015-01-15
公开日:2021-07-13
发明作者:Flavio Fusarpoli；Giuliano Zanaboni；Serena STRACUZZI
申请人:Cryovac, Inc；
IPC主号:

专利说明:

Technical Field
[001] The present invention relates to multilayer PVDC heat shrink barrier films comprising high melting aromatic (co)polyesters and flexible containers made therefrom, such as bags, pouches and others still useful for packaging articles, in particular food items. The invention also relates to a process for the manufacture of such multilayer heat shrinkable barrier films. Background of the Invention
[002] Heat shrink barrier packaging films have long been used for packaging a variety of products.
[003] In particular, heat shrink barrier films comprising PVDC barrier layers are known and especially appreciated for their very good barrier properties - under dry and wet conditions - and for excellent moisture barrier performance.
[004] However, the incorporation of PVDC in multilayer films is not exempt from processability problems, due to its chemical and thermal instability, which results in the formation of hydrochloric acid, bubbles and brown coloration of the ribbon.
[005] In particular, in order to coextrude films comprising PVDC and high melting point polymers - such as polyolefins or polyamides with a melting point generally lower than 200 to 225°C - insulated extrusion dies together with Encapsulation techniques have been developed to prevent thermal degradation of PVDC. Furthermore, in order to be successful in PVDC extrusion, precise control of the extrusion process is required, in particular over residence time, equipment design and materials used.
[006] However, co-extrusion of PVDC together with higher melting point polymers, such as aromatic polyesters that have much higher melting temperatures, still represents a technical challenge.
[007] Over the years, various efforts have been made in the technical field to increase the stiffness of films comprising PVDC in order to increase their resistance to abuse and ease of machining.
[008] Greater film stiffness is generally desirable as it results in packages with fewer leaks, leaks that are due to accidental openings or breakages during the packaging process or handling of the packages. The stiffer films also provide improved ease of machining, which allows you to reduce scrap and increase the speed of packaging cycles. In fact, a film that has good machineability is less susceptible to creases, creases, sealing creases, edge curls, or jamming, and can be more easily used with any conditioning machine. In addition, harder films result in flexible containers that are easier to line up and load with product. Finally, they generally exhibit improved stability during bubble orientation and improved ease of printing.
[009] However, in the case of shrinkable films, it has been observed that an increase in stiffness - which can be obtained, for example, by increasing the polyamide content or the number of polyamide layers in the film - often results in shrinkage properties lower or, in the case where a high shrinkage is obtained anyway, on optical characteristics worsened after shrinkage (eg glare, haze). Furthermore, the resulting film is less planar, which makes subsequent converting operations much more difficult.
[0010] With regard to shrinkage properties, an ideal packaging film must have the correct balance of free shrinkage, maximum shrinkage stress and residual shrinkage stress in order to provide packages with an attractive appearance and satisfactory functionality, in that appearance and functionality must be preserved under the most common conditions of packaging and storage and over time for the lifetime of the packaging.
[0011] Any deviation from the ideal values of said shrinkage properties can be detrimental to the performance of the film in the final packaging.
[0012] For example, too low free shrinkage values can result in an unacceptable package appearance to the customer due to film looseness and the presence of wrinkling.
[0013] This is particularly true for the vacuum packaging of meat products, in particular fresh meat products. With evacuation of the atmosphere from the package followed by heat sealing of the film, the resulting closed package should contract without any gap around the meat product. A film provided with a sufficiently high free shrinkage shrinks against the product, reducing excess film protruding away from the packaged product and improving the appearance and function of the package.
[0014] In this shrinkage step, it is essential that the films develop proper free shrinkage values in both directions along with an appropriate shrinkage force. This force must be high enough to enclose the product within the film without slack, but without unraveling or excessively distorting the final packaging.
[0015] The free shrinkage and the maximum shrinkage stress, i.e. the maximum value of the stress developed by the films during the heating/shrinkage process, are therefore very important parameters to obtain an ideal appearance of the package.
[0016] Another important requirement is that the packages must remain tight over time, during handling and storage.
[0017] A common inconvenience that occurs during storage in the refrigerator is the so-called "packaging relaxation", that is, the loss of package tension and the appearance of unsightly wrinkles and creases in the packaging film. Packaging relaxation is not only undesirable for purely aesthetic reasons - the presence of wrinkles in the packaging film is not attractive in itself - but also because it can impair visual inspection of the packaged product, and thus instill doubts about freshness and proper storage of food.
[0018] As far as the applicant is aware, there are several patents that mention the possibility of associating aromatic polyester layers with a PVDC barrier layer in a multilayer shrink film.
[0019] However, these documents do not actually exemplify the structures that comprise both of these materials or, if they do, describe clearly inadequate manufacturing processes or do not provide sufficient disclosure to replicate said structures, since the details about the process and equipment, necessary to enable its actual manufacture without damaging the PVDC layer, are totally lacking.
[0020] Patent document EP2147783A1 describes shrinkable films with increased stack sealing capacity comprising an inner barrier layer of PVDC and an outer layer of polyester, wherein the polyester is a polyester with a high melting point. The only example describes a film comprising polybutylene terephthalate (melting point 225°C), characterized by a free shrinkage at 90°C of 32% on MD and 32% on DT. No other contraction properties are reported in it.
[0021] The description does not manifest itself regarding the specific equipment and conditions necessary for the coextrusion, the subsequent orientation of the ribbon and the final cooling of the films. With regard to co-extrusion, it only mentions that: "The preferred method for producing the film is co-extrusion in a multilayer die" (par. 0049). With regard to orientation and cooling conditions, it refers in very broad terms to "a double bubble method described in patent US3456044" (par. 0051), but does not provide any noteworthy details.
[0022] Patent document EP2030784 in the name of Cryovac Inc. describes films comprising an external heat-sealable layer, an internal PVDC barrier layer and an external abuse layer. None of the films exemplified herein actually include a layer of aromatic polyester, but lower melting point polyamides or polystyrenes. This document does not provide any specific shrinkage values for the exemplified films or any teaching as to specific maximum shrinkage stress and residual shrinkage stress values.
[0023] In the manufacturing process, the PVDC barrier layer is placed on the coating and extruded along with the outer layer. The exemplified films do not experience the thermal damage of PVDC as the polymers used in the outer layers, ie polyamides, their blends or polystyrenes, have significantly lower melting points than aromatic polyesters.
[0024] Patent document US8039070 in the name of Curwood Inc. relates to removable barrier shrink films. The description generally mentions polyesters among various other polymers as possible components of the outer layer of the film, but none of the films exemplified therein comprise PVDC and high melting polymers, especially high melting aromatic polyesters. Barrier materials can be selected from ethylene vinyl alcohol copolymers (EVOH), polyacrylonitriles, polyamides, vinylidene chloride copolymers (PVDC), polyglycolide copolymers, and mixtures thereof. All examples relate to EVOH barrier films.
[0025] Patent document WO2005011978 in the name of Cryovac Inc. describes biaxially oriented heat shrink films comprising a heat sealable layer, an outer polyester layer and an inner EVOH barrier layer. The manufacturing process comprises the co-extrusion of all layers (no substrate plus coating). The EVOH layer is resistant to thermal stress and is not damaged by the high temperatures applied to extrude the polyesters. The document does not consider PVDC as an alternative material for the barrier layer.
[0026] Patent document US6699549 in the name of Kureha Chemical Inc. describes films comprising a heat sealable layer, an outer polyester layer and optionally an EVOH barrier layer. PVDC as barrier material is not considered. In the manufacturing process, all layers are co-extruded together (no substrate plus coating) as preserving the barrier layer from thermal damage is not an issue here.
[0027] Patent document US6764729 in the name of Cryovac Inc. describes heat shrinkable films comprising a first outer heat shrinkable layer and an outer layer comprising polyolefin, polystyrene or a second polyamide. None of the films exemplified therein exhibit a polyester layer or a PVDC barrier layer. They are manufactured according to a process comprising co-extrusion, ie all layers extruded together (no substrate plus coating).
[0028] Patent document US4064296 in the name of Grace W R & Co. describes high barrier heat shrink crosslinked films. The barrier polymer is HEVA, the outer layer is made of polyolefin. Other materials are generally listed as possible components of additional layers, but none of the films exemplified therein comprise a polyester layer and/or a PVDC barrier layer. Invention Summary
[0029] The Applicant, with respect to heat shrinkable PVDC barrier films, explored the possibility of improving the rigidity of the film, while preserving the optical and shrinkage properties by introducing aromatic (co)polyesters into the film structure , particularly in the outer layer.
[0030] However, the applicant has found by experiments that films including high melting point polyesters such as aromatic (co)polyesters, together with a thermolabile PVDC barrier layer, would be poorly obtained with matrices and/ or conventional extrusion processes, i.e. by co-extrusion of all layers - as taught in patent documents WO2005011978 or EP2147783 - or by extrusion coating of a substrate with a coating, wherein the coating comprises PVDC and PET - as suggested in patent document EP2030784.
[0031] In fact, the applicant found that, by applying conventional processes with traditional extrusion dies for the manufacture of the present films, so much damage could occur to the PVDC layer that the final film would not be acceptable in terms of color, transmission oxygen and/or optics.
[0032] The temperatures required to extrude aromatic (co)polyesters - which can be up to 270 to 280°C - are so high that they induce partial degradation of the PVDC barrier layer, with the appearance of an unwanted yellowing - brown colors , and the possible deterioration of gas barrier performance.
[0033] To the best of the applicant's knowledge, a sufficiently detailed and reproducible complete description of a manufacturing process and equipment for the preparation of multilayer shrinkable films comprising barrier layer(s) of PVDC and aromatic (co)polyesters of high melting point has not been reported in the prior art.
[0034] For example, patent document EP2147783, which states that a film of this type was prepared, is totally silent as to the characteristics of the equipment and the peculiar conditions of the process, the characteristics and conditions that seem to be essential to successfully coextrude the PVDC and aromatic (co)polyesters.
[0035] The other documents do not show that such a film was actually manufactured, but simply mention PVDC or aromatic polyesters as possible replacements for other "compatible" resins (such as EVOH/PET or PVDC/polyolefins or polyamides): they ignore the specific technical problem of co-extrusion of PVDC with PET. In other words, the state of the art does not teach how to solve the problem of manufacturing such films.
[0036] On the other hand, the applicant has managed to manufacture PVDC barrier films comprising very high melting aromatic (co)polyesters, even using conventional equipment, thanks to a new extrusion-coating process.
The Applicant found that by placing the thermolabile PVDC layer on the substrate and the high melting point (co)polyester on the coating, it was possible to prevent the PVDC from being degraded. In fact, the PVDC layer within the substrate is not heated to too high a temperature, since high melting aromatic (co)polyesters are in the coating. In addition, the Applicant has also been able to further minimize heat transmission during substrate coating by inserting a certain thickness of insulating layers between the PVDC layer and the aromatic (co)polyester layer(s).
[0038] Finally, the applicant concluded that, by using the process described in this document, and in the presence of the aromatic polyester layer and the present specific layer arrangement, large amount(s) of polyamide may be incorporated without affecting the stability of the process and also improving the resistance to abuse. The films thus obtained were also easily oriented. These films exhibit very good barrier, mechanical and optical properties.
[0039] Furthermore, these films are also surprisingly endowed with very good total shrinkage properties. In particular, these films, together with high free shrinkage values, unexpectedly exhibit a marked residual shrinkage performance in cold. This property solves the drawbacks of package relaxation and fluid dripping when the shrunk package is stored in a refrigerator.
[0040] With regard to the problem of package relaxation, the applicant found that one of the most critical parameters to be measured and possibly adjusted appropriately in order to resolve package relaxation, is the residual tension of the film, i.e. , the shrinkage stress expressed by the film at low temperatures, in particular at refrigerator temperatures, generally around 4 to 5°C. For the foregoing shrink films, shrink stresses were conventionally measured at temperatures no lower than room temperature.
[0041] In addition, it has been found that the control of residual shrinkage stress at 5°C is essential for the solution of another need felt for a long time in the technical field of meat packaging, that is, how to minimize the drip loss inside of the packaging. When fresh meat primordia are vacuum-packed and stored, after the slaughtering or cooking processes, they begin to release a drip, that is, a liquid exudation, which is a mixture of whey, protein and water. This is particularly evident for meats such as pork, beef, veal, horse meat and processed meat such as, for example, cooked ham. The amount of drip varies with the meat's thermal history and quality. When the package is opened, the drip is a loss of net weight for the retailer or food processor, as the removal cannot be sold by weight.
[0042] In addition, the presence of exudates on the packaging reduces its attraction and makes the retailer suspicious about the processing and freshness of the meat.
Applicant has surprisingly found that films comprising an inner PVDC barrier layer and aromatic (co)polyester(s) retain the seal even after refrigeration and exhibit reduced drip loss. Specifically, the Applicant has found that in meat packages it is possible to minimize drip loss by using the new packaging films of the present invention endowed with ideal shrinkage properties, in particular an appropriate residual shrinkage stress under cold conditions.
[0044] Furthermore, these films exhibit very good processability, at extrusion, orientation and converting levels, and provide excellent package appearance and high resistance to abuse.
[0045] Thus, a first object of the present invention is a multi-layer coextruded biaxially oriented barrier heat shrinkable packaging film comprising at least one heat-sealable layer (a); a layer (b) which is not directly adhered to the heat-sealable layer (a), wherein said layer (b) comprises one or more aromatic (co)polyesters, at least one internal gas barrier layer (c) which comprises polyvinylidene chloride, wherein said film is characterized by - A) a total free shrinkage at 85°C of at least 45%, preferably of at least 55%, more preferably of at least 60%, and - B ) a maximum shrinkage stress in each of the longitudinal and transverse directions of at least 20 kg/cm2, preferably at least 25 kg/cm2, more preferably at least 25 kg/cm2 in each of the longitudinal and transverse directions and more than 30 kg/cm2 in at least one of the two directions, and - C) a residual shrinkage stress at 5°C in each of the longitudinal and transverse directions of at least 25 kg/cm2, preferably of at least 27 kg /cm2, more preferably at least 30 kg/cm2.
[0046] A second object of the present invention is an article for packaging in the form of a seamless tube, wherein the heat sealing layer is the innermost layer of the tube, or a flexible container such as a bag or a bag, which comprises a film in accordance with the first purpose.
[0047] A third objective of the present invention consists of a packaging comprising an article according to the second objective and a product packaged in said article.
[0048] A fourth objective of the present invention is a process for the manufacture of a film according to the first objective of the present invention.
[0049] A fifth objective of the present invention is the use of films according to the first objective of the present invention to package dripping products, preferably fresh or processed meat. Definitions
[0050] As used herein, the term "film" is inclusive of plastic mesh, regardless of whether it is film or sheet or tubing.
[0051] As used herein, the terms "inner layer" and "inner layer" refer to any layer of film that has both of its major surfaces directly adhered to another layer of film.
[0052] As used herein, the term "outer layer" or "outer layer" refers to any layer of film that has only one of its major surfaces directly adhered to another layer of film.
[0053] As used herein, the terms "sealing layer", "sealing layer", "heat sealing layer" and "sealing layer" refer to an outer layer involved in sealing the film itself the same, in particular the same outer sealing layer or another outer layer of the same film, another film, and/or an article other than a film.
[0054] As used herein, the words "bonding layer" or "adhesive layer" refer to any inner film layer which has the primary purpose of adhering two layers together.
[0055] As used herein, the expressions "longitudinal direction" and "machine direction", abbreviated herein by "LD" or "MD", refer to an "along the length" direction of the film , that is, in the film direction as the film is formed during co-extrusion.
[0056] As used herein, the term "transverse direction" or "transverse direction", abbreviated herein with "TD", refers to a direction through the film, perpendicular to the machine direction or longitudinal.
[0057] As used herein, the term "extrusion" is used with reference to the process of forming continuous shapes by forcing a molten plastic material through a die, followed by chemical cooling or hardening. Immediately prior to extrusion through the die, the relatively high viscosity polymeric material is generally fed into a variable pitch rotary screw, i.e., an extruder, which forces the polymeric material through the die.
[0058] As used herein, the term "co-extrusion" refers to the process of extrusion of two or more materials through a single die with two or more holes arranged so that the extruded materials fuse and are welded together. to the other in a laminar structure before cooling, that is, extinction. The term "co-extrusion", as used herein, also includes "extrusion coating".
[0059] As used herein, the term "extrusion coating" refers to processes whereby a "coating" of polymer(s) in melt(s), comprising(s) one or more layers , is extruded onto a solid "substrate" to coat the substrate with the molten polymer coating to bond the substrate and coating together, thereby obtaining a complete film.
[0060] As used herein, the terms "coextrusion", "coextruded", "extrusion coating" and the like refer to processes and multilayer films that are not obtained by lamination alone, i.e. , by means of glue or welding the pre-formed networks together.
[0061] As used herein, the term "orientation" refers to "solid state orientation", ie the process of stretching the cast film carried out at a temperature higher than the Tg (transition temperature) glass) of all the resins that make up the layers of the structure and lower than the temperature at which all the layers of the structure are in a molten state. The solid state orientation can be monoaxial, transverse or, preferably, longitudinal or, preferably, biaxial.
[0062] As used herein, the expressions "orientation ratio" and "stretch ratio" refer to the product of the multiplication of the extent to which the plastic film material is expanded in two directions perpendicular to each other , that is, the machine direction and the transverse direction. Thus, if a film has been oriented up to three times its original size in the longitudinal direction (3:1) and three times its original size in the transverse direction (3:1), then the total film has an orientation ratio of 3x3 or 9:1.
[0063] As used herein, the expressions "heat-shrink", "heat-shrink" and the like refer to the tendency of the solid state oriented film to contract on application of heat, i.e., shrinking when heated, such that the film size decreases while the film is in an unrestrained state.
[0064] As used herein, the term used refers to solid state oriented films with a free shrinkage in both machine and transverse directions, as measured by ASTM standard D 2732, of at least 10% , preferably at least 15%, and even more preferably at least 20% at 85°C.
[0065] As used herein the term "total free contraction" refers to a value determined by adding the percentage of free contraction in the (longitudinal) direction of the machine to the percentage of free contraction in the transverse (transverse) direction. Total free contraction is expressed as a percentage (%).
[0066] As used herein, the term "maximum shrinkage stress" refers to the maximum stress value developed by the trapped film samples when subjected to a heating-cooling cycle in accordance with the test method described under the present experimental section. The maximum shrinkage stress is expressed in this document as kg/cm2. By way of example, Figure 1 shows the course of the contraction force during a heating-cooling cycle; force (g) and temperature (°C) are indicated on the y-axis and x-axis, respectively.
[0067] As used herein, the term "residual cold shrinkage stress" refers to the shrinkage stress that films exhibit at a temperature of 5°C after the complete heating-cooling cycle of the test method has had carried out as described under this experimental section. The residual cold shrinkage stress is expressed in this document as kg/cm2.
[0068] As used herein, the term "process stability" is interchangeable with the term "processability" and refers to film stability during manufacturing, extrusion levels, orientation and conversion.
[0069] As used herein, the term "polymer" refers to the product of a polymerization reaction, and is inclusive of homopolymers and copolymers.
[0070] As used herein, the term "homopolymer" is used with reference to a polymer resulting from the polymerization of a single type of monomer, i.e., a polymer consisting essentially of a single type of monomer, i.e., repeating unit.
[0071] As used herein, the term "copolymer" refers to polymers formed by the polymerization reaction of at least two different types of monomers. For example, the term "copolymer" includes the copolymerization reaction product of ethylene and an alpha-olefin, such as 1-hexene. When used in generic terms, the term "copolymer" is also inclusive of, for example, terpolymers. The term "copolymer" is also inclusive of random copolymers, block copolymers and graft copolymers.
[0072] As used herein, the term "heterogeneous polymer" or "polymer obtained by heterogeneous catalysis" refers to polymerization reaction products of relatively wide variation in molecular weight and relatively wide variation in composition distribution, that is, typical polymers prepared, for example, using conventional Ziegler-Natta catalysts, for example, metal halides activated by an organometallic catalyst, i.e., titanium chloride, optionally containing magnesium chloride, complexed to trialkyl aluminum, and can be found in patents such as US Patent no. 4,302,565 issued to Goeke et al. and U.S. Patent no. 4,302,566 issued to Karol, et al. Heterogeneous catalyzed copolymers of ethylene and an olefin can include linear low density polyethylene, very low density polyethylene, and ultra low density polyethylene. Some copolymers of this type are available, for example, from the Dow Chemical Company of Midland, Mich., USA and sold under the trademark DOWLEX resins.
[0073] As used herein, the term "homogeneous polymer" or "polymer obtained by homogeneous catalysis" refers to polymerization reaction products of relatively narrow molecular weight distribution and relatively narrow composition distribution. Homogeneous polymers are structurally different from heterogeneous polymers in that homogeneous polymers exhibit a relatively uniform sequence arrangement of comonomers within a chain, a mirror image of the sequence distribution across all chains, and a similarity in length of all the chains, that is, a narrower molecular weight distribution. This term includes homogeneous polymers prepared using metallocenes, or other single-site type catalysts, as well as homogeneous polymers that are obtained using Ziegler Natta catalysts under homogeneous catalysis conditions.
[0074] The copolymerization of ethylene and alpha-olefin complexes under homogeneous catalysis, for example, the copolymerization with metallocene catalysis systems that include catalysts of restricted geometry, i.e., monocyclopentadienyl transition metal complexes, is described in the US Patent at the. 5,026,798 issued to Canich. Homogeneous ethylene/alpha-olefin (E/AO) copolymers may include modified or unmodified ethylene/alpha-olefin copolymers that have a long-chain branched alpha-olefin comonomer (8 to 20 pendant carbon atoms) available together to Dow Chemical Company, known as AFFINITY and ATTANE resins, linear TAFMER copolymers obtainable from Mitsui Petrochemical Corporation of Tokyo, Japan, and modified or unmodified ethylene/-olefin copolymers that have a branched-chain -olefin comonomer short (3 to 6 pendant carbon atoms) known as EXACT resins available from ExxonMobil Chemical Company of Houston, Texas, USA.
As used herein, the term "polyolefin" refers to any polymerized olefin, which may be linear, branched, cyclic, aliphatic, aromatic, substituted or unsubstituted. More specifically, the term polyolefin includes olefin homopolymers, olefin copolymers, copolymers of an olefin and a non-olefinic comonomer copolymerizable with the olefin, such as vinyl monomers, their modified polymers, and the like. Specific examples include polyethylene homopolymer, polypropylene homopolymer, polybutene homopolymer, ethylene-alpha-olefin which are copolymers of ethylene with one or more olefins (alpha-olefins) such as butene-1, hexene-1, octene -1, or another still as a comonomer, and still others, copolymer of propylene and alpha-olefin, copolymer of butene and alpha-olefin, copolymer of ethylene-unsaturated ester, copolymer of ethylene-unsaturated acid, (for example copolymer of ethylene-ethyl acrylate, ethylene-ethylene-butyl acrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-acrylic acid copolymer, and ethylene-methacrylic acid copolymer), ethylene-vinyl acetate copolymer, resin ionomer, polymethyl pentene, etc.
As used herein the term "ionomer" refers to the products of the polymerization of ethylene with an unsaturated organic acid, and optionally also with an (C1-C4) alkyl ester of unsaturated organic acid, partially neutralized with a mono or divalent metal ion, such as lithium, sodium, potassium, calcium, magnesium and zinc. Typical unsaturated organic acids are acrylic acid and methacrylic acid which are thermally stable and commercially available. The (C 1 -C 4 )alkyl esters of unsaturated organic acid are typically (meth)acrylate esters, for example, methyl acrylate and isobutyl acrylate. Mixtures of more than one unsaturated organic acid ester comonomer and/or more than one unsaturated organic acid (C1-C4) alkyl ester monomer can also be used in the preparation of the ionomer.
[0077] As used herein, the term "modified polymer", as well as more specific expressions such as "modified ethylene/vinyl acetate copolymer" and "modified polyolefin", refers to such polymers that have a functionality anhydride, as defined immediately above, grafted thereon and/or copolymerized therewith and/or mixed therewith. Preferably, such modified polymers have the anhydride functionality grafted onto them or polymerized therewith, rather than merely being mixed with them. As used herein, the term "modified" refers to a chemical derivative, for example, one that has any form of anhydride functionality, such as maleic acid anhydride, crotonic acid, citraconic acid, acid anhydride itaconic acid, fumaric acid, etc., if grafted onto a polymer, copolymerized with a polymer, or mixed with one or more polymers, and is also inclusive of derivatives of such functionalities, such as acids, esters and metal salts derived from same. As used herein, the term "anhydride-containing polymer" and "anhydride-modified polymer" refers to one or more of the following: (1) polymers obtained by copolymerizing an anhydride-containing monomer with a second, different monomer, and (2) anhydride grafted copolymers, and (3) a mixture of a polymer and an anhydride-containing compound.
[0078] As used herein, the term "ethylene-alpha-olefin copolymer" refers to heterogeneous and homogeneous polymers such as linear low density polyethylene (LLDPE) with a density typically in the range of about 0.900 g/cm3 to about 0.930 g/cm3, linear medium density polyethylene (LMDPE) with a density typically in the range of about 0.930 g/cm3 to about 0.945 g/cm3, and very low and ultra low density polyethylene ( VLDPE and ULDPE) with a density lower than about 0.915 g/cm3, typically in the range of 0.868 to 0.915 g/cm3, and like the homogeneous metallocene catalyzed resins EXACT™ and EXCEED™ obtainable from Exxon , AFFINITY™ single-site resins obtainable from Dow, and homogeneous ethylene-alpha-olefin copolymer resins obtainable from Mitsui. All of these materials generally include ethylene copolymers with one or more comonomers selected from alpha-olefins (C4-C10) such as butene-1, hexene-1, octene-1, etc., wherein the molecules of the copolymers comprise long chains with relatively few side chain branches or lattice structures.
[0079] As used herein, terms identifying polymers such as "polyamide", "polyester", "polyurethane", etc., are inclusive not only of polymers comprising repeating units derived from known monomers to polymerize so as to form a polymer of the named type, but they are also inclusive of comonomers, derivatives, etc., which can copolymerize with the known monomers to polymerize so as to produce the named polymer. For example, the term "polyamide" encompasses both polymers comprising repeating units derived from monomers, such as caprolactam, which polymerize to form a polyamide, as well as copolymers derived from the copolymerization of caprolactam with a comonomer which, when polymerized alone, it does not result in the formation of a polyamide. Furthermore, the terms identifying polymers are also inclusive of blends, blends, etc., of such polymers with other polymers of a different type.
[0080] As used herein, the term "polyamide" refers to high molecular weight polymers that have amide bonds along the molecular chain, and more specifically refers to synthetic polyamides such as nylons. Such term encompasses both homo-polyamides and co-(or ter-)polyamides. It also specifically includes aliphatic polyamides or copolyamides, aromatic polyamides or copolyamides, and partially aromatic polyamides or copolyamides, modifications thereof and mixtures thereof. Homopolyamides are derived from the polymerization of a single type of monomer comprising both chemical functions that are typical of polyamides, i.e. amino and acid groups, and such monomers are typically lactams or amino acids, or from polycondensation of two types of polyfunctional monomers, ie polyamines with polybasic acids. Co-, ter- and multi-polyamides are derived from the copolymerization of precursor monomers of at least two (three or more) different polyamides. As an example in the preparation of co-polyamides, two different lactams can be employed, or two types of polyamines and polyacids, or a lactam on one side and a polyamine and a polyacid on the other side. Exemplary polymers are polyamide 6, polyamide 6/9, polyamide 6/10, polyamide 6/12, polyamide 11, polyamide 12, polyamide 6/12, polyamide 6/66, polyamide 66/ 6/10, their modifications and their mixtures. Said term also includes crystalline or partially crystalline, aromatic or partially aromatic polyamides.
[0081] As used herein, the term "amorphous polyamide" refers to polyamides or nylons with an absence of a regular three-dimensional arrangement of molecules or subunits of molecules that span distances, which are large relative to atomic dimensions. However, the regularity of the structure exists in a local band. See, "Amorphous Polymers" in the Encyclopedia of Polymer Science and Engineering, 2nd Ed., pages 789 to 842 (J. Wiley & Sons, Inc.1985). This document has Library of Congress Catalog Card Number 84-19713. In particular, the term "amorphous polyamide" refers to a material recognized by the element versed in the technique of differential scanning calorimetry (DSC) as having no measurable melting point (less than 0.5 cal/g) or no heat. melting rate as measured by DSC using ASTM standard 3417-83. Such nylons include amorphous nylons prepared from the condensation polymerization reactions of diamines with dicarboxylic acids. For example, an aliphatic diamine is combined with an aromatic dicarboxylic acid, or an aromatic diamine is combined with an aliphatic dicarboxylic acid to obtain suitable amorphous nylons.
[0082] As used herein, the term "polyester" refers to homopolymers or copolymers (also known as "copolyesters") that have an ester bond between the monomer units that can be formed, for example, by reactions of condensation polymerization of lactones or by polymerization of acid(s) and glycol(ols). The term "(co)polyesters" refers to both homo- and copolymers.
As used herein, the term "aromatic polyester" refers to homopolymers or copolymers (also known as "copolyesters") that have an ester bond between one or more aromatic or alkyl-substituted dicarboxylic acids and one or more glycols. The term "(co)polyesters" refers to homo- and copolymers.
[0084] As used herein, the term "adhered" is inclusive of films that are directly adhered to each other when using a thermal solder or other means, as well as films that are adhered to each other when using an adhesive that is between the two sheets.
[0085] As used herein, the term "directly adhered", for layers, is defined as the adhesion of the subject layer to the object layer, without a bonding layer, adhesive, or another layer between them.
[0086] On the other hand, as used herein, the word "between", for a layer expressed as being between two other specific layers, both includes the direct adhesion of the subject layer to the two other layers that are in between, as well as a lack of any direct adhesion to one or both of the other two layers between which the subject is, i.e. one or more additional layers may be imposed between the subject layer and one or more of the layers in the middle of which is the subject's layer.
[0087] As used herein, the term "gas barrier" when referring to a layer, a resin contained in said layer, or a total structure, refers to the property of the layer, resin or structure , to limit the passage of gases through it to a certain extent.
[0088] When referring to a layer or a total structure, the term "gas barrier" is used in this document to identify layers or structures characterized by an oxygen transmission rate (assessed at 23°C and a relative humidity of 0% according to ASTM Standard D-3985) of less than 500 cm3 /m2^dia^atm, preferably less than 100 cm3 /m2^dia^atm, and even more preferably less than 50 cm3 . m2^day^atm.
[0089] As used herein, the term "PVDC" refers to homopolymers or copolymers of vinylidene chloride.
[0090] A PVDC copolymer comprises a greater amount of vinylidene chloride and a smaller amount of one or more comonomers. A larger amount is defined as greater than 50%.
[0091] As used herein, the term "flexible container" is inclusive of end-sealed bags, side-sealed bags, L-sealed bags, U-sealed bags (also referred to as "pouches"), gusset-reinforced bags, back-stitched piping, and seamless packaging.
[0092] As used herein, the term "a packaging article in the form of a seamless tube" refers to a tube devoid of any seal which is generally made of a multilayer film (co)extruded through of a round matrix, optionally oriented, in which the heat sealing layer a) is the innermost layer of the tube.
[0093] As used herein, the term "packaging" is inclusive of packages made of such articles, i.e. containers or tubes, by placing a product on the article and sealing the article so that the product is substantially surrounded by the heat shrinkable multilayer film from which the packaging container is made.
[0094] As used herein, the term "bag" refers to a packaging container that has an open top, side edges, and a bottom edge. The term "bag" covers flat bags, pouches, packaging (seamless packaging and back-stitched packaging, including sealed packaging with flaps, sealed packaging with flaps, and back-seaming packaging sealed with beads that have the back-seam tape in them). The various configurations of the packaging are disclosed in patent document US6764729 and the various configurations of the bag, including L-seal bags, back-seam bags and U-seal bags (also referred to as pouches), are disclosed in the patent document. US6790468.
[0095] As used herein, the term "drip products" refers to products that release drops of exudation.
As used herein, the terms "conventional or traditional extrusion dies" refer to extrusion dies that are not properly modified (insulated) to allow simultaneous extrusion of PVDC and high melting point polymers.
[0097] Unless otherwise indicated, all percentages must be percentages by weight. Detailed Description of the Invention
[0098] A first object of the present invention is a multi-layer coextruded biaxially oriented heat-shrinkable packaging film comprising at least: one heat-sealable layer (a); a layer (b) which is not directly adhered to the heat-sealable layer (a), wherein said layer (b) comprises one or more aromatic (co)polyesters, at least one internal gas barrier layer (c) which comprises polyvinylidene chloride, wherein said film is characterized by - A) a total free shrinkage at 85°C of at least 45%, preferably of at least 55%, more preferably of at least 60% and - B ) a maximum shrinkage stress in each of the longitudinal and transverse directions of at least 20 kg/cm2, preferably at least 25 kg/cm2, more preferably at least 25 kg/cm2 in each of the longitudinal and transverse directions and greater than 30 kg/cm2 in at least one of the two directions, and - C) a residual shrinkage stress at 5°C in each of the longitudinal and transverse directions of at least 25 kg/cm2, preferably at least 27 kg/cm2, more preferably at least 30 kg/cm2.
[0099] The films of the invention are characterized by one or more of the following characteristics, taken alone or in combination.
[00100] In one embodiment, the films of the present invention do not comprise any abuse-resistant layer d) as defined below.
[00101] In another embodiment, the films of the present invention comprise an external heat-sealable layer (a), an external layer (b), wherein said layer (b) comprises one or more aromatic (co)polyesters, by at least one internal gas barrier layer (c) comprising polyvinylidene chloride, and at least one internal abuse resistant layer (d).
[00102] In another embodiment, the films of the present invention comprise an external heat-sealable layer (a), an external layer (b), wherein said layer (b) comprises one or more aromatic (co)polyesters, by at least one internal gas barrier layer (c) comprising polyvinylidene chloride, and at least two internal abuse resistant layers (d') and (d'').
[00103] In another embodiment, the films of the present invention comprise an external heat-sealable layer (a), an external layer (b), wherein said layer (b) comprises one or more aromatic (co)polyesters, by at least one inner gas barrier layer (c) comprising polyvinylidene chloride, at least two inner abuse resistant layers (d') and (d''), at least one additional inner layer (e), and optionally at least minus one additional inner bonding layer (f).
[00104] At least one internal gas barrier layer (c) of the present films comprises at least 70%, at least 80%, at least 90%, at least 95% of polyvinylidene chloride, and preferably consists of polyvinylidene chloride. polyvinylidene. Polyvinylidene chloride refers to homopolymers of vinylidene chloride or its copolymers with other suitable monomers in a smaller amount. Preferred polymers for the PVDC layer are PVDC copolymers. Especially preferred copolymers are vinylidene chloride-methyl acrylate copolymers, vinylidene chloride-vinyl chloride copolymers, vinylidene chloride-acrylonitrile copolymers and vinylidene chloride-methyl acrylate-vinyl chloride terpolymers .
Preferably, the present films comprise only an internal gas barrier layer (c) which comprises polyvinylidene chloride.
[00106] In a preferred embodiment, the films of the present invention also comprise at least one abuse resistant layer d), wherein said abuse resistant layer d) comprises polyamides, preferably a mixture of aliphatic and aromatic polyamides such as PA6 /66 with PA6I/6T. Preferably, said abuse resistant layer (d) consists of said mixture. Said abuse resistant layer (d) is preferably interposed between the heat sealable layer (a) and the layer (b). Preferably, said layer b) is the outermost layer.
[00107] Preferably, the total amount of polyamide(s) in the entire film is between 10% and 55%, preferably between 15% and 50%, more preferably between 20% and 50%, and even more preferably between 20 % and 45% by weight.
[00108] In a preferred embodiment, when both layers (d') and (d'') are present, they have the same composition; in a preferred embodiment they comprise at least one polyamide, preferably a mixture of aliphatic and aromatic polyamides.
[00109] Preferably, in such a mixture the percentage of said aliphatic polyamides is at least 70%, and at least 80% by weight. More preferably, in such a mixture the aliphatic polyamide content is between 70% and 97%, more preferably between 85% and 95%, and the aromatic polyamide content is between 3% and 30%, more preferably between 5% and 15%.
[00110] Preferably, said layers (d') and (d'') consist of said mixture.
[00111] Preferably, the percentage by weight of the sum of the polyamide resin(s) of the layers (d') and (d'') in the entire film is comprised between 10% and 55%, preferably between 15% and 50 %, more preferably between 20% and 50%, and even more preferably between 20% and 45% by weight.
[00112] More preferably in this modality, the layers (d') and (d'') are positioned respectively between the external heat-sealable layer (a) and the internal PVDC gas barrier layer (c), and between the inner PVDC gas barrier layer (c) and the outer barrier (b).
[00113] In the latter case, the layer (d'') acts as an insulating layer during the coating of the substrate, thereby protecting the thermodegradable PVDC layer against excessive heating of the outer aromatic (co)polyester melting layer b) .
[00114] In one embodiment, one or more additional layers interposed between at least one inner PVDC layer (c) and the aromatic (co)polyester layer (b), the total thickness of said layer(s) ( s) interposed is at least 10%, at least 20%, at least 25%, at least 30% of the total film thickness.
[00115] Said one or more additional layers are preferably selected from abuse-resistant layers d), additional e) and bonding f), which are defined in this document below.
[00116] In the case where the present film includes more than one internal gas barrier layer comprising PVDC, said one or more additional layers are preferably interposed between the aromatic (co)polyester layer (b) and each of adjacent PVDC barrier layers.
[00117] The films according to the first objective of the present invention and the modalities described above are characterized by the following contraction properties A), B) and C): A) A total free contraction at 85°C of at least 45 %, or at least 55%, or at least 60%, and B) a maximum contraction stress of at least 20 kg/cm2 in each of the LD and TD, or at least 25 kg/cm2 in each of the LD and TD, or at least 25 kg/cm2 in each of the LD and TD and greater than 30 kg/cm2 in at least one of the LD and TD, and C) a residual contraction stress a 5°C in each of the LD and TD of at least 25 kg/cm2 or at least 27 kg/cm2 or at least 30 kg/cm2.
[00118] Particularly preferred embodiments of the films of the present invention are characterized by the following shrinkage properties A), B) and C): A) a total free shrinkage of at least 55% at 85°C, B) a shrinkage stress maximum of at least 25 kg/cm2 in each of LD and TD, and C) a residual shrinkage stress in each of LD and TD of at least 27 kg/cm2 at 5°C.
[00119] Most preferred embodiments of the films of the present invention are characterized by the following shrinkage properties A), B) and C): A) a total free shrinkage of at least 60% at 85°C, B) a tension of maximum contraction of at least 25 kg/cm2 in each of the LD and the TD and greater than 30 kg/cm2 in at least one of the LD and the TD, and C) a residual contraction stress in each of the the LD and TD of at least 30 kg/cm2 at 5°C.
[00120] Packaging films according to the first objective of the present invention result in sealed packages when shrunk around the product to be packaged, maintain the initial tension during handling and storage of the package under cold conditions, advantageously reducing loss drip, especially in the case of meat packaging. The shrinkage properties shown by the present films are mainly due to the presence of certain polymers, preferably in specific amounts and preferred positions within the structure, as further defined below, but they can also be adapted to the product to be packaged and its dimensions, for example by changing the orientation temperature as is known to the member skilled in the art.
[00121] The total thickness of the multilayer film is generally not greater than 250 microns and can be selected depending on the product to be packaged and the packaging process. The total film thickness is preferably from 10 to 150 microns, more preferably from 20 to 120 microns, and even more preferably from 30 to 100 microns.
[00122] The number of layers of the films according to the present invention are generally between 3 and 50, preferably between 5 and 35, more preferably between 7 and 20, and even more preferably less than 20. In the modality Preferably, the number of layers of the films according to the present invention are comprised between 6 and 15, and even more preferably between 7 and 12.
[00123] The films according to the first objective of the present invention comprise a first external heat-sealable layer (a).
[00124] The heat sealable layer (a) comprises one or more of the polymers described in the following paragraphs. Preferably, it comprises more than 50%, 70%, 80%, 90%, 95% by weight with respect to the same layer, and more preferably consists substantially of one or more of said polymers.
[00125] The polymer for the heat sealable layer is typically selected from ethylene-vinyl acetate (EVA) copolymers, homogeneous or heterogeneous linear ethylene-alpha-olefin copolymers, polypropylene (PP) copolymers, ethylene-propylene copolymers (EPC), ionomers, and mixtures of two or more of these resins.
[00126] As used herein, the term "EVA" refers to copolymers of ethylene and vinyl acetate. The vinyl acetate monomer unit can be represented by the general formula: [CH3COOCH=CH2].
[00127] EVA is a copolymer formed by ethylene and vinyl acetate monomers in which the ethylene units are present in a larger amount and the vinyl acetate units are present in a smaller amount. The typical amount of vinyl acetate can range from about 5 to about 20%.
[00128] The particularly preferred polymer for the heat sealable layer consists of heterogeneous materials such as linear low density polyethylene (LLDPE) with a density typically in the range of about 0.910 g/cm3 to about 0.930 g/cm3, linear medium density polyethylene (LMDPE) with a density typically in the range of about 0.930 g/cm3 to about 0.945 g/cm3, and very low and ultra low density polyethylene (VLDPE and ULDPE) with a lower density than about 0.915 g/cm3; and homogeneous polymers such as homogeneous metallocene-catalyzed EXACT™ and EXCEED™ resins obtainable from Exxon, single-site AFFINITY™ resins obtainable from Dow, QUEO from Borealis, copolymer resins from TAFMER™ homogeneous ethylene-alpha-olefins available from Mitsui. All such materials generally include ethylene copolymers with one or more selected alpha-olefin (C4-C10) comonomers such as butene-1, hexene-1, octene-1, etc., wherein the molecules of the copolymers comprise long chains with relatively few side chain branching or lattice structures.
[00129] These polymers can be advantageously mixed in various percentages to adapt to the sealing properties of the films depending on their use in packaging, also known to those skilled in the art.
Blends comprising VLDPE polymers, e.g. AFFINITY PL 1281G1 and AFFINITY PL 1845G or QUEO 1007, are particularly preferred.
[00131] In the most preferred embodiment, the sealing layer (a) consists of a mixture between two VLDPE resins.
[00132] In general, the preferred resins for the heat-sealable layer (a) have a seal initiation temperature lower than 110°C, more preferably a seal initiation temperature lower than 105°C , and even more preferably a seal initiation temperature lower than 100°C.
[00133] The heat sealable film of the present invention may have a typical thickness comprised within the range of 2 to 30 microns, preferably 3 to 25 microns, and more preferably 4 to 20 microns.
[00134] The films of the present invention also comprise a layer (b), which is not directly adhered to the heat-sealable layer (a).
[00135] Layer (b) comprises one or more aromatic polyesters or copolyesters, herein (co)polyesters, preferably in an amount greater than 50%, 70%, 80%, 90%, 95% by weight with respect the same weight of the layer, optionally mixed with a smaller amount of aliphatic polyesters. More preferably, layer (b) substantially consists of one or more aromatic (co)polyesters.
[00136] Said (co)polyester(s) is (are) characterized preferably by a melting point higher than 225°C, higher than 230°C, more higher than 235°C.
[00137] It was found that the aromatic polyester resin in conjunction with the manufacturing method is important to start the combination of free contraction, maximum shrinkage stress and residual shrinkage stress according to the first objective of the present invention.
[00138] Preferably, the percentage by weight of the (co)polyester(s) in the entire film ranges from 3 to 60%, preferably from 5 to 50%, preferably 10 to 40%, and with more preferably from 15 to 40%, from 20 to 40%.
[00139] Preferably, the percentage by weight of the aromatic (co)polyester(s) in the entire film is at least 3%, at least 5%, at least 10%, at least 12%, at least 15%, at least 20%, at least 25%.
[00140] Preferably, layer (b) is the only layer of the present multilayer film which comprises aromatic (co)polyester(s).
[00141] Layer b) can be an inner layer or the outermost layer of the film according to the first objective of the present invention. Preferably, layer (b) is the second outer layer of the present multilayer film.
[00142] Preferably, layer (b) is the second outer layer of the present multilayer film and is the only layer comprising aromatic (co)polyesters.
[00143] In a preferred embodiment, the aromatic (co)polyester(s) is (are) present only in the outer layer (b). In such a case, the percentage by weight of aromatic (co)polyester(s) in said outer layer (b), with respect to the weight of the entire film, is at least 3%, at least 5%, at least 10%, at least 12%, at least 15%, at least 20%, at least 25%. Preferably, it is in the range 3 to 60%, 5 to 50%, 20 to 40%, 12 to 40%, 15 to 40%, 20 to 40%, 25 to 40%.
[00144] Layer (b) may have a typical thickness comprised within the range of 1.5 to 35 microns, preferably 3 to 30 microns, and more preferably 4 to 25 microns.
[00145] In the preferred embodiment according to the first objective of the present invention, layer b) is the outermost layer of the film.
[00146] As used herein, the term "aromatic (co)polyester" refers to homopolymers or copolymers that have an ester bond between monomer units that can be formed, for example, by condensation polymerization reactions between one or more dicarboxylic acids and one or more glycols. The dicarboxylic acid can be aromatic or alkyl-substituted aromatic, for example, various phthalic acid (i.e., ortho-phthalic acid) isomers, such as isophthalic (i.e., meta-phthalic acid) and terephthalic acid. (ie, para-phthalic acid) as well as naphthalic acid. Specific examples of alkyl-substituted aromatic acids also referred to herein as aromatic polyesters include the various isomers of dimethyl phthalic acid, such as dimethyl isophthalic acid, dimethyl orthophthalic acid, dimethyl terephthalic acid, the various isomers of diethyl phthalic acid , such as diethyl isophthalic acid, diethyl orthophthalic acid, the various isomers of dimethyl naphthalic acid, such as 2,6-dimethyl naphthalic acid and 2,5-dimethyl naphthalic acid, and the various isomers of diethyl naphthalic acid. The dicarboxylic acid alternatively can be 2,5-furan dicarboxylic acid (FDCA). Glycols can be straight-chain or branched. Specific examples include ethylene glycol, propylene glycol, trimethylene glycol, 1,4-butane diol, neopentyl glycol, and the like. Glycols include modified glycols such as 1,4-cyclohexane dimethanol.
Suitable aromatic polyesters include poly(2,6-ethylene naphthalate), poly(butylene terephthalate), poly(ethylene terephthalate), and copolyesters obtained by reacting one or more dicarboxylic acids with one or plus dihydroxy alcohols, such as PETG, which is an amorphous copolyester of terephthalic acid with ethylene glycol and 1,4-cyclohexane dimethanol, and mixtures thereof.
[00148] In the case of mixtures of (co)polyesters, the aromatic (co)polyester having a melting point higher than 225°C, 230°C, 235°C is present in a larger amount, i.e. in an amount greater than 50%, preferably greater than 70%, and more preferably greater than 80%, 90% by weight.
Preferred aromatic (co)polyesters are polyethylene terephthalates (PET) which have melting points higher than 225°C, higher than 230°C, higher than 235°C.
[00150] Particularly preferred polyesters are PET polyester resins supplied as Artenius or Ramapet by Indorama or polyester resins from Eastman.
[00151] The aromatic (co)polyester in layer b) of the present films may comprise any of the above polyesters alone or in a blend.
[00152] In a preferred embodiment, the aromatic (co)polyester layer (b) consists of a single aromatic polyester resin, with Indorama's Ramapet N180 and Ramapet N1 PETs being preferred.
[00153] More than one layer of aromatic (co)polyester b) can be present in the films according to the first objective of the present invention.
[00154] The films of the present invention are characterized by a total content of polyamides - if present - and aromatic (co)polyesters, expressed as the sum of the percentage by weight of the polyamide(s) and the (s) ( aromatic co)polyester(s), preferably between 30% and 80%, more preferably between 40% and 70% and even more preferably between 45% and 65%.
[00155] The films of the present invention comprise at least one internal oxygen barrier layer c) comprising polyvinylidene chloride.
[00156] Preferably the PVDC comprises a thermal stabilizer (i.e. HCl scavenger, for example epoxidized soybean oil) and a lubrication processing aid, which comprises, for example, one or more acrylates.
[00157] Polyvinylidene chloride (PVDC) includes copolymers of vinylidene chloride and at least one monoethylenically unsaturated monomer copolymerizable with vinylidene chloride. The monoethylenically unsaturated monomer can be used in a proportion of 2 to 40% by weight, preferably 4 to 35% by weight, of the resulting PVDC. Examples of the monoethylenically unsaturated monomer may include vinyl chloride, vinyl acetate, vinyl propionate, alkyl acrylates, alkyl methacrylates, acrylic acid, methacrylic acid and acrylonitrile. The vinylidene chloride copolymer can also be a terpolymer. It is particularly preferable to use a copolymer with vinyl chloride or (C1-C8) alkyl(meth)acrylate, such as methyl acrylate, ethyl acrylate or methyl methacrylate, as comonomers. It is also possible to use a mixture of different PVDCs such as, for example, a mixture of vinylidene chloride-vinyl chloride copolymer with vinylidene chloride-methyl acrylate copolymer. Mixtures of PVDC and polycaprolactone (such as those described in patent EP2064056 B1, examples 1 to 7) are also possible and particularly useful for breathable food products such as some cheeses. PVDCs can contain suitable additives as known in the prior art, i.e. stabilizers, antioxidants, plasticizers, hydrochloric acid removers, etc., which can be added for processing reasons and/or control of gas barrier properties of resin. The particularly preferred PVDC is IXAN PV910 supplied by Solvin and SARAN 806 by Dow.
[00158] Preferably, the barrier layer comprises at least 70%, more preferably at least 80%, 90%, 95% PVDC.
[00159] In the most preferred embodiment, the barrier layer c) consists of PVDC. The term "consists of" refers to a percentage by weight greater than 98%.
[00160] The barrier layer typically has a thickness from 0.1 to 30 µm, preferably from 0.2 to 20 µm, more preferably from 0.5 to 10 µm and even more preferably from 1 to 8 µm.
[00161] Once the PVDC gas barrier resin has been selected, its thickness will be adjusted to provide the desired oxygen transmission rate (OTR). High barrier films will have an OTR (rated at 23°C and 0% relative humidity according to ASTM D-3985 standard) below 100 cm3/m2^dia^atm and preferably below 80 cm 3/average atm and will be particularly suitable for packaging meat, including fresh red meat and processed meat. A higher OTR for low barrier films will be preferred for packaging, for example, most cheeses where generally OTRs of from about 100 to about 500 cm 3 /m 2 ·dia·atm are preferred and of about 150 to about 450 cm 3 /m 2 ·dia·atm are most preferred.
[00162] The present manufacturing processes - in which the PVDC layer is placed inside the substrate and the layer(s) of aromatic (co)polyester(s) of high melting point in the coating and, preferably, where a thick stack of interposed layers is provided between the PVDC and the aromatic (co)polyester layers - they are particularly advantageous in the case of medium to low barrier films comprising thin layer(s) of PVDC , which must be further damaged by heat.
[00163] The films of the present invention may also comprise one or more abuse resistant layers d).
[00164] Layer d) is positioned as the inner layer. Preferably, layer d) is positioned between sealing layer a) and barrier layer c).
[00165] The abuse-resistant layer d) typically has a thickness of from 1 to 30 µm, preferably from 2 to 25 µm, more preferably from 3 to 20 µm and even more preferably from 5 to 15 µm.
[00166] In order to provide resistance to abuse, the resins contained in layer d) can be selected from the group consisting of polyamides, (co)polyesters and styrene-based polymers. Mixtures of such classes of resins can be used.
Polyamide homopolymers useful for layer d) include nylon 6 (polycaprolactam), nylon 11 (polyundecanolactam), nylon 12 (polylauryllactam), and so on. Other useful polyamide homopolymers also include nylon 4.2 (ethylene diamide), nylon 4.6 (polytetramethylene adipamide), nylon 6.6 (polytetramethylene adipamide), nylon 6.9 (polyhexamethylene azelamide), nylon 6.10 (polyhexamethylene sebacamide), nylon 6.12 (polyhexamethylene dodecanediamide), nylon 7.7 (polyhexamethylene pimelamide), nylon 8.8 (polyheptamethylene suberamide), nylon 9.9 (polyoctamethylene azelamide), nylon 10.9 (polynonamethylene azelamide), nylon 12.12 (polydecamethylene dodecanediamide), and others.
Polyamide copolymers useful for layer d) include nylon 6.6/6 copolymer (polyhexamethylene adipamide/caprolactam copolymer), nylon 6/6.6 copolymer (polycaprolactam/hexamethylene adipamide copolymer), nylon copolymer 6.2/6.2 (polyhexamethylene ethylene diamide/hexamethylene ethylene diamine copolymer), nylon 6.6/6.9/6 copolymer (polyhexamethylene adipamide/hexamethylene azelamide/caprolactam copolymer), as well as other nylons which are not particularly delineated herein. Additional polyamides include nylon 4.1, nylon 6.I, nylon 6.6/6I copolymer, nylon 6.6/6T copolymer, MXD6 (polym-xylylene adipamide), nylon copolymer 6T/6I, the copolymer of nylon 6/MXDT/I, nylon MXDI, poly-p-xylylene adipamide, polyhexamethylene terephthalamide, polydodecamethylene terephthalamide, and others.
Particularly preferred polyamides are ULTRAMID C33 L 01 supplied by BASF, Terpalex, 503X family grades from Ube and Grilon and Grivori from EMS.
[00170] In the case where at least one internal abuse layer (d) of the present films comprises polyamide(s), the percentage by weight of said polyamide(s) in said layer is preferably at least minus 70%, 80% 90% by weight, based on the weight of said layer(s), and more preferably consists of polyamide(s).
Suitable (co)polyesters for layer d) are the aromatic (co)polyesters mentioned for layer (b). Suitable (co)polyesters for layer d) can also be aliphatic (co)polyesters deriving from linear or aliphatic dicarboxylic acid, i.e. oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, and so on; glycols can be straight-chain or branched. Specific examples include ethylene glycol, propylene glycol, trimethylene glycol, 1,4-butane diol, neopentyl glycol, and the like. Glycols include modified glycols such as 1,4-cyclohexane dimethanol.
[00172] In the case where at least one internal abuse layer (d) comprises (co)polyester(s), the percentage by weight of said (co)polyester(s) is preferably between 5 % and 40%, preferably between 10% and 30% and even more preferably between 15% and 25% with respect to the weight of the entire film.
[00173] In one embodiment, at least one internal abuse layer d) comprises styrene-based polymers.
[00174] As used herein, the term "styrene-based polymer" refers to at least one polymer selected from the group consisting of polystyrene, styrene-ethylene-butylene-styrene copolymer, styrene-butadiene copolymer - styrene, styrene-isoprene-styrene copolymer, styrene-ethylene-butadiene-styrene copolymer and styrene(ethylene-propylene rubber)-styrene copolymer. As used herein, the use of a "dash" (ie, "-") in a styrene-based polymer formula is inclusive of block copolymers and random copolymers. More particularly, the term "styrene-based polymer" includes both copolymers wherein (i) all named monomers are present as a block, or (ii) any subset of named monomers are present as a block with the remaining monomers being randomly arranged, or (iii) all named monomers are randomly arranged.
[00175] The term "polystyrene", as used herein, refers to film grade homopolymers and copolymers of styrene and its analogs and homologs, including -methyl-styrene and ring substituted styrenes such as, for example, ring methylated styrenes. That term "polystyrene polymer" is used to identify individual polymers or blends of different polystyrene polymers as indicated above.
Particularly preferred resins are BASF's Styrolux 684D, BASF's Polystyrol 143E and Chevron Phillips Chemicals' KR53 resin which can be used alone or in a blend.
[00177] In the case where at least one internal abuse layer (d) comprises polystyrene(s), the percentage by weight of said polystyrene(s) is preferably between 5% and 30%, of preferably between 10% and 25%, with respect to the weight of the entire film.
[00178] In the case where more than one layer d) is used, its chemical nature can be independently selected from the group consisting of polyamides, (co)polyesters and styrene-based polymers, can be the same or different.
[00179] In one embodiment, two abuse-resistant layers d') and d'') are used.
[00180] In a preferred embodiment, d') and d'') are positioned respectively between the sealing layer a) and the inner polyvinylidene chloride gas barrier layer c) and between the chloride gas barrier layer of polyvinylidene c) and the outermost layer b).
[00181] In a more preferred embodiment, d') and d'') have an identical chemical nature.
[00182] In the case where both layers d') and d'') comprise (co)polyester(s), the percentage by weight of the sum of the polyester resin(s) of the layers d' ) and d'') in the entire film is preferably from 5% to 40%.
[00183] In the case where layers d') and d'') comprise polystyrene(s), the percentage by weight of the sum of the polystyrene resin(s) of layers d') and d' ') in the entire film is preferably from 5% to 20%.
[00184] Preferably, at least one of d') and d'') comprises at least one polyamide.
[00185] Even more preferably, d') and d'') both comprise one or more polyamides. In such a case, preferably d') and d'') consist of a mixture of an aliphatic polyamide with an aromatic polyamide, even more preferably each of d') and d'') consists of a mixture of PA6/66 (Poly-caprolactam/hexamethylene diamine/adipic acid) with PA 6I/6T (Polyhexamethylene diamine/isophthalic acid/terephthalic acid). Preferably, the aliphatic polyamide content is between 70% and 97%, more preferably between 85% and 95%, and the aromatic polyamide content is between 3% and 30%, and more preferably between 5% and 15% .
[00186] Preferably, the percentage by weight of the sum of the polyamide resin(s) of the layers d') and d'') in the entire film is comprised between 10% and 55%, preferably between 15% and 50%, more preferably 20% and 50% and even more preferably between 20% and 45%.
Preferably, in such a mixture the percentage of said aliphatic polyamides is at least 70%, 80%, and more preferably at least 90%.
[00188] Preferably, said layers (d') and (d'') consist of said mixture.
[00189] Preferably, the layers (d') and (d'') are positioned respectively between the external heat-sealable layer (a) and the internal PVDC gas barrier layer (c), and between the layer of inner PVDC gas barrier (c) and outer layer (b).
[00190] This large amount of polyamide(s) further increases the abuse resistance of these heat shrink films. It has been found that, by using the process described in this document with this layer configuration, very large amounts of polyamide(s) can be incorporated without affecting the stability of the process. The films thus obtained were also easily oriented.
[00191] The films of the present invention may also comprise one or more additional layers e) comprising the resin based on acrylate, ethylene-vinyl acetate (EVA) or polyolefin.
[00192] The additional layer(s) may be inner layer(s) and/or outermost layer(s) of the film. Preferably, layer e) is an inner layer.
[00193] Preferably, one or more additional layers e) is (are) placed between at least one inner PVDC barrier layer c) and preferably the outer aromatic (co)polyester layer b).
As used herein, the term "acrylate-based resin" refers to homopolymers, copolymers including, for example, bipolymers, terpolymers, etc., which have an acrylate moiety on at least one of the units of repeats that form the main chain of the polymer. Generally speaking, acrylate-based resins are also known as polyalkyl acrylates. Acrylate resins or polyalkyl acrylates can be prepared by any method known to those skilled in the art. Suitable examples of such resins for use in the present invention include ethylene/methacrylate (EMA) copolymers, ethylene/butyl acrylate (EBA) copolymers, ethylene/methacrylic acid (EMAA), ethylene/methyl methacrylate (EMMA) copolymers , optionally modified with carboxylic or preferably anhydride functionality, ionomers and the like. Such as LOTRIL 18 MA 002 from Arkema (EMA), Elvaloy AC 3117 from Du Pont (EBA), Nucrel 1202HC from Du Pont (EMAA), Surlyn 1061 from Du Pont (ionomer).
[00195] As used herein, the term "EVA" refers to the copolymers of ethylene and vinyl acetate. EVA is a copolymer formed from ethylene and vinyl acetate monomers in which the ethylene units are present in a larger amount and the vinyl acetate units are present in a smaller amount, optionally modified with carboxylic or preferably anhydride functionalities. The typical amount of vinyl acetate can range from about 5 to about 20%. Examples are Escorene FL0014 by Exxon, ELVAX 3165 by Du by Pont and EVA 1003 VN4 by Total.
[00196] The "polyolefin" useful for the composition of the additional layer consists of ethylene homopolymers and ethylene copolymers, and most preferred are ethylene-alpha-olefin copolymers, in particular those with a density of from about 0.895 to about from 0.925 g/cm3 and more preferably from about 0.900 to about 0.920 g/cm3 and mixtures thereof.
[00197] Particularly preferred ethylene polymers are Affinity or Attane supplied by Dow, Exceed by Exxon and Exact by Dex.
Among polyolefins, homopolymers or copolymers of "polypropylene" (PP) are particularly preferred. PP homopolymers refer to propylene polymers having a density greater than 0.890 g/cm3, preferably greater than 0.895 g/cm3 and/or an MFI melt flow index of 0.5 to 15 g/ 10 min (at 230°C and 2.16 kg), preferably from 1.0 to 10 g/10 min, and more preferably from 2.5 to 7.0 g/10 min.
[00199] PP copolymers refer to random copolymers of propylene with ethylene or butene, which have an ethylene or butene content not greater than 15%, preferably not greater than 10%, and have a higher density than 0.890 g/cm3, preferably greater than 0.895 g/cm3 and/or an MFI melt flow index of 0.5 to 15 g/10 min (at 230°C and 2.16 kg), preferably from 1.0 to 10 g/10 min, and more preferably from 2.5 to 7.0 g/10 min; random terpolymers of propylene with ethylene and butene, in which the total amount of ethylene and butene comonomers is not greater than 18%, preferably not greater than 14% and/or the butene/ethylene ratio is greater than than 2, preferably greater than 4, and have a density greater than 0.890 g/cm3, preferably greater than 0.895 g/cm3 and/or a melt flow index MFI of 0.5 to 15 g/10 min (at 230°C and 2.16 kg), preferably from 1.0 to 10 g/10 min, and more preferably from 2.5 to 7.0 g/10 min.
Particularly preferred propylene polymers are ELTEX PKS 607 from Solvay, ELTEX PKS359 or PKS350 from Ineos and Moplen HP515M from Lyondell Basell.
[00201] The thickness of layer e) may be within the range of 1 to 30 microns, more preferably 1 to 20 microns and even more preferably 1 to 10 microns.
[00202] In a preferred embodiment of the present films, these additional layers e), optionally with one or more layers d) and/or f), if present, act as insulating layers during substrate coating, thereby protecting the layer PVDC thermodegradable against excessive heating coming from the aromatic (co)polyester layer(s) b).
[00203] Additional bonding layers f) to improve adhesion between the layers may be present.
[00204] Furthermore, the bonding layers f) also act as insulating layers.
[00205] The bonding layers f) can be arranged between the respective layers in the case that a sufficient adhesion is not ensured between the adjacent layers. The adhesive resin can comprise one or more polyolefins, one or more modified polyolefins, or a mixture thereof. Specific non-limiting examples thereof may include: ethylene-vinyl acetate copolymers, ethylene-(meth)acrylate copolymers, ethylene-alpha-olefin copolymers, any of the above modified with carboxylic or preferably anhydride functionalities, elastomers , and a mixture of these resins.
Particularly preferred resins are ADMER NF 538E from Mitsui Chemical, Plexar PX3227X09 or Plexar PX3227 from Lyondell Basell, OREVAC 18211 from Arkema and BYNEL 3101 or Bynel 39E660 or Bynel CXA21E6787 from DuPont.
[00207] The bonding layer f) may comprise at least one styrene-based polymer selected from the group consisting of styrene-ethylene-butylene-styrene copolymer, styrene-butadiene-styrene copolymer, styrene-isoprene-styrene copolymer , styrene-ethylene-butadiene-styrene copolymer and styrene(ethylene-propylene rubber)-styrene copolymer.
[00208] In one embodiment, the inner bonding layer comprises the styrene-based polymer in an amount of at least 5% by weight, based on the weight of the layer; or from 5 to 100% by weight, or from 8 to 100% by weight, or from 10 to 100% by weight, or from 10 to 90% by weight, or from 10 to 80% by weight, or from 10 to 60 % by weight, or from 10 to 40% by weight, or from 10 to 30% by weight, or from 10 to 25% by weight, or from 10 to 20% by weight, or from 10 to 15% by weight, with based on layer weight.
[00209] In one embodiment, the styrene-based polymer comprises at least one member selected from the group consisting of: styrene-ethylene-butylene-styrene copolymer, styrene-butadiene-styrene copolymer, styrene-isoprene-styrene copolymer , styrene-ethylene-butadiene-styrene copolymer, styrene(ethylene-propylene rubber)-styrene copolymer.
[00210] In one embodiment, the binding layer f) comprises a mixture of a styrene-based polymer and an acrylate-based polymer. The styrene-based polymer can consist of 5 to 95% by weight of the mixture, and the acrylate-based polymer consists of 5 to 95% by weight of the mixture, and the styrene-based and acrylate-based polymers consist of together in at least 70% by weight of the mixture. The styrene-based polymer may consist of 5 to 40% by weight of the blend, and the acrylate-based polymer may consist of 60 to 95% by weight of the blend. In one embodiment, the styrene-based polymer may consist of 10 to 20% by weight of the blend, and the acrylate-based polymer may consist of 80 to 90% by weight of the blend.
[00211] In one embodiment, the binding layer f) comprises a blend of styrene-based polymer and a cyclic polymer. The styrene-based polymer may consist of 5 to 95% by weight of the blend, and the cyclic polymer may consist of 5 to 95% by weight of the blend, wherein the styrene-based polymer and the cyclic polymer consisting together in at least 70% by weight of the mixture. The styrene-based polymer may consist of 60 to 95% by weight of the blend, and the cyclic polymer may consist of 5 to 40% by weight of the blend. The styrene-based polymer may consist of 80 to 90% by weight of the blend, and the cyclic polymer may consist of 10 to 20% by weight of the blend.
[00212] In one embodiment, the binding layer f) comprises a blend of styrene-based polymer and a modified polyolefin. In one embodiment, the styrene-based polymer may consist of 5 to 95% by weight of the blend, and the modified polyolefin may consist of 5 to 95% by weight of the blend, and the styrene-based polymer and the modified polyolefin may consist of together in at least 70% by weight of the mixture. The styrene-based polymer may consist of 5 to 40% by weight of the blend, and the modified polyolefin may consist of 60 to 95% by weight of the blend. The styrene-based polymer may consist of 10 to 20% by weight of the blend, and the modified polyolefin may consist of 80 to 90% by weight of the blend.
[00213] In one embodiment, the binding layer f) comprises a mixture of the styrene-based polymer, an acrylate-based polymer and a cyclic polymer.
[00214] In one embodiment, the styrene-based polymer consists of 5 to 90% by weight of the blend, the acrylate-based polymer consists of 5 to 90% by weight of the blend, and the cyclic polymer consists of 5 to 90 % by weight of the mixture, and the styrene-based polymer, the acrylate-based polymer and the cyclic polymer together comprise at least 70% by weight of the mixture. The styrene-based polymer may consist of 5 to 40% by weight of the blend, the acrylate-based polymer may consist of 20 to 90% by weight of the blend, and the cyclic polymer may consist of 5 to 40% by weight of the blend. mixture. The styrene-based polymer may consist of 10 to 20% by weight of the blend, the acrylate-based polymer may consist of 30 to 80% by weight of the blend, and the cyclic polymer may consist of 10 to 20% by weight of the blend. .
[00215] In one embodiment, the binding layer f) comprises a blend of a styrene-based polymer, an acrylate-based polymer and a modified polyolefin. In one embodiment, the styrene-based polymer consists of 5 to 90% by weight of the blend, the acrylate-based polymer consists of 5 to 90% by weight of the blend, and the modified polyolefin consists of 5 to 90% by weight of the blend. of the mixture, and the styrene-based polymer, the acrylate-based polymer and the modified polyolefin together comprise at least 70% by weight of the mixture. The styrene-based polymer may consist of 5 to 40% by weight of the blend, the acrylate-based polymer may consist of 20 to 90% by weight of the blend, and the modified polyolefin may consist of 5 to 40% by weight of the blend . The styrene-based polymer may consist of 10 to 20% by weight of the blend, the acrylate-based polymer may consist of 30 to 80% by weight of the blend, and the modified polyolefin may consist of 10 to 20% by weight of the blend. mixture.
[00216] In one embodiment, the binding layer f) comprises a blend of styrene-based polymer, a cyclic polymer and a modified olefin copolymer. In one embodiment, the styrene-based polymer consists of 5 to 90% by weight of the blend, the cyclic polymer consists of 5 to 90% by weight of the blend, and the modified olefin copolymer consists of 5 to 90% by weight of the mixture, and the styrene-based polymer, the cyclic polymer and the modified polyolefin together comprise at least 70% by weight of the mixture. The styrene-based polymer may consist of 5 to 40% by weight of the blend, the cyclic polymer may consist of 20 to 90% by weight of the blend, and the modified olefin copolymer may consist of 5 to 40% by weight of the blend. The styrene-based polymer may consist of 10 to 20% by weight of the blend, the cyclic polymer may consist of 30 to 80% by weight of the blend, and the modified olefin copolymer may consist of 10 to 20% by weight of the blend.
[00217] In one embodiment, the binding layer f) comprises a blend of styrene-based polymer, an acrylate-based polymer, a cyclic polymer and a modified polyolefin. The styrene-based polymer may consist of 5 to 85% by weight of the blend, the acrylate-based polymer may consist of 5 to 85% by weight of the blend, the cyclic polymer may consist of 5 to 85% by weight of the blend and the modified polyolefin may consist of 5 to 85% by weight of the mixture, wherein the styrene-based polymer, the acrylate-based polymer, the cyclic polymer and the modified polyolefin together consist of at least 70% by weight of the mixture. The styrene-based polymer may consist of 10 to 40% by weight of the blend, the acrylate-based polymer may consist of 10 to 40% by weight of the blend, the cyclic polymer may consist of 10 to 40% by weight of the blend and the modified polyolefin may consist of 10 to 40% by weight of the mixture. The styrene-based polymer may consist of 10 to 20% by weight of the blend, the acrylate-based polymer may consist of 10 to 80% by weight of the blend, the cyclic polymer may consist of 5 to 20% by weight of the blend and the modified polyolefin can consist of 10 to 80% by weight of the mixture.
[00218] If the binding layer f) comprises a modified polyolefin, the modified polyolefin may comprise at least one member selected from the group consisting of a grafted anhydride functionality, a copolymerized anhydride functionality and a mixture of the polyolefin and another polymer which has an anhydride functionality.
[00219] If the bonding layer f) comprises an acrylate-based polymer, the acrylate-based polymer may comprise at least one member selected from the group consisting of ethylene/methyl acrylate copolymer, ethylene/methyl acrylate copolymer. ethyl, ethylene/butyl acrylate copolymer and ethylene/vinyl acetate copolymer.
[00220] If the binding layer f) comprises a cyclic polymer, the cyclic polymer may comprise at least one member selected from the group consisting of ethylene/norbornene copolymer and ethylene/tetracyclododecene copolymer, and cyclic olefin polymer.
[00221] The binding layer f) may comprise a polymer mixture comprising: - from 50% to 85% by weight of at least one copolymer of ethylene - modified alpha-olefin; - from 50% to 15% by weight of at least one copolymer of ethylene-modified vinyl acetate which has a percentage by weight of vinyl acetate between 6% and 15%, preferably: - from 60% to 80% by weight of at least one modified ethylene-alpha-olefin copolymer; - from 40% to 20% by weight of at least one copolymer of ethylene-vinyl acetate which has a percentage by weight of vinyl acetate between 6% and 15%, even more preferably: - from 65% to 75% by weight of at least one modified ethylene-alpha-olefin copolymer; - from 35% to 25% by weight of at least one copolymer of ethylene-vinyl acetate which has a percentage by weight of vinyl acetate between 6% and 15%.
[00222] In a preferred embodiment, the inner layer consists of said copolymers in said amounts.
[00223] Modified ethylene-alpha-olefin copolymer generally includes ethylene copolymers with one or more selected alpha-olefin comonomers (C4-C10) such as butene-1, hexene-1, octene-1, etc., in that copolymer molecules comprise long chains with relatively few side chain branching or crosslinked structures.
[00224] Modified ethylene-alpha-olefin copolymers, which can be used for blending in accordance with the first objective of the invention, are selected from modified heterogeneous and homogeneous polymers, such as modified linear low density polyethylene (LLDPE) having a density typically in the range of about 0.900 g/cm3 to about 0.930 g/cm3, the modified linear medium density polyethylene (LMDPE) having a density typically in the range of about 0.930 g/cm3 to about 0.945 g/ cm3, and very low and ultra-low density polyethylene (VLDPE and ULDPE) modified with a density lower than about 0.915 g/cm3, typically in the range of 0.868 to 0.915 g/cm3.
[00225] The term "modified ethylene alpha-olefin copolymer" refers to ethylene-alpha-olefin copolymer having an anhydride functionality, as defined immediately below, grafted thereto and/or copolymerized with the same and /or mixed with it.
[00226] Preferably, such modified polymers have the anhydride functionality grafted onto or polymerized therewith, rather than merely being mixed with them.
[00227] As used herein, the term "modified" refers to a chemical derivative, for example, one that has any form of anhydride functionality, such as maleic acid anhydride, crotonic acid, citraconic acid anhydride , itaconic acid, fumaric acid, etc., if grafted onto a polymer, copolymerized with a polymer, or blended with one or more polymers, and is also inclusive of derivatives of such functionalities, such as acids, esters, and salts of metals derived from them. Grades of maleic anhydride are particularly preferred.
In the preferred embodiment, the density of the modified ethylene-alpha-olefin copolymer is in the range of 0.905 g/cc to 0.927 g/cc and even more preferably in the range of 0.910 g/cc to 0.920 g/cc.
[00229] The melt flow index of the modified ethylene-alpha-olefin copolymer, measured at 190°C, 2.16 kg (ASTM standard D1238) is normally in the range of 2 to 10 g/10 min, preferably of at least 3 g/10 min, and even more preferably of at least 4 g/10 min.
Particularly preferred are Admer® NF 538E (anhydride modified very low density polyethylene, density 0.91 g/cc, melt index 4.1 g/10 min at 190°C, 2.16 kg) and Admer® NF518E (polyethylene modified with maleic anhydride, low linear density, density 0.91 g/cc, melt index 3.1 g/10 min at 190°C, 2.16 kg) marketed by Mitsui.
[00231] Other commercially available resins that can be used are, for example: Bynel 4125 from DuPont (melt flow rate 2.5 g/10 min at 190°C, 2.16 kg, density 0.926 g/cc ), Plexar PX3243 from Lyondell Basell (melt flux index 4.5 g/10 min at 190°C, 2.16 kg, density 0.927 g/cc), Amplify TY 1354 from Dow (melt flux index 3.0 g/10 min at 190°C, 2.16 kg, density 0.92 g/cc).
[00232] The copolymer of ethylene-vinyl acetate (EVA) is a copolymer between ethylene and vinyl acetate, (this monomer is represented by the general formula: CH3COOCH=CH2).
[00233] In the EVA modified copolymer, the ethylene units are present in a larger amount and the vinyl acetate units are present in a smaller amount. The typical amount of vinyl acetate can range from about 5 to about 20%. For the mixture according to the first object of the present invention, the percentage by weight of vinyl acetate must be between 6% and 15%, preferably between 8% and 13%.
[00234] The melt flow index of such resins is typically in the range of 2.0 to 5.5 g/10 min, preferably 2.5 to 4.5 g/10 min (measured at 190°C, 2.16 kg, as per ASTM standard D1238).
[00235] The melting point of such resins is preferably in the range of 87°C to 100°C.
[00236] The term "modified ethylene-vinyl acetate copolymer" refers to ethylene-vinyl acetate copolymer which has an anhydride functionality, as defined immediately below, grafted thereto and/or copolymerized therewith and/or mixed with it.
[00237] Preferably, such modified polymers have the anhydride functionality grafted onto or polymerized therewith, rather than merely being mixed with them.
[00238] As used herein, the term "modified" refers to a chemical derivative, for example, one that has any form of anhydride functionality, such as maleic acid anhydride, crotonic acid anhydride, acid anhydride citraconic, itaconic acid, fumaric acid, etc., if grafted onto a polymer, copolymerized with a polymer, or mixed with one or more polymers, and is also inclusive of derivatives of such functionalities, such as acids, esters and salts of metal derived from them. Grades of maleic anhydride are particularly preferred.
Exemplary commercially available modified EVA resins are: Bynel 3101 from DuPont, Bynel 30E671 from DuPont, Orevac 9314 from Arkema.
[00240] Preferably, the mixture used in the inner bonding layer comprises from 65% to 75% by weight of at least one modified ethylene-alpha-olefin copolymer having a density of between 0.910 and 0.920 g/cc and of 35 % to 25% by weight of at least one modified ethylene vinyl acetate copolymer having a vinyl acetate weight percentage of between 6% and 15%, and more preferably between 8% and 13%.
[00241] According to an embodiment, a bonding layer f) is directly adhered to the outer film layer.
[00242] According to another embodiment, a bonding layer (f) is adhered directly to each side of the barrier layer (c). The composition of the two bonding layers (f) can be the same or different depending on the chemical nature of the additional layers adjacent to said two bonding layers. In the preferred embodiment, the bonding layers (f) adjacent to the PVDC have the same composition.
[00243] According to another embodiment, a bonding layer (f) is adhered directly to one side of the abuse layer (d) or (d').
[00244] The thickness of one or more additional layers d) and/or e) and/or f) interposed between the inner PVDC layer (c) and the polyester layer (b), is at least 20%, preferably at least 25%, and more preferably at least 30% of the total film thickness.
[00245] In all film layers, the polymer components may contain appropriate amounts of additives normally included in such compositions. Some of these additives are preferably included in the outer layers or one of the outer layers, while others are preferably added to the inner layers. These additives include slip and anti-blocking agents such as talc, waxes, silica, and so on, antioxidants, stabilizers, plasticizers, fillers, pigments and dyes, crosslink inhibitors, crosslink enhancers, UV absorbers, odor absorbers, scavengers oxygen, antistatic agents, anti-fog agents or compositions, and other additives still known to those skilled in the art of packaging films.
[00246] The non-exhaustive exemplary sequences of the film layers of the present invention are listed below: a/f/c/f/b, a/f/d/f/c/f/b, a/f/c/ f/d/f/b, a/f/d'/c/d''/f/b, a/e/f/c/f/e/f/b, a/f/d'/f/ c/f/f/d''/f/b, a/f/d'/f/c/f/d''/f/ba/e/f/c/f/b, a/f/c /f/e/b, a/f/b/f/c/f/e, a/f/b/f/e/f/c/f/e, a/f/b/f/e/f /c/f/d, a/f/c/f/b/f/e, a/f/c/f/e/f/b, a/f/b/f/e/f/c/f /d, a/f/d'/c/d'Tf/e/b, a/e/f/dVc/dVf/e/b... where: - a, b, c, d, d' , d'' and f have the same meaning as described previously and - when the same letter is written more than once in a sequence, these letters can represent layers that have an identical or different chemical nature.
[00247] The preferred sequences of layers for the films of the present invention are as follows: a/f/c/f/b, a/f/d/f/c/f/b, a/f/c/f/ d/f/b, a/f/d'/c/d''/f/b, a/e/f/c/f/e/f/b, a/f/d'/f/c/ f/f/d''/f/b, a/f/d'/f/c/f/d''/f/ba/e/f/c/f/b, a/f/c/f /e/b, a/f/c/f/e/f/b, a/f/d'/c/d''/f/e/b, a/e/f/d'/c/d ''/f/e/b.
[00248] Most preferred sequences of layers for the films of the present invention are as follows: a/e/f/c/f/e/f/b, a/f/d'/c/d''/ f/b, a/f/d'/f/c/f/f/d''/f/b, a/f/d'/f/c/f/d''/f/b, a/ f/d'/c/d''/f/e/b, a/e/f/d'/c/d''/f/e/b.
[00249] The films according to the present invention are heat shrinkable, that is, they exhibit a % free shrinkage in each of the LD and TD directions of at least 10% at 85°C (according to D2732 standard of ASTM), preferably at least 15%, even more preferably at least 20% at 85°C and a total free contraction at 85°C of at least 45%, preferably at least 55% and still with most preferably at least 60%.
[00250] The films according to the present invention exhibit a maximum shrinkage stress of at least 20 kg/cm2 each between the LD and the TD, preferably of at least 25 kg/cm2 each between the LD and the TD, more preferably at least 25 kg/cm2 in one of the LD and the TD and greater than 30 kg/cm2 in the other of the two directions, measured as described under the experimental part of the present invention.
[00251] The films according to the present invention exhibit a maximum shrinkage stress of at most 55 kg/cm2, preferably 50 kg/cm2 and even more preferably 45 kg/cm2 in at least one of the two directions LD and TD
[00252] The films according to the present invention exhibit a residual shrinkage stress in each of the LD and the TD of at least 25 kg/cm2, preferably of at least 27 kg/cm2 and more preferably of at least 30 kg/cm2 at 5°C, measured as described under the experimental part of the present invention.
[00253] The films of the present invention exhibit very good processability and can support high orientation ratios in both directions.
[00254] Furthermore, due to their rigidity, the films of the present invention can be printed by any printing method known in the prior art.
[00255] The films of the present invention are endowed with good optical properties.
[00256] In particular, the present films are characterized by haze values before shrinkage lower than 20%, preferably lower than 15%, more preferably lower than 12, measured in accordance with the D1003 standard of ASTM.
[00257] Furthermore, the present films are characterized by gloss values before shrinkage greater than 110 g.u., preferably greater than 120 g.u. and even more preferably greater than 130 g.u., measured in accordance with ASTM Standard D2457.
Particularly preferred embodiments of the present films are as follows: a multi-layer coextruded biaxially oriented hot shrinkable barrier film comprising an external heat sealable layer (a); an outer layer (b) which is not directly adhered to the heat-sealable layer (a), wherein said layer (b) comprises one or more aromatic (co)polyesters having a melting point higher than 225° C, at least one internal gas barrier layer (c) consisting of polyvinylidene chloride, and said film is characterized by - A) a total free contraction at 85°C of at least 45%, and - B) a maximum contraction stress in each of the longitudinal and transverse directions of at least 20 kg/cm2 and - C) a residual shrinkage stress at 5°C in each of the longitudinal and transverse directions of at least 25 kg/cm2, where the contraction total free is measured according to ASTM standard D2732, maximum shrinkage stress and residual shrinkage stress are measured according to the method of the present invention, or ii) a coextruded biaxially oriented barrier heat shrink wrapping film layer comprising an external heat sealable layer. rna(a); an outer layer (b) which is not directly adhered to the heat-sealable layer (a), wherein layer (b) is the only layer comprising aromatic (co)polyesters and wherein said layer (b) comprises one or plus polyethylene terephthalates which have a melting point higher than 225°C and where the weight percentage of polyethylene terephthalates in the entire film is at least 15%, at least one internal gas barrier layer (c) which consists of polyvinylidene chloride, and said film is characterized by - A) a total free shrinkage at 85°C of at least 45%, and - B) a maximum shrinkage stress in each of the longitudinal and transverse directions of at least 20 kg/cm2 and - C) a residual shrinkage stress at 5°C in each of the longitudinal and transverse directions of at least 25 kg/cm2, where the total free shrinkage is measured in accordance with ASTM standard D2732, a maximum shrinkage stress and residual shrinkage stress are measured according to the prosthesis method. In the present invention, or iii) a multi-layer co-extruded biaxially oriented barrier heat shrink packaging film comprising an external heat-sealable layer (a); an outer layer (b) which is not directly adhered to the heat-sealable layer (a), wherein layer (b) is the only layer comprising aromatic (co)polyesters and wherein said layer (b) comprises one or plus polyethylene terephthalates which have a melting point higher than 225°C and where the weight percentage of polyethylene terephthalates in the entire film is at least 5%, at least one internal gas barrier layer (c) consisting of polyvinylidene chloride, at least two internal abuse-resistant layers (d') and (d''), which have the same composition and comprise at least 90% by weight of a mixture of aliphatic and aromatic polyamides; wherein the percentage by weight of said polyamides in the entire film is between 20% and 50%; and said film is characterized by - A) a total free contraction at 85°C of at least 45%, and - B) a maximum shrinkage stress in each of the longitudinal and transverse directions of at least 20 kg/cm2 and - C ) a residual shrinkage stress at 5°C in each of the longitudinal and transverse directions of at least 25 kg/cm2, where the total free shrinkage is measured in accordance with ASTM standard D2732, the maximum shrinkage stress and the stress residual shrinkage are measured according to the method of the present invention, or iv) a multi-layer coextruded biaxially oriented barrier heat shrinkable packaging film comprising an external heat-sealable layer (a); an outer layer (b) which is not directly adhered to the heat-sealable layer (a), wherein layer (b) is the only layer comprising aromatic (co)polyesters and wherein said layer (b) comprises one or plus polyethylene terephthalates which have a melting point higher than 225°C and where the weight percentage of polyethylene terephthalates in the entire film is at least 5%, at least one internal gas barrier layer (c) consisting of polyvinylidene chloride, wherein one or more additional layers selected from abuse-resistant layers d), additional e) and bonding f) are interposed between at least one inner PVDC layer (c) and the polyester layer outer (b), wherein the total thickness of said interposed layers is at least 20% of the total film thickness, and said film is characterized by - A) a total free contraction at 85°C of at least 45%, and - B) a maximum shrinkage stress in each of the longitudinal and transverse directions of at least 20 kg/cm2 and - C) a residual shrinkage stress at 5°C in each of the longitudinal and transverse directions of at least 25 kg/cm2, where the total free shrinkage is measured in accordance with ASTM standard D2732 , the maximum shrinkage stress and the residual shrinkage stress are measured according to the method of the present invention.
[00259] A second object of the present invention is an article for packaging in the form of a seamless tube wherein the heat sealing layer is the innermost layer of the tube or in the form of a flexible container such as a pouch or a bag which comprises a film according to the first objective.
[00260] The article in the form of a seamless tube can be manufactured by extrusion coating through a round matrix of the layers of the present films as previously defined, followed by optional irradiation, and orientation of trapped bubbles, as described in follow.
[00261] The resulting seamless tube can be directly processed to provide flexible packaging containers or, alternatively, can be converted to a flat film by means of slits before being wound into rolls or further reprocessed.
[00262] The flexible container can be obtained by heat sealing the film to itself.
[00263] The self-sealing of the film to form a flexible container according to the present invention can be carried out in a fin seal mode and/or a flap seal mode, preferably by heat sealing the heat sealable layer therein same, that is, in a finned sealing mode.
[00264] Flexible heat-shrinkable containers may be in the form of an end-sealed (ES) bag, a side-sealed (or transverse TS) bag, or a pouch.
[00265] In one embodiment, the flexible container is a flat end-sealing bag made from seamless tubing, wherein the end-sealing bag has an open top, first and second folded side edges, and a seal. end through a bottom of the bag.
[00266] In one embodiment, the flexible container is a flat side seal bag made from seamless tubing, wherein the side seal bag has an open top, a folded bottom edge, and first and second side seals.
[00267] In one embodiment, the flexible container is a flat V-shaped side seal bag made from seamless tubing, wherein the side seal bag has an open top, a folded bottom edge, and first and second side seals. Said first and second side seals can be fully folded with respect to the open top, thereby forming a triangular or nearly triangular bag or, preferably, they can be partially straight (i.e. perpendicular to the open top) and partially folded, giving a trapeze-like shape.
[00268] In one embodiment, the flexible container is a flat pouch made by heat sealing two flat films together, wherein the pouch has an open top, a first side seal, a second side seal and a seal bottom.
[00269] The flexible container optionally comprises at least one tear initiator.
[00270] The films of the present invention can be supplied in rolls and formed as pouches on a conventional horizontal machine such as, for example, the Flow Wrapper (HFFS) supplied by ULMA. In this type of packaging machine, the product is packed in a shrunk bag around the product and has three seals: two transverse seals and one longitudinal seal.
[00271] Pouch can also be formed immediately before being filled, eg according to Vertical Form Fill Seal (VFFS) packaging systems. The VFFS process is known to those skilled in the art and is described, for example, in patent document US4589247. The product is introduced through a central vertical filling tube into a formed tubular film that has been sealed longitudinally and transversely at its lower end. The pouch is then completed by sealing the upper end of the tubular segment, and tearing the pouch from the tubular film above it.
[00272] Other methods of manufacturing bags and pouches known in the prior art can be readily adapted to make receptacles or containers from the multilayer film according to the present invention.
[00273] A third object of the present invention is a packaging comprising an article for packaging according to the second objective and a product packaged in said article.
[00274] In the packaging, the product will be loaded in a heat shrink bag made of the film of the invention, the bag will be evacuated normally, and the open end of the same will be closed by means of heat sealing or by applying a clip, for example , of metal. This process is advantageously carried out inside a vacuum chamber where the evacuation and application of the clamp or heat seal is done automatically. After the bag is removed from the chamber, it is heat contracted by applying heat. This can be done, for example, by immersing the filled bag in a heat water bath or by conducting it through a heat water shower or hot air tunnel, or by means of infrared radiation. The heat treatment will produce a tight wrap that will conform very close to the contour of the product contained therein.
[00275] A common method of packaging food and non-food products is by means of pouches made on form-fill-seal machines, such as a Horizontal Form-Fill-Seal (HFFS) machine or a Vertical Form-Fill-Seal machine (VFFS).
[00276] An FFS machine, horizontal or vertical, typically includes a former to form a flat web of film in a tubular configuration, a longitudinal seal to seal the overlapping longitudinal edges of the film in the tubular configuration, a conveyor to feed the products into the film. tubular one after another in an appropriately spaced configuration, or a feed tube in the case of a VFFS machine, and a transverse seal to seal the tubular film transversely in one direction to separate the products into separate packages.
[00277] The transverse seal can be operated to simultaneously seal the bottom of the front pouch and the front of the next pouch pouch and to tear off the two seals as well as the front package from the sealed tubing from the front.
[00278] Alternatively, in the HFFS process, the transverse seal can be operated to tear the previous package from the next tubular portion and seal the front part of said tubular portion, thereby creating the sealed bottom of the next previous pouch. In this way, the anterior bag containing the product to be packaged has a longitudinal seal and only a transverse seal. It can then be subjected to vacuum before a second transverse seal hermetically seals it. Also in this case, the oriented heat shrinkable thermoplastic film of the present invention is employed as the packaging material, and the package subjected to vacuum is then shrunk to achieve the desired appearance.
[00279] In FFS processes, although the transverse seals are always fin seals, the longitudinal seal can be a fin seal or a flap seal, i.e. a seal where the innermost heat sealable layer of the film is sealed to the outermost layer of the same film.
[00280] The polymers used for the thermoplastic packaging material and in particular for the heat sealing layer are selected in such a way that high sealing forces are provided. This effectively ensures that the final flexible container will properly protect the packaged product from the outside environment, without accidental openings or leaks.
[00281] The outermost or outer layer must also be selected with care as to its heat resistance during the sealing step. For example, it is advantageous to select a polymer for this layer that has a melting point higher than the sealing temperature.
[00282] A film barrier heat shrink bag of the invention has wide applications, preferably for food packaging, in particular for meat, poultry, cheese, processed and smoked meat, pork and lamb. The shrinkage properties of the film will in fact ensure complete shrinkage of the bag around the product so that the bag does not wrinkle, thereby offering an attractive packaging that also reduces drip loss. The bag will have adequate abuse resistance in order to physically survive the process of filling, evacuating, sealing, closing, heat shrinking, crating, shipping, unloading and storing in the supermarket retailer, and sufficient rigidity to also improve your retailer process. loading.
[00283] A fourth objective of the present invention is a process for the manufacture of a film according to the first objective of the present invention.
[00284] The manufacturing process according to the present invention provides for the coextrusion of a substrate comprising barrier layer(s) based on thermolabile PVDC(s), under moderate temperatures and conditions, and the subsequent coating of the substrate with a sequence of layers comprising the high melting aromatic (co)polyester layer (b) heated to higher temperatures.
[00285] In this way, the applicant was able to prevent the thermal degradation of the PVDC barrier layer c), even without using thermally insulated extrusion dies. Advantageously, the new process avoids costly interruptions to production cycles and prevents the generation of toxic gases associated with PVDC burning.
[00286] In the case where the present film includes more than one internal PVDC gas barrier layer (c), they will all be conveniently placed within the substrate structure.
[00287] In this way, the applicant was able to prevent the thermal degradation of the PVDC barrier layer(s) (c), by using traditional non-insulated extrusion dies.
[00288] Therefore, a process for the manufacture of the film of the first objective of the present invention comprises the steps of: - co-extrusion, through a round die, of a tubular substrate comprising at least one layer of sealant a) inside the tube and a barrier layer c) comprising PVDC; - sudden cooling of such substrate tube at temperatures between 5 and 15°C, preferably 8 to 10°C, after extrusion; - extrusion coating the substrate with a coating comprising at least one layer b), thereby obtaining an unoriented tubular film; - sudden cooling of the non-oriented tubular film at temperatures between 5°C and 30°C, preferably between 20 and 30°C; - heating the tubular film to a temperature that is higher than the Tg of all the polymeric resins that make up the layers and lower than the melting temperature of at least one of the resins used; - biaxial orientation of the tubular film at orientation ratios of about 2 to about 6, preferably between 3 and 5, and even more preferably between 3.1 and 4.5 in each of the longitudinal and transverse directions; - sudden cooling of the oriented tubular film, preferably in cold air, at a temperature of 4°C to 30°C, preferably of 5°C to 10°C.
[0288] It has been found that this combination of process and layer configuration is particularly advantageous for preparing the films of the present invention which comprise barrier resins such as PVDC and its copolymers, which tend to degrade at high temperatures.
[00289] Preferably, the process according to the present invention comprises the steps of: - co-extrusion, through a round die, of a tubular substrate comprising at least one sealing layer a) inside the tube, at least one barrier layer c) comprising PVDC and optionally an abuse resistant layer d') preferably between the sealant layer a) and the PVDC barrier layer c); - sudden cooling of such substrate tube at temperatures between 5 and 15°C, preferably 8 to 10°C, after extrusion; - extrusion coating the substrate with a coating comprising at least one layer b), and optionally, an abuse-resistant layer d''), thereby obtaining an unoriented tubular film; - sudden cooling of such unoriented tubular film at temperatures between 5°C and 30°C, preferably between 20 and 30°C; - heating the tubular film to a temperature that is higher than the Tg of all the polymeric resins that make up the layers and lower than the melting temperature of at least one of the resins used; - biaxial orientation of the tubular film at orientation ratios of about 2 to about 6, preferably between 3 and 5, even more preferably between 3.1 and 4.5 in each of the longitudinal and transverse directions, and - cooling blunt of the oriented tubular film, preferably in cold air, at a temperature of 4°C to 30°C, preferably of 5°C to 10°C.
[00290] Another process according to the present invention comprises the steps of: - co-extrusion, through a flat die, of a flat substrate comprising at least one sealing layer a), at least one barrier layer c) which comprises PVDC and optionally an abuse resistant layer d'); - sudden cooling of such substrate at temperatures between 5 and 15°C, preferably 8 to 10°C, after extrusion; - extrusion coating the substrate with a coating comprising at least one layer b), and optionally, an abuse-resistant layer d''), thereby obtaining a flat non-oriented tape; - sudden cooling of such non-oriented tape at temperatures between 5°C and 30°C, preferably between 20 and 30°C; - heating the tape to a temperature that is higher than the Tg of all the polymeric resins that make up the layers and lower than the melting temperature of at least one of the resins used; - biaxial orientation of the tape by means of a stretching arm, sequentially or simultaneously, preferably simultaneously, at orientation ratios of about 2 to about 6, preferably between 3 and 5, even more preferably between 3.1 and 4 .5 in each of the longitudinal and transverse directions, e - sudden cooling of the oriented film, preferably in cold air, at a temperature of 4°C to 30°C, preferably of 5°C to 10°C.
[00291] The multilayer substrate can be manufactured by means of co-extrusion, for example, as described in patent document US3891008, by using a flat or circular film matrix that allows the molding of the polymer melting mass into a one. tape or a tube.
[00292] According to a preferred process, the multilayer substrate is co-extruded through a round die to obtain a tube of molten polymeric material which is immediately quenched after extrusion without being expanded, and is optionally crosslinked.
[00293] The co-extrusion of the substrate is carried out in general at temperatures not higher than 250°C, preferably from 160 to 240°C, preferably from 170 to 230°C.
[00294] The coating step can be simultaneous, by coextrusion of all the remaining layers together, in order to simultaneously adhere all of them, one over the other, to the quench cooled pipe obtained in the first coextrusion step, or this coating step can be repeated as many times as the layers to be added.
[00295] Substrate coating is generally carried out by heating the coating resins to temperatures up to 280°C, typically 200°C to 270°C.
[00296] During extrusion coating, the tube is slightly inflated just to keep it in the shape of a tube and to prevent it from collapsing.
[00297] The optionally crosslinked tape or tube is then biaxially oriented.
[00298] In the case of a tube, the orientation is preferably carried out according to the so-called trapped bubble process. The tube is heated to a temperature that is greater than the Tg of all resins employed and less than the melting temperature of at least one of the resins employed, typically by being passed through a heat water bath or alternatively, by being passed through an IR oven or a hot air tunnel, and expanded, still at that temperature by the internal air pressure to achieve the transverse orientation and by a differential speed of the retaining rollers that hold "the trapped bubble" thereby obtained, to achieve the orientation longitudinal.
[00299] The heating temperature of the tube or tape varies from 70 to 98°C, depending on various factors such as the nature and amount of each resin inside the tube, the thickness of the tube, the orientation ratios to be obtained as it is known if an element versed in the state of the art.
[00300] Typical orientation ratios for the films of the present invention may be between about 2 and about 6 in each of the longitudinal and transverse directions, preferably between 3 and 5 in each direction, and even more preferably between 3.1 and 4.5 in each direction.
[00301] After being stretched, the film is rapidly cooled, preferably in cold air, to a temperature between 4 and 30°C, preferably between 5 and 10°C, while substantially maintaining its stretched dimensions to freeze from somehow the film molecules in their oriented state, and rolled up for further processing.
[00302] In a preferred embodiment, the films according to the first object of the present invention are manufactured by extrusion coating followed by the orientation of trapped bubbles.
[00303] Alternatively, the film according to the present invention can be obtained by coating by flat extrusion and biaxial stretching by a simultaneous or sequential frame process in stretcher.
[00304] In a preferred embodiment, the films according to the first objective of the present invention are manufactured by means of extrusion coating in round die followed by the process of orientation of the trapped bubbles.
[00305] The present manufacturing method includes preparing a first substrate by co-extruding some of the structure layers (at least the sealant layer a) and the PVDC barrier layer c) and subsequent deposition thereon of a coating comprising at least one layer of aromatic (co)polyester b) and the remaining optional layers, by means of extrusion coating.
[00306] Preferably, one or more additional layers, selected from abuse-resistant layers d), additional e) and bonding f), is present in the substrate and/or coating in order to improve the abuse performance of the final films, to join the adjacent layers and contribute to the thermal insulation of the PVDC barrier layer c).
[00307] These layers are properly placed on the substrate and/or coating, thereby providing a protective stack of the layers interposed between the gas barrier layer (c) and the polyester layer (b). Preferably, the total thickness of said interposed layers is at least 20%, at least 25%, at least 30% of the total film thickness.
[00308] If desired, the film or a portion thereof can be crosslinked, chemically or, preferably, by means of irradiation, in order to improve the mechanical properties and orientability. Typically, to produce the crosslink, the substrate or coated substrate is treated with an appropriate dosage of high energy electron radiation, preferably using an electron accelerator, where the dosage level is determined by standard dosimetry methods. Depending on the characteristics desired, such irradiation dosage may range from about 20 to about 200 kGi, preferably from about 30 to about 150 kGi.
[00309] Other accelerators, such as a Van der Graff generator or a resonant transformer, can be used.
[00310] Radiation is not limited to the electrons of an accelerator, since any ionizing radiation can be used.
[00311] The films according to the first objective of the present invention are preferably not irradiated. In particular, this is the case when at least one abuse-resistant layer d) as described herein is present in the film structure.
[00312] In such a case, the films already have the appropriate mechanical properties to be easily oriented, to support the packaging process and the handling of the packages obtained in this way and that do not need to be irradiated. Advantageously, the non-irradiated film will have better sealing properties.
[00313] In the most preferred embodiment of all, the layers d') and d'') comprise at least one polyamide and the percentage by weight of the sum of the polyamide resins of the layers d') and d'') in the entire film remains between 10% and 55%, preferably between 15% and 50%, more preferably between 20% and 50%, and even more preferably between 20% and 45% by weight.
[00314] This large amount of polyamide is desirable to impart high abuse resistance to these heat-shrinkable films, and it has been found that, by using the process described herein with this layer configuration, a large amount of polyamide can be incorporated without affecting process stability and shrinkage properties. The films thus obtained were also easily oriented.
[00315] The films of the present invention exhibit very good processability and can support high orientation ratios.
[00316] The films of the present invention can be printed easily.
[00317] The methods for printing the films of the present invention include any conventional method of printing plastic materials well known in the art.
[00318] A film that can be obtained according to any of the processes described in this document is also an object of the present invention.
[00319] A fifth objective of the present invention is the use of the films according to the first objective of the present invention to package dripping products, preferably fresh or processed meat, as illustrated by the experiments below. Examples
The present invention may also be understood by reference to the following examples, which are merely illustrative and should not be construed as limiting the scope of the present invention which is defined by the appended claims.
[00321] In the examples below, the polymers indicated in Table 1 below were employed. Table 1



[00322] The examples according to the invention and the comparative examples were collected in Table 2.
[00323] The film of Comparative Example 2 was manufactured according to the process shown in patent document EP2030784 for the preparation of films having an outer layer of polyamide instead of the outer layer of aromatic (co)polyester. In particular, the process described in Example 1 of patent document EP2030784 comprises extrusion coating a substrate with a coating comprising both the PVDC layers and the outer polyamide layer. In addition, the film of Comparative Example 2 comprises a stack of insulation layers between the barrier and the outer layer which has a thickness of about 9.7% of the total film thickness, i.e. a thickness within the range used for the corresponding interposed layers of similar films preceding disclosed in patent documents EP2030784 and WO2005011978. As can be appreciated from the experimental data below, the teachings of the prior art did not allow for the manufacture of the present films: in fact, neither did the extrusion coating disclosed in patent document EP2030784 - in which the PVDC layer and the layer of high melting point polymer are in fact coextruded - not even the plausibility of coextrusion taught in patent document WO2005011978, preserved the thermolabile PVDC layer from damage. Table 2


[00324] The layers in Table 2 are indicated in their extrusion order, from the sealing layer indicated as layer 1 to the outermost layer (the last one listed).
[00325] The multilayer films according to the present invention (Examples 1 to 3) and comparative films 1 and 2 were prepared by means of extrusion coating through a round matrix of a substrate consisting of: - layer 1 to layer 6 for Examples 2 and 3; - layer 1 to layer 5 for Example 1; - layer 1 to layer 3 for Comparative Examples 1 and 2.
[00326] The extruded multilayer tubular substrates thus obtained were then - quenched with a cascade of water to 8°C, - irradiated at 64 KGis (only for Comparative Example 1, whereas Examples 1, 2, 3 and Comparative Example 2 were not irradiated), and - coated by extrusion with: layers 7 to layers 10 for Examples 2 and 3, layers 6 to layers 8 for Example 1 and layers 4 to layers 6 for Comparative Examples 1 and 2.
[00327] The coated tube obtained in Examples 1 to 3 and Comparative Example 2 is then rapidly quenched to 25°C in water, the tube obtained in Comparative Example 1 is quenched to 12°C in water; and then the tubes obtained for all examples and Comparative Example 2 (with the exception of Comp Ex. 1) were biaxially oriented by being passed through a heat water bath maintained at a temperature of 94°C, while stopping o Ex. Comp. 1 the temperature was 90°C, so the tubes were inflated to begin transverse orientation and stretched by retaining rollers to begin longitudinal orientation.
[00328] The orientation ratios were: - about 3.4:1 in the longitudinal direction and 3.4:1 in the transverse direction for Ex. 1; - about 3.7:1 in the longitudinal direction and 4:1 in the transverse direction for Ex. Comp. 1; - about 3.4:1 in the longitudinal direction and 3.3:1 in the transverse direction for Ex. Comp. 2. Finally, the tubes obtained were cooled in cold air to 7°C.
[00329] During the manufacture of the films of the present invention (Examples 1 to 3), a very good process stability, in particular in the extrusion coating in terms of tube quality, and in the orientation of no bubble burst, a higher speed in-line and high tensile ratios, even if the films were not crosslinked, and with no negative effect on optical properties, were observed with respect to the comparative examples.
[00330] In addition, no degradation of the PVDC layer was observed, due to overheating during extrusion or contact with other hot layers present in the structure.
[00331] On the contrary, during the manufacture of the tube of comparative film 2, in particular during the coating of the substrate, degradation of PVDC was observed. In fact, bubbles formed in the molten mass and the resulting ribbon color was brown. After 20 minutes of extrusion coating, the situation was even worse, with the matrix barbs forming due to extensive degradation, and then tube collection was stopped.
[00332] Regardless of the unacceptable appearance of the tape, brown because of the thermal degradation of the PVDC and not transparent due to the presence of trapped bubbles, it was biaxially oriented as described above. The resulting film (Comparative Example 2) was not suitable for use because it was opaque, due to the presence of the same bubbles but enlarged, and slightly yellow to the naked eye.
[00333] The very bad appearance and optics - see the picture of the tube in Figure 2 - were enough by itself to discard the film.
[00334] The test methods used for property evaluations are summarized in Table 3 below. Table 3


[00335] Free Contraction: is the percentage of dimensional change in a 10 cm x 10 cm specimen of the film when subjected to a selected heat; it was measured following ASTM's standard test method D 2732 by immersing the specimen for 5 seconds in a heat bath of water at 85°C. The results of this test are shown in Table 4.
[00336] The Maximum Contraction Tension (kg/cm2) and the residual cold contraction tension (at 5°C) (kg/cm2) were measured by an internal method.
[00337] The maximum shrinkage stress is the maximum value of the stress developed by the materials during the heating/shrinkage process. The film specimens (2.54 cm x 14.0 cm, of which 10 cm are free for testing) are cut in the longitudinal (LD) and transverse (TD) directions of the film and clamped between two jaws, one of which is connected to a load cell. The two jaws hold the specimen in the center of a channel where an impeller blows hot or cold air and two thermocouples measure the temperature. Thermocouples are positioned as close as possible (less than 3 mm) to and in the middle of the specimens. The signals provided by the thermocouples (which are at a test temperature) and the load cell (which is the force) are sent to a computer where the software records these signals. The impeller starts blowing hot air and the force released by the sample is recorded in grams. The temperature is increased from 23°C to 90°C at a rate of about 3.2°C/s when blowing hot air and then decreased from 90°C to 5°C at a rate of 0.9°C/ s when blowing cold air. The maximum contraction stress is calculated by dividing the maximum force value in kg (peak force) of the specimen by the width (expressed in cm) and the average thickness of the specimen (expressed in cm) and expressed as kg/cm2. Residual cold shrinkage stress is calculated by dividing the force (in kg) exerted by the specimen at 5°C and the specimen width (in cm) and the average specimen thickness (in cm) and expressed as kg/cm2. Three specimens were measured for each film in each direction. The results of this test are shown in Table 4.
[00338] The drip loss was measured using an internal method. The meat was kept in the carcass for 24 hours at 2°C and then it was deboned, trimmed and cut before being vacuum-conditioned.
[00339] 32 pieces of loin (weighing 1.7 to 3.4 kg each, 4 pieces cut from 8 oxen) were packed with each of the bags tested (Example 1 and Comparative Example 1) in a Cryovac machine VS30 with the following values: - vacuum level: 5 mBar - sealing time, 1.5 seconds - cooling time, 2 seconds - Ultraseal sealing adjustment, 350 T - shrinkage of the packages at 85°C, through immersion in a heat water immersion tank for 3 seconds.
[00340] The packages were stored for 19 days under vacuum at 2 ± 2°C. 32 packages were evaluated for Example 1 and 32 packages were evaluated for Comparative Example 1. Drip loss was calculated (in percent by weight of meat) by subtracting the total weight of each block from the dry package weight and of dried meat, where the difference is a weight of the liquid that was exuded during storage. The average results of this test are shown in Table 4. The 0.3% difference in the total drop loss values between the pieces conditioned using Example 1 and Comparative Example 1 is significant at the 95% confidence level when subjected to a Student test.
Perforations at 23°C: puncture resistance is the resistance force that occurs when a perforator is pushed against a surface of the flexible film. A film sample is fixed to a specimen holder connected to a compression cell mounted on a dynamometer (an Instron strain tester); when the dynamometer is turned on, a perforator (a perforating ball, 5 mm in diameter, welded to a plunger) is applied against the film sample at a constant speed (30 cm/min) and the force required to perforate the sample is recorded graphically. This test is representative of the abuse resistance of packaging films. The results of this test are shown in Table 5.
[00342] Tensile Strength and Elongation at Break (ASTM standard D 882).
[00343] The tensile strength represents the maximum tensile load per unit area unit of the original cross-section of the test specimen required to break it, expressed as kg/cm2.
[00344] The elongation at break represents the increase in specimen length, measured at the time of break expressed as a percentage of the original length. Measurements were taken with an Instron strain tester equipped with a CM-type load cell (1 to 50 kg), in an environmental chamber set at 23°C, on specimens previously stored at 23°C and 50% relative humidity for a minimum of 24 hours. Tension and elongation measurements were recorded simultaneously and the results indicated are the mean values. The results of this test are shown in Table 5.
[00345] Elastic modulus at 23°C: was evaluated in accordance with ASTM D 882 standard. The results of this test are shown in Table 5.
[00346] Haze: was evaluated in accordance with ASTM D1003 standard. The results of this test are shown in Table 5.
[00347] Brightness at 60°: it was evaluated in accordance with ASTM standard D2457. The mean value of measurements made in the longitudinal and transverse directions was indicated. The results of this test are shown in Table 5.
[00348] As shown in Figure 2, which is an enlarged photo of a sample (A) taken from the tube of Comparative Example 2 and a sample (B) taken from the tube of Example 3, the simultaneous presence in the coating of the layer of PVDC and the PET layer, according to the manufacturing process suggested in patent document EP2030784, resulted in a damaged tape with a brown coloration. In fact, it is evident from the photo the presence of several bubbles.
[00349] As shown in Table 4, the films of the present invention exhibited high values of free shrinkage and high values of maximum shrinkage stress. Furthermore, the result is that these films were able to develop high values of residual shrinkage stress in cold conditions, thereby guaranteeing a very good appearance of the package during storage of the packages and a reduction in the drip loss of the meat.
[00350] Furthermore, these films have very good mechanical and optical properties, as demonstrated by the data indicated in Table 5.
[00351] In conclusion, the films of the present invention allow to obtain an excellent appearance of the package and a reduction of meat drip loss, while still maintaining a very good processability in extrusion and conversion level and ensuring a high resistance to abuse. Table 4
Table 5

While the present invention has been described with reference to preferred embodiments, it is to be understood that modifications and variations of the invention may occur without departing from the principles and scope of the invention, as those skilled in the art will readily understand. Therefore, such modifications are in accordance with the claims set out below.

权利要求:
Claims (23)
[0001]
1. A multi-layer coextruded biaxially oriented heat shrink barrier packaging film comprising at least: one external heat-sealable layer (a); a layer (b) which is not directly adhered to the heat-sealable layer (a), wherein said layer (b) comprises one or more aromatic (co)polyesters, wherein preferably said(s) Aromatic (co)polyester(s) has(have) a melting point higher than 225°C, higher than 230°C, higher than 235°C, at least one barrier layer to internal gases (c) comprising polyvinylidene chloride, wherein said film is characterized by the fact that: A) a total free contraction at 85°C of at least 45%, and B) a maximum contraction stress in each of the longitudinal and transverse directions of at least 20 kg/cm2 and C) a residual contraction stress at 5°C in each of the longitudinal and transverse directions of at least 25 kg/cm2, where the total free contraction is measured in accordance with ASTM standard D2732, maximum shrinkage stress and residual shrinkage stress are measured in accordance with the method of the present invention.
[0002]
2. Film according to claim 1, characterized in that layer (b) is the second outer layer.
[0003]
3. Film according to claim 1 or 2, characterized in that layer (b) is the only layer comprising aromatic (co)polyesters.
[0004]
4. Film according to any one of claims 1 to 3, characterized in that the percentage by weight of aromatic (co)polyester(s) in the entire film is at least 3%, at least 5% , at least 10%, at least 12%, at least 15%, at least 20%, at least 25%, or in the range from 3 to 60%, from 5 to 50%, from 10 to 40%, from 15 to 40%, from 20 to 40%.
[0005]
5. Film according to any one of claims 1 to 4, characterized in that the aromatic (co)polyesters are polyethylene terephthalates (PET) that have melting points higher than 225°C, higher than 230°C, higher than 235°C.
[0006]
6. Film according to any one of claims 1 to 5, characterized in that at least one internal gas barrier layer (c) comprises at least 70%, at least 80%, at least 90%, at least 95% polyvinylidene chloride, preferably consists of polyvinylidene chloride, and/or wherein the polymer for the heat sealable layer (a) is selected from ethylene-vinyl acetate (EVA) copolymers, ethylene-alpha-copolymers homogeneous or heterogeneous linear olefins, polypropylene (PP) copolymers, ethylene-propylene (EPC) copolymers, ionomers, and their mixtures.
[0007]
7. Film according to any one of claims 1 to 6, characterized in that it further comprises at least one internal abuse-resistant layer (d).
[0008]
8. Film according to claim 7, characterized in that it comprises at least two internal abuse-resistant layers (d') and (d''), said layers (d') and (d''), preferably having the same composition.
[0009]
9. Film according to claim 8, characterized in that the layers (d') and (d'') are positioned respectively between the external heat-sealable layer (a) and the internal gas barrier layer ( c), and between the inner gas barrier layer (c) and the outer layer (b).
[0010]
10. Film according to any one of claims 7 to 9, characterized in that at least one internal abuse-resistant layer (d) or at least two internal abuse-resistant layers (d') and (d'' ) comprise a resin selected from the group consisting of polyamides, polyesters and styrene-based polymers, preferably comprise polyamide(s), more preferably polyamide in an amount of at least 70%, 80%, 90% by weight based by weight of said layer(s), and more preferably said layer(s) consist of polyamide(s).
[0011]
11. Film according to any one of claims 7 to 10, characterized in that the at least one internal abuse-resistant layer (d) or at least two internal abuse-resistant layers (d') and (d' '), comprise a mixture of aliphatic and aromatic polyamides, and preferably consist of said mixture, more preferably of said mixture, the content of aliphatic polyamide(s) is between 70% and 97%, and the content of polyamide Aromatic(s) is between 3% and 30%.
[0012]
12. Film according to any one of claims 7 to 11, characterized in that the total amount of polyamide(s) in the entire film is between 10% and 55%, preferably between 15% and 50%, with more preferably 20% and 50%, and even more preferably between 20% and 45% by weight, and/or wherein the sum of the percentage by weight of the polyamide(s) and polyester(s) in the entire film is between 30% and 80%, preferably between 40% and 70%, and more preferably between 45% and 65%.
[0013]
13. Film according to any one of claims 1 to 12, characterized in that it further comprises one or more additional layers (e) comprising resin based on acrylate, ethylene-vinyl acetate (EVA) and/or polyolefins.
[0014]
14. Film according to any one of claims 1 to 13, characterized in that it comprises: at least two internal abuse-resistant layers (d') and (d''), at least one additional internal layer (e) , and optionally at least one additional inner bonding layer (f).
[0015]
15. Film according to any one of claims 1 to 14, characterized in that it further comprises one or more additional bonding layers (f), wherein said bonding layer(s) comprises (m) preferably: at least one styrene-based polymer; or a polymer blend comprising from 50% to 85% by weight of at least one modified ethylene-alpha-olefin copolymer; and from 50% to 15% by weight of at least one modified ethylene-vinyl acetate copolymer having a weight percentage of vinyl acetate between 6% and 15%.
[0016]
16. Film according to any one of claims 1 to 15, characterized in that one or more additional layers, selected from the abuse-resistant (d), additional (e) and bonding (f) layers are interposed between the at least one inner gas barrier layer (c) and the aromatic (co)polyester layer (b), wherein the total thickness of said interposed layer(s) being at least minus 20%, at least 25%, at least 30% of the total film thickness.
[0017]
17. Film according to any one of claims 1 to 16, characterized in that A) a total free contraction at 85°C of at least 55%, more preferably of at least 60%, B) a tension of maximum contraction in each of the longitudinal and transverse directions of at least 25 kg/cm2, more preferably at least 25 kg/cm2 in one of the longitudinal and transverse directions and greater than 30 kg/cm2 in the other of the two directions, and C) a residual shrinkage stress at 5°C in each of the longitudinal and transverse directions of at least 27 kg/cm2, more preferably at least 30 kg/cm2.
[0018]
18. Film according to any one of claims 1 to 17, characterized in that it has haze values lower than 20%, preferably lower than 15%, preferably lower than 12%, measured according to ASTM standard D1003, and/or brightness values greater than 110 gu, preferably greater than 120 gu, even more preferably greater than 130 gu, measured in accordance with ASTM standard D2457.
[0019]
19. An article for packaging in the form of a seamless tube, characterized in that the heat sealing layer (a) is the innermost layer of the tube, or in the form of a flexible container, comprising a film as defined in the claims 1 to 18.
[0020]
20. Packaging, characterized in that it comprises an article as defined in claim 19 and a product packaged in said article.
[0021]
21. Process for manufacturing a film as defined in claims 1 to 18, characterized in that it comprises the steps of: co-extruding, through a round or flat matrix, a tubular or flat substrate comprising at least one layer of sealant (a ) inside the tube and at least one barrier layer (c) comprising PVDC; abruptly cooling such tubular or flat substrate to temperatures between 5 and 15°C, preferably 8 to 10°C, after extrusion; extrusion coating the substrate with a coating comprising at least one layer of aromatic (co)polyester(s) (b), thereby obtaining an unoriented flat tubular film or tape; abruptly cool such unoriented tubular film or tape to temperatures between 5°C and 30°C, preferably between 20 and 30°C; heating the tubular film or flat tape to a temperature that is higher than the Tg of all polymeric resins that make up the layers and lower than the melting temperature of at least one of the resins employed; biaxially orienting the tubular film or the flat strip, said flat strip sequentially or simultaneously, preferably simultaneously, by stretching at orientation ratios of about 2 to about 6, preferably between 3 and 5, and with even greater preferably between 3.1 and 4.5 in each of the longitudinal and transverse directions, and abruptly cool the oriented or flat tubular film, preferably in cold air, to a temperature of 4°C to 30°C, preferably 5 °C to 10 °C.
[0022]
22. Process according to claim 21, characterized in that: coextruding the substrate is carried out at a temperature not higher than 250°C, preferably from 160 to 240°C, preferably from 170 to 230° Ç; and/or coating the substrate is carried out at temperatures of up to 280°C, typically 200°C to 270°C; and/or the heating temperature of the tube or ribbon ranges from 70 to 98°C; and/or the orientation ratios are between about 2 and about 6 in each direction, preferably between 3 and 5 in each direction, and even more preferably between 3.1 and 4.5 in each direction; and/or cooling the film is carried out at a temperature between 4 and 30°C, preferably between 5 and 10°C.
[0023]
23. Use of a film as defined in any one of claims 1 to 18, characterized in that it is for packaging dripping products, preferably fresh or processed meat.

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同族专利:

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公开号 | 公开日

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AU2015206003B2|2018-08-16|

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EP3094494B1|2018-01-03|

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US20170066228A1|2017-03-09|

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RU2016132829A3|2018-05-16|

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PL3094494T3|2018-06-29|

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ES2663514T3|2018-04-13|

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RU2658045C2|2018-06-19|

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BR112016015680A2|2017-08-08|

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US10239296B2|2019-03-26|

---

MX2016008983A|2016-12-08|

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JP2017507042A|2017-03-16|

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EP3094494A1|2016-11-23|

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CN105899358A|2016-08-24|

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BR112016015680A8|2020-06-09|

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WO2015107127A1|2015-07-23|

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RU2016132829A|2018-02-20|

---

CN105899358B|2019-08-13|

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NZ722752A|2021-11-26|

---

JP6489557B2|2019-03-27|

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CA2935440A1|2015-07-23|

---

AU2015206003A1|2016-08-18|

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法律状态:
2019-12-17| B06U| Preliminary requirement: requests with searches performed by other patent offices: procedure suspended [chapter 6.21 patent gazette]|

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2021-06-01| B09A| Decision: intention to grant [chapter 9.1 patent gazette]|

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2021-07-13| B16A| Patent or certificate of addition of invention granted [chapter 16.1 patent gazette]|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 15/01/2015, OBSERVADAS AS CONDICOES LEGAIS. |

优先权:

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申请号 | 申请日 | 专利标题

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EP14151344|2014-01-15|

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EP14151344.0|2014-01-15|

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PCT/EP2015/050718|WO2015107127A1|2014-01-15|2015-01-15|Multilayer pvdc barrier heat shrinkable films|

---