• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
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  • 优先权
    • 专利摘要:
    The present invention encompasses a process for preparing a substantially phenol-free impregnating resin, as well as the composition and end uses of the resin prepared by this process or otherwise. The process uses essentially only tannin as a substance containing phenolic OH groups, which is condensed with formaldehyde in the presence of a catalyst at an elevated temperature.
    公开号:FI20195118A1
    申请号:FI20195118
    申请日:2019-02-15
    公开日:2020-08-16
    发明作者:Tiina Pesonen；Peter Lingenfelter；Marika Jänis
    申请人:Prefere Resins Finland Oy；
    IPC主号:
    专利说明:

    BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a process for preparing a substantially phenol-free impregnating resin, to a resin prepared by this process or otherwise having a similar composition, and to end uses of the resin.
    Background Art In general, the resins used in impregnation are either phenolic resins or melamine resins, depending on the intended use of the impregnated paper. In many applications, phenolic resins - are a viable option, but melamine resins are used to achieve improved water resistance and similar properties. Some applications require the properties of both resins, so then a mixture of melamine and phenolic resin is used. Melamine resins are more expensive than phenolic resins in their raw materials, but they are safer because they do not contain free phenol, which is toxic.
    The structure and properties of the finished resin depend on the reaction conditions used in the preparation, such as, for example, the condensation temperature, the condensation time, the catalyst system, the solvent system and the formaldehyde / phenol molar ratio. The choice of reaction conditions depends on the end use for which the resin is prepared. 2 25 N The sufficiency of petrochemical raw materials such as phenol is limited and it would therefore be important 1 to replace them in the future with renewable natural raw materials such as lignin or tannin with a polyphenolic structure obtained from wood z. At the same time, a © e.g. environmental damage caused by phenol. D 30 S Replacement of phenol in phenol-formaldehyde resins with renewable natural raw materials is
    N already known.
    Efforts have been made to make binders from tannin using formaldehyde and aqueous sodium hydroxide. However, the compositions have been found to have, for example, poor workability time and insufficient water resistance. Thus, it has not been possible to produce a tannin resin with optimal properties.
    U.S. Pat. No. 3,254,438 discloses a modified phenolic resin composition in which tannin, paraformaldehyde and sodium hydroxide have been added to a finished phenolic formaldehyde resin, and a condensed reaction mixture in which a part of the phenolic resin formed has been replaced by tannin.
    WO2004058843 describes a resin composition consisting of a copolymer of tannin, an amino compound and an aldehyde prepared by reacting tannin with an aminoaldehyde. AU492815 in turn discloses the formation of a phenolic or amino resin utilizing a modified tannin condensate.
    US2582266 and GB703408 describe the modification of tannin with monochloroacetic acid and its condensation with formaldehyde in the presence of an alkaline catalyst. The preparation of formaldehyde resin using tannin and an alkaline catalyst is also described in KR20070104037, US2007125890 and ZA8001583. o According to known solutions, there is also a risk that the temperature of the reaction mixture> 25 rises uncontrollably, which affects the quality of the final product. At the same time, the consumption of N formaldehyde increases significantly.
    SUMMARY OF THE INVENTION It is an object of the present invention to obviate at least some of the problems associated with the prior art and to provide an improved process for preparing a phenol-free impregnating resin.
    The present invention comprises a process for preparing a substantially phenol-free impregnating resin using substantially only tannin as a phenolic OH group-containing substance, and a resin prepared by this process or otherwise having a similar composition. In the process, formaldehyde is condensed with tannin in the presence of a catalyst at an elevated temperature. The invention is based on the idea that the tannin is first introduced into the liquid phase by dissolving it in a solvent or solvent mixture, after which formaldehyde is added to the mixture thus obtained in the presence of an alkaline catalyst to effect a condensation reaction between formaldehyde and tannin.
    Preferably, the alkali is then introduced into the liquid phase gradually, so that the reaction of formaldehyde with the phenolic groups can be completed.
    The invention thus provides a substantially phenol-free impregnating resin comprising a condensation product of formaldehyde and tannin with a free formaldehyde content of at most 5% by weight, in particular at most 1% by weight, for example 0.1-1.0% by weight, preferably 0, 1-0.5% by weight. Most preferably, the finished impregnating resin is in the form of an aqueous mixture having a dry matter content relative to the resin of greater than about 20% by weight and usually up to about 70% by weight, typically between 25 and 50% by weight of the resin, e.g. 45% by weight. More specifically, the solution according to the invention is mainly characterized by what is set out in the independent claims.
    2 25 N The present invention provides significant advantages. In the invention, the phenol of the phenol-formaldehyde impregnation resin is completely or substantially completely replaced by tannin, = whereby the use of toxic phenol in the resin can alternatively be completely avoided.
    a co = 30 By means of the invention, the reactivity 2 of the condensation reaction between tannin and formaldehyde can be controlled and regulated. In the process, the resin can be condensed so that virtually all of the free formaldehyde is reacted. The cooking system according to the invention thus achieves really low concentrations of free formaldehyde, which means that the solution can be used in many applications where low levels of formaldehyde are required.
    At the same time, however, the viscosity of the resin is kept at such a level that it can still be used in paper impregnation applications. Such impregnated fibrous sheets can be used, for example, to make multilayer veneer products.
    In addition, tannins improve the water resistance of resins made from them. Thus, a resin prepared by the method according to the invention or corresponding to its composition is generally suitable for use as a substitute for a conventional impregnating resin, e.g. in film and frame papers. In addition to the impregnation resin, possible applications include - various fiberboards.
    BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows photographs of the finished extrudates of tannin impregnates, Figure 2 shows a schematic drawing of the structure of a compact laminate open and Figure 3 shows a photograph of birch plywood coated with tannin resin impregnated film paper made at 120 ° C / 7min / 20 bar.
    Embodiments In the present context, percentages are by weight, unless otherwise stated.
    o “Resin” means the reaction product of a starting material containing phenolic OH groups and formaldehyde S 25, which is obtained by a polymerization reaction.
    N <Q O “Tannins” are water-soluble polyphenols that are typically isolated from single and perennial plants, especially woody plants. The tannins have a molecular weight α, for example about 500-3000 Da. They can be polymeric tannins consisting of o 30 - flavonoids and phenolic acids. O OF
    Tannins are usually divided into condensable and hydrolyzable tannins. The latter are represented, for example, by gallotannins and ellagitannins. Condensed tannins are typically oligomeric compounds and are also called proanthocyanidins.
    5 For example, tannins can be isolated from wood and leaves by extraction using, for example, lyophilic solvents such as lower alcohols such as isopropanol or acetone. Generally, the tannin is obtained as a solution of about 10-30% by weight, especially as a viscous solution, which is diluted and purified by an ion exchanger.
    - In the present context, the various tannin compounds are commonly referred to as 'tannin'. It includes e.g. the condensable and hydrolyzable tannins mentioned above. It is possible to form derivatives of tannin, such as salts, ethers and esters. “Unmodified tannin” means tannin from which no derivative has been formed - by chemical modification. In one application, “unmodified tannin” is tannin obtained directly from the plant starting material by extraction and possibly concentration of the extract. In one embodiment, the phenol-free resin is prepared using substantially tannin alone as the phenolic OH group-containing agent. In practice, at least 90% by weight, preferably at least 95% by weight, more preferably at least 98% by weight, or most preferably up to 100% by weight of the raw material containing phenolic OH groups is tannin. 2 SC 25 According to a preferred embodiment, the phenol-free resin is prepared using only tannin, i.e. 100% tannin, as the substance containing phenolic N OH groups. © = “Phenol-free” means that essentially no phenol (CcHsOF), also called phenyl alcohol, = 30-hydroxybenzene or carboxylic acid is used in the preparation of the resin.
    R In one application, in addition to tannin, another biomass, such as lignin, is used as the substance containing phenolic OH groups.
    It is also possible to use small amounts (10% by weight, preferably at most 5% by weight, in particular at most 2% by weight) of phenol, cresol or resorcinol or a mixture thereof in the process. The tannin used in the present invention is in particular tannin obtained from biomass, such as wood or annual or perennial plants. In particular, a substance isolated from biomass as a water-soluble extract which can be used as such or dried to a powder is used as the tannin starting material.
    Examples of tannin starting materials include guebracho, mimosa, catechu, gambier, acacia, eucalyptus, hemlock, spruce, beech or magrove wood tannin. - According to a preferred embodiment, tannin from polyphenolic guebracho wood is used to replace the phenol. Mixtures of the various tannin starting materials mentioned above, for example, can also be used as the tannin starting material.
    According to a preferred embodiment, the present invention specifically uses unmodified tannin. o In addition to tannin, the tannin starting material may contain other substances, such as extractants or> 25 - carbohydrates, such as cellulose or hemicellulose or their degradation products. N In general, the tannin starting material contains at least 90% by weight, preferably at least 95% by weight, in particular at least 98% by weight of tannin.
    I = © The tannin starting material may be in the form of a solid, such as a powder. Such = 30 - tannin starting materials are represented, for example, by several commercially available tannin products.
    The powdered tannin typically has a dry matter content of more than 90% by weight, for example about 95% by weight.
    It is also possible to use tannin in the liquid stage, i.e. an aqueous tannin slurry. The dry matter content of the tannin aqueous slurry is typically 50% by weight or more. According to one embodiment, the preparation takes place by dissolving the tannin starting material in a solvent containing an alkaline substance as a catalyst. Formaldehyde, especially an aqueous solution of formaldehyde, i.e. formalin, is added to the solution. The tannin and formaldehyde are then condensed at elevated temperature. According to a preferred embodiment, the next part of the alkaline catalyst is then added in one or more parts and the condensation is continued until practically all of the formaldehyde, i.e. at least 90% by weight, more preferably at least 95% by weight, preferably at least 99% by weight, has reacted. The resin thus formed is recovered.
    Preferably, the tannin and formaldehyde are condensed in the liquid phase formed by the tannin solvent or mixture thereof. In particular, the condensation reaction takes place at a temperature of about 50-90 ° C until all the formaldehyde has reacted, after which the resin is recovered.
    In one embodiment, water is used as the solvent for the tannin.
    - According to another embodiment, in the process of preparing the resin, the tannin starting material is dissolved at the beginning of the resin cooking in a solvent mixture which contains not only water but also an alkaline catalyst but also the actual solvent. The addition of solvent and water at the beginning of the resin cooking helps to control the viscosity during condensation so that the viscosity does not become too high o at any stage of the reaction.
    > 25 N According to a preferred embodiment, the catalyst is metered in in several batches, which in particular helps to control the smooth progress of the condensation reactions. Thanks to the dosing of water and catalyst E, and possibly the actual solvent, as well as the dosing methods ©, the resin can be condensed to the point that the free formaldehyde is practically completely reacted.
    N As mentioned above, according to one embodiment, only water is used as the solvent for the tannin. According to another embodiment, a solvent mixture is used which contains, in addition to water, also the actual solvent, which is typically a polar liquid that is miscible with water. Examples of the actual solvent include aliphatic and aromatic alcohols, such as methanol, and aliphatic ketones, such as acetone. In one embodiment, the solvent is used in an amount sufficient to maintain a suitable dry matter content of the mixture, i.e., between about 20 and 70% by weight, especially between 30 and 70% by weight, for further reaction. Usually methanol or mixtures thereof are used as the actual solvent.
    For example, in the case of methanol, the methanol content of the water is usually about 1.5 to 15% by weight, such as 1.6 to 12% by weight. With the actual solvent involved in the cooking step, the resin can be condensed for a longer time without increasing the viscosity too quickly and a low formaldehyde content is achieved.
    When the tannin is dissolved in the water / methanol mixture, the resin remains soluble for a longer time and helps to control the viscosity during the condensation reaction. This, in turn, makes it possible to react virtually all of the free formaldehyde, whereby after the reaction the content of free formaldehyde is at most 5% by weight, based on the resin, in particular at most 1% by weight, for example 0.1-1.0% by weight. According to one embodiment, sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonia (NH 3), especially as ammonium hydroxide, or a mixed catalyst system such as> 25 - a mixture of sodium hydroxide and ammonia or sodium hydroxide and potassium hydroxide can be used as a catalyst in the reaction. Other nitrogen bases, such as organic amines, can also be used as catalysts. © = Preferably, the catalysts are added to the mixture as aqueous solutions, the concentration of which varies slightly according to the N catalyst. According to one embodiment, for example, the concentrations of sodium and = 30 to potassium hydroxide are between 40 and 60% by weight, preferably about 50% by weight for sodium hydroxide and preferably about 46% by weight for potassium hydroxide.
    N Aqueous sodium hydroxide is also referred to below as “lye”.
    Catalysts can influence the formation of the polymerization chain during the reaction by accelerating the condensation reaction between formaldehyde and tannin. The catalysts allow virtually all of the formaldehyde to react in a reasonable amount of time, alternatively at either normal pressure or elevated pressure.
    In one embodiment, the reaction uses formaldehyde as an aqueous solution having a formaldehyde content of 30-60% by weight, typically 50-60% by weight. According to one application, technical grade formaldehyde is used. The technical grade formaldehyde starting material may contain e.g. metallic impurities as well as some, typically up to 12% by weight methanol. According to a preferred embodiment, the technical grade formaldehyde used preferably has a formaldehyde content of at least 95% by weight. According to a preferred embodiment, the resin of the present invention is prepared under phenol-formaldehyde-free conditions. In this case, during the tannin condensation reaction, the reaction mixture does not contain phenol formaldehyde. According to one embodiment, the method for preparing the resin according to the present invention is in several steps, comprising 2 to 10 steps. Typically, the process is a 2-3 step, preferably a 3 step, with the addition of the alkaline catalyst taking place gradually in several steps during the process. With the gradual addition of the alkaline catalyst, the solids content of the mixture can be kept low during the reaction, which allows effective control of the viscosity. This in turn makes it possible to keep the viscosity of the reaction mixture so low that the condensation reaction can be carried out efficiently.
    S 0 “Gradual increment” means that the incremental time is longer than z would be if the pre-calculated amount were incremented at once (i.e., a “one-time increment”) was performed without interrupting N increments. In general, the addition time is at least 2 times longer than a one-time addition = 30 - would require, preferably 5-100 times longer, e.g. 10-50 times longer.
    In the process of the present invention, the catalyst is added in two or more portions, whereby after the addition of one batch of catalyst, the reaction is allowed to proceed before the addition of the next batch of catalyst.
    According to a preferred embodiment, the catalyst is added at least immediately at the beginning to the solvent or solvent mixture before the tannin is dissolved and after the condensation reaction, after which the condensation reaction is continued.
    According to a preferred embodiment, in the first step of the process, the tannin is dissolved in a mixture of a solvent, i.e. either water or water and the actual solvent, and a catalyst, in particular a water-soluble alkaline catalyst (first part). Preferably, the tannin is dissolved by stirring the mixture - at room temperature (about 20 ° C) or at elevated temperature. The temperature generally used is below 70 ° C, preferably below 65 ° C, for example at most 60 ° C. In one embodiment, the operation is at 30-50 ° C, especially at 30-35 ° C. The soaking time is affected by the selected reaction conditions as well as substances such as the tannin used, the solvent / solvent mixture, the catalyst and the dissolution temperature. The dissolution time is typically about 0.5 to 2 hours, for example about 1 hour. When the tannin is completely, i.e. at least 90%, preferably at least 95%, dissolved in the mixture, the temperature of the solution is raised to more than 60 °, for example to about 60-100 ° C, - preferably to about 65 ". Water is then added to the solution. Next, a calculated amount of formaldehyde is added to the solution in stages with stirring over about 0.1 to 2 hours, preferably about 15 to 60 minutes. In one embodiment, after about 40 minutes, the temperature of the solution is raised to more than 80 ° C, for example to about 80-100 ° C, preferably to about 85 ° C. At this temperature, condensation reactions take place between tannin and N 25 - formaldehyde. The condensation reaction is continued for 0.1 to 2 hours for a period of time, typically about 15 to 45 minutes, for example about 30 minutes.
    According to one embodiment, the alkaline catalyst can also be added during the condensation reaction in one or more portions. The next portion of the alkaline catalyst (optionally a second, or for example a third or fourth portion) is then added, the mixture is cooled to 80 ° C or below, for example to a temperature in the range of 20 to 80 ° C, and the condensation reaction is continued. In this way, the condensation reaction can be completed.
    According to one embodiment, the catalyst can also be added at this stage of the process in more than one part, for example 2-5, typically in two parts.
    After each catalyst addition, the condensation is continued for 0.1 to 1 hour, for example about 1 hour.
    When all the catalyst has been added, the condensation reaction is complete.
    The resin prepared as described above is typically cooled to room temperature, i.e., about 20 ° C, which is its typical storage temperature.
    In one embodiment, the condensation reaction is continued until virtually all of the formaldehyde has reacted.
    As stated above, in a preferred embodiment this means that at least 95% by weight of the formaldehyde required for condensation has reacted, preferably at least 99% by weight, for example 99.0-99.9% by weight, of the formaldehyde required for condensation has reacted.
    In the process, the resin can be boiled in a non-pressurized reaction vessel, i.e. a conventional reactor operated at normal pressure, or alternatively in a pressure cooker.
    In both cases, the condensing reactor is preferably equipped with reactor heating and cooling devices as well as temperature sensors and controls.
    In addition, the non-pressurized reaction vessel preferably has a condenser, such as a vertical condenser, which can be used to condense any volatile solvent and return it to the reaction vessel.
    This ensures that the resin solvent is always present during the condensation reaction. o The rate of development of the viscosity of the resin is affected by the catalyst system and the dry matter. > 25 - By carrying out the condensation reaction as described above, in which a tannin solvent such as N water and possibly methanol is present during the reaction and the catalyst is gradually added to the reaction mixture, the dry matter content can be increased without increasing the viscosity Ek, i.e. above 10,000 cP: n, especially above 300 cP / 20 ° C. a co = 30 - As mentioned above, the dry matter content of the reaction mixture with respect to the resin is typically about 20-70% by weight. From the finished resin, it is possible to evaporate, if necessary, any actual solvent used, such as methanol, ethanol or acetone. This makes the resin more suitable for various end uses in which the actual solvent must not be present.
    According to one embodiment, the content of the actual solvent in the finished resin is - typically 0-15% by weight. Thus, the resin can also be recovered completely free of the actual solvent, even if it has been used in the resin preparation step.
    In one application, the finished resin has a Brookfield viscosity of 20-10,000 cP, especially 20-1000 cP, e.g. 20-300 cP or 20-100 cP.
    According to one preferred embodiment, the viscosity of the resin prepared is at the same level as that of normal impregnation resins. A resin with a Brookfield viscosity of 20-50 cP is particularly suitable for impregnating the backing paper. A resin with a Brookfield viscosity of 100-300 cP is particularly suitable for impregnating film paper.
    - The actual solvents can also be added back to the resin after evaporation, if necessary, or the actual solvent evaporated, such as methanol, ethanol or acetone, can be completely or partially replaced by water, for example in applications where no solvent is present or above a certain limit, such as more than 5 % by weight of the total weight of the resin.
    The resin prepared according to the method is itself thermosetting, i.e. the addition of additives is not necessary to formulate it as an adhesive. However, the composition of the resin can still be modified, for example, by mixing it with extenders and crosslinkers.
    Compounds known per se, such as amide or N amine compounds, such as urea, or monomeric, oligomeric or polymeric carbohydrates, can be used as extenders. These lower the viscosity of the resin and thus z improve the absorption of the resin into the impregnation paper. In addition, carbohydrates, such as sugars, for example, can be used as a resin plasticizer to provide additional flexibility in the 5-30 compression step.
    According to one embodiment, aliphatic and / or aromatic alcohols, for example, can also be added to the resin at the end to reduce the viscosity of the resin and thus to promote the absorption of the resin into the paper.
    As crosslinkers, compounds known per se can be used, such as amine compounds, such as hexamethylenetetraamine, or vinyl compounds, such as divinylbenzene.
    In one embodiment, the finished tannin resin is crosslinked with a normal impregnating resin (e.g., phenol-formaldehyde resin) to improve the bond strengths of the tannin resin. In one application, such a phenol-formaldehyde resin suitable for impregnation has a Brookfield viscosity of 20-1000 cP, e.g. 20-300 cP or 20-100 cP.
    In one application, 70-90 parts by weight of finished tannin resin and 10-30 parts by weight of phenol-formaldehyde resin, in particular phenol-formaldehyde resin suitable for impregnation, are added to the reactor. The temperature of the mixture is raised to 80-85 ° C and condensed for 20-60 minutes, after which the product is cooled. This makes it possible to further improve the bond strengths of the tannin resin, while leaving the free phenol content of the final product at only 0.05-0.2%. The resin thus obtained can be impregnated into the paper as such or formulated with additives and then compressed into a laminate under the influence of heat and pressure.
    Paper impregnated with the resin prepared by the method of the present invention or corresponding to its composition can be compressed into a laminate. o For example, a multi-intermediate press can be used for compression, where the compression takes place at a pressure of more than 70> 25 bar at about 140-150 ° C.
    S 0 Alternatively, a high speed press, a continuous press or some other method commonly used in the industry may be used. The high speed press used is typically 1-3 and has a processing temperature of 170-200 ° C. 5 30 - When using a continuous press, typical process parameters are a pressure of 20-50 bar 5 and a temperature of 170-180 ° C. The following non-limiting examples represent applications of the present technology.
    Example The resin was boiled in a conventional reactor at normal pressure. In the first step - water I and catalyst I, i.e. the first part of the catalyst, comprising sodium hydroxide alone or sodium hydroxide together with either ammonia or potassium hydroxide, were fed to the reactor. At this point, the pH of the mixture was 7-8.5. To this mixture was added tannin from guebracho wood, after which the mixture was stirred for about 1 hour, keeping the temperature below 50 ° C, generally between 30-35 ° C. After stirring, the temperature of the mixture was raised to about 65 ° C and water II was added. Next, formalin was added to the mixture at a constant rate over about 40 minutes. After the addition, the temperature of the mixture was raised to about 85 ° C and condensed for about 30 minutes. Catalyst II, i.e. another part of the catalyst, was then added to the mixture and the mixture was cooled slightly, to about 80 ° C. The mixture was condensed at this temperature for about 1 hour. Catalyst III, i.e. a third part of the catalyst, was added and the mixture was condensed for another hour.
    Finally, the resin was cooled. The following examples illustrate soups made by the method described above: Soup Example 1
    N 5
    N 7 Cooking example 2>
    N: 3 S
    Soup Example 3 Usage Examples The present method can be used to prepare a substantially phenol-free impregnating resin and a resin prepared according to the method or corresponding to its composition - generally as a substitute for a conventional impregnating resin. The finished end product can be used as such for paper impregnation or as a mixture with normal impregnation resins. The finished resin can be impregnated on film / frame paper (60-160 g / m 2). The amount of resin in the paper varies between 20 and 60% by weight, depending on the end use. The amount of volatile substances in the impregnate is between 5 and 10% by weight. Figure 1 shows specimens of the finished extrudates of tannin impregnates with different catalyst systems.
    In particular, the present method is suitable for the preparation of a backing paper impregnation resin and its use in a compact laminate (Figure 2) as an adhesive. o 2 In addition to impregnation resins, the following applications can be mentioned in particular: plywood, S 20 LVL, chipboard production, MDF (medium-density fiberboard), HDF 2 (high-density fiberboard), ie various fiberboards in general. In addition to these, mention should also be made of the manufacture of E abrasive paper, beam adhesive and wool resins, in particular mineral wool resins such as glass wool and rock wool resins. io S 25 References N Patent Literature: US3254038
    WO2004058843 AU492815 US2582266 GB703408 KR20070104037 US2007125890 ZA8001583 o O OF OF
    O 0
    I a a 00 O O OF
    权利要求:
    Claims (1)
    [1]
    Claims:
    A process for preparing a phenol-free impregnating resin, which process comprises - condensing formaldehyde with a substance containing phenolic OH groups in the presence of an alkaline catalyst to form a resin, characterized in that - unmodified tannin is used as the phenolic OH group-containing substance dissolved in water , - formaldehyde is added to the tannin solution, and - the tannin and formaldehyde are condensed at an elevated temperature, and - the last part of the alkaline catalyst is added to the solution in one or more portions and the condensation is continued until practically all the formaldehyde has reacted. Process according to Claim 1, characterized in that only tannin, i.e. 100% tannin, is used as the substance containing phenolic OH groups.
    Process according to Claim 1 or 2, characterized in that the tannin used is polyphenol guebracho wood tannin, either as an aqueous slurry or the like - tannin powder, the tannin having a dry matter content of more than 50% by weight, in particular at least 90% by weight, for example about 95% by weight. weight-%.
    Process according to one of the preceding claims, characterized in that, in addition to water, an actual solvent is used to dissolve the tannin, which is a polar liquid which is miscible with water, such as an aliphatic or aromatic alcohol, such as S methanol or ethanol, or an aliphatic ketone, such as acetone.
    Process according to one of the preceding claims, characterized in that NaOH or KOH or ammonia or an organic amine or a mixture of two or more substances is used as catalyst.
    O
    Process according to one of the preceding claims, characterized in that the formaldehyde is used as an aqueous solution with a formaldehyde content of about 30 to 60% by weight.
    Process according to one of the preceding claims, characterized in that the resin is condensed under phenol-formaldehyde-free conditions.
    Process according to one of the preceding claims, characterized in that the resin is prepared in several stages, the addition of the alkaline catalyst taking place - in several steps during the process to keep the viscosity of the reaction mixture so low that condensation can be carried out efficiently, especially some alkaline catalyst before dissolution and some formaldehyde addition after.
    Process according to one of the preceding claims, characterized in that - the tannin is first dissolved in a mixture of water, optionally the actual solvent, and a water-soluble alkaline catalyst (first part), stirring the mixture at room temperature or at a slightly elevated temperature below 70 ° C.
    Process according to Claim 10, characterized in that when the tannin is completely dissolved, the temperature of the solution is raised above 60 ° C, for example to about 65 ° C, and water is added, after which the calculated amount of formaldehyde is added stepwise with stirring.
    Process according to Claim 11, characterized in that, after the addition of formaldehyde S, the temperature is raised above 80 ° C, for example to about 85 ° C, at which temperature a condensation reaction between tannin and formaldehyde takes place.
    = a 00 13. Process according to Claim 11, characterized in that the next portion of the alkaline catalyst is added in one or more portions, the mixture is cooled to> 80 ° C or below and the condensation reaction is continued after each catalyst addition.
    Process according to one of the preceding claims, characterized in that the condensation reaction is continued until at least 90%, preferably at least 95%, and in particular at least 99% of the formaldehyde required for condensation has reacted, after which the resin is recovered.
    Process according to one of the preceding claims, characterized in that the resin obtained is condensed with a phenol-formaldehyde resin in order to crosslink them with one another in order to improve the bond strength.
    Process according to one of the preceding claims, characterized in that 70-90 parts by weight of the resin obtained are condensed with a phenol-formaldehyde resin of 10-30 parts by weight, for example at 80-85 ° C for about 20-60 minutes, after which the product is cooled.
    An impregnating resin prepared by a method according to any one of the preceding claims.
    Impregnation resin according to Claim 17, characterized in that the product has a free phenol content of 0.05 to 0.2% by weight.
    Impregnation resin according to one of Claims 17 or 18, characterized in that it is in the form of an aqueous mixture having a dry matter content relative to the resin of about 20 to 70%.
    Use of an N impregnating resin prepared by a method according to any one of claims 1 to 16 or an impregnating resin 0 according to any one of claims 17 to 19 for impregnating backing paper, impregnating film paper, making plywood, LVL, z chipboard or fibreboards such as MDF (medium density fiberboard (N semi-hard fiberboard) or HDF (high-density fiberboard), = 30 - for the production of abrasive paper, as a beam adhesive, in wool resins, especially mineral wool, = such as glass wool or stone wool.
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