FI129275B - Phenol-free impregnation resin - Google Patents

Abstract

The present invention comprises 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 the like. The process uses essentially only lignin as a substance containing phenolic OH groups, which is condensed with formaldehyde in the presence of a catalyst at an elevated temperature.

Description

BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a process for preparing a substantially phenol-free impregnation resin, and to a resin prepared by this process or otherwise having a similar composition, and to end uses of the resin.

BACKGROUND OF THE INVENTION The resins commonly 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 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 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 final application for which the resin is prepared.

N <25 s The adequacy of petrochemical raw materials such as phenol is limited and it would therefore be important to replace them with renewable natural raw materials in the future, such as lignin from wood z, which has a polyphenolic structure. At the same time, e.g. environmental damage caused by phenol a e. © 3 30 S Replacing phenol in phenol-formaldehyde resins with renewable natural raw materials is

N already known.

WO2014080033 discloses a process for preparing a phenol-formaldehyde impregnation resin, wherein 60-100% of the phenol is replaced by lignin. According to the publication, mixtures of water and tetrahydrofuran, water and ammonia and water and ethyl acetate are mentioned for dissolving lignin.

In U.S. Pat. No. 5,177,169, an organic solvent that is typically polar and at least partially immiscible in water, such as ethyl acetate, is added to the aqueous solution containing lignin. The mixture is oxidized to provide an aqueous layer and an organic solvent layer containing demethylated lignin. The demethylated lignin is dissolved in an alkaline solution to which an aldehyde source has been added to prepare a resin. As the aldehyde source, for example, formaldehyde in the solution phase can be used. Both WO2015044528 and US2002065400 describe a process for preparing a phenol-free impregnation resin. In publications, lignin is dissolved in a mixture of water and an alkaline catalyst, followed by the addition of formaldehyde to form a resin. According to known solutions, there is a risk that the temperature of the reaction mixture rises uncontrollably, which affects the quality of the final product. At the same time, formaldehyde consumption is increasing significantly. SUMMARY OF THE INVENTION It is an object of the present invention to obviate at least some of the O 25 problems associated with the prior art and to provide an improved process for preparing phenol-free impregnation resin 3.

NN z The present invention comprises a process for preparing a substantially phenol-free impregnation resin N using substantially only ε-lignin as a phenolic OH-containing substance, and a resin prepared by this process or otherwise having a similar composition. In the process, formaldehyde is condensed with lignin in the presence of a catalyst N at an elevated temperature.

The invention is based on the idea that lignin 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 lignin.

The alkali is then gradually introduced into the liquid phase, so that the reaction of formaldehyde with the phenolic groups can be completed. According to the invention, there is thus provided a substantially phenol-free impregnation resin which - comprises a condensation product of formaldehyde and lignin 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. 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 not more than about 70% by weight, typically a dry matter content of the resin of between 30-40% by weight.

More specifically, the solution according to the invention is mainly characterized by what is stated in the independent claims.

- The present invention provides significant advantages. In the invention, the phenol of the phenol-formaldehyde impregnation resin is substantially completely replaced by lignin, whereby the use of toxic phenol in the resin can alternatively be completely avoided.

By means of the invention, the reactivity of the condensation reaction between lignin and formaldehyde O 25 - 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 S according to the invention thus achieves really low concentrations of free formaldehyde, which means that solution z can be used in many applications where a low level of formaldehyde is required. N At the same time, however, the viscosity of the resin is kept at such a level that it can also be used in paper impregnation applications. Such impregnated = fibrous sheets can be used, for example, for the production of multilayer veneer products.

Thus, a resin prepared by the method of 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 impregnating resin, possible applications are, for example, various fibreboards. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows photographs of the finished extrudates of the lignin impregnates as well as an image of a reference sample, and Figure 2 shows a schematic diagram of the open structure of a compact laminate. Embodiments In the present context, percentages are by weight unless otherwise stated. - 'Resin' means the reaction product of a starting material containing phenolic OH groups and formaldehyde, obtained by a polymerisation reaction. In one embodiment, the phenol-free resin is prepared using essentially lignin alone as the phenolic OH group-containing agent. In practice, at least 90% by weight, preferably at least 95% by weight, most preferably at least 98% by weight, or even 100% by weight of the raw material containing phenolic OH groups is lignin. In one application, in addition to lignin, another biomass, such as tannin, is used as the substance containing phenolic OH groups.

N <25 s It is also possible to use small amounts (10% by weight, preferably <up to 5% by weight, in particular up to 2% by weight) of phenol, cresol or resorcinol or a mixture of these in the process. a

S 2 30 - The lignin used in the present invention is especially from biomass, such as wood or

N S lignin from annual or perennial plants or lignocellulose, respectively.

N In particular, a substance isolated from used cooking broth from biomass cooking is used as the lignin feedstock.

Examples of the lignin feedstock to be used include lignin isolated from biomass by an alkaline cooking process, such as kraft lignin (i.e., sulphate cooking lignin) or soda lignin (i.e., soda cooking lignin). Organosolv lignin (i.e., lignin from organosolv cooking) can also be used in the process. Mention may also be made of pyrolytic lignin, vaporized lignin, dilute acid lignin and basic oxidative lignin. Mixtures of the above-mentioned lignin starting materials can also be used as the lignin starting material.

In addition to lignin, the lignin starting material may contain other substances, such as extractants or carbohydrates, such as cellulose or hemicellulose, or degradation products thereof. In general, the lignin starting material contains at least 90% by weight, preferably at least 95% by weight, in particular at least 98% by weight of lignin.

The lignin starting material may be in the form of a solid, such as a powder. Such lignin starting materials are represented by commercially available lignin products. It is also possible to use lignin in the liquid phase, as described in more detail below.

- The preparation takes place by dissolving the lignin starting material in a solvent containing an alkaline substance as a catalyst. Formaldehyde is added to the solution, especially an aqueous solution of formaldehyde, i.e. formalin. The lignin and formaldehyde are then condensed at elevated temperature 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, of the formaldehyde O 25 - has reacted. The resin thus formed is recovered.

3 S In particular, lignin and formaldehyde are condensed at a temperature of about 50-90 ° C until x all the formaldehyde has reacted, after which the resin is recovered.

O 2 30 - Preferably the lignin and formaldehyde are condensed in the liquid phase formed by the lignin solvent or mixture thereof.

According to a preferred embodiment, in the resin preparation process, lignin is dissolved at the beginning of the resin cooking in a solvent mixture containing a solvent, water and an alkaline catalyst. The addition of solvent and water at the beginning of the resin cooking allows the viscosity to be controlled during condensation so that the viscosity does not rise too high at any stage of the reaction. Catalyst dosing can also be done in several batches, which also helps to control the smooth progress of the condensation reactions. Due to the dosing of the solvent, water and catalyst, as well as the dosing methods, the resin can be condensed to the point where the free formaldehyde is practically completely reacted.

In a preferred embodiment, kraft lignin is used to replace the phenol. Such commercially available lignin is generally supplied as a powder with a dry matter content of more than 90% by weight, e.g. about 93% by weight. The process may also use - an aqueous lignin slurry having a dry matter content of about 50% by weight or more.

The solvent for lignin is typically a polar liquid that is miscible with water.

Examples of solvents are aliphatic and aromatic alcohols, such as methanol, and aliphatic ketones, such as acetone. A sufficient amount of solvent is used to keep the dry matter content of the mixture suitable, i.e. between about 20-70% by weight, especially between 30-70% by weight, for further reaction.

O 25 Methanol or mixtures thereof are usually used as the solvent.

3 S In one application, lignin is dissolved in a mixture of the actual solvent and water.

For example, in the case of methanol, the concentration of methanol in the water is usually about 1.5 to 15% by weight, such as 1.6 to 12% by weight. With the aid of the solvent present in the cooking step, the resin = can be condensed for a longer time without increasing the viscosity too quickly and a low formaldehyde content of N is achieved.

When lignin is dissolved in a water / methanol mixture, the resin remains soluble longer and allows viscosity to be controlled during the condensation reaction.

This, in turn, makes it possible to react virtually all of the free formaldehyde, the content of free formaldehyde after the reaction being at most 5% by weight of 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 a mixture of sodium hydroxide and ammonia or a mixture of 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 depending on the catalyst.

According to one embodiment, for example, the concentrations of sodium and 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. An aqueous solution of sodium hydroxide is also referred to below as "lye". Catalysts can affect the formation of the polymerization chain during the reaction - by accelerating the condensation reaction between formaldehyde and lignin.

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 an O 25 to formaldehyde content of 30 to 60% by weight, typically 50 to 60% by weight. & <According to one application, technical grade formaldehyde is used.

The technical grade z formaldehyde starting material may contain e.g. metallic impurities and to some extent, N typically up to 12% by weight of methanol.

According to a preferred embodiment, the formaldehyde content of the technical grade formaldehyde used is preferably at least 95% by weight. According to one embodiment, the method for preparing the resin according to the present invention is multi-step, comprising 2 to 10 steps.

Typically, the process is in 2-3 steps, preferably in 3 steps, with the addition of the alkaline catalyst gradually taking place in several steps during the process. By gradually adding 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 allows the viscosity of the reaction mixture to be kept so low that the condensation reaction can be carried out efficiently.

“Gradual addition” means that the addition takes longer than it would take if the pre-calculated amount is added at once (i.e., a “one-off addition”) is made without interrupting the addition. In general, the addition time is at least 2 times longer than the one-time addition - would require, preferably 5 to 100 times longer, e.g. 10-50 times longer.

Usually 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.

In a preferred embodiment, in the first step of the process according to the invention, the lignin is dissolved in a mixture of a solvent, in particular water and a solvent, and a catalyst, in particular a water-soluble alkaline catalyst (optionally a first part). Dissolution is by stirring the mixture at room temperature (about ° C) or at elevated temperature. In general, the temperature is below 70 ° C, preferably below 65 ° C, for example at most 60 ° C. In one embodiment, the operation is at 30-50 ° C, usually at 30-35 ° C.

The dissolution time is affected by the selected reaction conditions as well as the substances such as lignin used, = solvent / solvent mixture, catalyst and dissolution temperature. The dissolution time ranges from 0.5 to 2 hours N 25 - typically about 1 hour. When the lignin is completely, i.e. at least 90%, preferably at least 95%, dissolved in the mixture E, the temperature of the solution is typically raised above 60 ° C, for example about 60-100 ° C, preferably about 65 ° C. * To C, and add water. A solution of formaldehyde 3 is then added stepwise with stirring, typically over about 0.1 to 2 hours,> preferably about 15 to 60 minutes. After the addition of formaldehyde, the temperature is raised above 80 ° C, for example about 80-100 ° C, preferably about 85 ° C. At this temperature, condensation reactions between lignin and formaldehyde take place. The reaction is continued for 0.1 to 2 hours, typically about 15 to 45 minutes. In a multi-step embodiment, a second portion of the alkaline catalyst is then added, the mixture is cooled to 80 ° C or below, e.g. to a temperature in the range of 20-80 ° C, and the condensation reaction is continued. The condensation reaction can thus be completed, but if necessary, a second portion of the catalyst can be metered in even more steps, for example 2-5, typically in two steps. After the addition of the second catalyst portion, the mixture is condensed. Condensation takes place for about 0.1 to 2 hours, e.g. about 1 hour. A third of the catalyst is then added and condensed again for about 0.1 to 2 hours, e.g. about 1 hour. Similarly, the same procedure is continued if the catalyst is further divided. When all the catalyst has been added, the condensation reaction is complete. Typically, when the condensation reaction is complete, the resulting resin is 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. O 25 3 In both cases, the condensing reactor is preferably equipped with heating and cooling devices for the reactor S as well as temperature sensors and controls. In addition, the non-pressurized reaction vessel E preferably has a condenser, such as a vertical condenser, by means of which the potentially volatile solvent can be condensed and returned to the reaction vessel. In this case, it is ensured that the resin solvent is always present during the condensation reaction.

R The rate of development of the viscosity of the resin is affected by the catalyst system and the dry matter. By carrying out the condensation reaction as described above, in which a lignin solvent such as 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 too much, i.e., above 10,000 cP. As mentioned above, the dry matter content of the reaction mixture relative to the resin is - typically about 20-70% by weight. The solvent, such as methanol, ethanol or acetone, can be evaporated from the finished resin as needed. This makes the resin more suitable for various end uses in which the solvent must not be present. The concentration of solvent in the finished resin is typically 0-15% by weight. The resin can thus also be recovered completely solvent-free.

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 50-300 cP.

According to one preferred embodiment, the viscosity of the resin prepared is at the same level as that of normal impregnating 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.

If necessary, the solvents can also be added back to the resin after evaporation, or the evaporated solvent, such as methanol, ethanol or acetone, can be completely or partially replaced, for example with water, in applications where the solvent is not present at all or above a certain limit, such as more than 5% by weight. of the total weight of the resin.

S 25 The resin prepared according to the method is in itself thermosetting, i.e. the addition of additives s is not necessary to formulate it into an adhesive. However, the composition of the resin can be further modified, for example, by mixing it with extenders and crosslinkers.

I = e Extenents which can be used are compounds known per se, such as amide or 2-amine compounds, such as urea, or monomeric, oligomeric or polymeric compounds.

N S carbohydrates such as sugars. As the crosslinkers, compounds known per se can be used, such as amine compounds, such as hexamethylenetetraamine, or vinyl compounds, such as divinylbenzene.

The finished resin 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.

For example, a multi-intermediate press can be used for compression, where the compression takes place at a pressure of more than 70 bar at about 140-150 ° C. 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 between 1 and 3 and has a processing temperature between 170 and 200 ° C. When using a continuous press, typical process parameters are a pressure of 20-50 bar and a temperature of 170-180 ° C. - The following non-limiting examples represent applications of the present technology. Examples The resin was boiled in a conventional reactor at normal pressure. The reaction was equipped with a condenser to condense any solvent that evaporated back into the reaction mixture. In the first stage, water I, methanol 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 charged to the reactor. At this point, the pH of the mixture was _ 7-8.5. To this mixture was added kraft lignin, after which the mixture was stirred for about 1 hour with O 25 - keeping the temperature below 50 ° C, generally between 30-35 ° C. After stirring, the temperature of the mixture 3 was raised to about 65 ° C and water II was added. Next, formalin was added to mixture S at a constant rate over about 40 minutes. After the addition, the temperature of mixture E was raised to about 85 ° C and condensed for about 30 minutes. 9 Catalyst II, i.e. a second portion of 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 Soup Example 2 Soup Example 3 _ ©? Soup Example 4

R i

Z

E 2

Examples of Use 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 into film / body paper (60-200 g / m 2). The amount of resin in the paper varies between 20 and 50% by weight, depending on the end use. The amount of volatiles in the impregnate is between 5 and 10% by weight. Figure 1 shows on the right side specimens (6 pieces) of finished lignin impregnates with different catalyst systems. On the left is a reference sample made of phenol formaldehyde resin. In particular, the present method is suitable for the preparation of an impregnating resin of a backing paper and its use in a compact laminate (Fig. 2) as an adhesive. In addition to impregnation resins, the following applications can be mentioned in particular: plywood, LVL, chipboard production, MDF (medium-density fiberboard), HDF (high-density fiberboard), ie various fiberboards in general. In addition to these, mention should also be made of the production of abrasive paper, beam glue and wool resins, in particular mineral wool resins such as glass wool and rock wool resins. S 25

N s List of reference publications

S

N z Patent literature: a

O> 30 WO 2014/080033

MN 5 U.S. 5,177,169

OF

Claims (22)

Patent claims: A process for the preparation of a substantially phenol-free impregnation resin, the content of which is free of formaldehyde of not more than 5% by weight, in which process - formaldehyde is condensed with a phenolic OH group-containing substance in the presence of an alkaline catalyst to form resin , characterized in that the process comprises the following steps in the order mentioned: - as phenolic OH groups containing substance, kraft lignin, soda equation or organosolvlignin is used, - the lignin is dissolved to form a solution in a mixture of water, an alkaline catalyst and a solvent by to use a solvent consisting of a polar liquid which can be mixed with water, which solvent consists of aliphatic or aromatic alcohol or an aliphatic ketone, - the lignin solution is added to formaldehyde and - the lignin and formaldehyde are condensed in a liquid phase, - part of the the alkaline catalyst is added after the addition of formaldehyde and the condensation is continued until at least 9 5% by weight of the formaldehyde reacted, after which - the resin thus formed is recovered. Process according to Claim 1, characterized in that kraft lignin is used as lignin either as an aqueous suspension or a corresponding lignin powder, the dry matter content of the lignin amounting to more than 50% by weight, e.g. to about 75% by weight. Process according to Claim 1 or 2, characterized in that a solvent consisting of methanol, ethanol or acetone is used to dissolve the lignin. NE 4. A process according to any one of the preceding claims, characterized in that the solvent is used in a sufficient amount to maintain the dry matter content of the mixture suitable for further reaction, for example in the case of methanol the content of 9 methanol in water to about 1.6-12% by weight. Process according to any 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. Process according to any one of the preceding claims, characterized in that formaldehyde is used as aqueous solution, the formaldehyde content of which amounts to about 30-60% by weight. Process according to any one of the preceding claims, characterized in that - lignin and formaldehyde are condensed at a temperature of about 50-90 ° C until all formaldehyde has reacted, after which the resin is recovered. Process according to any one of the preceding claims, characterized in that lignin and formaldehyde are condensed in the liquid phase formed by the solvent of the lignin - or its mixture. Process according to any one of the preceding claims, characterized in that the preparation of resin is carried out in several steps, the alkaline catalyst being fed during the process in more than two steps to keep the viscosity of the reaction mixture so low that the condensation can be carried out efficiently. Process according to any one of the preceding claims, characterized in that first the lignin is dissolved in the mixture formed by water and the solvent and the water-soluble alkaline catalyst (first part) by mixing the mixture at room temperature or at slightly elevated temperature, which is below 70 ° C. S o Process according to Claim 10, characterized in that when the lignin is completely dissolved E, the temperature of the solution is raised to above 60 ° C, for example to about 65 ° C, and 9 water is added, after which the calculated amount of formaldehyde is added stepwise while dissolving. - 3 30 - the mixture is mixed at the same time. O Process according to Claim 10, characterized in that after the addition of formaldehyde the temperature is raised to above 80 ° C, for example to about 85 ° C, at which temperature a condensation reaction takes place between the lignin and the formaldehyde. Process according to Claim 12, characterized in that the second part of the alkaline catalyst is added, the mixture is cooled to 80 ° C or below and the condensation reaction is continued. Process according to one of the preceding claims, characterized in that the condensation reaction is continued until the formaldehyde content does not exceed 5%, preferably not more than 1% by weight, e.g. to 0.1-1.0%, and its Brookfield viscosity is at least 20 cP and at most 10,000 cP. Process according to any one of the preceding claims, characterized in that the condensation reaction is carried out in the presence of the solvent of the lignin in order to keep the viscosity of the reaction mixture sufficiently low. Process according to Claim 15, characterized in that the condensation reaction is carried out in a reaction vessel without pressure or in an overpressure boiler, the reactor being most suitably equipped with devices for heating and cooling the reactor and with temperature sensors and control. Process according to one of the preceding claims, characterized in that the resin is recovered without solvent or containing not more than 15% by weight of solvent. S S Resin prepared according to any one of the preceding claims. x a 2 A substantially phenol-free impregnating resin according to claim 18, which impregnating resin comprises a condensation product of formaldehyde and lignin, the content of free = formaldehyde of not more than 5% by weight. Impregnation resin according to claim 18 or 19, characterized in that it is present in the form of such a water mixture, the dry matter content of which in relation to the resin amounts to about 30-70%. Impregnation resin according to any one of claims 18-20, which impregnation resin is obtained by evaporation of the solvent residues which the resin contains in a separate evaporation phase. The use of impregnating resin according to any one of claims 18-21 for impregnating base paper, impregnating film paper, producing a veneer, LVL, clamping board or for producing fibreboard, such as MDF (medium-density fiberboard, semi-hard fiberboard) ) or HDF (high-density fiberboard) boards, for the production of abrasive paper, such as bale glue, in wool resins, in particular in mineral wool, such as glass wool or rock wool. N O N © IN O N I a a 0 O O LO MN O N