JP6793341B2 - Manufacturing method of powder adhesive for thermal pressure molding - Google Patents

Description

The present invention relates to a method for producing a powder adhesive for hot pressure molding.

Conventionally, as an adhesive for hot pressure molding, one derived from biomass has been known, and examples thereof include casein, soybean glue, and nikawa. However, these biomass-derived thermosetting adhesives do not always have sufficient physical properties such as adhesive strength, and are used as adhesives containing petroleum-derived thermosetting resins such as urea, melamine, and phenol as main components. It was replaced. At present, wood boards such as plywood, particle board, and fiberboard are manufactured using an adhesive containing these petroleum-derived thermosetting resins as main components.

In such a thermosetting adhesive containing a petroleum-derived thermosetting resin as a main component, an organic solvent is used as a diluent or a solvent, and formaldehyde is often added as a curing agent. Emission of formaldehyde from wood boards manufactured using such thermal pressure molding adhesives has become a problem, and various reduction measures have been taken, but it is not possible to completely suppress the emission of formaldehyde. Not done. In addition, isocyanate-based adhesives, which are petroleum-derived thermosetting resins that do not emit formaldehyde, have also been developed, but have not been widely used due to problems such as reaction with water and bonding with metals.

On the other hand, tannins and lignins, which are polyphenols contained in wood and bark, become wastes in lumber and pulp utilization, and attempts have been made for a long time to effectively utilize them. For example, since tannin and lignin have a chemical structure similar to that of a phenol resin, it has been studied to react and condense with formaldehyde in the same manner as the phenol resin and use it as an adhesive (see Patent Document 1). Furthermore, in anticipation of a reaction with the methylol group of the phenol resin, studies have been made on adding tannins and lignins to the phenol resin and incorporating these polyphenol compounds into the polymer skeleton of the phenol resin (non-patent documents). See 1 and 2).

Further, as another attempt for effective utilization of tannin or lignin, for example, reaction of a phenolic hydroxyl group of tannin or lignin with a polyisocyanate to form a urethane resin has been studied (Non-Patent Document 2). reference).

However, when tannin or lignin is reacted with formaldehyde, there is a problem that residual unreacted formaldehyde and formaldehyde generated by hydrolysis of the reaction product are released into the atmosphere. Further, since the reactivity of tannin and lignin is lower than that of the conventional phenol resin, the physical properties such as adhesive strength and productivity are inferior, and the above-mentioned technique has not been widely put into practical use at present.

Under these circumstances, it has been proposed to produce a wood board made of small wood pieces by using a thermal pressure molding adhesive containing polyvalent carboxylic acid and saccharides as main components (see Patent Documents 2 and 3). Patent Document 3 further proposes the addition of paratoluenesulfonic acid, phosphate, or an organic titanium compound as a catalyst.

When a wood board used for a floor material or the like is manufactured by using the thermal pressure molding adhesive described in Patent Documents 2 and 3 described above, for example, a polyvalent carboxylic acid is directly applied to a wood piece or the like as a raw material. Acids, sugars, catalysts, etc. are dispersed and mixed, and this is hot-press molded to form a wood board.

Japanese Patent No. 3796604 International Publication No. 2010/001988 Japanese Unexamined Patent Publication No. 2012-214687

"New Wood Material Handbook" Gihodo Publishing p.361 "New Developments in Wood Chemicals" CMC Publishing p.225 (2007)

However, the adhesives for thermal pressure molding described in Patent Documents 2 and 3 are all liquid adhesives, and since the adhesive is supplied to a wood board raw material such as a small piece of wood and then the adhesive is cured, the adhesive is used. A step of evaporating and drying the water and organic solvent inside was required. Therefore, there are problems that formaldehyde is released into the work environment, aerosol of volatilized organic solvent is released, and the molding time of the wood board becomes long, which improves the work environment and shortens the drying process. There was room for further improvement in improving productivity. Further, in the adhesives for thermal pressure molding of Patent Documents 2 and 3, it is necessary to contain saccharides, particularly sucrose, in the adhesive composition, and it has been desired to reduce the production cost of the adhesive raw material.

The present invention has been made in view of the above circumstances, and is for thermal pressure molding in a semi-cured state, which is low cost, has a small burden on the environment, and can improve the working environment and shorten the drying process. The subject is to provide a powder adhesive.

The present invention is characterized by the following in order to solve the above problems.

That is, the powder adhesive for hot pressure molding in the semi-cured state of the present invention is characterized in that wood powder is steamed or steamed and then mixed with a polyvalent carboxylic acid and heat treated.

According to the present invention, it is possible to provide a powder adhesive for hot pressure molding which is in a semi-cured state, which is low in cost, has less burden on the environment, and can improve the working environment and shorten the drying process.

Hereinafter, embodiments of the present invention will be described. The method for producing a powder adhesive for hot pressure molding in a semi-cured state of the present embodiment is characterized in that wood powder is steamed or steamed and then mixed with a polyvalent carboxylic acid and heat treated.

In the method for producing a powder adhesive for thermal pressure molding of the present embodiment, hemicellulose in the wood flour is hydrolyzed by steaming or heat-steaming the wood flour, and can react with the polyvalent carboxylic acid described later. It is considered that saccharides such as oligosaccharides, disaccharides and monosaccharides are produced. Such a hydrolysis reaction of hemicellulose is not observed when the wood powder is simply heated using a heating device such as a dryer or a hot plate, and the wood powder is subjected to wet conditions such as steaming treatment or heated steam treatment. It can be remarkably confirmed when heated. Therefore, unlike the adhesives for thermal pressure molding described in Patent Documents 2 and 3, even if saccharides are not directly added to the adhesive raw material, wood chips and the like can be produced by the saccharides produced by decomposing hemicellulose derived from wood flour. It is possible to impart sufficient adhesiveness to the adhesive so that it can be adhered to each other. This leads to cost reduction of the adhesive raw material.

In the method for producing a powder adhesive for hot pressure molding of the present embodiment, a conventionally known method can be appropriately used as the steaming treatment of wood powder, but the loss of heated steam is suppressed and the temperature is in a high temperature state of 100 ° C. or higher. It is preferably considered that the autoclave treatment is performed from the viewpoint that the above can be maintained. Examples of the conditions for the steaming treatment include a treatment time of about 10 to 30 minutes at a temperature in the range of 120 ° C. to 200 ° C. If the conditions during the steaming treatment are within the above ranges, hemicellulose can be decomposed to produce a sufficient amount of saccharides necessary for imparting adhesiveness.

Further, in the method for producing a powder adhesive for hot pressure molding of the present embodiment, it is preferably considered that the heated steam treatment is a superheated steam treatment. The superheated steam treatment can be carried out by appropriately using a device such as a conventionally known batch type superheated steam treatment device or a superheated steam continuous furnace. Examples of the conditions for the heated steam treatment and the superheated steam treatment include a treatment time of about 10 minutes to 30 minutes at a temperature in the range of 120 ° C. to 300 ° C. When the conditions during the heated steam treatment and the superheated steam treatment are within the above ranges, hemicellulose can be decomposed to produce a sufficient amount of saccharides necessary for imparting adhesiveness.

Examples of wood powder that can be used in the method for producing a powder adhesive for thermal pressure molding of the present embodiment include thinned wood and building demolition wood. Examples of wood flour derived from thinned wood include crushed coniferous trees such as pine, sugi, and cypress, and hardwoods such as lauan, kapol, and poplar. Examples of wood powder derived from building demolition materials include crushed waste wood boards such as wood plywood, particle board, medium density fiberboard, and oriented strand board. Further, cut and crushed agricultural waste such as bamboo and rice husks can be appropriately used. Such wood flour may be used alone or in combination of two or more.

Although the particle size of the wood powder is not particularly limited, it is used as a powder adhesive. Therefore, for example, the range of 0.1 mm to 2 mm is exemplified, and it is preferable that the particle size is smaller in consideration of dispersibility.

The polyvalent carboxylic acid that can be used in the method for producing a powder adhesive for thermal pressure molding of the present embodiment is not particularly limited as long as it is a compound having a plurality of carboxyl groups. Examples of these polyvalent carboxylic acids include citric acid, tartaric acid, malic acid, succinic acid, oxalic acid, adipic acid, malonic acid, phthalic acid, sebacic acid, maleic acid, fumaric acid, itaconic acid and the like. it can. In addition, glutaric acid (1,5-pentanedioic acid), gluconic acid, glutaconic acid, pentendioic acid and the like can also be mentioned. In addition, anhydrides of these polyvalent carboxylic acids can also be used. Among them, citric acid, tartaric acid, malic acid, gluconic acid, sebacic acid, itaconic acid and the like can be used more preferably because they are produced from plants, and in particular, the polyvalent carboxylic acid is citric acid. Is even more preferably considered. When a polyvalent carboxylic acid made from a plant is used, the use of fossil resources can be suppressed, so that a powder adhesive for thermal pressure molding can be obtained with less burden on the environment. These polyvalent carboxylic acids may be used alone or in combination of two or more. The polycarboxylic acid may be referred to as a polycarboxylic acid depending on the literature.

In such a method for producing a powder adhesive for thermal pressure molding, when wood powder is steam-treated or heat-steam-treated and a mixture obtained by mixing with a polyvalent carboxylic acid is heat-treated, the following reaction occurs and adhesion occurs. It is presumed that a reaction product having sex is produced.

That is, acid hydrolysis of oligosaccharides, which are decomposition products of hemicellulose derived from wood flour, and disaccharides such as sucrose, proceeds. This acid hydrolysis produces monosaccharides such as glucose and fructose, and these monosaccharides are heated in the coexistence with a polyvalent carboxylic acid to cause a dehydration reaction. In particular, the dehydration reaction of fructose, which is a monosaccharide, produces 5- (hydroxymethyl) furfural as a reaction product. Furfural, which is a kind of sugar-modified product, becomes a thermosetting resin, furan resin, by further heating, and the furan resin can be cured in the presence of a polyvalent carboxylic acid. Therefore, a mixture obtained by steaming or steaming wood powder and mixing it with a polyvalent carboxylic acid can be used as a thermosetting adhesive. Among the monosaccharides, glucose becomes a sugar ester polymer by a dehydration condensation reaction, and is filled in the voids between the wood pieces, which are the raw materials of the wood board, and hardened. Therefore, like the furan resin, the sugar ester polymer can be used as a thermosetting adhesive. It is considered that the polyvalent carboxylic acid after the heat treatment is not significantly modified, and remains in the form of the polyvalent carboxylic acid.

The blending ratio of the wood powder and the polyvalent carboxylic acid is not particularly limited, but usually, the wood powder is about 80 to 20% by mass and the polyvalent carboxylic acid is 20 with respect to the total amount of the powder adhesive for hot pressure molding. It is considered that it is about 80% by mass. When the blending ratio of the wood powder and the polyvalent carboxylic acid is within the above range, it is possible to produce a furan resin and a sugar ester polymer necessary and sufficient for imparting adhesiveness to the obtained powder adhesive for hot pressure molding. It is possible. Further, the obtained powder adhesive for hot pressure molding can be put into a semi-cured state (so-called B stage), which facilitates handling.

The temperature conditions for heat-treating the mixture obtained by steaming or heat-steaming wood powder and mixing it with a polyvalent carboxylic acid are not particularly limited, and examples thereof include a range of 100 ° C. to 200 ° C. ..

In this way, the wood powder is steamed or heated with steam, and the mixture obtained by mixing with the polyvalent carboxylic acid is heat-treated, and then powdered as necessary to obtain a heat pressure in a semi-cured state. A powder adhesive for molding can be obtained. Examples of the pulverization method include a method of pulverizing using a conventionally known pulverizing means such as a crusher. Further, as long as the function of the powder adhesive for hot pressure molding is not impaired, it is considered to add an excipient or the like.

In addition, the adhesive raw material containing the reaction product of the polyvalent carboxylic acid and the sugar-modified product in the state where the reaction by the heat treatment as described above is completed as an adhesive component exhibits water solubility and thermoplastic properties. Shown. Therefore, it is also possible to obtain a powder adhesive for thermal pressure molding in a semi-cured state by once dispersing the adhesive raw material in water and then drying and powdering it by a conventionally known method.

In the method for producing a powder adhesive for thermal pressure molding of the present embodiment, it is preferable to add ammonium sulfate or ammonium chloride to a mixture obtained by steaming or heat-steaming wood powder and mixing it with a polyvalent carboxylic acid. Will be considered. Ammonium sulfate and ammonium chloride are used for the esterification reaction between the hydroxyl group of cellulose in the wood piece, which is the raw material of the wood board, and the polyvalent carboxylic acid when the wood board is manufactured using the powder adhesive for hot pressure molding of the present invention. It is compounded as a reaction catalyst that promotes.

Usually, the esterification reaction between a polyvalent carboxylic acid and a hydroxyl group of cellulose in a piece of wood proceeds relatively slowly over time. Therefore, the reaction time of esterification can be shortened by blending at least ammonium sulfate or ammonium chloride as a catalyst.

The blending ratio of ammonium sulfate or ammonium chloride is not particularly limited, but it is usually considered that it is 20% by mass or less, preferably less than 10% by mass, based on the total amount of the powder adhesive for hot pressure molding. By setting the mixing ratio of the catalyst in the above range, the reaction time for esterification can be further shortened, and the water resistance of the obtained wood board can be improved. Since these reaction catalysts are relatively weak salts, the strength of the base metal is maintained.

When the powder adhesive for hot pressure molding thus obtained is mixed with an aggregate of wood pieces as described above and further heated, the curing reaction of the powder adhesive for hot pressure molding proceeds and the powder adhesive is completely cured. Complete. In this curing reaction, the reaction products of sugar-modified products such as the furan resin and the sugar ester polymer have a relatively large molecular weight and act as a tough auxiliary adhesive. On the other hand, the polyvalent carboxylic acid undergoes an esterification reaction with the hydroxyl group of cellulose in the woody small pieces, and is firmly cured in a state where the molecular weight is relatively small. That is, when a wood board is manufactured using the powder adhesive for thermal pressure molding of the present embodiment, it can withstand practical use without impairing the bending strength due to different curing reactions of the reaction product of the sugar modified product and the polyvalent carboxylic acid. It is possible to produce a wood board having water resistance.

Further, as described above, the adhesive obtained by the method for producing a powder adhesive for thermal pressure molding of the present embodiment does not contain an organic solvent or formaldehyde in the reaction system, and formaldehyde is generated by decomposition. Does not contain secondary amines. Therefore, the emission of formaldehyde can be suppressed. In addition, it is possible to suppress the emission of the aerosol of the organic solvent derived from the adhesive. Furthermore, since wood flour and polyvalent carboxylic acid, which are generally available as materials, are used, and it is not necessary to supply sugars added to the conventional biomass-derived adhesive from the outside, the raw material cost of the adhesive is reduced. It can be reduced and it is possible to manufacture a powder adhesive for thermal pressure molding at low cost.

In the method for producing a powder adhesive for hot pressure molding of the present embodiment, other components such as a thickener and a reaction accelerator are used as components other than the above as long as the effect of the powder adhesive for hot pressure molding is not impaired. It may be contained. Further, the catalyst for the esterification reaction is not limited to ammonium sulfate or ammonium chloride, and other catalysts such as paratoluenesulfonic acid may be used in combination.

The production of a wood board using the heat-pressure molding powder adhesive of the present embodiment is carried out by supplying the heat-pressure molding powder adhesive to an aggregate of wood pieces that are the raw material of the wood board and performing hot-press molding. Will be.

The molding pressure, molding temperature, molding time, etc. in hot pressure molding are appropriately set according to the type, shape, surface texture, thickness of the wood board, etc. of the wood piece. Considering that the physical properties of the wood board do not deteriorate, the reaction rate does not decrease easily, and the curing tends to be sufficient, the molding temperature, that is, the curing temperature of the powder adhesive for thermal pressure molding is, for example, 140 to 230 ° C. It is preferably in the range of. That is, it is preferably considered that the heating temperature of the heat treatment after mixing with the polyvalent carboxylic acid is lower than the curing temperature of the powder adhesive for thermal pressure molding. In this way, by setting the heat treatment conditions to be milder than the heating temperature at the time of curing molding, the powder adhesive for thermal pressure molding can be put into a semi-cured state.

Further, in consideration of improving the strength of the wood board by sufficiently crimping the powder adhesive for hot pressure molding and the wood small piece of the adherend, and considering the moldability, the molding pressure is, for example, 0.5 to 4 MPa. It is preferably in the range of.

As the wood pieces of the wood board raw material, those obtained from wood parts such as vegetation, bark, seeds, leaves and the like can be used. For example, wood strands, wood chips, wood fibers, plant fibers, commercially available plant powder (for example, bark powder), chips obtained by crushing recycled materials and the like can be mentioned. Examples of the wood board produced by adhering an aggregate of such wood pieces with the powder adhesive for thermal pressure molding of the present embodiment include a particle board, a fiber board, and MDF.

In the above embodiment, when a catalyst of ammonium sulfate or ammonium chloride is used, the wood powder is steamed or heat-steamed, and the catalyst is mixed with the mixture obtained by mixing with the polyvalent carboxylic acid, and the catalyst is heat-treated to heat pressure. Although it is a powder adhesive for molding, the catalyst can be dispersed in wood pieces in advance.

Examples of the method for dispersing the catalyst of ammonium sulfate and ammonium chloride in the aggregate of woody small pieces include a method using an aqueous dispersion of the catalyst, a method using a powder of the catalyst, and the like. The aqueous dispersion of the catalyst means a liquid in which the catalyst is dissolved or uniformly dispersed in water.

The method using the aqueous dispersion of the catalyst can be carried out, for example, by mixing the aqueous dispersion of the catalyst of ammonium sulfate or ammonium chloride with an aggregate of woody pieces and then drying the mixture. The drying is preferably in an air-dried state by curing, but it may be in a touch-dried state.

Further, in consideration of promoting the activity of the esterification reaction between the hydroxyl group of the cellulose of the wood small piece as the base material and the polyvalent carboxylic acid, the concentration of the aqueous dispersion of the catalyst is preferably 5% by mass or more. As a method of mixing the aqueous dispersion of the catalyst and the aggregate of wood pieces, a method of spraying the water dispersion of the catalyst on the aggregate of wood pieces by spraying or the like, or an assembly of wood pieces in the aqueous dispersion of the catalyst. Examples thereof include a method of impregnating the body.

In the method using the catalyst powder, the catalyst can be dispersed in the aggregate of the wood pieces by mixing the catalyst powder and the aggregate of the wood pieces. Examples of the mixing method include a method in which catalyst powder is sprayed on an aggregate of woody small pieces and mechanically mixed as needed.

By dispersing the catalyst in small pieces of wood in advance, it is possible to improve the reactivity by using the powder adhesive for thermal pressure molding of the present embodiment which does not contain the catalyst.

According to the powder adhesive for hot pressure molding of the present embodiment described above, the powder adhesive for hot pressure molding is provided at low cost, less burden on the environment, and can improve the working environment and shorten the drying process. can do.

The adherend of the powder adhesive for thermal pressure molding is not limited to small pieces of wood, and for example, a wood plate-like member such as a veneer or a thin plate may be used. Further, the shape to be molded is not limited to the board, and a three-dimensional molded product may be molded.

Claims (5)

A method for producing a powder adhesive for thermal pressure molding in a semi-cured state, which comprises steaming or heat-steaming wood powder, then mixing it with a polyvalent carboxylic acid, and heat-treating it. The method for producing a powder adhesive for thermal pressure molding according to claim 1, wherein the heated steam treatment is a superheated steam treatment. The method for producing a powder adhesive for thermal pressure molding according to claim 1 or 2 , wherein ammonium sulfate or ammonium chloride is added to the mixture of the wood powder and the polyvalent carboxylic acid, and then the heat treatment is performed. .. The thermal pressure according to any one of claims 1 to 3, wherein the heating temperature of the heat treatment after mixing with the polyvalent carboxylic acid is lower than the curing temperature of the powder adhesive for hot pressure molding. A method for producing a powder adhesive for molding. The method for producing a powder adhesive for thermal pressure molding according to any one of claims 1 to 4, wherein the polyvalent carboxylic acid is citric acid.