JP6973597B2 - Adhesive for wood boards - Google Patents

Description

The present invention relates to an adhesive for wood boards.

Wood boards can be freely designed in thickness and size compared to natural materials such as wood. Moreover, the wooden board is lightweight and has excellent heat insulation, sound insulation, and shear rigidity. Therefore, the wood board is used as a building material for a wide range of purposes, such as being used as a base material for floors and walls, and being processed into furniture by attaching a decorative board to the surface.
A wood board is usually obtained by mixing a wood material such as wood chips or wood fibers with an adhesive, heat-press molding the wood material, and curing the adhesive to bond the wood materials to each other.
Formaldehyde-based resins such as urea-formaldehyde resin (urea resin), melamine-formaldehyde resin (melamine resin), phenol-formaldehyde resin (phenol resin), and resorcinol-formaldehyde resin (resorcinol resin) are used as adhesives for wood boards. It is used.

However, formaldehyde caused by the adhesive may be emitted from the wood board using the formaldehyde-based resin as the adhesive for the wood board. In recent years, due to the revision of the Building Standard Law, the indoor concentration of formaldehyde has been strictly regulated, and the amount of formaldehyde emitted from building materials such as wooden boards has also been regulated.
Therefore, starch is used as an adhesive for wood boards with reduced formaldehyde emission (for example, Patent Documents 1 to 5).

Japanese Unexamined Patent Publication No. 2003-147307 Japanese Unexamined Patent Publication No. 2007-331286 Japanese Unexamined Patent Publication No. 2008-105246 Japanese Patent Publication No. 2008-545043 Special Table 2009-541809 Publication No.

When starch is heated in the presence of sufficient water, it gelatinizes and exerts an adhesive effect, but when the water content is low, starch is difficult to gelatinize and sufficient adhesive strength is difficult to obtain.
Among the wood boards, particle boards and medium density fiberboards are usually manufactured by dry forming (dry method), so that starch is heated in a state of low water content in the process of manufacturing wood boards. Therefore, the wood board using starch as an adhesive has insufficient strength.

The present invention provides an adhesive for a wood board that can obtain a wood board having reduced formaldehyde emission and sufficient strength, and a wood board having reduced formaldehyde emission and sufficient strength and a method for producing the same. The purpose is to do.

The present invention has the following aspects.
[1] An adhesive for a wood board (however, a carboxyl group) containing starch and an epoxy resin, and the mass ratio of the starch to the epoxy resin is starch: epoxy resin = 8: 1 to 30: 1. An aqueous resin emulsion obtained by emulsifying and polymerizing a radically polymerizable monomer copolymerizable with the contained monomer and the carboxyl group-containing monomer, the aqueous resin emulsion containing acetacetylated polyvinyl alcohol, and the aqueous resin emulsion. Except for those containing at least one of the ethylene-vinyl acetate copolymer emulsions).
[2] The adhesive for wood board according to [1], wherein the starch is modified starch.
[3] The adhesive for wood board according to [2], wherein the modified starch is a phosphoric acid monoesterified starch.

According to the present invention, an adhesive for a wood board that can obtain a wood board having reduced formaldehyde emission and sufficient strength, and a wood board having reduced formaldehyde emission and sufficient strength and a method for producing the same. Can be provided.

Hereinafter, the present invention will be described in detail.
In the present specification, the term "total mass" includes the mass of a medium such as water. In addition, the term "total mass in terms of solid content" does not include the mass of a medium such as water, but refers only to the amount of solid content.

[Adhesive for wood board]
The adhesive for wood boards of the present invention (hereinafter, also simply referred to as “adhesive”) contains starch and an epoxy resin.

<Starch>
The starch contained in the adhesive is in a non-gelatinized (pregelatinized) state.
Here, "gelatinization" means that water enters the inside of starch particles in which starch molecules are aggregated by hydrogen bonds or steric entanglement, blocks hydrogen bonds, disperses the starch molecules, and hydrates to a colloidal solution. It means to be in a state.

Examples of the starch include, but are not limited to, starches of plant origin that are widely used, such as cornstarch, tapioca, and potato starch, and starches of any origin can be used.

The starch may be unprocessed starch (unprocessed starch) or processed starch (modified starch). Modified starch is preferable from the viewpoint that the gelatinization start temperature is low and the gelatinization tends to be easy even in a low water content state.
Examples of the modified starch include those obtained by subjecting the starch to one or more treatments such as esterification treatment, etherification treatment, oxidation treatment, acid treatment and enzyme treatment. Among these, esterified starch such as phosphoric acid monoesterified starch and etherified starch such as cationized starch are preferable from the viewpoint of easy gelatinization even in a low water content state. In particular, the phosphoric acid monoesterified starch has a highly hydrophilic phosphoric acid group. Therefore, water existing around the starch particles such as water vapor generated in the production of the wood board is easily taken into the starch particles. Therefore, phosphoric acid monoesterified starch is suitable because it is easy to gelatinize even in a state of lower water content.
In the present invention, the above-mentioned modified starch or modified starch can be used alone or in combination of two or more.

Phosphoric acid monoesterified starch is obtained by subjecting phosphoric acid to an esterification reaction of phosphoric acid (including a phosphate), and one of the bonds of the phosphoric acid group is ester-bonded to the hydroxy group of the starch.
The ratio of bound phosphorus in the phosphoric acid monoesterified starch, that is, the mass of phosphorus esterified with the hydroxy group with respect to the total mass of the phosphoric acid monoesterified starch is preferably 0.05% by mass or more. When the ratio of bound phosphorus is 0.05% by mass or more, the phosphoric acid monoesterified starch is easily gelatinized in a low water state and low energy (low temperature). The higher the proportion of bound phosphorus, the lower the gelatinization start temperature, and it tends to be easier to gelatinize even in a low water content state, but if the proportion of bound phosphorus is too high, the proportion of the starch skeleton excluding the phosphoric acid portion becomes Since the amount is reduced, the adhesive strength may decrease. Therefore, the ratio of bound phosphorus is preferably 5% by mass or less with respect to the total mass of the phosphoric acid monoesterified starch.

The ratio of bound phosphorus is determined as follows.
First, the sample (phosphoric acid monoesterified starch) is dispersed in water and filtered using filter paper or the like to remove components such as chemicals that are not bound to the starch. When the starch component is easily eluted in water, it is preferable to add ethanol to the water as necessary to suppress the elution of the starch component when dispersing the sample in water.
A sample from which components such as chemicals have been removed is wet-decomposed with a mixed acid of sulfuric acid / nitric acid and perchloric acid to obtain a decomposition solution. After wet decomposition, water is added to the decomposition liquid and sufficiently heated in a boiling bath to hydrolyze the phosphoric acid component in the decomposition liquid into orthophosphoric acid.
The molybdenum blue specific color of the obtained decomposed sample is measured by the Fishe-Subbarow method, and the ratio of bound phosphorus is determined.

Phosphoric acid monoesterified starch is obtained, for example, by mixing phosphoric acid, at least one of phosphoric acid and phosphate, and optionally an inorganic acid or an organic acid, and then roasting. At this time, further addition of urea gives carbamic acid phosphate monoesterified starch.
As the roasting method, for example, a known method described in Japanese Patent Publication No. 45-20512 can be adopted. The following is an example of a method for producing phosphoric acid monoesterified starch.

First, a phosphoric acid aqueous solution in which at least one of phosphoric acid and phosphate and, if necessary, an inorganic acid or an organic acid is dissolved in water is impregnated with starch. Alternatively, the phosphoric acid aqueous solution is sprayed onto the starch by spraying or the like. Then, the aqueous phosphoric acid solution and the starch are stirred until uniform to obtain a starch mixture. The obtained starch mixture is dried to a desired moisture content, if necessary, and then a heating reaction is carried out using a dry roasting device such as a belt dryer, a flash dryer, a stirring dryer, or a static dryer. By the reaction, the hydroxy group of the starch is ester-bonded with phosphoric acid or phosphate to obtain a phosphoric acid monoesterified starch.
Examples of the phosphate include sodium phosphate, potassium phosphate, ammonium phosphate, sodium polyphosphate and the like.

When urea is added to the aqueous phosphoric acid solution, phosphoric acid esterification of the starch tends to proceed at a low temperature. Since urea decomposes and reacts with the hydroxy group of the starch to form a carbamic acid ester, the carbamic acid monoesterified starch (carbamic acid phosphate monoesterified starch) is a carbamic acid monoesterified and carbamic acid esterified starch. Is obtained.

<Epoxy resin>
The epoxy resin is a resin having two or more epoxy groups in one molecule, or a resin produced by a ring-opening reaction of the epoxy groups.
In the present invention, even a monomer is referred to as an "epoxy resin" as long as it has two or more epoxy groups in one molecule.

The mass average molecular weight of the epoxy resin is preferably 5000 or less, more preferably 100 to 3000, and even more preferably 150 to 1000. If the mass average molecular weight of the epoxy resin is 5000 or less, the handling property is excellent, and if it is 150 or more, the adhesive strength is further improved when used for a wood board.
The mass average molecular weight of the epoxy resin is a value calculated by polystyrene conversion using gel permeation chromatography (GPC).

The epoxy equivalent of the epoxy resin is preferably 1000 g / eq or less, more preferably 100 to 500 g / eq. When the epoxy equivalent of the epoxy resin is within the above range, the adhesive strength is further improved when used for a wood board.
The epoxy equivalent of the epoxy resin is a value measured according to JIS K-7236: 2009.

Examples of the epoxy resin include aromatic epoxy compounds, and specific examples thereof include bisphenol type epoxy resins (for example, bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, brominated bisphenol A diglycidyl ether, etc.). , Novolak type epoxy resin (for example, phenol novolac type epoxy resin, cresol novolac type epoxy resin, etc.), biphenyl type epoxy resin, hydroquinone diglycidyl ether, resorcin diglycidyl ether, terephthalic acid diglycidyl ester, phthalic acid diglycidyl ester, styrene- Examples thereof include an epoxie of a butadiene copolymer, an epoxie of a styrene-isoprene copolymer, and an addition reaction product of a terminal carboxylate polybutadiene and a bisphenol A type epoxy resin.

Further, as the epoxy resin, for example, a polyamide epoxy resin may be used in addition to the above-mentioned aromatic epoxy compound.
Examples of the polyamide epoxy resin include those having an epoxy group in the molecule, which is obtained by reacting epichlorohydrin such as epichlorohydrin on the polyamide resin, and specifically, polyamide epichlorohydrin having a side chain of an epoxy ring. Examples thereof include a phosphorus resin and a polyamide amine epichlorohydrin resin.

The epoxy resin can be obtained by reacting a compound (A) having an epoxy group, such as epihalohydrin, with a compound (B) having a functional hydrogen. When, for example, 4,4'-dihydroxy-2,2'-diphenylpropane is used as the compound (B), a bisphenol A type epoxy resin can be obtained.

The epoxy resin may be a liquid or a solid at room temperature (25 ° C.).
Further, the epoxy resin may be dissolved or dispersed in an aqueous medium. Examples of the aqueous medium include water and a mixture of water and a water-soluble organic solvent. Examples of the water-soluble organic solvent include alcohols such as methanol, ethanol and propanol; ketones such as acetone and methyl ethyl ketone; ethers such as diethyl ether and ethylene glycol monotarsial butyl ether.
When a liquid epoxy resin at room temperature or an epoxy resin dissolved or dispersed in an aqueous medium is used as the epoxy resin, even if part or all of the starch in the adhesive is dispersed in the epoxy resin or the aqueous medium. good.

<Water>
The adhesive of the present invention may contain water from the viewpoint of facilitating the gelatinization of starch when used in the production of wood boards.
When the starch contains water, the water in the starch is contained in the solvent. When a epoxy resin dissolved or dispersed in water is used, the solvent also contains water in which the epoxy resin is dissolved or dispersed.

<Arbitrary ingredient>
The adhesive of the present invention may contain components (arbitrary components) other than starch, epoxy resin and water.
Examples of the optional component include resins other than epoxy resins (other resins), solvents other than water, additives and the like.
Examples of other resins include urea resin, melamine resin, phenol resin, resorcinol resin, vinyl acetate resin, urethane resin and the like.
Examples of the solvent include the water-soluble organic solvent exemplified above in the description of the epoxy resin.
Examples of the additive include known additives to be blended in adhesives for wood boards, and specifically, flame retardant, compatibilizer, plasticizer, antioxidant, mold release agent, light resistant agent, and weather resistant agent. Agents, colorants, pigments, modifiers, anti-drip agents, antistatic agents, antioxidants, fillers, reinforcing agents (eg glass fiber, carbon fiber, talc, clay, mica, glass flakes, milled glass, etc. Glass beads, crystalline silica, alumina, silicon nitride, alumina nitride, boron nitride, etc.) and the like.

From the viewpoint of reducing the emission of formaldehyde, it is preferable that the adhesive does not substantially contain a substance that emits formaldehyde. Examples of the substance that dissipates formaldehyde include formaldehyde-based resins such as urea resin, melamine resin, phenol resin, and resorcinol resin.
Here, "substantially free" means that the content of the substance that emits formaldehyde is less than 0.1% by mass with respect to the total mass of the adhesive.
Since the adhesive of the present invention contains starch and an epoxy resin, when a formaldehyde-based resin is contained in the adhesive, sufficient adhesiveness can be exhibited even in a small amount. Therefore, the amount of formaldehyde-based resin used can be reduced.

<Ratio>
The mass ratio of starch in the adhesive to the epoxy resin is preferably starch: epoxy resin = 4: 1 to 50: 1, more preferably 8: 1 to 40: 1, and 10: 1 to 30: in terms of solid content. 1 is more preferable. When the mass ratio of starch and epoxy resin is within the above range, the adhesive strength is further improved when used for a wood board.

The total content of starch and epoxy resin in the adhesive is preferably 50% by mass or more, more preferably 60% by mass or more, still more preferably 70% by mass or more, based on the total mass of the adhesive in terms of solid content. .. When the total content of the starch and the epoxy resin is 50% by mass or more, the adhesive strength is further improved when used for a wood board.
The total content of starch and epoxy resin in the adhesive is preferably 95% by mass or less, more preferably 90% by mass or less, and further preferably 85% by mass or less, based on the total mass of the adhesive in terms of solid content. preferable.

In the present invention, it is preferable to contain phosphoric acid monoesterified starch as the starch contained in the adhesive, and the ratio of the phosphoric acid monoesterified starch to the total mass of the starch contained in the adhesive is 50% by mass or more. Is preferable, 70% by mass or more is more preferable, 80% by mass or more is further preferable, 90% by mass or more is particularly preferable, and 100% by mass is most preferable.

The content of the optional component in the adhesive is preferably 35% by mass or less, more preferably 10% by mass or less, still more preferably 5% by mass or less, based on the total mass of the adhesive.
However, the total of the starch and epoxy resin contained in the adhesive in terms of solid content, the water content, and the content of any component exceeds 100% by mass with respect to the total mass of the adhesive. Make it not exist.

<Manufacturing method>
The adhesive of the present invention can be obtained by mixing starch, an epoxy resin, and an optional component, if necessary. At this time, water may be further added.
Further, at least the starch and the epoxy resin may be stored in a non-contact state until immediately before the use of the adhesive. In the present invention, an aggregate of containers containing at least starch and epoxy resin separately is also referred to as an "adhesive kit for wood board".

<Action effect>
As described above, since wood boards such as particle boards and medium density fiberboards are usually manufactured by dry forming, starch is heated in a state of low water content in the process of manufacturing wood boards. Therefore, starch is difficult to gelatinize and it is difficult to obtain sufficient adhesive strength.
However, since the adhesive of the present invention contains an epoxy resin in addition to starch, sufficient adhesive strength can be exhibited even if the adhesive is used in a low water content state in the process of manufacturing a wood board. In particular, when modified starch (preferably phosphoric acid monoesterified starch) is used as the starch, the starch is easily gelatinized even in a low water content state, and the adhesive strength tends to be further increased. Therefore, if the adhesive of the present invention is used, a wood board having sufficient strength can be obtained.
Further, since the adhesive of the present invention contains an epoxy resin, a wood board having excellent water resistance can be obtained. Since the epoxy resin does not contain formaldehyde, the adhesive of the present invention can reduce the emission of formaldehyde. Further, since the adhesive of the present invention contains starch and an epoxy resin, sufficient adhesiveness can be exhibited even in a small amount when a formaldehyde-based resin is used in combination. Therefore, since the amount of formaldehyde-based resin used can be reduced, the emission of formaldehyde can be reduced.
When the adhesive does not contain starch, it is difficult to develop adhesiveness only with the epoxy resin, and a wood board having sufficient strength cannot be obtained.

<Use>
Since the adhesive of the present invention easily develops sufficient adhesive strength even when used in a low moisture state, it is used for producing a wood board (for example, particle board, medium density fiberboard) manufactured by dry forming. Suitable as an adhesive.

[Wood board]
The wood board of the present invention contains a wood raw material, starch, and an epoxy resin.

<Wood-based materials>
Examples of the form of the wood-based material include small pieces such as chips, flakes, wafers, and strands; and fibrous forms. For example, a chip-shaped wood raw material is called "wood chip", and a fibrous wood raw material is called "wood fiber".
As the wood raw material, waste wood from sawing, building demolition wood, thinned wood and the like can be used. If these woods are used, the environmental load can be reduced and the wood can be manufactured at low cost.

<Starch>
The starch contained in the wood board is in a gelatinized (pregelatinized) state.
Examples of the starch include the starch exemplified above in the description of the adhesive for wood board of the present invention. Of these, modified starch is preferable, and among them, phosphoric acid monoesterified starch is more preferable.

<Epoxy resin>
Examples of the epoxy resin include the epoxy resin exemplified above in the description of the adhesive for wood board of the present invention.

<Water>
Wood boards usually contain moisture.
Examples of the water content of the wood board include water derived from wood raw materials and water derived from starch. When a epoxy resin dissolved or dispersed in water is used, water derived from the epoxy resin is also contained in the water content of the wood board. Further, as will be described in detail later, when water is used in the production of a wood board, a part of this water is also contained in the water content of the wood board.

<Arbitrary ingredient>
The adhesive of the present invention may contain components (arbitrary components) other than starch, epoxy resin and water.
Examples of the optional component include optional components (other resins, solvents other than water, additives) exemplified above in the description of the adhesive for wood board of the present invention.
From the viewpoint of reducing the emission of formaldehyde, it is preferable that the wood board does not substantially contain a substance that emits formaldehyde.
Here, "substantially free" means that the content of the substance that emits formaldehyde is less than 0.1% by mass with respect to the total mass of the wood board.

<Ratio>
The content of the wood-based material in the wood board is preferably 70% by mass or more, more preferably 79% by mass or more, still more preferably 84% by mass or more, based on the total mass of the wood board in terms of solid content. .. The content of the wood raw material in the wood board is preferably 95% by mass or less, more preferably 93% by mass or less, still more preferably 90% by mass or less, based on the total mass of the wood board in terms of solid content. When the content of the wood-based material is within the above range, a wood-based board in which the wood-based materials are sufficiently adhered to each other can be obtained while maintaining the texture of the wood-based board.

The content of starch in the wood board is preferably 1% by mass or more, more preferably 4% by mass or more, still more preferably 9% by mass or more, based on the total mass of the wood board in terms of solid content. Further, the content of starch in the wood board is preferably 25% by mass or less, more preferably 20% by mass or less, and further preferably 15% by mass or less, based on the total mass of the wood board in terms of solid content. preferable. When the starch content is within the above range, a wood board having sufficient strength can be obtained.

The content of the epoxy resin in the wood board is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and 1% by mass, based on the total mass of the wood board in terms of solid content. The above is more preferable. When the content of the epoxy resin is 0.1% by mass or more, a wood board having sufficient strength and water resistance can be obtained. The effect of improving the strength and water resistance of the wood board tends to increase as the content of the epoxy resin increases, but even if the content of the epoxy resin is too high, it reaches a plateau. Considering the balance between the strength and water resistance of the wood board and the manufacturing cost, the content of the epoxy resin in the wood board is 10% by mass or less in terms of solid content with respect to the total mass in terms of solid content of the wood board. It is preferable, 5% by mass or less is more preferable, and 3% by mass or less is further preferable.
However, the total content of the wood raw material, starch and epoxy resin contained in the wood board in terms of solid content shall not exceed 100% by mass with respect to the total mass of wood board in terms of solid content.

The mass ratio of starch in the wood board to the epoxy resin is preferably starch: epoxy resin = 4: 1 to 50: 1, more preferably 8: 1 to 40: 1, and 10: 1 to 1 in terms of solid content. 30: 1 is more preferred. When the mass ratio of starch and epoxy resin is within the above range, the adhesive strength is further improved when used for a wood board.

The total content of the wood raw material, starch and epoxy resin in the wood board is preferably 75% by mass or more, more preferably 80% by mass or more, and 85% by mass or more with respect to the total mass of the wood board in terms of solid content. Is even more preferable. When the total content of the wood-based material, starch, and epoxy resin is 75% by mass or more, a wood-based board in which the wood-based materials are sufficiently adhered to each other can be obtained while maintaining the texture of the wood-based board.
The total content of the wood raw material, starch and epoxy resin in the wood board is preferably 95% by mass or less with respect to the total mass of the wood board in terms of solid content.

In the present invention, it is preferable to contain phosphoric acid monoesterified starch as the starch contained in the wood board, and the ratio of the phosphoric acid monoesterified starch to the total mass of the starch contained in the wood board is 50% by mass or more. Is preferable, 70% by mass or more is more preferable, 80% by mass or more is further preferable, 90% by mass or more is particularly preferable, and 100% by mass is most preferable.

The water content (moisture content) in the wood board is preferably 5 to 20% by mass, more preferably 5 to 15% by mass, still more preferably 5 to 10% by mass, based on the total mass of the wood board.
However, the total of the solid content of wood-based materials, starch and epoxy resin contained in the wood board and the water content shall not exceed 100% by mass with respect to the total mass of the wood board. ..

The content of the optional component in the wood board is preferably 20% by mass or less, more preferably 15% by mass or less, still more preferably 10% by mass or less, based on the total mass of the wood board.
However, the total of the solid content of wood-based materials, starch and epoxy resin contained in the wood board, the water content and the content of any component is 100 mass with respect to the total mass of the wood board. It shall not exceed%.

<Form of wood board>
Examples of the wood board include particle board, fiber board, oriented strand board and the like. Standards such as various strengths, types of adhesives, formaldehyde emission, flame retardancy, etc. are set by JIS of the Japanese Industrial Standards Committee according to the type of wood board. For example, for particle board, various standards are set in JIS A 5908: 2015. For fiber plates, various standards are set in JIS A 5905: 2014.

Particle board is a board that is hot-pressed by molding using an adhesive, using small pieces such as wood as the main raw material. Particle board includes base particle board, veneer particle board with veneer on both sides of particle board as a base material, decorative particle board with decorative paper on both sides or one side of particle board, structural particle board, etc. Can be mentioned.

The fiber board is a board made of fibers such as wood as a main raw material and heat-pressed by molding using an adhesive.
The fiberboard is roughly classified into three types according to the density and the manufacturing method. Specifically, an insulation fiberboard (soft fiberboard) having a density of less than ^{0.35 g / cm 3 and a density of 0.35 g / cm 3} or more. Examples thereof include medium density fiberboard (medium density fiberboard) and hard fiberboard (hard fiberboard) having ^{a density of 0.80 g / cm 3 or more.}
In the present invention, particle boards and medium density fiberboards manufactured by dry forming are suitable.

<Manufacturing method>
Wood boards can be manufactured by dry forming. Specifically, it is obtained by mixing the above-mentioned adhesive of the present invention and a wood-based raw material, and heat-press molding the obtained raw material mixture. By heating and pressurizing the raw material mixture, the wood-based raw materials in the raw material mixture are bound to each other by starch and epoxy resin.

When mixing the adhesive of the present invention with the wood-based material, water may be further added if necessary. The addition of water facilitates the gelatinization of starch.
Further, a wood-based raw material and starch may be mixed, and an aqueous solution of an epoxy resin and an optional component may be sprayed on the mixture, and then the mixture may be sufficiently stirred to prepare a raw material mixture.
If the proportion of water in the raw material mixture is too large, a large amount of steam may be generated during heat and pressure molding, which may cause a puncture. The content of water in the raw material mixture is preferably 10 to 25% by mass, more preferably 15 to 25% by mass, still more preferably 18 to 25% by mass, based on the total mass of the raw material mixture.

As the heat-press molding, a known method can be adopted, and examples thereof include press molding. Further, the mold may be filled with the raw material mixture, and the temporarily molded molding material (mat) may be main-molded by hot pressing. Further, instead of temporarily molding the raw material mixture, the raw material mixture may be formed into a predetermined shape, heated, precompressed, and then press-molded.
The conditions for heat and pressure molding are not particularly limited, but for example, the temperature is preferably 120 to 250 ° C., the pressure is preferably 0.5 to 15 MPa, and the molding time is preferably 1 to 20 minutes.

<Action effect>
The wood board of the present invention described above has sufficient strength because the wood raw materials are bonded to each other by gelatinized starch and an epoxy resin. Further, since the wood board of the present invention contains an epoxy resin, it is also excellent in water resistance. Since the epoxy resin does not contain formaldehyde, the wood board of the present invention can reduce the emission of formaldehyde. When the wood board does not contain starch, it is difficult to develop adhesiveness only with the epoxy resin, so that sufficient strength cannot be obtained. Further, since the wood board of the present invention is bonded with starch obtained by gelatinizing wood raw materials and an epoxy resin, when a formaldehyde-based resin is used in combination, even a small amount has sufficient strength. Therefore, since the amount of formaldehyde-based resin used can be reduced, the emission of formaldehyde can be reduced.
Further, in the method for producing a wood board of the present invention, since the adhesive of the present invention containing starch and an epoxy resin is used as the adhesive for the wood raw material, the emission of formaldehyde is reduced and sufficient strength is provided. It is possible to manufacture a wood-based board with starch.

<Use>
The wood board of the present invention is, for example, a roof base, a floor base, building members such as walls; interior materials such as floor materials, furniture, home appliances, kitchen utensils, housing equipment members such as storage; automobile interiors. It can be used for materials and the like.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited thereto.
The method used for measurement and evaluation in each example, and the method for producing phosphoric acid monoesterified starch are shown below.
Examples 1 to 3, 10, 13 to 15 are examples, and examples 4 to 9, 11 and 12 are comparative examples.

[Measurement / evaluation method]
<Measurement of bound phosphorus>
The sample (phosphoric acid monoesterified starch) was dispersed in a mixed solvent of water and ethanol, and filtered with a filter paper to remove components such as chemicals not bound to the starch.
A sample from which components such as chemicals had been removed was wet-decomposed with a mixed acid of sulfuric acid and nitric acid and perchloric acid to obtain a decomposition solution. After wet decomposition, water was added to the decomposition solution and sufficiently heated in a boiling bath to hydrolyze the phosphoric acid component in the decomposition solution to orthophosphoric acid.
The molybdenum blue specific color of the obtained decomposed sample was measured by the Fishe-Subbarow method, and the ratio of bound phosphorus was determined.

<Measurement of density>
The density of the particle board was measured according to JIS A 5908: 2015.

<Measurement of bending strength>
The bending strength of the particle board was measured according to JIS A 5908: 2015.
The bending strength is affected by the density. For example, the particle board manufactured in the same manner as in Example 1 described later had a density of 0.82 g / cm ³ and a bending strength of 13.4 N / mm ² . The bending strength of the particle board manufactured in the same manner as in Example 1 is that the density is different, except that the conditions of heat and pressure molding are separately changed so that the density is 0.68 ^{g / cm 3} or 0.75 g / cm ^3. was 9.9N / mm ² in the case of 0.68 g / cm ^3, a density of 11.2 N / mm ² in the case of 0.75 g / cm ^3. Table 1 shows the results of particle board density and bending strength.

When the density of the particle board was plotted on the horizontal axis (x-axis) and the bending strength of the particle board was plotted on the vertical axis (y-axis) to obtain a regression line, y = 25x-7.25, and the regression at this time. The coefficient of determination (R ² ) of the straight line was 0.9784. In this way, the density of the particle board and the bending strength were in a proportional relationship.
In each example, it is difficult to manufacture particle boards so that the densities of the particle boards match. Therefore, in order to prevent the bending strength of the particle board in each example from being affected by the individual densities, the measured values are ^{converted to the case where the density is 0.82 g / cm 3} to obtain the bending strength of the particle board. rice field. Specifically, the bending strength (converted value) was obtained from the following formula.
Bending strength (converted value) = bending strength (measured value) + (0.82-density (measured value)) x 25

<Measurement of formaldehyde emission>
The amount of formaldehyde emission from the wood board was measured according to JIS A 1460: 2015.
If it is below the detection limit (0.05 mg / L or less), it is referred to as "ND".

[Method for producing phosphoric acid monoesterified starch]
A phosphoric acid aqueous solution prepared by dissolving 10.2 parts by mass of urea and 2.7 parts by mass of orthophosphoric acid in water was impregnated with 100 parts by mass of corn starch and stirred until uniform to obtain a starch mixture. Water was distilled off until the content of water with respect to the total mass of the obtained starch mixture became 10% by mass or less, and then a heating reaction (roasting) was carried out at 140 ° C. for 25 minutes using a stirring dryer to carry out starch. Obtained phosphoric acid monoesterified and carbamate-esterified phosphoric acid monoesterified starch (carbamic acid phosphoric acid monoesterified starch).
The ratio of bound phosphorus to the total mass of the obtained phosphoric acid monoesterified starch was 0.55% by mass, and the water content was 9.3% by mass. The gelatinization start temperature of the phosphoric acid monoesterified starch was 44 ° C.

[Example 1]
As the epoxy resin, 25.3 g of a polyamide epichlorohydrin resin (manufactured by Seiko PMC Corporation, trade name "WS4030", water content 75% by mass) and 67.5 g of water were mixed to prepare an aqueous solution of the epoxy resin. ..
678.4 g of wood chips (water content 13.6% by mass) as a wood raw material and 72.6 g of phosphoric acid monoesterified starch (water content 9.3% by mass) as starch are mixed, and an aqueous solution of epoxy resin is mixed with this. After spraying, the mixture was sufficiently stirred to obtain 843.8 g of a raw material mixture. The solid content of the obtained raw material mixture was 78% by mass (658.2 g), and the water content was 22% by mass (185.6 g). Further, the content of the wood raw material (in terms of solid content) is 89% by mass and the content of starch (in terms of solid content) is 10% by mass with respect to the total mass of the raw material mixture in terms of solid content. The content (in terms of solid content) was 1% by mass.
Then, the raw material mixture was filled in a mold (300 × 300 mm), and the temporarily molded molding material (mat) was main-molded by hot pressing. In the press molding, the molding material was sandwiched between two iron plates heated to 150 ° C. together with the mold and held for 10 minutes until the distance between the two iron plates became 10 mm, and heat and pressure molding was performed. After heat and pressure molding for 10 minutes, the mold was removed and left at room temperature (25 ° C.) for 12 hours to obtain a particle board.
The water content of the particle board was 5% by mass with respect to the total mass of the particle board. The contents of the wood-based material, starch and epoxy resin in terms of solid content with respect to the total mass of the particle board in terms of solid content are the same as those of the raw material mixture.
The density, bending strength and formaldehyde emission of the obtained particle board were measured. These results are shown in Table 2.

[Examples 2 to 15]
Same as Example 1 except that the types of starch and resin and the contents of wood-based materials, starch and resin in terms of solid content with respect to the total mass of particle board in terms of solid content were changed as shown in Table 2. A particle board was manufactured and various measurements were made. The results are shown in Table 2. The water content of the obtained particle board was 5 to 11% by mass with respect to the total mass of the particle board.

As is clear from the results in Table 2, the particle boards of Examples 1, 3, 10, 13 to 15 had high bending strength and the amount of formaldehyde emission was below the detection limit. In particular, the particle boards of Examples 1 to 3 and 13 in which phosphoric acid monoesterified starch or cationized starch was used as the starch had higher bending strength.

On the other hand, the particle board of Example 4 in which starch and epoxy resin were not used had low bending strength.
The particle board of Example 5 using phosphoric acid monoesterified starch and no epoxy resin had lower bending strength than the particle board of Example 1 using phosphoric acid monoesterified starch and epoxy resin.
The particle boards of Examples 6 and 7 using the epoxy resin and not the starch had lower bending strength than the particle boards of Examples 1, 3, 10, 13 to 15 using the starch and the epoxy resin.
The particle boards of Examples 8 and 9 in which urea resin was used instead of epoxy resin without using starch were easy to emit formaldehyde. In addition, the particle board of Example 8 had a low bending strength.
The particle board of Example 11 using unmodified starch and no epoxy resin had lower bending strength than the particle board of Example 10 using unmodified starch and epoxy resin.
The particle board of Example 12 in which phosphoric acid monoesterified starch was used and urea resin was used instead of epoxy resin was easy to dissipate formaldehyde.

Although the particle boards of Examples 9 and 12 easily dissipate formaldehyde, the bending strength was high, and the bending strength was about the same as that of the particle boards of Examples 1 to 13 and, for example. The content of the urea resin in terms of solid content with respect to the total mass in terms of solid content of the particle board is 10% by mass in the case of Example 9 and 5% by mass in the case of Example 12. On the other hand, the content of the epoxy resin in terms of solid content with respect to the total mass in terms of solid content of the particle board is 1% by mass in each of Examples 1 to 13 and 13.
As described above, according to the present invention, it is possible to reduce the emission of formaldehyde while exhibiting high bending strength even with a small amount of epoxy resin as compared with the case of using urea resin.

Claims (3)

Contains starch and epoxy resin,
The mass ratio of the starch to the epoxy resin is starch: epoxy resin = 8: 1 to 30: 1, which is the same as that of the wood board adhesive (however, the carboxyl group-containing monomer and the carboxyl group-containing monomer). An aqueous resin emulsion obtained by emulsion polymerization of a polymerizable radically polymerizable monomer, which comprises at least one of an aqueous resin emulsion containing acetacetylated polyvinyl alcohol and an ethylene-vinyl acetate copolymer system emulsion. (Excluding those). The adhesive for wood board according to claim 1, wherein the starch is modified starch. The adhesive for wood board according to claim 2, wherein the modified starch is a phosphoric acid monoesterified starch.