JP5511145B2 - Adhesive composition for wood - Google Patents

Description

  The present invention relates to an adhesive composition for wood having high adhesive strength, excellent workability, durability, water resistance, warm water resistance and hot water resistance.

  Conventionally, thermosetting adhesives such as melamine-formaldehyde resin, urea-formaldehyde resin, phenol resin, resorcinol resin, resorcinol-phenol copolymer resin have been mainly used as adhesives for plywood. However, due to health problems caused by indoor contamination of formaldehyde, that is, sick house syndrome, these thermosetting adhesives have been developed with low formaldehyde emission, but it is virtually impossible to reduce formaldehyde emission to zero. Impossible.

  Therefore, vinyl acetate resin emulsion adhesives and ethylene-vinyl acetate resin emulsion adhesives are partly used as adhesives that do not contain formaldehyde, but these adhesives have extremely insufficient water resistance and hot water resistance. For example, it cannot be put into practical use in applications that require a high degree of adhesiveness, such as structural adhesives.

  Therefore, as a water-resistant adhesive not containing formaldehyde, an aqueous emulsion adhesive or an aqueous polymer-isocyanate adhesive obtained by blending an aqueous polymer and an isocyanate compound has been widely used. As the water-based emulsion adhesive, styrene butadiene rubber latex (SBR) is often used in order to have excellent hot water resistance and hot water resistance.

Further, as an aqueous polymer-isocyanate adhesive, an adhesive comprising an aqueous emulsion obtained by polymerizing an unsaturated monomer composition containing a primary hydroxyl group-containing ethylenically unsaturated monomer and a polyvalent isocyanate compound. An adhesive (for example, Patent Document 2), an aqueous emulsion obtained by polymerizing an unsaturated monomer composition containing a hydroxyl group-containing vinyl monomer and an isocyanate compound (for example, Patent Document 2) An adhesive containing an aqueous resin emulsion obtained by polymerizing an unsaturated monomer composition containing a hydroxyl group-containing monomer and an ethylenically unsaturated monomer and an isocyanate compound (for example, Patent Document 3) Are used).
However, these conventional techniques have not yet been developed that sufficiently satisfy adhesive strength, workability, durability, water resistance, hot water resistance and hot water resistance.

JP 05-279648 A JP 2002-155252 A JP 2006-238889 A

  Accordingly, an object of the present invention is to provide an adhesive composition for wood that does not disperse formaldehyde and has excellent adhesive strength, workability, durability, water resistance, hot water resistance and hot water resistance.

  As a result of intensive studies, the present inventors have found that an adhesive composition containing a specific acrylic resin emulsion, polyvinyl alcohol, an inorganic pigment, and an isocyanate group-containing compound can solve the above problems, and the present invention. Was completed.

That is, the present invention relates to (A) 100 parts by mass of a radical polymerizable unsaturated monomer composition containing 1% by mass to 15% by mass of an acetoacetyl group-containing radical polymerizable unsaturated monomer, and 1 part by mass of polyvinyl alcohol. ~ 20 parts by mass and an acrylic resin emulsion obtained by emulsion copolymerization in the presence of a water-soluble azo polymerization initiator having carboxyl groups at both ends, and (B) on the basis of solid content, (A) acrylic resin emulsion 100 15 to 80 parts by weight of polyvinyl alcohol with respect to parts by weight (however, (A) the one used for the preparation of the acrylic resin emulsion is not included in the amount of polyvinyl alcohol in (B)) , (C) an inorganic pigment, (D) It is an adhesive composition for wood characterized by including an isocyanate group containing compound.

In the wood adhesive composition, it is preferable that 50 mass parts to 350 mass parts of ( C) inorganic pigment is blended with respect to 100 mass parts of (A) acrylic resin emulsion on a solid basis.
Moreover, in the adhesive composition for wood, (D) isocyanate group containing compound is 20 mass parts-with respect to a total of 100 mass parts of (A) acrylic resin emulsion and (B) polyvinyl alcohol on the solid content basis. 150 parts by mass is preferably blended.

  ADVANTAGE OF THE INVENTION According to this invention, the adhesive composition for wood which does not disperse formaldehyde and has the outstanding adhesive strength, workability | operativity, durability, water resistance, warm water resistance, and hot water resistance can be provided.

Hereinafter, the present invention will be described in detail.
The wood adhesive composition according to the present invention is characterized in that (A) an acrylic resin emulsion, (B) polyvinyl alcohol, (C) an inorganic pigment, and (D) an isocyanate group-containing compound are blended as essential components. There is.

(A) Acrylic resin emulsion (A) Acrylic resin emulsion used in the adhesive composition for wood of the present invention uses polyvinyl alcohol (PVA) as a protective colloid and contains an acetoacetyl group-containing radical polymerizable unsaturated monomer. The radically polymerizable unsaturated monomer composition to be contained can be obtained by emulsion copolymerization in the presence of a specific polymerization initiator in accordance with a normal emulsion polymerization method.

Examples of the acetoacetyl group-containing radical polymerizable unsaturated monomer include allyl acetoacetate, vinyl acetoacetate, 2-acetoacetoxyethyl acrylate, 2-acetoacetoxyethyl methacrylate, 2-acetoacetoxypropyl acrylate, 2-acetoacetoxy (Meth) acrylic acid acetoacetate of alkylene glycol such as propyl methacrylate, 2-cyanoacetoacetoxyethyl methacrylate, crotonic acid acetoacetate of alkylene glycol such as 2-acetoacetoxyethyl crotonate, 2-acetoacetoxypropyl crotonate, N- (acetoacetoxymethyl) acrylamide, N- (acetoacetoxymethyl) methacrylamide, N- (acetoacetoxyethyl) acrylamido N-alkylol (meth) acrylamide acetoacetate such as N- (acetoacetoxyethyl) methacrylamide, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, hydroxypropyl acrylate, 2-hydroxy-3-chloropropyl methacrylate 1,4-butylene glycol monoacrylate, 1,4-butylene glycol monomethacrylate, N-methylol acrylamide, N-methylol methacrylamide, acetoacetylated ethylenically unsaturated monomers such as hydroxystyrene It is done. These may be used individually by 1 type and may be used in combination of 2 or more type.
The acetoacetyl group-containing radical polymerizable unsaturated monomer needs to be blended in an amount of 1% by mass to 15% by mass with respect to the entire radical polymerizable unsaturated monomer composition, and is blended by 2% by mass to 12% by mass. It is preferable. When the blending amount of the acetoacetyl group-containing radically polymerizable unsaturated monomer is less than 1% by mass, the peeling rate, which is a physical property of the wood adhesive composition, is lowered, and when it exceeds 15% by mass, it is stable. An emulsion cannot be obtained.

  Other radical polymerizable unsaturated monomers that can be copolymerized with the above-mentioned acetoacetyl group-containing radical polymerizable unsaturated monomer are not particularly limited, but include methyl (meth) acrylate, (meta ) Ethyl acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, sec-butyl (meth) acrylate, (meth) acryl T-butyl acid, n-pentyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, (meth) acrylic Cyclohexyl acid, 2-methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, (meth) acrylic acid -Methoxypropyl, 3-methoxypropyl (meth) acrylate, 2-methoxybutyl (meth) acrylate, 3-methoxybutyl (meth) acrylate, 4-methoxybutyl (meth) acrylate, hydroxy (meth) acrylate (Meth) acrylic esters such as ethyl, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, and monomers copolymerizable therewith, such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid Α, β-ethylenically unsaturated carboxylic acids such as Styrene may be used as another radical polymerizable unsaturated monomer copolymerizable with an acetoacetyl group-containing radical polymerizable unsaturated monomer, but styrene is a VOC (volatile organic compound) for building materials. ) It may be a problem in the future due to regulations, so it is preferable to reduce the amount used as much as possible.

  The amount of polyvinyl alcohol used as a protective colloid in the emulsion copolymerization of a radical polymerizable unsaturated monomer composition containing an acetoacetyl group-containing radical polymerizable unsaturated monomer is determined based on the radical polymerizable unsaturated monomer. 1 mass part-20 mass parts are preferable with respect to 100 mass parts of compositions, and 4 mass parts-15 mass parts are more preferable. By making the usage-amount of polyvinyl alcohol into the above-mentioned range, emulsion viscosity can be made into a more practical range, improving the reactivity of a radically polymerizable unsaturated monomer composition more. The polyvinyl alcohol used as the protective colloid in the present invention is preferably polyvinyl alcohol having a mercapto group at the end of the molecular chain because the polymerization reactivity and the stability of the obtained emulsion are further improved. Among polyvinyl alcohols having a mercapto group at the molecular chain end, those having a saponification degree of 80 mol% to 99.9 mol% and a polymerization degree of 300 to 2,500 are preferable, and the saponification degree is 86 mol% to 90 mol%. A degree of 500 to 1,500 is more preferred. Moreover, when carrying out emulsion copolymerization, you may use together an emulsifier, such as anionic property and nonionic property.

  In addition, for the purpose of adjusting the molecular weight of the obtained copolymer, a chain transfer agent such as lauryl mercaptan, octyl mercaptan, 2-mercaptoethyl alcohol, 2-mercaptopropionic acid, octyl thioglycolate may be used. In addition, known additives frequently used in synthetic resin emulsions such as film-forming aids and plasticizers can be added as necessary.

The polymerization initiator used at the time of emulsion copolymerization in the present invention is a water-soluble azo polymerization initiator having carboxyl groups at both ends, such as 4,4′-azobis (4-cyanovaleric acid), 2,2 ′. -Azobis [N- (2-carboxyethyl) -2-methylpropionamidine] hydrate and the like. Among these, 4,4′-azobis (4-cyanovaleric acid) is preferable because the polymerization reactivity is further improved. The amount of the water-soluble azo polymerization initiator used is 0.1 parts by mass to 20 parts by mass with respect to 100 parts by mass of the radical polymerizable unsaturated monomer composition (total of radical polymerizable unsaturated monomers to be used). Parts, preferably 0.3 parts by weight to 15 parts by weight. When the amount of the water-soluble azo polymerization initiator used is less than 0.1 parts by mass, the polymerization reactivity is remarkably lowered and a stable emulsion cannot be obtained. When the amount exceeds 20 parts by mass, the emulsion viscosity becomes too high. Deviate from the practical range. The water-soluble azo polymerization initiator having carboxyl groups at both ends is preferably introduced into the polymerization system as an aqueous solution diluted with aqueous ammonia.
Further, instead of the water-soluble azo polymerization initiator having carboxyl groups at both ends, (4,4′-azobis (4-cyanovaleric acid), 2,2′-azobis (2-methylpropionamidine) Dihydrochloride, (2,2′-azobis (2-amidinepropane) dihydrochloride, 2,2′-azobis [2- (2-imidoazolin-2-yl) propane], 2,2′-azobis [2 -(2-Imidazolin-2-yl) propane] typical water-soluble azo initiators such as dihydrochloride, water-soluble inorganic peroxides such as hydrogen peroxide, potassium persulfate, ammonium persulfate, persulfates, cumene When organic peroxides such as hydroperoxide and benzoyl peroxide are used, the particle size is large and the viscosity is increased due to aggregation of emulsion particles. In addition, when these polymerization initiators are used in combination with a water-soluble azo polymerization initiator having a carboxyl group at both ends, the physical properties of the wood adhesive composition are remarkably lowered. Absent.

  (A) Although the addition method of the radically polymerizable unsaturated monomer composition at the time of manufacturing an acrylic resin emulsion is not particularly limited, the radically polymerizable unsaturated monomer composition is changed prior to polymerization. A method of adding to a polymerization system all at once, a part of a radically polymerizable unsaturated monomer composition is previously added to the polymerization system, and the remaining radically polymerizable unsaturated monomer composition in the polymerization process A continuous dropping method, a method in which all radical polymerizable unsaturated monomer compositions are continuously dropped into a polymerization system, a polymerization system in which a radical polymerizable unsaturated monomer composition, PVA and water are pre-emulsified. For example, a method of continuously dripping is used.

Furthermore, (A) The glass transition temperature of the acrylic resin contained in the acrylic resin emulsion is preferably in the range of −10 ° C. to 50 ° C., more preferably in the range of 0 ° C. to 35 ° C. If the glass transition temperature of the acrylic resin is lower than −10 ° C., it is not preferable because the adhesive strength and water resistance of the wood adhesive composition may be lowered. If the glass transition temperature is higher than 50 ° C., it is not preferable. This is not preferable because the film-forming property of the adhesive composition may decrease, or the adhesive strength and water resistance may decrease.
(A) It is preferable that the non volatile matter of an acrylic resin emulsion is the range of 40 mass%-50 mass%. If the non-volatile content is less than 40% by mass, the initial adhesiveness when used as an aqueous polymer-isocyanate adhesive is lowered, which is not preferable. If the non-volatile content is more than 50% by mass, the emulsion viscosity becomes high. It is not preferable because it is too much.
(A) The viscosity of the acrylic resin emulsion is preferably in the range of 50 mPa · s to 10,000 mPa · s. If the viscosity is lower than 50 mPa · s, the viscosity when used as an aqueous polymer-isocyanate-based adhesive may be difficult to adjust, and if the viscosity is higher than 10,000 mPa · s, Since the non-volatile content at the time of using as a molecule-isocyanate adhesive decreases, it is not preferable. In addition, the viscosity here is TOKIMEC INC. This is a value measured at 10 rpm and 23 ° C. using a manufactured BH viscometer.

(B) Polyvinyl alcohol (B) Polyvinyl alcohol used in the adhesive composition for wood of the present invention may be any of ordinary full saponified products and partially saponified products, and has different degrees of polymerization and saponification. More than one kind of polyvinyl alcohol may be used in combination. Moreover, modified polyvinyl alcohols such as mercapto group-modified products and acetoacetyl group-modified products can also be used as (B) polyvinyl alcohol.

  The blending amount of (B) polyvinyl alcohol in the wood adhesive composition of the present invention is preferably 10 to 100 parts by mass with respect to 100 parts by mass of (A) acrylic resin emulsion on a solid basis. More preferably, it is 15 to 80 parts by mass. However, the blending amount of (B) polyvinyl alcohol does not include polyvinyl alcohol used as a protective colloid in (A) acrylic resin emulsion. (B) When the compounding quantity of polyvinyl alcohol is less than 10 mass parts, the viscosity of the adhesive composition for wood finally obtained after mix | blending the (D) isocyanate group containing compound demonstrated below increases. This is not preferable because workability may be reduced. Moreover, when the compounding quantity of (B) polyvinyl alcohol exceeds 100 mass parts, since the water resistance of the wood adhesive composition finally obtained may fall, it is unpreferable.

(C) Inorganic pigment Examples of the (C) inorganic pigment used in the wood adhesive composition of the present invention include calcium carbonate, barium sulfate, clay, talc, and titanium oxide. These may be used individually by 1 type and may be used in combination of 2 or more type. Moreover, you may use together organic pigments, such as wheat flour, starch, and wood flour, in the range which does not impair the effect of this invention.

  The blending amount of (C) inorganic pigment in the wood adhesive composition of the present invention is preferably 50 to 350 parts by mass with respect to 100 parts by mass of (A) acrylic resin emulsion on a solid basis. 100 parts by mass to 300 parts by mass is more preferable. When the blending amount of the inorganic pigment (C) is less than 50 parts by mass, the cohesive force of the wood adhesive composition is insufficient and a sufficient adhesive strength may not be obtained, which is not preferable. Moreover, when the compounding quantity of (C) inorganic pigment exceeds 350 mass parts, since the film forming property of the adhesive composition for wood may fall, or adhesive strength and water resistance may fall, it is unpreferable.

(D) Isocyanate group-containing compound The (D) isocyanate group-containing compound used in the adhesive composition for wood of the present invention is particularly limited as long as it contains two or more isocyanate groups in one molecule. For example, aliphatic isocyanates such as hexamethylene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, tolylene-2,4-diisocyanate, tolylene-2,6-diisocyanate, diphenylmethane-4,4′-diisocyanate, Aromatic isocyanates such as diphenylene-4,4′-diisocyanate, 4,4′-diisocyanate-3,3′-dimethyldiphenyl, 3-methyl-diphenylmethane-4,4′-diisocyanate, diphenylether diisocyanate, cyclohexa 2,4-diisocyanate, cyclohexane-2,3-diisocyanate, alicyclic isocyanates such as isophorone diisocyanate. These may be used individually by 1 type and may be used in combination of 2 or more type. (D) as isocyanate group-containing compound, an isocyanate-terminated prepolymer produced by reaction of an excess diisocyanate or polyfunctional polyisocyanate with a hydroxyl-terminated polyester or hydroxyl-terminated polyether, and an excess of diisocyanate or polyfunctional polyisocyanate; Products obtained by reaction with monomeric polyols such as ethylene glycol, trimethylolpropane or 1,3-butanediol, or mixtures thereof can also be used.

  The blending amount of the (D) isocyanate group-containing compound used in the wood adhesive composition of the present invention may be appropriately determined according to the use of the wood adhesive composition. The amount is preferably 20 parts by mass to 150 parts by mass, more preferably 50 parts by mass to 120 parts by mass with respect to 100 parts by mass in total of the acrylic resin emulsion and (B) polyvinyl alcohol. (D) It is unpreferable that the compounding quantity of an isocyanate group containing compound is less than 20 mass parts since sufficient adhesive strength may not be obtained. In addition, when the blending amount of the (D) isocyanate group-containing compound exceeds 150 parts by mass, the pot life after blending may be shortened, and the viscosity of the wood adhesive composition increases and workability is increased. Since it may decrease, it is not preferable.

  Other additives can be added to the wood adhesive composition of the present invention as long as the effects of the present invention are not impaired. Examples of such additives include cellulose derivatives such as hydroxycellulose and carboxymethylcellulose, water-soluble polymers such as casein, starch and polyacrylamide, phthalic acid derivatives such as dibutyl phthalate, glycolic acid derivatives such as phenyl glycol, and adipic acid. Derivatives, sulfonic acid derivatives, fatty acid derivatives, sulfonic acid derivatives, fumaric acid derivatives, paraffin derivatives, polyester derivatives and other plasticizers, tackifiers, fillers, pigments, dyes, antifoaming agents, antiseptics, rust inhibitors, organic A solvent etc. are mentioned.

  Moreover, the adhesive composition for wood of this invention can be used with the well-known application | coating method and the adhesion | attachment method. For example, a pressing method in which the wood adhesive composition of the present invention is applied to an adhesive surface of wood or the like with a brush, the surfaces coated with the wood adhesive composition are bonded together, and pressure is applied to fix the surface. Can be mentioned. Moreover, the adhesive composition for wood of the present invention can obtain sufficient adhesive strength by any method of room temperature drying and heat drying.

  As described above, the wood adhesive composition of the present invention can obtain sufficient adhesive strength by drying at room temperature, has excellent workability, does not dissipate formaldehyde (no need to add formaldehyde) ), Because there is no need to add styrene that can be subject to VOC regulations, and hardwood and softwood can be glued, so various wood substrates such as laminated timber, plywood, decorative plywood, fiberboard, etc. It is useful as an adhesive for materials.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited to these Examples.

[Preparation of wood adhesive composition]
<Example 1>
In a 1 liter separable flask equipped with a stirrer, dropping funnel, reflux condenser and thermometer, polyvinyl alcohol having a mercapto group at the molecular chain end (trade name: PVA-M205, polymerization degree 500, saponification degree 88 mol%) (Manufactured by Kuraray Co., Ltd.) was charged with 160 parts by mass of 15% aqueous solution and 400 parts by mass of water, and the internal temperature was raised to 75 ° C. in a nitrogen stream. Then, 6 parts by weight of methyl methacrylate, was added to 1 part by weight 6 parts by weight of butyl acrylate and acetoacetoxyethyl methacrylate, 4,4 ^'- azobis (4-cyanovaleric acid) aqueous ammonia 1.5 parts by The solution added with 0.75 part by mass was diluted with water to make a total amount of 40 parts by mass, and polymerization was started. 15 minutes after starting the dropping of the aqueous solution, 174 parts by mass of methyl methacrylate, 174 parts by mass of butyl acrylate and 35 parts by mass of acetoacetoxyethyl methacrylate were added dropwise over 4 hours, and emulsified at an internal temperature of 80 ° C to 85 ° C. Copolymerization was performed. After completion of dropping, the mixture was kept at 85 ° C. for 1 hour and then cooled to obtain an acrylic resin emulsion. The obtained acrylic resin emulsion had a nonvolatile content of 42% by mass and a viscosity of 125 mPa · s. The glass transition temperature of the acrylic resin contained in the emulsion was 6 ° C.

  Polyvinyl alcohol mixture (trade name: PVA224 (polymerization degree 2,400, saponification degree 88 mol%, so that polyvinyl alcohol becomes 30 parts by mass with respect to 100 parts by mass of the obtained acrylic resin emulsion on a solid basis) 15% aqueous solution of Kuraray Co., Ltd.) and trade name: PVA210 (polymerization degree 1,000, saponification degree 88 mol%, manufactured by Kuraray Co., Ltd.) mixed at a mass ratio of 1: 1). Next, 250 parts by mass of calcium carbonate as an inorganic pigment was blended with respect to 100 parts by mass of the acrylic resin emulsion on a solid basis. Furthermore, polymethylene polyphenyl isocyanate (trade name: Lupranate (registered trademark) M20S, manufactured by BASF INOAC Polyurethane Co., Ltd.) as an isocyanate-containing compound with respect to a total of 100 parts by mass of the acrylic resin emulsion and polyvinyl alcohol on a solid basis. ) Was blended and mixed well to prepare the wood adhesive composition of Example 1.

<Example 2>
In a 1 liter separable flask equipped with a stirrer, a dropping funnel, a reflux condenser and a thermometer, polyvinyl alcohol having a mercapto group at the molecular chain end (polymerization degree 500, saponification degree 88 mol%, PVA-manufactured by Kuraray Co., Ltd.) 160 parts by mass of a 15% aqueous solution of M205) and 400 parts by mass of water were charged, and the internal temperature was raised to 75 ° C. in a nitrogen stream. Then, 6 parts by weight of methyl methacrylate, 6 parts by weight of butyl acrylate, was added to 2-hydroxyethyl 0.6 parts by mass of 0.3 mass parts acetoacetoxyethyl methacrylate acrylate, 4,4 ^'- azobis (4 -Cyanovaleric acid) An aqueous solution obtained by diluting 1.5 parts by mass of 0.75 parts by mass of ammonia water with water to make 40 parts by mass in total was added to initiate polymerization. 15 minutes after the start of dropping of the aqueous solution, 174 parts by weight of methyl methacrylate, 174 parts by weight of butyl acrylate, 17.4 parts by weight of 2-hydroxyethyl acrylate and 10 parts by weight of acetoacetoxyethyl methacrylate were dropped over 4 hours. The emulsion was copolymerized at an internal temperature of 80 ° C to 85 ° C. After completion of dropping, the mixture was kept at 85 ° C. for 1 hour and then cooled to obtain an acrylic resin emulsion. The obtained acrylic resin emulsion had a nonvolatile content of 42% by mass and a viscosity of 25 mPa · s. Moreover, the glass transition temperature of the acrylic resin contained in the emulsion was 5 ° C.
A wood adhesive composition of Example 2 was prepared in the same manner as in Example 1 except that this acrylic resin emulsion was used.

<Comparative Example 1>
An acrylic resin emulsion was obtained in the same manner as in Example 1 except that acetoacetoxyethyl methacrylate was not used. The obtained acrylic resin emulsion had a nonvolatile content of 42% by mass and a viscosity of 100 mPa · s. The glass transition temperature of the acrylic resin contained in the emulsion was 6 ° C.
A wood adhesive composition of Comparative Example 1 was prepared in the same manner as in Example 1 except that this acrylic resin emulsion was used.

<Comparative example 2>
An acrylic resin emulsion was obtained in the same manner as in Example 1 except that the total amount of acetoacetoxyethyl methacrylate was reduced to 3.6 parts by mass. The obtained acrylic resin emulsion had a nonvolatile content of 42% by mass and a viscosity of 100 mPa · s. The glass transition temperature of the acrylic resin contained in the emulsion was 6 ° C.
A wood adhesive composition of Comparative Example 2 was prepared in the same manner as in Example 1 except that this acrylic resin emulsion was used.

<Comparative Example 3>
Except that the total amount of acetoacetoxyethyl methacrylate was increased to 64 parts by mass, the procedure was the same as in Example 1. However, the obtained acrylic resin emulsion had a high residual monomer and a large amount of coarse particles in the emulsion, so that it was stable. An emulsion could not be obtained.

<Comparative Example 4>
4,4 ^'- azobis except for using potassium sulfate instead of (4-cyanovaleric acid) in the same manner as in Example 1, to obtain an acrylic resin emulsion. The obtained acrylic resin emulsion had a nonvolatile content of 42% by mass and a viscosity of 5,000 mPa · s. The glass transition temperature of the acrylic resin contained in the emulsion was 6 ° C.
A wood adhesive composition of Comparative Example 4 was prepared in the same manner as in Example 1 except that this acrylic resin emulsion was used.

[Evaluation of adhesion performance]
The adhesive performance of the wood adhesive compositions obtained in Examples 1-2 and Comparative Examples 1-4 was evaluated by the following items.
<Compressive shear strength>
Test pieces were prepared using the wood adhesive composition, and the compression shear strength was measured. Adhesion conditions, test methods and measurement conditions are described below. The measurement results are shown in Table 1. In addition, it can be said that the higher the wood breaking rate in the table, the higher the adhesive strength.
(1) Adhesion conditions Base material: birch plate, moisture content 11%
Application amount: 250 g / m ² (double-sided application)
Crushing: normal temperature, 1177 kPa (12 kg / cm ² ), 24 hours (2) Test method Compressive shear test according to JIS K-6806 (3) Measurement conditions Normal state: Measured in a standard state at 23 ° C. and 65% RH Hot water resistant: Measured after immersing in warm water at 60 ° C for 3 hours and then chilling in room temperature water. Hot water resistance: immersed in boiling water for 4 hours, dried at 60 ° C for 20 hours, and further immersed in boiling water for 4 hours And then immersed in room temperature water until cooled

<Tensile shear strength>
A softwood veneer was bonded to a plywood using the wood adhesive composition, and the tensile shear strength of the plywood was measured. Adhesion conditions, test methods and measurement conditions are described below. The measurement results are shown in Table 2.
(1) Adhesion conditions Base material: larch / radiata pine veneer (thickness 2/3/2/3 / 2mm cloth pasted 5ply), moisture content 8%
Application amount: 435.7 g / m ² (double-sided application)
Crushing: 1471 kPa (15 kg / cm ² ) at room temperature, pressing for 20 minutes, then 981 kPa (10 kg / cm ² ) at 110 ° C. for 5 minutes (2) Test method JAS plywood tensile shear test (3) Measurement conditions Normal state: Measured in a standard state at 23 ° C. and 65% RH Class 1: Steaming test After being immersed in room temperature water for 2 hours or more, steaming is performed at 120 ° C. for 3 hours, and then cooled to room temperature until cooled. Measured in the wet state after immersion Special feature: Depressurization / Pressurization test Immerse in room temperature water, perform decompression of 0.085 MPa or more for 30 minutes, and further pressurize 0.45 MPa to 0.48 MPa for 30 minutes. Measured while wet

<Peel test>
Test pieces were prepared using the wood adhesive composition, and the peel rate was measured. Adhesion conditions, test methods and measurement conditions are described below. The measurement results are shown in Table 3. In addition, it can be said that adhesive strength is so high that the peeling rate in a table | surface is low.
(1) Bonding conditions Base material: Yonematsu, water content 11%
Application amount: 240 g / m ² (double-sided application)
Clamping: normal temperature, 981 kPa (10 kg / cm ² ), 20 minutes (2) Test method JAS laminated material peeling test (3) Measurement conditions Depressurization / pressurization test: The test piece was immersed in room temperature water, 0.08 MPa The process of reducing the pressure for 5 minutes and further applying the pressure of 0.48 MPa to 0.54 MPa for 1 hour was repeated twice and then placed in a constant temperature dryer at 70 ± 3 ° C., and the moisture content was below the moisture content before the treatment. After drying for 18 hours or more until it becomes, measure the peel length in the adhesive layer on both ends

  From the results of Tables 1 to 3, it is clear that the wood adhesive composition of the present invention is excellent in adhesive strength, workability, durability, water resistance, hot water resistance and hot water resistance.

Claims (6)

(A) 100 parts by mass of a radically polymerizable unsaturated monomer composition containing 1% by mass to 15% by mass of an acetoacetyl group-containing radically polymerizable unsaturated monomer, 1 part by mass to 20 parts by mass of polyvinyl alcohol, and both An acrylic resin emulsion obtained by emulsion copolymerization in the presence of a water-soluble azo polymerization initiator having a carboxyl group at the end;
(B) 15-80 parts by weight of polyvinyl alcohol and 100 parts by weight of acrylic resin emulsion (A) based on solid content (however, (A) used for the preparation of acrylic resin emulsion is polyvinyl of (B) Not included in the amount of alcohol)
(C) an inorganic pigment;
(D) An adhesive composition for wood, comprising an isocyanate group-containing compound containing two or more isocyanate groups in one molecule .   The said acetoacetyl group containing radically polymerizable unsaturated monomer contained in the said radically polymerizable unsaturated monomer composition is 2 mass%-12 mass%, It is characterized by the above-mentioned. Wood adhesive composition.   The wood adhesive composition according to claim 1 or 2, wherein the radical polymerizable unsaturated monomer composition further comprises hydroxyethyl (meth) acrylate.   4. The composition according to claim 1, wherein 50 parts by weight to 350 parts by weight of the inorganic pigment (C) is blended with respect to 100 parts by weight of the (A) acrylic resin emulsion on a solid basis. The adhesive composition for wood according to one item.   Based on solid content, the (D) isocyanate group-containing compound is blended in an amount of 20 to 150 parts by mass with respect to a total of 100 parts by mass of the (A) acrylic resin emulsion and the (B) polyvinyl alcohol. The wood adhesive composition according to any one of claims 1 to 4, wherein:   The adhesive composition for wood according to any one of claims 1 to 5, wherein the polyvinyl alcohol used for the preparation of the acrylic resin emulsion (A) is a polyvinyl alcohol having a mercapto group at a molecular chain terminal. object.