Aqueous adhesive composition and wood-based composite material

Abstract

To provide an aqueous adhesive composition that enables adhesion between adherends in a short time even when used in a low-temperature environment.SOLUTION: The aqueous adhesive composition of the present invention comprises: a main agent that comprises (A) polyvinyl alcohol; (B) an ethylene-vinyl acetate copolymer resin; and (C) a styrene-butadiene copolymer resin having a functional group capable of reacting with an isocyanate, where the content ratio of the (C) styrene-butadiene copolymer resin (solid content) is 20 mass% or more relative to 100 mass% of the total solid content of (A) to (C); and a curing agent containing an isocyanate compound.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an aqueous adhesive composition and a wood composite material. More specifically, the present invention relates to an aqueous adhesive composition preferably used for bonding wood materials.

Background Art

[0002] As wood materials used in buildings, solid wood and glued laminated timber are used. Glued laminated timber is produced by integrally bonding sawn wood with an adhesive. For this reason, glued laminated timber is less likely to warp compared to solid wood, and is also sold at a lower price range than solid wood, and is widely used in various buildings. Examples of glued laminated timber include structural glued laminated timber and carpentry glued laminated timber.

[0003] An aqueous vinyl urethane adhesive is often used for bonding sawn wood together when producing glued laminated timber. An aqueous vinyl urethane adhesive is a composition containing an emulsion containing a compound having a hydroxy group and an isocyanate compound, and while evaporating water to solidify, it reacts the compound having a hydroxy group with the isocyanate compound to exhibit adhesive strength.

[0004] As such an aqueous vinyl urethane adhesive, for example, an emulsion composition for wood panels containing an EVA emulsion, an SBR emulsion, and an acrylic emulsion is known (Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] When in use, the water-based vinyl urethane adhesive evaporates water to solidify and at the same time reacts a compound having a hydroxy group with an isocyanate compound, so it is desirable to use it in a temperature environment of normal temperature or higher. However, for example, when manufacturing glued laminated wood in a low temperature environment such as winter, the adhesiveness may be insufficient.

[0007] According to the emulsion composition for wood-based panels of Patent Document 1, it is described that good results can be obtained even when a durability test is carried out using test pieces prepared in a low temperature environment such as 5°C. However, in a low temperature environment, the evaporation of water and the progress of the above reaction are slow, and it takes a long time for adhesion to exhibit sufficient adhesiveness.

[0008] Therefore, an object of the present invention is to provide an aqueous adhesive composition capable of adhering adherends to each other in a short time even in a low temperature environment.

Means for Solving the Problems

[0009] As a result of intensive studies to solve the above problems, the present inventor has found that a main agent containing polyvinyl alcohol, an ethylene-vinyl acetate copolymer resin, and a styrene-butadiene copolymer resin having a functional group capable of reacting with an isocyanate, and the styrene-butadiene copolymer resin having a specific content ratio, and a curing agent containing an isocyanate compound, can adhere adherends to each other in a short time even in a low temperature environment. The present invention relates to one completed based on these findings.

[0010] That is, the present invention provides an aqueous adhesive composition comprising (A) polyvinyl alcohol, (B) an ethylene-vinyl acetate copolymer resin, and (C) a styrene-butadiene copolymer resin having a functional group capable of reacting with an isocyanate, wherein the content ratio of the (C) styrene-butadiene copolymer resin (solid content) is 20% by mass or more based on 100% by mass of the total solid content of (A) to (C), and a curing agent containing an isocyanate compound.

[0011] In the styrene-butadiene copolymer resin having a functional group capable of reacting with an isocyanate, the functional group capable of reacting with the isocyanate is preferably a hydroxy group and / or a carboxy group.

[0012] (A) The saponification degree of polyvinyl alcohol is preferably 80% mol or more.

[0013] The above aqueous adhesive composition is preferably for bonding wood materials to each other.

[0014] The present invention also provides a wood composite material in which two or more wood materials are bonded by a cured product of the above aqueous adhesive composition. [Advantages of the Invention]

[0015] According to the aqueous adhesive composition of the present invention, adherends can be bonded to each other in a short time even in a low-temperature environment. [Brief Description of the Drawings]

[0016]

Figure 1

[0017] [Aqueous Adhesive Composition] The aqueous adhesive composition of the present invention comprises a main agent containing at least (A) polyvinyl alcohol, (B) ethylene-vinyl acetate copolymer resin, and (C) styrene-butadiene copolymer resin having a functional group capable of reacting with an isocyanate, and a curing agent containing an isocyanate compound. In this specification, the styrene-butadiene copolymer resin having a functional group capable of reacting with the above (C) isocyanate may be referred to as "(C) styrene-butadiene copolymer resin".

[0018] [Main Agent] [((A) Polyvinyl Alcohol)] (A) Polyvinyl alcohol (sometimes referred to as "PVA") has at least structural units derived from vinyl alcohol. (A) Polyvinyl alcohol may be unmodified or modified. Examples of modified polyvinyl alcohol include carboxy group-modified polyvinyl alcohol, hydroxy group-modified polyvinyl alcohol, alkyl group-modified polyvinyl alcohol, thiol group-modified polyvinyl alcohol, acrylamide-modified polyvinyl alcohol, and the like. (A) Polyvinyl alcohol may be used alone or in combination of two or more.

[0019] Examples of the above carboxy group-modified polyvinyl alcohol include random copolymers obtained by copolymerizing vinyl ester monomers with ethylenically unsaturated carboxylic acids or their acid anhydrides and then saponifying; block copolymers obtained by radically polymerizing the above ethylenically unsaturated carboxylic acids in the presence of a polyvinyl alcohol-based polymer having a thiol group at the terminal; and terminal-modified copolymers obtained by copolymerizing vinyl ester monomers with ethylenically unsaturated carboxylic acids in the presence of thiol compounds such as thiolacetic acid and mercaptopropionic acid and then saponifying.

[0020] Examples of the above vinyl ester monomers include vinyl acetate, vinyl formate, vinyl propionate, vinyl versatate, vinyl pivalate, and the like. Examples of the above ethylenically unsaturated carboxylic acids include acrylic acid, methacrylic acid, fumaric acid, maleic acid, itaconic acid, crotonic acid, citraconic acid, aconitic acid, and their acid anhydrides.

[0021] (A) Polyvinyl alcohol may further contain other monomers as monomer components. Examples of the other monomers include ethylene, isobutylene, (meth)acrylonitrile, (meth)acrylamide, trimethyl-(3-acrylamido-3-dimethylpropyl)-ammonium chloride, ethyl vinyl ether, butyl vinyl ether, N-vinylpyrrolidone, vinyl chloride, vinyl bromide, vinyl fluoride, vinylidene chloride, vinylidene fluoride, tetrafluoroethylene, sodium vinyl sulfonate, sodium allyl sulfonate, and the like.

[0022] (A) The saponification degree of polyvinyl alcohol is preferably 80 mol% or more, more preferably 85 mol% or more. When the saponification degree is 80 mol% or more, it is easy to disperse in water and an even adhesive composition is easily obtained. Also, many hydroxy groups will be present, and the reactivity with the isocyanate compound under a low-temperature environment will be higher. The saponification degree is, for example, 98 mol% or less. The saponification degree of the polyvinyl alcohol can be measured, for example, based on JIS K6726:1994.

[0023] (A) The content ratio of polyvinyl alcohol (solid content) is preferably 5 to 30 mass%, more preferably 7 to 20 mass%, based on 100 mass% of the total (solid content) of (A) polyvinyl alcohol, (B) ethylene-vinyl acetate copolymer resin, and (C) styrene-butadiene copolymer resin. When the content ratio is 5 mass% or more, (B) ethylene-vinyl acetate copolymer resin and (C) styrene-butadiene copolymer resin are easily dispersed in water and an even adhesive composition is easily obtained. When the content ratio is 30 mass% or less, (B) ethylene-vinyl acetate copolymer resin and (C) styrene-butadiene copolymer resin can be sufficiently blended. Also, when the content ratio is within the above range, the viscosity of the aqueous adhesive composition becomes appropriate and the handleability is excellent. Note that the contents of (A) polyvinyl alcohol, (B) ethylene-vinyl acetate copolymer resin, and (C) styrene-butadiene copolymer resin are the solid content contents.

[0024] ((B) Ethylene-vinyl acetate copolymer resin) (B) Ethylene-vinyl acetate copolymer resin (sometimes referred to as "EVA") is a copolymer composed of ethylene and vinyl acetate as essential monomer components. That is, (B) ethylene-vinyl acetate copolymer resin is a copolymer having at least structural units derived from ethylene and structural units derived from vinyl acetate. (B) Ethylene-vinyl acetate copolymer resin may be used alone or in combination of two or more kinds.

[0025] (B) Ethylene-vinyl acetate copolymer resin may be unmodified or modified. Examples of modified ethylene-vinyl acetate copolymer resin include carboxy group-modified ethylene-vinyl acetate copolymer resin and hydroxy group-modified ethylene-vinyl acetate copolymer resin.

[0026] Examples of the above-mentioned modified ethylene-vinyl acetate copolymer resin include those containing other monomers other than ethylene and vinyl acetate as monomer components. Examples of the above-mentioned other monomers include vinyl-based monomers such as vinyl chloride; unsaturated carboxylic acids such as (meth)acrylic acid, maleic acid, fumaric acid, crotonic acid, itaconic acid, citraconic acid, and 5-norbornene-2,3-dicarboxylic acid; unsaturated anhydrous carboxylic acids such as maleic anhydride, citraconic anhydride, 5-norbornene-2,3-dicarboxylic anhydride, and tetrahydrophthalic anhydride; unsaturated carboxylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, glycidyl (meth)acrylate, monoethyl maleate, and diethyl maleate; unsaturated amides or imides such as acrylamide, methacrylamide, and maleimide; and unsaturated carboxylates such as sodium (meth)acrylate and zinc (meth)acrylate. The above-mentioned other monomers may be used alone or in combination of two or more kinds.

[0027] (B) The content ratio of ethylene-vinyl acetate copolymer resin (solid content) is preferably 30 to 70% by mass, more preferably 40 to 60% by mass, based on 100% by mass of the total (solid content) of (A) polyvinyl alcohol, (B) ethylene-vinyl acetate copolymer resin, and (C) styrene-butadiene copolymer resin. When the above content ratio is 30% by mass or more, the cohesive force is improved and the adhesive force becomes higher. Also, the water resistance of the adhesive layer formed by curing the aqueous adhesive composition is excellent. When the above content ratio is 70% by mass or less, the (B) ethylene-vinyl acetate copolymer resin is easily dispersed in water and a uniform adhesive composition is easily obtained. Also, (A) polyvinyl alcohol and (C) styrene-butadiene copolymer resin can be sufficiently blended. Note that the contents of (A) polyvinyl alcohol, (B) ethylene-vinyl acetate copolymer resin, and (C) styrene-butadiene copolymer resin are the contents of the solid components.

[0028] ((C) Styrene-butadiene copolymer resin) (C) Styrene-butadiene copolymer resin is a copolymer composed of styrene-based monomer and butadiene as essential monomer components and having a functional group reactive with isocyanate. That is, (C) styrene-butadiene copolymer resin is a polymer having a functional group reactive with isocyanate and containing at least a structural unit derived from a styrene-based monomer and a structural unit derived from butadiene in the molecule (in one molecule). (C) Styrene-butadiene copolymer resin may be used alone or in combination of two or more.

[0029] The above styrene-based monomer is not particularly limited, and examples thereof include styrene, α-methylstyrene, m-methylstyrene, p-methylstyrene, p-ethylstyrene, p-isobutylstyrene, p-t-butylstyrene, chloromethylstyrene, etc. Among them, styrene is preferred.

[0030] Examples of the functional group having reactivity with the isocyanate include a hydroxy group, a carboxy group (including an acid anhydride group), a sulfonic acid group, an amino group, an amide group, a phosphoric acid group, a mercapto group, an epoxy group, an N-methylol group, an N-alkoxymethyl group, and the like. Among them, a hydroxy group and a carboxy group are preferable, and a hydroxy group is more preferable.

[0031] (C) The styrene-butadiene copolymer resin is obtained by copolymerizing the above styrene monomer, the above butadiene, and a monomer having the above functional group. Examples of the monomer having the above functional group include hydroxyalkyl (meth) acrylates such as hydroxyethyl (meth) acrylate and hydroxy group-containing monomers such as allyl alcohol; maleic acid, maleic acid monoester, maleic acid diester, fumaric acid, fumaric acid monoester, itaconic acid, itaconic acid monoester, citraconic acid, citraconic acid monoester, mesaconic acid, mesaconic acid monoester, ethylenically unsaturated dicarboxylic acids such as 5-norbornene-2,3-dicarboxylic acid or esters thereof; unsaturated monocarboxylic acids such as crotonic acid and (meth) acrylic acid; and the like unsaturated carboxylic acids; unsaturated anhydrous carboxylic acids such as maleic anhydride, citraconic anhydride, 5-norbornene-2,3-dicarboxylic anhydride, and tetrahydrophthalic anhydride; and unsaturated amides or imides such as acrylamide, methacrylamide, and maleimide.

[0032] (C) The styrene-butadiene copolymer resin may contain, as monomer components, other monomers other than the above styrene monomer, the above butadiene, and the monomer having the above functional group. Examples of the other monomers include other conjugated dienes other than butadiene, vinyl monomers such as vinyl chloride; and unsaturated carboxylic acid esters such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate.

[0033] (C) The forms of styrene monomer and butadiene in the styrene-butadiene copolymer resin are not particularly limited, and examples include random copolymers, block copolymers, graft copolymers, and the like.

[0034] (C) The content ratio of the styrene-butadiene copolymer resin (solid content) is 20% by mass or more, preferably 25% by mass or more, more preferably 30% by mass or more, and still more preferably 35% by mass or more, based on 100% by mass of the total (solid content) of (A) polyvinyl alcohol, (B) ethylene-vinyl acetate copolymer resin, and (C) styrene-butadiene copolymer resin. When the above content ratio is 20% by mass or more, the reaction with the isocyanate compound proceeds in a short time under a low-temperature environment. The above content ratio is preferably 65% by mass or less, more preferably 50% by mass or less. When the above content ratio is 65% by mass or less, (A) polyvinyl alcohol and (B) ethylene-vinyl acetate copolymer resin can be sufficiently blended. The contents of (A) polyvinyl alcohol, (B) ethylene-vinyl acetate copolymer resin, and (C) styrene-butadiene copolymer resin are the solid content contents.

[0035] (Filler) The above main agent may contain a filler. By containing a filler, the cohesive force of the aqueous adhesive composition is improved, and the impregnation of the aqueous adhesive composition into the adherend is suppressed, resulting in excellent adhesiveness. Only one kind of the above filler may be used, or two or more kinds may be used.

[0036] Examples of the above filler include inorganic fillers and organic fillers. Examples of the above inorganic fillers include calcium carbonate, talc, silica, kaolin, calcined kaolin, clay, calcium silicate, calcium sulfate, aluminum oxide (alumina), aluminum hydroxide, aluminum silicate, titanium oxide, zinc oxide, magnesium carbonate, magnesium silicate, zeolite, glass beads, and shirasu balloon.

[0037] Examples of the organic filler include wheat flour, soybean flour, blood meal, wood flour, walnut shell powder, polyethylene, polypropylene, polymethyl methacrylate, ethylene-(meth)acrylic acid copolymer, ethylene-(meth)acrylate copolymer, ethylene-vinyl acetate copolymer, nylon, polyethylene terephthalate, polybutylene terephthalate, polystyrene, ABS resin, acrylonitrile-styrene copolymer, polycarbonate, and the like.

[0038] Among the above fillers, inorganic fillers are preferred, and calcium carbonate is more preferred.

[0039] The content ratio of the filler in the main agent is preferably 30 to 70% by mass, more preferably 35 to 65% by mass, based on 100% by mass of the total solid content in the main agent.

[0040] The main agent preferably contains a dispersant in order to improve the dispersibility of the filler. Examples of the dispersant include inorganic dispersants such as sodium metaphosphate and ammonium dihydrogen phosphate; and polymer dispersants such as sodium dodecylbenzenesulfonate. Only one kind of the dispersant may be used, or two or more kinds may be used.

[0041] <Hardener> (Isocyanate compound) The isocyanate compound used as the hardener is a polyisocyanate having two or more isocyanate groups such as diisocyanate. Examples thereof include aliphatic polyisocyanate, alicyclic polyisocyanate, and aromatic polyisocyanate. Only one kind of the isocyanate compound may be used, or two or more kinds may be used.

[0042] Examples of the aliphatic polyisocyanate include aliphatic diisocyanates such as 1,4-tetramethylene diisocyanate, 1,5-pentamethylene diisocyanate, 1,6-hexamethylene diisocyanate, 1,7-heptamethylene diisocyanate, 1,8-octamethylene diisocyanate, 1,9-nonamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, 1,10-decamethylene diisocyanate, and the like.

[0043] Examples of the alicyclic polyisocyanate include alicyclic diisocyanates such as 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, 1,4-bis(isocyanatomethyl)cyclohexane, 4,4'-dicyclohexylmethane diisocyanate, isophorone diisocyanate, norbornene diisocyanate, and the like.

[0044] Examples of the aromatic polyisocyanate include aromatic diisocyanates such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), 4,4'-diisocyanato-3,3'-dimethylbiphenyl (tolidine diisocyanate (TODI)), 4,4'-dibenzyl diisocyanate, 1,5-naphthylene diisocyanate (NDI), xylylene diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate (PPDI), and the like.

[0045] Among the above isocyanate compounds, aromatic diisocyanate is preferable, and MDI is more preferable. Examples of MDI include 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, polymeric MDI, and the like.

[0046] The content of the above isocyanate compound (especially MDI) is preferably 5 to 30 parts by mass, more preferably 10 to 20 parts by mass, based on 100 parts by mass of the total amount of the above main agent. When the above content is within the above range, it has appropriate film cohesion and adhesion strength.

[0047] The above curing agent may contain other curing agents other than the above isocyanate compound. The content ratio (active ingredient) of the above isocyanate compound in the above curing agent is preferably 80% by mass or more, more preferably 90% by mass or more, based on 100% by mass of the total amount of the above curing agent.

[0048] The aqueous adhesive composition of the present invention may contain other components other than the above-mentioned components. Examples of the above other components include solvents such as water, defoamers, preservatives, fire retardants, ant repellents, fungicides, insecticides, foam stabilizers, foaming agents, rust preventives, wetting agents, surfactants, wetting agents, etc. The above other components may be used alone or in combination of two or more. Further, the above other components may be contained in the main agent or the curing agent.

[0049] The content ratio of the total of (A) to (C) (solid content) in the aqueous adhesive composition of the present invention is preferably 30 to 60% by mass, more preferably 45 to 55% by mass, based on 100% by mass of the total solid content of the aqueous adhesive composition of the present invention excluding the curing agent.

[0050] The aqueous adhesive composition of the present invention may be provided with additives in addition to the above main agent and the above curing agent, within a range that does not prevent the effects of the present invention. The above additives are prepared separately from the above main agent and the above curing agent and are added to the above main agent or the above curing agent immediately before use.

[0051] The aqueous adhesive composition of the present invention may contain resins other than (A) to (C). For example, it is conceivable to blend the resin with the above main agent or the above curing agent, or to add the resin to the above main agent or the above curing agent before use as the above additive. From the viewpoint of not inhibiting the reaction promotion under a low-temperature environment, the content of the resin (solid content) other than (A) to (C) is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, based on 100 parts by mass in total (solid content) of (A) to (C). In particular, it is preferable that the content of the compound having a functional group (particularly, an epoxy group) capable of reacting with an isocyanate other than (A) to (C) is within the above range.

[0052] The aqueous adhesive composition of the present invention can be produced by a known or conventional method. For example, first, the above main agent and the above curing agent are prepared separately. For the above main agent, for example, PVA is first dissolved in water. When a filler is to be blended, the filler is added thereafter. Then, an EVA emulsion and an emulsion of (C) styrene-butadiene copolymer resin (SBR emulsion) are added and mixed. When other components are to be added, they are added thereafter. By preparing in such an order, a main agent in which various components are uniformly dispersed can be prepared.

[0053] The aqueous adhesive composition of the present invention can adhere adherends to each other in a short time not only under normal temperature and high-temperature environments but also under a low-temperature environment. Therefore, even in a period or region with a low-temperature environment, the adhesion time between adherends can be shortened, contributing to a reduction in man-hours.

[0054] The aqueous adhesive composition of the present invention can be used for adhering various adherends. Among them, the aqueous adhesive composition of the present invention is preferably used for adhering woody materials, and more preferably used for adhesion for bonding woody materials to each other. Further, the aqueous adhesive composition of the present invention can also be used as a coating composition or a paint composition.

[0055] Examples of the above-mentioned wood materials include wood fiber boards such as plywood, LVL, veneer, decorative boards, particle boards, etc., as well as furniture, fixtures, sports equipment, and the like. Further, the material of the above-mentioned wood material is not particularly limited, and it may be either a softwood or a hardwood. Even a softwood with annual rings and uneven specific gravity, which is generally difficult to adhere, can be preferably used.

[0056] Examples of the above-mentioned other adherends when used for adhering the wood material to another adherend include cardboard, paper, cloth, metal, ceramics, glass, wood wool boards, plastic boards (such as vinyl chloride resin boards, ABS boards, FRP boards, styrene resin boards, etc.), inorganic boards (such as mineral fiber boards like asbestos, rock wool, etc.), cement-based inorganic boards (such as asbestos slate boards, pulp cement boards, concrete boards, etc.).

[0057] The aqueous adhesive composition of the present invention is used by mixing the above-mentioned main agent and the above-mentioned curing agent immediately before use. Then, the aqueous adhesive composition of the present invention is applied to one adherend, the other adherend is bonded, and then the aqueous adhesive composition is cured while applying pressure using a press to form a cured product, whereby the adherends can be adhered to each other. During adhesion, pressure application, heating, or heating by high frequency may be performed.

[0058] [Wood composite material] By adhering two or more wood materials using the aqueous adhesive composition of the present invention, a wood composite material can be produced. The above-mentioned wood composite material has a structure in which two or more wood materials are adhered by a cured product of the aqueous adhesive composition of the present invention.

[0059] Examples of the above-mentioned wood composite material preferably include glued laminated timber such as structural glued laminated timber and glued laminated timber for construction, and more preferably structural glued laminated timber. The above-mentioned glued laminated timber can be produced, for example, by applying the aqueous adhesive composition of the present invention to a first wood board (sawn board), stacking a second wood board (sawn board), repeating this operation according to the number of wood boards (sawn boards), obtaining a laminate of wood boards filled with the aqueous adhesive composition of the present invention between each wood board, and then curing the aqueous adhesive composition of the present invention to form an adhesive layer.

[0060] The coating amount of the aqueous adhesive composition between each wood board is, for example, 100 to 300 g / m 2 and preferably 150 to 280 g / m 2 The aqueous adhesive composition of the present invention can be cured in a short time under a low temperature environment. For example, it can be cured by holding at 10°C under pressure for 30 minutes. The pressure during pressurization is preferably 0.5 to 2.0 MPa, more preferably 0.7 to 1.4 MPa. After pressurization, curing can proceed sufficiently by curing for 3 days or more.

Examples

[0061] The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

[0062] Example 1 (Preparation of main agent) Into a container, 20.0 parts by mass of water for dissolving PVA, 3.0 parts by mass of PVA, and 0.05 parts by mass of an antifoaming agent were added, and stirred with a paddle spring at 90°C for 60 minutes to dissolve PVA. Then, after cooling to 70°C or lower and adding 0.2 parts by mass of a dispersant, 32.1 parts by mass of calcium carbonate was added to the container, and stirred sufficiently for 120 minutes or more to disperse uniformly. Then, 25.0 parts by mass of an EVA emulsion and 20.0 parts by mass of an SBR emulsion were added to the container, and stirred for 20 minutes or more to make it uniform, and the main agent of Example 1 was obtained.

[0063] Examples 2, 3 and Comparative Examples 1 to 3 (Preparation of main agent) The main agents of each example were prepared in the same manner as in Example 1 except that the raw materials and the addition amounts were changed as shown in Table 1 or Table 2. In Table 1 and Table 2, the "proportion of PVA", "proportion of EVA", and "proportion of SBR" are all the proportions of the solid content with respect to the total amount of the solid content of PVA, EVA, and SBR (100% by mass).

[0064]

Table 1

[0065]

Table 2

[0066] In addition, each raw material in the table is as follows. <pva> PVA1: Trade name "Denka Poval H-17", manufactured by Denka Co., Ltd., saponification degree 95.0 - 96.0 mol%, solid content 100 mass% PVA2: Trade name "Kuraray Poval 22-88", manufactured by Kuraray Co., Ltd., saponification degree 87.0 - 89.0 mol%, solid content 100 mass% <eva> EVA1: Trade name "SumikaFlex S-400HQ", non-modified, manufactured by Sumitomo Chemical Tex Co., Ltd., emulsion (solid content 55% by mass) EVA2: Trade name "SumikaFlex S-456HQ", manufactured by Sumitomo Chemical Tex Co., Ltd., carboxyl group-containing, emulsion (solid content 55% by mass) <sbr> SBR1: Trade name "A-7901", manufactured by Asahi Kasei Corporation, carboxy group-containing, emulsion (solid content 50% by mass) SBR2: Trade name "L-3200", manufactured by Asahi Kasei Corporation, containing functional groups capable of reacting with isocyanate, emulsion (solid content 48% by mass) SBR3: Trade name "DL-612", manufactured by Asahi Kasei Corporation, unmodified, emulsion (solid content 48% by mass) <Others> Defoaming agent: Trade name "Noputam 8034-F", manufactured by San Nopco Limited Dispersant: Trade name "Sodium hexametaphosphate, primary grade", manufactured by Kishida Chemical Co., Ltd. Calcium carbonate: Trade name "Super SSS", manufactured by Maruo Calcium Co., Ltd.

[0067] <Evaluation> The following evaluations were performed on the main agents obtained in the examples and comparative examples. The results are shown in a table. In the evaluation, the adhesive compositions and test pieces prepared as follows were used.

[0068] (Preparation of aqueous adhesive composition) 100 parts by mass of the main agent obtained in the examples and comparative examples and 15 parts by mass of MDI (trade name "Bond CUS hardener", manufactured by Konishi Co., Ltd., conforming to JIS K6806 (2003)) were put into a container and thoroughly stirred with a paddle spring for 1 minute to make it uniform, and an aqueous adhesive composition was obtained. The above preparation of the aqueous adhesive composition was carried out immediately before lamination and used within 2 minutes after mixing.

[0069] (Preparation of peel test sample) Japanese cypress lumber (thickness 27 mm × width 110 mm × length 280 mm) used as the adherend was temperature-controlled in a 10°C environment (hereinafter, all carried out in a 10°C environment until the curing was completed) for 24 hours or more, and planar processing was carried out. After the planar processing, it was further temperature-controlled for 12 hours or more (material temperature 8 - 9°C, moisture content 9.4 - 10.6% (core penetrometer)). The coating amount of the above adhesive composition was 230 g / m 2 Apply it to three pieces of cypress laminates so as to achieve [the required state], then stack four pieces (a combination of wood surface / wood back / wood surface / wood back) and compress them with a press machine (open deposition time: 1 minute, closed deposition time: 1 minute, 1.2 MPa for 30 minutes). After compression, release the pressure and cure for 3 days to produce a glued laminated wood sample. Then, cut the above glued laminated wood sample to obtain a delamination test sample with a thickness of 108 mm × width of 110 mm × length of 75 mm. Figure 1 shows a cross-sectional view of the above delamination test sample. The delamination test sample (1) has a structure of [cypress laminate 1 (21) / adhesive layer 1 (31) / cypress laminate 2 (22) / adhesive layer 2 (32) / cypress laminate 3 (23) / adhesive layer 3 (33) / cypress laminate 4 (24)].

[0070] (Vacuum-pressure delamination test (in accordance with Japanese Agricultural and Forestry Standard for Structural Glued Laminated Timber)) Immerse the above delamination test sample in water at room temperature, reduce the pressure to 0.085 MPa and maintain it for 5 minutes, then pressurize it to 0.51 MPa and maintain it for 1 hour. After performing this vacuum and pressure operation for 2 cycles, take it out of the water and dry it in a dryer at 70 ± 3 °C so that the mass becomes 100 - 110% of the mass before immersion. Then, for the dried delamination test sample, measure the length of the delaminated part (delamination length) between each cypress laminate, and calculate the total delamination length, delamination length ratio, and delamination rate. The results are shown in Table 3. Specifically, first, measure the delaminated lengths on one side and the other side of each adhesive layer respectively and record them in the "delamination length" of the table. The numerical value enclosed in "()" indicates the delamination length at the end. The numerical value enclosed in "< >" indicates the delamination length at the knot part of the cypress laminate, which is not regarded as delamination. Then, show the total of the delamination lengths on one side and the other side of each adhesive layer (that is, the total excluding the numerical value enclosed in "< >") in the "total delamination length". The delamination length ratio is the ratio of the total delamination length to the total length of one side and the other side (110 mm × 2 sides) in the same adhesive layer. The delamination rate is the ratio of the total delamination length to the total length of the adhesive layer (110 mm × 2 sides × 3 layers). The delamination test samples using the main agent of each example were evaluated with n = 2.

[0071]

Table 3

[0072] As shown in Table 3, when the aqueous adhesive composition using the main agent of the example was used, the delamination length ratio of each adhesive layer of the laminated wood sample prepared in a short time in an environment of 10°C or lower was 1 / 4 (0.25) or less, and the delamination rate was 5% or less. It was evaluated that the adhesiveness was sufficient even when adhesion was performed in a low-temperature environment for a short time. On the other hand, as shown in Table 3, in Comparative Examples 1 and 2 using unmodified SBR and Comparative Example 3 with a low SBR content ratio, the delamination length ratio in one or more adhesive layers was large, or the delamination rate was high. When adhesion was performed in a low-temperature environment for a short time, it was evaluated that the adhesiveness was poor.

[0073] Hereinafter, variations of the invention according to the present specification will be described. [Appendix 1] An aqueous adhesive composition comprising (A) polyvinyl alcohol, (B) ethylene-vinyl acetate copolymer resin, and (C) a styrene-butadiene copolymer resin having a functional group capable of reacting with isocyanate, wherein the content ratio of the (C) styrene-butadiene copolymer resin (solid content) is 20% by mass or more based on 100% by mass of the total solid content of (A) to (C), and a curing agent containing an isocyanate compound. [Appendix 2] The aqueous adhesive composition according to Appendix 1, wherein the functional group capable of reacting with isocyanate in the (C) styrene-butadiene copolymer resin having a functional group capable of reacting with isocyanate is a hydroxy group and / or a carboxy group. [Appendix 3] The aqueous adhesive composition according to Appendix 1 or 2, wherein the saponification degree of (A) polyvinyl alcohol is 80 mol% or more. [Appendix 4] The aqueous adhesive composition according to any one of Appendices 1 to 4, which is for adhesion for bonding wooden materials to each other. [Appendix 5] A wood composite material in which two or more wooden materials are bonded by a cured product of the aqueous adhesive composition according to any one of Appendices 1 to 4.

Explanation of symbols

[0074] 1 Delamination test sample 21 Cypress Mite 1 22 Cypress Mite 2 23 Cypress Mite 3 24 Cypress Mite 4 31 Adhesive Layer 1 32 Adhesive Layer 2 33 Adhesive Layer 3< / sbr> < / eva> < / pva>

Claims

1. An aqueous adhesive composition comprising: (A) polyvinyl alcohol, (B) an ethylene-vinyl acetate copolymer resin, and (C) a styrene-butadiene copolymer resin having a functional group capable of reacting with an isocyanate, wherein the content ratio of the (C) styrene-butadiene copolymer resin (solid content) is 20% by mass or more based on 100% by mass of the total solid content of (A) to (C), and a curing agent containing an isocyanate compound.

2. The aqueous adhesive composition according to Claim 1, wherein the functional group capable of reacting with the isocyanate in the (C) styrene-butadiene copolymer resin having a functional group capable of reacting with an isocyanate is a hydroxy group and / or a carboxy group.

3. The aqueous adhesive composition according to Claim 1 or 2, wherein the saponification degree of (A) polyvinyl alcohol is 80 mol% or more.

4. The aqueous adhesive composition according to Claim 1 or 2, which is for bonding wood materials to each other.

5. A wood composite material in which two or more wood materials are bonded by a cured product of the aqueous adhesive composition according to Claim 1 or 2.

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