JP2005179471A - Aqueous emulsion-based adhesive - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aqueous emulsion giving an adhesive that has high adhesive strength, initial adhesive strength and adhesive strength even after undergoing repeated boiling, and is good in workability with slight viscosity change with time. <P>SOLUTION: The aqueous emulsion-based adhesive contains a (meth)acrylic copolymer and a thiol group-modified polyvinyl alcohol. In this adhesive, the (meth)acrylic copolymer has a glass transition point of -30 to 50°C and a gel fraction of 10-70 wt.%, being obtained by copolymerization of a monomer group comprising an ethylenically unsaturated carboxylic acid and a (meth)acrylic monomer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an aqueous emulsion adhesive containing a (meth) acrylic copolymer having an acidic group.

  An aqueous emulsion containing a water-soluble polymer and an adhesive mainly composed of an isocyanate compound are different from conventional aminoplast adhesives as shown in Patent Document 1 and Patent Document 2, and formalin. This material is used as an adhesive for wood because it has a very high adhesive strength and water resistance simply by pressing at room temperature for a relatively short time. Patent Document 3 discloses a water-resistant adhesive composition comprising a polyvinyl acetate emulsion using polyvinyl alcohol as a protective colloid (dispersant) and a polyvalent isocyanate compound.

JP-A-48-94739 JP 50-69139 A JP-A-3-33178

  Recently, with the expansion of objects to be bonded, it has become necessary to further improve the bonding performance level. Specifically, the structural adhesive may be required to have higher durability, and may be required to further improve the initial adhesiveness in individual applications.

  In the latter case, if an aqueous emulsion of a vinyl acetate resin using polyvinyl alcohol as a dispersant is frequently used, the initial adhesiveness is improved, but there is a problem that the boiling repetition strength is not sufficient. On the other hand, SBR latex adhesives with good boiling repetition strength have insufficient initial adhesiveness, and the two-part formulation containing a polyvalent isocyanate compound has a short pot life and thickening gelation phenomenon. There is a problem in workability such as the occurrence of

  Furthermore, in order to use an acrylic copolymer as an aqueous emulsion adhesive, a monomer group containing a (meth) acrylic monomer is used as a dispersant using ordinary polyvinyl alcohol or partially saponified polyvinyl acetate. Even when polymerization was attempted, gelation occurred due to destabilization of the system, and a desired polymer could not be obtained.

  Accordingly, the present invention eliminates the problems in the prior art and has an excellent adhesive strength, initial strength and boiling repetition strength, and provides an adhesive with good workability with little change in viscosity over time. The purpose is to provide.

  This invention has a glass transition point of −30 to 50 ° C. obtained by polymerizing a monomer group containing an ethylenically unsaturated carboxylic acid and a (meth) acrylic monomer, and a gel fraction. By using an aqueous emulsion adhesive containing 10 to 70% by weight of a (meth) acrylic copolymer and a thiol group-modified polyvinyl alcohol, the above problem has been solved.

  By using thiol group-modified polyvinyl alcohol as a dispersant, stable polymerization of (meth) acrylic monomers becomes possible, and (meth) acrylic copolymers having a predetermined glass transition point and gel fraction are obtained. Can be obtained. When the (meth) acrylic copolymer thus obtained is used, the change in viscosity over time is small, the workability is good, and the adhesive strength, initial strength, and boiling repetition strength are all excellent. An aqueous emulsion adhesive that is satisfactory in terms of points is obtained.

Hereinafter, the present invention will be described in detail.
An aqueous emulsion adhesive according to the present invention includes a copolymer obtained by polymerizing a monomer group containing an ethylenically unsaturated carboxylic acid and a (meth) acrylic monomer, and a thiol group-modified polyvinyl alcohol. It contains.

  The monomer group mainly includes one or a plurality of (meth) acrylic monomers and contains an ethylenically unsaturated carboxylic acid as an essential component. Examples of the ethylenically unsaturated carboxylic acid include monobasic acids such as (meth) acrylic acid, dibasic acids such as itaconic acid, (anhydrous) maleic acid, and fumaric acid, or monoester derivatives thereof, and 2-methacryloyl. And ethylenically unsaturated group adducts of succinic acid such as oxyethyl succinic acid. Among these, acrylic acid is particularly preferable.

  The (meth) acrylic acid means at least one of methacrylic acid and acrylic acid. In addition, the description of other "(meth) acryl" is based on this. The (meth) acrylic monomer means a monomer containing a (meth) acrylic group (excluding (meth) acrylic acid).

  Examples of (meth) acrylic monomers other than the (meth) acrylic acid include (meth) acrylic acid esters. Examples of the (meth) acrylic acid ester include (meth) acrylic acid alkyl esters having a carbon molecule having 1 to 10 alkyl groups. This alkyl group may be linear or branched. Examples of such (meth) acrylic acid alkyl esters include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and hydroxyethyl (meth) acrylate. , Hydroxypropyl (meth) acrylate, n-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and the like. The above (meth) acrylic means acrylic or methacrylic.

  The combination and ratio of these (meth) acrylic monomers needs to satisfy the conditions of the gel fraction and glass transition point described later, the (meth) acrylic copolymer that is the above-described copolymer. is there.

  The content of the ethylenically unsaturated carboxylic acid in the monomer group is preferably 0.1 to 5% by weight, and more preferably 0.3 to 3% by weight. If the amount is less than 0.1% by weight, the polymerization stability and reactivity may be insufficient, and the resulting emulsion emulsion may become unstable or the conversion rate of the reaction may be insufficient. On the other hand, when the amount is more than 5% by weight, the water-resistant adhesive property and boiling repeated strength may be lowered.

  In addition to each of the above monomers, the monomer group may contain other copolymerizable monomers as necessary. Specific examples include aromatic vinyl monomers such as α-methylstyrene and chlorostyrene, nitriles such as (meth) acrylonitrile, acrylamides such as N-methylolacrylamide and N-butoxymethylacrylamide, and butadiene. Conjugated dienes such as isoprene, and allyl compounds such as allyl sulfonate, diallyl phthalate, triallyl cyanurate and triallyl isocyanurate.

  The thiol group-modified polyvinyl alcohol is obtained by modifying the end of polyvinyl alcohol or partially saponified polyvinyl acetate with a thiol group. The average saponification degree of the partially saponified polyvinyl acetate used here is desirably 80 mol% or more, and more desirably 85 mol% or more. When it is lower than 80 mol%, sufficient emulsion polymerization stability may not be obtained. When the average saponification degree is 100 mol%, polyvinyl alcohol is obtained. The modification method can be produced by, for example, saponifying thiol group-containing polyvinyl acetate obtained by polymerizing vinyl acetate in the presence of thiolic acid such as thioacetic acid by a conventional method. Due to the reactivity of the terminal thiol group, the reaction with the monomer proceeds and a stable aqueous emulsion can be obtained.

  This thiol group-modified polyvinyl alcohol is used as a protective colloid when the monomer group is copolymerized, particularly emulsion polymerized. 100-3000 are preferable and, as for the average degree of polymerization of this thiol group modified polyvinyl alcohol, 300-1500 are more preferable. If it is less than 100, water resistance such as boiling repetition strength tends to deteriorate. On the other hand, if it exceeds 3000, a sufficient polymerization stabilizing effect may not be obtained.

  The amount of the thiol group-modified polyvinyl alcohol used is preferably 3 to 10 parts by weight, preferably 4 to 8 parts by weight, based on 100 parts by weight of the monomer group. If it is less than 3 parts by weight, sufficient emulsion polymerization stability cannot be obtained. On the other hand, if it is 10 parts by weight or more, the viscosity of the resulting aqueous emulsion tends to be high, and the handleability tends to deteriorate.

  As a protective colloid used in the above emulsion polymerization, in addition to the thiol group-modified polyvinyl alcohol, fully saponified or partially saponified polyvinyl alcohol, sodium polyacrylate, sodium alginate, carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, styrene A maleic acid copolymer resin or the like may be added as necessary.

  As a polymerization method of the monomer group, a general emulsion polymerization method can be used, and specifically, it can be produced by the following method. That is, ion-exchanged water is charged into a reaction kettle equipped with a stirring blade and a reflux condenser, and a protective colloid containing the thiol group-modified polyvinyl alcohol is added, and heated and dissolved. Next, after making the inside of the reaction kettle into a nitrogen atmosphere, the temperature is adjusted to about 40 to 80 ° C., and a polymerization catalyst such as persulfate, hydrogen peroxide, alkyl hydroperoxide such as t-butyl hydroperoxide is used. An aqueous emulsion adhesive containing the (meth) acrylic copolymer is obtained by adding an oxidizing agent or a reducing agent such as sodium hyposulfite, and dropping the monomer group continuously and emulsion polymerization. Manufactured.

  In the above emulsion polymerization, anionic, cationic and nonionic surfactants can be used as long as the objects and effects of the present invention are not impaired. Examples of the anionic surfactant include ammonium or sodium sulfonate of polyoxyethylene alkyl (and / or aryl) ether, sodium dodecylbenzene sulfate, and the like. Examples of the nonionic surfactant include polyoxyethylene alkyl ether, polyoxyethylene alkyl aryl ether, and oxyethylene / oxypropylene block polymer.

  The amount of the surfactant used is preferably 1 part by weight or less, preferably 0.5 parts by weight or less, per 100 parts by weight of the monomer group used. When the amount is more than 1 part by weight, the usable time of the adhesive obtained in the present invention is shortened, and a sufficient workability improvement effect may not be obtained.

  Thus, the glass transition point of the (meth) acrylic-type copolymer obtained needs to be -30-50 degreeC, and it is desirable that it is -20-30 degreeC. When the temperature is lower than −30 ° C., the heat resistance is lowered. On the other hand, when the temperature is higher than 50 ° C., the adhesiveness tends to be lowered. In addition, the glass transition temperature in the case of using the said monomer in combination can be calculated | required by the formula of FOX from the glass transition temperature of the homopolymer of each monomer.

  Further, the gel fraction of the (meth) acrylic copolymer needs to be 10 to 70% by weight, and preferably 15 to 60% by weight. If it is less than 10% by weight, the water resistance such as boiling repetition strength tends to decrease, while if it is more than 70% by weight, the polymerization becomes unstable and many coarse particles may be formed, which is not preferable.

  Furthermore, the weight average molecular weight of the (meth) acrylic copolymer is preferably 100,000 to 800,000, more preferably 150,000 to 750,000.

  In addition to the (meth) acrylic copolymer and the thiol group-modified polyvinyl alcohol, the aqueous emulsion adhesive can contain a polyvalent isocyanate compound and the like. By including this polyvalent isocyanate compound and the like, the adhesive strength and the boiling repetition strength can be further improved.

  The polyvalent isocyanate compound refers to a compound having two or more isocyanate groups in the molecule, such as tolylene diisocyanate (hereinafter abbreviated as “TDI”), hydrogenated trimethylolpropane / TDI adduct, triphenyl. Examples include methane triisocyanate, methylene bis (diphenyl isocyanate) (hereinafter abbreviated as “MDI”), hydrogenated MDI, polymerized MDI, hexamethylene diisocyanate, xylylene diisocyanate, 4,4-dicyclohexylmethane diisocyanate, and isophorone diisocyanate.

  Furthermore, as the polyvalent isocyanate compound, a prepolymer in which an excess polyisocyanate is added to a polyol and polymerized in advance and the terminal group has an isocyanate group may be used, and two or more polyvalent isocyanate compounds may be used. It may be used. By containing such a polyvalent isocyanate compound, the components of the aqueous emulsion adhesive such as the (meth) acrylic copolymer and the thiol group-modified polyvinyl alcohol can be crosslinked. Thereby, improvement of the above-mentioned adhesive strength is realized.

  The mixing ratio of the copolymer and the polyvalent isocyanate compound in the aqueous emulsion adhesive is 5 to 150 parts by weight of the polyvalent isocyanate compound relative to 100 parts by weight of the solid content of the copolymer. It is preferably 20 to 100 parts by weight. If it is less than 5 parts by weight, sufficient adhesive strength and boiling repetition strength may not be obtained. On the other hand, although it may be more than 150 parts by weight, an increase in the effect commensurate with the increase in the amount of addition is not obtained, it is not economical, and the usable time of the adhesive after blending is shortened.

  The aqueous emulsion adhesive may be blended with the thiol group-modified polyvinyl alcohol or partially saponified polyvinyl acetate after the (meth) acrylic copolymer is polymerized.

  Furthermore, you may contain the aqueous | water-based emulsion of another polymer in the range which does not reduce the performance as an adhesive agent as needed. Examples of such aqueous emulsion include polybutadiene emulsion, styrene / butanediene copolymer emulsion, acrylonitrile / butadiene copolymer emulsion, polyvinyl acetate emulsion, poly (meth) acrylate emulsion, polyvinyl chloride emulsion, polychloroprene emulsion, Polyvinylidene chloride emulsion, ethylene-vinyl acetate copolymer emulsion, vinyl acetate- (meth) acrylic acid ester copolymer emulsion, ethylene-vinyl acetate-vinyl chloride terpolymer emulsion, ethylene-vinyl acetate- (meth) Examples thereof include aqueous emulsions such as an acrylate terpolymer emulsion and an ethylene-vinyl acetate-vinyl versatic acid terpolymer emulsion.

  Among these, an aqueous emulsion of a polymer compound containing a functional group that reacts with an isocyanate group, such as a hydroxyl group or a carboxyl group, such as the above-described thiol group-modified polyvinyl alcohol or poly (meth) acrylate emulsion, is preferable.

  The aqueous emulsion adhesive further includes, for example, thermosetting resins such as urea resin, melamine resin, and phenol resin, fillers such as clay, kaolin, talc, and calcium carbonate, antiseptics, rust inhibitors, and antifoams. You may contain compounding agents, such as pigments, such as an agent, a foaming agent, a thickener, a viscosity modifier, a flame retardant, and a titanium oxide.

  By applying the aqueous emulsion adhesive to a porous material, a laminate having an adhesive layer made of the aqueous emulsion adhesive and a layer made of a porous material is obtained. Examples of the porous material include natural fibers such as cotton, hemp, and silk, chemical fibers such as viscose rayon and cellulose acetate, paper, cloth, and wood.

  Another layer may be provided outside the adhesive layer constituting the laminate. This layer may be a porous material similar to the above, and for example, metals such as iron, steel, gold, silver, copper, aluminum, glass, gypsum, ceramics, inorganic materials such as ceramics, polyolefins, Non-plastic materials such as polycarbonate, polystyrene, polyester, polyether, polyimide, polyamide, epoxy, polyurethane, ABS, rubber, or plastics containing synthetic fiber, fiber reinforced composite material, inorganic filler, etc. It may be a porous material layer.

  Examples of the coating method of the aqueous emulsion adhesive in the production of the laminate include brushing, tampo coating, spray coating, spray coating, electrostatic coating, roller coating, curtain flow coating, flow coating, and dipping. Examples thereof include coating, electrodeposition coating, powder coating, roll coater coating, blade coater coating, screen coating, and a method using a spin coater.

The coating amount of the adhesive layer in the laminate, 100 to 500 g / m ² selfishness, 200 to 400 g / m ² is preferred. It is preferable that the thickness satisfies the above range because the adhesiveness tends to be improved.

  The laminated body is, for example, a laminated wood veneer, a laminated material for construction, a laminated material such as a construction laminated material, a flooring material such as a composite floor, a wooden composite material such as a heat insulating panel, paper, fiber, wood, and metals. It can be used for composite materials such as inorganic materials and various plastics. Especially, it uses suitably for woody laminated bodies, such as a laminated material which adhere | attached timber.

EXAMPLES Hereinafter, although this invention is demonstrated in detail using an Example, this invention is not limited to a following example, unless the summary is exceeded.
First, tests and evaluation methods performed in Examples and Comparative Examples, and reagents used will be described.

[Evaluation methods]
(Normal adhesive strength)
The laminates obtained in the examples and comparative examples were cured at 20 ° C. and 60% RH for 7 days, and then the compression shear bond strength was measured according to JIS K 6852 as it was.

(Initial bond strength)
The laminates obtained in Examples and Comparative Examples were immediately measured for compression shear adhesive strength of 30 minutes in accordance with JIS K 6853.

(Boiling repeat strength)
The laminates obtained in Examples and Comparative Examples were cured at 20 ° C. and 60% RH for 7 days, then immersed in boiling water for 4 hours, dried in an oven at 60 ° C. for 20 hours, and further immersed in boiling water. After soaking for 4 hours, the specimen was immersed in room temperature water for 15 minutes or more, the specimen was cooled to room temperature, and the compression shear adhesive strength was measured in accordance with JIS K 6852 while the specimen was still wet.

(Glass transition temperature (hereinafter abbreviated as “Tg”))
The glass transition temperature of the (meth) acrylic copolymer is calculated from the FOX formula (Emulsion Latex Handbook, Taiseisha Co., Ltd.) from the glass transition temperature of the homopolymer of each monomer constituting the monomer group. 280-281). Moreover, about the commercial item with unknown composition ratio, Tg was measured using the differential scanning calorimeter (DSC, Seiko Instruments Co., Ltd. product thermal analysis system SSC5200).

(Gel fraction)
First, the sample was dried at room temperature and reduced pressure over 5 hours. The solid content of 40 mg of the obtained sample was adjusted to a 0.2 wt% THF solution at room temperature over 24 hours. This solution was filtered under reduced pressure with a 100 μm membrane filter and dried at 105 ° C. for 3 hours, and the residue was taken as a gel content, and the percentage of the solid content of the sample was determined.

(Weight average molecular weight: Mw)
First, the sample was dried at room temperature and reduced pressure over 5 hours. The solid content of 40 mg of the obtained sample was adjusted to a 0.2 wt% THF solution at room temperature over 10 hours. This solution was filtered through a 0.45 μm filter, and the filtrate was used as a GPC sample.
The weight average molecular weight of the obtained GPC sample was measured by gel permeation chromatography (GPC) under the following measurement conditions.
-Column temperature: 40 ° C
・ Eluent (THF) flow rate: 1 ml / min
Sample injection volume: 100 μl
Column: PL gel 10 μm mix B x 2 (manufactured by Polymer Laboratories)
-Detector: RI (UV254 nm)
Standard sample: monodisperse PS

(Viscosity measurement)
It measured at 10 rpm and 25 degreeC using the Brookfield type | mold viscosity meter (made by Tokimec Co., Ltd.).

(PH measurement)
Measurement was performed using a pH meter.

(Solid content measurement)
It measured based on JISK6828-1996.

(Auxiliaries used)
-Thiol group-modified polyvinyl alcohol (Kuraray Co., Ltd .: Kuraray M polymer: M-205 Average degree of polymerization: 500 End of partially saponified polyvinyl acetate having a saponification degree of about 88 mol% modified with thiol group)
T-butyl hydroperoxide: Kayaku Akzo Co., Ltd .: Kayabutyl H-70
Ascorbic acid: Takeda Pharmaceutical Co., Ltd. n-butyl methacrylate: Wako Pure Chemical Industries, Ltd .: Reagent grade (Tg of homopolymer: -20 ° C., hereinafter abbreviated as “BMA”)
・ 2-ethylhexyl acrylate: Wako Pure Chemical Industries, Ltd .: reagent grade (Tg of homopolymer: −70 ° C., hereinafter abbreviated as “2EHA”)
・ Methyl methacrylate: Wako Pure Chemical Industries, Ltd .: reagent grade (Tg of homopolymer: 105 ° C., hereinafter abbreviated as “MMA”)
Acrylic acid: Wako Pure Chemical Industries, Ltd .: reagent grade (Tg of homopolymer: 106 ° C., hereinafter abbreviated as “AA”)
・ Butyl acrylate: Wako Pure Chemical Industries, Ltd .: reagent grade (Tg of homopolymer: −50 ° C., hereinafter abbreviated as “BA”)
・ Polyvinyl alcohol: Kuraray Co., Ltd .: PVA217
・ Polymethylene polyisocyanate: Sumitomo Bayer Urethane Co., Ltd .: Sumijour 44V-20
・ Ethylene vinyl acetate emulsion: Sumitomo Chemical Co., Ltd .: S-400HQ
・ Styrene butadiene rubber latex: manufactured by Asahi Kasei Corporation: DL-612
・ Calcium carbonate: Nitto Flourishing Co., Ltd .: NS-100

(Example 1)
[Production of aqueous emulsion]
In a reaction vessel equipped with a stirring blade and a reflux condenser, 94 parts by weight of water and 5.6 parts by weight of thiol group-modified polyvinyl alcohol were charged and dissolved at elevated temperature. It was adjusted.
Next, 0.4 parts by weight of t-butyl peroxide and 0.04 parts by weight of ascorbic acid are added to the reaction kettle, and immediately after that, a monomer group consisting of 90 parts by weight of BMA, 10 parts by weight of 2EHA and 0.5 parts by weight of AA. The liquid mixture was continuously added dropwise to initiate polymerization, and the liquid mixture was added dropwise in about 4 hours while maintaining the liquid temperature in the reaction vessel at 60 ° C. Further, the liquid temperature was set at 75 ° C. and aged for 3 hours, followed by cooling to obtain a purified aqueous emulsion.

[Manufacture of adhesives]
The obtained aqueous emulsion, polyvinyl alcohol (PVA217, 15% by weight aqueous solution), and calcium carbonate in an apparent (solid) weight ratio of 42/29/29 (solid content weight ratio of 39/8/53) The main ingredient was blended at a ratio of An aqueous emulsion adhesive was obtained by adding and mixing 15 parts by weight of polymethylene polyisocyanate as a polyvalent isocyanate to 100 parts by weight of the main agent.

[Manufacture of laminates]
120 g / m ^{2 of} each obtained aqueous emulsion adhesive was applied to each side of two pieces of glazed glazing (10 mm × 25 mm × 30 mm, water content 8%), and the coated surfaces were bonded to each other. The laminate was obtained by pressing under the conditions of The pressing condition of the laminate for measuring the normal adhesive strength and the boiling repetition strength is 0.8 MPa × 24 hours, and the pressing condition of the laminate for the initial adhesion measurement is 0.8 MPa × 30 minutes.

[Measurement]
About this main ingredient and aqueous emulsion, the compounding ratio and viscosity of the non-volatile content were measured. Moreover, about the (meth) acrylic-type copolymer in aqueous emulsion, THF gel fraction and THF soluble part molecular weight Mw were measured, and Tg was computed. Furthermore, about the laminated body, normal-state adhesive strength, initial stage adhesive strength, and boiling repetition strength were measured. The results are shown in Table 1.

(Example 2)
An aqueous emulsion adhesive was obtained in the same manner as in Example 1 except that the monomer group of Example 1 was changed to MMA 60 parts by weight, 2EHA 40 parts by weight, and AA 0.5 part by weight. And calculated. The results are shown in Table 1.

(Comparative Example 1)
An aqueous emulsion adhesive was obtained in the same manner as in Example 1 except that the monomer group in Example 1 was changed to 50 parts by weight of MMA and 50 parts by weight of BA, and the same measurement and calculation as in Example 1 were performed. The results are shown in Table 1.

(Comparative Example 2)
Instead of the aqueous emulsion of Example 1, the same measurement and calculation as in Example 1 were performed using an ethylene vinyl acetate emulsion. The results are shown in Table 1. The measured Tg is that of ethylene vinyl acetate.

(Comparative Example 3)
Instead of the aqueous emulsion of Example 1, styrene butadiene rubber latex was used, and the same measurements and calculations as in Example 1 were performed. The results are shown in Table 1. The measured Tg is that of styrene butadiene rubber.

(result)
In the aqueous emulsion adhesive of Comparative Example 1 in which the monomer group does not contain AA and the gel fraction does not satisfy the conditions, the boiling repetition strength is remarkably reduced as compared with the two examples.
In addition, both of the two examples showed higher boiling repetition strength than Comparative Example 2 using ethylene vinyl acetate as an aqueous emulsion, and higher initial adhesiveness than Comparative Example 3 using styrene butadiene rubber as an aqueous emulsion. Indicated.

Claims (5)

  A glass transition point obtained by polymerizing a monomer group containing an ethylenically unsaturated carboxylic acid and a (meth) acrylic monomer is -30 to 50 ° C, and a gel fraction is 10 to 70 weights. % Aqueous (meth) acrylic copolymer and thiol group-modified polyvinyl alcohol.   The aqueous emulsion adhesive according to claim 1, wherein the content of the ethylenically unsaturated carboxylic acid in the monomer group is 0.1 to 5% by weight.   The aqueous emulsion adhesive according to claim 1 or 2, further comprising a polyvalent isocyanate compound in addition to the (meth) acrylic copolymer and the thiol group-modified polyvinyl alcohol.   The (meth) acrylic monomer is a (meth) acrylic acid alkyl ester having a linear or branched alkyl group having 1 to 10 carbon atoms. An aqueous emulsion adhesive.   The aqueous emulsion adhesive according to any one of claims 1 to 4, wherein the ethylenically unsaturated carboxylic acid is acrylic acid and / or methacrylic acid.