JP2012176999A - Aqueous adhesive - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the strength of water resistant adhesion of an aqueous adhesive using a polyvinyl alcohol emulsion type of a polychloroprene latex.SOLUTION: The aqueous adhesive contains a polychloroprene latex and zinc oxide. The polychloroprene latex is obtained by emulsification polymerization in the presence of acetoacetylated polyvinyl alcohol. The chloroprene polymer in the polychloroprene latex is preferably a copolymer of vinyl monomers containing chloroprene and carboxy groups. The toluene insoluble of the chloroprene polymer in polychloroprene latex is preferably 10-90%. Also, the acetoacetylation degree of acetoacetylated polyvinyl alcohol is preferably 0.05-15 mol%. The amount of zinc oxide contained in the aqueous adhesive is 0.1-6.0 mass parts based on 100 mass parts of polychloroprene latex, on solid content conversion basis.

Description

  The present invention relates to a polychloroprene latex obtained using a specific polyvinyl alcohol as an emulsifier, and an aqueous adhesive containing zinc oxide.

  Polychloroprene latex using polyvinyl alcohol as an emulsifier (hereinafter referred to as “PVA emulsified polychloroprene latex”) has excellent compatibility with various compounding agents such as tackifier resin emulsions and thickeners, and has a compounding design. It is characterized in that it has a high degree of freedom and is excellent in tackiness after being applied to various adherends. Therefore, taking advantage of these characteristics, it is used as a water-based adhesive for bonding wood such as plywood, or foam insulation and concrete. However, these water-based adhesives may cause the polyvinyl alcohol to bleed on the surface when the adhesive layer is dried, and may cause poor adhesion when used in places where the humidity is high or where water is easily wet. . Therefore, improvement of water-resistant adhesive strength is examined by various methods. Conventional techniques for improving water-resistant adhesive strength include (1) a method of adding an additive other than polyvinyl alcohol to polychloroprene latex, (2) a method of improving the structure of polychloroprene, and (3) improving the structure of polyvinyl alcohol. It can be roughly divided into methods.

As an example of (1), an aqueous system excellent in initial adhesive strength, normal adhesive strength, and water-resistant adhesive strength by emulsion polymerization of chloroprene in the temperature range of 0 to 20 ° C. in the presence of a nonionic emulsifier having a specific structure. It is known that polychloroprene latex for adhesives can be obtained. (See Patent Document 1)
In another patent document, in the presence of polyvinyl alcohol, chloroprene and a specific amount of an ethylenically unsaturated carboxylic acid are emulsion-copolymerized, and a weak acid salt and a radical scavenger are added thereto to improve storage stability and water-resistant adhesive strength. It is described that an excellent polychloroprene latex can be obtained. (See Patent Document 2)
Also known is a technique for improving water-resistant adhesive strength by blending polychloroprene latex with a thiourea compound. (See Patent Document 3)

  As an example of (2), a gel content of 10 to 70% by mass, pH 6 to 9, produced by emulsion copolymerization of chloroprene and ethylenically unsaturated carboxylic acid in the presence of polyvinyl alcohol and a nonionic emulsifier Polychloroprene latex is known. (See Patent Document 4)

As an example of (3), it is known that polychloroprene latex excellent in water-resistant adhesion and contact property can be obtained by using polyvinyl alcohol containing 1 to 15 mol% of ethylene units in the molecule as an emulsifier. Yes. (See Patent Document 5)
Moreover, polychloroprene latex excellent in adhesive performance such as water-resistant adhesive force, contact property, and heat-resistant creep property can be obtained by using polyvinyl alcohol having 1.9 mol% or more of 1,2-glycol bond as an emulsifier. It is known. (See Patent Document 6)

JP 2006-16084 A Patent No. 4342706 Patent No. 4244253 JP2007-63370 JP 2001-139611 A JP 2004-346183 A

  Although the water-resistant adhesive strength of water-based adhesives using PVA emulsified polychloroprene latex has been improved by the above-mentioned existing technology, it is high such as adhesion of rubber members of shoes and adhesion of foam rubber and cloth of wet suit fabrics. Further improvements were necessary for use in fields where water-resistant adhesion was required.

  This invention makes it a subject to improve the water-resistant adhesive force of the water-system adhesive agent using PVA emulsification type polychloroprene latex.

  The present invention is a water-based adhesive comprising polychloroprene latex obtained by emulsion polymerization in the presence of acetoacetylated polyvinyl alcohol and zinc oxide.

  The chloroprene polymer in the polychlorolatex is preferably a copolymer of chloroprene and a carboxyl group-containing vinyl monomer, and the toluene-insoluble content of the chloroprene polymer in the polychlorolatex is 10 to 90%. Is preferred. Moreover, it is preferable that the acetoacetylation degree of acetoacetylated polyvinyl alcohol is 0.05-15 mol%, and content of the zinc oxide in a water-system adhesive is a polychloroprene latex with respect to 100 mass parts in conversion of solid content. It is preferably 0.1 to 6.0 parts by mass in terms of solid content.

  ADVANTAGE OF THE INVENTION According to this invention, the water-resistant adhesive force of the water-system adhesive using PVA emulsification type polychloroprene latex can be improved.

  Hereinafter, embodiments for carrying out the present invention will be described in detail. Note that the present invention is not limited to the embodiments described below.

  The aqueous adhesive of the present invention comprises a polychloroprene latex produced by radical emulsion polymerization of chloroprene monomer in water using acetoacetylated polyvinyl alcohol (hereinafter referred to as “AA-modified PVA”) as an emulsifier. And zinc oxide as an essential component.

AA-PVA is polyvinyl alcohol having a structural unit represented by the following chemical formula (1) and having a hydroxyl group in a vinyl alcohol unit acetoacetylated.

  AA-modified PVA is produced by reacting diketene, acetoacetate, acetoacetate, or the like with polyvinyl alcohol obtained by radical polymerization of a vinyl ester monomer and then saponification.

  The vinyl ester monomer is not particularly limited, but vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate and Examples include vinyl versatate. Among these, it is desirable to use vinyl acetate that is excellent in stability during polymerization.

  When producing polyvinyl alcohol, if necessary, other monomers copolymerizable with the above-described monomers may be copolymerized. In this case, the copolymerizable monomer is not particularly limited, and examples thereof include olefins such as ethylene, propylene, 1-butene and isobutene, acrylic acid, methacrylic acid, crotonic acid, phthalic acid, maleic acid. Acids, unsaturated acids such as itaconic acid, or salts thereof, esters of the unsaturated acids, acrylamide, N-alkyl acrylamide having 1 to 18 carbon atoms, N, N-dialkyl acrylamide, diacetone acrylamide, 2-acrylamide propane Acrylamides such as sulfonic acid and its salt, acrylamidopropyldimethylamine and its salt or quaternary salt thereof, methacrylamide, N-alkylmethacrylamide having 1 to 18 carbon atoms, N, N-dialkylmethacrylamide, diacetone methacrylamide , 2-methacrylamide Vinyl ethers such as lopansulfonic acid and salts thereof, methacrylamides such as methacrylamide dimethyldimethylamine and salts thereof or quaternary salts thereof, alkyl vinyl ethers having an alkyl chain length of 1 to 18 carbon atoms, hydroxyalkyl vinyl ethers and alkoxyalkyl vinyl ethers N-vinylamides such as N-vinylpyrrolidone, N-vinylformamide, N-vinylacetamide, vinyl cyanides such as acrylonitrile, methacrylonitrile, vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, bromide Vinyl halides such as vinyl and vinylidene bromide, vinylsilanes such as trimethoxyvinylsilane, allyl compounds such as allyl acetate, allyl chloride, allyl alcohol, dimethylallyl alcohol, Such as vinyl silyl compounds and isopropenyl acetate such as sulfonyl trimethoxysilane.

  In addition, although the usage-amount of these other copolymerizable monomers is not specifically limited, It is preferable that it is 0.001 mol% or more and less than 20 mol% with respect to the monomer whole quantity.

  A known radical polymerization method can be adopted as a polymerization method of these monomers. Generally, it is produced by solution polymerization using alcohol such as methanol, ethanol and isopropyl alcohol as a solvent, but may be produced by bulk polymerization, emulsion polymerization, suspension polymerization or the like. Moreover, when performing bulk polymerization or solution polymerization, continuous polymerization or batch polymerization may be used. Furthermore, the monomers may be charged all at once, may be charged separately, or may be added continuously or intermittently.

  The polymerization initiator used in radical polymerization is not particularly limited, but azobisisobutyronitrile, azobis-2,4-dimethylpareronitrile, azobis (4-methoxy-2,4-dimethylpareronitrile). ), Etc., peroxides such as acetyl peroxide, benzoyl peroxide, lauroyl peroxide, acetylcyclohexylsulfonyl peroxide, 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate, diisopropylpropyloxy Percarbonate compounds such as dicarbonate, di-2-ethylhexyl peroxydicarbonate, diethoxyethyl peroxydicarbonate, t-butylperoxyneodecanate, α-cumylperoxyneodecanate, t-butylperoxy Perester compounds such as Odekaneto, azobisdimethylvaleronitrile can be used a known radical polymerization initiator such as azo-bis-methoxy valeronitrile. In addition, the polymerization reaction temperature is not particularly limited, but can usually be set in a range of about 30 to 90 ° C.

  Examples of chain transfer agents include mercaptan compounds and aldehyde compounds. When an aldehyde compound is used, a double bond is introduced into the resulting polyvinyl alcohol molecule. Therefore, by using this as an emulsifier, a polychloroprene latex having higher water resistance can be obtained. Examples of the aldehyde compound include acetaldehyde, propionaldehyde, acrolein (vinyl aldehyde), and benzaldehyde, and examples of the ketone compound include acetone and methyl ethyl ketone. Of these, acetaldehyde is most preferred because it is easy to control the amount of carbon-carbon double bonds in the polyvinyl alcohol molecule. As for the usage-amount of a chain transfer agent, 0.1-3.0 mass parts is preferable with respect to 100 mass parts of total monomers. The chain transfer agent may be added all at once in the initial stage, or may be added in a divided or continuous manner during the polymerization reaction.

  On the other hand, the saponification method for producing polyvinyl alcohol may be saponified by a known method. Generally, it can carry out by hydrolyzing the ester part in a molecule | numerator in presence of an alkali catalyst or an acid catalyst. At this time, although the density | concentration of the copolymer in alcohol which is a polymerization solvent is not specifically limited, It is desirable that it is 10-80 mass%.

  Examples of the alkali catalyst used include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, sodium methylate, sodium ethylate and potassium methylate, alcoholates, and the like. As the acid catalyst, for example, an inorganic acid aqueous solution such as hydrochloric acid and sulfuric acid, or an organic acid such as p-toluenesulfonic acid can be used, and sodium hydroxide is particularly preferable.

  Further, the temperature of the saponification reaction is not particularly limited, but is preferably in the range of 10 to 70 ° C, more preferably 30 to 40 ° C. Although reaction time is not specifically limited, It is desirable to carry out in 30 minutes-3 hours.

  The saponification degree of polyvinyl alcohol is preferably 85 to 99 mol%. When the degree of saponification is less than 85 mol%, the dissolution rate of polyvinyl alcohol in water becomes slow, and the productivity is lowered. On the other hand, when the degree of saponification exceeds 99 mol%, the emulsification performance of polyvinyl alcohol is lowered, and there is a possibility that stable emulsion polymerization cannot be performed. In addition, the saponification degree prescribed | regulated here is the value measured by the method prescribed | regulated to JISK6726.

  Polyvinyl alcohol preferably has an aqueous solution viscosity (viscosity at 20 ° C. of an aqueous solution having a concentration of 4% by mass) measured by a method defined in JIS K 6726 of 3 to 50 mPa · s. When this aqueous solution viscosity is less than 3 mPa · s, the aqueous solution tends to scatter. Moreover, when aqueous solution viscosity exceeds 20 mPa * s, the melt | dissolution rate with respect to the water of polyvinyl alcohol will become slow, or the adhesion amount to the inner wall of a melt | dissolution tank will increase.

  In the case of modified polyvinyl alcohol, when the degree of polymerization is measured by the method defined in JIS K 6726, it is crosslinked and insolubilized in the pretreatment stage in which unsaponified vinyl acetate units are completely saponified, An accurate degree of polymerization may not be obtained. Therefore, in the present invention, instead of the degree of polymerization, a preferred range of aqueous solution viscosity defined in JIS K 6726 is described. A suitable polymerization degree range when not insolubilizing by pretreatment is 200-2600.

  The saponified polyvinyl alcohol is washed as necessary and dried by heating. In the saponification reaction, an inorganic salt such as sodium acetate is by-produced, so the content of the inorganic salt varies depending on the washing conditions. Since the inorganic salt also acts as a catalyst for the acetoacetylation reaction, it is preferably contained to some extent. On the other hand, if the content of the inorganic salt is large, emulsification failure may occur when emulsion polymerization of the chloroprene monomer. For these reasons, the content of the inorganic salt is preferably 0.01 to 2.0% by mass.

  The average particle size of the dried and pulverized polyvinyl alcohol powder is preferably 100 to 1000 μm, more preferably 200 to 400 μm. If it is finer than 100 μm, powdering becomes a problem, and if it is coarser than 1000 μm, it is difficult to make the acetoacetylation reaction proceed uniformly.

  The method for acetoacetylating the polyvinyl alcohol thus obtained is not particularly limited. For example, when a method of reacting diketene with polyvinyl alcohol is selected, as a suitable method, the polyvinyl alcohol dry powder is stirred in an inert gas while being heated in the range of 20 to 120 ° C., and an organic acid such as acetic acid is stirred. The method of spraying diketene in presence is mentioned.

The degree of acetoacetylation of AA-modified PVA is preferably 0.05 to 15 mol%. If the degree of acetoacetylation is less than 0.05 mol%, the water resistance of an adhesive using polychloroprene latex may be lowered. Moreover, when the acetoacetylation degree exceeds 15 mol%, the property as an emulsifier of AA-PVA becomes insufficient, and the storage stability of the polychloroprene latex may be lowered. The degree of acetoacetylation can be calculated by the area ratio of the main chain methylene proton-derived peak to the acetocetyl group methylene proton-derived peak in the ¹ H-NMR spectrum.
In order to increase the degree of acetoacetylation of AA-PVA, for example, the heating temperature of polyvinyl alcohol is increased, the particle size of polyvinyl alcohol powder is increased, the amount of diketene sprayed is increased, The reaction time may be lengthened.

  The polychloroprene latex used in the aqueous adhesive of the present invention is composed of 2-chloro-1,3-butadiene (hereinafter referred to as chloroprene) or chloroprene and a monomer copolymerizable with chloroprene. Is a polychloroprene latex obtained by emulsion polymerization in the presence of That is, it is a latex (emulsion) obtained by emulsifying a chloroprene polymer in water through the above-described AA-PVA.

  Examples of monomers copolymerizable with chloroprene include 2,3-dichloro-1,3-butadiene, 1-chloro-1,3-butadiene, sulfur, methacrylic acid and esters thereof, and acrylic acid and esters thereof. Two or more types may be used as necessary. The chloroprene polymer of the present invention is preferably a copolymer of chloroprene and a carboxyl group-containing vinyl monomer. As the carboxyl group-containing vinyl monomer, methacrylic acid is most preferable, and the charging amount is preferably 0.01 to 5 parts by mass of the carboxyl group-containing vinyl monomer out of a total of 100 parts by mass of the monomers. When a carboxyl group-containing vinyl monomer is copolymerized, when a metal oxide such as zinc oxide or magnesium oxide is added to the adhesive, cross-linking of divalent metal ions and carboxyl groups occurs, resulting in adhesion such as heat resistance and solvent resistance. This is because the performance can be improved.

  As for the preparation amount of AA-ized PVA, 0.5-10 mass parts is preferable with respect to a total of 100 mass parts of initial preparation monomers. If it is less than 0.5 part by mass, the emulsifying power is not sufficient, and if it exceeds 10 parts by mass, the water resistance of the adhesive is lowered.

  It should be noted that an emulsifier other than AA-PVA can be used in combination for the purpose of improving the storage stability of the polychloroprene latex and preventing freezing in winter. In this case, the type of the emulsifier used in combination is not particularly limited, and any of anionic, nonionic, and cationic may be selected. Specific examples of the anionic emulsifier include carboxylic acid type and sulfate ester type. For example, alkali metal salt of rosin acid, alkyl sulfonate having 8 to 20 carbon atoms, alkyl aryl sulfate, sodium naphthalene sulfonate and formaldehyde And the like. Specific examples of nonionic emulsifiers include polyvinyl alcohol which is not acetoacetylated or a copolymer thereof (for example, a copolymer with acrylamide), polyvinyl ether or a copolymer thereof (for example, a copolymer with maleic acid). , Polyoxyethylene alkyl ether, polyoxyethylene alkylphenol, sorbitan fatty acid ester, polyoxyethylene acyl ester and the like. Specific examples of the cationic emulsifier include aliphatic amine salts, aliphatic quaternary ammonium salts, and the like, for example, octadecyltrimethylammonium chloride, dodecyltrimethylammonium chloride, dilauryldimethylammonium chloride and the like. In the case of using an emulsifier other than PVA, the charging amount is preferably 0.1 to 2.0 parts by mass with respect to 100 parts by mass in total of the monomers.

  The polymerization conditions for the chloroprene monomer are not particularly limited. By arbitrarily selecting the polymerization temperature, polymerization initiator, chain transfer agent, polymerization terminator, polymerization rate, etc., molecular weight, molecular weight distribution, gel content It is possible to control the amount, molecular end structure, and crystallization rate.

  The polymerization temperature for emulsion polymerization of the chloroprene monomer is not particularly limited, but is preferably 5 to 50 ° C. in order to smoothly perform the polymerization reaction. The initiator is a persulfate such as potassium persulfate, an organic peroxide such as 3-butyl hydroperoxide, and the like, and is not particularly limited.

  The type of chain transfer agent used for emulsion polymerization of chloroprene monomer is not particularly limited, and those usually used for emulsion polymerization of chloroprene can be used. For example, n-dodecyl mercaptan and tert-dodecyl mercaptan can be used. Long chain alkyl mercaptans such as diisopropyl xanthogen disulfide and dialkyl xanthogen disulfide such as diethyl xanthogen disulfide, and known chain transfer agents such as iodoform can be used.

  The polymerization terminator (polymerization inhibitor) is not particularly limited, and for example, 2,6-tertiarybutyl-4-methylphenol, phenothiazine, hydroxyamine and the like can be used.

  Although the final polymerization rate is not particularly limited, it can be arbitrarily adjusted at 70 to 100%. Removal of the unreacted monomer (demonomer) is performed by a known method such as heating under reduced pressure.

  The toluene-insoluble content of the chloroprene polymer in the polychloroprene latex in the present invention is preferably 10 to 90%, more preferably 20 to 80%. If it is this range, the adhesive agent excellent in the balance of initial stage adhesive force and normal state adhesive force can be made.

  Zinc oxide is blended in conventional aqueous adhesives as an acid acceptor for hydrochloric acid released from polychloroprene, and is blended for the purpose of improving the storage stability of aqueous adhesives. However, in the present invention, it is added in order to improve the adhesive force by the chelate reaction between the acetoacetyl group of AA-modified PVA and zinc, and has an effect that cannot be exhibited by the conventional polychloroprene latex using non-modified PVA. Have.

The blending amount of zinc oxide is preferably 0.1 to 6.0 parts by mass in terms of solid content with respect to 100 parts by mass in terms of solid content of polychloroprene latex. When the amount is less than 0.1 parts by mass, the effect of improving the adhesive strength is hardly exhibited, and when the amount exceeds 6.0 parts by mass, the zinc oxide itself moves to the surface after drying the adhesive and causes poor adhesion. There is.
When the viscosity of the latex is high, zinc oxide can be added in a powder state, but it is preferable to blend after emulsifying / dispersing in water using an emulsifier.

The water-based adhesive preferably contains 20 to 60 parts by mass of a tackifier resin in terms of solid content with respect to 100 parts by mass of polychloroprene latex in terms of solid content. When tackifying resin is mix | blended in the quantity of this range, the time (open time) after apply | coating an adhesive agent to an adherend and sticking together can be extended. Examples of tackifying resins, rosin resins, rosin ester resins, hydrogenated rosin resins, polymerized rosin resins, alpha-pinene resins, beta-pinene resins, terpene phenol resins, C ₅ fraction petroleum resin, C ₉ fraction Examples thereof include branched petroleum resins, C ₅ / C ₉ fraction petroleum resins, DCPD petroleum resins, alkylphenol resins, xylene resins, coumarone resins, coumarone indene resins, and the like. As a method for adding the tackifying resin, it is preferable to add it as an emulsion in order to uniformly mix it in the adhesive. Furthermore, the method for producing a tackifying resin emulsion includes a method in which an organic solvent such as toluene is emulsified / dispersed in water using an emulsifier, and then the organic solvent is removed while heating under reduced pressure. The former method, which can produce a finer particle emulsion, is preferred.

  Furthermore, for water-based adhesives, thickeners, vulcanization accelerators, fillers (reinforcing agents), pigments, colorants, antioxidants, ultraviolet absorbers, antifungal agents, antiseptics, depending on the application and required performance. An agent, an antibacterial agent, a plasticizer, a pH adjuster, an antifoaming agent, a rust preventive agent, a polymer latex other than polychloroprene may be optionally added. Moreover, it is also possible to combine with a hardening | curing agent to make a two-component adhesive.

  Specific examples of thickeners include organic thickeners such as polyacrylic acid-based, polyacrylamide-based, HUR-based (polymers in which both ends of polyethylene oxide are end-capped with hydrophobic groups), silicate compounds such as hectorite and montmorillonite. Inorganic thickeners such as Among these, the HEUR system is suitable because a large thickening effect can be obtained with a small addition amount and the viscosity stability after blending is excellent.

  Examples of the vulcanization accelerator include thiourea, dithiocarbamate and xanthate. Specific examples of the thiourea compound include ethylenethiourea, dibutylthiourea, dilaurylthiourea, N, N′-diphenylthiourea, trimethylthiourea (TMU), N, N′-diethylthiourea (EUR), and the like. Examples of dithiocarbamates include zinc dimethylcarbamate, zinc diethyldithiocarbamate, zinc dibutylthiocarbamate, zinc N-pentamethylenedithiocarbamate, zinc dibenzyldithiocarbamate, copper (II) dimethyldithiocarbamate, iron dimethyldithiocarbamate (III), tellurium dimethyldithiocarbamate (IV) and the like. Examples of xanthates include zinc butyl xanthate, zinc isopropyl xanthate, gallium (III) ethyl xanthate, and the like.

  In the case of a two-component adhesive using a curing agent, it is preferable to combine a water-dispersed isocyanate compound. If a curing agent is used, the water resistance of the adhesive can be further improved. The water-dispersed isocyanate compound is obtained by introducing a hydrophilic group into a polyisocyanate polymer obtained from an aliphatic and / or alicyclic diisocyanate and having a structure such as burette, isocyanurate, urethane, uretdione, or allophanate in the molecule. is there. That is, it is a self-emulsifying isocyanate compound that can be dispersed as fine particles in water when added and stirred in water. Examples of the aliphatic and / or alicyclic isocyanate include tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate (HDI), trimethylhexamethylene diisocyanate, lysine diisocyanate (LDI), isophorone diisocyanate (IPDI), and hydrogenated xylylene diene. Isocyanate (hydrogenated XDI), tolylene diisocyanate (TDI), 4,4′-diphenylmethane diisocyanate (MDI), polymerized MDI, xylylene diisocyanate (XDI), naphthylene diisocyanate (NDI), paraphenylene diisocyanate (PPDI), tetra Methylxylylene diisocyanate (TMXDI), dicyclohexylmethane diisocyanate (HMDI), isopropylide Bis (4-cyclohexyl isocyanate) (IPC), cyclohexyl diisocyanate (CHPI), tolidine diisocyanate (TODI), and the like. Among these, HDI, MDI, IPDI, and hydrogenated XDI are industrially easily available and good. The hydrophilic group is introduced by reacting an emulsifier having an ethylene oxide repeating unit with a part of the molecular chain of a polymer obtained from the above aliphatic and / or alicyclic diisocyanate. As the emulsifier having an ethylene oxide repeating unit, polyethylene glycol monomethyl ether is particularly preferable in view of dispersibility in water. The effect as a curing agent depends on the isocyanate group content calculated by the method defined in JIS K-7301 rather than the raw material compound. In order to obtain good adhesive strength, the isocyanate group content of the isocyanate compound used is preferably 17 to 25% by mass.

  When using a water-dispersed isocyanate compound as a curing agent to form a two-component adhesive, the polychloroprene latex in the main agent is 100 parts by mass in solid content, and the water-dispersed isocyanate compound in the curing agent is solid content. It is preferable to mix so that it may become 0.5-15 mass parts. If it is less than 0.5 parts by mass, the adhesive strength is insufficient, and if it is added more than 15 parts by mass, the pot life (usable time) after mixing the main agent and the curing agent may be shortened.

  Hereinafter, the effects of the present invention will be specifically described with reference to Examples and Comparative Examples of the present invention. As polyvinyl alcohol, AA-modified PVA-A to E within the scope of the present invention and general-purpose PVA-F to I which are not acetoacetylated and depart from the scope of the present invention were produced. Subsequently, using these PVA-A to I as emulsifiers, emulsion polymerization of polychloroprene is performed, and an adhesive is prepared by blending zinc oxide or the like into the obtained polychloroprene latex, and its adhesive strength. Evaluated. Below, manufacture of PVA-A to I is described.

<Production of AA PVA-A>
A reactor equipped with a reflux condenser was charged with 3500 g of vinyl acetate and 1.8 g of acetic acid. After purging with nitrogen, 154 g of acetaldehyde was charged and the temperature was raised to the boiling point of the mixed solution. When refluxing started, 50 g of a 0.5% methanol solution of azobisisobutyronitrile in methanol was added dropwise over 6 hours, and the polymerization was stopped when the polymerization rate reached 70%.

  The reactor is heated while blowing methanol vapor to remove unreacted vinyl acetate, and the resulting polymer methanol solution is mixed with sodium hydroxide methanol solution, and the saponification reaction proceeds at a reaction temperature of 35 ° C. I let you. The solidified saponification reaction liquid was wet pulverized in methanol, the slurry was filtered, and then dried in a gear oven at 90 ° C. for 2 hours to prepare PVA-A. In a Brabender kneader, 100 parts by mass of PVA-A powder, 1 part by mass of water, and 30 parts by mass of acetic acid were added and stirred at 60 ° C. for 2 hours. Next, 30 parts by mass of diketene was added little by little over 3 hours, and after completion of the addition, stirring was performed for 4 hours. Furthermore, it wash | cleaned 3 times with methanol, and it dried in 90 degreeC gear oven for 1 hour, and obtained AA-ized PVA-A.

<Production of AA PVA-B>
A reactor equipped with a reflux condenser was charged with 3000 g of vinyl acetate, 220 g of methanol, and 1.5 g of acetic acid, purged with nitrogen, charged with 65.9 g of acetaldehyde, and heated to the boiling point of the mixed solution. When refluxing started, 60 g of a 0.5% methanol solution of azobisisobutyronitrile in methanol was added dropwise over 5 hours, and the polymerization was stopped when the polymerization rate reached 71%.

  The reactor is heated while blowing methanol vapor to remove unreacted vinyl acetate, and the resulting polymer methanol solution is mixed with sodium hydroxide methanol solution, and the saponification reaction proceeds at a reaction temperature of 35 ° C. I let you. The solidified saponification reaction liquid was wet pulverized in methanol, the slurry was filtered, and then dried in a gear oven at 80 ° C. for 1 hour to obtain PVA-B. In a Brabender kneader, 100 parts by mass of PVA-B powder, 1 part by mass of water, and 30 parts by mass of acetic acid were added and stirred at 80 ° C. for 3 hours. Next, 30 parts by mass of diketene was added little by little over 3 hours, and after completion of the addition, stirring was performed for 4 hours. Furthermore, it wash | cleaned 3 times with methanol, and it dried in 90 degreeC gear oven for 1 hour, and obtained AA-ized PVA-B.

<Production of AA-PVA-C>
A reactor equipped with a reflux condenser was charged with 3000 g of vinyl acetate, 616.3 g of methanol, 40.8 g of dimethyl maleate and 2.5 g of azobisisobutyronitrile, heated after nitrogen substitution, and heated to the boiling point. The polymerization was stopped when the polymerization rate reached 70%.

  The reactor is heated while blowing methanol vapor to remove unreacted vinyl acetate, and the resulting polymer methanol solution is mixed with sodium hydroxide methanol solution, and the saponification reaction proceeds at a reaction temperature of 35 ° C. I let you. The solidified saponification reaction liquid was wet pulverized in methanol, the slurry was filtered, and then dried in a gear oven at 90 ° C. for 2 hours to prepare PVA-C. In a Brabender kneader, 100 parts by mass of PVA-C powder, 1 part by mass of water, and 30 parts by mass of acetic acid were added and stirred at 70 ° C. for 3 hours. Next, 30 parts by mass of diketene was added little by little over 3 hours, and after completion of the addition, stirring was performed for 2 hours. Furthermore, it wash | cleaned 3 times with methanol, and it dried in 90 degreeC gear oven for 1 hour, and obtained AA-ized PVA-C.

<Production of AA-PVA-D>
A reactor equipped with a reflux condenser was charged with 1640 g of vinyl acetate, 500 g of methanol, 4.0 g of dimethyl fumarate and 2.0 g of azobisisobutyronitrile, and the temperature was raised to the boiling point of the mixed solution after nitrogen substitution. When refluxing started, a mixture of 510 g vinyl acetate, 230 g methanol, and 33 g dimethyl fumarate was dripped little by little over 5 hours from the top of the reactor, and polymerization was performed when the polymerization rate reached 55%. Stopped.

  The reactor is heated while blowing methanol vapor to remove unreacted vinyl acetate, and the resulting polymer methanol solution is mixed with sodium hydroxide methanol solution, and the saponification reaction proceeds at a reaction temperature of 35 ° C. I let you. The solidified saponification reaction liquid was wet pulverized in methanol, and the slurry was filtered, followed by drying in a gear oven at 90 ° C. for 90 minutes to obtain PVA-D. In a Brabender kneader, 100 parts by mass of PVA-D powder, 1 part by mass of water, and 30 parts by mass of acetic acid were added and stirred at 70 ° C. for 3 hours. Next, 20 parts by mass of diketene was added little by little over 3 hours, and after completion of the addition, stirring was performed for 2 hours. Furthermore, it wash | cleaned 3 times with methanol, and it dried in 90 degreeC gear oven for 1 hour, and obtained AA-ized PVA-D.

<Production of AA-PVA-E>
A polymerization reactor was charged with 120 g of vinyl acetate, 560 g of methanol, and 1.6 g of a 1% methanol solution of azobisisobutyronitrile, and after heating with nitrogen, heated to the boiling point. Next, 1720 g of methyl acetate, 607 g of methanol, and 406 g of 1% methanol solution of azobisisobutyronitrile were continuously added over 14 hours, and after 1 hour from the end of continuous addition, the polymerization rate of vinyl acetate reached 99%. After confirming this, the polymerization reaction was stopped.

  The reactor is heated while blowing methanol vapor to remove unreacted vinyl acetate, and the resulting polymer methanol solution is mixed with sodium hydroxide methanol solution, and the saponification reaction proceeds at a reaction temperature of 35 ° C. I let you. The solidified saponification reaction solution was wet-divided in methanol and the slurry was filtered, and then dried in a gear oven at 90 ° C. for 90 minutes to obtain PVA-E. In a Brabender kneader, 100 parts by mass of PVA-E powder, 2 parts by mass of water, and 30 parts by mass of acetic acid were added and stirred at 60 ° C. for 2 hours. Next, 20 parts by mass of diketene was added little by little over 2 hours, and stirred for 2 hours after the addition was completed. Furthermore, it wash | cleaned 3 times with methanol, and it dried in 90 degreeC gear oven for 1 hour, and obtained AA-ized PVA-E.

<Production of non-modified PVA-F to I>
A polymerization reactor was charged with 120 g of vinyl acetate, 560 g of methanol, and 1.6 g of a 1% methanol solution of azobisisobutyronitrile, and after heating with nitrogen, heated to the boiling point. Next, 1720 g of methyl acetate, 607 g of methanol, and 406 g of 1% methanol solution of azobisisobutyronitrile were continuously added over 14 hours, and after 1 hour from the end of continuous addition, the polymerization rate of vinyl acetate reached 99%. After confirming this, the polymerization reaction was stopped.

  The reactor is heated while blowing methanol vapor to remove unreacted vinyl acetate, and the resulting polymer methanol solution is mixed with sodium hydroxide methanol solution, and the saponification reaction proceeds at a reaction temperature of 35 ° C. I let you. The solidified saponification reaction liquid was wet-dispersed in methanol, the slurry was filtered, and then dried in a gear oven at 90 ° C. for 90 minutes to prepare PVA-F to I. PVA-F to I are conventional PVA that is not acetoacetylated, and the saponification degree is adjusted by adjusting the amount of sodium hydroxide used in the polymerization reaction and the temperature and time of the saponification reaction.

<Characteristic analysis of PVA>
Next, the saponification degree, the sodium acetate content, the polymerization degree, the aqueous solution viscosity, and the AA degree of the obtained AA-PVA-A to E and non-modified PVA-F to I were measured by the following methods.

a) Degree of saponification: Measured according to JIS K6726.
b) Sodium acetate content: Measured according to JIS K6726.
c) Degree of polymerization: measured in accordance with JIS K6726.
d) Viscosity of aqueous solution: measured in accordance with JIS K6726.
e) Degree of AA: Calculated by the area ratio of the main chain methylene proton-derived peak to the acetocetyl group methylene proton-derived peak in the ¹ H-NMR spectrum.

<Production of polychloroprene latex A to I>
Using a reactor having an internal volume of 3 liters, 86 parts by mass of water, 3.2 parts by mass of AA-modified PVA-AE and non-modified PVA-F-I were dissolved at 60 ° C. under a nitrogen stream. It was. After cooling this polyvinyl alcohol aqueous solution to room temperature, 97 mass parts of chloroprene monomers, 4 mass parts of methacrylic acid, and 0.3 mass part of octyl mercaptan were added. While maintaining this at 40 ° C., emulsion polymerization was performed using potassium persulfate as an initiator. 20% by mass diethanolamine aqueous solution is added to the reaction finished solution to adjust the pH to 7 and after removing unreacted monomers under reduced pressure, the water is further evaporated under reduced pressure to perform concentration to obtain a solid content concentration. A 50% polychloroprene latex was obtained. Polychloroprene latexes A to I having different gel contents were prepared by changing the types of PVA (A to I) and adjusting the addition amount of octyl mercaptan. The solid content concentration and gel content were measured by the following methods.

<Concentration of solid content>
Let A be the mass of the aluminum dish alone. Let B be the mass of an aluminum dish containing 2 ml of a latex sample. Let C be the mass after the aluminum dish containing the latex sample is dried at 125 ° C. for 1 hour. The solid content concentration (%) was calculated by the following formula.
Solid content concentration = {(C−A) / (B−A)} × 100

<Gel content (toluene insoluble matter)>
The latex sample was lyophilized and weighed to A. It was dissolved in toluene (adjusted to 0.6%) at 23 ° C. for 20 hours, and the gel was separated using a centrifuge and a 200-mesh wire mesh. The gel was air-dried, dried in an atmosphere at 110 ° C. for 1 hour, and weighed to give B. The gel content (%) was calculated according to the following formula.
Gel content = (B / A) × 100

The adhesion test method will be described below.
According to the prescription shown in Table 1, polychloroprene latex A to I is 100 parts by mass in terms of solid content, and zinc oxide emulsion (AZ-SW / Osaki Kogyo Co., Ltd.) is 0 to 7 parts by mass in terms of solid content. Solid terpene phenol resin emulsion (Tamanol E-100 / Arakawa Chemical Industries Co., Ltd.) 40 parts by mass in terms of solid content, zinc isopropyl xanthate (Noxeller ZIX / Ouchi Shinsei Chemical Co., Ltd.) in water dispersion 5 parts by weight of wet silica (Tokushiru U / manufactured by Tokuyama Corporation) with 2 parts by mass, average particle size: 10 μm, specific surface area: 191 m ² / g, HEUR thickener (RM-8W / Rohm and Haas) Japan Co., Ltd.) was blended in an amount of 0.1 parts by mass in terms of solid content to prepare an adhesive.

150 g (wet) / m ² of adhesive is applied to each of two canvases (size of glue margin is 25 mm wide x 70 mm long) with a brush and dried in an atmosphere at 23 ° C. for 3 hours. To 300 g (wet) / m2 of adhesive was applied with a brush, dried in an atmosphere at 70 ° C. for 5 minutes, and then bonded and pressure-bonded with a hand roller.
<Initial adhesive strength>
One day after the pressure bonding, 180 ° peel strength was measured with a tensile tester at a tensile speed of 200 mm / min.
<Normal adhesive strength>
Seven days after the pressure bonding, 180 ° peel strength was measured with a tensile tester at a tensile speed of 200 mm / min.
<Water-resistant adhesive strength>
One day after the pressure bonding, the film was immersed in pure water for 7 days, and the 180 ° peel strength was measured with a tensile tester at a tensile speed of 200 mm / min.

The evaluation results are summarized in Table 1. The “amount of sodium hydroxide” in Table 1 is a value representing the molar ratio of vinyl acetate units / sodium hydroxide in the polymer.

As can be seen from Table 1, it was shown that the polychloroprene latexes of Examples 1 to 7 were superior to the polychloroprene latexes of Comparative Examples 1 to 6 in terms of the water-resistant adhesive strength of the adhesive.
Moreover, when AA-ized PVA is used, when the blending amount of zinc oxide is in an appropriate range (Examples 5 to 7), when zinc oxide is not blended (Comparative Example 5), or when the blending amount is excessive ( It was shown that the adhesive strength was higher than that of Comparative Example 6).

Claims (5)

  A water-based adhesive comprising polychloroprene latex obtained by emulsion polymerization in the presence of acetoacetylated polyvinyl alcohol and zinc oxide.   The aqueous adhesive according to claim 1, wherein the chloroprene polymer in the polychlorolatex is a copolymer of chloroprene and a carboxyl group-containing vinyl monomer.   The aqueous adhesive according to claim 1 or 2, wherein the toluene-insoluble content of the chloroprene polymer in the polychlorolatex is 10 to 90%. The aqueous adhesive according to any one of claims 1 to 3, wherein the degree of acetoacetylation of the acetoacetylated polyvinyl alcohol is 0.05 to 15 mol%. Content of zinc oxide is 0.1-6.0 mass parts in conversion of solid content with respect to 100 mass parts of polychloroprene latex in conversion of solid content, Any one of Claims 1-4 characterized by the above-mentioned. The water-based adhesive according to item.