JP5715867B2 - Adhesive composition - Google Patents

Description

  The present invention relates to an improvement in viscosity and pot life of an aqueous polymer-isocyanate adhesive.

  Water-based polymer-isocyanate adhesives are safe because they do not use formaldehyde or formaldehyde-producing raw materials, and instead of phenol adhesives or resorcinol adhesives, where formaldehyde emission cannot be avoided, plywood And is used to manufacture laminated timber.

  Aqueous polymer-isocyanate adhesive consists of a resin emulsion such as acrylic resin emulsion, ethylene-vinyl acetate copolymer resin emulsion, styrene-butadiene copolymer resin emulsion, etc., and a main agent and isocyanate compound containing polyvinyl alcohol, calcium carbonate, etc. It is obtained by mixing a curing agent. After mixing the main agent and the curing agent, the viscosity gradually increases as the reaction starts.

  Since the water-based polymer-isocyanate adhesive is used as a substitute for the phenol-based adhesive and the resorcinol adhesive, a high degree of adhesion performance is required. Therefore, the adhesive performance is improved by introducing a hydroxyl group capable of reacting with an isocyanate compound into the resin emulsion or by increasing the solid content of the adhesive. On the other hand, when such improvements are made, there are problems that the thixotropy of the resin emulsion is increased, and that the pot life is shortened due to an abrupt increase in viscosity after mixing the curing agent. When the thixotropy of the adhesive is increased, the applicability is lowered or the amount of application is difficult to adjust, and the workability is lowered when the pot life is shortened.

Patent Documents 1 and 2 disclose an aqueous polymer-isocyanate-based adhesive using an acrylic resin emulsion having a hydroxyl group, and describe that it has a sufficient pot life. However, when the solid content of the adhesive is increased, there is a problem that the pot life is remarkably lowered.
JP 2002-155252 JP JP 2006-273889 A

  An object of the present invention is to provide an aqueous polymer-isocyanate-based adhesive excellent in pot life after mixing a curing agent, even when the solid content of the adhesive is increased, the thixotropy of the adhesive is not too high. Is to provide.

As a result of repeated studies by the present inventors, the above-mentioned problem can be obtained by using an acrylic resin emulsion obtained by polymerizing a monomer containing methoxypolyethylene glycol methacrylate in addition to a hydroxyl group-containing monomer as a resin emulsion. The present invention has been completed by finding that the problem can be solved.
The present invention contains an acrylic resin emulsion (A) obtained by polymerizing a hydroxyl group-containing monomer and a monomer containing methoxypolyethylene glycol methacrylate, a hydroxyl group-containing aqueous polymer (B), and an isocyanate compound (C). It is an adhesive composition characterized by these.

  The adhesive composition of the present invention is excellent in pot life after mixing the curing agent without increasing the thixotropy of the adhesive even when the solid content of the adhesive is increased. Therefore, it is suitable for the production of plywood and laminated wood that require high bonding performance.

  The adhesive composition of the present invention contains an acrylic resin emulsion (A) obtained by polymerizing a monomer containing a hydroxyl group-containing monomer and methoxypolyethylene glycol methacrylate.

The hydroxyl group-containing monomer is a compound having a hydroxyl group and a polymerizable group such as a (meth) acryloyl group in the molecule, and specific examples thereof include hydroxyethyl (meth) acrylate. Note that N-methylol acrylamide whose hydroxyl group is a methylol group, N-butoxymethyl acrylamide obtained by etherifying a methylol group, etc. are not suitable for the present invention because formaldehyde may be by-produced and released.
The hydroxyl group-containing monomer is preferably used in an amount of 0.1 to 20% by weight, more preferably 1 to 10% by weight, based on the total amount of monomers. If it is less than this range, the thixotropy of the resulting adhesive composition may not be reduced. Moreover, when it uses exceeding this range, while the thixotropy reduction effect reaches a peak, there exists a possibility that the polymerizability of an acrylic resin emulsion may fall.

By polymerizing monomers containing methoxypolyethylene glycol methacrylate in addition to the hydroxyl group-containing monomer, the viscosity of the resulting acrylic resin emulsion and adhesives using it is lowered, improving the pot life after mixing the curing agent. it can.
It is preferable to use 0.05 to 10% by weight of methoxypolyethylene glycol methacrylate, and more preferably 0.1 to 3% by weight, based on the total amount of monomers. When it is less than this range, the pot life of the resulting adhesive composition may be reduced. Moreover, when it uses exceeding this range, while the extension effect of a pot life will reach a peak, there exists a possibility that the polymeric property of an acrylic resin emulsion may fall.

  Acrylic resin emulsion (A) is acrylic such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, isononyl acrylate, lauryl acrylate, stearyl acrylate, etc. Acid alkyl ester monomers, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate and other methacrylic acid alkyl ester monomers, styrene, α-methylstyrene, vinyl toluene, ethyl vinyl benzene, etc. Aromatic vinyl monomers, vinyl acetate, vinyl propionate, vinyl versatate and other saturated fatty acid vinyl monomers, acrylonitrile, Vinyl cyanide monomers such as acrylonitrile, olefin monomers such as ethylene, propylene and butadiene, monoalkyl esters of ethylene dicarboxylic acids such as monobutylmaleic acid, and ammonium salts or alkali metal salts thereof Ethylene carboxylates such as acrylamide, acid amides of ethylene carboxylic acids such as acrylamide, methacrylamide and diacetone acrylamide, hydroxy of ethylene carboxylic acids such as 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate and 2-hydroxy methacrylate Alkyl esters, esters of ethylene carboxylic acids such as dimethylaminoethyl methacrylate and diethylaminoethyl methacrylate and alcohols having amino groups, etc., alone or 2 A combination of more than one species can be used. Further, if necessary, a polyfunctional monomer such as divinylbenzene, ethylene glycol dimethacrylate, diallyl phthalate can be used. In addition, when using ethylene-based carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, citraconic acid, itaconic acid, maleic acid, fumaric acid, and maleic anhydride, Since the pot life is shortened, it is necessary to keep it at an amount that does not use it at all or does not affect the pot life.

The acrylic resin emulsion (A) can be produced by emulsion polymerization of these monomers in the presence of an emulsifier such as a surfactant. At this time, as a polymerization initiator, persulfates such as ammonium persulfate and sodium persulfate; Aqueous radical polymerization initiators such as hydrogen oxide water and t-butyl hydroperoxide or a mixture thereof can be used.
The usage-amount of a polymerization initiator is 0.1-5 weight part normally with respect to the polymerizable monomer whole quantity, Preferably it is 0.1-2 weight part.

Moreover, a redox system can be formed by using a polymerization initiator in the presence of a reducing agent.
Examples of such a reducing agent include alkali metal salts such as sulfites, hydrogen sulfites, and pyrosulfites, and carboxylic acids such as ammonium salts, L-ascorbic acid, and tartaric acid. Sodium formaldehyde sulfonate (Longalite) is preferably not used in the present invention because it may formaldehyde. The amount of the reducing agent used is 0.1 to 5 parts by weight, preferably 0.1 to 2 parts by weight, based on the total amount of polymerizable monomers.

  Note that irons such as ferrous sulfate, ferrous ammonium sulfate and cuprous naphthenate, salts of transition metals such as copper, nickel, cobalt, chromium, molybdenum, vanadium and cerium can be used as the reducing agent. However, since there is a possibility of coloring, it is not suitable for use where coloring is not preferred.

Examples of emulsifiers used in emulsion polymerization include anionic surfactants, nonionic surfactants, and amphoteric surfactants.
Examples of anionic surfactants include alkali metal salts such as alkyl or alkyl allyl sulfates, alkyl or alkyl allyl sulfonates, dialkyl sulfosuccinates, polyoxyethylene alkyl ether sulfates, or ammonium salts.
Examples of nonionic surfactants include polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, and polyoxyethylene fatty acid ester.
Examples of amphoteric surfactants include betaine and amino acid derivatives.
Moreover, the reactive surfactant which has an unsaturated group can also be used.

  These surfactants can be used alone or in combination of two or more, and the amount used is 0.1 to 5 parts by weight, preferably 0.3 to 3 parts by weight, based on the total amount of the polymerizable monomer. . When the amount used is less than 0.1 parts by weight, the reaction becomes unstable and aggregates may be generated. Moreover, when it exceeds 5 weight part, drying property and water resistance may worsen.

  In addition to the surfactant, a water-soluble polymer can be used as the emulsifier. In particular, by using thiol-modified polyvinyl alcohol, thixotropy can be reduced even when the amount of the hydroxyl group-containing monomer is small. However, since it tends to increase the viscosity of the acrylic resin emulsion when used from the early stage of emulsion polymerization like a surfactant, it is preferably added at the later stage of emulsion polymerization, and in the aging stage after completion of monomer addition It is more preferable to add.

Emulsion polymerization is carried out in the presence of a chelating agent such as ethylenediaminetetraacetic acid sodium, a dispersant such as polycarboxylate, an inorganic salt such as phosphate and carbonate, a chain transfer agent such as thiol compound and halogen compound, if necessary. You may go to
The polymerization is usually carried out at a temperature of 100 ° C. or lower until the monomer addition rate reaches 99% or higher.

  The hydroxyl group-containing aqueous polymer (B) is an aqueous polymer containing a hydroxyl group that reacts with isocyanate, and examples thereof include cellulose derivatives such as polyvinyl alcohol (PVA), starches, saccharides, hydroxyethyl cellulose, methyl cellulose, and carboxymethyl cellulose. PVA is preferred. PVA generally has a degree of polymerization of about 300 to 4000 and a degree of saponification of about 75 to 99.5%, and may contain a functional group such as an acetoacetyl group. The hydroxyl group-containing aqueous polymer may be added to the resin emulsion, or may be used as a protective colloid during polymerization of the resin emulsion.

  As the isocyanate compound (C), 4,4′-diphenylmethane diisocyanate (MDI), 2,4′-MDI, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, tolylene diisocyanate, hexamethylene diisocyanate , Isophorone diisocyanate, trifunctional compounds derived from the aforementioned isocyanates (adduct, isocyanurate, burette). Among them, crude MDI including MDI and liquid polymeric MDI has good performance and is suitable for use. The blending amount of the isocyanate compound relative to the main agent (adhesive composition other than the isocyanate compound) varies depending on the type of adherend and the required performance, but is preferably used in an amount of about 0.1 to 30 parts by weight with respect to 100 parts by weight of the main agent. Is about 1 to 20 parts by weight.

  It is preferable to mix | blend a filler (D) with the adhesive composition of this invention. Specific examples include clay, kaolin, talc, calcium carbonate, wheat flour, eggplant powder, and wood flour. Among these, calcium carbonate is preferable.

  In the adhesive composition of the present invention, in addition to the components (A) to (D), an ethylene-vinyl acetate copolymer resin emulsion, a styrene-butadiene copolymer resin emulsion, and the like can be used as the resin emulsion. Moreover, additives, such as tackifying resin, an antifoamer, antiseptic | preservative, and anti-aging agent, can be used.

  In the adhesive composition of the present invention, each component may be mixed immediately before use, but in consideration of workability, the isocyanate compound (C) is used as a curing agent, and other than the isocyanate compound is mixed in advance as a main agent, and immediately before use. It is preferable to use a mixture of two components.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and demonstrated in detail about this invention, a specific example is shown and it does not specifically limit to these.

Synthesis of acrylic resin emulsion Reactive anionic surfactant in a mixture of 47.5 parts by weight of styrene, 48.2 parts by weight of butyl acrylate, 4 parts by weight of 2-hydroxyethyl methacrylate, and 0.3 parts by weight of methoxypolyethylene glycol methacrylate Aqueous BC-1025 (Daiichi Kogyo Seiyaku Co., Ltd., trade name, 25% effective) 2 parts by weight of a solution prepared by dissolving in 24 parts by weight of ion-exchanged water was added and stirred with a homodisper to prepare a monomer emulsion. did.
In a separable flask provided with a stirrer, a thermometer, a reflux condenser, and a dropping hole, 55 parts by weight of ion-exchanged water was placed, the inside was purged with nitrogen, and the temperature was raised to 80 ° C. While maintaining the reaction vessel at 80 ° C., the monomer emulsion and an aqueous solution prepared by dissolving 0.6 parts by weight of ammonium persulfate in 6.6 parts by weight of ion-exchanged water were dropped over 4 hours, respectively, to perform emulsion polymerization. The acrylic resin emulsion of Example 1 was obtained by completing the emulsion polymerization by further stirring for 2 hours at the same temperature.

  In addition to the monomers used in the production of the acrylic resin emulsions of the examples, methyl methacrylate and acrylic acid were used, and in addition to the surfactants used in the production of the acrylic resin emulsions of the examples, Hytenol W- which is an anionic surfactant 1725 (Daiichi Kogyo Seiyaku Co., Ltd., trade name), Teika Power BN2060 (Taika Corporation, trade name), Kuraray Poval M-205 (Kuraray Co., trade name) which is polyvinyl alcohol, Except for the emulsifier composition (described based on the effective content) as shown in Table 1, the same procedure as for the acrylic resin emulsion of Example 1 was performed to obtain each acrylic resin emulsion of Examples 2-6 and Comparative Examples 1-3. It was. In addition, about Kuraray Poval M-205 of Example 7, it added, after dripping a monomer emulsion over 4 hours. About the obtained acrylic resin emulsion, pH was measured.

Preparation of main agent In a water solution in which 6.6 parts by weight of polyvinyl alcohol (Denkapoval B-17, manufactured by Denki Kagaku Kogyo Co., Ltd.) was dissolved in 30 parts by weight of ion-exchanged water, a dispersant (Nopco Santo R, manufactured by San Nopco, Product name) 1.4 parts by weight and 0.2 parts by weight of an antifoaming agent (SN deformer 485, manufactured by San Nopco) were added and stirred and mixed well. After confirming the mixing, stirring was performed at 1000 rpm, and 65 parts by weight of calcium carbonate (Whiteon SB, manufactured by Bihoku Flour Industries, trade name) was gradually added under stirring. After confirming the dispersion of Whiten SB, 86.6 parts by weight of each acrylic resin emulsion was added and stirred well to obtain the main agent. About each main ingredient, the 6 rpm value in 23 degreeC and the 30 rpm value were measured using the Brookfield rotational viscometer, and TI value used as the standard of thixotropy was computed from the ratio. When the TI exceeds 2, the coating workability is lowered.

Preparation of Adhesive Composition Weigh out 100 parts by weight of the main agent, add 22.5 parts by weight of an isocyanate compound (Millionate MR-100, manufactured by Nippon Polyurethane Industry Co., Ltd.) under stirring, and stir for 1 minute. Thus, an adhesive composition was obtained. Using a Brookfield rotational viscometer, the viscosity immediately after mixing (0 minutes) at 23 ° C. and 10 rpm and the viscosity after 20 minutes in an atmosphere at 30 ° C. were measured, and the viscosity increase ratio was calculated from the values.

Adhesive strength test About the adhesive composition prepared using the acrylic resin emulsion of Example 1 and Example 2, the compression shear adhesive strength in a normal state and a boiling repetition condition was evaluated based on JISK6806.

In each example, the thixotropy of the main agent was low, and the viscosity increase after mixing with the curing agent was also low. Moreover, it has confirmed that it had the outstanding adhesive performance. On the other hand, in each comparative example, there existed problems, such as the viscosity of a main ingredient being high, TI of the main ingredient exceeding 2, and the thickening after mixing with a hardening | curing agent being high, and workability was inferior.

Claims (4)

  It contains an acrylic resin emulsion (A) obtained by polymerizing a hydroxyl group-containing monomer and a monomer containing methoxypolyethylene glycol methacrylate, a hydroxyl group-containing aqueous polymer (B), and an isocyanate compound (C). An adhesive composition.   The adhesive composition according to claim 1, wherein the hydroxyl group-containing aqueous polymer (B) is polyvinyl alcohol.   The adhesive composition according to claim 1 or 2, further comprising a filler (D). The adhesive composition according to claim 3, wherein the filler (D) is calcium carbonate.