Adhesive composition

Abstract

To provide an adhesive composition that does not contain resorcinol or formalin and has excellent adhesive strength and pot life. [Solution] An adhesive composition comprising rubber latex, a crosslinking agent, and a polymerization initiator, wherein the polymerization initiator is contained in an amount of 0.1% by mass or more and less than 10% by mass of the total solid content of the adhesive composition.

Description

Technical Field

[0001] The present invention relates to an adhesive composition.

Background Art

[0002] Adhesives using latex have conventionally been used for bonding different base materials in a wide range of fields such as furniture, shoes, packaging materials, building materials, rubber products, etc. Among them, an RFL (resorcinol - formalin - latex) adhesive containing resorcinol, formaldehyde, and latex is widely known (Patent Document 1). However, both resorcinol and formaldehyde are highly toxic substances, and in recent years, there has been a growing demand to reduce their usage amounts from the viewpoints of environmental burden and harmfulness to health. Therefore, studies on adhesive compositions that do not use these raw materials have been proposed.

[0003] For example, in Patent Document 2, an adhesive composition for organic fiber cords containing a blocked isocyanate compound and / or an amine - based curing agent, an epoxy compound, and a rubber latex has been proposed. In Patent Document 3, an adhesive composition for organic fiber cords containing an epoxy compound, a compound containing an amide group and an amino group in one molecule, and a rubber latex has been proposed. In Patent Document 4, a rubber - resin interfacial adhesive composition containing a water - soluble carbodiimide, a thermally cross - linkable compound which is a blocked isocyanate compound or an epoxy compound, and a rubber latex has been proposed. In Patent Document 5, a reinforcing fiber having a surface - modified layer containing one or more nitrogen - containing functional groups and an adhesive layer containing a conjugated diene - based rubber has been proposed.

[0004] Although the adhesive compositions of the above patent documents do not contain resorcinol and thus have no concerns such as environmental burden, these adhesive compositions are insufficient in terms of the high adhesive strength required in recent years, and improvement thereof is demanded.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Special Publication No. 52-020490 [Patent Document 2] International Publication No. 2010 / 125992 [Patent Document 3] International Publication No. 2021 / 221075 [Patent Document 4] International Publication No. 2022 / 065206 [Patent Document 5] Japanese Patent Publication No. 2025-026645 [Overview of the project] [Problems that the invention aims to solve]

[0006] This invention has been made in view of these circumstances, and aims to provide an adhesive composition that does not contain resorcinol or formalin and has excellent adhesive strength and pot life. [Means for solving the problem]

[0007] As a result of diligent research to achieve the above objective, the inventors of the present invention have found that a composition containing rubber latex, a crosslinking agent, and a predetermined amount of polymerization initiator does not contain resorcinol and formalin, thus having low environmental impact and harm to the human body, and exhibiting excellent adhesive strength and pot life, thus completing the present invention.

[0008] In other words, the present invention is 1. Containing rubber latex, crosslinking agent, and polymerization initiator, The aforementioned polymerization initiator is contained in an amount of 0.1% by mass or more and less than 10% by mass of the total solid content of the adhesive composition. 2. One adhesive composition in which the crosslinking agent is at least one selected from a blocked isocyanate compound, an epoxy compound, a carbodiimide compound, an oxazoline compound, and a phenolic resin. 3. The crosslinking agent is one of two adhesive compositions containing a blocked isocyanate compound. 4. The polymerization initiator is an adhesive composition containing a thermal radical polymerization initiator. 5. The adhesive composition of 4 in which the thermal radical polymerization initiator is an azo polymerization initiator, 6. One adhesive composition that does not contain organic solvents, 7. Any adhesive composition from 1 to 6 for bonding organic fibers to rubber. To provide. [Effects of the Invention]

[0009] The adhesive composition of the present invention does not contain resorcinol and formalin, thus having a low environmental impact and low harm to the human body. Furthermore, because it is a composition containing rubber latex, a crosslinking agent, and a polymerization initiator, it has superior adhesive strength and pot life compared to conventionally known RF (resorcinol and formalin)-free adhesives. [Modes for carrying out the invention]

[0010] The present invention will be described in more detail below. The adhesive composition according to the present invention comprises rubber latex, a crosslinking agent, and a polymerization initiator, but does not contain resorcinol and formalin, and is characterized in that the polymerization initiator is contained in an amount of 0.1% by mass or more and less than 10% by mass of the total solid content of the adhesive composition.

[0011] (A) Rubber latex Rubber latex is a material obtained by dispersing fine particles of rubber components in water or the like. The concentration of rubber components in the rubber latex is preferably in the range of 10 to 60% by mass, and more preferably in the range of 20 to 50% by mass. The rubber components constituting the rubber latex can be appropriately selected from those conventionally known, such as natural rubber, styrene-butadiene copolymer rubber (SBR), styrene-butadiene-vinylpyridine copolymer rubber (VP), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), chlorosulfonated polyethylene (CSM), ethylene-propylene copolymer rubber (EPM), and ethylene-propylene-diene copolymer rubber (EPDM). These may be used individually or in combination of two or more.

[0012] Various commercially available rubber latex products can be used, and specific examples include PYRATEX, PYRATEX-LB, and PYRATEX-HM, which are VP latex products from Nippon A&L Co., Ltd.; SBL 2108, an SBR latex product from ENEOS Material Co., Ltd.; LX415M and LX432M, SBR latex products from Nippon Zeon Co., Ltd.; Showprene 842A, a CR latex product from Resonac Co., Ltd.; and Seporex CSM-N, a CSM latex product from Sumitomo Seika Co., Ltd., but are not limited to these.

[0013] In the adhesive composition of the present invention, the rubber latex content is preferably 15 to 90% by mass, more preferably 20 to 80% by mass, and even more preferably 20 to 70% by mass, as solid content (rubber component).

[0014] (B) Crosslinking agent The crosslinking agent contained in the adhesive composition of the present invention is a component that, for example, when used as an adhesive composition for rubber and fibers, has the function of improving adhesive strength by crosslinking with fibers. The crosslinking agent is not particularly limited, and examples thereof include blocked isocyanate compounds, epoxy compounds, carbodiimide compounds, oxazoline compounds, phenolic resins, etc. These may be used alone or in combination of two or more. However, from the viewpoint of improving the adhesive strength and pot life of the adhesive composition, the crosslinking agent preferably contains a blocked isocyanate compound, more preferably contains 50% by mass or more of the blocked isocyanate compound, and even more preferably contains only the blocked isocyanate compound.

[0015] (1) Blocked isocyanate compound The blocked isocyanate compound is an addition product of an aliphatic diisocyanate or an aromatic diisocyanate and a blocking agent. The addition reaction of the isocyanate and the blocking agent can be carried out by a known method.

[0016] Specific examples of the aliphatic diisocyanate include hexamethylene diisocyanate, 1,4-tetramethylene diisocyanate, 2-methylpentane-1,5-diisocyanate, dodecamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, etc. Specific examples of the aromatic diisocyanate include diphenylmethane diisocyanate such as methylene diphenyl 4,4'-diisocyanate (4,4'-diphenylmethane diisocyanate), 2,4'-diphenylmethane diisocyanate, 4,4'-diphenyl ether diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, 3,3'-dimethoxy-4,4'-biphenyl diisocyanate, 2,4,6-triisopropylbenzene-1,3-diyl diisocyanate, o-tolidine diisocyanate, naphthylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 3,3'-dimethyl-4,4'-diphenyl ether diisocyanate, 3,3'-dimethyl-4,4'-diphenyl ether diisocyanate, etc.

[0017] Specific examples of blocking agents include phenols such as phenol, thiophenol, chlorophenol, cresol, resorcinol, p-sec-butylphenol, p-tert-butylphenol, p-sec-amylphenol, p-octylphenol, and p-nonylphenol; secondary or tertiary alcohols such as isopropyl alcohol and tert-butyl alcohol; aromatic secondary amines such as diphenylamine and xylidine; phthalimides; lactams such as δ-valerolactam; caprolactams such as ε-caprolactam; active methylene compounds such as dialkyl malonates, acetylacetone, and alkyl acetoacetate; oximes such as acetoxime, 2-butanone oxime (methyl ethyl ketonexime), and cyclohexanone oxime; basic nitrogen compounds such as 3-hydroxypyridine; and acidic sodium sulfite.

[0018] The blocked isocyanate compound used in the adhesive composition of the present invention is preferably used in the form of an aqueous dispersion. Blocked isocyanate compounds in aqueous dispersion form are available commercially. Specific examples of commercially available products include Trixiene Aqua BI 120, BI 200, BI 201, BI 202, BI 220, and BI 522, which are aqueous aliphatic blocked isocyanate compounds manufactured by LANXESS, and BN-27, BN-69, and BN-77, which are aqueous aromatic blocked isocyanate compounds manufactured by Daiichi Kogyo Seiyaku Co., Ltd.

[0019] (2) Epoxy compounds The epoxy compound is preferably a polyfunctional epoxy compound. Specific examples include reaction products of polyhydric alcohols such as diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, glycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, and sorbitol polyglycidyl ether with epichlorohydrin; novolac-type epoxy resins such as phenol novolac-type epoxy resins and cresol novolac-type epoxy resins; and bisphenol A-type epoxy resins.

[0020] These epoxy compounds are available commercially. Specific examples of commercially available products include Denacol EX-612, 614, 614B, 313, 314, 421, 512, 521, 1610, 321, 321L, and 622, manufactured by Nagase ChemteX Corporation.

[0021] (3) Carbodiimide compounds Carbodiimide compounds are those that have one or more carbodiimide groups in a single molecule. The isocyanate compound used as a raw material for the carbodiimide compound is not particularly limited as long as it has two or more isocyanate groups in one molecule, and can be appropriately selected from various conventionally known diisocyanate compounds, etc. Specific examples include aliphatic isocyanates such as hexamethylene diisocyanate, 1,4-tetramethylene diisocyanate, 2-methylpentane-1,5-diisocyanate, dodecamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, and lysine diisocyanate; 1,3-bis(isocyanatomethyl)cyclohexane, 1,4-bis(isocyanatomethyl)cyclohexane, and 2,2-bis(4-isocyanatomethyl) Alicyclic diisocyanates such as cyclohexyl)propane, isophorone diisocyanate, norbornane diisocyanate, dicyclomethane diisocyanate (HMDI), hydrogenated tolylene diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated diphenylmethane diisocyanate, and hydrogenated tetramethylxylylene diisocyanate; 1,5-naphthalene diisocyanate, 2,2'-diphenylmethane diisocyanate, methylenediphenyl Diphenylmethane diisocyanates such as 4,4'-diisocyanate (4,4'-diphenylmethane diisocyanate), 2,4'-diphenylmethane diisocyanate, 4,4'-diphenyl ether diisocyanate, p-phenylenediisocyanate, m-phenylenediisocyanate, 3,3'-dimethoxy-4,4'-biphenyl diisocyanate, 2,4,6-triisopropylbenzene-1,3-diyl diisocyanate, o-tolidine diisocyanate, naphthylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diiso Examples include aromatic diisocyanates such as cyanates, 3,3'-dimethyl-4,4'-diphenyl ether diisocyanate, and 3,3'-dimethyl-4,4'-diphenyl ether diisocyanate; xylylene diisocyanates such as m-xylylene diisocyanate (m-xylylene diisocyanate); aromatic aliphatic diisocyanates such as tetramethylxylylene diisocyanate; and nurates, adducts, biurets, and end-capsulated compounds of these obtained by trimerization. These may be used individually or in combination of two or more.

[0022] Furthermore, in the production of carbodiimide compounds, it is also possible to control the degree of polymerization by encapsulating all or part of the remaining terminal isocyanates using a terminal-encapsulating compound having a functional group that can react with isocyanate groups. Examples of end-capturing compounds include compounds having one group selected from an amino group, an isocyanate group, an epoxy group, a carboxyl group, and a hydroxyl group. The end-capping compound may be either a hydrophobic or hydrophilic compound, but a hydrophilic compound is preferred.

[0023] Examples of compounds having one amino group include monoamines having hydrocarbon groups with 1 to 18 carbon atoms. Specific examples include methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, octylamine, dodecylamine, diethylamine, dipropylamine, dibutylamine, cyclohexylamine, adamantaneamine, allylamine, aniline, diphenylamine, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, 2,2-difluoroamine, fluorobenzylamine, trifluoroethylamine, [[4-(trifluoromethyl)cyclohexyl]methyl]amine, and derivatives thereof, which may be used individually or in combination of two or more. Furthermore, when encapsulated with a compound containing one amino group, the terminal isocyanate group forms a urea bond through a reaction with the amino group.

[0024] Examples of compounds having one isocyanate group include monoisocyanates having a hydrocarbon group with 1 to 18 carbon atoms. Specific examples include butyl isocyanate, pentyl isocyanate, hexyl isocyanate, octyl isocyanate, dodecyl isocyanate, cyclohexyl isocyanate, 1-adamantyl isocyanate, 3-isocyanate-propyltriethoxysilane, 2-isocyanatoethyl acrylate, benzyl isocyanate, 2-phenylethyl isocyanate, and derivatives thereof, which may be used individually or in combination of two or more. Furthermore, when a compound containing one isocyanate group is used for encapsulation, the terminal isocyanate group reacts with the isocyanate group of the terminal-encapsulating compound to form a carbodiimide bond (carbodiimide group).

[0025] Specific examples of compounds having one epoxy group include 1,2-epoxyheptane, 1,2-epoxyhexane, 1,2-epoxydecane, 1,2-epoxy-5-hexene, ethylglycidyl ether, 2-ethylhexylglycidyl ether, glycidyl lauryl ether, allylglycidyl ether, diethoxy(3-glycidyloxypropyl)methylsilane, 3-[2-(perfluorohexyl)ethoxy]-1,2-epoxypropane, and derivatives thereof. These may be used individually or in combination of two or more.

[0026] Specific examples of compounds having one carboxyl group include acetic acid, propionic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, cyclohexanecarboxylic acid, adamantaneic acid, phenylacetic acid, benzoic acid, undecenoic acid, and their derivatives. These can be used individually or in combination of two or more.

[0027] Specific examples of compounds having one hydroxyl group include cyclohexanol, oleyl alcohol, benzyl alcohol, dodecyl alcohol, octanol, hexanol, pentanol, butanol, propanol, ethanol, alkylene glycol monoethers such as ethylene glycol monomethyl ether, and alkylene glycol monoesters. These may be used individually or in combination of two or more.

[0028] The above carbodiimide compounds can be produced by various methods using the various diisocyanate compounds exemplified above as raw materials. Representative examples of production methods include the method of producing isocyanate-terminated carbodiimide compounds by a decarboxylation condensation reaction involving the decarbonation of diisocyanate compounds (e.g., U.S. Patent No. 2941956, Japanese Patent Publication No. 47-33279, J. Org. Chem, 28, 2069-2075 (1963), Chemical Review 1981, Vol. 81, No. 4, pp. 619-621). When end-capping is required, the carbodiimide compound can be reacted with a predetermined end-capping compound after synthesis, or simultaneously with its synthesis. In addition to diisocyanate compounds, compounds having three or more isocyanate groups can also be used as reaction raw materials.

[0029] Carbodiimide catalysts are typically used in the decarboxylation condensation reaction of diisocyanate compounds. Specific examples of carbodiimide catalysts include phosphone oxides such as 1-phenyl-2-phosphorene-1-oxide, 3-methyl-1-phenyl-2-phosphorene-1-oxide, 1-ethyl-2-phosphorene-1-oxide, 3-methyl-2-phosphorene-1-oxide, and their 3-phosphorene isomers. These may be used individually or in combination of two or more. The amount of carbodiimide catalyst used is not particularly limited, but 0.01 to 2.0 parts by mass per 100 parts by mass of the diisocyanate compound is preferred.

[0030] The above decarboxylation condensation reaction can be carried out without a solvent, but a solvent may also be used. Specific examples of usable solvents include alicyclic ethers such as tetrahydrofuran, 1,3-dioxane, and dioxolane; 1-(2-methoxy-2-methylethoxy)-2-propanol, diethylene glycol methyl ethyl ether, diethylene glycol diethyl ether, diethylene glycol dimethyl ether, dipropylene glycol methyl ethyl ether, dipropylene glycol diethyl ether, dipropylene glycol dimethyl ether, triethylene glycol methyl ethyl ether, triethylene glycol diethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol methyl ethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol Examples of aprotic water-soluble solvents include didimethyl ether, diethylene glycol monoethyl ether acetate, diethylene glycol monomethyl ether acetate, dipropylene glycol monoethyl ether acetate, dipropylene glycol monomethyl ether acetate, γ-butyrolactone, N-methylpyrrolidone, N-ethylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide; aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene; halogenated hydrocarbons such as chlorobenzene, dichlorobenzene, trichlorobenzene, perchloroene, trichloroethane, and dichloroethane; and cyclohexanone. These may be used individually or in combination of two or more.

[0031] The reaction temperature is not particularly limited, but is preferably 40 to 250°C, and more preferably 80 to 195°C. Furthermore, when the reaction is carried out in a solvent, it is preferably between 40°C and the boiling point of the solvent. The reaction time is preferably 0.5 to 80 hours, and more preferably 1 to 70 hours. While the reaction atmosphere is not particularly limited, an inert gas atmosphere such as nitrogen gas or a noble gas is preferred.

[0032] When performing end-capturing, if the end-capturing compound is a compound having one isocyanate group, for example, in the presence of a carbodiimide catalyst, the end-capturing compound and the diisocyanate compound can be stirred and mixed for about 10 to 70 hours at a temperature preferably of 40 to 200°C, more preferably of 80 to 195°C, to obtain an end-capturing carbodiimide compound. Furthermore, if the end-capped compound is not a compound having one isocyanate group, for example, the end-capped compound can be added to an isocyanate-terminated carbodiimide compound at a temperature of preferably 40 to 250°C, more preferably 80 to 195°C, and then stirred and mixed at approximately 80 to 200°C for about 0.5 to 5 hours to obtain a end-capped carbodiimide compound.

[0033] Furthermore, in the adhesive composition of the present invention, water-soluble salts of carbodiimide compounds, such as hydrochloride or sulfate salts (water-soluble carbodiimide compounds), can also be used as the carbodiimide compound. Specific examples include 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC); water-soluble salts of 1-cyclohexyl-3-(2-morpholinoethyl)carbodiimide such as 1-cyclohexyl-3-(2-morpholinoethyl)carbodiimidemetho-p-toluenesulfate; and triazine-based condensing agents such as 4-(4,6-dimethoxy-1,3,5-triazine-2-yl)-4-methylmorpholinium chloride (DMT-MM). Among these, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) is preferred.

[0034] These water-soluble carbodiimide compounds are available commercially. Specific examples of commercially available products include WSCD·HCl (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride) from Peptide Laboratories, Inc., 1-cyclohexyl-3-(2-morpholinoethyl)carbodiimidemetho-p-toluenesulfate and 4-(4,6-dimethoxy-1,3,5-triazine-2-yl)-4-methylmorpholinium chloride from Tokyo Chemical Industries, Ltd., and Carbodilite V-02, V-02-L2, SV-02, E-02, and E-05 from Nisshinbo Chemical Inc.

[0035] (4) Oxazoline compounds Examples of oxazoline compounds include acrylic polymers having oxazoline groups in their side chains, and acrylic / styrene copolymers having oxazoline groups in their side chains. Oxazoline compounds are available commercially. Specific examples of commercially available products include Epocross K-2010E, 2020E, 2035E, and WS-300, 500, and 700, all manufactured by Nippon Shokubai Co., Ltd.

[0036] (5) Phenolic resin As the phenolic resin, it can be appropriately selected from conventionally known novolac-type phenolic resins and resol-type phenolic resins.

[0037] In the adhesive composition of the present invention, the content of the crosslinking agent is not particularly limited, but in terms of improving the adhesive strength of the adhesive composition, it is preferably 10 to 100 parts by mass, more preferably 20 to 80 parts by mass, and even more preferably 30 to 70 parts by mass, as solid content per 100 parts by mass of rubber latex solid content.

[0038] (C) Polymerization initiator In the adhesive composition of the present invention, the polymerization initiator acts on the rubber component in the rubber latex to generate active species such as radicals and cations, thereby promoting crosslinking between the rubber component in the latex and the adherend, and improving adhesive strength. As the polymerization initiator, one can be appropriately selected from polymerization initiators commonly used in polymerization reactions of compounds having carbon-carbon unsaturated bonds. For example, azo compounds, organic and inorganic peroxides, and thermal cationic polymerization initiators can be used, but among these, thermal radical polymerization initiators are preferred, and azo-based thermal radical polymerization initiators are more preferred.

[0039] Specific examples of azo compounds (azo-based thermal radical polymerization initiators) include azobisisobutyronitrile, 2,2'-di(2-hydroxyethyl)azobisisobutyronitrile, 2,2'-azobis(2-methylpropionic acid)dimethyl, 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride, 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide], and 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine]tetrahydrate, which may be used alone or in combination of two or more. Among these, since latex contains water, water-soluble 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride, 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide], and 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine]tetrahydrate are preferred. These compounds are available commercially, and specific examples of commercially available products include VA-044 (2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride), 086 (2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide]), and 057 (2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine]tetrahydrate) manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

[0040] Specific examples of organic and inorganic peroxides include ketone peroxides (methyl ethyl ketone peroxide, cyclohexanone peroxide, etc.), diacyl peroxides (acetyl peroxide, benzoyl peroxide, etc.), hydroperoxides (hydrogen peroxide, tert-butyl hydroperoxide, cumene hydroperoxide, etc.), dialkyl peroxides (di-tert-butyl peroxide, dicumyl peroxide, dilauroyl peroxide, etc.), peroxyketals (dibutyl peroxycyclohexane, etc.), alkyl peresters (tert-butyl peroxyneodecanoate, tert-butyl peroxypivalate, tert-amyl peroxy2-ethylcyclohexanoate, etc.), and persulfates (potassium persulfate, sodium persulfate, ammonium persulfate, etc.). These may be used individually or in combination of two or more.

[0041] Specific examples of thermal cationic polymerization initiators include benzenesulfonic acid esters and alkylsulfonium salts, which may be used alone or in combination of two or more.

[0042] In the adhesive composition of the present invention, the polymerization initiator is contained in an amount of 0.1% by mass or more and less than 10% by mass of the total solid content of the adhesive composition, but from the viewpoint of balancing the adhesive strength and pot life of the composition, 0.1 to 7% by mass is preferred, 0.1 to 5% by mass is more preferred, and 0.1 to 3% by mass is even more preferred.

[0043] (D) Other ingredients The adhesive composition of the present invention may contain other components, as long as they do not impair the effects of the present invention. Specifically, depending on the intended use and application of the adhesive composition, it may contain, as necessary, organic solvents and various additives such as colorants, fillers, dispersants, plasticizers, thickeners, defoamers, surfactants, UV absorbers, antioxidants, pH adjusters, and lubricants.

[0044] As organic solvents, those soluble in water are preferred, such as alcohol solvents like methanol and ethanol; polyhydric alcohol solvents like diethylene glycol and glycerin; and ketone solvents like acetone. When organic solvents are used, the amount used is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less, and still more preferably 5% by mass or less, but the adhesive composition of the present invention is optimally a completely aqueous composition that does not contain organic solvents. Note that "does not contain organic solvents" means that it is substantially free of organic solvents, and for example, trace amounts on the order of ppm in the raw materials used are acceptable.

[0045] Specific examples of surfactants include anionic surfactants such as alkylbenzene sulfonates, alkyl sulfates, polyoxyethylene alkyl ether sulfates, and fatty acid salts; and nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, and polyoxyalkylene alkyl ethers.

[0046] Specific examples of thickeners include acrylic thickeners, urethane thickeners, polyether thickeners, water-soluble polymer thickeners, polyvinyl alcohol, cellulose derivatives, and inorganic thickeners such as clay minerals.

[0047] Specific examples of fillers include carbon black, silica, clay, talc, calcium carbonate, and alumina.

[0048] Specific examples of lubricants include stearic acid, waxes, silicone oils, polyethylene glycol, and fatty acid esters.

[0049] There are no particular restrictions on the method for producing the adhesive composition of the present invention; it can be prepared by mixing the above-mentioned components (A) to (C) and component (D), which may be used as needed, in any order.

[0050] The adhesive composition of the present invention, as described above, does not contain resorcinol and formalin, and therefore has a low environmental impact and is less harmful to the human body. Furthermore, it is a composition containing rubber latex, a crosslinking agent, and a polymerization initiator, and has superior adhesive strength compared to conventionally known RF (resorcinol and formalin) free adhesives. For this reason, it can be suitably used as a composition for bonding organic fibers, carbon fibers obtained by firing organic fibers, and especially organic fiber cords to rubber.

[0051] The types of organic fibers to which the adhesive composition of the present invention is applied are not particularly limited, but include polyester fibers, nylon fibers, aramid fibers, acrylic fibers, vinylon fibers, polyurethane fibers, and cellulose fibers. On the other hand, while there are no particular limitations on the rubber components, examples include natural rubber, polyisoprene rubber, polybutadiene rubber, styrene-butadiene copolymer rubber, nitrile rubber, chloroprene rubber, butyl rubber, and other conjugated diene synthetic rubbers, as well as ethylene-propylene copolymer rubber, ethylene-propylene-diene copolymer rubber, and polysiloxane rubber. These rubber components may be used individually or in combination of two or more. [Examples]

[0052] The present invention will be described in more detail below with reference to manufacturing examples, embodiments, and comparative examples, but the present invention is not limited to the embodiments described below.

[0053] Details of the compounds used are as follows: (A) Rubber latex (A)-1 PYRATEX (VP Latex, manufactured by Nippon A&L Co., Ltd., solids content 41% by mass) (A)-2 PYRATEX-LB (VP Latex, manufactured by Nippon A&L Co., Ltd., solids content 38% by mass) (A)-3 PYRATEX-HM (VP Latex, manufactured by Nippon A&L Co., Ltd., solids content 41% by mass) (A)-4 SBL 2108 (SBR latex, ENEOS Material Co., Ltd., solids content 40% by mass) (A)-5 LX415M (SBR latex, manufactured by Nippon Zeon Co., Ltd., solids content 43% by mass) (A)-6 LX432M (SBR latex, manufactured by Nippon Zeon Co., Ltd., solids content 41% by mass) (A)-7 Showprene 842A (CR latex, manufactured by Resonac Co., Ltd., solids content 50% by mass) (A)-8 Ceporex CSM-N (CSM latex, manufactured by Sumitomo Seika Co., Ltd., solids content 40% by mass) (B) Crosslinking agent (B)-1 Production Example 1: Aromatic Blocked Isocyanate Compound (B)-2 Trixiene Aqua BI 120 (Aliphatic blocked isocyanate adduct, manufactured by LANXESS, solids content 40% by mass) (B)-3 Denacol EX-614B (epoxy compound, Nagase ChemteX Corporation) (B)-4 WSCD·HCl (Carbodiimide compound, Peptide Research Institute Co., Ltd.) (C) Polymerization initiator (C)-1 VA-044 (Thermal radical polymerization initiator, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) (C)-2 VA-086 (Thermal radical polymerization initiator, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) (C)-3 VA-057 (Thermal radical polymerization initiator, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) (Other ingredients) Pascol NJ-1 (urethane compound, manufactured by T&K TOKA Corporation, solid content 40% by mass) Tomid TXS-53-C (amidoamine compound, manufactured by Meisei Chemical Industry Co., Ltd., solid content 30% by mass) Resorcinol (manufactured by Tokyo Chemical Industry Co., Ltd.) Formaldehyde solution (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0054] [1] Synthesis of aromatic block isocyanate compounds [Manufacturing Example 1] In a separable flask equipped with a stirrer and reflux condenser, 100 parts by mass of 4,4'-diphenylmethane diisocyanate and 170 parts by mass of methyl ethyl ketone were charged, and stirring was started. After raising the temperature to 50°C, 70 parts by mass of butanone oxime were added, and IR measurement was performed to obtain the peak wavelength of the isocyanate group, which is 2200 cm⁻¹. -1 The mixture was stirred until it disappeared, and a blocked isocyanate compound was obtained. 25 parts by mass of Hythenol NF-13 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as an anionic surfactant was mixed to form a homogenized solution. 230 parts by mass of ion-exchanged water were gradually added while stirring, and the mixture was emulsified using a homogenizer. Subsequently, methyl ethyl ketone was removed under reduced pressure, and deionized water was added to obtain an aqueous dispersion of the isocyanate compound with a solid content of 40% by mass.

[0055] [2] Preparation of adhesive composition [Examples 1-34, Comparative Examples 1-15] Various rubber latexes, blocked isocyanate compounds as crosslinking agents, polymerization initiators, and other components were mixed in the predetermined proportions shown in Tables 1 to 4. Water, or water and methanol (Examples 32 to 34) as an organic solvent, was added to the mixture so that the solid content concentration of the composition was 18% by mass, and the mixture was then thoroughly stirred to obtain an adhesive composition.

[0056] [Comparative Example 16] 588.29 parts by mass of water, 16.61 parts by mass of resorcinol, 20.80 parts by mass of formaldehyde solution (37% by mass), and 3.79 parts by mass of caustic soda (10% by mass) were mixed and aged at room temperature for 7 hours to obtain a matured liquid containing resorcinol and formaldehyde. Next, 370.51 parts by mass of vinylpyridine-styrene-butadiene copolymer rubber latex was added to 629.49 parts by mass of the matured liquid and aged at room temperature for 16 hours to obtain an adhesive composition (RFL composition).

[0057] The adhesive compositions obtained in each of the above examples and comparative examples were evaluated for their adhesive strength and pot life using the following method. The results are shown in Tables 1 to 3. [Adhesive strength] A polyethylene terephthalate cord was used as the organic fiber cord. The cord was immersed in an adhesive composition until the concentration of the adhesive composition impregnating the cord was 10% of the mass of the organic fiber. Then, it was dried at 80°C for 10 minutes and heat-treated at 180°C for 10 minutes to obtain a cord coated with the adhesive composition. The organic fiber cords for rubber reinforcement obtained as described above were embedded in unvulcanized SBR rubber, and after vulcanization, a T-type peel was performed and the adhesive strength was measured. [Pot Life] The compositions obtained in each example and comparative example were left to stand at room temperature, and the time until aggregates formed was evaluated according to the following criteria. A period of 7 days or more was considered acceptable. ◎: No change for more than 30 days ○: 14 days or more but less than 30 days △: 7 days or more but less than 14 days ×: Less than 7 days ××: Within 1 day

[0058] [Table 1]

[0059] [Table 2]

[0060] [Table 3]

[0061] [Table 4]

[0062] As shown in Tables 1-4, the adhesive compositions of the present invention prepared in each example exhibit superior adhesion to organic fiber cords and better pot life compared to the adhesive compositions prepared in the comparative examples (conventional RF-free compositions and RFL compositions).

Claims

1. Contains rubber latex, crosslinking agent, and polymerization initiator. The rubber latex comprises styrene-butadiene-vinylpyridine copolymer rubber, The crosslinking agent is at least one selected from blocked isocyanate compounds, epoxy compounds, carbodiimide compounds, oxazoline compounds, and phenolic resins, and includes a blocked isocyanate compound. An adhesive composition wherein the polymerization initiator comprises an azo polymerization initiator and is present in an amount of 0.1% by mass or more and less than 10% by mass of the total solid content of the adhesive composition.

2. The adhesive composition according to claim 1, wherein the polymerization initiator is contained in an amount of 0.1 to 7% by mass of the total solid content of the adhesive composition.

3. The adhesive composition according to claim 1, wherein the crosslinking agent comprises 50% by mass or more of a blocked isocyanate compound.

4. The adhesive composition according to claim 3, wherein the crosslinking agent comprises only a blocked isocyanate compound.

5. The adhesive composition according to claim 1, wherein the azo polymerization initiator is a water-soluble azo polymerization initiator.

6. The adhesive composition according to claim 1, which does not contain an organic solvent.

7. An adhesive composition according to any one of claims 1 to 6, for bonding organic fibers to rubber.

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