Aqueous pressure-sensitive adhesive and coated product thereof

Abstract

To provide an aqueous pressure-sensitive adhesive which, when used to bond a foam substrate to an adherend, is good in substrate adhesion and initial tack, is excellent in holding power, and has such a sufficient pressure-sensitive adhesive force as to cause no practical trouble.SOLUTION: The aqueous pressure-sensitive adhesive according to claim 1, which is an aqueous pressure-sensitive adhesive for bonding a foam substrate to an adherend, comprising a copolymer containing at least 2-octyl (meth) acrylate and a monomer (A) having an acid group as monomers constituting the copolymer, wherein the content of 2-octyl (meth) acrylate in the monomers is preferably 40% by mass or more and 99% by mass or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a water-based pressure-sensitive adhesive and a coated product thereof. [Background technology]

[0002] Conventionally, two types of adhesives have been mainly used to form the adhesive layer of adhesive coatings for foam substrates: organic solvent-based adhesives and emulsion-based adhesives. However, organic solvent-based adhesives require the organic solvent to be evaporated during the drying process during coating, which poses problems from the perspective of environmental protection. On the other hand, emulsion-based adhesives are superior to organic solvent-based adhesives in terms of environmental, safety, hygiene, and other aspects, and therefore, in recent years, emulsion-based adhesives have been increasingly used as adhesives to form the adhesive layer of adhesive sheets.

[0003] For example, Patent Document 1 discloses an aqueous emulsion-type pressure-sensitive adhesive for foams, which contains an acrylic copolymer containing a hydrophobic acrylic acid ester and / or methacrylic acid ester and an unsaturated carboxylic acid as essential copolymerization components, a petroleum resin-based tackifier resin, and an elastomer.

[0004] Patent Document 2 discloses an aqueous emulsion-type pressure-sensitive adhesive for foams, which contains 100 parts by weight of an acrylic copolymer emulsion obtained by emulsion polymerization of 70 to 99.9% by weight of a (meth)acrylic acid ester and 30 to 0.1% by weight of a functional group monomer, and which has an average particle size of 75 to 250 nm and a glass transition point of -70°C to -10°C, and 1 to 50 parts by weight of a rosin-based tackifying resin with a softening temperature of 140 to 200°C.

[0005] Patent Document 3 discloses an aqueous dispersion of a composite resin composition for pressure-sensitive adhesives, which is obtained by polymerizing a mixture containing 0.5 to 50 parts by weight of a solid resin (d) having a softening point above 85°C, relative to 100 parts by weight of a total of monomers containing 70 to 99.8% by weight of (a) an alkyl (meth)acrylate ester having 1 to 14 carbon atoms in the alkyl chain, 0.1 to 15% by weight of (b) a hydroxyalkyl (meth)acrylate having 1 to 8 carbon atoms in the alkyl chain, and 0.1 to 15% by weight of a copolymerizable monomer (c) other than (a) and (b), in an aqueous medium containing a surfactant (e) as an essential component. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 7-179835 [Patent Document 2] Japanese Patent Application Publication No. 11-131034 [Patent Document 3] Japanese Patent Application Laid-Open No. 2008-81691 Summary of the Invention [Problem to be solved by the invention]

[0007] However, while the aqueous pressure-sensitive adhesives disclosed in Patent Documents 1 to 3 have high cohesive strength, such as holding power and heat resistance, when adhering a foam substrate to an adherend, their adhesive strength is not sufficient for actual use conditions. Cohesive strength and substrate adhesion generally have a trade-off relationship. That is, attempts to improve practically required adhesive strength, initial tack, and substrate adhesion result in a deterioration in cohesive strength, such as holding power. Conversely, attempts to improve cohesive strength, such as holding power, result in a decrease in adhesive strength, initial tack, and substrate adhesion. Therefore, the problem to be solved by the present invention is to provide an aqueous pressure-sensitive adhesive that, when adhering a foam substrate to an adherend, has good substrate adhesion and initial tack, excellent holding power, and sufficient adhesive strength to prevent practical problems. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to solve the above problems and have arrived at the present invention. That is, the present invention is an aqueous adhesive for adhering a foam substrate to an adherend, which contains a copolymer containing at least 2-octyl (meth)acrylate and a monomer (A) having an acid group as monomers constituting the copolymer.

[0009] The present invention also relates to the aqueous pressure-sensitive adhesive, wherein the content of 2-octyl(meth)acrylate in the monomer is 40% by mass or more and 99% by mass or less.

[0010] The present invention also relates to the aqueous pressure-sensitive adhesive, wherein the content of the acid group-containing monomer (A) in the monomers is 1.0% by mass or more and 10% by mass or less.

[0011] In addition, in the present invention, the particle size at which the cumulative frequency from the small particle size side in the volume-based cumulative particle size distribution is 50% is defined as D 50 When the D of the copolymer particles in the aqueous pressure-sensitive adhesive is 50 is the above aqueous pressure-sensitive adhesive, wherein the average particle size is 100 nm or more and 900 nm or less.

[0012] The present invention also relates to the aqueous pressure-sensitive adhesive, further comprising 1.0 part by mass or more and 20 parts by mass or less of a tackifier resin per 100 parts by mass of the copolymer.

[0013] The present invention also relates to the aqueous pressure-sensitive adhesive, wherein the gel fraction is 20% by mass or more and 60% by mass or less.

[0014] The present invention also relates to a coated article in which the above-mentioned aqueous pressure-sensitive adhesive is coated on a foam substrate. [Effects of the Invention]

[0015] The present invention makes it possible to provide an aqueous pressure-sensitive adhesive that, when adhering a foam substrate to an adherend, has good substrate adhesion and initial tack, excellent holding power, and sufficient adhesive strength to the extent that it does not cause any practical problems. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention will be described in detail below. In this specification, "(meth)acrylate" refers to either acrylate or methacrylate, and "(meth)acrylic" and the like are also used in this specification. In this specification, a numerical range specified using "to" includes the numerical values ​​before and after "to" as the lower and upper limit values. In addition, D 50 This means the particle size (median size) at which the cumulative frequency from the small particle size side in the volume-based cumulative particle size distribution is 50%.

[0017] <Water-based adhesive> The aqueous pressure-sensitive adhesive of the present invention is an aqueous pressure-sensitive adhesive for adhering a foam substrate to an adherend, and contains a copolymer containing at least 2-octyl(meth)acrylate and a monomer (A) having an acid group as constituent monomers of the copolymer. First, the copolymer contained in the aqueous pressure-sensitive adhesive of the present invention will be described.

[0018] <2-octyl (meth)acrylate> The content of 2-octyl (meth)acrylate in the monomers constituting the copolymer is preferably 40 to 99 mass %, and particularly preferably 70 to 95 mass %, based on 100 mass % of the monomers. A content in the range of 40 to 99 mass % provides an appropriate cohesive strength, and a good balance between holding power and substrate adhesion is achieved.

[0019] <Monomer (A) Having an Acid Group> Examples of the monomer (A) having an acid group, which is one of the monomers constituting the copolymer, include acrylic acid, methacrylic acid, itaconic acid, maleic acid, β-carboxyethyl acrylate, etc. These may be used alone or in combination of two or more.

[0020] The content of the monomer (A) having an acid group is preferably 1 to 10 mass %, more preferably 2 to 5 mass %, based on 100 mass % of the monomers constituting the copolymer. When the content is in the range of 1 to 10 mass %, an appropriate cohesive force is obtained, and the holding power tends to be good.

[0021] The monomers constituting the copolymer may contain other monomers in addition to the above-mentioned 2-octyl(meth)acrylate and the acid group-containing monomer (A). The other monomers are not particularly limited, but include alkyl(meth)acrylates, glycidyl group-containing (meth)acrylates, hydroxyl group-containing (meth)acrylates, amino group-containing (meth)acrylates, cyano group-containing monomers, carboxylic acid amide group-containing monomers, aromatic ring-containing monomers, heterocyclic vinyl compounds, and polyfunctional group-containing vinyl monomers.

[0022] Examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, (meth)acrylate, (meth)acrylate, (meth)acrylate, 2-ethylhexyl (meth)acrylate, etc. Examples of glycidyl group-containing (meth)acrylates include glycidyl (meth)acrylate, etc. Examples of hydroxyl group-containing (meth)acrylates include 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate, etc. Examples of amino group-containing (meth)acrylates include N,N-dimethylaminoethyl (meth)acrylate and N,N-diethylaminoethyl (meth)acrylate, etc. Examples of cyano group-containing monomers include (meth)acrylonitrile, etc. Examples of carboxylic acid amide group-containing monomers include (meth)acrylamide, etc. Examples of aromatic ring-containing monomers include styrene, α-methylstyrene, benzyl methacrylate, etc. Examples of heterocyclic vinyl compounds include vinylpyrrolidone, etc. Examples of polyfunctional vinyl monomers include diallyl phthalate, etc. Other monomers may be used alone or in combination of two or more.

[0023] As the other monomer, alkyl(meth)acrylate is preferred, alkyl(meth)acrylate having an alkyl group with 1 to 18 carbon atoms is more preferred, and alkyl(meth)acrylate having an alkyl group with 4 to 8 carbon atoms is even more preferred.

[0024] <Method for producing copolymer> The copolymer is obtained by polymerizing a monomer mixture containing 2-octyl (meth)acrylate and a monomer (A) having an acid group, and optionally other monomers. Examples of the polymerization method include known polymerization methods such as solution polymerization and emulsion polymerization. Among these, emulsion polymerization is preferred, and the D of the copolymer particles can be controlled by appropriately adjusting the internal temperature, dropping rate, reaction time, etc. during emulsion polymerization. 50 In particular, the D of the copolymer particles can be controlled. 50 From the viewpoint of easy control of the temperature, it is preferable to produce the polyimide by emulsion polymerization in the presence of an emulsifier.

[0025] The emulsion polymerization is preferably a method of preparing an emulsion of the monomers and then synthesizing them (a so-called pre-emulsion method). The emulsion polymerization can be carried out by a known method, such as a method of charging the entire amount of the pre-emulsion into the emulsion polymerization site and carrying out the reaction, or a method of charging a part of the pre-emulsion into the emulsion polymerization site and adding the remaining amount of the pre-emulsion in portions or dropwise after the start of the reaction.

[0026] <Emulsifier> Examples of emulsifiers used in emulsion polymerization include anionic emulsifiers, nonionic emulsifiers, etc. The emulsifier may be a reactive emulsifier having a radically polymerizable functional group, or a non-reactive emulsifier having no radically polymerizable functional group, or both may be used in combination.

[0027] Among reactive emulsifiers, reactive anionic emulsifiers are anionic emulsifiers having one or more radically polymerizable unsaturated double bonds in the molecule. Examples of reactive anionic emulsifiers include polyoxyalkylene alkyl ether sulfate emulsifiers, sulfosuccinate emulsifiers, alkylphenol ether emulsifiers, etc. Examples of reactive nonionic emulsifiers include polyoxyethylene alkyl ethers.

[0028] Examples of non-reactive anionic emulsifiers include polyoxyethylene polycyclic phenyl ether sulfates, higher fatty acid salts such as sodium stearate, alkylarylsulfonates such as sodium dodecylbenzenesulfonate, alkyl sulfates such as sodium lauryl sulfate, polyoxyethylene alkyl ether sulfates such as sodium polyoxyethylene lauryl ether sulfate, and polyoxyethylene alkylaryl ether sulfates such as sodium polyoxyethylene nonylphenyl ether sulfate.

[0029] Examples of non-reactive nonionic emulsifiers include polyoxyethylene alkyl phenyl ethers such as polyoxyethylene nonylphenyl ether and polyoxyethylene octylphenyl ether; polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether, polyoxyethylene stearyl ether and polyoxyethylene oleyl ether; polyoxypolycyclic phenyl ethers such as polyoxyethylene distyrenated phenyl ether; and polyoxyethylene sorbitan fatty acid esters.

[0030] The emulsifier is preferably used in an amount of 0.5 to 3 parts by mass per 100 parts by mass of the monomer (a) mixture, as this range improves polymerization stability.

[0031] <Polymerization initiator> The polymerization initiator used in the emulsion polymerization is not particularly limited, and may be appropriately selected from water-soluble polymerization initiators and oil-soluble polymerization initiators.

[0032] Examples of the water-soluble polymerization initiator include potassium persulfate, sodium persulfate, ammonium persulfate, hydrogen peroxide, and 4,4'-azobis-4-cyanovalerinium (amine) salt.

[0033] Examples of oil-soluble polymerization initiators include alkyl peroxides, t-butyl hydroperoxide, cumene hydroperoxide, p-methane hydroperoxide, lauroyl peroxide, 3,5,5-trimethylhexanoyl peroxide, octanoyl peroxide, t-butylcumyl peroxide, benzoyl peroxide, dichlorobenzoyl peroxide, dicumyl peroxide, di-t-butyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 3,3,5-trimethylcyclohexanone peroxide, methylcyclohexanone peroxide, di-isobutyl peroxydicarbonate, and di-2-ethylhexyl peroxide. dicarbonate, organic peroxides such as t-butylperoxyisobutyrate, and azo compounds such as 2,2'-azobisisobutyronitrile, dimethyl-2,2'-azobisisobutyrate, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2-methylamidoxime) dihydrochloride, 2,2'-azobis(2-methylbutanamidoxime) dihydrochloride tetrahydrate, 2,2'-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]-propionamide}, and 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)-propionamide].

[0034] Redox initiators, which use a combination of an oxidizing agent and a reducing agent, are also preferred as polymerization initiators. Examples of the oxidizing agent include ammonium persulfate, potassium persulfate, sodium persulfate, hydrogen peroxide, t-butyl hydroperoxide, and benzoyl peroxide. Examples of the reducing agent include sodium sulfite, acidic sodium sulfite, Rongalite, and ascorbic acid.

[0035] <Buffering agent> During emulsion polymerization, a buffer can be used to adjust the pH as needed. The buffer is not particularly limited as long as it has a pH buffering effect on the reaction solution of emulsion polymerization. Examples of the buffer include sodium bicarbonate, potassium bicarbonate, monosodium phosphate, monopotassium phosphate, disodium phosphate, trisodium phosphate, sodium acetate, ammonium acetate, sodium formate, ammonium formate, and trisodium citrate.

[0036] <Chain transfer agent> During emulsion polymerization, the molecular weight of the copolymer can be appropriately adjusted using a chain transfer agent, such as a mercaptan compound, a thioglycol compound, or a thiol compound such as β-mercaptopropionic acid.

[0037] <D of copolymer particles 50 > D of copolymer particles in water-based pressure sensitive adhesives 50 The particle diameter is preferably 100 to 900 nm, and more preferably 300 to 600 nm. When the particle diameter is 100 to 900 nm, the film-forming property of the coating film is good, and the cohesive force due to the film formation is not too strong, so that both the holding power and the tackiness can be achieved. 50 The particle size can be measured using a light scattering particle size analyzer such as the Microtrac MT3000II (product name) manufactured by Nikkiso Co., Ltd. The measurement is carried out by diluting with water, and the measured concentration is adjusted so that it falls within the range of the optimum concentration gauge displayed on the screen.

[0038] <Tackifying resin> The aqueous pressure-sensitive adhesive of the present invention may contain a tackifying resin. By including a tackifying resin, sufficient adhesion to polyolefins can be ensured while also achieving processability. Examples of tackifying resins include rosin-based resins such as rosin esters, polymerized rosins, hydrogenated rosins, maleic acid-modified rosins, fumaric acid-modified rosins, and rosin phenolic resins; terpene-based resins such as α-pinene resins, β-pinene resins, dipentene resins, aromatic-modified terpene resins, hydrogenated terpene resins, terpene phenolic resins, acid-modified terpene resins, and styrenated terpene resins; petroleum-based hydrocarbon resins such as C5 aliphatic hydrocarbon resins, C9 aromatic hydrocarbon resins, hydrogenated C9 hydrocarbon resins, C5-C9 copolymer resins, and dicyclopentadiene monohydric resins; and coumarone-indene resins, styrene-based resins, alkylphenol resins, and xylene resins. Among these, rosin-based resins and terpene-based resins are preferred from the standpoint of ease of preparing aqueous dispersions and adhesive strength. The content of the tackifier resin is preferably 1.0 to 20 parts by mass, and more preferably 5 to 15 parts by mass, relative to 100 parts by mass of the copolymer. This content allows for both holding power and tackiness.

[0039] <Gel fraction> The gel fraction of the aqueous pressure-sensitive adhesive is preferably 20 to 60% by mass, more preferably 30 to 50% by mass. A gel fraction of 20 to 60% by mass allows for both adequate cohesive strength and wettability, thereby achieving both holding power and tackiness. The method for measuring the gel fraction will be described in detail in the Examples.

[0040] The aqueous pressure-sensitive adhesive of the present invention may contain, as necessary, various additives used in general aqueous pressure-sensitive adhesives, such as defoamers, wetting agents, coloring pigments, thickeners, plasticizers, antioxidants, ultraviolet absorbers, preservatives, and curing agents.

[0041] The curing agent is added later to the aqueous pressure-sensitive adhesive to adjust the cohesive strength, and examples thereof include metal crosslinking agents such as titanium chelate compounds, aluminum chelate compounds, zirconium chelate compounds, and zinc oxide, and organic crosslinking agents such as aziridine compounds, epoxy compounds, isocyanate compounds, carbodiimide compounds, and hydrazide compounds.

[0042] The aqueous pressure-sensitive adhesive of the present invention preferably has an adhesive strength to a polypropylene plate of 20 N / 25 mm or more, which can prevent the pressure-sensitive adhesive sheet from falling off during general use.

[0043] <Coated materials> The coated article of the present invention is obtained by coating a foam substrate with the aqueous pressure-sensitive adhesive of the present invention. One example of a method for producing the coated article of the present invention is to coat a release sheet with the aqueous pressure-sensitive adhesive of the present invention, dry it, and then laminate it to a foam substrate. Alternatively, the coated article of the present invention can be produced by directly coating the foam substrate with the aqueous pressure-sensitive adhesive, and then, if necessary, drying it and then laminating it to a release sheet.

[0044] <Foam base material> The foam substrate is not particularly limited and any desired one can be used, including, for example, polyurethane foams such as polyether-based urethane foam and polyester-based urethane foam, polystyrene foam, ABS resin foam, polyethylene foam, polypropylene foam, ethylene propylene diene rubber (EPDM) foam, chloroprene foam, vinyl chloride resin foam, phenolic resin foam, acrylic resin foam, natural rubber latex foam, and styrene butadiene rubber (SBR) foam.

[0045] <Removable sheet> The release sheet may be a paper or plastic film that has been treated with a release agent such as silicone.

[0046] The aqueous pressure-sensitive adhesive can be applied to a foam substrate or a release sheet using a known coating device, such as a roll coater such as a comma coater, blade coater, or gravure coater, a slot die coater, a lip coater, or a curtain coater. The thickness of the pressure-sensitive adhesive layer obtained after coating is preferably within the range of 0.1 to 200 μm.

[0047] The coated article of the present invention may be configured with a plurality of pressure-sensitive adhesive layers, in which case a core layer or the like may be provided.

[0048] The coated product of the present invention can be widely used as a fixing tape for industrial and domestic use. [Example]

[0049] The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples. The numerical values ​​of materials other than water during polymerization and blending are non-volatile content equivalents. In the examples, "parts" means "parts by mass" and "%" means "mass %."

[0050] [Example 1] 38.0 parts of 2-octyl acrylate, 29.0 parts of 2-ethylhexyl acrylate, 29.5 parts of butyl acrylate, 1.5 parts of acrylic acid, and 2.0 parts of methacrylic acid were mixed and dissolved in a glass container as monomers, along with 0.06 parts of octyl thioglycolate as a chain transfer agent. Furthermore, 1.0 parts of "Aqualon KH-10" (polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfate ester ammonium salt, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as a reactive anionic emulsifier and 28.8 parts of water were added to the glass container and stirred to obtain an emulsion. This emulsion was then placed in a dropping funnel. Separately, 50.5 parts of water and 1.0 part of the emulsion were charged into a four-neck flask equipped with a stirrer, condenser, thermometer, and the dropping funnel. The flask was filled with nitrogen gas and heated with stirring until the temperature inside the flask reached 78°C. Next, 3.0 parts of a 10% aqueous solution of ammonium persulfate was added to the flask as a polymerization initiator. After 10 minutes, the remaining emulsion was added dropwise from the dropping funnel. While maintaining the temperature inside the flask at 78°C, the emulsion was added dropwise over 180 minutes, and stirring was continued for another hour. Subsequently, 1.0 part of a 10% aqueous solution of t-butyl hydroperoxide and 1.0 part of a 10% aqueous solution of sodium ascorbate were added to the flask, and stirring was continued for another hour. The mixture was then cooled to 30°C, neutralized with 25% aqueous ammonia, and water was added to obtain an aqueous dispersion containing the copolymer at pH 7. To 100 parts of the obtained aqueous dispersion (based on non-volatile content), 0.05 parts of Levanax BX-150 (manufactured by Shoei Chemical Co., Ltd.) as a preservative, 0.5 parts of SN Defomer 364 (manufactured by San Nopco Co., Ltd.) as a defoaming agent, and 10.0 parts of a tackifying resin (Superester E-788, manufactured by Arakawa Chemical Industries, Ltd., rosin ester) were added, and the mixture was then mixed with a thickener and aqueous ammonia to obtain a non-volatile content of 49.6%, pH of 7.5, viscosity of 5000 mPa·s (BL type viscometer), and D 50 The obtained aqueous pressure-sensitive adhesive had a particle diameter of 499 nm and a gel fraction of 43%. 50 The gel fraction of the aqueous pressure-sensitive adhesive was determined by the following method.

[0051] <D of copolymer particles 50 > D of copolymer particles contained in water-based adhesive 50 The particle size was measured using a light scattering particle size measuring device "Microtrac MT3000II" (trade name), manufactured by Nikkiso Co., Ltd. For the measurement, the aqueous pressure sensitive adhesive was diluted 100 times with water.

[0052] <Gel fraction measurement> The resulting aqueous pressure-sensitive adhesive was applied to a polyethylene terephthalate (PET) film (50 μm thick) to a dry film thickness of approximately 100 μm, and then dried at 23°C for 7 days to form a coating film. The mass of a 200-mesh wire mesh was then measured (referred to as M). The coated film was then cut into 5 cm x 5 cm test pieces, which were then attached to the 200-mesh wire mesh. The mass of the test pieces was then measured (referred to as A). The 200-mesh mesh specified in JIS G-3555 was used for the measurements. The test pieces were left in 50 mL of ethyl acetate at 50°C for 1 day, then removed and dried at 100°C for 20 minutes, and then their mass was measured (referred to as T). The polyethylene terephthalate (PET) film was then removed from the test pieces, and the pressure-sensitive adhesive layer was removed using ethyl acetate. The mass of the PET film was then measured (referred to as K). The resulting values ​​were substituted into the following formula (1) to determine the gel fraction. Equation (1): (TMK)×100 / (AMK)

[0053] [Examples 2 to 42, Comparative Examples 1 to 3] Aqueous pressure-sensitive adhesives (Examples 2 to 42, Comparative Examples 1 to 3) were produced in the same manner as in Example 1, except that the composition of the monomer mixture was changed as shown in Tables 1 and 2. In addition, the D 50 The gel fraction of the water-based adhesive was adjusted appropriately by adjusting the amount of chain transfer agent added and the initial amount of emulsion added to the flask. By increasing the amount of chain transfer agent added, the gel fraction was lowered, and by decreasing the amount of chain transfer agent, the gel fraction was increased. In addition, by increasing the initial amount of emulsion added to the flask, the gel fraction of the water-based adhesive was adjusted appropriately. 50 is small, and by reducing the initial division amount, D 50 The results are shown in Table 1.

[0054] The abbreviations in Tables 1 and 2 are as follows: 2-OA: 2-octyl acrylate 2-OMA: 2-octyl methacrylate <Other monomers> 2EHA: 2-ethylhexyl acrylate BA: butyl acrylate MMA: Methyl methacrylate Vac: Vinyl acetate PEGDMA: Polyethylene glycol dimethacrylate HEMA: 2-hydroxyethyl methacrylate NVP: N-vinylpyrrolidone PEGMA: polyethylene oxide methacrylate (NK Ester M90G, manufactured by Shin-Nakamura Chemical Co., Ltd.) Nass: Sodium styrene sulfonate <Monomer (A) Having an Acid Group> AA: acrylic acid MAA: methacrylic acid

[0055] [Table 1]

[0056] [Table 1]

[0057] [Table 1]

[0058] [Table 2]

[0059] [Preparation of coated material] The aqueous pressure-sensitive adhesives obtained in the Examples and Comparative Examples were coated onto a commercially available release sheet using a doctor blade to a dry thickness of 50 μm, and then dried in a drying oven at 105°C for 2 minutes to form a pressure-sensitive adhesive layer. Next, a polyether-based urethane foam (ECS foam manufactured by Inoac Corporation, thickness: 10 mm), a polyester-based urethane foam (Moltopren manufactured by Inoac Corporation, thickness: 10 mm), or an EPDM foam (OP foam manufactured by Sanwa Kako Co., Ltd., thickness: 10 mm) was laminated to the pressure-sensitive adhesive layer as a foam substrate to produce each coated product.

[0060] <Adhesive strength> The coated product was cut into a 100mm long x 25mm wide sample at 23°C and 50% RH. The release sheet was then peeled off from the sample, and the sample was attached to a polypropylene plate (manufactured by Nippon Test Panel Co., Ltd., 2mm thick, hereinafter referred to as PP plate) and pressed against the plate using a 2kg roll. After pressing, the sample was left in a 23°C atmosphere for 24 hours, after which its adhesive strength was measured. The adhesive strength was measured using an RTG-1210 tester manufactured by A&G Company, at a peel speed of 300mm / min and a peel angle of 180°.

[0061] <Adhesion to substrate> The release sheet of the sample was peeled off, and the exposed adhesive layer was rubbed with a finger. The state of peeling from the substrate was visually observed and evaluated according to the following criteria. ◎: No peeling observed even after rubbing 10 times. Excellent Good: Peeling was observed after rubbing 8 times. △: Peeling was observed after rubbing five times. No practical problems.

[0062] <60℃ holding power> The coated material was cut into a 100 mm long x 25 mm wide sample under a 23°C, 50% RH environment. The release sheet was then peeled off from the sample, and the exposed adhesive layer was attached to the edge of a PP plate in a 15 mm x 15 mm area under a 23°C, 50% RH atmosphere. The sample was then pressed back and forth with a 5 kg roll. The resulting pressed sample was left in a 60°C atmosphere for 10 minutes, after which a 500 g load was applied to the pressed sample using a Tester Sangyo BE-501. The slippage was measured after leaving the sample for 24 hours. ◎: The deviation width is less than 0.3 mm. Excellent Good: The deviation is 0.3 mm or more and less than 1.0 mm. △: The deviation is 1.0 mm or more, but the device did not fall. There is no practical problem. ×: Dropped. Unusable.

[0063] <Initial Tack> The coated material was cut into a size of 280 mm long x 25 mm wide at 23°C and 50% RH to prepare a sample. The release sheet was removed from this sample, and the exposed adhesive layer was placed on the outside to form a ring. This ring was then attached to the upper chuck of a tensile tester (RTG-1210, manufactured by A&G Company). The ring-shaped sample was brought into contact with the PP plate (adherend) at a speed of 300 mm / min until the gap between the top and bottom of the ring-shaped sample became 60 mm. 15 seconds after the gap became 60 mm, the sample was peeled off at a speed of 300 mm / min, and the maximum adhesive strength was measured and evaluated according to the following criteria. ◎: Adhesion strength 15.0N / 25mm or more. Extremely good 〇: Adhesive strength 12.5N / 25mm or more, less than 15.0N / 25mm Good △: Adhesive strength 10.0N / 25mm or more, less than 12.5N / 25mm, no practical problems ×: Adhesive strength less than 10.0N / 25mm, not practical

[0064] [Table 3]

[0065] [Table 3]

[0066] [Table 3]

[0067] [Table 4]

[0068] As can be seen from the results in the table, the Examples using the aqueous pressure-sensitive adhesive of the present invention exhibited good adhesive strength, initial tack, substrate adhesion, and holding power, all of which are satisfactory for practical use. On the other hand, the aqueous pressure-sensitive adhesives of the Comparative Examples were found to be unable to satisfy one or more of the above properties.

Claims

1. An aqueous pressure-sensitive adhesive for adhering a foam substrate to an adherend, the aqueous pressure-sensitive adhesive comprising a copolymer containing at least 2-octyl(meth)acrylate and a monomer (A) having an acid group as monomers constituting the copolymer.

2. 2. The aqueous pressure-sensitive adhesive according to claim 1, wherein the content of 2-octyl (meth)acrylate in the monomer is 40% by mass or more and 99% by mass or less.

3. The aqueous pressure-sensitive adhesive according to claim 1, wherein the content of the monomer (A) having an acid group in the monomers is 1.0% by mass or more and 10% by mass or less.

4. The particle size at which the cumulative frequency from the small particle size side in the volume-based cumulative particle size distribution is 50% is defined as D 50 When the D of the copolymer particles in the aqueous pressure-sensitive adhesive is 50 The aqueous pressure-sensitive adhesive according to claim 1, wherein the particle size is 100 nm or more and 900 nm or less.

5. The aqueous pressure-sensitive adhesive according to claim 1, further comprising 1.0 part by mass or more and 20 parts by mass or less of a tackifier resin per 100 parts by mass of the copolymer.

6. The aqueous pressure-sensitive adhesive according to claim 1, wherein the gel fraction is 20% by mass or more and 60% by mass or less.

7. A coated product in which the aqueous pressure-sensitive adhesive according to any one of claims 1 to 6 is applied to a foam substrate.

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