Water-dispersible pressure-sensitive adhesive composition and pressure-sensitive adhesive sheet

Abstract

To provide a water-dispersible adhesive composition suitable for ensuring adhesive strength while achieving both low viscosity during filtering and appropriate viscosity recoverability during a coating process, and an adhesive sheet having an adhesive layer formed from the composition.SOLUTION: The water-dispersible adhesive composition of the present invention contains a water-dispersible polymer, a carboxylic acid-based copolymer thickener, a polyacrylic acid-based thickener, and water. The proportion of the carboxylic acid-based copolymer thickener in the solid content of the water-dispersible adhesive composition is 0.1 mass% or more and 1.5 mass% or less. The proportion of the polyacrylic acid-based thickener in the solid content is 1 mass% or more and 3.7 mass% or less. The adhesive sheet X of the present invention has an adhesive layer 10 formed from the water-dispersible adhesive composition.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a water-dispersible pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet. [Background technology]

[0002] Display panels have a laminated structure including elements such as a pixel panel, a polarizing film, a touch panel, and a cover film. In the manufacturing process of such display panels, optically transparent adhesive sheets are used to bond the elements included in the laminated structure. For adhesive sheets used in display panels of personal devices such as mobile devices and wearable devices, development of adhesive sheets formed from aqueous dispersion adhesive compositions is underway, not only for the purpose of environmental protection but also to avoid the effects of organic solvents on the human body. Technology related to aqueous dispersion adhesive compositions is described, for example, in Patent Document 1 listed below. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-134274 Summary of the Invention [Problem to be solved by the invention]

[0004] The above-mentioned PSA sheet is produced, for example, as follows. First, a water-dispersed PSA composition is prepared by mixing water as a solvent, a water-dispersed base polymer, and various components (water-dispersed tackifier resin, leveling agent, antifoaming agent, thickener, etc.) that are added as needed. Next, the water-dispersed PSA composition is filtered through a filter (filtering step). Next, the water-dispersed PSA composition is applied to a plastic substrate using a coater to form a coating film (coating step). Next, the coating film on the plastic substrate is dried to form a PSA layer.

[0005] A high level of cleanliness is required for PSA sheets used in display panels. Therefore, in the above-mentioned filtering step, a filter with a small pore size is used to remove minute foreign matter from the aqueous PSA composition. From the viewpoint of filter liquid permeability during such filtering, it is preferable that the aqueous PSA composition has a low viscosity.

[0006] Meanwhile, in the coating process described above, the water-dispersed PSA composition is applied to a plastic substrate using a coater. During coating, a relatively large shear force acts on the water-dispersed PSA composition, temporarily reducing the viscosity of the composition. After being applied to the plastic substrate, the water-dispersed PSA composition is released from the shear force and recovers its viscosity. However, if the viscosity of the water-dispersed PSA composition immediately after viscosity recovery is too low, the water-dispersed PSA composition will be repelled by the plastic substrate (occurrence of repelling). In the coating process, from the viewpoint of preventing repelling, it is preferable that the viscosity of the water-dispersed PSA composition immediately after viscosity recovery is high. Furthermore, if the viscosity of the water-dispersed PSA composition immediately after viscosity recovery is too high, streaky coating marks will remain on the coated water-dispersed PSA composition. From the viewpoint of preventing coating marks, it is preferable that the viscosity of the water-dispersed PSA composition immediately after viscosity recovery is not too high.

[0007] Furthermore, a pressure-sensitive adhesive sheet formed from a water-dispersible pressure-sensitive adhesive composition is also required to have sufficient adhesive strength to ensure reliable bonding between adherends.

[0008] The present invention provides a water-dispersible pressure-sensitive adhesive composition suitable for ensuring adhesive strength while achieving both low viscosity during filtering and appropriate viscosity recovery in the coating process, and a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed from the composition. [Means for solving the problem]

[0009] The present invention [1] is a water-dispersible pressure-sensitive adhesive composition containing a water-dispersible polymer, a carboxylic acid copolymer thickener, a polyacrylic acid thickener, and water, wherein the proportion of the carboxylic acid copolymer thickener in the solid content of the water-dispersible pressure-sensitive adhesive composition is from 0.1% by mass to 1.5% by mass, and the proportion of the polyacrylic acid thickener in the solid content is from 1% by mass to 3.7% by mass.

[0010] The present invention [2] includes the water-dispersible pressure-sensitive adhesive composition according to the above [1], in which the total proportion of the carboxylic acid copolymer thickener and the polyacrylic acid thickener in the solid content is 2% by mass or more and 4.2% by mass or less.

[0011] The present invention [3] is a shear rate of 4 s -1 and the water-dispersible PSA composition according to the above item [1] or [2], which has a viscosity at 30°C of 0.8 Pa·s or less.

[0012] The present invention [4] is a shear rate of 1 × 10 4 s -1 After shearing at 30°C, the shear rate was 4 s -1 and the water-dispersible PSA composition according to any one of [1] to [3] above, which has a viscosity at 30°C of 0.9 Pa·s or more and 1.5 Pa·s or less.

[0013] The present invention [5] includes the water-dispersed PSA composition according to any one of the above [1] to [4], which further contains a tackifier.

[0014] The present invention [6] includes the water-dispersed pressure-sensitive adhesive composition according to any one of the above [1] to [5], which further contains a leveling agent.

[0015] The present invention [7] includes a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to any one of the above [1] to [6].

[0016] The present invention [8] includes the pressure-sensitive adhesive sheet according to the above [7], wherein the pressure-sensitive adhesive layer has a thickness of 40 μm or less. [Effects of the Invention]

[0017] The water-dispersible PSA composition of the present invention contains, in addition to the water-dispersible polymer and water, 0.1 to 1.5 mass % (proportion of the solid content) of a carboxylic acid copolymer thickener and 1 to 3.7 mass % of a polyacrylic acid thickener, as described above. This water-dispersible PSA composition is suitable for ensuring adhesive strength while achieving both low viscosity during filtering and adequate viscosity recovery during the coating process. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a cross-sectional view of an embodiment of a pressure-sensitive adhesive sheet of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] The water-dispersible PSA composition according to one embodiment of the present invention is an aqueous emulsion containing a water-dispersible polymer, a carboxylic acid copolymer thickener, a polyacrylic acid thickener, and water.

[0020] Examples of water-dispersible polymers include water-dispersible acrylic polymers, water-dispersible urethane polymers, water-dispersible polyaniline polymers, and water-dispersible polyester polymers, with water-dispersible acrylic polymers being preferred. The acrylic polymer is a polymer of a monomer component containing 50% or more by mass of alkyl (meth)acrylate. "(Meth)acrylic" refers to acrylic and / or methacrylic.

[0021] Examples of (meth)acrylic acid alkyl esters include (meth)acrylic acid alkyl esters having a linear or branched alkyl group having 1 to 20 carbon atoms. Examples of such (meth)acrylic acid alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, and isopropyl (meth)acrylate. Examples of the alkyl (meth)acrylate include isooctyl, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, isotridodecyl (meth)acrylate, tetradecyl (meth)acrylate, isotetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isooctadecyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate. The alkyl (meth)acrylate esters may be used alone or in combination of two or more. As the (meth)acrylic acid alkyl ester, preferably, an acrylic acid alkyl ester having an alkyl group with 1 to 12 carbon atoms is used, more preferably, methyl acrylate and an acrylic acid alkyl ester having an alkyl group with 2 to 8 carbon atoms are used, and even more preferably, methyl acrylate and 2-ethylhexyl acrylate are used.

[0022] From the viewpoint of properly exhibiting basic properties such as adhesiveness in the adhesive layer formed from the water-dispersible adhesive composition, the proportion of the (meth)acrylic acid alkyl ester in the monomer components is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, and is preferably 99.5% by mass or less, more preferably 99% by mass or less.

[0023] The monomer component may contain a copolymerizable monomer copolymerizable with the (meth)acrylic acid alkyl ester. Examples of the copolymerizable monomer include polar group-containing monomers. Examples of the polar group-containing monomer include carboxy group-containing monomers, hydroxy group-containing monomers, monomers having a nitrogen atom-containing ring, silanol group-containing monomers, sulfo group-containing monomers, cyano group-containing monomers, and glycidyl group-containing monomers. The polar group-containing monomer is useful for modifying the acrylic polymer, for example, by ensuring the cohesive strength of the acrylic polymer. The copolymerizable monomer may be used alone or in combination of two or more types.

[0024] Examples of the carboxy group-containing monomer include acrylic acid, methacrylic acid, 2-carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid. From the viewpoint of ensuring the adhesiveness of the PSA layer formed from the water-dispersible PSA composition, the monomer component preferably contains a carboxy group-containing monomer, more preferably contains acrylic acid or methacrylic acid, and particularly preferably uses acrylic acid and methacrylic acid in combination.

[0025] The proportion of the carboxyl group-containing monomer in the monomer components is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 1.5% by mass or more, from the viewpoint of ensuring the cohesive strength of the pressure-sensitive adhesive layer formed from the water-dispersible pressure-sensitive adhesive composition. The proportion of the carboxyl group-containing monomer in the monomer components is preferably 8% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less, from the viewpoint of avoiding the risk of corrosion of the adherend by acid.

[0026] Examples of hydroxyl group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate.

[0027] Examples of monomers having a nitrogen atom-containing ring include N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-(meth)acryloyl-2-pyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine, N-vinylmorpholine, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholinedione, N-vinylpyrazole, N-vinylisoxazole, N-vinylthiazole, N-vinylisothiazole, and acryloylmorpholine.

[0028] Examples of silanol group-containing monomers include 3-methacryloxypropyltrimethoxysilane and 3-acryloxypropyltrimethoxysilane.

[0029] Examples of sulfo group-containing monomers include styrene sulfonic acid, allyl sulfonic acid, sodium vinyl sulfonate, 2-(meth)acrylamido-2-methylpropanesulfonic acid, (meth)acrylamidopropanesulfonic acid, sulfopropyl (meth)acrylate, and (meth)acryloyloxynaphthalenesulfonic acid.

[0030] An example of a phosphate group-containing monomer is 2-hydroxyethyl acryloyl phosphate.

[0031] Cyano group-containing monomers include, for example, acrylonitrile and methacrylonitrile.

[0032] Examples of the glycidyl group-containing monomer include glycidyl (meth)acrylate and 2-ethyl (meth)acrylate glycidyl ether.

[0033] The water-dispersible acrylic polymer can be formed, for example, by emulsion polymerization of the above-mentioned monomer components. In emulsion polymerization, for example, first, a mixture containing the monomer components, an emulsifier, and water is stirred to prepare a monomer emulsion. Next, a polymerization initiator is added to the monomer emulsion to start the polymerization reaction. A chain transfer agent may be used in this polymerization reaction to adjust the molecular weight of the acrylic polymer. The polymerization method may be dropwise polymerization or batch polymerization. The polymerization time is, for example, 0.5 to 10 hours. The polymerization temperature is, for example, 50°C to 80°C.

[0034] Examples of emulsifiers include anionic emulsifiers, nonionic emulsifiers, and radical polymerizable emulsifiers (reactive emulsifiers).

[0035] Examples of anionic emulsifiers include polyoxyethylene sodium lauryl sulfate, sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecylbenzenesulfonate, polyoxyethylene alkyl ether sodium sulfate, polyoxyethylene alkylphenyl ether ammonium sulfate, polyoxyethylene alkylphenyl ether sodium sulfate, and polyoxyethylene alkylsulfosuccinate.

[0036] Examples of nonionic emulsifiers include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene fatty acid esters, and polyoxyethylene polyoxypropylene block polymers.

[0037] Examples of radically polymerizable emulsifiers (reactive emulsifiers) include emulsifiers obtained by introducing a radically polymerizable functional group into the above-mentioned anionic emulsifiers or nonionic emulsifiers. Examples of such radically polymerizable functional groups include vinyl groups, propenyl groups, isopropenyl groups, vinyl ether groups, and allyl ether groups. A specific example of a reactive emulsifier is ammonium-α-sulfonato-ω-1-(allyloxymethyl)alkyloxypolyoxyethylene. When a reactive emulsifier is used as the emulsifier, the water-dispersible acrylic polymer obtained by emulsion polymerization contains a monomer unit derived from the reactive emulsifier. In other words, the emulsifier is incorporated into the acrylic polymer. Therefore, when a pressure-sensitive adhesive layer formed from the water-dispersible pressure-sensitive adhesive composition is applied to an adherend, contamination of the adherend by the emulsifier (low-molecular-weight component) can be suppressed.

[0038] The emulsifier may be used alone or in combination of two or more kinds. The amount of the emulsifier to be added is, for example, 0.5 parts by mass or more and, for example, 5 parts by mass or less, per 100 parts by mass of the monomer component.

[0039] Examples of polymerization initiators include azo polymerization initiators and peroxide polymerization initiators. Examples of azo polymerization initiators include 2,2'-azobis{2-[N-(2-carboxyethyl)amidino]propane}, 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-amidinopropane)dihydrochloride, 2,2'-azobis[2-(5-methyl-2-imidazolin-2-yl)propane]dihydrochloride, and 2,2'-azobis(N,N'-dimethyleneisobutylamidine). Examples of peroxide polymerization initiators include benzoyl peroxide, t-butyl hydroperoxide, and hydrogen peroxide. Polymerization initiators may be used alone or in combination of two or more. The amount of polymerization initiator added is, for example, 0.01 parts by mass or more and, for example, 2 parts by mass or less per 100 parts by mass of the monomer components.

[0040] Examples of chain transfer agents include glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, t-lauryl mercaptan, t-dodecanethiol, thioglycolic acid, 2-ethylhexyl thioglycolate, and 2,3-dimercapto-1-propanol. The chain transfer agents may be used alone or in combination. The amount of the chain transfer agent is, for example, 0.001 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of the monomer components.

[0041] By such emulsion polymerization, the water-dispersible acrylic polymer is prepared as a polymer emulsion (aqueous dispersion in which the water-dispersible acrylic polymer is dispersed in water).

[0042] The weight-average molecular weight (Mw) of the water-dispersible acrylic polymer is, for example, 100,000 or more, preferably 300,000 or more, and, for example, 5,000,000 or less, preferably 3,000,000 or less. The weight-average molecular weight of the acrylic polymer is measured by gel permeation chromatography (GPC) and calculated in terms of polystyrene.

[0043] The glass transition temperature (Tg) of the water-dispersible polymer is, for example, 20°C or lower, and preferably 0°C or lower.

[0044] The carboxylic acid copolymer thickener is an emulsion-type thickener made of a carboxylic acid copolymer. The carboxylic acid copolymer is, for example, a copolymer of monomer components containing a carboxyl group-containing acrylic monomer. Commercially available carboxylic acid copolymer thickeners include "Aron B-300K," "Aron B-500," "Aron A-7055," and "Aron A-7075" manufactured by Toa Gosei Co., Ltd., with "Aron B-500" being preferred. The viscosity of a 1% diluted solution of a commercially available carboxylic acid copolymer thickener (aqueous solution) measured at 25°C, pH 8-9, and 60 rpm using a BM-type viscometer is preferably 10,000 mPa·s or less, more preferably 1,200 mPa·s or less, and preferably 10 mPa·s or more, more preferably 1,000 mPa·s or more. The carboxylic acid copolymer thickeners may be used alone or in combination.

[0045] The proportion of the carboxylic acid copolymer thickener in the solid content of the water-dispersed PSA composition is 0.1% by mass or more, preferably 0.3% by mass or more, more preferably 0.4% by mass or more, and even more preferably 0.5% by mass or more, from the viewpoint of ensuring thickening by the carboxylic acid copolymer thickener in the water-dispersed PSA composition. The proportion of the carboxylic acid copolymer thickener in the solid content of the water-dispersed PSA composition is 1.5% by mass or less, preferably 1.3% by mass or less, more preferably 1.1% by mass or less, and even more preferably 0.9% by mass or less, from the viewpoint of avoiding excessive thickening by the carboxylic acid copolymer thickener in the water-dispersed PSA composition. The solid content of the water-dispersed PSA composition refers to the components other than water in the water-dispersed PSA composition, specifically, the combination of the water-dispersed polymer, the carboxylic acid copolymer thickener, the polyacrylic acid thickener, and other components (such as a leveling agent and a tackifier) ​​that are blended as needed.

[0046] Examples of polyacrylic acid thickeners include polyacrylic acid (a homopolymer of acrylic acid), sodium polyacrylate, and ammonium polyacrylate. Commercially available polyacrylic acid thickeners include "Aron A-10H" (polyacrylic acid), "Aron A-20L" (sodium polyacrylate), "Aron A-7100" (sodium polyacrylate), "Aron A-30" (ammonium polyacrylate), and "Aron A-7195" (sodium ammonium polyacrylate), all manufactured by Toa Gosei Co., Ltd., with "Aron A-10H" being preferred. The viscosity of commercially available polyacrylic acid thickeners (aqueous solutions) at 25°C is preferably 50,000 mPa·s or less, more preferably 40,000 mPa·s or less, and preferably 1,000 mPa·s or more, and preferably 5,000 mPa·s or more. Polyacrylic acid thickeners may be used alone or in combination. The molecular weight of a polyacrylic acid thickener exhibiting such a viscosity is preferably 1,000,000 or less, more preferably 600,000 or less, and is preferably 50,000 or more, more preferably 100,000 or more.

[0047] The proportion of the polyacrylic acid thickener in the solid content of the water-dispersed PSA composition is 1% by mass or more, preferably 1.4% by mass or more, more preferably 1.8% by mass or more, and even more preferably 2% by mass or more, from the viewpoint of ensuring thickening by the polyacrylic acid thickener in the water-dispersed PSA composition. The proportion of the polyacrylic acid thickener in the solid content of the water-dispersed PSA composition is 3.7% by mass or less, preferably 3% by mass or less, more preferably 2.8% by mass or less, and even more preferably 2.6% by mass or less, from the viewpoint of avoiding excessive thickening by the polyacrylic acid thickener in the water-dispersed PSA composition.

[0048] The total proportion of the carboxylic acid copolymer thickener and polyacrylic acid thickener in the solid content of the water-dispersible pressure-sensitive adhesive composition is preferably 2% by mass or more, more preferably 2.5% by mass or more, even more preferably 2.7% by mass or more, from the viewpoint of the balance between the first viscosity η1 and the second viscosity η2 described below, and is preferably 4.2% by mass or less, more preferably 3.5% by mass or less, even more preferably 2.9% by mass or less.

[0049] The aqueous PSA composition may contain other components, such as a leveling agent, a tackifier, a silane coupling agent, a preservative, a surfactant, a crosslinking agent, and an antistatic agent.

[0050] Examples of leveling agents include "Neocol SW-C" (dialkylsodium sulfosuccinate, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), "Neocol P" (dialkylsodium sulfosuccinate, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), "Surfynol 420" (acetylene glycol ethylene oxide surfactant, manufactured by Nissin Chemical Industry Co., Ltd.), and "Pelex OT-P" (dialkylsodium sulfosuccinate, manufactured by Kao Corporation). Other examples of leveling agents include "Nopco Wet 50" (sulfonic acid-based anionic surfactant), "SN Wet 126" (modified silicone / special polyether surfactant), "SN Wet FST2" (polyoxyalkyleneamine nonionic wetting agent), "SN Wet S" (polyoxyalkyleneamine ether nonionic wetting agent), and "SN Wet 125" (modified silicone surfactant) (all manufactured by San Nopco). Leveling agents may be used alone or in combination. From the viewpoint of ensuring good leveling properties in the water-dispersible PSA composition, the leveling agent used is preferably at least one selected from "Neocol SW-C," "Neocol P," and "Pelex OT-P."

[0051] The amount of the leveling agent to be added is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 0.8 parts by mass or more, relative to 100 parts by mass of the water-dispersible polymer, from the viewpoint of suppressing cissing of the water-dispersible PSA composition. The amount of the leveling agent to be added is preferably 3 parts by mass or less, more preferably 2 parts by mass or less, and even more preferably 1 part by mass or less, from the viewpoint of ensuring the adhesive properties of the water-dispersible PSA composition.

[0052] Examples of the tackifier include tackifier resins such as rosin resins, rosin derivative resins, petroleum resins, terpene resins, phenolic resins, ketone resins, etc. From the viewpoint of the balance between the viscosity of the water-dispersible PSA composition and the adhesiveness of the PSA layer formed from the composition, the amount of tackifier blended is preferably 5 parts by mass or more, more preferably 15 parts by mass or more, even more preferably 20 parts by mass or more, particularly preferably 25 parts by mass or more, and is preferably 50 parts by mass or less, more preferably 45 parts by mass or less, and even more preferably 40 parts by mass or less, relative to 100 parts by mass of the water-dispersible polymer.

[0053] Examples of the silane coupling agent include 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, and 3-methacryloxypropyltriethoxysilane, and preferably 3-methacryloxypropyltrimethoxysilane is used. The amount of the silane coupling agent to be added is, for example, 0.005 parts by mass or more and, for example, 1 part by mass or less, relative to 100 parts by mass of the water-dispersible polymer.

[0054] The water-dispersible PSA composition does not contain an organic solvent, and such a water-dispersible PSA composition is preferred from the viewpoint of reducing the environmental load.

[0055] The water-dispersible PSA composition can be prepared, for example, by adding various components to an emulsion of a water-dispersible polymer. The solids concentration of the water-dispersible PSA composition can be adjusted by increasing or decreasing the water content.

[0056] From the viewpoint of the balance between the first viscosity η1 and the second viscosity η2 described below, the solids concentration of the water-dispersible pressure-sensitive adhesive composition is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and particularly preferably 25% by mass or more, and is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 35% by mass or less, even more preferably 30% by mass or less, and particularly preferably 27% by mass or less.

[0057] Shear rate of 4s for water-dispersed PSA composition -1 The viscosity (first viscosity η1) under the conditions of 1000 kJ / min and 30°C is preferably 0.8 Pa·s or less, more preferably 0.7 Pa·s or less, and even more preferably 0.6 Pa·s or less, from the viewpoint of ensuring filter passability in the filtering step described below. The first viscosity η1 is preferably 0.1 Pa·s or more, more preferably 0.3 Pa·s or more, and more preferably 0.5 Pa·s or more, from the viewpoint of suppressing repelling when coated on a substrate after passing through a filter. The method for measuring the first viscosity η1 is as described below in the examples.

[0058] In the water-dispersed pressure-sensitive adhesive composition, the shear rate is 1×10 4 s -1 After shearing at 30°C, the shear rate was 4 s -1 The viscosity (second viscosity η2) under the conditions of 100°C and 30°C is preferably 0.9 Pa·s or more, and more preferably 1.0 Pa·s or more, from the viewpoint of suppressing repelling and streaks in the coating process described below. The second viscosity η2 is preferably 1.5 Pa·s or less, more preferably 1.3 Pa·s or less, and even more preferably 1.2 Pa·s or less, from the viewpoint of suppressing streaks in the coating process. The method for measuring the second viscosity η2 is as described below in the examples.

[0059] From the viewpoint of a balance between ensuring filterability in the filtering process and suppressing repelling and streaks in the coating process, the ratio of the second viscosity η2 to the first viscosity η1 (η2 / η1) is preferably 1.6 or more, more preferably 1.7 or more, and also preferably 3 or less, more preferably 2.5 or less, even more preferably less than 2, and particularly preferably 1.9 or less.

[0060] As described above, the water-dispersible PSA composition contains, in addition to the water-dispersible polymer and water, 0.1 to 1.5 mass % (proportion of the solid content) of a carboxylic acid copolymer thickener and 1 to 3.7 mass % of a polyacrylic acid thickener. Such a water-dispersible PSA composition is suitable for ensuring adhesive strength while achieving both low viscosity during filtering and adequate viscosity recovery during the coating process. Specific examples are shown in the examples and comparative examples below.

[0061] FIG. 1 is a cross-sectional schematic diagram of a pressure-sensitive adhesive sheet X according to one embodiment of the present invention. The pressure-sensitive adhesive sheet X has a pressure-sensitive adhesive layer 10. The pressure-sensitive adhesive layer 10 has a sheet shape with a predetermined thickness. The pressure-sensitive adhesive layer 10 extends in a direction (plane direction) perpendicular to the thickness direction. The pressure-sensitive adhesive layer 10 has an adhesive surface 11 and an adhesive surface 12 opposite the adhesive surface 11. FIG. 1 exemplarily illustrates a state in which release liners L1 and L2 are bonded to the adhesive surfaces 11 and 12 of the pressure-sensitive adhesive layer 10. The release liner L1 is disposed on the adhesive surface 11. The release liner L2 is disposed on the adhesive surface 12. The pressure-sensitive adhesive sheet X is, for example, an optical adhesive sheet disposed at a light passage point in a display panel. Examples of display panels include display panels for personal devices such as mobile devices and wearable devices. The display panel has a laminated structure including elements such as a pixel panel, a polarizing film, a touch panel, and a cover glass. The adhesive sheet X is used, for example, in the manufacturing process of a display panel to bond elements included in a laminated structure together.

[0062] The pressure-sensitive adhesive layer 10 is a pressure-sensitive adhesive layer formed from the above-mentioned aqueous dispersion-type pressure-sensitive adhesive composition. From the viewpoints of handleability and processability, the thickness of the pressure-sensitive adhesive layer 10 is preferably 50 μm or less, more preferably 40 μm or less, even more preferably 30 μm or less, and particularly preferably 20 μm or less. From the viewpoint of ensuring sufficient adhesion to the adherend, the thickness of the pressure-sensitive adhesive layer 10 is preferably 3 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more.

[0063] The release liners L1 and L2 are elements that cover and protect the pressure-sensitive adhesive sheet X (pressure-sensitive adhesive layer 10), and are peeled off from the pressure-sensitive adhesive sheet X when the pressure-sensitive adhesive sheet X is used. The release liner L1 is, for example, a flexible plastic film. Examples of such plastic films include polyethylene terephthalate film, polyethylene film, polypropylene film, and polyester film. The thickness of the release liners L1 and L2 is, for example, 3 μm or more and, for example, 200 μm or less. The surfaces of the release liners L1 and L2 are preferably release-treated.

[0064] The adhesive sheet X can be produced, for example, as follows.

[0065] First, the water-dispersed PSA composition is filtered through a filter (filtering step). Examples of the mesh size of the filter used for filtration include 188 μm, 154 μm, 109 μm, 75 μm, 50 μm, 25 μm, 10 μm, 5 μm, 3 μm, 2 μm, and 1 μm.

[0066] Next, the above-mentioned aqueous dispersion PSA composition is applied onto the release liner L1 using a coater to form a coating film (coating film forming step). Coating methods include, for example, roll coating, kiss roll coating, gravure coating, reverse coating, roll brush, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, and die coating. In this step, a coater appropriate for the coating method is used.

[0067] Next, the coating film on the release liner L1 is dried to form the pressure-sensitive adhesive layer 10 (drying step). The drying temperature is, for example, room temperature to 140° C. The drying time is, for example, 1 to 10 minutes.

[0068] Next, if necessary, a release liner L2 is attached to the exposed surface of the pressure-sensitive adhesive layer 10 on the release liner L1.

[0069] In this manner, the pressure-sensitive adhesive sheet X can be produced from the water-dispersible pressure-sensitive adhesive composition.

[0070] As described above, the water-dispersible PSA composition contains, in addition to the water-dispersible polymer and water, 0.1 to 1.5 mass % (proportion of the solid content) of a carboxylic acid copolymer thickener and 1 to 3.7 mass % of a polyacrylic acid thickener. Such a water-dispersible PSA composition is suitable for ensuring the adhesive strength of the PSA sheet X while achieving both low viscosity in the filtering step and appropriate viscosity recovery in the coating step.

[0071] In the filtering step, the lower the viscosity of the water-dispersed PSA composition, the easier it is for the water-dispersed PSA composition to pass through the filter, thereby enabling the time required for the filtering step to be shortened.

[0072] When a water-dispersed PSA composition is applied by a coater in the coating process, a relatively large shear force acts on the water-dispersed PSA composition, causing a temporary decrease in the viscosity of the composition. After being applied to a plastic substrate (release liner), the water-dispersed PSA composition is released from the shear force and recovers its viscosity. If the viscosity of the water-dispersed PSA composition immediately after viscosity recovery is too low, the water-dispersed PSA composition will be repelled by the plastic substrate (occurrence of cissing). If the viscosity immediately after viscosity recovery is too high, streaks will form in the coating film of the water-dispersed PSA composition (occurrence of streaks). However, the above-mentioned water-dispersed PSA composition has appropriate viscosity recovery after coating, thereby suppressing the occurrence of cissing and streaks. [Example]

[0073] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to these examples. The specific numerical values ​​of the blending amounts (contents), physical property values, parameters, etc. described below can be substituted for the upper limits (numerical values ​​defined as "equal to or less than") or lower limits (numerical values ​​defined as "equal to or more than") of the corresponding blending amounts (contents), physical property values, parameters, etc. described in the above-mentioned "Description of the Invention."

[0074] Example 1 <Preparation of Water-Dispersed Polymer> A mixture containing 30 parts by mass of ion-exchanged water, 85 parts by mass of 2-ethylhexyl acrylate, 13 parts by mass of methyl acrylate, 1.25 parts by mass of acrylic acid, 0.75 parts by mass of methacrylic acid, 0.035 parts by mass of t-lauryl mercaptan as a chain transfer agent, 1.88 parts by mass of a reactive emulsifier (trade name "Aqualon KH-1025", ammonium-α-sulfonato-ω-1-(allyloxymethyl)alkyloxypolyoxyethylene, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and 0.02 parts by mass of a silane coupling agent (trade name "KBM-503", 3-methacryloxypropyltrimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd.) was stirred in a container using a homomixer to prepare a monomer emulsion.

[0075] Meanwhile, in a reaction vessel equipped with a reflux condenser, nitrogen inlet, thermometer, and stirrer, a mixture containing 73 parts by mass of ion-exchanged water and 0.07 parts by mass of a reactive emulsifier (Aqualon KH-1025) was stirred at 60°C for 1 hour under a nitrogen atmosphere. Next, 0.1 parts by mass of 2,2'-azobis{2-[N-(2-carboxyethyl)amidino]propane} tetrahydrate was added as a polymerization initiator to the mixture, and the above-mentioned monomer emulsion was added dropwise to the mixture over 4 hours to allow the emulsion polymerization reaction to proceed. The reaction solution was then maintained at 60°C for 3 hours (aging). The resulting solution was then cooled to room temperature, and the pH of the solution was adjusted to 6.0 by adding 10% by mass of aqueous ammonia. Next, 0.03 parts by mass of a preservative (trade name "Levanax BX-150", manufactured by Shoei Chemical Co., Ltd.) was added to the solution. In this manner, an acrylic polymer emulsion containing a water-dispersible acrylic polymer as the water-dispersible polymer was prepared.

[0076] <Preparation of Water-Dispersed Pressure-Sensitive Adhesive Composition> To the acrylic polymer emulsion, 1.00 parts by weight (solids equivalent) of a carboxylic acid copolymer thickener (product name "Aron B-500", manufactured by Toagosei Co., Ltd.), 3.15 parts by weight (solids equivalent) of a polyacrylic acid thickener (product name "Aron A-10H", polyacrylic acid, weight average molecular weight 200,000, manufactured by Toagosei Co., Ltd.), 35 parts by weight (solids equivalent) of a tackifier (product name "Tamanol E-200NT", terpene resin, manufactured by Arakawa Chemical Industries, Ltd.), and 0.89 parts by weight (solids equivalent) of a leveling agent (product name "Neocol SW-C", dialkyl sodium sulfosuccinate, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) were added and mixed per 100 parts by weight of water-dispersible acrylic polymer. Next, the mixture was adjusted to a solids concentration of 25.5% by weight by adding ion-exchanged water, and then adjusted to pH 9.0 by adding 10% by weight aqueous ammonia solution. In this manner, the water-dispersible PSA composition of Example 1 (solid content concentration: 25.5% by mass) was prepared (in Tables 1 and 2, the units of each numerical value representing the composition are "parts by mass"). The prepared water-dispersible PSA composition was filtered through a nylon mesh filter (product name "N / Sher 4300KK", thickness 110 μm, 80 mesh, opening size 188 μm, manufactured by Koyo Synthetic Fiber Processing Co., Ltd.).

[0077] <Preparation of adhesive sheet> First, a water-dispersible pressure-sensitive adhesive composition was applied to the release-treated surface of a silicone-release-treated polyethylene terephthalate (PET) film (trade name "Diafoil MRF38", manufactured by Mitsubishi Chemical Corporation) to form a coating film. Next, the coating film on the PET film was dried in an oven for 3 minutes to form a 10 μm-thick pressure-sensitive adhesive layer. The drying temperature was 100°C. In this manner, the pressure-sensitive adhesive sheet of Example 1 (a pressure-sensitive adhesive sheet with a PET film) was produced.

[0078] [Examples 2 to 8, Comparative Examples 1 to 10] The water-dispersible PSA compositions of Examples 2 to 8 and Comparative Examples 1 to 10 were prepared in the same manner as the water-dispersible PSA composition of Example 1, except that the blending amounts of the carboxylic acid copolymer thickener and polyacrylic acid thickener were changed as shown in Tables 1 and 2. In Comparative Examples 1 and 3, no carboxylic acid copolymer thickener was used. In Comparative Examples 8 to 10, no polyacrylic acid thickener was used.

[0079] The adhesive sheets (PET film-attached adhesive sheets) of Examples 1 to 8 and Comparative Examples 3 to 5, 7, and 9 were prepared in the same manner as the adhesive sheet of Example 1, except that the amounts of the carboxylic acid copolymer thickener and the polyacrylic acid thickener were changed as shown in Tables 1 and 2.

[0080] The PSA sheets of Comparative Examples 1, 2, 6, 8, and 10 were produced in the same manner as the PSA sheet of Example 1, except that the blending amounts of the carboxylic acid copolymer thickener and polyacrylic acid thickener were changed as shown in Table 2. However, repelling occurred in the aqueous PSA composition applied to the PET film, and the PSA sheets of Comparative Examples 1, 2, 6, 8, and 10 could not be produced.

[0081] <Viscosity measurement> The viscosity of each of the water-dispersed pressure-sensitive adhesive compositions of Examples 1 to 8 and Comparative Examples 1 to 10 was measured. Specifically, the measurements were as follows.

[0082] First, a rheometer viscometer (product name "RheoStress1", manufactured by Haake) was used to measure the shear rate of 4 s -1 The viscosity of the water-dispersible PSA composition was measured under conditions of 1000 kJ / min and 30°C (first viscosity measurement). In this measurement, a cone-type rotor (cone No. 222-1267, cone diameter 35 mm, cone angle 0.5 degrees) was used as the rotor to apply shear to the water-dispersible PSA composition (the same applies to the second viscosity measurement described below). The measured viscosity is shown in Tables 1 and 2 as the first viscosity η1 (Pa s).

[0083] Next, the shear rate is increased to 1 × 10 4 s -1 and the shear rate was increased to 1 x 104 s -1 The water-dispersible PSA composition was subjected to shear for 10 seconds at a temperature of 100°C and 30°C. -1 After 3 seconds from the shear rate reduction, the rheometer viscometer (RheoStress1) measured the shear rate at 4 s -1 The viscosity of the water-dispersible PSA composition was measured under conditions of 100°C and 30°C (second viscosity measurement). The measured viscosity is shown as the second viscosity η2 (Pa s) in Tables 1 and 2. The ratio of the second viscosity η2 to the first viscosity η1 (η2 / η1) is also shown in Tables 1 and 2.

[0084] <Filter passability> The filter-passing ability of each of the water-dispersed PSA compositions of Examples 1 to 8 and Comparative Examples 1 to 10 was examined. Specifically, 1 mL of the water-dispersed PSA composition was gently dispensed (placed) using a dropper onto a horizontally placed nylon mesh filter (product name "N / Sher 4300KK", 110 μm thick, 80 mesh, 188 μm opening size, manufactured by Koyo Synthetic Fiber Processing Co., Ltd.), and it was observed whether the composition passed through the filter under its own weight. Regarding the filter-passing ability of the water-dispersed PSA composition, if the water-dispersed PSA composition passed through the filter under its own weight within 3 seconds, it was evaluated as "good," and if it did not pass through within 3 seconds, it was evaluated as "poor." The results are shown in Tables 1 and 2.

[0085] <Wettability> The wettability of each of the water-dispersed pressure-sensitive adhesive compositions of Examples 1 to 8 and Comparative Examples 1 to 10 to plastic substrates was examined. Specifically, the results are as follows.

[0086] First, an aqueous PSA composition was applied to the release-treated surface of a silicone-release-treated polyethylene terephthalate (PET) film (product name "Diafoil MRF38," manufactured by Mitsubishi Chemical Corporation) to form a coating film approximately 40 μm thick. The coating film was then visually observed. Regarding the repelling resistance (suppression of cissing) of the aqueous PSA composition, a case in which no cissing occurred in the coating film (aqueous PSA composition) on the PET substrate was evaluated as "good," and a case in which cissing occurred was evaluated as "poor." Furthermore, regarding the resistance to streak formation (suppression of streaks) of the aqueous PSA composition, a case in which no streaks occurred in the coating film (aqueous PSA composition) on the PET substrate was evaluated as "good," and a case in which streaks occurred was evaluated as "poor." The evaluation results are shown in Tables 1 and 2. The repelling resistance and streak resistance of the aqueous PSA composition are indicators of the wettability of the aqueous PSA composition. For the water-dispersible pressure-sensitive adhesive compositions of Comparative Examples 1, 2, 6, 8 and 10, repelling occurred after coating on the PET film, and a coating film could not be properly formed, so that the appearance of streaks in the coating film could not be confirmed.

[0087] <Drop impact resistance test> The adhesive strength of each of the pressure-sensitive adhesive sheets of Examples 1 to 8 and Comparative Examples 3 to 5, 7, and 9 was examined by a drop impact resistance test. Specifically, the test was carried out as follows.

[0088] First, a rectangular frame-shaped adhesive sheet piece (24.5 mm × 24.5 mm, 2 mm wide) was obtained by punching the adhesive sheet with the PET film. Next, the adhesive sheet piece with the PET film was attached to a square first stainless steel plate (25 mm × 25 mm, 3 mm thick) along its four sides. Next, the PET film was peeled off from the adhesive sheet piece on the first stainless steel plate. Next, the first stainless steel plate and a square second stainless steel plate (50 mm × 50 mm, 2 mm thick) with a central opening (20 mm × 20 mm) were bonded together through the adhesive sheet on the first stainless steel plate, with the centers of the plates aligned in a plan view, under conditions of a bonding force of 62 N and a bonding time of 10 seconds. This resulted in a bonded assembly. Next, this bonded assembly was left to stand at 80°C for 30 minutes. Next, the bonded assembly was allowed to cool to 23°C.

[0089] Next, a cylindrical pedestal (height 50 mm, outer diameter 49 mm, inner diameter 43 mm) was placed on the stage of a DuPont impact tester (manufactured by Toyo Seiki Seisakusho), and the above-mentioned bonded assembly was placed on the pedestal. Specifically, the second stainless steel plate of the bonded assembly was positioned on top, with the underside of the second stainless steel plate in contact with the upper end of the pedestal, and the lower first stainless steel plate was placed within the cylindrical cavity of the pedestal (the first stainless steel plate was exposed upward through the opening in the second stainless steel plate). Next, a stainless steel cylindrical striking die (bottom diameter 6.2 mm) was placed on the first stainless steel plate facing the opening in the second stainless steel plate in the bonded assembly.

[0090] Then, a drop impact resistance test was conducted using a DuPont impact testing machine, in which a weight was dropped vertically onto the impact die on the assembly. In the test for each assembly, the weight was dropped multiple times, varying in mass (50g, 100g) and drop height so that the impact energy acting on the assembly through the impact die would increase in succession, until peeling occurred between the first and second stainless steel plates of the assembly. When using a 50g weight, the drop height was changed from 50mm to 500mm in 50mm increments. Then, when using a 100g weight, the drop height was changed from 300mm to 500mm in 50mm increments. The potential energy of the weight used before peeling occurred between the first and second stainless steel plates of the assembly [load (kg) × gravitational acceleration 9.8 (m / s 2 ) × height (m)] was taken as the drop impact energy (J).

[0091] The average drop impact energy obtained from the above drop impact resistance test three times (n=3) is shown as drop impact energy (J) in Tables 1 and 2. In addition, the drop impact resistance of the PSA sheet was evaluated as "good" when the drop impact energy was 0.4 J or more, and as "poor" when the drop impact energy was less than 0.4 J. The results are also shown in Tables 1 and 2.

[0092] [Table 1]

[0093] [Table 2]

[0094] [evaluation] Each of the water-dispersed PSA compositions of Examples 1 to 8 contained, in addition to a water-dispersed polymer and water, 0.1 to 2.2 mass% (proportion of the solid content) of a carboxylic acid copolymer thickener and 1.2 to 5.2 mass% of a polyacrylic acid thickener. These water-dispersed PSA compositions exhibited good filterability, suppressed cissing and streaking during coating, and were able to form PSA sheets with good drop impact resistance.

[0095] In contrast, the water-dispersed PSA composition of Comparative Example 1 (containing no carboxylic acid copolymer thickener and a polyacrylic acid thickener ratio of 2.27% by mass) exhibited cissing during coating, and a PSA sheet could not be formed. The water-dispersed PSA composition of Comparative Example 2 (containing 0.04% by mass of carboxylic acid copolymer thickener and 2.26% by mass of polyacrylic acid thickener) exhibited cissing during coating, and a PSA sheet could not be formed. The water-dispersed PSA composition of Comparative Example 3 (containing no carboxylic acid copolymer thickener and a polyacrylic acid thickener ratio of 4.23% by mass) could not form a PSA sheet with good drop impact resistance. The water-dispersed PSA composition of Comparative Example 4 (containing 1.77% by mass of carboxylic acid copolymer thickener and 2.23% by mass of polyacrylic acid thickener) exhibited poor filterability and produced streaks during coating. The water-dispersed PSA composition of Comparative Example 5 (carboxylic acid copolymer thickener ratio: 2.11 mass%, polyacrylic acid thickener ratio: 2.22 mass%) exhibited poor filterability, produced streaks during coating, and failed to form a PSA sheet with good drop impact resistance. The water-dispersed PSA composition of Comparative Example 6 (carboxylic acid copolymer thickener ratio: 0.73 mass%, polyacrylic acid thickener ratio: 0.73 mass%) produced repelling during coating, and failed to form a PSA sheet. The water-dispersed PSA composition of Comparative Example 7 (carboxylic acid copolymer thickener ratio: 0.70 mass%, polyacrylic acid thickener ratio: 3.86 mass%) failed to form a PSA sheet with good drop impact resistance. The water-dispersed PSA composition of Comparative Example 8 (carboxylic acid copolymer thickener ratio: 1.81 mass%, no polyacrylic acid thickener) produced repelling during coating, and failed to form a PSA sheet. The water-dispersible PSA composition of Comparative Example 9 (carboxylic acid copolymer thickener ratio of 2.86 mass%, no polyacrylic acid thickener) had poor filterability and could not form a PSA sheet with good drop impact resistance. The water-dispersible PSA composition of Comparative Example 10 (carboxylic acid copolymer thickener ratio of 2.51 mass%, no polyacrylic acid thickener) caused repelling during coating and could not form a PSA sheet. [Explanation of symbols]

[0096] X adhesive sheet 10 adhesive layer L1, L2 release liner

Claims

1. A water-dispersible PSA composition comprising a water-dispersible polymer, a carboxylic acid copolymer thickener, a polyacrylic acid thickener, and water, the proportion of the carboxylic acid copolymer thickener in the solid content of the aqueous PSA composition is 0.1% by mass or more and 1.5% by mass or less; The proportion of the polyacrylic acid thickener in the solid content is 1% by mass or more and 3.7% by mass or less, the water-dispersible polymer is a water-dispersible acrylic polymer, The water-dispersible pressure-sensitive adhesive composition has a solids concentration of 10% by mass or more and 50% by mass or less.

2. The aqueous PSA composition according to claim 1, wherein the total amount of the carboxylic acid copolymer thickener and the polyacrylic acid thickener in the solid content is 2% by mass or more and 4.2% by mass or less.

3. Shear rate 4 s －１ 2. The aqueous dispersion pressure-sensitive adhesive composition according to claim 1, which has a viscosity of 0.8 Pa·s or less under conditions of 0.1 Pa·s and 30°C.

4. Shear rate 1 x 10 ４ s －１ After shearing under the conditions of 30 ° C., the shear rate was 4 s －１ 2. The aqueous dispersion pressure-sensitive adhesive composition according to claim 1, wherein the viscosity at 30°C is 0.9 Pa·s or more and 1.5 Pa·s or less.

5. The water-dispersed pressure-sensitive adhesive composition according to claim 1 , further comprising a tackifier.

6. The water-dispersed pressure-sensitive adhesive composition according to claim 1 , further comprising a leveling agent.

7. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to claim 1 .

8. The pressure-sensitive adhesive sheet according to claim 7 , wherein the pressure-sensitive adhesive layer has a thickness of 40 μm or less.

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