Aqueous adhesive and adhesive sheet

Abstract

To provide an aqueous adhesive that can form an adhesive layer having appropriate adhesive strength and peelability, with a high non-volatile content and good dispersion stability during high speed shearing, and an adhesive sheet having appropriate adhesive strength and peelability, using the adhesive.SOLUTION: Provided is an aqueous adhesive with a non-volatile content of 40 to 60 wt%, comprising acrylic polymer particles having an average particle diameter (D50) of 40 to 100 μm and acrylic polymer fine particles having an average particle diameter (D50) of 0.1 to 0.6 μm, in which a particle diameter distribution of the aqueous adhesive, measured by laser diffraction scattering, shows only an average particle diameter (D50) of 40 to 100 μm derived from the acrylic polymer, and change rates in viscosity and average particle diameter after high speed shearing are within specified ranges.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] An embodiment of the present invention relates to a water-based pressure-sensitive adhesive and a pressure-sensitive adhesive sheet. [Background technology]

[0002] As a pressure-sensitive adhesive sheet, a pressure-sensitive adhesive sheet having removability is known. For example, a pressure-sensitive adhesive sheet that includes a pressure-sensitive adhesive layer and a substrate, contains polymer particles in the pressure-sensitive adhesive layer, is used by attaching the pressure-sensitive adhesive layer surface of the pressure-sensitive adhesive sheet to an adherend, and can be repeatedly peeled from and attached to the adherend as necessary is widely used.

[0003] For example, Patent Document 1 describes a removable adhesive sheet in which an adhesive containing a spherical adhesive and an emulsion-type binder adhesive is applied to one side of a base sheet to form an adhesive layer, and the spherical adhesive is either spherical adhesive (A) obtained by polymerizing an ethylenically unsaturated monomer in the presence of 0.1 to 3 parts by mass of polyacrylic acid per 100 parts by mass of the ethylenically unsaturated monomer component, or spherical adhesive (B) obtained by adding 0.1 to 7 parts by mass of polyacrylic acid per 100 parts by mass of the solid content of the spherical adhesive to the spherical adhesive obtained by polymerizing the ethylenically unsaturated monomer.

[0004] Furthermore, Patent Document 2 describes an aqueous removable adhesive and adhesive sheet comprising acrylic particles (I) having a D50 average particle size of 20 to 60 μm, acrylic particles (i) having a D50 average particle size of 0.1 to 0.6 μm, and a crosslinking agent, the acrylic particles (i) being obtained by polymerizing a monomer mixture containing a carboxyl group-containing monomer, a hydroxyl group-containing monomer, and other monomers in the presence of an alkali metal salt of an oxyacid and an alkali metal salt of polyphosphoric acid, an anionic reactive emulsifier, and a nonionic nonreactive emulsifier having a repeating number of 7 to 20 ethylene oxide units. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2006 / 104235 [Patent Document 2] JP 2015-105353 A Summary of the Invention [Problem to be solved by the invention]

[0006] A pressure-sensitive adhesive sheet having removability is required to have appropriate adhesion and releasability.However, generally, a pressure-sensitive adhesive layer having sufficient adhesion tends to have poor releasability, while a pressure-sensitive adhesive layer having good releasability tends to have insufficient adhesion.Furthermore, in order to develop appropriate adhesion, it is necessary to reduce the moisture of the pressure-sensitive adhesive and increase the non-volatile content of the pressure-sensitive adhesive, while there is a problem that the dispersion stability of the pressure-sensitive adhesive decreases when the pressure-sensitive adhesive is subjected to high-speed shearing in a coating machine.

[0007] Therefore, an object of the present invention is to provide an aqueous adhesive that can form an adhesive layer having appropriate adhesive strength and peelability, has a high non-volatile content, and has good dispersion stability of the adhesive during high-speed shearing.Another object of the present invention is to provide an aqueous adhesive sheet having appropriate adhesive strength and peelability. [Means for solving the problem]

[0008] Examples of embodiments are given below. The present invention is not limited to the following embodiments. (1) Acrylic polymer particles (I) having an average particle size (D50) of 40 to 100 μm; and (i) acrylic polymer fine particles having an average particle size (D50) of 0.10 to 0.6 μm, The particle size distribution of the water-based adhesive measured by the laser diffraction scattering method showed that only acrylic polymer particles (I) with an average particle size (D50) of 40 to 100 μm were observed. The present invention is characterized in that the following (1) and (2) are simultaneously satisfied: A water-based adhesive with a non-volatile content of 40 to 60% by mass. (1) (X2 / X1) × 100≦20(%) X1: Initial viscosity (mPas s), X2: Viscosity after high-speed shear (mPas s) (2) (Y2 / Y1) × 100≦20(%) Y1: Initial average particle size (D50) (μm), Y2: Average particle size after high-speed shear (D50) (μm) Note that "after high-speed shearing" refers to the state after the water-based adhesive is rotated and stirred for 10 minutes at a rotation speed of 10,000 rpm using a homomixer.

[0009] (2) The above aqueous pressure-sensitive adhesive, wherein the content ratio of the acrylic polymer particles (I) to the acrylic polymer fine particles (i) is 70 / 30 to 50 / 50.

[0010] (3) The acrylic polymer microparticles (i) contain a (meth)acrylic acid alkyl ester monomer (a), a carboxyl group-containing monomer (b) and a hydroxyl group-containing monomer (c), The aqueous pressure-sensitive adhesive comprises acrylic polymer microparticles (i') which are emulsion polymers of a monomer mixture in which the content of the carboxyl group-containing monomer (b) is 1 to 10 mass% and the content of the hydroxyl group-containing monomer (c) is 1 to 10 mass% based on 100 mass% of the monomer mixture.

[0011] (4) The above aqueous pressure-sensitive adhesive, wherein the acrylic polymer fine particles (i') are an emulsion polymer of a monomer composition containing 2 to 10 parts by mass of an anionic emulsifier (d) per 100 parts by mass of a monomer mixture.

[0012] (5) A pressure-sensitive adhesive sheet comprising a substrate and a pressure-sensitive adhesive layer formed from the water-based pressure-sensitive adhesive on at least one surface of the substrate. Effect of the Invention

[0013] According to an embodiment of the present invention, it is possible to provide an aqueous adhesive capable of forming an adhesive layer having appropriate adhesive strength and peelability, and further to provide an aqueous adhesive having a high non-volatile content and good dispersion stability of the adhesive when subjected to high speed shear, and an adhesive sheet having an adhesive layer made of the aqueous adhesive. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 shows the particle size distribution measured by a laser diffraction scattering method using the water-based pressure sensitive adhesive of Example 1. [Diagram 2] FIG. 2 shows the particle size distribution measured by a laser diffraction scattering method using the aqueous pressure sensitive adhesive of Comparative Example 6. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] An embodiment of the present invention will be described below, but the present invention is not limited to the following embodiment.

[0016] In this specification, any numerical range specified using "to" is intended to include the numerical values ​​before and after "to" as the lower and upper limit values ​​of the range.

[0017] <Water-based adhesive> The aqueous pressure-sensitive adhesive according to one embodiment of the present invention contains acrylic polymer particles (I) having an average particle size of 40 to 100 μm and acrylic polymer fine particles (i) having an average particle size of 0.1 to 0.6 μm. The aqueous pressure-sensitive adhesive of the present invention may further contain any component other than the acrylic polymer particles (I) and the acrylic polymer fine particles (i).

[0018] The aqueous pressure-sensitive adhesive of the present invention has only a peak of average particle size (D50) of 40 to 100 μm, mainly composed of acrylic polymer particles (I), in the particle size distribution measured by a laser diffraction scattering method. According to a preferred embodiment, the aqueous pressure-sensitive adhesive includes acrylic polymer particles (i') obtained by polymerizing a monomer mixture in which the acrylic polymer particles (i) contain a (meth)acrylic acid alkyl ester monomer (a), a carboxyl group-containing monomer (b) and a hydroxyl group-containing monomer (c), and the monomer mixture contains 1 to 10 mass% of the monomer (b) containing a carboxyl group-containing monomer and 1 to 10 mass% of the monomer (c) containing a hydroxyl group-containing monomer, based on 100 mass% of the monomer mixture. The "average particle size of acrylic polymer particles (I) as the main component" refers to the "average particle size of acrylic polymer particles (I) to which at least some of the acrylic polymer microparticles (i) are attached" in the case where at least some of the acrylic polymer microparticles are attached to the surface of the acrylic polymer particles in the aqueous pressure sensitive adhesive.

[0019] [Acrylic polymer particles (I)] The average particle size (D50) of the acrylic polymer particles (I) is 40 μm or more, preferably 50 μm or more, and more preferably 60 μm or more. The average particle size of the acrylic polymer particles is 100 μm or less, preferably 95 μm or less, and more preferably 90 μm or less. In this specification, the average particle size of the acrylic polymer particles is the median size (D50) determined by the volume-based particle size distribution.

[0020] The average particle size can be measured using a laser diffraction scattering type particle size measuring device (for example, "Microtrac MT-3300" manufactured by Microtrac Bell Co., Ltd.). The measurement conditions are a particle refractive index of 1.44 and a non-spherical particle shape. For the measurement, a sample prepared by diluting the suspension polymer with water as necessary to a concentration suitable for the measurement can be used. The suspension polymer will be described later.

[0021] When the average particle size (D50) is 40 μm or more, good peelability can be obtained, and when the average particle size is 100 μm or less, appropriate adhesive strength can be obtained.

[0022] The acrylic polymer particles (I) preferably include acrylic polymer particles obtained by suspension polymerization of monomers including a (meth)acrylic acid alkyl ester monomer (A) and a carboxyl group-containing monomer (B). The monomer (A) and suspension polymerization will be described later. The acrylic polymer particles more preferably include the acrylic polymer particles (I') of the following embodiment.

[0023] (Acrylic polymer particles (I')) The acrylic polymer particles (I') according to one embodiment of the present invention are obtained by suspension polymerization of the monomers in a monomer composition containing, relative to 100 mass% of a monomer mixture containing a (meth)acrylic acid alkyl ester monomer (A) and a carboxyl group-containing monomer (B), 0.5 to 5 mass% of an anionic emulsifier (D) containing an ethylene oxide structure in the molecule, 20 to 90 mol% of an alkali metal hydroxide (E) relative to the molar amount of carboxyl groups contained in the carboxyl group-containing monomer (B), and 0.01 to 1 mass% of a cellulose-based polymer (F) relative to 100 mass% of the monomer (A). The acrylic polymer particles (I') can be produced, for example, by the production method described below.

[0024] (Meth)acrylic acid alkyl ester monomer (A) The (meth)acrylic acid alkyl ester monomer (A) is a monomer having one (meth)acryloyloxy group and one alkyl group in the molecule. In this specification, "(meth)acrylic" is used as a general term for "acrylic" and "methacrylic". In this specification, "(meth)acryloyl" is used as a general term for "acryloyl" and "methacryloyl".

[0025] The alkyl group contained in the (meth)acrylic acid alkyl ester monomer may be linear, branched, or cyclic, and is preferably linear or branched. By using a linear or branched group, polymerization stability during suspension polymerization is further improved. The number of carbon atoms in the alkyl group is preferably 1 to 20, more preferably 1 to 15, and even more preferably 1 to 10.

[0026] Examples of the (meth)acrylic acid alkyl ester monomer include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, dodecyl (meth)acrylate, tetradecyl (meth)acrylate, hexadecyl (meth)acrylate, octadecyl (meth)acrylate, lauryl (meth)acrylate, etc. The (meth)acrylic acid alkyl ester monomer (A) can be used alone or in combination of two or more. The (meth)acrylic acid alkyl ester monomer (A) preferably contains an acrylic acid alkyl ester monomer, more preferably contains at least one selected from butyl acrylate and 2-ethylhexyl acrylate. By containing an acrylic acid alkyl ester monomer, the flexibility of the obtained adhesive is further increased.

[0027] Carboxyl group-containing monomer (B) The carboxyl group-containing monomer (B) is a monomer having at least one polymerizable unsaturated group and at least one carboxyl group in the molecule. The polymerizable unsaturated group is preferably a polymerizable carbon-carbon double bond-containing group, more preferably a CH 2 =CH- group (vinyl group), CH 2 =C(CH 3)-group, (meth)acryloyl group, and (meth)acryloyloxy group. Examples of the carboxyl group-containing monomer include (meth)acrylic acid, monohydroxyethyl phthalate (meth)acrylate, p-carboxybenzyl (meth)acrylate, monohydroxyethyl succinate (meth)acrylate, β-carboxyethyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid. The carboxyl group-containing monomer (B) may be used alone or in combination of two or more. The carboxyl group-containing monomer (B) preferably contains (meth)acrylic acid, and more preferably contains acrylic acid. By containing (meth)acrylic acid, the polymerization stability during suspension polymerization and the dispersion stability of the adhesive are further improved.

[0028] The monomer mixture constituting the acrylic polymer particles (I') may contain other monomers other than the (meth)acrylic acid alkyl ester monomer (A) and the carboxyl group-containing monomer (B). Examples of other monomers include polyfunctional (meth)acrylic acid alkyl ester monomers such as alkyl di(meth)acrylate and alkyl tri(meth)acrylate; aromatic ring-containing (meth)acrylic acid ester monomers such as phenyl (meth)acrylate, phenoxyethyl (meth)acrylate, and benzyl (meth)acrylate; styrene-based monomers such as styrene and α-methylstyrene; vinyl ether-based monomers such as ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, and isobutyl vinyl ether; fatty acid vinyl-based monomers such as vinyl acetate and vinyl propionate; and functional group-containing monomers other than carboxyl groups such as hydroxyl groups, amino groups, mercapto groups, and oxetanyl groups.

[0029] The content of the (meth)acrylic acid alkyl ester monomer (A) is preferably 90 mass % or more, more preferably 92 mass % or more, and even more preferably 95 mass % or more, in 100 mass % of the monomer mixture. When the content is 90% by mass or more, the polymerization rate increases, and the polymerization stability during suspension polymerization and the dispersion stability of the adhesive are further improved. The content of the (meth)acrylic acid alkyl ester monomer (A) may be, for example, 99.5% by mass or less, 99.0% by mass or less, or 98.0% by mass or less based on the total mass of the monomers, taking into account the content of the carboxyl group-containing monomer (B).

[0030] From the viewpoint of dispersion stability of the monomer composition during polymerization, the content of the carboxyl group-containing monomer (B) is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and even more preferably 2.0% by mass or more, based on 100% by mass of the monomer mixture. By being 0.5% by mass or more, the polymerization stability during suspension polymerization and the dispersion stability of the adhesive are further improved. The content of the carboxyl group-containing monomer (B) is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less, based on 100% by mass of the monomer mixture. When the content is 20% by mass or less, the viscosity of the suspension polymer obtained by suspension polymerization can be reduced.

[0031] The content of the other monomer is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less, based on 100% by mass of the monomer mixture. When the content is 20% by mass or less, the polymerization rate can be increased.

[0032] The content of the monomer in the monomer composition for producing the acrylic polymer particles (I') is preferably 70% by mass or more and less than 100% by mass, based on 100% by mass of the solid content of the monomer composition excluding the solvent. When the content of the monomer is 70% by mass or more, the polymerization rate can be increased. The content of the monomer is preferably 75% by mass or more, more preferably 80% by mass or more.

[0033] Anionic emulsifiers (D) The monomer composition for producing the acrylic polymer particles (I') contains an anionic emulsifier (D) containing an ethylene oxide structure in the molecule. The anionic emulsifier (D) contains an ethylene oxide structure in the molecule, and further has at least one anionic functional group and at least one lipophilic group as a hydrophilic group. The anionic emulsifier (D) can be used alone or in combination of two or more.

[0034] Examples of anionic functional groups include carboxylic acid groups, carboxylate groups, sulfonic acid groups, sulfonate groups, phosphoric acid groups, and phosphoric acid groups. The cation contained in the salt may be, for example, sodium, potassium, ammonium, and the like. The lipophilic group may be a monovalent group containing carbon atoms, and examples of the lipophilic group include alkyl groups, alkenyl groups, aryl groups, heteroaryl groups, arylalkyl groups, and alkylaryl groups. The lipophilic group is preferably a monovalent group having 6 or more carbon atoms. By using a monovalent group having 6 or more carbon atoms, the emulsifying power is increased, and the stability during suspension polymerization and the dispersion stability of the adhesive are further improved.

[0035] The ethylene oxide structure contained in the anionic emulsifier (D) may be a polyethylene oxide structure. The anionic emulsifier (D) contains, for example, an anionic emulsifier containing a polyethylene oxide structure having 2 or more ethylene oxide structures. The number of ethylene oxide structures contained in the polyethylene oxide structure is preferably 5 or more, more preferably 7 or more, and even more preferably 10 or more. When the anionic emulsifier (D) contains a polyethylene oxide structure, the hydrophilicity of the emulsifier increases, and the stability during suspension polymerization tends to be improved. The number of ethylene oxide structures contained in the polyethylene oxide structure is, for example, 100 or less, preferably 80 or less, and more preferably 60 or less. When the number of ethylene oxide structures is 100 or less, the balance between hydrophilicity and lipophilicity is good, and the stability during suspension polymerization tends to be improved.

[0036] The weight average molecular weight of the anionic emulsifier (D) is preferably 200 or more, more preferably 300 or more, and even more preferably 500 or more. When the weight average molecular weight is 200 or more, the hydrophilicity of the emulsifier increases, and the stability during suspension polymerization tends to be improved. The weight average molecular weight of the anionic emulsifier (D) is preferably 6,000 or less, more preferably 5,000 or less, and even more preferably 4,000 or less. When the weight average molecular weight is 6,000 or less, the balance between hydrophilicity and lipophilicity is good, and the stability during suspension polymerization tends to be improved.

[0037] In this specification, the weight average molecular weight refers to the weight average molecular weight calculated using standard polystyrene standards by gel permeation chromatography (GPC).

[0038] The anionic emulsifier (D) may be, for example, a compound represented by the following formula (I) or a compound represented by the following formula (II).

[0039] Formula (I) [ka]

[0040] In formula (I), R represents a monovalent group containing a carbon atom, X represents an anionic functional group, and n represents an integer of 1 or more.

[0041] Formula (II) [ka]

[0042] In formula (II), R represents a monovalent group containing a carbon atom, R' represents a divalent group containing a carbon atom, X represents an anionic functional group, and n represents an integer of 1 or more.

[0043] Examples of R include an alkyl group, an alkenyl group, an aryl group, a heteroaryl group, an arylalkyl group, and an alkylaryl group. The alkyl group may be linear, branched, or cyclic. The number of carbon atoms in the alkyl group is preferably 6 to 20, more preferably 8 to 18, and even more preferably 8 to 16. The alkenyl group may be linear, branched, or cyclic. The number of carbon atoms in the alkenyl group is preferably 8 to 20, more preferably 8 to 18, and even more preferably 8 to 16. The aryl group may be a monocyclic ring, a condensed ring containing multiple rings (naphthalene, anthracene, etc.), or a polycyclic ring containing multiple rings bonded by covalent bonds (biphenyl, terphenyl, etc.). The number of carbon atoms in the aryl group is preferably 6 to 20, more preferably 6 to 18, and even more preferably 6 to 16. The heteroaryl group may be a monocyclic ring, a condensed ring containing multiple rings (benzothiophene, benzopyridine, etc.), or a polycyclic ring containing multiple rings bonded by covalent bonds (bithiophene, bipyridine, etc.). The heteroaryl group preferably has 2 to 20 carbon atoms, more preferably 2 to 18 carbon atoms, and further preferably 2 to 16 carbon atoms.

[0044] R is preferably an alkyl group or an aryl group. Preferred examples of the alkyl group include a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group, and an icosyl group. Preferred examples of the aryl group include a phenyl group, a naphthyl group, an anthryl group, a phenanthryl group, a pyrenyl group, a fluorenyl group, and a biphenyl group.

[0045] Examples of R' include an alkylene group and an alkenylene group. The alkylene group may be linear, branched, or cyclic. The number of carbon atoms in the alkylene group is preferably 1 to 10, more preferably 1 to 8, and even more preferably 1 to 5. The alkenylene group may be linear, branched, or cyclic. The number of carbon atoms in the alkenylene group is preferably 1 to 10, more preferably 1 to 8, and even more preferably 1 to 5.

[0046] X represents an anionic functional group. Examples of X include -COO - Y + , -SO 3 - Y + , -PO(O - Y + ) 2 etc. + Examples of each independently include H + , Na + , K + , N.H. 4 + etc.

[0047] n represents an integer of 1 or more, and is preferably 2 or more. n is preferably 10 or more, more preferably 20 or more or 30 or more, and even more preferably 50 or more. n is preferably 100 or less, more preferably 90 or less, and even more preferably 80 or less.

[0048] Examples of the anionic emulsifier (D) include carboxylate-type anionic emulsifiers, sulfonic acid-type anionic emulsifiers, sulfate-type anionic emulsifiers, phosphate-type anionic emulsifiers, etc. From the viewpoint of stability during suspension polymerization, sulfate-type anionic emulsifiers are preferred.

[0049] Commercially available anionic emulsifiers (D) include, for example, "Newcol(R) 1000-SN", "Newcol(R) 1105-SN", "Newcol(R) 1305-SN", "Newcol(R) 1703-SFD", "Newcol(R) 707-SF", "Newcol(R) 707-SFC", "Newcol(R) 707-SN", "Newcol(R) 723-SF", and "Newcol(R) 740-SF" (a compound represented by formula (I) (R is an aryl group, X is -SO) manufactured by Nippon Nyukazai Co., Ltd.) 3 - Y + , Y is NH 4 + ) manufactured by Kao Corporation, "Latemul E-118B" and "Latemul E-150" (a compound represented by the formula (I) (R is an alkyl group, X is -SO 3- Y + , Y is Na + ) manufactured by Lion Corporation; "Sunol TD-3130" (a compound represented by the formula (I) (R is an alkyl group, X is -SO 3 - Y + , Y is Na + )) etc.

[0050] The content of the anionic emulsifier (D) is 0.5 to 5 parts by mass relative to 100 parts by mass of the monomer mixture containing the (meth)acrylic acid alkyl ester monomer (A) and the carboxyl group-containing monomer (B). When the content of the anionic emulsifier (D) is 0.5 parts by mass or more, the stability during suspension polymerization tends to be excellent. The content of the anionic emulsifier (D) is preferably 0.6 parts by mass or more, more preferably 0.7 parts by mass or more. When the content of the anionic emulsifier (D) is 5 parts by mass or less, the adhesive strength of the obtained pressure-sensitive adhesive sheet tends to be increased. The content of the anionic emulsifier (D) is preferably 4 parts by mass or less, more preferably 3 parts by mass or less.

[0051] Alkali metal hydroxides (E) The monomer composition for producing the acrylic polymer particles (I') contains an alkali metal hydroxide (E). Examples of the alkali metal hydroxide (E) include sodium hydroxide and potassium hydroxide.

[0052] The content of the alkali metal hydroxide (E) is 20 to 90 mol % based on the molar amount of the carboxyl group contained in the carboxyl group-containing monomer (B). When the content of the alkali metal hydroxide (E) is 20 mol % or more, the stability during suspension polymerization tends to be excellent. The content of the alkali metal hydroxide (E) is preferably 25 mol % or more, more preferably 30 mol % or more. When the content of the alkali metal hydroxide (E) is 90 mol % or less, the stability during suspension polymerization tends to be excellent. The content of the alkali metal hydroxide (E) is preferably 85 mol % or less, more preferably 80 mol % or less.

[0053] Cellulosic polymers (F) The monomer composition for producing the acrylic polymer particles (I') contains a cellulose-based polymer (F). Examples of the cellulose-based polymer (F) include cellulose and cellulose in which some or all of the hydroxyl groups are substituted with monovalent groups containing carbon atoms. The cellulose-based polymer (F) can be used alone or in combination of two or more.

[0054] Examples of the monovalent group containing a carbon atom include an alkyl group (e.g., having 1 to 3 carbon atoms), an alkoxy group (e.g., having 1 to 3 carbon atoms), a carboxyalkyl group (e.g., an alkyl group having 1 to 3 carbon atoms), a hydroxyalkyl group (e.g., an alkyl group having 1 to 3 carbon atoms), an alkylene oxide-containing group (e.g., an alkylene group having 2 or 3 carbon atoms), etc. Examples of the alkylene oxide-containing group include an alkoxyalkyl group, a carboxyalkoxy group, a hydroxyalkoxy group, a poly(alkylene oxide)-containing group, etc.

[0055] The etherification degree of the cellulose-based polymer (F) is preferably 0.7 to 2.0, more preferably 0.8 to 1.8, and even more preferably 0.9 to 1.5. The etherification degree is the average number of hydroxyl groups reacted with a substitute (carboxymethyl group) per anhydrous glucose unit. When the etherification degree is 0.7 or more, the viscosity during suspension polymerization becomes sufficient, and the stability of the particles obtained by suspension polymerization can be improved. When the etherification degree is 2.0 or less, the cellulose-based polymer (F) has a high solubility in water and tends to be easy to handle.

[0056] The degree of etherification can be determined by weighing out approximately 1 g of the sample, wrapping it in filter paper, placing it in a magnetic crucible, and incinerating it at 600°C. The sodium hydroxide produced is titrated with 0.1 N sulfuric acid using phenolphthalein as an indicator, and the amount of sulfuric acid required for the neutralization titration (A (ml)) and the potency of 0.1 N sulfuric acid (f) are calculated using the following formula. Degree of etherification = (162 x A x f) ÷ {10,000 - (80 x A x f)}

[0057] When an aqueous solution containing a cellulose-based polymer (F) at a concentration of 1% by mass is prepared and the viscosity of the aqueous solution is measured, the viscosity is preferably 500 mPas·s or more, more preferably 1,000 mPas·s or more, and even more preferably 1,500 mPas·s or more. When the viscosity is 500 mPas·s or more, the viscosity during suspension polymerization is sufficient, and the stability of the particles obtained by suspension polymerization can be increased. The viscosity of the aqueous solution is preferably 20,000 mPas·s or less, more preferably 15,000 mPas·s or less, and even more preferably 10,000 mPas·s or less. When the viscosity is 20,000 mPas·s or less, the solubility of the cellulose-based polymer (F) in water is high, and handling tends to be easy. The viscosity can be measured using a BL type viscometer at 25°C, rotor No. 4, and 60 rpm.

[0058] The cellulose-based polymer (F) may be, for example, a polymer containing a structure represented by the following formula (III).

[0059] Formula (III) [ka]

[0060] In formula (III), each R independently represents a monovalent group containing a hydrogen atom or a carbon atom. n represents an integer of 2 or more. Examples of the monovalent group containing a carbon atom include -C p H 2p+1 , -C p H 2p COOH, -C p H 2p COO - Y + , -C p H 2p OH, -(C p H 2p O) q C r H 2r+1 p represents an integer of 1 or more, q represents an integer of 1 or more, and r represents an integer of 0 or more. Y represents H+ , Na + , K + , N.H. 4 + and the like cations.

[0061] Examples of the cellulose-based polymer (F) include methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, etc. From the viewpoint of stability during suspension polymerization, carboxymethyl cellulose is preferred.

[0062] As a commercially available product of the cellulose-based polymer (F), for example, “CMC Daicel (sodium carboxymethylcellulose, product numbers 1180, 1190, 1380, 1390, 2200, 2260, 2280)” manufactured by Daicel Miraizu Co., Ltd. (polymer having a structure represented by formula (III) (each R is independently -H or -CH 2 COONa)), "HEC DAICEL (hydroxyethyl cellulose, product numbers SP600, SP850, SP900, SE600, SE850, SE900)" (polymers containing a structure represented by formula (III) (each R is independently -H or -(CH 2 CH 2 O) q H (q is a number of 2 or more)); "Metolose(R) methylcellulose for food additives (MCE type), grades: 1500, 4000" manufactured by Shin-Etsu Chemical Co., Ltd. (a polymer having a structure represented by formula (III) (each R is independently -H or -CH 3 )), "Metolose(R) Hydroxypropyl methylcellulose (HPMC) for food additives (SFE type, SE type, NE type), Grade: 4000" (polymer containing a structure represented by formula (III) (R is each independently -H, -CH 3 or -CH 2 CHOHCH 3 )), "Metolose(R) methylcellulose (MC) (SM type), grade: 4000, 8000" (polymer containing a structure represented by formula (III) (each R is independently -H or -CH 3)), "Metolose(R) Hydroxypropylmethylcellulose (HPMC) (60SH type, 65SH type, 90SH type), Grades: 4000, 10000, 15000, 30000" (polymer containing a structure represented by formula (III) (R is each independently -H, -CH 3 or -CH 2 CHOHCH 3 )), "Metolose(R) Hydroxyethylmethylcellulose (HEMC) (SEB type, SNB type), Grades: 04T, 30T, 60T" (polymer containing a structure represented by formula (III) (R is each independently -H, -CH 3 or -CH 2 CHOH) etc.

[0063] The content of the cellulose-based polymer (F) is 0.01 to 1 mass% relative to 100 mass parts of the monomer (A). It is preferably 0.02 mass parts or more, more preferably 0.04 mass% or more, and even more preferably 0.06 mass parts or more. By making the content of the cellulose-based polymer (F) 0.01 mass parts or more, the viscosity during suspension polymerization becomes sufficient, and the stability of the particles obtained by suspension polymerization can be increased. The content of the cellulose-based polymer (F) is preferably 0.9 mass parts or less, more preferably 0.8 mass parts or less, and even more preferably 0.7 mass parts or less. By making the content of the cellulose-based polymer (F) 1 mass part or less, it becomes easy to adjust the particle size of the acrylic polymer particles (I').

[0064] Optional ingredients The monomer composition for producing the acrylic polymer particles (I') may further contain any component other than the components (A), (B), (D), (E) and (F). The monomer composition usually contains a solvent. The solvent preferably contains water. The solvent may be, for example, a solvent consisting of only water, or a mixed solvent containing water and a hydrophilic solvent such as alcohol. Optional components include a polymerization initiator; a chain transfer agent; a thickener; a polymer other than a cellulose-based polymer; and an emulsifier such as a nonionic emulsifier or an anionic emulsifier not containing an ethylene oxide structure in the molecule.

[0065] The polymerization initiator is preferably an oil-soluble polymerization initiator. Examples of the oil-soluble polymerization initiator include benzoyl peroxide, lauroyl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxypivalate, t-butyl peroxybenzoate, t-butyl peroxy-2-ethylhexanoate, 2,2'-azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis-2,4-dimethylvaleronitrile, 2,2'-azobis-4-methoxy-2,4-dimethylvaleronitrile, and 2,2'-azobismethylisobutyrate. The polymerization initiator can be used alone or in combination of two or more. From the viewpoint of the reaction rate during suspension polymerization, organic peroxides are preferred, and benzoyl peroxide is more preferred.

[0066] The content of the polymerization initiator is preferably 0.01 to 1 part by mass, more preferably 0.05 to 0.8 parts by mass, and even more preferably 0.1 to 0.5 parts by mass, relative to 100 parts by mass of the monomer composition. When the content is 0.01 part by mass or more, the polymerization reaction during suspension polymerization tends to proceed quickly. When the content is 1 part by mass or less, the polymerization reaction during suspension polymerization does not occur suddenly, and the reaction heat can be controlled.

[0067] The chain transfer agent may be, for example, a compound having a sulfhydryl group or a hydroxyl group. Examples of the compound having a sulfhydryl group include thiols such as lauryl mercaptan, 2-mercaptoethyl alcohol, dodecyl mercaptan, and mercaptosuccinic acid; alkyl mercaptopropionates such as n-butyl mercaptopropionate and octyl mercaptopropionate; and alkoxyalkyl mercaptopropionates such as methoxybutyl mercaptopropionate. Examples of the compound having a hydroxyl group include alcohols such as methyl alcohol, n-propyl alcohol, isopropyl alcohol, t-butyl alcohol, and benzyl alcohol. The chain transfer agent can be used alone or in combination of two or more.

[0068] The content of the chain transfer agent is preferably 0 to 0.5 parts by mass, more preferably 0 to 0.4 parts by mass, and even more preferably 0 to 0.3 parts by mass, relative to 100 parts by mass of the monomer composition. When the content is 0.5 parts by mass or less, the gel fraction of the acrylic particles obtained by suspension polymerization increases, and the adhesive sheet obtained from the acrylic particles has good removability.

[0069] (Method of producing acrylic polymer particles (I')) The method for producing acrylic polymer particles (I') according to one embodiment of the present invention includes preparing a monomer composition containing a specific amount of (meth)acrylic acid alkyl ester monomer (A), a carboxyl group-containing monomer (B), an anionic emulsifier (D) containing an ethylene oxide structure in the molecule, an alkali metal hydroxide (E) and a cellulose-based polymer (F); and suspending and polymerizing the monomer (A) and the monomer (B). In this specification, preparing the monomer composition may be referred to as a "preparation step", and suspending and polymerizing the monomers containing the monomer (A) and the monomer (B) may be referred to as a "polymerization step". The method for producing acrylic polymer particles (I') may further include any step.

[0070] (Preparation process) In the preparation step, a monomer composition is prepared that contains at least 0.5 to 5 parts by mass of an anionic emulsifier (D) containing an ethylene oxide structure in the molecule, 20 to 80 mol % of an alkali metal hydroxide (E) relative to the molar amount of the carboxyl group contained in the carboxyl group-containing monomer (B), and 0.01 to 1 part by mass of a cellulose-based polymer (F) relative to 100 parts by mass of the monomer (A), relative to a total of 100 parts by mass of the monomers including the (meth)acrylic acid alkyl ester monomer (A) and the carboxyl group-containing monomer (B). The monomer composition may further contain any component other than the components (A), (B), (D), (E), and (F). The mixing method is not particularly limited, and a method of adding all the components in order into a container and stirring the mixture can be used. Alternatively, a method of adding some of the components in order into one container and stirring the mixture to obtain a composition, adding the remaining components in order into another container and stirring the mixture to obtain a composition, and then mixing the two compositions and stirring the mixture can be used.

[0071] (Polymerization process) In the polymerization step, the monomer (A) and the carboxyl group-containing monomer (B) are suspension polymerized. From the viewpoint of increasing the polymerization rate, the polymerization reaction temperature is preferably 70° C. or higher, and more preferably 80° C. or higher. From the viewpoint of safety, the polymerization reaction temperature is preferably 96° C. or lower, and more preferably 90° C. or lower. From the viewpoint of safety, the polymerization reaction time is preferably 4 hours or longer, and more preferably 5 hours or longer. From the viewpoint of productivity, the polymerization reaction time is preferably 12 hours or shorter, and more preferably 10 hours or shorter.

[0072] A suspension polymer containing acrylic polymer particles (I') is obtained by suspension polymerization of a monomer using a monomer composition. The acrylic polymer particles (I') are particles obtained by suspension polymerization of a monomer. The suspension polymer may further contain each component remaining without reacting, reaction by-products, etc.

[0073] (Optional process) The method for producing the acrylic polymer particles (I') may further include, as optional steps, a step of neutralizing the acrylic polymer particles (I'), a step of separating the acrylic polymer particles (I') from the suspension polymer, a step of washing the acrylic polymer particles (I'), etc. A basic compound can be used for the neutralization. Examples of the basic compound include ammonia; amines such as monoethylamine, dimethylethanolamine, and methylpropanolamine, etc.

[0074] According to the manufacturing method of the embodiment of the present invention, it is possible to manufacture acrylic polymer particles (I') having a desired average particle size, particularly a large average particle size. The monomer composition used in the manufacturing method contains an anionic emulsifier (D) containing an ethylene oxide structure in the molecule and a cellulose polymer (F). This is thought to improve the dispersion stability of the monomer composition in suspension polymerization, and to allow the monomer to be dispersed in the monomer composition at an appropriate size and high concentration. Furthermore, it is thought to prevent the monomer composition from separating into a layer containing the monomer and a layer containing the solvent. As a result, it is possible to obtain acrylic polymer particles (I') having a high concentration and a large average particle size.

[0075] The average particle size of the acrylic polymer particles (I') can be adjusted, for example, by changing the contents of the components contained in the monomer composition, such as the anionic emulsifier (D) and the alkali metal hydroxide (C). The average particle size of the acrylic polymer particles (I') tends to be large when the dispersion stability of the monomer composition is good.

[0076] For example, the larger the content of the anionic emulsifier (D), the smaller the average particle size of the acrylic polymer particles (I'), and the smaller the content of the anionic emulsifier (D), the larger the average particle size of the acrylic polymer particles (I').For example, the larger the content of the alkali metal hydroxide (E), the smaller the average particle size of the acrylic polymer particles (I'), and the smaller the content of the alkali metal hydroxide (C), the larger the average particle size of the acrylic polymer particles (I').

[0077] [Acrylic polymer particles (i)] The average particle size (D50) of the acrylic polymer fine particles (i) is 0.1 μm or more, preferably 0.12 μm or more, more preferably 0.15 μm or more, and the average particle size of the acrylic polymer particles is 0.6 μm or less, preferably 0.5 μm or less, more preferably 0.4 μm or less.

[0078] The average particle size can be measured using a laser diffraction scattering type particle size measuring device (for example, Microtrac MT-3300 manufactured by Microtrac Bell Co., Ltd.). The measurement conditions are a particle refractive index of 1.44 and a non-spherical particle shape. In this case, a sample prepared by diluting the emulsion polymer with water as necessary to a concentration suitable for the measurement can be used for the measurement. The emulsion polymer will be described later.

[0079] When the average particle size is 0.1 μm or more, the viscosity of the composition containing the acrylic polymer particles (i) can be kept low, and the dispersion stability of the adhesive can be improved. When the average particle size is 0.6 μm or less, after mixing with the acrylic polymer particles (I), one peak can be obtained in the particle size distribution measured by the laser diffraction scattering method.

[0080] The acrylic polymer microparticles (i) preferably contain (meth)acrylic acid alkyl ester (a) monomer, carboxyl group-containing monomer (b) and hydroxyl group-containing monomer (c), and include acrylic polymer microparticles (i') obtained by emulsion polymerization of a monomer mixture containing 1 to 10 mass% of monomer (b) including a carboxyl group-containing monomer and 1 to 10 mass% of monomer (c) including a hydroxyl group-containing monomer in 100 mass% of the monomer mixture. The monomers and emulsion polymerization are as described below for the acrylic polymer microparticles (i').

[0081] (Acrylic polymer particles (i')) The acrylic polymer microparticles (i') according to one embodiment of the present invention are obtained by emulsion polymerization of a monomer mixture containing specific amounts of (meth)acrylic acid alkyl ester monomer (a), carboxyl group-containing monomer (b), and hydroxyl group-containing monomer (c). For the emulsion polymerization, it is preferable to use an anionic emulsifier (d). The acrylic polymer microparticles (i') are preferably obtained by emulsion polymerization of the monomers in a monomer composition containing 2 to 10 mass% of anionic emulsifier (d) relative to 100 mass% of the monomer mixture. The acrylic polymer fine particles (i') can be preferably produced, for example, by the production method described below.

[0082] Examples of the (meth)acrylic acid alkyl ester monomer (a) and the carboxyl group-containing monomer (b) include the above-mentioned (meth)acrylic acid alkyl ester monomer (A) and the carboxyl group-containing monomer (B) as well as the monomers exemplified below. Examples of the hydroxyl group-containing monomer (c) include the above-mentioned monomers in which the carboxyl group in the carboxyl group-containing monomer (B) is replaced with a hydroxyl group as well as the monomers exemplified below.

[0083] The (meth)acrylic acid alkyl ester monomer (a) preferably contains at least one selected from the group consisting of 2-ethylhexyl acrylate, butyl acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, and cyclohexyl (meth)acrylate. By using the above-mentioned (meth)acrylic acid alkyl ester monomer (a), the stability during emulsion polymerization and the dispersion stability of the adhesive are further improved. It is more preferable to contain at least one selected from the group consisting of 2-ethylhexyl acrylate, butyl acrylate, and methyl methacrylate.

[0084] The carboxyl group-containing monomer (b) preferably contains at least one selected from the group consisting of (meth)acrylic acid, β-carboxyethyl (meth)acrylate, itaconic acid, crotonic acid, fumaric acid, fumaric anhydride, maleic acid, maleic anhydride, and butyl maleate. By using the above-mentioned (carboxyl group-containing monomer (b), the stability during emulsion polymerization and the dispersion stability of the adhesive are further improved. It is more preferable that the monomer contains (meth)acrylic acid, and even more preferable that the monomer contains acrylic acid.

[0085] The hydroxyl group-containing monomer (c) preferably contains at least one selected from the group consisting of 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 6-hydroxyhexyl (meth)acrylate, as well as polyalkylene glycol (meth)acrylates such as polyethylene glycol (meth)acrylate and polypropylene glycol (meth)acrylate. By using the above-mentioned hydroxyl group-containing monomer (c), the stability during emulsion polymerization and the dispersion stability of the adhesive are further improved. It is more preferable to contain at least one selected from the group consisting of 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, and 4-hydroxybutyl acrylate.

[0086] The content of the (meth)acrylic acid alkyl ester monomer (a) is preferably 80% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more, in 100% by mass of the monomer mixture. When the content is 80% by mass or more, the polymerization rate can be increased. As a result, the cohesive force of the acrylic polymer fine particles is increased, and the removability is further improved. The content of the (meth)acrylic acid alkyl ester monomer (a) may be, for example, 98% by mass or less, 97% by mass or less, or 95% by mass or less, based on the total mass of the monomers, taking into account the contents of the carboxyl group-containing monomer (b) and the hydroxyl group-containing monomer (c).

[0087] The content of the carboxyl group-containing monomer (b) is preferably 1% by mass or more, more preferably 1.2% by mass or more, and even more preferably 1.5% by mass or more in 100% by mass of the monomer mixture, from the viewpoint of the dispersion stability of the monomer composition during polymerization and the stability when mixed with acrylic polymer particles. If the stability after mixing is excellent, the particle size distribution measured by the laser diffraction scattering method tends to have one peak. The content of the carboxyl group-containing monomer (b) is preferably 10% by mass or less, more preferably 7% by mass or less, and even more preferably 5% by mass or less, based on the total mass of the monomers. When the content is 10% by mass or less, the viscosity of the emulsion polymer obtained by emulsion polymerization can be reduced.

[0088] The content of the hydroxyl group-containing monomer (c) is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more in 100% by mass of the monomer mixture, from the viewpoint of the dispersion stability of the monomer composition during polymerization and the stability when mixed with acrylic polymer particles. If the stability after mixing is excellent, the particle size distribution measured by the laser diffraction scattering method tends to have one peak. The content of the hydroxyl group-containing monomer (c) is preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 7% by mass or less, based on the total mass of the monomers. When the content is 10% by mass or less, the viscosity of the emulsion polymer obtained by emulsion polymerization can be reduced.

[0089] The monomer mixture constituting the acrylic polymer fine particles (i') may further contain any monomer other than the (meth)acrylic acid alkyl ester monomer (a), the carboxyl group-containing monomer (b) and the hydroxyl group-containing monomer (c). The content of the optional monomer is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less, based on the total mass of the monomers. When the content is 20% by mass or less, the polymerization rate can be increased.

[0090] The content of the monomer in the monomer composition for producing the acrylic polymer particles (i') is preferably 70% by mass or more and less than 100% by mass, based on 100% by mass of the solid content of the monomer composition excluding the solvent. When the content of the monomer is 70% by mass or more, the polymerization rate can be increased. The content of the monomer is preferably 75% by mass or more, more preferably 80% by mass or more.

[0091] Anionic emulsifiers (d) The monomer composition for producing the acrylic polymer particles (i') preferably contains 2 to 10 parts by mass of an anionic emulsifier (d) relative to 100 parts by mass of the monomer mixture. The anionic emulsifier (d) is not particularly limited, but is preferably an anionic emulsifier containing an ethylene oxide structure in the molecule. The above-mentioned anionic emulsifier (D) can be used as the anionic emulsifier containing an ethylene oxide structure in the molecule. The anionic emulsifier (d) can be used alone or in combination of two or more kinds.

[0092] When the content of the anionic emulsifier (d) relative to 100 parts by mass of the monomer mixture is 2 parts by mass or more, the stability during emulsion polymerization tends to be excellent. The content of the anionic emulsifier (d) relative to 100 parts by mass of the monomer mixture is preferably 3 parts by mass or more, more preferably 4 parts by mass or more. When the content of the anionic emulsifier (d) is 10 parts by mass or less, the adhesive strength of the obtained pressure-sensitive adhesive sheet tends to be increased. The content of the anionic emulsifier (d) is preferably 9 parts by mass or less, more preferably 7 parts by mass or less.

[0093] Optional ingredients The monomer composition for producing the acrylic polymer particles (i') may further contain any component other than the components (a) to (c). The monomer composition usually contains a solvent. The solvent preferably contains water. The solvent may be, for example, a solvent consisting of only water, or a mixed solvent containing water and a hydrophilic solvent such as alcohol. Examples of the optional components include the above-mentioned component (E); the above-mentioned component (F); a polymerization initiator; a chain transfer agent; a thickener; a polymer; and an emulsifier such as a nonionic emulsifier.

[0094] The polymerization initiator is preferably a water-soluble polymerization initiator. The water-soluble polymerization initiator is preferably a peroxide, and may be used in combination with a reducing agent (hereinafter, also referred to as a redox initiator). When a redox initiator is used, the molecular structure of the acrylic polymer fine particles (i') tends to be a linear structure with few branches, and removability is further improved.

[0095] Examples of the peroxide include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate, and tertiary butyl hydroperoxide, etc. Examples of the reducing agent include sodium pyrosulfite, L-ascorbic acid, and iron (II) salts, etc.

[0096] Specific preferred combinations of peroxide and reducing agent in the redox initiator include, for example, a combination of peroxide and ascorbic acid (such as a combination of hydrogen peroxide and ascorbic acid), a combination of peroxide and iron (II) salt (such as a combination of hydrogen peroxide and iron (II) salt), a combination of persulfate and sodium hydrogen sulfite, etc. From the viewpoint of further improving removability, a combination of ammonium persulfate and sodium pyrosulfite is more preferred.

[0097] The content of the polymerization initiator is preferably 0.2 to 1 part by mass, more preferably 0.2 to 0.6 parts by mass, based on 100 parts by mass of the solid content of the monomer composition. When it is 0.2 to 1 part by mass, emulsion polymerization property and removability tend to be further improved. The redox initiator is preferably a peroxide / reducing agent (mass ratio) of about 2 / 1.

[0098] The monomer composition preferably contains a chain transfer agent, which is as described above.

[0099] (Method of producing acrylic polymer fine particles (i')) The method for producing acrylic polymer particles (i') according to one embodiment of the present invention includes preparing a monomer composition containing a monomer mixture containing specific amounts of (meth)acrylic acid alkyl ester monomer (a), carboxyl group-containing monomer (b) and hydroxyl group-containing monomer (c) and 2 to 10 mass% of anionic emulsifier (d) relative to 100 mass% of the monomer mixture; and emulsion-polymerizing the monomers. As in the method for producing acrylic polymer particles (I'), in this specification, preparing the monomer composition may be referred to as a "preparation step" and emulsion-polymerizing the monomers may be referred to as a "polymerization step". The method for producing acrylic polymer particles (i') may further include any optional steps.

[0100] (Preparation process) In the preparation step, a monomer composition is prepared that contains at least a monomer mixture containing (meth)acrylic acid alkyl ester monomer (a), a carboxyl group-containing monomer (b) and a hydroxyl group-containing monomer (c), the monomer mixture containing 1-10 mass% of the carboxyl group-containing monomer (b) and 1-10 mass% of the hydroxyl group-containing monomer (c) in 100 mass% of the monomer mixture, and 2-10 mass parts of an anionic emulsifier (d) relative to 100 mass parts of the monomer mixture. The monomer composition may further contain any component other than the components (a) to (c). The mixing method and the like are the same as those explained in the acrylic polymer particles (I').

[0101] (Polymerization process) In the polymerization step, the monomer mixture is emulsion-polymerized. In the emulsion polymerization, the polymerization reaction temperature is preferably 70° C. or higher, more preferably 80° C. or higher, from the viewpoint of increasing the polymerization rate. The polymerization reaction temperature is preferably 96° C. or lower, more preferably 90° C. or lower, from the viewpoint of safety. The polymerization reaction time is preferably 1 hour or longer, more preferably 2 hours or longer, from the viewpoint of safety. The polymerization reaction time is preferably 12 hours or shorter, more preferably 10 hours or shorter, from the viewpoint of productivity.

[0102] An emulsion polymer containing acrylic polymer fine particles (i') is obtained by emulsion polymerization of monomers using the monomer composition. The acrylic polymer fine particles (i') are particles obtained by emulsion polymerization of monomers. The emulsion polymer may further contain each component remaining without reacting, reaction by-products, etc.

[0103] (Optional process) The method for producing the acrylic polymer fine particles (i') may include any steps, similar to those for producing the acrylic polymer particles (I').

[0104] (Acid value and hydroxyl value) The theoretical acid value of the acrylic polymer fine particles (i') is preferably 5 to 100 mgKOH / g, more preferably 7 to 90 mgKOH / g, and more preferably 10 to 80 mgKOH / g. The theoretical hydroxyl value of the acrylic polymer fine particles (i') is preferably 1 to 50 mgKOH / g, more preferably 2 to 45 mgKOH / g, and more preferably 3 to 40 mgKOH / g.

[0105] The theoretical acid value is calculated as the number of milligrams of potassium hydroxide required to neutralize the acrylic polymer particles contained in 1 g of sample. In other words, the theoretical acid value can be calculated by calculating the number of moles of carboxyl groups contained in 1 g of sample and multiplying this number of moles by the formula weight of potassium hydroxide (KOH), 56.1. The theoretical hydroxyl value is calculated as the number of milligrams of potassium hydroxide required to neutralize the acetic acid bonded to the hydroxyl groups when 1 g of sample is acetylated. In other words, the theoretical acid value can be calculated by calculating the number of moles of hydroxyl groups contained in 1 g of sample and multiplying this number of moles by the formula weight of potassium hydroxide (KOH), 56.1.

[0106] [Properties of water-based adhesive] The aqueous pressure-sensitive adhesive of the present invention has only one peak mainly composed of the acrylic polymer particles (I) in the particle size distribution measured by the laser diffraction scattering method. That is, when the particle size distribution of the particles contained in the aqueous pressure-sensitive adhesive is measured by the laser diffraction scattering method, the obtained particle size distribution has only a peak at an average particle size (D50) of 40 to 100 μm mainly composed of the acrylic polymer particles (I).

[0107] The particle size distribution can be measured for the water-based adhesive using a measuring device that uses the laser diffraction scattering method. For example, the "Microtrack MT-3300" manufactured by Microtrack Bell Co., Ltd. can be used as the measuring device. The measurement conditions are a particle refractive index of 1.44 and a non-spherical particle shape.

[0108] As a method for obtaining an aqueous pressure sensitive adhesive having only one peak, for example, a method for adjusting the affinity of the acrylic polymer microparticles (i) to water can be mentioned. As a method for increasing the affinity to water, a method for increasing the amount of carboxyl group and / or hydroxyl group of the acrylic polymer microparticles (i) by increasing the amount of carboxyl group-containing monomer (b) and / or hydroxyl group-containing monomer (c) in the monomer (a) can be mentioned; a method for increasing the amount of anionic emulsifier (d) in the monomer composition can be mentioned. As a method for decreasing the affinity to water, a method for decreasing the amount of carboxyl group and / or hydroxyl group of the acrylic polymer microparticles by decreasing the amount of carboxyl group-containing monomer (b) and / or hydroxyl group-containing monomer (c) in the monomer (a) can be mentioned; a method for decreasing the amount of anionic emulsifier (d) in the monomer composition can be mentioned.

[0109] The acrylic polymer fine particles (i), which exhibit moderate hydrophilicity, are assumed to behave as if they themselves were an emulsifier, even though they are in the form of fine particles. As a result, in the aqueous pressure-sensitive adhesive, at least a part of the acrylic polymer fine particles (i) adheres to the surface of the acrylic polymer particles (I), and the particle size distribution originating from the acrylic polymer fine particles (i) with an average particle size of 0.1 to 0.6 μm is no longer observed. On the other hand, only the particle size distribution with an average particle size of 40 to 100 μm, which is mainly composed of the acrylic polymer particles (I) covered with the acrylic polymer fine particles (i), is observed. Therefore, when the particle size distribution is obtained by measuring the particle size of all the particles (including the acrylic polymer particles (I) and the acrylic polymer fine particles (i)) contained in the aqueous pressure-sensitive adhesive by the laser diffraction scattering method, the aqueous pressure-sensitive adhesive has only one peak mainly composed of the acrylic polymer particles (I).

[0110] It is believed that the aqueous pressure-sensitive adhesive can form a pressure-sensitive adhesive layer having appropriate adhesive strength and peelability by containing such acrylic polymer particles. Furthermore, it is believed that the dispersion stability of the aqueous pressure-sensitive adhesive after high-speed shearing is improved by covering the acrylic polymer particles (I) with low dispersion stability with the acrylic polymer fine particles (i) with high dispersion stability. The above is a conjecture and does not limit the present invention.

[0111] The aqueous pressure sensitive adhesive of the present invention satisfies the following (1) and (2) at the same time. (1) (X2 / X1) × 100≦20(%) X1: Initial viscosity (mPas s), X2: Viscosity after high-speed shear (mPas s) (2) (Y2 / Y1) × 100≦20(%) Y1: Initial average particle size (D50) (μm), Y2: Average particle size after high-speed shear (D50) (μm) The dispersion stability of the aqueous adhesive after high-speed shearing is measured by stirring the aqueous adhesive for 10 minutes at a rotation speed of 10,000 rpm using a homomixer disperser, and measuring the viscosity and average particle size (D50) before and after stirring. The viscosity can be measured using a BL type viscometer under conditions of 25°C, rotor No. 4, and a rotation speed of 60 rpm. The average particle size (D50) can be measured using a measuring device using the above-mentioned laser diffraction scattering method. Details are described in the Examples section.

[0112] When the values ​​of the formulas (1) and (2) are 20% or less, the dispersion stability of the water-based pressure-sensitive adhesive after high-speed shearing is improved, and the stability of the pressure-sensitive adhesive during coating, which is an issue in coaters such as gravure coaters and knife coaters, is improved. More preferably, the values ​​of the formulas (1) and (2) are 15% or less, and even more preferably, the values ​​of the formulas (1) and (2) are 10% or less.

[0113] The gel fraction of the aqueous pressure-sensitive adhesive is preferably 70 to 100% by mass. When the gel fraction is 70% by mass or more, the removability tends to be good. The gel fraction is more preferably 70 to 95% by mass, and even more preferably 70 to 90% by mass. In this specification, the "gel fraction of the aqueous pressure-sensitive adhesive" refers to the gel fraction of the aqueous pressure-sensitive adhesive excluding the solvent, and can be measured using a pressure-sensitive adhesive layer obtained by applying the aqueous pressure-sensitive adhesive to a substrate and then drying it.

[0114] Specifically, the obtained water-based adhesive was applied to a polyethylene terephthalate (PET) film to a dry thickness of about 20 g / m 2 After coating so that the adhesive layer was dried at 100° C. for 2 minutes, an adhesive layer was formed. Next, an 80 μm-thick release sheet (glassine paper) was attached to this adhesive layer, and aged for 24 hours under conditions of a temperature of 23° C. and a relative humidity of 50%, producing an adhesive sheet with a configuration of "release sheet / adhesive layer / PET film." The gel fraction of the adhesive can be measured by the following method.

[0115] (Adhesive gel fraction (%)) The mass of the 200 mesh wire mesh is measured (this mass is called M). The obtained adhesive sheet is cut into a size of 5 cm x 5 cm and attached to the 200 mesh wire mesh to obtain a test piece. The mass of the obtained test piece is measured (this mass is called A). Note that 200 mesh is the mesh specified in JIS G3555. The test piece is left in 50 ml of ethyl acetate at 50°C for one day. It is then removed and dried at 100°C for 20 minutes, after which its mass is measured (this mass is referred to as T). Next, the polyethylene terephthalate (PET) film is removed from the test piece, the adhesive layer is removed using ethyl acetate, and the mass of the PET film is measured (this mass is referred to as K). The obtained value is substituted into the following formula (1) to calculate the gel fraction. Formula (1) Gel fraction = (TMK) x 100 / (AMK)

[0116] [Composition, manufacturing method, etc. of water-based adhesive] In a preferred embodiment, the mass ratio of the content of the acrylic polymer particles (I) to the content of the acrylic polymer microparticles (i) in the aqueous pressure sensitive adhesive is preferably 70 / 30 to 50 / 50, i.e., the content of the acrylic polymer particles (I) / the content of the acrylic polymer microparticles (i). The mass ratio of 70 / 30 to 50 / 50 tends to improve the adhesive strength and removability. The mass ratio of the content of the acrylic polymer particles (I) to the content of the acrylic polymer microparticles (i) is more preferably 68 / 32 to 52 / 48, and even more preferably 65 / 35 to 55 / 45.

[0117] The aqueous adhesive contains water as a solvent. The aqueous adhesive may contain additives used in general aqueous adhesives as necessary. Examples of additives include neutralizers, defoamers, preservatives, wetting agents, leveling agents, thickeners, coloring pigments, plasticizers, antioxidants, and ultraviolet absorbing agents.

[0118] The nonvolatile content of the aqueous pressure-sensitive adhesive is 40 to 60% by mass. When the nonvolatile content is 40% by mass or more, the adhesive dries well when applied and has high adhesive strength. When the nonvolatile content is 60% by mass or less, the aqueous pressure-sensitive adhesive has good storage stability. The nonvolatile content is preferably 42 to 55% by mass, more preferably 45 to 50% by mass.

[0119] The method for producing the water-based adhesive is not particularly limited. For example, the method for producing the water-based adhesive includes a method of mixing an acrylic polymer particle-containing composition containing acrylic polymer particles (I) having an average particle size of 40 to 100 μm with acrylic polymer fine particles (i) having an average particle size of 0.1 to 0.6 μm. For mixing, a dispersing machine such as a paint conditioner, a ball mill, a sand mill, an attritor, a pearl mill, a co-ball mill, a homomixer, a homogenizer, a wet jet mill, or a microbead mill can be used.

[0120] <Adhesive sheet> The pressure-sensitive adhesive sheet according to one embodiment of the present invention has a substrate and a pressure-sensitive adhesive layer in contact with at least one surface of the substrate, and the pressure-sensitive adhesive layer is formed using the aqueous pressure-sensitive adhesive according to the embodiment. The coating amount of the pressure-sensitive adhesive layer is, for example, 1 to 20 g / m in a dry state. 2 It is.

[0121] Examples of the substrate include paper such as fine paper, coated paper, impregnated paper, synthetic paper, and plastic films such as polyethylene terephthalate film and polyolefin film. Paper is classified into acidic paper and neutral paper depending on the method for fixing the sizing agent. When neutral paper is used as the substrate, there is a tendency to obtain an adhesive layer whose adhesive strength is not likely to decrease over time.

[0122] The pressure-sensitive adhesive sheet may further have a release sheet on the surface of the pressure-sensitive adhesive layer opposite to the surface in contact with the substrate. Examples of the release sheet include paper or plastic film having releasability provided by silicone or the like.

[0123] The pressure-sensitive adhesive sheet can be produced, for example, by applying an aqueous pressure-sensitive adhesive to a release sheet, drying the sheet, and then laminating the sheet to a substrate. Alternatively, the pressure-sensitive adhesive sheet can be produced, for example, by applying an aqueous pressure-sensitive adhesive to a substrate, drying the sheet, and then laminating the sheet to a release sheet. For coating the pressure-sensitive adhesive, known coating devices such as roll coaters such as comma coaters, blade coaters, and gravure coaters, slot die coaters, lip coaters, and curtain coaters can be used.

[0124] In the adhesive layer formed from the aqueous adhesive, the acrylic polymer particles function as a binder and impart adhesiveness to the adhesive layer. The acrylic polymer particles (I) are dispersed in the acrylic polymer particles (i) and form a large number of protrusions on the surface of the adhesive layer. The protrusions (convex portions) have the function of reducing the tack of the adhesive layer. The aqueous adhesive contains the acrylic polymer particles (I) and the acrylic polymer particles (i), and can form an adhesive layer that has a suitable adhesive strength and is easy to peel off. Furthermore, the acrylic polymer particles (I) with low dispersion stability are covered with the acrylic polymer particles (i) with high dispersion stability, thereby improving the dispersion stability of the aqueous adhesive during high-speed shearing. In particular, a good adhesive layer can be obtained when the particle size of the acrylic polymer particles (I) is 40 to 100 μm. EXAMPLES

[0125] 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. In the examples, "parts" means "parts by mass" and "%" means "% by mass".

[0126] (Measurement of weight average molecular weight) The weight average molecular weight was measured using a GPC measuring device under the following conditions: Apparatus: Shodex GPC System-21 (Showa Denko Co., Ltd.) Column: One Shodex KF-602.5 and two Shodex KF-606M (manufactured by Showa Denko K.K.) were used in total three columns connected together. Solvent: Tetrahydrofuran Flow rate: 0.5ml / min Temperature: 40℃ Sample concentration: 0.1wt% Sample injection volume: 50 μl

[0127] (Measurement of average particle size of acrylic polymer particles (I)) The average particle diameter D50 of the acrylic polymer particles (I) was measured using a laser particle size measuring device (Microtrack MT-3300 manufactured by Microtrack Bell Co., Ltd.). The measurement conditions were a particle refractive index of 1.44 and a particle shape of asphericity. The average D50 value of the measurement results obtained three times was used as the average particle diameter D50.

[0128] (Measurement of average particle size of acrylic polymer fine particles (i)) The average particle diameter D50 of the acrylic polymer microparticles (i) was measured using a laser diffraction scattering type particle diameter measuring device (Microtrac MT-3300 manufactured by Microtrac-Bell Co., Ltd.). The measurement conditions were a particle refractive index of 1.44 and a particle shape of asphericity. The average D50 value of the measurement results obtained three times was used as the average particle diameter D50.

[0129] (Measurement of the average particle size of water-based adhesive) The average particle diameter D50 of the water-based adhesive was measured using a laser diffraction scattering particle size measuring device (Microtrack MT-3300, manufactured by Microtrack Bell Co., Ltd.). The measurement conditions were a particle refractive index of 1.44 and a particle shape of asphericity. The average D50 value of the measurement results obtained three times was used as the average particle diameter D50.

[0130] (Measurement of viscosity of cellulosic polymers) The viscosity of the cellulose-based polymer (F) was measured using a BL type viscometer at 25° C. with a rotor No. 4 at 60 rpm.

[0131] (Viscosity measurement of water-based adhesives) The viscosity of the water-based adhesive was measured using a BL type viscometer at 25° C. with a No. 4 rotor at 60 rpm.

[0132] <Production of Acrylic Polymer Particles (I)> (Manufacturing example I-1) [Preparation of monomer dispersion] 95 parts of 2-ethylhexyl acrylate was added to the vessel as the (meth)acrylic acid alkyl ester monomer (a), and 0.27 parts of "Niper BW" (75% benzoyl peroxide powder, manufactured by Nippon Oil & Fats Co., Ltd.) was added as an oil-soluble initiator to dissolve the oil-soluble initiator in 2-ethylhexyl acrylate. Then, 5 parts of acrylic acid was added to the vessel as a carboxyl group-containing monomer to obtain a monomer component. Next, in a separate container, 67.3 parts of deionized water as a solvent, 3.3 parts of "Newcol 707SF" (30% aqueous solution of polyoxyethylene polycyclic phenyl ether sulfate ester ammonium salt, weight average molecular weight 1,000, manufactured by Nippon Nyukazai Co., Ltd.) as an anionic emulsifier (D) containing an ethylene oxide structure in the molecule, 8.0 parts of a 25% aqueous solution of sodium hydroxide as an alkali metal hydroxide (E), and 0.2 parts of "CMC Daicel 2260" (sodium carboxymethylcellulose, degree of etherification 0.9, viscosity 3,000 mPa·s, manufactured by Daicel Miraize Co., Ltd.) as a cellulose-based polymer (F) were added to obtain a water component. The monomer component was added to the water component and mixed by stirring to obtain a monomer dispersion with a viscosity of 50 mPa·s and pH 5. [Suspension polymerization of monomer] The obtained monomer dispersion was placed in a dropping funnel. Separately, 26.3 parts of deionized water was added to a four-neck flask equipped with a stirrer, a cooling tube, a thermometer, and the dropping funnel, and the flask was replaced with nitrogen gas and heated to an internal temperature of 80°C while stirring. Then, the monomer dispersion was added to start the suspension polymerization reaction. The monomer dispersion was dropped over 120 minutes while keeping the internal temperature at 80°C, and the reaction was continued for 6 hours while keeping the internal temperature at 80°C and stirring. Then, the composition obtained after the suspension polymerization was cooled to obtain an acrylic polymer particle-containing composition containing acrylic polymer particles as a suspension polymer. The non-volatile content of the acrylic polymer particle-containing composition was 50%, and the average particle diameter D50 of the acrylic polymer particles was 70 μm.

[0133] (Production examples I-2~I-13, IX-1~IX-8> An acrylic polymer particle-containing composition containing acrylic polymer particles was obtained in the same manner as in Production Example I-1, except that the compounds and contents were changed to those shown in Table 1. In Production Example I-11, a 25% aqueous solution of potassium hydroxide was used. However, in the case of IX-6, even when the monomer component was added to the water component and mixed by stirring, emulsification was insufficient, and a monomer dispersion liquid could not be prepared. In the cases of IX-7 and IX-8, the polymerization stability during suspension polymerization was insufficient, and an acrylic polymer particle-containing composition containing acrylic polymer particles could not be obtained. In Table 2, "-" for the average particle size of IX-6 to IX-8 indicates that it was not possible to measure.

[0134] [Table 1]

[0135] [Table 2]

[0136] The abbreviations in Tables 1 and 2 are as follows. The products used as ingredients in Tables 1 and 2 are as follows. EHA: 2-Ethylhexyl acrylate ·BA: Butyl acrylate ·AA: Acrylic acid Newcol 707SF: Polyoxyethylene polycyclic phenyl ether sulfate ammonium salt, weight average molecular weight 1,000, manufactured by Nippon Nyukazai Co., Ltd. RA9612: Polyoxyethylene (EO20) sodium alkyl sulfate, weight average molecular weight 3000, manufactured by Nippon Nyukazai Co., Ltd. Newcol 740SF: Polyoxyethylene polycyclic phenyl ether sulfate ammonium salt, weight average molecular weight 3,000, manufactured by Nippon Nyukazai Co., Ltd. CMC Daicel 2260: Sodium carboxymethylcellulose, manufactured by Daicel Miraize Co., Ltd. (Etherification degree: 0.9, viscosity 3,000 mPa s) Daicel SP900: Hydroxyethyl cellulose HEC, manufactured by Daicel Miraize Co., Ltd. (Etherification degree: 1.3, viscosity 4,000 mPa s) Metrose MCE-100TS: Methylcellulose, manufactured by Shin-Etsu Chemical Co., Ltd. (Etherification degree: 1.8, viscosity 5,000 mPa s)

[0137] <Production of acrylic polymer particles (i)> (Manufacturing example i-1) [Preparation of monomer dispersion] Into the vessel, 80 parts of 2-ethylhexyl acrylate and 13 parts of methyl methacrylate were added as (meth)acrylic acid alkyl ester monomer (a), 2 parts of acrylic acid as carboxyl group-containing monomer (b), 5.0 parts of 2-ethylhexyl acrylate as hydroxyl group-containing monomer (c), and 0.05 parts of OTG (2-ethylhexyl thioglycolate) as a chain transfer agent. In addition, 26.1 parts of deionized water and 10 parts of "Hitenol NF-08" (20% aqueous solution of sodium polyoxyethylene alkyl ether sulfate, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as an anionic emulsifier (d) were added and stirred to obtain a monomer dispersion. The obtained monomer dispersion was placed in a dropping funnel. The content of each component (solid content (parts)) is shown in Table 2. [Emulsion polymerization of monomers] Separately, 55.6 parts of deionized water was added to a four-neck flask equipped with a stirrer, a cooling tube, a thermometer, and the dropping funnel, and the flask was replaced with nitrogen gas and heated to an internal temperature of 80°C while stirring. Then, 8.3 parts of potassium persulfate with a concentration of 3% was added to the flask to start the emulsion polymerization reaction. After the monomer dispersion was added dropwise over 240 minutes while keeping the internal temperature at 80°C, the reaction was continued for 1 hour while stirring while keeping the internal temperature at 80°C. Then, 0.6 parts of potassium persulfate with a concentration of 3% was added twice to the flask at 30 minute intervals, and the reaction was continued for another 1 hour. Then, the mixture was cooled to obtain an aqueous dispersion containing acrylic polymer fine particles (i) as an emulsion polymer. The non-volatile content of the aqueous dispersion was 50%, and the average particle diameter D50 of the acrylic polymer fine particles (i) was 0.2μm.

[0138] [Table 3]

[0139] <Manufacturing examples i-2~i-19, ix-1~ix-2> Except for changing the compounds and amounts thereof as shown in Table 3, the same method as in Production Example i-1 was used to obtain an aqueous dispersion containing acrylic polymer fine particles.

[0140] The abbreviations in Table 3 are as follows. The products used as the ingredients in Table 3 are as follows. EHA: 2-Ethylhexyl acrylate ·BA: Butyl acrylate MMA: Methyl methacrylate ·AA: Acrylic acid ·MAA: Methacrylic acid HEMA: 2-hydroxyethyl methacrylate ·HEA: 2-hydroxyethyl acrylate 4HBA: 4-hydroxybutyl acrylate - Hitenol NF-08: 20% aqueous solution of sodium polyoxyethylene alkyl ether sulfate, manufactured by Daiichi Kogyo Seiyaku Co., Ltd. Newcol 707SF: Polyoxyethylene polycyclic phenyl ether sulfate ammonium salt, manufactured by Nippon Nyukazai Co., Ltd.

[0141] <Example 1> [Preparation of water-based adhesive] To 60 parts of the aqueous dispersion containing acrylic polymer particles obtained in Production Example I-1, 40 parts of the aqueous dispersion containing acrylic polymer microparticles obtained in Production Example i-1, 0.5 parts of 25% ammonia water as a neutralizing agent, 0.3 parts of "Noptam 2364" (mineral oil-based antifoaming agent, manufactured by San Nopco) as an antifoaming agent, 0.2 parts of "Levanax BX-150" (containing an isothiazolinone-based preservative, manufactured by Shoei Chemical Co., Ltd.) as a preservative, and 1.0 parts of "Primal ASE-60" (polyacrylic acid, manufactured by Dow Chemical Co.) as an alkaline thickener were added to obtain an aqueous adhesive. The viscosity of the aqueous adhesive was 2,000 mPa·s. Although the aqueous pressure sensitive adhesive contains acrylic polymer particles (I-1) with an average particle size D50 of 70 μm and acrylic polymer fine particles (i-1) with an average particle size D50 of 0.2 μm, the average particle size D50 measured by the laser diffraction scattering method was only 70 μm derived from (I-1). Figure 1 shows the particle size distribution of Example 1.

[0142] [Increase in viscosity and average particle size of water-based adhesive after high-speed shearing] The viscosity and average particle size (D50) of the water-based adhesive were measured before and after high-speed shearing. The high-speed shearing conditions were as follows: Tokushu Kika Kogyo TK HOMOMIXXER MARK 2 Rotation speed: 10000 times / min Rotation time: 10 minutes The viscosity was measured using a BL type viscometer at 25° C. with rotor No. 4 at a rotation speed of 60 rpm. The average particle size (D50) was measured by the laser diffraction scattering method described in (Measurement of the average particle size of water-based adhesives). The viscosity increase rate and the average particle size increase rate were calculated based on the following formula. Viscosity increase rate=(X2 / X1)×100 X1: Initial viscosity (mPas s), X2: Viscosity after high-speed shear (mPas s) Average particle size increase rate = (Y2 / Y1) x 100 Y1: Initial average particle size (D50) (μm), Y2: Average particle size after high-speed shear (D50) (μm)

[0143] [Preparation of adhesive sheet (copy paper)] The obtained water-based adhesive was applied to a 70 μm thick copy paper so that the thickness after drying was 8 g / m 2 The adhesive layer was formed by applying the adhesive with an applicator so that the adhesive layer was coated with the adhesive and dried at 100°C for 1 minute. Next, a release paper was attached to the adhesive layer and aged for 24 hours under conditions of a temperature of 23°C and a relative humidity of 50%, to obtain an adhesive sheet with a composition of "copy paper / adhesive layer / release paper."

[0144] <Evaluation of adhesive sheets> The adhesive sheets obtained in the Examples and Comparative Examples were evaluated for adhesive strength, removability, and holding power according to the following methods.

[0145] (Adhesive strength) The adhesive sheet (copy paper) was cut to a size of 100 mm long x 25 mm wide in an environment of 23°C and 50% relative humidity (hereinafter referred to as 50% RH) to prepare a sample. The sample was then left for 24 hours in an environment of 23°C and 50% RH, after which the release paper was peeled off and the sample was attached to a copy paper not coated with an adhesive, and a 2 kg roll was run back and forth once on the sample. The sample was then left for 24 hours in an environment of 23°C and 50% RH, after which the two sheets of copy paper were peeled off and the adhesive strength was measured. The adhesive strength was measured using a tensile tester (Tensilon RTG-1210) in a 180° direction at a peeling speed of 300 mm / min to measure the adhesive strength. The adhesive strength was evaluated according to the following criteria. ◎: Adhesive strength of 0.5N / 25mm or more. Extremely good. 〇: Adhesive strength 0.3N / 25mm or more, less than 0.5N / 25mm. Good. △: Adhesive strength is 0.1N / 25mm or more, but less than 0.3N / 25mm. Practical use is possible. ×: Adhesive strength is less than 0.1N / 25mm. Not practical.

[0146] (removability) The adhesive sheet (copy paper) was cut to a size of 100 mm long x 25 mm wide in an environment of 23°C and 50% RH to prepare a sample. The release paper was then peeled off, and the sample was attached to a copy paper that was not coated with adhesive, and a 2 kg roll was rolled back and forth once on the sample. The two sheets of copy paper were then peeled off by hand, and the sample was then attached to the copy paper again, and the procedure of rolling the 2 kg roll back and forth once on the sample was repeated 50 times to measure removability. The removability was evaluated based on the ratio of the area of ​​torn paper to the total area of ​​the sample according to the following criteria. ◎: No tears in the paper at all. Very good. Good: Paper tears occurred over less than 5% of the area. Good. △: Paper tears occurred over an area of ​​5% or more but less than 10%. Usable. ×: Paper tears occurred over 10% or more of the surface area. Not usable.

[0147] <Examples 2 to 31 and Comparative Examples 1 to 15> Except for changing the compositions shown in Tables 4 to 6, the water-based pressure sensitive adhesives and pressure sensitive adhesive sheets were produced in the same manner as in Example 1 and evaluated. In the aqueous pressure-sensitive adhesives of Examples 2 to 31 and Comparative Examples 1 to 5, only a peak derived from the acrylic polymer particles was observed in the particle size distribution measured by the laser diffraction scattering method, as in Example 1. On the other hand, in the aqueous pressure-sensitive adhesives of Comparative Examples 6 to 13, two peaks were observed in the particle size distribution measured by the laser diffraction scattering method. Figure 2 shows the particle size distribution of Comparative Example 6.

[0148] [Table 4]

[0149] [Table 5]

[0150] [Table 6]

[0151] In addition to those shown in Tables 4 to 6, pressure-sensitive adhesive sheets having excellent adhesive strength, removability and holding power could be produced using aqueous pressure-sensitive adhesives containing the acrylic polymer particles of Production Examples 1 to 13 shown in Table 1 and the acrylic polymer microparticles of Production Examples 22 to 40 shown in Table 3. The aqueous pressure-sensitive adhesive according to an embodiment of the present invention can be preferably used for producing pressure-sensitive adhesive sheets having excellent adhesive strength and removability.

Claims

1. Acrylic polymer particles (I) having an average particle size (D50) of 40 to 100 μm; and (i) acrylic polymer fine particles having an average particle diameter (D50) of 0.10 to 0.6 μm; The particle size distribution of the aqueous pressure sensitive adhesive measured by a laser diffraction scattering method shows that only acrylic polymer particles (I) having an average particle size (D50) of 40 to 100 μm are observed as the main component. The present invention is characterized in that the following (1) and (2) are simultaneously satisfied: A water-based adhesive with a non-volatile content of 40 to 60% by mass. (1) (X2 / X1)×100≦20(%) X1: Initial viscosity (mPas·s), X2: Viscosity after high speed shear (mPas·s) (2) (Y2 / Y1)×100≦20(%) Y1: initial average particle size (D50) (μm), Y2: average particle size after high speed shear (D50) (μm) Incidentally, "after high speed shearing" refers to the state after the aqueous pressure sensitive adhesive is rotationally stirred for 10 minutes at a rotation speed of 10,000 rpm using a homomixer.

2. 2. The aqueous pressure-sensitive adhesive according to claim 1, wherein the content ratio of the acrylic polymer particles (I) to the acrylic polymer fine particles (i) is from 70 / 30 to 50 / 50.

3. the acrylic polymer fine particles (i) contain a (meth)acrylic acid alkyl ester monomer (a), a carboxyl group-containing monomer (b) and a hydroxyl group-containing monomer (c); The aqueous pressure-sensitive adhesive according to claim 1, comprising acrylic polymer fine particles (i') which are an emulsion polymer of a monomer mixture in which the content of the carboxyl group-containing monomer (b) is 1 to 10 mass% and the content of the hydroxyl group-containing monomer (c) is 1 to 10 mass% based on 100 mass% of the monomer mixture.

4. The aqueous pressure-sensitive adhesive according to claim 3, wherein the acrylic polymer fine particles (i') are an emulsion polymer of a monomer composition containing 2 to 10 parts by mass of an anionic emulsifier (d) per 100 parts by mass of a monomer mixture.

5. 5. A pressure-sensitive adhesive sheet comprising a substrate and a pressure-sensitive adhesive layer formed from the water-based pressure-sensitive adhesive according to claim 1 on at least one surface of the substrate.

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