Aqueous adhesive and adhesive sheet for surface protection

Abstract

To provide an aqueous adhesive capable of obtaining an adhesive sheet for surface protection having good releasability of an adhesive sheet, short aging and good coating appearance.SOLUTION: There is provided an aqueous adhesive used for an adhesive sheet for surface protection which contains an acrylic polymer (A) and a compound (B) having two or more aziridinyl groups in the molecule (B), wherein the acrylic polymer (A) is an emulsion polymerization product of a monomer mixture containing a (meth)acrylic acid alkyl ester (a1) having an alkyl group having 4 to 12 carbon atoms, a carboxyl group-containing monomer (a2) and a hydroxyl group-containing monomer (a3), contains 0.1 to 3.0 mass% of the carboxyl group-containing monomer (a2) and 0.5 to 5.0 mass% of the hydroxyl group-containing monomer (a3) in 100 mass% of the monomer mixture and has a gel fraction of 80 to 100%.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to an aqueous adhesive and an adhesive sheet for surface protection applications.

Background Art

[0002] Adhesives are used in various applications such as masking tapes, double-sided tapes, surface protection films, packaging tapes, etc. From the viewpoints of environmental measures, resource conservation, safety, etc., aqueous adhesives that do not use organic solvents are widely used. For such aqueous adhesives, acrylic adhesives that are low-cost and easy to satisfy various physical properties are used.

[0003] The required qualities for surface protection film applications include having adhesion that does not peel off from the film substrate, excellent adhesion workability that allows for uniform attachment to adherends such as various resin plates, glass plates, and metal plates used in industrial, electrical / electronic / optical fields, etc., without wrinkles or entraining air, having an appropriate adhesive force such that no lifting or peeling occurs during storage, transportation, etc. when the film is adhered to the adherend, having little change in adhesive force over time even under high-temperature and high-humidity atmospheres during storage and being easily peelable without contaminating the surface of the adherend after peeling, etc. In recent years, having a good coating appearance has been required for applications such as protecting optical members.

[0004] Patent Document 1 discloses a re-peelable aqueous pressure-sensitive adhesive containing a water-dispersion copolymer of a monomer mixture containing an acrylic monomer and a carboxyl group-containing monomer as essential components and a carbodiimide compound.

[0005] Patent Document 2 discloses a re-peelable aqueous adhesive composition containing an emulsion polymer obtained by emulsion-polymerizing a monomer mixture containing an alkyl acrylate, a carboxyl group-containing unsaturated monomer, a polyfunctional unsaturated monomer, and other unsaturated monomers in the presence of an anionic reactive emulsifier, and a crosslinking agent.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, the aqueous adhesives of Patent Documents 1 and 2 had a low gel fraction after curing with a carbodiimide curing agent and had problems with re-peelability. In addition, there was a problem that the reaction rate with the curing agent was slow and the coating appearance deteriorated.

[0008] The present invention has been made in view of the above problems, and the problem to be solved by the present invention is to provide an aqueous adhesive that can obtain a surface protection adhesive sheet having good re-peelability even under high temperature and high humidity environments, short aging, and good coating appearance.

Means for Solving the Problems

[0009] As a result of intensive studies by the present inventors, it has been found that the problems of the present disclosure can be solved in the following aspects, and the present disclosure has been completed. That is, the present invention relates to an acrylic polymer (A) which is an emulsion polymer of a monomer mixture containing an alkyl (meth)acrylate (a1) having 4 to 12 carbon atoms in the alkyl group, a carboxyl group-containing monomer (a2), and a hydroxyl group-containing monomer (a3), and a compound (B) having two or more aziridinyl groups in the molecule, and is used for a surface protection adhesive sheet containing 0.5 to 5.0% by mass of a hydroxyl group-containing monomer (a3) and 0.1 to 3.0% by mass of a carboxyl group-containing monomer (a2) in the monomer mixture.

[0010] The present invention also relates to the aqueous adhesive for use in a pressure-sensitive adhesive sheet for surface protection, wherein the compound (B) having two or more aziridinyl groups in the molecule is used in the pressure-sensitive adhesive sheet having a 2-methylaziridinyl group.

[0011] The present invention also relates to the aqueous adhesive for use in a pressure-sensitive adhesive sheet for surface protection, wherein the acrylic polymer (A) is in a particulate form and has an average particle diameter measured by a dynamic light scattering method of 100 to 300 nm.

[0012] The present invention also relates to the aqueous adhesive for use in a pressure-sensitive adhesive sheet for surface protection, which does not contain a thickener and a plasticizer.

[0013] The present invention also relates to a pressure-sensitive adhesive sheet for surface protection, which includes a film substrate and an adhesive layer formed from the aqueous adhesive.

Advantages of the Invention

[0014] According to the present disclosure, it has become possible to provide a pressure-sensitive adhesive sheet for surface protection that has good re-peelability even under high-temperature and high-humidity environments, short aging, and good coating appearance.

Modes for Carrying Out the Invention

[0015] Hereinafter, the terms related to the present disclosure will be described in order. “(Meth)acrylic acid alkyl ester” means “acrylic acid alkyl ester” and “methacrylic acid alkyl ester”. Monomer means an ethylenically unsaturated double bond-containing monomer. Adherend means the object to which the adhesive tape is attached. Also, unless otherwise specified, “part” means part by mass and “%” means mass %. Note that “~” indicating a numerical range includes the lower limit value and the upper limit value thereof unless otherwise specified.

[0016] <Acrylic polymer (A)> The acrylic polymer (A) is an emulsion polymer of a monomer mixture including a (meth)acrylic acid alkyl ester (a1) in which the alkyl group has 4 to 12 carbon atoms, a carboxyl group-containing monomer (a2), and a hydroxyl group-containing monomer (a3).

[0017] ((Meth)acrylic acid alkyl ester (a1) having an alkyl group with 4 to 12 carbon atoms) (Meth)acrylic acid alkyl ester (a1) having an alkyl group with 4 to 12 carbon atoms means a (meth)acrylic acid alkyl ester having an alkyl group with 4 to 12 carbon atoms. For example, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, cyclopentyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, 2-octyl (meth)acrylate, isononyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, etc. can be mentioned. These (meth)acrylic acid alkyl esters (a1) can be used alone or in combination of two or more kinds.

[0018] By using (meth)acrylic acid alkyl ester (a1) having an alkyl group with 4 to 12 carbon atoms, a compound (B) having two or more aziridinyl groups in the molecule is easily incorporated into the particles of the acrylic polymer (A), and the short aging property is improved. Along with that, since the curing reaction easily proceeds, a surface protective adhesive sheet having good heat-resistant re-peelability and moisture-heat-resistant re-peelability can be obtained. From the viewpoint of improving the short aging property, heat-resistant re-peelability, and moisture-heat-resistant re-peelability, the content of (meth)acrylic acid alkyl ester (a1) with 4 to 12 carbon atoms is preferably 40% by mass in 100% by mass of the monomer mixture. The upper limit of the content of (a1) is not particularly limited as long as a predetermined amount of the carboxyl group-containing monomer (a2) and the hydroxyl group-containing monomer (a3) can be contained. For example, the upper limit of the content of (a1) is 99.4% by mass or less.

[0019] (Carboxyl group-containing monomer (a2)) The carboxyl group-containing monomer (a2) includes, for example, (meth)acrylic acid, β-carboxyethyl acrylate, itaconic acid, crotonic acid, fumaric acid, maleic anhydride, maleic acid, and butyl maleate. The carboxyl group-containing monomer can be used alone or in combination of two or more. The carboxyl group-containing monomer includes the acid anhydride group-containing monomer.

[0020] The acrylic polymer (A) in the present invention contains 0.1 to 3.0% by mass of the carboxyl group-containing monomer (a2) in 100% by mass of the monomer mixture. By setting the content of the carboxyl group-containing monomer (a2) to 0.1% by mass or more, the generation of aggregates when producing an aqueous adhesive by blending the acrylic polymer (A) and the compound (B) having two or more aziridinyl groups in the molecule is suppressed (the blending stability is improved), and the coating appearance is improved. Also, the heat-resistant re-peelability and the wet heat-resistant re-peelability are similarly improved. On the other hand, by setting the content of the carboxyl group-containing monomer (a2) to 3.0% by mass or less, the blending stability can be maintained, and the coating appearance is good. Also, the wet heat-resistant re-peelability can be maintained. From the viewpoint of further improving the blending stability, the coating appearance, the heat-resistant re-peelability, and the wet heat-resistant re-peelability, the carboxyl group-containing monomer (a2) is preferably 0.5 to 2.5% by mass, and more preferably 1.0 to 2.0% by mass.

[0021] (Hydroxyl group-containing monomer (a3)) The hydroxyl group-containing monomer (a3) includes, for example, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 6-hydroxyhexyl (meth)acrylate, and polyalkylene glycol (meth)acrylates such as polyethylene glycol (meth)acrylate and polypropylene glycol (meth)acrylate. The hydroxyl group-containing monomer can be used alone or in combination of two or more.

[0022] The acrylic polymer (A) in the present invention contains 0.5 to 5.0% by mass of a hydroxyl group-containing monomer (a3) in 100% by mass of the monomer mixture. By setting the content of the hydroxyl group-containing monomer (a3) to 0.5% by mass or more, the heat-resistant re-peelability is improved. On the other hand, by setting the content of the hydroxyl group-containing monomer (a3) to 5.0% by mass or less, the moisture and heat-resistant re-peelability can be maintained. Also, the blending stability can be maintained, and the coating appearance becomes good. From the viewpoint of further improving the blending stability, coating appearance, heat-resistant re-peelability, and moisture and heat-resistant re-peelability, the content of the hydroxyl group-containing monomer (a3) is preferably 1.0 to 4.0% by mass, and more preferably 1.5 to 3.0% by mass.

[0023] The total content of the carboxyl group-containing monomer (a2) and the hydroxyl group-containing monomer (a3) is preferably 2.5 to 5.0% by mass, and more preferably 3.5 to 4.5% by mass in 100% by mass of the monomer mixture. By setting it within the above range, the coating appearance is improved.

[0024] (Other monomers) The monomer mixture constituting the acrylic polymer (A) may contain "other monomers" other than (meth)acrylic acid alkyl esters (a1) in which the alkyl group has 4 to 12 carbon atoms, carboxyl group-containing monomers (a2), and hydroxyl group-containing monomers (a3). Examples of other monomers include ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, cyclohexyl (meth)acrylate, aminomethyl (meth)acrylate, dimethylaminomethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylate, (meth)acrylamide, acetoacetoxyethyl methacrylate, diacetone (meth)acrylamide, (meth)acrylonitrile, N-cyclohexylmaleimide, N-isopropylmaleimide, N-laurylmaleimide, N-phenylmaleimide, N-methylitaconimide, N-ethylitaconimide, N-butylitaconimide, N-cyclohexylitaconimide, N-(meth)acryloyloxymethylenesuccinimide, N-(meth)acryloyl-6-oxyhexamethylenesuccinimide, N-(meth)acryloyl-8-oxyoctamethylenesuccinimide, glycidyl (meth)acrylate, vinyl acetate, styrene, 2-methoxyethyl (meth)acrylate, and 2-ethoxyethyl (meth)acrylate, etc. Also, known (meth)acrylates such as polyethylene glycol di(meth)acrylate and neopentyl glycol adipate di(meth)acrylate, etc. may be mentioned. Other monomers can be used alone or in combination of two or more kinds.

[0025] <Method for producing acrylic polymer (A)> The acrylic polymer (A) can be produced by emulsion polymerization of the aforementioned monomer mixture. In the present invention, emulsion polymerization is preferably carried out, for example, by emulsifying the monomers to form an emulsion and then synthesizing (pre-emulsification method). As the method of emulsion polymerization, known methods can be used, such as a method in which the total amount of the emulsion is charged into a reaction vessel in advance and then reacted, or a method in which a part of the emulsion is charged into a reaction vessel and the remaining portion of the emulsion is added in several portions or continuously dropped.

[0026] (Emulsifier) The emulsifier used in emulsion polymerization is preferably appropriately selected from anionic emulsifiers and nonionic emulsifiers. Further, as the emulsifier, a reactive emulsifier having a radically polymerizable functional group is preferred.

[0027] The reactive emulsifier is an anionic emulsifier having one or more unsaturated double bonds capable of radical polymerization in the molecule. Examples thereof include sulfosuccinate ester-based emulsifiers and alkylphenol ether-based emulsifiers.

[0028] Among the emulsifiers, it is preferable to use a reactive anionic emulsifier in order to obtain good polymerization stability and coating appearance. In particular, reactive polyoxyethylene alkyl ether sulfates are more preferable, and ammonium salts of polyoxyethylene alkyl ether sulfates having an alkyl group with 9 to 14 carbon atoms are even more preferable. The emulsifier is preferably used in an amount of 2.0 to 6.0 parts by mass based on 100 parts by mass of the monomer mixture. By setting the emulsifier within the above range, the synthesis stability is improved.

[0029] (Polymerization initiator) As the polymerization initiator used in emulsion polymerization, it is preferable to use a water-soluble polymerization initiator. Examples of the water-soluble polymerization initiator include potassium persulfate, sodium persulfate, ammonium persulfate, ammonium (amine) salts of 4,4'-azobis-4-cyanovaleric acid, 2,2'-azobis(2-methylamidoxime) dihydrochloride, 2,2'-azobis(2-methylbutanamideoxime) dihydrochloride tetrahydrate, 2,2'-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]-propionamide}, 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)-propionamide], and the like. Among these, potassium persulfate and sodium persulfate are preferable.

[0030] Furthermore, as the polymerization initiator, a redox polymerization initiator (using an oxidizing agent and a reducing agent in combination) can be used. Examples of the oxidizing agent include ammonium persulfate, potassium persulfate, sodium persulfate, hydrogen peroxide, t-butyl hydroperoxide, benzoyl peroxide, cumene hydroperoxide, p-methane hydroperoxide, and the like. Examples of the reducing agent include sodium sulfite, acidic sodium sulfite, Rongalit, ascorbic acid, and the like. Among these, since they are excellent in polymerization reactivity, it is preferable to use a combination of an oxidizing agent: potassium persulfate or sodium persulfate, and a reducing agent: sodium sulfite or acidic sodium sulfite.

[0031] (Particle size) The acrylic polymer (A) is in a particulate form, and the average particle size (D 50 ) measured by the dynamic light scattering method is preferably 100 to 300 nm, more preferably 150 to 250 nm. By adjusting the particle size of the emulsion polymer to 100 to 300 nm, the blending stability and film-forming property become good, and the coating appearance becomes good. The method for measuring the average particle size will be described in detail in the examples.

[0032] <Compound (B) having two or more aziridinyl groups in the molecule> The compound (B) having two or more aziridinyl groups in the molecule (hereinafter sometimes referred to as aziridine curing agent (B)) means a compound containing two or more three-membered ring skeletons containing a nitrogen atom. For example, 2,2-bis({[3-(2-methyl-1-aziridinyl)propanoyl]oxy}methyl)butyl = 3-(2-methyl-1-aziridinyl)propanoate, N,N'-diphenylmethane-4,4'-bis(1-aziridine carboxylate), N,N'-toluene-2,4-bis(1-aziridine carboxylate), bisisophthaloyl-1-(2-methylaziridine), tri-1-aziridinylphosphine oxide, N,N'-hexamethylene-1,6-bis(1-aziridine carboxylate), 2,2'-bis(hydroxymethyl)butanol-tris[3-(1-aziridinyl)propionate], trimethylolpropane tri-β-aziridinylpropionate, tetramethylolmethane tri-β-aziridinylpropionate, and tris-2,4,6-(1-aziridinyl)-1,3,5-triazine, etc. can be mentioned. From the viewpoint of coating appearance, a compound having a 2-methylaziridinyl group is preferable, and a compound having only a 2-methylaziridinyl group is more preferable. From the viewpoint of improving heat-resistant re-peelability and moisture-heat-resistant re-peelability, the content of the aziridine curing agent (B) is preferably 0.3 to 3.0 parts by mass with respect to 100 parts by mass of the acrylic polymer (A).

[0033] ≪Water-based adhesive≫ The water-based adhesive of the present invention contains an acrylic polymer (A) and a compound (B) having two or more aziridinyl groups in the molecule. Each component may be mixed, and the production method is not particularly limited.

[0034] (Thickener) The aqueous pressure-sensitive adhesive of the present invention preferably does not contain a thickener. Examples of the thickener include known celluloses, polyesters, polyamides, polyethers, polyglycols, polyvinyl alcohols, polyurethanes, and polyacrylic acid compounds. By not containing these thickeners, it is possible to obtain an aqueous pressure-sensitive adhesive used for a surface protection adhesive sheet having a good coating appearance because it does not inhibit the incorporation of the aziridine curing agent (B) into the particles.

[0035] (Plasticizer) The aqueous pressure-sensitive adhesive of the present invention preferably does not contain a plasticizer. Examples of the plasticizer include known phthalic acid esters, adipic acid esters, phosphoric acid esters, trimellitic acid esters, citric acid esters, and fatty acid esters. By not containing these plasticizers, the blending stability is improved, and it is possible to obtain an aqueous pressure-sensitive adhesive used for a surface protection adhesive sheet having a good coating appearance.

[0036] (Neutralizing agent) For the aqueous pressure-sensitive adhesive of the present invention, a known neutralizing agent can be used to adjust the pH. Examples of the neutralizing agent include ammonia, triethylamine, sodium hydroxide, and the like. The pH of the aqueous pressure-sensitive adhesive is preferably in the range of 8.0 to 11, and more preferably 9.0 to 10 from the viewpoint of improving the coating appearance. By setting the pH within the above range, it is possible to reduce the shock due to the pH difference when adding the aziridine curing agent (improve the blending stability) and obtain a surface protection sheet with a good coating appearance.

[0037] (Others) The aqueous pressure-sensitive adhesive of the present invention can be blended with known other additives such as a leveling agent, a preservative, an antifoaming agent, a pigment dispersion, and resin fine particles as optional components.

[0038] <Gel fraction> The gel fraction of the aqueous adhesive of the present invention is 80 to 100%. When the gel fraction is 80 to 100%, the strength of the adhesive coating film is improved, and the heat-resistant re-peelability and the wet-heat-resistant re-peelability are improved. From the viewpoint of improving the heat-resistant re-peelability and the wet-heat-resistant re-peelability, the gel fraction is preferably 85% or more. Details of the method for measuring the gel fraction are described in the examples.

[0039] <Chain transfer agent> In the present invention, a chain transfer agent can be used to adjust the gel fraction. As the chain transfer agent, compounds having a thiol group or a hydroxyl group are generally known. Examples of the compound having a thiol group include mercaptans 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. Further, alcohols such as methyl alcohol, n-propyl alcohol, isopropyl alcohol (IPA), t-butyl alcohol, and benzyl alcohol are also included. The chain transfer agents can be used alone or in combination of two or more.

[0040] ≪Adhesive sheet for surface protection≫ The adhesive sheet for surface protection of the present invention includes a film substrate and an adhesive layer formed from the aqueous adhesive of the present invention. Since the adhesive sheet for surface protection of the present invention has a good coating appearance, it is used for the purpose of protecting an adherend at the time of shipment, manufacture, etc. Illustrative of the manufacturing method are (1) a method of forming an adhesive layer by coating and drying an aqueous adhesive on a release sheet and then transferring the adhesive layer onto a substrate, and (2) a method of forming an adhesive layer by coating and drying an aqueous adhesive on a substrate and then laminating a release sheet. The thickness of the adhesive layer is not particularly limited, but is more preferably 1 to 10 μm.

[0041] Coating methods include known methods such as Meyer bar, applicator, brush, spray, roller, gravure coater, die coater, lip coater, comma coater, knife coater, reverse coater, spin coater, etc. During coating, drying is usually carried out. Drying is not particularly limited, and known methods such as hot air drying, infrared heater, and reduced pressure method can be appropriately selected and used. The drying temperature is usually about 60 to 180 °C.

[0042] Examples of the film substrate include sheets such as cellophane and plastic sheets. The substrate may be a single layer or a plurality of laminates. Also, the substrate can be subjected to a release treatment or an antistatic treatment on the back surface (the surface not in contact with the adhesive layer). Further, the substrate can improve the adhesion to the adhesive layer by performing a known easy adhesion treatment. The thickness of the substrate is generally about 10 to 100 μm, and more preferably 30 to 80 μm.

[0043] The adherend of the pressure-sensitive adhesive sheet for surface protection of the present invention can be used for a wide range of materials such as metals, glass, plastic films, rubbers, woods, cardboard, papers, and painted surfaces as materials.

Examples

[0044] Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto.

[0045] (Synthesis Example 1) To 96.0 parts of 2-ethylhexyl acrylate as an alkyl (meth)acrylate ester (a1) having 4 to 12 carbon atoms in the alkyl group, 1.5 parts of acrylic acid as a carboxyl group-containing monomer (a2), and 2.5 parts of hydroxyethyl methacrylate as a hydroxyl group-containing monomer (a3), 4.0 parts of KH-10 as an anionic reactive emulsifier and 20.7 parts of deionized water were added and stirred to obtain an emulsion. Separately, 69.0 parts of deionized water and 1.2 parts of the above emulsion were charged into a four-necked flask equipped with a stirrer, a cooling pipe, a thermometer and the above dropping funnel. The inside of the flask was replaced with nitrogen gas, and while stirring, the internal temperature was heated to 70°C. Then, 5.5 parts of 1% potassium persulfate and 5.5 parts of 1% sodium bisulfite were added to start the reaction. The remaining emulsion was put into the dropping funnel, and while maintaining the internal temperature at 70°C, the emulsion was added dropwise over 180 minutes. Then, the reaction was continued for 0.5 hour while maintaining the internal temperature at 70°C with further stirring. Thereafter, 0.5 part of a 5% aqueous solution of "Perbutyl H-69" (manufactured by NOF Corporation) as an oxidizing agent and 0.5 part of a 5% aqueous solution of sodium bisulfite as a reducing agent were added twice at 30-minute intervals, and the reaction was continued for another 2 hours. Then, it was cooled, and 25% aqueous ammonia was added at 30°C for neutralization to obtain an acrylic polymer (A-1). The acrylic polymer (A-1) is an emulsion (emulsion polymer), and the average particle diameter (D 50 ) was 200 nm.

[0046] [Particle Size Measurement] The average particle diameter (D 50 ) of the acrylic polymer (A) was measured using a particle size measuring device (Nanotrac WAVE EX, manufactured by Microtrac Bell Corporation). The measurement conditions were that the particle refractive index was 1.59, the particle shape was a perfect sphere, and the loading index was 8 to 12. In addition, the sample was prepared by diluting with water so that the acrylic polymer (A) had a concentration suitable for measurement as needed.

[0047] (Synthesis Examples 2 to 32) Acrylic polymers (A-2 to A-26, A'-1 to A'-6) of Synthesis Examples 2 to 32 were produced in the same manner as in Synthesis Example 1 except that the formulation of the monomer mixture was changed to the raw materials and formulation amounts described in Tables 1 to 3, and the particle size was measured. The measurement results of the particle size are shown in Tables 1 to 3.

[0048] The abbreviations in Tables 1 to 3 are as follows. ((Meth)acrylic acid alkyl ester (a1) in which the alkyl group has 4 to 12 carbon atoms) · LA: Lauryl acrylate (alkyl group with 12 carbon atoms) · 2EHA: 2-Ethylhexyl acrylate (alkyl group with 8 carbon atoms) · BA: Butyl acrylate (alkyl group with 4 carbon atoms) <Carboxyl group-containing monomer (a2)> · AA: Acrylic acid · MAA: Methacrylic acid <Hydroxyl group-containing monomer (a3)> · HEMA: Hydroxyethyl methacrylate · 4HBA: 4-Hydroxybutyl acrylate <Other monomers> · SA: Stearyl acrylate (alkyl group with 18 carbon atoms) · EA: Ethyl acrylate (alkyl group with 2 carbon atoms) <Emulsifier> · KH-10: "Aquaron KH-10" (anionic reactive emulsifier, polyoxyethylene-1-(allyloxymethyl)alkyl ether sulfate ammonium salt, non-volatile content 100%, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) · RA-9612: "Newcol RA-9612" (anionic non-reactive emulsifier, polyoxyethylene alkyl ether sulfate ammonium salt, non-volatile content 25%, manufactured by Nippon Emulsifier Co., Ltd.)

[0049]

Table 1

[0050]

Table 2

[0051]

Table 3

[0052] (Example 1: Production of aqueous adhesive) To 100 parts of an acrylic polymer (A-1), 0.3 part of 25% aqueous ammonia as a neutralizing agent, 0.1 part of Adekanate B-940 (manufactured by ADEKA) as an antifoaming agent, 0.18 part of Revanax BX-150 (manufactured by Shoei Chemical Co., Ltd.) as a preservative, 0.7 part of “Pelec OT-P” (manufactured by Kao Corporation) as a leveling agent, 14.4 parts of deionized water, and 0.5 part of HD-100A as an aziridine curing agent (B) were added to obtain an aqueous adhesive. The pH of the obtained aqueous adhesive was 9.3, and the viscosity was 50 mPa·s. Also, the gel fraction was 90%.

[0053] [pH Measurement] The pH of the aqueous adhesive was measured at 25°C using a pH meter (LAQUAact, manufactured by HORIBA). Calibration of the pH meter was performed using a standard buffer solution (borate pH standard solution) pH 9.18 (25°C) (manufactured by Fujifilm Wako Pure Chemical Corporation) and a standard buffer solution (neutral phosphate pH standard solution) pH 6.86 (25°C) (manufactured by Fujifilm Wako Pure Chemical Corporation).

[0054] [Viscosity Measurement] The viscosity of the aqueous adhesive was measured at 25°C, rotor No. 4, and 60 rpm using a BL type viscometer (TVB10 type viscometer, manufactured by Toki Sangyo Co., Ltd.).

[0055] [Gel Fraction] An aqueous adhesive was coated on a polyethylene terephthalate film (hereinafter referred to as PET film) so that the thickness of the dry film became 20 μm, dried in a drying oven at 100°C for 120 seconds, and cured for 144 hours in an environment of 23°C and relative humidity of 50% (hereinafter 50% RH) to produce a coated article for gel fraction measurement. Next, the mass of a 200-mesh wire mesh was measured (mass M). The obtained coated article was cut into a size of 5 cm × 5 cm and bonded to a 200-mesh wire mesh to obtain a test piece. The mass of the obtained test piece was measured (mass A). Note that 200 mesh is the mesh specified in JIS G3555. The test piece was left in 50 ml of ethyl acetate at 50 °C for one day. Then it was taken out, dried at 100 °C for 20 minutes, and its mass was measured (mass T). Subsequently, the polyethylene terephthalate (PET) film was taken out from the test piece, and the adhesive layer was removed using ethyl acetate, and the mass of the PET film was measured (mass K). The obtained numerical values were substituted into the following formula (1) to determine the gel fraction. Formula (1) Gel fraction = (T - M - K) × 100 / (A - M - K)

[0056] (Examples 2 to 42, Comparative Examples 1 to 9: Production of aqueous adhesives) Except for changing the acrylic polymer, other raw materials and compounding amounts described in Tables 4 to 7, aqueous adhesives of Examples 2 to 38 and Comparative Examples 1 to 9 were produced in the same manner as in Example 1. For Examples 39 to 42, except for changing the acrylic polymer, other raw materials and compounding amounts described in Table 7, and further setting the amounts of the neutralizing agent to 0.2 part, 0.35 part, 0.15 part, and 0.4 part, respectively, aqueous adhesives were produced in the same manner as in Example 1. Also, the pH, viscosity, and gel fraction of the aqueous adhesives were measured, and the results are described in Tables 4 to 7. Note that the numerical unit in the table represents parts unless otherwise specified.

[0057] The abbreviations in Tables 4 to 7 are as follows. <Hardener (B)> · HD-100A: Methyl aziridine hardener, 2,2-bis({[3-(2-methyl-1-aziridinyl)propanoyl]oxy}methyl)butyl = 3-(2-methyl-1-aziridinyl)propanoate, non-volatile content 100%, manufactured by Ningxia Joie material Co., Ltd. · PZ-33: "Chemite PZ-33" (aziridine hardener, 2,2'-bis(hydroxymethyl)butanol-tris[3-(1-aziridinyl)propionate], volatile content 100%, manufactured by Nippon Shokubai Co., Ltd.) · DZ-22E: "Chemite DZ-22E" (aziridine hardener, 4,4-bis(ethyleneiminocarbonylamino)diphenylmethane, non-volatile content 31%, manufactured by Nippon Shokubai Co., Ltd.) <Other hardeners> ·V-04: "Carbodilite V-04" (carbodiimide curing agent, modified carbodiimide, manufactured by Nisshinbo Industries, Inc.) ·EX-313: "Denacol EX-313" (epoxy curing agent, glycerol polyglycidyl ether, non-volatile content 100%, manufactured by Nagase ChemteX Corporation) <Plasticizer> ·TMS: "Kasozai TMS" (citric acid ester, tributyl acetylcitrate, non-volatile content 100%, manufactured by Tago Chemical Industry Co., Ltd.) ·C-101: "Ricizer C-101" (castor oil-based fatty acid ester, non-volatile content 100%, manufactured by Ito Oil Co., Ltd.) <Thickener> ·ASE-60: "Primal TM ASE-60" (polyacrylic acid thickener, non-volatile content 28%, manufactured by DOW) ·UH-420: "Adekanol UH-420" (special non-ionic polymer surfactant, non-volatile content 30%, manufactured by ADEKA)

[0058] <Evaluation of aqueous adhesive> (Blending stability) The obtained aqueous adhesive was filtered through a 400-mesh filter, and the residue was dried at 100 °C for 20 minutes, and then the mass was measured. The blending stability was confirmed by the ratio of the residue to the total mass of the monomers used (coagulation rate during blending). The coagulation rate can be obtained according to Equation 2. (Equation 2) Coagulation rate during blending (%) = {(Residue mass after drying) / (Total mass of monomers)} × 100 The blending stability was also classified according to the following criteria. ◎: Coagulation rate during blending is less than 0.1%, extremely stable. 〇: Coagulation rate during blending is 0.1% or more and less than 0.3%, stable. △: Coagulation rate during blending is 0.3% or more and less than 1.5%, slightly unstable. ×: Coagulation rate during blending is 1.5% or more, unstable.

[0059] (Examples 1 to 42, Comparative Examples 1 to 9: Production of pressure-sensitive adhesive sheet for surface protection) The obtained aqueous adhesive was applied onto a commercially available polyolefin film (hereinafter referred to as PO film) using a Mayer bar so that the thickness after drying would be 3 μm, and then dried in a drying oven at 80 °C for 180 seconds to obtain a surface protective adhesive sheet. The performance was evaluated by the method described below, and the results are shown in Tables 4 to 7.

[0060] <Evaluation of Surface Protective Adhesive Sheet> (1) Short Aging Property The surface protective adhesive sheet produced above was cured for 24 hours or 144 hours in an environment of 23 °C and 50% RH. The obtained adhesive sheet was cut into a size of 100 mm in length × 25 mm in width in an environment of 23 °C and 50% RH. The one with a curing time of 24 hours was used as a sample for measuring the short aging adhesive force, and the one with a curing time of 144 hours was used as a sample for measuring the long aging adhesive force. Next, in accordance with JIS Z 0237, the release sheet was peeled off from each sample, and the exposed adhesive layer was attached to a stainless steel plate (hereinafter referred to as SUS) whose surface was polished. A 2 kg roll was reciprocated once, and the adhesive force after 20 minutes was measured. The measurement of the adhesive force was carried out using a tensile tester at a peeling speed of 300 mm / min and a peeling angle of 180°. The presence or absence of short aging property was evaluated by obtaining the adhesive force reduction rate from the measured short aging adhesive force (S) and long aging adhesive force (L). The adhesive force reduction rate was obtained by the following formula (3), and the evaluation was carried out according to the following criteria. (Formula 3) Adhesive force reduction rate (%) = {1 - (L / S)} × 100 [Evaluation Criteria] 〇: The adhesive force reduction rate is less than 50%, and there is short aging property. Practical. ×: The adhesive force reduction rate is 50% or more, and there is no short aging property. Not practical.

[0061] (2) Heat Resistance and Repealable Property Samples were prepared in the same manner as the samples for long-term aging adhesion measurement. Next, the release sheet was peeled off from the sample, and the exposed adhesive layer was attached to polished SUS, and a 2 kg roll was reciprocated once. After pressure bonding, the sample was left in an atmosphere of 70°C - 0% RH for 24 hours. Then, it was transferred to an atmosphere of 23°C and 50% RH, and after 3 hours, a tensile tester was used to peel it off at a peeling speed of 300 mm / min and a peeling angle of 180°. The sample after peeling was visually inspected and evaluated according to the degree of glue residue on the adherend of the adhesive. The determination of heat-resistant re-peelability was evaluated according to the following criteria. ◎: There is no glue residue on the SUS surface at all, extremely good. 〇: There is glue residue on less than 5% of the SUS surface, good. △: There is glue residue on 5% or more and less than 10% of the SUS surface, practical. ×: There is glue residue on 10% or more of the SUS surface, not practical.

[0062] (3) Moisture and heat-resistant re-peelability Samples were prepared in the same manner as the samples for long-term aging adhesion measurement. Next, the release sheet was peeled off from the sample, and the exposed adhesive layer was attached to polished SUS, and a 2 kg roll was reciprocated once. After pressure bonding, the sample was left in an atmosphere of 60°C - 95% RH for 72 hours. Then, it was transferred to an atmosphere of 23°C and 50% RH, and after 3 hours, a tensile tester was used to peel it off at a peeling speed of 300 mm / min and a peeling angle of 180°. The sample after peeling was visually inspected and evaluated according to the degree of glue residue on the adherend of the adhesive. The determination of moisture and heat-resistant re-peelability was evaluated according to the following criteria. ◎: There is no glue residue on the SUS surface at all, extremely good. 〇: There is glue residue on less than 5% of the SUS surface, good. △: There is glue residue on 5% or more and less than 10% of the SUS surface, practical. ×: There is glue residue on 10% or more of the SUS surface, not practical.

[0063] (4) Coating appearance The evaluation of the coating appearance was carried out using each surface protection adhesive sheet. The surface protection adhesive sheet was cut into a size of 100 mm in length × 100 mm in width to obtain a test piece. The coating appearance was observed at a magnification of 20 times using a digital microscope VHX-7000 (manufactured by KEYENCE Corporation). The number of white circular defects of 1 μm or more observed on the screen was measured to determine the coating appearance. ◎: Less than 100 defects of 1 μm or more on the surface of the surface protection adhesive sheet, extremely good. 〇: 100 or more and less than 200 defects of 1 μm or more on the surface of the surface protection adhesive sheet, good. △: 200 or more and less than 500 defects of 1 μm or more on the surface of the surface protection adhesive sheet, practical. ×: 500 or more defects of 1 μm or more on the surface of the surface protection adhesive sheet, not practical.

[0064]

Table 4

[0065]

Table 5

[0066]

Table 6

[0067]

Table 7

Claims

1. An aqueous adhesive comprising an acrylic polymer (A) and a compound (B) having two or more aziridinyl groups in the molecule, The acrylic polymer (A) is an emulsion polymer of a monomer mixture containing an alkyl (meth)acrylate (a1) having 4 to 12 carbon atoms in the alkyl group, a carboxyl group-containing monomer (a2), and a hydroxyl group-containing monomer (a3), The monomer mixture contains 0.1 to 3.0% by mass of the carboxyl group-containing monomer (a2) and 0.5 to 5.0% by mass of the hydroxyl group-containing monomer (a3) per 100% by mass, Characterized in that the gel fraction is 80 to 100%, An aqueous adhesive for use in a surface protection adhesive sheet.

2. The compound (B) having two or more aziridinyl groups in the molecule has a 2-methylaziridinyl group, and the aqueous adhesive for use in the surface protection adhesive sheet according to Claim 1.

3. The acrylic polymer (A) is in a particulate form, and the average particle diameter measured by the dynamic light scattering method is 100 to 300 nm, and the aqueous adhesive for use in the surface protection adhesive sheet according to Claim 1.

4. The aqueous adhesive according to Claim 1 does not contain a thickening agent and a plasticizer, and the aqueous adhesive for use in a surface protection adhesive sheet.

5. A surface protection adhesive sheet comprising a film substrate and an adhesive layer formed from the aqueous adhesive according to any one of Claims 1 to 4.

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