Adhesive composition, adhesive sheet, and bonded body

Abstract

The present invention provides: an adhesive composition capable of forming an adhesive layer that has particularly excellent adhesive characteristics when voltage is not applied thereto, exhibits a sufficient reduction in adhesive force when voltage is applied thereto, and has excellent impact resistance; an adhesive sheet provided with an adhesive layer formed from the adhesive composition; and a bonded body of the adhesive sheet and an adherend. The present invention relates to an adhesive composition containing an emulsion-type acrylic polymer (A) and an electrolyte (B), wherein the emulsion-type acrylic polymer (A) contains a monomer unit derived from a cyano group–containing monomer.

Description

Pressure-sensitive adhesive composition, pressure-sensitive adhesive sheet, and bonded body

[0001] The present invention relates to a pressure-sensitive adhesive composition, a pressure-sensitive adhesive sheet including a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition, and a bonded body of the pressure-sensitive adhesive sheet and an adherend.

[0002] In electronic component manufacturing processes, etc., there is an increasing demand for rework to improve yields and recycling, such as disassembling and recovering components after use. To meet these demands, double-sided PSA sheets that have a certain level of adhesive strength and releasability are sometimes used to join components in electronic component manufacturing processes, etc.

[0003] As a pressure-sensitive adhesive composition for forming a double-sided pressure-sensitive adhesive sheet that achieves the above-mentioned adhesive strength and releasability, a solvent-based pressure-sensitive adhesive composition in which a base polymer is dissolved in an organic solvent has conventionally been used (Patent Document 1, etc.).

[0004] Furthermore, from the viewpoint of reducing the environmental load, etc., investigations have been conducted into emulsion-based pressure-sensitive adhesive compositions in which a base polymer is dispersed in an aqueous medium. For example, Patent Document 2 discloses an electrically peelable pressure-sensitive adhesive composition comprising an emulsion-type acrylic pressure-sensitive adhesive containing an emulsion-type acrylic polymer and a (poly)alkylene polyol having a number-average molecular weight of 2,000 or less.

[0005] Japanese Patent No. 5296446 Japanese Patent No. 6097112

[0006] However, it was found that the pressure-sensitive adhesive composition described in Patent Document 2 contains a (poly)alkylene polyol, and although the adhesive strength decreases and the electrical peelability improves when a voltage is applied to the pressure-sensitive adhesive layer, the results are still insufficient, and furthermore, the adhesive properties such as the adhesive strength and creep resistance when no voltage is applied deteriorate.

[0007] The present invention was completed in view of the above, and aims to provide a pressure-sensitive adhesive composition that has particularly excellent adhesive properties when no voltage is applied and whose adhesive strength is sufficiently reduced by the application of a voltage, a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition, and a bonded body of the pressure-sensitive adhesive sheet and an adherend.

[0008] As a result of extensive investigations, the present inventors have found that by using a pressure-sensitive adhesive composition containing an emulsion-type acrylic polymer including a monomer unit derived from a cyano group-containing monomer and an electrolyte, it is possible to form a pressure-sensitive adhesive layer that exhibits particularly excellent adhesive properties when no voltage is applied and whose adhesive strength is sufficiently reduced by the application of a voltage.The present inventors have also found that by using this pressure-sensitive adhesive composition, the pressure-sensitive adhesive layer formed also has excellent impact resistance.

[0009] Here, the monomer unit refers to a constituent unit derived from a monomer in a polymer.

[0010] Means for solving the above problems are as follows. [1] A pressure-sensitive adhesive composition containing an emulsion-type acrylic polymer (A) and an electrolyte (B), wherein the emulsion-type acrylic polymer (A) contains a monomer unit derived from a cyano group-containing monomer. [2] The pressure-sensitive adhesive composition according to [1], wherein the cyano group-containing monomer contains at least one selected from the group consisting of acrylonitrile and methacrylonitrile. [3] The pressure-sensitive adhesive composition according to [1], wherein the content of the cyano group-containing monomer in all monomer components constituting the emulsion-type acrylic polymer (A) is 0.1 to 10 mass%. [4] The pressure-sensitive adhesive composition according to [1], further comprising a crosslinking agent. [5] The pressure-sensitive adhesive composition according to [1], further comprising a thickener (C). [6] The pressure-sensitive adhesive composition according to [1], wherein the electrolyte (B) is an ionic substance. [7] The pressure-sensitive adhesive composition according to [6], wherein the ionic substance is an ionic liquid, and the anion of the ionic liquid comprises at least one selected from the group consisting of a bis(fluorosulfonyl)imide anion and a bis(trifluoromethanesulfonyl)imide anion. [8] The pressure-sensitive adhesive composition according to [5], wherein the thickener (C) comprises at least one selected from the group consisting of a urethane association-type thickener, an alkali swelling-type thickener, and a cellulose-type thickener. [9] The pressure-sensitive adhesive composition according to [1], which is for electrical peeling.

[10] A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to any one of [1] to [9].

[11] A bonded body comprising the pressure-sensitive adhesive sheet according to

[10] and an adherend, wherein the pressure-sensitive adhesive layer is attached to the adherend.

[0011] The pressure-sensitive adhesive composition of the present invention is particularly excellent in adhesive properties when no voltage is applied, and is capable of forming a pressure-sensitive adhesive layer that exhibits excellent impact resistance and whose adhesive strength is sufficiently reduced by the application of a voltage.

[0012] Fig. 1 is a cross-sectional view showing an example of the pressure-sensitive adhesive sheet of the present invention. Fig. 2 is a cross-sectional view showing an example of the laminate structure of the pressure-sensitive adhesive sheet of the present invention. Fig. 3 is a cross-sectional view showing another example of the laminate structure of the pressure-sensitive adhesive sheet of the present invention. Fig. 4 is a cross-sectional view showing an outline of a method for a 180° peel test in Examples.

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes in detail the preferred embodiments of the present invention, but the present invention is not limited to the following preferred embodiments.

[0014] [Adhesive Composition] The adhesive composition according to an embodiment of the present invention is an adhesive composition containing an emulsion-type acrylic polymer (A) and an electrolyte (B), and the emulsion-type acrylic polymer (A) contains a monomer unit derived from a cyano group-containing monomer. The adhesive composition according to an embodiment of the present invention is preferably for electropeeling. The adhesive composition will be described below.

[0015] In this specification, the adhesive strength when no voltage is applied is sometimes referred to as "normal peel strength." The property of adhesive strength decreasing with voltage application is sometimes referred to as "electrical peelability," and a large rate of decrease in adhesive strength due to voltage application is sometimes referred to as "excellent electrical peelability."

[0016] [Components of Pressure-Sensitive Adhesive Composition] <Emulsion-Type Acrylic Polymer (A)> The pressure-sensitive adhesive composition according to an embodiment of the present invention contains an emulsion-type acrylic polymer (A) containing a monomer unit derived from a cyano group-containing monomer. The use of an acrylic polymer containing such a monomer unit not only provides a cost-effective and productive pressure-sensitive adhesive composition, but also allows for the formation of a pressure-sensitive adhesive layer that exhibits particularly excellent adhesive properties in the absence of applied voltage, such as peel strength and creep resistance. Furthermore, the use of a pressure-sensitive adhesive composition containing an emulsion-type polymer dispersed in an aqueous medium (hereinafter also referred to as an emulsion-type pressure-sensitive adhesive composition) reduces the amount of organic solvent used, thereby reducing the environmental impact, compared to the use of a pressure-sensitive adhesive composition containing a solvent-based polymer dissolved in an organic solvent (hereinafter also referred to as a solvent-based pressure-sensitive adhesive composition). Impact resistance can also be improved. While the reason for the improved impact resistance of the resulting pressure-sensitive adhesive layer using an emulsion-type pressure-sensitive adhesive composition is unclear, it is believed that one contributing factor is the interfacial energy dissipation of emulsion particles formed by the emulsion-type acrylic polymer (A). Furthermore, the emulsifier used in emulsion polymerization also functions as an ionic charge transport agent, which may be responsible for the excellent electrical peeling properties.

[0017] The total content of the emulsion-type acrylic polymer (A) in all polymers contained in the pressure-sensitive adhesive composition according to the embodiment of the present invention is preferably 60% by mass or more, and more preferably 80% by mass or more.

[0018] In the pressure-sensitive adhesive composition according to an embodiment of the present invention, the emulsion-type acrylic polymer (A) contains monomer units derived from a cyano group-containing monomer. Examples of the cyano group-containing monomer include acrylonitrile, methacrylonitrile, 3-acryloyloxypropionitrile, 4-[(6-acryloyloxy)hexyloxy]-4'-cyanobiphenyl, and methacrylonitrile. The cyano group-containing monomer preferably contains at least one selected from the group consisting of acrylonitrile and methacrylonitrile.

[0019] The content of the cyano group-containing monomer in all monomer components constituting the emulsion-type acrylic polymer (A) is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 1% by mass or more, and particularly preferably 3% by mass or more. The upper limit is preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 15% by mass or less, particularly preferably 10% by mass or less, and most preferably 5% by mass or less. By setting the content of the cyano group-containing monomer to 0.1% by mass or more, it is easy to obtain an improved adhesive property of the pressure-sensitive adhesive layer when no voltage is applied. Furthermore, by setting the content to 30% by mass or less, it is possible to form a pressure-sensitive adhesive layer that is particularly excellent in adhesive properties when no voltage is applied, such as normal peel strength and creep resistance. The content of the cyano group-containing monomer in all monomer components constituting the emulsion-type acrylic polymer (A) is preferably 0.1 to 10% by mass, more preferably 1 to 5% by mass.

[0020] The emulsion-type acrylic polymer (A) preferably contains a monomer unit derived from a (meth)acrylic acid alkyl ester (the following formula (1)) having an alkyl group having 1 to 14 carbon atoms. Such a monomer unit is suitable for obtaining a large normal peel strength. Furthermore, in order to improve the adhesive strength and electrical peelability of the resulting pressure-sensitive adhesive layer when no voltage is applied, the alkyl group R in the following formula (1) ｂ The number of carbon atoms in is preferably small, particularly preferably 8 or less, and more preferably 4 or less. ２ = C(R ａ ) COOR ｂ (1) [R in formula (1)] ａ is a hydrogen atom or a methyl group, and R ｂ is an alkyl group having 1 to 14 carbon atoms.

[0021] Examples of (meth)acrylic acid alkyl esters having an alkyl group having 1 to 14 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, sec-butyl (meth)acrylate, 1,3-dimethylbutyl acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylbutyl (meth)acrylate, and methylbutyl (meth)acrylate. Examples of suitable acrylates include n-butyl (meth)acrylate, heptyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, n-dodecyl (meth)acrylate, n-tridecyl (meth)acrylate, and n-tetradecyl (meth)acrylate. Among these, n-butyl acrylate, 2-ethylhexyl acrylate, and isononyl acrylate are preferred. The (meth)acrylic acid alkyl esters having an alkyl group having 1 to 14 carbon atoms can be used alone or in combination of two or more.

[0022] The proportion of the (meth)acrylic acid alkyl ester having an alkyl group having 1 to 14 carbon atoms relative to the total amount (100% by mass) of all monomer components constituting the emulsion-type acrylic polymer (A) is not particularly limited, but is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 85% by mass or more. When the proportion of the (meth)acrylic acid alkyl ester having an alkyl group having 1 to 14 carbon atoms is 70% by mass or more, a large normal peel strength is easily obtained.

[0023] For the purpose of improving cohesive strength, heat resistance, crosslinkability, etc., the emulsion-type acrylic polymer (A) preferably contains, in addition to monomer units derived from cyano group-containing monomers and monomer units derived from (meth)acrylic acid alkyl esters having an alkyl group of 1 to 14 carbon atoms, monomer units derived from polar group-containing monomers containing polar groups other than cyano groups that are copolymerizable therewith (hereinafter, sometimes simply referred to as polar group-containing monomers). Monomer units derived from polar group-containing monomers can impart crosslinking points and are suitable for obtaining a large normal peel strength. Furthermore, from the viewpoint of improving adhesive strength and electrical peelability when no voltage is applied, it is also preferable to contain monomer units derived from polar group-containing monomers.

[0024] Examples of polar group-containing monomers include carboxy group-containing monomers, alkoxy group-containing monomers, hydroxyl group-containing monomers, vinyl group-containing monomers, aromatic vinyl monomers, amide group-containing monomers, imide group-containing monomers, amino group-containing monomers, epoxy group-containing monomers, vinyl ether monomers, N-acryloylmorpholine, sulfo group-containing monomers, phosphate group-containing monomers, and acid anhydride group-containing monomers. Among these, carboxy group-containing monomers, alkoxy group-containing monomers, hydroxyl group-containing monomers, and amide group-containing monomers are preferred due to their excellent cohesive properties, with carboxy group-containing monomers being particularly preferred. Carboxy group-containing monomers are particularly suitable for achieving high normal peel strength. Furthermore, they form a protective layer on the surface of emulsion particles formed from the emulsion-type acrylic polymer (A), thereby preventing shear fracture of the particles and improving creep resistance. This effect is further enhanced by neutralizing the carboxy group with a base. The polar group-containing monomers can be used alone or in combination of two or more.

[0025] Examples of carboxyl group-containing monomers include acrylic acid, methacrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid. Acrylic acid is particularly preferred. The carboxyl group-containing monomers can be used alone or in combination.

[0026] Examples of the alkoxy group-containing monomer include methoxy group-containing monomers and ethoxy group-containing monomers, and examples of the methoxy group-containing monomer include 2-methoxyethyl acrylate.

[0027] Examples of hydroxyl group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, (4-hydroxymethylcyclohexyl)methyl (meth)acrylate, N-methylol (meth)acrylamide, vinyl alcohol, allyl alcohol, 2-hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether, and diethylene glycol monovinyl ether. 2-Hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are particularly preferred. The hydroxyl group-containing monomers may be used alone or in combination of two or more.

[0028] Examples of amide group-containing monomers include acrylamide, methacrylamide, N-vinylpyrrolidone, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylacrylamide, N,N-diethylmethacrylamide, N-isopropylacrylamide, N,N'-methylenebisacrylamide, N-propylacrylamide, N-propylmethacrylamide, N-benzylacrylamide, N-benzylmethacrylamide, N-dodecylacrylamide, N-dodecylmethacrylamide, N,N-dimethylaminopropylacrylamide, N,N-dimethylaminopropylmethacrylamide, and diacetoneacrylamide. The amide group-containing monomers can be used alone or in combination of two or more.

[0029] Examples of vinyl group-containing monomers include vinyl esters such as vinyl acetate, vinyl propionate, and vinyl laurate, with vinyl acetate being particularly preferred.

[0030] Examples of aromatic vinyl monomers include styrene, chlorostyrene, chloromethylstyrene, α-methylstyrene, and other substituted styrenes.

[0031] Examples of imide group-containing monomers include cyclohexylmaleimide, isopropylmaleimide, N-cyclohexylmaleimide, and itaconimide.

[0032] Examples of amino group-containing monomers include aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, and N,N-dimethylaminopropyl (meth)acrylate.

[0033] Examples of epoxy group-containing monomers include glycidyl (meth)acrylate, methyl glycidyl (meth)acrylate, and allyl glycidyl ether.

[0034] Examples of vinyl ether monomers include methyl vinyl ether, ethyl vinyl ether, and isobutyl vinyl ether.

[0035] The content of the polar group-containing monomer in the total monomer components constituting the emulsion-type acrylic polymer (A) is preferably 0.1% by mass or more and 35% by mass or less, and preferably 2.5% by mass or more and 6.0% by mass or less. The upper limit of the proportion of the polar group-containing monomer is more preferably 25% by mass, even more preferably 20% by mass, even more preferably 6.0% by mass, even more preferably 5.5% by mass, particularly preferably 5.0% by mass, and most preferably 4.5% by mass, and the lower limit is more preferably 0.5% by mass, even more preferably 1% by mass, even more preferably 2% by mass, even more preferably 2.5% by mass, particularly preferably 3.0% by mass, and most preferably 3.5% by mass. When the content of the polar group-containing monomer is 0.1% by mass or more, cohesion is easily obtained, so that adhesive residue is less likely to occur on the adherend surface after peeling off the pressure-sensitive adhesive layer, and the electrical peelability is improved. Furthermore, when the content of the polar group-containing monomer is 35% by mass or less, it is easy to prevent the pressure-sensitive adhesive layer from adhering excessively to the adherend and causing heavy peeling. In particular, when the content is 2% by mass or more and 20% by mass or less, it is easy to achieve both good releasability from the adherend and good adhesion between the pressure-sensitive adhesive layer and other layers.

[0036] When a carboxyl group-containing monomer is contained as the polar group-containing monomer, its content is preferably 2.5% by mass or more and 6.0% by mass or less of the total monomer components constituting the emulsion-type acrylic polymer (A). The upper limit of the carboxyl group-containing monomer content is more preferably 5.5% by mass, even more preferably 5.0% by mass, and particularly preferably 4.5% by mass, and the lower limit is more preferably 3.0% by mass, even more preferably 3.5% by mass. When the carboxyl group-containing monomer content is 2.5% by mass or more, the normal peel strength is improved. Furthermore, when the carboxyl group-containing monomer content is 6.0% by mass or less, it is preferable from the viewpoint of suppressing corrosion of the metal adherend. In particular, when the content is 3.0% by mass or more and 4.5% by mass or less, it is easy to achieve both normal peel strength and corrosion suppression of the metal adherend.

[0037] Furthermore, the monomer components constituting the emulsion type acrylic polymer (A) may contain a polyfunctional monomer in order to introduce a crosslinked structure into the emulsion type acrylic polymer (A) and make it easier to obtain the required cohesive strength.

[0038] Examples of polyfunctional monomers include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, divinylbenzene, and N,N'-methylenebisacrylamide. The polyfunctional monomers can be used alone or in combination of two or more.

[0039] The content of the polyfunctional monomer in the total monomer components (100% by mass) constituting the emulsion-type acrylic polymer (A) is preferably 0.1% by mass or more and 15% by mass or less. The upper limit of the polyfunctional monomer content is more preferably 10% by mass, and the lower limit is more preferably 3% by mass. When the content of the polyfunctional monomer is 0.1% by mass or more, the flexibility and adhesiveness of the pressure-sensitive adhesive layer are easily improved, which is preferable. When the content of the polyfunctional monomer is 15% by mass or less, the cohesive force is not too high, and appropriate adhesiveness is easily obtained.

[0040] The glass transition temperature (Tg) of the emulsion-type acrylic polymer (A) is not particularly limited, but a temperature of 0° C. or lower is preferable because a decrease in peel strength can usually be suppressed, more preferably −10° C. or lower, and even more preferably −20° C. or lower. A temperature of −40° C. or lower is particularly preferable because the rate of decrease in adhesive strength due to voltage application becomes particularly large, and most preferably −50° C. or lower.

[0041] The glass transition temperature (Tg) can be calculated, for example, based on the following formula (Y) (Fox formula): 1 / Tg=W1 / Tg1+W2 / Tg2+ ... +Wn / Tgn (Y) [In formula (Y), Tg is the glass transition temperature (unit: K) of the polymer, Tgi (i = 1, 2, ... n) is the glass transition temperature (unit: K) when monomer i forms a homopolymer, and Wi (i = 1, 2, ... n) is the mass fraction of monomer i in all monomer components] The above formula (Y) is a calculation formula when a polymer is composed of n types of monomer components, i.e., monomer 1, monomer 2, ..., monomer n.

[0042] The glass transition temperature when a homopolymer is formed refers to the glass transition temperature of a homopolymer of the monomer, and refers to the glass transition temperature (Tg) of a polymer formed using only a certain monomer (sometimes referred to as "monomer X") as the monomer component. Specific values ​​are listed in "Polymer Handbook" (3rd Edition, John Wiley & Sons, Inc., 1989). The glass transition temperature (Tg) of a homopolymer not described in this document refers to a value obtained, for example, by the following measurement method. Specifically, 100 parts by mass of monomer X, 0.2 parts by mass of 2,2'-azobisisobutyronitrile, and 200 parts by mass of ethyl acetate as a polymerization solvent are placed in a reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser, and the mixture is stirred for 1 hour while introducing nitrogen gas. After removing oxygen from the polymerization system in this way, the temperature is raised to 63°C and the reaction is allowed to proceed for 10 hours. The mixture is then cooled to room temperature to obtain a homopolymer solution with a solids concentration of 33% by mass. Next, this homopolymer solution is cast onto a release liner and dried to prepare a test sample (sheet-like homopolymer) with a thickness of approximately 2 mm. Approximately 1 to 2 mg of this test sample is weighed into an aluminum open cell, and the reversing heat flow (specific heat component) behavior of the homopolymer is measured using a temperature-modulated DSC (trade name "Q-2000" manufactured by TA Instruments) at a heating rate of 5°C / min under a nitrogen atmosphere of 50 ml / min. With reference to JIS-K-7121, the glass transition temperature (Tg) of the homopolymer is determined as the temperature at the point where a line equidistant in the vertical direction from a line extending the low-temperature baseline and the high-temperature baseline of the obtained reversing heat flow intersects with the curve representing the stepwise change in the glass transition.

[0043] The emulsion type acrylic polymer (A) used in the present invention can be obtained by emulsion polymerization of the monomer components constituting the emulsion type acrylic polymer (A) using an emulsifier and a polymerization initiator.

[0044] The emulsifier used in the emulsion polymerization of the emulsion-type acrylic polymer (A) is preferably a reactive emulsifier having a radically polymerizable functional group introduced into the molecule (a reactive emulsifier containing a radically polymerizable functional group). These emulsifiers may be used alone or in combination of two or more.

[0045] (Emulsifier) ​​Examples of the emulsifier include anionic emulsifiers, nonionic emulsifiers, cationic emulsifiers, amphoteric emulsifiers, and polymeric emulsifiers.

[0046] Examples of the anionic emulsifier include polyoxyethylene sodium lauryl sulfate, sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecylbenzenesulfonate, polyoxyethylene alkyl ether sodium sulfate, polyoxyethylene alkyl phenyl ether ammonium sulfate, polyoxyethylene alkyl phenyl ether sodium sulfate, and polyoxyethylene alkyl sodium sulfosuccinate.

[0047] Examples of the nonionic emulsifier include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene fatty acid esters, and polyoxyethylene polyoxypropylene block polymers.

[0048] Examples of the cationic emulsifier include dodecyl ammonium chloride, lauryl trimethyl ammonium chloride, and lauryl dimethyl ethyl ammonium ethyl sulfate.

[0049] Examples of the amphoteric emulsifier include betaine ester emulsifiers.

[0050] Examples of the polymeric emulsifier include poly(meth)acrylates such as sodium polyacrylate, polyvinyl alcohol, polyvinylpyrrolidone, polyhydroxyethyl acrylate, copolymers containing one or more of the monomers constituting polyhydroxyethyl acrylate as copolymerization components, styrene-maleic acid copolymer ammonium salt, and sodium carboxymethyl cellulose.

[0051] Alternatively, a reactive emulsifier having a polymerizable group (hereinafter referred to as a "reactive emulsifier") can be used as the emulsifier. Use of a reactive emulsifier is preferred because the emulsifier is incorporated into the polymer, thereby reducing contamination caused by the emulsifier.

[0052] Examples of the reactive emulsifier include emulsifiers obtained by introducing a radically polymerizable functional group such as a vinyl group, a propenyl group, an isopropenyl group, a vinyl ether group, or an allyl ether group into the anionic emulsifiers, nonionic emulsifiers, or cationic emulsifiers. Specific examples include polyoxyethylene styrenated propenyl phenyl ether sulfate ammonium, polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfate ammonium, polyoxyethylene styrenated propenyl phenyl ether, polyoxyethylene-1-(allyloxymethyl) alkyl ether, and ammonium-α-sulfonato-ω-1-(allyloxymethyl) alkyloxy polyoxyethylene. When a reactive emulsifier is used, the acrylic polymer, which is a water-dispersible polymer obtained by emulsion polymerization, contains monomer units derived from the reactive emulsifier.

[0053] As the reactive emulsifier, for example, commercially available products such as those under the trade name "ADEKA REASOAP SE-10N" (manufactured by ADEKA Corporation), those under the trade name "AQUALON HS-10" (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), those under the trade name "AQUALON HS-05" (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), those under the trade name "AQUALON HS-1025" (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and those under the trade name "AQUALON KH-1025" (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) can also be used.

[0054] In particular, impurity ions can be a problem, so the impurity ions are removed and the SO ４ ２－ It is preferable to use an emulsifier with an ion concentration of 100 μg / g or less. In the case of an anionic emulsifier, it is preferable to use an ammonium salt emulsifier. As a method for removing impurities from the emulsifier, an appropriate method such as an ion exchange resin method, a membrane separation method, or a method of precipitating and filtering impurities using alcohol can be used.

[0055] The amount of the reactive emulsifier blended (used) is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 6 parts by mass, and even more preferably 1 to 4 parts by mass, relative to 100 parts by mass of the total amount of raw material monomers (all raw material monomers) constituting the emulsion-type acrylic polymer (A). A blending amount of 0.1 parts by mass or more is preferred because stable emulsification can be maintained. On the other hand, a blending amount of 10 parts by mass or less is preferred because the cohesive strength of the pressure-sensitive adhesive (pressure-sensitive adhesive layer) is improved, contamination of the adherend can be suppressed, and contamination by the emulsifier can be suppressed.

[0056] (pH Buffering Agent) Furthermore, when emulsion polymerizing a monomer mixture using an emulsifier, a pH buffering agent may be used in combination as needed to adjust the pH. The pH buffering agent is not particularly limited as long as it has a pH buffering effect, and examples thereof include sodium hydrogen carbonate, potassium hydrogen carbonate, monosodium phosphate, monopotassium phosphate, disodium phosphate, trisodium phosphate, sodium acetate, ammonium acetate, sodium formate, and ammonium formate.

[0057] (Polymerization initiator) The emulsion type acrylic polymer (A) is preferably a polymer polymerized using a polymerization initiator. The polymerization initiator used for emulsion polymerization of the acrylic emulsion polymer of the present invention is not particularly limited, and examples thereof include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis[2-(5-methyl-2-imidazolin-2-yl)propane] dihydrochloride, 2,2'-azobis(2-methylpropionamidine) disulfate, 2,2'-azobis(N,N'-dimethyleneisobutylamidine), 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine]n Examples of polymerization initiators that can be used include azo-based polymerization initiators such as hydrates; persulfates such as potassium persulfate and ammonium persulfate; peroxide-based polymerization initiators such as benzoyl peroxide, t-butyl hydroperoxide, and hydrogen peroxide; and redox-based initiators obtained by combining a peroxide with a reducing agent, such as a combination of a peroxide and ascorbic acid (e.g., a combination of aqueous hydrogen peroxide and ascorbic acid), a combination of a peroxide and an iron (II) salt (e.g., a combination of aqueous hydrogen peroxide and an iron (II) salt), and a combination of a persulfate and sodium hydrogen sulfite.

[0058] The blending amount (usage amount) of the polymerization initiator can be appropriately determined depending on the types of polymerization initiator and raw material monomers, and is not particularly limited, but is preferably 0.01 to 1 part by mass, and more preferably 0.02 to 0.5 parts by mass, relative to 100 parts by mass of the total amount of raw material monomers (all raw material monomers) constituting the emulsion-type acrylic polymer (A). The blending (dropping) of the polymerization initiator can be carried out by total drop polymerization, in which the initiator is added dropwise all at once, or two-stage polymerization, in which the initiator is added dropwise in two stages. The former is preferred because it makes it easier to control the particle size of the emulsion and is advantageous in terms of antistatic properties.

[0059] (Chain Transfer Agent) The emulsion-type acrylic polymer (A) is preferably a polymer polymerized using a chain transfer agent. Examples of the chain transfer agent that can be preferably used include terpene compounds such as α-pinene, β-pinene, limonene, and terpinolene. Compounds having a thiol group or a hydroxyl group are also commonly known.

[0060] Examples of the compound having a thiol group include mercaptans such as lauryl mercaptan, 2-mercaptoethyl alcohol, t-dodecyl mercaptan, and mercaptosuccinic acid, alkyl mercaptopropionates such as n-butyl mercaptopropionate and octyl mercaptopropionate, and alkoxyalkyl mercaptopropionates such as methoxybutyl mercaptopropionate, etc. Examples of the compound having a hydroxyl group include alcohols such as methyl alcohol, n-propyl alcohol, isopropyl alcohol (IPA), t-butyl alcohol, and benzyl alcohol.

[0061] The amount of the chain transfer agent used is preferably 0 to 1 part by mass per 100 parts by mass of the total monomer mixture used in the emulsion polymerization. By using an amount of 1 part by mass or less, it is possible to prevent a decrease in water resistance, heat resistance, etc. due to a decrease in molecular weight, and to prevent the problem of guide roll contamination from occurring, which is preferable.

[0062] Emulsion polymerization of the emulsion-type acrylic polymer (A) can be carried out by emulsifying the monomer components in an aqueous medium using a conventional method, followed by emulsion polymerization. This allows for the preparation of an aqueous dispersion (polymer emulsion) containing the emulsion-type acrylic polymer (A). The emulsion polymerization method is not particularly limited, and known emulsion polymerization methods such as a batch polymerization method (bulk polymerization method), a monomer dropping method, and a monomer emulsion dropping method can be used. In the monomer dropping method and the monomer emulsion dropping method, continuous dropping (total dropping) or divided dropping (including two-stage dropping, where divided dropping refers to dividing the polymerization process by changing the dropping rate or dropping amount, such as slowing the first dropping and speeding up the second dropping) can be appropriately selected, but continuous dropping (total dropping) is particularly preferred. By employing continuous dropping (total dropping), the average particle size of the emulsion particles of the emulsion-type acrylic polymer (A) used in the present invention can be adjusted to the desired range, making this a preferred embodiment. Polymerization by two-stage dropping is sometimes called two-stage (dropping) polymerization.

[0063] To explain the full-amount dropping polymerization in more detail, when full-amount dropping polymerization is employed, there is insufficient emulsifier in the reaction system (aqueous solution to which a polymerization initiator has been added) to form micelles at the initial stage of dropping, so no reaction occurs (since the reaction occurs within the emulsifier micelles in emulsion dropping polymerization). However, once a certain amount of monomer emulsion is dropped and reaches a concentration sufficient for micelles (critical micelle concentration), the monomer is present in large amounts in the system, resulting in large particle sizes upon reaction. Therefore, by controlling the amount of emulsifier initially charged, taking into account the critical micelle concentration of the emulsifier, it is possible to adjust the average particle size within the desired range. These methods can be combined as appropriate. While reaction conditions can be appropriately selected, the polymerization temperature is preferably about 40 to 95°C, and the polymerization time is preferably about 30 minutes to 24 hours. The average particle size of emulsion particles can also be adjusted by increasing the dropping rate of the monomer emulsion or the polymerization temperature.

[0064] (Average Particle Diameter of Emulsion Particles) The average particle diameter of the emulsion particles of the emulsion-type acrylic polymer (A) used in the present invention is preferably 100 nm to 500 nm. The particle size distribution of the emulsion particles is preferably 1.0 to 4.0.

[0065] As described above, the average particle size of emulsion particles can be controlled by the polymerization conditions such as the method of dropping the polymerization initiator and raw material monomers, the polymerization temperature and polymerization time, as well as the type and concentration of the emulsifier added during polymerization, the concentration of the polymerization initiator, etc. Here, the average particle size of emulsion particles is based on the volume-based median diameter value obtained by measurement using a laser diffraction / scattering particle size distribution analyzer.

[0066] The solvent-insoluble content of the emulsion-type acrylic polymer (A) (the proportion of solvent-insoluble components, sometimes referred to as the "gel fraction") is preferably 40% (mass%) or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more, from the viewpoints of low contamination and appropriate peel strength (adhesive strength). If the solvent-insoluble content is less than 40% by mass, the emulsion-type acrylic polymer (A) contains a large amount of low-molecular-weight components, and the low-molecular-weight components in the adhesive layer cannot be sufficiently reduced by the crosslinking effect alone. This may result in contamination of the adherend due to the low-molecular-weight components, or excessively high peel strength (adhesive strength). The solvent-insoluble content can be controlled by the polymerization initiator, reaction temperature, the type of emulsifier, the raw material monomer, etc. The upper limit of the solvent-insoluble content is not particularly limited, but is, for example, 99% by mass. In the present invention, the solvent-insoluble content of the emulsion-type acrylic polymer (A) is a value calculated by the "Method for Measuring Solvent-Insoluble Content" below.

[0067] -Method for measuring solvent-insoluble content Approximately 0.1 g of emulsion-type acrylic polymer (A) was collected, wrapped in a porous tetrafluoroethylene sheet (trade name "NTF1122", manufactured by Nitto Denko Corporation) with an average pore size of 0.2 μm, and tied with kite string. The weight at this time was measured, and this weight was recorded as the weight before immersion. The weight before immersion was the total weight of the emulsion-type acrylic polymer (A) (collected above), the tetrafluoroethylene sheet, and the kite string. The total weight of the tetrafluoroethylene sheet and the kite string was also measured, and this weight was recorded as the bag weight. Next, the emulsion-type acrylic polymer (A) wrapped in a tetrafluoroethylene sheet and tied with kite string (referred to as the "sample") was placed in a 50 ml container filled with ethyl acetate and allowed to stand at 23°C for 7 days. The sample (after the ethyl acetate treatment) is then removed from the container, transferred to an aluminum cup, and dried in a dryer at 130°C for 2 hours to remove the ethyl acetate. The weight is then measured and used as the post-immersion weight. The solvent-insoluble content is then calculated using the following formula: Solvent-insoluble content (wt%) = (a - b) / (c - b) x 100 (2) (In formula (2), a is the post-immersion weight, b is the bag weight, and c is the pre-immersion weight.)

[0068] The weight-average molecular weight (Mw) of the solvent-soluble fraction (sometimes referred to as the "sol fraction") of the emulsion-type acrylic polymer (A) is preferably 40,000 to 200,000, more preferably 50,000 to 150,000, and even more preferably 60,000 to 100,000. When the weight-average molecular weight of the solvent-soluble fraction of the emulsion-type acrylic polymer (A) is 40,000 or more, the wettability of the PSA composition to the adherend is improved, thereby improving adhesion to the adherend. Furthermore, when the weight-average molecular weight of the solvent-soluble fraction of the emulsion-type acrylic polymer (A) is 200,000 or less, the amount of residual PSA composition on the adherend is reduced, thereby improving low contamination of the adherend. The weight-average molecular weight of the solvent-soluble fraction of the acrylic emulsion polymer can be determined by measuring, by gel permeation chromatography (GPC), a sample (the solvent-soluble fraction of the acrylic emulsion polymer) obtained by air-drying at room temperature the treatment liquid (ethyl acetate solution) after ethyl acetate treatment obtained in the measurement of the solvent-insoluble fraction of the emulsion-type acrylic polymer (A) described above. Specific measurement methods include the following.

[0069] -Method for measuring weight average molecular weight GPC measurement is performed using a GPC device "HLC-8220GPC" manufactured by Tosoh Corporation, and the molecular weight is determined in polystyrene equivalent value. The measurement conditions are as follows. Sample concentration: 0.2 wt% (THF solution) Sample injection amount: 10 μl Eluent: THF Flow rate: 0.6 ml / min Measurement temperature: 40°C Columns: Sample column; 1 TSKguard column SuperHZ-H + 2 TSKgel SuperHZM-H Reference column; 1 TSKgel SuperH-RC Detector: Differential refractometer

[0070] The content of the emulsion-type acrylic polymer (A) in the total solid content of the PSA composition according to the embodiment of the present invention is preferably 50% by mass or more and 99.9% by mass or less, with the upper limit being more preferably 99.5% by mass, still more preferably 99% by mass, and the lower limit being more preferably 60% by mass, still more preferably 70% by mass. In this specification, the solid content of the PSA composition refers to other components excluding water and other dispersion media, and the solid content concentration refers to the mass percentage of the mass of other components excluding water and other dispersion media with respect to the total mass of the PSA composition.

[0071] <Electrolyte (B)> The pressure-sensitive adhesive composition according to the embodiment of the present invention preferably contains an electrolyte, particularly for electro-peeling applications. The electrolyte is a substance that can be ionized into anions and cations, and an ionic substance is preferred as such an electrolyte. An ionic substance is a general term for substances that are in a state other than gas at room temperature (25°C) and are composed of at least one pair of anions and cations. Ionic substances at room temperature (25°C) may be solid, liquid, or in an intermediate state between solid and liquid (e.g., liquid crystal, plastic crystal, viscous solid, viscous liquid). The state of an ionic substance at room temperature (25°C) varies depending on its molecular structure. Examples of ionic substances include ionic liquids, plastic ionic crystals, ionic surfactants, alkali metal salts, alkaline earth metal salts, organic quaternary ammonium salts, etc. From the viewpoint of achieving good electro-peeling properties, ionic liquids are more preferred as the electrolyte contained in the pressure-sensitive adhesive composition.

[0072] (Ionic Liquid) The ionic liquid is not particularly limited as long as it is a molten salt (room-temperature molten salt) composed of a pair of anion and cation and is liquid at 25° C. Examples of anions and cations are given below, but among the ionic substances obtained by combining these, those that are liquid at 25° C. are ionic liquids, and those that are solid at 25° C. are not ionic liquids but ionic solids described below. Among ionic substances, ionic liquids have high ionic conductivity and high thermal stability, so that they can exist as liquids over a wide temperature range, and therefore the effects of the technology disclosed herein tend to be preferably exhibited.

[0073] The anion of the ionic liquid is, for example, (FSO ２ ) ２ N － , (CF ３ SO ２ ) ２ N － , (CF ３ CF ２ SO ２ ) ２ N － , (CF ３ SO ２ ) ３ C － ,Br － , AlCl ４ － , Al ２ Cl ７ － , NO ３ － , B.F. ４ － , P.F. ６ － , C.H. ３ COO － , C.F. ３ COO － , C.F. ３ CF ２ CF ２ COO － , C.F. ３ SO ３ － , C.F. ３ (CF ２ ) ３ SO ３ － , AsF ６ － , SbF ６ － , and F(HF) ｎ － Among them, the anion is (FSO ２ ) ２ N － [bis(fluorosulfonyl)imide anion], and (CF ３ SO ２ ) ２ N －Anions of sulfonylimide compounds such as bis(trifluoromethanesulfonyl)imide anions are preferred because they are chemically stable and suitable for improving electrical peelability. That is, the anion of the ionic liquid preferably includes at least one anion selected from the group consisting of bis(fluorosulfonyl)imide anions and bis(trifluoromethanesulfonyl)imide anions.

[0074] As the cation in the ionic liquid, nitrogen-containing onium, sulfur-containing onium, and phosphorus-containing onium cations are preferred because they are chemically stable and suitable for improving electrical peeling properties, and imidazolium-based, ammonium-based, pyrrolidinium-based, and pyridinium-based cations are more preferred.

[0075] Examples of imidazolium cations include 1-methylimidazolium cation, 1-ethyl-3-methylimidazolium cation, 1-propyl-3-methylimidazolium cation, 1-butyl-3-methylimidazolium cation, 1-pentyl-3-methylimidazolium cation, 1-hexyl-3-methylimidazolium cation, 1-heptyl-3-methylimidazolium cation, 1-octyl-3-methylimidazolium cation, 1-nonyl-3-methylimidazolium cation, 1-undecyl-3-methylimidazolium cation, and 1-dodecyl-3-methylimidazolium cation. imidazolium cation, 1-tridecyl-3-methylimidazolium cation, 1-tetradecyl-3-methylimidazolium cation, 1-pentadecyl-3-methylimidazolium cation, 1-hexadecyl-3-methylimidazolium cation, 1-heptadecyl-3-methylimidazolium cation, 1-octadecyl-3-methylimidazolium cation, 1-undecyl-3-methylimidazolium cation, 1-benzyl-3-methylimidazolium cation, 1-butyl-2,3-dimethylimidazolium cation, and 1,3-bis(dodecyl)imidazolium cation.

[0076] Examples of pyridinium cations include 1-butylpyridinium cation, 1-hexylpyridinium cation, 1-butyl-3-methylpyridinium cation, 1-butyl-4-methylpyridinium cation, and 1-octyl-4-methylpyridinium cation.

[0077] Examples of pyrrolidinium cations include 1-ethyl-1-methylpyrrolidinium cation and 1-butyl-1-methylpyrrolidinium cation.

[0078] Examples of ammonium-based cations include tetraethylammonium cation, tetrabutylammonium cation, methyltrioctylammonium cation, tetradecyltrihexylammonium cation, glycidyltrimethylammonium cation, and trimethylaminoethylacrylate cation.

[0079] From the viewpoint of increasing the rate of decrease in adhesive strength when a voltage is applied, it is preferable to select a cation having a molecular weight of 160 or less as the constituent cation of the ionic liquid. ２ ) ２ N － [bis(fluorosulfonyl)imide anion] or (CF ３ SO ２ ) ２ N －Particularly preferred is an ionic liquid containing a bis(trifluoromethanesulfonyl)imide anion and a cation having a molecular weight of 160 or less. Examples of the cation having a molecular weight of 160 or less include a 1-methylimidazolium cation, a 1-ethyl-3-methylimidazolium cation, a 1-propyl-3-methylimidazolium cation, a 1-butyl-3-methylimidazolium cation, a 1-pentyl-3-methylimidazolium cation, a 1-butylpyridinium cation, a 1-hexylpyridinium cation, a 1-butyl-3-methylpyridinium cation, a 1-butyl-4-methylpyridinium cation, a 1-ethyl-1-methylpyrrolidinium cation, a 1-butyl-1-methylpyrrolidinium cation, a tetraethylammonium cation, a glycidyltrimethylammonium cation, and a trimethylaminoethyl acrylate cation.

[0080] Furthermore, as the cation of the ionic liquid, cations represented by the following formulas (2-A) to (2-D) are also preferred.

[0081]

[0082] R in formula (2-A) １ represents a hydrocarbon group having 4 to 10 carbon atoms (preferably a hydrocarbon group having 4 to 8 carbon atoms, more preferably a hydrocarbon group having 4 to 6 carbon atoms), which may contain a heteroatom; R ２ and R ３ are the same or different and represent a hydrogen atom or a hydrocarbon group having 1 to 12 carbon atoms (preferably a hydrocarbon group having 1 to 8 carbon atoms, more preferably a hydrocarbon group having 2 to 6 carbon atoms, and even more preferably a hydrocarbon group having 2 to 4 carbon atoms), and may contain a heteroatom. However, when a nitrogen atom forms a double bond with an adjacent carbon atom, R ３ does not exist.

[0083] R in formula (2-B) ４ represents a hydrocarbon group having 2 to 10 carbon atoms (preferably a hydrocarbon group having 2 to 8 carbon atoms, more preferably a hydrocarbon group having 2 to 6 carbon atoms), which may contain a heteroatom; R ５ , R ６ , and R ７are the same or different and represent a hydrogen atom or a hydrocarbon group having 1 to 12 carbon atoms (preferably a hydrocarbon group having 1 to 8 carbon atoms, more preferably a hydrocarbon group having 2 to 6 carbon atoms, and even more preferably a hydrocarbon group having 2 to 4 carbon atoms), which may contain a heteroatom.

[0084] R in formula (2-C) ８ represents a hydrocarbon group having 2 to 10 carbon atoms (preferably a hydrocarbon group having 2 to 8 carbon atoms, more preferably a hydrocarbon group having 2 to 6 carbon atoms), which may contain a heteroatom; R ９ , R １０ , and R １１ are the same or different and represent a hydrogen atom or a hydrocarbon group having 1 to 16 carbon atoms (preferably a hydrocarbon group having 1 to 10 carbon atoms, more preferably a hydrocarbon group having 1 to 8 carbon atoms), which may contain a heteroatom.

[0085] In formula (2-D), X represents a nitrogen, sulfur, or phosphorus atom; １２ , R １３ , R １４ , and R １５ are the same or different and represent a hydrocarbon group having 1 to 16 carbon atoms (preferably a hydrocarbon group having 1 to 14 carbon atoms, more preferably a hydrocarbon group having 1 to 10 carbon atoms, even more preferably a hydrocarbon group having 1 to 8 carbon atoms, and particularly preferably a hydrocarbon group having 1 to 6 carbon atoms), which may contain a heteroatom. However, when X is a sulfur atom, R １２ does not exist.

[0086] In an embodiment of the present invention, the cation of the ionic liquid preferably includes at least one selected from the group consisting of nitrogen-containing onium cations, sulfur-containing onium cations, and phosphorus-containing onium cations.

[0087] Examples of commercially available ionic liquids include "E1452", "E0599", "M2098", "M2980", "M2981", and "M2998" manufactured by Tokyo Chemical Industry Co., Ltd., "HMI-FSI" manufactured by Mitsubishi Materials Corporation, and "CIL-312" and "CIL-313" manufactured by Nippon Carlit Co., Ltd.

[0088] (Plastic Ionic Crystal) A plastic ionic crystal is a substance that has a pair of anions and cations, is composed of a regularly aligned three-dimensional crystal lattice, and has disorder at the ionic level, such as local orientation and rotational disorder. Plastic ionic crystals have higher plasticity than ionic solids, and are superior in electrochemical stability and heat resistance among ionic substances, so the effects of the technology disclosed herein tend to be favorably exhibited.

[0089] The anion of the plastic ionic crystal is, for example, (FSO ２ ) ２ N － , (CF ３ SO ２ ) ２ N － , (CF ３ CF ２ SO ２ ) ２ N － , (FSO ２ ) (CF ３ SO ２ ) N － ,Br － , B.F. ４ － , P.F. ６ － , N (CN) ２ － , and F(HF) ｎ － Among them, the anion is (FSO ２ ) ２ N － [bis(fluorosulfonyl)imide anion], and (CF ３ SO ２ ) ２ N － Anions of sulfonylimide compounds such as bis(trifluoromethanesulfonyl)imide anions are preferred because they are chemically stable and suitable for improving electrical peelability. That is, the anion of the plastic ionic crystal preferably includes at least one anion selected from the group consisting of bis(fluorosulfonyl)imide anions and bis(trifluoromethanesulfonyl)imide anions.

[0090] Examples of the cation in the plastic ionic crystal include imidazolium-based, ammonium-based, pyrrolidinium-based, and phosphonium-based cations. Among these, imidazolium-based and pyrrolidinium-based cations are preferred because they are chemically stable and suitable for improving electrical peelability.

[0091] Examples of imidazolium cations include 1-ethyl-3-methylimidazolium cation and 1-butyl-3-methylimidazolium cation.

[0092] Examples of pyrrolidinium cations include 1-ethyl-1-methylpyrrolidinium cation and 1-butyl-1-methylpyrrolidinium cation.

[0093] As for the plastic ionic crystal, from the viewpoint of increasing the rate of decrease in adhesive strength when a voltage is applied, it is preferable to select a cation having a molecular weight of 160 or less as the constituent cation. ２ ) ２ N － [bis(fluorosulfonyl)imide anion] or (CF ３ SO ２ ) ２ N － Particularly preferred is a plastic ionic crystal containing a bis(trifluoromethanesulfonyl)imide anion and a cation having a molecular weight of 160 or less. Examples of the cation having a molecular weight of 160 or less include a 1-ethyl-3-methylimidazolium cation, a 1-butyl-3-methylimidazolium cation, a 1-ethyl-1-methylpyrrolidinium cation, and a 1-butyl-1-methylpyrrolidinium cation.

[0094] An example of a commercially available plastic ionic crystal is "ETHYLMETHYLPYRROLIDINIUM BIS(FLUOROSULFONYL)IMIDE" manufactured by Boron Molecular Inc.

[0095] (Ionic Surfactant) Examples of the ionic surfactant include anionic surfactants and cationic surfactants, and examples thereof include the emulsifiers described above, such as polyoxyethylene sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecylbenzenesulfonate, lauryltrimethylammonium chloride, and polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfate ester ammonium.

[0096] (Alkali Metal Salt) Examples of alkali metal salts include LiCl, Li ２ SO ４ , LiBF ４ , LiPF ６ , LiClO ４ , LiAsF ６ , LiCF ３ SO ３ , LiN(SO ２ CF ３ ) ２ , LiN(SO ２ C ２ F ５ ) ２ , LiC(SO ２ CF ３ ) ３ These examples are lithium salts, but sodium salts or potassium salts may also be used.

[0097] (Alkaline Earth Metal Salt) Examples of alkaline earth metal salts include calcium salts, magnesium salts, barium salts, cesium salts, and halides thereof.

[0098] (Organic Quaternary Ammonium Salt) Examples of organic quaternary ammonium salts include tetrabutylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium iodide, tetramethylammonium hydroxide, and tetramethylammonium fluoride tetrahydrate.

[0099] The molecular weight of the cation in the ionic substance is, for example, 500 or less, preferably 400 or less, more preferably 300 or less, even more preferably 250 or less, particularly preferably 200 or less, and most preferably 160 or less. It is usually 50 or more. It is believed that the cation in the ionic substance has the property of migrating to the cathode side in the pressure-sensitive adhesive layer upon application of a voltage and becoming concentrated near the interface between the pressure-sensitive adhesive layer and the adherend. For this reason, in the present invention, the adhesive strength decreases with application of a voltage relative to the normal peel strength, resulting in electro-separability. Cations with a small molecular weight, such as a molecular weight of 500 or less, are suitable for facilitating the migration of the cation to the cathode side in the pressure-sensitive adhesive layer and increasing the rate of decrease in adhesive strength upon application of a voltage.

[0100] The ionic conductivity of the ionic substance is preferably 0.1 mS / cm or more. More preferably, it is 1 mS / cm or more, even more preferably 3 mS / cm or more, even more preferably 5 mS / cm or more, even more preferably 10 mS / cm or more, particularly preferably 15 mS / cm or more, and most preferably 20 mS / cm or more. There is no particular upper limit, but by having the above ionic conductivity, the adhesive strength is sufficiently reduced even at low voltages. The ionic conductivity can be measured, for example, by the AC impedance method using a Solartron 1260 frequency response analyzer.

[0101] The content (blending amount) of the electrolyte (B) in the pressure-sensitive adhesive composition according to the embodiment of the present invention is preferably 0.5 parts by mass or more relative to 100 parts by mass of the emulsion-type acrylic polymer (A) from the viewpoint of reducing adhesive strength by voltage application, and 30 parts by mass or less is preferred from the viewpoint of increasing peel strength. From the same viewpoint, it is more preferably 20 parts by mass or less, even more preferably 15 parts by mass or less, particularly preferably 10 parts by mass or less, and most preferably 5 parts by mass or less. Furthermore, it is more preferably 0.6 parts by mass or more, even more preferably 0.8 parts by mass or more, particularly preferably 1.0 part by mass or more, and most preferably 1.5 parts by mass or more.

[0102] <Thickener (C)> The pressure-sensitive adhesive composition according to the embodiment of the present invention preferably further contains a thickener (C) for the purpose of improving adhesive properties when no voltage is applied, impact resistance, and electrical peelability.

[0103] Examples of the thickener (C) include urethane association type thickeners, alkali swelling type thickeners, cellulose type thickeners, and natural polymer type thickeners.

[0104] Examples of urethane associative thickeners include urethane compounds having urethane bonds and polyether chains in the molecule, which exhibit a thickening effect when the urethane bonds associate with each other in water. The urethane associative thickener may be a thickener obtained by reacting an isocyanate compound with a polyol compound, and examples of the urethane associative thickener include ester-based, ether-based, and carbonate-based thickeners depending on the type of polyol.

[0105] Examples of alkali-swelling thickeners include polyacrylic acid-based thickeners. Examples of polyacrylic acid-based thickeners include polyacrylic acid and polyacrylic acid-poly(meth)acrylic acid alkyl ester copolymers (acrylic acid-based copolymers). Examples of polyacrylic acid-based thickeners include neutralized products of the above-mentioned polyacrylic acids, i.e., polyacrylates. Examples of polyacrylates include sodium polyacrylate and potassium polyacrylate. Examples of polyacrylic acid-based thickeners include hydrophobic-modified polyacrylic acids in which some of the carboxyl groups have been modified with hydrophobic groups such as styrene groups or alkyl groups.

[0106] The acid value of the polyacrylic acid thickener is, for example, 30 to 300 mg / KOH, or preferably 80 to 280 mg / KOH.

[0107] Examples of cellulose-based thickeners include methyl cellulose, ethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropylmethyl cellulose, and carboxymethyl cellulose.

[0108] Examples of natural polymer thickeners include xanthan gum, gellan gum, guar gum, sodium alginate, carrageenan, and pectin.

[0109] Other examples of thickeners include polyacrylamide, polyethylene oxide, and polyvinyl alcohol.

[0110] These thickeners can be used alone or in combination of two or more.

[0111] The thickener (C) preferably contains at least one selected from the group consisting of a urethane association type thickener, an alkali swelling type thickener, and a cellulose type thickener.

[0112] These thickeners (C) can be commercially available products. Specific examples of urethane associative thickeners include ADEKA NOL UH-462, ADEKA NOL UH-752, ADEKA NOL UH-140S, ADEKA NOL UH-420, ADEKA NOL UH-438, ADEKA NOL UH-472, ADEKA NOL UH-450, ADEKA NOL UH-450VF, ADEKA NOL UH-540, ADEKA NOL UH-550, and ADEKA NOL UH-541. Examples of suitable thickeners include VF, ADEKA NOL UH-526, ADEKA NOL UH-530 (all manufactured by ADEKA Corporation), RHEOLATE 266, RHEOLATE 288, RHEOLATE 244, RHEOLATE 255, RHEOLATE 278 (all manufactured by RHEOX Corporation), SN Thickener A-803, SN Thickener A-804, SN Thickener A-807, SN Thickener A-812, SN Thickener A-814 (all manufactured by San Nopco Ltd.).

[0113] Examples of alkali swelling thickeners include Primal ASE-60, Primal TT-615, Primal ASE-75, Primal ASE-95, Primal ASE-108, and Primal RM-5 (all manufactured by Rohm and Haas Company), Zogen 100, Zogen 150, Zogen 200, Zogen 250, and Zogen 350 (all manufactured by RHEOX), SN Thickener A-815, SN Thickener A-818, and SN Thickener A-850 (all manufactured by San Nopco Ltd.), and RHEOVIS Examples include CR (manufactured by Ipposha Yushi Co., Ltd.), Aron B-300K, Aron B-500 (acrylic acid copolymer), Aron A-7070 (all manufactured by Toagosei Co., Ltd.), Thixol K-150B (manufactured by Kyoeisha Yushi Chemical Industry Co., Ltd.), Acryset WR-503, Acryset WR-650 (all manufactured by Nippon Shokubai Co., Ltd.), etc. Further examples include SN Thickener 640 (hydrophobic group-modified polyacrylic acid, manufactured by San Nopco Ltd.).

[0114] Examples of cellulose-based thickeners include Rheocrysta I-2SX (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), Rheocrysta I-2AX (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and Rheocrysta I-2SXS (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.).

[0115] The above-mentioned thickeners are prepared in the form of, for example, powder (particle) type, aqueous solution type, emulsion type, or the like.

[0116] Furthermore, the thickener (C) has a turbidity when prepared as a 1% by mass aqueous solution and further adjusted to pH 8 of, for example, 100 NTU or less, preferably 50 NTU or less, more preferably 20 NTU or less, and usually 0.1 NTU or more.

[0117] To adjust a 1% by mass aqueous solution to pH 8, for example, an aqueous alkali solution such as an aqueous ammonia solution having a concentration of 5 to 15% by weight is added to a 1% by mass aqueous solution of the thickener. The amount of the aqueous alkali solution added is adjusted so that the rate of decrease in the concentration of the thickener due to its addition is, for example, within 1%.

[0118] The turbidity is measured using a turbidimeter, and NTU is the Nephelometric Turbidity Unit.

[0119] By setting the turbidity of a 1% by mass aqueous solution of the thickener after pH adjustment to the above-mentioned range, insoluble matter (particles) of the thickener remains, and the thickener remains as relatively large particles in the adhesive layer, making it less likely that the adhesive layer will become cloudy due to a decrease in transparency.

[0120] The molecular weight of the thickener (C) is preferably, for example, 5,000 to 2,000,000 in terms of weight average molecular weight.

[0121] The content of the thickener (C) in the pressure-sensitive adhesive composition according to the embodiment of the present invention is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, relative to 100 parts by mass of the emulsion-type acrylic polymer (A), and the upper limit is preferably 15 parts by mass or less, more preferably 10 parts by mass or less, even more preferably 7 parts by mass or less, and even more preferably 5 parts by mass or less.

[0122] The pressure-sensitive adhesive composition according to the embodiment of the present invention further comprises a thickener (C), and the content of the thickener (C) is preferably 0.01 to 15 parts by mass, more preferably 0.01 to 10 parts by mass, even more preferably 0.01 to 7 parts by mass, and even more preferably 0.05 to 5 parts by mass, relative to 100 parts by mass of the emulsion-type acrylic polymer (A). The content of the thickener (C) indicates the content as solid content.

[0123] <Other Components> The pressure-sensitive adhesive composition according to the embodiment of the present invention may contain one or more components (hereinafter, sometimes referred to as "other components") other than the emulsion-type acrylic polymer (A), the electrolyte (B), and the thickener (C), as needed, within a range that does not impair the effects of the present invention. Hereinafter, other components that may be contained in the pressure-sensitive adhesive composition according to the embodiment of the present invention will be described.

[0124] The pressure-sensitive adhesive composition according to the embodiment of the present invention may contain an ionic additive for the purpose of controlling the electric peeling force. As the ionic additive, for example, an ionic solid can be used.

[0125] The ionic solid is an ionic substance that is solid at 25°C. The ionic solid is not particularly limited, and for example, a solid ionic substance obtained by combining an anion and a cation as exemplified in the section describing the ionic liquid above can be used. When the pressure-sensitive adhesive composition contains an ionic solid, the content of the ionic solid is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 2.5 parts by mass or less, relative to 100 parts by mass of the emulsion-type acrylic polymer (A).

[0126] The pressure-sensitive adhesive composition according to the embodiment of the present invention may contain a crosslinking agent, if necessary, for the purpose of improving creep properties and shear properties by crosslinking the emulsion-type acrylic polymer (A). Examples of crosslinking agents include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, carbodiimide-based crosslinking agents, melamine-based crosslinking agents, peroxide-based crosslinking agents, urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, and amine-based crosslinking agents. Examples of isocyanate-based crosslinking agents include toluene diisocyanate and methylene bisphenyl isocyanate. Examples of epoxy-based crosslinking agents include N,N,N',N'-tetraglycidyl-m-xylylene diamine, diglycidyl aniline, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, and 1,6-hexanediol diglycidyl ether. Examples of carbodiimide crosslinking agents include low molecular weight compounds or high molecular weight compounds having two or more carbodiimide groups. Low molecular weight compounds having carbodiimide groups are, for example, represented by the following general formula: R １ -N=C=N-R ２ -N=C=N-R ３ (In the general formula, R １ , R ２ and R ３ are different and represent a hydrocarbon group.) The polymer compound having a carbodiimide group is a polycarbodiimide, and preferably has a moiety with excellent affinity for water, specifically, ethylene oxide (—CH２ -CH ２ Examples of the polymer compound having a carbodiimide group include a polymer compound having a —O— moiety. Commercially available products are used as the polymer compound having a carbodiimide group, and specific examples include the "Carbodilite" series manufactured by Nisshinbo Chemical Inc. Examples of the series include water-soluble types (for example, grade names "V-04," "V-02," and "V-02-L2"), emulsion types (for example, "E-02" and "E-05"), solvent types (for example, "V-03," "V-07," and "V-09"), and solventless types (for example, "V-05").

[0127] When a crosslinking agent is contained, the content thereof is preferably 0.1 parts by mass or more, more preferably 0.7 parts by mass or more, and is preferably 50 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 7 parts by mass or less, relative to 100 parts by mass of the emulsion-type acrylic polymer (A). The crosslinking agents may be used alone or in combination of two or more.

[0128] The pressure-sensitive adhesive composition according to the embodiment of the present invention may contain polyethylene glycol or tetraethylene glycol dimethyl ether, if necessary, for the purpose of aiding the movement of the electrolyte (B) during voltage application. Polyethylene glycol or tetraethylene glycol dimethyl ether having a number-average molecular weight of 100 to 6,000 can be used. When these components are contained, the content is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 15 parts by mass or less, per 100 parts by mass of the emulsion-type acrylic polymer (A). It is preferable that the pressure-sensitive adhesive composition according to the embodiment of the present invention does not contain these components, from the viewpoint of suppressing deterioration of adhesive properties and impact resistance during no voltage application.

[0129] The pressure-sensitive adhesive composition according to the embodiment of the present invention may contain a conductive filler, if necessary, for the purpose of imparting electrical conductivity to the pressure-sensitive adhesive composition. The conductive filler is not particularly limited, and a commonly known or commonly used conductive filler can be used, such as graphite, carbon black, carbon fiber, or metal powder such as silver or copper. When a conductive filler is contained, the content thereof is preferably 0.1 parts by mass or more and 200 parts by mass or less relative to 100 parts by mass of the emulsion-type acrylic polymer (A).

[0130] The pressure-sensitive adhesive composition according to the embodiment of the present invention may contain a corrosion inhibitor, if necessary, for the purpose of inhibiting corrosion of the metal adherend. The corrosion inhibitor is not particularly limited, and a commonly known or commonly used corrosion inhibitor can be used, such as a carbodiimide compound, an adsorptive inhibitor, or a chelating metal deactivator.

[0131] Examples of carbodiimide compounds include 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, N,N'-dicyclohexylcarbodiimide, N,N'-diisopropylcarbodiimide, 1-ethyl-3-tert-butylcarbodiimide, N-cyclohexyl-N'-(2-morpholinoethyl)carbodiimide, N,N'-di-tert-butylcarbodiimide, 1,3-bis(p-tolyl)carbodiimide, and polycarbodiimide resins containing these as monomers. These carbodiimide compounds can be used alone or in combination of two or more. When a carbodiimide compound is contained in the pressure-sensitive adhesive composition according to the embodiment of the present invention, the content thereof is preferably 0.01 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the emulsion-type acrylic polymer (A).

[0132] Examples of the adsorptive inhibitor include alkylamines, carboxylates, carboxylic acid derivatives, and alkyl phosphates. The adsorptive inhibitors can be used alone or in combination of two or more. When the pressure-sensitive adhesive composition according to the embodiment of the present invention contains an alkylamine as the adsorptive inhibitor, the content is preferably 0.01 to 20 parts by mass per 100 parts by mass of the emulsion-type acrylic polymer (A). When the pressure-sensitive adhesive composition according to the embodiment of the present invention contains a carboxylate as the adsorptive inhibitor, the content is preferably 0.01 to 10 parts by mass per 100 parts by mass of the emulsion-type acrylic polymer (A). When the pressure-sensitive adhesive composition according to the embodiment of the present invention contains a carboxylic acid derivative as the adsorptive inhibitor, the content is preferably 0.01 to 10 parts by mass per 100 parts by mass of the emulsion-type acrylic polymer (A). When an alkyl phosphate is contained as an adsorptive inhibitor in the pressure-sensitive adhesive composition according to an embodiment of the present invention, the content thereof is preferably 0.01 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the emulsion-type acrylic polymer (A).

[0133] As the chelating metal deactivator, for example, a triazole group-containing compound or a benzotriazole group-containing compound can be used. These are preferred because they have a high effect of deactivating the surface of metals such as stainless steel and aluminum, and their inclusion in the adhesive component does not affect adhesiveness. The chelating metal deactivators can be used alone or in combination of two or more. When a chelating metal deactivator is contained in the adhesive composition according to the embodiment of the present invention, the content thereof is preferably 0.01 to 20 parts by mass per 100 parts by mass of the emulsion-type acrylic polymer (A). The total content (blending amount) of the corrosion inhibitor is preferably 0.01 to 30 parts by mass per 100 parts by mass of the emulsion-type acrylic polymer (A).

[0134] The pressure-sensitive adhesive composition according to the embodiment of the present invention may also contain various additives such as a tackifying resin, a filler, a plasticizer, an antioxidant, an antioxidant, a pigment (dye), a flame retardant, a solvent, a surfactant (leveling agent), a rust inhibitor, an adhesion promoter, and an antistatic agent. The total content of these components is not particularly limited as long as the effects of the present invention are achieved, but is preferably 0.01 parts by mass or more and 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less, per 100 parts by mass of the emulsion-type acrylic polymer (A).

[0135] Examples of tackifier resins include various tackifier resins such as rosin-based resins, rosin derivative resins, petroleum-based resins, terpene-based resins, phenol-based resins, and ketone-based resins, and preferably rosin-based resins and terpene-based resins.

[0136] The content of the tackifier resin is, relative to 100 parts by mass of the water-dispersible polymer, for example, 5 parts by mass or more, preferably 15 parts by mass or more, more preferably 25 parts by mass or more, even more preferably 33 parts by mass or more, and for example, 50 parts by mass or less, preferably 45 parts by mass or less, more preferably 38 parts by mass or less.

[0137] Examples of fillers include silica, iron oxide, zinc oxide, aluminum oxide, titanium oxide, barium oxide, magnesium oxide, calcium carbonate, magnesium carbonate, zinc carbonate, pyrophyllite clay, kaolin clay, and calcined clay.

[0138] The plasticizer can be a known and commonly used plasticizer used in general resin compositions and the like, and examples thereof include oils such as paraffin oil and process oil; liquid rubbers such as liquid polyisoprene, liquid polybutadiene, and liquid ethylene-propylene rubber; tetrahydrophthalic acid, azelaic acid, benzoic acid, phthalic acid, trimellitic acid, pyromellitic acid, adipic acid, sebacic acid, fumaric acid, maleic acid, itaconic acid, citric acid, and derivatives thereof; dioctyl phthalate (DOP), dibutyl phthalate (DBP), dioctyl adipate, diisononyl adipate (DINA), and isodecyl succinate.

[0139] Examples of antioxidants include hindered phenol compounds, aliphatic and aromatic hindered amine compounds, etc. Examples of antioxidants include butylhydroxytoluene (BHT) and butylhydroxyanisole (BHA), etc. Examples of pigments include inorganic pigments such as titanium dioxide, zinc oxide, ultramarine, red iron oxide, lithopone, lead, cadmium, iron, cobalt, aluminum, hydrochloride, and sulfate, and organic pigments such as azo pigments and copper phthalocyanine pigments.

[0140] Examples of the rust inhibitor include zinc phosphate, tannic acid derivatives, phosphoric acid esters, basic sulfonates, and various rust inhibitor pigments. Examples of the adhesion promoter include titanium coupling agents and zirconium coupling agents. Examples of the antistatic agent generally include quaternary ammonium salts or hydrophilic compounds such as polyglycolic acid and ethylene oxide derivatives.

[0141] [Normal Peel Strength and Electrical Peel Strength] The adhesive strength of the pressure-sensitive adhesive composition according to the embodiment of the present invention can be evaluated by various methods, for example, the 180° peel strength test described in the Examples section.

[0142] The pressure-sensitive adhesive composition according to the embodiment of the present invention preferably has a normal peel strength of 4.0 N / cm or more, more preferably 4.5 N / cm or more, even more preferably 5.0 N / cm or more, particularly preferably 5.5 N / cm or more, and most preferably 6.0 N / cm or more, as measured by forming a pressure-sensitive adhesive sheet as described in the Examples section and conducting a 180° peel test. When the normal peel strength is 4.0 N / cm or more, the adhesion to the adherend is particularly excellent, and the adherend is less likely to peel off or slip.

[0143] Furthermore, it is preferable that the adhesive composition according to the embodiment of the present invention forms an adhesive sheet as described in the Examples section, and the adhesive strength, i.e., the electric peel strength, measured in a 180° peel test immediately after applying a voltage of 30 V for 30 seconds is sufficiently smaller than the normal peel strength.

[0144] The pressure-sensitive adhesive composition according to the embodiment of the present invention is formed into a pressure-sensitive adhesive sheet as described in the Examples section, and the electrical peel strength measured in a 180° peel test immediately after applying a voltage of 30 V for 30 seconds is preferably less than 2.0 N / cm, more preferably 0.5 N / cm or less, even more preferably 0.3 N / cm or less, particularly preferably 0.1 N / cm or less, and most preferably less than 0.01 N / cm. When the electrical peel strength is less than 2.0 N / cm, the electrical peeling property is particularly excellent, making it possible to rework even fragile adherends without destruction.

[0145] The applied voltage and voltage application time during electrical peeling are not limited to those described above, and are not particularly limited as long as the pressure-sensitive adhesive sheet can be peeled off. The preferred ranges for these are shown below. The applied voltage is preferably 1 V or more, more preferably 3 V or more, and even more preferably 6 V or more. It is also preferably 100 V or less, more preferably 50 V or less, even more preferably 30 V or less, and particularly preferably 15 V or less. The voltage application time is preferably 60 seconds or less, more preferably 40 seconds or less, even more preferably 20 seconds or less, and particularly preferably 10 seconds or less. In such cases, workability is excellent. The shorter the application time, the better, but it is usually 1 second or more.

[0146] [Uses of Pressure-Sensitive Adhesive Composition] The uses of the pressure-sensitive adhesive composition according to the embodiment of the present invention are not particularly limited, but it can be preferably used as a pressure-sensitive adhesive composition for electrical peeling and / or for fixing components in electrical and electronic devices. Specific aspects of the pressure-sensitive adhesive composition when applied to such uses are the same as those described below for the uses of the pressure-sensitive adhesive sheet.

[0147] [Method for Producing Pressure-Sensitive Adhesive Composition] The pressure-sensitive adhesive composition according to the embodiment of the present invention is not particularly limited, and can be produced by appropriately stirring and mixing an emulsion solution obtained by emulsion polymerization of an emulsion-type acrylic polymer (A), an electrolyte (B), and optionally a thickener (C), a crosslinker, and the like. The solids concentration of the pressure-sensitive adhesive composition according to the embodiment of the present invention is not particularly limited, and can be, for example, 20 to 60 mass %, and from the viewpoint of coatability, for example, can be, for example, 40 to 55 mass %. As described above, the solids concentration of the pressure-sensitive adhesive composition refers to the mass percentage of the mass of the other components, excluding water and other dispersion media, relative to the total mass of the pressure-sensitive adhesive composition. In the pressure-sensitive adhesive composition according to the embodiment of the present invention, the mass of water relative to the total mass of water and other dispersion media is preferably 50 to 100 mass %, and more preferably 95 to 100 mass %.

[0148] [Adhesive Sheet] [Configuration of Adhesive Sheet] The adhesive sheet according to the embodiment of the present invention is not particularly limited as long as it comprises an adhesive layer (hereinafter also referred to as an "electrically peelable adhesive layer") formed from the adhesive composition according to the embodiment of the present invention described above. The adhesive sheet according to the embodiment of the present invention may also comprise an adhesive layer (hereinafter sometimes referred to as an "other adhesive layer") other than the electrically peelable adhesive layer that does not contain the electrolyte (B). The adhesive sheet according to the embodiment of the present invention may also comprise a substrate, a conductive layer, a conductive substrate, an intermediate layer, an undercoat layer, etc. in addition to the above. The adhesive sheet according to the embodiment of the present invention may be in the form of, for example, a roll or a sheet. It should be noted that the term "adhesive sheet" also encompasses the meaning of "adhesive tape." That is, the adhesive sheet according to the embodiment of the present invention may be an adhesive tape in the form of a tape.

[0149] The pressure-sensitive adhesive sheet according to the embodiment of the present invention may be a double-sided pressure-sensitive adhesive sheet that does not have a substrate and is composed only of an electrically releasing pressure-sensitive adhesive layer, i.e., does not include a substrate layer (substrate-less). The pressure-sensitive adhesive sheet according to the embodiment of the present invention may be a double-sided pressure-sensitive adhesive sheet that has a substrate, and both sides of the substrate are pressure-sensitive adhesive layers (electrically releasing pressure-sensitive adhesive layers or other pressure-sensitive adhesive layers). The pressure-sensitive adhesive sheet according to the embodiment of the present invention may also be a single-sided pressure-sensitive adhesive sheet that has a substrate, and only one side of the substrate is a pressure-sensitive adhesive layer (electrically releasing pressure-sensitive adhesive layer or other pressure-sensitive adhesive layer). The pressure-sensitive adhesive sheet according to the embodiment of the present invention may have a release liner for the purpose of protecting the surface of the pressure-sensitive adhesive layer, but such a release liner is not included in the pressure-sensitive adhesive sheet according to the embodiment of the present invention.

[0150] The structure of the pressure-sensitive adhesive sheet according to the embodiment of the present invention is not particularly limited, and preferred examples include pressure-sensitive adhesive sheet X1 shown in FIG. 1 , pressure-sensitive adhesive sheet X2 shown in FIG. 2 with a laminated structure, and pressure-sensitive adhesive sheet X3 shown in FIG. 3 with a laminated structure. Pressure-sensitive adhesive sheet X1 is a substrate-less double-sided pressure-sensitive adhesive sheet consisting only of an electrically releasing pressure-sensitive adhesive layer 1. Pressure-sensitive adhesive sheet X2 is a substrate-attached double-sided pressure-sensitive adhesive sheet having a layer structure of an adhesive layer 2, an electrically conducting substrate 5 (substrate 3 and conductive layer 4), and an electrically releasing pressure-sensitive adhesive layer 1. Pressure-sensitive adhesive sheet X3 is a substrate-attached double-sided pressure-sensitive adhesive sheet having a layer structure of an adhesive layer 2, an electrically conducting substrate 5 (substrate 3 and conductive layer 4), an electrically releasing pressure-sensitive adhesive layer 1, an electrically conducting substrate 5 (substrate 3 and conductive layer 4), and an adhesive layer 2. In the electrically conducting substrate 5 of pressure-sensitive adhesive sheets X2 and X3 shown in FIGS. 2 and 3 , the substrate 3 is not essential, and only the conductive layer 4 may be present. Furthermore, pressure-sensitive adhesive sheet X2 of FIG. 2 may be a single-sided pressure-sensitive adhesive sheet without the adhesive layer 2.

[0151] The substrate 3 is not particularly limited, but examples thereof include paper-based substrates such as paper, fiber-based substrates such as cloth and nonwoven fabric, plastic-based substrates such as films and sheets made of various plastics (polyolefin-based resins such as polyethylene and polypropylene, polyester-based resins such as polyethylene terephthalate, acrylic resins such as polymethyl methacrylate, etc.), and laminates thereof. The substrate may have a single layer structure or a multi-layer structure. The substrate may be subjected to various treatments such as back surface treatment, antistatic treatment, and primer treatment as necessary.

[0152] The conductive layer 4 is not particularly limited as long as it is a layer having conductivity, but may be a metal substrate such as a metal (e.g., aluminum, magnesium, copper, iron, tin, gold, etc.) foil or a metal plate (e.g., aluminum, magnesium, copper, iron, tin, silver, etc.), a conductive polymer, or the like, or may be a metal vapor deposition film provided on the substrate 3.

[0153] The conductive substrate 5 is not particularly limited as long as it is a substrate having a conductive layer (conductive), but examples thereof include a substrate having a metal layer formed on the surface thereof, such as a substrate having a metal layer formed on the surface thereof by plating, chemical vapor deposition, sputtering, etc. Examples of the metal layer include the metals, metal plates, conductive polymers, etc. exemplified above.

[0154] In the pressure-sensitive adhesive sheet X1, the adherends on both sides preferably have metal adherend surfaces. In the pressure-sensitive adhesive sheet X2, the adherend on the electrically peelable pressure-sensitive adhesive layer 1 side preferably has a metal adherend surface.

[0155] Examples of metal-coated surfaces include conductive surfaces made of metals primarily composed of aluminum, copper, iron, magnesium, tin, gold, silver, and lead, with surfaces made of metals containing iron or aluminum (e.g., stainless steel) being preferred. Examples of adherends having a metal-coated surface include sheets, parts, and plates made of metals primarily composed of aluminum, copper, iron, magnesium, tin, gold, silver, and lead. Adherends other than those having a metal-coated surface include, but are not limited to, fiber sheets such as paper, cloth, and nonwoven fabric, and various plastic films and sheets.

[0156] From the viewpoint of peel strength, the thickness of the electrically peeling pressure-sensitive adhesive layer 1 is preferably 1 μm or more and 1000 μm or less. The upper limit of the thickness of the electrically peeling pressure-sensitive adhesive layer 1 is more preferably 500 μm, even more preferably 300 μm, still more preferably 200 μm, particularly preferably 150 μm, even more particularly preferably 100 μm, even more preferably 80 μm, still more preferably 70 μm, very preferably 60 μm, and most preferably 50 μm, and the lower limit is more preferably 5 μm, even more preferably 10 μm, still more preferably 20 μm, and particularly preferably 30 μm.

[0157] The thickness of the electrically peelable pressure-sensitive adhesive sheet of this embodiment is preferably 20 μm or more and 3000 μm or less. The upper limit of the thickness is more preferably 1000 μm, even more preferably 500 μm, still more preferably 300 μm, particularly preferably 250 μm, even more particularly preferably 200 μm, even more preferably 150 μm, and still more preferably 100 μm, and the lower limit is more preferably 30 μm, even more preferably 50 μm.

[0158] From the viewpoint of adhesive strength, the thickness of the pressure-sensitive adhesive layer 2 is preferably 1 μm or more and 2000 μm or less. The upper limit of the thickness of the pressure-sensitive adhesive layer 2 is more preferably 1000 μm, even more preferably 500 μm, and particularly preferably 100 μm, and the lower limit is more preferably 3 μm, even more preferably 5 μm, and particularly preferably 8 μm.

[0159] The thickness of the substrate 3 is preferably 10 μm or more and 1000 μm or less. The upper limit of the thickness is more preferably 500 μm, even more preferably 300 μm, and particularly preferably 100 μm, and the lower limit is more preferably 12 μm, even more preferably 25 μm.

[0160] The thickness of the conductive layer 4 is preferably 0.001 μm or more and 1000 μm or less. The upper limit of the thickness is more preferably 500 μm, even more preferably 300 μm, particularly preferably 50 μm, and most preferably 10 μm, and the lower limit is more preferably 0.01 μm, even more preferably 0.03 μm, and particularly preferably 0.05 μm.

[0161] The thickness of the conductive substrate 5 is preferably 10 μm or more and 1000 μm or less. The upper limit of the thickness is more preferably 500 μm, even more preferably 300 μm, and particularly preferably 100 μm, and the lower limit is more preferably 12 μm, even more preferably 25 μm.

[0162] The surfaces of the electrically releasable pressure-sensitive adhesive layer and other pressure-sensitive adhesive layers of the pressure-sensitive adhesive sheet according to an embodiment of the present invention may be protected by a release liner. Examples of the release liner include, but are not limited to, a release liner in which the surface of a substrate (liner substrate) such as paper or plastic film is silicone-treated, and a release liner in which the surface of a substrate (liner substrate) such as paper or plastic film is laminated with a polyolefin resin. The thickness of the release liner is not particularly limited, but is preferably 10 μm or more and 100 μm or less.

[0163] The thickness of the pressure-sensitive adhesive sheet according to the embodiment of the present invention is preferably 5 μm or more and 3000 μm or less. The upper limit of the thickness is more preferably 1000 μm, even more preferably 500 μm, still more preferably 300 μm, particularly preferably 250 μm, even more particularly preferably 200 μm, even more preferably 150 μm, and still more preferably 100 μm. The lower limit is more preferably 20 μm, even more preferably 35 μm, and still more preferably 50 μm.

[0164] In particular, in the case of the pressure-sensitive adhesive sheet X2 shown in Fig. 2, the thickness of the pressure-sensitive adhesive sheet is preferably 15 µm or more and 2000 µm or less. The upper limit of the thickness is more preferably 1000 µm, even more preferably 500 µm, still more preferably 300 µm, particularly preferably 250 µm, even more particularly preferably 200 µm, and even more preferably 150 µm, and the lower limit is more preferably 35 µm, even more preferably 50 µm, still more preferably 80 µm, and particularly preferably 100 µm.

[0165] In particular, in the case of the pressure-sensitive adhesive sheet X3 shown in Fig. 3, the thickness of the pressure-sensitive adhesive sheet is preferably 25 µm or more and 3000 µm or less. The upper limit of the thickness is more preferably 1000 µm, even more preferably 500 µm, still more preferably 300 µm, particularly preferably 250 µm, even more particularly preferably 200 µm, and even more preferably 150 µm, and the lower limit is more preferably 50 µm, even more preferably 80 µm, and still more preferably 100 µm.

[0166] The pressure-sensitive adhesive sheet according to an embodiment of the present invention may further comprise a coating layer. The coating layer is preferably provided between the electrically-releasing pressure-sensitive adhesive layer and the conductive layer. By further comprising a coating layer, the electrically-releasing pressure-sensitive adhesive sheet according to this embodiment acts as a barrier to the electrolyte (B) contained in the electrically-releasing pressure-sensitive adhesive layer from penetrating into the conductive layer upon application of voltage, thereby preventing the conductive layer from peeling off from the substrate. Furthermore, the coating layer being in contact with the electrically-releasing pressure-sensitive adhesive layer improves the adhesion between the electrically-releasing pressure-sensitive adhesive layer and the conductive layer, thereby preventing the electrically-releasing pressure-sensitive adhesive layer from being thermally cured when exposed to a high-temperature environment, thereby reducing the interfacial adhesion between the electrically-releasing pressure-sensitive adhesive layer and the adherend (e.g., a conductive material), which would otherwise result in peeling off within the electrically-releasing pressure-sensitive adhesive sheet.

[0167] The coating layer is a layer mainly composed of a resin or an inorganic material, and can be formed from a resin composition mainly composed of a resin component or a composition mainly composed of an inorganic material. The coating layer is made of at least one resin selected from polyester resins, acrylic resins, epoxy resins, and urethane resins, or SiNx, SiOx, Al ２ O ３ It is preferable that the material contains at least one inorganic substance selected from the group consisting of Ni, NiCr, and NiAl.

[0168] [Method for manufacturing pressure-sensitive adhesive sheet] The pressure-sensitive adhesive sheet according to the embodiment of the present invention can be manufactured by a known or commonly used manufacturing method. For the electrically releasable pressure-sensitive adhesive layer in the pressure-sensitive adhesive sheet according to the embodiment of the present invention, a method can be used in which the pressure-sensitive adhesive composition according to the embodiment of the present invention is applied to a release liner, followed by drying and / or curing. For the other pressure-sensitive adhesive layer, a method can be used in which a solution of a pressure-sensitive adhesive composition containing no electrolyte (B) or additives, dissolved in a solvent as necessary, is applied to a release liner, followed by drying and / or curing. The release liners listed above can be used.

[0169] For application, a conventional coater (for example, a gravure roll coater, a reverse roll coater, a kiss roll coater, a dip roll coater, a bar coater, a knife coater, a spray roll coater, etc.) can be used.

[0170] The above-mentioned method can produce an electrically releasing pressure-sensitive adhesive layer and other pressure-sensitive adhesive layers, and the pressure-sensitive adhesive sheet according to the embodiment of the present invention can be produced by laminating the electrically releasing pressure-sensitive adhesive layer and other pressure-sensitive adhesive layers appropriately on a substrate, a conductive layer, and a conductive substrate. Note that the pressure-sensitive adhesive sheet may also be produced by applying the pressure-sensitive adhesive composition to a substrate, a conductive layer, and a conductive substrate instead of a release liner.

[0171] [Method for Electrically Peeling Pressure-Sensitive Adhesive Sheets] The pressure-sensitive adhesive sheet according to an embodiment of the present invention can be peeled from an adherend by applying a voltage to the electrically-peelable pressure-sensitive adhesive layer, thereby generating a potential difference in the thickness direction of the electrically-peelable pressure-sensitive adhesive layer. For example, a bonded structure in which pressure-sensitive adhesive sheet X1 is attached to a conductive adherend can be peeled by passing a current through the conductive adherend and applying a voltage to the electrically-peelable pressure-sensitive adhesive layer. In the case of pressure-sensitive adhesive sheet X2, when the adherend has a metal surface on the electrically-peelable pressure-sensitive adhesive layer side, peeling can be achieved by passing a current through the conductive adherend and the conductive layer 4 and applying a voltage to the electrically-peelable pressure-sensitive adhesive layer. In the case of pressure-sensitive adhesive sheet X3, peeling can be achieved by passing a current through the conductive layer 4 on both sides and applying a voltage to the electrically-peelable pressure-sensitive adhesive layer. The current is preferably applied by connecting terminals to one end and the other end of the pressure-sensitive adhesive sheet so that a voltage is applied to the entire electrically-peelable pressure-sensitive adhesive layer. In addition, when the adherend has a metal surface, the one end and the other end may be part of the adherend having a metal surface. When peeling, water may be added to the interface between the metal adherend surface and the electrically peelable pressure-sensitive adhesive layer before applying voltage.

[0172] [Uses of Pressure-Sensitive Adhesive Sheets] Conventional removable technologies include adhesive layers that are cured and removed by ultraviolet (UV) irradiation, and adhesive layers that are removed by heat. Pressure-sensitive adhesive sheets using such adhesive layers cannot be used in cases where ultraviolet (UV) irradiation is difficult or where heat damages the adherend. Pressure-sensitive adhesive sheets according to embodiments of the present invention that include the electrically releasable adhesive layer do not use ultraviolet or heat, and therefore can be easily removed by applying a voltage without damaging the adherend. Therefore, pressure-sensitive adhesive sheets according to embodiments of the present invention are suitable for use in fixing secondary batteries (e.g., lithium-ion battery packs) used in mobile devices such as smartphones, mobile phones, laptops, video cameras, and digital cameras to their housings, and for fixing the display panels of these devices to their housings.

[0173] In addition, examples of rigid members that can be bonded with the pressure-sensitive adhesive sheet according to the embodiment of the present invention include silicon substrates for semiconductor wafers, sapphire substrates for LEDs, SiC substrates and metal-based substrates, TFT substrates and color filter substrates for displays, display units, display unit protective members, housings, and base substrates for organic EL panels. Examples of fragile members that can be bonded with the double-sided pressure-sensitive adhesive sheet include semiconductor substrates such as compound semiconductor substrates, silicon substrates for MEMS devices, passive matrix substrates, surface cover glass for smartphones, OGS (One Glass Solution) substrates in which a touch panel sensor is attached to the cover glass, organic substrates and organic-inorganic hybrid substrates mainly composed of silsesquioxane, flexible glass substrates for flexible displays, and graphene sheets.

[0174] [Jointed Structure] The joined structure according to an embodiment of the present invention is a joined structure comprising the pressure-sensitive adhesive sheet according to an embodiment of the present invention and an adherend, with the pressure-sensitive adhesive layer being adhered to the adherend. More specifically, the joined structure is a joined structure comprising the pressure-sensitive adhesive sheet according to an embodiment of the present invention and an adherend, with the electrically peelable pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet being adhered to the adherend. The adherend is preferably an adherend having a metal adherend surface, and an adherend having a metal adherend surface may be an electrically conductive adherend or may be made of an electrically conductive material, such as one made of a metal primarily composed of aluminum, copper, iron, magnesium, tin, gold, silver, lead, or the like, with aluminum being preferred.

[0175] Examples of the bonded body of this embodiment include a bonded body in which an adhesive sheet X2 and the electrically peelable adhesive layer 1 side of the adhesive sheet X2 are attached to a conductive adherend having, for example, a metal adherend surface.

[0176] Examples of the bonded body of this embodiment include a bonded body in which the other adhesive layer 2 on both sides of the adhesive sheet X3 is attached to a conductive material having, for example, a metal coating surface, and a bonded body in which any of the other adhesive layers 2 on the adhesive sheet X3 is attached to a non-conductive material.

[0177] Examples of the bonded body according to the embodiment of the present invention include a bonded body which is an adhesive sheet X1 and which includes adherends having metal adherend surfaces on both sides of the electrically peeling adhesive layer 1, a bonded body which is an adhesive sheet X2 and which includes an adherend having a metal adherend surface on the electrically peeling adhesive layer 1 side and an adherend on the adhesive layer 2 side, and a bonded body which is an adhesive sheet X3 and which includes adherends on both sides of the adhesive layer 2.

[0178] As explained above, the present specification discloses the following. [1] A pressure-sensitive adhesive composition containing an emulsion-type acrylic polymer (A) and an electrolyte (B), wherein the emulsion-type acrylic polymer (A) contains a monomer unit derived from a cyano group-containing monomer. [2] The pressure-sensitive adhesive composition according to [1], wherein the cyano group-containing monomer contains at least one selected from the group consisting of acrylonitrile and methacrylonitrile. [3] The pressure-sensitive adhesive composition according to [1] or [2], wherein the content of the cyano group-containing monomer in all monomer components constituting the emulsion-type acrylic polymer (A) is 0.1 to 10 mass%. [4] The pressure-sensitive adhesive composition according to any one of [1] to [3], further comprising a crosslinking agent. [5] The pressure-sensitive adhesive composition according to any one of [1] to [4], further comprising a thickener (C). [6] The pressure-sensitive adhesive composition according to any one of [1] to [5], wherein the electrolyte (B) is an ionic substance. [7] The pressure-sensitive adhesive composition according to [6], wherein the ionic substance is an ionic liquid, and the anion of the ionic liquid comprises at least one selected from the group consisting of a bis(fluorosulfonyl)imide anion and a bis(trifluoromethanesulfonyl)imide anion. [8] The pressure-sensitive adhesive composition according to [5], wherein the thickener (C) comprises at least one selected from the group consisting of a urethane association-type thickener, an alkali swelling-type thickener, and a cellulose-type thickener. [9] The pressure-sensitive adhesive composition according to any one of [1] to [8], which is for electrical peeling.

[10] A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to any one of [1] to [9].

[11] A bonded body comprising the pressure-sensitive adhesive sheet according to

[10] and an adherend, wherein the pressure-sensitive adhesive layer is attached to the adherend.

[0179] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The weight average molecular weights shown below were measured by gel permeation chromatography (GPC).

[0180] <Preparation of emulsion-type acrylic polymer (A)> (Preparation of emulsion (Em)-type acrylic polymer 1) 93 parts by mass of n-butyl acrylate (BA), 4 parts by mass of acrylic acid (AA), 3 parts by mass of acrylonitrile (AN), 0.05 parts by mass of t-dodecanethiol (chain transfer agent), 2.70 parts by mass of Aqualon KH-1025 (emulsifier), and 53 parts by mass of distilled water were blended into a vessel and then stirred and mixed to prepare a monomer emulsion. Next, 0.3 parts by mass of Aqualon KH-1025 (emulsifier, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) and 50 parts by mass of distilled water were added to a reaction vessel equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser, and the atmosphere was replaced with nitrogen at room temperature (25°C) for 1 hour with stirring. Thereafter, 0.1 parts by mass of VA-057 (polymerization initiator, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to the mixture, and the temperature was raised to 60°C. Next, the monomer emulsion was added dropwise to the reaction vessel over 4 hours, and polymerization was carried out with stirring while maintaining the liquid temperature in the reaction vessel at around 60°C. Thereafter, the mixture was cooled to room temperature, and the pH was adjusted to 6 using 10% aqueous ammonia as a pH adjuster, thereby obtaining an Em-based acrylic polymer 1 solution with a solids concentration of 50% by mass.

[0181] (Preparation of Em-based acrylic polymers 2 to 4) Solutions of Em-based acrylic polymers 2 to 4 with a solid content concentration of 50% by mass were obtained in the same manner as for the Em-based acrylic polymer 1, except that the monomer components were changed to the monomer types and blending amounts shown in Tables 1 to 3. Note that MMA in Tables 1 to 3 represents methyl methacrylate.

[0182] Examples 1 to 12, Comparative Examples 1 to 5 Preparation of Pressure-Sensitive Adhesive Compositions The Em-based acrylic polymer solutions containing the emulsion-type acrylic polymer (A) obtained above, the electrolyte (B), the crosslinking agent, and the thickener (C) were used as shown in Tables 1 to 3, and were stirred and mixed to obtain electropeelable pressure-sensitive adhesive compositions (solutions) of Examples 1 to 12 and Comparative Examples 1 to 5, each adjusted to a solids concentration of 40% by mass. Tables 1 to 3 show the blending amount of each component. The values ​​for each component in Tables 1 to 3 below refer to parts by mass. The blending amount (parts by mass) of the emulsion-type acrylic polymer (A) indicates the blending amount (parts by mass) of the solids in the Em-based acrylic polymer solution. Distilled water was used to adjust the solids concentration.

[0183] <Preparation of Electrically Peelable Pressure-Sensitive Adhesive Layer> The electrically peelable pressure-sensitive adhesive composition (solution) obtained above was applied to a uniform thickness using an applicator onto the release-treated surface of a polyethylene terephthalate release liner (trade name "MRF38", manufactured by Mitsubishi Chemical Corporation) whose surface had been release-treated. Next, the coating was dried by heating at 150°C for 3 minutes, and the release-treated surface of another polyethylene terephthalate release liner (trade name "MRE38", manufactured by Mitsubishi Chemical Corporation) whose surface had been release-treated was laminated onto the pressure-sensitive adhesive using a hand roller, to obtain an electrically peelable pressure-sensitive adhesive layer (pressure-sensitive adhesive sheet) having a thickness of 60 µm.

[0184] <Preparation of a single-sided pressure-sensitive adhesive sheet with a substrate> The obtained electrically peelable pressure-sensitive adhesive layer (adhesive sheet) was cut into a sheet measuring 10 mm × 80 mm, the release liner (MRE38) was peeled off, and the metal layer side of a film with a metal layer (product name "1005CR", manufactured by Toray Industries, Inc., thickness 12 μm, size 10 mm × 100 mm) was bonded to the exposed surface of the electrically peelable pressure-sensitive adhesive layer to prepare a single-sided pressure-sensitive adhesive sheet with a substrate.

[0185] <Preparation of Bonded Assembly> The release liner (MRF38) was peeled off from the substrate-attached single-sided PSA sheet, and a stainless steel plate was attached as an adherend to the peeled surface so that one edge of the PSA sheet protruded from the adherend by approximately 20 mm. The sheet was then pressed back and forth once with a 2 kg roller and left to stand in an environment of 23°C for 72 hours, yielding a bonded assembly consisting of stainless steel plate 6 / electrically peelable PSA layer (PSA sheet 1' / metal layer-attached film (current-carrying substrate) 5'. An overview of this bonded assembly is shown in Figure 4.

[0186] <Evaluation> (180° Peel Force) A 180° peel force test was carried out using the bonded structures of the Examples and Comparative Examples. Using a peel tester (product name "Variable Angle Peel Tester YSP", manufactured by Asahi Seiko Co., Ltd.), peeling was performed in the direction of the arrow in FIG. 4 , and the adhesive strength in the 180° peel test (tensile speed: 300 mm / min, peel temperature 23° C.) was measured. The 180° peel force was measured and defined as the normal peel force. The evaluation was based on the following criteria: 5.0 [N / cm] or more: Good; 4.0 [N / cm] or more to less than 5.0 [N / cm]: Fair; and Less than 4.0 [N / cm]: Bad.

[0187] (Electrical Peeling Force) The electrical peeling force was measured using the bonded bodies of the Examples and Comparative Examples. Before peeling, the positive and negative electrodes of a DC current machine were attached to the bonded bodies at the positions α and β in FIG. 4, respectively, and a voltage of 30 V was applied for 30 seconds. Immediately after that, peeling was performed in the same manner as in the above-mentioned 180° peeling force measurement, and the adhesive strength immediately after voltage application was measured and used as the electrical peeling force. The evaluation was also based on the following criteria: Less than 0.01 [N / cm]: ○ 0.01 [N / cm] or more to less than 2.0 [N / cm]: △ 2.0 [N / cm] or more: ×

[0188] (Impact resistance) Two strips of the electrically peelable pressure-sensitive adhesive layer (adhesive sheet) of each Example and Comparative Example were cut into 5 mm wide x 20 mm long strips to be used as evaluation samples. The evaluation samples were placed on two opposing sides of a 2 mm thick, 50 mm x 50 mm square stainless steel plate with a 20 mm long x 20 mm wide hole in the center, and a square stainless steel plate (outer diameter 30 mm square, thickness 3 mm) was placed on top of it. Then, the samples were pressed together so that a uniform force was applied in the direction of gravity (70 N x 15 s), and left to stand at 50 ° C for 3 hours. The evaluation sample was then removed and returned to 23 ° C. Next, a measurement table was placed on the base of a DuPont impact tester (manufactured by Toyo Seiki Seisakusho Co., Ltd.), and the evaluation sample was placed on top of it with the square stainless steel plate facing down. Furthermore, a stainless steel impact core with a tip radius of 3.1 mm was placed on the evaluation sample, and the weight and height of the falling weight were changed in 50 mm increments from 50 mm to 500 mm at 50 g, in 50 mm increments from 50 mm to 500 mm at 100 g, in 50 mm increments from 50 mm to 500 mm at 150 g, in 50 mm increments from 350 mm to 500 mm at 200 g, in 50 mm increments from 400 mm to 500 mm at 200 g, and in 50 mm increments from 350 mm to 500 mm at 300 g, until peeling occurred. The energy was increased until peeling occurred. For previously evaluated energies, the test was not repeated, and the load and height were set so that the amount of energy would not overlap. The energy before peeling was then calculated as load x height, and the result was determined. Evaluation was also based on the following criteria: 0.25 J or more: Good; 0.20 J or more but less than 0.25 J: Fair; and Less than 0.20 J: Bad.

[0189] (Creep Resistance) The electrically peelable pressure-sensitive adhesive layer (adhesive sheet) of each Example and Comparative Example was cut to a size of 25 mm x 25 mm to prepare a sample. The release liner (MRE38) was peeled off from this sample, and the exposed electrically peelable pressure-sensitive adhesive layer surface was attached to the tip of a stainless steel plate (SUS316, size: 30 mm x 120 mm) of a first adherend. Next, the other release liner (MRF38) was peeled off, and the tip of a stainless steel plate (SUS316, size: 30 mm x 120 mm) of a second adherend was brought into contact with the exposed electrically peelable pressure-sensitive adhesive layer surface to obtain a laminate (first adherend / electrically peelable pressure-sensitive adhesive layer (adhesive sheet) / second adherend) in which the two adherends were bonded together. Next, the laminate was pressed back and forth once with a 2 kg roller and left in an environment at 23°C for 72 hours (hr), and the attachment position of the laminate after leaving it for 72 hours was designated as the initial attachment position. Thereafter, a load of 5 kg was applied to one end of the laminate, and the laminate was left for one week in an environment at a temperature of 23°C. After one week of leaving the laminate, the amount of displacement (mm) from the initial attachment position was measured. If the laminate peeled off and fell within one week, it was recorded as "Fall". The evaluation was also made according to the following criteria: Displacement less than 10 mm: ○ Displacement 10 mm or more or Fall: ×

[0190] The measurement results are shown in Tables 1 to 3.

[0191]

[0192]

[0193]

[0194] The abbreviations for the electrolyte (B), ion promoter, crosslinking agent, and thickener (C) in Tables 1 to 3 are as follows:

[0195] (Electrolyte (B)) Ionic liquid Ionic liquid 1: cation: 1-ethyl-3-methylimidazolium cation, anion: bis(fluorosulfonyl)imide anion, trade name "E1452" manufactured by Tokyo Chemical Industry Co., Ltd. Plastic ionic crystal Plastic ionic crystal 1: cation: 1-ethyl-1-methylpyrrolidinium cation, anion: bis(fluorosulfonyl)imide anion, trade name "ETHYLMETHYLPYRROLIDINIUM BIS(FLUOROSULFONYL)IMIDE" manufactured by Boron Molecular Inc.

[0196] (Ion accelerator) PEG400: polyethylene glycol 400 (average molecular weight 380 to 420), manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

[0197] (Crosslinking agent) E-02: Polycarbodiimide resin, trade name "Carbodilite E-02", manufactured by Nisshinbo Chemical Inc.

[0198] (Thickeners (C)) Urethane associative type UH-450VF: trade name "ADEKA NOL UH-450VF", manufactured by ADEKA Corporation UH-420: trade name "ADEKA NOL UH-420", manufactured by ADEKA Corporation UH-550: trade name "ADEKA NOL UH-550", manufactured by ADEKA Corporation UH-530: trade name "ADEKA NOL UH-530", manufactured by ADEKA Corporation Alkali swelling type B-500: acrylic thickener, trade name "Aron B-500", manufactured by Toagosei Co., Ltd. Cellulose type Rheocrysta: trade name "Rheocrysta I-2SX", manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.

[0199] The electrically peelable pressure-sensitive adhesive layers formed using the pressure-sensitive adhesive compositions of Examples 1 to 12 were particularly excellent in adhesive properties (normal peel strength and creep resistance) when no voltage was applied, and also had excellent impact resistance, and the adhesive strength was sufficiently reduced by the application of voltage.

[0200] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0201] Although various embodiments have been described above with reference to the drawings, it goes without saying that the present invention is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention. Furthermore, the components of the above-described embodiments may be combined in any manner without departing from the spirit of the invention.

[0202] The pressure-sensitive adhesive composition of the present invention is particularly excellent in adhesive properties when no voltage is applied, and is capable of forming a pressure-sensitive adhesive layer that exhibits excellent impact resistance and whose adhesive strength is sufficiently reduced by the application of a voltage.

[0203] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 2023-185744) filed on October 30, 2023, the contents of which are incorporated herein by reference.

[0204] X1, X2, X3 Adhesive sheet 1 Electrically peelable adhesive layer 2 Adhesive layer 3 Substrate 4 Conductive layer 5 Conductive substrate

Claims

1. A pressure-sensitive adhesive composition comprising an emulsion-type acrylic polymer (A) and an electrolyte (B), wherein the emulsion-type acrylic polymer (A) contains a monomer unit derived from a cyano group-containing monomer.

2. The pressure-sensitive adhesive composition according to claim 1, wherein the cyano group-containing monomer comprises at least one selected from the group consisting of acrylonitrile and methacrylonitrile.

3. The pressure-sensitive adhesive composition according to claim 1, wherein the content of the cyano group-containing monomer in all monomer components constituting the emulsion-type acrylic polymer (A) is 0.1 to 10 mass %.

4. The pressure-sensitive adhesive composition according to claim 1, further comprising a crosslinking agent.

5. The pressure-sensitive adhesive composition according to claim 1, further comprising a thickener (C).

6. The pressure-sensitive adhesive composition according to claim 1, wherein the electrolyte (B) is an ionic substance.

7. The pressure-sensitive adhesive composition according to claim 6, wherein the ionic substance is an ionic liquid, and the anion of the ionic liquid includes at least one anion selected from the group consisting of a bis(fluorosulfonyl)imide anion and a bis(trifluoromethanesulfonyl)imide anion.

8. The pressure-sensitive adhesive composition according to claim 5, wherein the thickener (C) comprises at least one selected from the group consisting of urethane association type thickeners, alkali swelling type thickeners, and cellulose type thickeners.

9. The pressure-sensitive adhesive composition according to claim 1, which is for electrical peeling.

10. A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to any one of claims 1 to 9.

11. A bonded body comprising the adhesive sheet according to claim 10 and an adherend, the adhesive layer being attached to the adherend.

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