Adhesive composition, adhesive sheet, and bonded body

Abstract

The purpose of the present invention is to provide: an adhesive composition from which an adhesive layer, which firmly bonds members when a voltage is not applied thereto, and the adhesive strength of which is sufficiently reduced by applying a voltage thereto, can be formed; an adhesive sheet comprising an adhesive layer that is formed from said adhesive composition; and a bonded body. The present invention relates to: an adhesive composition which contains a polymer, an ionic liquid, and a tackifier, wherein the product of the acid value [mgKOH / g] of the tackifier and the content [parts by mass] of the tackifier with respect to 100 parts by mass of the polymer is less than 1,200; an adhesive sheet comprising an adhesive layer that is formed from said adhesive composition; and a bonded body.

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] Known double-sided pressure-sensitive adhesive sheets that achieve the above-mentioned adhesive strength and releasability include pressure-sensitive adhesive sheets that are peeled off by applying a voltage to the pressure-sensitive adhesive layer (electrically peelable pressure-sensitive adhesive sheets) (Patent Documents 1 to 3). The electrically peelable pressure-sensitive adhesive sheet in Patent Document 3 uses an ionic liquid consisting of cations and anions as a component that forms the pressure-sensitive adhesive composition, and describes that upon application of a voltage, the cations of the ionic liquid migrate to the cathode side and become unevenly distributed near the interface between the pressure-sensitive adhesive layer and the adherend, thereby weakening the adhesive strength at the adhesive interface and making peeling easier.

[0004] Furthermore, Patent Documents 1 to 3 disclose that a tackifier may be contained as an additive in the adhesive layer that forms the adhesive sheet in order to improve adhesive strength when no voltage is applied.

[0005] Japanese Patent No. 6152288 Japanese Patent No. 6097112 Japanese Patent Application Laid-Open No. 2020-164778

[0006] It is preferable that the electrically peelable pressure-sensitive adhesive sheet firmly bonds members when no voltage is applied, and can be peeled off with little force when a voltage is applied.

[0007] However, as a result of investigations by the present inventors, a new problem was discovered in that, in conventional technology, although the addition of a tackifier improves the bonding strength when no voltage is applied, the peelability may deteriorate when a voltage is applied.

[0008] The present invention was completed in view of the above, and aims to provide a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer that firmly bonds members when no voltage is applied and whose adhesive strength is sufficiently reduced when a voltage is applied, and a pressure-sensitive adhesive sheet including a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition.

[0009] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by setting the product of the acid value [mg KOH / g] of the tackifier and the content [parts by mass] of the tackifier per 100 parts by mass of the polymer within a specific range, and have thus completed the present invention.

[0010] That is, the present invention is as follows. [1] A pressure-sensitive adhesive composition comprising a polymer, an ionic liquid, and a tackifier, wherein the product of the acid value [mg KOH / g] of the tackifier and the content [parts by mass] of the tackifier per 100 parts by mass of the polymer is less than 1,200. [2] The pressure-sensitive adhesive composition according to [1], wherein the softening point of the tackifier is 100°C or higher. [3] The pressure-sensitive adhesive composition according to [1], wherein the content of the tackifier is 5 to 50 parts by mass per 100 parts by mass of the polymer. [4] The pressure-sensitive adhesive composition according to [1], wherein the tackifier is a terpene-based tackifier resin or a rosin-based tackifier resin. [5] The pressure-sensitive adhesive composition according to [1], wherein 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. [6] The pressure-sensitive adhesive composition according to [1], wherein the polymer comprises at least one selected from the group consisting of polyester-based polymers, urethane-based polymers, and acrylic-based polymers. [7] The pressure-sensitive adhesive composition according to [1], further comprising a second polymer having a glass transition temperature (Tg) of 40 to 180°C. [8] The pressure-sensitive adhesive composition according to [7], wherein the content of the second polymer is 1 to 50 parts by mass per 100 parts by mass of the polymer. [9] The pressure-sensitive adhesive composition according to [1], which is used 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 a conductive material, wherein the pressure-sensitive adhesive layer is adhered to the conductive material.

[0011] According to the present invention, it is possible to provide a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer that firmly bonds members when no voltage is applied and whose adhesive strength is sufficiently reduced when a voltage is applied, as well as a pressure-sensitive adhesive sheet and a bonded body that include a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition.

[0012] Fig. 1 is a cross-sectional view showing an example of a pressure-sensitive adhesive sheet of the present invention. Fig. 2 is a cross-sectional view showing an example of a laminate structure of a pressure-sensitive adhesive sheet of the present invention. Fig. 3 is a cross-sectional view showing another example of a laminate structure of a 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 the 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 contains a polymer, an ionic liquid, and a tackifier, and the product of the acid value [mg KOH / g] of the tackifier and the content [parts by mass] of the tackifier per 100 parts by mass of the polymer is less than 1200. The inventors have conducted studies and found that when a tackifier having an acid value is added to an adhesive composition containing a polymer and an ionic liquid so that the product of the acid value [mg KOH / g] of the tackifier and the content [parts by mass] of the tackifier per 100 parts by mass of the polymer is 1200 or more, the adhesive strength when no voltage is applied is improved, but the decrease in adhesive strength due to the application of a voltage is insufficient. This is thought to be due to the following two factors: (i) poor compatibility between the polymer and the tackifier results in poor dispersibility of the tackifier in the adhesive layer formed from the adhesive composition, resulting in precipitation of the tackifier and phase separation of the adhesive layer, and (ii) tackifiers with an acid value have the ability to capture ionic liquids, which prevents cations in the ionic liquid from migrating to the cathode when voltage is applied, preventing uneven distribution near the interface between the adhesive layer and the adherend.

[0015] In the pressure-sensitive adhesive composition according to an embodiment of the present invention, the product of the acid value [mg KOH / g] of the tackifier and the content [parts by mass] of the tackifier per 100 parts by mass of the polymer is set to less than 1200. This improves the dispersion state of the tackifier in the pressure-sensitive adhesive layer and suppresses the capture of the ionic liquid by the tackifier, making it possible to achieve both improved adhesive strength when no voltage is applied and a sufficient decrease in adhesive strength when a voltage is applied. The pressure-sensitive adhesive composition is suitable as an electrically peelable pressure-sensitive adhesive composition. The pressure-sensitive adhesive composition will be described below.

[0016] In this specification, the adhesive strength when no voltage is applied is sometimes referred to as "initial adhesive strength." The property of adhesive strength decreasing with voltage application is sometimes referred to as "electrical releasability," and a large rate of decrease in adhesive strength due to voltage application is sometimes referred to as "excellent electrical releasability."

[0017] <Components of Pressure-Sensitive Adhesive Composition> (Polymer) The pressure-sensitive adhesive composition according to the embodiment of the present invention contains a polymer. The polymer according to the embodiment of the present invention is not particularly limited as long as it is a general organic polymer compound, and is, for example, a polymer or partial polymer of a monomer. The monomer may be one type of monomer or a mixture of two or more types of monomers. Note that a partial polymer refers to a polymer in which at least a part of the monomer or monomer mixture is partially polymerized.

[0018] The polymer in the embodiment of the present invention is not particularly limited as long as it is normally used as an adhesive and has adhesive properties, and examples thereof include acrylic polymers, rubber polymers, vinyl alkyl ether polymers, silicone polymers, polyester polymers, polyamide polymers, urethane polymers, fluorine-containing polymers, and epoxy polymers. The above polymers can be used alone or in combination of two or more.

[0019] The polymer in the embodiment of the present invention preferably includes at least one selected from the group consisting of polyester polymers, urethane polymers, and acrylic polymers. The acrylic polymer preferably has a carboxyl group, an alkoxy group, a hydroxyl group, and / or an amide bond. Since polyester polymers and urethane polymers have easily polarizable hydroxyl groups at their terminals, and since acrylic polymers having carboxyl groups, alkoxy groups, hydroxyl groups, and / or amide bonds have easily polarizable carboxyl groups, alkoxy groups, hydroxyl groups, and / or amide bonds, the use of these polymers makes it possible to obtain a pressure-sensitive adhesive layer that exhibits excellent adhesive strength when no voltage is applied.

[0020] The total content of the polyester polymer, urethane polymer, and acrylic polymer in all polymers contained in the pressure-sensitive adhesive composition according to an embodiment of the present invention is preferably 60% by mass or more, and more preferably 80% by mass or more.

[0021] In particular, in order to improve costs, productivity, and initial adhesive strength, the polymer in the embodiment of the present invention is preferably an acrylic polymer, and more preferably an acrylic polymer having a carboxyl group, an alkoxy group, a hydroxyl group, and / or an amide bond. That is, the pressure-sensitive adhesive composition according to the embodiment of the present invention is preferably an acrylic pressure-sensitive adhesive composition containing an acrylic polymer as the polymer.

[0022] The acrylic polymer 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 initial adhesive strength. Furthermore, in order to improve the adhesive strength and electrical peelability when no voltage is applied to the resulting pressure-sensitive adhesive layer, it is preferable to use a monomer unit derived from an alkyl (meth)acrylic acid ester (the following formula (1)) having an alkyl group having 1 to 14 carbon atoms. ｂ The number of carbon atoms in CH 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.

[0023] 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, and 2-ethylbutyl (meth)acrylate. Examples of the (meth)acrylate include n-butyl acrylate, n-butyl acrylate, n-ethyl acrylate, n-octyl acrylate, n-isooctyl acrylate, n-ethyl acrylate, n-octyl acrylate, n-isooctyl acrylate, n-ethyl acrylate, n-butyl ...

[0024] The proportion of the (meth)acrylic acid alkyl ester having an alkyl group having 1 to 14 carbon atoms relative to all monomer components (100% by mass) constituting the acrylic polymer 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 initial adhesive strength is easily obtained.

[0025] For the purpose of improving cohesive strength, heat resistance, crosslinkability, etc., the acrylic polymer preferably contains a monomer unit derived from a polar group-containing monomer copolymerizable with a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 14 carbon atoms, in addition to the monomer unit. The monomer unit can impart crosslinking points and is suitable for obtaining a large initial adhesive strength. Furthermore, from the viewpoint of improving adhesive strength and electrical peelability when no voltage is applied, it is also preferable to contain a monomer unit derived from a polar group-containing monomer.

[0026] Examples of polar group-containing monomers include carboxyl group-containing monomers, alkoxy group-containing monomers, hydroxyl group-containing monomers, cyano 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, carboxyl group-containing monomers, alkoxy group-containing monomers, hydroxyl group-containing monomers, and amide group-containing monomers are preferred from the viewpoint of excellent cohesion properties, and carboxyl group-containing monomers are particularly preferred. Carboxyl group-containing monomers are particularly suitable for obtaining high initial adhesive strength. Polar group-containing monomers can be used alone or in combination of two or more.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] Examples of amide group-containing monomers include acrylamide, methacrylamide, N-vinylpyrrolidone, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylacrylamide, N,N-diethylmethacrylamide, N,N'-methylenebisacrylamide, N,N-dimethylaminopropylacrylamide, N,N-dimethylaminopropylmethacrylamide, and diacetoneacrylamide. The amide group-containing monomers can be used alone or in combination of two or more.

[0031] Examples of cyano group-containing monomers include acrylonitrile and methacrylonitrile.

[0032] Examples of vinyl group-containing monomers include vinyl esters such as vinyl acetate, vinyl propionate, and vinyl laurate, with vinyl acetate being particularly preferred.

[0033] Examples of aromatic vinyl monomers include styrene, chlorostyrene, chloromethylstyrene, α-methylstyrene, and other substituted styrenes.

[0034] Examples of imide group-containing monomers include cyclohexylmaleimide, isopropylmaleimide, N-cyclohexylmaleimide, and itaconimide.

[0035] Examples of amino group-containing monomers include aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, and N,N-dimethylaminopropyl (meth)acrylate.

[0036] Examples of epoxy group-containing monomers include glycidyl (meth)acrylate, methyl glycidyl (meth)acrylate, and allyl glycidyl ether.

[0037] Examples of vinyl ether monomers include methyl vinyl ether, ethyl vinyl ether, and isobutyl vinyl ether.

[0038] The proportion of the polar group-containing monomer relative to the total monomer components (100% by mass) constituting the acrylic polymer is preferably 0.1% by mass or more and 35% 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, and the lower limit is more preferably 0.5% by mass, even more preferably 1% by mass, and particularly preferably 2% by mass. When the proportion of the polar group-containing monomer is 0.1% by mass or more, cohesive strength is easily obtained, so that adhesive residue is less likely to remain on the adherend surface after peeling the pressure-sensitive adhesive layer, and electrical peelability is improved. Furthermore, when the proportion of the polar group-containing monomer is 35% by mass or less, it is easy to prevent the pressure-sensitive adhesive layer from excessively adhering to the adherend and causing heavy peeling. In particular, when the proportion is 2% by mass or more and 20% by mass or less, it is easy to achieve both releasability from the adherend and adhesion between the pressure-sensitive adhesive layer and other layers.

[0039] Furthermore, the monomer components constituting the acrylic polymer may contain a polyfunctional monomer in order to introduce a crosslinked structure into the acrylic polymer and make it easier to obtain the required cohesive strength.

[0040] 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.

[0041] The content of the polyfunctional monomer relative to the total monomer components (100% by mass) constituting the acrylic polymer 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.

[0042] Polyester-based polymers are typically polymers having a structure formed by condensation of a polycarboxylic acid such as a dicarboxylic acid or a derivative thereof (hereinafter also referred to as a "polycarboxylic acid monomer") with a polyhydric alcohol such as a diol or a derivative thereof (hereinafter referred to as a "polyhydric alcohol monomer").

[0043] The polycarboxylic acid monomer is not particularly limited, but examples thereof include adipic acid, azelaic acid, dimer acid, sebacic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 4-methyl-1,2-cyclohexanedicarboxylic acid, dodecenylsuccinic anhydride, fumaric acid, succinic acid, dodecanedioic acid, hexahydrophthalic anhydride, tetrahydrophthalic anhydride, maleic acid, maleic anhydride, itaconic acid, citraconic acid, and derivatives thereof. The polycarboxylic acid monomers can be used alone or in combination of two or more.

[0044] The polyhydric alcohol monomer is not particularly limited, but examples thereof include ethylene glycol, 1,2-propylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 2,2,4-trimethyl-1,5-pentanediol, 2-ethyl-2-butylpropanediol, 1,9-nonanediol, 2-methyloctanediol, 1,10-decanediol, and derivatives thereof. The polyhydric alcohol monomers can be used alone or in combination of two or more.

[0045] Examples of urethane polymers include ether polyurethanes and polyester polyurethanes.

[0046] Examples of ether-based polyurethanes include urethane acrylate resins. Coating compositions for forming resin films using urethane acrylate resins can be prepared, for example, by polymerizing a precursor containing a polyether segment, a (meth)acrylic segment, and a urethane segment under conditions that allow control of the molecular weight to produce an oligomer, and then adding various additives to the oligomer. This oligomer can be applied to a support substrate and crosslinked to obtain a urethane acrylate resin film on the support substrate. More specifically, coating compositions for forming resin films using urethane acrylate resins can be prepared by prepolymerizing a polyether polyol, an isocyanate group-containing compound, and a hydroxyalkyl (meth)acrylate, or an acrylic-modified polyether polyol and an isocyanate group-containing compound, to produce a urethane acrylate oligomer, and then adding appropriate additives to the oligomer. This oligomer can be applied to a support substrate and crosslinked to obtain a urethane acrylate resin film on the support substrate.

[0047] Examples of polyether polyols include polyalkylene glycols such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol, and various derivatives thereof.

[0048] Examples of ester-based polyurethanes include adipate-based (ester-based) polyurethanes and polycaprolactone-based (ester-based) polyurethanes.

[0049] In an embodiment of the present invention, a polymer can be obtained by (co)polymerizing monomer components. The polymerization method is not particularly limited, but examples thereof include solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization (active energy ray polymerization). In particular, from the viewpoints of cost and productivity, solution polymerization is preferred. When copolymerized, the polymer may be any of a random copolymer, a block copolymer, an alternating copolymer, a graft copolymer, and the like.

[0050] The solution polymerization method is not particularly limited, but examples thereof include a method in which a monomer component, a polymerization initiator, etc. are dissolved in a solvent and heated to polymerize, thereby obtaining a polymer solution containing a polymer.

[0051] As the solvent used in the solution polymerization method, various common solvents can be used. Examples of such solvents (polymerization solvents) include organic solvents such as aromatic hydrocarbons such as toluene, benzene, and xylene; esters such as ethyl acetate and n-butyl acetate; aliphatic hydrocarbons such as n-hexane and n-heptane; alicyclic hydrocarbons such as cyclohexane and methylcyclohexane; and ketones such as methyl ethyl ketone and methyl isobutyl ketone. The solvents can be used alone or in combination of two or more.

[0052] The amount of the solvent used is not particularly limited, but is preferably 10 parts by mass or more and 1,000 parts by mass or less relative to the total monomer components (100 parts by mass) constituting the polymer. The upper limit of the amount of the solvent used is more preferably 500 parts by mass, and the lower limit is more preferably 50 parts by mass.

[0053] The polymerization initiator used in the solution polymerization method is not particularly limited, but examples thereof include peroxide-based polymerization initiators, azo-based polymerization initiators, etc. Examples of the peroxide-based polymerization initiator are not particularly limited, but examples thereof include peroxycarbonate, ketone peroxide, peroxyketal, hydroperoxide, dialkyl peroxide, diacyl peroxide, and peroxyester, and more specific examples thereof include benzoyl peroxide, t-butyl hydroperoxide, di-t-butyl peroxide, t-butyl peroxybenzoate, dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, and 1,1-bis(t-butylperoxy)cyclododecane, etc. The azo polymerization initiator is not particularly limited, but examples thereof include 2,2'-azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-methylpropionate)dimethyl, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), 2,2'-azobis(2,4,4-trimethylpentane), 4,4'-azobis Examples of polymerization initiators include 4-cyanovaleric acid, 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) hydrochloride, and 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine] hydrate. The polymerization initiators can be used alone or in combination of two or more.

[0054] The amount of the polymerization initiator used is not particularly limited, but is preferably 0.01 to 5 parts by mass relative to the total monomer components (100 parts by mass) constituting the polymer. The upper limit of the amount of the polymerization initiator used is more preferably 3 parts by mass, and the lower limit is more preferably 0.05 parts by mass.

[0055] In the solution polymerization method, the heating temperature when polymerizing by heating is not particularly limited, but is, for example, 50° C. to 80° C. The heating time is not particularly limited, but is, for example, 1 hour to 24 hours.

[0056] The weight-average molecular weight of the polymer is not particularly limited, but is preferably 100,000 or more and 5,000,000 or less. The upper limit of the weight-average molecular weight is more preferably 4,000,000, even more preferably 3,000,000, and the lower limit is more preferably 200,000, even more preferably 300,000. When the weight-average molecular weight is 100,000 or more, the cohesive force is reduced, and the problem of adhesive residue remaining on the adherend surface after peeling off the pressure-sensitive adhesive layer can be effectively suppressed. Furthermore, when the weight-average molecular weight is 5,000,000 or less, the problem of insufficient wettability on the adherend surface after peeling off the pressure-sensitive adhesive layer can be effectively suppressed.

[0057] The weight average molecular weight is obtained by measurement by gel permeation chromatography (GPC). More specifically, for example, it can be measured using a GPC measurement device with the trade name "HLC-8220GPC" (manufactured by Tosoh Corporation) under the following conditions, and calculated as a value converted into standard polystyrene.

[0058] (Weight-average molecular weight measurement conditions) Sample concentration: 0.2% by mass (tetrahydrofuran solution) Sample injection volume: 10 μL Sample column: TSKguard column Super HZ-H (1 column) + TSKgel Super HZM-H (2 columns) Reference column: TSKgel Super H-RC (1 column) Eluent: tetrahydrofuran (THF) Flow rate: 0.6 mL / min Detector: differential refractometer (RI) Column temperature (measurement temperature): 40°C

[0059] The glass transition temperature (Tg) of the polymer is not particularly limited, but is preferably 0° C. or lower because this can suppress a decrease in the initial adhesive strength, more preferably −10° C. or lower, and even more preferably −20° C. or lower. Furthermore, if it is −40° C. or lower, the rate of decrease in adhesive strength due to voltage application becomes particularly large, so it is particularly preferred, and most preferably −50° C. or lower.

[0060] 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.

[0061] 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.

[0062] The polymer content in the pressure-sensitive adhesive composition according to the embodiment of the present invention is preferably 50% by mass or more and 99.9% by mass or less, relative to the total amount (100% by mass) of the pressure-sensitive adhesive composition, the upper limit is more preferably 99.5% by mass, and even more preferably 99% by mass, and the lower limit is more preferably 60% by mass, and even more preferably 70% by mass.

[0063] (Ionic Liquid) The ionic liquid in the embodiment of the present invention 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 are ionic solids described below.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] Examples of pyrrolidinium cations include 1-ethyl-1-methylpyrrolidinium cation and 1-butyl-1-methylpyrrolidinium cation.

[0069] Examples of ammonium-based cations include tetraethylammonium cation, tetrabutylammonium cation, methyltrioctylammonium cation, tetradecitrihexylammonium cation, glycidyltrimethylammonium cation, and trimethylaminoethylacrylate cation.

[0070] 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.

[0071] Furthermore, as the cation of the ionic liquid, cations represented by the following formulas (2-A) to (2-D) are also preferred.

[0072]

[0073] 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 ３are 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.

[0074] 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 ７ 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), which may contain a heteroatom.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] The molecular weight of the cation in the ionic liquid 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 liquid has the property of migrating to the cathode side in the pressure-sensitive adhesive layer when a voltage is applied, and being biased toward the interface between the pressure-sensitive adhesive layer and the adherend. For this reason, in the present invention, the adhesive strength during voltage application decreases relative to the initial adhesive 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 cations to the cathode side in the pressure-sensitive adhesive layer and increasing the rate of decrease in adhesive strength when a voltage is applied.

[0079] Examples of commercially available ionic liquids include "ELEXEL AS-110," "ELEXEL MP-442," "ELEXEL IL-210," "ELEXEL MP-471," "ELEXEL MP-456," and "ELEXEL AS-804" manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.; "HMI-FSI" manufactured by Mitsubishi Materials Corporation; and "CIL-312" and "CIL-313" manufactured by Nippon Carlit Co., Ltd.

[0080] The ionic conductivity of the ionic liquid 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.

[0081] The content (blending amount) of the ionic liquid 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 polymer from the viewpoint of reducing adhesive strength during voltage application, and preferably 30 parts by mass or less from the viewpoint of increasing initial adhesive 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 parts by mass or more, and most preferably 1.5 parts by mass or more.

[0082] (Tackifier) ​​In the tackifier according to an embodiment of the present invention, the product of the acid value [mg KOH / g] of the tackifier and the content [parts by mass] of the tackifier relative to 100 parts by mass of the polymer (hereinafter simply referred to as the "product of acid value and content") is less than 1200. The product of acid value and content may be less than 1200, but since electrical peelability tends to deteriorate as the amount of carboxylic acid groups contained in the PSA increases, it is preferably 1000 or less, more preferably 750 or less, even more preferably 500 or less, and most preferably 300 or less. There are no particular restrictions on the lower limit, but from the viewpoint of electrical peelability, it can be, for example, 10 or more.

[0083] Here, the acid value can be a value measured by potentiometric titration as specified in JIS K0070: 1992. The specific measurement method is as follows.

[0084] [Method for measuring acid value] 1. Reagents (1) A mixture of diethyl ether and ethanol in a volume ratio of 4:1 is used as the solvent. (2) A 0.1 mol / L potassium hydroxide ethanol solution is used as the measurement reagent. (3) A phenolphthalein solution is used as the indicator.

[0085] 2. Procedure (1) Add a few drops of phenolphthalein solution to the solvent and neutralize with 0.1 mol / L potassium hydroxide ethanol solution. (2) Accurately weigh out approximately 5 g of sample into a beaker, add 50 mL of the solvent neutralized in 1) above, and stir and dissolve completely on a panel heater (80°C). (3) Perform potentiometric titration with 0.1 mol / L potassium hydroxide ethanol solution. The inflection point of the obtained titration curve is the endpoint.

[0086] 3. Calculation Calculate the acid value using the following formula: Acid value (mg KOH / g) = (B × f × 5.611) / S Where, B: Amount (mL) of 0.1 mol / L potassium hydroxide ethanol solution used in the sample, f: Factor of the 0.1 mol / L potassium hydroxide ethanol solution, S: Mass (g) of the sample, 5.611: 1 / 10 of the molecular weight of potassium hydroxide, 56.11.

[0087] The hydroxyl value of the tackifier is not particularly limited, and may be more than 0 mgKOH / g, but is preferably 0 mgKOH / g.

[0088] The tackifier preferably has a softening point of 100°C or higher, more preferably 120°C or higher, even more preferably 130°C or higher, and most preferably 145°C or higher. By adjusting the softening point of the tackifier to 100°C or higher, it is possible to further improve the adhesive strength when no voltage is applied, i.e., the initial adhesive strength. Furthermore, the softening point is preferably 200°C or lower, more preferably 180°C or lower, even more preferably 170°C or lower, and most preferably 160°C or lower. By adjusting the softening point of the tackifier to 200°C or lower, the dispersibility of the tackifier in the adhesive layer is improved, precipitation or phase separation of the tackifier is less likely to occur, and the movement of the ionic liquid in the adhesive layer when a voltage is applied is less likely to be hindered.

[0089] The softening point of the tackifier is defined as the value measured based on the softening point test method (ring and ball method) specified in JIS K5902 and JIS K2207. Specifically, the sample is melted as quickly as possible at the lowest possible temperature and carefully filled into a ring placed on a flat metal plate, avoiding the formation of bubbles. After cooling, any raised portion of the ring, including the top edge, is cut off with a slightly heated knife. Next, a holder (ring stand) is placed in a glass container (heating bath) with a diameter of at least 85 mm and a height of at least 127 mm, and glycerin is poured in to a depth of at least 90 mm. Next, a steel ball (diameter 9.5 mm, weight 3.5 g) and the ring filled with the sample are immersed in the glycerin without touching each other, and the glycerin temperature is maintained at 20°C ± 5°C for 15 minutes. Next, the steel ball is placed in the center of the surface of the sample in the ring and placed in its fixed position on the holder. Next, keeping the distance from the top of the ring to the glycerin surface at 50 mm, place a thermometer, align the center of the thermometer's mercury bulb with the center of the ring, and heat the container. The flame of the Bunsen burner used for heating should be aimed midway between the center of the bottom and the edge of the container, ensuring even heating. After heating begins and reaching 40°C, the rate of increase in bath temperature must be 5.0 ± 0.5°C per minute. The sample gradually softens, flows down the ring, and finally touches the bottom plate, at which point the temperature is read and considered the softening point. Two or more samples should be measured at the same time, and the average value should be used.

[0090] As the tackifier, for example, a tackifying resin is used. Specific examples of the tackifying resin include phenol-based tackifying resins, terpene-based tackifying resins, rosin-based tackifying resins, hydrocarbon-based tackifying resins, epoxy-based tackifying resins, polyamide-based tackifying resins, elastomer-based tackifying resins, and ketone-based tackifying resins.

[0091] Examples of phenolic tackifying resins include terpene phenolic resins, hydrogenated terpene phenolic resins, alkylphenolic resins, rosin phenolic resins, and xylene-formaldehyde resins. Terpene phenolic resins refer to polymers containing terpene and phenol residues, and encompass both copolymers of terpenes and phenolic compounds (terpene-phenolic copolymer resins) and phenol-modified terpene homopolymers or copolymers of terpenes (phenol-modified terpene resins). Terpenes constituting such terpene phenolic resins include, for example, monoterpenes such as α-pinene, β-pinene, and limonene (including d-, l-, and d / l-(dipentene)). Hydrogenated terpene phenolic resins, sometimes referred to as hydrogenated terpene phenolic resins, are those obtained by hydrogenating such terpene phenolic resins. Alkylphenolic resins are resins (oil-based phenolic resins) obtained from alkylphenols and formaldehyde. Examples of alkylphenolic resins include novolac and resol types. Examples of rosin phenolic resins include phenol-modified products of rosins or various rosin derivatives (including rosin esters, unsaturated fatty acid-modified rosins, and unsaturated fatty acid-modified rosin esters). Examples of rosin phenolic resins include rosin phenolic resins obtained by adding phenol to rosins or various rosin derivatives using an acid catalyst and then thermally polymerizing the resulting phenol.

[0092] Examples of terpene-based tackifying resins include terpene resins, terpene phenol resins, styrene-modified terpene resins, aromatic-modified terpene resins, and hydrogenated terpene resins. Examples of terpene resins include polymers of terpenes (typically monoterpenes) such as α-pinene, β-pinene, d-limonene, 1-limonene, and dipentene. Examples of homopolymers of one type of terpene include α-pinene polymers, β-pinene polymers, and dipentene polymers.

[0093] The concept of rosin-based tackifying resins encompasses both rosins and rosin derivative resins, including, for example, unmodified rosins (raw rosins) such as gum rosin, wood rosin, and tall oil rosin, and modified rosins obtained by modifying these unmodified rosins through hydrogenation, disproportionation, polymerization, etc. (hydrogenated rosin, disproportionated rosin, polymerized rosin, and other chemically modified rosins).

[0094] Examples of rosin derivative resins include rosin esters such as unmodified rosin esters, which are esters of unmodified rosin and alcohols, and modified rosin esters, which are esters of modified rosin and alcohols; unsaturated fatty acid-modified rosins obtained by modifying rosin with unsaturated fatty acids; unsaturated fatty acid-modified rosin esters obtained by modifying rosin esters with unsaturated fatty acids; rosin alcohols obtained by reducing the carboxyl groups of rosins or rosin derivative resins (rosin esters, unsaturated fatty acid-modified rosins, unsaturated fatty acid-modified rosin esters, etc.); rosin phenols; metal salts thereof; etc. Examples of rosin esters include methyl esters, triethylene glycol esters, glycerin esters, pentaerythritol esters, and maleic acid esters of unmodified rosin or modified rosin (e.g., hydrogenated rosin, disproportionated rosin, polymerized rosin, etc.).

[0095] Examples of hydrocarbon tackifying resins include aliphatic hydrocarbon resins, aromatic hydrocarbon resins (e.g., styrene-based resins, xylene-based resins, etc.), aliphatic cyclic hydrocarbon resins, aliphatic / aromatic petroleum resins (styrene-olefin copolymers, etc.), aliphatic / alicyclic petroleum resins, hydrogenated hydrocarbon resins, coumarone-based resins, and coumarone-indene-based resins.

[0096] Among these, terpene-based tackifying resins or rosin-based tackifying resins are preferred. The tackifiers may be used alone or in combination of two or more. When two or more tackifiers are used in combination in the embodiment of the present invention, the product of the acid value and the content of each tackifier is calculated, and the sum of these values ​​is less than 1,200. When two or more tackifiers are used in combination, the preferred range of the sum of the products of the acid value and the content of each tackifier is the same as the preferred range when each tackifier is used alone.

[0097] The preferred acid value of the tackifier according to the embodiment of the present invention varies depending on the content of the tackifier used, but generally, from the viewpoint of electrical peelability, it is preferably, for example, 50 mgKOH / g or less, more preferably 30 mgKOH / g or less, and most preferably 10 mgKOH / g. There are no particular restrictions on the lower limit. The acid value of the tackifier is preferably 1 to 200 mgKOH / g.

[0098] The content of the tackifier in the pressure-sensitive adhesive composition according to the embodiment of the present invention varies depending on the acid value of the tackifier used. Generally, from the viewpoint of electrical peelability, it is preferably 5 parts by mass or more, more preferably 7.5 parts by mass or more, even more preferably 10 parts by mass or more, and most preferably 15 parts by mass or more, per 100 parts by mass of the polymer. By setting the content of the tackifier to 5 parts by mass or more, the effect of adding the tackifier, i.e., the effect of achieving both initial adhesive strength and electrical peelability, is easily obtained. The upper limit is preferably 50 parts by mass or less, more preferably 45 parts by mass or less, even more preferably 40 parts by mass or less, and most preferably 30 parts by mass. By setting the content of the tackifier to 50 parts by mass or less, the dispersibility of the tackifier in the resin can be maintained, making it easier to obtain initial adhesive strength. The content of the tackifier in the pressure-sensitive adhesive composition is preferably 5 to 50 parts by mass per 100 parts by mass of the polymer.

[0099] (Second Polymer) The pressure-sensitive adhesive composition according to the embodiment of the present invention may further contain a second polymer having a glass transition temperature (Tg) of 40 to 180°C.

[0100] In the pressure-sensitive adhesive composition according to an embodiment of the present invention, the second polymer is required to have a glass transition temperature (Tg) of 40 to 180°C. It is sufficient that the second polymer is different from the polymer. By including a second polymer having a glass transition temperature (Tg) of 40 to 180°C, the pressure-sensitive adhesive composition according to an embodiment of the present invention can obtain the effect of improving the elastic modulus, and can form a pressure-sensitive adhesive layer that exhibits excellent adhesive strength when no voltage is applied, and whose adhesive strength is sufficiently reduced by the application of a voltage even after storage in a high-temperature, high-humidity environment, and has excellent humidity and heat stability.

[0101] The glass transition temperature (Tg) of the second polymer is preferably 40°C or higher, more preferably 50°C or higher, even more preferably 60°C or higher, and preferably 70°C or higher, from the viewpoint of adhesive properties. Furthermore, from the viewpoint of adhesive properties, it must be 180°C or lower, more preferably 160°C or lower, even more preferably 140°C or lower, even more preferably 120°C or lower, and preferably 100°C or lower. The glass transition temperature (Tg) of the second polymer can be calculated in the same manner as the glass transition temperature (Tg) of the polymer. Furthermore, the glass transition temperature (Tg) of the second polymer can be adjusted by the type and amount of monomers constituting the second polymer.

[0102] In the embodiment of the present invention, the second polymer is not particularly limited as long as its Tg satisfies the above-mentioned specific range, and a general organic polymer compound can be used, including a polymer or partial polymer of a monomer. The monomer may be a single type of monomer or a mixture of two or more types of monomers. The partial polymer refers to a polymer in which one or more components of the monomer or monomer mixture are partially polymerized.

[0103] The second polymer may be adhesive or may be the tackifier resin described above. Preferably, the second polymer further comprises an organic polymer compound in addition to the tackifier resin described above. The pressure-sensitive adhesive composition preferably includes a second polymer, particularly an organic polymer compound as the second polymer, because this further improves the initial adhesive strength and electrical peelability. Examples of organic polymer compounds included in the second polymer include acrylic polymers, rubber polymers, vinyl alkyl ether polymers, silicone polymers, polyester polymers, polyamide polymers, urethane polymers, fluorine-containing polymers, and epoxy polymers. In this specification, the organic polymer compound in the second polymer refers to a compound that is a polymer or partial polymer of a monomer, and refers to a component that is different from the tackifier resin and the polymer.

[0104] Among the above, it is preferable to use an acrylic polymer or a polyester polymer from the viewpoint of adhesive properties. In the embodiment of the present invention, the acrylic polymer used as the organic polymer compound in the second polymer may be a commercially available product, or may be obtained by polymerizing an acrylic monomer component.

[0105] Examples of commercially available acrylic polymers used as the organic polymer compound in the second polymer include ARUFON UH2170 and UC3000 (manufactured by Toagosei Co., Ltd.).

[0106] As the acrylic monomer component, any acrylic monomer can be used, and examples thereof include hydroxyl group-containing acrylic monomers and polymerizable acrylic monomers.

[0107] The acrylic monomer component constituting the organic polymer compound in the second polymer preferably contains a polymerizable acrylic monomer. The polymerizable acrylic monomer contained in the acrylic monomer component may be of one type or two or more types.

[0108] Examples of polymerizable monomers include acrylic acid (AA), N-vinyl-2-pyrrolidone, dicyclopentanyl methacrylate, methyl acrylate (MA), methyl methacrylate (MMA), cyclohexyl acrylate, cyclohexyl methacrylate (CHMA), isobornyl acrylate (IBXMA), β-carboxyethyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, acrylonitrile, acrylamide, dimethylacrylamide, isopropylacrylamide, hydroxyethylacrylamide, hydroxymethylacrylamide, hydroxybutylacrylamide, acrylic acid, acrylic acid esters ... Examples of the acrylic acid copolymer include acryloylmorpholine (ACMO) and 1-vinylimidazole. In terms of being able to more effectively exhibit the effects of the present invention, preferred is at least one selected from acrylic acid, methyl acrylate (MA), methyl methacrylate (MMA), cyclohexyl acrylate, cyclohexyl methacrylate (CHMA), isobornyl acrylate (IBXMA), and acryloylmorpholine (ACMO), and more preferred is at least one selected from acrylic acid (AA), cyclohexyl acrylate, cyclohexyl methacrylate (CHMA), and isobornyl acrylate (IBXMA).

[0109] From the viewpoint of adhesive properties, the content of the polymerizable monomer in the acrylic monomer component is preferably 1% by mass or more, more preferably 10% by mass or more, even more preferably 30% by mass or more, even more preferably 50% by mass or more, and preferably 80% by mass or more.

[0110] Specific examples of the hydroxyl group-containing monomer include hydroxyalkyl (meth)acrylates such as 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl acrylate (4HBA), 4-hydroxybutyl methacrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, and 12-hydroxylauryl (meth)acrylate; hydroxyalkyl cycloalkane (meth)acrylates such as (4-hydroxymethylcyclohexyl)methyl (meth)acrylate; and other hydroxyl group-containing monomers such as hydroxyethyl (meth)acrylamide, allyl alcohol, 2-hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether, and diethylene glycol monovinyl ether.

[0111] Among these, the hydroxyl group-containing monomer is preferably a hydroxyalkyl(meth)acrylate from the viewpoint of ease of handling and the ability to further exhibit the effects of the present invention, and more preferably a hydroxyalkyl(meth)acrylate having a hydroxyalkyl group having 2 to 6 carbon atoms. Specifically, it is preferably at least one selected from 2-hydroxyethyl(meth)acrylate and 4-hydroxybutyl(meth)acrylate, and more preferably 4-hydroxybutyl acrylate (4HBA).

[0112] The content of the hydroxyl group-containing monomer in the acrylic monomer component is preferably 1% by mass or more, more preferably 3% by mass or more, even more preferably 5% by mass or more, even more preferably 10% by mass or more, and preferably 15 parts by mass, from the viewpoint of adhesive properties. Also, from the viewpoint of adhesive properties, it is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less.

[0113] The organic polymer compound in the second polymer according to an embodiment of the present invention can be produced by any appropriate polymerization method as long as the effects of the present invention are not impaired. Examples of methods for polymerizing the organic polymer compound in the second polymer according to an embodiment of the present invention include solution polymerization, emulsion polymerization, bulk polymerization, and polymerization by active energy ray irradiation (active energy ray polymerization). Among these, bulk polymerization and solution polymerization are preferred, and solution polymerization is more preferred.

[0114] Examples of solvents that can be used in the polymerization include organic solvents such as esters such as ethyl acetate and n-butyl acetate, aromatic hydrocarbons such as toluene and benzene, aliphatic hydrocarbons such as n-hexane and n-heptane, alicyclic hydrocarbons such as cyclohexane and methylcyclohexane, and ketones such as methyl ethyl ketone and methyl isobutyl ketone. Only one type of solvent may be used, or two or more types may be used.

[0115] In the polymerization, any appropriate polymerization initiator (for example, a thermal polymerization initiator or a photopolymerization initiator) can be used as long as it does not impair the effects of the present invention. The polymerization initiator may be one type or two or more types. When solution polymerization is performed, it is preferable to use an oil-soluble polymerization initiator.

[0116] As the thermal polymerization initiator, any appropriate thermal polymerization initiator can be used as long as it does not impair the effects of the present invention. The thermal polymerization initiator may be one type only or two or more types. Examples of the thermal polymerization initiator include 2,2'-azobisisobutyronitrile (AIBN), 2,2'-azobis-2-methylbutyronitrile (AMBN), 2,2'-azobis(2-methylpropionic acid) dimethyl, 4,4'-azobis-4-cyanovaleric acid, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 1,1'-azobis(cyclohexane-1- azo-based initiators such as 2,2'-azobis(2,4,4-trimethylpentane) and 2,2'-azobis(2,4,4-trimethylpentane); and peroxide-based initiators such as benzoyl peroxide, t-butyl hydroperoxide, di-t-butyl peroxide, t-butyl peroxybenzoate, dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, and 1,1-bis(t-butylperoxy)cyclododecane.

[0117] The amount of the thermal polymerization initiator used is, for example, preferably 0.1 to 15 parts by mass relative to 100 parts by mass of all monomers (monomer composition) that can be used to constitute the organic polymer compound in the second polymer.

[0118] As the photopolymerization initiator, any appropriate photopolymerization initiator can be used as long as it does not impair the effects of the present invention. The photopolymerization initiator may be a single type or two or more types. Examples of such photopolymerization initiators include benzoin ether-based photopolymerization initiators, acetophenone-based photopolymerization initiators, α-ketol-based photopolymerization initiators, aromatic sulfonyl chloride-based photopolymerization initiators, photoactive oxime-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzyl-based photopolymerization initiators, benzophenone-based photopolymerization initiators, ketal-based photopolymerization initiators, thioxanthone-based photopolymerization initiators, and acylphosphine oxide-based photopolymerization initiators.

[0119] The amount of the photopolymerization initiator used is, for example, preferably 0.001 to 0.5 parts by mass relative to 100 parts by mass of all monomers (monomer composition) that can be used to constitute the organic polymer compound in the second polymer.

[0120] In polymerizing the organic polymer compound for the second polymer, a chain transfer agent may be used to adjust the molecular weight. Examples of the chain transfer agent include 2-mercaptoethanol, α-thioglycerol, 2,3-dimercapto-1-propanol, octyl mercaptan, t-nonyl mercaptan, dodecyl mercaptan (lauryl mercaptan), t-dodecyl mercaptan, glycidyl mercaptan, thioglycolic acid, methyl thioglycolate, ethyl thioglycolate, propyl thioglycolate, butyl thioglycolate, t-butyl thioglycolate, 2-ethylhexyl thioglycolate, octyl thioglycolate, isooctyl thioglycolate, decyl thioglycolate, dodecyl thioglycolate, thioglycolic acid esters of ethylene glycol, thioglycolic acid esters of neopentyl glycol, thioglycolic acid esters of pentaerythritol, and α-methylstyrene dimer. Among these, from the viewpoint of suppressing whitening of the double-sided pressure-sensitive adhesive tape of the present invention, 2-mercaptoethanol and methyl thioglycolate are preferred, and 2-mercaptoethanol is particularly preferred. Only one type of chain transfer agent may be used, or two or more types may be used.

[0121] The amount of the chain transfer agent used is, for example, preferably 0.1 to 20 parts by mass, more preferably 0.2 to 15 parts by mass, and even more preferably 0.3 to 10 parts by mass, relative to 100 parts by mass of all monomers (monomer composition) that can be used to constitute the organic polymer compound in the second polymer.

[0122] The weight-average molecular weight of the organic polymer compound in the second polymer is not particularly limited, but is preferably 500 or more and 1,000,000 or less. The upper limit of the weight-average molecular weight is more preferably 800,000, even more preferably 600,000, even more preferably 400,000, even more preferably 200,000, even more preferably 100,000, even more preferably 100,000, and the lower limit is more preferably 1,000, even more preferably 2,000, even more preferably 3,000, and even more preferably 4,000. When the weight-average molecular weight is 500 or more, the problem of contamination of the adherend surface due to surface segregation after peeling of the pressure-sensitive adhesive layer can be effectively suppressed. Furthermore, when the weight-average molecular weight is 1,000,000 or less, the problem of adhesive residue remaining on the adherend after peeling due to a decrease in the cohesive strength of the pressure-sensitive adhesive layer can be effectively suppressed.

[0123] From the viewpoint of adhesive properties, the content of the organic polymer compound in the second polymer is preferably 1 to 40 parts by mass, more preferably 1 to 30 parts by mass, even more preferably 1 to 20 parts by mass, and particularly preferably 1 to 10 parts by mass, per 100 parts by mass of the polymer.

[0124] The second polymers may be used alone or in combination of two or more.

[0125] The content of the second polymer in the pressure-sensitive adhesive composition according to the embodiment of the present invention is preferably 1 part by mass or more, more preferably 5 parts by mass or more, even more preferably 10 parts by mass or more, particularly preferably 15 parts by mass or more, even more preferably 20 parts by mass or more, even more preferably 25 parts by mass or more, and most preferably 30 parts by mass or more, per 100 parts by mass of the polymer or 100 parts by mass of the monomer mixture that is the raw material for the polymer, from the viewpoint of adhesive properties. Furthermore, from the viewpoint of adhesive properties, the content is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 30 parts by mass or less. The content of the second polymer may be 1 to 50 parts by mass per 100 parts by mass of the polymer.

[0126] These second polymers may be added after the polymer is obtained, or may be blended together with the monomer mixture that is the raw material for the polymer and subjected to a polymerization reaction before the polymer is obtained. However, it is preferable that the polymer and the second polymer are blended after each has undergone a polymerization reaction.

[0127] (Other Components) The pressure-sensitive adhesive composition according to the embodiment of the present invention may contain one or more components other than the polymer, the ionic liquid, and the second polymer (hereinafter, these may be referred to as "other components"), 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.

[0128] (Catalyst) The pressure-sensitive adhesive composition according to the embodiment of the present invention may contain a catalyst. Examples of the catalyst include organometallic compounds and tertiary amine compounds. The catalyst may be one type or two or more types.

[0129] Examples of organometallic compounds include iron-based compounds, tin-based compounds, titanium-based compounds, zirconium-based compounds, lead-based compounds, cobalt-based compounds, and zinc-based compounds. Among these, iron-based compounds and tin-based compounds are preferred in terms of reaction rate and pot life of the adhesive layer.

[0130] Examples of iron compounds include iron acetylacetonate and iron 2-ethylhexanoate.

[0131] Examples of tin compounds include dibutyltin dichloride, dibutyltin oxide, dibutyltin dibromide, dibutyltin maleate, dibutyltin dilaurate, dibutyltin diacetate, dibutyltin sulfide, tributyltin methoxide, tributyltin acetate, triethyltin ethoxide, tributyltin ethoxide, dioctyltin oxide, dioctyltin dilaurate, tributyltin chloride, tributyltin trichloroacetate, and tin 2-ethylhexanoate.

[0132] Examples of titanium compounds include dibutyltitanium dichloride, tetrabutyltitanate, and butoxytitanium trichloride.

[0133] Examples of zirconium compounds include zirconium naphthenate and zirconium acetylacetonate.

[0134] Examples of lead compounds include lead oleate, lead 2-ethylhexanoate, lead benzoate, and lead naphthenate.

[0135] Examples of the cobalt-based compound include cobalt 2-ethylhexanoate and cobalt benzoate.

[0136] Examples of zinc compounds include zinc naphthenate and zinc 2-ethylhexanoate.

[0137] Examples of the tertiary amine compound include triethylamine, triethylenediamine, and 1,8-diazabis(2-(5,4,0)-undecene-7-ene.

[0138] The amount of the catalyst is preferably 0.02 to 0.50% by weight, more preferably 0.05 to 0.40% by weight, and even more preferably 0.07% by weight, based on the polyol (A).

[0139] (Ionic Additive) 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.

[0140] The ionic solid is an ionic substance that is solid at 25°C. The ionic solid is not particularly limited, but 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 polymer.

[0141] (Crosslinking Agent) The pressure-sensitive adhesive composition according to the embodiment of the present invention may contain a crosslinking agent as needed to improve creep resistance and shear resistance by crosslinking the polymer. Examples of crosslinking agents include isocyanate-based crosslinking agents, carbodiimide-based crosslinking agents, epoxy-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 carbodiimide-based crosslinking agents include polycarbodiimide resins. Examples of epoxy-based crosslinking agents include N,N,N',N'-tetraglycidyl-m-xylylenediamine, diglycidylaniline, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, and 1,6-hexanediol diglycidyl ether. When a crosslinking agent is contained, the content is preferably 0.1 parts by mass or more, more preferably 0.7 parts by mass or more, and preferably 50 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 3 parts by mass or less, relative to 100 parts by mass of the polymer. The crosslinking agents can be used alone or in combination of two or more.

[0142] (Polyethylene glycol, tetraethylene glycol dimethyl ether) 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 assisting the movement of the ionic liquid when a voltage is applied. As the polyethylene glycol or tetraethylene glycol dimethyl ether, those having a number average molecular weight of 100 to 6000 can be used. When these components are contained, the content thereof is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 1 part by mass or more, and 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, relative to 100 parts by mass of the polymer.

[0143] (Conductive Filler) 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 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 is preferably 0.1 parts by mass or more and 200 parts by mass or less relative to 100 parts by mass of the polymer.

[0144] (Corrosion inhibitor) 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.

[0145] 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, and 1,3-bis(p-tolyl)carbodiimide. 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 relative to 100 parts by mass of the polymer.

[0146] 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 relative to 100 parts by mass of the polymer. 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 relative to 100 parts by mass of the polymer. 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 relative to 100 parts by mass of the polymer. When the pressure-sensitive adhesive composition according to the embodiment of the present invention contains an alkyl phosphate as the adsorptive inhibitor, the content is preferably 0.01 to 10 parts by mass relative to 100 parts by mass of the polymer.

[0147] 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 significantly 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 an embodiment of the present invention, the content is preferably 0.01 to 20 parts by mass per 100 parts by mass of the polymer. 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 polymer.

[0148] (Various Additives) The pressure-sensitive adhesive composition according to the embodiment of the present invention may also contain various additives such as fillers, plasticizers, antioxidants, antioxidants, pigments (dyes), flame retardants, solvents, surfactants (leveling agents), rust inhibitors, and antistatic agents. 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 polymer.

[0149] 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.

[0150] 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.

[0151] 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.

[0152] 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.

[0153] <Initial Adhesion Strength and Electrical Peel Strength> The adhesion 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 test described in the Examples section.

[0154] The pressure-sensitive adhesive composition according to the embodiment of the present invention preferably has an initial adhesive 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 initial adhesive strength is 4.0 N / cm or more, adhesion to the adherend is sufficient, and the adherend is unlikely to peel off or slip.

[0155] Furthermore, it is preferable that the adhesive strength of the pressure-sensitive adhesive composition according to the embodiment of the present invention, which is measured by forming a pressure-sensitive adhesive sheet as described in the Examples section, applying a voltage of 30 V for 30 seconds, and then conducting a 180° peel test while applying a voltage of 30 V, i.e., the electrical peel strength, is sufficiently smaller than the initial adhesive strength.

[0156] The pressure-sensitive adhesive composition according to the embodiment of the present invention is prepared by forming a pressure-sensitive adhesive sheet as described in the Examples section, applying a voltage of 30 V for 30 seconds, and then performing a 180° peel test while applying a voltage of 30 V. The electrical peel strength measured is preferably 1.0 N / cm or less, 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 0.05 N / cm or less. An electrical peel strength of 1.0 N / cm or less provides excellent electrical releasability, improving reworkability and facilitating recycling.

[0157] 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.

[0158] <Method for producing pressure-sensitive adhesive composition> The pressure-sensitive adhesive composition of the present invention is not particularly limited, and can be produced by appropriately stirring and mixing a polymer, an ionic liquid, a tackifier, and, if necessary, a crosslinking agent, polyethylene glycol, a conductive filler, and the like.

[0159] [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 has at least one adhesive layer (hereinafter also referred to as "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 have an adhesive layer other than the electrically peelable adhesive layer that does not contain an ionic liquid (hereinafter sometimes referred to as "another adhesive layer"). The adhesive sheet according to the embodiment of the present invention may also have 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 a roll or a sheet. It should be noted that the term "adhesive sheet" also includes 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.

[0160] 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.

[0161] 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.

[0162] 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.

[0163] 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.

[0164] 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.

[0165] 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.

[0166] 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.

[0167] From the viewpoint of initial adhesive strength, the thickness of the electrically peeling pressure-sensitive adhesive layer 1 is preferably 1 μm or more and 1,000 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, even more preferably 200 μm, even more preferably 150 μm, even more preferably 100 μm, even more preferably 80 μm, even more preferably 70 μm, even more preferably 60 μm, even more preferably 50 μm, and the lower limit is more preferably 5 μm, even more preferably 10 μm, even more preferably 20 μm, even more preferably 30 μm.

[0168] 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, even more preferably 300 μm, even more preferably 250 μm, even more preferably 200 μm, even more preferably 150 μm, and even more preferably 100 μm, and the lower limit is more preferably 30 μm, even more preferably 50 μm.

[0169] 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.

[0170] 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.

[0171] 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, even more preferably 50 μm, and even more preferably 10 μm, and the lower limit is more preferably 0.01 μm, more preferably 0.03 μm, and even more preferably 0.05 μm.

[0172] 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.

[0173] 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.

[0174] The thickness of the pressure-sensitive adhesive sheet according to the embodiment of the present invention 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, even more preferably 300 μm, even more preferably 250 μm, even more preferably 200 μm, even more preferably 150 μm, even more preferably 100 μm, and the lower limit is more preferably 30 μm, even more preferably 50 μm.

[0175] 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 50 µm or more and 2000 µm or less. The upper limit of the thickness is more preferably 1000 µm, even more preferably 500 µm, even more preferably 300 µm, even more preferably 250 µm, even more preferably 200 µm, and even more preferably 150 µm, and the lower limit is more preferably 80 µm, even more preferably 100 µm.

[0176] 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 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, even more preferably 300 µm, even more preferably 250 µm, even more preferably 200 µm, even more preferably 150 µm, and the lower limit is more preferably 50 µm, even more preferably 80 µm, even more preferably 100 µm.

[0177] 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 the coating layer, the electrically-releasing pressure-sensitive adhesive sheet according to this embodiment acts as a barrier to the ionic liquid 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 peeling within the electrically-releasing pressure-sensitive adhesive sheet due to a decrease in the interfacial adhesion between the electrically-releasing pressure-sensitive adhesive layer and a conductive material (e.g., an adherend) caused by thermal curing of the electrically-releasing pressure-sensitive adhesive layer exposed to a high-temperature environment.

[0178] 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 ３It is preferable that the material contains at least one inorganic substance selected from the group consisting of Ni, NiCr, and NiAl.

[0179] (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 releasing pressure-sensitive adhesive layer in the pressure-sensitive adhesive sheet according to the embodiment of the present invention, a method can be exemplified in which a solution of the pressure-sensitive adhesive composition according to the embodiment of the present invention dissolved in a solvent as needed is applied to a release liner, followed by drying and / or curing. For the other pressure-sensitive adhesive layers, a method can be exemplified in which a solution of the pressure-sensitive adhesive composition not containing an ionic liquid dissolved in a solvent as needed is applied to a release liner, followed by drying and / or curing. The solvents and release liners listed above can be used.

[0180] 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.

[0181] The above 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 onto a substrate, a conductive layer, and a conductive substrate. Note that a pressure-sensitive adhesive sheet may also be produced by applying a pressure-sensitive adhesive composition to a substrate, a conductive layer, and a conductive substrate instead of a release liner.

[0182] (Method for Electrically Peeling Pressure-Sensitive Adhesive Sheet) 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.

[0183] (Uses of Pressure-Sensitive Adhesive Sheets) Conventional removable technologies include pressure-sensitive adhesive layers that are cured and released by ultraviolet (UV) irradiation, and pressure-sensitive adhesive layers that are released by heat. Pressure-sensitive adhesive sheets using such pressure-sensitive 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, which include the electrically peelable pressure-sensitive adhesive layer, do not use ultraviolet or heat, and therefore can be easily removed by applying a voltage without damaging the adherend. Due to the above properties, 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. Pressure-sensitive adhesive sheets according to embodiments of the present invention are also suitable for use in fixing automotive components (e.g., batteries, motors, etc.). Pressure-sensitive adhesive sheets according to embodiments of the present invention are also suitable for use in fixing components (e.g., ceramic capacitors, lithium-ion batteries, etc.) in semiconductor manufacturing processes and inspections. Pressure-sensitive adhesive sheets according to embodiments of the present invention are also suitable for use in protecting metal processing processes (e.g., stainless steel plates for railways, etc.).

[0184] 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, 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.

[0185] [Joint] The joined structure according to the embodiment of the present invention comprises the pressure-sensitive adhesive sheet according to the embodiment of the present invention and a conductive material, and the electrically peelable pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet is attached to the conductive material. The conductive material is preferably an adherend having a metal adhesion surface, and examples of the adherend having a metal adhesion surface include those made of a metal primarily composed of aluminum, copper, iron, magnesium, tin, gold, silver, lead, etc., and among these, metals containing aluminum are preferred.

[0186] 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.

[0187] As described above, the present specification discloses the following: <1> A pressure-sensitive adhesive composition comprising a polymer, an ionic liquid, and a tackifier, wherein the product of the acid value [mg KOH / g] of the tackifier and the content [parts by mass] of the tackifier per 100 parts by mass of the polymer is less than 1,200. <2> The pressure-sensitive adhesive composition according to <1>, wherein the softening point of the tackifier is 100°C or higher. <3> The pressure-sensitive adhesive composition according to <1> or <2>, wherein the content of the tackifier is 5 to 50 parts by mass per 100 parts by mass of the polymer. <4> The pressure-sensitive adhesive composition according to any one of <1> to <3>, wherein the tackifier is a terpene-based tackifier resin or a rosin-based tackifier resin. <5> The pressure-sensitive adhesive composition according to any one of <1> to <4>, wherein 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. <6> The pressure-sensitive adhesive composition according to any one of <1> to <5>, wherein the polymer comprises at least one selected from the group consisting of polyester-based polymers, urethane-based polymers, and acrylic-based polymers. <7> The pressure-sensitive adhesive composition according to any one of <1> to <6>, further comprising a second polymer having a glass transition temperature (Tg) of 40 to 180°C. <8> The pressure-sensitive adhesive composition according to <7>, wherein the content of the second polymer is 1 to 50 parts by mass per 100 parts by mass of the polymer. <9> The pressure-sensitive adhesive composition according to any one of <1> to <8>, which is used 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 structure comprising the pressure-sensitive adhesive sheet according to <10> and a conductive material, wherein the pressure-sensitive adhesive layer is adhered to the conductive material.

[0188] 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 below were measured by gel permeation chromatography (GPC). The Tg of the acrylic polymer and the second polymer was determined using the above-mentioned FOX formula, and the Tg of the polyester polymer was determined using catalog values. Furthermore, the acid value, hydroxyl value, Tg, and softening point of the tackifier are generally catalog values, and if no catalog values ​​are available, measured values ​​are used. If there is a range in the catalog values, the median value is generally used.

[0189] <Polymer> (Preparation of Acrylic Polymer 1 Solution) As monomer components, 87 parts by mass of n-butyl acrylate (BA), 10 parts by mass of 2-methoxyethyl acrylate (MEA), 3 parts by mass of acrylic acid (AA), and 150 parts by mass of ethyl acetate as a polymerization solvent were charged into a separable flask and stirred for 1 hour while introducing nitrogen gas. After removing oxygen from the polymerization system in this way, 0.2 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) was added as a polymerization initiator, and the temperature was raised to 63°C and reacted for 6 hours. Ethyl acetate was then added to obtain an acrylic polymer 1 solution with a solids concentration of 40% by mass. The weight average molecular weight of the obtained acrylic polymer 1 was 750,000. The Tg was -45°C.

[0190] (Preparation of Acrylic Polymer 2 Solution) 95 parts by mass of n-butyl acrylate (BA) and 5 parts by mass of acrylic acid (AA) as monomer components, and 150 parts by mass of ethyl acetate as a polymerization solvent were charged into a separable flask and stirred for 1 hour while introducing nitrogen gas. After removing oxygen from the polymerization system in this manner, 0.2 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) was added as a polymerization initiator, and the mixture was heated to 63°C and reacted for 6 hours. Ethyl acetate was then added to obtain an acrylic polymer 2 solution with a solids concentration of 40% by mass. The weight-average molecular weight of the obtained acrylic polymer 2 was 600,000. The Tg was -47°C.

[0191] <Second Polymer> 95 parts by mass of cyclohexyl methacrylate (CHMA) as monomer components, 5 parts by mass of acrylic acid (AA), 300 parts by mass of ethyl acetate as a polymerization solvent, and 3 parts by mass of 2-mercaptoethanol (thioglycol) as a chain transfer agent were charged into a separable flask and stirred for 1 hour while introducing nitrogen gas. After removing oxygen from the polymerization system in this manner, 0.2 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) as a polymerization initiator was added, and the mixture was heated to 65°C and reacted for 3 hours, followed by reaction at 75°C for 2 hours to obtain a second polymer solution with a solids concentration of 25% by mass. The Tg of the obtained second polymer was 68°C.

[0192] Examples 1 to 20, Comparative Examples 1 to 5 Preparation of Pressure-Sensitive Adhesive Compositions The acrylic polymer solutions, second polymer solutions, and ethyl acetate solutions of tackifiers adjusted to a solids concentration of 50% by mass were used as described above, along with the crosslinking agent, ionic liquid, and catalyst components shown below, as described in Tables 1 and 2. These components were stirred and mixed to obtain electro-peelable pressure-sensitive adhesive compositions (solutions) adjusted to a solids concentration of 25% by mass for Examples 1 to 20 and Comparative Examples 1 to 5. Ethyl acetate was used to adjust the solids concentration of the pressure-sensitive adhesive compositions. Tables 1 and 2 show the blending amounts of each component. The values ​​for each component in Tables 1 and 2 refer to parts by mass. The blending amounts (parts by mass) of the polymer, second polymer, and tackifier refer to the blending amounts (parts by mass) as the solids.

[0193] <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 a 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 layer using a hand roller, to obtain an electrically peelable pressure-sensitive adhesive layer (pressure-sensitive adhesive sheet) having a thickness of 60 µm.

[0194] <Preparation of single-sided pressure-sensitive adhesive sheet with 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 attached to the exposed surface of the electrically peelable pressure-sensitive adhesive layer to prepare a single-sided pressure-sensitive adhesive sheet with substrate.

[0195] <Preparation of Bonded Structure> The release liner (MRF38) was peeled off from the substrate-attached single-sided PSA sheet, and a stainless steel plate was attached to the peeled surface as an adherend so that one edge of the PSA sheet protruded from the adherend by about 2 mm, and the sheet was pressed back and forth once with a 2 kg roller and left to stand for 30 minutes in an environment of 23°C, yielding a bonded structure consisting of stainless steel plate 6 / electrically peelable PSA layer (adhesive sheet) 1' / metal layer-attached film (conductive substrate) 5'. An overview of this bonded structure is shown in Figure 4.

[0196] <Product of Acid Value and Content> The product of the acid value and the content was calculated by multiplying the acid value [mg KOH / g] of the tackifier by the content [parts by mass] of the tackifier relative to 100 parts by mass of the polymer. The results are shown in Tables 1 and 2.

[0197] <Evaluation> (180° Peel Force) A 180° peel test was performed using the bonded structures of the Examples and Comparative Examples. The adherends used were stainless steel plates (SUS304, size: 30 mm x 120 mm). 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 Figure 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 used as the initial adhesive strength. An initial adhesive strength of 4.0 N / cm or more was evaluated as ◯, and an initial adhesive strength of less than 4.0 N / cm was evaluated as ×. The measurement results are shown in Tables 1 and 2.

[0198] (Electrical Peel Force) Stainless steel plates (SUS316, size: 30 mm x 120 mm) were used as adherends. A bonded structure was prepared by pressing it back and forth with a 2 kg roller once and left in an environment at 23°C for 30 minutes. Prior to peeling, the negative and positive electrodes of a DC current machine were attached to the bonded structure at the positions α and β in Figure 4, respectively. A voltage of 30 V was applied for 30 seconds. While the voltage was still applied, the bonded structure was peeled in the same manner as in the 180° peel force measurement described above, and the adhesive strength during voltage application was measured and used as the electrical peel force. An electrical peel force of 1.0 N / cm or less was evaluated as ◯, and an electrical peel force of more than 1.0 N / cm was evaluated as ×. The measurement results are shown in Tables 1 and 2.

[0199]

[0200]

[0201] The abbreviations for the ester polymer, urethane polymer, tackifier, ionic liquid, crosslinker, and catalyst in Tables 1 and 2 are as follows: Unless otherwise specified, the hydroxyl value of the following tackifiers is 0 mgKOH / g.

[0202] (Polyester-based polymer) NP-110S50EO: polyester resin, manufactured by Mitsubishi Chemical Corporation, Tg=-50°C (Urethane-based polymer) UR-V8700: urethane-modified polyester resin, trade name "Vylon UR-V8700", manufactured by Toyobo Co., Ltd.

[0203] (Tackifiers) Pine Crystal KE-311: rosin-based tackifying resin, manufactured by Arakawa Chemical Industries, Ltd., acid value 6 mg KOH / g, Tg = 50°C, softening point 100°C Pencel D-125: rosin-based tackifying resin, manufactured by Arakawa Chemical Industries, Ltd., acid value 10 mg KOH / g, Tg = 75°C, softening point 125°C Haritack 4740: rosin-based tackifying resin, manufactured by Harima Chemical Group Co., Ltd., acid value 30 mg KOH / g, Tg = 70°C, softening point 120°C Pencel AZ: rosin-based tackifying resin, manufactured by Arakawa Chemical Industries, Ltd., acid value 43 mg KOH / g, Tg = 50°C, softening point 100°C Pencel KK: rosin-based tackifying resin, manufactured by Arakawa Chemical Industries, Ltd., acid value 15 mg KOH / g, Tg = 120°C, softening point 170°C Hariestar MSR-4: rosin-based tackifying resin, manufactured by Harima Chemicals Group Co., Ltd., acid value 135 mg KOH / g, Tg = 75°C, softening point 125°C

[0204] (Ionic liquid) AS-110: cation: 1-ethyl-3-methylimidazolium cation, anion: bis(fluorosulfonyl)imide anion, trade name "Elexcel AS-110", manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.

[0205] (Crosslinking agent) V-05: Polycarbodiimide resin, trade name "Carbodilite V-05", manufactured by Nisshinbo Chemical Inc. Coronate L: Isocyanate-based crosslinking agent, manufactured by Tosoh Corporation

[0206] (Catalyst) ZC-150: Zirconium tetraacetylacetate, trade name "Orgatix ZC-150", manufactured by Matsumoto Fine Chemical Co., Ltd.

[0207] The electrically releasing pressure-sensitive adhesive layers formed from the PSA compositions of Examples 1 to 20 all had high initial adhesive strength and excellent electrical releasability, because the product of the acid value [mg KOH / g] of the tackifier and the content [parts by mass] of the tackifier per 100 parts by mass of the polymer was less than 1200. Furthermore, the electrically releasing pressure-sensitive adhesive layers formed from the PSA compositions of Examples 11 to 20 further contained a second polymer, and thus showed further improvements in initial adhesive strength and electrical releasability.

[0208] 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.

[0209] 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.

[0210] This application is based on a Japanese patent application filed on September 30, 2021 (Patent Application No. 2021-161475), a Japanese patent application filed on January 7, 2022 (Patent Application No. 2022-001918), and a Japanese patent application filed on February 24, 2022 (Patent Application No. 2022-026642), the contents of which are incorporated by reference into this application.

[0211] 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 containing a polymer, an ionic liquid, and a tackifier, wherein the product of the acid value [mg KOH / g] of the tackifier and the content [parts by mass] of the tackifier with respect to 100 parts by mass of the polymer is less than 1200.

2. The pressure-sensitive adhesive composition according to claim 1, wherein the softening point of the tackifier is 100°C or higher.

3. The pressure-sensitive adhesive composition according to claim 1, wherein the content of the tackifier is 5 to 50 parts by mass with respect to 100 parts by mass of the polymer.

4. The pressure-sensitive adhesive composition according to claim 1, wherein the tackifier is a terpene-based tackifying resin or a rosin-based tackifying resin.

5. The pressure-sensitive adhesive composition according to claim 1, wherein the anion of the ionic liquid contains at least one selected from the group consisting of bis(fluorosulfonyl)imide anion and bis(trifluoromethanesulfonyl)imide anion.

6. The pressure-sensitive adhesive composition according to claim 1, wherein the polymer contains at least one selected from the group consisting of polyester-based polymers, urethane-based polymers, and acrylic-based polymers.

7. The pressure-sensitive adhesive composition according to claim 1, further containing a second polymer having a glass transition temperature (Tg) of 40 to 180°C.

8. The pressure-sensitive adhesive composition according to claim 7, wherein the content of the second polymer is 1 to 50 parts by mass with respect to 100 parts by mass of the polymer.

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 joined body comprising the pressure-sensitive adhesive sheet according to claim 10 and a conductive material, wherein the pressure-sensitive adhesive layer is adhered to the conductive material.