JP7699859B2 - Electrically peelable adhesive sheet and method for producing same - Google Patents

Description

The present invention relates to an electrically peelable adhesive sheet. The present invention relates to a method for producing an electrically peelable adhesive sheet.

Adhesives and adhesive sheets that have adhesion to and releasability from an adherend are used in a variety of applications (e.g., surface protection films, masking tapes for painting, peelable memos, etc.). In addition to physical methods, known methods for peeling an adhesive from an adherend include methods that use stimulation by light, heat, vibration, or electrical current. For example, Patent Document 1 describes that by using a polymer and an ionic liquid in the adhesive, an adhesive that can be peeled from an adherend by application of voltage (electrically peelable adhesive) can be provided. Patent Document 2 describes that by examining the conditions of the transfer promoter used together with the polymer and ionic liquid, an electrically peelable adhesive that does not leave any adhesive residue even when a low voltage is applied can be provided.

JP 2010-037354 A U.S. Patent Application 17/602,212

In order to achieve good electrical peelability in an electrically peelable adhesive sheet, it is necessary to select the material of the core material. For example, films such as polyethylene terephthalate (PET) used in general adhesive tapes are insulators, so double-sided tapes using PET as the core material do not exhibit electrical peelability. For this reason, adhesive sheets such as double-sided tapes with electrical peelability had to use porous materials such as nonwoven fabric as the core material. However, conventional electrically peelable adhesive sheets using nonwoven fabric required a thick adhesive layer to achieve electrical peeling, which made the adhesive sheet thick. In addition, electrically peelable adhesives without a core material were prone to changes in the shape of the adhesive surface, making them difficult to apply to the adherend. For this reason, there was a demand for an electrically peelable adhesive sheet that was thin and easy to apply to the adherend.

The present inventors have discovered that by using a core material having a basis weight of 10.0 g/ ^m2 or less and a thickness of 10 μm to 35 μm, it is possible to provide an electrically peelable pressure-sensitive adhesive sheet that is thin and easy to apply to an adherend without affecting electrical peelability, and have arrived at the present invention.
Thus, the present invention provides an electrically peelable adhesive sheet comprising a planar core material and an adhesive layer comprising an electrically peelable adhesive composition, wherein the core material has a basis weight of 10.0 g/ ^m2 or less and a thickness of 10 μm to 35 μm, the electrically peelable adhesive composition is a composition comprising an acrylic polymer and an ionic liquid, and the adhesive sheet is a double-sided adhesive sheet.

Furthermore, according to the present invention, ^there is provided a method for producing an electrically peelable adhesive sheet, which comprises the step of contacting an electrically peelable adhesive composition containing an acrylic polymer and an ionic liquid with a planar core material having a basis weight of 10.0 g/m2 or less and a thickness of 10 μm to 35 μm to form an adhesive layer.

According to the present invention, an electrically peelable adhesive sheet is provided which is thin and easy to apply to an adherend without affecting electrical peelability.

FIG. 2 is a diagram showing an example of a cross section of an electrically peelable adhesive sheet on which an electrically peelable adhesive layer is formed. FIG. 2 is a diagram showing an example of a cross section of an electrically peelable adhesive sheet made of a core material permeated with an electrically peelable adhesive composition. FIG. 1 is a diagram showing an example of a circuit in which a voltage is applied to a conductive adherend and a conductive object to be fixed, and the conductive object to be fixed is peeled off from an electrically peelable adhesive sheet. 13A and 13B are diagrams showing an example in which a conductive object to be fixed is peeled off by applying a voltage. FIG. 1 is a diagram showing an example of a circuit for peeling a non-conductive object to be fixed from an electrically peelable adhesive sheet by applying a voltage to a conductive adherend and a conductive auxiliary material. 13A and 13B are diagrams showing an example in which a non-conductive object to be fixed is peeled off by applying a voltage. FIG. 13 is a diagram showing an example of a circuit for peeling off the conductive object from the electrically peelable adhesive sheet by applying a voltage to the conductive auxiliary material and the conductive object to be fixed. 13A and 13B are diagrams showing an example in which a conductive object to be fixed is peeled off by applying a voltage. FIG. 1 is a diagram showing an example of a circuit in which a voltage is applied to a conductive auxiliary material adhered to a non-conductive adherend and a conductive auxiliary material adhered to a non-conductive object to be fixed, thereby peeling the non-conductive object to be fixed from the electrically peelable adhesive sheet. 13A and 13B are diagrams showing an example in which a non-conductive object to be fixed is peeled off by applying a voltage. FIG. 1 is a diagram showing an example of a circuit in which a voltage is applied to a conductive adherend and a conductive object to be fixed, and the conductive object to be fixed is peeled off from an electrically peelable adhesive sheet. 13A and 13B are diagrams showing an example in which a conductive object to be fixed is peeled off by applying a voltage.

In this specification, "x~y" (x and y are specific values) means greater than or equal to x and less than or equal to y, unless otherwise specified.

[Electrically peelable adhesive sheet]
The electrically peelable adhesive sheet of this embodiment (hereinafter also simply referred to as "adhesive sheet") comprises an adhesive layer containing a planar core material and an electrically peelable adhesive composition (hereinafter also simply referred to as the composition), and a part or all of each of both sides of the sheet has adhesiveness. That is, the adhesive sheet of the present invention is in the form of, for example, a double-sided sheet or a double-sided tape. The adhesive sheet of this embodiment also has electrical peeling properties. This electrical peeling property refers to the fact that the adhesive sheet is used to adhere and fix an adherend or an object to be fixed, which will be described later, and that the adhesiveness of the adhesive sheet is reduced by applying a voltage, thereby making it possible to remove the adherend or the object to be fixed. It is preferable that the adhesive sheet has an adhesive strength of 10 N/25 mm or more before the voltage is applied.

The thickness of the adhesive sheet is not particularly limited, but is preferably 1 to 200 μm, more preferably 1 to 100 μm, more preferably 1 to 80 μm, more preferably 1 μm or more and less than 80 μm, more preferably 5 to 60 μm, more preferably 5 to 50 μm, and more preferably 10 to 50 μm. The upper limit of the thickness of the adhesive sheet is, for example, 200, 150, 100, 90, 80, 79, 75, 70, 65, 60, 55, or 50 μm. The lower limit of the thickness of the adhesive sheet is, for example, 1, 3, 5, 10, 15, 20, 25, 29, or 30 μm.

The thickness of the adhesive sheet and core material can be measured using a known thickness gauge. An example of a thickness gauge is the Peacock Precision Measuring Instrument. The thickness here refers to the average value measured using the thickness gauge at least five randomly selected points on the object to be measured.

(Core material)
The core material in this embodiment refers to a planar object that can form an adhesive layer together with the electrically peelable adhesive composition described later. The core material does not have to be completely planar, and may be partially or entirely uneven. The core material may also have at least one through hole. The core material is not particularly limited as long as the adhesive layer is ionically conductive when a voltage is applied to the adhesive sheet and the following properties (thickness, basis weight) are satisfied.

In order for the adhesive layer of the adhesive sheet to exhibit ionic conductivity, for example, the core material can be made of fibers and the composition can be allowed to penetrate into the gaps between the fibers.

The material of the core material is not particularly limited as long as it satisfies the following properties (thickness, basis weight). Examples of the core material include fibers such as plant fibers, inorganic and chemical fibers, and porous films. Of these, it is preferable that the core material is made of fibers, and more preferably that the core material is made of plant fibers. Examples of the core material made of plant fibers include Western paper and Japanese paper. Examples of the core material made of inorganic and chemical fibers include nonwoven fabrics and woven fabrics such as polyester (particularly nonwoven fabrics made of polyethylene terephthalate), carbon fibers, and glass fibers. Examples of the porous film include films made of polyimide and polyester. Since the core material is made of fibers, the composition can penetrate into the gaps between the fibers, and the core material exhibits ionic conductivity when a voltage is applied. The core material is preferably an insulator, and more preferably a fiber made of an insulator. Examples of the fiber made of an insulator include plant fibers and polyester fibers.

The thickness of the core material is 10 to 35 μm, and preferably 10 to 30 μm. The upper limit of the thickness of the core material is, for example, 35, 34, 33, 32, 31, or 30 μm. The lower limit of the thickness of the core material is, for example, 10, 11, 12, 13, or 14 μm.

The basis weight of the core material is 10.0 g/m2 or ^less , preferably 2.0 to 10.0 g/ ^m2 , more preferably 2.0 to 9.0 g/ ^m2 , and even more preferably 2.0 to 8.0 g/ ^m2 . The upper limit of the basis weight is, for example, 10.0, 9.5, 9.0, 8.5, 8.4, 8.3, 8.2, 8.1, or 8.0 g/ ^m2 . The lower limit of the basis weight is, for example, 2.0, 2.3, 2.5, 2.7, 2.9, 3.0, 3.2, 3.5, 3.8, 3.9, or 4.0 g/ ^m2 .

If the core material is thicker than 35 μm, the thickness of the adhesive sheet will be large. Also, if the fibers used for the core material are non-conductive fibers and the basis weight of the core material is greater than 10.0 g/ ^m2 , the composition will not easily penetrate into the gaps between the fibers, and the adhesive strength of the manufactured adhesive sheet may not decrease even when a voltage is applied. If the core material has a basis weight of 10.0 g/ ^m2 or less and a thickness of 10 μm to 35 μm, a thin adhesive sheet can be produced without affecting the electrical peelability.

The adhesive layer may consist only of the electrically peelable adhesive composition permeated into the core material, or the electrically peelable adhesive composition may be in contact with one or both sides of the core material to form a layer of the electrically peelable adhesive composition. In this case, the layer of the electrically peelable adhesive composition is also called an electrically peelable adhesive layer. When the adhesive layer consists only of the composition permeated into the core material, both sides of the core material are in a state of adhesiveness due to the composition.

The electrically peelable adhesive sheet of the present invention may be defined by its density. That is, the electrically peelable adhesive sheet of the present invention is an electrically peelable adhesive sheet comprising a planar core material and an adhesive layer containing an electrically peelable adhesive composition, wherein the core material has a density of 2.0 g/ ^cm3 or less and a thickness of 10 μm to 35 μm, the electrically peelable adhesive composition is a composition containing an acrylic polymer and an ionic liquid, and the adhesive sheet is a double-sided adhesive sheet.

The density of the core material is 2.0 g/cm3 or ^less , preferably 0.1 to 1.5 g/ ^cm3 , more preferably 0.1 to 1.0 g/ ^cm3 , more preferably 0.1 to 0.8 g/cm3, more preferably 0.1 to 0.6 g/ ^cm3 , and more preferably 0.1 to 0.5 g/ ^cm3 . The upper limit of the density is, for example, 2.0, 1.9, 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1, 1.0, 0.9, 0.8, 0.7, ^0.6, or 0.5 g/ ^cm3 . The lower limit of the density is, for example, 0.1, 0.15, or 0.2 g/ ^cm3 .

[Electrically peelable adhesive composition]
The electrically peelable pressure-sensitive adhesive composition of the present embodiment contains at least an acrylic polymer and an ionic liquid.
(Acrylic polymer)
The acrylic polymer of the present embodiment can be obtained by polymerizing an acrylic monomer in the presence of any polymerization initiator. Any polymer can be used as the acrylic polymer as long as it can adhere to a conductive object. The conductive object refers to a conductive adherend, a conductive auxiliary material, a conductive core material, or a conductive object to be fixed (these definitions will be described later). From the viewpoint of adhesion, the weight average molecular weight of the acrylic polymer is preferably 100,000 to 5,000,000, more preferably 200,000 to 4,000,000, and more preferably 300,000 to 3,000,000. Here, the weight average molecular weight refers to the weight average molecular weight in terms of polystyrene. Specifically, it may be the weight average molecular weight in terms of polystyrene calculated using GPC (System21) by Shodex Co., Ltd., with tetrahydrofuran as the mobile phase.

The glass transition temperature (Tg) of the acrylic polymer is preferably not higher than 0° C., more preferably not higher than −20° C., and even more preferably not higher than −40° C. The Tg can be calculated, for example, based on the following Fox equation.

1/Tg=(W1/Tg1)+(W2/Tg2)+・・・・・・+(Wn/Tgn)

The glass transition temperature can be measured, for example, by differential thermal analysis (DTA).

The acrylic polymer may be crosslinked by the action of a crosslinking agent. Examples of crosslinking agents include isocyanate-based crosslinking agents such as toluene diisocyanate and methylene bisphenyl isocyanate. The amount of crosslinking agent is preferably 1 to 10 parts by weight or less, more preferably 3 to 10 parts by weight or less, and even more preferably 5 to 10 parts by weight or less, per 100 parts by weight of the acrylic polymer. By crosslinking the acrylic polymer, when the composition is formed as a layer on a core material, the creep resistance and/or shear resistance of the layer can be improved.

It is more preferable that the acrylic polymer contains a copolymer of an alkyl (meth)acrylate having an alkyl group with 1 to 8 carbon atoms, a carboxyl group-containing acrylic monomer, and/or a hydroxyl group-containing acrylic monomer. When the acrylic polymer contains these copolymers, it becomes a composition with excellent adhesive strength.

(Acrylic Monomer)
The acrylic monomer preferably contains, as a main component (50% by weight or more), an alkyl(meth)acrylate having an alkyl group with a carbon number of 1 to 14. Here, (meth)acrylate means methacrylate or acrylate.

Examples of alkyl (meth)acrylates having an alkyl group with 1 to 14 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, sec-butyl (meth)acrylate, t-butyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isononyl (meth)acrylate, and dodecyl (meth)acrylate. These alkyl (meth)acrylates may be used alone or in combination of two or more. Among these alkyl (meth)acrylates, alkyl (meth)acrylates having an alkyl group with 1 to 8 carbon atoms are preferred, alkyl (meth)acrylates having an alkyl group with 1 to 4 carbon atoms are more preferred, n-butyl (meth)acrylate is more preferred, and n-butyl acrylate is more preferred.

Examples of other acrylic monomers include carboxyl group-containing monomers such as acrylic acid, methacrylic acid, and carboxyethyl acrylate, and hydroxyl group-containing monomers such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and (4-hydroxymethylcyclohexyl)-methyl acrylate. These other acrylic monomers may be used alone or in combination of two or more. The other acrylic monomers preferably include either a carboxyl group-containing monomer or a hydroxyl group-containing monomer, or both.

The acrylic monomer may be composed of only alkyl (meth)acrylate without using the other acrylic monomers mentioned above. From the viewpoint of easily obtaining a composition with the desired performance, it is preferable that the other acrylic monomer is contained in an amount of 1% by weight or more and less than 50% by weight, more preferably 5 to 30% by weight, and even more preferably 5 to 15% by weight.

In addition, when either a carboxyl group-containing monomer or a hydroxyl group-containing monomer, or both, are included, the total content of these two monomers is not particularly limited, but is preferably 1 to 20 parts by weight when the total monomer amount is 100 parts by weight. By using both monomers in this range, the adhesive properties can be improved. Furthermore, it is more preferable that the total content of both monomers is 1 to 10 parts by weight.

Furthermore, a vinyl monomer may be added to the (meth)acrylate as necessary. Examples of the vinyl monomer include itaconic acid, maleic acid, crotonic acid, maleic anhydride, itaconic anhydride, vinyl acetate, N-vinylpyrrolidone, N-vinyl carboxylic acid amides, styrene, and N-vinyl caprolactam. These vinyl monomers may be used alone or in combination of two or more.
(Polymerization initiator)
Examples of polymerization initiators that may be used optionally include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylpropionamidine) disulfide, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), 2,2'-azobis(2,4,4-trimethylpentane), dimethyl-2,2'-azobis(2-methylpropionate), 2,2'-azobis[2-methyl-N-(phenylmethyl)-propionamidine]dihydrochloride, 2,2'-azobis[2-(3,4,5,6-tetrahydropyrimidin-2-yl)propane]dihydrochloride, and the like. Examples of the polymerization initiator include azo-based polymerization initiators such as 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride and 2,2'-azobis[2-(2-imidazolin-2-yl)propane]; persulfate-based polymerization initiators such as potassium persulfate and ammonium persulfate; peroxide-based polymerization initiators such as benzoyl peroxide, hydrogen peroxide, t-butyl hydroperoxide, di-t-butyl peroxide, t-butyl peroxybenzoate, dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclododecane, 3,3,5-trimethylcyclohexanoyl peroxide and t-butyl peroxypivalate; and redox-based polymerization initiators composed of persulfates and sodium hydrogen sulfite. These polymerization initiators may be used alone or in combination of two or more. In addition, ultraviolet irradiation or radiation irradiation may be performed. The polymerization initiator is preferably used in an amount of 0.005 to 1 part by weight based on 100 parts by weight of the acrylic monomer. By using the polymerization initiator in this range, an acrylic polymer with excellent adhesive properties can be formed.

(Ionic Liquid)
Ionic liquids are a combination of cations and anions that are liquid at room temperature, and are also called room temperature molten salts. Ionic liquids have properties such as non-flammability, non-volatility, and chemical stability. When a voltage is applied to an ionic liquid, anions move to the anode side and cations move to the cathode side. It is believed that the adhesion of the composition is weakened by the movement of anions and cations to the vicinity of the electrode or the occurrence of an oxidation-reduction reaction of anions or cations at the interface between the electrode and the composition, resulting in improved peelability.

The ionic conductivity of the ionic liquid is not particularly limited, but is preferably 10 ^-7 S/cm or more, more preferably 10 ^-6 to 10 ^-1 S/cm, more preferably 10 ^-4 to 10 ^-2 S/cm, and even more preferably 10 ^-3 to 10 ^-2 S/cm. The ionic conductivity can be measured, for example, by the AC impedance method. The ionic conductivity of the ionic liquid can be measured, for example, as follows by the AC impedance method.

At room temperature, an ionic liquid is placed on a stainless steel plate using a bipolar cell, and another stainless steel plate is placed on top of the ionic liquid to sandwich the ionic liquid between the stainless steel plates, and a sample is obtained by controlling the shape of the ionic liquid to a disk of a certain area and thickness using a spacer. A voltage is applied to this sample, and the bulk resistance (Ω) is calculated by curve fitting the Cole-Cole plot obtained when the frequency that defines the amplitude is changed using an equivalent circuit. The ionic conductivity δ of the ionic liquid can be calculated by substituting the sample area A, sample thickness L, and bulk resistance Rb into the following formula.

δ＝L/(Rb×A)
[δ: ionic conductivity, Rb: bulk resistivity, L: sample thickness (cm), A: sample area (cm ² )]

Examples of ionic liquids include combinations of cyclic cations and anions represented by the following formula (1):

[式中、R¹は、ヘテロ原子を含んでもよい炭素数2～8の二価の炭化水素基であり、式中のN⁺と共に環を構成し、R²及びR³は、同一又は異なって、水素原子又は炭素数1～6のアルキル基であり(但し、窒素原子が隣接する炭素原子と二重結合を形成している場合は、R³は存在しない)、
X^-は、Cl^-、Br^-、I^-、AlCl₄ ^-、Al₂Cl₇ ^-、NO₃ ^-、BF₄ ^-、PF₆ ^-、ClO₄ ^-、CH₃COO^-、CF₃COO^-、CF₃SO₃ ^-、(CF₃SO₂)₂N^-、(FSO₂)₂N^-、(CF₃SO₂)₃C^-、AsF₆ ^-、SbF₆ ^-、NbF₆-、F(HF)_n ^-、B(C₆H₅)₄ ^-、C₄F₉SO₃ ^-、CF₃(CF₂)₃SO₃ ^-、(CF₃CF₂SO₂)₂N^-及びCF₃CF₂COO^-から選択されるアニオンである]

[In the formula, R ¹ is a divalent hydrocarbon group having 2 to 8 carbon atoms which may contain a heteroatom and forms a ring together with N ⁺ in the formula, R ² and R ³ are the same or different and are a hydrogen atom or an alkyl group having 1 to 6 carbon atoms (however, when the nitrogen atom forms a double bond with the adjacent carbon atom, R ³ does not exist),
^X- is ^{an anion selected} _from Cl- ^, Br-, ^I- , ^AlCl4- , _{Al2Cl7- ,} ^NO3- , _{BF4- , PF6-} ^{, ClO4-} , _{CH3COO- ,} ^CF3COO- , ^CF3SO3- _, ⁽ _{CF3SO2 ) 2N- , ( FSO2} ) ^2N- , _{( CF3SO2 )} ^3C- _, AsF6-, ^SbF6- _{, NbF6-} ^, _F ⁽ _HF ^{) n- , B} _{( C6H5} ) _{4- , C4F9SO3- , CF3 ( CF2 ) 3SO3-} , ⁽ _{CF3CF2SO2 ) 2N- and} ^CF3CF2COO- _.

In the above formula, the ring composed of ^R1 and N ⁺ includes rings in which at least one carbon atom constituting a hydrocarbon ring, such as saturated alicyclic hydrocarbons such as cyclopropane, cyclobutane, cyclopentane, cyclohexane, cycloheptane, and cyclooctane, and unsaturated cyclic hydrocarbons such as cyclopropene, cyclobutene, cyclopentene, cyclohexene, cycloheptene, cyclooctene, cyclopentadiene, and benzene, is replaced with a nitrogen atom. Examples of heteroatoms include N, O, S, and P, and N is preferred.

Examples of alkyl groups having 1 to 6 carbon atoms include methyl, ethyl, propyl, butyl, pentyl, and hexyl groups. Alkyl groups having 3 to 8 carbon atoms include structural isomers.

Other examples of ionic liquids include combinations of cations and anions represented by the following formulas (2) or (3):

[式中、YはN又はPであり、R⁴～R⁷は、同一又は異なって、水素原子(但し、R⁴～R⁷の全てが水素原子ではない)又は炭素数1～20の、置換基を有していてもよい、直鎖若しくは分岐又は環状のアルキル基であり(但し、窒素原子が隣接する炭素原子と二重結合を形成している場合は、R⁷は存在しない)、置換基は、ハロゲン原子、ヒドロキシ基、ニトロ基、シアノ基からなる群より選択され、
X^-は、Cl^-、Br^-、I^-、AlCl₄ ^-、Al₂Cl₇-、NO₃ ^-、BF₄ ^-、PF₆ ^-、ClO₄ ^-、CH₃COO^-、CF₃COO^-、CF₃SO₃ ^-、(CF₃SO₂)₂N^-、(FSO₂)₂N^-、(CF₃SO₂)₃C^-、AsF₆ ^-、SbF₆ ^-、NbF₆-、F(HF)_n ^-、B(C₆H₅)₄ ^-、C₄F₉SO₃ ^-、CF₃(CF₂)₃SO₃ ^-、(CF₃CF₂SO₂)₂N^-及びCF₃CF₂COO^-から選択されるアニオンである]

[wherein Y is N or P, R ⁴ to R ⁷ are the same or different and each is a hydrogen atom (provided that all of R ⁴ to R ⁷ are not hydrogen atoms) or a linear, branched or cyclic alkyl group having 1 to 20 carbon atoms which may have a substituent (provided that R ⁷ does not exist when a nitrogen atom forms a double bond with an adjacent carbon atom), and the substituent is selected from the group consisting of a halogen atom, a hydroxy group, a nitro group and a cyano group;
^X- is ^{an anion selected} _from Cl- ^, Br-, ^I- , ^AlCl4- , _{Al2Cl7- ,} ^NO3- , _{BF4- , PF6-} ^, _ClO4- , _{CH3COO- ,} ^CF3COO- , ^CF3SO3- _, ( _{CF3SO2 ) 2N- ,} ⁽ _FSO2 ) ^2N- , _{( CF3SO2 )} ^3C- _, AsF6-, ^SbF6- _{, NbF6-} ^, _F ⁽ _HF ^{) n- , B} _{( C6H5} ) _{4- , C4F9SO3- , CF3 ( CF2 ) 3SO3-} , ⁽ _{CF3CF2SO2 ) 2N- and} ^CF3CF2COO- _.

[式中、R⁸～R¹⁰は、同一又は異なって、水素原子(但し、R⁸～R¹⁰の全てが水素原子ではない)又は炭素数1～20の、置換基を有していてもよい、直鎖若しくは分岐又は環状のアルキル基であり、置換基は、ハロゲン原子、ヒドロキシ基、ニトロ基、シアノ基からなる群より選択され、
X^-は、Cl^-、Br^-、I^-、AlCl₄ ^-、Al₂Cl₇-、NO₃ ^-、BF₄ ^-、PF₆ ^-、ClO₄ ^-、CH₃COO^-、CF₃COO^-、CF₃SO₃ ^-、(CF₃SO₂)₂N^-、(FSO₂)₂N^-、(CF₃SO₂)₃C^-、AsF₆ ^-、SbF₆ ^-、NbF₆-、F(HF)_n ^-、B(C₆H₅)₄ ^-、C₄F₉SO₃ ^-、CF₃(CF₂)₃SO₃ ^-、(CF₃CF₂SO₂)₂N^-及びCF₃CF₂COO^-から選択されるアニオンである]

[In the formula, R ⁸ to R ¹⁰ are the same or different and each is a hydrogen atom (provided that all of R ⁸ to R ¹⁰ are not hydrogen atoms) or a linear, branched or cyclic alkyl group having 1 to 20 carbon atoms which may have a substituent, and the substituent is selected from the group consisting of a halogen atom, a hydroxy group, a nitro group and a cyano group;
^X- is ^{an anion selected} _from Cl- ^, Br-, ^I- , ^AlCl4- , _{Al2Cl7- ,} ^NO3- , _{BF4- , PF6-} ^, _ClO4- , _{CH3COO- ,} ^CF3COO- , ^CF3SO3- _, ( _{CF3SO2 ) 2N- ,} ⁽ _FSO2 ) ^2N- , _{( CF3SO2 )} ^3C- _, AsF6-, ^SbF6- _{, NbF6-} ^, _F ⁽ _HF ^{) n- , B} _{( C6H5} ) _{4- , C4F9SO3- , CF3 ( CF2 ) 3SO3-} , ⁽ _{CF3CF2SO2 ) 2N- and} ^CF3CF2COO- _.

The cation in the ionic liquid preferably has a weight average molecular weight of 700 or less, more preferably a weight average molecular weight of 50 to 600, more preferably a weight average molecular weight of 50 to 500, and even more preferably a weight average molecular weight of 50 to 400. The upper limit of the weight average molecular weight of the cation in the ionic liquid is, for example, 700, 650, 600, 550, 500, 450, 400, 350, 300, 250, 200, or 150. The lower limit of the weight average molecular weight of the cation in the ionic liquid is, for example, 30, 40, 50, 60, 70, 80, 90, 99, or 100. The weight average molecular weight here refers to the weight average molecular weight in terms of polystyrene.

The ionic liquid is preferably a combination of a cyclic cation represented by formula (1) and an anion, more preferably a combination of a cation selected from a ^pyridinium -based cation, a cyclic aliphatic ammonium cation, and an imidazolium-based cation, and an ^anion selected from ( _FSO2 ) _{2N- ,} ( _CF3SO2 ) ^2N- _, and _{BF4- ,} and more preferably a combination of a cation selected from _an imidazolium-based cation and an anion selected from (FSO2) _2N- , ( _CF3SO2 ) _2N- , and _BF4- from the viewpoint of improving peelability after application of a voltage.

Ionic liquids are available from Daiichi Kogyo Seiyaku, Kanto Chemical, Koei Chemical Industry, and others. For example, 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMI-FSI) and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-TFSI) can be obtained from Daiichi Kogyo Seiyaku, 1-hexylpyridinium bis(trifluoromethanesulfonyl)imide, N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide and 1-ethyl-3-methylimidazolium tetrafluoroborate can be obtained from Kanto Chemical, and 1-ethyl-3-methylimidazolium hexafluorophosphate (IL-C3), 1-butylpyridinium tetrafluoroborate (IL-P10) and 1-hexylpyridinium bis(trifluoromethanesulfonyl)imide (IL-P14) can be obtained from Koei Chemical Industry. The combinations of cations and anions contained in EMI-FSI and EMI-TFSI are as follows:

The amount of ionic liquid contained in the composition is not particularly limited, but is preferably 1 to 90 parts by weight, more preferably 5 to 80 parts by weight, more preferably 5 to 60 parts by weight, more preferably 5 to 50 parts by weight, more preferably 5 to 40 parts by weight, and more preferably 5 to 30 parts by weight, relative to 100 parts by weight of the acrylic polymer. The upper limit of the amount of ionic liquid contained in the composition is, for example, 90 parts by weight, 85 parts by weight, 80 parts by weight, 70 parts by weight, 60 parts by weight, 50 parts by weight, 45 parts by weight, 40 parts by weight, 35 parts by weight, 33 parts by weight, 32 parts by weight, 31 parts by weight, or 30 parts by weight, relative to 100 parts by weight of the acrylic polymer. The lower limit of the amount of ionic liquid contained in the composition is, for example, 1 part by weight, 3 parts by weight, 5 parts by weight, 7 parts by weight, 9 parts by weight, 10 parts by weight, 12 parts by weight, 14 parts by weight, 15 parts by weight, 16 parts by weight, 17 parts by weight, 18 parts by weight, 19 parts by weight, or 20 parts by weight relative to 100 parts by weight of the acrylic polymer. The ionic liquid may be a combination of one cation and one anion, or a combination of multiple types of cations and anions.

(Mobility promoter)
In this embodiment, the composition may contain a transport promoter that aids in the transport of ions when a voltage is applied. Examples of the transport promoter include polyethylene glycol and alkyl ethers of polyethylene glycol, and alkyl ethers of polyethylene glycol are preferred.

The molecular weight of the migration promoter is not particularly limited, but it is preferable that the weight average molecular weight is 120 to 600, more preferably 120 to 550, more preferably 120 to 500, and even more preferably 120 to 360. The upper limit of the weight average molecular weight of the migration promoter is, for example, 600, 590, 580, 570, 560, 550, 540, 530, 520, 510, 500, 490, 480, 470, 460, 450, 440, 430, 420, 410, 400, 390, 380, 370, 360, 355, 350, and 340. The lower limit of the weight average molecular weight of the migration promoter is, for example, 120, 125, 130, 135, 140, 145, 150, 155, 160, or 170. The weight average molecular weight referred to here refers to the weight average molecular weight calculated in terms of polystyrene.

Examples of alkyl ethers of polyethylene glycol include polyethylene glycol mono(di)methyl ether, polyethylene glycol mono(di)ethyl ether, polyethylene glycol mono(di)propyl ether, polyethylene glycol mono(di)isopropyl ether, polyethylene glycol mono(di)butyl ether, polyethylene glycol mono(di)isobutyl ether, polyethylene glycol mono(di)methyl ether, and polyethylene glycol mono(di)pentyl ether. Among these, alkyl ethers of polyethylene glycol having a weight average molecular weight of 120 to 360 are preferred, and polyethylene glycol mono(di)methyl ether having a weight average molecular weight of 120 to 360 is more preferred, and those selected from tetraethylene glycol dimethyl ether (dimethyl tetraglycol), diethylene glycol dibutyl ether, triethylene glycol butyl methyl ether, dimethyl triglycol, and triethylene glycol monomethyl ether are more preferred, and tetraethylene glycol dimethyl ether is more preferred. Alkyl ethers of polyethylene glycol are available from Nippon Nyukazai, Toho Chemical Industry, and the like. The alkyl ethers of polyethylene glycol used may be used alone or in combination of two or more.

The amount of the migration promoter contained in the composition is not particularly limited, but may be, for example, 1 to 90 parts by weight, 5 to 80 parts by weight, 5 to 50 parts by weight, 5 to 40 parts by weight, or 5 to 30 parts by weight, relative to 100 parts by weight of the acrylic polymer. The upper limit of the migration promoter contained in the composition is, for example, 90 parts by weight, 80 parts by weight, 70 parts by weight, 60 parts by weight, 50 parts by weight, 40 parts by weight, or 30 parts by weight, relative to 100 parts by weight of the acrylic polymer. The lower limit of the migration promoter contained in the composition is, for example, 1 part by weight, 3 parts by weight, 5 parts by weight, 7 parts by weight, 9 parts by weight, 10 parts by weight, 12 parts by weight, 14 parts by weight, 15 parts by weight, 16 parts by weight, 17 parts by weight, 18 parts by weight, 19 parts by weight, or 20 parts by weight, relative to 100 parts by weight of the acrylic polymer.

(Organic solvent)
The composition may contain an organic solvent. The organic solvent is not particularly limited, and may be any known organic solvent that can be used for a pressure-sensitive adhesive. As the organic solvent, either a hydrophilic organic solvent or a hydrophobic organic solvent may be used. Examples of hydrophilic organic solvents include methanol, ethanol, 1-propanol, 2-propanol, n-butyl alcohol, sec-butyl alcohol, isobutanol, tert-butyl alcohol, acetonitrile, acetone, and dimethylformamide. Examples of hydrophobic organic solvents include aliphatic hydrocarbons such as hexane, heptane, and isooctane, esters such as methyl acetate, ethyl acetate, and propyl acetate, aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene, halogenated hydrocarbons such as dichloromethane, 1,2-dichloroethane, chloroform, 1-chlorobutane, or chlorobenzene, ethers such as diethyl ether and t-butyl methyl ether, and ketones such as methyl ethyl ketone and methyl isobutyl ketone. These organic solvents may be used alone or in combination of two or more. When an organic solvent is used, it is preferable to adjust the usage ratio so that the solid content of the acrylic polymer is 10% by weight or more, and more preferably, the usage ratio is adjusted so that the solid content is 20% by weight or more and 50% by weight or less.

(Additives)
In addition to the above components, the composition of the present embodiment may contain additives such as a conductive material, a filler, a plasticizer, an antioxidant, a flame retardant, a colorant, a surfactant, or an adhesive other than the acrylic polymer.

Conductive materials are mainly classified into carbon-based conductive materials and metal-based conductive materials. Examples of carbon-based conductive materials include nanocarbon or carbon fiber [e.g., vapor-grown carbon fiber (VGCF) or carbon nanofiber], and more specifically, natural graphite, artificial graphite, acetylene black, ketjen black, furnace black, etc. Examples of metal-based conductive materials include metals such as Cu, Ni, Al, Ag, Au, Pt, Zn, or Mn, or alloys thereof. Conductive materials may be used alone or in combination.

Examples of fillers include silica, diatomaceous earth, alumina, zinc oxide, magnesium oxide, calcium carbonate, magnesium carbonate, calcium sulfate, barium sulfate, calcium silicate, talc, mica, bentonite, activated clay, glass fiber, aluminum nitride, etc. Fillers may be used alone or in combination.

Examples of plasticizers include polyols such as glycerin, diglycerin, triglycerin, ethylene glycol, propylene glycol, and polyethylene glycol; aliphatic polycarboxylates such as adipates, citric acids, sebacates, azelates, and maleates; aromatic polycarboxylates such as terephthalates, isophthalates, phthalates, trimellitates, and benzoates; and polyesters. Plasticizers may be used alone or in combination.

Examples of antioxidants include phenol-based antioxidants, amine-based antioxidants, lactone-based antioxidants, phosphorus-based antioxidants, sulfur-based antioxidants, etc. The antioxidants may be used alone or in combination.

Examples of flame retardants include phosphorus- and halogen-containing organic compounds, bromine- or chlorine-containing organic compounds, ammonium polyphosphate, aluminum hydroxide, antimony oxide, and reactive flame retardants. Flame retardants may be used alone or in combination.

Examples of colorants include inorganic pigments such as carbon black, titanium oxide, zinc oxide, iron oxide, and mica, and organic pigments such as coupling azo, condensed azo, anthraquinone, thioindigo, dioxazone, and phthalocyanine. Colorants may be used alone or in combination.

Examples of surfactants include anionic surfactants such as alkylbenzenesulfonates, α-olefinsulfonates, and phosphate esters; cationic surfactants such as amine salts (alkylamine salts, imidazolines, etc.) and quaternary ammonium salts (dialkyldimethylammonium salts, alkylbenzyldimethylammonium salts, pyridinium salts, benzethonium chloride, etc.); and nonionic surfactants such as sorbitan tristearate, sorbitan monopalmitate, sorbitan trioleate, stearic acid monoglyceride, polyoxyethylene nonylphenyl ether, and polyoxyethylene dodecyl ether. The surfactants may be used alone or in combination.

Examples of adhesives other than the acrylic polymers include silicone adhesives, polyester adhesives, urethane adhesives, and rubber adhesives. Examples of silicone adhesives include dimethylsiloxane and diphenylsiloxane adhesives. Examples of polyester adhesives include polyesters obtained by polycondensation of a carboxylic acid component having two or more functional groups and a diol component. Examples of urethane adhesives include urethane polymers obtained by reacting a polyol with a polyisocyanate compound. Examples of rubber adhesives include synthetic rubbers such as styrene-isoprene block copolymers, styrene-butadiene-styrene block copolymers, styrene-butadiene rubber, polyisoprene rubber, polyisobutylene, and butyl rubber, as well as natural rubbers.

The amount of these adhesives other than the above acrylic polymers is less than 100 parts by weight, preferably 90 parts by weight or less, more preferably 80 parts by weight or less, more preferably 70 parts by weight or less, more preferably 60 parts by weight or less, more preferably 50 parts by weight or less, more preferably 40 parts by weight or less, more preferably 30 parts by weight or less, more preferably 20 parts by weight or less, more preferably 10 parts by weight or less, more preferably 5 parts by weight or less, more preferably 3 parts by weight or less, and it is more preferable that no adhesives other than the acrylic polymer are included.

The amount of these additives (excluding adhesives other than the above acrylic polymer) contained in the composition is not particularly limited, but can be, for example, 0.1 to 200 parts by weight, or 1 to 100 parts by weight, per 100 parts by weight of the acrylic polymer.

The method of forming the adhesive layer or the electrically peelable adhesive layer is not particularly limited, and for example, the composition can be applied to a film (release film) of polyethylene terephthalate that has been subjected to a release treatment, and a core material can be laminated thereto. After applying the composition to the release film, the composition may be heated to dry the composition. Another example of forming the adhesive layer or the electrically peelable adhesive layer is to apply the composition to a core material. The method of applying these compositions is not particularly limited, and examples include directly applying the composition with a brush or using a coating device used in the manufacture of adhesive tapes. Examples of the coating device that can be used include a spin coater, a gravure coater, an applicator, a multi-coater, a die coater, a bar coater, a roll coater, a blade coater, or a knife coater. The thickness of the electrically peelable adhesive layer is not particularly limited, and is preferably 1 to 100 μm, more preferably 1 to 50 μm, and more preferably 5 to 30 μm. When an electrically peelable adhesive layer is formed on both sides of the adhesive layer, the two electrically peelable adhesive layers may have the same thickness or may have different thicknesses.

The adhesive sheet of this embodiment functions as a substance that fixes a substance (called a fixing target) that is to be fixed to an adherend by the adhesive sheet to the adherend. The surface of the adhesive sheet that is to be used may be protected by a release film or release paper until use.

The adherend in this embodiment refers to an object that provides a place where an object to be fixed is fixed via the adhesive sheet of this embodiment. Here, fixing can be direct or indirect, with direct fixing referring to a state in which the adherend and the object to be fixed are in direct contact with the adhesive sheet, and indirect fixing referring to a state in which the adherend and/or the object to be fixed are not in direct contact with the adhesive sheet but are in contact via a conductive auxiliary material. As long as the object to be fixed can be fixed to the adherend, the fixing method may be direct or indirect.

The adherend may be either conductive (conductive adherend) or non-conductive (non-conductive adherend). When the adherend is conductive, the adhesive sheet may be directly attached to the adherend. When the adherend is non-conductive, it is essential to attach a conductive auxiliary material to the non-conductive adherend. When attaching the conductive auxiliary material, any adhesive such as a commercially available adhesive may be used.

Examples of conductive substrates include metal plates, metal products, and metal workbenches made of metals such as iron, aluminum, copper, silver, and gold, or alloys of these metals. Examples of non-conductive substrates include wooden plywood, plastic products, and non-metallic workbenches.

The object to be fixed in this embodiment is not particularly limited, but if the object to be fixed is conductive, the object to be fixed may be directly attached to the adhesive sheet. If the object to be fixed is non-conductive, it is essential to attach a conductive auxiliary material to the object to be fixed and then attach it to the adhesive sheet, as in the case of a non-conductive adherend.

Examples of conductive objects to be fixed include foils (thickness less than 100 μm) and plates (thickness 100 μm or more) made of metals such as iron, aluminum, copper, silver, gold, etc., or alloys of these metals, meshes or cloths containing fibers mixed or coated with these metals or alloys, resin sheets containing these metals or alloys, and resin plates with a layer containing these metals, alloys, or conductive metal oxides. Examples of non-conductive objects to be fixed include resin, wood, or plastic plates, etc.

There are no particular limitations on the conductive auxiliary material as long as it is conductive, and examples include metals such as aluminum, copper, silver, gold, etc., alloys of these metals, or films on which conductive metal oxides (such as indium tin oxide: ITO) are vapor-deposited; fabrics containing fibers mixed with or coated with these metals or alloys; resin sheets containing these metals or alloys; and resin plates with a layer containing these metals, alloys, or conductive metal oxides.

1A shows an example of a cross section of an adhesive sheet on which an electrically peelable adhesive layer is formed (a cross section of a tape applied to a horizontal surface cut vertically; the same applies below). FIG. 1B shows an example of a cross section of an adhesive sheet made of a core material permeated with an electrically peelable adhesive composition. FIGS. 2A to 5B show examples of circuits when a voltage is applied to the electrically peelable adhesive layer of an adhesive sheet on which an electrically peelable adhesive layer is formed through a conductive object, and an example of peeling after the voltage is applied. FIGS. 6A and 6B show examples of circuits when a voltage is applied to both sides of an adhesive layer of an adhesive sheet made of a core material permeated with an electrically peelable adhesive composition through a conductive object, and an example of peeling after the voltage is applied. The use form of the adhesive sheet of the present invention is not limited to the following circuit examples and peeling examples. Note that in the following peeling examples, the adhesive sheet is described as remaining on the adherend side, but peeling can be performed so that the adhesive sheet remains on the object to be fixed by reversing the positive and negative directions of the DC power sources in each example. Incidentally, which side of the power source the adhesive sheet remains on varies depending on the composition of the adhesive sheet, and is not particularly limited.

In each drawing, 1 denotes an electrically peelable adhesive layer, 2 denotes a core material, 3 denotes a conductive adherend, 4 denotes a DC power source, 5 denotes a conductive object to be fixed, 6 denotes a non-conductive object to be fixed, 7 denotes an optional adhesive, 8 denotes a conductive auxiliary material, 9 denotes a non-conductive adherend, and 10 denotes an adhesive layer. In FIG. 1A, an electrically peelable adhesive layer 1 is formed on each side of a core material 2 of an adhesive sheet, and an adhesive layer 10 is formed by the core material 2 and the electrically peelable adhesive layer 1 (the same applies to the examples shown in FIGS. 2A to 5B). In FIG. 1B, an electrically peelable adhesive composition permeates the core material 2, and the core material 2 itself forms an adhesive layer 10 (the same applies to the examples shown in FIGS. 6A and 6B). In FIG. 1A and FIG. 1B, the adhesive layer 10 is also the adhesive sheet itself.

Figure 2A shows an example of a cross section in which a conductive object to be fixed 5 is adhered to a conductive adherend 3 using an adhesive sheet and a voltage is applied. As shown in Figure 2A, terminals are connected to the conductive object to be fixed 5 and the conductive adherend 3, and a circuit is formed with a DC power source 4, thereby applying a voltage to the electrically peelable adhesive layer 1, and the adhered conductive object to be fixed 5 can be peeled off from the conductive adherend 3 as shown in Figure 2B.

Figure 3A shows an example of a cross section in which a non-conductive object 6 is attached to a conductive adherend 3 using an adhesive sheet and a voltage is applied. As shown in Figure 3A, an aluminum plate is attached to the non-conductive object 6 as a conductive auxiliary material 8 using any adhesive 7, and the non-conductive object 6, the conductive auxiliary material 8, and the conductive adherend 3 are attached using an adhesive sheet. By connecting terminals to the conductive auxiliary material 8 and the conductive adherend 3 and forming a circuit with a DC power source 4, a voltage is applied to the electrically peelable adhesive layer 1, and the non-conductive object 6 that has been attached can be peeled off from the conductive adherend 3 as shown in Figure 3B. In this case, the conductive auxiliary material 8 attached to the non-conductive object 6 remains on the non-conductive object 6.

Figure 4A shows an example of a cross section in which a conductive object to be fixed 5 is adhered to a non-conductive adherend 9 using an adhesive sheet and a voltage is applied. As shown in Figure 4A, an aluminum plate is attached to the non-conductive adherend 9 as a conductive auxiliary material 8 using any adhesive 7, and the conductive object to be fixed 5, the conductive auxiliary material 8, and the non-conductive adherend 9 are adhered to each other using an adhesive sheet. By connecting terminals to the conductive object to be fixed 5 and the conductive auxiliary material 8 and forming a circuit with a DC power source 4, a voltage is applied to the electrically peelable adhesive layer 1, and the adhered conductive object to be fixed 5 can be peeled off from the non-conductive adherend 9 as shown in Figure 4B.

Figure 5A shows an example of a cross section in which a non-conductive object 6 is attached to a non-conductive adherend 9 using an adhesive sheet and a voltage is applied. As shown in Figure 5A, an aluminum plate is attached as a conductive auxiliary material 8 to each of the non-conductive object 6 and the non-conductive adherend 9 using an arbitrary adhesive 7, and the conductive auxiliary material 8 to which the non-conductive object 6 is attached and the conductive auxiliary material 8 to which the non-conductive adherend 9 is attached are attached using an adhesive sheet. By connecting terminals to each conductive auxiliary material 8 and forming a circuit with a DC power source 4, a voltage is applied to the electrically peelable adhesive layer 1, and the non-conductive object 6 attached to the non-conductive adherend 9 can be peeled off from the non-conductive adherend 9 as shown in Figure 5B. In this case, the conductive auxiliary material 8 attached to the non-conductive object 6 remains on the non-conductive object 6.

Figure 6A shows an example of a cross section in which a conductive object to be fixed 5 is adhered to a conductive adherend 3 using an adhesive sheet made of a core material impregnated with an electrically peelable adhesive composition, and a voltage is applied. As shown in Figure 6A, terminals are connected to the conductive object to be fixed 5 and the conductive adherend 3, and a circuit is formed with a DC power source 4, thereby applying a voltage to the core material 2 (adhesive layer 10), and the adhered conductive object to be fixed 5 can be peeled off from the conductive adherend 3 as shown in Figure 6B.

(Applications of Electrically Peelable Adhesive Sheets)
The electrically peelable adhesive sheet of this embodiment can be easily peeled off from a conductive object without UV irradiation or heat treatment by applying a low voltage of 30V or less. Therefore, the adhesive sheet can be suitably used for adhesive fixation of non-transparent members that cannot be irradiated with UV or members that are weak against heat. In addition, since the composition of the present invention has excellent adhesive fixation properties for conductive objects, it can be suitably used for fixing members that require high processing accuracy or members that are difficult to physically fix, such as thin metal plates and substrates. For example, the composition can be used for temporary fixing of parts in the electronic component manufacturing process (for example, temporary fixing of wafers during dicing of LSI chips), and the temporary fixing of parts can be easily released by applying a voltage. In addition, the electrically peelable adhesive sheet of this embodiment is thin and easy to attach uniformly to the adherend. Therefore, even when fixing parts in an assembly line, it is possible to work efficiently.

(Method of producing electrically releasing adhesive composition)
The electrically peelable adhesive composition of the present embodiment can be produced by stirring and mixing an acrylic polymer, an ionic liquid, and optionally a migration promoter, a crosslinking agent, etc. The stirring method is not particularly limited, and a known mixing method can be used. Specifically, for example, an acrylic polymer, an ionic liquid, and optionally a migration promoter, a crosslinking agent, etc. can be stirred with a V-type mixer or a mixer (such as a dissolver, homomixer, or planetary mixer). The above-mentioned additives may be added during stirring.

(Method of manufacturing electrically peelable adhesive sheet)
One embodiment of the present invention is a method for producing an electrically peelable adhesive sheet. The electrically peelable adhesive sheet can be produced by contacting an electrically peelable adhesive composition containing an acrylic polymer and an ionic liquid with a planar core material having a basis weight of 10.0 g/ ^m2 or less and a thickness of 10 μm to 35 μm to form an adhesive layer. The electrically peelable adhesive composition, the core material, and the electrically peelable adhesive sheet are as described above.

Contacting the core material with the electrically peelable adhesive composition includes, for example, permeating the core material with the electrically peelable adhesive composition, or contacting both sides of the core material with the electrically peelable adhesive composition to form a layer of the electrically peelable adhesive composition.

The electrically peelable adhesive composition can be made to permeate the core material, or the electrically peelable adhesive composition can be brought into contact with both sides of the core material to form a layer of the electrically peelable adhesive composition, for example, by applying the electrically peelable adhesive composition onto a release film and attaching the core material to the release film. A release film to which the electrically peelable adhesive composition has been applied may be attached to the side of the core material to which the release film is not attached. If the core material is made of fibers or has holes, the attached electrically peelable adhesive composition permeates into the fibers or holes. At this time, pressure may be applied to the attached core material. By applying pressure, the electrically peelable adhesive composition can be easily permeated into the core material. Pressure may be applied only from one side of the core material, or may be applied to both sides. The electrically peelable adhesive composition may be completely contained in the core material by permeating the core material. At that time, the adhesive sheet becomes an adhesive sheet made of a core material permeated with the electrically peelable adhesive composition. The electrically peelable adhesive composition may form a layer of the electrically peelable adhesive composition while permeating the core material. In the above-mentioned method, a film coated with the electrically peelable adhesive composition is attached to the core material, but the electrically peelable adhesive composition may be directly coated on the core material. The method for coating the electrically peelable adhesive composition is as described above.

(Removal method)
The adhesive sheet of the present embodiment can be peeled off from the conductive object by applying a voltage after the adhesive sheet is attached to the conductive object.

As a peeling method, for example, if the object to be fixed and the adherend are conductive, the adhesive sheet can be peeled off from the object to be fixed or the adherend by connecting terminals to the object to be fixed and the adherend and applying a voltage between the terminals. If the object to be fixed and/or the adherend are not conductive, fixing and peeling operations can be performed even on non-conductive objects by adhesively adhering an aluminum plate or the like as a conductive auxiliary material. These fixing and peeling operations are shown in the adhesive sheet peeling examples above.

There are no particular limitations on the voltage to be applied as long as it is possible to peel off the adhesive sheet, but a low voltage is preferable, taking into consideration the size of the voltage application device, the effect on the object to be fixed, and the risk to the human body in the event of an accident during work. The range of the applied voltage is, for example, 690V, 650V, 600V, 550V, 500V, 480V, 450V, 415V, 400V, 380V, 350V, 347V, 300V, 250V, 240V, 230V, 220V, 210V, 208V, 200V, 180V, 160V, 150V, 130V, 125V, 120V, 115V, 110V, 105V, 100V, 90V, 80V, 70V, 60V, 50V, 40V, and 30V with the upper limit set to 0.5V, 1V, 2V, 3V, The lower limit can be selected from the voltages of 4 V, 5 V, 6 V, 7 V, 8 V, 9 V, and 10 V. Among these, it is preferable to operate at a voltage of 1 to 30 V, because a compact application device is required, and in terms of safety and the effect on the object to be fixed.

The adhesive sheet of this embodiment can be peeled off from a conductive object even with an applied voltage as low as a few volts, so the peeling operation can be performed even if the power source is, for example, a commercially available dry cell battery. This shows that this embodiment is safe for the operator and allows the peeling operation to be performed using a simple, portable voltage application device.

The duration of voltage application is not particularly limited as long as the adhesive sheet can be peeled off, but taking into consideration the effect on the object to be fixed, it is preferable for it to be within 10 minutes, more preferably within 5 minutes, more preferably within 3 minutes, and even more preferably within 1 minute.

The temperature during peeling is not particularly specified, but it is preferable to perform the peeling at room temperature. As described above, the adhesive sheet of this embodiment can be peeled off from a conductive object at a low voltage in a short time, so that the effect of heat on the object to be fixed can be minimized.

The electrically peelable adhesive sheet of this embodiment includes a core material having a basis weight of 10.0 g/ ^m2 or less and a thickness of 10 μm to 35 μm, so that the adhesive sheet is easy to handle. Specifically, when using the adhesive sheet of this embodiment, when the release film attached to both sides is peeled off, the shape of the adhesive sheet does not tear or stretch, making it easy to apply. If a substrate (core material) is not used when using the composition, the shape of the adhesive layer is easily changed when the release film attached to the adhesive layer is peeled off, making it difficult to apply. If a thick core material that does not satisfy the basis weight of 10.0 g/ ^m2 or less and the thickness of 10 μm to 35 μm, for example, exceeds 35 μm, is used as the core material, the adhesive sheet becomes thick, although it is easy to apply, or the electrical peelability is reduced, making it difficult to peel off the adhesive sheet after the voltage is applied. Whether an adhesive sheet can be easily peeled off after application of a voltage can be determined by determining whether the adhesive strength reduction rate calculated by the following formula (4) is 70% or more. The reduction rate is preferably 75% or more, more preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. By using a core material with a basis weight of 10.0 g/ ^m2 or less and a thickness of 10 μm to 35 μm, an electrically peelable adhesive sheet that is easy to apply can be obtained.

(式中、未印加の粘着シートの粘着力とは、粘着シートを導電性の被着体及び導電性の固定対象物を固定した後、JIS-Z-0237(2009)に準拠して測定した粘着力を指し、
印加処理後の粘着シートの粘着力とは、粘着シートを導電性の被着体及び導電性の固定対象物を固定した後、10Vの電圧を10秒間印加してからJIS-Z-0237(2009)に準拠して測定した粘着力を指す)

(In the formula, the adhesive strength of the adhesive sheet before application of the voltage refers to the adhesive strength measured in accordance with JIS-Z-0237 (2009) after the adhesive sheet is fixed to a conductive adherend and a conductive object to be fixed.
The adhesive strength of the adhesive sheet after voltage application refers to the adhesive strength measured in accordance with JIS-Z-0237 (2009) after fixing the adhesive sheet to a conductive adherend and a conductive object to be fixed, and then applying a voltage of 10V for 10 seconds.

One embodiment of the present invention involves the use of a core material having a basis weight of 10.0 g/ ^m2 or less and a thickness of 10 μm to 35 μm for the production of an electrically peelable adhesive sheet. By using a core material having a basis weight of 10.0 g/m2 or ^less and a thickness of 10 μm to 35 μm, an electrically peelable adhesive sheet having excellent electrical peelability and excellent workability can be produced. The electrically peelable adhesive sheet and the core material are as described above.

The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited by these in any way.

(Production of Electrically Peelable Adhesive Composition 1)
An electrically peelable pressure-sensitive adhesive composition was prepared using an acrylic polymer, an ionic liquid, and a migration promoter as follows.

1. Preparation of acrylic polymer
A monomer mixture consisting of 91 parts by weight of n-butyl acrylate (Mitsubishi Chemical), 8 parts by weight of acrylic acid (Mitsubishi Chemical), and 1 part by weight of 2-hydroxyethyl methacrylate (Nippon Shokubai) and 186 parts by weight of polymerization solvent (ethyl acetate:toluene (weight ratio) = 9:1) were placed in a glass flask and replaced with nitrogen gas. 0.2 parts by weight of azobisisobutyronitrile (AIBN, Junsei Chemical) was added as a polymerization initiator, and the temperature was raised to 85°C and polymerization reaction was carried out for 5 hours to obtain an acrylic adhesive. The obtained acrylic adhesive contained 35% by weight of an acrylic polymer (weight average molecular weight about 800,000, Tg-46°C) and had a viscosity of 7,000 mPa s.

2. Preparation of Electrically Peelable Adhesive Composition To 100 parts by weight of the above acrylic adhesive (including 35 parts by weight of acrylic polymer), 3.85 parts by weight of Coronate (registered trademark) L-55E (Tosoh Corporation) as an isocyanate crosslinking agent, 7.0 parts by weight of Elexcel (registered trademark) AS-110 (EMI-FSI: Daiichi Kogyo Seiyaku Co., Ltd.) as an ionic liquid, and 7.0 parts by weight of dimethyl tetraglycol (Nippon Nyukazai Co., Ltd.: molecular weight approximately 220) as a mobility promoter were added, and the mixture was stirred with a dissolver at room temperature for 10 minutes and allowed to stand to defoam, to obtain electrically peelable adhesive composition A (composition A).

(Production of Electrically Peelable Adhesive Composition 2)
A composition was prepared using an acrylic polymer and an ionic liquid as follows: The acrylic polymer prepared in the above "1. Preparation of acrylic polymer" was used as the acrylic polymer.
To 100 parts by weight of acrylic adhesive (including 35 parts by weight of acrylic polymer), 3.85 parts by weight of Coronate L-55E (Tosoh Corporation) as an isocyanate crosslinking agent and 14.0 parts by weight of EMI-FSI as an ionic liquid were added, and the mixture was stirred with a dissolver at room temperature for 10 minutes and allowed to stand to degas, thereby obtaining electrically peelable adhesive composition B (composition B).

Example 1
Manufacturing of electrically peelable adhesive sheets 1
An electrically peelable adhesive sheet (hereinafter, simply referred to as a double-sided sheet) in the form of a double-sided adhesive sheet was produced using composition A. As the core material of the double-sided sheet, Japanese paper (manufactured by Hidaka Washi Co., Ltd.) with a basis weight of 5.0 g/m ² and a thickness of 30 μm was used.
Composition A was applied to a polyethylene terephthalate film (hereinafter also referred to as a release film) with a silicone-treated surface in an amount such that the composition A would have a thickness of 22 μm after drying, and then dried at 100° C. for 5 minutes. The composition-coated surface of the dried film was attached to one side of Japanese paper. Similarly, composition A was applied to a release film in an amount such that the composition A would have a thickness of 22 μm after drying, and dried to prepare a film, which was then attached to the side of the Japanese paper to which the film was not attached. The film was then left to stand at 40° C. for 3 days to produce the double-sided sheet of Example 1.

Example 2
Manufacturing of electrically peelable adhesive sheets 2
A double-sided sheet of Example 2 was produced in the same manner as in Production of Electrically Peelable Pressure Sensitive Adhesive Sheet 1, except that Composition A was applied to each side of the release film in an amount such that the dried thickness would be 12 μm.

Example 3
Manufacturing of electrically peelable adhesive sheets 3
A double-sided sheet of Example 3 was produced in the same manner as in Production 1 of an electrically releasing pressure sensitive adhesive sheet, except that Composition B was used instead of Composition A.

Example 4
Manufacture of electrically peelable adhesive sheets 4
The double-sided sheet of Example ⁴ was manufactured in the same manner as in Manufacturing of Electrically Peelable Adhesive Sheet 1, except that a polyester nonwoven fabric (UT-PET(A)8S: manufactured by Nippon Paper Papylia Co., Ltd.) with a basis weight of 8.0 g/m2 and a thickness of 14 μm was used as the core material.

Example 5
Manufacture of electrically peelable adhesive sheets 5
A double-sided sheet of Example 5 was produced in the same manner as in Production of Electrically Peelable Adhesive Sheet 1, except that paper with a basis weight of 6.0 g/m ² and a thickness of 17 μm (thin base paper: manufactured by Nippon Paper Papylia Co., Ltd.) was used as the core material.

Example 6
Manufacture of electrically peelable adhesive sheets 6
The double-sided sheet of Example 6 was produced in the same manner as in Production of Electrically Peelable Adhesive Sheet ¹ , except that paper with a basis weight of 6.0 g/m2 and a thickness of 17 μm (thin base paper: manufactured by Nippon Paper Papylia Co., Ltd.) was used as the core material, and an amount of Composition A was applied to each side of the release film in such an amount that the thickness after drying would be 12 μm.

Comparative Example 1
A polyester nonwoven fabric [Milife (registered trademark) TY0503FE (ENEOS Techno Materials)] with a basis weight of 8.0 g/ ^m2 and a thickness of 40 μm was used as the core material, and a double-sided sheet for Comparative Example 1 was produced in the same manner as in Production of Electrically Peelable Adhesive Sheet 1, except that an amount of Composition A was applied to each side of the release film in such a way that the thickness after drying would be 30 μm.

(Comparative Example 2)
A polyester nonwoven fabric [Milife (registered trademark) TY0503FE] with a basis weight of 8.0 g/ ^m2 and a thickness of 40 μm was used as the core material, and a double-sided sheet of Comparative Example 2 was produced in the same manner as in Production of Electrically Peelable Adhesive Sheet 1, except that an amount of Composition A was applied to each side of the release film in such a way that the thickness after drying would be 20 μm.

(Comparative Example 3)
A polyester nonwoven fabric [Milife (registered trademark) TY0503FE] with a basis weight of 8.0 g/ ^m2 and a thickness of 40 μm was used as the core material, and a double-sided sheet of Comparative Example 3 was produced in the same manner as in Production of Electrically Peelable Adhesive Sheet 1, except that an amount of Composition A was applied to each side of the release film so that the thickness after drying would be 15 μm.

(Comparative Example 4)
A double-sided sheet of Comparative Example 4 was produced by applying composition A to a polyethylene terephthalate film whose surface had been treated with silicone so that the thickness after drying would be 50 μm, and attaching a release film to the applied surface.

(Comparative Example 5)
Composition A was applied onto a polyethylene terephthalate film whose surface had been treated with silicone so that the thickness after drying would be 30 μm, and a release film was attached to the applied surface to produce a double-sided sheet of Comparative Example 5.

(Comparative Example 6)
A polyester film (E5007: Toyobo Co., Ltd.: PET film) with a basis weight of 35.0 g/ ^m2 and a thickness of 25 μm was used as the core material, and a double-sided sheet for Comparative Example 6 was produced in the same manner as in Production of Electrically Peelable Pressure-Sensitive Adhesive Sheet 1, except that Composition A was applied to each side of the release film in an amount such that the dried thickness would be 12 μm. Unlike the polyester nonwoven fabric used in Example 4, this PET film is a non-fibrous, non-porous film.

(Comparative Example 7)
A double-sided sheet for Comparative Example 7 was produced in the same manner as in Production of Electrically Peelable Adhesive Sheet 1, except that a nonwoven fabric (manufactured by Daio Paper Co., Ltd.) with a basis weight of 23.0 g/ ^m2 and a thickness of 40 μm was used as the core material, and an amount of Composition A was applied to each side of the release film in such an amount that the thickness after drying would be 10 μm.

(Comparative Example 8)
The double-sided sheet of Comparative Example 8 was produced in the same manner as in Production of Electrically Peelable Adhesive Sheet 1, except that rayon (manufactured by Nippon Paper Papylia Co., Ltd.) with a basis weight of 14.0 g/ ^m2 and a thickness of 40 μm was used as the core material, and an amount of Composition A so that the dried thickness would be 15 μm was applied to each side of the release film.

(Evaluation of double-sided sheets)
The thickness, workability, adhesive strength, and electrical peelability of the prepared double-sided sheets were evaluated. Note that the core materials used in each of the Examples and Comparative Examples were not electrically conductive. Each procedure is described below.

(Thickness measurement)
The thickness of the double-sided sheet was measured using a Peacock precision measuring device. Measurements were taken at five points on the double-sided sheet, and the average of the measurements was taken as the thickness of the double-sided sheet. If the thickness of the double-sided sheet was 50 μm or less, it was evaluated as a thin sheet, and if it was more than 50 μm, it was evaluated as a thick double-sided sheet.

(Evaluation of workability)
The workability of the double-sided sheet was evaluated as excellent if the shape of the double-sided sheet was not torn or stretched and was easy to apply when the polyethylene terephthalate films attached to both sides of the double-sided sheet were peeled off, and the double-sided sheet was evaluated as having poor workability if the shape of the double-sided sheet was torn or stretched and was difficult to apply when the release film was peeled off.

(Adhesiveness Evaluation)
The release film on one side of each double-sided sheet of Examples 1 to 6 and Comparative Examples 1 and 5 to 8 was peeled off, and a 50 μm thick aluminum foil (fixed object) was attached. After the aluminum foil was attached, the double-sided sheet was cut together with the aluminum foil to a length of 250 mm x 25 mm (three pieces per double-sided sheet. Hereinafter, these are referred to as double-sided tape). The release film on the other side of each cut double-sided tape was peeled off, and a 100 mm x 25 mm piece was attached to a polished stainless steel plate (conductive adherend: 125 mm x 50 mm). A 2 kg rubber roller was used to make one reciprocating motion in the long side direction of the sample piece at a speed of 300 mm/min to press the adherend, adhesive product, and fixed object, thereby preparing an evaluation sample. Thirty minutes after the adherend, double-sided tape, and object to be fixed were pressed together, each evaluation sample was measured using an Autograph (registered trademark) AGS-H manufactured by Shimadzu Corporation in accordance with JIS Z-0237 (2009), at a tensile speed of 300 mm/min, to measure the force (adhesive strength: N/25 mm) required to peel the double-sided tape in the evaluation sample from the adherend at an angle of 180° (180° peel), and the average value measured for each evaluation sample was recorded as the measured value.

Three evaluation samples were prepared for each double-sided sheet from Examples 1 to 6 and Comparative Examples 1 and 5 to 8 in the same manner as above. Electrodes were attached to each evaluation sample so that the conductive adherend side was the negative electrode and the fixed object side was the positive electrode, and a voltage of 10 V was applied to the evaluation samples for 10 seconds using a DC power source and a transformer to adjust the voltage. After the voltage was applied, the force required to peel the adhesive tape 180° from the adherend was measured in the same manner as above.

The degree of decrease in adhesive strength of the double-sided tape after voltage application (decrease rate) was evaluated. The decrease rate was calculated using the following formula (5). If the decrease rate is 70% or more, peeling by applying voltage is easy. If it is less than 70%, peeling is difficult.

The composition, tape thickness, thickness evaluation, and adhesiveness evaluation of each double-sided tape of Examples 1 to 6 and Comparative Examples 1 to 8 are shown in Tables 1 and 2 below, respectively. In the tables, A in the composition column indicates composition A, B indicates composition B, and the composition thickness indicates the thickness of the composition after drying on one side (total amount for Comparative Examples 4 and 5).

As in Examples 1 to 6, the double-sided tapes using a thin core material with a small basis weight were thin and had excellent workability, and were excellent in electrical peeling properties. In Examples 1 to 6 and Comparative Examples 1, 2, and 6 to 8, the final thickness of the double-sided tape was smaller than the sum of the thickness of the core material and the thickness of the composition after drying. This is because part of the composition penetrated into the gaps in the core material when applied. As in Comparative Examples 1 to 3 and 6 to 8, the double-sided tapes using a large basis weight or a thick core material were thick. In Comparative Examples 2 to 4, the adhesive strength was not measured, but the double-sided tapes of Comparative Examples 2 and 3 had very uneven surfaces on which the composition was applied and had uneven thicknesses, making them unsuitable as double-sided tapes, and the adhesive strength could not be properly evaluated, so it was not measured. The inventors believe that the results of Comparative Example 4 will be similar to those of Comparative Example 5, which does not use a core material. As in Comparative Examples 4 and 5, the double-sided tapes without a core material were thin, but because there was no core material, the shape of the tape was lost when the release film was peeled off, and workability was poor. In the case of a core material that was neither electrically conductive nor permeated by the composition, as in Comparative Example 6, the ionic liquid did not migrate even when a voltage was applied, and the adhesiveness did not decrease. In the cases of Comparative Examples 7 and 8, when the core material was too thick, sufficient electrical peeling properties could not be obtained even if a thin double-sided tape was formed.

The above experimental results show that by using a thin core material with a small basis weight, an electrically peelable adhesive sheet can be produced that is thin, has excellent workability, and also has excellent electrical peeling properties.

Reference Signs List 1 Electrically peelable adhesive layer 2 Core material 3 Conductive adherend 4 DC power source 5 Conductive object to be fixed 6 Non-conductive object to be fixed 7 Optional adhesive 8 Conductive auxiliary material 9 Non-conductive adherend 10 Adhesive layer

Claims (21)

An electrically peelable adhesive sheet comprising a planar core material and an adhesive layer comprising an electrically peelable adhesive composition,
the core material has a basis weight of 10.0 g/ ^m2 or less and a thickness of 10 μm to 35 μm, and is permeated with the electrically peelable pressure-sensitive adhesive composition;
the electrically releasing pressure sensitive adhesive composition is a composition containing an acrylic polymer and an ionic liquid,
the pressure-sensitive adhesive sheet is a double-sided pressure- sensitive adhesive sheet,
The thickness of the pressure-sensitive adhesive sheet is 10 to 50 μm.
Electrically peelable adhesive sheet. The adhesive sheet according to claim 1, wherein the electrically peelable adhesive composition is in contact with both sides of the core material in the adhesive layer. The pressure-sensitive adhesive sheet according to claim 1 , wherein the core material is made of fibers. The pressure-sensitive adhesive sheet according to claim 1 , wherein the core material has at least one through hole. The pressure-sensitive adhesive sheet according to claim 1 or 3 , wherein the pressure-sensitive adhesive sheet comprises the core material permeated with the electrically peelable pressure-sensitive adhesive composition. The pressure-sensitive adhesive sheet according to any one of claims 1 to 5 , wherein the core material has a basis weight of 2.0 to 8.0 g/ ^m2 . The pressure-sensitive adhesive sheet according to any one of claims 1 to 6 , wherein the pressure-sensitive adhesive sheet has a thickness of 15 to 50 µm. The pressure-sensitive adhesive sheet according to any one of claims 1 to 7 , wherein the electrically peelable pressure-sensitive adhesive composition comprises a migration promoter. The pressure-sensitive adhesive sheet according to claim 8 , wherein the migration promoter is an alkyl ether of polyethylene glycol. The pressure-sensitive adhesive sheet according to claim 9 , wherein the alkyl ether of polyethylene glycol is polyethylene glycol mono(di)methyl ether having a weight average molecular weight of 120 to 360. The pressure-sensitive adhesive sheet according to any one of claims 8 to 10 , wherein the content of the migration promoter is 5 to 30 parts by weight based on 100 parts by weight of the acrylic polymer. The pressure-sensitive adhesive sheet according to any one of claims 1 to 11 , wherein the ionic conductivity of the ionic liquid is 10 ^-4 to 10 ^-2 S/cm. The pressure-sensitive adhesive sheet according to any one of claims 1 to 12 , wherein the ionic liquid is represented by the following formula (1):
(In the formula, R ¹ is a divalent hydrocarbon group having 2 to 8 carbon atoms which may contain a heteroatom and forms a ring together with N ⁺ in the formula,
R ² and R ³ are the same or different and each is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms (however, when a nitrogen atom forms a double bond with an adjacent carbon atom, R ³ does not exist);
^X- is ^{an anion selected} _from Cl- ^, Br-, ^I- , ^AlCl4- , _{Al2Cl7- ,} ^NO3- , _{BF4- , PF6-} ^{, ClO4-} , _{CH3COO- ,} ^CF3COO- , ^CF3SO3- _, ⁽ _{CF3SO2 ) 2N-} ^, _{( FSO2} ) ^2N- , _{( CF3SO2 )} ^3C- _, AsF6-, ^SbF6- _{, NbF6-} ^, _F ⁽ _HF ^{) n- , B} _{( C6H5 ) 4- , C4F9SO3- , CF3} ( _{CF2 ) 3SO3-} , ⁽ _{CF3CF2SO2 ) 2N- , and} ^CF3CF2COO- _. The pressure-sensitive ^adhesive sheet according to any one of ^claims 1 to ₁₃ , wherein the ionic liquid is a salt of a cation selected from a pyridinium-based cation, a cyclic aliphatic ammonium cation, and an imidazolium-based cation, and an anion selected from ( _FSO2 ) _2N- , _{( CF3SO2} ) _2N- , and BF4- ^. The pressure-sensitive adhesive sheet according to any one of claims 1 to 14 , wherein the content of the ionic liquid is 5 to 60 parts by weight based on 100 parts by weight of the acrylic polymer. The pressure-sensitive adhesive sheet according to any one of claims 1 to 15 , wherein the acrylic polymer comprises an alkyl(meth)acrylate having an alkyl group having 1 to 8 carbon atoms, a carboxyl group-containing acrylic monomer, and/or a copolymer with a hydroxyl group-containing acrylic monomer. The pressure-sensitive adhesive sheet according to any one of claims 1 to 16 , further comprising a peelable release film, the release film being attached to both sides of the pressure-sensitive adhesive layer. The pressure-sensitive adhesive sheet according to any one of claims 1 to 17 , wherein the adhesive strength reduction rate calculated by the following formula (2) is 70% or more:
(In the formula, the adhesive strength of the pressure-sensitive adhesive sheet before application of pressure is meant to refer to the adhesive strength measured in accordance with JIS-Z-0237 (2009) after the pressure-sensitive adhesive sheet is fixed to a conductive adherend and a conductive object to be fixed,
The adhesive strength of the adhesive sheet after voltage application refers to the adhesive strength measured in accordance with JIS-Z-0237 (2009) after fixing the adhesive sheet to a conductive adherend and a conductive object to be fixed, and then applying a voltage of 10 V for 10 seconds. The method includes a step of contacting both sides of a planar core material having a basis weight of 10.0 g/ ^m2 or less and a thickness of 10 μm to 35 μm with an electrically peelable adhesive composition containing an acrylic polymer and an ionic liquid to form an adhesive layer ,
The total thickness of the core material and the adhesive layers formed on both sides of the core material is 10 to 50 μm,
The contacting is performed by allowing the electrically releasing adhesive composition to permeate the core material.
A method for producing an electrically releasable adhesive sheet. The method according to claim 19 , wherein the contacting comprises contacting the electrically releasing adhesive composition with each of both sides of the core material to form a layer of the electrically releasing adhesive composition. The method of claim 19 or 20 , wherein the electrically releasing adhesive composition further comprises a migration promoter.