JPWO2018230323A1 - Adhesive sheet and electronic equipment - Google Patents

Abstract

The problem to be solved by the present invention is to have a re-peeling performance that enables an organic EL information display device or the like to be easily peeled at the time of disassembly of an electronic device, and for a high step portion of an adherend. An object of the present invention is to provide a pressure-sensitive adhesive sheet having good followability. The present invention is a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer directly or via another layer on one or both surfaces of a foam base material, wherein the foam base material is ethylene-vinyl acetate copolymer (EVA) and / or An ethylene acrylic acid copolymer (EAA) is contained in an amount of 30 to 90% by mass, the apparent density of the foam base material is 0.20 g / cm3 to 0.60 g / cm3, and the tensile modulus in the flow direction is 10 MPa to 35 MPa. It relates to an adhesive sheet.

Description

  The present invention relates to a pressure-sensitive adhesive sheet that can be used in the production of various articles including electronic devices such as car navigation systems, personal computers, televisions, and smartphones.

  BACKGROUND ART Adhesive sheets based on foams are widely used, for example, in situations where two or more housings, rechargeable batteries, circuit boards, and the like that constitute an electronic device are fixed.

  The pressure-sensitive adhesive sheet is, for example, a resin foam obtained by foaming a resin composition containing a polyolefin resin and an incompatible resin with respect to the polyolefin resin in a ratio of 90:10 to 60:40. 2. Description of the Related Art An adhesive sheet using a foamed sheet as a base material, wherein an average major axis of an island portion of a sea-island structure formed by an incompatible resin is 1 μm or more, is known (for example, see Patent Document 1).

By the way, waterproofing of electronic devices such as televisions and smartphones is progressing. For this reason, pressure-sensitive adhesive sheets used for fixing members have been required to have conformability to a stepped portion such as a housing or a circuit board and to have high adhesive strength in order to prevent water entry. In recent years, from the viewpoint of design, a panel having a curved surface or a complicated shape is often used, and the adhesive sheet is required to have a performance of following irregularities and high steps.
Furthermore, in recent years, in order to achieve higher definition of information display, use of an organic EL information display device is progressing. Since such an organic EL display device is expensive, it is required to reuse it when repairing an electronic device. Accordingly, a pressure-sensitive adhesive sheet used for fixing the information display device has been required to have a re-peeling performance that enables easy peeling without breaking the organic EL information display device during disassembly for repair.

  As a means for solving such a problem, it is generally effective to increase the strength of the foam base material of the pressure-sensitive adhesive sheet. However, a pressure-sensitive adhesive sheet using a high-strength foam has a stepped portion of the adherend. However, there is a problem that the ability to follow water is not sufficient, and that water is likely to be flooded from outside.

JP 2008-240773 A

  The problem to be solved by the present invention is to have a re-peeling performance that enables an organic EL information display device or the like to be easily peeled off at the time of disassembly of an electronic device, and for a high step portion of an adherend. An object of the present invention is to provide a pressure-sensitive adhesive sheet having good followability.

  In order to achieve both the re-peeling performance that enables the organic EL information display device and the like to be easily peeled off and the followability, the present inventors have specified a specific configuration for the foam base material used for the adhesive tape. It has been found that the above problem can be solved when the components are contained, a specific range of apparent density is selected, and a specific tensile modulus is selected, and they are combined.

That is, the present invention is a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer directly or via another layer on one or both surfaces of a foam base material, wherein the foam base material is ethylene vinyl acetate copolymer (EVA) and And / or an ethylene acrylic acid copolymer (EAA) in an amount of 30 to 90% by mass, an apparent density of the foam base material of 0.20 g / cm ^{3 to} 0.60 g / cm ³ and a tensile modulus in a flow direction. The present invention relates to a pressure-sensitive adhesive sheet having a pressure of 10 MPa to 35 MPa.

  The pressure-sensitive adhesive sheet of the present invention can be peeled off without breaking an organic EL information display device or the like at the time of disassembly of an electronic device or the like, and has good followability even at a high step portion. The pressure-sensitive adhesive sheet can be used in various situations including, for example, manufacturing electronic devices such as portable electronic terminals, fixing automobile parts, fixing interior and exterior of buildings, and the like.

FIG. 2 is a diagram in which the pressure-sensitive adhesive sheet of the present invention is attached to an acrylic plate. FIG. 2 is a diagram in which the acrylic plate with an adhesive sheet of FIG. 1 is attached to a SUS plate. It is a figure which shows the method of measuring the indentation adhesive strength of the adhesive sheet of this invention with a tensile tester. FIG. 2 is a diagram in which the pressure-sensitive adhesive sheet of the present invention is attached to an acrylic plate. FIG. 3 is a diagram in which a single-sided adhesive tape of a polyethylene terephthalate substrate is attached to an acrylic plate. FIG. 5 is a view in which FIG. FIG. 2 is a diagram in which the pressure-sensitive adhesive sheet of the present invention is attached to an acrylic plate. It is a figure showing the evaluation method of re-peelability of the pressure sensitive adhesive sheet of the present invention. It is a figure showing the evaluation method of re-peelability of the pressure sensitive adhesive sheet of the present invention.

The pressure-sensitive adhesive sheet of the present invention is a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer directly or via another layer on one or both sides of a foam base material, wherein the foam base material is ethylene vinyl acetate copolymer (EVA) And / or an ethylene acrylic acid copolymer (EAA) in an amount of 30 to 90% by mass, an apparent density of the foam base material of 0.20 g / cm ^{3 to} 0.60 g / cm ³ and a tensile modulus in a flow direction. Is 10 MPa to 35 MPa.

(Foam substrate)
The pressure-sensitive adhesive sheet of the present invention has a foam containing 30 to 90% by mass of an ethylene vinyl acetate copolymer (EVA) and / or an ethylene acrylic acid copolymer (EAA) as a material constituting the base material (core). Use body substrate.
The content of the ethylene-vinyl acetate copolymer and / or the ethylene acrylic acid copolymer is more preferably from 40 to 80% by mass, and most preferably from 50 to 70% by mass. By setting the content of the ethylene vinyl acetate copolymer and / or the ethylene acrylic acid copolymer within the above range, the strength of the foam which is not broken at the time of re-peeling is secured, and the flexibility required for the followability of the step portion is secured. Easy to secure.
The ethylene vinyl acetate copolymer more preferably has a vinyl acetate content (copolymerization ratio) of 20% by mass or less, 5% by mass or more and 15% by mass or less. By keeping the vinyl acetate content in the ethylene-vinyl acetate copolymer within the above range, it is possible to secure the strength of the foam which is not torn at the time of re-peeling, and to easily secure the flexibility required for the followability of the step portion. .

The foam substrate has an apparent density using the range of ^{0.20g / cm 3 ~0.60g / cm 3} .

The apparent density of the foam substrate is in ^the range of 0.25g / cm ³ ~0.55g / cm 3 are ^preferred, the range of 0.30g / cm ³ ~0.50g / cm 3 is more preferable. By setting the apparent density of the foam base material within the above range, it is possible to secure the strength of the foam which is not broken at the time of re-peeling, and to secure the flexibility required for the followability of the step portion. The apparent density refers to the apparent density measured according to JIS K6767, and a foam cut into a rectangle of 4 cm × 5 cm is prepared for about 15 cm ³ minutes, and its mass is measured. Based on the mass and the volume, Refers to the value calculated by

  The foam base material preferably has a thickness of 50 μm to 300 μm, more preferably 70 μm to 300 μm, and most preferably 100 μm to 250 μm. If the thickness of the foam base material is too small, it is difficult to secure a foam strength that does not break when re-peeled. On the other hand, if the thickness of the foam is too large, the thickness of the electronic device itself is increased, which is not desirable from the viewpoint of design and portability of the electronic device.

  The foam has a tensile modulus in the flow direction of 10 MPa to 35 MPa. The tensile elastic modulus in the flow direction is preferably from 12 MPa to 33 MPa, and most preferably from 14 MPa to 29 MPa. By setting the tensile modulus in this range, it is possible to secure the strength of the foam that is not torn at the time of re-peeling and to secure the flexibility necessary for the followability of the step portion.

The tensile modulus in the flow direction of the foam refers to a value measured according to JIS K7161. More specifically, a foam having a grip-to-grip distance (L) of 20 mm and a test piece width (W) of 10 mm was subjected to a tensile speed of 10 mm / min using a Tensilon tensile tester at 23 ° C. and 50% RH. The tensile modulus is calculated by the following method. This evaluation method is an evaluation suitable as an index of whether or not the foam can be peeled without tearing when the tape is peeled again.
(1) E = (σ2-σ1) / ε2-ε1
E: Tensile modulus [Mpa],
σ1: stress at strain 0.0005 [MPa]
σ2: stress [MPa] at a strain of 0.0025
ε1: strain 0.0005
ε2: strain 0.0025
(2) σ1 = F1 / (t × W)
F1: Tensile load [N] at strain 0.0005
t: thickness of test piece [mm]
W: width of test piece [mm]
(3) σ2 = F2 / (t × W)
F2: Tensile load at strain 0.0025 [N]
t: thickness of test piece [mm]
W: width of test piece [mm]
In addition, the tensile load at the time of each strain uses the tensile load at the time of the increase of the distance between grips calculated based on the following formula.
(4) ε = Lt / L
Lt: Increase in distance between grips [mm]
L: Initial distance between grips [mm]

  The foam may further contain at least one selected from the group consisting of polyolefins, polyurethanes and acrylic polymers. As the polyolefin, polyethylene, polypropylene and ethylene-propylene copolymer are preferable, and as the acrylic polymer, acrylic rubber and other elastomers are preferable. Among them, one or more selected from linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), medium-density polyethylene (MDPE), and high-density polyethylene (HDPE) to increase the tensile strength at the time of re-peeling It is preferred to contain. The content of these is preferably 5 to 60% by mass, more preferably 10 to 50% by mass, and most preferably 20 to 40% by mass. By setting the content in this range, it is easy to achieve both the flexibility required for following steps. Further, it is preferable to contain an elastomer for improving the followability. As the elastomer, ethylene-propylene rubber (EPDM) is preferable. The content of the elastomer is preferably 5 to 40% by mass, more preferably 10 to 30% by mass.

  As the foam, for example, a foam having a crosslinked structure can be used.

  The method for producing the foam is not particularly limited. For example, in addition to ethylene vinyl acetate copolymer (EVA) and / or ethylene acrylic acid copolymer (EAA), polyolefin resins such as polyethylene resins A foamable resin composition containing a pyrolytic foaming agent, a foaming aid, and a coloring agent, if necessary, is supplied to an extruder, melt-kneaded, and extruded from the extruder into a sheet to form a foam. A method includes a step of manufacturing a resin sheet, a step of crosslinking the foamed resin sheet as necessary, and a step of foaming the foamable resin sheet.

  The foam obtained by the above method may be melted or softened as necessary, and may be stretched in one or both of the flow direction and the width direction. The stretching may be performed a plurality of times as necessary.

  As a method of producing the foamable resin sheet, for example, the foamable resin sheet can be produced by coating or casting a foamable resin composition on the surface of a release liner or the like, followed by drying.

  The step of crosslinking the foamable resin sheet obtained by the above method is, for example, a method of irradiating the foamable resin sheet with ionizing radiation, preparing a foamable resin composition containing an organic peroxide, and using the same. The heating can be performed by a method of heating the obtained foamable resin sheet.

  Examples of the ionizing radiation include an electron beam, α-ray, β-ray, and γ-ray. The dose of the ionizing radiation is appropriately adjusted so that the gel fraction of the resin foam falls within the above-mentioned preferable range, but is preferably in the range of 5 to 200 kGy. Irradiation with ionizing radiation is preferably performed on both surfaces of the foamable resin sheet, since it is easy to obtain a uniform foaming state, and it is more preferable to irradiate both surfaces with the same dose.

  Examples of the organic peroxide include 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane, and 2,2-bis ( (t-butylperoxy) octane, n-butyl-4,4-bis (t-butylperoxy) valerate, di-t-butyl peroxide, t-butylcumyl peroxide, dicumyl peroxide, α, α ′ -Bis (t-butylperoxy-m-isopropyl) benzene, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, 2,5-dimethyl-2,5-di (t-butyl Peroxy) hexyne-3, benzoyl peroxide, cumylperoxyneodecane, t-butylperoxybenzoate, 2,5-dimethyl-2,5-di (ben Examples include zoylperoxy) hexane, t-butylperoxyisopropyl carbonate, and t-butylperoxyallyl carbonate. These may be used alone or two or more of them may be used in combination.

  The addition amount of the organic peroxide is preferably from 0.01 to 5 parts by mass, more preferably from 0.1 to 3 parts by mass, based on 100 parts by mass of the base resin.

  The step of foaming the foamable resin sheet can be performed by, for example, a method of heating with hot air, a method of heating with infrared rays, a method of using a salt bath, a method of using an oil bath, or the like. Among them, a method of heating with hot air and a method of heating with infrared rays are preferable.

  When foaming the foamable resin sheet, a foamable resin sheet containing a pyrolytic foaming agent can be used.

  The pyrolytic blowing agent may be appropriately determined according to the expansion ratio of the foam, but is preferably used in a range of 1 part by mass to 40 parts by mass with respect to 100 parts by mass of the base resin, It is more preferable to use it in the range of 1 part by mass to 30 parts by mass.

  The stretching step may be performed on the foam obtained by the above method, or may be performed in parallel with the step of foaming the foamable resin sheet.

  The stretching step may be performed continuously while maintaining the molten state in the foaming step, or may be cooled and heated again after the foaming step.

  Here, the molten state of the foam refers to a state in which the foam is heated to a temperature equal to or higher than the melting point of a resin such as a base resin constituting the foam. The softening of the foam refers to a state where the foam is heated to a temperature equal to or higher than the softening point and lower than the melting point of the base resin constituting the foam.

As the foam of the present invention, a colored foam can be used for the purpose of imparting design properties, light-shielding properties, hiding properties, light-reflecting properties, and light resistance. As the coloring agent usable for coloring, for example, a black coloring agent can be used, and specifically, carbon black, graphite, copper oxide, manganese dioxide, aniline black, perylene black, titanium black, cyanine black, Activated carbon, ferrite, magnetite, chromium oxide, iron oxide, molybdenum disulfide, chromium complex, composite oxide black dye, anthraquinone organic black dye, and the like can be used. Above all, it is preferable to use carbon black as a coloring agent in order to maintain cost, availability, insulation properties and heat resistance.

  As the colorant, a white colorant can be used, and specifically, titanium oxide, zinc oxide, aluminum oxide, silicon oxide, magnesium oxide, zirconium oxide, calcium oxide, tin oxide, barium oxide, oxide Cesium, yttrium oxide, magnesium carbonate, calcium carbonate, barium carbonate, zinc carbonate, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, zinc hydroxide, aluminum silicate, calcium silicate, barium sulfate, calcium sulfate, barium stearate , Zinc white, talc, silica, alumina, clay, kaolin, titanium phosphate, mica, gypsum, white carbon, diatomaceous earth, bentonite, lithopone, zeolite, sericite, etc., inorganic white colorants, silicone resin particles, acrylic Resin particles, c Tan resin particles, such as organic white colorants such as melamine resin particles can be used. Above all, it is preferable to use aluminum oxide or zinc oxide as the coloring agent in order to maintain cost, availability, color tone, and heat resistance.

  In addition, as the foam of the present invention, a plasticizer, an antioxidant, a foaming auxiliary such as zinc oxide, a foam nucleus adjusting material, a heat stabilizer, an aluminum hydroxide, as needed, as long as the physical properties are not impaired. Containing additives such as flame retardants such as aluminum and magnesium hydroxide, antistatic agents, glass or plastic hollow balloon beads, fillers such as metal powders and metal compounds, conductive fillers, and thermal conductive fillers Can be used.

  As the foam, in order to maintain appropriate followability and cushioning property, the additive is preferably used in an amount of 0.1% by mass to 10% by mass, and more preferably 1% by mass to 7% by mass with respect to a base resin. Is preferred.

  When producing a foam containing an additive such as the coloring agent or the thermally decomposable foaming agent or a foaming aid, in order to prevent color unevenness or partial excessive foaming or insufficient foaming, the foamable resin composition It is preferable to use a thermoplastic resin having high compatibility with the above-mentioned additive and the above-mentioned additive, which are kneaded in advance and made into a master batch.

  As the foam, it is preferable to use a foam having a surface having a wetting index of 36 mN / m or more with a wetting reagent for the purpose of improving the adhesion to the pressure-sensitive adhesive layer and other layers, and 40 mN / It is more preferable to use one having a surface of at least 48 mN / m. Examples of a method for adjusting the wetting index of the surface of the foam to the above range include surface treatment methods such as corona treatment, flame treatment, plasma treatment, hot air treatment, ozone treatment, ultraviolet treatment, and application of an easy-adhesion treatment agent. .

(Adhesive layer)
As the pressure-sensitive adhesive sheet, a sheet having a pressure-sensitive adhesive layer directly or via another layer on one side or both sides of the foam can be used.

  Examples of the pressure-sensitive adhesive that can be used for forming the pressure-sensitive adhesive layer include an acrylic pressure-sensitive adhesive, a urethane-based pressure-sensitive adhesive, a synthetic rubber-based pressure-sensitive adhesive, a natural rubber-based pressure-sensitive adhesive, and a silicone-based pressure-sensitive adhesive. Use of an acrylic pressure-sensitive adhesive containing an acrylic polymer obtained by polymerizing a monomer component containing a (meth) acrylic monomer and, if necessary, a tackifying resin or a crosslinking agent. Is preferred.

  Examples of (meth) acrylic monomers that can be used in the production of the acrylic polymer include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, and t- Carbon such as butyl (meth) acrylate, n-hexyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate, isononyl (meth) acrylate, cyclohexyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate (Meth) acrylate having an alkyl group having 1 to 12 atoms can be used.

  Among them, as the (meth) acrylic monomer, it is preferable to use a (meth) acrylate having an alkyl group having 4 to 12 carbon atoms, and having an alkyl group having 4 to 8 carbon atoms. It is more preferable to use (meth) acrylate, and it is particularly preferable to use one or both of n-butyl acrylate and 2-ethylhexyl acrylate in order to achieve both excellent adhesive strength and excellent followability. .

  The (meth) acrylate having an alkyl group having 1 to 12 carbon atoms is preferably used in an amount of 60% by mass or more, and more preferably 80% by mass or more based on the total amount of the monomers used for producing the acrylic polymer. It is more preferable to use it in the range of 98.5% by mass, and it is even more preferable to use it in the range of 90% by mass to 98.5% by mass in order to achieve both excellent adhesive strength and excellent followability.

  In producing the acrylic polymer, a high-polarity vinyl monomer can be used as a monomer. As the high-polarity vinyl monomer, one kind or a combination of two or more kinds of a vinyl monomer having a hydroxyl group, a vinyl monomer having a carboxyl group, a vinyl monomer having an amide group, and the like can be used.

  Examples of the monomer having a hydroxyl group include a hydroxyl group such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, and 6-hydroxyhexyl (meth) acrylate. (Meth) acrylates can be used.

  As the vinyl monomer having a carboxyl group, for example, acrylic acid, methacrylic acid, itaconic acid, maleic acid, (meth) acrylic acid dimer, crotonic acid, ethylene oxide-modified succinic acrylate, and the like can be used. Among them, it is preferable to use acrylic acid.

  As the monomer having an amide group, for example, N-vinylpyrrolidone, N-vinylcaprolactam, acryloylmorpholine, acrylamide, N, N-dimethylacrylamide and the like can be used.

  As the high polar vinyl monomer, in addition to those described above, vinyl acetate, ethylene oxide-modified succinic acrylate, 2-acrylamido-2-methylpropanesulfonic acid, and the like can also be used.

  The high-polarity vinyl monomer is preferably used in a range of 1.5% by mass to 20% by mass relative to the total amount of the monomers used for producing the acrylic polymer, and is preferably 1.5% by mass. It is more preferably used in the range of 10 to 10% by mass, and further preferably used in the range of 2% to 8% by mass in order to achieve both excellent adhesive strength and excellent followability.

  When using a pressure-sensitive adhesive containing a crosslinking agent described below, it is preferable to use an acrylic polymer having a functional group that reacts with a functional group of the crosslinking agent as the acrylic polymer. Examples of the functional group which the acrylic polymer may have include a hydroxyl group.

  The hydroxyl group can be introduced into the acrylic polymer by using, for example, a vinyl monomer having a hydroxyl group as the monomer.

  The vinyl monomer having a hydroxyl group is preferably used in a range of 0.01% by mass to 1.0% by mass with respect to the total amount of the monomers used for producing the acrylic polymer, and 0.03% by mass. It is more preferable to use it in the range of mass% to 0.3 mass%.

  The acrylic polymer can be produced by polymerizing the monomer by a method such as a solution polymerization method, a bulk polymerization method, a suspension polymerization method, and an emulsion polymerization method. Is preferable in improving the production efficiency of the acrylic polymer.

  Examples of the solution polymerization method include a method in which the monomer, the polymerization initiator, and the organic solvent are mixed and stirred at a temperature of preferably 40 ° C. to 90 ° C. to perform radical polymerization.

  Examples of the polymerization initiator include peroxides such as benzoyl peroxide and lauryl peroxide, azo-based thermal polymerization initiators such as azobisisobutylnitrile, acetophenone-based photopolymerization initiator, benzoin ether-based photopolymerization initiator, and benzyl. Ketal-based photopolymerization initiators, acylphosphine oxide-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzophenone-based photopolymerization initiators, and the like can be used.

  The acrylic polymer obtained by the above method may be in a state of being dissolved or dispersed in an organic solvent, for example, when produced by a solution polymerization method.

  As the acrylic polymer, those having a weight average molecular weight of 400,000 to 3,000,000 are preferably used, and those having a weight average molecular weight of 700,000 to 2.5 million are more preferable.

  The weight average molecular weight refers to a value measured by gel permeation chromatography (GPC) and calculated in terms of standard polystyrene. Specifically, the weight average molecular weight can be measured using a GPC device (HLC-8320GPC) manufactured by Tosoh Corporation under the following conditions.

Sample concentration: 0.5% by mass (tetrahydrofuran solution)
Sample injection volume: 100 μL
Eluent: tetrahydrofuran Flow rate: 1.0 mL / min Measurement temperature: 40 ° C
Main column: 2 TSKgel GMHHR-H (20) Guard column: TSKgel HXL-H
Detector: Differential refractometer Weight average molecular weight of standard polystyrene: 10,000 to 20 million (manufactured by Tosoh Corporation)

  As the pressure-sensitive adhesive that can be used for forming the pressure-sensitive adhesive layer, in order to achieve both excellent adhesion to adherends and foams and excellent followability, it is possible to use a material containing a tackifier resin. preferable.

  As the tackifying resin, for example, rosin-based tackifying resin, polymerized rosin-based tackifying resin, polymerized rosin-ester-based tackifying resin, rosin-phenol-based tackifying resin, stabilized rosin-ester-based tackifying resin, disproportionated rosin ester Tackifier resin, hydrogenated rosin ester tackifier resin, terpene tackifier resin, terpene phenol tackifier resin, petroleum resin tackifier resin, (meth) acrylate resin tackifier resin, etc. can be used. . When an emulsion-type adhesive is used as the adhesive, it is preferable to use an emulsion-type adhesive resin also as the tackifier resin.

  Examples of the tackifying resin include a disproportionated rosin ester-based tackifying resin, a polymerized rosin ester-based tackifying resin, a rosin phenol-based tackifying resin, a hydrogenated rosin ester-based tackifying resin, and a (meth) acrylate-based resin. It is preferable to use one or more of resins, terpene phenol resins and petroleum resins in combination.

  As the tackifying resin, those having a softening point in the range of 30 ° C. to 180 ° C. are preferably used, and those having a softening point in the range of 70 ° C. to 140 ° C. are preferably used. This is more preferable in order to achieve both excellent adhesion to ()) and excellent followability. When using the (meth) acrylate tackifier resin, it is preferable to use a (meth) acrylate tackifier resin having a glass transition temperature of 30 ° C to 200 ° C, and to use a resin having a glass transition temperature of 50 ° C to 160 ° C. Is more preferable.

  The tackifier resin is preferably used in a range of 5 parts by mass to 65 parts by mass, and more preferably in a range of 8 parts by mass to 55 parts by mass with respect to 100 parts by mass of the acrylic polymer. It is more preferable to achieve both excellent adhesion to a body or a foam and excellent followability.

  As the pressure-sensitive adhesive used for forming the pressure-sensitive adhesive layer, it is preferable to use a cross-linking agent in order to ensure excellent adhesive strength to adherends and foams.

  As the crosslinking agent, for example, an isocyanate-based crosslinking agent, an epoxy-based crosslinking agent, a metal chelate-based crosslinking agent, an aziridine-based crosslinking agent, and the like can be used. Among them, as the cross-linking agent, it is preferable to use one or both of an isocyanate-based cross-linking agent and an epoxy-based cross-linking agent having high reactivity with an acrylic polymer, and it is preferable to use an isocyanate-based cross-linking agent. More preferred.

  Examples of the isocyanate-based cross-linking agent include tolylene diisocyanate, naphthylene-1,5-diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, and trimethylolpropane-modified tolylene diisocyanate. It is preferable to use trimethylolpropane-modified tolylene diisocyanate.

  The cross-linking agent is preferably selected and used in such an amount that the gel fraction of the pressure-sensitive adhesive layer with respect to toluene is 40 to 80%, and is selected and used in an amount such that the gel fraction is 30 to 70% by mass. More preferably, selecting and using an amount that gives a gel fraction of 35% by mass to 65% by mass achieves both excellent adhesion to adherends and foam base materials and excellent conformability. It is more preferable to obtain an adhesive sheet.

  In addition, the said gel fraction points out the value measured by the method shown below.

  After applying the above-mentioned adhesive to the release-treated surface of the release liner so that the thickness after drying becomes 50 μm, the coating is dried at 100 ° C. for 3 minutes, and then dried at 40 ° C. in an environment of 2 ° C. The adhesive layer was formed by aging for days.

  A test piece was obtained by cutting the pressure-sensitive adhesive layer into a square having a length of 50 mm and a width of 50 mm.

  After measuring the mass (G1) of the test piece, the test piece was immersed in toluene at 23 ° C. for 24 hours.

  After the immersion, the mixture of the test piece and toluene was filtered using a 300-mesh wire net to extract components insoluble in toluene. The mass (G2) of the insoluble component dried at 110 ° C. for one hour was measured.

  The gel fraction was calculated based on the mass (G1), the mass (G2) and the following equation.

    Gel fraction (% by mass) = (G2 / G1) × 100

  Examples of the adhesive include plasticizers, softeners, antioxidants, flame retardants, glass and plastic fibers and balloons, beads, metals, metal oxides, fillers such as metal nitrides, pigments, dyes, and the like. Those containing additives such as a coloring agent, a leveling agent, a thickener, a water repellent, and an antifoaming agent can be used.

  The pressure-sensitive adhesive layer that can be formed using the pressure-sensitive adhesive preferably has a temperature at which a peak value of a loss tangent (tan δ) at a frequency of 1 Hz is obtained, and more preferably the temperature is −40 ° C. to 15 ° C. By setting the peak value of the loss tangent of the pressure-sensitive adhesive layer in the above range, it becomes easy to provide good adhesion to the adherend at normal temperature.

  The loss tangent (tan δ) at a frequency of 1 Hz is obtained from the storage elastic modulus (G ′) and the loss elastic modulus (G ″) obtained by the dynamic viscoelasticity measurement based on the temperature dispersion according to the equation of tan δ = G ″ / G ′. Can be In the measurement of the dynamic viscoelasticity, the pressure-sensitive adhesive layer formed to a thickness of about 2 mm was measured using a viscoelasticity tester (trade name: ARES G2, manufactured by TIA Instruments Japan). The test piece is sandwiched between parallel disks having a diameter of 8 mm, which is a measuring part, and the storage elastic modulus (G ′) and the loss elastic modulus (G ″) are measured at a frequency of 1 Hz from −50 ° C. to 150 ° C.

  The thickness of the pressure-sensitive adhesive layer used in the present invention is preferably 5 μm to 100 μm, and more preferably 15 μm to 80 μm, in order to achieve both excellent adhesion to adherends and foams and excellent followability. More preferably, it is particularly preferably from 25 μm to 75 μm.

(Adhesive sheet)
The pressure-sensitive adhesive sheet of the present invention preferably has a strength value of at least 40 N / cm ^2, more preferably at least 50 N / cm ² , and preferably at least 60 N / cm ² when measuring the adhesive strength by indentation in a frame shape having a width of 1 mm. Most preferably, it is ² or more. By increasing the adhesive strength by this method, it is possible to secure the adhesive strength necessary for securing members and ensuring waterproofness.

  The pressure-sensitive adhesive sheet of the present invention is, for example, a direct method in which the pressure-sensitive adhesive is directly applied to the foam and dried, or a pressure-sensitive adhesive layer is formed by applying and drying a pressure-sensitive adhesive on a release sheet, and then foamed. It can be manufactured by a transfer method of sticking to a body. When using an adhesive containing an acrylic polymer and a cross-linking agent as the adhesive forming the pressure-sensitive adhesive layer, one obtained by laminating an adhesive layer on one or both surfaces of a foam by the direct method or the transfer method is used. Aging is preferably performed for about 2 days to 7 days in an environment of preferably 20 ° C. to 50 ° C., more preferably 23 ° C. to 45 ° C., and has excellent adhesive strength to adherends and foam base materials. It is preferable in terms of achieving both the follow-up property.

  As the pressure-sensitive adhesive sheet of the present invention, the thickness is preferably 400 μm or less because it is easy to contribute to thinning of electronic devices, more preferably 100 μm to 300 μm, further preferably 150 μm to 300 μm, and still more preferably 200 μm. Most preferably, it is 300 μm. Since the pressure-sensitive adhesive sheet uses a foam having the specific apparent density and tensile elastic modulus, as described above, when the total thickness of the pressure-sensitive adhesive sheet is peeled off at the time of re-peeling, the foam may be used. It is difficult to be torn off, and it is possible to achieve both good followability to the step portion.

  As the pressure-sensitive adhesive sheet, a sheet having other layers as necessary in addition to the foam and the pressure-sensitive adhesive layer can be used.

  As the other layer, for example, in order to impart dimensional stability of the pressure-sensitive adhesive sheet, good tensile strength, suitability for re-peeling, etc., heat conduction of a laminate layer such as a polyester film, a light shielding layer, a light reflection layer, a metal layer, etc. Layers.

  As the pressure-sensitive adhesive sheet of the present invention, a release sheet may be laminated on the surface of the pressure-sensitive adhesive layer.

  As the release sheet, for example, a film, a paper, a nonwoven fabric, a cloth, a foamed sheet, a metal substrate, and a laminate obtained by using a synthetic resin such as polyethylene, polypropylene, and polyester are used. And those subjected to a release treatment such as a long-chain alkyl-based treatment and a fluorine-based treatment can be used.

  The pressure-sensitive adhesive sheet of the present invention is used particularly preferably for fixing and the like which is required to be adhered and fixed to, for example, a portion having unevenness or a large step, and is not required to break the adhered member upon re-peeling. it can.

  The member having the irregularities and large steps is often used as a member in an industrial terminal such as an electronic terminal such as a car navigation system or a smartphone, an automobile, a building material, an office automation (OA), and a home appliance industry.

  Specific examples of the member include two or more housings, lens members, and the like that constitute the electronic terminal.

  An article such as an electronic terminal to which two or more casings or lens members are fixed using the pressure-sensitive adhesive sheet of the present invention has excellent adhesive strength, can be re-peeled at the time of disassembly, etc. It has waterproofness.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

[Preparation Example 1] Method for producing acrylic polymer (A-1) 95.9 parts by mass of n-butyl acrylate and 4 parts by mass of acrylic acid were placed in a reaction vessel equipped with a stirrer, a reflux condenser, a nitrogen inlet tube, and a thermometer. , 2-hydroxyethyl acrylate, and 200 parts by mass of ethyl acetate were charged, and the temperature was raised to 72 ° C. while blowing nitrogen under stirring.

  Next, 2 parts by mass (solid content: 0.1% by mass) of a 2,2′-azobis (2-methylbutyronitrile) solution previously dissolved in ethyl acetate was added to the mixture, and the mixture was stirred at 72 ° C. After holding for 4 hours, it was held at 75 ° C. for 5 hours.

  Next, the mixture was filtered through a 200 mesh wire mesh to obtain an acrylic polymer (A-1) solution having a weight average molecular weight of 1.86 million (a nonvolatile content of 33% by mass).

[Preparation Example 2] Method for producing acrylic polymer (A-2) In a reaction vessel equipped with a stirrer, a reflux condenser, a nitrogen inlet tube, and a thermometer, 63.9 parts by mass of n-butyl acrylate and 2-ethylhexyl acrylate 32 were added. Parts by mass, 4 parts by mass of acrylic acid, 0.1 part by mass of 4-hydroxybutyl acrylate, and 200 parts by mass of ethyl acetate were charged, and the temperature was increased to 72 ° C. while blowing nitrogen with stirring.

  Next, 2 parts by mass (solid content: 0.1% by mass) of a 2,2′-azobis (2-methylbutyronitrile) solution previously dissolved in ethyl acetate was added to the mixture, and the mixture was stirred at 72 ° C. After holding for 4 hours, it was held at 75 ° C. for 5 hours.

  Next, the mixture was filtered through a 200-mesh wire net to obtain a solution of an acrylic polymer (A-2) having a weight average molecular weight of 750,000 (a nonvolatile content of 33% by mass).

[Adhesive composition (A)]
In a container, based on 100 parts by mass of the acrylic polymer (A-1), 10 parts by mass of a polymerized rosin ester-based tackifying resin D-125 (manufactured by Arakawa Chemical Industries, Ltd.) and a disproportionated rosin ester-based tackifying resin After mixing and stirring with 15 parts by mass of A-100 (manufactured by Arakawa Chemical Industries, Ltd.), ethyl acetate was added to obtain a pressure-sensitive adhesive composition (A) having a solid content of 31% by mass.

[Adhesive composition (B)]
In a container, 10 parts by mass of a polymerized rosin ester-based tackifying resin D-125 (manufactured by Arakawa Chemical Industry Co., Ltd.) and disproportionated rosin ester-based tackifying resin with respect to 100 parts by mass of the acrylic polymer (A-2) After mixing and stirring with 15 parts by mass of A-100 (manufactured by Arakawa Chemical Industry Co., Ltd.), ethyl acetate was added to obtain a pressure-sensitive adhesive composition (B) having a solid content of 31% by mass.

[Adhesive (A1)]
Vernock D-40 (manufactured by DIC Co., Ltd., trimethylolpropane adduct of tolylene diisocyanate, isocyanate group content: 7% by mass, non-volatile content: 40% by mass, based on 100 parts by mass of the pressure-sensitive adhesive composition (A)) %), Stirred and mixed so as to be uniform, and then filtered through a 100-mesh wire net to obtain an adhesive (A1) having a gel fraction of 50%.

[Adhesive (A2)]
0.7 parts by mass of Vernock D-40 as a crosslinking agent was added to 100 parts by mass of the pressure-sensitive adhesive composition (A), and the mixture was stirred and mixed so as to be uniform. 30% of an adhesive (A2) was obtained.

[Adhesive (A3)]
2.1 parts by mass of Vernock D-40 as a cross-linking agent was added to 100 parts by mass of the pressure-sensitive adhesive composition (A), and the mixture was stirred and mixed so as to be uniform. 70% of an adhesive (A3) was obtained.

[Adhesive (B)]
Next, 1.4 parts by mass of Vernock D-40 as a crosslinking agent was added to 100 parts by mass of the pressure-sensitive adhesive composition (B), and the mixture was stirred and mixed so as to be uniform, and then filtered through a 100-mesh wire net. An adhesive (B) having a gel fraction of 50% was obtained.

[Example 1]
The pressure-sensitive adhesive (A1) is applied to the surface of the release liner using a bar coater so that the thickness of the pressure-sensitive adhesive layer after drying becomes 50 μm, and the pressure-sensitive adhesive is dried at 80 ° C. for 3 minutes. Layers were made.

  Next, the pressure-sensitive adhesive layer was affixed to both surfaces of the foam 1 shown in Table 1 whose surface was adjusted to 50 mN / m by corona treatment and cured for 48 hours in a 40 ° C environment. Thereby, an adhesive sheet was produced.

[Example 2]
A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1, except that the foam 2 shown in Table 1 was used instead of the foam 1.

[Example 3]
A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1, except that the foam 3 shown in Table 1 was used instead of the foam 1.

[Example 4]
A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1, except that the foam 4 shown in Table 1 was used instead of the foam 1.

[Example 5]
A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1, except that the foam 5 shown in Table 1 was used instead of the foam 1.

[Example 6]
A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1, except that the foam 6 shown in Table 1 was used instead of the foam 1.

[Example 7]
A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1, except that the foam 7 shown in Table 1 was used instead of the foam 1.

Example 8
A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1, except that the foam 8 shown in Table 1 was used instead of the foam 1.

[Example 9]
A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1, except that the foam 9 shown in Table 1 was used instead of the foam 1.

[Example 10]
The pressure-sensitive adhesive (A1) is applied to the surface of the release liner using a bar coater so that the thickness of the pressure-sensitive adhesive layer after drying is 15 μm, and dried at 80 ° C. for 3 minutes. Layers were made.

Next, the pressure-sensitive adhesive layer was affixed to both sides of the foam 10 shown in Table 1 whose surface was adjusted to 50 mN / m by corona treatment and cured for 48 hours in a 40 ° C environment. This produced an adhesive sheet [Example 11].
The pressure-sensitive adhesive (A1) is applied to the surface of the release liner using a bar coater so that the thickness of the pressure-sensitive adhesive layer after drying is 15 μm, and dried at 80 ° C. for 3 minutes. Layers were made.

  Next, the pressure-sensitive adhesive layer was affixed to both surfaces of the foam 11 shown in Table 1 whose surface was adjusted to 50 mN / m by corona treatment and cured for 48 hours in a 40 ° C environment. Thereby, an adhesive sheet was produced.

[Example 12]
The above pressure-sensitive adhesive (A1) is applied to the surface of the release liner using a bar coater so that the thickness of the pressure-sensitive adhesive layer after drying is 25 μm, and the pressure-sensitive adhesive is dried at 80 ° C. for 3 minutes. Layers were made.

  Next, the pressure-sensitive adhesive layer was affixed to both surfaces of the foam 12 shown in Table 1 whose surface was adjusted to 50 mN / m by corona treatment and cured for 48 hours in a 40 ° C environment. Thereby, an adhesive sheet was produced.

Example 13
The pressure-sensitive adhesive (A1) is applied to the surface of the release liner using a bar coater so that the thickness of the pressure-sensitive adhesive layer after drying becomes 50 μm, and the pressure-sensitive adhesive is dried at 80 ° C. for 3 minutes. Layers were made.

  Next, the pressure-sensitive adhesive layer was affixed to both sides of the foam 13 shown in Table 1 whose surface was adjusted to 50 mN / m by corona treatment and cured for 48 hours in an environment of 40 ° C. Thereby, an adhesive sheet was produced.

[Example 14]
The pressure-sensitive adhesive (A1) is applied to the surface of the release liner using a bar coater so that the thickness of the pressure-sensitive adhesive layer after drying becomes 50 μm, and the pressure-sensitive adhesive is dried at 80 ° C. for 3 minutes. Layers were made.

  Next, the pressure-sensitive adhesive layer was affixed to both surfaces of the foam 14 shown in Table 1 whose surface was adjusted to 50 mN / m by corona treatment and cured for 48 hours in a 40 ° C environment. Thereby, an adhesive sheet was produced.

[Example 15]
The above pressure-sensitive adhesive (A2) is applied to the surface of the release liner using a bar coater so that the thickness of the pressure-sensitive adhesive layer after drying becomes 50 μm, and dried at 80 ° C. for 3 minutes. Layers were made.

  Next, the pressure-sensitive adhesive layer was adhered to both surfaces of the foam 5 shown in Table 1 whose surface was adjusted to 50 mN / m by corona treatment and cured for 48 hours in a 40 ° C environment. Thereby, an adhesive sheet was produced.

[Example 16]
The above pressure-sensitive adhesive (A3) is applied to the surface of the release liner using a bar coater so that the thickness of the pressure-sensitive adhesive layer after drying becomes 50 μm, and the pressure-sensitive adhesive is dried at 80 ° C. for 3 minutes. Layers were made.

  Next, the pressure-sensitive adhesive layer was adhered to both surfaces of the foam 5 shown in Table 1 whose surface was adjusted to 50 mN / m by corona treatment and cured for 48 hours in a 40 ° C environment. Thereby, an adhesive sheet was produced.

[Example 17]
The pressure-sensitive adhesive (B) is applied to the surface of the release liner using a bar coater so that the thickness of the pressure-sensitive adhesive layer after drying is 50 μm, and dried at 80 ° C. for 3 minutes. Layers were made.

  Next, the pressure-sensitive adhesive layer was adhered to both surfaces of the foam 5 shown in Table 1 whose surface was adjusted to 50 mN / m by corona treatment and cured for 48 hours in a 40 ° C environment. Thereby, an adhesive sheet was produced.

[Comparative Example 1]
The pressure-sensitive adhesive (A1) is applied to the surface of the release liner using a bar coater so that the thickness of the pressure-sensitive adhesive layer after drying becomes 50 μm, and the pressure-sensitive adhesive is dried at 80 ° C. for 3 minutes. Layers were made.

  Next, the pressure-sensitive adhesive layer was affixed to both surfaces of the foam 15 shown in Table 1 whose surface was adjusted to 50 mN / m by corona treatment and cured for 48 hours in a 40 ° C environment. Thereby, an adhesive sheet was produced.

[Comparative Example 2]
A pressure-sensitive adhesive sheet was obtained in the same manner as in Comparative Example 1, except that the foam 16 shown in Table 1 was used instead of the foam 15.

[Comparative Example 3]
An adhesive sheet was obtained in the same manner as in Comparative Example 1, except that the foam 17 shown in Table 1 was used instead of the foam 15.

[Comparative Example 4]
A pressure-sensitive adhesive sheet was obtained in the same manner as in Comparative Example 1, except that the foam 18 shown in Table 1 was used instead of the foam 15.

  The apparent density and tensile modulus of the foam in Table 1 were measured by the same method as described in the present specification.

[Evaluation method of indentation adhesive strength]
1) At 23 ° C., a 2 mm-thick, 20 mm square acrylic plate (Mitsubishi Rayon Co., Ltd. Acrylite MR200 “brand name”, hue: transparent, the same applies hereinafter) was applied to the above-obtained adhesive sheet with a 15 mm square outer shape. A 1 mm wide window frame is cut out and attached (Fig. 1).

  2) Next, on a rectangular SUS plate having a hole of 10 mm in the center and a thickness of 2 mm and a size of 30 × 60 mm, attach the acrylic plate with the adhesive sheet prepared in 1) to the center of the acrylic plate and the center of the SUS plate. And pressurized once with a 2 kg roller, and allowed to stand at 23 ° C. for 1 hour to obtain a test piece (FIG. 2).

  3) The acrylic plate was pressed at 10 mm / min with a tensile tester equipped with a stainless steel probe having a diameter of 8 mm from the SUS side of the test piece through a hole of the SUS plate, and the peeling strength of the acrylic plate was measured (FIG. 3).

[Evaluation method of step followability]
1) Using the pressure-sensitive adhesive sheet obtained above, a frame-shaped sample having an outer size of 64 mm x 43 mm and a width of 1 mm is prepared and attached to an acrylic plate having a thickness of 2 mm and an outer size of 65 mm x 45 mm (Fig. 4).

  2) Next, a polyethylene terephthalate (PET) of each thickness (30 μm, 40 μm, 50 μm, 60 μm), width 5 mm, and length 45 mm is placed at the center of another acrylic plate having a thickness of 2 mm and an outer diameter of 65 mm × 45 mm. Two single-sided pressure-sensitive adhesive tapes (for forming a step) of a base material are stuck in parallel in a vertical direction at an interval of 1 cm to form a stepped acrylic plate (FIG. 5).

  3) The acrylic plate with the adhesive sheet is placed on the adhesive tape portion of the stepped acrylic plate at 23 ° C., and then one reciprocating pressure is applied from the end with a 2 kg roller (FIG. 6).

  4) The follow-up state of the pressure-sensitive adhesive sheet near the step from the side of the stepped acrylic plate is visually evaluated.

  A: No gap such as air bubbles was present at the interface between the step and the pressure-sensitive adhesive sheet up to the step of 60 μm.

  B: No gap such as air bubbles was present at the interface between the step portion and the pressure-sensitive adhesive sheet up to the step difference of 50 μm, but when the step was 60 μm, a space such as air bubbles was present at the interface between the step portion and the pressure-sensitive adhesive sheet.

  C: No gap such as air bubbles was present at the interface between the step portion and the pressure-sensitive adhesive sheet up to the step difference of 40 μm, but when the step was 50 μm or more, a space such as air bubbles was present at the interface between the step portion and the pressure-sensitive adhesive sheet.

  D: No gap such as air bubbles was present at the interface between the step portion and the pressure-sensitive adhesive sheet up to the step difference of 30 μm, but there was a gap such as air bubbles at the interface between the step portion and the pressure-sensitive adhesive sheet at a step difference of 40 μm or more.

  E: At a step of 30 μm, voids such as bubbles were present at the interface between the step and the pressure-sensitive adhesive sheet.

[Removability]
1) Two samples of a pressure-sensitive adhesive sheet having a length of 40 mm and a width of 2 mm are prepared and attached to an acrylic plate having a thickness of 2 mm and an outer shape of 50 mm × 50 mm so that the two sheets are parallel (FIG. 7).
Next, a PET film plate having a thickness of 0.05 mm and an outer shape of 50 mm × 50 mm is adhered, and each sample is pressed back and forth with a 2 kg roller once, and then left at 23 ° C. for 24 hours to obtain a test piece.

  2) The state of the tape when the test piece was peeled off the PET film in the vertical direction at 23 ° C. was evaluated (FIG. 8).

  3) Next, the ease with which the pressure-sensitive adhesive sheet remaining on the PET film or acrylic plate was peeled off by hand at a peel angle of about 135 degrees was evaluated (FIG. 9).

  A: When the PET film was peeled off in the vertical direction, it could be peeled off without interlayer cracking of the foam base material. Furthermore, even when the pressure-sensitive adhesive sheet remaining on the PET film or the acrylic plate was peeled off, it could be peeled off without any interlayer crack of the substrate.

  B: When the PET film was peeled off in the vertical direction, it could be peeled off without interlayer cracking of the foam base material. When the pressure-sensitive adhesive sheet remaining on the PET film or the acrylic plate was peeled off, although the interlayer crack of the foam base material occurred, the tape could be peeled off by pulling again.

  C: When the PET film was peeled off in the vertical direction, it could be peeled off without any interlayer cracking of the foam base material. When the pressure-sensitive adhesive sheet remaining on the PET film or the acrylic plate was peeled off, interlayer cracking of the foam base material occurred, and even if it was pulled again by hand, interlayer cracking occurred and could not be peeled off.

  D: When the PET film was peeled off in the vertical direction, interlayer cracking of the foam base material occurred. Further, when the pressure-sensitive adhesive sheet remaining on the PET film or the acrylic plate was peeled off, interlayer cracking of the base material occurred, and even if the substrate was pulled by hand again, interlayer cracking occurred and could not be peeled off.

  From the above results, it can be seen that Examples 1 to 17 of the present invention succeeded in achieving both step followability and removability while maintaining appropriate adhesive strength. On the other hand, it can be seen that in Comparative Examples 1 and 3, the step followability is deteriorated, and in Comparative Examples 2 to 4, the removability is deteriorated.

DESCRIPTION OF SYMBOLS 1 Acrylic plate 2 Adhesive sheet 3 SUS plate 4 Stainless steel probe 21 Adhesive sheet 22 Acrylic plate 23 Acrylic plate 24 One-sided adhesive tape of polyethylene terephthalate base material 25 Surface for evaluating step followability 31 Acrylic plate 32 Adhesive sheet 33 PET film

Claims (10)

A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer on one or both sides of a foam base material directly or via another layer, wherein the foam base material is formed of ethylene vinyl acetate copolymer (EVA) and / or ethylene acrylic acid copolymer. An adhesive containing 30 to 90% by mass of a polymer (EAA), an apparent density of the foam base material of 0.20 g / cm ^{3 to} 0.60 g / cm ^3, and a tensile modulus in a flow direction of 10 MPa to 35 MPa. Sheet. The pressure-sensitive adhesive sheet according to claim 1, wherein the foam base material has a thickness of 50 to 300 m. The pressure-sensitive adhesive sheet according to claim 1, wherein the sheet has a thickness of 80 to 400 μm. The pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein the pressure-sensitive adhesive layer has a gel fraction of 40 to 80%. The pressure-sensitive adhesive sheet according to any one of claims 1 to 4, wherein the foam base material further contains at least one selected from the group consisting of a polyolefin, a polyurethane, and an acrylic polymer. The pressure-sensitive adhesive sheet according to claim 5, wherein the content of at least one selected from the group consisting of polyolefin, polyurethane, and acrylic polymer is 5 to 60% by mass. The polyolefin according to claim 5 or 6, wherein the polyolefin is at least one selected from the group consisting of linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), medium-density polyethylene (MDPE), and high-density polyethylene (HDPW). The pressure-sensitive adhesive sheet according to the above. The pressure-sensitive adhesive sheet according to any one of claims 1 to 7, wherein the foam base material further contains an elastomer. The pressure-sensitive adhesive sheet according to any one of claims 1 to 8, wherein the pressure-sensitive adhesive sheet has a strength value of 40 N / cm ² or more when measured with a frame shape having a width of 1 mm to measure the adhesive strength. An electronic device having a configuration in which two or more adherends are bonded by the pressure-sensitive adhesive sheet according to any one of claims 1 to 9.

Images