double-sided adhesive sheet

Abstract

To provide a double-sided adhesive sheet excellent in followability to an adherend when adhered onto the adherend, difficult to break at drawing separation, capable of being drawn and easily separated, and unlikely to leave an adhesive residue on the adherend after separation.SOLUTION: A double-sided adhesive sheet 1 includes a substrate layer 2, and adhesive layers 3, 4 respectively laminated on two sides of the substrate layer 2. The substrate layer 2 contains a foam body. The adhesive layers 3, 4 contain a filler. A content ratio of the filler is 2 mass% or more based on a total amount of the adhesive layers 3, 4 of 100 mass%. The double-sided adhesive sheet 1 has a 25% compressive load of 2 MPa or less. The double-sided adhesive sheet 1 at a width 10 mm has a rupture elongation of 600% or more and a rupture stress of 2 MPa or more at a tensile test conducted under a condition of an initial distance between chucks of 10 mm, room temperature and a tensile speed of 300 mm / min.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a double-sided pressure-sensitive adhesive sheet. [Background technology]

[0002] In recent years, mobile devices such as mobile phones, digital cameras, and PDAs (Personal Digital Assistants) have become increasingly smaller. Consequently, efforts are being made to make the various electronic components they contain smaller and thinner. For example, in mobile phones, a typical example of a mobile device, each of the major components tends to be made thinner. The display section of a mobile device typically consists primarily of an LCD module and a backlight unit, with various sheet-like components layered on top of each other to achieve functions such as light emission, reflection, light blocking, and light guidance. Therefore, double-sided pressure-sensitive adhesive sheets (double-sided pressure-sensitive adhesive tapes) are used to assemble (bond) these components.

[0003] Double-sided PSA sheets are required to exhibit a certain level of adhesive strength to prevent adhesion defects such as peeling or slippage during their use. On the other hand, when repairing, replacing, inspecting, recycling, etc. a component having an adherend to which the double-sided PSA sheet is attached, it may be necessary to peel the double-sided PSA sheet. In such cases, the double-sided PSA sheet is required to be easily peelable from the adherend, i.e., to have reworkability.

[0004] As a method for peeling a double-sided pressure-sensitive adhesive sheet while suppressing damage to the adherend, a method (stretch-peeling method) has been proposed in which a portion of the double-sided pressure-sensitive adhesive sheet attached to the adherend is gripped and pulled, causing the double-sided pressure-sensitive adhesive sheet to elongate and deform, reducing the adhesive area, and then being removed from the adherend in the horizontal direction (shear direction). Double-sided pressure-sensitive adhesive sheets that can be peeled by such stretch-peeling methods are disclosed in, for example, Patent Documents 1 to 3. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2019 / 167922 [Patent Document 2] International Publication No. 2019 / 003933 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-8288 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, mobile assembly parts have become increasingly complex, and the surfaces of these parts often have minute irregularities. For this reason, double-sided PSA sheets are required to be able to conform to the irregularities on the adherend surface.

[0007] However, double-sided PSA sheets using a non-foamed plastic film as the base layer, such as those disclosed in Patent Documents 1 and 2, lack sufficient compressibility and are insufficient in their ability to conform to fine irregularities on the surface of the adherend. Furthermore, conventional double-sided PSA sheets using a foamed base layer, such as the double-sided PSA sheet disclosed in Patent Document 3, are compressible, but the base is prone to fracture when stretch-peeled. Even when stretch-peeling is possible without breaking the base, the adhesive of the double-sided PSA sheet may remain on the adherend, leaving adhesive residue. In particular, when the surface of the adherend has fine irregularities, the double-sided PSA sheet is stretch-peeled from a compressed state, which may easily destroy the adhesive layer and leave adhesive residue during stretch-peeling, and the base layer may also be easily destroyed.

[0008] The present invention was devised under these circumstances, and its object is to provide a double-sided pressure-sensitive adhesive sheet that has excellent conformability to an adherend when attached to the adherend, is resistant to tearing when stretch-peeled, can be easily peeled off by stretching, and leaves little adhesive residue on the adherend after peeling. [Means for solving the problem]

[0009]

[0006] As a result of extensive research to achieve the above object, the inventors have found that a double-sided PSA sheet having a substrate layer, which uses a foam as the substrate layer, which contains a specific amount of filler in the PSA layer, and which has a breaking elongation and breaking stress within specific ranges under specific conditions, exhibits excellent conformability to the adherend when attached to the adherend, is less likely to break when stretch-peeled, can be easily stretched and peeled, and is less likely to leave adhesive residue on the adherend after peeling. The present invention was completed based on these findings.

[0010] That is, the present invention provides a double-sided PSA sheet comprising a base layer and PSA layers laminated on both sides of the base layer, the substrate layer comprises a foam, the pressure-sensitive adhesive layer contains a filler, the content of the filler is 2% by mass or more relative to 100% by mass of the total amount of the pressure-sensitive adhesive layer, The double-sided PSA sheet has a 25% compressive load of 2 MPa or less, Provided is a double-sided pressure-sensitive adhesive sheet that has a breaking elongation of 600% or more and a breaking stress of 2 MPa or more in a tensile test conducted on a 10 mm wide double-sided pressure-sensitive adhesive sheet under conditions of an initial chuck distance of 10 mm, room temperature, and a tensile speed of 300 mm / min.

[0011] The foam preferably has a thickness of 80 μm or more.

[0012] The thickness of each of the pressure-sensitive adhesive layers is preferably 50 μm or more.

[0013] The density of the foam is 0.05 g / cm 3 More than 1g / cm 3 It is preferable that it is less than 10 ...

[0014] The content of the filler is preferably 20% by mass or less relative to 100% by mass of the total amount of the pressure-sensitive adhesive layer.

[0015] The thickness of the double-sided pressure-sensitive adhesive sheet is preferably 200 to 1500 μm.

[0016] The foam is preferably made of one or more resins selected from the group consisting of polyolefin resins, acrylic resins, and polyurethanes.

[0017] The pressure-sensitive adhesive layer is preferably an acrylic pressure-sensitive adhesive layer containing an acrylic polymer as a base polymer.

[0018] The double-sided pressure-sensitive adhesive sheet is preferably used for fixing electrical and electronic components. [Effects of the Invention]

[0019] The double-sided pressure-sensitive adhesive sheet of the present invention, when attached to an adherend, exhibits excellent conformability to the adherend even when the adherend has a finely uneven surface, and is resistant to tearing during stretch-peeling, can be easily stretched and peeled, and is less likely to leave adhesive residue on the adherend after peeling. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a cross-sectional view of a double-sided pressure-sensitive adhesive sheet according to one embodiment of the present invention. [Figure 2] FIG. 1 is a side view schematic illustrating one embodiment of stretch-peeling from an adherend using a double-sided pressure-sensitive adhesive sheet according to one embodiment of the present invention. [Figure 3] FIG. 1 is a top view schematic diagram illustrating one embodiment of stretch-peeling from an adherend using a double-sided pressure-sensitive adhesive sheet according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] [Double-sided adhesive sheet] The double-sided pressure-sensitive adhesive sheet of the present invention comprises at least a substrate layer and pressure-sensitive adhesive layers laminated on both sides of the substrate layer. In this specification, the structure of the double-sided pressure-sensitive adhesive sheet of the present invention from one adhesive surface to the other adhesive surface may be referred to as the "adhesive body." When the double-sided pressure-sensitive adhesive sheet of the present invention comprises a release liner, the release liner is not included in the adhesive body.

[0022] Figure 1 is a cross-sectional schematic diagram showing one embodiment of the double-sided pressure-sensitive adhesive sheet of the present invention. As shown in Figure 1, the double-sided pressure-sensitive adhesive sheet 1 comprises a base layer 2, a pressure-sensitive adhesive layer 3 provided on one side of the base layer 2, and a pressure-sensitive adhesive layer 4 provided on the other side of the base layer 2. Release liners may be provided on the surfaces of the pressure-sensitive adhesive layer 3 and the pressure-sensitive adhesive layer 4, respectively.

[0023] The 25% compression load of the double-sided PSA sheet is 2 MPa or less, preferably 1.5 MPa or less, and more preferably 1.0 MPa or less. When the 25% compression load is 2 MPa or less, the double-sided PSA sheet has excellent compressibility and can be held between adherends in a compressed state, resulting in excellent conformability to uneven shapes.

[0024] The 25% compression load can be measured in accordance with JIS K6767, and specifically refers to the resilience measured per unit area after compressing the adhesive body of the double-sided pressure-sensitive adhesive sheet in the thickness direction to a compression rate of 25% (a height corresponding to a thickness that is 75% of the initial thickness) and holding this for 10 seconds in an atmosphere of room temperature (25±5°C).

[0025] The double-sided PSA sheet has a breaking elongation (the ratio of the elongated length at break to the length before elongation) of 600% or more, preferably 650% or more, more preferably 680% or more, and even more preferably 700% or more, in a tensile test using a 10 mm wide test piece, with an initial chuck distance of 10 mm, at room temperature (25±5°C), and at a tensile speed of 300 mm / min. A breaking elongation of 600% or more allows the double-sided PSA sheet to be stretched and easily peeled. From the viewpoint of superior stretch-peelability, the breaking elongation is, for example, 1500% or less, preferably 1200% or less, and more preferably 1000% or less.

[0026] The double-sided PSA sheet has a breaking stress of 2 MPa or more, preferably 3 MPa or more, and more preferably 5 MPa or more, in a tensile test using a 10 mm wide test piece, with an initial chuck distance of 10 mm, at room temperature (25±5°C), and at a tensile speed of 300 mm / min. Having a breaking stress of 2 MPa or more makes the double-sided PSA sheet less likely to break even when fully stretched. The breaking stress is, for example, 100 MPa or less, preferably 50 MPa or less, and more preferably 30 MPa or less.

[0027] The breaking elongation and breaking stress can be measured in accordance with JIS K7311 (1995). Specifically, they can be measured using, for example, a tensile tester (product name "Autograph AG-10G", manufactured by Shimadzu Corporation). The breaking elongation of the double-sided pressure-sensitive adhesive sheet can be adjusted as appropriate by controlling the amount of filler blended in the pressure-sensitive adhesive layer, the type of monomer component constituting the base polymer in the pressure-sensitive adhesive layer, etc. The breaking stress of the double-sided pressure-sensitive adhesive sheet can be adjusted as appropriate by controlling the amount of filler blended in the pressure-sensitive adhesive layer, the type of monomer component constituting the base polymer in the pressure-sensitive adhesive layer, the thickness, density, and type of constituent resin of the foam in the substrate layer, etc.

[0028] (base material layer) The substrate layer is an element that functions as a support in the double-sided pressure-sensitive adhesive sheet. The substrate layer contains a foam. By containing a foam, the double-sided pressure-sensitive adhesive sheet has compressibility and can be held between adherends in a compressed state, resulting in excellent conformability to uneven shapes. The substrate layer may be a single layer or a laminate of substrates of the same or different types. The substrate layer may also contain a layer other than the foam, but the thickness of the foam is preferably 50% or more, more preferably 80% or more, and even more preferably 90% or more of the total thickness of the substrate layer.

[0029] The thickness of the foam is not particularly limited, but is preferably 80 μm or more, more preferably 100 μm or more, and even more preferably 130 μm or more. When the thickness is 80 μm or more, the double-sided PSA sheet has excellent compressibility and can be held between adherends in a compressed state, resulting in excellent conformability to uneven shapes. The thickness is, for example, 1000 μm or less, preferably 800 μm or less, and more preferably 600 μm or less. It is also preferable that the thickness of the substrate layer is within the above range.

[0030] The density of the foam is not particularly limited, but is preferably 1 g / cm 3 It is preferable that the density is less than 0.9 g / cm 3 or less, more preferably 0.8 g / cm 3 The density is 1 g / cm or less. 3 When the density is less than 0.03 g / cm, the double-sided PSA sheet has excellent compressibility and can be held between adherends in a compressed state, resulting in excellent conformability to uneven shapes. 3 In this specification, the density of the foam means the "apparent density."

[0031] The foam is preferably a resin foam made of a resin. The resin foam can be made of a resin composition containing a resin (polymer). The resin constituting the resin foam is not particularly limited, and any known or well-known resin material constituting a foam can be used. Examples of the resin include polyolefin resins, styrene resins, polyamide resins, polyamideimides, polyurethanes, polyimides, polyetherimides, acrylic resins, polyvinyl chloride, polyvinyl fluorides, alkenyl aromatic resins, polyester resins, polycarbonates, polyacetals, and polyphenylene sulfides. Among these, polyolefin resins, acrylic resins, and polyurethanes are preferred. One or more of the resins may be used.

[0032] The polyolefin resin may be a homopolymer or a copolymer containing two or more types of monomers. When the polyolefin resin is a copolymer, it may be a random copolymer or a block copolymer. The polyolefin resin may be used alone or in combination of two or more types.

[0033] The polyolefin resin is not particularly limited, but is preferably a polymer constructed (formed) with an α-olefin as an essential monomer component, i.e., a polymer having at least one structural unit derived from an α-olefin in the molecule (per molecule). The polyolefin resin may be, for example, a polymer constructed solely from an α-olefin, or a polymer constructed from an α-olefin and a monomer component other than an α-olefin.

[0034] Examples of the α-olefin include α-olefins having 2 to 8 carbon atoms (e.g., ethylene, propylene, butene-1, pentene-1, hexene-1, 4-methyl-pentene-1, heptene-1, octene-1, etc.). One or more of the α-olefins may be used.

[0035] Examples of the monomer component other than the α-olefin include ethylenically unsaturated monomers such as vinyl acetate, acrylic acid, acrylic acid esters, methacrylic acid, methacrylic acid esters, vinyl alcohol, etc. The monomer component other than the α-olefin may be used singly or in combination of two or more.

[0036] Examples of the polyolefin resin include low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, polypropylene (propylene homopolymer), copolymers of ethylene and propylene, copolymers of ethylene and an α-olefin other than ethylene, copolymers of propylene and an α-olefin other than propylene, copolymers of ethylene, propylene and an α-olefin other than ethylene and propylene, and copolymers of propylene and an ethylenically unsaturated monomer.

[0037] The polyolefin resin is preferably a polymer (polyethylene resin) composed of ethylene as an essential monomer component, i.e., a polymer having at least ethylene-derived structural units. Examples of the polyethylene resin include polyethylene (ethylene homopolymer), a copolymer of ethylene and propylene, and a copolymer of ethylene and an α-olefin other than ethylene. The α-olefin other than ethylene may be used singly or in combination of two or more.

[0038] The content of the α-olefin in the polyolefin resin is not particularly limited, but is preferably 0.1 to 10 mass %, and more preferably 1 to 5 mass %, relative to the total amount (100 mass %) of the monomer components constituting the polyolefin resin.

[0039] When the foam contains the polyolefin resin, the resin constituting the foam preferably contains, in addition to the polyolefin resin, an elastomer component such as rubber or a thermoplastic elastomer, etc. The inclusion of an elastomer component tends to improve the flexibility and breaking stress of the foam.

[0040] The rubber is not particularly limited, but examples thereof include natural or synthetic rubbers such as natural rubber, polyisobutylene, isoprene rubber, chloroprene rubber, butyl rubber, nitrile butyl rubber, etc. Only one type of the rubbers may be used, or two or more types may be used.

[0041] The thermoplastic elastomer is not particularly limited, but examples thereof include thermoplastic olefin-based elastomers such as ethylene-propylene copolymer elastomers, ethylene-propylene-diene copolymer elastomers, ethylene-vinyl acetate copolymer elastomers, polybutene elastomers, polyisobutylene elastomers, and chlorinated polyethylene elastomers; thermoplastic styrene-based elastomers such as styrene-butadiene-styrene copolymer elastomers, styrene-isoprene-styrene copolymer elastomers, styrene-isoprene-butadiene-styrene copolymer elastomers, and hydrogenated versions thereof; thermoplastic polyester-based elastomers; thermoplastic polyurethane-based elastomers; and thermoplastic acrylic-based elastomers. One or more of the thermoplastic elastomers may be used.

[0042] Among the elastomer components, thermoplastic olefin elastomers are preferred, and particularly preferred are olefin elastomers having a microphase-separated structure of a polyolefin resin component and an olefin rubber component. The olefin elastomer having a microphase-separated structure of a polyolefin resin component and an olefin rubber component is preferably an elastomer composed of polypropylene (PP) and ethylene-propylene rubber (EPM) or ethylene-propylene-diene rubber (EPDM). However, the polyolefin resin component in the olefin elastomer having a microphase-dispersed structure is not included in the thermoplastic resin contained in the foam, but is included in the elastomer component. From the viewpoint of compatibility, the mass ratio of the polyolefin resin component to the olefin rubber component (polyolefin resin component / olefin rubber component) is preferably 90 / 10 to 10 / 90, more preferably 80 / 20 to 20 / 80.

[0043] When the foam contains an elastomer component, the content of the elastomer component in the foam is not particularly limited, but is preferably more than 0 mass % and not more than 70 mass %, more preferably 20 to 60 mass %, and even more preferably 20 to 50 mass %, relative to the mass of the foam (100 mass %).

[0044] When the resin foam contains a polyolefin resin, the density of the resin foam is 0.5 g / cm 3 It is preferable that the concentration is 0.3 g / cm or less, and more preferably 0.3 g / cm 3 The density is 0.08 g / cm 3 It is preferable that the concentration is equal to or higher than 0.1 g / cm. 3 That's all.

[0045] The acrylic polymer is preferably an acrylic polymer formed from essential monomer components that are a monomer having a glass transition temperature (Tg) of -10°C or higher when forming a homopolymer, and a monomer having a Tg of less than -10°C when forming a homopolymer.

[0046] In this specification, the "glass transition temperature (Tg) when a homopolymer is formed" (sometimes simply referred to as "Tg of the homopolymer") refers to the "glass transition temperature (Tg) of a homopolymer of the monomer," and specific numerical values ​​are listed in "Polymer Handbook" (3rd Edition, John Wiley & Sons, Inc., 1987). The Tg of a homopolymer of a monomer not described in the above literature refers to, for example, a value obtained by the following measurement method (see JP 2007-51271 A). Specifically, 100 parts by mass of the monomer, 0.2 parts by mass of 2,2'-azobisisobutyronitrile, and 200 parts by mass of ethyl acetate as a polymerization solvent were placed in a reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser, and the mixture was stirred for 1 hour while introducing nitrogen gas. After removing oxygen from the polymerization system in this way, the temperature was raised to 63°C and the reaction was continued for 10 hours. The mixture was then cooled to room temperature to obtain a homopolymer solution with a solids concentration of 33% by mass. The homopolymer solution was then cast onto a separator and dried to prepare a test sample (sheet-like homopolymer) approximately 2 mm thick. This test sample was then punched into a 7.9 mm diameter disk, sandwiched between parallel plates, and subjected to a 1 Hz shear strain using a viscoelasticity tester (ARES, manufactured by Rheometrics) in a shear mode at a temperature range of -70 to 150°C and a heating rate of 5°C / min. The peak top temperature of tan δ was taken as the Tg of the homopolymer.

[0047] In the case of a monomer having a homopolymer Tg of -10°C or higher, the Tg is, for example, -10°C to 250°C, preferably 10 to 230°C, and more preferably 50 to 200°C.

[0048] Examples of the monomers having a homopolymer Tg of −10° C. or higher include (meth)acrylonitrile; amide group-containing monomers such as (meth)acrylamide and N-hydroxyethyl(meth)acrylamide; (meth)acrylic acid; (meth)acrylic acid alkyl esters having a homopolymer Tg of −10° C. or higher such as methyl methacrylate and ethyl methacrylate; isobornyl (meth)acrylate; heterocycle-containing vinyl monomers such as N-vinyl-2-pyrrolidone; and hydroxyl group-containing monomers such as 2-hydroxyethyl methacrylate. These may be used alone or in combination of two or more.

[0049] In the case of a monomer whose homopolymer has a Tg of less than -10°C, the Tg is, for example, not less than -70°C and less than -10°C, preferably from -70°C to -12°C, and more preferably from -65°C to -15°C.

[0050] Examples of the monomer having a homopolymer Tg of less than −10° C. include (meth)acrylic acid alkyl esters such as ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate, which have a homopolymer Tg of less than −10° C. These may be used alone or in combination of two or more.

[0051] The content of monomers having a homopolymer Tg of -10°C or higher relative to all monomer components (total amount of monomer components) forming the acrylic polymer is, for example, 2 to 30% by mass, with a lower limit of preferably 3% by mass, more preferably 4% by mass, and an upper limit of preferably 25% by mass, more preferably 20% by mass. The content of monomers having a homopolymer Tg of less than -10°C relative to all monomer components (total amount of monomer components) forming the acrylic polymer is, for example, 70 to 98% by mass, with a lower limit of preferably 75% by mass, more preferably 80% by mass, and an upper limit of preferably 97% by mass, more preferably 96% by mass.

[0052] When the resin foam contains an acrylic polymer, the density of the resin foam is 0.5 g / cm 3 More than 1g / cm3 It is preferably less than 0.6 to 0.9 g / cm 3 , and more preferably 0.7 to 0.8 g / cm 3 is.

[0053] Examples of the urethane polymer include polycarbonate polyurethane, polyester polyurethane, and polyether polyurethane.

[0054] When the resin foam contains a urethane polymer, the density of the resin foam is 0.5 g / cm 3 It is preferably 0.4 g / cm or less, and more preferably 0.4 g / cm 3 The following is the result.

[0055] The content of the resin in the resin foam is not particularly limited, but is preferably 50% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, relative to the total amount (100% by mass) of the resin foam. The upper limit of the content is not particularly limited, but may be 100% by mass, 99% by mass, or 95% by mass.

[0056] The foam may contain additives in addition to the resins described above, provided that the effects of the present invention are not impaired. Examples of the additives include antioxidants, weathering agents, ultraviolet absorbers, dispersants, plasticizers, colorants (pigments, dyes, etc.), antistatic agents, surfactants, tension modifiers, flow modifiers, lubricants, antioxidants, fillers, reinforcing agents, surface treatment agents, shrinkage inhibitors, vulcanizing agents, and flame retardants. One or more of the additives may be used.

[0057] The substrate layer may include an auxiliary layer, such as a colored layer, a reflective layer, an undercoat layer, or an antistatic layer, provided on the surface of the substrate layer.

[0058] The surface of the substrate layer may be subjected to surface treatments such as physical treatments such as corona discharge treatment, plasma treatment, sand matting treatment, ozone exposure treatment, flame exposure treatment, high-voltage shock exposure treatment, and ionizing radiation treatment; chemical treatments such as chromic acid treatment; and adhesion-enhancing treatment, for the purpose of improving adhesion and retention with the pressure-sensitive adhesive layer. The surface treatment for improving adhesion is preferably applied to the entire surface of the substrate layer.

[0059] (Adhesive layer) In the double-sided pressure-sensitive adhesive sheet, the two pressure-sensitive adhesive layers provided on both sides of the base layer may be the same pressure-sensitive adhesive layer, or may be pressure-sensitive adhesive layers with different compositions, thicknesses, physical properties, etc. Each of the pressure-sensitive adhesive layers may be a single layer, or may be a multilayer composed of the same or different layers.

[0060] Each of the pressure-sensitive adhesive layers contains at least a base polymer and a filler that exhibits adhesiveness. By including a filler in the pressure-sensitive adhesive layer, the adhesive layer exhibits excellent releasability from the adherend, allowing the double-sided pressure-sensitive adhesive sheet to be peeled off while suppressing adhesive residue on the adherend. In this specification, the term "base polymer" refers to the main component of the polymer components in the pressure-sensitive adhesive that constitutes the pressure-sensitive adhesive layer, for example, a polymer component that accounts for more than 50% by mass.

[0061] The content of the base polymer in the pressure-sensitive adhesive layer is preferably 60% by mass or more, and more preferably 70% by mass or more, relative to 100% by mass of the total amount of the pressure-sensitive adhesive layer.

[0062] The adhesive constituting the adhesive layer is not particularly limited, but examples thereof include acrylic adhesives, rubber adhesives (natural rubber-based, synthetic rubber-based, and mixtures thereof), silicone adhesives, polyester adhesives, urethane adhesives, polyether adhesives, polyamide adhesives, and fluorine-based adhesives. Among these, acrylic adhesives are preferred as adhesives constituting the adhesive layer in terms of adhesion, weather resistance, cost, and ease of adhesive design. The adhesive layer is preferably an acrylic adhesive layer composed of an acrylic adhesive. One type of adhesive may be used, or two or more types may be used.

[0063] The acrylic pressure-sensitive adhesive layer contains an acrylic polymer as a base polymer. The acrylic polymer is a polymer containing an acrylic monomer (a monomer having a (meth)acryloyl group in the molecule) as a monomer component constituting the polymer. That is, the acrylic polymer contains a structural unit derived from the acrylic monomer. Only one type of acrylic polymer may be used, or two or more types may be used.

[0064] The content of the acrylic polymer in the acrylic pressure-sensitive adhesive layer is preferably 60% by mass or more, and more preferably 70% by mass or more, relative to 100% by mass of the total amount of the acrylic pressure-sensitive adhesive layer.

[0065] The acrylic polymer is preferably a polymer constituted (formed) with a (meth)acrylic acid alkyl ester as an essential monomer component. That is, the acrylic polymer preferably contains a (meth)acrylic acid alkyl ester as a constituent unit. In this specification, "(meth)acrylic" refers to "acrylic" and / or "methacrylic" (either one or both of "acrylic" and "methacrylic"), and the same applies to other terms.

[0066] The (meth)acrylic acid alkyl ester as an essential monomer component is preferably a (meth)acrylic acid alkyl ester having a linear or branched alkyl group, and one or more (meth)acrylic acid alkyl esters may be used.

[0067] The (meth)acrylic acid alkyl ester having a linear or branched alkyl group is not particularly limited, and examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, and methyl (meth)acrylate. Examples of (meth)acrylic acid alkyl esters having a linear or branched alkyl group having 1 to 20 carbon atoms include isononyl acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate (lauryl (meth)acrylate), tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate (stearyl (meth)acrylate), isostearyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate. Among these, the (meth)acrylic acid alkyl esters having a linear or branched alkyl group having 4 to 10 carbon atoms (preferably 4 to 8 carbon atoms) are preferred from the viewpoint of excellent releasability from adherends.

[0068] The proportion of the (meth)acrylic acid alkyl ester in the total of all monomer components constituting the acrylic polymer (100% by mass) is not particularly limited, but is preferably 50% by mass or more (e.g., 50 to 100% by mass), more preferably 60% by mass or more, and even more preferably 70% by mass or more. The proportion is preferably less than 100% by mass, more preferably 95% by mass or less, even more preferably 90% by mass or less, and particularly preferably 80% by mass or less. When the proportion is within the above range, a good quantitative balance with the copolymerizable monomer is achieved, making it possible to form a pressure-sensitive adhesive layer that has good adhesion even when thin.

[0069] The acrylic polymer may contain a copolymerizable monomer together with the (meth)acrylic acid alkyl ester as a monomer component constituting the polymer. That is, the acrylic polymer may contain a copolymerizable monomer as a structural unit. The copolymerizable monomer may be used alone or in combination of two or more.

[0070] The copolymerizable monomer is preferably a carboxyl group-containing monomer and / or an acid anhydride monomer, from the viewpoint of being able to form a thin pressure-sensitive adhesive layer having good adhesion. Examples of the carboxyl group-containing monomer include acrylic acid, methacrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid. Examples of the acid anhydride monomer include maleic anhydride and itaconic anhydride.

[0071] The proportion of the carboxyl group-containing monomer and / or acid anhydride monomer in the total amount (100% by mass) of all monomer components constituting the acrylic polymer is not particularly limited, but is preferably 0.2% by mass or more, more preferably 1% by mass or more, and even more preferably 5% by mass or more. The proportion is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 11% by mass or less. When the proportion is within the above range, a good quantitative balance with the (meth)acrylic acid alkyl ester can be achieved, making it possible to form a pressure-sensitive adhesive layer that has good adhesion even when thin.

[0072] The copolymerizable monomer may further contain a functional group-containing monomer for the purpose of introducing crosslinking points into the acrylic polymer or increasing the cohesive strength of the acrylic polymer. Examples of the functional group-containing monomer include hydroxy group-containing monomers, epoxy group-containing monomers, nitrogen atom-containing monomers, keto group-containing monomers, alkoxysilyl group-containing monomers, sulfonic acid group-containing monomers, and phosphate group-containing monomers. Among these, hydroxy group-containing monomers and nitrogen atom-containing monomers are preferred. The functional group-containing monomers may be used alone or in combination of two or more.

[0073] Examples of the hydroxy group-containing monomer include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate; unsaturated alcohols such as vinyl alcohol and allyl alcohol; and polypropylene glycol mono(meth)acrylate.

[0074] Examples of the epoxy group-containing monomer include glycidyl group-containing monomers such as glycidyl (meth)acrylate, methyl glycidyl (meth)acrylate, and allyl glycidyl ether.

[0075] Examples of the nitrogen atom-containing monomer include amide group-containing monomers, amino group-containing monomers, cyano group-containing monomers, and monomers having a nitrogen atom-containing ring. Examples of the amide group-containing monomer include (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-butyl(meth)acrylamide, N-methylol(meth)acrylamide, N-methylolpropane(meth)acrylamide, N-methoxymethyl(meth)acrylamide, and N-butoxymethyl(meth)acrylamide. Examples of the amino group-containing monomer include aminoethyl(meth)acrylate, N,N-dimethylaminoethyl(meth)acrylate, and t-butylaminoethyl(meth)acrylate. Examples of the cyano group-containing monomer include acrylonitrile and methacrylonitrile. Examples of the monomer having a nitrogen atom-containing ring include N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-vinylmorpholine, N-vinylcaprolactam, and N-(meth)acryloylmorpholine.

[0076] Examples of the keto group-containing monomer include diacetone (meth)acrylamide, diacetone (meth)acrylate, vinyl methyl ketone, vinyl ethyl ketone, allyl acetoacetate, and vinyl acetoacetate.

[0077] Examples of the alkoxysilyl group-containing monomer include 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, and 3-(meth)acryloxypropylmethyldiethoxysilane.

[0078] Examples of the sulfonic acid group-containing monomer include styrenesulfonic acid, allylsulfonic acid, 2-(meth)acrylamido-2-methylpropanesulfonic acid, (meth)acrylamidopropanesulfonic acid, sulfopropyl (meth)acrylate, and (meth)acryloyloxynaphthalenesulfonic acid.

[0079] Examples of the phosphate group-containing monomer include 2-hydroxyethyl acryloyl phosphate.

[0080] The proportion of the functional group-containing monomer in the total of all monomer components constituting the acrylic polymer (100% by mass) may be, for example, 0.1% by mass or more, 0.5% by mass or more, 1% by mass or more, 5% by mass or more, or 10% by mass or more. The proportion may be, for example, 40% by mass or less, 20% by mass or less, or may be substantially free. In this specification, "substantially free" refers to unintentional inclusion, such as unavoidable mixing, rather than intentional incorporation, and is, for example, 0.05% by mass or less, 0.01% by mass or less.

[0081] The copolymerizable monomer may further contain other monomers. Examples of the other monomers include vinyl ester monomers such as vinyl acetate, vinyl propionate, and vinyl laurate; aromatic vinyl compounds such as styrene, substituted styrenes (α-methylstyrene, etc.), and vinyltoluene; (meth)acrylic acid esters having a cyclic structure in the molecule; olefin monomers such as ethylene, propylene, isoprene, butadiene, and isobutylene; chlorine-containing monomers such as vinyl chloride and vinylidene chloride; isocyanate group-containing monomers such as 2-(meth)acryloyloxyethyl isocyanate; alkoxy group-containing monomers such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; and vinyl ether monomers such as methyl vinyl ether and ethyl vinyl ether.

[0082] The cyclic structure in the (meth)acrylic acid ester having a cyclic structure within the molecule may be either an aromatic ring or a non-aromatic ring. Examples of the aromatic ring include a monocyclic carbocycle such as a benzene ring, an aromatic carbocycle such as a condensed carbocycle such as a naphthalene ring, and an aromatic heterocycle. Examples of the non-aromatic ring include a non-aromatic aliphatic ring (a non-aromatic alicyclic ring) (e.g., a cycloalkane ring such as a cyclopentane ring, a cyclohexane ring, a cycloheptane ring, or a cyclooctane ring; a cycloalkene ring such as a cyclohexene ring), a non-aromatic bridged ring (e.g., a bicyclic hydrocarbon ring such as pinane, pinene, bornane, norbornane, or norbornene; a tricyclic or higher aliphatic hydrocarbon ring (bridged hydrocarbon ring) such as adamantane), and a non-aromatic heterocycle (e.g., an epoxy ring, an oxolane ring, or an oxetane ring). Examples of the tricyclic or higher aliphatic hydrocarbon ring (tricyclic or higher bridged hydrocarbon ring) include a dicyclopentanyl group, a dicyclopentenyl group, an adamantyl group, a tricyclopentanyl group, and a tricyclopentenyl group.

[0083] Specific examples of the (meth)acrylic acid ester having a cyclic structure in the molecule include (meth)acrylic acid cycloalkyl esters such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, and cyclooctyl (meth)acrylate; (meth)acrylic acid esters having a bicyclic aliphatic hydrocarbon ring such as isobornyl (meth)acrylate; dicyclopentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, tricyclopentanyl (meth)acrylate, Examples of (meth)acrylic acid esters include (meth)acrylic acid esters having three or more aliphatic hydrocarbon rings, such as 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate; and (meth)acrylic acid esters having aromatic rings, such as (meth)acrylic acid aryl esters, such as phenyl (meth)acrylate; (meth)acrylic acid aryloxyalkyl esters, such as phenoxyethyl (meth)acrylate; and (meth)acrylic acid arylalkyl esters, such as benzyl (meth)acrylate.

[0084] The proportion of the other monomers in the total of all monomer components constituting the acrylic polymer (100% by mass) may be, for example, 0.05% by mass or more, 0.5% by mass or more, and may be, for example, 20% by mass or less, 10% by mass or less, 5% by mass or less, or may be substantially zero.

[0085] From the viewpoint of achieving superior stretch-peelability, the acrylic polymer preferably contains, as a constituent unit, a monomer whose homopolymer has a Tg of 0° C. or higher. Examples of the monomer whose homopolymer has a Tg of 0° C. or higher include a carboxy group-containing monomer, an acid anhydride monomer, a nitrogen atom-containing monomer, a (meth)acrylic acid ester having a cyclic structure in the molecule, and methyl methacrylate.

[0086] The proportion of the monomers having a Tg of 0°C or higher in the homopolymer relative to the total of all monomer components constituting the acrylic polymer (100% by mass) is preferably 1 to 50% by mass, more preferably 5 to 40% by mass, even more preferably 8 to 30% by mass, and particularly preferably 10 to 25% by mass. If the proportion is within this range, the hardness of the pressure-sensitive adhesive layer can be made appropriate, and the breaking elongation and breaking stress of the double-sided pressure-sensitive adhesive sheet can be made appropriately high.

[0087] The acrylic polymer may contain a polyfunctional monomer copolymerizable with the monomer components forming the acrylic polymer to form a crosslinked structure in the polymer backbone. Examples of the polyfunctional monomer include polyfunctional (meth)acrylates such as hexanediol di(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and dipentaerythritol hexa(meth)acrylate; and monomers having a (meth)acryloyl group and other reactive functional groups in the molecule, such as epoxy (meth)acrylates (e.g., polyglycidyl (meth)acrylate), polyester (meth)acrylate, and urethane (meth)acrylate. The polyfunctional monomers may be used singly or in combination.

[0088] The proportion of the polyfunctional monomer in the total amount (100% by mass) of all monomer components constituting the acrylic polymer is preferably 0.001 to 0.5% by mass, more preferably 0.005 to 0.3% by mass, and even more preferably 0.01 to 0.2% by mass, from the viewpoint of providing an appropriate hardness to the pressure-sensitive adhesive layer and appropriately increasing the breaking elongation and breaking stress of the double-sided pressure-sensitive adhesive sheet.

[0089] The shape of the filler is not particularly limited, and particulate or fibrous fillers can be used. Among these, particulate fillers are preferred. The filler may be either organic or inorganic, but inorganic fillers (particularly inorganic particles) are preferred. Only one type of filler may be used, or two or more types may be used.

[0090] Examples of materials constituting the filler include metals such as copper, silver, gold, platinum, nickel, aluminum, chromium, iron, and stainless steel; metal oxides such as aluminum oxide, silicon oxide (silicon dioxide), titanium oxide, zirconium oxide, zinc oxide, tin oxide, copper oxide, and nickel oxide; aluminum hydroxide, boehmite, magnesium hydroxide, calcium hydroxide, zinc hydroxide, silicic acid, iron hydroxide, copper hydroxide, barium hydroxide, zirconium oxide hydrate, tin oxide hydrate, basic magnesium carbonate, and hydrotalcite. Examples of suitable inorganic materials include metal hydroxides and hydrated metal compounds such as dawsonite, borax, and zinc borate; carbides such as silicon carbide, boron carbide, nitrogen carbide, and calcium carbide; nitrides such as aluminum nitride, silicon nitride, boron nitride, and gallium nitride; carbonates such as calcium carbonate; titanates such as barium titanate and potassium titanate; carbon-based materials such as carbon black, carbon tubes (carbon nanotubes), carbon fiber, and diamond; inorganic materials such as glass; and natural raw material particles such as volcanic silt, clay, and sand. Among these, inorganic metals, metal hydroxides, and hydrated metal compounds are preferred, with aluminum hydroxide being more preferred.

[0091] Examples of materials that constitute the organic matter include polymers such as polystyrene, acrylic resin (e.g., polymethyl methacrylate), phenolic resin, benzoguanamine resin, urea resin, silicone resin, polyester, polyurethane, polyethylene, polypropylene, polyamide (e.g., nylon), polyimide, and polyvinylidene chloride.

[0092] The particulate filler has an average particle size of, for example, 1.0 to 50 μm, preferably 4.0 to 50 μm, more preferably 4.1 to 50 μm, even more preferably 5.0 to 45 μm, even more preferably 5.5 to 40 μm, even more preferably 6.0 to 35 μm, even more preferably 6.5 to 30 μm, and particularly preferably 7.0 to 30 μm. When the average particle size is within the above range, the hardness of the pressure-sensitive adhesive layer can be made appropriate, and the breaking elongation and breaking stress of the double-sided pressure-sensitive adhesive sheet can be made appropriately high. The average particle size is the median diameter (D50) measured by dynamic light scattering.

[0093] The content of the filler in the pressure-sensitive adhesive layer is 2% by mass or more, preferably 5% by mass or more, and more preferably 8% by mass or more, relative to 100% by mass of the total amount of the pressure-sensitive adhesive layer. A content of 2% by mass or more provides excellent releasability from the adherend, allowing the double-sided pressure-sensitive adhesive sheet to be peeled off while suppressing adhesive residue on the adherend. Furthermore, the pressure-sensitive adhesive layer has an appropriate hardness, allowing the double-sided pressure-sensitive adhesive sheet to have an appropriately high breaking elongation and breaking stress. From the viewpoint of ensuring adhesiveness to the adherend by the base polymer, the content is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 12% by mass or less.

[0094] The pressure-sensitive adhesive layer can be produced, for example, by applying (coating) a pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer onto the substrate layer or release liner and drying and curing the resulting pressure-sensitive adhesive composition layer, or by applying (coating) the pressure-sensitive adhesive composition onto the substrate layer or release liner and irradiating the resulting pressure-sensitive adhesive composition layer with active energy rays to cure it. Furthermore, if necessary, the resulting pressure-sensitive adhesive composition may be further dried by heating.

[0095] The pressure-sensitive adhesive composition forming the pressure-sensitive adhesive layer may be in any form. For example, the pressure-sensitive adhesive composition may be an emulsion type, a solvent type (solution type), an active energy ray curable type, a hot melt type (hot melt type), or the like. Among these, a solvent type or an active energy ray curable type pressure-sensitive adhesive composition is preferred from the viewpoint of easily obtaining a pressure-sensitive adhesive layer with excellent productivity. In particular, an active energy ray curable type pressure-sensitive adhesive composition is preferred from the viewpoint of more excellent stretch-releasability.

[0096] Examples of the active energy rays include ionizing radiation such as α-rays, β-rays, γ-rays, neutron rays, and electron beams, as well as ultraviolet rays, and ultraviolet rays are particularly preferred. That is, the active energy ray-curable pressure-sensitive adhesive composition is preferably an ultraviolet-curable pressure-sensitive adhesive composition.

[0097] When polymerizing the above-mentioned monomer components, a polymerization initiator such as a thermal polymerization initiator or a photopolymerization initiator (photoinitiator) may be used depending on the type of polymerization reaction. Note that only one type of polymerization initiator may be used, or two or more types may be used.

[0098] The thermal polymerization initiator is not particularly limited, but examples thereof include azo polymerization initiators, peroxide polymerization initiators (e.g., persulfates such as dibenzoyl peroxide, tert-butyl permaleate, and potassium persulfate, benzoyl peroxide, and hydrogen peroxide), substituted ethane initiators such as phenyl-substituted ethane, aromatic carbonyl compounds, and redox polymerization initiators. Among these, the azo polymerization initiators disclosed in JP-A-2002-69411 are preferred. Examples of the azo polymerization initiator include 2,2'-azobisisobutyronitrile (hereinafter sometimes referred to as "AIBN"), 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis(2-methylpropionate)dimethyl, and 4,4'-azobis-4-cyanovaleric acid. The amount of the thermal polymerization initiator used may be any amount that is normally used, and can be selected, for example, from the range of 0.005 to 1 part by mass, preferably 0.01 to 1 part by mass, per 100 parts by mass of the monomer component.

[0099] The photopolymerization initiator is not particularly limited, but examples thereof include benzoin ether-based photopolymerization initiators, acetophenone-based photopolymerization initiators, α-ketol-based photopolymerization initiators, aromatic sulfonyl chloride-based photopolymerization initiators, photoactive oxime-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzyl-based photopolymerization initiators, benzophenone-based photopolymerization initiators, ketal-based photopolymerization initiators, and thioxanthone-based photopolymerization initiators. Other examples include acylphosphine oxide-based photopolymerization initiators and titanocene-based photopolymerization initiators. Examples of the benzoin ether-based photopolymerization initiators include benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, benzoin isobutyl ether, 2,2-dimethoxy-1,2-diphenylethan-1-one, and anisole methyl ether. Examples of the acetophenone-based photopolymerization initiator include 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexylphenyl ketone, 4-phenoxydichloroacetophenone, and 4-(t-butyl)dichloroacetophenone. Examples of the α-ketol-based photopolymerization initiator include 2-methyl-2-hydroxypropiophenone and 1-[4-(2-hydroxyethyl)phenyl]-2-methylpropan-1-one. Examples of the aromatic sulfonyl chloride-based photopolymerization initiator include 2-naphthalenesulfonyl chloride. Examples of the photoactive oxime-based photopolymerization initiator include 1-phenyl-1,1-propanedione-2-(O-ethoxycarbonyl)-oxime. Examples of the benzoin-based photopolymerization initiator include benzoin. Examples of the benzyl-based photopolymerization initiator include benzil. Examples of the benzophenone-based photopolymerization initiator include benzophenone, benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, polyvinylbenzophenone, α-hydroxycyclohexylphenyl ketone, etc. Examples of the ketal-based photopolymerization initiator include benzyl dimethyl ketal, etc.Examples of the thioxanthone-based photopolymerization initiator include thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-diisopropylthioxanthone, and dodecylthioxanthone. Examples of the acylphosphine oxide-based photopolymerization initiator include 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide. Examples of the titanocene-based photopolymerization initiator include bis(η). 5 -2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)-phenyl)titanium. The amount of the photopolymerization initiator used may be a normal amount, and can be selected, for example, from the range of 0.01 to 3 parts by mass, preferably 0.1 to 1.5 parts by mass, per 100 parts by mass of the monomer component.

[0100] Examples of the pressure-sensitive adhesive composition (acrylic pressure-sensitive adhesive composition) forming the acrylic pressure-sensitive adhesive layer include an acrylic pressure-sensitive adhesive composition containing an acrylic polymer and a filler as essential components, and an acrylic pressure-sensitive adhesive composition containing a mixture of monomers (sometimes referred to as a "monomer mixture") constituting an acrylic polymer or a partial polymer thereof and a filler as essential components. Examples of the former include so-called solvent-based acrylic pressure-sensitive adhesive compositions. Examples of the latter include so-called active energy ray-curable acrylic pressure-sensitive adhesive compositions. The "monomer mixture" refers to a mixture containing the monomer components constituting the polymer. The "partially polymerized product" is sometimes referred to as a "prepolymer" or "syrup," and refers to a composition in which one or more of the monomer components in the monomer mixture are partially polymerized.

[0101] From the viewpoint of achieving superior releasability from an adherend, the pressure-sensitive adhesive composition preferably contains a partial polymer of an acrylic monomer (A), an acrylic monomer (B), a polyfunctional monomer, a photopolymerization initiator, and a filler.

[0102] The acrylic monomer (A) preferably contains a (meth)acrylic acid alkyl ester, more preferably a (meth)acrylic acid alkyl ester having a linear or branched alkyl group having 4 to 10 carbon atoms (preferably 4 to 8). The acrylic monomer (A) preferably contains the functional group-containing monomer (preferably a hydroxy group-containing monomer). The acrylic monomer (A) more preferably contains a monomer having a homopolymer Tg of 0°C or higher.

[0103] The partially polymerized product differs from the fully polymerized product of the acrylic monomer (A) and is obtained by polymerizing the acrylic monomer (A) at a polymerization conversion rate of, for example, 95% by mass or less. The polymerization conversion rate is preferably 70% by mass or less, more preferably 60% by mass or less, even more preferably 50% by mass or less, even more preferably 40% by mass or less, and particularly preferably 35% by mass or less. The polymerization conversion rate is preferably 1% by mass or more, more preferably 5% by mass or more.

[0104] The content of the (meth)acrylic acid alkyl ester in the acrylic monomer (A) is preferably 30 to 99% by mass, more preferably 40 to 95% by mass, even more preferably 50 to 90% by mass, even more preferably 60 to 85% by mass, and particularly preferably 70 to 80% by mass. The content of the hydroxy group-containing monomer in the acrylic monomer (A) is preferably 0.1 to 30% by mass, more preferably 0.5 to 20% by mass, even more preferably 1 to 10% by mass, and particularly preferably 2 to 7% by mass. The content of the monomer having a homopolymer Tg of 0°C or higher in the acrylic monomer (A) is preferably 1 to 50% by mass, more preferably 5 to 40% by mass, even more preferably 8 to 30% by mass, even more preferably 10 to 25% by mass, and particularly preferably 15 to 20% by mass.

[0105] The partially polymerized product can be prepared by polymerizing the acrylic monomer (A) by a known or conventional method. The polymerization may be carried out using the photopolymerization initiator.

[0106] The acrylic monomer (B) preferably contains a (meth)acrylic acid alkyl ester, more preferably a (meth)acrylic acid alkyl ester having a linear or branched alkyl group having 4 to 10 carbon atoms (preferably 4 to 8). The acrylic monomer (B) also preferably contains the above-mentioned functional group-containing monomer, more preferably a monomer whose homopolymer has a Tg of 0°C or higher. Among them, preferred monomers whose homopolymer has a Tg of 0°C or higher are carboxy group-containing monomers, acid anhydride monomers, and nitrogen atom-containing monomers, more preferably (meth)acrylic acid and N-vinyl-2-pyrrolidone.

[0107] The content of the monomer having a homopolymer Tg of 0°C or higher in the acrylic monomer (B) is preferably 10 to 90 parts by mass, more preferably 12 to 80 parts by mass, even more preferably 15 to 70 parts by mass, even more preferably 20 to 65 parts by mass, still more preferably 25 to 65 parts by mass, and particularly preferably 30 to 60 parts by mass, relative to 100 parts by mass of the (meth)acrylic acid alkyl ester.

[0108] The content of the (meth)acrylic acid alkyl ester in the acrylic monomer (B) is preferably 53 to 91 mass%, more preferably 56 to 89 mass%, even more preferably 59 to 87 mass%, still more preferably 61 to 83 mass%, and particularly preferably 63 to 77 mass%. The content of the monomer having a homopolymer Tg of 0°C or higher in the acrylic monomer (B) is preferably 9 to 47 mass%, more preferably 11 to 44 mass%, even more preferably 13 to 41 mass%, still more preferably 17 to 39 mass%, and particularly preferably 23 to 37 mass%.

[0109] The content of the polyfunctional monomer in the acrylic pressure-sensitive adhesive composition is preferably 0.001 to 0.5 parts by mass, more preferably 0.005 to 0.3 parts by mass, even more preferably 0.01 to 0.2 parts by mass, and particularly preferably 0.05 to 0.1 parts by mass, relative to 100 parts by mass of the acrylic monomer (A).

[0110] The acrylic pressure-sensitive adhesive composition may contain an acrylic oligomer as another component to further improve elongation at break. The weight-average molecular weight of the acrylic oligomer is preferably 1,000 to 30,000, more preferably 1,000 to 20,000, even more preferably 1,500 to 10,000, and particularly preferably 2,000 to 8,000. When the acrylic pressure-sensitive adhesive composition contains an acrylic oligomer, the stretch-removal properties are improved. Only one type of acrylic oligomer may be used, or two or more types may be used. The weight-average molecular weight can be determined in polystyrene equivalent terms by the GPC method. For example, it can be measured using a high-speed GPC device "HPLC-8120GPC" manufactured by Tosoh Corporation under the following conditions. Column: TSKgel SuperHZM-H / HZ4000 / HZ3000 / HZ2000 Solvent: tetrahydrofuran Flow rate: 0.6ml / min

[0111] The acrylic oligomer contains an acrylic monomer as a structural unit. The acrylic oligomer preferably contains a (meth)acrylic acid ester having a cyclic structure in the molecule as a structural unit, and more preferably further contains a (meth)acrylic acid alkyl ester having a linear or branched alkyl group as a structural unit. The acrylic monomer contained as the structural unit may be of only one type or two or more types.

[0112] The (meth)acrylic acid ester having a cyclic structure in the molecule is preferably a non-aromatic ring-containing (meth)acrylic acid ester, more preferably cyclohexyl acrylate (CHA), cyclohexyl methacrylate (CHMA), dicyclopentanyl acrylate (DCPA), dicyclopentanyl methacrylate (DCPMA), and even more preferably dicyclopentanyl acrylate (DCPA) and dicyclopentanyl methacrylate (DCPMA). The proportion of the (meth)acrylic acid ester having a cyclic structure in the molecule of all monomer components constituting the acrylic oligomer is preferably 10 to 90% by mass, more preferably 20 to 80% by mass.

[0113] Of the (meth)acrylic acid alkyl esters having a linear or branched alkyl group, methyl methacrylate (MMA) is preferred. The proportion of the (meth)acrylic acid alkyl esters having a linear or branched alkyl group in all monomer components constituting the acrylic oligomer is preferably 10 to 90 mass%, more preferably 20 to 80 mass%, and even more preferably 20 to 60 mass%.

[0114] The pressure-sensitive adhesive layer may further contain, as necessary, additives such as crosslinking accelerators, antioxidants, colorants (pigments, dyes, etc.), antioxidants, plasticizers, softeners, surfactants, antistatic agents, surface lubricants, leveling agents, light stabilizers, UV absorbers, polymerization inhibitors, foil-like materials, and rust inhibitors, within the range that does not impair the effects of the present invention. Only one of the above additives may be used, or two or more thereof may be used.

[0115] The thickness of the pressure-sensitive adhesive layer (thickness of the pressure-sensitive adhesive layer on one side) is not particularly limited, but is preferably 50 μm or more, more preferably 100 μm or more, and even more preferably 150 μm or more. When the thickness is 50 μm or more, the breaking elongation tends to be high. In addition, the compressive load can be made smaller, resulting in better conformability to the adherend. The thickness of the pressure-sensitive adhesive layer is, for example, 500 μm or less, preferably 300 μm or less. When the thickness is 500 μm or less, the thickness of the double-sided pressure-sensitive adhesive sheet can be made thinner. The thicknesses of the pressure-sensitive adhesive layers on both sides may be the same or different.

[0116] (double-sided adhesive sheet) The thickness of the double-sided pressure-sensitive adhesive sheet is preferably 200 to 1500 μm, more preferably 400 to 1200 μm, and even more preferably 500 to 1000 μm. When the thickness is 200 μm or more, the compressive load can be reduced, resulting in better conformability to the adherend. When the thickness is 1500 μm or less, the thickness of the double-sided pressure-sensitive adhesive sheet can be made thinner. The thickness of the double-sided pressure-sensitive adhesive sheet refers to the thickness from one adhesive surface to the other adhesive surface, i.e., the thickness of the adhesive body, and does not include the release liner.

[0117] The double-sided pressure-sensitive adhesive sheet may have a release liner on the surface (adhesive surface) of the pressure-sensitive adhesive layer until use. Each adhesive surface of the double-sided pressure-sensitive adhesive sheet may be protected by two release liners, or may be protected by a single release liner with release surfaces on both sides in a rolled form (rolled body). The release liner is used as a protective material for the pressure-sensitive adhesive layer and is peeled off when the sheet is attached to the adherend. The release liner is not necessarily provided.

[0118] The release liner can be a conventional release paper, and is not particularly limited. Examples include substrates with a release treatment layer, low-adhesion substrates made of fluoropolymers, and low-adhesion substrates made of non-polar polymers. Examples of substrates with a release treatment layer include plastic films and papers surface-treated with release agents such as silicones, long-chain alkyls, fluorines, and molybdenum sulfide. Examples of fluorine-based polymers in the low-adhesion substrates made of fluoropolymers include polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymers, and chlorofluoroethylene-vinylidene fluoride copolymers. Examples of non-polar polymers include olefin resins (e.g., polyethylene, polypropylene, etc.). The release liner can be formed by known or conventional methods. The thickness of the release liner is also not particularly limited.

[0119] The double-sided PSA sheet has excellent stretch-releasability, i.e., excellent ability to be removed by pulling it out from between adherends. Here, stretch-releasability refers to the ease of removal, such as by exposing a portion (typically a tab) of the double-sided PSA sheet from two adherends fixed together via the sheet, and then pulling this exposed portion to remove the double-sided PSA sheet, thereby releasing the fixation (typically bonding) of the adherends. The two adherends may be two locations on a single member. This will be explained in detail below with reference to Figures 2 and 3.

[0120] Fig. 2 is a schematic side view illustrating one embodiment of stretch-peeling, with Fig. 2(a) showing the start of stretch-peeling of a double-sided pressure-sensitive adhesive sheet, Fig. 2(b) showing the state in which the double-sided pressure-sensitive adhesive sheet is being stretched and peeled, and Fig. 2(c) showing the state after stretch-peeling of the double-sided pressure-sensitive adhesive sheet has been completed. Fig. 3 is a schematic top view illustrating one embodiment of stretch-peeling, with Figs. 3(a) to 3(c) being top views corresponding to Figs. 2(a) to 2(c), respectively.

[0121] As shown in Figures 2(a) and 3(a), the double-sided pressure-sensitive adhesive sheet 1 has a tab 11 that is exposed to the outside when the adherends 5 and 6 are joined together. This double-sided pressure-sensitive adhesive sheet 1 is used to join the adherends 5 and 6. After the joining is achieved, the double-sided pressure-sensitive adhesive tape 1 is stretched (pulled) by pinching the tab 11 with the fingers and pulling it out from between the adherends 4 and 5. As a result, the double-sided pressure-sensitive adhesive sheet 1 begins to stretch and contracts in a direction perpendicular to the stretching direction, and begins to peel from the adherends 5 and 6 (see Figures 2(b) and 3(b)). Finally, the entire adhesive region of the double-sided pressure-sensitive adhesive sheet 1 peels off, completing the peeling of the double-sided pressure-sensitive adhesive sheet 1 from between the adherends 5 and 6 (see Figures 2(c) and 3(c)). At the same time, the removal of the adherend 6 that was joined to the adherend 5 is also completed.

[0122] The double-sided PSA sheets are preferably used for fixing or temporarily fixing components in electrical and electronic devices (for fixing electrical and electronic components). For example, when a double-sided PSA sheet is used for fixing or temporarily fixing components in electrical and electronic devices, there are cases where a defect occurs during the application of the double-sided PSA sheet, and the double-sided PSA sheet must be peeled off and reworked. There are also cases where the double-sided PSA sheet must be peeled off to repair, replace, inspect, recycle, or the like a component equipped with an adherend to which the double-sided PSA sheet is attached. Thus, when a double-sided PSA sheet is used for fixing or temporarily fixing components in electrical and electronic devices, for example, the double-sided PSA sheet must be removed particularly frequently. However, in order to peel the double-sided PSA sheet from the adherend, if there are adherends on both sides of the double-sided PSA sheet, as shown in Figures 2 and 3, for example, it is necessary to first flip over one of the adherends to expose one side of the double-sided PSA sheet, and then peel the double-sided PSA sheet. Furthermore, if there are adherends on one side of the double-sided PSA sheet, for example, it is necessary to carefully peel the double-sided PSA sheet from the adherend. However, since the components provided in electrical and electronic devices are often expensive, the above-mentioned turning over or peeling operations are likely to damage the components, creating a cost problem. Here, the double-sided pressure-sensitive adhesive sheet of the present invention has excellent stretch-peelability, and can be removed from the adherend in the horizontal direction (shear direction), as shown in Figures 2 and 3, so damage to the adherend caused by removal of the double-sided pressure-sensitive adhesive sheet can be suppressed.

[0123] Depending on the position of the adherend (for example, the position of a component serving as the adherend in an electrical or electronic device), the double-sided PSA sheet may not be able to be removed from the adherend in the horizontal direction (shear direction). In such cases, the double-sided PSA sheet may be stretch-peeled at any appropriate angle relative to the adhesive surface, as long as the effects of the present invention are not impaired. For example, the angle relative to the horizontal direction (shear direction) is preferably greater than 0° but not greater than 90°, more preferably greater than 0° but not greater than 45°, even more preferably greater than 0° but not greater than 30°, and particularly preferably greater than 0° but not greater than 20°.

[0124] The term "electrical and electronic devices" refers to devices that fall into at least either an electrical device or an electronic device. Examples of the electrical and electronic devices include image display devices such as liquid crystal displays, electroluminescence displays, and plasma displays, as well as portable electronic devices. The double-sided pressure-sensitive adhesive sheet is preferably used by adhering it to an internal component of an optical component (particularly an electrical and electronic device), and is particularly preferably used to fix an internal component of an optical component (particularly an electrical and electronic device).

[0125] Examples of the portable electronic device include mobile phones, smartphones, tablet computers, notebook computers, various wearable devices (for example, wristwear devices worn on the wrist like a wristwatch, modular devices worn on a part of the body with a clip or strap, eyewear devices including eyeglasses (monocular and binocular, including head-mounted devices), clothing devices attached to shirts, socks, hats, etc. as accessories, and earwear devices attached to the ears like earphones), digital cameras, digital video cameras, audio equipment (portable music players, IC recorders, etc.), calculators (calculators, etc.), portable game devices, electronic dictionaries, electronic organizers, e-books, in-car information devices, portable radios, portable televisions, portable printers, portable scanners, and portable modems. In this specification, "portable" does not simply mean being portable, but also means having a level of portability that allows an individual (average adult) to carry it relatively easily. The double-sided PSA sheet is used, for example, so that the adhesive layer adheres to components of the portable electronic device. [Example]

[0126] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0127] <Tg of representative monomers> The Tg values ​​of the representative monomers used in the Production Examples, Examples, and Comparative Examples when they form homopolymers are as follows: 2EHA:-70℃ NVP: 80℃ HEA:-15℃ AA: 106℃ DCPMA: 175℃ MMA: 105℃

[0128] Production Example 1: Synthesis of syrup A liquid monomer mixture (monomer composition) containing 78 parts by weight of 2-ethylhexyl acrylate (2EHA), 18 parts by weight of N-vinyl-2-pyrrolidone (NVP), and 4 parts by weight of 2-hydroxyethyl acrylate (HEA) was mixed with 0.05 parts by weight of 2,2-dimethoxy-1,2-diphenylethan-1-one (trade name "OMNIRAD651", manufactured by IGM Resins BV) as a photopolymerization initiator. The mixture was then irradiated with pulsed ultraviolet light until the viscosity (BH viscometer No. 5 rotor, 10 rpm, measurement temperature: 30°C) reached approximately 15 Pa·s, yielding a syrup (partially polymerized product) containing a partial polymer in which some of the monomer components had polymerized (polymerization rate: approximately 8%).

[0129] Production Example 2: Synthesis of acrylic oligomer A flask was charged with 58 parts by mass of dicyclopentanyl methacrylate (DCPMA), 39 parts by mass of methyl methacrylate (MMA), 3 parts by mass of α-thioglycerol, 0.2 parts by mass of 2,2'-azobisisobutyronitrile, and 65 parts by mass of ethyl acetate. The flask was thoroughly filled with nitrogen, and polymerization was carried out at 70°C for 5 hours. After that, 0.1 parts by mass of 2,2'-azobisisobutyronitrile was added, and polymerization was carried out at 80°C for 8 hours. Thereafter, ethyl acetate was distilled off from the reaction solution, and the reaction solution was further dried in a vacuum dryer to obtain an acrylic oligomer.

[0130] Manufacturing Example 3: Synthesis of acrylic foam 100 parts by mass of an acrylic emulsion solution (solid content 55%, ethyl acrylate-butyl acrylate-acrylonitrile copolymer (mass ratio 45:48:7)), 1.5 parts by mass of a fatty acid ammonium surfactant (aqueous dispersion of ammonium stearate, solid content 33%), 1 part by mass of a carboxybetaine-type amphoteric surfactant ("Amogen CB-H", manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), 0.35 parts by mass of an oxazoline-based crosslinker ("Epocross WS-500", manufactured by Nippon Shokubai Co., Ltd., solid content 39%), 0.78 parts by mass of a polyacrylic acid-based thickener (ethyl acrylate-acrylic acid copolymer (acrylic acid 20% by mass), solid content 28.7%), and 0.5 parts by mass of a benzotriazole-based rust inhibitor ("SEETEC BT-NA", manufactured by Shipro Kasei Co., Ltd.) were stirred and mixed in a disperser ("Robomix", manufactured by Primix Corporation) to generate foam. This foaming composition was applied to a release-treated PET (polyethylene terephthalate) film (thickness: 38 μm, product name "MRF#38", manufactured by Mitsubishi Chemical Corporation), and dried at 70°C for 4.5 minutes and at 140°C for 4.5 minutes to produce a foam with a thickness of 130 μm and a density of 0.33 g / cm. 3 An acrylic foam (foam sheet) having an open-cell structure was obtained.

[0131] Example 1 100 parts by mass of the syrup obtained in Production Example 1, 3 parts by mass of the acrylic oligomer obtained in Production Example 2, 30 parts by mass of 2-ethylhexyl acrylate (2EHA), 15 parts by mass of acrylic acid (AA), 0.08 parts by mass of 1,6-hexanediol diacrylate (HDDA), 15 parts by mass of aluminum hydroxide (product name "B103", manufactured by Nippon Light Metal Co., Ltd., average particle size 7 μm) as a filler, and 0.05 parts by mass of 2,2-dimethoxy-1,2-diphenylethan-1-one (product name "OMNIRAD651", manufactured by IGM Resins BV) as a photopolymerization initiator were blended, and then the mixture was mixed uniformly using a disper, followed by degassing to obtain an acrylic pressure-sensitive adhesive composition.

[0132] The obtained acrylic pressure-sensitive adhesive composition was applied using an applicator to a 38 μm thick polyethylene terephthalate film (product name "MRF#38", manufactured by Mitsubishi Chemical Corporation) whose one side had been treated with a silicone release agent to give a pressure-sensitive adhesive layer thickness of 100 μm, thereby forming a coating layer.

[0133] Next, a 25 μm thick polyethylene terephthalate film (product name "MRE#25", manufactured by Mitsubishi Chemical Corporation) with one side treated with silicone for release was used to cover the coating layer, with the release-treated side facing the coating layer, to block oxygen. After that, a black light lamp was used to illuminate the top surface of this film at an illuminance of 4 mW / cm. 2 The film was irradiated with ultraviolet light (UV checker "UVR-T1", manufactured by Topcon Corporation, maximum sensitivity during measurement was approximately 350 nm) for 180 seconds to obtain a pressure-sensitive adhesive layer having a thickness of 100 μm.

[0134] One of the polyethylene terephthalate films of the obtained adhesive layer was peeled off to expose the adhesive layer, and the exposed adhesive layer was bonded to both sides of an acrylic foam (product name "Hyperjoint H9004", manufactured by Nitto Denko Corporation) as a base layer to produce the double-sided adhesive sheet of Example 1.

[0135] Example 2 A double-sided PSA sheet of Example 2 was produced in the same manner as in Example 1, except that the thickness of each PSA layer was 200 μm.

[0136] Example 3 A double-sided PSA sheet of Example 3 was produced in the same manner as in Example 1, except that the thickness of each PSA layer was 250 μm.

[0137] Example 4 A double-sided PSA sheet of Example 4 was produced in the same manner as in Example 3, except that the amount of aluminum hydroxide added was 20 parts by mass when producing the PSA composition.

[0138] Example 5 A double-sided PSA sheet of Example 5 was produced in the same manner as in Example 3, except that the amount of aluminum hydroxide added was 10 parts by mass when producing the PSA composition.

[0139] Example 6 A double-sided PSA sheet of Example 6 was produced in the same manner as in Example 3, except that the amount of aluminum hydroxide added was 5 parts by mass when producing the PSA composition.

[0140] Example 7 A double-sided PSA sheet of Example 7 was produced in the same manner as Example 2, except that an acrylic foam (product name "Hyperjoint H8004", manufactured by Nitto Denko Corporation) was used as the substrate layer.

[0141] Example 8 A double-sided PSA sheet of Example 8 was produced in the same manner as Example 2, except that a polyethylene foam (product name "Volara XL-H #05003", manufactured by Sekisui Chemical Co., Ltd.) was used as the substrate layer.

[0142] Example 9 A double-sided PSA sheet of Example 9 was produced in the same manner as in Example 2, except that a polyethylene foam (product name "Volara XL-H #0270015", manufactured by Sekisui Chemical Co., Ltd.) was used as the substrate layer.

[0143] Example 10 A double-sided PSA sheet of Example 10 was produced in the same manner as Example 2, except that a polyethylene foam (product name "Volara XL-H #10005", manufactured by Sekisui Chemical Co., Ltd.) was used as the substrate layer.

[0144] Example 11 A double-sided PSA sheet of Example 11 was produced in the same manner as Example 2, except that the acrylic foam obtained in Production Example 3 was used as the substrate layer.

[0145] Example 12 A double-sided PSA sheet of Example 12 was produced in the same manner as Example 2, except that a polyurethane foam (product name "PureCell 020", manufactured by Inoac Corporation) was used as the substrate layer.

[0146] Comparative Example 1 A double-sided PSA sheet of Comparative Example 1 was produced in the same manner as in Example 3, except that a polypropylene foam (product name "SCF400TT", manufactured by Nitto Denko Corporation) was used as the base layer.

[0147] Comparative Example 2 A double-sided PSA sheet of Comparative Example 2 was produced in the same manner as in Example 1, except that a non-foamed polyethylene terephthalate film was used as the base layer.

[0148] Comparative Example 3 A double-sided PSA sheet of Comparative Example 3 was produced in the same manner as in Example 3, except that aluminum hydroxide was not added during the production of the PSA composition.

[0149] Comparative Example 4 A double-sided PSA sheet of Comparative Example 4 was produced in the same manner as in Example 8, except that aluminum hydroxide was not added when producing the PSA composition and the thickness of the PSA layer was set to 250 μm.

[0150] <Evaluation> The double-sided PSA sheets obtained in the examples and comparative examples were evaluated as follows, and the results are shown in the table below.

[0151] (1) 25% compression load The compression hardness was measured according to the compression hardness measurement method described in JIS K6767. Specifically, the double-sided PSA sheet was cut into a sheet-like test piece with a width of 30 mm and a length of 30 mm. The test piece was then compressed in the thickness direction at a compression rate of 10 mm / min until the compression rate reached 25% (75% of the original thickness), and the stress (MPa) was measured.

[0152] (2) Breaking elongation, breaking stress The double-sided PSA sheet was punched into a No. 1 dumbbell shape (JIS K6251 compliant, 10 mm wide), and set in a tensile testing machine "Autograph AG-10G" (Shimadzu Corporation) with a chuck distance of 10 mm in the longitudinal direction. The sheet was stretched at a tensile speed of 300 mm / min until it broke. The elongation at break (breaking elongation) and load (breaking stress) at break were then measured.

[0153] (3) Stretch releasability The double-sided PSA sheet was punched into a rectangle measuring 10 mm wide x 100 mm long to obtain a test piece. A 50 mm length of the test piece was sandwiched between two polycarbonate plates (2 mm thick) to prepare a test sample. The test piece exposed from the test sample was pulled in the plane direction of the polycarbonate plate (adherend) at a pulling speed of 300 mm / min. The stretch-peelability was then evaluated according to the following evaluation criteria. ◯ (Good): The test piece was able to be stretch-peeled without destroying the base layer, and no adhesive residue was observed on the polycarbonate plate after peeling. × (bad): The test piece could not be stretched and peeled, or adhesive residue was observed on the polycarbonate plate after peeling.

[0154] [Table 1]

[0155] As shown in Table 1, the double-sided pressure-sensitive adhesive sheet of the present invention has compressibility because the 25% compression load is 2 MPa or less, and therefore has excellent conformability to the adherend. Furthermore, when two adherends were attached together, the base layer could be stretched and peeled without breaking, and no adhesive residue was observed on the adherend. On the other hand, when the breaking stress was high (Comparative Example 1), the base layer broke when the test piece was pulled in the stretch-peeling test, and stretch-peeling was not possible. When the breaking elongation was low (Comparative Example 2), it was difficult to stretch the test piece, and stretch-peeling was not possible. Furthermore, when a non-foamed material was used as the base layer (Comparative Example 2), the 25% compression load exceeded 2 MPa, resulting in insufficient compressibility and poor conformability to the adherend. When the pressure-sensitive adhesive layer did not contain a filler (Comparative Examples 3 and 4), adhesive residue was observed on the polycarbonate plate after stretch-peeling. [Explanation of symbols]

[0156] 1 double-sided adhesive sheet 2 Base material layer 3,4 Adhesive layer

Claims

1. A double-sided PSA sheet comprising a base layer and PSA layers laminated on both sides of the base layer, the substrate layer comprises a foam; the pressure-sensitive adhesive layer contains a filler, the pressure-sensitive adhesive layer is an acrylic pressure-sensitive adhesive layer formed from an active energy ray-curable acrylic pressure-sensitive adhesive composition, the acrylic pressure-sensitive adhesive composition contains a photopolymerization initiator, the content of the filler is 2% by mass or more relative to 100% by mass of the total amount of the pressure-sensitive adhesive layer, the double-sided PSA sheet has a 25% compressive load of 2 MPa or less; A double-sided pressure-sensitive adhesive sheet having a width of 10 mm, in a tensile test conducted under conditions of an initial chuck distance of 10 mm, room temperature, and a tensile speed of 300 mm / min, which has a breaking elongation of 600% or more and a breaking stress of 2 MPa or more.

2. The double-sided pressure-sensitive adhesive sheet according to claim 1 , wherein the foam has a thickness of 80 μm or more.

3. 3. The double-sided pressure-sensitive adhesive sheet according to claim 1, wherein each of the pressure-sensitive adhesive layers has a thickness of 50 [mu]m or more.

4. The density of the foam is 0.05 g / cm ３ 1g / cm or more ３ The double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein the thickness is less than 1 / 2 mm.

5. The double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 4, wherein the filler content is 20% by mass or less relative to 100% by mass of the total amount of the pressure-sensitive adhesive layer.

6. The double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 5, which has a thickness of 200 to 1500 µm. to.

7. The double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 6, wherein the foam is composed of at least one material selected from the group consisting of polyolefin resins, acrylic resins, and polyurethanes.

8. The double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 7, wherein the pressure-sensitive adhesive layer is an acrylic pressure-sensitive adhesive layer containing an acrylic polymer as a base polymer.

9. The double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 8, which is used for fixing electrical and electronic components.

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