Double-sided pressure-sensitive adhesive sheet

Abstract

[Problem] To provide a double-sided pressure-sensitive adhesive sheet having excellent impact resistance, high shear adhesive force, and excellent initial tackiness. [Solution] A double-sided pressure-sensitive adhesive sheet 1 includes a pressure-sensitive adhesive layer 2, wherein the pressure-sensitive adhesive layer 2 is an active-ray-curable acrylic pressure-sensitive adhesive layer comprising an acrylic polymer as a base polymer. The acrylic polymer comprises 50 mass% or more constituent units derived from an alkyl (meth)acrylate (A) in which the alkyl group is a linear or branched C2-C7 alkyl. The pressure-sensitive adhesive layer 2 has a glass transition temperature of 0°C or higher, a -20°C storage modulus G' of 10 MPa or greater, and a 65°C storage modulus G' of 0.05 MPa or greater. The double-sided pressure-sensitive adhesive sheet 1 has a 180° peel strength in application to a stainless-steel plate of 20 N / 20 mm or greater when examined at 23°C in the state of having a 50 μm-thick poly(ethylene terephthalate) film adherent to one pressure-sensitive adhesive surface thereof.

Description

double-sided adhesive sheet

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

[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, which are a representative example of mobile devices, each of the major components tends to be made thinner. Typically, the display section of a mobile device is primarily composed of an LCD module and a backlight unit, and various sheet-like components are layered 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] For example, portable electronic devices are often exposed to the risk of being dropped depending on how they are used, and therefore double-sided PSA sheets used in portable electronic devices are required to have impact resistance so that they are less likely to break or peel off from components due to the impact of the portable electronic device being dropped.

[0004] Known double-sided pressure-sensitive adhesive sheets that are used in portable electronic devices and have excellent impact resistance are disclosed in, for example, Patent Documents 1 to 3.

[0005] JP 2020-128453 A JP 2020-128454 A JP 2021-24907 A

[0006] Portable electronic devices may be subjected to various types of impacts when not in use, and therefore double-sided PSA sheets used in portable electronic devices are required to have high shear adhesive strength to prevent peeling due to deformation of the adherend.

[0007] However, in general, when the adhesive layer of a double-sided pressure-sensitive adhesive sheet is flexible, it tends to have excellent impact resistance but low shear adhesive strength. Furthermore, when the adhesive layer of a double-sided pressure-sensitive adhesive sheet is hard, it tends to have high shear adhesive strength but low surface adhesiveness, which tends to result in poor adhesiveness (initial adhesiveness) when the double-sided pressure-sensitive adhesive sheet is attached to an adherend. For this reason, it has been considered difficult to realize a double-sided pressure-sensitive adhesive sheet that has excellent impact resistance, high shear adhesive strength, and excellent initial adhesiveness. Patent Documents 1 to 3 do not mention excellent impact resistance, high shear adhesive strength, and excellent initial adhesiveness.

[0008] The present invention was conceived under these circumstances, and its object is to provide a double-sided PSA sheet that has excellent impact resistance, high shear adhesive strength, and excellent initial adhesiveness.

[0009] As a result of extensive research to achieve the above object, the inventors have found that a substrate-free double-sided PSA sheet can have excellent impact resistance, high shear adhesive strength, and excellent initial tackiness by specifying the base polymer composition in the PSA layer that constitutes the double-sided PSA sheet, the storage modulus G' and glass transition temperature of the PSA layer under two temperature conditions, and the 180° peel strength of the double-sided PSA sheet from a stainless steel plate. The present invention was completed based on these findings.

[0010] That is, the present invention provides a double-sided pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer, wherein the pressure-sensitive adhesive layer is an active energy ray-curable acrylic pressure-sensitive adhesive layer that contains an acrylic polymer as a base polymer, and the acrylic polymer contains 50 mass % or more of structural units derived from a (meth)acrylic acid alkyl ester (A) having a linear or branched alkyl group having 2 to 7 carbon atoms, and the pressure-sensitive adhesive layer has a glass transition temperature of 0°C or higher, a storage modulus G' at -20°C of 10 MPa or higher, and a storage modulus G' at 65°C of 0.05 MPa or higher, and a 180° peel strength from a stainless steel plate measured at 23°C with a 50 μm-thick polyethylene terephthalate film attached to one adhesive surface of the double-sided pressure-sensitive adhesive sheet of 20 N / 20 mm or higher.

[0011] The alkyl (meth)acrylate (A) preferably contains butyl (meth)acrylate, and the proportion of structural units derived from butyl (meth)acrylate in the acrylic polymer is preferably 50% by mass or more.

[0012] The acrylic polymer preferably contains a polyfunctional monomer as a monomer component constituting the polymer.

[0013] The acrylic polymer preferably has a structural portion derived from a photopolymerization initiator.

[0014] The acrylic polymer preferably contains a structural unit derived from a monomer component (B) having a non-aromatic ring and a glass transition temperature of the homopolymer of the polymer being 0° C. or higher.

[0015] The double-sided pressure-sensitive adhesive sheet is preferably used for fixing components together in an electric or electronic device.

[0016] The present invention also provides an electric / electronic device comprising the double-sided pressure-sensitive adhesive sheet, wherein both adhesive surfaces of the double-sided pressure-sensitive adhesive sheet fix components together.

[0017] The double-sided pressure-sensitive adhesive sheet of the present invention has excellent impact resistance, high shear adhesive strength, and excellent initial adhesiveness, and therefore, when used in, for example, portable electronic devices, it can sufficiently secure components to each other and is resistant to peeling even when subjected to a drop impact or when the adherend is deformed.

[0018] 1 is a cross-sectional view of a double-sided pressure-sensitive adhesive sheet according to an embodiment of the present invention. 2 is an explanatory view showing a method for measuring shear adhesive strength.

[0019] [Double-Sided Pressure-Sensitive Adhesive Sheet] The double-sided pressure-sensitive adhesive sheet of the present invention is a double-sided pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer, and is a so-called "substrate-less" double-sided pressure-sensitive adhesive sheet that does not have a substrate.

[0020] The pressure-sensitive adhesive layer is an active energy ray-curable acrylic pressure-sensitive adhesive layer containing an acrylic polymer as a base polymer, and has a glass transition temperature of 0°C or higher, a storage modulus G' of 10 MPa or higher at -20°C, and a storage modulus G' of 0.05 MPa or higher at 65°C. The acrylic polymer contained in the acrylic pressure-sensitive adhesive layer contains 50% by mass or more of structural units derived from a (meth)acrylic acid alkyl ester having a linear or branched alkyl group having 2 to 7 carbon atoms. In this specification, the pressure-sensitive adhesive layer may be referred to as the "pressure-sensitive adhesive layer of the present invention."

[0021] The pressure-sensitive adhesive layer constituting the double-sided pressure-sensitive adhesive sheet of the present invention may be a single layer or multiple layers. When the double-sided pressure-sensitive adhesive sheet of the present invention is composed of multiple pressure-sensitive adhesive layers, all of the multiple pressure-sensitive adhesive layers are the pressure-sensitive adhesive layer of the present invention. The multiple pressure-sensitive adhesive layers may be the same pressure-sensitive adhesive layer, or may be pressure-sensitive adhesive layers with different compositions, thicknesses, physical properties, etc.

[0022] Fig. 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 Fig. 1, the double-sided pressure-sensitive adhesive sheet 1 is composed of a single layer of the pressure-sensitive adhesive layer 2 of the present invention. Release liners 3 and 4 are bonded to the adhesive surfaces of the pressure-sensitive adhesive layer 2, respectively.

[0023] (Pressure-sensitive adhesive layer of the present invention) The pressure-sensitive adhesive layer of the present invention is an acrylic pressure-sensitive adhesive layer containing an acrylic polymer as a base polymer that exhibits adhesiveness. In this specification, the base polymer refers to a main component of the polymer components in the pressure-sensitive adhesive that constitutes the pressure-sensitive adhesive layer, for example, a polymer component that is contained in an amount of more than 50 mass %.

[0024] The proportion 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.

[0025] 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. Furthermore, the acrylic polymer may contain only one type of acrylic monomer as a monomer component, or two or more types. In this specification, "(meth)acrylic" represents "acrylic" and / or "methacrylic" (either one or both of "acrylic" and "methacrylic"), and the same applies to other terms.

[0026] The acrylic polymer is a polymer constructed (formed) using, as an essential monomer component, a (meth)acrylic acid alkyl ester (sometimes referred to as "(meth)acrylic acid alkyl ester (A)") having a linear or branched alkyl group having 2 to 7 carbon atoms. That is, the acrylic polymer contains the (meth)acrylic acid alkyl ester (A) as a structural unit. The acrylic polymer may contain only one type of (meth)acrylic acid alkyl ester (A) as a monomer component, or may contain two or more types.

[0027] The (meth)acrylic acid alkyl ester (A) is not particularly limited, but examples thereof include 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, etc. Among these, butyl (meth)acrylate is preferred from the viewpoint of selecting a lower storage modulus G'.

[0028] The proportion of (meth)acrylic acid alkyl ester (A) in the total amount (100% by mass) of all monomer components constituting the acrylic polymer is 50% by mass or more, preferably 60% by mass or more, more preferably 65% ​​by mass or more. By having the proportion of 50% by mass or more, it is possible to form a pressure-sensitive adhesive layer that has good adhesion even when it is thin. The proportion is preferably 94% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less. In addition, it is preferable that the proportion of butyl (meth)acrylate is within the above range.

[0029] The acrylic polymer is preferably a polymer constituted (formed) using, as monomer components, a (meth)acrylic acid alkyl ester (A) and a monomer component (sometimes referred to as "monomer component (B)") whose homopolymer glass transition temperature is 0° C. or higher and which has a non-aromatic ring. The acrylic polymer may contain only one type of monomer component (B) as the monomer component, or two or more types.

[0030] Examples of the non-aromatic ring include a non-aromatic hydrocarbon ring and a non-aromatic heterocycle. The non-aromatic ring may be saturated or unsaturated. Examples of the non-aromatic hydrocarbon ring include an aliphatic hydrocarbon ring, such as 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; or a bridged hydrocarbon ring such as a bicyclic hydrocarbon ring or a tricyclic or higher aliphatic hydrocarbon ring. Examples of the bicyclic hydrocarbon ring include a pinane ring, a pinene ring, a bornane ring, a norbornane ring, or a norbornene ring. Examples of the tricyclic or higher aliphatic hydrocarbon ring (a tricyclic or higher bridged hydrocarbon ring) include a dicyclopentane ring, a dicyclopentene ring, an adamantane ring, a tricyclopentane ring, and a tricyclopentene ring.

[0031] Examples of the non-aromatic heterocycle include an oxygen atom-containing heterocycle, a nitrogen atom-containing heterocycle, and a sulfur atom-containing heterocycle. Examples of the oxygen atom-containing heterocycle include an oxolane ring, an oxane ring, an oxole ring, a pyran ring, a caprolactone ring, a caprolactam ring, and a heterocycle containing an oxygen atom and a nitrogen atom. Examples of the nitrogen atom-containing heterocycle include an azolidine ring, an azinane ring, an azole ring, a piperidine ring, a caprolactam ring, a heterocycle containing an oxygen atom and a nitrogen atom, and a heterocycle containing a nitrogen atom and a sulfur atom. Examples of the sulfur atom-containing heterocycle include a thiolane ring, a thiol ring, and a heterocycle containing a nitrogen atom and a sulfur atom. Examples of the oxygen atom- and nitrogen atom-containing heterocycle include a morpholine ring. Examples of the nitrogen atom- and sulfur atom-containing heterocycle include a thiazine ring and a thiazole ring.

[0032] The number of atoms constituting the ring in the non-aromatic ring is preferably 5 to 12, more preferably 6 to 10. Furthermore, the monomer component (B) is preferably a monomer component having an active energy ray-polymerizable carbon-carbon double bond (e.g., a (meth)acryloyl group, a vinyl group, etc.) and a non-aromatic ring, such as a (meth)acrylic acid ester having a non-aromatic ring in the ester moiety, or a monomer component having a vinyl group and a non-aromatic heterocyclic ring. In the (meth)acrylic acid ester, the non-aromatic ring is preferably bonded directly to the (meth)acryloyl group or bonded to the (meth)acryloyl group via an oxygen atom or an oxyalkylene group. Among these, an aliphatic hydrocarbon ring or a nitrogen-containing heterocyclic ring is preferred as the non-aromatic ring.

[0033] Specific examples of the monomer component (B) in which the non-aromatic ring is an aliphatic hydrocarbon ring 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; and (meth)acrylic acid esters having a tricyclic or higher aliphatic hydrocarbon ring such as dicyclopentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, tricyclopentanyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate.

[0034] Specific examples of the monomer component (B) in which the non-aromatic ring is a nitrogen atom-containing heterocycle include N-(meth)acryloylmorpholine, N-vinyl-2-pyrrolidone, N-vinyl-2-piperidone, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholinedione, N-vinylpiperazine, N-vinylpyrazine, N-vinylmorpholine, N-vinylpyrazole, vinylpyrimidine, 2-vinyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, vinylpyridazine, (meth)acryloylpyrrolidone, (meth)acryloylpyrrolidine, and (meth)acryloylpiperidine.

[0035] The Tg of the homopolymer of monomer component (B) is 0°C or higher, preferably 10°C or higher, and more preferably 60°C or higher. When the Tg is 0°C or higher, the initial adhesiveness is excellent, while the storage modulus G' is high, and the impact resistance is excellent. From the viewpoint of excellent initial adhesiveness, the Tg is preferably 50°C or lower, and more preferably 20°C or lower.

[0036] In this specification, the "glass transition temperature (Tg) when a homopolymer is formed" (sometimes simply referred to as "Tg of the homopolymer") means 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 document refers to, for example, a value obtained by the following measurement method (see JP 2007-51271 A). That is, 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 are placed in a reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser, and the mixture is stirred for 1 hour while introducing nitrogen gas. After removing oxygen from the polymerization system in this way, the temperature is raised to 63°C and the reaction is carried out for 10 hours. The mixture was then cooled to room temperature to obtain a homopolymer solution with a solids concentration of 33% by mass. This homopolymer solution was then cast onto a release liner and dried to prepare a test sample (sheet-like homopolymer) with a thickness of approximately 2 mm. This test sample was then punched into a disk with a diameter of 7.9 mm, sandwiched between parallel plates, and its viscoelasticity was measured in shear mode using a viscoelasticity tester (product name "ARES", manufactured by Rheometrics) at a temperature range of -70 to 150°C and a heating rate of 5°C / min while applying a shear strain of 1 Hz. The peak top temperature of tan δ was taken as the Tg of the homopolymer.

[0037] The proportion of monomer component (B) in the total 100% by mass of all monomer components constituting the acrylic polymer is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more. When this proportion is 5% by mass or more, the storage modulus G' (particularly the storage modulus G' at -20°C) becomes high, and the proportion of monomer component (B) which has better impact resistance is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less. When this proportion is 60% by mass or less, flexibility is improved, and adhesion to adherends and shear adhesive strength can be improved.

[0038] The acrylic polymer may contain a copolymerizable monomer as a monomer component constituting the polymer, in addition to the (meth)acrylic acid alkyl ester (A) and the monomer component (B). 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.

[0039] 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 with good adhesion, and also improving cohesion and impact resistance. 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.

[0040] 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 10% by mass or less. When the proportion is within the above range, the (meth)acrylic acid alkyl ester (A) and the monomer component (B) are well balanced in quantity, and a pressure-sensitive adhesive layer having excellent impact resistance and good adhesion even when thin can be formed.

[0041] 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, nitrogen atom-containing monomers (excluding those corresponding to the monomer component (B)), keto group-containing monomers, alkoxysilyl group-containing monomers, sulfonic acid group-containing monomers, and phosphoric acid group-containing monomers. The functional group-containing monomers may be used alone or in combination of two or more.

[0042] 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.

[0043] Examples of the nitrogen atom-containing monomer include amide group-containing monomers, amino group-containing monomers, and cyano group-containing monomers. 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.

[0044] 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.

[0045] Examples of the alkoxysilyl group-containing monomer include 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, and 3-(meth)acryloxypropylmethyldiethoxysilane.

[0046] 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.

[0047] The phosphate group-containing monomer may, for example, be 2-hydroxyethyl acryloyl phosphate.

[0048] The proportion of the functional group-containing monomer in the total 100% by mass of all monomer components constituting the acrylic polymer 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" means that the monomer is unintentionally included, such as when it is unavoidably mixed in rather than being actively mixed in, and is, for example, 0.05% by mass or less, 0.01% by mass or less.

[0049] The copolymerizable monomer may further contain other monomers. Examples of the other monomers include vinyl ester-based monomers such as vinyl acetate, vinyl propionate, and vinyl laurate; aromatic vinyl compounds such as styrene, substituted styrene (α-methylstyrene, etc.), and vinyltoluene; olefin-based 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; vinyl ether-based monomers such as methyl vinyl ether and ethyl vinyl ether; methyl (meth)acrylate; octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, and (meth)acrylic acid. and (meth)acrylic acid alkyl esters having a linear or branched alkyl group having 8 to 20 carbon atoms, such as 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; and (meth)acrylic acid esters having an aromatic ring, 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.

[0050] The proportion of the other monomers in the total amount (100% by mass) of all monomer components constituting the acrylic polymer 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.

[0051] The acrylic polymer may contain a polyfunctional monomer copolymerizable with the monomer components forming the acrylic polymer as a monomer component constituting the polymer in order to form a crosslinked structure in the polymer skeleton. 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)acrylate (e.g., polyglycidyl (meth)acrylate), polyester (meth)acrylate, and urethane (meth)acrylate. The polyfunctional monomer may be used alone or in combination of two or more.

[0052] The proportion of the polyfunctional monomer in the total amount (100% by mass) of all monomer components constituting the acrylic polymer is preferably 0.05% by mass or more, more preferably 0.07% by mass or more, and even more preferably 0.10% by mass or more. The proportion may be 5% by mass or less, 3% by mass or less, or may be substantially zero.

[0053] The acrylic polymer preferably has a structural part derived from a photopolymerization initiator.The acrylic polymer has a structural part derived from a photopolymerization initiator, which means that the acrylic polymer and the pressure-sensitive adhesive layer of the present invention are polymerized by active energy ray irradiation or a cured pressure-sensitive adhesive layer.The photopolymerization initiator may be one described later.

[0054] The acrylic polymer is preferably a polymerization reaction product obtained by polymerizing a composition containing one or more selected from the group consisting of an acrylic partial polymer, an acrylic oligomer, and a monomer component. In the case of a polymerization reaction product obtained by polymerizing a composition consisting only of a monomer component, the monomer component contains at least an acrylic monomer. The "partial polymer" may also be referred to as a "prepolymer," "syrup," etc. Only one type of acrylic partial polymer, acrylic oligomer, and monomer component may be used, or two or more types may be used. The monomer component that may be contained in the composition may also be referred to as "monomer component (C)."

[0055] The acrylic polymer is preferably a polymerization reaction product of a composition containing an acrylic partial polymer, and particularly preferably a polymerization reaction product of a composition containing an acrylic partial polymer and monomer component (C).When the acrylic polymer is a polymerization reaction product of a composition containing an acrylic partial polymer and monomer component (C), it is presumed that this is because the monomer component (C) forms a low-molecular-weight polymer in the pressure-sensitive adhesive layer of the present invention, and a double-sided pressure-sensitive adhesive sheet with particularly excellent initial adhesiveness can be easily produced.

[0056] The acrylic partial polymer and the acrylic oligomer are both compounds constituted by an acrylic monomer as an essential monomer component. Examples of the monomer components constituting the acrylic partial polymer and the acrylic oligomer, as well as the monomer component (C), include those exemplified and explained above as the monomer components constituting the acrylic polymer.

[0057] Unlike fully polymerized acrylic polymers, the partially polymerized acrylic polymers are obtained by polymerizing the monomer components 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.

[0058] The acrylic partial polymer contains an acrylic monomer as a constituent unit. The acrylic partial polymer preferably contains a (meth)acrylic acid alkyl ester (A) as a constituent unit. The (meth)acrylic acid alkyl ester (A) is preferably butyl (meth)acrylate. The (meth)acrylic acid alkyl ester (A) contained as the constituent unit may be one type or two or more types.

[0059] The proportion of the (meth)acrylic acid alkyl ester (A) in the total amount (100% by mass) of all monomer components constituting the acrylic partial polymer is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 65% ​​by mass or more, and is preferably 94% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less.

[0060] The acrylic partially polymerized product preferably contains a monomer component (B) as a structural unit. The monomer component (B) contained as the structural unit may be one type or two or more types.

[0061] The proportion of monomer component (B) in the total 100% by mass of all monomer components constituting the acrylic partially polymerized product is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more. When the proportion is 5% by mass or more, the storage modulus G' (particularly the storage modulus G' at -20°C) becomes high, resulting in better impact resistance. The proportion of monomer component (B) is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less. When the proportion is 60% by mass or less, flexibility is improved, and adhesion to adherends and shear adhesive strength can be further improved.

[0062] The acrylic partial polymer may contain the copolymerizable monomer as a constituent unit. Among these, the copolymerizable monomer is preferably a carboxy group-containing monomer and / or an acid anhydride monomer, from the viewpoints of improving cohesive strength and providing more excellent impact resistance, and of being able to form a pressure-sensitive adhesive layer that has good adhesion even when thin.

[0063] 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 partially polymerized product 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, and is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 11% by mass or less.

[0064] The acrylic polymer may be a polymerization reaction product of a composition containing an acrylic partial polymer and an acrylic oligomer, in which case the storage modulus G' at -20°C is further improved.

[0065] The weight-average molecular weight of the acrylic oligomer is preferably 2,500 to 10,000, and more preferably 3,000 to 8,000. The weight-average molecular weight can be determined in polystyrene equivalent terms by GPC. For example, it can be measured using a high-speed GPC device "HPLC-8120GPC" manufactured by Tosoh Corporation under the following conditions: Column: TSKgel Super HZM-H / HZ4000 / HZ3000 / HZ2000 Solvent: Tetrahydrofuran Flow rate: 0.6 ml / min

[0066] The acrylic oligomer contains an acrylic monomer as a constituent unit. The acrylic oligomer preferably contains a monomer component (B) as a constituent unit. The monomer component contained as the constituent unit may be one type or two or more types.

[0067] The proportion of the monomer component (B) in the total amount (100% by mass) of all the monomer components constituting the acrylic oligomer is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 55% by mass or more, and is preferably 90% by mass or less, more preferably 80% by mass or less.

[0068] The acrylic oligomer preferably contains methyl methacrylate (MMA) as a structural unit. The proportion of methyl methacrylate in all monomer components constituting the acrylic oligomer is preferably 10% by mass or more, more preferably 20% by mass or more. The proportion is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 45% by mass or less. The acrylic oligomer may also contain the copolymerizable monomer as a structural unit.

[0069] The content of the acrylic oligomer is preferably 0.5 to 35 parts by mass, more preferably 2 to 20 parts by mass, and even more preferably 4 to 10 parts by mass, relative to 100 parts by mass of the total amount of the acrylic partial polymer. When the content is within the above range, the storage modulus G' at -20°C tends to be high.

[0070] Examples of the monomer component (C) include those exemplified and explained as monomer components that the above-mentioned acrylic polymer may contain as a structural unit. The monomer component (C) preferably contains a monomer copolymerizable with the monomer component (B) and / or the monomer component that forms the above-mentioned acrylic partial polymer. Examples of the copolymerizable monomer include the above-mentioned copolymerizable monomer.

[0071] When the monomer component (C) contains the monomer component (B), the proportion of the monomer component (B) in the monomer component (C) is preferably 60% by mass or more, more preferably 70% by mass or more.

[0072] Among the monomers copolymerizable with the monomer component that forms the acrylic partial polymer, from the viewpoint of being able to form a thin pressure-sensitive adhesive layer that has good adhesion, a carboxy group-containing monomer and / or an acid anhydride monomer are preferred. When the monomer component (C) contains the copolymerizable monomer, the proportion of the copolymerizable monomer in the monomer component (C) is not particularly limited, but is preferably 5% by mass or more, more preferably 10% by mass or more.

[0073] When the monomer component (C) contains the monomer component (B) and the copolymerizable monomer, the proportion of the monomer component (B) in the monomer component (C) is preferably 60 to 95% by mass, more preferably 70 to 90% by mass. In the above case, the proportion of the copolymerizable monomer in the monomer component (C) is not particularly limited, but is preferably 5 to 40% by mass, more preferably 10 to 30% by mass.

[0074] The content of the monomer component (C) is preferably 1 to 30 parts by mass, more preferably 10 to 20 parts by mass, per 100 parts by mass of the total amount of the acrylic partially polymerized product. When the content is within the above range, the initial adhesive strength is further improved. In addition, the storage modulus G' is further improved, and the shear adhesive strength is further increased.

[0075] The acrylic partial polymer and the acrylic oligomer are obtained by polymerizing a monomer component. The acrylic polymer is obtained by polymerizing a composition containing one or more selected from the group consisting of the acrylic partial polymer, the acrylic oligomer, and the monomer component (C). The polymerization method is not particularly limited, but examples thereof include solution polymerization, emulsion polymerization, bulk polymerization, thermal polymerization, and polymerization by active energy ray irradiation (active energy ray polymerization). Among these, the bulk polymerization, thermal polymerization, and active energy ray polymerization are preferred in terms of the transparency of the pressure-sensitive adhesive layer, cost, etc.

[0076] Furthermore, various common solvents may be used when polymerizing the above-mentioned monomer components, etc. Examples of the solvent include organic solvents such as esters such as ethyl acetate and n-butyl acetate; aromatic hydrocarbons such as toluene and benzene; aliphatic hydrocarbons such as n-hexane and n-heptane; alicyclic hydrocarbons such as cyclohexane and methylcyclohexane; and ketones such as methyl ethyl ketone and methyl isobutyl ketone. Note that only one type of solvent may be used, or two or more types may be used.

[0077] 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. Only one type of polymerization initiator may be used, or two or more types may be used.

[0078] 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, 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.

[0079] 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-hydroxycyclohexyl phenyl 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 benzyl. 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 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 from 0.1 to 1.5 parts by mass, per 100 parts by mass of the monomer component.

[0080] The pressure-sensitive adhesive layer of the present invention preferably further contains a filler. By incorporating a filler, it becomes easy to adjust the storage modulus G' at -20°C and 65°C. Only one type of filler may be used, or two or more types may be used.

[0081] The shape of the filler is not particularly limited, and particulate or fibrous fillers can be used. Particulate fillers are preferred. The filler may be either organic or inorganic.

[0082] Examples of materials constituting the inorganic substance 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. carbides such as silicon carbide, boron carbide, nitrogen carbide, calcium carbide; nitrides such as aluminum nitride, silicon nitride, boron nitride, gallium nitride; carbonates such as calcium carbonate; titanates such as barium titanate, potassium titanate; carbon-based substances such as carbon black, carbon tubes (carbon nanotubes), carbon fiber, diamond; inorganic materials such as glass; and natural raw material particles such as volcanic silt, clay, and sand.

[0083] Examples of materials constituting 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.

[0084] The filler may have a hollow structure. The hollow portion (the space inside the hollow particle) of the filler having the hollow structure may be in a vacuum state or may be filled with a medium. Examples of the medium include an inert gas such as nitrogen or argon, air, and a volatile solvent.

[0085] Among the fillers, fillers whose surfaces are composed of organic or inorganic materials other than acrylic resins and fillers having a hollow structure are preferred. These fillers have little interaction with the acrylic component in the acrylic pressure-sensitive adhesive layer or have a hollow structure, so they are less likely to break when the pressure-sensitive adhesive layer is stretched and have excellent releasability (reworkability) when peeling off the double-sided pressure-sensitive adhesive sheet after it has been stuck to an adherend.

[0086] The particulate filler has an average particle size of, for example, 0.5 to 80 μm, preferably 1 to 40 μm. When the average particle size is within the above range, the pressure-sensitive adhesive layer can have an appropriate hardness. The average particle size is the median diameter (D50) measured by dynamic light scattering.

[0087] The proportion of the filler in the pressure-sensitive adhesive layer of the present invention is preferably 0.5 to 10% by mass, more preferably 1 to 5% by mass, relative to 100% by mass of the total amount of the pressure-sensitive adhesive layer. When the proportion is within the above range, the pressure-sensitive adhesive layer can have an appropriate hardness. In addition, the pressure-sensitive adhesive layer has excellent reworkability.

[0088] The pressure-sensitive adhesive layer of the present invention may contain a colorant. The inclusion of a colorant colors the pressure-sensitive adhesive layer, and the double-sided pressure-sensitive adhesive sheet of the present invention exhibits excellent visibility and design. The colorant may be a pigment or a dye. Examples of colorants include black colorants, cyan colorants, magenta colorants, and yellow colorants. From the viewpoint of superior visibility and design, black colorants are preferred. The pressure-sensitive adhesive layer may contain only one type of colorant, or two or more types. The content of the colorant in the pressure-sensitive adhesive layer of the present invention is preferably 0.05 to 5% by mass, and more preferably 0.1 to 2% by mass, relative to 100% by mass of the total amount of the pressure-sensitive adhesive layer.

[0089] Examples of black colorants include carbon black, carbon nanotubes, graphite, copper oxide, manganese dioxide, azo pigments such as azomethine azo black, aniline black, perylene black, titanium black, cyanine black, activated carbon, ferrite, magnetite, chromium oxide, iron oxide, molybdenum disulfide, complex oxide black pigments, anthraquinone organic black dyes, and azo organic black dyes. Examples of carbon black include furnace black, channel black, acetylene black, thermal black, and lamp black. Examples of black colorants include C.I. Solvent Black 3, 7, 22, 27, 29, 34, 43, and 70; C.I. Direct Black 17, 19, 22, 32, 38, 51, and 71; C.I. Acid Black 1, 2, 24, 26, 31, 48, 52, 107, 109, 110, 119, 154; C.I. Disperse Black 1, 3, 10, 24; C.I. Pigment Black 1, 7, and the like.

[0090] Examples of cyan colorants include C.I. Solvent Blue 25, 36, 60, 70, 93, and 95; C.I. Acid Blue 6 and 45; C.I. Pigment Blue 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:4, 15:5, 15:6, 16, 17, 17:1, 18, 22, 25, 56, 60, 63, 65, and 66; C.I. Bat Blue 4; 60, and C.I. Pigment Green 7.

[0091] Examples of magenta colorants include C.I. Solvent Red 1, 3, 8, 23, 24, 25, 27, 30, 49, 52, 58, 63, 81, 82, 83, 84, 100, 109, 111, 121, and 122; C.I. Disperse Red 9; C.I. Solvent Violet 8, 13, 14, 21, and 27; C.I. Disperse Violet 1; C.I. C.I. Basic Red 1, 2, 9, 12, 13, 14, 15, 17, 18, 22, 23, 24, 27, 29, 32, 34, 35, 36, 37, 38, 39, 40; C.I. Basic Violet 1, 3, 7, 10, 14, 15, 21, 25, 26, 27, 28, etc. Examples of magenta colorants include, for example, C.I. Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 21, 22, 23, 30, 31, 32, 37, 38, 39, 40, 41, 42, 48:1, 48:2, 48:3, 48:4, 49, 49:1, 50, 51, 52, 52:2, 53:1, 54, 55, 56, 57:1, 58, 60, 60:1, 63, 63:1, 63:2, 64, 64:1, 6 C.I.7, 68, 81, 83, 87, 88, 89, 90, 92, 101, 104, 105, 106, 108, 112, 114, 122, 123, 139, 144, 146, 147, 149, 150, 151, 163, 166, 168, 170, 171, 172, 175, 176, 177, 178, 179, 184, 185, 187, 190, 193, 202, 206, 207, 209, 219, 222, 224, 238, 245; C.I. Pigment Violet 3, 9, 19, 23, 31, 32, 33, 36, 38, 43, and 50; C.I. Bat Red 1, 2, 10, 13, 15, 23, 29, and 35.

[0092] Examples of yellow colorants include C.I. Solvent Yellow 19, 44, 77, 79, 81, 82, 93, 98, 103, 104, 112, and 162; C.I. Pigment Orange 31 and 43; C.I. Pigment Yellow 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 15, 16, 17, 23, 24, 34, 35, 37, 42, 53, 55, 65, 73, 74, 75, 81, 83, 93, 94, 95, 97, 98, and 100, C.I. Bat Yellow 1, 3, 20, and the like.

[0093] The pressure-sensitive adhesive layer of the present invention may further contain, as necessary, additives such as crosslinking agents, crosslinking accelerators, antiaging agents, 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.

[0094] As described above, the pressure-sensitive adhesive layer of the present invention has a storage modulus G' at -20°C of 10 MPa or more, preferably 50 MPa or more, more preferably 100 MPa or more, even more preferably 200 MPa or more, and particularly preferably 300 MPa or more. The storage modulus G' at -20°C is a property of the pressure-sensitive adhesive layer at low temperatures and can be expressed as the property when subjected to an impact at a relatively high speed. Such a storage modulus G' at a temperature as low as -20°C of 10 MPa or more provides excellent impact resistance, for example, when a member to which the double-sided pressure-sensitive adhesive sheet is applied is dropped at high speed. The storage modulus G' can be calculated using a dynamic mechanical analysis (DMA) device.

[0095] As described above, the pressure-sensitive adhesive layer of the present invention has a storage modulus G' at 65°C of 0.05 MPa or more, preferably 0.06 MPa or more, more preferably 0.08 MPa or more, and even more preferably 0.10 MPa or more. The storage modulus G' at 65°C is a property of the pressure-sensitive adhesive layer at relatively high temperatures and can be expressed as the property when subjected to a low-speed impact. When the storage modulus G' at 65°C is 0.05 MPa or more, the pressure-sensitive adhesive layer of the present invention has high shear adhesive strength. The storage modulus G' can be calculated using a dynamic mechanical analysis (DMA) device.

[0096] The pressure-sensitive adhesive layer of the present invention preferably has a storage modulus G' at 23°C of 0.10 MPa or more, more preferably 0.21 MPa or more, and even more preferably 0.25 MPa or more. When the storage modulus G' at 23°C is 0.10 MPa or more, the pressure-sensitive adhesive layer has appropriate hardness at room temperature and excellent reworkability. The storage modulus G' can be calculated using a dynamic mechanical analysis (DMA) device.

[0097] The pressure-sensitive adhesive layer of the present invention has a glass transition temperature (Tg) of 0°C or higher, preferably 2°C or higher, and more preferably 5°C or higher. When the Tg is 0°C or higher, the storage modulus G' is high and the impact resistance is excellent. The Tg is, for example, 50°C or lower. The Tg can be calculated using a dynamic mechanical analysis (DMA) device.

[0098] The pressure-sensitive adhesive layer of the present invention preferably has a peak top value of tan δ of 0.5 or more, more preferably 1.0 or more, and even more preferably 1.5 or more. When the peak top value of tan δ is 0.5 or more, the impact resistance is more excellent. The tan δ can be calculated using a dynamic mechanical analysis (DMA) device.

[0099] The pressure-sensitive adhesive layer of the present invention is an active energy ray-curable pressure-sensitive adhesive layer. That is, the pressure-sensitive adhesive layer of the present invention is a pressure-sensitive adhesive layer formed from an active energy ray-curable pressure-sensitive adhesive composition. This allows the double-sided pressure-sensitive adhesive sheet of the present invention to have dense crosslinks, resulting in a high-strength pressure-sensitive adhesive, excellent impact resistance, and high shear adhesive strength.

[0100] 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 layer is preferably an ultraviolet-curable pressure-sensitive adhesive layer.

[0101] The pressure-sensitive adhesive layer of the present invention can be produced, for example, by applying (coating) the pressure-sensitive adhesive composition onto a release liner, drying and solidifying the composition by volatilizing the solvent by heating or the like as necessary, and curing the resulting pressure-sensitive adhesive composition layer by irradiating it with active energy rays. If necessary, the composition may be further dried by heating.

[0102] Examples of the pressure-sensitive adhesive composition (acrylic pressure-sensitive adhesive composition) that forms the pressure-sensitive adhesive layer of the present invention include an acrylic pressure-sensitive adhesive composition containing, as an essential component, the above-mentioned acrylic partial polymer, the above-mentioned acrylic oligomer, or a monomer mixture containing monomer component (C).

[0103] From the viewpoint of achieving superior initial adhesiveness, the pressure-sensitive adhesive composition preferably contains at least a partial polymer of a monomer mixture containing a (meth)acrylic acid alkyl ester (A) and a monomer component (B), a monomer component (C), a polyfunctional monomer, and a photopolymerization initiator. In addition, the pressure-sensitive adhesive composition may contain an acrylic oligomer, a filler, a colorant, etc.

[0104] (Double-Sided Pressure-Sensitive Adhesive Sheet) The double-sided pressure-sensitive adhesive sheet of the present invention is composed of the pressure-sensitive adhesive layer of the present invention. The thickness of the double-sided pressure-sensitive adhesive sheet is preferably 50 to 500 μm, more preferably 100 to 300 μm. A thickness of 50 μm or more provides excellent adhesion and conformability to the adherend. A thickness of 500 μm or less allows the double-sided pressure-sensitive adhesive sheet to 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.

[0105] The double-sided pressure-sensitive adhesive sheet of the present invention, with a 50 μm-thick polyethylene terephthalate (PET) film attached to one adhesive surface, has a 180° peel strength against a stainless steel plate, measured at 23°C, of ​​20 N / 20 mm or more, preferably 25 N / 20 mm or more, and more preferably 30 N / 20 mm or more. A peel strength of 20 N / 20 mm or more provides excellent initial adhesion, enabling the sheet to sufficiently secure components together when used, for example, to bond components together in electrical and electronic devices. The peel strength is, for example, 50 N / 20 mm or less. It is preferable that the 180° peel strength of at least one adhesive surface of the double-sided pressure-sensitive adhesive sheet of the present invention is within the above range, and it is more preferable that the 180° peel strength of both adhesive surfaces is within the above range. When a release liner is attached to the double-sided pressure-sensitive adhesive sheet of the present invention, the peel strength is a value measured with the release liner peeled off, and detailed methods are as shown in the examples.

[0106] The double-sided pressure-sensitive adhesive sheet of the present invention is sandwiched between two stainless steel plates, both adhesive surfaces of which are bonded together, and measured at a tensile speed of 10 mm / min and a peel angle of 0°. When the shear adhesive strength to one of the stainless steel plates is measured, it is preferably 1.0 MPa or more, more preferably 1.3 MPa or more, and more preferably 1.5 MPa or more. A shear adhesive strength of 1.0 MPa or more provides excellent adhesion when bonded to an adherend. From the viewpoint of excellent reworkability, the shear adhesive strength is preferably 10 MPa or less, more preferably 5.0 MPa or less, and even more preferably 3.0 MPa or less. When a release liner is bonded to the double-sided pressure-sensitive adhesive sheet of the present invention, the peel strength is a value measured with the release liner peeled off; detailed methods are as shown in the examples.

[0107] The energy (load x height) of the double-sided pressure-sensitive adhesive sheet of the present invention before one of the stainless steel plates peels off, as measured by the DuPont impact test described below, is preferably 0.3 or more, more preferably 0.4 or more. <Impact Resistance Test> A frame-shaped double-sided pressure-sensitive adhesive sheet measuring 24.5 mm square in outer diameter and 2 mm wide is sandwiched and pressed between a 2 mm thick, 50 mm square stainless steel plate with a hole in the center and a 3 mm thick, 25 mm square stainless steel plate, and left to stand in an environment at 50°C for 2 hours, and then returned to room temperature to obtain an evaluation sample. Using a DuPont impact tester, the weight and height of the drop weight on the evaluation sample were changed in 50 mm increments from 50 to 500 mm at 100 g, in 50 mm increments from 350 to 500 mm at 150 g, in 50 mm increments from 400 to 500 mm at 200 g, and in 50 mm increments from 350 to 500 mm at 300 g, increasing the energy until peeling occurred. At this time, the energy already evaluated was not tested, and the load and height were set so that the amount of energy did not overlap. The energy until at least one of the stainless steel plates peeled off was then calculated using the formula: load x height.

[0108] The double-sided PSA sheet may have a release liner attached to the surface (adhesive surface) of the PSA layer until use. Each adhesive surface of the double-sided PSA 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 PSA layer and is peeled off when the sheet is attached to the adherend. The release liner is not necessarily provided.

[0109] 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 silicone-based, long-chain alkyl-based, fluorine-based, and molybdenum sulfide-based release agents. 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-based 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.

[0110] The double-sided PSA sheet is preferably used for attaching electrical and electronic components by being attached to components included in electrical and electronic devices. The double-sided PSA sheet is particularly preferably used for applications in which components included in electrical and electronic devices are attached to each of the two adhesive surfaces of the double-sided PSA sheet, i.e., for fixing components to each other in electrical and electronic devices. The double-sided PSA sheet may be used for either fixing or temporarily fixing the components to each other. For example, when a double-sided PSA sheet is used to fix or temporarily fix components included in electrical and electronic devices, there may be cases where the double-sided PSA sheet needs to be peeled off and reworked due to a malfunction in the application of the double-sided PSA sheet, or there may be cases where the double-sided PSA sheet needs to be peeled off to repair, replace, inspect, recycle, or the like of a component including an adherend to which the double-sided PSA sheet is attached. Thus, when a double-sided PSA sheet is used to fix or temporarily fix components included in electrical and electronic devices, for example, the double-sided PSA sheet needs to be removed frequently.

[0111] The double-sided pressure-sensitive adhesive sheet is preferably used to bond the outer frames of optical components (particularly electrical and electronic devices) together, and therefore the double-sided pressure-sensitive adhesive sheet can be preferably used even if it has a width of 5 mm or less, preferably 3 mm or less.

[0112] 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.

[0113] 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 PSA layer adheres to components of the portable electronic device.

[0114] 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.

[0115] Production Example 1 Synthesis of Syrup (1) A liquid monomer mixture (monomer composition) containing 70 parts by mass of butyl acrylate (BA), 7 parts by mass of acrylic acid (AA), and 23 parts by mass of isobornyl acrylate (IBXA, Tg: 97°C) as monomer components was blended with 0.05 parts by mass of 2,2-dimethoxy-1,2-diphenylethan-1-one (trade name "OMNIRAD651", manufactured by IGM Resins B.V.) as a photopolymerization initiator, and the mixture was then irradiated with pulsed ultraviolet light until the viscosity (BH viscometer No. 5 rotor, 10 rpm, measurement temperature: 30°C) reached about 15 Pa s, thereby obtaining a syrup (partially polymerized product) containing a partial polymer in which a portion of the monomer components had polymerized (polymerization rate: about 8%).

[0116] Production Example 2: Synthesis of syrup (2) A liquid monomer mixture (monomer composition) containing 70 parts by mass of butyl acrylate (BA), 7 parts by mass of acrylic acid (AA), and 23 parts by mass of dicyclopentanyl acrylate (DCPA, Tg: approximately 100°C) as monomer components was blended with 0.05 parts by mass of 2,2-dimethoxy-1,2-diphenylethan-1-one (trade name "OMNIRAD651", manufactured by IGM Resins B.V.) as a photopolymerization initiator, and 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, thereby obtaining a syrup (partially polymerized product) containing a partial polymer (polymerization rate: approximately 8%) in which a portion of the monomer components had polymerized.

[0117] Production Example 3 Synthesis of Syrup (3) A liquid monomer mixture (monomer composition) containing 78 parts by mass of butyl acrylate (BA), 7 parts by mass of acrylic acid (AA), and 15 parts by mass of acryloylmorpholine (ACMO, Tg: approximately 145°C) as monomer components was blended with 0.05 parts by mass of 2,2-dimethoxy-1,2-diphenylethan-1-one (trade name "OMNIRAD651", manufactured by IGM Resins B.V.) as a photopolymerization initiator, and 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, thereby obtaining a syrup (partially polymerized product) containing a partial polymer in which a portion of the monomer components had polymerized (polymerization rate: approximately 8%).

[0118] Production Example 4 Synthesis of Syrup (4) A liquid monomer mixture (monomer composition) containing 70 parts by mass of butyl acrylate (BA), 7 parts by mass of acrylic acid (AA), and 23 parts by mass of cyclohexyl acrylate (CHA, Tg: 15°C) as monomer components was blended with 0.05 parts by mass of 2,2-dimethoxy-1,2-diphenylethan-1-one (trade name "OMNIRAD651", manufactured by IGM Resins B.V.) as a photopolymerization initiator, and the mixture was then irradiated with pulsed ultraviolet light until the viscosity (BH viscometer No. 5 rotor, 10 rpm, measurement temperature: 30°C) reached about 15 Pa s, thereby obtaining a syrup (partially polymerized product) containing a partial polymer in which a portion of the monomer components had polymerized (polymerization rate: about 8%).

[0119] Example 1 100 parts by mass of the syrup (1) obtained in Production Example 1, 13 parts by mass of cyclohexyl acrylate (CHA), 2 parts by mass of acrylic acid (AA), 0.2 parts by mass of a black pigment containing carbon black (trade name "Multilac A903" manufactured by Toyocolor Co., Ltd.), 2 parts by mass of polyethylene powder (trade name "Flothane UF-80" manufactured by Sumitomo Seika Chemicals Co., Ltd.) as a filler, 0.12 parts by mass of 1,6-hexanediol diacrylate (HDDA), and 0.1 part by mass of 2,2-dimethoxy-1,2-diphenylethan-1-one (trade name "OMNIRAD651" manufactured by IGM Resins B.V.) as a photopolymerization initiator were blended and then uniformly mixed using a disper, followed by degassing to obtain an acrylic pressure-sensitive adhesive composition.

[0120] 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) one side of which had been subjected to a release treatment with silicone, so that the pressure-sensitive adhesive layer had a thickness of 200 μm, thereby forming a coating layer.

[0121] 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, thereby blocking 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 sheet 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 form a 200 μm thick adhesive layer, thereby producing a double-sided adhesive sheet.

[0122] Example 2 A double-sided PSA sheet of Example 2 was produced in the same manner as in Example 1, except that the syrup (2) obtained in Production Example 2 was used instead of the syrup (1) obtained in Production Example 1.

[0123] Example 3 100 parts by mass of the syrup (2) obtained in Production Example 2, 2 parts by mass of acrylic acid (AA), 0.2 parts by mass of a black pigment containing carbon black (trade name "Multilac A903", manufactured by Toyocolor Co., Ltd.), 2 parts by mass of polyethylene powder (trade name "Flothane UF-80", manufactured by Sumitomo Seika Chemicals Co., Ltd.) as a filler, 0.12 parts by mass of 1,6-hexanediol diacrylate (HDDA), and 0.1 part by mass of 2,2-dimethoxy-1,2-diphenylethan-1-one (trade name "OMNIRAD651", manufactured by IGM Resins B.V.) as a photopolymerization initiator were blended and then uniformly mixed using a disper, followed by degassing to obtain an acrylic pressure-sensitive adhesive composition.

[0124] A double-sided PSA sheet of Example 3 was produced in the same manner as in Example 1, except that the acrylic PSA composition obtained above was used.

[0125] Example 4 100 parts by mass of the syrup (2) obtained in Production Example 2, 20 parts by mass of cyclohexyl acrylate (CHA), 0.2 parts by mass of a black pigment containing carbon black (trade name "Multilac A903", manufactured by Toyocolor Co., Ltd.), 2 parts by mass of polyethylene powder (trade name "Flothane UF-80", manufactured by Sumitomo Seika Chemicals Co., Ltd.) as a filler, 0.12 parts by mass of 1,6-hexanediol diacrylate (HDDA), and 0.1 part by mass of 2,2-dimethoxy-1,2-diphenylethan-1-one (trade name "OMNIRAD651", manufactured by IGM Resins B.V.) as a photopolymerization initiator were blended and then uniformly mixed using a disper, followed by degassing to obtain an acrylic pressure-sensitive adhesive composition.

[0126] A double-sided PSA sheet of Example 4 was produced in the same manner as in Example 1, except that the acrylic PSA composition obtained above was used.

[0127] Example 5 A double-sided PSA sheet of Example 5 was produced in the same manner as in Example 1, except that the syrup (3) obtained in Production Example 3 was used instead of the syrup (1) obtained in Production Example 1.

[0128] Example 6 A double-sided PSA sheet of Example 6 was produced in the same manner as in Example 1, except that 2 parts by mass of silicone rubber particles (product name "Trefil E-606", manufactured by Toray Industries, Inc.) were used as the filler.

[0129] Example 7 A double-sided PSA sheet of Example 7 was produced in the same manner as Example 1, except that 2 parts by mass of polyethylene particles (product name "Flow Beads FBRP", manufactured by Sumitomo Seika Chemicals Co., Ltd.) was used as the filler.

[0130] Comparative Example 1 100 parts by mass of the syrup (2) obtained in Production Example 2, 0.2 parts by mass of a black pigment containing carbon black (trade name "Multilac A903" manufactured by Toyocolor Co., Ltd.), 2 parts by mass of polyethylene powder (trade name "Flothane UF-80" manufactured by Sumitomo Seika Chemicals Co., Ltd.) as a filler, 0.12 parts by mass of 1,6-hexanediol diacrylate (HDDA), and 0.1 part by mass of 2,2-dimethoxy-1,2-diphenylethan-1-one (trade name "OMNIRAD651" manufactured by IGM Resins B.V.) as a photopolymerization initiator were blended and then mixed uniformly using a disper, followed by degassing to obtain an acrylic pressure-sensitive adhesive composition.

[0131] A double-sided PSA sheet of Comparative Example 1 was produced in the same manner as in Example 1, except that the acrylic PSA composition obtained above was used.

[0132] Comparative Example 2 A double-sided PSA sheet of Comparative Example 2 was prepared in the same manner as in Comparative Example 1, except that the amount of 2,2-dimethoxy-1,2-diphenylethan-1-one (trade name "OMNIRAD651", manufactured by IGM Resins B.V.) blended as a photopolymerization initiator was set to 0.05 parts by mass.

[0133] Comparative Example 3 A double-sided PSA sheet of Comparative Example 3 was produced in the same manner as Comparative Example 1, except that the syrup (4) obtained in Production Example 4 was used instead of the syrup (2) obtained in Production Example 2.

[0134] <Evaluation> The double-sided PSA sheets obtained in the examples and comparative examples were evaluated as follows. The results are shown in the table below. The blend amount of each component in the table is shown in parts by mass.

[0135] (1) Dynamic Viscoelasticity Measurement A pressure-sensitive adhesive layer approximately 2 mm thick was prepared by stacking multiple double-sided pressure-sensitive adhesive sheets prepared in the Examples and Comparative Examples. A sample was punched out from this pressure-sensitive adhesive layer into a disk shape with a diameter of 7.9 mm, and sandwiched and fixed between parallel plates. Dynamic viscoelasticity measurement was performed under the following conditions using a viscoelasticity tester (trade name "ARES Rheometer", manufactured by T.A. Instruments) in an environment of 23°C and 50% RH, and the storage modulus G' (-20°C), storage modulus G' (23°C), storage modulus G' (65°C), glass transition temperature, and peak top value of tan δ were calculated. Measurement mode: Shear mode Temperature range: -70°C to 150°C Heating rate: 5°C / min Measurement frequency: 1 Hz

[0136] (2) Shear Adhesion Strength Measurement samples were prepared by cutting the double-sided PSA sheets prepared in the Examples and Comparative Examples to a size of 20 mm x 20 mm. In an environment of 23°C and 50% RH, each adhesive surface of the measurement sample was placed on the surface of two stainless steel plates, and a 2 kg roller was rolled back and forth once to press the sheets together. After leaving the sheets in the same environment for 30 minutes, the shear adhesion strength was measured using a tensile tester at a pulling rate of 10 mm / min and a peel angle of 0°. Specifically, as shown in Figure 2, one adhesive surface 10a of measurement sample 10 was bonded to stainless steel plate 21, and the other adhesive surface 10b of measurement sample 10 was bonded to stainless steel plate 22 and pressed together. The sheets were pulled at the above-mentioned speed in the direction of the arrow in Figure 2 (i.e., the shear direction), and the peel strength per 20 mm x 20 mm was measured. The shear adhesion strength [MPa] was calculated from the obtained value. The tensile tester used was a universal tension / compression tester (product name "TG-1kN", manufactured by Minebea Co., Ltd.).

[0137] (3) Impact Resistance The double-sided PSA sheets sandwiched between release liners prepared in the Examples and Comparative Examples were punched into frames measuring 24.5 mm square in outer diameter and 2 mm wide. The release liners were then peeled off from the double-sided PSA sheets, and the sheets were sandwiched and pressure-bonded between a 2 mm thick, 50 mm square stainless steel plate with a central hole and a 3 mm thick, 25 mm square stainless steel plate. The sheets were then left to stand in an environment at 50°C for 2 hours, and then returned to room temperature to obtain evaluation samples. A cylindrical measurement platform measuring 50 mm in length, 49 mm in outer diameter, and 43 mm in inner diameter was placed on the base of a DuPont impact tester (manufactured by Toyo Seiki Seisakusho, Ltd.), and the test specimen was placed on top of the platform with the square stainless steel plate (without a hole) facing downwards. A stainless steel impact core with a tip radius of 3.1 mm was placed on the test piece, and the weight and height of the falling weight were changed in 50 mm increments from 50 to 500 mm at 100 g, in 50 mm increments from 350 to 500 mm at 150 g, in 50 mm increments from 400 to 500 mm at 200 g, and in 50 mm increments from 350 to 500 mm at 300 g, increasing the energy until peeling occurred. For energies that had already been evaluated, the test was not repeated, and the load and height were set so that the amount of energy did not overlap. The energy until at least one of the stainless steel plates peeled off was then calculated as the load x height, and the result was obtained.

[0138] (4) 180° Peel Strength For the double-sided PSA sheets prepared in the Examples and Comparative Examples, the release liner was peeled from one adhesive surface under a measurement environment of 23°C and 50% RH, and a 50 μm thick PET film was attached as a backing. A measurement sample was then cut to a size of 25 mm wide and 100 mm long. For the prepared measurement sample, the release liner was peeled from the other adhesive surface under an environment of 23°C and 50% RH, and the adhesive surface was pressure-bonded to the surface of a stainless steel plate (SUS304BA plate) by rolling a 2 kg roller back and forth once. After leaving this under the same environment for 30 minutes, the peel strength was measured using a universal tension-compression tester in accordance with JIS Z0237 (2000) at a tension speed of 300 mm / min and a peel angle of 180°. A universal tension-compression tester under the trade name "Tension-Compression Tester, TG-1kN" (manufactured by Minebea Co., Ltd.) was used.

[0139]

[0140] As shown in Table 1, the double-sided pressure-sensitive adhesive sheets of the present invention were confirmed to have excellent impact resistance, high shear adhesive strength, and excellent initial adhesiveness. On the other hand, when the Tg of the pressure-sensitive adhesive layer was low and the 180° peel strength was small (Comparative Example), the initial adhesiveness was judged to be poor.

[0141] REFERENCE SIGNS LIST 1 double-sided pressure-sensitive adhesive sheet 2 pressure-sensitive adhesive layer 3, 4 release liner 10 measurement sample 10a, 10b adhesive surface 21, 22 stainless steel plate

Claims

1. A double-sided pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer, the pressure-sensitive adhesive layer is an active energy ray-curable acrylic pressure-sensitive adhesive layer containing an acrylic polymer as a base polymer, The acrylic polymer contains 50% by mass or more of structural units derived from a (meth)acrylic acid alkyl ester (A) having a linear or branched alkyl group having 2 to 7 carbon atoms, The pressure-sensitive adhesive layer has a glass transition temperature of 0° C. or higher, a storage modulus G′ of 10 MPa or higher at −20° C., and a storage modulus G′ of 0.05 MPa or higher at 65° C.; A double-sided pressure-sensitive adhesive sheet, the 180° peel strength against a stainless steel plate being 20 N / 20 mm or more when measured at 23° C. with a 50 μm thick polyethylene terephthalate film attached to one adhesive surface of the double-sided pressure-sensitive adhesive sheet.

2. 2. The double-sided pressure-sensitive adhesive sheet according to claim 1, wherein the (meth)acrylic acid alkyl ester (A) contains butyl (meth)acrylate, and the proportion of structural units derived from butyl (meth)acrylate in the acrylic polymer is 50 mass% or more.

3. The double-sided pressure-sensitive adhesive sheet according to claim 1 , wherein the acrylic polymer contains a polyfunctional monomer as a monomer component constituting the polymer.

4. The double-sided pressure-sensitive adhesive sheet according to claim 1 , wherein the acrylic polymer has a structural portion derived from a photopolymerization initiator.

5. 3. The double-sided pressure-sensitive adhesive sheet according to claim 1, wherein the acrylic polymer contains a structural unit derived from a monomer component (B) having a homopolymer glass transition temperature of 0°C or higher and having a non-aromatic ring.

6. The double-sided pressure-sensitive adhesive sheet according to claim 1 or 2, which is used for fixing components together in an electric / electronic device.

7. A double-sided pressure-sensitive adhesive sheet according to claim 6, The double-sided pressure-sensitive adhesive sheet fixes components together using both adhesive surfaces of the sheet, in an electric / electronic device.