Double-sided 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

Technical Field

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

Background Art

[0002] In recent years, miniaturization of portable devices such as mobile phones, digital cameras, and PDAs (Personal Digital Assistants) has been progressing. Therefore, various electronic components to be mounted are also being miniaturized and thinned. For example, in a mobile phone, which is a typical portable device, the main components are each tending to be thinner. Usually, the display portion of a portable device mainly consists of an LCD module and a backlight unit, and various sheet-like components are laminated to exhibit functions such as light emission, reflection, light shielding, and light guiding. Therefore, a double-sided adhesive sheet (double-sided adhesive tape) is used for assembling (bonding) these components.

[0003] For example, portable electronic devices are often exposed to the risk of dropping depending on their usage form. Therefore, the double-sided adhesive sheet used for portable electronic devices is required to have impact resistance so that it is not easily damaged or peeled off from components due to the impact of dropping the portable electronic device.

[0004] As double-sided adhesive sheets used for portable electronic devices and having excellent impact resistance, for example, those disclosed in Patent Documents 1 to 3 are known.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] Because portable electronic devices can be subjected to various impacts when not in use, double-sided adhesive 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, generally speaking, double-sided adhesive sheets with a flexible adhesive layer tend to have superior impact resistance, but also tend to have lower shear adhesion. Conversely, if the adhesive layer of a double-sided adhesive sheet is rigid, the shear adhesion is higher, but the surface adhesion tends to be lower, resulting in poor adhesion (initial adhesion) when bonding the double-sided adhesive sheet to a substrate. For this reason, it has been considered difficult to realize a double-sided adhesive sheet that has superior impact resistance, high shear adhesion, and excellent initial adhesion. Patent documents 1 to 3 do not mention anything about having superior impact resistance, high shear adhesion, and excellent initial adhesion.

[0008] The present invention was conceived under these circumstances, and its purpose is to provide a double-sided adhesive sheet that has excellent impact resistance, high shear adhesion, and excellent initial adhesion. [Means for solving the problem]

[0009] As a result of diligent research to achieve the above objectives, the present inventors have found that a double-sided adhesive sheet without a substrate has excellent impact resistance, high shear adhesion, and excellent initial adhesion by specifying the base polymer composition in the adhesive layer constituting the double-sided adhesive sheet, the storage modulus G' and glass transition temperature of the adhesive layer under two temperature conditions, and the 180° peel strength of the double-sided adhesive sheet to a stainless steel plate. The present invention was completed based on these findings.

[0010] In other words, the present invention is a double-sided adhesive sheet comprising an adhesive layer, The above adhesive layer is an active energy ray curable acrylic adhesive layer containing an acrylic polymer as the base polymer. The above acrylic polymer contains 50% by mass or more of constituent units derived from alkyl (meth)acrylate (A) having a linear or branched alkyl group having 2 to 7 carbon atoms. The above 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. The present invention provides a double-sided adhesive sheet in which a polyethylene terephthalate film with a thickness of 50 μm is attached to one of the adhesive surfaces of the double-sided adhesive sheet, and the 180° peel strength against a stainless steel plate measured at 23°C is 20 N / 20 mm or more.

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

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

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

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

[0015] The above-mentioned double-sided adhesive sheet is preferably used for fixing components together in electrical and electronic equipment.

[0016] Furthermore, the present invention provides an electrical and electronic device comprising the above-mentioned double-sided adhesive sheet, wherein the double-sided adhesive sheet fixes components together on both adhesive surfaces. [Effects of the Invention]

[0017] The double-sided adhesive sheet of the present invention is excellent in impact resistance, has a high shear adhesive strength, and is excellent in initial adhesiveness. Therefore, for example, when used in a portable electronic device, members can be sufficiently fixed to each other, and even when it is subjected to a dropping impact or the adherend is deformed, it is difficult to peel off.

Brief Description of the Drawings

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

Modes for Carrying Out the Invention

[0019] [Double-sided Adhesive Sheet] The double-sided adhesive sheet of the present invention is a double-sided adhesive sheet composed of an adhesive layer and is a so-called "substrate-free" double-sided adhesive sheet having no substrate.

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

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

[0022] Figure 1 is a schematic cross-sectional view showing one embodiment of the double-sided adhesive sheet of the present invention. As shown in Figure 1, the double-sided adhesive sheet 1 is composed of a single layer of adhesive layer 2 of the present invention. Release liners 3 and 4 are attached to the adhesive surface of the adhesive layer 2, respectively.

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

[0024] The proportion of the base polymer in the adhesive layer is preferably 60% by mass or more, and more preferably 70% by mass or more, based on 100% by mass of the total amount of the adhesive layer.

[0025] The above-mentioned acrylic polymer is a polymer that contains an acrylic monomer (a monomer having a (meth)acryloyl group in its molecule) as a monomer component constituting the polymer. That is, the above-mentioned acrylic polymer contains constituent units derived from an acrylic monomer. Note that only one type of acrylic polymer may be used, or two or more types may be used. Furthermore, the above-mentioned acrylic polymer may contain only one type of acrylic monomer as a monomer component, or two or more types may be contained. 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.

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

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

[0028] The proportion of alkyl (meth)acrylate (A) in 100% by mass of the total amount of all monomer components constituting the above acrylic polymer is 50% by mass or more, preferably 60% by mass or more, and more preferably 65% ​​by mass or more. A proportion of 50% by mass or more allows for the formation of an adhesive layer with good adhesion even when 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. Furthermore, it is preferable that the proportion of butyl (meth)acrylate is within the above range.

[0029] The above acrylic polymer is preferably a polymer composed (formed) of a monomer component (sometimes referred to as "monomer component (B)") having a homopolymer glass transition temperature of 0°C or higher and having a non-aromatic ring, together with an alkyl (meth)acrylate ester (A). The above acrylic polymer may contain only one type of monomer component (B) or two or more types.

[0030] Examples of the above non-aromatic rings include non-aromatic hydrocarbon rings and non-aromatic heterocycles. The above non-aromatic rings may be saturated or unsaturated. Examples of the above non-aromatic hydrocarbon group rings include aliphatic hydrocarbon rings, such as cycloalkane rings such as cyclopentane rings, cyclohexane rings, cycloheptane rings, and cyclooctane rings; cycloalkene rings such as cyclohexene rings; and bridged hydrocarbon rings such as bicyclic hydrocarbon rings and aliphatic hydrocarbon rings with three or more rings. Examples of bicyclic hydrocarbon rings include pinan rings, pinene rings, bornane rings, norbornane rings, and norbornene rings. Examples of aliphatic hydrocarbon rings with three or more rings (bridged hydrocarbon rings with three or more rings) include dicyclopentane rings, dicyclopentene rings, adamantane rings, tricyclopentane rings, and tricyclopentene rings.

[0031] Examples of the above non-aromatic heterocycles include oxygen-containing heterocycles, nitrogen-containing heterocycles, and sulfur-containing heterocycles. Examples of oxygen-containing heterocycles include oxolane rings, oxane rings, oxol rings, pyran rings, caprolactone rings, caprolactam rings, and heterocycles containing oxygen and nitrogen atoms. Examples of nitrogen-containing heterocycles include azolidine rings, adinane rings, azole rings, piperidine rings, caprolactam rings, heterocycles containing oxygen and nitrogen atoms, and heterocycles containing nitrogen and sulfur atoms. Examples of sulfur-containing heterocycles include thiolane rings, thiol rings, and heterocycles containing nitrogen and sulfur atoms. Examples of heterocycles containing oxygen and nitrogen atoms include morpholine rings. Examples of heterocycles containing nitrogen and sulfur atoms include thiazine rings and thiazole rings.

[0032] The number of atoms constituting the ring in the above non-aromatic ring is preferably 5 to 12, and more preferably 6 to 10. Furthermore, monomer component (B) is preferably a monomer component having a carbon-carbon double bond (e.g., a (meth)acryloyl group, a vinyl group, etc.) that is polymerizable by active energy rays and a non-aromatic ring, and examples include (meth)acrylic acid esters having a non-aromatic ring in the ester portion, and monomer components having a vinyl group and a non-aromatic heterocycle. In the above (meth)acrylic acid ester, the non-aromatic ring is preferably directly bonded to the (meth)acryloyl group, or bonded to the (meth)acryloyl group via an oxygen atom or an oxyalkylene group. Among the above non-aromatic rings, aliphatic hydrocarbon rings and nitrogen atom-containing heterocycles are preferred.

[0033] Examples of monomer components (B) in which the non-aromatic ring is an aliphatic hydrocarbon ring include, for example, cycloalkyl (meth)acrylates such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, and cyclooctyl (meth)acrylate; (meth)acrylate esters having a bicyclic aliphatic hydrocarbon ring such as isobornyl (meth)acrylate; and (meth)acrylate esters having three or more aliphatic hydrocarbon rings 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] Examples of monomer components (B) in which the non-aromatic ring is a nitrogen-containing heterocycle include, for example, 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-morpholindione, 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 monomer component (B) homopolymer is 0°C or higher, preferably 10°C or higher, and more preferably 60°C or higher. A Tg of 0°C or higher results in excellent initial tackiness while also increasing the storage modulus G', leading to superior impact resistance. From the viewpoint of superior initial tackiness, the Tg is preferably 50°C or lower, and more preferably 20°C or lower.

[0036] In this specification, "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 the monomer homopolymer," and specifically, the numerical value is given in "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1987). For Tg of a monomer homopolymer not listed in the above-mentioned literature, the value refers to a value obtained by, for example, the following measurement method (see Japanese Patent Publication No. 2007-51271). Specifically, 100 parts by mass of monomer, 0.2 parts by mass of 2,2'-azobisisobutyronitrile, and 200 parts by mass of ethyl acetate as a polymerization solvent are added to a reactor equipped with a thermometer, stirrer, nitrogen inlet tube, and 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. Then, it is cooled to room temperature to obtain a homopolymer solution with a solid content of 33% by mass. Next, this homopolymer solution is cast onto a release liner and dried to produce a test sample (sheet-like homopolymer) with a thickness of approximately 2 mm. This test sample is then punched out into a disc shape with a diameter of 7.9 mm, sandwiched between parallel plates, and the viscoelasticity is measured using a viscoelasticity tester (product name "ARES", manufactured by Rheometrics) in shear mode while applying a shear strain at a frequency of 1 Hz, in a temperature range of -70 to 150°C, with a heating rate of 5°C / min. The peak top temperature of tanδ is defined as the Tg of the homopolymer.

[0037] The proportion of monomer component (B) in the total amount of all monomer components constituting the above 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 the above proportion is 5% by mass or more, the storage modulus G' (especially the storage modulus G' at -20°C) is high, and the proportion of monomer component (B) which is superior in 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 the above proportion is 60% by mass or less, flexibility is improved, and adhesion to the adherend and shear adhesion strength can be improved.

[0038] The above acrylic polymer may contain copolymerizable monomers as monomer components, along with (meth)acrylate (A) and monomer component (B). That is, the above acrylic polymer may contain copolymerizable monomers as constituent units. Only one type of copolymerizable monomer may be used, or two or more types may be used.

[0039] As the copolymerizable monomers mentioned above, carboxyl group-containing monomers and / or acid anhydride monomers are preferred from the viewpoint of being able to form an adhesive layer with good adhesion even when thin, and having improved cohesive strength and superior impact resistance. Examples of the carboxyl group-containing monomers 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 monomers include maleic anhydride and itaconic anhydride.

[0040] The proportion of carboxyl group-containing monomers and / or acid anhydride monomers in 100% by mass of the total amount of all monomer components constituting the above 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 above 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 above proportion is within the above range, a good quantitative balance is achieved between the alkyl (meth)acrylate ester (A) and the monomer component (B), making it possible to form an adhesive layer that has excellent impact resistance and good adhesion even when thin.

[0041] The copolymerizable monomers described above may further include functional group-containing monomers for the purpose of introducing crosslinking points into the acrylic polymer or enhancing the cohesive strength of the acrylic polymer. Examples of functional group-containing monomers include hydroxyl group-containing monomers, nitrogen atom-containing monomers (excluding those corresponding to monomer component (B)), keto group-containing monomers, alkoxysilyl group-containing monomers, sulfonic acid group-containing monomers, and phosphate group-containing monomers. Only one type of functional group-containing monomer may be used, or two or more types may be used.

[0042] Examples of the above-mentioned hydroxyl group-containing monomers 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 nitrogen atom-containing monomers include amide group-containing monomers, amino group-containing monomers, and cyano group-containing monomers. Examples of amide group-containing monomers 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 amino group-containing monomers include aminoethyl(meth)acrylate, N,N-dimethylaminoethyl(meth)acrylate, and t-butylaminoethyl(meth)acrylate. Examples of cyano group-containing monomers include acrylonitrile and methacrylonitrile.

[0044] Examples of the above-mentioned keto group-containing monomers include diacetone(meth)acrylamide, diacetone(meth)acrylate, vinyl methyl ketone, vinyl ethyl ketone, allyl acetacetate, and vinyl acetacetate.

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

[0046] Examples of the above-mentioned sulfonic acid group-containing monomers include styrene sulfonic acid, allyl sulfonic acid, 2-(meth)acrylamide-2-methylpropanesulfonic acid, (meth)acrylamidepropanesulfonic acid, sulfopropyl (meth)acrylate, and (meth)acryloyloxynaphthalenesulfonic acid.

[0047] Examples of the above-mentioned phosphate group-containing monomers include 2-hydroxyethyl acryloyl phosphate.

[0048] The proportion of the functional group-containing monomer in 100% by mass of the total amount of all monomer components constituting the above 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 above proportion may be, for example, 40% by mass or less, 20% by mass or less, or substantially absent. In this specification, substantially absent means that it is included unintentionally, such as when it is inevitably mixed in, rather than being actively blended, for example, 0.05% by mass or less, or 0.01% by mass or less.

[0049] The copolymerizable monomers mentioned above may further include other monomers. Examples of these other monomers include vinyl ester monomers such as vinyl acetate, vinyl propionate, and vinyl laurate; aromatic vinyl compounds such as styrene, substituted styrene (α-methylstyrene, etc.), and vinyltoluene; 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; vinyl ether 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 methyl (meth)acrylate. Examples include alkyl (meth)acrylates having linear or branched alkyl groups with 8 to 20 carbon atoms, such as isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (lauryl (meth)acrylate), tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (stearyl (meth)acrylate), isostearyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate; and aryl (meth)acrylates having aromatic rings, such as aryl (meth)acrylates such as phenyl (meth)acrylate, aryloxyalkyl (meth)acrylates such as phenoxyethyl (meth)acrylate, and arylalkyl (meth)acrylates such as benzyl (meth)acrylate.

[0050] The proportion of the other monomers in the total amount of all monomer components constituting the above acrylic polymer (100% by mass) may be, for example, 0.05% by mass or more, or 0.5% by mass or more. The above proportion may also be, for example, 20% by mass or less, 10% by mass or less, or 5% by mass or less, and may be substantially absent.

[0051] The above-mentioned acrylic polymer may contain polyfunctional monomers copolymerizable with the monomer components forming the acrylic polymer as monomer components constituting the polymer, in order to form a crosslinked structure within its polymer backbone. Examples of the above-mentioned polyfunctional monomers 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; 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. Only one of the above-mentioned polyfunctional monomers may be used, or two or more may be used.

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

[0053] The above-mentioned acrylic polymer preferably has a structural component derived from a photopolymerization initiator. The presence of a structural component derived from a photopolymerization initiator in the above-mentioned acrylic polymer means that the above-mentioned acrylic polymer and the adhesive layer of the present invention are polymers polymerized by active energy ray irradiation or adhesive layers cured by active energy ray irradiation. Examples of the above-mentioned photopolymerization initiator are those described below.

[0054] The above acrylic polymer is preferably a polymerization product obtained by polymerizing a composition containing one or more selected from the group consisting of acrylic partial polymers, acrylic oligomers, and monomer components. If the polymerization product is obtained by polymerizing a composition consisting only of monomer components, the monomer components contain at least an acrylic monomer. The above "partial polymer" may also be referred to as "prepolymer," "syrup," etc. The acrylic partial polymer, acrylic oligomer, and monomer component may each be used individually or in combination of two or more. The monomer component that may be included in the above composition may be referred to as "monomer component (C)."

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

[0056] The above-mentioned acrylic partial polymers and acrylic oligomers are both compounds composed of acrylic monomers as essential monomer components. Examples of monomer components and monomer component (C) constituting the above-mentioned acrylic partial polymers and acrylic oligomers include those exemplified and described as monomer components constituting the above-mentioned acrylic polymers.

[0057] Unlike the complete polymer, the above-mentioned acrylic partial polymer is obtained by polymerizing the monomer component, for example, with a polymerization conversion rate of 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 above acrylic partial polymer contains an acrylic monomer as a constituent unit. The above acrylic partial polymer preferably contains an alkyl (meth)acrylate (A) as a constituent unit. Butyl (meth)acrylate is preferred as the alkyl (meth)acrylate (A). The alkyl (meth)acrylate (A) included as a constituent unit may be one type or two or more types.

[0059] The proportion of alkyl (meth)acrylate (A) in 100% by mass of the total amount of all monomer components constituting the above 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. The above proportion 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 above acrylic partial polymer preferably contains monomer component (B) as a constituent unit. The monomer component (B) included as a constituent unit may be one type or two or more types.

[0061] The proportion of monomer component (B) in the total amount of all monomer components constituting the above acrylic partial 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 the above proportion is 5% by mass or more, the storage modulus G' (especially the storage modulus G' at -20°C) is increased, resulting in superior 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 above proportion is 60% by mass or less, flexibility is improved, and adhesion to the adherend and shear adhesion strength can be further improved.

[0062] The above acrylic partial polymer may contain the above copolymerizable monomer as a constituent unit. Among the above copolymerizable monomers, carboxyl group-containing monomers and / or acid anhydride monomers are preferred from the viewpoint of improving cohesive strength and having superior impact resistance, and from the viewpoint of being able to form an adhesive layer with good adhesion even when thin.

[0063] The proportion of carboxyl group-containing monomers and / or acid anhydride monomers in 100% by mass of the total amount of all monomer components constituting the above acrylic partial 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 above proportion 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 above-mentioned acrylic polymer may be a polymerization product of a composition containing an acrylic partial polymer and an acrylic oligomer. In this case, the storage modulus G' at -20°C is further improved.

[0065] The weight-average molecular weight of the above acrylic oligomer is preferably 2500 to 10000, and more preferably 3000 to 8000. The weight-average molecular weight can be determined by converting it to polystyrene equivalent using the GPC method. For example, it can be measured using the high-speed GPC instrument "HPLC-8120GPC" manufactured by Tosoh Corporation under the following conditions. Column: TSKgel SuperHZM-H / HZ4000 / HZ3000 / HZ2000 Solvent: tetrahydrofuran Flow rate: 0.6ml / min

[0066] The above acrylic oligomer contains an acrylic monomer as a constituent unit. Preferably, the above acrylic oligomer contains monomer component (B) as a constituent unit. The monomer component included as a constituent unit may be one or two or more.

[0067] The proportion of monomer component (B) in the total amount of all monomer components constituting the above 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. The above proportion is preferably 90% by mass or less, and more preferably 80% by mass or less.

[0068] The above acrylic oligomer preferably contains methyl methacrylate (MMA) as a constituent unit. The proportion of methyl methacrylate in the total monomer components constituting the above acrylic oligomer is preferably 10% by mass or more, more preferably 20% by mass or more. The above 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 above acrylic oligomer may also contain the above copolymerizable monomer as a constituent unit.

[0069] The content of the above 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, per 100 parts by mass of the total amount of the above 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 monomer component (C) include those exemplified and described as monomer components that the above-mentioned acrylic polymer may contain as constituent units. Preferably, monomer component (C) contains monomers copolymerizable with monomer component (B) and / or monomer components that form the above-mentioned acrylic partial polymer. Examples of copolymerizable monomers include the copolymerizable monomers described above.

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

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

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

[0074] The content of monomer component (C) is preferably 1 to 30 parts by mass, and more preferably 10 to 20 parts by mass, per 100 parts by mass of the total amount of the acrylic partial polymer. 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 higher.

[0075] The above-mentioned acrylic partial polymers and acrylic oligomers are obtained by polymerizing monomer components. The above-mentioned acrylic polymers are obtained by polymerizing a composition containing one or more selected from the group consisting of the above-mentioned acrylic partial polymers, acrylic oligomers, and monomer component (C). The polymerization methods are not particularly limited, but examples include solution polymerization, emulsion polymerization, bulk polymerization, thermal polymerization, and polymerization by active energy ray irradiation (active energy ray polymerization). Among these, bulk polymerization, thermal polymerization, and active energy ray polymerization are preferred in terms of transparency of the adhesive layer and cost.

[0076] Furthermore, various general solvents may be used in the polymerization of the above-mentioned monomer components. Examples of such solvents include 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 organic solvents such as ketones such as methyl ethyl ketone and methyl isobutyl ketone. Note that one solvent may be used alone, or two or more solvents may be used.

[0077] When polymerizing the above monomer components, polymerization initiators such as thermal polymerization initiators and photopolymerization initiators (photoinitiators) may be used depending on the type of polymerization reaction. Note that one polymerization initiator may be used alone, or two or more may be used.

[0078] The above-mentioned thermal polymerization initiators are not particularly limited, but examples include azo polymerization initiators, peroxide polymerization initiators (e.g., persulfates such as dibenzoyl peroxide, tert-butyl permaleate, potassium persulfate, benzoyl peroxide, hydrogen peroxide, etc.), substituted ethane initiators such as phenyl-substituted ethane, aromatic carbonyl compounds, redox polymerization initiators, etc. Among these, the azo polymerization initiator disclosed in Japanese Patent Application Publication No. 2002-69411 is preferred. Examples of the above-mentioned azo polymerization initiators include 2,2'-azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis(2-methylpropionic acid)dimethyl, and 4,4'-azobis-4-cyanovaleric acid. The amount of thermal polymerization initiator used can be the usual amount, for example, it can be selected from a range of 0.005 to 1 part by mass, preferably 0.01 to 1 part by mass, per 100 parts by mass of monomer component.

[0079] The above-mentioned photopolymerization initiators are not particularly limited, but examples 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 above-mentioned 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-diphenylethane-1-one, and anisole methyl ether. Examples of the above acetophenone-based photopolymerization initiators include 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexylphenyl ketone, 4-phenoxydichloroacetophenone, and 4-(t-butyl)dichloroacetophenone. Examples of the above α-ketol-based photopolymerization initiators include 2-methyl-2-hydroxypropiophenone and 1-[4-(2-hydroxyethyl)phenyl]-2-methylpropan-1-one. Examples of the above aromatic sulfonyl chloride-based photopolymerization initiators include 2-naphthalenesulfonyl chloride. Examples of the above photoactive oxime-based photopolymerization initiators include 1-phenyl-1,1-propanedione-2-(O-ethoxycarbonyl)-oxime. Examples of the above benzoin-based photopolymerization initiators include benzoin. Examples of the above benzyl-based photopolymerization initiators include benzyl. Examples of the benzophenone-based photopolymerization initiators include benzophenone, benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, polyvinylbenzophenone, and α-hydroxycyclohexylphenyl ketone. Examples of the ketal-based photopolymerization initiators include benzyldimethyl ketal.Examples of the thioxanthone-based photopolymerization initiators include thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-diisopropylthioxanthone, and dodecylthioxanthone. Examples of the acylphosphine oxide-based photopolymerization initiators include 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide. Examples of the titanocene-based photopolymerization initiators include bis(η. 5 Examples include -2,4-cyclopentadiene-1-yl)bis(2,6-difluoro-3-(1H-pyrrole-1-yl)-phenyl)titanium. The amount of photopolymerization initiator used can be the usual amount, for example, it can be selected from a range of 0.01 to 3 parts by mass, preferably 0.1 to 1.5 parts by mass, per 100 parts by mass of monomer component.

[0080] The adhesive layer of the present invention preferably further contains a filler. By incorporating a filler, it becomes easier to adjust the storage modulus G' at -20°C and 65°C. 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 above inorganic substances include metals such as copper, silver, gold, platinum, nickel, aluminum, chromium, iron, and stainless steel; metal oxides such as aluminum 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 include metal hydroxides and hydrated metal compounds such as dosonite, 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 fibers, and diamonds; inorganic materials such as glass; and natural raw material particles such as volcanic ash, clay, and sand.

[0083] Examples of materials constituting the above-mentioned 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 described above may have a hollow structure. The hollow portion of the filler having the hollow structure (the space inside the hollow particle) may be in a vacuum state or may be filled with a medium. Examples of the medium include inert gases such as nitrogen and argon, air, and volatile solvents.

[0085] Among the above fillers, fillers whose surface is 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 components in the acrylic adhesive layer, or have a hollow structure, so they are less likely to break when the adhesive layer is stretched, and have excellent peelability (reworkability) when peeling off the double-sided adhesive sheet after it has been attached to the substrate.

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

[0087] The proportion of the filler in the adhesive layer of the present invention is preferably 0.5 to 10% by mass, and more preferably 1 to 5% by mass, based on 100% by mass of the total amount of the adhesive layer. When the proportion is within the above range, the hardness of the adhesive layer can be made appropriate. Furthermore, it exhibits excellent reworkability.

[0088] The adhesive layer of the present invention may contain a coloring agent. By including a coloring agent, the adhesive layer is colored, and the double-sided adhesive sheet of the present invention has excellent visibility and design. The coloring agent may be a pigment or a dye. Examples of coloring agents include black coloring agents, cyan coloring agents, magenta coloring agents, and yellow coloring agents. From the viewpoint of superior visibility and design, black coloring agents are preferred. The adhesive layer of the present invention may contain only one type of coloring agent or two or more types. The proportion of the coloring agent in the adhesive layer of the present invention is preferably 0.05 to 5% by mass, and more preferably 0.1 to 2% by mass, based on 100% by mass of the total amount of the adhesive layer.

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

[0090] Examples of cyan-based colorants include CI Solvent Blue 25, 36, 60, 70, 93, 95; CI Acid Blue 6, 45; CI 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, 66; CI Bat Blue 4, 60, and CI Pigment Green 7.

[0091] Examples of magenta-based colorants include CI Solvent Red 1, 3, 8, 23, 24, 25, 27, 30, 49, 52, 58, 63, 81, 82, 83, 84, 100, 109, 111, 121, 122; CI Disperse Red 9; CI Solvent Violet 8, 13, 14, 21, 27; CI Disperse Examples include Violet 1; CI Basic Red 1, 2, 9, 12, 13, 14, 15, 17, 18, 22, 23, 24, 27, 29, 32, 34, 35, 36, 37, 38, 39, 40; CI Basic Violet 1, 3, 7, 10, 14, 15, 21, 25, 26, 27, 28, etc. Furthermore, as magenta-based colorants, for example, CI 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, Same 48:2, same 48:3, same 48:4, same 49, same 49:1, same 50, same 51, same 52, same 52:2, same 53:1, same 54, same 55, same 56, same 57:1, same 58, same 60, same 60:1, same 63, same 63:1, same 63:2, same 64, same 64:1, same 67, same 68, same 81, same 83, same 87, same 88, same 89, same 90, same 92, same 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 Examples include 193, 202, 206, 207, 209, 219, 222, 224, 238, and 245; CI Pigment Violet 3, 9, 19, 23, 31, 32, 33, 36, 38, 43, and 50; CI Bat Red 1, 2, 10, 13, 15, 23, 29, and 35.

[0092] Examples of yellow colorants include CI Solvent Yellow 19, 44, 77, 79, 81, 82, 93, 98, 103, 104, 112, 162; CI Pigment Orange 31, 43; CI 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. Examples include 75, 81, 83, 93, 94, 95, 97, 98, 100, 101, 104, 108, 109, 110, 113, 114, 116, 117, 120, 128, 129, 133, 138, 139, 147, 150, 151, 153, 154, 155, 156, 167, 172, 173, 180, 185, 195; CI Bat Yellow 1, 3, 20, etc.

[0093] The adhesive layer of the present invention may optionally further contain additives such as crosslinking agents, crosslinking accelerators, anti-aging agents, antioxidants, plasticizers, softeners, surfactants, antistatic agents, surface lubricants, leveling agents, light stabilizers, ultraviolet absorbers, polymerization inhibitors, foil-like materials, and rust inhibitors, to the extent that they do not impair the effects of the present invention. Each of the above additives may be used individually or in combination of two or more.

[0094] As described above, the adhesive layer of the present invention has a storage modulus G' of 10 MPa or more at -20°C, 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 represents the properties of the adhesive layer at low temperatures and can be replaced with the properties when subjected to impact at relatively high speeds. Having a storage modulus G' of 10 MPa or more at such low temperatures as -20°C provides excellent impact resistance, for example, when a component to which a double-sided adhesive sheet is applied is dropped at high speed. The above storage modulus G' can be calculated using a dynamic viscoelasticity measurement (DMA) device.

[0095] As described above, the adhesive layer of the present invention has a storage modulus G' of 0.05 MPa or higher at 65°C, preferably 0.06 MPa or higher, more preferably 0.08 MPa or higher, and even more preferably 0.10 MPa or higher. The storage modulus G' at 65°C represents the properties of the adhesive layer at relatively high temperatures and can be replaced with the properties when subjected to low-speed impact. By having such a storage modulus G' at 65°C of 0.05 MPa or higher, the adhesive layer of the present invention has high shear adhesion. The above storage modulus G' can be calculated using a dynamic viscoelasticity measurement (DMA) device.

[0096] The adhesive layer of the present invention preferably has a storage modulus G' of 0.10 MPa or higher at 23°C, more preferably 0.21 MPa or higher, and even more preferably 0.25 MPa or higher. A storage modulus G' of 0.10 MPa or higher at 23°C provides appropriate hardness at room temperature and excellent reworkability. The above storage modulus G' can be calculated using a dynamic viscoelasticity measurement (DMA) device.

[0097] The glass transition temperature (Tg) of the adhesive layer of the present invention is 0°C or higher, preferably 2°C or higher, and more preferably 5°C or higher. A Tg of 0°C or higher results in a high storage modulus G', providing excellent impact resistance. For example, the Tg can be 50°C or lower. The Tg can be calculated using a dynamic viscoelasticity measurement (DMA) device.

[0098] The peak-top value of tanδ in the adhesive layer of the present invention is preferably 0.5 or higher, more preferably 1.0 or higher, and even more preferably 1.5 or higher. When the peak-top value of tanδ is 0.5 or higher, the impact resistance is superior. The above tanδ can be calculated using a dynamic viscoelasticity measurement (DMA) device.

[0099] The adhesive layer of the present invention is an active energy ray-curable adhesive layer. That is, the adhesive layer of the present invention is an adhesive layer formed from an active energy ray-curable adhesive composition. As a result, the double-sided adhesive sheet of the present invention can produce an adhesive with dense crosslinking and high strength, excellent impact resistance and high shear adhesion.

[0100] Examples of the active energy rays mentioned above include ionizing radiation such as alpha rays, beta rays, gamma rays, neutron rays, and electron beams, as well as ultraviolet rays, with ultraviolet rays being particularly preferred. In other words, the active energy ray-curable adhesive layer is preferably an ultraviolet-curable adhesive layer.

[0101] The adhesive layer of the present invention can be manufactured, for example, by applying the above-mentioned adhesive composition onto a release liner, drying and solidifying it by volatilizing the solvent by heating or other means as needed, and curing the resulting adhesive composition layer by irradiating it with active energy rays. Alternatively, it may be further heated and dried as needed.

[0102] Examples of adhesive compositions (acrylic adhesive compositions) that form the adhesive layer of the present invention include acrylic adhesive compositions that contain the above-mentioned acrylic partial polymer, the above-mentioned acrylic oligomer, or a monomer mixture containing monomer component (C) as essential components.

[0103] From the viewpoint of superior initial tackiness, the above adhesive composition preferably contains at least a partially polymerized monomer mixture containing an alkyl (meth)acrylate (A) and a monomer component (B), a monomer component (C), a polyfunctional monomer, and a photopolymerization initiator. It may also contain acrylic oligomers, fillers, colorants, etc.

[0104] (Double-sided adhesive sheet) The double-sided adhesive sheet of the present invention is composed of the adhesive layer of the present invention. The thickness of the double-sided adhesive sheet is preferably 50 to 500 μm, and more preferably 100 to 300 μm. When the thickness is 50 μm or more, it has excellent adhesion and conformability to the adherend. When the thickness is 500 μm or less, the thickness of the double-sided adhesive sheet can be made thinner. Note that the thickness of the double-sided adhesive sheet refers to the thickness from one adhesive surface to the other adhesive surface, i.e., the thickness of the adhesive, and does not include the release liner.

[0105] The double-sided adhesive sheet of the present invention has a 180° peel strength against a stainless steel plate measured at 23°C with a 50 μm thick polyethylene terephthalate (PET) film attached to one adhesive surface, which is 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, allowing for sufficient fixation of components when used, for example, in bonding components in electrical and electronic equipment. 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 adhesive sheet of the present invention is within the above range, and more preferably that the 180° peel strength of both adhesive surfaces is within the above range. When a release liner is attached to the double-sided adhesive sheet of the present invention, the above peel strength is measured with the release liner removed, and the detailed method is shown in the examples.

[0106] The double-sided adhesive sheet of the present invention preferably has a shear adhesive strength of 1.0 MPa or more, more preferably 1.3 MPa or more, and more preferably 1.5 MPa or more, when the adhesive surfaces of both sides of the sheet are bonded together by sandwiching it between two stainless steel plates, and measured under conditions of a tensile speed of 10 mm / min and a peel angle of 0°, to one of the stainless steel plates. 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 adhesive sheet of the present invention, the above peel strength is the value measured with the release liner removed, and the detailed method is shown in the examples.

[0107] The energy (load × height) of the double-sided adhesive sheet of the present invention, measured by the DuPont impact test described below, before either stainless steel plate peels off, is preferably 0.3 or more, and more preferably 0.4 or more. <Impact Resistance Test> A frame-shaped double-sided adhesive sheet with an outer diameter of 24.5 mm and a width of 2 mm is sandwiched and pressed between a stainless steel plate with a thickness of 2 mm and an outer diameter of 50 mm with a hole in the center, and a stainless steel plate with a thickness of 3 mm and an outer diameter of 25 mm. The sheet is left to stand in an environment of 50°C for 2 hours, and then returned to room temperature to be used as an evaluation sample. Using a DuPont impact tester, the evaluation sample is subjected to the following changes: the weight of the drop and the drop height are changed in 50 mm increments from 50 to 500 mm with a 100 g weight, in 50 mm increments from 350 to 500 mm with a 150 g weight, in 50 mm increments from 400 to 500 mm with a 200 g weight, and in 50 mm increments from 350 to 500 mm with a 300 g weight, so that the energy increases until peeling occurs. At this time, energy levels that have already been evaluated are not tested, and the load and height are set so that the amount of energy does not overlap. Subsequently, the energy expended before at least one of the stainless steel plates detached is calculated as load × height.

[0108] The above-mentioned double-sided adhesive sheet may have a release liner attached to the surface (adhesive side) of the adhesive layer until use. The adhesive surfaces on both sides of the above-mentioned double-sided adhesive sheet may each be protected by two release liners, or they may be protected by a single release liner with both sides being release surfaces, in a roll-like winding form (winding body). The release liner is used as a protective material for the adhesive layer and is peeled off when the sheet is applied to the substrate. The release liner is not necessarily required.

[0109] The above-mentioned release liner can be conventional release paper or the like, and is not particularly limited, but examples include a substrate having a release treatment layer, a low-adhesion substrate made of a fluoropolymer, or a low-adhesion substrate made of a nonpolar polymer. Examples of the substrate having the release treatment layer include plastic films and paper surface-treated with release agents such as silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide. Examples of fluorine-based polymers in the low-adhesion substrate made of a fluoropolymer include polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, and chlorofluoroethylene-vinylidene fluoride copolymer. Examples of the above-mentioned nonpolar polymer 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.

[0110] The above-mentioned double-sided adhesive sheet is preferably used for attaching electrical and electronic components, by being bonded to components provided in electrical and electronic equipment. In particular, the above-mentioned double-sided adhesive sheet is preferably used for applications in which components provided in electrical and electronic equipment are bonded to each of the adhesive surfaces of the double-sided adhesive sheet, that is, for fixing components together in electrical and electronic equipment. The above-mentioned double-sided adhesive sheet may be used for either fixing components together or for temporary fixing. For example, when a double-sided adhesive sheet is used for fixing or temporarily fixing components provided in electrical and electronic equipment, there may be cases where the double-sided adhesive sheet must be peeled off and reworked due to a problem in the application process, or where the double-sided adhesive sheet must be peeled off in order to repair, replace, inspect, or recycle a component to which the double-sided adhesive sheet has been bonded. Thus, when a double-sided adhesive sheet is used, for example, for fixing or temporarily fixing components provided in electrical and electronic equipment, the frequency of removing the double-sided adhesive sheet is particularly high.

[0111] The above-mentioned double-sided adhesive sheet is preferably used to bond the outer frames of optical components (especially electrical and electronic equipment) together. For this reason, the above-mentioned double-sided adhesive sheet can preferably be used even if it has a width of 5 mm or less, and more preferably 3 mm or less.

[0112] Furthermore, "electrical and electronic equipment" refers to equipment that falls under either electrical equipment or electronic equipment. Examples of such electrical and electronic equipment include image display devices such as liquid crystal displays, electroluminescent displays, and plasma displays, as well as portable electronic devices.

[0113] Examples of the above-mentioned portable electronic devices include mobile phones, smartphones, tablet computers, notebook computers, various wearable devices (for example, wristwear-type devices worn on the wrist like watches, modular-type devices attached to a part of the body with clips or straps, eyewear-type devices including glasses (monocular and binocular types, including head-mounted types), clothing-type devices attached to shirts, socks, hats, etc. as accessories, earwear-type devices attached to the ears like earphones, etc.), digital cameras, digital video cameras, audio equipment (portable music players, IC recorders, etc.), calculators (calculators, etc.), portable game consoles, electronic dictionaries, electronic organizers, e-books, in-car information equipment, portable radios, portable televisions, portable printers, portable scanners, and portable modems. In this specification, "portable" means not merely being able to carry something, but having a level of portability that allows an individual (a typical adult) to carry it relatively easily. The above-mentioned double-sided adhesive sheet is used, for example, so that the adhesive layer adheres closely to the components of the above-mentioned portable electronic device. [Examples]

[0114] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by these examples.

[0115] Manufacturing Example 1: Synthesis of Syrup (1) A liquid monomer mixture (monomer composition) was prepared by mixing 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. 0.05 parts by mass of 2,2-dimethoxy-1,2-diphenylethane-1-one (trade name "OMNIRAD651", manufactured by IGM Resins BV) was added as a photopolymerization initiator. The mixture was then pulsed with ultraviolet light until the viscosity (BH viscometer No. 5 rotor, 10 rpm, measurement temperature: 30°C) reached approximately 15 Pa·s, yielding a syrup (partial polymer) containing a partial polymer (polymerization rate: approximately 8%) in which a portion of the monomer components had polymerized.

[0116] Manufacturing Example 2: Synthesis of Syrup (2) A liquid monomer mixture (monomer composition) was prepared by mixing 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. 0.05 parts by mass of 2,2-dimethoxy-1,2-diphenylethane-1-one (trade name "OMNIRAD651", manufactured by IGM Resins BV) was added as a photopolymerization initiator. The mixture was then pulsed with ultraviolet light until the viscosity (BH viscometer No. 5 rotor, 10 rpm, measurement temperature: 30°C) reached approximately 15 Pa·s, yielding a syrup (partial polymer) containing a partial polymer (polymerization rate: approximately 8%) in which a portion of the monomer components had polymerized.

[0117] Manufacturing Example 3: Synthesis of Syrup (3) A liquid monomer mixture (monomer composition) was prepared by mixing 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. 0.05 parts by mass of 2,2-dimethoxy-1,2-diphenylethane-1-one (trade name "OMNIRAD651", manufactured by IGM Resins BV) was added as a photopolymerization initiator. The mixture was then pulsed with ultraviolet light until the viscosity (BH viscometer No. 5 rotor, 10 rpm, measurement temperature: 30°C) reached approximately 15 Pa·s, yielding a syrup (partial polymer) containing a partial polymer (polymerization rate: approximately 8%) in which a portion of the monomer components had polymerized.

[0118] Manufacturing Example 4: Synthesis of Syrup (4) A liquid monomer mixture (monomer composition) was prepared by mixing 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℃) as monomer components. 0.05 parts by mass of 2,2-dimethoxy-1,2-diphenylethane-1-one (trade name "OMNIRAD651", manufactured by IGM Resins BV) was added as a photopolymerization initiator. The mixture was then pulsed with ultraviolet light until the viscosity (BH viscometer No. 5 rotor, 10 rpm, measurement temperature: 30℃) reached approximately 15 Pa·s, yielding a syrup (partial polymer) containing a partial polymer (polymerization rate: approximately 8%) in which a portion of the monomer components had polymerized.

[0119] Example 1 In the preparation of the syrup (1) obtained in Production Example 1, 100 parts by mass were used to combine cyclohexyl acrylate (CHA), 2 parts by mass were used to combine acrylic acid (AA), 0.2 parts by mass were used to combine black pigment containing carbon black (product name "Multi-Rack A903", manufactured by Toyo Color Co., Ltd.), 2 parts by mass were used to combine polyethylene powder as a filler (product name "Flosen UF-80", manufactured by Sumitomo Seika Co., Ltd.), 0.12 parts by mass were used to combine 1,6-hexanediol diacrylate (HDDA), and 0.1 parts by mass were used to combine 2,2-dimethoxy-1,2-diphenylethane-1-one (product name "OMNIRAD651", manufactured by IGM Resins BV) as a photopolymerization initiator. The mixture was then uniformly mixed using a disperser, and subsequently degassed to obtain an acrylic adhesive composition.

[0120] The obtained acrylic adhesive composition was applied using an applicator to a 38 μm thick polyethylene terephthalate film (product name "MRF#38", manufactured by Mitsubishi Chemical Corporation) that had been peel-treated on one side with silicone, so that the adhesive layer thickness was 200 μm, thereby forming a coated layer.

[0121] Next, a 25 μm thick polyethylene terephthalate film (product name "MRE#25", manufactured by Mitsubishi Chemical Corporation), with one side of which had been peel-treated with silicone, was covered with the coating layer so that the peel-treated side faced the coating layer, thereby blocking oxygen. After that, a black light lamp was used to illuminate the top surface of the film at an illuminance of 4 mW / cm². 2 A 200 μm thick adhesive layer was formed by irradiating the sheet with ultraviolet light (UV checker "UVR-T1", manufactured by Topcon Corporation, with a maximum sensitivity of approximately 350 nm during measurement) for 180 seconds, thereby creating a double-sided adhesive sheet.

[0122] Example 2 The double-sided adhesive sheet of Example 2 was prepared 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 In the syrup (2) obtained in Production Example 2, 100 parts by mass, acrylic acid (AA), black pigment containing carbon black (product name "Multi-Rack A903", manufactured by Toyo Color Co., Ltd.), 2 parts by mass of polyethylene powder as a filler (product name "Flosen UF-80", manufactured by Sumitomo Seika Co., Ltd.), 0.12 parts by mass of 1,6-hexanediol diacrylate (HDDA), and 0.1 parts by mass of 2,2-dimethoxy-1,2-diphenylethane-1-one (product name "OMNIRAD651", manufactured by IGM Resins BV) as a photopolymerization initiator were mixed uniformly using a disperser, and then degassed to obtain an acrylic adhesive composition.

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

[0125] Example 4 In the preparation of the syrup (2) obtained in Production Example 2, 100 parts by mass were used, along with 20 parts by mass of cyclohexyl acrylate (CHA), 0.2 parts by mass of a black pigment containing carbon black (product name "Multi-Rack A903", manufactured by Toyo Color Co., Ltd.), 2 parts by mass of polyethylene powder as a filler (product name "Flosen UF-80", manufactured by Sumitomo Seika Co., Ltd.), 0.12 parts by mass of 1,6-hexanediol diacrylate (HDDA), and 0.1 parts by mass of 2,2-dimethoxy-1,2-diphenylethane-1-one (product name "OMNIRAD651", manufactured by IGM Resins BV) as a photopolymerization initiator. These were then mixed uniformly using a disperser, and subsequently degassed to obtain an acrylic adhesive composition.

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

[0127] Example 5 The double-sided adhesive sheet of Example 5 was prepared 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 adhesive sheet for Example 6 was prepared in the same manner as in Example 1, except that 2 parts by mass of silicone rubber particles (product name "Torefil E-606", manufactured by Toray Industries, Inc.) were used as fillers.

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

[0130] Comparative Example 1 In the syrup (2) obtained in Production Example 2, 100 parts by mass, a black pigment containing carbon black (product name "Multi-Rack A903", manufactured by Toyo Color Co., Ltd.), 0.2 parts by mass, polyethylene powder as a filler (product name "Flosen UF-80", manufactured by Sumitomo Seika Co., Ltd.), 0.12 parts by mass, 1,6-hexanediol diacrylate (HDDA), and 0.1 parts by mass of 2,2-dimethoxy-1,2-diphenylethane-1-one (product name "OMNIRAD651", manufactured by IGM Resins BV) as a photopolymerization initiator were blended together, then uniformly mixed using a disperser, and subsequently degassed to obtain an acrylic adhesive composition.

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

[0132] Comparative Example 2 A double-sided adhesive sheet for Comparative Example 2 was prepared in the same manner as for Comparative Example 1, except that the amount of 2,2-dimethoxy-1,2-diphenylethane-1-one (trade name "OMNIRAD651", manufactured by IGM Resins BV) used as a photopolymerization initiator was 0.05 parts by mass.

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

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

[0135] (1) Dynamic viscoelasticity measurement A layer of adhesive approximately 2 mm thick was prepared by stacking multiple double-sided adhesive sheets prepared in the examples and comparative examples. A sample of this adhesive layer, punched out in the shape of a 7.9 mm diameter disc, was sandwiched and fixed between parallel plates. Dynamic viscoelasticity measurements were performed under the following conditions using a viscoelasticity tester (product name "ARES Rheometer", manufactured by T.A. Instruments Co., Ltd.) at 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 tanδ were calculated. Measurement mode: Shear mode Temperature range: -70℃ to 150℃ Heating rate: 5°C / min Measurement frequency: 1Hz

[0136] (2) Shear bond strength Measurement samples were prepared by cutting the double-sided adhesive sheets prepared in the examples and comparative examples to a size of 20 mm x 20 mm. Under conditions 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 pressed down once back and forth. After leaving this in the same conditions for 30 minutes, the shear adhesive strength was measured using a tensile testing machine under the conditions of a tensile speed of 10 mm / min and a peel angle of 0°. Specifically, as shown in Figure 2, one adhesive surface 10a of the measurement sample 10 was attached to a stainless steel plate 21, and the other adhesive surface 10b of the measurement sample 10 was attached to a stainless steel plate 22 and pressed down. This was pulled in the direction of the arrow in Figure 2 (i.e., the shear direction) at the speed described above, and the peel strength per 20 mm x 20 mm was measured. The shear adhesive strength [MPa] was determined from the obtained value. A universal tensile and compression testing machine (product name "TG-1kN", manufactured by Minebea Co., Ltd.) was used as the tensile testing machine.

[0137] (3) Impact resistance The double-sided adhesive sheets, sandwiched between release liners as prepared in the examples and comparative examples, were punched out into a frame shape with an outer diameter of 24.5 mm and a width of 2 mm. Then, the release liners were peeled off the double-sided adhesive sheets, and the sheets were sandwiched 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 pressed together. The samples were left to stand for 2 hours at a temperature of 50°C, and then returned to room temperature to be used as evaluation samples. A cylindrical measuring stand with a length of 50 mm, an outer diameter of 49 mm, and an inner diameter of 43 mm was placed on the base of a DuPont impact tester (manufactured by Toyo Seiki Seisakusho Co., Ltd.), and the test pieces were placed on it with the square stainless steel plate (the stainless steel plate without the hole) facing downwards. A stainless steel impact pin with a tip radius of 3.1 mm was placed on the test piece, and the drop weight and drop height were varied in 50 mm increments from 50 to 500 mm with a 100 g weight, from 350 to 500 mm with a 150 g weight, from 400 to 500 mm with a 200 g weight, and from 350 to 500 mm with a 300 g weight, so that the energy increased until peeling occurred. At this time, tests were not conducted for energy levels that had already been evaluated, and the load and height were set so that the amount of energy did not overlap. Subsequently, the energy before at least one of the stainless steel plates peeled off was calculated as load × height and the result was obtained.

[0138] (4) 180° peel strength For the double-sided adhesive sheets prepared in the examples and comparative examples, the release liner was peeled off one adhesive surface, a 50 μm thick PET film was attached as a backing, and the sheets were cut to a size of 25 mm wide and 100 mm long to prepare measurement samples under a measurement environment of 23°C and 50% RH. For the prepared measurement samples, the release liner was peeled off the other adhesive surface under a measurement environment of 23°C and 50% RH, and this adhesive surface was pressed onto the surface of a stainless steel plate (SUS304BA plate) by applying pressure with a 2 kg roller for one back-and-forth motion. After leaving this in the same environment for 30 minutes, the peel strength was measured using a universal tensile and compression testing machine in accordance with JIS Z0237 (2000), under conditions of a tensile speed of 300 mm / min and a peel angle of 180°. The universal tensile and compression testing machine used was the product name "Tensile and Compression Testing Machine, TG-1kN" (manufactured by Minebea Co., Ltd.).

[0139] [Table 1]

[0140] As shown in Table 1, the double-sided adhesive sheet of the present invention was confirmed to have excellent impact resistance, high shear adhesion, and excellent initial tackiness. On the other hand, when the Tg of the adhesive layer was low and the 180° peel strength was low (comparative example), it was determined that the initial tackiness was poor. [Explanation of Symbols]

[0141] 1. Double-sided adhesive sheet 2. Adhesive layer 3,4 Peel-off liner 10 measurement samples 10a,10b Adhesive side 21,22 Stainless steel plate

Claims

1. It is a double-sided adhesive sheet consisting of an adhesive layer, The adhesive layer is an active energy ray curable acrylic adhesive layer containing an acrylic polymer as the base polymer. The acrylic polymer contains 50% by mass or more of constituent units derived from an alkyl (meth)acrylate (A) having a linear or branched alkyl group having 2 to 7 carbon atoms. The 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. The double-sided adhesive sheet has a polyethylene terephthalate film with a thickness of 50 μm attached to one of its adhesive surfaces, and the 180° peel strength against a stainless steel plate measured at 23°C is 20 N / 20 mm or more.

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

3. The double-sided adhesive sheet according to claim 1 or 2, wherein the acrylic polymer includes a polyfunctional monomer as a monomer component constituting the polymer.

4. The double-sided adhesive sheet according to claim 1 or 2, wherein the acrylic polymer has a structural component derived from a photopolymerization initiator.

5. The double-sided adhesive sheet according to claim 1 or 2, wherein the acrylic polymer comprises a constituent unit derived from a monomer component (B) having a non-aromatic ring and a glass transition temperature of the homopolymer of 0°C or higher.

6. A double-sided adhesive sheet according to claim 1 or 2, for fixing components together in electrical and electronic equipment.

7. The double-sided adhesive sheet described in claim 6 is provided, The aforementioned double-sided adhesive sheet is used to fix components together on both adhesive surfaces in an electrical and electronic device.

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