Adhesive sheet

Abstract

Provided is an adhesive sheet having excellent bending resistance in various environments. The pressure-sensitive adhesive sheet (1) is provided with a pressure-sensitive adhesive layer (2). The pressure-sensitive adhesive layer (2) contains: an acrylic polymer which has a glass transition temperature of less than-55 DEG C as determined on the basis of the Fox formula and which contains one or more types of monomers containing functional groups as structural units; the adhesive layer (2) has an elastic modulus of 4.0 MPa or less at-20 DEG C, a 180 DEG peel adhesive force of 6.0 N / 20 mm or more at room temperature with respect to an SUS stainless steel plane, and a temperature of 60 DEG C and a relative humidity of 90% RH of 2.5 N / 20 mm or more.

Description

Technical Field

[0001] The present invention relates to an adhesive sheet. Background Art

[0002] Adhesive sheets for image display devices such as mobile phones, smartphones, digital cameras, liquid crystal displays (LCDs), organic EL displays, and portable electronic devices are required to have various performances represented by high adhesive force.

[0003] In recent years, organic EL panels using bendable substrates (flexible substrates) such as resin films have been put into practical use, and bendable flexible displays have been proposed. In a flexible display, in addition to the display panel such as an organic EL panel being bendable, the constituent members are also bendable, and these members are bonded via an adhesive sheet. In a foldable flexible display, bending is repeatedly performed at the same position. At the bending portion, compressive stress is applied to the inner side and tensile stress is applied to the outer side, and strain is generated at the bending portion and its periphery. Therefore, there is a concern that breakage, marks, or peeling of the adhesive layer may occur at the bending portion.

[0004] For example, in Patent Documents 1 to 7, adhesive sheets for the purpose of having bend resistance are disclosed.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2018-111754

[0008] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2019-108498

[0009] Patent Document 3: Japanese Unexamined Patent Application Publication No. 2020-111734

[0010] Patent Document 4: Japanese Unexamined Patent Application Publication No. 2020-139034

[0011] Patent Document 5: Japanese Unexamined Patent Application Publication No. 2020-164575

[0012] Patent Document 6: Japanese Unexamined Patent Application Publication No. 2018-27996

[0013] Patent Document 7: Japanese Unexamined Patent Application Publication No. 2019-218513 Summary of the Invention

[0014] Problems to be Solved by the Invention

[0015] When considering the possibility of using flexible displays in the world, it is not enough that the bending resistance at normal temperature is excellent only in Japan. Excellent bending resistance in various environments is required. However, even when conventional adhesive sheets have bending resistance at normal temperature, they sometimes have poor bending resistance in low-temperature, high-temperature / high-humidity environments.

[0016] In order to improve the bending resistance at low temperature, it is considered to use a polymer with a low glass transition temperature as the base polymer in the adhesive layer constituting the adhesive sheet. And in order to improve the bending resistance in high-temperature, high-humidity environments, it is considered to incorporate a large amount of tackifier in the above-mentioned adhesive layer. However, if a large amount of tackifier is added, the bending resistance at low temperature will decrease. Therefore, it is difficult to produce an adhesive sheet with excellent bending resistance from low temperature to high temperature. It should be noted that although an adhesive layer with excellent bending resistance at -20°C to 85°C is disclosed in Patent Document 7, higher bending resistance is required.

[0017] The present invention is an invention conceived based on such actual situations, and its object is to provide an adhesive sheet with excellent bending resistance in various environments.

[0018] Solution to the problem

[0019] The inventors of the present invention conducted in-depth research to achieve the above object, and as a result, found that according to a specific adhesive sheet, the bending resistance is excellent in various environments. The present invention was completed based on these insights.

[0020] That is, the present invention provides an adhesive sheet having an adhesive layer containing an acrylic polymer and a tackifier. Regarding the acrylic polymer, the glass transition temperature calculated based on the Fox formula is less than -55°C, and it contains one or more monomers containing functional groups as structural units. The elastic modulus of the adhesive layer at -20°C is 4.0 MPa or less, the 180° peel adhesion force to a SUS stainless steel plane is 6.0 N / 20 mm or more at room temperature, and 2.5 N / 20 mm or more at a temperature of 60°C and a relative humidity of 90%RH.

[0021] Preferably, the tackifier contains an oligomer or a tackifying resin.

[0022] Preferably, the content ratio of the tackifier exceeds 0% by mass and is less than 20% by mass relative to the total amount of the adhesive layer.

[0023] Preferably, the thickness of the adhesive layer is 50 μm or less.

[0024] Alternatively, the adhesive sheet may be a double-sided adhesive sheet for fixing components of electrical and electronic devices to each other.

[0025] In addition, the present invention provides an electrical and electronic device including the adhesive sheet, which fixes components to each other through two adhesive surfaces.

[0026] Advantages of the Invention

[0027] The adhesive sheet according to the present invention has excellent bend resistance in various environments. Therefore, even when used in a part where bending is repeatedly performed, breakage, traces, or peeling of the adhesive sheet are not likely to occur at the bent part. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a schematic cross-sectional view of an adhesive sheet according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0029] [Adhesive Sheet]

[0030] The adhesive sheet according to an embodiment of the present invention includes at least an adhesive layer containing an acrylic polymer and a tackifier. For the acrylic polymer, the glass transition temperature calculated based on the Fox formula is less than -55°C, and contains one or more monomers containing functional groups as structural units. The elastic modulus of the adhesive layer at -20°C is 4.0 MPa or less, the 180° peel adhesion to a SUS stainless steel plane is 6.0 N / 20 mm or more at room temperature, and 2.5 N / 20 mm or more at a temperature of 60°C and a relative humidity of 90% RH. It should be noted that in this specification, the above-mentioned adhesive layer is sometimes referred to as "the adhesive layer of the present invention".

[0031] The adhesive sheet of the present invention may be a so-called "substrate-free type" adhesive sheet without a substrate (substrate layer), or may be an adhesive sheet with a substrate. It should be noted that in this specification, the "substrate-free type" adhesive sheet is sometimes referred to as "substrate-free adhesive sheet", and the adhesive sheet with a substrate is sometimes referred to as "adhesive sheet with a substrate". Examples of the substrate-free adhesive sheet include: a double-sided adhesive sheet composed only of the adhesive layer of the present invention, a double-sided adhesive sheet composed of the adhesive layer of the present invention and other adhesive layers (adhesive layers other than the adhesive layer of the present invention), etc. In addition, examples of the adhesive sheet with a substrate include: a single-sided adhesive sheet having the adhesive layer of the present invention on one side of the substrate, a double-sided adhesive sheet having the adhesive layer of the present invention on both sides of the substrate, a double-sided adhesive sheet having the adhesive layer of the present invention on one side of the substrate and other adhesive layers on the other side, etc. It should be noted that the above-mentioned "substrate (substrate layer)" is a support, and is the part that is attached to the adherend together with the adhesive layer when the adhesive sheet of the present invention is used (attached) to the adherend. The release liner peeled off when the adhesive sheet is used (attached) is not included in the above substrate.

[0032] Figure 1 This is a schematic cross-sectional view showing an embodiment of the adhesive sheet of the present invention. Figure 1 The shown adhesive sheet 1 is a substrate-free double-sided adhesive sheet composed of a single adhesive layer 2 which is the adhesive layer of the present invention, and release liners 3 and 4 are provided on its two adhesive surfaces respectively.

[0033] (Adhesive layer of the present invention)

[0034] The adhesive sheet of the present invention may have only one adhesive layer, or may have two or more adhesive layers. In the case of having two or more layers, at least one layer is the adhesive layer of the present invention, and the other adhesive layers may be the adhesive layer of the present invention or other adhesive layers. In the case of having two or more adhesive layers of the present invention, the multiple adhesive layers of the present invention may be the same adhesive layer, or may be adhesive layers with different compositions, thicknesses, physical properties, etc. In addition, in the case of an adhesive sheet with a substrate, the adhesive layer provided on one surface of the substrate may be a single layer, or may be a multi-layer composed of the same layer or layers with different compositions, thicknesses, physical properties, etc.

[0035] The elastic modulus of the adhesive layer of the present invention at -20°C is 4.0 MPa or less, preferably 3.0 MPa or less, more preferably 2.0 MPa or less. Since the above elastic modulus is 4.0 MPa or less, even when repeatedly bent at low temperatures, it is not easy to have breakage, marks at the bending part or peeling of the adhesive sheet, and the bending resistance is excellent. The above elastic modulus is, for example, 0.1 MPa or more, preferably 0.5 MPa or more.

[0036] It should be noted that the "elastic modulus" in this specification refers to the dynamic shear storage modulus (G'), for example, it can be measured by a viscoelasticity tester while applying a shear strain of 1 Hz and heating at a rate of 5°C / minute in the temperature range of -50 to 150°C in a shear mode, and the peak value of G' at any temperature is obtained as the elastic modulus.

[0037] The 180° peel adhesion force of the adhesive layer of the present invention with respect to the SUS stainless steel plane at room temperature is 6.0 N / 20 mm or more, preferably 6.5 N / 20 mm or more, more preferably 7.0 N / 20 mm or more, and further preferably 7.5 N / 20 mm or more. Since the above peel adhesion force is 6.0 N / 20 mm or more, even when repeatedly bent near room temperature, it is not easy to have peeling of the adhesive sheet, and the bending resistance is excellent. The higher the above peel adhesion force, the less likely it is to have peeling, but it is, for example, 20.0 N / 20 mm or less. The above room temperature refers to an environment of a temperature of 23°C and a relative humidity of 50% RH, for example.

[0038] The 180° peel adhesion of the adhesive layer of the present invention with respect to the SUS stainless steel plane at a temperature of 60°C and a relative humidity of 90% RH is 2.5 N / 20 mm or more, preferably 3.0 N / 20 mm or more, and more preferably 3.5 N / 20 mm or more. Since the above-mentioned peel adhesion is 2.5 N / 20 mm or more, even when repeatedly bent in a high-temperature and high-humidity environment, the adhesive sheet is not easily peeled off, and the bending resistance is excellent. The higher the above-mentioned peel adhesion, the less likely it is to peel off, but for example, it is 20.0 N / 20 mm or less.

[0039] As the adhesive constituting the adhesive layer of the present invention, known or conventional adhesives can be used, and there is no particular limitation. For example, acrylic adhesives, rubber adhesives (natural rubber-based, synthetic rubber-based, their mixed systems, etc.), silicone adhesives, polyester adhesives, urethane adhesives, polyether adhesives, polyamide adhesives, fluorine adhesives, styrene adhesives, etc. can be cited. Among them, as the adhesive constituting the adhesive layer, acrylic adhesives are preferred in terms of adhesiveness, weather resistance, cost, and ease of design of the adhesive. The above-mentioned adhesives can be used alone or in combination of two or more.

[0040] The above-mentioned acrylic adhesive may contain an acrylic polymer as the basic polymer. It should be noted that in this specification, the basic polymer refers to the main component in the polymer components of the adhesive constituting the adhesive layer, for example, containing more than 50% by mass of the polymer components. The content ratio of the basic polymer in the above-mentioned adhesive layer is preferably 60% by mass or more, and more preferably 70% by mass or more, based on the total amount of the adhesive layer of 100% by mass.

[0041] The adhesive layer of the present invention contains at least an acrylic polymer and a tackifier. For the acrylic polymer, the glass transition temperature calculated based on the Fox formula is less than -55°C, and contains one or more monomers containing functional groups as structural units. Sometimes the above-mentioned acrylic polymer is referred to as "the acrylic polymer of the present invention". The adhesive layer of the present invention may contain only one acrylic polymer of the present invention, or may contain two or more acrylic polymers of the present invention.

[0042] The glass transition temperature (Tg) of the acrylic polymer of the present invention is less than -55°C, preferably -60°C or lower, and more preferably -62°C or lower. Since the above-mentioned glass transition temperature is less than -55°C, even when repeatedly bent at low temperatures, it is not easy to have breakage, marks or peeling of the adhesive sheet at the bending part. The above-mentioned glass transition temperature is preferably -80°C or higher, more preferably -70°C or higher, and further preferably -66°C or higher.

[0043] The above glass transition temperature is a value calculated based on the following formula (X) (Fox formula).

[0044] 1 / Tg = W1 / Tg1 + W2 / Tg2 + …… + Wn / Tgn (X)

[0045] [In formula (X), Tg represents the glass transition temperature of the polymer (unit: K), Tgi (i = 1, 2, …… n) represents the glass transition temperature of the homopolymer formed by monomer i (unit: K), and Wi (i = 1, 2, …… n) represents the mass fraction of monomer i in all monomer components.]

[0046] The above formula (X) is the calculation formula for the case where the polymer is composed of n monomer components of monomer 1, monomer 2, ……, monomer n.

[0047] It should be noted that the "glass transition temperature (Tg) when forming a homopolymer" in this specification (sometimes only referred to as "Tg of the homopolymer") refers to "the glass transition temperature (Tg) of the homopolymer of this monomer". Specifically, the values in "Polymer Handbook" (Third Edition, John Wiley & Sons, Inc, 1987) can be cited. It should be noted that for the Tg of the homopolymer of a monomer not recorded in the above literature, except for monomers having a polysiloxane backbone, for example, it refers to the value obtained by the following measurement method (refer to Japanese Patent Laid-Open No. 2007-51271). That is, into a reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser, 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 charged, and nitrogen is introduced while stirring for 1 hour. In this way, the oxygen in the polymerization system is removed, and then the temperature is raised to 63°C and reacted for 10 hours. Then, it is cooled to room temperature to obtain a homopolymer solution with a solid content concentration of 33 mass%. Then, the homopolymer solution is cast and coated on a release liner, dried, and a test sample (sheet-like homopolymer) with a thickness of about 2 mm is prepared. Then, the test sample is punched into a disk shape with a diameter of 7.9 mm, clamped with parallel plates, and using a viscoelasticity tester (trade name "ARES", manufactured by Rheometrics Corporation), while applying a shear strain of 1 Hz, the viscoelasticity is measured in the temperature range of -70 to 150°C at a heating rate of 5°C / minute through the shear mode, and the peak temperature of tanδ is set as the Tg of the homopolymer.

[0048] The acrylic polymer of the present invention 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 above acrylic polymer contains a structural unit derived from an acrylic monomer. It should be noted that only one kind of acrylic polymer may be used, or two or more kinds may be used. In addition, the above acrylic polymer may contain only one kind of acrylic monomer as a monomer component, or may contain two or more kinds of acrylic monomers as a monomer component. It should be noted that in this specification, "(meth)acrylic acid" means "acrylic acid" and / or "methacrylic acid" (either one or both of "acrylic acid" and "methacrylic acid"), and the same applies to others.

[0049] The above acrylic polymer is preferably a polymer containing the largest amount of a structural unit derived from a (meth)acrylate in terms of mass ratio. Examples of the above (meth)acrylate include a (meth)acrylate containing a hydrocarbon group. Examples of the above (meth)acrylate containing a hydrocarbon group include: a (meth)acrylic acid alkyl ester having a linear or branched aliphatic hydrocarbon group, a (meth)acrylic acid cycloalkyl ester such as a (meth)acrylic acid ester having an alicyclic hydrocarbon group, and a (meth)acrylic acid aryl ester such as a (meth)acrylic acid ester having an aromatic hydrocarbon group. Only one kind of the above (meth)acrylate containing a hydrocarbon group may be used, or two or more kinds may be used.

[0050] Examples of the above (meth)acrylic acid alkyl ester include: methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate (lauryl (meth)acrylate), tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, eicosyl (meth)acrylate, etc.

[0051] As the above-mentioned (meth)acrylic acid alkyl ester, preferably, it is a (meth)acrylic acid alkyl ester having a linear or branched aliphatic hydrocarbon group with 1 to 20 carbon atoms (preferably 2 to 12 carbon atoms, more preferably 6 to 10 carbon atoms). If the number of carbon atoms is within the above range, it is easy to adjust the glass transition temperature of the above acrylic polymer, and it is easy to make the bending resistance at low temperature more appropriate.

[0052] As the above-mentioned (meth)acrylic acid ester having an alicyclic hydrocarbon group, for example, (meth)acrylic acid cyclopentyl ester, (meth)acrylic acid cyclohexyl ester, (meth)acrylic acid cycloheptyl ester, (meth)acrylic acid cyclooctyl ester and other (meth)acrylic acid esters having a monocyclic aliphatic hydrocarbon ring can be cited; (meth)acrylic acid isobornyl ester and other (meth)acrylic acid esters having a bicyclic aliphatic hydrocarbon ring; (meth)acrylic acid dicyclopentyl ester, (meth)acrylic acid dicyclopentyloxyethyl ester, (meth)acrylic acid tricyclopentyl ester, (meth)acrylic acid 1-adamantyl ester, (meth)acrylic acid 2-methyl-2-adamantyl ester, (meth)acrylic acid 2-ethyl-2-adamantyl ester and other (meth)acrylic acid esters having an aliphatic hydrocarbon ring with three or more rings, etc.

[0053] As the above-mentioned (meth)acrylic acid ester having an aromatic hydrocarbon group, for example, phenyl (meth)acrylate, benzyl (meth)acrylate, etc. can be cited.

[0054] In order to appropriately exhibit the basic properties such as adhesiveness brought by the above-mentioned hydrocarbon group-containing (meth)acrylic acid ester in the adhesive layer, the proportion of the above-mentioned hydrocarbon group-containing (meth)acrylic acid ester in all monomer components constituting the above acrylic polymer is preferably 50% by mass or more, more preferably 60% by mass or more, further preferably 70% by mass or more, and may also be 80% by mass or more, 90% by mass or more, 95% by mass or more, relative to the total amount (100% by mass) of all monomer components. In addition, from the viewpoint of being able to copolymerize with other monomer components and obtaining the effects of other monomer components, the above proportion can be 99.9% by mass or less, and can also be 98% by mass or less, 95% by mass or less, 90% by mass or less.

[0055] The acrylic polymer of the present invention contains at least a monomer containing a functional group as a structural unit. As the above-mentioned monomer containing a functional group, monomers containing polar groups such as a hydroxyl group-containing monomer, a nitrogen atom-containing monomer, a carboxyl group-containing monomer, an acid anhydride monomer, a keto group-containing monomer, an alkoxysilyl group-containing monomer, a glycidyl group-containing monomer, a sulfonic acid group-containing monomer, a phosphoric acid group-containing monomer, etc. can be cited. As the above-mentioned monomer containing a functional group, preferably, a hydroxyl group-containing monomer and a carboxyl group-containing monomer. The above-mentioned monomer containing a functional group can be used alone or in combination of two or more.

[0056] Examples of the above-mentioned hydroxyl group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, methyl (4-hydroxymethylcyclohexyl) (meth)acrylate, etc.

[0057] Examples of the above-mentioned nitrogen atom-containing monomers include amide group-containing monomers, amino group-containing monomers, cyano group-containing monomers, monomers having a nitrogen atom-containing ring, etc. Examples of the above-mentioned amide group-containing monomers include (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-butyl(meth)acrylamide, N-hydroxymethyl(meth)acrylamide, N-hydroxymethylpropane(meth)acrylamide, N-methoxymethyl(meth)acrylamide, N-butoxymethyl(meth)acrylamide, etc. Examples of the above-mentioned amino group-containing monomers include aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, tert-butylaminoethyl (meth)acrylate, etc. Examples of the above-mentioned cyano group-containing monomers include acrylonitrile, methacrylonitrile. Examples of the above-mentioned monomers having a nitrogen atom-containing ring include N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-vinylmorpholine, N-vinylcaprolactam, N-(meth)acryloylmorpholine, etc.

[0058] Examples of the above-mentioned carboxyl group-containing monomers include acrylic acid, methacrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, etc. Examples of the above-mentioned acid anhydride monomers include maleic anhydride, itaconic anhydride, etc.

[0059] Examples of the above-mentioned keto group-containing monomers include diacetone (meth)acrylamide, diacetone (meth)acrylate, vinyl methyl ketone, vinyl ethyl ketone, allyl acetoacetate, vinyl acetoacetate, etc.

[0060] Examples of the above-mentioned alkoxysilyl group-containing monomers include 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, 3-(meth)acryloxypropylmethyldiethoxysilane, etc.

[0061] As the glycidyl group-containing monomer described above, examples thereof include glycidyl (meth)acrylate, methyl glycidyl (meth)acrylate, and the like.

[0062] As the sulfonic acid group-containing monomer described above, examples thereof include styrene sulfonic acid, allyl sulfonic acid, 2-(meth)acrylamide-2-methylpropanesulfonic acid, (meth)acrylamidopropanesulfonic acid, (meth)acrylic acid sulfopropyl ester, (meth)acryloyloxynaphthalene sulfonic acid, and the like.

[0063] As the phosphoric acid group-containing monomer described above, examples thereof include 2-hydroxyethyl acryloyl phosphate and the like.

[0064] The total proportion of the functional group-containing monomers in all the monomer components (100% by mass) constituting the acrylic polymer of the present invention is not particularly limited. From the viewpoint of better exerting the effects brought about by using the functional group-containing monomers, it is preferably 0.1% by mass or more, more preferably 1% by mass or more. In addition, the total of the above proportions is preferably 10% by mass or less, more preferably 8% by mass or less. If the above proportion is 10% by mass or less, peeling is less likely to occur even when repeatedly subjected to bending in a high-temperature and high-humidity environment.

[0065] As the monomer components constituting the acrylic polymer of the present invention, other monomers may be further included. As the above other monomers, examples thereof include vinyl ester monomers such as vinyl acetate, vinyl propionate, vinyl laurate; aromatic vinyl compounds such as styrene, substituted styrene (α-methylstyrene, etc.), vinyltoluene; olefin monomers such as ethylene, propylene, isoprene, butadiene, isobutene; chlorine-containing monomers such as vinyl chloride, vinylidene chloride; alkoxy group-containing monomers such as (meth)acrylic acid 2-methoxyethyl ester, (meth)acrylic acid 2-ethoxyethyl ester; vinyl ether monomers such as methyl vinyl ether, ethyl vinyl ether, and the like. Each of the above other monomer components may be used alone or two or more thereof may be used.

[0066] As the alkoxy group-containing monomer, monomers obtained by substituting one or more hydrogen atoms in the hydrocarbon group of the above hydrocarbon group-containing (meth)acrylate with an alkoxy group can be mentioned. For example, alkoxy group-containing hydrocarbon group-containing (meth)acrylates such as (meth)acrylic acid methoxymethyl ester, (meth)acrylic acid 2-methoxyethyl ester, (meth)acrylic acid 2-methoxybutyl ester, (meth)acrylic acid 2-ethoxyethyl ester, (meth)acrylic acid ethoxyethoxyethyl ester (ethyl carbitol (meth)acrylate), and the like can be mentioned.

[0067] The proportion of the above-mentioned other monomers in the total amount of 100% by mass of all monomer components constituting the acrylic polymer of the present invention may be, for example, 0.05% by mass or more, 0.5% by mass or more, 5% by mass or more, 10% by mass or more. The above proportion may be, for example, 20% by mass or less, 10% by mass or less, 5% by mass or less, and may also be substantially free of the above-mentioned other monomers.

[0068] The weight average molecular weight (Mw) of the acrylic polymer of the present invention is preferably 50×10 4 or more, more preferably 80×10 4 or more, still more preferably 90×10 4 or more, particularly preferably 110×10 4 or more. If the above Mw is 50×10 4 or more, it is easy to obtain an adhesive showing good cohesiveness. In addition, the above Mw is preferably 500×10 4 or less, more preferably 200×10 4 or less. If the above Mw is 500×10 4 or less, it is easy to form an adhesive showing appropriate fluidity (mobility of polymer chains), and thus the bending resistance is more excellent.

[0069] The acrylic polymer of the present invention is obtained by polymerizing a composition containing at least an acrylic monomer. As their polymerization methods, there is no particular limitation, and examples thereof include: solution polymerization method, emulsion polymerization method, bulk polymerization method, thermal polymerization method, polymerization method using active energy ray irradiation (active energy ray polymerization method), etc. Among them, from the viewpoints of transparency, cost, etc. of the adhesive layer, the bulk polymerization method, thermal polymerization method, and active energy ray polymerization method are preferred. In addition, the obtained acrylic polymer may be any one of random copolymer, block copolymer, graft copolymer, etc.

[0070] In the polymerization of monomer components, various ordinary solvents can be used. Examples of the above 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; ketones such as methyl ethyl ketone and methyl isobutyl ketone, etc. organic solvents. The above solvents may be used alone or in combination of two or more.

[0071] There is no particular limitation on the polymerization initiator, chain transfer agent, emulsifier, etc. for the radical polymerization of monomer components, and they can be appropriately selected and used. It should be noted that the weight average molecular weight of the polymer can be controlled by the usage amounts of the polymerization initiator and chain transfer agent and the reaction conditions, and the appropriate usage amounts are adjusted according to their types.

[0072] As a polymerization initiator for the polymerization of monomer components, a thermal polymerization initiator, a photo-polymerization initiator (photoinitiator), etc. can be used according to the type of polymerization reaction. The above polymerization initiator can be used alone or in combination of two or more.

[0073] The above thermal polymerization initiator is not particularly limited, and examples thereof include: azo polymerization initiators, peroxide polymerization initiators (such as dibenzoyl peroxide, tert-butyl peroxy maleate, persulfates such as potassium persulfate, benzoyl peroxide, hydrogen peroxide, etc.), substituted ethane-based initiators such as phenyl-substituted ethane, aromatic carbonyl compounds, redox polymerization initiators, etc. Among them, the azo polymerization initiator disclosed in JP-A No. 2002-69411 is preferably used. Examples of the above azo polymerization initiator include: 2,2'-azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis(2-methylpropionic acid) dimethyl ester, 4,4'-azobis-4-cyanovaleric acid, etc. The amount of the thermal polymerization initiator used may be a usual amount. For example, it can be selected from the range of, for example, 0.01 to 5 parts by mass, preferably 0.05 to 3 parts by mass, relative to 100 parts by mass of the monomer component.

[0074] As the above-mentioned photoinitiator, there is no particular limitation, and examples thereof include: benzoin ether-based photoinitiators, acetophenone-based photoinitiators, α-ketol-based photoinitiators, aromatic sulfonyl chloride-based photoinitiators, photoactive oxime-based photoinitiators, benzoin-based photoinitiators, benzil-based photoinitiators, benzophenone-based photoinitiators, ketal-based photoinitiators, thioxanthone-based photoinitiators, etc. In addition, acylphosphine oxide-based photoinitiators and titanocene-based photoinitiators can also be cited. As the above-mentioned benzoin ether-based photoinitiators, for example, benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, benzoin isobutyl ether, 2,2-dimethoxy-1,2-diphenylethane-1-one, anisole methyl ether, etc. can be cited. As the above-mentioned acetophenone-based photoinitiators, for example, 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexyl phenyl ketone, 4-phenoxydichloroacetophenone, 4-(tert-butyl)dichloroacetophenone, etc. can be cited. As the above-mentioned α-ketol-based photoinitiators, for example, 2-methyl-2-hydroxypropiophenone, 1-[4-(2-hydroxyethyl)phenyl]-2-methylpropan-1-one, etc. can be cited. As the above-mentioned aromatic sulfonyl chloride-based photoinitiators, for example, 2-naphthalenesulfonyl chloride, etc. can be cited. As the above-mentioned photoactive oxime-based photoinitiators, for example, 1-phenyl-1,1-propanedione-2-(O-ethoxycarbonyl)-oxime, etc. can be cited. As the above-mentioned benzoin-based photoinitiators, for example, benzoin can be cited. As the above-mentioned benzil-based photoinitiators, for example, benzil can be cited. As the above-mentioned benzophenone-based photoinitiators, for example, benzophenone, benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, polyvinylbenzophenone, α-hydroxycyclohexyl phenyl ketone, etc. can be cited. As the above-mentioned ketal-based photoinitiators, for example, benzil dimethyl ketal, etc. can be cited. As the above-mentioned thioxanthone-based photoinitiators, for example, thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-diisopropylthioxanthone, dodecylthioxanthone, etc. can be cited. As the above-mentioned acylphosphine oxide-based photoinitiators, for example, 2,4,6-trimethylbenzoyl diphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, etc. can be cited. As the above-mentioned titanocene-based photoinitiators, for example, bis(η5-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)-phenyl)titanium, etc. can be cited. The usage amount of the photoinitiator may be the usual usage amount. For example, it can be selected from the range of, for example, 0.01 to 5 parts by mass, preferably 0.05 to 3 parts by mass, relative to 100 parts by mass of the monomer component.

[0075] The acrylic polymer of the present invention may also contain a structural part derived from the above crosslinking agent. That is, the acrylic polymer of the present invention may be a polymer crosslinked with the above crosslinking agent. By using a crosslinking agent, a crosslinked structure can be formed in the acrylic polymer of the acrylic adhesive layer to control the gel fraction. The above crosslinking agent may be used alone or in combination of two or more.

[0076] The above crosslinking agent is not particularly limited, and examples thereof include: isocyanate-based crosslinking agents, epoxy-based crosslinking agents, melamine-based crosslinking agents, peroxide-based crosslinking agents, urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, carbodiimide-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, amine-based crosslinking agents, hydrazine-based crosslinking agents, silicone-based crosslinking agents, silane-based crosslinking agents (silane coupling agents), etc.

[0077] The content of the above crosslinking agent is not particularly limited, and is preferably 0.001 to 20 parts by mass, more preferably 0.01 to 15 parts by mass, and particularly preferably 0.5 to 10 parts by mass, based on 100 parts by mass of the total amount of the monomer components constituting the acrylic polymer of the present invention.

[0078] The above isocyanate-based crosslinking agent is a compound having an average of two or more isocyanate groups per molecule (polyfunctional isocyanate compound). Examples of the above isocyanate-based crosslinking agent include: aliphatic polyisocyanates, alicyclic polyisocyanates, aromatic polyisocyanates, etc.

[0079] Examples of the above aliphatic polyisocyanates include: 1,2-ethylene diisocyanate; 1,2-tetramethylene diisocyanate, 1,3-tetramethylene diisocyanate, 1,4-tetramethylene diisocyanate, etc. of tetramethylene diisocyanate; 1,2-hexamethylene diisocyanate, 1,3-hexamethylene diisocyanate, 1,4-hexamethylene diisocyanate, 1,5-hexamethylene diisocyanate, 1,6-hexamethylene diisocyanate, 2,5-hexamethylene diisocyanate, etc. of hexamethylene diisocyanate; 2-methyl-1,5-pentane diisocyanate, 3-methyl-1,5-pentane diisocyanate, lysine diisocyanate, etc.

[0080] Examples of the above alicyclic polyisocyanates include: isophorone diisocyanate; 1,2-cyclohexyl diisocyanate, 1,3-cyclohexyl diisocyanate, 1,4-cyclohexyl diisocyanate, etc. of cyclohexyl diisocyanate; 1,2-cyclopentyl diisocyanate, 1,3-cyclopentyl diisocyanate, etc. of cyclopentyl diisocyanate; hydrogenated benzene dimethylene diisocyanate, hydrogenated toluene diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated tetramethylxylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, etc.

[0081] Examples of the above-mentioned aromatic polyisocyanates include 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 4,4'-diphenyl ether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, 2,2'-diphenylpropane-4,4'-diisocyanate, 3,3'-dimethyl diphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropane diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, naphthylene-1,4-diisocyanate, naphthylene-1,5-diisocyanate, 3,3'-dimethoxy diphenyl-4,4'-diisocyanate, benzene dimethylene-1,4-diisocyanate, benzene dimethylene-1,3-diisocyanate, etc.

[0082] In addition, examples of the above-mentioned isocyanate-based crosslinking agents include commercially available products such as trimethylolpropane / toluene diisocyanate adduct (trade name "CORONATE L", manufactured by TOSOH Corporation), trimethylolpropane / hexamethylene diisocyanate adduct (trade name "CORONATE HL", manufactured by TOSOH Corporation), trimethylolpropane / benzene dimethylene diisocyanate adduct (trade name "TAKENATE D-110N", manufactured by Mitsui Chemicals, Inc.).

[0083] It should be noted that in the aqueous dispersion of the modified acrylic polymer prepared by emulsion polymerization, an isocyanate-based crosslinking agent may not be used, but in cases where it is required, a blocked isocyanate-based crosslinking agent may also be used for easy reaction with water.

[0084] When using an isocyanate-based crosslinking agent as the above-mentioned crosslinking agent, the content of the isocyanate-based crosslinking agent is not particularly limited. Relative to 100 parts by mass of the total amount of the monomer components constituting the acrylic polymer of the present invention, it is preferably 0.5 part by mass or more, more preferably 1 part by mass or more, and further preferably 1.5 part by mass or more. The above content is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and further preferably 5 parts by mass or less.

[0085] Examples of the epoxy crosslinking agent (polyfunctional epoxy compound) described above include: N,N,N',N'-tetraglycidyl-m-xylenediamine, diglycidylaniline, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, sorbitol polyglycidyl ether, glycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitan polyglycidyl ether, trimethylolpropane polyglycidyl ether, adipic acid diglycidyl ester, phthalic acid diglycidyl ester, triglycidyl tris(2-hydroxyethyl)isocyanurate, resorcinol diglycidyl ether, bisphenol-S-diglycidyl ether, and epoxy resins having two or more epoxy groups in the molecule. In addition, examples of the epoxy crosslinking agent described above include commercially available products such as the product named "TETRAD C" (manufactured by MITSUBISHI GAS CHEMICAL COMPANY, INC.).

[0086] When using an epoxy crosslinking agent as the above crosslinking agent, the content of the epoxy crosslinking agent is not particularly limited. Relative to 100 parts by mass of the total monomer components constituting the acrylic polymer of the present invention, it is preferably more than 0 part by mass and 1 part by mass or less, more preferably 0.001 to 0.5 part by mass, further preferably 0.002 to 0.2 part by mass, further preferably 0.005 to 0.1 part by mass, further preferably 0.008 to 0.1 part by mass, and particularly preferably 0.009 to 0.05 part by mass.

[0087] As the peroxide crosslinking agent, any crosslinking agent that generates free radical active species by heat and crosslinks the base polymer can be appropriately used. However, considering workability and stability, peroxides having a 1-minute half-life temperature of 80 to 160 °C are preferably used, and peroxides having a 1-minute half-life temperature of 90 to 140 °C are more preferably used.

[0088] Examples of the peroxide crosslinking agent described above include: bis(2-ethylhexyl) peroxydicarbonate (1-minute half-life temperature: 90.6 °C), bis(4-tert-butylcyclohexyl) peroxydicarbonate (1-minute half-life temperature: 92.1 °C), di-sec-butyl peroxydicarbonate (1-minute half-life temperature: 92.4 °C), tert-butyl peroxyneodecanoate (1-minute half-life temperature: 103.5 °C), tert-hexyl peroxyneopentanoate (1-minute half-life temperature: 109.1 °C), tert-butyl peroxyneopentanoate (1-minute half-life temperature: 110.3 °C), dilauroyl peroxide (1-minute half-life temperature: 116.4 °C), di-n-octanoyl peroxide (1-minute half-life temperature: 117.4 °C), 1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanoate (1-minute half-life temperature: 124.3 °C), bis(4-methylbenzoyl) peroxide (1-minute half-life temperature: 128.2 °C), benzoyl peroxide (1-minute half-life temperature: 130.0 °C), tert-butyl peroxyisobutyrate (1-minute half-life temperature: 136.1 °C), 1,1-bis(tert-hexylperoxy) cyclohexane (1-minute half-life temperature: 149.2 °C), etc.

[0089] The half-life of the above peroxide crosslinking agent is an index indicating the decomposition rate of the peroxide, which refers to the time until the residual amount of the peroxide becomes half. The decomposition temperature for obtaining the half-life at any time and the half-life time at any temperature are described in the manufacturer's catalog, etc., for example, in "Organic Peroxide Catalog Ninth Edition (May 2003)" of NOF Corporation, etc. It should be noted that as a method for measuring the decomposition amount of the peroxide remaining after the reaction treatment, for example, it can be measured by HPLC (high performance liquid chromatography). More specifically, for example, about 0.2 g of the adhesive after the reaction treatment is successively taken out, immersed in 10 ml of ethyl acetate, and shaken and extracted at 25 °C at 120 rpm for 3 hours, and then left standing at room temperature for 3 days. Then, 10 ml of acetonitrile is added, shaken at 25 °C at 120 rpm for 30 minutes, filtered using a membrane filter (0.45 μm), and about 10 μl of the obtained extract is injected into HPLC for analysis, so as to obtain the amount of peroxide after the reaction treatment.

[0090] When using a peroxide crosslinking agent as the above crosslinking agent, the content of the above crosslinking agent is not particularly limited. Relative to 100 parts by mass of the total amount of the monomer components constituting the acrylic polymer of the present invention, it is preferably contained in an amount of 2 parts by mass or less, more preferably 0.02 - 2 parts by mass, and further preferably 0.05 - 1 part by mass.

[0091] In addition, as the above-mentioned crosslinking agent, an organic crosslinking agent and a polyfunctional metal chelate may also be used in combination. The polyfunctional metal chelate is a polyfunctional metal chelate formed by covalently bonding or coordinately bonding a polyvalent metal with an organic compound. Examples of the polyvalent metal atom include: Al, Cr, Zr, Co, Cu, Fe, Ni, V, Zn, In, Ca, Mg, Mn, Y, Ce, Sr, Ba, Mo, La, Sn, Ti, etc. Examples of the atom in the organic compound that undergoes covalent bonding or coordinate bonding include an oxygen atom, and examples of the organic compound include: alkyl esters, alcohol compounds, carboxylic acid compounds, ether compounds, ketone compounds, etc.

[0092] As the above-mentioned crosslinking agent, preferably, an isocyanate-based crosslinking agent is included. In addition, it is more preferable to include other crosslinking agents together with the isocyanate-based crosslinking agent. As the above-mentioned other crosslinking agent, an epoxy-based crosslinking agent is preferred. When such a crosslinking agent is used, an adhesive layer having more excellent adhesiveness even when thin can be formed with the acrylic polymer of the present invention.

[0093] The adhesive layer of the present invention contains a tackifier. The adhesive layer of the present invention contains the acrylic polymer of the present invention and a tackifier. As a result, the adhesive layer of the present invention has excellent adhesiveness to the adherend, and is not easily peeled off under various environments even when repeatedly subjected to bending, and has excellent bending resistance. The above-mentioned tackifier may be used alone or in combination of two or more.

[0094] Examples of the above-mentioned tackifier include a tackifying resin and an oligomer. The above-mentioned oligomer may exist in the form of an oligomer in the adhesive layer of the present invention, or may exist in the acrylic polymer of the present invention as a structural part derived from the above-mentioned oligomer. That is, the acrylic polymer of the present invention may have a structural part derived from the above-mentioned oligomer.

[0095] Examples of the above-mentioned tackifying resin include: phenolic tackifying resins, terpene-based tackifying resins, rosin-based tackifying resins, hydrocarbon-based tackifying resins, epoxy-based tackifying resins, polyamide-based tackifying resins, elastomeric tackifying resins, ketone-based tackifying resins, etc. The above-mentioned tackifying resin may be used alone or in combination of two or more.

[0096] Examples of the phenolic tackifying resins described above include terpene phenol resins, hydrogenated terpene phenol resins, alkylphenol formaldehyde resins, and rosin phenol formaldehyde resins. The above-mentioned terpene phenol resin is a polymer containing terpene residues and phenol residues, and examples thereof include copolymers of terpenes and phenolic compounds (terpene-phenol copolymer resins), and resins obtained by phenol-modifying homopolymers or copolymers of terpenes (phenol-modified terpene resins). Examples of the terpenes constituting the above terpene phenol resin include monoterpenes such as α-pinene, β-pinene, limonene (d-form, l-form, d / l-form (dipentene), etc.). The above hydrogenated terpene phenol resin is a resin having a structure obtained by hydrogenating the above terpene phenol resin. The above alkylphenol formaldehyde resin is a resin obtained from alkylphenol and formaldehyde (oil-based phenolic resin). Examples of the above alkylphenol formaldehyde resin include alkylphenol formaldehyde resins of the novolak type and resole type. The above rosin phenol formaldehyde resin is a phenol-modified product of rosin or various rosin derivatives described below. The above rosin phenol formaldehyde resin is obtained, for example, by a method of adding phenol to rosin or various rosin derivatives described below using an acid catalyst and then performing thermal polymerization.

[0097] Examples of the above terpene tackifying resins include polymers of terpenes such as α-pinene, β-pinene, d-limonene, l-limonene, dipentene, etc. (typically, monoterpenes). The polymers of the above terpenes may be homopolymers of one type of terpene or copolymers of two or more types of terpenes. Examples of homopolymers of one type of terpene include α-pinene polymer, β-pinene polymer, dipentene polymer, etc. The above modified terpene tackifying resin is a resin obtained by modifying the above terpene resin (modified terpene resin). Examples of the above modified terpene resin include styrene-modified terpene resin, hydrogenated terpene resin, etc.

[0098] As the above-mentioned rosin-based tackifying resins, rosin and rosin derivative resins can be cited. As the above-mentioned rosins, for example, unmodified rosins (raw rosins) such as gum rosin, wood rosin, and tall oil rosin can be cited; modified rosins (hydrogenated rosin, disproportionated rosin, polymerized rosin, and other chemically modified rosins, etc.) obtained by modifying these unmodified rosins through hydrogenation, disproportionation, polymerization, etc. As the above-mentioned rosin derivative resins, derivatives of the above-mentioned rosins can be cited. As the above-mentioned rosin derivative resins, for example, rosin esters such as esters of unmodified rosin and alcohols (i.e., unmodified rosin esters) and esters of modified rosin and alcohols (i.e., modified rosin esters); unsaturated fatty acid-modified rosins obtained by modifying rosins with unsaturated fatty acids; unsaturated fatty acid-modified rosin esters obtained by modifying rosin esters with unsaturated fatty acids; rosin alcohols obtained by reducing the carboxyl groups of rosins or the above-mentioned various rosin derivatives; metal salts of rosins or the above-mentioned various rosin derivatives. As specific examples of the above-mentioned rosin esters, methyl esters, triethylene glycol esters, glycerol esters, pentaerythritol esters, etc. of unmodified rosin or modified rosin can be cited.

[0099] As the above-mentioned hydrocarbon-based tackifying resins, aliphatic hydrocarbon resins, aromatic hydrocarbon resins, aliphatic cyclic hydrocarbon resins, aliphatic-aromatic petroleum resins (such as styrene-olefin copolymers), aliphatic-alicyclic petroleum resins, hydrogenated hydrocarbon resins, coumarone resins, coumarone-indene resins, etc. can be cited.

[0100] The softening point of the above-mentioned tackifying resin is preferably 160 °C or lower, more preferably 150 °C or lower, further preferably 140 °C or lower, and particularly preferably 120 °C or lower. If the above-mentioned softening point is low, the elastic modulus can be maintained low even when added in a small amount, and the bending resistance is further excellent in various environments. The above-mentioned softening point is, for example, 60 °C or higher, preferably 70 °C or higher.

[0101] The weight average molecular weight of the above-mentioned oligomer is preferably 2500 to 10000, more preferably 3000 to 8000. It should be noted that the above-mentioned weight average molecular weight can be determined by the GPC method in terms of polystyrene conversion. For example, a high-speed GPC device "HPLC-8120GPC" manufactured by TOSOH Corporation can be used for measurement under the following conditions.

[0102] Chromatographic column: TSKgel SuperHZM-H / HZ4000 / HZ3000 / HZ2000.

[0103] Solvent: Tetrahydrofuran.

[0104] Flow rate: 0.6 ml / minute.

[0105] The above oligomer is preferably an acrylic oligomer composed of acrylic monomers as essential monomer components. As for the acrylic monomers that are monomer components constituting the above acrylic oligomer, the monomers exemplified and described as monomer components constituting the acrylic polymer of the present invention can be cited. The above acrylic oligomer preferably contains a (meth)acrylate having an alicyclic hydrocarbon group as a structural unit. The acrylic monomer contained as the above structural unit may be only one kind, or two or more kinds.

[0106] The proportion of the (meth)acrylate having an alicyclic hydrocarbon group in the total amount of 100% by mass of all monomer components constituting the above acrylic oligomer is preferably 40% by mass or more, more preferably 50% by mass or more, and further preferably 55% by mass or more. The above proportion is preferably 99% by mass or less, and may be 97% by mass or less.

[0107] As for the above acrylic oligomer, as one embodiment, it preferably contains a (meth)acrylic acid alkyl ester as a structural unit. As the (meth)acrylic acid alkyl ester, methyl methacrylate (MMA) is preferred. The proportion of the (meth)acrylic acid alkyl ester in all 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 further preferably 45% by mass or less. In addition, the above acrylic oligomer may contain the above copolymerizable monomer as a structural unit.

[0108] As for the above acrylic oligomer, as one embodiment, it preferably contains a monomer containing a functional group as a structural unit. As the monomer containing a functional group, a monomer containing a polar group is preferred, and a monomer containing a carboxyl group is more preferred. The proportion of the monomer containing a functional group in all monomer components constituting the above acrylic oligomer is preferably 3% by mass or more, more preferably 4% by mass or more. The above proportion is preferably 20% by mass or less, more preferably 10% by mass or less, and further preferably 8% by mass or less. In addition, the above acrylic oligomer may contain the above copolymerizable monomer as a structural unit.

[0109] The above oligomers are obtained by polymerizing a composition containing monomer components constituting the above oligomers. As their polymerization methods, the methods exemplified and described as the polymerization methods of the above acrylic polymers can be cited. Among them, bulk polymerization methods, thermal polymerization methods, and active energy ray polymerization methods are preferred. When polymerizing the monomer components, various common solvents can be used. As the above solvents, the solvents exemplified and described as the solvents that can be used in the polymerization of the above acrylic polymers can be cited. The above solvents can be used alone or in combination of two or more. There are no particular limitations on polymerization initiators, chain transfer agents, emulsifiers, etc. for the radical polymerization of monomer components, and they can be appropriately selected and used.

[0110] The content of the above tackifier in the adhesive layer of the present invention is not particularly limited. For example, it is 1 part by mass or more (for example, 1 to 100 parts by mass), preferably 4 parts by mass or more, based on 100 parts by mass of the total amount of the acrylic polymer of the present invention. If the above content is 1 part by mass or more, peeling is less likely to occur even when repeatedly bent in various environments. From the viewpoint that peeling is less likely to occur even when repeatedly bent at low temperatures, the above content is preferably less than 30 parts by mass, more preferably 25 parts by mass or less, and further preferably less than 20 parts by mass.

[0111] The content ratio of the above tackifier in the adhesive layer of the present invention is not particularly limited. Based on 100% by mass of the total amount of the adhesive layer of the present invention, it is preferably more than 0% and less than 20%, more preferably 3 to 18%. If the above content ratio is more than 0%, peeling is less likely to occur even when repeatedly bent in various environments. If the above content ratio is less than 20%, peeling is less likely to occur even when repeatedly bent at low temperatures.

[0112] The adhesive layer of the present invention may contain a colorant. The above colorant can be a pigment or a dye. As the colorant, for example, the following can be cited: black-based colorants, cyan-based colorants, magenta-based colorants, yellow-based colorants, etc. From the viewpoint of more excellent visibility and designability, black-based colorants are preferred. The above colorant can contain only one kind or two or more kinds.

[0113] As black colorants, examples 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, composite oxide-based black pigments, anthraquinone-based organic black dyes, azo-based organic black dyes, etc. As carbon black, examples include: furnace black, channel black, acetylene black, thermal black, lamp black, etc. As black colorants, there are also: C.I. Solvent Black 3, C.I. Solvent Black 7, C.I. Solvent Black 22, C.I. Solvent Black 27, C.I. Solvent Black 29, C.I. Solvent Black 34, C.I. Solvent Black 43, C.I. Solvent Black 70; C.I. Direct Black 17, C.I. Direct Black 19, C.I. Direct Black 22, C.I. Direct Black 32, C.I. Direct Black 38, C.I. Direct Black 51, C.I. Direct Black 71; C.I. Acid Black 1, C.I. Acid Black 2, C.I. Acid Black 24, C.I. Acid Black 26, C.I. Acid Black 31, C.I. Acid Black 48, C.I. Acid Black 52, C.I. Acid Black 107, C.I. Acid Black 109, C.I. Acid Black 110, C.I. Acid Black 119, C.I. Acid Black 154; C.I. Disperse Black 1, C.I. Disperse Black 3, C.I. Disperse Black 10, C.I. Disperse Black 24; C.I. Pigment Black 1, C.I. Pigment Black 7, etc.

[0114] As cyan colorants, examples include: C.I. Solvent Blue 25, C.I. Solvent Blue 36, C.I. Solvent Blue 60, C.I. Solvent Blue 70, C.I. Solvent Blue 93, C.I. Solvent Blue 95; C.I. Acid Blue 6, C.I. Acid Blue 45; C.I. Pigment Blue 1, C.I. Pigment Blue 2, C.I. Pigment Blue 3, C.I. Pigment Blue 15, C.I. Pigment Blue 15:1, C.I. Pigment Blue 15:2, C.I. Pigment Blue 15:3, C.I. Pigment Blue 15:4, C.I. Pigment Blue 15:5, C.I. Pigment Blue 15:6, C.I. Pigment Blue 16, C.I. Pigment Blue 17, C.I. Pigment Blue 17:1, C.I. Pigment Blue 18, C.I. Pigment Blue 22, C.I. Pigment Blue 25, C.I. Pigment Blue 56, C.I. Pigment Blue 60, C.I. Pigment Blue 63, C.I. Pigment Blue 65, C.I. Pigment Blue 66; C.I. Vat Blue 4; C.I. Vat Blue 60, C.I. Pigment Green 7, etc.

[0115] Examples of magenta colorants include: C.I. Solvent Red 1, C.I. Solvent Red 3, C.I. Solvent Red 8, C.I. Solvent Red 23, C.I. Solvent Red 24, C.I. Solvent Red 25, C.I. Solvent Red 27, C.I. Solvent Red 30, C.I. Solvent Red 49, C.I. Solvent Red 52, C.I. Solvent Red 58, C.I. Solvent Red 63, C.I. Solvent Red 81, C.I. Solvent Red 82, C.I. Solvent Red 83, C.I. Solvent Red 84, C.I. Solvent Red 100, C.I. Solvent Red 109, C.I. Solvent Red 111, C.I. Solvent Red 121, C.I. Solvent Red 122; C.I. Disperse Red 9; C.I. Solvent Violet 8, C.I. Solvent Violet 13, C.I. Solvent Violet 14, C.I. Solvent Violet 21, C.I. Solvent Violet 27; C.I. Disperse Violet 1; C.I. Basic Red 1, C.I. Basic Red 2, C.I. Basic Red 9, C.I. Basic Red 12, C.I. Basic Red 13, C.I. Basic Red 14, C.I. Basic Red 15, C.I. Basic Red 17, C.I. Basic Red 18, C.I. Basic Red 22, C.I. Basic Red 23, C.I. Basic Red 24, C.I. Basic Red 27, C.I. Basic Red 29, C.I. Basic Red 32, C.I. Basic Red 34, C.I. Basic Red 35, C.I. Basic Red 36, C.I. Basic Red 37, C.I. Basic Red 38, C.I. Basic Red 39, C.I. Basic Red 40; C.I. Basic Violet 1, C.I. Basic Violet 3, C.I. Basic Violet 7, C.I. Basic Violet 10, C.I. Basic Violet 14, C.I. Basic Violet 15, C.I. Basic Violet 21, C.I. Basic Violet 25, C.I. Basic Violet 26, C.I. Basic Violet 27, C.I. Basic Violet 28, etc. In addition, examples of magenta colorants include: C.I. Pigment Red 1, C.I. Pigment Red 2, C.I. Pigment Red 3, C.I. Pigment Red 4, C.I. Pigment Red 5, C.I. Pigment Red 6, C.I. Pigment Red 7, C.I. Pigment Red 8, C.I. Pigment Red 9, C.I. Pigment Red 10, C.I. Pigment Red 11, C.I. Pigment Red 12, C.I. Pigment Red 13, C.I. Pigment Red 14, C.I. Pigment Red 15, C.I. Pigment Red 16, C.I. Pigment Red 17, C.I. Pigment Red 18, C.I. Pigment Red 19, C.I. Pigment Red 21, C.I. Pigment Red 22, C.I. Pigment Red 23, C.I. Pigment Red 30, C.I. Pigment Red 31, C.I. Pigment Red 32, C.I. Pigment Red 37, C.I. Pigment Red 38, C.I. Pigment Red 39, C.I. Pigment Red 40, C.I. Pigment Red 41, C.I. Pigment Red 42, C.I. Pigment Red 48:1, C.I. Pigment Red 48:2, C.I. Pigment Red 48:3, C.I. Pigment Red 48:4, C.I.Pigment Red 49, C.I. Pigment Red 49:1, C.I. Pigment Red 50, C.I. Pigment Red 51, C.I. Pigment Red 52, C.I. Pigment Red 52:2, C.I. Pigment Red 53:1, C.I. Pigment Red 54, C.I. Pigment Red 55, C.I. Pigment Red 56, C.I. Pigment Red 57:1, C.I. Pigment Red 58, C.I. Pigment Red 60, C.I. Pigment Red 60:1, C.I. Pigment Red 63, C.I. Pigment Red 63:1, C.I. Pigment Red 63:2, C.I. Pigment Red 64, C.I. Pigment Red 64:1, C.I. Pigment Red 67, C.I. Pigment Red 68, C.I. Pigment Red 81, C.I. Pigment Red 83, C.I. Pigment Red 87, C.I. Pigment Red 88, C.I. Pigment Red 89, C.I. Pigment Red 90, C.I. Pigment Red 92, C.I. Pigment Red 101, C.I. Pigment Red 104, C.I. Pigment Red 105, C.I. Pigment Red 106, C.I. Pigment Red 108, C.I. Pigment Red 112, C.I. Pigment Red 114, C.I. Pigment Red 122, C.I. Pigment Red 123, C.I. Pigment Red 139, C.I. Pigment Red 144, C.I. Pigment Red 146, C.I. Pigment Red 147, C.I. Pigment Red 149, C.I. Pigment Red 150, C.I. Pigment Red 151, C.I. Pigment Red 163, C.I. Pigment Red 166, C.I. Pigment Red 168, C.I. Pigment Red 170, C.I. Pigment Red 171, C.I. Pigment Red 172, C.I. Pigment Red 175, C.I. Pigment Red 176, C.I. Pigment Red 177, C.I. Pigment Red 178, C.I. Pigment Red 179, C.I. Pigment Red 184, C.I. Pigment Red 185, C.I. Pigment Red 187, C.I. Pigment Red 190, C.I. Pigment Red 193, C.I. Pigment Red 202, C.I. Pigment Red 206, C.I. Pigment Red 207, C.I. Pigment Red 209, C.I. Pigment Red 219, C.I. Pigment Red 222, C.I. Pigment Red 224, C.I. Pigment Red 238, C.I. Pigment Red 245; C.I. Pigment Violet 3, C.I. Pigment Violet 9, C.I. Pigment Violet 19, C.I. Pigment Violet 23, C.I. Pigment Violet 31, C.I. Pigment Violet 32, C.I. Pigment Violet 33, C.I. Pigment Violet 36, C.I. Pigment Violet 38, C.I. Pigment Violet 43, C.I. Pigment Violet 50; C.I. Vat Red 1, C.I. Vat Red 2, C.I. Vat Red 10, C.I. Vat Red 13, C.I. Vat Red 15, C.I. Vat Red 23, C.I. Vat Red 29, C.I. Vat Red 35, etc..

[0116] As yellow colorants, examples include: C.I. Solvent Yellow 19, C.I. Solvent Yellow 44, C.I. Solvent Yellow 77, C.I. Solvent Yellow 79, C.I. Solvent Yellow 81, C.I. Solvent Yellow 82, C.I. Solvent Yellow 93, C.I. Solvent Yellow 98, C.I. Solvent Yellow 103, C.I. Solvent Yellow 104, C.I. Solvent Yellow 112, C.I. Solvent Yellow 162; C.I. Pigment Orange 31, C.I. Pigment Orange 43; C.I. Pigment Yellow 1, C.I. Pigment Yellow 2, C.I. Pigment Yellow 3, C.I. Pigment Yellow 4, C.I. Pigment Yellow 5, C.I. Pigment Yellow 6, C.I. Pigment Yellow 7, C.I. Pigment Yellow 10, C.I. Pigment Yellow 11, C.I. Pigment Yellow 12, C.I. Pigment Yellow 13, C.I. Pigment Yellow 14, C.I. Pigment Yellow 15, C.I. Pigment Yellow 16, C.I. Pigment Yellow 17, C.I. Pigment Yellow 23, C.I. Pigment Yellow 24, C.I. Pigment Yellow 34, C.I. Pigment Yellow 35, C.I. Pigment Yellow 37, C.I. Pigment Yellow 42, C.I. Pigment Yellow 53, C.I. Pigment Yellow 55, C.I. Pigment Yellow 65, C.I. Pigment Yellow 73, C.I. Pigment Yellow 74, C.I. Pigment Yellow 75, C.I. Pigment Yellow 81, C.I. Pigment Yellow 83, C.I. Pigment Yellow 93, C.I. Pigment Yellow 94, C.I. Pigment Yellow 95, C.I. Pigment Yellow 97, C.I. Pigment Yellow 98, C.I. Pigment Yellow 100, C.I. Pigment Yellow 101, C.I. Pigment Yellow 104, C.I. Pigment Yellow 108, C.I. Pigment Yellow 109, C.I. Pigment Yellow 110, C.I. Pigment Yellow 113, C.I. Pigment Yellow 114, C.I. Pigment Yellow 116, C.I. Pigment Yellow 117, C.I. Pigment Yellow 120, C.I. Pigment Yellow 128, C.I. Pigment Yellow 129, C.I. Pigment Yellow 133, C.I. Pigment Yellow 138, C.I. Pigment Yellow 139, C.I. Pigment Yellow 147, C.I. Pigment Yellow 150, C.I. Pigment Yellow 151, C.I. Pigment Yellow 153, C.I. Pigment Yellow 154, C.I. Pigment Yellow 155, C.I. Pigment Yellow 156, C.I. Pigment Yellow 167, C.I. Pigment Yellow 172, C.I. Pigment Yellow 173, C.I. Pigment Yellow 180, C.I. Pigment Yellow 185, C.I. Pigment Yellow 195; C.I. Vat Yellow 1, C.I. Vat Yellow 3, C.I. Vat Yellow 20, etc.

[0117] The adhesive layer of the present invention may further contain, as needed and within the range not impairing the effects of the present invention: crosslinking accelerators, anti-aging agents, antioxidants, plasticizers, softeners, surfactants, antistatic agents, surface lubricants, leveling agents, light stabilizers, ultraviolet absorbers, polymerization inhibitors, foils, rust inhibitors, and other additives. Each of the above additives may be used alone or in combination of two or more.

[0118] The above-mentioned rust inhibitor is a compound that prevents rust (rust) and corrosion of metal. When the adherend is a metal, rust and corrosion can be suppressed when the above-mentioned adhesive sheet is attached. Examples of the above-mentioned rust inhibitor include: amine compounds, benzotriazole compounds, nitrites, etc. Other examples include: ammonium benzoate, ammonium phthalate, ammonium stearate, ammonium palmitate, ammonium oleate, ammonium carbonate, dicyclohexylamine benzoate, urea, urotropine, thiourea, phenyl carbamate, cyclohexyl ammonium-N-cyclohexylcarbamate (CHC), etc. The above-mentioned rust inhibitor can be used alone or in combination of two or more.

[0119] The content of the rust inhibitor is not particularly limited, but is preferably 0.02 to 15 parts by mass relative to 100 parts by mass of the base polymer. If the content is 0.02 parts by mass or more, good corrosion protection is easily obtained. If the content is 15 parts by mass or less, transparency is easily ensured.

[0120] Among them, the rust inhibitor is preferably a benzotriazole compound from the viewpoint of being able to obtain balanced and high levels of properties such as compatibility with the base polymer, adhesion reliability, transparency and corrosion resistance, and from the viewpoint of being able to obtain excellent appearance.

[0121] The content of the benzotriazole compound is not particularly limited, but is preferably 0.02 to 3 parts by mass, more preferably 0.02 to 2.5 parts by mass, and even more preferably 0.02 to 2 parts by mass, based on 100 parts by mass of the base polymer.

[0122] The thickness of the adhesive layer of the present invention is preferably 50 μm or less, more preferably 40 μm or less, and further preferably 30 μm or less. If the thickness is 50 μm or less, the difference between the inner and outer diameters when subjected to bending is small, and the stress applied when bent is easily relieved. The thickness is not particularly limited, but is preferably 6 μm or more, more preferably 10 μm or more, and further preferably 20 μm or more from the viewpoint of better adhesion and less prone to peeling when subjected to bending.

[0123] In the case where the adhesive sheet of the present invention is a double-sided adhesive sheet with a substrate, the total thickness of the adhesive layer on one side is not particularly limited, preferably 6 μm or more, more preferably 10 μm or more, and further preferably 20 μm or more. If the above thickness is 6 μm or more, the adhesiveness is more excellent and peeling is less likely to occur when bending is applied. The total thickness of the adhesive layer on one side is preferably 50 μm or less, more preferably 40 μm or less, and further preferably 30 μm or less. If the above thickness is 50 μm or less, the inner and outer diameter differences during bending are small, and it is easy to relieve the stress applied during bending. It should be noted that the thicknesses of the adhesive layers on the two sides in the case of a double-sided adhesive sheet with a substrate may be the same or different.

[0124] The adhesive layer constituting the adhesive sheet of the present invention can be in any form. For example, it can be an emulsion type, a solvent type (solution type), an active energy ray curable type, a hot melt type (hot melt type), etc. Among them, from the aspect of easily obtaining an adhesive layer with excellent productivity, a solvent type or an active energy ray curable type adhesive layer is preferred.

[0125] As the above active energy rays, for example, ionizing radiation rays such as α rays, β rays, γ rays, neutron rays, and electron rays, ultraviolet rays, etc. can be cited, and ultraviolet rays are particularly preferred. That is, the above active energy ray curable adhesive layer is preferably an ultraviolet curable adhesive layer.

[0126] The above adhesive layer can be manufactured as follows, for example: The adhesive composition for forming the adhesive layer is coated (applied) on a release liner, and the obtained adhesive composition layer is dried and cured, or the above adhesive composition is coated (applied) on a release liner, and the obtained adhesive composition layer is irradiated with active energy rays to cure it. In addition, heating and drying can be further performed as needed.

[0127] (Substrate)

[0128] The above substrate is an element that functions as a support in the adhesive sheet. The above substrate can be a single layer or a laminate of the same or different substrates.

[0129] As the above substrate, for example, plastic substrates (such as plastic films), paper, cloth, porous materials such as non-woven fabrics, nets, foamed sheets, etc. can be cited. As the above substrate, a plastic substrate (especially a plastic film) is preferred. In addition, the above substrate is preferably a non-foamed sheet.

[0130] Examples of the resin constituting the above-mentioned plastic substrate include: polyolefin resins such as low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, ultra-low-density polyethylene, random copolymer polypropylene, block copolymer polypropylene, homopolymer polypropylene, polybutene, polymethylpentene, ethylene-vinyl acetate copolymer (EVA), ionomer, ethylene-(meth)acrylic acid copolymer, ethylene-(meth)acrylate (random, alternating) copolymer, ethylene-butene copolymer, ethylene-hexene copolymer; polyurethane resins; rubber resins (natural rubber-based, synthetic rubber-based, their mixed systems, etc.); polyesters such as polyethylene terephthalate (PET), polyethylene naphthalate, polybutylene terephthalate (PBT); polycarbonate; polyimide; polyetheretherketone; polyetherimide; polyamides such as aramid and wholly aromatic polyamide; polyphenylene sulfide; fluororesin; polyvinyl chloride; polyvinylidene chloride; cellulose resin; silicone resin, etc. The above resins can be used alone or in combination of two or more.

[0131] The above substrate can be compounded with various additives such as fillers (inorganic fillers, organic fillers, etc.), colorants (pigments, dyes), dispersants (surfactants, etc.), anti-aging agents, antioxidants, ultraviolet absorbers, antistatic agents, lubricants, plasticizers, etc. The compounding ratio of various additives is less than 30% by mass (for example, less than 20% by mass, typically less than 10% by mass) with respect to the total mass of 100% by mass of the above substrate.

[0132] The above substrate can be a substrate including an auxiliary layer. Examples of the above auxiliary layer include a colored layer, a reflective layer, a primer layer, an antistatic layer, etc. provided on the surface of the above substrate.

[0133] For the surface of the above substrate, for the purpose of improving the adhesion, retention, etc. with the adhesive layer, physical treatments such as corona discharge treatment, plasma treatment, sandblasting treatment, ozone exposure treatment, flame exposure treatment, high-voltage electric shock exposure treatment, ionizing radiation treatment, etc. can be performed; chemical treatments such as chromic acid treatment; surface treatments such as easy adhesion treatment based on a coating agent (primer). The surface treatment for improving adhesion is preferably performed on the entire surface of the substrate.

[0134] (Adhesive sheet)

[0135] The thickness of the above-mentioned adhesive sheet is preferably 6 to 100 μm, more preferably 10 to 80 μm, and further preferably 20 to 70 μm. If the above thickness is 6 μm or more, the adhesiveness is more excellent and peeling is less likely to occur when subjected to bending. If the above thickness is 100 μm or less, the inner and outer diameter difference during bending is small, and it is easy to relieve the stress applied during bending. It should be noted that in the case of a single-sided adhesive sheet, the thickness of the above-mentioned adhesive sheet refers to the thickness from the surface of the base material where the adhesive layer is not formed to the adhesive surface. In the case of a double-sided adhesive sheet, the thickness of the above-mentioned adhesive sheet refers to the thickness from one adhesive surface to the other adhesive surface, that is, the thickness of the adhesive body, excluding the release liner.

[0136] Until use, a release liner can be attached to the surface (adhesive surface) of the adhesive layer of the adhesive sheet of the present invention. In the case where the above-mentioned adhesive sheet is a double-sided adhesive sheet, each adhesive surface of the two surfaces in the above-mentioned adhesive sheet can be protected by two release liners respectively, or can be protected in the form of a roll (wound body) by a release liner with a release surface on both sides. The release liner serves as a protective material for the adhesive layer and is peeled off when attached to the adherend. It should be noted that the release liner does not necessarily have to be provided.

[0137] As the above-mentioned release liner, conventional release paper, etc. can be used, and there is no particular limitation. For example, examples include: a base material having a release treatment layer, a low-adhesion base material formed of a fluoropolymer, a low-adhesion base material formed of a non-polar polymer, etc. As the base material having a release treatment layer, for example, examples include plastic films, papers, etc. that have been surface-treated with a release treatment agent such as a silicone-based, long-chain alkyl-based, fluorine-based, molybdenum disulfide-based release treatment agent. As the fluorine-based polymer in the above-mentioned low-adhesion base material formed of a fluoropolymer, for example, examples include: polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, chlorofluoroethylene-vinylidene fluoride copolymer, etc. In addition, as the above-mentioned non-polar polymer, for example, examples include: olefin-based resins (such as polyethylene, polypropylene, etc.). It should be noted that the release liner can be formed by a known or conventional method. In addition, the thickness of the release liner is not particularly limited.

[0138] The above-mentioned adhesive sheet is preferably used for attaching electrical and electronic components that are used for attaching to components included in electrical and electronic devices. The above-mentioned adhesive sheet is particularly preferably a double-sided adhesive sheet, which is used for attaching components included in an electrical and electronic device to each of the two adhesive surfaces of the double-sided adhesive sheet, that is, for fixing components to each other in an electrical and electronic device. The above-mentioned double-sided adhesive sheet can be used for any one of the uses of fixing the above-mentioned components to each other or temporarily fixing the above-mentioned components to each other.

[0139] It should be noted that the "electrical and electronic device" refers to a device equivalent to at least any one of electrical devices or electronic devices. Examples of the above-mentioned electrical and electronic devices include image display devices such as liquid crystal displays, electroluminescent displays, and plasma displays; portable electronic devices, etc.

[0140] Examples of the above-mentioned portable electronic devices include: mobile phones, smart phones, tablet personal computers, notebook personal computers, various wearable devices (for example, wrist-worn types like watches; modular types worn on a part of the body using clips, straps, etc.; eye-worn types including glasses types (monocular types, binocular types. Also includes head-mounted types); clothing types installed in the form of accessories on shirts, socks, hats, etc.; ear-worn types like earphones, etc.), digital cameras, digital video cameras, audio equipment (portable music players, IC recorders, etc.), calculators (electronic calculators, etc.), portable game devices, electronic dictionaries, electronic notebooks, e-books, in-vehicle information devices, portable radios, portable televisions, portable printers, portable scanners, portable modems, etc. It should be noted that in this specification, it is not sufficient to interpret "portable" as merely being able to be carried, but rather it means having a level of portability that an individual (standard adult) can relatively easily move. The above double-sided adhesive sheet is used, for example, in a manner such that the adhesive layer adheres to the components of the above portable electronic device.

[0141] The adhesive sheet of the present invention has excellent bending resistance in various environments. Therefore, even when used in a part where bending is repeatedly performed, it is not easy to have breakage, traces, or peeling of the adhesive sheet at the bending part. Specifically, even when repeatedly subjected to bending from low temperature to high temperature or in a high-humidity environment, it is not easy to peel from the adherend, and in addition, even at low temperature, it is not easy to have breakage or traces at the bending part. Therefore, the adhesive sheet of the present invention is preferably used in parts to be repeatedly bent. Therefore, the adhesive sheet of the present invention is preferably used for adhering components (especially between components) in electrical and electronic devices such as electrical and electronic devices having an image display device (flexible display) (especially a foldable image display device (foldable display)) that can be bent.

[0142] Examples

[0143] Examples are listed below to illustrate the present invention in more detail, and the present invention is not limited by any of these examples.

[0144] Preparation Example 1

[0145] (Preparation of acrylic polymer A)

[0146] Into a reaction vessel equipped with a stirrer, a thermometer, a nitrogen inlet tube, a reflux condenser, and a dropping funnel, 95 parts by mass of 2-ethylhexyl acrylate (2EHA) and 5 parts by mass of acrylic acid (AA) as monomer components and 160 parts by mass of ethyl acetate as a polymerization solvent were charged, and nitrogen was introduced while stirring for 2 hours. Thus, oxygen in the polymerization system was removed, and then 0.15 parts by mass of benzoyl peroxide as a polymerization initiator was added, and solution polymerization was carried out at 60 °C for 6 hours to obtain a solution of acrylic polymer A. The Mw of this acrylic polymer A was about 120×10 4 .

[0147] Preparation Example 2

[0148] (Preparation of Acrylic Polymer B)

[0149] Into a reaction vessel equipped with a stirrer, a thermometer, a nitrogen inlet tube, a reflux condenser, and a dropping funnel, 95 parts by mass of butyl acrylate (BA) and 5 parts by mass of AA as monomer components and 233 parts by mass of ethyl acetate as a polymerization solvent were charged, and nitrogen was introduced while stirring for 2 hours. Thus, oxygen in the polymerization system was removed, and then 0.2 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) as a polymerization initiator was added, and solution polymerization was carried out at 60 °C for 8 hours to obtain a solution of acrylic polymer B. The Mw of this acrylic polymer B was about 70×10 4 .

[0150] Preparation Example 3

[0151] (Preparation of Acrylic Polymer C)

[0152] Into a reaction vessel equipped with a stirrer, a thermometer, a nitrogen inlet tube, a reflux condenser, and a dropping funnel, 90 parts by mass of 2EHA and 10 parts by mass of AA as monomer components and 199 parts by mass of ethyl acetate as a polymerization solvent were charged, and nitrogen was introduced while stirring for 2 hours. Thus, oxygen in the polymerization system was removed, and then 0.2 parts by mass of benzoyl peroxide as a polymerization initiator was added, and solution polymerization was carried out at 60 °C for 6 hours to obtain a solution of acrylic polymer C. The Mw of this acrylic polymer C was about 120×10 4 .

[0153] Preparation Example 4

[0154] (Preparation of Acrylic Polymer D)

[0155] Into a reaction vessel equipped with a stirrer, a thermometer, a nitrogen inlet tube, a reflux condenser, and a dropping funnel, 85 parts by mass of 2EHA, 15 parts by mass of ethyl carbitol acrylate (CBA), 7 parts by mass of AA, and 0.15 parts by mass of 4-hydroxybutyl acrylate (4HBA) as monomer components, and 145 parts by mass of ethyl acetate as a polymerization solvent were charged, and nitrogen was introduced while stirring for 2 hours. Thus, oxygen in the polymerization system was removed, and then 1.3 parts by mass of AIBN as a polymerization initiator was added, and solution polymerization was carried out at 60 °C for 6 hours to obtain a solution of acrylic polymer D. The Mw of this acrylic polymer D was about 100×10 4 。

[0156] Production Example 5

[0157] (Preparation of Acrylic Polymer E)

[0158] Into a reaction vessel equipped with a stirrer, a thermometer, a nitrogen inlet tube, a reflux condenser, and a dropping funnel, 98 parts by mass of 2EHA and 2 parts by mass of AA as monomer components, and 100 parts by mass of toluene as a polymerization solvent were charged, and nitrogen was introduced while stirring for 2 hours. Thus, oxygen in the polymerization system was removed, and then 0.2 parts by mass of benzoyl peroxide as a polymerization initiator was added, and solution polymerization was carried out at 60 °C for 6 hours to obtain a solution of acrylic polymer E. The Mw of this acrylic polymer E was about 120×10 4 。

[0159] Production Example 6

[0160] (Preparation of Oligomer A)

[0161] 95 parts by mass of cyclohexyl methacrylate, 5 parts by mass of AA, 10 parts by mass of α-methylstyrene dimer as a chain transfer agent, 10 parts by mass of AIBN as a polymerization initiator, and 120 parts by mass of toluene as a polymerization solvent as monomer components were mixed, and reacted at 85 °C for 5 hours under a nitrogen atmosphere to obtain a solution of oligomer A with a solid content concentration of 50 mass%. The weight average molecular weight of oligomer A was 4300.

[0162] Production Example 7

[0163] (Preparation of Oligomer B)

[0164] 60 parts by mass of dicyclopentanyl methacrylate as a monomer component, 40 parts by mass of methacrylic acid, 3.5 parts by mass of α-thioglycerol as a chain transfer agent, and 100 parts by mass of toluene as a polymerization solvent were mixed and stirred at 70°C for 1 hour under a nitrogen atmosphere. Subsequently, 0.2 part by mass of AIBN as a thermal polymerization initiator was added, and the reaction was carried out at 70°C for 2 hours, and then the temperature was raised to 80°C and the reaction was carried out for 2 hours. Thereafter, the reaction solution was heated to 130°C, and toluene, the chain transfer agent, and unreacted monomers were removed by drying to obtain a solid acrylic oligomer (oligomer B). The weight-average molecular weight of oligomer B was 5,100.

[0165] Example 1

[0166] (Preparation of Adhesive Composition)

[0167] To the solution of the acrylic polymer A prepared in Preparation Example 1, 10 parts by mass of oligomer A prepared in Preparation Example 6 as a tackifier, 3 parts by mass of an isocyanate-based crosslinking agent (trade name “CORONATE L”, manufactured by TOSOH Corporation) as crosslinking agent A, and 0.03 part by mass of an epoxy crosslinking agent (trade name “TETRAD-C”, manufactured by Mitsubishi Gas Chemical Company, Inc.) as crosslinking agent B were added per 100 parts by mass of the acrylic polymer A, and the mixture was stirred and mixed to prepare an adhesive composition.

[0168] (Preparation of Adhesive Sheet)

[0169] The above adhesive composition was coated on the release treatment layer of a 75-μm-thick polyethylene terephthalate film (product name “DIAFOIL MRF”, manufactured by Mitsubishi Chemical Corporation) that had been release-treated with silicone on one side so that the thickness of the adhesive layer was 25 μm, and dried at 100°C for 2 minutes to form an adhesive layer. The release treatment layer of a 38-μm-thick polyethylene terephthalate film (product name “DIAFOIL MRF”, manufactured by Mitsubishi Chemical Corporation) that had been release-treated with silicone on one side was laminated with the above adhesive layer to produce the double-sided adhesive sheet of Example 1.

[0170] Example 2

[0171] The amount of oligomer A was changed to 5 parts by mass, and an adhesive composition and a double-sided adhesive sheet were produced in the same manner as in Example 1 except for this.

[0172] Example 3

[0173] As a tackifier, oligomer B prepared in Preparation Example 7 was used in place of oligomer A, and a pressure-sensitive adhesive composition and a double-sided pressure-sensitive adhesive sheet were produced in the same manner as in Example 1, except for this.

[0174] Example 4

[0175] As a tackifier, oligomer B prepared in Preparation Example 7 was used in place of oligomer A, and a pressure-sensitive adhesive composition and a double-sided pressure-sensitive adhesive sheet were produced in the same manner as in Example 2, except for this.

[0176] Example 5

[0177] As a tackifier, tackifying resin A (trade name “HARITACK SE10”, hydrogenated rosin glyceride, manufactured by Harima Chemicals, Inc., softening point of about 80°C) was used in place of oligomer A, and a pressure-sensitive adhesive composition and a double-sided pressure-sensitive adhesive sheet were produced in the same manner as in Example 2, except for this.

[0178] Example 6

[0179] The compounding amount of tackifying resin A was changed to 10 parts by mass, and a pressure-sensitive adhesive composition and a double-sided pressure-sensitive adhesive sheet were produced in the same manner as in Example 5, except for this.

[0180] Example 7

[0181] The compounding amount of tackifying resin A was changed to 20 parts by mass, and a pressure-sensitive adhesive composition and a double-sided pressure-sensitive adhesive sheet were produced in the same manner as in Example 5, except for this.

[0182] Example 8

[0183] As a tackifier, tackifying resin B (trade name “YS Polyster T80”, terpene phenol resin, manufactured by YASUHARA CHEMICAL CO., LTD., softening point of about 80°C) was used in place of oligomer A, and a pressure-sensitive adhesive composition and a double-sided pressure-sensitive adhesive sheet were produced in the same manner as in Example 2, except for this.

[0184] Example 9

[0185] The compounding amount of tackifying resin B was changed to 10 parts by mass, and a pressure-sensitive adhesive composition and a double-sided pressure-sensitive adhesive sheet were produced in the same manner as in Example 8, except for this.

[0186] Example 10

[0187] The compounding amount of tackifying resin B was changed to 20 parts by mass, and a pressure-sensitive adhesive composition and a double-sided pressure-sensitive adhesive sheet were produced in the same manner as in Example 8, except for this.

[0188] Example 11

[0189] As a tackifier, tackifying resin C (trade name “YS Polyster T115”, terpene phenol resin, manufactured by YASUHARA CHEMICAL CO., LTD., softening point of approximately 115°C) was used to replace oligomer A, and in other respects, an adhesive composition and a double-sided adhesive sheet were produced in the same manner as in Example 2.

[0190] Example 12

[0191] The blending amount of tackifying resin C was changed to 10 parts by mass, and in other respects, an adhesive composition and a double-sided adhesive sheet were produced in the same manner as in Example 11.

[0192] Example 13

[0193] As a tackifier, tackifying resin D (trade name “YS Polyster S145”, terpene phenol resin, manufactured by YASUHARA CHEMICAL COMPANY, softening point of approximately 145°C) was used to replace oligomer A, and in other respects, an adhesive composition and a double-sided adhesive sheet were produced in the same manner as in Example 1.

[0194] Example 14

[0195] (Production of Adhesive Composition)

[0196] To the solution of acrylic polymer A prepared in Preparation Example 1, with respect to 100 parts by mass of acrylic polymer A, 10 parts by mass of oligomer A prepared in Preparation Example 6 as a tackifier, 3 parts by mass of an isocyanate-based crosslinking agent (trade name “CORONATE L”, manufactured by TOSOH CORPORATION) as crosslinking agent A, 0.03 parts by mass of an epoxy crosslinking agent (trade name “TETRAD-C”, manufactured by MITSUBISHI GAS CHEMICAL COMPANY, INC.) as crosslinking agent B, and 15 parts by mass of a black pigment containing carbon black (trade name “Multilac A903”, manufactured by TOYOCOLOR CO., LTD.) were added, and stirring and mixing were performed to prepare an adhesive composition.

[0197] (Production of Adhesive Sheet)

[0198] Using the above adhesive composition, in other respects, a double-sided adhesive sheet was produced in the same manner as in Example 1.

[0199] Example 15

[0200] The solution of acrylic polymer D prepared in Preparation Example 4 was used to replace the solution of acrylic polymer A, and in other respects, an adhesive composition and a double-sided adhesive sheet were produced in the same manner as in Example 1.

[0201] Example 16

[0202] The solution of the acrylic polymer E prepared in Preparation Example 5 was used instead of the solution of the acrylic polymer A, and a pressure-sensitive adhesive composition and a double-sided pressure-sensitive adhesive sheet were produced in the same manner as in Example 1 except for this.

[0203] Comparative Example 1

[0204] The blending amount of the oligomer A was changed to 20 parts by mass, and a pressure-sensitive adhesive composition and a double-sided pressure-sensitive adhesive sheet were produced in the same manner as in Example 1 except for this.

[0205] Comparative Example 2

[0206] The blending amount of the oligomer B was changed to 20 parts by mass, and a pressure-sensitive adhesive composition and a double-sided pressure-sensitive adhesive sheet were produced in the same manner as in Example 3 except for this.

[0207] Comparative Example 3

[0208] The blending amount of the tackifying resin A was changed to 30 parts by mass, and a pressure-sensitive adhesive composition and a double-sided pressure-sensitive adhesive sheet were produced in the same manner as in Example 8 except for this.

[0209] Comparative Example 4

[0210] The blending amount of the tackifying resin C was changed to 20 parts by mass, and a pressure-sensitive adhesive composition and a double-sided pressure-sensitive adhesive sheet were produced in the same manner as in Example 11 except for this.

[0211] Comparative Example 5

[0212] The oligomer A was not blended, and a pressure-sensitive adhesive composition and a double-sided pressure-sensitive adhesive sheet were produced in the same manner as in Example 1 except for this.

[0213] Comparative Example 6

[0214] The solution of the acrylic polymer B prepared in Preparation Example 2 was used instead of the solution of the acrylic polymer A, and a pressure-sensitive adhesive composition and a double-sided pressure-sensitive adhesive sheet were produced in the same manner as in Example 1 except for this.

[0215] Comparative Example 7

[0216] The oligomer A was not blended, and a pressure-sensitive adhesive composition and a double-sided pressure-sensitive adhesive sheet were produced in the same manner as in Comparative Example 6 except for this.

[0217] Comparative Example 8

[0218] The solution of the acrylic polymer C prepared in Preparation Example 3 was used instead of the solution of the acrylic polymer A, and a pressure-sensitive adhesive composition and a double-sided pressure-sensitive adhesive sheet were produced in the same manner as in Example 1 except for this.

[0219] Comparative Example 9

[0220] Without using oligomer A, an adhesive composition and a double-sided adhesive sheet were produced in the same manner as in Comparative Example 8.

[0221] <Evaluation>

[0222] The adhesive sheets obtained in the examples and comparative examples were evaluated as follows. The results are shown in the table.

[0223] (1) 180° peel adhesion force (RT)

[0224] In a measurement environment of 23°C and 50% RH, the release liners of both sides were peeled off from the double-sided adhesive sheets produced in the examples and comparative examples. A PET film with a thickness of 25 μm was attached to one adhesive surface of the double-sided adhesive sheet for backing, and it was cut into a size of 20 mm in width and 100 mm in length to produce a measurement sample. Regarding the produced measurement sample, in an environment of 23°C and 50% RH, a 2 kg roller was reciprocated once to press the exposed adhesive surface of the above measurement sample against the surface of a stainless steel plate (SUS304BA plate). The measurement sample was left in the same environment for 24 hours, and then using a universal tensile-compression testing machine, under the conditions of a tensile speed of 300 mm / minute, a peel angle of 180°, a temperature of 23°C, and a relative humidity of 50% RH (room temperature), the 180° peel strength (adhesion force) [N / 20 mm] was measured. As the universal tensile-compression testing machine, a tensile-compression testing machine manufactured by MINEBEA Co., Ltd. (trade name “TG-1kN”) was used. It should be noted that in the case of a single-sided adhesive sheet, the above PET film backing is not required.

[0225] (2) 180° peel adhesion force (60°C, 90% RH)

[0226] In a measurement environment of 23°C and 50% RH, the release liners of both sides were peeled off from the double-sided adhesive sheets produced in the examples and comparative examples. A PET film with a thickness of 25 μm was attached to one adhesive surface of the double-sided adhesive sheet for backing, and it was cut into a size of 20 mm in width and 100 mm in length to produce a measurement sample. Regarding the produced measurement sample, in an environment of 23°C and 50% RH, a 2 kg roller was reciprocated once to press the exposed adhesive surface of the above measurement sample against the surface of a stainless steel plate (SUS304BA plate). The measurement sample was left in the same environment for 24 hours, and then using a universal tensile-compression testing machine, under the conditions of a tensile speed of 300 mm / minute, a peel angle of 180°, a temperature of 60°C, and a relative humidity of 90% RH, the 180° peel strength (adhesion force) [N / 20 mm] was measured. As the universal tensile-compression testing machine, a tensile-compression testing machine manufactured by MINEBEA Co., Ltd. (trade name “TG-1kN”) was used. It should be noted that in the case of a single-sided adhesive sheet, the above PET film backing is not required.

[0227] (3) Storage modulus G’ (-20 °C)

[0228] Peel the release liners on both sides from the double-sided adhesive sheets produced in the examples and comparative examples, and laminate the double-sided adhesive sheets to produce a test sample with a thickness of about 1 mm. Punch the test sample into a disc shape with a diameter of 7.9 mm, clamp it with parallel plates, and use a viscoelasticity tester (trade name “ARES”, manufactured by Rheometrics) to measure the viscoelasticity in the shear mode while applying a shear strain of 1 Hz and heating at a rate of 5 °C / min in the temperature range of -50 to 150 °C, and find the peak strength of G’ (dynamic shear storage modulus) at -20 °C.

[0229] (4) Light transmittance

[0230] It was determined using “SolidSpec-3700” manufactured by Shimadzu Corporation by measuring the intensity of light irradiated from one side of the double-sided adhesive sheet and transmitted to the other side at a measurement wavelength of 550 nm. It should be noted that the measurement was performed with the release liner peeled off.

[0231] (5) Flexural resistance test

[0232] At each of the environments of -20°C / 50%RH, 23°C / 50%RH, and 60°C / 90%RH, a release liner was peeled off from the double-sided adhesive sheets prepared in the examples and comparative examples, and the exposed adhesive surface was adhered to one surface of a polyethylene terephthalate film (thickness: 50 μm, Young's modulus: 4.5 GPa). Next, the other release liner was peeled off, and the exposed adhesive surface was adhered to one surface of another polyethylene terephthalate film (thickness: 50 μm, Young's modulus: 4.5 GPa). Then, it was pressurized at 0.5 MPa and 50°C for 20 minutes using an autoclave manufactured by Kurihara Seisakusho Co., Ltd., and then left for 24 hours under the conditions of 23°C and 50%RH. The laminate composed of [PET film / double-sided adhesive sheet / PET film] thus obtained was cut into strips 20 mm wide and 200 mm long and used as samples. Using a durability tester (product name "Sheet-like body non-load U-shaped expansion and contraction environmental tester CL09-TypeD01-FSC90", manufactured by YUASA SYSTEM Machine Co., Ltd.), the obtained samples were repeatedly bent under the following conditions. After that, it was visually confirmed whether there were creases at the bent part of the samples after the test at -20°C / 50%RH (flexural resistance (low temperature)), whether there was peeling at the interface between the double-sided adhesive sheet and the PET film as the adherend under the environment of 23°C / 50%RH (flexural resistance (RT)), and whether there was peeling at the interface between the double-sided adhesive sheet and the PET film as the adherend under each environment of 60°C / 90%RH (flexural resistance (60°C 90%RH)), and the flexural resistance was evaluated according to the following criteria.

[0233] <Test conditions>

[0234] Bending radius: 2 mm, number of bending cycles: 200,000 times, bending speed: 60 times / minute.

[0235] <Evaluation criteria for creases>

[0236] 〇: No creases, or slightly creased but at a level that can be used in practice.

[0237] △: Creases visible by light irradiation were generated, but at a level that can be used in practice.

[0238] ×: Creases or damages at a level that cannot be used in practice were generated.

[0239] <Evaluation criteria for peeling>

[0240] 〇: No peeling, or slightly peeling but at a level that can be used in practice. ×: Peeling at a level that cannot be used in practice was generated.

[0241] [Table 1]

[0242]

[0243] [Table 2]

[0244]

[0245] Hereinafter, modifications of the invention of the present disclosure will be described.

[0246] [Supplementary Note 1] An adhesive sheet having an adhesive layer containing an acrylic polymer and a tackifier. For the acrylic polymer, the glass transition temperature calculated based on the Fox formula is less than -55°C, and it contains one or more monomers containing functional groups as structural units. The elastic modulus of the adhesive layer at -20°C is 4.0 MPa or less, the 180° peel adhesion to a SUS stainless steel plane is 6.0 N / 20 mm or more at room temperature, and 2.5 N / 20 mm or more at a temperature of 60°C and a relative humidity of 90% RH.

[0247] [Supplementary Note 2] The adhesive sheet according to Supplementary Note 1, wherein the tackifier contains an oligomer or a tackifying resin.

[0248] [Supplementary Note 3] The adhesive sheet according to Supplementary Note 1 or 2, wherein the content ratio of the tackifier exceeds 0% by mass and is less than 20% by mass with respect to the total amount of the adhesive layer.

[0249] [Supplementary Note 4] The adhesive sheet according to any one of Supplementary Notes 1 to 3, wherein the thickness of the adhesive layer is 50 μm or less.

[0250] [Supplementary Note 5] The adhesive sheet according to any one of Supplementary Notes 1 to 4, wherein the adhesive sheet is a double-sided adhesive sheet for fixing components of an electrical and electronic device to each other.

[0251] [Supplementary Note 6] An electrical and electronic device, wherein the electrical and electronic device includes the adhesive sheet according to Supplementary Note 5, and the adhesive sheet fixes components to each other through two adhesive surfaces.

[0252] Explanation of Reference Numerals

[0253] 1: Double-sided adhesive sheet; 2: Adhesive layer; 3, 4: Release liner.

Claims

1. An adhesive sheet having an adhesive layer, wherein the adhesive layer contains an acrylic polymer and a tackifier. For the acrylic polymer, the glass transition temperature calculated based on the Fox formula is less than -55°C, and it contains one or more monomers having functional groups as structural units, the elastic modulus of the adhesive layer at -20°C is 4.0 MPa or less, the 180° peel adhesion to a SUS stainless steel plane is 6.0 N / 20 mm or more at room temperature, and 2.5 N / 20 mm or more at a temperature of 60°C and a relative humidity of 90% RH.

2. The adhesive sheet according to claim 1, wherein, the tackifier contains an oligomer or a tackifying resin.

3. The adhesive sheet according to claim 1 or 2, wherein, the content ratio of the tackifier is more than 0% by mass and less than 20% by mass relative to the total amount of the adhesive layer.

4. The adhesive sheet according to claim 1 or 2, wherein, the thickness of the adhesive layer is 50 μm or less.

5. The adhesive sheet according to claim 1 or 2, wherein, the adhesive sheet is a double-sided adhesive sheet for fixing components of an electrical and electronic device to each other.

6. An electrical and electronic device, wherein, the electrical and electronic device has the adhesive sheet according to claim 5, and the adhesive sheet fixes components to each other through two adhesive surfaces.

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