Adhesive sheet

Abstract

Provided is an adhesive sheet having excellent bending resistance in a low-temperature environment and excellent adhesiveness in a wide temperature range from normal temperature to high temperature. The adhesive sheet 1 is provided with an adhesive layer 2. The pressure-sensitive adhesive layer (2) contains: an acrylic polymer containing, as a constituent unit, an alkyl (meth) acrylate having a linear or branched alkyl group having 10 or more carbon atoms; and a tackifier. The adhesive layer (2) has an elastic modulus of 5.0 MPa or less at-30 DEG C and a gel fraction of 50% or more.

Description

Technical Field

[0001] This invention relates to an adhesive sheet. Background Technology

[0002] Adhesive sheets used in image display devices and portable electronic devices such as mobile phones, smartphones, digital cameras, liquid crystal displays (LCDs), and organic EL displays require various properties, with high adhesion being a key characteristic.

[0003] In recent years, organic EL panels using flexible substrates such as resin films have been put into practical use, leading to the development of flexible displays capable of bending. In flexible displays, in addition to the bendable display panel itself (such as the organic EL panel), the constituent components can also be bent; these components are bonded together via adhesive sheets. In foldable flexible displays, bending is repeatedly applied to the same location. At the bending point, compressive stress is applied to the inner side and tensile stress to the outer side, resulting in strain at and around the bending point. Therefore, there are concerns about creases, marks, or peeling of the adhesive layer at the bending point.

[0004] For example, Patent Documents 1 to 7 disclose adhesive sheets intended to have bend resistance.

[0005] Existing technical documents

[0006] Patent documents

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

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

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

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

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

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

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

[0014] The problem that the invention aims to solve

[0015] Considering the potential for the use of flexible displays worldwide, excellent bending resistance at room temperature only within Japan is insufficient; excellent bending resistance under various environments is required. However, even when existing adhesive sheets exhibit bending resistance at room temperature, this resistance sometimes deteriorates at low temperatures.

[0016] To improve flexural resistance at low temperatures, a polymer with a low glass transition temperature is considered as the base polymer in the adhesive layer constituting the adhesive sheet. However, in this case, both the elastic modulus at low and high temperatures decrease, resulting in reduced cohesion and adhesion at high temperatures, making it easier to peel off. Therefore, it is difficult to manufacture an adhesive sheet that exhibits excellent flexural resistance at low temperatures and excellent adhesion at high temperatures.

[0017] The present invention was conceived based on the following situation, and its purpose is to provide an adhesive sheet that exhibits excellent bending resistance at low temperatures and excellent adhesion over a wide temperature range from room temperature to high temperatures.

[0018] Solution for solving the problem

[0019] The inventors conducted in-depth research to achieve the above-mentioned objectives and discovered that, based on specific adhesive sheets, excellent flexural strength is achieved at low temperatures, and excellent adhesion is achieved over a wide temperature range from room temperature to high temperatures. This invention is based on these insights.

[0020] That is, the present invention provides an adhesive sheet having an adhesive layer comprising: an acrylic polymer comprising (meth)acrylate alkyl esters having alkyl groups having 10 or more carbon atoms as constituent units; and a tackifier, wherein the adhesive layer has an elastic modulus of 5.0 MPa or less at -30°C and a gel fraction of 50% or more.

[0021] Preferably, the above-mentioned acrylic polymer contains alkyl (meth)acrylates having straight-chain or branched alkyl groups having 1 to 8 carbon atoms as constituent units.

[0022] Preferably, the above-mentioned tackifier comprises oligomers or tackifying resins.

[0023] Yes, the adhesive sheet mentioned above is a double-sided adhesive sheet used to fix components in electrical and electronic equipment to each other.

[0024] Furthermore, the present invention provides an electrical and electronic device having the aforementioned adhesive sheet, wherein the adhesive sheet fixes components to each other through two adhesive surfaces.

[0025] Invention Effects

[0026] The adhesive sheet according to the present invention exhibits excellent flexural strength at low temperatures and excellent adhesion over a wide temperature range from room temperature to high temperatures. Therefore, it exhibits excellent adhesion over a wide temperature range, and even when used in locations where repeated bending occurs at low temperatures, it is not prone to leaving creases, marks, or peeling of the adhesive sheet at the bending location. Attached Figure Description

[0027] Figure 1 This is a cross-sectional schematic diagram of an adhesive sheet according to one embodiment of the present invention. Detailed Implementation

[0028] [Adhesive sheet]

[0029] An adhesive sheet according to one embodiment of the present invention comprises an acrylic polymer and a tackifier, has an elastic modulus of 5.0 MPa or less at -30°C, and has an adhesive layer with a gel fraction of at least 50%. It should be noted that, in this specification, the aforementioned adhesive layer is sometimes referred to as "the adhesive layer of the present invention".

[0030] The adhesive sheet of the present invention can be a so-called "substrate-free" adhesive sheet without a substrate (substrate layer), or it can be an adhesive sheet with a substrate. It should be noted that in this specification, the "substrate-free" adhesive sheet is sometimes referred to as a "substrate-free adhesive sheet," and the adhesive sheet with a substrate is sometimes referred to as a "substrate-supported adhesive sheet." Examples of the aforementioned substrate-free adhesive sheets include, for example, a double-sided adhesive sheet consisting solely of the adhesive layer of the present invention, and a double-sided adhesive sheet containing the adhesive layer of the present invention and other adhesive layers (adhesive layers other than the adhesive layer of the present invention). Furthermore, examples of the aforementioned substrate-supported adhesive sheets include, for example, 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, and 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. It should be noted that the aforementioned "substrate (substrate layer)" refers to a support body, which is the portion of the adhesive sheet of the present invention that is adhered to the adhered object along with the adhesive layer when the adhesive sheet of the present invention is used (attached). The release liner that is peeled off when using (adhesive sheet) is not included in the above-mentioned substrate.

[0031] Figure 1 This is a cross-sectional schematic diagram illustrating one embodiment of the adhesive sheet of the present invention. Figure 1 The adhesive sheet 1 shown is a substrate-free double-sided adhesive sheet containing a single layer of adhesive layer 2 as the adhesive layer of the present invention, and release liner 3 and release liner 4 are respectively provided on the adhesive surfaces on both sides.

[0032] (The adhesive layer of the present invention)

[0033] The adhesive sheet of the present invention may have a single adhesive layer or two or more adhesive layers. When it has two or more layers, at least one layer may be the adhesive layer of the present invention, while the other adhesive layers may be the adhesive layer of the present invention or other adhesive layers. When it has two or more adhesive layers of the present invention, the multiple adhesive layers may be the same adhesive layer or may be adhesive layers with different compositions, thicknesses, and physical properties. Furthermore, when the adhesive layer is provided on one side of the substrate in the case of the adhesive sheet with a substrate, it may be a single layer or multiple layers composed of the same layers or layers with different compositions, thicknesses, and physical properties.

[0034] The adhesive layer of the present invention has an elastic modulus of 5.0 MPa or less at -30°C, preferably 4.0 MPa or less, more preferably 3.0 MPa or less, even more preferably 2.0 MPa or less, and particularly preferably 1.0 MPa or less. With an elastic modulus of 5.0 MPa or less, even under repeated bending at low temperatures, it is not easy to leave creases, marks, or peeling of the adhesive at the bending points, exhibiting excellent bending resistance. The aforementioned elastic modulus is, for example, 0.1 MPa or more, preferably 0.2 MPa or more.

[0035] It should be noted that in this specification, "elastic modulus" refers to the dynamic shear storage modulus (G'). For example, by applying a shear strain at a frequency of 1 Hz using a viscoelasticity testing machine, and measuring the temperature in shear mode at a heating rate of 5 ℃ / min within the temperature range of -50 to 150 ℃, the peak of G' at any temperature can be obtained as the elastic modulus.

[0036] The gel fraction (mass ratio of solvent-insoluble components) of the adhesive layer of the present invention is 50% or more, preferably 60% or more, and more preferably 70% or more. By having a gel fraction of 50% or more, the cohesive strength of the adhesive layer is improved, resulting in excellent adhesion to the adhered object under high-temperature conditions. The gel fraction is, for example, 95% or less, preferably 90% or less. If the gel fraction is 95%, moderate flexibility is obtained, further improving adhesion. It should be noted that the gel fraction can be controlled, for example, by the monomer composition of the acrylic polymer, the weight-average molecular weight, and the amount of crosslinking agent used (addition amount).

[0037] Specifically, the gel fraction mentioned above is a value calculated, for example, by the following "Method for Determining Gel Fraction".

[0038] (Method for determining gel fraction)

[0039] Approximately 0.2g of the adhesive layer was collected from the adhesive sheet and wrapped in a porous tetrafluoroethylene sheet (trade name "NTF1122", manufactured by Nitto Denko Co., Ltd.) with an average pore size of 0.2μm. The sheet was then bound with cotton thread, and the mass at this point was measured. This mass is designated as the mass before impregnation. It should be noted that this mass before impregnation is the total mass of the adhesive layer (the adhesive layer collected above) (B), the tetrafluoroethylene sheet, and the cotton thread. Furthermore, the total mass of the tetrafluoroethylene sheet and the cotton thread was also measured beforehand, and this mass is designated as the bag mass (A).

[0040] Next, the object (referred to as the "sample"), which was wrapped with an adhesive layer of tetrafluoroethylene sheet and bound with cotton thread, was placed in a 50 ml container filled with ethyl acetate and left to stand at 23°C for 7 days. After that, the sample (after ethyl acetate treatment) was removed from the container, transferred to an aluminum cup, and dried in a desiccator at 130°C for 2 hours to remove the ethyl acetate. The mass was then measured and set as the mass after impregnation (C).

[0041] Then, the gel fraction is calculated according to the following formula.

[0042] Gel fraction [mass %] = 100 × (C - A) / B

[0043] The peel adhesion force of the adhesive layer of the present invention at 180° relative to the SUS plane at room temperature is preferably 5.0 N / 20 mm or more, more preferably 5.5 N / 20 mm or more, and even more preferably 6.0 N / 20 mm or more. If the peel adhesion force is 5.0 N / 20 mm or more, the adhesive sheet is less prone to peeling even under repeated bending near room temperature, exhibiting excellent bending resistance. A higher peel adhesion force makes peeling less likely; for example, 20.0 N / 20 mm or less. The aforementioned room temperature refers, for example, to an environment with a temperature of 23°C and a relative humidity of 50% RH.

[0044] The adhesive layer of the present invention is an adhesive layer comprising an acrylic polymer. Preferably, the adhesive layer of the present invention comprises an acrylic polymer as a matrix polymer for adhesive properties. It should be noted that, in this specification, the matrix polymer refers to the main component of the polymer composition in the adhesive constituting the adhesive layer, for example, a polymer component comprising more than 50% by mass. The proportion of the matrix polymer in the above-mentioned adhesive layer relative to 100% by mass of the total amount of the adhesive layer is preferably 60% by mass or more, more preferably 70% by mass or more.

[0045] The adhesive layer of the present invention comprises at least: an acrylic polymer, comprising (meth)acrylate alkyl esters having alkyl groups having 10 or more carbon atoms as constituent units; and a tackifier. The aforementioned acrylic polymer is sometimes referred to as "the acrylic polymer of the present invention". The adhesive layer of the present invention may comprise only one acrylic polymer of the present invention, or it may comprise two or more acrylic polymers of the present invention.

[0046] The acrylic polymer of the present invention is a polymer comprising acrylic monomers (monomers having (meth)acryloyl groups in the molecule) as monomeric components constituting the polymer. That is, the above-mentioned acrylic polymer comprises constitutive units derived from acrylic monomers. It should be noted that the acrylic polymer may use only one type or two or more types of acrylic monomers. Furthermore, the above-mentioned acrylic polymer may contain only one type of acrylic monomer as a monomeric component or may contain two or more types of acrylic monomers. It should be noted that in this specification, "(meth)acrylic acid" means "acrylic acid" and / or "methacrylic acid" (either or both of "acrylic acid" and "methacrylic acid"), and so on.

[0047] The acrylic polymer of the present invention comprises alkyl (meth)acrylates having a straight-chain or branched alkyl group having 10 or more carbon atoms as constituent units. Therefore, the adhesive sheet of the present invention does not exhibit reduced adhesion at room temperature and high temperature, and exhibits excellent flexural resistance at low temperature. Only one type of alkyl (meth)acrylate having 10 or more carbon atoms may be used, or two or more types may be used.

[0048] Examples of (meth)acrylate alkyl esters having a straight or branched alkyl group having 10 or more carbon atoms include decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate (lauryl)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecanyl (meth)acrylate, octadecyl (meth)acrylate, nonadecanyl (meth)acrylate, and eicosyl (meth)acrylate.

[0049] The number of carbon atoms in the alkyl (meth)acrylate having a straight-chain or branched alkyl group having 10 or more carbon atoms is preferably 10 to 18, more preferably 12 to 16.

[0050] The proportion of alkyl (meth)acrylates having straight-chain or branched alkyl groups having 10 or more carbon atoms in all monomer components constituting the acrylic polymer of the present invention is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, relative to the total amount of all monomer components (100% by mass). Furthermore, from the viewpoint of enabling copolymerization of other monomer components to obtain the effect of those other monomer components, the above proportion can be 70% by mass or less, or 60% by mass or less, 50% by mass or less, 20% by mass or less, 16% by mass or less, or 10% by mass or less.

[0051] The acrylic polymer of the present invention further preferably comprises alkyl (meth)acrylates having straight-chain or branched alkyl groups having 1 to 8 carbon atoms as constituent units. Therefore, the adhesive sheet of the present invention exhibits superior adhesion at both room temperature and high temperature. Only one type of alkyl (meth)acrylate having 1 to 8 carbon atoms may be used, or two or more types may be used.

[0052] Examples of alkyl (meth)acrylates having straight-chain or branched alkyl groups having 1 to 8 carbon atoms 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, isoamyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and isooctyl (meth)acrylate.

[0053] In alkyl methacrylates having a straight-chain or branched alkyl group having 1 to 8 or more carbon atoms, the number of carbon atoms of the alkyl group is preferably 2 to 8, more preferably 4 to 8.

[0054] The proportion of alkyl (meth)acrylates having straight-chain or branched alkyl groups having 1 to 8 carbon atoms in all monomer components constituting the acrylic polymer of the present invention is preferably 30% by mass or more, more preferably 40% by mass or more, further preferably 50% by mass or more, more preferably 60% by mass or more, and particularly preferably 70% by mass or more, relative to the total amount of all monomer components (100% by mass). Furthermore, from the viewpoint of enabling copolymerization of other monomer components to obtain the effect of those other monomer components, the above proportion can be 99% by mass or less, 96% by mass or less, or 93% by mass or less.

[0055] The acrylic polymer of the present invention is preferably the polymer containing the most constituent units derived from (meth)acrylates by mass ratio. Examples of the aforementioned (meth)acrylates include hydrocarbon-containing (meth)acrylates. Examples of hydrocarbon-containing (meth)acrylates include alkyl (meth)acrylates having linear or branched aliphatic hydrocarbon groups, cycloalkyl (meth)acrylates having alicyclic hydrocarbon groups, and aryl (meth)acrylates having aromatic hydrocarbon groups. Only one type of hydrocarbon-containing (meth)acrylate may be used, or two or more types may be used.

[0056] Examples of the above-mentioned alkyl methacrylates include compounds that are alkyl methacrylates having a straight-chain or branched alkyl group having 10 or more carbon atoms, compounds that are alkyl methacrylates having a straight-chain or branched alkyl group having 1 to 8 carbon atoms, nonyl methacrylate, isononyl methacrylate, etc.

[0057] Examples of (meth)acrylates having the aforementioned alicyclic hydrocarbon groups include: cyclopentyl methacrylate, cyclohexyl methacrylate, cycloheptyl methacrylate, cyclooctyl methacrylate, etc., which have a monocyclic aliphatic hydrocarbon ring; isobornyl methacrylate, etc., which have a bicyclic aliphatic hydrocarbon ring; and dicyclopentyl methacrylate, dicyclopentyloxyethyl methacrylate, tricyclopentyl methacrylate, 1-adamantane methacrylate, 2-methyl-2-adamantane methacrylate, 2-ethyl-2-adamantane methacrylate, etc., which have three or more aliphatic hydrocarbon rings.

[0058] Examples of (meth)acrylates having the aforementioned aromatic hydrocarbon groups include phenyl (meth)acrylate and benzyl (meth)acrylate.

[0059] In order to properly express the basic properties such as adhesiveness of the aforementioned hydrocarbon-containing (meth)acrylate in the adhesive layer, the proportion of the aforementioned hydrocarbon-containing (meth)acrylate in all monomer components constituting the aforementioned acrylic polymer relative to the total amount (100% by mass) of the aforementioned monomer components is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and can be 80% by mass or more, 90% by mass or more, or 95% by mass or more. Furthermore, from the viewpoint of enabling copolymerization of other monomer components to obtain the effects of those other monomer components, the aforementioned proportion can be 99.9% by mass or less, and can be 98% by mass or less, 95% by mass or less, or 90% by mass or less.

[0060] The acrylic polymer of the present invention, with the aim of improving cohesiveness and introducing crosslinking points, may contain constituent units derived from other monomer components capable of copolymerizing with the aforementioned hydrocarbon-containing (meth)acrylates. Examples of such other monomer components include, for instance, monomers containing carboxyl groups, acid anhydride monomers, hydroxyl groups, glycidyl groups, sulfonic acid groups, phosphate groups, nitrogen atoms, and other monomers containing polar groups. Only one of these other monomer components may be used, or two or more may be used.

[0061] Examples of hydroxyl-containing monomers mentioned above include: 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, 6-hydroxyhexyl methacrylate, 8-hydroxyoctyl methacrylate, 10-hydroxydecyl methacrylate, 12-hydroxylaurate methacrylate, and methyl methacrylate (4-hydroxymethylcyclohexyl)

[0062] Examples of nitrogen-containing monomers include amide-containing monomers, amino-containing monomers, cyano-containing monomers, and monomers with nitrogen-containing rings. Examples of amide-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, and N-butoxymethyl (meth)acrylamide. Examples of amino-containing monomers include aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, and tert-butylaminoethyl (meth)acrylate. Examples of cyano-containing monomers include acrylonitrile and methacrylonitrile. Examples of monomers having nitrogen-containing rings include N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazolium, N-vinylazole, N-vinylmorpholine, N-vinylcaprolactam, and N-(meth)acryloylmorpholine.

[0063] Examples of the aforementioned carboxyl-containing monomers include acrylic acid, methacrylic acid, carboxyethyl methacrylate, carboxypentyl methacrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid. Examples of the aforementioned acid anhydride monomers include maleic anhydride and itaconic anhydride.

[0064] Examples of ketone-containing monomers mentioned above include diacetone (meth)acrylamide, diacetone (meth)acrylate, vinyl methyl ketone, vinyl ethyl ketone, allyl acetoacetate, vinyl acetoacetate, etc.

[0065] Examples of alkoxysilyl monomers include 3-(meth)acryloyloxypropyltrimethoxysilane, 3-(meth)acryloyloxypropyltriethoxysilane, 3-(meth)acryloyloxypropylmethyldimethoxysilane, and 3-(meth)acryloyloxypropylmethyldiethoxysilane.

[0066] Examples of the monomers containing glycidyl groups mentioned above include glycidyl (meth)acrylate and methyl glycidyl (meth)acrylate.

[0067] Examples of the sulfonic acid-containing monomers mentioned above include styrene sulfonic acid, allyl sulfonic acid, 2-(meth)acrylamide-2-methylpropanesulfonic acid, (meth)acrylamide propanesulfonic acid, (meth)acrylate sulfonylpropyl ester, and (meth)acryloyloxynaphthalene sulfonic acid.

[0068] Examples of the aforementioned phosphate-containing monomers include 2-hydroxyethylacrylphosphate.

[0069] The polar monomers constituting the acrylic polymers of the present invention preferably contain hydroxyl-containing monomers and / or nitrogen-containing monomers. By using such polar monomers, the cohesiveness and polarity of the adhesive can be adjusted, thereby improving its adhesion at both room temperature and high temperature.

[0070] When the acrylic polymer of the present invention contains the above-mentioned hydroxyl-containing monomer as a monomer component constituting the polymer, the proportion of the above-mentioned hydroxyl-containing monomer in all monomer components (100% by mass) is not particularly limited, but is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.5% by mass or more. Furthermore, from the viewpoint of improving adhesion at room temperature and flexibility at low temperature, the proportion of the above-mentioned hydroxyl-containing monomer is preferably 30% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, and can be 3% by mass or less.

[0071] When the acrylic polymer of the present invention contains the above-mentioned nitrogen-containing monomer as a monomer component constituting the polymer, the proportion of the nitrogen-containing monomer in all the monomer components (100% by mass) is not particularly limited, but is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.5% by mass or more. Furthermore, from the viewpoint of improved adhesion at room temperature and improved flexibility at low temperature, the proportion of the nitrogen-containing monomer is preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, even more preferably 2% by mass or less, and particularly preferably 1% by mass or less.

[0072] The total proportion of the aforementioned polar monomers (particularly, the total of the aforementioned nitrogen-containing monomers and the aforementioned hydroxyl-containing monomers) in all monomer components (100% by mass) constituting the acrylic polymer of the present invention is not particularly limited, but from the viewpoint of better utilizing the effects of using polar monomers, it is preferably 0.1% by mass or more, more preferably 1% by mass or more. Furthermore, from the viewpoint of obtaining an adhesive layer with moderate flexibility, the total of the above proportions is preferably 10% by mass or less, more preferably 5% by mass or less, further preferably 4% by mass or less, and particularly preferably 2% by mass or less.

[0073] As monomer components constituting the acrylic polymers of the present invention, other monomers may also be included. Examples of such other monomers include: vinyl ester monomers such as vinyl acetate, vinyl propionate, and vinyl laurate; aromatic vinyl compounds such as styrene, substituted styrene (α-methylstyrene, etc.), and vinyltoluene; olefin monomers such as ethylene, propylene, isoprene, butadiene, and isobutylene; chlorine-containing monomers such as vinyl chloride and vinylidene chloride; alkoxy-containing monomers such as methoxyethyl methacrylate and ethoxyethyl methacrylate; and vinyl ether monomers such as methyl vinyl ether and ethyl vinyl ether. Only one of the above-mentioned other monomer components may be used, or two or more may be used.

[0074] As the aforementioned alkoxy-containing monomers, examples include monomers formed by replacing one or more hydrogen atoms in the hydrocarbon group of the aforementioned hydrocarbon-containing (meth)acrylates with alkoxy groups, such as methoxymethyl methacrylate, 2-methoxyethyl methacrylate, 2-methoxybutyl methacrylate, 2-ethoxyethyl methacrylate, ethoxyethoxyethyl methacrylate (ethyl carbitol methacrylate), and other hydrocarbon-containing (meth)acrylates with alkoxy groups.

[0075] The proportion of the other monomers in 100% by mass of all monomer components constituting the acrylic polymer of the present invention can be, for example, 0.05% by mass or more, 0.5% by mass or more, 5% by mass or more, or 10% by mass or more. The above proportions can be, for example, 20% by mass or less, 10% by mass or less, 5% by mass or less, or they can be substantially absent.

[0076] The weight-average molecular weight (Mw) of the acrylic polymer of the present invention is preferably 10 × 10⁻⁶. 4 The above is preferred, with 60×10 being more ideal. 4 The above is further preferred to be 100×10 4 That's all. If the above Mw is 10 × 10 4 The above methods readily yield adhesives exhibiting good cohesiveness. Furthermore, the preferred Mw value is 500 × 10⁻⁶.4 The following is more preferably 400×10 4 The following is a further preferred value: 300×10 4 Below. If the above Mw is 500×10 4 The following methods readily form adhesives exhibiting moderate flowability (polymer chain mobility), resulting in superior flexural strength. The weight-average molecular weights mentioned above were determined by gel permeation chromatography (GPC) and calculated based on polystyrene.

[0077] The glass transition temperature (Tg) of the acrylic polymer of the present invention is preferably below 0°C, more preferably below -10°C, and even more preferably below -20°C. If the glass transition temperature is below 0°C, even under repeated bending at low temperatures, creases, marks, or peeling of the adhesive sheet are less likely to occur at the bending location. The glass transition temperature is preferably above -80°C, more preferably above -70°C, and even more preferably above -66°C.

[0078] The glass transition temperature mentioned above is a value calculated based on the following formula (X) (Fox formula).

[0079] 1 / Tg=W1 / Tg1+W2 / Tg2+……+Wn / Tgn(X)

[0080] [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 monomer i when it forms a homopolymer (unit: K), and Wi (i = 1, 2, ..., n) represents the mass fraction of monomer i in the total monomer composition.]

[0081] The above formula (X) is a calculation formula for a polymer composed of n monomer components: monomer 1, monomer 2, ..., monomer n.

[0082] It should be noted that the "glass transition temperature (Tg) at which the homopolymer is formed" (sometimes simply referred to as "the Tg of the homopolymer") in this specification refers to the "glass transition temperature (Tg) of the homopolymer of that monomer," specifically, the values ​​listed in the "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1987). It should also be noted that the Tg of the homopolymer of monomers not described in the aforementioned literature refers to values ​​obtained, for example, by the following determination method (refer to Japanese Patent Application Publication No. 2007-51271), excluding monomers with a polyorganosiloxane backbone. Specifically, in a reactor equipped with a thermometer, stirrer, nitrogen inlet pipe, and reflux cooling pipe, 100 parts by mass of monomer, 0.2 parts by mass of 2,2'-azobisisobutyronitrile, and 200 parts by mass of ethyl acetate as the polymerization solvent are added, and nitrogen is introduced while stirring for 1 hour. After removing oxygen from the polymerization system in this way, the temperature is raised to 63°C and the reaction is carried out for 10 hours. Next, the mixture was cooled to room temperature to obtain a homopolymer solution with a solid content of 33% by mass. This homopolymer solution was then cast onto a release liner, dried, and used to prepare a test sample (sheet-like homopolymer) approximately 2 mm thick. The test sample was then punched into a disc shape with a diameter of 7.9 mm, clamped with parallel plates, and viscoelasticity was measured in shear mode using a viscoelasticity testing machine (trade name "ARES", manufactured by Rheometrics) at a frequency of 1 Hz, with a heating rate of 5 °C / min over a temperature range of -70 to 150 °C. The peak temperature of tanδ was taken as the Tg of the homopolymer.

[0083] The acrylic polymers of the present invention are obtained by polymerizing a composition comprising at least an acrylic monomer. These polymerization methods are not particularly limited, and examples include solution polymerization, emulsion polymerization, bulk polymerization, thermal polymerization, and polymerization using active energy rays (active energy ray polymerization). Among these, bulk polymerization, thermal polymerization, and active energy ray polymerization are preferred from the perspectives of adhesive layer transparency and cost. Furthermore, the obtained acrylic polymer can be any of a random copolymer, block copolymer, or graft copolymer.

[0084] Various conventional solvents can be used during the polymerization of monomer components. Examples of such solvents include esters such as ethyl acetate and n-butyl acetate; aromatic hydrocarbons such as toluene and benzene; aliphatic hydrocarbons such as n-hexane and n-heptane; alicyclic hydrocarbons such as cyclohexane and methylcyclohexane; and ketones such as methyl ethyl ketone and methyl isobutyl ketone. Only one of these solvents may be used, or two or more may be used.

[0085] There are no particular limitations on the polymerization initiators, chain transfer agents, emulsifiers, etc., used in the free radical polymerization of monomer components; they can be selected appropriately. It should be noted that the weight-average molecular weight of the polymer can be controlled by the amount of polymerization initiator and chain transfer agent used, as well as the reaction conditions; the appropriate amount should be adjusted according to these factors.

[0086] The polymerization initiators used in the polymerization of monomer components can be thermal polymerization initiators, photopolymerization initiators (photoinitiators), etc., depending on the type of polymerization reaction. Only one of these polymerization initiators can be used, or two or more can be used.

[0087] There are no particular limitations on the aforementioned thermal polymerization initiators. Examples include azo polymerization initiators, peroxide polymerization initiators (such as benzoyl peroxide, tert-butyl maleate peroxide, potassium persulfate and other persulfates, benzoyl peroxide, hydrogen peroxide, etc.), substituted ethane initiators such as phenyl-substituted ethane, aromatic carbonyl compounds, and redox polymerization initiators. Among these, the azo polymerization initiators disclosed in Japanese Patent Application Publication No. 2002-69411 are preferred. Examples of such azo polymerization initiators include 2,2'-azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis(2-methylpropionic acid) dimethyl ester, and 4,4'-azobis-4-cyanovaleric acid. The amount of thermal polymerization initiator used is the usual amount, for example, it can be selected from a 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.

[0088] There are no particular limitations on the photopolymerization initiators mentioned above. Examples include benzoin ether-based photopolymerization initiators, acetophenone-based photopolymerization initiators, α-keto alcohol-based photopolymerization initiators, aromatic sulfonyl chloride-based photopolymerization initiators, photoactive oxime-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzoyl (Benzil)-based photopolymerization initiators, benzophenone-based photopolymerization initiators, ketal-based photopolymerization initiators, and thioxanone-based photopolymerization initiators. Additionally, acylphosphine oxide-based photopolymerization initiators and titanium ceramsite-based photopolymerization initiators can also be listed. Examples of benzoin ether-based photopolymerization initiators include benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, benzoin isobutyl ether, 2,2-dimethoxy-1,2-diphenylethane-1-one, and anisole methyl ether. Examples of acetophenone-based photopolymerization initiators include 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexylphenyl ketone, 4-phenoxydichloroacetophenone, and 4-tert-butyldichloroacetophenone. Examples of α-keto-alcohol-based photopolymerization initiators include 2-methyl-2-hydroxyacetone and 1-[4-(2-hydroxyethyl)phenyl]-2-methylpropane-1-one. Examples of aromatic sulfonyl chloride-based photopolymerization initiators include 2-naphthalenesulfonyl chloride. Examples of photoactive oxime-based photopolymerization initiators include 1-phenyl-1,1-propanedione-2-(o-ethoxycarbonyl)-oxime. Examples of benzoin-based photopolymerization initiators include benzoin. Examples of benzoinyl-based photopolymerization initiators include benzoin. Examples of benzophenone-based photopolymerization initiators include benzophenone, benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, polyvinylbenzophenone, and α-hydroxycyclohexylphenyl ketone. Examples of benzyl dimethyl ketal-based photopolymerization initiators include benzyl dimethyl ketal. Examples of thioxanthone-based photopolymerization initiators include thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-diisopropylthioxanthone, and dodecylthioxanthone. Examples of acylphosphine oxide-based photopolymerization initiators include 2,4,6-trimethylbenzoyl-diphenylphosphine oxide and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide. Examples of titanium-based photopolymerization initiators include bis(n5-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrolo-1-yl)-phenyl)titanium. The amount of photopolymerization initiator used is the usual amount, for example, selected from a range of 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.

[0089] The acrylic polymer of the present invention may include structural portions derived from the aforementioned crosslinking agent. That is, the acrylic polymer of the present invention may be formed by crosslinking with the aforementioned crosslinking agent. By using a crosslinking agent, a crosslinked structure can be formed in the acrylic polymer within the acrylic adhesive layer, controlling the gel fraction. Only one type of crosslinking agent may be used, or two or more types may be used.

[0090] The crosslinking agents mentioned above are not particularly limited, and examples 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, organosilicon-based crosslinking agents, and silane-based crosslinking agents (silane coupling agents), etc.

[0091] The content of the crosslinking agent is not particularly limited, but is preferably 0.001 to 20 parts by mass relative to 100 parts by mass of the total monomer components constituting the acrylic polymer of the present invention, more preferably 0.01 to 15 parts by mass, further preferably 0.15 to 5 parts by mass, even more preferably 0.1 to 3 parts by mass, and particularly preferably 0.2 to 2 parts by mass.

[0092] The aforementioned isocyanate-based crosslinking agents are compounds (polyfunctional isocyanate compounds) having an average of two or more isocyanate groups per molecule. Examples of such isocyanate-based crosslinking agents include aliphatic polyisocyanates, alicyclic polyisocyanates, and aromatic polyisocyanates.

[0093] Examples of the aforementioned aliphatic polyisocyanates include: 1,2-ethylene diisocyanate; tetramethylene diisocyanates such as 1,2-tetramethylene diisocyanate, 1,3-tetramethylene diisocyanate, and 1,4-tetramethylene diisocyanate; hexamethylene diisocyanates such as 1,2-hexamethylene diisocyanate, 1,3-hexamethylene diisocyanate, 1,4-hexamethylene diisocyanate, 1,5-hexamethylene diisocyanate, 1,6-hexamethylene diisocyanate, and 2,5-hexamethylene diisocyanate; 2-methyl-1,5-pentane diisocyanate, 3-methyl-1,5-pentane diisocyanate, and lysine diisocyanate.

[0094] Examples of the aforementioned alicyclic polyisocyanates include isophorone diisocyanate; cyclohexyl diisocyanates such as 1,2-cyclohexyl diisocyanate, 1,3-cyclohexyl diisocyanate, and 1,4-cyclohexyl diisocyanate; cyclopentyl diisocyanates such as 1,2-cyclopentyl diisocyanate and 1,3-cyclopentyl diisocyanate; hydrogenated phenyl dimethyl diisocyanate, hydrogenated toluene diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated tetramethylxylene diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate.

[0095] Examples of the aforementioned 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, and 2,2'-diphenylpropane-4,4'-diisocyanate. Cyanides, 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropane diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, naphthalene-1,4-diisocyanate, naphthalene-1,5-diisocyanate, 3,3'-dimethoxydiphenyl-4,4'-diisocyanate, phenylenedimethyl-1,4-diisocyanate, phenylenedimethyl-1,3-diisocyanate, etc.

[0096] In addition, as the aforementioned isocyanate-based crosslinking agents, 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), and trimethylolpropane / phenylenedimethyl diisocyanate adduct (trade name "TAKENATE D-110N", manufactured by Mitsui Chemicals Co., Ltd.) can also be listed.

[0097] It should be noted that in the aqueous dispersion of modified acrylic polymers prepared by emulsion polymerization, isocyanate-based crosslinking agents can be omitted. However, if necessary, blocked isocyanate-based crosslinking agents can be used to facilitate reaction with water.

[0098] When an isocyanate-based crosslinking agent is used as the crosslinking agent described above, the content of the isocyanate-based crosslinking agent is not particularly limited. However, relative to 100 parts by mass of the total monomer components constituting the acrylic polymer of the present invention, it is preferably 0.01 parts by mass or more, more preferably 0.02 parts by mass or more. The above content is preferably 1 part by mass or less, more preferably 0.5 parts by mass or less, further preferably 0.3 parts by mass or less, even more preferably 0.2 parts by mass or less, and particularly preferably 0.1 parts by mass or less.

[0099] Examples of epoxy crosslinking agents (multifunctional epoxy compounds) include N,N,N',N'-tetraglycidyl-m-phenylenediamine, diglycidyl aniline, 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, and polyglycerol polyglycidyl ether. Polyglycidyl ether, sorbitol polyglycidyl ether, trimethylolpropane polyglycidyl ether, diglycidyl adipate, diglycidyl phthalate, triglycidyl-tris(2-hydroxyethyl) isocyanurate, resorcinol diglycidyl ether, bisphenol S diglycidyl ether, and epoxy resins having two or more epoxy groups in the molecule, etc. Furthermore, commercially available products under the trade name "TETRAD C" (manufactured by Mitsubishi Gas Chemical Co., Ltd.) can also be listed as examples of the aforementioned epoxy crosslinking agents.

[0100] When an epoxy-based crosslinking agent is used as the crosslinking agent, the content of the epoxy-based crosslinking agent is not particularly limited. It is preferably more than 0 parts by mass and less than 1 part by mass relative to 100 parts by mass of the total monomer components constituting the acrylic polymer of the present invention, more preferably 0.001 to 0.5 parts by mass, even more preferably 0.002 to 0.2 parts by mass, even more preferably 0.005 to 0.1 parts by mass, even more preferably 0.008 to 0.1 parts by mass, and particularly preferably 0.009 to 0.05 parts by mass.

[0101] As the aforementioned peroxide-based crosslinking agent, any peroxide that generates free radicals through heat to crosslink the matrix polymer can be used appropriately. However, considering workability and stability, it is preferable to use a peroxide with a 1-minute half-life temperature of 80 to 160°C, and more preferably a peroxide with a temperature of 90 to 140°C.

[0102] Examples of peroxide-based crosslinking agents include di(2-ethylhexyl) peroxide dicarbonate (1-minute half-life temperature: 90.6°C), di(4-tert-butylcyclohexyl) peroxide dicarbonate (1-minute half-life temperature: 92.1°C), disec-butyl peroxide dicarbonate (1-minute half-life temperature: 92.4°C), tert-butyl peroxide neodecanoate (1-minute half-life temperature: 103.5°C), tert-hexyl peroxide neopentanoate (1-minute half-life temperature: 109.1°C), tert-butyl peroxide neopentanoate (1-minute half-life temperature: 110.3°C), and lauric acid peroxide. Acyl peroxide (1-minute half-life temperature: 116.4℃), dioctanoyl peroxide (1-minute half-life temperature: 117.4℃), 1,1,3,3-tetramethylbutyl peroxide (1-minute half-life temperature: 124.3℃), di(4-methylbenzoyl peroxide) (1-minute half-life temperature: 128.2℃), benzoyl peroxide (1-minute half-life temperature: 130.0℃), tert-butyl peroxide (1-minute half-life temperature: 136.1℃), 1,1-di(tert-hexylperoxy)cyclohexane (1-minute half-life temperature: 149.2℃), etc.

[0103] The half-life of the aforementioned peroxide-based crosslinking agent refers to the time until the residual amount of peroxide is reduced to half, which is an indicator of the decomposition rate of the peroxide. The decomposition temperature used to obtain the half-life at any given time, and the half-life time at any given temperature, are described in manufacturer catalogs, such as in Nippon Oil Co., Ltd.'s "Organic Peroxide Catalog, Ninth Edition (May 2003)". It should be noted that the determination of the residual peroxide amount after reaction treatment can be performed, for example, by HPLC (High Performance Liquid Chromatography). More specifically, for example, approximately 0.2 g of the reacted adhesive is taken out and immersed in 10 ml of ethyl acetate. After extraction by shaking at 25°C and 120 rpm for 3 hours, the mixture is allowed to stand at room temperature for 3 days. Then, 10 ml of acetonitrile is added, and the mixture is shaken at 25°C and 120 rpm for 30 minutes. Approximately 10 μl of the extract obtained by filtration through a membrane filter (0.45 μm) is injected into the HPLC for analysis, which can be used as the amount of peroxide after reaction treatment.

[0104] When a peroxide-based crosslinking agent is used as the crosslinking agent, the content of the crosslinking agent is not particularly limited. It is preferably 2 parts by mass or less, more preferably 0.02 to 2 parts by mass, further preferably 0.05 to 1.5 parts by mass, more preferably 0.05 to 1 part by mass, and particularly preferably 0.1 to 1 part by mass, relative to 100 parts by mass of the monomer components constituting the acrylic polymer of the present invention.

[0105] Furthermore, organic crosslinking agents and multifunctional metal chelates can also be used in combination as the aforementioned crosslinking agents. Multifunctional metal chelates are compounds in which a multivalent metal is covalently or coordinately bonded to an organic compound. Examples of multivalent metal atoms include Al, Cr, Zr, Co, Cu, Fe, Ni, V, Zn, In, Ca, Mg, Mn, Y, Ce, Sr, Ba, Mo, La, Sn, and Ti. Examples of atoms in the covalently or coordinately bonded organic compounds include oxygen atoms, and examples of organic compounds include alkyl esters, alcohols, carboxylic acids, ethers, and ketones.

[0106] As the aforementioned crosslinking agent, an isocyanate-based crosslinking agent is preferably included. Furthermore, it is more preferable to include other crosslinking agents along with the isocyanate-based crosslinking agent. As the aforementioned other crosslinking agent, a peroxide-based crosslinking agent is preferred. Using such a crosslinking agent, an adhesive layer with thinner and more superior adhesion can be formed using the acrylic polymer of the present invention.

[0107] The adhesive layer of the present invention contains a tackifier. By incorporating the acrylic polymer and the tackifier of the present invention, the adhesive layer of the present invention exhibits excellent adhesion to the adherend and is not easily peeled off at low temperatures, even under repeated bending, demonstrating excellent flexural resistance. The aforementioned tackifier may be used alone or in combination with two or more.

[0108] Examples of tackifiers include tackifying resins and oligomers. In the adhesive layer of the present invention, the oligomers may exist as oligomers or as structural portions derived from the oligomers in the acrylic polymer of the present invention. That is, the acrylic polymer of the present invention may have structural portions derived from the oligomers.

[0109] Examples of tackifying resins include phenolic tackifying resins, terpene tackifying resins, rosin tackifying resins, hydrocarbon tackifying resins, epoxy tackifying resins, polyamide tackifying resins, elastic tackifying resins, and ketone tackifying resins. Only one of these tackifying resins may be used, or two or more may be used.

[0110] Examples of phenolic tackifying resins include terpene phenol resins, hydrogenated terpene phenol resins, alkylphenol resins, and rosin phenol resins. Terpene phenol resins are polymers containing terpene residues and phenol residues, and examples include copolymers of terpenes and phenolic compounds (terpene-phenol copolymer resins) and substances obtained by modifying homopolymers or copolymers of terpenes with phenol (phenol-modified terpene resins). Examples of terpenes constituting the above-mentioned terpene phenol resins include monoterpenes such as α-pinene, β-pinene, and limonene (d-form, l-form, d / l-form (dipentene)). Hydrogenated terpene phenol resins are resins having a structure obtained by hydrogenating the above-mentioned terpene phenol resins. Alkylphenol resins are resins obtained from alkylphenols and formaldehyde (oil-based phenolic resins). Examples of alkylphenol resins include phenolic varnish type and methyl phenolic type alkylphenol resins. Rosin phenol resins are phenol-modified products of rosin or various rosin derivatives described later. As the aforementioned rosin phenol resin, it can be obtained, for example, by a method of thermal polymerization in which phenol is added to rosin or various rosin derivatives described later using an acid catalyst.

[0111] Examples of terpene-based tackifying resins include polymers of terpenes (typically monoterpenes), such as α-pinene, β-pinene, d-limonene, l-limonene, and dipentene. These terpene polymers can be homopolymers of a single terpene or copolymers of two or more terpenes. Examples of terpene homopolymers include α-pinene polymers, β-pinene polymers, and dipentene polymers. The modified terpene-based tackifying resins are resins obtained by modifying the aforementioned terpene resins (modified terpene resins). Examples of modified terpene resins include styrene-modified terpene resins and hydrogenated terpene resins.

[0112] As rosin-based tackifying resins, examples include rosin-based resins and rosin derivative resins. Examples of rosin-based resins include: unmodified rosin (raw rosin) such as resin rosin, wood rosin, and tall oil rosin; and modified rosin (hydrogenated rosin, disproportionated rosin, polymerized rosin, and rosin with other chemical modifications) obtained by modifying these unmodified rosin through hydrogenation, disproportionation, polymerization, etc. Examples of rosin derivative resins include derivatives of the aforementioned rosin-based resins.

[0113] Examples of rosin derivative resins include: unmodified rosin esters (esters of unmodified rosin and alcohols), modified rosin esters (esters of modified rosin and alcohols), unsaturated fatty acid modified rosin (derived by modifying rosin with unsaturated fatty acids), unsaturated fatty acid modified rosin esters (derived by modifying rosin esters with unsaturated fatty acids), rosin alcohols (derived by reducing the carboxyl groups of rosin or the aforementioned rosin derivatives), and metal salts of rosin or the aforementioned rosin derivatives. Specific examples of the aforementioned rosin esters include: methyl esters, triethylene glycol esters, glyceryl esters, and pentaerythritol esters of unmodified or modified rosin.

[0114] Examples of hydrocarbon-based tackifying resins include 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, and coumarone-indene resins.

[0115] The softening point of the aforementioned tackifying resin is preferably below 160°C, more preferably below 150°C, and even more preferably below 140°C. A lower softening point allows for maintaining a lower elastic modulus with minimal addition, resulting in superior flexural resistance at low temperatures. For example, the softening point is above 60°C, preferably above 70°C.

[0116] The weight-average molecular weight of the above-mentioned oligomers is preferably 2,500 to 10,000, more preferably 3,000 to 8,000. It should be noted that the above-mentioned weight-average molecular weight can be determined by converting polystyrene using the GPC method. For example, a high-efficiency GPC apparatus, "HPLC-8120GPC," manufactured by Tosoh Corporation, can be used to determine it under the following conditions.

[0117] Column: TSKgel SuperHZM-H / HZ4000 / HZ3000 / HZ2000.

[0118] Solvent: Tetrahydrofuran.

[0119] Flow rate: 0.6 ml / min.

[0120] The aforementioned oligomers are preferably acrylic oligomers composed of acrylic monomers as essential monomer components. Examples of acrylic monomers constituting the aforementioned acrylic oligomers, i.e., acrylic monomers, are listed and described as monomer components constituting the acrylic polymers of the present invention. The aforementioned acrylic oligomers preferably contain (meth)acrylates having alicyclic hydrocarbon groups as constituent units. The acrylic monomers contained as the aforementioned constituent units may be only one type or may be two or more types.

[0121] The proportion of (meth)acrylates having alicyclic hydrocarbon groups in 100% of the total monomer components constituting the above-mentioned acrylic oligomers is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 55% by mass or more. The above proportion is preferably 99% by mass or less, and can be 97% by mass or less.

[0122] As one embodiment, the above-mentioned acrylic oligomer preferably contains alkyl (meth)acrylate as a constituent unit. The alkyl (meth)acrylate is preferably methyl methacrylate (MMA). The proportion of alkyl (meth)acrylate in all monomer components constituting the above-mentioned acrylic oligomer is preferably 10% by mass or more, more preferably 20% by mass or more. The above proportion is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 45% by mass or less. Furthermore, the above-mentioned acrylic oligomer may contain the above-mentioned copolymeric monomer as a constituent unit.

[0123] As one embodiment, the above-mentioned acrylic oligomer preferably contains monomers containing functional groups as constituent units. The monomers containing functional groups are preferably monomers containing polar groups, and more preferably monomers containing carboxyl groups. The proportion of monomers containing functional groups in all monomer components constituting the above-mentioned 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 even more preferably 8% by mass or less. Furthermore, the above-mentioned acrylic oligomer may contain the above-mentioned copolymerizable monomers as constituent units.

[0124] The aforementioned oligomers are obtained by polymerizing a composition containing monomeric components constituting the oligomers. Examples of polymerization methods include those for the polymerization of the aforementioned acrylic polymers. Bulk polymerization, thermal polymerization, and active energy radiation polymerization are preferred. Various conventional solvents can be used during the polymerization of the monomeric components. Examples of solvents that can be used in the polymerization of the aforementioned acrylic polymers are provided. Only one solvent may be used, or two or more may be used. The polymerization initiator, chain transfer agent, emulsifier, etc., used in the free radical polymerization of the monomeric components are not particularly limited, and can be appropriately selected.

[0125] The content of the tackifier in the adhesive layer of the present invention is not particularly limited, but is, for example, 0.6 parts by mass or more, preferably 2 parts by mass or more, relative to 100 parts by mass of the total amount of the acrylic polymer of the present invention. If the content is 0.6 parts by mass or more, peeling is less likely to occur even when repeatedly bent at low temperatures. From the viewpoint that peeling is less likely to occur even when repeatedly bent at low temperatures, the content is preferably less than 30 parts by mass, more preferably 25 parts by mass or less.

[0126] The proportion of the tackifier in the adhesive layer of the present invention is not particularly limited, but is preferably more than 0% by mass and less than 22% by mass relative to 100% of the total amount of the adhesive layer of the present invention, and more preferably 1 to 16% by mass. If the above proportion is within the above range, peeling is not likely to occur even when repeatedly bent at low temperatures.

[0127] The adhesive layer of the present invention may contain a colorant. The colorant may be a pigment or a dye. Examples of colorants include black, cyan, magenta, and yellow colorants. From the viewpoint of superior visual recognizability and design, a black colorant is preferred. The colorant may be one type or two or more.

[0128] Examples of black pigments include: carbon black, carbon nanotubes, graphite, copper oxide, manganese dioxide, azo dyes such as azobenzene black, aniline black, perylene black, titanium black, anthocyanin black, activated carbon, ferrite, magnetite, chromium oxide, iron oxide, molybdenum disulfide, complex oxide black pigments, anthraquinone organic black dyes, and azo organic black dyes. Examples of carbon blacks include furnace black, channel black, acetylene black, thermal cracking black, and lampblack. As black colorants, the following can also be listed: CI Solvent Black 3, CI Solvent Black 7, CI Solvent Black 22, CI Solvent Black 27, CI Solvent Black 29, CI Solvent Black 34, CI Solvent Black 43, CI Solvent Black 70; CI Direct Black 17, CI Direct Black 19, CI Direct Black 22, CI Direct Black 32, CI Direct Black 38, CI Direct Black 51, CI Direct Black 71; CI Acid Black 1, CI Acid Black 2, CI Acid Black 24, CI Acid Black 26, CI Acid Black 31, CI Acid Black 48, CI Acid Black 52, CI Acid Black 107, CI Acid Black 109, CI Acid Black 110, CI Acid Black 119, CI Acid Black 154; CI Dispersion Black 1, CI Dispersion Black 3, CI Dispersion Black 10, CI Dispersion Black 24; CI Pigment Black 1, CI Pigment Black 7, etc.

[0129] Examples of cyan colorants include: CI Solvent Blue 25, CI Solvent Blue 36, CI Solvent Blue 60, CI Solvent Blue 70, CI Solvent Blue 93, CI Solvent Blue 95; CI Acid Blue 6, CI Acid Blue 45; CI Pigment Blue 1, CI Pigment Blue 2, CI Pigment Blue 3, CI Pigment Blue 15, CI Pigment Blue 15:1, CI Pigment Blue 15:2, CI Pigment Blue 15:3, CI Pigment Blue 15:4, CI Pigment Blue 15:5, CI Pigment Blue 15:6, CI Pigment Blue 16, CI Pigment Blue 17, CI Pigment Blue 17:1, CI Pigment Blue 18, CI Pigment Blue 22, CI Pigment Blue 25, CI Pigment Blue 56, CI Pigment Blue 60, CI Pigment Blue 63, CI Pigment Blue 65, CI Pigment Blue 66; CI Vat Blue 4, CI Vat Blue 60; CI Pigment Green 7, etc.

[0130] Examples of magenta-based colorants include: CI Solvent Red 1, CI Solvent Red 3, CI Solvent Red 8, CI Solvent Red 23, CI Solvent Red 24, CI Solvent Red 25, CI Solvent Red 27, CI Solvent Red 30, CI Solvent Red 49, CI Solvent Red 52, CI Solvent Red 58, CI Solvent Red 63, CI Solvent Red 81, CI Solvent Red 82, CI Solvent Red 83, CI Solvent Red 84, CI Solvent Red 100, CI Solvent Red 109, CI Solvent Red 111, CI Solvent Red 121, CI Solvent Red 122; CI Disperse Red 9; CI Solvent Violet 8, CI Solvent Violet 13, CI Solvent Violet 14, CI Solvent Violet 21, CI Solvent Violet 27; CI Disperse Violet 1; CI Basic Red 1, CI Basic... Basic Red 2, CI Basic Red 9, CI Basic Red 12, CI Basic Red 13, CI Basic Red 14, CI Basic Red 15, CI Basic Red 17, CI Basic Red 18, CI Basic Red 22, CI Basic Red 23, CI Basic Red 24, CI Basic Red 27, CI Basic Red 29, CI Basic Red 32, CI Basic Red 34, CI Basic Red 35, CI Basic Red 36, CI Basic Red 37, CI Basic Red 38, CI Basic Red 39, CI Basic Red 40; CI Basic Violet 1, CI Basic Violet 3, CI Basic Violet 7, CI Basic Violet 10, CI Basic Violet 14, CI Basic Violet 15, CI Basic Violet 21, CI Basic Violet 25, CI Basic Violet 26, CI Basic Violet 27, CI Basic Violet 28, etc. In addition, examples of magenta-based colorants include: CI Pigment Red 1, CI Pigment Red 2, CI Pigment Red 3, CI Pigment Red 4, CI Pigment Red 5, CI Pigment Red 6, CI Pigment Red 7, CI Pigment Red 8, CI Pigment Red 9, CI Pigment Red 10, CI Pigment Red 11, CI Pigment Red 12, CI Pigment Red 13, CI Pigment Red 14, CI Pigment Red 15, CI Pigment Red 16, CI Pigment Red 17, CI Pigment Red 18, CI Pigment Red 19, CI Pigment Red 21, CI Pigment Red 22, CI Pigment Red 23, CI Pigment Red 30, CI Pigment Red 31, CI Pigment Red 32, CI Pigment Red 37, CI Pigment Red 38, CI Pigment Red 39, CI Pigment Red 40, CI Pigment Red 41, CI Pigment Red 42, CI Pigment Red 48:1, CI Pigment Red 48:2, CI Pigment Red 48:3, CI Pigment Red 48:4, CI Pigment Red 49, and C.I. Pigment Red 49:1, CI Pigment Red 50, CI Pigment Red 51, CI Pigment Red 52, CI Pigment Red 52:2, CI Pigment Red 53:1, CI Pigment Red 54, CI Pigment Red 55, CI Pigment Red 56, CI Pigment Red 57:1, CI Pigment Red 58, CI Pigment Red 60, CI Pigment Red 60:1, CI Pigment Red 63, CI Pigment Red 63:1, CI Pigment Red 63:2, CI Pigment Red 64, CI Pigment Red 64:1, CI Pigment Red 67, CI Pigment Red 68, CI Pigment Red 81, CI Pigment Red 49:1, CI Pigment Red 50, CI Pigment Red 51, CI Pigment Red 52:2, CI Pigment Red 53:1, CI Pigment Red 54, CI Pigment Red 55, CI Pigment Red 56, CI Pigment Red 57:1, CI Pigment Red 58, CI Pigment Red 60:1, CI Pigment Red 63, CI Pigment Red 63:1, CI Pigment Red 63:2, CI Pigment Red 64:1, CI Pigment Red 67, CI Pigment Red 68, CI Pigment Red 81, CI Pigment Red 59: ... CI Pigment Red 83, CI Pigment Red 87, CI Pigment Red 88, CI Pigment Red 89, CI Pigment Red 90, CI Pigment Red 92, CI Pigment Red 101, CI Pigment Red 104, CI Pigment Red 105, CI Pigment Red 106, CI Pigment Red 108, CI Pigment Red 112, CI Pigment Red 114, CI Pigment Red 122, CI Pigment Red 123, CI Pigment Red 139, CI Pigment Red 144, CI Pigment Red 146, CI Pigment Red 147, CI Pigment Red 149, CI Pigment Red 150, CI Pigment Red 151 CI Pigment Red 163, CI Pigment Red 166, CI Pigment Red 168, CI Pigment Red 170, CI Pigment Red 171, CI Pigment Red 172, CI Pigment Red 175, CI Pigment Red 176, CI Pigment Red 177, CI Pigment Red 178, CI Pigment Red 179, CI Pigment Red 184, CI Pigment Red 185, CI Pigment Red 187, CI Pigment Red 190, CI Pigment Red 193, CI Pigment Red 202, CI Pigment Red 206, CI Pigment Red 207, CI Pigment Red 209, CI Pigment Red 2 19. CI Pigment Red 222, CI Pigment Red 224, CI Pigment Red 238, CI Pigment Red 245; CI Pigment Violet 3, CI Pigment Violet 9, CI Pigment Violet 19, CI Pigment Violet 23, CI Pigment Violet 31, CI Pigment Violet 32, CI Pigment Violet 33, CI Pigment Violet 36, CI Pigment Violet 38, CI Pigment Violet 43, CI Pigment Violet 50; CI Reduce Red 1, CI Reduce Red 2, CI Reduce Red 10, CI Reduce Red 13, CI Reduce Red 15, CI Reduce Red 23, CI Reduce Red 29, CI Reduce Red 35, etc.

[0131] Examples of yellow colorants include: CI Solvent Yellow 19, CI Solvent Yellow 44, CI Solvent Yellow 77, CI Solvent Yellow 79, CI Solvent Yellow 81, CI Solvent Yellow 82, CI Solvent Yellow 93, CI Solvent Yellow 98, CI Solvent Yellow 103, CI Solvent Yellow 104, CI Solvent Yellow 112, CI Solvent Yellow 162; CI Pigment Orange 31, CI Pigment Orange 43; CI Pigment Yellow 1, CI Pigment Yellow 2, CI Pigment Yellow 3, CI Pigment Yellow 4, CI Pigment Yellow 5, CI Pigment Yellow 6, CI Pigment Yellow 7, CI Pigment Yellow 81, CI Solvent Yellow 82, CI Solvent Yellow 93, CI Solvent Yellow 98, CI Solvent Yellow 103, CI Solvent Yellow 104, CI Solvent Yellow 104, CI Solvent Yellow 112, CI Solvent Yellow 162; CI Pigment Orange 31, CI Pigment Orange 43; CI Pigment Yellow 1, CI Pigment Yellow 2, CI Pigment Yellow 3, CI Pigment Yellow 4, CI Pigment Yellow 5, CI Pigment Yellow 6, CI Pigment Yellow 7, CI Pigment Yellow 8, CI Pigment Yellow 9, ...1, CI CI Pigment Yellow 6, CI Pigment Yellow 7, CI Pigment Yellow 10, CI Pigment Yellow 11, CI Pigment Yellow 12, CI Pigment Yellow 13, CI Pigment Yellow 14, CI Pigment Yellow 15, CI Pigment Yellow 16, CI Pigment Yellow 17, CI Pigment Yellow 23, CI Pigment Yellow 24, CI Pigment Yellow 34, CI Pigment Yellow 35, CI Pigment Yellow 37, CI Pigment Yellow 42, CI Pigment Yellow 53, CI Pigment Yellow 55, CI Pigment Yellow 65, CI Pigment Yellow 73, CI Pigment Yellow 74, CI Pigment Yellow 75 CI Pigment Yellow 81, CI Pigment Yellow 83, CI Pigment Yellow 93, CI Pigment Yellow 94, CI Pigment Yellow 95, CI Pigment Yellow 97, CI Pigment Yellow 98, CI Pigment Yellow 100, CI Pigment Yellow 101, CI Pigment Yellow 104, CI Pigment Yellow 108, CI Pigment Yellow 109, CI Pigment Yellow 110, CI Pigment Yellow 113, CI Pigment Yellow 114, CI Pigment Yellow 116, CI Pigment Yellow 117, CI Pigment Yellow 120, CI Pigment Yellow 128, CI Pigment Yellow 129, CI Pigment Yellow 133, CI Pigment Yellow 138, CI Pigment Yellow 139, CI Pigment Yellow 147, CI Pigment Yellow 150, CI Pigment Yellow 151, CI Pigment Yellow 153, CI Pigment Yellow 154, CI Pigment Yellow 155, CI Pigment Yellow 156, CI Pigment Yellow 167, CI Pigment Yellow 172, CI Pigment Yellow 173, CI Pigment Yellow 180, CI Pigment Yellow 185, CI Pigment Yellow 195; CI Reduced Yellow 1, CI Reduced Yellow 3, CI Reduced Yellow 20, etc.

[0132] As needed, the adhesive layer of the present invention may also contain additives such as crosslinking accelerators, anti-aging agents, antioxidants, plasticizers, softeners, surfactants, antistatic agents, surface lubricants, leveling agents, light stabilizers, ultraviolet absorbers, polymerization inhibitors, foils, and rust inhibitors, within a range that does not impair the effects of the present invention. Only one of the above additives may be used, or two or more may be used.

[0133] The aforementioned rust inhibitors are compounds that prevent rusting and corrosion of metals. When the adhered object is metal, they inhibit rusting and corrosion during the bonding of the adhesive sheet. Examples of such rust inhibitors include amine compounds, benzotriazole compounds, and nitrites. Other examples include ammonium benzoate, ammonium phthalate, ammonium stearate, ammonium palmitate, ammonium oleate, ammonium carbonate, dicyclohexylamine benzoate, urea, hexamethylenetetramine, thiourea, phenyl carbamate, and cyclohexylammonium-N-cyclohexylcarbamate (CHC). Only one of these rust inhibitors may be used, or two or more may be used.

[0134] The content of the aforementioned rust inhibitor is not particularly limited, but is preferably 0.02 to 15 parts by weight relative to 100 parts by weight of the base polymer. If the content is 0.02 parts by weight or more, good anti-corrosion performance is easily obtained. If the content is 15 parts by weight or less, transparency is easily ensured.

[0135] Among these considerations, the rust inhibitor is preferably a benzotriazole compound, which can achieve a higher level of compatibility with the base polymer, reliable adhesion, transparency, and corrosion resistance, as well as excellent appearance.

[0136] The content of benzotriazole compounds is not particularly limited, but is preferably 0.02 to 3 parts by mass relative to 100 parts by mass of the matrix polymer, more preferably 0.02 to 2.5 parts by mass, and even more preferably 0.02 to 2 parts by mass.

[0137] The thickness of the adhesive layer of the present invention is preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 30 μm or less. If the thickness is 50 μm or less, the difference between the inner and outer diameters during bending is smaller, making it easier to alleviate the stress applied during bending. The thickness is not particularly limited, but from the viewpoint of superior adhesion and less likelihood of peeling during bending, it is preferably 6 μm or more, more preferably 10 μm or more, and even more preferably 20 μm or more.

[0138] When 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, but is preferably 6 μm or more, more preferably 10 μm or more, and even more preferably 20 μm or more. If the thickness is 6 μm or more, the adhesion is better and it is less likely to peel off when bent. The total thickness of the adhesive layer on one side is preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 30 μm or less. If the thickness is 50 μm or less, the difference between the inner and outer diameters when bent is smaller, and the stress applied during bending is more easily mitigated. It should be noted that, in the case of a double-sided adhesive sheet with a substrate, the thickness of the adhesive layer on both sides can be the same or different.

[0139] The adhesive layer constituting the adhesive sheet of the present invention can be of any form, such as emulsion type, solvent type (solution type), active energy ray curing type, hot melt type, etc. Among these, solvent type and active energy ray curing type adhesive layers are preferred from the viewpoint of easily obtaining an adhesive layer with excellent production performance.

[0140] Examples of such active energy rays include ionizing radiation such as alpha rays, beta rays, gamma rays, neutron rays, electron beams, and ultraviolet rays, with ultraviolet rays being particularly preferred. That is, the active energy ray-curable adhesive layer is preferably an ultraviolet-curable adhesive layer.

[0141] The adhesive layer described above can be manufactured, for example, by applying (coating) an adhesive composition for forming the adhesive layer onto a release liner and allowing the resulting adhesive composition layer to dry and cure; or by applying (coating) the adhesive composition onto a release liner and irradiating the resulting adhesive composition layer with active energy rays to cure it. Furthermore, heating and drying may be performed as needed.

[0142] (Substrate)

[0143] The aforementioned substrate is an element that functions as a support in the adhesive sheet. The aforementioned substrate can be a single layer or a laminate of the same or different substrates.

[0144] Examples of substrates include plastic substrates (e.g., plastic films), porous materials such as paper, cloth, and nonwoven fabrics, meshes, and foam sheets. Plastic substrates (especially plastic films) are preferred. Furthermore, non-foam sheets are more preferably used as substrates.

[0145] Examples of resins constituting the aforementioned plastic substrates include: 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), ionomers, ethylene-(meth)acrylic acid copolymer, ethylene-(meth)acrylic acid (random, alternating) copolymer, ethylene-butene copolymer, ethylene-hexene copolymer, and other polyolefin resins; polyurethane resins; rubber resins (natural rubber, synthetic rubber, and their mixtures): polyethylene terephthalate (PET), polyethylene naphthalate, polybutylene terephthalate (PBT), and other polyesters; polycarbonate; polyimide; polyetheretherketone; polyetherimide; aramid, fully aromatic polyamide, and other polyamides; polyphenylene sulfide; fluoropolymers; polyvinyl chloride; polyvinylidene chloride; cellulose resins; silicone resins, etc. The above-mentioned resins may be used in one or more ways.

[0146] The aforementioned substrate can be formulated 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, and plasticizers. The proportion of each additive relative to 100% of the total mass of the aforementioned substrate is approximately 30% by mass (e.g., less than 20% by mass, typically less than 10% by mass).

[0147] The aforementioned substrate may include auxiliary layers. Examples of such auxiliary layers include: a coloring layer, a reflective layer, a primer layer, and an antistatic layer disposed on the surface of the substrate.

[0148] To improve adhesion and retention with the adhesive layer, the surface of the substrate may be subjected to physical treatments such as corona discharge treatment, plasma treatment, sand mat processing, ozone exposure treatment, flame exposure treatment, high voltage electric shock exposure treatment, and ionized radiation treatment; chemical treatments such as chromic acid treatment; and surface treatments utilizing the adhesion-enhancing properties of the coating agent (primer). Surface treatments for improving adhesion are preferably applied to the entire surface of the substrate.

[0149] (Adhesive sheet)

[0150] The thickness of the adhesive sheet is preferably 6 to 100 μm, more preferably 100 to 80 μm, and even more preferably 20 to 70 μm. If the thickness is 6 μm or more, the adhesion is superior and peeling is less likely to occur when bent. If the thickness is 100 μm or less, the difference between the inner and outer diameters is smaller when bent, making it easier to alleviate the stress applied during bending. It should be noted that, in the case of a single-sided adhesive sheet, the thickness of the adhesive sheet refers to the thickness from the surface of the substrate without the adhesive layer to the adhesive surface; in the case of a double-sided adhesive sheet, it refers to the thickness from one adhesive surface to the other adhesive surface, i.e., the thickness of the adhesive body, excluding the release liner.

[0151] The adhesive sheet of the present invention has a release liner attached to the surface (adhesive surface) of the adhesive layer until use. When the adhesive sheet is a double-sided adhesive sheet, each adhesive surface on both sides can be protected by two separate release liners, or it can be protected by a single release liner with both sides serving as the release surface, wound into a roll (wound body). The release liner serves as a protective material for the adhesive layer and is peeled off when adhered to the object. It should be noted that the release liner may also be unnecessary.

[0152] As the release liner mentioned above, conventional release paper or the like can be used, without particular limitation. Examples include substrates with a release treatment layer, low-adhesion substrates containing fluoropolymers, and low-adhesion substrates containing non-polar polymers. Examples of substrates with a release treatment layer include plastic films and papers that have been surface-treated with release agents such as silicone-based, long-chain alkyl-based, fluorine-based, and molybdenum sulfide. Examples of fluoropolymers in the low-adhesion substrate containing fluoropolymers include polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, and chlorofluoroethylene-vinylidene fluoride copolymer. Furthermore, examples of non-polar polymers include olefin resins (e.g., polyethylene, polypropylene). It should be noted that the release liner can be formed by known or conventional methods. Furthermore, the thickness of the release liner is not particularly limited.

[0153] The aforementioned adhesive sheet is preferably used for bonding electrical and electronic components, that is, for attaching to components included in electrical and electronic equipment. The aforementioned adhesive sheet is particularly preferred for use where components included in electrical and electronic equipment are respectively bonded to the two adhesive surfaces of the double-sided adhesive sheet, i.e., as a double-sided adhesive sheet for fixing components in electrical and electronic equipment to each other. The aforementioned double-sided adhesive sheet can be used for either fixing the aforementioned components to each other or for temporary fixing.

[0154] It should be noted that "electrical and electronic equipment" refers to equipment that conforms to at least one of the categories of electrical equipment or electronic equipment. Examples of such electrical and electronic equipment include, for instance, image display devices such as liquid crystal displays, electroluminescent displays, and plasma displays, as well as portable electronic devices.

[0155] Examples of portable electronic devices include: mobile phones, smartphones, tablets, laptops, various wearable devices (such as wristwatches worn on the wrist; modular devices worn on the body using clips, straps, etc.; eyeglasses (monocular, binocular, and headband types); clothing accessories attached to shirts, socks, hats, etc.; ear-worn devices like headphones), digital cameras, digital camcorders, acoustic devices (portable music players, IC recorders, etc.), calculators (desktop computers, etc.), portable game consoles, 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 "portable" in this specification refers not only to the ability to carry, but also to a level of portability that allows a standard adult to handle it relatively easily. The aforementioned double-sided adhesive sheet is used, for example, as an adhesive layer to adhere tightly to the components of the portable electronic device.

[0156] The adhesive sheet of the present invention exhibits excellent bending resistance at low temperatures. Therefore, even in locations where repeated bending is required at low temperatures, creases, marks, or peeling of the adhesive sheet are unlikely to occur at the bending points. Furthermore, it exhibits excellent adhesion to the adhered object at both room temperature and high temperature. Therefore, the adhesive sheet of the present invention is preferably used in areas subject to repeated bending. Consequently, the adhesive sheet of the present invention is preferably used for bonding components (particularly between components) in electrical and electronic equipment used for bending, such as electrical and electronic equipment having a bendable image display device (flexible display) (especially a foldable image display device (foldable display)).

[0157] Example

[0158] The following examples illustrate the invention in more detail, but the invention is not limited to these examples.

[0159] Preparation Example 1

[0160] (Preparation of acrylic polymer A)

[0161] In a reaction vessel equipped with a stirrer, thermometer, nitrogen inlet pipe, reflux condenser, and dropping funnel, a mixture containing 70 parts by mass of 2-ethylhexyl acrylate (2EHA), 20 parts by mass of n-butyl acrylate (BA), 8 parts by mass of lauryl acrylate (LA), 1 part by mass of 4-hydroxybutyl acrylate (4HBA), 0.6 parts by mass of N-vinyl-2-pyrrolidone (NVP), 0.1 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) as a thermal polymerization initiator, and ethyl acetate as a polymerization solvent (solids concentration 47% by mass) was stirred at 56°C under a nitrogen atmosphere for 6 hours (polymerization reaction). This yielded a polymer solution containing acrylic polymer A. The acrylic polymer A in this polymer solution has a weight-average molecular weight of approximately 2 million and a glass transition temperature of -63°C.

[0162] Preparation Example 2

[0163] (Preparation of acrylic polymer B)

[0164] In a reaction vessel equipped with a stirrer, thermometer, nitrogen inlet pipe, reflux condenser, and dropping funnel, 95 parts by mass of 2EHA and 5 parts by mass of AA as monomers, and 199 parts by mass of ethyl acetate as polymerization solvent were added. The mixture was stirred for 2 hours while nitrogen was introduced. After removing oxygen from the polymerization system, 0.2 parts by mass of benzoyl peroxide was added as a polymerization initiator, and solution polymerization was carried out at 60°C for 6 hours to obtain a solution of acrylic polymer B. The Mw of this acrylic polymer B is approximately 120 × 10⁻⁶. 4.

[0165] Preparation Example 3

[0166] (Preparation of oligomer A)

[0167] A mixture of 60 parts by mass of dicyclopentyl methacrylate and 40 parts by mass of methacrylic acid as monomers, 3.5 parts by mass of α-thioglycerol as a chain transfer agent, and 100 parts by mass of toluene as a polymerization solvent was stirred at 70°C for 1 hour under a nitrogen atmosphere. Next, 0.2 parts by mass of AIBN was added as a thermal polymerization initiator, and the mixture was reacted at 70°C for 2 hours, followed by a further reaction at 80°C for 2 hours. The reaction mixture was then heated to 130°C, and the toluene, chain transfer agent, and unreacted monomers were dried to remove them, yielding a solid acrylic oligomer (oligomer A). The weight-average molecular weight of oligomer A was 5100.

[0168] Preparation Example 4

[0169] (Preparation of oligomer B)

[0170] A mixture of 95 parts by mass of cyclohexyl methacrylate as a monomer, 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 was reacted at 85°C for 5 hours under a nitrogen atmosphere to obtain a solution of oligomer B with a solid content concentration of 50% by mass. The weight average molecular weight of oligomer B is 4300.

[0171] Example 1

[0172] (Preparation of adhesive composition)

[0173] In the solution of acrylic polymer A prepared in Preparation Example 1, 3 parts by mass of oligomer A prepared in Preparation Example 3 as a tackifier, 0.26 parts by mass of benzoyl peroxide (trade name "NYPER BMT-40SV", manufactured by Nippon Oil Co., Ltd.) as crosslinking agent A, and 0.03 parts by mass of isocyanate crosslinking agent (trade name "CORONATE L", manufactured by Tosoh Co., Ltd.) as crosslinking agent B were added relative to 100 parts by mass of acrylic polymer A, and the mixture was stirred to prepare an adhesive composition.

[0174] (Making of adhesive sheets)

[0175] The adhesive composition described above was applied to the release layer of a 75 μm thick polyethylene terephthalate film (product name "Diafoil MRF", manufactured by Mitsubishi Chemical Co., Ltd.) that had undergone silicone release treatment on one side, with an adhesive layer thickness of 25 μm. The film was dried at 150°C for 3 minutes to form an adhesive layer. The release layer of a 38 μm thick polyethylene terephthalate film (product name "Diafoil MRF", manufactured by Mitsubishi Chemical Co., Ltd.) that had undergone silicone release treatment on one side was then overlapped on the adhesive layer to produce the double-sided adhesive sheet of Example 1.

[0176] Example 2

[0177] (Preparation of adhesive composition)

[0178] In the solution of acrylic polymer A prepared in Preparation Example 1, 6 parts by mass of oligomer A prepared in Preparation Example 3 as a tackifier, 0.52 parts by mass of benzoyl peroxide (trade name "NYPER BMT-40SV", manufactured by Nippon Oil Co., Ltd.) as crosslinking agent A, and 0.05 parts by mass of isocyanate crosslinking agent (trade name "CORONATE L", manufactured by Tosoh Co., Ltd.) as crosslinking agent B were added to prepare an adhesive composition by stirring and mixing.

[0179] (Making of adhesive sheets)

[0180] Using the adhesive composition described above, except that the double-sided adhesive sheet of Example 2 was produced in the same manner as in Example 1.

[0181] Example 3

[0182] The oligomer B prepared in Preparation Example 4 was used as a tackifier in 20 parts by weight. Otherwise, the adhesive composition and double-sided adhesive sheet were prepared in the same manner as in Example 2.

[0183] Example 4

[0184] Six parts by weight of oligomer A and six parts by weight of oligomer B were used as tackifiers. Otherwise, the adhesive composition and double-sided adhesive sheet were prepared in the same manner as in Example 2.

[0185] Example 5

[0186] Six parts by weight of oligomer A and 15 parts by weight of oligomer B were used as tackifiers. Otherwise, the adhesive composition and double-sided adhesive sheet were prepared in the same manner as in Example 2.

[0187] Example 6

[0188] As a tackifier, 20 parts by weight of tackifying resin B (trade name "Pensel D-125", rosin ester, manufactured by Arakawa Chemical Industry Co., Ltd., softening point about 125°C) were used. Otherwise, the adhesive composition and double-sided adhesive sheet were prepared in the same manner as in Example 2.

[0189] Example 7

[0190] As a tackifier, 10 parts by weight of oligomer A and 10 parts by weight of tackifying resin A (trade name "YS Polystar S145", terpene phenol resin, manufactured by Yasuhara Chemical Co., Ltd., softening point about 145°C) were used. Otherwise, the adhesive composition and double-sided adhesive sheet were prepared in the same manner as in Example 2.

[0191] Example 8

[0192] (Preparation of adhesive composition)

[0193] In the solution of acrylic polymer A prepared in Preparation Example 1, 10 parts by mass of oligomer B as a tackifier and 0.2 parts by mass of isocyanate crosslinking agent (trade name "CORONATE L", manufactured by Tosoh Co., Ltd.) as crosslinking agent B were added relative to 100 parts by mass of acrylic polymer A, and the mixture was stirred to prepare an adhesive composition.

[0194] (Making of adhesive sheets)

[0195] Using the adhesive composition described above, except that the double-sided adhesive sheet of Example 8 was produced in the same manner as in Example 1.

[0196] Comparative Example 1

[0197] Without the addition of a tackifier, the adhesive composition and double-sided adhesive sheet were prepared in the same manner as in Example 1.

[0198] Comparative Example 2

[0199] (Preparation of adhesive composition)

[0200] In the solution of acrylic polymer A prepared in Preparation Example 1, 30 parts by mass of tackifying resin B (trade name "Pensel D-125", rosin ester, manufactured by Arakawa Chemical Industry Co., Ltd., softening point about 125°C) as a tackifier, 0.78 parts by mass of benzoyl peroxide (trade name "NYPER BMT-40SV", manufactured by Nippon Oil Co., Ltd.) as crosslinking agent A, and 0.1 parts by mass of isocyanate crosslinking agent (trade name "CORONATE L", manufactured by Tosoh Co., Ltd.) as crosslinking agent B were added and stirred to prepare an adhesive composition.

[0201] (Making of adhesive sheets)

[0202] Using the adhesive composition described above, except that, the double-sided adhesive sheet of Comparative Example 2 was prepared in the same manner as in Example 1.

[0203] Comparative Example 3

[0204] (Preparation of adhesive composition)

[0205] In the solution of acrylic polymer B prepared in Preparation Example 2, 10 parts by mass of tackifying resin A (trade name "YS Polystar S145", terpene phenol resin, manufactured by Yasuhara Chemical Co., Ltd., softening point about 145°C) as tackifier, 3 parts by mass of isocyanate crosslinking agent B (trade name "CORONATE L", manufactured by Tosoh Co., Ltd.), and 0.03 parts by mass of epoxy crosslinking agent C (trade name "TETRAD-C", manufactured by Mitsubishi Gas Chemical Co., Ltd.) as crosslinking agent were added and stirred to prepare an adhesive composition.

[0206] (Making of adhesive sheets)

[0207] The adhesive composition described above was applied to the release layer of a 75 μm thick polyethylene terephthalate film (product name "Diafoil MRF", manufactured by Mitsubishi Chemical Co., Ltd.) that had undergone silicone release treatment on one side, with an adhesive layer thickness of 25 μm. The film was dried at 100°C for 2 minutes to form an adhesive layer. The release layer of a 38 μm thick polyethylene terephthalate film (product name "Diafoil MRF", manufactured by Mitsubishi Chemical Co., Ltd.) that had undergone silicone release treatment on one side was then overlapped on the adhesive layer to produce the double-sided adhesive sheet of Example 1.

[0208] Comparative Example 4

[0209] (Preparation of adhesive composition)

[0210] In the solution of acrylic polymer A prepared in Preparation Example 1, 20 parts by mass of tackifying resin B (trade name "Pensel D-125", rosin ester, manufactured by Arakawa Chemical Industry Co., Ltd., softening point about 125°C) as a tackifier, 0.26 parts by mass of benzoyl peroxide (trade name "NYPER BMT-40SV", manufactured by Nippon Oil Co., Ltd.) as crosslinking agent A, and 0.05 parts by mass of isocyanate crosslinking agent (trade name "CORONATE L", manufactured by Tosoh Co., Ltd.) as crosslinking agent B were added and stirred to prepare an adhesive composition.

[0211] (Making of adhesive sheets)

[0212] Using the adhesive composition described above, except that, the double-sided adhesive sheet of Comparative Example 4 was prepared in the same manner as in Example 1.

[0213] <Evaluation>

[0214] The adhesive sheets obtained in the examples and comparative examples were evaluated as follows. The results are shown in the table.

[0215] (1) Energy storage modulus G' (-30℃)

[0216] Peel the release liner from both sides of the double-sided adhesive sheet prepared in the examples and comparative examples, and stack the double-sided adhesive sheets to prepare a test sample with a thickness of about 1 mm. The test sample was punched into a disc shape with a diameter of 7.9 mm, clamped with parallel plates, and subjected to shear strain at a frequency of 1 Hz using a viscoelastic testing machine (trade name "ARES", manufactured by Rheometrics). The viscoelasticity was measured in shear mode at a temperature range of -50 to 150 °C and a heating rate of 5 °C / min. The peak strength of G' (dynamic shear storage modulus) at -30 °C was determined.

[0217] (2) Gel fraction

[0218] Approximately 0.2 g of adhesive was scraped from the adhesive sheet and wrapped in a porous polytetrafluoroethylene (PTFE) membrane (trade name "NTF-1122", manufactured by Nitto Denko Corporation) with a pore size of 0.2 μm and a diameter of 100 mm × 100 mm. The opening was then tied with cotton thread. The mass of the adhesive sample (B) was calculated by subtracting the total mass of the porous PTFE membrane and cotton thread (A) from the mass of the sample. The adhesive sample wrapped in the porous PTFE membrane was then immersed in approximately 50 mL of ethyl acetate at 23°C for 7 days to allow the sol component of the adhesive to dissolve out of the porous PTFE membrane. After immersion, the adhesive wrapped in the porous PTFE membrane was removed and dried at 130°C for 2 hours. After cooling for approximately 20 minutes, the dried mass (C) was measured. The gel fraction of the adhesive was calculated using the following formula.

[0219] Gel fraction (%) = 100 × (C - A) / B

[0220] (3) 180° peel adhesion (RT)

[0221] Under a testing environment of 23°C and 50% RH, release liner pads on both sides of the double-sided adhesive sheet prepared in the examples and comparative examples were peeled off. A 25 μm thick PET film was laminated onto one adhesive side of the double-sided adhesive sheet and mounted. The film was then cut into test samples with a width of 20 mm and a length of 100 mm. For the prepared test samples, under a testing environment of 23°C and 50% RH, the exposed adhesive side of the test sample was pressed against the surface of a stainless steel plate (SUS304BA plate) and pressed once by a 2 kg roller. After being placed in this environment for 24 hours, the 180° peel strength (adhesive force) [N / 20 mm] was measured using a universal tensile and compression testing machine under the conditions of a tensile speed of 300 mm / min, a peel angle of 180°, a temperature of 23°C, and a relative humidity of 50% RH (room temperature). A tensile and compression testing machine (trade name "TG-1kN") manufactured by Minebea Corporation was used as the universal tensile and compression testing machine. It should be noted that in the case of single-sided adhesive sheets, the aforementioned PET film lamination is not required.

[0222] (4) Bending resistance test

[0223] Under conditions of -30°C / 50% RH, the release liner of one side of the double-sided adhesive sheet prepared in the examples and comparative examples was peeled off, and the exposed adhesive surface was adhered to one side of a polyethylene terephthalate film (thickness: 50 μm, Young's modulus: 4.5 GPa). Next, the release liner of the other side was peeled off, and the exposed adhesive surface was adhered to one side of another polyethylene terephthalate film (thickness: 50 μm, Young's modulus: 4.5 GPa). Then, the film was pressurized at 0.5 MPa and 50°C for 20 minutes in an autoclave manufactured by Kurihara Manufacturing Co., Ltd., and then placed at 23°C and 50% RH for 24 hours. The laminate obtained in this way, consisting of [PET film / double-sided adhesive sheet / PET film], was cut into pieces 20 mm wide and 200 mm long, and used as samples. Using a durability testing machine (product name "Plane Unloaded U-Shaped Expansion Environmental Testing Machine CL09-TypeD01-FSC90", manufactured by YUASA SYSTEM Machinery Co., Ltd.), the obtained sample was repeatedly bent under the following conditions. Afterwards, the presence of creases (bending resistance (low temperature)) at the bent portion of the sample after the test at -30°C / 50%RH was visually confirmed, and the bending resistance was evaluated according to the following criteria.

[0224] <Experimental Conditions>

[0225] Bending radius: 2mm, number of bends: 200,000, bending speed: 60 times / minute.

[0226] <Evaluation Criteria>

[0227] 〇: No creases, or slight creases but still usable in practical condition.

[0228] △: Creates a horizontal crease that is visible when illuminated, but is a usable level.

[0229] ×: Creates a horizontal crease that is practically unusable.

[0230] (5) High temperature holding power

[0231] Under a testing environment of 23°C and 50% RH, the double-sided adhesive sheets prepared in the examples and comparative examples were cut to a size of 10mm × 20mm without glue overflow. The release liner (a 38μm thick polyethylene terephthalate film with silicone release treatment on one side) on the lightly peeled side was peeled off, and a 25μm thick PET film was laminated and mounted. Then, the release liner on the heavily peeled side was peeled off and laminated onto a stainless steel plate (SUS304BA plate). A 2kg roller was used to press the film back and forth once at a speed of 5mm / second, and the film was placed at 80°C for 30 minutes. Afterward, the film was removed under a testing environment of 23°C and 50% RH, and the distance of the offset between the PET film and the stainless steel plate (SUS304BA plate) from the starting point was measured. The high-temperature holding power was then evaluated according to the following evaluation criteria.

[0232] <Evaluation Criteria>

[0233] 〇: Not stripped.

[0234] ×: Already stripped.

[0235]

[0236] The following describes variations of the invention disclosed herein.

[0237] [Note 1] An adhesive sheet having an adhesive layer.

[0238] The adhesive layer comprises: an acrylic polymer containing (meth)acrylate alkyl esters having alkyl groups having 10 or more carbon atoms as constituent units; and a tackifier.

[0239] The adhesive layer has an elastic modulus of less than 5.0 MPa at -30°C and a gel fraction of more than 50%.

[0240] [Note 2] According to the adhesive sheet of Note 1, the acrylic polymer comprises (meth)acrylate alkyl esters having straight or branched alkyl groups having 1 to 8 carbon atoms as constituent units.

[0241] [Note 3] The adhesive sheet according to Note 1 or 2, wherein the tackifier comprises an oligomer or a tackifying resin.

[0242] [Note 4] The adhesive sheet according to any one of Notes 1 to 3 is a double-sided adhesive sheet for fixing components in electrical and electronic equipment to each other.

[0243] [Note 5] An electrical and electronic device comprising an adhesive sheet as described in Note 4, the adhesive sheet securing components to each other via two adhesive surfaces.

[0244] Explanation of reference numerals in the attached figures

[0245] 1: Double-sided adhesive sheet; 2: Adhesive layer; 3, 4: Release liner.

Claims

1. An adhesive sheet having an adhesive layer, The adhesive layer comprises: Acrylic polymers comprising (meth)acrylate alkyl esters having straight-chain or branched alkyl groups having 10 or more carbon atoms as constituent units; and Tackifier, The adhesive layer has an elastic modulus of less than 5.0 MPa at -30°C and a gel fraction of more than 50%.

2. The adhesive sheet according to claim 1, wherein, The acrylic polymer comprises (meth)acrylate alkyl esters with straight or branched alkyl groups having 1 to 8 carbon atoms as constituent units.

3. The adhesive sheet according to claim 1 or 2, wherein, The tackifier comprises oligomers or tackifying resins.

4. The adhesive sheet according to claim 1 or 2, which is a double-sided adhesive sheet for fixing components in electrical and electronic equipment to each other.

5. An electrical and electronic device comprising the adhesive sheet of claim 4. The adhesive sheet secures the components to each other through two adhesive surfaces.

Images