Acrylic adhesive composition, acrylic adhesive, acrylic adhesive sheet, and flexible device

Abstract

The present invention provides an acrylic adhesive capable of exhibiting a low elastic modulus in a low-temperature environment, a high adhesive strength in a room-temperature environment, and a high adhesive strength in a high-temperature environment, an acrylic adhesive composition forming the same, an acrylic adhesive sheet comprising an acrylic adhesive layer composed of the said acrylic adhesive, and a flexible device comprising the same. An acrylic adhesive composition according to an embodiment of the present invention comprises an acrylic polymer (A) having a specific weight average molecular weight Mw, an acrylic oligomer (B) having a specific weight average molecular weight Mw, and a crosslinking agent (C), wherein the amount of the acrylic oligomer (B) relative to 100 parts by weight of the acrylic polymer (A) is within a specific range, the acrylic polymer (A) is obtained by polymerizing a monomer component (M), the monomer component (M) comprises a specific alkyl (meth)acrylate (m1), and the content ratio of N-vinyl-2-pyrrolidone in the monomer component (M) is less than 0.5% by weight.

Description

Technology Field

[0001] The present invention relates to an acrylic adhesive composition, an acrylic adhesive, an acrylic adhesive sheet, and a flexible device. Background Technology

[0002] Adhesive sheets are used for reinforcing or surface protection of members of various shapes.

[0003] For example, when bonding an integrated circuit (IC) or a flexible printed circuit board (FPC) to a substrate of a semiconductor device (e.g., a TFT substrate, etc.), thermal compression is typically performed using an anisotropic conductive film (ACF). When performing such thermal compression, there are cases where an adhesive sheet is bonded to the other side of the semiconductor device substrate in advance to provide reinforcement (e.g., Patent Document 1).

[0004] In addition, as a method for manufacturing so-called flexible devices, such as foldable or rollable devices currently under development, a release layer and a flexible film substrate are generally formed on a support substrate such as glass, a TFT substrate is formed on the film substrate, and an organic EL layer is formed thereon. Then, the support substrate is released to manufacture the flexible device, but since the flexible display layer is very thin, problems may occur in the device due to handling, etc. For this reason, an adhesive sheet is bonded to this side to reinforce it (e.g., Patent Document 2).

[0005] Flexible devices can be repeatedly bent. For this reason, if the bending characteristics of the aforementioned adhesive sheet are poor, the recovery after repeated bending deteriorates, or in the worst case, it breaks due to repeated bending. Against this background, acrylic adhesive sheets having good bending characteristics have recently been developed and reported (e.g., Patent Documents 3 and 4). Prior art literature

[0006] Japanese Patent Publication No. 5600039 Japanese Patent Publication No. 6376271 Japanese Patent Publication No. 6993543 Japanese Patent Publication No. 2024-052821 The problem to be solved

[0007] As the development of various flexible devices becomes more active, acrylic adhesive sheets bonded to flexible devices require higher levels of bending characteristics. As for these higher levels of bending characteristics, a combination of low elastic modulus in low-temperature environments, high adhesive strength in room-temperature environments, and high adhesive strength in high-temperature environments is required. However, it is not easy to lower the elastic modulus in low-temperature environments, and if one attempts to lower the elastic modulus in low-temperature environments, it becomes difficult to achieve adhesive strength sufficient to withstand repeated bending, and in particular, it becomes difficult to achieve high adhesive strength in both room-temperature and high-temperature environments.

[0008] The objective of the present invention is to provide an acrylic adhesive capable of exhibiting a low elastic modulus in a low-temperature environment, a high adhesive strength in a room-temperature environment, and a high adhesive strength in a high-temperature environment, an acrylic adhesive composition forming the acrylic adhesive, an acrylic adhesive sheet comprising an acrylic adhesive layer composed of the acrylic adhesive, and a flexible device comprising the acrylic adhesive sheet. means of solving the problem

[0009] [1] An acrylic adhesive composition according to an embodiment of the present invention comprises an acrylic polymer (A) having a weight average molecular weight Mw of 500,000 or more, an acrylic oligomer (B) having a weight average molecular weight Mw of 1,000 to 30,000, and a crosslinking agent (C). The amount of the acrylic oligomer (B) per 100 parts by weight of the acrylic polymer (A) is 0.01 parts by weight or more and less than 10 parts by weight. The acrylic polymer (A) is obtained by polymerizing a monomer component (M), and the monomer component (M) comprises an alkyl (meth)acrylate (m1) having an alkyl group having 6 to 9 carbon atoms as an ester portion. The content ratio of the alkyl (meth)acrylate having an alkyl group selected from the group consisting of an ethyl group and a tert-butyl group as an ester portion among the alkyl (meth)acrylate (m1) is 80% by weight. It is less than, and the content ratio of N-vinyl-2-pyrrolidone in the corresponding monomer component (M) is less than 0.5 weight%.

[0010] [2] In the acrylic adhesive composition described in [1] above, the content ratio of the alkyl (meth)acrylate (m1) in the monomer component (M) may be 40% by weight or more.

[0011] [3] In the acrylic adhesive composition described in [1] or [2] above, the monomer component (M) may include a hydroxyl group-containing monomer (m2).

[0012] [4] In the acrylic adhesive composition described in [3] above, the content ratio of the hydroxyl group-containing monomer (m2) in the monomer component (M) may be 0.1% by weight or more.

[0013] [5] In the acrylic adhesive composition described in any one of [1] to [4] above, the content ratio of the alkyl (meth)acrylate having an alkyl group having 10 or more carbon atoms as an ester portion in the monomer component (M) may be less than 0.5 weight%.

[0014] [6] In the acrylic adhesive composition described in any one of [1] to [5] above, the glass transition temperature Tg of the acrylic oligomer (B), calculated by the formula of FOX, may be 50°C to 170°C.

[0015] [7] In the acrylic adhesive composition described in any one of [1] to [6] above, the amount of the crosslinking agent (C) per 100 parts by weight of the acrylic polymer (A) may be 0.01 to 5.00 parts by weight.

[0016] [8] The acrylic adhesive composition described in any one of [1] to [7] above may form an acrylic adhesive with a glass transition temperature Tg of less than -37.5°C obtained by measuring dynamic viscoelasticity.

[0017] [9] An acrylic adhesive according to an embodiment of the present invention is formed from an acrylic adhesive composition described in any one of claims [1] to [8].

[0018]

[10] An acrylic adhesive sheet according to an embodiment of the present invention comprises an acrylic adhesive layer composed of the acrylic adhesive described in [9].

[0019]

[11] A flexible device according to an embodiment of the present invention includes an acrylic adhesive sheet as described in

[10] . Effects of the invention

[0020] According to the present invention, an acrylic adhesive capable of exhibiting a low elastic modulus in a low-temperature environment, a high adhesive strength in a room-temperature environment, and a high adhesive strength in a high-temperature environment, an acrylic adhesive composition forming the acrylic adhesive, an acrylic adhesive sheet comprising an acrylic adhesive layer composed of the acrylic adhesive, and a flexible device comprising the acrylic adhesive sheet can be provided. Brief explanation of the drawing

[0021] FIG. 1 is a schematic cross-sectional view illustrating one embodiment of a flexible device of the present invention and one use form of an acrylic adhesive sheet according to an embodiment of the present invention. Specific details for implementing the invention

[0022] In this specification, if the expression “(meth)acrylic-based” is used, it means “acrylic-based and / or methacrylic-based.” In this specification, if the expression “(meth)acrylic” is used, it means “acrylic and / or methacrylic.” If the expression “(meth)acrylate” is used, it means “acrylate and / or methacrylate.” If the expression “(meth)allyl” is used, it means “allyl and / or metallyl.” If the expression “(meth)acrolein” is used, it means “acrolein and / or methacrolein.” Additionally, if the expression “acid (salt)” is used in this specification, it means “acid and / or its salt.” Examples of salts include alkali metal salts and alkaline earth metal salts, and specifically, examples include sodium salts and potassium salts.

[0023] In this specification, regarding the "Tg of the homopolymer" of various monomers, values ​​described in known materials may be adopted unless otherwise specified in this specification, and, for example, values ​​described in the "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989) may be used. If multiple values ​​are described in the "Polymer Handbook," the conventional values ​​shall be adopted. For monomers not described in the "Polymer Handbook," catalog values ​​from monomer manufacturers shall be adopted. For the Tg of the homopolymer of monomers not described in the "Polymer Handbook" and for which catalog values ​​from monomer manufacturers are not provided, the values ​​obtained by the measurement method described in Japanese Patent Publication No. 2007-51271 shall be used.

[0024] ≪≪1. Acrylic adhesive composition≫≫

[0025] An acrylic adhesive composition according to an embodiment of the present invention is an acrylic adhesive composition comprising an acrylic polymer (A) having a weight average molecular weight Mw of 500,000 or more, an acrylic oligomer (B) having a weight average molecular weight Mw of 1,000 to 30,000, and a crosslinking agent (C).

[0026] ≪1-1. Acrylic Polymer (A)≫

[0027] The acrylic polymer (A) may be a so-called “base polymer” in the field of adhesives.

[0028] The acrylic polymer (A) may be of only one type or two or more types.

[0029] The content ratio of the acrylic polymer (A) in the acrylic adhesive composition may be any appropriate content ratio within a range that does not impair the effects of the present invention. The content ratio of the acrylic polymer (A) in the acrylic adhesive composition may be, for example, 50% by weight or more, 60% by weight to 99.9% by weight, 70% by weight to 99% by weight, 80% by weight to 98% by weight, or 90% by weight to 97% by weight.

[0030] The weight-average molecular weight Mw of the acrylic polymer (A) is typically 500,000 or more, and may be between 500,000 and 2,500,000, between 600,000 and 2,400,000, or between 700,000 and 2,300,000. The method for measuring the weight-average molecular weight Mw will be explained in detail later.

[0031] The acrylic polymer (A) is typically obtained by polymerizing a monomer component (M).

[0032] The acrylic polymer (A) can be defined as being obtained by polymerizing the monomer component (M) in this manner. The acrylic polymer (A) can be formed by the monomer component (M) undergoing a polymerization reaction, and there may exist circumstances where it is impossible to directly identify the acrylic polymer (A) by its structure, and also circumstances where it is not practically feasible ("impossible / unfeasible circumstances"). For this reason, the acrylic polymer (A) can be validly identified as a "thing" by the definition that it is "obtained by polymerizing the monomer component (M)."

[0033] The monomer component (M) preferably comprises an alkyl (meth)acrylate (m1) having an alkyl group having 6 to 9 carbon atoms as an ester portion, in order to further express the effects of the present invention.

[0034] <1-1-a. Alkyl (meth)acrylate (m1)>

[0035] The alkyl (meth)acrylate (m1) may be of only one type or two or more types.

[0036] The number of carbon atoms in the alkyl group of the ester portion of the alkyl (meth)acrylate (m1) is typically 6 to 9 as described above, but may be 7 to 9 or 8. Adopting an alkyl (meth)acrylate (m1) having an alkyl group in the ester portion having a number of carbon atoms within the above range is one preferred embodiment for exhibiting the effects of the present invention, and can effectively lower the elastic modulus of the acrylic adhesive obtained, for example, under a low-temperature environment.

[0037] The content ratio of the alkyl (meth)acrylate having an alkyl group selected from the group consisting of at least one ethyl group and a tert-butyl group as an ester portion in the alkyl (meth)acrylate (m1) is typically less than 80 weight%, may be 0 weight% to 60 weight%, 0 weight% to 40 weight%, 0 weight% to 20 weight%, 0 weight% to 10 weight%, 0 weight% to 5 weight%, 0 weight% to 3 weight%, 0 weight% to 1 weight%, and substantially 0 weight%. Lowering the content ratio of the alkyl (meth)acrylate having an alkyl group selected from the group consisting of ethyl groups and tert-butyl groups as an ester portion in the alkyl (meth)acrylate (m1) as described above is one preferred embodiment for expressing the effects of the present invention. In particular, even if an alkyl (meth)acrylate having an alkyl group having 6 to 9 carbon atoms as an ester portion is adopted, it is inferred that if the content ratio of the alkyl (meth)acrylate having an alkyl group selected from the group consisting of ethyl groups and tert-butyl groups as an ester portion in the said alkyl (meth)acrylate is high, the structural rigidity increases, and for this reason, there is a concern that the elastic modulus of the acrylic adhesive obtained, for example, under a low-temperature environment cannot be effectively lowered.

[0038] The content ratio of the alkyl (meth)acrylate having an alkyl group selected from the group consisting of ethyl groups and tert-butyl groups as an ester portion in the alkyl (meth)acrylate (m1) can be confirmed by any suitable method. As such a method, for example, NMR ( 1 H-NMR or 13Examples include C-NMR and IR. Furthermore, the "ethyl group" and "tert-butyl group" mentioned here refer to the "ethyl group" and "tert-butyl group" named based on the IUPAC organic compound nomenclature, respectively.

[0039] In an acrylic adhesive composition according to an embodiment of the present invention, as described above, the alkyl (meth)acrylate (m1) is an alkyl (meth)acrylate having an alkyl group having 6 to 9 carbon atoms as an ester portion, and by employing an alkyl (meth)acrylate having an alkyl group having at least one selected from the group consisting of ethyl groups and tert-butyl groups as an ester portion, the elastic modulus of the acrylic adhesive obtained, for example, can be effectively lowered in a low-temperature environment.

[0040] The content ratio of alkyl (meth)acrylate (m1) in the monomer component (M) may be any appropriate content ratio within a range that does not impair the effects of the present invention. The content ratio of alkyl (meth)acrylate (m1) in the monomer component (M) may be, for example, 40% by weight or more, 40% by weight to 90% by weight, 45% by weight to 85% by weight, 50% by weight to 80% by weight, 55% by weight to 75% by weight, 55% by weight to 70% by weight, or 55% by weight to 65% by weight.

[0041] The alkyl (meth)acrylate (m1) may be an alkyl (meth)acrylate in which the Tg of the homopolymer is in the range of -70°C to -55°C or lower. The Tg may be in which -70°C to -58°C or lower. The alkyl (meth)acrylate (m1) being an alkyl (meth)acrylate in which the Tg of the homopolymer is in the above range is one preferred embodiment for expressing the effects of the present invention, and can effectively lower the elastic modulus of the acrylic adhesive obtained, for example, under a low-temperature environment.

[0042] As for alkyl (meth)acrylates (m1), specifically, examples include n-hexyl (meth)acrylate, n-octyl (meth)acrylate, and isononyl (meth)acrylate.

[0043] <1-1-b. N-vinyl-2-pyrrolidone>

[0044] In order to further express the effects of the present invention, it is preferable that the monomer component (M) does not contain N-vinyl-2-pyrrolidone as much as possible. The content ratio of N-vinyl-2-pyrrolidone in the monomer component (M) is typically less than 0.5 wt%, may be less than 0.4 wt%, may be less than 0.3 wt%, may be less than 0.2 wt%, may be less than 0.1 wt%, may be less than 0.05 wt%, and may substantially be 0 wt%. One preferred embodiment for expressing the effects of the present invention is that the monomer component (M) does not contain N-vinyl-2-pyrrolidone as much as possible. If the content ratio of N-vinyl-2-pyrrolidone in the monomer component (M) exceeds the above range, it is estimated that although there is a possibility of strengthening the interaction with the substrate, the glass transition point of the adhesive increases, and for this reason, the adhesive strength of the acrylic adhesive obtained, for example, may be increased, but there is a concern that the elastic modulus of the acrylic adhesive obtained under a low-temperature environment cannot be effectively lowered.

[0045] <1-1-c. Hydroxyl group-containing monomer (m2)>

[0046] The monomer component (M) may include a hydroxyl group-containing monomer (m2).

[0047] The hydroxyl group-containing monomer (m2) may be of only one type or two or more types.

[0048] The content ratio of the hydroxyl group-containing monomer (m2) in the monomer component (M) may be any appropriate content ratio within a range that does not impair the effects of the present invention. The content ratio of the hydroxyl group-containing monomer (m2) in the monomer component (M) may be, for example, 0.1% by weight or more, 1% by weight to 30% by weight, 3% by weight to 20% by weight, 5% by weight to 15% by weight, 6% by weight to 12% by weight, or 6% by weight to 10% by weight.

[0049] Examples of hydroxyl group-containing monomers (m2) include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; polypropylene glycol mono(meth)acrylate; and N-hydroxyethyl (meth)acrylamide.

[0050] The hydroxyl group-containing monomer (m2) may be a hydroxyl group-containing monomer in which the Tg of the homopolymer is within the range of -60°C to -10°C. Examples of such hydroxyl group-containing monomers (m2) include 2-hydroxyethyl acrylate (2HEA) (the Tg of the homopolymer = -15°C) and 4-hydroxybutyl acrylate (4HBA) (the Tg of the homopolymer = -32°C).

[0051] <1-1-d. Alkyl (meth)acrylate (m3) having an alkyl group having 1 to 5 carbon atoms as the ester portion>

[0052] The monomer component (M) may include an alkyl (meth)acrylate (m3) having an alkyl group having 1 to 5 carbon atoms as an ester portion.

[0053] The alkyl (meth)acrylate (m3) may be of only one type or two or more types.

[0054] The content ratio of alkyl (meth)acrylate (m3) in the monomer component (M) may be any appropriate content ratio within a range that does not impair the effects of the present invention. The content ratio of alkyl (meth)acrylate (m3) in the monomer component (M) may be, for example, 55% by weight or less, 1% to 55% by weight, 5% to 50% by weight, 10% to 45% by weight, 15% to 42% by weight, 20% to 40% by weight, or 25% to 35% by weight.

[0055] As for alkyl (meth)acrylates (m3), specifically, examples include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, and n-butyl (meth)acrylate.

[0056] The alkyl (meth)acrylate (m3) may be an alkyl (meth)acrylate in which the Tg of the homopolymer is in the range of -60°C and less than -40°C. Examples of such alkyl (meth)acrylate (m3) include n-butyl acrylate (BA) (the Tg of the homopolymer = -55°C).

[0057] <1-1-e. Carboxyl group-containing monomers>

[0058] The monomer component (M) may include a carboxyl group-containing monomer.

[0059] The carboxyl group-containing monomer may be just one type or two or more types.

[0060] The content ratio of the carboxyl group-containing monomer in the monomer component (M) may be any appropriate content ratio within a range that does not impair the effects of the present invention. The content ratio of the carboxyl group-containing monomer in the monomer component (M) may be, for example, 30% by weight or less, 0% by weight to 25% by weight, 0% by weight to 20% by weight, 0% by weight to 15% by weight, 0% by weight to 12% by weight, or 0% by weight to 10% by weight.

[0061] Examples of monomers containing carboxyl groups include (meth)acrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, isocrotonic acid, and their acid anhydrides (e.g., monomers containing acid anhydrides such as maleic anhydride and itaconic anhydride), and representative examples include (meth)acrylic acid.

[0062] When the monomer component (M) includes a carboxyl group-containing monomer, it is preferable to use an epoxy-based crosslinking agent as the crosslinking agent (C) described below.

[0063] <1-1-f. Alkyl (meth)acrylate having an alkyl group having 10 or more carbon atoms as the ester portion>

[0064] In order to further express the effects of the present invention, it is preferable that the monomer component (M) does not contain, as much as possible, an alkyl (meth)acrylate having an alkyl group having 10 or more carbon atoms as an ester portion. The content ratio of the alkyl (meth)acrylate having an alkyl group having 10 or more carbon atoms as an ester portion in the monomer component (M) is typically less than 0.5 wt%, may be less than 0.4 wt%, may be less than 0.3 wt%, may be less than 0.2 wt%, may be less than 0.1 wt%, may be less than 0.05 wt%, and may substantially be 0 wt%. One preferred embodiment for expressing the effects of the present invention is that the monomer component (M) does not contain, as much as possible, an alkyl (meth)acrylate having an alkyl group having 10 or more carbon atoms as an ester portion.

[0065] <1-1-g. Other monomers>

[0066] The monomer component (M) may include any other suitable monomer to the extent that it does not impair the effects of the present invention.

[0067] There may be only one type of other monomer, or two or more types.

[0068] Other monomers include, for example, monomers containing amide groups such as (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-methylol(meth)acrylamide, N-methoxymethyl(meth)acrylamide, N-butoxymethyl(meth)acrylamide, N-hydroxyethyl(meth)acrylamide; monomers containing amino groups such as (meth)acrylate aminoethyl, (meth)acrylate dimethylaminoethyl, (meth)acrylate t-butylaminoethyl; monomers containing epoxy groups such as (meth)acrylate glycidyl, (meth)acrylate methylglycidyl; monomers containing cyano groups such as acrylonitrile or methacrylonitrile; Heterocyclic vinyl monomers such as (meth)acryloylmorpholine, N-vinylpiperidone, N-vinylpiperazine, N-vinylpyrrole, N-vinylimidazole, vinylpyridine, vinylpyrimidine, vinyloxazole, etc. (excluding N-vinyl-2-pyrrolidone); sulfonic acid group-containing monomers such as sodium vinylsulfonate; phosphate group-containing monomers such as 2-hydroxyethylacryloylphosphate; imide group-containing monomers such as cyclohexylmaleimide, isopropylmaleimide, etc.; isocyanate group-containing monomers such as 2-methacryloyloxyethylisocyanate; (meth)acrylic acid esters having alicyclic hydrocarbon groups such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate; Examples include (meth)acrylic acid esters having aromatic hydrocarbon groups such as phenyl (meth)acrylate, phenoxyethyl (meth)acrylate, and benzyl (meth)acrylate; vinyl esters such as vinyl acetate and vinyl propionate; aromatic vinyl compounds such as styrene and vinyltoluene; olefins or dienes such as ethylene, butadiene, isoprene, and isobutylene; vinyl ethers such as vinylalkyl ethers; and vinyl chloride.

[0069] As other monomers, polyfunctional monomers may also be used. A polyfunctional monomer refers to a monomer having two or more ethylenically unsaturated groups in one molecule. Any suitable ethylenically unsaturated group may be used as long as it does not impair the effects of the present invention. Examples of such ethylenically unsaturated groups include radical polymerizable functional groups such as vinyl groups, propenyl groups, isopropenyl groups, vinyl ether groups (vinyloxy groups), and allyl ether groups (allyloxy groups). Examples of polyfunctional monomers include hexanediol di(meth)acrylate, butanediol di(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, allyl(meth)acrylate, vinyl(meth)acrylate, divinylbenzene, epoxy acrylate, polyester acrylate, and urethane acrylate.

[0070] As other monomers, (meth)acrylate alkoxyalkyl esters may also be used. Examples of (meth)acrylate alkoxyalkyl esters include (meth)acrylate 2-methoxyethyl, (meth)acrylate 2-ethoxyethyl, (meth)acrylate methoxytriethylene glycol, (meth)acrylate 3-methoxypropyl, (meth)acrylate 3-ethoxypropyl, (meth)acrylate 4-methoxybutyl, and (meth)acrylate 4-ethoxybutyl.

[0071] The content ratio of other monomers in the monomer component (M) may be any appropriate content ratio within a range that does not impair the effects of the present invention. The content ratio of other monomers in the monomer component (M) may be, for example, 15% by weight or less, 0% to 10% by weight, 0% to 5% by weight, 0% to 3% by weight, 0% to 1% by weight, 0% to 0.5% by weight, or 0% to 0.1% by weight.

[0072] <1-1-h. Preparation of acrylic polymer (A)>

[0073] As a method for preparing an acrylic polymer (A), various polymerization methods known as synthesis methods for acrylic polymers, such as solution polymerization, emulsion polymerization, bulk polymerization, and suspension polymerization, may be appropriately employed. Among these polymerization methods, solution polymerization may be preferably used. As a monomer supply method when performing solution polymerization, a batch feeding method in which the entire amount of monomer components is supplied at once, a continuous feeding (dropping) method, or a divided feeding (dropping) method may be appropriately employed. The polymerization temperature may be appropriately selected depending on the type of monomer and solvent used, the type of polymerization initiator, etc., and is preferably 20°C to 200°C, may be 30°C to 170°C, may be 35°C to 160°C, or may be 40°C to 140°C. As a method for preparing an acrylic polymer (A), photopolymerization performed by irradiating with UV light (typically performed in the presence of a photopolymerization initiator) or radiation polymerization performed by irradiating with β rays, γ rays, etc., may be employed.

[0074] As a solvent used for solution polymerization (polymerization solvent), any suitable organic solvent can be appropriately selected. Examples include aromatic compounds such as toluene (typically aromatic hydrocarbons), acetic acid esters such as ethyl acetate, and aliphatic or alicyclic hydrocarbons such as hexane or cyclohexane.

[0075] The initiator used for polymerization (polymerization initiator) can be appropriately selected from any suitable polymerization initiator depending on the type of polymerization method. There may be only one type of polymerization initiator, or two or more types.

[0076] Examples of polymerization initiators include thermal polymerization initiators and photopolymerization initiators.

[0077] A thermal polymerization initiator can be employed, for example, when obtaining an acrylic polymer (A) by solution polymerization. As such thermal polymerization initiators, for example, 2,2'-azobis-isobutyronitrile (AIBN), 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis(2-methylpropionic acid)dimethyl, 4,4'-azobis-4-cyanovaleric acid, azobis-isovaleronitrile, 2,2'-azobis(2-amidinopropane)dihydrochloride, 2,2'-azobis[2-(5-methyl-2-imidazoline-2-yl)propane]dihydrochloride, 2,2'-azobis(2-methylpropionamidine)disulfate, 2,2'-azobis(N,N'-dimethyleneisobutylamidine), and 2,2'-azobis Azo-based initiators such as [N-(2-carboxyethyl)-2-methylpropionamidine]hydrate (VA-057, manufactured by Wako Junyaku Kogyo Co., Ltd.); Persulfates such as potassium persulfate and ammonium persulfate, di(2-ethylhexyl)peroxydicarbonate, di(4-t-butylcyclohexyl)peroxydicarbonate, di-sec-butylperoxydicarbonate, t-butylperoxyneodecanoate, t-hexylperoxypivalate, t-butylperoxypivalate, dilauroylperoxide, di-n-octanoylperoxide, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, di(4-methylbenzoyl)peroxide, dibenzoylperoxide, t-butylperoxyisobutyrate, 1,1-di(t-hexylperoxy)cyclohexane, t-butylhydroperoxide, peroxide-based initiators such as hydrogen peroxide; Examples include redox initiators combining a peroxide and a reducing agent, such as a combination of persulfate and sodium bisulfite, or a combination of peroxide and sodium ascorbate; substituted ethane initiators such as phenyl-substituted ethane; and aromatic carbonyl compounds.

[0078] A photopolymerization initiator can preferably be employed when obtaining an acrylic polymer by active energy beam polymerization. Examples of photopolymerization initiators include benzoin ether-based photopolymerization initiators, acetophenone-based photopolymerization initiators, α-ketol-based photopolymerization initiators, aromatic sulfonyl chloride-based photopolymerization initiators, photoactive oxime-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzyl-based photopolymerization initiators, benzophenone-based photopolymerization initiators, ketal-based photopolymerization initiators, and thioxanthone-based photopolymerization initiators.

[0079] 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, anisole methyl ether, etc. Examples of acetophenone-based photopolymerization initiators include 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexylphenyl ketone, 4-phenoxydichloroacetophenone, and 4-(t-butyl)dichloroacetophenone. Examples of α-ketol photopolymerization initiators include 2-methyl-2-hydroxypropiophenone and 1-[4-(2-hydroxyethyl)phenyl]-2-methylpropan-1-one. Examples of aromatic sulfonyl chloride photopolymerization initiators include 2-naphthalenesulfonyl chloride. Examples of photoactive oxime photopolymerization initiators include 1-phenyl-1,1-propanedione-2-(o-ethoxycarbonyl)-oxime. Examples of benzoin photopolymerization initiators include benzoin. Examples of benzyl photopolymerization initiators include benzyl. Examples of benzophenone-based photopolymerization initiators include benzophenone, benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, polyvinylbenzophenone, and α-hydroxycyclohexylphenyl ketone. Examples of ketal-based photopolymerization initiators include benzyldimethylketal. Examples of thioxantone-based photopolymerization initiators include thioxantone, 2-chlorothioxantone, 2-methylthioxantone, 2,4-dimethylthioxantone, isopropylthioxantone, 2,4-diisopropylthioxantone, and dodecylthioxantone.

[0080] Any suitable amount of polymerization initiator may be used within a range that does not impair the effects of the present invention. As for the amount of polymerization initiator, for example, 0.001 to 10 parts by weight per 100 parts by weight of monomer component (M), it may be 0.005 to 5 parts by weight, 0.01 to 3 parts by weight, or 0.05 to 1 part by weight.

[0081] During polymerization, any other suitable additive may be added within a range that does not impair the effects of the present invention.

[0082] ≪1-2. Acrylic Oligomer (B)≫

[0083] The acrylic oligomer (B) may be of only one type or two or more types.

[0084] The weight-average molecular weight Mw of the acrylic oligomer (B) is typically 1,000 to 30,000, but may be 1,000 to 20,000, 1,500 to 10,000, or 2,000 to 8,000. The method for measuring the weight-average molecular weight Mw will be explained in detail later.

[0085] The content of the acrylic oligomer (B) in the acrylic adhesive composition is typically 0.01 parts by weight or more and less than 10 parts by weight, with respect to 100 parts by weight of the acrylic polymer (A), and may be 0.05 parts by weight or more and less than 9 parts by weight, 0.1 parts by weight or more and less than 8 parts by weight, 0.5 parts by weight or more and less than 7 parts by weight, or 1 part by weight or more and less than 6 parts by weight. Having the content of the acrylic oligomer (B) in the acrylic adhesive composition within the above range is one preferred embodiment for exhibiting the effects of the present invention. If the content of the acrylic oligomer (B) in the acrylic adhesive composition is excessively high, the adhesive strength of the acrylic adhesive obtained, for example, may be increased, but there is a concern that the elastic modulus of the acrylic adhesive obtained under a low-temperature environment may not be effectively lowered.

[0086] The acrylic oligomer (B) may adopt any suitable value for the Tg calculated by the FOX formula, as long as the Tg calculated by the FOX formula does not impair the effects of the present invention. The glass transition temperature Tg of the acrylic oligomer (B), calculated by the FOX formula, may be, for example, 50°C to 170°C, 55°C to 165°C, 60°C to 160°C, 60°C to 155°C, or 60°C to 150°C. Furthermore, if there are two or more types of acrylic oligomers (B), it means that the glass transition temperature Tg calculated by each FOX formula may be within the above range.

[0087] As for the acrylic oligomer (B), at least one type selected from the group consisting of an acrylic oligomer (B1) with a Tg of 50°C or more and less than 100°C calculated by the FOX formula and an acrylic oligomer (B2) with a Tg of 100°C or more and less than 170°C calculated by the FOX formula may be used.

[0088] The Tg calculated by the formula of FOX of the acrylic oligomer (B1) may be 50°C to 95°C, 50°C to 90°C, 55°C to 85°C, or 60°C to 80°C.

[0089] The Tg calculated by the formula of FOX of the acrylic oligomer (B2) may be 100°C to 165°C, 110°C to 160°C, 120°C to 155°C, or 130°C to 150°C.

[0090] The Tg calculated by the FOX formula of the acrylic oligomer (B) refers to a value obtained from the FOX formula based on the Tgi of the homopolymer of each monomer i constituting the acrylic oligomer (B) and the weight fraction (copolymerization ratio based on weight) Wi of the said monomer i. The FOX formula is a relationship between the Tg of the copolymer and the glass transition temperature Tgi of the homopolymer produced by homopolymerizing each of the monomers i constituting the copolymer, as shown below.

[0091] 1 / Tg=Σ(Wi / Tgi)

[0092] In the above FOX formula, Tg represents the glass transition temperature of the copolymer (unit: K), Wi represents the weight fraction of each monomer i in the copolymer (copolymer ratio based on weight), and Tgi represents the glass transition temperature of the homopolymer of each monomer i (unit: K).

[0093] As for the acrylic oligomer (B1), for example, an acrylic oligomer obtained from a monomer component having a (meth)acrylic acid ester having a cyclic structure within the molecule as an essential component, and preferably, an acrylic oligomer obtained from a monomer component having a (meth)acrylic acid ester having a cyclic structure within the molecule and a carboxyl group-containing monomer as essential components.

[0094] (Met)acrylic acid esters having a cyclic structure within the molecule may be of only one type or two or more types.

[0095] In (meth)acrylic acid esters having a cyclic structure within the molecule, the cyclic structure may be an aromatic ring or a non-aromatic ring.

[0096] Examples of aromatic rings include substituted or unsubstituted aromatic hydrocarbon rings (e.g., monocyclic hydrocarbon rings such as benzene rings, condensed hydrocarbon rings such as naphthalene rings), and substituted or unsubstituted aromatic heterocyclic rings.

[0097] Examples of non-aromatic rings include, for instance, substituted or unsubstituted non-aromatic aliphatic hydrocarbon rings (non-aromatic alicyclic hydrocarbon rings) (e.g., cycloalkane rings such as cyclophenethane ring, cyclohexane ring, cycloheptane ring, cyclooctane ring; cycloalkene rings such as cyclohexene ring), substituted or unsubstituted non-aromatic cross-linked hydrocarbon rings (e.g., bicyclic hydrocarbon rings in pinan, pinene, bornan, norbornan, norbornene, etc.; three or more aliphatic hydrocarbon rings (cross-linked hydrocarbon rings) in adamantane, etc.), and substituted or unsubstituted non-aromatic heterocyclic rings (e.g., epoxy ring, oxolan ring, oxetane ring). Examples of aliphatic hydrocarbon rings with three or more rings (cross-linked hydrocarbon rings with three or more rings) include dicyclofentanyl groups, dicyclofentenyl groups, adamantyl groups, tricyclofentanyl groups, and tricyclofentenyl groups.

[0098] As (meth)acrylic acid esters having a cyclic structure within the molecule, specifically, for example, (meth)acrylic acid cycloalkyl esters such as (meth)acrylic acid cyclopentyl, (meth)acrylic acid cyclohexyl, (meth)acrylic acid cycloheptyl, (meth)acrylic acid cyclooctyl; (meth)acrylic acid esters having a bicyclic aliphatic hydrocarbon ring such as (meth)acrylic acid isobornyl; (meth)acrylic acid esters having three or more aliphatic hydrocarbon rings such as dicyclofentanyl (meth)acrylate, dicyclofentanyloxyethyl (meth)acrylate, tricyclofentanyl (meth)acrylate, 1-adamanthyl (meth)acrylate, 2-methyl-2-adamanthyl (meth)acrylate, and 2-ethyl-2-adamanthyl (meth)acrylate; Examples include (meth)acrylic acid esters having an aromatic ring, such as (meth)acrylic acid aryl esters of (meth)acrylic acid phenyl, (meth)acrylic acid aryloxyalkyl esters of (meth)acrylic acid phenoxyethyl, (meth)acrylic acid arylalkyl esters of (meth)acrylic acid benzyl, (meth)acrylic acid arylalkyl esters.

[0099] As for (meth)acrylic acid esters having a cyclic structure within the molecule, (meth)acrylic acid esters containing a non-aromatic hydrocarbon ring are preferably used to further express the effects of the present invention, and examples include cyclohexyl acrylate (CHA), cyclohexyl methacrylate (CHMA), dicyclofentanyl acrylate (DCPA), and dicyclofentanyl methacrylate (DCPMA).

[0100] The carboxyl group-containing monomer may be just one type or two or more types.

[0101] Examples of carboxyl group-containing monomers include acid anhydride-containing monomers such as (meth)acrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, isocrotonic acid, and maleic anhydride.

[0102] The content ratio of (meth)acrylic acid ester having a cyclic structure within the molecule among the total monomer components that can be used to form the acrylic oligomer (B1) may be any appropriate content ratio within a range that does not impair the effects of the present invention. The content ratio of (meth)acrylic acid ester having a cyclic structure within the molecule among the total monomer components that can be used to form the acrylic oligomer (B1) may be, for example, 10 to 99.9 parts by weight with respect to 100 parts by weight of the total monomer components, 30 to 99.5 parts by weight, 50 to 99 parts by weight, 70 to 98.5 parts by weight, 80 to 98 parts by weight, 85 to 97.5 parts by weight, or 90 to 97 parts by weight.

[0103] The content ratio of the carboxyl group-containing monomer among the total monomer components that can be used to form the acrylic oligomer (B1) may be any appropriate content ratio within a range that does not impair the effects of the present invention. The content ratio of the carboxyl group-containing monomer among the total monomer components that can be used to form the acrylic oligomer (B1) may be, for example, 0.1 to 90 parts by weight, 0.5 to 70 parts by weight, 1 to 50 parts by weight, 1.5 to 30 parts by weight, 2 to 20 parts by weight, 2.5 to 15 parts by weight, or 3 to 10 parts by weight, with respect to 100 parts by weight of the total monomer components.

[0104] Among the total monomer components that can be used to form the acrylic oligomer (B1), other monomers may be included. The content of other monomers among the total monomer components that can be used to form the acrylic oligomer (B1) may be any appropriate content ratio within a range that does not impair the effects of the present invention. The content of other monomers among the total monomer components that can be used to form the acrylic oligomer (B1) may be, for example, less than 50 parts by weight, less than 40 parts by weight, less than 30 parts by weight, less than 20 parts by weight, less than 10 parts by weight, less than 5 parts by weight, or less than 3 parts by weight, with respect to 100 parts by weight of the total monomer components.

[0105] Other such monomers include, for example, alkyl esters of (meth)acrylate having straight-chain or branched-chain alkyl groups (e.g., methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate), alkoxyalkyl esters of (meth)acrylate (e.g., 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, methoxytriethyleneglycol (meth)acrylate), 3-methoxypropyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 4-methoxybutyl (meth)acrylate, 4-ethoxybutyl (meth)acrylate), and hydroxyl group-containing monomers (e.g., 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate). (meth)acrylate hydroxyalkyls such as (meth)acrylate 4-hydroxybutyl, (meth)acrylate 6-hydroxyhexyl, etc.; vinyl alcohol; allyl alcohol), amide group-containing monomers (e.g., (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-methylol(meth)acrylamide, N-methoxymethyl(meth)acrylamide, N-butoxymethyl(meth)acrylamide, N-hydroxyethyl(meth)acrylamide), amino group-containing monomers (e.g., (meth)acrylate aminoethyl, (meth)acrylate dimethylaminoethyl, (meth)acrylate t-butylaminoethyl), cyano group-containing monomers (e.g., acrylonitrile, methacrylonitrile), sulfonic acid group-containing monomers (e.g., sodium vinylsulfonate), phosphate group-containing monomers (e.g., Examples include 2-hydroxyethylacryloyl phosphate), isocyanate group-containing monomers (e.g., 2-methacryloyloxyethylisocyanate), and imide group-containing monomers (e.g., cyclohexylmaleimide, isopropylmaleimide).

[0106] As for the acrylic oligomer (B2), for example, an acrylic oligomer obtained from a monomer component having a (meth)acrylic acid ester having a cyclic structure within the molecule as an essential component, preferably an acrylic oligomer obtained from a monomer component having a (meth)acrylic acid ester having a cyclic structure within the molecule and a (meth)acrylic acid alkyl ester having a straight-chain or branched-chain alkyl group as essential components.

[0107] (Met)acrylic acid esters having a cyclic structure within the molecule may be of only one type or two or more types.

[0108] For (meth)acrylic acid esters having a cyclic structure within the molecule, the above description may be applied.

[0109] A (meth)acrylate alkyl ester having a straight-chain or branched-chain alkyl group may be one type or two or more types.

[0110] As alkyl esters of (meth)acrylate having a straight-chain or branched-chain alkyl group, examples include (meth)acrylate methyl, (meth)acrylate ethyl, (meth)acrylate propyl, (meth)acrylate isopropyl, (meth)acrylate butyl, (meth)acrylate isobutyl, (meth)acrylate s-butyl, (meth)acrylate t-butyl, (meth)acrylate pentyl, (meth)acrylate isopentyl, (meth)acrylate hexyl, (meth)acrylate heptyl, (meth)acrylate octyl, (meth)acrylate 2-ethylhexyl, (meth)acrylate isooctyl, (meth)acrylate nonyl, (meth)acrylate isononyl, (meth)acrylate decyl, (meth)acrylate isodecyl, (meth)acrylate undecyl. Examples include alkyl esters of (meth)acrylate having 1 to 20 carbon atoms in an alkyl group, such as (meth)acrylate dodecyl, (meth)acrylate tridecyl, (meth)acrylate tetradecyl, (meth)acrylate pentadecyl, (meth)acrylate hexadecyl, (meth)acrylate heptadecyl, (meth)acrylate octadecyl, (meth)acrylate nonadecyl, and (meth)acrylate eicosyl.

[0111] The content ratio of (meth)acrylic acid ester having a cyclic structure within the molecule among the total monomer components that can be used to form the acrylic oligomer (B2) may be any appropriate content ratio within a range that does not impair the effects of the present invention. The content ratio of (meth)acrylic acid ester having a cyclic structure within the molecule among the total monomer components that can be used to form the acrylic oligomer (B2) may be, for example, 20 to 99.9 parts by weight with respect to 100 parts by weight of the total monomer components, 25 to 95 parts by weight, 30 to 90 parts by weight, 35 to 85 parts by weight, 40 to 80 parts by weight, 45 to 75 parts by weight, 50 to 70 parts by weight, or 55 to 65 parts by weight.

[0112] The content ratio of (meth)acrylate alkyl ester having a straight-chain or branched-chain alkyl group in the total monomer components that can be used to form the acrylic oligomer (B2) may be any suitable content ratio within a range that does not impair the effects of the present invention. The content ratio of (meth)acrylate alkyl ester having a straight-chain or branched-chain alkyl group in the total monomer components that can be used to form the acrylic oligomer (B2) may be, for example, 1 to 80 parts by weight, 10 to 70 parts by weight, 15 to 65 parts by weight, 20 to 60 parts by weight, 25 to 55 parts by weight, 30 to 50 parts by weight, or 35 to 45 parts by weight, with respect to 100 parts by weight of the total monomer components.

[0113] Among the total monomer components that can be used to form the acrylic oligomer (B2), other monomers may be included. Any appropriate content ratio of other monomers among the total monomer components that can be used to form the acrylic oligomer (B2) may be adopted within a range that does not impair the effects of the present invention. The content ratio of other monomers among the total monomer components that can be used to form the acrylic oligomer (B2) may be, for example, less than 50 parts by weight, less than 40 parts by weight, less than 30 parts by weight, less than 20 parts by weight, less than 10 parts by weight, less than 5 parts by weight, or less than 3 parts by weight, with respect to 100 parts by weight of the total monomer components.

[0114] Other such monomers include, for example, carboxyl group-containing monomers (e.g., acid anhydride group-containing monomers such as (meth)acrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, isocrotonic acid, maleic anhydride), (meth)acrylic acid alkoxyalkyl esters (e.g., (meth)acrylic acid 2-methoxyethyl, (meth)acrylic acid 2-ethoxyethyl, (meth)acrylic acid methoxytriethylene glycol, (meth)acrylic acid 3-methoxypropyl, (meth)acrylic acid 3-ethoxypropyl, (meth)acrylic acid 4-methoxybutyl, (meth)acrylic acid 4-ethoxybutyl), and hydroxyl group-containing monomers (e.g., (meth)acrylic acid 2-hydroxyethyl, (meth)acrylic acid 3-hydroxypropyl, (meth)acrylic acid 4-hydroxybutyl, (meth)acrylate hydroxyalkyls such as (meth)acrylate 6-hydroxyhexyl; vinyl alcohol; allyl alcohol), amide group-containing monomers (e.g., (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-methylol(meth)acrylamide, N-methoxymethyl(meth)acrylamide, N-butoxymethyl(meth)acrylamide, N-hydroxyethyl(meth)acrylamide), amino group-containing monomers (e.g., (meth)acrylate aminoethyl, (meth)acrylate dimethylaminoethyl, (meth)acrylate t-butylaminoethyl), cyano group-containing monomers (e.g., acrylonitrile, methacrylonitrile), sulfonic acid group-containing monomers (e.g., sodium vinylsulfonate), phosphate group-containing monomers (e.g., 2-hydroxyethylacryloylphosphate), Examples include monomers containing isocyanate groups (e.g., 2-methacryloyloxyethyl isocyanate) and monomers containing imide groups (e.g., cyclohexyl maleimide, isopropyl maleimide).

[0115] The acrylic oligomer (B) can be prepared by any suitable method within a range that does not impair the effects of the present invention. Examples of such preparation methods include solution polymerization, emulsion polymerization, bulk polymerization, and polymerization by irradiation with active energy rays (active energy ray polymerization method). Among these, preferably, the bulk polymerization method and the solution polymerization method are used, and more preferably, the solution polymerization method is used.

[0116] Examples of solvents that can be used in polymerization include organic solvents such as esters such as ethyl acetate and n-butyl acetate; aromatic hydrocarbons such as toluene and benzene; aliphatic hydrocarbons such as n-hexane and n-heptane; alicyclic hydrocarbons such as cyclohexane and methylcyclohexane; and ketones such as methyl ethyl ketone and methyl isobutyl ketone. There may be only one type of solvent or two or more types.

[0117] In polymerization, any suitable polymerization initiator (e.g., a thermal polymerization initiator or a photopolymerization initiator, etc.) may be employed within a range that does not impair the effects of the present invention. There may be only one type of polymerization initiator or two or more types. In addition, when performing solution polymerization, it is preferable to use an oil-soluble polymerization initiator.

[0118] As a thermal polymerization initiator, any suitable thermal polymerization initiator may be employed within a range that does not impair the effects of the present invention. The thermal polymerization initiator may be one type or two or more types.

[0119] Examples of thermal polymerization initiators include azo-based initiators such as 2,2'-azobisisobutyronitrile (AIBN); peroxide-based initiators such as persulfates like potassium persulfate and ammonium persulfate, and hydrogen peroxide; redox-based initiators combining peroxide and a reducing agent, such as a combination of persulfate and sodium bisulfite, or a combination of peroxide and sodium ascorbate; substituted ethane-based initiators such as phenyl-substituted ethane; and aromatic carbonyl compounds.

[0120] As a photopolymerization initiator, any suitable photopolymerization initiator may be employed within a range that does not impair the effects of the present invention. The photopolymerization initiator may be one type or two or more types.

[0121] Examples of photopolymerization initiators include benzoin ether-based photopolymerization initiators, acetophenone-based photopolymerization initiators, α-ketol-based photopolymerization initiators, aromatic sulfonyl chloride-based photopolymerization initiators, photoactive oxime-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzyl-based photopolymerization initiators, benzophenone-based photopolymerization initiators, ketal-based photopolymerization initiators, and thioxanthone-based photopolymerization initiators.

[0122] Examples of benzoin ether-based photopolymerization initiators include benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, and dichloroacetophenone. Examples of α-ketol-based photopolymerization initiators include 2-methyl-2-hydroxypropiophenone and 1-[4-(2-hydroxyethyl)phenyl]-2-methylpropan-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 benzyl-based photopolymerization initiators include benzyl. Examples of benzophenone-based photopolymerization initiators include benzophenone and benzoylbenzoic acid. Examples of ketal-based photopolymerization initiators include benzyldimethylketal. Examples of thioxantone-based photopolymerization initiators include thioxantone, 2-chlorothioxantone, 2-methylthioxantone, and 2,4-dimethylthioxantone.

[0123] Any suitable amount of polymerization initiator may be used within a range that does not impair the effects of the present invention. Such amount may be, for example, 0.001 to 20 parts by weight, 0.005 to 10 parts by weight, 0.01 to 5 parts by weight, or 0.05 to 1 part by weight, based on 100 parts by weight of the total monomer component that can be used to form the acrylic oligomer (B).

[0124] When polymerizing to produce an acrylic oligomer (B), a chain transfer agent may be used to adjust the molecular weight. Examples of chain transfer agents include 2-mercaptoethanol, α-thioglycerol, octyl mercaptan, thioglycolic acid, methyl thioglycolate, and α-methylstyrene dimer. There may be only one type of chain transfer agent or two or more types.

[0125] Any suitable amount of chain transfer agent may be used within a range that does not impair the effects of the present invention. The amount of chain transfer agent used may be, for example, 0.1 to 20 parts by weight, 1 to 15 parts by weight, or 1 to 13 parts by weight, based on 100 parts by weight of the total monomer component that can be used to form the acrylic oligomer (B).

[0126] During polymerization, any other suitable additive may be added within a range that does not impair the effects of the present invention.

[0127] ≪1-3. Crosslinking Agent (C)≫

[0128] The crosslinking agent (C) may be of only one type or two or more types.

[0129] In order to further express the effects of the present invention, the crosslinking agent content in the acrylic adhesive composition is preferably 0.01 to 5.00 parts by weight per 100 parts by weight of the acrylic polymer (A), and may be 0.03 to 3.00 parts by weight, 0.05 to 1.00 parts by weight, 0.07 to 0.50 parts by weight, 0.075 to 0.25 parts by weight, 0.08 to 0.20 parts by weight, or 0.085 to 0.175 parts by weight.

[0130] As for the crosslinking agent (C), examples include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, silicone-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, silane-based crosslinking agents, alkyl etherified melamine-based crosslinking agents, metal chelate-based crosslinking agents, peroxides, etc., and in order to further express the effects of the present invention, preferably at least one is selected from the group consisting of isocyanate-based crosslinking agents, epoxy-based crosslinking agents, and peroxides.

[0131] As an isocyanate-based crosslinking agent, a compound having two or more isocyanate groups (including isocyanate regenerating polar groups in which the isocyanate groups are temporarily protected by blocking agents or merizing, etc.) in one molecule may be used. Examples of isocyanate-based crosslinking agents include aromatic isocyanates such as tolylene diisocyanate and xylene diisocyanate; alicyclic isocyanates such as isophorone diisocyanate; and aliphatic isocyanates such as hexamethylene diisocyanate.

[0132] As isocyanate-based crosslinking agents, for example, lower aliphatic polyisocyanates such as butylene diisocyanate and hexamethylene diisocyanate; alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate, and isophorone diisocyanate; aromatic diisocyanates such as 2,4-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate, and polymethylene polyphenyl isocyanate; Isocyanate adducts such as trimethylolpropane / tolylene diisocyanate trimer adducts (e.g., manufactured by Dosoh Co., trade name: Coronate L), trimethylolpropane / hexamethylene diisocyanate trimer adducts (e.g., manufactured by Dosoh Co., trade name: Coronate HL), and isocyanurate forms of hexamethylene diisocyanate (e.g., manufactured by Dosoh Co., trade name: Coronate HX); Trimethylolpropane adducts of xylylene diisocyanate (e.g., manufactured by Mitsui Chemicals, trade name: Takenate D110N), trimethylolpropane adducts of xylylene diisocyanate (e.g., manufactured by Mitsui Chemicals, trade name: Takenate D120N), trimethylolpropane adducts of isophorone diisocyanate (e.g., manufactured by Mitsui Chemicals, trade name: Takenate D140N), trimethylolpropane adducts of hexamethylene diisocyanate (e.g., manufactured by Mitsui Chemicals, trade name: Takenate D160N), trimethylolpropane adducts of tolylene diisocyanate (e.g., manufactured by Mitsui Chemicals, trade name: Takenate D101E); polyether polyisocyanates, polyester polyisocyanates, and adducts of these and various polyols; Examples include polyisocyanates polyfunctionalized with isocyanurate bonds, biuret bonds, allophanate bonds, etc.

[0133] As an epoxy-based crosslinking agent, a polyfunctional epoxy compound having two or more epoxy groups in one molecule can be used. As epoxy-based crosslinking agents, for example, N,N,N',N'-tetraglycidyl-m-xylenediamine, diglycidylaniline, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, sorbitol polyglycidyl ether, glycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitan polyglycidyl ether, trimethylolpropane polyglycidyl ether, adipic acid diglycidyl ester, o-phthalic acid diglycidyl ester, Examples include triglycidyl-tris(2-hydroxyethyl)isocyanurate, resorcinol diglycidyl ether, bisphenol-S-diglycidyl ether, and epoxy resins having two or more epoxy groups in the molecule. Examples of commercially available epoxy crosslinking agents include the trade names "Tetrad C" and "Tetrad X" manufactured by Mitsubishi Gas Corporation.

[0134] As peroxides, for example, dibenzoyl peroxide, dicumyl peroxide, di-t-butyl peroxide, di-t-butylperoxy-3,3,5-trimethylcyclohexane, t-butylhydroperoxide, t-butylcumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxin)hexine-3,2,5-dimethyl-2,5-di(benzoylperoxy)hexane, 2,5-dimethyl-2,5-mono(t-butylperoxy)-hexane, α,α'-bis(t-butylperoxy-m-isopropyl)benzene, di(2-ethylhexyl)peroxydicarbonate, di(4-t-butylcyclohexyl)peroxydicarbonate, di-sec-butylperoxydicarbonate, t-butylperoxyneodecanoate, Examples include t-hexyl peroxypivalate, t-butyl peroxypivalate, dilauroyl peroxide, di-n-octanoyl peroxide, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, di(4-methylbenzoyl)peroxide, t-butylperoxyisobutyrate, 1,1-di(t-hexylperoxy)cyclohexane, 1,1-di(t-butylperoxy)cyclohexane, t-butylperoxy-2-ethylhexyl carbonate, t-amylperoxyisopropyl carbonate, 3,5,5-trimethylhexanoyl peroxide, t-butylperoxy-2-hexanoate, t-butylperoxypivalate, and t-hexyl peroxypivalate. Examples of commercially available peroxides include the "Niper BMT" series and "Niper BW" series manufactured by Nippon Yushi Co., Ltd.

[0135] ≪1-4. Other Components≫

[0136] The acrylic adhesive composition may contain any suitable other components to the extent that it does not impair the effects of the present invention. Examples of such other components include crosslinking catalysts, crosslinking accelerators, crosslinking retardants, silane coupling agents, tackifying resins (rosin derivatives, polyterpene resins, petroleum resins, oil-soluble phenols, etc.), anti-aging agents, inorganic fillers, organic fillers, metal powders, coloring agents (pigments or dyes, etc.), film materials, ultraviolet absorbers, antioxidants, light stabilizers, nucleating agents, chain transfer agents, plasticizers, softeners, antistatic agents (ionic compounds, etc.), conductive agents, stabilizers, surface lubricants, leveling agents, corrosion inhibitors, heat stabilizers, polymerization inhibitors, lubricants, solvents, etc.

[0137] The content of other components in the acrylic adhesive composition may be any appropriate amount within a range that does not impair the effects of the present invention. The content of other components in the acrylic adhesive composition may be, for example, 0 to 30 parts by weight with respect to 100 parts by weight of the acrylic polymer (A), 0 to 20 parts by weight, 0 to 10 parts by weight, or 0 to 5 parts by weight.

[0138] ≪≪2. Acrylic Adhesives≫≫

[0139] The acrylic adhesive according to an embodiment of the present invention is formed from an acrylic adhesive composition according to an embodiment of the present invention.

[0140] Acrylic adhesives can be defined as being formed from an acrylic adhesive composition in this manner. Since an acrylic adhesive composition can become an acrylic adhesive by undergoing cross-linking reactions, such as those caused by heating or ultraviolet irradiation, there may exist circumstances where it is impossible to directly identify the acrylic adhesive by its structure, and furthermore, circumstances where such identification is approximately impractical ("impossible / impractical circumstances") may exist. For this reason, acrylic adhesives can be validly identified as "things" by the provision that they are "formed from an acrylic adhesive composition."

[0141] When an acrylic adhesive is formed from an acrylic adhesive composition, any suitable method for forming the acrylic adhesive may be employed within a range that does not impair the effects of the present invention. Examples of such methods for forming the acrylic adhesive include, for instance, a method of forming an acrylic adhesive on a substrate by applying an acrylic adhesive composition onto any suitable substrate, performing heating and drying as necessary, and curing as necessary; or a method of forming an acrylic adhesive on a substrate by applying an acrylic adhesive composition onto a film such as a release liner as necessary, performing heating and drying as necessary, and curing as necessary, and then forming an acrylic adhesive on the film, and finally bonding and transferring any suitable substrate onto the acrylic adhesive. Any suitable means for such application may be employed within a range that does not impair the effects of the present invention. Examples of such coating methods include roll coating, gravure roll coating, reverse roll coating, kiss roll coating, dip roll coating, bar coating, roll brush coating, spray coating, knife coating, air knife coating, comma coating, direct coating, and die coating. Any suitable means may be employed for heating and drying the acrylic adhesive composition within a range that does not impair the effects of the present invention. Examples of such heating and drying methods include heating to a temperature of 60°C to 180°C. Any suitable means may be employed for curing the acrylic adhesive composition within a range that does not impair the effects of the present invention. Examples of such curing methods include heat, ultraviolet irradiation, laser irradiation, alpha ray irradiation, beta ray irradiation, gamma ray irradiation, X-ray irradiation, and electron ray irradiation.

[0142] The acrylic adhesive according to an embodiment of the present invention may have a glass transition temperature Tg obtained by dynamic viscoelasticity measurement that is, for example, less than -37.5°C, less than -38.0°C, less than -38.5°C, less than -39.0°C, less than -39.5°C, less than -40.0°C, less than -40.5°C, or less than -41.0°C. The lower limit of the glass transition temperature Tg obtained by dynamic viscoelasticity measurement of the acrylic adhesive according to an embodiment of the present invention may be, for example, -70°C or higher, -65°C or higher, or -60°C or higher, from the perspective of compatibility with adhesive strength. The acrylic adhesive according to an embodiment of the present invention can effectively lower the elastic modulus in a low-temperature environment by having the glass transition temperature Tg obtained by dynamic viscoelasticity measurement within the above range. In addition, the acrylic adhesive composition according to an embodiment of the present invention may form an acrylic adhesive in which the glass transition temperature Tg obtained by dynamic viscoelasticity measurement is within the above-mentioned range. The measurement of the glass transition temperature Tg by dynamic viscoelasticity measurement will be explained in detail later.

[0143] The acrylic adhesive according to an embodiment of the present invention can exhibit a low elastic modulus under low-temperature conditions. The acrylic adhesive according to an embodiment of the present invention may have a storage modulus G' at -20°C that is, for example, less than 160 kPa, less than 155 kPa, less than 150 kPa, less than 145 kPa, less than 140 kPa, less than 135 kPa, or less than 130 kPa. The lower limit of the storage modulus G' at -20°C of the acrylic adhesive according to an embodiment of the present invention is, for example, 30 kPa or more, from the perspective of handling properties. The method for measuring the storage modulus G' at -20°C will be explained in detail later.

[0144] The acrylic adhesive according to an embodiment of the present invention can exhibit high adhesive strength under room temperature conditions. The acrylic adhesive according to an embodiment of the present invention, under a 25°C environment, a peel angle of 180 degrees, and a peel speed (tensile speed) of 300 mm / min, has an adhesive strength to a polyimide film (which may be referred to as "25°C adhesive strength") that is, for example, 5 N / 25 mm or more, 6 N / 25 mm or more, 7 N / 25 mm or more, 8 N / 25 mm or more, 9 N / 25 mm or more, or 10 N / 25 mm or more. The upper limit of the 25°C adhesive strength of the acrylic adhesive according to an embodiment of the present invention is, for example, 40 N / 25 mm or less, from the perspective of compatibility with the storage modulus G' at -20°C. The method for measuring the 25°C adhesive strength will be explained in detail later.

[0145] The acrylic adhesive according to an embodiment of the present invention can exhibit high adhesive strength under high temperature conditions. The acrylic adhesive according to an embodiment of the present invention has an adhesive strength (sometimes referred to as "85°C adhesive strength") to a polyimide film under an 85°C environment, a peel angle of 180 degrees, and a peel speed (tensile speed) of 300 mm / min, which may be, for example, 4 N / 25 mm or more, 4.5 N / 25 mm or more, 5 N / 25 mm or more, 5.5 N / 25 mm or more, 6 N / 25 mm or more, or 6.5 N / 25 mm or more. The upper limit of the 85°C adhesive strength of the acrylic adhesive according to an embodiment of the present invention is, for example, 40 N / 25 mm or less, from the perspective of compatibility with the storage modulus G' at -20°C. The method for measuring adhesive strength at 85℃ will be explained in detail later.

[0146] ≪≪3. Acrylic Adhesive Sheets≫≫

[0147] An acrylic adhesive sheet according to one embodiment of the present invention comprises an acrylic adhesive layer composed of an acrylic adhesive according to an embodiment of the present invention.

[0148] An acrylic adhesive sheet according to an embodiment of the present invention may be a substrate-free sheet consisting only of an acrylic adhesive layer, or a substrate-equipped sheet having a substrate and an acrylic adhesive layer. An acrylic adhesive sheet according to an embodiment of the present invention may include any other suitable layer in addition to the substrate and the acrylic adhesive layer, provided that the effects of the present invention are not impaired.

[0149] The substrate may be one layer or two or more layers. The substrate is preferably one layer in order to further express the effects of the present invention.

[0150] The acrylic adhesive layer may be one layer or two or more layers. The acrylic adhesive layer is preferably one layer in order to further express the effects of the present invention.

[0151] The acrylic adhesive sheet according to an embodiment of the present invention may be provided with any suitable release liner on the surface opposite to the side on which the acrylic adhesive layer substrate is provided, for protection until use.

[0152] Examples of release liners include a release liner in which the surface of the substrate (liner substrate), such as paper or plastic film, is silicone-treated, and a release liner in which the surface of the substrate (liner substrate), such as paper or plastic film, is laminated with a polyolefin resin. Examples of plastic films used as liner substrates include polyethylene film, polypropylene film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyethylene terephthalate film, polybutylene terephthalate film, polyurethane film, and ethylene-vinyl acetate copolymer film.

[0153] The thickness of the release liner is preferably 1 μm to 500 μm, may be 3 μm to 450 μm, may be 5 μm to 400 μm, or may be 10 μm to 300 μm.

[0154] The total thickness of the acrylic adhesive sheet according to an embodiment of the present invention is preferably 1 μm to 500 μm, may be 5 μm to 200 μm, or may be 10 μm to 150 μm.

[0155] ≪3-1. Recording≫

[0156] The thickness of the substrate is preferably 1 μm to 500 μm, and may be 5 μm to 300 μm, 10 μm to 100 μm, 15 μm to 80 μm, or 20 μm to 60 μm.

[0157] As for the material of the substrate, any suitable material may be adopted within a range that does not impair the effects of the present invention. Examples of such materials of the substrate include resin materials, metals, paper, and nonwoven fabrics, and preferably resin materials and metals.

[0158] Examples of resin materials used as the material for the base include, for instance, acrylic resins such as polyimide (PI), polyetheretherketone (PEEK), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), and polymethyl methacrylate (PMMA), polycarbonate, triacetylcellulose (TAC), polysulfone, polyarylate, polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer, ethylene-vinyl acetate copolymer (EVA), polyamide (nylon), fully aromatic polyamide (aramid), polyvinyl chloride (PVC), polyvinyl acetate, polyphenylene sulfide (PPS), fluorinated resins, and cyclic olefin polymers.

[0159] Examples of metals used as materials for the base include iron, copper, titanium, tin, zinc, stainless steel, aluminum alloy, aluminum, Galvalume steel (registered trademark), tungsten, chromium, cobalt, and nickel.

[0160] ≪3-2. Acrylic Adhesive Layer≫

[0161] The thickness of the acrylic adhesive layer in the acrylic adhesive sheet according to an embodiment of the present invention is preferably 100 μm or less, may be 70 μm or less, may be 50 μm or less, may be 30 μm or less, may be 1 μm to 30 μm, may be 5 μm to 30 μm, or may be 10 μm to 30 μm.

[0162] The acrylic adhesive layer is composed of an acrylic adhesive. More specifically, the acrylic adhesive layer is formed by forming an acrylic adhesive into a layer shape. Any suitable forming method may be employed as long as it does not impair the effects of the present invention. Examples of such forming methods include applying an acrylic adhesive composition onto any suitable substrate, performing heating and drying as necessary, and curing as necessary to form an adhesive layer composed of an acrylic adhesive on the said substrate. Any suitable means may be employed as long as it does not impair the effects of the present invention. Examples of such application means include a gravure roll coater, a reverse roll coater, a kiss roll coater, a dip roll coater, a bar coater, a knife coater, an air knife coater, a spray coater, a comma coater, a direct coater, and a roll brush coater. Any suitable means may be employed for heating and drying the acrylic adhesive composition as long as it does not impair the effects of the present invention. As means of such heating and drying, for example, heating to about 60°C to 180°C may be used. Any suitable means may be employed for curing the acrylic adhesive composition within a range that does not impair the effects of the present invention. Examples of such means of curing include ultraviolet irradiation, laser irradiation, alpha ray irradiation, beta ray irradiation, gamma ray irradiation, X-ray irradiation, and electron ray irradiation.

[0163] ≪≪4. Flexible Devices≫≫

[0164] A flexible device according to an embodiment of the present invention includes an acrylic adhesive sheet according to an embodiment of the present invention.

[0165] FIG. 1 is a schematic cross-sectional view illustrating one embodiment of a flexible device of the present invention as a representative example of one use form of an acrylic adhesive sheet according to an embodiment of the present invention. In FIG. 1, the flexible device (1000) according to an embodiment of the present invention comprises a cover film (10), an adhesive layer (20), a polarizing plate (30), an adhesive layer (40), a touch sensor (50), an adhesive layer (60), an OLED (70), and an acrylic adhesive sheet (100) according to an embodiment of the present invention. In FIG. 1, the acrylic adhesive sheet (100) according to an embodiment of the present invention is composed of an acrylic adhesive layer (80) and a substrate (90). The adhesive layer (20), adhesive layer (40), and adhesive layer (60) may be an acrylic adhesive layer containing an adhesive of the same composition as the acrylic adhesive layer (80) constituting the acrylic adhesive sheet (100) according to an embodiment of the present invention, or an adhesive layer containing an adhesive of a different composition.

[0166] The acrylic adhesive sheet according to an embodiment of the present invention comprises an acrylic adhesive layer composed of an acrylic adhesive according to an embodiment of the present invention, so that the acrylic adhesive layer can simultaneously exhibit a low elastic modulus under a low-temperature environment, a high adhesive strength under a room-temperature environment, and a high adhesive strength under a high-temperature environment. For this reason, it can be suitably provided for flexible devices such as bendable devices having movable bending parts, foldable devices, or rollable devices.

[0167] The flexible device of the present invention may include any other suitable member if it includes an acrylic adhesive sheet according to an embodiment of the present invention.

[0168] [Example]

[0169] The present invention will be explained in more detail below with reference to examples and comparative examples. However, the present invention is not limited thereto. Furthermore, in the following description, "parts" and "%" are based on weight unless otherwise specified.

[0170] The abbreviations and details of the raw materials, etc. used in the following manufacturing examples, examples, and comparative examples are as follows.

[0171] BA: n-butyl acrylate

[0172] HxA: n-hexyl acrylate

[0173] NOAA: n-octyl acrylate

[0174] 2EHA: 2-ethylhexyl acrylate

[0175] INAA: Isononyl acrylate

[0176] NA: Nonyl acrylate (content of nonyl acrylate having a nonyl group having a tert-butyl group as an ester portion is 80% by weight or more)

[0177] 4HBA: 4-hydroxybutyl acrylate

[0178] NVP: N-vinyl-2-pyrrolidone

[0179] DCPMA: Dicyclofentanyl methacrylate

[0180] MMA: Methyl methacrylate

[0181] CHMA: Cyclohexyl methacrylate

[0182] AA: Acrylic acid

[0183] AIBN: 2,2'-Azobisisobutyronitrile

[0184] C / HX: Coronate HX (manufactured by Toso Co., Ltd., isocyanate-based crosslinking agent)

[0185] <Measurement of Weight Average Molecular Weight Mw of Acrylic Polymers>

[0186] The weight-average molecular weight Mw of the acrylic polymer was measured by gel permeation chromatography (GPC). Specifically, using an "Alliance" (manufactured by Waters) as the GPC measuring device, a 0.1 wt% tetrahydrofuran solution was prepared considering the polymer concentration of the sample, left to stand for 20 hours, filtered through a 0.45 μm membrane filter, and GPC measurement was performed on the obtained filtrate. The following conditions were adopted for the GPC measurement.

[0187] · Sample concentration: 0.1 wt% (tetrahydrofuran solution)

[0188] · Sample injection volume: 30μL

[0189] · Column: Product Name "TSKgel SuperHZM-H" (Manufactured by Dosō Co.)

[0190] · Eluent: Tetrahydrofuran

[0191] · Flow rate: 0.2 mL / min

[0192] · Detector: Parallax Refractometer (RI)

[0193] · Column temperature (measurement temperature): 40℃

[0194] · Standard sample: Polystyrene (PS)

[0195] <Measurement of Weight Average Molecular Weight Mw of Acrylic Oligomers>

[0196] The weight-average molecular weight Mw of the acrylic oligomer was measured by gel permeation chromatography (GPC). Specifically, using the "HLC-8320GPC" (manufactured by Tosoh Co., Ltd.) as the GPC measuring device, a 0.1 wt% tetrahydrofuran solution was prepared considering the polymer concentration of the sample, left to stand for 20 hours, filtered through a 0.45 μm membrane filter, and GPC measurement was performed on the obtained filtrate. The following conditions were adopted for the GPC measurement.

[0197] · Sample concentration: 0.1 wt% (tetrahydrofuran solution)

[0198] · Sample injection volume: 100μL

[0199] · Column: Product Name "TSKgel SuperHZM-H / HZ4000 / HZ3000 / HZ2000" (Manufactured by Dososa)

[0200] · Eluent: Tetrahydrofuran

[0201] · Flow rate: 0.6 mL / min

[0202] · Detector: Parallax Refractometer (RI)

[0203] · Column temperature (measurement temperature): 40℃

[0204] · Standard sample: Polystyrene (PS)

[0205] <Preparation of Test Specimens for Measurement of Glass Transition Temperature Tg and Storage Modulus G' at -20℃ of Acrylic Adhesives>

[0206] Each of the coating solutions of the acrylic adhesive compositions (1) to (6) and (C1) to (C6) obtained in the examples and comparative examples was applied to a release liner (Mitsubishi Chemical, MRV50T100J) made of a polyester resin with a thickness of 50 μm and silicone treatment on one side, so that the thickness after drying was 15 μm, and dried under conditions of a drying temperature of 130°C and a drying time of 1 minute to form an acrylic adhesive layer composed of acrylic adhesives (1a) to (6a) and (C1a) to (C6a) on the release liner.

[0207] Next, the silicone-treated surface of a release liner (Mitsubishi Chemical, MRQ50T100J), made of a polyester resin with a thickness of 50 μm and silicone-treated on one side, was bonded to the surface of the obtained acrylic adhesive layer so as to contact it, thereby obtaining acrylic adhesive sheets (1a) to (6a) and (C1a) to (C6a). This was aged at 50°C for 1 day.

[0208] <Measurement of Glass Transition Temperature Tg and Storage Modulus G' at -20℃ of Acrylic Adhesives>

[0209] Only the acrylic adhesive layer was extracted from each of the acrylic adhesive sheets (1a) to (6a) and (C1a) to (C6a) prepared as test specimens for measuring the glass transition temperature Tg and storage modulus G' at -20°C of the acrylic adhesive, laminated to a thickness of about 1 mm, and then punched into a cylindrical pellet of φ8 mm to produce a sample for measurement.

[0210] Using a dynamic viscoelasticity measuring device (TA Instruments, DHR-2), the obtained measurement sample was fixed to a jig on a φ8 mm parallel plate, and the glass transition temperature Tg and storage modulus G' at -20°C were measured.

[0211] The measurement conditions are as follows.

[0212] Measurement: Shear mode

[0213] Temperature range: -50℃ to 200℃

[0214] Heating rate: 5℃ / min

[0215] Frequency: 1Hz

[0216] Strain: 0.1%

[0217] <Measurement of Adhesion Strength of Acrylic Adhesives at 25°C>

[0218] For the acrylic adhesive sheets (1b) to (6b) and (C1b) to (C6b) obtained in the examples and comparative examples, a width of 25 mm × a length of 100 mm was cut, and a release liner was peeled off to expose the acrylic adhesive layer, and the sheets were adhered to a polyimide film (product name "U-Fillers 50S", manufactured by Ube Kosan Co., Ltd.) with one round of a 2 kg hand roller to obtain a sample for evaluation.

[0219] The obtained evaluation sample was stored at room temperature for 30 minutes and then measured using a tensile testing machine. As the tensile testing machine, the Shimadzu Seisakusho "Autograph AG-Xplus HS 6000 mm / min high-speed model (AG-50NX plus)" was used. After setting the evaluation sample in the tensile testing machine, the tensile test was started. The conditions for the tensile test were set to a 25°C environment, a peel angle of 180 degrees, and a peel speed (tensile speed) of 300 mm / min. The load was measured when the adhesive film was peeled from the polyimide film (U-Fillers 50S), and the average load at that time was taken as the 25°C adhesive strength.

[0220] <Measurement of Adhesion Strength of Acrylic Adhesives at 85°C>

[0221] For the acrylic adhesive sheets (1b) to (6b) and (C1b) to (C6b) obtained in the examples and comparative examples, a width of 25 mm × a length of 100 mm was cut, and a release liner was peeled off to expose the acrylic adhesive layer, and the sheets were adhered to a polyimide film (product name "U-Fillers 50S", manufactured by Ube Kosan Co., Ltd.) with one round of a 2 kg hand roller to obtain a sample for evaluation.

[0222] Evaluation samples were prepared as test specimens by autoclaving at 50°C, 0.5 MPa, and for 15 minutes, and after being stored for 10 minutes in an 85°C environment using a tensile testing machine equipped with a constant temperature bath, the adhesive strength at 85°C was measured. As the tensile testing machine, the "Autograph AGX-V2 6000 mm / min model equipped with a constant temperature bath" manufactured by Shimadzu Seisakusho Co., Ltd. was used. The conditions for the tensile test were set to an 85°C environment, a peel angle of 180 degrees, and a peel speed (tensile speed) of 300 mm / min. The load was measured when the adhesive film was peeled from the above polyimide film (U-Fillers 50S), and the average load at that time was taken as the adhesive strength at 85°C.

[0223] [Preparation Example 1]: Preparation of acrylic polymer (1)

[0224] In a 4-neck flask equipped with a stirring blade, thermometer, nitrogen gas inlet tube, and condenser, 60 parts by weight of HxA, 32 parts by weight of BA, 8 parts by weight of 4HBA, and 0.1 parts by weight of AIBN as a polymerization initiator were added, and ethyl acetate was added so that the total concentration of these was 37% by weight. The system was then nitrogen-purified for 1 hour while stirring gently, and the liquid temperature in the flask was maintained at around 58°C to carry out a polymerization reaction for 5 hours. After the reaction was finished, ethyl acetate was added to adjust the polymer concentration to 30% by weight, and a solution of acrylic polymer (1) was obtained.

[0225] The results are shown in Table 1.

[0226] [Preparation Examples 2 to 7]: Preparation of acrylic polymers (2) to (7)

[0227] A solution of acrylic polymers (2) to (7) was obtained by performing the same procedure as in Preparation Example 1, except that the composition of the raw materials was changed as shown in Table 1.

[0228] The results are shown in Table 1.

[0229] [Preparation Example 8]: Preparation of acrylic oligomer (X)

[0230] In a four-necked flask equipped with a stirring blade, a thermometer, a nitrogen gas inlet tube, and a condenser, 57.7 parts by weight of DCPMA and 38.7 parts by weight of MMA were added as monomer components, 3.3 parts by weight of α-thioglycerol as a chain transfer agent, and 0.29 parts by weight of AIBN as a thermal polymerization initiator. Ethyl acetate was added so that the total concentration of these components was 60% by weight, and the mixture was reacted at 67°C for 2 hours under a nitrogen atmosphere. Next, the temperature was raised to 80°C and the mixture was reacted for 8 hours to obtain a solution of an acrylic oligomer (X). The weight-average molecular weight Mw of the acrylic oligomer (X) was 4900, and the glass transition temperature Tg was 144°C.

[0231] [Preparation Example 9]: Preparation of acrylic oligomer (Y)

[0232] In a four-necked flask equipped with a stirring blade, a thermometer, a nitrogen gas inlet tube, and a condenser, 95 parts by weight of CHMA and 5 parts by weight of AA were added as monomer components, 10 parts by weight of α-methylstyrene dimer (manufactured by Nippon Yushi Co., Ltd., trade name "Nopmer-MSD") as a chain transfer agent, and 10 parts by weight of AIBN as a thermal polymerization initiator. Toluene was added so that the total concentration of these components was 50% by weight, and the mixture was reacted at 85°C for 2 hours under a nitrogen atmosphere. Next, the temperature was raised to 86°C and the mixture was reacted for 1.5 hours to obtain a solution of acrylic oligomer (Y). The weight-average molecular weight Mw of the acrylic oligomer (Y) was 4000, and the glass transition temperature Tg was 67°C.

[0233] [Example 1]

[0234] A coating solution of an acrylic adhesive composition (1) was obtained by mixing 100 parts by weight of an acrylic polymer (1), 0.1 parts by weight of C / HX as a crosslinking agent, and 4 parts by weight of an acrylic oligomer (X), stirring thoroughly, and then diluting with ethyl acetate so that the total solid content is 21% by weight.

[0235] A coating solution of the obtained acrylic adhesive composition (1) was applied to a polyester film (Toray Lumirror #50-U48) as a substrate so that the thickness after drying was 15 μm, and dried under conditions of a drying temperature of 130°C and a drying time of 1 minute to form an acrylic adhesive layer composed of an acrylic adhesive (1b) on the substrate.

[0236] Next, an acrylic adhesive sheet (1b) was manufactured by bonding the silicone-treated surface of a release liner (Mitsubishi Chemical, MRQ50T100J), made of polyester resin with a thickness of 50 μm and silicone-treated on one side, to the surface of the obtained acrylic adhesive layer. This was aged at 50°C for 1 day.

[0237] The results are shown in Table 2.

[0238] [Examples 2 to 6]

[0239] Except for changing the composition of the raw materials as shown in Table 2, the same procedure as in Example 1 was performed to prepare acrylic adhesive sheets (2b) to (6b) having an acrylic adhesive layer composed of an acrylic adhesive (2b) to (6b) and an acrylic adhesive composition (2b) to (6b). These were aged at 50°C for 1 day.

[0240] The results are shown in Table 2.

[0241] [Comparative Examples 1 to 6]

[0242] Except for changing the composition of the raw materials as shown in Table 2, the same procedure as in Example 1 was performed to prepare acrylic adhesive sheets (C1b) to (C6b) having an acrylic adhesive layer composed of an acrylic adhesive (C1b) to (C6b) and an acrylic adhesive composition (C1b) to (C6b). These were aged at 50°C for 1 day.

[0243] The results are shown in Table 2.

[0244]

[0245] Industrial applicability

[0246] The acrylic adhesive and acrylic adhesive sheet according to an embodiment of the present invention can be used in so-called flexible devices, such as foldable devices or rollable devices.

Claims

Claim 1 An acrylic adhesive composition comprising an acrylic polymer (A) having a weight-average molecular weight Mw of 500,000 or more, an acrylic oligomer (B) having a weight-average molecular weight Mw of 1,000 to 30,000, and a crosslinking agent (C); wherein the amount of the acrylic oligomer (B) per 100 parts by weight of the acrylic polymer (A) is 0.01 parts by weight or more and less than 10 parts by weight; wherein the acrylic polymer (A) is obtained by polymerizing a monomer component (M), and the monomer component (M) comprises an alkyl (meth)acrylate (m1) having an alkyl group having 6 to 9 carbon atoms as an ester portion, wherein the content ratio of the alkyl (meth)acrylate having an alkyl group selected from the group consisting of an ethyl group and a tert-butyl group as an ester portion in the alkyl (meth)acrylate (m1) is less than 80% by weight, and wherein the monomer component (M) An acrylic adhesive composition having a content of less than 0.5 weight% of N-vinyl-2-pyrrolidone. Claim 2 An acrylic adhesive composition according to claim 1, wherein the content ratio of the alkyl (meth)acrylate (m1) in the monomer component (M) is 40% by weight or more. Claim 3 An acrylic adhesive composition according to claim 1, wherein the monomer component (M) comprises a hydroxyl group-containing monomer (m2). Claim 4 An acrylic adhesive composition according to claim 3, wherein the content ratio of the hydroxyl group-containing monomer (m2) in the monomer component (M) is 0.1 weight% or more. Claim 5 An acrylic adhesive composition according to claim 1, wherein the content ratio of an alkyl (meth)acrylate having an alkyl group having 10 or more carbon atoms as an ester portion in the monomer component (M) is less than 0.5 weight%. Claim 6 An acrylic adhesive composition according to claim 1, wherein the glass transition temperature Tg calculated by the FOX formula of the acrylic oligomer (B) is 50°C to 170°C. Claim 7 An acrylic adhesive composition according to claim 1, wherein the amount of the crosslinking agent (C) per 100 parts by weight of the acrylic polymer (A) is 0.01 to 5.00 parts by weight. Claim 8 An acrylic adhesive composition according to claim 1, wherein the glass transition temperature Tg obtained by dynamic viscoelasticity measurement is less than -37.5℃. Claim 9 An acrylic adhesive formed from an acrylic adhesive composition described in any one of claims 1 to 8. Claim 10 An acrylic adhesive sheet comprising an acrylic adhesive layer composed of the acrylic adhesive described in claim 9. Claim 11 A flexible device comprising an acrylic adhesive sheet as described in claim 10.

Images