Acrylic adhesives, acrylic adhesive sheets, and flexible devices

Abstract

The present invention provides an acrylic adhesive that, when a laminate formed by bonding an acrylic adhesive sheet containing an acrylic adhesive to an adherend is repeatedly bent under low pressure, can suppress the generation of air bubbles between the acrylic adhesive sheet and the adherend, even if fine particles are present between the acrylic adhesive sheet and the adherend. [Solution] The acrylic adhesive according to an embodiment of the present invention is an acrylic adhesive formed from an acrylic adhesive composition, wherein the acrylic adhesive composition comprises an acrylic polymer (A) as a base polymer and a crosslinking agent, the Tg of the acrylic polymer (A) calculated by the FOX formula is less than -50°C, the creep measured under specific conditions is 1.0% or more and less than 8.0%, and the adhesive strength to a polyimide film under specific conditions is 8.0 N / 25 mm or more.

Description

Technical Field

[0006] ,

[0007] ,

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

Background Art

[0002] Acrylic adhesive sheets are used for reinforcing members of various shapes and surface protection.

[0003] For example, an adhesive sheet is used for reinforcing the substrate of a semiconductor element (e.g., a TFT substrate, etc.). When joining an integrated circuit (IC) or a flexible printed circuit board (FPC) to the substrate of a semiconductor element, thermal compression bonding is usually performed using an anisotropic conductive film (ACF). When performing such thermal compression bonding, in some cases, an acrylic adhesive sheet is previously bonded to the back side of the substrate of the semiconductor element for reinforcement (e.g., Patent Document 1).

[0004] In addition, acrylic adhesive sheets are used for reinforcing so-called flexible devices such as foldable devices and rollable devices.

[0005] Typically, a flexible device is manufactured by forming a flexible substrate on a support substrate (e.g., carrier glass), forming a display layer on the flexible substrate, and finally peeling the flexible substrate from the support substrate. The display layer is formed, for example, by forming a TFT substrate on the flexible substrate and further forming an organic EL layer thereon.

[0006] However, the display layer formed on the flexible substrate is very thin. Therefore, the display layer is easily damaged during manufacturing such as during the peeling process, and defects are likely to occur in the obtained flexible device. To suppress the occurrence of such defects, in some cases, an acrylic adhesive sheet is bonded to the back side of the display layer for reinforcement (e.g., Patent Document 2).

[0007] Flexible devices can be repeatedly bent. Therefore, if the bending properties of the adhesive sheet are poor, the recovery after repeated bending will deteriorate, or in the worst case, the sheet may break due to repeated bending. Against this backdrop, acrylic adhesive sheets with good bending properties have been developed and reported in recent years (for example, Patent Documents 3 and 4). [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Patent No. 5600039 [Patent Document 2] Patent No. 6376271 [Patent Document 3] Patent No. 6993543 [Patent Document 4] Japanese Patent Publication No. 2024-052821 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] However, our research has revealed that even conventional acrylic adhesive sheets, which are considered to have good flexibility, have a problem in that air bubbles form between them and the adherend when bent in a low-pressure environment. Such bending of acrylic adhesive sheets in a low-pressure environment is a situation that can be expected, for example, in flexibility confirmation tests during the manufacturing process or when flexible devices containing acrylic adhesive sheets are used in a low-pressure environment (for example, in high-altitude areas).

[0010] Further research by the inventors revealed that the bubbles described above become particularly noticeable when fine particles are present between the acrylic adhesive sheet and the adherend. Such fine particles are thought to include, for example, foreign matter generated during the manufacturing process, components in the substrate or precipitates from the substrate, particles derived from the peel-off liner that has peeled off from the acrylic adhesive surface (such as silica particles), and components in the acrylic adhesive or precipitates from the acrylic adhesive.

[0011] The object of the present invention is to provide an acrylic adhesive that, when a laminate formed by bonding an acrylic adhesive sheet containing an acrylic adhesive to an adherend is repeatedly bent in a low-pressure environment, can suppress the generation of air bubbles between the acrylic adhesive sheet and the adherend, even if fine particles are present between the acrylic adhesive sheet and the adherend. Furthermore, the invention aims to provide an acrylic adhesive sheet containing such an acrylic adhesive. Additionally, it aims to provide a flexible device containing such an acrylic adhesive, and a flexible device containing such an acrylic adhesive sheet. [Means for solving the problem]

[0012] [1] The acrylic adhesive according to the embodiment of the present invention is An acrylic adhesive formed from an acrylic adhesive composition, The acrylic adhesive composition comprises an acrylic polymer (A) as a base polymer and a crosslinking agent. The Tg of the acrylic polymer (A), calculated by FOX's formula, is less than -50°C. The creep measured by pressing a 2mm diameter spherical indenter into the PET resin substrate surface of a laminate of the acrylic adhesive in layer form and a PET resin substrate with a thickness of 50μm at a measurement temperature of 25℃, an indentation load of 500mN, an indentation time of 20 seconds, and an indentation holding time of 5 seconds was 1.0% or more and less than 8.0%. At 23°C, with a peeling angle of 180 degrees and a peeling speed of 300 mm / min, the adhesive strength of the acrylic adhesive to the polyimide film is 8.0 N / 25 mm or more. [2] In the acrylic adhesive described in [1] above, the amount of the crosslinking agent in the acrylic adhesive composition may be 0.010 parts by weight to 5.000 parts by weight per 100 parts by weight of the acrylic polymer (A). [3] In the acrylic adhesive described in [1] or [2] above, the acrylic adhesive composition may contain an acrylic oligomer having a weight-average molecular weight Mw of 1,000 to 30,000. [4] In the acrylic adhesive described in [3] above, the content of the acrylic oligomer in the acrylic adhesive composition may be 0.1 to 20 parts by weight per 100 parts by weight of the acrylic polymer (A). [5] In the acrylic adhesive described in any one of the above items [1] to [4], the acrylic polymer (A) may be obtained by polymerizing the monomer component (M). [6] In the acrylic adhesive described in [5] above, the monomer component (M) may contain an alkyl (meth)acrylate (m1) having an alkyl group having 6 to 10 carbon atoms as an ester portion in an amount of 40% to 90% by weight. [7] In the acrylic adhesive described in [6] above, the Tg of the alkyl (meth)acrylate (m1) homopolymer may be in the range of -75°C to -55°C. [8] In the acrylic adhesive described in [6] or [7] above, the alkyl group may be a linear alkyl group. [9] In the acrylic adhesive described in any one of the above items [5] to [8], the monomer component (M) may include an alkyl (meth)acrylate (m2) having an alkyl group having 1 to 5 carbon atoms as an ester portion.

[10] In the acrylic adhesive described in [9] above, the glass transition temperature Tg of the alkyl (meth)acrylate (m2) homopolymer may be in the range of -60°C to less than -40°C.

[11] In the acrylic adhesive described in [9] or

[10] above, the content ratio of the alkyl (meth)acrylate (m2) in the monomer component (M) may be 1% by weight to 55% by weight.

[12] In the acrylic adhesive described in any one of the above items [5] to

[11] , the monomer component (M) may contain a hydroxyl group-containing monomer (m3).

[13] In the acrylic adhesive described in

[12] above, the Tg of the homopolymer of the hydroxyl group-containing monomer (m3) may be in the range of -60°C to -10°C.

[14] In the acrylic adhesive described in

[12] or

[13] above, the content ratio of the hydroxyl group-containing monomer (m3) in the monomer component (M) may be 0.01% by weight to 30% by weight.

[15] The acrylic adhesive sheet according to an embodiment of the present invention includes an acrylic adhesive layer composed of the acrylic adhesive described in any one of [1] to

[14] above.

[16] In the acrylic adhesive sheet described in

[15] above, the thickness of the acrylic adhesive layer may be 30 μm or less.

[17] The flexible device according to an embodiment of the present invention includes the acrylic adhesive sheet described in

[15] or

[16] above. [Effect of the Invention]

[0013] According to the present invention, when a laminate obtained by bonding an adhesive surface of an acrylic adhesive sheet containing an acrylic adhesive to an adherend is repeatedly bent in a low-pressure environment, even if fine particles are present between the acrylic adhesive sheet and the adherend, generation of bubbles between the acrylic adhesive sheet and the adherend can be suppressed, and the acrylic adhesive can be provided. Further, an acrylic adhesive sheet containing such an acrylic adhesive can be provided. Furthermore, a flexible device containing such an acrylic adhesive and a flexible device containing such an acrylic adhesive sheet can be provided. [Brief Description of the Drawings]

[0014] [Figure 1] FIG. 1 is a schematic cross-sectional view showing one embodiment of the flexible device of the present invention, and shows one usage form of the adhesive sheet according to the embodiment of the present invention. [Figure 2] FIG. 2 is a schematic explanatory view for explaining the preparation of a test piece in a reduced-pressure bending test. [Modes for Carrying Out the Invention]

[0015] Where the term "acrylic" is used herein, it means "acrylic and / or methacrylic." Where the term "(meth)acrylic" is used herein, it means "acrylic and / or methacrylic." Where the term "(meth)acrylate" is used herein, it means "acrylate and / or methacrylate." Where the term "(meth)allyl" is used herein, it means "allyl and / or methallyl." Where the term "(meth)acrolein" is used herein, it means "acrolein and / or methcrolein." Where the term "acid (salt)" is used herein, it means "acid and / or its salt." Examples of salts include alkali metal salts and alkaline earth metal salts, specifically, for example, sodium salts and potassium salts.

[0016] ≪≪1. Acrylic adhesive≫≫ The acrylic adhesive according to the embodiment of the present invention is formed from an acrylic adhesive composition.

[0017] Acrylic adhesives can thus be defined as those formed from acrylic adhesive compositions. Acrylic adhesives can be formed when acrylic adhesive compositions undergo crosslinking reactions such as heating or ultraviolet irradiation, and it is impossible and impractical to directly identify acrylic adhesives by their structure. For this reason, acrylic adhesives can be appropriately identified as "things" by the definition "those formed from acrylic adhesive compositions."

[0018] When an acrylic adhesive is formed from an acrylic adhesive composition, any suitable method can be used to form the acrylic adhesive, provided that it does not impair the effects of the present invention. Examples of such methods for forming an acrylic adhesive include: applying an acrylic adhesive composition onto a suitable substrate, heating and drying as necessary, and curing as necessary to form an acrylic adhesive on the substrate; applying an acrylic adhesive composition onto a suitable film such as a release liner, heating and drying as necessary, and curing as necessary to form an acrylic adhesive on the film; and then transferring a suitable substrate onto the acrylic adhesive to form an acrylic adhesive on the substrate. Any suitable means can be used for such application, provided that it does not impair the effects of the present invention. Examples of such application means 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. The heating and drying of the acrylic adhesive composition can be carried out by any suitable means, as long as it does not impair the effects of the present invention. For example, heating to 60°C to 180°C is one such heating and drying method. The curing of the acrylic adhesive composition can be carried out by any suitable means, as long as it does not impair the effects of the present invention. For example, curing methods include heat, ultraviolet irradiation, laser irradiation, alpha-ray irradiation, beta-ray irradiation, gamma-ray irradiation, X-ray irradiation, and electron beam irradiation.

[0019] The inventors investigated whether there was an appropriate indicator to show the degree of bubble generation between an acrylic adhesive sheet containing an acrylic adhesive and a substrate when the laminate is repeatedly bent under low pressure conditions, particularly when fine particles are present between the acrylic adhesive sheet and the substrate. They hypothesized that the durability of the acrylic adhesive against compression and expansion in the thickness direction might be related to the generation of bubbles when repeatedly bent under low pressure conditions, and conducted further investigations. As a result, they found that creep, measured by pressing a small-diameter indenter into the surface of the substrate under specific conditions, can serve as an indicator of the degree of bubble generation in a laminate of layered acrylic adhesive and a substrate.

[0020] In other words, the creep measured by pressing a 2 mm diameter spherical indenter into the PET resin substrate surface of a laminate of the acrylic adhesive in layer form and a PET resin substrate with a thickness of 50 μm at a measurement temperature of 25°C, an indentation load of 500 mN, an indentation time of 20 seconds, and an indentation holding time of 5 seconds is typically 1.0% or more and less than 8.0%, but may also be 1.0% or more and less than 7.5%, 1.0% or more and less than 7.0%, 1.0% or more and less than 6.5%, or 1.0% or more and less than 6.0%. If the creep is within the above range, the effects of the present invention can be more fully expressed, and when a laminate formed by bonding the adhesive surface of an acrylic adhesive sheet containing such an acrylic adhesive to an adherend is repeatedly bent in a low-pressure environment, even if fine particles are present between the acrylic adhesive sheet and the adherend, the generation of air bubbles between the acrylic adhesive sheet and the adherend can be effectively suppressed.

[0021] When the above-mentioned creep is within the above range, the acrylic adhesive becomes moderately soft in terms of compression and expansion in the thickness direction, but maintains a moderate hardness without becoming excessively soft. Therefore, when an acrylic adhesive sheet and an adherend are bonded together with fine particles interposed between them, the moderately soft acrylic adhesive deforms to enclose the fine particles and adhere closely to the adherend, thereby suppressing the generation of large air bubbles. Furthermore, even if minute air bubbles remaining around the fine particles, which are difficult to observe visually, expand due to repeated bending in a low-pressure environment, the acrylic adhesive, as described above, possesses a moderate hardness without being excessively soft, and can crush the minute air bubbles that are trying to expand with its moderately hard acrylic adhesive. As a result, the effects of the present invention can be realized.

[0022] If the above creep value is too large, from the viewpoint of solving the problems of the present invention, the acrylic adhesive becomes too soft in terms of compression and expansion in the thickness direction. Therefore, when minute air bubbles that are difficult to observe with the naked eye remaining around the fine particles expand due to repeated bending in a low-pressure environment, the acrylic adhesive may not be able to suppress the expansion of the air bubbles because it is too soft as described above, and furthermore, it may become difficult to crush the air bubbles that are trying to expand around the fine particles.

[0023] If the above creep value is too small, from the viewpoint of solving the problems of the present invention, the acrylic adhesive becomes too hard in terms of compression and expansion in the thickness direction. As a result, the acrylic adhesive becomes less able to deform to follow the shape of the fine particles, and the acrylic adhesive cannot deform to enclose the fine particles and adhere to the substrate, which may lead to the generation of large air bubbles. Furthermore, if the acrylic adhesive becomes too hard as described above, the adhesive strength may decrease, which can also cause air bubbles to form.

[0024] The acrylic adhesive according to the embodiment of the present invention has an adhesive strength to a polyimide film of 8.0 N / 25 mm or more at 23°C, with a peeling angle of 180 degrees and a peeling speed of 300 mm / min, but may also be 8.5 N / 25 mm or more, 9.0 N / 25 mm or more, 9.5 N / 25 mm or more, or 10.0 N / 25 mm or more. The upper limit of the adhesive strength is preferable as long as it is high, but in reality, from the viewpoint of handling and the like, it is, for example, 40 N / 25 mm or less. If the adhesive strength is within the above range, the effects of the present invention can be more fully expressed, and when a laminate formed by bonding the adhesive surface of an acrylic adhesive sheet containing such an acrylic adhesive to an adherend is repeatedly bent in a low-pressure environment, even if fine particles are present between the acrylic adhesive sheet and the adherend, the generation of air bubbles between the acrylic adhesive sheet and the adherend can be effectively suppressed.

[0025] The acrylic adhesive composition contains an acrylic polymer (A) as a base polymer and a crosslinking agent.

[0026] The content of the acrylic polymer (A) in the acrylic adhesive composition is preferably 50% by weight or more in terms of solid content, in order to better exhibit the effects of the present invention, and may be 70% to 99.999% by weight, 80% to 99.99% by weight, 90% to 99.9% by weight, or 92% to 99% by weight.

[0027] The amount of crosslinking agent in the acrylic adhesive composition is preferably 0.010 to 5.000 parts by weight per 100 parts by weight of acrylic polymer (A), but may also be 0.030 to 3.000 parts by weight, 0.050 to 1.000 parts by weight, 0.070 to 0.500 parts by weight, 0.075 to 0.250 parts by weight, 0.080 to 0.200 parts by weight, 0.080 to 0.175 parts by weight, 0.085 to 0.175 parts by weight, or 0.090 to 0.160 parts by weight, in order to better exhibit the effects of the present invention.

[0028] ≪1-1. Acrylic polymer (A)≫ The acrylic polymer (A) may be of one type or two or more types.

[0029] The weight-average molecular weight Mw of the acrylic polymer (A) is preferably 2.5 million or less, but may be between 500,000 and 2.4 million, between 500,000 and 2.3 million, between 500,000 and 2.2 million, or between 500,000 and 2.1 million. The method for measuring the weight-average molecular weight Mw will be described in detail later.

[0030] The acrylic polymer (A) typically has a Tg calculated by FOX's formula that is less than -50°C, but may be -80°C or higher but less than -50°C, -75°C or higher but less than -50°C, -70°C or higher but less than -50°C, -68°C or higher but less than -52°C, -66°C or higher but less than -54°C, or -65°C or higher but less than -55°C. If the Tg value calculated by FOX's formula for the acrylic polymer (A) is too high, the resulting acrylic adhesive may have poor flexibility at low temperatures, and for example, repeated bending at low temperatures may cause breakage. If the Tg value calculated by FOX's formula for the acrylic polymer (A) is too low, the resulting acrylic adhesive may have poor adhesive performance, and it may be impossible to achieve both flexibility and adhesive strength.

[0031] The Tg of an acrylic polymer (A), calculated using the FOX formula, is the value obtained from the FOX formula based on the Tgi of the homopolymer of each monomer i constituting the acrylic polymer (A) and the weight fraction (weight-based copolymerization ratio) Wi of the monomer i. The FOX formula is a relationship between the Tg of a copolymer and the glass transition temperature Tgi of the homopolymer obtained by homopolymerizing each monomer i constituting the copolymer, as shown below. 1 / Tg = Σ(Wi / Tgi)

[0032] 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 (weight-based copolymerization ratio), and Tgi represents the glass transition temperature of the homopolymer of each monomer i (unit: K).

[0033] Unless otherwise specified herein, the Tg of homopolymers may be the values ​​listed in publicly available documents, for example, the values ​​listed in the "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989). If multiple values ​​are listed in the "Polymer Handbook," the conventional value shall be adopted. For monomers not listed in the "Polymer Handbook," the catalog values ​​of the monomer manufacturers shall be adopted. For monomer homopolymers that are not listed in the "Polymer Handbook" and for which no catalog values ​​are provided by monomer manufacturers, the Tg obtained by the measurement method described in Japanese Patent Publication No. 2007-51271 shall be used. The above explanation may also be applied to the Tg of monomer homopolymers described later.

[0034] The acrylic polymer (A) is preferably obtained by polymerizing a monomer component (M).

[0035] Acrylic polymer (A) can thus be defined as something obtained by polymerizing monomer component (M). Acrylic polymer (A) can become acrylic polymer (A) when monomer component (M) undergoes a polymerization reaction, and it may be impossible and impractical to directly identify acrylic polymer (A) by its structure. For this reason, acrylic polymer (A) can be appropriately identified as a "substance" by the definition "something obtained by polymerizing monomer component (M)".

[0036] The monomer component (M) preferably contains an alkyl (meth)acrylate (m1) having an alkyl group with 6 to 10 carbon atoms as an ester portion in an amount of 40% to 90% by weight, in order to better express the effects of the present invention.

[0037] The alkyl (meth)acrylate (m1) may be one type or two or more types.

[0038] The number of carbon atoms in the alkyl group of the ester portion of alkyl(meth)acrylate (m1) is typically 6 to 10, as described above, but may also be 7 to 10, 7 to 9, 6 to 9, or 6 to 8.

[0039] The content of alkyl (meth)acrylate (m1) in the monomer component (M) may be 40% to 85% by weight, 45% to 80% by weight, 50% to 75% by weight, or 50% to 70% by weight.

[0040] Preferably, the alkyl (meth)acrylate (m1) is an alkyl (meth)acrylate whose homopolymer Tg is in the range of -75°C to -55°C. It is presumed that by using an alkyl (meth)acrylate (m1) whose homopolymer Tg is within the specific range of -75°C to -55°C, the resulting acrylic adhesive will be easier to achieve both sufficient flexibility so that the surrounding material does not break when bent in a low-temperature environment and sufficient adhesion so that it does not peel off the adherend when bent in a high-temperature environment, thereby allowing the effects of the present invention to be more fully realized. The Tg of the alkyl (meth)acrylate (m1) homopolymer may be -72°C to -57°C, -70°C to -58°C, -70°C to -59°C, or above -70°C and below -60°C.

[0041] The C6-C10 alkyl group in the ester portion of the alkyl(meth)acrylate (m1) is preferably a linear alkyl group. It is presumed that by having a linear alkyl group in the ester portion of the alkyl(meth)acrylate (m1), the polymer molecules in the resulting acrylic adhesive will intertwine appropriately while lowering the Tg, thereby making it easier to achieve both sufficient flexibility so that the surrounding material does not break when bent in a low-temperature environment and appropriate cohesive force so that cohesive failure does not occur when bent in a high-temperature environment, and thus the effects of the present invention can be more fully realized.

[0042] For the reasons mentioned above, the alkyl (meth)acrylate (m1) is particularly preferably an alkyl (meth)acrylate having a linear alkyl group with 6 to 10 carbon atoms as the ester portion, and the Tg of its homopolymer being in the range of -75°C to -55°C. In this case, the number of carbon atoms in the linear alkyl group may be 7 to 10, 7 to 9, 6 to 9, or 6 to 8. Furthermore, the Tg of the alkyl (meth)acrylate (m1) homopolymer in this case may be -72°C to -57°C, -70°C to -58°C, -70°C to -59°C, or above -70°C and below -60°C.

[0043] Examples of alkyl (meth)acrylates (m1) include n-hexyl acrylate (HxA, the alkyl group in the ester portion is a linear alkyl group with 6 carbon atoms) (Tg of its homopolymer = -60°C), n-octyl acrylate (NOAA, the alkyl group in the ester portion is a linear alkyl group with 8 carbon atoms) (Tg of its homopolymer = -65°C), 2-ethylhexyl acrylate (2EHA, the alkyl group in the ester portion is a branched alkyl group with 8 carbon atoms) (Tg of its homopolymer = -70°C), isononyl acrylate (INAA, the alkyl group in the ester portion is a branched alkyl group with 9 carbon atoms) (Tg of its homopolymer = -58°C), and isodecyl acrylate (IDAA, the alkyl group in the ester portion is a branched alkyl group with 10 carbon atoms) (Tg of its homopolymer = -62°C).

[0044] The monomer component (M) may include an alkyl (meth)acrylate (m2) having an alkyl group with 1 to 5 carbon atoms as the ester portion.

[0045] The alkyl (meth)acrylate (m2) may be one type or two or more types.

[0046] The number of carbon atoms in the alkyl group of the ester portion of alkyl(meth)acrylate(m2) is typically 1 to 5, as described above, but it may also be 2 to 5 or 3 to 5.

[0047] The alkyl (meth)acrylate (m2) is preferably an alkyl (meth)acrylate in which the Tg of the homopolymer is in the range of -60°C to less than -40°C.

[0048] By appropriately using alkyl (meth)acrylate (m2) in combination with alkyl (meth)acrylate (m1) as the monomer component (M), the appropriate softness of the resulting acrylic adhesive in terms of compression and expansion in the thickness direction (softness that is not excessively soft but maintains an appropriate level of hardness) can be further optimized, and as a result, the effects of the present invention can be more fully realized.

[0049] The content of alkyl (meth)acrylate (m2) in the monomer component (M) is preferably 55% by weight or less, and may be 1% to 55% by weight, 5% to 50% by weight, 10% to 45% by weight, 15% to 42% by weight, or 20% to 40% by weight.

[0050] Examples of alkyl (meth)acrylates (m2) include n-butyl acrylate (BA) (with a Tg of its homopolymer at -55°C).

[0051] The monomer component (M) may include a hydroxyl group-containing monomer (m3).

[0052] The hydroxyl group-containing monomer (m3) may be one type or two or more types.

[0053] By appropriately combining a hydroxyl group-containing monomer (m3) with an alkyl (meth)acrylate (m1) as the monomer component (M), the appropriate softness (softness that is not excessively soft but maintains an appropriate hardness) in terms of compression and expansion in the thickness direction of the acrylic adhesive obtained due to the presence of hydroxyl groups that act as reaction sites with the crosslinking agent can be further optimized, and the effects of the present invention can be further realized. Furthermore, high adhesion to the adherend can be achieved due to the presence of hydroxyl groups that interact with the adherend, and the effects of the present invention can be further realized.

[0054] The content of the hydroxyl group-containing monomer (m3) in the monomer component (M) is preferably 30% by weight or less, and may be 0.01% to 30% by weight, 0.05% to 25% by weight, 0.1% to 20% by weight, 0.5% to 17% by weight, 1% to 15% by weight, or 3% to 12% by weight.

[0055] Examples of hydroxyl group-containing monomers (m3) 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.

[0056] As the hydroxyl group-containing monomer (m3), a hydroxyl group-containing monomer whose homopolymer Tg is in the range of -60°C to -10°C may be used. By using a hydroxyl group-containing monomer whose homopolymer Tg is in the range of -60°C to -10°C as the hydroxyl group-containing monomer (m3), in addition to the effects mentioned above due to the presence of hydroxyl groups, the appropriate softness (softness that is not excessively soft but maintains an appropriate hardness) of the resulting acrylic adhesive in terms of compression and expansion in the thickness direction can be further optimized, and as a result, the effects of the present invention can be more fully realized.

[0057] Examples of hydroxyl group-containing monomers (m3) include 2-hydroxyethyl acrylate (2HEA) (Tg = -15°C for its homopolymer) and 4-hydroxybutyl acrylate (4HBA) (Tg = -32°C for its homopolymer).

[0058] The monomer component (M) may include other alkyl (meth)acrylates (m4) other than alkyl (meth)acrylate (m1) and alkyl (meth)acrylate (m2), as long as the effects of the present invention are not impaired.

[0059] The other alkyl (meth)acrylate (m4) may be one type or two or more types.

[0060] The content of other alkyl (meth)acrylates (m4) in the monomer component (M) is, for example, 15% by weight or less, and may be 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.

[0061] The monomer component (M) may include other monomers (m5) other than alkyl (meth)acrylate (m1), alkyl (meth)acrylate (m2), hydroxyl group-containing monomer (m3), and other alkyl (meth)acrylate (m4), as long as the effects of the present invention are not impaired.

[0062] The other monomer (m5) may be one type or two or more types.

[0063] Other monomers (m5) include, for example, carboxyl group-containing monomers such as (meth)acrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, isocrotonic acid, and their acid anhydrides (e.g., acid anhydride group-containing monomers such as maleic anhydride and itaconic anhydride); (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-methylol(meth)acrylamide, N-methoxymethyl(meth)acrylamide, N-butoxymethyl(meth)acrylamide, N-hydroxyethyl(meth)acrylamide, etc. Any amide group-containing monomer; amino group-containing monomers such as (meth)aminoethyl acrylate, (meth)dimethylaminoethyl acrylate, and (meth)butylaminoethyl acrylate; epoxy group-containing monomers such as (meth)glycidyl acrylate and (meth)methylglycidyl acrylate; cyano group-containing monomers such as acrylonitrile and methacrylonitrile; N-vinyl-2-pyrrolidone, (meth)acryloylmorpholine, N-vinylpiperidone, N-vinylpiperazine, N-vinylpyrrole, and N-vinylimidazole Examples include: heterocyclic vinyl monomers such as vinylpyridine, vinylpyrimidine, and vinyloxazole; sulfonic acid group-containing monomers such as sodium vinylsulfonate; phosphoric acid group-containing monomers such as 2-hydroxyethyl acryloyl phosphate; imide group-containing monomers such as cyclohexyl maleimide and isopropyl maleimide; isocyanate group-containing monomers such as 2-methacryloyloxyethyl isocyanate; (meth)acrylic acid esters having alicyclic hydrocarbon groups such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate; (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 and dienes such as ethylene, butadiene, isoprene, and isobutylene; vinyl ethers such as vinyl alkyl ethers; and vinyl chloride.

[0064] Other monomers (m5) may also be used, including polyfunctional monomers. A polyfunctional monomer is a monomer having two or more ethylenically unsaturated groups in one molecule. Any suitable ethylenically unsaturated group can be used as the ethylenically unsaturated group, 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.

[0065] Other monomers (m5) that can be used include alkoxyalkyl esters of (meth)acrylate. Examples of alkoxyalkyl esters of (meth)acrylate include 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, methoxytriethylene glycol (meth)acrylate, 3-methoxypropyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 4-methoxybutyl (meth)acrylate, and 4-ethoxybutyl (meth)acrylate.

[0066] The content of other monomers (m5) in monomer component (M) is, for example, 15% by weight or less, and may be 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.

[0067] As a method for preparing the acrylic polymer (A), various polymerization methods known as synthesis methods for acrylic polymers, such as solution polymerization, emulsion polymerization, bulk polymerization, and suspension polymerization, can be appropriately employed. Among these polymerization methods, solution polymerization is preferably used. As a method for supplying monomers when performing solution polymerization, a batch supply method in which the entire amount of monomer components is supplied at once, a continuous supply (dropping) method, a divided supply (dropping) method, etc., can be appropriately employed. The polymerization temperature can 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, but may also be 30°C to 170°C, 35°C to 160°C, or 40°C to 140°C. As a method for preparing the acrylic polymer (A), active energy ray irradiation polymerization such as photopolymerization (typically performed in the presence of a photopolymerization initiator) by irradiation with light such as UV, or radiation polymerization (perhaps performed by irradiation with radiation such as beta rays or gamma rays) may be employed.

[0068] The solvent used for solution polymerization (polymerization solvent) can be appropriately selected from any suitable organic solvent. 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 and cyclohexane.

[0069] The polymerization initiator used can be appropriately selected from any suitable polymerization initiator depending on the type of polymerization method. There may be only one polymerization initiator or two or more.

[0070] Examples of polymerization initiators include thermal polymerization initiators and photopolymerization initiators.

[0071] Thermal polymerization initiators can typically be used when obtaining acrylic polymers (A) by solution polymerization. Examples of such thermal polymerization initiators include 2,2'-azobisisobutyronitrile (AIBN), 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis(2-methylpropionic acid)dimethyl, 4,4'-azobis-4-cyanovaleric acid, azobisisovaleronitrile, 2,2'-azobis(2-amidinopropane)dihydrochloride, and 2,2'-azobis[2-(5-methyl-2-imidazoline-2-yl)pro Azo initiators such as pan-dihydrochloride, 2,2'-azobis(2-methylpropionamidine) disulfate, 2,2'-azobis(N,N'-dimethylene isobutylamidine), and 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine]hydrate (VA-057, manufactured by Wako Pure Chemical Industries, Ltd.); persulfates such as potassium persulfate and ammonium persulfate, and di(2-ethylhexyl) peroxydicarbonate. Examples include peroxide initiators such as di(4-t-butylcyclohexyl)peroxydicarbonate, di-sec-butylperoxydicarbonate, t-butylperoxyneodecanoate, t-hexylperoxypivalate, t-butylperoxypivalate, dilauroyl peroxide, di-n-octanoyl peroxide, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, di(4-methylbenzoyl)peroxide, dibenzoyl peroxide, t-butylperoxyisobutyrate, 1,1-di(t-hexylperoxy)cyclohexane, t-butylhydroperoxide, and hydrogen peroxide; redox initiators combining peroxides with reducing agents, such as combinations of persulfates and sodium bisulfite, and combinations of peroxides and sodium ascorbate; substituted ethane initiators such as phenyl-substituted ethane; and aromatic carbonyl compounds.

[0072] Photopolymerization initiators can preferably be used when obtaining acrylic polymers by active energy ray 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.

[0073] 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-(t-butyl)dichloroacetophenone. Examples of α-ketol-based photopolymerization initiators include 2-methyl-2-hydroxypropiophenone and 1-[4-(2-hydroxyethyl)phenyl]-2-methylpropan-1-one. An example of an aromatic sulfonyl chloride-based photopolymerization initiator is 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, benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, polyvinylbenzophenone, and α-hydroxycyclohexylphenyl ketone. Examples of ketal-based photopolymerization initiators include benzyldimethylketal. Examples of thioxanthone-based photopolymerization initiators include thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-diisopropylthioxanthone, and dodecylthioxanthone.

[0074] The amount of polymerization initiator used can be any appropriate amount, as long as it does not impair the effects of the present invention. Such an amount may be, for example, 0.001 to 10 parts by weight, 0.005 to 5 parts by weight, 0.01 to 3 parts by weight, or 0.05 to 1 part by weight per 100 parts by weight of monomer component (M).

[0075] During polymerization, any other suitable additives may be added, provided that they do not impair the effects of the present invention.

[0076] ≪1-2. Crosslinking Agents≫ The acrylic adhesive composition contains a crosslinking agent. The crosslinking agent may be one type or two or more types. The content of the crosslinking agent in the acrylic adhesive composition is as described above.

[0077] Examples of crosslinking agents 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, and peroxides. Preferably, at least one isocyanate-based crosslinking agent selected from the group consisting of isocyanate-based crosslinking agents, epoxy-based crosslinking agents, and peroxides, as this can better express the effects of the present invention.

[0078] Isocyanate-based crosslinking agents can be compounds having two or more isocyanate groups (including isocyanate-regenerating polar groups in which isocyanate groups are temporarily protected by a blocking agent or quantification, etc.) in one molecule. 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.

[0079] Examples of isocyanate crosslinking agents include: 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 adduct (e.g., manufactured by Tosoh Corporation, trade name: Coronate L), trimethylolpropane / hexamethylene diisocyanate trimer adduct (e.g., manufactured by Tosoh Corporation, trade name: Coronate HL), and isocyanurate derivatives of hexamethylene diisocyanate (e.g., manufactured by Tosoh Corporation, trade name: Coronate HX); xyl Examples include trimethylolpropane adducts of reylene diisocyanate (e.g., Mitsui Chemicals, trade name: Takenate D110N), trimethylolpropane adducts of xylylene diisocyanate (e.g., Mitsui Chemicals, trade name: Takenate D120N), trimethylolpropane adducts of isophorone diisocyanate (e.g., Mitsui Chemicals, trade name: Takenate D140N), trimethylolpropane adducts of hexamethylene diisocyanate (e.g., Mitsui Chemicals, trade name: Takenate D160N), trimethylolpropane adducts of tolylene diisocyanate (e.g., Mitsui Chemicals, trade name: Takenate D101E); polyether polyisocyanates, polyester polyisocyanates, and adducts thereof with various polyols; and polyfunctionalized polyisocyanates with isocyanurate bonds, biuret bonds, allophanate bonds, etc.

[0080] As epoxy crosslinking agents, polyfunctional epoxy compounds having two or more epoxy groups in one molecule can be used. Examples of epoxy crosslinking agents include N,N,N',N'-tetraglycidyl-m-xylenediline, 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, and sorbitol polyglycidyl ether. Examples of epoxy crosslinking agents include tel, glycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitan polyglycidyl ether, trimethylolpropane polyglycidyl ether, diglycidyl adipate ester, diglycidyl o-phthalate ester, triglycidyl-tris(2-hydroxyethyl) isocyanurate, resorcinol diglycidyl ether, bisphenol-S-diglycidyl ether, and epoxy resins having two or more epoxy groups in the molecule. Examples of commercially available epoxy crosslinking agents include the trade names "Tetrad C" and "Tetrad X" manufactured by Mitsubishi Gas Chemical Company.

[0081] Examples of peroxides include dibenzoyl peroxide, dicumyl peroxide, di-t-butyl peroxide, di-t-butylperoxy-3,3,5-trimethylcyclohexane, t-butyl hydroperoxide, t-butylcumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)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, and t-butylperoxy Examples include neodecanoate, t-hexyl peroxypivalate, t-butyl peroxypivalate, dilauroyl peroxide, di-n-octanoyl peroxide, 1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanoate, di(4-methylbenzoyl) peroxide, t-butyl peroxyisobutyrate, 1,1-di(t-hexyl peroxy)cyclohexane, 1,1-di(t-butyl peroxy)cyclohexane, t-butyl peroxy-2-ethylhexyl carbonate, t-amyl peroxyisopropyl carbonate, 3,5,5-trimethylhexanoyl peroxide, t-butyl peroxy-2-hexanoate, t-butyl peroxypivalate, and t-hexyl peroxypivalate. Examples of commercially available peroxides include the "Nipper BMT" series and "Nipper BW" series manufactured by Nippon Oil & Fats Co., Ltd.

[0082] ≪1-3. Acrylic Oligomers≫ The acrylic adhesive composition may contain acrylic oligomers. The acrylic oligomers may be one type or two or more types.

[0083] The weight-average molecular weight (Mw) of acrylic oligomers is typically between 1,000 and 30,000, but may also be between 1,000 and 20,000, 1,500 and 10,000, or 2,000 and 8,000. The method for measuring the weight-average molecular weight (Mw) will be described in detail later.

[0084] The content of the acrylic oligomer in the acrylic adhesive composition can be set to any appropriate content as long as it does not impair the effects of the present invention. The content of the acrylic oligomer in the acrylic adhesive composition is preferably 0.1 to 20 parts by weight, but may also be 1 to 15 parts by weight, 2 to 10 parts by weight, or 3 to 8 parts by weight, per 100 parts by weight of the acrylic polymer (A).

[0085] The acrylic oligomer has a Tg calculated by the FOX formula, preferably between 20°C and 300°C, but may also be between 30°C and 300°C, or between 40°C and 300°C.

[0086] For the specific method of calculating the Tg of acrylic oligomers using the FOX formula, the description of the Tg of acrylic polymer (A) calculated using the FOX formula mentioned above can be directly applied.

[0087] As acrylic oligomers, those obtained from monomer components having a (meth)acrylic acid ester having a cyclic structure within the molecule are preferred, and those obtained from monomer components having an alkyl (meth)acrylic acid ester having a cyclic structure within the molecule and a linear or branched alkyl group are more preferred.

[0088] The (meth)acrylic acid ester having a cyclic structure within the molecule may be one type or two or more types.

[0089] The alkyl (meth)acrylate having a linear or branched alkyl group may be one type or two or more types.

[0090] In (meth)acrylic acid esters having a cyclic structure within the molecule, the cyclic structure may be either an aromatic ring or a non-aromatic ring.

[0091] Examples of aromatic rings include aromatic carbon rings (e.g., monocyclic carbon rings such as benzene rings, fused carbon rings such as naphthalene rings) and various aromatic heterocycles.

[0092] Examples of non-aromatic rings include non-aromatic aliphatic rings (non-aromatic alicyclic rings) (e.g., cycloalkane rings such as cyclopentane, cyclohexane, cycloheptane, and cyclooctane rings; cycloalkene rings such as cyclohexene rings), non-aromatic bridged rings (e.g., bicyclic hydrocarbon rings in pinane, pinene, bornane, norbornane, norbornene, etc.; triplicate or more aliphatic hydrocarbon rings (bridged hydrocarbon rings) in adamantane, etc.), and non-aromatic heterocycles (e.g., epoxy rings, oxolane rings, oxetane rings). Examples of triplicate or more aliphatic hydrocarbon rings (triplicate or more bridged hydrocarbon rings) include dicyclopentanyl group, dicyclopentenyl group, adamantyl group, tricyclopentanyl group, and tricyclopentenyl group.

[0093] Examples of (meth)acrylic acid esters having a cyclic structure within the molecule include, specifically, cycloalkyl (meth)acrylic acid esters such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, and cyclooctyl (meth)acrylate; (meth)acrylic acid esters having a bicyclic aliphatic hydrocarbon ring such as isobornyl (meth)acrylate; dicyclopentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, tricyclopentanyl (meth)acrylate, 1 Examples include (meth)acrylic acid esters having three or more aliphatic hydrocarbon rings, such as adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate; and (meth)acrylic acid esters having aromatic rings, such as aryl (meth)acrylates like phenyl (meth)acrylate, aryloxyalkyl (meth)acrylates like phenoxyethyl (meth)acrylate, and arylalkyl (meth)acrylates like benzyl (meth)acrylate.

[0094] As (meth)acrylic acid esters having a cyclic structure within the molecule, non-aromatic ring-containing (meth)acrylic acid esters are preferred in that they can better express the effects of the present invention, for example, cyclohexyl acrylate (CHA), cyclohexyl methacrylate (CHMA), dicyclopentanyl acrylate (DCPA), and dicyclopentanyl methacrylate (DCPMA), with dicyclopentanyl acrylate (DCPA) and dicyclopentanyl methacrylate (DCPMA) being preferred.

[0095] The content of (meth)acrylic acid esters having a cyclic structure within the molecule in the total monomer components that can be used to constitute the acrylic oligomer is preferably 10 to 90 parts by weight, and may be 20 to 80 parts by weight, per 100 parts by weight of the total monomer components, in order to better express the effects of the present invention.

[0096] Examples of alkyl (meth)acrylates having linear or branched alkyl groups include 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, and methyl (meth)acrylate. Examples of alkyl esters of (meth)acrylates having 1 to 20 carbon atoms in the alkyl group include isooctyl acid, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate. Among these, methyl methacrylate (MMA) is preferred in that it can better exhibit the effects of the present invention.

[0097] The content of alkyl (meth)acrylate having a linear or branched alkyl group in the total monomer components that can be used to constitute the acrylic oligomer is preferably 10 to 90 parts by weight, but may also be 20 to 80 parts by weight, or 20 to 60 parts by weight, per 100 parts by weight of the total monomer components.

[0098] The total monomer components that can be used to constitute the acrylic oligomer may include, in addition to (meth)acrylic acid esters having a cyclic structure in the molecule and (meth)acrylic acid alkyl esters having linear or branched alkyl groups, other monomers that can copolymerize with these monomers (copolymerizable monomers). The content of other monomers (copolymerizable monomers) in the total monomer components that can be used to constitute the acrylic oligomer is preferably less than 50 parts by weight, more preferably 40 parts by weight or less, even more preferably 30 parts by weight or less, and particularly preferably 20 parts by weight or less, per 100 parts by weight of the total monomer components.

[0099] Other monomers (copolymerizable monomers) include, for example, alkoxyalkyl esters of (meth)acrylates (e.g., 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, methoxytriethylene glycol (meth)acrylate, 3-methoxypropyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 4-methoxybutyl (meth)acrylate, 4-ethoxybutyl (meth)acrylate, etc.), 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, etc.), hydroxyl group-containing monomers (e.g., hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, etc.); vinyl alcohol; allyl alcohol; Examples include monomers containing amide groups (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, etc.), monomers containing amino groups (e.g., aminoethyl(meth)acrylate, dimethylaminoethyl(meth)acrylate, t-butylaminoethyl(meth)acrylate, etc.), monomers containing cyano groups (e.g., acrylonitrile, methacrylonitrile, etc.), monomers containing sulfonic acid groups (e.g., sodium vinylsulfonate, etc.), monomers containing phosphate groups (e.g., 2-hydroxyethylacryloylphosphate, etc.), monomers containing isocyanate groups (e.g., 2-methacryloyloxyethyl isocyanate, etc.), and monomers containing imide groups (e.g., cyclohexylmaleimide, isopropylmaleimide, etc.).

[0100] The monomer components that can be used to constitute the acrylic oligomer are particularly preferably (1) at least one monomer selected from the group consisting of dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate, and (2) methyl methacrylate. In this case, the content of monomer (1) is preferably 30 to 70 parts by weight and the content of monomer (2) is preferably 30 to 70 parts by weight per 100 parts by weight of all monomer components that can be used to constitute the acrylic oligomer.

[0101] Acrylic oligomers can be produced by any suitable polymerization method, provided that the effects of the present invention are not impaired. Examples of such polymerization methods include solution polymerization, emulsion polymerization, bulk polymerization, and polymerization by active energy ray irradiation (active energy ray polymerization). Among these, bulk polymerization and solution polymerization are preferred, and solution polymerization is more preferred.

[0102] Examples of solvents that can be used in polymerization include organic solvents such as esters like ethyl acetate and n-butyl acetate; aromatic hydrocarbons like toluene and benzene; aliphatic hydrocarbons like n-hexane and n-heptane; alicyclic hydrocarbons like cyclohexane and methylcyclohexane; and ketones like methyl ethyl ketone and methyl isobutyl ketone. One solvent may be used, or two or more solvents may be used.

[0103] In polymerization, any suitable polymerization initiator (e.g., a thermal polymerization initiator or a photopolymerization initiator) can be used, as long as it does not impair the effects of the present invention. One polymerization initiator may be used, or two or more may be used. When performing solution polymerization, it is preferable to use an oil-soluble polymerization initiator.

[0104] As a thermal polymerization initiator, any suitable thermal polymerization initiator can be used as long as it does not impair the effects of the present invention. There may be only one thermal polymerization initiator or two or more. As a specific example of such a thermal polymerization initiator, the description of the thermal polymerization initiator that can be used when producing the acrylic polymer (A) described above can be directly applied.

[0105] As the photopolymerization initiator, any suitable photopolymerization initiator can be used as long as it does not impair the effects of the present invention. There may be only one type of photopolymerization initiator or two or more types. As a specific example of such a photopolymerization initiator, the description of the photopolymerization initiator that can be used when producing the acrylic polymer (A) described above can be directly applied.

[0106] The amount of polymerization initiator used can be any appropriate amount, as long as it does not impair the effects of the present invention. Such an amount may be, for example, 0.001 to 10 parts by weight, 0.005 to 5 parts by weight, 0.01 to 3 parts by weight, or 0.05 to 1 part by weight, per 100 parts by weight of all monomer components that can be used to constitute the acrylic oligomer.

[0107] In polymerization for producing acrylic oligomers, a chain transfer agent may be used to adjust the molecular weight (preferably to adjust the weight-average molecular weight to 1,000 to 30,000). Examples of chain transfer agents include 2-mercaptoethanol, α-thioglycerol, 2,3-dimercapto-1-propanol, octyl mercaptan, t-nonyl mercaptan, dodecyl mercaptan (lauryl mercaptan), t-dodecyl mercaptan, glycidyl mercaptan, thioglycolic acid, methyl thioglycolate, ethyl thioglycolate, propyl thioglycolate, butyl thioglycolate, t-butyl thioglycolate, 2-ethylhexyl thioglycolate, octyl thioglycolate, isooctyl thioglycolate, decyl thioglycolate, dodecyl thioglycolate, thioglycolic acid ester of ethylene glycol, thioglycolic acid ester of neopentyl glycol, thioglycolic acid ester of pentaerythritol, and α-methylstyrene dimer. The chain transfer agent may be one type or two or more types.

[0108] The amount of chain transfer agent used can be any appropriate amount, as long as it does not impair the effects of the present invention. Such an amount is preferably 0.1 to 20 parts by weight, but may also be 0.2 to 15 parts by weight, or 0.3 to 10 parts by weight, per 100 parts by weight of all monomer components that can be used to constitute the acrylic oligomer.

[0109] ≪1-4. Other Ingredients≫ The acrylic adhesive composition may contain any other suitable components as long as they do not impair the effects of the present invention. Examples of such other components include crosslinking catalysts, crosslinking accelerators, crosslinking retarders, silane coupling agents, tackifying resins (rosin derivatives, polyterpene resins, petroleum resins, oil-soluble phenols, etc.), anti-aging agents, inorganic fillers, organic fillers, metal powders, colorants (pigments, dyes, etc.), foils, 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, and the like.

[0110] The content of other components in the acrylic adhesive composition can be any appropriate amount depending on the purpose, as long as it does not impair the effects of the present invention. The content of other components in the acrylic adhesive composition is, for example, 0 to 30 parts by weight, on a solid content basis, per 100 parts by weight of acrylic polymer (A), and may be 0 to 20 parts by weight, 0 to 10 parts by weight, 0 to 10 parts by weight, or 0 to 5 parts by weight. If the other component is a solvent, it may be, for example, 0 to 1000 parts by weight.

[0111] ≪≪2. Acrylic Adhesive Sheet≫≫ An acrylic adhesive sheet according to one embodiment of the present invention includes an acrylic adhesive layer composed of an acrylic adhesive according to an embodiment of the present invention.

[0112] The acrylic adhesive sheet according to the embodiment of the present invention may be a substrate-less sheet consisting only of an acrylic adhesive layer, or a substrate-attached sheet having a substrate and an acrylic adhesive layer. In addition to the substrate and the acrylic adhesive layer, the acrylic adhesive sheet according to the embodiment of the present invention may include any other suitable layer, as long as it does not impair the effects of the present invention.

[0113] The substrate may be one layer or two or more layers. Preferably, the substrate is one layer, as this allows for better expression of the effects of the present invention.

[0114] The acrylic adhesive layer may be one layer or two or more layers. Preferably, the acrylic adhesive layer is one layer, as this allows for better expression of the effects of the present invention.

[0115] The acrylic adhesive sheet according to the embodiment of the present invention may be provided with an optional suitable release liner on the surface opposite to the surface on which the base layer of the adhesive layer is provided, for protection until use.

[0116] Examples of release liners include release liners in which the surface of a substrate (liner substrate) such as paper or plastic film is treated with silicone, and release liners in which the surface of a 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.

[0117] The thickness of the release liner is preferably 1 μm to 500 μm, but may also be 3 μm to 450 μm, 5 μm to 400 μm, or 10 μm to 300 μm.

[0118] The total thickness of the acrylic adhesive sheet according to the embodiment of the present invention is preferably 1 μm to 500 μm, but may also be 5 μm to 200 μm, 10 μm to 150 μm, 20 μm to 100 μm, or 30 μm to 80 μm.

[0119] ≪2-1. Base material≫ The thickness of the substrate is preferably 1 μm to 500 μm, but may also be 5 μm to 300 μm, 10 μm to 100 μm, 15 μm to 80 μm, or 2010 μm to 60 μm.

[0120] Any suitable material can be used as the base material, as long as it does not impair the effects of the present invention. Examples of such base material materials include resin materials, metals, paper, and nonwoven fabrics, with resin materials and metals being preferred.

[0121] Examples of resin materials used as base materials include acrylic resins such as polyimide (PI), polyether ether ketone (PEEK), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), and polymethyl methacrylate (PMMA), as well as 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), fluororesins, and cyclic olefin polymers.

[0122] Examples of metals used as base materials include iron, copper, titanium, tin, zinc, stainless steel, aluminum alloy, aluminum, galvalume steel (registered trademark), tungsten, chromium, cobalt, and nickel.

[0123] ≪2-2. Acrylic adhesive layer≫ The thickness of the acrylic adhesive layer in the acrylic adhesive sheet according to the embodiment of the present invention is preferably 100 μm or less, but may be 70 μm or less, 50 μm or less, 30 μm or less, 1 μm to 30 μm, 5 μm to 30 μm, or 10 μm to 30 μm.

[0124] The acrylic adhesive layer is composed of an acrylic adhesive. More specifically, the acrylic adhesive layer is an acrylic adhesive arranged in a layered form. Any suitable method can be used to form the acrylic adhesive layer, as long as it does not impair the effects of the present invention. For example, such a method involves applying an acrylic adhesive composition onto any suitable substrate, heating and drying as necessary, and curing as necessary to form an adhesive layer composed of an acrylic adhesive on the substrate. Any suitable means can be used for such application, as long as it does not impair the effects of the present invention. Examples of such application means include gravure roll coaters, reverse roll coaters, kiss roll coaters, dip roll coaters, bar coaters, knife coaters, air knife coaters, spray coaters, comma coaters, direct coaters, and roll brush coaters. Any suitable means can be used for heating and drying the acrylic adhesive composition, as long as it does not impair the effects of the present invention. Such heating and drying methods include, for example, heating to a temperature of approximately 60°C to 180°C. The curing of the acrylic adhesive composition can be carried out by any suitable means, as long as it does not impair the effects of the present invention. Such curing methods include, for example, ultraviolet irradiation, laser irradiation, alpha-ray irradiation, beta-ray irradiation, gamma-ray irradiation, X-ray irradiation, and electron beam irradiation.

[0125] ≪≪3. Flexible Devices≫≫ A flexible device according to an embodiment of the present invention includes an acrylic adhesive sheet according to an embodiment of the present invention.

[0126] The acrylic adhesive sheet according to an embodiment of the present invention includes an acrylic adhesive layer composed of an acrylic adhesive according to an embodiment of the present invention. Therefore, when a laminate formed by bonding the adhesive surface of the acrylic adhesive sheet to an adherend is repeatedly bent in a low-pressure environment, even if fine particles are present between the acrylic adhesive sheet and the adherend, the generation of air bubbles between the acrylic adhesive sheet and the adherend can be suppressed. For this reason, it can be suitably provided in flexible devices such as bendable devices, foldable devices, and rollable devices that have a movable bending portion.

[0127] The flexible device of the present invention may include any other suitable components, provided that it includes an acrylic adhesive sheet according to an embodiment of the present invention.

[0128] Figure 1 is a schematic cross-sectional view showing one embodiment of the flexible device of the present invention as a representative example of one use case of the acrylic adhesive sheet according to an embodiment of the present invention. In Figure 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 Figure 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 layers 20, 40, and 60 may be acrylic adhesive layers containing an adhesive with the same composition as the acrylic adhesive layer 80 that constitutes the acrylic adhesive sheet 100 according to an embodiment of the present invention, or they may be adhesive layers containing an adhesive with a different composition. [Examples]

[0129] The present invention will be described more specifically below with reference to examples and comparative examples. However, the present invention is not limited in any way to these. In the following description, "parts" and "%" refer to weight unless otherwise specified.

[0130] The abbreviations and details of the raw materials used in the following manufacturing examples, examples, and comparative examples are as follows. HxA:n-Hexylacrylate NOAA: n-Octylacrylate 2EHA:2-Ethylhexylacrylate INAA: Isononyl acrylate IDAA: Isodecyl acrylate BA: n-butyl acrylate 4HBA: 4-Hydroxybutyl acrylate HEA: 2-hydroxyethyl acrylate MMA: Methyl methacrylate NVP: N-vinyl-2-pyrrolidone DCPMA: Dicyclopentanyl methacrylate AIBN: 2,2'-Azobisisobutyronitrile C / HX: Coronate HX (manufactured by Tosoh Corporation, isocyanate-based crosslinking agent)

[0131] The Tg of the homopolymers of the following monomers is as follows: HxA (n-hexyl acrylate): Tg = -60℃ NOAA (n-octyl acrylate): Tg = -65℃ 2EHA (2-ethylhexyl acrylate): Tg = -70℃ INAA (Isononyl Acrylate): Tg = -58℃ IDAA (isodecyl acrylate): Tg = -62℃ BA (n-butyl acrylate): Tg = -55℃ 4HBA (4-hydroxybutyl acrylate): Tg = -32℃ HEA (2-hydroxyethyl acrylate): Tg = -15℃ MMA (Methyl Methacrylate): Tg = 105℃ NVP (N-vinyl-2-pyrrolidone): Tg = 80℃ DCPMA (Dicyclopentanyl methacrylate): Tg = 175℃

[0132] <Creep Measurement> An acrylic adhesive sheet (a laminate consisting of a release liner, a layered acrylic adhesive, and a PET resin substrate with a thickness of 50 μm) was cut to a width of 50 mm and a length of 50 mm. The release liner was peeled off to expose the acrylic adhesive, and the sheet was attached to a glass plate to obtain a sample for evaluation. Creep was measured using a PICODENTOR HM500 (manufactured by Fischer Instruments) by pressing a 2mm diameter spherical indenter into the PET resin substrate surface of the evaluation sample. The measurement conditions were: measurement temperature: 25°C, indentation load: 500mN, indentation time: 20 seconds, indentation holding time: 5 seconds. The indentation depth (creep: CIT1) that changed during the 5-second indentation holding time was read. CIT1 is calculated using the following formula, where T5 is the indentation depth at 5 seconds and T0 is the indentation depth at 0 seconds. CIT1 = [(T5-T0) / T0] × 100 (%)

[0133] <Adhesion to polyimide film at a peeling speed of 300 mm / min> The adhesive sheet was cut to a width of 25 mm and a length of 100 mm, the release liner was peeled off to expose the acrylic adhesive, and it was attached to a polyimide film (product name "UPIREX 50S", manufactured by Ube Industries, Ltd.) using a 2 kg hand roller in one pass-through motion to obtain a sample for evaluation. The obtained evaluation samples were stored at room temperature for 30 minutes and then measured using a tensile testing machine. The tensile testing machine used was the "Autograph AG-Xplus HS 6000mm / min high-speed model (AG-50NX plus)" manufactured by Shimadzu Corporation. After setting the evaluation samples in the tensile testing machine, the tensile test was started. The conditions for the tensile test were: peel angle: 180 degrees, peel speed (tensile speed): 300 mm / min. The load when peeling the adhesive sheet from the above polyimide film (UPIREX 50S) was measured, and the average load at that time was defined as the adhesive force.

[0134] <Decompression flexion test> The adhesive sheet was cut to a width of 30 mm and a length of 100 mm, and the release liner was peeled off to expose the acrylic adhesive. As shown in Figure 2, masking release liners 201 and 202 were attached to the adhesive sheet 100 at positions 20 mm to the left and right of the midpoint L in the longitudinal direction, thereby exposing the acrylic adhesive over a width of 40 mm within a length of 100 mm. Subsequently, plastic particles (Micropearl SP-203, manufactured by Sekisui Chemical Co., Ltd.) 300 were uniformly dispersed and applied to the entire exposed area of ​​the acrylic adhesive sandwiched between the masking release liners 201 and 202. Next, the masking release liners 201 and 202 were peeled off to obtain the adhesive sheet 101 for the test specimen. This was then laminated with a polyimide film (product name "UPIREX 50S", manufactured by Ube Industries, Ltd.), autoclaved at 50°C, 0.5 MPa, and for 15 minutes, and then cut into 25 mm wide x 100 mm long pieces to form the test specimen. The presence or absence of air bubbles in the test specimen was checked from the substrate side (the substrate side of the adhesive sheet) using a microscope (OLYMPUS BX51, objective lens: UMPlanFI 20× / 0.40 BD P). The observation conditions were 20x magnification and transmission mode. Air bubbles found at this stage were marked beforehand. The test specimen was set on a bending test machine (test fixture: DMX-CS-max Teardrop Controller BF0107MR, manufactured by Yuasa System Equipment Co., Ltd.) using double-sided tape No. 5000NS (thickness 0.16 mm, manufactured by Nitto Denko Corporation). At this time, the test specimen was set on the machine so that the polyimide film side of the test specimen was oriented to bend inward. Furthermore, the test specimen was set on the machine so that the fold of the bend was parallel to the width direction of the test specimen. The setting conditions were as follows, using side supporters and bottom supporters: PS1: 3 mm, PS2: 2 mm, TS1: 4 mm, TS2: 3.9 mm, RS: 4.25 mm, BRS: 5.55 mm, BS: 1.47 mm. 1000 and 3500 depressurized bending tests were performed under a reduced pressure of 0.06 MPa. After the tests, the specimens were observed under a microscope under the same conditions as above. Bubbles observed before the test (marked bubbles) were removed, and the presence or absence of newly formed bubbles after the test was checked. Evaluation was performed according to the following criteria. [1000 decompression bending tests] ○: No bubbles were generated. ×: Bubbles were generated. [3500 decompression bending tests] ○: No bubbles were generated. ×: Bubbles were generated. [Comprehensive evaluation of decompression bending test] ○: No bubbles were generated in either the 1000-cycle depressurization bending test or the 3500-cycle depressurization bending test. △: No bubbles were generated in the 1000-cycle depressurized bending test, but bubbles were generated in the 3500-cycle depressurized bending test. ×: Bubbles were generated in both the 1000-cycle depressurized bending test and the 3500-cycle depressurized bending test.

[0135] <-20℃ bending test> The adhesive sheet was cut to a width of 25 mm and a length of 100 mm, the release liner was peeled off to expose the acrylic adhesive, and it was attached to a polyimide film (product name "UPIREX 75S", manufactured by Ube Industries, Ltd.) using a 2 kg hand roller in one pass-through motion. Next, the sheet was autoclaved at 50°C, 0.5 MPa, and for 15 minutes to obtain a test specimen. The test specimen was set in a bending test machine (test fixture: CS-MAX, manufactured by Yuasa System Equipment Co., Ltd.) with the polyimide film side of the specimen bent inward, and the fold of the bend parallel to the width direction of the specimen. A bending test was performed 200,000 times at a bending diameter of 2 mm and in a -20°C environment. After the test, the appearance of the test specimen was checked, and the length of the adhesive sheet at break was measured. If it broke completely, the break length was considered to be 25 mm (width).

[0136] <Weight-average molecular weight (Mw) of acrylic polymers> The weight-average molecular weight (Mw) of acrylic polymers was measured by gel permeation chromatography (GPC). Specifically, an "Alliance" GPC analyzer (manufactured by Waters Corporation) was used. Considering the polymer concentration of the sample, a 0.1% by weight tetrahydrofuran solution was prepared, left for 20 hours, filtered through a 0.45 μm membrane filter, and the resulting filtrate was subjected to GPC measurement. The following GPC measurement conditions were adopted. • Sample concentration: 0.1% by weight (tetrahydrofuran solution) • Sample injection volume: 30 μL • Column: Product name "TSKgel SuperHZM-H" (manufactured by Tosoh Corporation) • Eluent: Tetrahydrofuran ·Flow rate: 0.2mL / min • Detector: Differential refractometer (RI) • Column temperature (measurement temperature): 40°C • Standard sample: Polystyrene (PS)

[0137] <Weight-average molecular weight (Mw) of acrylic oligomers> The weight-average molecular weight (Mw) of acrylic oligomers was measured by gel permeation chromatography (GPC). Specifically, an "HLC-8320GPC" (manufactured by Tosoh Corporation) was used as the GPC measuring instrument. Considering the polymer concentration of the sample, a 0.1% by weight tetrahydrofuran solution was prepared, left for 20 hours, filtered through a 0.45 μm membrane filter, and the resulting filtrate was subjected to GPC measurement. The following conditions were used for GPC measurement. • Sample concentration: 0.1% by weight (tetrahydrofuran solution) • Sample injection volume: 100 μL • Column: Product name "TSKgel SuperHZM-H / HZ4000 / HZ3000 / HZ2000" (manufactured by Tosoh Corporation) • Eluent: Tetrahydrofuran ·Flow rate: 0.6mL / min • Detector: Differential refractometer (RI) • Column temperature (measurement temperature): 40°C • Standard sample: Polystyrene (PS)

[0138] [Manufacturing Example 1]: Manufacturing of acrylic polymer (1) In a four-necked flask equipped with a stirring blade, thermometer, nitrogen gas inlet tube, and condenser, 60 parts by weight of NOAA, 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. Ethyl acetate was then added to bring the total concentration of these components to 37% by weight. The system was purged with nitrogen over 1 hour while gently stirring, and the polymerization reaction was carried out for 5 hours while maintaining the temperature of the liquid in the flask at around 58°C. After the reaction was complete, ethyl acetate was added to adjust the polymer concentration to 30% by weight to obtain a solution of acrylic polymer (1). The weight-average molecular weight Mw of the acrylic polymer (1) was 2 million. The Tg of the acrylic polymer (1), calculated using FOX's formula, was -59.5°C.

[0139] [Manufacturing Example 2]: Manufacturing of acrylic polymer (2) The procedure was carried out in the same manner as in Production Example 1, except that 60 parts by weight of HxA were used instead of 60 parts by weight of NOAA, to obtain a solution of acrylic polymer (2). The weight-average molecular weight Mw of the acrylic polymer (2) was 2 million. The Tg of the acrylic polymer (2), calculated using FOX's formula, was -56.4°C.

[0140] [Manufacturing Example 3]: Manufacturing of acrylic polymer (3) The procedure was carried out in the same manner as in Production Example 1, except that 60 parts by weight of 2EHA were used instead of 60 parts by weight of NOAA, to obtain a solution of acrylic polymer (3). The weight-average molecular weight Mw of the acrylic polymer (3) was 2 million. The Tg of the acrylic polymer (3), calculated using FOX's formula, was -62.7°C.

[0141] [Manufacturing Example 4]: Manufacturing of acrylic polymer (4) The procedure was carried out in the same manner as in Production Example 1, except that 60 parts by weight of INAA were used instead of 60 parts by weight of NOAA, to obtain a solution of acrylic polymer (4). The weight-average molecular weight Mw of the acrylic polymer (4) was 2 million. The Tg of the acrylic polymer (4), calculated using FOX's formula, was -55.1°C.

[0142] [Manufacturing Example 5]: Manufacturing of acrylic polymer (5) The procedure was carried out in the same manner as in Production Example 1, except that IDAA was used in place of NOAA at 60 parts by weight, to obtain a solution of acrylic polymer (5). The weight-average molecular weight Mw of the acrylic polymer (5) was 2 million. The Tg of the acrylic polymer (5), calculated using the FOX formula, was -57.6°C.

[0143] [Manufacturing Example 6]: Manufacturing of acrylic polymer (6) In a four-necked flask equipped with a stirring blade, thermometer, nitrogen gas inlet tube, and condenser, 63 parts by weight of 2EHA, 9 parts by weight of MMA, 13 parts by weight of HEA, 15 parts by weight of NVP, and 0.2 parts by weight of AIBN as a polymerization initiator were added. Ethyl acetate was then added to bring the total concentration of these components to 36% by weight. The system was purged with nitrogen over 1 hour while gently stirring, and the polymerization reaction was carried out for 5 hours while maintaining the temperature of the liquid in the flask at around 65°C. Then, the reaction was carried out for 2 hours while maintaining the temperature at around 70°C to obtain a solution of acrylic polymer (6). The weight-average molecular weight Mw of the acrylic polymer (6) was 800,000. The Tg of the acrylic polymer (6), calculated using FOX's formula, was -38.8°C.

[0144] [Manufacturing Example 7]: Manufacturing of acrylic oligomers In a four-necked flask equipped with a stirring blade, thermometer, nitrogen gas inlet tube, and condenser, 57.7 parts by weight of DCPMA, 38.7 parts by weight of MMA, 3.3 parts by weight of α-thioglycerol as a chain transfer agent, and 0.29 parts by weight of AIBN as a polymerization initiator were added. Ethyl acetate was then added to bring the total concentration of these components to 60% by weight. The mixture was reacted at 67°C for 2 hours under a nitrogen atmosphere, and then the temperature was raised to 80°C for 8 hours to obtain an acrylic oligomer. The weight-average molecular weight (Mw) of the acrylic oligomer was 4900. The Tg of the acrylic oligomer, calculated using the FOX formula, was 144°C.

[0145] [Example 1] A solution of acrylic adhesive composition (1) was obtained by mixing 100 parts by weight of acrylic polymer (1), 0.075 parts by weight of C / HX as a crosslinking agent, and 4 parts by weight of acrylic oligomer, stirring thoroughly, and then diluting with ethyl acetate so that the total solid content was 21% by weight. The solution of the obtained acrylic adhesive composition (1) was applied to a polyester film (Toray Industries, Inc., #50-U48) as a substrate so that the thickness after drying would be 15 μm, and it was dried at a drying temperature of 130°C for a drying time of 1 minute. This formed an acrylic adhesive layer with a thickness of 15 μm on the substrate, consisting of the acrylic adhesive (1). Next, an acrylic adhesive sheet (1) was obtained by laminating an acrylic adhesive layer with a release liner (Mitsubishi Chemical Corporation, MRQ50T100J) made of polyester resin with a thickness of 50 μm and one side treated with silicone, so that the silicone-treated side of the liner was in contact with the surface of the acrylic adhesive layer. The obtained acrylic adhesive sheet (1) was aged at 50°C for one day, and various evaluations were performed. The results are shown in Tables 1 and 2.

[0146] [Examples 2-8] Except for changing the amount of crosslinking agent and the thickness of the acrylic adhesive layer as shown in Tables 1 and 2, the procedure was carried out in the same manner as in Example 1 to obtain acrylic adhesive sheets (2) to (8) having solutions of acrylic adhesive compositions (2) to (8) and acrylic adhesive layers composed of acrylic adhesives (2) to (8). The obtained acrylic adhesive sheets (2) to (8) were aged at 50°C for one day, and various evaluations were performed. The results are shown in Tables 1 and 2.

[0147] [Example 9] The procedure was carried out in the same manner as in Example 3, except that 100 parts by weight of acrylic polymer (2) was used instead of 100 parts by weight of acrylic polymer (1), to obtain an acrylic adhesive sheet (9) having an acrylic adhesive layer composed of a solution of acrylic adhesive composition (9) and acrylic adhesive (9). The obtained acrylic adhesive sheet (9) was aged at 50°C for one day, and various evaluations were performed. The results are shown in Tables 1 and 2.

[0148] [Example 10] The procedure was carried out in the same manner as in Example 3, except that 100 parts by weight of acrylic polymer (3) was used instead of 100 parts by weight of acrylic polymer (1), to obtain an acrylic adhesive sheet (10) having an acrylic adhesive layer composed of a solution of acrylic adhesive composition (10) and acrylic adhesive (10). The obtained acrylic adhesive sheet (10) was aged at 50°C for one day, and various evaluations were performed. The results are shown in Tables 1 and 2.

[0149] [Example 11] The procedure was carried out in the same manner as in Example 3, except that 100 parts by weight of acrylic polymer (4) was used instead of 100 parts by weight of acrylic polymer (1), to obtain an acrylic adhesive sheet (11) having an acrylic adhesive layer composed of a solution of acrylic adhesive composition (11) and acrylic adhesive (11). The obtained acrylic adhesive sheet (11) was aged at 50°C for one day, and various evaluations were performed. The results are shown in Tables 1 and 2.

[0150] [Example 12] The procedure was carried out in the same manner as in Example 3, except that 100 parts by weight of acrylic polymer (5) was used instead of 100 parts by weight of acrylic polymer (1), to obtain an acrylic adhesive sheet (12) having an acrylic adhesive layer composed of a solution of acrylic adhesive composition (12) and acrylic adhesive (12). The obtained acrylic adhesive sheet (12) was aged at 50°C for one day, and various evaluations were performed. The results are shown in Tables 1 and 2.

[0151] [Comparative Examples 1 and 2] Except for changing the amount of crosslinking agent as shown in Tables 1 and 2, the procedure was carried out in the same manner as in Example 1 to obtain acrylic adhesive sheets (C1) and (C2) having acrylic adhesive layers composed of solutions of acrylic adhesive compositions (C1) and (C2) and acrylic adhesives (C1) and (C2). The obtained acrylic adhesive sheets (C1) and (C2) were aged at 50°C for one day, and various evaluations were performed. The results are shown in Tables 1 and 2.

[0152] [Comparative Example 3] Except for changing acrylic polymer (1):100 parts by weight to acrylic polymer (6):100 parts by weight and changing the amount of crosslinking agent as shown in Tables 1 and 2, the procedure was carried out in the same manner as in Example 1 to obtain an acrylic adhesive sheet (C3) having an acrylic adhesive layer composed of a solution of acrylic adhesive composition (C3) and acrylic adhesive (C3). The obtained acrylic adhesive sheet (C3) was aged at 50°C for one day, and various evaluations were performed. The results are shown in Tables 1 and 2.

[0153] [Table 1]

[0154] [Table 2] [Industrial applicability]

[0155] The acrylic adhesive and acrylic adhesive sheet according to the embodiments of the present invention can be used in so-called flexible devices such as foldable devices and rollable devices. [Explanation of symbols]

[0156] 1000 Flexible Devices 100 adhesive sheets 101 Adhesive sheet for test specimens 201 Masking Release Liner 202 Masking release liner 300 plastic particles 10 Cover film 20 Adhesive layer 30 Polarizing plates 40 Adhesive layer 50 touch sensors 60 Adhesive layer 70 OLED 80 Adhesive layer 90 Base material layer

Claims

1. An acrylic adhesive formed from an acrylic adhesive composition, The acrylic adhesive composition comprises an acrylic polymer (A) as a base polymer and a crosslinking agent. The Tg of the acrylic polymer (A), calculated by FOX's formula, is less than -50°C. The creep measured by pressing a 2 mm diameter spherical indenter into the PET resin substrate surface of a laminate of the acrylic adhesive in layer form and a PET resin substrate with a thickness of 50 μm, at a measurement temperature of 25°C, an indentation load of 500 mN, an indentation time of 20 seconds, and an indentation holding time of 5 seconds, was 1.0% or more and less than 8.0%. At 23°C, with a peeling angle of 180 degrees and a peeling speed of 300 mm / min, the adhesive strength of the acrylic adhesive to the polyimide film is 8.0 N / 25 mm or more. Acrylic adhesive.

2. The acrylic adhesive according to claim 1, wherein the amount of the crosslinking agent in the acrylic adhesive composition is 0.010 parts by weight to 5.000 parts by weight per 100 parts by weight of the acrylic polymer (A).

3. The acrylic adhesive according to claim 1, wherein the acrylic adhesive composition comprises an acrylic oligomer having a weight-average molecular weight Mw of 1,000 to 30,000.

4. The acrylic adhesive according to claim 3, wherein the content of the acrylic oligomer in the acrylic adhesive composition is 0.1 to 20 parts by weight per 100 parts by weight of the acrylic polymer (A).

5. The acrylic adhesive according to claim 1, wherein the acrylic polymer (A) is obtained by polymerizing a monomer component (M).

6. The acrylic adhesive according to claim 5, wherein the monomer component (M) contains 40% to 90% by weight of an alkyl (meth)acrylate (m1) having an alkyl group having 6 to 10 carbon atoms as an ester portion.

7. The acrylic adhesive according to claim 6, wherein the Tg of the alkyl (meth)acrylate (m1) homopolymer is in the range of -75°C to -55°C.

8. The acrylic adhesive according to claim 6, wherein the alkyl group is a linear alkyl group.

9. The acrylic adhesive according to claim 5, wherein the monomer component (M) comprises an alkyl (meth)acrylate (m2) having an alkyl group having 1 to 5 carbon atoms as an ester portion.

10. The acrylic adhesive according to claim 9, wherein the Tg of the alkyl (meth)acrylate (m2) homopolymer is in the range of -60°C to less than -40°C.

11. The acrylic adhesive according to claim 9, wherein the content of the alkyl (meth)acrylate (m2) in the monomer component (M) is 1% by weight to 55% by weight.

12. The acrylic adhesive according to claim 5, wherein the monomer component (M) comprises a hydroxyl group-containing monomer (m3).

13. The acrylic adhesive according to claim 12, wherein the Tg of the homopolymer of the hydroxyl group-containing monomer (m3) is in the range of -60°C to -10°C.

14. The acrylic adhesive according to claim 12, wherein the content of the hydroxyl group-containing monomer (m3) in the monomer component (M) is 0.01% by weight to 30% by weight.

15. An acrylic adhesive sheet comprising an acrylic adhesive layer composed of an acrylic adhesive according to any one of claims 1 to 14.

16. The acrylic adhesive sheet according to claim 15, wherein the thickness of the acrylic adhesive layer is 30 μm or less.

17. A flexible device comprising the acrylic adhesive sheet described in claim 15.

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