Pressure-sensitive adhesive sheet and flexible device

Abstract

To provide a pressure-sensitive adhesive sheet that realizes a balance between superior flexural recovery and strong anchoring strength, and to provide a flexible device comprising the pressure-sensitive adhesive sheet.SOLUTION: A pressure-sensitive adhesive sheet according to an embodiment of the present invention comprises a base material and a pressure-sensitive adhesive layer. The pressure-sensitive adhesive sheet contains a filler that is in contact with the surface of the pressure-sensitive adhesive layer on the base material side. The pressure-sensitive adhesive layer is composed of an acrylic pressure-sensitive adhesive formed from an acrylic pressure-sensitive adhesive composition. The acrylic pressure-sensitive adhesive composition includes an acrylic polymer, an acrylic oligomer, and two or more types of crosslinking agents.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive sheet and a flexible device. [Background technology]

[0002] Adhesive sheets are used to reinforce and protect the surfaces of components of various shapes. For example, when joining an integrated circuit (IC) or a flexible printed circuit board (FPC) to a semiconductor element substrate (e.g., a TFT substrate), thermocompression bonding is usually performed using an anisotropic conductive film (ACF). Before performing such thermocompression bonding, an adhesive sheet may be attached to the back side of the semiconductor element substrate to reinforce it (e.g., Patent Document 1).

[0003] In conventional pressure-sensitive adhesive sheets, a filler is usually contained in the substrate (typically a PET film) to prevent blocking and the like.

[0004] However, the presence of fillers in the substrate reduces the inspectability of foreign matter inspections during the PSA sheet manufacturing process. For example, even if a product contains only extremely fine foreign matter with a maximum length of less than 1 μm, which is the level at which a product passes inspection, the fillers may be recognized as foreign matter and the product may be judged as a reject, resulting in reduced productivity.

[0005] Recently, a highly transparent film has been known in which a thin, easily adhesive layer having an uneven surface is provided on a resin film that does not contain a filler. When such a highly transparent film is used as a substrate, the problem of reduced inspectability as described above can be resolved because the substrate does not contain a filler, and the unevenness of the thin, easily adhesive layer on the surface can also ensure prevention of blocking.

[0006] Meanwhile, in recent years, the development of so-called flexible devices, such as foldable devices and rollable devices, has progressed. Generally, a method for manufacturing such devices involves forming a release layer and a flexible film substrate on a support substrate such as glass, forming a TFT substrate on the film substrate, and then forming an organic EL layer on top of that. The support substrate is then peeled off to produce a flexible device. However, because the flexible display layer is very thin, problems can occur with handling, etc. For this reason, an adhesive sheet is sometimes attached to the backside to reinforce the device (see, for example, Patent Document 2).

[0007] Substrates of semiconductor elements and flexible devices may be repeatedly bent, and if the bending properties of the adhesive sheet attached to the substrate or the like are poor, the recovery after bending may be poor, or in the worst case, the sheet may break due to repeated bending. Therefore, as a means for imparting good bending properties to the adhesive sheet, it is considered to use an adhesive having a low elastic modulus as the adhesive of the adhesive sheet. Furthermore, since the elastic modulus in the low temperature range is higher than the elastic modulus in the normal temperature range, it is particularly desirable to use an adhesive having a low elastic modulus in the low temperature range. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 5600039 [Patent Document 2] Patent No. 6376271 Summary of the Invention [Problem to be solved by the invention]

[0009] In view of the above background art, the present inventors attempted to produce a pressure-sensitive adhesive sheet with excellent flex recovery by using the above-mentioned highly transparent film as a substrate and laminating a pressure-sensitive adhesive layer composed of a pressure-sensitive adhesive having a low elastic modulus to the substrate, but found that peeling occurred between the film and the pressure-sensitive adhesive layer when the sheet was bent.

[0010] An object of the present invention is to provide a pressure-sensitive adhesive sheet that can achieve both excellent flex recovery and high anchoring strength, and a flexible device that includes such a pressure-sensitive adhesive sheet. [Means for solving the problem]

[0011] [1] An adhesive sheet according to an embodiment of the present invention is an adhesive sheet comprising a substrate and an adhesive layer, and a filler in contact with the surface of the adhesive layer facing the substrate, the adhesive layer being composed of an acrylic adhesive formed from an acrylic adhesive composition, the acrylic adhesive composition comprising an acrylic polymer, an acrylic oligomer, and two or more types of crosslinking agents. [2] In the pressure-sensitive adhesive sheet according to the above item [1], the pressure-sensitive adhesive layer may have a storage modulus at −20° C. of less than 140 kPa. [3] In the pressure-sensitive adhesive sheet according to the above [1] or [2], the two or more types of crosslinking agents may include an epoxy-based crosslinking agent. [4] In the pressure-sensitive adhesive sheet according to the above item [3], the content of the epoxy-based crosslinking agent relative to 100 parts by weight of the acrylic polymer may be 0.05 parts by weight or more. [5] In the pressure-sensitive adhesive sheet according to any one of [1] to [4] above, the content of the acrylic oligomer may be 1 part by weight or more per 100 parts by weight of the acrylic polymer. [6] In the pressure-sensitive adhesive sheet according to any one of the above [1] to [5], the acrylic oligomer may be a carboxyl group-containing acrylic oligomer. [7] In the pressure-sensitive adhesive sheet according to any one of the above items [1] to [6], the acrylic polymer may be a hydroxyl group-containing acrylic polymer. [8] In the pressure-sensitive adhesive sheet according to any one of [1] to [7] above, the thickness of the substrate may be 90 μm or less. [9] A flexible device according to an embodiment of the present invention comprises the adhesive sheet according to any one of [1] to [8] above. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a pressure-sensitive adhesive sheet that can achieve both excellent flex recovery and high anchoring strength. According to the present invention, it is also possible to provide a flexible device comprising such a pressure-sensitive adhesive sheet. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic cross-sectional view illustrating a pressure-sensitive adhesive sheet according to one embodiment of the present invention. [Figure 2] FIG. 4 is a schematic cross-sectional view illustrating a pressure-sensitive adhesive sheet according to another embodiment of the present invention. [Figure 3] FIG. 4 is a schematic cross-sectional view illustrating a pressure-sensitive adhesive sheet according to another embodiment of the present invention. [Figure 4] FIG. 4 is a schematic cross-sectional view illustrating a pressure-sensitive adhesive sheet according to another embodiment of the present invention. [Figure 5] FIG. 2 is a schematic cross-sectional view for explaining in detail "a filler in contact with the surface of the pressure-sensitive adhesive layer on the substrate side." [Figure 6] FIG. 6 is a schematic cross-sectional view showing one embodiment of the flexible device of the present invention, and shows one mode of use of the pressure-sensitive adhesive sheet according to an embodiment of the present invention. [Figure 7] FIG. 7 is a schematic diagram illustrating a method for measuring flexion recovery. [Figure 8] FIG. 8 is a photograph of a cross-section of the vicinity of the interface between the substrate and the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet (1) obtained in Example 1, taken by TEM. [Figure 9] FIG. 9 is a photograph of a cross-section of the vicinity of the interface between the substrate and the adhesive layer of the adhesive sheet (6) obtained in Example 6, taken by TEM. [Figure 10] FIG. 10 is a photograph of a cross-section taken by TEM near the interface between the substrate and the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet (C1) obtained in Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0014] In this specification, the term "(meth)acrylic" means "acrylic and / or methacrylic," the term "(meth)acrylate" means "acrylate and / or methacrylate," the term "(meth)allyl" means "allyl and / or methallyl," and the term "(meth)acrolein" means "acrolein and / or methacrolein." Furthermore, in this specification, the term "acid (salt)" means "acid and / or its salt." Examples of salts include alkali metal salts and alkaline earth metal salts, and specific examples include sodium salts and potassium salts.

[0015] <<1. Adhesive sheet>> The pressure-sensitive adhesive sheet according to the embodiment of the present invention includes a substrate and a pressure-sensitive adhesive layer. The pressure-sensitive adhesive sheet according to the embodiment of the present invention may include any other appropriate layer in addition to the substrate and the pressure-sensitive adhesive layer, as long as the effects of the present invention are not impaired.

[0016] The pressure-sensitive adhesive sheet according to the embodiment of the present invention may be provided with any appropriate release liner on the surface of the pressure-sensitive adhesive layer opposite to the surface on which the substrate is provided, for protection until use, etc.

[0017] Examples of release liners include release liners in which the surface of a substrate (liner substrate) such as paper or plastic film is silicone-treated, 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 as liner substrates include polyethylene films, polypropylene films, polybutene films, polybutadiene films, polymethylpentene films, polyvinyl chloride films, vinyl chloride copolymer films, polyethylene terephthalate films, polybutylene terephthalate films, polyurethane films, and ethylene-vinyl acetate copolymer films.

[0018] The thickness of the release liner is preferably 1 μm to 500 μm, more preferably 3 μm to 450 μm, even more preferably 5 μm to 400 μm, and particularly preferably 10 μm to 300 μm.

[0019] The total thickness of the pressure-sensitive adhesive sheet according to the embodiment of the present invention is preferably 1 μm to 500 μm, more preferably 5 μm to 200 μm, even more preferably 10 μm to 150 μm, particularly preferably 20 μm to 100 μm, and most preferably 30 μm to 80 μm. When the thickness of the pressure-sensitive adhesive sheet according to the embodiment of the present invention is within the above range, the effects of the present invention can be more effectively exhibited.

[0020] The pressure-sensitive adhesive sheet according to the embodiment of the present invention comprises a filler in contact with the substrate-side surface of the pressure-sensitive adhesive layer, i.e., the pressure-sensitive adhesive sheet according to the embodiment of the present invention comprises a filler, and at least a portion of the filler is in contact with the substrate-side surface of the pressure-sensitive adhesive layer.

[0021] Fig. 1 is a schematic cross-sectional view illustrating a pressure-sensitive adhesive sheet according to one embodiment of the present invention. In Fig. 1, a pressure-sensitive adhesive sheet 100 includes a substrate 10 and a pressure-sensitive adhesive layer 20, and includes a filler 30 in contact with the surface of the pressure-sensitive adhesive layer 20 facing the substrate 10. In Fig. 1, the substrate 10 is made up of a main substrate layer. In Fig. 1, the filler 30 is present near the surface of the substrate 10. In the embodiment shown in Fig. 1, the filler 30 is present only near the surface of the substrate 10 facing the pressure-sensitive adhesive layer 20, but an embodiment in which the filler 30 is present near both surfaces of the substrate 10 may also be used, as shown in the schematic cross-sectional view of Fig. 2.

[0022] 1 and 2, the filler 30 includes not only the filler 30 that is entirely contained inside the substrate 10, but also the filler 30 that is partially exposed from the surface of the substrate 10.

[0023] 1 and 2, filler 30 that is partially exposed from the surface of substrate 10 and in contact with pressure-sensitive adhesive layer 20 can also be said to be partially exposed from the surface of pressure-sensitive adhesive layer 20 and in contact with substrate 10 from the perspective of the pressure-sensitive adhesive layer side. In this way, filler that is in contact with the surfaces of both substrate 10 and pressure-sensitive adhesive layer 20 is treated as filler contained in the substrate and in contact with the surface of the pressure-sensitive adhesive layer on the substrate side.

[0024] Fig. 3 is a schematic cross-sectional view illustrating a pressure-sensitive adhesive sheet according to another embodiment of the present invention. In Fig. 3, a pressure-sensitive adhesive sheet 100 includes a substrate 10 and a pressure-sensitive adhesive layer 20, and includes a filler 30a in contact with the surface of the pressure-sensitive adhesive layer 20 facing the substrate 10. In Fig. 3, the substrate 10 includes a main substrate layer 11 and a surface layer 12a provided on the pressure-sensitive adhesive layer 20 side of the main substrate layer 11. In Fig. 3, the filler 30a is included in the surface layer 12a. In the embodiment shown in Fig. 3, the surface layer 12a containing the filler 30a is provided only on the pressure-sensitive adhesive layer 20 side of the substrate 10, but as shown in the schematic cross-sectional view of Fig. 4, an embodiment in which a surface layer 12b containing a filler 30b is further provided on the side of the substrate 10 opposite the pressure-sensitive adhesive layer 20 may also be used.

[0025] 3 and 4, at least a portion of the filler 30a contained in the surface layer 12a is in contact with the surface of the pressure-sensitive adhesive layer facing the substrate. That is, the filler 30a contained in the surface layer 12a includes not only filler 30a that is entirely contained within the surface layer 12a, but also filler 30a that is partially exposed from the surface of the surface layer 12a facing the pressure-sensitive adhesive layer 20. Similarly, the filler 30b contained in the surface layer 12b includes not only filler 30b that is entirely contained within the surface layer 12b, but also filler 30b that is partially exposed from the surface of the surface layer 12b opposite to the main substrate layer 11.

[0026] 3 and 4, filler 30a partially exposed from the surface of surface layer 12a and in contact with pressure-sensitive adhesive layer 20 can also be said to be partially exposed from the surface of pressure-sensitive adhesive layer 20 and in contact with surface layer 12a from the perspective of the pressure-sensitive adhesive layer side. In this way, filler in contact with the surfaces of both surface layer 12a and pressure-sensitive adhesive layer 20 is treated as filler contained in the substrate (specifically, surface layer 12a) and in contact with the surface of the pressure-sensitive adhesive layer on the substrate (specifically, surface layer 12a) side.

[0027] In the pressure-sensitive adhesive sheet according to the embodiment of the present invention, "filler in contact with the surface of the pressure-sensitive adhesive layer facing the substrate" refers to a filler that is partially exposed from the surface of the substrate facing the pressure-sensitive adhesive layer, such as filler 30 shown in FIGS. 1 and 2 (filler 30 near the surface of the pressure-sensitive adhesive layer 20 in FIG. 2) or filler 30a shown in FIGS. 3 and 4, where the exposed portion of the filler is embedded in the pressure-sensitive adhesive layer. As one example, FIG. 5 is a schematic cross-sectional view illustrating in detail "filler in contact with the surface of the pressure-sensitive adhesive layer facing the substrate" using the embodiment shown in FIGS. 3 and 4 as an example, and is an enlarged view of a portion of the pressure-sensitive adhesive layer 20 and the surface layer 12a. FIG. 5 shows an example of "filler in contact with the surface of the pressure-sensitive adhesive layer facing the substrate" among fillers 30a contained in the surface layer 12a. The filler may be slightly embedded (slightly in contact) in the surface of the pressure-sensitive adhesive layer, as shown on the left, or may be largely embedded in the pressure-sensitive adhesive layer, as shown on the right. T in FIG. 5 indicates the height of the exposed portion of the filler that is partially exposed from the surface of the substrate on the pressure-sensitive adhesive layer side.

[0028] In the pressure-sensitive adhesive sheet according to an embodiment of the present invention, the number of fillers partially exposed from the surface of the substrate on the pressure-sensitive adhesive layer side, as observed within a 500 μm wide area on the surface of the substrate on the pressure-sensitive adhesive layer side when observed by cross-sectional TEM, is preferably 10 or more, more preferably 20 to 1500, even more preferably 25 to 1000, and particularly preferably 30 to 900.

[0029] In the pressure-sensitive adhesive sheet according to the embodiment of the present invention, the height T (see FIG. 5) of the exposed portion of the filler that is partially exposed from the surface of the substrate facing the pressure-sensitive adhesive layer may be greater than 0 nm, preferably greater than 0 nm and less than the average particle size of the filler, more preferably greater than 0 nm and less than 70% of the average particle size of the filler, and even more preferably greater than 0 nm and less than 50% of the average particle size of the filler. Such height T can be measured, for example, by cross-sectional TEM.

[0030] The pressure-sensitive adhesive sheet according to an embodiment of the present invention preferably has a flex recovery angle of 35 to 180 degrees, more preferably 40 to 180 degrees, even more preferably 43 to 180 degrees, and particularly preferably 45 to 180 degrees, as measured by the flex recovery test described below. The larger the flex recovery angle, the better the flex recovery property. As described above, the upper limit of the flex recovery angle measured by the flex recovery test described below is 180 degrees. If the flex recovery angle is within the above range, the pressure-sensitive adhesive sheet according to an embodiment of the present invention can exhibit excellent flex recovery property.

[0031] ≪1-1. Base material≫ The thickness of the entire substrate is preferably 5 μm to 500 μm, more preferably 10 μm to 200 μm, even more preferably 10 μm or more but less than 100 μm, even more preferably 20 μm to 90 μm, even more preferably 30 μm to 85 μm, even more preferably 30 μm to 80 μm, particularly preferably 35 μm to 75 μm, and most preferably 40 μm to 70 μm. When the thickness of the pressure-sensitive adhesive sheet according to the embodiment of the present invention is within the above range, the effects of the present invention can be more effectively exhibited.

[0032] The substrate typically contains a filler. Examples of the filler include inorganic fillers and organic fillers. The filler may be one type only, or two or more types may be used. Examples of the inorganic filler include inorganic oxides such as silica, titania, alumina, and zirconia; calcium carbonate; talc; clay; calcined kaolin; silicates such as calcined calcium silicate, hydrated calcium silicate, aluminum silicate, and magnesium silicate; and phosphates such as calcium phosphate. Examples of the organic filler include silicone resins, fluororesins, and acrylic resins. Among these, inorganic fillers are preferred, with inorganic oxides such as silica, titania, alumina, and zirconia being more preferred, and silica being particularly preferred.

[0033] The average particle diameter of the filler may be any appropriate average particle diameter as long as it does not impair the effects of the present invention. In order to further exhibit the effects of the present invention, the average particle diameter of the filler is preferably 10 nm to 400 nm, more preferably 20 nm to 350 nm, even more preferably 30 nm to 300 nm, and particularly preferably 50 nm to 250 nm. The average particle diameter of the filler can be measured, for example, by cross-sectional TEM.

[0034] The content of the filler in the substrate is preferably 10 ppm to 300 ppm, more preferably 20 ppm to 270 ppm, even more preferably 30 ppm to 250 ppm, and particularly preferably 40 ppm to 220 ppm by volume, in order to further exhibit the effects of the present invention. The content of the filler in the substrate can be calculated, for example, from a cross-sectional TEM image (planar image) as the proportion of the total area of ​​filler particles present in the area calculated by multiplying the thickness of the substrate by a predetermined width (for example, the width of the field of view of the image).

[0035] The substrate may have any appropriate structure as long as it does not impair the effects of the present invention. In order to further enhance the effects of the present invention, the substrate may be, for example, composed of only a main substrate layer as shown in Figures 1 and 2, or may be a two-layer structure of a surface layer / main substrate layer as shown in Figure 3, or may be a three-layer structure of a surface layer / main substrate layer / surface layer as shown in Figure 4.

[0036] When the substrate includes a main substrate layer and a surface layer (for example, the embodiment shown in Figures 3 and 4), the content of the filler included in the surface layer relative to the total filler included in the substrate is preferably 50% by weight to 100% by weight, more preferably 70% by weight to 100% by weight, even more preferably 90% by weight to 100% by weight, particularly preferably 95% by weight to 100% by weight, and most preferably 100% by weight, in order to further exhibit the effects of the present invention.

[0037] When the substrate includes a main substrate layer and a surface layer (for example, the embodiments shown in Figures 3 and 4), the content of the filler contained in the main substrate layer in the filler contained in the substrate is preferably 0% by weight to 50% by weight, more preferably 0% by weight to 30% by weight, even more preferably 0% by weight to 10% by weight, particularly preferably 0% by weight to 5% by weight, and most preferably 0% by weight, in order to further exhibit the effects of the present invention.

[0038] 1 and 2, when the substrate of the pressure-sensitive adhesive sheet according to the embodiment of the present invention is composed only of a main substrate layer without including a surface layer, it is preferable that all fillers contained in the substrate are present in a range from the outermost surface of the substrate toward the inside in the thickness direction to a depth d1, in order to better exhibit the effects of the present invention. In this case, when the thickness of the substrate is D1, the depth d1 is preferably (D1 x 0.3), more preferably (D1 x 0.2), even more preferably (D1 x 0.1), particularly preferably (D1 x 0.05), and most preferably (D1 x 0.01).

[0039] In the pressure-sensitive adhesive sheet according to an embodiment of the present invention, as shown in Figures 3 and 4, when a surface layer 12a contained in a substrate 10 contains a filler 30a, and at least a portion of the filler 30a is in contact with the pressure-sensitive adhesive layer, and the thickness of the surface layer 12a is D2, the effects of the present invention can be more effectively exhibited. In this regard, the filler 30a contained in the surface layer 12a preferably contains a filler having a particle diameter d2 that satisfies d2 > 0.01 × D2, more preferably contains a filler having a particle diameter d2 that satisfies d2 > 0.1 × D2, even more preferably contains a filler having a particle diameter d2 that satisfies d2 > 0.5 × D2, particularly preferably contains a filler having a particle diameter d2 that satisfies d2 > 0.8 × D2, and most preferably contains a filler having a particle diameter d2 that satisfies d2 > D2.

[0040] The thickness of the main substrate layer is preferably 5 μm to 500 μm per layer, more preferably 10 μm to 200 μm, even more preferably 10 μm or more but less than 100 μm, even more preferably 20 μm to 90 μm, even more preferably 30 μm to 85 μm, even more preferably 30 μm to 80 μm, particularly preferably 35 μm to 75 μm, and most preferably 40 μm to 70 μm, in order to further exert the effects of the present invention.

[0041] The thickness of the surface layer is preferably 10 nm to 400 nm per layer, more preferably 20 nm to 300 nm, even more preferably 30 nm to 200 nm, and particularly preferably 50 nm to 100 nm, in order to further exert the effects of the present invention.

[0042] As the main substrate layer, any appropriate main substrate layer can be used as long as the effects of the present invention are not impaired. A representative example of such a main substrate layer is a main substrate layer containing a resin material as a main component. Examples of such resin materials include polyester-based resins such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polybutylene terephthalate (PBT); acrylic-based resins such as polymethyl methacrylate (PMMA); olefin-based resins such as polyethylene (PE), polypropylene (PP), and ethylene-propylene copolymers; urethane-based resins; vinyl-based resins such as polyvinyl acetate; chlorine-based resins such as polyvinyl chloride (PVC); styrene-based resins; polycarbonate-based resins; cellulose-based resins such as triacetyl cellulose (TAC); polysulfone; polyethersulfone-based resins; polysulfone-based resins; polyarylate; ethylene-vinyl acetate copolymer (EVA); polyamide-based resins such as polyamide (nylon) and wholly aromatic polyamide (aramid); polyimide-based resins; polyphenylene sulfide (PPS); polyether ether ketone (PEEK); epoxy-based resins; melamine-based resins; oxazoline-based resins; silicone-based resins; fluorine-based resins; cyclic olefin-based polymers; and various graft-based resins. The resin material may be one type only, or two or more types.

[0043] When the substrate is composed only of a main substrate layer (for example, the embodiment shown in Figures 1 and 2), the content of the resin material in the main substrate layer is preferably 99.970% to 99.999%, more preferably 99.973% to 99.998%, even more preferably 99.975% to 99.997%, and particularly preferably 99.978% to 99.996% by volume. The content of the resin material in the main substrate layer can be calculated, for example, from a cross-sectional TEM image (planar image) as the percentage of the total area of ​​the resin material present in the area calculated by multiplying the thickness of the substrate by a predetermined width (for example, the width of the field of view of the image).

[0044] When the substrate includes a main substrate layer and a surface layer (for example, the embodiment shown in Figures 3 and 4), the content of the resin material in the main substrate layer is preferably 70% by weight to 100% by weight, more preferably 90% by weight to 100% by weight, even more preferably 95% by weight to 100% by weight, and particularly preferably 98% by weight to 100% by weight.

[0045] When the substrate includes a main substrate layer and a surface layer (for example, the embodiments shown in Figures 3 and 4), the content of the filler in the main substrate layer is preferably 0% by weight to 30% by weight, more preferably 0% by weight to 10% by weight, even more preferably 0% by weight to 5% by weight, particularly preferably 0% by weight to 2% by weight, and most preferably 0% by weight.

[0046] Any appropriate surface layer can be used as the surface layer as long as it does not impair the effects of the present invention.

[0047] The surface layer typically contains an organic component and a filler.

[0048] Examples of organic components that can be contained in the surface layer include the resin materials that can be contained in the main substrate layer, phthalate esters, sulfophthalic acid, ethylene glycol, polyvinyl alcohol, melamine, and nitrogen-containing organic substances.

[0049] The content of the organic component in the surface layer is preferably 70% to 99%, more preferably 75% to 99%, even more preferably 80% to 99%, and particularly preferably 85% to 99% by volume. The content of the organic component in the surface layer can be calculated, for example, from a cross-sectional TEM image (planar image) as the percentage of the total area of ​​the organic components present in the area calculated by multiplying the thickness of the surface layer by a predetermined width (for example, the width of the field of view of the image).

[0050] Examples of fillers that can be contained in the surface layer include the fillers that can be contained in the base layer described above.

[0051] The content of the filler in the surface layer is preferably 0.1% to 25%, more preferably 0.1% to 20%, even more preferably 0.1% to 17%, and particularly preferably 0.1% to 15% by volume. The content of the organic component in the surface layer can be calculated, for example, from a cross-sectional TEM image (planar image) as the proportion of the total area of ​​the filler present in the area calculated by multiplying the thickness of the surface layer by a predetermined width (for example, the width of the field of view of the image).

[0052] The surface layer can be formed by any appropriate method as long as it does not impair the effects of the present invention. For example, the surface layer can be formed from a surface layer-forming composition containing at least one selected from the group consisting of resin materials and monomer components capable of forming the resin material, and a filler. More specifically, the surface layer can be formed by, for example, applying a surface layer-forming composition containing at least one selected from the group consisting of resin materials and monomer components capable of forming the resin material, and a filler, to the surface of the main substrate layer to form a coating layer, and then drying the coating layer. Examples of coating methods include a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, bar coater, knife coater, air knife coater, spray coater, comma coater, direct coater, and roll brush coater.

[0053] When the resin component is an acrylic resin, examples of the monomer component include acrylic monomers such as acrylic acid and alkyl acrylate esters.

[0054] The surface layer-forming composition may contain any other appropriate components, such as a crosslinking agent and a solvent.

[0055] <1-2. Adhesive layer> The pressure-sensitive adhesive layer may be one layer or two or more layers. In one embodiment of the present invention, the pressure-sensitive adhesive layer is one layer.

[0056] The thickness of the pressure-sensitive adhesive layer is preferably 1 μm to 500 μm, more preferably 5 μm to 300 μm, even more preferably 10 μm to 100 μm, particularly preferably 10 μm to 80 μm, and most preferably 10 μm to 60 μm. When the thickness of the pressure-sensitive adhesive layer is within the above range, the effects of the present invention can be more effectively exhibited.

[0057] The pressure-sensitive adhesive layer is composed of an acrylic pressure-sensitive adhesive. More specifically, the pressure-sensitive adhesive layer is a layer of an acrylic pressure-sensitive adhesive. Any appropriate method for forming the pressure-sensitive adhesive layer can be used as long as it does not impair the effects of the present invention. Examples of such methods include applying an acrylic pressure-sensitive adhesive composition to a suitable substrate, optionally heating and drying the composition, and optionally curing the composition to form a pressure-sensitive adhesive layer composed of the acrylic pressure-sensitive adhesive on the substrate. Any appropriate method for applying the composition can be used as long as it does not impair the effects of the present invention. Examples of such application methods 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 appropriate method for heating and drying the acrylic pressure-sensitive adhesive composition can be used as long as it does not impair the effects of the present invention. Examples of such heating and drying methods include heating to approximately 60°C to 180°C. The acrylic pressure-sensitive adhesive composition may be cured by any suitable means as long as the effects of the present invention are not impaired, such as ultraviolet irradiation, laser irradiation, α-ray irradiation, β-ray irradiation, γ-ray irradiation, X-ray irradiation, and electron beam irradiation.

[0058] In the pressure-sensitive adhesive sheet according to an embodiment of the present invention, the pressure-sensitive adhesive layer preferably has a storage modulus at -20°C of less than 140 kPa, more preferably less than 135 kPa, even less than 130 kPa, particularly less than 125 kPa, and most preferably less than 120 kPa. From the viewpoint of ease of handling, the lower limit of the storage modulus is practically preferably 30 kPa or more. In the pressure-sensitive adhesive sheet according to an embodiment of the present invention, if the storage modulus at -20°C of the pressure-sensitive adhesive layer is within the above range, the pressure-sensitive adhesive layer will have a low modulus in the low temperature range, and therefore can exhibit excellent flex recovery. The method for measuring the storage modulus at -20°C will be described in detail below.

[0059] In the pressure-sensitive adhesive sheet according to an embodiment of the present invention, the pressure-sensitive adhesive layer preferably has a creep value at −20°C of 45% or more, more preferably 47% or more, even more preferably 49% or more, and particularly preferably 50% or more. The upper limit of the creep value is generally better, but taking into account the balance with other pressure-sensitive adhesive properties, etc., it is preferably 200% or less. The creep value at −20°C is an index of stress relaxation properties with respect to bending in a low-temperature environment; the higher the value, the better the stress relaxation properties with respect to bending in a low-temperature environment. If the creep value at −20°C is low, the stress relaxation properties with respect to bending in a low-temperature environment will be reduced, which may cause cracking or breakage of surrounding components when bending. The method for measuring the creep value at −20°C will be described in detail below.

[0060] In the pressure-sensitive adhesive sheet according to the embodiment of the present invention, the anchoring strength of the pressure-sensitive adhesive layer to the substrate is preferably 5.0 N / 25 mm or more, more preferably 6.0 N / 25 mm or more, even more preferably 7.0 N / 25 mm or more, particularly preferably 8.0 N / 25 mm or more, and most preferably 9.0 N / 25 mm or more. The upper limit of the anchoring strength is usually the higher the better, but in reality, it is usually preferably 30.0 N / 25 mm or less. In the pressure-sensitive adhesive sheet according to the embodiment of the present invention, if the anchoring strength of the pressure-sensitive adhesive layer to the substrate is within the above range, peeling between the substrate and the pressure-sensitive adhesive layer is unlikely to occur when the sheet is bent. If the anchoring strength of the pressure-sensitive adhesive layer to the substrate is too small, outside the above range, peeling between the substrate and the pressure-sensitive adhesive layer may occur when the sheet is bent.

[0061] <1-2-1. Acrylic adhesive> In the pressure-sensitive adhesive sheet according to the embodiment of the present invention, the acrylic pressure-sensitive adhesive is preferably formed from an acrylic pressure-sensitive adhesive composition.

[0062] In this way, an acrylic pressure-sensitive adhesive can be defined as something formed from an acrylic pressure-sensitive adhesive composition. Because an acrylic pressure-sensitive adhesive composition undergoes a crosslinking reaction or the like upon heating or ultraviolet irradiation to become an acrylic pressure-sensitive adhesive, it is impossible and practical to directly identify an acrylic pressure-sensitive adhesive by its structure ("impossible / impractical circumstances"). Therefore, the acrylic pressure-sensitive adhesive can be appropriately identified as a "product" by the definition of "something formed from an acrylic pressure-sensitive adhesive composition."

[0063] When the acrylic pressure-sensitive adhesive is formed from an acrylic pressure-sensitive adhesive composition, any appropriate method can be used to form the acrylic pressure-sensitive adhesive as long as it does not impair the effects of the present invention. Examples of methods for forming such acrylic pressure-sensitive adhesives include applying the acrylic pressure-sensitive adhesive composition to any appropriate substrate, optionally heating and drying it, and optionally curing it to form an acrylic pressure-sensitive adhesive on the substrate. Any appropriate 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 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 appropriate means can be used to heat and dry the acrylic pressure-sensitive adhesive composition as long as it does not impair the effects of the present invention. Examples of such heating and drying means include heating to approximately 60°C to 180°C. The acrylic pressure-sensitive adhesive composition can be cured by any appropriate means as long as the effects of the present invention are not impaired, including, for example, ultraviolet irradiation, laser irradiation, α-ray irradiation, β-ray irradiation, γ-ray irradiation, X-ray irradiation, and electron beam irradiation.

[0064] The pressure-sensitive adhesive sheet according to an embodiment of the present invention includes a pressure-sensitive adhesive layer composed of an acrylic pressure-sensitive adhesive, and the acrylic pressure-sensitive adhesive is preferably formed from an acrylic pressure-sensitive adhesive composition as described above. From the viewpoint of achieving the effects of the present invention, such an acrylic pressure-sensitive adhesive composition contains an acrylic polymer, an acrylic oligomer, and two or more crosslinking agents. The acrylic polymer is usually referred to as a base polymer. The effects of the present invention can be effectively achieved by the acrylic pressure-sensitive adhesive composition containing, in addition to the acrylic polymer as the base polymer, an acrylic oligomer and two or more crosslinking agents. If the acrylic pressure-sensitive adhesive composition does not contain an acrylic oligomer or contains only one type of crosslinking agent, the effects of the present invention may not be achieved.

[0065] The content of the acrylic polymer in the acrylic pressure-sensitive adhesive composition is preferably 50% by weight or more, more preferably 70% by weight or more, even more preferably 90% by weight or more, particularly preferably 95% by weight or more, and most preferably 97% by weight or more, in order to further exhibit the effects of the present invention. The upper limit of the content is preferably 99% by weight or less, more preferably 97% by weight or less, and even more preferably more than 95% by weight or less.

[0066] In the acrylic pressure-sensitive adhesive composition, the content of the acrylic oligomer relative to 100 parts by weight of the acrylic polymer is preferably 1 part by weight or more, more preferably 3 parts by weight or more but less than 17 parts by weight, even more preferably 5 parts by weight or more but less than 16 parts by weight, even more preferably 6 parts by weight or more but less than 15 parts by weight, particularly preferably 7 parts by weight or more but less than 14 parts by weight, and most preferably 8 parts by weight or more but less than 13 parts by weight. When the content of the acrylic oligomer is within the above range, the effects of the present invention can be more effectively exhibited. If the content of the acrylic oligomer is too low outside the above range, peeling may occur between the substrate and the pressure-sensitive adhesive layer, for example, when flexed. If the content of the acrylic oligomer is too high outside the above range, for example, the creep value at low temperatures may be low, stress relaxation may be reduced, and cracking or breakage of surrounding components may occur when flexed.

[0067] In the acrylic pressure-sensitive adhesive composition, the total content ratio of the two or more crosslinking agents relative to 100 parts by weight of the acrylic polymer is preferably 0.05 parts by weight or more, more preferably 0.10 parts by weight or more but less than 3.00 parts by weight, even more preferably 0.15 parts by weight or more but less than 2.50 parts by weight, even more preferably 0.20 parts by weight or more but less than 2.00 parts by weight, even more preferably 0.25 parts by weight or more but less than 1.50 parts by weight, even more preferably 0.30 parts by weight or more but less than 1.50 parts by weight, even more preferably 0.35 parts by weight or more but less than 1.40 parts by weight, particularly preferably 0.40 parts by weight or more but less than 1.30 parts by weight, and most preferably 0.45 parts by weight or more but less than 1.20 parts by weight.

[0068] [1-2-1-a. Acrylic polymer] The acrylic polymer may be of only one type, or of two or more types.

[0069] The weight average molecular weight Mw of the acrylic polymer is preferably 2.5 million or less, more preferably 2.4 million or less, even more preferably 2.3 million or less, still more preferably 2.2 million or less, and particularly preferably 2.1 million or less. The lower limit of the weight average molecular weight Mw is preferably 1 million or more.

[0070] The weight-average molecular weight can be measured, for example, by gel permeation chromatography (GPC). For example, an Agilent 1260 Infinity (manufactured by Agilent Technologies) is used as a GPC measurement device. Taking into account the polymer concentration of the sample, a 0.1 wt% amine-based component-added tetrahydrofuran solution is prepared, left to stand for 20 hours, filtered through a 0.45 μm membrane filter, and the resulting filtrate is subjected to GPC measurement. The GPC measurement conditions may be, for example, as follows: Sample concentration: 0.1% by weight (tetrahydrofuran solution with added amine components) Sample injection volume: 100 μL Column: Product name "TSKgel GMH-H(S)" (manufactured by Tosoh Corporation) Eluent: Tetrahydrofuran with added amine components ·Flow rate: 0.5mL / min Detector: Differential refractometer (RI) Column temperature (measurement temperature): 40℃ Standard sample: Polystyrene (PS)

[0071] The acrylic polymer can be obtained by polymerizing the monomer component (M).

[0072] In this way, an acrylic polymer can be defined as something obtained by polymerizing the monomer component (M). An acrylic polymer becomes an acrylic polymer through the polymerization reaction of the monomer component (M), and since there are circumstances that make it impossible and almost impractical to directly identify an acrylic polymer by its structure ("impossible / impractical circumstances"), an acrylic polymer can be properly identified as a "product" by the definition of "something obtained by polymerizing the monomer component (M)."

[0073] The monomer component (M) preferably contains an alkyl(meth)acrylate. The alkyl group in the ester moiety is preferably an alkyl group having 1 to 20 carbon atoms. The alkyl group in the ester moiety here does not include an alkyl group containing a polar group such as a hydroxyl group. The alkyl(meth)acrylate may be of only one type, or may be of two or more types.

[0074] The content of alkyl (meth)acrylate in the monomer component (M) is preferably 50 to 99% by weight, more preferably 70 to 99% by weight, even more preferably 80 to 99% by weight, still more preferably 90 to 99% by weight, particularly preferably 95 to 99% by weight, and most preferably 97 to 99% by weight, in order to further exhibit the effects of the present invention. When the content of alkyl (meth)acrylate in the monomer component (M) is within the above range, the effects of the present invention can be further exhibited.

[0075] As the alkyl(meth)acrylate, any appropriate alkyl(meth)acrylate can be used as long as it does not impair the effects of the present invention. As such an alkyl(meth)acrylate, for example, a compound represented by the following formula (1) can be suitably used. CH2=C(R 1 )COOR 2 (1)

[0076] Here, R in the above formula (1) 1 is a hydrogen atom or a methyl group, and R 2is an alkyl group having 1 to 20 carbon atoms.

[0077] R 2 is preferably an alkyl group having 1 to 16 carbon atoms, more preferably an alkyl group having 2 to 14 carbon atoms, even more preferably an alkyl group having 4 to 14 carbon atoms, and particularly preferably an alkyl group having 4 to 12 carbon atoms, in that the effects of the present invention can be more effectively exhibited.

[0078] The alkyl group is preferably a chain alkyl group, which can more effectively exhibit the effects of the present invention. Here, the term "chain" includes both linear and branched alkyl groups.

[0079] R 2 Examples of alkyl(meth)acrylates in which is a chain alkyl group having 1 to 20 carbon atoms include methyl(meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate, isopropyl(meth)acrylate, n-butyl(meth)acrylate, isobutyl(meth)acrylate, s-butyl(meth)acrylate, pentyl(meth)acrylate, isopentyl(meth)acrylate, hexyl(meth)acrylate, heptyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, octyl(meth)acrylate, and isooctyl(meth). ) acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isostearyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate.

[0080] In order to further demonstrate the effects of the present invention, the alkyl(meth)acrylate that can be contained in the monomer component (M) preferably has a glass transition temperature (Tg) of its homopolymer (homopolymer) of -10°C or lower, more preferably -12°C or lower, even more preferably -15°C or lower, particularly preferably -18°C or lower, and most preferably -20°C or lower. The lower limit of the glass transition temperature (Tg) is preferably -80°C or higher. The glass transition temperature (Tg) of the alkyl(meth)acrylate homopolymer that can be contained in the monomer component (M) can affect the adhesive properties and flexural properties of the acrylic polymer. By using an alkyl(meth)acrylate whose homopolymer (homopolymer) has a glass transition temperature (Tg) within the above range as the alkyl(meth)acrylate that can be contained in the monomer component (M), the adhesive properties and flexural properties of the acrylic polymer can be appropriately adjusted, thereby further demonstrating the effects of the present invention.

[0081] Here, the glass transition temperature Tg of a homopolymer of alkyl (meth)acrylate that may be contained in the monomer component (M) can be a value described in a publicly known document, such as the value described in "Polymer Handbook" (3rd Edition, John Wiley & Sons, Inc., 1989). When multiple values ​​are described in the "Polymer Handbook," the conventional value is used. For alkyl (meth)acrylates not described in the "Polymer Handbook," the value listed in the catalog of the monomer manufacturer is used. For alkyl (meth)acrylate homopolymers not described in the "Polymer Handbook" and for which no catalog value is provided by the monomer manufacturer, the value obtained by the measurement method described in JP 2007-51271 A is used.

[0082] Representative examples of the glass transition temperature Tg of a homopolymer of alkyl (meth)acrylate that can be contained in the monomer component (M) are as follows: 2-Ethylhexyl acrylate (2EHA): -70℃ Lauryl acrylate (LA): -23℃ n-Butyl acrylate (BA): -55℃

[0083] In order to further exert the effects of the present invention, the monomer component (M) preferably contains, as the alkyl (meth)acrylate, an alkyl (meth)acrylate (m1) whose homopolymer has a glass transition temperature Tg in the range of −80° C. to −60° C. When the monomer component (M) contains the alkyl (meth)acrylate (m1), in order to further exert the effects of the present invention, the content of the alkyl (meth)acrylate (m1) in the monomer component (M) is preferably 40% to 99% by weight, more preferably 50% to 90% by weight, even more preferably 55% to 85% by weight, particularly preferably 60% to 80% by weight, and most preferably 65% ​​to 75% by weight.

[0084] An example of the alkyl(meth)acrylate (m1) is 2-ethylhexyl acrylate (2EHA) (the glass transition temperature Tg of its homopolymer is −70° C.).

[0085] In order to further exert the effects of the present invention, the monomer component (M) preferably contains, as the alkyl (meth)acrylate, an alkyl (meth)acrylate (m2) whose homopolymer has a glass transition temperature Tg in the range of −40° C. to −10° C. When the monomer component (M) contains the alkyl (meth)acrylate (m2), in order to further exert the effects of the present invention, the content of the alkyl (meth)acrylate (m2) in the monomer component (M) is preferably 1 to 50% by weight, more preferably 3 to 30% by weight, even more preferably 4 to 20% by weight, particularly preferably 5 to 15% by weight, and most preferably 6 to 10% by weight.

[0086] An example of the alkyl (meth)acrylate (m2) is lauryl acrylate (LA) (the glass transition temperature Tg of its homopolymer is −23° C.).

[0087] In order to further exert the effects of the present invention, the monomer component (M) preferably contains, as the alkyl (meth)acrylate, an alkyl (meth)acrylate (m3) whose homopolymer has a glass transition temperature Tg in the range of more than −60° C. to less than −40° C. When the monomer component (M) contains the alkyl (meth)acrylate (m3), in order to further exert the effects of the present invention, the content of the alkyl (meth)acrylate (m3) in the monomer component (M) is preferably 1 to 45% by weight, more preferably 3 to 40% by weight, even more preferably 5 to 35% by weight, particularly preferably 10 to 30% by weight, and most preferably 15 to 25% by weight.

[0088] An example of the alkyl(meth)acrylate (m3) is n-butyl acrylate (BA) (the glass transition temperature Tg of its homopolymer is −55° C.).

[0089] In order to further exert the effects of the present invention, the monomer component (M) preferably contains at least one selected from the group consisting of alkyl (meth)acrylate (m1), alkyl (meth)acrylate (m2), and alkyl (meth)acrylate (m3), more preferably contains at least two selected from the group consisting of alkyl (meth)acrylate (m1), alkyl (meth)acrylate (m2), and alkyl (meth)acrylate (m3), and even more preferably contains all of alkyl (meth)acrylate (m1), alkyl (meth)acrylate (m2), and alkyl (meth)acrylate (m3).

[0090] In terms of being able to further exert the effects of the present invention, typically, the monomer component (M) preferably contains at least one selected from the group consisting of 2-ethylhexyl acrylate, lauryl acrylate, and n-butyl acrylate, more preferably contains at least two selected from the group consisting of 2-ethylhexyl acrylate, lauryl acrylate, and n-butyl acrylate, and even more preferably contains all of 2-ethylhexyl acrylate, lauryl acrylate, and n-butyl acrylate.

[0091] The monomer component (M) preferably contains a hydroxyl group-containing monomer (m4). The hydroxyl group-containing monomer (m4) may be one type only, or two or more types. When the monomer component (M) contains a hydroxyl group-containing monomer (m4), the acrylic polymer becomes a hydroxyl group-containing acrylic polymer.

[0092] When the monomer component (M) contains a hydroxyl group-containing monomer (m4), the content of the hydroxyl group-containing monomer (m4) in the monomer component (M) is preferably 0.01% by weight to 30% by weight, more preferably 0.05% by weight to 10% by weight, even more preferably 0.1% by weight to 5.0% by weight, particularly preferably 0.3% by weight to 3.0% by weight, and most preferably 0.5% by weight to 1.5% by weight, in order to further exert the effects of the present invention.

[0093] Examples of the hydroxyl group-containing monomer (m4) 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.

[0094] In order to further exert the effects of the present invention, the hydroxyl group-containing monomer (m4) preferably contains a hydroxyalkyl(meth)acrylate, and more preferably contains a hydroxyalkyl(meth)acrylate in which the alkyl group moiety is a linear alkyl group having 2 to 4 carbon atoms. Examples of the hydroxyalkyl(meth)acrylate include 2-hydroxyethyl acrylate (HEA) and 4-hydroxybutyl acrylate (4HBA), and in order to further exert the effects of the present invention, 4-hydroxybutyl acrylate is preferred.

[0095] In order to further enhance the effects of the present invention, the hydroxyl group-containing monomer (m4) that can be contained in the monomer component (M) preferably has a glass transition temperature (Tg) of its homopolymer (homopolymer) of -10°C or lower, more preferably -15°C or lower, even more preferably -20°C or lower, particularly preferably -25°C or lower, and most preferably -30°C or lower. The lower limit of the glass transition temperature (Tg) is preferably -80°C or higher. The glass transition temperature (Tg) of the homopolymer (homopolymer) of the hydroxyl group-containing monomer (m4) that can be contained in the monomer component (M) can affect the adhesive properties and flexural properties of the acrylic polymer. By using a hydroxyl group-containing monomer (m4) whose homopolymer (homopolymer) has a glass transition temperature (Tg) within the above range as the hydroxyl group-containing monomer (m4) that can be contained in the monomer component (M), the adhesive properties and flexural properties of the acrylic polymer can be appropriately adjusted, thereby further enhancing the effects of the present invention.

[0096] Here, the glass transition temperature Tg of a homopolymer of the hydroxyl group-containing monomer (m4) that can be contained in the monomer component (M) may be determined in the same manner as the glass transition temperature Tg of the homopolymer of the aforementioned alkyl (meth)acrylate.

[0097] Representative examples of the glass transition temperature Tg of the homopolymer of the hydroxyl group-containing monomer (m4) that can be contained in the monomer component (M) are as follows. 2-Hydroxyethyl acrylate: -15℃ 4-Hydroxybutyl acrylate: -40℃

[0098] In order to further exert the effects of the present invention, the monomer component (M) preferably contains at least one selected from the group consisting of alkyl (meth)acrylate (m1), alkyl (meth)acrylate (m2), and alkyl (meth)acrylate (m3), and a hydroxyl group-containing monomer (m4), more preferably contains at least two selected from the group consisting of alkyl (meth)acrylate (m1), alkyl (meth)acrylate (m2), and alkyl (meth)acrylate (m3), and a hydroxyl group-containing monomer (m4), and even more preferably contains all of alkyl (meth)acrylate (m1), alkyl (meth)acrylate (m2), and alkyl (meth)acrylate (m3), and a hydroxyl group-containing monomer (m4).

[0099] In terms of being able to further exert the effects of the present invention, the monomer component (M) typically preferably contains at least one selected from the group consisting of 2-ethylhexyl acrylate, lauryl acrylate, and n-butyl acrylate, and a hydroxyl group-containing monomer (m4), more preferably contains at least two selected from the group consisting of 2-ethylhexyl acrylate, lauryl acrylate, and n-butyl acrylate, and a hydroxyl group-containing monomer (m4), and even more preferably contains all of 2-ethylhexyl acrylate, lauryl acrylate, and n-butyl acrylate, and a hydroxyl group-containing monomer (m4).

[0100] The monomer component (M) may contain other monomers as long as the effects of the present invention are not impaired. The other monomers can be used, for example, for the purpose of adjusting the glass transition temperature (Tg) of the acrylic polymer, adjusting the adhesive properties, etc. The other monomers may be one type only, or two or more types.

[0101] Examples of other monomers include carboxy group-containing monomers, nitrogen-containing monomers, sulfonic acid group-containing monomers, phosphoric acid group-containing monomers, cyano group-containing monomers, acid anhydride group-containing monomers, vinyl esters (e.g., vinyl acetate (VAc), vinyl propionate, vinyl laurate), aromatic vinyl compounds, amide group-containing monomers, epoxy group-containing monomers, (meth)acryloylmorpholine, and vinyl ethers.

[0102] Examples of carboxy group-containing monomers include acrylic acid (AA), methacrylic acid (MAA), carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid.

[0103] Examples of nitrogen-containing monomers include nitrogen-containing vinyl monomers such as N-vinyl-2-pyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, (meth)acryloylmorpholine, N-vinylcarboxylic acid amides, and N-vinylcaprolactam; and cyano group-containing acrylic monomers such as acrylonitrile and methacrylonitrile.

[0104] As the other monomer, N-vinyl-2-pyrrolidone is preferred because it has a high effect of improving adhesive strength by improving cohesive strength.

[0105] The content of other monomers in the monomer component (M) is preferably 0% by weight to 20% by weight, more preferably 0% by weight to 10% by weight, even more preferably 0% by weight to 5% by weight, particularly preferably 0% by weight to 3% by weight, and most preferably 0% by weight to 1% by weight.

[0106] Acrylic polymers can be obtained by various polymerization methods known as acrylic polymer synthesis techniques, such as solution polymerization, emulsion polymerization, bulk polymerization, and suspension polymerization. Among these polymerization methods, solution polymerization is preferred. Monomer supply methods for solution polymerization include a batch feed method in which the entire amount of the monomer components is supplied at once, a continuous feed (dropping) method, and a divided feed (dropping) method. The polymerization temperature can be appropriately selected depending on the types of monomers and solvents used, the type of polymerization initiator, and the like, and is preferably 20°C or higher, more preferably 30°C or higher, and even more preferably 40°C or higher, and preferably 170°C or lower, more preferably 160°C or lower, and even more preferably 140°C or lower. Acrylic polymers can also be obtained by photopolymerization (typically in the presence of a photopolymerization initiator) using UV or other light, or by radiation polymerization using β-rays, γ-rays, or other radiation.

[0107] The solvent (polymerization solvent) used in solution polymerization can be appropriately selected from any suitable organic solvent, for example, aromatic compounds (typically aromatic hydrocarbons) such as toluene, acetate esters such as ethyl acetate, aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane, etc.

[0108] The initiator (polymerization initiator) used for polymerization can be appropriately selected from any appropriate polymerization initiator depending on the type of polymerization method. The polymerization initiator may be one type only, or two or more types may be used.

[0109] Examples of the polymerization initiator 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, 2,2'-azobis[2-(5-methyl-2-imidazolin-2-yl)propane]dihydrochloride, and azo initiators such as 2,2'-azobis(2-methylpropionamidine) disulfate, 2,2'-azobis(N,N'-dimethyleneisobutylamidine), and 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine]hydrate (VA-057, Wako Pure Chemical Industries, Ltd.); persulfates such as potassium persulfate and ammonium persulfate, di(2-ethylhexyl) peroxydicarbonate, and di( Examples of initiators include peroxide initiators such as 4-t-butylcyclohexyl)peroxydicarbonate, di-sec-butyl peroxydicarbonate, t-butyl peroxyneodecanoate, t-hexyl peroxypivalate, t-butyl peroxypivalate, dilauroyl peroxide, di-n-octanoyl peroxide, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, di(4-methylbenzoyl)peroxide, dibenzoyl peroxide, t-butyl peroxyisobutyrate, 1,1-di(t-hexylperoxy)cyclohexane, t-butyl hydroperoxide, and hydrogen peroxide; redox initiators that combine a peroxide with a reducing agent, such as a combination of a persulfate and sodium hydrogen sulfite or a combination of a peroxide and sodium ascorbate; substituted ethane initiators such as phenyl-substituted ethane; and aromatic carbonyl compounds.

[0110] The amount of the polymerization initiator used may be any appropriate amount within the range that does not impair the effects of the present invention, and is preferably 0.005 to 1 part by weight, more preferably 0.01 to 1 part by weight, per 100 parts by weight of the monomer component (M).

[0111] The polymerization may contain any other appropriate additives as long as they do not impair the effects of the present invention.

[0112] [1-2-1-b. Acrylic Oligomer] The acrylic oligomer may be of one kind or two or more kinds.

[0113] The weight average molecular weight Mw of the acrylic oligomer is preferably 1000 to 30000, more preferably 1500 to 10000, still more preferably 2000 to 8000, and particularly preferably 2000 to 5000. By using an acrylic oligomer having such a weight average molecular weight Mw, the adhesive properties and flexural properties of the acrylic pressure-sensitive adhesive can be improved.

[0114] The glass transition temperature Tg of the acrylic oligomer is preferably 20° C. or higher, more preferably 30° C. or higher, even more preferably 40° C. or higher, particularly preferably 50° C. or higher, and most preferably 60° C. or higher. The upper limit of the glass transition temperature Tg of the acrylic oligomer is preferably 200° C. or lower, more preferably 180° C. or lower, and even more preferably 160° C. or lower.

[0115] The glass transition temperature Tg of an acrylic oligomer is a value calculated from the Fox equation based on the Tg of a homopolymer of each constituent monomer and the weight fraction (copolymerization ratio by weight) of the monomer. The Fox equation, as shown below, is a relational expression between the Tg of a copolymer and the glass transition temperature Tgi of a homopolymer obtained by homopolymerizing each of the monomers constituting the copolymer. 1 / Tg=Σ(Wi / Tgi)

[0116] In the Fox formula, Tg represents the glass transition temperature (unit: K) of the copolymer, Wi represents the weight fraction of monomer i in the copolymer (copolymerization ratio by weight), and Tgi represents the glass transition temperature (unit: K) of a homopolymer of monomer i. The Tg of a homopolymer can be a value listed in a publicly available document, such as the value listed in the "Polymer Handbook" (3rd Edition, John Wiley & Sons, Inc., 1989). If multiple values ​​are listed in the "Polymer Handbook," the conventional value is used. For monomers not listed in the "Polymer Handbook," the catalog value from the monomer manufacturer is used. For the Tg of a homopolymer of a monomer not listed in the "Polymer Handbook" or for which no catalog value from the monomer manufacturer is provided, the value obtained by the measurement method described in JP 2007-51271 A is used.

[0117] The acrylic oligomer contains an alicyclic alkyl (meth)acrylate as a main constituent monomer component, and the alicyclic alkyl (meth)acrylate may be of one type only or of two or more types.

[0118] Examples of alicyclic alkyl (meth)acrylates include cycloalkyl (meth)acrylates 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; and (meth)acrylic acid esters having a tricyclic or higher aliphatic hydrocarbon ring such as dicyclopentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, tricyclopentanyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate.

[0119] As the alicyclic alkyl(meth)acrylate, cyclohexyl(meth)acrylate and dicyclopentanyl(meth)acrylate are preferred in that they can further exert the effects of the present invention.

[0120] The content of the alicyclic alkyl (meth)acrylate relative to the total amount of constituent monomer components of the acrylic oligomer is preferably 10% by weight to 99% by weight, more preferably 30% by weight to 99% by weight, even more preferably 50% by weight to 98% by weight, particularly preferably 70% by weight to 98% by weight, and most preferably 90% by weight to 98% by weight, in order to further exhibit the effects of the present invention.

[0121] The acrylic oligomer is preferably a carboxyl group-containing acrylic oligomer, as it can more effectively exhibit the effects of the present invention.

[0122] The carboxyl group-containing acrylic oligomer preferably contains (meth)acrylic acid as a constituent monomer component, and as the (meth)acrylic acid, acrylic acid is preferred in that the effects of the present invention can be more effectively exhibited.

[0123] The content of (meth)acrylic acid relative to the total amount of constituent monomer components of the acrylic oligomer is preferably 0.1 to 20% by weight, more preferably 1 to 10% by weight, even more preferably 2 to 8% by weight, and particularly preferably 3 to 7% by weight, in order to further exhibit the effects of the present invention.

[0124] The acrylic oligomer may contain, as a constituent monomer component, a chain alkyl (meth)acrylate having a chain alkyl group, and the chain alkyl (meth)acrylate having a chain alkyl group may be one type or two or more types. Here, chain includes both linear and branched.

[0125] The chain alkyl (meth)acrylate is preferably a chain alkyl (meth)acrylate having a chain alkyl group having 1 to 20 carbon atoms, and examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and octyl (meth)acrylate. acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isostearyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate.

[0126] As the chain alkyl (meth)acrylate, methyl methacrylate is preferred in that it can further exhibit the effects of the present invention.

[0127] The content of the chain alkyl (meth)acrylate relative to the total amount of the constituent monomer components of the acrylic oligomer is preferably 70% by weight or less, more preferably 50% by weight or less, even more preferably 30% by weight or less, particularly preferably 10% by weight or less, and most preferably 5% by weight or less.

[0128] The acrylic oligomer can be obtained by polymerizing the constituent monomer components by various polymerization methods. During the polymerization to obtain the acrylic oligomer, any appropriate additive may be used within a range that does not impair the effects of the present invention. Examples of such additives include a polymerization initiator and a chain transfer agent.

[0129] [1-2-1-c. Crosslinking Agents] The acrylic pressure-sensitive adhesive composition contains two or more types of crosslinking agents. If the acrylic pressure-sensitive adhesive composition contains only one type of crosslinking agent, the effects of the present invention may not be achieved.

[0130] The number of types of crosslinking agents is two or more, preferably two to five, more preferably two to four, still more preferably two to three, and particularly preferably two.

[0131] The two or more crosslinking agents contained in the acrylic pressure-sensitive adhesive composition may be any appropriate crosslinking agents as long as they do not impair the effects of the present invention. Examples of such crosslinking agents include at least two crosslinking agents selected from the group consisting of epoxy crosslinking agents, isocyanate crosslinking agents, silicone crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, silane crosslinking agents, alkyl etherified melamine crosslinking agents, metal chelate crosslinking agents, and peroxides.

[0132] The two or more crosslinking agents contained in the acrylic pressure-sensitive adhesive composition preferably include an epoxy-based crosslinking agent, and more preferably include two types of crosslinking agents, an epoxy-based crosslinking agent and an isocyanate-based crosslinking agent, in order to further enhance the effects of the present invention. The epoxy-based crosslinking agent may be of only one type, or may be of two or more types. The isocyanate-based crosslinking agent may be of only one type, or may be of two or more types.

[0133] When the crosslinking agent contains an epoxy-based crosslinking agent, the content of the epoxy-based crosslinking agent relative to 100 parts by weight of the acrylic polymer is preferably 0.05 parts by weight or more, more preferably 0.05 parts by weight or more but less than 2 parts by weight, even more preferably 0.1 parts by weight or more but less than 1.5 parts by weight, even more preferably 0.2 parts by weight or more but less than 1.0 parts by weight, particularly preferably 0.3 parts by weight or more but less than 1.0 parts by weight, and most preferably 0.4 parts by weight or more but less than 1.0 parts by weight. When the content of the epoxy-based crosslinking agent is within the above range, the effects of the present invention can be more effectively achieved. If the content of the epoxy-based crosslinking agent is too low, the effects of the present invention may not be achieved, for example, the anchoring strength may be significantly reduced. If the content of the epoxy-based crosslinking agent is too high, the effects of the present invention may not be achieved, for example, the anchoring strength may be reduced.

[0134] When the crosslinking agent contains an epoxy-based crosslinking agent and an isocyanate-based crosslinking agent, the content of the isocyanate-based crosslinking agent relative to 100 parts by weight of the acrylic polymer is preferably 0.06 parts by weight or more, more preferably 0.06 parts by weight or more but less than 0.20 parts by weight, even more preferably 0.07 parts by weight or more but less than 0.18 parts by weight, particularly preferably 0.07 parts by weight or more but less than 0.16 parts by weight, and most preferably 0.08 parts by weight or more but less than 0.15 parts by weight. When the content of the isocyanate-based crosslinking agent is within the above range, the effects of the present invention can be more effectively exhibited. If the content of the isocyanate-based crosslinking agent is too low, the effects of the present invention may not be exhibited, for example, the cohesive strength of the acrylic pressure-sensitive adhesive may be reduced. If the content of the isocyanate-based crosslinking agent is too high, the effects of the present invention may not be exhibited, for example, the adhesion between the acrylic pressure-sensitive adhesive and the adherend may be reduced.

[0135] The crosslinking agent may be contained in the acrylic PSA in a form after crosslinking reaction, a form before crosslinking reaction, a partially crosslinked form, an intermediate or composite form thereof, etc. The crosslinking agent is typically contained in the acrylic PSA in a form after crosslinking reaction.

[0136] As the epoxy-based crosslinking agent, a multifunctional epoxy compound having two or more epoxy groups in one molecule can be used. Examples of the epoxy-based crosslinking agent include N,N,N',N'-tetraglycidyl-m-xylenediamine, diglycidylaniline, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and sorbitol polyglycidyl ether. Examples of epoxy crosslinking agents include glycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitan polyglycidyl ether, trimethylolpropane polyglycidyl ether, adipic acid diglycidyl ester, o-phthalic acid diglycidyl ester, triglycidyl-tris(2-hydroxyethyl)isocyanurate, resorcinol diglycidyl ether, bisphenol-S-diglycidyl ether, and epoxy resins having two or more epoxy groups in the molecule. Commercially available epoxy crosslinking agents include, for example, "Tetrad C" and "Tetrad X" manufactured by Mitsubishi Gas Chemical Company, Inc.

[0137] The isocyanate crosslinking agent can be a compound having two or more isocyanate groups (including isocyanate-regenerating polar groups in which the isocyanate group is temporarily protected by a blocking agent or oligomerization) per molecule. Examples of the isocyanate crosslinking agent include aromatic isocyanates such as tolylene diisocyanate and xylene diisocyanate; alicyclic isocyanates such as isophorone diisocyanate; and aliphatic isocyanates such as hexamethylene diisocyanate.

[0138] Examples of the isocyanate crosslinking agent 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; 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 of hexamethylene diisocyanate (e.g., manufactured by Tosoh Corporation, trade name: Coronate HL). Examples of suitable polyisocyanates include isocyanate adducts such as those manufactured by Mitsui Chemicals under the trade name of Coronate HX; trimethylolpropane adducts of xylylene diisocyanate (for example, Mitsui Chemicals, Inc., trade name: Takenate D110N), trimethylolpropane adducts of xylylene diisocyanate (for example, Mitsui Chemicals, Inc., trade name: Takenate D120N), trimethylolpropane adducts of isophorone diisocyanate (for example, Mitsui Chemicals, Inc., trade name: Takenate D140N), and trimethylolpropane adducts of hexamethylene diisocyanate (for example, Mitsui Chemicals, Inc., trade name: Takenate D160N); polyether polyisocyanates, polyester polyisocyanates, and adducts of these with various polyols; and polyisocyanates multifunctionalized with isocyanurate bonds, biuret bonds, allophanate bonds, etc. Among these, aromatic isocyanates and alicyclic isocyanates are preferred because they can achieve a good balance between deformability and cohesive strength.

[0139] [1-2-1-d. Other ingredients] The acrylic pressure-sensitive adhesive composition may contain any other appropriate components as long as they do not impair the effects of the present invention.Such other components include, for example, polymer components other than acrylic polymers, crosslinking accelerators, crosslinking catalysts, silane coupling agents, tackifying resins (rosin derivatives, polyterpene resins, petroleum resins, oil-soluble phenols, etc.), antioxidants, inorganic fillers, organic fillers, metal powders, colorants (pigments, dyes, etc.), foil-like materials, UV absorbers, antioxidants, light stabilizers, nucleating agents, chain transfer agents, plasticizers, softeners, surfactants, antistatic agents, conductive agents, stabilizers, surface lubricants, leveling agents, corrosion inhibitors, heat stabilizers, polymerization inhibitors, lubricants, solvents, and catalysts.

[0140] 2. Flexible Devices A flexible device according to an embodiment of the present invention includes an adhesive sheet according to an embodiment of the present invention.

[0141] The adhesive sheet according to an embodiment of the present invention can combine excellent bending recovery and high anchoring strength, and therefore can be suitably provided in flexible devices such as bendable devices (devices that can be bent) having movable bending parts, foldable devices (devices that can be folded), and rollable devices (devices that can be rolled up).

[0142] The flexible device of the present invention may include any other appropriate member as long as it includes the pressure-sensitive adhesive sheet according to an embodiment of the present invention.

[0143] Fig. 6 is a schematic cross-sectional view showing one embodiment of a flexible device of the present invention as a representative example of one usage form of the pressure-sensitive adhesive sheet according to an embodiment of the present invention. In Fig. 6, flexible device 1000 according to an embodiment of the present invention includes cover film 200, pressure-sensitive adhesive layer 300, polarizer 400, pressure-sensitive adhesive layer 500, touch sensor 600, pressure-sensitive adhesive layer 700, OLED 800, and pressure-sensitive adhesive sheet 100 according to an embodiment of the present invention. In Fig. 6, pressure-sensitive adhesive sheet 100 according to an embodiment of the present invention is composed of substrate 10 and pressure-sensitive adhesive layer 20. Pressure-sensitive adhesive layer 300, pressure-sensitive adhesive layer 500, and pressure-sensitive adhesive layer 700 may be pressure-sensitive adhesive layers composed of a pressure-sensitive adhesive having the same composition as pressure-sensitive adhesive layer 20 constituting pressure-sensitive adhesive sheet 100 according to an embodiment of the present invention, or pressure-sensitive adhesive layers containing a pressure-sensitive adhesive having a different composition. [Example]

[0144] The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention is not limited to these examples. In the following description, "parts" and "%" are by weight unless otherwise specified.

[0145] The abbreviations and details of the raw materials used in the following Production Examples, Examples, and Comparative Examples are as follows: 2EHA: 2-ethylhexyl acrylate LA: Lauryl acrylate BA: n-butyl acrylate 4HBA: 4-hydroxybutyl acrylate NVP: N-vinyl-2-pyrrolidone AIBN: 2,2'-azobisisobutyronitrile CHMA: Cyclohexyl methacrylate AA: acrylic acid C / HX: Coronate HX (Tosoh Corporation, isocyanate crosslinking agent) TETRAD-C (Mitsubishi Gas Chemical Company, Inc., epoxy crosslinking agent) Nasem ferric: iron catalyst (manufactured by Nippon Chemical Industry Co., Ltd.)

[0146] <Substrate details> The substrates used in the examples and comparative examples are as follows. [Polyester film #50-U48 (manufactured by Toray Industries, Inc.)] This is a polyester film with a low-interference, easy-adhesion coating on both surfaces of a particle-free PET layer. Cross-sectional TEM observation revealed that a 90-nm-thick surface layer (low-interference, easy-adhesion coating) was provided on both surfaces of a 50-μm-thick main substrate layer (PET layer), and 38 particles with diameters of 140 nm to 160 nm were observed within a 500-μm-wide area of ​​the surface layer. [Polyester film #75-U48 (manufactured by Toray Industries, Inc.)] This is a polyester film with a low-interference, easy-adhesion coating on both surfaces of a particle-free PET layer. Cross-sectional TEM observation revealed that a 90-nm-thick surface layer (low-interference, easy-adhesion coating) was provided on both surfaces of the 75-μm-thick main substrate layer (PET layer), and 37 particles with diameters of 140 nm to 160 nm were observed within a 500-μm-wide area of ​​the surface layer. [Polyester film SRF (Cosmoshine SRF, manufactured by Toyobo Co., Ltd.)] This is a polyester film with easy-adhesion layers on both surfaces of a particle-free PET layer. Cross-sectional TEM observation revealed that it had 60 nm thick surface layers (easy-adhesion layers) on both surfaces of an 80 μm thick main substrate layer (PET layer), and 938 particles with diameters of 70 nm to 80 nm were observed within a 500 μm wide area of ​​the surface layers. [Polyester film T100C50 (Mitsubishi Chemical Corporation, Diafoil T100C50, thickness = 50 μm)] PET film with particles inside.

[0147] <Preparation of test specimens for measuring storage modulus at -20°C and creep value at -20°C> The coating solution of the acrylic pressure-sensitive adhesive composition was applied to a release sheet (manufactured by Mitsubishi Chemical Corporation, MRV50T100J) made of polyester resin with a thickness of 50 μm and one side of which had been silicone-treated, so that the thickness after drying would be 15 μm, and the coating was dried under conditions of a drying temperature of 135°C and a drying time of 1 minute. Next, a release sheet (manufactured by Mitsubishi Chemical Corporation, MRQ50T100J) made of polyester resin with a thickness of 50 μm and one side of which had been silicone-treated was attached to the surface of the obtained pressure-sensitive adhesive layer so that the silicone-treated surface was in contact with the surface, thereby preparing a pressure-sensitive adhesive sheet. This was then aged at 50°C for 1 day to prepare a test specimen.

[0148] <Storage modulus at -20℃> Only the adhesive layer was taken out from the test piece, laminated to a thickness of about 1 mm, and punched out to a diameter of 8 mm to prepare a cylindrical pellet, which was used as a measurement sample. The obtained measurement sample was fixed to a jig with a φ8 mm parallel plate using a dynamic viscoelasticity measuring device (manufactured by TA Instruments, DHR-2), and the storage modulus was calculated under the following measurement conditions. Measurement: Shear mode Temperature range: -50℃~200℃ Heating rate: 5°C / min Frequency: 1Hz Distortion: 0.1%

[0149] <Creep value at -20°C> Only the adhesive layer was taken out from the test piece, laminated to a thickness of about 1 mm, and punched out to a diameter of 8 mm to prepare a cylindrical pellet, which was used as a measurement sample. Using a dynamic viscoelasticity measuring device (TA Instruments, DHR-2), the obtained measurement sample was fixed to a φ8 mm parallel plate jig. A deformation stress of 10 kPa was applied at -20°C, and the deformation strain (%) after holding for 600 seconds was taken as the creep value at -20°C.

[0150] <Cross-sectional TEM observation> The obtained adhesive sheet was embedded in resin, and then a test piece was prepared by ultra-thin sectioning including noble metal staining. Cross-sectional TEM observation was performed using a Hitachi HT7820 microscope at an acceleration voltage of 100 kV and a magnification of 100,000 times. Observation was performed over a width of 500 μm, and the number of particles was counted. The number of particles was counted at two arbitrary locations on the cut surface, and the average value was calculated.

[0151] <Bending recovery> The pressure-sensitive adhesive sheets obtained in the Examples and Comparative Examples were attached to a polyimide film (trade name "Upilex 50S", manufactured by Ube Industries, Ltd.) using a 2 kg hand roller in one stroke. The sheets were then autoclaved at 50°C, 0.5 MPa, and 15 minutes, and then cut to a width of 25 mm and a length of 100 mm to prepare test specimens. The resulting test specimens were sandwiched between 1 mm thick glass plates 50 and bent as shown in Figure 7, and stored at 85°C for 120 hours. The test specimens were bent so that the polyimide film side faced inward. After storage, the test specimens were removed from the glass plates, and the bend recovery angle was measured using a protractor.

[0152] <Anchor power> The substrate side of the pressure-sensitive adhesive sheet obtained in the Examples and Comparative Examples was attached to a glass plate using double-sided tape, and the release liner of the pressure-sensitive adhesive sheet was peeled off to expose the pressure-sensitive adhesive layer. The treated surface of a PET (polyethylene terephthalate) film (product name "125 Tetolite OES", thickness = 125 μm, manufactured by Oike Industries Co., Ltd.) vapor-deposited with indium tin oxide was attached to the surface of the exposed pressure-sensitive adhesive layer, and the film was autoclaved at 50°C, 0.5 MPa, and 15 minutes to prepare a test specimen. The resulting test specimen was cut into a width of 25 mm and a length of 100 mm to serve as an evaluation sample. After storing the sample at room temperature for 30 minutes, the test specimen was measured using a tensile tester. The tensile tester used was an "Autograph AG-Xplus HS 6000 mm / min High-Speed ​​Model (AG-50NX plus)" manufactured by Shimadzu Corporation. After the evaluation sample was placed in the tensile tester, the PET film vapor-deposited with indium tin oxide was pulled to perform the test. The conditions for the tensile test were a peel angle of 180 degrees and a peel speed (pulling speed) of 300 mm / min. After confirming that the adhesive that constitutes the adhesive layer of the adhesive sheet was attached to the PET film vapor-deposited with indium tin oxide and that peeling had occurred between the adhesive sheet substrate and the adhesive layer, the measurement load was measured and the average load was taken as the anchoring force.

[0153] [Production Example 1]: Production of acrylic polymer A four-neck flask equipped with a stirring blade, a thermometer, a nitrogen gas inlet tube, and a condenser was charged with 70 parts by weight of 2EHA, 8 parts by weight of LA, 20 parts by weight of BA, 1 part by weight of 4HBA, 0.6 parts by weight of NVP, and 0.1 parts by weight of AIBN as a polymerization initiator, and ethyl acetate was added so that the total concentration of these was 47% by weight.The atmosphere in the system was purged with nitrogen over the course of 1 hour while gently stirring, and the liquid temperature in the flask was maintained at around 56°C to carry out a polymerization reaction for 6 hours.After completion of the reaction, ethyl acetate was added to adjust the polymer concentration to 24% by weight, yielding an acrylic polymer solution.

[0154] [Production Example 2]: Production of acrylic oligomer 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 NOF Corporation, trade name "Nofumer MSD") as a chain transfer agent, and 10 parts by weight of AIBN as a thermal polymerization initiator. Toluene was added to make the raw material concentration 50% by weight, and the mixture was reacted at 85°C for 2 hours under a nitrogen atmosphere. The temperature was then raised to 86°C and the mixture was reacted for 1.5 hours to obtain an acrylic oligomer. The weight-average molecular weight (Mw) of the acrylic oligomer was 4000, and the glass transition temperature (Tg) was 67°C.

[0155] Example 1 100 parts by weight of acrylic polymer, 10 parts by weight of acrylic oligomer, 0.5 parts by weight of TETRAD-C as an epoxy crosslinking agent, 0.1 parts by weight of C / HX as an isocyanate crosslinking agent, and 0.01 parts by weight of nursem ferric as a catalyst were mixed, stirred thoroughly, and diluted with ethyl acetate and acetyl acetone in an amount that was 1% by weight of the solvent so that the total solids content was 17% by weight, thereby obtaining a coating solution of an acrylic pressure-sensitive adhesive composition. The resulting acrylic pressure-sensitive adhesive composition coating solution was applied to a polyester film #50-U48 (manufactured by Toray Industries, Inc., thickness = 50 μm) as a substrate so that the dried thickness would be 15 μm, and then dried under conditions of a drying temperature of 135°C and a drying time of 1 minute. Next, a 50 μm-thick release sheet (manufactured by Mitsubishi Chemical Corporation, product name: MRQ50T100J) made of polyester resin and silicone-treated on one side was attached to the surface of the resulting pressure-sensitive adhesive layer so that the silicone-treated surface came into contact with it, thereby obtaining a pressure-sensitive adhesive sheet (1). This was then aged at 50°C for 1 day, and various evaluations were performed. The results are shown in Table 1. FIG. 8 shows a cross-sectional TEM photograph of the area near the interface between the substrate and the adhesive layer of the adhesive sheet (1). The cross-sectional TEM observation was performed over a width of 500 μm, and FIG. 8 is an enlarged photograph of a portion approximately 1000 nm wide. As shown in FIG. 8, filler was observed in contact with the surface of the adhesive layer on the substrate side in the adhesive sheet (1). Furthermore, the particle diameter of the filler shown in FIG. 8 was 150 nm, and the thickness of the surface layer was 90 nm, so it was observed that the surface layer contained filler with a particle diameter larger than the thickness of the surface layer.

[0156] Example 2 A pressure-sensitive adhesive sheet (2) was obtained in the same manner as in Example 1, except that polyester film #75-U48 (manufactured by Toray Industries, Inc., thickness = 75 μm) was used as the substrate instead of polyester film #50-U48 (manufactured by Toray Industries, Inc., thickness = 50 μm). This was aged at 50°C for 1 day and various evaluations were performed. The results are shown in Table 1.

[0157] Example 3 A pressure-sensitive adhesive sheet (3) was obtained in the same manner as in Example 1, except that the amount of acrylic oligomer was changed to 15 parts by weight. This was aged at 50°C for 1 day and various evaluations were performed. The results are shown in Table 1.

[0158] Example 4 A pressure-sensitive adhesive sheet (4) was obtained in the same manner as in Example 1, except that the amount of TETRAD-C, an epoxy-based crosslinking agent, was changed to 0.1 parts by weight. This was aged at 50°C for 1 day and various evaluations were performed. The results are shown in Table 1.

[0159] Example 5 A pressure-sensitive adhesive sheet (5) was obtained in the same manner as in Example 1, except that the amount of TETRAD-C, an epoxy-based crosslinking agent, was changed to 1 part by weight. This was aged at 50°C for 1 day and various evaluations were performed. The results are shown in Table 1.

[0160] Example 6 An adhesive sheet (6) was obtained in the same manner as in Example 1, except that a polyester film SRF (Cosmoshine SRF, manufactured by Toyobo Co., Ltd., thickness = 80 μm) was used as the substrate instead of polyester film #50-U48 (manufactured by Toray Industries, Inc., thickness = 50 μm). This was aged at 50°C for 1 day and various evaluations were performed. The results are shown in Table 1. FIG. 9 shows a cross-sectional TEM photograph of the area near the interface between the substrate and the adhesive layer of the adhesive sheet (6). The cross-sectional TEM observation was performed over a width of 500 μm, and FIG. 9 is an enlarged photograph of a portion approximately 1000 nm wide. As shown in FIG. 9, filler was observed in contact with the surface of the adhesive layer on the substrate side of the adhesive sheet (6). Furthermore, the particle diameter of the filler shown in FIG. 9 was 75 nm, and the thickness of the surface layer was 60 nm, indicating that the surface layer contained filler with a particle diameter larger than the thickness of the surface layer.

[0161] Example 7 A pressure-sensitive adhesive sheet (7) was obtained in the same manner as in Example 1, except that the amount of acrylic oligomer was changed to 5 parts by weight. This was aged at 50°C for 1 day and various evaluations were performed. The results are shown in Table 1.

[0162] Comparative Example 1 An adhesive sheet (C1) was obtained in the same manner as in Example 1, except that polyester film T100C50 (Diafoil T100C50, manufactured by Mitsubishi Chemical Corporation, thickness = 50 μm) was used as the substrate instead of polyester film #50-U48 (manufactured by Toray Industries, Inc., thickness = 50 μm). This was aged at 50°C for 1 day and various evaluations were performed. The results are shown in Table 1. Furthermore, a cross-sectional TEM photograph of the vicinity of the interface between the substrate and the pressure-sensitive adhesive layer of pressure-sensitive adhesive sheet (C1) is shown in Figure 10. Note that the cross-sectional TEM observation was performed over a width of 500 µm, and Figure 10 is an enlarged photograph of a portion approximately 1000 nm wide. As shown in Figure 10, in pressure-sensitive adhesive sheet (C1), filler was observed in the substrate, but no filler was observed in contact with the surface of the pressure-sensitive adhesive layer facing the substrate.

[0163] Comparative Example 2 A pressure-sensitive adhesive sheet (C2) was obtained in the same manner as in Example 1, except that the amount of the epoxy crosslinking agent TETRAD-C was changed to 0 parts by weight. This was aged at 50°C for 1 day and various evaluations were performed. The results are shown in Table 1.

[0164] [Table 1] [Industrial Applicability]

[0165] The pressure-sensitive adhesive sheet according to the embodiment of the present invention can be used for so-called flexible devices such as foldable devices and rollable devices. [Explanation of symbols]

[0166] 100 adhesive sheets 10 Base material 20 adhesive layer 1000 Flexible Devices 200 cover film 300 adhesive layer 400 Polarizer 500 adhesive layer 600 Touch Sensor 700 adhesive layer 800 OLED 150 test specimens 50 Glass Plate

Claims

1. A pressure-sensitive adhesive sheet comprising a substrate and a pressure-sensitive adhesive layer, a filler in contact with the surface of the pressure-sensitive adhesive layer facing the substrate, the pressure-sensitive adhesive layer is composed of an acrylic pressure-sensitive adhesive formed from an acrylic pressure-sensitive adhesive composition, The acrylic pressure-sensitive adhesive composition comprises an acrylic polymer, an acrylic oligomer, and two or more crosslinking agents. Adhesive sheet.

2. The pressure-sensitive adhesive sheet according to claim 1, wherein the pressure-sensitive adhesive layer has a storage modulus at −20° C. of less than 140 kPa.

3. The pressure-sensitive adhesive sheet according to claim 1 , wherein the two or more types of crosslinking agents include an epoxy-based crosslinking agent.

4. The pressure-sensitive adhesive sheet according to claim 3 , wherein the content of the epoxy-based crosslinking agent relative to 100 parts by weight of the acrylic polymer is 0.05 parts by weight or more.

5. The pressure-sensitive adhesive sheet according to claim 1 , wherein the content of the acrylic oligomer is 1 part by weight or more relative to 100 parts by weight of the acrylic polymer.

6. The pressure-sensitive adhesive sheet according to claim 1 , wherein the acrylic oligomer is a carboxyl group-containing acrylic oligomer.

7. The pressure-sensitive adhesive sheet according to claim 1 , wherein the acrylic polymer is a hydroxyl group-containing acrylic polymer.

8. The pressure-sensitive adhesive sheet according to claim 1 , wherein the substrate has a thickness of 90 μm or less.

9. A flexible device comprising the pressure-sensitive adhesive sheet according to any one of claims 1 to 8.

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