Adhesive layer, adhesive sheet, and optical member

Abstract

The present invention relates to an adhesive layer, an adhesive sheet, and an optical member. The adhesive layer is formed from an adhesive composition comprising: a (meth)acrylic polymer containing a structural unit derived from a (meth)acrylic monomer having a hydroxyl group and having a ratio of z+1 average molecular weight (Mz+1) to weight average molecular weight (Mw) (Mz+1 / Mw) of 5.5 or greater; and a crosslinking agent; wherein the adhesive composition has an adhesive strength of 4.0 N / 25 mm or greater as measured under condition A and an adhesive strength of 0.05 N / 25 mm to 2.0 N / 25 mm as measured under condition B [the adhesive layer having a thickness of 15 μm adhered to a PET film is peeled off from the PET film at a peel angle (condition A: 45°, condition B: 180°) and a peel speed of 300 mm / min under an ambient temperature of 23° C. and 50% relative humidity].

Description

Technical Field

[0001] The present invention relates to an adhesive layer, an adhesive sheet, and an optical member. Background Art

[0002] To prevent product yield reductions caused by incorrect application, adhesive layers have traditionally been designed with reapplyability in mind. For example, silicone compounds are commonly incorporated into adhesives used in displays to ensure relatively easy peeling from the adherend when reapplying is necessary. In recent years, with the increasing thinning of substrates, there has been a demand for adhesive sheets with adhesive layers exhibiting even easier peelability.

[0003] For example, a pressure-sensitive adhesive sheet has been reported, comprising a substrate and a pressure-sensitive adhesive layer laminated on at least one side of the substrate, wherein the pressure-sensitive adhesive layer has a weight-average molecular weight of 10,000 or more and less than 50,000, and comprises a (meth)acrylic polymer containing, as a monomer unit, a monomer having a polyorganosiloxane skeleton. The pressure-sensitive adhesive layer has an adhesive strength of 1.0 N / 20 mm or less 30 minutes after being affixed to an ABS (Acrylonitrile-Butadiene-Styrene) plate, an adhesive strength of 2.5 N / 20 mm or less 24 minutes after being affixed to an ABS plate, and an adhesive strength of 6.5 N / 20 mm or more after being affixed to an ABS plate and heated at 80° C. for 5 minutes and at 23° C. for 30 minutes (see, for example, International Publication No. 2015 / 190441). Summary of the Invention

[0004] In recent years, with the popularity of displays of various shapes, there are more and more cases of pasting adhesive layers on adherends with an inclination angle. However, for the adhesive layer pasted on the adherend with an inclination angle, there is a tendency to easily peel off at the edge portion (so-called end). For example, the adhesive layer with relatively low adhesion described in International Publication No. 2015 / 190441 cannot withstand the stress applied to the end and is easily peeled off at an unexpected opportunity. Therefore, for the adhesive layer pasted on the adherend with an inclination angle, it is required to be less likely to be unintentionally peeled off and to show light peelability when intentionally peeled off.

[0005] An embodiment of the present disclosure aims to provide a pressure-sensitive adhesive layer that is less likely to be unintentionally peeled off even when attached to an adherend at an inclined angle and exhibits easy peelability when intentionally peeled off.

[0006] Another embodiment of the present disclosure aims to provide a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer that is less likely to be unintentionally peeled off even when attached to an adherend at an inclined angle and exhibits easy peelability when intentionally peeled off.

[0007] Another embodiment of the present disclosure aims to provide an optical member having a pressure-sensitive adhesive layer that is less likely to be unintentionally peeled off even when attached to an adherend at an inclined angle and exhibits easy peelability when intentionally peeled off.

[0008] Specific methods for solving the problem include the following.

[0009] <1> An adhesive layer formed from an adhesive composition comprising a (meth)acrylic polymer and a crosslinking agent,

[0010] The (meth)acrylic polymer contains a structural unit derived from a (meth)acrylic monomer having a hydroxyl group, and has a ratio (Mz+1 / Mw) of z+1 average molecular weight (Mz+1) to weight average molecular weight (Mw) of 5.5 or more;

[0011] The adhesive force measured under the following condition A is 4.0 N / 25 mm or more, and the adhesive force measured under the following condition B is 0.05 N / 25 mm to 2.0 N / 25 mm.

[0012] <Condition A>

[0013] Under an ambient temperature of 23° C. and 50% RH, a 15 μm thick adhesive layer adhered to the polyethylene terephthalate film was peeled from the polyethylene terephthalate film at a peeling angle of 45° and a peeling speed of 300 mm / min.

[0014] Condition B

[0015] Under an ambient temperature of 23° C. and 50% RH, a 15 μm thick adhesive layer adhered to the polyethylene terephthalate film was peeled from the polyethylene terephthalate film at a peeling angle of 180° and a peeling speed of 300 mm / min.

[0016] <2> The pressure-sensitive adhesive layer according to <1>, wherein the (meth)acrylic polymer has a weight average molecular weight (Mw) of 50,000 to 300,000 and a z+1 average molecular weight (Mz+1) of 500,000 or more.

[0017] <3> The pressure-sensitive adhesive layer according to <1> or <2>, wherein the (meth)acrylic polymer includes a structural unit derived from an alkyl (meth)acrylate monomer.

[0018] <4> The pressure-sensitive adhesive layer according to <1> or <2>, wherein the (meth)acrylic polymer includes a structural unit derived from a monomer having a carboxyl group.

[0019] <5> A pressure-sensitive adhesive sheet comprising the pressure-sensitive adhesive layer according to any one of <1> to <4>.

[0020] <6> An optical member comprising the pressure-sensitive adhesive layer according to any one of <1> to <4>.

[0021] According to one embodiment of the present disclosure, there is provided a pressure-sensitive adhesive layer that is less likely to be unintentionally peeled off even when attached to an adherend at an inclined angle and exhibits easy peelability when intentionally peeled off.

[0022] According to another embodiment of the present disclosure, a pressure-sensitive adhesive sheet is provided, comprising a pressure-sensitive adhesive layer that is less likely to be unintentionally peeled off even when attached to an adherend at an inclined angle and exhibits easy peelability when intentionally peeled off.

[0023] According to another embodiment of the present disclosure, an optical member is provided that includes a pressure-sensitive adhesive layer that is less likely to be unintentionally peeled off even when attached to an adherend at an inclined angle and exhibits easy peelability when intentionally peeled off. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a diagram showing a schematic configuration of an evaluation sample in a durability evaluation test. DETAILED DESCRIPTION

[0025] The pressure-sensitive adhesive layer, pressure-sensitive adhesive sheet, and optical member of the present disclosure are described in detail below. The following description of the elements is based on representative embodiments of the present disclosure, but the present disclosure is not limited to such embodiments and can be implemented with appropriate modifications within the scope of the present disclosure.

[0026] In the present disclosure, a numerical range expressed using “to” means a range including the numerical values ​​described before and after “to” as the lower limit and the upper limit, respectively.

[0027] In the numerical ranges described in stages in this disclosure, the upper limit or lower limit described in a certain numerical range may be replaced by the upper limit or lower limit of another numerical range described in stages. In addition, in the numerical ranges described in this disclosure, the upper limit or lower limit described in a certain numerical range may also be replaced by the value shown in the Examples.

[0028] In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment.

[0029] In the present disclosure, when a plurality of substances corresponding to components are present in the PSA composition, the amount of each component in the PSA composition represents the total amount of the plurality of substances present in the PSA composition unless otherwise specified.

[0030] In the present disclosure, a "(meth)acrylic polymer" refers to a polymer in which the content of structural units derived from a monomer having a (meth)acryloyl group is 50% by mass or more of all structural units (ie, all structural units of the (meth)acrylic polymer).

[0031] In the present disclosure, a "(meth)acrylic monomer" refers to a monomer having a (meth)acryloyl group.

[0032] In the present disclosure, “(meth)acrylic acid” is a term encompassing both “acrylic acid” and “methacrylic acid”, “(meth)acrylate” is a term encompassing both “acrylate” and “methacrylate”, and “(meth)acryloyl” is a term encompassing both “acryloyl” and “methacryloyl”.

[0033] In the present disclosure, "n-" represents normal, "i-" represents iso, "s-" represents secondary, and "t-" represents tertiary.

[0034] [Adhesive layer]

[0035] The adhesive layer of the present disclosure is formed from an adhesive composition comprising a (meth)acrylic polymer and a cross-linking agent. The (meth)acrylic polymer contains structural units derived from a (meth)acrylic monomer having a hydroxyl group and has a ratio (Mz+1 / Mw) of z+1 average molecular weight (Mz+1) to weight average molecular weight (Mw) of 5.5 or greater (hereinafter also referred to as a "specific (meth)acrylic polymer"). The adhesive strength measured under the following condition A is 4.0 N / 25 mm or greater, and the adhesive strength measured under the following condition B is 0.05 N / 25 mm to 2.0 N / 25 mm.

[0036] The pressure-sensitive adhesive layer of the present disclosure is unlikely to be unintentionally peeled even when attached to an adherend having an inclined angle, and exhibits easy peelability when intentionally peeled.

[0037] <Condition A>

[0038] Under an ambient temperature of 23° C. and 50% RH, a 15 μm thick adhesive layer adhered to the polyethylene terephthalate film was peeled from the polyethylene terephthalate film at a peeling angle of 45° and a peeling speed of 300 mm / min.

[0039] Condition B

[0040] Under an ambient temperature of 23° C. and 50% RH, a 15 μm thick adhesive layer attached to the polyethylene terephthalate film was peeled from the polyethylene terephthalate film at a peeling angle of 180° and a peeling speed of 300 mm / min.

[0041] In recent years, with the popularity of displays of various shapes, there are more and more cases of pasting adhesive layers on adherends with tilt angles. However, the adhesive layer pasted on the adherend with tilt angles has the problem of being easily peeled off at the edge portion (so-called end portion). The present inventors have conducted in-depth research on the adhesive layer pasted on the adherend with tilt angles, and found that when the edge portion (so-called end portion) of the adhesive layer pasted on the adherend is unintentionally peeled off, the angle (so-called peeling angle) when peeling off is very different from that when the adhesive layer pasted on the adherend is intentionally peeled off from the adherend. That is, it is known that the unintentional peeling of the end portion of the adhesive layer occurs at a smaller angle, while the intentional peeling of the adhesive layer is carried out at a larger angle. The present disclosure has the following features: in order to realize an adhesive layer that is not easily unintentionally peeled off even when attached to an adherend at an inclined angle and exhibits easy peelability when peeled off intentionally, the adhesive force of the adhesive layer is controlled so that the adhesive force is increased when the adhesive layer is peeled off from the adherend at a small angle and decreased when the adhesive layer is peeled off from the adherend at a large angle; and in order to control the adhesive force of the adhesive layer, the ratio (Mz+1 / Mw) of the z+1 average molecular weight (Mz+1) to the weight average molecular weight (Mw) of the (meth)acrylic polymer contained in the adhesive composition and the composition are focused on.

[0042] [Adhesive composition]

[0043] The adhesive composition of the present disclosure comprises a (meth)acrylic polymer and a crosslinking agent. The (meth)acrylic polymer contains a structural unit derived from a (meth)acrylic monomer having a hydroxyl group and has a ratio (Mz+1 / Mw) of z+1 average molecular weight (Mz+1) to weight average molecular weight (Mw) of 5.5 or more (i.e., a specific (meth)acrylic polymer).

[0044] The pressure-sensitive adhesive layer of the present disclosure is formed from a pressure-sensitive adhesive composition containing a specific (meth)acrylic polymer and a cross-linking agent, and is a cured product of the pressure-sensitive adhesive composition.

[0045] <Specific (meth)acrylic acid polymer>

[0046] The specific (meth)acrylic polymer contains a structural unit derived from a (meth)acrylic monomer having a hydroxyl group, and has a ratio (Mz+1 / Mw) of z+1 average molecular weight (Mz+1) to weight average molecular weight (Mw) of 5.5 or more.

[0047] The specific (meth)acrylic polymer may be a homopolymer of a (meth)acrylic monomer having a hydroxyl group, or a copolymer of a (meth)acrylic monomer having a hydroxyl group and a monomer other than a (meth)acrylic monomer having a hydroxyl group.

[0048] As an embodiment of the specific (meth)acrylic polymer, for example, a copolymer embodiment of a (meth)acrylic monomer having a hydroxyl group and a monomer other than a (meth)acrylic monomer having a hydroxyl group is preferred from the viewpoint of easily controlling the adhesive strength of the pressure-sensitive adhesive layer.

[0049] Hereinafter, after describing the structural unit of the specific (meth)acryl-based polymer, the molecular weight of the specific (meth)acryl-based polymer will be described.

[0050] <<Structural Unit of Specific (Meth)Acrylic Polymer>>

[0051] -Structural unit derived from a (meth)acrylic monomer having a hydroxyl group-

[0052] The specific (meth)acrylic polymer contains a structural unit derived from a (meth)acrylic monomer having a hydroxyl group.

[0053] The structural unit derived from the (meth)acrylic monomer having a hydroxyl group contributes to improving the easy peelability of the PSA layer when the PSA layer is intentionally peeled from an adherend.

[0054] In the present disclosure, the “structural unit derived from a (meth)acrylic monomer having a hydroxyl group” refers to a structural unit formed by addition polymerization of a (meth)acrylic monomer having a hydroxyl group.

[0055] The type of the (meth)acrylic monomer having a hydroxyl group is not particularly limited.

[0056] Specific examples of the (meth)acrylic monomer having a hydroxyl group include 2-hydroxymethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, 3-methyl-3-hydroxybutyl (meth)acrylate, , 1,1-dimethyl-3-hydroxybutyl (meth)acrylate, 1,3-dimethyl-3-hydroxybutyl (meth)acrylate, 2,2,4-trimethyl-3-hydroxypentyl (meth)acrylate, 2-ethyl-3-hydroxyhexyl (meth)acrylate, N-hydroxyethyl (meth)acrylamide, glycerol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, polyethylene glycol mono(meth)acrylate and poly(ethylene glycol-propylene glycol) mono(meth)acrylate.

[0057] As the (meth)acrylic monomer having a hydroxyl group, for example, from the viewpoint of good copolymerizability with other monomers, hydroxyalkyl (meth)acrylates are preferred. From the viewpoint of good compatibility with other monomers and good reactivity with a cross-linking agent (particularly an isocyanate-based cross-linking agent), hydroxyalkyl (meth)acrylates having a hydroxyalkyl group having 1 to 5 carbon atoms are more preferred. hydroxyalkyl (meth)acrylates having a hydroxyalkyl group having 2 to 4 carbon atoms are further preferred. At least one selected from 2-hydroxyethyl acrylate (2HEA) and 4-hydroxybutyl acrylate (4HBA) is particularly preferred.

[0058] The specific (meth)acrylic polymer may include only one type of structural unit derived from a (meth)acrylic monomer having a hydroxyl group, or may include two or more types.

[0059] The content of the structural unit derived from the (meth)acrylic monomer having a hydroxyl group in the specific (meth)acrylic polymer is not particularly limited, but is preferably 0.1% by mass to 10% by mass, more preferably 0.3% by mass to 8% by mass, further preferably 0.5% by mass to 6% by mass, and particularly preferably 1% by mass to 3% by mass, based on the total structural units of the specific (meth)acrylic polymer.

[0060] The fact that the content of the structural unit derived from the (meth)acrylic monomer having a hydroxyl group in the specific (meth)acrylic polymer is 0.1% by mass or more relative to all the structural units of the specific (meth)acrylic polymer means that the specific (meth)acrylic polymer actively contains the structural unit derived from the (meth)acrylic monomer having a hydroxyl group.

[0061] When the content of the structural units derived from the (meth)acrylic monomer having a hydroxyl group in the specific (meth)acrylic polymer is 10% by mass or less relative to all the structural units of the specific (meth)acrylic polymer, the reaction with the cross-linking agent does not become excessive, and an increase in the viscosity of the pressure-sensitive adhesive composition tends to be suppressed.

[0062] -Structural unit derived from an alkyl (meth)acrylate monomer-

[0063] The specific (meth)acrylic polymer preferably includes a structural unit derived from an alkyl (meth)acrylate monomer.

[0064] The structural unit derived from the alkyl (meth)acrylate monomer contributes to adjusting the adhesive force of the adhesive layer.

[0065] In the present disclosure, the “structural unit derived from an alkyl (meth)acrylate monomer” refers to a structural unit formed by addition polymerization of an alkyl (meth)acrylate monomer.

[0066] In addition, the "alkyl (meth)acrylate monomer" in the present disclosure does not include monomers corresponding to the above-mentioned (meth)acrylic monomer having a hydroxyl group and monomers corresponding to the (meth)acrylic monomer having a carboxyl group described later.

[0067] The type of the alkyl (meth)acrylate monomer is not particularly limited.

[0068] The alkyl (meth)acrylate monomer is preferably an unsubstituted alkyl (meth)acrylate monomer.

[0069] The (meth)acrylic acid alkyl ester monomer may be a methacrylic acid alkyl ester monomer or an acrylic acid alkyl ester monomer. For example, from the viewpoint of good copolymerizability with other monomers, an acrylic acid alkyl ester monomer is preferred.

[0070] The alkyl group of the (meth)acrylate monomer may be linear, branched, or cyclic.

[0071] The number of carbon atoms in the alkyl group is preferably 1 to 18, and more preferably 1 to 12, for example.

[0072] Specific examples of the alkyl (meth)acrylate monomer include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, n-octyl (meth)acrylate, i-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-nonyl (meth)acrylate, i-nonyl (meth)acrylate, n-decyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, cyclohexyl (meth)acrylate, and i-bornyl (meth)acrylate.

[0073] The (meth)acrylic acid alkyl ester monomer is preferably at least one selected from n-butyl acrylate (n-BA) and 2-ethylhexyl acrylate (2EHA).

[0074] When the specific (meth)acrylic polymer contains a structural unit derived from an alkyl (meth)acrylate monomer, it may contain only one type of structural unit derived from an alkyl (meth)acrylate monomer, or may contain two or more types.

[0075] When the specific (meth)acrylic acid-based polymer contains a structural unit derived from an alkyl (meth)acrylate monomer, the content of the structural unit derived from the alkyl (meth)acrylate monomer is not particularly limited, but for example, is preferably 50% by mass or more, more preferably 50% by mass to 99.9% by mass, further preferably 60% by mass to 99.7% by mass, further preferably 70% by mass to 99.5% by mass, and particularly preferably 80% by mass to 99% by mass, relative to all the structural units of the specific (meth)acrylic acid-based polymer.

[0076] Here, the content of the structural unit derived from the alkyl (meth)acrylate monomer in the specific (meth)acrylic polymer is 50% by mass or more relative to all the structural units of the specific (meth)acrylic polymer. This means that the structural unit derived from the alkyl (meth)acrylate monomer is contained as the main component of the structural units constituting the specific (meth)acrylic polymer.

[0077] -Structural unit derived from a (meth)acrylic acid-based monomer having a carboxyl group-

[0078] The specific (meth)acrylic polymer may include a structural unit derived from a (meth)acrylic monomer having a carboxyl group.

[0079] In the present disclosure, the “structural unit derived from a (meth)acrylic monomer having a carboxyl group” refers to a structural unit formed by addition polymerization of a (meth)acrylic monomer having a carboxyl group.

[0080] The type of the (meth)acrylic monomer having a carboxyl group is not particularly limited.

[0081] Specific examples of the (meth)acrylic acid monomer having a carboxyl group include acrylic acid (AA), methacrylic acid (MAA), ω-carboxy-polycaprolactone mono(meth)acrylate [e.g., ω-carboxy-polycaprolactone (n≈2) monoacrylate], and 2-propenyloxyethyl succinate.

[0082] As the monomer having a carboxyl group, acrylic acid (AA) is preferred, for example, from the viewpoint of good reactivity with a cross-linking agent (particularly an isocyanate-based cross-linking agent).

[0083] When the specific (meth)acrylic polymer contains a structural unit derived from a (meth)acrylic monomer having a carboxyl group, it may contain only one type of (meth)acrylic monomer derived from a carboxyl group, or may contain two or more types.

[0084] When the specific (meth)acrylic polymer contains a structural unit derived from a (meth)acrylic monomer having a carboxyl group, the content of the structural unit derived from the (meth)acrylic monomer having a carboxyl group is not particularly limited, but is, for example, preferably 0.1% by mass to 3% by mass, more preferably 0.1% by mass to 2% by mass, and even more preferably 0.1% by mass to 1% by mass, relative to all the structural units of the specific (meth)acrylic polymer.

[0085] The content of the structural units derived from the (meth)acrylic monomer having a carboxyl group in the specific (meth)acrylic polymer is 0.1% by mass or more relative to all the structural units of the specific (meth)acrylic polymer. This means that the specific (meth)acrylic polymer actively contains structural units derived from the monomer having a carboxyl group.

[0086] When the content of the structural units derived from the (meth)acrylic monomer having a carboxyl group in the specific (meth)acrylic polymer is 3% by mass or less relative to all the structural units of the specific (meth)acrylic polymer, the reaction with the cross-linking agent does not become excessive, and an increase in the viscosity of the pressure-sensitive adhesive composition tends to be suppressed.

[0087] -Other structural units-

[0088] The specific (meth)acrylic polymer may contain structural units other than the above-mentioned structural units (so-called other structural units) as needed within a range not impairing the effects of the pressure-sensitive adhesive layer of the present disclosure.

[0089] Specific examples of monomers constituting other structural units include (meth)acrylates having an aromatic ring, such as benzyl (meth)acrylate and phenoxyethyl (meth)acrylate; alkoxyalkyl (meth)acrylates, such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; monovinyl aromatics, such as styrene, α-methylstyrene, t-butylstyrene, p-chlorostyrene, chloromethylstyrene, and vinyltoluene; vinyl cyanides, such as acrylonitrile and methacrylonitrile; vinyl esters, such as vinyl formate, vinyl acetate, vinyl propionate, and vinyl versatate; and 1,6-hexanediol diacrylate. Various derivatives of these monomers are also included.

[0090] When the specific (meth)acrylic polymer contains other structural units, it may contain only one type of other structural units, or may contain two or more types.

[0091] When the specific (meth)acrylic polymer contains other structural units, the content of the other structural units is not particularly limited and can be appropriately set depending on the intended purpose.

[0092] <<Molecular Weight of Specific (Meth)Acrylic Polymer>>

[0093] -Ratio of the z+1 average molecular weight (Mz+1) to the weight average molecular weight (Mw) (Mz+1 / Mw)

[0094] The Mz+1 / Mw of the specific (meth)acrylic polymer is 5.5 or more.

[0095] If the Mz+1 / Mw of the specific (meth)acrylic polymer is 5.5 or greater, there is a tendency to form an adhesive layer that is not easily peeled off even when attached to an adherend at an inclined angle and exhibits easy peelability when intentionally peeled off. In addition, if the Mz+1 / Mw of the specific (meth)acrylic polymer is 5.5 or greater, there is a tendency to form an adhesive layer that is not easily peeled off even when attached to an adherend at an inclined angle and exposed to a high temperature environment and has excellent durability. From this viewpoint, the Mz+1 / Mw of the specific (meth)acrylic polymer is 5.5 or greater, preferably 6.5 or greater, more preferably 7 or greater, further preferably 8 or greater, and particularly preferably 9 or greater.

[0096] The upper limit of Mz+1 / Mw of the specific (meth)acrylic polymer is not particularly limited, but is, for example, preferably 200 or less, more preferably 150 or less, even more preferably 100 or less, even more preferably 80 or less, even more preferably 40 or less, even more preferably 25 or less, even more preferably 15 or less, and particularly preferably 10 or less.

[0097] When Mz+1 / Mw of the specific (meth)acrylic polymer is 200 or less, when adjusting Mz+1 / Mw of the (meth)acrylic polymer to a desired value by controlling the polymerization reaction of the monomers, the control tends to be easier.

[0098] -Weight average molecular weight (Mw)-

[0099] The Mw of the specific (meth)acrylic polymer is not particularly limited, but is preferably 50,000 to 300,000.

[0100] When the Mw of the specific (meth)acrylic polymer is 50,000 or greater, a PSA layer exhibiting easier peelability when intentionally peeled off tends to be formed. From this viewpoint, the Mw of the specific (meth)acrylic polymer is preferably 50,000 or greater, more preferably 80,000 or greater, and even more preferably 100,000 or greater.

[0101] When the Mw of the specific (meth)acrylic polymer is 300,000 or less, a PSA layer that is less likely to be unintentionally peeled off even when attached to an adherend at an inclined angle tends to be formed. From this viewpoint, the Mw of the specific (meth)acrylic polymer is preferably 300,000 or less, more preferably 250,000 or less, and even more preferably 200,000 or less.

[0102] -z+1 average molecular weight (Mz+1)-

[0103] The Mz+1 of the specific (meth)acrylic polymer is not particularly limited, but is preferably 500,000 or more.

[0104] When the Mz+1 of the specific (meth)acrylic polymer is 500,000 or greater, a PSA layer exhibiting easier peelability when intentionally peeled tends to be formed. From this viewpoint, the Mz+1 of the specific (meth)acrylic polymer is preferably 500,000 or greater, more preferably 800,000 or greater, even more preferably 900,000 or greater, and particularly preferably 1,000,000 or greater.

[0105] The upper limit of Mz+1 of the specific (meth)acrylic polymer is not particularly limited, but, for example, from the viewpoint of the coating properties of the adhesive composition, is preferably 20 million or less, more preferably 15 million or less, further preferably 10 million or less, further preferably 5 million or less, and particularly preferably 3 million or less.

[0106] The specific (meth)acrylic polymer preferably has an Mw of 50,000 to 300,000, an Mz+1 of 500,000 or more, and an Mz+1 / Mw of 5.5 or more, more preferably an Mw of 50,000 to 300,000, an Mz+1 of 500,000 to 20 million, and an Mz+1 / Mw of 5.5 to 80, and further preferably an Mw of 50,000 to 300,000, an Mz+1 of 800,000 to 10 million, and an Mz+1 / Mw of 6.5 to 40. The embodiment in which Mw is 100,000 to 250,000, Mz+1 is 900,000 to 5,000,000 and Mz+1 / Mw is 7 to 25 is further preferred, the embodiment in which Mw is 100,000 to 250,000, Mz+1 is 1,000,000 to 5,000,000 and Mz+1 / Mw is 8 to 15 is further preferred, and the embodiment in which Mw is 100,000 to 200,000, Mz+1 is 1,000,000 to 3,000,000 and Mz+1 / Mw is 9 to 10 is particularly preferred.

[0107] The Mw and Mz+1 of the specific (meth)acrylic polymer are values ​​determined by the following method. Specifically, they are determined according to the following (1) to (3).

[0108] (1) A solution of a specific (meth)acrylic acid-based polymer was applied to release paper and dried at 100° C. for 1 minute to obtain a film-like specific (meth)acrylic acid-based polymer.

[0109] (2) Using the film-like specific (meth)acrylic acid-based polymer obtained in (1) above and tetrahydrofuran, a sample solution having a solid content concentration of 0.2% by mass was obtained. It should be noted that the "solid content concentration" herein refers to the mass ratio of the specific (meth)acrylic acid-based polymer in the sample solution.

[0110] (3) Gel permeation chromatography (GPC) measurement was performed under the following conditions, and Mw and Mz+1 of the specific (meth)acrylic polymer were determined by conversion to standard polystyrene.

[0111] Here, when there are Ni polymers having a molecular weight Mi, Mw and Mz+1 are calculated by the following formula.

[0112] Mw=Σ(Mi 2 ×Ni) / Σ(Mi×Ni)

[0113] Mz+1=Σ(Mi 4 ×Ni) / Σ(Mi 3 ×Ni)

[0114] ~Conditions~

[0115] Measuring apparatus: High-speed GPC [Model: HLC-8220GPC, manufactured by Tosoh Corporation]

[0116] Detector: Differential refractometer (RI) [Built-in HLC-8220, manufactured by Tosoh Corporation]

[0117] Column: 4 TSKgel GMH XL [Made by Tosoh Corporation]

[0118] Column temperature: 40°C

[0119] Eluent: tetrahydrofuran

[0120] Injection volume of sample solution: 100 μL

[0121] Flow rate: 0.8 mL / min

[0122] The Mw and Mz+1 of the (meth)acrylic polymer can be adjusted to desired values ​​by adjusting the polymerization temperature, polymerization time, the amount of the organic solvent used, the type and amount of the polymerization initiator used, etc., when polymerizing the monomers.

[0123] Mz+1 / Mw can be adjusted by controlling the polymerization reaction of the monomers. For example, Mz+1 / Mw can be adjusted by first polymerizing a portion of the monomers to synthesize a high molecular weight polymer, and then polymerizing the remaining monomers to synthesize a low molecular weight polymer. As a specific example, the following method can be cited: using an organic peroxide as a polymerization initiator, a portion of the monomers are polymerized at a relatively low temperature (e.g., 50°C to 70°C), and then using an azo compound as a polymerization initiator, the remaining monomers are polymerized at a higher temperature (e.g., 85°C to 95°C).

[0124] Furthermore, Mz+1 / Mw can be adjusted by using a polyfunctional monomer as a monomer. For example, when polymerizing monomers, if a small amount of a polyfunctional monomer is added as a monomer, a high molecular weight polymer can be synthesized in a small amount.

[0125] Furthermore, Mz+1 / Mw can also be adjusted by, for example, mixing a (meth)acrylic polymer having a low Mw and a (meth)acrylic polymer having a high Mw.

[0126] <<Content of specific (meth)acrylic acid-based polymer>>

[0127] The content of the specific (meth)acrylic polymer in the adhesive composition of the present disclosure is not particularly limited, but is preferably 80% to 100% by mass, more preferably 85% to 100% by mass, further preferably 90% to 100% by mass, and particularly preferably 95% to 100% by mass, relative to the total solid content of the adhesive composition.

[0128] In the present disclosure, when the adhesive composition does not contain a solvent, "the total solid content in the adhesive composition" refers to the total mass of the adhesive composition; when the adhesive composition contains a solvent, it refers to the total mass of the components excluding the solvent from the adhesive composition.

[0129] In the present disclosure, "solvent" refers to water and organic solvents.

[0130] <<Method for producing specific (meth)acrylic acid-based polymer>>

[0131] The method for producing the specific (meth)acrylic polymer is not particularly limited.

[0132] The method for adjusting Mw, Mz+1, and Mz+1 / Mw of the specific (meth)acrylic polymer is as described above, and therefore, description thereof is omitted here.

[0133] The specific (meth)acrylic polymer can be produced by polymerizing the above-mentioned monomers using a known polymerization method, such as solution polymerization, emulsion polymerization, suspension polymerization, and bulk polymerization. As a polymerization method, solution polymerization is preferred because it simplifies the handling process and can be performed in a short time when preparing the adhesive composition after production.

[0134] In solution polymerization, a predetermined organic solvent, monomers, a polymerization initiator, and, if necessary, a chain transfer agent are generally placed in a polymerization tank, and the mixture is heated and reacted for several hours, for example, at the reflux temperature of the organic solvent while stirring. In this case, at least a portion of the organic solvent, monomers, polymerization initiator, and / or chain transfer agent may be added gradually.

[0135] Examples of the organic solvent used in the polymerization reaction include aromatic hydrocarbon compounds, aliphatic or alicyclic hydrocarbon compounds, ester compounds, ketone compounds, glycol ether compounds, and alcohol compounds.

[0136] More specifically, examples of the organic solvent used in the polymerization reaction include aromatic hydrocarbon compounds represented by benzene, toluene, ethylbenzene, n-propylbenzene, t-butylbenzene, o-xylene, m-xylene, p-xylene, tetralin, decalin, and aromatic naphtha; aliphatic or alicyclic hydrocarbon compounds represented by n-hexane, n-heptane, n-octane, i-octane, n-decane, dipentene, petroleum spirit, naphtha, and turpentine; ethyl acetate, n-butyl acetate, n-amyl acetate, 2-hydroxyethyl acetate, Ester compounds represented by 2-butoxyethyl acetate, 3-methoxybutyl acetate and methyl benzoate, ketone compounds represented by acetone, methyl ethyl ketone, methyl-i-butyl ketone, isophorone, cyclohexanone and methylcyclohexanone, glycol ether compounds represented by ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether and diethylene glycol monobutyl ether, and alcohol compounds represented by methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, s-butanol and t-butanol.

[0137] When producing the specific (meth)acrylic polymer, it is preferred to use an organic solvent such as an aromatic hydrocarbon compound, an ester compound, or a ketone compound that is less likely to cause chain transfer during the polymerization reaction. In particular, ethyl acetate is preferably used from the viewpoints of the solubility of the specific (meth)acrylic polymer and the ease of the polymerization reaction.

[0138] During the polymerization reaction, only one organic solvent may be used, or two or more organic solvents may be used.

[0139] Examples of the polymerization initiator include organic peroxides and azo compounds used in general solution polymerization methods.

[0140] Examples of the organic peroxide include t-butyl peroxide, cumyl peroxide, dicumyl peroxide, benzoyl peroxide, lauroyl peroxide, hexanoyl peroxide, di-i-propyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxypivalate, 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane, 2,2-bis(4,4-di-t-pentylperoxycyclohexyl)propane, 2,2-bis(4,4-di-t-octylperoxycyclohexyl)propane, 2,2-bis(4,4-di-α-cumylperoxycyclohexyl)propane, 2,2-bis(4,4-di-t-butylperoxycyclohexyl)butane, and 2,2-bis(4,4-di-t-octylperoxycyclohexyl)butane.

[0141] Examples of the azo compound include 2,2'-azobis-i-butyronitrile [AIBN], 2,2'-azobis(2,4-dimethylvaleronitrile) [ABVN], 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), and 2,2'-azobis(dimethylisobutyrate).

[0142] When producing a specific (meth)acrylic polymer, an organic peroxide or an azo compound can be used as a polymerization initiator. Organic peroxides are more likely to undergo a grafting reaction during polymerization, while azo compounds are less likely to undergo a grafting reaction during polymerization. Therefore, the organic peroxide can be appropriately selected according to the intended purpose.

[0143] During the polymerization reaction, only one polymerization initiator may be used, or two or more polymerization initiators may be used.

[0144] The amount of the polymerization initiator used is not particularly limited and can be appropriately set according to, for example, the molecular weight of the intended specific (meth)acrylic polymer.

[0145] When producing the specific (meth)acrylic polymer, a chain transfer agent may be used as needed.

[0146] Examples of the chain transfer agent include cyanoacetic acid, alkyl ester compounds of cyanoacetic acid having 1 to 8 carbon atoms, bromoacetic acid, alkyl ester compounds of bromoacetic acid having 1 to 8 carbon atoms, aromatic compounds represented by α-methylstyrene, anthracene, phenanthrene, fluorene, and 9-phenylfluorene, aromatic nitro compounds represented by p-nitroaniline, nitrobenzene, dinitrobenzene, p-nitrobenzoic acid, p-nitrophenol, and p-nitrotoluene, benzoquinone derivatives represented by benzoquinone and 2,3,5,6-tetramethyl-p-benzoquinone, and borane derivatives represented by tributylborane. , halogenated hydrocarbon compounds represented by carbon tetrabromide, carbon tetrachloride, 1,1,2,2-tetrabromoethane, tribromoethylene, trichloroethylene, bromotrichloromethane, bromoform and 3-chloro-1-propene, aldehyde compounds represented by chloral and furfural, alkyl mercaptan compounds having 1 to 18 carbon atoms, aromatic mercaptan compounds represented by thiophenol and toluene mercaptan, thioglycolic acid, alkyl ester compounds having 1 to 10 carbon atoms of thioglycolic acid, hydroxyalkyl mercaptan compounds having 1 to 12 carbon atoms, and terpene compounds represented by pinene and terpinolene.

[0147] When a chain transfer agent is used in producing the specific (meth)acrylic polymer, the amount of the chain transfer agent used is not particularly limited and can be appropriately set according to, for example, the molecular weight of the intended specific (meth)acrylic polymer.

[0148] The polymerization temperature is not particularly limited and can be appropriately set according to, for example, the molecular weight of the intended specific (meth)acrylic polymer.

[0149] Cross-linking agent

[0150] The adhesive composition of the present disclosure includes a cross-linking agent.

[0151] The type of the cross-linking agent is not particularly limited.

[0152] Examples of the cross-linking agent include isocyanate-based cross-linking agents, epoxy-based cross-linking agents, and metal chelate-based cross-linking agents.

[0153] In this disclosure, an "isocyanate crosslinking agent" refers to a compound having two or more isocyanate groups in one molecule (so-called polyisocyanate compounds). Furthermore, an "epoxy crosslinking agent" refers to a compound having two or more epoxy groups in one molecule (so-called bifunctional or higher epoxy compounds). Furthermore, a "metal chelate crosslinking agent" refers to a metal chelate compound that functions as a crosslinking agent.

[0154] The type of the isocyanate-based cross-linking agent is not particularly limited.

[0155] Examples of the isocyanate crosslinking agent include aromatic polyisocyanate compounds such as xylene diisocyanate (XDI), diphenylmethane diisocyanate, triphenylmethane triisocyanate, and toluene diisocyanate (TDI); aliphatic or alicyclic polyisocyanate compounds such as hexamethylene diisocyanate (HMDI), pentamethylene diisocyanate (PDI), isophorone diisocyanate, and hydrogenated aromatic polyisocyanate compounds.

[0156] Examples of the isocyanate crosslinking agent include dimers, trimers, or pentamers of the aforementioned polyisocyanate compounds, adducts of the aforementioned polyisocyanate compounds with polyol compounds such as trimethylolpropane, and biuret forms of the aforementioned polyisocyanate compounds.

[0157] As the isocyanate-based cross-linking agent, a commercially available product can be used.

[0158] Examples of commercially available isocyanate crosslinking agents include "CORONATE (registered trademark) HX", "CORONATE (registered trademark) HL-S", "CORONATE (registered trademark) L", "CORONATE (registered trademark) L-45E", "CORONATE (registered trademark) 2031", "CORONATE (registered trademark) 2030", "CORONATE (registered trademark) 2234", "CORONATE (registered trademark) 2785", "AQUANATE (registered trademark) 200", and "AQUANATE (registered trademark) 210" (all manufactured by Tosoh Corporation), "SUMIDUR (registered trademark) N3300", "DESMODUR (registered trademark) N3400", and "SUMIDUR (registered trademark) N75" (all manufactured by Sumika Covestro Urethane Co., Ltd.], "DURANATE (registered trademark) E-405-80T", "DURANATE (registered trademark) AE700-100", "DURANATE (registered trademark) 24A-100" and "DURANATE (registered trademark) TSE-100" [all manufactured by Asahi Kasei Corporation] and "TAKENATE (registered trademark) D-110N", "TAKENATE

[0159] (Registered Trademark) D-120N", "TAKENATE (Registered Trademark) M-631N", "MT-OLESTER (Registered Trademark) NP1200" and "STABIO (Registered Trademark) XD-340N"

[0160] [The above products are manufactured by Mitsui Chemicals, Inc.]

[0161] The type of the epoxy-based crosslinking agent is not particularly limited.

[0162] Examples of epoxy crosslinking agents include ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, tripropylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, polytetramethylene glycol diglycidyl ether, glycerol diglycidyl ether, glycerol triglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, and resorcinol diglycidyl ether. Water glyceryl ether, 2,2-dibromoneopentyl glycol diglycidyl ether, trimethylolpropane triglycidyl ether, pentaerythritol polyglycidyl ether, sorbitol polyglycidyl ether, diglycidyl adipate, diglycidyl phthalate, tris(glycidyl)isocyanurate, tris(glycidyloxyethyl)isocyanurate, 1,3-bis(N,N-glycidylaminomethyl)cyclohexane, N,N,N',N'-tetraglycidyl-1,3-phenylenedi(methaneamine), etc.

[0163] As the epoxy-based crosslinking agent, a commercially available product can be used.

[0164] Examples of commercially available epoxy crosslinking agents include "TETRAD (registered trademark)-X" and "TETRAD (registered trademark)-C" [both manufactured by Mitsubishi Gas Chemical Co., Ltd.].

[0165] The type of the metal chelate-based cross-linking agent is not particularly limited.

[0166] Examples of the metal chelate crosslinking agent include aluminum chelate compounds represented by monoacetylacetonate bis(ethyl acetoacetate)aluminum, tris(ethyl acetoacetate)aluminum, and tris(acetylacetonate)aluminum, titanium chelate compounds, zirconium chelate compounds, and cobalt chelate compounds.

[0167] As the metal chelate-based cross-linking agent, a commercially available product can be used.

[0168] Examples of commercially available metal chelate crosslinking agents include aluminum chelate A [trade name, aluminum tris(acetylacetonate), manufactured by Kawaken Fine Chemicals Co., Ltd.], aluminum chelate D [trade name, aluminum monoacetylacetonate bis(ethyl acetoacetate), manufactured by Kawaken Fine Chemicals Co., Ltd.], and ALCH-TR [trade name, aluminum tris(ethyl acetoacetate), manufactured by Kawaken Fine Chemicals Co., Ltd.].

[0169] The adhesive composition of the present disclosure may contain only one cross-linking agent, or may contain two or more cross-linking agents.

[0170] The content of the crosslinking agent in the adhesive composition of the present disclosure is not particularly limited, but is preferably 0.01 to 5 parts by mass, more preferably 0.1 to 5 parts by mass, and even more preferably 0.1 to 3 parts by mass, based on 100 parts by mass of the specific (meth)acrylic polymer.

[0171] The fact that the content of the crosslinking agent in the PSA composition of the present disclosure is 0.01 parts by mass or more relative to 100 parts by mass of the specific (meth)acrylic polymer means that the PSA composition of the present disclosure actively contains the crosslinking agent.

[0172] When the content of the crosslinking agent in the PSA composition of the present disclosure is 5 parts by mass or less relative to 100 parts by mass of the specific (meth)acrylic polymer, a PSA layer that is less likely to be unintentionally peeled off even when attached to an adherend at an inclined angle tends to be formed.

[0173] Organic solvents

[0174] The adhesive composition of the present disclosure may include an organic solvent.

[0175] If the adhesive composition of the present disclosure includes an organic solvent, coating properties may be improved.

[0176] Examples of the organic solvent include the same organic solvents as those used in the polymerization reaction of the specific (meth)acrylic polymer.

[0177] When the pressure-sensitive adhesive composition of the present disclosure contains an organic solvent, it may contain only one organic solvent or two or more organic solvents.

[0178] When the pressure-sensitive adhesive composition of the present disclosure contains an organic solvent, the content of the organic solvent is not particularly limited and can be appropriately set depending on the intended purpose.

[0179] <Other ingredients>

[0180] The adhesive composition of the present disclosure may contain components other than the above components (so-called other components) as needed within a range that does not impair the effects of the formed adhesive layer.

[0181] Other components include various additives such as crosslinking catalysts, silane coupling agents, surfactants (e.g., compounds containing polyethylene glycol chains), release regulators, tackifiers, antioxidants, colorants (e.g., dyes and pigments), light stabilizers (e.g., ultraviolet absorbers), and antistatic agents.

[0182] When the adhesive composition of the present disclosure contains other components, the content of the other components can be appropriately set within a range that does not impair the effects of the adhesive layer formed from the adhesive composition of the present disclosure.

[0183] [Thickness of adhesive layer]

[0184] The thickness of the adhesive layer of the present disclosure is not particularly limited, but is generally 1 μm to 100 μm, preferably 5 μm to 50 μm, and more preferably 10 μm to 30 μm.

[0185] The “thickness of the adhesive layer” in the present disclosure refers to the average thickness of the adhesive layer.

[0186] The average thickness of the pressure-sensitive adhesive layer is a value measured by the following method.

[0187] The arithmetic mean of the thickness of the adhesive layer measured at 10 randomly selected locations in the thickness direction of the adhesive layer was determined, and the obtained value was defined as the average thickness of the adhesive layer. The thickness of the adhesive layer was measured using a film thickness meter.

[0188] [Method for forming adhesive layer]

[0189] The method for forming the adhesive layer of the present disclosure is not particularly limited.

[0190] The adhesive layer of the present disclosure can be formed, for example, by the following method.

[0191] An adhesive composition comprising the specific (meth)acrylic polymer and a crosslinking agent is applied to a support (e.g., a substrate or a release film) to form a coating film. The coating film is then dried to form an adhesive film. The adhesive film is then aged to form an adhesive layer.

[0192] The method for applying the adhesive composition is not particularly limited.

[0193] Examples of the method for applying the adhesive composition include known methods using a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, knife coater, spray coater, bar coater, or applicator.

[0194] The amount of the adhesive composition applied is not particularly limited and can be appropriately set according to, for example, the thickness of the adhesive layer to be formed.

[0195] The method for drying the coating film is not particularly limited.

[0196] Examples of a method for drying the coating film include natural drying, heat drying, hot air drying, and vacuum drying.

[0197] The drying temperature and drying time of the coating film are not particularly limited and can be appropriately set according to the thickness of the coating film, the amount of the organic solvent in the coating film, and the like.

[0198] An example of drying conditions is drying at 70° C. to 120° C. for 30 seconds to 3 minutes using a hot air dryer.

[0199] Aging is performed for 3 days in an environment with an atmospheric temperature of 20° C. to 35° C. and a relative humidity of 45% to 55% (ie, 45% RH to 55% RH), for example.

[0200] [Adhesive strength of adhesive layer]

[0201] The adhesive layer of the present disclosure has an adhesive strength of 4.0 N / 25 mm or more as measured under the following condition A and an adhesive strength of 0.05 N / 25 mm to 2.0 N / 25 mm as measured under the following condition B.

[0202] In the adhesive layer of the present disclosure, the adhesive force measured under the following condition A is preferably 4.5 N / 25 mm or more and the adhesive force measured under the following condition B is preferably 0.05 N / 25 mm to 1.5 N / 25 mm, and the adhesive force measured under the following condition A is more preferably 5.0 N / 25 mm or more and the adhesive force measured under the following condition B is preferably 0.05 N / 25 mm to 1.0 N / 25 mm.

[0203] The upper limit of the adhesive strength measured under the following condition A is not particularly limited, but is preferably 15.0 N / 25 mm or less, for example.

[0204] <Condition A>

[0205] Under an ambient temperature of 23° C. and 50% RH, a 15 μm thick adhesive layer adhered to a polyethylene terephthalate (PET) film was peeled from the PET film at a peeling angle of 45° and a peeling speed of 300 mm / min.

[0206] Condition B

[0207] Under an ambient temperature of 23° C. and 50% RH, a 15 μm thick adhesive layer adhered to a polyethylene terephthalate (PET) film was peeled from the PET film at a peeling angle of 180° and a peeling speed of 300 mm / min.

[0208] The "15 μm thick adhesive layer adhered to the PET film" in Condition A and Condition B specifically refers to the following adhesive layer: a laminated body is produced by pressing and pasting a 250 μm thick PET film and a 15 μm thick adhesive layer using a desktop laminator, and the laminated body is left to stand for 24 hours in an environment with an ambient temperature of 23°C and a relative humidity of 50% (i.e., 50% RH).

[0209] The adhesive force measured under condition A and the adhesive force measured under condition B are specifically adhesive forces measured by the methods described in the examples described later.

[0210] [Adhesive sheet]

[0211] The pressure-sensitive adhesive sheet of the present disclosure includes the pressure-sensitive adhesive layer of the present disclosure.

[0212] The PSA sheet of the present disclosure, because it includes the PSA layer of the present disclosure, is less susceptible to unintentional peeling even when attached to an adherend at an oblique angle and exhibits easy peelability when intentionally peeled. Therefore, it can be advantageously used for adherends at oblique angles.

[0213] Furthermore, the PSA sheet of the present disclosure is unlikely to peel even when attached to an adherend at an oblique angle and exposed to a high-temperature environment. Therefore, it is suitable for use not only at room temperature but also at high temperatures.

[0214] The PSA sheet disclosed herein may be a substrate-less PSA sheet having no substrate, or a substrate-attached PSA sheet having a PSA layer on at least one side of a substrate.

[0215] In the pressure-sensitive adhesive sheet of the present disclosure, the exposed surface of the pressure-sensitive adhesive layer may be protected by a release film.

[0216] The release film is not particularly limited as long as it can be easily released from the pressure-sensitive adhesive layer. Examples thereof include resin films surface-treated with a release agent on one or both sides (so-called easy-release treatment).

[0217] Examples of the resin film include polyester films such as polyethylene terephthalate (PET) films, and examples of the release agent include silicone release agents (e.g., silicone), wax release agents (e.g., paraffin), and fluorine release agents (e.g., fluorine resins).

[0218] The release film protects the surface of the adhesive layer before the adhesive sheet is put to practical use and is released during use.

[0219] When the pressure-sensitive adhesive sheet of the present disclosure includes a substrate, the substrate is not particularly limited.

[0220] Examples of the substrate include films comprising resins such as polyester resins [e.g., polyethylene terephthalate (PET)], acetate resins (e.g., cellulose triacetate resins), polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins (e.g., polyethylene and polypropylene), acrylic resins, vinyl chloride resins, ABS (Acrylonitrile Butadiene Styrene, acrylonitrile-butadiene-styrene) resins, and fluorine-based resins.

[0221] From the viewpoint of improving the adhesion between the substrate and the adhesive layer, the surface of the substrate on which the adhesive layer is provided may be subjected to a surface treatment such as corona discharge treatment or plasma discharge treatment (so-called adhesion-facilitating treatment).

[0222] The substrate may contain various additives such as plasticizers, colorants (such as dyes and pigments), heat stabilizers, light stabilizers, antistatic agents, flame retardants, antioxidants, and the like.

[0223] The substrate may be patterned over a portion or the entirety.

[0224] The thickness of the substrate is not particularly limited.

[0225] The thickness of the substrate is generally 10 μm to 500 μm, preferably 20 μm to 300 μm, and more preferably 25 μm to 200 μm.

[0226] The "thickness of a substrate" in the present disclosure refers to the average thickness of the substrate.

[0227] The average thickness of the substrate is a value measured by a method according to the above-mentioned method for measuring the average thickness of the pressure-sensitive adhesive layer of the present disclosure.

[0228] The thickness of the PSA layer in the PSA sheet of the present disclosure is the same as the thickness of the PSA layer of the present disclosure, and therefore, description thereof is omitted here.

[0229] The adherend of the pressure-sensitive adhesive sheet of the present disclosure is not particularly limited.

[0230] The PSA sheet of the present disclosure is less likely to be unintentionally peeled off even when attached to an adherend having an oblique angle, and exhibits easy peelability when intentionally peeled off. Therefore, it can also be preferably used for adherends having an oblique angle.

[0231] Examples of the material of the adherend of the pressure-sensitive adhesive sheet of the present disclosure include resin, glass, stainless steel, and copper.

[0232] Examples of the resin include polyolefin resins (such as polyethylene and polypropylene), acrylic resins, polyester resins [such as polyethylene terephthalate (PET)], polyimide resins, and cellulose triacetate resins.

[0233] [Method for producing adhesive sheet]

[0234] The pressure-sensitive adhesive sheet of the present disclosure can be produced by known methods.

[0235] As a method for producing the pressure-sensitive adhesive sheet of the present disclosure, for example, the following method can be mentioned.

[0236] In the case of a substrate-less PSA sheet, the PSA composition of the present disclosure is first applied to the easily releasable surface of a release film to form a coating film on the release film. The formed coating film is then dried to form an adhesive film on the release film. The exposed surface of the formed adhesive film is then superimposed and affixed to the easily releasable surface of a separate release film, followed by aging. This allows the production of a substrate-less PSA sheet having a laminated structure of release film / adhesive layer / release film.

[0237] In the case of a substrate-based PSA sheet, the PSA composition of the present disclosure is first applied to the easily adhesive surface of the substrate to form a coating film on the substrate. The formed coating film is then dried to form an adhesive film on the substrate. The exposed surface of the formed adhesive film is then superimposed and affixed to the easily adhesive surface of a release film, followed by aging, to produce a substrate-based PSA sheet having a laminated structure of release film / adhesive layer / substrate.

[0238] As other methods, for example, the following methods can also be mentioned.

[0239] The adhesive composition of the present disclosure is applied to the easily releasable surface of a release film to form a coating film on the release film. The formed coating film is then dried to form an adhesive film on the release film. The exposed surface of the formed adhesive film is then superimposed and affixed to the easily adhesive surface of a substrate, followed by aging, to produce a substrate-containing adhesive sheet having a laminated structure of substrate / adhesive layer / release film.

[0240] The coating method of the adhesive composition, the coating amount of the adhesive composition, the drying method of the coating film, the drying temperature and drying time of the coating film, and the aging conditions in the method for preparing the adhesive sheet disclosed in the present invention are the same as the coating method of the adhesive composition, the coating amount of the adhesive composition, the drying method of the coating film, the drying temperature and drying time of the coating film, and the aging conditions in the method for forming the adhesive layer disclosed in the present invention, and therefore their description is omitted here.

[0241] [Optical components]

[0242] The optical member of the present disclosure is an optical member including the pressure-sensitive adhesive layer of the present disclosure.

[0243] Since the optical member of the present disclosure includes the pressure-sensitive adhesive layer of the present disclosure, unintentional peeling is unlikely to occur even when attached to an adherend having an inclined angle, and exhibits easy peelability when intentionally peeled.

[0244] Furthermore, the optical member of the present disclosure is unlikely to peel even when exposed to a high-temperature environment while attached to an adherend having an oblique angle, and is therefore suitable for use not only at room temperature but also at high temperatures.

[0245] The optical member is not particularly limited, and examples thereof include members constituting devices such as image display devices and input devices (so-called optical devices) or members used in these devices.

[0246] Specific examples of optical components include polarizing plates, AG (Anti-Glare) polarizing plates, wavelength plates, phase difference plates including 1 / 2, 1 / 4 and other wavelength plates, viewing angle compensation films, optical compensation films, brightness enhancement films, light guide plates, reflective films, anti-reflection films, transparent conductive films such as ITO (Indium-Tin Oxide) films, prism sheets, lens sheets, diffuser plates, etc.

[0247] Examples of materials for optical components include polyester resins [e.g., polyethylene terephthalate (PET)], acetate resins (e.g., cellulose triacetate resins), polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins (e.g., polyethylene and polypropylene), acrylic resins, vinyl chloride resins, ABS (Acrylonitrile Butadiene Styrene, acrylonitrile-butadiene-styrene) resins, and fluorine-based resins.

[0248] Example

[0249] Hereinafter, the adhesive layer and the like of the present disclosure will be described in more detail with reference to examples. The present disclosure is not limited to the following examples unless the gist of the disclosure is exceeded.

[0250] [Production of (meth)acrylic acid polymer]

[0251] [Production Example A-1]

[0252] 13.0 parts by mass of ethyl acetate (organic solvent) was added to a reaction vessel equipped with a thermometer, a stirrer, and a reflux cooler. Subsequently, 98.2 parts by mass of n-butyl acrylate (n-BA; alkyl acrylate monomer), 1.5 parts by mass of 2-hydroxyethyl acrylate (2HEA; hydroxyl group-containing monomer), and 0.3 parts by mass of acrylic acid (AA; carboxyl group-containing monomer) were added to a separate vessel and mixed to prepare a monomer mixture. 5.0% by mass of this monomer mixture was added to the above reaction vessel. The temperature of the contents in the reaction vessel was then raised to 85°C while stirring. A mixture of 10.0 parts by mass of ethyl acetate and 0.002 parts by mass of t-butyl peroxypivalate (trade name: PERBUTYL (registered trademark) PV, manufactured by NOF Corporation; polymerization initiator) was then gradually added dropwise to the reaction vessel. The reactants in the reaction vessel were allowed to react for 30 minutes to obtain reaction product (a1). Then, the remaining 95.0% by mass of the monomer mixture and a solution prepared by dissolving 3.0 parts by mass of 2,2'-azobis-i-butyronitrile [AIBN; polymerization initiator] in 10.0 parts by mass of ethyl acetate were gradually added dropwise over 2 hours, while the reactants in the reaction vessel were reacted. After the completion of the dropwise addition, the reaction was continued for another 2 hours to obtain a reaction product (a2). The obtained reaction product (a2) was diluted with ethyl acetate to a solids concentration of 65% by mass to obtain a solution of (meth)acrylic polymer A-1.

[0253] The "solid content concentration" referred to here refers to the mass ratio of the (meth)acrylic acid-based polymer A-1 in the solution of the (meth)acrylic acid-based polymer A-1.

[0254] The same applies to each solution of the following (meth)acrylic polymers A-2 to A-24.

[0255] [Manufacturing Examples A-2 to A-7, A-11 and A-20]

[0256] In Production Examples A-2 to A-7, A-11, and A-20, the weight average molecular weight (Mw) and z+1 average molecular weight (Mz+1) of the (meth)acrylic polymer were adjusted to the weight average molecular weight (Mw) and z+1 average molecular weight (Mz+1) shown in Table 1 by adjusting the ratio of the monomer mixture used at the beginning of the reaction, the amount of the polymerization initiator used, and the reaction time. The same procedures as in Production Example A-1 were performed to obtain solutions of (meth)acrylic polymers A-2 to A-7, A-11, and A-20 having a solid content concentration of 65% by mass.

[0257] [Manufacturing Examples A-8 to A-10, A-12, A-13, A-15, A-16 and A-24]

[0258] In Production Examples A-8 to A-10, A-12, A-13, A-15, A-16, and A-24, the monomer composition of the (meth)acrylic acid polymer was changed to the monomer composition shown in Table 1, and the weight average molecular weight (Mw) and z+1 average molecular weight (Mz+1) of the (meth)acrylic acid polymer were adjusted to the weight average molecular weight (Mw) and z+1 average molecular weight (Mz+1) shown in Table 1 by adjusting the ratio of the monomer mixture used at the beginning of the reaction, the amount of the polymerization initiator used, and the reaction time. The same procedures as in Production Example A-1 were performed to obtain solutions of (meth)acrylic acid polymers A-8 to A-10, A-12, A-13, A-15, A-16, and A-24 having a solid content concentration of 65% by mass.

[0259] [Production Example A-14]

[0260] 154 parts by mass (100 parts by mass in terms of solid content) of a solution of a (meth)acrylic polymer A-17 described below and 0.77 parts by mass (0.5 parts by mass in terms of solid content) of a solution of a (meth)acrylic polymer A-23 described below were mixed, and then diluted with ethyl acetate to a solid content concentration of 60% by mass to obtain a solution of a (meth)acrylic polymer A-14.

[0261] [Production Example A-17]

[0262] 30.0 parts by mass of ethyl acetate (organic solvent) was added to a reaction vessel equipped with a thermometer, a stirrer, and a reflux cooler. Subsequently, 65.0 parts by mass of n-butyl acrylate (n-BA; alkyl acrylate monomer), 33.2 parts by mass of 2-ethylhexyl acrylate (2EHA; alkyl acrylate monomer), 1.5 parts by mass of 2-hydroxyethyl acrylate (2HEA; hydroxyl group-containing monomer), and 0.3 parts by mass of acrylic acid (AA; carboxyl group-containing monomer) were added to a separate vessel and mixed to prepare a monomer mixture. 8.0% by mass of this monomer mixture was added to the above reaction vessel. Then, 0.6 parts by mass of 2,2'-azobis-i-butyronitrile (AIBN; polymerization initiator) was added, and the temperature of the contents of the reaction vessel was raised to 85°C while stirring to initiate the initial reaction. After the initial reaction was substantially completed, the remaining 92.0% by mass of the monomer mixture and a mixture of 10.0 parts by mass of ethyl acetate and 3.0 parts by mass of AIBN were gradually added dropwise to the reaction vessel over 2 hours. The reactants in the reaction vessel were then allowed to react. After the addition was complete, the reaction was continued for an additional 2 hours to obtain a reaction product. The obtained reaction product was diluted with ethyl acetate to a solids concentration of 65% by mass, thereby obtaining a solution of (meth)acrylic polymer A-17.

[0263] [Production Examples A-18 and A-19]

[0264] In Production Examples A-18 and A-19, the weight average molecular weight (Mw) and z+1 average molecular weight (Mz+1) of the (meth)acrylic polymer were adjusted to the weight average molecular weight (Mw) and z+1 average molecular weight (Mz+1) shown in Table 1 by adjusting the ratio of the monomer mixture used at the beginning of the reaction, the amount of the polymerization initiator used, and the reaction time. The same procedures as in Production Example A-17 were performed to obtain solutions of (meth)acrylic polymers A-18 and A-19 having a solid content concentration of 65% by mass.

[0265] [Production Example A-21]

[0266] In Production Example A-21, except that the monomer composition of the (meth)acrylic acid polymer was changed to the monomer composition shown in Table 1, and the weight average molecular weight (Mw) and z+1 average molecular weight (Mz+1) of the (meth)acrylic acid polymer were adjusted to the weight average molecular weight (Mw) and z+1 average molecular weight (Mz+1) shown in Table 1 by adjusting the ratio of the monomer mixture used at the beginning of the reaction, the amount of the polymerization initiator used, and the reaction time, the same procedures as in Production Example A-1 were performed to obtain a solution of (meth)acrylic acid polymer A-21 having a solid content concentration of 40% by mass.

[0267] [Production Example A-22]

[0268] In Production Example A-22, the weight average molecular weight (Mw) and z+1 average molecular weight (Mz+1) of the (meth)acrylic acid polymer were adjusted to the weight average molecular weight (Mw) and z+1 average molecular weight (Mz+1) shown in Table 1 by adjusting the ratio of the monomer mixture used at the beginning of the reaction, the amount of the polymerization initiator used, and the reaction time. Except for this, the same procedures as in Production Example A-17 were performed to obtain a solution of the (meth)acrylic acid polymer A-22 having a solid content concentration of 30% by mass.

[0269] [Production Example A-23]

[0270] In Production Example A-23, the weight average molecular weight (Mw) and z+1 average molecular weight (Mz+1) of the (meth)acrylic acid polymer were adjusted to the weight average molecular weight (Mw) and z+1 average molecular weight (Mz+1) shown in Table 1 by adjusting the ratio of the monomer mixture used at the beginning of the reaction, the amount of the polymerization initiator used, and the reaction time. Except for this, the same procedures as in Production Example A-17 were performed to obtain a solution of the (meth)acrylic acid polymer A-23 having a solid content concentration of 24% by mass.

[0271] The monomer composition (unit: mass %), weight average molecular weight (Mw) of (meth)acrylic polymers A-1 to A-24 [unit: ten thousand (indicated as “×10 4 ”)〕、z+1 average molecular weight (Mz+1)〔Unit: ten thousand (marked as “×10 4 Table 1 shows the solid content concentrations (unit: mass %) of the solutions of the (meth)acrylic polymers A-1 to A-24, the ratio of the z+1 average molecular weight (Mz+1) to the weight average molecular weight (Mw) [Mz+1 / Mw].

[0272] The weight average molecular weight (Mw) and z+1 average molecular weight (Mz+1) of the (meth)acrylic polymers A-1 to A-24 were measured by the same method as the method for measuring the weight average molecular weight (Mw) and z+1 average molecular weight (Mz+1) of the above-mentioned specific (meth)acrylic polymer.

[0273] Among the (meth)acrylic polymers A-1 to A-24 obtained above, (meth)acrylic polymers A-1 to A-16 correspond to the specific (meth)acrylic polymers in the present disclosure.

[0274]

[0275] The details of each monomer described in Table 1 are as follows.

[0276] "n-BA"; n-butyl acrylate (alkyl acrylate monomer)

[0277] "2EHA"; 2-ethylhexyl acrylate (alkyl acrylate monomer)

[0278] "2HEA"; 2-hydroxyethyl acrylate (a monomer having a hydroxyl group)

[0279] "4HBA"; 4-hydroxybutyl acrylate (a monomer having a hydroxyl group)

[0280] "AA"; acrylic acid (monomer with carboxyl group)

[0281] "1,6-HX"; 1,6-hexanediol diacrylate (other monomers)

[0282] In Table 1, all the numerical values ​​described in the column "Monomer composition [mass %]" are values ​​based on solid content.

[0283] In Table 1, "-" in the monomer composition column indicates that the monomer corresponding to that column is not included.

[0284] In Table 1, “weight average molecular weight” is indicated as “Mw”, “z+1 average molecular weight” is indicated as “Mz+1”, and “ratio of z+1 average molecular weight (Mz+1) to weight average molecular weight (Mw)” is indicated as “Mz+1 / Mw”.

[0285] [Preparation of adhesive sheet]

[0286] [Example 1]

[0287] 133.3 parts by mass (100 parts by mass based on solid content) of a solution of the (meth)acrylic polymer A-1 and 0.5 parts by mass of SUMIDUR (registered trademark) N-3300 [trade name, trimer of hexamethylene diisocyanate (HMDI), solid content concentration: 100% by mass, manufactured by Sumika Covestro Urethane Co., Ltd.] as an isocyanate crosslinking agent were thoroughly mixed to prepare an adhesive composition.

[0288] The prepared adhesive composition was then applied to the adhesive-treated surface of an adhesive-treated polyethylene terephthalate (PET) film (trade name: TEIJIN (registered trademark) TETORON (registered trademark) film, model: G2, thickness: 38 μm, manufactured by Teijin Film Solutions Limited) to a film thickness of 15 μm after drying, forming a coating film. The resulting coating film was then dried using a hot air circulation dryer at 100°C for 1 minute to form an adhesive film on the PET film. The exposed surface of the adhesive film was then overlaid with the surface-treated surface of a separately prepared release film (trade name: FILMBYNA (registered trademark) 100E-0010 No. 23, thickness: 100 μm, manufactured by Fujimori Industries Co., Ltd.) that had been surface-treated with a silicone release agent. The film was then pressed and bonded using a pressurized nip roller. The film was then left to stand for 3 days in an environment of 23°C and 50% relative humidity for aging to produce an adhesive sheet. The produced pressure-sensitive adhesive sheet had a laminated structure of release film / pressure-sensitive adhesive layer (thickness: 15 μm) / PET film (base material).

[0289] [Examples 2 to 18]

[0290] In Example 1, except that the composition of the adhesive composition was changed to the composition shown in Table 2, the same operation as in Example 1 was carried out to prepare an adhesive composition and produce an adhesive sheet.

[0291] [Comparative Examples 1 to 8]

[0292] In Example 1, except that the composition of the adhesive composition was changed to the composition shown in Table 3, the same operation as in Example 1 was carried out to prepare an adhesive composition and produce an adhesive sheet.

[0293] [Measurement and evaluation]

[0294] 1. Adhesion

[0295] (1) Peeling angle: 45°

[0296] The adhesive sheet prepared above was cut into a size of 25 mm x 150 mm to prepare an adhesive sheet A-1. The peeling film of the prepared adhesive sheet A-1 (composition: peeling film / adhesive layer / PET film (substrate)) was then peeled off, and the surface of the adhesive layer exposed by the peeling was overlapped with the surface of the PET film (trade name: COSMOSHINE (registered trademark) A4300, thickness: 250 μm, manufactured by Toyobo Co., Ltd.) as the adherend. The two were then pressed and pasted together using a desktop laminator to produce a laminate. The laminate produced had a laminate structure of PET film (adherend) / adhesive sheet A-2 (composition: adhesive layer (thickness: 15 μm) / PET film (substrate)). The laminate was then allowed to stand for 24 hours in an environment with an ambient temperature of 23°C and 50% RH to produce a test piece. The test pieces were measured using an adhesive / film peeling analyzer (Model: VPA-H200) manufactured by Kyowa Interface Science Co., Ltd., at a peeling rate of 300 mm / min under an ambient temperature of 23°C and 50% RH. The adhesive strength (unit: N / 25 mm) was measured when the adhesive sheet A-2 was peeled 45° along the long side (150 mm) from the PET film (adherend). Evaluation was then performed according to the following criteria.

[0297] The results are shown in Tables 2 and 3.

[0298] If the evaluation result is "A", "B", or "C", it is judged that the pressure-sensitive adhesive layer is unlikely to be unintentionally peeled even when attached to an adherend having an inclined angle.

[0299] -Evaluation Criteria-

[0300] A: Adhesive force is 5.0 N / 25 mm or more.

[0301] B: The adhesive force is 4.5 N / 25 mm or more and less than 5.0 N / 25 mm.

[0302] C: Adhesive force is 4.0 N / 25 mm or more and less than 4.5 N / 25 mm.

[0303] D: Adhesion force less than 4.0N / 25mm

[0304] (2) Peeling angle: 180°

[0305] The adhesive sheet prepared above was cut into a size of 25 mm x 150 mm to prepare an adhesive sheet B-1. The peeling film of the prepared adhesive sheet B-1 (composition: peeling film / adhesive layer / PET film (substrate)) was then peeled off, and the surface of the adhesive layer exposed by the peeling was overlapped with the surface of the PET film (trade name: COSMOSHINE (registered trademark) A4300, thickness: 250 μm, manufactured by Toyobo Co., Ltd.) as the adherend. The two were then pressed and pasted together using a desktop laminator to produce a laminate. The laminate produced had a laminate structure of PET film (adherend) / adhesive sheet B-2 (composition: adhesive layer (thickness: 15 μm) / PET film (substrate)). The laminate was then allowed to stand for 24 hours in an environment with an ambient temperature of 23°C and 50% RH to produce a test piece. The test piece was tested using an adhesive / film peeling analyzer (Model: VPA-H200) manufactured by Kyowa Interface Science Co., Ltd. The adhesive strength (unit: N / 25 mm) was measured when the adhesive sheet B-2 was peeled 180° along the long side (150 mm) from the PET film (adherend) at a peeling speed of 300 mm / min under an ambient temperature of 23°C and 50% RH. Evaluation was performed according to the following criteria.

[0306] The results are shown in Tables 2 and 3.

[0307] If the evaluation result was "A," "B," or "C," the pressure-sensitive adhesive layer was judged to exhibit easy peelability when intentionally peeled.

[0308] -Evaluation Criteria-

[0309] A: Adhesion force is 0.05N / 25mm to 1.0N / 25mm.

[0310] B: The adhesive force exceeds 1.0 N / 25 mm and is 1.5 N / 25 mm or less.

[0311] C: Adhesive strength exceeds 1.5 N / 25 mm and is 2.0 N / 25 mm or less.

[0312] D: Adhesion force is less than 0.05 N / 25 mm or exceeds 2.0 N / 25 mm.

[0313] 2. Durability

[0314] Preparation of evaluation samples

[0315] The adhesive sheet prepared above was cut into a size of 25 mm x 150 mm to prepare adhesive sheet C-1. The release film of the prepared adhesive sheet C-1 (composition: release film / adhesive layer / PET film (substrate)) was then peeled off, and the surface of the adhesive layer exposed by the peeling was press-bonded and adhered to a sample in the shape of a regular square pyramid (8 cm upper base x 14 cm lower base x 3 cm height, 45° side inclination angle) wrapped around a PET film (trade name: COSMOSHINE (registered trademark) A4300, thickness: 250 μm, manufactured by Toyobo Co., Ltd.) to prepare an evaluation sample. The evaluation sample prepared had a laminated structure of sample / adhesive sheet C-2 (composition: adhesive layer (thickness: 15 μm) / PET film (substrate)). Figure 1 This is a diagram showing the schematic structure of the evaluation sample. Figure 1 As shown, in the evaluation sample 100 , the adhesive layer 20 including the base material 10 is attached to the surface of the adherend 30 having a regular quadrilateral pyramidal shape at an inclined angle.

[0316] (1) Durability at 23°C

[0317] The prepared evaluation samples were left to stand in a thermostatic chamber set at 23° C. for 7 days (ie, 168 hours), then taken out of the thermostatic chamber and visually observed.

[0318] Then, evaluation was performed based on the following evaluation criteria.

[0319] The results are shown in Tables 2 and 3.

[0320] If the evaluation result is "A" or "B", it is judged that the pressure-sensitive adhesive layer is unlikely to peel even when attached to an adherend having an inclined angle and has excellent durability.

[0321] -Evaluation Criteria-

[0322] A: None of wrinkles, lifting, and peeling were observed.

[0323] B: Wrinkles were observed at the edge, but neither lifting nor peeling was observed.

[0324] C: Lifting and peeling were observed at the edge.

[0325] (2) Durability at 80°C

[0326] The prepared evaluation samples were left to stand in a thermostatic chamber set at 80° C. for 7 days (ie, 168 hours), then taken out of the thermostatic chamber and visually observed.

[0327] Then, evaluation was performed based on the following evaluation criteria.

[0328] The results are shown in Tables 2 and 3.

[0329] If the evaluation result is "A" or "B", it is judged that the pressure-sensitive adhesive layer is not easily peeled even when it is attached to an adherend at an inclined angle and exposed to a high-temperature environment and has excellent durability.

[0330] -Evaluation Criteria-

[0331] A: None of wrinkles, lifting, and peeling were observed.

[0332] B: Wrinkles were observed at the edge, but neither lifting nor peeling was observed.

[0333] C: Lifting and peeling were observed at the edge.

[0334]

[0335]

[0336] In Tables 2 and 3, all the numerical values ​​described in the "compounding amount" column are values ​​calculated based on the solid content.

[0337] The details of the cross-linking agents described in Tables 2 and 3 are shown below.

[0338] "HMDI" [Trade name: SUMIDUR (registered trademark) N-3300, trimer of hexamethylene diisocyanate (HMDI), solid content concentration: 100% by mass, manufactured by Sumika Covestro Urethane Co., Ltd.]

[0339] "TDI" [Trade name: CORONATE (registered trademark) L-45E, an adduct of toluene diisocyanate (TDI) and trimethylolpropane (TMP), solid content concentration: 45% by mass, manufactured by Tosoh Corporation]

[0340] "XDI" [Trade name: TAKENATE (registered trademark) D-110N, an adduct of xylene diisocyanate (XDI) and trimethylolpropane (TMP), solid content concentration: 75% by mass, manufactured by Mitsui Chemicals, Inc.]

[0341] As shown in Table 2, the adhesive layers of Examples 1 to 18 were confirmed to be less susceptible to unintentional peeling even when attached to adherends at an inclined angle and to exhibit easy peelability when intentionally peeled. Furthermore, the adhesive layers of Examples 1 to 18 were confirmed to be less susceptible to peeling even when attached to adherends at an inclined angle and exposed to high temperatures, demonstrating excellent durability.

[0342] On the other hand, as shown in Table 3, it was confirmed that the pressure-sensitive adhesive layers of Comparative Examples 1 to 8 were easily unintentionally peeled when attached to an adherend having an inclined angle, or did not exhibit easy peelability when intentionally peeled.

Claims

1. An adhesive layer formed from an adhesive composition comprising a (meth)acrylic polymer and a crosslinking agent, The (meth)acrylic acid polymer contains a structural unit derived from a (meth)acrylic acid monomer having a hydroxyl group in a ratio of 0.1% by mass to 10% by mass relative to all structural units of the (meth)acrylic acid polymer, and has a weight average molecular weight (Mw) of 50,000 to 300,000, a z+1 average molecular weight (Mz+1) of 500,000 or more, and a ratio (Mz+1 / Mw) of the z+1 average molecular weight (Mz+1) to the weight average molecular weight (Mw) of 5.5 or more. The adhesive force measured under the following condition A is 4.0 N / 25 mm or more and the adhesive force measured under the following condition B is 0.05 N / 25 mm to 2.0 N / 25 mm, Condition A is: Under an ambient temperature of 23° C. and 50% RH, a 15 μm thick adhesive layer adhered to a polyethylene terephthalate film was peeled off from the polyethylene terephthalate film at a peeling angle of 45° and a peeling speed of 300 mm / min. Condition B is: Under an ambient temperature of 23° C. and 50% RH, a 15 μm thick adhesive layer adhered to a polyethylene terephthalate film was peeled from the polyethylene terephthalate film at a peeling angle of 180° and a peeling speed of 300 mm / min.

2. The adhesive layer according to claim 1, wherein The (meth)acrylic polymer includes a structural unit derived from an alkyl (meth)acrylate monomer.

3. The adhesive layer according to claim 1 or 2, wherein The (meth)acrylic polymer includes a structural unit derived from a monomer having a carboxyl group. 4 . A pressure-sensitive adhesive sheet comprising the pressure-sensitive adhesive layer according to claim 1 . An optical member comprising the pressure-sensitive adhesive layer according to claim 1 .

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