Photocurable composition and transparent adhesive sheet

Abstract

A photocurable composition which contains a (meth)acryloyloxy group-containing polyurethane (A), an ethylenically unsaturated group-containing monomer (B), an antistatic agent (C) and a photopolymerization initiator (D), wherein: the (meth)acryloyloxy group-containing polyurethane (A) contains a polyurethane (a1) which has a skeleton containing a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate, while having a (meth)acryloyloxy group at a plurality of ends; the ethylenically unsaturated group-containing monomer (B) contains a first monomer (B-0) that is a hydroxy group-containing (meth)acrylate; and the antistatic agent (C) is a fluorine-containing alkali metal imide salt.

Description

[Technical Field]

[0001] The present invention relates to a photocurable composition and a transparent adhesive sheet. This application claims priority based on Japanese Patent Application No. 2020-112950, ​​filed on June 30, 2020, the contents of which are incorporated herein by reference. [Background technology]

[0002] In recent years, touch panels that serve as both a display device and an input means have become increasingly popular in fields such as smartphones, tablets, personal computers, and game consoles. Some touch panels incorporate a liquid crystal display (LCD) as the display section and a capacitive sensor as the touch sensor section.

[0003] A liquid crystal display generally comprises a liquid crystal cell in which a liquid crystal compound is sealed between two transparent electrode substrates, and polarizing films attached to both sides of the liquid crystal cell via adhesive layers. Polarizing films have high electrical insulation properties. Therefore, they are prone to generating static electricity. Therefore, it is necessary to prevent the static electricity generated in the polarizing film from disrupting the orientation of the liquid crystal molecules in the liquid crystal cell.

[0004] As a method for preventing the disturbance of the alignment of liquid crystal molecules due to static electricity, there is a method in which a liquid crystal cell and a polarizing film are bonded together using an adhesive sheet having an adhesive layer containing an antistatic agent. Patent Document 1 describes a pressure-sensitive adhesive sheet in which the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer contains an antistatic agent. Patent Document 1 also describes that the pressure-sensitive adhesive contains a (meth)acrylic acid ester polymer or a crosslinked product thereof. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-015801 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the pressure-sensitive adhesive sheet described in Patent Document 1, the pressure-sensitive adhesive layer is formed by crosslinking the pressure-sensitive adhesive composition through a heat treatment, which has the disadvantage of being time-consuming to form the pressure-sensitive adhesive layer. Furthermore, pressure-sensitive adhesive sheets having a pressure-sensitive adhesive layer containing an antistatic agent are required to suppress a decrease in adhesive strength over time.

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a photocurable composition that contains an antistatic agent and that can form, by a simple method, a pressure-sensitive adhesive layer that can maintain adhesive strength over a long period of time. Another object of the present invention is to provide a transparent adhesive sheet having an adhesive layer that has antistatic properties, can maintain adhesive strength over a long period of time, and can be formed by a simple method. [Means for solving the problem]

[0008] The present invention achieves the above object by the following configurations [1] to [9].

[0009] That is, a first aspect of the present invention is a photocurable composition described in the following [1]. [1] A (meth)acryloyloxy group-containing polyurethane (A), an ethylenically unsaturated group-containing monomer (B); an antistatic agent (C); A photopolymerization initiator (D) is contained, The (meth)acryloyloxy group-containing polyurethane (A) comprises a polyurethane (a1) having a skeleton including a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate, and having (meth)acryloyloxy groups at a plurality of terminals; the ethylenically unsaturated group-containing monomer (B) includes a first monomer (B-0) that is a hydroxy group-containing (meth)acrylate, The photocurable composition, wherein the antistatic agent (C) is a fluorine-containing alkali metal imide salt.

[0010] The first aspect of the present invention preferably includes the following features described in [2] to [8]. Two or more of the following features can be preferably combined. [2] The photocurable composition according to [1], wherein the antistatic agent (C) is at least one selected from the group consisting of a salt of an alkali metal cation and a bis(fluorosulfonyl)imide anion and a salt of an alkali metal cation and a bis(perfluoroalkylsulfonyl)imide anion. [3] The photocurable composition according to [2], wherein the alkali metal cation of the antistatic agent (C) is a lithium cation.

[0011] [4] The photocurable composition according to any one of [1] to [3], wherein the ethylenically unsaturated group-containing monomer (B) further comprises a second monomer (B-1) having a homopolymer glass transition temperature (Tg) of −5°C or higher, and a third monomer (B-2) having a homopolymer glass transition temperature (Tg) of less than −5°C. [5] The second monomer (B-1) is a cyclic alkyl (meth)acrylate, The photocurable composition according to [4], wherein the third monomer (B-2) is an alkyl(meth)acrylate.

[0012] [6] 10 to 60% by mass of the (meth)acryloyloxy group-containing polyurethane (A), 39 to 89% by mass of the ethylenically unsaturated group-containing monomer (B), 0.1 to 5 mass% of the antistatic agent (C), The photocurable composition according to any one of [1] to [5], which contains the photopolymerization initiator (D) in an amount of 0.01 to 5% by mass. [7] The photocurable composition according to any one of [1] to [6], which contains the first monomer (B-0) in an amount of 3 to 25 mass %.

[0013] [8] 5 to 40 mass% of the second monomer (B-1), The third monomer (B-2) is contained in an amount of 10 to 60% by mass, The photocurable composition according to [4], wherein the mass ratio ((B-1):(B-2)) of the second monomer (B-1) to the third monomer (B-2) is 20:80 to 50:50.

[0014] A second aspect of the present invention is a transparent adhesive sheet according to the following item [9]. [9] A transparent adhesive sheet having an adhesive layer made of a cured product of the photocurable composition according to any one of [1] to [8]. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a photocurable composition that can form, by a simple method, a pressure-sensitive adhesive layer that contains an antistatic agent and can maintain adhesive strength over a long period of time. The transparent adhesive sheet of the present invention has an adhesive layer that has antistatic properties, can maintain adhesive strength over a long period of time, and can be formed by a simple method. DETAILED DESCRIPTION OF THE INVENTION

[0016] The photocurable composition and transparent adhesive sheet of the present invention will be described in detail below. The present invention is not limited to the following embodiments, and the number, type, position, amount, ratio, material, configuration, and the like may be added, omitted, substituted, or changed without departing from the spirit of the present invention.

[0017] In this specification and claims, the term "(meth)acryloyloxy group" refers to one or more groups selected from the group represented by the chemical formula "CH2=CH-(C=O)-O-" and the group represented by the chemical formula "CH2=C(CH3)-(C=O)-O-". Additionally, the term "isocyanato group" refers to a group represented by the chemical formula "-N=C=O".

[0018] <Photocurable composition> The photocurable composition of this embodiment contains a (meth)acryloyloxy group-containing polyurethane (A), an ethylenically unsaturated group-containing monomer (B), an antistatic agent (C), and a photopolymerization initiator (D). The photocurable composition of this embodiment is preferably used as a material for forming the adhesive layer of a transparent adhesive sheet.

[0019] [(Meth)acryloyloxy group-containing polyurethane (A)] The (meth)acryloyloxy group-containing polyurethane (A) of the present embodiment (hereinafter also referred to simply as "polyurethane (A)") includes a polyurethane (hereinafter also referred to as "polyurethane (a1)") having a skeleton containing a polyoxyalkylene polyol-derived structure and a polyisocyanate-derived structure, and having (meth)acryloyloxy groups at multiple terminals.

[0020] As used herein, the term "multiple ends" of a polyurethane refers to both ends when the polyurethane is a linear polymer, or to two or more ends out of the same number as the number of branched chains when the polyurethane is a branched polymer.

[0021] The polyurethane (A) may contain not only polyurethane (a1) but also polyurethanes other than polyurethane (a1). Examples of polyurethanes other than polyurethane (a1) include polyurethanes (hereinafter also referred to as "polyurethane (a2)") that, like polyurethane (a1), have a skeleton containing a structure derived from polyoxyalkylene polyol and a structure derived from polyisocyanate, but, unlike polyurethane (a1), have a (meth)acryloyloxy group at only one end.

[0022] The terminal of the polyurethane (a2) that does not have a (meth)acryloyloxy group preferably has any one selected from an isocyanato group, a structure derived from an alkyl alcohol, or a structure derived from an alkyl isocyanate, and more preferably has a structure derived from an alkyl alcohol. The polyurethane (a2) has the function of adjusting the cohesive strength of the cured product of the photocurable composition containing the polyurethane (A).

[0023] The polyurethane (A) preferably does not contain any components other than the polyurethane (a1) and the polyurethane (a2) that is contained as needed.

[0024] "Polyoxyalkylene polyol-derived structure" The polyoxyalkylene polyol (polyoxyalkylene polyol used as a raw material) having a structure derived from polyoxyalkylene polyol contained in the skeleton of polyurethane (a1) and the skeleton of polyurethane (a2) preferably has an alkylene chain having 2 to 4 carbon atoms. Specific examples include polyoxyethylene polyol, polyoxypropylene polyol, and polyoxybutylene polyol.

[0025] The polyoxyalkylene polyol having a structure derived from polyoxyalkylene polyol may contain one type of alkylene chain, or may contain two or more types of alkylene chains. The polyoxyalkylene polyol having a structure derived from polyoxyalkylene polyol is preferably one having two or three hydroxyl groups at the terminals (diol-type or triol-type polyoxyalkylene polyol), more preferably a polyoxyalkylene glycol (diol-type), and particularly preferably a polypropylene glycol having an alkylene chain with three carbon atoms.

[0026] For example, when the polyoxyalkylene polyol is polypropylene glycol, it preferably has a hydroxyl value of 20 to 120 mgKOH / g, more preferably 30 to 100 mgKOH / g, and even more preferably 40 to 80 mgKOH / g. Specific examples of polypropylene glycol include polypropylene glycol having a hydroxyl group (hydroxy group) at its terminal and a hydroxyl value of 56 mgKOH / g (Actocol D-2000 (trade name); manufactured by Mitsui Chemicals, number average molecular weight 2000, diol type).

[0027] The hydroxyl value of a polyoxyalkylene polyol is the hydroxyl value of the polyoxyalkylene polyol measured according to JIS K0070. That is, it means the number of milligrams of potassium hydroxide required to neutralize free acetic acid when 1 g of polyoxyalkylene polyol is acetylated. Specifically, it can be determined by acetylating the hydroxyl groups in a sample (polyoxyalkylene polyol) with acetic anhydride and titrating the free acetic acid generated during this process with a potassium hydroxide solution.

[0028] The number-average molecular weight of the polyoxyalkylene polyol is preferably 500 to 5,000, more preferably 800 to 4,000, and even more preferably 1,000 to 3,000. When the number-average molecular weight of the polyoxyalkylene polyol is 500 or more, the adhesive layer formed from the cured product of the photocurable composition containing the polyurethane (A) synthesized therewith has high adhesive strength. When the number-average molecular weight of the polyoxyalkylene polyol is 5,000 or less, the polyurethane (A) synthesized therewith contains a sufficient amount of urethane bonds. Therefore, the adhesive layer formed from the cured product of the photocurable composition containing the polyurethane (A) has good cohesion.

[0029] The structure derived from a polyoxyalkylene polyol contained in the skeleton of the polyurethane (a1) and the structure derived from a polyoxyalkylene polyol contained in the skeleton of the polyurethane (a2) may be the same as or different from each other. The polyoxyalkylene polyol-derived structure contained in the skeleton of polyurethane (a1) and the skeleton of polyurethane (a2) may each be of one type or may contain two or more types. The polyurethane (a1) and the polyurethane (a2) may have a structure in which two or more types of structures derived from polyoxyalkylene polyols are bonded together with a structure derived from polyisocyanate sandwiched therebetween.

[0030] "Polyisocyanate-derived structure" The polyisocyanate (polyisocyanate used as a raw material) that forms the structure derived from the polyisocyanate contained in the skeleton of polyurethane (a1) and the skeleton of polyurethane (a2) is a compound having multiple isocyanato groups, and diisocyanate is preferably used. Examples of diisocyanates include tolylene diisocyanate and its hydrogenated products, xylylene diisocyanate and its hydrogenated products, diphenylmethane diisocyanate and its hydrogenated products, 1,5-naphthylene diisocyanate and its hydrogenated products, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, tetramethylxylylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexyl diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, and norbornane diisocyanate.

[0031] Among these polyisocyanates, it is preferable to use a hydrogenated product of isophorone diisocyanate or diphenylmethane diisocyanate from the viewpoint of light resistance of the polyurethane (A) synthesized using the same and control of reactivity with polyoxyalkylene polyol, and it is more preferable to use a hydrogenated product of diphenylmethane diisocyanate from the viewpoint of reactivity with polyoxyalkylene polyol.

[0032] Specific examples of polyisocyanates with a polyisocyanate-derived structure include Desmodur W (trade name: manufactured by Sumika Covestro Urethane Co., Ltd.), which is a hydrogenated product of diphenylmethane diisocyanate, and VESTANT IPDI (trade name: manufactured by EVONIK), which is isophorone diisocyanate.

[0033] The polyisocyanate-derived structure contained in the skeleton of the polyurethane (a1) and the polyisocyanate-derived structure contained in the skeleton of the polyurethane (a2) may be the same as or different from each other. The polyisocyanate-derived structures contained in the skeleton of polyurethane (a1) and the skeleton of polyurethane (a2) may each be of one type only, or may each be of two or more types.

[0034] When polyurethane (A) contains polyurethane (a2), the polyurethane (a1) and polyurethane (a2) may have the same or different polyisocyanate-derived structure and polyoxyalkylene polyol-derived structure in their skeletons. When polyurethane (a1) and polyurethane (a2) have the same polyisocyanate-derived structure and polyoxyalkylene polyol-derived structure in their skeletons, polyurethane (a1) and polyurethane (a2) can be synthesized simultaneously, allowing polyurethane (A) to be produced efficiently.

[0035] The proportion of polyurethane (a1) contained in polyurethane (A) is preferably 80 to 100% of polyurethane (A) on a molecular number basis, more preferably 90 to 100%, and even more preferably 100%. That is, polyurethane (A) preferably consists solely of polyurethane (a1). When the proportion of polyurethane (a1) contained in polyurethane (A) is 80% or more, the cured product of the photocurable composition containing polyurethane (A) has a high cohesive force, which is preferable. The proportion of polyurethane (a2) contained in polyurethane (A) is preferably 0 to 20% of polyurethane (A) in terms of the number of molecules, more preferably 0 to 10%, and even more preferably 0%.

[0036] Of the total number of terminals contained in polyurethane (A) (the total number of terminals of polyurethane (a1) and the number of terminals of polyurethanes other than polyurethane (a1) contained as needed), it is preferable that 90 to 100% of the terminals, based on the number of terminals, have a (meth)acryloyloxy group. If the proportion of the terminals having (meth)acryloyloxy groups introduced, based on the number of terminals, of the total number of terminals contained in polyurethane (A), is 90% or more, based on the number of terminals, the cohesive strength of the cured product obtained by curing a photocurable composition containing polyurethane (A) is sufficiently high.

[0037] The proportion of the number of terminals into which a (meth)acryloyloxy group has been introduced to the total number of terminals contained in polyurethane (A) can be calculated using the results of analyzing polyurethane (A) using infrared absorption spectroscopy (IR) or nuclear magnetic resonance spectroscopy (NMR), for example.

[0038] The ratio of the content of polyurethane (a1) to the content of polyurethane (a2) contained in polyurethane (A), i.e., the ratio of the number of terminals into which a (meth)acryloyloxy group has been introduced, to the total number of terminals contained in polyurethane (A), can be adjusted by the production method of polyurethane (A) described below.

[0039] The weight average molecular weight of the polyurethane (A) (the total of the polyurethane (a1) and polyurethanes other than the polyurethane (a1) that are contained as needed) is preferably 30,000 to 200,000, more preferably 50,000 to 150,000, and even more preferably 60,000 to 100,000. When the weight average molecular weight of the polyurethane (A) is 30,000 or more, the flexibility of the cured product obtained by curing the photocurable composition containing the polyurethane (A) is good. Furthermore, when the weight average molecular weight of the polyurethane (A) is 200,000 or less, the photocurable composition containing the polyurethane (A) is easy to handle and has good workability.

[0040] (Method for measuring the mass average molecular weight of polyurethane (A)) The weight average molecular weight of polyurethane (A) is a value calculated as polystyrene equivalent, measured by gel permeation chromatography (GPC-101; Shodex (registered trademark) manufactured by Showa Denko K.K.) (hereinafter referred to as GPC). The GPC measurement conditions are as follows: Column: LF-804 (Showa Denko K.K.) Column temperature: 40℃ Sample: 0.2% by mass solution of polyurethane (A) in tetrahydrofuran Flow rate: 1 ml / min Eluent: tetrahydrofuran Detector: RI detector (differential refractive index detector)

[0041] The content of polyurethane (A) in the photocurable composition of this embodiment is preferably 10 to 60% by mass, more preferably 15 to 55% by mass, and even more preferably 25 to 45% by mass. When the content of polyurethane (A) is 10% by mass or more, the cured product obtained by curing the photocurable composition has sufficient cohesive strength and excellent adhesive strength. Furthermore, the pressure-sensitive adhesive layer formed from this cured product has an appropriate range of softness, making it less likely for air bubbles to be trapped between the pressure-sensitive adhesive layer and the adherend. When the content of polyurethane (A) is 60% by mass or less, the cured product obtained by curing the photocurable composition has sufficient flexibility. Therefore, the pressure-sensitive adhesive layer formed from this cured product has good wettability with respect to the adherend. When the content of polyurethane (A) is 60% by mass or less, the content of ethylenically unsaturated group-containing monomer (B) in the photocurable composition can be sufficiently ensured. As a result, the cured product obtained by curing the photocurable composition has even better adhesive strength.

[0042] [Ethylenically unsaturated group-containing monomer (B)] The ethylenically unsaturated group-containing monomer (B) is a monomer other than the polyurethane (A) that has an ethylenically unsaturated group such as a vinyl group and a (meth)acryloyloxy group. The ethylenically unsaturated group-containing monomer (B) may be a monofunctional monomer or a polyfunctional monomer.

[0043] In this specification, the term "monofunctional" in a monofunctional monomer means that the number of ethylenically unsaturated groups is only 1. In addition, in this specification, the term "polyfunctional" in a polyfunctional monomer means that the number of ethylenically unsaturated groups is 2 or more. The ethylenically unsaturated group-containing monomer (B) contains a first monomer (B-0) that is a hydroxyl group-containing (meth)acrylate. The ethylenically unsaturated group-containing monomer (B) may contain not only the first monomer (B-0) but also a monomer that does not contain a hydroxyl group in addition to the first monomer (B-0).

[0044] [First Monomer (B-0)] The first monomer (B-0) is not particularly limited as long as it is a (meth)acrylate containing a hydroxy group. The first monomer (B-0) preferably does not have a carboxy group that interacts with the antistatic agent (C). The first monomer (B-0) may be used alone or in combination of two or more. A preferred example of the first monomer (B-0) is a hydroxyalkyl(meth)acrylate. The alkyl group of the hydroxyalkyl(meth)acrylate preferably has 2 to 10 carbon atoms, more preferably 2 to 6 carbon atoms, and even more preferably 2 to 4 carbon atoms.

[0045] Specific examples of the first monomer (B-0) include 2-hydroxyethyl acrylate (Tg=-15°C), 2-hydroxyethyl methacrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl acrylate (Tg=-32°C), 4-hydroxybutyl methacrylate, and caprolactone-modified (meth)acrylate (manufactured by Daicel Corporation, Placcel FA, FM series, Tg=-8 to -53°C). Among these, it is particularly preferable to use 2-hydroxyethyl (meth)acrylate and / or 2-hydroxybutyl (meth)acrylate as the first monomer (B-0), since a pressure-sensitive adhesive layer having excellent adhesive strength can be obtained.

[0046] When the ethylenically unsaturated group-containing monomer (B) contains two or more types of monomers, it is preferable to appropriately select and use a combination of the two or more types of monomers so that the glass transition temperature (Tg) of the cured product obtained by curing the photocurable composition falls within a desired range. For example, the ethylenically unsaturated group-containing monomer (B) can be a combination of a first monomer (B-0), a second monomer (B-1) that does not contain a hydroxy group and whose homopolymer has a glass transition temperature (Tg) of -5°C or higher, and a third monomer (B-2) that does not contain a hydroxy group and whose homopolymer has a glass transition temperature (Tg) of less than -5°C.

[0047] The glass transition temperature (Tg) of the homopolymer in the present invention is the glass transition temperature (Tg) of the homopolymer (a homopolymer of a monomer). The Tg of various homopolymers is described in publicly known sources such as "Adhesive Technology Handbook" published by Nikkan Kogyo Shimbun Ltd. (published March 1997) and "Polymer Handbook, 4th Edition" published by Wiley-Interscience (published 1999). For the Tg of a homopolymer of a monomer not described in the above-mentioned publicly known documents, a value determined by the following method is used. Specifically, a homopolymer solution obtained by solution polymerization of the target monomer is cast onto a release liner and dried to prepare a test sample. This test sample is subjected to differential scanning calorimetry (DSC) by changing the temperature from -120°C to 280°C at a heating rate of 10°C / min, and the endothermic onset temperature due to glass transition is taken as the Tg of the homopolymer.

[0048] [Second Monomer (B-1)] Specific examples of the second monomer (B-1) having a homopolymer glass transition temperature (Tg) of -5°C or higher include methyl acrylate (Tg = 8°C), methyl methacrylate (Tg = 105°C), propyl methacrylate (Tg = 35°C), isopropyl acrylate (Tg = -3°C), tert-butyl acrylate (Tg = 43°C), tert-butyl methacrylate (Tg = 20°C), isobutyl methacrylate (Tg = 48°C), isobutyl acrylate (Tg = 43°C), pentyl acrylate (Tg = 48 ... alkyl (meth)acrylates such as butyl acrylate (Tg = 22°C), pentyl methacrylate (Tg = -5°C), hexyl methacrylate (Tg = -5°C), ethoxyethyl methacrylate (Tg = 15°C), stearyl acrylate (Tg = 35°C), lauryl acrylate (Tg = 10°C), tetradecyl acrylate (Tg = 24°C), hexadecyl acrylate (Tg = 35°C), hexadecyl methacrylate (Tg = 15°C); cyclohexyl acrylate (Tg = 15°C), Cyclic alkyl (meth)acrylates such as isobornyl methacrylate (Tg = 180°C) and isobornyl acrylate (Tg = 97°C); aromatic ring-containing (meth)acrylates such as benzyl acrylate (Tg = 6°C); vinyl compounds such as vinyl acetate (Tg = 32°C); dialkylaminoalcohols such as N,N-dimethylaminoethyl acrylate (Tg = 18°C), N,N-dimethylaminoethyl methacrylate (Tg = 18°C), and N,N-diethylaminoethyl methacrylate (Tg = 20°C). (meth)acrylate; styrene (Tg = 100°C); polyfunctional (meth)acrylates such as dipropylene glycol diacrylate (Tg = 104°C), neopentyl glycol dimethacrylate (Tg = 32.5°C), and 1,6-hexanediol diacrylate (Tg = 43°C); 2-(2-vinyloxyethoxy)ethyl acrylate (Tg = 39°C), acrylonitrile (Tg = 97°C), acrylamide (Tg = 165°C), and glycidyl methacrylate (Tg = 46°C).

[0049] Among these second monomers (B-1), from the viewpoint of the heat yellowing resistance of the cured product obtained by curing the photocurable composition, it is preferable to use one having a homopolymer glass transition temperature (Tg) of 0 to 100° C. As the second monomer (B-1), it is more preferable to use a cyclic alkyl (meth)acrylate, and it is particularly preferable to use cyclohexyl acrylate and / or isobornyl acrylate, because this gives a cured product with excellent adhesive strength.

[0050] [Third Monomer (B-2)] Specific examples of the third monomer (B-2) having a homopolymer glass transition temperature (Tg) of less than -5°C include ethyl acrylate (Tg = -22°C), n-butyl acrylate (Tg = -55°C), isobutyl acrylate (Tg = -26°C), octyl acrylate (Tg = -65°C), iso-octyl acrylate (Tg = -70°C), iso-octyl methacrylate (Tg = -45°C), 2-ethylhexyl acrylate (Tg = -70°C), 2-ethylhexyl methacrylate (Tg = -10°C), tetradecyl methacrylate (Tg = -72°C), lauryl methacrylate (Tg = -65°C), isobutyl acrylate (Tg = -26°C), octyl acrylate (Tg = -65°C), isobutyl acrylate (Tg = -26°C), octyl acrylate (Tg = -65°C), isobutyl acrylate (Tg = -70°C), isobutyl methacrylate (Tg = -45°C), 2-ethylhexyl acrylate (Tg = -70°C), 2-ethylhexyl methacrylate (Tg = -10°C), tetradecyl methacrylate (Tg = -72°C), lauryl methacrylate (Tg = -65°C), isobutyl ... Examples of suitable acrylates include alkyl (meth)acrylates such as methyl acrylate (Tg = -45°C); alkoxyalkyl (meth)acrylates such as 2-methoxyethyl acrylate (Tg = -50°C) and methoxy methacrylate (Tg = -16°C); alkoxy (poly)alkylene glycol (meth)acrylates such as ethoxydiethylene glycol acrylate (Tg = -70°C) and methoxytriethylene glycol acrylate (Tg = -50°C); ethyl carbitol acrylate (Tg = -67°C), tetrahydrofurfuryl acrylate (Tg = -12°C), and phenoxyethyl acrylate (Tg = -22°C).

[0051] Among these third monomers (B-2), it is preferable to use one having a homopolymer glass transition temperature (Tg) of -100 to -20°C, as this gives a cured product with excellent adhesive strength. As the third monomer (B-2), from the viewpoint of the heat yellowing resistance of the cured product obtained by curing the photocurable composition, it is more preferable to use an alkyl (meth)acrylate, even more preferable to use an alkyl (meth)acrylate having an alkyl group having 4 to 12 carbon atoms, and it is particularly preferable to use n-butyl acrylate and / or 2-ethylhexyl acrylate.

[0052] The content of the ethylenically unsaturated group-containing monomer (B) in the photocurable composition of this embodiment is preferably 39 to 89 mass%, more preferably 43 to 82 mass%, and even more preferably 55 to 70 mass%. When the content of the ethylenically unsaturated group-containing monomer (B) is 39 mass% or more, a cured product with superior adhesive strength can be obtained. When the content of the ethylenically unsaturated group-containing monomer (B) is 89 mass% or less, the cohesive strength of the cured product obtained by curing the photocurable composition is improved, and a cured product with superior adhesive strength can be obtained.

[0053] The content of the first monomer (B-0), which is a hydroxy group-containing (meth)acrylate, in the photocurable composition of this embodiment is preferably 3 to 25 mass%, more preferably 3 to 20 mass%, and even more preferably 8 to 15 mass%. When the content of the first monomer (B-0) is 3 mass% or more, a cured product with superior adhesive strength is obtained. When the content of the first monomer (B-0) is 25 mass% or less, a cured product with good water resistance is obtained.

[0054] The content of the second monomer (B-1) in the photocurable composition of this embodiment is preferably 5 to 40 mass%, more preferably 10 to 35 mass%, and even more preferably 15 to 30 mass%. When the content of the second monomer (B-1) is 5 mass% or more, a cured product with good heat resistance can be obtained. When the content of the second monomer (B-1) is 40 mass% or less, a cured product with better adhesive strength can be obtained.

[0055] The content of the third monomer (B-2) in the photocurable composition of this embodiment is preferably 10 to 60 mass%, more preferably 15 to 50 mass%, and even more preferably 20 to 40 mass%. When the content of the third monomer (B-2) is 10 mass% or more, a cured product with good flexibility is obtained. When the content of the third monomer (B-2) is 60 mass% or less, a cured product with better adhesive strength is obtained.

[0056] In the photocurable composition of this embodiment, the mass ratio of the second monomer (B-1) to the third monomer (B-2) [(B-1):(B-2)] is preferably 20:80 to 50:50, and more preferably 30:70 to 40:60. When the mass ratio is within the above range, a cured product having excellent adhesion and durability can be obtained.

[0057] [Antistatic agent (C)] The antistatic agent (C) of this embodiment is a fluorine-containing alkali metal imide salt composed of an alkali metal cation and a fluorine-containing imide anion. Examples of the alkali metal cation contained in the fluorine-containing alkali metal imide salt include lithium cation, sodium cation, and potassium cation, with the lithium cation being preferred due to its high ionic conductivity.

[0058] In the photocurable composition of this embodiment, since the polyurethane (A) contains the polyurethane (a1), the cured product is less likely to whiten and maintains transparency for a long period of time, even when the composition contains a fluorine-containing lithium metal imide salt as the antistatic agent (C). This is because the polyoxyalkylene polyol-derived structure contained in the polyurethane (a1) skeleton forms a complex with the lithium ions contained in the antistatic agent (C), improving the compatibility of the antistatic agent (C) in the photocurable composition.

[0059] In contrast, for example, in a photocurable composition containing a fluorine-containing lithium metal imide salt as the antistatic agent (C) and an acrylic copolymer or polyurethane not containing a structure derived from polyoxyalkylene polyol instead of the polyurethane (A), the cured product is prone to whitening. Whitening is particularly likely to occur under high temperature and high humidity conditions. A cured product prone to whitening is not suitable as a pressure-sensitive adhesive layer used to bond optical components. However, if the content of the antistatic agent (C) is reduced in order to suppress the whitening of the cured product, a cured product with sufficient antistatic properties cannot be obtained.

[0060] The antistatic agent (C) of this embodiment is preferably one or more selected from salts of alkali metal cations and bis(fluorosulfonyl)imide anions and salts of alkali metal cations and bis(perfluoroalkylsulfonyl)imide anions, and the alkali metal cation of the antistatic agent (C) is more preferably a lithium cation. That is, it is more preferably one or more selected from salts of lithium cations and bis(fluorosulfonyl)imide anions and salts of lithium cations and bis(perfluoroalkylsulfonyl)imide anions.

[0061] The bis(fluorosulfonyl)imide anion is (SO2F)2N - It is an anion represented by the formula: The bis(perfluoroalkylsulfonyl)imide anion is (C n F 2n+1 SO2)2N - (where n is an integer from 1 to 10) or (C p F 2p+1 SO2)N - (C q F 2q+1 SO2) (wherein p and q are integers of 1 to 10). In the above formula, n is preferably 1 to 6, and more preferably 1 to 4. In the above formula, p is preferably 1 to 6, and more preferably 1 to 4. In the above formula, q is preferably 1 to 6, and more preferably 1 to 4.

[0062] Among these, the fluorine-containing imide anion is (SO2F)2N - and / or (CF3SO2)2N - is preferred. This is because the antistatic agent (C) has high ionic conductivity, and therefore a pressure-sensitive adhesive layer with good antistatic performance can be obtained even with a low content of the antistatic agent (C). When the content of the antistatic agent (C) in the photocurable composition is low, the pressure-sensitive adhesive layer obtained by curing the composition has good durability with the adhesive strength further suppressed from decreasing over time, which is preferred.

[0063] The total content of the antistatic agent (C) in the photocurable composition of this embodiment is preferably 0.1 to 5 mass%, more preferably 0.3 to 4 mass%, and even more preferably 0.5 to 3 mass%. When the content of the antistatic agent (C) is 0.1 mass% or more, the effect of reducing the surface resistivity of the cured product obtained by curing the photocurable composition is obtained. Therefore, a cured product suitable for use as an adhesive layer in a transparent adhesive sheet is obtained. Furthermore, when the content of the antistatic agent (C) is 5 mass% or less, the adhesive layer obtained by curing this composition is further prevented from losing adhesive strength over time.

[0064] [Photopolymerization initiator (D)] The photopolymerization initiator (D) is not particularly limited, but it is preferable to use a photoradical polymerization initiator. Examples of the photopolymerization initiator (D) that can be used include carbonyl-based photopolymerization initiators, sulfide-based photopolymerization initiators, acylphosphine oxide-based photopolymerization initiators, quinone-based photopolymerization initiators, sulfochloride-based photopolymerization initiators, and thioxanthone-based photopolymerization initiators. Among these photopolymerization initiators (D), from the viewpoint of the transparency of the cured product obtained by photocuring the pressure-sensitive adhesive composition, it is preferable to use a carbonyl-based photopolymerization initiator and / or an acylphosphine oxide-based photopolymerization initiator. Specifically, it is preferable to use 2,4,6-trimethylbenzoyldiphenylphosphine oxide and / or 1-hydroxycyclohexylphenyl ketone.

[0065] The content of the photopolymerization initiator (D) in the pressure-sensitive adhesive composition of this embodiment is preferably 0.01 to 5 mass%, more preferably 0.05 to 3 mass%, and even more preferably 0.1 to 2 mass%. When the content of the photopolymerization initiator (D) is 0.01 mass% or more, the photocuring of the photocurable composition proceeds sufficiently. Furthermore, when the content of the photopolymerization initiator (D) is 5 mass% or less, the amount of low-molecular-weight components does not become too large during photocuring of the photocurable composition. This is preferable because the adhesive strength of the cured product is sufficiently improved.

[0066] (tackifying resin) In the photocurable composition of this embodiment, a tackifying resin may be added as needed to improve the adhesive strength of the cured product obtained by curing the composition, within a range that does not reduce the transparency of the cured product. Examples of tackifying resins include rosin-based resins such as rosin and rosin esters; terpene-based resins such as diterpene polymers and α-pinene-phenol copolymers; aliphatic (C5) and aromatic (C9) petroleum resins; and styrene-based resins, phenolic resins, xylene resins, etc. From the viewpoint of light resistance of the cured product, it is preferable to use, as the tackifying resin, hydrogenated rosin with few unsaturated double bonds, esters of disproportionated rosin, aliphatic and aromatic petroleum resins, and high-Tg acrylic resins.

[0067] The amount of tackifier resin added is preferably in the range of 1 to 10 parts by mass per 100 parts by mass of the photocurable composition (per 100 parts by mass of the total of components (A) to (D)). From the viewpoint of preventing adhesive residue on an adherend from a cured product of the photocurable composition, it is preferable that the photocurable composition does not contain a tackifying resin.

[0068] (solvent) The photocurable composition of this embodiment may or may not contain a solvent. The photocurable composition of this embodiment is preferably a solvent-free composition that does not substantially contain a solvent. When the photocurable composition of the present embodiment contains a solvent, the solvent can be used as, for example, a viscosity modifier, a leveling agent, and / or a softener. Specific examples of the solvent include methyl ethyl ketone, acetone, ethyl acetate, tetrahydrofuran, dioxane, cyclohexanone, n-hexane, toluene, xylene, n-propanol, and isopropanol.

[0069] When the pressure-sensitive adhesive composition of this embodiment is solvent-free, the step of heat-drying the solvent can be omitted when using it to prepare a pressure-sensitive adhesive layer of a transparent pressure-sensitive adhesive sheet. Therefore, excellent productivity can be obtained. In particular, when using the photocurable composition of this embodiment to produce a transparent pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer with a thickness of more than 50 μm, the productivity improvement effect of omitting the step of heat-drying the solvent is remarkable. Therefore, it is preferable that the composition is solvent-free.

[0070] In the present invention, the photocurable composition being "substantially free of solvent" means that the content of solvent in the photocurable composition is 0 to 1 mass %, preferably 0 to 0.5 mass %, and more preferably 0 to 0.1 mass %.

[0071] (others) The photocurable composition of the present embodiment may contain additives as needed, provided that the effects of the present invention are not impaired. Examples of additives include plasticizers, surface lubricants, antioxidants, antiaging agents, light stabilizers, ultraviolet absorbers, polymerization inhibitors, benzotriazole-based light stabilizers, phosphate ester-based and other flame retardants, and dyes.

[0072] The photocurable composition of this embodiment preferably has an acid value of 0 to 5 mgKOH / g, more preferably 0 to 0.5 mgKOH / g, and even more preferably 0 to 0.1 mgKOH / g. An acid value of 5 mgKOH / g or less is preferable because, for example, when the adhesive layer of the transparent adhesive sheet is attached to the conductive layer surface of a transparent conductive film of a touch panel, the conductive layer surface is not corroded.

[0073] The acid value of the photocurable composition is a value measured in accordance with JIS K 0070. Specifically, the acid value of the photocurable composition is determined by the method shown below. Approximately 2 g of sample is weighed out accurately into a 100 ml Erlenmeyer flask using a precision balance, and 10 ml of a 1:1 (by weight) ethanol / diethyl ether mixed solvent is added to dissolve it. One to three drops of phenolphthalein ethanol solution are added to the solution in the Erlenmeyer flask as an indicator, and the mixture is thoroughly stirred until homogenous. The solution is titrated with 0.1 N potassium hydroxide-ethanol solution, and the neutralization endpoint is determined when the indicator remains pale red for 30 seconds. The acid value of the photocurable composition is calculated from the results using the following formula (1):

[0074] Acid value (mgKOH / g)=[B×f×5.661] / S (1) In addition, B, f, and S in the calculation formula (1) are as follows: B: Amount (ml) of 0.1N potassium hydroxide-ethanol solution used f: Factor of 0.1N potassium hydroxide-ethanol solution (correction for variations due to reagent lots) S: Amount of sample collected (g)

[0075] <Transparent adhesive sheet> The transparent adhesive sheet of this embodiment has an adhesive layer made of a cured product of the photocurable composition. The transparent adhesive sheet of this embodiment may be a single-sided adhesive sheet in which an adhesive layer made of a cured product of the photocurable composition is provided on one side of a substrate formed of a transparent resin sheet such as polyethylene terephthalate (PET), or may be a double-sided adhesive sheet that does not have a substrate and is made only of an adhesive layer. From the viewpoints of ensuring transparency and shape conformability (step absorbability), the transparent adhesive sheet of this embodiment is preferably a double-sided adhesive sheet that does not have a substrate and is made only of an adhesive layer.

[0076] The adhesive layer of the transparent adhesive sheet of this embodiment may have a single layer structure or a multilayer structure in which multiple layers are laminated. A specific example of a multilayer adhesive layer is a three-layer structure in which the composition of the central layer is different from the composition of the outer layers sandwiching the central layer. In such an adhesive layer, the cohesive strength and adhesive strength of the adhesive layer can be balanced by adjusting the composition of the photocurable composition used as the material for the central layer and the composition of the photocurable composition used as the material for the outer layers. From the perspective of simplifying the manufacturing process of the transparent adhesive sheet, it is preferable that the adhesive layer of the transparent adhesive sheet be a single layer.

[0077] The thickness of the pressure-sensitive adhesive layer in this embodiment is preferably 5 to 1000 μm, more preferably 10 to 500 μm, and even more preferably 15 to 300 μm. When the thickness of the pressure-sensitive adhesive layer is 5 μm or more, workability when laminating the transparent pressure-sensitive adhesive sheet is improved. Furthermore, when the thickness of the pressure-sensitive adhesive layer is 1000 μm or less, film thickness control of the pressure-sensitive adhesive layer is easy.

[0078] The glass transition temperature (Tg) of the pressure-sensitive adhesive layer of this embodiment is preferably −40 to 20° C., more preferably −30 to 10° C. When the glass transition temperature (Tg) is −40° C. or higher, the pressure-sensitive adhesive layer has an appropriate hardness, resulting in a transparent pressure-sensitive adhesive sheet with sufficient adhesive strength. When the glass transition temperature (Tg) is 20° C. or lower, the pressure-sensitive adhesive layer has an appropriate softness, resulting in a transparent pressure-sensitive adhesive sheet with good level difference absorbency on the adherend.

[0079] The glass transition temperature (Tg) of the cured product of the photocurable composition is a value measured by the following method: Using a differential scanning calorimeter (DSC), differential scanning calorimetry is performed on approximately 10 mg of a sample, changing the temperature from -80°C to 280°C at a heating rate of 10°C / min, and the endothermic initiation temperature due to glass transition is taken as the glass transition temperature (Tg) of the cured product.

[0080] From the viewpoint of practicality, the surface resistivity of the adhesive layer in the transparent adhesive sheet of this embodiment is 1.0×10 8 ~5.0×1010 Ω / □ is preferred, and 1.0×10 8 ~1.0×10 10 Ω / □ is more preferable, and 1.0×10 8 ~5.0×10 9 It is more preferable that the surface resistivity is 1.0×10 Ω / □. The smaller the surface resistivity and the more excellent the antistatic performance of the pressure-sensitive adhesive layer, the less likely it is to be charged during the step of laminating an optical member, and therefore it is preferable. 8 When the surface resistivity is 5.0×10 Ω / □ or more, the transparent adhesive sheet has an adhesive layer in which the charge decays relatively quickly. 10 When the resistivity is Ω / □ or less, the transparent adhesive sheet has an adhesive layer with better antistatic properties.

[0081] The gel fraction of the adhesive layer is preferably 55 to 90% by mass, and more preferably 60 to 80% by mass. A gel fraction of 55% by mass or more improves workability when laminating or cutting (punching) the transparent adhesive sheet. A gel fraction of 90% by mass or less results in a transparent adhesive sheet having an adhesive layer with good level difference absorbency on the adherend.

[0082] The surface of the transparent adhesive sheet of this embodiment (surface of the adhesive layer) may be protected by a release film (separator) until use. When the transparent adhesive sheet is a double-sided adhesive sheet, both sides of the double-sided adhesive sheet may be protected by two release films, respectively, or may be protected by a single release film with both sides serving as release surfaces in a rolled form. The release film is used as a protective material for the adhesive layer and is peeled off when the adhesive layer is attached to an adherend. The release film does not have to be provided on the surface of the adhesive layer.

[0083] The release film may be any commonly used release film, and is not particularly limited. Examples of the release film include plastic films whose surfaces are treated with a release treatment agent such as a silicone-based, long-chain alkyl-based, or fluorine-based release agent. The release film may be formed by a known method. The thickness of the release film is not particularly limited. For example, when the surfaces (both sides) of the pressure-sensitive adhesive layer are protected by two release films, the thicknesses of the two release films may be the same or different. In this case, the two release films may be made of the same material or different materials. For example, the releasability of the release films can be controlled by changing the rigidity of the two release films.

[0084] The transparent adhesive sheet of this embodiment is suitable for use in bonding optical components that are easily charged. The optical components to be bonded include components having optical properties, and are not particularly limited, but include, for example, components constituting image display devices or touch panels, or components used in these devices. Specific examples include polarizing films, retardation films, optical compensation films, brightness enhancement films, light-guiding films, reflective films, anti-reflection films, transparent conductive films, design films, decorative films, surface protection films, prisms, lenses, color filters, transparent substrates, and components in which these are laminated.

[0085] <Method for producing photocurable composition> Next, the method for producing the photocurable composition of this embodiment will be described in detail using examples. Among the components contained in the photocurable composition of this embodiment, a preferred synthesis method for polyurethane (A) will be described below by citing an example. Of the components contained in the photocurable composition of this embodiment, the ethylenically unsaturated group-containing monomer (B), antistatic agent (C), photopolymerization initiator (D), and other components other than polyurethane (A) are readily available as commercially available products, and the synthesis method for each component differs depending on the type of compound used, so explanations of the synthesis methods will be omitted.

[0086] <Method for synthesizing (meth)acryloyloxy group-containing polyurethane (A)> An example of a preferred method for synthesizing the polyurethane (A) contained in the photocurable composition of this embodiment will be described below. The method for synthesizing the polyurethane (A) is not limited to the synthesis method shown below, and can be changed as appropriate depending on conditions such as the raw materials and equipment used in the synthesis.

[0087] In the synthesis method of polyurethane (A) shown below, the reaction between hydroxyl groups and isocyanato groups is carried out in the presence of an organic solvent inert to isocyanato groups using a urethanization catalyst in every step. Examples of the urethanization catalyst that can be used include dibutyltin dilaurate, dibutyltin diethylhexoate, and dioctyltin dilaurate. The amount of the urethanization catalyst used is preferably 50 to 500 ppm by mass relative to the total mass of the reactants (raw materials). In addition, the reaction between the hydroxy group and the isocyanato group is preferably carried out continuously at 30 to 100° C. for 1 to 5 hours in any step.

[0088] To synthesize polyurethane (A), first, a polyoxyalkylene polyol and a polyisocyanate are charged in a ratio such that the amount of isocyanato groups (based on the total number of functional groups, the same applies hereinafter) is greater than the amount of hydroxyl groups (based on the total number of functional groups, the same applies hereinafter). The polyoxyalkylene polyol and the polyisocyanate are then reacted to synthesize a polyurethane having isocyanato groups at its terminals as a precursor of polyurethane (A). Specific examples of the polyoxyalkylene polyol and polyisocyanate used as raw materials are as exemplified in the section on polyurethane (A).

[0089] At this time, the molecular weight (degree of polymerization) of the polyurethane having isocyanato groups at its terminals can be adjusted by adjusting the ratio of the amount of isocyanato groups to the amount of hydroxy groups contained in the raw materials. Specifically, the smaller the excess amount of isocyanato groups relative to the amount of hydroxy groups, the higher the molecular weight of the polyurethane having isocyanato groups at its terminals. Furthermore, the greater the excess amount of isocyanato groups relative to the amount of hydroxy groups, the lower the molecular weight of the polyurethane having isocyanato groups at its terminals. In this embodiment, the weight average molecular weight of the target polyurethane (A) is adjusted by adjusting the molecular weight of the polyurethane having isocyanato groups at its terminals.

[0090] Next, a polyurethane having an isocyanato group at a terminal is reacted with a compound having a hydroxy group and a (meth)acryloyloxy group to produce a polyurethane (A) having a skeleton containing a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate, and containing a polyurethane (a1) having (meth)acryloyloxy groups at a plurality of terminals.

[0091] Compounds having a hydroxy group and a (meth)acryloyloxy group include, but are not limited to, hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; and monools having a (meth)acryloyloxy group derived from various polyols, such as 1,3-butanediol mono(meth)acrylate, 1,4-butanediol mono(meth)acrylate, 1,6-hexanediol mono(meth)acrylate, and 3-methylpentanediol mono(meth)acrylate. These compounds having a hydroxy group and a (meth)acryloyloxy group may be used alone or in combination of two or more. Among these compounds having a hydroxy group and a (meth)acryloyloxy group, 2-hydroxyethyl (meth)acrylate is preferred in terms of reactivity with the isocyanato group of a polyurethane having an isocyanato group at its terminal and the photocurability of the photocurable composition.

[0092] Alternatively, polyurethane (A) may be produced by reacting a compound having a hydroxy group and a (meth)acryloyloxy group with an alkyl alcohol having one hydroxy group but no (meth)acryloyloxy group, and the resulting mixture with a polyurethane having an isocyanato group at its terminal. The alkyl alcohol is not particularly limited as long as it does not have a (meth)acryloyloxy group and has one hydroxy group, and may be a linear, branched, or alicyclic alkyl alcohol, etc. The alkyl alcohol may be used alone or in combination of two or more.

[0093] The amount of (meth)acryloyloxy groups introduced into the polyurethane having terminal isocyanato groups can be adjusted by reacting a compound having a hydroxy group and a (meth)acryloyloxy group with an alkyl alcohol having no (meth)acryloyloxy groups but one hydroxy group, and a polyurethane having terminal isocyanato groups to produce polyurethane (A).

[0094] More specifically, the above reaction produces polyurethane (A) containing multiple types of polyurethanes with different amounts of (meth)acryloyloxy groups introduced at their terminals. The multiple types of polyurethanes include polyurethane (a1) having multiple terminals with (meth)acryloyloxy groups. Furthermore, the multiple types of polyurethanes include not only polyurethane (a1) but also polyurethanes in which at least some of the terminals have a structure derived from the alkyl alcohol. Therefore, the multiple types of polyurethanes produced include polyurethanes in which at least some of the terminals do not have (meth)acryloyloxy groups. Furthermore, the multiple types of polyurethanes produced may also include polyurethane (a2) having a (meth)acryloyloxy group at only one terminal.

[0095] <Another example of a method for synthesizing polyurethane (A)> Next, another preferred example of the synthesis method for polyurethane (A) will be described. In the synthesis method of polyurethane (A) shown below, as in the example of the synthesis method described above, the reaction between hydroxyl groups and isocyanato groups is carried out in the presence of an organic solvent inert to isocyanato groups using a urethanization catalyst in every step. Examples of the urethanization catalyst that can be used include dibutyltin dilaurate, dibutyltin diethylhexoate, and dioctyltin dilaurate. The amount of the urethanization catalyst used is preferably 50 to 500 ppm by mass relative to the total mass of the reactants (raw materials). In addition, the reaction between the hydroxy group and the isocyanato group is preferably carried out continuously at 30 to 100° C. for 1 to 5 hours in any step.

[0096] When polyurethane (A) is synthesized using this synthesis method, unlike the above-mentioned examples of synthesis methods, a polyurethane having a terminal hydroxy group is synthesized as a precursor of polyurethane (A). Specifically, first, a polyoxyalkylene polyol and a polyisocyanate are charged in a ratio such that the amount of hydroxy groups (based on the total number of functional groups, the same applies hereinafter) is greater than the amount of isocyanato groups (based on the total number of functional groups, the same applies hereinafter).The polyoxyalkylene polyol and the polyisocyanate are then reacted to synthesize a polyurethane having hydroxy groups at its terminals as a precursor of polyurethane (A).

[0097] At this time, the molecular weight (degree of polymerization) of the polyurethane having terminal hydroxy groups can be adjusted by adjusting the ratio of the amount of hydroxy groups to the amount of isocyanato groups contained in the raw materials. Specifically, the smaller the excess amount of hydroxy groups relative to the amount of isocyanato groups, the higher the molecular weight of the polyurethane having terminal hydroxy groups. Furthermore, the greater the excess amount of hydroxy groups relative to the amount of isocyanato groups, the lower the molecular weight of the polyurethane having terminal hydroxy groups. In this embodiment, the mass average molecular weight of the target polyurethane (A) is adjusted by adjusting the molecular weight of the polyurethane having terminal hydroxy groups.

[0098] Next, a polyurethane having a hydroxy group at its terminal is reacted with a compound having an isocyanato group and a (meth)acryloyloxy group to produce a polyurethane (A) having a skeleton containing a polyoxyalkylene polyol-derived structure and a polyisocyanate-derived structure, and containing a polyurethane (a1) having (meth)acryloyloxy groups at multiple terminals.

[0099] The compound having an isocyanato group and a (meth)acryloyloxy group is not particularly limited, but includes 2-(meth)acryloyloxyethyl isocyanate, 2-(meth)acryloyloxypropyl isocyanate, 1,1-bis(acryloyloxymethyl)ethyl isocyanate, etc. Examples of commercially available compounds having an isocyanato group and a (meth)acryloyloxy group include Karenz MOI (registered trademark) and Karenz AOI (registered trademark) manufactured by Showa Denko K.K. These compounds having an isocyanato group and a (meth)acryloyloxy group may be used alone or in combination of two or more. Among these compounds having an isocyanato group and a (meth)acryloyloxy group, 2-(meth)acryloyloxyethyl isocyanate is preferred in terms of reactivity with the hydroxyl group of a polyurethane having a terminal hydroxyl group and the photocurability of the pressure-sensitive adhesive composition.

[0100] Alternatively, polyurethane (A) may be produced by reacting a compound having an isocyanato group and a (meth)acryloyloxy group with an alkyl isocyanate having one isocyanato group but no (meth)acryloyloxy group, and the resulting mixture with polyurethane having a terminal hydroxy group. The alkyl isocyanate is not particularly limited as long as it does not have a (meth)acryloyloxy group and has one isocyanato group, and linear, branched, alicyclic alkyl isocyanates, etc. can be used. The alkyl isocyanates may be used alone or in combination of two or more.

[0101] The amount of (meth)acryloyloxy groups introduced into the polyurethane having hydroxy groups at its terminals can be adjusted by reacting a compound having an isocyanato group and a (meth)acryloyloxy group with an alkyl isocyanate having one isocyanato group but no (meth)acryloyloxy group, and a polyurethane having hydroxy groups at its terminals to produce polyurethane (A).

[0102] More specifically, the above reaction produces polyurethane (A) containing multiple types of polyurethanes with different amounts of (meth)acryloyloxy groups introduced at their terminals. The multiple types of polyurethanes include polyurethane (a1) having multiple terminals with (meth)acryloyloxy groups. Furthermore, the multiple types of polyurethanes include not only polyurethane (a1) but also polyurethanes in which at least some of the terminals have a structure derived from the alkyl isocyanate. Therefore, the multiple types of polyurethanes produced include polyurethanes in which at least some of the terminals do not have (meth)acryloyloxy groups. Furthermore, the multiple types of polyurethanes produced may also include polyurethane (a2) having a (meth)acryloyloxy group at only one terminal.

[0103] The amount of (meth)acryloyloxy groups introduced into the polyurethane (A) at its terminals is preferably 50 to 100 mol %, more preferably 80 to 100 mol %, and even more preferably 90 to 100 mol %, based on the total number (total amount) of terminals possessed by the polyurethane (A). When the amount introduced is 50 mol % or more, the cohesive strength of the cured product obtained by curing the photocurable composition is sufficiently high.

[0104] <Method of mixing components contained in photocurable composition> The photocurable composition of this embodiment can be produced by mixing the polyurethane (A) obtained by the above synthesis method, the ethylenically unsaturated group-containing monomer (B), the antistatic agent (C), the photopolymerization initiator (D), and other additives that are added as needed. The method for mixing the components contained in the photocurable composition of this embodiment is not particularly limited, and can be carried out using, for example, a stirring device equipped with stirring blades such as a homodisper or paddle blade.

[0105] <Manufacturing method of transparent adhesive tape> Next, a method for producing the transparent adhesive tape of this embodiment will be described. The method for producing the transparent adhesive tape of the present embodiment is not particularly limited, and the tape can be produced using a known method. The transparent adhesive tape of this embodiment can be produced, for example, by a method of applying a photocurable composition to a substrate or a release film, and directly irradiating the applied photocurable composition with ultraviolet light using an ultraviolet irradiation device or the like to photocure the photocurable composition. Alternatively, the transparent adhesive tape of this embodiment may be produced by a method of applying a photocurable composition to a substrate or a release film, laminating a transparent release film thereon, and irradiating the transparent release film with ultraviolet light using an ultraviolet irradiation device or the like to photocure the photocurable composition.

[0106] The method for applying the photocurable composition to the substrate or the release film is not particularly limited and can be selected appropriately. For example, examples of the method for applying the pressure-sensitive adhesive composition to the substrate or the release film include a method using various coaters such as a gravure roll coater, a reverse roll coater, a kiss roll coater, a dip roll coater, a bar coater, a knife coater, a spray coater, a comma coater, and a direct coater, and a screen printing method.

[0107] Examples of light sources used to photocure the photocurable composition include black lights, low-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, metal halide lamps, and xenon lamps. The light irradiation dose is, for example, 50 to 3000 mJ / cm 2 If the amount of light irradiation is too small, it takes a long time to cure the photocurable composition, resulting in a decrease in productivity. When the substrate or release film onto which the photocurable composition is applied is transparent, the photocurable composition may be irradiated with ultraviolet light from the substrate or release film side.

[0108] <Uses and required performance of transparent adhesive sheets> The transparent adhesive tape of the present embodiment can be suitably used for bonding optical members together, specifically, when bonding two plate-like optical members together, such as bonding a liquid crystal cell and a polarizing film in a touch panel. When the transparent adhesive tape of this embodiment is used to bond optical components, the transparent adhesive sheet preferably has high transparency. Specifically, the total light transmittance of the transparent adhesive sheet is preferably 90% or more, more preferably 91% or more. The haze value is preferably 1% or less, more preferably 0.5% or less.

[0109] The peel strength of the transparent adhesive tape used for the above applications is preferably 15 to 40 (N / 25 mm), more preferably 20 to 35 (N / 25 mm). A specific method for measuring the peel strength of the transparent adhesive sheet will be described later in the examples. When a transparent adhesive sheet is used to bond optical components of a touch panel, the transparent adhesive sheet is affected by heat emitted from the touch panel. The transparent adhesive sheet of this embodiment has good durability against heat and exhibits little change over time in the haze value and adhesive strength (peel strength). Therefore, it can be preferably used to bond optical components of a touch panel.

[0110] The photocurable composition of this embodiment contains a (meth)acryloyloxy group-containing polyurethane (A), an ethylenically unsaturated group-containing monomer (B), an antistatic agent (C), and a photopolymerization initiator (D). In the photocurable composition of this embodiment, the (meth)acryloyloxy group-containing polyurethane (A) has a backbone containing a polyoxyalkylene polyol-derived structure and a polyisocyanate-derived structure, and includes a polyurethane (a1) having (meth)acryloyloxy groups at multiple terminals. The ethylenically unsaturated group-containing monomer (B) includes a first monomer (B-0) that is a hydroxyl group-containing (meth)acrylate. The antistatic agent (C) is a fluorine-containing alkali metal imide salt. Therefore, a transparent adhesive sheet having an adhesive layer made of a cured product of the photocurable composition of this embodiment has antistatic properties, is resistant to deterioration in adhesive strength over time, and can maintain adhesive strength over a long period of time. Furthermore, the adhesive layer in the transparent adhesive sheet of this embodiment can be formed by a method of photocuring a photocurable composition, and can be formed by a simple method without requiring time-consuming and complicated steps such as heat treatment. [Example]

[0111] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0112] <Synthesis of polyurethane (a1-1)> A reactor consisting of a four-neck flask equipped with a thermometer, a stirrer, a dropping funnel, and a condenser with a drying tube was charged with 21 mol of a hydrogenated product of diphenylmethane diisocyanate (trade name: Desmodur W, manufactured by Sumika Covestro Urethane Co., Ltd.), 20 mol of polypropylene glycol having a hydroxyl group at its terminal and a hydroxyl value of 56 mg KOH / g (trade name: Actocol D-2000, manufactured by Mitsui Chemicals, Inc., number average molecular weight 2000), and 8 g of a urethanization catalyst dioctyltin (trade name: Neostan U-810, manufactured by Nitto Kasei Co., Ltd.).

[0113] The reactor was then heated to 60°C and reacted for 4 hours to obtain a polyurethane having isocyanato groups at both ends as a precursor of polyurethane (A). 20 mol of 2-hydroxyethyl acrylate was then added to the reactor, and the temperature was raised to 70°C to react for 2 hours to obtain polyurethane (a1-1).

[0114] The resulting polyurethane (a1-1) was analyzed using infrared absorption spectroscopy (IR). As a result, no peaks derived from isocyanato groups were observed. Therefore, it was confirmed that polyurethane (a1-1) was polyurethane (a1) in which acryloyloxy groups had been introduced at all terminals. The weight-average molecular weight of the resulting polyurethane (a1-1) was 70,000.

[0115] <Synthesis of polyurethane (a1-2)> The reaction was carried out in the same manner as in the synthesis of polyurethane (a1-1), except that 20 mol of a hydrogenated product of diphenylmethane diisocyanate (Desmodur W) and 21 mol of polypropylene glycol (Actocol D-2000) were used, to obtain a polyurethane having hydroxy groups at both ends as a precursor of polyurethane (A). Next, 20 mol of 2-acryloyloxyethyl isocyanate (product name: MOI-AOI, manufactured by Showa Denko K.K.) was added to the reactor, and the temperature was raised to 70°C and the reaction was carried out for 2 hours to obtain polyurethane (a1-2).

[0116] The resulting polyurethane (a1-2) was analyzed using infrared absorption spectroscopy (IR). As a result, no peaks derived from isocyanato groups were observed. Therefore, it was confirmed that polyurethane (a1-2) was polyurethane (a1) in which acryloyloxy groups had been introduced at all terminals. The weight-average molecular weight of the resulting polyurethane (a1-2) was 70,000.

[0117] <Synthesis of polyurethane (a3-1)> A reactor consisting of a four-neck flask equipped with a thermometer, a stirrer, a dropping funnel, and a condenser with a drying tube was charged with 15 mol of isophorone diisocyanate (trade name: VESTANT IPDI, manufactured by EVONIK), 14 mol of hydroxyl-terminated hydrogenated polybutadiene (trade name: GI-3000, manufactured by Nippon Soda Co., Ltd., hydroxyl value 25 mg KOH / g), and 8 g of a urethanization catalyst, dioctyltin (trade name: Neostan U-810, manufactured by Nitto Kasei Co., Ltd.).

[0118] The reactor was then heated to 60°C and reacted for 4 hours to obtain a polyurethane having a polybutadiene-derived structure and isocyanato groups at both ends. 2 mol of 2-hydroxyethyl acrylate was then added to the reactor, and the temperature was raised to 70°C to allow the reaction for 2 hours to obtain polyurethane (a3-1).

[0119] The resulting polyurethane (a3-1) was analyzed using infrared absorption spectroscopy (IR). As a result, no peaks derived from isocyanato groups were observed. Therefore, it was confirmed that polyurethane (a3-1) was a polyurethane in which acryloyloxy groups were introduced at all terminals. The weight-average molecular weight of the resulting polyurethane (a3-1) was 70,000.

[0120] (Example 1 9. Refer to Example 10 , Comparative Examples 1 to 4) Any of the polyurethanes (a1-1) to (a3-1) obtained by the above synthesis method was blended with the ethylenically unsaturated group-containing monomer (B), antistatic agent (C), and photopolymerization initiator (D) shown in Table 1 or Table 2 in the ratios shown in Table 1 or Table 2, and mixed at 25°C using a disper. 9. Refer to Example 10 Photocurable compositions of Comparative Examples 1 to 4 were prepared.

[0121] [Table 1]

[0122] [Table 2]

[0123] The symbols shown below in Tables 1 and 2 represent the compounds shown below. For the compounds shown below, the glass transition temperature (Tg) values ​​shown in parentheses are the glass transition temperature values ​​when each compound is made into a homopolymer. "Ethylenically unsaturated group-containing monomer (B)" HEA: Hydroxyethyl acrylate (Osaka Organic Chemical Industry Co., Ltd., Tg = -15°C) 4HBA: 4-hydroxybutyl acrylate (Osaka Organic Chemical Industry Ltd., Tg = -32°C) CHA: cyclohexyl acrylate (Osaka Organic Chemical Industry Co., Ltd., Tg = 15°C) IBA: isobornyl acrylate (Nippon Shokubai Co., Ltd., Tg = 97°C) BUA: n-butyl acrylate (Nippon Shokubai Co., Ltd., Tg = -55°C) EHA: 2-ethylhexyl acrylate (Toagosei Co., Ltd., Tg = -70°C)

[0124] "Antistatic agent (C)" LiFSI: LiN(SO2F)2 (trade name: Ionel LF-101, manufactured by Nippon Shokubai Co., Ltd.) LiTFSI: LiN(CF3SO2)2 (product name: F-Top EF-N115, manufactured by Mitsubishi Materials Electronic Chemicals Co., Ltd.) PFMLi: LiSO3CF3 (product name: F-Top EF-15, manufactured by Mitsubishi Materials Electronic Chemicals Co., Ltd.) AS-804: 1-octyl-4-methylpyridinium bis(fluorosulfonyl)imide (Dai-ichi Kogyo Seiyaku Co., Ltd.) "Photopolymerization initiator (D)" OMN184: 1-hydroxycyclohexyl-phenyl ketone (trade name: Omnirad 184, manufactured by IGM)

[0125] The obtained Examples 1 to 9. Refer to Example 10 The acid value was measured by the above method for each of the photocurable compositions of Comparative Examples 1 to 4. The results are shown in Table 1 or Table 2.

[0126] "Manufacturing transparent adhesive sheets" Examples 1 to 3 were prepared by the following method. 9. Refer to Example 10 The photocurable compositions of Examples 1 to 4 were used, respectively. 9. Refer to Example 10 Transparent adhesive sheets of Comparative Examples 1 to 4 were produced. A 75 μm thick release PET film (200 mm long, 150 mm wide, manufactured by Higashiyama Film Co., Ltd., product name: S-10-2) was prepared. The photocurable composition was applied to the release surface of the release PET film using an applicator so that the film thickness after curing was 150 μm. The applied surface was then covered with a 50 μm thick release PET film (manufactured by Toyobo Co., Ltd., product name: E7006).

[0127] Next, an ultraviolet irradiation device (metal halide lamp, UV irradiation device 4 kW × 1, output: 160 W / cm, manufactured by Japan Battery Co., Ltd.) was used, the irradiation distance was 12 cm, the lamp movement speed was 20 m / min, and the irradiation dose was approximately 500 mJ / cm 2 The photocurable composition was irradiated with ultraviolet light through a 50 μm thick release PET film under the conditions of 100 μm to cure. By the above process, the photocurable composition of Examples 1 to 3 having a pressure-sensitive adhesive layer sandwiched between release PET films on both sides was obtained. 9. Refer to Example 10 Thus, transparent adhesive sheets of Comparative Examples 1 to 4 were obtained.

[0128] Example 1 9. Refer to Example 10 The glass transition temperature (Tg), surface resistivity, adhesive strength, total light transmittance, and resistance to wet heat whitening were measured by the methods described below for the transparent adhesive sheets of Comparative Examples 1 to 4. The results are shown in Table 1 or Table 2.

[0129] (glass transition temperature (Tg)) The PET release films were peeled off from both sides of the transparent adhesive sheet, and approximately 10 mg of the adhesive layer was measured. Using a differential scanning calorimeter (DSC), the temperature of the approximately 10 mg sample was changed from -80°C to 280°C at a heating rate of 10°C / min. The temperature at which heat absorption due to the glass transition began was taken as the glass transition temperature (Tg) of the cured product.

[0130] (Surface resistivity) The transparent adhesive sheet was cut into a size of 120 mm long and 120 mm wide, and the 50 μm thick release PET film was peeled off to expose the adhesive layer. The sheet was then left to stand for 3 hours in an environment at 23°C and 50% RH (relative humidity) to condition the humidity. The surface resistivity of the adhesive layer side was then measured using a high resistivity meter (HIRESTA-UX, manufactured by Mitsubishi Chemical Analytech Co., Ltd.) under the condition of an applied voltage of 100 V for 60 seconds.

[0131] (Adhesive strength) The 50 μm-thick release PET film was peeled off from the transparent adhesive sheet, and a 50 μm-thick PET film (Toyobo Ester Film E5100, manufactured by Toyobo Co., Ltd.) with one side corona-treated was reattached. The transparent adhesive sheet was cut into a size of 25 mm length and 150 mm width, and the 75 μm-thick release PET film was peeled off to expose the adhesive layer (measurement surface). The adhesive layer was attached to a glass plate, and a 2 kg rubber roller (width: approximately 50 mm) was rolled back and forth once to prepare a measurement sample.

[0132] The obtained measurement samples were left in an environment of 23°C and 50% RH (relative humidity) for 0.5 hours, 24 hours, and 500 hours. After leaving, the measurement samples were subjected to measurement of adhesive strength using the method described below. Specifically, each measurement sample was subjected to a tensile test in the 180° direction at a peel rate of 300 mm / min according to JIS K6854, and the obtained measurement value was taken as the adhesive strength (N / 25 mm) of the transparent adhesive sheet to the glass plate.

[0133] (Total light transmittance) The transparent adhesive sheet was cut into a size of 30 mm long and 30 mm wide, and the 50 μm thick release PET film was peeled off to expose the adhesive layer. The exposed adhesive layer was attached to a 0.7 mm thick glass plate. Next, the 75 μm thick release PET film on the opposite side was peeled off to expose the adhesive layer. The exposed adhesive layer was attached to the glass plate. This yielded a measurement sample consisting of an adhesive layer sandwiched between glass plates on both sides. The total light transmittance of the measurement sample was measured using a haze meter "HR-100 (manufactured by Murakami Color Research Laboratory Co., Ltd.)".

[0134] (Heat and humidity whitening resistance) A measurement sample was prepared in the same manner as in the measurement of total light transmittance, and the obtained measurement sample was left to stand for 500 hours under conditions of a temperature of 85°C and a humidity of 85% RH (relative humidity). Thereafter, the measurement sample was subjected to measurement of diffuse transmittance and total luminous transmittance using a haze meter "NM-150 (manufactured by Murakami Color Research Laboratory Co., Ltd.)" to calculate the haze value. The haze value (%) was calculated by dividing the diffuse transmittance by the total luminous transmittance and multiplying the result by 100. The glass plate used for the measurement sample was also used as a blank. The number of measurements (n) used to calculate the haze value was three, and the average value was used. The smaller the haze value, the higher the transparency. The results are shown in Table 1 or Table 2.

[0135] As shown in Table 1 or Table 2, Examples 1 to 9. Refer to Example 10 It was confirmed that the transparent adhesive sheet of Examples 1 to 3 has a low surface resistivity and antistatic properties. 9. Refer to Example 10 It was confirmed that the transparent adhesive sheet of this example did not lose its adhesive strength even after being left for 500 hours, and had an adhesive layer that could maintain its adhesive strength for a long period of time. Furthermore, Examples 1 to 9. Refer to Example 10 The transparent adhesive sheet had a total light transmittance of 91.0% or more and was highly transparent.

[0136] In contrast, Comparative Example 1, which contained polyurethane (a3-1) that did not contain a structure derived from polyoxyalkylene polyol, had a higher surface resistivity than Example 7, which contained the same amount of polyurethane (A) and antistatic agent (C). Similarly, in Comparative Example 2, which contained polyurethane (a3-1) that did not contain a structure derived from polyoxyalkylene polyol, the surface resistivity was higher than that of Example 3.

[0137] Furthermore, in Comparative Example 3, which contained an antistatic agent (C) that was not a fluorine-containing alkali metal imide salt, the surface resistivity was higher than in Example 1, which contained the same polyurethane (A), despite the content of the antistatic agent (C) being twice as high. Furthermore, in Comparative Examples 3 and 4, which contained an antistatic agent (C) that was not a fluorine-containing alkali metal imide salt, the surface resistivity was higher than that of Example 9, which contained the same polyurethane (A) and ethylenically unsaturated group-containing monomer (B) and also contained the same amounts thereof. In Comparative Example 4, which contained an antistatic agent (C) that was an ionic liquid rather than a fluorine-containing alkali metal imide salt, the adhesive strength decreased over time. This is presumably due to the bleed-out of the antistatic agent (C). [Industrial Applicability]

[0138] The present invention can provide a photocurable composition that can form a pressure-sensitive adhesive layer that contains an antistatic agent and can maintain adhesive strength over a long period of time using a simple method. According to the present invention, there are provided a transparent adhesive sheet having an adhesive layer that can be formed by a simple method, has antistatic properties, and is inhibited from losing adhesive strength over time, and a photocurable composition that is suitably used as a raw material for the adhesive layer of the transparent adhesive sheet. The transparent adhesive sheet of the present invention has excellent transparency and durability. The transparent adhesive sheet of the present invention can be preferably used for bonding optical components that are easily charged.

Claims

1. a (meth)acryloyloxy group-containing polyurethane (A); an ethylenically unsaturated group-containing monomer (B); an antistatic agent (C); A photopolymerization initiator (D) is contained, The (meth)acryloyloxy group-containing polyurethane (A) includes a polyurethane (a1) having a skeleton including a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate, and having (meth)acryloyloxy groups at a plurality of terminals; The ethylenically unsaturated group-containing monomer (B) includes a first monomer (B-0) which is a hydroxy group-containing (meth)acrylate, a second monomer (B-1) which does not contain a hydroxy group and has a homopolymer glass transition temperature (Tg) of 0 to 100°C, and a third monomer (B-2) which does not contain a hydroxy group and has a homopolymer glass transition temperature (Tg) of -100 to -20°C, 5 to 40% by mass of the second monomer (B-1), The third monomer (B-2) is contained in an amount of 10 to 60% by mass, the mass ratio of the second monomer (B-1) to the third monomer (B-2) ((B-1):(B-2)) is 20:80 to 50:50; the antistatic agent (C) is a fluorine-containing alkali metal imide salt, 10 to 60% by mass of the (meth)acryloyloxy group-containing polyurethane (A), 39 to 89% by mass of the ethylenically unsaturated group-containing monomer (B), 0.1 to 5% by mass of the antistatic agent (C), A photocurable composition comprising the photopolymerization initiator (D) in an amount of 0.01 to 5% by mass.

2. 2. The photocurable composition according to claim 1, wherein the antistatic agent (C) is at least one selected from the group consisting of a salt of an alkali metal cation and a bis(fluorosulfonyl)imide anion and a salt of an alkali metal cation and a bis(perfluoroalkylsulfonyl)imide anion.

3. 3. The photocurable composition according to claim 2, wherein the alkali metal cation of the antistatic agent (C) is a lithium cation.

4. the second monomer (B-1) is a cyclic alkyl (meth)acrylate, 2. The photocurable composition according to claim 1, wherein the third monomer (B-2) is an alkyl(meth)acrylate.

5. The photocurable composition according to any one of claims 1 to 4, comprising the first monomer (B-0) in an amount of 3 to 25% by mass.

6. A transparent adhesive sheet having an adhesive layer made of a cured product of the photocurable composition according to any one of claims 1 to 5.

7. 2. The photocurable composition according to claim 1, wherein 90 to 100% of all terminals contained in the (meth)acryloyloxy group-containing polyurethane (A) are (meth)acryloyloxy groups.

8. The photocurable composition according to claim 7 , wherein 100% of all the terminals contained in the (meth)acryloyloxy group-containing polyurethane (A) have a (meth)acryloyloxy group.

9. The bis(fluorosulfonyl)imide anion (SO ２ F) ２ N － is an anion represented by The bis(perfluoroalkylsulfonyl)imide anion is (C ｎ F ２ｎ＋１ SO ２ ) ２ N － (where n is an integer from 1 to 10) or (C ｐ F ２ｐ＋１ SO ２ ) N － (C ｑ F ２ｑ＋１ SO ２ 3. The photocurable composition according to claim 2, wherein p and q are integers of 1 to 10.

10. The photocurable composition according to claim 5, wherein the first monomer (B-0) is contained in an amount of 8 to 15% by mass.

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