Pressure-sensitive adhesive composition

Abstract

To provide a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer hardly causing peeling by sebum in a state of being stuck to an adherend.SOLUTION: A pressure-sensitive adhesive composition, which is an active energy ray-curable pressure-sensitive adhesive composition, wherein the pressure-sensitive adhesive composition has an adhesive force change rate represented by the following formula (1) of 80% or less and a water contact ratio change rate represented by the following formula (2) of less than - 1.5%: Adhesive force change rate [%] = (adhesive force after stabilization-adhesive force at the time of rising) / adhesive force after stabilization] * 100 (1) Water contact rate change rate [%] = (water contact angle before oil permeation-water contact angle after oil permeation) / water contact angle after oil permeation * 100 (2) SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive composition. [Background technology]

[0002] In recent years, image display devices such as liquid crystal displays (LCDs) and organic light-emitting diode (OLED) displays, as well as touch panels incorporating touch sensors into these image display devices, have become widely used in various fields. Such image display devices and touch panels have a configuration in which various optical components, such as a polarizing film, a retardation film, an optical compensation film, a touch sensor film, and a cover film, are laminated on an image display panel. Pressure-sensitive adhesive sheets having a pressure-sensitive adhesive layer are used to bond these optical components. For example, optical pressure-sensitive adhesive sheets are used to bond various optical components in image display devices (see, for example, Patent Documents 1 to 3).

[0003] Meanwhile, development of repeatedly foldable display panels for, for example, smartphones and tablet terminals is progressing. Specifically, foldable display panels can be repeatedly deformed between a bent shape and a flat, unbent shape. In such foldable display panels, each element in the laminated structure is made to be repeatedly foldable, and a thin optical adhesive sheet is used to bond such elements. Optical adhesive sheets for flexible devices such as foldable display panels are described, for example, in Patent Document 4 listed below. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-238915 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-342542 [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-231723 [Patent Document 4] Japanese Patent Application Publication No. 2018-111754 Summary of the Invention [Problem to be solved by the invention]

[0005] Since the touch panel is used in a state where it is touched by bare hands, sebum from the hands may transfer to the touch panel. The sebum transferred to the surface of the touch panel gradually transfers to the pressure-sensitive adhesive layer inside the touch panel, causing the pressure-sensitive adhesive layer to swell due to the sebum, which may result in peeling or lifting of adherends. In particular, pressure-sensitive adhesive layers used in optical components such as portable electronic devices, which are required to be thin, are becoming thinner, and thinner pressure-sensitive adhesive layers are more likely to swell due to sebum and to peel or lift.

[0006] The present invention is intended to solve these problems, and an object of the present invention is to provide a pressure-sensitive adhesive composition that can form a pressure-sensitive adhesive layer that is resistant to peeling due to sebum when attached to an adherend. [Means for solving the problem]

[0007] The present invention provides an active energy ray-curable pressure-sensitive adhesive composition, The pressure-sensitive adhesive composition has a rate of change in adhesive strength represented by the following formula (1) of 80% or less, and a rate of change in water contact ratio represented by the following formula (2) of less than −1.5%. Adhesive strength change rate [%] = (adhesive strength after stabilization - adhesive strength at start-up) / adhesive strength after stabilization × 100 (1) (A 25 mm wide adhesive layer formed from the adhesive composition is attached to glass and stored for 15 minutes under conditions of a pressure of 0.5 MPa and a temperature of 50°C, and then 25 μL of a mixture of oleic acid and squalene (volume ratio 1:1) is added to the interface between the adhesive layer and the glass and allowed to settle, after which the adhesive strength is measured under conditions of a peel angle of 180°, a peel speed of 50 mm / min, and a peel distance of 90 mm. The adhesive strength that finally stabilizes is defined as the post-stable adhesive strength, and the adhesive strength that temporarily stabilizes before rising to the post-stable adhesive strength is defined as the initial adhesive strength.) Change in water contact rate [%] = (water contact angle before oil penetration - water contact angle after oil penetration) / water contact angle after oil penetration × 100 (2) (Water contact angle before oil penetration: Water contact angle on the glass surface before the adhesive strength measurement) Water contact angle after oil penetration: Water contact angle on the glass surface after the adhesive strength measurement

[0008] The pressure-sensitive adhesive composition preferably has a shear storage modulus (G') at -20°C of 150 kPa or less.

[0009] The adhesive strength at the time of rising is preferably 2.0 N / 25 mm or more.

[0010] The water contact angle after the oil penetration is preferably 120° or more.

[0011] The pressure-sensitive adhesive composition is preferably used for bonding components of a foldable optical member together. [Effects of the Invention]

[0012] The pressure-sensitive adhesive composition of the present invention can form a pressure-sensitive adhesive layer that is resistant to peeling due to sebum when attached to an adherend. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic diagram (cross-sectional view) illustrating one embodiment of the pressure-sensitive adhesive sheet of the present invention. [Figure 2] 1 is a schematic diagram (cross-sectional view) showing one embodiment of an optical laminate of the present invention. [Figure 3] FIG. 2 is a schematic view (cross-sectional view) showing another embodiment of the optical laminate of the present invention. [Figure 4] FIG. 2 is a schematic view (cross-sectional view) showing still another embodiment of the optical laminate of the present invention. [Figure 5] FIG. 2 is an external view showing a method for measuring adhesive strength in the examples. [Figure 6] 1 is a graph showing the relationship between adhesive strength and peel distance of the adhesive layer obtained in Example 3. [Figure 7] 1 is a graph showing the relationship between adhesive strength and peel distance of the adhesive layer obtained in Comparative Example 1. [Figure 8] 1 is a graph showing the relationship between adhesive strength and peel distance of the adhesive layer obtained in Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0014] [Adhesive composition] The pressure-sensitive adhesive composition of the present invention is an active energy ray-curable pressure-sensitive adhesive composition, which has an adhesive strength change rate represented by the following formula (1) of 80% or less. Adhesive strength change rate [%] = (adhesive strength after stabilization - adhesive strength at start-up) / adhesive strength after stabilization × 100 (1)

[0015] In the above formula (1), the "adhesive strength at the time of rising" and the "adhesive strength after stabilization" can be obtained by the following adhesive strength measurement. Specifically, the adhesive strength measurement can be performed by the method described in the examples below. <Adhesive strength measurement> A 25 mm wide adhesive layer formed from the adhesive composition was attached to glass and stored for 15 minutes under conditions of a pressure of 0.5 MPa and a temperature of 50°C. 25 μL of a mixture of oleic acid and squalene (volume ratio 1:1) was then added to the interface between the adhesive layer and the glass, and allowed to settle. After this, the adhesive strength was measured under conditions of a peel angle of 180°, a peel speed of 50 mm / min, and a peel distance of 90 mm. The adhesive strength that finally stabilizes is defined as the "post-stabilization adhesive strength," and the adhesive strength that temporarily stabilizes before rising to the post-stabilization adhesive strength is defined as the "initial adhesive strength."

[0016] The post-stabilization adhesive strength is a value measured as a general adhesive strength (peel strength) under the conditions described in the adhesive strength measurement. The initial adhesive strength is the adhesive strength when it temporarily stabilizes before rising to the post-stabilization adhesive strength, for example, the adhesive strength that remains stable for a peel distance of 5 mm or more (preferably 10 mm or more). For example, Figures 6 to 8 are graphs showing the relationship between peel distance and adhesive strength measured in the examples and comparative examples described below. In Figures 6 to 8, F0 represents the initial adhesive strength, and F1 represents the post-stabilization adhesive strength.

[0017] The adhesive strength change rate is 80% or less, preferably 75% or less, more preferably 70% or less, and may be 65% or less, 60% or less, or 55% or less. An adhesive strength change rate of 80% or less indicates that the initial adhesive strength is closer to the adhesive strength after stabilization, and the adhesive layer is less likely to peel when sebum penetrates the interface between the adhesive layer and the adherend and attempts to peel it off. The adhesive strength change rate is, for example, 1% or more, and may be 5% or more or 10% or more.

[0018] The initial adhesive strength is preferably 2.0 N / 25 mm or more, more preferably 2.5 N / 25 mm or more, and even more preferably 4.5 N / 25 mm or more. When the initial adhesive strength is 2.0 N / 25 mm or more, the adhesive layer is less likely to peel when sebum penetrates the interface between the adhesive layer and the adherend and attempts to peel it off. The initial adhesive strength may be lower than the post-stabilization adhesive strength, for example, 50 N / 25 mm or less.

[0019] The adhesive strength after stabilization is higher than the initial adhesive strength, and is preferably 7.6 N / 25 mm or more, more preferably 8.0 N / 25 mm or more, and even more preferably 8.5 N / 25 mm or more. When the adhesive strength after stabilization is 7.6 N / 25 mm or more, the adhesive layer is less likely to peel when sebum penetrates the interface between the adhesive layer and the adherend and attempts to peel it off. The adhesive strength after stabilization is, for example, 100 N / 25 mm or less.

[0020] The rate of change in adhesive strength, adhesive strength at start-up, and adhesive strength after stabilization can be adjusted, for example, by adjusting the type of base polymer constituting the adhesive composition, the monomer composition and content, etc.

[0021] The pressure-sensitive adhesive composition has a rate of change in water contact rate, represented by the following formula (2), of less than −1.5%. Change in water contact rate [%] = (water contact angle before oil penetration - water contact angle after oil penetration) / water contact angle after oil penetration × 100 (2)

[0022] In the above formula (2), the "water contact angle before oil penetration" is the water contact angle of the glass surface before the above adhesive strength measurement, and is the water contact angle of the glass surface before lamination in the area where the pressure-sensitive adhesive layer is to be laminated. The "water contact angle after oil penetration" is the water contact angle of the glass surface after the above adhesive strength measurement, and is the water contact angle of the glass surface in the area where the pressure-sensitive adhesive layer was laminated after the pressure-sensitive adhesive layer was peeled off after the above adhesive strength measurement. The water contact angles before and after oil penetration can be specifically measured by the method described in the Examples below.

[0023] The mixture of oleic acid and squalene is an oil component that mimics human sebum. The change in water contact angle is less than -1.5%, preferably -2.0% or less, more preferably -2.5% or less, and may be -3.0% or less, -3.5% or less, or -4.0% or less. A low change in water contact angle indicates that the water contact angle on the glass surface after the adhesive layer is applied, oil is added to the interface between the adhesive layer and the glass, and the adhesive layer is then peeled off is larger than the water contact angle on the glass surface before the adhesive layer is applied. A water contact angle of less than -1.5% is presumed to indicate that a moderate amount of oil remains on the glass surface after the adhesive layer is peeled off. This means that the adhesive layer is less likely to absorb oil and therefore less likely to swell, and the adhesive layer is less likely to peel off when sebum penetrates the interface between the adhesive layer and the adherend. The change in water contact angle may be, for example, -20% or more, -15% or more, or -10% or more.

[0024] The water contact angle before oil penetration is preferably smaller than the water contact angle after oil penetration. The water contact angle before oil penetration is preferably 130° or less, more preferably 125° or less. The water contact angle before oil penetration is, for example, 100° or more, and may be 110° or more.

[0025] The water contact angle after oil penetration is preferably 120° or more, more preferably 122° or more. If the water contact angle after oil penetration is 120° or more, the pressure-sensitive adhesive layer is less likely to peel when sebum penetrates the interface between the pressure-sensitive adhesive layer and the adherend. The water contact angle after oil penetration may be, for example, 170° or less, 160° or less, or 150° or less.

[0026] The rate of change in the water contact angle, the water contact angle before the oil penetration, and the water contact angle after the oil penetration can be adjusted, for example, by adjusting the type of base polymer constituting the PSA composition, the monomer composition and content, etc.

[0027] The pressure-sensitive adhesive composition preferably has a shear storage modulus (G') at -20°C of 150 kPa or less, more preferably 140 kPa or less, and even more preferably 130 kPa or less. When the shear storage modulus is 150 kPa or less, the pressure-sensitive adhesive sheet has high flexibility and excellent bending resistance at low temperatures. Furthermore, from the viewpoint of ensuring the cohesive strength of the pressure-sensitive adhesive sheet at low temperatures, the shear storage modulus (G') at -20°C is preferably 50 kPa or more, more preferably 60 kPa or more, and even more preferably 70 kPa or more.

[0028] The shear storage modulus (G') at -20°C can be obtained by measuring the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition. The shear storage modulus (G') at -20°C can be adjusted by adjusting the type of base polymer constituting the pressure-sensitive adhesive composition, the monomer composition, the molecular weight of the base polymer, the type and content of additives such as crosslinking agents, etc.

[0029] Examples of the pressure-sensitive adhesive composition of the present invention include a mixture of polymerizable components that form a polymer when a pressure-sensitive adhesive layer is formed (sometimes referred to as a "monomer mixture") or a composition containing a partially polymerized product thereof as an essential component.

[0030] The mixture of polymerizable components may be composed of a single polymerizable component or two or more polymerizable components. The "partially polymerized product" may also be referred to as a "prepolymer" or "syrup," and refers to a composition in which one or more polymerizable components in the monomer mixture are partially polymerized.

[0031] In this specification, the term "polymerizable component" in the pressure-sensitive adhesive composition is used to include polymerizable components constituting a partial polymer. Furthermore, in this specification, the term "polymerizable component" refers to a compound having only one polymerizable functional group, and does not include compounds having two or more polymerizable functional groups, such as polyfunctional (meth)acrylates.

[0032] The base polymer contained in the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention is not particularly limited, and examples thereof include an acrylic polymer contained as a base polymer in an acrylic pressure-sensitive adhesive layer, a rubber polymer contained as a base polymer in a rubber pressure-sensitive adhesive layer (such as a natural rubber pressure-sensitive adhesive layer or a synthetic rubber pressure-sensitive adhesive layer), a silicone polymer contained as a base polymer in a silicone pressure-sensitive adhesive layer, a polyester polymer contained as a base polymer in a polyester pressure-sensitive adhesive layer, a urethane polymer contained as a base polymer in a urethane pressure-sensitive adhesive layer, a polyamide polymer contained as a base polymer in a polyamide pressure-sensitive adhesive layer, an epoxy polymer contained as a base polymer in an epoxy pressure-sensitive adhesive layer, a vinyl alkyl ether polymer contained as a base polymer in a vinyl alkyl ether pressure-sensitive adhesive layer, and a fluorine-based polymer contained as a base polymer in a fluorine-based pressure-sensitive adhesive layer. Among these, acrylic polymers are preferred as the base polymer because of their transparency, weather resistance, adhesive reliability, and the wide variety of monomers available, which makes it easy to design the function of the pressure-sensitive adhesive layer. That is, the pressure-sensitive adhesive composition of the present invention is preferably an acrylic pressure-sensitive adhesive composition in which the pressure-sensitive adhesive layer to be formed contains an acrylic polymer as a base polymer. The base polymer may be one type or two or more types.

[0033] The content of the base polymer in the pressure-sensitive adhesive layer is not particularly limited, but is preferably 75% by mass or more (e.g., 75 to 99.9% by mass) relative to the total amount (100% by mass) of the pressure-sensitive adhesive layer, and more preferably 85% by mass or more (e.g., 85 to 99.9% by mass).

[0034] The acrylic pressure-sensitive adhesive composition is not particularly limited, but examples thereof include a mixture of polymerizable components constituting an acrylic polymer (monomer mixture) or a composition containing a partially polymerized product thereof as an essential component.

[0035] The acrylic pressure-sensitive adhesive composition contains an acrylic monomer as the polymerizable component. In other words, the acrylic pressure-sensitive adhesive composition contains an acrylic monomer, or contains a partial polymer of a monomer mixture containing an acrylic monomer. In this specification, "(meth)acrylic" refers to either or both of "acrylic" and "methacrylic", and the same applies to other terms. The weight-average molecular weight of the acrylic polymer is not particularly limited, but is preferably 100,000 to 5,000,000.

[0036] The acrylic monomer preferably contains a (meth)acrylic acid alkyl ester. The (meth)acrylic acid alkyl ester is preferably a (meth)acrylic acid alkyl ester having an alkyl group with 1 to 20 carbon atoms. The (meth)acrylic acid alkyl ester may have a linear or branched alkyl group, or may have a cyclic alkyl group such as an alicyclic alkyl group. The (meth)acrylic acid alkyl ester may be used alone or in combination of two or more.

[0037] Examples of (meth)acrylic acid alkyl esters having a linear or branched alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, and ) isononyl acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate (i.e., lauryl (meth)acrylate), isotridecyl (meth)acrylate, tetradecyl (meth)acrylate, isotetradecyl (meth)acrylate, pentadecyl (meth)acrylate, cetyl (meth)acrylate, heptadecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, and nonadecyl (meth)acrylate.

[0038] Examples of (meth)acrylic acid alkyl esters having an alicyclic alkyl group include (meth)acrylic acid cycloalkyl esters, (meth)acrylic acid alkyl esters having a bicyclic aliphatic hydrocarbon ring, and (meth)acrylic acid alkyl esters having a tricyclic or higher aliphatic hydrocarbon ring. Examples of (meth)acrylic acid cycloalkyl esters include cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, and cyclooctyl (meth)acrylate. Examples of (meth)acrylic acid alkyl esters having a bicyclic aliphatic hydrocarbon ring include isobornyl (meth)acrylate. Examples of (meth)acrylic acid alkyl esters having three or more aliphatic hydrocarbon rings include dicyclopentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, tricyclopentanyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate.

[0039] The (meth)acrylic acid alkyl ester is preferably an acrylic acid alkyl ester having an alkyl group of 3 to 15 carbon atoms, more preferably an acrylic acid alkyl ester having an alkyl group of 4 to 10 carbon atoms, and even more preferably at least one selected from the group consisting of n-butyl acrylate (BA), 2-ethylhexyl acrylate (2EHA), and n-octyl acrylate (NOAA). From the viewpoints of achieving good conformability to the adherend when the pressure-sensitive adhesive layer is attached to the adherend and excellent adhesion at the time of setting up, and of preventing the pressure-sensitive adhesive layer from swelling in the presence of sebum and peeling due to sebum, it is preferable for the pressure-sensitive adhesive layer to contain an acrylic acid alkyl ester having an alkyl group of 6 to 10 carbon atoms, and more preferably to additionally contain an acrylic acid alkyl ester having an alkyl group of 4 or less carbon atoms. It is particularly preferable to use BA and NOAA in combination, or BA and 2EHA in combination.

[0040] From the viewpoint of appropriately exhibiting basic properties such as adhesiveness in the PSA sheet, the proportion of the (meth)acrylic acid alkyl ester is preferably 55% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more, relative to the total amount (100% by mass) of polymerizable components constituting the base polymer. This proportion is, for example, 99% by mass or less or 96% by mass or less. Furthermore, the proportion of the acrylic acid alkyl ester having an alkyl group with 3 to 15 carbon atoms, the proportion of the acrylic acid alkyl ester having an alkyl group with 4 to 10 carbon atoms, the proportion of the acrylic acid alkyl ester having an alkyl group with 6 to 10 carbon atoms, the proportion of at least one selected from the group consisting of BA, 2EHA, and NOAA, the total proportion of BA and NOAA, or the total proportion of BA and 2EHA is preferably within the above range.

[0041] The polymerizable component may contain a copolymerizable monomer copolymerizable with the (meth)acrylic acid alkyl ester. Examples of the copolymerizable monomer include a monomer having a polar group. Examples of the polar group-containing monomer include a hydroxy group-containing monomer, a carboxy group-containing monomer, and a monomer having a nitrogen atom-containing ring. The polar group-containing monomer is useful for modifying the acrylic polymer, such as by introducing crosslinking points into the acrylic polymer and ensuring the cohesive strength of the acrylic polymer. The copolymerizable monomer may be used alone or in combination of two or more.

[0042] Examples of hydroxy group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, and 12-hydroxylauryl (meth)acrylate. The hydroxy group-containing monomer is preferably at least one selected from the group consisting of 2-hydroxyethyl acrylate (HEA) and 4-hydroxybutyl acrylate (4HBA).

[0043] The proportion of the hydroxy group-containing monomer is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, relative to the total amount (100% by mass) of polymerizable components constituting the base polymer, from the viewpoints of introducing a crosslinked structure into the acrylic polymer and ensuring cohesive strength in the pressure-sensitive adhesive layer of the present invention. From the viewpoint of adjusting the polarity of the acrylic polymer (which is related to the compatibility between the acrylic polymer and various additive components in the pressure-sensitive adhesive layer of the present invention), the proportion is preferably 15% by mass or less, more preferably 12% by mass or less, and even more preferably 10% by mass or less.

[0044] Examples of carboxy group-containing monomers include acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid.

[0045] The proportion of the carboxyl group-containing monomer is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, relative to the total amount (100% by mass) of polymerizable components constituting the base polymer, from the viewpoints of introducing a crosslinked structure into the acrylic polymer, ensuring cohesive strength in the pressure-sensitive adhesive layer, and ensuring adhesive strength to the adherend in the pressure-sensitive adhesive layer of the present invention. From the viewpoints of adjusting the glass transition temperature of the acrylic polymer and avoiding the risk of corrosion of the adherend by acid, the proportion is preferably 3% by mass or less, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less.

[0046] Examples of monomers having a nitrogen atom-containing ring include N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-(meth)acryloyl-2-pyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine, N-vinylmorpholine, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholinedione, N-vinylpyrazole, N-vinylisoxazole, N-vinylthiazole, and N-vinylisothiazole.

[0047] The proportion of the monomer having a nitrogen atom-containing ring relative to the total amount (100% by mass) of polymerizable components constituting the base polymer is, for example, 0.5% by mass or more, or may be 1% by mass or more, or 1.5% by mass or more. From the viewpoint of more easily achieving a low shear storage modulus at −20° C., the proportion is preferably 10% by mass or less, more preferably 7% by mass or less, even more preferably 5% by mass or less, even more preferably 1% by mass or less, and particularly preferably 0.5% by mass or less, and may be substantially free of the monomer. In the pressure-sensitive adhesive composition, the phrase “substantially free of” a monomer having a nitrogen atom-containing ring means that the monomer having a nitrogen atom-containing ring is not actively blended in, except in cases where the monomer having a nitrogen atom-containing ring is inevitably mixed in.

[0048] The polymerizable component may contain other copolymerizable monomers. Examples of the other copolymerizable monomers include acid anhydride monomers, sulfonic acid group-containing monomers, phosphoric acid group-containing monomers, epoxy group-containing monomers, cyano group-containing monomers, alkoxy group-containing monomers, and aromatic vinyl compounds. One or more of the other copolymerizable monomers may be used.

[0049] The pressure-sensitive adhesive composition may contain a polymerization initiator such as a photopolymerization initiator. The base polymer may be formed, for example, by photopolymerizing the polymerizable component. The photopolymerization initiator may be used alone or in combination of two or more types.

[0050] Examples of the photopolymerization initiator include a radical photopolymerization initiator, a cationic photopolymerization initiator, and an anionic photopolymerization initiator.

[0051] Examples of the radical photopolymerization initiator include an acylphosphine oxide photopolymerization initiator, a benzoin ether photopolymerization initiator, an acetophenone photopolymerization initiator, an α-ketol photopolymerization initiator, an aromatic sulfonyl chloride photopolymerization initiator, a photoactive oxime photopolymerization initiator, a benzoin photopolymerization initiator, a benzyl photopolymerization initiator, a benzophenone photopolymerization initiator, a ketal photopolymerization initiator, and a thioxanthone photopolymerization initiator.

[0052] Examples of acylphosphine oxide photopolymerization initiators include bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-2,4-di-n-butoxyphenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, and bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide. Examples of benzoin ether photopolymerization initiators include benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, benzoin isobutyl ether, and 2,2-dimethoxy-1,2-diphenylethan-1-one. Examples of acetophenone photopolymerization initiators include 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexylphenyl ketone, 4-phenoxydichloroacetophenone, and 4-(t-butyl)dichloroacetophenone. Examples of α-ketol photopolymerization initiators include 2-methyl-2-hydroxypropiophenone and 1-[4-(2-hydroxyethyl)phenyl]-2-methylpropan-1-one. Examples of aromatic sulfonyl chloride photopolymerization initiators include 2-naphthalenesulfonyl chloride. Examples of photoactive oxime photopolymerization initiators include 1-phenyl-1,1-propanedione-2-(o-ethoxycarbonyl)-oxime. Examples of benzoin photopolymerization initiators include benzoin. Examples of benzyl photopolymerization initiators include benzyl. Examples of benzophenone photopolymerization initiators include benzophenone, benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, and polyvinylbenzophenone. Examples of ketal photopolymerization initiators include benzyl dimethyl ketal. Examples of thioxanthone photopolymerization initiators include thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-diisopropylthioxanthone, and dodecylthioxanthone.

[0053] The photopolymerization initiator is preferably at least one selected from the group consisting of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, 2,2-dimethoxy-1,2-diphenylethan-1-one, and 1-hydroxycyclohexyl phenyl ketone.

[0054] The amount of the photopolymerization initiator used (the total amount of the photopolymerization initiators when multiple photopolymerization initiators are used) is, for example, 0.01 part by mass or more, preferably 0.03 part by mass or more, more preferably 0.05 part by mass or more, relative to 100 parts by mass of the total amount of the polymerizable components, and is, for example, 1 part by mass or less, preferably 0.5 part by mass or less, more preferably 0.3 part by mass or less, and even more preferably 0.2 part by mass or less.

[0055] The pressure-sensitive adhesive composition may contain a crosslinking agent. Use of the crosslinking agent results in the base polymer having a crosslinked structure. Examples of methods for introducing a crosslinked structure into the base polymer include the following first and second methods. In the first method, a base polymer having a functional group reactive with the crosslinking agent and the crosslinking agent are blended into the pressure-sensitive adhesive composition, and the base polymer and the crosslinking agent are reacted in the pressure-sensitive adhesive layer. In the second method, a polyfunctional compound (crosslinking agent) such as a polyfunctional monomer is added together with a polymerizable component, and a base polymer having a branched structure (crosslinked structure) introduced into the polymer chain is formed by polymerization of the polymerizable component. These methods may be used in combination.

[0056] Examples of the crosslinking agent used in the first method include compounds that react with the polar groups (such as hydroxyl and carboxyl groups) in the polar group-containing monomers. Examples of such crosslinking agents include isocyanate crosslinking agents, peroxide crosslinking agents, epoxy crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, carbodiimide crosslinking agents, and metal chelate crosslinking agents. Only one type of crosslinking agent may be used, or two or more types may be used.

[0057] In the first method, the amount of crosslinking agent to be blended is preferably 0.01 parts by mass or more, more preferably 0.02 parts by mass or more, and even more preferably 0.05 parts by mass or more, per 100 parts by mass of the total amount of polymerizable components (or the total amount of base polymers), from the viewpoint of ensuring the cohesive strength of the adhesive layer, and is also preferably 3 parts by mass or less, more preferably 1 part by mass or less, and even more preferably 0.5 parts by mass or less.

[0058] In the second method, the monofunctional monomer and the polyfunctional compound, such as the polyfunctional monomer for introducing a crosslinked structure, may be polymerized in one step or in multiple steps. In the multi-step polymerization method, the monofunctional monomer is first polymerized (preliminary polymerization), thereby preparing a prepolymer composition containing a partial polymer (a mixture of a low-polymerization polymer and unreacted monomer). Next, a polyfunctional compound is added as a crosslinking agent to the prepolymer composition, and then the partial polymer and the polyfunctional compound are polymerized (main polymerization).

[0059] Examples of polyfunctional compounds include polyfunctional monomers and polyfunctional oligomers containing two or more ethylenically unsaturated double bonds in one molecule. Examples of polyfunctional monomers include polyfunctional (meth)acrylates.

[0060] Examples of the polyfunctional (meth)acrylate include difunctional (meth)acrylate, trifunctional (meth)acrylate, and tetrafunctional or higher polyfunctional (meth)acrylate.

[0061] Examples of difunctional (meth)acrylates include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, glycerin di(meth)acrylate, ethoxylated bisphenol A diacrylate (BPAEODE), and neopentyl glycol di(meth)acrylate.

[0062] Examples of trifunctional (meth)acrylates include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and tris(acryloyloxyethyl)isocyanurate.

[0063] Examples of tetrafunctional or higher polyfunctional (meth)acrylates include ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol monohydroxypenta(meth)acrylate, alkyl-modified dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate.

[0064] Examples of polyfunctional oligomers include urethane (meth)acrylate oligomers, polyester (meth)acrylate oligomers, polyether (meth)acrylate oligomers, polyol (meth)acrylate oligomers, epoxy (meth)acrylate oligomers, polyethylene glycol di(meth)acrylate, and polypropylene glycol di(meth)acrylate.

[0065] In the second method, one or more polyfunctional compounds may be used as the crosslinking agent. The polyfunctional compound is preferably at least one selected from the group consisting of 1,6-hexanediol diacrylate (HDDA) and dipentaerythritol hexaacrylate (DPHA).

[0066] When a polyfunctional monomer is used as the polyfunctional compound, the amount of the polyfunctional monomer is, from the viewpoint of ensuring the cohesive strength of the pressure-sensitive adhesive layer, preferably 0.01 parts by mass or more, more preferably 0.03 parts by mass or more, and even more preferably 0.05 parts by mass or more, per 100 parts by mass of the total amount of the monofunctional monomers. From the viewpoint of ensuring the flexible deformation property of the pressure-sensitive adhesive layer, the amount of the polyfunctional monomer is, from the viewpoint of ensuring the flexible deformation property of the pressure-sensitive adhesive layer, preferably 3 parts by mass or less, more preferably 2 parts by mass or less, and even more preferably 1 part by mass or less, per 100 parts by mass of the total amount of the monofunctional monomers.

[0067] When a polyfunctional oligomer is used as the polyfunctional compound, the blending amount of the polyfunctional oligomer in the polymerizable component is preferably 0.2 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 0.7 parts by mass or more per 100 parts by mass of the total amount of the monofunctional monomers, from the viewpoint of ensuring the cohesive strength of the pressure-sensitive adhesive layer. The blending amount of the polyfunctional oligomer is preferably 8 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less per 100 parts by mass of the total amount of the monofunctional monomers, from the viewpoint of ensuring the flexible deformation property of the pressure-sensitive adhesive layer.

[0068] In the polymerization, a chain transfer agent may be used for the purpose of molecular weight adjustment, etc. That is, the PSA composition may contain a chain transfer agent. Examples of the chain transfer agent include α-thioglycerol, lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolate, 2,3-dimercapto-1-propanol, and α-methylstyrene dimer. One or more types of chain transfer agents may be used.

[0069] The pressure-sensitive adhesive composition may contain a silane coupling agent. The content of the silane coupling agent is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, per 100 parts by mass of the total amount of polymerizable components (or the total amount of base polymers). The content is preferably 5 parts by mass or less, more preferably 3 parts by mass or less.

[0070] The pressure-sensitive adhesive composition may contain other components in addition to the above-mentioned components, as long as the effects of the present invention are not impaired. Examples of such other components include curing agents, curing catalysts, crosslinking accelerators, tackifying resins (rosin derivatives, polyterpene resins, petroleum resins, oil-soluble phenols, etc.), antioxidants, fillers (metal powders, organic fillers, inorganic fillers, etc.), colorants (pigments, dyes, etc.), antioxidants, plasticizers, softeners, surfactants, antistatic agents, surface lubricants, leveling agents, light stabilizers, UV absorbers, polymerization inhibitors, rust inhibitors, granular materials, foil-like materials, flame retardants, and ion trapping agents. Only one of the above other components may be used, or two or more may be used.

[0071] The pressure-sensitive adhesive composition is preferably a solvent-free type. That is, the pressure-sensitive adhesive composition preferably does not contain or substantially does not contain an organic solvent. A solvent-free pressure-sensitive adhesive composition does not require a step of volatilizing and removing the solvent from a coating film of the composition in the process of producing a pressure-sensitive adhesive layer from the composition. Therefore, a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention is suitable for reducing the environmental load.

[0072] The organic solvent is not particularly limited as long as it is an organic compound that can be used as a solvent, and examples thereof include hydrocarbon solvents such as cyclohexane, hexane, heptane, etc.; aromatic solvents such as toluene and xylene; ester solvents such as ethyl acetate and methyl acetate; ketone solvents such as acetone and methyl ethyl ketone; and alcohol solvents such as methanol, ethanol, butanol, isopropyl alcohol, etc. The organic solvent may be a mixed solvent containing two or more organic solvents.

[0073] In the PSA composition, "substantially free of" organic solvent means that the organic solvent is not actively blended in, except in cases where the organic solvent is inevitably mixed in. Specifically, a PSA composition having an organic solvent content of 1.0% by mass or less (preferably 0.5% by mass or less, and more preferably 0.2% by mass or less) relative to the total amount of the PSA composition (total mass, 100% by mass) can be said to be substantially free of organic solvent.

[0074] The pressure-sensitive adhesive composition can be prepared by a known or conventional method, for example, by mixing an additive, if necessary, with a mixture of polymerizable components or a partially polymerized product thereof.

[0075] The pressure-sensitive adhesive composition of the present invention can form a pressure-sensitive adhesive layer that is resistant to peeling due to sebum when attached to an adherend. In particular, in recent years, optical components have become thinner, and accordingly, pressure-sensitive adhesive layers used in optical components are also required to be thinner. The pressure-sensitive adhesive composition of the present invention can form a pressure-sensitive adhesive layer that is resistant to peeling due to sebum when attached to an adherend, even if the pressure-sensitive adhesive layer is thin.

[0076] [Adhesive layer] A pressure-sensitive adhesive layer can be formed using the pressure-sensitive adhesive composition of the present invention. A pressure-sensitive adhesive layer formed using the pressure-sensitive adhesive composition of the present invention may be referred to as the "pressure-sensitive adhesive layer of the present invention." The pressure-sensitive adhesive layer can be produced, for example, by applying the pressure-sensitive adhesive composition to a release-treated surface of a release liner or a substrate to form a pressure-sensitive adhesive composition layer, and then solidifying the pressure-sensitive adhesive composition layer by polymerization via active energy ray irradiation. If necessary, heating, drying, etc. may be performed in addition to the active energy ray irradiation. Polymerization via active energy ray irradiation can smooth the surface of the pressure-sensitive adhesive layer and reduce the permeability of sebum-derived components into the pressure-sensitive adhesive layer.

[0077] Examples of the active energy rays include ionizing radiation such as α rays, β rays, γ rays, neutron rays, and electron beams, as well as ultraviolet rays, and ultraviolet rays are particularly preferred. That is, the active energy ray-curable pressure-sensitive adhesive composition is preferably an ultraviolet-curable pressure-sensitive adhesive composition.

[0078] The PSA composition may be applied (coated) using a known coating method, such as a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, bar coater, knife coater, spray coater, comma coater, or direct coater.

[0079] After forming a pressure-sensitive adhesive layer by curing a monomer mixture or a partially polymerized product thereof with active energy radiation, a solution containing an additive may be applied to the pressure-sensitive adhesive layer, and the additive may be allowed to penetrate the pressure-sensitive adhesive layer in the thickness direction from one side. The additive can impart the desired properties to the pressure-sensitive adhesive layer. Furthermore, the transparency of the pressure-sensitive adhesive layer is maintained by the additive penetrating the pressure-sensitive adhesive layer in solution form. The pressure-sensitive adhesive layer is then dried by heating or the like. This process restores the pressure-sensitive adhesive layer to a state close to that before coating. In other words, since the pressure-sensitive adhesive layer has been cured once, its physical properties, such as adhesive strength and elastic modulus, are restored to a state close to that before coating the solution. Because the pressure-sensitive adhesive layer is cured before the additive is added, once the composition, curing conditions, physical properties, etc. of the pressure-sensitive adhesive composition are determined, there is no need to redesign the composition by incorporating the additive, and the thickness of the pressure-sensitive adhesive layer can be easily changed. The desired properties imparted to the pressure-sensitive adhesive layer can then be controlled by changing the coating conditions of the additive solution. In this way, it is possible to separate the control of the physical properties of the adhesive layer from the control of the required characteristics using additives, so there is no need to design the adhesive layer from scratch when changing the thickness of the adhesive layer or the amount of additive added, which is more efficient.

[0080] The additives can be used without any particular limitation, and those added in the field of pressure-sensitive adhesives can be used.For example, polymerization initiators, crosslinking agents, ultraviolet absorbers, rust inhibitors, antistatic agents, crosslinking accelerators, silane coupling agents, tackifying resins, antioxidants, colorants such as dyes, antioxidants, chain transfer agents, plasticizers, softeners, surfactants, etc.From the viewpoint of easily achieving the desired effects of the present invention, polymerization initiators, crosslinking agents, ultraviolet absorbers, rust inhibitors, and antistatic agents are preferred.

[0081] [Adhesive sheet] A pressure-sensitive adhesive sheet can be obtained using the pressure-sensitive adhesive layer of the present invention. A pressure-sensitive adhesive sheet comprising the pressure-sensitive adhesive layer of the present invention may be referred to as the "pressure-sensitive adhesive sheet of the present invention." The pressure-sensitive adhesive sheet may be a double-sided pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer surface on both sides, or a single-sided pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer surface on only one side. Among these, a double-sided pressure-sensitive adhesive sheet is preferred from the viewpoint of bonding two members together. In this specification, the term "pressure-sensitive adhesive sheet" also includes a tape-like material, i.e., an "adhesive tape." In this specification, the surface of the pressure-sensitive adhesive layer may be referred to as the "adhesive surface."

[0082] The PSA sheet may be a so-called "substrate-less" PSA sheet that does not have a substrate (substrate layer) (hereinafter, this may be referred to as a "substrate-less PSA sheet"), or may be a PSA sheet that has a substrate (hereinafter, this may be referred to as a "substrate-attached PSA sheet"). Examples of the substrate-less PSA sheet include a double-sided PSA sheet consisting only of the PSA layer of the present invention, and a double-sided PSA sheet consisting of the PSA layer of the present invention and a PSA layer other than the PSA layer of the present invention (hereinafter, this may be referred to as an "other PSA layer"). On the other hand, examples of substrate-attached PSA sheets include PSA sheets having the PSA layer of the present invention on at least one side of a substrate. Among these, substrate-less PSA sheets (substrate-less double-sided PSA sheets) are preferred, and substrate-less double-sided PSA sheets consisting only of the PSA layer of the present invention are more preferred. PSA sheets having PSA layers on both sides of a substrate (substrate-attached double-sided PSA sheets) are also preferred. The PSA layers on both sides of the substrate-attached double-sided PSA sheet may both be the PSA layer of the present invention, or one may be the PSA layer of the present invention and the other may be another PSA layer. The above "substrate (substrate layer)" does not include a release liner that is peeled off when the pressure-sensitive adhesive sheet is used (applied).

[0083] When the pressure-sensitive adhesive sheet is a pressure-sensitive adhesive sheet with a substrate, radiation loss of millimeter waves may occur due to the substrate, so it is preferable that the pressure-sensitive adhesive sheet is a substrate-less pressure-sensitive adhesive sheet. However, when the substrate is made of a material with a low dielectric constant and low dielectric loss, the pressure-sensitive adhesive sheet may be a substrate-attached pressure-sensitive adhesive sheet.

[0084] The substrate is an element that functions as a support for the pressure-sensitive adhesive layer in the pressure-sensitive adhesive sheet. Examples of the substrate include plastic substrates (particularly plastic films). The substrate may be a single layer or a laminate of the same or different types of substrates.

[0085] The substrate is not particularly limited, and examples thereof include various optical films such as plastic films, antireflection (AR) films, antiglare (AG) films, polarizing plates, and retardation plates. Examples of materials for the plastic films include polyester resins such as polyethylene terephthalate (PET), acrylic resins such as polymethyl methacrylate (PMMA), polycarbonate, triacetyl cellulose (TAC), polysulfone, polyarylate, polyimide, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, ethylene-propylene copolymers, cyclic olefin polymers such as "ARTON" (cyclic olefin polymer, manufactured by JSR Corporation) and "ZEONOR" (cyclic olefin polymer, manufactured by Zeon Corporation), and fluorine-based polymers. These plastic materials may be used alone or in combination.

[0086] The surface of the substrate on which the pressure-sensitive adhesive layer is provided may be subjected to surface treatments such as physical treatments such as corona discharge treatment, plasma treatment, sand matting treatment, ozone exposure treatment, flame exposure treatment, high-voltage shock exposure treatment, and ionizing radiation treatment; chemical treatments such as chromic acid treatment; and adhesion-enhancing treatments using a coating agent (primer), for the purpose of improving adhesion and retention with the pressure-sensitive adhesive layer. The surface treatment for improving adhesion is preferably applied to the entire surface of the substrate on which the pressure-sensitive adhesive layer is provided.

[0087] The substrate may be a noise-reducing film. The noise-reducing film is not particularly limited as long as it has noise-reducing properties, but examples include a film substrate having a noise-reducing layer formed on at least one side thereof. The noise-reducing layer may be a single layer or multiple layers, and is not particularly limited as long as it has the function of reducing electromagnetic noise, but a transparent conductive layer is preferred from the viewpoint of transparency. The transparent conductive layer may be a thin film layer formed from a conductive organic or inorganic material, or a conductive layer formed by partial contact of conductive organic or inorganic materials.

[0088] The pressure-sensitive adhesive sheet may have a release liner on its adhesive surface until use. The release liner protects the adhesive surface that contacts the pressure-sensitive adhesive layer until use, and is peeled off when the pressure-sensitive adhesive layer is used. When the pressure-sensitive adhesive sheet is a double-sided pressure-sensitive adhesive sheet, each adhesive surface may be protected by two release liners, or may be protected by a single release liner with release surfaces on both sides and wound into a roll. The release liner is used as a protective material for the pressure-sensitive adhesive layer, and is peeled off when the pressure-sensitive adhesive sheet is attached to the adherend. When the pressure-sensitive adhesive sheet is a substrate-less pressure-sensitive adhesive sheet, the release liner also serves as a support for the pressure-sensitive adhesive layer. The release liner is not necessarily provided.

[0089] Examples of the substrate for the release liner include polyethylene films, polypropylene films, polybutene films, polybutadiene films, polymethylpentene films, polyvinyl chloride films, vinyl chloride copolymer films, polyethylene terephthalate films, polyethylene naphthalate films, polybutylene terephthalate films, polyurethane films, ethylene vinyl acetate films, ionomer resin films, ethylene-(meth)acrylic acid copolymer films, ethylene-(meth)acrylic acid ester copolymer films, polystyrene films, polycarbonate films, polyimide films, and fluororesin films. Crosslinked films of these films are also included. Furthermore, laminated films of these films may also be used.

[0090] The release surface of the release liner (particularly the surface that comes into contact with the pressure-sensitive adhesive layer) is preferably subjected to a release treatment. Examples of release agents used for the release treatment include alkyd-based, silicone-based, fluorine-based, unsaturated polyester-based, polyolefin-based, and wax-based release agents.

[0091] The thickness of the release liner is not particularly limited, but is, for example, about 20 to 150 μm.

[0092] Figure 1 is a cross-sectional schematic diagram showing one embodiment of a pressure-sensitive adhesive sheet of the present invention. Pressure-sensitive adhesive sheet 10 shown in Figure 1 is a substrate-less double-sided pressure-sensitive adhesive sheet consisting of two single pressure-sensitive adhesive layers, which are the pressure-sensitive adhesive layers of the present invention, and release liners 11a and 11b are provided on both adhesive surfaces, respectively.

[0093] [Application] The pressure-sensitive adhesive composition of the present invention, the pressure-sensitive adhesive layer of the present invention, and the pressure-sensitive adhesive sheet of the present invention are used for optical applications, i.e., for applications in which they are attached to optical members. More specifically, they are used, for example, for applications in which optical members are attached (for optical member attachment) and for the production of products (optical products) in which the optical members are used. The pressure-sensitive adhesive composition of the present invention, the pressure-sensitive adhesive layer of the present invention, and the pressure-sensitive adhesive sheet of the present invention are used for optical applications, and are therefore highly reliable.

[0094] The pressure-sensitive adhesive composition of the present invention, the pressure-sensitive adhesive layer of the present invention, and the pressure-sensitive adhesive sheet of the present invention are useful for bonding an adherend having a small linear expansion coefficient to an adherend having a large linear expansion coefficient. Specifically, the pressure-sensitive adhesive composition of the present invention, the pressure-sensitive adhesive layer of the present invention, and the pressure-sensitive adhesive sheet of the present invention are preferably used for bonding a glass adherend (e.g., glass plate, chemically strengthened glass, glass lens, etc.) to the above-mentioned resin substrate having a large linear expansion coefficient.

[0095] As described above, the pressure-sensitive adhesive composition of the present invention, the pressure-sensitive adhesive layer of the present invention, and the pressure-sensitive adhesive sheet of the present invention are useful for bonding adherends made of various materials together, and are particularly useful for bonding glass adherends to plastic adherends.

[0096] The pressure-sensitive adhesive composition of the present invention, the pressure-sensitive adhesive layer of the present invention, and the pressure-sensitive adhesive sheet of the present invention are used, for example, in optical components of electrical and electronic devices, when attaching (mounting) various members or components to predetermined locations (e.g., housings, front panels, window portions, etc.). The term "electrical and electronic devices" refers to devices that fall into at least either electrical or electronic categories. Examples of the electrical and electronic devices include image display devices such as liquid crystal displays, organic / inorganic electroluminescence displays, and plasma displays, as well as portable electronic devices. Examples of the image display devices include image display devices for portable electronic devices, in-vehicle displays, and digital signage (electronic signboards and electronic bulletin boards). The image display devices may be of a form (structure) such as a so-called "rigid type" or a so-called "flexible type," or may be of a form (structure) that can be bent or folded, such as a so-called "foldable type" or "rollable type."

[0097] Examples of the portable electronic devices include mobile phones, smartphones, tablet computers, notebook computers, various wearable devices (for example, wristwear devices worn on the wrist like a wristwatch, modular devices worn on a part of the body with a clip or strap, eyewear devices including eyeglasses (monocular and binocular, including head-mounted devices), clothing devices attached to shirts, socks, hats, etc. as accessories, and earwear devices attached to the ears like earphones), digital cameras, digital video cameras, audio equipment (portable music players, IC recorders, etc.), calculators (calculators, etc.), portable game devices, electronic dictionaries, electronic organizers, e-books, in-car information devices, portable radios, portable televisions, portable printers, portable scanners, and portable modems. Note that in this specification, "portable" does not simply mean being portable, but rather means having a level of portability that allows an individual (average adult) to carry it relatively easily.

[0098] In particular, the pressure-sensitive adhesive composition of the present invention, the pressure-sensitive adhesive layer of the present invention, and the pressure-sensitive adhesive sheet of the present invention are preferably used for bonding components of foldable optical components together, from the viewpoint of excellent resistance to bending in low temperature ranges and being less susceptible to peeling due to sebum.

[0099] Specifically, the pressure-sensitive adhesive composition of the present invention, the pressure-sensitive adhesive layer of the present invention, and the pressure-sensitive adhesive sheet of the present invention are preferably used for bonding a touch sensor and an image display device, which are provided between the touch sensor and the image display device. It is particularly preferred that the pressure-sensitive adhesive layer of the present invention is directly laminated to the touch sensor. Furthermore, the pressure-sensitive adhesive layer of the present invention may be directly laminated to the image display device, or may be laminated via another layer such as a polarizing film. The pressure-sensitive adhesive layer of the present invention is less likely to cause noise amplification, and therefore can prevent noise emitted from the image display device from being transmitted to the touch sensor.

[0100] Furthermore, the pressure-sensitive adhesive composition of the present invention, the pressure-sensitive adhesive layer of the present invention, and the pressure-sensitive adhesive sheet of the present invention are useful for bonding components constituting an antenna (millimeter-wave antenna) used in millimeter-wave communication. The pressure-sensitive adhesive layer of the present invention has low dielectric constant and dielectric loss in high-frequency bands such as millimeter waves, and can therefore suppress radiation loss of millimeter waves. In this specification, "millimeter-wave communication" refers to communication in a frequency band of 20 GHz to 300 GHz.

[0101] [Optical components with adhesive layers] By laminating the sheet of the present invention to an optical member, it is possible to obtain an optical member with a pressure-sensitive adhesive layer, which comprises an optical member and the pressure-sensitive adhesive sheet of the present invention attached to at least one surface of the optical member. The pressure-sensitive adhesive layer of the pressure-sensitive adhesive layer-attached optical member may or may not have a release liner on the adhesive surface until use.

[0102] The pressure-sensitive adhesive layer-attached optical member of the present invention may be one in which the pressure-sensitive adhesive sheet of the present invention is attached to an optical member (touch sensor film) having metal wiring such as a metal mesh film or a silver nanowire film. In this case, it is preferable that the pressure-sensitive adhesive sheet of the present invention is attached to the surface of the touch sensor film on the side having the metal wiring.

[0103] [Optical laminate] By providing the pressure-sensitive adhesive layer of the present invention or the pressure-sensitive adhesive sheet of the present invention between a touch sensor and an image display device, an optical laminate (optical laminate of the present invention) is obtained which includes, in this order, a touch sensor, the pressure-sensitive adhesive layer of the present invention, and an image display device. The optical laminate may include a single layer of the touch sensor and the pressure-sensitive adhesive layer, or multiple layers. When a plurality of touch sensors are provided, it is preferable that the touch sensors are laminated with a pressure-sensitive adhesive layer interposed therebetween. When a plurality of pressure-sensitive adhesive layers are provided, the plurality of pressure-sensitive adhesive layers may be the same or different layers in terms of composition, thickness, etc. When a plurality of pressure-sensitive adhesive layers are provided, at least one layer is the pressure-sensitive adhesive layer of the present invention. It is preferable that all of the pressure-sensitive adhesive layers provided between the touch sensor and the image display device are the pressure-sensitive adhesive layers of the present invention.

[0104] Examples of the image display device include those described above. The touch sensor is a capacitance-type touch sensor, and is, for example, a transparent conductive film in which a transparent conductive layer is provided on a glass plate or a transparent plastic film (particularly a PET film, a polycarbonate film, or a cyclic olefin polymer film). The pressure-sensitive adhesive layer of the present invention is preferably attached so as to come into contact with the transparent conductive layer.

[0105] Examples of the transparent conductive layer include thin films of ITO (indium tin oxide), ZnO, SnO, and CTO (cadmium tin oxide). The transparent conductive layer can also be formed of silver, copper, CNT (carbon nanotube), or the like. Metal mesh sensors such as Ag nanowires and Ag / Cu can also be used for the transparent conductive layer. The touch sensor may also have wiring at its end formed of thin copper or silver paste.

[0106] The optical laminate may include a cover member. The cover member is provided on the surface of the touch sensor opposite to the side where the image display device is provided, and protects the touch sensor and the image display device in the optical laminate. Examples of the cover member include a cover glass and a plastic cover. The cover member may be attached to a layer constituting the optical laminate, such as the touch sensor, via an adhesive layer. The adhesive layer may be the adhesive layer of the present invention, but may also be another adhesive layer, since the function of suppressing the amplification of noise emitted by the image display device is not required. Furthermore, the optical laminate may include a polarizing film on the surface of the image display device (the surface on the side where the touch sensor is provided).

[0107] The optical laminate may include a noise reduction layer (such as a noise reduction film). The noise reduction layer is preferably provided between the touch sensor and the image display device, since it is required to have the function of suppressing the amplification of noise emitted by the image display device. The noise reduction layer and the touch sensor, and the noise reduction layer and the image display device, are bonded together via an adhesive layer (preferably the adhesive layer of the present invention). The noise reduction layer may be a single layer or multiple layers. When multiple noise reduction layers are provided, the multiple noise reduction layers may be the same or different in terms of composition, thickness, etc.

[0108] 2 to 4 show one embodiment of the optical laminate of the present invention. The optical laminate 1 shown in FIG. 2 includes, in this order, an image display device 5, a polarizing film 6 provided on the image display device 5, a touch sensor 41, a touch sensor 42, and a cover member 3. The polarizing film 6 and the touch sensor 41 are bonded together by an adhesive layer (adhesive sheet) 21, and the touch sensors 41 and 42 are bonded together by an adhesive layer (adhesive sheet) 22. The adhesive layers 21 and 22 are the adhesive layer of the present invention. The touch sensor 42 and the cover member 3 are bonded together by an adhesive layer (adhesive sheet) 23. The adhesive layer 23 is another adhesive layer.

[0109] The optical laminate 1 shown in FIG. 3 includes, in this order, an image display device 5, a polarizing film 6 provided on the image display device 5, a touch sensor 43, and a cover member 3. The touch sensor 43 combines the functions of both touch sensors 41 and 42 in FIG. 2, for example. The polarizing film 6 and the touch sensor 43 are bonded together by an adhesive layer 21. The adhesive layer 21 is the adhesive layer of the present invention. The touch sensor 43 and the cover member 3 are bonded together by an adhesive layer 23. The adhesive layer 23 is another adhesive layer.

[0110] The optical laminate 1 shown in FIG. 4 includes, in this order, an image display device 5, a polarizing film 6 provided on the image display device 5, a noise reduction layer 44, a touch sensor 43, and a cover member 3. The polarizing film 6 and the noise reduction layer 44 are bonded together by an adhesive layer 21, and the noise reduction layer 44 and the touch sensor 43 are bonded together by an adhesive layer 22. The adhesive layers 21 and 22 are adhesive layers of the present invention. The touch sensor 43 and the cover member 3 are bonded together by an adhesive layer 23. The adhesive layer 23 is another adhesive layer.

[0111] 2 to 4, the polarizing film 6 does not necessarily have to be provided. In this case, the image display device 5 and the touch sensors 41 and 43 or the noise reduction layer 44 are bonded together by the adhesive layer 21. The image display device 5 and the polarizing film 6 may also be bonded together via an adhesive sheet.

[0112] The above-described embodiments have been described to facilitate understanding of the present invention, and are not intended to limit the present invention. [Example]

[0113] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Note that the number of blended parts (parts by mass) all refers to the number of blended parts of each component described.

[0114] [Example 1] (Preparation of Prepolymer Composition) A monomer mixture containing 65 parts by weight of n-octyl acrylate (NOAA), 30 parts by weight of n-butyl acrylate (BA), and 5 parts by weight of 4-hydroxybutyl acrylate (4HBA) was placed in a flask. 0.05 parts by weight of a first photoinitiator (product name "Omnirad 184," 1-hydroxycyclohexyl phenyl ketone, IGM Resins) and 0.05 parts by weight of a second photoinitiator (product name "Omnirad 819," bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, IGM Resins) were then added. The mixture was then irradiated with UV light under a nitrogen atmosphere to partially polymerize the polymerizable components in the mixture, yielding a first prepolymer composition. A black light was used for UV irradiation. UV irradiation was continued until the viscosity of the composition reached approximately 20 Pa·s. This viscosity was measured using a Brookfield viscometer with a No. 5 rotor at a rotor rotation speed of 10 rpm and a temperature of 30°C (the same applies to the viscosity described below). The obtained prepolymer composition is a partial polymer containing a photopolymerized product and a polymerizable component (residual monomer) that has not undergone a polymerization reaction.

[0115] (Preparation of Pressure-Sensitive Adhesive Composition) A pressure-sensitive adhesive composition was prepared by mixing 100 parts by mass of the above prepolymer composition, 0.04 parts by mass of dipentaerythritol hexaacrylate (DPHA) as a crosslinking agent, and 0.3 parts by mass of a silane coupling agent (trade name "KBM-403", manufactured by Shin-Etsu Chemical Co., Ltd.).

[0116] (Formation of adhesive layer) The coating process, first lamination process, photo-curing process, peeling process, heating process, and second lamination process were carried out in sequence while the long first release liner was run in the length direction of the release liner (roll-to-roll process). The first release liner was a 75 μm thick polyethylene terephthalate (PET) film with one side treated with silicone release. The running speed of the first release liner was 4.0 m / min.

[0117] In the coating step, the pressure-sensitive adhesive composition was applied to the release-treated surface of the first release liner using a roll coater to form a coating film. In the first laminating step, the release-treated surface of a second release liner, one side of which had been treated with a silicone release agent, was laminated to the coating film on the first release liner. The second release liner was a long PET film (75 μm thick) with one side treated with a silicone release agent.

[0118] In the photo-curing process, ultraviolet (UV) rays were irradiated onto the coating film between the release liners, and the coating film was photo-cured to form a 25 μm thick adhesive layer. For UV irradiation, a black light was used as the irradiation light source, and the irradiation intensity was approximately 6.5 mW / cm. 2 The cumulative irradiation dose was 390 mJ / cm 2 It was decided.

[0119] In the peeling step, the second release liner was peeled from the pressure-sensitive adhesive layer on the first release liner. In the heating step, first and second heating steps were carried out sequentially in a hot air heating oven to dry the pressure-sensitive adhesive layer on the first release liner. In the first heating step, the heating temperature (first heating temperature) was set to 120°C. In the second heating step, the heating temperature (second heating temperature) was set to 90°C.

[0120] In the second lamination step, the release-treated surface of a third release liner, one side of which had been treated with a silicone release agent, was laminated to the adhesive layer on the first release liner. The third release liner was a long PET film (75 μm thick) with one side treated with a silicone release agent.

[0121] In this manner, a substrate-less double-sided PSA sheet with double-sided release liners of Example 1 was produced.

[0122] Examples 2 and 3, Comparative Examples 1 and 2 The PSA layer and substrate-less double-sided PSA sheet of each example were produced in the same manner as in Example 1, except that in preparing the prepolymer composition, the monomer composition was changed as shown in Table 1. In Table 1, "2EHA" represents 2-ethylhexyl acrylate, "LA" represents lauryl acrylate, and "NVP" represents N-vinyl-2-pyrrolidone.

[0123] Comparative Example 3 (Preparation of Pressure-Sensitive Adhesive Composition) A reaction vessel equipped with a stirrer, thermometer, nitrogen gas inlet tube, reflux condenser, and dropping funnel was charged with 99 parts by mass of n-butyl acrylate (BA) as polymerizable components, 1 part by mass of 4-hydroxybutyl acrylate (4HBA), and 160 parts by mass of ethyl acetate as a polymerization solvent, and the mixture was stirred for 2 hours while introducing nitrogen gas. After removing oxygen from the polymerization system in this way, 0.15 parts by mass of benzoyl peroxide was added as a polymerization initiator, and solution polymerization was carried out at 60°C for 6 hours to obtain an acrylic polymer solution.

[0124] To the above acrylic polymer solution, 3 parts by mass of an isocyanate crosslinking agent (trade name "Coronate L", manufactured by Tosoh Corporation) was added as a crosslinking agent per 100 parts by mass of the acrylic polymer, and the mixture was stirred and mixed to prepare a pressure-sensitive adhesive composition.

[0125] (Formation of adhesive layer) A substrate-less double-sided PSA sheet with double-sided release liners of Comparative Example 3 was produced in the same manner as in Example 1, except that the above PSA composition was used.

[0126] [evaluation] The substrate-less double-sided PSA sheets of the Examples and Comparative Examples were subjected to the following measurements and evaluations. The evaluation results are shown in Table 1.

[0127] (1) Shear storage modulus The required number of measurement samples were prepared for each substrate-less double-sided PSA sheet. Specifically, first, multiple substrate-less double-sided PSA sheet pieces cut from the substrate-less double-sided PSA sheet were laminated together to prepare a sample sheet approximately 1.5 mm thick. Next, this sheet was punched out to obtain cylindrical pellets (7.9 mm in diameter) as measurement samples. Then, the measurement samples were fixed to a 7.9 mm diameter parallel plate jig using a dynamic viscoelasticity measuring device (product name "Discovery Hybrid Reometer-2 (DHR-2)", manufactured by TA Instruments), and dynamic viscoelasticity measurement was performed. In this measurement, the measurement mode was shear mode, the measurement temperature range was -50°C to 150°C, the heating rate was 5°C / min, and the frequency was 1 Hz. The shear storage modulus at -20°C was read from the measurement results.

[0128] (2) Adhesive strength The method for measuring adhesive strength will be described using Figure 5. A substrate-less double-sided PSA sheet was punched out to a width of 25 mm and a length of 100 mm to obtain measurement sample 7. The third release liner was peeled off from measurement sample 7 to expose the adhesive surface, and the exposed adhesive surface was attached to glass plate 8 (product name "Blue Plate Cutout (1 OF Position)", manufactured by Matsunami Glass Industry Co., Ltd.) at a temperature of 23°C and a humidity of 40%. The glass plate was then left to stand for 15 minutes in an atmosphere of 0.5 MPa pressure and 50°C temperature, and then left to stand for 2 hours in an atmosphere of 23°C and a humidity of 40%. Measurement sample 7 was attached to the center of glass plate 8 in the width direction so that the length of the adhesive region was 90 mm or more, and so that the upper end of measurement sample 7 was within the plane of glass plate 8 and the lower end was outside the plane of glass plate 8. Next, 25 μL of a mixture 9 of oleic acid and squalene (volume ratio 1:1) was added to the upper end of the interface between the measurement sample 7 and the glass plate 8 using a dropper and allowed to blend. The glass plate 8 was then inverted vertically to allow the mixture 9 to be spread over the adhesive area (length 90 mm or more). The measurement sample 7 was then turned upward and adhesive strength measurements were performed at a peel angle of 180°, a peel rate of 50 mm / min, and a peel distance of 90 mm. The final stable adhesive strength was defined as the post-stable adhesive strength, and the temporarily stable initial adhesive strength before increasing to the post-stable adhesive strength was defined as the initial adhesive strength. Graphs showing the relationship between peel distance (peel distance) and adhesive strength obtained from the adhesive strength measurements are shown in Figures 6 to 8. Figure 6 is a graph for Example 3, Figure 7 is a graph for Comparative Example 1, and Figure 8 is a graph for Comparative Example 2. In Figures 6 to 8, F0 indicates the initial adhesive strength, and F1 indicates the post-stable adhesive strength.

[0129] (3) Water contact angle In measuring the adhesive strength, before the adhesive layer was bonded, a water droplet of approximately 3 μL was dropped by the drop method using a water contact angle measuring device (trade name "DM700", manufactured by Kyowa Interface Science Co., Ltd.) on the surface of a glass plate (trade name "Blue Plate Cutout (1 OF)", manufactured by Matsunami Glass Industrial Co., Ltd.) to which the adhesive layer was to be bonded, in an atmosphere of 23°C temperature and 40% humidity.The angle formed by the tangent line between the adherend surface and the end of the dropped water droplet 1 second after the drop was measured to measure the "water contact angle (°)" (water contact angle before oil penetration). Furthermore, after peeling off the adhesive layer in the measurement of the adhesive strength, a water droplet of approximately 3 μL was dropped by the drop method using the water contact angle measuring device on the surface of the glass plate in the area where the adhesive layer had been attached, in an atmosphere of 23°C temperature and 40% humidity, and the angle formed by the tangent line of the end of the dropped water droplet with the adherend surface 1 second after the drop was measured to measure the "water contact angle (°)" (water contact angle after oil penetration).

[0130] [Table 1]

[0131] As shown in Table 1, the substrate-less double-sided PSA sheets of the Examples had a low rate of change in water contact angle, and after oil penetration, a small amount of oil remained on the glass surface, suggesting that the PSA layer was not swollen by the oil. They also had a small rate of change in adhesive strength, and were evaluated as being less susceptible to peeling due to sebum. On the other hand, when the rate of change in adhesive strength or the rate of change in water contact was large (Comparative Examples 1 to 3), after oil penetration, no oil remained on the glass surface, suggesting that the PSA layer was swollen by the oil, they were evaluated as being more susceptible to peeling due to sebum.

[0132] Variations of the invention according to the present disclosure are described below. [Appendix 1] An active energy ray-curable pressure-sensitive adhesive composition, The pressure-sensitive adhesive composition has a rate of change in adhesive strength represented by the following formula (1) of 80% or less, and a rate of change in water contact ratio represented by the following formula (2) of less than −1.5%. Adhesive strength change rate [%] = (adhesive strength after stabilization - adhesive strength at start-up) / adhesive strength after stabilization × 100 (1) (A 25 mm wide adhesive layer formed from the adhesive composition is attached to glass and stored for 15 minutes under conditions of a pressure of 0.5 MPa and a temperature of 50°C, and then 25 μL of a mixture of oleic acid and squalene (volume ratio 1:1) is added to the interface between the adhesive layer and the glass and allowed to settle, after which the adhesive strength is measured under conditions of a peel angle of 180°, a peel speed of 50 mm / min, and a peel distance of 90 mm. The adhesive strength that finally stabilizes is defined as the post-stable adhesive strength, and the adhesive strength that temporarily stabilizes before rising to the post-stable adhesive strength is defined as the initial adhesive strength.) Change in water contact rate [%] = (water contact angle before oil penetration - water contact angle after oil penetration) / water contact angle after oil penetration × 100 (2) (Water contact angle before oil penetration: Water contact angle of the glass surface before the adhesive strength measurement) Water contact angle after oil penetration: Water contact angle on the glass surface after the adhesive strength measurement [Appendix 2] The pressure-sensitive adhesive composition according to Appendix 1, which has a shear storage modulus (G') at -20°C of 150 kPa or less. [Appendix 3] The pressure-sensitive adhesive composition according to appendix 1 or 2, wherein the adhesive strength at rise is 2.0 N / 25 mm or more. [Appendix 4] The pressure-sensitive adhesive composition according to any one of Appendices 1 to 3, wherein the water contact angle after the oil penetration is 120° or more. [Appendix 5] The pressure-sensitive adhesive composition according to any one of Appendices 1 to 4, which is used for bonding components of a foldable optical member together. [Explanation of symbols]

[0133] 1 Optical laminate 2. Adhesive layer 21, 22, 23 Adhesive layer (adhesive sheet) 3 Cover member 41, 42, 43 Touch sensor 44 Noise Reduction Layer 5 Image display device 6. Polarizing film 10 adhesive sheet 11a, 11b Release liner

Claims

1. an active energy ray-curable pressure-sensitive adhesive composition, The pressure-sensitive adhesive composition has a rate of change in adhesive strength represented by the following formula (1) of 80% or less, and a rate of change in water contact ratio represented by the following formula (2) of less than −1.5%: Adhesive strength change rate [%] = (adhesive strength after stabilization - adhesive strength at start-up) / adhesive strength after stabilization × 100 (1) (A 25 mm wide adhesive layer formed from the adhesive composition was attached to glass and stored for 15 minutes under conditions of a pressure of 0.5 MPa and a temperature of 50°C, and then 25 μL of a mixture of oleic acid and squalene (volume ratio 1:1) was added to the interface between the adhesive layer and the glass and allowed to settle, after which the adhesive strength was measured under conditions of a peel angle of 180°, a peel speed of 50 mm / min, and a peel distance of 90 mm, the adhesive strength that finally stabilizes is defined as the post-stable adhesive strength, and the adhesive strength that temporarily stabilizes before rising to the post-stable adhesive strength is defined as the initial adhesive strength.) Change in water contact rate [%] = (water contact angle before oil penetration - water contact angle after oil penetration) / water contact angle after oil penetration × 100 (2) (Water contact angle before oil penetration: Water contact angle on the glass surface before the adhesive strength measurement) Water contact angle after oil penetration: Water contact angle on the glass surface after the adhesive strength measurement

2. The pressure-sensitive adhesive composition according to claim 1, which has a shear storage modulus (G') at -20°C of 150 kPa or less.

3. The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the adhesive strength at rise is 2.0 N / 25 mm or more.

4. The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the water contact angle after the oil penetration is 120° or more.

5. The pressure-sensitive adhesive composition according to claim 1 or 2, which is used for bonding components of a foldable optical member together.

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