Adhesive composition, adhesive sheet, laminate, and display comprising said laminate

Abstract

Provided is an adhesive composition comprising an acrylic polymer (A) and a curing agent (B), wherein: the acrylic polymer (A) is a copolymer of a monomer mixture containing the following monomer (a1), monomer (a2), monomer (a3), and monomer (a4) and other monomers, and satisfies expression (1); the content of (a2) is 40-95 parts by mass in 100 parts by mass of the monomer mixture; the content of (a3) is at most 10 parts by mass in 100 parts by mass of the monomer mixture; the content of (a4) is 0.1-20 parts by mass in 100 parts by mass of the monomer mixture; the content of the other monomers is at most 15 parts by mass in 100 parts by mass of the monomer mixture; the amount of the curing agent (B) added is 0.01-5 parts by mass with respect to 100 parts by mass of the acrylic polymer (A); and the gel fraction of an adhesive layer composed of the adhesive composition is 55-90%. Here, (a1) is a (meth)acrylic acid ester monomer which has a glass transition temperature of a homopolymer of at least 0ºC and does not have a functional group, (a2) is 2-octyl (meth)acrylate, (a3) is a carboxy group-containing monomer, (a4) is a hydroxy group-containing monomer, and expression (1) is 1,500≤Σ(T2×MA / 100)≤38,000, where T is the glass transition temperature (K) of the homopolymer of (a1), and MA is the content (parts by mass) of (a1) in 100 parts by mass of the monomer mixture.

Description

Pressure-sensitive adhesive composition, pressure-sensitive adhesive sheet, laminate, and display including said laminate

[0001] The present disclosure relates to a pressure-sensitive adhesive composition, a pressure-sensitive adhesive sheet, a laminate, and a display including the laminate, which are suitable for fixing polarizing plates.

[0002] Display devices such as liquid crystal displays (LCDs) used in various devices, including electronic calculators, electronic watches, mobile phones, televisions, and other home and commercial electrical appliances, are becoming larger, with LCD and plasma TVs becoming particularly large. Furthermore, touch-panel LCDs, including those used in smartphones and tablets, have rapidly become more popular in recent years, and significant market expansion is expected in the future. Meanwhile, LCDs are also used in in-vehicle devices such as car navigation systems, and they must be durable enough to withstand harsh in-vehicle environments, including high temperatures and humidity. Liquid crystal displays incorporate polarizing plates and retardation plates with various optical functions, which are attached to substrates such as glass or transparent plastic liquid crystal cells via adhesives.

[0003] The polarizing plate is generally a laminate in which a polyvinyl alcohol film is sandwiched between triacetyl cellulose-based films or cycloolefin-based films. These films have different mechanical properties and therefore different dimensional change rates when heated, so that the laminate often warps when placed in a high-temperature atmosphere.

[0004] For example, if a liquid crystal cell component consisting of a polarizing plate / adhesive layer / glass (the glass is the surface component of the liquid crystal cell) is left in a high-temperature atmosphere, problems such as warping due to the dimensional change rate between the components of the polarizing plate, bubbles (foaming) at the bonding interface between the adhesive layer and the glass, or the polarizing plate lifting off the glass may occur. Furthermore, the warping may cause uneven stress distribution in the liquid crystal cell component, resulting in stress concentration at the peripheral edges of the liquid crystal cell component, leading to a problem known as "light leakage," in which light leaks from the four corners or peripheral edges of the liquid crystal cell component. The above-mentioned problems also occur in high-temperature, high-humidity atmospheres.

[0005] On the other hand, in the manufacturing process of liquid crystal displays and the like, when a polarizing plate is bonded to an optical component such as a liquid crystal cell, if a misalignment occurs in the bonding position, the polarizing plate is peeled off after a certain time has passed since bonding, and the expensive liquid crystal cell is reused. Therefore, the adhesive is required to have the property (reworkability) that allows the polarizing plate to be re-peeled from the liquid crystal cell after a certain time has passed since bonding.

[0006] In addition, for convenient coating during the production of adhesive sheets, adhesives are generally diluted and adjusted to a low viscosity before use. Regarding the solvent used for viscosity adjustment, it is desirable to reduce the content as much as possible from the viewpoint of cost and handling. Furthermore, if the non-volatile content of the adjusted solution is low, it tends to be difficult to apply the adhesive thickly and uniformly, so there is a demand for low-viscosity adhesives that can achieve a higher non-volatile content.

[0007] To solve these problems, Patent Document 1 discloses a technology for improving stress relaxation properties and preventing light leakage by incorporating an acrylic copolymer using an aromatic ring-containing monomer. However, the pressure-sensitive adhesive using the aromatic ring-containing monomer disclosed in Patent Document 1 has problems such as white spots occurring in light leakage evaluations and poor optical properties. Furthermore, the inventors' investigations revealed that a non-volatile content of 25% would result in excessively high viscosity, making coating difficult, and therefore it was not possible to increase the non-volatile content.

[0008] Patent Document 2 discloses a technique for imparting removability by blending a low-molecular-weight acrylic polymer having a high acid value and a weight-average molecular weight of 0.2 to 100,000 with a high-molecular-weight acrylic polymer having a weight-average molecular weight of 500,000 or more. However, the pressure-sensitive adhesive described in Patent Document 2 has a problem in that the drying conditions for the pressure-sensitive adhesive are limited.

[0009] Patent Document 3 discloses a technique for improving durability and adhesive properties under heated and humid conditions by using a block polymer containing two or more monomers. However, the adhesive described in Patent Document 3 has a problem in that the transmittance decreases under heated and / or humid conditions.

[0010] Patent Document 4 discloses a technology that makes polarization less likely to occur and provides reworkability and recyclability by using a water-dispersible pressure-sensitive adhesive containing an acrylic copolymer having a glass transition temperature of −55° C. or more and less than 0° C. and an acrylic copolymer having a glass transition temperature of 0° C. or more and 180° C. or less. However, the pressure-sensitive adhesive described in Patent Document 4 has a problem in that it lacks reworkability after being applied for a long period of time due to various additives used in the pressure-sensitive adhesive.

[0011] Patent Document 5 discloses a technology for suppressing peeling and lifting in a high-temperature, high-humidity environment by constructing an interpenetrating network structure in a cured state using a hydroxyl group- and alkylene oxide group-containing acrylic copolymer and a polyfunctional isocyanate curing agent. However, the pressure-sensitive adhesive described in Patent Document 5 has a problem in that when left in a high-temperature, high-humidity environment for a long period of time, the alkylene oxide groups decompose, causing peeling and lifting.

[0012] Furthermore, Patent Document 6 discloses a technology for suppressing lifting and peeling of an adhesive sheet when placed in a high-temperature, high-humidity environment for a long period of time using an acrylic copolymer containing a hydroxyl group and a carboxyl group, a mercapto group-containing silane compound, and an alcohol. However, the adhesive described in Patent Document 6 uses a highly volatile silane compound, so when the adhesive is coated and dried, the silane compound volatilizes, and a sufficient amount of the silane compound does not remain in the adhesive layer after coating, resulting in the problem of lifting and peeling.

[0013] JP 2007-169329 A JP 2010-100710 A JP 2013-82772 A JP 2014-1365 A JP 2014-55299 A JP 2004-59711 A

[0014] The problem to be solved by the present invention is to provide a pressure-sensitive adhesive composition that exhibits excellent low viscosity when adjusted to a predetermined nonvolatile content, exhibits excellent releasability when used in a pressure-sensitive adhesive sheet, and is resistant to lifting or peeling from an adherend after exposure to a high temperature or a high temperature / high humidity environment, and a pressure-sensitive adhesive sheet using the same, in order to solve the above problems.Furthermore, the present invention aims to provide a pressure-sensitive adhesive composition that exhibits extremely low light leakage when used to fix a polarizing plate, has good adhesive strength that allows it to maintain high transparency even when exposed to a high temperature / high humidity environment, and does not contaminate an adherend such as glass, and a pressure-sensitive adhesive sheet using the same.

[0015] The present inventors have conducted extensive research to solve the above-mentioned problems, and have arrived at the present invention. Specifically, the present invention relates to a pressure-sensitive adhesive composition comprising an acrylic polymer (A) and a curing agent (B), wherein the acrylic polymer (A) is a copolymer of a monomer mixture comprising the following monomers (a1), (a2), (a3), and (a4), and other monomers, and the pressure-sensitive adhesive composition satisfies the following formula (1), wherein the content of (a2) is 40 to 95 parts by mass per 100 parts by mass of the monomer mixture, the content of (a3) ​​is 10 parts by mass or less per 100 parts by mass of the monomer mixture, the content of (a4) is 0.1 to 20 parts by mass per 100 parts by mass of the monomer mixture, the content of the other monomers is 15 parts by mass or less per 100 parts by mass of the monomer mixture, the amount of curing agent (B) added is 0.01 to 5 parts by mass per 100 parts by mass of the acrylic polymer (A), and the pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive composition has a gel fraction of 55 to 90%. (a1) A (meth)acrylic acid ester monomer having a glass transition temperature of 0°C or higher and having no functional group, (a2) 2-octyl (meth)acrylate, (a3) ​​a monomer having a carboxy group, and (a4) a monomer having a hydroxy group. Formula (1) 1500≦Σ(T ２ × MA / 100)≦38000, where T: glass transition temperature (K) of the homopolymer of (a1), MA: content (parts by mass) of (a1) in 100 parts by mass of the monomer mixture.

[0016] The present disclosure also provides a pressure-sensitive adhesive composition comprising an acrylic polymer (A) and a curing agent (B), wherein the acrylic polymer (A) is a copolymer of a monomer mixture comprising the following monomers (a1), (a2), (a3), and (a4), and other monomers, and satisfies the following formula (1): the content of (a2) is 40 to 95 parts by mass, the content of (a3) ​​is 10 parts by mass or less, and the content of (a4) is 0.1 to 20 parts by mass, per 100 parts by mass of the monomer mixture; The pressure-sensitive adhesive composition has a gel fraction of 55 to 90%. The pressure-sensitive adhesive composition comprises: (a1) a (meth)acrylic acid ester monomer having a glass transition temperature of 0°C or higher and having no functional group; (a2) 2-octyl(meth)acrylate; (a3) ​​a monomer having a carboxy group; and (a4) a monomer having a hydroxy group, the content of which is 1500≦Σ(T ２ × MA / 100)≦38000, where T: glass transition temperature (K) of the homopolymer of (a1), MA: content (parts by mass) of (a1) in 100 parts by mass of the monomer mixture.

[0017] The present disclosure also provides a pressure-sensitive adhesive composition comprising an acrylic polymer (A) and a curing agent (B), wherein the acrylic polymer (A) is a copolymer of a monomer mixture comprising the following monomers (a1), (a2), (a3), and (a4), and other monomers, and satisfies the following formula (1), in which the content of (a2) is 40 to 95 parts by mass in 100 parts by mass of the monomer mixture, the content of (a3) ​​is 10 parts by mass or less in 100 parts by mass of the monomer mixture, and the content of (a4) is 10 parts by mass or less in 100 parts by mass of the monomer mixture. The present invention relates to a pressure-sensitive adhesive composition, wherein the content of the other monomers is 15 parts by mass or less per 100 parts by mass of the monomer mixture, and when a nitrogen-containing monomer is included as the other monomer, the content of at least one of the nitrogen-containing monomer and the monomer (a4) per 100 parts by mass of the monomer mixture is less than 10 parts by mass, the amount of the curing agent (B) added is 0.01 to 5 parts by mass per 100 parts by mass of the acrylic polymer (A), and the gel fraction of the pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive composition is 55 to 90%. The present invention relates to a pressure-sensitive adhesive composition, wherein the content of the other monomers is 15 parts by mass or less per 100 parts by mass of the acrylic polymer (A), and the content of the other monomers is 0.1 to 20 parts by mass per 100 parts by mass of the monomer mixture, and when a nitrogen-containing monomer is included as the other monomer, the content of at least one of the nitrogen-containing monomer and the monomer (a4) per 100 parts by mass of the acrylic polymer (A) is less than 10 parts by mass, the amount of the curing agent (B) added is 0.01 to 5 parts by mass per 100 parts by mass of the acrylic polymer (A), and the gel fraction of the pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive composition is 55 to 90%. ２ × MA / 100)≦38000, where T: glass transition temperature (K) of the homopolymer of (a1), MA: content (parts by mass) of (a1) in 100 parts by mass of the monomer mixture.

[0018] The present disclosure also relates to the pressure-sensitive adhesive composition, wherein the content of the monomer (a4) is 0.1 to 5 parts by mass based on 100 parts by mass of the monomer mixture.

[0019] The present disclosure also relates to the pressure-sensitive adhesive composition, wherein the curing agent (B) contains an isocyanate-based curing agent.

[0020] The present disclosure also relates to the pressure-sensitive adhesive composition, which further comprises an organosilane (C).

[0021] The present disclosure also relates to the pressure-sensitive adhesive composition, wherein the content of the carboxyl group-containing monomer (a3) ​​in 100 parts by mass of the monomer mixture constituting the acrylic polymer (A) is 10 parts by mass or less.

[0022] The present disclosure also relates to the pressure-sensitive adhesive composition used for fixing a polarizing plate.

[0023] The present disclosure also relates to a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive composition.

[0024] The present disclosure also relates to a laminate comprising a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive composition and a light-transmitting substrate.

[0025] The present disclosure also relates to a polarizing plate with a pressure-sensitive adhesive layer, which includes a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive composition.

[0026] The present disclosure also relates to a display comprising a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive composition, a light-transmitting substrate, a polarizing plate, and an optical element.

[0027] The present disclosure makes it possible to provide a pressure-sensitive adhesive composition that exhibits excellent low viscosity when adjusted to a predetermined non-volatile content, exhibits excellent removability when used in a pressure-sensitive adhesive sheet, and is resistant to lifting and peeling from adherends, such as glass and plastics, after exposure to a high-temperature environment or a high-temperature, high-humidity environment, and is resistant to light leakage.

[0028] Fig. 1 is a schematic cross-sectional view partially showing an example of a laminate according to the present disclosure;Fig. 2 is a schematic cross-sectional view partially showing a display, which is an example of use of an example of a laminate according to the present disclosure;Fig. 3 is a schematic cross-sectional view partially showing an example of a pressure-sensitive adhesive sheet according to the present disclosure.

[0029] The pressure-sensitive adhesive composition, pressure-sensitive adhesive sheet, laminate, and display of the present disclosure are described below, but are not limited thereto. In this specification, (meth)acrylic acid esters include acrylic acid esters and methacrylic acid esters, and (meth)acryloxy groups include acryloxy groups and methacryloxy groups. A monomer is a monomer having an ethylenically unsaturated group. In this specification, a numerical range specified using "to" includes the numerical values ​​before and after "to" as the lower and upper limits of the range. Furthermore, "film" and "sheet" are not distinguished by thickness. In other words, in this specification, "sheet" includes thin film-like objects, and "film" in this specification includes thick sheet-like objects. Furthermore, an adherend refers to a surface to which the pressure-sensitive adhesive layer of a pressure-sensitive adhesive sheet is attached. Unless otherwise noted, the various components mentioned in this specification may be used independently, either singly or in combination of two or more types.

[0030] <<Adhesive Composition>> The adhesive composition of the present disclosure contains an acrylic polymer (A) and a curing agent (B).

[0031] <Acrylic Polymer (A)> The acrylic polymer (A) is a copolymer of a monomer mixture containing the following monomer (a1) and monomer (a2).

[0032] Monomer (a1) is a (meth)acrylate monomer having no functional group and having a homopolymer glass transition temperature of 0° C. or higher. The glass transition temperature (° C.) of the homopolymer can be obtained from information provided by the vendor of the monomer or from the values ​​listed in "Polymer Handbook 3rd Edition" (A Wiley-Interscience Publication, 1989).

[0033] Examples of monomer (a1) include methyl (meth)acrylate, ethyl methacrylate, ter-butyl methacrylate, sec-butyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, isopropyl methacrylate, stearyl (meth)acrylate, isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenyl (meth)acrylate, etc. From the viewpoint of improving cohesive strength and adhesive strength, monomer (a1) is preferably at least one selected from the group consisting of methyl (meth)acrylate, ethyl methacrylate, isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, and phenyl (meth)acrylate.

[0034] The acrylic polymer (A) satisfies the following formula (1): 1500≦Σ(T ２ × MA / 100)≦38000, where T: glass transition temperature (K) of the homopolymer of (a1); MA: content (parts by mass) of (a1) in 100 parts by mass of the monomer mixture. By setting the content of monomer (a1) so that the acrylic polymer (A) satisfies formula (1), the cohesive strength of the pressure-sensitive adhesive composition is improved and a tough pressure-sensitive adhesive layer is obtained. This can suppress lifting and peeling when exposed to a high-temperature atmosphere, and can also ensure the removability required for re-adhesion to optical components. The lower limit of formula (1) is preferably 3900, more preferably 7100. The upper limit of formula (1) is preferably 32000, more preferably 24000.

[0035] [Monomer (a2)] Monomer (a2) is 2-octyl(meth)acrylate. Since biologically derived materials are available as monomer (a2), the use of these materials can increase the proportion of biologically derived materials. Furthermore, the flexibility of the pressure-sensitive adhesive layer is improved, the adhesive layer's adhesion to the substrate is further improved, and lifting and peeling can be further suppressed when exposed to a high-temperature atmosphere or a high-temperature, high-humidity atmosphere. Furthermore, by including monomer (a2), even if the acrylic polymer (A) has a high molecular weight, the viscosity tends to be lower than that of a polymer of the same molecular weight that does not contain monomer (a2). Therefore, even if the pressure-sensitive adhesive composition has a high non-volatile content, the viscosity does not increase too much, making it easy to handle.

[0036] The content of monomer (a2) is 40 to 95 parts by mass per 100 parts by mass of the monomer mixture, preferably 50 to 95 parts by mass, more preferably 60 to 90 parts by mass, and most preferably 70 to 85 parts by mass. By setting the content of monomer (a2) to 40 to 95 parts by mass, an increase in viscosity of the PSA composition can be suppressed, and both adhesiveness and durability when exposed to a high-temperature atmosphere or a high-temperature, high-humidity atmosphere can be achieved.

[0037] The proportion of 2-octyl acrylate in 100% by mass of monomer (a2) is preferably 75% by mass or more, more preferably 85% by mass or more, and most preferably 95% by mass or more. By making it 75% by mass or more, adhesion to various optical members can be ensured and, when a polarizing plate is formed, lifting and peeling can be further suppressed when the polarizing plate is exposed to a high-temperature atmosphere or a high-temperature, high-humidity atmosphere.

[0038] [Monomer (a3)] The monomer mixture constituting the acrylic polymer (A) may further contain a monomer having a carboxy group as the monomer (a3).

[0039] The content of (a3) ​​is 10 parts by mass or less, preferably 5 parts by mass or less, more preferably less than 0.5 parts by mass, and most preferably 0.1 parts by mass or less, per 100 parts by mass of the monomer mixture. By setting the content to 10 parts by mass or less, corrosion resistance when the pressure-sensitive adhesive sheet is attached to a transparent electrode can be improved, and lifting and peeling can be further suppressed when the formed polarizing plate is exposed to a high-temperature atmosphere or a high-temperature, high-humidity atmosphere.

[0040] The monomer (a3) ​​having a carboxy group is not limited as long as it is a monomer having a carboxy group in the molecule, and specific examples include (meth)acrylic acid, p-carboxybenzyl acrylate, β-carboxyethyl acrylate, maleic acid, monoethyl maleate, itaconic acid, citraconic acid, fumaric acid, etc. Among these, (meth)acrylic acid is preferred from the viewpoint of adhesive strength, and acrylic acid is more preferred.

[0041] [Monomer (a4)] The monomer mixture constituting the acrylic polymer (A) further contains a monomer having a hydroxy group as the monomer (a4). The inclusion of a monomer having a hydroxy group suppresses an increase in the viscosity of the adhesive, making it easier to achieve both adhesiveness and durability when exposed to a high-temperature or high-humidity atmosphere. The hydroxy group-containing monomer (a4) is not limited as long as it contains a hydroxy group in the molecule. Specific examples include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate, and these can be used alone or in combination of two or more. The average carbon number of the alkyl chain of the hydroxy group-containing monomer (a4) is preferably 2.5 or more, and more preferably 3 or more. This improves reactivity with the curing agent and imparts cohesive strength to the adhesive layer, making it easier to suppress lifting and peeling when exposed to a high-temperature or high-humidity atmosphere when a polarizing plate is formed.

[0042] The content of the hydroxyl group-containing monomer (a4) is 0.1 to 20 parts by mass, preferably 0.1 to 5 parts by mass, and most preferably 0.2 to 1.5 parts by mass, per 100 parts by mass of the monomer mixture. By setting the content of the hydroxyl group-containing monomer to 0.1 to 20 parts by mass, an increase in viscosity of the pressure-sensitive adhesive composition can be suppressed, and it becomes easier to achieve both adhesion to optical members, removability, and durability when exposed to a high-temperature atmosphere or a high-temperature, high-humidity atmosphere.

[0043] [Other Monomers] The monomer mixture constituting the acrylic polymer (A) contains other monomers in addition to the above (a1) to (a4). Examples of such monomers include (meth)acrylic acid ester monomers having no functional group and having a homopolymer glass transition temperature (Tg) of less than 0°C (ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, dodecyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, dodecyl (meth)acrylate, and octadecyl (meth)acrylate), alkoxy (meth)acrylic acid esters such as methoxyethyl acrylate, vinyl monomers such as vinyl acetate and styrene, monomers having a glycidyl group such as glycidyl (meth)acrylate, and monomers containing a nitrogen atom.

[0044] Examples of nitrogen atom-containing monomers include N-vinyl lactams, cyclic amides such as vinylpyridine, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, and (meth)acryloylmorpholine, N-vinylcarboxylic acid amides such as N-vinylformamide and N-vinylacetamide, acrylonitrile, acrylamide, N,N-dimethylacrylamide, etc. N-vinyl lactams are monomers having a cyclic lactam ring, and examples thereof include N-vinyl-2-pyrrolidone, N-vinyl-2-piperidone, N-vinyl-ε-caprolactam, and compounds having a structure in which one or more hydrogen atoms of these are substituted with a substituent. Examples of the substituent include an alkyl group having 1 to 20 carbon atoms, an alkyl group having 2 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a carboxy ester group having 3 to 20 carbon atoms, and an amino group having 1 to 20 carbon atoms, and do not include acidic groups such as a hydroxy group, a carboxylic acid (salt) group, a sulfonic acid (salt) group, or a hypophosphorous acid (salt) group. Among these, cyclic amides and N-vinyl lactams are preferred, and N-vinyl lactams are more preferred.

[0045] The content of the other monomer is 15 parts by mass or less, preferably 10 parts by mass or less, and most preferably 5 parts by mass or less, per 100 parts by mass of the monomer mixture.

[0046] When isobornyl (meth)acrylate is contained as the monomer (a1) and a nitrogen-containing monomer is contained as another monomer, the content of at least one of isobornyl (meth)acrylate, the nitrogen-containing monomer, and the monomer (a4) is less than 10 parts by mass per 100 parts by mass of the monomer mixture. If the content of isobornyl (meth)acrylate, the nitrogen-containing monomer, or the monomer (a4) is high, the cohesive strength becomes too high, resulting in a decrease in adhesive strength. Therefore, it is important that the content of at least one of the three isobornyl (meth)acrylate, the nitrogen-containing monomer, and the monomer (a4) is less than 10 parts by mass.

[0047] When the monomer mixture contains a nitrogen-containing monomer as another monomer, the content of at least one of the nitrogen-containing monomer and the monomer (a4) is less than 10 parts by mass per 100 parts by mass of the monomer mixture. If the content of the nitrogen-containing monomer and the monomer (a4) is high, the cohesive strength becomes too high, resulting in a decrease in adhesive strength. Therefore, it is important that the content of at least one of them is less than 10 parts by mass.

[0048] (Production of Acrylic Polymer (A)) The acrylic polymer (A) can be produced by polymerizing the monomer mixture. Although known polymerization methods such as solution polymerization, bulk polymerization, emulsion polymerization, and suspension polymerization are possible, solution polymerization is preferred. Preferred solvents used in solution polymerization include, for example, acetone, methyl acetate, ethyl acetate, toluene, xylene, anisole, methyl ethyl ketone, and cyclohexanone. The polymerization temperature is preferably a boiling point reaction at 60 to 120°C. The polymerization time is preferably about 5 to 12 hours.

[0049] The polymerization initiator used in the polymerization is preferably a radical polymerization initiator. Radical polymerization initiators are generally peroxides and azo compounds. Examples of peroxides include dialkyl peroxides such as di-t-butyl peroxide, dicumyl peroxide, t-butylcumyl peroxide, α,α'-bis(t-butylperoxy-m-isopropyl)benzene, and 2,5-di(t-butylperoxy)hexyne-3; peroxy esters such as t-butyl peroxybenzoate, t-butyl peroxyacetate, and 2,5-dimethyl-2,5-di(benzoylperoxy)hexane; ketone peroxides such as cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide, and methylcyclohexanone peroxide; Examples of the peroxyketals include 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane, 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, and n-butyl-4,4-bis(t-butylperoxy)valerate; hydroperoxides such as cumene hydroperoxide, diisopropylbenzene hydroperoxide, and 2,5-dimethylcyclohexane-2,5-dihydroperoxide; diacyl peroxides such as benzoyl peroxide, decanoyl peroxide, lauroyl peroxide, and 2,4-dichlorobenzoyl peroxide; and peroxydicarbonates such as bis(t-butylcyclohexyl)peroxydicarbonate.

[0050] Examples of the azo compound include 2,2'-azobisbutyronitrile such as 2,2'-azobisisobutyronitrile (abbreviation: AIBN) and 2,2'-azobis(2-methylbutyronitrile); 2,2'-azobisvaleronitrile such as 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) and 2,2'-azobis(2,4-dimethylvaleronitrile); 2,2'-azobispropionitrile such as 2,2'-azobis(2-hydroxymethylpropionitrile); and 1,1'-azobis-1-alkanenitrile such as 1,1'-azobis(cyclohexane-1-carbonitrile).

[0051] The polymerization initiator is preferably used in an amount of 0.01 to 10 parts by mass, more preferably 0.1 to 2 parts by mass, based on 100 parts by mass of the monomer mixture.

[0052] (Weight-average molecular weight (Mw)) The weight-average molecular weight of the acrylic polymer (A) is preferably 800,000 to 1,800,000, and more preferably 1,000,000 to 1,700,000. By setting the weight-average molecular weight within the above-mentioned range, it becomes easier to ensure adhesion to optical components, removability, and durability when exposed to a high-temperature atmosphere. The weight-average molecular weight is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0053] <Curing Agent (B)> The pressure-sensitive adhesive composition of the present disclosure contains 0.01 to 5 parts by mass of curing agent (B) per 100 parts by mass of acrylic polymer (A). The curing agent incorporated into the pressure-sensitive adhesive composition is preferably one that reacts with the carboxy group of the monomer (a3) ​​and / or the hydroxy group of the monomer (a4) by heat or other means to form a bond. By incorporating the curing agent in the above ratio, the cohesive strength of the pressure-sensitive adhesive layer is improved, and adhesion to optical components, removability, and durability when exposed to a high-temperature atmosphere or a high-temperature, high-humidity atmosphere can all be achieved. The curing agent (B) is preferably incorporated in an amount of 0.1 to 2 parts by mass per 100 parts by mass of acrylic polymer (A).

[0054] The curing agent can be selected from known curing agents such as epoxy-based curing agents, isocyanate-based curing agents, oxazoline-based curing agents, aziridine-based curing agents, carbodiimide-based curing agents, metal chelate-based curing agents, and melamine-based curing agents, taking into consideration the reactivity with the functional groups of the polymer in the pressure-sensitive adhesive composition. From the viewpoint of removability, it is preferable to include an isocyanate-based curing agent.

[0055] Examples of epoxy curing agents include N,N,N',N'-tetraglycidyl-m-xylylenediamine, tetraglycidyl-3,3'-diaminodiphenylsulfone, tetraglycidyldiaminodiphenylmethane, 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane, N,N,N',N'-tetraglycidylaminophenylmethane (all of which are examples of tetrafunctional epoxy compounds), glycerin diglycidyl ether, 1,6-hexanediol diglycidyl ether, and the like, and one or more of these can be selected as appropriate.

[0056] The isocyanate curing agent is an isocyanate having two or more isocyanate groups. Examples of the isocyanate include aromatic polyisocyanates, aliphatic polyisocyanates, araliphatic polyisocyanates, alicyclic polyisocyanates, and their biuret forms, nurate forms, and adduct forms, and from the viewpoint of yellowing resistance, aliphatic polyisocyanates, alicyclic polyisocyanates, and their biuret forms, nurate forms, and adduct forms are more preferred.

[0057] The biuret compound is a self-condensation product having a biuret bond formed by self-condensation of an isocyanate monomer, such as a biuret compound of hexamethylene diisocyanate.

[0058] The nurate derivative is a trimer of an isocyanate monomer, such as a trimer of hexamethylene diisocyanate, a trimer of isophorone diisocyanate, or a trimer of tolylene diisocyanate.

[0059] The adduct is a bifunctional or higher isocyanate compound obtained by reacting an isocyanate monomer with a bifunctional or higher low-molecular-weight active hydrogen-containing compound. Examples of the adduct include a compound obtained by reacting trimethylolpropane with hexamethylene diisocyanate, a compound obtained by reacting trimethylolpropane with tolylene diisocyanate, a compound obtained by reacting trimethylolpropane with xylylene diisocyanate, a compound obtained by reacting trimethylolpropane with isophorone diisocyanate, and a compound obtained by reacting 1,6-hexanediol with hexamethylene diisocyanate.

[0060] The isocyanate compound is preferably a trifunctional isocyanate compound from the viewpoint of forming a sufficient crosslinked structure. The isocyanate compound is more preferably an adduct or nurate, which is a reaction product of an isocyanate monomer and a trifunctional low-molecular-weight active hydrogen-containing compound. The isocyanate compound is preferably a trimethylolpropane adduct of hexamethylene diisocyanate, a nurate of hexamethylene diisocyanate, a trimethylolpropane adduct of tolylene diisocyanate, a nurate of tolylene diisocyanate, a trimethylolpropane adduct of isophorone diisocyanate, or a nurate of isophorone diisocyanate, and more preferably a trimethylolpropane adduct of hexamethylene diisocyanate, a trimethylolpropane adduct of tolylene diisocyanate, or a trimethylolpropane adduct of isophorone diisocyanate.

[0061] The oxazoline-based curing agent has two or more oxazoline groups in the molecule and may be a low molecular weight compound or a polymer. Examples of the low molecular weight oxazoline-based curing agent include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline, 2,2'-bis-(2-oxazoline), 2,2'-methylene-bis-(2-oxazoline), 2,2'-ethylene-bis-(2-oxazoline), 2,2'-trimethylene-bis-(2-oxazoline), and 2,2'-tetramethylene-bis-(2-oxazoline). , 2,2'-hexamethylene-bis-(2-oxazoline), 2,2'-octamethylene-bis-(2-oxazoline), 2,2'-ethylene-bis-(4,4'-dimethyl-2-oxazoline), 2,2'-p-phenylene-bis-(2-oxazoline), 2,2'-m-phenylene-bis-(2-oxazoline), 2,2'-m-phenylene-bis-(4,4'-dimethyl-2-oxazoline), 2,2'-(1,3-phenylene)-bis-(2-oxazoline), bis-(2-oxazolinylcyclohexane) sulfide, bis-(2-oxazolinylnorbornane) sulfide, etc. Examples of polymeric oxazoline-based curing agents include polymers containing an addition-polymerizable oxazoline as an essential component. Examples of the addition-polymerizable oxazoline include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline.

[0062] Examples of the aziridine curing agent include N,N'-diphenylmethane-4,4'-bis(1-aziridinecarboxite), tris-2,4,6-(1-aziridinyl)-1,3,5-triazine, and 4,4'-bis(ethyleneiminocarbonylamino)diphenylmethane.

[0063] The carbodiimide compound is preferably a high-molecular-weight polycarbodiimide produced by a decarboxylation condensation reaction of a diisocyanate compound in the presence of a carbodiimidization catalyst. Commercially available high-molecular-weight polycarbodiimides are preferably the Carbodilite series manufactured by Nisshinbo Industries, Inc. Among these, Carbodilite V-03, 07, and 09 are preferred due to their excellent compatibility with organic solvents.

[0064] The metal chelate is preferably a coordination compound of a polyvalent metal such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, or zirconium with acetylacetone or ethyl acetoacetate. Examples of the metal chelate include aluminum ethyl acetoacetate diisopropylate, aluminum trisacetylacetonate, aluminum bisethyl acetoacetate monoacetylacetonate, and aluminum alkyl acetoacetate diisopropylate.

[0065] Typical examples of the melamine-based hardener include fully alkyl-etherified melamine resins, methylol group-type melamine resins, and imino group-type melamine resins partially containing imino groups.

[0066] <Organic Silane (C)> The pressure-sensitive adhesive composition of the present disclosure preferably contains an organic silane (C). By containing the organic silane (C), it becomes easier to achieve both adhesion to optical members, removability, and durability when exposed to a high-temperature atmosphere or a high-temperature, high-humidity atmosphere. The organic silane (C) is preferably contained in an amount of 0.001 to 1 part by mass, and more preferably 0.005 to 0.8 parts by mass, per 100 parts by mass of the acrylic polymer (A). By setting the amount within the above range, it becomes easier to achieve both adhesion to optical members, removability, and durability when exposed to a high-temperature atmosphere or a high-temperature, high-humidity atmosphere.

[0067] Examples of the organic silane (C) include alkoxysilane compounds having a (meth)acryloxy group, alkoxysilane compounds having a vinyl group, alkoxysilane compounds having an amino group, alkoxysilane compounds having a mercapto group, and alkoxysilane compounds having an epoxy group, among which alkoxysilane compounds having an epoxy group are preferred. Specific examples of commercially available products include alkoxysilane compounds having an epoxy group such as KBM-403 (3-glycidoxypropyltrimethoxysilane), KBE-403 (3-glycidoxypropyltriethoxysilane), and KBM-303 (2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane) (all manufactured by Shin-Etsu Chemical Co., Ltd.), and examples of other organic amines include BYK-325N (polyether-modified polymethylalkylsiloxane) (manufactured by BYK Japan KK).

[0068] The pressure-sensitive adhesive composition of the present disclosure may also contain other compounds, such as chlorinated polyolefins, antistatic agents, silicone oils, and tackifying resins, within the scope of the present invention.

[0069] (Chlorinated Polyolefin) Examples of chlorinated polyolefin include chlorinated polypropylene, acid-modified chlorinated polypropylene, acrylic-modified chlorinated polypropylene, chlorinated polyethylene, chlorinated ethylene vinyl acetate copolymer, etc., and chlorinated polypropylene or chlorinated ethylene vinyl acetate copolymer is preferred from the viewpoint of good compatibility with acrylic polymers, etc. and effective reduction of polarity. Specific examples of commercially available products include Superchlor 390S (chlorinated polypropylene, chlorine content 36%) and Superchlor BX (chlorinated EVA, chlorine content 18%) (both manufactured by Nippon Paper Industries Co., Ltd.).

[0070] (Antistatic Agent) Examples of antistatic agents include inorganic salts, ionic liquids, ionic solids, surfactants, etc. Among these, ionic liquids are preferred. Note that "ionic liquids" are also called room temperature molten salts and exhibit liquid properties at 25°C.

[0071] Examples of inorganic salts include sodium chloride, potassium chloride, lithium chloride, lithium perchlorate, ammonium chloride, potassium chlorate, aluminum chloride, copper chloride, ferrous chloride, ferric chloride, ammonium sulfate, potassium nitrate, sodium nitrate, sodium carbonate, and sodium thiocyanate.

[0072] The ionic liquid is a salt of a cation and an anion, and the cation is preferably, for example, an imidazolium ion, a pyridinium ion, an ammonium ion, etc. Examples of ionic liquids containing imidazolium ions include 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide, and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide.

[0073] Examples of ionic liquids containing pyridinium ions include 1-methylpyridinium bis(trifluoromethylsulfonyl)imide, 1-butylpyridinium bis(trifluoromethylsulfonyl)imide, 1-hexylpyridinium bis(trifluoromethylsulfonyl)imide, 1-octylpyridinium bis(trifluoromethylsulfonyl)imide, 1-hexyl-4-methylpyridinium bis(trifluoromethylsulfonyl)imide, 1-hexyl-4-methylpyridinium hexafluorophosphate, 1-octyl-4-methylpyridinium bis(trifluoromethylsulfonyl)imide, 1-octyl-4-methylpyridinium bis(fluorosulfonyl)imide, 1-methylpyridinium bis(perfluoroethylsulfonyl)imide, and 1-methylpyridinium bis(perfluorobutylsulfonyl)imide.

[0074] Examples of ionic liquids containing ammonium ions include trimethylheptylammonium bis(trifluoromethanesulfonyl)imide, N,N-diethyl-N-methyl-N-propylammonium bis(trifluoromethanesulfonyl)imide, N,N-diethyl-N-methyl-N-pentylammonium bis(trifluoromethanesulfonyl)imide, N,N-diethyl-N-methyl-N-heptylammonium bis(trifluoromethanesulfonyl)imide, and tri-n-butylmethylammonium bistrifluoromethanesulfonimide.

[0075] In addition, known ionic liquids in which the cation is a pyrrolidinium ion, a phosphonium ion, a sulfonium ion, or the like can be used as appropriate.

[0076] Like ionic liquids, ionic solids are salts of cations and anions, but exhibit solid properties at normal pressure and 25° C. Preferred cations include, for example, alkali metal ions, phosphonium ions, pyridinium ions, and ammonium ions.

[0077] Examples of ionic solids containing alkali metal ions include lithium bisfluorosulfonylimide, lithium bistrifluoromethylsulfonylimide, lithium bispentafluoroethylsulfonylimide, lithium bisheptafluoropropylsulfonylimide, lithium bisnonanefluorobutylsulfonylimide, sodium bisfluorosulfonylimide, sodium bistrifluoromethylsulfonylimide, sodium bispentafluoroethylsulfonylimide, sodium bisheptafluoropropylsulfonylimide, sodium bisnonanefluorobutylsulfonylimide, potassium bisfluorosulfonylimide, potassium bistrifluoromethylsulfonylimide, potassium bispentafluoroethylsulfonylimide, potassium bisheptafluoropropylsulfonylimide, and potassium bisnonanefluorobutylsulfonylimide.

[0078] Examples of the ionic solid containing a phosphonium ion include tetrabutylphosphonium bisfluorosulfonylimide, tetrabutylphosphonium bistrifluoromethylsulfonylimide, tetrabutylphosphonium bispentafluoroethylsulfonylimide, tetrabutylphosphonium bisheptafluoropropylsulfonylimide, tetrabutylphosphonium bisnonanefluorobutylsulfonylimide, tributylhexadecylphosphonium bisfluorosulfonylimide, tributylhexadecylphosphonium bistrifluoromethylsulfonylimide, tributylhexadecylphosphonium bispentafluoroethylsulfonylimide, tributylhexadecylphosphonium bisheptafluoropropylsulfonylimide, tributylhexadecylphosphonium bisnonanefluorobutylsulfonylimide, tetraoctylphosphonium bisfluorosulfonylimide, tetraoctylphosphonium bistrifluoromethylsulfonylimide, tetraoctylphosphonium bispentafluoroethylsulfonylimide, tetraoctylphosphonium bisheptafluoropropylsulfonylimide, and tetraoctylphosphonium bisnonanefluorobutylsulfonylimide.

[0079] Examples of ionic solids containing pyridinium ions include 1-hexadecyl-4-methylpyridinium bisfluorosulfonylimide, 1-hexadecyl-4-methylpyridinium bistrifluoromethylsulfonylimide, 1-hexadecyl-4-methylpyridinium bispentafluoroethylsulfonylimide, 1-hexadecyl-4-methylpyridinium bisheptafluoropropylsulfonylimide, and 1-hexadecyl-4-methylpyridinium bisnonanefluorobutylsulfonylimide.

[0080] Examples of ionic solids containing ammonium ions include tributylmethylbistrifluoromethylsulfonylimide, tributylmethylbispentafluoroethylsulfonylimide, tributylmethylbisheptafluoropropylsulfonylimide, tributylmethylbisnonanefluorobutylsulfonylimide, octyltributylbistrifluoromethylsulfonylimide, octyltributylbispentafluoroethylsulfonylimide, octyltributylbisheptafluoropropylsulfonylimide, octyltributylbisnonanefluorobutylsulfonylimide, tetrabutylbisfluorosulfonylimide, tetrabutylbistrifluoromethylsulfonylimide, tetrabutylbispentafluoroethylsulfonylimide, tetrabutylbisheptafluoropropylsulfonylimide, tetrabutylbisnonanefluorobutylsulfonylimide, etc. In addition, known ionic solids in which the cation is a pyrrolidinium ion, imidazolium ion, sulfonium ion, etc. can be used as appropriate.

[0081] Surfactants can be classified into nonionic, anionic, cationic, and amphoteric types.

[0082] Examples of nonionic surfactants include glycerin fatty acid esters, polyoxyalkylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene alkylamines, polyoxyethylene alkylamine fatty acid esters, fatty acid diethanolamides, polyether ester amide types, ethylene oxide-epichlorohydrin types, and polyether ester types.

[0083] Examples of anionic surfactants (excluding ionic liquids and ionic solids) include alkyl sulfonates, alkyl benzene sulfonates, alkyl phosphates, and polystyrene sulfonates. Examples of cationic surfactants include tetraalkyl ammonium salts, trialkyl benzyl ammonium salts, and quaternary ammonium base-containing acrylate polymers.

[0084] Examples of amphoteric surfactants include amino acid type amphoteric surfactants such as alkyl betaines, alkyl imidazolium betaines, and higher alkyl aminopropionates, and betaine type amphoteric surfactants such as higher alkyl dimethyl betaines and higher alkyl dihydroxyethyl betaines.

[0085] The antistatic agents may be used alone or in combination of two or more.

[0086] When an antistatic agent is added, the blending amount is preferably 0.01 to 3 parts by mass, more preferably 0.03 to 2 parts by mass, and even more preferably 0.06 to 1 part by mass, per 100 parts by mass of the acrylic polymer (A). Blending an appropriate amount of antistatic agent makes it difficult for the removability to decrease when exposed to a high-temperature, high-humidity atmosphere, and improves the yield when producing a pressure-sensitive adhesive sheet.

[0087] (Silicone Oil) Examples of silicone oils include dimethyl silicone oil, methylphenyl silicone oil, methylhydrogen silicone oil, side-chain type polyether-modified silicone oil, aralkyl-modified silicone oil, fluoroalkyl-modified silicone oil, long-chain alkyl-modified silicone oil, higher fatty acid ester-modified silicone oil, higher fatty acid amide-modified silicone oil, polyether-long-chain alkyl-modified silicone oil-aralkyl-modified silicone oil, phenyl-modified silicone oil, both-end type polyether-modified silicone oil, and polyether-methoxy-modified silicone oil.

[0088] When silicone oil is added, the blending amount is preferably 1 to 10 parts by mass, more preferably 1 to 5 parts by mass, per 100 parts by mass of the acrylic polymer (A). Blending an appropriate amount of silicone oil makes it difficult for the removability to decrease when exposed to a high-temperature, high-humidity atmosphere, and improves the yield when producing a pressure-sensitive adhesive sheet.

[0089] (Tackifying Resin) Examples of tackifying resins include aliphatic petroleum resins, aromatic petroleum resins, synthetic hydrocarbon resins, terpene resins, rosin resins (rosin, polymerized rosin, hydrogenated rosin, and their esters with glycerin, pentaerythritol, etc., resin acid dimers, etc.), and acrylic resins.

[0090] When a tackifier resin is added, the blending amount is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, even more preferably 10 parts by mass or less, and most preferably substantially none, per 100 parts by mass of the acrylic polymer (A). By setting the amount of the tackifier resin to be added within this range, it is possible to prevent a decrease in adhesive strength due to softening of the pressure-sensitive adhesive layer even in a high-temperature atmosphere, and further to ensure the removability required for re-attachment to an optical component.

[0091] Examples of aliphatic petroleum resins include Quinton B170 manufactured by Zeon Corporation; examples of aromatic petroleum resins include Nisseki Neopolymer L-90 manufactured by ENEOS Materials Corporation; examples of aliphatic / aromatic petroleum resins include FTR6100 manufactured by Mitsui Chemicals, Inc.; and examples of rosin derivatives include SylvatacRE85 manufactured by Arizona Chemical Company and Superester A-75 manufactured by Arakawa Chemical Industries, Ltd.

[0092] Examples of synthetic hydrocarbon resins include aliphatic petroleum resins, aromatic petroleum resins, aliphatic / aromatic petroleum resins, hydrogenated petroleum resins, coumarone-indene resins, and phenol resins.

[0093] Examples of terpene resins include α-pinene resins, β-pinene resins, dipentene resins, aromatic modified terpene resins, hydrogenated terpene resins, terpene phenol resins, acid modified terpene resins, styrenated terpene resins, and styrene-aliphatic hydrocarbon copolymer resins.

[0094] Examples of rosin-based resins include rosin ester, polymerized rosin, hydrogenated rosin, disproportionated rosin, maleic acid-modified rosin, fumaric acid-modified rosin, rosin phenolic resin, and natural rosin.

[0095] The viscosity of the pressure-sensitive adhesive composition is not particularly limited, but the viscosity when adjusted to a predetermined nonvolatile content according to the weight-average molecular weight of the acrylic polymer (A) contained therein is preferably 7000 mPa s or less. Specifically, when the weight-average molecular weight of the acrylic polymer (A) is 1.5 million or more, the viscosity at a nonvolatile content of 20.0 ± 0.5% is preferably less than 7000 mPa s. When the weight-average molecular weight of the acrylic polymer (A) is 1 million or more but less than 1.5 million, the viscosity at a nonvolatile content of 25.0 ± 0.5% is preferably less than 7000 mPa s. When the weight-average molecular weight of the acrylic polymer (A) is less than 1 million, the viscosity at a nonvolatile content of 30.0 ± 0.5% is preferably less than 7000 mPa s. Such a viscosity facilitates handling during coating, making it easier to obtain a defect-free pressure-sensitive adhesive layer.

[0096] <<Adhesive Layer>> The adhesive layer of the present disclosure has a gel fraction of 55 to 90% by mass. 60 to 80% by mass is more preferable. A gel fraction of 55% by mass or more improves the cohesive strength of the adhesive composition, resulting in a strong adhesive layer, and making it less likely for the adhesive layer to protrude from the edges when folded. A gel fraction of 55% by mass or more improves the cohesive strength of the adhesive and provides a strong adhesive layer, thereby preventing lifting and peeling when exposed to a high-temperature atmosphere and ensuring the removability required for re-attachment to an optical component. A gel fraction of 90% by mass or less facilitates the formation of a flexible adhesive layer, further improving the adhesion of the adhesive layer to the substrate (hereinafter referred to as substrate adhesion), and further preventing lifting and peeling when exposed to a high-temperature atmosphere or a high-temperature, high-humidity atmosphere. Generally, the gel fraction of a polymer is equal to the degree of crosslinking; the more crosslinked portions in the polymer, the higher the gel fraction. The gel fraction (amount of crosslinked structure introduced) can be adjusted to the desired range by adjusting the method for introducing the crosslinked structure, the type and amount of crosslinking agent, etc. The method for measuring the gel fraction will be described in detail in the Examples.

[0097] <<Adhesive Sheet>> The adhesive sheet includes an adhesive layer made of the adhesive composition of the present disclosure.

[0098] The pressure-sensitive adhesive sheet of the present disclosure preferably has a configuration in which a release film is attached to at least one surface of the pressure-sensitive adhesive layer, specifically, a configuration in which release films are formed on both surfaces of the pressure-sensitive adhesive layer, or a configuration in which a release film is formed on one surface of the pressure-sensitive adhesive layer and a light-transmitting substrate is provided on the other surface of the pressure-sensitive adhesive, and the pressure-sensitive adhesive layer is formed from the pressure-sensitive adhesive composition of the present disclosure.

[0099] <Release Film> The release film is not particularly limited, but a transparent plastic substrate can be suitably used. Examples of materials for the transparent plastic substrate include polyesters such as polyethylene terephthalate (PET), acrylic resins such as polymethyl methacrylate (PMMA), and plastic materials such as polycarbonate, triacetyl cellulose, polysulfone, polyarylate, and polycycloolefin. The plastic materials can be used alone or in combination of two or more.

[0100] As the release film, among the transparent plastic substrates described above, a transparent plastic substrate having excellent heat resistance, i.e., a transparent plastic substrate that is suppressed or prevented from deforming under severe conditions such as high temperature, high temperature and high humidity, etc. PET film or sheet is particularly suitable as the transparent plastic substrate.

[0101] The thickness of the transparent plastic substrate is not particularly limited, but is preferably, for example, 10 to 200 μm, and more preferably 25 to 150 μm.

[0102] The pressure-sensitive adhesive sheet of the present disclosure has adhesiveness and removability to optical components, and durability when exposed to high-temperature or high-temperature, high-humidity atmospheres, making it suitable as a pressure-sensitive adhesive for forming optical display components such as LCD, OLED, and other display devices, and input devices such as touch panels, and for bonding these components together. However, since it has excellent durability in high-temperature, high-humidity environments when attached to a polarizing plate, it is preferable that at least one side of the pressure-sensitive adhesive layer is attached to the polarizing plate. The optical component is not particularly limited, and examples thereof include PET films, COP films, polarizing plates, retardation plates, elliptically polarizing plates, optical compensation films, brightness-enhancing films, infrared / electromagnetic wave-blocking films, front-face anti-reflection films, surface protective films, films with an ITO (indium tin oxide) layer, films with a zinc oxide (ZnO) layer, films obtained by coating or printing metal nanoparticles, films obtained by coating or printing dispersions containing carbon nanotubes, films obtained by coating or printing dispersions containing graphene, films obtained by coating or printing dispersions containing conductive polymers, metal plates made of SUS or the like, metal meshes, and even laminates thereof.

[0103] When applying the pressure-sensitive adhesive composition, the viscosity can be adjusted by adding a suitable liquid medium.Specific examples include hydrocarbon solvents such as toluene, xylene, hexane, and heptane; ester solvents such as ethyl acetate and butyl acetate; ketone solvents such as acetone and methyl ethyl ketone; halogenated hydrocarbon solvents such as dichloromethane and chloroform; ether solvents such as diethyl ether, methoxytoluene, and dioxane, or other hydrocarbon solvents.However, water and alcohols must be used carefully because they may inhibit the reaction between the acrylic polymer (A) and the isocyanate curing agent (B).

[0104] The coating method is not particularly limited, and examples thereof include various coating methods using a Mayer bar, applicator, brush, spray, roller, gravure coater, die coater, lip coater, comma coater, knife coater, reverse coater, spin coater, etc. The drying and curing method is also not particularly limited, and examples thereof include hot air drying, infrared rays, reduced pressure methods, and methods using active energy rays, but hot air or steam heating at 60 to 180°C is preferred from the viewpoint of outgassing resistance.

[0105] The thickness of the pressure-sensitive adhesive layer is preferably 2 to 1000 μm, more preferably 5 to 500 μm, still more preferably 10 to 100 μm, and most preferably 20 to 50 μm. The pressure-sensitive adhesive layer may be in the form of a single layer or a laminate of two or more layers.

[0106] The laminate includes a light-transmitting substrate and a pressure-sensitive adhesive layer, and the pressure-sensitive adhesive layer is formed using the pressure-sensitive adhesive sheet of the present disclosure. Specifically, for example, the laminate can be formed by peeling the release film from the pressure-sensitive adhesive sheet of the present disclosure and attaching the pressure-sensitive adhesive layer to the light-transmitting substrate.

[0107] <Light-Transmitting Substrate> A transparent plastic substrate is used as the light-transmitting substrate. Examples of materials for such light-transmitting substrates include acrylic resins such as polyethylene terephthalate (PET), polyethylene naphthalate, and polymethyl methacrylate (PMMA), and plastic materials such as polycarbonate (PC), polycycloolefin (COP), polyimide, polyphenylene ether, polysulfone, polyethersulfone, polystyrene, and polypropylene. In particular, PET film or PC is preferred, and PC is even more preferred in terms of durability. The plastic materials can be used alone or in combination of two or more. In addition, the light-transmitting substrate may be subjected to an appropriate surface treatment, such as a physical treatment such as corona discharge treatment or plasma treatment, or a chemical treatment such as a primer treatment.

[0108]

[0033] The polarizing plate with a pressure-sensitive adhesive layer includes a polarizing plate and a pressure-sensitive adhesive layer, and the pressure-sensitive adhesive layer is formed using the pressure-sensitive adhesive sheet of the present disclosure. Specifically, for example, the polarizing plate with a pressure-sensitive adhesive layer can be formed by peeling the release film from the pressure-sensitive adhesive sheet of the present disclosure and attaching the pressure-sensitive adhesive layer to the polarizing plate.

[0109] An example of a schematic cross-sectional view partially illustrating the laminate of the present disclosure is shown in Figure 1. In Figure 1, 3 is a light-transmitting substrate (cover panel), 1 is a pressure-sensitive adhesive layer, and 4 is a polarizing plate.

[0110] In the laminate shown in Fig. 1, a light-transmitting substrate (cover panel) is attached to a polarizing plate via an adhesive layer. In the laminate shown in Fig. 1, a light-transmitting substrate (cover panel) is attached to a polarizing plate via an adhesive layer.

[0111]

[0023] Figure 3 shows a schematic cross-sectional view partially illustrating an example of a pressure-sensitive adhesive sheet according to the present disclosure. In Figure 3, 3 denotes a light-transmitting substrate (cover panel), 1 denotes a pressure-sensitive adhesive layer, and 2 denotes a release film. In the release sheet shown in Figure 3, the release film 2 can be peeled off, and the light-transmitting substrate (cover panel) 1 can be attached to a polarizing plate or the like via the pressure-sensitive adhesive layer 1.

[0112] <Production of Laminate and Adhesive-Attached Polarizing Plate> A laminate and a polarizing plate with adhesive can be produced, for example, by peeling the release film from a pressure-sensitive adhesive sheet having release films on both sides of the pressure-sensitive adhesive layer, and then attaching the pressure-sensitive adhesive layer to a light-transmitting substrate or a polarizing plate. Alternatively, the laminate and the polarizing plate can be produced by peeling the release film from a pressure-sensitive adhesive sheet having a release film on one side of the pressure-sensitive adhesive layer and a light-transmitting substrate on the other side, and then attaching the pressure-sensitive adhesive layer to a light-transmitting substrate or a polarizing plate. Furthermore, a pressure-sensitive adhesive layer can be formed directly on a light-transmitting substrate, and then a pressure-sensitive adhesive layer provided on an adherend or another pressure-sensitive adhesive sheet can be attached to the pressure-sensitive adhesive layer to form a laminate.

[0113] The display of the present disclosure includes a light-transmitting substrate, a pressure-sensitive adhesive layer, a polarizing plate, and an optical element. This provides the display with excellent visibility. The optical element is not particularly limited, and examples thereof include a liquid crystal element and an organic EL element.

[0114] Figure 2 shows an example of a schematic cross-sectional view partially illustrating a display, which is an example of use of an example of the pressure-sensitive adhesive sheet of the present disclosure. In Figure 2, 3 is a light-transmitting substrate (cover panel), 1 is a pressure-sensitive adhesive layer 1, 4 is a polarizing plate, 5 is a pressure-sensitive adhesive layer 2, 6 is a barrier layer such as silicon nitride, 7 is an organic EL layer, 8 is a support such as polyimide, and 9 is an organic EL cell. It should be noted that the configuration of the display is not limited to that shown in Figure 2.

[0115] In the display shown in FIG. 2 , a light-transmitting substrate (cover panel) is attached to a polarizing plate via a pressure-sensitive adhesive layer (pressure-sensitive adhesive layer 1) of the present disclosure, and is further attached to an organic EL cell via a pressure-sensitive adhesive layer for a polarizing plate (pressure-sensitive adhesive layer 2). In this way, the pressure-sensitive adhesive sheet of the present disclosure can be used in a form in which a transparent pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition is attached to a light-transmitting substrate (cover panel) and a polarizing plate, and the laminate is further attached to an organic EL cell via a pressure-sensitive adhesive layer for a polarizing plate. For example, in FIG. 2 , the pressure-sensitive adhesive composition of the present disclosure can be used for both pressure-sensitive adhesive layer 1 and pressure-sensitive adhesive layer 2. Generally, when pressure-sensitive adhesive layer 1 and pressure-sensitive adhesive layer 2 are compared, the pressure-sensitive adhesive layer requires higher quality, whereas the pressure-sensitive adhesive composition of the present disclosure is preferably used for pressure-sensitive adhesive layer 1 because of its excellent adhesion and adhesion to the substrate. In this case, the pressure-sensitive adhesive for forming pressure-sensitive adhesive layer 2 may be the pressure-sensitive adhesive composition of the present disclosure, or a conventionally known pressure-sensitive adhesive may be used.

[0116] The uses of the display are not particularly limited, but examples include organic EL televisions, organic EL smartphones, organic EL tablets, and organic EL smart watches.

[0117] The present disclosure will be explained in more detail below using examples, but the present disclosure is not limited to these examples. In the examples, unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass". The amounts in the tables are in parts by mass, and amounts other than the solvent are calculated as non-volatile contents. Blank spaces in the tables indicate that no ingredients were added. The method for measuring the weight average molecular weight of the acrylic polymer is as follows:

[0118] <Measurement of Weight-Average Molecular Weight (Mw)> The weight-average molecular weight (Mw) was measured by gel permeation chromatography (GPC). The apparatus used was a GPC apparatus: LC-GPC system "Prominence" manufactured by Shimadzu Corporation. The columns used were TSKgel α-M manufactured by Tosoh Corporation, with two columns connected in series. N,N-dimethylformamide (DMF) was used as the eluent, and measurements were carried out at 40°C. Mw was determined by conversion using polystyrene with a known Mw as the standard substance. Based on the measurement results of the weight-average molecular weight, the samples were classified into H, M, and L categories according to the following criteria: H: molecular weight of 1.5 million or more M: molecular weight of 1 million or more but less than 1.5 million L: molecular weight less than 1 million

[0119] <Acrylic Polymer Production Example> (Acrylic Polymer (A-1)) Using a reaction apparatus equipped with a stirrer, reflux condenser, nitrogen inlet pipe, thermometer, and dropping tube, 10 parts of methyl acrylate (MA, Tg = 8°C) as monomer (a1), 88.5 parts of 2-octyl acrylate (2OA) as monomer (a2), 1.5 parts of 4-hydroxybutyl acrylate (4HBA) as monomer (a4), and 110 parts of methyl acetate as solvent were charged into a reaction vessel, and polymerization was carried out at 70°C for 5 hours under a nitrogen atmosphere, with the viscosity being adjusted appropriately by dropwise addition of ethyl acetate during polymerization. After completion of the reaction, the mixture was cooled and diluted with ethyl acetate to obtain an acrylic polymer solution (A-1) with a non-volatile content of 30.0 ± 0.5%. The weight average molecular weight (Mw) of the obtained acrylic polymer is shown in Table 1.

[0120] (Acrylic Polymers (A-2 to A-34, A'-1 to A'-4)) Acrylic polymers (A-2 to A-33, A'-1 to A'-4) were synthesized in the same manner as in the production of acrylic polymer (A-1), except that the compositions and blending amounts (parts by mass) were changed to those shown in Tables 1 to 4. The weight-average molecular weights of the obtained acrylic polymers are shown in Tables 1 to 3.

[0121]

[0122]

[0123]

[0124] The abbreviations are as follows: [Monomer (a1)] MA: methyl acrylate (alkyl group carbon number: 1, Tg = 8°C) BzA: benzyl acrylate (Tg = 6°C) CHA: cyclohexyl acrylate (Tg = 15°C) IBXA: isobornyl acrylate (Tg = 97°C) MMA: methyl methacrylate (alkyl group carbon number: 1, Tg = 105°C) IBXMA: isobornyl methacrylate (Tg = 180°C) [Monomer (a2)] 2OA: 2-octyl acrylate 2OMA: 2-octyl methacrylate [Monomer (a3)] AA: acrylic acid [Monomer (a4)] HEA: hydroxyethyl acrylate 4HBA: 4-hydroxybutyl acrylate [Other monomers] 2EHA: 2-ethylhexyl acrylate (alkyl group carbon number: 8, Tg = -70°C) DDA: normal dodecyl acrylate (alkyl group carbon number: 12, Tg = -23°C)

[0125] The materials used in the examples and comparative examples are listed below. <Curing agent B> [Isocyanate-based curing agents] B-1: ("NP-1200", manufactured by Mitsui Chemicals, Inc., biuret form of hexamethylene diisocyanate) B-2: ("D-172N", manufactured by Mitsui Chemicals, Inc., nurate form of hexamethylene diisocyanate) B-3: ("D-160N", manufactured by Mitsui Chemicals, Inc., trimethylolpropane-modified hexamethylene diisocyanate) B-4: ("Desmodur 2565", manufactured by Covestro, nurate form of isophorone diisocyanate) B-5: ("Coronate L", manufactured by Tosoh Corporation, trimethylolpropane-modified toluene diisocyanate) [Other curing agents] B-6: zirconium tetraacetylacetonate ("Orgatix ZC-700", manufactured by Matsumoto Fine Chemical Co., Ltd.) B-7: N,N,N',N'-tetraglycidyl-m-xylylenediamine (TETRAD-X)

[0126] <Organic silane (C)> KBE-403: (3-glycidoxypropyltriethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd.) KBM-303: ([2-(3,4-epoxycyclohexyl)ethyl]trimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd.)

[0127] <Tackifying Resins> SE10: (Haritack SE10, hydrogenated rosin, manufactured by Harima Chemicals Co., Ltd.) FTR6100: (FTR6100, aliphatic / aromatic petroleum resin, manufactured by Mitsui Chemicals, Inc.) A-100: (Super Ester A-100, rosin-based resin, manufactured by Arakawa Chemical Industries, Ltd.) T130: (YS Polystar T130, terpene phenol resin, manufactured by Yasuhara Chemical Co., Ltd.)

[0128] Example 1 100 parts of acrylic polymer (A-1) were blended with 0.4 parts of B-1 ("NP-1200", manufactured by Mitsui Chemicals, Inc., biuret form of hexamethylene diisocyanate) as curing agent (B) and 0.1 parts of KBE-403 (3-glycidoxypropyltriethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd.) as organosilane (C), and diluted with ethyl acetate to a non-volatile content of 25.0±0.5%, to obtain a pressure-sensitive adhesive composition. The obtained pressure-sensitive adhesive composition was applied to a 38 μm thick polyethylene terephthalate release sheet (Cerapeel MF, manufactured by Toray Advanced Film Co., Ltd.) using a comma coater to a dry thickness of 25 μm, and then dried at 100° C. for 2 minutes to obtain a pressure-sensitive adhesive sheet. Next, one side of a 100 μm thick polyethylene terephthalate film (hereinafter referred to as PET film, product name: A-4300, manufactured by Toyobo Co., Ltd.) was bonded to the adhesive surface of this adhesive sheet, yielding a laminate having a "release sheet / adhesive layer / cycloolefin film" configuration. The resulting laminate was then aged for one week at a temperature of 25°C and a relative humidity of 55% to obtain a laminate (hereinafter referred to as Laminate A). Furthermore, a polarizing plate (layer structure: triacetyl cellulose film / polyvinyl alcohol film / polymethyl methacrylate film) was used instead of the PET film, and the adhesive layer was bonded to the polymethyl methacrylate film side of the polarizing plate so that it was in contact with the polarizing plate, yielding a polarizing plate with an adhesive having a "release sheet / adhesive layer / polarizing plate" configuration. The resulting polarizing plate with an adhesive was then aged for one week at a temperature of 25°C and a relative humidity of 55%. This was designated Laminate B.

[0129] Examples 2 to 51, Comparative Examples 1 to 6 As shown in Table 4, the types and blending amounts of the acrylic polymer, curing agent, and organosilane were changed, and depending on the weight average molecular weight category of the acrylic polymer, if it was H, it was diluted with ethyl acetate so that the non-volatile content was 20.0±0.5%, if it was M, it was diluted with ethyl acetate so that the non-volatile content was 25.0±0.5%, and if it was L, it was not diluted, and other than that, a pressure-sensitive adhesive composition, a pressure-sensitive adhesive sheet laminate A, and a laminate B were obtained in the same manner as in Example 1. However, Examples 18, 24, 28, and 29 are reference examples.

[0130] [Method for measuring gel fraction] A 30 mm x 100 mm sample for measuring gel fraction was cut from the pressure-sensitive adhesive sheet obtained above, and the release sheet was peeled off to obtain a free film of the pressure-sensitive adhesive layer. The gel fraction of the pressure-sensitive adhesive layer was determined as the mass fraction (unit: mass%) of the insoluble components after immersing the pressure-sensitive adhesive layer in ethyl acetate at 50°C for 1 day relative to the pressure-sensitive adhesive layer before immersion, as represented by the following formula 1: (Formula 1) Gel fraction (mass%) = ((X-Y) / X) x 100 X = mass (g) of the pressure-sensitive adhesive layer before immersion Y = mass (g) of the pressure-sensitive adhesive layer after immersion

[0131]

[0132] <<Physical Properties and Evaluation of Pressure-Sensitive Adhesive Composition and Laminate>> The low viscosity of the pressure-sensitive adhesive composition of the present disclosure and the adhesion (to glass, acrylic plate, ITO / PET), heat resistance, moist heat resistance, corrosion resistance, light leakage, and removability of the laminate were evaluated by the following methods. The results are shown in Table 5.

[0133] <Low Viscosity> The viscosity of the pressure-sensitive adhesive compositions of Examples 1 to 51 and Comparative Examples 1 to 6 was measured using a Brookfield viscometer (rotor No. 3, rotation speed 12 rpm). Low viscosity was evaluated based on the following criteria. [Evaluation criteria] ◎: Viscosity less than 7000 mPa·s (excellent) ○: Viscosity 7000 mPa·s or more and less than 8000 mPa·s (good) △: Viscosity 8000 mPa·s or more and less than 9000 mPa·s (fairly good) ▲: Viscosity 9000 mPa·s or more and less than 10000 mPa·s (usable) ×: Viscosity 10000 mPa·s or more (unusable)

[0134] <Adhesion> A test laminate A was prepared by preparing the laminate A obtained above in a size of 25 mm wide x 100 mm long. The release sheet was peeled off from the test laminate A, and the pressure-sensitive adhesive layer was attached to a glass plate in an atmosphere of 23°C and 50% relative humidity, followed by pressure bonding with a roll in accordance with JIS Z-0237. After 24 hours of pressure bonding, the adhesive strength (peel angle 180°, peel rate 300 mm / min; unit N / 25 mm width) was measured using a universal tensile tester. Separately, the adherend was replaced from the glass plate with an acrylic plate and an ITO / PET film, and the adhesive strength was measured in the same manner as above. The ITO / PET film was a PET film vapor-deposited with indium tin oxide, and the test pressure-sensitive adhesive sheet was attached to the ITO-deposited surface. Adhesion was evaluated based on adhesive strength according to the following criteria. [Evaluation Criteria] ⊚: Adhesion strength of 5.0 N / 25 mm or more. (Excellent) ○: Adhesive strength is 3.0 N / 25 mm or more and less than 5.0 N / 25 mm (Good) △: Adhesive strength is 2.0 N / 25 mm or more and less than 3.0 N / 25 mm (Fairly good) ▲: Adhesive strength is 1.0 N / 25 mm or more and less than 2.0 N / 25 mm (Usable) ×: Adhesive strength is less than 1.0 N / 25 mm (Poor)

[0135] <Evaluation 1 of Heat Resistance and Moist Heat Resistance> The laminate A obtained above was cut into a size of 930 mm wide and 523 mm long (equivalent to 42 inches). Next, the release sheet was peeled off from the cut laminate A, and the laminate A was attached to an ITO-sputtered glass plate (80Ω: manufactured by Nippon Sheet Glass Co., Ltd.) using a laminator. Next, the glass plate to which the laminate A was attached was held in an autoclave at 50°C and 5 atmospheres for 20 minutes to tightly adhere each component, thereby obtaining a measurement sample. The heat resistance of this measurement sample was evaluated as an evaluation of resistance in a high-temperature atmosphere. That is, the measurement sample was left at 105°C for 1000 hours, and then visually observed for the presence or absence of bubbling, lifting, and peeling. The measurement sample was also evaluated for the moist heat resistance as an evaluation of resistance in a high-temperature, high-humidity atmosphere. That is, the measurement sample was left at 85°C and a relative humidity of 85% for 500 hours, and then visually observed for the presence or absence of bubbling, lifting, and peeling. The heat resistance and moist heat resistance were both evaluated based on the following criteria. [Evaluation criteria] ◎: No foaming, lifting, or peeling was observed (Excellent) ○: Foaming, lifting, or peeling of 0.5 mm or less was observed (Good) △: Foaming, lifting, or peeling of more than 0.5 mm but not more than 1 mm was observed (Fairly good) ▲: Foaming, lifting, or peeling of more than 1 mm but not more than 1.5 mm was observed (Usable) ×: Foaming, lifting, or peeling was observed over the entire surface (Unusable)

[0136] <Corrosion Resistance> A PET film (IPF-05H125: manufactured by Gunze Co., Ltd.) having a 5 μm thick ITO transparent conductive film was cut to a width of 40 mm and a length of 100 mm and attached to a 40 mm wide, 160 mm long ITO transparent conductive film. The release sheet was peeled off from the laminate A and attached to the laminate. Subsequently, this laminate was held in an autoclave at 50°C and 5 atmospheres for 20 minutes to adhere the components together, thereby obtaining a measurement sample having a layered structure of PET film / adhesive layer / ITO film. Electrodes were connected to both ends of this measurement sample, and the initial electrical resistance was measured. Furthermore, the measurement sample was left at 85°C and 85% relative humidity for 1000 hours, and then the electrical resistance after aging was measured in the same manner as above. Corrosion resistance was evaluated based on the following criteria. The electrical resistance was measured using a Laresta-GP MCP-T600 (manufactured by Mitsubishi Chemical Corporation). Electrical resistance increase rate = ((electrical resistance value after aging - initial electrical resistance value) / initial electrical resistance value) [Evaluation criteria] ◎: Electrical resistance increase rate is less than 0.5 (excellent) ○: Electrical resistance increase rate is 0.5 or more and less than 1.0 (good) △: Electrical resistance increase rate is 1.0 or more and less than 1.5 (fairly good) ▲: Electrical resistance increase rate is 1.5 or more and less than 2.0 (usable) ×: Electrical resistance increase rate is 2.0 or more (unusable)

[0137] <Evaluation 2 of Heat Resistance and Moist Heat Resistance> The laminate B obtained above was cut into a size of 930 mm wide and 523 mm long (equivalent to 42 inches). Next, the release sheet was peeled off from the cut laminate B, and the laminate was attached to an ITO-sputtered glass plate (80Ω: manufactured by Nippon Sheet Glass Co., Ltd.) using a laminator. Next, the glass plate with laminate B attached was held in an autoclave at 50°C and 5 atmospheres for 20 minutes to tightly adhere each component, thereby obtaining a measurement sample. The heat resistance of this measurement sample was evaluated as an evaluation of resistance in a high-temperature atmosphere. That is, the measurement sample was left at 105°C for 1000 hours, and then visually observed for the presence or absence of bubbling, lifting, and peeling. The measurement sample was also evaluated for the moist heat resistance as an evaluation of resistance in a high-temperature, high-humidity atmosphere. That is, the measurement sample was left at 85°C and a relative humidity of 95% for 1000 hours, and then visually observed for the presence or absence of bubbling, lifting, and peeling. The heat resistance and moist heat resistance were both evaluated based on the following criteria. [Evaluation criteria] ◎: No foaming, lifting, or peeling was observed (Excellent) ○: Foaming, lifting, or peeling of 0.5 mm or less was observed (Good) △: Foaming, lifting, or peeling of more than 0.5 mm but not more than 1 mm was observed (Fairly good) ▲: Foaming, lifting, or peeling of more than 1 mm but not more than 1.5 mm was observed (Usable) ×: Foaming, lifting, or peeling was observed over the entire surface (Unusable)

[0138] <Light Leakage> The laminate B obtained above was cut into a size of 930 mm wide and 523 mm long (equivalent to 42 inches). Next, the release sheet was peeled off from the cut laminate B, and two sheets of laminate B were attached to both sides of an ITO-sputtered glass plate (80Ω: manufactured by Nippon Sheet Glass Co., Ltd.) using a laminator so that the absorption axes of the polarizing plates were perpendicular to each other, thereby obtaining a pressure-bonded product. The pressure-bonded product was then held in an autoclave at 50°C and 5 atmospheres for 20 minutes to tightly bond the components together, thereby obtaining a measurement sample. This measurement sample was left at 105°C for 1,000 hours, and then light leakage was visually observed when light was transmitted through the polarizing plate. Light leakage was evaluated based on the following criteria. [Evaluation Criteria] ⊚: No white spots were observed (Excellent) ○: White spots were observed in 1 to 2 places (Good) △: White spots were observed in 3 to 5 places (fairly good) ▲: White spots are observed in 6 to 10 places (usable) ×: White spots are observed in 11 or more places (unusable)

[0139] <Removability> The laminate B obtained above was cut into a size of 100 mm wide and 100 mm long. The release sheet was then peeled off from the cut laminate B, and the laminate was attached to an ITO-sputtered glass plate (80Ω: manufactured by Nippon Sheet Glass Co., Ltd.) using a laminator. Subsequently, the laminate was placed in an autoclave at 50°C and 5 atmospheres for 20 minutes to adhere the components together, thereby obtaining a measurement sample. After leaving the measurement sample at 105°C for 7 days, a peel test was performed in which the sample was pulled in a 180° direction at a rate of 300 mm / min using a tensile tester ("Tensilon" manufactured by Orientec Co., Ltd.) at 23°C and 50% relative humidity. The glass surface after peeling was then visually observed for cloudiness. The above evaluation was performed on five samples per laminate type, and the evaluation was based on the following criteria. [Evaluation Criteria] ⊚: No adhesive residue or cloudiness was observed in any of the five samples. (Excellent) ○: Of the five samples, only one sample had adhesive residue or cloudiness of 5% or less of the measured area. (Good) △: Of the five samples, two samples each had adhesive residue or cloudiness of 5% or less of the measured area. (Fairly good) ▲: Of the five samples, three samples each had adhesive residue or cloudiness of 5% or less of the measured area. (Usable) ×: Of the five samples, four or more samples each had adhesive residue or cloudiness of 5% or less of the measured area, or one or more samples each had adhesive residue or cloudiness of more than 5%. (Unusable)

[0140]

[0141] As shown in Table 5, the pressure-sensitive adhesive composition of the present disclosure achieved excellent results in terms of low viscosity, adhesion (glass, acrylic plate, ITO / PET), heat resistance and moist heat resistance evaluation, corrosion resistance, light leakage, and removability. On the other hand, the pressure-sensitive adhesive composition of the comparative example failed to satisfy all of the following: low viscosity, adhesion (glass, acrylic plate, ITO / PET), heat resistance and moist heat resistance evaluation, corrosion resistance, light leakage, and removability. These results indicate that the pressure-sensitive adhesive composition of the present disclosure can be suitably used for bonding optical components.

[0142] Although the present invention has been described with reference to the above-mentioned several embodiments, the present invention is not limited to these several embodiments. Various modifications can be made to the configuration and details of the present invention within the scope of the present invention.

[0143] The disclosure of this application is related to the subject matter described in Japanese Patent Application No. 2023-151063 filed on September 19, 2023, and the subject matter described in Japanese Patent Application No. 2023-175423 filed on October 10, 2023, the entire disclosures of which are incorporated herein by reference.

[0144] The symbols in Figures 1, 2 and 3 are explained below: 1 adhesive layer 1, 2 release film, 3 film substrate (cover panel), 4 polarizing plate, 5 adhesive layer 2, 6 barrier layer, 7 organic EL layer, 8 support, 9 organic EL cell

Claims

1. A pressure-sensitive adhesive composition comprising an acrylic polymer (A) and a curing agent (B), wherein the acrylic polymer (A) is a copolymer of a monomer mixture comprising the following monomers (a1), (a2), (a3), and (a4), and other monomers, and wherein the pressure-sensitive adhesive composition satisfies the following formula (1), wherein the content of (a2) is 40 to 95 parts by mass per 100 parts by mass of the monomer mixture, the content of (a3) ​​is 10 parts by mass or less per 100 parts by mass of the monomer mixture, the content of (a4) is 0.1 to 20 parts by mass per 100 parts by mass of the monomer mixture, and the content of the other monomers is 15 parts by mass or less per 100 parts by mass of the monomer mixture, the amount of the curing agent (B) added is 0.01 to 5 parts by mass relative to 100 parts by mass of the acrylic polymer (A), and the pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive composition has a gel fraction of 55 to 90%. (a1) A (meth)acrylic acid ester monomer having no functional group and having a glass transition temperature of 0° C. or higher when the homopolymer is formed. (a2) 2-octyl (meth)acrylate. (a3) ​​A monomer having a carboxy group. (a4) A monomer having a hydroxy group. Formula (1) 1500≦Σ(T ２ × MA / 100)≦38000 T: glass transition temperature (K) of homopolymer of (a1) MA: content (parts by mass) of (a1) in 100 parts by mass of monomer mixture 2. A pressure-sensitive adhesive composition comprising an acrylic polymer (A) and a curing agent (B), wherein the acrylic polymer (A) is a copolymer of a monomer mixture comprising the following monomers (a1), (a2), (a3), and (a4), and other monomers, and satisfies the following formula (1), wherein the content of (a2) is 40 to 95 parts by mass in 100 parts by mass of the monomer mixture, the content of (a3) ​​is 10 parts by mass or less in 100 parts by mass of the monomer mixture, the content of (a4) is 0.1 to 20 parts by mass in 100 parts by mass of the monomer mixture, and the content of the other monomers is 15 parts by mass or less in 100 parts by mass of the monomer mixture, A pressure-sensitive adhesive composition comprising: when isobornyl (meth)acrylate is contained as the monomer (a1) and a nitrogen-containing monomer is contained as the other monomer, the content of at least one of isobornyl (meth)acrylate, the nitrogen-containing monomer and the monomer (a4) in 100 parts by mass of the monomer mixture is less than 10 parts by mass; the amount of the curing agent (B) added is 0.01 to 5 parts by mass relative to 100 parts by mass of the acrylic polymer (A); and the gel fraction of a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive composition is 55 to 90%. (a1) A (meth)acrylic acid ester monomer having no functional group and having a homopolymer glass transition temperature of 0°C or higher; (a2) 2-octyl (meth)acrylate; (a3) ​​A monomer having a carboxy group; and (a4) A monomer having a hydroxy group. ２ × MA / 100)≦38000 T: glass transition temperature (K) of homopolymer of (a1) MA: content (parts by mass) of (a1) in 100 parts by mass of monomer mixture 3. A pressure-sensitive adhesive composition comprising an acrylic polymer (A) and a curing agent (B), wherein the acrylic polymer (A) is a copolymer of a monomer mixture comprising the following monomers (a1), (a2), (a3), and (a4), and other monomers, and satisfies the following formula (1), the content of (a2) is 40 to 95 parts by mass in 100 parts by mass of the monomer mixture, the content of (a3) ​​is 10 parts by mass or less in 100 parts by mass of the monomer mixture, the content of (a4) is 0.1 to 20 parts by mass in 100 parts by mass of the monomer mixture, the content of the other monomers is 15 parts by mass or less in 100 parts by mass of the monomer mixture, and when a nitrogen-containing monomer is contained as the other monomer, the content of at least one of the nitrogen-containing monomer and the monomer (a4) in 100 parts by mass of the monomer mixture is less than 10 parts by mass, The amount of the curing agent (B) added is 0.01 to 5 parts by mass relative to 100 parts by mass of the acrylic polymer (A), and the gel fraction of the adhesive layer made of the adhesive composition is 55 to 90%. (a1) A (meth)acrylic acid ester monomer having no functional group, the homopolymer of which has a glass transition temperature of 0°C or higher, (a2) 2-octyl (meth)acrylate, (a3) ​​A monomer having a carboxy group, and (a4) A monomer having a hydroxy group. Formula (1) 1500≦Σ(T ２ × MA / 100)≦38000 T: glass transition temperature (K) of homopolymer of (a1) MA: content (parts by mass) of (a1) in 100 parts by mass of monomer mixture 4. The pressure-sensitive adhesive composition according to claim 1, wherein the content of monomer (a4) is 0.1 to 5 parts by mass per 100 parts by mass of the monomer mixture.

5. The pressure-sensitive adhesive composition according to claim 1, wherein the curing agent (B) comprises an isocyanate-based curing agent.

6. The pressure-sensitive adhesive composition according to claim 1, further comprising an organosilane (C).

7. The pressure-sensitive adhesive composition according to claim 1, wherein the upper limit of formula (1) is 24,000 or less.

8. The pressure-sensitive adhesive composition according to any one of claims 1 to 7, which is used for fixing a polarizing plate.

9. An adhesive sheet having an adhesive layer made of the adhesive composition according to any one of claims 1 to 7.

10. A laminate comprising a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive composition according to any one of claims 1 to 7 and a light-transmitting substrate.

11. A polarizing plate having an adhesive layer comprising the adhesive composition according to claim 8.

12. A display comprising an adhesive layer made of the adhesive composition according to any one of claims 1 to 7, a light-transmitting substrate, a polarizing plate, and an optical element.

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