Adhesive, adhesive composition, adhesive sheet, multilayer body, and display provided with said multilayer body

Abstract

The present invention provides an adhesive which contains an acrylic polymer (A) that is a copolymer of a monomer mixture, wherein, in 100% by mass of the monomer mixture, there are contained more than 30% by mass but less than 99.5% by mass of the monomer (a1) described below, and not less than 0.1% by mass but less than 70% by mass of the monomer (a2) and the monomer (a3) described below in total, and there may be additionally contained at least one selected from the group consisting of 30% by mass or less of the monomer (a4) described below and less than 0.5% by mass of a monomer that has a carboxy group. Monomer (a1): 2-octyl (meth)acrylate Monomer (a2): a monomer having a glass transition temperature of a homopolymer of 0°C or higher (excluding the monomer (a3), a monomer having a carboxy group and a monomer having a hydroxy group) Monomer (a3): isobornyl (meth)acrylate Monomer (a4): a monomer other than the monomer (a1), the monomer (a2), the monomer (a3), a monomer having a carboxy group, and a monomer having a hydroxy group.

Description

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

[0001] The present disclosure relates to a pressure-sensitive adhesive and a pressure-sensitive adhesive composition, a pressure-sensitive adhesive sheet, a laminate, and a display including the laminate.

[0002] Due to their ease of handling, adhesive sheets with adhesive layers formed from adhesives are used in a wide range of fields, including label applications and medical applications. They are also widely used in various optical displays, such as liquid crystal displays (LCDs) and organic electroluminescence displays (OLEDs). Optical displays are also used as input devices, such as touch panels, in addition to their use as display devices. Touch panels are equipped with cover panels for surface protection. The components constituting these optical displays are typically bonded together via an adhesive layer. Among these, adhesives used in applications expected to be used for long periods, such as marking films, window films, automotive components, and optical displays, require high adhesion to the substrate to prevent peeling during use. When adhesive sheets are bonded to metal substrates, corrosion-resistant adhesives are required because corrosion of the substrate due to components contained in the adhesive can cause product degradation.

[0003] On the other hand, for convenient coating during the production of adhesive sheets, adhesives are generally diluted and adjusted to 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 solid 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 be made with a higher solid content.

[0004] The adhesives described in Patent Documents 1 and 2 are adjusted to a solids content of about 35%. The inventors' investigations revealed that the adhesives described in Patent Documents 1 and 2 could not have an increased solids content because adjusting the solids content to 35% or more would result in excessively high viscosity, making coating difficult. As a result, the high cost of the solvent used and the difficulty of applying a thick layer of adhesive have become major issues.

[0005] Furthermore, Patent Document 3 discloses a pressure-sensitive adhesive composition with low viscosity, but the adhesive strength to the adherend is problematic. In addition to the increasing performance requirements described above, the depletion of petroleum resources and carbon dioxide emissions from the combustion of petroleum-derived products are becoming issues in industries that use pressure-sensitive adhesive sheets. Therefore, efforts to conserve petroleum resources by replacing petroleum-derived materials with bio-derived materials have been attempted in various industries, starting with the packaging field and including the optical and semiconductor fields. One method for increasing the proportion of bio-derived materials in pressure-sensitive adhesives primarily composed of acrylic polymers is to obtain an acrylic polymer by copolymerizing a monomer mixture containing a (meth)acrylic acid alkyl ester monomer obtained by esterifying a linear alkyl alcohol produced by a living organism with (meth)acrylic acid. Furthermore, there are also tackifying resins made from naturally derived components, and selective use of these can achieve environmentally friendly products. Increasing the proportion of environmentally friendly materials can contribute to the conservation of petroleum resources, but this requires the use of limited environmentally friendly materials, which currently poses challenges to the performance originally achieved, such as adhesive strength and other fixation properties.

[0006] JP 2007-264092 A JP 2012-173354 A JP 2010-506979 A

[0007] The problem that the present invention aims to solve is to provide an adhesive that can contribute to the conservation of petroleum resources by increasing the proportion of environmentally friendly materials, and that has high adhesive strength performance to adherends, excellent corrosion resistance, and low viscosity with high solidification, as well as an adhesive sheet and laminate using the same, and a display equipped with the laminate.

[0008] The present inventors have conducted extensive research and have found that the problems of the present invention can be solved in the following manner, thereby completing the present invention. Specifically, the present disclosure relates to a pressure-sensitive adhesive containing an acrylic polymer (A) that is a copolymer of a monomer mixture, wherein the pressure-sensitive adhesive contains, based on 100% by mass of the monomer mixture, more than 30% by mass and less than 99.5% by mass of the following monomer (a1), and 0.1% by mass or more and less than 70% by mass of the following monomer (a2) and monomer (a3), and may further contain 30% by mass or less of the following monomer (a4), and at least one selected from the group consisting of less than 0.5% by mass of monomers having a carboxy group. (a1) 2-octyl (meth)acrylate (a2) Monomers whose homopolymer glass transition temperature is 0°C or higher (excluding monomer (a3), monomers having a carboxy group, and monomers having a hydroxy group) (a3) ​​isobornyl (meth)acrylate (a4) Other monomers other than monomer (a1), monomer (a2), monomer (a3), monomers having a carboxy group, and monomers having a hydroxy group.

[0009] The present disclosure makes it possible to provide an adhesive that can contribute to the conservation of petroleum resources, has high adhesive strength performance to adherends, has low viscosity and is capable of high solidification, as well as an adhesive sheet and laminate using the same, and a display equipped with the laminate.

[0010] 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.

[0011] The pressure-sensitive adhesive composition, pressure-sensitive adhesive sheet, laminate, and display including the laminate according to the present disclosure have the following configurations [1] to

[28] .

[0012] [1] A pressure-sensitive adhesive comprising an acrylic polymer (A) that is a copolymer of a monomer mixture, wherein the monomer mixture contains, based on 100% by mass, more than 30% by mass and less than 99.5% by mass of the following monomer (a1), and 0.1% by mass or more and less than 70% by mass of the following monomer (a2) and monomer (a3), in total, and may further contain 30% by mass or less of the following monomer (a4), and less than 0.5% by mass of at least one monomer selected from the group consisting of monomers having a carboxy group: (a1) 2-octyl(meth)acrylate, (a2) a monomer whose homopolymer glass transition temperature is 0°C or higher (excluding monomer (a3), monomers having a carboxy group, and monomers having a hydroxy group), (a3) ​​isobornyl(meth)acrylate, and (a4) another monomer other than monomer (a1), monomer (a2), monomer (a3), monomers having a carboxy group, and monomers having a hydroxy group. [2] A pressure-sensitive adhesive comprising an acrylic polymer (A) that is a copolymer of a monomer mixture, wherein the monomer mixture contains, in 100% by mass, more than 30% by mass and less than 99.5% by mass of the following monomer (a1), and the following monomer (a2) and monomer (a3) ​​in a total amount of 0.1% by mass or more and less than 70% by mass, and may further contain 30% by mass or less of the following monomer (a4), less than 0.5% by mass of a monomer having a carboxy group, and at least one selected from the group consisting of a monomer having a hydroxy group, and a monomer having a carboxy group in a total amount of 0.5% by mass or more and 30% by mass or less, and when the pressure-sensitive adhesive contains a nitrogen-containing monomer as monomer (a2) and also contains monomer (a3) ​​and a monomer having a hydroxy group, the content of at least one of the nitrogen-containing monomer, monomer (a3) ​​and hydroxy group-containing monomer in 100% by mass of the monomer mixture is less than 10% by mass.(a1) 2-octyl (meth)acrylate (a2) a monomer having a glass transition temperature of 0°C or higher as a homopolymer (excluding the monomer (a3), a monomer having a carboxy group, and a monomer having a hydroxy group); (a3) ​​isobornyl (meth)acrylate (a4) a monomer other than the monomer (a1), the monomer (a2), the monomer (a3), a monomer having a carboxy group, and a monomer having a hydroxy group [3] A pressure-sensitive adhesive comprising an acrylic polymer (A) which is a copolymer of a monomer mixture, A PSA comprising, based on 100% by mass of the monomer mixture, more than 30% by mass and less than 99.5% by mass of the following monomer (a1), and 0.1% by mass or more and less than 70% by mass of the following monomer (a2) and monomer (a3), and optionally further comprising 30% by mass or less of the following monomer (a4), less than 0.5% by mass of a monomer having a carboxy group, and at least one monomer having a hydroxy group, the total of which, together with the monomer having the carboxy group, accounts for 0.5% by mass or more and 30% by mass or less; and when the monomer (a2) contains a nitrogen-containing monomer and a monomer having a hydroxy group, the content of at least one of the nitrogen-containing monomer and the hydroxy group-containing monomer in 100% by mass of the monomer mixture is less than 10% by mass. (a1) 2-octyl (meth)acrylate, (a2) a monomer having a glass transition temperature of 0°C or higher when forming a homopolymer (excluding monomer (a3), monomers having a carboxy group, and monomers having a hydroxy group), (a3) ​​isobornyl (meth)acrylate, and (a4) another monomer other than monomer (a1), monomer (a2), monomer (a3), monomers having a carboxy group, and monomers having a hydroxy group. [4] The pressure-sensitive adhesive according to any one of [1] to [3], wherein the total amount of monomer (a2) and monomer (a3) ​​is 0.1% by mass or more and less than 50% by mass based on 100% by mass of the monomer mixture. [5] The pressure-sensitive adhesive according to any one of [1] to [4], wherein monomer (a2) comprises at least one selected from the group consisting of methyl (meth)acrylate, ethyl methacrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, and phenyl (meth)acrylate.[6] The pressure-sensitive adhesive according to any one of [1] to [5] above, wherein the monomer mixture further contains a monomer having a hydroxy group. [7] The pressure-sensitive adhesive according to [6] above, wherein a total of 0.5% by mass or more and 30% by mass or less of a monomer having a carboxy group and a monomer having a hydroxy group is contained in 100% by mass of the monomer mixture. [8] The pressure-sensitive adhesive according to any one of [1] to [7] above, wherein the biomass content is 30% or more. [9] A pressure-sensitive adhesive composition comprising the pressure-sensitive adhesive according to any one of [1] to [8] above and a curing agent (B).

[10] The pressure-sensitive adhesive composition according to [9] above, wherein the curing agent (B) contains at least one of an isocyanate-based curing agent and an epoxy-based curing agent.

[11] The pressure-sensitive adhesive composition according to [9] or

[10] above, further containing a silane coupling agent (C).

[12] The pressure-sensitive adhesive composition according to any one of [9] to

[11] above, wherein the gel fraction is 40% or more.

[13] The pressure-sensitive adhesive composition according to any one of [9] to

[12] , further comprising less than 50 parts by mass of a tackifier resin (D) per 100 parts by mass of the acrylic polymer (A).

[14] The pressure-sensitive adhesive composition according to any one of

[13] , wherein the tackifier resin (D) has a biomass content of 80% or more.

[15] A pressure-sensitive adhesive layer obtained using the pressure-sensitive adhesive according to any one of [1] to [8] or the pressure-sensitive adhesive composition according to any one of [9] to

[14] .

[16] The pressure-sensitive adhesive layer according to any one of

[15] to

[16] , wherein the haze is 1.0 or less.

[17] The pressure-sensitive adhesive layer according to any one of

[15] or

[16] , wherein the dielectric constant at 40 GHz is 5.0 or less.

[18] The pressure-sensitive adhesive layer according to any one of

[17] to

[18] , wherein the dielectric dissipation factor at 40 GHz is 0.1 or less.

[19] The pressure-sensitive adhesive layer according to any one of

[15] to

[18] , wherein the refractive index is 1.45 or more but less than 1.52.

[20] The pressure-sensitive adhesive layer according to any one of

[15] to

[18] above, having a glass adhesive strength of 10 N / 25 mm or more.

[21] The pressure-sensitive adhesive layer according to

[20] above, having an SUS adhesive strength of 5 N / 25 mm or more.

[22] A pressure-sensitive adhesive sheet comprising the pressure-sensitive adhesive layer according to any one of

[15] to

[21] above and a release film.

[23] The pressure-sensitive adhesive sheet according to

[22] above, wherein the release film has a thickness of less than 200 μm.

[24] A laminate comprising the pressure-sensitive adhesive layer according to any one of

[15] to

[21] above and a substrate.

[25] The laminate according to

[24] above, wherein the substrate has a thickness of less than 500 μm.

[26] The laminate according to any one of

[24] to

[25] above, wherein the substrate is a light-transmitting substrate.

[27] The laminate according to any one of

[24] to

[26] above, wherein the total light transmittance is 60% or more.

[28] A display comprising the laminate according to any one of

[24] to

[27] above, a polarizing plate, and an optical element.

[0013] The composition, pressure-sensitive adhesive sheet, laminate, and display of the present disclosure are described below, but are not limited thereto. In this specification, (meth)acrylate includes acrylate and methacrylate, and (meth)acryloxy group includes acryloxy group and methacryloxy group. 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 limit values. 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.

[0014] <<Adhesive>> The adhesive of the present disclosure contains an acrylic polymer (A).

[0015] <Acrylic Polymer (A)> The acrylic polymer (A) is a copolymer of a monomer mixture, and the acrylic polymer (A) contains, based on 100% by mass of the monomer mixture, more than 30% by mass and less than 99.5% by mass of the following monomer (a1), and 0.1% by mass or more and less than 70% by mass of the following monomer (a2) and monomer (a3), in total, and may further contain 30% by mass or less of the following monomer (a4), and less than 0.5% by mass of at least one monomer selected from the group consisting of monomers having a carboxy group: (a1) 2-octyl(meth)acrylate (a2) a monomer whose homopolymer glass transition temperature is 0°C or higher (excluding monomer (a3), monomers having a carboxy group, and monomers having a hydroxy group) (a3) ​​isobornyl(meth)acrylate (a4) another monomer other than monomer (a1), monomer (a2), monomer (a3), monomers having a carboxy group, and monomers having a hydroxy group

[0016] [Monomer (a1)] Monomer (a1) refers to 2-octyl(meth)acrylate and is represented by the following formula (1). Monomer (a1) is a biomass monomer. (Formula 1) (R1 = H, CH ３ The content of (a1) is greater than 30% by mass and less than 99.5% by mass based on 100% by mass of the monomer mixture. A content of (a1) less than 30% by mass is undesirable because the viscosity of the PSA increases or the adhesive strength decreases. The lower limit of the content of (a1) is preferably 50% by mass or more, more preferably 70% by mass or more, although the desired effect can be achieved if the content is greater than 30% by mass. A higher content of (a1) is preferable because it contributes to the conservation of petroleum resources. The content of (a1) may be 99.5% by mass or less, 95% by mass or less, or 91% by mass or less. For example, it may be greater than 30% by mass and less than 99.5% by mass, 50 to 95% by mass, or 70 to 91% by mass.

[0017] [Monomer (a2)] Monomer (a2) is a monomer having a glass transition temperature of 0°C or higher when it forms a homopolymer. However, even if the monomer has a glass transition temperature of 0°C or higher when it forms a homopolymer, monomer (a3) ​​and those having a carboxy group and a hydroxy group are excluded. The glass transition temperature (°C) of the homopolymer can be known from information provided by the vendor of the various monomers or from the values ​​described in "Polymer Handbook 3rd Edition" (A Wiley-Interscience Publication, 1989).

[0018] Examples of monomer (a2) include nitrogen-containing monomers such as acrylamide, N,N-dimethylacrylamide, methacrylonitrile, acrylonitrile, and diacetone acrylamide, alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl methacrylate, ter-butyl methacrylate, sec-butyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, isopropyl methacrylate, and stearyl (meth)acrylate, and (meth)acrylates having an alicyclic or aromatic ring such as cyclohexyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, and phenyl (meth)acrylate. From the viewpoint of improving cohesive strength and / or adhesive strength, monomer (a2) is preferably at least one selected from the group consisting of methyl (meth)acrylate, ethyl methacrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, and phenyl (meth)acrylate.

[0019] When the monomer mixture contains a nitrogen-containing monomer as the monomer (a2), and also contains the monomer (a3) ​​and a monomer having a hydroxy group, the content of at least one of the nitrogen-containing monomer, the monomer (a3), and the hydroxy group-containing monomer is less than 10% by mass. If the content of the nitrogen-containing monomer as the monomer (a2), the monomer (a3), and the hydroxy group-containing monomer 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 types is less than 10% by mass.

[0020] When the monomer mixture contains a nitrogen-containing monomer and a hydroxyl-containing monomer as the monomer (a2), the content of at least one of the nitrogen-containing monomer and the hydroxyl-containing monomer is less than 10% by mass. If the content of the nitrogen-containing monomer and the hydroxyl-containing monomer as the monomer (a2) is too 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% by mass.

[0021] The total content of (a2) and monomer (a3) ​​is 0.1% by mass or more and less than 70% by mass based on 100% by mass of the monomer mixture. By including 0.1% by mass or more and less than 70% by mass, cohesive strength and / or adhesive strength can be ensured. It is more preferably 1% by mass or more and less than 50% by mass, and even more preferably 3% by mass or more and less than 30% by mass.

[0022] [Monomer (a3)] Monomer (a3) ​​is isobornyl (meth)acrylate, which is a biomass monomer. In order to increase the biomass content of the PSA, it is preferable to contain monomer (a3).

[0023] [Monomer (a4)] The monomer (a4) is a monomer other than the monomer (a1), the monomer (a2), the monomer (a3), the monomer having a carboxy group, and the monomer having a hydroxy group, and is not particularly limited. In consideration of the environment, it is preferable to use a (meth)acrylate, which is a biomass monomer, as the monomer (a4), and it is more preferable to use a (meth)acrylate with a high biomass content.

[0024] (a4) may or may not be contained, but if it is contained, the content is 30% by mass or less relative to 100% by mass of the monomer mixture. By containing 30% by mass or less, an increase in viscosity of the PSA can be suppressed. In order to suppress the increase in viscosity, the content is preferably 20% by mass or less, more preferably 10% by mass or less.

[0025] The monomer mixture constituting the acrylic polymer (A) preferably further contains at least one of a monomer having a carboxy group and a monomer having a hydroxy group. It may contain both a monomer having a carboxy group and a monomer having a hydroxy group, or only one of them. By containing at least one of a monomer having a carboxy group and a monomer having a hydroxy group, the cohesive strength of the adhesive layer is increased, and the adhesive strength and heat resistance are easily improved. It is more preferable to contain a monomer having a hydroxy group in order to prevent corrosion of the adherend by acid.

[0026] The total content of the carboxyl group-containing monomer and the hydroxyl group-containing monomer is preferably 0.5% by mass or more and 30% by mass or less, more preferably 0.5% by mass or more and 21% by mass or less, and even more preferably 0.5% by mass or more and less than 10% by mass, based on 100% by mass of the monomer mixture. A content of 0.5% by mass or more and 30% by mass or less can accelerate curing and prevent wet heat whitening. When a carboxyl group-containing monomer is included to prevent corrosion of the adherend by acid, the content of the carboxyl group-containing monomer is less than 0.5% by mass based on 100% by mass of the monomer mixture. The total content of the carboxyl group-containing monomer and the hydroxyl group-containing monomer may be 30% by mass or less, 21% by mass or less, less than 10% by mass, or 0.5% by mass or more. These ranges can provide better effects. For example, the content may be 0.5 to 30% by mass, 0.5 to 21% by mass, or 0.5% by mass or more and less than 10% by mass.

[0027] The monomer having a carboxy group is not limited as long as it has 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. Of these, (meth)acrylic acid is preferred from the viewpoint of adhesive strength, and acrylic acid is more preferred.

[0028] The monomer having a hydroxy group is not limited as long as it is a monomer having a hydroxy group in the molecule, and specific examples include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, etc. Of these, 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are preferred from the viewpoints of adhesive strength and moist heat resistance.

[0029] (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.

[0030] 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; 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane; Examples of the peroxyketals include 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.

[0031] 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).

[0032] 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.

[0033] (Weight-average molecular weight (Mw)) The weight-average molecular weight of the acrylic polymer (A) is not particularly limited, but is preferably 2,000,000 or less, and more preferably 1,000,000 or less. The weight-average molecular weight is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0034] <<Pressure-Sensitive Adhesive Composition>> The pressure-sensitive adhesive composition of the present disclosure contains a pressure-sensitive adhesive containing an acrylic polymer (A) and a curing agent (B). It may also contain a silane coupling agent (C) and a tackifier resin (D) as needed.

[0035] <Curing Agent (B)> The pressure-sensitive adhesive composition of the present disclosure contains a curing agent (B), and the curing agent (B) can be used without any particular limitation as long as it provides a crosslinked structure to the pressure-sensitive adhesive composition. The incorporation of a curing agent improves the cohesive strength of the pressure-sensitive adhesive layer, thereby improving adhesive strength, heat resistance, and light resistance. The curing agent (B) is preferably one of an isocyanate-based curing agent and an epoxy-based curing agent, which can appropriately increase the cohesive strength of the pressure-sensitive adhesive and is less likely to adversely affect other physical properties. As long as the pressure-sensitive adhesive composition contains at least one of an isocyanate-based curing agent and an epoxy-based curing agent, known curing agents other than an isocyanate-based curing agent and an epoxy-based curing agent may be used in combination.

[0036] 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.

[0037] Examples of aromatic polyisocyanates include 1,3-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,4-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-toluidine diisocyanate, 2,4,6-triisocyanate toluene, 1,3,5-triisocyanate benzene, dianisidine diisocyanate, 4,4'-diphenyl ether diisocyanate, and 4,4',4"-triphenylmethane triisocyanate.

[0038] Examples of aliphatic polyisocyanates include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (also known as HMDI), pentamethylene diisocyanate, 1,2-propylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, dodecamethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate.

[0039] Examples of the aromatic aliphatic polyisocyanate include ω,ω'-diisocyanate-1,3-dimethylbenzene, ω,ω'-diisocyanate-1,4-dimethylbenzene, ω,ω'-diisocyanate-1,4-diethylbenzene, 1,4-tetramethylxylylene diisocyanate, and 1,3-tetramethylxylylene diisocyanate.

[0040] Examples of alicyclic polyisocyanates include 3-isocyanatemethyl-3,5,5-trimethylcyclohexyl isocyanate (also known as IPDI, isophorone diisocyanate), 1,3-cyclopentane diisocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), and 1,4-bis(isocyanatemethyl)cyclohexane.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] Examples of epoxy curing agents include glycerin diglycidyl ether, 1,6-hexanediol diglycidyl ether, N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane, and N,N,N',N'-tetraglycidylaminophenylmethane.

[0046] The curing agent (B) is preferably contained in an amount of 0.02 to 4 parts by mass, and more preferably 0.04 to 1 part by mass, per 100 parts by mass of the acrylic polymer (A). When the content is 0.02 part by mass or more, the cohesive strength is further improved, and when the content is 4 parts by mass or less, it becomes easier to achieve both cohesive strength and flexibility, making it easier to obtain sufficient adhesive strength, heat resistance, and light resistance.

[0047] <Silane Coupling Agent (C)> The pressure-sensitive adhesive composition of the present disclosure preferably contains a silane coupling agent (C). By including the silane coupling agent (C), it is possible to improve adhesive strength, heat resistance, resistance to wet heat whitening, and light fastness. The silane coupling agent (C) is preferably included in an amount of 0.05 to 0.2 parts by mass per 100 parts by mass of the acrylic polymer (A). By including the silane coupling agent (C) in an amount of 0.05 to 0.2 parts by mass, it becomes easy to achieve both heat resistance, outgassing resistance, and light fastness.

[0048] Examples of the silane coupling agent (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. Specific examples of commercially available products include KBM-403 (3-glycidoxypropyltrimethoxysilane), KBE-403 (3-glycidoxypropyltriethoxysilane), KBM-303 (2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane) (all manufactured by Shin-Etsu Chemical Co., Ltd.), and BYK-325N (polyether-modified polymethylalkylsiloxane) (manufactured by BYK Japan KK).

[0049] <Tackifier Resin (D)> The pressure-sensitive adhesive composition of the present disclosure preferably further contains a tackifier resin (D). As the tackifier resin (D), any of the existing resins can be used, such as 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. The tackifier resin may be used alone or in combination of two or more.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] The content of the tackifier resin (D) is preferably less than 50 parts by mass, more preferably 40 parts by mass or less, per 100 parts by mass of the acrylic polymer (A) in the pressure-sensitive adhesive composition. By including the tackifier resin (D), the adhesive strength to the adherend can be improved.

[0055] In consideration of the environment, it is more preferable to use a tackifier resin (D) having a biomass content of 80% or more. The softening point of the tackifier resin (D) is preferably a high-softening-point grade, in order to enhance durability at high temperatures, and is preferably 90°C or higher, more preferably 120°C or higher, and even more preferably 140°C or higher.

[0056] The pressure-sensitive adhesive composition of the present disclosure may contain various resins, chlorinated polyolefins described below, oils, softeners, dyes, pigments, antioxidants, and ultraviolet absorbers as optional components, as long as the problem can be solved.

[0057] Examples of chlorinated polyolefins include chlorinated polypropylene, acid-modified chlorinated polypropylene, acrylic-modified chlorinated polypropylene, chlorinated polyethylene, and chlorinated ethylene-vinyl acetate copolymers. Chlorinated polypropylene and chlorinated ethylene-vinyl acetate copolymers are preferred from the viewpoints of good compatibility with acrylic polymers and the like 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.).

[0058] The pressure-sensitive adhesive composition of the present disclosure preferably has a gel fraction of 40% or more. However, depending on the application, a gel fraction of 40% or less may also be used. The method for measuring the gel fraction will be described in detail in the Examples.

[0059] The pressure-sensitive adhesive composition of the present disclosure contains an acrylic polymer (A), which is a copolymer of a monomer mixture containing a specific monomer, thereby suppressing the increase in viscosity when using an acrylic polymer and ensuring high adhesive strength to an adherend. This allows for a significant reduction in the amount of organic solvent used to adjust the viscosity during application compared to conventional methods. In the present disclosure, when the weight-average molecular weight of the acrylic polymer (A) is 1.9 million to 2 million, the viscosity at a solids content of 15% (±1%) is preferably 3,000 mPas·s or less; when it is 700,000 to 900,000, the viscosity at a solids content of 35% (±1%) is preferably 3,000 mPas·s or less; and when it is 400,000 to 500,000, the viscosity at a solids content of 50% (±1%) is preferably 3,000 mPas·s or less. Details of the solids content adjustment method and viscosity measurement method are described in the Examples.

[0060] <<Pressure-Sensitive Adhesive Layer>> The pressure-sensitive adhesive layer is a layer obtained using the pressure-sensitive adhesive or pressure-sensitive adhesive composition of the present disclosure. The method for forming the pressure-sensitive adhesive layer is not particularly limited, and may be the same as the coating method described below in the description of the pressure-sensitive adhesive sheet.

[0061] The pressure-sensitive adhesive layer of the present disclosure preferably has a haze of 1.0 or less. A haze of 1.0 or less results in higher transparency, making it less noticeable during use, and providing superior transmittance for optical applications. In order to achieve a haze of 1.0 or less, it is necessary to consider the type and ratio of monomers used in the pressure-sensitive adhesive to prevent the pressure-sensitive adhesive's glass transition temperature from becoming too high. Furthermore, some monomers used exhibit crystallinity, and the development of crystallinity can increase the haze, so it is also necessary to consider the type and blending ratio of the monomers used with crystallinity in mind. The measurement method will be described in detail in the Examples.

[0062] The pressure-sensitive adhesive layer of the present disclosure preferably has a dielectric constant of 5.0 or less at 40 GHz. A dielectric constant of 5.0 or less at 40 GHz can improve optimal operation of touch sensors and the like. In order to achieve a dielectric constant of 5.0 or less, it is necessary to reduce the polarity of the pressure-sensitive adhesive. It is necessary to use a compound that is inherently low in polarity or to increase the number of carbon atoms contained in the compound. The measurement method will be described in detail in the Examples.

[0063] The pressure-sensitive adhesive layer of the present disclosure preferably has a dielectric loss tangent of 0.1 or less at 40 GHz. A dielectric constant of 0.1 or less at 40 GHz can suppress radiation loss of millimeter waves in high frequency bands such as millimeter waves. In order to achieve a dielectric loss tangent of 0.1 or less, it is necessary to reduce the polarity of the pressure-sensitive adhesive. It is necessary to use a compound with low polarity to begin with, or to increase the number of carbon atoms contained in the compound. The measurement method will be described in detail in the Examples.

[0064] The pressure-sensitive adhesive layer of the present disclosure preferably has a refractive index of 1.45 or more but less than 1.52. A refractive index of 1.45 or more but less than 1.52 is useful for reducing light reflection at the interface between the pressure-sensitive adhesive layer and the optical component when used for bonding between layers of optical components. In order to keep the refractive index within the above range, it is necessary to consider the balance between high-refractive index materials and low-refractive index materials. This can be adjusted by the composition of the pressure-sensitive adhesive. For example, this can be adjusted by the type of base polymer, the composition ratio of the monomer components, the presence or absence, type and amount of additives, etc. The measurement method is described in detail in the Examples.

[0065] The adhesive sheet of the present disclosure preferably has a higher glass adhesion strength for the purpose of product fixation, etc. Although a lower adhesive strength may be used depending on the product, for multi-purpose use, a peel strength of 10 N / 25 mm or more is preferred, and 20 N / 25 mm or more is even more preferred. The measurement method is described in detail in the examples. The adhesive sheet of the present disclosure preferably has a higher SUS adhesion strength for the purpose of product fixation, etc. Although a lower adhesive strength may be used depending on the product, for multi-purpose use, a peel strength of 5 N / 25 mm or more is preferred, and 10 N / 25 mm or more is even more preferred. The measurement method is described in detail in the examples.

[0066] <<Adhesive Sheet>> The adhesive sheet comprises an adhesive layer made of the adhesive or adhesive composition of the present disclosure and a release film.

[0067] The pressure-sensitive adhesive sheet of the present disclosure may have a configuration in which a release film is formed on one or both sides of the pressure-sensitive adhesive layer.

[0068] <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.

[0069] As the release film, among the above-mentioned transparent plastic substrates, 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.

[0070] The thickness of the release film is preferably less than 200 μm. The thickness should be adjusted depending on the handling of the member to be used, but by being less than 200 μm, the material itself is not too stiff, making it easy to wind up into a roll and allowing for comfortable use when laminating sheets or the like.

[0071] The pressure-sensitive adhesive sheet of the present disclosure has excellent adhesiveness and is therefore suitable for forming optical display components such as display devices such as LCDs and OLEDs, and input devices such as touch panels, and for bonding these components together. Examples of optical components include, but are not limited to, PET films, polarizing plates, retardation plates, elliptically polarizing plates, optical compensation films, brightness-enhancing films, infrared / electromagnetic wave-blocking films, front-surface anti-reflection films, surface protection films, films having an ITO (indium tin oxide) layer, films having a zinc oxide (ZnO) layer, films obtained by coating or printing metal nanoparticles, films obtained by coating or printing a dispersion containing carbon nanotubes, films obtained by coating or printing a dispersion containing graphene, films obtained by coating or printing a dispersion containing a conductive polymer, metal plates made of SUS or the like, metal meshes, and laminates of these.

[0072] When applying the adhesive or adhesive composition, a suitable liquid medium can be added to adjust the viscosity.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).

[0073] 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.

[0074] The thickness of the adhesive layer is preferably 2 to 1000 μm, more preferably 5 to 500 μm. The adhesive layer may be in the form of a single layer or a laminate of two or more layers.

[0075] <Laminate> The laminate of the present disclosure includes a substrate and a pressure-sensitive adhesive layer. 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 substrate.

[0076] <Substrate> The substrate refers to the surface to which the pressure-sensitive adhesive layer of a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer is attached, and is not limited to a specific material. Examples of substrates that can be used include resins such as polyolefins including polyethylene and polypropylene, polycarbonate, and phenol; metals such as iron, stainless steel (SUS), aluminum, and copper; and other materials such as cement, mortar, glass, nonwoven fabric, woven fabric, paper, rubber, foam sheets, and laminates thereof. The pressure-sensitive adhesive and pressure-sensitive adhesive composition of the present disclosure exhibit excellent adhesive strength to at least one type of adherend. The thickness of the substrate is not particularly limited, and is preferably less than 500 μm, more preferably 10 to 200 μm, and even more preferably 25 to 150 μm.

[0077] <Light-Transmitting Substrate> The laminate of the present disclosure can also use a light-transmitting substrate as the 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, polyimide, polyphenylene ether, polysulfone, polyethersulfone, polystyrene, and polypropylene. PET film or PC is preferred, and PC is more preferred in terms of durability. The plastic materials can be used alone or in combination of two or more. The light-transmitting substrate may also 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.

[0078] For a laminate including a light-transmitting substrate, the total light transmittance of the pressure-sensitive adhesive sheet is preferably 60% or more. A laminate including a light-transmitting substrate has, for example, a configuration of a light-transmitting substrate / pressure-sensitive adhesive layer / polarizing plate. In this case, it is preferable to provide the light-transmitting substrate, pressure-sensitive adhesive layer, and polarizing plate in this order. This allows for a laminate with excellent transparency.

[0079] Fig. 1 shows a schematic cross-sectional view partially illustrating an example of a laminate according to the present disclosure. In Fig. 1, 3 is a light-transmitting substrate (cover panel), 1 is a pressure-sensitive adhesive layer, and 4 is a polarizing plate. In the laminate shown in Fig. 1, the light-transmitting substrate (cover panel) is attached to the polarizing plate via the pressure-sensitive adhesive layer.

[0080]

[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.

[0081] <Production of Laminate> A laminate can be produced, for example, by peeling off a release film from a pressure-sensitive adhesive sheet having release films on both sides of the pressure-sensitive adhesive layer, and attaching the pressure-sensitive adhesive layer to a substrate such as a light-transmitting flexible substrate or a polarizing plate, etc. Alternatively, a pressure-sensitive adhesive layer can be directly formed on a light-transmitting flexible substrate, and then an adhesive layer provided on a substrate or another pressure-sensitive adhesive sheet can be attached to the pressure-sensitive adhesive layer to form a laminate.

[0082] <Display> A display includes the laminate of the present disclosure, a polarizing plate, and an optical element. This allows the display of the present disclosure to have excellent visibility. The optical element is not particularly limited, and examples thereof include a liquid crystal element and an organic EL element.

[0083] 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.

[0084] 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 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 layer 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 1 has higher quality requirements, while the pressure-sensitive adhesive of the present disclosure is preferably used for pressure-sensitive adhesive layer 1 because of its excellent adhesion and bondability to the substrate. In this case, the pressure-sensitive adhesive for forming pressure-sensitive adhesive layer 2 may be the pressure-sensitive adhesive of the present disclosure or a conventionally known pressure-sensitive adhesive.

[0085] 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.

[0086] In view of the recent trend toward environmentally friendly materials, the adhesive and adhesive composition of the present disclosure can be made partially or entirely from biologically derived materials by using a biomass monomer as the monomer constituting the acrylic polymer (A) or by using a biomass tackifier. The biomass ratio is preferably 30% or more. The higher the biomass ratio, more preferably 39% or more, and even more preferably 60% or more, the greater the usefulness as an environmentally friendly material. The method for calculating the biomass ratio is described in the Examples.

[0087] The present disclosure will be further described in detail below using examples, but the present disclosure is not limited to these examples. In the examples, unless otherwise specified, "parts" and "%" refer to "parts by mass" and "% by mass," respectively. Furthermore, the blend amounts in the tables are in parts by mass, and values ​​other than the solvent are calculated as nonvolatile components. Blank spaces in the tables indicate that no blend is present. It is common technical knowledge that the viscosity of a pressure-sensitive adhesive composition increases or decreases depending on the Mw of the acrylic polymer (A) contained therein. Since the Mw of the acrylic polymer (A) can be adjusted as appropriate, it is not realistic to confirm the effects of the present disclosure over the entire Mw range of the acrylic polymer (A). Therefore, in the examples, acrylic polymers (A) were produced and evaluated so that the Mw was 400,000 to 500,000, 700,000 to 900,000, or 1,900,000 to 2,000,000. The method for measuring the weight-average molecular weight of the acrylic polymer is as follows.

[0088] <Method for measuring weight-average molecular weight (Mw) and evaluating Mw classification> The weight-average molecular weight (Mw) was measured by gel permeation chromatography (GPC). The apparatus used was a GPC apparatus manufactured by Shimadzu Corporation: LC-GPC system "Prominence". Furthermore, a column manufactured by Tosoh Corporation: TSKgel α-M was used, with two columns connected in series. N,N-dimethylformamide (DMF) was used as the eluent, and measurements were taken at 40°C. Mw was determined by conversion using polystyrene with a known Mw as the standard substance. The weight-average molecular weight (Mw) of the acrylic polymer was measured, and the evaluation results were determined as follows: if it was 1.9 million to 2 million, the Mw classification was U; if it was 700,000 to 900,000, the Mw classification was H; and if it was 400,000 to 500,000, the Mw classification was L.

[0089] (Production of Acrylic Polymer) Example 1: Production of (A-1) Using a reaction apparatus equipped with a stirrer, a reflux condenser, a nitrogen inlet tube, a thermometer, and a dropping tube, ethyl acetate was added to a reaction vessel as a polymerization solvent, and a monomer mixture of 19.75 parts of 2-octyl acrylate (2-OA) as monomer (a1), 20 parts of methyl acrylate (MA) as monomer (a2), 3 parts of isobornyl acrylate (IBXA) as monomer (a3), 7 parts of 2-hydroxyethyl acrylate (HEA), and 0.25 parts of 4-hydroxybutyl acrylate (4HBA), and 0.04 parts of azobisisobutyronitrile as an initiator, was reacted. A reaction vessel was charged with a monomer mixture of 19.75 parts of 2-octyl acrylate (2-OA), 20 parts of methyl acrylate (MA) as monomer (a2), 3 parts of isobornyl acrylate (IBXA) as monomer (a3), 7 parts of 2-hydroxyethyl acrylate (HEA), and 0.25 parts of 4-hydroxybutyl acrylate (4HBA), ethyl acetate as a polymerization solvent, and 0.02 parts of azobisisobutyronitrile as an initiator. The resulting solution was added dropwise from the dropping tube over approximately 2 hours and polymerized for 6 hours at approximately 80°C under a nitrogen atmosphere. After completion of the reaction, the mixture was cooled and diluted with ethyl acetate to obtain an acrylic polymer solution. The resulting acrylic polymer was designated (A-1). The weight average molecular weight (Mw) of the resulting acrylic polymer was measured, and the results are shown in Table 1.

[0090] <Production of Examples 2 to 7, Comparative Production Examples 1 to 7: (A-2 to A-7, A'-1 to A'-7)> Acrylic polymers (A-2 to A-7, A'-1 to A'-7) were produced in the same manner as the production of the acrylic polymer (Example 1), except that the compositions and blending amounts (parts by mass) were changed to those shown in Table 1. The Mw classification of the obtained acrylic polymers is also shown in Table 1.

[0091]

[0092] <Examples 21 to 24, Examples 30 to 35: Production of (A-8 to A-17), Comparative Production Examples 8 to 12: (A'-8 to A'-10)> Acrylic polymers (A-8 to A-17, A'-8 to A'-10) were produced in the same manner as the production of the acrylic polymer (Example 1), except that the compositions and blending amounts (parts by mass) were changed to those shown in Tables 2 and 3. The Mw classification of the obtained acrylic polymers is shown in Table 2.

[0093]

[0094]

[0095] The abbreviations are as follows: Regarding biomass content, only confirmed cases are listed. [Monomer (a1)] 2-OA: 2-octyl acrylate (biomass degree 73%) 2-OMA: 2-octyl methacrylate (biomass degree 67%) [Monomer (a2)] MA: methyl acrylate (Tg: 8°C) MMA: methyl methacrylate (Tg: 105°C) BMA: butyl methacrylate (Tg: 20°C) [Monomer (a3)] IBXA: isobornyl acrylate (Tg: 97°C, biomass degree 76%) [Monomer having a hydroxy group (OH monomer) / monomer having a carboxy group (COOH monomer)] HEA: hydroxyethyl acrylate 4HBA: 4-hydroxy-normal-butyl acrylate AA: acrylic acid [Other monomers (a4)] 2EHA: 2-ethylhexyl acrylate (Tg: -70°C) BA: n-butyl acrylate (Tg: -55°C, biomass degree 57%) LA: Lauryl acrylate (Tg: -23°C, biomass content 80%)

[0096] Example 8 A pressure-sensitive adhesive composition was obtained by blending 0.2 parts of "D-165N" (a biuret of hexamethylene diisocyanate manufactured by Mitsui Chemicals, Inc.) as the curing agent (B) with 100 parts of the acrylic polymer (A-1). The resulting pressure-sensitive adhesive composition was applied using a comma coater to a 38 μm thick release liner (SP-PET-O1-BU, manufactured by Mitsui Chemicals Tohcello, Inc.) as a release sheet so that the thickness after drying would be 25 μm. After drying at 110°C for 3 minutes, a 75 μm thick release liner (SP-PET-O3-B3, manufactured by Mitsui Chemicals Tohcello, Inc.) as a release sheet was laminated to the pressure-sensitive adhesive layer, and the resulting mixture was aged in this state at 23°C for 7 days to obtain a pressure-sensitive adhesive sheet.

[0097] Examples 9 to 17, Examples 19 to 20, Examples 25 to 29, Examples 36 to 45, Comparative Examples 1 to 15 As shown in Table 4, pressure-sensitive adhesive compositions and pressure-sensitive adhesive sheets were obtained in the same manner as in Example 8, except that the types and blending amounts of the acrylic polymer, curing agent (B), silane coupling agent (C), and tackifier resin (D) were changed.

[0098] Example 18 A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 8, except that the acrylic polymer (A-5) obtained in Example 5 was used as the pressure-sensitive adhesive.

[0099] <Gel Fraction Measurement> The 38 μm release liner was peeled off from the obtained pressure-sensitive adhesive sheet, and the pressure-sensitive adhesive layer was attached to a PET film substrate (Cosmoshine A-4360, manufactured by Toyobo Co., Ltd., thickness 100 μm), which was then cut into a size of 30 mm wide x 100 mm long to prepare a test pressure-sensitive adhesive sheet. The release liner on the other side of the pressure-sensitive adhesive tape was then peeled off to prepare a test specimen, and its weight was measured. The test specimen was immersed in ethyl acetate at 23°C for 24 hours, then removed from the ethyl acetate and dried at 150°C for 30 minutes. The weight of the test specimen after drying was measured, and the gel fraction was calculated using the following formula (1). In Table 4, "40%<" means that the gel fraction is greater than 40%. Gel fraction (wt%)=100×(W2−W0) / (W1−W0) (1) (W0: weight of substrate (PET film), W1: weight of test piece before immersion, W2: weight of test piece after immersion and drying)

[0100] <Calculation of Biomass Degree> The biomass degree of the PSA composition was calculated using the following formula (2): (In the case of a system consisting of two monomer components (A, B) and one tackifier component (C)) Biomass degree = {(Aw x Ab) + (Bw x Bb) + (Cw x Cb)} / (Aw + Bw + Cw) (2) Aw: weight of monomer A, Bw: weight of monomer B, Cw: weight of tackifier, Ab: biomass degree (%) of monomer A, Bb: biomass degree (%) of monomer B, Cb: biomass degree (%) of monomer C. When the biomass degree was specified as a range, the minimum value was used for the calculation.

[0101] The materials used in the examples and comparative examples are listed below. <Curing agent (B)> D-165N: biuret of hexamethylene diisocyanate, manufactured by Mitsui Chemicals, Inc. Tetrad X: multifunctional epoxy resin, manufactured by Mitsubishi Gas Chemical Company, Inc. Aluminum Chelate A: chelate curing agent, manufactured by Kawaken Fine Chemicals Co., Ltd.

[0102] <Silane coupling agent (C)> KBE-403: (3-glycidoxypropyltriethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd.) <Tackifying resin (D)> A-100: (Super Ester A-100, manufactured by Arakawa Chemical Industries, Ltd., biomass degree 95 to 100%, softening point 95°C to 105°C) YS-T160: (YS Polystar T160, manufactured by Yasuhara Chemical Co., Ltd., biomass degree 70%, softening point 160°C)

[0103] The adhesives and adhesive compositions obtained in Examples 8 to 20, 25 to 29, 36 to 45, and Comparative Examples 1 to 15 were evaluated for low viscosity, and the adhesive strength and corrosion resistance of the adhesive sheets were measured and evaluated using the methods described below. Adhesion was judged to be practical if the adhesive strength to either glass or SUS adherends was evaluated as "usable" or better; if the adhesive strength to one adherend was evaluated as "good," evaluation of the adhesive strength to the other adherend was omitted. The diagonal lines in Table 5 indicate that no evaluation was performed. The results are shown in Table 5.

[0104] <Low Viscosity> The viscosity of the pressure-sensitive adhesives and pressure-sensitive adhesive compositions of Examples 8 to 20, 25 to 29, 36 to 45, and Comparative Examples 1 to 15 was measured by the following method to evaluate low viscosity. When the weight average molecular weight (Mw) of the contained acrylic polymer was 1,900,000 to 2,000,000 (U), the solids content was adjusted to 15% (±1); when the Mw was 700,000 to 900,000 (H), the solids content was adjusted to 35% (±1); and when the Mw was 400,000 to 500,000 (L), the solids content was adjusted to 50% (±1), and the viscosity was measured using a Brookfield viscometer (rotor number: M3, rotation speed: 12 rpm). The solids content was adjusted using ethyl acetate. [Evaluation criteria] A: Viscosity less than 3000 mPas·s: Good B: Viscosity 3000 mPas·s or more but less than 4000 mPas·s: Usable C: Viscosity 4000 mPas·s or more: Unusable

[0105] <Glass Adhesion Strength> The 38 μm release liner was peeled off from the resulting pressure-sensitive adhesive sheet, and the pressure-sensitive adhesive layer was attached to a PET film substrate (Cosmoshine A-4360, 100 μm thick, manufactured by Toyobo Co., Ltd.), and cut into a size of 25 mm wide x 100 mm long to prepare a test pressure-sensitive adhesive sheet. The other 75 μm release liner was peeled off from this test pressure-sensitive adhesive sheet, and the pressure-sensitive adhesive layer was attached to a glass plate in an atmosphere of 23°C and 50% relative humidity (50% RH), and further pressed with a roll in accordance with JIS Z-0237. After 24 hours of pressing, the peel strength (peel angle 180°, peel rate 300 mm / min; unit N / 25 mm width) was measured using a tensile tester (Tensilon, manufactured by Orientec Co., Ltd.). [Evaluation Criteria] A: Peel strength of 20 N / 25 mm or more. : Good B: Peel strength is 10N / 25mm or more and less than 20N / 25mm. : Usable C: Peel strength is less than 10N / 25mm. : Unusable

[0106] <SUS Adhesion Strength> Measurement was performed in the same manner as in the glass adhesion strength measurement above, except that the adherend was changed from a glass plate to a SUS plate. [Evaluation Criteria] A: Peel strength of 10 N / 25 mm or more: Good B: Peel strength of 5 N / 25 mm or more but less than 10 N / 25 mm: Usable C: Peel strength of less than 5 N / 25 mm: Unusable

[0107] <Corrosion Resistance> After laminating the pressure-sensitive adhesive sheet onto aluminum foil, it was left under high-temperature and high-humidity conditions of 60°C x 90% RH for 48 hours. Thereafter, the pressure-sensitive adhesive sheet was peeled off from the aluminum foil, and the aluminum foil surface was visually inspected and evaluated according to the following criteria. A: No discoloration was observed on the aluminum foil surface. B: Partial discoloration was observed on the aluminum foil surface. C: Discoloration was observed on the aluminum foil surface.

[0108]

[0109] The pressure-sensitive adhesive layers of the Examples and Comparative Examples were measured for haze, dielectric constant, dielectric loss tangent, refractive index, corrosiveness, and total light transmittance by the following methods. The measurement results are shown in Table 5.

[0110] <Measurement of Haze and Total Light Transmittance> One separator was peeled from the double-sided pressure-sensitive adhesive sheet, and the double-sided pressure-sensitive adhesive sheet was attached to a glass slide (manufactured by Matsunami Glass Industrial Co., Ltd., "White Polish No. 1," thickness 0.8 to 1.0 mm, total light transmittance 92%, haze 0.2%). The other separator was then peeled off to prepare a test piece having a layer structure of double-sided pressure-sensitive adhesive sheet (adhesive layer) / glass slide. The total light transmittance and haze in the visible light range of the test piece were measured using a haze meter (device name "HM-150," manufactured by Murakami Color Research Institute Co., Ltd.) in an environment of 23±1°C and 52±1% RH. Three samples were prepared for each specimen, and the average measured values ​​of the three samples were used as the total light transmittance and haze in the visible light range.

[0111] <Measurement of dielectric constant and dielectric loss tangent> Samples were prepared by laminating 25 microns of PET to both sides of the adhesive layer obtained in the Examples or Comparative Examples, and the dielectric constant and dielectric loss at a frequency of 40 GHz were measured using the following device. Three samples were prepared for each specimen, and the averages of the measurements for these three samples were used as the relative dielectric constant and dielectric loss. After the measurement, the measurement value for the PET alone was subtracted from the value for the three-layer structure of PET-adhesive layer-PET to obtain the measurement value for the adhesive layer itself. Measurement method: Cavity resonator method JIS R1641 IPC-TM650 2.5.5.13 Device: Dielectric constant measurement device, cavity resonator TE mode, manufactured by AET Corporation Measurement environment: 23±1°C, 52±1% RH

[0112] <Method for measuring refractive index> The refractive index of the adhesive layer at 23°C is measured using an Abbe refractometer (manufacturer: ERMA, model: ER-2S). [Evaluation criteria] A: Refractive index is 1.45 or more and less than 1.52: Usable C: Refractive index is less than 1.45 or 1.52 or more: Unusable

[0113]

[0114] 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.

[0115] The disclosure of this application is related to the subject matter described in Japanese Patent Application No. 2023-144832 filed on September 6, 2023, the subject matter described in Japanese Patent Application No. 2023-181269 filed on October 20, 2023, and the subject matter described in Japanese Patent Application No. 2024-015205 filed on February 2, 2024, the entire disclosures of which are incorporated herein by reference.

[0116] REFERENCE SIGNS LIST 1 Pressure-sensitive adhesive layer 1, 2 Release film, 3 Substrate, 4 Polarizing plate, 5 Pressure-sensitive adhesive layer 2, 6 Barrier layer, 7 Organic EL layer, 8 Support, 9 Organic EL cell

Claims

1. An adhesive comprising an acrylic polymer (A) which is a copolymer of a monomer mixture, the adhesive comprising, based on 100% by mass of the monomer mixture, more than 30% by mass and less than 99.5% by mass of the following monomer (a1), and a total of 0.1% by mass or more and less than 70% by mass of the following monomer (a2) and monomer (a3), and may further comprise at least one selected from the group consisting of 30% by mass or less of the following monomer (a4), and less than 0.5% by mass of a monomer having a carboxy group: (a1) 2-octyl (meth)acrylate (a2) a monomer having a homopolymer glass transition temperature of 0°C or more (excluding monomer (a3), a monomer having a carboxy group, and a monomer having a hydroxy group) (a3) ​​isobornyl (meth)acrylate (a4) other monomers other than monomer (a1), monomer (a2), monomer (a3), a monomer having a carboxy group, and a monomer having a hydroxy group.

2. An adhesive comprising an acrylic polymer (A) which is a copolymer of a monomer mixture, the adhesive comprising, in 100% by mass of the monomer mixture, more than 30% by mass and less than 99.5% by mass of the following monomer (a1), and a total of the following monomer (a2) and monomer (a3), which are 0.1% by mass or more and less than 70% by mass, and which may further comprise at least one selected from the group consisting of 30% by mass or less of the following monomer (a4), less than 0.5% by mass of a monomer having a carboxy group, and a monomer having a hydroxy group, which together with the monomer having a carboxy group accounts for 0.5% by mass or more and 30% by mass or less; and when the adhesive comprises a nitrogen-containing monomer as monomer (a2) and also monomer (a3) ​​and a monomer having a hydroxy group, the content of at least one of the nitrogen-containing monomer, monomer (a3) ​​and hydroxy group-containing monomer in 100% by mass of the monomer mixture is less than 10% by mass. (a1) 2-octyl (meth)acrylate (a2) Monomers having a glass transition temperature of a homopolymer of 0°C or higher (excluding monomer (a3), monomers having a carboxy group, and monomers having a hydroxy group) (a3) ​​isobornyl (meth)acrylate (a4) Other monomers other than monomer (a1), monomer (a2), monomer (a3), monomers having a carboxy group, and monomers having a hydroxy group 3. An adhesive comprising an acrylic polymer (A) which is a copolymer of a monomer mixture, the adhesive comprising, in 100% by mass of the monomer mixture, more than 30% by mass and less than 99.5% by mass of the following monomer (a1), and a total of the following monomer (a2) and monomer (a3), which are 0.1% by mass or more and less than 70% by mass, and which may further comprise at least one selected from the group consisting of 30% by mass or less of the following monomer (a4), less than 0.5% by mass of a monomer having a carboxy group, and a monomer having a hydroxy group, the total of which, together with the monomer having a carboxy group, is 0.5% by mass or more and 30% by mass or less, and when the monomer (a2) contains a nitrogen-containing monomer and a monomer having a hydroxy group, the content of at least one of the nitrogen-containing monomer and the hydroxy group-containing monomer in 100% by mass of the monomer mixture is less than 10% by mass. (a1) 2-octyl (meth)acrylate (a2) Monomers having a glass transition temperature of a homopolymer of 0°C or higher (excluding monomer (a3), monomers having a carboxy group, and monomers having a hydroxy group) (a3) ​​isobornyl (meth)acrylate (a4) Other monomers other than monomer (a1), monomer (a2), monomer (a3), monomers having a carboxy group, and monomers having a hydroxy group 4. The adhesive according to claim 1, containing a total of 0.1% by mass or more and less than 50% by mass of monomer (a2) and monomer (a3) ​​based on 100% by mass of the monomer mixture.

5. The adhesive according to claim 1, wherein the monomer (a2) comprises at least one member selected from the group consisting of methyl (meth)acrylate, ethyl methacrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate and phenyl (meth)acrylate.

6. The pressure-sensitive adhesive according to claim 1, wherein the monomer mixture further contains a monomer having a hydroxy group.

7. The adhesive according to claim 4, comprising a monomer having a carboxy group and a monomer having a hydroxy group in a total amount of 0.5% by mass or more and 30% by mass or less based on 100% by mass of the monomer mixture.

8. The pressure-sensitive adhesive according to claim 1, having a biomass ratio of 30% or more.

9. A pressure-sensitive adhesive composition comprising the pressure-sensitive adhesive according to claim 1 and a curing agent (B).

10. The pressure-sensitive adhesive composition according to claim 9, wherein the curing agent (B) comprises at least one of an isocyanate-based curing agent and an epoxy-based curing agent.

11. The pressure-sensitive adhesive composition according to claim 9, further comprising a silane coupling agent (C).

12. The pressure-sensitive adhesive composition according to claim 9, which has a gel fraction of 40% or more.

13. The pressure-sensitive adhesive composition according to claim 9, further comprising less than 50 parts by mass of a tackifier resin (D) per 100 parts by mass of the acrylic polymer (A).

14. The pressure-sensitive adhesive composition according to claim 11, wherein the tackifier resin (D) has a biomass content of 80% or more.

15. A pressure-sensitive adhesive layer obtained by using the pressure-sensitive adhesive according to any one of claims 1 to 8 or the pressure-sensitive adhesive composition according to any one of claims 9 to 14.

16. The pressure-sensitive adhesive layer according to claim 15, which has a haze of 1.0 or less.

17. The pressure-sensitive adhesive layer according to claim 15, which has a dielectric constant of 5.0 or less at 40 GHz.

18. The pressure-sensitive adhesive layer according to claim 15, which has a dielectric loss tangent of 0.1 or less at 40 GHz.

19. The pressure-sensitive adhesive layer according to claim 15, which has a refractive index of 1.45 or more and less than 1.

52.

20. The pressure-sensitive adhesive layer according to claim 15, having a glass adhesion strength of 10 N / 25 mm or more.

21. The pressure-sensitive adhesive layer according to claim 15, which has an adhesive strength to SUS of 5 N / 25 mm or more.

22. An adhesive sheet comprising the adhesive layer according to claim 15 and a release film.

23. The pressure-sensitive adhesive sheet according to claim 22, wherein the release film has a thickness of less than 200 μm.

24. A laminate comprising the pressure-sensitive adhesive layer according to claim 15 and a substrate.

25. The laminate according to claim 24, wherein the thickness of the substrate is less than 500 μm.

26. The laminate according to claim 24, wherein the substrate is a light-transmitting substrate.

27. The laminate according to claim 26, having a total light transmittance of 60% or more.

28. A display comprising the laminate according to claim 26, a polarizing plate, and an optical element.

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