Adhesive sheet, method for producing same, and optical laminate

Abstract

The present invention pertains to an adhesive sheet that is characterized by having a substrate layer and an adhesive agent layer, and that is characterized in that the thickness of the adhesive agent layer is 100 μm or more, and the adhesive agent layer is formed from an adhesive agent that exhibits, when an adhesive agent layer having a thickness of 500 μm is obtained, a chromaticity b* value of -3.0 or more stipulated by the CIE1976L*a*b* color system in a reflection mode of the adhesive agent layer. The present invention also pertains to: a method for producing the adhesive sheet; and an optical laminate provided with the adhesive sheet. The present invention provides: an adhesive sheet that improves, when an adhesive sheet having a thick adhesive agent layer is applied to the outermost surface of an optical laminate, the phenomenon in which the optical laminate appears bluish white; a method for producing the adhesive sheet; and an optical laminate comprising the adhesive sheet.

Description

Pressure-sensitive adhesive sheet, manufacturing method thereof, and optical laminate

[0001] The present invention relates to an adhesive sheet having a thick adhesive layer with a thickness of 100 μm or more, which is improved in the phenomenon of appearing pale blue and has excellent durability, a method for producing the same, and an optical laminate including the adhesive sheet.

[0002] In a display, a protective panel or the like is placed on the display module on which the image is displayed to protect the display module. Conventionally, the protective panel has been placed on the display module via a gap (air gap) made of an air layer. This configuration makes it easy to manufacture the display.

[0003] However, there is a problem that the display light from the display module is easily reflected or scattered in the air gap, which reduces the visibility of the image. To address this problem, in recent years, a technology has been adopted in which a thick layer of optically clear adhesive (OCA) is provided to fill the air gap.

[0004] In relation to the present invention, Patent Document 1 describes an adhesive composition, an adhesive, and an adhesive sheet containing (A) an acrylic polymer having a weight-average molecular weight of 800,000 to 2,000,000 and containing a specific acrylic monomer as a monomer unit, (B) a hydrogen abstraction photopolymerization initiator, and (C) a silane coupling agent in a specific blending ratio.

[0005] Furthermore, Patent Document 2 describes an adhesive sheet used to bond a protective plate and a display panel, which is formed from an adhesive composition containing a specific acrylic polymer having a weight-average molecular weight of 200,000 to 900,000, an epoxy crosslinking agent, and a hydrogen abstraction photopolymerization initiator, and which is characterized in that the thickness of the adhesive layer formed from the adhesive composition is 50 μm or more.

[0006] The pressure-sensitive adhesive compositions described in these documents use a solvent as a diluent, and therefore there is a limit to the thickness of the pressure-sensitive adhesive layer that can be formed. For example, when a thick pressure-sensitive adhesive layer having a thickness of 100 μm or more is required, it is difficult to form it all at once.

[0007] Patent No. 5534584 Patent No. 6545488

[0008] In recent years, UV-curable adhesives have been developed that do not contain solvents but instead contain low-molecular-weight materials. These adhesives facilitate thick-film coating because the low-molecular-weight materials act as diluents and react with UV light to form covalent bonds with the resin material. Furthermore, because no solvent is used, a drying process is unnecessary, which also has the advantage of being environmentally friendly.

[0009] However, when a pressure-sensitive adhesive sheet having a thick pressure-sensitive adhesive layer formed using a pressure-sensitive adhesive having such advantages is used in an optical laminate for an image display device or the like, the pressure-sensitive adhesive layer may take on a bluish-white color, causing the optical laminate to appear bluish-white in appearance. In such cases, there is a problem of a decrease in the quality of the optical laminate.

[0010] The present invention has been made to solve such problems, and has an object to provide an adhesive sheet having an adhesive layer that improves the phenomenon in which an optical laminate appears bluish-white when an adhesive sheet having a thick adhesive layer is applied to the optical laminate, a method for manufacturing the adhesive sheet, and an optical laminate including the adhesive sheet.

[0011] In order to solve the above problems, the present inventors have conducted extensive research into a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer with a thickness of 100 μm or more. As a result, when the thickness of the pressure-sensitive adhesive layer is set to 500 μm, the CIE 1976L ＊ a ＊ b ＊ Chromaticity b defined by the color system ＊ The present inventors have found that when a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed from a pressure-sensitive adhesive having a viscosity index of -3.0 or more is applied to an optical laminate, the phenomenon in which the optical laminate appears pale is improved, and have completed the present invention. Furthermore, the present inventors have found that a pressure-sensitive adhesive layer having excellent durability, blister resistance, resistance to wet heat whitening, and weather resistance can be obtained.

[0012] Thus, according to the present invention, there are provided the pressure-sensitive adhesive sheets described in the following items [1] to

[10] , the methods for producing pressure-sensitive adhesive sheets described in items

[11] and (12), and the optical laminate described in item

[13] .

[0013] [1] A pressure-sensitive adhesive sheet having a base layer and a pressure-sensitive adhesive layer, wherein the pressure-sensitive adhesive layer has a thickness of 100 μm or more, and the pressure-sensitive adhesive layer has a CIE1976L reflection coefficient in a reflection mode of the pressure-sensitive adhesive layer when the film thickness is 500 μm. ＊ a ＊ b ＊ Chromaticity b defined by the color system ＊ [2] A pressure-sensitive adhesive sheet characterized in that the pressure-sensitive adhesive layer has a CIE 1976L value in a transmission mode of the pressure-sensitive adhesive layer when the film thickness is 500 μm. ＊ a ＊ b ＊ Chromaticity b defined by the color system ＊ [3] The pressure-sensitive adhesive sheet according to [1] or [2], which is formed from a pressure-sensitive adhesive having a total light transmittance of 85% or more.

[0014] [4] The pressure-sensitive adhesive sheet according to [1] or [2], wherein the difference between the initial total light transmittance (%) and the total light transmittance (%) after irradiating the surface side of the pressure-sensitive adhesive layer with ultraviolet light for 1000 hours using an ultraviolet fade meter in accordance with JIS B7751: 2007 is 4.0% or less. [5] The pressure-sensitive adhesive sheet according to [1] or [2], wherein the change in the initial haze (%) and the haze (%) after irradiating the surface side of the pressure-sensitive adhesive layer with ultraviolet light for 1000 hours using an ultraviolet fade meter in accordance with JIS B7751: 2007 is 1% or less. [6] The pressure-sensitive adhesive sheet according to [1] or [2], wherein the pressure-sensitive adhesive layer is made of an acrylic pressure-sensitive adhesive.

[0015] [7] The pressure-sensitive adhesive sheet according to [1] or [2], wherein the pressure-sensitive adhesive layer comprises a cured product of an active energy ray-curable pressure-sensitive adhesive composition containing one or more photopolymerizable components selected from the group consisting of polymerizable vinyl monomers, polymerizable vinyl prepolymers, polyfunctional (meth)acrylate monomers, and polyfunctional (meth)acrylate oligomers, and a hydrogen abstraction photopolymerization initiator. [8] The pressure-sensitive adhesive sheet according to [7], wherein the active energy ray-curable pressure-sensitive adhesive composition does not contain a solvent. [9] The pressure-sensitive adhesive sheet according to [7], wherein the pressure-sensitive adhesive layer contains 5,000 ppm or less of low-molecular-weight components having a molecular weight of 3,000 or less.

[10] The pressure-sensitive adhesive sheet according to [7], wherein the active energy ray-curable pressure-sensitive adhesive composition contains an oxygen absorber.

[0016]

[11] A method for producing a pressure-sensitive adhesive sheet having a base layer and a pressure-sensitive adhesive layer, comprising the steps of: forming a coating film of an active energy ray-curable pressure-sensitive adhesive composition containing one or more photopolymerizable components selected from the group consisting of polymerizable vinyl monomers, polymerizable vinyl prepolymers, polyfunctional (meth)acrylate monomers and polyfunctional (meth)acrylate oligomers, and a hydrogen abstraction photopolymerization initiator on the base layer; and irradiating the coating film with active energy rays to cure the active energy ray-curable pressure-sensitive adhesive composition to form a pressure-sensitive adhesive layer.

[12] The method for producing the pressure-sensitive adhesive sheet according to

[11] , wherein the active energy ray-curable pressure-sensitive adhesive composition does not contain a solvent.

[13] An optical laminate comprising the pressure-sensitive adhesive sheet according to [1] or [2] above.

[0017] According to the present invention, there are provided an adhesive sheet that improves the phenomenon in which an optical laminate appears bluish-white even when an adhesive sheet having a thick adhesive layer with a film thickness of 100 μm or more is applied to the optical laminate, a method for manufacturing the same, and an optical laminate including the adhesive sheet.

[0018] 1 is a cross-sectional view of the layer structure of an example of an optical laminate of the present invention.

[0019] Hereinafter, the present invention will be described in detail by dividing it into the following sections: 1) pressure-sensitive adhesive sheet, 2) method for producing a pressure-sensitive adhesive sheet, and 3) optical laminate.

[0020] The pressure-sensitive adhesive sheet of the present invention is a pressure-sensitive adhesive sheet having a base layer and a pressure-sensitive adhesive layer, wherein the pressure-sensitive adhesive layer has a thickness of 100 μm or more, and the pressure-sensitive adhesive layer has a CIE 1976L reflection coefficient in a reflection mode of the pressure-sensitive adhesive layer when the film thickness is 500 μm. ＊ a ＊ b ＊ Chromaticity b defined by the color system ＊ The adhesive is characterized in that it is formed from a pressure-sensitive adhesive having a value of -3.0 or more.

[0021] A cross-sectional view of the layer structure of a pressure-sensitive adhesive sheet 10 of the present invention is shown in Fig. 1. In Fig. 1, 1 denotes a substrate layer, and 2 denotes a pressure-sensitive adhesive layer.

[0022] (Substrate layer) The substrate layer used in the pressure-sensitive adhesive sheet of the present invention is not particularly limited, and plastic films made of various materials can be used. For example, it may be an optical component incorporated in an image display device or the like, or a release film that is peeled off and removed during use. From the perspective of the SDGs, the material constituting the substrate layer may be a material with a high biomass content, a material that can be recycled or reused, or a recycled or reused material.

[0023] Examples of plastic film materials include polyester films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; polyurethane films, polyethylene films, polypropylene films, cellulose films such as triacetyl cellulose (TAC); plastic films such as polyvinyl chloride films, polyvinylidene chloride films, polyvinyl alcohol films, ethylene-vinyl acetate copolymer films, polystyrene films, polycarbonate films, acrylic resin films, norbornene resin films, and cycloolefin resin (COP) films; laminates of two or more of these plastic films; and plastic films on one or both sides of which a functional layer such as a release agent layer, hard coat layer, antiglare layer, reflective layer, transparent conductive film, or colored layer is provided.

[0024] Examples of optical members include polarizing plates (polarizing films), polarizers, retardation plates (retardation films), viewing angle compensation films, brightness enhancement films, contrast enhancement films, liquid crystal polymer films, diffusion films, and semi-transmissive reflective films.

[0025] The release film refers to, for example, a plastic film such as those mentioned above, on at least one side of which a release agent layer is provided. The release agent layer is composed of an alkyd-based, silicone-based, fluorine-based, unsaturated polyester-based, polyolefin-based, wax-based, or other release agent. When the base layer is made of a release film, the release film is peeled off and removed when the pressure-sensitive adhesive sheet is used.

[0026] The thickness of the base film is preferably 10 to 500 μm, more preferably 20 to 300 μm, and particularly preferably 30 to 200 μm, from the viewpoint of suppressing thermal shrinkage that occurs when forming a pressure-sensitive adhesive layer by ultraviolet irradiation and from the viewpoint of suppressing dents. The thickness of the base film can be measured in accordance with JIS K7130:1990.

[0027] (Adhesive Layer) The adhesive layer of the adhesive sheet of the present invention preferably has a thickness of 100 μm or more, more preferably 200 to 5000 μm, particularly preferably 300 to 3000 μm, even more preferably 400 to 2000 μm, and of these, 500 to 1000 μm is preferred. An adhesive layer having such a thickness will not reduce the visibility of the screen. The thickness of the adhesive layer can be measured in accordance with JIS K7130:1990.

[0028] The pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet of the present invention has a thickness of 500 μm and a reflectance of 1000 μm. ＊ a ＊ b ＊ Chromaticity b defined by the color system ＊ value (hereinafter simply "b ＊ It is preferable that the optical laminate is formed from a pressure-sensitive adhesive having a b value of -3.0 or more. This improves the phenomenon that the obtained optical laminate appears pale. From this viewpoint,＊ The value is preferably −2.8 or more, more preferably −2.5 or more, and particularly preferably −2.2 or more.

[0029] Here, the reflection mode refers to a mode in which light reflected from a sample is collected as an optical signal, and the transmission mode refers to a mode in which light transmitted through a sample is collected as an optical signal.

[0030] The inventors have found that if the obtained optical laminate appears pale, light on the low wavelength side is scattered backward during irradiation, and b is scattered to the minus side in the reflection mode. ＊ The value of b in the reflective mode of the adhesive layer becomes lower. ＊ Focusing on the value, b in the reflection mode when the adhesive layer is an adhesive layer with a thickness of 500 μm ＊ It has been found that when the value is adjusted to -3.0 or more and the pressure-sensitive adhesive layer is applied to an optical laminate such as an image display device, the phenomenon in which the optical laminate appears pale is improved.

[0031] Also, if the adhesive sheet looks pale, it means that the positive side is b in the transmission mode. ＊ Therefore, from the viewpoint of further improving the phenomenon of appearing pale, the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet of the present invention has a thickness of 500 μm, and the b value in the transmission mode of the pressure-sensitive adhesive layer is also found to be high. ＊ The value is preferably +1.0 or less, more preferably +0.7 or less, and even more preferably +0.5 or less. ＊ The lower limit of the value is not particularly limited, but is preferably 0 or more.

[0032] b in the reflective mode of the adhesive sheet ＊ The value can be calculated, for example, by using a laminate obtained by laminating the pressure-sensitive adhesive sheet on the pressure-sensitive adhesive layer side of the pressure-sensitive adhesive sheet to a blackboard as a measurement sample, measuring the total reflectance using a known haze meter, and performing hue conversion from the obtained total reflection spectrum. ＊The value can be calculated by using a laminate having a layer structure of soda glass / adhesive layer / base layer obtained by laminating the adhesive layer side of the adhesive sheet to a soda glass plate as a measurement sample, irradiating light from the base layer side, and performing hue conversion from the total light spectrum of the transmitted light.

[0033] The adhesive constituting the adhesive layer of the adhesive sheet of the present invention has a thickness of b ＊ There are no particular restrictions on the material, etc., as long as the adhesive is formed from an adhesive having a value of −3.0 or more.

[0034] The pressure-sensitive adhesive used may be any of an acrylic pressure-sensitive adhesive, a polyester pressure-sensitive adhesive, a polyurethane pressure-sensitive adhesive, a rubber pressure-sensitive adhesive, a silicone pressure-sensitive adhesive, etc. The pressure-sensitive adhesive may be any of an emulsion type, a solvent type, or a solventless type, and may be either a cross-linked type or a non-cross-linked type. Among these, an acrylic pressure-sensitive adhesive is preferred because of its excellent adhesive properties and optical properties. From the perspective of the SDGs, an emulsion type pressure-sensitive adhesive or a solventless pressure-sensitive adhesive is preferred, and a solventless pressure-sensitive adhesive is particularly preferred.

[0035] The adhesive constituting the adhesive layer of the adhesive sheet of the present invention is preferably composed of a cured product of an active energy ray-curable adhesive composition (hereinafter, sometimes referred to as the "adhesive composition of the present invention") containing a photopolymerization component and a hydrogen abstraction photopolymerization initiator. In this specification, "active energy ray-curable adhesive composition" refers to an adhesive composition that has the property of curing to form a cured product (adhesive) when irradiated with active energy rays. The adhesive composition of the present invention is preferred because it is less likely to undergo cure shrinkage due to active energy rays, making it easier to produce the above-mentioned adhesive sheet. In this specification, "(meth)acrylate" refers to both acrylate and methacrylate. The same applies to other similar terms.

[0036] The pressure-sensitive adhesive composition forming the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet of the present invention has an appropriate viscosity due mainly to the photopolymerizable component, and can therefore be used as a coating solution as is without adding a diluent, etc. Various additives may also be added as needed.

[0037] (Photopolymerizable Component) The photopolymerizable component is not particularly limited as long as it is a component that is cured by irradiation with active energy rays in the presence of a photopolymerization initiator described below. For example, it may be any of a monomer, an oligomer, a polymer, or a mixture thereof.

[0038] In the present invention, the photopolymerizable component is preferably at least one selected from the group consisting of a polymerizable vinyl monomer, a polymerizable vinyl prepolymer, a polyfunctional (meth)acrylate monomer, and a polyfunctional (meth)acrylate oligomer. Each component will be described in detail below.

[0039] (Polymerizable vinyl monomer) The polymerizable vinyl monomer is not particularly limited as long as it has a vinyl group-containing group, and conventionally known polymerizable vinyl monomers can be used appropriately. Note that the polymerizable vinyl monomer in the present invention means a polymerizable vinyl monomer having one vinyl group-containing group, and does not overlap with the polyfunctional (meth)acrylate monomer described below.

[0040] Specific examples of the polymerizable vinyl monomer include (meth)acrylates that do not have any functional groups other than vinyl group-containing groups in the molecule, such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, myristyl (meth)acrylate, palmityl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, isobornyl (meth)acrylate, phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, and polyoxyalkylene-modified (meth)acrylates. Among these, it is preferable to use 2-ethylhexyl (meth)acrylate, butyl (meth)acrylate, and isobornyl (meth)acrylate, from the viewpoint of easily exhibiting the above-mentioned optical properties and favorable adhesive properties.

[0041] The polymerizable vinyl monomer may further contain a functional group other than the vinyl group-containing group in the molecule. Examples of such functional groups include a hydroxy group, a carboxy group, a thiol group, and a primary or secondary amino group. Specific examples of polymerizable vinyl monomers having such functional groups include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; hydroxy group-containing (meth)acrylamides such as N-methylolacrylamide and N-methylolmethacrylamide; and ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, and citraconic acid. Among these, from the viewpoint of providing the resulting pressure-sensitive adhesive with suitable cohesive strength and good resistance to wet heat whitening, hydroxyalkyl (meth)acrylates are preferred, and 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate are more preferred.

[0042] Other polymerizable vinyl monomers include vinyl esters such as vinyl acetate and vinyl propionate; olefins such as ethylene, propylene, and isobutylene; halogenated olefins such as vinyl chloride and vinylidene chloride; styrene-based monomers such as styrene and α-methylstyrene; diene-based monomers such as butadiene, isoprene, and chloroprene; nitrile-based monomers such as acrylonitrile and methacrylonitrile; amide-based monomers such as acrylamide, methacrylamide, N-methylacrylamide, N-methylmethacrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, and N-vinylpyrrolidone; and tertiary amino group-containing monomers such as N,N-diethylaminoethyl (meth)acrylate and N-(meth)acryloylmorpholine.

[0043] (Polymerizable vinyl prepolymer) The polymerizable vinyl prepolymer is not particularly limited, and conventionally known ones can be used as appropriate, but it is preferable to use a polymerizable vinyl prepolymer obtained by polymerizing the above-mentioned polymerizable vinyl monomer. In this specification, the term "prepolymer" refers to a compound obtained by polymerizing a monomer and capable of constituting a polymer by further polymerization.

[0044] When the polymerizable vinyl monomer is polymerized to obtain a polymerizable vinyl prepolymer, one type of the monomer may be polymerized alone, or two or more types may be copolymerized. The polymerizable vinyl prepolymer may be obtained by free radical polymerization, may be obtained by living polymerization, or may be a polymer having a RAFT (Reversible Addition-Fragmentation Chain Transfer Polymerization) terminal.

[0045] The weight-average molecular weight of the polymerizable vinyl prepolymer is preferably 6,000 to 1,500,000, particularly preferably 7,500 to 1,000,000, and even more preferably 10,000 to 100,000. This makes it easy to adjust the viscosity of the pressure-sensitive adhesive composition to a desired range. Note that the weight-average molecular weight in this specification is a value measured by gel permeation chromatography (GPC) in terms of standard polystyrene.

[0046] (Polyfunctional (meth)acrylate Monomer) The polyfunctional (meth)acrylate monomer is not particularly limited, and conventionally known ones can be used as appropriate.

[0047] Preferred examples of polyfunctional (meth)acrylate monomers include monomers having two or more (meth)acryloyl groups in one molecule. Examples of such monomers include 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, neopentyl glycol adipate di(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, dicyclopentanyl di(meth)acrylate, caprolactone-modified dicyclopentenyl di(meth)acrylate, ethylene oxide-modified phosphate di(meth)acrylate, di(acryloxyethyl)isocyanurate, allylated cyclohexyl di(meth)acrylate, trimethylolpropane tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, and propionic acid-modified dipentaerythritol. tri(meth)acrylate, pentaerythritol tri(meth)acrylate, propylene oxide-modified trimethylolpropane tri(meth)acrylate, tris(acryloxyethyl)isocyanurate, bis(acryloxyethyl)hydroxyethyl isocyanurate, ethylene oxide isocyanurate-modified diacrylate, ethylene oxide isocyanurate-modified triacrylate, ε-caprolactone-modified tris(acryloxyethyl)isocyanurate, diglycerin tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, propionic acid-modified dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and caprolactone-modified dipentaerythritol hexa(meth)acrylate.

[0048] (Polyfunctional (meth)acrylate oligomer) The polyfunctional (meth)acrylate oligomer is not particularly limited, and conventionally known oligomers can be used as appropriate, and it is preferable to use a polyfunctional (meth)acrylate oligomer having two or more (meth)acryloyl groups in one molecule. Examples of such oligomers include urethane acrylate-based, polyester acrylate-based, epoxy acrylate-based, polyether acrylate-based, polybutadiene acrylate-based, and silicone acrylate-based oligomers.

[0049] The urethane acrylate oligomer can be obtained by esterifying a polyurethane oligomer obtained by reacting a compound such as a polyalkylene polyol, a polyether polyol, a polyester polyol, a hydroxy-terminated hydrogenated isoprene, or a hydroxy-terminated hydrogenated butadiene with a polyisocyanate, with (meth)acrylic acid or a (meth)acrylic acid derivative.

[0050] Examples of polyalkylene polyols used in the production of urethane acrylate oligomers include polypropylene glycol, polyethylene glycol, polybutylene glycol, polyhexylene glycol, etc., and polypropylene glycol is particularly preferred. When the number of functional groups of the resulting urethane acrylate oligomer is to be 3 or more, an appropriate combination of glycerin, trimethylolpropane, triethanolamine, pentaerythritol, ethylenediamine, diethylenetriamine, sorbitol, sucrose, etc. may be used.

[0051] Examples of polyisocyanates include aliphatic diisocyanates such as hexamethylene diisocyanate and trimethylene diisocyanate; aromatic diisocyanates such as tolylene diisocyanate, xylylene diisocyanate and diphenyl diisocyanate; and alicyclic diisocyanates such as dicyclohexylmethane diisocyanate and isophorone diisocyanate. Among these, it is preferable to use an aliphatic diisocyanate, and it is particularly preferable to use hexamethylene diisocyanate. Note that the polyisocyanate is not limited to bifunctional ones, and trifunctional or higher functional ones can also be used.

[0052] Examples of the (meth)acrylic acid derivative include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate; 2-isocyanate ethyl acrylate, 2-isocyanate ethyl methacrylate, and 1,1-bis(acryloxymethyl)ethyl isocyanate, and it is particularly preferable to use 2-isocyanate ethyl acrylate.

[0053] Another method for producing a urethane acrylate oligomer is to react a hydroxy group contained in a compound such as polyalkylene polyol, polyether polyol, polyester polyol, hydroxy-terminated hydrogenated isoprene, or hydroxy-terminated hydrogenated butadiene with an —N═C═O moiety contained in an isocyanate alkyl (meth)acrylate, to obtain the urethane acrylate oligomer. In this case, the isocyanate alkyl (meth)acrylate may be, for example, the above-mentioned 2-isocyanate ethyl acrylate, 2-isocyanate ethyl methacrylate, or 1,1-bis(acryloxymethyl)ethyl isocyanate.

[0054] The polyester acrylate oligomer can be obtained, for example, by esterifying with (meth)acrylic acid the hydroxy groups of a polyester oligomer having hydroxy groups at both ends, which is obtained by condensation of a polycarboxylic acid and a polyhydric alcohol, or by esterifying with (meth)acrylic acid the terminal hydroxy groups of an oligomer obtained by adding an alkylene oxide to a polycarboxylic acid.

[0055] Epoxy acrylate oligomers can be obtained, for example, by esterifying the oxirane ring of a relatively low molecular weight bisphenol epoxy resin or novolac epoxy resin with (meth)acrylic acid. Alternatively, carboxyl-modified epoxy acrylate oligomers can be used, in which epoxy acrylate oligomers are partially modified with dibasic carboxylic acid anhydrides.

[0056] The polyether acrylate oligomer can be obtained, for example, by esterifying the hydroxy group of a polyether polyol with (meth)acrylic acid.

[0057] The weight average molecular weight of the polyfunctional (meth)acrylate oligomer is preferably 10,000 to 350,000, and particularly preferably 20,000 to 200,000.

[0058] (Bulking ratio) The ratio obtained by dividing the mass of the polymerizable vinyl monomer by the mass of the polymerizable vinyl monomer having a functional group other than a vinyl group-containing group among the polymerizable vinyl monomers is preferably 1.5 to 10, particularly preferably 2 to 7, and further preferably 3 to 5. This makes it easier for the resulting pressure-sensitive adhesive to exhibit good resistance to wet heat whitening and the above-mentioned optical properties.

[0059] When two types of polymerization components, a polymerizable vinyl monomer and a polyfunctional (meth)acrylate oligomer, are used, the ratio obtained by dividing the mass of the polymerizable vinyl monomer by the mass of the polyfunctional (meth)acrylate oligomer is preferably 0.18 to 999, more preferably 1 to 100, and even more preferably 1.5 to 10. This makes it easier for the resulting pressure-sensitive adhesive to exhibit suitable adhesive strength and the above-mentioned optical properties.

[0060] [Photopolymerization initiator (C)] The pressure-sensitive adhesive composition of the present invention preferably contains a photopolymerization initiator (C), which enables efficient curing of the active energy ray-curable component in the pressure-sensitive adhesive composition and reduces the polymerization curing time and the active energy ray irradiation dose.

[0061] Examples of the photopolymerization initiator (C) include an intramolecular cleavage type photopolymerization initiator, a hydrogen abstraction type photopolymerization initiator, and a cationic photopolymerization initiator.

[0062] Examples of the intramolecular cleavage type photopolymerization initiator include 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy-1,2-diphenylethan-1-one, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2-hydroxy-2-methyl-1-phenylpropan-1-one, etc. These may be used alone or in combination of two or more.

[0063] Examples of hydrogen abstraction photopolymerization initiators include benzophenones such as 2-ethylanthraquinone, 2,4-diethylthioxanthone, benzophenone, and derivatives thereof; and aromatic ketones such as acetophenone, benzophenone, P,P'-dimethoxybenzophenone, P,P'-dichlorobenzophenone, P,P'-dimethylbenzophenone, and acetonaphthone. These may be used alone or in combination of two or more. Commercially available products such as Omnirad. MBF (manufactured by IGM) and Omnirad. 754 (manufactured by IGM) are also preferred.

[0064] Examples of the photocationic polymerization initiator include sulfonium salt compounds, iodonium salt compounds, phosphonium salt compounds, ammonium salt compounds, antimonate compounds, diazonium salt compounds, selenium salt compounds, oxonium salt compounds, and bromine salt compounds.

[0065] Among these, a hydrogen abstraction photopolymerization initiator is preferred as the photopolymerization initiator. This improves the reactivity of each material in the pressure-sensitive adhesive composition of the present invention, ensuring appropriate cohesion while facilitating the formation of a crosslinked structure that is less likely to cause wavelength shifts in the visible light region, and making it easier to satisfy the optical properties described above. This improves the phenomenon of the bluish white appearance.

[0066] It is also preferable to use an intramolecular cleavage-type photopolymerization initiator in combination with a hydrogen abstraction-type photopolymerization initiator, which further improves the reactivity of the materials in the pressure-sensitive adhesive composition of the present invention, makes it difficult for layer separation to occur, and more effectively improves the phenomenon of pale appearance.

[0067] The content of the photopolymerization initiator (C) in the adhesive composition is preferably 0.01 to 10 parts by mass, particularly preferably 0.1 to 5 parts by mass, and even more preferably 0.2 to 2 parts by mass, relative to 100 parts by mass of the photopolymerization component.

[0068] The pressure-sensitive adhesive composition of the present invention may contain, if desired, various additives commonly used in pressure-sensitive adhesives, such as a silane coupling agent, a heat curing agent, an oxygen absorber, an antistatic agent, a tackifier, an antioxidant, an ultraviolet absorber, an infrared absorber, a light stabilizer, a softener, a light diffusing agent, a colorant, a filler, a refractive index adjuster, etc.

[0069] [Silane Coupling Agent (D)] The pressure-sensitive adhesive composition of the present invention preferably further contains a silane coupling agent (D). This improves the adhesion of the resulting pressure-sensitive adhesive to a glass member when the adherend is a glass member. Furthermore, even when the adherend is a plastic plate, the resulting pressure-sensitive adhesive improves the adhesion of the resulting pressure-sensitive adhesive to the plastic plate.

[0070] The silane coupling agent (D) is preferably an organosilicon compound having at least one alkoxysilyl group in the molecule, which has good compatibility with the (meth)acrylic acid ester polymer (A) and has optical transparency.

[0071] Examples of the silane coupling agent (D) include polymerizable unsaturated group-containing silicon compounds such as vinyltrimethoxysilane, vinyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, and 3-methacryloxypropyltrimethoxysilane; silicon compounds having an epoxy structure such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, and 3-mercaptopropyldimethoxysilane; Examples of suitable silicon compounds include mercapto group-containing silicon compounds such as dimethylsilane; amino group-containing silicon compounds such as 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, and N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane; 3-chloropropyltrimethoxysilane; 3-isocyanatepropyltriethoxysilane; and condensates of at least one of these with alkyl group-containing silicon compounds such as methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, and ethyltrimethoxysilane. These may be used alone or in combination of two or more.

[0072] The content of the silane coupling agent (D) in the pressure-sensitive adhesive composition of the present invention is preferably 0.01 to 2 parts by mass, more preferably 0.05 to 1.5 parts by mass, particularly preferably 0.1 to 1 part by mass, and even more preferably 0.15 to 0.5 parts by mass, relative to 100 parts by mass of the photopolymerizable component, thereby improving adhesion to the adherend.

[0073] [Oxygen Absorber (E)] The pressure-sensitive adhesive composition of the present invention may contain an oxygen absorber (E). The oxygen absorber has oxygen absorbing ability, and therefore can sufficiently promote the crosslinking reaction and curing reaction of the pressure-sensitive adhesive composition. In addition, the pressure-sensitive adhesive sheet after the weather resistance test can be * It is possible to suppress the increase in value to within Δ±2.0.

[0074] Examples of oxygen absorbers include unsaturated double bond-containing compounds represented by the following formula:

[0075]

[0076] The oxygen absorber used in the present invention may further contain a transition metal salt from the viewpoint of improving oxygen absorption performance. Examples of transition metals constituting the transition metal salt include iron, nickel, copper, manganese, cobalt, rhodium, titanium, chromium, vanadium, and ruthenium. In terms of compatibility, the counter ion of the transition metal in the transition metal salt is preferably an anion species derived from an organic acid. Examples of organic acids include acetic acid, stearic acid, dimethyldithiocarbamic acid, palmitic acid, 2-ethylhexanoic acid, neodecanoic acid, linoleic acid, oleic acid, capric acid, and naphthenic acid.

[0077] When the pressure-sensitive adhesive composition of the present invention contains an oxygen absorber, the content of the oxygen absorber is preferably 0.01 to 5 parts by mass, more preferably 0.05 to 3 parts by mass, particularly preferably 0.1 to 1 part by mass, and even more preferably 0.2 to 0.6 parts by mass, relative to 100 parts by mass of the photopolymerizable component. This makes it easier to satisfy the above-mentioned optical properties.

[0078] The adhesive composition of the present invention preferably does not contain a solvent. A solvent refers to a substance that is not involved in the curing reaction and acts as a diluent to reduce the viscosity of the adhesive composition. If the adhesive composition contains a solvent, it is difficult to form a thick adhesive layer having a thickness of 100 μm or more. Furthermore, if the adhesive composition contains a solvent, a drying process is required, and the photopolymerization initiator (C) may decompose, volatilize, or sublimate. Even if the adhesive composition of the present invention does not contain a solvent, it is easy to adjust the viscosity to a level suitable for coating, and it is possible to appropriately produce an adhesive layer of a desired thickness.

[0079] In the pressure-sensitive adhesive sheet of the present invention, the content of low-molecular-weight components having a molecular weight of less than 3,000 contained in the pressure-sensitive adhesive is preferably 5,000 ppm or less, more preferably 4,000 ppm or less, particularly preferably 3,000 ppm or less, and even more preferably 2,200 ppm or less. The lower limit of the amount of such components is usually 0 ppm or more. This makes it possible to suppress appearance defects such as foaming even when the pressure-sensitive adhesive sheet is subjected to a high-temperature environment or a high-temperature, high-humidity environment. Furthermore, when a large amount of residual monomer components remains, the generation of unpleasant odors during the process of peeling off the release film can be suppressed. The content of low-molecular-weight components in the pressure-sensitive adhesive layer can be measured, for example, by gas chromatography analysis.

[0080] The gel fraction of the adhesive in the pressure-sensitive adhesive sheet of the present invention is preferably 30 to 100%, more preferably 40 to 95%, particularly preferably 50 to 90%, and even more preferably 60 to 85%. This makes it easier to obtain an adhesive with a moderate crosslinked structure, and to form a crosslinked structure that is less likely to cause wavelength changes in the visible light region, making it easier to satisfy the optical properties described above. This makes it easier to improve the phenomenon of appearing bluish-white. The gel fraction of the adhesive can be measured and calculated using the method described in the Examples.

[0081] The pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet of the present invention has excellent adhesive strength. The initial adhesive strength of the pressure-sensitive adhesive layer is preferably 28 (N / 25 mm) or more, more preferably 30 (N / 25 mm) or more. Furthermore, the adhesive strength measured in accordance with JIS Z0237:2009 under an environment of 85°C and 85% RH for 1000 hours and then under an environment of 23°C and 50% RH is preferably 18 (N / 25 mm) or more, more preferably 30 (N / 25 mm) or more. The adhesive strength of the pressure-sensitive adhesive layer can be measured by the method described in the Examples. Note that "α°C, β% RH" means "under an environment of temperature α°C and relative humidity β%."

[0082] The total light transmittance of the pressure-sensitive adhesive sheet of the present invention is preferably 85% or more, more preferably 88% or more, and even more preferably 90% or more. The upper limit of the total light transmittance is usually 100%. This makes the pressure-sensitive adhesive sheet of the present invention excellent in transparency and easily satisfies the above-mentioned optical properties. It can also be preferably used for optical components that require transparency. The total light transmittance of the pressure-sensitive adhesive sheet can be measured by the method described in the examples.

[0083] The haze of the pressure-sensitive adhesive sheet of the present invention is preferably 10% or less, more preferably 5% or less, particularly preferably 2% or less, and even more preferably 1% or less. The lower limit of the haze is usually 0%. This makes the pressure-sensitive adhesive sheet of the present invention excellent in transparency and easily satisfies the above-mentioned optical properties. It can also be preferably used for optical components that require transparency. The haze of the pressure-sensitive adhesive sheet can be measured by the method described in the examples.

[0084] The pressure-sensitive adhesive sheet of the present invention has excellent resistance to wet heat whitening. The difference between the initial haze (%) of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet of the present invention, measured by the method described in the Examples, and the haze (%) after a durability test is 1.5 or more and less than 8.0, and more preferably less than 1.5.

[0085] The pressure-sensitive adhesive sheet of the present invention has excellent blister resistance. The difference between the initial total light transmittance (%) of the pressure-sensitive adhesive sheet of the present invention and the total light transmittance (%) after irradiating the surface side of the pressure-sensitive adhesive layer with ultraviolet light for 1000 hours using an ultraviolet fade meter in accordance with JIS B7751:2007 is usually 4.0% or less, preferably 3.5% or less, and more preferably 3.0% or less.

[0086] The pressure-sensitive adhesive sheet of the present invention has excellent durability. The excellent durability of the pressure-sensitive adhesive sheet of the present invention can be confirmed, for example, by a change in the initial haze (%) of the pressure-sensitive adhesive sheet of the present invention and the haze (%) after irradiating the surface side of the pressure-sensitive adhesive layer with ultraviolet light for 1000 hours using an ultraviolet fade meter in accordance with JIS B7751:2007 being 1% or less. More specifically, this is determined by the method described in the examples.

[0087] Furthermore, a sample having a layer structure of soda glass / adhesive layer (500 μm) / soda glass was autoclaved (50°C, 0.5 MPa, 20 minutes), and the sample was left overnight. After that, no bubbles, lifting, or peeling were observed before or after placing the sample under durable conditions (85°C, 85% RH).

[0088]

[0023] 2) Method for Producing Pressure-Sensitive Adhesive Sheet

[0024] The method for producing a pressure-sensitive adhesive sheet of the present invention is a method for producing a pressure-sensitive adhesive sheet having a substrate layer and a pressure-sensitive adhesive layer, and preferably includes the steps of forming, on the substrate layer, a coating film of an active energy ray-curable pressure-sensitive adhesive composition containing one or more photopolymerizable components selected from the group consisting of polymerizable vinyl monomers, polymerizable vinyl prepolymers, polyfunctional (meth)acrylate monomers, and polyfunctional (meth)acrylate oligomers, and a hydrogen abstraction photopolymerization initiator, and irradiating the coating film with active energy rays to cure the active energy ray-curable pressure-sensitive adhesive composition to form a pressure-sensitive adhesive layer. The active energy ray-curable pressure-sensitive adhesive composition is preferably a solvent-free composition.

[0089] The active energy ray-curable pressure-sensitive adhesive composition can be prepared by uniformly mixing one or more photopolymerization components selected from the group consisting of polymerizable vinyl monomers, polymerizable vinyl prepolymers, polyfunctional (meth)acrylate monomers, and polyfunctional (meth)acrylate oligomers, and a hydrogen abstraction photopolymerization initiator.

[0090] First, a coating film of the pressure-sensitive adhesive composition of the present invention is formed on a substrate layer. Examples of coaters used to form the coating film of the pressure-sensitive adhesive composition of the present invention include spin coaters, spray coaters, bar coaters, knife coaters, roll coaters, knife roll coaters, blade coaters, gravure coaters, curtain coaters, and die coaters.

[0091] The thickness of the coating film to be formed is preferably 100 μm or more. In this case, it is preferable to use an active energy ray-curable pressure-sensitive adhesive composition containing one or more photopolymerizable components selected from the group consisting of polymerizable vinyl monomers, polymerizable vinyl prepolymers, polyfunctional (meth)acrylate monomers, and polyfunctional (meth)acrylate oligomers, and a hydrogen abstraction photopolymerization initiator, as the pressure-sensitive adhesive composition. This effectively improves the phenomenon of the bluish-white appearance even when a thick pressure-sensitive adhesive layer is formed, and allows for the efficient formation of a pressure-sensitive adhesive layer that is excellent in transparency, durability, blister resistance, moist heat resistance, and weather resistance.

[0092] Furthermore, by using an active energy ray-curable pressure-sensitive adhesive composition that does not contain a solvent, a pressure-sensitive adhesive layer having a thickness of 100 μm or more can be easily formed, and this is also preferable because there is no need to dry the coating film and the burden on the environment can be reduced.

[0093] Next, the resulting coating film is irradiated with active energy rays to cure the curable composition, thereby forming a pressure-sensitive adhesive layer.

[0094] The active energy ray refers to an electromagnetic wave or a charged particle beam that has an energy quantum. Specifically, ultraviolet light; an electron beam; laser light such as a semiconductor laser, an argon laser, or a He—Cd laser; ionizing radiation such as α-rays, β-rays, γ-rays, neutron beams, X-rays, or accelerated electron beams; and the like can be used. Among these, ultraviolet light and an electron beam are preferred as active energy rays, as they can be generated using a relatively simple device, and ultraviolet light is more preferred.

[0095] When ultraviolet rays are used as the active energy rays, the ultraviolet rays can be irradiated by a high-pressure mercury lamp, a fusion H lamp, a xenon lamp, etc. The irradiation amount of ultraviolet rays is set to an illuminance of 50 to 1000 mW / cm. ２ The light intensity is preferably about 50 to 10,000 mJ / cm. ２ is preferably 80 to 5000 mJ / cm ２ More preferably, it is 300 to 2000 mJ / cm ２ On the other hand, the electron beam irradiation can be carried out by an electron beam accelerator or the like, and the irradiation dose of the electron beam is preferably about 10 to 1000 krad.

[0096] In this way, a pressure-sensitive adhesive sheet having a layer structure of a substrate layer / a pressure-sensitive adhesive layer can be produced. In this case, a release film may be laminated on the pressure-sensitive adhesive layer for the purpose of protecting the surface of the pressure-sensitive adhesive layer. The release film may be the same as those listed as being used as the substrate layer. The release film is peeled off and removed when the pressure-sensitive adhesive sheet is used.

[0097] [Optical Laminate] The optical laminate of the present invention includes the pressure-sensitive adhesive sheet of the present invention. The optical laminate of the present invention is not limited in any way as long as it is a structure that requires a thick pressure-sensitive adhesive layer. For example, preferred examples include a laminate formed by sandwiching a transparent conductive film made of tin-doped indium oxide (ITO) between two glass substrates (or plastic films) laminated with the pressure-sensitive adhesive layer so that the transparent conductive film side is in contact with the pressure-sensitive adhesive layer, and a laminate formed by filling the gap between hard plates formed by laminating a polarizing plate or a retardation plate on a glass substrate with a thick pressure-sensitive adhesive layer.

[0098] An example of an optical laminate 20 of the present invention is shown in Figure 2. In Figure 2, 3 is a liquid crystal display, 10 is the pressure-sensitive adhesive sheet of the present invention, and 4 is a top panel. The optical laminate of the present invention is improved in the phenomenon of appearing bluish-white, even when it has a thick pressure-sensitive adhesive layer. Therefore, the optical laminate has a good appearance and is highly valuable as a product.

[0099] The above-described embodiments have been described to facilitate understanding of the present invention, and are not intended to limit the present invention. Therefore, each element disclosed in the above embodiments is intended to include all design modifications and equivalents that fall within the technical scope of the present invention.

[0100] In this specification, when it is stated that "α to β" (α and β are any numbers), it means "not less than α and not more than β" unless otherwise specified, and also includes the meaning of "preferably greater than α" or "preferably smaller than β." Furthermore, when it is stated that "not less than α" (α is any number), it also includes the meaning of "preferably greater than α" unless otherwise specified, and when it is stated that "not more than β" (β is any number), it also includes the meaning of "preferably smaller than β" unless otherwise specified.

[0101] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0102] (1) Preparation of Urethane Acrylate Oligomer A urethane acrylate oligomer was prepared as follows. A mixture of 100 parts by mass (solids equivalent; the same applies below) of polypropylene glycol having a weight average molecular weight of 3,000, 4 parts by mass of hexamethylene diisocyanate, and 0.02 parts by mass of dioctyltin dilaurate was polymerized to obtain a reaction product. Measurement of the IR spectrum of the resulting reaction product by infrared spectroscopy confirmed that the isocyanate groups had almost completely disappeared.

[0103] Thereafter, 1 part by mass of 2-isocyanatoethyl acrylate was mixed with the total amount of the obtained reaction product, and polymerization was carried out to obtain a urethane acrylate oligomer (a1) as a polyfunctional (meth)acrylate oligomer. When the IR spectrum of the obtained urethane acrylate oligomer (A1) was measured by infrared spectroscopy, it was confirmed that the isocyanate groups had almost completely disappeared. Furthermore, when the molecular weight of the obtained urethane acrylate oligomer (a1) was measured by the method described below, the weight average molecular weight (Mw) was 25,000.

[0104] The weight average molecular weight (Mw) is a weight average molecular weight converted to standard polystyrene measured using gel permeation chromatography (GPC) under the following conditions (GPC measurement). <Measurement conditions> GPC measurement device: HLC-8020, manufactured by Tosoh Corporation GPC columns (passed in the following order): TSK guard column HXL-H, TSK gel GMHXL (x2), TSK gel G2000HXL, manufactured by Tosoh Corporation Measurement solvent: tetrahydrofuran Measurement temperature: 40°C

[0105] (2) (Meth)acrylic acid ester monomers The following (meth)acrylic acid ester monomers were prepared: (b1) 2-ethylhexyl acrylate (b2) isobornyl acrylate (b3) 4-hydroxybutyl acrylate

[0106] (3) Photopolymerization initiator The following were prepared as photopolymerization initiators: (C1): 1-hydroxycyclohexyl phenyl ketone (C2): Blend of oxy-phenyl-acetic acid 2-[2-oxo-2-phenyl-acetoxyethoxy]-ethyl ester and oxy-phenyl-acetic acid 2-[2-hydroxyethoxy]-ethyl ester (Omnirad. 754, manufactured by IGM) (C3): Benzophenone

[0107] (4) Silane Coupling Agent The following silane coupling agents were prepared: (D1): 3-glycidoxypropyltrimethoxysilane (D2): 3-acryloxypropyltrimethoxysilane (D3): 3-mercaptopropyltrimethoxysilane (D4): 3-glycidoxypropyltrimethoxysilane

[0108] (5) Oxygen Absorber The following oxygen absorbers were prepared: (E1): Diprenyl Glycerin Ether (DPNG, manufactured by Kuraray Co., Ltd.)

[0109] [Example 1] (Preparation of adhesive composition) 30 parts by mass of the urethane acrylate oligomer (a1) prepared as described above, 40 parts by mass of 2-ethylhexyl acrylate (b1) as a polymerizable vinyl monomer, 10 parts by mass of isobornyl acrylate (b2) as a polymerizable vinyl monomer, and 20 parts by mass of 4-hydroxybutyl acrylate (b3) as a polymerizable vinyl monomer were mixed and stirred to obtain a liquid mixture (A1).

[0110] To 100 parts by mass of the liquid mixture (A1) obtained above, 0.5 parts by mass of 1-hydroxycyclohexyl phenyl ketone as a photopolymerization initiator (C1), 0.5 parts by mass of a blend of oxy-phenyl-acetic acid 2-[2-oxo-2-phenyl-acetoxyethoxy]-ethyl ester and oxy-phenyl-acetic acid 2-[2-hydroxyethoxy]-ethyl ester (Omnirad.754, manufactured by IGM) as a photopolymerization initiator (C2), and 0.2 parts by mass of 3-glycidoxypropyltrimethoxysilane (D1) as a silane coupling agent were added, and the mixture was thoroughly stirred to obtain an ultraviolet-curable pressure-sensitive adhesive composition.

[0111] (Production of adhesive sheet) A predetermined amount of the adhesive composition obtained above was applied using a knife coater to the release-treated surface of a release sheet S1 (thickness: 100 μm) made by treating one side of a polyethylene terephthalate film with a silicone-based release agent.

[0112] Next, the coating layer on the release sheet S1 obtained above was bonded to a release sheet S2 (thickness: 75 μm) made of a polyethylene terephthalate film with one side treated with a silicone-based release agent so that the release-treated surface of the release sheet S2 was in contact with the coating layer.

[0113] Thereafter, the coating layer was irradiated with active energy rays through the release sheet S2 under the following conditions to cure the adhesive composition and form an adhesive layer, thereby producing an adhesive sheet with a release sheet having a configuration of release sheet S1 / adhesive layer (thickness: 500 μm) / release sheet S2. (Active energy ray irradiation conditions) Light source: high-pressure mercury lamp Light intensity: 1000 mJ / cm ２ ・Illuminance: 100mW / cm ２

[0114] [Examples 2 to 7, Comparative Example 1] Pressure-sensitive adhesive sheets with release sheets were produced in the same manner as in Example 1, except that the type and amount of photopolymerization initiator, the type and amount of silane coupling agent, and the amount of oxygen absorber were changed as shown in Table 1.

[0115] The thickness of the adhesive layer was measured using a constant pressure thickness measuring device (manufactured by Teclock Corporation, product name "PG-02") in accordance with JIS K 7130. Furthermore, regarding the release strength of release sheets S1 and S2 in the obtained adhesive sheets (Examples 2 to 7, Comparative Example 1), it was confirmed that release sheet S1 had a greater release strength than release sheet S2.

[0116]

[0117] (Test and Evaluation Methods) The release sheet-attached pressure-sensitive adhesive sheets produced above were subjected to the following evaluation tests.

[0118] (1) Gel fraction The pressure-sensitive adhesive sheets with release sheets produced in the Examples and Comparative Examples were cut to a size of 80 mm x 80 mm, the pressure-sensitive adhesive layer was wrapped in a polyester mesh (mesh size 200), and the mass was weighed on a precision balance. The mass of the mesh alone was subtracted to calculate the mass of the pressure-sensitive adhesive alone. This mass was designated M1.

[0119] Next, the adhesive wrapped in the polyester mesh was immersed in ethyl acetate at room temperature (23°C) for 24 hours. The adhesive was then removed and dried in an oven at 100°C for 6 hours, and then left in an environment of 23°C and 50% RH for 24 hours. The mass of the adhesive wrapped in the mesh was then weighed using a precision balance, and the mass of the mesh alone was subtracted to calculate the mass of the adhesive alone. This mass was designated M2. The gel fraction (%) was expressed as (M2 / M1) x 100. The results are shown in Table 2.

[0120] (2) Adhesive Strength In an environment of 23 ° C. and 50% RH, the release sheet S2 was peeled from the release sheet-attached adhesive sheet produced in the Examples and Comparative Examples, and the exposed adhesive layer was attached to an easy-adhesion layer of a polyethylene terephthalate (PET) film (Toyobo Co., Ltd., Cosmoshine A4160, thickness: 100 μm) having an easy-adhesion layer to obtain a release sheet S1 / adhesive layer / PET film laminate. The resulting laminate was cut into a width of 25 mm and a length of 100 mm. Then, the release sheet S1 was peeled from the cut laminate, and the exposed adhesive layer was attached to soda glass, and then pressurized in an autoclave (Kurihara Seisakusho Co., Ltd.) at 0.5 MPa and 50 ° C. for 20 minutes. The sample was then left for 24 hours in an environment of 23 ° C. and 50% RH.

[0121] The adhesive strength (N / 25 mm) of the sample was measured at 23°C and 50% RH using a tensile tester (manufactured by A&D Co., Ltd., product name "Tensilon") at a peel speed of 300 mm / min and a peel angle of 180°, and this was taken as the initial adhesive strength. Measurements were conducted under conditions other than those described here in accordance with JIS Z0237:2009. The results are shown in Table 2.

[0122] The above samples were also left for 1000 hours in an environment of 85°C and 85% RH. Thereafter, the adhesive strength (N / 25 mm) was measured under the same conditions as the initial adhesive strength in an environment of 23°C and 50% RH. The results are shown in Table 2.

[0123] (3) Evaluation Test of Humidity and Heat Whitening Resistance The adhesive layer of the release-sheet-attached adhesive sheet obtained in the Examples and Comparative Examples was sandwiched between two ITO-deposited films (manufactured by Oike Kogyo Co., Ltd., product name "Tetlite TCFKH150NMH2-125-U6 / T2") to obtain a laminate. The obtained laminate was autoclaved for 20 minutes under conditions of 50°C and 0.5 MPa, and then left at atmospheric pressure, 23°C, and 50% RH for 24 hours. The haze (%) of the laminate was measured in accordance with JIS K7136:2000 using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "NDH5000"), and this was recorded as the initial haze (%) before the evaluation test of humidity and heat whitening resistance. The results are shown in Table 2.

[0124] Next, the laminate was stored under humid heat conditions of 85°C and 85% RH for 120 hours, and then left in an environment of 23°C and 50% RH for 24 hours. The haze (%) of the laminate was measured in the same manner as above. The measurement result was taken as the haze (%) after the evaluation test for humidity and heat whitening resistance (immediately after removal). The results are shown in Table 2.

[0125] Resistance to wet heat whitening was evaluated according to the following criteria based on the difference in haze value before and after the evaluation test for resistance to wet heat whitening. Examples 1 to 7 and Comparative Example 1 were all rated as excellent, demonstrating excellent resistance to wet heat whitening: Excellent: The difference in haze value is less than 1.5. Good: The difference in haze value is 1.5 or more and less than 8.0. Bad: The difference in haze value is 8.0 or more.

[0126] The adhesive layer evaluated as "◎" in the humidity and heat whitening resistance test shows no whitening at all and can be said to be suitable for use in displays, etc. The adhesive layer evaluated as "◯" shows whitening, but can also be said to be suitable for use in displays, etc. The adhesive layer evaluated as "×" shows whitening, and can be said to be unsuitable for use in displays, etc.

[0127] (4) Evaluation test for blister resistance The release sheet S2 was peeled off from the release-sheet-attached pressure-sensitive adhesive sheets obtained in the Examples and Comparative Examples, and the exposed pressure-sensitive adhesive layer was attached to an ITO vapor-deposited film (manufactured by Oike Kogyo Co., Ltd., product name "Tetlite TCFKH150NMH2-125-U6 / T2"). Furthermore, the release sheet S1 was peeled off from the release-sheet-attached pressure-sensitive adhesive sheet, and the exposed pressure-sensitive adhesive layer was attached to the polycarbonate resin plate side of a resin plate (manufactured by Mitsubishi Gas Chemical Company, Inc., product name "Iupilon Sheet MR58U", containing an ultraviolet absorber, thickness: 0.8 mm) in which a polymethyl methacrylate resin layer was laminated on a polycarbonate resin plate, thereby obtaining an evaluation sample.

[0128] The obtained evaluation sample was autoclaved for 20 minutes under conditions of 50°C and 0.5 MPa, and then left for 12 hours at normal pressure, 23°C, and 50% RH. After storing for 72 hours in an environment of 85°C and 85% RH, the condition of the interface between the pressure-sensitive adhesive layer and the adherend was visually inspected, and blister resistance was evaluated according to the following criteria. The results are shown in Table 2. ○: No bubbles or lifting / peeling occurred. △: Slight micro-bubbles occurred (no large bubbles or peeling), and whitening of the pressure-sensitive adhesive layer was observed. ×: Bubbles, bubble marks, or lifting / peeling occurred.

[0129] (5) Total Light Transmittance The release sheet S2 was peeled off from the release sheet-attached pressure-sensitive adhesive sheets obtained in the Examples and Comparative Examples, and the exposed pressure-sensitive adhesive layer was attached to soda-lime glass, which was used as an initial measurement sample (sample A).

[0130] Sample A obtained above was stored in a humid and hot environment of 85°C and 85% RH for 72 hours, and then left in an environment of 23°C and 50% RH for 1 hour, and this was used as a measurement sample (Sample B) after the humid and heat resistance durability test.

[0131] The measurement sample obtained above after the wet heat durability test was placed in a weather resistance tester (manufactured by Suga Test Instruments Co., Ltd., product name "Ultraviolet Fade Meter U48", light source: carbon arc lamp) and irradiated with ultraviolet light for 1000 hours in accordance with JIS B7751-2007. Thereafter, the sample was left in an environment of 23°C and 50% RH for 1 hour, and this was used as the measurement sample (Sample C) after the weather resistance test.

[0132] For each of the samples A, B, and C obtained above, the total light transmittance was measured in accordance with JIS 7361-1:1997 using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "SH7000"). This resulted in the total light transmittance of the initial pressure-sensitive adhesive layer, the pressure-sensitive adhesive layer after the moist heat durability test, and the pressure-sensitive adhesive layer after the weather resistance test. Furthermore, the difference between the total light transmittance of the initial pressure-sensitive adhesive layer and the total light transmittance of the pressure-sensitive adhesive layer after the weather resistance test was calculated. The results are shown in Table 3. The total light transmittance was measured by irradiating light from the pressure-sensitive adhesive layer side of the laminate after blank correction. In Table 3, "T.T (%)" represents the total light transmittance, "85°C, 85% RH" represents the total light transmittance of the measurement sample (Sample B) after the moist heat durability test, and "fade 1000h" represents the total light transmittance of the measurement sample (Sample C) after the weather resistance test. Furthermore, "initial - after durability" represents the difference between the total light transmittance of measurement sample A and the total light transmittance of the measurement sample (sample C) after the weather resistance test.

[0133] (6) Haze Value Samples A, B, and C were prepared in the same manner as in the measurement of total light transmittance described above. For Samples A, B, and C, the haze values ​​(%) were measured in accordance with JIS K7136:2000 using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "SH7000"). This resulted in the haze values ​​(%) of the initial pressure-sensitive adhesive layer, the pressure-sensitive adhesive layer after the moist heat durability test, and the pressure-sensitive adhesive layer after the weather resistance test. Furthermore, the difference between the haze value of the initial pressure-sensitive adhesive layer and the haze value of the pressure-sensitive adhesive layer after the weather resistance test was calculated. The results are shown in Table 3. The haze values ​​(%) were measured by irradiating light from the pressure-sensitive adhesive layer side of the laminate after blank correction. In Table 3, "Haze (%)" represents the haze value, "85°C, 85% RH" represents the haze value of the measurement sample (sample B) after the moist heat durability test, "fade 1000h" represents the haze value of the measurement sample (sample C) after the weather resistance test, and "initial - after durability" represents the difference between the haze value of measurement sample A and the haze value of the measurement sample (sample C) after the weather resistance test.

[0134] (7) Color measurement (reflective mode) The release sheet S2 was peeled off from the release-sheet-attached adhesive sheets obtained in the Examples and Comparative Examples, and the exposed adhesive layer was attached to a blackboard to prepare a sample. Next, a UV-VIS-NIR measuring instrument (Shimadzu Corporation, product name "UV-3600") was used to perform background measurement without placing anything inside the measuring instrument, and then light was irradiated onto the adhesive layer surface of the sample to obtain a total reflectance spectrum. The obtained total reflectance spectrum was subjected to hue conversion to obtain b ＊ The value was calculated.

[0135] (8) Color measurement (transmission mode) Samples A, B, and C were prepared in the same manner as in the measurement of total light transmittance described above. The color values ​​of these samples were measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "SH7000"). After blank correction, light was irradiated from the pressure-sensitive adhesive layer side for measurement. The results are shown in Table 3. In Table 3, "initial" refers to the b * The value of "85°C, 85% RH" is the value of the measurement sample (sample B) after the humidity and heat durability test. ＊ The value, "fade1000h", is the b of the measurement sample (sample C) after the weather resistance test. ＊ Each represents a value.

[0136] (9) Paleness Evaluation The release sheet S2 was peeled off from the release-sheet-attached pressure-sensitive adhesive sheets obtained in the Examples and Comparative Examples, and the exposed pressure-sensitive adhesive layer was attached to a blackboard to prepare a sample. The color of the samples of the Examples and Comparative Examples was observed and evaluated under fluorescent light. The evaluation results are shown in Table 3. ◯: No paleness was observed. ×: A paleness was observed.

[0137] (10) Residual Monomer Concentration 0.1 g of adhesive was isolated from the adhesive layer of the adhesive sheets with release sheets obtained in the Examples and Comparative Examples, placed in a 22 mL vial, and maintained at 120°C for 30 minutes. The gas phase components in the vial were then introduced into a gas chromatograph (manufactured by Hewlett-Packard, product name "6890 Model") using a headspace sampler (manufactured by PerkinElmer, product name "TerphoMatrix 40"), and component analysis was performed to confirm the residual monomer concentration (ppm). The separation column used was an HP-5 manufactured by Hewlett-Packard. The measurement results are shown in Table 3.

[0138]

[0139]

[0140] The following can be seen from Tables 2 and 3. The samples of Examples 1 to 7 using the pressure-sensitive adhesive sheets of the present invention exhibited b ＊ The value was -3.0 or more, and the pressure-sensitive adhesive sheet did not appear pale. Therefore, when these pressure-sensitive adhesive sheets are used, it is expected that the phenomenon in which the optical laminate appears pale will be significantly improved. ＊ The pressure-sensitive adhesive sheet of Comparative Example 1, which had a value of -4.3, appeared pale. The pressure-sensitive adhesive sheets of Examples 1 to 5 were excellent in all of transparency, durability, blister resistance, resistance to moist heat whitening, and weather resistance. The pressure-sensitive adhesive sheet of Example 6, which had a pressure-sensitive adhesive layer formed from a pressure-sensitive adhesive composition containing no silane coupling agent and no oxygen absorber, was poor in adhesive strength and blister resistance. The pressure-sensitive adhesive sheet of Example 7, which had a pressure-sensitive adhesive layer formed from a pressure-sensitive adhesive composition containing a photopolymerization initiator containing C1 and C3 but no C2, was somewhat poor in weather resistance and blister resistance. Furthermore, the pressure-sensitive adhesive sheet of Comparative Example 1, which had a pressure-sensitive adhesive layer formed from a pressure-sensitive adhesive composition containing a photopolymerization initiator containing only C1, was poor in adhesive strength and somewhat poor in blister resistance, and exhibited a b ＊ The value was low at -4.3, the paleness evaluation test also gave an unfavorable result ("x"), and the residual monomer concentration was also high.

[0141] DESCRIPTION OF SYMBOLS 1: Base layer 2: Pressure-sensitive adhesive layer 3: Liquid crystal display 4: Top panel 10: Pressure-sensitive adhesive sheet 20: Optical laminate

Claims

1. A pressure-sensitive adhesive sheet having a substrate layer and a pressure-sensitive adhesive layer, wherein the thickness of the pressure-sensitive adhesive layer is 100 μm or more, and the pressure-sensitive adhesive layer has a CIE 1976L reflection coefficient in the reflection mode of the pressure-sensitive adhesive layer when the film thickness is 500 μm. ＊ a ＊ b ＊ Chromaticity b defined by the color system ＊ A pressure-sensitive adhesive sheet characterized by being formed from a pressure-sensitive adhesive having a value of -3.0 or more.

2. The pressure-sensitive adhesive layer has a thickness of 500 μm and a CIE 1976L ＊ a ＊ b ＊ Chromaticity b defined by the color system ＊ The pressure-sensitive adhesive sheet according to claim 1 , which is formed from a pressure-sensitive adhesive having a value of +1.0 or less.

3. The pressure-sensitive adhesive sheet according to claim 1 or 2, which has a total light transmittance of 85% or more.

4. A pressure-sensitive adhesive sheet as described in claim 1 or 2, in which the difference between the initial total light transmittance (%) and the total light transmittance (%) after irradiating the surface side of the pressure-sensitive adhesive layer with ultraviolet light for 1000 hours using an ultraviolet fade meter in accordance with JIS B7751:2007 is 4.0% or less.

5. An adhesive sheet as described in claim 1 or 2, in which the change in haze (%) between the initial haze (%) and the haze (%) after irradiating the surface side of the adhesive layer with ultraviolet light for 1000 hours using an ultraviolet fade meter in accordance with JIS B7751:2007 is 1% or less.

6. The adhesive sheet according to claim 1 or 2, wherein the adhesive layer is made of an acrylic adhesive.

7. The adhesive sheet according to claim 1 or 2, wherein the adhesive layer comprises a cured product of an active energy ray-curable adhesive composition containing one or more photopolymerizable components selected from the group consisting of polymerizable vinyl monomers, polymerizable vinyl prepolymers, polyfunctional (meth)acrylate monomers, and polyfunctional (meth)acrylate oligomers, and a hydrogen abstraction photopolymerization initiator.

8. The pressure-sensitive adhesive sheet according to claim 7, wherein the active energy ray-curable pressure-sensitive adhesive composition does not contain a solvent.

9. The pressure-sensitive adhesive sheet according to claim 7, wherein the content of low-molecular-weight components having a molecular weight of 3,000 or less in the pressure-sensitive adhesive layer is 5,000 ppm or less.

10. The pressure-sensitive adhesive sheet according to claim 7, wherein the active energy ray-curable pressure-sensitive adhesive composition contains an oxygen absorber.

11. A method for producing a pressure-sensitive adhesive sheet having a base layer and a pressure-sensitive adhesive layer, comprising the steps of: forming, on the base layer, a coating film of an active energy ray-curable pressure-sensitive adhesive composition containing one or more photopolymerizable components selected from the group consisting of polymerizable vinyl monomers, polymerizable vinyl prepolymers, polyfunctional (meth)acrylate monomers, and polyfunctional (meth)acrylate oligomers, and a hydrogen abstraction photopolymerization initiator; and irradiating the coating film with active energy rays to cure the active energy ray-curable pressure-sensitive adhesive composition, thereby forming a pressure-sensitive adhesive layer.

12. The method for producing a pressure-sensitive adhesive sheet according to claim 11, characterized in that the active energy ray-curable pressure-sensitive adhesive composition does not contain a solvent.

13. An optical laminate comprising the pressure-sensitive adhesive sheet according to claim 1 or 2.

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