Pressure-sensitive adhesive composition, pressure-sensitive adhesive layer, pressure-sensitive adhesive film, and pressure-sensitive

Abstract

Disclosed are a pressure-sensitive adhesive composition, a pressure-sensitive adhesive layer, a pressure-sensitive adhesive film and an optical film with a pressure-sensitive adhesive layer, which have high adhesive strength and high adhesive properties despite being thin films having a thickness of 1-20 μm.SOLUTION: A pressure-sensitive adhesive composition comprising an acrylic polymer and (E) a crosslinking agent, wherein the acrylic polymer is obtained by copolymerizing (A) at least one or more alkyl (meth) acrylate monomers having an alkyl group with C1 to C14 carbon atoms, (B) at least one or more (meth) acrylate monomers containing an aromatic group, (C) at least one or more nitrogen-containing vinyl monomers containing neither carboxyl groups nor hydroxyl groups, and (D) at least one or more copolymerizable vinyl monomers containing carboxyl groups and / or copolymerizable vinyl monomers containing hydroxyl groups, the crosslinking agent (E) is selected from an adduct of tolylene diisocyanate and an adduct of xylylene diisocyanate.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive layer that has high adhesive strength and high adhesion properties despite being a thin film with a thickness of 1 μm to 20 μm, and is used for bonding between layers of optical components, and a pressure-sensitive adhesive film using the same. [Background technology]

[0002] BACKGROUND ART Various pressure-sensitive adhesive films have been proposed for bonding optical members such as polarizing plates and retardation plates to adherends such as liquid crystal cells via pressure-sensitive adhesive layers (see, for example, Patent Documents 1 and 2). Patent Document 1 describes an optical pressure-sensitive adhesive composition containing butyl acrylate or the like as a main monomer component and containing an acrylamide compound or the like. Patent Document 2 describes an optical pressure-sensitive adhesive composition containing a (meth)acrylate having an alkyl group with 4 to 8 carbon atoms as a main component monomer, a carboxyl group-containing monomer, and a nitrogen-containing vinyl monomer. Furthermore, various pressure-sensitive adhesive films have been proposed that incorporate various techniques to increase the refractive index of the pressure-sensitive adhesive layer (see, for example, Patent Documents 3 to 8). Patent Document 3 describes an optical pressure-sensitive adhesive composition containing a tackifier having an aromatic ring and a refractive index of 1.51 to 1.75. Patent Document 4 describes a pressure-sensitive adhesive sheet containing a pressure-sensitive adhesive composition containing a copolymerizable polymer of an acrylic acid-modified monomer containing an aromatic ring. Patent Document 5 describes an optical pressure-sensitive adhesive composition containing a tackifier resin having an aromatic ring and an aromatic phosphate ester-based plasticizer. Patent Document 6 describes a pressure-sensitive adhesive obtained by curing a pressure-sensitive adhesive composition containing an acrylic resin and an aromatic compound containing one ethylenically unsaturated group. Patent Document 7 describes an optical component in which a retardation film and a birefringent plate are fixed to each other via an acrylic adhesive containing an aromatic monomer. Patent Document 8 describes a pressure-sensitive adhesive composition containing a urethane resin obtained by reacting an aromatic diisocyanate with an aromatic polyester diol. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-177022 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-201734 [Patent Document 3] Japanese Patent Application Laid-Open No. 2007-084762 [Patent Document 4] Japanese Patent Application Laid-Open No. 2011-153169 [Patent Document 5] Japanese Patent Application Laid-Open No. 2012-167188 [Patent Document 6] Japanese Patent Application Laid-Open No. 2012-021148 [Patent Document 7] Japanese Patent Application Laid-Open No. 2006-293281 [Patent Document 8] Japanese Patent Application Laid-Open No. 2009-091522 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, a requirement for adhesive films used to bond layers of optical components has been to reduce the thickness of the adhesive layer to 20 μm or less in order to facilitate the thinning of optical components. Generally, the adhesive strength of a pressure-sensitive adhesive layer is approximately proportional to the thickness of the pressure-sensitive adhesive layer, and therefore, when the thickness of the pressure-sensitive adhesive layer is reduced, the adhesive strength decreases accordingly.

[0005] However, in recent years, adhesive films have been required to have adhesive strength equivalent to that of conventional adhesive films (thick adhesive layers of approximately 30 μm) even when the thickness of the adhesive layer is reduced, and also to have durability equivalent to or better than that of conventional adhesive films after being left in a high-temperature, high-humidity environment for long periods of time. Furthermore, because it is possible to make the adhesive layer thinner and to form an adhesive layer that does not require aging treatment (curing at a constant temperature), there is a demand for an NCF (Non Carrier Film) configuration consisting of only the adhesive layer, omitting the adhesive film substrate, and consisting of a "release film / adhesive layer / release film" component.

[0006] Furthermore, with conventional pressure-sensitive adhesive films, an aging treatment is carried out after the pressure-sensitive adhesive film is attached to an adherend, which has enabled improvement in the adhesion between the adherend and the pressure-sensitive adhesive layer. However, because the adhesive layer of an NCF-type PSA film has already undergone aging, the adhesive strength between the adherend and the adhesive layer is insufficient, which necessitates surface treatment such as corona treatment of the adherend surface. There is a need for a self-adhesive film that overcomes these requirements and problems.

[0007] The present invention has been made in view of the above circumstances, and aims to provide an adhesive layer that has high adhesive strength and high adhesion properties despite being a thin film having a thickness of 1 μm to 20 μm, and an adhesive film using the same. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention has a technical concept of providing a pressure-sensitive adhesive layer obtained by crosslinking a pressure-sensitive adhesive composition made of an acrylic polymer, in which at least one alkyl (meth)acrylate monomer having an alkyl group with a carbon number of C1 to C14 is used as the main monomer, and at least one or more copolymerizable nitrogen-containing vinyl monomers are contained as other copolymerizable monomers, and by copolymerizing and crosslinking the resulting layer, the pressure-sensitive adhesive layer has strong adhesive strength and high adhesion properties.

[0009] In order to solve the above-mentioned problems, the present invention provides a pressure-sensitive adhesive layer obtained by crosslinking a pressure-sensitive adhesive composition containing an acrylic polymer and (E) a crosslinking agent, wherein the acrylic polymer is a copolymer obtained by copolymerizing 100 parts by weight of a total of (A) at least one or more alkyl (meth)acrylate monomers having an alkyl group of C1 to C14 carbon atoms and (B) at least one or more (meth)acrylate monomers containing an aromatic group, and 5 to 50 parts by weight of (C) at least one or more nitrogen-containing vinyl monomers, and 0.1 to 2.0 parts by weight of (D) at least one or more copolymerizable vinyl monomers containing a carboxyl group and / or 0.1 to 5.0 parts by weight of at least one or more copolymerizable vinyl monomers containing a hydroxyl group, as other copolymerizable monomers. the (C) nitrogen-containing vinyl monomer is one or more selected from the group consisting of N-vinylpyrrolidone, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide, N,N-diisopropyl(meth)acrylamide, N,N-dibutyl(meth)acrylamide, N,N-dimethylaminopropyl(meth)acrylamide, N,N-diethylaminopropyl(meth)acrylamide, N,N-dimethylaminoethyl(meth)acrylamide, and N-vinylcaprolactam; the pressure-sensitive adhesive composition contains 0.01 to 1 part by weight of the (E) crosslinking agent per 100 parts by weight of the total of the (A) and the (B); and the pressure-sensitive adhesive layer has a thickness of 1 μm to 20 μm.

[0010] Furthermore, it is preferable that the adhesive strength when the thickness of the adhesive layer is 5 μm is 4.0 (N / 25 mm) or more.

[0011] The pressure-sensitive adhesive layer preferably has a refractive index of 1.47 to 1.50.

[0012] The present invention also provides a pressure-sensitive adhesive film, characterized in that the pressure-sensitive adhesive layer is formed on one side of a release film, and has a structure of release film / pressure-sensitive adhesive layer / release film.

[0013] The present invention also provides a pressure-sensitive adhesive film comprising the pressure-sensitive adhesive layer laminated on one surface of a substrate.

[0014] The present invention also provides a film for peripheral members of polarizing plates, which uses the pressure-sensitive adhesive film.

[0015] The present invention also provides a film for a touch panel, which uses the pressure-sensitive adhesive film.

[0016] The present invention also provides a film for electronic paper, which uses the pressure-sensitive adhesive film.

[0017] The present invention also provides a film for organic EL devices, which uses the pressure-sensitive adhesive film.

[0018] The present invention also provides a pressure-sensitive adhesive layer-attached optical film, which comprises an optical film and the pressure-sensitive adhesive layer laminated on at least one surface of the optical film. [Effects of the Invention]

[0019] According to the present invention, it is possible to overcome the conventional requirements and problems and provide a pressure-sensitive adhesive layer that has high adhesive strength and high adhesion properties despite being a thin film with a thickness of 1 μm to 20 μm, and a pressure-sensitive adhesive film using the same. DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention will be described below based on preferred embodiments. The pressure-sensitive adhesive layer of the present invention is a pressure-sensitive adhesive layer obtained by crosslinking a pressure-sensitive adhesive composition made of an acrylic polymer, wherein the pressure-sensitive adhesive composition contains, as a main component (meth)acrylate monomer, at least one alkyl (meth)acrylate monomer having an alkyl group with a carbon number of C1 to C14 and at least one (meth)acrylate monomer containing an aromatic group, and contains, as other copolymerizable monomers, at least one nitrogen-containing vinyl monomer and at least one copolymerizable vinyl monomer containing a carboxyl group and / or at least one copolymerizable vinyl monomer containing a hydroxyl group, and wherein the thickness of the pressure-sensitive adhesive layer is 1 μm to 20 μm, and the adhesive strength at a thickness of 5 μm is 4.0 (N / 25 mm) or more.

[0021] Examples of alkyl (meth)acrylate monomers having an alkyl group with a carbon number of C1 to C14 include at least one of methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, cyclopentyl (meth)acrylate, and cyclohexyl (meth)acrylate. The alkyl group of the alkyl (meth)acrylate monomer may be linear, branched, or cyclic. The proportion of the (meth)acrylic acid ester monomer having an alkyl group with a carbon number of C1 to C14 per 100 parts by weight of the acrylic polymer (copolymer) in the pressure-sensitive adhesive composition is preferably 50 to 95 parts by weight.

[0022] Examples of the (meth)acrylate monomer containing an aromatic group include benzyl (meth)acrylate, naphthyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxybutyl (meth)acrylate, 2-(1-naphthyloxy)ethyl (meth)acrylate, 2-(2-naphthyloxy)ethyl (meth)acrylate, 6-(1-naphthyloxy)hexyl (meth)acrylate, 6-(2-naphthyloxy)hexyl (meth)acrylate, 8-(1-naphthyloxy)octyl (meth)acrylate, and 8-(2-naphthyloxy)octyl (meth)acrylate. In order to obtain a pressure-sensitive adhesive layer with a high refractive index, it is preferable to blend at least one (meth)acrylate monomer containing an aromatic group. By mixing these aromatic group-containing (meth)acrylate monomers with alkyl (meth)acrylate monomers having C1 to C14 carbon atoms in the alkyl group, which is the main component monomer, the refractive index of the resulting pressure-sensitive adhesive layer can be increased and adjusted, reducing the refractive index difference between optical components and reducing total reflection, thereby improving total light transmittance.When the aromatic group-containing (meth)acrylate monomer is contained in the pressure-sensitive adhesive composition of the pressure-sensitive adhesive layer according to the present invention, it is preferably contained in an amount of 5 to 30 parts by weight per 100 parts by weight of the main component (meth)acrylate monomer.

[0023] Examples of the nitrogen-containing vinyl monomer include cyclic nitrogen vinyl compounds such as N-vinylpyrrolidone, N-vinylcaprolactam, and (meth)acryloylmorpholine; dialkyl-substituted (meth)acrylamides such as N-ethyl-N-methyl(meth)acrylamide, N-methyl-N-propyl(meth)acrylamide, N-methyl-N-isopropyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide, N,N-diisopropyl(meth)acrylamide, and N,N-dibutyl(meth)acrylamide; N-ethyl-N-methylaminoethyl(meth)acrylate, N-methyl-N-propylaminoethyl(meth)acrylate, N-methyl-N-isopropylaminoethyl(meth)acrylate, N,N-dimethylaminomethyl(meth)acrylate, and N,N-dimethylaminoethyl(meth)acrylamide; acrylate, dialkylamino(meth)acrylates such as N,N-dimethylaminopropyl(meth)acrylate, N,N-dimethylaminobutyl(meth)acrylate, N,N-dipropylaminoethyl(meth)acrylate, and N,N-dibutylaminoethyl(meth)acrylate, and dialkyl-substituted aminoalkyl(meth)acrylamides such as N-ethyl-N-methylaminopropyl(meth)acrylamide, N-methyl-N-propylaminopropyl(meth)acrylamide, N-methyl-N-isopropylaminopropyl(meth)acrylamide, N,N-dimethylaminopropyl(meth)acrylamide, N,N-diethylaminopropyl(meth)acrylamide, N,N-dipropylaminopropyl(meth)acrylamide, N,N-dimethylaminoethyl(meth)acrylamide, and N,N-diethylaminoethyl(meth)acrylamide, can be mentioned as at least one or more of the above.

[0024] The nitrogen-containing vinyl monomer is preferably one that does not contain a hydroxyl group, more preferably one that does not contain a hydroxyl group or a carboxyl group, so as to be distinguishable from the compound (D) described later. Examples of such a monomer include the above-mentioned monomers, such as acrylic monomers containing an N,N-dialkyl-substituted amino group or an N,N-dialkyl-substituted amide group; N-vinyl-substituted lactams such as N-vinylpyrrolidone and N-vinylcaprolactam; and N-(meth)acryloyl-substituted cyclic amines such as N-(meth)acryloylmorpholine.

[0025] In the pressure-sensitive adhesive layer according to the present invention, the nitrogen-containing vinyl monomer contained in the pressure-sensitive adhesive composition can impart the necessary adhesive strength and durability to the pressure-sensitive adhesive layer. In the pressure-sensitive adhesive layer according to the present invention, the nitrogen-containing vinyl monomer contained in the pressure-sensitive adhesive composition is preferably 5 to 50 parts by weight per 100 parts by weight of the (meth)acrylate monomer as the main component. In the pressure-sensitive adhesive layer according to the present invention, particularly preferred nitrogen-containing vinyl monomers to be contained in the pressure-sensitive adhesive composition include N-vinylpyrrolidone, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide, N,N-diisopropyl(meth)acrylamide, N,N-dibutyl(meth)acrylamide, N,N-dimethylaminopropyl(meth)acrylamide, N,N-diethylaminopropyl(meth)acrylamide, N,N-dimethylaminoethyl(meth)acrylamide, and N-vinylcaprolactam.

[0026] Examples of copolymerizable vinyl monomers containing a carboxyl group (carboxyl group-containing monomers) include at least one of (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, 2-(meth)acryloyloxyethyl hexahydrophthalate, 2-(meth)acryloyloxypropyl hexahydrophthalate, 2-(meth)acryloyloxyethyl phthalate, 2-(meth)acryloyloxyethyl succinate, 2-(meth)acryloyloxyethyl maleate, carboxypolycaprolactone mono(meth)acrylate, and 2-(meth)acryloyloxyethyl tetrahydrophthalate. In the pressure-sensitive adhesive layer according to the present invention, the carboxyl group-containing monomer contained in the pressure-sensitive adhesive composition can impart the necessary cohesive strength to the pressure-sensitive adhesive layer. In the pressure-sensitive adhesive layer according to the present invention, the carboxyl group-containing monomer contained in the pressure-sensitive adhesive composition is preferably 0.1 to 5 parts by weight per 100 parts by weight of the (meth)acrylate monomer as the main component.

[0027] Examples of copolymerizable vinyl monomers containing a hydroxyl group (hydroxyl group-containing monomers) include at least one of hydroxyalkyl (meth)acrylates such as 8-hydroxyoctyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and hydroxyethyl (meth)acrylate, and hydroxyl group-containing (meth)acrylamides such as N-hydroxy(meth)acrylamide, N-hydroxymethyl (meth)acrylamide, and N-hydroxyethyl (meth)acrylamide. Furthermore, in the pressure-sensitive adhesive layer according to the present invention, the hydroxyl group-containing monomer contained in the pressure-sensitive adhesive composition can be used as a copolymerizable monomer to reduce the content of carboxyl group-containing monomers, which are believed to affect the corrosiveness of the resulting pressure-sensitive adhesive layer to easily corroded substrates such as the ITO surface of a transparent conductive film. Therefore, the hydroxyl group-containing monomer can be used to improve the adhesive strength of the pressure-sensitive adhesive layer and reduce its corrosiveness. In the pressure-sensitive adhesive layer according to the present invention, the hydroxyl group-containing monomer contained in the pressure-sensitive adhesive composition is preferably 0.1 to 5 parts by weight per 100 parts by weight of the (meth)acrylate monomer, which is the main component.

[0028] The copolymer of the pressure-sensitive adhesive composition used in the pressure-sensitive adhesive layer of the present invention preferably contains, relative to 100 parts by weight of the main component (meth)acrylate monomers combined, which are 70 to 95 parts by weight of (A) at least one alkyl (meth)acrylate monomer having an alkyl group with a carbon number of C1 to C14 and 5 to 30 parts by weight of (B) at least one (meth)acrylate monomer containing an aromatic group, 5 to 50 parts by weight of (C) at least one nitrogen-containing vinyl monomer, and 0.1 to 5 parts by weight of (D) at least one copolymerizable vinyl monomer containing a carboxyl group and / or at least one copolymerizable vinyl monomer containing a hydroxyl group. It is also preferred that the composition contains 2.0 parts by weight or less of one or more copolymerizable vinyl monomers containing a carboxyl group and / or 5.0 parts by weight or less of one or more copolymerizable vinyl monomers containing a hydroxyl group per 100 parts by weight of the (meth)acrylate monomer as the main component.

[0029] The polymerization method for the copolymer is not particularly limited, and any known polymerization method can be used as appropriate, such as solution polymerization, emulsion polymerization, etc. The weight-average molecular weight of the copolymer is preferably 200,000 to 2,000,000. The copolymer is preferably an acrylic polymer, and preferably contains 50 to 100% by weight of an acrylic monomer such as a (meth)acrylic acid ester monomer, (meth)acrylic acid, or a (meth)acrylamide.

[0030] The properties of the pressure-sensitive adhesive composition, such as required physical properties, can be adjusted by blending a crosslinking agent and / or any additives with the copolymer. Examples of the crosslinking agent include at least one of biuret-modified or isocyanurate-modified diisocyanates such as hexamethylene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, tolylene diisocyanate, and xylylene diisocyanate, polyisocyanate compounds such as adducts with trivalent or higher polyols such as trimethylolpropane and glycerin, metal chelate compounds, and epoxy compounds. The pressure-sensitive adhesive may also be crosslinked by photocrosslinking using ultraviolet light or the like. When the copolymer is crosslinked using a crosslinking agent, it is preferable that the copolymer has a functional group capable of crosslinking with the crosslinking agent (such as a hydroxyl group or a carboxyl group, depending on the type of crosslinking agent), and it is also preferable that the copolymer contains a monomer having such a functional group in its side chain. Furthermore, it is preferable that the pressure-sensitive adhesive composition contains 0.01 to 5 parts by weight of (E) a crosslinking agent. The weight parts are the same as those for (A) to (D) in the copolymer.

[0031] Other optional components that can be appropriately blended include known additives such as silane coupling agents, antioxidants, surfactants, curing accelerators, plasticizers, fillers, crosslinking catalysts, crosslinking retarders, curing retarders, processing aids, and antioxidants. These may be used alone or in combination of two or more.

[0032] The pressure-sensitive adhesive layer of the present invention can be obtained by applying the pressure-sensitive adhesive composition to a substrate or a release film, and then crosslinking the pressure-sensitive adhesive composition. When used for bonding layers of optical components, a thin pressure-sensitive adhesive layer is desirable, and the thickness of the pressure-sensitive adhesive layer is preferably 1 μm to 20 μm. In general, the adhesive strength of a pressure-sensitive adhesive layer is approximately proportional to the thickness of the pressure-sensitive adhesive layer, and the adhesive strength at a thickness of 5 μm is preferably 4.0 (N / 25 mm) or more. If the thickness of the pressure-sensitive adhesive layer is not 5 μm, the "adhesive strength at a thickness of 5 μm" (N / 25 mm) can be estimated by the formula "(adhesive strength at a thickness of 5 μm) = 5F / T," where T (μm) is the thickness of the pressure-sensitive adhesive layer and F (N / 25 mm) is the adhesive strength of the pressure-sensitive adhesive layer.

[0033] When the pressure-sensitive adhesive layer according to the present invention is used for bonding between layers of optical components, it is desirable that the difference in refractive index between the pressure-sensitive adhesive layer and the optical component is as small as possible in order to reduce light reflection at the interface between the pressure-sensitive adhesive layer and the optical component. Therefore, the refractive index of the pressure-sensitive adhesive layer is preferably 1.47 to 1.50.

[0034] The pressure-sensitive adhesive film of the present invention can be produced by forming the pressure-sensitive adhesive layer of the present invention on one side of a substrate or a release film. As the base film used to form the adhesive layer and the release film (separator) to protect the adhesive surface, a resin film such as a polyester film can be used. The substrate film may be subjected to an antifouling treatment using a silicone-based or fluorine-based release agent or coating agent, or silica microparticles, or an antistatic treatment by coating or kneading an antistatic agent on the surface opposite to the side on which the pressure-sensitive adhesive layer of the resin film is formed.

[0035] The release film is subjected to a release treatment with a silicone-based or fluorine-based release agent on the surface thereof that faces the adhesive surface of the adhesive layer. A "release film / adhesive layer / release film" configuration can also be achieved by attaching the release-treated surfaces of release films to both sides of a single adhesive layer. In this case, the release films on both sides can be peeled off sequentially or simultaneously to expose the adhesive surface, making it possible to bond it to an optical component such as an optical film. Examples of optical films include polarizing films, retardation films, anti-reflection films, anti-glare films, ultraviolet absorbing films, infrared absorbing films, optical compensation films, and brightness enhancing films.

[0036] The adhesive film of the present invention can be used to bond various optical films for peripheral components of liquid crystal display devices, mainly polarizing plates, various optical films for touch panels, various optical films for electronic paper, various optical films for organic EL, etc. Furthermore, the pressure-sensitive adhesive layer may be laminated on at least one surface of these optical films to form a pressure-sensitive adhesive layer-attached optical film. Specific examples of such optical films include "optical film / pressure-sensitive adhesive layer / optical film," "optical film / pressure-sensitive adhesive layer / release film," "optical film / pressure-sensitive adhesive layer," "optical film / pressure-sensitive adhesive layer / optical film / pressure-sensitive adhesive layer / optical film," "optical film / pressure-sensitive adhesive layer / optical film / pressure-sensitive adhesive layer / release film," and the like. For example, in the case of an "optical film / adhesive layer / release film" structure having a pressure-sensitive adhesive layer protected by a release film, the release film can be peeled off to expose the pressure-sensitive adhesive layer as in "optical film / adhesive layer," and then the structure can be laminated to another optical film, thereby obtaining a structure such as "optical film / adhesive layer / optical film" in which the pressure-sensitive adhesive layer is used for lamination between layers. [Example]

[0037] The present invention will be specifically described below with reference to examples.

[0038] <Production of acrylic copolymer> [Example 1] Nitrogen gas was introduced into a reactor equipped with a stirrer, thermometer, reflux condenser, and nitrogen inlet tube, and the air in the reactor was replaced with nitrogen gas. Then, 90 parts by weight of butyl acrylate, 10 parts by weight of phenoxyethyl acrylate, 10 parts by weight of diethylacrylamide, 1.0 part by weight of acrylic acid, 1.0 part by weight of 4-hydroxybutyl acrylate, and 60 parts by weight of solvent (ethyl acetate) were added to the reactor. Then, 0.1 parts by weight of azobisisobutyronitrile as a polymerization initiator was added dropwise over 2 hours, and the mixture was allowed to react at 65°C for 6 hours, yielding an acrylic copolymer solution 1 used in Example 1 with a weight-average molecular weight of 500,000. A portion of the acrylic copolymer was sampled and used as a sample for measuring the acid value, as described below. [Examples 2 to 5 and Comparative Examples 1 to 3] The acrylic copolymer solutions used in Examples 2 to 5 and Comparative Examples 1 to 3 were obtained in the same manner as the acrylic copolymer solution 1 used in Example 1, except that the monomer compositions were as shown in (A), (B), (C), (D-1), and (D-2) in Table 1. Although no specific measurement results are shown, the weight-average molecular weights of the copolymers contained in the acrylic copolymer solutions of Examples 2 to 5 and Comparative Examples 1 to 3 were in the range of 200,000 to 2,000,000.

[0039] <Production of Pressure-Sensitive Adhesive Composition, Pressure-Sensitive Adhesive Layer, and Pressure-Sensitive Adhesive Film> [Example 1] To the acrylic copolymer solution 1 of Example 1 produced as described above, 0.1 parts by weight of Coronate L-45 (an adduct of a tolylene diisocyanate (TDI) compound) and 0.1 parts by weight of aluminum chelate (aluminum trisacetylacetonate) were added and mixed by stirring to obtain a pressure-sensitive adhesive composition of Example 1. This pressure-sensitive adhesive composition was applied to a release film made of a silicone resin-coated polyethylene terephthalate (PET) film, and then dried at 90°C to remove the solvent. After that, the film was aged for 7 days in an atmosphere of 23°C and 50% RH to obtain a pressure-sensitive adhesive film of Example 1 having a pressure-sensitive adhesive layer formed by crosslinking the pressure-sensitive adhesive composition on one side of the release film. [Examples 2 to 5 and Comparative Examples 1 to 3] PSA films of Examples 2 to 5 and Comparative Examples 1 to 3 were obtained in the same manner as the PSA film of Example 1 above, except that the compositions of the additives were each as shown in Table 1 (E).

[0040] [Table 1]

[0041] In Table 1, the total of Group (A) and Group (B) is taken as 100 parts by weight, and the addition ratios of Groups (C) to (E) are shown in parts by weight enclosed in parentheses. The compound names of the abbreviations of each component used in Table 1 are shown in Table 2. Coronate (registered trademark) L-45 is a trade name of Nippon Polyurethane Industry Co., Ltd., and D-110N is a trade name of Mitsui Chemicals, Inc. TDI means tolylene diisocyanate, and XDI means xylylene diisocyanate.

[0042] [Table 2]

[0043] <Test method and evaluation> The release film (silicone resin-coated PET film) was peeled off from the pressure-sensitive adhesive film in Examples 1 to 5 and Comparative Examples 1 to 3 to expose the pressure-sensitive adhesive layer, which was then transferred to one side of a polarizing plate (film).

[0044] <Method for measuring adhesive strength> An adhesive layer was transferred onto one surface of a polarizing plate (film) having a thickness of 180 μm to obtain an adhesive film (optical film with an adhesive layer) as a sample. The adhesive film was laminated with a pressure roller to the non-tin surface of soda lime glass that had been washed with acetone, and then autoclaved at 50°C and 0.5 MPa for 20 minutes. After that, the film was returned to an atmosphere of 23°C and 50% RH. After 1 hour, the peel strength of the adhesive film was measured using a tensile tester in accordance with JIS Z0237 "Test method for adhesive tapes and adhesive sheets." The peel strength when peeled in a 180° direction at a speed of 300 mm / min was taken as the adhesive strength of the adhesive layer of the adhesive film.

[0045] <Adhesion test method> After measuring the adhesive strength, the adhesive layer of the adhesive film sample was visually inspected, and the adhesion was judged based on the state of the substrate layer dropping off from the polarizing plate (film). ◯: The adhesive layer did not fall off at all from the base layer. △: Part of the adhesive layer has lifted off from the base layer and fallen off. × The adhesive layer has fallen off the base layer and transferred to the glass substrate.

[0046] <Durability test method> A 10cm square adhesive film prepared in the same manner as in measuring adhesive strength was attached to the non-tin side of soda lime glass in the same manner to create a sample.The sample was then left in an atmosphere of 60°C x 90% RH for 250 hours, then removed to an atmosphere of 23°C x 50% RH, and the condition of the adhesive film was visually observed after 1 hour to determine its durability. ○··No peeling or foaming of the adhesive film. △: Peeling and bubbling occurred in some parts of the adhesive film. × Peeling and bubbling has occurred over the entire adhesive film.

[0047] <Refractive index measurement method> The refractive index of the adhesive layer at 23° C. is measured using an Abbe refractometer (manufacturer: ERMA, model: ER-2S).

[0048] Table 3 shows the evaluation results.

[0049] [Table 3]

[0050] The adhesive films of Examples 1 to 5 had an adhesive strength of 4.0 N / 25 mm or more for a 5 μm thick adhesive layer, a refractive index of the adhesive layer within the range of 1.47 to 1.50, and excellent adhesion and durability. In other words, the adhesive films of Examples 1 to 5 were able to overcome the requirements and problems. Table 4 shows the results of measuring the adhesive strength of the adhesive layer of adhesive films with thicknesses of 3 μm, 5 μm, 10 μm, 15 μm, and 20 μm, which were produced in the same manner using the adhesive composition of Example 1. It can be seen that the adhesive strength of the adhesive layer using the adhesive composition of Example 1 is generally proportional to the thickness of the adhesive layer, as is generally known.

[0051] [Table 4]

[0052] The adhesive film of Comparative Example 1 had a weak adhesive strength of a 5 μm-thick adhesive layer, possibly because the adhesive composition did not contain a nitrogen-containing monomer. Furthermore, because the adhesive composition did not contain a (meth)acrylate monomer containing an aromatic group, the refractive index of the adhesive layer was low. Furthermore, the adhesive film was also poor in adhesion and durability. The adhesive film of Comparative Example 2 had a weak adhesive strength of a 5 μm-thick adhesive layer, possibly due to the fact that the amount of copolymerizable vinyl monomer containing a carboxyl group in the adhesive composition was too high. Furthermore, the refractive index of the adhesive layer was low because it did not contain a (meth)acrylate monomer containing an aromatic group. Furthermore, the adhesive strength and durability were also somewhat poor. The adhesive film of Comparative Example 3 had weak adhesive strength of the 5 μm thick adhesive layer and was also poor in adhesion and durability, probably because the adhesive composition did not contain either a copolymerizable vinyl monomer containing a carboxyl group or a copolymerizable vinyl monomer containing a hydroxyl group. As described above, the pressure-sensitive adhesive films of Comparative Examples 1 to 3 were unable to overcome the conventional requirements and problems.

Claims

1. A pressure-sensitive adhesive composition containing an acrylic polymer and (E) a crosslinking agent, The acrylic polymer (A) at least one alkyl (meth)acrylate monomer having an alkyl group with a carbon number of C1 to C14; (B) at least one (meth)acrylate monomer containing an aromatic group; Other copolymerizable monomers include: (C) at least one nitrogen-containing vinyl monomer that does not contain a carboxyl group or a hydroxyl group; (D) a copolymer having a weight average molecular weight of 200,000 to 2,000,000 obtained by copolymerizing at least one copolymerizable vinyl monomer containing a carboxyl group and / or at least one copolymerizable vinyl monomer containing a hydroxyl group, the (C) at least one nitrogen-containing vinyl monomer not containing a carboxyl group or a hydroxyl group is 5 to 50 parts by weight, and the (D) at least one copolymerizable vinyl monomer containing a carboxyl group and / or a hydroxyl group is 0.1 to 2.0 parts by weight of the at least one copolymerizable vinyl monomer containing a carboxyl group and / or 0.1 to 5.0 parts by weight of the at least one copolymerizable vinyl monomer containing a hydroxyl group, relative to a total of 100 parts by weight of the (A) at least one alkyl (meth)acrylate monomer having an alkyl group with a carbon number of C1 to C14 and the (B) at least one (meth)acrylate monomer containing an aromatic group, the (E) crosslinking agent is at least one selected from the group consisting of an adduct of tolylene diisocyanate and an adduct of xylylene diisocyanate, A pressure-sensitive adhesive composition comprising the (E) crosslinking agent in an amount of 0.01 to 5 parts by weight per 100 parts by weight of the total of the (A) at least one alkyl (meth)acrylate monomer having an alkyl group with a carbon number of C1 to C14 and the (B) at least one (meth)acrylate monomer containing an aromatic group.

2. A pressure-sensitive adhesive layer obtained by crosslinking the pressure-sensitive adhesive composition according to claim 1.

3. 3. A pressure-sensitive adhesive film comprising the pressure-sensitive adhesive layer according to claim 2 formed on one side of a release film, and having a structure of release film / pressure-sensitive adhesive layer / release film.

4. A pressure-sensitive adhesive film comprising a substrate and the pressure-sensitive adhesive layer according to claim 2 laminated on one surface of the substrate.

5. An optical film with a pressure-sensitive adhesive layer, comprising an optical film and the pressure-sensitive adhesive layer according to claim 2 laminated on at least one surface of the optical film.

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