Adhesive layer and adhesive film

Abstract

To provide an adhesive layer capable of forming an adhesive layer having excellent reworkability and high adhesiveness in spite of being a thin film.SOLUTION: There is provided an adhesive layer in which an acrylic polymer, which is a copolymer having an acid value of 0.1 or less and a weight average molecular weight of 1000000 or more obtained by copolymerization of (A) a total of 100 pts.wt. of a monomer group consisting of an alkyl (meth)acrylate monomer having an alkyl group having 1 to 14 carbon atoms and a (meth)acrylate monomer having an aromatic group and (B) 0.1 to 3.5 pts.wt. of a hydroxyl group-containing copolymerizable vinyl monomer without containing a carboxyl group-containing copolymerizable vinyl monomer and an amino group-containing (meth)acrylate, contains butyl acrylate in a ratio of at least 30 pts.wt. or more and which contains an isocyanate compound as a crosslinking agent and a silane coupling agent and the adhesive layer has a thickness of 1 to 25 μm and has a gel fraction of 40 to 75%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive composition and a pressure-sensitive adhesive film used for bonding optical members such as polarizing plates. [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 make the thickness of the adhesive layer thinner in order to reduce the thickness of the 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 an object of the present invention is to provide a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer that has excellent reworkability and high adhesion performance despite being a thin film, and a pressure-sensitive adhesive film using the same. [Means for solving the problem]

[0008] In order to solve the above problems, the pressure-sensitive adhesive composition of the present invention is characterized in that it uses butyl acrylate as an essential monomer, does not use a carboxyl group-containing copolymerizable vinyl monomer as a functional group-containing monomer, but uses a hydroxyl group-containing copolymerizable vinyl monomer, and has a weight-average molecular weight of 1,000,000 or more, and uses an isocyanate compound as a crosslinking agent for the copolymer, and more preferably uses a silane coupling agent in combination with the copolymer.

[0009] Furthermore, in order to solve the above-mentioned problems, the present invention provides a pressure-sensitive adhesive composition comprising: (1) an acrylic polymer which is a copolymer having an acid value of 0.1 or less and a weight-average molecular weight of 1,000,000 or more, the acrylic polymer containing, as a main component (meth)acrylate monomer, at least one selected from the group consisting of alkyl (meth)acrylate monomers having an alkyl group carbon number of C1 to C14 and (meth)acrylate monomers having an aromatic group, wherein, out of a total of 100 parts by weight of the main component (meth)acrylate monomers, at least 30 parts by weight of butyl acrylate is contained; and the acrylic polymer does not contain a carboxyl group-containing copolymerizable vinyl monomer; (2) 0.1 to 3.5 parts by weight of a hydroxyl group-containing copolymerizable vinyl monomer is contained per 100 parts by weight of the main component (meth)acrylate monomers; and (3) 0.01 to 0.8 parts by weight of an isocyanate compound as a crosslinking agent per 100 parts by weight of the main component (meth)acrylate monomers.

[0010] Furthermore, it is preferable that (4) a silane coupling agent be contained in an amount of 0.01 to 0.5 parts by weight relative to 100 parts by weight of the total of the (meth)acrylate monomers as the main component.

[0011] The isocyanate compound is preferably a trimethylolpropane adduct of tolylene diisocyanate.

[0012] Furthermore, it is preferable that the (2) hydroxyl group-containing copolymerizable vinyl monomer is at least one selected from the group consisting of 8-hydroxyoctyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate.

[0013] The present invention also provides a pressure-sensitive adhesive layer obtained by crosslinking the pressure-sensitive adhesive composition, wherein the pressure-sensitive adhesive layer has a gel fraction of 40 to 75% after crosslinking and an adhesive strength of 1.5 to 6.0 N / 25 mm when the pressure-sensitive adhesive layer has a thickness of 25 μm.

[0014] Furthermore, it is preferable that the adhesive layer has an adhesive strength of 1.5 to 10 N / 25 mm after being attached to an adherend and left at 70° C. for 10 days.

[0015] The present invention also provides a pressure-sensitive adhesive film comprising the pressure-sensitive adhesive layer laminated on one surface of a substrate.

[0016] The present invention also provides an adhesive film that uses the adhesive film and is used to bond a polarizing plate to a display panel.

[0017] The present invention also provides the pressure-sensitive adhesive layer used as a pressure-sensitive adhesive layer of a polarizing plate with a pressure-sensitive adhesive layer.

[0018] The present invention also provides the pressure-sensitive adhesive layer used as a pressure-sensitive adhesive layer of a pressure-sensitive adhesive layer-attached polarizing plate in which a retardation film having a retardation of λ / 4 or λ / 2 is used as a constituent material of the polarizing plate.

[0019] The present invention also provides a pressure-sensitive adhesive layer-attached optical film, in which the pressure-sensitive adhesive layer is laminated on at least one surface of an optical film. [Effects of the Invention]

[0020] According to the present invention, a pressure-sensitive adhesive layer having a high gel fraction after crosslinking can be obtained while reducing the amount of crosslinking agent and the amount of functional groups compared to conventional pressure-sensitive adhesive layers, and a pressure-sensitive adhesive layer having flexibility, rigidity, durability, and reworkability, and a pressure-sensitive adhesive film using the same can be obtained. The pressure-sensitive adhesive film of the present invention has excellent reworkability and high adhesiveness despite being a thin film. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention will be described below based on preferred embodiments. The pressure-sensitive adhesive composition of the present invention is characterized by comprising: (1) a main component (meth)acrylate monomer containing at least one selected from the group consisting of alkyl (meth)acrylate monomers having an alkyl group carbon number of C1 to C14 and (meth)acrylate monomers having an aromatic group, wherein at least 30 parts by weight of butyl acrylate is contained in a total of 100 parts by weight of the main component (meth)acrylate monomers; and (2) 0.1 to 3.5 parts by weight of a hydroxyl group-containing copolymerizable vinyl monomer is contained relative to 100 parts by weight of the main component (meth)acrylate monomers; the acrylic polymer is a copolymer having an acid value of 0.1 or less and a weight-average molecular weight of 1,000,000 or more; and (3) 0.01 to 0.8 parts by weight of an isocyanate compound as a crosslinking agent relative to 100 parts by weight of the main component (meth)acrylate monomers.

[0022] In the pressure-sensitive adhesive composition according to the present invention, examples of the alkyl (meth)acrylate monomer 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. Of the total 100 parts by weight of the (meth)acrylate monomers that are the main component, the total amount of alkyl (meth)acrylate monomers having a carbon number of C1 to C14 in the alkyl group is preferably 70 parts by weight or more, and may be 100 parts by weight. The proportion of the alkyl (meth)acrylate monomers having a carbon number of C1 to C14 in the alkyl group relative to 100 parts by weight of the acrylic polymer (copolymer) in the pressure-sensitive adhesive composition is preferably 50 to 99.9 parts by weight. In the present invention, butyl acrylate is an essential monomer. Of the total 100 parts by weight of the (meth)acrylate monomers that are the main component, it is preferable that at least 30 parts by weight or more of butyl acrylate is contained. Furthermore, in the present invention, the pressure-sensitive adhesive composition contains 20 parts by weight or more of methyl acrylate monomer out of a total of 100 parts by weight of (meth)acrylate monomers as the main component, which are one or more alkyl (meth)acrylate monomers having an alkyl group with a carbon number of C1 to C14, thereby making it possible to increase the refractive index of the pressure-sensitive adhesive layer to 1.47 or more.

[0023] The pressure-sensitive adhesive composition of the present invention may further contain one or more (meth)acrylate monomers having an aromatic group as the main (meth)acrylate monomer. Examples of (meth)acrylate monomers having 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. To obtain a pressure-sensitive adhesive layer with a high refractive index, it is preferable to incorporate at least one (meth)acrylate monomer having an aromatic group.

[0024] By mixing these (meth)acrylate monomers having an aromatic group with alkyl (meth)acrylate monomers having C1 to C14 carbon atoms in the alkyl group, which are the main component monomers, 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 a (meth)acrylate monomer having an aromatic group 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 out of a total of 100 parts by weight of the main component (meth)acrylate monomers. Furthermore, by copolymerizing a (meth)acrylate monomer having an aromatic group, the refractive index of the adhesive layer can be increased even further than the effect of increasing the refractive index of the adhesive layer by including 20 parts by weight or more of methyl acrylate monomer out of a total of 100 parts by weight of the above-mentioned main component (meth)acrylate monomers. As mentioned above, there are two methods for increasing the refractive index of the adhesive layer: one is to include 20 parts by weight or more of methyl acrylate monomer out of a total of 100 parts by weight of the main component (meth)acrylate monomer, and the other is to copolymerize a (meth)acrylate monomer having an aromatic group. Each method can be used alone, but it is more preferable to use the two methods in combination.

[0025] In the pressure-sensitive adhesive composition of the present invention, the acrylic polymer does not contain a carboxyl group-containing copolymerizable vinyl monomer as the functional group-containing monomer, but contains a hydroxyl group-containing copolymerizable vinyl monomer. As the functional group-containing monomer, only the hydroxyl group-containing copolymerizable vinyl monomer may be used.

[0026] Examples of the hydroxyl group-containing copolymerizable vinyl monomer include at least one of hydroxyl group-containing alkyl (meth)acrylates such as 8-hydroxyoctyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate, and hydroxyl group-containing (meth)acrylamides such as N-hydroxy(meth)acrylamide, N-hydroxymethyl (meth)acrylamide, and N-hydroxyethyl (meth)acrylamide. Among these, it is preferable that the hydroxyl group-containing copolymerizable vinyl monomer is at least one selected from the group consisting of 8-hydroxyoctyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate. Furthermore, in the pressure-sensitive adhesive layer of the present invention, the hydroxyl group-containing copolymerizable vinyl monomer contained in the pressure-sensitive adhesive composition can be used as a copolymerizable monomer to reduce the content of carboxyl group-containing copolymerizable vinyl 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 copolymerizable vinyl 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 of the present invention, the hydroxyl group-containing copolymerizable vinyl monomer contained in the pressure-sensitive adhesive composition is preferably 0.1 to 3.5 parts by weight out of a total of 100 parts by weight of the (meth)acrylate monomers, which are the main components.

[0027] The acrylic polymer of the pressure-sensitive adhesive composition used in the pressure-sensitive adhesive layer of the present invention is a copolymer having an acid value of 0.1 or less and a weight-average molecular weight of 1,000,000 or more, and containing (1) as a main component (meth)acrylate monomer at least one selected from the group consisting of alkyl (meth)acrylate monomers having an alkyl group carbon number of C1 to C14 and (meth)acrylate monomers having an aromatic group, at least 30 parts by weight of butyl acrylate out of a total of 100 parts by weight of the main component (meth)acrylate monomers, and no carboxyl group-containing copolymerizable vinyl monomer, and containing (2) 0.1 to 3.5 parts by weight of a hydroxyl group-containing copolymerizable vinyl monomer per 100 parts by weight of the main component (meth)acrylate monomers.

[0028] 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 acrylic polymer preferably contains 50 to 100% by weight of an acrylic monomer such as a (meth)acrylate monomer or a (meth)acrylamide.

[0029] 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 as appropriate with the acrylic polymer. (3) Examples of crosslinking agents include at least one polyisocyanate compound, such as biuret-modified or isocyanurate-modified diisocyanates such as hexamethylene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, tolylene diisocyanate, and xylylene diisocyanate, and adducts with trivalent or higher polyols such as trimethylolpropane and glycerin. The acrylic polymer preferably has a hydroxyl group as a functional group capable of crosslinking with the isocyanate compound of the crosslinking agent, and preferably contains a monomer having such a functional group in its side chain. The pressure-sensitive adhesive composition preferably contains 0.01 to 0.8 parts by weight of the isocyanate compound per 100 parts by weight of the total of the (meth)acrylate monomers as the main component. (3) The isocyanate compound may be used alone as the crosslinking agent. As the isocyanate compound, an adduct of tolylene diisocyanate is preferred, and an adduct of tolylene diisocyanate with trimethylolpropane is particularly preferred.

[0030] The pressure-sensitive adhesive composition preferably further contains (4) a silane coupling agent. Examples of (4) silane coupling agents include compounds having at least one organic functional group and at least one hydrolyzable group in one molecule, where the hydrolyzable group is an alkoxy group or the like bonded to a silicon atom. The silane coupling agent preferably has at least one organic functional group selected from the group consisting of an epoxy group, a (meth)acryloxy group, a mercapto group, and an amino group. Here, the (meth)acryloxy group refers to an acryloxy group (CH2=CHCOO-) or a methacryloxy group (CH2=C(CH3)COO-).

[0031] Examples of silane coupling agents having an epoxy group include 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethylmethyldimethoxysilane, 2-(3,4-epoxycyclohexyl)ethylmethyldiethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, 5,6-epoxyhexyltrimethoxysilane, 5,6-epoxyhexylmethyldimethoxysilane, 5,6-epoxyhexylmethyldiethoxysilane, and 5,6-epoxyhexyltriethoxysilane. Examples of silane coupling agents having a (meth)acryloxy group include 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropylmethyldiethoxysilane, 3-(meth)acryloxypropyldimethylethoxysilane, and 3-(meth)acryloxypropyldimethylmethoxysilane. Examples of silane coupling agents having a mercapto group include 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropylmethyldiethoxysilane, and 3-mercaptopropyltriethoxysilane. Examples of silane coupling agents having an amino group include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldiethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltriethoxysilane, 3-(methylamino)propyltrimethoxysilane, and 3-(methylamino)propyltriethoxysilane. Furthermore, alkoxy oligomers (silicone alkoxy oligomers) containing the organic functional groups and oligomerized can also be used as silane coupling agents.

[0032] (4) The content of the silane coupling agent is preferably 0.01 to 0.5 parts by weight per 100 parts by weight of the total of the (meth)acrylate monomers as the main component.

[0033] Other optional components that can be appropriately blended include known additives such as 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.

[0034] 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. The gel fraction of the pressure-sensitive adhesive layer after crosslinking is preferably 40 to 75%. 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 25 μm, more preferably 5 μm to 25 μm. Generally, the adhesive strength of a pressure-sensitive adhesive layer is approximately proportional to the thickness of the pressure-sensitive adhesive layer, and a pressure-sensitive adhesive layer with a thickness of 25 μm preferably has an adhesive strength of 1.5 to 6.0 N / 25 mm. Furthermore, after the pressure-sensitive adhesive layer is bonded to an adherend, the adhesive strength after 10 days at 70°C is preferably 1.5 to 10 N / 25 mm. Examples of adherends include glass plates such as alkali-free glass, and resin films.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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 optical film may have the pressure-sensitive adhesive layer laminated on at least one surface thereof, 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. The pressure-sensitive adhesive film of the present invention is suitable for use in bonding a polarizing plate and a display panel. For example, it is used as the pressure-sensitive adhesive layer of a polarizing plate with a pressure-sensitive adhesive layer. A retardation film having a phase difference of λ / 4 or λ / 2 may be used as a constituent material of the polarizing plate. [Example]

[0039] The present invention will be specifically described below with reference to examples.

[0040] <Production of acrylic polymers> [Example 1] Nitrogen gas was introduced into a reactor equipped with a stirrer, thermometer, reflux condenser, and nitrogen inlet tube, and the air inside the reactor was replaced with nitrogen gas. Subsequently, 100 parts by weight of butyl acrylate, 0.2 parts by weight of 8-hydroxyoctyl acrylate, and 60 parts by weight of a 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 polymer solution 1 used in Example 1, with a weight-average molecular weight of 1,000,000 or more. A portion of the acrylic polymer was collected and used as a sample for measuring the acid value, which will be described later. [Examples 2 to 5 and Comparative Examples 1 to 3] The acrylic polymer solutions used in Examples 2 to 5 and Comparative Examples 1 to 3 were obtained in the same manner as the acrylic polymer solution 1 used in Example 1, except that the monomer compositions were as shown in Groups (1) and (2) in Table 1. Although no specific measurement results are shown, the weight-average molecular weights of the acrylic polymers contained in the acrylic polymer solutions of Examples 2 to 5 and Comparative Examples 1 to 3 were 1,000,000 or more.

[0041] <Production of Pressure-Sensitive Adhesive Composition, Pressure-Sensitive Adhesive Layer, and Pressure-Sensitive [Example 1] To the acrylic polymer solution 1 of Example 1 produced as described above, 0.2 parts by weight of Coronate L (a trimethylolpropane (TMP) adduct of a tolylene diisocyanate (TDI) compound) and 0.05 parts by weight of KBM-403 (3-glycidoxypropyltrimethoxysilane) were added and stirred 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 aging for 7 days in an atmosphere of 23°C and 50% RH, a pressure-sensitive adhesive film of Example 1 was obtained, which had a 25 μm-thick 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] The adhesive films of Examples 2 to 5 and Comparative Examples 1 to 3 were obtained in the same manner as the adhesive film of Example 1 above, except that the compositions of the additives were as described in Groups (3) and (4) of Table 1, respectively.

[0042] [Table 1]

[0043] In Table 1, the total of group (1) is set to 100 parts by weight, and the addition ratios of groups (2) to (4) 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 is a trade name of Nippon Polyurethane Industry Co., Ltd., D-110N is a trade name of Mitsui Chemicals, Inc., and KBM-403 and KBM-803 are trade names of Shin-Etsu Chemical Co., Ltd. TDI means tolylene diisocyanate, TMP means trimethylolpropane, and XDI means xylylene diisocyanate. In Tables 1 and 2, carboxyl group-containing copolymerizable vinyl monomers are listed in group (2) together with hydroxyl group-containing copolymerizable vinyl monomers.

[0044] [Table 2]

[0045] <Test method and evaluation> The release film (a 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).

[0046] <Method for measuring adhesive strength> A 25 μm thick adhesive layer was transferred onto one surface of a 180 μm thick polarizing plate (film) to obtain an adhesive film (optical film with an adhesive layer) as a sample. The resulting adhesive film was laminated with a pressure roller to the non-tin surface of alkali-free glass, which had been cleaned with acetone, and then autoclaved at 50°C and 0.5 MPa for 20 minutes. It was then returned to an atmosphere of 23°C and 50% RH for 1 hour. The peel strength of the adhesive film was then measured using a tensile tester in accordance with JIS Z0237 "Test Method for Adhesive Tape and Adhesive Sheet." The peel strength when peeled in a 180° direction at a rate of 300 mm / min was taken as the adhesive strength of the adhesive layer of the adhesive film (N / 25 mm).

[0047] <Acid value measurement method> The acid value of the acrylic polymer was measured by dissolving the sample in a solvent (a 2:1 volume mixture of diethyl ether and ethanol) and titrating it with an automatic potentiometric titrator (Kyoto Electronics Manufacturing Co., Ltd., AT-610) using a 0.1 mol / L potassium hydroxide ethanol solution. The amount of potassium hydroxide ethanol solution required to neutralize the sample was measured, and the acid value was calculated using the following formula. Acid value = (B × f × 5.611) / S B = Amount (ml) of 0.1 mol / l potassium hydroxide ethanol solution used in titration f = Factor of 0.1 mol / l potassium hydroxide ethanol solution S = mass of solids in the sample (g)

[0048] <Method for measuring gel fraction> After aging, the mass of the measurement sample before bonding to the polarizing plate was accurately measured, immersed in toluene for 24 hours, and then filtered through a 200-mesh wire netting. The filtered material was then dried at 100°C for 1 hour, and the mass of the residue was accurately measured, and the gel fraction of the pressure-sensitive adhesive layer (pressure-sensitive adhesive after crosslinking) was calculated using the following formula. Gel fraction (%) = insoluble portion mass (g) / adhesive mass (g) × 100

[0049] <Durability test method> A 10cm square adhesive film prepared in the same manner as in measuring adhesive strength was attached to the non-tin surface of alkali-free glass in the same manner to create a sample.The sample was then left in a specified atmosphere (80°C dry atmosphere or 60°C x 90% RH atmosphere) for 250 hours, then removed from the sample and placed in a 23°C x 50% RH atmosphere.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.

[0050] <Reworkability 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 alkali-free glass in the same manner to create a sample. The sample was left in an atmosphere of 70°C for 10 days, then removed to an atmosphere of 23°C, and the adhesive strength of the adhesive film was measured after leaving it for 1 hour to determine its reworkability. ○··Adhesive strength after 10 days at 70℃ is 1.5~10N / 25mm. △··The adhesive strength after 10 days at 70℃ is greater than 10N / 25mm but less than 20N / 25mm. ×··Adhesive strength after 10 days at 70℃ is greater than 20N / 25mm (cannot be peeled off).

[0051] The evaluation results are shown in Table 3. Regarding the acid value, it was confirmed that the acrylic polymers of Examples 1 to 5 and Comparative Examples 2 and 3, which did not contain a carboxyl group-containing copolymerizable vinyl monomer, had an acid value of 0.1 or less, and that the acrylic polymer of Comparative Example 1, which contained a carboxyl group-containing copolymerizable vinyl monomer, had an acid value of more than 0.1.

[0052] [Table 3]

[0053] The adhesive films of Examples 1 to 5 had an adhesive strength of 1.5 to 6.0 N / 25 mm for a 25 μm thick adhesive layer, and a gel fraction of 40 to 75% for the adhesive layer after crosslinking, demonstrating excellent adhesion and durability. Furthermore, after being attached to an adherend, the adhesive strength after 10 days at 70°C was in the range of 1.5 to 10 N / 25 mm, demonstrating excellent reworkability. In other words, the adhesive films of Examples 1 to 5 were able to overcome the requirements and problems.

[0054] The adhesive film of Comparative Example 1 did not contain butyl acrylate as the main component (meth)acrylate monomer, but contained a carboxyl group-containing copolymerizable vinyl monomer as the functional group-containing monomer. Perhaps due to the high gel fraction, the adhesive strength of the 25 μm-thick adhesive layer was strong, but its durability and reworkability in an atmosphere of 60°C x 90% RH were poor. The adhesive film of Comparative Example 2 had poor durability in an atmosphere of 60°C x 90% RH, and was also somewhat poor in durability and reworkability in an 80°C dry atmosphere, probably because the amount of hydroxyl group-containing copolymerizable vinyl monomer blended in the adhesive composition was too high, resulting in a high gel fraction. In the adhesive film of Comparative Example 3, the adhesive composition did not contain either a carboxyl group-containing copolymerizable vinyl monomer or a hydroxyl group-containing copolymerizable vinyl monomer, so the acrylic polymer was not crosslinked, the gel fraction was 0, and the adhesive strength of the 25 μm-thick adhesive layer was very strong. As a result, the durability and reworkability were poor. 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 layer obtained by crosslinking a pressure-sensitive adhesive composition containing an acrylic polymer and a crosslinking agent, The acrylic polymer (A) 100 parts by weight in total of at least two or more monomers selected from the group consisting of alkyl (meth)acrylate monomers having an alkyl group with a carbon number of C1 to C14 and (meth)acrylate monomers having an aromatic group; (B) an acrylic polymer that is a copolymer having an acid value of 0.1 or less and a weight-average molecular weight of 1,000,000 or more, obtained by copolymerizing 0.1 to 3.5 parts by weight of a hydroxyl group-containing copolymerizable vinyl monomer without containing a carboxyl group-containing copolymerizable vinyl monomer or an amino group-containing (meth)acrylate; The (A) monomers are selected from the group consisting of alkyl (meth)acrylate monomers having an alkyl group carbon number of C1 to C14 and (meth)acrylate monomers having an aromatic group, and the monomers contain at least 30 parts by weight of butyl acrylate and 20 parts by weight of methyl acrylate, or the (A) monomers are selected from the group consisting of benzyl (meth)acrylate, naphthyl (meth)acrylate, and the like, and the ... alkyl (meth)acrylate monomers having an aromatic group and benzyl (meth)acrylate, naphthyl (meth)acrylate, and the like, and the monomers are selected from the group consisting of alkyl (meth)acrylate monomers having an aromatic group, and the monomers are selected from the group consisting of alkyl (meth)acrylate monomers having an alkyl group carbon number of C1 to C14 and (meth)acrylate monomers having an aromatic group, and the monomers are selected from the group consisting of alkyl (meth)acrylate monomers having an alkyl group carbon number of C1 to C14 and (meth)acrylate monomers having an aromatic group, and the monomers are selected from the group consisting of alkyl (meth)acrylate monomers having an alkyl group carbon number of C1 to C14 and (meth)acrylate monomers having an aromatic group, and the monomers are selected from the group consisting of alkyl ) 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 an amount of 5 to 30 parts by weight, the pressure-sensitive adhesive composition further comprises, relative to 100 parts by weight in total of at least two or more monomers (A) selected from the group consisting of alkyl (meth)acrylate monomers having an alkyl group carbon number of C1 to C14 and (meth)acrylate monomers having an aromatic group, 0.01 to 0.8 parts by weight of an isocyanate compound as the crosslinking agent, and 0.01 to 0.5 parts by weight of a silane coupling agent; the silane coupling agent has at least one organic functional group selected from the group consisting of an epoxy group, a (meth)acryloxy group, and a mercapto group; The thickness of the pressure-sensitive adhesive layer is 1 to 25 μm, A pressure-sensitive adhesive layer characterized in that the gel fraction of the pressure-sensitive adhesive layer measured by the gel fraction measurement method described below is 40 to 75%. -Method of measuring gel fraction: After aging, the mass of the measurement sample before being attached to the polarizing plate was accurately measured, and the sample was immersed in toluene for 24 hours and then filtered through a 200-mesh wire netting. The filtered product was then dried at 100°C for 1 hour, and the mass of the residue was accurately measured, and the gel fraction of the pressure-sensitive adhesive layer (pressure-sensitive adhesive after crosslinking) was calculated using the following formula (1). Gel fraction (%) = mass of insoluble portion (g) / mass of adhesive (g) × 100 Formula (1)

2. An adhesive film comprising a substrate and the adhesive layer according to claim 1 laminated on one surface thereof.

3. The pressure-sensitive adhesive layer according to claim 1 , which is used as a pressure-sensitive adhesive layer of a polarizing plate with a pressure-sensitive adhesive layer.

4. An optical film with a pressure-sensitive adhesive layer, comprising an optical film and the pressure-sensitive adhesive layer according to claim 1 laminated on at least one surface of the optical film.

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