Adhesive layer for optical film, picture display device, and polarizing plate with adhesive layer

Abstract

To provide: an adhesive layer for an optical film, which is used for sticking an optical film to be incorporated in a picture display device and has excellent heat resistance and durability; the picture display device; and a polarizing plate with the adhesive layer.SOLUTION: An adhesive layer for an optical film, which is formed by crosslinking a composition of an adhesive for an optical film containing an acrylic polymer with Tg of -60°C or higher and -30°C or below formed by copolymerizing (A) 100 pts.wt. of total of at least two kinds or more monomers selected from a 1-14C alkyl (meth)acrylate monomer, a (meth)acrylate monomer having an aromatic group, and a nitrogen-containing vinyl monomer, (B) 0.1-10.0 pts.wt. of a carboxy group-containing copolymerizable vinyl monomer, and (C) 0.05-4.5 pts.wt. of a hydroxy group-containing copolymerizable vinyl monomer, and a two or more functional epoxy-based compound as a crosslinking compound has a gel fraction of 60-90% and thickness of 5-25 μm.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a pressure-sensitive adhesive layer for an optical film, a pressure-sensitive adhesive film for an optical film, and a pressure-sensitive adhesive composition for producing them. More specifically, the present invention relates to a pressure-sensitive adhesive layer for an optical film, a pressure-sensitive adhesive film for an optical film, and a pressure-sensitive adhesive composition for producing them, which are used for laminating an optical film incorporated in an image display device and have excellent heat resistance and durability. [Background technology]

[0002] In recent years, various optical films are used in various image display devices. For example, optical films such as polarizing films and retardation films are used for the purpose of improving contrast and preventing reflection of external light. In order to attach these optical films to adherends such as liquid crystal panels and organic EL (electroluminescence) panels, various adhesive films have been proposed (see, for example, Patent Document 1). It is also known that reflection of external light can be suppressed by disposing one 1 / 4λ retardation film with an angle of -45° with respect to the polarization axis of the polarizing film between the reflective layer on the back of the organic EL panel and the polarizing film, or by disposing one 1 / 2λ retardation film with an angle of -15° and one 1 / 4λ retardation film with an angle of -75°. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2012-201734 A Summary of the Invention [Problem to be solved by the invention]

[0004] As described above, in order to prevent reflection of external light from the organic EL panel, a 1 / 4λ retardation film with reverse wavelength dispersion (birefringence increases with longer wavelength) is provided between the polarizing film and the organic EL panel. In addition, in the conventional technology, a retardation film made of a polycarbonate-based film is widely used as the 1 / 4λ retardation film. However, when a polycarbonate-based film is used, there is a problem that foaming due to outgassing from polycarbonate cannot be suppressed.

[0005] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a pressure-sensitive adhesive layer for an optical film, a pressure-sensitive adhesive film for an optical film, and a pressure-sensitive adhesive composition for producing the same, which have excellent heat resistance and durability and are used for bonding an optical film to be incorporated into an image display device. [Means for solving the problem]

[0006] In order to solve the above problems, the present invention has the technical idea of ​​obtaining a pressure-sensitive adhesive layer having excellent heat resistance and durability by forming an acrylic polymer consisting of a copolymer having a Tg of -60°C or more and -30°C or less, obtained by copolymerizing a total of 100 parts by weight of at least two or more monomers selected from the group of monomers consisting of alkyl (meth)acrylate monomers having an alkyl group carbon number of C1 to C14, (meth)acrylate monomers having an aromatic group, and nitrogen-containing vinyl monomers, 0.1 to 10.0 parts by weight of a carboxyl group-containing copolymerizable vinyl monomer, and 0.05 to 4.5 parts by weight of a hydroxyl group-containing copolymerizable vinyl monomer, into a crosslinked pressure-sensitive adhesive layer.

[0007] In order to solve the above problems, the present invention provides a pressure-sensitive adhesive composition for optical films, comprising an acrylic polymer and a crosslinkable compound, the acrylic polymer comprising 100 parts by weight of a total of at least two or more monomers selected from the group consisting of (A) alkyl (meth)acrylate monomers (a1) having an alkyl group carbon number of C1 to C14, (meth)acrylate monomers (a2) having an aromatic group, and nitrogen-containing vinyl monomers (a3) ​​(provided that one of the monomers belonging to (a1) is 5 parts by weight). The present invention provides a pressure-sensitive adhesive composition for optical films, characterized in that the composition comprises a copolymer having a Tg of -60°C or more and -30°C or less, obtained by copolymerizing (a) 1 part by weight or more and 95 parts by weight or less of (a1) to (a3) ​​and a total of 5 parts by weight or more and 49 parts by weight or less of one or more other monomers selected from the monomer group consisting of (a1) to (a3), (B) 0.1 to 10.0 parts by weight of a carboxyl group-containing copolymerizable vinyl monomer, and (C) 0.05 to 4.5 parts by weight of a hydroxyl group-containing copolymerizable vinyl monomer.

[0008] It is preferable that the crosslinkable compound is a bifunctional or higher epoxy compound, and that the content of the crosslinkable compound is 0.001 to 0.5 parts by weight per 100 parts by weight in total of at least two or more monomers selected from the monomer group consisting of (a1) to (a3).

[0009] the (B) carboxyl group-containing copolymerizable vinyl monomer copolymerized with the acrylic polymer is selected from the group consisting of (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, 2-(meth)acryloyloxyethyl hexahydrophthalic acid, 2-(meth)acryloyloxyethyl phthalic acid, 2-(meth)acryloyloxyethyl succinic acid, 2-(meth)acryloyloxyethyl maleic acid, carboxypolycaprolactone mono(meth)acrylate, and 2-(meth)acryloyloxyethyl tetrahydrophthalic acid; It is preferable that the (C) hydroxyl group-containing copolymerizable vinyl monomer copolymerized with the acrylic polymer is at least one type selected from the group consisting of 8-hydroxyoctyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, N-hydroxy(meth)acrylamide, N-hydroxymethyl (meth)acrylamide, and N-hydroxyethyl (meth)acrylamide.

[0010] The (a2) (meth)acrylate monomer having an aromatic group copolymerized with the acrylic polymer is preferably at least one selected from the group consisting of benzyl (meth)acrylate, naphthyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxybutyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, 2-(1-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.

[0011] The present invention also provides a pressure-sensitive adhesive layer for an optical film, the pressure-sensitive adhesive layer being obtained by crosslinking the pressure-sensitive adhesive composition for an optical film, the pressure-sensitive adhesive layer having a gel fraction of 60 to 90% and a thickness of 5 to 25 μm.

[0012] The present invention also provides a pressure-sensitive adhesive layer for an optical film, characterized in that the pressure-sensitive adhesive layer for an optical film is transferred to both sides of a retardation film made of a polycarbonate resin film, and a polarizing film is laminated to one side of the pressure-sensitive adhesive layer-attached optical film laminate, which is laminated to alkali-free glass and then stored in a dry atmosphere at 85°C for 200 hours.The pressure-sensitive adhesive layer for an optical film is then taken out of the optical film and placed in a 23°C x 50% RH atmosphere, and checked one hour later to show durability with no foaming.

[0013] The present invention also provides an adhesive film for optical films, characterized in that the adhesive composition for optical films is applied to one side of a release film to form an adhesive layer for optical films, and the adhesive layer has a structure of release film / adhesive layer for optical films / release film.

[0014] The present invention also provides a pressure-sensitive adhesive film for an optical film, characterized in that a pressure-sensitive adhesive layer for an optical film obtained by crosslinking the pressure-sensitive adhesive composition for an optical film is laminated on one surface of a substrate.

[0015] The present invention also provides an image display device in which a pressure-sensitive adhesive layer for an optical film obtained by crosslinking the pressure-sensitive adhesive composition for an optical film is used for laminating an optical film.

[0016] The present invention also provides a polarizing plate with a pressure-sensitive adhesive layer, which uses a pressure-sensitive adhesive layer for an optical film obtained by crosslinking the pressure-sensitive adhesive composition for an optical film.

[0017] The present invention also provides a polarizing plate with a pressure-sensitive adhesive layer, in which a pressure-sensitive adhesive layer for an optical film obtained by crosslinking the pressure-sensitive adhesive composition for an optical film is used, and a retardation film having a phase difference of 1 / 4λ is used as a constituent material.

[0018] The present invention also provides a pressure-sensitive adhesive layer-attached optical film, comprising an optical film and a pressure-sensitive adhesive layer for an optical film formed by crosslinking the pressure-sensitive adhesive composition for an optical film, laminated on at least one surface of the optical film. Effect of the Invention

[0019] According to the present invention, by forming an adhesive layer by crosslinking an acrylic polymer consisting of a copolymer having a Tg of -60°C or more and -30°C or less, which is obtained by copolymerizing a total of 100 parts by weight of at least two or more monomers selected from the monomer group consisting of alkyl (meth)acrylate monomers, (meth)acrylate monomers having an aromatic group, and nitrogen-containing vinyl monomers, 0.1 to 10.0 parts by weight of a carboxyl group-containing copolymerizable vinyl monomer, and 0.05 to 4.5 parts by weight of a hydroxyl group-containing copolymerizable vinyl monomer, it is possible to provide an adhesive layer for optical films, an adhesive film for optical films, and an adhesive composition for optical films used therein, which have excellent heat resistance and durability. In addition, the pressure-sensitive adhesive layer for optical film according to the present invention is transferred to both sides of a retardation film made of a polycarbonate resin film, and a polarizing film is attached to one side of the optical film laminate, which is attached to an alkali-free glass and then stored in a dry atmosphere at 85°C for 200 hours. After that, the laminate is taken out of the glass and placed in a 23°C x 50% RH atmosphere and checked one hour later, and has durability without foaming. Therefore, the pressure-sensitive adhesive layer for optical film according to the present invention can exhibit extremely excellent functions in attaching a retardation film made of a polycarbonate resin film. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, the present invention will be described based on preferred embodiments. The pressure-sensitive adhesive composition for an optical film of the present invention contains an acrylic polymer and a crosslinkable compound. The pressure-sensitive adhesive composition for an optical film of the present invention is crosslinked to form the pressure-sensitive adhesive layer for an optical film of the present invention. The pressure-sensitive adhesive composition for optical films of the present invention contains: (A) 100 parts by weight of at least two or more monomers selected from the group of monomers consisting of alkyl (meth)acrylate monomers (a1) having an alkyl group carbon number of C1 to C14, (meth)acrylate monomers (a2) having an aromatic group, and nitrogen-containing vinyl monomers (a3) ​​(wherein the total of 100 parts by weight is 51 parts by weight or more and 95 parts by weight or less of one of the monomers belonging to (a1) and 5 parts by weight or more and 49 parts by weight or less of the other one or more monomers selected from the group of monomers consisting of (a1) to (a3)); (B) 0.1 to 10.0 parts by weight of a carboxyl group-containing copolymerizable vinyl monomer; and (C) 0.05 to 4.5 parts by weight of a hydroxyl group-containing copolymerizable vinyl monomer, and an acrylic polymer composed of a copolymer having a Tg of -60°C or more and -30°C or less, obtained by copolymerizing the above-mentioned monomers; and a crosslinkable compound. In addition, the pressure-sensitive adhesive layer for optical films of the present invention has durability such that no foaming is observed when a laminate of an optical film with a pressure-sensitive adhesive layer, which is formed by transferring the pressure-sensitive adhesive layer for optical films to both sides of a retardation film made of a polycarbonate resin film and laminating a polarizing film to one side of the laminate, is laminated to alkali-free glass and then stored in a dry atmosphere at 85°C for 200 hours, and then taken out into a 23°C x 50% RH atmosphere and checked one hour later.

[0021] The acrylic polymer in the pressure-sensitive adhesive composition for optical film of the present invention is a copolymer obtained by copolymerizing two or more kinds selected from the group of compounds belonging to the monomers (main component monomers) belonging to group (A) with one or more kinds selected from the group of compounds belonging to the monomers (functional group monomers) belonging to groups (B) and (C). As the monomers belonging to group (A), at least two or more kinds selected from the group of monomers consisting of alkyl (meth)acrylate monomers (a1) having an alkyl group with carbon number of C1 to C14, (meth)acrylate monomers (a2) having an aromatic group, and nitrogen-containing vinyl monomers (a3) ​​can be used. As the monomers belonging to group (B), at least one or more kinds of copolymerizable vinyl monomers containing a carboxyl group can be used, and as the monomers belonging to group (C), at least one or more kinds of copolymerizable vinyl monomers containing a hydroxyl group can be used. In this specification, (meth)acrylate is a general term for acrylate and methacrylate.

[0022] In the pressure-sensitive adhesive composition for the pressure-sensitive adhesive layer for optical film of the present invention, examples of the alkyl (meth)acrylate monomer (a1) having an alkyl group with a carbon number of C1 to C14 belonging to group (A) include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, isohexyl (meth)acrylate, heptyl (meth)acrylate, isoheptyl (meth)acrylate, and tert-butyl (meth)acrylate. At least one selected from the group consisting of acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, isoundecyl (meth)acrylate, dodecyl (meth)acrylate, isododecyl (meth)acrylate, tridecyl (meth)acrylate, isotridecyl (meth)acrylate, tetradecyl (meth)acrylate, and isotetradecyl (meth)acrylate. The alkyl group of the alkyl (meth)acrylate monomer may be linear, branched, or cyclic (alicyclic). The acrylic polymer in the pressure-sensitive adhesive composition for optical films of the present invention preferably contains 51 to 95 parts by weight of one kind of monomer selected from the compound group consisting of (a1) alkyl (meth)acrylate monomers having an alkyl group carbon number of C1 to C14 out of a total of 100 parts by weight of at least two or more kinds of monomers selected from the monomer group consisting of (a1) to (a3) ​​belonging to group (A). In addition, (a1) alkyl (meth)acrylate monomer having an alkyl group with a carbon number of C1 to C14 is an extremely common compound used in large quantities in the chemical industry, and is therefore an easily available and relatively inexpensive material, and is a compound that can be effectively used to reduce the production costs of the pressure-sensitive adhesive composition product. In addition, (a1) alkyl (meth)acrylate monomers having an alkyl group with a carbon number of C1 to C14 include many compounds having a polymer glass transition temperature (Tg) of -30°C or lower, and therefore are highly useful compounds in that they can be easily selected as a method for adjusting the physical properties of the pressure-sensitive adhesive layer for optical films according to the present invention.

[0023] In the pressure-sensitive adhesive composition relating to the pressure-sensitive adhesive layer for optical films of the present invention, examples of the (a2) (meth)acrylate monomer having an aromatic group belonging to group (A) include at least one selected from the group of compounds consisting of benzyl (meth)acrylate, naphthyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxybutyl (meth)acrylate, phenoxydiethylene glycol (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 for an optical film having a high refractive index, it is preferable to copolymerize the acrylic polymer with at least one or more (meth)acrylate monomers having an aromatic group. The acrylic polymer in the pressure-sensitive adhesive composition for optical films of the present invention may contain 0 to 30 parts by weight of (a2) a (meth)acrylate monomer having an aromatic group, out of a total of 100 parts by weight of at least two or more monomers selected from the monomer group consisting of (a1) to (a3) ​​belonging to group (A). When the acrylic polymer of the present invention contains (a2) a (meth)acrylate monomer having an aromatic group, it more preferably contains 3 to 25 parts by weight, and particularly preferably 8 to 20 parts by weight, of a total of 100 parts by weight of at least two or more monomers selected from the monomer group consisting of (a1) to (a3) ​​belonging to group (A).

[0024] In the pressure-sensitive adhesive composition relating to the pressure-sensitive adhesive layer for optical film of the present invention, the nitrogen-containing vinyl monomer (a3) ​​belonging to group (A) includes (meth)acrylic monomers containing an amide bond, (meth)acrylic monomers containing an amino group, etc. More specifically, cyclic nitrogen-containing vinyl compounds having an N-(meth)acryloyl-substituted heterocyclic structure such as N-(meth)acryloylmorpholine, N-(meth)acryloylpiperazine, N-(meth)acryloylaziridine, N-(meth)acryloylazetidine, N-(meth)acryloylpyrrolidine, N-(meth)acryloylpiperidine, N-(meth)acryloylazepane, and N-(meth)acryloylazocane; (meth)acrylamide, N- Unsubstituted or monoalkyl-substituted (meth)acrylamides such as methyl(meth)acrylamide, N-isopropyl(meth)acrylamide, and Nt-butyl(meth)acrylamide; N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropylacrylamide, N,N-diisopropyl(meth)acrylamide, N,N-dibutyl(meth)acrylamide, and N-ethyl-N-methyl(meth)acrylamide dialkyl-substituted (meth)acrylamides such as N-methyl-N-propyl (meth)acrylamide and N-methyl-N-isopropyl (meth)acrylamide; dialkylamino (meth)acrylates such as N,N-dimethylaminomethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylate, N,N-dimethylaminoisopropyl (meth)acrylate, N,N-dimethylaminobutyl (meth)acrylate, N,N-diethylaminomethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, N-ethyl-N-methylaminoethyl (meth)acrylate, N-methyl-N-propylaminoethyl (meth)acrylate, N-methyl-N-isopropylaminoethyl (meth)acrylate, N,N-dibutylaminoethyl (meth)acrylate, and t-butylaminoethyl (meth)acrylate;At least one selected from the group consisting of N,N-dialkyl-substituted aminopropyl(meth)acrylamides such as N,N-dimethylaminopropyl(meth)acrylamide, N,N-diethylaminopropyl(meth)acrylamide, N,N-dipropylaminopropyl(meth)acrylamide, N,N-diisopropylaminopropyl(meth)acrylamide, N-ethyl-N-methylaminopropyl(meth)acrylamide, N-methyl-N-propylaminopropyl(meth)acrylamide, and N-methyl-N-isopropylaminopropyl(meth)acrylamide; and (meth)acrylonitrile. (a3) ​​The nitrogen-containing vinyl monomer is preferably one that does not contain a hydroxyl group, and more preferably one that does not contain a hydroxyl group or a carboxyl group.; The acrylic polymer in the pressure-sensitive adhesive composition for optical films of the present invention may contain 0 to 20 parts by weight of a nitrogen-containing vinyl monomer (a3) ​​out of a total of 100 parts by weight of at least two or more monomers selected from the monomer group consisting of (a1) to (a3) ​​belonging to group (A). When the acrylic polymer according to the present invention contains the nitrogen-containing vinyl monomer (a3), it is more preferable that the monomers selected from the monomer group consisting of (a1) to (a3) ​​belonging to group (A) are contained in an amount of 2 to 20 parts by weight, and particularly preferably 2 to 12 parts by weight, based on a total of 100 parts by weight of at least two or more monomers selected from the monomer group consisting of (a1) to (a3).

[0025] The monomers (functional group monomers) belonging to groups (B) and (C) have a functional group capable of reacting with a crosslinking compound. Such functional groups include a carboxyl group, a hydroxyl group, etc. The monomers belonging to group (A) do not need to have a functional group capable of reacting with a crosslinking compound.

[0026] In the pressure-sensitive adhesive composition relating to the pressure-sensitive adhesive layer for optical films of the present invention, the (B) carboxyl group-containing copolymerizable vinyl monomer may be at least one selected from the group consisting of (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, 2-(meth)acryloyloxyethyl hexahydrophthalic acid, 2-(meth)acryloyloxyethyl phthalic acid, 2-(meth)acryloyloxyethyl succinic acid, 2-(meth)acryloyloxyethyl maleic acid, carboxypolycaprolactone mono(meth)acrylate, and 2-(meth)acryloyloxyethyl tetrahydrophthalic acid. The acrylic polymer according to the present invention preferably contains 0.1 to 10.0 parts by weight, more preferably 0.3 to 9.0 parts by weight, and particularly preferably 0.5 to 9.0 parts by weight of (B) a carboxyl group-containing copolymerizable vinyl monomer per 100 parts by weight in total of at least two or more monomers selected from the monomer group consisting of (a1) to (a3) ​​belonging to (A).

[0027] In the pressure-sensitive adhesive composition relating to the pressure-sensitive adhesive layer for optical film of the present invention, examples of the hydroxyl group-containing copolymerizable vinyl monomer (C) 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, 2-hydroxypropyl (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 them, 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, 2-hydroxypropyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, N-hydroxy(meth)acrylamide, N-hydroxymethyl (meth)acrylamide, and N-hydroxyethyl (meth)acrylamide. The acrylic polymer for the pressure-sensitive adhesive layer for optical films of the present invention preferably contains 0.05 to 4.5 parts by weight, more preferably 0.05 to 1.2 parts by weight, and particularly preferably 0.05 to 0.5 parts by weight of (C) a hydroxyl group-containing copolymerizable vinyl monomer relative to 100 parts by weight in total of at least two or more monomers selected from the monomer group consisting of (a1) to (a3) ​​belonging to group (A).

[0028] The polymerization method of the copolymer used as the acrylic polymer is not particularly limited, and a known polymerization method such as a solution polymerization method or an emulsion polymerization method can be used as appropriate. In the monomer composition of the acrylic polymer, among the total of 100 parts by weight of at least two or more monomers selected from the monomer group consisting of (a1) to (a3) ​​belonging to group (A), one type of monomer belonging to (a1) alkyl (meth)acrylate monomer having a carbon number of C1 to C14 in the alkyl group is 51 parts by weight or more and 95 parts by weight or less (abbreviated as M1), and the total of one or more other monomers selected from the monomer group consisting of (a1) to (a3) ​​is 5 parts by weight or more and 49 parts by weight or less (abbreviated as M2), and the total of M1 and M2 is 100 parts by weight. M1 consists of only one type of monomer, and M2 consists of a monomer other than M1. As long as each monomer constituting M2 belongs to any of (a1) to (a3), M2 may or may not contain a monomer belonging to (a1) (excluding monomers corresponding to M1), M2 may or may not contain a monomer belonging to (a2), and M2 may or may not contain a monomer belonging to (a3). In the present invention, the glass transition temperature (hereinafter referred to as Tg) of the acrylic polymer is preferably -60°C or more and -30°C or less. If the Tg exceeds -30°C, the foaming resistance (durability) decreases, which is not preferable. Furthermore, the Tg of the acrylic polymer according to the present invention is more preferably -50°C to -30°C. Furthermore, the weight average molecular weight of the acrylic polymer according to the present invention is preferably 1 million or more, and more preferably in the range of 1 million to 2 million.

[0029] The pressure-sensitive adhesive composition for the pressure-sensitive adhesive layer for an optical film of the present invention can have required physical property values ​​adjusted by blending the above-mentioned acrylic polymer with a crosslinkable compound and / or any appropriate additives.

[0030] The crosslinkable compound in the pressure-sensitive adhesive composition for optical films of the present invention is a compound (crosslinking agent) used for crosslinking acrylic polymers. As the crosslinkable compound, a bifunctional or higher functional epoxy compound is preferred. The bifunctional or higher functional epoxy compound is not particularly limited as long as it is a compound having two or more epoxy groups in one molecule, and examples thereof include at least one selected from polyglycidyl amines such as 1,3-bis(diglycidylaminomethyl)cyclohexane, 1,3-bis(diglycidylaminomethyl)benzene (also known as N,N,N',N'-tetraglycidyl-m-xylylenediamine), and diglycidylaniline; polyglycidyl ethers such as sorbitol polyglycidyl ether, (poly)ethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, glycerin polyglycidyl ether, trimethylolpropane polyglycidyl ether, and bisphenol A diglycidyl ether; and polyglycidyl esters such as hexahydrophthalic acid diglycidyl ester and maleic acid diglycidyl ester. Furthermore, examples of commonly available commercially available epoxy compounds include 1,3-bis(diglycidylaminomethyl)cyclohexane and 1,3-bis(diglycidylaminomethyl)benzene. The pressure-sensitive adhesive composition for optical films of the present invention preferably contains 0.001 to 0.5 parts by weight of a crosslinkable compound relative to 100 parts by weight in total of at least two or more monomers selected from the monomer group consisting of (a1) to (a3) ​​belonging to group (A). As the crosslinkable compound, only a bifunctional or higher epoxy compound may be used.

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

[0032] The pressure-sensitive adhesive layer for optical film according to the present invention can be formed 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 for optical film after crosslinking is preferably 60 to 90%. If the gel fraction of the pressure-sensitive adhesive layer for optical film is outside this range, the heat resistance and durability are reduced, which is not preferable.

[0033] When the pressure-sensitive adhesive layer for optical films according to the present invention is used for bonding between layers of optical members, it is preferable that the pressure-sensitive adhesive layer is thin. The thickness of the pressure-sensitive adhesive layer for optical films is preferably 5 to 25 μm. In addition, in order to reduce the reflection of light at the interface between the pressure-sensitive adhesive layer for optical films and the optical member, it is preferable that the difference in refractive index between the adherend and the pressure-sensitive adhesive layer for optical films is as small as possible.

[0034] The adhesive film for optical film of the present invention can be produced by forming the adhesive layer for optical film of the present invention on one side of a substrate, an optical film, or a release film. A resin film such as a polyester film can be used as the substrate film used to form the adhesive layer for optical film and the release film (separator) to protect the adhesive surface. The substrate film can be subjected to an antifouling treatment using a silicone-based or fluorine-based release agent or coating agent, silica fine particles, or an antistatic treatment by coating or kneading an antistatic agent on the side opposite to the side on which the adhesive layer for optical 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 that is to be joined to the adhesive surface of the pressure-sensitive adhesive layer for optical films. A "release film / pressure-sensitive adhesive layer for optical films / release film" configuration can be achieved by joining the release-treated surfaces of the release film to both sides of one pressure-sensitive adhesive layer for optical films. In this case, the release films on both sides are peeled off sequentially or simultaneously to expose the adhesive surface, making it possible to attach it to an optical member 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 pressure-sensitive adhesive layer for optical films according to the present invention has excellent heat resistance and durability, and is therefore suitable for applications in which a retardation film is bonded to a polarizing film or an organic EL panel in a configuration of polarizing film / pressure-sensitive adhesive layer for optical films / retardation film / pressure-sensitive adhesive layer for optical films / organic EL panel.

[0037] The pressure-sensitive adhesive layer for optical films and the pressure-sensitive adhesive film for optical films of the present invention can be used for bonding various optical films incorporated in image display devices, various optical films for touch panels, various optical films for electronic paper, various optical films incorporated in liquid crystal panels, and various optical films incorporated in organic EL panels. In addition, the pressure-sensitive adhesive layer for optical films can be laminated on at least one surface of these optical films to form an optical film with a pressure-sensitive adhesive layer. When the pressure-sensitive adhesive layer for optical films is protected by a release film, the release film is peeled off to expose the pressure-sensitive adhesive layer for optical films as in "optical film / pressure-sensitive adhesive layer for optical films", and the optical film is bonded to another optical film, thereby obtaining a configuration such as "optical film / pressure-sensitive adhesive layer for optical films / optical film" in which the pressure-sensitive adhesive layer for optical films is used between the layers.

[0038] The pressure-sensitive adhesive layer for optical films of the present invention is preferably used for bonding various optical films incorporated in image display devices. The pressure-sensitive adhesive layer for optical films of the present invention can also be preferably used in configurations such as "polarizing film / pressure-sensitive adhesive layer for optical films", "polarizing film / pressure-sensitive adhesive layer for optical films / release film", "polarizing film / pressure-sensitive adhesive layer for optical films / retardation film / pressure-sensitive adhesive layer for optical films", "polarizing film / pressure-sensitive adhesive layer for optical films / retardation film / pressure-sensitive adhesive layer for optical films / release film", etc.

[0039] Examples of image display devices according to the present invention include, but are not limited to, liquid crystal display devices (liquid crystal panels), organic EL display devices (liquid crystal panels), touch panels, electronic paper, etc. In the following, an organic EL panel will be described as a representative example, but the present invention based on these concepts can also be applied to other image display devices such as liquid crystal panels. The material of the retardation film incorporated in the organic EL panel includes polycarbonate compounds, and preferably has reverse wavelength dispersion (birefringence increases with longer wavelength). Polycarbonate compounds are resins containing carbonate bonds (-O-CO-O-) in the repeating units of the polymer, and various types of chemical structures such as aromatic and aliphatic are known to be contained between each carbonate bond. The repeating units may be one type or two or more types. The retardation of the retardation film may be 1 / 4λ or 1 / 2λ (1 / 4 or 1 / 2 times the wavelength λ). In recent years, organic EL panels have come to require a circular polarizer to prevent external light reflection. A circular polarizer is made up of two layers of a linear polarizing film and a 1 / 4λ retardation film, and the retardation film surface is bonded to the organic EL panel. This has the drawback of poor durability and foaming resistance due to the polycarbonate resin. The pressure-sensitive adhesive layer for optical films of the present invention is highly useful for bonding optical films, such as polarizing films incorporating 1 / 4λ retardation films made of polycarbonate resins and organic EL panels.

[0040] A commonly used polarizing film is a layer of polyvinyl alcohol (PVA) containing iodine molecules (I2) that serves as a polarizer, and on both sides of the layer are laminated protective layers (sometimes called protective films for the polarizer) made of materials with excellent optical properties (such as transparency), such as triacetyl cellulose (TAC), COP (cycloolefin polymer), acrylic resin, and polypropylene (PP). Furthermore, the resin film of the protective layer may also function as a retardation film.

[0041] An example of an organic EL panel is a light-emitting element having an organic light-emitting diode (OLED) structure, in which a plurality of functional layers, such as a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, and an electron injection layer, are formed and stacked between positive and negative electrodes. Examples of electrodes include a transparent electrode layer having translucency and an opaque metal electrode layer. Flexible organic EL panels can also be manufactured, and electrodes, wiring, functional layers, and the like can be formed on a flexible substrate such as a resin by foil, plating, printing, vapor deposition, sputtering, and the like. EXAMPLES

[0042] The present invention will now be described in detail with reference to examples.

[0043] <Production of acrylic polymer> [Example 1] Nitrogen gas was introduced into a reaction apparatus equipped with a reaction vessel, a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet tube, and the air in the reaction vessel was replaced with nitrogen gas. Then, 70 parts by weight of 2-ethylhexyl acrylate, 30 parts by weight of t-butyl acrylate, 0.5 parts by weight of 2-acryloyloxyethylhexahydrophthalic acid, 0.3 parts by weight of 8-hydroxyoctyl acrylate, and 60 parts by weight of a solvent (ethyl acetate) were added to the reaction vessel. Then, 0.1 parts by weight of azobisisobutyronitrile was dropped as a polymerization initiator over 2 hours, and the mixture was reacted at 65°C for 6 hours to obtain an acrylic polymer solution of Example 1. [Examples 2 to 5 and Comparative Examples 1 to 3] The acrylic polymer solutions of Examples 2 to 5 and Comparative Examples 1 to 3 were obtained in the same manner as in Example 1 above, except that the types and mixing ratios of the monomers constituting the acrylic polymer were set as shown in Table 1, groups (A) to (C).

[0044] <Production of Pressure-Sensitive Adhesive Composition, Pressure-Sensitive Adhesive Layer for Optical Film, and Pressure-Sensitive Adhesive Film for Optical Film> [Example 1] 0.01 parts by weight of 1,3-bis(diglycidylaminomethyl)cyclohexane was added to the acrylic polymer solution of Example 1 in the reaction vessel produced as described above, and the mixture was stirred and mixed to obtain a pressure-sensitive adhesive composition of Example 1. This pressure-sensitive adhesive composition was applied onto a release film (a silicone resin-coated polyethylene terephthalate (PET) film) so that the thickness after drying was 10 μm, and then dried at 90° C. for 5 minutes to form a pressure-sensitive adhesive layer. Thereafter, a release-treated release film was superimposed on the dried pressure-sensitive adhesive layer to form a layer structure consisting of release film / pressure-sensitive adhesive layer for optical film / release film. Furthermore, aging (aging) was performed for 7 days under an atmosphere of 23° C. and 50% RH to obtain a pressure-sensitive adhesive film for optical film of Example 1. [Examples 2 to 5 and Comparative Examples 1 to 3] The types and blending ratios of the crosslinkable compounds were each as described in Group (D) of Table 1, and the thickness of the adhesive layer after drying was the value in Table 3. Except for this, adhesive films for optical films of Examples 2 to 5 and Comparative Examples 1 to 3 were obtained in the same manner as in Example 1 above.

[0045] [Table 1]

[0046] In Table 1, the total of two or more monomers selected from the monomer group consisting of alkyl (meth)acrylate monomers (a1) having an alkyl group carbon number of C1 to C14, (meth)acrylate monomers (a2) having an aromatic group, and nitrogen-containing vinyl monomers (a3) ​​in group (A) is 100 parts by weight (wherein the total of 51 to 95 parts by weight of one of the monomers belonging to (a1) and 5 to 49 parts by weight of the other one or more monomers selected from the monomer group consisting of (a1) to (a3) ​​is 100 parts by weight). In addition, the weight parts are shown in parentheses as the addition ratios of groups (B) to (D). Group (B) is a copolymerizable vinyl monomer containing a carboxyl group, group (C) is a copolymerizable vinyl monomer containing a hydroxyl group, and group (D) is a crosslinkable compound.

[0047] Table 2 shows the compound names corresponding to the abbreviations of the components shown in Table 1. TETRAD (registered trademark)-C and -X are product names of Mitsubishi Gas Chemical Co., Inc., and Coronate (registered trademark) HX and L are product names of Tosoh Corporation. TDI means tolylene diisocyanate, TMP means trimethylolpropane, and HDI means hexamethylene diisocyanate.

[0048] [Table 2]

[0049] <Test methods and evaluation> The release films (silicone resin-coated PET films) were peeled off from the obtained adhesive films for optical films of Examples 1 to 5 and Comparative Examples 1 to 3 to expose the adhesive layers for optical films, which were used as samples for various measurements and tests.

[0050] <Method for measuring gel fraction of pressure-sensitive adhesive layer for optical film> The mass of the pressure-sensitive adhesive layer of the measurement sample was accurately measured, and then the sample was immersed in toluene at room temperature for 24 hours to elute the dissolved components, and then filtered through a 200-mesh wire screen. 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 for optical films (pressure-sensitive adhesive layer for optical films after crosslinking) was calculated from the following formula. Gel fraction (%) of pressure-sensitive adhesive layer for optical film = mass of insoluble portion (g) / mass of pressure-sensitive adhesive layer (g) × 100

[0051] <Durability test method> A pressure-sensitive adhesive layer for optical films was transferred onto both sides of a retardation film made of a polycarbonate resin film (Teijin Limited, model PURE-ACE WR), and a polarizing film was further laminated onto one side to obtain an optical film laminate with a pressure-sensitive adhesive layer. The laminate was then laminated onto alkali-free glass (Corning Incorporated, EAGLE-XG, thickness 0.7 mm), autoclaved (50°C, 5 atm x 20 minutes), stored in a 85°C dry atmosphere for 200 hours, and then removed from the glass in a 23°C x 50% RH atmosphere for 1 hour, after which the durability was visually inspected and judged. The criteria for visual inspection were as follows: ◯: There is absolutely no peeling or foaming of the pressure-sensitive adhesive layer for optical films. △ Peeling and bubbling occurred in the pressure-sensitive adhesive layer for the optical film. × Peeling and bubbling occurred over the entire pressure-sensitive adhesive layer for the optical film.

[0052] The evaluation results are shown in Table 3. "Thickness of pressure-sensitive adhesive layer for optical film" indicates the thickness of the pressure-sensitive adhesive layer for optical film used in the durability test.

[0053] [Table 3]

[0054] The pressure-sensitive adhesive layer for optical films according to the present invention, which is the pressure-sensitive adhesive layer for optical films exposed from the pressure-sensitive adhesive films for optical films of Examples 1 to 5, had a configuration of polarizing film / pressure-sensitive adhesive layer for optical films / retardation film / pressure-sensitive adhesive layer for optical films / alkali-free glass, and after preparing a laminate simulating an organic EL panel, it did not foam during durability after 200 hours at 85° C. That is, the pressure-sensitive adhesive layer for optical films according to the present invention has excellent heat resistance and durability when used for interlayer bonding between a retardation film and a polarizing film or an organic EL panel.

[0055] In the adhesive film for optical films in Comparative Example 1, the amount of carboxyl group-containing copolymerizable vinyl monomer used in the acrylic polymer of the adhesive composition for optical films was too small, the Tg of the acrylic polymer was high, and the gel fraction of the adhesive layer for optical films was high. In the durability test, partial foaming was observed in the adhesive layer for optical films. In the adhesive film for optical films of Comparative Example 2, in the acrylic polymer of the adhesive composition for optical films, no hydroxyl group-containing copolymerizable vinyl monomer was used, but instead an excessive amount of carboxyl group-containing copolymerizable vinyl monomer was used. As a result, the reactivity of the acrylic polymer with the crosslinking agent was high, and gelation progressed before coating, making it impossible to coat (in this case, the gel fraction after crosslinking can be said to be approximately 100%). The pressure-sensitive adhesive film for an optical film of Comparative Example 3 had a low gel fraction in the pressure-sensitive adhesive layer for an optical film, and significant foaming was observed in the durability test. As described above, in the pressure-sensitive adhesive films for an optical film of Comparative Examples 1 to 3, the pressure-sensitive adhesive layer for an optical film was not provided with durability.

Claims

1. A pressure-sensitive adhesive layer for an optical film, which is obtained by crosslinking a pressure-sensitive adhesive composition for an optical film containing an acrylic polymer and a crosslinkable compound (excluding those containing a polyisocyanate compound), The acrylic polymer is as group (A), a total of 100 parts by weight of at least two or more monomers selected from the monomer group consisting of (a1) alkyl (meth)acrylate monomers having an alkyl group with a carbon number of C1 to C14, (a2) (meth)acrylate monomers having an aromatic group, and (a3) ​​nitrogen-containing vinyl monomers (provided that the monomer contains 51 parts by weight or more and 95 parts by weight or less of one monomer belonging to the (a1) alkyl (meth)acrylate monomers having an alkyl group with a carbon number of C1 to C14, and 3 to 25 parts by weight of one or more (a2) (meth)acrylate monomers having an aromatic group); (B) 0.1 to 10.0 parts by weight of a carboxyl group-containing copolymerizable vinyl monomer, (C) 0.05 to 4.5 parts by weight of a hydroxyl group-containing copolymerizable vinyl monomer, and having a Tg of -60°C or more and -30°C or less, the crosslinkable compound is a di- or higher functional epoxy compound, The pressure-sensitive adhesive layer for an optical film has a gel fraction of 60 to 90%, and the pressure-sensitive adhesive layer for an optical film has a thickness of 5 to 25 μm.

2. An image display device, in which the pressure-sensitive adhesive layer for optical films according to claim 1 is used for bonding an optical film.

3. A polarizing plate having a pressure-sensitive adhesive layer, comprising the pressure-sensitive adhesive layer for an optical film according to claim 1 .

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