Adhesive composition for polarizing plate, polarizing plate, and optical display apparatus

Abstract

This document discloses an adhesive composition for a polarizing plate, a polarizing plate, and an optical display device. The adhesive composition for the polarizing plate comprises a curable compound and a photoinitiator, wherein the curable compound includes an epoxy compound and a (meth)acrylate compound, the epoxy compound including a mixture of bifunctional alicyclic epoxy compounds and bifunctional alicyclic epoxy compounds, and the (meth)acrylate compound including a mixture of hydrophilic bifunctional (meth)acrylate compounds, hydrophobic bifunctional (meth)acrylate compounds, and vinyl-containing (meth)acrylate compounds, wherein the hydrophobic bifunctional (meth)acrylate compound is a bifunctional (meth)acrylate compound having a straight-chain extended alkyl chain containing 9 or more carbon atoms, and wherein the vinyl-containing (meth)acrylate compound is present in an amount of 10 to 15 parts by weight relative to 100 parts by weight of the curable compound.

Description

Adhesive composition for polarizing plates, polarizing plates and optical display devices This invention relates to an adhesive composition for a polarizing plate, a polarizing plate, and an optical display device. Cross-Reference to Related Applications This application claims priority and benefit to Korean Patent Application No. 10-2024-0002026, filed on January 5, 2024, with the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference. A polarizing plate includes a polarizer and polarizer protective films formed on both surfaces of the polarizer. The polarizer protective film can be an optically clear protective film, such as a triacetylcellulose (TAC) film, a polyethylene terephthalate (PET) film, an acrylic film, a polycarbonate film, or a cyclic olefin polymer (COP) film, or it can be a protective layer formed from a curable resin (e.g., epoxy resin and acrylate). TAC films are highly moisture-permeable protective films, and therefore easily bonded with water-based adhesives due to their moisture permeability. However, TAC films have limited ability to improve the reliability of the polarizing plate. Bonding polarizer protective films other than TAC films requires solvent-free, photocurable adhesives because these protective films prevent the removal of moisture from the adhesive. For example, PET, COP, or acrylic films are protective films with low moisture permeability and require photocurable adhesives for bonding. COP films manufactured through solution casting and stretching to high elongation (e.g., COP films manufactured by Konica Minolta of Japan) are preferred as polarizer protective films because they allow for easy adjustment of the phase retardation required for vertical alignment (VA) liquid crystal display (LCD) panels. However, bonding COP films using typical photocurable adhesives is difficult. The background technology of this invention is disclosed in Japanese Patent Publication No. 2014-032270. The object of the present invention is to provide an adhesive composition for a polarizing plate, the adhesive composition providing an adhesive layer that can: ensure good adhesion between the polarizing plate and a COP film produced by solution casting and stretching to high elongation; and maintain good adhesion after exposure to high temperature and high humidity conditions. Another object of the present invention is to provide an adhesive composition for a polarizing plate, the adhesive composition providing an adhesive layer that can improve the reliability of the polarizing plate by preventing discoloration of the polarizing film after exposure to high temperature and high humidity conditions. One aspect of the present invention relates to an adhesive composition for a polarizing plate. The adhesive composition for polarizing plates comprises: a curable compound; and a photoinitiator, wherein the curable compound includes (A) an epoxy compound and (B) a (meth)acrylate compound, the epoxy compound including a mixture of bifunctional cycloaliphatic epoxy compounds and bifunctional aliphatic epoxy compounds, the (meth)acrylate compound including a mixture of hydrophilic bifunctional (meth)acrylate compounds, hydrophobic bifunctional (meth)acrylate compounds and vinyl-containing (meth)acrylate compounds, the hydrophobic bifunctional (meth)acrylate compound being a bifunctional (meth)acrylate compound having a straight-chain extended alkyl chain containing 9 or more carbon atoms, and the vinyl-containing (meth)acrylate compound being present in an amount of 10 to 15 parts by weight relative to 100 parts by weight of the curable compound. Another aspect of the present invention relates to a polarizing plate. The polarizing plate includes a polarizing film and a protective film formed on the lower surface of the polarizing film, wherein the polarizing film is bonded to the protective film by an adhesive layer, and the adhesive layer contains a cured product of an adhesive composition for a polarizing plate according to the present invention. Another aspect of the present invention relates to an optical display device. The optical display device includes a polarizing plate according to the present invention. Embodiments of the present invention provide an adhesive composition for a polarizing plate, the adhesive composition providing an adhesive layer that can: ensure good adhesion between the polarizing film and a COP film produced by solution casting and stretching to high elongation; and have good adhesion after exposure to high temperature and high humidity conditions. Embodiments of the present invention provide an adhesive composition for a polarizing plate, the adhesive composition providing an adhesive layer capable of improving the reliability of the polarizing plate by preventing discoloration of the polarizing film after exposure to high temperature and high humidity conditions. Exemplary embodiments of the invention will be described in detail with reference to the accompanying drawings to facilitate practice by those skilled in the art. It should be understood that the invention may be implemented in different ways and is not limited to the following embodiments. In the accompanying drawings, details not relevant to the description are omitted for clarity. Throughout the specification, the same components are indicated by the same reference numerals. The lengths, sizes, and similar elements of the components in the accompanying drawings are for illustrative purposes only, and the invention is not limited thereto. In this document, spatial relative terms such as "upper" and "lower" are defined with reference to the accompanying drawings. Therefore, it should be understood that the term "upper surface" is used interchangeably with the term "lower surface". The terminology used herein is for the purpose of illustrating exemplary embodiments and is not intended to limit the invention. Unless the context clearly indicates otherwise, the singular forms "a" and "the" as used herein are intended to include the plural forms as well. The adhesive composition for polarizing plates according to the present invention is used to bond polarizing films to polarizing film protective films. The adhesive composition for the polarizing plate provides an adhesive layer that ensures good adhesion between the polarizer and the protective film of the polarizer. This adhesion remains strong even after prolonged exposure to high temperature and humidity conditions, and the reliability of the polarizing plate is improved by preventing discoloration of the polarizer after prolonged exposure to these conditions. Specifically, the adhesive composition for the polarizing plate provides an adhesive layer that ensures good adhesion (initial adhesion) between the polarizer and a COP film manufactured by solution casting and stretching to high elongation. This adhesion remains strong even after prolonged exposure to high temperature and humidity conditions, and the reliability of the polarizing plate is improved by preventing discoloration of the polarizer after prolonged exposure to these conditions. In one embodiment, in the stack of polarizer / adhesive layer / polarizer protective film (e.g., a COP film manufactured by solution casting and stretching to high elongation), the adhesive strength (initial adhesive strength) between the polarizer and the polarizer protective film can be 130 gf / 25 mm or greater (e.g., 130 gf / 25 mm to 500 gf / 25 mm). Within this range, the polarizer can exhibit good reliability and durability. In one embodiment, after stacking the polarizer / adhesive layer / polarizer protective film (e.g., a COP film manufactured by solution casting and stretching to high elongation) at 60°C and 95% relative humidity (RH) for 2 days, the adhesion strength between the polarizer and the polarizer protective film can be 150 gf / 25 mm or greater (e.g., 150 gf / 25 mm to 500 gf / 25 mm). Within this range, the polarizer can exhibit good reliability and durability. In one embodiment, after placing the polarizer / adhesive layer / polarizer protective film (e.g., a COP film manufactured by solution casting and stretching to high elongation) at 60°C and 95% RH for 500 hours, the length at which the iodine color disappears can be less than 1 mm (e.g., 0 mm to less than 1 mm). Within this range, the polarizer can exhibit good reliability and durability. In one embodiment, the polarizing protective film used to measure peel strength may be a COP film manufactured by solution casting and stretching to high elongation. The adhesive composition for polarizing plates includes a curable compound and a photoinitiator, wherein: the curable compound includes (A) an epoxy compound and (B) a (meth)acrylate compound; the epoxy compound (A) includes a mixture of bifunctional alicyclic epoxy compounds and bifunctional alicyclic epoxy compounds; the (meth)acrylate compound (B) includes a mixture of hydrophilic bifunctional (meth)acrylate compounds, hydrophobic bifunctional (meth)acrylate compounds and vinyl-containing (meth)acrylate compounds; the hydrophobic bifunctional (meth)acrylate compound is a bifunctional (meth)acrylate compound having a straight-chain extended alkyl chain containing 9 or more carbon atoms; and the vinyl-containing (meth)acrylate compound is present in an amount of 10 to 15 parts by weight relative to 100 parts by weight of the curable compound. According to the present invention, a bifunctional aliphatic epoxy compound and a hydrophobic bifunctional (meth)acrylate compound having a straight-chain extended alkyl chain containing nine or more carbon atoms are further incorporated into an adhesive composition, said adhesive composition comprising the curable compound as described above, namely, the bifunctional alicyclic epoxy compound, the hydrophilic bifunctional (meth)acrylate compound, and the vinyl-containing (meth)acrylate compound, and the content of the vinyl-containing (meth)acrylate compound in the adhesive composition is adjusted to a specific range, namely, 10 to 15 parts by weight relative to 100 parts by weight of the curable compound. Therefore, the adhesive composition according to the present invention can improve both the initial adhesion between the polarizer and the polarizer protective film (especially COP film manufactured by solution casting and stretching to high elongation) and the adhesion between the polarizer and the polarizer protective film after long-term exposure to high temperature and high humidity conditions, while improving the reliability of the polarizer by suppressing discoloration of the polarizer after long-term exposure to high temperature and high humidity conditions. The curable compound is a photocurable compound, making the adhesive composition a photocurable adhesive composition for use with polarizing plates. In one embodiment, the curable compound may be present in the adhesive composition in an amount of 90% by weight or greater than 90% by weight, for example 90% by weight, 91% by weight, 92% by weight, 93% by weight, 94% by weight, 95% by weight, 96% by weight, 97% by weight, 98% by weight, 99% by weight, or 100% by weight, for example 90% to 100% by weight or 93% to 100% by weight. In one embodiment, the total amount of epoxy compound (A) and (meth)acrylate compound (B) relative to 100 parts by weight of the curable compound may be 95 parts by weight or greater than 95 parts by weight, for example 95 parts by weight, 96 parts by weight, 97 parts by weight, 98 parts by weight, 99 parts by weight, or 100 parts by weight, preferably 99 parts by weight to 100 parts by weight, more preferably 100 parts by weight. Within this range, the adhesive composition can readily provide the desired effects of the present invention. Epoxy compounds The epoxy compound (A) may be present in an amount of 30 to 70 parts by weight relative to 100 parts by weight of the curable compound. Within this range, insufficient adhesion of the adhesive layer to the polarizer can be prevented by enhancing the bonding between the adhesive layer and the hydroxyl groups in the polarizer, while preventing the deterioration of the color-changing suppression properties due to the decrease in the overall glass transition temperature of the adhesive layer and insufficient bonding between the adhesive layer and the polarizer. Preferably, the epoxy compound (A) is present in an amount of 40 to 60 parts by weight relative to 100 parts by weight of the curable compound. Epoxy compounds (A) include bifunctional alicyclic epoxy compounds and bifunctional alicyclic epoxy compounds. In one embodiment, relative to 100 parts by weight of epoxy compound (A), the difunctional alicyclic epoxy compound and the difunctional alicyclic epoxy compound may be present in a total amount of 95 parts by weight or more, for example 95 parts by weight, 96 parts by weight, 97 parts by weight, 98 parts by weight, 99 parts by weight, or 100 parts by weight, preferably 99 parts by weight to 100 parts by weight, more preferably 100 parts by weight. Within this range, the epoxy compound can be beneficial in achieving the desired effects of the present invention. Bifunctional alicyclic epoxy compounds exhibit relatively high initial reaction rates and, therefore, due to their high glass transition temperatures, can have a beneficial effect on the dimensional stability of polarizers. Furthermore, bifunctional alicyclic epoxy compounds can improve the peel strength of polarizers relative to the protective film by bonding hydroxyl groups to the polarizer. Bifunctional alicyclic epoxy compounds can refer to compounds having two epoxide alicyclic groups. For example, bifunctional alicyclic epoxy compounds may include, but are not limited to, at least one of 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylate, 3,4-epoxy-6-methylcyclohexylmethyl-3',4'-epoxy-6'-methylcyclohexane carboxylate, bis(3,4-epoxy-6-methylcyclohexyl) adipic acid ester, dicyclohexyl diepoxide (3,4,3',4'-diepoxy-dicyclohexane), or 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylate-modified ε-caprolactone. The bifunctional alicyclic epoxy compound may be present in amounts from 10 parts by weight to 40 parts by weight, for example, 10 parts by weight, 11 parts by weight, 12 parts by weight, 13 parts by weight, 14 parts by weight, 15 parts by weight, 16 parts by weight, 17 parts by weight, 18 parts by weight, 19 parts by weight, 20 parts by weight, 21 parts by weight, 22 parts by weight, 23 parts by weight, 24 parts by weight, 25 parts by weight, 26 parts by weight, 27 parts by weight, 28 parts by weight, 29 parts by weight, 30 parts by weight, 31 parts by weight, 32 parts by weight, 33 parts by weight, 34 parts by weight, 35 parts by weight, 36 parts by weight, 37 parts by weight, 38 parts by weight, 39 parts by weight, or 40 parts by weight, preferably from 15 parts by weight to 30 parts by weight or from 20 parts by weight to 30 parts by weight, relative to 100 parts by weight of the curable compound. Within the specified range, bifunctional alicyclic epoxy compounds, due to their relatively high polymerization rate, can stabilize the structure of the adhesive layer, thereby ensuring a stable reaction while preventing delamination between films. Relative to 100 parts by weight of epoxy compound (A), the difunctional alicyclic epoxy compound can be 20 to 60 parts by weight, for example, 20 parts by weight, 21 parts by weight, 22 parts by weight, 23 parts by weight, 24 parts by weight, 25 parts by weight, 26 parts by weight, 27 parts by weight, 28 parts by weight, 29 parts by weight, 30 parts by weight, 31 parts by weight, 32 parts by weight, 33 parts by weight, 34 parts by weight, 35 parts by weight, 36 parts by weight, 37 parts by weight, 3 The amount present is 8 parts by weight, 39 parts by weight, 40 parts by weight, 41 parts by weight, 42 parts by weight, 43 parts by weight, 44 parts by weight, 45 parts by weight, 46 parts by weight, 47 parts by weight, 48 parts by weight, 49 parts by weight, 50 parts by weight, 51 parts by weight, 52 parts by weight, 53 parts by weight, 54 parts by weight, 55 parts by weight, 56 parts by weight, 57 parts by weight, 58 parts by weight, 59 parts by weight, or 60 parts by weight, preferably 40 parts by weight to 60 parts by weight. Within the range described, the bifunctional alicyclic epoxy compound is beneficial for achieving the desired effects of the present invention. Compared to bifunctional alicyclic epoxy compounds, bifunctional alicyclic epoxy compounds have relatively low reaction rates. During cationic polymerization, bifunctional alicyclic epoxy compounds do not cause a delay in the growth reaction of the epoxy compound. Conversely, due to the proton-trapping properties of the epoxy compound, bifunctional alicyclic epoxy compounds delay the growth reaction of the epoxy compound during cationic polymerization. In this invention, based on the growth-retarding effect of the bifunctional alicyclic epoxy compound, by providing sufficient time for the hydrophobic bifunctional (meth)acrylate compound to permeate the COP film before the fluidity of the hydrophobic bifunctional (meth)acrylate compound disappears, and then performing post-curing to impart good adhesion and reliability to the adhesive layer, a non-adhesive polarizer protective film, especially a COP film manufactured by solution casting and stretching to high elongation, is cured together with the hydrophobic bifunctional (meth)acrylate compound. In one embodiment, relative to 100 parts by weight of the bifunctional aliphatic epoxy compound, the hydrophobic bifunctional (meth)acrylate compound can be from 50 parts by weight to 300 parts by weight, for example, 50 parts by weight, 55 parts by weight, 60 parts by weight, 65 parts by weight, 70 parts by weight, 75 parts by weight, 80 parts by weight, 85 parts by weight, 90 parts by weight, 95 parts by weight, 100 parts by weight, 105 parts by weight, 110 parts by weight, 115 parts by weight, 120 parts by weight, 125 parts by weight, 130 parts by weight, 135 parts by weight, 140 parts by weight, 145 parts by weight, 150 parts by weight, 155 parts by weight, 160 parts by weight, and 165 parts by weight. It is present in amounts of 170 parts by weight, 175 parts by weight, 180 parts by weight, 185 parts by weight, 190 parts by weight, 195 parts by weight, 200 parts by weight, 205 parts by weight, 210 parts by weight, 215 parts by weight, 220 parts by weight, 225 parts by weight, 230 parts by weight, 235 parts by weight, 240 parts by weight, 245 parts by weight, 250 parts by weight, 255 parts by weight, 260 parts by weight, 265 parts by weight, 270 parts by weight, 275 parts by weight, 280 parts by weight, 285 parts by weight, 290 parts by weight, 295 parts by weight, or 300 parts by weight, preferably from 50 parts by weight to 200 parts by weight or from 60 parts by weight to 150 parts by weight. Within the specified range, due to the interaction between the bifunctional aliphatic epoxy compound and the hydrophobic bifunctional (meth)acrylate compound, the adhesive layer can exhibit good adhesion to COP films manufactured by solution casting and stretching to high elongation. Furthermore, by enabling the cationic protonated epoxy ring of the bifunctional alicyclic epoxy compound to be structurally held by the non-covalent electron pairs of the ether groups in the epoxy chain of the bifunctional alicyclic epoxy compound to restrict the polymerization of the epoxy ring, the bifunctional alicyclic epoxy compound can ensure the structural stability of the adhesive layer. Adhesive compositions containing aromatic epoxy compounds rather than bifunctional aliphatic epoxy compounds are unsuitable for improving peel strength because aromatic epoxy compounds have short carbon chains that make it difficult to trap protons in the adhesive composition. Bifunctional aliphatic epoxy compounds may include at least one of diglycidyl ether compounds having a straight-chain extended alkyl chain containing four or more carbon atoms, and diglycidyl ether compounds of ethylene oxide or propylene oxide having 2 moles or more. These bifunctional aliphatic epoxy compounds can be useful in ensuring that adhesive compositions according to the invention provide the desired effects described herein. Diglycidyl ether compounds having a straight-chain extended alkyl chain containing four or more carbon atoms can help provide the desired effects of the present invention because the straight-chain extended alkyl chain having four or more carbon atoms provides the above-mentioned reaction delay effect. Diglycidyl ether compounds having a straight-chain extended alkyl chain containing four or more carbon atoms may have a straight-chain or branched extended alkyl chain containing four or more, preferably four to ten, more preferably four to six carbon atoms. For example, the diglycidyl ether compound may include at least one of 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane diglycidyl ether, or neopentyl glycol diglycidyl ether. Preferably, the diglycidyl ether compound has an unsubstituted straight-chain C... 4 to C A diglycidyl ether compound with a 6-alkyl chain, such as at least one of 1,4-butanediol diglycidyl ether or 1,6-hexanediol diglycidyl ether. Since ethylene oxide or propylene oxide containing 2 moles or more provides the above-mentioned reaction delay effect, diglycidyl ether compounds containing 2 moles or more of ethylene oxide or propylene oxide may help to provide the desired effects of the present invention. The diglycidyl ether compound containing 2 moles or more of ethylene oxide or propylene oxide may be a diglycidyl ether compound containing 2 to 10 moles of ethylene oxide or propylene oxide. For example, the diglycidyl ether compound may include at least one of polyethylene glycol diglycidyl ether or polypropylene glycol diglycidyl ether. The bifunctional aliphatic epoxy compound may be present in amounts from 10 parts by weight to 40 parts by weight, for example, 10 parts by weight, 11 parts by weight, 12 parts by weight, 13 parts by weight, 14 parts by weight, 15 parts by weight, 16 parts by weight, 17 parts by weight, 18 parts by weight, 19 parts by weight, 20 parts by weight, 21 parts by weight, 22 parts by weight, 23 parts by weight, 24 parts by weight, 25 parts by weight, 26 parts by weight, 27 parts by weight, 28 parts by weight, 29 parts by weight, 30 parts by weight, 31 parts by weight, 32 parts by weight, 33 parts by weight, 34 parts by weight, 35 parts by weight, 36 parts by weight, 37 parts by weight, 38 parts by weight, 39 parts by weight, or 40 parts by weight, preferably from 15 parts by weight to 30 parts by weight or from 20 parts by weight to 30 parts by weight, relative to 100 parts by weight of the curable compound. Within the aforementioned range, bifunctional aliphatic epoxy compounds can provide sufficient time for hydrophobic bifunctional (meth)acrylate compounds to penetrate the COP film, preventing insufficient peel strength by ensuring enhanced bonding between the adhesive layer and the hydroxyl groups in the polarizer, and ultimately can be used to cure the adhesive composition to connect medium-sized polymers to form macromolecular polymers. This is because bifunctional aliphatic epoxy compounds have a relatively low curing rate compared to alicyclic epoxy compounds, thus ensuring good durability of the final product. Relative to 100 parts by weight of epoxy compound (A), the bifunctional aliphatic epoxy compound can be 40 to 80 parts by weight, for example, 40 parts by weight, 41 parts by weight, 42 parts by weight, 43 parts by weight, 44 parts by weight, 45 parts by weight, 46 parts by weight, 47 parts by weight, 48 parts by weight, 49 parts by weight, 50 parts by weight, 51 parts by weight, 52 parts by weight, 53 parts by weight, 54 parts by weight, 55 parts by weight, 56 parts by weight, 57 parts by weight, 58 parts by weight, etc. The amount present is 59 parts by weight, 60 parts by weight, 61 parts by weight, 62 parts by weight, 63 parts by weight, 64 parts by weight, 65 parts by weight, 66 parts by weight, 67 parts by weight, 68 parts by weight, 69 parts by weight, 70 parts by weight, 71 parts by weight, 72 parts by weight, 73 parts by weight, 74 parts by weight, 75 parts by weight, 76 parts by weight, 77 parts by weight, 78 parts by weight, 79 parts by weight, or 80 parts by weight, preferably 40 parts by weight to 60 parts by weight. Within the range described, the bifunctional aliphatic epoxy compound is beneficial for achieving the desired effects of the present invention. In one embodiment, in the composition, at least one of an aromatic group-containing epoxy compound or a hydrogenated aromatic group-containing epoxy compound may be present in an amount of less than 5 parts by weight, for example, 0 to less than 5 parts by weight or 0 parts by weight, relative to 100 parts by weight of the curable compound. ( methyl ) Acrylic compounds The (meth)acrylate compound (B) may be present in an amount of 30 to 70 parts by weight, for example, 40 to 60 parts by weight, relative to 100 parts by weight of the curable compound. Within this range, the (meth)acrylate compound can be beneficial in achieving the desired effects of the present invention. (Meth)acrylate compounds (B) include mixtures of hydrophilic bifunctional (meth)acrylate compounds, hydrophobic bifunctional (meth)acrylate compounds, and vinyl-containing (meth)acrylate compounds. In one embodiment, relative to 100 parts by weight of the (meth)acrylate compound (B), the total amount of the vinyl-containing (meth)acrylate compound, the hydrophilic bifunctional (meth)acrylate compound, and the hydrophobic bifunctional (meth)acrylate compound may be 95 parts by weight or more, for example 95 parts by weight, 96 parts by weight, 97 parts by weight, 98 parts by weight, 99 parts by weight, or 100 parts by weight, preferably 99 parts by weight to 100 parts by weight, more preferably 100 parts by weight. Within this range, the (meth)acrylate compound can be beneficial in achieving the desired effects of the present invention. The hydrophilic bifunctional (meth)acrylate compound can be a bifunctional (meth)acrylate compound having two (meth)acrylate groups and an epoxy alkyl group between the (meth)acrylate groups. This bifunctional (meth)acrylate compound exhibits good adhesion to hydrophilic substrates with hydroxyl groups (e.g., polarizers) and also has high affinity for polyester films treated with a primer, thereby enhancing the adhesion of the adhesive layer. Preferably, the epoxy alkyl group is ethylene oxide or propylene oxide. In the bifunctional (meth)acrylate compound, the epoxy alkyl group may be present in an amount of 2 mol or greater, for example, from 2 mol to 5 mol. Within this range, the bifunctional (meth)acrylate compound may be advantageous in achieving the desired effects of the present invention. For example, the hydrophilic bifunctional (meth)acrylate compound may include at least one of diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, or tripropylene glycol di(meth)acrylate. Relative to 100 parts by weight of the curable compound, the hydrophilic bifunctional (meth)acrylate compound may be present in an amount of 5 to 20 parts by weight, for example, 5 parts by weight, 6 parts by weight, 7 parts by weight, 8 parts by weight, 9 parts by weight, 10 parts by weight, 11 parts by weight, 12 parts by weight, 13 parts by weight, 14 parts by weight, 15 parts by weight, 16 parts by weight, 17 parts by weight, 18 parts by weight, 19 parts by weight, or 20 parts by weight, preferably 10 to 20 parts by weight. Within this range, due to the affinity of the hydrophilic bifunctional (meth)acrylate compound for the epoxy compound, the adhesive composition can stably maintain a liquid phase, and the (meth)acrylate compound does not penetrate into the COP membrane. Therefore, through polymerization with the hydrophobic bifunctional (meth)acrylate that has already penetrated the COP membrane, the adhesive composition can be cured over a large area, thereby facilitating the achievement of the desired effects of the present invention. The preferred amount relative to 100 parts by weight of (meth)acrylate compound (B) is the sum of hydrophilic difunctional (meth)acrylate compound, hydrophobic difunctional (meth)acrylate compound, and vinyl-containing (meth)acrylate compound. The hydrophilic difunctional (meth)acrylate compound can range from 10 parts by weight to 60 parts by weight, for example, 10 parts by weight, 11 parts by weight, 12 parts by weight, 13 parts by weight, 14 parts by weight, 15 parts by weight, 16 parts by weight, 17 parts by weight, 18 parts by weight, 19 parts by weight, 20 parts by weight, 21 parts by weight, 22 parts by weight, 23 parts by weight, 24 parts by weight, 25 parts by weight, 26 parts by weight, 27 parts by weight, 28 parts by weight, etc. It is present in parts by weight, 29 parts by weight, 30 parts by weight, 31 parts by weight, 32 parts by weight, 33 parts by weight, 34 parts by weight, 35 parts by weight, 36 parts by weight, 37 parts by weight, 38 parts by weight, 39 parts by weight, 40 parts by weight, 41 parts by weight, 42 parts by weight, 43 parts by weight, 44 parts by weight, 45 parts by weight, 46 parts by weight, 47 parts by weight, 48 parts by weight, 49 parts by weight, 50 parts by weight, 51 parts by weight, 52 parts by weight, 53 parts by weight, 54 parts by weight, 55 parts by weight, 56 parts by weight, 57 parts by weight, 58 parts by weight, 59 parts by weight, or 60 parts by weight, preferably in amounts of 10 to 50 parts by weight, 10 to 30 parts by weight, or 20 to 30 parts by weight. Within the specified range, the ratio between the hydrophilic bifunctional (meth)acrylate compound remaining in the adhesive without penetrating the COP membrane and the (meth)acrylate compound that has permeated the COP membrane can be adjusted to an appropriate level, thereby ensuring sufficient adhesion of the adhesive layer and thus facilitating the achievement of the desired effects of the present invention. Hydrophobic bifunctional (meth)acrylate compounds have very low polarity and therefore penetrate extensively into low-polarity polarizing protective films (especially COP films manufactured by solution casting and stretching to high elongation), thereby contributing to improved adhesion of the adhesive layer to the protective film. However, in this invention, the aforementioned bifunctional aliphatic epoxy compound and the following vinyl-containing (meth)acrylate compound are incorporated into the adhesive composition in specific amounts to ensure not only the adhesion of the adhesive layer to the COP film, but also good adhesion and improved reliability of the adhesive layer after long-term exposure to high temperature and high humidity conditions. Hydrophobic bifunctional (meth)acrylate compounds have two (meth)acrylate groups. Hydrophobic monofunctional (meth)acrylate compounds with one (meth)acrylate group, although exhibiting good permeability to polarizer protective films, especially COP films, may be less effective in improving peel strength due to their limited crosslinking degree. Hydrophobic bifunctional (meth)acrylate compounds have an alkyl group between the (meth)acrylate groups, said alkyl group having an unsubstituted alkyl chain containing nine or more carbon atoms. (meth)acrylate compounds having a straight-chain alkyl group containing fewer than nine carbon atoms have poor permeability to polarizer protective films, especially COP films, due to their high polarity, and are therefore less effective in improving the adhesion of adhesive layers. Hydrophobic bifunctional (meth)acrylate compounds may not have an ether functional group (epoxyalkyl group), such as ethylene oxide or propylene oxide. In one embodiment, the hydrophobic bifunctional (meth)acrylate compound has a straight-chain or branched alkyl group having 9 or more carbon atoms, such as 9, 10, 11, 12, 13, 14, or 15 carbon atoms, preferably an unsubstituted straight-chain alkyl group with 9 to 15 carbon atoms, and the hydrophobic bifunctional (meth)acrylate compound may include, for example, at least one of 1,9-nonanediol di(meth)acrylate or 1,10-decanediol di(meth)acrylate. Preferably, the hydrophobic bifunctional (meth)acrylate compound is 1,9-nonanediol di(meth)acrylate. The hydrophobic bifunctional (meth)acrylate compound may be present in amounts from 10 parts by weight to 40 parts by weight, for example, 10 parts by weight, 11 parts by weight, 12 parts by weight, 13 parts by weight, 14 parts by weight, 15 parts by weight, 16 parts by weight, 17 parts by weight, 18 parts by weight, 19 parts by weight, 20 parts by weight, 21 parts by weight, 22 parts by weight, 23 parts by weight, 24 parts by weight, 25 parts by weight, 26 parts by weight, 27 parts by weight, 28 parts by weight, 29 parts by weight, 30 parts by weight, 31 parts by weight, 32 parts by weight, 33 parts by weight, 34 parts by weight, 35 parts by weight, 36 parts by weight, 37 parts by weight, 38 parts by weight, 39 parts by weight, or 40 parts by weight, preferably 20 parts by weight to 30 parts by weight, relative to 100 parts by weight of the curable compound. Within the specified range, hydrophobic bifunctional (meth)acrylate compounds can fully penetrate the COP membrane and can fully bond to hydrophilic bifunctional (meth)acrylate compounds in the adhesive composition, thereby contributing to the improvement of the overall adhesion of the adhesive layer. The preferred ratio relative to 100 parts by weight of (meth)acrylate compound (B) is the sum of hydrophilic bifunctional (meth)acrylate compound, hydrophobic bifunctional (meth)acrylate compound, and vinyl-containing (meth)acrylate compound. The hydrophobic bifunctional (meth)acrylate compound can be from 30 parts by weight to 80 parts by weight, for example, 30 parts by weight, 31 parts by weight, 32 parts by weight, 33 parts by weight, 34 parts by weight, 35 parts by weight, 36 parts by weight, 37 parts by weight, 38 parts by weight, 39 parts by weight, 40 parts by weight, 41 parts by weight, 42 parts by weight, 43 parts by weight, 44 parts by weight, 45 parts by weight, 46 parts by weight, and 47 parts by weight. The product is present in parts by weight, 48 parts by weight, 49 parts by weight, 50 parts by weight, 51 parts by weight, 52 parts by weight, 53 parts by weight, 54 parts by weight, 55 parts by weight, 56 parts by weight, 57 parts by weight, 58 parts by weight, 59 parts by weight, 60 parts by weight, 61 parts by weight, 62 parts by weight, 63 parts by weight, 64 parts by weight, 65 parts by weight, 66 parts by weight, 67 parts by weight, 68 parts by weight, 69 parts by weight, 70 parts by weight, 71 parts by weight, 72 parts by weight, 73 parts by weight, 74 parts by weight, 75 parts by weight, 76 parts by weight, 77 parts by weight, 78 parts by weight, 79 parts by weight, or 80 parts by weight, preferably in amounts from 30 to 60 parts by weight or from 40 to 60 parts by weight. Within the specified range, the ratio between the (meth)acrylate compound permeating the COP membrane and the hydrophilic bifunctional (meth)acrylate compound remaining in the adhesive composition can be adjusted to an appropriate range to ensure sufficient peel strength and thus facilitate the achievement of the desired effects of the present invention. Vinyl-containing (meth)acrylate compounds possess both (meth)acrylate groups and vinyl groups. Therefore, vinyl-containing (meth)acrylate compounds form covalent bonds between the epoxy compound and the (meth)acrylate compound, simultaneously causing physical entanglement between them. This suppresses intermolecular movement even under high temperature and high humidity conditions, thus improving the adhesion of the adhesive layer after long-term exposure to these conditions. Furthermore, it improves the reliability of the polarizer by suppressing discoloration of the polarizer after prolonged exposure to high temperature and high humidity. The vinyl-containing (meth)acrylate compound may be present in an amount of 10 to 15 parts by weight relative to 100 parts by weight of the curable compound. If the content of the vinyl-containing (meth)acrylate compound is less than 10 parts by weight, it may be difficult to provide the desired effects of the present invention, such as improved adhesion of the adhesive layer and suppression of polarizer discoloration. If the content of the vinyl-containing (meth)acrylate compound exceeds 15 parts by weight, this may reduce the effect of the vinyl-containing (meth)acrylate in suppressing interfacial delamination between other components of the adhesive composition, and may reduce the bonding strength of the adhesive layer to the hydrophilic polarizer due to the increased hydrophobicity of the adhesive composition. The vinyl-containing (meth)acrylate compounds have both (meth)acrylate groups and vinyl groups. Therefore, the (meth)acrylate groups are bonded to both hydrophilic and hydrophobic bifunctional (meth)acrylate compounds, and the vinyl groups are bonded to mixtures of bifunctional alicyclic epoxy compounds and bifunctional alicyclic epoxy compounds, thereby facilitating the achievement of the desired effects of this invention. In one embodiment, the vinyl-containing (meth)acrylate compound may be a monofunctional (meth)acrylate compound containing a monofunctional vinyl group. The vinyl-containing (meth)acrylate compound differs from hydrophilic bifunctional (meth)acrylate compounds and hydrophobic bifunctional (meth)acrylate compounds. In one embodiment, the vinyl-containing (meth)acrylate compound may have an alkylene oxide group. The alkylene oxide group is present between the (meth)acrylate group and the vinyl group of the vinyl-containing (meth)acrylate compound to increase the compatibility of the vinyl-containing (meth)acrylate compound with the aforementioned bifunctional aliphatic epoxy compounds and hydrophobic bifunctional (meth)acrylate compounds. For example, the alkylene oxide group may be an ethylene oxide group or an propylene oxide group, preferably an ethylene oxide group. In one embodiment, the vinyl-containing (meth)acrylate compound may be a compound represented by Formula 1: CH 2=CH–(-O-CH 2CH 2-) n -O-(C=O)-CHR=CH 2 where R is hydrogen or methyl, and n is an integer from 1 to 5. For example, a vinyl-containing (meth)acrylate compound may be 2-(2-vinyloxyethoxy)ethyl (meth)acrylate or a similar compound. The preferred amount relative to 100 parts by weight of (meth)acrylate compound (B) is the sum of hydrophilic bifunctional (meth)acrylate compound, hydrophobic bifunctional (meth)acrylate compound, and vinyl-containing (meth)acrylate compound, wherein the vinyl-containing (meth)acrylate compound can be from 10 parts by weight to 40 parts by weight, for example 10 parts by weight, 11 parts by weight, 12 parts by weight, 13 parts by weight, 14 parts by weight, 15 parts by weight, 16 parts by weight. The amount present is in parts by weight, 17 parts by weight, 18 parts by weight, 19 parts by weight, 20 parts by weight, 21 parts by weight, 22 parts by weight, 23 parts by weight, 24 parts by weight, 25 parts by weight, 26 parts by weight, 27 parts by weight, 28 parts by weight, 29 parts by weight, 30 parts by weight, 31 parts by weight, 32 parts by weight, 33 parts by weight, 34 parts by weight, 35 parts by weight, 36 parts by weight, 37 parts by weight, 38 parts by weight, 39 parts by weight, or 40 parts by weight, preferably 20 parts by weight to 30 parts by weight. Within the range described, due to the copolymerization properties of the vinyl-containing (meth)acrylate compound, the epoxy resin curing zone and the acrylate curing zone can be connected to each other, thereby ensuring sufficient peel strength and improved durability of the adhesive layer. Photoinitiators include a mixture of radical photoinitiators and cationic photoinitiators. The photoinitiator may be present in an amount of 1 to 15 parts by weight, preferably 1 to 10 parts by weight, relative to 100 parts by weight of the curable compound. Within this range, incomplete curing of the adhesive composition can be prevented, while also preventing a decrease in the light transmittance of the adhesive layer due to excessive photoinitiator. Free radical photoinitiators may include cyclohexyl phenyl ketone photoinitiators and thioxanthone photoinitiators, etc. The free radical photoinitiator can be present in an amount of 0.5 to 10 parts by weight, for example, 1 to 6 parts by weight, relative to 100 parts by weight of the curable compound. Within this range, sufficient curing of the adhesive composition can be ensured, while preventing a decrease in the adhesiveness of the adhesive layer and the exudation of the free radical photoinitiator. Cationic photoinitiators may include onium salts formed by onium ions as cations and anions. Examples of onion ions may include: diaryliodonium, such as diphenyliodonium, 4-methoxydiphenyliodonium, bis(4-methylphenyl)iodonium, bis(4-tert-butylphenyl)iodonium, bis(dodecylphenyl)iodonium, and (4-methylphenyl)((4-(2-methylpropyl)phenyl)iodonium; triarylstromium, such as triphenylstromium, diphenyl-4-thiophenoxyphenylstromium, and diphenyl-4-(phenylthio)phenylstromium; bis[4-(diphenylstromium)-phenyl]sulfide; bis[4-(di(4-(2-hydroxyethyl)phenyl)stromium)-phenyl]sulfide; and 5-2,4-(cyclopentadienyl)[1,2,3,4,5,6-n]-(methylethyl)-phenyl]-iron(1+), etc. Examples of anions may include tetrafluoroborate (BF). 4 - ), hexafluorophosphate (PF6) 6 - ), hexafluoroantimonate (SbF) 6 - ), hexafluoroarsenate (AsF) 6 - ) and hexachloroantimonate (SbCl 6 - )wait. The cationic photoinitiator can be present in amounts from 0.5 to 10 parts by weight, for example, from 1 to 6 parts by weight, relative to 100 parts by weight of the curable compound. Within this range, sufficient curing of the adhesive composition can be ensured, while preventing a decrease in the adhesiveness of the adhesive layer and the exudation of free radical photoinitiators. Adhesive compositions can be prepared by mixing a curable compound with a photoinitiator. Adhesive compositions can be solvent-free, or may include a solvent to increase applicability (coatability). The adhesive composition may also include typical additives, such as antioxidants, ultraviolet (UV) absorbers, ionic conductors, conductivity imparters (e.g., conductive metal oxide particles), light diffusing imparters, and viscosity modifiers, without altering the desired effects of the invention. The polarizing plate according to the invention comprises an adhesive layer formed from an adhesive composition for polarizing plates according to the invention. The polarizing plate includes a polarizer and a protective film formed on one surface of the polarizer, wherein the polarizer is bonded to the protective film via the adhesive layer, and the adhesive layer comprises a cured product of the adhesive composition according to the invention. Referring to FIG1, the polarizing plate may include: a polarizing film 10; an adhesive layer 20 and a lower polarizing film protective film 30, which are sequentially formed on one surface of the polarizing film 10; and an upper polarizing film protective layer 40, which is formed on the other surface of the polarizing film 10. polarizer Polarizer 10 is used to polarize external or internal light. The polarizer 10 may include a polyvinyl alcohol (PVA) polarizer obtained by dyeing a PVA film with iodine or a similar substance. For example, a PVA polarizer is manufactured by dyeing a PVA film with iodine or a dichroic dye and then stretching it in a specific direction. Specifically, the polarizer is manufactured through a swelling step, a dyeing step, and a stretching step. Methods for performing each step are well known in the art. The polarizer 10 may have a thickness from 1 μm to 50 μm. Within this range, the polarizer 10 can be used in optical display devices. Adhesive layer The adhesive layer 20 can be formed directly on the polarizer and the lower polarizer protective film to bond the polarizer to the lower polarizer protective film. The adhesive layer 20 can be formed from the aforementioned adhesive composition. Specifically, the adhesive layer 20 can be formed by coating the adhesive composition onto a surface of the polarizer or the lower polarizer protective film to a predetermined thickness, followed by photocuring the adhesive composition. Here, photocuring refers to a process of curing the composition by irradiation with UV light, wherein the energy density and wavelength of the UV light used can be adjusted according to the coating thickness of the adhesive composition. The adhesive layer 20 can have a thickness of 0.01 μm to 10 μm, preferably 1 μm to 5 μm. Within this range, the adhesive layer 20 ensures adhesion between the polarizer and the polarizer protective film. Lower polarizer protective film A lower polarizer protective film can be formed on the lower surface of the polarizer (the surface of the polarizer through which internal light enters the polarizer) to provide additional properties to the polarizer plate. The lower polarizer protective film can be any typical polarizer protective film known in the art, such as the polarizer protective film described below regarding the upper polarizer protective layer. In this invention, a COP film manufactured by solution casting and stretching to high elongation as a non-adhesive protective film can be used as the lower polarizer protective film. Advantageously, this COP film, manufactured by solution casting and stretching to high elongation, can easily adjust the phase delay required for vertically oriented (VA) LCD panels when used in polarizers. Upper polarizer protective layer An upper polarizer protective layer 40 may be formed on the upper surface of the polarizer (the surface through which internal light exits the polarizer) to support the polarizer. The upper polarizer protective layer may include at least one of an optically transparent protective film or an optically transparent protective coating. When the upper polarizer protective layer is a protective film, the upper polarizer protective layer may include a protective film formed of an optically transparent resin. The protective film can be formed by melt extrusion of the resin. If desired, the resin may be further subjected to a stretching process. The resin may include at least one of the following: cellulose ester resin (e.g., cellulose triacetate (TAC)), cyclic polyolefin resin (e.g., cyclic olefin polymer (COP)), polycarbonate resin, polyester resin (e.g., polyethylene terephthalate (PET)), polyether resin, polyurethane resin, polyamide resin, polyimide resin, acyclic polyolefin resin, poly(meth)acrylate resin (e.g., poly(methyl methacrylate)), polyvinyl alcohol resin, polyvinyl chloride resin, or polyvinylidene chloride resin. Preferably, the protective film may be a film formed of a cyclic polyolefin resin (e.g., cyclic olefin polymer (COP)). When the upper polarizer protective layer is a protective coating, it can exhibit good properties in terms of polarizer adhesion, transparency, mechanical strength, thermal stability, moisture barrier capability, and durability. In one embodiment, the protective coating may be formed from a photochemical radiation-curable resin composition comprising a photochemical radiation-curable compound and a polymerization initiator. Actinic radiation-curable compounds may include at least one of cationic polymerizable curable compounds, radical polymerizable curable compounds, urethane resins, or silicone resins. Cationic polymerizable curable compounds may be epoxy compounds having at least one epoxy group or oxetane compounds having at least one oxetane ring. Radical polymerizable curable compounds may be (meth)acrylic acid compounds having at least one (meth)acrylic acid group. The upper polarizer protective layer 40 may have a thickness of 5 μm to 200 μm, specifically 30 μm to 120 μm, more specifically 50 μm to 100 μm (in the case of a protective film) or 5 μm to 50 μm (in the case of a protective coating). Within this range, the upper polarizer protective layer 40 can be used in light-emitting diode display devices. Although not shown in Figure 1, the polarizer may also include a functional coating formed on the upper surface of the upper polarizer protective layer 40, wherein the functional coating may include a hard coating, an anti-fingerprint layer, and an anti-reflective layer, etc. Although not shown in Figure 1, when the upper polarizer protective layer 40 is a protective film, the polarizer may also include an adhesive layer sandwiched between the upper polarizer protective layer and the polarizer. This adhesive layer may be formed from typical adhesives used for polarizers (e.g., water-based adhesives, photocurable adhesives, or pressure-sensitive adhesives). Although not shown in Figure 1, the polarizing plate may also include a polarizer protective film, an anti-reflective film, and a delay film (liquid crystal layer or non-liquid crystal layer) commonly used in polarizing plates. An optical display device according to one embodiment of the present invention includes a polarizing plate according to the present invention. For example, the optical display device may be a light-emitting diode display device or a liquid crystal display device, etc. The invention will now be described in more detail with reference to some examples. However, it should be noted that these examples are provided for illustrative purposes only and should not be construed as limiting the invention in any way. Example 1 ( 1 Preparation of photocurable adhesive composition for polarizing plates As epoxy compounds, 20 parts by weight of a difunctional alicyclic epoxy compound (2021P, Daicel Corporation) and 20 parts by weight of a difunctional alicyclic epoxy compound (1,4-butanediol diglycidyl ether, Kukdo Chemical Co., Ltd.) were used. As (meth)acrylate compounds, 15 parts by weight of dipropylene glycol diacrylate (M222, Miwon Chemical Co., Ltd.) and 30 parts by weight of 1,9-nonanediol diacrylate (NDDA, Kyoeisha Chemical Co., Ltd.) and 15 parts by weight of 2-(2-vinyloxyethoxy)ethyl acrylate (VEEA, Nippon Catalyst Co., Ltd.) were used. After mixing an epoxy compound with a (meth)acrylate compound, 1 part by weight of a cationic photoinitiator (1-hydroxycyclohexylphenyl ketone, Irgacure 184, BASF Corporation) and 6 parts by weight of a photoacid generator (CPI-100P, San-Apro Ltd.) are added to the mixture and mixed together to prepare a solvent-free photocurable adhesive composition for polarizing plates. ( 2 Manufacturing of polarizing plates A polyvinyl alcohol film (saponification degree: 99.5%, thickness: 60 μm PS # 60, Kuraray Co., Ltd.) was immersed in a 0.3% iodine aqueous solution for dyeing, and then the polyvinyl alcohol film was uniaxially stretched to 6 times its original length in the machine direction (MD). The stretched polyvinyl alcohol film was immersed in a 3% boric acid solution and a 2% potassium iodide aqueous solution for color correction, and then dried at 50°C for 4 minutes to produce a polarizer (light transmittance: 45%, thickness: 7 μm). As the upper polarizer protective film, a polyethylene terephthalate (PET) film (thickness: 80 μm, uniaxially stretched in the transverse direction (TD), Toyobo Co., Ltd.) is used, wherein the surface of the PET film coated with the adhesive composition is treated with an undercoat. As the lower polarizer protective film, a cyclic olefin polymer (COP) film (manufactured by solution casting and stretching to high elongation, thickness: 37 μm, Konica Minolta, Inc.) is used, wherein the surface of the COP film coated with the adhesive composition is treated with a dose of 100 using corona discharge. The prepared photocurable adhesive composition is coated to a predetermined thickness on each of the undercoat-treated surface of the upper polarizer protective film and the corona-treated surface of the lower polarizer protective film. The manufactured polarizer is then bonded to each of the upper and lower polarizer protective films, and then subjected to a metal halide lamp at 400 mW / cm². 2 and 1000 mJ / cm 2 Under certain conditions, the adhesive composition is cured by irradiating it with UV light from the direction of the lower polarizer protective film, thereby manufacturing a polarizing plate in which the upper polarizer protective film, adhesive layer, polarizer, adhesive layer, and lower polarizer protective film are stacked in that order. The polarizing plate is manufactured at a temperature of 22°C to 25°C and at 20% RH to 60% RH. Example 2 To instance 9 In the preparation of the solvent-free, photocurable adhesive composition for polarizing plates, the polarizing plates were manufactured in the same manner as in Example 1, except that the content and / or type of each component were varied as shown in Table 1. In Table 1, "-" indicates that the corresponding component was not used. Comparative example 1 To the comparative example 8 In the preparation of the solvent-free, photocurable adhesive composition for polarizing plates, the polarizing plates are manufactured in the same manner as in Example 1, except that the content and / or type of each component are varied as shown in Table 1. The properties of each of the polarizing plates prepared in Examples 1 to 9 and Comparative Examples 1 to 8, as shown in Table 2, were evaluated. The results are shown in Table 2. (1) Adhesion at room temperature (initial adhesion) (unit: gf / 25 mm): Double-sided foam adhesive tape (VHS, 3M) was applied to the lower polarizer protective film of each of the polarizers manufactured in Examples 1 to 9 and Comparative Examples 1 to 8. The polarizers were then cut into 25 mm × 150 mm (MD × TD) sizes, and the release film of the double-sided foam adhesive tape was removed. The polarizers were then applied to an alkali-free glass plate (thickness: 0.5 t) and placed indoors for 30 minutes to prepare the sample. Next, a cutting blade is inserted between the polarizer and the lower polarizer protective film of the sample to create a small gap therebetween. The sample is then mounted on a texture analyzer (TA Instruments Inc.) and subsequently on an upper load cell, with the polarizer clamped in a 90-degree fixture and the lower polarizer protective film clamped in another fixture. The peel strength is measured while peeling the polarizer from the lower polarizer protective film under conditions of a peel angle of 90°, a peel rate of 300 mm / min, and a temperature of 25°C. This process is repeated three times, and the average peel strength is then calculated. (2) Adhesion after exposure to high temperature and high humidity: Samples were prepared in the same manner as in (1). The samples were then placed in a chamber at 60°C and 95% RH for 2 days, after which the samples were removed from the chamber and left at room temperature for 30 minutes. The peel strength was then measured three times in the same manner as in (1), and the average peel strength was calculated. (3) Discoloration after exposure to high temperature and high humidity: Each of the polarizing plates prepared in Examples 1 to 9 and Comparative Examples 1 to 8 was cut into a 50 mm × 50 mm square, wherein the absorption axis of the polarizer was tilted at an angle of 45°, and then bonded to a glass plate by an acrylic adhesive layer. The samples were then placed in a chamber at 60°C and 95% RH for 500 hours. After the samples were removed from the chamber, the length (5) of the iodine color disappearance in sample (1) was measured diagonally from the four corners of the sample, as shown in Figure 2, and then evaluated according to the following criteria: ◎: less than 1 mm; ○: 1 mm to less than 2 mm; △: 2 mm to less than 3 mm; ×: 3 mm or greater than 3 mm. Table 1 A) 2021P: Alicyclic epoxy resin (Daicel Corporation) B) DE200: 1,4-Butanediol diglycidyl ether (Kokto Chemical Co., Ltd.) C) DE202: 1,6-Hexanediol diglycidyl ether (Kokto Chemical Co., Ltd.) D) EX821: Polyethylene glycol diglycidyl ether (Nagase Chemtex Corporation) E) EX920: Polypropylene glycol diglycidyl ether (Nagase Chemtex Corporation) F) YD128: Bisphenol A diglycidyl ether (Kokto Chemical Co., Ltd.) G) M222: Dipropylene glycol diacrylate (Migen Chemical Co., Ltd.) H) NDDA: 1,9-Nonanediol diacrylate (Kyoeisha Chemical Co., Ltd.) I) VEEA: 2-(2-Vinyloxyethoxy)ethyl acrylate (Nippon Catalyst Co., Ltd.) J) M232: Triethylene glycol diacrylate (Migen Chemical Co., Ltd.) K) M200: 1,6-Hexanediol diacrylate (Meiyuan Chemical Co., Ltd.) L) M120: Lauryl acrylate (Meiyuan Chemical Co., Ltd.) Table 2 As can be seen from the table, the adhesive composition for polarizing plates according to the present invention can provide the following adhesive layer: the adhesive layer ensures good adhesion between the polarizing film and the COP film manufactured by solution casting and stretching to high elongation, has good adhesion after exposure to high temperature and high humidity conditions, and improves the reliability of the polarizing plate by preventing the polarizing film from discoloring after exposure to high temperature and high humidity conditions. Conversely, the adhesive compositions of Comparative Examples 1 to 8, which do not meet the requirements of the present invention, cannot provide all the desired effects of the present invention. It should be understood that various modifications, alterations, changes, and equivalent embodiments can be made by those skilled in the art without departing from the spirit and scope of the invention. 1: Sample 5: Length 10: Polarizing film 20: Adhesive layer 30: Lower polarizing film protective film 40: Upper polarizing film protective layer Figure 1 is a cross-sectional view of a polarizing plate according to an embodiment of the present invention. Figure 2 is a schematic diagram illustrating a method for evaluating the discoloration (disappearance of iodine color) of a polarizing plate. 10: Polarizing film 20: Adhesive layer 30: Lower polarizer protective film 40: Upper polarizer protective layer

Claims

1. An adhesive composition for a polarizing plate, comprising: a curable compound; and a photoinitiator, wherein the curable compound comprises an epoxy compound and a (meth)acrylate compound, the epoxy compound comprising a mixture of bifunctional alicyclic epoxy compounds and bifunctional alicyclic epoxy compounds, the (meth)acrylate compound comprising a mixture of hydrophilic bifunctional (meth)acrylate compounds, hydrophobic bifunctional (meth)acrylate compounds and vinyl-containing (meth)acrylate compounds, wherein the hydrophobic bifunctional (meth)acrylate compound is a bifunctional (meth)acrylate compound having a straight-chain extended alkyl chain containing 9 or more carbon atoms, and wherein the vinyl-containing (meth)acrylate compound is present in an amount of 10 to 15 parts by weight relative to 100 parts by weight of the curable compound, wherein the vinyl-containing (meth)acrylate compound is a compound represented by Formula 1: CH2=CH–(-O-CH2CH2-)nO-(C=O)-CHR=CH2 Where R is hydrogen or methyl, and n is an integer from 1 to 5.

2. The adhesive composition as claimed in claim 1, wherein the hydrophobic bifunctional (meth)acrylate compound is present in an amount of 50 to 300 parts by weight relative to 100 parts by weight of the bifunctional aliphatic epoxy compound.

3. The adhesive composition as claimed in claim 1, wherein the bifunctional aliphatic epoxy compound comprises at least one of a diglycidyl ether compound having a straight-chain extended alkyl chain containing 4 or more carbon atoms, and a diglycidyl ether compound having 2 moles or more of ethylene oxide or propylene oxide.

4. The adhesive composition as claimed in claim 1, wherein the bifunctional aliphatic epoxy compound is present in an amount of 10 to 40 parts by weight relative to 100 parts by weight of the curable compound.

5. The adhesive composition as claimed in claim 1, wherein the hydrophobic bifunctional (meth)acrylate compound is present in an amount of 10 to 40 parts by weight relative to 100 parts by weight of the curable compound.

6. The adhesive composition as claimed in claim 1, wherein the hydrophilic bifunctional (meth)acrylate compound is a bifunctional (meth)acrylate compound having an epoxy alkyl group between two (meth)acrylate groups.

7. The adhesive composition as claimed in claim 1, wherein the hydrophilic bifunctional (meth)acrylate compound is present in an amount of 5 to 20 parts by weight relative to 100 parts by weight of the curable compound.

8. The adhesive composition as claimed in claim 1, wherein the epoxy compound is present in an amount of 30 to 70 parts by weight relative to 100 parts by weight of the curable compound.

9. The adhesive composition as claimed in claim 1, wherein the difunctional alicyclic epoxy compound and the total amount of the difunctional alicyclic epoxy compound are present in an amount of 95 parts by weight or greater than 95 parts by weight relative to 100 parts by weight of the epoxy compound.

10. The adhesive composition as claimed in claim 1, wherein the vinyl-containing (meth)acrylate compound, the hydrophilic bifunctional (meth)acrylate compound, and the hydrophobic bifunctional (meth)acrylate compound are present in an amount of 95 parts by weight or greater than 95 parts by weight relative to 100 parts by weight of the (meth)acrylate compound.

11. The adhesive composition as claimed in claim 1, wherein the epoxy compound and the (meth)acrylate compound are present in an amount of 95 parts by weight or more relative to 100 parts by weight of the curable compound.

12. The adhesive composition as claimed in claim 1, wherein the curable compound is present in the adhesive composition in an amount of 90% by weight or greater than 90% by weight, based on solids content.

13. A polarizing plate, comprising: Polarizing film; A protective film is formed on the lower surface of the polarizer, wherein the polarizer is bonded to the protective film by an adhesive layer, and the adhesive layer comprises a cured product of an adhesive composition for a polarizer as described in any one of claims 1 to 12.

14. An optical display device comprising a polarizing plate as described in claim 13.

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