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

Abstract

Disclosed herein are an adhesive composition for a polarizing plate, a polarizing plate, and an optical display device. The adhesive composition for a polarizing plate includes a curable compound including an epoxy compound and a (meth) acrylate compound, the epoxy compound including a mixture of a bifunctional alicyclic epoxy compound and a bifunctional aliphatic epoxy compound, and a photoinitiator. The (methyl) acrylate compound comprises a mixture of a hydrophilic bifunctional (methyl) acrylate compound, a hydrophobic bifunctional (methyl) acrylate compound and a vinyl-containing (methyl) acrylate compound; wherein the hydrophobic bifunctional (meth) acrylate compound is a bifunctional (meth) acrylate compound having a linear alkylene chain having 9 or more carbon atoms, and wherein the vinyl group-containing (meth) acrylate compound is present in an amount of 10 parts by weight to 15 parts by weight with respect to 100 parts by weight of the curable compound.

Description

[0001] Cross - reference to related applications

[0002] This application claims the priority and benefits of Korean Patent Application No. 10 - 2024 - 0002026, filed with the Korean Intellectual Property Office on January 5, 2024, the entire disclosure of which is incorporated herein by reference. Technical field

[0003] The present invention relates to an adhesive composition for a polarizing plate, a polarizing plate, and an optical display device. Background art

[0004] A polarizing plate includes a polarizer and polarizer protective films formed on two surfaces of the polarizer. The polarizer protective film may be an optically clear protective film, such as a triacetylcellulose (TAC) film, a polyethylene terephthalate (PET) film, an acrylic film, a polycarbonate film, and a cyclic olefin polymer (COP) film, or may be a protective layer formed of a curable resin (such as an epoxy resin and an acrylate). The TAC film is a high - moisture - permeability protective film, and thus it is easy to bond using a water - based adhesive due to the moisture permeability of the TAC film. However, the TAC film is limited in its ability to improve the reliability of the polarizing plate. The bonding of polarizer protective films other than the TAC film requires a solvent - free photocurable adhesive because these protective films make it impossible to remove moisture in the adhesive.

[0005] For example, PET, COP, or acrylic films are protective films with low moisture permeability, and a photocurable adhesive needs to be used for the bonding of the protective films. Among them, a COP film (e.g., a COP film manufactured by Konica Minolta of Japan) manufactured by solution casting and stretching to a high elongation rate is preferably used as a polarizer protective film because the COP film can easily adjust the phase retardation required for a vertical alignment (VA) liquid crystal display (LCD) panel. However, it is difficult to bond a COP film using a typical photocurable adhesive.

[0006] The background art of the present invention is disclosed in Japanese Patent Laid - Open No. 2014 - 032270. Summary of the invention

[0007] An object of the present invention is to provide an adhesive composition for a polarizing plate, the adhesive composition providing an adhesive layer capable of: ensuring good adhesiveness between a polarizing film and a cyclic olefin polymer (COP) film produced by solution casting and stretching to a high elongation rate; and having good adhesiveness after being exposed to high temperature and high humidity conditions.

[0008] Another object of the present invention is to provide an adhesive composition for a polarizing plate, the adhesive composition providing an adhesive layer capable of improving the reliability of a polarizing plate by preventing discoloration of a polarizing film after being exposed to high temperature and high humidity conditions.

[0009] One aspect of the present invention relates to an adhesive composition for a polarizing plate.

[0010] The adhesive composition for a polarizing plate 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 includes a mixture of a bifunctional cycloaliphatic epoxy compound and a bifunctional aliphatic epoxy compound, the (meth)acrylate compound includes a mixture of a hydrophilic bifunctional (meth)acrylate compound, a hydrophobic bifunctional (meth)acrylate compound, and a vinyl-containing (meth)acrylate compound, the hydrophobic bifunctional (meth)acrylate compound is a bifunctional (meth)acrylate compound having a linear alkylene 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 based on 100 parts by weight of the curable compound.

[0011] Another aspect of the present invention relates to a polarizing plate.

[0012] 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 adhered to the protective film through an adhesive layer, and the adhesive layer contains a cured product of the adhesive composition for a polarizing plate according to the present invention.

[0013] Still another aspect of the present invention relates to an optical display device.

[0014] The optical display device includes the polarizing plate according to the present invention.

[0015] 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 a polarizing film and a COP film produced by solution casting and stretching to a high elongation rate; and have good adhesion after being exposed to high temperature and high humidity conditions.

[0016] Embodiments of the present invention 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 the polarizing film from discoloring after being exposed to high temperature and high humidity conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a cross-sectional view of a polarizing plate according to an example of the present invention.

[0018] Figure 2 is a schematic diagram showing a method for evaluating the discoloration (disappearance of iodine color) of a polarizing film. DETAILED DESCRIPTION

[0019] Exemplary embodiments of the present invention will be described in detail with reference to the drawings so as to be practiced by those of ordinary skill in the art to which the present invention pertains. It should be understood that the present invention can be implemented in different ways and is not limited to the following embodiments. In the drawings, parts not relevant to the description are not described in detail for clarity. Throughout the specification, the same components will be denoted by the same reference numerals. The lengths, sizes, and similar elements of the components in the drawings are for the purpose of illustrating the present invention, and the present invention is not limited thereto.

[0020] In this document, spatial relative terms such as "upper" and "lower" are defined with reference to the drawings. Therefore, it should be understood that the term "upper surface" can be used interchangeably with the term "lower surface".

[0021] The terms used herein are for the purpose of describing exemplary embodiments and are not intended to limit the present invention. Unless the context clearly indicates otherwise, the singular forms "a" and "an" and "the" used herein are also intended to include the plural forms.

[0022] The adhesive composition for a polarizing plate according to the present invention is used to bond a polarizing film to a polarizing film protective film.

[0023] The adhesive composition for a polarizing plate provides an adhesive layer that can ensure good adhesiveness between the polarizing film and the polarizing film protective film, can have good adhesiveness after long-term exposure to high temperature and high humidity conditions, and can improve the reliability of the polarizing plate by preventing the polarizing film from discoloring after long-term exposure to high temperature and high humidity conditions. Specifically, the adhesive composition for a polarizing plate provides an adhesive layer that can ensure good adhesiveness (initial adhesiveness) between the polarizing film and a COP film manufactured by solution casting and stretching to a high elongation rate, can have good adhesiveness after long-term exposure to high temperature and high humidity conditions, and can improve the reliability of the polarizing plate by preventing the polarizing film from discoloring after long-term exposure to high temperature and high humidity conditions.

[0024] In one embodiment, in the stack of polarizing film / adhesive layer / polarizing film protective film (e.g., a COP film manufactured by solution casting and stretching to a high elongation rate), the adhesive strength (initial adhesive strength) between the polarizing film and the polarizing film protective film can be 130 gf / 25 mm or greater than 130 gf / 25 mm (e.g., 130 gf / 25 mm to 500 gf / 25 mm). Within this range, the polarizing plate can have good reliability and durability.

[0025] In one embodiment, after placing the stack of polarizing film / adhesive layer / polarizing film protective film (e.g., a COP film manufactured by solution casting and stretching to a high elongation rate) at 60 °C and 95% relative humidity (RH) for 2 days, the adhesive strength between the polarizing film and the polarizing film protective film can be 150 gf / 25 mm or greater than 150 gf / 25 mm (e.g., 150 gf / 25 mm to 500 gf / 25 mm). Within this range, the polarizing plate can have good reliability and durability.

[0026] In one embodiment, after placing the polarizing film / adhesive layer / polarizing film protective film (e.g., a COP film manufactured by solution casting and stretching to a high elongation rate) at 60 °C and 95% RH for 500 hours, the length of iodine color disappearance can be less than 1 mm (e.g., 0 mm to less than 1 mm). Within this range, the polarizing plate can have good reliability and durability.

[0027] In one embodiment, the polarizing film protective film for measuring the peel strength can be a COP film manufactured by solution casting and stretching to a high elongation rate.

[0028] The adhesive composition for a polarizing plate contains 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 a bifunctional alicyclic epoxy compound and a bifunctional aliphatic epoxy compound; the (meth)acrylate compound (B) includes a mixture of a hydrophilic bifunctional (meth)acrylate compound, a hydrophobic bifunctional (meth)acrylate compound, and a vinyl-containing (meth)acrylate compound; the hydrophobic bifunctional (meth)acrylate compound is a bifunctional (meth)acrylate compound having a linear alkylene chain containing 9 or more carbon atoms; and the vinyl-containing (meth)acrylate compound is present in an amount of 10 parts by weight to 15 parts by weight based on 100 parts by weight of the curable compound.

[0029] According to the present invention, a bifunctional aliphatic epoxy compound and a hydrophobic bifunctional (meth)acrylate compound having a linear alkylene chain containing 9 or more carbon atoms are further incorporated into the adhesive composition, which contains the curable compounds as described above, i.e., a bifunctional alicyclic epoxy compound, a hydrophilic bifunctional (meth)acrylate compound, and a 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, i.e., a range of 10 parts by weight to 15 parts by weight based on 100 parts by weight of the curable compound. Therefore, the adhesive composition according to the present invention can improve both the initial adhesiveness between the polarizing plate and the polarizing plate protective film (especially a COP film manufactured by solution casting and stretching to a high elongation rate) and the adhesiveness between the polarizing plate and the polarizing plate protective film after long-term exposure to high temperature and high humidity conditions, and at the same time improve the reliability of the polarizing plate by suppressing the discoloration of the polarizing plate after long-term exposure to high temperature and high humidity conditions.

[0030] The curable compound is a photocurable compound, so that the adhesive composition is a photocurable adhesive composition for a polarizing plate.

[0031] In one embodiment, based on the solid content, the curable compound may be present in the adhesive composition in an amount of 90% by weight or more than 90% by weight, such as 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, such as in a range of 90% by weight to 100% by weight or 93% by weight to 100% by weight.

[0032] In one embodiment, relative to 100 parts by weight of the curable compound, the total amount of the epoxy compound (A) and the (meth)acrylate compound (B) can be 95 parts by weight or more than 95 parts by weight, such as 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 in an amount of 99 parts by weight to 100 parts by weight, more preferably 100 parts by weight. Within this range, the adhesive composition can easily provide the desired effects of the present invention.

[0033] Epoxy compound

[0034] Relative to 100 parts by weight of the curable compound, the epoxy compound (A) can be present in an amount of 30 parts by weight to 70 parts by weight. Within this range, insufficient adhesion of the adhesive layer to the polarizing plate can be prevented by enhancing the bond between the adhesive layer and the hydroxyl groups in the polarizing plate, while deterioration of the discoloration inhibition property due to a decrease in the overall glass transition temperature of the adhesive layer and insufficient bonding between the adhesive layer and the polarizing plate can be prevented. Preferably, relative to 100 parts by weight of the curable compound, the epoxy compound (A) is present in an amount of 40 parts by weight to 60 parts by weight.

[0035] The epoxy compound (A) includes a bifunctional alicyclic epoxy compound and a bifunctional aliphatic epoxy compound.

[0036] In one embodiment, relative to 100 parts by weight of the epoxy compound (A), the total amount of the bifunctional alicyclic epoxy compound and the bifunctional aliphatic epoxy compound can be 95 parts by weight or more than 95 parts by weight, such as 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 in an amount of 99 parts by weight to 100 parts by weight, more preferably 100 parts by weight. Within this range, the epoxy compound can be conducive to achieving the desired effects of the present invention.

[0037] The bifunctional alicyclic epoxy compound has a relatively high initial reaction rate, and thus can have a favorable effect on the dimensional stability of the polarizing plate due to its high glass transition temperature. In addition, the bifunctional alicyclic epoxy compound can improve the peel strength of the polarizing plate relative to the protective film by bonding to the hydroxyl groups in the polarizing plate.

[0038] A bifunctional alicyclic epoxy compound may refer to a compound having two epoxy alicyclic groups. For example, the bifunctional alicyclic epoxy compound may include at least one of 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate, 3,4-epoxy-6-methylcyclohexylmethyl-3',4'-epoxy-6'-methylcyclohexanecarboxylate, bis(3,4-epoxy-6-methylcyclohexyl) adipate, dicyclohexyl diepoxide (3,4,3',4'-diepoxy-biscyclohexane), or 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate-modified ε-caprolactone, without limitation thereto.

[0039] Relative to 100 parts by weight of the curable compound, the bifunctional alicyclic epoxy compound may be present in an amount of 10 to 40 parts by weight, such as 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 15 to 30 parts by weight or 20 to 30 parts by weight. Within this range, the bifunctional alicyclic epoxy compound can stabilize the structure of the adhesive layer due to its relatively high polymerization rate, thus ensuring a stable reaction while preventing delamination between the films.

[0040] Relative to 100 parts by weight of the epoxy compound (A), the bifunctional alicyclic epoxy compound may be present in an amount of 20 to 60 parts by weight, such as 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, 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 to 60 parts by weight. Within this range, the bifunctional alicyclic epoxy compound can facilitate achieving the desired effects of the present invention.

[0041] Compared with bifunctional alicyclic epoxides, bifunctional aliphatic epoxides have a relatively low reaction rate. Bifunctional alicyclic epoxides do not cause a delay in the growth reaction of epoxides during cationic polymerization. In contrast, due to the proton-trapping nature in the epoxides, bifunctional aliphatic epoxides cause a delay in the growth reaction of epoxides during cationic polymerization. In the present invention, based on the growth-retarding effect of bifunctional aliphatic epoxides, before the fluidity of the hydrophobic bifunctional (meth)acrylate compound disappears, sufficient time is provided for the hydrophobic bifunctional (meth)acrylate compound to penetrate the COP film, and then post-curing is carried out to impart good adhesiveness and reliability to the adhesive layer, thereby curing a non-adhesive polarizer protective film, especially a COP film manufactured by solution casting and stretching to a high elongation rate, together with the following hydrophobic bifunctional (meth)acrylate compound.

[0042] In one embodiment, relative to 100 parts by weight of the bifunctional aliphatic epoxide, the hydrophobic bifunctional (meth)acrylate compound may be present in an amount of 50 to 300 parts by weight, such as 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, 200, 205, 210, 215, 220, 225, 230, 235, 240, 245, 250, 255, 260, 265, 270, 275, 280, 285, 290, 295 or 300 parts by weight, preferably in an amount of 50 to 200 parts by weight or 60 to 150 parts by weight. Within the said range, due to the interaction between the bifunctional aliphatic epoxide and the hydrophobic bifunctional (meth)acrylate compound, the adhesive layer can have good adhesiveness to the COP film manufactured by solution casting and stretching to a high elongation rate.

[0043] In addition, by enabling the cationic protonated epoxy ring of the bifunctional alicyclic epoxide to be structurally held by the non-covalent electron pair of the ether group in the epoxy chain of the bifunctional aliphatic epoxide to limit the polymerization of the epoxy ring, the bifunctional aliphatic epoxide can ensure the structural stability of the adhesive layer.

[0044] An adhesive composition containing an aromatic epoxide instead of a bifunctional aliphatic epoxide is not suitable for improving the peel strength because the aromatic epoxide has a short carbon chain that makes it difficult to capture protons in the adhesive composition.

[0045] The bifunctional aliphatic epoxide may include at least one of a diglycidyl ether compound having a straight-chain alkylene chain containing 4 or more carbon atoms and a diglycidyl ether compound having 2 moles or more than 2 moles of ethylene oxide or propylene oxide therein. These bifunctional aliphatic epoxides may be useful in ensuring that the adhesive composition according to the present invention provides the desired effects described herein.

[0046] The diglycidyl ether compound having a straight-chain alkylene chain containing 4 or more carbon atoms may contribute to providing the desired effects of the present invention because the straight-chain alkylene chain containing 4 or more carbon atoms provides the above-described reaction delay effect.

[0047] The diglycidyl ether compound having a straight-chain alkylene chain containing 4 or more carbon atoms may have a straight-chain or branched-chain alkylene chain containing 4 or more, preferably 4 to 10, more preferably 4 to 6 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 is a diglycidyl ether compound having an unsubstituted straight-chain C4 to C6 alkylene chain, such as at least one of 1,4-butanediol diglycidyl ether or 1,6-hexanediol diglycidyl ether.

[0048] Since 2 moles or more than 2 moles of ethylene oxide or propylene oxide therein provide the above-described reaction delay effect, the diglycidyl ether compound having 2 moles or more than 2 moles of ethylene oxide or propylene oxide therein may contribute to providing the desired effects of the present invention.

[0049] The diglycidyl ether compound having 2 moles or more than 2 moles of ethylene oxide or propylene oxide may be a diglycidyl ether compound having 2 moles 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.

[0050] Relative to 100 parts by weight of the curable compound, the bifunctional aliphatic epoxy compound may be present in an amount of 10 parts by weight to 40 parts by weight, such as 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 in an amount of 15 parts by weight to 30 parts by weight or 20 parts by weight to 30 parts by weight. Within this range, the bifunctional aliphatic epoxy compound can provide sufficient time for the hydrophobic bifunctional (meth)acrylate compound to penetrate the COP film, can prevent insufficient peel strength by ensuring enhanced bonding between the adhesive layer and the hydroxyl groups in the polarizer, and can ultimately be used to cure the adhesive composition to connect medium-sized polymers to form macromolecular polymers, because the curing rate of the bifunctional aliphatic epoxy compound is relatively low compared to the alicyclic epoxy compound, thus ensuring good durability of the final product.

[0051] Based on 100 parts by weight of the epoxy compound (A), the difunctional aliphatic epoxy compound may be present in an amount of 40 to 80 parts by weight, such as 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, 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 an amount of 40 to 60 parts by weight. Within the said range, the difunctional aliphatic epoxy compound can be conducive to achieving the desired effects of the present invention.

[0052] In one embodiment, in the composition, based on 100 parts by weight of the curable compound, at least one of the aromatic group-containing epoxy compound or the hydrogenated aromatic group-containing epoxy compound may be present in an amount of less than 5 parts by weight, such as from 0 to less than 5 parts by weight or 0 parts by weight.

[0053] (Meth)acrylate compound

[0054] Based on 100 parts by weight of the curable compound, the (meth)acrylate compound (B) may be present in an amount of 30 to 70 parts by weight, such as 40 to 60 parts by weight. Within the said range, the (meth)acrylate compound can be conducive to achieving the desired effects of the present invention.

[0055] (Meth)acrylate compound (B) comprises a mixture of a hydrophilic difunctional (meth)acrylate compound, a hydrophobic difunctional (meth)acrylate compound and a vinyl-containing (meth)acrylate compound.

[0056] 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 difunctional (meth)acrylate compound, and the hydrophobic difunctional (meth)acrylate compound may be 95 parts by weight or more than 95 parts by weight, such as 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 in an amount of 99 parts by weight to 100 parts by weight, and more preferably 100 parts by weight. Within this range, the (meth)acrylate compound can facilitate achieving the desired effects of the present invention.

[0057] The hydrophilic difunctional (meth)acrylate compound can be a difunctional (meth)acrylate compound having two (meth)acrylate groups and an epoxyalkyl group between the (meth)acrylate groups. Such a difunctional (meth)acrylate compound exhibits good adhesion to hydrophilic adherends having a hydroxyl group (such as a polarizing film), and also has a high affinity for a polyester film treated with a primer, thereby enhancing the adhesion of the adhesive layer. Preferably, the epoxyalkyl group is ethylene oxide or propylene oxide.

[0058] In the difunctional (meth)acrylate compound, the epoxyalkyl group can be present in an amount of 2 moles or more than 2 moles, such as 2 moles to 5 moles. Within this range, the difunctional (meth)acrylate compound can facilitate achieving the desired effects of the present invention. For example, the hydrophilic difunctional (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.

[0059] Relative to 100 parts by weight of the curable compound, the hydrophilic difunctional (meth)acrylate compound may be present in an amount of 5 to 20 parts by weight, such as 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 difunctional (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 film. Therefore, through the polymerization reaction with the hydrophobic difunctional (meth)acrylate that has penetrated the COP film, the adhesive composition can be cured over a large area, thus facilitating the achievement of the desired effects of the present invention.

[0060] Relative to 100 parts by weight of the (meth)acrylate compound (B), preferably relative to the total of 100 parts by weight of the hydrophilic difunctional (meth)acrylate compound, the hydrophobic difunctional (meth)acrylate compound, and the vinyl-containing (meth)acrylate compound, the hydrophilic difunctional (meth)acrylate compound may be present in an amount of 10 to 60 parts by weight, such as 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, 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 10 to 50 parts by weight, 10 to 30 parts by weight, or 20 to 30 parts by weight. Within this range, the ratio between the hydrophilic difunctional (meth)acrylate compound remaining in the adhesive without penetrating the COP film and the (meth)acrylate compound that has penetrated the COP film can be adjusted to an appropriate level, thereby ensuring sufficient adhesiveness of the adhesive layer and thus facilitating the achievement of the desired effects of the present invention.

[0061] The hydrophobic bifunctional (meth)acrylate compound has a very low polarity and thus highly penetrates into a polarizer protective film having a low polarity, especially a COP film manufactured by solution casting and stretching to a high elongation ratio, thereby contributing to improving the adhesion of the adhesive layer to the protective film. However, in the present invention, the above bifunctional aliphatic epoxy compound and the following vinyl-containing (meth)acrylate compound are incorporated into the adhesive composition in a specific amount so as to ensure not only the adhesion of the adhesive layer to the COP film but also the good adhesion and improved reliability of the adhesive layer after long-term exposure to high temperature and high humidity conditions.

[0062] The hydrophobic bifunctional (meth)acrylate compound has two (meth)acrylate groups. The hydrophobic monofunctional (meth)acrylate compound having one (meth)acrylate group, although having good permeability to the polarizer protective film, especially the COP film, may have a poor effect in improving the peel strength due to its limited crosslinking degree.

[0063] The hydrophobic bifunctional (meth)acrylate compound has an alkylene group between the (meth)acrylate groups, and the alkylene group has an unsubstituted alkylene chain containing 9 or more carbon atoms. The (meth)acrylate compound having a straight-chain alkylene group containing less than 9 carbon atoms has poor permeability to the polarizer protective film, especially the COP film, due to its high polarity and thus has a poor effect in improving the adhesion of the adhesive layer.

[0064] The hydrophobic bifunctional (meth)acrylate compound may not have an ether functional group (epoxyalkyl group), such as ethylene oxide or propylene oxide.

[0065] In one embodiment, the hydrophobic bifunctional (meth)acrylate compound has a straight-chain or branched-chain alkylene group having an unsubstituted straight-chain alkylene chain containing 9 or more carbon atoms, such as 9, 10, 11, 12, 13, 14 or 15 carbon atoms, preferably 9 to 15 carbon atoms, and the hydrophobic bifunctional (meth)acrylate compound may include at least one of, for example, 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.

[0066] Relative to 100 parts by weight of the curable compound, the hydrophobic difunctional (meth)acrylate compound may be present in an amount of 10 to 40 parts by weight, such as 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 in an amount of 20 to 30 parts by weight. Within this range, the hydrophobic difunctional (meth)acrylate compound can sufficiently penetrate the COP film and can sufficiently bond to the hydrophilic difunctional (meth)acrylate compound in the adhesive composition, thus facilitating the improvement of the overall adhesiveness of the adhesive layer.

[0067] Relative to 100 parts by weight of the (meth)acrylate compound (B), preferably relative to the total of 100 parts by weight of the hydrophilic difunctional (meth)acrylate compound, the hydrophobic difunctional (meth)acrylate compound, and the vinyl-containing (meth)acrylate compound, the hydrophobic difunctional (meth)acrylate compound may be present in an amount of 30 to 80 parts by weight, such as 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, 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 an amount of 30 to 60 parts by weight or 40 to 60 parts by weight. Within this range, the ratio between the (meth)acrylate compound that penetrates the COP film and the hydrophilic difunctional (meth)acrylate compound remaining in the adhesive composition can be adjusted to an appropriate range, thus ensuring sufficient peel strength and therefore facilitating the achievement of the desired effects of the present invention.

[0068] The vinyl-containing (meth)acrylate compound has both a (meth)acrylate group and a vinyl group. Therefore, the vinyl-containing (meth)acrylate compound forms a covalent bond between the epoxy compound and the (meth)acrylate compound, while causing physical entanglement between the epoxy compound and the (meth)acrylate compound, thereby suppressing intermolecular movement even under high temperature and high humidity conditions, and thus improving the adhesiveness of the adhesive layer after long-term exposure to high temperature and high humidity conditions, and at the same time improving the reliability of the polarizing plate by suppressing the discoloration of the polarizing film after long-term exposure to high temperature and high humidity conditions.

[0069] Relative to 100 parts by weight of the curable compound, the vinyl-containing (meth)acrylate compound may be present in an amount of 10 to 15 parts by weight. 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 improving the adhesiveness of the adhesive layer and suppressing the discoloration of the polarizing film. If the content of the vinyl-containing (meth)acrylate compound exceeds 15 parts by weight, it may reduce the effect of the vinyl-containing (meth)acrylate in suppressing the interfacial detachment between other components of the adhesive composition, and due to the increased hydrophobicity of the adhesive composition, the bonding strength of the adhesive layer to the hydrophilic polarizing film may be reduced.

[0070] The vinyl-containing (meth)acrylate compound has both a (meth)acrylate group and a vinyl group. Therefore, the (meth)acrylate group is bonded to both the hydrophilic difunctional (meth)acrylate compound and the hydrophobic difunctional (meth)acrylate compound, and the vinyl group is bonded to a mixture of the difunctional alicyclic epoxy compound and the difunctional aliphatic epoxy compound, thereby facilitating the achievement of the desired effects of the present invention.

[0071] 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 is different from the hydrophilic difunctional (meth)acrylate compound and the hydrophobic difunctional (meth)acrylate compound.

[0072] 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 above-mentioned difunctional aliphatic epoxy compound and the hydrophobic difunctional (meth)acrylate compound. For example, the alkylene oxide group may be an ethylene oxide group or a propylene oxide group, preferably an ethylene oxide group.

[0073] In one embodiment, the vinyl-containing (meth)acrylate compound may be a compound represented by Formula 1:

[0074] CH2=CH–(-O-CH2CH2-) n -O-(C=O)-CHR=CH2

[0075] wherein R is hydrogen or methyl, and

[0076] n is an integer from 1 to 5.

[0077] For example, the vinyl-containing (meth)acrylate compound may be 2-(2-vinyloxyethoxy)ethyl (meth)acrylate or a similar compound.

[0078] Relative to 100 parts by weight of the (meth)acrylate compound (B), preferably relative to the total of 100 parts by weight of the hydrophilic difunctional (meth)acrylate compound, the hydrophobic difunctional (meth)acrylate compound, and the vinyl-containing (meth)acrylate compound, the vinyl-containing (meth)acrylate compound may be present in an amount of 10 to 40 parts by weight, such as 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 in an amount of 20 to 30 parts by weight. Within this range, due to the copolymerization properties of the vinyl-containing (meth)acrylate compound, the epoxy resin curing region and the acrylate curing region can be connected to each other, thereby ensuring sufficient peel strength and improved durability of the adhesive layer.

[0079] The photoinitiator includes a mixture of a radical photoinitiator and a cationic photoinitiator.

[0080] Relative to 100 parts by weight of the curable compound, the photoinitiator may be present in an amount of 1 to 15 parts by weight, preferably 1 to 10 parts by weight. Within this range, incomplete curing of the adhesive composition can be prevented, while a reduction in the light transmittance of the adhesive layer due to an excessive photoinitiator can be prevented.

[0081] The free radical photoinitiator may include cyclohexyl phenyl ketone photoinitiator, thioxanthone photoinitiator, etc.

[0082] Relative to 100 parts by weight of the curable compound, the free radical photoinitiator may be present in an amount of 0.5 to 10 parts by weight, for example, 1 to 6 parts by weight. Within this range, sufficient curing of the adhesive composition can be ensured while preventing a decrease in the adhesiveness of the adhesive layer and bleeding of the free radical photoinitiator.

[0083] The cationic photoinitiator may include an onium salt formed by an onium ion as a cation and an anion. Examples of the onium ion 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; triarylsulfonium, such as triphenylsulfonium, diphenyl-4-thiophenoxyphenylsulfonium, and diphenyl-4-(phenylthio)phenylsulfonium; bis[4-(diphenylsulfonium)phenyl]sulfide; bis[4-(bis(4-(2-hydroxyethyl)phenyl)sulfonium)phenyl]sulfide; and 5-2,4-(cyclopentadienyl)[1,2,3,4,5,6-η]-(methylethyl)-benzene]-iron(1+), etc. Examples of the anion may include tetrafluoroborate (BF4 - ), hexafluorophosphate (PF6 - ), hexafluoroantimonate (SbF6 - ), hexafluoroarsenate (AsF6 - ), and hexafluoroantimonate (SbCl6 - ), etc.

[0084] Relative to 100 parts by weight of the curable compound, the cationic photoinitiator may be present in an amount of 0.5 to 10 parts by weight, for example, 1 to 6 parts by weight. Within this range, sufficient curing of the adhesive composition can be ensured while preventing a decrease in the adhesiveness of the adhesive layer and bleeding of the free radical photoinitiator.

[0085] The adhesive composition can be prepared by mixing the curable compound and the photoinitiator. The adhesive composition may be solvent-free or may also include a solvent to increase its applicability (coating ability).

[0086] The adhesive composition may also include typical additives, such as antioxidants, ultraviolet (UV) absorbers, ion conductors, conductivity-imparting agents (such as conductive metal oxide particles), light diffusibility-imparting agents, and viscosity modifiers, etc., without changing the desired effects of the present invention.

[0087] The polarizing plate according to the present invention includes an adhesive layer formed of the adhesive composition for a polarizing plate according to the present invention. The polarizing plate includes a polarizer and a protective film formed on one surface of the polarizer, wherein the polarizer is attached to the protective film through the adhesive layer, and the adhesive layer contains a cured product of the adhesive composition according to the present invention.

[0088] Referring to Figure 1 , the polarizing plate may include: a polarizer 10; an adhesive layer 20 and a lower polarizer protective film 30, which are sequentially formed on one surface of the polarizer 10; and an upper polarizer protective layer 40, which is formed on the other surface of the polarizer 10.

[0089] Polarizer

[0090] The polarizer 10 is used to polarize external light or internal light.

[0091] The polarizer 10 may include a polyvinyl alcohol-based polarizer obtained by dyeing a polyvinyl alcohol film with iodine or the like. For example, the polyvinyl alcohol-based polarizer is manufactured by dyeing a polyvinyl alcohol 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. The methods for implementing each step are well known in the art. The polarizer 10 may have a thickness of 1 μm to 50 μm. Within this range, the polarizer 10 can be used in an optical display device.

[0092] Adhesive layer

[0093] The adhesive layer 20 may be directly formed on the polarizer and the lower polarizer protective film to bond the polarizer to the lower polarizer protective film.

[0094] The adhesive layer 20 may be formed of the above-mentioned adhesive composition. Specifically, the adhesive layer 20 can be formed by coating the adhesive composition on one surface of the polarizer or the lower polarizer protective film to a predetermined thickness and then photocuring the adhesive composition. Here, photocuring refers to a process of curing the composition by irradiating it with UV light, and the energy density (fluence) and wavelength of the UV light used can be adjusted according to the coating thickness of the adhesive composition. The adhesive layer 20 may have a thickness of 0.01 μm to 10 μm, preferably 1 μm to 5 μm. Within this range, the adhesive layer 20 can ensure the adhesiveness between the polarizer and the polarizer protective film.

[0095] Lower polarizer protective film

[0096] The 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 polarizing plate.

[0097] The lower polarizer protective film can be any typical polarizer protective film known in the art, such as the polarizer protective film described below for the upper polarizer protective layer. In the present invention, a COP film manufactured by solution casting and stretching to a high elongation rate as a non-adhesive protective film can be used as the lower polarizer protective film.

[0098] Advantageously, such a COP film manufactured by solution casting and stretching to a high elongation rate is easy to adjust the phase retardation required for a vertically aligned (VA) LCD panel when used for a polarizing plate.

[0099] Upper polarizer protective layer

[0100] The upper polarizer protective layer 40 can be formed on the upper surface of the polarizer (the surface of the polarizer through which internal light exits the polarizer) to support the polarizer. The upper polarizer protective layer can include at least one of an optically transparent protective film or an optically transparent protective coating.

[0101] When the upper polarizer protective layer is a protective film, the upper polarizer protective layer can include a protective film formed of an optically transparent resin. The protective film can be formed by melt-extruding the resin. If necessary, the resin can be further subjected to a stretching process. The resin can include at least one of a cellulose ester resin (such as triacetyl cellulose (TAC)), a cyclic olefin resin (such as cycloolefin polymer (COP)), a polycarbonate resin, a polyester resin (such as polyethylene terephthalate (PET)), a polyethersulfone resin, a polysulfone resin, a polyamide resin, a polyimide resin, an acyclic olefin resin, a poly(meth)acrylate resin (such as poly(methyl methacrylate)), a polyvinyl alcohol resin, a polyvinyl chloride resin, or a polyvinylidene chloride resin. Preferably, the protective film can be a film formed of a cyclic olefin resin (such as cycloolefin polymer (COP)).

[0102] When the upper polarizer protective layer is a protective coating, the upper polarizer protective layer can have good properties in terms of adhesiveness to the polarizer, transparency, mechanical strength, thermal stability, moisture barrier ability, and durability. In one embodiment, the protective coating can be formed of a photo-radiation-curable resin composition containing a photo-radiation-curable compound and a polymerization initiator.

[0103] The actinic radiation-curable compound may include at least one of a cationically polymerizable curable compound, a free-radically polymerizable curable compound, a urethane resin, or a silicone resin. The cationically polymerizable curable compound may be an epoxy compound having at least one epoxy group therein or an oxetane compound having at least one oxetane ring therein. The free-radically polymerizable curable compound may be a (meth)acrylic acid compound having at least one (meth)acryloyloxy group therein.

[0104] 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 a light-emitting diode display device.

[0105] Although not shown in Figure 1 the polarizer may further include a functional coating formed on the upper surface of the upper polarizer protective layer 40, and the functional coating may include a hard coating, an anti-fingerprint layer, an anti-reflection layer, etc.

[0106] Although not shown in Figure 1 when the upper polarizer protective layer 40 is a protective film, the polarizer may further include an adhesive layer sandwiched between the upper polarizer protective layer and the polarizer. Such an adhesive layer may be formed of a typical adhesive for a polarizer (such as an aqueous adhesive, a photocurable adhesive, or a pressure-sensitive adhesive).

[0107] Although not shown in Figure 1 the polarizer may further include a polarizer protective film, an anti-reflection film, and a retardation film (liquid crystal layer or non-liquid crystal layer) commonly used in a polarizer.

[0108] An optical display device according to an embodiment of the present invention includes a polarizer 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.

[0109] Next, the present invention will be described in more detail with reference to some examples. However, it should be noted that these examples are provided only for illustration and should not be construed as limiting the present invention in any way.

[0110] Example 1

[0111] (1) Preparation of a photocurable adhesive composition for a polarizer

[0112] As the epoxy compound, 20 parts by weight of a bifunctional alicyclic epoxy compound (2021P, Daicel Corporation) and 20 parts by weight of a bifunctional aliphatic epoxy compound (1,4-butanediol diglycidyl ether, Kukdo Chemical Co., Ltd.) were used. As the (meth)acrylate compound, 15 parts by weight of dipropylene glycol diacrylate (M222, Miwon Chemical Co., Ltd.), 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.

[0113] After mixing the epoxy compound and the (meth)acrylate compound, 1 part by weight of a cationic photoinitiator (1-hydroxycyclohexyl phenyl ketone, Irgacure 184, BASF Corporation) and 6 parts by weight of a photoacid generator (CPI-100P, San-Apro Ltd.) were added to and mixed with the mixture to prepare a solvent-free photocurable adhesive composition for a polarizing plate.

[0114] (2) Manufacture of a polarizing plate

[0115] A polyvinyl alcohol film (saponification degree: 99.5%, thickness: 60 μm PS # 60, Kuraray Co., Ltd.) was immersed in an aqueous solution of 0.3% iodine for dyeing, and then the polyvinyl alcohol film was uniaxially stretched 6 times its original length in the machine direction (MD). The stretched polyvinyl alcohol film was immersed in an aqueous solution of 3% boric acid and 2% potassium iodide for color correction, and then dried at 50 °C for 4 minutes to manufacture a polarizing sheet (light transmittance: 45%, thickness: 7 μm).

[0116] 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, and the surface of the PET film coated with the adhesive composition is treated with an undercoat. As the lower polarizer protective film, a cycloolefin polymer (COP) film (manufactured by solution casting and stretching to a high elongation rate, thickness: 37 μm, Konica Minolta, Inc.) is used, and the surface of the COP film to which the adhesive composition will be coated is treated with corona discharge at a dose of 100.

[0117] 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. Subsequently, the manufactured polarizer is bonded to each of the upper polarizer protective film and the lower polarizer protective film, and then the adhesive composition is irradiated with UV light from the direction of the lower polarizer protective film under the conditions of 400 mW / cm 2 and 1000 mJ / cm 2 to cure the adhesive composition, thereby manufacturing a polarizing plate in which the upper polarizer protective film, the adhesive layer, the polarizer, the adhesive layer, and the lower polarizer protective film are stacked in this order. The manufacturing of the polarizing plate is carried out at a temperature of 22°C to 25°C and a relative humidity (RH) of 20% to 60%.

[0118] Examples 2 to 9

[0119] In the preparation of a solvent-free photocurable adhesive composition for a polarizing plate, except for changing the content and / or type of each component as shown in Table 1, the polarizing plate is manufactured in the same manner as in Example 1. In Table 1, "-" means that the corresponding component is not used.

[0120] Comparative Examples 1 to 8

[0121] In the preparation of a solvent-free photocurable adhesive composition for a polarizing plate, except for changing the content and / or type of each component as shown in Table 1, the polarizing plate is manufactured in the same manner as in Example 1.

[0122] The properties shown in Table 2 of each of the polarizing plates prepared in Examples 1 to 9 and Comparative Examples 1 to 8 are evaluated. The results are shown in Table 2.

[0123] (1)Adhesion at room temperature (initial adhesion) (unit: gf / 25 mm): A double-sided foam adhesive tape (VHS, 3M Company) was attached to the lower polarizer protective film of each of the polarizing plates manufactured in Examples 1 to 9 and Comparative Examples 1 to 8. Subsequently, the polarizing plate was cut into a size of 25 mm × 150 mm (MD × TD), and the release film of the double-sided foam adhesive tape was removed. Then, the polarizing plate was attached to a non-alkali glass plate (thickness: 0.5 t) and placed indoors for 30 minutes to prepare a specimen.

[0124] Thereafter, a cutting blade was inserted between the polarizer and the lower polarizer protective film of the specimen to form a small gap therebetween. Thereafter, the specimen was mounted on a texture analyzer (TA Instruments Inc.), and then mounted on an upper load cell, where the polarizer was clamped in one 90-degree fixture and the lower polarizer protective film was clamped in another fixture. Under the conditions of a peeling angle of 90°, a peeling rate of 300 mm / min, and a temperature of 25 °C, the peeling strength was measured while peeling the polarizer from the lower polarizer protective film. This process was repeated three times, and then the average peeling strength was calculated.

[0125] (2)Adhesion after exposure to high temperature and high humidity conditions: Samples were prepared in the same manner as in (1). Thereafter, the samples were placed in a chamber at 60 °C and 95% RH for 2 days. Subsequently, the specimens were taken out of the chamber, and then the specimens were placed at room temperature for 30 minutes. Thereafter, the peeling strength was measured three times in the same manner as in (1), and then the average peeling strength was calculated.

[0126] (3)Color change after exposure to high temperature and high humidity conditions: Each of the polarizing plates prepared in Examples 1 to 9 and Comparative Examples 1 to 8 was cut into a square of 50 mm × 50 mm, where the absorption axis of the polarizer was inclined at an angle of 45°, and then attached to a glass plate through an acrylic adhesive layer. Thereafter, the specimens were placed in a chamber at 60 °C and 95% RH for 500 hours. After taking out the specimens from the chamber, the length (5) at which iodine color disappearance occurred in the specimens in (1) was measured diagonally from the four corners of the specimens, as Figure 2 shown, and then evaluated according to the following criteria.

[0127] ◎: Less than 1 mm

[0128] ○: 1 mm to less than 2 mm

[0129] △: 2 mm to less than 3 mm

[0130] ×: 3 mm or greater than 3 mm

[0131] Table 1

[0132]

[0133] A) 2021P: Alicyclic epoxy resin (Daicel Corporation)

[0134] B) DE200: 1,4-Butanediol diglycidyl ether (Guodu Chemical Co., Ltd.)

[0135] C) DE202: 1,6-Hexanediol diglycidyl ether (Guodu Chemical Co., Ltd.)

[0136] D) EX821: Polyethylene glycol diglycidyl ether (Nagase Chemtex Corporation)

[0137] E) EX920: Polypropylene glycol diglycidyl ether (Nagase Chemtex Corporation)

[0138] F) YD128: Bisphenol A diglycidyl ether (Guodu Chemical Co., Ltd.)

[0139] G) M222: Dipropylene glycol diacrylate (Meiyuan Chemical Co., Ltd.)

[0140] H) NDDA: 1,9-Nonanediol diacrylate (Kyoeisha Chemical Co., Ltd.)

[0141] I) VEEA: 2-(2-Vinyloxyethoxy)ethyl acrylate (Nippon Catalyst Co., Ltd.)

[0142] J) M232: Triethylene glycol diacrylate (Meiyuan Chemical Co., Ltd.)

[0143] K) M200: 1,6-Hexanediol diacrylate (Meiyuan Chemical Co., Ltd.)

[0144] L) M120: Lauryl acrylate (Meiyuan Chemical Co., Ltd.)

[0145] Table 2

[0146]

[0147] As can be seen from the table, the adhesive composition for a polarizing plate according to the present invention can provide the following adhesive layer: the adhesive layer ensures good adhesiveness between the polarizing film and a COP film manufactured by solution casting and stretching to a high elongation rate, has good adhesiveness after being exposed to high temperature and high humidity conditions, and improves the reliability of the polarizing plate by preventing the polarizing film from discoloring after being exposed to high temperature and high humidity conditions.

[0148] In contrast, the adhesive compositions of Comparative Examples 1 to 8 that do not meet the requirements of the present invention cannot provide all the desired effects of the present invention.

[0149] It should be understood that various modifications, changes, alterations, and equivalent embodiments can be made by those skilled in the art without departing from the spirit and scope of the present invention.

Claims

1. An adhesive composition for a polarizing plate, comprising: a curable compound; and a photoinitiator, wherein the curable compound includes an epoxy compound and a (meth)acrylate compound, the epoxy compound includes a mixture of a bifunctional alicyclic epoxy compound and a bifunctional aliphatic epoxy compound, the (meth)acrylate compound includes a mixture of a hydrophilic bifunctional (meth)acrylate compound, a hydrophobic bifunctional (meth)acrylate compound, and a vinyl-containing (meth)acrylate compound, wherein the hydrophobic bifunctional (meth)acrylate compound is a bifunctional (meth)acrylate compound having a straight-chain alkylene chain containing 9 or more carbon atoms, and wherein the vinyl-containing (meth)acrylate compound is present in an amount of 10 parts by weight to 15 parts by weight relative to 100 parts by weight of the curable compound.

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

3. The adhesive composition according to claim 1, wherein the bifunctional aliphatic epoxy compound includes at least one of a diglycidyl ether compound having a straight-chain alkylene chain containing 4 or more carbon atoms and a diglycidyl ether compound having 2 moles or more of ethylene oxide or propylene oxide therein.

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

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

6. The adhesive composition according to claim 1, wherein the vinyl-containing (meth)acrylate compound is a compound represented by Formula 1: CH2=CH–(-O-CH2CH2-) n -O-(C=O)-CHR=CH2 wherein R is hydrogen or methyl, and n is an integer from 1 to 5.

7. The adhesive composition according to claim 1, wherein the hydrophilic bifunctional (meth)acrylate compound is a bifunctional (meth)acrylate compound having an epoxyalkyl group between two (meth)acrylate groups.

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

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

10. The adhesive composition according to claim 1, wherein the bifunctional alicyclic epoxy compound and the bifunctional aliphatic epoxy compound are present in a total amount of 95 parts by weight or more than 95 parts by weight relative to 100 parts by weight of the epoxy compound.

11. The adhesive composition according to claim 1, wherein the vinyl-containing (meth)acrylate compound, the hydrophilic difunctional (meth)acrylate compound, and the hydrophobic difunctional (meth)acrylate compound are present in a total amount of 95 parts by weight or more than 95 parts by weight relative to 100 parts by weight of the (meth)acrylate compound.

12. The adhesive composition according to claim 1, wherein the epoxy compound and the (meth)acrylate compound are present in a total amount of 95 parts by weight or more than 95 parts by weight relative to 100 parts by weight of the curable compound.

13. The adhesive composition according to claim 1, wherein the curable compound is present in the adhesive composition in an amount of 90% by weight or more than 90% by weight based on the solid content.

14. A polarizing plate, comprising: a polarizing film; and a protective film formed on the lower surface of the polarizing film, wherein the polarizing film is adhered to the protective film through an adhesive layer, and the adhesive layer contains a cured product of the adhesive composition for a polarizing plate according to any one of claims 1 to 13.

15. An optical display device, comprising the polarizing plate according to claim 14.

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