# Patent

## Title
Polarizing plate and image display device comprising same

## Abstract

The present invention relates to a polarizing plate including: a polarizer; and a protective layer formed on at least one surface of the polarizer, in which the protective layer is a cured product of a radical curable composition including: (A) a radical polymerizable compound having at least one hydrophilic functional group in a molecule thereof; (B) a phosphate-based compound having three (meth)acryl groups in a molecule thereof; and (C) a radical initiator, and an image display device including the same.

## Background
This application is a National Stage Entry of International Application No. PCT/KR2014/009133, filed on Sep. 29, 2014, and claims the benefit of and priority to Korean Application No. 10-2013-0117043, filed on Sep. 30, 2013, and Korean Application No. 10-2014-0129390, filed on Sep. 26, 2014, all of which are incorporated herein by reference in their entirety for all purposes as if fully set forth herein.
TECHNICAL FIELD
The present invention relates to a polarizing plate and an image display device including the same, and more specifically, to a polarizing plate which has excellent adhesion between a polarizer and a protective layer, is excellent in water resistance and heat resistance, and may be manufactured as a thin-type, and an image display device including the same.
BACKGROUND ART
A polarizing plate has been usually used in a structure, in which a protective film is stacked on both surfaces of a polarizer formed of a polyvinyl alcohol (hereinafter, referred to as ‘PVA’)-based resin dyed with a dichroic dye or iodine. In this case, a triacetyl cellulose (TAC)-based film has been frequently used as the protective film because the film is excellent in optical transparency or moisture permeability.
Meanwhile, as a liquid crystal display device has recently been developed into a mobile device such as a laptop personal computer, a cellular phone and a car navigation system, it is required that a polarizing plate which constitutes a liquid crystal display device is thin and light weight. However, in a polarizing plate in which a TAC film and the like are laminated as the protective film as described above, it is difficult to maintain a thickness of the protective film at 20 μm or less from the viewpoint of handling property or durability performance during the operation, so that there is a limitation for the liquid crystal device to be thin and light weight.
In order to solve the aforementioned problems, a technology has been suggested, in which a protective film is provided on only one surface of a polarizer, and a transparent thin film layer is formed by coating an active energy ray curable composition on the other surface thereof. Meanwhile, the active energy ray curable composition which has been suggested may be classified into a radical curable composition and a cationic curable composition according to the curing method. In this case, when a transparent thin film layer is formed using a cationic curable composition, there is an advantage in that excellent adhesion with the polarizer is achieved, but there are many disadvantages in the manufacturing process due to a slow curing rate and a low degree of curing.
In order to solve such problems of the cationic curable composition, a technology has been suggested, in which a transparent thin film layer is formed by using a radical curable composition which includes an acrylic or acrylamide-based compound as a main component. However, in the case of a radical curable composition including an acrylic or acrylamide-based compound as a main component, there are problems in that the curing rate is fast compared to a cationic curable composition, but the curing rate becomes slow under a high humidity atmosphere, and water resistance is not good such that a transparent protective layer formed by using the same does not have sufficient adhesion with a polarizer, and iodide ions in the polarizer are affected. Further, in the case of a radical curable composition including the acrylic or acrylamide-based compound as a main component, there is a problem in that the heat resistance reliability of a polarizing plate including the same is not good because a protective layer has a low glass transition temperature after curing.
Therefore, there is a need for a new polarizing plate, which is excellent in adhesion between a polarizer and a protective layer, and is excellent in water resistance and heat resistance while having a thin protective layer which may be formed by curing radicals.
DISCLOSURE
Technical Problem
The present invention has been made in an effort to solve the aforementioned problem and provide a polarizing plate, which has excellent adhesion between a polarizer and a protective layer and is excellent in water resistance and heat resistance, and may be manufactured as a thin-type, and an image display device including the same.
Technical Solution
In one aspect, the present invention provides a polarizing plate including: a polarizer; and a protective layer formed on at least one surface of the polarizer, in which the protective layer is a cured product of a radical curable composition including: (A) a radical polymerizable compound having at least one hydrophilic functional group in a molecule thereof; (B) a phosphate-based compound having three (meth)acryl groups in a molecule thereof; and (C) a radical initiator.
Meanwhile, the radical curable composition preferably includes: 40 to 93 parts by weight of (A) the radical polymerizable compound; 1 to 30 parts by weight of (B) the phosphate-based compound; and 0.5 to 20 parts by weight of the radical initiator, based on 100 parts by weight of the radical curable composition.
Meanwhile, (A) the radical polymerizable compound is particularly preferably a mixture of (a-1) a radical polymerizable first compound including at least one hydroxy group and at least one (meth)acryl group in a molecule thereof and (a-2) a radical polymerizable second compound including at least two hydroxy groups, at least one benzene ring or cyclohexane ring, and at least two (meth)acryl groups in a molecule thereof.
In this case, (a-1) the first compound may be one or more selected from the group consisting of the following [Formula 1] to [Formula 21].







Also, (a-2) the second compound may be one or more selected from the group consisting of the following [Formula 22] to [Formula 24].




Meanwhile, (B) the phosphate-based compound is preferably a compound represented by the following [Formula I].




In [Formula 1], R1, R2 and R3 are each independently a substituted or unsubstituted C1 ̃10 alkylene group, a substituted or unsubstituted C4 ̃14 cycloalkylene group, a substituted or unsubstituted C6 ̃14 arylene group, or a combination thereof; R4, R5 and R6 are each independently hydrogen or a methyl group; and X1, X2 and X3 are each independently O (oxygen) or N (nitrogen).
Meanwhile, the radical curable composition may further include (D) a phosphate-based compound having one or two (meth)acryl groups in a molecule thereof.
In this case, (D) the phosphate-based compound is more preferably included in an amount of 5 to 40 parts by weight based on 100 parts by weight of the radical curable composition.
Further, (D) the phosphate-based compound is more preferably a compound represented by the following [Formula II] and/or [Formula III].




In [Formula II], R7 and R8 are each independently a substituted or unsubstituted C1 ̃10 alkylene group, a substituted or unsubstituted C4 ̃14 cycloalkylene group, a substituted or unsubstituted C6 ̃14 arylene group, or a combination thereof; R9 and R10 are each independently hydrogen or a methyl group; and X4 and X5 are each independently O (oxygen) or N (nitrogen).




In [Formula III], R11 is a substituted or unsubstituted C1 ̃10 alkylene group, a substituted or unsubstituted C4 ̃14 cycloalkylene group, a substituted or unsubstituted C6 ̃14 arylene group, or a combination thereof; R12 is each independently hydrogen or a methyl group; and X6 is each independently O (oxygen) or N (nitrogen).
Meanwhile, the radical curable composition may further include (E) a polyfunctional (meth)acrylic compound.
In this case, (E) the polyfunctional (meth)acrylic compound is more preferably included in an amount of 5 to 40 parts by weight based on 100 parts by weight of the radical curable composition.
In addition, (E) the polyfunctional (meth)acrylic compound is more preferably one or more selected from the group consisting of compounds represented by the following [Formula IV] to [Formula VI].




In [Formula IV], R13 and R14 are each independently a (meth)acryloyloxy group or a (meth)acryloyloxy alkyl group.




In [Formula V], R15, R16 and R17 are each independently a (meth)acryloyloxy group, or a (meth)acryloyloxy alkyl group, and R18 is a (meth)acryloyloxy group, a (meth)acryloyloxy alkyl group, a hydroxy group, or a substituted or unsubstituted C1 ̃10 alkyl group.




In [Formula VI], R19 is a substituted or unsubstituted C1 ̃10 alkylene, and R20 and R21 are each independently a (meth)acryloyloxy group or a (meth)acryloyloxy alkyl group.
Meanwhile, the radical curable composition preferably has a glass transition temperature of 50° C. or more after curing.
Furthermore, the radical curable composition preferably has a viscosity of 70 cP or less.
Meanwhile, the protective layer preferably has a thickness of 0.5 to 20 μm.
Meanwhile, in the polarizing plate of the present invention, a protective film may be further attached to a surface opposite to a surface of the polarizer, on which a protective layer is formed, through an adhesive layer.
Further, the polarizing plate of the present invention may further include an adhesion layer at the upper portion of the protective layer.
In another aspect, the present invention provides an image display device including the polarizing plate.
Advantageous Effects
The polarizing plate of the present invention has excellent adhesion between the polarizer and the protective layer, excellent water resistance which may prevent iodide ions in the polarizer from being discolored even under high humidity environment, and has a high glass transition temperature of the protective layer after curing, and thus is excellent in heat resistance.
In addition, in the polarizing plate of the present invention, a composition for forming a protective layer has excellent water resistance such that discoloration of the polarizer does not occur even under a high humidity situation, and furthermore has low viscosity, and thus the polarizing plate may be manufactured as a thin type, and workability is also excellent.


MODE FOR INVENTION
Hereinafter, preferred exemplary embodiments of the present invention will be described. However, exemplary embodiments of the present invention may be modified in various forms, and the scope of the present invention is not limited to the exemplary embodiments which will be described below. Further, exemplary embodiments of the present invention are provided to more completely explain the present invention to a person with ordinary skill in the art.
1. Polarizing Plate
As a result of repeated studies, the present inventors have found that when a phosphate-based compound having three (meth)acryl groups in a molecule thereof is mixed with a radical curable composition having a hydrophilic functional group for forming a protective layer, and the mixture is used, adhesion is excellent, water resistance and heat resistance are excellent, and furthermore, low viscosity may be implemented, thereby completing the present invention.
More specifically, the radical curable composition of the present invention provides a polarizing plate including: a polarizer; and a protective layer formed on at least one surface of the polarizer, in which the protective layer is a cured product of a radical curable composition including: (A) a radical polymerizable compound having at least one hydrophilic functional group in a molecule thereof; (B) a phosphate-based compound having three (meth)acryl groups in a molecule thereof; and (C) a radical initiator.
1-1. Polarizer
First, as the polarizer of the present invention, it is possible to use a polarizer well known in the art, for example, a film composed of polyvinyl alcohol (PVA) including iodine or a dichroic dye. The polarizer may be manufactured by dyeing iodine or a dichromatic dye to the PVA film, but the manufacturing method thereof is not particularly limited. In the present specification, the polarizer refers to a state in which the polarizer does not include a protective layer (or a protective film), and the polarizing plate refers to a state in which the polarizing plate includes a polarizer and a protective layer (or a protective film).
Meanwhile, when the polarizer is a polyvinyl alcohol-based film, the polyvinyl alcohol-based film may be used without particular limitation as long as the film includes a polyvinyl alcohol resin or a derivative thereof. In this case, examples of the derivative of the polyvinyl alcohol resin include, but are not limited to, a polyvinyl formal resin, a polyvinyl acetal resin and the like. Also, as the polyvinyl alcohol-based film, it is also possible to use a commercially available polyvinyl alcohol-based film generally used in the manufacture of a polarizer in the art, for example, P30, PE30 and PE60 manufactured by Kuraray Co., Ltd., and M3000 and M6000 manufactured by Nippon Synthetic Chemical Industry Co., Ltd., and the like.
Meanwhile, the degree of polymerization of the polyvinyl alcohol-based film may be in a range of 1,000 to 10,000, preferably, in a range of 1,500 to 5,000, but is not limited thereto. This is because when the degree of polymerization satisfies the range, molecules freely move, and may be flexibly mixed with iodine or a dichroic dye, and the like.
1-2. Protective Layer
Next, the protective layer of the present invention is formed by using the radical curable composition in order to support and protect a polarizer, and may be formed by a method well known in the art. For example, the protective layer may be formed by a method of applying the radical curable composition on one surface of a polarizer to form a protective layer by a coating method well known in the art, for example, a method such as spin coating, bar coating, roll coating, gravure coating and blade coating, and then curing the protective layer through irradiation of an active energy ray. The method of irradiating an active energy ray is not particularly limited, and for example, may be performed by irradiating UV light at 10 to about 2,500 mJ/cm2 using a UV light irradiation device (fusion lamp, D bulb).
In this case, the radical curable composition of the present invention includes: (A) a radical polymerizable compound having at least one hydrophilic functional group in a molecule thereof; (B) a phosphate-based compound having three (meth)acryl groups in a molecule thereof; and (C) a radical initiator, as described above.
More preferably, the radical curable composition of the present invention includes: 40 to 93 parts by weight of (A) the radical polymerizable compound; 1 to 30 parts by weight of (B) the phosphate-based compound; and 0.5 to 20 parts by weight of (C) the radical initiator, based on 100 parts by weight of the radical curable composition.
A. Radical Polymerizable Compound Including Hydrophilic Group (A)
First, (A) the radical polymerizable compound having at least one hydrophilic functional group in a molecule thereof, which is included in the radical curable composition according to the present invention, is a component for implementing adhesion of a protective layer, may have at least one hydrophilic functional group in a molecule thereof to implement adhesion through a hydrogen bond, and may be used without particular limitation as long as the radical polymerizable compound may achieve the radical polymerization due to the presence of an unsaturated double bond between carbons in a molecule thereof. In this case, the hydrophilic functional group is not particularly limited as long as the hydrophilic functional group may obtain a hydrogen bond, such as a hydroxy group, a carboxyl group, a urethane group, an amine group, and an amide group, but among them, particularly, a hydroxy group is more preferred for implementing excellent adhesion.
Meanwhile, (A) the radical polymerizable compound is not limited to, but is particularly preferably a mixture of (a-1) a radical polymerizable first compound including at least one hydroxy group and at least one (meth)acryl group in a molecule thereof and (a-2) a radical polymerizable second compound including at least two hydroxy groups, at least one benzene ring or cyclohexane ring, and at least two (meth)acryl groups in a molecule thereof, in order to implement the effect of the present invention.
In this case, (a-1) the first compound may be used without particular limitation as long as the compound includes at least one hydroxy group and at least one (meth)acryl group in a molecule thereof, but a compound corresponding to (a-2) the second compound to be described below in the present specification is excluded from (a-1) the first compound.
More specifically, (a-1) the first compound may be, but is not limited to, one or more selected from the group consisting of the following [Formula 1] to [Formula 21].







Further, (a-2) the second compound may be used without particular limitation as long as the compound includes at least two hydroxy groups, at least one benzene ring or cyclohexane ring, and at least two (meth)acryl groups in a molecule thereof.
More specifically, (a-2) the second compound may be, but is not limited to, one or more selected from the group consisting of the following [Formula 22] to [Formula 24].




Meanwhile, the content of the radical polymerizable compound of the present invention may be 40 to 93 parts by weight, preferably 40 to 90 parts by weight, and more preferably 45 to 90 parts by weight, based on 100 parts by weight of the entire radical curable composition. This is because when the radical polymerizable compound is included in this content, excellent adhesion may be implemented.
B. Trifunctional Phosphate-Based Compound (B)
Next, (B) the phosphate-based compound having three (meth)acryl groups in a molecule thereof, which is included in the radical curable composition according to the present invention is a component for further enhancing adhesion of an adhesive, and furthermore, securing excellent water resistance and heat resistance, and it is possible to use various phosphate-based compounds including three (meth)acryl groups in a molecule thereof.
According to the study results of the present inventors of the present invention, particularly when a compound including three (meth)acryl groups in a molecule thereof is used among the phosphate-based compounds, excellent thermal impact stability and heat resistance may also be secured compared to the case of using a compound including one or two (meth)acryl groups in a molecule thereof, and furthermore, it is easier to implement low viscosity.
Meanwhile, (B) the phosphate-based compound is not limited to, but is more preferably a compound represented by the following [Formula I]. This is because the aforementioned effect is particularly excellent.




In [Formula I], R1, R2 and R3 are each independently a substituted or unsubstituted C1 ̃10 alkylene group, a substituted or unsubstituted C4 ̃14 cycloalkylene group, a substituted or unsubstituted C6 ̃14 arylene group, or a combination thereof; R4, R5 and R6 are each independently hydrogen or a methyl group; and X1, X2 and X3 are each independently O (oxygen) or N (nitrogen).
In this case, in R1, R2 and R3, the alkylene group refers to a straight-chained or branch-chained divalent hydrocarbon moiety having 1 to 10, or 1 to 8, or 1 to 4 carbon atoms, and the alkylene group in the present specification may also include at least one unsaturated bond in a molecule thereof. Meanwhile, examples of the alkylene group include, but are not limited to, methylene, ethylene, trimethylene, tetramethylene, pentamethylene, hexamethylene, heptamethylene, nonamethylene, decamethylene and the like. One or more hydrogen atoms included in the alkylene group may be substituted with any substituent.
In addition, in R1, R2 and R3, the cycloalkylene group refers to a non-aromatic divalent monocyclic, bicyclic or tricyclic hydrocarbon moiety of 4 to 14, or 4 to 10, or 4 to 6 ring carbons, and the alkylene group in the present specification may also include at least one unsaturated bond in a molecule thereof. Meanwhile, examples of the cycloalkylene group include, but are not limited to, a divalent cyclopentane ring, a divalent cyclohexane ring and the like. One or more hydrogen atoms included in the cycloalkylene group may be substituted with any substituent.
Furthermore, in R1, R2 and R3, the arylene group refers to a divalent monocyclic, bicyclic or tricyclic aromatic hydrocarbon moiety having 6 to 14, or 6 to 12 ring atoms, and examples thereof include, but are not limited to, a divalent benzene ring, a divalent naphthalene ring, a divalent anthracene ring, a divalent biphenyl ring and the like. One or more hydrogen atoms included in the arylene group may be substituted with any substituent.
Meanwhile, R1, R2 and R3 are not limited thereto, but among them, are preferably a substituted or unsubstituted C1 ̃10 alkylene group, more preferably a substituted or unsubstituted C1 ̃8 alkylene group, and even more preferably a substituted or unsubstituted C1 ̃4 alkylene group.
More specifically, (B) the phosphate-based compound may be, but is not limited to, a compound represented by the following [Formula 25] to [Formula 30].







Meanwhile, the content of (B) the phosphate-based compound of the present invention may be 1 to 30 parts by weight, preferably 5 to 30 parts by weight, and more preferably 6 to 29 parts by weight, based on 100 parts by weight of the entire composition. When the phosphate-based compound is used in an amount less than the aforementioned content, it is difficult to secure thermal impact stability and water resistance, and the viscosity thereof is high. Further, when the phosphate-based compound is used in an amount more than the aforementioned content, adhesion deteriorates.
C. Radical Initiator (C)
Next, (C) the radical initiator included in the radical curable composition according to the present invention is for promoting radical polymerizability to enhance the curing rate.
In this case, as the radical initiator, radical initiators generally used in the art may be used without limitation, and the radical initiator may be, for example, one or more selected from the group consisting of 1-hydroxy-cyclohexyl-phenyl-ketone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone, methylbenzoylformate, oxy-phenyl-acetic acid-2-[2-oxo-2-phenyl-acetoxy-ethoxy]-ethyl ester, oxy-phenyl-acetic acid-2-[2-hydroxy-ethoxy]-ethyl ester, alpha-dimethoxy-alpha-phenylacetophenone, 2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone, 2-methyl-1-[4-(methylthio)phenyl]-2-(4-morpholinyl)-1-propanone, diphenyl (2,4,6-trimethylbenzoyl)-phosphine oxide, and phenylbis(2,4,6-trimethylbenzoyl)-phosphineoxide. Particularly, in the present invention, the radical initiator is preferably phenylbis(2,4,6-trimethylbenzoyl)-phosphineoxide.
Meanwhile, it is preferred that (C) the content of the radical initiator is, for example, 0.5 to 20 parts by weight, 0.5 to 15 parts by weight, or 0.5 to 10 parts by weight, based on 100 parts by weight of the radical curable composition. This is because when the content of the radical initiator satisfies the numerical range, the protective layer may be smoothly cured.
D. Additional Phosphate-Based Compound (D)
The radical curable composition according to the present invention may further include (D) a phosphate-based compound having one or two (meth)acryl groups in a molecule thereof in order to obtain further excellent adhesion and water resistance effects.
That is, the radical curable composition according to the present invention may be a composition including: (A) a radical polymerizable compound having at least one hydrophilic functional group in a molecule thereof; (B) a phosphate-based compound having three (meth)acryl groups in a molecule thereof; (C) a radical initiator; and (D) a phosphate-based compound having one or two (meth)acryl groups in a molecule thereof.
In this case, (D) the phosphate-based compound is not particularly limited, and it is possible to use various phosphate-based compounds including one or two (meth)acryl groups in a molecule thereof.
Meanwhile, (D) the phosphate-based compound is not limited but, is more preferably a compound represented by the following [Formula II] and/or [Formula III]. This is because the aforementioned effect is particularly excellent.




In [Formula II], R7 and R8 are each independently a substituted or unsubstituted C1 ̃10 alkylene group, a substituted or unsubstituted C4 ̃14 cycloalkylene group, a substituted or unsubstituted C6 ̃14 arylene group, or a combination thereof; R9 and R10 are each independently hydrogen or a methyl group; and X4 and X5 are each independently O (oxygen) or N (nitrogen).
In this case, in R7 and R8, the alkylene group refers to a straight-chained or branch-chained divalent hydrocarbon moiety having 1 to 10, or 1 to 8, or 1 to 4 carbon atoms, and the alkylene group in the present specification may also include at least one unsaturated bond in a molecule thereof. Meanwhile, examples of the alkylene group include, but are not limited to, methylene, ethylene, trimethylene, tetramethylene, pentamethylene, hexamethylene, heptamethylene, nonamethylene, decamethylene and the like. One or more hydrogen atoms included in the alkylene group may be substituted with any substituent.
In addition, in R7 and R8, the cycloalkylene group refers to a non-aromatic divalent monocyclic, bicyclic or tricyclic hydrocarbon moiety of 4 to 14, or 4 to 10, or 4 to 6 ring carbons, and the alkylene group in the present specification may also include at least one unsaturated bond in a molecule thereof. Meanwhile, examples of the cycloalkylene group include, but are not limited to, a divalent cyclopentane ring, a divalent cyclohexane ring and the like. One or more hydrogen atoms included in the cycloalkylene group may be substituted with any substituent.
Furthermore, in R7 and R8, the arylene group refers to a divalent monocyclic, bicyclic or tricyclic aromatic hydrocarbon moiety having 6 to 14, or 6 to 12 ring atoms, and examples thereof include, but are not limited to, a divalent benzene ring, a divalent naphthalene ring, a divalent anthracene ring, a divalent biphenyl ring and the like. One or more hydrogen atoms included in the arylene group may be substituted with any substituent.
Meanwhile, R7 and R8 are not limited thereto, but among them, are preferably a substituted or unsubstituted C1 ̃10 alkylene group, more preferably a substituted or unsubstituted C1 ̃8 alkylene group, and even more preferably a substituted or unsubstituted C1 ̃4 alkylene group.




In [Formula III], R11 is a substituted or unsubstituted C1 ̃10 alkylene group, a substituted or unsubstituted C4 ̃14 cycloalkylene group, a substituted or unsubstituted C6 ̃14 arylene group, or a combination thereof; R12 is each independently hydrogen or a methyl group; and X6 is each independently O (oxygen) or N (nitrogen).
In this case, in R11, the alkylene group refers to a straight-chained or branch-chained divalent hydrocarbon moiety having 1 to 10, or 1 to 8, or 1 to 4 carbon atoms, and the alkylene group in the present specification may also include at least one unsaturated bond in a molecule thereof. Meanwhile, examples of the alkylene group include, but are not limited to, methylene, ethylene, trimethylene, tetramethylene, pentamethylene, hexamethylene, heptamethylene, nonamethylene, decamethylene and the like. One or more hydrogen atoms included in the alkylene group may be substituted with any substituent.
In addition, in R11, the cycloalkylene group refers to a non-aromatic divalent monocyclic, bicyclic or tricyclic hydrocarbon moiety of 4 to 14, or 4 to 10, or 4 to 6 ring carbons, and the alkylene group in the present specification may also include at least one unsaturated bond in a molecule thereof. Meanwhile, examples of the cycloalkylene group include, but are not limited to, a divalent cyclopentane ring, a divalent cyclohexane ring and the like. One or more hydrogen atoms included in the cycloalkylene group may be substituted with any substituent.
Furthermore, in R11, the arylene group refers to a divalent monocyclic, bicyclic or tricyclic aromatic hydrocarbon moiety having 6 to 14, or 6 to 12 ring atoms, and examples thereof include, but are not limited to, a divalent benzene ring, a divalent naphthalene ring, a divalent anthracene ring, a divalent biphenyl ring and the like. One or more hydrogen atoms included in the arylene group may be substituted with any substituent.
Meanwhile, R12 is not limited thereto, but among them, is preferably a substituted or unsubstituted C1 ̃10 alkylene group, more preferably a substituted or unsubstituted C1 ̃8 alkylene group, and even more preferably a substituted or unsubstituted C1 ̃4 alkylene group.
More specifically, (D) the phosphate-based compound may be, but is not limited to, one or more selected from the group consisting of the following [Formula 31] to
[Formula 34].




Meanwhile, (D) the phosphate-based compound may be included in an amount of preferably 5 to 40 parts by weight, more preferably 5 to 35 parts by weight, and even more preferably 5 to 30 parts by weight, based on 100 parts by weight of the radical curable composition. When the content of (D) the phosphate-based compound is more than the range, adhesion may not be sufficient, and when the content is less than the range, water resistance may be reduced.
E. Polyfunctional (Meth)Acrylic Compound (E)
The radical curable composition according to the present invention may also be a composition further including (E) a polyfunctional (meth)acrylic compound in order to obtain further excellent adhesion and water resistance effects.
That is, the radical curable composition according to the present invention may be a composition including: (A) a radical polymerizable compound having at least one hydrophilic functional group in a molecule thereof; (B) a phosphate-based compound having three (meth)acryl groups in a molecule thereof; (C) a radical initiator; and (D) a phosphate-based compound having one or two (meth)acryl groups in a molecule thereof and/or (E) a polyfunctional (meth)acrylic compound.
In this case, (E) the polyfunctional (meth)acrylic compound is not particularly limited, and it is possible to use various polyfunctional (meth)acrylic compounds, which are widely known in the art as a compound having at least two (meth)acryl groups in a molecule thereof, without particular limitation. However, in the present specification, except for the following polyfunctional (meth)acrylic compounds enumerated as an example, a compound corresponding to the above-described (A) and (D) compounds is excluded from the polyfunctional (meth)acrylic compounds.
In the present invention, examples of (E) the polyfunctional (meth)acrylic compound include ethylene glycol di(meth)acrylate, 1,3-butanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, trimethylol propane di(meth)acrylate, pentaerythritol di(meth)acrylate, ditrimethylol propane di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, silicone di(meth)acrylate, hydroxypivalic acid ester neopentyl glycol di(meth)acrylate, 2,2-bis[4-(meth)acryloyloxyethoxyethoxyphenyl]propane, 2,2-bis[4-(meth)acryloyloxyethoxyethoxycyclohexyl]propane, hydrogenated dicyclopentadienyl di(meth)acrylate, tricyclodecane dimethaneol di(meth)acrylate, 1,3-dioxane-2,5-diyl di(meth)acrylate, di(meth)acrylate of 2-(2-hydroxy-1,1-dimethylethyl)-5-ethyl-5-hydroxymethyl-1,3-dioxane, tris(hydroxyethyl)isocyanurate di(meth)acrylate, glycerin tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, di trimethyolpropane tri(meth)acrylate, di trimethylol propane tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, di pentaerythritol tetra(meth)acrylate, di pentaerythritol penta(meth)acrylate, di pentaerythritol hexa(meth)acrylate and the like. These may be used either alone or in a mixture.
Meanwhile, (E) the polyfunctional (meth)acrylic compound is more preferably one or more selected from the group consisting of compounds represented by the following [Formula IV] to [Formula VI], but is not limited thereto. This is because water resistance improvement effects are still excellent in this case.




In [Formula IV], R13 and R14 are each independently a (meth)acryloyloxy group or a (meth)acryloyloxy alkyl group.
In this case, in R13 and R14, the alkyl of the (meth)acryloyloxy alkyl group refers to a straight-chained or branch-chained hydrocarbon moiety having 1 to 10, or 1 to 8, or 1 to 4 carbon atoms, and the (meth)acryloyloxy group may be substituted at any position of the alkyl group. The remaining one or more hydrogen atoms included in the alkyl may be substituted with any substituent.




In [Formula V], R15, R16 and R17 are each independently a (meth)acryloyloxy group, or a (meth)acryloyloxy alkyl group, and R18 is a (meth)acryloyloxy group, a (meth)acryloyloxy alkyl group, a hydroxy group, or a substituted or unsubstituted C1 ̃10 alkyl group.
In this case, in R15, R16, R17 and R18, the alkyl of the (meth)acryloyloxy alkyl group refers to a straight-chained or branch-chained hydrocarbon moiety having 1 to 10, or 1 to 8, or 1 to 4 carbon atoms, and the (meth)acryloyloxy group may be substituted at any position of the alkyl group. The remaining one or more hydrogen atoms included in the alkyl may be substituted with any substituent.
Further, in R18, the alkyl group refers to a straight-chained or branch-chained hydrocarbon moiety having 1 to 10, or 1 to 8, or 1 to 4 carbon atoms, and one or more hydrogen atoms included in the alkyl group may be substituted with any substituent.




In [Formula VI], R19 is a substituted or unsubstituted C1 ̃10 alkylene, and R20 and R21 are each independently a (meth)acryloyloxy group or a (meth)acryloyloxy alkyl group.
In this case, in R19, the alkylene refers to a straight-chained or branch-chained divalent hydrocarbon moiety having 1 to 10, or 1 to 8, or 1 to 6 carbon atoms, and the alkylene group in the present specification may also include at least one unsaturated bond in a molecule thereof. Meanwhile, examples of the alkylene group include, but are not limited to, methylene, ethylene, trimethylene, tetramethylene, pentamethylene, hexamethylene, heptamethylene, nonamethylene, decamethylene and the like. One or more hydrogen atoms included in the alkylene may be substituted with any substituent.
Furthermore, in R20 and R21, the alkyl of the (meth)acryloyloxy alkyl group refers to a straight-chained or branch-chained hydrocarbon moiety having 1 to 10, or 1 to 8, or 1 to 4 carbon atoms, and the (meth)acryloyloxy group may be substituted at any position of the alkyl group. The remaining one or more hydrogen atoms included in the alkyl may be substituted with any substituent.
More specifically, (E) the polyfunctional (meth)acrylic compound is particularly preferably one or more selected from the group consisting of compounds represented by the following [Formula 35] to [Formula 38], but is not limited thereto.




Meanwhile, the content of (E) the polyfunctional (meth)acrylic compound of the present invention may be 5 to 40 parts by weight, preferably 5 to 35 parts by weight, and more preferably 5 to 30 parts by weight, based on 100 parts by weight of the entire composition. When the content of (E) the polyfunctional (meth)acrylic compound is more than the range, adhesion may not be sufficient, and when the content is less than the range, water resistance may be reduced.
F. Physical Properties of Composition
Meanwhile, the glass transition temperature of the aforementioned radical curable composition of the present invention after curing is 50° C. or more, and may be, for example, 70 to 140° C., or 70 to 130° C. When the radical curable composition has a glass transition temperature in the numerical range as described above, the protective layer may have excellent heat resistance and water resistance.
Further, the viscosity of the radical curable composition is 70 cP or less, and may be, for example, 10 to 70 cP or 10 to 65 cP. When the viscosity of the composition satisfies the numerical range, there is an advantage in that workability is excellent because the protective layer may be thinly formed, and has a low viscosity.
Meanwhile, the thickness of a protective layer formed by using the radical curable composition is preferably 0.5 to 20 μm, and may be, for example, 0.5 to 15 μm or 0.5 to 10 μm. This is because a polarizing plate manufactured may become thin and light weight when the thickness of the protective layer satisfies the range. When the thickness is less than 0.5 μm, thermal impact stability and curl characteristics of the polarizer are vulnerable, and when the thickness is 20 μm or more, it is difficult to make the polarizing plate thin and light weight.
1-3. Protective Film
Meanwhile, the polarizing plate of the present invention may further include a protective film on one surface of the polarizer, if necessary. More specifically, when the protective layer is formed on one surface of the polarizer in the polarizing plate of the present invention, a separate protective film may be attached to a surface opposite to the surface, on which a protective layer is formed, through an adhesive layer in order to support and protect the polarizer.
In this case, the protective film is provided for supporting and protecting a polarizer, and it is possible to use protective films formed of various materials generally known in the art, for example, a cellulose-based film, a polyethylene terephthalate (PET) film, a cycloolefin polymer (COP) film, an acrylic film and the like without limitation. Among them, it is particularly preferred that an acrylic film is used in consideration of optical properties, durability, economic efficiency and the like.
Meanwhile, the acrylic film which may be used in the present invention may be obtained by molding a molding material including a (meth)acrylate-based resin as a main component by extrusion molding. In this case, the (meth)acrylate-based resin includes a resin including a (meth)acrylate-based unit as a main component, and is a concept which includes not only a homopolymer resin composed of a (meth)acrylate-based unit but also a copolymer resin in which other monomer units other than the (meth)acrylate-based unit are copolymerized, and a blend resin in which other resins are blended with the aforementioned (meth)acrylate-based resin.
Meanwhile, the (meth)acrylate-based unit may be, for example, an alkyl(meth)acrylate-based unit. Here, the alkyl(meth)acrylate-based unit refers to both an alkyl acrylate-based unit and an alkyl methacrylate-based unit, and the alkyl group of the alkyl(meth)acrylate-based unit has preferably 1 to 10 carbon atoms, and more preferably 1 to 4 carbon atoms.
Further, examples of a monomer unit capable of being copolymerized with the (meth)acrylate-based unit include a styrene-based unit, a maleic anhydride-based unit, a maleimide-based unit and the like. In this case, examples of the styrene-based unit include, but are not limited to, styrene, α-methylstyrene and the like; examples of the maleic anhydride-based monomer include, but are not limited to, maleic anhydride, methyl maleic anhydride, cyclohexyl maleic anhydride, phenyl maleic anhydride, and the like; and examples of the maleimide-based monomer include, but are not limited to, maleimide, N-methyl maleimide, N-cyclohexyl maleimide, N-phenyl maleimide and the like. These may be used either alone or in a mixture.
Meanwhile, the acrylic film may be a film including a (meth)acrylate-based resin having a lactone ring structure. Specific examples of the (meth)acrylate-based resin having a lactone ring structure include (meth)acrylate-based resins having a lactone ring structure, which are described in, for example, the official gazettes of Japanese Patent Application Laid-Open Nos. 2000-230016, 2001-151814, and 2002-120326, and the like.
The method of manufacturing the acrylic film is not particularly limited, and for example, the acrylic film may be manufactured by sufficiently mixing a (meth)acrylate-based resin, other polymers, an additive and the like by any appropriate mixing method to manufacture a thermoplastic resin composition, and then film-molding the resin composition, or may also be manufactured by preparing the (meth)acrylate-based resin, other polymers, an additive and the like in separate solutions, mixing the solutions to form a homogeneous mixture solution, and then film-molding the mixture solution. In addition, the acrylic film may be an unstretched film, or a stretched film. The stretched film may be a uniaxially stretched film or a biaxially stretched film, and the biaxially stretched film may be a simultaneous biaxially stretched film or a sequential biaxially stretched film.
Meanwhile, the polarizing plate of the present invention may further include a primer layer between the adhesive layer and the protective film in order to further enhance adhesive strength. In this case, the primer layer may be formed by a method of applying a coating solution including a water-dispersible polymer resin, a water-dispersible particulate and water on a protective film by using a bar coating method, a gravure coating method and the like, and drying the coating solution. The water-dispersible polymer resin may be, for example, a water-dispersible polyurethane-based resin, a water-dispersible acrylic resin, a water-dispersible polyester-based resin or a combination thereof, and the like, and for the water-dispersible particulate, it is possible to use an inorganic-based particulate such as silica, titania, alumina and zirconia, or an organic-based particulate composed of a silicone-based resin, a fluorine-based resin, a (meth)acrylic resin, a crosslinked polyvinyl alcohol and a melamine-based resin, or a combination thereof, but the particulate is not limited thereto.
Meanwhile, the polarizer and the protective film may be attached by a method of applying an adhesive on the surface of the polarizer or the protective film by using a roll coater, a gravure coater, a bar coater, a knife coater, or a capillary coater, and the like, and then heating and paper-laminating the polarizer or the protective film by a laminated paper roll, or laminating paper by compressing the polarizer and the protective film at normal temperature, a method of irradiating UV after the paper-lamination, or the like. Meanwhile, as the adhesive, various adhesives for a polarizing plate used in the art, for example, a polyvinyl alcohol-based adhesive, a polyurethane-based adhesive, an acrylic adhesive, a cationic or radical adhesive and the like may be used without limitation.
1-4. Adhesion Layer
Meanwhile, the polarizing plate of the present invention may include an adhesion layer at the upper portion of the protective layer, if necessary, for attachment to an optical film such as a display device panel or a phase difference film.
In this case, the adhesion layer may be formed by using various gluing agents well known in the art, and the kind thereof is not particularly limited. For example, the adhesion layer may be formed by using a rubber-based gluing agent, an acrylic gluing agent, a silicone-based gluing agent, a urethane-based gluing agent, a polyvinyl alcohol-based gluing agent, a polyvinyl pyrrolidone-based gluing agent, a polyacryl amide-based gluing agent, a cellulose-based gluing agent, a vinyl alkyl ether-based gluing agent and the like. Among them, it is particularly preferred that an acrylic gluing agent is used in consideration of transparency, heat resistance and the like.
Meanwhile, the adhesion layer may be formed by a method of applying a gluing agent at the upper portion of the protective layer, and may also be formed by a method of attaching an adhesion sheet, which is manufactured by applying a gluing agent on a release sheet, and then drying the gluing agent, at the upper portion of the protective layer.
2. Image Display Device
The aforementioned polarizing plate of the present invention may be usefully applied to an image display device such as a liquid crystal display device. The image display device may be, for example, a liquid crystal display device including a liquid crystal panel and polarizing plates each provided on both surfaces of the liquid crystal panel, and in this case, at least one of the polarizing plates may be the polarizing plate according to the present invention. In this case, the kind of liquid crystal panel included in the liquid crystal display device is not particularly limited. For example, it is possible to apply all the publicly known panels such as a passive matrix type panel such as a twisted nematic (TN)-type, a super twisted nematic (STN)-type, a ferroelectric (F)-type, or a polymer dispersed (PD)-type; an active matrix type panel such as a two terminal or three terminal; an in plane switching (IPS) panel and a vertical alignment (VA) panel without being limited to the kind thereof. Furthermore, the kinds of other configurations which constitute the liquid crystal display device, for example, the kinds of upper and lower substrates (e.g., a color filter substrate, or an array substrate) and the like are not particularly limited, and the configuration publicly known in the field may be adopted without limitation.
BEST MODE
Hereinafter, the present invention will be described in more detail with reference to specific Examples.
Preparation Example 1
Manufacture of Acrylic Protective Film
A raw material pellet was manufactured by supplying a resin composition, in which poly(N-cyclohexylmaleimide-co-methylmethacrylate), a styrene-maleic anhydride copolymer resin and a phenoxy-based resin were uniformly mixed with each other at a weight ratio of 100:2.5:5, to a 24Φ extruder in which a portion from a raw material hopper to the extruder was substituted with nitrogen, and melting the mixed resin composition at 250° C.
PKFE (Mw=60,000, Mn=16,000, Tg=95° C.) manufactured by InChemRez® Co., Ltd., was used as the phenoxy-based resin, Dylaeck 332 with a content of 85 wt % of styrene and 15 wt % of anhydrous maleic anhydride was used as the styrene-maleic anhydride copolymer resin, and as the poly(N-cyclohexylmaleimide-co-methylmethacrylate) resin, a resin with a content of 6.5 wt % of N-cyclohexylmaleimide as a result of NMR analysis was used.
The obtained raw material pellet was dried under vacuum, melted by the extruder at 260° C., allowed to pass through a coat hanger-type T-die, and allowed to pass through a chrome plating casting roll and a drying roll and the like to manufacture a film having a thickness of 150 μm. A pilot stretching device was used to stretch the film at a ratio of 170% in the MD direction at 125° C. by using the difference between speeds of the rolls, thereby manufacturing an acrylic film.
After the acrylic film manufactured by the aforementioned process was subjected to corona treatment, a primer composition, in which 20 parts by weight of an oxazoline crosslinking agent (Nippon Shokubai Co., Ltd., WS700) was added to a primer composition with a solid content of 10 wt % that is prepared by diluting CK-PUD-F (Chokwang urethane dispersion) with pure water, was coated on one surface of the acrylic film with a #7 bar, and then the acrylic film was stretched at a ratio of 190% in a TD direction at 130° C. using a tenter, thereby finally manufacturing an acrylic protective film having a primer layer thickness of 400 nm.
Preparation Example 2
Preparation of Radical Curable Composition
(1) Radical Curable Composition A
Radical curable composition A for a polarizing plate was prepared by adding 3 parts by weight of a radical initiator Irgacure-819 (Ciba Chemical Specialty Chemicals) to 100 parts by weight of a resin composition prepared by putting 66.7 wt % of hydroxyethyl acrylate (HEA), 16.6 wt % of BPA type epoxy di-acrylate (EB600, product of Cytec Industries Inc.), and 16.7 wt % of tri(acryloyloxy ethyl)phosphate.
(2) Radical Curable Composition B
Radical curable composition B for a polarizing plate was prepared by adding 3 parts by weight of a radical initiator Irgacure-819 (Ciba Chemical Specialty Chemicals) to 100 parts by weight of a resin composition prepared by adding 50 wt % of hydroxyethyl acrylate (HEA), 21.4 wt % of BPA type epoxy di-acrylate (EB600, product of Cytec Industries Inc.), 14.3 wt % of tri(acryloyloxy ethyl)phosphate, and 14.3 wt % of di-(methacryloyloxy ethyl)phosphate.
(3) Radical Curable Composition C
Radical curable composition C for a polarizing plate was prepared by adding 3 parts by weight of a radical initiator Irgacure-819 (Ciba Chemical Specialty Chemicals) to 100 parts by weight of a resin composition prepared by adding 50 wt % of hydroxyethyl acrylate (HEA), 21.4 wt % of BPA type epoxy di-acrylate (EB600, product of Cytec Industries Inc.), 21.4 wt % of tri(acryloyloxy ethyl)phosphate, and 7.2 wt % of di-(methacryloyloxy ethyl)phosphate.
(4) Radical Curable Composition D
Radical curable composition D for a polarizing plate was prepared by adding 3 parts by weight of a radical initiator Irgacure-819 (Ciba Chemical Specialty Chemicals) to 100 parts by weight of a resin composition prepared by adding 50 wt % of hydroxyethyl acrylate (HEA), 21.4 wt % of BPA type epoxy di-acrylate (EB600, product of Cytec Industries Inc.), 14.3 wt % of tri(acryloyloxy ethyl)phosphate, and 14.3 wt % of dimethylol tricyclodecane diacrylate (DCPDA).
(5) Radical Curable Composition E
Radical curable composition E for a polarizing plate was prepared by adding 3 parts by weight of a radical initiator Irgacure-819 (Ciba Chemical Specialty Chemicals) to 100 parts by weight of a resin composition prepared by adding 16.7 wt % of hydroxyethyl acrylate (HEA), 50 wt % of glyceryl methacrylate (GLM), 16.6 wt % of BPA type epoxy di-acrylate (EB600, product of Cytec Industries Inc.), and 16.7 wt % of tri(acryloyloxy ethyl)phosphate.
(6) Radical Curable Composition F
Radical curable composition F for a polarizing plate was prepared by adding 3 parts by weight of a radical initiator Irgacure-819 (Ciba Chemical Specialty Chemicals) to 100 parts by weight of a resin composition prepared by adding 50 wt % of hydroxyethyl acrylate (HEA), 16.7 wt % of 1,4-cyclohexanedimethanol mono-acrylate, 16.6 wt % of BPA type epoxy di-acrylate (EB600, product of Cytec Industries Inc.), and 16.7 wt % of tri(acryloyloxy ethyl)phosphate.
(7) Radical Curable Composition G
Radical curable composition G for a polarizing plate was prepared by adding 3 parts by weight of a radical initiator Irgacure-819 (Ciba Chemical Specialty Chemicals) to 100 parts by weight of a resin composition prepared by putting 50 wt % of hydroxyethyl acrylate (HEA), 21.4 wt % of BPA type epoxy di-acrylate (EB600, product of Cytec Industries Inc.), 14.3 wt % of 2-(acrylamido)ethyl bis(2-(acryloyloxy)ethyl)phosphate, and 14.3 wt % of dimethylol tricyclodecane diacrylate (DCPDA).
(8) Radical Curable Composition H
Radical curable composition H for a polarizing plate was prepared by adding 3 parts by weight of a radical initiator Irgacure-819 (Ciba Chemical Specialty Chemicals) to 100 parts by weight of a resin composition prepared by putting 30 wt % of hydroxyethyl acrylate (HEA), and 70 wt % of BPA type epoxy di-acrylate (EB600, product of Cytec Industries Inc.).
(9) Radical Curable Composition I
Radical curable composition I for a polarizing plate was prepared by adding 3 parts by weight of a radical initiator Irgacure-819 (Ciba Chemical Specialty Chemicals) to 100 parts by weight of a resin composition prepared by putting 66.7 wt % of hydroxyethyl acrylate (HEA), 16.6 wt % of BPA type epoxy di-acrylate (EB600, product of Cytec Industries Inc.), and 16.7 wt % of di-(methacryloyloxy ethyl)phosphate.
(10) Radical Curable Composition J
Radical curable composition J for a polarizing plate was prepared by adding 3 parts by weight of a radical initiator Irgacure-819 (Ciba Chemical Specialty Chemicals) to 100 parts by weight of a resin composition prepared by adding 66.7 wt % of hydroxyethyl acrylate (HEA), 16.6 wt % of BPA type epoxy di-acrylate (EB600, product of Cytec Industries Inc.), and 16.7 wt % of mono-(methacryloyloxy ethyl)phosphate.
Example 1
Radical curable composition A was applied on a primer layer of an acrylic film-based protective film prepared in Preparation Example 1 by using a dropper, and lamination was performed on one surface of a polarizer (PVA device), a condition was set such that the thickness of the final adhesive layer became 1 to 2 μm, and then the film was allowed to pass through a laminator (5 m/min). Then, a polarizing plate including a protective film on one surface of a polarizer was manufactured by irradiating UV light with 1,000 mJ/cm2 on a surface, on which the acrylic film was laminated, using a UV irradiation device (metal halide lamp).
Next, Radical curable composition A was applied on the other surface of the surface on which the protective film of the polarizer of the polarizing plate manufactured above was laminated, a PET film having a release force was laminated, a condition was set such that the thickness of the final protective layer became 4 to 5 μm, and then the film was allowed to pass through a laminator (5 m/min). Then, a polarizing plate including a protective film on one surface of a polarizer and a protective layer on the other surface thereof was manufactured by irradiating UV light with 1,000 mJ/cm2 on a surface, on which a release PET film was laminated, using a UV irradiation device (metal halide lamp), and removing the PET film.
Example 2
A polarizing plate was manufactured in the same manner as in Example 1, except that Radical curable composition B was used.
Example 3
A polarizing plate was manufactured in the same manner as in Example 1, except that Radical curable composition C was used.
Example 4
A polarizing plate was manufactured in the same manner as in Example 1, except that Radical curable composition D was used.
Example 5
A polarizing plate was manufactured in the same manner as in Example 1, except that Radical curable composition E was used.
Example 6
A polarizing plate was manufactured in the same manner as in Example 1, except that Radical curable composition F was used.
Example 7
A polarizing plate was manufactured in the same manner as in Example 1, except that Radical curable composition G was used.
Comparative Example 1
A polarizing plate was manufactured in the same manner as in Example 1, except that Radical curable composition H was used.
Comparative Example 2
A polarizing plate was manufactured in the same manner as in Example 1, except that Radical curable composition I was used.
Comparative Example 3
A polarizing plate was manufactured in the same manner as in Example 1, except that Radical curable composition J was used.
Experimental Example 1
Evaluation of Adhesion
Adhesion of the protective layers of the polarizing plates manufactured in the Examples and the Comparative Examples were measured, and are shown in the following [Table 1]. Specifically, the radical curable compositions used in the Examples and the Comparative Examples were applied at a thickness of 4 to 5 μm on a polarizer (PVA device), a polarizer (PVA device) was laminated thereon and allowed to pass through a laminator, and then a UV irradiation device (metal halide lamp) was used to irradiate UV rays thereon at 1,000 mJ/cm2, thereby preparing a peel strength sample composed of a polarizer/a protective layer/a polarizer. The prepared sample was left to stand under conditions of a temperature of 20° C. and a humidity of 70% for 4 days, and then cut into a width of 20 mm and a length of 100 mm, and a texture analyzer device (TA-XT Plus manufactured by Stable Micro Systems Ltd.) was used to measure a peel strength at a speed of 300 m/min and an angle of 90 degrees. In this case, the sample was indicated as excellent, good and bad when the peel strength thereof is 1.0 N/2 cm to 2.0 N/2 cm, 0.5 N/2 cm or more and less than 1.0 N/2 cm, and less than 0.5 N/2 cm, respectively.
Experimental Example 2
Evaluation of Water Resistance
Water resistance of the polarizing plates manufactured in the Examples and the Comparative Examples was measured, and is shown in the following [Table 1]. Specifically, the polarizing plates in the Examples and the Comparative Examples were laminated on a glass substrate, and then immersed in a thermostat at 60° C., and the water resistance was judged by observing whether the end portions of the polarizing plate had been discolored after 8 hours, and the cases in which no change was observed, discoloration partially occurred, and a lot of discoloration occurred were indicated as excellent, good, and bad, respectively.
Experimental Example 3
Evaluation of Thermal Impact Properties
Thermal impact properties of the polarizing plates manufactured in the Examples and the Comparative Examples were measured, and are shown in the following [Table 1]. Specifically, the evaluation was performed by repeating 100 times a process of laminating the polarizing plates manufactured in the Examples and the Comparative Examples on a glass substrate, leaving the laminates to stand at −40° C. for 30 minutes, and then leaving the laminates to stand again at 80° C. for 30 minutes. Then, it was visually evaluated whether the external appearance of the polarizing plate changed. The cases, in which cracks with a size of 2 mm or less were generated only at the end portions, cracks with a short line shape of 5 mm or more were only confirmed at the portions other than the end portions, and a plurality of cracks was generated on the entire surface of the polarizing plate in the external appearance of the polarizing plate, were indicated as excellent, good, and bad, respectively.
Experimental Example 4
Measurement of Viscosity of Composition
The viscosity of each of compositions used in the Examples and the Comparative Examples was measured at 25° C. using Viscometer TV-22 (TOKI SANGYO), and is shown in the following [Table 1].












TABLE 1









Thermal




Compo-

Water
impact
Viscosity


Classification
sition
Adhesion
resistance
stability
[cP]







Example 1
A
Good
Excellent
Excellent
42


Example 2
B
Excellent
Excellent
Excellent
65


Example 3
C
Good
Excellent
Excellent
55


Example 4
D
Excellent
Excellent
Excellent
63


Example 5
E
Excellent
Excellent
Good
50


Example 6
F
Good
Excellent
Good
47


Example 7
G
Excellent
Good
Excellent
68


Comparative
H
Bad
Bad
Bad
90


Example 1


Comparative
I
Good
Bad
Good
72


Example 2


Comparative
J
Good
Bad
Good
75


Example 3









As can be seen in Table 1, it can be known that in Examples 1 to 7 of the present invention, adhesion is excellent, water resistance and thermal impact stability are also excellent, and viscosity is low.
In contrast, it can be known that when a trifunctional phosphate-based compound is not included as in Comparative Example 1, all of the adhesion, water resistance, thermal impact stability and viscosity characteristics were bad.
Further, it can be known that when a bifunctional phosphate-based compound is used instead of a trifunctional phosphate-based compound as in Comparative Example 2, adhesion and thermal impact stability were good, but water resistance and viscosity characteristics were still bad.
In addition, it can be known that when a monofunctional phosphate-based compound is used instead of a trifunctional phosphate-based compound as in Comparative Example 3, adhesion and thermal impact stability were good, but water resistance and viscosity characteristics were still bad.
Meanwhile, in the case of the Examples, the adhesive layer and the protective layer were manufactured by using the same radical curable composition for convenience when the polarizing plate was manufactured, but the present invention is not limited thereto.
As described above, exemplary embodiments of the present invention have been described in detail, but it will be obvious to a person with ordinary skill in the art that the scope of the present invention is not limited thereto, and various modifications and changes may be made without departing from the technical spirit of the present invention described in the claims.

## Claims

1. A polarizing plate comprising:
a polarizer; and
a protective layer formed on at least one surface of the polarizer,
wherein the protective layer is a cured product of a radical curable composition including: (A) a radical polymerizable compound having at least one hydrophilic functional group in a molecule thereof; (B) a phosphate-based compound having three (meth)acryl groups in a molecule thereof; and (C) a radical initiator.

2. The polarizing plate of claim 1, wherein the radical curable composition comprises: 40 to 93 parts by weight of (A) the radical polymerizable compound; 1 to 40 parts by weight of (B) the phosphate-based compound; and 0.5 to 20 parts by weight of the radical initiator, based on 100 parts by weight of the radical curable composition.

3. The polarizing plate of claim 1, wherein (A) the radical polymerizable compound is a mixture of (a-1) a radical polymerizable first compound comprising at least one hydroxy group and at least one (meth)acryl group in a molecule thereof and (a-2) a radical polymerizable second compound comprising at least two hydroxy groups, at least one benzene ring or cyclohexane ring, and at least two (meth)acryl groups in a molecule thereof.

4. The polarizing plate of claim 3, wherein (a-1) the first compound is one or more selected from the group consisting of the following [Formula 1] to [Formula 21]:

5. The polarizing plate of claim 3, wherein (a-2) the second compound is one or more selected from the group consisting of the following [Formula 22] to [Formula 24]:

6. The polarizing plate of claim 1, wherein (B) the phosphate-based compound is a compound represented by the following [Formula I]:



in [Formula 1], R1, R2 and R3 are each independently a substituted or unsubstituted C1 ̃10 alkylene group, a substituted or unsubstituted C4 ̃14 cycloalkylene group, a substituted or unsubstituted C6 ̃14 arylene group, or a combination thereof; R4, R5 and R6 are each independently hydrogen or a methyl group; and X1 , X2 and X3 are each independently O (oxygen) or N (nitrogen).

7. The polarizing plate of claim 1, wherein the radical curable composition further comprises (D) a phosphate-based compound having one or two (meth)acryl groups in a molecule thereof.

8. The polarizing plate of claim 7, wherein (D) the phosphate-based compound is comprised in an amount of 5 to 40 parts by weight based on 100 parts by weight of the polarizing plate.

9. The polarizing plate of claim 7, wherein (D) the phosphate-based compound is one or more selected from the group consisting of compounds represented by the following [Formula II] and [Formula III]:



in [Formula III], R7 and R8 are each independently a substituted or unsubstituted C1 ̃10 alkylene group, a substituted or unsubstituted C4 ̃14 cycloalkylene group, a substituted or unsubstituted C6 ̃14 arylene group, or a combination thereof; R9 and R10 are each independently hydrogen or a methyl group; and X4 and X5 are each independently O(oxygen) or N (nitrogen),




in [Formula III], R11 is a substituted or unsubstituted C1 ̃10 alkylene group, a substituted or unsubstituted C4 ̃14 cycloalkylene group, a substituted or unsubstituted C6 ̃14 arylene group, or a combination thereof; R12 is each independently hydrogen or a methyl group; and X6 is each independently O (oxygen) or N (nitrogen).

10. The polarizing plate of claim 1, wherein the radical curable composition further comprises (E) a polyfunctional (meth)acrylic compound.

11. The polarizing plate of claim 10, wherein (E) the polyfunctional (meth)acrylic compound is comprised in an amount of 5 to 40 parts by weight based on 100 parts by weight of the polarizing plate.

12. The polarizing plate of claim 10, wherein (E) the polyfunctional (meth)acrylic compound is one or more selected from the group consisting of compounds represented by the following [Formula IV] to [Formula VI]:



in [Formula IV], R13 and R14 are each independently a (meth)acryloyloxy group or a (meth)acryloyloxy alkyl group,




in [Formula V], R15, R16 and R17 are each independently a (meth)acryloyloxy group, or a (meth)acryloyloxy alkyl group, and R18 is a (meth)acryloyloxy group, a (meth)acryloyloxy alkyl group, a hydroxy group, or a substituted or unsubstituted C1 ̃10 alkyl group,




in [Formula VI], R19 is a substituted or unsubstituted C1 ̃10 alkylene, and R20 and R21 are each independently a (meth)acryloyloxy group or a (meth)acryloyloxy alkyl group.

13. The polarizing plate of claim 1, wherein the radical curable composition has a glass transition temperature of 50° C. or more after curing.

14. The polarizing plate of claim 1, wherein the radical curable composition has a viscosity of 70 cP or less.

15. The polarizing plate of claim 1, wherein the protective film has a thickness of 0.5 to 20 μm.

16. The polarizing plate of claim 1, wherein a protective film is attached to a surface opposite to a surface of the polarizer, on which the protective layer is formed, through an adhesive layer.

17. The polarizing plate of claim 1, further comprising: an adhesion layer at an upper portion of the protective layer.

18. An image display device comprising the polarizing plate of claims 1.