JP2012018360A - Polarizer protective film and display device including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizer protective film having superior optical transparency, heat resistance and mechanical strength; and to provide a display device including the same.SOLUTION: This polarizer protective film includes a polymer which has at least one structural unit (i) selected from a group consisting of a structural unit represented by a specific formula and a structural unit represented by the following formula (2). (In the formula (2), Rto Reach represents an univalent organic group having 1-12 carbon numbers, and a to d are integers from 0 to 4. Y represents a single bond, -SO- or >C=O, Rand Reach represents independently a halogen atom, an univalent organic group having 1-12 carbon numbers, or a nitro group, g and h represent integers from 0 to 4 respectively and m represents 0 or 1.)

Description

  The present invention relates to a polarizer protective film and a display device including the same.

  A polarizing plate is used on the front surface of a display device such as a liquid crystal display in order to improve contrast of the display device and prevent reflection of light from the outside.

  Conventionally, as a polarizer protective film used for such a polarizing plate, a triacetyl cellulose (TAC) film is used because of its excellent adhesion to a polyvinyl alcohol film used as a polarizer and excellent light transmittance. (Patent Document 1).

  However, the TAC film does not have sufficient heat resistance, and when the TAC film is used as a polarizer protective film, the properties of the polarizing plate may deteriorate at high temperatures, and the polyvinyl alcohol film may shrink, expand and deform. There was a case where it could not endure.

JP 2003-262725 A

  This invention is made | formed in view of such a problem, and it aims at providing the polarizer protective film excellent in light transmittance, heat resistance, and mechanical strength, and a display apparatus including the same.

  As a result of intensive studies to solve the above problems, the present inventors have found that a film containing a polymer having a specific structural unit can solve the above problems, and further, the retardation of the film is small. The present invention was completed by finding that it can be suitably used as a polarizer protective film.

That is, the present invention provides the following [1] to [10].
[1] A polarizer protective film comprising a polymer having at least one structural unit (i) selected from the group consisting of a structural unit represented by the following formula (1) and a structural unit represented by the following formula (2).

(In Formula (1), R < ¹ > -R < ⁴ > shows a C1-C12 monovalent organic group each independently, and ad shows the integer of 0-4, respectively.)

(In the formula ^(2), R 1 to R ⁴ and a~d are respectively the same as ^R 1 to R ⁴ and a~d of the formula (1), Y is a single bond, -SO ₂ -, or > C = O, R ⁷ and R ⁸ each independently represent a halogen atom, a monovalent organic group having 1 to 12 carbon atoms or a nitro group, and g and h each represents an integer of 0 to 4 M represents 0 or 1. However, when m is 0, R ⁷ is not a cyano group.)
[2] The polymer further has at least one structural unit (ii) selected from the group consisting of a structural unit represented by the following formula (3) and a structural unit represented by the following formula (4): [1] ] The polarizer protective film of description.

(In Formula (3), R ⁵ and R ⁶ each independently represent a monovalent organic group having 1 to 12 carbon atoms, and Z represents a single bond, —O—, —S—, —SO ₂ —, > C═O, —CONH—, —COO— or a divalent organic group having 1 to 12 carbon atoms, e and f each represents an integer of 0 to 4, and n represents 0 or 1.)

(In the formula ^(4), R ^7, R 8, Y, m, g and h are the ^R 7 of each of the formulas ^(2), R 8, Y, m, and g and h synonymous, ^{R 5} , R ⁶ , Z, n, e and f have the same meanings as R ⁵ , R ⁶ , Z, n, e and f in the formula (3), respectively.
[3] The polarizer protective film according to [1] or [2], wherein the polymer has a molar ratio of the structural unit (i) to the structural unit (ii) of 80:20 to 100: 0. .

  [4] The polarizer protective film according to any one of [1] to [3], wherein the polymer has a polystyrene-reduced weight average molecular weight of 5,000 to 500,000 by gel permeation chromatography (GPC). .

  [5] The glass transition temperature (Tg) according to differential scanning calorimetry (DSC, heating rate 20 ° C./min) of the polymer is 230 to 350 ° C., according to any one of [1] to [4]. Polarizer protective film.

  [6] The polarizer protective film according to any one of [1] to [5], wherein the total light transmittance by a JIS K7105 transparency test method at a thickness of 30 μm is 85% or more.

  [7] The polarizer protective film according to any one of [1] to [6], wherein a YI value (yellow index) at a thickness of 30 μm is 3.0 or less.

  [8] The polarizer protective film according to any one of [1] to [7], wherein a thickness direction retardation (Rth) at a thickness of 30 μm is 100 nm or less.

  [9] A polarizing plate comprising the polarizer protective film according to any one of [1] to [8] on at least one surface of the polarizer.

  [10] A display device comprising the polarizing plate according to [9].

  The polarizer protective film of the present invention is excellent in light transmittance, heat resistance and mechanical strength, and has a small retardation in the thickness direction. Therefore, the polarizer protective film of this invention is used suitably for a polarizing plate and a display apparatus.

≪Polarizer protective film≫
The polarizer protective film of the present invention has a structural unit represented by the following formula (1) (hereinafter also referred to as “structural unit (1)”) and a structural unit represented by the following formula (2) (hereinafter “structural unit (2)”. And a polymer having at least one structural unit (i) selected from the group consisting of:

  By including such a polymer, it is excellent in balance in light transmittance, heat resistance and mechanical strength, and has a low phase difference (optical isotropy). Therefore, the polarizer can be suitably protected.

In said formula (1), R < ¹ > -R < ⁴ > shows a C1-C12 monovalent organic group each independently, and ad shows the integer of 0-4, respectively.

  The monovalent organic group having 1 to 12 carbon atoms includes a monovalent hydrocarbon group having 1 to 12 carbon atoms and 1 to 1 carbon atoms containing at least one atom selected from the group consisting of an oxygen atom and a nitrogen atom. And 12 monovalent hydrocarbon groups.

  Examples of the monovalent hydrocarbon group having 1 to 12 carbon atoms include a linear or branched hydrocarbon group having 1 to 12 carbon atoms, an alicyclic hydrocarbon group having 3 to 12 carbon atoms, and 6 to 12 carbon atoms. An aromatic hydrocarbon group etc. are mentioned.

  The linear or branched hydrocarbon group having 1 to 12 carbon atoms is preferably a linear or branched hydrocarbon group having 1 to 8 carbon atoms, and the linear or branched carbon group having 1 to 5 carbon atoms. A hydrogen group is more preferable.

  Preferable specific examples of the linear or branched hydrocarbon group include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, and n-pentyl. Group, n-hexyl group, n-heptyl group and the like.

  As said C3-C12 alicyclic hydrocarbon group, a C3-C8 alicyclic hydrocarbon group is preferable, and a C3-C4 alicyclic hydrocarbon group is more preferable.

  Preferable specific examples of the alicyclic hydrocarbon group having 3 to 12 carbon atoms include cycloalkyl groups such as cyclopropyl group, cyclobutyl group, cyclopentyl group, and cyclohexyl group; cyclobutenyl group, cyclopentenyl group, and cyclohexenyl group. And the like. The bonding site of the alicyclic hydrocarbon group may be any carbon on the alicyclic ring.

  Examples of the aromatic hydrocarbon group having 6 to 12 carbon atoms include a phenyl group, a biphenyl group, and a naphthyl group. The bonding site of the aromatic hydrocarbon group may be any carbon on the aromatic ring.

  As a C1-C12 hydrocarbon group containing an oxygen atom, a C1-C12 hydrocarbon group which has an ether bond, a carbonyl group, and an ester group etc. can be mentioned.

  As C1-C12 hydrocarbon group which has an ether bond, C1-C12 alkoxy group, C2-C12 alkenyloxy group, C2-C12 alkynyloxy group, C6-C12 And an aryloxy group having 1 to 12 carbon atoms and the like. Specific examples include a methoxy group, an ethoxy group, a propoxy group, an isopropyloxy group, a butoxy group, a phenoxy group, a propenyloxy group, a cyclohexyloxy group, and a methoxymethyl group.

  Moreover, as a C1-C12 hydrocarbon group which has a carbonyl group, a C2-C12 acyl group etc. can be mentioned. Specific examples include an acetyl group, a propionyl group, an isopropionyl group, and a benzoyl group.

  As a C1-C12 hydrocarbon group which has ester group, a C2-C12 acyloxy group etc. are mentioned. Specific examples include an acetyloxy group, a propionyloxy group, an isopropionyloxy group, and a benzoyloxy group.

  As a C1-C12 hydrocarbon group containing a nitrogen atom, an imidazole group, a triazole group, a benzimidazole group, a benztriazole group, etc. are mentioned.

  Specific examples of the hydrocarbon group having 1 to 12 carbon atoms including an oxygen atom and a nitrogen atom include an oxazole group, an oxadiazole group, a benzoxazole group, and a benzoxadiazole group.

In the formula ^(2), R 1 to R ⁴ and a~d are respectively the same as ^R 1 to R ⁴ and a~d of the formula (1), Y is a single bond, -SO ₂ -, or > C = O, R ⁷ and R ⁸ each independently represent a halogen atom, a monovalent organic group having 1 to 12 carbon atoms or a nitro group, and g and h each represents an integer of 0 to 4 , M represents 0 or 1. However, when m is 0, R ⁷ is not a cyano group.
Examples of the monovalent organic group having 1 to 12 carbon atoms include the same functional groups as described above.

  In the polymer, the molar ratio between the structural unit (1) and the structural unit (2) (however, the total of the structural unit (1) and the structural unit (2) is 100) is optical. From the viewpoint of properties, heat resistance and mechanical properties, the structural unit (1): structural unit (2) is preferably 50:50 to 100: 0, and the structural unit (1): structural unit (2) = 70: More preferably, it is 30-100: 0, and it is further more preferable that it is structural unit (1): structural unit (2) = 80: 20-100: 0.

  Here, the mechanical properties refer to properties such as the tensile strength, breaking elongation and tensile elastic modulus of the polymer.

  The polymer may further have at least one structural unit (ii) selected from the group consisting of a structural unit represented by the following formula (3) and a structural unit represented by the following formula (4). Good. It is preferable that the polymer has such a structural unit (ii) because the mechanical properties of the film having the polymer are improved.

In the formula (3), R ⁵ and R ⁶ each independently represent a monovalent organic group having 1 to 12 carbon atoms, Z represents a single bond, —O—, —S—, —SO ₂ —, > C═O, —CONH—, —COO— or a divalent organic group having 1 to 12 carbon atoms, e and f each represents an integer of 0 to 4, and n represents 0 or 1.

  Examples of the monovalent organic group having 1 to 12 carbon atoms include the same functional groups as described above.

  The divalent organic group having 1 to 12 carbon atoms includes a divalent hydrocarbon group having 1 to 12 carbon atoms, a divalent halogenated hydrocarbon group having 1 to 12 carbon atoms, an oxygen atom, and a nitrogen atom. A divalent hydrocarbon group having 3 to 12 carbon atoms containing at least one atom selected from the above, and a divalent hydrocarbon having 3 to 12 carbon atoms containing at least one atom selected from the group consisting of an oxygen atom and a nitrogen atom And halogenated hydrocarbon groups.

  Examples of the divalent hydrocarbon group having 1 to 12 carbon atoms include a linear or branched divalent hydrocarbon group having 1 to 12 carbon atoms, a divalent alicyclic hydrocarbon group having 3 to 12 carbon atoms, and Examples thereof include a bivalent aromatic hydrocarbon group having 6 to 12 carbon atoms.

  Examples of the linear or branched divalent hydrocarbon group having 1 to 12 carbon atoms include a methylene group, an ethylene group, a trimethylene group, an isopropylidene group, a pentamethylene group, a hexamethylene group, and a heptamethylene group.

  Examples of the divalent alicyclic hydrocarbon group having 3 to 12 carbon atoms include cycloalkylene groups such as cyclopropylene group, cyclobutylene group, cyclopentylene group and cyclohexylene group; cyclobutenylene group, cyclopentenylene group and And cycloalkenylene groups such as a cyclohexenylene group.

  Examples of the divalent aromatic hydrocarbon group having 6 to 12 carbon atoms include a phenylene group, a naphthylene group, and a biphenylene group.

  Examples of the divalent halogenated hydrocarbon group having 1 to 12 carbon atoms include a linear or branched divalent halogenated hydrocarbon group having 1 to 12 carbon atoms and a divalent halogenated fat having 3 to 12 carbon atoms. Examples thereof include a cyclic hydrocarbon group and a divalent halogenated aromatic hydrocarbon group having 6 to 12 carbon atoms.

  Examples of the linear or branched divalent halogenated hydrocarbon group having 1 to 12 carbon atoms include a difluoromethylene group, a dichloromethylene group, a tetrafluoroethylene group, a tetrachloroethylene group, a hexafluorotrimethylene group, and a hexachlorotrimethylene group. Group, hexafluoroisopropylidene group, hexachloroisopropylidene group and the like.

  As the divalent halogenated alicyclic hydrocarbon group having 3 to 12 carbon atoms, at least a part of the hydrogen atoms exemplified in the divalent alicyclic hydrocarbon group having 3 to 12 carbon atoms is a fluorine atom. , A group substituted with a chlorine atom, a bromine atom, or an iodine atom.

  As the divalent halogenated aromatic hydrocarbon group having 6 to 12 carbon atoms, at least a part of the hydrogen atoms exemplified in the divalent aromatic hydrocarbon group having 6 to 12 carbon atoms is a fluorine atom, chlorine And a group substituted with an atom, a bromine atom, or an iodine atom.

  Examples of the C1-C12 hydrocarbon group containing at least one atom selected from the group consisting of an oxygen atom and a nitrogen atom include an ether bond, a carbonyl group, an ester group, and an amide group. Valent hydrocarbon group and the like.

  Specifically, the divalent halogenated hydrocarbon group having 1 to 12 carbon atoms containing at least one atom selected from the group consisting of oxygen atom and nitrogen atom is specifically selected from the group consisting of oxygen atom and nitrogen atom A group in which at least part of the hydrogen atoms exemplified in the divalent hydrocarbon group having 1 to 12 carbon atoms containing at least one kind of atom is substituted with a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, etc. Is mentioned.

In said formula (4), R < ⁷ >, R < ⁸ >, Y, m, g, and h are synonymous with R < ⁷ >, R < ⁸ >, Y, m, g, and h in said formula (2), respectively, R < ⁵ > , R ⁶ , Z, n, e and f have the same meanings as R ⁵ , R ⁶ , Z, n, e and f in the formula (3), respectively. When m is 0, R ⁷ is not a cyano group.

  In the polymer, the molar ratio between the structural unit (i) and the structural unit (ii) (however, the sum of both ((i) + (ii)) is 100) has optical properties and heat resistance. From the viewpoints of sex and mechanical properties, (i) :( ii) = 50: 50 to 100: 0 is preferable, and (i) :( ii) = 70: 30 to 100: 0 is more preferable. , (I) :( ii) = 80: 20 to 100: 0 is more preferable.

Here, the mechanical properties refer to properties such as the tensile strength, breaking elongation and tensile elastic modulus of the polymer.
The polymer preferably contains 70 mol% or more of the structural unit (i) and the structural unit (ii) in the total structural unit from the viewpoints of optical properties, heat resistance and mechanical properties, and 95 mol in the total structural unit. It is more preferable that it contains more than%.

  Examples of the polymer include a compound represented by the following formula (5) (hereinafter also referred to as “compound (5)”) and a compound represented by the following formula (7) (hereinafter also referred to as “compound (7)”). A component containing at least one compound selected from the group consisting of (hereinafter also referred to as “component (A)”) and a component containing a compound represented by the following formula (6) (hereinafter also referred to as “component (B)”). ) Can be obtained by reaction.

  In said formula (5), X shows a halogen atom independently.

In the formula ^(7), R ^7, R 8, Y, m, g and h are the ^R 7 of each of the formulas ^(2), R 8, Y, m, and g and h synonymous, X is And has the same meaning as X in the formula (5). However, when m is 0, R ⁷ is not a cyano group.

In the formula (6), R ^a represents a hydrogen atom, a methyl group, an ethyl group, an acetyl group, a methanesulfonyl group or a trifluoromethylsulfonyl group, and among them, a hydrogen atom is preferable. In the formula ^(6), R 1 to R ⁴ and a~d are respectively the same as ^R 1 to R ⁴ and a~d of the formula (1).

  Specific examples of the compound (5) include 2,6-difluorobenzonitrile, 2,5-difluorobenzonitrile, 2,4-difluorobenzonitrile, 2,6-dichlorobenzonitrile, and 2,5-dichloro. Mention may be made of benzonitrile, 2,4-dichlorobenzonitrile and its reactive derivatives. In particular, 2,6-difluorobenzonitrile and 2,6-dichlorobenzonitrile are preferably used from the viewpoints of reactivity and economy. These compounds can be used in combination of two or more.

  As the compound represented by the above formula (6) (hereinafter also referred to as “compound (6)”), specifically, 9,9-bis (4-hydroxyphenyl) fluorene, 9,9-bis (3- Phenyl-4-hydroxyphenyl) fluorene, 9,9-bis (3,5-diphenyl-4-hydroxyphenyl) fluorene, 9,9-bis (4-hydroxy-3-methylphenyl) fluorene, 9,9-bis (4-hydroxy-3,5-dimethylphenyl) fluorene, 9,9-bis (4-hydroxy-3-cyclohexylphenyl) fluorene, and reactive derivatives thereof. Among the above-mentioned compounds, 9,9-bis (4-hydroxyphenyl) fluorene and 9,9-bis (3-phenyl-4-hydroxyphenyl) fluorene are preferably used. These compounds can be used in combination of two or more.

  Specific examples of the compound (7) include 4,4′-difluorobenzophenone, 4,4′-difluorodiphenylsulfone, 2,4′-difluorobenzophenone, 2,4′-difluorodiphenylsulfone, 2,2 '-Difluorobenzophenone, 2,2'-difluorodiphenylsulfone, 3,3'-dinitro-4,4'-difluorobenzophenone, 3,3'-dinitro-4,4'-difluorodiphenylsulfone, 4,4'- Dichlorobenzophenone, 4,4'-dichlorodiphenylsulfone, 2,4'-dichlorobenzophenone, 2,4'-dichlorodiphenylsulfone, 2,2'-dichlorobenzophenone, 2,2'-dichlorodiphenylsulfone, 3,3 ' -Dinitro-4,4'-dichlorobenzophenone and 3,3 ' Dinitro-4,4'-dichloro diphenyl sulfone, and the like. These compounds can be used in combination of two or more.

  At least one compound selected from the group consisting of compound (5) and compound (7) is preferably contained in 80 mol% to 100 mol% in 100 mol% of component (A), preferably 90 mol% to 100 mol. More preferably, it is contained in mol%.

  Moreover, it is preferable that (B) component contains the compound represented by following formula (8) as needed. Compound (6) is preferably contained in 80 mol% to 100 mol%, and more preferably 90 mol% to 100 mol%, in 100 mol% of component (B).

In the formula ^(8), R ^5, R 6, Z, n, e and f are the ^R 5 of each of the formulas ^(3), R 6, Z, and n, e and f synonymous, ^{R a} Is synonymous with R ^a in the formula (6).

  Examples of the compound represented by the formula (8) include hydroquinone, resorcinol, 2-phenylhydroquinone, 4,4′-biphenol, 3,3′-biphenol, 4,4′-dihydroxydiphenylsulfone, and 3,3′-dihydroxy. Diphenylsulfone, 4,4′-dihydroxybenzophenone, 3,3′-dihydroxybenzophenone, 1,1′-bi-2-naphthol, 1,1′-bi-4-naphthol, 2,2-bis (4-hydroxy) Phenyl) propane, 2,2-bis (4-hydroxyphenyl) -1,1,1,3,3,3-hexafluoropropane and reactive derivatives thereof. These compounds can be used in combination of two or more.

  Among the above-mentioned compounds, 4,4′-biphenol is preferably used from the viewpoint of reactivity and mechanical properties.

More specifically, the polymer can be synthesized by the following method (I).
The compound (6) contained in the component (B) is reacted with an alkali metal compound in an organic solvent to obtain the alkali metal salt of the compound (6), and then the obtained alkali metal salt and the component (A) The contained compound (5) and / or compound (7) are reacted. The reaction between the compound (6) and the alkali metal compound is carried out in the presence of the compound (5) and / or the compound (7), so that the alkali metal salt of the compound (6) and the compound (5) and / or the compound are used. (7) can also be reacted.

  Examples of the alkali metal compound used in the reaction include alkali metals such as lithium, potassium and sodium; alkali hydrides such as lithium hydride, potassium hydride and sodium hydride; lithium hydroxide, potassium hydroxide and sodium hydroxide And alkali metal carbonates such as lithium hydrogen carbonate, potassium hydrogen carbonate and sodium hydrogen carbonate. These can be used alone or in combination of two or more.

The amount of the alkali metal compound is usually 1 to 3 times equivalent to one ^{-O-R a} in the formula (6), preferably 1.1 to 2 equivalents, more preferably 1. It is 2-1.5 times equivalent.

  Examples of the organic solvent used in the reaction include N, N-dimethylacetamide, N, N-dimethylformamide, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, γ-butyllactone, Sulfolane, dimethyl sulfoxide, diethyl sulfoxide, dimethyl sulfone, diethyl sulfone, diisopropyl sulfone, diphenyl sulfone, diphenyl ether, benzophenone, dialkoxybenzene (1 to 4 carbon atoms of alkoxy group) and trialkoxybenzene (1 to 4 carbon atoms of alkoxy group) ) Etc. can be used. Among these solvents, polar organic solvents having a high dielectric constant such as N-methyl-2-pyrrolidone, N, N-dimethylacetamide, sulfolane, diphenylsulfone, and dimethylsulfoxide are particularly preferably used.

  Further, in the reaction, a solvent azeotropic with water such as benzene, toluene, xylene, hexane, cyclohexane, octane, chlorobenzene, dioxane, tetrahydrofuran, anisole and phenetole can be further used.

  The proportion of component (A) and component (B) used is preferably 45 mol% or more and 55 mol% or less when component (A) is 100 mol% when the total of component (A) and component (B) is 100 mol%. More preferably, it is 50 mol% or more and 52 mol% or less, More preferably, it exceeds 50 mol% and is 52 mol% or less, and (B) component becomes like this. Preferably it is 45 mol% or more and 55 mol% or less, More preferably, it is 48 mol%. It is at least 50 mol%, more preferably at least 48 mol% but less than 50 mol%.

  Moreover, reaction temperature becomes like this. Preferably it is 60 to 250 degreeC, More preferably, it is the range of 80 to 200 degreeC. The reaction time is preferably in the range of 15 minutes to 100 hours, more preferably 1 hour to 24 hours.

  The polymer preferably has a weight average molecular weight (Mw) in terms of polystyrene measured by an HLC-8220 GPC apparatus (column: TSKgel α-M, developing solvent: tetrahydrofuran (hereinafter also referred to as “THF”) manufactured by TOSOH. It is 5,000-500,000, More preferably, it is 15,000-400,000, More preferably, it is 30,000-300,000.

  The polymer preferably has a glass transition temperature (Tg) of 230-350 ° C., preferably 240-330 ° C., measured by a Rigaku 8230 DSC measuring device (heating rate 20 ° C./min). Is more preferable, and it is more preferable that it is 250-300 degreeC.

  The polarizer protective film of the present invention has excellent heat resistance by including a polymer having such a glass transition temperature. Therefore, the obtained polarizing plate can be disposed close to the light source, and by using such a polarizing plate, the display device can be reduced in height.

  The polymer has a thermal decomposition temperature measured by thermogravimetric analysis: TGA of preferably 450 ° C. or higher, more preferably 475 ° C. or higher, and further preferably 490 ° C. or higher.

  Although it does not restrict | limit especially as a manufacturing method of the polarizer protective film of this invention, apply | coat the resin composition containing the said polymer on a board | substrate, form a coating film, and then remove an organic solvent from this coating film And a method of forming a film on the substrate.

  By forming the film by such a method, it is possible to prevent the resin molecules from being oriented in a certain direction, so that a film having a smaller retardation can be obtained.

  The resin composition preferably contains the polymer and an organic solvent.

  As such a resin composition, a mixture of the polymer obtained by the method (I) and an organic solvent can be used as it is. By using such a resin composition, a polarizer protective film can be easily produced at a low cost.

  The resin composition is prepared by isolating (purifying) the polymer as a solid component from the mixture of the polymer and the organic solvent obtained by the above method, and then re-dissolving the resin composition in the organic solvent. It can also be prepared.

  The method for isolating (purifying) the polymer as a solid component can be performed, for example, by reprecipitation of the polymer in a poor solvent of the polymer such as methanol, followed by filtration and then drying under reduced pressure. As the organic solvent for dissolving the polymer, for example, methylene chloride, tetrahydrofuran, cyclohexanone, N, N-dimethylformamide, N, N-dimethylacetamide, N-methylpyrrolidone and γ-butyrolactone are preferably used. From the viewpoint of coatability and economy, methylene chloride, N, N-dimethylacetamide and N-methylpyrrolidone are preferably used. These solvents can be used alone or in combination of two or more.

  The polymer concentration in the resin composition in which the polymer is dissolved is usually 5 to 40% by weight, preferably 7 to 25% by weight, although it depends on the molecular weight of the polymer. If it is less than 5% by weight, it is difficult to form a thick film, and pinholes are likely to be generated. On the other hand, if it exceeds 40% by weight, the viscosity of the resin composition is so high that it is difficult to form a film, and surface smoothness may be lacking.

  The viscosity of the resin composition is usually 2,000 to 100,000 mPa · s, preferably 3,000 to 50,000 mPa · s, although it depends on the molecular weight and concentration of the polymer. If it is less than 2,000 mPa · s, the resin composition during film formation is poorly retained and may flow down from the substrate. On the other hand, when it exceeds 100,000 mPa · s, the viscosity is too high, it is difficult to adjust the film thickness, and it may be difficult to form the film.

  Moreover, an anti-aging agent can be further contained in the resin composition, and the durability of the resulting film can be further improved by containing the anti-aging agent.

  As the anti-aging agent, a hindered phenol compound having a molecular weight of 500 or more is preferable.

  Examples of hindered phenol compounds having a molecular weight of 500 or more that can be used in the present invention include triethylene glycol-bis [3- (3-tert-butyl-5-methyl-4-hydroxyphenyl) proonate], 1,6. -Hexanediol-bis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5- Di-tert-butylanilino) -3,5-triazine, pentaerythritol tetrakis [3- (3,5-tert-butyl-4-hydroxyphenyl) propionate], 1,1,3-tris [2-methyl-4- [3- (3,5-Di-tert-butyl-4-hydroxyphenyl) propionyloxy] -5-tert-buty Phenyl] butane, 2,2-thio-diethylenebis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], octadecyl-3- (3,5-di-tert-butyl-4 -Hydroxyphenyl) propionate), N, N-hexamethylenebis (3,5-di-tert-butyl-4-hydroxy-hydrocinnamamide), 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) benzene, tris- (3,5-di-tert-butyl-4-hydroxybenzyl) -isocyanurate and 3,9-bis [2 -[3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propionyloxy] -1,1-dimethylethyl] -2,4,8,10- , And the like tiger-oxa-spiro [5.5] undecane.

  In the present invention, the hindered phenol compound having a molecular weight of 500 or more with respect to 100 parts by weight of the polymer is preferably used in an amount of 0.01 to 10 parts by weight.

  Examples of a method for forming a coating film by applying the resin composition on a substrate include a roll coating method, a gravure coating method, a spin coating method, and a method using a doctor blade. Although the thickness of a coating film is not specifically limited, For example, it is 1-250 micrometers, Preferably it is 2-150 micrometers, More preferably, it is 5-125 micrometers. Examples of the substrate include a polyethylene terephthalate (PET) film and a SUS plate.

  Further, the method for removing the organic solvent from the coating film is not particularly limited, and examples thereof include a method of heating the coating film. By heating the coating film, the organic solvent in the coating film can be evaporated and removed. The heating condition may be determined as long as the organic solvent evaporates, and may be appropriately determined according to the substrate and the polymer. For example, the heating temperature is preferably 30 ° C to 300 ° C, and preferably 40 ° C to 250 ° C. Is more preferable, and it is still more preferable that it is 50 to 230 degreeC.

  Further, the heating time is preferably 10 minutes to 5 hours. Heating may be performed in two stages. Specifically, after drying at a temperature of 30 to 80 ° C. for 10 minutes to 2 hours, heating is further performed at 100 to 250 ° C. for 10 minutes to 2 hours. Further, if necessary, drying may be performed under a nitrogen atmosphere or under reduced pressure.

  The obtained film can be used after being peeled off from the substrate, or can be used as it is without being peeled off.

Although the thickness of the film of this invention is suitably selected according to a desired use, Preferably it is 1-250 micrometers, More preferably, it is 2-150 micrometers, More preferably, it is 10-125 micrometers.
In consideration of film retardation, polarizing plate and weight reduction of display measures, etc., it is preferable that the film thickness is thin.

  The film of the present invention preferably has a glass transition temperature (Tg) of 230-350 ° C., 240-330 ° C., measured by Rigaku 8230 DSC measuring device (temperature increase rate 20 ° C./min). Is more preferable, and it is more preferable that it is 250-300 degreeC. It can use suitably as a polarizer protective film because a glass transition temperature exists in such a range.

  Moreover, when the film of this invention is 30 micrometers in thickness, it is preferable that the total light transmittance in a JIS K7105 transparency test method is 85% or more, and it is more preferable that it is 88% or more. The total light transmittance can be measured using a haze meter SC-3H (manufactured by Suga Test Instruments Co., Ltd.).

  When the thickness of the film of the present invention is 30 μm, the light transmittance at a wavelength of 400 nm is preferably 70% or more, more preferably 75% or more, and further preferably 80% or more. The light transmittance at a wavelength of 400 nm can be measured using an ultraviolet / visible spectrophotometer V-570 (manufactured by JASCO).

  When the transmittance of the film of the present invention is in such a range, it has a particularly high light transmittance. For this reason, it can use suitably for a polarizing plate.

  When the thickness of the film of the present invention is 30 μm, the YI value (yellow index) is preferably 3.0 or less, more preferably 2.5 or less, and 2.0 or less. Is more preferable. The YI value can be measured using an SM-T color measuring device manufactured by Suga Test Co., Ltd. When the YI value is in such a range, a film that is difficult to be colored can be obtained, and can be suitably used as a polarizer protective film.

  Moreover, when the film of this invention is 30 micrometers in thickness, it is preferable that YI value after heating for 1 hour at 230 degreeC in air | atmosphere with a hot air dryer is 3.0 or less. It is more preferably 5 or less, and further preferably 2.0 or less. When the YI value is in such a range, a film that is difficult to be colored even at high temperatures can be obtained, and can be suitably used as a polarizer protective film.

  The film of the present invention preferably has a refractive index of 1.55 to 1.75, more preferably 1.60 to 1.70 with respect to light having a wavelength of 633 nm. The refractive index can be measured using a haze meter SC-3H (manufactured by Suga Test Instruments Co., Ltd.).

  The film of the present invention preferably has a tensile strength of 50 to 200 MPa, and more preferably 80 to 150 MPa. The tensile strength can be measured using a tensile tester 5543 (manufactured by INSTRON).

  The film of the present invention preferably has an elongation at break of 10 to 100%, more preferably 15 to 100%. The elongation at break can be measured using a tensile tester 5543 (manufactured by INSTRON).

  The film of the present invention preferably has a tensile modulus of 2.5 to 4.0 GPa, more preferably 2.7 to 3.7 GPa. The tensile elastic modulus can be measured using a tensile tester 5543 (manufactured by INSTRON).

  When the film of the present invention has such a mechanical characteristic, the strength of the polarizer can be sufficiently reinforced even if the film is thin. Therefore, a light and thin polarizing plate with excellent optical properties can be manufactured.

  When the film of the present invention has a thickness of 30 μm, the thickness direction retardation (Rth) is preferably 100 nm or less, more preferably 50 nm or less, and even more preferably 10 nm or less. The phase difference can be measured using a RETS spectrometer manufactured by Otsuka Electronics.

  When the film of the present invention has such a low retardation, an optically isotropic film can be obtained, and when a polarizing plate comprising the film is used in a display device or the like, uneven color on the display surface Interference fringes appear and display quality and deterioration of polarization characteristics can be suitably prevented. Therefore, the film of the present invention can be suitably used as a polarizer protective film for polarizing plates used in display devices and the like.

  The film of the present invention has a linear expansion coefficient of preferably 80 ppm / K or less, more preferably 75 ppm / K or less, measured using an SSC-5200 type TMA measuring device manufactured by Seiko Instruments.

  The film of the present invention preferably has a humidity expansion coefficient of 15 ppm / K or less, and more preferably 12 ppm / K or less. The humidity expansion coefficient can be measured using MA (SII Nanotechnology, TMA-SS6100) humidity control option. When the expansion coefficient of the film is in the above range, it indicates that the dimensional stability (environmental reliability) of the film is high, so that it can be more suitably used as a polarizer protective film.

<Polarizing plate>
The polarizing plate of the present invention is characterized by comprising the polarizer protective film of the present invention on at least one surface of a polarizer.
For this reason, even when a polarizer containing polyvinyl alcohol, which will be described later, is used as the polarizer, it is possible to obtain a polarizing plate having excellent optical characteristics that can withstand the contraction and expansion of the polarizer.
In addition, since the polarizer protective film has high heat resistance, it is possible to dispose the polarizing plate close to the light source. By using such a polarizing plate, it is possible to reduce the height of the display device.

  The structure of the polarizing plate of the present invention is not particularly limited, and may be a structure in which a polarizer protective film is laminated on one surface of a polarizer, or a structure in which a polarizer protective film is laminated on both sides of a polarizer. It may be.

  The polarizer used in the present invention is not particularly limited. For example, a polarizer obtained by uniaxial stretching after dyeing a polyvinyl alcohol film with iodine and / or a dichroic dye; It is a known polarizer such as a polyene polarizer such as polyvinyl chloride treated with hydrochloric acid; a reflective polarizer using a multilayer laminate or a cholesteric liquid crystal; a polarizer comprising a thin film crystal film; The thickness of the polarizer is not particularly limited, and is generally about 5 to 100 μm.

  The method for laminating the polarizer and the polarizer protective film is not particularly limited, but an adhesive or an adhesive can be used. These pressure-sensitive adhesives and adhesives are preferably excellent in transparency. Specific examples include natural rubber, synthetic rubber, vinyl acetate / vinyl chloride copolymer, polyvinyl ether, acrylic, modified polyolefin, and isocyanates. Examples thereof include a curable pressure-sensitive adhesive to which a curing agent such as nate is added, an adhesive for dry lamination in which a polyurethane resin solution and a polyisocyanate resin solution are mixed, a synthetic rubber adhesive, and an epoxy adhesive. Moreover, as long as the function of a polarizer is not impaired, you may laminate | stack by thermocompression bonding.

  The polarizing plate of the present invention may have any member in addition to the polarizer and the polarizer protective film of the present invention. Examples of the member include a TAC film, a polycarbonate film, a cyclic polyolefin film, an acrylic resin film, a polyethylene terephthalate film, and a polynaphthalene terephthalate film.

  In addition, the polarizing plate of the present invention may have a hard coat layer for the purpose of improving its surface characteristics, for example, scratch resistance, and is subjected to a known antiglare treatment such as an antireflection treatment or a low reflection treatment. You may go.

≪Display device≫
The display device of the present invention includes the polarizing plate of the present invention. Therefore, a display device with excellent display characteristics can be obtained.
Examples of the display device include various liquid crystal display devices such as a touch panel, a mobile phone, a digital information terminal, a pager, navigation, an in-vehicle liquid crystal display, a liquid crystal monitor, a light control panel, a display for OA equipment, and a display for AV equipment. It is done.

  Hereinafter, the present invention will be specifically described by way of examples.

(1) Structural analysis The structural analysis of the polymers obtained in the following examples was performed by IR (ATR method, FT-IR, 6700, manufactured by NICOLET) and NMR (ADVANCE500 type, manufactured by BRUKAAR).

(2) Weight average molecular weight (Mw), number average molecular weight (Mw) and molecular weight distribution The weight average molecular weight (Mw), number average molecular weight (Mw) and molecular weight distribution of the polymers obtained in the following examples are the HLC manufactured by TOSOH. -8220 type GPC apparatus (column: TSKgel α-M, developing solvent: tetrahydrofuran (hereinafter also referred to as “THF”)).

(3) Glass transition temperature (Tg)
The glass transition temperatures of the polymers or films obtained in the following examples and comparative examples were measured using a Rigaku 8230 type DSC measuring apparatus at a temperature rising rate of 20 ° C./min.

(3 ') Thermal decomposition temperature The thermal decomposition temperature of the polymers obtained in the following examples and comparative examples was determined by thermogravimetric analysis (TGA: temperature increase rate of 10 ° C / min under nitrogen atmosphere, 5% weight loss temperature). It was measured.

(4) Mechanical strength The film obtained in the following examples and comparative examples was measured for the tensile strength, breaking elongation, and tensile modulus at room temperature according to JIS K7127 using a tensile tester 5543 (manufactured by INSTRON). did.

(5) Environmental stability The linear expansion coefficient of the film obtained by the following Example and the comparative example was measured using SSC-5200 type | mold TMA measuring apparatus by Seiko Instruments. Once the temperature was raised to 280 ° C., the linear expansion coefficient was calculated from the gradient at 200 to 100 ° C. when the temperature was lowered at 3 ° C./min.

The humidity expansion coefficient of the films obtained in the following examples and comparative examples was measured under the following conditions using MA (manufactured by SII Nanotechnology, TMA-SS6100) humidity control option.
Humidity condition: 40% RH → 70% RH (Tensile method: Weight 5 g) Temperature: 23 ° C.

(6) Optical properties The films obtained in the following examples and comparative examples were measured for total light transmittance and yellow index (YI value) according to the JIS K7105 transparency test method. Specifically, the total light transmittance and YI value of the base material were measured using a SM-T type color measuring instrument manufactured by Suga Test Co., Ltd. (YI before heating). Moreover, after heating the base material obtained by the following Example and the comparative example at 230 degreeC in air | atmosphere for 1 hour with a hot air dryer, YI value was used for the Suga Test Co., Ltd. SM-T type | mold color measuring device. (YI after heating). The measurement was performed according to JIS Z 8722 conditions.

  Moreover, the phase difference (Rth) of the base materials obtained in the following Examples and Comparative Examples was measured using a RETS spectrometer manufactured by Otsuka Electronics. In addition, the reference wavelength at the time of measurement was 589 nm, and the evaluation film thickness of the retardation was shown as a value normalized to 30 μm.

(7) Evaluation of Polarizing Plate Two 10 cm × 10 cm polarizing plates were cut out as test pieces from the polarizing plates obtained in the following Examples and Comparative Examples. Each polarizing plate was observed obliquely for color unevenness and interference fringes, and evaluated according to the following criteria. In addition, the two polarizing plates were overlapped so that their polarization axes were orthogonal to each other, visually observed to observe light leakage, and evaluated according to the following criteria.
<Evaluation of uneven color>
○: Uneven color is not visible.
Δ: Color unevenness is slightly visible.
X: Color irregularity is conspicuous.
<Evaluation of interference fringes>
○: Interference fringes are not visible.
Δ: Interference fringes are slightly visible.
X: Interference fringes are conspicuous.
<Evaluation of light leakage>
○: No light leakage is visible over the entire surface.
Δ: Some light leakage is visible.
X: Light leakage is conspicuous.

[Example 1]
In a 3 L four-necked flask, component (A): 35.12 g (0.253 mol) of 2,6-difluorobenzonitrile (hereinafter also referred to as “DFBN”), component (B): 9,9-bis (4 -Hydroxyphenyl) fluorene (hereinafter also referred to as “BPFL”) 70.08 g (0.200 mol), resorcinol (hereinafter also referred to as “RES”) 5.51 g (0.050 mol), 41.46 g of potassium carbonate ( 0.300 mol), 443 g of N, N-dimethylacetamide (hereinafter also referred to as “DMAc”) and 111 g of toluene were added. Subsequently, a thermometer, a stirrer, a three-way cock with a nitrogen introduction tube, a Dean-Stark tube and a cooling tube were attached to the four-necked flask.
Next, after the atmosphere in the flask was replaced with nitrogen, the obtained solution was reacted at 140 ° C. for 3 hours, and water produced was removed from the Dean-Stark tube as needed. When no more water was observed, the temperature was gradually raised to 160 ° C. and reacted at that temperature for 6 hours.
After cooling to room temperature (25 ° C.), the produced salt was removed with a filter paper, the filtrate was poured into methanol for reprecipitation, and the filtrate (residue) was isolated by filtration. The obtained filtrate was vacuum dried at 60 ° C. overnight to obtain a white powder (polymer) (yield 95.67 g, yield 95%).

Table 1 shows the physical properties of the obtained polymer. The obtained polymer was subjected to a structural analysis and a weight average molecular weight measurement. As a result, the characteristic absorption of the infrared absorption spectrum is 3035 (C—H stretching), 2229 cm ⁻¹ (CN), 1574 cm ⁻¹ , 1499 cm ⁻¹ (aromatic ring skeleton absorption), 1240 cm ⁻¹ (—O—). The weight average molecular weight was 130,000.

  Next, the obtained polymer was redissolved in DMAc to obtain a resin composition having a polymer concentration of 20% by mass. The resin composition is applied onto a substrate made of polyethylene terephthalate (PET) using a doctor blade, dried at 70 ° C. for 30 minutes, and then dried at 100 ° C. for 30 minutes to form a film. It peeled. Thereafter, the film was fixed to a metal frame and further dried at 230 ° C. for 2 hours to obtain an evaluation film having a thickness of 30 μm.

    Table 1 shows the physical properties of the obtained film for evaluation.

  In addition, a PVA film (75 μm) manufactured by Kuraray Co., Ltd. was immersed in an aqueous solution of 0.3 g / L iodine and 18.0 g / L potassium iodide at 25 ° C., and further 80 g / L boric acid, 30 g potassium iodide / L, stretched 5.0 times in an aqueous solution of 10 g / L of ferrous chloride and 50 ° C. Dry at 60 ° C. for 5 minutes. A polarizing plate was produced by sticking the film to both sides of the polarizer thus produced via a silicone adhesive [Konishi Co., Ltd., Silex Clear]. As a result of evaluating the obtained polarizing plate, uneven color, interference fringes and light leakage were not observed.

[Example 2]
The same procedure as in Example 1 was performed except that 11.41 g (0.050 mol) of 2,2-bis (4-hydroxyphenyl) propane was used instead of resorcinol. Table 1 shows the physical properties of the obtained polymer, film and polarizing plate.

[Example 3]
As component (B), instead of 70.08 g of BPFL and 5.51 g of RES, 78.84 g (0.225 mol) of 9,9-bis (4-hydroxyphenyl) fluorene and 2,2-bis (4-hydroxyphenyl)- The same operation as in Example 1 was conducted except that 8.41 g (0.025 mol) of 1,1,1,3,3,3-hexafluoropropane was used. Table 1 shows the physical properties of the obtained polymer, film and polarizing plate.

[Example 4]
As component (B), in the same manner as in Example 1, except that 87.60 g (0.250 mol) of 9,9-bis (4-hydroxyphenyl) fluorene was used instead of 70.08 g of BPFL and 5.51 g of RES. . Table 1 shows the physical properties of the obtained polymer, film and polarizing plate.

[Example 5]
As component (B), instead of 70.08 g of BPFL and 5.51 g of RES, 78.84 g (0.225 mol) of 9,9-bis (4-hydroxyphenyl) fluorene and 9,9-bis (4-hydroxyphenyl) cyclohexane The same operation as in Example 1 was conducted except that 6.71 g (0.025 mol) was used. Table 1 shows the physical properties of the obtained polymer, film and polarizing plate.

[Example 6]
Example (A) Except for using 35.12 g of DFBN, 28.10 g (0.202 mol) of 2,6-difluorobenzonitrile and 11.02 g (0.051 mol) of 4,4-difluorobenzophenone were used instead of 35.12 g of DFBN. Same as 5 Table 1 shows the physical properties of the obtained polymer, film and polarizing plate.

[Example 7]
(A) It is the same as that of Example 7 except having changed the compounding quantity of the component into 17.56 g (0.126 mol) of 2, 6- difluoro benzonitrile and 27.55 g (0.126 mol) of 4, 4- difluoro benzophenone. went. Table 1 shows the physical properties of the obtained polymer, film and polarizing plate.

[Example 8]
The same procedure as in Example 5 was performed except that 78.84 g (0.250 mol) of 4,4-difluorodiphenylsulfone (DFDS) was used as the component (A). Table 1 shows the physical properties of the obtained polymer and film.

[Comparative Example 1]
As component (B), instead of 70.08 g of BPFL and 5.51 g of RES, 84.06 g of 2,2-bis (4-hydroxyphenyl) -1,1,1,3,3,3-hexafluoropropane (0. 250 mol) was used in the same manner as in Example 1. Table 1 shows the physical properties of the obtained polymer, film and polarizing plate.

[Comparative Example 2]
Polyethylene naphthalate film manufactured by Teijin Limited: Neotex was used, and evaluation and production of a polarizing plate were carried out in the same manner as in Example 1 (film thickness 125 μm). Table 1 shows the physical properties of the obtained film and polarizing plate.

[Comparative Example 3]
9.70 g (23.6 mmol) of 2,2-bis [4- (4-aminophenoxy) phenyl] propane was added to a 300 mL four-necked flask equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a condenser tube. did. Next, after the atmosphere in the flask was replaced with nitrogen, N-methyl-2-pyrrolidone (NMP) (60 ml) was added and stirred until uniform. To the resulting solution, 5.30 g (23.6 mmol) of 2,3,5-tricarboxycyclopentylacetic acid dianhydride was added at room temperature, and the reaction was continued for 12 hours at the same temperature to obtain a solution containing polyamic acid. Obtained.
After diluting the resulting polyamic acid-containing solution with NMP (75 ml), pyridine (7.5 ml) and acetic anhydride (6.7 ml) were added, and the mixture was stirred at 110 ° C. for 6 hours for imidization. . Then, after cooling to room temperature, it poured into a lot of methanol, and the filtrate was isolated by filtration. The obtained filtrate was vacuum dried at 60 ° C. overnight to obtain a white powder (polymer) (yield 13.5 g, yield 95.3%).

  Next, the obtained polymer was redissolved in DMAc to obtain a 20% by mass resin solution. The resin solution is applied onto a substrate made of polyethylene terephthalate (PET) using a doctor blade (100 μm gap), dried at 100 ° C. for 30 minutes, and then dried at 150 ° C. for 60 minutes to form a film. Peeled from the substrate. Thereafter, the film was further dried at 150 ° C. under reduced pressure for 3 hours to obtain an evaluation film having a thickness of 30 μm. Evaluation and production of the polarizing plate were carried out in the same manner as in Example 1. The results are shown in Table 1.

Claims (10)

A polarizer protective film comprising a polymer having at least one structural unit (i) selected from the group consisting of a structural unit represented by the following formula (1) and a structural unit represented by the following formula (2).

(In Formula (1), R < ¹ > -R < ⁴ > shows a C1-C12 monovalent organic group each independently, and ad shows the integer of 0-4, respectively.)

(In the formula ^(2), R 1 to R ⁴ and a~d are respectively the same as ^R 1 to R ⁴ and a~d of the formula (1), Y is a single bond, -SO ₂ -, or > C = O, R ⁷ and R ⁸ each independently represent a halogen atom, a monovalent organic group having 1 to 12 carbon atoms or a nitro group, and g and h each represents an integer of 0 to 4 M represents 0 or 1. However, when m is 0, R ⁷ is not a cyano group.) 2. The polymer according to claim 1, further comprising at least one structural unit (ii) selected from the group consisting of a structural unit represented by the following formula (3) and a structural unit represented by the following formula (4). Polarizer protective film.

(In Formula (3), R ⁵ and R ⁶ each independently represent a monovalent organic group having 1 to 12 carbon atoms, and Z represents a single bond, —O—, —S—, —SO ₂ —, > C═O, —CONH—, —COO— or a divalent organic group having 1 to 12 carbon atoms, e and f each represents an integer of 0 to 4, and n represents 0 or 1.)

(In the formula ^(4), R ^7, R 8, Y, m, g and h are the ^R 7 of each of the formulas ^(2), R 8, Y, m, and g and h synonymous, ^{R 5} , R ⁶ , Z, n, e and f have the same meanings as R ⁵ , R ⁶ , Z, n, e and f in the formula (3), respectively.   The polarizer protective film of Claim 1 or 2 whose molar ratio of the said structural unit (i) and the said structural unit (ii) is 80: 20-100: 0 in the said polymer.   The polarizer protective film of any one of Claims 1-3 whose weight average molecular weight of polystyrene conversion by the gel permeation chromatography (GPC) of the said polymer is 5,000-500,000.   Polarizer protection according to any one of claims 1 to 4, wherein the polymer has a glass transition temperature (Tg) of 230 to 350 ° C by differential scanning calorimetry (DSC, heating rate 20 ° C / min). the film.   The polarizer protective film of any one of Claims 1-5 whose total light transmittance by JISK7105 transparency test method in thickness of 30 micrometers is 85% or more.   The polarizer protective film of any one of Claims 1-6 whose YI value (yellow index) in thickness of 30 micrometers is 3.0 or less.   The polarizer protective film of any one of Claims 1-7 whose retardation (Rth) of the thickness direction in thickness 30 micrometers is 100 nm or less.   A polarizing plate comprising the polarizer protective film according to claim 1 on at least one surface of the polarizer.   A display device comprising the polarizing plate according to claim 9.