Slowing membrane, circular polarizer plate using this slowing membrane, and image display device.

Abstract

The invention relates to a reverse dispersion retardation film of excellent strength in high temperature and high humidity environments. The retardation film of the invention consists of: a resin with positive refractive index anisotropy, which contains: at least one linkage group selected from the group of: carbonate linkage; and ester linkage; and at least one structural unit selected from the group of: the structural unit represented by general formula (1); and the structural unit represented by general formula (2); and compound (A) containing an aromatic structure and having a molecular weight greater than or equal to 500 and less than or equal to 2,000. The content of compound (A) is greater than 0.5% by weight and less than or equal to 4.0% by weight. The retardation film has Re(550) from 100 nm to 200 nm, and the ratio "Re(450) / Re(550)" is greater than 0.5 and less than 1.0.

Description

Retardation film, circularly polarizing plate using said retardation film, and image display device

[0001] The present invention relates to a retardation film, a circular polarizing plate using the retardation film, and an image display device.

[0002] In recent years, smart devices such as smartphones, as well as display devices such as digital signage and window displays, have increasingly been used under strong ambient light. This has led to problems such as ambient light reflection and background glare caused by the display device itself or by reflectors such as touch panels, glass substrates, and metal wiring used in the display device. In particular, organic electroluminescence (EL) display devices, which have been put into practical use in recent years, are prone to problems such as ambient light reflection and background glare due to their highly reflective metal layers. Therefore, it is known that these problems can be prevented by providing a circular polarizer with a retardation film (typically a λ / 4 plate) as an anti-reflection film on the viewing side. Furthermore, to achieve good retardation characteristics at each wavelength in the visible range, development is underway for retardation films that exhibit wavelength dependence of so-called reverse dispersion, in which the retardation value increases with the wavelength of the measured light (hereinafter sometimes simply referred to as reverse dispersion retardation films). Continuous research is being conducted to further improve the properties of reverse dispersion retardation films.

[0003] Patent No. 3325560

[0004] A primary object of the present invention is to provide a reverse dispersion retardation film that is excellent in durability under high-temperature and high-humidity environments.

[0005] The retardation film of the present invention contains: a resin having positive refractive index anisotropy, the resin including at least one bonding group selected from the group consisting of a carbonate bond and an ester bond, and at least one structural unit selected from the group consisting of a structural unit represented by the following general formula (1) and a structural unit represented by the following general formula (2): In general formulas (1) and (2), R １ ~R ３ are each independently a direct bond or a substituted or unsubstituted alkylene group having 1 to 4 carbon atoms, R ４ ~R ９ are each independently a hydrogen atom, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted aryl group having 4 to 10 carbon atoms, a substituted or unsubstituted acyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 10 carbon atoms, a substituted or unsubstituted aryloxy group having 1 to 10 carbon atoms, a substituted or unsubstituted amino group, a substituted or unsubstituted vinyl group having 1 to 10 carbon atoms, a substituted or unsubstituted ethynyl group having 1 to 10 carbon atoms, a sulfur atom having a substituent, a silicon atom having a substituent, a halogen atom, a nitro group, or a cyano group; ４ ~R ９ may be the same or different, R ４ ~R ９At least two adjacent groups among these may be bonded to each other to form a ring. Re(550) is the in-plane retardation of the film measured at 23°C with light having a wavelength of 550 nm, and Re(450) is the in-plane retardation of the film measured at 23°C with light having a wavelength of 450 nm. In one embodiment, the resin having positive refractive index anisotropy contains 1% by mass to 40% by mass of at least one structural unit selected from the group consisting of structural units represented by general formula (1) and structural units represented by general formula (2). In one embodiment, the resin having positive refractive index anisotropy further contains a structural unit represented by the following general formula (3): In one embodiment, the resin having positive refractive index anisotropy further includes a structural unit represented by the following general formula (4). In one embodiment, the retardation film further contains an acrylic resin, and the content of the acrylic resin is 0.5% by mass or more and 2.0% by mass or less. In one embodiment, the content of the compound (A) is 1.0% by mass or more and 3.0% by mass or less. In one embodiment, the compound (A) is characterized by having a partial structure represented by the following formula (5): According to yet another aspect of the present invention, there is provided a circular polarizing plate. This circular polarizing plate has a polarizer and the above-mentioned retardation film, and the angle between the absorption axis of the polarizer and the slow axis of the retardation film is 40° to 50° or 130° to 140°. According to yet another aspect of the present invention, there is provided an image display device. This image display device includes the above-mentioned circular polarizing plate on the viewing side, and the polarizer of the circular polarizing plate is arranged on the viewing side.

[0006] According to an embodiment of the present invention, by blending a specific compound with a resin having a specific positive refractive index anisotropy (typically, a polycarbonate-based resin, a polyester-based resin, or a polyestercarbonate-based resin), it is possible to obtain a reverse dispersion retardation film having excellent durability in a high-temperature, high-humidity environment.

[0007] 1 is a schematic cross-sectional view of a circular polarizer according to one embodiment of the present invention.

[0008] Representative embodiments of the present invention will be described below, but the present invention is not limited to these embodiments.

[0009] (Definition of Terms and Symbols) The definitions of terms and symbols used in this specification are as follows. (1) Refractive Index (nx, ny, nz) "nx" is the refractive index in the direction in which the in-plane refractive index is maximum (i.e., the slow axis direction), "ny" is the refractive index in the in-plane direction perpendicular to the slow axis (i.e., the fast axis direction), and "nz" is the refractive index in the thickness direction. (2) In-Plane Retardation (Re) "Re(λ)" is the in-plane retardation of a film measured with light having a wavelength of λ nm at 23°C. For example, "Re(450)" is the in-plane retardation of a film measured with light having a wavelength of 450 nm at 23°C. Re(λ) is calculated by the formula: Re = (nx - ny) × d, where d (nm) is the thickness of the film. (3) Thickness Direction Retardation (Rth) "Rth(λ)" is the retardation of a film measured with light having a wavelength of λ nm at 23°C. For example, "Rth(450)" is the retardation in the thickness direction of the film measured with light having a wavelength of 450 nm at 23°C. Rth(λ) is calculated by the formula: Rth = (nx - nz) x d, where d (nm) is the thickness of the film. (4) Nz coefficient The Nz coefficient is calculated by Nz = Rth / Re. (5) Angle When an angle is referred to in this specification, the angle includes angles in both clockwise and counterclockwise directions unless otherwise specified.

[0010] A. Retardation Film The retardation film of the present invention comprises a resin having positive refractive index anisotropy, which contains at least one bonding group selected from the group consisting of a carbonate bond and an ester bond, and at least one structural unit selected from the group consisting of a structural unit represented by the following general formula (1) and a structural unit represented by the following general formula (2):

[0011] A-1. Materials Constituting the Retardation Film The retardation film according to an embodiment of the present invention contains a resin containing at least one bonding group selected from the group consisting of a carbonate bond and an ester bond. In other words, the retardation film contains a polycarbonate-based resin, a polyester-based resin, or a polyestercarbonate-based resin (hereinafter, these may be collectively referred to as polycarbonate-based resins, etc.). The polycarbonate-based resins, etc. contain at least one structural unit selected from the group consisting of structural units represented by the above general formula (1) and / or structural units represented by the above general formula (2). These structural units are structural units derived from divalent oligofluorene, and may be referred to hereinafter as oligofluorene structural units. Such polycarbonate-based resins, etc. have positive refractive index anisotropy.

[0012] The retardation film according to an embodiment of the present invention further contains a modifier. The modifier is a compound (A) containing an aromatic structure and having a molecular weight of 500 or more and 2000 or less. As described above, the content of compound (A) is more than 0.5% by mass and 4.0% by mass or less. In this specification, percentages or parts in "mass" units are synonymous with percentages or parts in "weight" units.

[0013] The retardation film may further contain an acrylic resin, the content of which is 0.5% by mass to 1.5% by mass as described above.

[0014] A-1-1. Polycarbonate Resin, etc. <Oligofluorene Structural Unit> The oligofluorene structural unit is represented by the above general formula (1) or (2). In general formulas (1) and (2), R １ ~R ３ are each independently a direct bond or a substituted or unsubstituted alkylene group having 1 to 4 carbon atoms, R ４ ~R ９ are each independently a hydrogen atom, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted aryl group having 4 to 10 carbon atoms, a substituted or unsubstituted acyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 10 carbon atoms, a substituted or unsubstituted aryloxy group having 1 to 10 carbon atoms, a substituted or unsubstituted amino group, a substituted or unsubstituted vinyl group having 1 to 10 carbon atoms, a substituted or unsubstituted ethynyl group having 1 to 10 carbon atoms, a sulfur atom having a substituent, a silicon atom having a substituent, a halogen atom, a nitro group, or a cyano group, provided that R ４ ~R ９ may be the same or different, R ４ ~R ９ At least two adjacent groups among these may be bonded to each other to form a ring.

[0015] R １ and R ２ As R, for example, the following alkylene groups can be used: linear alkylene groups such as methylene, ethylene, n-propylene, and n-butylene; and branched alkylene groups such as methylmethylene, dimethylmethylene, ethylmethylene, propylmethylene, (1-methylethyl)methylene, 1-methylethylene, 2-methylethylene, 1-ethylethylene, 2-ethylethylene, 1-methylpropylene, 2-methylpropylene, 1,1-dimethylethylene, 2,2-dimethylpropylene, and 3-methylpropylene. １ and R ２The positions of the branched chains in the formula (I) are indicated by numbers assigned so that the carbon atom on the fluorene ring side is at the first position.

[0016] R １ and R ２ The selection of R may be related to the expression of the reverse dispersion wavelength dependency. Polycarbonate resins and the like exhibit the strongest reverse dispersion wavelength dependency when the fluorene rings are oriented perpendicular to the main chain direction (stretching direction). In order to bring the orientation state of the fluorene rings closer to this state and to express a strong reverse dispersion wavelength dependency, it is necessary to select R in which the number of carbon atoms on the main chain of the alkylene group is 2 to 3. １ and R ２ It is preferable to employ the above. When the carbon number is 1, unexpectedly, the reverse dispersion wavelength dependency may not be exhibited. This may be due to the steric hindrance of the carbonate group and / or ester group, which are the linking groups of the oligofluorene structural unit, causing the orientation of the fluorene ring to be fixed in a direction that is not perpendicular to the main chain direction. On the other hand, when the carbon number is too large, the fixation of the orientation of the fluorene ring becomes weak, which may result in insufficient reverse dispersion wavelength dependency. Furthermore, the heat resistance of polycarbonate-based resins and the like may be reduced.

[0017] R ３ As R, for example, the following alkylene groups can be used: linear alkylene groups such as methylene, ethylene, n-propylene, and n-butylene; and branched alkylene groups such as methylmethylene, dimethylmethylene, ethylmethylene, propylmethylene, (1-methylethyl)methylene, 1-methylethylene, 2-methylethylene, 1-ethylethylene, 2-ethylethylene, 1-methylpropylene, 2-methylpropylene, 1,1-dimethylethylene, 2,2-dimethylpropylene, and 3-methylpropylene. ３ The alkylene group preferably has 1 to 2 carbon atoms on the main chain, and more preferably has 1 carbon atom. When the number of carbon atoms on the main chain is too large, R １ and R ２As in the case of (1), the fixation of the fluorene rings is weakened, which may lead to a decrease in the wavelength dependency of reverse dispersion, an increase in the photoelastic coefficient, a decrease in heat resistance, etc. On the other hand, the fewer the number of carbon atoms on the main chain, the better the optical properties and heat resistance, but when the 9-positions of two fluorene rings are connected by a direct bond, the thermal stability may deteriorate.

[0018] R １ ~R ３ Examples of the substituent in include a halogen atom (a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom); an alkoxy group having 1 to 10 carbon atoms, such as a methoxy group or an ethoxy group; an acyl group having 1 to 10 carbon atoms, such as an acetyl group or a benzoyl group; an acylamino group having 1 to 10 carbon atoms, such as an acetamido group or a benzoylamido group; a nitro group; a cyano group; and an aryl group having 6 to 10 carbon atoms, such as a phenyl group or a naphthyl group, in which 1 to 3 hydrogen atoms may be substituted by the halogen atom, the alkoxy group, the acyl group, the acylamino group, the nitro group, the cyano group, or the like.

[0019] R ４ ~R ９ As the substituted or unsubstituted alkyl group in the above, for example, the following alkyl groups can be used: linear alkyl groups such as methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, and n-decyl; branched alkyl groups such as isopropyl, 2-methylpropyl, 2,2-dimethylpropyl, and 2-ethylhexyl; and cyclic alkyl groups such as cyclopropyl, cyclopentyl, cyclohexyl, and cyclooctyl. The number of carbon atoms in the alkyl group is preferably 4 or less, and more preferably 2 or less. When the number of carbon atoms is within this range, steric hindrance between fluorene rings is unlikely to occur, making it easy to obtain desired optical properties derived from the fluorene rings. As the substituent of the alkyl group, R １ ~R ３ Examples of the substituents include those described above for the group.

[0020] R ４ ~R ９As the substituted or unsubstituted aryl group in the above, for example, the following aryl groups can be used: aryl groups such as a phenyl group, a 1-naphthyl group, and a 2-naphthyl group; and heteroaryl groups such as a 2-pyridyl group, a 2-thienyl group, and a 2-furyl group. The number of carbon atoms in the aryl group is preferably 8 or less, and more preferably 7 or less. When the number of carbon atoms is within this range, steric hindrance between the fluorene rings is unlikely to occur, making it easy to obtain the desired optical properties derived from the fluorene rings. As the substituent of the aryl group, R １ ~R ３ Examples of the substituents include those described above for the group.

[0021] R ４ ~R ９ As the substituted or unsubstituted acyl group in the above, for example, the following acyl groups can be used: aliphatic acyl groups such as formyl group, acetyl group, propionyl group, 2-methylpropionyl group, 2,2-dimethylpropionyl group, and 2-ethylhexanoyl group; and aromatic acyl groups such as benzoyl group, 1-naphthylcarbonyl group, 2-naphthylcarbonyl group, and 2-furylcarbonyl group. The number of carbon atoms in the acyl group is preferably 4 or less, and more preferably 2 or less. When the number of carbon atoms is within this range, steric hindrance between the fluorene rings is unlikely to occur, making it easy to obtain the desired optical properties derived from the fluorene rings. As the substituent of the acyl group, R １ ~R ３ Examples of the substituents include those described above for the group.

[0022] R ４ ~R ９ As the substituted or unsubstituted alkoxy group or aryloxy group in the above, for example, the following can be used: methoxy group, ethoxy group, isopropoxy group, tert-butoxy group, trifluoromethoxy group, and phenoxy group. The number of carbon atoms in the alkoxy group or aryloxy group is preferably 4 or less, and more preferably 2 or less. When the number of carbon atoms is within this range, steric hindrance between the fluorene rings is unlikely to occur, making it easy to obtain the desired optical properties derived from the fluorene ring. As the substituent of the alkoxy group or aryloxy group, R １ ~R ３Examples of the substituents include those described above for the group.

[0023] R ４ ~R ９ Examples of the substituted or unsubstituted amino group in the above formula include the following amino groups: amino groups; aliphatic amino groups such as N-methylamino, N,N-dimethylamino, N-ethylamino, N,N-diethylamino, N,N-methylethylamino, N-propylamino, N,N-dipropylamino, N-isopropylamino, and N,N-diisopropylamino; aromatic amino groups such as N-phenylamino and N,N-diphenylamino; acylamino groups such as formamide, acetamide, decanoylamide, benzoylamide, and chloroacetamide; and alkoxycarbonylamino groups such as benzyloxycarbonylamino and tert-butyloxycarbonylamino. N,N-dimethylamino, N-ethylamino, and N,N-diethylamino groups are preferred, with N,N-dimethylamino being more preferred. These groups do not have highly acidic protons, have small molecular weights, and can increase the fluorene ratio.

[0024] R ４ ~R ９ As the substituted or unsubstituted vinyl group or ethynyl group in the above, for example, the following can be used: vinyl group, 2-methylvinyl group, 2,2-dimethylvinyl group, 2-phenylvinyl group, 2-acetylvinyl group, ethynyl group, methylethynyl group, tert-butylethynyl group, phenylethynyl group, acetylethynyl group, and trimethylsilylethynyl group. The number of carbon atoms in the vinyl group or ethynyl group is preferably 4 or less. When the number of carbon atoms is within this range, steric hindrance between fluorene rings is unlikely to occur, making it easier to obtain desired optical properties derived from the fluorene ring. Furthermore, by increasing the length of the conjugated system of the fluorene ring, it becomes easier to obtain stronger reverse dispersion wavelength dependence.

[0025] R ４ ~R ９As the sulfur atom having a substituent in the formula (I), for example, the following sulfur-containing groups can be used: a sulfo group; alkylsulfonyl groups such as a methylsulfonyl group, an ethylsulfonyl group, a propylsulfonyl group, and an isopropylsulfonyl group; arylsulfonyl groups such as a phenylsulfonyl group and a p-tolylsulfonyl group; alkylsulfinyl groups such as a methylsulfinyl group, an ethylsulfinyl group, a propylsulfinyl group, and an isopropylsulfinyl group; arylsulfinyl groups such as a phenylsulfinyl group and a p-tolylsulfinyl group; a methylthio group, an ethylthio group, etc. Alkylthio groups; arylthio groups such as phenylthio and p-tolylthio; alkoxysulfonyl groups such as methoxysulfonyl and ethoxysulfonyl; aryloxysulfonyl groups such as phenoxysulfonyl; aminosulfonyl groups; alkylsulfonyl groups such as N-methylaminosulfonyl, N-ethylaminosulfonyl, N-tert-butylaminosulfonyl, N,N-dimethylaminosulfonyl, and N,N-diethylaminosulfonyl; and arylaminosulfonyl groups such as N-phenylaminosulfonyl and N,N-diphenylaminosulfonyl. The sulfo group may form a salt with lithium, sodium, potassium, magnesium, ammonium, or the like. A methylsulfinyl group, an ethylsulfinyl group, or a phenylsulfinyl group is preferred, with a methylsulfinyl group being more preferred. These groups do not have a highly acidic proton, have a small molecular weight, and can increase the fluorene ratio.

[0026] R ４ ~R ９ As the silicon atom having a substituent in the formula (I), for example, the following silyl groups can be used: trialkylsilyl groups such as trimethylsilyl group and triethylsilyl group; and trialkoxysilyl groups such as trimethoxysilyl group and triethoxysilyl group. Trialkylsilyl groups are preferred because they are superior in stability and ease of handling.

[0027] The content of oligofluorene structural units in polycarbonate-based resins and the like is preferably 1% by mass to 40% by mass, more preferably 10% by mass to 35% by mass, even more preferably 15% by mass to 30% by mass, and particularly preferably 18% by mass to 25% by mass, based on the total resin. If the content of oligofluorene structural units is too high, problems such as an excessively high photoelastic coefficient, insufficient reliability, and insufficient retardation expression may occur. Furthermore, since the proportion of oligofluorene structural units in the resin increases, the molecular design flexibility narrows, and improvements may be difficult when modifications to the resin are required. On the other hand, even if the desired reverse dispersion wavelength dependence is obtained with a very small amount of oligofluorene structural units, in this case, the optical properties change sensitively depending on slight variations in the content of the oligofluorene structural units, making it difficult to manufacture the resin so that the various properties fall within a certain range.

[0028] The method for adjusting the ratio of oligofluorene structural unit in resin can be, for example, copolymerizing the monomer having oligofluorene structural unit with other monomer, or blending the resin containing oligofluorene structural unit with other resin.The method for copolymerizing the monomer having oligofluorene structural unit with other monomer is preferred, because it can precisely control the content of oligofluorene structural unit, obtain high transparency, and obtain uniform properties on the entire surface of the film.

[0029] <Other structural units> Polycarbonate resins etc. can typically comprise other structural units in addition to oligofluorene structural units.In one embodiment, other structural units can preferably be derived from dihydroxy compound or diester compound.In order to realize the desired reverse wavelength dispersion, it is necessary to incorporate the structural unit with positive intrinsic birefringence into polymer structure together with the oligofluorene structural unit with negative intrinsic birefringence, so as other monomers to be copolymerized, more preferably dihydroxy compound or diester compound that can be the raw material of the structural unit with positive birefringence.

[0030] The copolymerizable monomer may be a compound capable of introducing a structural unit containing an aromatic ring, or a compound having an aliphatic structure that does not introduce a structural unit containing an aromatic ring. Specific examples of the compound having an aliphatic structure are listed below. Dihydroxy compounds of straight-chain aliphatic hydrocarbons such as ethylene glycol, 1,3-propanediol, 1,2-propanediol, 1,4-butanediol, 1,3-butanediol, 1,2-butanediol, 1,5-heptanediol, 1,6-hexanediol, 1,9-nonanediol, 1,10-decanediol, and 1,12-dodecanediol; dihydroxy compounds of branched aliphatic hydrocarbons such as neopentyl glycol and hexylene glycol; dihydroxy compounds which are secondary and tertiary alcohols of alicyclic hydrocarbons, exemplified by 1,2-cyclohexanediol, 1,4-cyclohexanediol, 1,3-adamantanediol, hydrogenated bisphenol A, and 2,2,4,4-tetramethyl-1,3-cyclobutanediol; 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, tricyclodecanediol, and the like. dihydroxy compounds which are primary alcohols of alicyclic hydrocarbons, exemplified by dihydroxy compounds derived from terpene compounds such as norbornane dimethanol, pentacyclopentadecanedimethanol, 2,6-decalindimethanol, 1,5-decalindimethanol, 2,3-decalindimethanol, 2,3-norbornane dimethanol, 2,5-norbornane dimethanol, 1,3-adamantanedimethanol, and limonene; oxyalkylene glycols such as diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, and polypropylene glycol; dihydroxy compounds having a cyclic ether structure such as isosorbide; dihydroxy compounds having a cyclic acetal structure such as spiroglycol and dioxane glycol; alicyclic dicarboxylic acids such as 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid;Aliphatic dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid. Specific examples of compounds into which the structural unit containing an aromatic ring can be introduced are listed below. 2,2-bis(4-hydroxyphenyl)propane, 2,2-bis(3-methyl-4-hydroxyphenyl)propane, 2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane, 2,2-bis(4-hydroxy-3,5-diethylphenyl)propane, 2,2-bis(4-hydroxy-(3-phenyl)phenyl)propane, 2,2-bis(4-hydroxy-(3,5-diphenyl)phenyl)propane, 2,2-bis(4-hydroxy-3,5-dibromophenyl)propane, bis(4-hydroxyphenyl)methane, 1,1-bis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl)butane, 2,2-bis(4-hydroxyphenyl)pentane, 1,1-bis(4-hydroxyphenyl)-1-phenylethane, bis(4-hydroxyphenyl)diphenylmethane, 1,1-bis(4-hydroxyphenyl)-2 aromatic bisphenol compounds such as ethylhexane, 1,1-bis(4-hydroxyphenyl)decane, bis(4-hydroxy-3-nitrophenyl)methane, 3,3-bis(4-hydroxyphenyl)pentane, 1,3-bis(2-(4-hydroxyphenyl)-2-propyl)benzene, 1,3-bis(2-(4-hydroxyphenyl)-2-propyl)benzene, 2,2-bis(4-hydroxyphenyl)hexafluoropropane, 1,1-bis(4-hydroxyphenyl)cyclohexane, bis(4-hydroxyphenyl)sulfone, 2,4'-dihydroxydiphenyl sulfone, bis(4-hydroxyphenyl)sulfide, bis(4-hydroxy-3-methylphenyl)sulfide, bis(4-hydroxyphenyl)disulfide, 4,4'-dihydroxydiphenyl ether, and 4,4'-dihydroxy-3,3'-dichlorodiphenyl ether;Dihydroxy compounds having an ether group bonded to an aromatic group, such as 2,2-bis(4-(2-hydroxyethoxy)phenyl)propane, 2,2-bis(4-(2-hydroxypropoxy)phenyl)propane, 1,3-bis(2-hydroxyethoxy)benzene, 4,4'-bis(2-hydroxyethoxy)biphenyl, and bis(4-(2-hydroxyethoxy)phenyl)sulfone; and aromatic dicarboxylic acids such as terephthalic acid, phthalic acid, isophthalic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 4,4'-benzophenonedicarboxylic acid, 4,4'-diphenoxyethanedicarboxylic acid, 4,4'-diphenylsulfonedicarboxylic acid, and 2,6-naphthalenedicarboxylic acid. The aliphatic dicarboxylic acid and aromatic dicarboxylic acid components listed above can be used as raw materials for the polyester carbonate as dicarboxylic acids themselves, but depending on the production method, dicarboxylic acid esters such as methyl esters and phenyl esters, or dicarboxylic acid derivatives such as dicarboxylic acid halides can also be used as raw materials.

[0031] As the copolymerization monomer, dihydroxy compounds having a fluorene ring, such as 9,9-bis(4-(2-hydroxyethoxy)phenyl)fluorene, 9,9-bis(4-hydroxyphenyl)fluorene, and 9,9-bis(4-hydroxy-3-methylphenyl)fluorene, which are conventionally known as compounds having a structural unit with negative birefringence, and dicarboxylic acid compounds having a fluorene ring can also be used in combination with an oligofluorene compound.

[0032] From the viewpoint of optical properties, it is preferable that the resin used in the present invention does not contain aromatic components as structural units other than the oligofluorene structural unit. That is, it is preferable to use a compound composed of an aliphatic structure as a copolymerization monomer. If an aromatic component is contained in the main chain of the polymer, the reverse wavelength dispersion exhibited by the oligofluorene structural unit is canceled, so the content of the oligofluorene structural unit must be increased, which may result in deterioration of the photoelastic coefficient and mechanical properties. By adopting the other structural unit that does not contain an aromatic component, it is possible to prevent the aromatic component from being incorporated into the main chain due to the structural unit. Among compounds composed of an aliphatic structure, compounds having an alicyclic structure are more preferable, as they have excellent mechanical properties and heat resistance.

[0033] On the other hand, in order to ensure optical properties while balancing heat resistance, mechanical properties, etc., it may be effective to incorporate an aromatic component into the main chain or side chain of the polymer. From the viewpoint of balancing various properties, it is preferable that the content of structural units containing aromatic groups (excluding oligofluorene structural units) in the resin is 5 mass% or less.

[0034] The resin used in the present invention preferably contains a structural unit represented by the following formula (3) as a copolymerization component, among the structural units that can be introduced by the compound having an alicyclic structure.

[0035] As a dihydroxy compound capable of introducing the structural unit of the formula (3), spiroglycol can be used.

[0036] In the resin used in the present invention, the structural unit represented by formula (3) is preferably contained in an amount of 5% by mass or more and 90% by mass or less. The upper limit is more preferably 70% by mass or less, and particularly preferably 50% by mass or less. The lower limit is more preferably 10% by mass or more, more preferably 20% by mass or more, and particularly preferably 25% by mass or more. When the content of the structural unit represented by formula (3) is equal to or greater than the lower limit, sufficient mechanical properties, heat resistance, and a low photoelastic coefficient can be obtained. Furthermore, compatibility with acrylic resins is improved, and the transparency of the resulting resin composition can be further improved. In addition, since the polymerization reaction rate of spiroglycol is relatively slow, the polymerization reaction can be easily controlled by limiting the content to the upper limit or less.

[0037] The resin used in the present invention preferably further contains a structural unit represented by the following formula (4) as a copolymerization component.

[0038] Examples of dihydroxy compounds capable of introducing the structural unit represented by formula (4) include isosorbide (ISB), isomannide, and isoidet, which are stereoisomers. These may be used alone or in combination of two or more.

[0039] In the resin used in the present invention, the structural unit represented by formula (4) is preferably contained in an amount of 5% by mass or more and 90% by mass or less. The upper limit is more preferably 70% by mass or less, and particularly preferably 50% by mass or less. The lower limit is more preferably 10% by mass or more, and particularly preferably 15% by mass or more. When the content of the structural unit represented by formula (4) is equal to or greater than the lower limit, sufficient mechanical properties, heat resistance, and a low photoelastic coefficient can be obtained. Furthermore, since the structural unit represented by formula (4) has high water absorption properties, when the content of the structural unit represented by formula (4) is equal to or less than the upper limit, dimensional change of the molded body due to water absorption can be kept within an acceptable range.

[0040] The resin used in the present invention may further contain other structural units. Such structural units may be referred to as "other structural units." As monomers having other structural units, it is more preferable to use 1,4-cyclohexanedimethanol, tricyclodecane dimethanol, and 1,4-cyclohexanedicarboxylic acid (and derivatives thereof), with 1,4-cyclohexanedimethanol and tricyclodecane dimethanol being particularly preferable. Resins containing structural units derived from these monomers have an excellent balance of optical properties, heat resistance, mechanical properties, and the like. Furthermore, since the polymerization reactivity of diester compounds is relatively low, it is preferable not to use diester compounds other than diester compounds containing oligofluorene structural units, from the viewpoint of increasing reaction efficiency.

[0041] The dihydroxy compound or diester compound for introducing the other structural unit may be used alone or in combination of two or more depending on the required performance of the resulting resin. The content of the other structural unit in the resin is preferably 1% by mass or more and 50% by mass or less, more preferably 5% by mass or more and 40% by mass or less, and particularly preferably 10% by mass or more and 30% by mass or less. The other structural unit particularly plays a role in adjusting the heat resistance of the resin and imparting flexibility and toughness, so if the content is too low, the mechanical properties and melt processability of the resin may deteriorate, and if the content is too high, the heat resistance and optical properties may deteriorate.

[0042] The molecular weight of a polycarbonate-based resin can be expressed, for example, by reduced viscosity. The reduced viscosity is measured using methylene chloride as a solvent, precisely adjusting the concentration of the polycarbonate-based resin to 0.6 g / dL, and using an Ubbelohde viscosity tube at a temperature of 20.0°C ± 0.1°C. The lower limit of the reduced viscosity is usually preferably 0.30 dL / g or more, more preferably 0.35 dL / g or more, and particularly preferably 0.40 dL / g or more. The upper limit of the reduced viscosity is usually preferably 1.00 dL / g or less, more preferably 0.80 dL / g or less, and particularly preferably 0.60 dL / g or less. If the reduced viscosity is lower than the lower limit, the mechanical strength of the resulting film may be insufficient. On the other hand, if the reduced viscosity is higher than the upper limit, the moldability, handleability, and productivity may be insufficient.

[0043] The melt viscosity of polycarbonate resin is 240°C and the shear rate is 91.2 sec. －１ Under the measurement conditions, the viscosity is preferably 700 Pa s or more and 5000 Pa s or less. The upper limit is more preferably 4000 Pa s or less, more preferably 3500 Pa s or less, and particularly preferably 3000 Pa s or less. The lower limit is more preferably 1000 Pa s or more, more preferably 1500 Pa s or more, and particularly preferably 2000 Pa s or more. The melt viscosity is measured using a capillary rheometer (manufactured by Toyo Seiki Co., Ltd.).

[0044] The glass transition temperature (Tg) of the resin used in the present invention is preferably 110°C or higher and 160°C or lower. The upper limit is more preferably 155°C or lower, more preferably 150°C or lower, and particularly preferably 145°C or lower. The lower limit is more preferably 120°C or higher, and particularly preferably 130°C or higher. If the glass transition temperature is outside the above range, heat resistance tends to deteriorate, which may cause dimensional changes after film formation or may deteriorate the quality reliability of the retardation film under its usage conditions. On the other hand, if the glass transition temperature is excessively high, unevenness in film thickness may occur during film formation, the film may become brittle, stretchability may deteriorate, and the transparency of the film may be impaired.

[0045] Details of the composition and manufacturing method of polycarbonate-based resins and the like are described, for example, in International Publication No. WO 2015 / 159928, the disclosure of which is incorporated herein by reference.

[0046] A-1-2. Modifier The retardation film according to an embodiment of the present invention contains a modifier. As the modifier, a compound (A) containing an aromatic structure and having a molecular weight of 500 or more and 2000 or less is used. The content of the compound (A) is greater than 0.5% by mass and less than 4.0% by mass. By ensuring that the content of the compound (A) in the retardation film is within this range, a reverse dispersion retardation film with excellent durability in high-temperature, high-humidity environments can be obtained. This is presumably due to the combined effect of suppressing the mobility of polymer molecules by incorporating the compound (A) into the resin, thereby suppressing the orientation relaxation of polymer molecules caused by heat or moisture absorption, and suppressing moisture absorption by the resin. From the same viewpoint, the lower limit of the content is more preferably 1.0% by mass or more, and particularly preferably 1.5% by mass or more. The upper limit of the content is more preferably 3.5% by mass or less.

[0047] The molecular weight of the compound (A) is, as described above, 500 or more and 2000 or less. By setting it within the above range, the compound (A) is compatible with the resin, and the decrease in the glass transition temperature (Tg) of the resin is small, thereby achieving the effect of highly improving durability. Furthermore, during melt extrusion kneading or melt extrusion film formation, the compound (A) volatilizes or bleeds out, which can reduce the occurrence of problems such as contamination of vacuum vents or film-forming rolls. From the same viewpoint, the lower limit is more preferably 600 or more, even more preferably 700 or more, and particularly preferably 800 or more. The upper limit of the molecular weight is more preferably 1800 or less, particularly preferably 1500 or less.

[0048] The compound (A) preferably has a partial structure represented by the following formula (5): Compounds containing the partial structure have better compatibility with the polycarbonate resin used in the present invention, and it is presumed that the bulky structure thereof enhances the effect of suppressing the mobility of polymer molecules.

[0049] Examples of preferred compounds for the compound (A) include compounds known as antioxidants or ultraviolet absorbers having a hindered phenol structure, such as pentaerythritol-tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (trade name "Irganox 1010" manufactured by BASF), 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene (trade name "Irganox 1330" (manufactured by BASF Corporation), tris(3,5-di-tert-butyl-4-hydroxybenzyl)isocyanurate: trade name "Irganox 3114" (manufactured by BASF Corporation), 3-(3,5-di-tert-butyl-4-hydroxyphenyl)stearyl propionate: trade name "Irganox 1076" (manufactured by BASF Corporation), 2,2'-thiodiethylbis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]: trade name "Irganox 1035" (manufactured by BASF Corporation), N,N'-hexamethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanamide]: trade name "Irganox 1098" (manufactured by BASF Corporation), bis[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionic acid][ethylenebis(oxyethylene)]: trade name "Irganox 245" (manufactured by BASF Corporation), 1,6-hexanediol bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] trade name "Irg Examples of suitable phenols include 4-[[4,6-bis(octylthio)-1,3,5-triazin-2-yl]amino]-2,6-di-tert-butylphenol (trade name "Irganox 565") (manufactured by BASF Corporation), and 2,2'-methylenebis[6-(2H-benzotriazol-2-yl)-4-(1,1,3,3,-tetramethylbutyl)phenol (trade name "ADEKA STAB LA-31") and "ADEKA STAB LA-F70") (manufactured by ADEKA Corporation).Among these, from the viewpoint of having a high molecular weight and a bulky structure, the trade names "Irganox 1010" (manufactured by BASF), "Irganox 1330" (manufactured by BASF), "Irganox 3114" (manufactured by BASF), "ADK STAB LA-31" (manufactured by ADEKA), and "ADK STAB LA-F70" (manufactured by ADEKA) can be preferably used. In particular, pentaerythritol-tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] or 2,2'-methylenebis[6-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol is preferred, and pentaerythritol-tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] is most preferred.

[0050] A-1-3. Acrylic Resin The retardation film according to the embodiment of the present invention may contain an acrylic resin. By containing an acrylic resin, the breaking strength and the limit stretching ratio during film stretching are improved, and it is possible to achieve higher orientation. Furthermore, by reducing the frequency of breakage, it is possible to improve the yield of the stretching process.

[0051] As the acrylic resin, an acrylic resin as a thermoplastic resin is used. Examples of monomers that form the structural units of the acrylic resin include the following compounds: methyl methacrylate, methacrylic acid, methyl acrylate, acrylic acid, benzyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, stearyl (meth)acrylate, glycidyl (meth)acrylate, hydroxypropyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, norbornyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentanyl (meth)acrylate, and dicyclopentenyloxyethyl (meth)acrylate. Acrylate, tetrahydrofurfuryl (meth)acrylate, acrylic (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-(meth)acroyloxyethyl succinate, 2-(meth)acroyloxyethyl maleate, 2-(meth)acroyloxyethyl phthalate, 2-(meth)acryloyloxyethyl hexahydrophthalate, pentamethylpiperidyl (meth)acrylate, tetramethylpiperidyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, cyclopentyl methacrylate, cyclopentyl acrylate, cyclohexyl methacrylate, cyclohexyl acrylate, cycloheptyl methacrylate, cycloheptyl acrylate, cyclooctyl methacrylate, cyclooctyl acrylate, cyclododecyl methacrylate, and cyclododecyl acrylate. These may be used alone or in combination of two or more. Examples of the use of a combination of two or more monomers include copolymerization of two or more monomers, blends of two or more homopolymers of one monomer, and combinations thereof. Furthermore, other monomers copolymerizable with these acrylic monomers (e.g., olefinic monomers, vinylic monomers) may be used in combination.

[0052] The acrylic resin preferably contains a structural unit derived from methyl methacrylate. The content of the structural unit derived from methyl methacrylate in the acrylic resin is preferably 70% by mass or more and 100% by mass or less. The lower limit is more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. Within this range, excellent compatibility with the polycarbonate resin of the present invention can be obtained. As structural units other than methyl methacrylate, methyl acrylate, phenyl (meth)acrylate, benzyl (meth)acrylate, and styrene are preferably used. Copolymerization of methyl acrylate can improve thermal stability. The refractive index of the acrylic resin can be adjusted by using phenyl (meth)acrylate, benzyl (meth)acrylate, and styrene, and therefore, by matching the refractive index to that of the resin to be combined, the transparency of the resulting resin composition can be improved.

[0053] The weight average molecular weight Mw of the acrylic resin is preferably 10,000 or more and 200,000 or less. The lower limit is preferably 30,000 or more, particularly preferably 50,000 or more. The upper limit is preferably 180,000 or less, particularly preferably 150,000 or less. If the molecular weight is within this range, compatibility with the polycarbonate resin of the present invention can be obtained, thereby improving the transparency of the final retardation film and achieving the effect of sufficiently improving the extensibility during stretching. The weight average molecular weight is a molecular weight measured by GPC in terms of polystyrene. The measurement method will be described in detail later. Furthermore, from the viewpoint of compatibility, it is preferable that the acrylic resin does not substantially contain a branched structure. The absence of a branched structure can be confirmed by, for example, the GPC curve of the acrylic resin being unimodal.

[0054] The content of the acrylic resin in the resin composition (and consequently, the retardation film) is preferably 0% by mass or more and 2.0% by mass or less. The upper limit is preferably 1.5% by mass or less, more preferably 1.0% by mass or less, even more preferably 0.9% by mass or less, and particularly preferably 0.8% by mass or less. In this way, by blending the acrylic resin with the polycarbonate resin in a very limited ratio, the extensibility and retardation expression can be significantly increased. Furthermore, haze can be suppressed. Such an effect is not theoretically clear, but is an unexpectedly excellent effect obtained through trial and error. Note that if the content of the acrylic resin is too low, the above effect may not be obtained. On the other hand, if the content of the acrylic resin is too high, the haze may become high. Furthermore, the extensibility and retardation expression are often insufficient or even reduced compared to when they are within the above range.

[0055] A-1-4. Resin Composition A polycarbonate-based resin or the like is blended with the modifier and acrylic resin, and the resulting resin composition is used in the method for producing a retardation film (the production method will be described later in Section A-3). The polycarbonate-based resin or the like and the modifier and acrylic resin can be blended preferably in a molten state. A typical example of a method for blending in a molten state is melt-kneading using an extruder. The kneading temperature (molten resin temperature) is preferably 200°C to 280°C, more preferably 220°C to 270°C, and even more preferably 230°C to 260°C. If the kneading temperature is within this range, pellets of a resin composition in which the modifier and acrylic resin are uniformly blended can be obtained while suppressing thermal decomposition. If the molten resin temperature in the extruder exceeds 280°C, coloration and / or thermal decomposition of the resin may occur. On the other hand, if the temperature of the molten resin in the extruder falls below 200°C, the resin viscosity may become too high, placing an excessive load on the extruder or causing insufficient melting of the resin. Any appropriate configuration may be adopted for the extruder, screw configuration, etc. In order to obtain transparency and uniform dispersibility of the resin sufficient for optical film applications, it is preferable to use a twin-screw extruder. Furthermore, since there is a concern that residual low-molecular-weight components in the resin and low-molecular-weight thermally decomposed components during extrusion kneading may contaminate cooling rolls and conveying rolls in the film-forming process and stretching process, it is preferable to use an extruder equipped with a vacuum vent in order to remove these.

[0056] The resin composition may be further blended with synthetic resins such as aromatic polycarbonate, aliphatic polycarbonate, aromatic polyester, aliphatic polyester, polyamide, polystyrene, polyolefin, acrylic, amorphous polyolefin, ABS, AS, polylactic acid, polybutylene succinate, rubber, or combinations thereof, for the purpose of improving mechanical properties and / or solvent resistance.

[0057] The resin composition may further contain additives. Specific examples of additives include heat stabilizers, antioxidants, catalyst deactivators, UV absorbers, light stabilizers, release agents, dyes and pigments, impact modifiers, antistatic agents, slip agents, lubricants, plasticizers, compatibilizers, nucleating agents, flame retardants, inorganic fillers, and foaming agents. The type, number, combination, and content of the additives contained in the resin composition can be appropriately set depending on the purpose.

[0058] A-2. Characteristics of Retardation Film The in-plane retardation Re(550) of the retardation film is, as described above, 100 nm to 200 nm, preferably 110 nm to 180 nm, more preferably 120 nm to 160 nm, and even more preferably 130 nm to 150 nm. That is, the retardation film can function as a so-called λ / 4 plate.

[0059] The retardation film typically satisfies the relationship Re(450)<Re(550)<Re(650). That is, the retardation film exhibits wavelength dependency of inverse dispersion, in which the retardation value increases according to the wavelength of the measurement light. As described above, the Re(450) / Re(550) of the retardation film is greater than 0.5 and less than 1.0, preferably 0.7 to 0.95, more preferably 0.75 to 0.92, and even more preferably 0.8 to 0.9. The Re(650) / Re(550) is preferably 1.0 or more and less than 1.15, more preferably 1.03 to 1.1.

[0060] Since the retardation film has an in-plane retardation as described above, it has a relationship of nx > ny. The retardation film exhibits any appropriate index ellipsoid as long as it has the relationship nx > ny. The index ellipsoid of the retardation film typically exhibits the relationship nx > ny ≧ nz. Note that "ny = nz" here encompasses not only the case where ny and nz are completely equal, but also the case where they are substantially equal. Therefore, ny < nz may be satisfied within a range that does not impair the effects of the present invention. The Nz coefficient of the retardation film is preferably 0.9 to 2.0, more preferably 0.9 to 1.5, and even more preferably 0.9 to 1.2. By satisfying this relationship, when a circularly polarizing plate including a retardation film is used in an image display device, an extremely excellent reflection hue can be achieved.

[0061] The thickness of the retardation film can be set so that it can function most appropriately as a λ / 4 plate. In other words, the thickness can be set so that a desired in-plane retardation is obtained. Specifically, the thickness is preferably 15 μm to 60 μm, more preferably 20 μm to 55 μm, and most preferably 20 μm to 50 μm. According to an embodiment of the present invention, a retardation film having excellent retardation expression properties can be obtained, so that the thickness of the retardation film can be made thinner than that of a normal λ / 4 plate.

[0062] The haze value of the retardation film is preferably 1.5% or less, more preferably 1.0% or less, and even more preferably 0.5% or less. According to an embodiment of the present invention, a reverse dispersion retardation film excellent in both retardation expression and haze value can be realized. The smaller the haze value, the more preferable. The lower limit of the haze value can be, for example, 0.1%.

[0063] The birefringence Δn of the retardation film is preferably 0.0025 or more, more preferably 0.0030 or more, even more preferably 0.0035 or more, and particularly preferably 0.0040 or more. The upper limit of the birefringence Δn may be, for example, 0.0070. The birefringence can be determined by dividing the in-plane retardation Re of the film at the highest stretching ratio at which the film does not break by the film thickness d.

[0064] The absolute value of the photoelastic coefficient of the retardation film is preferably 20×10 －１２ (m ２ / N) or less, and more preferably 1.0 × 10 －１２ (m ２ / N) ~ 15 x 10 －１２ (m ２ / N), and more preferably 2.0 × 10 －１２ (m ２ / N) ~ 12 x 10 －１２ (m ２ When the absolute value of the photoelastic coefficient is within such a range, display unevenness can be suppressed when the retardation film is applied to an image display device.

[0065] A-3. Method for Producing Retardation Film The retardation films described in A-1 and A-2 above can be obtained by forming a film from the resin composition described in A-1 and then stretching the film. Any appropriate molding method can be used to form a film from the resin composition. Specific examples include compression molding, transfer molding, injection molding, extrusion molding, blow molding, powder molding, FRP molding, cast coating (e.g., casting), calendar molding, and heat pressing. Among these, extrusion molding and cast coating are preferred, as they can improve the smoothness of the resulting film and provide good optical uniformity. Since cast coating can cause problems due to residual solvent, extrusion molding is particularly preferred, and melt extrusion molding using a T-die is particularly preferred from the perspective of film productivity and ease of subsequent stretching. Molding conditions can be appropriately set depending on the composition and type of resin used, the properties desired for the retardation film, and the like. In this way, a resin film containing a polycarbonate-based resin or the like can be obtained.

[0066] The thickness of the resin film (unstretched film) can be set to any appropriate value depending on the desired thickness of the resulting retardation film, the desired optical properties, the stretching conditions described below, etc. It is preferably 50 μm to 300 μm.

[0067] The stretching may be performed using any suitable stretching method and conditions (e.g., stretching temperature, stretch ratio, stretching direction). Specifically, various stretching methods such as free-end stretching, fixed-end stretching, free-end shrinkage, and fixed-end shrinkage may be used alone, simultaneously, or sequentially. Stretching may be performed in various directions or dimensions, such as the length direction, width direction, thickness direction, and oblique direction.

[0068] By appropriately selecting the stretching method and stretching conditions, a retardation film having the desired optical properties (for example, refractive index properties, in-plane retardation, Nz coefficient) can be obtained.

[0069] In one embodiment, the retardation film is produced by uniaxially stretching or fixed-end uniaxially stretching a resin film. A specific example of uniaxial stretching is a method in which a resin film is stretched in the running direction (longitudinal direction) while running in the longitudinal direction. A specific example of fixed-end uniaxial stretching is a method in which a resin film is stretched in the width direction (transverse direction) while running in the longitudinal direction. The stretching ratio is preferably 1.1 to 3.5 times.

[0070] In another embodiment, the retardation film can be produced by continuously obliquely stretching a long resin film in a direction at a predetermined angle relative to the longitudinal direction. By employing oblique stretching, a long stretched film having an orientation angle (slow axis in the direction of the predetermined angle) relative to the longitudinal direction of the film can be obtained. For example, roll-to-roll lamination with a polarizer is possible, simplifying the manufacturing process. The predetermined angle can be the angle between the absorption axis of the polarizer and the slow axis of the retardation film in a circular polarizing plate (described below). As described below, the angle is preferably 40° to 50°, more preferably 42° to 48°, even more preferably 44° to 46°, and particularly preferably about 45°; or preferably 130° to 140°, more preferably 132° to 138°, even more preferably 134° to 136°, and particularly preferably about 135°.

[0071] Examples of stretching machines used for oblique stretching include tenter-type stretching machines that can apply feeding forces, pulling forces, or take-up forces at different speeds in the transverse and / or longitudinal directions. Tenter-type stretching machines include transverse uniaxial stretching machines and simultaneous biaxial stretching machines, but any appropriate stretching machine can be used as long as it can continuously obliquely stretch a long resin film.

[0072] By appropriately controlling the left and right speeds in the stretching machine, a retardation film (substantially a long retardation film) having the desired in-plane retardation and the slow axis in the desired direction can be obtained.

[0073] Examples of oblique stretching methods include those described in JP-A Nos. 50-83482, 2-113920, 3-182701, 2000-9912, 2002-86554, and 2002-22944.

[0074] In one embodiment, the stretching temperature of the film is a temperature below the glass transition temperature (Tg) of the polycarbonate-based resin or the like. Typically, when stretching a film of a polycarbonate-based resin or the like, the film is in a glassy state at temperatures below Tg, making stretching substantially impossible. According to an embodiment of the present invention, by blending a small amount of an acrylic resin (typically, polymethyl methacrylate), stretching at a temperature below Tg becomes possible without substantially changing the Tg of the polycarbonate-based resin or the like. Furthermore, although not theoretically clear, stretching at a temperature below Tg can produce a reverse dispersion retardation film that is excellent in stretchability and retardation expression and has low haze. Specifically, the stretching temperature is preferably Tg to Tg -10°C, more preferably Tg to Tg -8°C, and even more preferably Tg to Tg -5°C. The film can be appropriately stretched even at temperatures higher than Tg, for example, up to about Tg +5°C or, for example, up to about Tg +2°C.

[0075] B. Circular Polarizer The retardation film according to the embodiment of the present invention described in Section A above can be suitably used in a circular polarizer. Therefore, the embodiment of the present invention also encompasses a circular polarizer. FIG. 1 is a schematic cross-sectional view of a circular polarizer according to one embodiment of the present invention. The illustrated circular polarizer 100 includes a polarizer 10 and a retardation film 20. The retardation film 20 is the retardation film according to the embodiment of the present invention described in Section A above. The polarizer 10 includes a polarizer 11, a first protective layer 12 disposed on one side of the polarizer 11, and a second protective layer 13 disposed on the other side of the polarizer 11. Depending on the purpose, one of the first protective layer 12 and the second protective layer 13 may be omitted. For example, since the retardation film 20 according to the embodiment of the present invention can also function as a protective layer for the polarizer 11, the second protective layer 13 may be omitted. The angle formed by the slow axis of the retardation film 20 and the absorption axis of the polarizer 11 is preferably 40° to 50°, more preferably 42° to 48°, even more preferably 44° to 46°, and particularly preferably about 45°; alternatively, it is preferably 130° to 140°, more preferably 132° to 138°, even more preferably 134° to 136°, and particularly preferably about 135°.

[0076] In another embodiment, another retardation layer and / or a conductive layer or an isotropic substrate with a conductive layer may be provided (not shown). The other retardation layer and the conductive layer or the isotropic substrate with a conductive layer are typically provided on the outer side of the retardation film 20 (the side opposite the polarizing plate 10). The other retardation layer typically exhibits a refractive index characteristic of nz > nx = ny. By providing such another retardation layer, reflections in oblique directions can be effectively prevented, enabling a wide viewing angle of the anti-reflection function. The other retardation layer and the conductive layer or the isotropic substrate with a conductive layer are typically provided in this order from the retardation film 20 side. The other retardation layer and the conductive layer or the isotropic substrate with a conductive layer are typically optional layers provided as needed, and either one or both may be omitted. When the conductive layer or the isotropic substrate with a conductive layer is provided, the circular polarizer can be applied to a so-called inner touch panel type input display device in which a touch sensor is incorporated between an image display cell (e.g., an organic EL cell) and the polarizing plate.

[0077] The circularly polarizing plate may have an additional retardation layer. The additional retardation layer may be provided in combination with another retardation layer, or may be provided alone (i.e., without providing another retardation layer). The optical properties (e.g., refractive index characteristics, in-plane retardation, Nz coefficient, photoelastic coefficient), thickness, arrangement position, etc. of the additional retardation layer may be appropriately set according to the purpose.

[0078] The circular polarizing plate may be in the form of a sheet or a long sheet. In this specification, "long sheet" refers to an elongated shape in which the length is sufficiently longer than the width, and includes, for example, an elongated shape in which the length is 10 times or more, preferably 20 times or more, the width. A long circular polarizing plate can be wound into a roll. When the circular polarizing plate is elongated, the polarizing plate and the retardation film are also elongated. In this case, the polarizer preferably has an absorption axis in the longitudinal direction. As described above, the retardation film is preferably an obliquely stretched film having a slow axis in a direction forming an angle of 40° to 50° or 130° to 140° with respect to the longitudinal direction. When the polarizer and the retardation film have such a configuration, the circular polarizing plate can be produced by a roll-to-roll method.

[0079] In practice, a pressure-sensitive adhesive layer (not shown) is provided on the side of the retardation film opposite the polarizing plate, so that the circular polarizing plate can be attached to an image display cell. Furthermore, it is preferable that a release film is temporarily attached to the surface of the pressure-sensitive adhesive layer until the circular polarizing plate is used. Temporarily attaching the release film protects the pressure-sensitive adhesive layer and enables the circular polarizing plate to be formed into a roll.

[0080] The components of the circular polarizer will be described below.

[0081] B-1. Polarizer Any appropriate polarizer can be adopted as the polarizer 11. For example, the resin film forming the polarizer may be a single-layer resin film or a laminate of two or more layers.

[0082] Specific examples of polarizers composed of a single-layer resin film include hydrophilic polymer films such as polyvinyl alcohol (PVA) films, partially formalized PVA films, and partially saponified ethylene-vinyl acetate copolymer films that have been dyed with iodine or a dichroic substance such as a dichroic dye and stretched, and polyene-based oriented films such as dehydrated PVA films and dehydrochlorinated polyvinyl chloride films. Preferably, a polarizer obtained by dyeing a PVA film with iodine and uniaxially stretching it is used because of its excellent optical properties.

[0083] The dyeing with iodine is carried out, for example, by immersing the PVA-based film in an aqueous iodine solution. The stretching ratio of the uniaxial stretching is preferably 3 to 7 times. The stretching may be carried out after the dyeing treatment or while dyeing. Alternatively, the PVA-based film may be stretched and then dyed. If necessary, the PVA-based film may be subjected to a swelling treatment, a crosslinking treatment, a washing treatment, a drying treatment, or the like. For example, by immersing the PVA-based film in water and washing it before dyeing, it is possible to wash away dirt and antiblocking agents from the surface of the PVA-based film and also to swell the PVA-based film, thereby preventing uneven dyeing and the like.

[0084] Specific examples of polarizers obtained using laminates include a laminate of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate. A polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate can be produced, for example, by applying a PVA-based resin solution to the resin substrate and drying the solution to form a PVA-based resin layer on the resin substrate to obtain a laminate of the resin substrate and the PVA-based resin layer; and then stretching and dyeing the laminate to convert the PVA-based resin layer into a polarizer. In this embodiment, stretching typically involves immersing the laminate in an aqueous boric acid solution and stretching it. Furthermore, stretching may, if necessary, further involve in-air stretching of the laminate at an elevated temperature (e.g., 95°C or higher) before stretching in the aqueous boric acid solution. The obtained resin substrate / polarizer laminate may be used as is (i.e., the resin substrate may be used as a protective layer for the polarizer), or the resin substrate may be peeled from the resin substrate / polarizer laminate and any appropriate protective layer depending on the purpose may be laminated on the peeled surface. Details of such methods for producing polarizers are described in, for example, JP-A-2012-73580 (Patent No. 5414738) and JP-A-6470455. The descriptions of these patent documents are incorporated herein by reference.

[0085] The thickness of the polarizer is preferably 15 μm or less, more preferably 1 μm to 12 μm, even more preferably 3 μm to 10 μm, and particularly preferably 3 μm to 8 μm. When the polarizer thickness is within this range, curling during heating can be effectively suppressed, and good durability of appearance during heating can be obtained. Furthermore, when the polarizer thickness is within this range, it can contribute to a thinner circular polarizing plate (and, consequently, an organic EL display device).

[0086] The polarizer preferably exhibits absorptive dichroism at any wavelength between 380 nm and 780 nm. The single transmittance of the polarizer is preferably 43.0% to 46.0%, more preferably 44.5% to 46.0%. The degree of polarization of the polarizer is preferably 97.0% or more, more preferably 99.0% or more, and even more preferably 99.9% or more.

[0087] B-2. Protective Layer The first protective layer 12 and the second protective layer 13 are each formed of any appropriate film that can be used as a protective layer for a polarizer. Specific examples of materials that can be the main component of the film include cellulose-based resins such as triacetyl cellulose (TAC), and transparent resins such as polyesters, polyvinyl alcohols, polycarbonates, polyamides, polyimides, polyethersulfones, polysulfones, polystyrenes, polynorbornenes, polyolefins, (meth)acrylics, and acetates. Other examples include thermosetting or ultraviolet-curing resins such as (meth)acrylics, urethanes, (meth)acrylic urethanes, epoxy resins, and silicones. Other examples include glassy polymers such as siloxane polymers. Polymer films described in JP 2001-343529 A (WO 01 / 37007) can also be used. Examples of materials that can be used for this film include a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in its side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in its side chain, such as a resin composition containing an alternating copolymer of isobutene and N-methylmaleimide and an acrylonitrile-styrene copolymer. The polymer film can be, for example, an extrusion molded product of the above resin composition.

[0088] As described below, the circular polarizing plate is typically disposed on the viewing side of the image display device, and the first protective layer 12 is typically disposed on the viewing side. Therefore, the first protective layer 12 may be subjected to a surface treatment such as a hard coat treatment, an anti-reflection treatment, an anti-sticking treatment, or an anti-glare treatment, as needed. Furthermore, the first protective layer 12 may be subjected to a treatment to improve visibility when viewed through polarized sunglasses (typically, by imparting an (elliptical) circular polarization function or an ultra-high phase difference), as needed. By performing such a treatment, excellent visibility can be achieved even when the display screen is viewed through polarized lenses such as polarized sunglasses. Therefore, the circular polarizing plate can be suitably applied to image display devices that can be used outdoors.

[0089] The thickness of the first protective layer is typically 300 μm or less, preferably 100 μm or less, more preferably 5 μm to 80 μm, and even more preferably 10 μm to 60 μm. When a surface treatment is applied, the thickness of the outer protective layer includes the thickness of the surface treatment layer.

[0090] In one embodiment, the second protective layer 13 is preferably optically isotropic. In this specification, the term "optically isotropic" means that the in-plane retardation Re(550) is 0 nm to 10 nm and the retardation Rth(550) in the thickness direction is −10 nm to +10 nm.

[0091] C. Image Display Device The circular polarizer described in Section B above can be applied to an image display device. Accordingly, embodiments of the present invention also encompass image display devices using such circular polarizers. Representative examples of image display devices include liquid crystal display devices and organic EL display devices. An image display device according to an embodiment of the present invention includes the circular polarizer described in Section B above on its viewing side. The circular polarizer is arranged so that the polarizer is on the viewing side.

[0092] The present invention will be described in detail below using examples, but the present invention is not limited to these examples. The methods for measuring each property are as follows. (1) Thickness: Measured using a dial gauge (manufactured by PEACOCK, product name "DG-205 type pds-2"). (2) Glass transition temperature (Tg): The glass transition temperatures of the resin and film were measured using a differential scanning calorimeter DSC6220 manufactured by SII NanoTechnology. Approximately 10 mg of a resin sample was placed in an aluminum pan manufactured by the same company, sealed, and heated from 30°C to 200°C at a heating rate of 20°C / min under a nitrogen gas flow of 50 mL / min. After holding the temperature for 3 minutes, the sample was cooled to 30°C at a rate of 20°C / min. After holding at 30°C for 3 minutes, the sample was again heated to 200°C at a rate of 20°C / min. From the DSC data obtained in the second temperature rise, the extrapolated glass transition onset temperature, which is the temperature at the intersection of a straight line extending the low-temperature baseline toward the high-temperature side and a tangent drawn at the point where the gradient of the curve of the stepwise change in the glass transition is maximum, was determined, and this was taken as the glass transition temperature (Tg). (3) Water absorption Using the films obtained in the examples and comparative examples, measurement was made in accordance with the "Test method for water absorption and boiling water absorption of plastics" described in JIS K 7209. The size of the test piece was a square with sides of 50 mm, and it was determined by immersing the test piece in water at 25°C for 24 hours and measuring the weight change before and after immersion. The unit is %. (4) Content of modifier in resin The actual content of modifier (compound (A)) in the resin was １ Approximately 15 mg of the retardation film obtained in each of the examples and comparative examples was weighed out and dissolved in approximately 0.7 mL of deuterated chloroform. This was placed in an NMR tube with an inner diameter of 5 mm, and １ The H-NMR spectrum was measured. In addition, the resin containing no modifier and the modifier were each precisely weighed to prepare samples with known contents. １ H-NMR was measured. １From the H-NMR spectrum, the integral value per proton was calculated from the signals derived from each component constituting the resin and the signal derived from the modifier, and this value was multiplied by the molecular weight of each component to calculate the value corresponding to the weight of the resin and the weight of the modifier. If these values ​​are X and Y, respectively, the content of the modifier can be calculated using the following formula. Here, the coefficient α was determined from the measurement results of a sample with a known content. Modifier content [mass%] = α × Y / (X + Y) × 100 The equipment and conditions used are as follows: - Equipment: JNM-ECZ400S (manufactured by JEOL Ltd.) - Measurement temperature: 30 ° C - Relaxation time: 6 seconds - Number of accumulations: 64 times (5) Retardation Value A 50 mm × 50 mm sample was cut out from the retardation film obtained in the examples and comparative examples as a measurement sample, and was measured using an Axoscan manufactured by Axometrics. The measurement wavelengths were 450 nm, 550 nm, 590 nm, and 650 nm, and the measurement temperature was 23°C. (6) Retardation Change in Humidity Test The retardation films obtained in the Examples and Comparative Examples were bonded to glass via an adhesive layer to prepare samples, and the retardation was measured in the same manner as in the measurement of the retardation. After the measurement, the samples were placed in an environment of 60°C and 90% RH for 500 hours, and then removed and the retardation was measured again to determine the change rate (%) of Re (550). Good: The absolute value of the retardation change rate (%) is less than 1.40%. Poor: The absolute value of the retardation change rate (%) is 1.40% or more. (7) Dimensional Change in Humidity Test The stretched films or retardation films obtained in the Examples and Comparative Examples were cut into 20 mm (slow axis direction) x 4 mm (fast axis direction) to prepare measurement samples. The measurement sample was placed in an environment of 60°C and 90% RH for 500 hours, and then the dimensional change rate in the length direction of the measurement sample was measured. Good: The absolute value of the dimensional change rate (%) was less than 0.12%. Poor: The absolute value of the dimensional change rate (%) was 0.12% or more. (8) Dimensional Change in Heating and Humidifying Test The stretched films or retardation films obtained in the Examples and Comparative Examples were cut into 20 mm (slow axis direction) x 4 mm (fast axis direction) to prepare measurement samples. The measurement sample was placed in an environment of 85°C and 85% RH for 500 hours, and then the dimensional change rate in the length direction of the measurement sample was measured.Good: The absolute value of the dimensional change rate (%) is less than 0.30%. Poor: The absolute value of the dimensional change rate (%) is 0.30% or more.

[0093] [Compound Abbreviations] The abbreviations for the compounds used in the following synthesis examples, examples, and comparative examples are as follows: BPFM: bis[9-(2-phenoxycarbonylethyl)fluoren-9-yl]methane Synthesized by the method described in JP 2015-25111 A (Patent No. 6311264). ISB: Isosorbide [manufactured by Roquette Fleuret] SPG: Spiroglycol [manufactured by Mitsubishi Gas Chemical Company, Inc.] DPC: Diphenyl carbonate [manufactured by Mitsubishi Chemical Corporation] PHL: Phenol [manufactured by Mitsubishi Chemical Corporation] Irganox 1010: Pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] [manufactured by BASF] ... molecular weight 1178 Irganox 1330: 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene [manufactured by BASF] ... molecular weight 775 Irganox 3114: Tris(3,5-di-tert-butyl-4-hydroxybenzyl)isocyanurate [manufactured by BASF] ... Molecular weight: 784 LA-31: 2,2'-methylenebis[6-(2H-benzotriazol-2-yl)-4-(1,1,3,3,-tetramethylbutyl)phenol [manufactured by ADEKA Corporation] ... molecular weight: 659 LA-F70: 6,6',6''-(1,3,5-triazine-2,4,6-triyl)tris(3-hexyloxy-2-methylphenol) [manufactured by ADEKA Corporation] ... molecular weight: 700 TPP: triphenyl phosphate [manufactured by Tokyo Chemical Industry Co., Ltd.] ... molecular weight: 326 DMT: dimethyl terephthalate [manufactured by Tokyo Chemical Industry Co., Ltd.] ... molecular weight: 194 PEP36: 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane [manufactured by ADEKA Corporation]... molecular weight 633 BR80: acrylic resin [manufactured by Mitsubishi Chemical Corporation]

[0094] [Production Example 1] Polymerization of polyester carbonate resin was carried out using a continuous polymerization system consisting of three vertical stirred reactors, one horizontal stirred reactor, and a twin-screw extruder. In each dissolution tank, ISB, SPG and PHL, and BPFM and DPC were melted, respectively (PHL was used as a solvent to dissolve SPG). The weight ratio of SPG to PHL was 55.0 / 45.0, and the weight ratio of BPFM to DPC was 30.3 / 69.7. The ISB melt, the SPG-PHL mixed solution, and the BPFM-DPC mixed solution were continuously supplied to the first vertical stirred reactor at flow rates of 49.9 parts by weight / hr, 68.5 parts by weight / hr, and 75.3 parts by weight / hr (molar ratio ISB / SPG / BPFM / DPC = 0.734 / 0.266 / 0.126 / 0.874). Simultaneously, an aqueous solution of calcium acetate monohydrate, serving as a polymerization catalyst, was supplied to the first vertical stirred reactor in an amount such that 12 μmol of calcium acetate monohydrate was added per mol of the total dihydroxy compounds. The internal temperature, internal pressure, and residence time of each reactor were as follows: first vertical stirred reactor: 195°C, 27 kPa, 90 minutes; second vertical stirred reactor: 205°C, 20 kPa, 70 minutes; third vertical stirred reactor: 220°C, 10 kPa, 60 minutes; and fourth horizontal stirred reactor: 235°C, 0.1 to 1.0 kPa, 150 minutes. The vacuum pressure of the fourth horizontal stirred reactor was finely adjusted during operation so that the reduced viscosity of the final resin was 0.45 to 0.47 dL / g. The resin extracted from the fourth horizontal stirred reactor was fed in a molten state into a vented twin-screw extruder (manufactured by The Japan Steel Works, Ltd.). The extruder had two vacuum vents, where residual low-molecular-weight components in the resin were removed by volatilization. Phosphonic acid was added as a catalyst deactivator before the first vent at 3.7 ppm by weight relative to the polyester carbonate resin. After the second vent, Irganox 1010 and PEP36 were added as heat stabilizers at 1000 ppm by weight and 100 ppm by weight relative to the polyester carbonate resin, respectively. The Irganox 1010 and PEP36 added here are compounds corresponding to compound (A) in the present invention and are included in the content of the modifier. The polycarbonate resin that had passed through the extruder was then passed through a 10 μm Ultipleat candle filter (manufactured by PALL) while still in the molten state to filter out foreign matter.The molten resin was then extruded through a die into strands, water-cooled, solidified, and cut into pellets with a rotary cutter. The ratio of structural units derived from each monomer was BPFM / ISB / SPG / DPC=21.5 / 39.4 / 30.0 / 9.1% by mass.

[0095] [Example 1] Extrusion kneading was performed using the polyester carbonate resin obtained in Production Example 1. Polyester carbonate resin pellets were mixed with 2.0% by mass of Irganox 1010 as a modifier, and the mixture was fed into a twin-screw extruder TEX30HSS (manufactured by The Japan Steel Works, Ltd.) using a metering feeder. The extruder cylinder temperature was set to 240°C, and extrusion was performed at a throughput of 12 kg / hr and a screw rotation speed of 120 rpm. The extruder was also equipped with a vacuum vent, and the molten resin was extruded while devolatilizing under reduced pressure. The molten resin was extruded from a die into strands, water-cooled, solidified, and then cut with a rotary cutter to form pellets. The resin composition pellets thus obtained were vacuum-dried at 100°C for 6 hours or more, and then a film-forming apparatus equipped with a single-screw extruder (manufactured by Technovel Co., Ltd., screw diameter 30 mm, cylinder set temperature: 235°C, with vacuum vent), a T-die (width 400 mm, set temperature: 245°C), a chill roll (set temperature: 125-135°C), and a winder was used to produce a long unstretched film having a length of 10 m, a width of 350 mm, and a thickness of 110 μm. After the film was taken out, the chill roll surface was inspected and no dirt on the roll was found. The glass transition temperature (Tg) of the obtained film was 137°C and the water absorption rate was 1.6%. Next, a sample of 120 mm (direction of film conveyance during production: MD) x 150 mm (direction perpendicular to the conveyance direction: TD) was cut out from this long unstretched film. This sample was stretched uniaxially in the TD direction with a fixed end using a laboratory stretcher "Blackner KARO IV" at a stretching temperature set to "Tg + 4 ° C" of the resin sample and varying the stretching ratio, and the in-plane retardation Re (measurement wavelength 590 nm) was adjusted to 145 nm to produce a retardation film. The results are shown in Table 1.

[0096] [Example 2] A retardation film was produced in the same manner as in Example 1, except that 1% by mass of Irganox 1330 was added as a modifier. A small amount of deposit was confirmed on the chill roll surface. The Tg of the film was 140°C, and the water absorption rate was 1.7%. The obtained retardation film was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0097] [Example 3] A retardation film was produced in the same manner as in Example 1, except that 2% by mass of Irganox 1330 was blended as a modifier. A small amount of deposit was confirmed on the chill roll surface. The Tg of the film was 139°C, and the water absorption rate was 1.6%. The obtained retardation film was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0098] [Example 4] A retardation film was produced in the same manner as in Example 1, except that 2% by mass of Irganox 3114 was added as a modifier. A small amount of deposit was confirmed on the chill roll surface. The Tg of the film was 139°C, and the water absorption rate was 1.7%. The obtained retardation film was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0099] [Example 5] A retardation film was produced in the same manner as in Example 1, except that 2% by mass of LA-31 was blended as a modifier. No contamination was observed on the chill roll surface. The Tg of the film was 138°C, and the water absorption rate was 1.7%. The obtained retardation film was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0100] [Example 6] A retardation film was produced in the same manner as in Example 1, except that 2% by mass of Irganox 1010 was used as a modifier and 0.7% by mass of BR80 was used as an acrylic resin. No contamination was observed on the chill roll surface. The Tg of the film was 137°C, and the water absorption was 1.6%. Furthermore, a retardation film was obtained in the same manner as in Example 1, except that the stretching temperature was set to "Tg - 2°C" of the resin sample. The results are shown in Table 1.

[0101] [Example 7] A retardation film was produced in the same manner as in Example 1, except that 1.5 mass% of Irganox 1010, 0.3 mass% of LA-F70, and 0.7 mass% of BR80 were blended as modifiers and acrylic resins, respectively. No contamination was observed on the chill roll surface. The Tg of the film was 137°C, and the water absorption rate was 1.7%. The obtained retardation film was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0102] [Comparative Example 1] A retardation film was produced in the same manner as in Example 1, except that 0.2 mass% of Irganox 1010 was blended as a modifier. No contamination was observed on the chill roll surface. The Tg of the film was 140°C, and the water absorption rate was 1.8%. The obtained retardation film was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0103] Comparative Example 2 Extrusion kneading was carried out in the same manner as in Example 1, except that 5% by mass of Irganox 1010 was added as a modifier. However, the extrusion state of the molten resin was unstable, and a pellet-shaped sample could not be obtained.

[0104] [Comparative Example 3] A retardation film was produced in the same manner as in Example 1, except that 2% by mass of TPP was blended as a modifier. No contamination was observed on the chill roll surface. The Tg of the film was 134°C, and the water absorption rate was 1.5%. The obtained retardation film was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0105] [Comparative Example 4] A retardation film was produced in the same manner as in Example 1, except that 2% by mass of DMT was blended as a modifier. A small amount of deposit was confirmed on the chill roll surface. The Tg of the film was 131°C, and the water absorption rate was 1.5%. The obtained retardation film was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0106] [Evaluation] As is clear from Table 1, by having the configurations of the examples of the present invention, it is possible to obtain a retardation film in which the change in retardation and dimensional change under humid conditions and the dimensional change under heated and humid conditions are suppressed.

[0107] The retardation film of the present invention can be suitably used in a circular polarizing plate, and the circular polarizing plate can be suitably used in an image display device (typically, a liquid crystal display device or an organic EL display device).

[0108] REFERENCE SIGNS LIST 10 Polarizing plate 11 Polarizer 12 First protective layer 13 Second protective layer 20 Retardation film 100 Circular polarizing plate

Claims

1. A resin having a positive refractive index anisotropy, comprising at least one bonding group selected from the group consisting of a carbonate bond and an ester bond, and at least one structural unit selected from the group consisting of a structural unit represented by the following general formula (1) and a structural unit represented by the following general formula (2); a compound (A) containing an aromatic structure and having a molecular weight of 500 or more and 2000 or less; wherein the content of the compound (A) is more than 0.5% by mass and 4.0% by mass or less, Re(550) is 100 nm to 200 nm, and Re(450) / Re(550) is more than 0.5 and less than 1.0, a retardation film: In general formulas (1) and (2), R １ ~R ３ are each independently a direct bond, a substituted or unsubstituted alkylene group having 1 to 4 carbon atoms, and R ４ ~R ９ are each independently a hydrogen atom, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted aryl group having 4 to 10 carbon atoms, a substituted or unsubstituted acyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 10 carbon atoms, a substituted or unsubstituted aryloxy group having 1 to 10 carbon atoms, a substituted or unsubstituted amino group, a substituted or unsubstituted vinyl group having 1 to 10 carbon atoms, a substituted or unsubstituted ethynyl group having 1 to 10 carbon atoms, a sulfur atom having a substituent, a silicon atom having a substituent, a halogen atom, a nitro group, or a cyano group; provided that R ４ ~R ９ may be the same as or different from each other, and at least two adjacent groups among R ４ ~R ９ may be bonded to each other to form a ring; Re(550) is the in-plane retardation of the film measured with light having a wavelength of 550 nm at 23°C, and Re(450) is the in-plane retardation of the film measured with light having a wavelength of 450 nm at 23°C.

2. The retardation film according to claim 1, wherein the resin having positive refractive index anisotropy contains at least one structural unit selected from the group consisting of the structural unit represented by the general formula (1) and the structural unit represented by the general formula (2) in an amount of 1% by mass to 40% by mass.

3. The retardation film according to claim 1 or 2, wherein the resin having positive refractive index anisotropy further contains a structural unit represented by the following general formula (3).

4. The retardation film according to any one of claims 1 to 3, wherein the resin having positive refractive index anisotropy further contains a structural unit represented by the following general formula (4).

5. The retardation film according to any one of claims 1 to 4, further comprising an acrylic resin, wherein the content of the acrylic resin is 0.5% by mass or more and 2.0% by mass or less.

6. The retardation film according to any one of claims 1 to 5, wherein the content of the compound (A) is 1.0% by mass or more and 3.0% by mass or less.

7. The retardation film according to any one of claims 1 to 6, wherein the compound (A) has a partial structure represented by the following formula (5).

8. A circular polarizing plate having a polarizer and the retardation film according to any one of claims 1 to 7, wherein the angle formed by the absorption axis of the polarizer and the slow axis of the retardation film is 40° to 50° or 130° to 140°.

9. An image display device including the circular polarizing plate according to claim 8 on the viewing side, wherein the polarizer of the circular polarizing plate is disposed on the viewing side.

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