JP2010072135A - Optical film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical film containing an acrylic resin having ring structure in a principal chain, excellent in an optical characteristic, and having compatibly a film strength and flexibility. <P>SOLUTION: The film containing the acrylic resin having the ring structure in the principal chain is biaxially stretched to bring an in-plane phase difference Re and a thickness-directional phase difference into 10 nm or less, to bring a film impact strength into ≥0.2 J and to bring a folding endurance test frequency into ≥200 times. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical film excellent in optical properties and mechanical strength.

  A thermoplastic acrylic resin typified by polymethyl methacrylate (PMMA) has a high light transmittance, and has excellent optical properties, as well as excellent balance of mechanical strength, molding processability and surface hardness. Widely used for transparent materials and optical related applications in various industrial parts such as automobile parts and home appliances. In recent years, films using thermoplastic acrylic resins have been increasingly used as optical members for image display devices such as liquid crystal display devices, plasma displays, and organic EL display devices.

  One type of thermoplastic acrylic resin has a cyclic structure in the main chain. An acrylic resin having a ring structure in the main chain has a higher glass transition temperature (Tg) than an acrylic resin having no ring structure in the main chain. For this reason, a film containing such an acrylic resin as a main component has high heat resistance, and has various practical advantages such as easy arrangement in the vicinity of a heat generating part such as a light source in an image display device. As an example, an acrylic resin having a lactone ring structure in the main chain is disclosed in Japanese Patent Application Laid-Open No. 2000-230016 (Patent Document 1), and a resin film mainly comprising an acrylic resin having a lactone ring structure in the main chain is disclosed in Japanese Patent Application Laid-Open No. 2006-2006. No. 96960 (Patent Document 2).

  In image display devices, resin films are used as various optical films. With the increase in screen size of image display devices, there is a strong demand for thinning and large area of these films. For this purpose, improvement of mechanical properties such as strength and flexibility of resin films is desired. ing. In addition, a film having a low retardation is desired for improving the image quality.

  However, when the main component is an acrylic resin having a ring structure in the main chain, the heat resistance of the film is improved by the ring structure, while the film becomes hard, and this tendency increases the content of the ring structure in the resin film. It gets stronger. For this reason, it is difficult to improve the mechanical properties of the acrylic resin film by introducing a ring structure into the main component acrylic resin, and at the same time, it is difficult to improve the mechanical properties. Or tears when handling the film. For this reason, attempts have been made to improve flexibility by stretching a resin film, but the strength is insufficient, and an optical film having improved flexibility and strength with a low phase difference is not disclosed. It was.

JP 2000-230016 A JP 2006-96960 A

  Up to now, in a film containing an acrylic resin having a ring structure in the main chain, the flexibility could be improved by stretching, but the absolute strength of the film decreased as the thickness decreased. I was sorry. An object of the present invention is to provide an optical film having a low phase difference and excellent mechanical strength having both flexibility and strength.

  The optical film of the present invention is a film containing an acrylic resin having a ring structure in the main chain, the in-plane retardation Re is 10 nm or less, the thickness direction retardation Rth is 10 nm or less, the film impact strength is 0.2 J or more, The number of MIT folding endurance tests is 200 or more.

  The optical film of the present invention is a biaxially stretched optical film.

  According to the present invention, an optical film having excellent optical properties and having both strength and flexibility can be obtained. Moreover, the film excellent in heat resistance can be provided by including the acrylic resin which has ring structure in a principal chain.

  In the following description, unless otherwise specified, “%” means “% by mass”, “parts” means “parts by mass”, and “A to B” representing a range means “A or more and B or less”. To do.

[Acrylic resin (A)]
The acrylic resin (A) is not particularly limited as long as it is an acrylic resin having a ring structure in the main chain.

  The acrylic resin is a resin having a (meth) acrylic acid ester unit and / or a (meth) acrylic acid unit as a structural unit, and is derived from a (meth) acrylic acid ester or a derivative of (meth) acrylic acid. You may have a unit. The total of the proportion of the structural units derived from the (meth) acrylic acid ester unit, the (meth) acrylic acid unit and the derivative in all the structural units of the acrylic resin is usually 50% or more, preferably 60% or more, More preferably, it is 70% or more.

  (Meth) acrylic acid ester units are, for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, t- (meth) acrylic acid t- Butyl, n-hexyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, benzyl (meth) acrylate, dicyclopentanyloxyethyl (meth) acrylate, (meth) acryl Dicyclopentanyl acid, chloromethyl (meth) acrylate, 2-chloroethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, (meth) acrylic acid 2, 3,4,5,6-pentahydroxyhexyl, 2,3,4,5-tetrahydro (meth) acrylic acid Shipenchiru is a structural unit derived from 2- (hydroxymethyl) acrylate, 2- (hydroxymethyl) acrylate, a monomer such as 2- (hydroxyethyl) acrylate.

  The (meth) acrylic acid unit is a structural unit derived from a monomer such as acrylic acid, methacrylic acid, crotonic acid, 2- (hydroxymethyl) acrylic acid, 2- (hydroxyethyl) acrylic acid, and the like.

  The acrylic resin (A) may have two or more of these structural units as a (meth) acrylic acid ester unit and a (meth) acrylic acid unit. The acrylic resin (A) preferably has a methyl methacrylate unit. In this case, the thermal stability of a film obtained by molding the composition containing the acrylic resin (A) and the acrylic resin (A) is improved.

  Since the acrylic resin (A) has a ring structure in the main chain, the glass transition temperature (Tg) of the acrylic resin (A) is increased, and the heat resistance of the film containing the acrylic resin (A) is improved. As described above, the film containing the acrylic resin (A) having a ring structure in the main chain is suitable for use as an optical member because it can be easily arranged in the vicinity of a heat generating part such as a light source in an image display device.

  The Tg of the acrylic resin (A) is preferably 115 ° C. or higher, more preferably 120 ° C. or higher, and further preferably 130 ° C. or higher because the heat resistance of the resulting film is improved.

  Although the kind of ring structure is not specifically limited, For example, it is at least 1 sort (s) chosen from lactone ring structure, glutaric anhydride structure, glutarimide structure, N-substituted maleimide structure, and maleic anhydride structure.

  The following general formula (1) shows a glutaric anhydride structure and a glutarimide structure.

In the general formula (1), R ¹ and R ² are each independently a hydrogen atom or a methyl group, and X ¹ is an oxygen atom or a nitrogen atom. When X ¹ is an oxygen atom, R ³ does not exist, and when X ¹ is a nitrogen atom, R ³ is a hydrogen atom, a linear alkyl group having 1 to 6 carbon atoms, a cyclopentyl group, a cyclohexyl group, or a phenyl group. It is.

X ¹ is the ring structure represented by the general formula (1) when the oxygen atom is the glutaric anhydride structure. The glutaric anhydride structure can be formed, for example, by subjecting a copolymer of (meth) acrylic acid ester and (meth) acrylic acid to dealcoholization cyclocondensation in the molecule.

When X ¹ is a nitrogen atom, the ring structure represented by the general formula (1) is a glutarimide structure. The glutarimide structure can be formed, for example, by imidizing a (meth) acrylic acid ester polymer with an imidizing agent such as methylamine.

  The following general formula (2) shows a maleic anhydride structure and an N-substituted maleimide structure.

In the general formula (2), R ⁴ and R ⁵ are each independently a hydrogen atom or a methyl group, and X ² is an oxygen atom or a nitrogen atom. When X ² is an oxygen atom, R ⁶ is not present, and when X ² is a nitrogen atom, R ⁶ is a hydrogen atom, a linear alkyl group having 1 to 6 carbon atoms, a cyclopentyl group, a cyclohexyl group, or a phenyl group. It is.

When X ² is an oxygen atom, the ring structure represented by the general formula (2) is a maleic anhydride structure. The maleic anhydride structure can be formed, for example, by copolymerizing maleic anhydride and (meth) acrylic acid ester.

When X ² is a nitrogen atom, the ring structure represented by the general formula (2) is an N-substituted maleimide structure. The N-substituted maleimide structure can be formed, for example, by polymerizing an N-substituted maleimide such as phenylmaleimide and a (meth) acrylic acid ester.

  In each method for forming the ring structure exemplified in the description of the general formulas (1) and (2), all polymers used for forming each ring structure have a (meth) acrylate unit as a single unit. The resin obtained by this method is an acrylic resin.

  The lactone ring structure that the acrylic resin (A) may have in the main chain is not particularly limited, and may be, for example, a 4- to 8-membered ring. Alternatively, a 6-membered ring is preferable, and a 6-membered ring is more preferable. The lactone ring structure which is a 6-membered ring is, for example, the structure disclosed in Japanese Patent Application Laid-Open No. 2004-168882. However, the lactone ring structure is high due to the high polymerization yield of the precursor and the cyclization condensation reaction of the precursor. A structure represented by the following general formula (3) is preferable because an acrylic resin (A) having a ring content can be obtained and a polymer having a methyl methacrylate unit as a constituent unit can be used as a precursor.

In the general formula (3), R ⁷ , R ⁸ and R ⁹ are each independently a hydrogen atom or an organic residue having 1 to 20 carbon atoms. The organic residue may contain an oxygen atom.

  The organic residue in the general formula (3) is, for example, an alkyl group having 1 to 20 carbon atoms such as a methyl group, an ethyl group, or a propyl group. An aromatic hydrocarbon group having 1 to 20 carbon atoms, such as a saturated aliphatic hydrocarbon group, a phenyl group, or a naphthyl group, and the alkyl group, the unsaturated aliphatic hydrocarbon group, and the aromatic hydrocarbon group are One or more hydrogen atoms may be substituted with at least one group selected from a hydroxyl group, a carboxyl group, an ether group, and an ester group.

  Although the content rate of the said ring structure except the lactone ring structure in an acrylic resin (A) is not specifically limited, For example, it is 5-90%, Preferably it is 10-70%, More preferably, it is 10-60% More preferably, it is 10 to 50%.

  When the acrylic resin (A) has a lactone ring structure in the main chain, the content of the lactone ring structure in the resin is not particularly limited, but is, for example, 5 to 90%, preferably 10 to 80%, more Preferably it is 10-70%, More preferably, it is 20-60%.

  When the content of the ring structure in the acrylic resin (A) becomes transiently small, the heat resistance of the film may be lowered, and the solvent resistance and surface hardness may be insufficient. On the other hand, when the above content rate increases transiently, the moldability and mechanical properties of the film deteriorate.

  The acrylic resin (A) having a ring structure in the main chain can be produced by a known method. An acrylic resin whose ring structure is a glutaric anhydride structure or a glutarimide structure can be produced, for example, by the method described in WO2007 / 26659 or WO2005 / 108438. An acrylic resin whose ring structure is a maleic anhydride structure or an N-substituted maleimide structure can be produced, for example, by the method described in JP-A-57-153008 and JP-A-2007-31537. An acrylic resin whose ring structure is a lactone ring structure can be produced by, for example, the method described in JP-A-2006-96960, JP-A-2006-171464, or JP-A-2007-63541.

  The acrylic resin (A) may have a structural unit other than the (meth) acrylic acid ester unit and the (meth) acrylic acid unit. Examples of such a structural unit include styrene, vinyltoluene, and α-methyl. Styrene, α-hydroxymethylstyrene, α-hydroxyethylstyrene, acrylonitrile, methacrylonitrile, methallyl alcohol, allyl alcohol, ethylene, propylene, 4-methyl-1-pentene, vinyl acetate, 2-hydroxymethyl-1-butene , A structural unit derived from monomers such as methyl vinyl ketone, N-vinyl pyrrolidone and N-vinyl carbazole. The acrylic resin (A) may have two or more of these structural units.

  The acrylic resin (A) may have a structural unit having an effect of giving negative intrinsic birefringence to the resin. In this case, the degree of freedom in controlling the birefringence in the film made of the acrylic resin (A) is improved, and the use application of the optical film in the present invention is expanded.

  Intrinsic birefringence refers to the orientation axis from the refractive index n1 of light in a direction parallel to the direction (orientation axis) in which molecular chains are oriented in a layer (for example, a sheet or film) in which resin molecular chains are uniaxially oriented. A value obtained by subtracting the refractive index n2 of the light in the direction perpendicular to (i.e., "n1-n2"). The positive / negative of the intrinsic birefringence of the acrylic resin (A) itself is determined by the balance between the action of the structural unit with respect to the intrinsic birefringence and the action of the other structural unit of the acrylic resin (A).

  An example of a structural unit having an effect of giving negative intrinsic birefringence to the acrylic resin (A) is a styrene unit.

  The weight average molecular weight of an acrylic resin (A) is the range of 1000-300000, for example, Preferably it is the range of 5000-250,000, More preferably, it is the range of 10,000-200000, More preferably, it is the range of 50,000-200000. is there.

  The acrylic resin (A) may have an ultraviolet absorbing ability as long as the heat resistance, physical properties, and optical properties are not impaired. Specifically, a method using an ultraviolet-absorbing monomer and / or an ultraviolet-stable monomer as a monomer component when producing the acrylic resin (A), an ultraviolet absorber and / or an ultraviolet stabilizer There exists a method of mix | blending with the said acrylic resin (A). Moreover, as long as there is no trouble in the optical film containing an acrylic resin (A), you may use these methods together. In order to maintain the ultraviolet absorbing function, it is preferable to use an ultraviolet absorbing monomer and an ultraviolet stabilizing monomer in combination, or to use an ultraviolet absorber and an ultraviolet stabilizer in combination. It is also preferable to use an ultraviolet absorber and / or an ultraviolet stabilizer in combination with the ultraviolet absorbing monomer and / or the ultraviolet stabilizing monomer.

  Examples of the ultraviolet absorbing monomer include benzotriazole compounds, benzophenone compounds or triazine compounds and acrylic monomers having a polymerizable unsaturated group. Examples of benzotriazole compounds include 2- [2′-hydroxy-5 ′-(meth) acryloyloxymethylphenyl] -2H-benzotriazole, 2- [2′-hydroxy-5 ′-(meth) acryloyloxyethyl. Phenyl] -2H-benzotriazole, 2- [2′-hydroxy-5 ′-(meth) acryloyloxypropylphenyl] -2H-benzotriazole, 2- [2′-hydroxy-5 ′-(meth) acryloyloxyhexyl Phenyl] -2H-benzotriazole, 2- [2′-hydroxy-3′-tert-butyl-5 ′-(meth) acryloyloxyethylphenyl] -2H-benzotriazole, 2- [2′-hydroxy-5 ′ -(Β- (Meth) acryloyloxyethoxy) -3′-tert-butyl Enyl] -5-tert-butyl-2H-benzotriazole, 2- [2′-hydroxy-3′-methacrylaminomethyl-5 ′-(1 ″, 1 ″, 3 ″, 3 ″ -tetramethyl) butylphenyl ] -2H-benzotriazole and the like can be used. Examples of the benzophenone compounds include 2-hydroxy-4- [2- (meth) acryloyloxy] ethoxybenzophenone, 2-hydroxy-4- [2- (meth) acryloyloxy] butoxybenzophenone, 2,2 ′. -Dihydroxy-4- [2- (meth) acryloyloxy] ethoxybenzophenone, 2-hydroxy-4- [2- (meth) acryloyloxy] ethoxy-4 '-(2-hydroxyethoxy) benzophenone, and the like can be used. . Examples of the triazine compound include 4-diphenyl-6- [2-hydroxy-4- (2-acryloyloxyethoxy)]-s-triazine, 2,4-bis (2-methylphenyl) -6- [2-Hydroxy-4- (2-acryloyloxyethoxy)]-s-triazine, 2,4-bis (2-methoxyphenyl) -6- [2-hydroxy-4- (2-acryloyloxyethoxy)]- An s-triazine or the like can be used. When using such an ultraviolet-absorbing monomer, it is preferably copolymerized in an amount of 0.1 to 25% by weight, more preferably 1 to 15% by weight of all monomers. . If the content is small, the contribution to improving the weather resistance is low, and if the content is too large, the hot water resistance and solvent resistance may decrease or yellowing may occur.

  As the UV-stable monomer, a monomer having a polymerizable unsaturated group bonded to a hindered amine compound can be used, and specific examples include 4- (meth) acryloyloxy-2,2,6,6. -Tetramethylpiperidine, 4- (meth) acryloylamino-2,2,6,6-tetramethylpiperidine, 4- (meth) acryloyloxy-1,2,2,6,6-pentamethylpiperidine, 4- ( (Meth) acryloylamino-1,2,2,6,6-pentamethylpiperidine, 4-cyano-4- (meth) acryloylamino-2,2,6,6-tetramethylpiperidine, 4-crotonoyloxy-2 , 2,6,6-tetramethylpiperidine, 4-crotonoylamino-2,2,6,6-tetramethylpiperidine, 1- (meth) acryloyl-4- (me ) Acryloylamino-2,2,6,6-tetramethylpiperidine, 1- (meth) acryloyl-4-cyano-4- (meth) acryloylamino-2,2,6,6-tetramethylpiperidine, 1-crotonoyl -4-crotonoyloxy-2,2,6,6-tetramethylpiperidine and the like. When such an ultraviolet-stable monomer is used, it is preferably copolymerized in an amount of 0.1 to 25% by weight, more preferably 1 to 15% by weight of all monomers. . If the content is small, the contribution to improving the weather resistance is low, and if the content is too large, the hot water resistance and solvent resistance may decrease or yellowing may occur.

  Examples of the ultraviolet absorber include benzophenone compounds, salicinate compounds, benzoate compounds, triazole compounds, and triazine compounds. Examples of the benzophenone compounds include 2,4-dihydroxybenzophenone, 4-n-octyloxy-2-hydroxybenzophenone, 2,2′-dihydroxy-4,4′-dimethoxybenzophenone, 2-hydroxy-4-n-octyl. Examples thereof include oxybenzophenone, bis (5-benzoyl-4-hydroxy-2-methoxyphenyl) methane, 1,4-bis (4-benzoyl-3-hydroxyphenone) -butane and the like. Examples of the silicate compound include pt-butylphenyl silicate. Examples of the benzoate compound include 2,4-di-t-butylphenyl-3 ', 5'-di-t-butyl-4'-hydroxybenzoate. Examples of triazole compounds include 2,2′-methylenebis [4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol], 2- (3 , 5-Di-tert-butyl-2-hydroxyphenyl) -5-chlorobenzotriazole, 2- (2H-benzotriazol-2-yl) -p-cresol, 2- (2H-benzotriazol-2-yl) -4,6-bis (1-methyl-1-phenylethyl) phenol, 2-benzotriazol-2-yl-4,6-di-tert-butylphenol, 2- [5-chloro (2H) -benzotriazole- 2-yl] -4-methyl-6-tert-butylphenol, 2- (2H-benzotriazol-2-yl) -4,6-di-tert-butylphenol, 2- 2H-benzotriazol-2-yl) -4- (1,1,3,3-tetramethylbutyl) phenol, 2- (2H-benzotriazol-2-yl) -4-methyl-6- (3,4) , 5,6-tetrahydrophthalimidylmethyl) phenol, methyl 3- (3- (2H-benzotriazol-2-yl) -5-tert-butyl-4-hydroxyphenyl) propionate / polyethylene glycol 300 reaction product 2- (2H-benzotriazol-2-yl) -6- (linear and side chain dodecyl) -4-methylphenol, 2- (5-methyl-2-hydroxyphenyl) benzotriazole, 2- [2- Hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2H-benzotriazole, 3- (2H-benzotriazol-2-yl ) -5- (1,1-dimethylethyl) -4-hydroxy -C7-9 side chain and straight chain alkyl esters. Further, triazine compounds include 2,4-diphenyl-6- (2-hydroxy-4-methoxyphenyl) -1,3,5-triazine, 2,4-diphenyl-6- (2-hydroxy-4-). Ethoxyphenyl) -1,3,5-triazine, 2,4-diphenyl- (2-hydroxy-4-propoxyphenyl) -1,3,5-triazine, 2,4-diphenyl- (2-hydroxy-4-) Butoxyphenyl) -1,3,5-triazine, 2,4-diphenyl-6- (2-hydroxy-4-butoxyphenyl) -1,3,5-triazine, 2,4-diphenyl-6- (2- Hydroxy-4-hexyloxyphenyl) -1,3,5-triazine, 2,4-diphenyl-6- (2-hydroxy-4-octyloxyphenyl) -1,3,5-tria 2,4-diphenyl-6- (2-hydroxy-4-dodecyloxyphenyl) -1,3,5-triazine, 2,4-diphenyl-6- (2-hydroxy-4-benzyloxyphenyl)- 1,3,5-triazine, 2,4-diphenyl-6- (2-hydroxy-4-butoxyethoxy) -1,3,5-triazine, 2,4-bis (2-hydroxy-4-butoxyphenyl) And -6- (2,4-dibutoxyphenyl) -1,3-5-triazine. Among these, 2,4-bis (2,4-dimethylphenyl) -6- [2-hydroxy-4- (3-alkyloxy-2- (2)-(2-alkyloxy-2-) has a high compatibility with acrylic resins and excellent absorption characteristics. (Hydroxypropyloxy) -5-α-cumylphenyl] -s-triazine skeleton (alkyloxy; long-chain alkyloxy groups such as octyloxy, nonyloxy, decyloxy, etc.) is more preferred, and is represented by the following chemical formula (4). Particularly preferred is an ultraviolet absorber containing as a main component an ultraviolet absorber having the structure described above. As a commercial item, Tinuvin 477 (made by Ciba Specialty Chemicals) etc. are mentioned, for example.

These can be used alone or in combination of two or more. Although the compounding quantity of the said ultraviolet absorber is not specifically limited, It is preferable that it is 0.01-25 mass% in the film containing an acrylic resin (A), More preferably, it is 0.05-10 mass%. If the amount added is too small, the contribution to improving weather resistance is low, and if it is too large, the mechanical strength may be lowered or yellowing may be caused.

  The acrylic resin (A) may contain other resins as long as the effects of the present invention are not impaired. The content of other resins is preferably 0 to 50% by mass, more preferably 0 to 25% by mass, and still more preferably 0 to 10% by mass.

  Examples of other resin components include olefin polymers such as polyethylene, polypropylene, ethylene-propylene copolymer, and poly (4-methyl-1-pentene); halogen-containing polymers such as vinyl chloride and chlorinated vinyl resins; Acrylic polymers such as polymethyl methacrylate; styrene polymers such as polystyrene, styrene-methyl methacrylate copolymer, styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene block copolymer; polyethylene terephthalate, polybutylene terephthalate, Polyester such as polyethylene naphthalate; biodegradable polyester such as polylactic acid and polybutylene succinate; polyamide such as nylon 6, nylon 66, nylon 610; polyacetal: polycarbonate Polyphenylene oxide; Polyphenylene sulfide: Polyether ether ketone; Polyether nitrile; Polysulfone; Polyether sulfone: Polyoxypentylene; Polyamideimide; Rubber weight such as ABS resin and ASA resin blended with polybutadiene rubber and acrylic rubber And the like; From the viewpoint of compatibility, a styrene-acrylonitrile copolymer is preferable. The rubbery polymer preferably has a graft portion having a composition compatible with the acrylic resin (A) on the surface, and the average particle diameter of the rubbery polymer is from the viewpoint of improving transparency when formed into a film. Therefore, the thickness is preferably 100 nm or less, and more preferably 70 nm or less.

  The acrylic resin (A) may contain other additives. The content of other additives in the acrylic resin (A) is preferably 0 to 5% by mass, more preferably 0 to 2% by mass, and still more preferably 0 to 0.5% by mass. Examples of other additives include hindered phenol-based, phosphorus-based and sulfur-based antioxidants; light-resistant stabilizers, weather-resistant stabilizers, heat-stabilizers, and other stabilizers; reinforcing materials such as glass fibers and carbon fibers. Near infrared absorbers; flame retardants such as tris (dibromopropyl) phosphate, triallyl phosphate, antimony oxide; antistatic agents such as anionic, cationic and nonionic surfactants; inorganic pigments, organic pigments, dyes, etc. Colorants; organic fillers and inorganic fillers; resin modifiers; plasticizers; lubricants.

  A known antioxidant can be used as the antioxidant. Examples of phenolic antioxidants include n-octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, n-octadecyl-3- (3,5-di-t-butyl). -4-hydroxyphenyl) acetate, n-octadecyl-3,5-di-t-butyl-4-hydroxybenzoate, n-hexyl-3,5-di-t-butyl-4-hydroxyphenylbenzoate, n-dodecyl 3,5-di-t-butyl-4-hydroxyphenylbenzoate, neododecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, dodecyl-β- (3,5-di- t-butyl-4-hydroxyphenyl) propionate, ethyl-α- (4-hydroxy-3,5-di-t-butylphenyl) isobutyrate Octadecyl-α- (4-hydroxy-3,5-di-t-butylphenyl) isobutyrate, octadecyl-α- (4-hydroxy-3,5-di-t-butyl-4-hydroxyphenyl) propionate, 2- (n-octylthio) ethyl-3,5-di-t-butyl-4-hydroxybenzoate, 2- (n-octylthio) ethyl-3,5-di-t-butyl-4-hydroxyphenyl acetate, 2 -(N-octadecylthio) ethyl-3,5-di-t-butyl-4-hydroxyphenyl acetate, 2- (n-octadecylthio) ethyl-3,5-di-t-butyl-4-hydroxybenzoate, 2- (2-hydroxyethylthio) ethyl-3,5-di-t-butyl-4-hydroxybenzoate, diethyl glycol bis- (3,5 -Di-t-butyl-4-hydroxy-phenyl) propionate, 2- (n-octadecylthio) ethyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, stearamide-N, N -Bis- [ethylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], n-butylimino-N, N-bis- [ethylene-3- (3,5-di-t -Butyl-4-hydroxyphenyl) propionate], 2- (2-stearoyloxyethylthio) ethyl-3,5-di-t-butyl-4-hydroxybenzoate, 2- (2-stearoyloxyethylthio) ethyl- 7- (3-Methyl-5-tert-butyl-4-hydroxyphenyl) heptanoate, 1,2-propylene glycol bis- [3- (3,5 Di-t-butyl-4-hydroxyphenyl) propionate], ethylene glycol bis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], neopentyl glycol bis- [3- (3 , 5-di-t-butyl-4-hydroxyphenyl) propionate], ethylene glycol bis- (3,5-di-t-butyl-4-hydroxyphenyl acetate), glycerin-1-n-octadecanoate- 2,3-bis- (3,5-di-t-butyl-4-hydroxyphenyl acetate), pentaerythritol tetrakis- [3- (3 ', 5'-di-t-butyl-4'-hydroxyphenyl) Propionate], 1,1,1-trimethylolethanetris- [3- (3,5-di-tert-butyl-4-hydroxypheny ) Propionate], sorbitol hexa- [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], 2-hydroxyethyl-7- (3-methyl-5-tert-butyl-4-hydroxy Phenyl) propionate, 2-stearoyloxyethyl-7- (3-methyl-5-tert-butyl-4-hydroxyphenyl) heptanoate, 1,6-n-hexanediol bis-[(3 ', 5'-di- t-butyl-4-hydroxyphenyl) propionate], pentaerythritol tetrakis- (3,5-di-t-butyl-4-hydroxyhydrocinnamate), 3,9-bis [1,1-dimethyl-2- [ [beta]-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionyloxy] ethyl] 2,4,8,10-tetrao Saspiro [5,5] -undecane, 2,4-di-t-amyl-6- [1- (3,5-di-t-amyl-2-hydroxyphenyl) ethyl] phenyl acrylate and 2-t-butyl -6- (3-t-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate.

  Examples of the thioether-based antioxidant include pentaerythrityl tetrakis (3-lauryl thiopropionate), dilauryl-3,3′-thiodipropionate, dimyristyl-3,3′-thiodipropionate, and distearyl. -3,3'-thiodipropionate.

Examples of phosphorus antioxidants include tris (2,4-di-t-butylphenyl) phosphite, 2-[[2,4,8,10-tetrakis (1,1-dimethylethyl) dibenzo [d. , F] [1,3,2] dioxaphosphin-6-yl] oxy] -N, N-bis [2-[[2,4,8,10-tetrakis (1,1 dimethylethyl) dibenzo [D, f] [1,3,2] dioxaphosphin-6-yl] oxy] -ethyl] ethanamine, diphenyltridecyl phosphite, triphenyl phosphite, 2,2-methylenebis (4,6- Di-t-butylphenyl) octyl phosphite, bis (2,6-di-t-butyl-4-methylphenyl) pentaerythritol diphosphite, distearyl pentaerythritol diphosphite DOO, cyclic neopentanetetraylbis (2,6-di -t- butyl-4-methylphenyl) phosphite and the like.
[Optical film]
Since the optical film of the present invention contains an acrylic resin (A) having a ring structure in the main chain, it is excellent in heat resistance. The Tg of the film is, for example, 110 ° C. or higher, and is 115 ° C. or higher, 120 ° C. or higher, and further 130 ° C. or higher depending on the composition of the acrylic resin (A) and the acrylic resin (A) content in the optical film. . Such an optical film having a high Tg is suitable for optical applications because it can be easily disposed near a heat generating part such as a light source in an image display device.

  The optical film of the present invention has an in-plane retardation Re and a thickness direction retardation Rth of 10 nm or less, preferably 5 nm or less, and more preferably 3 nm or less. In-plane retardation and thickness direction retardation are indicators of birefringence, and the optical film of the present invention has low birefringence. When the in-plane retardation and the thickness direction retardation exceed 10 nm, the anisotropy of the refractive index increases, and it may not be used for applications requiring low birefringence.

  The optical film of the present invention has a film impact strength measured in accordance with ASTM D3420-95 of 0.2 J or more, preferably 0.3 J or more. When the film impact strength is less than 0.2 J, the mechanical strength as a film may be insufficient.

  In the optical film of the present invention, the number of MIT folding resistance tests at a load of 200 g measured in accordance with JIS P8115 is 200 times or more, preferably 300 times or more, more preferably 400 times or more. When the number of folding resistance tests is less than 200, the flexibility as a film may be insufficient.

  The optical film of the present invention is preferably biaxially stretched, and either sequential biaxial stretching or simultaneous biaxial stretching may be used. The stretching temperature is not particularly limited, and a temperature in the vicinity of Tg of the resin composition containing the acrylic resin (A) is preferable, for example, in the range of (Tg-20) to (Tg + 50), and more preferably (Tg-10). To (Tg + 30). When it is (Tg-20) degrees or less, the film cannot follow the stretching during stretching and is easily broken, and when it is (Tg + 50) degrees or more, the effect of stretching may be insufficient. The stretching speed is not particularly limited and is, for example, in the range of 10 to 20000% / min, and more preferably in the range of 100 to 10000% / min. If the stretching speed is slower than 10% / min, it takes time to perform stretching, resulting in an increase in production cost. If the stretching speed is faster than 20000% / min, the film may be broken.

  It is preferable that the draw ratio of the optical film of the present invention is formed by stretching at an area ratio of 4.1 times or more. If the magnification is 4.1 times or less, it is difficult to achieve both impact strength and flexibility of the film.

  The thickness of the optical film of the present invention is 1 to 250 μm, preferably 10 to 100 μm, and more preferably 20 to 60 μm.

  The method for forming the optical film of the present invention is not particularly limited, and for example, a known technique such as cast molding, melt extrusion molding, press molding or the like may be used.

  As a method of forming the optical film of the present invention, there is an extrusion method. As a specific example, after each component constituting the acrylic resin (A) is pre-blended with a mixer such as an omni mixer, the obtained mixture may be extrusion kneaded from a kneader. The kneader used for the extrusion kneading is not particularly limited, and for example, a known kneader such as a single screw extruder, a twin screw extruder, or a pressure kneader can be used.

  Alternatively, separately formed acrylic resin (A) may be melt-extruded. Examples of the melt extrusion method include a T-die method and an inflation method, and the molding temperature at that time is preferably 200 to 350 ° C., more preferably 250 to 300 ° C., further preferably 255 to 300 ° C., particularly Preferably it is 260 to 300 degreeC.

  When the T-die method is used, a resin film wound into a roll can be obtained by attaching a T-die to the tip of the extruder and winding the film extruded from the T-die. At this time, it is also possible to control the temperature and speed of winding and to stretch (uniaxial stretching) in the extrusion direction of the film.

  When an extruder is used for extrusion molding, the type is not particularly limited and may be uniaxial, biaxial, or multiaxial, but its L / D value is (L is the value of the extruder) The length of the cylinder, D is the cylinder inner diameter), in order to sufficiently plasticize the acrylic resin to obtain a good kneaded state, it is preferably 10 or more and 100 or less, more preferably 15 or more and 80 or less, and still more preferably 20 or more and 60 or less. When the L / D value is less than 10, the acrylic resin cannot be sufficiently plasticized and a good kneaded state may not be obtained. On the other hand, when the L / D value exceeds 100, the resin in the composition may be thermally decomposed due to excessive shearing heat generation on the acrylic resin.

  In this case, the set temperature of the cylinder is preferably 200 ° C. or higher and 300 ° C. or lower, and more preferably 250 ° C. or higher and 300 ° C. or lower. If setting temperature is less than 200 degreeC, the melt viscosity of an acrylic resin will become high too much, and the productivity of a resin film will fall. On the other hand, when the set temperature exceeds 300 ° C., the acrylic resin may be thermally decomposed.

  When an extruder is used for extrusion molding, the shape is not particularly limited, but the extruder preferably has one or more open vent portions. By using such an extruder, the decomposition gas can be sucked from the open vent portion, and the amount of volatile components remaining in the obtained resin film can be reduced. In order to suck the decomposition gas from the open vent portion, for example, the open vent portion may be in a reduced pressure state, and the degree of pressure reduction is preferably in the range of 931 to 1.3 hPa as the pressure of the open vent portion, 798 A range of ˜13.3 hPa is more preferable. When the pressure in the open vent portion is higher than 931 hPa, volatile components or monomer components generated by decomposition of the resin tend to remain in the resin. On the other hand, it is industrially difficult to keep the pressure of the open vent part lower than 1.3 hPa.

  The optical film of the present invention is preferably formed by molding an acrylic resin filtered through a polymer filter. Since the polymer filter can remove foreign substances present in the acrylic resin, defects in the appearance of the obtained film can be reduced. In addition, at the time of filtration by a polymer filter, an acrylic resin will be in a high temperature molten state. For this reason, the acrylic resin deteriorates when passing through the polymer filter, and gas components and colored deterioration products formed by the deterioration flow into the composition, and the resulting film is perforated, flow pattern, flow streak. Such defects may be observed. This defect is particularly easily observed during continuous molding of a resin film. For this reason, when molding an acrylic resin filtered with a polymer filter, the molding temperature is, for example, 255 to 300 ° C. in order to reduce the melt viscosity of the resin and shorten the residence time of the resin in the polymer filter. 260 to 320 ° C is preferable.

  The configuration of the polymer filter is not particularly limited, but a polymer filter in which a large number of leaf disk filters are arranged in a housing can be suitably used. The filter material of the leaf disk type filter may be any of a type in which a metal fiber nonwoven fabric is sintered, a type in which metal powder is sintered, a type in which several metal meshes are laminated, or a hybrid type in which they are combined. The sintered type is most preferred.

  The filtration accuracy by the polymer filter is not particularly limited, but is usually 15 μm or less, preferably 10 μm or less, more preferably 5 μm or less. If the filtration accuracy is 1 μm or less, the residence time of the resin becomes longer, so that the thermal degradation of the composition increases, and the productivity of the resin film decreases. On the other hand, when the filtration accuracy exceeds 15 μm, it is difficult to remove foreign substances in the acrylic resin.

  The shape of the polymer filter is not particularly limited. For example, an inner flow type having a plurality of resin flow ports and a resin flow path in the center pole; the inner peripheral surface of the leaf disk filter at a plurality of vertices or faces And an external flow type having a resin flow path on the outer surface of the center pole. In particular, it is preferable to use an external flow type in which the resin stays are small.

  Although there is no restriction | limiting in particular in the residence time of the resin in a polymer filter, Preferably it is 20 minutes or less, More preferably, it is 10 minutes or less, More preferably, it is 5 minutes or less. Further, the filter inlet pressure and the filter outlet pressure during filtration are, for example, 3 to 15 MPa and 0.3 to 10 MPa, respectively, and the pressure loss (the pressure difference between the filter inlet pressure and the outlet pressure) is 1 MPa to 15 MPa. A range is preferred. When the pressure loss is 1 MPa or less, the flow path through which the resin passes through the filter tends to be biased, and the quality of the obtained resin film tends to deteriorate. On the other hand, when the pressure loss exceeds 15 MPa, the polymer filter is easily damaged.

  What is necessary is just to set suitably the temperature of resin introduce | transduced into a polymer filter according to the melt viscosity, for example, it is 250-300 degreeC, Preferably it is 255-300 degreeC, More preferably, it is 260-300 degreeC.

  The specific process of obtaining an optical film with few foreign substances and colored substances by filtration using a polymer filter is not particularly limited. For example, (1) a process of forming and filtering an acrylic resin in a clean environment, and subsequently molding the acrylic resin in a clean environment; (2) an acrylic resin having foreign matter or colored substances in a clean environment Examples of the process include a process in which an acrylic resin is subsequently molded in a clean environment after the filtration process, and (3) a process in which an acrylic resin having a foreign substance or a colored substance is filtered in a clean environment and simultaneously molded. You may perform the filtration process of the acrylic resin by a polymer filter in multiple times for each process.

  When the acrylic resin is filtered by the polymer filter, it is preferable to install a gear pump between the extruder and the polymer filter to stabilize the pressure of the resin in the filter.

  In order to stabilize the optical properties and mechanical properties of the optical film, heat treatment (annealing) may be performed as necessary after stretching.

<Measurement method>
The physical properties in the present invention are measured by the following method. The same method was used in the examples and comparative examples.

<Glass transition temperature>
The glass transition temperature (Tg) of each sample was determined in accordance with JIS K7121 regulations. Specifically, using a differential scanning calorimeter (manufactured by Rigaku, DSC-8230), a sample of about 10 mg was heated from a normal temperature to 200 ° C. at a heating rate of 20 ° C./min in a nitrogen gas atmosphere. It calculated by the starting point method from the DSC curve. Α-alumina was used as a reference.

<Weight average molecular weight>
The weight average molecular weight of the acrylic resin was determined by gel permeation chromatography (GPC) under the following conditions.
System: GPC system HLC-8220 manufactured by Tosoh Corporation
Developing solvent: Chloroform (made by Wako Pure Chemical Industries, special grade), flow rate: 0.6 ml / min Standard sample: TSK standard polystyrene (manufactured by Tosoh Corporation, PS-oligomer kit)
Measurement side column configuration: guard column (manufactured by Tosoh Corp., TSKguardcolumn SuperHZ-L), separation column (manufactured by Tosoh Corp., TSKgel SuperHZM-M) 2 series connection reference side column configuration: reference column (manufactured by Tosoh Corp., TSKgel SuperH-RC) )
<Thickness of film>
Measurement was performed using a Digimatic Micrometer (manufactured by Mitutoyo Corporation).

<Haze>
The total light transmittance and haze were measured using a turbidimeter (Nippon Denshoku Industries Co., Ltd., NDH 5000).

<Refractive index anisotropy>
Refractive index anisotropy (retardation: in-plane retardation Re) was measured using KOBRA-WR manufactured by Oji Scientific Instruments. Thickness direction retardation Rth was measured by tilting it by 40 ° with the measurement wavelength as 589 nm and the slow axis as the tilt axis.

<Film impact>
The film impact strength was measured according to ASTM D3420 using a film impact tester (manufactured by Tester Sangyo) under the conditions of 23 ° C. and 50% RH.

<Folding resistance>
The number of folding times of the film was 15 mm in width and 90 mm in length using a MIT folding resistance tester (manufactured by Tester Sangyo Co., Ltd., model BE-201) and allowed to stand at 23 ° C. and 50% RH for 1 hour or longer The test film was measured under the condition of a load of 200 g in accordance with JIS P8115.

  Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to the examples shown below. In the following description, for convenience, “part by mass” may be simply referred to as “part”, and “liter” may be simply referred to as “L”.

(Production Example 1) Production of acrylic resin (A-1) In a 1000 L reaction kettle equipped with a stirrer, thermometer, cooler and nitrogen introduction tube, 40 parts of methyl methacrylate, 10 methyl 2- (hydroxymethyl) acrylate Part, toluene 50 parts and Adeka Stub 2112 (made by ADEKA) 0.025 part, while nitrogen was passed through this, the temperature was raised to 105 ° C. and refluxed. Manufactured under the trade name: Lupazole 570) and at the same time adding 0.10 parts of t-amylperoxyisononanoate dropwise over a period of 2 hours while refluxing (about 105-110 ° C.) Polymerization was performed, and further aging was performed for 4 hours.

  0.05 parts of stearyl phosphate (manufactured by Sakai Chemical Industry, trade name: Phoslex A-18) was added to the above polymer solution, and the cyclization condensation reaction was allowed to proceed for 2 hours under reflux (about 90 to 110 ° C.). .

  Next, the polymer solution obtained by the cyclization condensation reaction was completed through a multi-tube heat exchanger heated to 240 ° C., and then the barrel temperature was 240 ° C., the rotation speed was 120 rpm, and the degree of vacuum was 13 .3 to 400 hPa, 1 rear vent, 4 fore vents (referred to as the first, second, third, and fourth vents from the upstream side) Vent having a side feeder between the third vent and the fourth vent It was introduced into a type screw twin screw extruder (φ = 44 mm, L / D = 52.5) at a treatment rate of 20 kg / hour in terms of resin amount, and devolatilization was performed. At that time, the separately prepared antioxidant / deactivator mixed solution was injected after the second vent at a charging rate of 0.3 kg / hour using a high-pressure pump. Further, after the first vent and after the side feeder, ion exchange water was injected at a charging rate of 0.33 kg / hour using a high-pressure pump.

  Further, AS resin (manufactured by Asahi Kasei Chemicals, trade name: Stylac AS783L) was added from the side feeder at a supply rate of 2.12 kg / hour.

  Further, the melt-kneaded resin was filtered with a leaf disk type polymer filter (manufactured by Nagase Sangyo, filtration accuracy of 5 μm).

  An antioxidant / deactivator mixed solution was prepared by dissolving 50 parts of ADK STAB AO-60 (manufactured by ADEKA) and 40 parts of zinc octylate (manufactured by Nippon Chemical Industry Co., Ltd., 3.6% of Nikka octix zinc) in 210 parts of toluene. did.

  By the devolatilization operation, a pellet of the thermoplastic acrylic resin composition (A-1) was obtained. The weight average molecular weight of the resin part was 132000, and the glass transition temperature was 125 ° C.

(Example 1) Production of optical film (C-1) A-1 pellet obtained in Production Example 1 was coated on a hanger at 280 ° C using a single screw extruder (φ = 20 mm, L / D = 25). Melt extrusion was carried out from a type T die (width 150 mm) and discharged onto a cooling roll having a temperature of 110 ° C. to produce an unstretched film (B-1) having a thickness of 198 μm.

  After the obtained B-1 film was cut out to 96 mm × 96 mm, it was longitudinally and transversely (MD) at 150 ° C. and a speed of 800 mm / min using a sequential biaxial stretching machine (X-6S, manufactured by Toyo Seiki Seisakusho). -The biaxial stretching was successively performed so that the ratio was 2.2 times in the order of (TD direction). After stretching, the film was quickly taken out from the test apparatus and cooled to obtain an optical film (C-1) having a thickness of 36 μm. The in-plane retardation Re of the obtained optical film C-1 was 1 nm, the thickness direction retardation Rth was 2 nm, the total light transmittance was 93%, and the haze was 0.2%.

Example 2 Production of Optical Film (C-2) An unstretched film (B-2) having a thickness of 312 μm was produced in the same manner as in Example 1.

  The obtained B-2 film was sequentially biaxially stretched so as to be 2.7 times in the order of the machine direction and the transverse direction (MD and TD directions) in the same manner as in Example 1. After stretching, the film was promptly taken out from the test apparatus and cooled to obtain an optical film (C-2) having a thickness of 38 μm. The in-plane retardation Re of the obtained optical film C-2 was 1 nm, the thickness direction retardation Rth was 3 nm, the total light transmittance was 93%, and the haze was 0.2%.

Example 3 Production of Optical Film (C-3) An unstretched film (B-3) having a thickness of 406 μm was produced in the same manner as in Example 1.

  The obtained B-3 film was sequentially biaxially stretched in the same manner as in Example 1 so as to be 3.1 times in the order of the longitudinal and transverse directions (MD and TD directions). After stretching, the film was promptly taken out from the test apparatus and cooled to obtain an optical film (C-3) having a thickness of 41 μm. The in-plane retardation Re of the obtained optical film C-3 was 1 nm, the thickness direction retardation Rth was 4 nm, the total light transmittance was 93%, and the haze was 0.3%.

(Example 4) Production of optical film (C-4) An optical film (C-4) having a thickness of 37 µm was obtained in the same manner as in Example 1 except that the stretching temperature was set to 142 ° C. The in-plane retardation Re of the obtained optical film C-4 was 2 nm, the thickness direction retardation Rth was 4 nm, the total light transmittance was 92%, and the haze was 0.3%. Example 5 Optical Film An optical film (C-5) having a thickness of 38 μm was obtained in the same manner as in Example 2 except that the production stretching temperature of (C-5) was set to 142 ° C. In-plane retardation Re of the obtained optical film C-5 was 3 nm, thickness direction retardation Rth was 5 nm, total light transmittance was 92%, and haze was 0.4%. Example 6 Optical Film An optical film (C-6) having a thickness of 40 μm was obtained in the same manner as in Example 3 except that the production stretching temperature of (C-6) was set to 142 ° C. The in-plane retardation Re of the obtained optical film C-6 was 3 nm, the thickness direction retardation Rth was 6 nm, the total light transmittance was 92%, and the haze was 0.4%. (Comparative Example 1) Optical Film In the same manner as in Production Example 1 of (D-1), an unstretched film (B-4) having a thickness of 152 μm was produced.

  The obtained B-4 film was successively biaxially stretched in the same manner as in Example 1 so as to be 1.8 times in the longitudinal and lateral directions (MD and TD directions). After stretching, the film was promptly taken out from the test apparatus and cooled to obtain an optical film (D-1) having a thickness of 41 μm. The in-plane retardation Re of the obtained optical film D-1 was 1 nm, the thickness direction retardation Rth was 2 nm, the total light transmittance was 93%, and the haze was 0.3%.

(Comparative example 2) Production of optical film (D-2) Using unstretched film B-1 obtained in Example 1, in the same manner as in Example 1, in the order of length and width (MD and TD directions). Sequential biaxial stretching was performed so as to be 1.8 times each. After stretching, the film was quickly taken out from the test apparatus and cooled to obtain an optical film (D-2) having a thickness of 58 μm. The obtained optical film D-2 had an in-plane retardation Re of 2 nm, a thickness direction retardation Rth of 3 nm, a total light transmittance of 91%, and a haze of 0.5%.

(Comparative Example 3) Production of optical film (D-3) The unstretched film B-4 obtained in Comparative Example 1 was treated in the same manner as in Example 1 in the order of length and width (MD and TD directions). Sequential biaxial stretching was performed so as to be doubled. After stretching, the film was promptly taken out from the test apparatus and cooled to obtain an optical film (D-3) having a thickness of 29 μm. The obtained optical film D-3 had an in-plane retardation Re of 1 nm, a thickness direction retardation Rth of 3 nm, a total light transmittance of 93%, and a haze of 0.2%.

  Various test results of Examples 1 to 6 and Comparative Examples 1 to 3 are shown in Table 1.

  According to the present invention, by including an acrylic resin having a ring structure in the main chain, it is possible to provide an optical film that is excellent in heat resistance and has excellent optical properties, film strength, and flexibility. The optical film of the present invention can be suitably used for various image display devices (liquid crystal display devices, organic EL display devices, PDPs, etc.). Specifically, it can be used for various optical film applications such as a protective film, an antireflection film, a retardation film, and a polarizing film, which are used in flat panel display devices. In particular, it is suitable for a polarizer protective film.

Claims (3)

A film made of an acrylic resin having a ring structure in the main chain, with an in-plane retardation Re of 10 nm or less, a thickness direction retardation Rth of 10 nm or less, a film impact strength of 0.2 J or more, and a MIT folding resistance test number of times An optical film that is 200 times or more. The optical film according to claim 1, which is a biaxially stretched film. The optical film according to claim 1 or 2, wherein the draw ratio is 4.1 times or more in terms of area ratio.