Optical film

Abstract

To provide an optical film in which antiblocking properties are imparted to a surface layer composed of a polycarbonate resin composition.SOLUTION: The optical film includes a first surface layer comprising a first polycarbonate resin composition, an intermediate layer comprising a (meth) acrylic resin composition, and a second surface layer comprising a second polycarbonate resin composition in this order in the thickness direction, wherein the first surface layer and the second surface layer contain fine particles.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to optical films. [Background technology]

[0002] It is known that (meth)acrylic resin has excellent optical properties, and polycarbonate resin has excellent mechanical strength. As an optical film used in an image display device, an optical film utilizing the characteristics of these two resins is known, and for example, an optical film in which an intermediate layer is made of (meth)acrylic resin and a surface layer is made of polycarbonate resin has been disclosed (Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-232504 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-114427 [Patent Document 3] Japanese Patent Application Publication No. 2017-165086 Summary of the Invention [Problem to be solved by the invention]

[0004] The optical films disclosed in Patent Documents 1 to 3 need further study from the viewpoint of anti-blocking properties. First, Patent Documents 1 and 2 do not disclose anything about anti-blocking properties. On the other hand, Patent Document 3 discloses providing a predetermined urethane coating layer on the surface of a surface layer made of a polycarbonate resin, but this method does not improve anti-blocking properties unless a new urethane coating layer is provided.

[0005] The present disclosure has been made in light of the above-mentioned circumstances, and an object of the present disclosure is to provide an optical film in which anti-blocking properties are imparted to a surface layer made of a polycarbonate resin composition. [Means for solving the problem]

[0006] As a result of extensive investigation, the inventors have found an optical film that is endowed with anti-blocking properties by incorporating fine particles into a surface layer made of a polycarbonate resin composition.

[0007] That is, the present disclosure includes the following configurations. [1] An optical film comprising, in the thickness direction, a first surface layer made of a first polycarbonate resin composition, an intermediate layer made of a (meth)acrylic resin composition, and a second surface layer made of a second polycarbonate resin composition, in this order, wherein the first surface layer and the second surface layer contain fine particles. [2] The optical film according to [1], wherein the fine particles include organic fine particles. [3] The optical film according to [2], wherein the organic fine particles contain structural units derived from aromatic vinyl. [4] The optical film according to [3], wherein the organic fine particles have a core made of a (meth)acrylic resin and a shell made of a resin containing a structural unit derived from an aromatic vinyl. [5] The optical film according to [3] or [4], wherein the aromatic vinyl contains styrene. [6] The optical film according to any one of [1] to [5], wherein the (meth)acrylic resin composition has a glass transition temperature of 115 to 160°C. [7] The optical film according to any one of [1] to [6], wherein the (meth)acrylic resin composition has a positive stress optical coefficient. [8] The optical film according to any one of [1] to [7], wherein the (meth)acrylic resin composition contains a (meth)acrylic resin that includes a ring structural unit having a ring structure in the main chain and has a positive stress optical coefficient. [9] The optical film according to [8], wherein the ring structural unit is at least one selected from the group consisting of a lactone ring structural unit, an N-substituted succinimide structural unit, and a glutarimide structural unit.

[10] The optical film according to any one of [1] to [9], wherein the glass transition temperature of the first polycarbonate resin composition and the glass transition temperature of the second polycarbonate resin composition are both lower than the glass transition temperature of the (meth)acrylic resin composition.

[11] The optical film according to any one of [1] to

[10] above, which is a stretched film.

[12] A polarizer protective film comprising the optical film according to

[11] above.

[13] A polarizing plate comprising the polarizer protective film according to

[12] above.

[14] An image display device comprising the polarizing plate according to

[13] above. [Effects of the Invention]

[0008] The optical film of the present disclosure has excellent anti-blocking properties because the surface layer made of a polycarbonate resin composition contains fine particles. DETAILED DESCRIPTION OF THE INVENTION

[0009] The optical film of the present disclosure comprises a first surface layer made of a first polycarbonate resin composition, an intermediate layer made of a (meth)acrylic resin composition, and a second surface layer made of a second polycarbonate resin composition, in this order in the thickness direction. In other words, the optical film of the present disclosure comprises the first surface layer on one surface and the second surface layer on the other surface. The optical film of the present disclosure may further comprise another layer between the first surface layer and the intermediate layer or between the intermediate layer and the second surface layer, as long as the optical properties of the optical film are not significantly impaired.

[0010] In the present disclosure, the term "(meth)acrylic acid" encompasses both methacrylic acid and acrylic acid. Furthermore, the numerical range indicated as X to Y means not less than X and not more than Y.

[0011] [First and second surface layers] As described above, the first surface layer is made of a first polycarbonate resin composition, and the second surface layer is made of a second polycarbonate resin composition. The same explanation can be applied to the first polycarbonate resin composition and the second polycarbonate resin composition. Therefore, in the following explanation, except for the explanation of the glass transition temperature, the two will not be distinguished and will simply be referred to as "polycarbonate resin compositions."

[0012] The polycarbonate resin composition contains a polycarbonate resin. The polycarbonate resin may be one in which structural units constituting the resin are bonded via carbonate groups, and typically, structural units derived from a dihydroxy compound are bonded via carbonate groups. The dihydroxy compound may be an aromatic dihydroxy compound, an aliphatic dihydroxy compound, or the like.

[0013] Specific examples of the aromatic dihydroxy compound include biphenols (e.g., 4,4'-dihydroxybiphenyl, 3,3',5,5'-tetramethyl-4,4'-dihydroxybiphenyl), bisphenols {e.g., bis(hydroxyphenyl)alkanes [e.g., 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), 2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane, 2,2-bis(4-hydroxy-3,5-diethylphenyl)propane, Bis(hydroxyphenyl)C such as 2,2-bis(4-hydroxy-(3,5-diphenyl)phenyl)propane, 2,2-bis(4-hydroxy-3,5-dibromophenyl)propane, 2,2-bis(4-hydroxyphenyl)pentane, 2,4'-dihydroxy-diphenylmethane, bis(4-hydroxyphenyl)methane, bis(4-hydroxy-5-nitrophenyl)methane, 1,1-bis(4-hydroxyphenyl)ethane, and 3,3-bis(4-hydroxyphenyl)pentane 1-10 alkanes]}, bis(hydroxyphenyl)cycloalkanes [e.g., bis(hydroxyphenyl)C such as 1,1-bis(4-hydroxyphenyl)cyclohexane], 4-20Cycloalkanes], bis(hydroxyphenyl) sulfones [e.g., bis(4-hydroxyphenyl) sulfone, 2,4'-dihydroxydiphenyl sulfone], bis(hydroxyphenyl) ethers [e.g., 4,4'-dihydroxydiphenyl ether, 4,4'-dihydroxy-3,3'-dichlorodiphenyl ether, 4,4'-dihydroxy-2,5-diethoxydiphenyl ether], bis(hydroxyphenyl) sulfides [e.g., bis(4-hydroxyphenyl) sulfide], bis(hydroxyphenyl) ethers [e.g., bis(4-hydroxyphenyl) sulfide], bis(hydroxyphenyl)ketones [e.g., bis(4-hydroxyphenyl)ketone], dihydroxy compounds having a fluorene skeleton {e.g., bis(hydroxyphenyl)fluorenes [e.g., 9,9-bis(4-hydroxyphenyl)fluorene]}, bis(hydroxyalkoxy)fluorenes {e.g., 9,9-bis[(hydroxy C) such as 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene and 9,9-bis[4-(2-hydroxyethoxy-2-methyl)phenyl]fluorene}, 2-4 alkoxy)phenyl]fluorenes}, and the like.

[0014] The aliphatic dihydroxy compound may be an alicyclic dihydroxy compound (e.g., an alicyclic dihydroxy compound having 70 or less carbon atoms, an alicyclic dihydroxy compound having a 5- or 6-membered ring structure, an alicyclic dihydroxy compound having 70 or less carbon atoms and a 5- or 6-membered ring structure, etc.), a non-alicyclic dihydroxy compound, or the like.

[0015] Specific examples of the alicyclic dihydroxy compound include cycloalkanediols {for example, mono(monocyclic) cycloalkanediols [for example, C4-10 (mono)cycloalkanediols such as cyclohexanediols (e.g., 1,2-cyclohexanediol, 1,3-cyclohexanediol, 1,4-cyclohexanediol, 2-methyl-1,4-cyclohexanediol)], poly(polycyclic) cycloalkanediols [for example, tricyclodecanediol, pentacyclopentadecanediol, dicyclohexanediol, decalindiol (or tricyclotetradecanediol, for example, 2,6-decalindiol, 1,5-decalindiol, 2,3-decalindiol), norbornanediol (for example, 2,3-norbornanediol, 2,5-norbornanediol), adamantanediol (for example, 1,3-adamantanediol), etc.}, di(hydroxyalkyl)cycloalkanes {for example, mono(monocyclic)cycloalkanedialkanols [for example, cyclohexanedimethanols ( C4-10 (mono)cycloalkane diC1-4 alkanols such as 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, and 1,4-cyclohexanedimethanol), poly(polycyclic) cycloalkane dialkanols or bridged cyclic cycloalkane dialkanols [for example, tricyclodecane dimethanol, pentacyclopentadecanedimethanol, decalin dimethanol (or tricyclotetradecane dimethanol, for example, 2,6-decalin dimethanol, dimethanol (e.g., 1,5-decalin dimethanol, 2,3-decalin dimethanol), norbornane dimethanol (e.g., 2,3-norbornane dimethanol, 2,5-norbornane dimethanol), adamantane dimethanol (e.g., 1,3-adamantanedimethanol), etc.}, heterocyclic aliphatic dihydroxy compounds {e.g., heteromonocyclic aliphatic dihydroxy compounds (e.g., tetrahydrofuran-2,2-dimethanol), heteropolycyclic aliphatic dihydroxy compounds, etc.}, and the like.

[0016] Specific examples of the non-alicyclic dihydroxy compound include C alkanediols (e.g., ethylene glycol, 1,3-propanediol, 1,2-propanediol, 1,4-butanediol, 1,3-butanediol, 1,2-butanediol, 1,5-heptanediol, and 1,6-hexanediol). 2-20 Alkanediols), polyalkanediols (e.g., polyC such as diethylene glycol, triethylene glycol, and tetraethylene glycol) 2-6 Alkanediols) and the like.

[0017] The polycarbonate resin may contain only one type of structural unit derived from the above-mentioned dihydroxy compound, or may contain two or more types.

[0018] The polycarbonate resin content in the polycarbonate resin composition is sufficient as long as it is more than 50% by mass, preferably 70% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. The polycarbonate resin composition may contain only polycarbonate resin as a resin component.

[0019] The polycarbonate resin composition may contain a thermoplastic resin other than the polycarbonate resin. Such a thermoplastic resin may be an acrylic resin, a styrene resin, or the like. Specific examples of the acrylic resin include polymethyl methacrylate, polymethyl methacrylate-styrene copolymer (MS resin), and partially hydrogenated MS resin obtained by partially hydrogenating the aromatic ring of the MS resin. Specific examples of the styrene resin include polystyrene, styrene-methyl methacrylate copolymer, styrene-acrylonitrile copolymer, and acrylonitrile-butadiene-styrene block copolymer. The content of the other thermoplastic resin in the polycarbonate resin composition may be less than 50% by mass, preferably 30% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. The polycarbonate resin composition may not contain a thermoplastic resin other than the polycarbonate resin as a resin component.

[0020] The polycarbonate resin composition may contain additives such as stabilizers, processing aids, plasticizers, impact resistance aids, retardation adjusters, matting agents, antibacterial agents, antifungal agents, and antistatic agents. The additives in the present disclosure do not include the fine particles described below. The content of the additives in the polycarbonate resin composition may be adjusted appropriately and is not particularly limited. However, the content of the additives in the polycarbonate resin composition may be 10% by mass or less, preferably 5% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less.

[0021] The glass transition temperatures of the first and second polycarbonate resin compositions are not particularly limited, but are preferably 95°C or higher and 155°C or lower, more preferably 105°C or higher and 130°C or lower, and even more preferably 115°C or higher and 125°C or lower.

[0022] The glass transition temperatures of the first and second polycarbonate resin compositions are preferably lower than the glass transition temperature of the (meth)acrylic resin composition. From the viewpoint of enhancing mechanical strength, the optical film of the present disclosure is preferably a stretched film produced by stretching. However, when stretched, polycarbonate resin compositions tend to exhibit orientation birefringence. However, by lowering the glass transition temperatures of the first and second polycarbonate resin compositions below the glass transition temperature of the (meth)acrylic resin composition, orientation birefringence is less likely to be exhibited even when stretched, thereby reducing the absolute values ​​of the in-plane retardation and thickness direction retardation. Based on the glass transition temperature Tgi of the (meth)acrylic resin composition constituting the intermediate layer, the glass transition temperatures of the first and second polycarbonate resin compositions are more preferably (Tgi - 40) to (Tgi - 1)°C, even more preferably (Tgi - 20) to (Tgi - 3)°C, and particularly preferably (Tgi - 10) to (Tgi - 6)°C.

[0023] The glass transition temperatures of the first and second polycarbonate resin compositions can be adjusted, for example, by the type of structural unit derived from a dihydroxy compound contained in the polycarbonate resin. Furthermore, when two or more types of structural units derived from dihydroxy compounds are contained, the glass transition temperature can be adjusted by the ratio of their contents. Furthermore, the addition of a plasticizer tends to lower the glass transition temperature. The glass transition temperatures of the resin compositions constituting each layer can be determined by separating each layer and performing differential scanning calorimetry (DSC).

[0024] <Fine particles> In the optical film of the present disclosure, both the first surface layer and the second surface layer contain fine particles, and each of the first surface layer and the second surface layer may contain only one type of fine particles or may contain two or more types of fine particles.

[0025] The same explanation can be applied to the fine particles contained in the first surface layer and the fine particles contained in the surface layer. Therefore, in the following explanation, they will not be distinguished and will simply be referred to as "fine particles." The fine particles preferably contain at least one type selected from organic fine particles and inorganic fine particles, and more preferably contain organic fine particles. Examples of organic fine particles include hard fine particles and elastic fine particles, and hard fine particles are preferred. Note that elastic materials refer to soft materials that undergo large elastic deformation due to external forces, such as rubber (thermosetting elastomers) and thermoplastic elastomers, and have a glass transition temperature in the range below 0°C. Hard fine particles refer to organic fine particles that are not elastic fine particles, and the fine particles (P-1) and fine particles (P-2) described in the examples are hard fine particles.

[0026] The organic fine particles may contain fine particles having a single layer structure or may contain fine particles having a multilayer structure. However, from the viewpoint of improving the antiblocking properties of the optical film while suppressing a decrease in tensile strength, it is preferable that the organic fine particles contain fine particles having a multilayer structure, and it is more preferable that the organic fine particles contain fine particles having a core-shell structure composed of a core portion and a shell portion provided on the outside of the core portion.

[0027] The organic fine particles preferably contain structural units derived from aromatic vinyl, and more preferably the aromatic vinyl contains styrene, i.e., contains structural units derived from styrene. Because aromatic vinyl has high affinity with polycarbonate resin, by including organic fine particles containing structural units derived from aromatic vinyl in the polycarbonate resin composition, the antiblocking property of the optical film can be improved while suppressing a decrease in tensile strength and a decrease in transparency.

[0028] In the case of organic fine particles having a core-shell structure, they preferably have a core portion and a shell portion made of a resin containing structural units derived from aromatic vinyl, and more preferably have a core portion containing structural units derived from a (meth)acrylic acid ester monomer (hereinafter sometimes referred to as "(meth)acrylic acid ester units") and a shell portion made of a resin containing structural units derived from aromatic vinyl. By incorporating organic fine particles having a shell portion made of a resin containing structural units derived from aromatic vinyl into a polycarbonate resin composition, it is possible to improve the antiblocking properties of an optical film while suppressing a decrease in tensile strength and a decrease in transparency.

[0029] The structural unit derived from aromatic vinyl is not particularly limited as long as it is derived from a compound in which a vinyl group is bonded to an aromatic ring. One or more types of aromatic vinyl can be used. Examples of aromatic vinyl include styrene-based monomers such as styrene, vinyltoluene, methoxystyrene, α-methylstyrene, α-hydroxymethylstyrene, and α-hydroxyethylstyrene; polycyclic aromatic hydrocarbon ring vinyls such as 2-vinylnaphthalene; and aromatic heterocyclic vinyls such as N-vinylcarbazole, 2-vinylpyridine, vinylimidazole, and vinylthiophene. Styrenic monomers include not only styrene but also styrene derivatives in which any substituent is bonded to the polymerizable double bond carbon or benzene ring of styrene. Examples of the substituent include, but are not limited to, alkyl groups, alkoxy groups, hydroxy groups, halogen groups, amino groups, nitro groups, and sulfo groups. The aromatic vinyl is preferably a styrene-based monomer, and more preferably styrene.

[0030] In organic fine particles containing structural units derived from aromatic vinyl, from the viewpoint of crosslinking aromatic vinyl monomers, the organic fine particles preferably contain structural units derived from a crosslinkable monomer. When the organic fine particles have a core-shell structure, the shell preferably contains structural units derived from a crosslinkable monomer. One or more crosslinkable monomers can be used. The crosslinkable monomer is preferably a polyfunctional ethylenically unsaturated monomer. The polyfunctional ethylenically unsaturated monomer preferably has two or more ethylenically unsaturated bonds, more preferably has two ethylenically unsaturated bonds. Specific examples of polyfunctional ethylenically unsaturated monomers include divinylbenzene, 1,3-butadiene, trivinylbenzene, divinylnaphthalene, trivinylcyclohexane, divinyl ether, diallyl ether, and polyvalent methacrylate esters. Examples of diallyl ethers include dialkylene glycol diallyl ethers such as diethylene glycol diallyl ether, dipropylene glycol diallyl ether, and dibutylene glycol diallyl ether; and polyalkylene glycol diallyl ethers such as polyethylene glycol diallyl ether, polypropylene glycol diallyl ether, and polybutylene glycol diallyl ether. Furthermore, examples of polyvalent methacrylic acid esters include monomers such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate, 1,9-nonanediol dimethacrylate, neopentyl glycol dimethacrylate, dipropylene glycol dimethacrylate, polypropylene glycol dimethacrylate, trimethylolpropane trimethacrylate, pentaerythritol trimethacrylate, pentaerythritol tetramethacrylate, dipentaerythritol hexamethacrylate, and methacrylic-modified polydimethylsiloxane.The crosslinkable monomer is more preferably at least one of divinylbenzene, 1,3-butadiene, diallyl ether, and polyvalent methacrylic acid ester, and even more preferably at least one of divinylbenzene and polyvalent methacrylic acid ester.

[0031] The (meth)acrylic acid ester monomer that can be contained in the core portion is not particularly limited, and examples thereof include (meth)acrylic acid alkyl esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, n-hexyl (meth)acrylate, benzyl (meth)acrylate, and phenyl (meth)acrylate; (meth)acrylic acid cycloalkyl esters such as cyclopropyl (meth)acrylate, cyclobutyl (meth)acrylate, and cyclohexyl (meth)acrylate; and (meth)acrylic acid hydroxyalkyl esters such as 2-methoxyethyl (meth)acrylate, 2-hydroxymethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2,3,4,5,6-pentahydroxyhexyl (meth)acrylate, and 2,3,4,5-tetrahydroxypentyl (meth)acrylate. The (meth)acrylic acid ester monomer is preferably a (meth)acrylic acid alkyl ester, and the alkyl group bonded to the oxygen atom of the ester bond of the (meth)acrylic acid alkyl ester preferably has 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms, even more preferably 1 to 4 carbon atoms, and particularly preferably 1 to 2 carbon atoms.

[0032] When the core portion contains a (meth)acrylic acid ester monomer, the core portion may contain a structural unit derived from a crosslinkable monomer from the viewpoint of crosslinking the (meth)acrylic acid ester monomers with each other. The crosslinkable monomer used is the same as that used for the organic fine particles, but is preferably at least one of divinylbenzene, 1,3-butadiene, diallyl ether, and polyvalent methacrylic acid ester, and more preferably polyvalent methacrylic acid ester.

[0033] Known hard microparticles can be used as the hard microparticles. The hard microparticles may contain either single-layer or multilayer hard microparticles, but preferably contain multilayer hard microparticles. From the viewpoints of further improving antiblocking properties, further suppressing a decrease in tensile strength, and further suppressing a decrease in transparency, core-shell hard microparticles are preferred, more preferably core-shell hard microparticles having a shell containing structural units derived from aromatic vinyl, even more preferably core-shell hard microparticles having a core made of a (meth)acrylic resin containing (meth)acrylic acid ester units and a shell made of a resin containing structural units derived from aromatic vinyl, particularly preferred core-shell hard microparticles having a core made of a (meth)acrylic resin containing (meth)acrylic acid ester units and a shell made of a resin containing structural units derived from aromatic vinyl and a crosslinkable monomer, and most preferably core-shell hard microparticles having a core made of a (meth)acrylic resin containing (meth)acrylic acid ester units and a shell made of a resin containing structural units derived from styrene and a crosslinkable monomer. The (meth)acrylic acid ester units and aromatic vinyl used are the same as those of the organic fine particles, and the preferred embodiments are also the same as those of the organic fine particles.

[0034] Hard microparticles can be produced by a known production method, for example, by adding core particles obtained by suspension polymerization to an aqueous solvent, adding a shell monomer having a different composition from the monomer composition of the core particles to the solvent, dispersing and suspending the mixture to prepare a shell suspension, polymerizing the monomer component, and coating the core particles with the polymer (shell).The hard microparticles can be produced by, for example, the production method described in JP 2012-219148 A, or commercially available products.

[0035] As the elastomer microparticles, known elastomer microparticles can be used. The elastomer microparticles may contain elastomer microparticles of a single layer structure or of a multilayer structure, but preferably contain elastomer microparticles of a multilayer structure, more preferably elastomer microparticles having a core-shell structure, and even more preferably elastomer microparticles having a core-shell structure composed of a core portion which is a rubber-like polymer and a shell portion obtained by graft polymerization to the rubber-like polymer. The elastomer microparticles having a core-shell structure have good dispersibility in polycarbonate resins, making it easy to obtain high impact strength.

[0036] The elastomer microparticles preferably have a core portion which is a rubber polymer and a shell portion which is made of a resin containing structural units derived from aromatic vinyl, more preferably have a core portion which is a rubber polymer containing (meth)acrylic acid ester units and a shell portion which is made of a resin containing structural units derived from aromatic vinyl, and even more preferably have a core portion which is a rubber polymer containing (meth)acrylic acid ester units and a shell portion which is made of a resin containing structural units derived from styrene. The (meth)acrylic acid ester units and aromatic vinyl used are the same as those for organic microparticles, and the preferred embodiments are also the same as those for organic microparticles.

[0037] The elastic microparticles may be produced by a known production method, such as those produced by the production method described in JP 2020-073697 A, or commercially available products such as Kane Ace M-590 manufactured by Kaneka Corporation, Metablen W-341, W-377, and W-341 manufactured by Mitsubishi Chemical Corporation, and Acrypet IR377, IR441, and IR491 manufactured by Mitsubishi Chemical Corporation.

[0038] Examples of inorganic fine particles include fine particles made of silica, titania, alumina, zirconia, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, calcium phosphate, and the like.

[0039] The content of fine particles in the first and second surface layers is preferably 0.01 to 3 mass%, more preferably 0.02 to 2 mass%, and even more preferably 0.03 to 1 mass%, in order to improve the internal haze and lubricity of the optical film. When hard fine particles are contained in the surface layers, the content of fine particles can be reduced, and is preferably 0.01 to 0.5 mass%, more preferably 0.02 to 0.2 mass%, and even more preferably 0.03 to 0.1 mass%. The average primary particle diameter (median diameter) of the fine particles is preferably 0.1 to 2.0 μm, more preferably 0.5 to 2.0 μm, in order to improve both the haze and lubricity (anti-blocking properties) of the optical film.

[0040] [Middle layer] The intermediate layer is made of a (meth)acrylic resin composition, and the (meth)acrylic resin composition contains structural units derived from a (meth)acrylic acid ester monomer. The (meth)acrylic acid ester monomer is not particularly limited and is the same as the (meth)acrylic acid ester unit that may be contained in the organic fine particles, and the preferred embodiments are also the same as those for the organic fine particles. The (meth)acrylic resin composition may contain only one type of (meth)acrylic acid ester unit, or may contain two or more types.

[0041] From the viewpoint of increasing the glass transition temperature, the (meth)acrylic resin composition preferably contains, in addition to the (meth)acrylic acid ester unit, a (meth)acrylic resin containing a structural unit having a ring structure in the main chain (hereinafter referred to as a ring structural unit). Details of the ring structural unit will be described later.

[0042] The (meth)acrylic resin composition may contain a third structural unit different from the (meth)acrylic acid ester unit and the ring structural unit. The third structural unit is a structural unit derived from a monomer copolymerizable with the monomer for forming the (meth)acrylic acid ester unit or the ring structural unit. Specific examples include structural units derived from monomers such as styrene, vinyltoluene, α-methylstyrene, α-hydroxymethylstyrene, α-hydroxyethylstyrene, acrylonitrile, methacrylonitrile, ethylene, propylene, 4-methyl-1-pentene, vinyl acetate, 2-hydroxymethyl-1-butene, methyl vinyl ketone, N-vinylpyrrolidone, and N-vinylcarbazole. The (meth)acrylic resin composition may contain only one type of third structural unit, or may contain two or more types.

[0043] The content of each structural unit in the (meth)acrylic resin composition is not particularly limited, but is preferably as follows: The content of the (meth)acrylic acid ester unit may be, for example, 50 to 99% by mass, preferably 65 to 90% by mass, and more preferably 65 to 85% by mass. The content of the ring structural unit may be, for example, 1 to 50% by mass, preferably 10 to 35% by mass, and more preferably 15 to 30% by mass. The content of the third structural unit may be, for example, 0 to 20% by mass. The content of each structural unit in the (meth)acrylic resin composition is determined by dissolving the copolymer in a heavy solvent and 1 It is determined by measuring H-NMR and calculating the area ratio of the peaks corresponding to each structural unit.

[0044] The content of the (meth)acrylic resin having a ring structure in the main chain in the (meth)acrylic resin composition may be more than 50% by mass, is preferably 70% by mass or more, and more preferably 90% by mass or more.

[0045] The (meth)acrylic resin composition may contain a thermoplastic resin other than the (meth)acrylic resin having a ring structure in the main chain. Such a thermoplastic resin may be an acrylic resin, a styrene resin, a polycarbonate resin, a polyvinylidene fluoride resin, or the like. Specific examples of the acrylic resin include polymethyl methacrylate, polymethyl methacrylate-styrene copolymer (MS resin), and partially hydrogenated MS resin obtained by partially hydrogenating the aromatic ring of an MS resin. Specific examples of the styrene resin include polystyrene, a styrene-acrylonitrile copolymer, and an acrylonitrile-butadiene-styrene block copolymer.

[0046] The content of the thermoplastic resin other than the (meth)acrylic resin having a ring structure in the main chain in the (meth)acrylic resin composition may be less than 50% by mass, preferably 30% by mass or less, and more preferably 10% by mass or less. The (meth)acrylic resin composition may contain only the (meth)acrylic resin having a ring structure in the main chain as a resin component.

[0047] The (meth)acrylic resin composition may contain additives such as stabilizers, processing aids, plasticizers, impact resistance aids, retardation adjusters, matting agents, antibacterial agents, antifungal agents, antistatic agents, etc. The content of the additives in the (meth)acrylic resin composition may be adjusted as appropriate and is, for example, about 0.1 to 40 mass %, preferably 0.2 to 10 mass %, more preferably 0.3 to 5 mass %, and even more preferably 0.5 to 2 mass % in total.

[0048] The glass transition temperature Tgi of the (meth)acrylic resin composition is not particularly limited, but is preferably 115°C or higher and 160°C or lower, more preferably 120 to 150°C, and even more preferably 125 to 140°C.

[0049] The glass transition temperature of the (meth)acrylic resin composition can be adjusted, for example, by the content of the ring structural unit in the (meth)acrylic resin having a ring structure in the main chain. As the content of the ring structural unit in the (meth)acrylic resin having a ring structure in the main chain increases, the glass transition temperature of the (meth)acrylic resin composition tends to increase.

[0050] The (meth)acrylic resin composition preferably has a positive stress optical coefficient. The (meth)acrylic resin composition preferably contains a (meth)acrylic resin that includes a ring structural unit having a ring structure in the main chain and has a positive stress optical coefficient.

[0051] The weight-average molecular weight of the (meth)acrylic resin composition is preferably from 5,000 to 350,000, more preferably from 10,000 to 300,000, even more preferably from 30,000 to 250,000, particularly preferably from 50,000 to 200,000, and most preferably from 100,000 to 150,000. By setting the weight-average molecular weight of the (meth)acrylic resin composition within the above range, it becomes easier to improve the molding processability of the resin composition, and the mechanical strength of the obtained optical film can be ensured.

[0052] The number average molecular weight of the (meth)acrylic resin composition is preferably from 5,000 to 250,000, more preferably from 10,000 to 200,000, even more preferably from 20,000 to 150,000, particularly preferably from 30,000 to 100,000, and most preferably from 50,000 to 80,000. By setting the number average molecular weight of the (meth)acrylic resin composition within the above range, it becomes easier to improve the molding processability of the resin composition, and the mechanical strength of the obtained optical film can be ensured.

[0053] <Ring structural unit> The ring structure constituting the ring structural unit preferably contained in the (meth)acrylic resin composition may be any of a 4-membered ring structure, a 5-membered ring structure, a 6-membered ring structure, a 7-membered ring structure, an 8-membered ring structure, etc., and is preferably a 5-membered ring structure or a 6-membered ring structure.

[0054] The ring structure constituting the ring structural unit may be introduced by polymerizing a (meth)acrylic monomer having a ring structure, or may be introduced by polymerizing a (meth)acrylic monomer having a group for forming a ring structure and then chemically reacting the polymer.

[0055] Specific examples of the ring structural unit include, but are not limited to, a lactone ring structural unit, a lactam ring structural unit, a succinic anhydride structural unit, an N-substituted succinimide structural unit, a glutaric anhydride structural unit, and a glutarimide structural unit. The ring structural unit may contain only one type of these structural units, or may contain two or more types.

[0056] The lactone ring structural unit has a lactone ring structure, but the number of ring members in the lactone ring structure is not particularly limited, and may be, for example, any of a 4-membered ring to an 8-membered ring. From the viewpoint of increasing the stability of the ring structure, the lactone ring structure is preferably a 5-membered or 6-membered ring, more preferably a 6-membered ring, and particularly preferably a structural unit represented by the following formula (1a):

[0057] The lactam ring structural unit is preferably a structural unit represented by the following formula (1b).

[0058] [ka]

[0059] In formula (1a), R 11 and R 12 are each independently, but are not particularly limited to, a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms. The hydrocarbon group may be linear, branched, or cyclic. The hydrocarbon group may be either an aliphatic hydrocarbon group or an aromatic hydrocarbon group. R 13 is a hydrogen atom or a methyl group.

[0060] In formula (1b), R 15 and R 16are each independently, but are not particularly limited to, a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms. The hydrocarbon group may be linear, branched, or cyclic. The hydrocarbon group may be either an aliphatic hydrocarbon group or an aromatic hydrocarbon group. R 14 is a hydrogen atom or a methyl group.

[0061] In formula (1a), R 11 and R 12 are preferably each independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and more preferably each independently a hydrogen atom or a methyl group. 15 and R 16 are preferably each independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and more preferably each independently a hydrogen atom or a methyl group.

[0062] The structural unit represented by formula (1a) can be formed, for example, by polymerizing a group of monomers containing methyl 2-(hydroxymethyl)acrylate and methyl (meth)acrylate, followed by dealcoholization condensation between the hydroxy group and the ester bond. The structural unit represented by formula (1b) can be formed, for example, by polymerizing a group of monomers containing N-vinylacetamide and methyl (meth)acrylate, followed by dealcoholization condensation between the amide group and the ester bond.

[0063] The ring structural unit may contain only one type or two or more types of lactone ring structural unit represented by formula (1a).The ring structural unit may contain only one type or two or more types of lactam ring structural unit represented by formula (1b).

[0064] The succinic anhydride structural unit (structural unit derived from a maleic anhydride monomer) is preferably a structural unit represented by the following formula (2a): The N-substituted succinimide structural unit (structural unit derived from a maleimide monomer) is preferably a structural unit represented by the following formula (2b):

[0065] [ka]

[0066] In formula (2a), R 21 and R 22 are each independently a hydrogen atom or a methyl group.

[0067] In formula (2b), R 23 and R 24 R each independently represents a hydrogen atom or a methyl group. 25 is not particularly limited, but is, for example, a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms. The hydrocarbon group may be linear, branched, or cyclic. The hydrocarbon group may be either an aliphatic hydrocarbon group or an aromatic hydrocarbon group. R 25 is preferably a methyl group, an ethyl group, a cyclohexyl group, a phenyl group, a naphthyl group or a benzyl group, and more preferably a cyclohexyl group or a phenyl group.

[0068] The structural unit represented by formula (2a) can be formed, for example, by polymerizing a group of monomers including a maleic anhydride monomer. The structural unit represented by formula (2b) can be formed, for example, by polymerizing a group of monomers including a maleimide monomer or an N-substituted maleimide monomer.

[0069] The ring structural unit may contain only one type of succinic anhydride structural unit represented by formula (2a), or may contain two or more types of succinimide structural unit represented by formula (2b).

[0070] The glutaric anhydride structural unit is preferably a structural unit represented by the following formula (3a): The glutarimide structural unit is preferably a structural unit represented by the following formula (3b):

[0071] [ka]

[0072] In formula (3a), R 31 ~R 33 each independently represents a hydrogen atom or a methyl group.

[0073] In formula (3b), R 34 ~R 36 R each independently represents a hydrogen atom or a methyl group. 37 is not particularly limited, but is, for example, a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms. The hydrocarbon group may be linear, branched, or cyclic. The hydrocarbon group may be either an aliphatic hydrocarbon group or an aromatic hydrocarbon group. R 37 is preferably a hydrogen atom, a methyl group, a cyclohexyl group, a phenyl group or a tolyl group, and more preferably a hydrogen atom or a methyl group.

[0074] The structural unit represented by formula (3a) can be formed, for example, by polymerizing a monomer group containing a (meth)acrylic acid monomer and a methyl (meth)acrylate monomer, followed by dehydration condensation between a carboxy group and an ester bond. The structural unit represented by formula (3b) can be formed, for example, by polymerizing a monomer group containing a methyl (meth)acrylate monomer, followed by imidization between two ester bonds.

[0075] The ring structural unit may contain only one type of glutaric anhydride structural unit represented by formula (3a), or may contain two or more types of glutarimide structural unit represented by formula (3b).

[0076] From the viewpoint of stability of the ring structure, the ring structural unit preferably contains at least one ring structural unit selected from a lactone ring structural unit, a lactam ring structural unit, a succinic anhydride structural unit, an N-substituted succinimide structural unit, a glutaric anhydride structural unit, and a glutarimide structural unit, more preferably contains at least one selected from the group consisting of a lactone ring structural unit, an N-substituted succinimide structural unit, and a glutarimide structural unit, still more preferably contains at least one selected from the group consisting of a lactone ring structural unit and a glutarimide structural unit, and particularly preferably contains a lactone ring structural unit (i.e., the (meth)acrylic resin composition contains a (meth)acrylic resin having a (meth)acrylic acid ester unit and a lactone ring structural unit). Furthermore, when the (meth)acrylic resin composition contains a (meth)acrylic resin having a ring structure in the main chain, the (meth)acrylic resin preferably has at least one ring structure selected from a lactone ring structural unit, a lactam ring structural unit, a succinic anhydride structural unit, an N-substituted succinimide structural unit, a glutaric anhydride structural unit, and a glutarimide structural unit in the main chain, more preferably has at least one ring structure selected from a lactone ring structural unit, an N-substituted succinimide structural unit, and a glutarimide structural unit in the main chain, still more preferably has at least one ring structure selected from the group consisting of a lactone ring structural unit and a glutarimide structural unit in the main chain, and particularly preferably has a lactone ring structural unit in the main chain.

[0077] [Physical properties of optical films] The thickness of the optical film of the present disclosure may be, for example, 1 to 200 μm, but from the viewpoint of improving the mechanical strength of the optical film, it is preferably 5 to 100 μm, and more preferably 10 to 60 μm.

[0078] The ratio of the total thickness of the first surface layer and the second surface layer to the thickness of the intermediate layer may be, for example, 1:99 to 40:60. From the viewpoint of achieving a better balance between the mechanical strength of the polycarbonate resin composition and the transparency of the (meth)acrylic resin composition, and from the viewpoint of improving the optical isotropy of the optical film, the ratio is preferably 2:98 to 35:65, and more preferably 3:97 to 30:70.

[0079] The in-plane retardation Re at a wavelength of 550 nm and the thickness direction retardation Rth at a wavelength of 550 nm can be calculated from the following formula: where nx is the refractive index in the slow axis direction of the film in the plane, ny is the refractive index in the fast axis direction of the film in the plane, nz is the refractive index in the thickness direction of the film, and d is the thickness of the film. In-plane phase difference Re=|nx-ny|×d Thickness direction retardation Rth=[(nx+ny) / 2-nz]×d

[0080] From the viewpoint of optical isotropy, the absolute value of the in-plane retardation Re in the optical film of the present disclosure is preferably 50 nm or less, more preferably 30 nm or less, even more preferably 20 nm or less, and particularly preferably 10 nm or less. The absolute value of the thickness direction retardation Rth in the optical film of the present disclosure is preferably 60 nm or less, more preferably 50 nm or less, even more preferably 40 nm or less, and particularly preferably 20 nm or less.

[0081] From the viewpoint of enhancing anti-blocking properties, the static friction coefficient of the optical film of the present disclosure is preferably 1.0 or less, more preferably 0.8 or less, even more preferably 0.6 or less, and particularly preferably 0.5 or less.

[0082] From the viewpoint of increasing the tensile strength, the elongation at break of the optical film of the present disclosure may be, for example, 10% or more, and is preferably 20% or more.

[0083] From the viewpoint of improving transparency, the haze of the optical film of the present disclosure is preferably 2% or less, more preferably 1.5% or less, and even more preferably 1% or less.

[0084] [Method of manufacturing optical film] The optical film of the present disclosure can be produced, for example, by coextrusion. Coextrusion can be performed using a vent-type extruder equipped with a single or twin screw extrusion screw. For example, three extruders can be used, and the (meth)acrylic resin composition for forming the intermediate layer and the polycarbonate resin compositions for forming the first and second surface layers can be fed into separate melt extrusion devices to obtain a molten resin composition.

[0085] The molten resin compositions are each metered using a gear pump, laminated using a pinol or feed block, and then extruded into a film using a T-die nozzle or a multi-manifold nozzle. To prevent coloration, the resin compositions are preferably melt-kneaded under reduced pressure using a vent provided in the extruder, or under a nitrogen gas flow. To reduce the amount of foreign matter, the molten resin composition is preferably filtered using a filter after being metered using a gear pump.

[0086] The extruded resin composition is cooled and solidified by a casting drum to form an unstretched film. At this time, it is preferable that the unstretched film is pressed against the casting drum using a metal nip roll or an elastic metal nip roll equipped with a metal sleeve on a rubber roll, so as to prevent the formation of irregularities (so-called die lines, etc.) in the unstretched film.

[0087] From the viewpoint of increasing mechanical strength, the optical film of the present disclosure is preferably a stretched film produced by stretching, and more preferably a biaxially stretched film produced by biaxial stretching. The biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching, but it is preferable to stretch an unstretched film in the machine direction (MD) and then stretch it in the transverse direction (TD). In addition, heat treatment (annealing) may be performed after biaxial stretching.

[0088] The stretching ratios in both the longitudinal and transverse directions are preferably 1.4 to 3.0, and more preferably 1.7 to 2.5. The stretching speed is not particularly limited as long as the properties of the optical film according to this embodiment are not impaired. For example, the stretching speeds in both the longitudinal and transverse directions may be 150% / min to 400% / min.

[0089] The stretching temperature is generally set based on the glass transition temperature of the resin composition that mainly constitutes the intermediate layer. Therefore, in the optical film of the present disclosure, the stretching temperature is set based on Tgi, which is the glass transition temperature of the (meth)acrylic resin composition that constitutes the intermediate layer. The stretching temperatures in both the longitudinal and transverse directions are preferably Tgi + 10°C to Tgi + 35°C, and more preferably Tgi + 15°C to Tgi + 30°C. By setting the stretching temperature within the above range, the obtained optical film is less likely to exhibit retardation due to orientation birefringence resulting from the orientation of the polycarbonate resin contained in the first and second surface layers.

[0090] The resulting optical film may be wound onto a cylindrical core to form a roll of optical film.

[0091] [Optical film applications] The optical film according to an embodiment of the present disclosure is suitable for use as, for example, a polarizer protective film or a retardation film, and is more suitable for use as a polarizer protective film. The polarizer protective film is a film that can be included in a polarizing plate included in an image display device.

[0092] That is, the present disclosure includes not only an optical film according to one embodiment, but also a polarizer protective film including the optical film according to one embodiment, a polarizing plate including the polarizer protective film, and an image display device including the polarizing plate.

[0093] The optical film according to an embodiment of the present disclosure is also suitable for use in a zero-phase retardation film, a viewing angle compensation film, a light diffusion film, a reflective film, an anti-reflection film, an anti-glare film, a brightness enhancement film, a conductive film for a touch panel, a diffuser plate, a light guide, a retardation plate, a zero-phase retardation plate, a prism sheet, and the like. [Example]

[0094] The present disclosure will be described below with reference to examples, but the present disclosure is not limited to these examples. The evaluation methods used in each example, comparative example, and reference example are as follows.

[0095] (1) Glass transition temperature Tg The glass transition temperatures of the (meth)acrylic resin composition and the polycarbonate resin composition were measured in accordance with the provisions of Japanese Industrial Standards (JIS) K 7121. Using a differential scanning calorimeter (Rigaku Corporation; Thermo plus EVO DSC-8230), approximately 10 mg of a sample was heated from room temperature to 200°C (heating rate: 20°C / min) in a nitrogen gas atmosphere, and the measurements were made from the DSC curve by the starting point method. α-Alumina was used as a reference.

[0096] (2) Weight-average molecular weight and number-average molecular weight The weight average molecular weight and number average molecular weight of the (meth)acrylic resin composition were determined in terms of polystyrene using gel permeation chromatography (GPC) using the following measuring device and conditions. Measurement system: Tosoh GPC system HLC-8220 Measurement column configuration: Guard column (Tosoh Corporation, TSK Gel guard column SuperHZ-L) Separation columns (Tosoh Corporation, TSK Gel Super HZM-M), two connected in series Reference column configuration: Reference column (Tosoh Corporation, TSK gel SuperH-RC) Developing solvent: chloroform (Fujifilm Wako Pure Chemical Industries, Ltd., special grade) Developing solvent flow rate: 0.6 mL / min Standard sample: TSK standard polystyrene (Tosoh Corporation, PS-oligomer kit) Column temperature: 40℃

[0097] (3) Optical film thickness The thickness of the optical film was measured using a Digimatic Micrometer (manufactured by Mitutoyo Corporation). The thickness of each layer constituting the optical film was measured by observing the cross section of the optical film with a scanning electron microscope (FE-SEM S-4800 manufactured by Hitachi High-Technologies Corporation) under the following measurement conditions: acceleration voltage 20 kV, emission current 5 μA or 10 μA, and WD = 8 mm.

[0098] (4) Coefficient of static friction (slipperiness) The static friction coefficient of the optical film was measured in accordance with the provisions of Japanese Industrial Standards (JIS) K 7125.

[0099] (5) Tensile strength (elongation at break) The tensile strength of the optical film was measured using an autograph (Shimadzu Corporation; AGS-X) in accordance with JIS K 7127:1999. Specifically, a test film 150 mm long and 10 mm wide, with the longitudinal direction as the MD, was left standing at 23°C and 50% RH for at least one hour, and then tested at a test speed of 5 mm / min and a gauge length of 25 mm to measure the breaking elongation. Another test film 150 mm long and 10 mm wide, with the longitudinal direction as the TD, was also prepared, and the breaking elongation was measured in the same manner as for the test film with the longitudinal direction as the MD. The breaking elongation was measured for a total of 10 test films, five with the longitudinal direction as the MD and five with the longitudinal direction as the TD, and the average value was used as the measurement result.

[0100] (6) Hayes The haze of the optical film was measured using a turbidity meter (manufactured by Nippon Denshoku Industries Co., Ltd.; NDH5000).

[0101] (7) MIT strength The MIT strength of the optical film was measured in accordance with JIS P8115. Specifically, a test film 90 mm long and 15 mm wide, with the longitudinal direction in the MD direction, was left standing at 23°C and 50% RH for at least one hour, and then tested using an MIT folding fatigue tester (Model DA, manufactured by Toyo Seiki Seisaku-sho, Ltd.) under conditions of a bending angle of 135°, a bending speed of 175 cpm, and a load of 200 g, to measure the number of times the film broke. Additionally, a test film 90 mm long and 15 mm wide, with the longitudinal direction in the TD direction, was prepared, and the number of times the film broke was measured in the same way as for the test film with the longitudinal direction in the MD direction. The number of times the film broke was measured for a total of 10 test films, five with the longitudinal direction in the MD direction and five with the longitudinal direction in the TD direction, and the average was used as the measurement result.

[0102] (8) Phase difference The in-plane retardation Re at a wavelength of 550 nm and the retardation Rth in the thickness direction at a wavelength of 550 nm of the optical film were measured using a retardation film / optical material testing device (Axometrics Inc., AxoScan Mueller Matrix Polarimeter).

[0103] (9) Sign of the stress optical coefficient Cr The stress optical coefficient Cr was evaluated as follows. A resin composition (1) described below was formed into a film by melt pressing to prepare an unstretched film (thickness: 100 μm). Next, the prepared unstretched film was cut into a rectangle of 60 mm × 20 mm to prepare an evaluation sample. 2A weight selected to apply the following stress to the sample was attached to one of the short sides of the sample. Next, the sample was placed in a constant temperature dryer (DOV-450A, AS ONE Corporation) with a chuck distance of 40 mm, with the attached weight at the bottom. The temperature setting of the constant temperature dryer was set to 3°C higher than the Tg of resin composition (1), and the constant temperature dryer was preheated to that temperature before placing the sample. After placing the sample, the constant temperature dryer was maintained at the same temperature setting for approximately 30 minutes, allowing uniaxial stretching of the sample based on the load of the attached weight. Next, the constant temperature dryer was cooled at a cooling rate of approximately 1°C / min until the temperature inside the dryer reached a temperature 40°C lower than the Tg of resin composition (1). After cooling, the film was removed from the dryer, and the length and thickness of the stretched film, the weight of the weight, and the in-plane retardation (Re) of the stretched film for light with a wavelength of 590 nm were measured using the methods described below. The same measurement was carried out four times for one film while changing the weight of the weight, and the stress optical coefficient Cr of the resin composition (1) was calculated from the results. The calculation method of Cr was in accordance with the method described in pp. 37-44 of "Frontiers of Transparent Plastics (edited by the Society of Polymer Science)". Specifically, Δn (= nx - ny) of the film was calculated from the in-plane retardation Re and thickness of the film after stretching, and the stretching stress σ (unit: N / m 2 ) was determined, and the Δn and σ obtained from each of the four measurements were plotted on a coordinate system with Δn as the vertical axis value and σ as the horizontal axis value. Next, the slope of the approximation line connecting the four plotted points was determined by the least squares method, and this was taken as the Cr of the resin composition (1). When the sign of Cr was determined from this value, the Cr of the resin composition (1) was found to be positive.

[0104] <Manufacturing method> [Production of Resin Composition (1)] A 30 L reactor equipped with a stirrer, thermometer, condenser, and nitrogen inlet tube was charged with 40 parts by weight of methyl methacrylate, 10 parts by weight of methyl 2-(hydroxymethyl)acrylate, 50 parts by weight of toluene, and 0.025 parts by weight of tris(2,4-di-tert-butylphenyl)phosphite (ADEKA Corporation: ADK STAB® 2112) as an antioxidant. While nitrogen was passed through the mixture, the temperature was raised to 105°C. Upon reflux, 0.05 parts by weight of tert-amyl peroxyisononanoate (Arkema Yoshitomi Corporation: Luperox® 570) as a polymerization initiator was added, and 0.10 parts by weight of the polymerization initiator was added dropwise over 2 hours. Solution polymerization was allowed to proceed under reflux at approximately 105-110°C. After the dropwise addition, the mixture was aged for an additional 4 hours at the same temperature. 0.05 parts by mass of 2-ethylhexyl phosphate (Phoslex A-8, manufactured by Sakai Chemical Industry Co., Ltd.) was added, and a dealcoholization condensation reaction was carried out for 2 hours under reflux at approximately 90 to 110°C. Thereafter, the mixture was heated in an autoclave at 240°C for 30 minutes to further promote the dealcoholization condensation reaction. The mixture was then introduced into a vent-type twin-screw extruder (φ=30 mm, L / D=40) with a barrel temperature of 240°C, a rotation speed of 120 rpm, a vacuum level of 13.3 to 400 hPa, one rear vent, four fore vents (referred to as the first, second, third, and fourth vents from the upstream side), and a side feeder between the third and fourth vents, at a processing rate of 2.0 kg / h (equivalent to the resin amount), and devolatilization was performed. A separately prepared mixed solution of antioxidant and deactivator was then injected from the first vent using a high-pressure pump at a rate of 0.03 kg / h. A benzotriazole-based UV absorber (KEMISORB 279RC, manufactured by Chemipro Chemicals) was also injected from the side feeder at a rate of 0.09 kg / h. Ion-exchanged water was then injected from the third vent using a high-pressure pump at a rate of 0.01 kg / h. The mixed solution was prepared by dissolving 50 parts by mass of the antioxidant Irganox 1010 (manufactured by Ciba Specialty Chemicals) and 65 parts by mass of the deactivator zinc octylate (manufactured by Nippon Chemical Industry Co., Ltd., Nikka Octyx Zinc 3.6%) in 185 parts by mass of toluene. Finally, the (meth)acrylic resin composition in the extruder was passed through a polymer filter and then extruded from an extrusion die. The extruded acrylic resin composition was immersed in cooling water to obtain strands. The cooling water was filtered through a filter with a pore size of 1 μm (Micropore Filter 1EU, manufactured by Organo Corporation) and maintained at a temperature within the range of 30±10°C. The strands were introduced into a pelletizer to obtain pellets of resin composition (1). The resin composition (1) had a weight average molecular weight of 132,000, a number average molecular weight of 55,000, and a glass transition temperature of 128°C.

[0105] [Production of (meth)acrylic crosslinked fine particles (P-1)] Preparation of shell suspension A flask was charged with 181 parts of deionized water in which 0.35 parts of polyoxyethylene distyrylphenyl ether sulfate ester ammonium salt (Dai-ichi Kogyo Seiyaku Co., Ltd., "Hitenol (registered trademark) NF-08") had been dissolved, and a mixture of 34 parts of styrene (St) and 2.5 parts of DVB-570 (divinylbenzene purity 57%, Nippon Steel Chemical Co., Ltd.) was further added. The mixture in the flask was stirred at 4500 rpm for 2 minutes using a TK homomixer (suspended type, Primix Corporation) to prepare a suspension for the shell.

[0106] Core Polymerization Into another flask was charged 331 parts of a deionized water solution in which 2.4 parts of the polyoxyethylene distyryl phenyl ether sulfate ester ammonium salt had been dissolved. A core mixture was prepared by thoroughly stirring 216 parts of methyl methacrylate (MMA), 24 parts of ethylene glycol dimethacrylate (EGDMA), 12 parts of isopropyl alcohol, and 4.8 parts of lauryl peroxide, and then added to the flask. The mixture was stirred at 7,000 rpm for 20 minutes using a TK homomixer to form a uniform suspension. This suspension was transferred to a flask equipped with a stirrer, an inert gas inlet tube, a reflux condenser, a thermometer, and a dropping funnel, and 600 parts of deionized water was added. While blowing nitrogen gas into the flask, the flask was immersed in an oil bath set to 65°C to raise the temperature inside the flask and initiate polymerization of the core.

[0107] Shell Polymerization After the core polymerization was initiated, the internal temperature of the flask exceeded the oil bath temperature (65°C) and reached a peak temperature. Immediately after the maximum value was reached, the shell suspension was added dropwise using a dropping funnel. After the dropwise addition was completed, the oil bath temperature was set to 75°C, and the internal temperature of the flask was raised to 75°C, and the reaction was allowed to proceed for 1 hour. The oil bath temperature was then further set to 85°C, and the internal temperature of the flask was raised to 85°C. Stirring was continued at this temperature for 3 hours, and then the mixture was cooled. The particle suspension (polymerization reaction solution) after the reaction was measured using a Coulter Multisizer, and the volume average particle diameter of the produced particles was 1.2 μm. The particle concentration in the polymerization reaction solution was 17.5% by mass.

[0108] Classification The obtained particles were fed into a swirling air classifier ("AC-20", manufactured by Nisshin Engineering Co., Ltd.), and classified by adjusting the balance between the centrifugal force and drag force exerted on the pulverized particles by a high-speed swirling air current and a suction blower, to obtain (meth)acrylic crosslinked microparticles (P-1) with a volume average particle size of 1.0 μm. The recovery rate of the microparticles (P-1) relative to the particles fed to the classifier was 60 mass%.

[0109] [Production of (meth)acrylic crosslinked fine particles (P-2)] The (meth)acrylic crosslinked microparticles (P-2) without shell polymerization were obtained by the same method as the core polymerization described in the preparation of (meth)acrylic crosslinked microparticles (P-1), except that the shell portion was not polymerized.The volume average particle diameter of the (meth)acrylic crosslinked microparticles (P-2) was 0.9 μm.

[0110] [Production of Resin Composition (2-A)] A commercially available polycarbonate resin (Mitsubishi Gas Chemical Company, Inc.: Iupizeta FPC-0330, glass transition temperature: 120°C) was introduced into a twin-screw extruder (L / D = 30) at a rate of 100 parts by mass / hour. The twin-screw extruder was equipped with a side feeder and a vent, and a leaf disk-type polymer filter (filtration accuracy: 10 μm) was placed at the tip. The barrel temperature was set to 280°C. In addition, (meth)acrylic crosslinked microparticles (P-1) were introduced from the side feeder at a rate of 0.04 parts by mass / hour. In this way, the polycarbonate resin and the (meth)acrylic crosslinked microparticles (P-1) were kneaded to obtain a mixture. The mixture was filtered through a polymer filter and then extruded through an extrusion die. The extruded mixture was immersed in cooling water to obtain strands. The cooling water was filtered through a filter with a pore size of 1 μm (Micropore Filter 1EU, manufactured by Organo Corporation) and maintained at a temperature within the range of 30±10°C. The obtained strands were introduced into a pelletizer to obtain pellets of resin composition (2-A). The glass transition temperature of resin composition (2-A) was 120°C.

[0111] [Production of Resin Composition (2-B)] Pellets of resin composition (2-B) were obtained in the same manner as for resin composition (2-A), except that instead of introducing (meth)acrylic crosslinked microparticles (P-1) from the side feeder, commercially available acrylic rubber microparticles (Mitsubishi Chemical Corporation: Metablen W-377) were introduced at a rate of 0.50 parts by mass / hour. Note that Metablen W-377 is a rubber microparticle with a core-shell structure. The glass transition temperature of resin composition (2-B) was 120°C.

[0112] [Production of Resin Composition (2-C)] Pellets of resin composition (2-C) were obtained in the same manner as resin composition (2-A), except that instead of introducing (meth)acrylic crosslinked microparticles (P-1) from the side feeder, commercially available acrylic rubber microparticles (Mitsubishi Chemical Corporation: Metablen W-377) were introduced at a rate of 2.00 parts by mass / hour. The glass transition temperature of resin composition (2-C) was 120°C.

[0113] [Production of Resin Composition (2-D)] Pellets of resin composition (2-D) were obtained in the same manner as resin composition (2-A), except that instead of introducing (meth)acrylic crosslinked microparticles (P-1) from the side feeder, commercially available silica microparticles (manufactured by Nippon Aerosil Co., Ltd., trade name: AEROSIL R972, average primary particle diameter: 16 nm) were introduced at a rate of 0.10 parts by mass / hour. The glass transition temperature of resin composition (2-D) was 120°C.

[0114] [Production of Resin Composition (2-E)] Pellets of resin composition (2-E) were obtained in the same manner as resin composition (2-B), except that (meth)acrylic crosslinked microparticles (P-2) were introduced at a rate of 0.04 parts by mass / hour instead of (meth)acrylic crosslinked microparticles (P-1) from the side feeder. The glass transition temperature of resin composition (2-E) was 120°C.

[0115] Example 1 An optical film having a first surface layer, an intermediate layer, and a second surface layer laminated in this order was obtained by the following manufacturing method. Resin composition (1) and resin composition (2-A) were dried in a hot air oven at 80°C for 8 hours. Single-screw extruders P, Q, and R equipped with leaf-disk polymer filters with a filtration accuracy of 5 μm were prepared. Resin composition (2-A) for forming the first surface layer was fed into single-screw extruder P, resin composition (1) for forming the intermediate layer was fed into single-screw extruder Q, and resin composition (2-A) for forming the second surface layer was fed into single-screw extruder R. These were co-extruded into a sheet to obtain a molten film in which the first surface layer, intermediate layer, and second surface layer were laminated together in this order. The thickness ratio of the first surface layer, intermediate layer, and second surface layer was set to 1:8:1. The resulting molten film was passed through two rolls (a cooling roll and a touch roll) adjusted to 90°C, and then passed sequentially through multiple pass rolls to obtain an unstretched film with a thickness of 80 μm. The unstretched film was stretched 2.0 times in the MD direction at a stretching rate of 300% / min using a biaxial stretching tester (manufactured by Toyo Seiki Seisakusho, Ltd.) at a stretching temperature of 154°C, and then stretched 2.0 times in the TD direction at a stretching rate of 300% / min, thereby obtaining an optical film with a thickness of 20 μm.

[0116] <Example 2> An optical film was obtained in the same manner as in Example 1, except that the polycarbonate resin composition (2-B) was charged into the single-screw extruders P and R instead of the polycarbonate resin composition (2-A).

[0117] Example 3 An optical film was obtained in the same manner as in Example 1, except that the polycarbonate resin composition (2-C) was charged into the single-screw extruders P and R instead of the polycarbonate resin composition (2-A).

[0118] <Comparative Example 1> An optical film was obtained in the same manner as in Example 1, except that a commercially available polycarbonate resin (2-F) (Iupizeta FPC-0330, manufactured by Mitsubishi Gas Chemical Company, Inc., glass transition temperature: 120°C) was fed into the single-screw extruders P and R instead of the polycarbonate resin composition (2-A).

[0119] Example 4 An optical film was obtained in the same manner as in Example 1, except that the stretching temperature was changed from 154°C to 144°C.

[0120] <Example 5> An optical film was obtained in the same manner as in Example 4, except that the polycarbonate resin composition (2-D) was charged into the single-screw extruders P and R instead of the polycarbonate resin composition (2-A).

[0121] Example 6 An optical film was obtained in the same manner as in Example 4, except that the polycarbonate resin composition (2-E) was charged into the single-screw extruders P and R instead of the polycarbonate resin composition (2-A).

[0122] <Comparative Example 2> An optical film was obtained in the same manner as in Example 4, except that a commercially available polycarbonate resin (2-F) was charged into the single-screw extruders P and R instead of the polycarbonate resin composition (2-A).

[0123] Table 1 shows various physical properties of the optical films of Examples 1 to 6 and Comparative Examples 1 and 2. Table 1 also shows details of the surface layers provided on the optical films.

[0124] [Table 1]

[0125] Compared with Comparative Examples 1 and 2 in which no fine particles were included in the surface layer, Examples 1 to 6 in which fine particles were included in the surface layer had a lower static friction coefficient and exhibited high anti-blocking properties.

Claims

1. An optical film comprising, in a thickness direction, a first surface layer made of a first polycarbonate resin composition, an intermediate layer made of a (meth)acrylic resin composition, and a second surface layer made of a second polycarbonate resin composition, in this order, An optical film, wherein the first surface layer and the second surface layer contain fine particles.

2. The optical film according to claim 1 , wherein the fine particles comprise organic fine particles.

3. The optical film according to claim 2 , wherein the organic fine particles contain structural units derived from an aromatic vinyl.

4. 4. The optical film according to claim 3, wherein the organic fine particles have a core portion made of a (meth)acrylic resin and a shell portion made of a resin containing a structural unit derived from an aromatic vinyl.

5. 5. The optical film according to claim 3, wherein the aromatic vinyl comprises styrene.

6. 2. The optical film according to claim 1, wherein the (meth)acrylic resin composition has a glass transition temperature of 115 to 160°C.

7. The optical film according to claim 6, wherein the (meth)acrylic resin composition has a positive stress optical coefficient.

8. The optical film according to claim 7 , wherein the (meth)acrylic resin composition contains a (meth)acrylic resin that includes a ring structural unit having a ring structure in the main chain and has a positive stress optical coefficient.

9. 9. The optical film according to claim 8, wherein the ring structural unit is at least one selected from the group consisting of a lactone ring structural unit, an N-substituted succinimide structural unit, and a glutarimide structural unit.

10. 2. The optical film according to claim 1, wherein the glass transition temperature of the first polycarbonate resin composition and the glass transition temperature of the second polycarbonate resin composition are each lower than the glass transition temperature of the (meth)acrylic resin composition.

11. 2. The optical film according to claim 1, which is a stretched film.

12. A polarizer protective film comprising the optical film according to claim 1 .

13. A polarizing plate comprising the polarizer protective film according to claim 12 .

14. An image display device comprising the polarizing plate according to claim 13.

Images