Optical film, polarizer protective film, polarizing plate, and image display device

Abstract

This optical film is provided with: a first polycarbonate resin layer formed from a first polycarbonate resin composition; a second polycarbonate resin layer formed from a second polycarbonate resin composition; and a (meth) acrylic resin layer formed from a (meth) acrylic resin composition containing a (meth) acrylic resin having a ring structure in the main chain, the (meth) acrylic resin layer being disposed between the first polycarbonate resin layer and the second polycarbonate resin layer. The glass transition temperature (Tga) of the first polycarbonate resin composition, the glass transition temperature (Tgb) of the second polycarbonate resin composition, and the glass transition temperature (Tgc) of the (meth) acrylic resin composition satisfy formula (A) and formula (B). Formula (A): Tga < = Tgc + 6, Formula (B): Tgb < = Tgc + 6.

Description

Technical Field

[0001] The present disclosure relates to an optical film, a polarizer protective film, a polarizing plate, and an image display device. Background Art

[0002] (Meth)acrylic resins have excellent optical properties and are used as materials for optical films constituting liquid crystal displays, for example.

[0003] For example, Example 1 of Patent Document 1 discloses a laminate comprising a polycarbonate resin layer containing a polycarbonate resin and a (meth)acrylic resin layer containing an acrylic thermoplastic resin having a lactone ring structure in the main chain. This laminate has excellent mechanical strength (particularly flexibility) due to the polycarbonate resin layer. The laminate can be used as an optical film.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2008-273028 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] A laminate is sometimes stretched to increase mechanical strength. Stretching the laminate may cause phase difference due to orientational birefringence caused by the orientation of the polycarbonate resin contained in the polycarbonate resin layer. This is because the polycarbonate resin has a high glass transition temperature, making it difficult for the polycarbonate resin layer to soften during stretching. Therefore, there is room for improvement in the use of the laminate as a film requiring optical isotropy, such as a polarizer protective film.

[0009] An object of the present disclosure is to provide an optical film suitable for use as a film requiring optical isotropy. In addition, another object of the present disclosure is to provide an optical member including such an optical film.

[0010] Solutions for solving problems

[0011] The present disclosure provides the following optical film described in [1], the polarizing plate protective film described in [2], the polarizing plate described in [3], and the image display device described in [4].

[0012] [1] An optical film comprising: a first polycarbonate resin layer formed from a first polycarbonate resin composition; a second polycarbonate resin layer formed from a second polycarbonate resin composition; and a (meth)acrylic resin layer formed from a (meth)acrylic resin composition containing a (meth)acrylic resin having a ring structure in its main chain, the layer being disposed between the first polycarbonate resin layer and the second polycarbonate resin layer, wherein the glass transition temperature Tga of the first polycarbonate resin composition, the glass transition temperature Tgb of the second polycarbonate resin composition, and the glass transition temperature Tgc of the (meth)acrylic resin composition satisfy the following formula (A) and the following formula (B): Formula (A): Tga≤Tgc+6, Formula (B): Tgb≤Tgc+6, and the first polycarbonate resin layer, the second polycarbonate resin layer, and the (meth)acrylic resin layer are stretched.

[0013] [2] A polarizing plate protective film comprising the optical film according to [1].

[0014] [3] A polarizing plate comprising the polarizer protective film according to [2].

[0015] [4] An image display device comprising the polarizing plate according to [3].

[0016] Effects of the Invention

[0017] According to the present disclosure, an optical film suitable for use as a film requiring optical isotropy can be provided. In addition, according to the present disclosure, an optical member including such an optical film can be provided. DETAILED DESCRIPTION

[0018] The embodiments of the present disclosure are described. Of course, the present disclosure is not limited to the following embodiments. In the following description, "(meth)acrylic acid" is used as a term including both "methacrylic acid" and "acrylic acid". Resin and polymer are used as terms with the same meaning. Resin composition is used as a term to indicate a composition that contains at least one resin and may contain other resins, additives, etc. When a numerical range is expressed as X to Y, it means greater than X and less than Y. For example, "1 to 200 μm" means greater than 1 μm and less than 200 μm.

[0019] [Optical Film]

[0020] An optical film according to one embodiment of the present disclosure includes a first polycarbonate resin layer formed from a first polycarbonate resin composition; a second polycarbonate resin layer formed from a second polycarbonate resin composition; and a (meth)acrylic resin layer formed from a (meth)acrylic resin composition including a (meth)acrylic resin having a ring structure in its main chain, disposed between the first and second polycarbonate resin layers. The first and second polycarbonate resin layers serve as surface layers of the optical film.

[0021] The first polycarbonate resin layer, the second polycarbonate resin layer, and the (meth)acrylic resin layer are integrally laminated. "Integrated" as used herein means, for example, that they do not separate naturally due to their own weight or are not easily separated by manual operation by a person handling the optical film. For example, temporarily laminating multiple layers using adhesion forces with the intention of separation is not included in this embodiment.

[0022] The glass transition temperature Tga (unit: ° C.) of the first polycarbonate resin composition, the glass transition temperature Tgb (unit: ° C.) of the second polycarbonate resin composition, and the glass transition temperature Tgc (unit: ° C.) of the (meth)acrylic resin composition including a (meth)acrylic resin having a ring structure in the main chain satisfy the following formula (A) and the following formula (B).

[0023] Formula (A): Tga≤Tgc+6.

[0024] Formula (B): Tgb≤Tgc+6.

[0025] The glass transition temperatures of the first polycarbonate resin composition, the second polycarbonate resin composition, and the (meth)acrylic resin composition may satisfy the above-mentioned formulas (A) and (B) when determined by the same measurement method. The glass transition temperature of the resin composition constituting each layer can be determined by separating each layer and measuring it by differential scanning calorimetry (DSC).

[0026] The glass transition temperature Tgc of the (meth)acrylic resin composition, the glass transition temperature Tga of the first polycarbonate resin composition, and the glass transition temperature Tgb of the second polycarbonate resin composition may satisfy at least one of the following formula (A1) and the following formula (B1).

[0027] Formula (A1): Tga≤Tgc.

[0028] Formula (B1): Tgb≤Tgc.

[0029] The first polycarbonate-based resin layer, the second polycarbonate-based resin layer, and the (meth)acrylic-based resin layer are stretched.

[0030] The thickness of the optical film may be, for example, 1 to 200 μm. From the viewpoint of improving the mechanical strength of the optical film, the thickness is preferably 5 to 100 μm, and more preferably 10 to 60 μm.

[0031] The ratio of the total thickness of the first polycarbonate resin layer and the thickness of the second polycarbonate resin layer to the thickness of the (meth)acrylic resin layer can 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 further 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.

[0032] In this embodiment, the (meth)acrylic resin layer is in contact with the first polycarbonate resin layer and the second polycarbonate resin layer. The optical film may further include other layers between the first polycarbonate resin layer and the (meth)acrylic resin layer, or between the first polycarbonate resin layer and the (meth)acrylic resin layer, as long as the properties of the optical film of this embodiment are not impaired.

[0033] (First Polycarbonate-Based Resin Layer and Second Polycarbonate-Based Resin Layer)

[0034] The first polycarbonate-based resin layer is formed from a first polycarbonate resin composition. The second polycarbonate-based resin layer is formed from a second polycarbonate resin composition. The same description applies to the first and second polycarbonate resin compositions, and therefore, in the following description, the two are not distinguished and are simply referred to as the polycarbonate resin composition. Furthermore, the same description applies to the first and second polycarbonate-based resin layers, and therefore, in the following description, the two are not distinguished and are simply referred to as the polycarbonate resin layer.

[0035] The polycarbonate resin composition comprises a polycarbonate resin. The polycarbonate resin may be any resin having structural units bonded via carbonate groups. 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.

[0036] Specifically, the aromatic dihydroxy compound may be 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, 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, 3,3-bis(4-hydroxyphenyl)pentane, etc. 1-10 Alkanes]}, bis(hydroxyphenyl)cycloalkanes [such as 1,1-bis(4-hydroxyphenyl)cyclohexane and other bis(hydroxyphenyl) C 4-20 Cycloalkanes], bis(hydroxyphenyl)sulfones [e.g., bis(4-hydroxyphenyl)sulfone, 2,4'-dihydroxydiphenylsulfone], 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)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[4-(2-hydroxyethoxy)phenyl]fluorene, 9,9-bis[4-(2-hydroxyethoxy-2-methyl)phenyl]fluorene, etc., 9,9-bis[(hydroxyC 2-4 alkoxy)phenyl]fluorenes}, etc.

[0037] 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-membered ring or 6-membered ring structure, an alicyclic dihydroxy compound having 70 or less carbon atoms and a 5-membered ring or 6-membered ring structure, etc.], a non-alicyclic dihydroxy compound, etc.

[0038] Specifically, the alicyclic dihydroxy compound may be: cycloalkanediols {e.g., mono (monocyclic) cycloalkanediols [e.g., cyclohexanediols (e.g., 1,2-cyclohexanediol, 1,3-cyclohexanediol, 1,4-cyclohexanediol, 2-methyl-1,4-cyclohexanediol) and other C4-10 (mono)cycloalkanediols)], poly (polycyclic) cycloalkanediols [e.g., tricyclodecanediol, pentacyclopentadecanediol, decahydronaphthalene diol] (or tricyclotetradecanediol, for example, 2,6-decalinanediol, 1,5-decalinanediol, 2,3-decalinanediol), norbornanediol (for example, 2,3-norbornanediol, 2,5-norbornanediol), adamantanediol (for example, 1,3-adamantanediol), etc.], etc.}, di(hydroxyalkyl)cycloalkanes {for example, mono(monocyclic)cycloalkanediols [for example, cyclohexanedimethanols (for example) Such as 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol) and other C4-10 (mono) cycloalkanediC1-4 alkanols) etc.], poly (polycyclic) cycloalkanediols or cross-linked cyclic cycloalkanediols [such as tricyclodecanedimethanol, pentacyclopentadecanedimethanol, decahydronaphthalenedimethanol (or tricyclotetradecane dimethanol, such as 2,6-decahydronaphthalenedimethanol, 1,5-decahydronaphthalenedimethanol, 2,3-decahydronaphthalenedimethanol), norbornane dimethanol (such as 2,3-norbornane dimethanol, 2,5-norbornane dimethanol), adamantane dimethanol (such as 1,3-adamantanedimethanol) etc.], etc., heterocyclic aliphatic dihydroxy compounds {such as heteromonocyclic aliphatic dihydroxy compounds (such as tetrahydrofuran-2,2-dimethanol, etc.), heteropolycyclic aliphatic dihydroxy compounds, etc.}, etc.

[0039] Specifically, the non-alicyclic dihydroxy compound may be an alkanediol (e.g., ethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, 1,4-butanediol, 1,3-butanediol, 1,2-butanediol, 1,5-heptanediol, 1,6-hexanediol, etc.) 2-20 Alkylene glycols), polyalkylene glycols (such as diethylene glycol, triethylene glycol, tetraethylene glycol, etc. 2-6 Alkanediols) etc.

[0040] 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 of structural units derived from the above-mentioned dihydroxy compound.

[0041] The content of the polycarbonate resin in the polycarbonate resin composition may be more than 50% by mass, preferably 70% by mass or more, and more preferably 90% by mass or more. The polycarbonate resin composition may contain only the polycarbonate resin as a resin component.

[0042] The polycarbonate resin composition may also contain a thermoplastic resin other than the polycarbonate resin. Such thermoplastic resins may include acrylic resins, styrene resins, and the like. Specifically, acrylic resins include polymethyl methacrylate, polymethyl methacrylate-styrene copolymers (MS resins), and partially hydrogenated MS resins obtained by partially hydrogenating the aromatic rings of MS resins. Specifically, styrene resins include polystyrene, styrene-methyl methacrylate copolymers, styrene-acrylonitrile copolymers, and acrylonitrile-butadiene-styrene block copolymers.

[0043] The content of other thermoplastic resins in the polycarbonate resin composition may be less than 50% by mass, preferably 30% by mass or less, and more preferably 10% by mass or less.

[0044] The polycarbonate resin composition may also contain hard particles. Hard particles refer to inorganic or organic particles that do not have a glass transition temperature below 0°C. The inclusion of hard particles in the polycarbonate resin composition improves the anti-blocking properties of the optical film. The glass transition temperature is determined by the onset method.

[0045] Specifically, the inorganic particles may be particles composed of silica, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, calcium phosphate, and the like. Specifically, the organic particles may be particles composed of silicone resin, fluororesin, (meth)acrylic crosslinked particles, and the like. The polycarbonate resin composition may contain only one type of hard particle or two or more types of hard particles. The hard particles preferably include at least one selected from silica particles and (meth)acrylic crosslinked particles.

[0046] From the perspective of achieving better internal haze and lubricity of the optical film, the content of hard particles in the polycarbonate resin composition is preferably 0.001 to 1% by mass, more preferably 0.01 to 0.20% by mass, and even more preferably 0.05 to 0.15% by mass. From the perspective of achieving better internal haze and lubricity of the optical film, the average primary particle size (median particle size) of the hard particles is preferably 0.1 to 2.0 μm, more preferably 0.5 to 2.0 μm.

[0047] The polycarbonate resin composition may also contain additives such as stabilizers, processing aids, plasticizers, impact-resistant additives, phase difference reducing agents, matting agents, antibacterial agents, antifungal agents, and antistatic agents. The content of the additives in the polycarbonate resin composition can be adjusted appropriately, but is generally about 0.1 to 30% by weight in total.

[0048] The glass transition temperature of the polycarbonate resin composition is not particularly limited, but from the perspective of improving the heat resistance of the optical film, it is preferably (Tgc-40)°C or higher, based on the glass transition temperature Tgc of the (meth)acrylic resin composition. Specifically, the glass transition temperature Tga of the first polycarbonate resin composition and the glass transition temperature Tgb of the second polycarbonate resin composition preferably satisfy the following formulas (C) and (D).

[0049] Formula (C): Tgc-40≤Tga≤Tgc+6.

[0050] Formula (D): Tgc-40≤Tgb≤Tgc+6.

[0051] From the perspective of facilitating stretching during the production of the optical film, the glass transition temperature of the polycarbonate resin composition is preferably lower than Tgc. That is, the glass transition temperature Tga of the first polycarbonate resin composition and the glass transition temperature Tgb of the second polycarbonate resin composition preferably satisfy the following formula (E) and formula (F).

[0052] Formula (E): Tgc-40≤Tga <Tgc。

[0053] Formula (F): Tgc-40≤Tgb <Tgc。

[0054] The glass transition temperature of a polycarbonate resin composition can be adjusted, for example, by the type of dihydroxy compound-derived structural units contained in the polycarbonate resin. Furthermore, when two or more dihydroxy compound-derived structural units are contained, the glass transition temperature can be adjusted by adjusting the ratio of their contents. Furthermore, the addition of a plasticizer tends to lower the glass transition temperature.

[0055] The glass transition temperature of the polycarbonate resin composition may be lower than 150°C, may be 120°C or higher and lower than 150°C, or may be 120°C or higher and 145°C or lower.

[0056] ((Meth)acrylic resin layer)

[0057] The (meth)acrylic resin layer is formed from a (meth)acrylic resin composition. The (meth)acrylic resin composition includes a (meth)acrylic resin having a ring structure in its main chain. The (meth)acrylic resin having a ring structure in its main chain includes a structural unit derived from a (meth)acrylate monomer (hereinafter referred to as a (meth)acrylate unit) and a structural unit including a ring structure formed in the main chain (hereinafter referred to as a ring structural unit).

[0058] Specifically, the (meth)acrylate unit can be a structural unit derived from the following monomers: methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, n-hexyl (meth)acrylate, cyclohexyl (meth)acrylate, cyclopropyl (meth)acrylate, cyclobutyl (meth)acrylate, phenyl (meth)acrylate, benzyl (meth)acrylate, o-cresyl (meth)acrylate, phenoxyethyl (meth)acrylate, chloromethyl (meth)acrylate, 2-chloroethyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 2-hydroxymethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2,3,4,5,6-pentahydroxyhexyl (meth)acrylate, 2,3,4,5-tetrahydroxypentyl (meth)acrylate, glycidyl (meth)acrylate, etc. The (meth)acrylic resin having a ring structure in its main chain may contain only one type of (meth)acrylate unit, or may contain two or more types of (meth)acrylate units.

[0059] Specifically, the ring structural unit may be a glutaric anhydride structural unit, a glutarimide structural unit, a maleic anhydride structural unit, an N-substituted maleimide structural unit, a lactone ring structural unit, etc. The (meth)acrylic resin having a ring structure in the main chain may contain only one type of ring structural unit or two or more types of ring structural units.

[0060] The following general formula (1) represents a glutaric anhydride structural unit and a glutarimide structural unit.

[0061] [Chemical Formula 1]

[0062]

[0063] R in the general formula (1) 1 、R 2 are independently a hydrogen atom or a methyl group. 1 is an oxygen atom or a nitrogen atom. 1 When it is an oxygen atom, R 3 Does not exist. When X 1 When it 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, a benzyl group or a phenyl group. 1 When X is an oxygen atom, the general formula (1) represents a glutaric anhydride structural unit. 1 When it is a nitrogen atom, the general formula (1) represents a glutarimide structural unit.

[0064] The following general formula (2) represents a maleic anhydride structural unit and an N-substituted maleimide structural unit.

[0065] [Chemical Formula 2]

[0066]

[0067] R in general formula (2) 4 、R 5 are independently a hydrogen atom or a methyl group. 2 is an oxygen atom or a nitrogen atom. 2 When it is an oxygen atom, R 6 Does not exist. When X 2 When it 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, a benzyl group or a phenyl group. 2 When X is an oxygen atom, the general formula (2) represents a maleic anhydride structural unit. 2 When it is a nitrogen atom, the general formula (2) represents an N-substituted maleimide structural unit.

[0068] The following general formula (3) represents a lactone ring structural unit.

[0069] [Chemical Formula 3]

[0070]

[0071] In the general formula (3), R 7 、R 8 and R 9 Each of the groups is independently a hydrogen atom or an organic group having 1 to 20 carbon atoms. The organic group may contain an oxygen atom.

[0072] Organic groups include alkyl groups, unsaturated aliphatic hydrocarbon groups, aromatic hydrocarbon groups, and the like. Examples of alkyl groups include groups having 1 to 20 carbon atoms, specifically, methyl, ethyl, and propyl groups. Examples of unsaturated aliphatic hydrocarbon groups include groups having 2 to 20 carbon atoms, specifically, vinyl and propenyl groups. Examples of aromatic hydrocarbon groups include groups having 6 to 20 carbon atoms, specifically, phenyl and naphthyl groups. In alkyl groups, unsaturated aliphatic hydrocarbon groups, and aromatic hydrocarbon groups, one or more hydrogen atoms may be substituted with at least one group selected from the group consisting of a hydroxyl group, a carboxyl group, an ether group, and an ester group.

[0073] The lactone ring structural unit represented by the general formula (3) can be formed, for example, by subjecting a copolymer of methyl methacrylate and methyl 2-(hydroxymethyl)acrylate to dealcoholization and cyclocondensation within the molecule.

[0074] The lactone ring structural unit represented by general formula (3) can be said to be a lactone ring structural unit in which two or more carbon atoms among the carbon atoms constituting the lactone ring structure form the main chain of the (meth)acrylic resin. General formula (3) shows a 6-membered lactone ring structural unit. The number of ring members in the lactone ring may be 4 to 8, but the number of ring members in the lactone ring is preferably 5 to 6 from the viewpoint of excellent ring structure stability.

[0075] The following general formula (4) represents another lactone ring structural unit.

[0076] [Chemical Formula 4]

[0077]

[0078] R in the general formula (4) 10 ~R 13 are independently a hydrogen atom or a hydrocarbon group having 1 to 18 carbon atoms. The hydrocarbon group is an aliphatic hydrocarbon group or an aromatic hydrocarbon group. An example of an aliphatic hydrocarbon group is an alkyl group. An alkyl group is a group having 1 to 10 carbon atoms and can be a linear structure, a branched structure, or a cyclic structure. Specifically, it can be a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a tert-butyl group, an n-pentyl group, an n-hexyl group, a cyclopentyl group, a cyclohexyl group, etc. Specifically, an aromatic hydrocarbon group can be a phenyl group, a tolyl group, a benzyl group, etc. R 10 ~R 13 Preferably, they are independently hydrogen atoms or alkyl groups having 1 to 10 carbon atoms, and more preferably, all of them are hydrogen atoms.

[0079] The lactone ring structural unit represented by the general formula (4) can be formed by polymerizing a compound represented by the following formula (5).

[0080] [Chemical Formula 5]

[0081]

[0082] R in general formula (5) 10 ~R 13 and R in general formula (4) 10 ~R 13 same.

[0083] The lactone ring structural unit represented by general formula (4) can be said to be a lactone ring structural unit in which one of the carbon atoms constituting the lactone ring structure forms the main chain of the (meth)acrylic resin. General formula (4) shows a 5-membered lactone ring structural unit. The number of ring members in the lactone ring may be 4 to 8, but the number of ring members in the lactone ring is preferably 5 to 6 from the viewpoint of excellent ring structure stability.

[0084] The (meth)acrylic resin having a cyclic structure in its main chain preferably comprises at least one cyclic structural unit selected from the group consisting of glutaric anhydride structural units, glutarimide structural units, maleic anhydride structural units, N-substituted maleimide structural units, and lactone ring structural units, and more preferably comprises at least one cyclic structural unit selected from the group consisting of glutarimide structural units and lactone ring structural units. In other words, the (meth)acrylic resin having a cyclic structure in its main chain preferably comprises at least one cyclic structure selected from the group consisting of glutaric anhydride structures, glutarimide structures, maleic anhydride structures, N-substituted maleimide structures, and lactone ring structures, and more preferably comprises at least one cyclic structure selected from the group consisting of glutarimide structures and lactone ring structures.

[0085] The (meth)acrylic resin having a ring structure in the main chain may also contain a third structural unit different from the (meth)acrylate unit and the ring structural unit. The third structural unit is a structural unit derived from a monomer that can be copolymerized with the monomer used to form the (meth)acrylate unit and the ring structural unit. Specifically, it can be a structural unit derived from the following monomers: 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-vinyl pyrrolidone, N-vinyl carbazole, etc. The (meth)acrylic resin having a ring structure in the main chain may contain only one third structural unit, or may contain two or more third structural units.

[0086] The content of each structural unit in the (meth) acrylic resin having a ring structure in the main chain is not particularly limited, and is preferably as follows. The content of the (meth) acrylate unit can be, for example, 50 to 99 mass%, preferably 65 to 90 mass%, and more preferably 65 to 85 mass%. The content of the ring structural unit can be, for example, 1 to 50 mass%, preferably 10 to 35 mass%, and more preferably 15 to 35 mass%. The content of the third structural unit can be, for example, 0 to 20 mass%. It should be noted that the content of each structural unit in the (meth) acrylic resin having a ring structure in the main chain is obtained as follows: the copolymer is dissolved in a deuterated solvent, and the content is measured. 1 For H-NMR, the area ratio of the peak corresponding to each structural unit was calculated.

[0087] The (meth)acrylic resin having a ring structure in its main chain may be a block copolymer or a graft copolymer.

[0088] An example of a block copolymer is a block copolymer having an XYX or XY structure, wherein the block X is formed of a (meth)acrylic resin having a ring structure in the main chain and the block Y is formed of an aliphatic acrylate such as butyl acrylate.

[0089] An example of a graft copolymer is a (meth)acrylic resin having a ring structure in the main chain of a polymer having units derived from a diene and / or olefin as a graft chain. Specifically, the polymer having units derived from a diene and / or olefin may be a styrene-butadiene block copolymer, a styrene-butadiene-styrene block copolymer, a hydrogenated product of a styrene-butadiene-styrene block copolymer (e.g., a styrene-ethylene / butylene-styrene block copolymer, a styrene-butadiene / butylene-styrene block copolymer), a styrene-isoprene block copolymer, a styrene-isoprene-styrene block copolymer, and a hydrogenated product of a styrene-isoprene-styrene block copolymer (e.g., a styrene-ethylene / propylene-styrene block copolymer).

[0090] The weight average molecular weight of the (meth)acrylic resin having a ring structure in its main chain may be, for example, 10,000 to 500,000, or 50,000 to 300,000.

[0091] 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, preferably 70% by mass or more, and more preferably 90% by mass or more.

[0092] The (meth)acrylic resin composition may also contain a thermoplastic resin different from the (meth)acrylic resin having a ring structure in the main chain. Such thermoplastic resins may include acrylic resins, styrene resins, polycarbonate resins, polyvinylidene fluoride resins, and the like. Specifically, acrylic resins may include polymethyl methacrylate, polymethyl methacrylate-styrene copolymers (MS resins), and partially hydrogenated MS resins obtained by partially hydrogenating the aromatic rings of MS resins. Specifically, styrene resins may include polystyrene, styrene-acrylonitrile copolymers, and acrylonitrile-butadiene-styrene block copolymers.

[0093] 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.

[0094] The (meth)acrylic resin composition preferably contains a UV absorber. Examples of UV absorbers include triazine-based UV absorbers, triazole-based UV absorbers, benzophenone-based UV absorbers, salicylate-based UV absorbers, and benzoate-based UV absorbers. The (meth)acrylic resin layer may contain only one UV absorber or two or more. The UV absorber preferably includes at least one selected from triazine-based UV absorbers and triazole-based UV absorbers.

[0095] Specific examples of the triazine-based ultraviolet absorbers 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-triazine, and 2,4-diphenyl-6-(2-hydroxy-4-propoxyphenyl)-1,3,5-triazine. UV absorbers having a 2,4-bis(2,4-dimethylphenyl)-6-[2-hydroxy-4-(3-alkoxy-2-hydroxypropoxy)-5-α-cumylphenyl]-s-triazine skeleton (alkoxy group; long-chain alkoxy groups such as octyloxy, nonyloxy, and decyloxy groups) and the like.

[0096] Specific examples of triazole-based ultraviolet absorbers 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, and 2-[5-chloro(2H)-benzotriazol-2-yl]-4-methyl-6-(tert-butyl)phenol. Phenol, 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-tetrahydrophthalimidomethyl)phenol, reaction products of methyl 3-(3-(2H-benzotriazol-2-yl)-5-tert-butyl-4-hydroxyphenyl)propionate / polyethylene glycol 300, 2-(2H-benzotriazol-2-yl)-6-(straight chain and side chain dodecyl)-4-methylphenol, etc. The (meth)acrylic resin layer may be made of 2,2′-methylenebis[4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazol-2-yl)phenol], 2-[5-chloro(2H)-benzotriazol-2-yl]-4-methyl-6-(tert-butyl)phenol, or the like.

[0097] The ultraviolet absorber may be a commercially available product. Examples of commercially available products include "Tinuvin (registered trademark) 326" (2-[5-chloro(2H)-benzotriazol-2-yl]-4-methyl-6-(tert-butyl)phenol) manufactured by BASF Japan Co., Ltd. and "ADKSTAB (registered trademark) LA-31" (2,2'-methylenebis[4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazol-2-yl)phenol) manufactured by ADEKA Corporation.

[0098] The content of the ultraviolet absorber in the (meth)acrylic resin composition is preferably 0.1 to 5% by mass, more preferably 1 to 4% by mass.

[0099] The (meth)acrylic resin composition may also contain additives such as stabilizers, processing aids, plasticizers, impact-resistant additives, retardation modifiers, matting agents, antibacterial agents, antifungal agents, and antistatic agents. The content of the additives in the (meth)acrylic resin composition can be adjusted appropriately, but is generally about 0.1 to 40% by weight in total.

[0100] The glass transition temperature Tgc of the (meth)acrylic resin composition is not particularly limited, but is preferably 115°C or higher from the viewpoint of improving the heat resistance of the optical film, and is preferably 160°C or lower from the viewpoint of facilitating stretching during the production of the optical film. In other words, it is preferably 115°C or higher and 160°C or lower.

[0101] The glass transition temperature of a (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 its main chain. As the content of the ring structural unit in the (meth)acrylic resin having a ring structure in its main chain increases, the glass transition temperature of the (meth)acrylic resin composition tends to increase.

[0102] (Method for producing optical film)

[0103] The optical film can be produced by, for example, co-extrusion molding.

[0104] In co-extrusion molding, a vented extruder equipped with a single or twin extrusion screw can be used. For example, two extruders can be used to feed the resin composition for forming the (meth)acrylic resin layer and the resin composition for forming the first and second polycarbonate resin layers into separate melt extruders to produce molten resin compositions. It should be noted that when the first and second polycarbonate resin layers have different compositions, three extruders may be used.

[0105] The resin composition in a molten state is extruded into a film-like shape by the following method: after being measured with a gear pump, a sleeve (pinole) and a feed block (feed block) are used for lamination, and then a T-die discharge method is used; a method of discharging using a multi-manifold die, etc. At this time, from the viewpoint of suppressing coloration, it is preferably melt-mixed under reduced pressure using an exhaust port provided in an extruder, or melt-mixed under a nitrogen stream. In addition, from the viewpoint of suppressing the amount of foreign matter, the resin composition in a molten state is preferably filtered with a filter after being measured with a gear pump.

[0106] The extruded resin composition is cooled and solidified by passing through a casting drum to form an unstretched film. To prevent unevenness (so-called die lines, etc.) from forming on the unstretched film, the casting drum is preferably pressed by a metal nip roll, an elastic metal nip roll with a metal sleeve attached to a rubber roll, or the like.

[0107] The unstretched film is stretched while being heated to form an optical film. The stretching temperature is set based on the glass transition temperature of the resin composition constituting the unstretched film. In particular, in the manufacture of a multi-layer optical film, it is usually set based on the glass transition temperature of the resin composition that mainly constitutes the intermediate layer of the optical film. From this point of view, the stretching temperature can be, for example, about (Tgc+20)°C based on the glass transition temperature Tgc of the (meth)acrylic resin composition. The stretching method can be uniaxial stretching or biaxial stretching (sequential biaxial stretching, simultaneous biaxial stretching). The stretching ratio can be, for example, about 2 times. The stretching speed can be, for example, about 1 m / min.

[0108] The obtained optical film can be wound around a cylindrical core to form an optical film roll.

[0109] (Characteristics of optical films)

[0110] The optical film described above comprises a first polycarbonate resin layer and a second polycarbonate resin layer. Thus, the film has excellent flexibility. Furthermore, the glass transition temperature Tga of the first polycarbonate resin composition, the glass transition temperature Tgb of the second polycarbonate resin composition, and the glass transition temperature Tgc of the (meth)acrylic resin composition comprising a (meth)acrylic resin having a ring structure in the main chain satisfy the above-mentioned formulas (A) and (B). Thus, in the manufacture of the optical film, particularly in the process of obtaining a stretched optical film from an unstretched film, even if the stretching temperature is set based on the glass transition temperature of the (meth)acrylic resin composition, the first polycarbonate resin layer and the second polycarbonate resin layer can be fully softened and stretched. Thus, in the obtained optical film, it is difficult to exhibit phase difference due to orientational birefringence caused by the orientation of the polycarbonate resins contained in the first and second polycarbonate resin layers.

[0111] [Applications of optical films]

[0112] The optical film according to one embodiment of the present disclosure is suitable for use as, for example, a polarizer protective film or a retardation film, and is more preferably used 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.

[0113] That is, the present disclosure includes not only the optical film of one embodiment but also a polarizing plate protective film including the optical film of one embodiment, a polarizing plate including the polarizing plate protective film, and an image display device including the polarizing plate.

[0114] The optical film of one embodiment of the present disclosure is also suitable for use in zero phase difference film, viewing angle compensation film, light diffusion film, reflective film, anti-reflective film, anti-glare film, brightness enhancement film, conductive film for touch panel, diffuser plate, light guide, phase difference plate, zero phase difference plate, prism sheet, etc.

[0115] Example

[0116] The following describes the examples of the present disclosure. Of course, the present disclosure is not limited to the following examples. Before describing the examples, the following describes the evaluation methods in the examples.

[0117] (1) Weight average molecular weight (Mw)

[0118] The weight average molecular weight was determined in terms of polystyrene using gel permeation chromatography (GPC). The apparatus and conditions for the measurement were as follows.

[0119] -System: GPC system HLC-8220 manufactured by TOSOH Corporation.

[0120] - Determine the side column structure

[0121] Guard column: manufactured by TOSOH, TSKguardcolumn SuperHZ-L.

[0122] Separation columns: Two TSKgel SuperHZM-M columns manufactured by TOSOH Corporation were connected in series.

[0123] - Reference jamb composition

[0124] Reference column: TSKgel SuperH-RC manufactured by TOSOH Corporation.

[0125] - Developing solvent: chloroform (manufactured by FUJIFILM Wako Pure Chemical Co., Ltd., special grade).

[0126] -Flow rate of developing solvent: 0.6 mL / min.

[0127] - Standard sample: TSK standard polystyrene (manufactured by TOSOH Corporation, PS-Oligomer Kit).

[0128] - Column temperature: 40°C.

[0129] (2) Glass transition temperature

[0130] The glass transition temperature was determined according to Japanese Industrial Standard (JIS) K 7121. The glass transition temperature was determined by the onset point method using a differential scanning calorimeter (Rigaku Thermoplus EVO DSC-8230) obtained by heating approximately 10 mg of a sample from room temperature to 200°C (heating rate 20°C / min) under a nitrogen atmosphere. It should be noted that α-alumina was used as a reference.

[0131] (3)Thickness of optical film

[0132] The thickness of the optical film was measured using a digital micrometer (manufactured by Mitutoyo). The thickness of each layer constituting the optical film was measured by observing a cross-section of the optical film using a scanning electron microscope (FE-SEM S-4800, manufactured by Hitachi High-Technologies Corporation (currently Hitachi High-Tech Corporation)). The measurement conditions were an accelerating voltage of 20 kV, an emission current of 5 μA or 10 μA, and a WD of 8 mm.

[0133] (4) Evaluation of flexibility

[0134] The flexibility of optical films was evaluated according to Japanese Industrial Standards (JIS) K5600-5-1:1999. Five test films, 50 mm wide and 100 mm long, were prepared and allowed to stand for at least one hour at 23°C and 50% RH. The number of folding cycles was measured for each test film. The average number of folding cycles reported for each of the five test films was used for evaluation as follows.

[0135] A: The folding endurance is more than 500 times.

[0136] B: The folding endurance is 200 times or more and less than 500 times.

[0137] C: The folding endurance is 100 times or more and less than 200 times.

[0138] D: Folding times are less than 100 times.

[0139] The case where the bending line was parallel to the film forming direction was defined as an MD test, and the case where the bending line was perpendicular to the film forming direction was defined as a TD test.

[0140] (5) Evaluation of birefringence

[0141] The in-plane phase difference Re and the phase difference Rth in the thickness direction of the optical film were determined using a phase difference film-optical material inspection device (manufactured by Otsuka Electronics Co., Ltd., RETS-100). The phase difference Rth in the thickness direction was calculated using the refractive indices nx, ny, and nz and the thickness d (nm) of the optical film using the formula Rth = {(nx + ny) / 2-nz} × d. The refractive indices nx, ny, and nz were determined based on the average refractive index of the optical film measured using an Abbe refractometer and the in-plane phase difference Re (40°) measured using the above device with the optical film tilted 40° relative to the tilt axis. nx is the refractive index in the slow axis direction of the optical film. ny is the refractive index in the direction perpendicular to the slow axis direction (fast axis direction) of the optical film in the plane of the optical film. nz is the refractive index in the thickness direction of the optical film. Re(40°) is set to a larger value selected from Re(S40°) obtained with the slow axis as the tilt axis and Re(F40°) with the direction perpendicular to the slow axis in the plane of the optical film as the tilt axis.

[0142] A: The absolute value of Rth is less than 50 nm.

[0143] B: The absolute value of Rth is 50 nm or more and less than 150 nm.

[0144] C: The absolute value of Rth is 150 nm or more.

[0145] [Manufacture of Resin Composition 1A]

[0146] A reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen inlet tube was charged with a mixed solvent of 79.4 parts by mass of methyl methacrylate, 20.6 parts by mass of methacrylic acid, 90.0 parts by mass of toluene, and 22.5 parts by mass of methanol, and 0.05 parts by mass of an antioxidant [manufactured by ADEKA Corporation, trade name: ADK STAB 2112]. While nitrogen was flowing into the reaction vessel, the temperature was raised to 73°C. At the start of reflux associated with the temperature increase, 0.25 parts by mass of 2,2'-azobis(2-methylpropionic acid)dimethyl ester [Fujifilm Wako Pure Chemical Co., Ltd., trade name: V-601] was added to the reactor. A solution of 0.35 parts by mass of 2,2'-azobis(2-methylpropionic acid)dimethyl ester [Fujifilm Wako Pure Chemical Co., Ltd., trade name: V-601] dissolved in a mixed solvent of 7.3 parts by mass of toluene and 1.8 parts by mass of methanol was then added dropwise to the reactor over 2 hours. Solution polymerization was carried out under reflux at approximately 71-76°C. After the addition of the 2,2'-azobis(2-methylpropionic acid)dimethyl ester was completed, the reaction mixture was aged for a further 4 hours. The (meth)acrylic resin contained in the resulting polymer solution contained 20.6% by weight of structural units derived from methacrylic acid. The weight-average molecular weight of the (meth)acrylic resin was 110,000.

[0147] A solution of 0.05 parts by mass of a cyclization catalyst (sodium methoxide) dissolved in 9.9 parts by mass of methanol was added dropwise to the obtained polymerization solution over 20 minutes to carry out a cyclization reaction.

[0148] The cyclized polymer solution was introduced into a vented twin-screw extruder (15 mm bore diameter, L / D: 45) at a barrel temperature of 280°C, a rotation speed of 238 rpm, a reduced pressure of 13.3 to 400 hPa (10 to 300 mmHg), and two front vents at a processing rate of 624 g / h (based on the resin content). Devolatilization was performed within the extruder. Extrusion was continued with a residence time within the extruder of approximately 2.6 minutes to obtain (meth)acrylic resin pellets. The resulting (meth)acrylic resin had a weight-average molecular weight of 98,000 and a glass transition temperature of 130°C.

[0149] The resulting pellets were introduced from a hopper into a vented twin-screw extruder (15 mm bore diameter, L / D: 45) at a processing rate of 420 g / h (based on the resin content). The extruder had a barrel temperature of 290°C, a rotation speed of 300 rpm, a reduced pressure of 13.3 to 400 hPa (10 to 300 mmHg), and one vent port. Aniline was then injected downstream of the hopper at a rate of 202 g / h. Extrusion was continued with a residence time within the extruder of approximately 5.5 minutes to produce (meth)acrylic resin pellets. The resulting (meth)acrylic resin had a weight-average molecular weight of 92,000 and a glass transition temperature of 178°C.

[0150] The resulting pellets were introduced from a hopper into a vented twin-screw extruder (15 mm bore diameter, L / D: 45) at a processing rate of 420 g / h (based on the resin amount), with a barrel temperature of 290°C, a rotation speed of 300 rpm, a reduced pressure of 13.3 to 400 hPa (10 to 300 mmHg), and one vent port. A mixed solution of dimethyl carbonate (DBC) and diazabicycloundecene (DBU) was injected downstream of the hopper using a liquid addition pump to provide 20 parts by mass of DBC and 0.5 parts by mass of DBU per 100 parts by mass of the resin. Extrusion was performed with a residence time in the shaft of approximately 5.2 minutes, thereby producing pellets of a (meth)acrylic resin having a phenylglutarimide structure in its main chain. The (meth)acrylic resin having a phenylglutarimide structure in its main chain had a weight-average molecular weight of 83,000 and a glass transition temperature of 158°C. This resin was designated as resin composition 1A.

[0151] [Manufacture of Resin Composition 2A]

[0152] A (meth)acrylic resin having an N-substituted maleimide structure in its main chain (manufactured by Nippon Shokubai Co., Ltd., trade name: POLYIMILEX PML203, glass transition temperature: 139° C.) was used as resin composition 2A.

[0153] [Production of Resin Composition 3A]

[0154] A reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen inlet was charged with 83.5 parts of methyl methacrylate (MMA), 12 parts of 2-hydroxymethyl (meth)acrylate (MHMA), 88.7 parts of toluene, and 0.05 parts of an antioxidant (manufactured by ADEKA, trade name: ADK STAB (registered trademark) 2112). Nitrogen was then introduced and the temperature was raised to 105°C. At the start of reflux accompanying the temperature increase, 0.435 parts of a 20% by weight toluene solution of t-amyl peroxyisononanoate (manufactured by ARKEMA, trade name: Luperox (registered trademark) 570T20) was added as a polymerization initiator. Subsequently, 4.5 parts of styrene (St) and 0.15 parts of n-dodecyl mercaptan (nDM) were added dropwise over 2 hours. Furthermore, 0.865 parts of a 20% by weight toluene solution of t-amyl peroxyisononanoate was added dropwise over 4 hours. During the dropwise addition, the mixed solution was refluxed at about 105 to 110° C. to carry out solution polymerization. After the dropwise addition was completed, aging was further carried out at the same temperature for 2 hours.

[0155] To the obtained polymerization solution was added 0.075 parts of stearyl phosphate (manufactured by SC Organic Chemical Co., Ltd., trade name: Phoslex A-18), and a cyclization condensation reaction was carried out under reflux at about 90 to 110° C. for 2 hours to form a lactone ring structure.

[0156] The polymer solution that has undergone the cyclization condensation reaction is passed through a multi-tubular heat exchanger heated to 240°C to complete the cyclization condensation reaction. Then, the polymer solution is introduced into a vented twin-screw extruder (L / D=52) at a processing speed of 31.2 parts / hour (resin amount conversion). The barrel temperature of the above-mentioned vented twin-screw extruder is 250°C, and it is equipped with a rear exhaust port, four front exhaust ports (called the first exhaust port, the second exhaust port, the third exhaust port, and the fourth exhaust port from the upstream side) and a side feeder located between the third exhaust port and the fourth exhaust port. A blade disk-type polymer filter (filtration accuracy 10μm) is arranged at the front end. The decompression degree of each exhaust port is set to 798hPa for the rear exhaust port, 266hPa for the first exhaust port, and 27hPa for the second exhaust port to the fourth exhaust port, and devolatilization is implemented. At this time, ion exchange water is added from the rear of the second exhaust port and the fourth exhaust port at an input rate of 0.47 parts / hour.

[0157] After the devolatilization is completed, the molten resin composition is discharged from the front end of the extruder while being filtered with the above-mentioned polymer filter. Then, it is passed through the die head equipped at the front end of the extruder and cooled in a water tank filled with cooling water to obtain a strand of the resin composition. The above-mentioned cooling water is filtered with a filter with a pore size of 1 μm (Organo Co., Ltd., trade name: microporefilter1EU) and maintained at a temperature within the range of 30±10°C. The cooled strand is introduced into a cutting machine to obtain particles of a (meth) acrylic resin having a lactone ring structure in the main chain. The weight-average molecular weight of the (meth) acrylic resin having a lactone ring structure in the main chain is 133,000, and the content of the lactone ring structure is 19.6% by mass. In addition, the glass transition temperature of the (meth) acrylic resin is 123°C. In addition, this resin is used as resin composition 3A.

[0158] [Manufacture of Resin Composition 4A]

[0159] Pellets of a (meth)acrylic resin composition containing a (meth)acrylic resin having a lactone ring structure in its main chain were obtained in the same manner as for resin composition 3A, except that 2.2 parts by mass of an ultraviolet absorber (manufactured by ADEKA Corporation, trade name: ADK STAB (registered trademark) LA-31) was added from a side feeder relative to 100 parts by mass of the resin. The (meth)acrylic resin having a lactone ring structure in its main chain had a weight-average molecular weight of 133,000 and a lactone ring structure content of 19.6% by mass. The glass transition temperature of the (meth)acrylic resin composition was 120°C. This resin composition was designated as resin composition 4A.

[0160] [Manufacture of Resin Composition 1B]

[0161] A commercially available polycarbonate resin (manufactured by Sumika Polycarbonate Co., Ltd., trade name: SD POLYCA 301-15, glass transition temperature: 145° C.) was used as resin composition 1B.

[0162] [Production of Resin Composition 2B]

[0163] Using a twin-screw extruder (manufactured by PLABOR Research Laboratory of Plastics Technology Co., Ltd., BT-30-S21C-30-1), 99.9 parts by mass of a commercially available polycarbonate resin (manufactured by Sumika Polycarbonate Co., Ltd., trade name: SD POLYCA 301-10) and 0.1 parts by mass of silica-based fine particles having an average particle size of 0.3 μm (manufactured by Nippon Shokubai Co., Ltd., trade name: SEAHOSTAR (registered trademark) KE-P30) were melt-kneaded at 260°C to produce resin composition 2B. The glass transition temperature of resin composition 2B was 140°C.

[0164] [Production of Resin Composition 3B]

[0165] A commercially available polycarbonate resin (manufactured by Mitsubishi Gas Chemical Co., Ltd., trade name: Iupizeta FPC-0330, glass transition temperature: 120° C.) was used as resin composition 3B.

[0166] [Manufacturing of Optical Film 1]

[0167] Resin compositions 1A and 3B were dried in a hot air oven at 80°C for 8 hours. Single-screw extruders A and B, each equipped with a bladed-disc polymer filter with a filtration accuracy of 5μm, were prepared. Resin composition 1A was fed into single-screw extruder A, and resin composition 3B was fed into single-screw extruder B. Co-extrusion molding was performed to obtain a molten film composed of a first polycarbonate resin layer, a (meth)acrylic resin layer, and a second polycarbonate resin layer, laminated in sequence. The layer thickness ratio was 1:38:1. The resulting molten film was passed through a first cooling roll adjusted to 120°C, a second cooling roll adjusted to 95°C, and multiple conveyor rolls to obtain an unstretched film.

[0168] The resulting film was uniaxially stretched in the longitudinal direction using an oven stretching machine to produce a longitudinally stretched film. The stretching temperature was set at 176°C and the stretch ratio was set at 215%. The longitudinally stretched film was then stretched in the transverse direction using a tenter stretching machine. Specifically, while heating the longitudinally stretched film, the film was clamped between 2-inch clamps at a position 20 mm from each end and stretched in the transverse direction. The stretching temperature was set at 176°C and the stretch ratio was set at 265%. The resulting optical film 1 had a thickness of 40 μm.

[0169] [Manufacturing of Optical Films 2 to 9]

[0170] Optical Films 2 to 9 were obtained by varying the resin composition and stretching conditions used to form each layer. The resin composition used to form each layer, its glass transition temperature (Tg), and the stretching conditions (stretching temperature, stretch ratio) are shown in Table 1. The first and second polycarbonate resin layers are referred to as surface layers, and the (meth)acrylic resin layer is referred to as the intermediate layer.

[0171] [Table 1]

[0172]

[0173] Table 2 shows the evaluation results of the values obtained by subtracting the glass transition temperature of the (meth)acrylic resin composition from the glass transition temperatures of the first and second polycarbonate resin compositions (Tg difference), flexibility (folding endurance), and birefringence (absolute value of Rth) of Optical Films 1 to 9.

[0174] [Table 2]

[0175]

[0176] The flexibility evaluations of Optical Films 1 to 7 were also good, and the birefringence evaluations were also good. Therefore, it can be said that Optical Films 1 to 7 are suitable for use as films requiring optical isotropy.

[0177] The flexibility of optical film 8 was evaluated as good, but its birefringence was evaluated as poor. In optical film 8, the glass transition temperatures of the first and second polycarbonate resin compositions are sufficiently higher than the glass transition temperature of the (meth)acrylic resin composition. Furthermore, the stretching temperatures during longitudinal and transverse stretching are set based on the relatively low glass transition temperature of the (meth)acrylic resin composition. Therefore, it is believed that the first and second polycarbonate resin layers were stretched in an insufficiently softened state, resulting in phase difference due to orientational birefringence caused by the orientation of the polycarbonate resins contained in the first and second polycarbonate resin layers.

[0178] Optical Film 9 not only received poor evaluations for flexibility, but also poor evaluations for birefringence. In Optical Film 9, the glass transition temperatures of the first and second polycarbonate resin compositions are significantly higher than the glass transition temperature of the (meth)acrylic resin composition. Furthermore, the stretching temperatures during longitudinal and transverse stretching are set based on the glass transition temperatures of the first and second polycarbonate resin compositions, which have relatively high glass transition temperatures. Therefore, it can be assumed that the first and second polycarbonate resin layers are stretched while softened to some extent. On the other hand, since the first and second polycarbonate resin layers are stretched while softened to some extent, it can also be assumed that the improvement in mechanical strength associated with stretching cannot be effectively achieved.

[0179] It should be noted that, for reference, when a single-layer optical film 10 (thickness: 40 μm) formed by the resin composition 2A is manufactured at a longitudinal stretching temperature of 157°C / a longitudinal stretching ratio of 2.15 times and a transverse stretching temperature of 157°C / a transverse stretching ratio of 2.65 times, the flexibility in the MD direction and the TD direction is evaluated as C, and the birefringence is evaluated as A.

Claims

1. An optical film comprising: a first polycarbonate-based resin layer formed from a first polycarbonate resin composition; a second polycarbonate-based resin layer formed from a second polycarbonate resin composition; and The (meth)acrylic resin layer is formed of a (meth)acrylic resin composition containing a (meth)acrylic resin having a ring structure in its main chain, and is disposed between the first polycarbonate resin layer and the second polycarbonate resin layer. The glass transition temperature Tga of the first polycarbonate resin composition, the glass transition temperature Tgb of the second polycarbonate resin composition, and the glass transition temperature Tgc of the (meth)acrylic resin composition satisfy the following formula (A) and the following formula (B), Formula (A): Tga≤Tgc+6, Formula (B): Tgb≤Tgc+6, The first polycarbonate-based resin layer, the second polycarbonate-based resin layer, and the (meth)acrylic-based resin layer are stretched.

2. The optical film according to claim 1, wherein The ring structure comprises at least one selected from the group consisting of a glutaric anhydride structure, a glutarimide structure, a maleic anhydride structure, an N-substituted maleimide structure, and a lactone ring structure.

3. The optical film according to claim 1, wherein The (meth)acrylic resin composition has a glass transition temperature Tgc of 115° C. or higher and 160° C. or lower. 4 . A polarizing plate protective film comprising the optical film according to claim 1 . A polarizing plate comprising the polarizer protective film according to claim 4 . An image display device comprising the polarizing plate according to claim 5 .

Images