Polarizer protective film, polarizing plate, liquid crystal panel, and acrylic resin composition

Abstract

To provide a polarizer protective film which reduces yellowness when being viewed from an oblique direction of a liquid crystal panel, and can improve heat resistance of a biaxially oriented film.SOLUTION: A polarizer protective film contains an acrylic resin composition, and has a retardation Rth in a thickness direction at a wavelength of 590 nm of -35.0 nm or more and -5.0 nm or less. The acrylic resin composition contains an acrylic resin having a ring structure at a main chain, and has a glass transition temperature of 120°C or higher. The polarizer protective film has an absolute value of an Nz coefficient of 2.0 or more and 5.0 or less, a ratio Rth(447) / Rth(548) of a retardation Rth (447) in a thickness direction at a wavelength of 447 nm to a retardation Rth (548) in a thickness direction at a wavelength of 548 nm is 1.00 or more and 1.30 or less, and a ratio Rth(628) / Rth(548) of a retardation Rth (628) in a thickness direction at a wavelength of 628 nm to the retardation Rth (548) in a thickness direction at a wavelength of 548 nm is 1.00 or more and 1.30 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polarizer protective film, a polarizing plate, a liquid crystal panel, and an acrylic resin composition. [Background technology]

[0002] Acrylic resins have excellent transparency, color tone, appearance, heat resistance, and processability, and are therefore used, for example, in polarizer protective films (see, for example, Patent Document 1). Here, the polarizer protective films are attached to both sides of a polarizer to form polarizing plates, which are then placed on both sides of a liquid crystal cell to be used in liquid crystal panels.

[0003] On the other hand, IPS type liquid crystal panels are preferably used for applications such as liquid crystal televisions because of their wide viewing angle and excellent color reproducibility. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2017-25333 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when a polarizer protective film containing an acrylic resin is applied to an IPS liquid crystal panel, the liquid crystal panel may appear slightly yellowish when displayed in black and viewed from an oblique direction. Furthermore, it is desirable to improve the heat resistance of the polarizer protective film.

[0006] The present invention aims to provide a polarizer protective film and an acrylic resin composition that can reduce the yellowness when viewed from an oblique direction of a liquid crystal panel and improve the heat resistance of a biaxially stretched film. [Means for solving the problem]

[0007] [1] A polarizer protective film comprising an acrylic resin composition, the thickness direction retardation Rth at a wavelength of 590 nm being -35.0 nm or more and -5.0 nm or less, the acrylic resin composition comprising an acrylic resin having a ring structure in its main chain, the glass transition temperature being 120°C or more, the absolute value of the Nz coefficient being 2.0 or more and 5.0 or less, the ratio Rth(447) / Rth(548) of the thickness direction retardation Rth(447) at a wavelength of 447 nm to the thickness direction retardation Rth(548) at a wavelength of 548 nm being 1.00 or more and 1.30 or less, and the ratio Rth(628) / Rth(548) of the thickness direction retardation Rth(628) at a wavelength of 628 nm to the thickness direction retardation Rth(548) at a wavelength of 548 nm being 1.00 or more and 1.30 or less.

[0008] [2] The polarizer protective film described in (1), wherein the acrylic resin having a ring structure in the main chain has a structural unit containing, in the main chain, one or more ring structures selected from the group consisting of a glutarimide ring, a lactone ring, a maleic anhydride ring, a maleimide ring, and a glutaric anhydride ring.

[0009] [3] The polarizer protective film according to [2], wherein the acrylic resin having a ring structure in the main chain has a structural unit represented by the following formula (1):

[0010] [ka] (In the formula, R 1 and R 2 are each independently a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and R 3 is a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, or a cycloalkyl group having 3 to 12 carbon atoms.

[0011] [4] The polarizer protective film according to any one of [1] to [3], wherein the acrylic resin composition has an aromatic vinyl unit content of 1.0% by weight or more and 10.0% by weight or less.

[0012] [5] The polarizer protective film according to [4], wherein the aromatic vinyl unit is a styrene unit.

[0013] [6] The polarizer protective film according to any one of [1] to [5], wherein the acrylic resin composition further contains a copolymer containing a (meth)acrylonitrile unit and an aromatic vinyl unit.

[0014] [7] The polarizer protective film according to any one of [1] to [6], wherein the acrylic resin composition has a 1% weight loss temperature of 320°C or higher.

[0015] [8] The polarizer protective film according to any one of [1] to [7], which does not contain an ultraviolet absorber.

[0016] [9] The polarizer protective film according to any one of [1] to [8], which is a biaxially stretched film.

[0017]

[10] The polarizer protective film according to any one of [1] to [9], which has a yellowness index of 0.01 or more and 5.00 or less.

[0018]

[11] The polarizer protective film according to any one of [1] to

[10] , which has an absorbance at a wavelength of 380 nm of 0.01 or more and 1.00 or less.

[0019]

[12] A polarizing plate comprising the polarizer protective film according to any one of [1] to

[10] .

[0020]

[13] A liquid crystal panel comprising the polarizing plate according to

[12] .

[0021]

[14] An acrylic resin composition comprising an acrylic resin having a ring structure in the main chain and a copolymer containing (meth)acrylonitrile units and aromatic vinyl units, wherein the glass transition temperature is 120°C or higher, the content of the aromatic vinyl units is 1% by weight or more and 10% by weight or less, and when the acrylic resin composition is formed into a biaxially stretched film, the absolute value of the Nz coefficient at a thickness of 40 μm is 2.0 or more and 5.0 or less.

[0022]

[15] The acrylic resin composition according to

[14] , which has a 1% weight loss temperature of 320°C or higher.

[0023]

[16] An acrylic resin composition comprising an acrylic resin having a ring structure in its main chain, the acrylic resin composition having a glass transition temperature of 120°C or higher, an aromatic vinyl unit content of 1% by weight or more and 10% by weight or less, a 1% weight loss temperature of 320°C or higher, and an absolute value of the Nz coefficient at a thickness of 40 μm when the acrylic resin composition is formed into a biaxially stretched film of 2.0 or more and 5.0 or less.

[0024]

[17] The acrylic resin composition according to any one of

[14] to

[16] , wherein the acrylic resin having a ring structure in its main chain has a structural unit containing, in its main chain, one or more ring structures selected from the group consisting of a glutarimide ring, a lactone ring, a maleic anhydride ring, a maleimide ring, and a glutaric anhydride ring.

[0025]

[18] The acrylic resin composition according to

[17] , wherein the acrylic resin having a ring structure in the main chain has a structural unit represented by the following formula (1):

[0026] [ka] (In the formula, R 1 and R 2 are each independently a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and R 3 is a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, or a cycloalkyl group having 3 to 12 carbon atoms.

[0027]

[19] The acrylic resin composition according to any one of

[14] to

[18] , wherein the aromatic vinyl unit is a styrene unit.

[0028]

[20] The acrylic resin composition according to any one of

[14] to

[19] , which does not contain an ultraviolet absorber.

[0029]

[21] The acrylic resin composition according to any one of

[14] to

[20] , wherein the acrylic resin composition is formed into a biaxially stretched film, and the yellowness index at a thickness of 40 μm is 0.01 or more and 5.00 or less.

[0030]

[22] The acrylic resin composition according to any one of

[14] to

[21] , wherein the acrylic resin composition, when molded into a biaxially stretched film, has an absorbance at a wavelength of 380 nm at a thickness of 40 μm of 0.01 or more and 1.00 or less.

[0031]

[23] The acrylic resin composition according to any one of

[14] to

[22] , which is used for an optical film.

[0032]

[24] The acrylic resin composition according to

[23] , wherein the optical film is a polarizer protective film. [Effects of the Invention]

[0033] According to the present invention, it is possible to provide a polarizer protective film and an acrylic resin composition that can reduce the yellowness when viewed from an oblique direction of a liquid crystal panel and improve the heat resistance of a biaxially stretched film. DETAILED DESCRIPTION OF THE INVENTION

[0034] Hereinafter, an embodiment of the present invention will be described.

[0035] [First embodiment] (Polarizer protective film) The polarizer protective film of the present embodiment contains an acrylic resin composition.

[0036] The thickness direction retardation Rth at a wavelength of 590 nm of the polarizer protective film of this embodiment is -35.0 nm or more and -5.0 nm or less, preferably -30.0 nm or more and -6.0 nm or less, preferably -20.0 nm or more and -7.0 nm or less, more preferably -15.0 nm or more and -8.0 nm or less, and particularly preferably -14.0 nm or more and -9.0 nm or less. When Rth is -35.0 nm or more and -5.0 nm or less, the yellowness index when viewed from an oblique direction of the liquid crystal panel is reduced. In this case, the polarizer protective film of this embodiment preferably has a yellowness index of 50 or less when viewed from an oblique direction of the liquid crystal panel.

[0037] Rth is expressed by the formula Rth=[(nx+ny) / 2-nz]×d where nx, ny, and nz are the refractive indices in the X-axis direction, Y-axis direction, and Z-axis direction, respectively, where the MD direction is the X-axis, the TD direction is the Y-axis, and the thickness direction of the film is the Z-axis. Also, d is the thickness of the film.

[0038] The absolute value of the Nz coefficient of the polarizer protective film of this embodiment is from 2.0 to 5.0, and preferably from 3.0 to 4.5. When the absolute value of the Nz coefficient of the polarizer protective film of this embodiment is from 2.0 to 5.0, the yellowness of the liquid crystal panel when viewed from an oblique direction is reduced.

[0039] The ratio Rth(447) / Rth(548), which is the thickness direction retardation Rth(447) at a wavelength of 447 nm to the thickness direction retardation Rth(548) at a wavelength of 548 nm, of the polarizer protective film of this embodiment is 1.00 or more and 1.30 or less, and preferably 1.01 or more and 1.28 or less. When Rth(447) / Rth(548) of the polarizer protective film of this embodiment is 1.00 or more and 1.30 or less, the yellowness when viewed from an oblique direction of the liquid crystal panel is reduced.

[0040] The ratio Rth(628) / Rth(548), which is the thickness direction retardation Rth(628) at a wavelength of 628 nm to the thickness direction retardation Rth(548) at a wavelength of 548 nm, of the polarizer protective film of this embodiment is 1.00 or more and 1.30 or less, and preferably 1.01 or more and 1.15 or less. When Rth(628) / Rth(548) of the polarizer protective film of this embodiment is 1.00 or more and 1.30 or less, the yellowness when viewed from an oblique direction of the liquid crystal panel is reduced.

[0041] The yellowness index of the polarizer protective film of this embodiment is preferably 0.01 to 5.00, and more preferably 0.1 to 2.0. When the yellowness index of the polarizer protective film of this embodiment is 5.00 or less, the polarizer protective film of this embodiment is less colored and has less effect on the color rendering properties of the display.

[0042] The absorbance of the polarizer protective film of this embodiment at a wavelength of 380 nm is preferably 0.01 or more and 1.00 or less, and more preferably 0.10 or more and 0.80 or less. When the absorbance of the polarizer protective film of this embodiment at a wavelength of 380 nm is 1.00 or less, the polarizer protective film of this embodiment is substantially free of an ultraviolet absorber.

[0043] The polarizer protective film of this embodiment can be attached to a polarizer to form a polarizing plate. The polarizer is not particularly limited, and known polarizers can be used. The polarizing plate can also be combined with a liquid crystal cell to form a liquid crystal panel. In this case, it is preferable to use an IPS liquid crystal cell with a wide viewing angle. When the polarizer protective film of this embodiment is disposed on the side facing the liquid crystal cell, it may not contain an ultraviolet absorber, or may not substantially contain an ultraviolet absorber.

[0044] (Acrylic resin composition) The acrylic resin composition contains an acrylic resin having a ring structure in the main chain. The glass transition temperature of the acrylic resin composition is 120°C or higher, preferably greater than 120°C, more preferably 121°C or higher, and even more preferably 122°C or higher. If the glass transition temperature of the acrylic resin composition is lower than 120°C, orientation relaxation may proceed in a high-temperature, high-humidity environment, resulting in a decrease in retardation stability. The glass transition temperature of the acrylic resin composition is, for example, 160°C or lower.

[0045] In this specification and claims, acrylic resin refers to a polymer of a monomer having an acryloyl group and / or a monomer having a methacryloyl group. In this case, the acrylic resin may be either a homopolymer or a copolymer. When the acrylic resin is a copolymer, it may also be a copolymer of a monomer not having an acryloyl group or a methacryloyl group.

[0046] The content of aromatic vinyl units in the acrylic resin composition is preferably 1.0% by weight or more and 10.0% by weight or less, more preferably 2.5% by weight or more and 9.5% by weight or less, even more preferably 3.0% by weight or more and 9.0% by weight or less, even more preferably 3.2% by weight or more and 8.5% by weight or less, and particularly preferably 3.5% by weight or more and 8.0% by weight or less. When the content of aromatic vinyl units in the acrylic resin composition is 1.0% by weight or more and 10.0% by weight or less, the yellowness of the liquid crystal panel when viewed from an oblique direction is reduced.

[0047] The acrylic resin composition may further contain, for example, a copolymer containing (meth)acrylonitrile units and aromatic vinyl units. The content of the aromatic vinyl units in the copolymer is not particularly limited, but is, for example, 50% by weight or more and 90% by weight or less. The weight ratio of the copolymer to the acrylic resin is also not particularly limited, but is, for example, 5% by weight or more and 90% by weight or less. It is preferable that the acrylic resin contained in the acrylic resin composition does not contain aromatic vinyl units.

[0048] The aromatic vinyl is not particularly limited, but examples thereof include styrene, α-methylstyrene, methoxystyrene, vinyltoluene, and halostyrene. Among these, styrene is preferred from the viewpoint of reducing yellowness when the liquid crystal panel is viewed from an oblique direction. Here, the (meth)acrylonitrile is acrylonitrile or methacrylonitrile.

[0049] The 1% weight loss temperature of the acrylic resin composition is preferably 320°C or higher, more preferably 325°C or higher, and even more preferably 330°C or higher. When the 1% weight loss temperature of the acrylic resin composition is 320°C or higher, contamination of the cooling roll during production of raw film is suppressed, improving the film formability of the raw film. The 1% weight loss temperature of the acrylic resin composition is, for example, 380°C or lower.

[0050] The weight-average molecular weight of the acrylic resin composition is preferably from 50,000 to 200,000, and more preferably from 90,000 to 150,000. When the weight-average molecular weight of the acrylic resin composition is 50,000 or more, the mechanical properties of a molded product of the acrylic resin composition tend to be improved, and when it is 200,000 or less, the moldability of the acrylic resin composition tends to be improved.

[0051] The ratio of the weight average molecular weight to the number average molecular weight of the acrylic resin composition (polydispersity) is preferably 1.5 or more and 2.5 or less, and more preferably 1.5 or more and 2.2 or less. When the polydispersity of the acrylic resin composition is 1.5 or more, the flowability of the acrylic resin composition tends to be improved and it tends to be easier to mold, and when it is 2.5 or less, the mechanical properties such as impact resistance, toughness, and flex resistance of an article molded from the acrylic resin composition tend to be improved.

[0052] The number-average molecular weight and weight-average molecular weight of the acrylic resin composition are values ​​measured by gel permeation chromatography (GPC) in terms of standard polystyrene. The number-average molecular weight and weight-average molecular weight of the acrylic resin composition can be controlled by the types and amounts of polymerization initiators and chain transfer agents used in synthesizing the acrylic resin.

[0053] The acrylic resin composition may further contain additives within a range that does not impair the object of the present invention. The additives are not particularly limited, but examples thereof include antioxidants, heat stabilizers, light stabilizers, ultraviolet absorbers, specific wavelength absorbers or specific wavelength absorbing dyes for cutting blue light, light resistance stabilizers such as radical scavengers, retardation adjusters, catalysts, plasticizers, lubricants, antistatic agents, colorants, shrinkage inhibitors, antibacterial and deodorizing agents, fluorescent brighteners, and compatibilizers, and two or more of these may be used in combination.

[0054] (acrylic resin with a ring structure in the main chain) The acrylic resin having a ring structure in the main chain (hereinafter referred to as "acrylic resin") preferably has a structural unit containing one or more ring structures selected from the group consisting of a glutarimide ring, a lactone ring, a maleic anhydride ring, a maleimide ring, and a glutaric anhydride ring in the main chain.

[0055] A structural unit containing a glutarimide ring in the main chain is represented by, for example, the following formula (1).

[0056] [ka] (In the formula, R 1 and R 2 are each independently a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and R 3 is a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, or a cycloalkyl group having 3 to 12 carbon atoms.

[0057] The acrylic resin having the structural unit represented by formula (1) can be produced by a known method. An example of the method for producing the acrylic resin having the structural unit represented by formula (1) will be described below.

[0058] First, a twin-screw extruder equipped with a die at the outlet is used to melt the methyl methacrylate resin, which is then imidized, and a strand is extruded from the die. Next, the strand is cooled using a water bath and then pelletized using a pelletizer to obtain an imidized methyl methacrylate resin. Next, a twin-screw extruder equipped with a die at the outlet is used to melt the imidized methyl methacrylate resin, which is then esterified, and a strand is extruded from the die. Next, the strand is cooled using a water bath and then pelletized using a pelletizer to obtain an acrylic resin having a structural unit represented by formula (1).

[0059] Examples of the imidizing agent include ammonia and primary amines represented by the following formula (2): Among these, monomethylamine is preferred.

[0060] R 3 NH2(2) (In the formula, R 3 is the same as formula (1).

[0061] Examples of the esterifying agent include dimethyl carbonate, 2,2-dimethoxypropane, dimethyl sulfoxide, triethyl orthoformate, trimethyl orthoacetate, trimethyl orthoformate, diphenyl carbonate, dimethyl sulfate, methyl toluene sulfonate, methyl trifluoromethyl sulfonate, methyl acetate, methanol, ethanol, methyl isocyanate, p-chlorophenyl isocyanate, dimethylcarbodiimide, dimethyl-t-butylsilyl chloride, isopropenyl acetate, dimethyl urea, tetramethylammonium hydroxide, dimethyldiethoxysilane, tetra-n-butoxysilane, dimethyl(trimethylsilane) phosphite, trimethyl phosphite, trimethyl phosphate, tricresyl phosphate, diazomethane, ethylene oxide, propylene oxide, cyclohexene oxide, 2-ethylhexyl glycidyl ether, phenyl glycidyl ether, and benzyl glycidyl ether. Of these, dimethyl carbonate is preferred.

[0062] The content of structural units containing a ring structure in the main chain in the acrylic resin is preferably 1% by weight or more and 80% by weight or less, and the glass transition temperature of the acrylic resin is preferably 120°C or more and 160°C or less.

[0063] The acrylic resin may further have a structural unit derived from a (meth)acrylic acid ester.

[0064] Examples of (meth)acrylic acid esters include alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, and isobutyl (meth)acrylate; aryl (meth)acrylates such as phenyl (meth)acrylate; aralkyl (meth)acrylates such as benzyl (meth)acrylate; and cycloalkyl (meth)acrylates such as cyclohexyl (meth)acrylate, and two or more of these may be used in combination. Among these, alkyl methacrylates are preferred, and methyl methacrylate is particularly preferred.

[0065] The content of structural units derived from alkyl methacrylate in the acrylic resin is preferably 50% by weight or more, more preferably 75% by weight or more, and particularly preferably 90% by weight or more.

[0066] The content of structural units derived from acrylic acid ester in the acrylic resin is preferably less than 1% by weight, more preferably less than 0.5% by weight, and particularly preferably less than 0.3% by weight.

[0067] The acrylic resin may further contain structural units derived from other monomers, including, but not limited to, aromatic monomers such as styrene and methylstyrene, and nitrile monomers such as acrylonitrile and methacrylonitrile.

[0068] (Method of manufacturing polarizer protective film) The polarizer protective film of this embodiment can be produced by a known method. An example of the method for producing the polarizer protective film of this embodiment will be described below.

[0069] First, an acrylic resin is kneaded, if necessary, together with a copolymer containing (meth)acrylonitrile units and aromatic vinyl units using an extruder equipped with a die at the outlet, and a strand is extruded from the die. Next, the strand is cooled using a water bath and then pelletized using a pelletizer to obtain an acrylic resin composition. Next, the acrylic resin composition is melted using an extruder equipped with a T-die at the outlet, and a sheet is extruded from the T-die and cooled with a cooling roll to obtain a raw film. Next, the raw film is biaxially stretched to obtain the polarizer protective film of this embodiment. In this case, the biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching.

[0070] The temperature when biaxially stretching the raw film is preferably (Tg + 5)°C or higher (Tg + 20)°C or lower, more preferably (Tg + 6)°C or higher (Tg + 18)°C or lower, and even more preferably (Tg + 7)°C or higher (Tg + 15)°C or lower, where Tg is the glass transition temperature of the acrylic resin composition. The areal stretching ratio when biaxially stretching the raw film is not particularly limited, but is, for example, 2 times or higher and 10 times or lower. The stretching speed when biaxially stretching the raw film is not particularly limited, but is, for example, 1.1 times / min or higher and 100 times / min or lower. When sequentially biaxially stretching the raw film, the stretching speeds in the first stage and the second stage may be the same or different. In sequential biaxial stretching, the first stage stretching is usually stretching in the longitudinal direction (MD), and the second stage stretching is stretching in the transverse direction (TD).

[0071] [Second embodiment] (Acrylic resin composition) The acrylic resin composition of this embodiment contains an acrylic resin having a ring structure in the main chain. The glass transition temperature of the acrylic resin composition of this embodiment is 120°C or higher, preferably greater than 120°C, more preferably 121°C or higher, and even more preferably 122°C or higher. If the glass transition temperature of the acrylic resin composition of this embodiment is lower than 120°C, the heat resistance of the biaxially stretched film may decrease, and in a high-temperature, high-humidity environment, the orientation relaxation of the biaxially stretched film may proceed, resulting in a decrease in the stability of the retardation. The glass transition temperature of the acrylic resin composition of this embodiment is, for example, 160°C or lower.

[0072] In this specification and claims, acrylic resin refers to a polymer of a monomer having an acryloyl group and / or a monomer having a methacryloyl group. In this case, the acrylic resin may be either a homopolymer or a copolymer. When the acrylic resin is a copolymer, it may also be a copolymer of a monomer not having an acryloyl group or a methacryloyl group.

[0073] The content of aromatic vinyl units in the acrylic resin composition of this embodiment is 1.0 wt% or more and 10.0 wt% or less, preferably 2.5 wt% or more and 9.5 wt% or less, more preferably 3.0 wt% or more and 9.0 wt% or less, even more preferably 3.2 wt% or more and 8.5 wt% or less, and particularly preferably 3.5 wt% or more and 8.0 wt% or less. When the content of aromatic vinyl units in the acrylic resin composition is 1.0 wt% or more and 10.0 wt% or less, the yellowness index when viewed obliquely from a liquid crystal panel is reduced. In this case, the yellowness index when viewed obliquely from a liquid crystal panel is preferably 50 or less.

[0074] When the acrylic resin composition of this embodiment is formed into a biaxially stretched film, the absolute value of the Nz coefficient at a thickness of 40 μm is 2.0 or more and 5.0 or less, and preferably 3.0 or more and 4.5 or less. When the acrylic resin composition of this embodiment is formed into a biaxially stretched film, the absolute value of the Nz coefficient at a thickness of 40 μm is 2.0 or more and 5.0 or less, and the yellowness when viewed from an oblique direction of the liquid crystal panel is reduced.

[0075] A first aspect of the acrylic resin composition of this embodiment further includes a copolymer containing (meth)acrylonitrile units and aromatic vinyl units. The content of the aromatic vinyl units in the copolymer is not particularly limited, but is, for example, 50% by weight or more and 90% by weight or less. The weight ratio of the copolymer to the acrylic resin is also not particularly limited, but is, for example, 5% by weight or more and 90% by weight or less. It is preferable that the acrylic resin contained in the acrylic resin composition does not have aromatic vinyl units.

[0076] The 1% weight loss temperature of the second aspect of the acrylic resin composition of this embodiment is 320°C or higher, preferably 325°C or higher, and more preferably 330°C or higher. When the 1% weight loss temperature of the second aspect of the acrylic resin composition of this embodiment is 320°C or higher, contamination of the cooling roll during production of raw film is suppressed, and the film formability of the raw film is improved. The 1% weight loss temperature of the second aspect of the acrylic resin composition of this embodiment is, for example, 380°C or lower.

[0077] The second aspect of the acrylic resin composition of the present embodiment may also serve as the first aspect of the acrylic resin composition of the present embodiment.

[0078] The aromatic vinyl is not particularly limited, but examples thereof include styrene, α-methylstyrene, methoxystyrene, vinyltoluene, and halostyrene. Among these, styrene is preferred from the viewpoint of reducing yellowness when the liquid crystal panel is viewed from an oblique direction. Here, the (meth)acrylonitrile is acrylonitrile or methacrylonitrile.

[0079] The acrylic resin composition of the present embodiment may not contain an ultraviolet absorber, or may be substantially free of an ultraviolet absorber.

[0080] When the acrylic resin composition of this embodiment is formed into a biaxially stretched film, the yellowness index at a thickness of 40 μm is preferably 0.01 or more and 5.00 or less, and more preferably 0.1 or more and 2.0 or less. When the acrylic resin composition of this embodiment is formed into a biaxially stretched film, the yellowness index at a thickness of 40 μm is 5.00 or less, and the biaxially stretched film is less colored, and the color rendering properties of the display are less affected.

[0081] When the acrylic resin composition of this embodiment is formed into a biaxially stretched film, the absorbance at a wavelength of 380 nm at a thickness of 40 μm is preferably 0.01 or more and 1.00 or less, and more preferably 0.10 or more and 0.80 or less. When the acrylic resin composition of this embodiment is formed into a biaxially stretched film, the absorbance at a wavelength of 380 nm at a thickness of 40 μm is 1.00 or less, the acrylic resin composition of this embodiment is substantially free of an ultraviolet absorber.

[0082] The weight-average molecular weight of the acrylic resin composition of the present embodiment is preferably from 50,000 to 200,000, and more preferably from 90,000 to 150,000. When the weight-average molecular weight of the acrylic resin composition of the present embodiment is 50,000 or more, the mechanical properties of a molded article of the acrylic resin composition of the present embodiment tend to be improved, and when it is 200,000 or less, the moldability of the acrylic resin composition of the present embodiment tends to be improved.

[0083] The ratio of the weight average molecular weight to the number average molecular weight (polydispersity) of the acrylic resin composition of this embodiment is preferably 1.5 or more and 2.5 or less, and more preferably 1.5 or more and 2.2 or less. When the acrylic resin composition of this embodiment has a polydispersity of 1.5 or more, the flowability of the acrylic resin composition of this embodiment tends to be improved and it tends to be easier to mold, and when it is 2.5 or less, the mechanical properties such as impact resistance, toughness, and flex resistance of an article molded from the acrylic resin composition of this embodiment tend to be improved.

[0084] The number-average molecular weight and weight-average molecular weight of the acrylic resin composition of this embodiment are values ​​calculated as standard polystyrene as measured by gel permeation chromatography (GPC). The number-average molecular weight and weight-average molecular weight of the acrylic resin composition of this embodiment can be controlled by the types and amounts of polymerization initiators and chain transfer agents used in synthesizing the acrylic resin.

[0085] The acrylic resin composition of the present embodiment may further contain additives within a range that does not impair the object of the present invention. The additives are not particularly limited, but examples thereof include antioxidants, heat stabilizers, light stabilizers, ultraviolet absorbers, specific wavelength absorbers or specific wavelength absorbing dyes for the purpose of cutting blue light, light resistance stabilizers such as radical scavengers, retardation adjusters, catalysts, plasticizers, lubricants, antistatic agents, colorants, shrinkage inhibitors, antibacterial and deodorizing agents, fluorescent brighteners, and compatibilizers, and two or more of these may be used in combination.

[0086] (acrylic resin with a ring structure in the main chain) The acrylic resin having a ring structure in the main chain is the same as that in the first embodiment.

[0087] (Method of producing acrylic resin composition) The acrylic resin composition of the present embodiment can be produced by a known method. An example of the method for producing the acrylic resin composition of the present embodiment will be described below.

[0088] First, an acrylic resin is mixed with a copolymer containing (meth)acrylonitrile units and aromatic vinyl units, if necessary, in an extruder equipped with a die at the outlet, and then extruded into strands from the die. Next, the strands are cooled in a water bath and then pelletized using a pelletizer to obtain the acrylic resin composition of the present embodiment.

[0089] (Method of manufacturing biaxially stretched film) The biaxially stretched film can be produced by a known method, and an example of the method for producing the biaxially stretched film will be described below.

[0090] First, the acrylic resin composition of the present embodiment is melted using an extruder equipped with a T-die at the outlet, and then a sheet is extruded from the T-die and cooled with a cooling roll to obtain a raw film. Next, the raw film is biaxially stretched to obtain a biaxially stretched film. At this time, the biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching.

[0091] The temperature when biaxially stretching the raw film is preferably (Tg + 5)°C or higher (Tg + 20)°C or lower, more preferably (Tg + 6)°C or higher (Tg + 18)°C or lower, and even more preferably (Tg + 7)°C or higher (Tg + 15)°C or lower, where Tg is the glass transition temperature of the acrylic resin composition of this embodiment. The areal stretching ratio when biaxially stretching the raw film is not particularly limited, but is, for example, 2 times or higher and 10 times or lower. The stretching speed when biaxially stretching the raw film is not particularly limited, but is, for example, 1.1 times / min or higher and 100 times / min or lower. When sequentially biaxially stretching the raw film, the stretching speeds in the first stage and the second stage may be the same or different. In sequential biaxial stretching, the first stage stretching is usually stretching in the longitudinal direction (MD), and the second stage stretching is usually stretching in the transverse direction (TD).

[0092] (Uses of acrylic resin composition) The acrylic resin composition of the present embodiment is used for optical films such as a polarizer protective film, etc. The polarizer protective film will be described below.

[0093] (Polarizer protective film) The thickness direction retardation Rth of the polarizer protective film at a wavelength of 590 nm is preferably -35.0 nm or more and -5.0 nm or less, more preferably -30.0 nm or more and -6.0 nm or less, even more preferably -20.0 nm or more and -7.0 nm or less, even more preferably -15.0 nm or more and -8.0 nm or less, and particularly preferably -14.0 nm or more and -9.0 nm or less. When Rth is -35.0 nm or more and -5.0 nm or less, the yellowness index when viewed from an oblique direction of the liquid crystal panel is reduced. In this case, the polarizer protective film preferably has a yellowness index of 50 or less when viewed from an oblique direction of the liquid crystal panel.

[0094] Rth is expressed by the formula Rth=[(nx+ny) / 2-nz]×d where nx, ny, and nz are the refractive indices in the X-axis direction, Y-axis direction, and Z-axis direction, respectively, where the MD direction is the X-axis, the TD direction is the Y-axis, and the thickness direction of the film is the Z-axis. Also, d is the thickness of the film.

[0095] The ratio Rth(447) / Rth(548), which is the thickness direction retardation Rth(447) at a wavelength of 447 nm to the thickness direction retardation Rth(548) at a wavelength of 548 nm of the polarizer protective film, is preferably 1.00 or more and 1.30 or less, more preferably 1.01 or more and 1.28 or less. When Rth(447) / Rth(548) of the polarizer protective film is 1.00 or more and 1.30 or less, the yellowness when viewed from an oblique direction of the liquid crystal panel is reduced.

[0096] The ratio Rth(628) / Rth(548), which is the thickness direction retardation Rth(628) at a wavelength of 628 nm to the thickness direction retardation Rth(548) at a wavelength of 548 nm of the polarizer protective film, is preferably 1.00 or more and 1.30 or less, more preferably 1.01 or more and 1.15 or less. When Rth(628) / Rth(548) of the polarizer protective film is 1.00 or more and 1.30 or less, the yellowness when viewed from an oblique direction of the liquid crystal panel is reduced.

[0097] The polarizer protective film can be attached to a polarizer to form a polarizing plate. The polarizer is not particularly limited, and known polarizers can be used. The polarizing plate can also be combined with a liquid crystal cell to form a liquid crystal panel. In this case, it is preferable to use an IPS liquid crystal cell with a wide viewing angle. When the polarizer protective film is disposed on the side facing the liquid crystal cell, it may not contain an ultraviolet absorber, or may not substantially contain an ultraviolet absorber.

[0098] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and the above-described embodiments may be modified as appropriate within the scope of the spirit of the present invention. [Example]

[0099] Examples of the present invention will be described below, but the present invention is not limited to these examples.

[0100] (Content of structural units containing glutarimide rings in the main chain) Using a nuclear magnetic resonance spectrometer Avance III (manufactured by BRUKER) with a proton resonance frequency of 400 MHz, 1 H-NMR spectra were measured. The molar ratio of the structural units derived from methyl methacrylate to the structural units containing glutarimide rings in the main chain was converted into weight, and the content of structural units containing glutarimide rings in the main chain was calculated. The molar ratio was determined from the peak area A derived from the O-CH3 protons of methyl methacrylate around 3.5 to 3.8 ppm and the peak area B derived from the N-CH3 protons of glutarimide around 3.0 to 3.3 ppm.

[0101] (glass transition temperature) Using a high-sensitivity differential scanning calorimeter DSC7000X (manufactured by Hitachi High-Tech Science), 10 mg of the acrylic resin or acrylic resin composition was heated at a heating rate of 10°C / min in a nitrogen atmosphere, and the glass transition temperature was determined by the midpoint method.

[0102] (1% weight loss temperature) Using a thermogravimetric and differential thermal analyzer STA7200 (manufactured by Hitachi High-Tech Science), 10 mg of the acrylic resin composition was heated from room temperature at a heating rate of 10°C / min in a nitrogen atmosphere to determine the 1% weight loss temperature.

[0103] (Thickness direction retardation Rth) The thickness direction retardation Rth of the polarizer protective film at a wavelength of 590 nm was measured using a retardation measurement device KOBRA-WR (manufactured by Oji Scientific Instruments).

[0104] (Rth(447) / Rth(548), Rth(628) / Rth(548) and Nz coefficient) The retardation of the polarizer protective film was measured at wavelengths λ (λ = 446.7 nm, 547.9 nm, 628.2 nm) using a retardation measurement device KOBRA-WR (manufactured by Oji Scientific Instruments). Specifically, the in-plane retardation Re(λ) at each wavelength and the retardation R40(λ) measured at a 40° tilt with the absorption axis as the tilt axis were measured, and then the three-dimensional refractive index calculation software N-Calc (manufactured by Oji Scientific Instruments) was used to calculate the three-dimensional refractive indexes nx(λ), ny(λ), and nz(λ) at each wavelength. Next, the three-dimensional refractive indexes nx(λ), ny(λ), and nz(λ) were used to calculate the formula Rth(λ)=[{nx(λ)+ny(λ)} / 2-nz(λ)]×d The thickness direction retardation Rth(λ) at each wavelength was calculated using the formula: Rth(447) / Rth(548) and Rth(628) / Rth(548). The in-plane retardation Re(548) and thickness direction retardation Rth(548) at a wavelength of 548 nm were used to calculate the wavelength dispersion characteristics Rth(447) / Rth(548). Nz coefficient = [Rth(548) / Re(548)] + 0.5 The Nz coefficient was calculated by the following equation.

[0105] (yellowness) The polarizer protective film was cut into a 3 cm square, and the yellowness index (YI) was measured using a color meter SC-P (manufactured by Suga Test Instruments) in accordance with JIS K7373:2006.

[0106] (Absorbance at wavelength 380 nm) The absorbance of the polarizer protective film at a wavelength of 380 nm was measured using an ultraviolet-visible-near-infrared spectrophotometer UV-560 (manufactured by JASCO Corporation).

[0107] (Yellowness when viewing the LCD panel from an oblique angle) A liquid crystal panel simulation was performed using the LCD Master liquid crystal simulator (manufactured by Shintech). A polarizer was placed on the light source side, an IPS-mode liquid crystal cell with an in-plane retardation Re of 295 nm, and a polarizer was placed on the viewing side. Measurement results for the thickness direction retardation Rth were input as the optical properties of the polarizer protective film on the light source side and the viewing side facing the liquid crystal cell. Next, the XYZ colorimetric values ​​when viewed from a polar angle of 70° and an azimuthal angle of 40° with the liquid crystal cell set to the dark state were determined by simulation. The yellowness index (YI) was calculated using the following formula in accordance with JIS K7373:2006. YI=100(1.2985X-1.1335Z) / Y

[0108] (Production of acrylic resin 1) A 40mm diameter co-rotating intermeshing twin-screw extruder (L / D = 90) equipped with a die at the outlet was set at a temperature of 250-280°C in each temperature control zone and a screw rotation speed of 85 rpm. Methyl methacrylate resin Parapet HM (Kuraray) was melted and filled using a kneading block. Next, 1.8% by weight of monomethylamine (Mitsubishi Gas Chemical) was added to the methyl methacrylate resin through the nozzle to imidize the methyl methacrylate resin. The strand extruded from the die was then cooled in a water bath and pelletized using a pelletizer to obtain Resin (I).

[0109] A 40mm diameter co-rotating intermeshing twin-screw extruder (L / D = 90) equipped with a die at the outlet was melted and filled with resin (I) using a kneading block at a temperature setting of 240-260°C and a screw speed of 85 rpm. Next, 0.56 wt% of dimethyl carbonate was added to resin (I) through the nozzle to esterify the carboxyl groups in resin (I). The by-products and excess dimethyl carbonate were removed after the reaction. The strands extruded from the die were cooled in a water bath and then pelletized using a pelletizer to obtain acrylic resin 1. Acrylic resin 1 had a glass transition temperature of 123°C and a glutarimide ring-containing structural unit content of 6 wt% in the main chain.

[0110] (Production of acrylic resin 2) Acrylic resin 2 was obtained in the same manner as acrylic resin 1, except that the amount of monomethylamine added was changed to 4.3% by weight relative to the methyl methacrylate resin. Acrylic resin 2 had a glass transition temperature of 125°C and a content of structural units containing glutarimide rings in the main chain of 15% by weight.

[0111] Example 1 Using a 15mm diameter, co-rotating, intermeshing twin-screw extruder (L / D = 45) equipped with a die at the outlet, 95% by weight of acrylic resin 1 and 5% by weight of acrylonitrile-styrene copolymer AS-61 7200NT (manufactured by Shin Chemical Shoji Co., Ltd.), which has a styrene unit content of 74% by weight, were kneaded. Next, a water bath was used to cool the strand extruded from the die at the extruder outlet, and the strand was pelletized using a pelletizer to obtain an acrylic resin composition. The acrylic resin composition had a glass transition temperature of 122°C and a 1% weight loss temperature of 333°C.

[0112] The acrylic resin composition was dried at 100°C for 5 hours and then melted using a 15mm diameter co-rotating twin-screw extruder (L / D = 45) equipped with a T-die at the outlet. The sheet extruded from the T-die was then cooled using a cooling roll to obtain a raw film having a width of 160mm and a thickness of 160µm.

[0113] Using a film biaxial stretching device IMC-1905 (manufactured by Imoto Machinery Co., Ltd.), the raw film was simultaneously biaxially stretched at a temperature 10°C higher than the glass transition temperature of the acrylic resin composition so that the stretching ratio in the longitudinal and transverse directions was 2 times, thereby obtaining a polarizer protective film of 280 mm x 280 mm.

[0114] Example 2 A polarizer protective film was obtained in the same manner as in Example 1, except that the mixing ratios of acrylic resin 1 and AS-61 7200NT (manufactured by Shin Chemical Shoji Co., Ltd.) were changed to 92.5 wt % and 7.5 wt %, respectively. The acrylic resin composition had a glass transition temperature of 122°C and a 1% weight loss temperature of 337°C.

[0115] Example 3 A polarizer protective film was obtained in the same manner as in Example 1, except that the mixing ratios of acrylic resin 1 and AS-61 7200NT (manufactured by Shin Chemical Shoji Co., Ltd.) were changed to 90 wt % and 10 wt %, respectively. The acrylic resin composition had a glass transition temperature of 121°C and a 1% weight loss temperature of 334°C.

[0116] (Comparative Example 1) Except for not using AS-61 7200NT (manufactured by Shin Chemical Shoji Co., Ltd.), a polarizer protective film was obtained in the same manner as in Example 1. The acrylic resin composition had a glass transition temperature of 123°C and a 1% weight loss temperature of 310°C.

[0117] (Comparative Example 2) A polarizer protective film was obtained in the same manner as in Comparative Example 1, except that acrylic resin 2 was used instead of acrylic resin 1, and the raw film was simultaneously biaxially stretched at a temperature 15°C higher than the glass transition temperature of the acrylic resin composition. In this case, the acrylic resin composition had a glass transition temperature of 125°C and a 1% weight loss temperature of 315°C.

[0118] (Comparative Example 3) A polarizer protective film was obtained in the same manner as in Example 1, except that acrylic resin 1 was not used, a methyl methacrylate-styrene copolymer KT-89 (manufactured by Denka) having a styrene unit content of 11% by weight was used instead of an acrylonitrile-styrene copolymer having a styrene unit content of 74% by weight, and the raw film was simultaneously biaxially stretched at a temperature 20°C higher than the glass transition temperature of the acrylic resin composition. At this time, the acrylic resin composition had a glass transition temperature of 117°C and a 1% weight loss temperature of 297°C.

[0119] Comparative Example 4 A polarizer protective film was obtained in the same manner as in Comparative Example 3, except that a methyl methacrylate-styrene copolymer MS800 (Nippon Steel Chemical Co., Ltd.) having a styrene unit content of 20% by weight was used instead of KT-89 (Denka Co., Ltd.), and the raw film was simultaneously biaxially stretched at a temperature 30°C higher than the glass transition temperature of the acrylic resin composition. At this time, the acrylic resin composition had a glass transition temperature of 115°C and a 1% weight loss temperature of 296°C.

[0120] Table 1 shows the properties and evaluation results of the acrylic resin composition and the polarizer protective film.

[0121] [Table 1]

[0122] Table 1 shows that the polarizer protective films (biaxially stretched films) of Examples 1 to 3 have reduced YI when viewed obliquely from the liquid crystal panel. In contrast, the polarizer protective film (biaxially stretched film) of Comparative Example 1 has an Rth of 0.0 nm, an Nz coefficient of −1.4, and an Rth(447) / Rth(548) of 0.958, resulting in a high YI when viewed obliquely from the liquid crystal panel. The polarizer protective film (biaxially stretched film) of Comparative Example 2 has an Rth of 10.2 nm and an Nz coefficient of 51.5, resulting in a high YI when viewed obliquely from the liquid crystal panel. The polarizer protective films (biaxially stretched films) of Comparative Examples 3 and 4 have poor heat resistance because the Tg of the acrylic resin composition is 117°C and 115°C. Furthermore, the acrylic resin compositions of Comparative Examples 3 and 4 have low 1% weight loss temperatures.

Claims

1. An acrylic resin composition is included, a thickness direction retardation Rth at a wavelength of 590 nm of −35.0 nm or more and −5.0 nm or less; the acrylic resin composition contains an acrylic resin having a ring structure in its main chain and has a glass transition temperature of 120°C or higher; The absolute value of the Nz coefficient is 2.0 or more and 5.0 or less, a ratio Rth(447) / Rth(548) of a thickness direction retardation Rth(447) at a wavelength of 447 nm to a thickness direction retardation Rth(548) at a wavelength of 548 nm is 1.00 or more and 1.30 or less; A polarizer protective film, wherein the ratio Rth(628) / Rth(548) of thickness direction retardation Rth(628) at a wavelength of 628 nm to thickness direction retardation Rth(548) at a wavelength of 548 nm is 1.00 or more and 1.30 or less.

2. 2. The polarizer protective film according to claim 1, wherein the acrylic resin having a ring structure in its main chain has a structural unit having one or more ring structures in its main chain selected from the group consisting of a glutarimide ring, a lactone ring, a maleic anhydride ring, a maleimide ring, and a glutaric anhydride ring.

3. The polarizer protective film according to claim 2 , wherein the acrylic resin having a ring structure in its main chain has a structural unit represented by the following formula (1): 【Chemical 1】 (In the formula, R １ and R ２ are each independently a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and R ３ is a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, or a cycloalkyl group having 3 to 12 carbon atoms.

4. The polarizer protective film according to claim 1 , wherein the acrylic resin composition has an aromatic vinyl unit content of 1.0% by weight or more and 10.0% by weight or less.

5. The polarizer protective film according to claim 4 , wherein the aromatic vinyl unit is a styrene unit.

6. The polarizer protective film according to claim 1 , wherein the acrylic resin composition further contains a copolymer containing a (meth)acrylonitrile unit and an aromatic vinyl unit.

7. The polarizer protective film according to claim 1 , wherein the acrylic resin composition has a 1% weight loss temperature of 320° C. or higher.

8. The polarizer protective film according to claim 1 , which does not contain an ultraviolet absorber.

9. The polarizer protective film according to claim 1 , which is a biaxially stretched film.

10. The polarizer protective film according to claim 1 , having a yellowness index of 0.01 or more and 5.00 or less.

11. The polarizer protective film according to claim 1 , having an absorbance at a wavelength of 380 nm of 0.01 or more and 1.00 or less.

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

13. A liquid crystal panel comprising the polarizing plate according to claim 12.

14. An acrylic resin composition comprising an acrylic resin having a ring structure in its main chain and a copolymer containing a (meth)acrylonitrile unit and an aromatic vinyl unit, The glass transition temperature is 120°C or higher, the content of the aromatic vinyl unit is 1% by weight or more and 10% by weight or less, The acrylic resin composition has an absolute value of Nz coefficient of 2.0 or more and 5.0 or less at a thickness of 40 μm when formed into a biaxially stretched film.

15. The acrylic resin composition according to claim 14, wherein the 1% weight loss temperature is 320°C or higher.

16. An acrylic resin composition containing an acrylic resin having a ring structure in its main chain, The glass transition temperature is 120°C or higher, the content of aromatic vinyl units is 1% by weight or more and 10% by weight or less, The 1% weight loss temperature is 320°C or higher, The acrylic resin composition has an absolute value of Nz coefficient of 2.0 or more and 5.0 or less at a thickness of 40 μm when formed into a biaxially stretched film.

17. 17. The acrylic resin composition according to claim 14, wherein the acrylic resin having a ring structure in its main chain has a structural unit including, in its main chain, one or more ring structures selected from the group consisting of a glutarimide ring, a lactone ring, a maleic anhydride ring, a maleimide ring, and a glutaric anhydride ring.

18. The acrylic resin composition according to claim 17, wherein the acrylic resin having a ring structure in the main chain has a structural unit represented by the following formula (1): 【Chemistry 2】 (In the formula, R １ and R ２ are each independently a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and R ３ is a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, or a cycloalkyl group having 3 to 12 carbon atoms.

19. 17. The acrylic resin composition according to claim 14, wherein the aromatic vinyl unit is a styrene unit.

20. 17. The acrylic resin composition according to any one of claims 14 to 16, which does not contain an ultraviolet absorber.

21. The acrylic resin composition according to any one of claims 14 to 16, wherein the acrylic resin composition is formed into a biaxially stretched film having a yellowness index of 0.01 or more and 5.00 or less at a thickness of 40 µm.

22. The acrylic resin composition according to any one of claims 14 to 16, wherein the acrylic resin composition is formed into a biaxially stretched film having an absorbance at a wavelength of 380 nm at a thickness of 40 µm of 0.01 or more and 1.00 or less.

23. The acrylic resin composition according to any one of claims 14 to 16, which is used for an optical film.

24. The acrylic resin composition according to claim 23, wherein the optical film is a polarizer protective film.

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