Method for manufacturing resin film and biaxially oriented optical film

Abstract

The present invention provides a method for manufacturing a resin film that reduces the degree of yellowness when viewing a liquid crystal panel from an oblique angle, and also reduces the in-plane phase difference R0. [Solution] The method for manufacturing a resin film includes a step of sequentially biaxially stretching a raw film containing acrylic resin and having a glass transition temperature of 120°C or higher, such that the in-plane phase difference R0 at a wavelength of 590 nm is greater than 0.0 nm and less than or equal to 5.0 nm, and the thickness direction phase difference Rth at a wavelength of 590 nm is between -35 nm and -5.0 nm.

Description

[Technical Field]

[0001] This invention relates to a method for manufacturing a resin film and a biaxially oriented optical film. [Background technology]

[0002] Optical films containing acrylic resin 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 film is applied to a liquid crystal panel by laminating it to both sides of a polarizer to form a polarizing plate, and then placing it on both sides of a liquid crystal cell.

[0003] On the other hand, IPS-type liquid crystal panels are preferred for applications such as LCD televisions because they offer a wide viewing angle and excellent color reproduction. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2017-25333 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, when an optical film containing acrylic resin is applied to an IPS-type liquid crystal panel, the black display on the panel may appear slightly yellowish when viewed from an oblique angle.

[0006] Furthermore, when manufacturing optical films, sequential biaxial stretching can increase the in-plane phase difference R0 of the optical film. If such an optical film is placed opposite a liquid crystal cell, it can cause color unevenness.

[0007] The present invention aims to provide a method for manufacturing a resin film that can reduce the degree of yellowness when viewed from an oblique direction on a liquid crystal panel, and also reduce the in-plane phase difference R0. [Means for solving the problem]

[0008] [1] A method for manufacturing a resin film, comprising the step of sequentially biaxially stretching a raw film containing an acrylic resin and having a glass transition temperature of 120°C or higher, such that the in-plane phase difference R0 at a wavelength of 590 nm is greater than 0.0 nm and less than or equal to 5.0 nm, and the thickness direction phase difference Rth at a wavelength of 590 nm is between -35 nm and -5.0 nm.

[0009] [2] After stretching the raw film in the MD direction, and then stretching it in the TD direction, if the ratio of the in-plane phase difference R0 to the thickness direction phase difference Rth at a wavelength of 590 nm for the raw film stretched in the MD direction is [R0 / Rth]1st, and the ratio of the in-plane phase difference R0 to the thickness direction phase difference Rth at a wavelength of 590 nm for the raw film stretched in the TD direction is [R0 / Rth]2nd, then the formula [R0 / Rth]2nd / [R0 / Rth]1st<0.4 A method for manufacturing a resin film as described in [1], which satisfies the requirements.

[0010] [3] The method for producing a resin film according to [1] or [2], wherein the raw film comprises aromatic vinyl units.

[0011] [4] The method for producing a resin film according to any one of [1] to [3], wherein the acrylic resin has a methyl methacrylate unit content of 98% by weight or more and a triple-representation syndiotacticity of 55% or more.

[0012] [5] The method for producing a resin film according to any one of [1] to [4], wherein the acrylic resin comprises a ring structure in the main chain.

[0013] [6] The acrylic resin comprises 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, as described in [5].

[0014] [7] A biaxially oriented optical film comprising an acrylic resin having a methyl methacrylate unit content of 98% by weight or more and a triple-representation syndiotacticity of 55% or more, having a glass transition temperature of 120°C or higher, an in-plane phase difference R0 at a wavelength of 590 nm greater than 0.0 nm and less than or equal to 5.0 nm, a thickness direction phase difference Rth at a wavelength of 590 nm greater than or equal to -35 nm and less than or equal to -5.0 nm, and a thickness of 20 μm or more and less than or equal to 60 μm.

[0015] [8] A biaxially oriented optical film comprising an acrylic resin having a ring structure in its main chain, having a glass transition temperature of 120°C or higher, an in-plane phase difference R0 at a wavelength of 590 nm greater than 0.0 nm and less than or equal to 5.0 nm, a thickness direction phase difference Rth at a wavelength of 590 nm greater than or equal to -35 nm and less than or equal to -5.0 nm, and a thickness of 20 μm or more and less than or equal to 60 μm.

[0016] [9] A biaxially oriented optical film according to [7] or [8], wherein the in-plane phase difference R0 at a wavelength of 590 nm is greater than 0.7 nm.

[0017]

[10] A biaxially oriented optical film according to any one of [7] to [9], comprising aromatic vinyl units.

[0018]

[11] A biaxially oriented optical film according to any one of items [7] to

[10] , wherein the glass transition temperature is 135°C or less. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide a method for manufacturing a resin film that can reduce the degree of yellowness when viewed from an oblique direction on a liquid crystal panel, and also reduce the in-plane phase difference R0. [Modes for carrying out the invention]

[0020] Hereinafter, embodiments of the present invention will be described.

[0021] (Method for producing a resin film) The method for producing a resin film according to this embodiment includes a step of sequentially biaxially stretching a raw film containing an acrylic resin and having a glass transition temperature of 120°C or higher so that the in-plane retardation R0 at a wavelength of 590 nm is more than 0.0 nm and 5.0 nm or less, and the thickness-direction retardation Rth is -35 nm or more and -5.0 nm or less.

[0022] In this specification and the claims, the acrylic resin means a polymer containing a structural unit derived from a monomer having an acryloyl group and / or a monomer having a methacryloyl group. At this time, the acrylic resin may be either a homopolymer or a copolymer. When the acrylic resin is a copolymer, the acrylic resin may be a copolymer with a monomer having no acryloyl group or methacryloyl group.

[0023] The glass transition temperature of the raw film is 120°C or higher, preferably more than 120°C, more preferably 121°C or higher, still more preferably 122°C or higher, and even more preferably 123°C or higher. Since the glass transition temperature of the raw film is 120°C or higher, in a high-temperature and high-humidity environment, the orientation relaxation of the resin film is less likely to proceed, and the stability of the retardation is improved. The glass transition temperature of the raw film is, for example, 160°C or lower, preferably 135°C or lower, more preferably 133°C or lower, and still more preferably 130°C or lower.

[0024] The in-plane retardation R0 at a wavelength of 590 nm of the sequentially biaxially stretched raw film is more than 0.0 nm and 5.0 nm or less, preferably more than 0.7 nm and 5.0 nm or less, and more preferably 1.0 nm or more and 4.0 nm or less. Since R0 is more than 0.0 nm and 5.0 nm or less, the uniformity of the in-plane retardation R0 of the resin film is improved.

[0025] The phase difference Rth in the thickness direction of the sequentially biaxially stretched raw film at a wavelength of 590 nm is -35.0 nm or more and -5.0 nm or less, but is 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 even more 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 when the liquid crystal panel is viewed from an oblique direction is reduced. In this case, it is preferable that the yellowness when the liquid crystal panel is viewed from an oblique direction is 40 or less.

[0026] Note that R0 and Rth are given by the formula R0 = (nx - ny) × d Rth = [(nx + ny) / 2 - nz] × d It is calculated by the following formula. Here, nx, ny, and nz are the refractive indices in the X-axis direction, Y-axis direction, and Z-axis direction, respectively, with the slow axis being the X-axis, the fast axis being the Y-axis, and the film thickness direction being the Z-axis. Also, d is the thickness of the film.

[0027] When sequentially biaxially stretching a raw film roll, it is preferable to stretch the raw film roll in the MD direction first, and then in the TD direction. In this case, when stretching the raw film roll in the MD direction, for example, the difference in peripheral speed between the rolls can be utilized, and when stretching the raw film roll in the TD direction, for example, a heating furnace can be utilized.

[0028] If the ratio of the in-plane phase difference R0 to the thickness-direction phase difference Rth at a wavelength of 590 nm for a raw film stretched in the MD direction is [R0 / Rth]1st, and the ratio of the in-plane phase difference R0 to the thickness-direction phase difference Rth at a wavelength of 590 nm for a raw film stretched in the TD direction is [R0 / Rth]2nd, then the equation [R0 / Rth]2nd / [R0 / Rth]1st<0.4 It is preferable that the following conditions be met: [R0 / Rth]2nd / [R0 / Rth]1st<0.35 It is more preferable that the following conditions are met. If [R0 / Rth]2nd / [R0 / Rth]1st is less than 0.4, the in-plane phase difference R0 of the resin film becomes small. [R0 / Rth]2nd / [R0 / Rth]1st is, for example, 0.1 or more. In this case, it is preferable that [R0 / Rth]1st is -2.5 or more and less than -0.5, and [R0 / Rth]2nd is -0.5 or more and less than -0.1.

[0029] The following describes an example of a method for manufacturing the resin film of this embodiment.

[0030] First, using an extruder equipped with a die at the outlet, acrylic resin is kneaded together with a copolymer containing aromatic vinyl units as needed, and then the strand is extruded from the die. Next, the strand is cooled in a water bath, and then pelletized using a pelletizer to obtain a resin composition. Next, using an extruder equipped with a T-die at the outlet, the resin composition is melted, 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 successively biaxially stretched to obtain a resin film.

[0031] The temperature during sequential biaxial stretching of the raw film is preferably (Tg+5)°C to (Tg+30)°C, more preferably (Tg+6)°C to (Tg+18)°C, and even more preferably (Tg+7)°C to (Tg+15)°C, where Tg is the glass transition temperature of the raw film. The surface ratio during sequential biaxial stretching of the raw film is not particularly limited, but for example, it is between 2 and 10 times. The stretching speed during sequential biaxial stretching of the raw film is not particularly limited, but for example, it is between 1.1 times / min and 100 times / min. In this case, the stretching speed in the MD direction and the stretching speed in the TD direction may be the same or different.

[0032] (Original film roll) The raw film may contain aromatic vinyl units. In this case, the raw film may contain an acrylic resin containing aromatic vinyl units, but it is preferable to contain an acrylic resin that does not contain aromatic vinyl units and a copolymer that contains aromatic vinyl units.

[0033] The aromatic vinyl unit content in the raw film is preferably 0% to 8% by weight, more preferably 0.5% to 5% by weight, even more preferably 0.5% to 3% by weight, even more preferably 0.5% to 2.5% by weight, and particularly preferably 1.0% to 2.5% by weight. When the aromatic vinyl unit content in the raw film is 8% by weight or less, the yellowness when the liquid crystal panel is viewed from an oblique direction is reduced.

[0034] Aromatic vinyls are not particularly limited, but examples include styrene, α-methylstyrene, methoxystyrene, vinyltoluene, and halostyrene. Among these, styrene is preferred from the viewpoint of reducing the degree of yellowness when the liquid crystal panel is viewed from an oblique angle.

[0035] The base film preferably further comprises a methyl methacrylate-styrene copolymer or an acrylonitrile-styrene copolymer.

[0036] The raw film may further contain additives, provided that they do not impair the objectives of the present invention. The additives are not particularly limited, but examples include antioxidants, heat stabilizers, light stabilizers, ultraviolet absorbers, specific wavelength absorbers or specific wavelength absorbing dyes for blue light filtering, light-resistant stabilizers such as radical scavengers, phase difference adjusters, catalysts, plasticizers, lubricants, antistatic agents, colorants, shrinkage inhibitors, antibacterial and deodorizing agents, fluorescent whitening agents, compatibilizers, antiblocking agents, and toughness modifiers. Two or more of these may be used in combination.

[0037] (Acrylic resin) The acrylic resin is not particularly limited as long as it is possible to set the glass transition temperature of the raw film to 120°C or higher. Examples include an acrylic resin (A1) containing a ring structure in the main chain, or an acrylic resin (A2) having a methyl methacrylate unit content of 98% by weight or more and a triple-represented syndiotacticity of 55% or more.

[0038] Here, the ring structure is preferably one or more selected from the group consisting of a glutarimide ring, a lactone ring, a maleic anhydride ring, a maleimide ring, and a glutaric anhydride ring.

[0039] (Acrylic resin (A1) containing a ring structure in the main chain) Acrylic resin (A1) containing a glutarimide ring in its main chain includes, for example, a structural unit represented by the following formula (1) as a structural unit containing a ring structure.

[0040] [ka] (In the formula, R 1 and R 2 Each is independently a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and R 3 (These are a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, or an aryl group having 6 to 10 carbon atoms.)

[0041] Acrylic resin (A1) containing the constituent units represented by formula (1) can be manufactured using known methods. An example of a method for manufacturing acrylic resin (A1) containing the constituent units represented by formula (1) is described below.

[0042] First, methyl methacrylate resin is melted using a twin-screw extruder equipped with a die at the outlet, and then an imidizing agent is injected to imidize the methyl methacrylate resin. Next, the strand extruded from the die is cooled in a water bath, and then pelletized in a pelletizer to obtain acrylic resin (A1) containing the constituent units represented by formula (1).

[0043] Examples of imidizing agents include ammonia and primary amines represented by the following formula (2). Among these, monomethylamine is preferred.

[0044] R 3 NH2(2) (In the formula, R 3 This is equivalent to equation (1).

[0045] Acrylic resin (A1) containing a lactone ring in the main chain can be obtained, for example, by polymerizing a monomer represented by the following formula (3), and then forming the lactone ring by heat treatment.

[0046] [ka] (In the formula, R 4 and R 5 Each of these is independently either a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.

[0047] Examples of monomers represented by formula (3) include methyl 2-(hydroxymethyl)acrylate, ethyl 2-(hydroxymethyl)acrylate, isopropyl 2-(hydroxymethyl)acrylate, n-butyl 2-(hydroxymethyl)acrylate, and t-butyl 2-(hydroxymethyl)acrylate, and two or more may be used in combination. Among these, methyl 2-(hydroxymethyl)acrylate and ethyl 2-(hydroxymethyl)acrylate are preferred, and methyl 2-(hydroxymethyl)acrylate is particularly preferred.

[0048] The content of ring-structured constituent units in the acrylic resin (A1) is not particularly limited, but is, for example, 1% by weight or more and 40% by weight or less.

[0049] The acrylic resin (A1) may further have (meth)acrylic acid ester units. 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. Two or more of these may be used in combination. Among these, alkyl methacrylate is preferred, and methyl methacrylate is particularly preferred.

[0050] The acrylic resin (A1) may further have constituent units derived from other monomers. Examples of other monomers, though not particularly limited, include aromatic monomers such as styrene and methylstyrene; and nitrile monomers such as acrylonitrile and methacrylonitrile.

[0051] Examples of acrylic resins (A1) containing maleic anhydride rings in the main chain include styrene-N-phenylmaleimide-maleic anhydride copolymers. Examples of acrylic resins (A1) containing maleimide rings in the main chain include olefin-maleimide copolymers described in Japanese Patent Publication No. 2004-45893. Examples of acrylic resins (A1) containing glutaric anhydride rings in the main chain include heat-resistant copolymers described in Japanese Patent Publication No. 2003-137937.

[0052] (Acrylic resin (A2) having a methyl methacrylate unit content of 98% by weight or more and a triple-representation syndiotacticity of 55% or more) The methyl methacrylate unit content in the acrylic resin (A2) is 98% by weight or more, preferably 99% by weight or more, and more preferably 100% by weight. When the methyl methacrylate unit content in the acrylic resin (A2) is 98% by weight or more, the chemical recyclability of the acrylic resin (A2) is enhanced.

[0053] The triple-representation syndiotacticity of acrylic resin (A2) is 55% or higher, preferably 56% or higher, and more preferably 57% or higher. When the triple-representation syndiotacticity of acrylic resin (A2) is 55% or higher, the glass transition temperature of acrylic resin (A2) tends to increase, and the heat resistance tends to improve. In addition, when the triple-representation syndiotacticity of acrylic resin (A2) is 55% or higher, the solvent resistance of the resulting molded article tends to improve, and the moisture permeability tends to decrease. There is no particular upper limit to the triple-representation syndiotacticity of acrylic resin (A2), but from the viewpoint of molding temperature, toughness of the molded article, and secondary processability, it is preferably 70% or lower, more preferably 67% or lower, even more preferably 65% ​​or lower, and particularly preferably 63% or lower.

[0054] The syndiotacticity of the triplet representation of acrylic resin (A2) is the ratio of two diads (doubletactic) within a chain of three consecutive constituent units (triad) that are both racemo (rr). In polymer molecules, diads of constituent units with the same stereochemistry are called meso, and those with the opposite stereochemistry are called racemo, denoted as m and r, respectively.

[0055] The synthesis method for acrylic resin (A2) is not particularly limited, but examples include anionic polymerization and radical polymerization. Among these, radical polymerization is preferred from an environmental standpoint (see, for example, International Publication No. 2023 / 238886). Here, the glass transition temperature and the triple-represented syndiotacticity of acrylic resin (A2) can be controlled by the polymerization temperature of acrylic resin (A2). For example, lowering the polymerization temperature of acrylic resin (A2) increases the glass transition temperature and syndiotacticity of acrylic resin (A2). Furthermore, the glass transition temperature of acrylic resin (A2) can also be controlled by the molecular weight of acrylic resin (A2).

[0056] Other monomers that can be used when synthesizing acrylic resin (A2) are not particularly limited, but include, for example, alkyl acrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate; aryl acrylates such as phenyl acrylate; cycloalkyl acrylates such as cyclohexyl acrylate and norborneyl acrylate; alkyl methacrylates other than methyl methacrylate such as ethyl methacrylate, propyl methacrylate, and butyl methacrylate; aryl methacrylates such as phenyl methacrylate; cycloalkyl methacrylates such as cyclohexyl methacrylate and norborneyl methacrylate; aromatic vinyl compounds such as styrene and α-methylstyrene; acrylamide; methacrylamide; acrylonitrile; and methacrylonitrile.

[0057] (Biaxially oriented optical film) The first aspect of the biaxially oriented optical film of this embodiment contains an acrylic resin having a methyl methacrylate unit content of 98% by weight or more and a triple-representation syndiotacticity of 55% or more, a glass transition temperature of 120°C or higher, an in-plane phase difference R0 at a wavelength of 590 nm greater than 0.0 nm and 5.0 nm or less, a thickness direction phase difference Rth at a wavelength of 590 nm greater than or equal to -35 nm and 5.0 nm or less, and a thickness of 20 μm or more and 60 μm or less.

[0058] A second aspect of the biaxially oriented optical film of this embodiment contains an acrylic resin with a ring structure in its main chain, has a glass transition temperature of 120°C or higher, an in-plane phase difference R0 at a wavelength of 590 nm greater than 0.0 nm and less than or equal to 5.0 nm, a thickness direction phase difference Rth at a wavelength of 590 nm greater than or equal to -35 nm and less than or equal to -5.0 nm, and a thickness of 20 μm or more and less than or equal to 60 μm.

[0059] The glass transition temperature of the biaxially oriented optical film of this embodiment is 120°C or higher, but is preferably greater than 120°C, more preferably 121°C or higher, even more preferably 122°C or higher, and even more preferably 123°C or higher. Because the glass transition temperature of the biaxially oriented optical film of this embodiment is 120°C or higher, the orientation relaxation of the resin film is less likely to occur in a high-temperature, high-humidity environment, and the stability of the phase difference is improved. The glass transition temperature of the biaxially oriented optical film of this embodiment is, for example, 160°C or lower, but is preferably 135°C or lower, more preferably 133°C or lower, and even more preferably 130°C or lower.

[0060] The in-plane phase difference R0 of the biaxially oriented optical film of this embodiment at a wavelength of 590 nm is greater than 0.0 nm and less than or equal to 5.0 nm, but is preferably greater than 0.7 nm and less than or equal to 5.0 nm, and more preferably between 1.0 nm and 4.0 nm. Because R0 is greater than 0.0 nm and less than or equal to 5.0 nm, the uniformity of the in-plane phase difference R0 of the biaxially oriented optical film of this embodiment is improved.

[0061] The biaxially oriented optical film of this embodiment may contain aromatic vinyl units. In this case, the biaxially oriented optical film of this embodiment may contain an acrylic resin containing aromatic vinyl units, but it is preferable to contain an acrylic resin that does not contain aromatic vinyl units and a copolymer that contains aromatic vinyl units.

[0062] Furthermore, the biaxially oriented optical film of this embodiment can be manufactured using the resin film manufacturing method of this embodiment.

[0063] The biaxially stretched optical film of this embodiment can be applied to, for example, a polarizer protection film. In this case, the biaxially stretched optical film of this embodiment can be laminated with a polarizer to form a polarizing plate. The polarizer is not particularly limited, and a known polarizer can be used. Further, the polarizing plate can be combined with a liquid crystal cell to form a liquid crystal panel. In this case, it is preferable to use an IPS mode liquid crystal cell with a wide viewing angle. Further, when the biaxially stretched optical film of this embodiment is disposed on the side facing the liquid crystal cell, it may not contain an ultraviolet absorber, and may not substantially contain an ultraviolet absorber.

[0064] As described above, the embodiments of the present invention have been described. However, the present invention is not limited to the above embodiments, and the above embodiments may be appropriately modified within the scope of the gist of the present invention.

Example

[0065] Hereinafter, examples of the present invention will be described. However, the present invention is not limited to the examples.

[0066] (Conversion rate) The ratio of the solid content weight of the acrylic resin after drying for 30 minutes in an oven heated to 150 °C to the weight of the monomer charged, that is, the formula (Solid content weight of acrylic resin) × 100 / (Weight of monomer charged) was used to determine the conversion rate.

[0067] (Syndiotacticity rr of triad display) The syndiotacticity (rr) of the triad display of the acrylic resin was calculated as follows. First, using a 400 MHz nuclear magnetic resonance apparatus AVANCEIII (manufactured by Bruker), in a deuterated chloroform solution, at 22 °C, and with an integration number of 16 times, the 1 1H-NMR spectrum of the acrylic resin was measured. 1From the 1H-NMR spectrum, the area (X) of the region between 0.60 ppm and 0.95 ppm, with tetramethylsilane (TMS) set to 0 ppm, and the area (Y) of the region between 0.60 ppm and 1.25 ppm were measured, and then the formula was used. (X / Y) × 100 The syndiotacticity rr in triple representation was calculated based on this.

[0068] (Weight-average molecular weight Mw, number-average molecular weight Mn, and polydispersity Mw / Mn) The weight-average molecular weight (Mw), number-average molecular weight (Mn), and polydispersity (Mw / Mn) of the acrylic resin were calculated using a standard polystyrene-based method with gel permeation chromatography (GPC). Specifically, a sample solution prepared by dissolving 20 mg of acrylic resin in 10 mL of tetrahydrofuran was used for analysis under the following instrumentation and conditions. Measuring instrument: HLC-8220GPC (manufactured by Tosoh) Detector: RI detector Eluent: Tetrahydrofuran Guard column: TSKgel guardcolumn SuperHL (manufactured by Tosoh) Analysis column: TSKgel SuperH5000, SuperH4000, SuperH3000, and SuperH2000 (manufactured by Tosoh) connected in series. Eluent flow rate: 0.60 mL / min Measurement temperature: 40℃ Standard material: Standard polystyrene (manufactured by Tosoh Corporation)

[0069] (Glass transition temperature Tg) Using a high-sensitivity differential scanning calorimeter DSC7000X (manufactured by Hitachi High-Tech Science), 10 mg of acrylic resin or resin composition was heated at a heating rate of 10°C / min under a nitrogen atmosphere, and the glass transition temperature Tg was determined by the midpoint method.

[0070] (Phase difference in the thickness direction Rth and phase difference in the plane R0) The phase difference Rth in the thickness direction and the in-plane phase difference R0 of the film at a wavelength of 590 nm were measured using the KOBRA-WR phase difference measuring device (manufactured by Oji Instruments).

[0071] (Yellowness YI when viewed from an oblique angle on the LCD panel) A liquid crystal panel simulation was performed using the LCD Master (manufactured by Syntec) liquid crystal simulator. The setup involved arranging a polarizer on the light source side, an IPS-type liquid crystal cell with an in-plane phase difference Re of 295 nm, and another polarizer on the viewing side. The measurement results of the thickness-direction phase difference Rth were input as the optical properties of the polarizer protective film on the side facing the liquid crystal cell on both the light source and viewing sides. Next, the XYZ color values ​​were simulated when the liquid crystal cell was viewed from an extreme angle of 70° and an azimuth angle of 40° with the liquid crystal cell set to a dark state. The yellowness YI was then calculated using the following formula in accordance with JIS K7373:2006. YI = 100(1.2985X - 1.1335Z) / Y

[0072] <Manufacturing of acrylic resin 1> A 40mm diameter, co-rotating, interlocking twin-screw extruder (L / D=90) was used as the extruder, with the temperature of each temperature control zone set to 250°C to 280°C and the screw rotation speed set to 85 rpm. After melting and filling the extruder with polymethyl methacrylate resin using a kneading block, 1.8 parts by weight of monomethylamine (manufactured by Mitsubishi Gas Chemical) was injected per 100 parts by weight of polymethyl methacrylate resin. The resin that came out as strands from the die at the extruder outlet was cooled in a water bath and then pelletized in a pelletizer to obtain resin (I). Next, the temperature of each temperature control zone of the 40mm diameter, co-rotating, interlocking twin-screw extruder was set to 240°C to 260°C, and resin (I) was supplied from a hopper. 0.56 parts by weight of dimethyl carbonate was injected from a nozzle per 100 parts by weight of polymethyl methacrylate resin to reduce the number of carboxyl groups in resin (I). Furthermore, by-products and excess dimethyl carbonate were removed after the reaction. The resin, which emerged as strands from a die at the extruder outlet, was cooled in a water bath and then pelletized in a pelletizer to obtain acrylic resin 1 containing glutarimide rings in the main chain. Acrylic resin 1 had a Tg of 123°C, a Mw of 98000, a Mw / Mn ratio of 2.2, and a glutarimide ring content of 6% by weight.

[0073] <Manufacturing of Acrylic Resin 2> In a 4L glass reactor equipped with a stirrer having H-type impellers, 150 parts by weight of deionized water, 0.20 parts by weight of tricalcium phosphate as a dispersant, 0.0075 parts by weight of sodium α-olefin sulfonate, and 0.30 parts by weight of sodium chloride were charged. Next, under a nitrogen atmosphere, while stirring at 250 rpm, 100 parts by weight of methyl methacrylate (MMA), 0.289 parts by weight of n-octyl mercaptan as a chain transfer agent, and 0.065 parts by weight of V-601 (2,2'-azobis(isobutyrate)dimethyl) (manufactured by Fujifilm Wako Pure Chemical Industries) as a polymerization initiator were added to the reactor. Then, the temperature of the liquid in the reactor was raised to 70°C to start polymerization, and 0.10 parts by weight of tricalcium phosphate was added to the reactor 2 hours after the start of polymerization. At this time, an exothermic peak associated with the gel effect was observed 4 hours and 20 minutes after the start of polymerization. Next, heating was started 7 hours after the start of polymerization, and the temperature of the liquid in the reactor was raised to 95°C. The conversion rate after 7 hours from the start of polymerization was 93%. Then, 2 hours after the temperature of the liquid in the reactor reached 95°C, the temperature of the liquid in the reactor was cooled to room temperature to terminate polymerization and obtain an acrylic resin dispersion. The conversion rate at the end of polymerization was 99%.

[0074] The acrylic resin dispersion was acid-washed with 1 N hydrochloric acid in a weight ratio of 0.1 times the weight of the monomer, and then washed with water to remove the dispersant. Next, the washed acrylic resin dispersion was dehydrated and dried to obtain bead-shaped acrylic resin 2. Acrylic resin 2 had a Tg of 120°C, an rr of 57%, a Mw of 83,000, a Mw / Mn ratio of 1.63, and an MMA unit content of 100% by weight.

[0075] <Example 1> Using a 15 mm diameter, co-rotating twin-screw extruder (L / D=45) equipped with a die at the outlet, 90 parts by weight of acrylic resin 1 and 10 parts by weight of methyl methacrylate-styrene copolymer MS-750 (manufactured by Toyo Styrene) (hereinafter referred to as "MS resin 1"), which has a styrene unit content of 25% by weight, were kneaded. The strands extruded from the die were cooled in a water bath, pelletized in a pelletizer, and then dried at 100°C for 5 hours to obtain the resin composition. The resin composition had a Tg of 123°C.

[0076] Using a 15mm diameter, co-rotating twin-screw extruder (L / D=45) equipped with a T-die at the outlet, the resin composition was melted, and then the sheet extruded from the T-die was cooled using a cooling roll to obtain a raw film with a width of 160mm and a thickness of 160μm.

[0077] A biaxially oriented optical film was obtained by sequentially biaxially stretching the raw film. Specifically, using a uniaxial stretching apparatus, the free end was uniaxially stretched in the MD direction at a stretching temperature of 128 (Tg+5)°C and a stretching ratio of 1.8 times. Then, using a biaxial stretching apparatus IMC-1905 (manufactured by Imoto Seisakusho), the fixed end was uniaxially stretched in the TD direction at a stretching temperature of 128 (Tg+5)°C and a stretching ratio of 2.0 times.

[0078] <Example 2> A biaxially oriented optical film was obtained in the same manner as in Example 1, except that the stretching temperature during free-end uniaxial stretching was changed to 138 (Tg + 15) °C, and the stretching temperature and stretching ratio during fixed-end uniaxial stretching were changed to 138 (Tg + 15) °C and 2.5 times, respectively.

[0079] <Example 3> A resin composition was obtained in the same manner as in Example 1, except that the stretching temperature during uniaxial stretching of the free end was changed to 138 (Tg + 15) °C, and the stretching temperature during uniaxial stretching of the fixed end was changed to 138 (Tg + 15) °C.

[0080] <Example 4> Using a 15mm diameter, coaxial twin-screw extruder (L / D=45) equipped with a die at the outlet, 95 parts by weight of acrylic resin 1 and 5 parts by weight of acrylonitrile-styrene copolymer AS-61NT7200 (manufactured by Shin Chemical Trading Co., Ltd.) (hereinafter referred to as "AS resin 1"), which has a styrene unit ratio of 74% by weight and contains a colorant, were kneaded. The strands extruded from the die were cooled in a water bath, pelletized in a pelletizer, and then dried at 100°C for 5 hours to obtain the resin composition. The resin composition had a Tg of 122°C.

[0081] Using a 15mm diameter, co-rotating twin-screw extruder (L / D=45) equipped with a T-die at the outlet, the resin composition was melted, and then the sheet extruded from the T-die was cooled using a cooling roll to obtain a raw film with a width of 160mm and a thickness of 160μm.

[0082] A biaxially oriented optical film was obtained by sequentially biaxially stretching the raw film. Specifically, using a uniaxial stretching apparatus, the free end was uniaxially stretched in the MD direction at a stretching temperature of 137 (Tg + 15) °C and a stretching ratio of 1.8 times. Then, using a biaxial stretching apparatus IMC-1905 (manufactured by Imoto Seisakusho), the fixed end was uniaxially stretched in the TD direction at a stretching temperature of 137 (Tg + 15) °C and a stretching ratio of 1.5 times.

[0083] <Example 5> Using a 15 mm diameter, co-rotating, interlocking twin-screw extruder (L / D=45) equipped with a die at the outlet, 92.5 parts by weight of acrylic resin 1 and 7.5 parts by weight of AS resin 1 were kneaded together. The strand extruded from the die was cooled in a water bath, pelletized in a pelletizer, and then dried at 100°C for 5 hours to obtain the resin composition. The resin composition had a Tg of 122°C.

[0084] Using a 15mm diameter, co-rotating twin-screw extruder (L / D=45) equipped with a T-die at the outlet, the resin composition was melted, and then the sheet extruded from the T-die was cooled using a cooling roll to obtain a raw film with a width of 160mm and a thickness of 160μm.

[0085] A biaxially oriented optical film was obtained by sequentially biaxially stretching the raw film. Specifically, using a uniaxial stretching apparatus, the free end was uniaxially stretched in the MD direction at a stretching temperature of 127 (Tg+5)°C and a stretching ratio of 1.8 times. Then, using a biaxial stretching apparatus IMC-1905 (manufactured by Imoto Seisakusho), the fixed end was uniaxially stretched in the TD direction at a stretching temperature of 148 (Tg+26)°C and a stretching ratio of 3.0 times.

[0086] <Example 6> Using a 15mm diameter, co-rotating, interlocking twin-screw extruder (L / D=45) equipped with a die at the outlet, 100 parts by weight of acrylic resin 2 were kneaded. The strands extruded from the die were cooled in a water bath, pelletized in a pelletizer, and then dried at 100°C for 5 hours.

[0087] Using a 15mm diameter, co-rotating, interlocking twin-screw extruder (L / D=45) equipped with a T-die at the outlet, the pelletized acrylic resin 2 was melted, and then the sheet extruded from the T-die was cooled using a cooling roll to obtain a raw film with a width of 160mm and a thickness of 160μm.

[0088] A biaxially oriented optical film was obtained by sequentially biaxially stretching the raw film. Specifically, using a uniaxial stretching apparatus, the free end was uniaxially stretched in the MD direction at a stretching temperature of 125 (Tg+5)°C and a stretching ratio of 2.0x. Then, using a biaxial stretching apparatus IMC-1905 (manufactured by Imoto Seisakusho), the fixed end was uniaxially stretched in the TD direction at a stretching temperature of 135 (Tg+15)°C and a stretching ratio of 2.0x.

[0089] <Example 7> A biaxially oriented optical film was obtained in the same manner as in Example 6, except that the stretching ratio during uniaxial stretching of the free end was changed to 2.2 times.

[0090] <Example 8> A biaxially oriented optical film was obtained in the same manner as in Example 7, except that the stretching ratio during uniaxial stretching at the fixed end was changed to 2.5 times.

[0091] <Example 9> A biaxially oriented optical film was obtained in the same manner as in Example 6, except that the stretching temperature and stretching ratio when performing uniaxial stretching at the free end were changed to 140 (Tg+20)°C and 1.8 times, and the stretching temperature and stretching ratio when performing uniaxial stretching at the fixed end were changed to 140 (Tg+20)°C and 2.7 times.

[0092] <Comparative Example 1> A biaxially oriented optical film was obtained in the same manner as in Example 1, except that the stretching ratio when uniaxially stretching the free end was changed to 1.4 times and the stretching ratio when uniaxially stretching the fixed end was changed to 3.0 times.

[0093] <Comparative Example 2> A biaxially oriented optical film was obtained in the same manner as in Example 1, except that the stretching temperature during free-end uniaxial stretching was changed to 148 (Tg + 25) °C, and the stretching temperature and stretching ratio during fixed-end uniaxial stretching were changed to 148 (Tg + 25) °C and 3.0 times, respectively.

[0094] <Comparative Example 3> A biaxially oriented optical film was obtained in the same manner as in Comparative Example 1, except that the stretching ratio during uniaxial stretching of the free end was changed to 1.8 times.

[0095] <Comparative Example 4> A biaxially oriented optical film was obtained in the same manner as in Example 4, except that the stretching ratio when uniaxially stretching the free end was changed to 1.4 times, and the stretching ratio when uniaxially stretching the fixed end was also changed to 1.4 times.

[0096] <Comparative Example 5> A biaxially oriented optical film was obtained in the same manner as in Example 4, except that the stretching ratio when uniaxially stretching the free end was changed to 1.8 times and the stretching ratio when uniaxially stretching the fixed end was changed to 3.0 times.

[0097] <Comparative Example 6> A biaxially oriented optical film was obtained in the same manner as in Example 4, except that the stretching temperature and stretching ratio during free-end uniaxial stretching were changed to 127 (Tg+5)°C and 1.4 times the medium, and the stretching temperature and stretching ratio during fixed-end uniaxial stretching were changed to 127 (Tg+5) and 3.0 times.

[0098] <Comparative Example 7> A biaxially oriented optical film was obtained in the same manner as in Example 6, except that the stretching ratio when uniaxially stretching the free end was changed to 1.6 times and the stretching ratio when uniaxially stretching the fixed end was changed to 2.5 times.

[0099] Table 1 shows the properties and evaluation results of the resin composition and biaxially oriented optical film.

[0100] [Table 1]

[0101] Table 1 shows that the biaxially oriented optical films of Examples 1-9 have reduced YI when viewed from an oblique direction on the liquid crystal panel, and also have a small R0. In contrast, the biaxially oriented optical films of Comparative Examples 1, 3-7 have a large R0. Furthermore, the biaxially oriented optical film of Comparative Example 2 has an Rth of -3.2 nm, resulting in a large YI when viewed from an oblique direction on the liquid crystal panel.

Claims

1. A method for manufacturing a resin film, comprising the step of sequentially biaxially stretching a raw film containing an acrylic resin and having a glass transition temperature of 120°C or higher, such that the in-plane phase difference R0 at a wavelength of 590 nm is greater than 0.0 nm and less than or equal to 5.0 nm, and the thickness direction phase difference Rth at a wavelength of 590 nm is between -35 nm and -5.0 nm.

2. After stretching the aforementioned raw film in the MD direction, it is stretched in the TD direction. If the ratio of the in-plane phase difference R0 to the thickness-direction phase difference Rth at a wavelength of 590 nm for the raw film stretched in the MD direction is [R0 / Rth]1st, and the ratio of the in-plane phase difference R0 to the thickness-direction phase difference Rth at a wavelength of 590 nm for the raw film stretched in the TD direction is [R0 / Rth]2nd, then the formula [R0 / Rth] 2nd / [R0 / Rth] 1st<0.4 A method for producing a resin film according to claim 1, which satisfies the requirements.

3. The method for producing a resin film according to claim 1 or 2, wherein the raw material film contains aromatic vinyl units.

4. The method for producing a resin film according to claim 1 or 2, wherein the acrylic resin has a methyl methacrylate unit content of 98% by weight or more and a triple-representation syndiotacticity of 55% or more.

5. The method for producing a resin film according to claim 1 or 2, wherein the acrylic resin includes a ring structure in its main chain.

6. The method for producing a resin film according to claim 5, wherein the acrylic resin contains 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.

7. It contains an acrylic resin having a methyl methacrylate unit content of 98% by weight or more and a triple-symbol syndiotacticity of 55% or more. The glass transition temperature is 120°C or higher. The in-plane phase difference R0 at a wavelength of 590 nm is greater than 0.0 nm and less than or equal to 5.0 nm. The phase difference Rth in the thickness direction at a wavelength of 590 nm is between -35 nm and -5.0 nm. A biaxially oriented optical film with a thickness of 20 μm or more and 60 μm or less.

8. The main chain contains an acrylic resin with a ring structure, The glass transition temperature is 120°C or higher. The in-plane phase difference R0 at a wavelength of 590 nm is greater than 0.0 nm and less than or equal to 5.0 nm. The phase difference Rth in the thickness direction at a wavelength of 590 nm is between -35 nm and -5.0 nm. A biaxially oriented optical film with a thickness of 20 μm or more and 60 μm or less.

9. The biaxially oriented optical film according to claim 7 or 8, wherein the in-plane phase difference R0 at a wavelength of 590 nm is greater than 0.7 nm.

10. A biaxially oriented optical film according to claim 7 or 8, comprising aromatic vinyl units.

11. A biaxially oriented optical film according to claim 7 or 8, wherein the glass transition temperature is 135°C or lower.

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