Optical films, polarizing plates, and liquid crystal panels

Abstract

The present invention provides an optical film that can simultaneously achieve heat resistance, uniformity of in-plane phase difference, and reduction of yellowness when viewing the liquid crystal panel from an oblique angle. [Solution] The optical film comprises a resin composition, and the thickness direction phase difference Rth at a wavelength of 590 nm is between -35.0 nm and -5.0 nm. The resin composition comprises an acrylic resin, has a glass transition temperature of 118°C or higher, and a birefringence Δnxy of -1.0 × 10⁻⁶. -3 Above -0.1 × 10 -3 The following conditions apply: The acrylic resin has a methyl methacrylate unit content of 98% by weight or more, and a triplet syndiotacticity of 55% or more.

Description

[Technical Field]

[0001] This invention relates to optical films, polarizing plates, and liquid crystal panels. [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 Initiative] [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, a slight yellowish tint may appear when viewing a black display from an oblique angle. On the other hand, if such color tone issues are optically compensated for by the phase difference of the optical film, variations in the in-plane phase difference of the optical film may result in unevenness in the display of the liquid crystal panel.

[0006] The present invention aims to provide an optical film that can achieve both heat resistance, uniformity of in-plane phase difference, and reduction of yellowness when viewed from an oblique direction on a liquid crystal panel. [Means for solving the problem]

[0007] [1] An optical film comprising a resin composition, having a thickness-direction retardation Rth at a wavelength of 590 nm of -35.0 nm or more and -5.0 nm or less, the resin composition containing an acrylic resin having a glass transition temperature of 118 °C or more and a birefringence development property Δnxy of -1.0×10 -3 or more and -0.1×10 -3 or less, the acrylic resin having a methyl methacrylate unit content of 98% by weight or more and a syndiotacticity of triplets of 55% or more.

[0008] [2] An optical film comprising a resin composition, having an in-plane retardation Re with an average value of 0.8 nm or more and 4.0 nm or less and a thickness-direction retardation Rth at a wavelength of 590 nm of -35.0 nm or more and -5.0 nm or less, the resin composition containing an acrylic resin having a glass transition temperature of 118 °C or more, the acrylic resin having a methyl methacrylate unit content of 98% by weight or more and a syndiotacticity of triplets of 55% or more.

[0009] [3] The acrylic resin in the optical film according to [1] or [2], having a weight-average molecular weight of 80,000 or more and 200,000 or less and a polydispersity of 1.6 or more and 2.5 or less.

[0010] [4] The optical film according to any one of [1] to [3], wherein the resin composition has an aromatic vinyl unit content of 0% by weight or more and 8% by weight or less.

[0011] [5] The optical film according to [4], wherein the resin composition has a styrene unit content of 0% by weight or more and 8% by weight or less.

[0012] [6] The optical film according to any one of [1] to [5], wherein the resin composition further contains a methyl methacrylate-styrene copolymer.

[0013] [7] The optical film according to [6], wherein the methyl methacrylate-styrene copolymer has a weight average molecular weight of 80,000 or more and 200,000 or less, and a polydispersity of 1.6 or more and 2.5 or less.

[0014] [8] The optical film according to any one of [1] to [7], wherein the resin composition has a 5% weight loss temperature of 330 °C or more.

[0015] [9] The optical film according to any one of [I] to [8], wherein the internal haze is 1.0% or less.

[0016]

[10] The optical film according to any one of [1] to [9], which does not contain an ultraviolet absorber.

[0017]

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

[10] , which is a biaxially stretched film.

[0018]

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

[11] .

[0019]

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

[12] .

[0020]

[14] A resin composition containing an acrylic resin, having a glass transition temperature of 118 °C or more, a birefringence development property Δnxy of -1.0 × 10 -3 or more and -0.1 × 10 -3 or less, an aromatic vinyl unit content of 0 wt% or more and 8 wt% or less, a 5% weight loss temperature of 330 °C or more, wherein the acrylic resin has a methyl methacrylate unit content of 98 wt% or more and a syndiotacticity of triads of 55% or more.

[0021]

[15] The resin composition according to

[14] , wherein the styrene unit content is 0 wt% or more and 8 wt% or less.

[0022]

[16] The resin composition according to

[14] or

[15] , further comprising a methyl methacrylate-styrene copolymer.

Advantages of the Invention

[0023] According to the present invention, it is possible to provide an optical film capable of achieving both heat resistance, uniformity of in-plane retardation, and reduction of yellowness when viewed from an oblique direction of a liquid crystal panel.

Modes for Carrying Out the Invention

[0024] Hereinafter, embodiments of the present invention will be described.

[0025] (Optical Film) The optical film of the present embodiment contains a resin composition.

[0026] The retardation in the thickness direction Rth of the optical film of the present embodiment at a wavelength of 590 nm is -35.0 nm or more and -5.0 nm or less, preferably -30.0 nm or more and -6.0 nm or less, more preferably -20.0 nm or more and -7.0 nm or less, further 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. Since Rth is -35.0 nm or more and -5.0 nm or less, the yellowness when viewed from an oblique direction of the liquid crystal panel is reduced. At this time, the yellowness of the optical film of the present embodiment when viewed from an oblique direction of the liquid crystal panel is preferably 50 or less.

[0027] In a first aspect of the optical film of the present embodiment, the birefringence development property Δnxy of the resin composition is -1.0×10 -3 or more and -0.1×10 -3 or less, preferably -0.8×10 -3 or more and -0.25×10 -3 or less, more preferably -0.8×10 -3 or more and -0.20×1,0 -3 or less, and even more preferably -0.8×10 -3 or more and -0.12×10 -3 or less. When Δnxy is -1.0×10 -3Therefore, when the resin composition is biaxially stretched, it becomes easier to achieve the desired thickness-direction phase difference, -0.1 × 10 -3 Therefore, when the resin composition is biaxially stretched, the in-plane phase difference tends to become uniform.

[0028] In this specification and in the claims, the birefringence Δnxy of a resin composition means the birefringence that occurs when an unstretched film of the resin composition is uniaxially stretched at its free end at a temperature 5°C higher than the glass transition temperature of the resin composition, such that the stretching ratio in the longitudinal direction (longitudinal direction) becomes twice as large.

[0029] Note that Δnxy is expressed by the formula Δnxy = nx - ny = Re / d It is calculated by the following formula. Here, nx and ny are the refractive indices in the X-axis and Y-axis directions, respectively, with the MD direction as the X-axis, the TD direction as the Y-axis, and the film thickness direction as the Z-axis. Re is the in-plane phase difference of the film, and d is the thickness of the film.

[0030] In the second embodiment of the optical film of this embodiment, the average value of the in-plane phase difference Re is 0.8 nm or more and 4.0 nm or less, and preferably 0.9 nm or more and 3.5 nm or less. Since the average value of Re is 0.8 nm or more and 4.0 nm or less, the uniformity of the in-plane phase difference Re is improved. In this case, it is preferable that the standard deviation of the in-plane phase difference Re of the optical film of this embodiment is less than 1.0.

[0031] Note that Re and Rth are expressed in formula Re=(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 MD direction being the X-axis, the TD direction being the Y-axis, and the film thickness direction being the Z-axis. Also, d is the thickness of the film.

[0032] In this case, the first embodiment of the optical film of this embodiment may also serve as the second embodiment of the optical film of this embodiment.

[0033] The internal haze of the optical film in this embodiment is preferably 1.0% or less, more preferably 0.8% or less, and even more preferably 0.5% or less. When the internal haze of the optical film in this embodiment is 1.0% or less, the transparency of the optical film in this embodiment is maintained. For example, the internal haze of the optical film in this embodiment is 0.1% or more.

[0034] The yellowness of the optical film in this embodiment is preferably 0.01 to 5.00, and more preferably 0.1 to 2.0. When the yellowness of the optical film in this embodiment is 5.00 or less, the coloration of the optical film in this embodiment is minimal, and the impact on the color rendering of the display is small.

[0035] The absorbance of the optical 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. If the absorbance of the optical film of this embodiment at a wavelength of 380 nm is 1.00 or less, the optical film of this embodiment is substantially free of ultraviolet absorbers.

[0036] The photoelastic coefficient of the optical film in this embodiment is -10 × 10 -12 Pa -1 The above 10 x 10 -12 Pa -1 Preferably, it is -5.5 × 10 -12 Pa -1 The above 5.5 x 10 -12 Pa -1 It is more preferable that the following conditions are met: -4.5 × 10 -12 Pa -1 The above 4.5 × 10 -12 Pa -1 It is even more preferable that the optical film of this embodiment has a photoelastic coefficient of -10 × 10 -12 Pa -1 The above 10 x 10 -12 Pa-1 The following conditions make it less likely for color unevenness to occur in the optical film of this embodiment, and this tendency becomes particularly pronounced in high-temperature and high-humidity environments.

[0037] (Resin composition) The resin composition includes an acrylic resin.

[0038] In this specification and in the claims, acrylic resin means a polymer of monomers 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. If the acrylic resin is a copolymer, it may be a copolymer of monomers that do not have an acryloyl group or a methacryloyl group.

[0039] The glass transition temperature of the resin composition is 118°C or higher, preferably 119°C or higher, more preferably 120°C or higher, and even more preferably greater than 120°C. Because the glass transition temperature of the resin composition is 118°C or higher, the heat resistance of the optical film in this embodiment is enhanced. Furthermore, orientation relaxation is less likely to occur in high-temperature, high-humidity environments, improving the stability of the phase difference. The glass transition temperature of the resin composition is, for example, 160°C or lower.

[0040] The resin composition may contain aromatic vinyl units. In this case, the resin composition 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.

[0041] The content of aromatic vinyl units in the resin composition is preferably 0% to 8% by weight, more preferably 0.05% to 5% by weight, even more preferably 0.05% to 3% by weight, even more preferably 0.05% to 2.5% by weight, and particularly preferably 0.1% to 2.5% by weight. When the content of aromatic vinyl units in the resin composition is 8% by weight or less, the degree of yellowness when the liquid crystal panel is viewed from an oblique direction is reduced.

[0042] 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.

[0043] The resin composition preferably further comprises a methyl methacrylate-styrene copolymer.

[0044] The weight-average molecular weight of the methyl methacrylate-styrene copolymer is between 80,000 and 200,000, and preferably between 90,000 and 150,000. When the weight-average molecular weight of the methyl methacrylate-styrene copolymer is between 80,000 and 200,000, the compatibility with acrylic resin is increased.

[0045] The polydispersity (ratio of weight-average molecular weight to number-average molecular weight) of the methyl methacrylate-styrene copolymer is 1.6 or more and 2.5 or less, preferably 1.7 or more and 2.0 or less. Because the polydispersity of the methyl methacrylate-styrene copolymer is 1.6 or more and 2.5 or less, the extrusion processability of the resin composition of this embodiment is improved.

[0046] The resin composition 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, and compatibilizers. Two or more of these may be used in combination.

[0047] The 5% weight loss temperature of the resin composition is preferably 330°C or higher, more preferably 332°C or higher, and even more preferably 335°C or higher. When the 5% weight loss temperature of the resin composition is 330°C or higher, contamination of the cooling rolls during the production of the raw film is suppressed, and the film-forming properties of the raw film are improved. The 5% weight loss temperature of the resin composition is, for example, 380°C or lower.

[0048] The weight-average molecular weight of the resin composition is preferably 50,000 to 200,000, and more preferably 90,000 to 150,000. When the weight-average molecular weight of the resin composition is 50,000 or more, the mechanical properties of the molded article of the resin composition tend to improve, and when it is 200,000 or less, the moldability of the resin composition tends to improve.

[0049] The polydispersity of the resin composition (ratio of weight-average molecular weight to number-average molecular weight) 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 resin composition is 1.5 or more, the fluidity of the resin composition tends to improve and it tends to become easier to mold, and when it is 2.5 or less, the mechanical properties of the molded article of the resin composition, such as impact resistance, toughness, and bending resistance, tend to improve.

[0050] The number-average molecular weight and weight-average molecular weight of the resin composition are values ​​equivalent to standard polystyrene, measured by gel permeation chromatography (GPC). Furthermore, the number-average molecular weight and weight-average molecular weight of the resin composition can be controlled by the type and amount of polymerization initiator and chain transfer agent used in the synthesis of the acrylic resin.

[0051] The optical film of this embodiment can be applied, for example, to a polarizer protective film. In this case, the optical film of this embodiment can be bonded to a polarizer to form a polarizing plate. The polarizer is not particularly limited, and known polarizers can be used. 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 type liquid crystal cell with a wide viewing angle. Furthermore, when the optical film of this embodiment is placed on the side facing the liquid crystal cell, it does not need to contain an ultraviolet absorber, or may not contain an ultraviolet absorber at all.

[0052] (Acrylic resin) The syndiotacticity of the triple-marked acrylic resin is 55% or higher, preferably 57% or higher, and more preferably 58% or higher. Because the syndiotacticity of the triple-marked acrylic resin is 55% or higher, the heat resistance of the resin composition is increased.

[0053] The syndiotacticity of the triple-marked acrylic resin is preferably 70% or less, more preferably 67% or less, even more preferably 65% ​​or less, and even more preferably 60% or less. When the syndiotacticity of the triple-marked acrylic resin is 70% or less, the extrusion processability of the resin composition is improved.

[0054] The syndiotacticity of the triplet configuration of acrylic resin is the proportion of the three structural unit chains (triplets) that are rr. Note that in two structural unit chains (doublets), those with the same stereochemistry are called meso (m), and those with the opposite stereochemistry are called racemo (r).

[0055] The content of methyl methacrylate units in the acrylic resin is 98% by weight or more, preferably 99% by weight or more, and more preferably 100% by weight. When the content of methyl methacrylate units in the acrylic resin is 98% by weight or more, the chemical recyclability of the acrylic resin is enhanced.

[0056] The weight-average molecular weight of the acrylic resin is 80,000 to 200,000, and preferably 90,000 to 150,000. Because the weight-average molecular weight of the acrylic resin is 80,000 to 200,000, the extrusion processability of the resin composition of this embodiment is improved.

[0057] The polydispersity of the acrylic resin (ratio of weight-average molecular weight to number-average molecular weight) is 1.6 or more and 2.5 or less, preferably 1.7 or more and 2.0 or less. Because the polydispersity of the acrylic resin is 1.6 or more and 2.5 or less, the extrusion processability of the resin composition of this embodiment is improved.

[0058] The synthesis method for acrylic resin 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 syndiotacticity expressed in triplicate of the acrylic resin can be controlled by the polymerization temperature of the acrylic resin. For example, lowering the polymerization temperature of the acrylic resin increases the glass transition temperature and syndiotacticity of the acrylic resin. Furthermore, the glass transition temperature of the acrylic resin can also be controlled by the molecular weight of the acrylic resin.

[0059] Monomers other than methyl methacrylate that can be used when synthesizing acrylic resins 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 norbornenyl 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 norbornenyl methacrylate; aromatic vinyl compounds such as styrene and α-methylstyrene; acrylamide; methacrylamide; acrylonitrile; and methacrylonitrile.

[0060] (Method of manufacturing optical film) The optical film of this embodiment can be manufactured using known methods. An example of a method for manufacturing the optical film of this embodiment is described below.

[0061] First, using an extruder equipped with a die at the outlet, the acrylic resin is kneaded together with methyl methacrylate-styrene copolymer 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 the resin composition. Next, using an extruder equipped with a T-die at the outlet, the resin composition is melted, and then the sheet is extruded from the T-die and cooled with a cooling roll to obtain the raw film. Next, the raw film is biaxially stretched to obtain the optical film of this embodiment. At this time, the biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching.

[0062] The temperature at which the raw film is biaxially stretched is preferably (Tg+5)°C to (Tg+20)°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 resin composition. The surface ratio at which the raw film is biaxially stretched is not particularly limited, but for example, it is between 2 and 10 times. The stretching speed at which the raw film is biaxially stretched is not particularly limited, but for example, it is between 1.1 times / min and 100 times / min. When the raw film is sequentially biaxially stretched, the stretching speed of the first stage and the stretching speed of the second stage may be the same or different. In sequential biaxial stretching, the first stage stretching is usually in the longitudinal direction (MD direction), and the second stage stretching is in the width direction (TD direction).

[0063] Although embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and the above embodiments may be modified as appropriate within the scope of the spirit of the present invention. [Examples]

[0064] The following describes embodiments of the present invention, but the present invention is not limited to these embodiments.

[0065] (polymerization rate) The polymerization conversion rate [%] was determined by the gravimetric method, based on the ratio of the solid content weight of the polymerization solution to the weight of the added monomer. The solid content weight of the polymerization solution was determined by drying it in an oven set to 150°C for 30 minutes.

[0066] (Syndiotacticity rr with triple display) Using a 400MHz nuclear magnetic resonance spectrometer AVANCEIII (manufactured by Bruker), acrylic resin was subjected to a deuterated chloroform solution under the conditions of 22°C and 16 cumulative cycles. 1 The 1H-NMR spectrum was measured. Next, the area (X) of the region from 0.60 to 0.95 ppm and the area (Y) of the region from 0.60 to 1.25 ppm were measured, with tetramethylsilane (TMS) set to 0 ppm, and then the formula was applied. (X / Y) × 100 The syndiotacticity rr in triple representation was calculated based on this.

[0067] (Weight-average molecular weight Mw and polydispersity Mw / Mn) Using a high-speed GPC instrument HLC-8220GPC (manufactured by Tosoh), the weight-average molecular weight (Mw) and polydispersity (Mw / Mn) of the acrylic resin were calculated using the standard polystyrene equivalent method. Specifically, a sample solution prepared by dissolving 20 mg of acrylic resin in 10 mL of chloroform was used, and the analysis was performed under the following conditions. Detector: RI detector Solvent: Chloroform Guard column: TSKgel guardcolumn SuperHZ-H (manufactured by Tosoh) Analytical columns: TSKgel SuperHZM-H x 2 (manufactured by Tosoh) Measurement temperature: 40℃ Standard material: Standard polystyrene (manufactured by Tosoh Corporation)

[0068] (Glass transition temperature Tg) Using a high-sensitivity differential scanning calorimeter DSC7000X (manufactured by Hitachi High-Tech Science), 10 mg of 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.

[0069] (5% weight loss temperature Td5) Using a differential thermogravimetric analyzer STA7200 (manufactured by Hitachi High-Tech Science), 10 mg of the resin composition was heated from room temperature at a heating rate of 10°C / min under a nitrogen atmosphere, and the 5% weight loss temperature Td5 was determined.

[0070] (Birefringence-producing Δnxy) After cutting a 30 × 100 mm area from the original film, the free end was uniaxially stretched at a temperature 5°C higher than the glass transition temperature of the original film so that the stretching ratio in the longitudinal direction (longitudinal direction) was doubled, thereby obtaining a uniaxially oriented film. Next, the in-plane phase difference at the center of the uniaxially oriented film was measured using a phase difference measuring device KOBRA-WR (manufactured by Oji Keisoku Kiki), and then divided by the thickness of the uniaxially oriented film to determine the birefringence Δnxy.

[0071] (Phase difference in the thickness direction Rth) The phase difference Rth in the thickness direction of an optical film at a wavelength of 590 nm was measured using a phase difference measuring device KOBRA-WR (manufactured by Oji Instruments). After measuring the Rth of the optical film, the value was converted to a value equivalent to a film thickness of 40 μm.

[0072] (Mean and standard deviation of in-plane phase difference Re) After cutting out a 150 x 150 mm area from the center of the optical film, the mean and standard deviation of the in-plane phase difference Re were measured using a 2D birefringence evaluation system WPA-200 (manufactured by Photonic Lattice). At this time, three lines were drawn in both the MD and TD directions, and the mean and standard deviation of the in-plane phase difference Re were calculated using the line analysis function.

[0073] (Internal haze) In accordance with JIS K7136:2000, the internal haze of the optical film was measured using a HZ-V3 haze meter (manufactured by Suga Test Instruments). The internal haze of the optical film was measured twice, with glycerin and then glass sandwiched between both sides, and the average value was calculated. Furthermore, the measured internal haze was converted to a value equivalent to a film thickness of 40 μm.

[0074] (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 polarizing plate on the light source side, an IPS-type liquid crystal cell with an in-plane phase difference Re of 295 nm, and another polarizing plate on the viewing side. The measurement results of the thickness-direction phase difference Rth were input as the optical properties of the optical film on the side of the polarizing plates facing the liquid crystal cell. Next, the XYZ color values ​​were simulated when the liquid crystal cell was viewed from a polar 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

[0075] (Manufacturing of acrylic resin 1) In a 4L glass reactor equipped with an H-type agitator, 150 parts by weight of deionized water, 0.20 parts by weight of tricalcium phosphate, 0.0075 parts by weight of sodium α-olefin sulfonate, and 0.30 parts by weight of sodium chloride were charged as dispersants. 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 0.074 parts by weight of 2,2'-azobis(isobutyrate)dimethyl V-601 (manufactured by Fujifilm Wako Pure Chemical Industries) as a polymerization initiator were added to the reactor. Subsequently, the temperature of the liquid in the reactor was raised to 70°C to start polymerization. Two hours after the start of polymerization, 0.10 parts by weight of tricalcium phosphate was added to the polymerization solution. At this time, an exothermic peak associated with the gel effect was observed 4 hours and 20 minutes after the start of polymerization. Seven hours after the start of polymerization, the temperature was increased to 95°C. At the seven-hour mark, the polymerization conversion rate was 93%. Two hours after the temperature reached 95°C, the reactor was cooled to room temperature to terminate polymerization and obtain an acrylic resin dispersion. At this point, the polymerization conversion rate was 99%. Next, the acrylic resin dispersion was washed with 0.1 times the weight of the charged monomer in 1N hydrochloric acid, and then washed with water to remove the dispersant. The acrylic resin washed with water was then dehydrated and dried to obtain bead-shaped acrylic resin 1. Acrylic resin 1 had a Tg of 120°C, an rr of 57%, an Mw of 83,000, an Mw / Mn ratio of 1.63, and an MMA unit content of 100% by weight.

[0076] (Example 1) Using a 15mm diameter, coaxial twin-screw extruder (L / D=45) equipped with a die at the outlet, 100 parts by weight of acrylic resin 1 and 2 parts by weight of methyl methacrylate-styrene copolymer KT-89 (manufactured by Denka) (hereinafter referred to as MS resin 1), which has a styrene unit content of 11% by weight, an Mw of 104,000, and an Mw / Mn ratio of 1.89, were kneaded. Next, the strand extruded from the die at the outlet of the extruder was cooled using a water bath, and the strand was pelletized using a pelletizer. After that, it was dried at 100°C for 5 hours to obtain a resin composition. The resin composition had a Tg of 121.0°C, a Td5 of 337.6°C, and a Δnxy of -0.41 × 10⁻⁶. -3 That was the case.

[0077] 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.

[0078] Using a biaxial film stretching machine IMC-1905 (manufactured by Imoto Seisakusho), the raw film was simultaneously biaxially stretched at a temperature 15°C higher than the glass transition temperature of the resin composition, so that the stretching ratio in the longitudinal and transverse directions was doubled, to obtain an optical film measuring 280 mm x 280 mm.

[0079] (Example 2) An optical film was obtained in the same manner as in Example 1, except that the amount of MS resin 1 added was changed to 5 parts by weight. At this time, the resin composition had a Tg of 120.1°C, a 5% weight loss temperature of 336.7°C, and a Δnxy of -0.45 × 10⁻⁶. -3 That was the case.

[0080] (Example 3) An optical film was obtained in the same manner as in Example 1, except that the amount of MS resin 1 added was changed to 10 parts by weight. At this time, the resin composition had a Tg of 119.6°C, a 5% weight loss temperature of 336.0°C, and a Δnxy of -0.47 × 10⁻⁶. -3 That was the case.

[0081] (Example 4) An optical film was obtained in the same manner as in Example 3, except that methyl methacrylate-styrene copolymer MS-750 (manufactured by Toyo Styrene) (hereinafter referred to as MS resin 2), which has a styrene unit content of 25% by weight, an Mw of 97,000, and an Mw / Mn of 1.82, was used instead of MS resin 1. At this time, the resin composition had a Tg of 118.9°C, a 5% weight loss temperature of 336.6°C, and a Δnxy of -0.64 × 10⁻⁶. -3 That was the case.

[0082] (Example 5) An optical film was obtained in the same manner as in Example 3, except that the raw film was simultaneously biaxially stretched at a temperature 7°C higher than the glass transition temperature of the resin composition.

[0083] (Example 6) An optical film was obtained in the same manner as in Example 3, except that the raw film was simultaneously biaxially stretched at a temperature 20°C higher than the glass transition temperature of the resin composition.

[0084] (Comparative Example 1) An optical film was obtained in the same manner as in Example 3, except that a methyl methacrylate resin parapet HM (manufactured by Kuraray) (hereinafter referred to as acrylic resin 2), which has a Tg of 116°C, an rr of 51%, an Mw of 91,000, an Mw / Mn ratio of 1.68, and an MMA unit content of 98% by weight or more, was used instead of acrylic resin 1. In this case, the resin composition had a Tg of 116.7°C, a 5% weight loss temperature of 338.1°C, and a Δnxy of -0.62 × 10⁻⁶. -3 That was the case.

[0085] Table 1 shows the properties of acrylic resin.

[0086] [Table 1]

[0087] Table 2 shows the properties of MS resin.

[0088] [Table 2]

[0089] Table 3 shows the properties and evaluation results of the resin composition and optical film.

[0090] [Table 3]

[0091] Table 3 shows that the optical films of Examples 1 to 6 achieve a balance between heat resistance, standard deviation of Re, and reduction of YI when viewed from an oblique angle on the liquid crystal panel. In contrast, the optical film of Comparative Example 1 has low heat resistance because the Tg of the resin composition is 116.7°C.

Claims

1. Includes a resin composition, The phase difference Rth in the thickness direction at a wavelength of 590 nm is between -35.0 nm and -5.0 nm. The aforementioned resin composition contains an acrylic resin, has a glass transition temperature of 118°C or higher, and a birefringence Δnxy of -1.0 × 10⁻¹⁰. －３ Above -0.1 × 10 －３ The following: The acrylic resin is an optical film having a methyl methacrylate unit content of 98% by weight or more and a triple-link syndiotacticity of 55% or more.

2. Includes a resin composition, The average value of the in-plane phase difference Re is 0.8 nm or more and 4.0 nm or less. The phase difference Rth in the thickness direction at a wavelength of 590 nm is between -35.0 nm and -5.0 nm. The aforementioned resin composition contains an acrylic resin and has a glass transition temperature of 118°C or higher. The acrylic resin is an optical film having a methyl methacrylate unit content of 98% by weight or more and a triple-link syndiotacticity of 55% or more.

3. The optical film according to claim 1 or 2, wherein the acrylic resin has a weight-average molecular weight of 80,000 or more and 200,000 or less, and a polydispersity of 1.6 or more and 2.5 or less.

4. The optical film according to claim 1 or 2, wherein the resin composition has an aromatic vinyl unit content of 0% by weight or more and 8% by weight or less.

5. The optical film according to claim 4, wherein the resin composition has a styrene unit content of 0% by weight or more and 8% by weight or less.

6. The optical film according to claim 1 or 2, further comprising a methyl methacrylate-styrene copolymer in the resin composition.

7. The optical film according to claim 6, wherein the methyl methacrylate-styrene copolymer has a weight-average molecular weight of 80,000 or more and 200,000 or less, and a polydispersity of 1.6 or more and 2.5 or less.

8. The optical film according to claim 1 or 2, wherein the resin composition has a 5% weight loss temperature of 330°C or higher.

9. The optical film according to claim 1 or 2, wherein the internal haze is 1.0% or less.

10. An optical film according to claim 1 or 2, which does not contain an ultraviolet absorber.

11. The optical film according to claim 1 or 2, wherein the optical film is a biaxially oriented film.

12. A polarizing plate comprising the optical film according to claim 1 or 2.

13. A liquid crystal panel comprising the polarizing plate described in claim 12.

14. A resin composition containing an acrylic resin, The glass transition temperature is 118°C or higher. The birefringence-producing Δnxy is -1.0 × 10⁻⁶ －３ Above -0.1 × 10 －３ The following: The aromatic vinyl unit content is 0% by weight or more and 8% by weight or less. The temperature at which the 5% weight loss occurs is 330°C or higher. The acrylic resin is a resin composition having a methyl methacrylate unit content of 98% by weight or more and a triplet syndiotacticity of 55% or more.

15. The resin composition according to claim 14, wherein the styrene unit content is 0% by weight or more and 8% by weight or less.

16. The resin composition according to claim 14 or 15, further comprising a methyl methacrylate-styrene copolymer.

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