Polarizing plates and liquid crystal display devices

Abstract

To provide a polarizing plate which is composed of an optical film that exhibits negative birefringence, and which has high productivity and process adaptability and excels in view angle characteristic.SOLUTION: Provided is a polarizing plate that is arranged, on at least one face side of a polarizer, with an optical film having: a refractive index measured at wavelength 589 nm, of 1.50 or less; an out-of-place phase difference Rth indicated by formula (a), measured at wavelength 589nm, of -200 to -20 nm; an in-plane phase difference Re indicated by formula (b), measured at wavelength 589 nm, of 30 to 300 nm; and a ratio (R450 / R550) of an in-plane phase difference Re (R450) measured at wavelength 450 nm with respect to an in-plane phase difference Re (R550) measured at wavelength 550 nm, of less than 1.03. (a): Rth=[(nx+ny) / 2-nz]×d, (b):Re=(ny-nx)×d. In the formulas, nx indicates a refractive index in a fast axis direction in plane of a film, ny indicates a refractive index in a slow axis direction in plane of a film, nz indicates a refractive index in a vertical direction out of plane of a film, and d indicates thickness of a film.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a polarizing plate that can be suitably used for a liquid crystal display device, an organic electroluminescence (organic EL) display, etc., and the present invention also relates to a liquid crystal display device using the above polarizing plate.

Background Art

[0002] Liquid crystal displays are widely used in mobile phones, computer monitors, notebook computers, televisions, etc. as the most important display devices in the multimedia society. Many optical films are used for the polarizing plates used in liquid crystal displays to improve display characteristics such as contrast improvement when viewed from the front or obliquely, and color tone compensation.

[0003] Typical examples of optical films related to polarizing plates include retardation films. Retardation films are used as antireflection layers for liquid crystal display devices, touch panels, and organic ELs.

[0004] Conventional retardation films use polycarbonate and cyclic polyolefin, and these polymers all have polymers with positive birefringence. Here, the positive and negative of birefringence are defined as follows.

[0005] The optical anisotropy of a polymer film with molecular orientation by stretching or the like can be represented by a refractive index ellipsoid in which the refractive index in the direction of the fast axis in the film plane when the film is stretched is nx, the refractive index in the direction in the film plane perpendicular to it (slow axis) is ny, and the refractive index in the film thickness direction is nz.

[0006] That is, in the uniaxial stretching of a polymer having negative birefringence, the refractive index in the stretching axis direction is small (fast axis: stretching direction), and in the uniaxial stretching of a polymer having positive birefringence, the refractive index in the axis direction perpendicular to the stretching axis direction is small (fast axis: direction perpendicular to the stretching direction).

[0007] Furthermore, the in-plane phase difference (Re) is expressed as the product of the refractive index in the direction perpendicular to the phase-advancing axis (ny) minus the refractive index in the phase-advancing axis direction (nx) multiplied by the film thickness.

[0008] Many polymers exhibit positive birefringence. Acrylic resins and polystyrene are examples of polymers with negative birefringence, but acrylic resins exhibit little phase difference and are not sufficiently suitable as optical compensation films. Polystyrene has challenges in terms of phase difference stability, such as a large photoelastic coefficient at room temperature which causes the phase difference to change with even slight stress, as well as challenges in optical properties such as a large wavelength dependence of the phase difference, and practical challenges such as low heat resistance, so it is not currently used.

[0009] Wavelength dependence of phase difference means that the phase difference changes depending on the measurement wavelength, and can be expressed as the ratio R450 / R550 of the phase difference measured at a wavelength of 450 nm (R450) and the phase difference measured at a wavelength of 550 nm (R550). Generally, polymers with aromatic structures tend to have a large R450 / R550 ratio, which reduces contrast and viewing angle characteristics in the low-wavelength region.

[0010] Stretched polymer films exhibiting negative birefringence have a high refractive index in the film's thickness direction, resulting in unique phase difference performance. This is expected to improve viewing angle characteristics through the use of unprecedented polarizing plate and liquid crystal display device configurations.

[0011] There is strong market demand for polarizers having phase difference films that exhibit such negative birefringence. Various phase difference films have been developed to meet the above-mentioned required characteristics.

[0012] Methods have been proposed for manufacturing films in which the refractive index in the thickness direction of the film is increased using polymers with positive birefringence. One method involves bonding a heat-shrinkable film to one or both sides of a polymer film and then heat-stretching the laminate to apply a shrinking force in the thickness direction of the polymer film (see, for example, Patent Documents 1-3). Another method has been proposed in which the polymer film is uniaxially stretched in plane while an electric field is applied to it (see, for example, Patent Document 4).

[0013] Furthermore, a phase difference film consisting of fine particles with negative optical anisotropy and a transparent polymer has been proposed (see, for example, Patent Document 5).

[0014] Furthermore, Patent Document 6.7 proposes an optical film with a high refractive index in the thickness direction. [Prior art documents] [Patent Documents]

[0015] [Patent Document 1] Patent No. 2818983 [Patent Document 2] Japanese Patent Application Publication No. 05-297223 [Patent Document 3] Japanese Patent Application Publication No. 05-323120 [Patent Document 4] Japanese Patent Application Publication No. 06-088909 [Patent Document 5] Japanese Patent Publication No. 2005-156862 [Patent Document 6] Japanese Patent Publication No. 2008-064817 [Patent Document 7] Japanese Patent Publication No. 2011-107281 [Overview of the project] [Problems that the invention aims to solve]

[0016] However, the methods proposed in Patent Documents 1-4 have drawbacks, such as low productivity due to the extremely complex manufacturing process. Furthermore, controlling the uniformity of the phase difference becomes significantly more difficult compared to conventional stretching methods.

[0017] Furthermore, the optical compensation film obtained in Patent Document 5 is a phase difference film having negative birefringence due to the addition of fine particles having negative optical anisotropy, and it has problems with uniform dispersion of fine particles, uniform orientation control, and film transparency.

[0018] There is a demand for a polarizing plate that is highly productive and process adaptable, made of an optical film exhibiting negative birefringence, and has excellent viewing angle characteristics.

[0019] In recent years, there has been a demand for a polarizing plate and a liquid crystal display device that have excellent viewing angle characteristics with a low luminance (black luminance) when viewed from an oblique direction. This is because a high-contrast polarizing plate and liquid crystal display device can be obtained by reducing the black luminance. However, Patent Documents 6 and 7 do not describe or suggest a polarizing plate and liquid crystal display device with a low black luminance.

Means for Solving the Problems

[0020] As a result of intensive studies by the present inventors, it has been found that a polarizing plate using an optical film having specific properties can solve the above problems, and the present invention has been completed.

[0021] That is, it relates to a polarizing plate characterized in that an optical film having a refractive index measured at a wavelength of 589 nm of 1.50 or less, an out-of-plane retardation Rth measured at a wavelength of 589 nm represented by the following formula (a) of -400 to -20 nm, an in-plane retardation Re measured at a wavelength of 589 nm represented by the following formula (b) of 30 to 400 nm, and a ratio (R450 / R550) of Re (R450) measured at a wavelength of 450 nm to Re (R550) measured at a wavelength of 550 nm of less than 1.03 is disposed on at least one side of the polarizer. Rth = [(nx + ny) / 2 - nz] × d (a) Re = (ny - nx) × d (b) (In the formula, nx represents the refractive index in the advancing axis direction in the film plane, ny represents the refractive index in the slow axis direction in the film plane, nz represents the refractive index in the vertical direction outside the film plane, and d represents the film thickness.)

Effects of the Invention

[0022] According to the present invention, by placing an optical film exhibiting specific negative birefringence on at least one side of a polarizer, a polarizer with high productivity, process adaptability, and excellent viewing angle characteristics can be obtained. By using a polarizer with a different phase difference combination than conventional polarizers with a film having a positive phase difference, further improvements in the viewing angle characteristics of displays can be made. The polarizer is useful as a polarizer for liquid crystal displays and as an anti-reflective polarizer.

[0023] Furthermore, in a liquid crystal display device equipped with a polarizing plate of the present invention having an optical film that exhibits a specific negative birefringence, and a polarizing plate having an optical film that exhibits negative birefringence with a different phase difference, viewing angle characteristics such as low black brightness and high contrast can be improved. [Modes for carrying out the invention]

[0024] A polarizing plate according to one aspect of the present invention (hereinafter referred to as "the polarizing plate of the present invention") will be described in detail below.

[0025] The polarizing plate of the present invention is characterized in that an optical film (hereinafter referred to as optical film (A)) is placed on at least one side of the polarizer, having a refractive index of 1.50 or less measured at a wavelength of 589 nm, an out-of-plane phase difference Rth measured at a wavelength of 589 nm as shown in formula (a) below, an in-plane phase difference Re measured at a wavelength of 589 nm as shown in formula (b) below, an in-plane phase difference Re (R450 / R550) of less than 1.03 measured at a wavelength of 450 nm (R450 / R550). Rth = [(nx + ny) / 2 - nz] × d (a) Re = (ny - nx) × d (b) (In the formula, nx represents the refractive index in the phase-advancing axis direction within the film plane, ny represents the refractive index in the phase-slow axis direction within the film plane, nz represents the refractive index in the perpendicular direction outside the film plane, and d represents the film thickness.) An optical film can be represented by a refractive index ellipsoid, where nx is the refractive index in the direction of the phase-advancing axis within the film plane, ny is the refractive index in the direction perpendicular to it within the film plane, and nz is the refractive index in the thickness direction of the film.

[0026] Negative birefringence is when the direction of stretching is aligned with the phase-advancing axis, while positive birefringence is when the direction perpendicular to the stretching is aligned with the phase-advancing axis.

[0027] In other words, resins in which the refractive index in the axial direction perpendicular to the stretching axis decreases when uniaxially stretched (progressive axis: perpendicular to the stretching direction) are said to exhibit positive birefringence, and resins in which the refractive index in the axial direction of the stretching axis decreases when uniaxially stretched (progressive axis: stretching direction) are said to exhibit negative birefringence.

[0028] Resins exhibiting positive birefringence have a smaller refractive index in the thickness direction perpendicular to the stretching direction, resulting in a larger positive out-of-plane phase difference (Rth). On the other hand, resins exhibiting negative birefringence have a larger refractive index in the thickness direction perpendicular to the stretching direction, resulting in a larger negative out-of-plane phase difference (Rth). Rth is expressed by equation (a). Furthermore, both resins exhibiting positive and negative birefringence exhibit a refractive index difference in the axial direction perpendicular to the stretching direction when stretched, resulting in an in-plane phase difference (Re) expressed by equation (b).

[0029] In the optical film (A) used in the polarizing plate of the present invention, the polarizing plate has excellent viewing angle characteristics such as low black brightness and high contrast, and therefore the refractive index measured at a wavelength of 589 nm is 1.50 or less, preferably 1.49 or less, more preferably 1.30 to 1.49, and particularly preferably 1.30 to 1.48.

[0030] The Rth measured at 589 nm as shown in formula (a) above is -400 to -20 nm, preferably -160 to -40 nm, and particularly preferably -140 to -60 nm, as this results in a polarizer with excellent viewing angle characteristics such as low black brightness and high contrast.

[0031] In the optical film (A), the Re measured at 589 nm as shown in formula (b) above is 30 to 400 nm, preferably 40 to 250 nm, and particularly preferably 60 to 230 nm, because this results in a polarizing plate with excellent viewing angle characteristics such as low black brightness and high contrast.

[0032] In optical film (A), the ratio (R450 / R550) of Re(R450) measured at a wavelength of 450 nm to Re(R550) measured at a wavelength of 550 nm is less than 1.03, preferably 1.02 or less, more preferably 0.70 to 1.02, and particularly preferably 0.80 to 1.01, in order to produce a polarizer with excellent viewing angle characteristics.

[0033] In the optical film (A), the thickness is preferably 30.0 μm or less, more preferably 0.1 to 25.0 μm, and most preferably 1 to 20.0 μm, from the viewpoint of suitability for thinning of optical components.

[0034] Examples of resins used as raw materials for the optical film (A) include fumarate ester resins, itaconic acid ester resins such as dimethyl itaconic acid ester, diethyl itaconic acid ester, diisopropyl itaconic acid ester, di-s-butyl itaconic acid ester, di-t-butyl itaconic acid ester, and dicyclohexyl itaconic acid ester, and β-glucan resins such as β-1,3-glucan, β-(1,3)-(1,4)-glucan, and β-(1,3)-(1,6)-glucan. Among these, fumarate ester resins are preferred because they exhibit excellent negative birefringence.

[0035] As a resin used as a raw material for optical film (A), a fumarate ester resin that is preferably used is one that contains 50 mol% or more, preferably 70 mol% or more, particularly preferably 80 mol% or more, and even more preferably 90 mol% or more, of the fumarate ester residue units represented by the following formula (1), as it makes a polarizing plate with excellent heat resistance and mechanical properties.

[0036] [ka]

[0037] (In the formula, R1 and R2 each independently represent one of the group consisting of a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 3 to 12 carbon atoms, or a cyclic alkyl group having 3 to 6 carbon atoms.) In formula (1), R1 and R2 each independently represent one of the group consisting of a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 3 to 12 carbon atoms, or a cyclic alkyl group having 3 to 6 carbon atoms. The alkyl group may be substituted with a halogen group such as a fluorine atom or a chlorine atom; an ether group; an ester group; or an amino group.

[0038] Specific examples of R1 and R2 include ethyl group, isopropyl group, s-butyl group, t-butyl group, s-pentyl group, t-pentyl group, s-hexyl group, t-hexyl group, cyclopropyl group, cyclopentyl group, and cyclohexyl group. Among these, it is preferable that R1 and R2 be one of the group consisting of ethyl group, isopropyl group, s-butyl group, t-butyl group, cyclopentyl group, and cyclohexyl group, as this results in a phase difference film with excellent heat resistance and mechanical properties. In particular, isopropyl group is preferred because it results in a polarizing plate with an excellent balance of heat resistance and mechanical properties.

[0039] Here, examples of fumarate diester residue units represented by formula (1) include diisopropyl fumarate, di-s-butyl fumarate, di-t-butyl fumarate, di-s-pentyl fumarate, di-t-pentyl fumarate, di-s-hexyl fumarate, di-t-hexyl fumarate, dicyclopropyl fumarate, dicyclopentyl fumarate, and dicyclohexyl fumarate, with diisopropyl fumarate, di-s-butyl fumarate, di-t-butyl fumarate, dicyclopentyl fumarate, and dicyclohexyl fumarate being preferred, and diisopropyl fumarate being particularly preferred.

[0040] The fumarate diester resin may contain residue units other than the residue unit shown in formula (1). Examples of residue units other than the residue unit shown in formula (1) include one or more of the following: styrene residues such as styrene residues and α-methylstyrene residues; acrylic acid residues; acrylic acid ester residues such as methyl acrylate residues, ethyl acrylate residues, and butyl acrylate residues; methacrylic acid residues; methacrylic acid ester residues such as methyl methacrylate residues, ethyl methacrylate residues, and butyl methacrylate residues; vinyl ester residues such as vinyl acetate residues and vinyl propionate residues; acrylonitrile residues; methacrylonitrile residues; olefin residues such as ethylene residues and propylene residues.

[0041] Fumarate ester resins exhibit particularly excellent mechanical properties and superior stretchability as single films. Therefore, the number-average molecular weight (Mn) obtained from the elution curve measured by gel permeation chromatography (GPC), in terms of standard polystyrene, is preferably 100,000 or more, more preferably between 100,000 and 5,000,000, and particularly preferably between 120,000 and 300,000.

[0042] In the polarizing plate of the present invention, the optical film (A) contains, from the viewpoint of in-plane phase difference expression, preferably 81 to 100% by weight, more preferably 90 to 100% by weight, and particularly preferably 95 to 100% by weight, an ester resin with a number average molecular weight of 100,000 or more, which contains 50 mol% or more of fumarate ester residue units represented by formula (1).

[0043] The fumarate ester resin can be produced by any method as long as the fumarate ester resin can be obtained, and it can be produced by radical polymerization.

[0044] Any of the following methods can be used for radical polymerization: bulk polymerization, solution polymerization, suspension polymerization, precipitation polymerization, emulsion polymerization, etc.

[0045] The polarizing plate of the present invention can also be characterized in that an optical film (B) is laminated on an optical film (A) and has an optical film (B) on at least one side of the polarizer, the optical film (B) having a refractive index of 1.70 or less measured at a wavelength of 589 nm, an out-of-plane phase difference Rth of 20 to 200 nm measured at a wavelength of 589 nm as shown in formula (a), an in-plane phase difference Re of 0 to 100 nm measured at a wavelength of 589 nm as shown in formula (b), and a ratio (R450 / R550) of 1.09 or less between the in-plane phase difference Re(R450) measured at a wavelength of 450 nm and the in-plane phase difference Re(R550) measured at a wavelength of 550 nm.

[0046] The polarizing plate of the present invention exhibits excellent viewing angle characteristics such as low black brightness and high contrast by laminating optical film (A) and optical film (B).

[0047] Because the out-of-plane phase difference Rth of optical film (A) is negative and the out-of-plane phase difference Rth of optical film (B) is positive, it becomes possible to adjust the out-of-plane phase difference Rth during lamination to any desired value.

[0048] Stretched polymer films exhibiting negative birefringence exhibit unique phase difference performance. Therefore, by combining them with films that have a positive phase difference and other films with different phase differences than conventional ones, it becomes possible to compensate for the viewing angle characteristics of displays and polarizers.

[0049] The in-plane phase difference Re measured at a wavelength of 589 nm, as shown by formula (b) for the laminated film in which optical film (A) and optical film (B) are laminated, used in the polarizing plate of the present invention, can be controlled by adjusting the in-plane phase difference Re of film (A) and film (B). Since this results in a polarizing plate with excellent viewing angle characteristics such as low black brightness and high contrast, the wavelength is preferably 30 to 300 nm, more preferably 60 to 200 nm, and particularly preferably 100 to 150 nm.

[0050] The out-of-plane phase difference Rth of the laminated film, measured at a wavelength of 589 nm as shown in equation (a), can be controlled by adjusting the out-of-plane phase difference Rth of film (A) and film (B). Since this results in a polarizer with excellent viewing angle characteristics such as low black brightness and high contrast, the phase difference is preferably -100 to 100 nm, more preferably -40 to 40 nm, and particularly preferably -20 to 20 nm.

[0051] The ratio (R450 / R550) of the in-plane phase difference Re(R450) measured at a wavelength of 450 nm to the in-plane phase difference Re(R550) measured at a wavelength of 550 nm of the laminated film is preferably 1.06 or less, more preferably 1.02 or less, even more preferably 0.70 to 1.00, and particularly preferably 0.80 to 0.98, as this results in a polarizer with excellent viewing angle characteristics.

[0052] From the viewpoint of suitability for thinning of optical components, the thickness of the laminated film is preferably 110.0 μm or less, more preferably 0.2 to 70.0 μm, and most preferably 2 to 50.0 μm.

[0053] In laminated films, the angle between the phase advance axes of optical film (A) and optical film (B) and the direction of transport and stretching of the film's longitudinal axis can be set according to the purpose. Among these, a polarizing plate exhibits excellent viewing angle characteristics such as low black brightness and high contrast, and improves productivity and process adaptability during film lamination. Therefore, an angle of 0 degrees ± 10 degrees or less, or 90 degrees ± 10 degrees or less, is preferable.

[0054] The optical film (B) in the laminated film in which optical film (A) and optical film (B) are laminated, used in the polarizing plate of the present invention, will be described in detail below.

[0055] From the viewpoint of suitability for thinning of optical components, the thickness of the optical film (B) is preferably 80.0 μm or less, more preferably 0.1 to 40.0 μm, and most preferably 1 to 25.0 μm.

[0056] In the optical film (B) used in the polarizing plate of the present invention, the refractive index measured at a wavelength of 589 nm is preferably 1.70 or less, more preferably 1.30 to 1.52, and particularly preferably 1.30 to 1.48, in order to produce a polarizing plate with excellent viewing angle characteristics such as low black brightness and high contrast.

[0057] The in-plane phase difference Re of optical film (B), measured at a wavelength of 589 nm as shown in equation (b), is 0 to 100 nm, more preferably 0 to 80 nm, and particularly preferably 0 to 60 nm, because the laminated film is a thin film with low black brightness and excellent viewing angle characteristics such as high contrast, making it a polarizer. Since the stretched film (A) has a large in-plane phase difference Re, even in the case of film (B) with a small in-plane phase difference Re, excellent optical properties can be exhibited in the laminated film.

[0058] The out-of-plane phase difference Rth of optical film (B), measured at a wavelength of 589 nm as shown in equation (a), is 20 to 200 nm, more preferably 50 to 170 nm, and particularly preferably 80 to 140 nm, because the laminated film of film (A) and film (B) is a polarizer with excellent viewing angle characteristics such as low black brightness and high contrast in a thin film.

[0059] The ratio (R450 / R550) of the in-plane phase difference Re(R450) measured at a wavelength of 450 nm to the in-plane phase difference Re(R550) measured at a wavelength of 550 nm of the optical film (B) is 1.09 or less, more preferably 1.02 or less, even more preferably 0.70 to 1.01, and particularly preferably 0.80 to 0.98, in order to produce a polarizer with excellent viewing angle characteristics.

[0060] Such a film (B) can be obtained, for example, by forming a film of a polymer with positive birefringence, or by stretching the formed film. The polymer with positive birefringence is not particularly limited as long as it is a polymer with positive birefringence, and examples of such polymers with good heat resistance and transparency include polycarbonate resin, polyethersulfone resin, polyarylate resin, polyimide resin, cyclic olefin resin, cellulose resin, and N-substituted maleimide resin. Among these, cyclic olefin resin and cellulose resin are particularly preferred because they produce a polarizer with excellent viewing angle characteristics when laminated with an optical film (A).

[0061] The polarizing plate of the present invention is suitably used in polarizing plates for applications such as liquid crystal display devices and organic EL display devices.

[0062] The polarizer used in the polarizing plate of the present invention converts natural light or any polarized light into linearly polarized light. Any suitable polarizer can be used depending on the purpose. For example, hydrophilic polymer films such as polyvinyl alcohol-based films, partially formalized polyvinyl alcohol-based films, and partially saponified ethylene-vinyl acetate copolymer films are uniaxially stretched after adsorbing dichroic substances such as iodine or dichroic dyes, and polyene-based oriented films such as dehydrated polyvinyl alcohol or dehydrochlorinated polyvinyl chloride are also used. In addition, guest-host type polarizers in which a liquid crystalline composition containing a dichroic substance and a liquid crystalline compound is oriented in a certain direction, as disclosed in U.S. Patent No. 5523863, etc., and E-type polarizers in which lyotropic liquid crystals are oriented in a certain direction, as disclosed in U.S. Patent No. 6049428, etc., can also be used.

[0063] The polarizing plate of the present invention can be suitably used in liquid crystal displays, organic electroluminescent (OLED) displays, and the like by arranging the optical film (A) of the present invention, or a laminated film of optical film (A) and optical film (B), on at least one side of the polarizer.

[0064] Specific arrangements of the optical film (A) or the laminated film of optical film (A) and optical film (B) in the polarizing plate include optical film (A) / polarizer, optical film (A) / polarizer / optical film (A), optical film (A) / optical film (B) / polarizer, optical film (B) / optical film (A) / polarizer, optical film (A) / optical film (B) / polarizer / optical film (B) / optical film (A), optical film (B) / optical film (A) / polarizer / optical film (A) / optical film (B), etc. Additional optical films may be added to the polarizing plate as needed to improve the strength or environmental stability of the polarizing plate.

[0065] There are no particular limitations on the type of liquid crystal display device used in the polarizing plate of the present invention, and any type of transmissive, reflective, or reflective-semitransmissive device can be used. Examples of liquid crystal cells used in the liquid crystal display device include various liquid crystal cells such as twisted nematic (TN) mode, super-twisted nematic (STN) mode, horizontal alignment (ECB) mode, vertical alignment (VA) mode, in-plane switching (IPS) mode, bend nematic (OCB) mode, ferroelectric liquid crystal (SSFLC) mode, and antiferroelectric liquid crystal (AFLC) mode. Of these, it is particularly preferable to use a liquid crystal cell of TN mode, VA mode, IPS mode, or OCB mode in the optical film and polarizing plate of the present invention.

[0066] By using the polarizing plate according to the present invention in such various liquid crystal cells, contrast, hue, and viewing angle characteristics can be improved.

[0067] A liquid crystal display device according to one aspect of the present invention (hereinafter referred to as "the liquid crystal display device of the present invention") will be described in detail below.

[0068] The liquid crystal display device of the present invention comprises a polarizing plate of the present invention (hereinafter referred to as the "first polarizing plate") and a second polarizing plate on which an optical film (C) having a thickness of 40 μm or less, with a refractive index of 1.70 or less measured at a wavelength of 589 nm as shown in formula (a) and an out-of-plane phase difference Rth of -200 to -20 nm measured at a wavelength of 589 nm as shown in formula (b) and an in-plane phase difference Re of 0 to 10 nm measured at a wavelength of 589 nm as shown in formula (b), is disposed on at least one side of the polarizing plate, and a liquid crystal cell is disposed between the first polarizing plate and the second polarizing plate.

[0069] The liquid crystal display device of the present invention includes a first polarizing plate having an optical film (A) exhibiting negative birefringence or a laminated film of optical film (A) and optical film (B), and a second polarizing plate having an optical film (C) exhibiting negative birefringence with a different phase difference from optical films (A) and (B), thereby improving contrast, hue, and viewing angle characteristics.

[0070] The optical film (C) used in the liquid crystal display device of the present invention will be described in detail below.

[0071] From the viewpoint of suitability for thinning liquid crystal display devices, the thickness of the optical film (C) is preferably 40.0 μm or less, more preferably 0.1 to 30.0 μm, and most preferably 1 to 25.0 μm.

[0072] The in-plane phase difference Re of the optical film (C), measured at a wavelength of 589 nm as shown in equation (b), is preferably 0 to 10 nm, more preferably 0 to 5 nm, and particularly preferably 0 to 3 nm, in order to obtain a liquid crystal display device with better optical properties at a thinner film.

[0073] The out-of-plane phase difference Rth of the optical film (C), measured at a wavelength of 589 nm as shown in equation (a), is preferably -200 to -20 nm, more preferably -160 to -60 nm, and particularly preferably -140 to -80 nm, in order to produce a liquid crystal display device with thinner films and superior viewing angle characteristics.

[0074] In the optical film (C) used in the polarizing plate of the present invention, the refractive index measured at a wavelength of 589 nm is preferably 1.70 or less, more preferably 1.52 or less, even more preferably 1.30 to 1.52, and particularly preferably 1.30 to 1.48, in order to produce a polarizing plate with excellent viewing angle characteristics such as low black brightness and high contrast.

[0075] Since the optical film (C) is a film with an excellent balance of heat resistance and mechanical properties, it is preferable that it contains 81 to 100% by weight of a fumarate ester resin with a number average molecular weight of 100,000 or more, which contains 50 mol% or more of the fumarate ester residue units represented by formula (1).

[0076] The liquid crystal cells in the liquid crystal display device of the present invention are not particularly limited, and various liquid crystal cells can be used, such as those in twisted nematic (TN) mode, super-twisted nematic (STN) mode, horizontal alignment (ECB) mode, vertical alignment (VA) mode, in-plane switching (IPS) mode, bend nematic (OCB) mode, ferroelectric liquid crystal (SSFLC) mode, and antiferroelectric liquid crystal (AFLC) mode. Of these, the liquid crystal display device of the present invention preferably contains liquid crystal molecules that are homogeneously oriented in a field-free state. The orientation direction of liquid crystal molecules in a field-free state is referred to as the orientation direction of the liquid crystal molecules. Homogeneously oriented liquid crystal molecules are those in which the orientation vector of the liquid crystal molecules is parallel and uniformly oriented with respect to the substrate plane. The orientation vector of the liquid crystal molecules is slightly tilted with respect to the substrate plane and has pre-tilt. The liquid crystal cells used in the liquid crystal display device of the present invention preferably have a pre-tilt angle of 0.5° or less, and particularly preferably 0.3° or less. By having a pre-tilt angle of 0.5° or less for the liquid crystal cell, a liquid crystal panel can be obtained that exhibits high contrast even when viewed from an oblique angle, and has minimal hue change with changes in the viewing azimuth angle.

[0077] Liquid crystal cells containing homogeneously oriented liquid crystal molecules in an electroless state include in-plane switching (IPS) mode, fringe-field switching (FFS) mode, and ferroelectric liquid crystal (FLC) mode. Nematic liquid crystals and smectic liquid crystals are used as liquid crystal molecules. Generally, nematic liquid crystals are used in IPS mode and FFS mode liquid crystal cells, while smectic liquid crystals are used in FLC mode liquid crystal cells.

[0078] The difference Re2-Re1 between the in-plane phase difference Re(Re1) of the optical film (optical film (A), or a laminated film of optical film (A) and optical film (B)) of the first polarizing plate used in the liquid crystal display device of the present invention, measured at a wavelength of 589 nm as shown by formula (b), and the in-plane phase difference Re(Re2) of the liquid crystal cell, measured at a wavelength of 589 nm as shown by formula (b), is preferably 100-200 nm, more preferably 120-170 nm, and particularly preferably 130-160 nm, as this results in a thinner film with superior optical properties.

[0079] The out-of-plane phase difference Rth of the optical film (optical film (A), or a laminated film of optical film (A) and optical film (B)) used in the liquid crystal display device of the present invention, measured at a wavelength of 589 nm as shown by formula (a), is preferably -50 to 50 nm, more preferably -30 to 30 nm, and particularly preferably -20 to 20 nm relative to -0.6 × Re1, as this results in a thinner film with superior optical properties.

[0080] The polarizing plates and optical films (A), (B), and (C) used in the liquid crystal display devices of the present invention may contain plasticizers to improve processability. Examples of such plasticizers include aliphatic dibasic acid esters or phthalate esters.

[0081] Optical films (A), (B), and (C) may contain antioxidants to improve thermal stability. Examples of such antioxidants include hindered phenol antioxidants, phosphorus antioxidants, sulfur antioxidants, lactone antioxidants, amine antioxidants, hydroxylamine antioxidants, vitamin E antioxidants, and other antioxidants. These antioxidants may be used individually or in combination of two or more types.

[0082] Optical films (A), (B), and (C) may contain hindered amine-based light stabilizers or ultraviolet absorbers to enhance weather resistance. Examples of ultraviolet absorbers include benzotriazole, benzophenone, triazine, and benzoate.

[0083] Optical films (A), (B), and (C) may contain other polymers, surfactants, polymer electrolytes, conductive complexes, pigments, dyes, antistatic agents, antiblocking agents, lubricants, etc., to the extent that they do not exceed the spirit of the invention.

[0084] The optical films (A), (B), and (C) have a transmittance of preferably 85% or more, and more preferably 90% or more, in film form to avoid a decrease in the light intensity of the image display device. Here, the light transmittance represents the total light transmittance and is the value measured at a wavelength of 380 to 780 nm using a transmittance measuring device equipped with a white light source, in accordance with JIS K 7361-1 (1997 edition). Here, the total light transmittance is the value measured when the optical films (A), (B), and (C) of the present invention are formed into films with a thickness of 20 μm.

[0085] The haze of the optical films (A), (B), and (C) is preferably 3.0% or less, and more preferably 1.0% or less. By controlling the haze within the above range, a high-contrast image can be obtained when the films are incorporated into a display device as polarizing plates. Here, the haze is a value measured at a wavelength of 380 to 780 nm using a general haze meter equipped with a white light source, in accordance with JIS-K 7136 (2000 edition).

[0086] Optical films can be further laminated with films containing other resins as needed. Examples of other resins include polyethersulfone, polyarylate, polyethylene terephthalate, polynaphthalene terephthalate, polycarbonate, cyclic polyolefin, maleimide resins, fluororesins, and polyimides. It is also possible to laminate liquid crystal layers, hard coat layers, gas barrier layers, and layers with controlled refractive index (low-reflection layers).

[0087] There are no particular restrictions on the manufacturing method of the optical films (A) and (B). For example, they can be manufactured by forming a long film from the raw material resin using a method such as solution casting, and then stretching the film uniaxially or biaxially or more.

[0088] There are no particular restrictions on the manufacturing method of the optical film (C). For example, it can be manufactured by forming a long film from the raw material resin using a method such as solution casting. Alternatively, after manufacturing the film from a long film, the film may be further stretched uniaxially or biaxially or more.

[0089] Here, the solution casting method is a method in which a resin solution (generally called dope) is cast onto a support substrate, and then the solvent is evaporated by heating and drying, allowing the film to be peeled off the substrate.

[0090] In the solution casting method, any solvent capable of dissolving resins can be used as the solvent for the resin solution. However, to minimize residual solvent when obtaining the film, the boiling point of the solvent is preferably 200°C or lower, and more preferably 170°C or lower.

[0091] Examples of such solvents include halogenated hydrocarbons such as chloroform, dichloromethane, carbon tetrachloride, dichloroethane, tetrachloroethane, trichloroethylene, tetrachloroethylene, chlorobenzene, and dichlorobenzene; phenols such as phenol and chlorophenol; aromatic hydrocarbons such as benzene, toluene, xylene, methoxybenzene, mesitylene, and dimethoxybenzene; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, cyclopentanone, 2-pyrrolidone, and N-methyl-2-pyrrolidone; and ester solvents such as ethyl acetate and butyl acetate. Solvents include alcohol-based solvents such as t-butyl alcohol, glycerin, ethylene glycol, triethylene glycol, ethylene glycol monomethyl ether, diethylene glycol dimethyl ether, propylene glycol, dipropylene glycol, and 2-methyl-2,4-pentanediol; amide-based solvents such as dimethylformamide and dimethylacetamide; nitrile-based solvents such as acetonitrile and butyronitrile; ether-based solvents such as diethyl ether, dibutyl ether, and tetrahydrofuran; and solvents such as carbon disulfide, ethyl cellosolve, and butyl cellosolve, either alone or in combination.

[0092] The viscosity of the resin solution can be adjusted by the molecular weight, concentration, and type of solvent of each component. There are no particular restrictions on the viscosity of the resin solution, but to facilitate film casting, it is preferably 100 to 30,000 cps, more preferably 300 to 20,000 cps, and most preferably 300 to 15,000 cps.

[0093] In the present invention, the concentration of the raw material resin relative to the dope is not particularly limited as long as dissolution and film formation are possible. The dissolution method may be carried out by dissolving the resin to a predetermined concentration at the dissolution stage, or by preparing a low-concentration solution in advance and then adjusting it to a predetermined high-concentration solution in a concentration step. Furthermore, a predetermined low-concentration resin solution may be obtained by adding various additives to a high-concentration resin solution in advance.

[0094] Furthermore, there are no particular restrictions on the supporting substrate used, and examples include polymer substrates made of polyesters such as polyethylene terephthalate and polyethylene naphthalate, polycarbonates, polystyrene, polyethylene, polypropylene, polyacrylic, polyvinyl chloride and polyvinylidene chloride, cellulose such as cellulose acetate and cellulose ether, polyvinyl alcohol, polyamide, polyimide, polyarylate, polysulfone and polyethersulfone, polyetherketone, phenolic resin, epoxy resin, aliphatic cyclic polyolefin, norbornene-based thermoplastic transparent resin, etc., glass substrates such as glass plates and quartz substrates, metal substrates such as aluminum, stainless steel and ferrotype, and inorganic substrates such as ceramic substrates. Preferably, the above substrates are polymer substrates such as polyesters such as polyethylene terephthalate and polyethylene naphthalate, polypropylene, polyacrylic, cellulose such as cellulose acetate and cellulose ether, polyimide, aliphatic cyclic polyolefin, norbornene-based thermoplastic transparent resin. Particularly preferred are polymer substrates such as polyesters such as polyethylene terephthalate and polyethylene naphthalate, polypropylene, polyimide, aliphatic cyclic polyolefin, norbornene-based thermoplastic transparent resin.

[0095] The casting method is not particularly limited, and any conventional method can be used. Examples include the T-die method, doctor blade method, bar coater method, slot die method, lip coater method, reverse gravure coating method, microgravure method, spin coating method, brush coating method, roll coating method, and flexographic printing method.

[0096] The drying method in the drying process is not particularly limited, and conventional heating methods can be used. Examples include hot air blowers, heating rollers, and far-infrared heaters.

[0097] The drying temperature is preferably 30 to 200°C, and particularly preferably 40 to 160°C. It is also acceptable to use a single drying stage, or to maintain appearance and shorten drying time, a multi-stage drying method is used, where the first stage is dried at a low temperature and subsequent stages at high temperatures.

[0098] The film peeling speed in the substrate peeling process can preferably be in the range of 0.1 to 30 m / min, and more preferably in the range of 1 to 30 m / min, considering factors such as productivity, mechanical precision, and stability.

[0099] The phase difference can be controlled by stretching the obtained film uniaxially or biaxially to obtain the optical films (A), (B), and (C) of the present invention. Examples of uniaxial stretching methods include longitudinal uniaxial stretching, which stretches between rolls, and transverse axial stretching, which stretches using a tenter. Examples of biaxial stretching methods include stretching using a tenter and stretching by inflating into a tube shape.

[0100] The temperature during stretching is preferably 90 to 300°C, and particularly preferably 105 to 250°C, as this minimizes thickness variations and results in a polarizing plate with excellent mechanical and optical properties.

[0101] The stretching ratio of the film (hereinafter referred to as "stretching ratio") is preferably 1.05 to 4.0 times, more preferably 1.05 to 3.5 times, and particularly preferably 1.1 to 3.0 times, in order that the resulting film is thin and exhibits good phase difference characteristics.

[0102] The thickness of the film subjected to the stretching process is preferably 5 to 200 μm, more preferably 5 to 150 μm, and particularly preferably 5 to 100 μm, from the viewpoint of ease of stretching and suitability for thinning of optical components.

[0103] In this way, by adjusting the stretching temperature and stretching ratio, the in-plane phase difference of the resulting optical films (A), (B), and (C) can be controlled.

[0104] The film transport speed in the stretching process can preferably be in the range of 0.5 to 30 m / min, and more preferably in the range of 1 to 20 m / min, based on mechanical precision, stability, etc.

[0105] The manufacturing method of the present invention may include a shrinkage step in which the optical films (A), (B), and (C) obtained by the present invention are subjected to shrinkage treatment. Specifically, the stretched optical films (A), (B), and (C) are shrunk in the direction opposite to the stretching direction. This relieves residual stress accumulated in the stretched film, and the resulting optical films (A), (B), and (C) exhibit a high phase difference even after a long period of time. [Brief explanation of the drawing]

[0106] [Figure 1] A liquid crystal display device consisting of a polarizing plate (polarizer / film I), a liquid crystal cell, a polarizing plate (polarizer), and a light source. [Figure 2] A liquid crystal display device consisting of a polarizing plate (polarizer / film II / film I), liquid crystal cell, polarizing plate (polarizer), and light source. [Figure 3] A liquid crystal display device consisting of a polarizing plate (polarizer / film I), a liquid crystal cell, a polarizing plate (film III / polarizer), and a light source. [Figure 4] A liquid crystal display device consisting of a polarizing plate (polarizer / film II / film I), liquid crystal cell, polarizing plate (film III / polarizer), and light source. [Examples]

[0107] The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

[0108] The physical properties shown in the examples were measured by the following method. <Analysis of polymers (resins)> Structural analysis of the polymer was performed using a nuclear magnetic resonance spectrometer (JEOL, product name: JNM-GX270), specifically proton nuclear magnetic resonance spectroscopy. 1 The result was obtained from 1H-NMR spectral analysis. <Measurement of number-average molecular weight> Gel Permeation Chromatography (GPC) system (manufactured by Tosoh, product name: C0-8011 (column GMH) HRUsing a device equipped with -H, measurements were taken at 40°C with tetrahydrofuran or dimethylformamide as the solvent, and the value was determined as a standard polystyrene equivalent. <Measurement of phase difference characteristics (Rth, Re)> Using a polarization phase difference measurement system (manufactured by AxometrIcs, product name: AxoScan), the phase difference characteristics of the optical film were measured using light at a wavelength of 589 nm, the out-of-plane phase difference Rth measured at a wavelength of 589 nm as shown in equation (a), and the in-plane phase difference Re measured at a wavelength of 589 nm as shown in equation (b). <Measurement of wavelength dispersion characteristics (R450 / R550)> The wavelength dispersion characteristics of the optical film were measured using a polarization phase difference measurement system (manufactured by AxometrIcs, product name: AxoScan) as the ratio (R450 / R550) of the in-plane phase difference Re(450) measured at a wavelength of 450 nm and the in-plane phase difference Re(550) measured at a wavelength of 550 nm. <Measuring refractive index> The refractive index of the optical film was measured at a wavelength of 589 nm using a multi-wavelength Abbe refractometer (manufactured by Atago, product name: DR-M2).

[0109] Synthesis Example 1 In a 1-liter reactor equipped with a stirrer, condenser, nitrogen inlet tube, and thermometer, 600 g of distilled water, 3.4 g of hydroxypropyl methylcellulose (Shin-Etsu Chemical Co., Ltd., trade name Metroze 60SH-50) as a dispersant, 350.9 g of diisopropyl fumarate, 49.1 g of diethyl fumarate (14.0 parts by weight per 100 parts by weight of diisopropyl fumarate), and 8.3 g of t-butyl peroxypivalate as an oil-soluble radical initiator were added. After 1 hour of nitrogen bubbling, radical suspension polymerization was carried out by holding the mixture at 50°C for 28 hours while stirring at 400 rpm. After the polymerization reaction was complete, the contents were collected from the reactor, the polymer was filtered off, washed twice with distilled water and twice with methanol, and then dried under reduced pressure at 80°C (yield: 75%).

[0110] The number-average molecular weight of the obtained fumarate ester polymer was 138,000. 11H-NMR measurements confirmed that the polymer particles are a diisopropyl fumarate / diethyl fumarate copolymer with a diisopropyl fumarate residue unit / diethyl fumarate residue unit ratio of 86.7 / 13.3 (mol%).

[0111] Synthesis Example 2 In a 1-liter reactor equipped with a stirrer, condenser, nitrogen inlet tube, and thermometer, 600 g of distilled water, 3.4 g of hydroxypropyl methylcellulose (Shin-Etsu Chemical Co., Ltd., trade name Metroze 60SH-50) as a dispersant, 400.0 g of diisopropyl fumarate, and 8.3 g of t-butyl peroxypivalate as an oil-soluble radical initiator were added. After 1 hour of nitrogen bubbling, radical suspension polymerization was carried out by holding the mixture at 50°C for 24 hours while stirring at 400 rpm. After the polymerization reaction was complete, the contents were collected from the reactor, the polymer was filtered off, washed twice with distilled water and twice with methanol, and then dried under reduced pressure at 80°C (yield: 77%). The number-average molecular weight of the obtained diisopropyl fumarate polymer was 129,000.

[0112] Synthesis Example 3 In a 1-liter reactor equipped with a stirrer, condenser, nitrogen inlet tube, and thermometer, 600 g of distilled water, 3.4 g of hydroxypropyl methylcellulose (Shin-Etsu Chemical Co., Ltd., trade name Metroze 60SH-50) as a dispersant, 387.5 g of diisopropyl fumarate, 12.5 g of 3-ethyl-3-oxetanyl methyl acrylate (3.2 parts by weight per 100 parts by weight of diisopropyl fumarate), and 8.3 g of t-butyl peroxypivalate as an oil-soluble radical initiator were added. After 1 hour of nitrogen bubbling, radical suspension polymerization was carried out by holding the mixture at 50°C for 24 hours while stirring at 400 rpm. After the polymerization reaction was complete, the contents were collected from the reactor, the polymer was filtered off, washed twice with distilled water and twice with methanol, and then dried under reduced pressure at 80°C (yield: 73%).

[0113] The number-average molecular weight of the obtained fumarate ester polymer was 147,000. 1¹H-NMR measurement confirmed that the polymer particles are a diisopropyl fumarate-3-ethyl-3-oxetanyl methyl acrylate copolymer with a ratio of diisopropyl fumarate residue units to 3-ethyl-3-oxetanyl methyl acrylate residue units of 96.1 / 3.9 (mol%).

[0114] Synthesis Example 4 24.0 g of diisopropyl fumarate, 0.99 g of monoisopropyl fumarate (manufactured by Tokyo Chemical Industry Co., Ltd.), and 0.26 g of t-butyl peroxypivalate, a radical initiator, were placed in a 75 mL glass ampoule. After repeated nitrogen purging and pressure release, the ampoule was sealed under reduced pressure. Radical polymerization was carried out by placing this ampoule in a 50°C constant temperature bath and maintaining it for 24 hours. After the polymerization reaction was complete, the polymer was removed from the ampoule and dissolved in 200 g of tetrahydrofuran. This polymer solution was precipitated by dropping it into 4 L of hexane, and then vacuum dried at 80°C for 10 hours (yield: 76%).

[0115] The number-average molecular weight of the obtained fumarate ester polymer was 138,000. 1 ¹H-NMR measurements confirmed that the polymer particles are a diisopropyl fumarate / monoisopropyl fumarate copolymer with a ratio of diisopropyl fumarate residue units to monoisopropyl fumarate residue units of 93.4 / 6.6 (mol%).

[0116] Film (A) Example 1 19.4 g of the fumarate ester resin obtained in Synthesis Example 1 and 0.6 g of diisodecyl phthalate were dissolved in a methyl ethyl ketone solution to prepare an 18% by weight resin solution. This solution was poured onto a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray) using a coater, and dried in three stages at drying temperatures of 60°C, 120°C, and 140°C to produce a film with a thickness of 28 μm. The obtained film was cut into a 7 cm × 5 cm rectangle and uniaxially stretched longitudinally at 110°C to 1.35 times its length using a batch-type biaxial film stretching apparatus. The film thickness, refractive index, phase difference characteristics, and wavelength dispersion characteristics of the obtained optical film were measured. The results are shown in Table 1.

[0117] Film (A) Example 2 19.4 g of the fumarate ester resin obtained by Synthesis Example 1 and 0.6 g of diisodecyl phthalate were dissolved in a methyl ethyl ketone solution to prepare an 18% by weight resin solution. This solution was poured onto a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray) using a coater, and dried in three stages at drying temperatures of 60°C, 120°C, and 140°C to produce a film with a thickness of 24 μm. The obtained film was cut into a 7 cm × 5 cm rectangle and uniaxially stretched longitudinally to 1.4 times its length at 110°C using a batch-type biaxial film stretching apparatus. The film thickness, refractive index, phase difference characteristics, and wavelength dispersion characteristics of the obtained optical film were measured. The results are shown in Table 1.

[0118] Film (A) Example 3 19.2 g of the fumarate ester resin obtained by Synthesis Example 2 and 0.8 g of diisodecyl phthalate were dissolved in a toluene / methyl ethyl ketone = 4 / 6 (weight ratio) solution to prepare a 20% by weight resin solution. This solution was poured onto a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray) using a coater, and dried in three stages at drying temperatures of 80°C, 120°C, and 130°C to produce a film with a thickness of 17 μm. The obtained film was cut into a 7 cm × 5 cm rectangle and uniaxially stretched longitudinally to 1.4 times its length at 140°C using a batch-type biaxial film stretching apparatus. The film thickness, refractive index, phase difference characteristics, and wavelength dispersion characteristics of the obtained optical film were measured. The results are shown in Table 1.

[0119] Film (A) Example 4 19.2 g of the fumarate ester resin obtained by Synthesis Example 3 and 0.8 g of the ultraviolet absorber UV-1164 were dissolved in a toluene / methyl ethyl ketone = 1 / 9 (by weight) solution to prepare a 20% by weight resin solution. This solution was poured onto a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray) using a coater, and dried in two stages at drying temperatures of 80°C and 130°C to produce a film with a thickness of 20 μm. The obtained film was cut into a 7 cm × 5 cm rectangle and uniaxially stretched 1.6 times in the longitudinal direction of the film at 140°C using a batch-type biaxial film stretching apparatus. The film thickness, refractive index, phase difference characteristics, and wavelength dispersion characteristics of the obtained optical film were measured. The results are shown in Table 1.

[0120] Film (A) Example 5 19.4 g of the fumarate ester resin obtained in Synthesis Example 1 and 0.6 g of diisodecyl phthalate were dissolved in a methyl ethyl ketone solution to prepare a 20% by weight resin solution. This solution was poured onto a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray) using a coater, and dried in three stages at drying temperatures of 30°C, 50°C, and 80°C to produce a film with a thickness of 17 μm. The obtained film was cut into a 7 cm × 5 cm rectangle and uniaxially stretched longitudinally at 110°C to 1.75 times its length using a batch-type biaxial film stretching apparatus. The film thickness, refractive index, phase difference characteristics, and wavelength dispersion characteristics of the obtained optical film were measured. The results are shown in Table 1.

[0121] Film (A) Example 6 18.8 g of fumarate ester resin obtained by Synthesis Example 1, silicone 1.2 g of oil KF-54 (manufactured by Shin-Etsu Chemical Co., Ltd.) was dissolved in a methyl ethyl ketone solution to prepare an 18% by weight resin solution. This solution was poured onto a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray Industries) using a coater, and dried in three stages at drying temperatures of 60°C, 120°C, and 140°C to produce a film with a thickness of 31 μm. The obtained film was cut into a 7 cm × 5 cm rectangle and uniaxially stretched longitudinally at 120°C to 1.15 times its length using a batch-type biaxial film stretching apparatus. The film thickness, refractive index, phase difference characteristics, and wavelength dispersion characteristics of the obtained optical film were measured. The results are shown in Table 1.

[0122] Film (A) Example 7 20.0 g of the fumarate ester resin obtained by Synthesis Example 3 was mixed with toluene / A 20% by weight resin solution was prepared by dissolving the methyl ethyl ketone in a 4 / 6 (by weight) solution. This solution was poured onto a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray) using a coater, and dried in three stages at drying temperatures of 60°C, 120°C, and 140°C to produce a film with a thickness of 20 μm. The obtained film was cut into a 7 cm × 5 cm rectangle and uniaxially stretched longitudinally to 1.1 times its length at 140°C using a batch-type biaxial film stretching apparatus. The film thickness, refractive index, phase difference characteristics, and wavelength dispersion characteristics of the obtained optical film were measured. The results are shown in Table 1.

[0123] Film (A) Example 8 19.4 g of the fumarate ester resin obtained in Synthesis Example 1 and 0.6 g of diisodecyl phthalate were dissolved in a methyl ethyl ketone solution to prepare an 18% by weight resin solution. This solution was poured onto a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray) using a coater, and dried in two stages at drying temperatures of 30°C and 130°C to produce a film with a thickness of 22 μm. The obtained film was cut into a 7 cm × 5 cm rectangle and uniaxially stretched longitudinally at 110°C to 1.15 times its length using a batch-type biaxial film stretching apparatus. The film thickness, refractive index, phase difference characteristics, and wavelength dispersion characteristics of the obtained optical film were measured. The results are shown in Table 1.

[0124] Film (A) Example 9 20.0 g of the fumarate ester resin obtained by Synthesis Example 4 was dissolved in a toluene / methyl ethyl ketone = 4 / 6 (weight ratio) solution to obtain a 20% by weight resin solution. This solution was poured onto a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray) using a coater, and dried in three stages at drying temperatures of 60°C, 120°C, and 140°C to produce a film with a thickness of 24 μm. The obtained film was cut into a 7 cm × 5 cm rectangle and uniaxially stretched longitudinally at 140°C to 1.1 times its length using a batch-type biaxial film stretching apparatus. The film thickness, refractive index, phase difference characteristics, and wavelength dispersion characteristics of the obtained optical film were measured. The results are shown in Table 1.

[0125] Film (A) Example 10 19.4 g of the fumarate ester resin obtained by Synthesis Example 1 and 0.6 g of diisodecyl phthalate were dissolved in a methyl ethyl ketone solution to prepare an 18% by weight resin solution. This solution was poured onto a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray) using a coater, and dried in three stages at drying temperatures of 60°C, 120°C, and 140°C to produce a film with a thickness of 24 μm. The obtained film was cut into a 7 cm × 5 cm rectangle and uniaxially stretched longitudinally by 1.7 times at 110°C using a batch-type biaxial film stretching apparatus. The film thickness, refractive index, phase difference characteristics, and wavelength dispersion characteristics of the obtained optical film were measured. The results are shown in Table 1.

[0126] Film (A) Example 11 20.0 g of the fumarate ester resin obtained by Synthesis Example 4 was dissolved in a toluene / methyl ethyl ketone = 4 / 6 (weight ratio) solution to obtain a 20% by weight resin solution. This solution was poured onto a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray) using a coater, and dried in three stages at drying temperatures of 60°C, 120°C, and 140°C to produce a film with a thickness of 23 μm. The obtained film was cut into a 7 cm × 5 cm rectangle and uniaxially stretched longitudinally to 1.2 times its length at 140°C using a batch-type biaxial film stretching apparatus. The film thickness, refractive index, phase difference characteristics, and wavelength dispersion characteristics of the obtained optical film were measured. The results are shown in Table 1.

[0127] Film (A) Example 12 19.4 g of the fumarate ester resin obtained in Synthesis Example 1 and 0.6 g of diisodecyl phthalate were dissolved in a methyl ethyl ketone solution to prepare an 18% by weight resin solution. This solution was poured onto a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray) using a coater, and dried in three stages at drying temperatures of 60°C, 120°C, and 140°C to produce a film with a thickness of 28 μm. The obtained film was cut into a 7 cm × 5 cm rectangle and uniaxially stretched longitudinally to 1.2 times its length at 110°C using a batch-type biaxial film stretching apparatus. The film thickness, refractive index, phase difference characteristics, and wavelength dispersion characteristics of the obtained optical film were measured. The results are shown in Table 1.

[0128] Film (B) Example 1 20.0 g of cellulose acetate resin (manufactured by Fujifilm Wako Pure Chemical Industries) was dissolved in methylene chloride / methanol = 9 / 1 (by weight ratio) to prepare a 15% by weight resin solution. This solution was poured onto a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray Industries) using a coater, and dried in three stages at drying temperatures of 50°C, 80°C, and 130°C to form a film with a thickness of 26 μm. The thickness, refractive index, phase difference characteristics, and wavelength dispersion characteristics of the obtained optical film were measured. The results are shown in Table 2.

[0129] Film (B) Example 2 20.0 g of polycarbonate resin (manufactured by Mitsubishi Chemical) was dissolved in methylene chloride to prepare a 12% by weight resin solution. This solution was poured onto a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray) using a coater, and dried in three stages at drying temperatures of 50°C, 80°C, and 155°C to form a film with a thickness of 10 μm. The thickness, refractive index, phase difference characteristics, and wavelength dispersion characteristics of the obtained optical film were measured. The results are shown in Table 2.

[0130] Film (B) Example 3 20.0 g of ethylcellulose resin (manufactured by Dow Chemical) was dissolved in ethyl acetate to prepare a 15% by weight resin solution. This solution was poured onto a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray) using a coater, and a 30 μm thick film was formed by three-stage drying at drying temperatures of 50°C, 130°C, and 155°C. The film thickness, refractive index, phase difference characteristics, and wavelength dispersion characteristics of the obtained optical film were measured. The results are shown in Table 2.

[0131] Film (B) Example 4 20.0 g of polycarbonate resin (manufactured by Mitsubishi Chemical) was dissolved in methylene chloride to prepare a 12% by weight resin solution. This solution was poured onto a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray) using a coater, and dried in three stages at drying temperatures of 50°C, 80°C, and 155°C to produce a film with a thickness of 21 μm. The obtained film was cut into a 7 cm × 5 cm rectangle and uniaxially stretched longitudinally to 1.05 times its length at 150°C using a batch-type biaxial film stretching apparatus. The film thickness, refractive index, phase difference characteristics, and wavelength dispersion characteristics of the obtained optical film were measured. The results are shown in Table 1.

[0132] Film (B) Example 5 20.0 g of cellulose acetate resin (manufactured by Fujifilm Wako Pure Chemical Industries) was dissolved in methylene chloride / methanol = 9 / 1 (by weight ratio) to prepare a 15% by weight resin solution. This solution was poured onto a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray Industries) using a coater, and dried in three stages at drying temperatures of 50°C, 80°C, and 130°C to produce a film with a thickness of 26 μm. The obtained film was cut into a 7 cm × 5 cm rectangle and uniaxially stretched longitudinally to 1.40 times its length at 170°C using a batch-type biaxial film stretching apparatus. The film thickness, refractive index, phase difference characteristics, and wavelength dispersion characteristics of the obtained optical film were measured. The results are shown in Table 1.

[0133] Film (B) Example 6 20.0 g of cyclic olefin resin (manufactured by JSR) was dissolved in methylene chloride to prepare a 25% by weight resin solution. This solution was poured onto a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray) using a coater, and dried in three stages at drying temperatures of 50°C, 80°C, and 130°C to produce a film with a thickness of 46 μm. The obtained film was cut into a 7 cm × 5 cm rectangle and uniaxially stretched 1.5 times in the longitudinal direction of the film at 146°C using a batch-type biaxial film stretching apparatus. The film thickness, refractive index, phase difference characteristics, and wavelength dispersion characteristics of the obtained optical film were measured. The results are shown in Table 1.

[0134] Film (B) Example 7 20.0 g of ethylcellulose resin (manufactured by Dow Chemical) was dissolved in ethyl acetate to prepare a 15% by weight resin solution. This solution was poured onto a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray) using a coater, and dried in three stages at drying temperatures of 50°C, 130°C, and 155°C to produce a film with a thickness of 42 μm. The obtained film was cut into a 7 cm × 5 cm rectangle and uniaxially stretched longitudinally to 1.1 times its length at 140°C using a batch-type biaxial film stretching apparatus. The film thickness, refractive index, phase difference characteristics, and wavelength dispersion characteristics of the obtained optical film were measured. The results are shown in Table 2.

[0135] Film (C) Example 1 19.4 g of the fumarate ester resin obtained in Synthesis Example 3 and 0.6 g of diisodecyl phthalate were dissolved in a methyl ethyl ketone solution to prepare an 18% by weight resin solution. This solution was poured onto a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray) using a coater, and dried in three stages at drying temperatures of 60°C, 120°C, and 140°C to form a film with a thickness of 24 μm. The thickness, refractive index, and phase difference characteristics of the obtained optical film were measured. The results are shown in Table 3.

[0136] Film (C) Example 2 20.0 g of the fumarate ester resin obtained by Synthesis Example 4 was dissolved in a toluene / methyl ethyl ketone = 4 / 6 (weight ratio) solution to obtain a 20% by weight resin solution. This solution was poured onto a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray) using a coater, and dried in three stages at drying temperatures of 60°C, 120°C, and 140°C to form a film with a thickness of 23 μm. The thickness, refractive index, and phase difference characteristics of the obtained optical film were measured. The results are shown in Table 3.

[0137] Film (C) Example 3 18.8 g of fumarate ester resin obtained by Synthesis Example 3, silicone 1.2 g of oil KF-54 (manufactured by Shin-Etsu Chemical Co., Ltd.) was dissolved in a methyl ethyl ketone solution to prepare an 18% by weight resin solution. This solution was poured onto a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray Industries) using a coater, and a film with a thickness of 31 μm was formed by three-stage drying at drying temperatures of 60°C, 120°C, and 140°C. The thickness, refractive index, and phase difference characteristics of the obtained optical film were measured. The results are shown in Table 3.

[0138] Film (C) Example 4 19.2 g of the fumarate ester resin obtained by Synthesis Example 1 and 0.8 g of diisodecyl phthalate were dissolved in a toluene / methyl ethyl ketone = 4 / 6 (weight ratio) solution to prepare a 20% by weight resin solution. This solution was poured onto a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray) using a coater, and dried in three stages at drying temperatures of 80°C, 120°C, and 130°C to form a film with a thickness of 17 μm. The thickness, refractive index, and phase difference characteristics of the obtained optical film were measured. The results are shown in Table 3.

[0139] Film (D) Example 1 20.0 g of poly(N-vinylcarbazole) (manufactured by Tokyo Chemical Industry Co., Ltd.) was dissolved in cyclopentanone to prepare a 12% by weight resin solution. This solution was poured onto a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray Industries) using a coater, and dried in four stages at drying temperatures of 50°C, 80°C, 130°C, and 155°C to produce a film with a thickness of 12 μm. The obtained film was cut into a 7 cm × 5 cm rectangle and uniaxially stretched longitudinally to 1.20 times its length at 142°C using a batch-type biaxial film stretching apparatus. The film thickness, refractive index, phase difference characteristics, and wavelength dispersion characteristics of the obtained optical film were measured. The results are shown in Table 4.

[0140] [Table 1]

[0141] [Table 2]

[0142] [Table 3]

[0143] [Table 4]

[0144] <Evaluation of polarizing plates> The simulation was conducted using the LCDDMASTER simulator for liquid crystal displays manufactured by Syntec Corporation. The transmissive liquid crystal display device and liquid crystal cell were set to a dark state (black display), and calculations were performed at 5° intervals for an azimuth angle of 0° to 360° with a polar angle of 60°, to calculate the brightness (black brightness) when displaying black, and to find the maximum value.

[0145] Examples 1-2 A simulation was performed using a liquid crystal display device as the simulation model, which has a polarizer, an IPS liquid crystal cell, a film I, and another polarizer arranged in that order from the light source side. The arrangement of each element is as shown in Figure 1.

[0146] As shown in Table 5, simulations were performed using the refractive index, Re, Rth, and R450 / R550 measurements of film I, and the Re setting value of the liquid crystal cell. The simulation results are shown in Table 5. It can be seen that a liquid crystal display device with low black brightness and high contrast can be obtained even when viewed from an oblique direction.

[0147] Comparative Examples 1-4 A simulation was performed using a liquid crystal display device as the simulation model, which has a polarizer, an IPS liquid crystal cell, a film I, and another polarizer arranged in that order from the light source side. The arrangement of each element is as shown in Figure 1.

[0148] As shown in Table 5, simulations were performed using the measured values ​​of the refractive index, Re, Rth, and R450 / R550 of film I, and the Re setting value of the liquid crystal cell. The simulation results are shown in Table 5. Film (A) is either absent or does not meet the requirements for refractive index, Re, Rth, and R450 / R550 of film (A), and the black brightness is high and the contrast is low even when viewed from an oblique direction, making it unsuitable as a liquid crystal display device.

[0149] Examples 3-15 A simulation was performed using a liquid crystal display device as the simulation model, which had the following components arranged in this order from the light source side: polarizer, IPS liquid crystal cell, film I, film II, and polarizer. The arrangement of each component was as shown in Figure 2.

[0150] As shown in Table 6, simulations were performed using the measured refractive indices, Re, Rth, and R450 / R550 values ​​of Film I and Film II, as well as the Re setting value of the liquid crystal cell. The simulation results are shown in Table 6. It can be seen that a liquid crystal display device with low black brightness and high contrast can be obtained even when viewed from an oblique direction.

[0151] Comparative Examples 5-7 A simulation was performed using a liquid crystal display device as the simulation model, which had the following components arranged in this order from the light source side: polarizer, IPS liquid crystal cell, film I, film II, and polarizer. The arrangement of each component was as shown in Figure 2.

[0152] As shown in Table 6, simulations were performed using the measured refractive indices, Re, Rth, and R450 / R550 values ​​of film I and film II, as well as the Re setting value of the liquid crystal cell. The simulation results are shown in Table 6. Because optical film (A) is absent or does not meet the Re or Rth requirements, and the black brightness is high and the contrast is low even when viewed from an oblique angle, it is unsuitable as a liquid crystal display device.

[0153] Examples 16-26 A simulation was performed using a liquid crystal display device as the simulation model, which had the following components arranged in this order from the light source side: polarizer, film III, IPS liquid crystal cell, film I, and polarizer. The arrangement of each component was as shown in Figure 3.

[0154] As shown in Table 7, simulations were performed using the measured refractive indices, Re, Rth, and R450 / R550 values ​​of Film I and Film III, as well as the Re setting value of the liquid crystal cell. The simulation results are shown in Table 7. It can be seen that a liquid crystal display device with low black brightness and high contrast can be obtained even when viewed from an oblique direction.

[0155] Comparative Examples 8-10 A simulation was performed using a liquid crystal display device as the simulation model, which had the following components arranged in this order from the light source side: polarizer, film III, IPS liquid crystal cell, film I, and polarizer. The arrangement of each component was as shown in Figure 3.

[0156] As shown in Table 7, simulations were performed using the measured refractive indices, Re, Rth, and R450 / R550 values ​​of Film I and Film III, as well as the Re setting value of the liquid crystal cell. The simulation results are shown in Table 7. Because optical film (A) is absent or does not meet the Re or Rth requirements, and the black brightness is high and the contrast is low even when viewed from an oblique angle, it is unsuitable as a liquid crystal display device.

[0157] Example 27 A liquid crystal display device was used as the simulation model, with the elements arranged in the following order from the light source side: polarizer, film III, IPS liquid crystal cell, film I, film II, and polarizer. The arrangement of each element was as shown in Figure 4.

[0158] As shown in Table 8, simulations were performed using the measured refractive indices, Re, Rth, and R450 / R550 values ​​of Film I, Film II, and Film III, along with the Re setting value of the liquid crystal cell. The simulation results are shown in Table 8. It can be seen that a liquid crystal display device with low black brightness and high contrast can be obtained even when viewed from an oblique direction.

[0159] [Table 5]

[0160] [Table 6]

[0161] [Table 7]

[0162] [Table 8] [Explanation of symbols]

[0163] 10 light source 20, 70 polarizers 21, 71 Absorption axis of polarizer 30 LCD cells 31 Orientation direction of liquid crystal molecules 40 Film I 50 Film II 41 Axial axis when film I has a phase-advancing axis 51 Axial axis when film II has a phase-advancing axis 60 Film III 100 LCD display device 200,300 polarizing plates

Claims

1. Optical film containing 81 to 100% by weight of a fumarate ester resin with a number average molecular weight of 100,000 or more, which contains 50 mol% or more of fumarate ester residue units as shown in formula (1) below, where the refractive index measured at a wavelength of 589 nm is 1.50 or less, the out-of-plane phase difference Rth measured at a wavelength of 589 nm as shown in formula (a) below is -160 to -40 nm, the in-plane phase difference Re measured at a wavelength of 589 nm as shown in formula (b) below is 60 to 230 nm, and the ratio of the in-plane phase difference Re (R450) measured at a wavelength of 450 nm to the in-plane phase difference Re (R550) measured at a wavelength of 550 nm (R450 / R550) is less than 1.

03. Hereinafter referred to as optical film (A), an optical film (B) is laminated with an optical film (A) having a refractive index of 1.30 to 1.52 measured at a wavelength of 589 nm, an out-of-plane phase difference Rth measured at a wavelength of 589 nm as shown in formula (a) of 80 to 140 nm, an in-plane phase difference Re measured at a wavelength of 589 nm as shown in formula (b) of 0 to 100 nm, and a ratio (R450 / R550) of 1.02 or less of the in-plane phase difference Re(R450) measured at a wavelength of 450 nm to the in-plane phase difference Re(R550) measured at a wavelength of 550 nm. A polarizing plate characterized by having a laminated optical film on at least one side of a polarizer, wherein the in-plane phase difference Re measured at a wavelength of 589 nm as shown in formula (b) is 100 to 150 nm, the out-of-plane phase difference Rth measured at a wavelength of 589 nm as shown in formula (a) is -40 to 40 nm, and the film thickness is 0.2 to 70.0 μm. Rth=[(nx+ny) / 2-nz]×d (a) Re=(ny-nx)×d (b) (In the formula, nx represents the refractive index in the phase-advancing axis direction within the film plane, ny represents the refractive index in the phase-lagging axis direction within the film plane, nz represents the refractive index in the perpendicular direction outside the film plane, and d represents the film thickness.) 【Chemistry 1】 (In the formula, R １ and R ２ Each of these independently represents one of the group consisting of a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 3 to 12 carbon atoms, or a cyclic alkyl group having 3 to 6 carbon atoms.

2. The polarizing plate according to claim 1, wherein the phase advance axes of optical film (A) and optical film (B) make an angle with respect to the longitudinal direction of the film of 0 degrees ± 10 degrees, or 90 degrees ± 10 degrees.

3. A liquid crystal display device comprising a polarizing plate (first polarizing plate) according to any one of claims 1 to 2, and a polarizing plate (second polarizing plate) having an optical film (C) with a thickness of 40 μm or less, wherein the optical film (C) has a refractive index of 1.70 or less measured at a wavelength of 589 nm, an out-of-plane phase difference Rth measured at a wavelength of 589 nm as shown in formula (a) of -200 to -20 nm, and an in-plane phase difference Re measured at a wavelength of 589 nm as shown in formula (b) of 0 to 10 nm, and a liquid crystal cell is disposed between the first polarizing plate and the second polarizing plate.

4. The liquid crystal display device according to claim 3, characterized in that the optical film (C) contains 81 to 100% by weight of a fumarate ester resin with a number average molecular weight of 100,000 or more, which contains 50 mol% or more of fumarate ester residue units represented by formula (1).

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