JP2007133296A - Polarizing plate and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarizing plate which contributes improvement of front contrast without degrading a contrast viewing angle of a liquid crystal display device. <P>SOLUTION: In the polarizing plate which has at least an optical compensation film having an in-plane retardation of 20 nm or more and a polarizer, a retardation value (Re) determined such that a measurement of transmittance I for 0°≤θ≤360° is most closely approximated to the transmittance I calculated according to equation [1] is 0.2 nm to 5 nm, wherein I is the transmittance, K is a constant, θ is an angle between a polarizer transmission axis and an analyzer transmission axis and λ is a measurement wavelength (therein, visible light region wavelength). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a polarizing plate and a liquid crystal display device provided with an optical compensation film.

  Optical compensation sheets are used in various liquid crystal display devices in order to eliminate image coloring and expand the viewing angle. Conventionally, stretched birefringent films have been used as optical compensation sheets. In recent years, it has been proposed to use an optical compensation sheet having an optically anisotropic layer made of a discotic liquid crystalline compound on a transparent support instead of a stretched birefringent film. This optically anisotropic layer is usually formed by applying a discotic liquid crystal composition containing a discotic liquid crystal compound on an alignment film, and heating it at a temperature higher than the alignment temperature to align the discotic liquid crystal compound, It is formed by fixing its orientation state. In general, the discotic liquid crystalline compound has a large birefringence and various alignment forms. By using a discotic liquid crystalline compound, it has become possible to realize optical properties that cannot be obtained with conventional stretched birefringent films.

Along with the widening of the viewing angle, the improvement of the contrast at the front is also important for the display performance. In order to improve the front contrast, there has been proposed a method (Patent Document 1) in which a birefringent medium having a phase difference equal to the residual phase difference of the liquid crystal during black display is disposed between the polarizing plate and the like. However, the method of adjusting the birefringence phase difference as described above has a problem that the viewing angle contrast becomes insufficient.
Japanese Patent No. 3321559

  An object of the present invention is to improve the front contrast while maintaining the wide contrast viewing angle of the liquid crystal display device. It is another object of the present invention to provide a polarizing plate that contributes to improving the front contrast without reducing the contrast viewing angle.

  As a result of intensive studies, the present inventors have found that the front contrast can be remarkably improved while maintaining the contrast viewing angle by controlling the apparent retardation value of the polarizing plate within a certain range.

That is, the means for solving the above problems are as follows.
(1) A polarizing plate having at least an optical compensation film having an in-plane retardation of 20 nm or more and a polarizer, and a transmittance I of light passing through the polarizing plate with respect to a transmission axis of the polarizer When measured using an analyzer having a transmission axis in the direction of the angle θ, the transmittance I measured for 0 ° ≦ θ ≦ 360 ° is determined so as to best match the following equation [1]. Is a polarizing plate having a thickness of 0.2 nm to 5 nm.

（Ｉ：透過率、Ｋ：定数、θ：偏光子透過軸と検光子透過軸なす角度、λ：測定波長（但し可視光域波長））

(I: transmittance, K: constant, θ: angle between polarizer transmission axis and analyzer transmission axis, λ: measurement wavelength (however, visible light wavelength))

(2) The polarized light according to (1), wherein the optical compensation film has at least one optically anisotropic layer formed of a support and a composition containing a liquid crystal compound on the support. Board.
(3) The polarizing plate according to (1) or (2), wherein the liquid crystalline compound is a discotic liquid crystal.
(4) A liquid crystal display device having the polarizing plate of any one of (1) to (3).

  ADVANTAGE OF THE INVENTION According to this invention, while improving the contrast viewing angle of a liquid crystal display device, the polarizing plate which contributes to the improvement of front contrast can be provided. In addition, according to the present invention, it is possible to provide a liquid crystal display device in which the contrast viewing angle is improved and the front contrast is improved.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described in detail below. In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.
Further, in this specification, “parallel” and “orthogonal” mean that the angle is within a range of strictly less than ± 10 °. In this range, an error from a strict angle is preferably less than ± 5 °, and more preferably less than ± 2 °. Further, the “slow axis” means a direction in which the refractive index is maximized. Further, the measurement wavelengths of the refractive index and the phase difference are values at λ = 550 nm in the visible light region unless otherwise specified.
Further, in this specification, the “polarizing plate” is cut into a size to be incorporated into a long polarizing plate and a liquid crystal device unless otherwise specified (in this specification, “cutting” includes “punching” and The term “includes“ cutout ”and the like” is used to include both polarizing plates. Further, in this specification, “polarizer” and “polarizing plate” are used separately, but “polarizing plate” means a laminate having a transparent protective film for protecting the polarizer on at least one side of the “polarizer”. It shall be.

[Polarizer]
The polarizing plate of the present invention has at least an optical compensation film having an in-plane retardation of 20 nm or more and a polarizer. In one embodiment of the polarizing plate of the present invention, an optical compensation film having an in-plane retardation of 20 nm or more, a polarizer, and a protective film are sequentially laminated and integrated from the side disposed on the liquid crystal cell side. It is a polarizing plate.
The polarizing plate of the present invention is measured with respect to 0 ° ≦ θ ≦ 360 ° when the transmittance I is measured by changing the angle θ between the transmission axis of the analyzer of the measurement system and the transmission axis of the polarizer. The retardation value Re (hereinafter referred to as the apparent retardation) at which the transmittance I is determined so as to best fit the following formula [1] is 0.2 nm to 5 nm.

（Ｉ：透過率、Ｋ：定数、θ：偏光子透過軸と検光子透過軸なす角度）

(I: transmittance, K: constant, θ: angle between polarizer transmission axis and analyzer transmission axis)

  In general, it is known that the transmittance I when light passing through a polarizer passes through a birefringent medium such as an optical compensation film is represented by the following formula [0].

  In the above formula [0], I is the transmittance, K is a constant, θ is the angle formed by the polarizer transmission axis and the analyzer transmission axis of the measurement system, and φ is a birefringent medium such as the polarizer transmission axis and the optical compensation film. Λ is a measurement wavelength (however, visible light wavelength), and Re is a retardation value of the birefringent medium. As a result of the inventor's extensive studies on the polarizing plate in which the optical compensation film and the polarizer are integrated, an equation assuming that the angle φ formed by the polarizer transmission axis and the slow axis of the optical compensation film is 45 °. When the Re determined by fitting so as to best fit (the above formula [1]) is 0.2 to 5 nm, the width of the contrast viewing angle is maintained when such a polarizing plate is used in a liquid crystal display device. As it is, it was found that the residual retardation at the time of black display of the liquid crystal cell can be compensated and the front contrast can be remarkably improved.

The apparent retardation of the polarizing plate can be determined, for example, by the following method.
The polarizing plate of the measurement sample is arranged with the optical compensation film on the analyzer side, and the angle θ formed when the transmission axis of the polarizer and the transmission axis of the analyzer are projected on the same plane is 0 ° ≦ θ While changing within a range of ≦ 360 °, light having a wavelength λ (where λ is a visible light region) is incident from the lower part of the polarizing plate (the side opposite to the side where the analyzer is disposed), and the light is emitted from the analyzer. Measure the intensity of the light. The transmittance I is calculated from the measured value, and the curve obtained by plotting with respect to θ is optimized so as to best fit the above equation [1], and Re is determined. The constant K in the equation is determined by the maximum transmittance when θ is changed. These measurements and calculations can be performed automatically using a commercially available optical measurement system. For example, when KOBRA 21ADH (manufactured by Oji Scientific Instruments) is used, the transmittance of the polarizing plate can be automatically measured by changing θ, and from the relationship between the measured transmittance and θ, Apparent retardation can be calculated automatically. However, in KOBRA 21ADH, optimization is performed based on the above equation [0]. Therefore, in measurement, it is necessary to input an angle φ formed by the polarizer transmission axis and the optical compensation film slow axis, and φ = 45 An apparent retardation Re that best fits the above equation [1] can be obtained by inputting and measuring the angle.

The apparent retardation of the polarizing plate determined by the above formula [1] depends on the relationship between the slow axis of the optical compensation film and the axial angle of the transmission axis of the polarizer and / or in-plane retardation of the optical compensation film. , And can be adjusted to the above range (0.2 to 5 nm).
Hereinafter, materials used for the polarizing plate of the present invention, production methods, and the like will be described in detail.

[Optical compensation film]
The optical compensation film of the polarizing plate of the present invention preferably has an in-plane retardation of 20 nm or more in order to improve the contrast at the viewing angle.
The material of the optical compensation film is not particularly limited, and any optical compensation film can be used as long as the above optical characteristics are satisfied. For example, the optical compensation film may be made of a transparent polymer film having birefringence developed by stretching or the like. Examples of the polymer constituting the polymer film include cellulose esters (eg, cellulose acetate, cellulose diacetate), norbornene-based polymers, and polymethyl methacrylate. A commercially available polymer (for Norbornene-based polymers, both Arton and Zeonex are trade names)) may be used. Even in the case of conventionally known polymers such as polycarbonate and polysulfone that easily develop birefringence, the birefringence expression can be controlled by modifying the molecule as described in WO00 / 26705. Can also be used.

  The optical compensation film may be composed of only one layer or may be a laminate of two or more layers, but at least one optically anisotropic layer composed of a liquid crystalline composition is formed on a support composed of a polymer film or the like. It is preferable that it is the structure which has.

(Optically anisotropic layer)
The optically anisotropic layer is preferably designed so as to compensate for the liquid crystalline compound in the liquid crystal cell in the black display of the liquid crystal display device. The alignment state of the liquid crystal compound molecules in the liquid crystal cell in black display varies depending on the mode of the liquid crystal display device. The alignment state of the liquid crystal compound molecules in the liquid crystal cell is described in IDW'00, P411 to 414 of FMC7-2, and the like.
The optically anisotropic layer is formed directly from the liquid crystalline composition on the support or from the liquid crystalline composition via an alignment film. The alignment film preferably has a thickness of 10 μm or less.
The liquid crystalline composition used for forming the optically anisotropic layer contains at least one liquid crystalline compound. The liquid crystal compound includes a rod-like liquid crystal compound and a discotic liquid crystal compound. The rod-like liquid crystal compound and the discotic liquid crystal compound may be a polymer liquid crystal or a low-molecular liquid crystal, and the low-molecular liquid crystal is in a cross-linked state in the optically anisotropic layer and no longer exhibits liquid crystallinity. included. The optically anisotropic layer can be formed by applying a liquid crystal compound and, if necessary, a coating liquid containing a polymerizable initiator and optional components on the alignment film. A preferred example of the alignment film is described in JP-A-8-338913.

(Bar-shaped liquid crystalline compound)
Examples of rod-like liquid crystalline compounds include azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines. , Phenyldioxanes, tolanes and alkenylcyclohexylbenzonitriles are preferably used.
The rod-like liquid crystalline compound includes a metal complex. Moreover, the liquid crystal polymer which contains a rod-shaped liquid crystalline compound in a repeating unit can also be used as the rod-shaped liquid crystalline compound of the present invention. In other words, the rod-like liquid crystalline compound may be bonded to a (liquid crystal) polymer.
Regarding rod-like liquid crystalline compounds, for example, Quarterly Chemical Review Vol. 22, Liquid Crystal Chemistry (1994), Chapter 4, Chapter 7 and Chapter 11 of the Chemical Society of Japan and Liquid Crystal Device Handbook, Japan Society for the Promotion of Science, 142nd Committee The one described in Chapter 3 of the edition can be adopted.
The birefringence of the rod-like liquid crystalline compound is preferably in the range of 0.001 to 0.7.

  The rod-like liquid crystalline compound preferably has a polymerizable group in order to fix its alignment state. The polymerizable group is preferably an unsaturated polymerizable group or an epoxy group, more preferably an unsaturated polymerizable group, and most preferably an ethylenically unsaturated polymerizable group.

(Discotic liquid crystalline compounds)
Examples of discotic liquid crystalline compounds include C.I. Benzene derivatives described in a research report of Destrade et al. (Mol. Cryst. 71, 111 (1981)), C.I. Destrode et al. (Mol. Cryst. 122, 141 (1985), Physics lett, A, 78, 82 (1990)) described in The cyclohexane derivatives described in the research report of Kohne et al. (Angew. Chem. 96, 70 (1984)) and M.M. Lehn et al. (JCS, Chem. Commun., 1794 (1985)), J.C. Azacrown-type and phenylacetylene-type macrocycles described in the research report of Zhang et al. (J. Am. Chem. Soc. 116, 2655 (1994)) are included.

  The discotic liquid crystalline compound also includes a compound having a structure in which a linear alkyl group, an alkoxy group, and a substituted benzoyloxy group are radially substituted as a side chain of the mother nucleus with respect to the mother nucleus at the center of the molecule. The molecule or the assembly of molecules is preferably a compound having rotational symmetry and imparting a certain orientation. Note that the discotic liquid crystalline compound finally contained in the optically anisotropic layer does not need to be discotic liquid crystalline. For example, the discotic liquid crystalline compound has a group in which a low molecular weight discotic liquid crystalline molecule reacts with heat or light. As a result, it may be polymerized or cross-linked by reaction with heat and light to increase the molecular weight and lose liquid crystallinity. Preferred examples of the discotic liquid crystalline compound are described in JP-A-8-50206. Moreover, about superposition | polymerization of a discotic liquid crystalline compound, Unexamined-Japanese-Patent No. 8-27284 has description.

  In order to fix the discotic liquid crystalline compound by polymerization, it is necessary to bond a polymerizable group as a substituent to the discotic core of the discotic liquid crystalline compound. However, when the polymerizable group is directly connected to the disc-shaped core, it becomes difficult to maintain the orientation state in the polymerization reaction. Therefore, a linking group is introduced between the discotic core and the polymerizable group. Therefore, the discotic liquid crystalline compound having a polymerizable group is preferably a compound represented by the following formula (5).

General formula (5)
D (-LQ) _r
(In General Formula (5), D is a discotic core, L is a divalent linking group, Q is a polymerizable group, and r is an integer of 4 to 12.)

  An example of the disk-shaped core (D) is shown below. In each of the following examples, LQ (or QL) means a combination of a divalent linking group (L) and a polymerizable group (Q).

  In the general formula (5), the divalent linking group (L) is selected from the group consisting of an alkylene group, an alkenylene group, an arylene group, —CO—, —NH—, —O—, —S—, and combinations thereof. It is preferable that it is a bivalent coupling group. The divalent linking group (L) is a divalent combination of at least two divalent groups selected from the group consisting of an alkylene group, an arylene group, -CO-, -NH-, -O-, and -S-. More preferably, it is a linking group. The divalent linking group (L) is most preferably a divalent linking group in which at least two divalent groups selected from the group consisting of an alkylene group, an arylene group, -CO- and -O- are combined. . The alkylene group preferably has 1 to 12 carbon atoms. The alkenylene group preferably has 2 to 12 carbon atoms. The number of carbon atoms in the arylene group is preferably 6-10.

Examples of the divalent linking group (L) are shown below. The left side is bonded to the discotic core (D), and the right side is bonded to the polymerizable group (Q). AL represents an alkylene group or an alkenylene group, and AR represents an arylene group. The alkylene group, alkenylene group and arylene group may have a substituent (eg, an alkyl group).
L1: -AL-CO-O-AL-,
L2: -AL-CO-O-AL-O-,
L3: -AL-CO-O-AL-O-AL-,
L4: -AL-CO-O-AL-O-CO-,
L5: -CO-AR-O-AL-,
L6: -CO-AR-O-AL-O-,
L7: -CO-AR-O-AL-O-CO-,
L8: -CO-NH-AL-,
L9: -NH-AL-O-,
L10: -NH-AL-O-CO-,

L11: -O-AL-,
L12: -O-AL-O-,
L13: -O-AL-O-CO-,
L14: -O-AL-O-CO-NH-AL-,
L15: -O-AL-S-AL-,
L16: -O-CO-AL-AR-O-AL-O-CO-,
L17: -O-CO-AR-O-AL-CO-,
L18: -O-CO-AR-O-AL-O-CO-,
L19: -O-CO-AR-O-AL-O-AL-O-CO-,
L20: -O-CO-AR-O-AL-O-AL-O-AL-O-CO-,
L21: -S-AL-,
L22: -S-AL-O-,
L23: -S-AL-O-CO-,
L24: -S-AL-S-AL-,
L25: -S-AR-AL-.

  The polymerizable group (Q) of the general formula (5) is determined according to the type of polymerization reaction. Examples of the polymerizable group (Q) are shown below.

  The polymerizable group (Q) is preferably an unsaturated polymerizable group (Q1, Q2, Q3, Q7, Q8, Q15, Q16, Q17) or an epoxy group (Q6, Q18). More preferably, it is most preferably an ethylenically unsaturated polymerizable group (Q1, Q7, Q8, Q15, Q16, Q17). A specific value of r is determined according to the type of the disk-shaped core (D). In addition, although the combination of several L and Q may differ, it is preferable that it is the same.

  In the hybrid alignment, the angle between the major axis (disk surface) of the discotic liquid crystalline compound and the surface of the support, that is, the inclination angle is in the direction of the depth of the optically anisotropic layer (that is, perpendicular to the transparent support). And it increases or decreases with increasing distance from the plane of the polarizer. The angle preferably decreases with increasing distance. Further, the change in the tilt angle can be continuous increase, continuous decrease, intermittent increase, intermittent decrease, change including continuous increase and continuous decrease, or intermittent change including increase and decrease. . The intermittent change includes a region where the inclination angle does not change in the middle of the thickness direction. Even if a region where the angle does not change is included, it may be increased or decreased as a whole. However, it is preferred that the tilt angle changes continuously.

The average direction of the major axis (disk surface) of the discotic liquid crystalline compound (average of the major axis direction of each molecule) is generally selected by selecting the discotic liquid crystalline compound or the material of the alignment film, or selecting the rubbing treatment method. By doing so, it can be adjusted. The major axis (disk surface) direction of the discotic liquid crystalline compound on the surface side (air side) is generally adjusted by selecting the type of additive used together with the discotic liquid crystalline compound or the discotic liquid crystalline compound. be able to.
Examples of the additive used together with the discotic liquid crystalline compound include a plasticizer, a surfactant, a polymerizable monomer and a polymer. The degree of change in the orientation direction of the major axis can also be adjusted by selecting liquid crystalline molecules and additives as described above.

  The plasticizer, surfactant and polymerizable monomer used together with the discotic liquid crystalline compound are compatible with the discotic liquid crystalline compound, and can change the tilt angle of the discotic liquid crystalline compound or change the orientation. It is preferable not to inhibit. Among the additive components, addition of a polymerizable monomer (eg, a compound having a vinyl group, a vinyloxy group, an acryloyl group and a methacryloyl group) is preferable. The amount of the compound added is generally in the range of 1 to 50% by mass and preferably in the range of 5 to 30% by mass with respect to the discotic liquid crystalline compound. In addition, when a monomer having 4 or more polymerizable reactive functional groups is mixed and used, the adhesion between the alignment film and the optically anisotropic layer can be improved.

The optically anisotropic layer may contain a polymer together with the discotic liquid crystalline compound. The polymer preferably has a certain degree of compatibility with the discotic liquid crystalline compound and can change the tilt angle of the discotic liquid crystalline compound. A cellulose ester can be mentioned as an example of a polymer. Preferable examples of the cellulose ester include cellulose acetate, cellulose acetate propionate, hydroxypropyl cellulose and cellulose acetate butyrate. The addition amount of the polymer is preferably in the range of 0.1 to 10% by mass with respect to the discotic liquid crystalline compound so as not to inhibit the orientation of the discotic liquid crystalline compound, and 0.1 to 8% by mass. More preferably, it is in the range of 0.1 to 5% by mass.
The discotic nematic liquid crystal phase-solid phase transition temperature of the discotic liquid crystalline compound is preferably 70 to 300 ° C, more preferably 70 to 170 ° C.

(Fixing the alignment state of liquid crystalline molecules)
The aligned liquid crystal molecules can be fixed while maintaining the alignment state. The immobilization is preferably performed by a polymerization reaction. The polymerization reaction includes a thermal polymerization reaction using a thermal polymerization initiator and a photopolymerization reaction using a photopolymerization initiator. A photopolymerization reaction is preferred.
Examples of photopolymerization initiators include α-carbonyl compounds (described in US Pat. Nos. 2,367,661 and 2,367,670), acyloin ethers (described in US Pat. No. 2,448,828), α-hydrocarbon substituted aromatic acyloin compounds ( US Pat. No. 2,722,512), a polynuclear quinone compound (described in US Pat. Nos. 3,046,127 and 2,951,758), a combination of triarylimidazole dimer and p-aminophenyl ketone (described in US Pat. No. 3,549,367), acridine Phenazine compounds (described in JP-A-60-105667 and US Pat. No. 4,239,850) and oxadiazole compounds (described in US Pat. No. 4,221,970) are included.

The amount of the photopolymerization initiator used is preferably in the range of 0.01 to 20% by mass, more preferably in the range of 0.5 to 5% by mass, based on the solid content of the coating solution.
Light irradiation for polymerizing liquid crystalline molecules is preferably performed using ultraviolet rays.
The irradiation energy is preferably in the range of ^{20mJ / cm 2 ~50J / cm 2} , more preferably in the range of ^{20mJ / cm 2 ~5000mJ / cm 2} , a range of 100mJ / cm ² ~800mJ / cm ² More preferably. In order to accelerate the photopolymerization reaction, light irradiation may be performed under heating conditions.
A protective layer may be provided on the optically anisotropic layer.

  The optically anisotropic layer may contain a copolymer containing a repeating unit derived from a fluoroaliphatic group-containing monomer (sometimes abbreviated as “fluorine polymer”). The fluoropolymer is preferably an acrylic resin or a methacrylic resin, and may be an acrylic resin or a methacrylic resin obtained by copolymerizing a vinyl monomer copolymerizable with these monomers. Regarding the fluorine-based polymer usable in the present invention, [0016] to [0057] of JP-A No. 2004-198511, [0013] to [0065] of JP-A No. 2004-333852, and JP-A No. 2005-179636. Details are described in [0020] to [0118].

  Specific examples of the fluoroaliphatic group-containing copolymer preferably used in the present invention as the fluorine-based polymer are shown below, but the present invention is not limited to these specific examples. The numerical value in a formula here is a mass percentage which shows the composition ratio of each monomer, respectively, and Mw is the mass mean molecular weight of PS conversion measured by GPC. Numerical values such as a, b, c, and d represent mass ratios.

  The fluoropolymer used in the present invention can be produced by a publicly known and commonly used method. For example, it can be produced by adding a general-purpose radical polymerization initiator to an organic solvent containing the above-described monomer having a fluoroaliphatic group, a monomer having a hydrogen bonding group, and the like, and polymerizing the mixture. Further, in some cases, other addition-polymerizable unsaturated compounds can be further added and produced by the same method as described above. Depending on the polymerizability of each monomer, a dropping polymerization method in which a monomer and an initiator are added dropwise to a reaction vessel is also effective for obtaining a polymer having a uniform composition.

  The content of the fluoropolymer is preferably 0.005 to 8% by mass, and 0.01 to 5% by mass in the composition (a composition excluding the solvent in the case of a coating solution). Is more preferable, and it is further more preferable that it is 0.05-2.5 mass%. When the addition amount of the fluoropolymer is within the above range, the effect can be sufficiently exerted, the coating film can be sufficiently dried, and the performance as an optical compensation film (for example, uniformity of retardation) is further improved. it can.

The optically anisotropic layer is prepared by preparing a coating solution containing at least one of the liquid crystalline compounds and, optionally, an additive such as a polymerizable initiator and a fluorine-based polymer, and applying the coating solution to the alignment film surface. It can be formed by drying. As the solvent used for preparing the coating solution, an organic solvent is preferably used. Examples of organic solvents include amides (eg, N, N-dimethylformamide), sulfoxides (eg, dimethyl sulfoxide), heterocyclic compounds (eg, pyridine), hydrocarbons (eg, benzene, hexane), alkyl halides (eg, , Chloroform, dichloromethane, tetrachloroethane), esters (eg, methyl acetate, butyl acetate), ketones (eg, acetone, methyl ethyl ketone), ethers (eg, tetrahydrofuran, 1,2-dimethoxyethane). Alkyl halides and ketones are preferred. Two or more organic solvents may be used in combination.
When producing an optical compensation film with high uniformity, the surface tension of the coating solution is preferably 25 mN / m or less, and more preferably 22 mN / m or less.

  The coating liquid can be applied by a known method (eg, extrusion coating method, direct gravure coating method, reverse gravure coating method, die coating method).

Next, the support body which the said optical compensation film has is demonstrated.
(Support)
The support that the optical compensation film has is preferably glass or a transparent polymer film.
The support preferably has a light transmittance of 80% or more. Examples of the polymer constituting the polymer film include cellulose esters (eg, cellulose acetate, cellulose diacetate), norbornene-based polymers, and polymethyl methacrylate. A commercially available polymer (for Norbornene-based polymers, both Arton and Zeonex are trade names)) may be used.
Among these, cellulose esters are preferable, and lower fatty acid esters of cellulose are more preferable. Lower fatty acid means a fatty acid having 6 or less carbon atoms. The number of carbon atoms is particularly preferably 2 (cellulose acetate), 3 (cellulose propionate) or 4 (cellulose butyrate). Cellulose acetate is particularly preferred. Mixed fatty acid esters such as cellulose acetate propionate and cellulose acetate butyrate may be used.

  Even in the case of conventionally known polymers such as polycarbonate and polysulfone that easily develop birefringence, the birefringence expression can be controlled by modifying the molecule as described in WO00 / 26705. For example, it can be used as a support for the optical compensation film.

  In an aspect in which the optical compensation film also serves as a protective film for the polarizer (for example, an aspect in which the optical compensation film is bonded to the surface of the polarizer), the polymer film used as the support has an acetylation degree of 55.0 to 62.5%. It is preferable to use cellulose acetate. The acetylation degree is more preferably 57.0 to 62.0%.

The degree of acetylation means the amount of bound acetic acid per unit mass of cellulose. The degree of acetylation is determined by measurement and calculation of the degree of acetylation in ASTM: D-817-91 (test method for cellulose acetate and the like).
The viscosity average degree of polymerization (DP) of cellulose acetate is preferably 250 or more, and more preferably 290 or more. Cellulose acetate preferably has a narrow molecular weight distribution of Mw / Mn (Mw is a mass average molecular weight, Mn is a number average molecular weight) by gel permeation chromatography. The specific value of Mw / Mn is preferably 1.0 to 1.7, more preferably 1.0 to 1.65, and most preferably 1.0 to 1.6. preferable.

In cellulose acetate, the hydroxyl groups at the 2-position, 3-position and 6-position of cellulose are not evenly substituted, but the substitution degree at the 6-position tends to be small. In the polymer film used in the present invention, it is preferable that the degree of substitution at the 6-position of cellulose is the same or greater than that at the 2- and 3-positions.
The ratio of the substitution degree at the 6-position to the total substitution degree at the 2-position, the 3-position, and the 6-position is preferably 30 to 40%, more preferably 31 to 40%, and more preferably 32 to 40%. Most preferably it is. The substitution degree at the 6-position is preferably 0.88 or more.
The degree of substitution at each position can be measured by NMR.
Cellulose acetate having a high degree of substitution at the 6-position is described in Synthesis Example 1 described in Paragraph Nos. 0043 to 0044, Synthesis Example 2 described in Paragraph Nos. 0048 to 0049, and Paragraph Nos. 0051 to 0052. It can be synthesized with reference to the method of Synthesis Example 3.

Next, the polarizer which the polarizing plate of this invention has is demonstrated.
(Polarizer)
The polarizer that can be used in the polarizing plate of the present invention is preferably a coating type polarizer typified by Optiva, or a polarizer comprising a binder and iodine or a dichroic dye.
The iodine and the dichroic dye in the polarizer exhibit a polarizing performance by being oriented in the binder. It is preferable that the iodine and the dichroic dye are aligned along the binder molecule, or the dichroic dye is aligned in one direction by self-assembly such as liquid crystal.

A general-purpose polarizer can be prepared, for example, by immersing a stretched polymer in a solution of iodine or dichroic dye in a bath and allowing the iodine or dichroic dye to penetrate into the binder. it can.
In general-purpose polarizers, iodine or dichroic dye is distributed about 4 μm from the polymer surface (about 8 μm on both sides), and a thickness of at least 10 μm is necessary to obtain sufficient polarization performance. The penetrability can be controlled by the solution concentration of iodine or dichroic dye, the temperature of the bath, and the immersion time.
As described above, the lower limit of the binder thickness is preferably 10 μm. On the other hand, the upper limit of the thickness is not particularly limited, but the thinner the better, from the viewpoint of the light leakage phenomenon that occurs when the polarizing plate is used in a liquid crystal display device. Currently, it is preferably a general-purpose polarizing plate (about 30 μm) or less, preferably 25 μm or less, and more preferably 20 μm or less. When it is 20 μm or less, the light leakage phenomenon is not observed in a 17-inch liquid crystal display device.

The binder of the polarizer may be cross-linked. As the crosslinked binder, a polymer that can be crosslinked per se can be used. A polarizer can be formed by reacting a polymer having a functional group or a binder obtained by introducing a functional group into a polymer between the binders by light, heat, or pH change.
Moreover, you may introduce | transduce a crosslinked structure into a polymer with a crosslinking agent. It can be formed by cross-linking between binders by introducing a bonding group derived from the cross-linking agent between binders using a cross-linking agent which is a compound having high reaction activity.
Crosslinking is generally carried out by applying a coating solution containing a polymer or a mixture of a polymer and a crosslinking agent on a transparent support and then heating. Since it is only necessary to ensure durability at the final product stage, the crosslinking treatment may be performed at any stage until the final polarizing plate is obtained.

  As the binder of the polarizer, either a polymer that can be crosslinked by itself or a polymer that is crosslinked by a crosslinking agent can be used. Examples of polymers include polymethyl methacrylate, polyacrylic acid, polymethacrylic acid, polystyrene, gelatin, polyvinyl alcohol, modified polyvinyl alcohol, poly (N-methylolacrylamide), polyvinyltoluene, chlorosulfonated polyethylene, nitrocellulose, chlorinated Polyolefin (eg, polyvinyl chloride), polyester, polyimide, polyvinyl acetate, polyethylene, carboxymethyl cellulose, polypropylene, polycarbonate and copolymers thereof (eg, acrylic acid / methacrylic acid polymer, styrene / maleimide polymer, styrene / vinyl) Toluene polymer, vinyl acetate / vinyl chloride polymer, ethylene / vinyl acetate polymer). Water-soluble polymers (eg, poly (N-methylolacrylamide), carboxymethylcellulose, gelatin, polyvinyl alcohol and modified polyvinyl alcohol) are preferred, gelatin, polyvinyl alcohol and modified polyvinyl alcohol are more preferred, and polyvinyl alcohol and modified polyvinyl alcohol are most preferred. .

The saponification degree of polyvinyl alcohol and modified polyvinyl alcohol is preferably 70 to 100%, more preferably 80 to 100%, and most preferably 95 to 100%. As for the polymerization degree of polyvinyl alcohol, 100-5000 are preferable.
The modified polyvinyl alcohol is obtained by introducing a modifying group into polyvinyl alcohol by copolymerization modification, chain transfer modification or block polymerization modification. In the copolymerization modification, —COONa, —Si (OH) ₃ , N (CH ₃ ) ₃ .Cl, C ₉ H ₁₉ COO—, —SO ₃ Na, —C ₁₂ H ₂₅ may be introduced as modifying groups. it can. In chain transfer modification, —COONa, —SH, or —SC ₁₂ H ₂₅ can be introduced as a modifying group. The degree of polymerization of the modified polyvinyl alcohol is preferably 100 to 3000. The modified polyvinyl alcohol is described in JP-A-8-338913, JP-A-9-152509 and JP-A-9-316127.
Unmodified polyvinyl alcohol and alkylthio-modified polyvinyl alcohol having a saponification degree of 85 to 95% are particularly preferable.
Two or more kinds of polyvinyl alcohol and modified polyvinyl alcohol may be used in combination.

When a large amount of the crosslinking agent for the binder is added, the wet heat resistance of the polarizer can be improved. However, when 50 mass% or more of a crosslinking agent is added to the binder, the orientation of iodine or the dichroic dye is lowered. 0.1-20 mass% is preferable with respect to a binder, and, as for the addition amount of a crosslinking agent, 0.5-15 mass% is more preferable.
The binder contains some crosslinking agent that has not reacted even after the crosslinking reaction has been completed. However, the amount of the remaining crosslinking agent is preferably 1.0% by mass or less in the binder, and more preferably 0.5% by mass or less. When the crosslinking agent is contained in the binder layer in an amount exceeding 1.0% by mass, there may be a problem in durability. That is, when a polarizer with a large amount of residual crosslinking agent is incorporated in a liquid crystal display device and used for a long time or left in a high-temperature and high-humidity atmosphere for a long time, the degree of polarization may decrease.
The crosslinking agent is described in US Reissue Patent 23297. Boron compounds (eg, boric acid, borax) can also be used as a crosslinking agent.

As the dichroic dye, an azo dye, stilbene dye, pyrazolone dye, triphenylmethane dye, quinoline dye, oxazine dye, thiazine dye or anthraquinone dye is used. The dichroic dye is preferably water-soluble. The dichroic dye preferably has a hydrophilic substituent (eg, sulfo, amino, hydroxyl).
Examples of dichroic dyes include C.I. I. Direct Yellow 12, C.I. I. Direct Orange 39, C.I. I. Direct Orange 72, C.I. I. Direct Red 39, C.I. I. Direct Red 79, C.I. I. Direct Red 81, C.I. I. Direct Red 83, C.I. I. Direct Red 89, C.I. I. Direct Violet 48, C.I. I. Direct Blue 67, C.I. I. Direct Blue 90, C.I. I. Direct Green 59, C.I. I. Acid Red 37 is included. As for the dichroic dyes, those described in JP-A-1-161202, 1-172906, 1-172907, 1-183602, 1-248105, 1-265205, 7-261024 are used. There are descriptions in each publication. The dichroic dye is used as a free acid or an alkali metal salt, ammonium salt or amine salt. By blending two or more types of dichroic dyes, polarizers having various hues can be produced. A polarizer using a compound (pigment) that exhibits black when the polarization axes are orthogonal to each other, or a polarizer or polarizing plate that is blended with various dichroic molecules so as to exhibit a black color, has both a single plate transmittance and a polarization rate. It is excellent and preferable.

  In order to increase the contrast ratio of the liquid crystal display device, the transmittance of the polarizing plate is preferably higher and the degree of polarization is preferably higher. The transmittance of the polarizing plate is preferably in the range of 30 to 50%, more preferably in the range of 35 to 50%, and in the range of 40 to 50% in the light having a wavelength of 550 nm (of the polarizing plate). Most preferably, the maximum value of the single plate transmittance is 50%. The degree of polarization is preferably in the range of 90 to 100%, more preferably in the range of 95 to 100%, and most preferably in the range of 99 to 100% in light having a wavelength of 550 nm. Here, the transmittance refers to the transmittance with respect to natural light (non-polarized light) incidence, and an analyzer or the like is not installed in the measurement system.

  It is also possible to arrange the polarizer and the optical compensation film via an adhesive layer. As the adhesive, a polyvinyl alcohol resin (including a modified polyvinyl alcohol with an acetoacetyl group, a sulfonic acid group, a carboxyl group, or an oxyalkylene group) or an aqueous boron compound solution can be used. Of these, polyvinyl alcohol resins are preferred. The thickness of the adhesive layer is preferably in the range of 0.01 to 10 μm after drying, and particularly preferably in the range of 0.05 to 5 μm. In the aspect in which the optical compensation film has a support made of a polymer film and an optically anisotropic layer made of a liquid crystalline composition, the back surface of the support (the surface on which the optically anisotropic layer is not formed) is It is preferable to laminate on the polarizer surface side.

  The polarizing plate of the present invention has an apparent letter determined on the basis of the above formula [1], and has a Re of 0.2 to 5 nm. In order to produce a polarizing plate having such optical characteristics, for example, there is a method in which the transmission axis of the polarizer and the slow axis of the optically anisotropic layer are shifted from each other by about 0.1 to 2.5 °. Generally, when a polarizer and an optical compensation film are produced in a roll shape, the transmission axis (or absorption axis) of the polarizer and the slow axis of the optical compensation film are parallel or orthogonal to the longitudinal direction. When laminated in a roll form, both optical axes are parallel or orthogonal to each other, and the apparent retardation of the produced polarizing plate becomes zero. In order to make this 0.2 to 5 nm, the transmission axis of the polarizer and the slow axis of the optically anisotropic phase are shifted by an angle in the above range (both axes when projected on the same plane). The angle is preferably within the above range. For example, an optical compensation film in which the slow axis is not parallel (or orthogonal) to the longitudinal direction by adjusting the rubbing direction when producing the optical compensation film, and the transmission axis is parallel (or orthogonal) to the longitudinal direction. It may be combined with a polarizer, or a polarizer whose transmission axis is not parallel (or orthogonal) to the longitudinal direction is prepared by adjusting the stretching direction when producing the polarizer, and the slow axis is parallel to the longitudinal direction. (Or orthogonal) may be combined with an optical compensation film, or both the optical compensation film and the polarizer may be prepared parallel (or orthogonal) to the longitudinal direction, and the angle may be adjusted when the two are bonded. .

  In the polarizing plate of the present invention, an optical compensation film is disposed on one surface of the polarizer, and a polymer film is disposed on the other surface as a protective film (arrangement of optical compensation film / polarizer / polymer film). It is preferable.

In this specification, Re and Rth respectively represent in-plane retardation and retardation in the thickness direction at a wavelength λ. Re is measured by making light incident in the normal direction of the film in KOBRA 21ADH (manufactured by Oji Scientific Instruments). Rth is a retardation value measured by making light incident from a direction inclined by + 40 ° with respect to the film normal direction, with the in-plane slow axis (determined by KOBRA 21ADH) as the tilt axis (rotary axis), And the retardation value measured in three directions, the retardation value measured by making light incident from a direction inclined by -40 ° with respect to the film normal direction with the in-plane slow axis as the tilt axis (rotation axis). KOBRA 21ADH is calculated based on the above. Here, as the assumed value of the average refractive index, values in the polymer handbook (John Wiley & Sons, Inc.) and catalogs of various optical films can be used. Those whose average refractive index is not known can be measured with an Abbe refractometer. The average refractive index values of main optical films are exemplified below: cellulose acylate (1.48), cycloolefin polymer (1.52), polycarbonate (1.59), polymethyl methacrylate (1.49), Polystyrene (1.59). The KOBRA 21ADH calculates nx, ny, and nz by inputting the assumed value of the average refractive index and the film thickness.
In addition, as a support body of this invention, the thing in which Rth shows a positive value and shows negative birefringence is preferable.

[Liquid Crystal Display]
The polarizing plate of the present invention can be used in various modes of liquid crystal display devices. In particular, it is effective for a mode using a twisted orientation in which a slight residual retardation occurs during black display. The optical compensation film used for the polarizing plate of the present invention has an in-plane retardation (Re) of 20 nm or more, and a preferable Re and thickness direction retardation (Rth) can be set according to the mode of the liquid crystal display device. it can.
Hereinafter, preferred forms of the optically anisotropic layer in each liquid crystal mode will be described.

(TN mode liquid crystal display)
The TN mode liquid crystal cell is most frequently used as a color TFT liquid crystal display device, and is described in many documents.
The alignment state in the liquid crystal cell in the TN mode black display is an alignment state in which a rod-like liquid crystalline molecule rises at the center of the cell and the rod-like liquid crystalline compound lies in the vicinity of the cell substrate.

The rod-like liquid crystalline compound in the center of the cell is compensated with a discotic liquid crystalline compound of the homeotropic orientation (horizontal orientation in which the disk surface is lying) or a (transparent) support, and the rod-like liquid crystalline property in the vicinity of the cell substrate The compound can be compensated with a discotic liquid crystalline compound having a hybrid orientation (an orientation in which the inclination of the major axis changes with the distance from the polarizer).
In addition, the rod-like liquid crystalline compound at the center of the cell is compensated with a rod-like liquid crystalline compound having a homogeneous orientation (horizontal orientation in which the major axis lies) or a (transparent) support, and the rod-like liquid crystalline property in the vicinity of the cell substrate The compound can be compensated with a discotic liquid crystalline compound having a hybrid alignment.

The homeotropic alignment liquid crystal compound is aligned in a state where the angle between the average alignment direction of the major axis of the liquid crystal compound and the plane of the polarizer is 85 to 95 degrees.
The liquid crystal compound of homogeneous alignment is aligned in a state where the angle between the average alignment direction of the major axis of the liquid crystal compound and the plane of the polarizer is less than 5 degrees.
In the hybrid alignment liquid crystal compound, the angle between the long axis average alignment direction of the liquid crystal compound and the plane of the polarizer is preferably 15 degrees or more, and more preferably 15 degrees to 85 degrees.

(Transparent) Optically anisotropic layer in which the support or discotic liquid crystalline compound is homeotropically oriented, optically anisotropic layer in which rod-like liquid crystalline compound is homogeneously oriented, or even homeotropically oriented discotic When using an optical compensation film having an optically anisotropic layer made of a mixture of a liquid crystal compound and a homogeneously oriented rod-like liquid crystal compound, the Rth retardation value of the optically anisotropic layer is 40 nm to 200 nm, The Re retardation value is preferably 20 to 70 nm.
Regarding the discotic liquid crystal compound layer having homeotropic alignment (horizontal alignment) and the rod-like liquid crystal compound layer having homogeneous alignment (horizontal alignment), Japanese Patent Laid-Open Nos. 12-304931 and 12-304932 describe them. Are listed. The discotic liquid crystal compound layer having a hybrid orientation is described in JP-A-8-50206.

(OCB mode liquid crystal display)
The OCB mode liquid crystal cell is a bend alignment mode liquid crystal cell in which a rod-like liquid crystal compound is aligned in a substantially opposite direction (symmetrically) between an upper portion and a lower portion of the liquid crystal cell. Liquid crystal display devices using a bend alignment mode liquid crystal cell are disclosed in US Pat. Nos. 4,583,825 and 5,410,422. Since the rod-like liquid crystal compounds are symmetrically aligned at the upper and lower portions of the liquid crystal cell, the bend alignment mode liquid crystal cell has a self-optical compensation function. Therefore, this liquid crystal mode is called an OCB (Optically Compensatory Bend) liquid crystal mode.
Similarly to the TN mode, the liquid crystal cell in the OCB mode is in a black display, and the alignment state in the liquid crystal cell is such that the rod-like liquid crystal compound rises at the center of the cell and the rod-like liquid crystal compound lies in the vicinity of the cell substrate. .

  Since the TN mode and the alignment of the liquid crystal are the same in black display, the preferred mode is the same for the TN mode. However, since the OCB mode has a larger range in which the liquid crystal compound has risen at the center of the cell than the TN mode, an optically anisotropic layer in which the discotic liquid crystal compound is homeotropically aligned or a rod-like liquid crystal It is necessary to slightly adjust the retardation value of the optically anisotropic layer in which the functional compound is homogeneously oriented. Specifically, the optically anisotropic layer in which the discotic liquid crystalline compound on the (transparent) support is homeotropically aligned, or the optically anisotropic layer in which the rod-like liquid crystalline compound is homogeneously aligned is Rth The retardation value is preferably 150 nm to 500 nm, and the Re retardation value is preferably 20 to 70 nm.

(VA mode liquid crystal display device)
In the VA mode liquid crystal cell, the rod-like liquid crystalline compound is aligned substantially vertically when no voltage is applied.
The VA mode liquid crystal cell includes (1) a narrowly defined VA mode liquid crystal cell in which a rod-like liquid crystal compound is aligned substantially vertically when no voltage is applied, and is substantially horizontally aligned when a voltage is applied (Japanese Patent Laid-Open No. 2). 176625 (in Japanese Patent Publication No. 176625), and (2) a liquid crystal cell (SID97, Digest of tech. Papers (Proceedings) 28 (1997) 845 in which the VA mode is converted into a multi-domain (for MVA mode) in order to enlarge the viewing angle. ), (3) A liquid crystal cell in a mode (n-ASM mode) in which a rod-like liquid crystalline compound is substantially vertically aligned when no voltage is applied and twisted multi-domain alignment is applied when a voltage is applied (Preliminary Collection 58-59 of the Japan Liquid Crystal Society) (1998)) and (4) SURVAVAL mode liquid crystal cells (announced at LCD International 98).

  In the black display of the VA mode liquid crystal display device, most of the rod-like liquid crystalline compounds in the liquid crystal cell are in a standing state, so that the optically anisotropic layer in which the discotic liquid crystalline compounds are homeotropically aligned, Alternatively, the liquid crystalline compound is compensated by an optically anisotropic layer in which the rod-like liquid crystalline compound is homogeneously aligned, and separately, the rod-like liquid crystalline compound is homogeneously oriented, and the average orientation direction of the major axis of the rod-like liquid crystalline compound and the polarizer It is preferable to compensate the viewing angle dependency of the polarizing plate with an optically anisotropic layer having an angle with respect to the transmission axis direction of less than 5 degrees.

  (Transparent) The optically anisotropic layer in which the support or the discotic liquid crystalline compound is homeotropically oriented, or the optically anisotropic layer in which the rod-like liquid crystalline compound is homogeneously oriented has an Rth retardation value of 150 nm to It is preferably 500 nm and the Re retardation value is 20 to 70 nm.

(Other liquid crystal display devices)
The ECB mode and STN mode liquid crystal display devices can be optically compensated in the same way as described above.

The present invention will be described more specifically with reference to the following examples. The materials, reagents, ratios, operations, and the like shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the following examples.
[Example 1]
(Production of polymer substrate)
The following composition was put into a mixing tank and stirred while heating to 30 ° C. to dissolve each component to prepare a cellulose acetate solution.
────────────────────────────────────
Cellulose acetate solution composition (parts by mass) Inner layer Outer layer ────────────────────────────────────
Cellulose acetate with an acetylation degree of 60.9% 100 100
Triphenyl phosphate (plasticizer) 7.8 7.8
Biphenyl diphenyl phosphate (plasticizer) 3.9 3.9
Methylene chloride (first solvent) 293 314
Methanol (second solvent) 71 76
1-butanol (third solvent) 1.5 1.6
Silica fine particles (AEROSIL R972, manufactured by Nippon Aerosil Co., Ltd.)
0 0.8
The following retardation increasing agent 1.7 0
────────────────────────────────────

  The obtained inner layer dope and outer layer dope were cast on a drum cooled to 0 ° C. using a three-layer co-casting die. The film having a residual solvent amount of 70% by mass was peeled off from the drum, both ends were fixed with a pin tenter, and the film was dried at 80 ° C. while transporting at a draw ratio of 110% in the transport direction, resulting in a residual solvent amount of 10%. By the way, it was dried at 110 ° C. Thereafter, it was dried at 140 ° C. for 30 minutes to produce a cellulose acetate film (outer layer: 3 μm, inner layer: 74 μm, outer layer: 3 μm) having a residual solvent of 0.3 mass%. The optical properties of the produced cellulose acetate film (CF-02) were measured.

The width of the obtained cellulose acetate was 1340 mm, and the thickness was 80 μm. It was 6 nm when the retardation value (Re) in wavelength 500nm was measured by the said method. Moreover, it was 90 nm when the retardation value (Rth) in wavelength 500nm was measured.
The produced cellulose acetate was immersed in a 2.0N potassium hydroxide solution (25 ° C.) for 2 minutes, neutralized with sulfuric acid, washed with pure water and dried. The surface energy of this PK-1 was determined by the contact angle method and found to be 63 mN / m.

<Preparation of alignment film for optically anisotropic layer>
On this cellulose acetate film, a coating solution having the following composition was applied at 28 mL / m ² with a # 16 wire bar coater. Drying was performed with warm air of 60 ° C. for 60 seconds and further with warm air of 90 ° C. for 150 seconds.
(Orientation film coating solution composition)
The following modified polyvinyl alcohol 20 parts by mass Water 360 parts by mass Methanol 120 parts by mass Glutaraldehyde (crosslinking agent) 1.0 part by mass

<Preparation of optically anisotropic layer>
On the alignment film, a rubbing treatment was performed by rotating at 500 rpm in a direction shifted by 1 ° from the conveying direction with a rubbing roll. Then, the following coating solution is continuously rotated on the alignment film surface of the roll film being conveyed at 30 m / min by rotating the wire bar of # 3.2 at 1171 rpm in the same direction as the film conveying direction. It was applied to. In the step of continuously heating from room temperature to 100 ° C., the solvent is dried, and then the film surface wind speed corresponding to the discotic liquid crystal compound layer is 1.5 m / sec in parallel with the film conveyance direction in the 135 ° C. drying zone. And heated for about 90 seconds to align the discotic liquid crystal compound. Next, the film is transported to a drying zone at 80 ° C., and an ultraviolet ray with an illuminance of 600 mW is applied by an ultraviolet irradiation device (ultraviolet lamp: output 160 W / cm, emission length 1.6 m) with the surface temperature of the film being about 100 ° C. Irradiation was carried out for 4 seconds to advance the crosslinking reaction, and the discotic liquid crystal compound was fixed to the orientation. Then, it was allowed to cool to room temperature and wound into a cylindrical shape to form a roll.

(Coating solution composition of optically anisotropic layer)
The following composition was dissolved in 107 parts by mass of methyl ethyl ketone to prepare a coating solution.
The following discotic liquid crystalline compound (1) 41.01 parts by mass Ethylene oxide-modified trimethylolpropane triacrylate (V # 360, manufactured by Osaka Organic Chemical Co., Ltd. 4.06 parts by mass Cellulose acetate butyrate (CAB551-0.2) 0.27 parts by mass Cellulose acetate butyrate (CAB531-1, manufactured by Eastman Chemicals) 0.09 parts by mass The following fluoroaliphatic group-containing polymer 1 0.03 parts by mass The following fluoroaliphatic groups Containing polymer 2 0.23 parts by mass Photopolymerization initiator (Irgacure 907, manufactured by Ciba Geigy) 1.35 parts by mass Sensitizer (Kayacure DETX, manufactured by Nippon Kayaku Co., Ltd.) 0.45 parts by mass

  When the polarizing plate was placed in a crossed Nicol arrangement and the unevenness of the obtained optical compensation film was observed, the unevenness was not detected even when viewed from the front and the direction inclined to 60 degrees from the normal line. The in-plane retardation of the obtained optical compensation film was 50 nm, and the slow axis angle viewed from the front was an angle of 89 ° with the film conveyance direction.

(Preparation of polarizing plate)
A polyvinyl alcohol (PVA) film having a thickness of 80 μm is dyed by immersing it in an aqueous iodine solution having an iodine concentration of 0.05% by mass at 30 ° C. for 60 seconds, and then in an aqueous boric acid solution having a boric acid concentration of 4% by mass. The film was longitudinally stretched 5 times the original length during the second immersion, and then dried at 50 ° C. for 4 minutes to obtain a polarizer having a thickness of 20 μm.
The optical compensation film was immersed in an aqueous sodium hydroxide solution at 55 ° C. at 1.5 mol / L, and then the sodium hydroxide was sufficiently washed away with water. Then, after being immersed in a diluted sulfuric acid aqueous solution at 35 ° C. for 1 minute at 0.005 mol / L, the diluted sulfuric acid aqueous solution was sufficiently washed away by immersion in water. Finally, the sample was thoroughly dried at 120 ° C.
An optical compensation film that has been saponified as described above is combined with a commercially available cellulose acylate film that has also been saponified, and a polarizing plate is laminated using a polyvinyl alcohol adhesive so as to sandwich the polarizer. Obtained. Here, Fujitac TF80UL (Fuji Photo Film Co., Ltd.) was used as a commercially available cellulose acylate film. At this time, since the polarizer and the protective films on both sides of the polarizer are manufactured in a roll form, the longitudinal directions of the roll films are parallel to each other and are continuously bonded. Therefore, the longitudinal direction of the optical compensation film roll (the casting direction of the cellulose acylate film) and the polarizer absorption axis were parallel to each other.
The angle formed between the polarizer transmission axis and the slow axis of the optical compensation film was 1 °.
When the apparent retardation of the obtained polarizing plate was calculated by inputting 45 ° as the angle φ between the polarizer transmission axis and the optical compensation film slow axis with KOBRA 21ADH (manufactured by Oji Scientific Instruments), It was 2 nm.

(Evaluation with TN liquid crystal cell)
A pair of polarizing plates provided in a liquid crystal display device (Syncmster 172X, manufactured by Samsung Electronics Co., Ltd.) using a TN type liquid crystal cell is peeled off. Instead, the above-prepared polarizing plate is replaced with an optical compensation film on the liquid crystal cell side. In this manner, the sheets were attached to the observer side and the backlight side one by one through an adhesive. The transmission axis of the polarizing plate on the viewer side and the transmission axis of the polarizing plate on the backlight side were arranged to be in the O mode.
About the produced liquid crystal display device, the transmittance | permeability of a black display (L0) and a white display (L7) is measured using a measuring machine (EZ-Contrast160D, ELDIM company make), and a front contrast ratio (white transmittance / black). And the angle at which the contrast ratio is 10 or more in the vertical and horizontal directions. The measurement results are shown in Table 1.

(Evaluation of unevenness on LCD panel)
When the display panel of the produced liquid crystal display device was adjusted to a halftone on the entire surface and unevenness was evaluated, unevenness was not detected in the panel.

[Example 2]
An optical compensation film and a polarizing plate were prepared and evaluated in the same manner as in Example 1 except that the rubbing angle on the alignment film was 0.1 ° and 2.5 ° with respect to the transport direction, respectively. The results are shown in Table 1.

[Comparative Example 1]
An optical compensation film and a polarizing plate were produced in the same manner as in Example 1 except that the rubbing direction on the alignment film was parallel to the film transport direction. The retardation of the produced optical compensation film was 50 nm, and the apparent retardation of the produced polarizing plate was 0 nm.

[Comparative Example 2]
In the cellulose acetate solution composition, the addition amount of the retardation increasing agent is changed to 1.5 parts by mass, the coating solution composition of the optically anisotropic layer is changed as follows, and the wire bar used for coating the optically anisotropic layer An optical compensation film was prepared in the same manner as in Comparative Example 1 except that # was changed to # 4.0. The retardation of the produced optical compensation film was 40 nm, and the apparent retardation of the produced polarizing plate was 0 nm.

(Coating solution composition of optically anisotropic layer)
The following composition was dissolved in 107 parts by mass of methyl ethyl ketone to prepare a coating solution.
The following discotic liquid crystalline compound (1) 41.01 parts by mass Ethylene oxide-modified trimethylolpropane triacrylate (V # 360, manufactured by Osaka Organic Chemical Co., Ltd. 4.06 parts by mass Cellulose acetate butyrate (CAB551-0.2) 0.72 parts by mass Cellulose acetate butyrate (CAB531-1, manufactured by Eastman Chemicals Co., Ltd.) 0.18 parts by mass MegaFuck F780 (manufactured by Dainippon Ink Co., Ltd.) 0.48 parts by mass light Polymerization initiator (Irgacure 907, manufactured by Ciba Geigy) 1.35 parts by mass Sensitizer (Kayacure DETX, manufactured by Nippon Kayaku Co., Ltd.) 0.45 parts by mass

[Comparative Example 3]
An optical compensation film was produced in the same manner as in Example 1 except that the wire bar used for coating the optically anisotropic layer was changed to # 1.0. The retardation of the produced optical compensation film was 16 nm, and the apparent retardation of the produced polarizing plate was 0.8 nm.

[Comparative Example 4]
An optical compensation film and a polarizing plate were prepared and evaluated in the same manner as in Example 1 except that the rubbing angle on the alignment film was 5 ° with respect to the transport direction. The results are shown in Table 1.

  As can be seen from the results shown in Table 1, in the embodiment of the present invention, the front contrast ratio can be improved while maintaining the wide contrast viewing angle of the liquid crystal display device.

[Example 3]
In the same manner as in Example 1, except that the addition amount of the retardation increasing agent used in Example 1 was changed to prepare a cellulose acetate film having Rth of 76, 85, 100, and 110 nm, an optical compensation film, Furthermore, a polarizing plate with an optical compensation film was prepared. Even when Rth of the polymer substrate was changed to 76, 85, 100, and 110 nm, it was confirmed that the surface was uniform. It was confirmed that the contrast ratio of these polarizing plates can be improved while maintaining the contrast viewing angle in the same manner as described above.

[Example 4]
Example 1 except that the retardation increasing agent used in Example 1 was replaced with the following retardation increasing agent, and the addition amount of the inner layer was 1.2 parts by mass, and a polymer substrate having an Rth of 90 nm was prepared. In the same manner, an optical compensation film and a polarizing plate with an optical compensation film were produced. It was confirmed that the surface had no unevenness. It was confirmed that both optical compensation films can improve the contrast ratio while maintaining the contrast viewing angle.

[Example 5]
In the same manner as in Example 1 except that the polymer base material having Rth of 76, 85, 100, and 110 nm was prepared by changing the addition amount of the retardation increasing agent used in Example 4, an optical compensation film, Furthermore, a polarizing plate with an optical compensation film was prepared. Even when Rth of the polymer substrate was changed to 76, 85, 100, and 110 nm, it was confirmed that the surface was uniform. It was confirmed that any optical compensation film can improve the contrast ratio while maintaining the contrast viewing angle.

Claims (4)

A polarizing plate having at least an optical compensation film having an in-plane retardation of 20 nm or more and a polarizer, and having a transmittance I of light passing through the polarizing plate at an angle θ with respect to the transmission axis of the polarizer When measured using an analyzer having a transmission axis in the direction, Re is determined such that the transmittance I measured with respect to 0 ° ≦ θ ≦ 360 ° is best matched with the following equation [1]: A polarizing plate that is 2 nm to 5 nm.

(I: transmittance, K: constant, θ: angle between polarizer transmission axis and analyzer transmission axis, λ: measurement wavelength (however, visible light wavelength)) 2. The polarizing plate according to claim 1, wherein the optical compensation film has at least one optically anisotropic layer formed of a support and a composition containing a liquid crystal compound on the support. . The polarizing plate according to claim 1, wherein the liquid crystal compound is a discotic liquid crystal. The liquid crystal display device which has a polarizing plate of any one of Claims 1-3.