JP2002055230A - Optical compensation sheet, elliptically polarizing plate and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device having excellent display quality and being easy to reuse the liquid crystal cell. SOLUTION: An optical compensation sheet, which is used for the liquid crystal display device, is characterized by comprising a transparent supporting body having an alignment layer and an optically anisotropic layer composed of a compound with a discotic structural unit arranged thereon in this order where the alignment layer is a cross-linked film, of a polymer mixture containing a polymer of a lower degree of polymerization and a polymer of a higher degree of polymerization with difference in their respective degrees of polymerization 50 or more, rubbing treated on the surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical compensation sheet,
The present invention relates to an elliptically polarizing plate and a liquid crystal display using the same.

[0002]

2. Description of the Related Art A liquid crystal display device comprises a polarizing plate and a liquid crystal cell. In a TN mode TFT liquid crystal display device that is currently mainstream, as described in JP-A-8-50206, the display quality is improved by inserting an optical compensation sheet (retardation plate) between a polarizing plate and a liquid crystal cell. , A liquid crystal display device having a high density is realized. However, this method has a problem that the liquid crystal display device itself becomes thicker. Japanese Patent Application Laid-Open No. 1-68940 discloses that an elliptically polarizing plate having an optical compensatory sheet on one surface of a polarizing film and a protective film on the other surface is used to increase the front contrast without increasing the thickness of the liquid crystal display device. There is a statement that it can be done. However, the optical compensation sheet of the present invention
It was found that a phase difference was easily generated by distortion such as heat, and there was a problem in durability. Japanese Patent Application Laid-Open No. Hei 7-191217 and European Patent Publication 0 disclose the problem of phase difference generation due to distortion.
In the specification of 911656A2, a liquid crystal display device is obtained by using an optical compensatory sheet in which an optically anisotropic layer made of a discotic compound is applied on a transparent support, and using an elliptically polarizing plate as a direct protective film for the polarizing plate. The above-mentioned problem of durability was solved without increasing the thickness.

The optical compensation sheet is bonded to a glass substrate of a liquid crystal cell as a part of a polarizing plate (protective film) via an adhesive. When an abnormality occurs during inspection or the like, the polarizing plate is peeled off from the glass substrate of the liquid crystal cell, and the expensive liquid crystal cell is reused. The peeling of the polarizing plate from the glass substrate of the liquid crystal cell is hereinafter referred to as rework. However, when reworking, once every few times,
There was a problem that the optically anisotropic layer of the optical compensation sheet was peeled off on the glass substrate. At the time of rework, there is a high possibility that the interface between the alignment film and the optically anisotropic layer and the breakdown of the alignment film in the layer occur. The destruction occurring at the interface between the alignment film and the optically anisotropic layer could be prevented by using the modified polyvinyl alcohol described in JP-A-8-338913. However, although the in-layer fracture of the alignment film was considerably improved by the addition of the crosslinking agent described in JP-A-8-338913, when the thickness of the optically anisotropic layer was increased, the alignment film layer was reworked. In some cases, the strain (stress) applied to the substrate becomes large, causing breakage in the alignment film layer.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical compensatory sheet which can be easily manufactured, enlarges the viewing angle of a liquid crystal display device, and has excellent reworkability. It is another object of the present invention to facilitate the reuse of a liquid crystal cell and reduce the manufacturing cost of a liquid crystal display device by using the optical compensation sheet. Further, the object of the present invention is to increase the viewing angle without increasing the thickness of the liquid crystal panel, and due to a change in the viewing angle, a decrease in contrast, gradation or black-and-white inversion, and little change in hue, etc., occur. Another object of the present invention is to provide a liquid crystal display device having improved durability.

[0005]

The inventor of the present invention has found that the cause of the intra-layer breakdown of the alignment film is that the degree of polymerization of the polymer used for the alignment film material is low, and when a large stress is applied, the inter-molecular It is presumed that the entanglement is broken and destroyed.
Therefore, this destruction can be prevented by increasing the molecular weight of the polymer used for the alignment film material. However, the orientation film has a role of orienting the discotic compound in the upper layer by rubbing treatment. If the degree of polymerization is too high, rubbing requires a large amount of energy. By earnest research of the inventor,
By using two kinds of polymers having different degrees of polymerization in combination for the alignment film of the optical compensation sheet, it has been found that the frequency of occurrence of the peeling of the optically anisotropic layer during rework can be reduced.

Accordingly, an object of the present invention is to provide the following (1) to
This was achieved by the optical compensation sheet of (8), the elliptically polarizing plate of the following (9) and (10), and the liquid crystal display of the following (11) and (12). (1) An optical compensation sheet in which an alignment film and an optically anisotropic layer made of a compound having a disc-shaped structural unit are provided in this order on a transparent support, wherein the alignment films have a degree of polymerization of 50 or more. An optical compensation sheet, wherein a rubbing treatment is applied to the surface of a crosslinked film of a polymer mixture containing a polymer having a different degree of polymerization and a polymer having a higher degree of polymerization. (2) The degree of polymerization of the polymer having a low degree of polymerization is 100 to 500.
Wherein the degree of polymerization of the polymer having a high degree of polymerization is in the range of 750 to 2,000. (3) The optical compensation sheet according to (1) or (2), wherein the polymer having a low degree of polymerization and the polymer having a high degree of polymerization are either unmodified polyvinyl alcohol or modified polyvinyl alcohol.

(4) One of the polymer having a low polymerization degree and the polymer having a high polymerization degree is a modified polyvinyl alcohol, and the other is an unmodified polyvinyl alcohol. (1)
The optical compensation sheet according to any one of (1) to (3). (5) The method according to any one of (1) to (4), wherein the mass ratio of the polymer having a low polymerization degree to the polymer having a high polymerization degree is in the range of 50:50 to 99.8: 0.2. Optical compensation sheet. (6) The optically compensatory sheet according to (3) or (4), wherein the modified polyvinyl alcohol is a modified product of polyvinyl alcohol with the following compound:

Embedded image [Wherein, R ¹ represents an alkyl group, an acryloylalkyl group, a methacryloylalkyl group, or an epoxyalkyl group; W represents a halogen atom, an alkyl group, or an alkoxy group; X represents an active ester, an acid anhydride Or the group of atoms necessary to form an acid halide; p represents 0 or 1;
Represents an integer of 0 to 4].

(7) The above transparent support is represented by the following formula (I)
Re retardation value defined by
And the Rth retardation value defined by the following formula (II) is from 70 to 400 nm.
(1) Re = (nx−ny) × d (II) Rth = {(nx + ny) / 2−nz} × d where nx is the refractive index in the slow axis direction in the film plane; ny is the refractive index in the fast axis direction in the film plane; nz is the refractive index in the film thickness direction. And d is the thickness of the film]. (8) The polymer film contains 0.01% of an aromatic compound having at least two aromatic rings per 100 parts by mass of cellulose acetate having an acetylation degree of 59.0 to 61.5% and 100 parts by mass of cellulose acetate. The optical compensation sheet according to (7), wherein the optical compensation sheet contains from 20 to 20 parts by mass.

(9) An optical compensatory sheet comprising an optically anisotropic layer comprising a transparent support, an alignment film and a compound having a disc-shaped structural unit is adhered to at least one surface of the polarizing film. A polymer film having a Re retardation value defined by the following formula (I) in the range of 20 to 200 nm and an Rth retardation value defined by the following formula (II) in the range of 70 to 400 nm: Elliptically polarized light, wherein the alignment film is obtained by rubbing the surface of a crosslinked film of a polymer mixture containing a polymer having a low polymerization degree and a polymer having a high polymerization degree, each having a polymerization degree different from each other by 50 or more. Plate: (I) Re = (nx−ny) × d (II) Rth = {(nx + ny) / 2−nz} × d [where nx is a value in the slow axis direction in the film plane] It is a folding rate; ny is an fast axis direction of the refractive index in the film plane; nz is a refractive index thickness direction of the film; and, d is the thickness of the film.

(10) The polymer film comprises cellulose acetate having an acetylation degree of 59.0 to 61.5% and an aromatic compound having at least two aromatic rings per 100 parts by mass of cellulose acetate. The elliptically polarizing plate according to (9), comprising 0.01 to 20 parts by mass. (11) A liquid crystal display device including a liquid crystal cell and two polarizing plates disposed on both sides of the liquid crystal cell, wherein at least one of the polarizing plates is the polarizing plate according to (9) or (10), and optical compensation is performed. A liquid crystal display device, wherein a sheet is disposed so as to be on a liquid crystal cell side. (12) The liquid crystal display device according to (11), wherein the liquid crystal cell is an OCB mode or TN mode liquid crystal cell.

[0011]

The optical compensatory sheet of the present invention is provided with an alignment film and an optically anisotropic layer made of a compound having a disc-shaped structural unit on a transparent support. Then, as the alignment film, a crosslinked film of a polymer mixture containing two kinds of polymers having different degrees of polymerization is formed, and the surface thereof is subjected to a rubbing treatment, whereby the optically anisotropic layer is left unremoved during rework. It is possible to provide an optical compensation sheet that is performed less frequently. By using this alignment film, the rubbing treatment of the alignment film for aligning the compound having the disc-shaped structural unit does not cause any problem in the same process as the conventional one, and the alignment ability as the alignment film can be sufficiently maintained. . By using the optical compensatory sheet of the present invention or a polarizing plate using the same in a liquid crystal display device, the liquid crystal cell is optically compensated without adverse effects while maintaining the conventional thickness, and a liquid crystal with excellent display quality is provided. A display device can be provided. Furthermore, due to the excellent reworkability of the optical compensation sheet of the present invention, the liquid crystal cell can be easily reused, the productivity of the liquid crystal display device can be improved, and the manufacturing cost can be reduced.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The optical compensatory sheet of the present invention comprises an alignment film and an optically anisotropic layer having a disc-shaped structural unit provided in this order on a transparent support. Then, two kinds of polymers having different degrees of polymerization are used as the polymer for forming the alignment film. Examples of the compound having a discotic structural unit used in the optically anisotropic layer include a polymer obtained by polymerization of a low molecular weight discotic liquid crystalline compound such as a monomer or a polymerizable discotic liquid crystalline compound. . Discotic compounds (discotic compounds) can generally be broadly classified into compounds having a discotic liquid crystal phase (that is, a discotic nematic phase) and compounds having no discotic liquid crystal phase. Discotic compounds generally have negative birefringence. The optically anisotropic layer in the invention utilizes the negative birefringence of the discotic compound. The optical compensation sheet of the present invention has a basic structure including a transparent support, an alignment film provided thereon, and an optically anisotropic layer having a disc-shaped structural unit formed on the alignment film.

[Alignment Film] The alignment film can be formed by forming a crosslinked film of a polymer mixture containing two types of polymers having different degrees of polymerization, and subjecting the surface to a rubbing treatment. By using a polymer having a small degree of polymerization and a polymer having a large degree of polymerization as the two kinds of polymers, an optical compensation sheet having excellent reworkability can be provided. Further, the alignment film may further contain another polymer in addition to the two types of polymers having different degrees of polymerization. Further, a crosslinked film may be formed from these polymers and a crosslinking agent. The difference in the degree of polymerization between the two types of polymers may be 50 or more, and may be 250 or more.
It is preferably at least 500, and more preferably at least 500. The degree of polymerization of the polymer having a small degree of polymerization is 1
00 to 500 is preferable, and 150 to 350 is more preferable. The polymerization degree of the polymer having a large polymerization degree is 750.
To 2,000, more preferably 850 to 1500. The ratio of the polymer having a large degree of polymerization to the polymer having a small degree of polymerization is preferably in the range of 0.5 to 50% by mass, more preferably in the range of 5 to 30% by mass, and 7.5 to 25% by mass. % Is more preferable.

Further, as at least one kind of polymer used for the alignment film, it is preferable to use a polymer which is crosslinkable by itself or a polymer which is crosslinked by a crosslinking agent. The alignment film is a polymer having a functional group or a polymer having a functional group introduced therein.
It is formed by reacting between polymers by light, heat, pH change or the like, or by introducing a crosslinking group derived from a crosslinking agent between polymers by using a crosslinking agent which is a compound having high reaction activity. Can be formed by crosslinking.

[0015] Such crosslinking is usually carried out by applying a coating solution containing the above polymer or a mixture of the polymer and a crosslinking agent on a transparent support, followed by heating or the like. As long as durability can be ensured at the stage of the final product, crosslinking treatment may be performed at any stage after coating the alignment film on the transparent support until obtaining the final optical compensation sheet. Considering the orientation of the compound having a disc-shaped structure (optically anisotropic layer) formed on the orientation film,
After orienting the compound having a disc-like structure, it is also preferable to perform sufficient crosslinking. That is, the optical compensation sheet is formed by applying a coating solution containing a polymer and a crosslinking agent capable of crosslinking the polymer on a transparent support, heating and drying, and then performing a rubbing treatment to form an alignment film. A coating solution containing a compound having a disc-shaped structural unit is applied on a film, heated to a temperature higher than a discotic nematic phase formation temperature, and then cooled to form an optically anisotropic layer. When the alignment film coating liquid is heated and dried, the alignment film is cross-linked. However, when the heating temperature is low, the cross-linking of the alignment film further proceeds when the alignment film is heated to the discotic nematic phase forming temperature.

As the polymer used for the alignment film of the present invention, any of a polymer which can be crosslinked by itself and a polymer which is crosslinked by a crosslinking agent can be used. Of course, both possible polymers can also be used.
Examples of the polymer include polymethyl methacrylate, acrylic acid / methacrylic acid copolymer, styrene / maleimide copolymer, polyvinyl alcohol, modified polyvinyl alcohol, poly (N-methylol acrylamide), styrene / vinyl toluene copolymer, Polymers such as chlorosulfonated polyethylene, nitrocellulose, polyvinyl chloride, chlorinated polyolefin, polyester, polyimide, vinyl acetate / vinyl chloride copolymer, ethylene / vinyl acetate copolymer, carboxymethyl cellulose, polyethylene, polypropylene, and polycarbonate; Compounds such as silane coupling agents can be mentioned. Examples of preferred polymers include water-soluble polymers such as poly (N-methylolacrylamide), carboxymethylcellulose, gelatin, polyvinyl alcohol and modified polyvinyl alcohol.
Gelatin, polyvinyl alcohol and modified polyvinyl alcohol are preferred, and polyvinyl alcohol and modified polyvinyl alcohol are more preferred.

Polyvinyl alcohol having a different degree of polymerization or
It is further possible to use two types of modified polyvinyl alcohol in combination.
preferable. Examples of polyvinyl alcohol include saponification degree
Polyvinyl alcohol in the range of 70 to 100% is listed.
I can do it. Generally, the degree of saponification is in the range of 80-100%.
More preferably in the range of 85 to 95%.
No. The degree of polymerization of polyvinyl alcohol is 100 to
It is preferably in the range of 3000. Modified polyvinyl
Examples of alcohols include copolymerization modification and chain transfer
Polyvinyl modified or modified by block polymerization
Alcohol and the like can be mentioned. Copolymerize
Examples of modifying groups in this case include COONa, Si (OX)
_Three, N (CH_Three)_Three・ Cl, C₉, H₁₉COO, S
O_Three, Na, C₁₂H_{twenty five}And the like. By chain transfer
Examples of the modifying group for the modification include COONa,
SH, C₁₂H_{twenty five}And the like. Also, block polymerization
Examples of the modifying group when modifying with COO include COO
H, CONH_Two, COOR, C₆H_FiveEtc.
You. Among these, the degree of saponification is in the range of 80 to 100%.
Certain unmodified or modified polyvinyl alcohols are preferred
No. In addition, an unmodified polysaccharide having a saponification degree of 85 to 95%
Rivinyl alcohol and modified polyvinyl alcohol
More preferred.

As the modified polyvinyl alcohol, it is particularly preferable to use a modified polyvinyl alcohol with a compound represented by the following general formula. This modified polyvinyl alcohol is hereinafter referred to as a specific modified polyvinyl alcohol.

[0019]

Embedded image [Wherein, R ¹ represents an alkyl group, an acryloylalkyl group, a methacryloylalkyl group, or an epoxyalkyl group; W represents a halogen atom, an alkyl group, or an alkoxy group; X represents an active ester, an acid anhydride Or the group of atoms necessary to form an acid halide; p represents 0 or 1;
Represents an integer of 0 to 4]. The above-mentioned specific modified polyvinyl alcohol is preferably a modified product of polyvinyl alcohol with a compound represented by the following general formula.

[0020]

Embedded image [Wherein, X ¹ represents an atomic group necessary for forming an active ester, an acid anhydride, or an acid halide, and m represents an integer of 2 to 24. ]

The polyvinyl alcohol used for reacting with the compound represented by these general formulas includes:
Examples of the above-mentioned unmodified polyvinyl alcohol and modified polyvinyl alcohol such as those modified by copolymerization, that is, those modified by chain transfer and those modified by block polymerization can be mentioned. A preferred example of the specific modified polyvinyl alcohol is described in Japanese Patent Application No. 7-2058.
No. 3 describes this in detail. Methods for synthesizing these polymers, measuring the visible absorption spectrum, and determining the introduction rate y are described in detail in JP-A-8-338913.

Examples of the crosslinking agent include aldehydes, N-
Examples include methylol compounds, dioxane derivatives, compounds that act by activating carboxyl groups, active vinyl compounds, active halogen compounds, isoxazoles, and dialdehyde starch. Examples of aldehydes include formaldehyde, glyoxal, and glutaraldehyde. Examples of N-methylol compounds include dimethylol urea and methylol dimethylhydantoin. Examples of the dioxane derivative include 2,3-dihydroxydioxane. Examples of compounds that act by activating a carboxyl group include carbenium, 2-naphthalene sulfonate, 1,1-bispyrrolidino-1-.
Chloropyridinium, and 1-morpholinocarbonyl-3- (sulfonatoaminomethyl). Examples of active vinyl compounds include 1,3,5-triacloyl-hexahydro-s-triazine, bis (vinylsulfone) methane, and N, N′-methylenebis- [β- (vinylsulfonyl) propionamide]. . Examples of the active halogen compound include 2, 4
-Dichloro-6-hydroxy-S-triazine. These can be used alone or in combination. These are preferred when used in combination with the above water-soluble polymers, particularly polyvinyl alcohol and modified polyvinyl alcohol (including the above-mentioned specific modified products). When productivity is considered, the use of aldehydes having high reaction activity, particularly glutaraldehyde, is preferred.

The amount of the crosslinking agent added to the polymer is not particularly limited. Moisture resistance tends to improve when a large amount of a crosslinking agent is added. However, when the cross-linking agent is added in an amount of 50% by mass or more based on the polymer, the alignment ability as an alignment film decreases. Therefore, the amount of the crosslinking agent added to the polymer,
It is preferably in the range of 0.1 to 20% by mass,
More preferably, it is in the range of 0.5 to 15% by mass. Although the alignment film contains a certain amount of a cross-linking agent that has not reacted even after the cross-linking reaction is completed, the amount of the cross-linking agent is preferably 1.0% by mass or less in the alignment film. More preferably, it is at most 5% by mass. If the unreacted crosslinking agent is contained in the alignment film in an amount exceeding 1.0 mass, sufficient durability cannot be obtained. That is, when used in a liquid crystal display device, reticulation may occur when used for a long time or when left in an atmosphere of high temperature and high humidity for a long time.

The alignment film in the present invention is formed by applying a solution containing the above polymer or a solution containing the above polymer and a crosslinking agent on a transparent support, and then drying by heating (crosslinking).
Then, it can be formed by rubbing. The cross-linking reaction may be performed at any time after coating on the transparent support. When using a water-soluble polymer such as polyvinyl alcohol as the alignment film forming material,
The solvent for preparing the coating liquid is preferably an organic solvent such as methanol having defoaming action, or a mixed solvent of an organic solvent and water. When methanol is used as the organic solvent, the ratio is generally water: methanol in a mass ratio of 0: 100 to 99: 1, and 0:10 to 100: 1.
The ratio is more preferably 0 to 91: 9. Thereby, generation of bubbles is suppressed, and defects on the surface of the alignment film and the optically anisotropic layer are significantly reduced. Examples of the coating method include a spin coating method, a dip coating method, a curtain coating method, an extrusion coating method, a bar coating method, and an E-type coating method. Among them, the E-type coating method is particularly preferable.

The thickness of the alignment film is 0.1 to 10 μm.
Is preferred. Heating drying, the heating temperature is 20 ~ 110 ℃
Can be performed in the range of In order to form a sufficient crosslink, the heating temperature is preferably in the range of 60 to 100 ° C, more preferably in the range of 80 to 100 ° C. The drying time can be 1 minute to 36 hours. Preferably, it is 5 minutes to 30 minutes. The pH is also preferably set to an optimum value for the crosslinking agent to be used. When glutaraldehyde is used, the pH is adjusted to 4.5 to 5.5.
It is preferably in the range of 5, particularly preferably pH 5.

The alignment film is provided on the transparent support or on the undercoat layer. The orientation film can be obtained by subjecting the surface to rubbing after crosslinking the polymer layer as described above. The alignment film functions to define the alignment direction of the liquid crystalline discotic compound provided thereon.

For the rubbing treatment, a treatment method widely used as a liquid crystal alignment treatment step of an LCD can be used. That is, a method of rubbing the surface of the alignment film in a certain direction using paper, gauze, felt, rubber, nylon, polyester fiber, or the like can be used to obtain the alignment. Generally, rubbing is performed several times using a cloth or the like on which fibers having a uniform length and thickness are planted on average.

[Optical Anisotropic Layer] In the present invention, the optically anisotropic layer is formed on the alignment film. The optically anisotropic layer is a layer having a negative birefringence made of a compound having a disc-shaped structural unit. That is, the optically anisotropic layer is a layer of a low molecular weight liquid crystalline discotic compound such as a monomer or a layer of a polymer obtained by polymerization (curing) of a polymerizable liquid crystalline discotic compound. Examples of discotic (discotic) compounds include C.I. Destrade et al., Mol. Cr
yst. 71, p. 111 (1981); Destrade et al., Mol. Cryst. 122, 141 pages (198
5 years), Physics lett, A, Vol. 78, 82
Truxene derivatives described on page (1990),
B. Kohne et al., Angew. Chem.
Vol. 96, p. 70 (1984) and cyclohexane derivatives described in J. Am. M. J. Lehn et al. C
hem. Commun. , P. 1794 (1985),
J. Research report by Zhang et al. Am. Chem. S
oc. 116, p. 2655 (1994), and azacrown-based and phenylacetylene-based macrocycles.

Discotic (disk-like) compounds generally have a structure in which these are used as a core of a molecular center, and linear alkyl groups, alkoxy groups, substituted benzoyloxy groups and the like are radially substituted as the linear chains. , Which exhibit liquid crystallinity and include those generally called discotic liquid crystals. However, the molecule is not limited to the above example as long as the molecule itself has negative uniaxiality and can impart a certain orientation. In the present invention, the term "formed from a discotic compound" does not mean that the final product need be the above-described compound. For example, a group in which the low-molecular-weight discotic liquid crystal reacts with heat, light, or the like. As a result, those which have been polymerized or cross-linked by reaction with heat, light, or the like to have a high molecular weight and have lost liquid crystallinity are also included. Preferred examples of the discotic compound are described in JP-A-8-50206.

The optically anisotropic layer is a layer having a negative birefringence made of a compound having a discotic structural unit, and the surface of the discotic structural unit is inclined with respect to the transparent support surface, and It is preferable that the angle between the surface of the structural unit and the surface of the transparent support changes in the depth direction of the optically anisotropic layer. Generally, the angle (tilt angle) of the surface of the discotic structural unit increases or decreases in the depth direction of the optically anisotropic layer and as the distance from the bottom surface of the optically anisotropic layer increases. Preferably, the tilt angle increases with increasing distance. Further, the change in the inclination angle includes a continuous increase, a continuous decrease, an intermittent increase, an intermittent decrease, a change including the continuous increase and the continuous decrease, and an intermittent change including the increase and the decrease. it can. The intermittent change includes a region where the inclination angle does not change in the thickness direction. It is preferable that the tilt angle increases or decreases as a whole, even if it includes a region that does not change. Further, the inclination angle is preferably increased as a whole, and is particularly preferably changed continuously.

The optically anisotropic layer is generally formed by applying a solution in which a discotic compound and another compound are dissolved in a solvent onto an orientation film, drying the solution, and then heating the solution to a discotic nematic phase forming temperature. (Discotic nematic phase) is obtained by cooling. Alternatively, the optically anisotropic layer is formed by applying a solution in which a discotic compound and other compounds (for example, a polymerizable monomer and a photopolymerization initiator) are dissolved in a solvent onto the alignment film, drying, and then discotic nematic It is obtained by heating to a phase forming temperature, polymerizing (by irradiation with UV light or the like), and further cooling. The discotic liquid crystalline compound used in the present invention has a discotic nematic liquid crystal phase-solid phase transition temperature of 70 to 3
It is preferably in the range of 00 ° C, particularly preferably in the range of 70 to 170 ° C.

The tilt angle of the discotic unit on the support side can be generally adjusted by selecting a discotic compound or a material of an alignment film, or by selecting a rubbing method. The tilt angle of the discotic unit on the surface side (air side) can be generally adjusted by selecting a discotic compound or another compound used together with the discotic compound. Examples of compounds used with discotic compounds include plasticizers, surfactants,
Examples include polymerizable monomers and polymers. Further, the degree of change of the inclination angle can be adjusted by the same selection as described above.

The plasticizer, surfactant and polymerizable monomer used together with the discotic compound are compatible with the discotic compound and can change the tilt angle of the liquid crystalline discotic compound, or have an orientation. Any compound can be used as long as it does not inhibit. Among these, 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 1 to 50 relative to the discotic compound.
% By mass, preferably in the range of 5 to 30% by mass.

As the polymer to be used together with the discotic compound, any polymer can be used as long as it has compatibility with the discotic compound and can change the tilt angle of the liquid crystalline discotic compound. Examples of the polymer include a cellulose ester. Preferred examples of the cellulose ester include cellulose acetate, cellulose acetate propionate, hydroxypropylcellulose and cellulose acetate butyrate. In order not to hinder the orientation of the liquid crystalline discotic compound, the amount of the polymer is generally in the range of 0.1 to 10% by mass relative to the discotic compound,
More preferably, it is in the range of 0.1 to 8% by mass,
More preferably, it is in the range of 0.1 to 5% by mass.

[Transparent Support] As the polymer film used in the present invention, a polymer film having a light transmittance of 80% or more is preferably used. As the polymer film, a film that does not easily exhibit birefringence due to external force is preferable. Examples of the polymer film include cellulosic polymers, norbornene-based polymers such as Arton (trade name, manufactured by JSR Corporation) and Zeonex (trade name, manufactured by Zeon Corporation), and polymethyl methacrylate. As the cellulosic polymer, a cellulose ester is preferable, and a lower fatty acid ester of cellulose is more preferable. Lower fatty acids are those with 6 carbon atoms.
The following fatty acids are meant: The number of carbon atoms is preferably 2 (cellulose acetate), 3 (cellulose propionate) or 4 (cellulose butyrate).
As the cellulose ester, cellulose acetate is preferable, and examples thereof include diacetyl cellulose and triacetyl cellulose. Mixed fatty acid esters such as cellulose acetate propionate and cellulose acetate butyrate may be used.

The viscosity average degree of polymerization (DP) of the polymer film is preferably at least 250,
More preferably, it is the above. Further, the polymer film 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. Specific M
The value of w / Mn is preferably from 1.0 to 1.7, more preferably from 1.3 to 1.65, and most preferably from 1.4 to 1.6. Surface treatment (eg, glow discharge treatment, corona discharge treatment, ultraviolet treatment) on the polymer film to improve the adhesion between the polymer film and the layer provided thereon (adhesive layer, alignment film, or optically anisotropic layer) , Flame treatment). These polymer films preferably contain an ultraviolet absorber or the like. In addition, Japanese Patent Application Laid-Open No. 7-33343
An adhesive layer (undercoat layer) may be provided on the polymer film as described in Japanese Patent Publication No. 3 (JP-A) No. 3 (1999). The thickness of the adhesive layer is preferably 0.1 to 2 μ, more preferably 0.2 to 1 μ. As the polymer film of the present invention, it is preferable to use a cellulose acetate film having an acetylation degree of 59.0 to 61.5%. The acetylation degree means the amount of bound acetic acid per unit mass of cellulose. The degree of acetylation follows the measurement and calculation of the degree of acetylation in ASTM: D-817-91 (test method for cellulose acetate and the like).

[Retardation Control] In order to adjust the retardation of a polymer film, a method of applying an external force such as stretching is generally used.
Aromatic compounds having at least two aromatic rings, such as those described in 6A2, can also be used as retardation increasing agents. When a cellulose acetate film is used as the transparent support of the optical compensation sheet of the present invention, the aromatic compound is cellulose acetate 100
It is used in the range of 0.01 to 20 parts by mass with respect to parts by mass. The aromatic compound is preferably used in a range of 0.05 to 15 parts by mass, more preferably in a range of 0.1 to 10 parts by mass, based on 100 parts by mass of cellulose acetate. Two or more aromatic compounds may be used in combination. The aromatic ring of the aromatic compound includes an aromatic hetero ring in addition to the aromatic hydrocarbon ring.

[Retardation of Film] The Re retardation value and Rth retardation value of the film are defined by the following formulas (I) and (II), respectively. (I) Re = (nx−ny) × d (II) Rth = {(nx + ny) / 2−nz} × d In the formulas (I) and (II), nx is a slow axis direction in the film plane ( (The direction in which the refractive index becomes the maximum). In the formulas (I) and (II), ny is the refractive index in the fast axis direction (direction in which the refractive index is minimum) in the film plane. In the formula (II), nz is the refractive index in the thickness direction of the film. In formulas (I) and (II), d
Is the film thickness in nm. In the present invention, the polymer film has a Re retardation value of 20.
To 200 nm, and the Rth retardation value is adjusted to 70 to 400 nm. Particularly preferred are aromatic heterocycles, which are generally unsaturated heterocycles. A 1,3,5-triazine ring is particularly preferred.

The number of aromatic rings in the aromatic compound is 2
To 20, preferably 2 to 12, more preferably 2 to 8, and most preferably 3 to 6. The bonding relationship between two aromatic rings is as follows: (a) when forming a condensed ring, (b)
It can be classified into a case where a single bond is directly bonded and a case where it is bonded via a (c) linking group (a spiro bond cannot be formed due to an aromatic ring). The connection relationship may be any of (a) to (c).

Examples of the condensed ring of (a) (condensed ring of two or more aromatic rings) include an indene ring, a naphthalene ring, an azulene ring, a fluorene ring, a phenanthrene ring, an anthracene ring, an acenaphthylene ring, a naphthacene ring, Pyrene ring, indole ring, isoindole ring, benzofuran ring, benzothiophene ring, indolizine ring, benzoxazole ring, benzothiazole ring, benzimidazole ring, benzotriazole ring, purine ring, indazole ring, chromene ring, quinoline ring, isoquinoline Ring, quinolidine ring, quinazoline ring, cinnoline ring, quinoxaline ring, phthalazine ring, pteridine ring, carbazole ring, acridine ring,
Phenanthridine ring, xanthene ring, phenazine ring, phenothiazine ring, phenoxatiin ring, phenoxazine ring and thianthrene ring are included. Preferred are a naphthalene ring, an azulene ring, an indole ring, a benzoxazole ring, a benzothiazole ring, a benzimidazole ring, a benzotriazole ring and a quinoline ring. The single bond in (b) is preferably a bond between carbon atoms of two aromatic rings. Two aromatic rings may be linked by two or more single bonds to form an aliphatic ring or a non-aromatic heterocyclic ring between the two aromatic rings.

The connecting group (c) is also preferably bonded to carbon atoms of two aromatic rings. The linking group is an alkylene group, alkenylene group, alkynylene group, -CO-, -O
-, -NH-, -S- or a combination thereof is preferred. Examples of the linking group consisting of a combination are shown below. Note that the left and right relationships in the following examples of the linking group may be reversed. c1: -CO-O-c2: -CO-NH-c3: -alkylene-O-c4: -NH-CO-NH-c5: -NH-CO-O-c6: -O-CO-O-c7: -O-alkylene-O-c8: -CO-alkenylene-c9: -CO-alkenylene-NH-c10: -CO-alkenylene-O-c11: -alkylene-CO-O-alkylene-O-CO
-Alkylene-c12: -O-alkylene-CO-O-alkylene-O-
CO-alkylene-O-c13: -O-CO-alkylene-CO-O-c14: -NH-CO-alkenylene- c15: -O-CO-alkenylene-

The aromatic ring and the linking group may have a substituent. Examples of the substituent include a halogen atom (F, C
l, Br, I), hydroxyl, carboxyl, cyano, amino, nitro, sulfo, carbamoyl, sulfamoyl, ureido, alkyl, alkenyl, alkynyl, aliphatic acyl, aliphatic acyloxy, alkoxy, alkoxycarbonyl , Alkoxycarbonylamino group, alkylthio group, alkylsulfonyl group, aliphatic amide group, aliphatic sulfonamide group, aliphatic substituted amino group, aliphatic substituted carbamoyl group, aliphatic substituted sulfamoyl group, aliphatic substituted ureido group and non-aromatic Group heterocyclic groups.

The alkyl group preferably has 1 to 8 carbon atoms. A chain alkyl group is preferable to a cyclic alkyl group, and a linear alkyl group is particularly preferable.
The alkyl group may further have a substituent (eg, hydroxy, carboxy, alkoxy group, alkyl-substituted amino group). Examples of alkyl groups (including substituted alkyl groups) include methyl, ethyl, n-butyl, n-hexyl,
-Hydroxyethyl, 4-carboxybutyl, 2-methoxyethyl and 2-diethylaminoethyl. The alkenyl group preferably has 2 to 8 carbon atoms. A chain alkenyl group is preferable to a cyclic alkenyl group, and a linear alkenyl group is particularly preferable.
The alkenyl group may further have a substituent. Examples of the alkenyl group include vinyl, allyl and 1-hexenyl. The alkynyl group preferably has 2 to 8 carbon atoms. A chain alkynyl group is preferable to a cyclic alkynyl group, and a linear alkynyl group is particularly preferable. The alkynyl group may further have a substituent. Examples of the alkynyl group include ethynyl, 1-butynyl and 1-hexynyl.

The number of carbon atoms of the aliphatic acyl group is 1 to 1
It is preferably 0. Examples of the aliphatic acyl group include acetyl, propanoyl and butanoyl. The aliphatic acyloxy group preferably has 1 to 10 carbon atoms. Examples of the aliphatic acyloxy group include acetoxy. The alkoxy group preferably has 1 to 8 carbon atoms. The alkoxy group may further have a substituent (eg, an alkoxy group). Examples of alkoxy groups (including substituted alkoxy groups) include methoxy, ethoxy, butoxy and methoxyethoxy. The alkoxycarbonyl group preferably has 2 to 10 carbon atoms. Examples of the alkoxycarbonyl group include methoxycarbonyl and ethoxycarbonyl. The alkoxycarbonylamino group preferably has 2 to 10 carbon atoms. Examples of the alkoxycarbonylamino group include methoxycarbonylamino and ethoxycarbonylamino.

The number of carbon atoms of the alkylthio group is 1 to 1
It is preferably 2. Examples of the alkylthio group include methylthio, ethylthio and octylthio.
The alkylsulfonyl group preferably has 1 to 8 carbon atoms. Examples of the alkylsulfonyl group include methanesulfonyl and ethanesulfonyl. The aliphatic amide group preferably has 1 to 10 carbon atoms. Examples of the aliphatic amide group include acetamide. The aliphatic sulfonamide group preferably has 1 to 8 carbon atoms. Examples of the aliphatic sulfonamide group include methanesulfonamide, butanesulfonamide and n-octanesulfonamide. The aliphatic substituted amino group preferably has 1 to 10 carbon atoms. Examples of the aliphatic substituted amino group include dimethylamino, diethylamino and 2-carboxyethylamino. The aliphatic substituted carbamoyl group preferably has 2 to 10 carbon atoms. Examples of the aliphatic substituted carbamoyl group include methylcarbamoyl and diethylcarbamoyl. The aliphatic substituted sulfamoyl group preferably has 1 to 8 carbon atoms. Examples of the aliphatic substituted sulfamoyl group include methylsulfamoyl and diethylsulfamoyl. The aliphatic substituted ureido group preferably has 2 to 10 carbon atoms. Examples of the aliphatic substituted ureido group include methyl ureide. Examples of the non-aromatic heterocyclic group include piperidino and morpholino. The molecular weight of the retardation increasing agent is preferably from 300 to 800.

[Production of polymer film] It is preferable to produce a polymer film by a solvent casting method. In the solvent casting method, a film is manufactured using a solution (dope) in which a polymer material is dissolved in an organic solvent. The production of the polymer film of the present invention will be specifically described using cellulose acetate as an example. Organic solvents include ethers having 3 to 12 carbon atoms and 3 to 1 carbon atoms.
It is preferable to include a solvent selected from ketones having 2 carbon atoms, esters having 3 to 12 carbon atoms and halogenated hydrocarbons having 1 to 6 carbon atoms. Ethers, ketones and esters may have a cyclic structure. ether,
Functional groups of ketones and esters (ie, -O-,-
A compound having two or more of any of CO- and -COO-) can also be used as the organic solvent. The organic solvent may have another functional group such as an alcoholic hydroxyl group. In the case of an organic solvent having two or more types of functional groups, the number of carbon atoms may be within the specified range of the compound having any one of the functional groups.

Examples of the ethers having 3 to 12 carbon atoms include diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolan, tetrahydrofuran, anisole and phenetole. Examples of the ketones having 3 to 12 carbon atoms include acetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone, cyclohexanone and methylcyclohexanone. Examples of the esters having 3 to 12 carbon atoms include ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate and pentyl acetate. Examples of the organic solvent having two or more types of functional groups include
Includes 2-ethoxyethyl acetate, 2-methoxyethanol and 2-butoxyethanol. The number of carbon atoms of the halogenated hydrocarbon is preferably 1 or 2, and most preferably 1. The halogen of the halogenated hydrocarbon is preferably chlorine. The proportion of halogen atoms substituted by halogen atoms in halogenated hydrocarbons is preferably 25 to 75 mol%, and preferably 3 to 75 mol%.
The content is more preferably 0 to 70 mol%, still more preferably 35 to 65 mol%, and 40 to 60 mol%.
Most preferably, it is mol%. Methylene chloride is a typical halogenated hydrocarbon. Two or more organic solvents may be used as a mixture.

A cellulose acetate solution can be prepared by a general method. The general method means that the treatment is performed at a temperature of 0 ° C. or higher (normal temperature or high temperature). The solution can be prepared using a dope preparation method and apparatus in a usual solvent casting method. In the case of a general method, it is preferable to use a halogenated hydrocarbon (particularly, methylene chloride) as the organic solvent. The amount of cellulose acetate is adjusted so that the obtained solution contains 10 to 40% by mass. More preferably, the amount of cellulose acetate is 10 to 30% by mass. In the organic solvent (main solvent), any additives described below may be added. The solution can be prepared by stirring cellulose acetate and an organic solvent at normal temperature (0 to 40 ° C.). The highly concentrated solution may be stirred under pressure and heating conditions. Specifically, the cellulose acetate and the organic solvent are put in a pressurized container and hermetically sealed, and the mixture is stirred while being heated under pressure to a temperature not lower than the boiling point of the solvent at normal temperature and in a range where the solvent does not boil. The heating temperature is usually 40 ° C. or higher, preferably 60 to 200 ° C., and more preferably 80 to 110 ° C.

The components may be roughly mixed in advance and then placed in a container. Moreover, you may put in a container sequentially. The container must be configured to be able to stir. The container can be pressurized by injecting an inert gas such as nitrogen gas. Further, an increase in the vapor pressure of the solvent due to heating may be used.
Alternatively, each component may be added under pressure after the container is sealed. When heating, it is preferable to heat from outside the container. For example, a jacket-type heating device can be used. Alternatively, a plate heater may be provided outside the container, and the entire container may be heated by circulating the liquid through piping. It is preferable to provide a stirring blade inside the container and stir using the stirring blade. The stirring blade preferably has a length reaching the vicinity of the container wall. At the end of the stirring blade, a scraping blade is preferably provided to renew the liquid film on the container wall. Instruments such as a pressure gauge and a thermometer may be installed in the container. Dissolve each component in the solvent in the container.
The prepared dope is taken out of the vessel after cooling, or is taken out and then cooled using a heat exchanger or the like.

A solution can be prepared by a cooling dissolution method. In the cooling dissolution method, cellulose acetate can be dissolved even in an organic solvent that is difficult to dissolve by a normal dissolution method. In addition, even if it is a solvent which can dissolve cellulose acetate by an ordinary dissolution method, the cooling dissolution method has an effect that a uniform solution can be obtained quickly. In the cooling dissolution method, first, cellulose acetate is gradually added to an organic solvent at room temperature while stirring. It is preferable to adjust the amount of cellulose acetate so that the mixture contains 10 to 40% by mass. More preferably, the amount of cellulose acetate is 10 to 30% by mass. Further, an optional additive described below may be added to the mixture.

Next, the mixture is heated to -100 to -10 ° C (preferably -80 to -10 ° C, more preferably -50 to -10 ° C).
To -20 ° C, most preferably -50 to -30 ° C). The cooling can be performed, for example, in a dry ice / methanol bath (−75 ° C.) or a cooled diethylene glycol solution (−30 to −20 ° C.). Upon such cooling, the mixture of cellulose acetate and the organic solvent solidifies. The cooling rate is preferably 4 ° C./min or more, more preferably 8 ° C./min or more.
Most preferably, the temperature is at least ° C / min. The cooling rate is preferably as fast as possible, but 10,000 ° C./sec is the theoretical upper limit, 1000 ° C./sec is the technical upper limit, and
00 ° C / sec is a practical upper limit. The cooling rate is
This is a value obtained by dividing the difference between the temperature at which the cooling is started and the final cooling temperature by the time from when the cooling is started to when the final cooling temperature is reached.

Further, the temperature is raised to 0 to 200 ° C (preferably 0 to 150 ° C, more preferably 0 to 120 ° C,
When heated to the temperature (most preferably 0 to 50 ° C.), the cellulose acetate dissolves in the organic solvent. The temperature may be raised only by leaving it at room temperature or may be heated in a warm bath. The heating rate is preferably 4 ° C./min or more, and 8 ° C./min.
Minutes or more, and most preferably 12 ° C./minute or more. The heating rate is preferably as high as possible, but the theoretical upper limit is 10,000 ° C./sec.
0 ° C./sec is a technical upper limit, and 100 ° C./sec is a practical upper limit. Note that the heating rate is a value obtained by dividing the difference between the temperature at which heating is started and the final heating temperature by the time from when the heating is started until the final heating temperature is reached. . As described above, a uniform solution is obtained. If the dissolution is insufficient, the operation of cooling and heating may be repeated. Whether or not the dissolution is sufficient can be determined only by visually observing the appearance of the solution.

In the cooling dissolution method, it is desirable to use a closed container in order to avoid water contamination due to dew condensation during cooling. Also, in the cooling and heating operation, pressurization during cooling,
By reducing the pressure during the heating, the dissolution time can be shortened. In order to perform pressurization and decompression, it is desirable to use a pressure-resistant container. According to differential scanning calorimetry (DSC), a 20% by mass solution of cellulose acetate (degree of acetylation: 60.9%, viscosity average polymerization degree: 299) dissolved in methyl acetate by a cooling dissolution method was 3%.
A pseudo phase transition point between the sol state and the gel state exists near 3 ° C., and below this temperature, the gel state becomes uniform. Therefore,
This solution must be maintained at a temperature equal to or higher than the pseudo phase transition temperature, preferably at a temperature of about 10 ° C. plus the gel phase transition temperature. However, the pseudo phase transition temperature varies depending on the acetylation degree of cellulose acetate, the viscosity average polymerization degree, the solution concentration, and the organic solvent used.

From the prepared cellulose acetate solution (dope), a cellulose acetate film is produced by a solvent casting method. It is preferable to add the above-mentioned retardation increasing agent to the dope. The dope is cast on a drum or band and the solvent is evaporated to form a film. The dope before casting has a solid content of 1
It is preferable to adjust the concentration so as to be 8 to 35%. It is preferable that the surface of the drum or the band is finished in a mirror state. The casting and drying methods in the solvent casting method are described in US Pat. No. 2,336,310.
No. 2367603, No. 2492078, No. 24
No. 92977, No. 2492978, No. 2607704
Nos. 2739069 and 2739070; British Patent Nos. 640731 and 736892; Japanese Patent Publication Nos. 45-4554 and 49-5614;
-176834, 60-203430, 62-
It is described in each publication of No. 115035. The dope is preferably cast on a drum or band having a surface temperature of 10 ° C. or less. After casting, it is preferable to dry by blowing on air for 2 seconds or more. The obtained film can be peeled off from the drum or band, and further dried with high-temperature air whose temperature is gradually changed from 100 to 160 ° C. to evaporate the residual solvent. The above method is described in JP-B-5-17844. According to this method, the time from casting to stripping can be reduced. In order to carry out this method, it is necessary that the dope gels at the surface temperature of the drum or band during casting.

A plasticizer can be added to the cellulose acetate film in order to improve the mechanical properties or to increase the drying speed. As a plasticizer,
Phosphate or carboxylate esters are used. Examples of phosphate esters include triphenyl phosphate (TPP) and tricresyl phosphate (TCC).
P) is included. Representative carboxylic esters include phthalic esters and citric esters. Examples of phthalate esters include dimethyl phthalate (DM
P), diethyl phthalate (DEP), dibutyl phthalate (DBP), dioctyl phthalate (DOP), diphenyl phthalate (DPP) and diethylhexyl phthalate (DEHP). Examples of citrate esters include O-acetyl triethyl citrate (OACT
E) and tributyl O-acetylcitrate (OACT
B) is included. Examples of other carboxylic esters include butyl oleate, methylacetyl ricinoleate,
It includes dibutyl sebacate and various trimellitate esters. Phthalate ester plasticizers (DMP, DE
P, DBP, DOP, DPP, DEHP) are preferably used. DEP and DPP are particularly preferred. The amount of the plasticizer added is 0.1 to 25 times the amount of the cellulose ester.
%, More preferably 1 to 20% by mass, most preferably 3 to 15% by mass.

The cellulose acetate film may contain a deterioration inhibitor (eg, an antioxidant, a peroxide decomposer, a radical inhibitor, a metal deactivator, an acid scavenger, an amine). Regarding the deterioration inhibitor, see JP-A-3-19920.
No. 1, 5-1907073, 5-194789
And JP-A-5-271471 and JP-A-6-107854. The amount of the deterioration inhibitor added is preferably 0.01 to 1% by mass, more preferably 0.01 to 0.2% by mass of the solution (dope) to be prepared. When the amount is less than 0.01% by mass, the effect of the deterioration inhibitor is hardly recognized. 1% by mass
Exceeding the limit may cause bleed-out (bleeding-out) of the deterioration inhibitor to the film surface. Particularly preferred examples of the deterioration inhibitor include butylated hydroxytoluene (BHT) and tribenzylamine (TBA).

The retardation of the cellulose acetate film can be adjusted by a stretching treatment. The stretching ratio is preferably 3 to 100%. The thickness of the cellulose acetate film is preferably 40 to 140 μm, more preferably 70 to 120 μm.
Is more preferable.

[Surface Treatment of Polymer Film] The polymer film is preferably subjected to a surface treatment. Examples of the surface treatment include saponification treatment, plasma treatment, flame treatment, and ultraviolet irradiation treatment. The saponification treatment includes an acid saponification treatment and an alkali saponification treatment. The plasma treatment includes a corona discharge treatment and a glow discharge treatment. In these surface treatments, the temperature of the polymer film is preferably set to a glass transition temperature (Tg) or lower in order to maintain the flatness of the film.

When used as a transparent protective film of a polarizing plate,
From the viewpoint of adhesiveness to the polarizing film, it is particularly preferable to perform an acid treatment or an alkali treatment. Hereinafter, an example of performing the alkali saponification treatment will be specifically described. The alkali saponification treatment is preferably performed in a cycle in which the polymer film is immersed in an alkaline solution, neutralized with an acidic solution, washed with water, and dried. Examples of alkaline solutions include:
Potassium hydroxide solution, and sodium hydroxide solution. The specified concentration of the hydroxide ion in the alkaline solution is preferably in the range of 0.1N to 3.0N, and more preferably in the range of 0.5N to 2.0N. The temperature of the alkaline solution is preferably in the range of 0 to 90 ° C, more preferably in the range of 40 to 70 ° C.

[Polarizing Plate] In general, a polarizing plate used in a liquid crystal display device comprises a polarizing film and two transparent protective films disposed on both sides thereof. For the polarizing film, an iodine-based polarizing film,
There are a dye-based polarizing film using a dichroic dye and a polyene-based polarizing film. The iodine-based polarizing film and the dye-based polarizing film are generally manufactured using a polyvinyl alcohol-based film. Then, by using one of the protective films of the polarizing plate as the above-mentioned optical compensation sheet, the polarizing plate of the present invention can be manufactured.
In addition, a normal cellulose acetate film may be laminated as the other protective film of the polarizing film. Thus, the polarizing plate of the present invention can be obtained by laminating the optical compensation sheet having excellent reworkability and the polarizing film (via an adhesive). In the polarizing plate of the present invention, the relationship between the slow axis of the optical compensation sheet and the transmission axis of the polarizing film is preferably arranged as follows depending on the type of the applied liquid crystal display device. TN, MVA, and OC
When used in a B-mode liquid crystal display device, the slow axis of the optical compensation sheet and the transmission axis of the polarizing film are arranged so as to be substantially parallel to each other. It is preferable to dispose the slow axis and the transmission axis of the polarizing film substantially at 45 degrees.

[Liquid crystal display device] The optical compensatory sheet of the present invention and a polarizing plate using the same are advantageously used for a liquid crystal display device. TN, MVA, and OCB mode liquid crystal display devices include a liquid crystal cell and two polarizing plates disposed on both sides of the liquid crystal cell. A liquid crystal cell carries a liquid crystal between two electrode substrates. When the optical compensation sheet of the present invention is used for a liquid crystal display device, one sheet is disposed between the liquid crystal cell and one polarizing plate, or two sheets are disposed between the liquid crystal cell and both polarizing plates. . The optical compensation sheet of the present invention has an optically anisotropic layer made of a compound having a disc-shaped structural unit on a polymer film. The optically anisotropic layer is formed by orienting the discotic compound and fixing the orientation state. Discotic compounds generally have a large birefringence. In addition, the discotic compound has various orientation forms. Therefore, by using a discotic compound, an optical compensatory sheet having optical properties that cannot be obtained with a conventional stretched birefringent film can be produced.
An optical compensatory sheet using a discotic compound is disclosed in JP-A-6-214116, US Pat. No. 5,583,679.
No. 5,646,703, West German Patent Publication 3911620
It is described in each specification of A1.

When the polarizing plate of the present invention is used for a liquid crystal display device, the optical compensation sheet of the present invention is used as a transparent protective film disposed between a liquid crystal cell and a polarizing film. The optical compensatory sheet is used only for the transparent protective film (between the liquid crystal cell and the polarizing film) of one polarizing plate, or two transparent protective films (between the liquid crystal cell and the polarizing film) of both polarizing plates Then, an optical compensation sheet may be used.

The liquid crystal cell is preferably of OCB mode or TN mode. The OCB mode liquid crystal cell
This is a liquid crystal display device using a bend alignment mode liquid crystal cell in which rod-like liquid crystal molecules are aligned (symmetrically) in substantially opposite directions at the top and bottom of the liquid crystal cell.
Nos. 825 and 5410422. Since the rod-like liquid crystal molecules 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 also called OCB (Optically Compensatory Bend) liquid crystal mode. The bend alignment mode liquid crystal display device has an advantage that the response speed is high. In a TN mode liquid crystal cell, rod-like liquid crystalline molecules are substantially horizontally aligned when no voltage is applied, and further twisted at 60 to 120 °. TN mode liquid crystal cells are most frequently used as color TFT liquid crystal display devices, and are described in many documents.

[0064]

EXAMPLES Example 1 The following composition was put into a mixing tank, and stirred while heating to dissolve each component.
A cellulose acetate solution was prepared.

<< Composition of Cellulose Acetate Solution >>セ ル ロ ー ス 100% by mass of cellulose acetate having a degree of acetylation of 60.9% triphenyl phosphate (plasticizer) 7 0.8 parts by mass Biphenyldiphenyl phosphate (plasticizer) 3.9 parts by mass Methylene chloride (first solvent) 300 parts by mass Methanol (second solvent) 54 parts by mass 1-butanol (third solvent) 11 parts by mass ────────────────────────────────

Into another mixing tank, 16 parts by mass of the following retardation increasing agent, 80 parts by mass of methylene chloride and 20 parts by mass of methanol were added, and the mixture was stirred with heating to prepare a retardation increasing agent solution.
11 parts by mass of the retardation increasing agent solution was mixed with 488 parts by mass of the cellulose acetate solution, and the mixture was sufficiently stirred to prepare a dope. The addition amount of the retardation enhancer
It was 1.5 parts by mass with respect to 100 parts by mass of cellulose acetate.

[0067]

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With respect to the produced cellulose acetate film, the Re retardation value and the Rth retardation value at a wavelength of 633 nm were measured using an ellipsometer (M-150, manufactured by JASCO Corporation). Re was 10 nm and Rth was 81 nm.

(Preparation of Undercoat Layer) The above cellulose acetate
28 cc / m2 of a coating solution of the following composition
^TwoIt was applied and dried to provide a 0.1 μm gelatin layer.組成 Composition of coating solution for first undercoat layer ─────── ───────────────────────────── Gelatin 0.542 parts by mass Formaldehyde 0.136 parts by mass Salicylic acid 0.160 parts by mass Acetone 39. 1 part by weight Methanol 15.8 parts by weight Methylene chloride 40.6 parts by weight Water 1.2 parts by weight ──────────────────────────── ──────── A 7cc / m coating solution of the following composition^TwoCoating dry
Dried.組成 Composition of coating solution for second undercoat layer ─────── ───────────────────────────── 0.079 parts by mass of the following anionic copolymer: monoethyl citrate 1.01 part by mass Parts acetone 20 parts by weight methanol 87.7 parts by weight water 4.05 parts by weight ───────────────────────────────── ───

[0070]

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Further, a coating solution having the following composition was applied to the layer on the side opposite to that described above at 25 cc / m ^{2 and} dried to form a back layer. ──────────────────────────────────── Back layer coating solution composition ─────────セ ル ロ ー ス 0.656 parts by mass of cellulose diacetate having a degree of acetylation of 55% ) 0.065 parts by mass acetone 67.9 parts by mass methanol 10.4 parts by mass ──────────────────────────────── ８０ Further, as a transparent protective film used for a polarizing plate, an 80 μm cellulose acetate film obtained without adding a retardation increasing solution was prepared.

(Preparation of Alignment Layer) A coating solution having the following composition was applied onto the gelatin layer of the cellulose acetate film at a rate of 28 ml / m ² using a # 16 wire bar coater. As the polymer for the alignment film, modified polyvinyl alcohol having a polymerization degree of 350 (described below) and polyvinyl alcohol having a polymerization degree of 1700 (PVA217, manufactured by Kuraray Co., Ltd.)
Was used. It was dried with hot air at 60 ° C. for 60 seconds and further with hot air at 90 ° C. for 150 seconds. Next, in the direction of the slow axis (measured at a wavelength of 632.8 nm) of the cellulose acetate film,
A rubbing treatment was performed on the formed film.

<< Composition of Alignment Film Coating Solution >>変 性 The following modified polyvinyl alcohol 8 parts by mass polyvinyl alcohol (PVA217, manufactured by Kuraray Co., Ltd.) 2 Parts by mass Water 371 parts by mass Methanol 119 parts by mass Glutaraldehyde (crosslinking agent) 0.5 parts by mass ───────────────────────────── ───────

[0074]

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(Formation of Optically Anisotropic Layer) On the alignment film, 41.01 g of the following discotic (liquid crystalline) compound, ethylene oxide-modified trimethylolpropane triacrylate (V # 360, manufactured by Osaka Organic Chemical Co., Ltd.) ) 4.06 g, cellulose acetate butyrate (CAB551-0.
2, 0.90 g of Eastman Chemical Co., Ltd., 0.23 g of cellulose acetate butyrate (CAB531-1, manufactured by Eastman Chemical Co.), 1.35 g of photopolymerization initiator (Irgacure 907, Ciba Geigy), sensitization (Kayacure DETX, manufactured by Nippon Kayaku Co., Ltd.) 0.4
A coating solution of 5 g dissolved in 102 g of methyl ethyl ketone was applied with a # 4 wire bar. This was attached to a metal frame and heated in a thermostat at 130 ° C. for 2 minutes to orient the discotic compound. Next, at 130 ° C., 120 W /
UV irradiation was performed for 1 minute using a cm high-pressure mercury lamp to polymerize the discotic compound. Then, it was left to cool to room temperature. Thus, an optically anisotropic layer was formed. The Re retardation value of the optically anisotropic layer measured at a wavelength of 633 nm is 48 n
m. The angle (tilt angle) between the disk surface and the first transparent support surface was 42 ° on average.

[0076]

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Comparative Example 1 A coating solution having the following composition was applied onto the cellulose acetate film having an undercoat layer obtained in Example 1 using a # 16 wire bar coater at 28 ml / m 2.
^{2 were} applied. As a polymer for an alignment film, a polymerization degree of 300
(MP203, manufactured by Kuraray Co., Ltd.) was used. 60 ° C for 60 seconds, 90 ° C
For 150 seconds. Next, a rubbing treatment was performed on the formed film in the direction of the slow axis (measured at a wavelength of 632.8 nm) of the cellulose acetate film.

<< Composition of Alignment Film Coating Solution >> ────────────────────────────── Modified polyvinyl alcohol (MP203, manufactured by Kuraray Co., Ltd.) 10 parts by mass Water 371 parts by mass Methanol 119 parts by mass Glutaraldehyde (crosslinking agent) 0.5 parts by mass ────────────────────────────────────

(Formation of Optically Anisotropic Layer) An optically anisotropic layer was formed on the alignment film in the same manner as in Example 1. Wavelength 633
The Re retardation value of the optically anisotropic layer measured in nm was 48 nm. The angle (tilt angle) between the disk surface and the first transparent support surface was 42 ° on average, which was the same as in Example 1.

[Example 2] The addition amount of the retardation increasing agent was determined based on 100 parts by mass of cellulose acetate.
A dope obtained in the same manner as in Example 1 except that the amount was 3.0 parts by mass was cast using a band casting machine. A film having a residual solvent amount of 15% by mass was laterally stretched at a stretching ratio of 30% using a tenter at a temperature of 130 ° C. to produce a cellulose acetate film (thickness: 80 μm). About the produced cellulose acetate film,
The Re retardation value and the Rth retardation value at a wavelength of 633 nm were measured using an ellipsometer (M-150, manufactured by JASCO Corporation). Re was 20 nm in the tenter stretching direction, and Rth was 130 nm. (Preparation of Undercoat Layer) An undercoat layer was provided in the same manner as in Example 1.

(Preparation of Alignment Film Layer) On a gelatin layer of this cellulose acetate film, a coating solution having the following composition was applied at 28 ml / m ² using a # 16 wire bar coater. As the polymer for the alignment film, modified polyvinyl alcohol having a polymerization degree of 500 (described below) and polyvinyl alcohol having a polymerization degree of 1700 (PVA117, manufactured by Kuraray Co., Ltd.)
Was used. It was dried with hot air at 60 ° C. for 60 seconds and further with hot air at 90 ° C. for 150 seconds. Next, a rubbing treatment was performed on the formed film in a direction at an angle of 45 ° with the slow axis (measured at a wavelength of 632.8 nm) of the cellulose acetate film.

<< Composition of Alignment Film Coating Solution >>変 性 8.5 parts by mass of the following modified polyvinyl alcohol polyvinyl alcohol (PVA117, manufactured by Kuraray Co., Ltd.) 1.5 parts by mass Water 371 parts by mass Methanol 119 parts by mass Glutaraldehyde (crosslinking agent) 0.5 part by mass ───────────────────────── ───────────

[0083]

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(Formation of Optically Anisotropic Layer) On the alignment film, 41.01 g of the discotic (liquid crystalline) compound used in Example 1 and ethylene oxide-modified trimethylolpropane triacrylate (V # 360, Osaka Organic Chemical Co., Ltd.) 4.0
6 g, cellulose acetate butyrate (CAB551
-0.2, 0.90 g of Eastman Chemical Co., Ltd., 0.23 g of cellulose acetate butyrate (CAB531-1, manufactured by Eastman Chemical Co.), 1.35 of photopolymerization initiator (Irgacure 907, Ciba Geigy)
g, sensitizer (Kayacure DETX, Nippon Kayaku Co., Ltd.)
Co., Ltd.) was applied with a # 3 wire bar. This was attached to a metal frame and heated in a thermostat at 130 ° C. for 2 minutes to orient the discotic compound. Next, UV irradiation was performed at 130 ° C. for 1 minute using a 120 W / cm high pressure mercury lamp to polymerize the discotic compound. Then, it was left to cool to room temperature. Thus, an optically anisotropic layer was formed. Wavelength 6
The Re retardation value of the optically anisotropic layer measured at 33 nm was 38 nm. The angle (tilt angle) between the disk surface and the first transparent support surface was 40 ° on average.

Example 3 A polarizing film was prepared by adsorbing iodine on a stretched polyvinyl alcohol film, and the cellulose triacetate film prepared in Example 1 was applied to one side of the polarizing film using a polyvinyl alcohol-based adhesive. On the other side, a commercially available cellulose triacetate film (Fujitac TD80UF, manufactured by Fuji Photo Film Co., Ltd.) was subjected to a saponification treatment and attached, and then dried at 80 ° C. for 10 minutes. The transmission axis of the polarizing film and the slow axis of the optical compensation sheet prepared in Example 1 were arranged in parallel. The transmission axis of the polarizing film and the slow axis of the commercially available cellulose triacetate film were arranged so as to be orthogonal to each other. Thus, a polarizing plate was produced.

Example 4 Polarization was performed in the same manner as in Example 3 except that the optical compensation sheet produced in Example 2 was arranged so that the slow axis was at 45 ° to the transmission axis of the polarizing film. A plate was made.

Comparative Example 2 A polarizing film was prepared by adsorbing iodine on a stretched polyvinyl alcohol film, and the optical compensatory sheet prepared in Comparative Example 1 was placed on one side of the polarizing film using a polyvinyl alcohol-based adhesive. On the other side, a commercially available polycarbonate film (manufactured by Teijin Limited) was attached and dried at 80 ° C. for 30 minutes. However, the polarizing ability was lowered, and the function as a polarizing plate was not sufficiently performed.

Example 5 (Evaluation of Reworkability) The polarizing plates obtained in Examples 3 and 4 and Comparative Example 2 were bonded together with an adhesive so that the optical compensation sheet was on the glass surface side. 6 at 50 ° C and 5 atm
Aged for hours. This polarizing plate was heated at 25 ° C and 60 ° C.
Under the condition of% RH, it was peeled off from the glass surface. The results are shown in Table 1.

[Table 1] Table 1 枚 数 Number of polarizing plates Number of sheets ──────────────────────────────────── Example 3 100 0 Example 4 100 0 Comparative Example 2 100 50 ────────────────────────────────────

Example 6 (Preparation of Bend Alignment Liquid Crystal Cell) A polyimide film was provided as an alignment film on a glass substrate with an ITO electrode, and the alignment film was subjected to a rubbing treatment. The two glass substrates thus obtained were opposed to each other in an arrangement where the rubbing directions were parallel, and the cell gap was set to 6 μm. Δn is 0.13 in the cell gap
96 liquid crystal compounds (ZLI1132, manufactured by Merck Ltd.) were injected to prepare bend alignment liquid crystal cells. Two elliptically polarizing plates produced in Example 4 were attached so as to sandwich the produced bend alignment cell. The optically anisotropic layer of the elliptically polarizing plate was arranged so as to face the cell substrate, and the rubbing direction of the liquid crystal cell was antiparallel to the rubbing direction of the optically anisotropic layer facing the cell substrate. A rectangular wave voltage of 55 Hz was applied to the liquid crystal cell. A normally white mode of 2 V for white display and 5 V for black display was set. The transmittance ratio (white display / black display) is defined as a contrast ratio, and a measuring device (EZ-Contrast 160D, ELD
IM display) from black display (L1) to white display (L
The viewing angle was measured in eight steps up to 8). It was measured. The results are shown in Table 2.

[0090]

[Table 2] Table 2 ──────────────────────────────────── Liquid crystal viewing angle (contrast ratio Range of 10 or more without gradation inversion on the black side) Display device Upper Lower Left / Right ──────────────────────────────── ──── Example 6 80 ゜ 80 ゜ 80 ゜ ──────────────────────────────────── ( Note) Black side tone inversion: Inversion between L1 and L2

[Example 7] A pair of polarizing plates provided in a liquid crystal display device (6E-A3, manufactured by Sharp Corporation) using a TN type liquid crystal cell was peeled off, and the polarized light produced in Example 3 was used instead. One plate was attached to each of the observer side and the backlight side via an adhesive so that the cellulose acetate film produced in Example 1 was on the liquid crystal cell side. The transmission axis of the polarizing plate on the observer side and the transmission axis of the polarizing plate on the backlight side were arranged so as to be in the O mode. About the manufactured liquid crystal display device, a measuring machine (EZ-Contrast
160D, manufactured by ELDIM), and black display (L1)
The viewing angle was measured in eight stages from to white display (L8).
The results are shown in Table 3.

Comparative Example 3 A liquid crystal display device (6E-A3, manufactured by Sharp Corporation) using a TN type liquid crystal cell was displayed in black (L1) using a measuring machine (EZ-Contrast 160D, manufactured by ELDIM). ) To white display (L8), the viewing angle was measured in eight steps. The results are shown in Table 3.

[0093]

[Table 3] Table 3 視野 Liquid crystal viewing angle (contrast ratio Range of 10 or more without gradation inversion on the black side) Display device Upper Lower Left / Right ──────────────────────────────── ──── Example 7 70 ゜ 45 ゜ 160 ゜ Comparative Example 3 15 ゜ 25 ゜ 37 ゜──────── (Note) Black side gradation inversion: Inversion between L1 and L2

Continued on the front page F-term (reference) 2H049 BA02 BA04 BA06 BA42 BB03 BB43 BB51 BC04 BC22 2H091 FA11Y FC07 FC16 FC24 FC25 FC29 FC30 FD10 FD14 FD21 GA06 HA11 LA11 LA12 LA13 4F100 AH01A AJ06A AK01B10 BA04 BA10 BA04 BA10 BAK JA07B JA09B JA11B JM02B JN01A JN10D JN18A JN30C YY00A YY00B

Claims (12)

[Claims] 1. An optical compensation sheet comprising a transparent support and an alignment film and an optically anisotropic layer comprising a compound having a disc-shaped structural unit provided in this order, wherein the alignment films have a degree of polymerization of one another. An optical compensation sheet, wherein a rubbing treatment is performed on the surface of a crosslinked film of a polymer mixture containing a polymer having a low polymerization degree and a polymer having a high polymerization degree different from each other by 50 or more. 2. The optical compensation sheet according to claim 1, wherein the degree of polymerization of the polymer having a low degree of polymerization is in the range of 100 to 500, and the degree of polymerization of the polymer having a high degree of polymerization is in the range of 750 to 2,000. 3. The polymer having a low degree of polymerization and the polymer having a high degree of polymerization are either unmodified polyvinyl alcohol or modified polyvinyl alcohol.
Or the optical compensation sheet according to 2. 4. One of the low and high degree of polymerization polymers is a modified polyvinyl alcohol,
4. The optical compensation sheet according to claim 1, wherein the other is unmodified polyvinyl alcohol. 5. The method according to claim 1, wherein the mass ratio of the polymer having a low polymerization degree to the polymer having a high polymerization degree is in a range of 50:50 to 99.8: 0.2. Optical compensation sheet. 6. The optically compensatory sheet according to claim 3, wherein the modified polyvinyl alcohol is a modified product of polyvinyl alcohol with the following compound. [Wherein, R ¹ represents an alkyl group, an acryloylalkyl group, a methacryloylalkyl group, or an epoxyalkyl group; W represents a halogen atom, an alkyl group, or an alkoxy group; X represents an active ester, an acid anhydride Or the group of atoms necessary to form an acid halide; p represents 0 or 1;
Represents an integer of 0 to 4]. 7. The transparent support has a Re retardation value defined by the following formula (I) of 20 to 200.
2. The optical compensatory sheet according to claim 1, wherein the optical compensatory sheet comprises a polymer film having a Rth retardation value defined by the following formula (II) in the range of 70 to 400 nm. ) Re = (nx−ny) × d (II) Rth = {(nx + ny) / 2−nz} × d [where nx is the refractive index in the slow axis direction in the film plane; Is the refractive index in the fast axis direction in the film plane; nz is the refractive index in the film thickness direction; and d is the film thickness]. 8. The method according to claim 1, wherein the polymer film has an acetylation degree of 5.
9.0 to 61.5% of cellulose acetate and 100 parts by mass of cellulose acetate contain 0.01% of an aromatic compound having at least two aromatic rings.
The optical compensatory sheet according to claim 7, comprising from 20 to 20 parts by mass. 9. An optical compensatory sheet comprising an optically anisotropic layer comprising a transparent support, an alignment film and a compound having a disc-shaped structural unit is bonded to at least one surface of the polarizing film, and the transparent support is provided. A polymer film having a Re retardation value defined by the following formula (I) in the range of 20 to 200 nm, an Rth retardation value defined by the following formula (II) in the range of 70 to 400 nm, and And the alignment films have a degree of polymerization of 5
An elliptically polarizing plate characterized in that a rubbing treatment is applied to the surface of a crosslinked film of a polymer mixture containing a polymer having a low polymerization degree and a polymer having a high polymerization degree different from 0 or more: (I) Re = (nx−) ny) × d (II) Rth = {(nx + ny) / 2−nz} × d [where nx is the refractive index in the slow axis direction in the film plane; ny is the fast phase in the film plane] Is the refractive index in the axial direction; nz is the refractive index in the thickness direction of the film; and d is the thickness of the film. 10. The polymer film having an acetylation degree of 5
9.0 to 61.5% of cellulose acetate and 100 parts by mass of cellulose acetate contain 0.01% of an aromatic compound having at least two aromatic rings.
The elliptically polarizing plate according to claim 9, comprising from 20 to 20 parts by mass. 11. A liquid crystal display device comprising a liquid crystal cell and two polarizing plates disposed on both sides of the liquid crystal cell, wherein at least one of the polarizing plates is the polarizing plate according to claim 9 or 10, and is optically compensated. A liquid crystal display device, wherein a sheet is disposed so as to be on a liquid crystal cell side. 12. A liquid crystal cell in an OCB mode or a T
12. An N-mode liquid crystal cell.
3. The liquid crystal display device according to 1.