JP2003344856A - Liquid crystal display device and optical retardation thin film and laminated polarizing plate to be used for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To conveniently provide a vertical alignment (VA) mode liquid crystal display device with little viewing angle dependence and a wide viewing angle and further to provide a biaxial optical retardation film and a compensation polarizing plate to be used for the same. <P>SOLUTION: A wide viewing angle liquid crystal display device is provided with a VA mode liquid crystal cell and an optical retardation thin film composed of at least a kind of polymer selected from a group consisting of polyamide, polyimide, polyester, poly(etherketone), poly(amideimide) and poly(esterimide) and satisfying an inequality nx>ny>nz in the case its in-plane refractive indexes of two directions are represented by nx and ny and its refractive index in the thickness direction is represented by nz between two sheets of polarizing plates with their axes mutually perpendicularly intersecting. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to vertical alignment (VA:
The present invention relates to a vertical alignment mode liquid crystal display device, and a retardation film and a polarizing plate used for the same.

Conventionally, a so-called TN mode in which a liquid crystal having a positive dielectric anisotropy is horizontally aligned between mutually opposing substrates has been mainly used as a liquid crystal display device (hereinafter, also abbreviated as LCD). It is being appreciated. However, in such a TN mode, due to the driving characteristics, even if an attempt is made to display black, birefringence occurs due to liquid crystal molecules in the vicinity of the substrate, light leakage occurs, and it is difficult to perform complete black display. On the other hand, in the VA (Vertical Alignment) mode, since the liquid crystal molecules have an orientation substantially perpendicular to the substrate surface in the non-driving state, light passes through the liquid crystal layer with almost no change in its polarization plane. As a result, by arranging the polarizing plates above and below the substrate, it is possible to display almost perfect black in a non-driving state. As a specific display method, MVA (Multi-d
omain Vertical Alignment) method, PVA (Patterned Vein)
rtical Alignment) method.

However, in the VA mode, although almost perfect black display is possible in the normal direction of the panel, when the panel is observed from a direction deviated from the normal direction, light leakage occurs due to the influence of birefringence of the liquid crystal. As a result, there is a problem that the viewing angle becomes narrow.

In order to solve this problem, in order to compensate the birefringence of the liquid crystal layer that occurs when observing from an oblique direction,
It is effective if a retardation plate having a refractive index anisotropy such that ny = nx> nz is arranged between the liquid crystal layer and the polarizing plate.
Many have been disclosed so far. For example, there is Japanese Patent No. 2047880 that uses a polymer film,
There is Japanese Patent No. 2972892 as one utilizing the cholesteric alignment of liquid crystal molecules, and as one using a polyimide thin film, Japanese Patent Publication No. 8-511812 and USP5344.
916 and the like. However, even if the birefringence of the liquid crystal layer is compensated by these, due to the characteristics of the polarizing plate in the crossed Nicols state, light leakage due to the polarizing plate will occur in the direction deviated from the optical axis of the polarizing plate. Is caused, and there is a problem that a sufficient wide viewing angle cannot be achieved.

Therefore, in order to achieve a wide viewing angle in the VA mode, an optical anisotropic layer having a refractive index anisotropy of nx> ny = nz and a refractive index anisotropy of nx = ny> nz are provided. Structure (A) using at least one optically anisotropic layer
Alternatively, a configuration (B) using at least one optically anisotropic layer having a biaxial refractive index anisotropy of nx>ny> nz is required.

In the structure (A), two or more optically anisotropic layers are required to compensate for the birefringence of liquid crystal molecules in the cell and the viewing angle characteristics of the polarizing plate. An increase in thickness due to stacking and complication of the process become problems.

On the other hand, in the configuration (B), nx> ny
In order to obtain a biaxial retardation film such as> nz, a method of controlling a three-dimensional refractive index nx, ny and nz by stretching a polymer film is generally used. As a control method by stretching, fixed-end uniaxial stretching in which one side is fixed, such as stretching in two plane directions (x and y directions) and stretching by a tenter, is used. Thereby, the in-plane retardation value Δnd (= (nx-ny) d) and the thickness direction retardation value Rth (= (nx-nz) d) are controlled.

Currently, the optically transparent polymer film used for obtaining the biaxial retardation film mainly includes norbornene type and cellulose type. In widening the viewing angle of VA by the biaxial retardation film, the thickness direction retardation Rth plays an important role in compensating the birefringence of the liquid crystal layer. However, in the current material, since the in-plane orientation of the molecular chains is not high even when stretched, the birefringence in the thickness direction to be developed, that is, the difference between the in-plane maximum refractive index and the refractive index in the thickness direction is 0. 000
It is about 3 to 0.005. Therefore, in order to increase Rth in one film, it is necessary to thicken the film, or a plurality of retardation films are required.
Increased thickness and complication of the process become problems.

On the other hand, when a polymer selected from the group consisting of polyamide, polyimide, polyester, poly (ether ketone), poly (amide imide) and poly (ester imide) is used, the main chain direction of the polymer is increased. Since it has an aromatic ring or an aromatic heterocycle, it has a higher refractive index than the direction perpendicular to the main chain, so it has large birefringence as a molecule, and its molecular chain is easily oriented parallel to the substrate. In addition, there is an advantage that a material having a large difference between the maximum in-plane refractive index and the refractive index in the thickness direction can be easily obtained.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and can easily and easily achieve a wide viewing angle vertical alignment (VA: Vertical Alignment) with a small viewing angle dependency.
It is an object of the present invention to provide a liquid crystal display device of a ment mode. Furthermore, it aims at providing the biaxial retardation film and compensation polarizing plate used for it.

[0011]

In order to achieve the above object, the present invention provides a liquid crystal cell in a vertical alignment mode (that is, a cell in a non-driving state in which an external electric field is not applied) between two orthogonal polarizing plates. Selected from the group consisting of liquid crystal cells filled with liquid crystal molecules aligned in a direction substantially perpendicular to the substrate), and a group consisting of polyamide, polyimide, polyester, poly (ether ketone), poly (amide imide) and poly (ester imide). Of at least one polymer having a refractive index in the in-plane two directions of nx and ny,
When the refractive index in the thickness direction is nz, nx>ny> nz
A wide viewing angle liquid crystal display device having a very small viewing angle dependency, which is characterized by having a retardation thin film satisfying the relationship of

In the liquid crystal display device of the present invention, it is preferable that the retardation thin film has a difference between the maximum refractive index in the plane and the refractive index in the thickness direction of 0.01 to 0.4.

In the liquid crystal display device of the present invention, the retardation thin film and the polarizing plate are arranged such that the maximum refractive index azimuth in the plane of the retardation thin film and the absorption axis of the polarizing plate are orthogonal or parallel to each other. Preferably.

In the above liquid crystal display device, the in-plane retardation value Δnd = (nx-ny) d of the retardation thin film is 3.
It is more preferable that the thickness is 00 nm or less (however, d is the thickness of the thin film), and that the maximum refractive index direction in the plane and the absorption axis of the adjacent polarizing plate are orthogonal to each other.

Further, the present invention comprises at least one polymer selected from the group consisting of polyamide, polyimide, polyester, poly (etherketone), poly (amide imide) and poly (ester imide), and has two in-plane directions. Where nx and ny are the refractive indices of N and nz is the refractive index in the thickness direction, V satisfying the relationship of nx>ny> nz
The present invention provides a retardation thin film for an A-mode liquid crystal cell.

Further, the present invention comprises at least one polymer selected from the group consisting of polyamide, polyimide, polyester, poly (etherketone), poly (amide imide) and poly (ester imide), and has two in-plane directions. Where nx and ny are the refractive indices of the above, and nz is the refractive index in the thickness direction, a VA-mode liquid crystal characterized by being formed by laminating a retardation thin film satisfying the relationship of nx>ny> nz and a polarizing plate. A laminated polarizing plate for a cell is provided.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The liquid crystal display device of the present invention comprises a VA mode liquid crystal cell, a polyamide, a polyimide, a polyester, a poly (ether ketone), a poly (amide imide), and a poly (amide imide) between two orthogonal polarizing plates. Ester imide) and at least one type of polymer selected from the group consisting of
When the refractive index in the thickness direction is nz, nx>ny> nz
And a retardation thin film having the relationship of refractive index. Although the thickness of the retardation thin film is not particularly limited, it is preferably 0.1 to 50 μm, more preferably 0.5 to 30 μm from the viewpoint of providing a uniform film while achieving a thin liquid crystal display device. More preferably 1
It is 20 μm.

As the polymer forming the retardation thin film,
At least one selected from the group consisting of polyamide, polyimide, polyester, poly (ether ketone), poly (amide imide) and poly (ester imide) is used. Optically transparent materials are preferably used. Conventionally known polymer materials can be appropriately used as long as they can satisfy the characteristics of the retardation thin film of the present invention, and can be used alone or in any combination.

For example, as a polyimide, a special table 8-
A soluble polyimide composed of an aromatic dianhydride and a polyaromatic diamine as described in JP-A-511812 is preferably used. As the polyaryl ether ketone, there are JP-A Nos. 2001-64226 and 200.
The fluorine-containing aryl ether ketone polymer described in JP-A 1-49110 is preferably used.

The molecular weight of these polymers is not particularly limited, but the weight average molecular weight (Mw) is 1,000 to 1,
The range of, 000,000 is preferable, and the range of 2,000 to 500,000 is more preferable.

The manufacturing conditions and process of the retardation thin film are not particularly limited as long as they can satisfy the characteristics (nx>ny> nz) of the retardation thin film of the present invention. Rth
A large film with a large thickness can be efficiently manufactured in a thin layer with a simple process. Therefore, the polymer is coated on a polymer substrate such as a resin film or sheet, and stretched / extended as necessary.
It is preferable to perform a stretching process.

When the polymer is applied to a resin film or sheet, it may be applied by a heating and melting method, or it may be dissolved in a solvent and applied as a solution. From the viewpoint of production efficiency and control of optical anisotropy, a method of applying a polymer solution is preferable. As the solvent, for example, the solvent for dissolving the polyimide is not particularly limited as long as it can dissolve the polyimide, and can be appropriately selected according to the type of polymer. Examples of the solvent include halogenated hydrocarbons such as chloroform, dichloromethane, carbon tetrachloride, dichloroethane, tetrachloroethane, trichloroethylene, tetrachloroethylene, chlorobenzene, orthodichlorobenzene; phenols such as phenol and barachlorophenol; benzene, toluene, xylene. , Aromatic hydrocarbons such as methoxybenzene and 1,2-dimethoxybenzene; acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, cyclopentanone, 2-pyrrolidone, N-methyl-
Ketone-based solvents such as 2-pyrrolidone; ester-based solvents such as ethyl acetate and butyl acetate; t-butyl alcohol,
Alcoholic solvents such as glycerin, ethylene glycol, triethylene glycol, ethylene glycol monomethyl ether, diethylene glycol dimethyl ether, propylene glycol, dipropylene glycol, 2-methyl-2,4-pentanediol; amides such as dimethylformamide and dimethylacetamide. Examples of the solvent include nitrile solvents such as acetonitrile and butyronitrile; ether solvents such as diethyl ether, dibutyl ether and tetrahydrofuran; carbon disulfide, ethyl cellosolve, butyl cellosolve. These solvents can be used alone or as a mixture. From the viewpoint of viscosity, the polymer solution contains 5 to 5 parts of the above polymer per 100 parts by weight of the solvent.
It is advisable to mix 0 part by weight, preferably 10 to 40 parts by weight.

The above-mentioned polymer base material is preferably optically transparent from the viewpoint of being used as an integrated product with a polymer material. There is no particular limitation as long as it is optically transparent.

Examples of the material of the polymer base material include acetate resin such as triacetyl cellulose, polyester resin, polyether sulfone resin, polysulfone resin, polycarbonate resin, polyamide resin, polyimide resin and polyolefin resin. Resin, acrylic resin, polynorbornene resin, cellulose resin, polyarylate resin, polystyrene resin, polyvinyl alcohol resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyacrylic resin, liquid crystal polymer resin, etc. Can be mentioned.

The thickness of the polymer substrate can be appropriately determined according to the purpose of use, etc., but is preferably 5 to 500 μm, more preferably 10 from the viewpoint of strength and thinning.
˜200 μm, more preferably 15 to 150 μm.

Further, the coating treatment is carried out by an appropriate method such as a spin coating method, a roll coating method, a flow coating method, a printing method, a dip coating method, a casting film forming method, a bar coating method or a gravure printing method. You can

After coating, air dry or 40 ° C
By heating at ~ 200 ° C, the polymer is immobilized on the resin film or sheet to form a polymer layer on the resin film or sheet. The obtained optically anisotropic layer may be used in the form of a laminate as an integrated product of the resin film or sheet, or may be peeled from the resin film or sheet before use.

In order to satisfy the optical characteristics, the polymer layer may be subjected to the following stretching / shrinking treatment in the form of a laminate with the resin film or sheet, or the polymer layer may be formed from the resin film or sheet. You may peel and perform the following expansion / contraction processing. When forming the polymer layer, various additives such as stabilizers, plasticizers and metals can be blended as necessary.

The stretching / shrinking treatment is not particularly limited as long as it can satisfy the characteristics of the optically anisotropic layer of the present invention. A stretching method is generally used as the stretching method. Free end-axial stretching and fixed end-axial stretching are preferable, but sequential biaxial stretching and simultaneous biaxial stretching can also be used. Further, it is also possible to express Δnd by contraction. It is also possible to use a resin film or sheet that is a coating base material to shrink it by utilizing the dimensional change, or to use a material in which the base material positively has a shrinking performance. At this time, it is desirable to control the shrinkage ratio using a stretching machine or the like.

In the above retardation thin film, when the maximum refractive index azimuth in the plane and the absorption axis of the polarizing plate are arranged orthogonally, L
From the point of increasing the viewing angle of CD, the in-plane retardation value Δn
d is preferably 300 nm or less, more preferably 10 to 250 nm, still more preferably 20 nm to 20 nm.
It is 0 nm. The thickness direction retardation value Rth is 20 to 60.
It is preferably 0 nm, more preferably 30 to 50
It is 0 nm. By setting Δnd in the range of 10 to 300 nm, it is possible to obtain a wide viewing angle LCD that maintains a sufficient display contrast in all directions.

Polyamide, polyimide, polyester, poly (ether ketone), poly (amide imide)
When a polymer selected from the group consisting of and poly (ester imide) is used, since the polymer has an aromatic ring or an aromatic heterocycle in the main chain direction, the refractive index is higher than that in the direction perpendicular to the main chain. Has a large birefringence as a molecule, and its molecular chains are easily oriented in the horizontal plane, so that the difference between the maximum in-plane refractive index and the refractive index in the thickness direction (Δn)
The value of 0.01 to 0.4 is easily obtained. When the difference (Δn) between the maximum in-plane refractive index and the refractive index in the thickness direction is 0.01 or more, it is not necessary to laminate a plurality of retardation films, so that it is possible to reduce the thickness. Δn is 0.01 to 0.
The range of 2 is preferable, and more preferably 0.01 to 0.1.
It is preferably in the range of 5.

Since the retardation thin film of the present invention can be controlled mainly by coating Rth and Δnd by, for example, stretching, it is not necessary to laminate a plurality of sheets as in the conventional retardation film, and it is possible to easily and simply use one sheet. This thin film can be a retardation film necessary for compensating the birefringence of a VA mode liquid crystal cell. If necessary, a plurality of sheets may be laminated and used.

Next, a laminated polarizing plate obtained by laminating the retardation thin film of the present invention and a polarizing plate will be described. The laminated polarizing plate is used as a compensation polarizing plate having an optical compensation function.

The polarizing plate used in the present invention is not particularly limited, but its basic constitution is such that a suitable adhesive layer is formed on one or both sides of a polarizer made of a polyvinyl alcohol-based polarizing film containing a dichroic substance, For example, a transparent protective film serving as a protective layer is adhered via an adhesive layer made of vinyl alcohol polymer or the like.

As the polarizer (polarizing film), for example, a film made of a vinyl alcohol polymer such as polyvinyl alcohol or partially formalized polyvinyl alcohol is dyed with a dichroic substance such as iodine or a dichroic dye, and stretched. Appropriate treatments such as treatments and cross-linking treatments performed in an appropriate order or method and capable of transmitting linearly polarized light when natural light is incident can be used. A polarizing film formed of a polyene oriented film such as a dehydrated product of polyvinyl alcohol or a dehydrochlorinated product of polyvinyl chloride may be used. Among them, a polyvinyl alcohol-based film in which iodine or a dichroic dye is adsorbed and oriented is preferable. In particular, those having excellent light transmittance and polarization degree are preferable. The thickness of the polarizing film is generally 1 to 80 μm, but is not limited to this.

An appropriate transparent film can be used as the protective film material which is a transparent protective layer provided on one side or both sides of the polarizer (polarizing film). Above all, a film made of a polymer having excellent transparency, mechanical strength, thermal stability, moisture shielding property and the like is preferably used. Examples of the polymer include acetate resin such as triacetyl cellulose, polyester resin, polyether sulfone resin, polycarbonate resin, polyamide resin, polyimide resin, polynorbornene resin, polyolefin resin, acrylic resin. However, the present invention is not limited to this. A transparent protective film that can be particularly preferably used in terms of polarization characteristics and durability is a triacetyl cellulose film whose surface is saponified with an alkali or the like. Although the thickness of the transparent protective film is arbitrary, it is generally 500 μm or less, preferably 5 to 300 μm, for the purpose of thinning the polarizing plate.
Particularly preferably, the thickness is 5 to 150 μm. When the transparent protective films are provided on both sides of the polarizing film, the transparent protective films made of different polymers may be used on the front and back.

The transparent protective film used for the protective layer is
As long as the object of the present invention is not impaired, a hard coat treatment, an antireflection treatment, a treatment for the purpose of preventing sticking, diffusion or antiglare, or the like may be applied. The hard coat treatment is performed for the purpose of preventing scratches on the surface of the polarizing plate.
It is possible to form a cured skin film, which is made of a suitable ultraviolet-curable resin such as urethane-based, acrylic-based, or epoxy-based resin, and has excellent hardness and slipperiness, by a method of adding it to the surface of the transparent protective film.

On the other hand, the antireflection treatment is carried out for the purpose of preventing reflection of external light on the surface of the polarizing plate, and can be achieved by forming an antireflection film or the like according to the conventional method. In addition, anti-sticking is performed for the purpose of preventing adhesion with an adjacent layer, and anti-glare treatment is performed for the purpose of preventing external light from being reflected on the surface of the polarizing plate and hindering visual recognition of light transmitted through the polarizing plate. It can be formed by imparting a fine concavo-convex structure to the surface of the transparent protective film by an appropriate method such as a surface roughening method by a sand blast method or an embossing method or a method of blending transparent fine particles.

Examples of the transparent fine particles include silica and alumina having an average particle size of 0.5 to 20 μm, titania and zirconia, tin oxide and indium oxide, cadmium oxide and antimony oxide. Fine particles may be used, or organic fine particles made of crosslinked or non-crosslinked polymer particles may be used.
The amount of transparent fine particles used is 2 per 100 parts by weight of transparent resin.
It is generally 70 to 70 parts by weight, especially 5 to 50 parts by weight.

The antiglare layer containing transparent fine particles can be provided as the transparent protective film itself or as a coating layer on the surface of the transparent protective film. The anti-glare layer may also serve as a diffusion layer (viewing angle compensation function or the like) for diffusing light transmitted through the polarizing plate and expanding the viewing angle. The antireflection layer, the sticking prevention layer, the diffusion layer, the antiglare layer, and the like may be provided as an optical layer formed of a sheet provided with these layers, separately from the transparent protective film.

The adhesion treatment between the polarizer and the transparent protective film as the protective layer is not particularly limited, but for example, an adhesive made of an acrylic polymer or a vinyl alcohol polymer, or boric acid or borax. Alternatively, it can be carried out via an adhesive or the like made of at least a water-soluble crosslinking agent of a vinyl alcohol polymer such as glutaraldehyde, melamine, and oxalic acid. This makes it difficult to peel off due to the influence of humidity and heat, and makes it possible to provide excellent light transmittance and polarization degree. Such an adhesive layer is formed as a coating dry layer of an aqueous solution or the like, but other additives and a catalyst such as an acid can be added as necessary when preparing the aqueous solution. In particular, it is preferable to use an adhesive made of polyvinyl alcohol because of its excellent adhesion to the PVA film.

When the retardation thin film and the polarizing plate are integrated, the retardation thin film (birefringent layer) of the present invention is transferred / laminated onto a polarizer or a polarizing plate via an adhesive or a pressure-sensitive adhesive ( 1 and 2), a method of laminating a retardation thin film with a substrate formed on a polymer substrate as it is as a protective layer of a polarizer, and laminating via an adhesive or a pressure-sensitive adhesive (see FIG. 3), polymer A method of directly forming a retardation thin film of the present invention on a polarizer using a substrate as a polarizer (see FIG. 4), a retardation thin film with a substrate formed on a polymer substrate via an adhesive or an adhesive material. Examples thereof include a method of laminating with a polarizing plate (see FIG. 5).

Explaining the example in FIG. 1, the protective film is shown in FIG.
A polarizer (21) to which (22) is attached, and a contact (adhesive) layer
The retardation thin film (1) is laminated via (4).

In the example shown in FIG. 2, a protective layer (22) is laminated on both sides of a polarizer (21), and a protective film (22) is attached to one side of the protective film. The retardation thin films (1) are laminated via the above.

In the example shown in FIG. 3, the protective film substrate (2
2) A birefringent film with a substrate on which a retardation thin film is directly laminated is used as a protective layer for the polarizer (21). Another protective film (22) is attached to the other surface of the polarizer.

In the example shown in FIG. 4, the polarizer (21) is used as a polymer substrate, and the retardation thin film (1) is laminated on the polymer substrate to form a laminated polarizing plate. A protective film (22) is attached to the other surface of the polarizer.

In the example shown in FIG. 5, a polarizing plate (2) is provided with a polymer base material (that is, a film base material) (5) and a retardation thin film (1) via a viscous (adhesive) adhesion layer (4). One piece is pasted together. Further, on the outside of the film base material, a viscous (adhesion) adhesion layer (4) for bonding with a liquid crystal cell is formed. Although FIG. 5 shows an example in which the film substrate is on the liquid crystal cell side, the film substrate (5) may be laminated on the polarizing plate side and the retardation thin film (1) may be laminated on the liquid crystal cell side. .

The retardation thin film of the present invention can be used in combination with a polarizing plate, and can also be used in combination with various retardation plates, diffusion control films, brightness enhancement films and the like. The retardation plate, uniaxially stretched polymer,
Examples include biaxially stretched ones, Z-axis oriented treatments, and ones coated with a liquid crystalline polymer. As the diffusion control film, a film using diffusion, scattering, and refraction for controlling the viewing angle, a film using diffusion, scattering, and refraction for controlling glare related to resolution, scattered light, and the like can be used. The brightness enhancement film is a brightness enhancement film using selective reflection of cholesteric liquid crystal and a λ / 4 plate,
A scattering film or the like utilizing anisotropic scattering depending on the polarization direction can be used. Further, it may be used in combination with a wire grid polarizer.

The adhesive (adhesive) is not particularly limited, and a suitable pressure sensitive adhesive such as a transparent pressure sensitive adhesive such as acrylic, silicone, polyester, polyurethane, polyether, or rubber is used. Can be used. From the viewpoint of preventing changes in optical properties of optical films and the like, those that do not require a high temperature process at the time of curing or drying are preferable, and those that do not require a long curing treatment or drying time are desirable. Further, those which do not cause peeling under heating or humidifying conditions are preferably used.

The laminated polarizing plate according to the present invention can be preferably used for forming various liquid crystal display devices, etc., but in its application, a polarizing plate or a reflection plate is optionally bonded through the above-mentioned adhesive or pressure-sensitive adhesive. One or more layers of other optical layers such as a semi-transmissive reflector and a brightness enhancement film can be laminated.

The above-mentioned reflection plate is provided on a polarizing plate to form a reflection type polarizing plate. The reflective polarizing plate is usually placed on the back side of the liquid crystal cell and is on the viewing side (display side).
A liquid crystal display device (reflection-type liquid crystal display device) of a type that reflects and displays incident light from the device is formed. The reflective polarizing plate has an advantage that a light source such as a backlight can be omitted and the liquid crystal display device can be easily thinned. The reflective polarizing plate can be formed by an appropriate method such as a method in which a reflective layer made of metal or the like is attached to one surface of the polarizing plate. Specific examples thereof include a transparent protective film that is mat-treated if necessary, and a reflective layer formed by attaching a foil or a vapor deposition film made of a reflective metal such as aluminum to one surface of the transparent protective film.

Further, there may be mentioned a reflection type polarizing plate having a reflective layer reflecting the fine concavo-convex structure on the transparent protective film containing fine particles and having a fine concavo-convex structure on the surface. The reflective layer having a fine surface irregularity structure has an advantage of diffusing incident light by diffuse reflection, preventing directivity and glare, and suppressing uneven brightness. The reflective layer having a fine concavo-convex structure reflecting the surface fine concavo-convex structure of the transparent protective film is formed by an appropriate method such as a vacuum evaporation method, an ion plating method, a vapor deposition method such as a sputtering method, or a plating method. Can be directly formed on the surface of the transparent protective film.

The semi-transmissive type polarizing plate is a semi-transmissive type reflective layer in the above reflective type polarizing plate, and examples thereof include a half mirror which reflects and transmits light by the reflective layer.
The semi-transmissive polarizing plate is usually provided on the back side of the liquid crystal cell, and when a liquid crystal display device is used in a relatively bright atmosphere, it reflects incident light from the viewing side (display side) to display an image. In a relatively dark atmosphere, a liquid crystal display device of the type that displays an image using a built-in light source such as a backlight built in the back side of a semi-transmissive polarizing plate is formed. That is, the semi-transmissive polarizing plate is useful for forming a liquid crystal display device of a type that can save energy for using a light source such as a backlight in a bright atmosphere and can be used with a built-in light source in a relatively dark atmosphere. Is.

Further, as the above-mentioned brightness enhancement film,
For example, a dielectric multi-layered thin film or a multi-layered laminate of thin films having different refractive index anisotropies, which shows the property of transmitting linearly polarized light of a predetermined polarization axis and reflecting other light (“D” manufactured by 3M). -BEF ", etc.), a cholesteric liquid crystal layer, especially an oriented film of a cholesteric liquid crystal polymer, or one having an oriented liquid crystal layer supported on a film substrate (Nitto Denko Corporation" P
CF350 ", Merck" Transmax ")
As described above, an appropriate one can be used, such as one having a characteristic of reflecting either left-handed or right-handed circularly polarized light and transmitting other light.

The above-mentioned optical member in which two or more optical layers are laminated can be formed by a method of sequentially laminating separately in the manufacturing process of a liquid crystal display device or the like. The optical member is excellent in quality stability and assembling workability, and has an advantage that the manufacturing efficiency of the liquid crystal display device can be improved. In addition, for stacking,
Appropriate adhesion means such as the above-mentioned adhesive can be used.

The laminated polarizing plate of the present invention may be provided with an adhesive layer or an adhesive layer for adhering to other optical layers or other members such as liquid crystal cells. The adhesive (adhesive) layer can be appropriately formed by using a conventionally known adhesive such as acrylic. Among them, prevention of foaming phenomenon or peeling phenomenon due to moisture absorption, prevention of warpage of liquid crystal cell due to deterioration of optical characteristics due to thermal expansion difference, etc., and therefore, high moisture absorption rate in terms of formability of a liquid crystal display device having high quality, The adhesive layer is preferably low and has excellent heat resistance. Further, an adhesive layer or the like which contains fine particles and exhibits a light diffusing property can be used. The adhesive (adhesion) layer may be provided on a necessary surface as necessary.

When the adhesive (adhesive) layer provided on the laminated polarizing plate is exposed on the surface, the adhesive (adhesive) layer is temporarily attached with a separator for the purpose of preventing contamination until the adhesive (adhesive) layer is put to practical use. It is preferable to cover. The separator is formed by, for example, a method of providing a release coat with an appropriate release agent such as a silicone-based or long-chain alkyl-based, fluorine-based or molybdenum sulfide, etc., on an appropriate thin sheet according to the above transparent protective film or the like. be able to.

Each layer such as the above-mentioned polarizing plate or polarizer forming the optical member, the transparent protective film, the optical layer and the adhesive (adhesion) layer is, for example, a salicylic acid ester compound, a benzophenone compound, a benzotriazole compound. It may be one having an ultraviolet absorbing ability by an appropriate method such as a method of treating with an ultraviolet absorber such as a cyanoacrylate compound, a nickel complex salt compound or the like.

The retardation thin film and laminated polarizing plate of the present invention are V
The liquid crystal display device can be preferably used for forming an A-mode liquid crystal display device. For example, a liquid crystal display device of a reflective type, a semi-transmissive type, a transmissive / reflective type, etc., in which a polarizing plate is arranged on one side or both sides of a liquid crystal cell Can be used for. In particular, it can be most preferably used as a viewing angle compensation film for a reflective liquid crystal display in a vertical alignment mode, and can achieve excellent display quality in a wide viewing angle range of front and squint, and a liquid crystal display device with a wide viewing angle. I can.

In the present invention, the material and thickness of the substrate forming the liquid crystal cell are not particularly limited, and any suitable material such as a glass substrate or a plastic substrate can be used.

When polarizing plates and optical members are provided on both sides of the liquid crystal cell, they may be the same or different. Further, when forming the liquid crystal display device, one or two or more layers can be arranged at appropriate positions with appropriate components such as a prism array sheet, a lens array sheet, a light diffusion plate and a backlight.

FIG. 5 is a diagram showing an example of the liquid crystal display device of the present invention. The retardation thin film (1) of the present invention is laminated and arranged on the backlight side of the VA mode liquid crystal cell (3), and the polarizing plate (6) is laminated thereon. A polarizing plate (7) is laminated on the viewer side of the liquid crystal cell (3). In addition, a pressure-sensitive adhesive or an adhesive can be used for the lamination, if necessary.

FIG. 6 is a diagram showing the axial relationship of the liquid crystal display device of FIG. In the illustrated example, the maximum refractive index azimuth (nx) in the plane of the retardation thin film and the absorption axis (a) of the backlight side polarizing plate (6) are arranged so as to be substantially orthogonal to each other, and the viewing side polarizing plate (7) The absorption axis (a) of () is orthogonal to the absorption axis of the polarizing plate on the backlight side. Further, although FIG. 6 shows an example in which the retardation thin film (1) is arranged only on the backlight side, the retardation thin film (1) may be arranged on both sides of the liquid crystal cell (3), and the viewing side. It may be arranged only in.

The figure shows an example of the embodiment of the present invention. For example, in FIG. 6, instead of the retardation thin film (1), a polymer or polymer liquid crystal having a characteristic of nx> ny = nz, or a polymerizable liquid crystal is used. A combination of a retardation plate made of liquid crystal and the retardation thin film (1) may be used.

[0065]

EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples. The characteristics of the film were evaluated by the following methods.

(Measurement of Phase Difference) A phase difference meter (KOBRA21ADH manufactured by Oji Scientific Instruments) was used for measurement.

Example 1 2,2′-bis (3,4-dicarboxyphenyl) hexafluoropropane (≈6F
DA) and 2,2'-bis (trifluoromethyl)-
4,4'-diaminobiphenyl (≒ PFMB ≒ TFM
A solution in which the polyimide synthesized from B) was prepared at 15 wt% using cyclohexanone as a solvent was applied onto a 50 μm thick triacetyl cellulose film. Then, by drying at 100 ° C. for 10 minutes, a thin film having a residual solvent amount of 7% and a thickness of 6 μm was obtained. Thereafter, the thin film formed on the triacetyl cellulose film was stretched uniaxially in the longitudinal direction by 5% at a temperature of 160 ° C. together with the substrate.

The characteristics of the thin film peeled from the triacetyl cellulose film are as follows: Δnd = 60 nm, Rth = 250
nm, d = 5.5 μm, and Δn = (nx−nz) =
It had a property of a retardation thin film of 0.045 and nx>ny> nz.

This retardation thin film was attached via an adhesive so that the absorption axis of the polarizing plate was orthogonal to the nx direction. V with an adhesive so that the retardation thin film is on the liquid crystal cell side.
I stuck it on the A panel. In addition, on the opposite side, only the polarizing plate was attached to the VA panel via an adhesive so that the absorption axes of the polarizing plates were orthogonal to each other, to manufacture a liquid crystal display device.

Comparative Example 1 A polynorbornene film (ARTON film manufactured by JSR) was stretched at 175 ° C. by a fixed-end lateral stretching of 1.3 times to obtain a film having a thickness of 80 μm. This film has Δnd = 50 nm,
Rth = 120 nm, Δn = 0.015, nx
It was a retardation film of>ny> nz.

This retardation film was n-bonded through an adhesive.
The lamination was performed so that the x direction and the absorption axis of the polarizing plate were orthogonal to each other.
This was bonded to a VA panel with an adhesive so that the retardation film was on the liquid crystal cell side. In addition, on the opposite side, only the polarizing plate was attached to the VA panel via an adhesive so that the absorption axes of the polarizing plates were orthogonal to each other, to manufacture a liquid crystal display device.

Comparative Example 2 Using the same solution as in Example 1,
Coated on triacetyl cellulose. Then 100 ° C
After heat treatment for 10 minutes, a completely transparent and smooth film was obtained after peeling. This film has Δnd = 0.5 nm and Rth =
220 nm, d = 5.8 μm, Δn = nx−nz
= 0.038, nx≈ny> nz, which was a retardation thin film.

This retardation thin film was bonded via an adhesive so that the nx direction and the absorption axis of the polarizing plate were orthogonal to each other. V with an adhesive so that the retardation thin film is on the liquid crystal cell side.
I stuck it on the A panel. In addition, on the opposite side, only the polarizing plate was attached to the VA panel via an adhesive so that the absorption axes of the polarizing plates were orthogonal to each other, to manufacture a liquid crystal display device.

(Evaluation of Viewing Angle Characteristics) The viewing angle characteristics of the liquid crystal display device obtained above were measured. For measurement, ELDIM
EZContrast manufactured by the company was used. Table 1 shows the measurement results regarding the contrast reduction in the oblique azimuth, which is different from the absorption axis azimuth of the polarizing plate. The absorption axis direction of the polarizing plate is 0 ° on the observer side and 90 ° on the backlight side.

[0075]

[Table 1]                                               Contrast (10 or more)             Refractive index Retardation film Retardation film 45 ° 135 ° 225 ° 315 °             Anisotropy Thickness Number azimuth azimuth azimuth azimuth                (μm) Example 1 nx> ny> nz 5.5 1 80 ° 80 ° 80 ° 80 ° Comparative Example 1 nx> ny> nz 80 2 80 ° 80 ° 80 ° 80 ° Comparative Example 2 nx≈ny> nz 5.8 1 60 ° 60 ° 60 ° 60 °

As a result of the evaluation, in this example, a panel having a wide viewing angle in which the contrast was less dependent on the viewing angle was obtained by using one retardation thin film, but in the comparative example, a thick phase difference was obtained even at a wide viewing angle. Two films are required, or a display device having a wide viewing angle cannot be obtained only with the retardation thin film.

[0077]

As described above, according to the present invention,
It is possible to easily obtain a VA mode liquid crystal display device having a wide viewing angle with a small viewing angle dependency. That is, in order to achieve a wide viewing angle, an optically anisotropic layer having a refractive index anisotropy of nx> ny = nz and an optically anisotropic layer having a refractive index anisotropy of nx = ny> nz. Since the configuration in which at least one layer is used is not adopted, increase in thickness and complication of steps due to stacking optical members can be eliminated.

Since the retardation thin film of the present invention uses a polymer having an aromatic ring or an aromatic heterocycle in the main chain direction of the polymer, it has a larger refractive index in the main chain direction than in the vertical direction. Therefore, it has a large birefringence as a molecule,
In addition, since the molecular chains are likely to be oriented parallel to each other in the plane, the difference between the maximum in-plane refractive index and the refractive index in the thickness direction (R
th) is large. Therefore, unlike a norbornene-based or cellulose-based retardation film or the like, it is not necessary to laminate a plurality of sheets, and one sheet can be used, so that an increase in thickness and a complicated process due to lamination are eliminated. By arranging this in a VA mode liquid crystal cell in combination with a polarizing plate, a VA with a wide viewing angle with a small viewing angle dependency can be easily provided.
It is possible to obtain a mode liquid crystal display device.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an example of a laminated polarizing plate of the present invention.

FIG. 2 is a schematic cross-sectional view showing another example of the laminated polarizing plate of the present invention.

FIG. 3 is a schematic cross-sectional view showing another example of the laminated polarizing plate of the present invention.

FIG. 4 is a schematic cross-sectional view showing another example of the laminated polarizing plate of the present invention.

FIG. 5 is a schematic cross-sectional view showing another example of the laminated polarizing plate of the present invention.

FIG. 6 is a schematic sectional view showing an example of a liquid crystal display device of the present invention.

FIG. 7 is a diagram showing an axial relationship of an example of the liquid crystal display device of the present invention.

[Explanation of symbols]

1 Phase difference thin film (birefringent layer) 2 Polarizer 21 Polarizer 22 Protective film 3 Liquid crystal cell 4 Adhesive layer or adhesive layer 5 Polymer substrate 6 Backlight side polarizing plate 7 Viewing side polarizing plate

Continued front page    (72) Inventor Naho Murakami             1-2 1-2 Shimohozumi, Ibaraki City, Osaka Prefecture Nitto             Electric Works Co., Ltd. (72) Inventor Masatake Hayashi             1-2 1-2 Shimohozumi, Ibaraki City, Osaka Prefecture Nitto             Electric Works Co., Ltd. F-term (reference) 2H049 BA02 BA06 BA25 BA26 BA42                       BB03 BB23 BB26 BB33 BB36                       BB43 BB44 BB45 BB46 BB47                       BB48 BB49 BB51 BB63 BB65                       BB67 BC03 BC09 BC14 BC22                 2H091 FA08 FA11 FC09 FD10 FD12                       GA16 GA17 HA06 LA03 LA11                       LA12 LA13 LA17

Claims (6)

[Claims] 1. A liquid crystal cell in a vertical alignment mode between two orthogonal polarizing plates and selected from the group consisting of polyamide, polyimide, polyester, poly (ether ketone), poly (amide imide) and poly (ester imide). A retardation thin film made of at least one polymer and having a relationship of nx>ny> nz, where nx and ny are in-plane refractive indices and nz is a refractive index in the thickness direction. Liquid crystal display device. 2. The liquid crystal display device according to claim 1, wherein the retardation thin film has a difference between the maximum in-plane refractive index and the refractive index in the thickness direction of 0.01 to 0.4. 3. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is arranged so that the maximum refractive index direction in the plane of the retardation thin film and the absorption axis of the polarizing plate are orthogonal or parallel to each other. 4. A retardation value Δn in the plane of the retardation thin film.
d (= (nx-ny) d) is 300 nm or less (where d is the thickness of the thin film), and the maximum refractive index direction in the plane is orthogonal to the absorption axis of the adjacent polarizing plate. The liquid crystal display device according to any one of claims 1 to 3, wherein the liquid crystal display device is disposed in. 5. A polymer comprising at least one polymer selected from the group consisting of polyamide, polyimide, polyester, poly (ether ketone), poly (amide imide) and poly (ester imide), and having a refractive index in two in-plane directions. A retardation thin film for a VA mode liquid crystal cell, which satisfies the relationship of nx>ny> nz, where nx and ny and a refractive index in the thickness direction are nz. 6. A polymer comprising at least one polymer selected from the group consisting of polyamide, polyimide, polyester, poly (ether ketone), poly (amide imide) and poly (ester imide), and having a refractive index in two in-plane directions. nx and ny, where nz is the refractive index in the thickness direction, a retardation thin film satisfying the relationship of nx>ny> nz and a polarizing plate are laminated, and a laminated polarization for a VA mode liquid crystal cell is provided. Board.