JP2001042128A - Composite phase difference plate, optical compensation polarizing plate and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To develop a phase difference plate which can highly compensate the phase difference due to double refractivity of a liquid crystal and which can form a liquid crystal display device having excellent viewing angle and contrast and uniformity of these properties. SOLUTION: The composite phase difference plate consists of a combination of one or more phase difference films 1 having the main refractive indices nx, ny (nx>=ny) in the plane and the refractive index nz in the thickness direction satisfying that at least one of the refractive indices is different from others, and a double refraction film 2 having all different aforementioned refractive indices. The combination is determined so that each wavelength dependence of double refraction and Nz defined by Nz=(nx-nz)/(nx-ny) in the phase difference film and double refraction film differs from each other. The phase difference film and the double refraction film consist of films having an aligned non-liquid crystalline polymer. The optical compensation polarizing plate is obtained by disposing the composite phase difference plate on one face of an absorption type polarizing plate 3. The Liquid crystal display device has the optical compensation polarizing plate on at least one side of a liquid crystal cell.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite retardation plate and an optically compensating polarizing plate capable of forming a liquid crystal display device excellent in viewing angle and contrast by highly compensating for birefringence caused by liquid crystal.

[0002]

2. Description of the Related Art With the spread of liquid crystal display devices (LCDs) to televisions and personal computer monitors, it is desired to increase the viewing angle and increase the contrast. It has been proposed to improve the visibility by compensating a phase difference due to birefringence of a liquid crystal by a retardation plate, such as achieving black and white display by color compensation in an LCD. However, the conventional compensator cannot sufficiently cope with the phase difference characteristic of the liquid crystal, and there is a problem that the improvement of the visibility characteristic cannot be satisfied.

[0003] Incidentally, in the TN-LCD, a wide view film (trade name, manufactured by Fuji Photo Film Co., Ltd.)
H film (trade name, manufactured by Nippon Petrochemical Co., Ltd.) is known as a compensating plate for widening the viewing angle. However, inversion of gradation, remarkable reduction of contrast at a viewing angle of 60 ° or more, and black / white level There were problems such as coloring.

In view of the above, vertical alignment (VA) mode, horizontal alignment mode, ASM mode, etc.
A TFT-LCD using a compensator made of a biaxial retardation film exhibiting retardation characteristics such as nz has also been proposed.
However, for example, (nx-nz) d (thickness) is 200 nm
As described above, it is difficult to obtain a biaxial retardation film having a large phase difference and excellent accuracy due to restrictions on materials and the like, and at present, high-precision compensation has not been achieved.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to develop a retardation plate capable of highly compensating for a phase difference due to birefringence of a liquid crystal and forming a liquid crystal display device having an excellent viewing angle, contrast and uniformity.

[0006]

According to the present invention, the in-plane principal refractive index is nx,
ny, when the refractive index in the thickness direction is nz and nx ≧ ny, at least one of the refractive indexes is different from one or more retardation films, and all of the refractive indexes are different. One or two or more birefringent films are used in a combination in which the wavelength dependence of birefringence and Nz defined by the formula: (nx-nz) / (nx-ny) are different, and Wherein the retardation film and the birefringent film are composed of a film in which a non-liquid crystalline polymer is oriented.

Further, according to the present invention, an optically compensating polarizing plate characterized in that the composite retardation plate is provided on one side of an absorption type polarizing plate, and the optically compensating polarizing plate is provided on at least one side of a liquid crystal cell. A liquid crystal display device characterized by the following.

[0008]

According to the present invention, there is provided a retardation film in which a part or all of the refractive index in the plane and in the thickness direction is different, and the wavelength dependency (wavelength dispersion) of birefringence and Nz are different. By combining the retardation layer with the combination of birefringent films to control the wavelength dependence by its additive property, it is possible to obtain a retardation plate that can highly compensate for the retardation due to birefringence of the liquid crystal,
In particular, it is possible to form a liquid crystal display device excellent in viewing angle, contrast, and uniformity by compensating for coloring due to viewing angle with high accuracy.

That is, the birefringence characteristic of the liquid crystal changes in the alignment state even in the same liquid crystal, and in order to compensate for the change, particularly to compensate for the coloring phenomenon due to the viewing angle, in addition to the phase difference and the change due to the viewing angle, the birefringence characteristic is also changed. It is necessary to deal with the wavelength dependence, the configuration by the combination of the chromatic dispersion difference described above,
In particular, due to the combination of the difference in Nz with respect to the wavelength dispersion of △ nxy and △ nxz defined by (nx-ny) and (nx-nz), which have a large influence on the viewing angle change, △ nxzd: 200 nm
It is possible to obtain a retardation plate having abundant retardation characteristics, such as being able to accurately create even a large retardation such as that described above. Accordingly, it is possible to greatly improve the compensation accuracy of coloring due to the viewing angle. Therefore, the lack of compensation by the conventional compensator is considered to be due to the inability to adequately cope with the wavelength dependence of the phase difference and its change in viewing angle.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In a composite retardation plate according to the present invention, when nx ≧ ny, where nx and ny are the in-plane main refractive index and nz is the refractive index in the thickness direction, at least one of those refractive indices is different. And one or two or more retardation films different from the above, and one or two birefringent films having all the refractive indexes different from each other.
The number of sheets is referred to as the wavelength dependence of birefringence and the formula: (nx−nz) /
Nz defined by (nx-ny) is used in a different combination, and the retardation film and the birefringent film are made of a film in which a non-liquid crystalline polymer is oriented. An example is shown in FIG. 1 is a retardation film and 2 is a birefringent film. In the example of the figure, an optical compensating polarizer is shown, and 3 is an absorption polarizer.

As the retardation film and the birefringent film, a film in which a suitable non-liquid crystal polymer having the above-mentioned refractive index characteristics is oriented can be used, and there is no particular limitation. As an example, a stretched film obtained by stretching a film made of various non-liquid crystalline polymers by an appropriate method such as uniaxial or biaxial is exemplified. Above all, those having excellent light transmittance and little alignment unevenness and phase difference unevenness can be preferably used.

Examples of the non-liquid crystalline polymer include polyesters such as polycarbonate, polyarylate, polyethylene terephthalate, and polyethylene naphthalate, polysulfone, olefin-based polymers and norbornene-based polymers, acrylic polymers and styrene-based polymers, and triacetyl-based polymers. Cellulose-based polymers such as cellulose and polyvinyl alcohol;
Examples thereof include polymers of a kind or a mixture of three or more kinds.

By using a non-liquid crystalline polymer, the photoelastic coefficient can be easily controlled, and the change in birefringence characteristic (phase difference characteristic) due to temperature change, humidity, light, or stress generated by bonding treatment is suppressed. Means that the photoelastic coefficient is 50 × 10 ⁻¹² m ² / N or less in absolute value, especially 30 × 10
^A retardation film or a birefringent film made of a polymer film having a size of ⁻¹² m ² / N or less, particularly 20 × 10 ⁻¹² m ² / N or less is preferable.

Further, in the case of a birefringent film disposed as a transparent protective layer of a polarizing film in an optical compensation polarizing plate, the photoelastic coefficient is 15 × 1 in absolute value from the above point.
0 ^{- 12} m ² / N or less, especially ¹⁰ × 10 -12 ^m 2 / N
It is preferable that the film is composed of the following polymer film.

The retardation film used has an in-plane main refractive index of nx and ny, a refractive index in the thickness direction of nz, and nx ≧ n.
When y is used (the same applies hereinafter), at least one of the refractive indices is different from the others. Therefore, the refractive index characteristics are nx = ny> nz, nx>ny> nz, nx> ny = nz,
nx>nz> ny, nx = nz> ny, nz>nx> ny or nz
> Nx = ny. Further, as the birefringent film, a film having all of the above-mentioned refractive indices different from each other is used. Therefore, its refractive index characteristics are nx>ny> nz, nx> n
z> ny or nz>nx> ny.

The composite retardation plate can be formed by a method using one or more retardation films and one or more birefringent films to form a laminate. In the present invention, the wavelength dependence of birefringence between the retardation film and the birefringent film, and the formula: (nx−
Nz defined by (nz) / (nx-ny) is used in different combinations.

In the above, the wavelength dependence of birefringence and Nz
A combination of a retardation film and a birefringent film having different (index of viewing angle characteristics) is optional. By using a combination in which the wavelength dependence of birefringence is different, a composite retardation plate exhibiting different wavelength dependence characteristics different from the wavelength dependence characteristics of each member such as the used retardation film can be obtained.

By using a combination having different Nz, it is possible to obtain a composite retardation plate exhibiting different characteristics different from the Nz of each member used, and the wavelength dependence of the Nz can also be obtained. By exhibiting, it is possible to obtain a composite retardation plate exhibiting a retardation characteristic that cannot be obtained as a whole as a single product of each member, and to compensate for the difference in birefringence characteristics due to the alignment state of the liquid crystal. A retardation plate can be obtained.

Control of the wavelength dependence and the retardation characteristics such as Nz in the composite retardation plate can be performed by changing the combination of the retardation film and the birefringent film and the number of the combinations. In that case, the arrangement angle of the nx axis and the like in the retardation film and the birefringent film is arbitrary, and for example, by arranging their slow axes (nx axes) crosswise, (pseudo) optical rotation can be imparted. The phase difference characteristic can also be adjusted by controlling the angle. Note that the (pseudo) optical rotation due to the intersection of the nx axes also exhibits wavelength dependence.

In the above-described combination of wavelength-dependent combinations, the resulting composite retardation plate has the same wavelength dependence as the wavelength dependence of each member, and does not exhibit different wavelength dependence. Also, the wavelength dependency does not occur in Nz, and the Nz value does not depend on the wavelength while maintaining a constant Nz value similarly to each member.
Therefore, when two or more retardation films or birefringent films are used, it is preferable to use a combination in which the wavelength dependence of birefringence and Nz are different from the viewpoint of converting the retardation characteristics.

As described above, a new phase difference characteristic can be provided by compounding with a combination of wavelength dependency and Nz different, and a phase difference due to birefringence of liquid crystal and a change due to a viewing angle can be provided.
It is possible to obtain abundant retardation plates exhibiting various retardation characteristics that can compensate for the wavelength dependence of these characteristics, etc., with high accuracy even for differences in birefringence characteristics due to differences in the alignment state of the liquid crystal. Can compensate.

The refractive index characteristics of the above-mentioned retardation film and birefringent film can be controlled by the kind of polymer, stretching conditions and orientation conditions, and the refractive index nz in the thickness direction is, for example, the polymer to be treated. Adhering one or two or more layers of heat-shrinkable film to one or both sides of the film, and controlling the film by a method of stretching or shrinking the film under the action of the shrinkage force of the heat-shrinkable film by heating. Can be. The polymer film to be treated may be formed by an appropriate method according to the related art, such as a casting method or an extrusion molding method.

The thickness of the retardation film or birefringent film can be appropriately determined according to the desired retardation characteristics. Generally 1 to 500 μm, especially 3 to 3
A layer having a thickness of 50 μm, particularly 5 to 250 μm is used, but is not limited thereto.

The composite retardation plate according to the present invention can be put to practical use as it is, or as shown in FIG.
Can be put to practical use as an optically compensating polarizing plate. In forming the optically compensating polarizing plate, an appropriate absorbing polarizing plate exhibiting characteristics of transmitting linearly polarized light having a predetermined vibration plane and absorbing other light can be used, and the type thereof is not particularly limited.

In general, a film of a hydrophilic polymer such as polyvinyl alcohol, partially formalized polyvinyl alcohol, or a partially saponified ethylene / vinyl acetate copolymer film is coated with a dichroic dye such as iodine and / or a dichroic dye. A polarizing film or the like which has been subjected to a stretching orientation treatment by adsorbing a substance is used.

The absorption type polarizing plate may have a structure in which transparent protective layers 2 and 31 are provided on one or both sides of a polarizing film 32 as shown in the figure. The transparent protective layer is provided for various purposes such as reinforcing the polarizing film and improving heat resistance and moisture resistance. The transparent protective layer can be formed as a resin coating layer, a resin film laminating layer, or the like, and may contain fine particles for diffusion or surface roughening.

The transparent protective layer may be provided as a birefringent film composed of the above-mentioned stretched cellulose polymer film. In this case, as shown in the figure, a birefringent film 2 forming a composite retardation plate according to the present invention is used.
Serves also as the transparent protective layer of the polarizing film 32 in the absorption polarizing plate 3, which is effective for reducing the thickness of the optical compensation polarizing plate. It is also advantageous for improving the assembling efficiency of the liquid crystal display device and improving the accuracy of compensating for birefringence caused by the liquid crystal.

Further, the absorption type polarizing plate may be provided with an antireflection layer or an antiglare treatment layer for the purpose of preventing surface reflection. The antireflection layer can be appropriately formed, for example, as a light interference film such as a fluorine polymer coat layer or a multilayer metal vapor deposition film. On the other hand, the anti-glare treatment layer also
For example, it may be a resin coating layer containing fine particles or formed by an appropriate method in which surface reflected light is diffused by imparting a fine uneven structure to the surface by an appropriate method such as embossing, sand blasting or etching. .

The above-mentioned fine particles may be made of a conductive material such as silica, calcium oxide, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, antimony oxide having an average particle size of 0.5 to 20 μm. One or more kinds of appropriate inorganic fine particles or crosslinked or uncrosslinked organic fine particles made of a suitable polymer such as polymethyl methacrylate or polyurethane may be used.

Each layer of the retardation film, birefringent film, absorption type polarizing plate and the like forming the composite retardation plate and the optically compensating polarizing plate according to the present invention may be in a separated state. It is preferable that a part, particularly, all of them, be fixed, in order to suppress reflection due to light, prevent displacement of the optical system, and prevent entry of foreign matter such as dust.

For the fixing treatment, an appropriate material such as a transparent adhesive can be used, and the kind of the adhesive is not particularly limited. From the viewpoint of preventing a change in the optical properties of the constituent members, it is preferable that a high-temperature process is not required for curing and drying at the time of the bonding process, and that a long curing process and a drying time are not required. From such a point, an adhesive layer can be preferably used.

For forming the pressure-sensitive adhesive layer, for example, a transparent pressure-sensitive adhesive using an appropriate polymer such as an acrylic polymer, a silicone-based polymer, polyester, polyurethane, polyether or synthetic rubber can be used. Above all, acrylic pressure-sensitive adhesives are preferred from the viewpoints of optical transparency, adhesive properties, weather resistance and the like.

The adhesive layer may be provided on one or both sides of a composite retardation plate or an optically compensating polarizing plate, if necessary, for the purpose of adhering to an adherend such as a liquid crystal cell. When the pressure-sensitive adhesive layer is exposed on the surface, it is preferable to temporarily attach a separator or the like to prevent the contamination or the like of the surface of the pressure-sensitive adhesive layer until the pressure-sensitive adhesive layer is put to practical use.

The arrangement relationship between the fast axis and the like of the composite retardation plate and the transmission axis and the like of the polarizing plate in the optical compensation polarizing plate is not particularly limited, and can be appropriately determined. Generally, the nx axis of the composite retarder and the transmission axis of the polarizer are arranged in a parallel or orthogonal relationship to control the oblique characteristics in which the viewing angle changes without affecting the characteristics in the front (vertical) direction. STN-L
When applied to a CD, the arrangement is such that the fast axis of the composite phase plate and the transmission axis of the polarizing plate intersect, and when applied to a TN-LCD, the fast axis of the composite phase plate and the polarizing plate In many cases, the transmission axis is arranged in a parallel or orthogonal relationship.

The composite retardation plate or optically compensating polarizing plate according to the present invention can be preferably used for forming a liquid crystal display device as a compensating plate for birefringence due to liquid crystal. A liquid crystal display device is generally formed by appropriately assembling components such as a polarizing plate, a liquid crystal cell, a compensating plate, and a backlight and a reflecting plate as necessary and incorporating a driving circuit. There is no particular limitation except that the above-described composite retardation plate or optically compensating polarizing plate is used, and a liquid crystal display device can be formed according to the related art.

Therefore, when forming the liquid crystal display device, for example, a light diffusion plate, an antiglare layer, a prism sheet, an antireflection film, a protective layer, a protective plate,
An appropriate optical element such as an optical path control plate such as a prism sheet provided in the backlight can be appropriately arranged. The compensator is usually disposed between the liquid crystal cell and the polarizing plate on the viewing side or / and the backlight side. Therefore, the composite retardation plate or the optically compensating polarizing plate according to the present invention may be disposed on at least one side of the liquid crystal cell.

[0037]

Example 1 Polarized light obtained by dyeing a 75 μm-thick polyvinyl alcohol film in an aqueous solution containing iodine, and then uniaxially stretching the film by a factor of 6 between rolls having different peripheral speeds in an aqueous solution containing boric acid. An 80 μm-thick triacetylcellulose film (having a phase difference of almost 0) is adhered to one surface of the film via a polyvinyl alcohol-based adhesive, and a birefringent film is adhered to the other surface of the polarizing film via a polyvinyl alcohol-based adhesive. An optical compensation polarizing plate was obtained by bonding a retardation film through an acrylic pressure-sensitive adhesive layer thereon.

The above-mentioned birefringent film has a thickness of 100
A μm triacetyl cellulose film is stretched at 200 ° C. with a tenter stretching machine, and has a refractive index characteristic of nx>ny> nz, where Δnxy · d is 10 nm and Δnxz · d is 6
0 nm and Nz is 6.

The above retardation film has a thickness of 100
Stretching a μm norbornene-based resin film (ARTON manufactured by JSR) at 175 ° C. with a tenter stretching machine,
It has a refractive index characteristic of nx>ny> nz, and Δnxy · d is 4
0 nm, Δnxz · d is 50 nm, and Nz is 1.25.

Comparative Example A triacetyl cellulose film having a thickness of 80 μm (having a phase difference of almost 0) was used in place of the birefringent film.
As a retardation film adhered on it, a thickness of 100μ
nx>ny> nz obtained by stretching a norbornene-based resin film of m at 175 ° C. with a tenter stretching machine, and Δnxy
A (optically compensated) polarizing plate was obtained according to Example 1 except that d was 30 nm, Δnxz · d was 110 nm, and Nz was 3.7.

Evaluation Test The (optically compensated) polarizing plates obtained in Example 1 and Comparative Example were adhered to both sides of a VA type liquid crystal cell such that the polarizing plates were on the outside, to obtain a liquid crystal display device. As a result, in Example 1, it was possible to obtain a liquid crystal display device which was excellent in uniformity of contrast, with little decrease in contrast and change in chromaticity due to the viewing angle. On the other hand, in the comparative example, a phenomenon occurs in which white display is colored yellow depending on the viewing angle, and the contrast is significantly reduced at a viewing angle of 70 ° or more, and the contrast is different between the central portion and the peripheral portion of the display screen. And its uniformity was poor.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an example of an optical compensation polarizing plate.

[Explanation of symbols]

 1: retardation film 2: birefringent film (also used as transparent protective layer) 3: absorption type polarizing plate 31: transparent protective layer 32: polarizing film

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Naoshi Yamaoka 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Inventor Yuichi Nishikoji 1-1-1, Shimohozumi, Ibaraki-shi, Osaka No. 2 Nitto Denko Corporation F term (reference) 2H049 BA02 BA06 BA42 BB03 BB42 BB44 BB46 BB47 BB48 BB49 BC22 2H091 FA11X FA11Z FB02 FC08 FC09 HA07 KA01 LA17 LA19

Claims (5)

[Claims] 1. When a main refractive index in a plane is nx and ny and a refractive index in a thickness direction is nz and nx ≧ ny, one of the retardation films in which at least one of these refractive indexes is different from the other. Alternatively, two or more sheets and one or two or more birefringent films having different refractive indices are defined by the wavelength dependence of birefringence and the formula: (nx−nz) / (nx−ny). Wherein the retardation film and the birefringent film are made of a film in which a non-liquid crystalline polymer is oriented. 2. The method according to claim 1, wherein the retardation film is formed.
The photoelastic coefficient of the formed polymer film is based on the absolute value.
50 × 10^-12m²/ N or less, or a birefringent film
Photoelastic coefficient of polymer film to be formed is based on absolute value
20 × 10 ^-12m²/ N or less. 3. An optically compensating polarizing plate comprising the composite retardation plate according to claim 1 provided on one side of an absorption type polarizing plate. 4. The optical compensation polarizing plate according to claim 3, wherein the birefringent film in the composite retardation plate is disposed as a transparent protective layer of the polarizing film in the absorption type polarizing plate. 5. A liquid crystal display device comprising the optical compensation polarizing plate according to claim 3 on at least one side of a liquid crystal cell.