JP2002236211A - Polarizing plate and liquid crystal display device which uses the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflection type polarizing plate having a thin polarizing layer, a thin reflecting layer and no parallax and to provide a thin reflection type or semi-transmission and reflection type liquid crystal display device having no parallax by using the above plate. SOLUTION: The polarizing plate has a polarizing layer 5 of 20 to 1,500 nm thickness on the surface of a layer 3 having reflective characteristics. The thin polarizing layer 5 can be made from a planar dye. Further, a light diffusing layer 7 can be formed in the side of the polarizing layer 5 of the polarizing plate. The reflection type or semi-transmission reflection type liquid crystal display device can be obtained by stacking the polarizing plate on a liquid crystal cell 9 with the polarizing layer 5 side in contact with the cell.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing plate having a reflective layer and an ultra-thin polarizing layer, and a liquid crystal display using the polarizing plate.

[0002]

2. Description of the Related Art Liquid crystal display devices include notebook personal computers, word processors, desk-top personal computer monitors, liquid crystal projectors, liquid crystal televisions, digital cameras, personal organizers, personal digital assistants, amusement equipment, stationery, and mobile phones. It is used in various fields such as car navigation systems, home appliances such as rice cookers, air conditioners, and microwave ovens. Along with this, demands for liquid crystal display devices have also been diverse,
For example, high brightness, high contrast, wide viewing angle, improved visibility, low power consumption, thinness, light weight, and the like are required. The reflective or transflective liquid crystal display device, which is stacked in the order of polarizer / liquid crystal cell / polarizer / reflector (or transflector), is effective in reducing power consumption and is relatively thin. Because of its light weight, it is widely used in mobile phones and personal digital assistants.

[0003] A polarizing plate used in a liquid crystal display device is usually made of a polyvinyl alcohol resin film on which iodine or a dichroic direct dye is adsorbed and oriented. It is common to laminate a transparent protective film such as a film, the thickness of which is only 20 to 30 μm in a polarizing film layer made of a polyvinyl alcohol-based resin.
Before and after the addition of the transparent protective film layer, a total of 19
It is around 0 μm. Such a polarizing film is produced, for example, by uniaxially stretching a polyvinyl alcohol-based resin film, adsorbing and orienting a dichroic direct dye having iodine or an azo group, and immersing in a boric acid-containing aqueous solution. .

On the other hand, a reflection plate or a semi-transmission reflection plate is a scattering type reflection plate or a semi-transmission reflection plate obtained by depositing aluminum or silver on one surface of a matt-treated white film having a thickness of about 50 μm. Also, a combination of a specular reflection plate or a transflective plate and a diffusion layer is often used.

[0005]

In recent years, lighter and thinner reflective or transflective liquid crystal display devices have been required to be lighter and thinner. Accordingly, a polarizing plate and a reflective plate or a semi-transmissive liquid crystal display device have been required. It is also required that the reflector be made thinner. Further, as described above, the current reflection type polarizing plate is a polarizing plate obtained by laminating a transparent protective film on both sides of a polyvinyl alcohol-based polarizing film layer and a reflecting plate or a transflective reflecting plate laminated on one surface of the polarizing plate. Therefore, the polarizing layer and the reflective layer are separated from each other by about 100 μm, and the parallax is large. Therefore, there is a problem in the visibility of the liquid crystal display device incorporating the same.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a reflective polarizing plate having a thin polarizing layer and a thin reflective layer and having no parallax. The present inventors have conducted intensive studies in order to solve such a problem, and as a result, have adopted a recently developed coating-type polarizing layer and found that the problem can be solved by combining it with a reflective layer in a specific form. Heading, and led to the present invention.

[0007]

That is, the present invention provides a polarizing plate in which a polarizing layer having a thickness of 20 to 1,500 nm is formed on a surface having reflection characteristics. It is advantageous that such an ultra-thin polarizing layer is made of a flat dye. In this polarizing plate, a light diffusion layer can be further provided on the polarizing layer. In addition, these polarizing plates can be formed as a reflective or transflective liquid crystal display device by laminating the polarizing layer side on a liquid crystal cell.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings as appropriate. FIG. 1 is a cross-sectional view schematically illustrating an example of the layer configuration of the polarizing plate according to the present invention. FIG. 2 is a cross-sectional view schematically illustrating another example of the layer configuration of the polarizing plate according to the present invention. FIG. 3 is a cross-sectional view schematically showing an example in which the polarizing plate of FIG. 1 is laminated on a liquid crystal cell. FIG.
FIG. 3 is a cross-sectional view schematically illustrating an example in which the polarizing plate of FIG. 2 is stacked on a liquid crystal cell.

The basic structure of the polarizing plate according to the present invention is shown in FIG.
As shown in (1), a polarizing layer 5 is formed directly on the surface of a layer (reflection layer) 3 having reflection characteristics. Reflective layer 3
Is usually formed on the surface of the substrate 1. In addition, the polarizing layer 5
A light diffusion layer 7 can be provided on the surface opposite to the surface in contact with the reflection layer 3 as shown in FIG. The substrate 1 can be, for example, a transparent resin film. Specific examples include a cellulose acetate film, a polyester film, a polyolefin film, an acrylic film, a polycarbonate film, a polyarylate film, and a polyethersulfone film. Examples of the cellulose acetate-based film include a triacetyl cellulose film and a diacetyl cellulose film. Examples of the polyester film include a polyethylene terephthalate film, a polyethylene naphthalate film, and a polybutylene terephthalate film. The polyolefin film is preferably an amorphous (amorphous) film, and particularly preferably a film having a polymerized unit of a cyclic olefin such as norbornene or a polycyclic norbornene monomer.
Further, a copolymer of a cyclic olefin and a chain olefin may be used. Among them, a film made of a norbornene-based resin is advantageously used. Further, those having a polar group introduced therein are also effective.

The substrate 1 is preferably thin, but if it is too thin, the processability is poor. For example, it is about 10 to 150 μm, preferably 20 to 100 μm, more preferably 30 to 90 μm.
μm. These substrates may contain an ultraviolet absorber or the like. As such a base material, a commercially available product can be used, and as a commercially available triacetyl cellulose film, for example, “Konica UV80SF” sold by Konica Corporation and Fuji Photo Film Co., Ltd. "SHI SH80" and other commercially available amorphous polyolefin resin films, such as "SCA50" sold by Sekisui Chemical Co., Ltd., "ARTON" sold by JSR Corporation, and Japan “ZEONEX” and “ZEON” sold by Zeon Corporation
OR "and" APO "and" Apel "sold by Mitsui Chemicals, Inc. Reflective layer 3 on the surface of transparent substrate 1
Is formed, and the polarizing layer 5 is formed on the upper surface, thereby obtaining a desired polarizing plate.

The reflecting layer 3 is provided so that light is reflected well.
It is preferred to be composed of a metal layer. Such a metal layer can be provided, for example, by forming a layer made of a metal having a high reflectance such as aluminum or silver. For the formation of the metal layer, for example, a vacuum evaporation method, a sputtering method,
An ordinary method used for providing a metal thin film, such as an ion plating method, can be adopted. If the thickness of the reflective layer 3 is usually about 10 to 100 nm, practically sufficient reflectance is exhibited. The reflective layer 3 may be a semi-transmissive reflective layer having a certain degree of transmissivity. The thickness of the metal layer for imparting transparency is usually about 10 to 30 nm.

When a silver layer is provided as a metal layer by a vapor deposition method or the like, it is preferable to provide a protective layer above and / or below the metal layer in order to prevent deterioration of the metal layer. The protective layer is not particularly limited, and examples thereof include a coating film of an acrylic resin, an epoxy resin, a polyester resin, a urethane resin, or an alkyd resin. These protective coating films can be provided by a usual method such as roll coating, gravure coating, spray coating and the like. Also,
Inorganic thin films such as aluminum oxide and silicon oxide,
It can be used as a protective layer. When such a protective layer is provided, its thickness is usually in the range of about 5 nm to 20 μm.

The reflecting surface of the reflecting layer 3 may be roughened. For example, a method in which the surface of the substrate 1 on which the reflecting layer is formed is subjected to sandblasting in advance, containing inorganic fine particles and / or organic fine particles. The surface of the substrate 1 can be roughened by previously coating the surface of the substrate 1 with a coating solution to be applied, or by preparing the substrate film 1 with a resin containing a filler.

On the reflection layer 3, a polarizing layer 5 is formed with a thickness of 20 to 1,500 nm. Such an ultra-thin polarizing layer 5 can be provided by applying and drying an aqueous solution containing a plate-like dye. Specifically, anthraquinone, phthalocyanine, porphyrin, naphthalocyanine, quinacridone, dioxazine, indanthrene, acridine, perylene, oxazole,
Plate-like pigments such as pyrazolone, acridone and pyranthrone are used. The thickness of the polarizing layer 5 is 20 to 1.5.
It is preferably from 100 to 1,000 nm, and is appropriately selected depending on the type of the plate-like dye and the characteristics of the obtained polarizing plate.

The polarizing layer 5 can be obtained by applying an aqueous solution containing the above-mentioned tabular dye on the reflecting layer 3 and drying. Therefore, the plate-like dye is preferably amphiphilic, and specifically, a dye having a structure having one or more sulfonic acid groups in the above-mentioned dye is mentioned. . The aqueous solution to be applied preferably contains a surfactant in addition to the above-mentioned tabular dye. As a suitable surfactant, for example, polyethylene glycol,
"Triton X-100" (a nonionic surfactant sold by Rohm and Haas) and the like. Examples of suitable tabular dyes or dichroic polarizers for use in the present invention are described in JP-A-8-511109 (= WO 94/28073). Further, an aqueous solution containing such a plate-like dye and suitable for forming a polarizing layer is manufactured by Optiva (Op.
tiva).

The application of the dye-containing aqueous solution may be performed by a general method, for example, a printing technique such as Meyer bar coating, gravure coating, die coating, dip coating, spraying, and screen printing. After application, the polarizing layer can be formed by evaporating the solvent water. The solvent may be evaporated by a usual drying method, and examples thereof include heating drying, room temperature drying, freeze drying, and far infrared drying.

As described above, the reflection surface of the reflection layer 3 can be roughened, and the polarizing layer 5 can be formed thereon.
On the other hand, when the reflection surface of the reflection layer 3 is a flat mirror surface,
As shown in FIG. 2, a light diffusion layer 7 made of a resin mixed with inorganic fine particles and / or organic fine particles may be provided on the polarizing layer 5. Examples of the inorganic fine particles used in this case include, for example, silica, calcium carbonate, and the like, pearl pigments such as synthetic or natural mica coated with titanium dioxide, plate-like fish scale foil, and pearls such as hexagonal plate-like basic lead carbonate. Examples of the organic fine particles include acrylic beads such as polymethyl methacrylate beads, polystyrene beads such as cross-linked polystyrene beads, polycarbonate beads, and melamine.
Examples include formaldehyde resin-based beads, benzoguanamine / formaldehyde resin-based beads, and organic silica-based beads such as "Tospearl" manufactured by Toshiba Silicone Co., Ltd.
The particle size of the fine particles is not particularly limited.
It is about 50 μm, preferably 1-20 μm, more preferably 1-10 μm. These fine particles may be used alone or in combination of two or more. The resin for forming the light diffusion layer 7 is not particularly limited, but examples thereof include an acrylic resin, a urethane resin, an epoxy resin, a polyester resin, and an alkyd resin. These resins may have adhesive properties. The combination of the fine particles and the resin binder is appropriately selected, but the difference in refractive index between the two is 0.01 to 0.1.
It is preferable to select a combination that results in 5. The mixing ratio between the fine particles and the resin binder is not particularly limited, either, but usually, for example, the fine particles are blended in an amount of 0.01 to 70 parts by weight with respect to 100 parts by weight of the resin binder. When the light diffusion layer 7 is provided, its thickness is usually about 1 to 100 μm, preferably about 5 to 30 μm.

In order to form the light diffusion layer 7, for example, fine particles and a resin are mixed and then applied by a usual method such as roll coating, gravure coating, spray coating and the like. Further, the light diffusion layer 7 can be provided by laminating films having light diffusion characteristics. As the light diffusing film used in this case, the same inorganic fine particles and / or organic fine particles and resin as described above are used, and a film obtained by casting a resin mixed with fine particles, a resin mixed with fine particles is used. After coating on the base film surface, a film obtained by peeling from the base film, a film obtained by embossing the surface of the film, a film obtained by heat or light curing a mixture of resins having different refractive indexes, and the like. Can be Such a light diffusing film may have a haze value of 5 to 99%, for example. The method for laminating the films is not particularly limited. For example, the films may be laminated by an ordinary method using an acrylic adhesive or the like.

The reflective polarizing plate thus obtained can be laminated on the back surface of the liquid crystal cell (the surface opposite to the viewing side) to form a liquid crystal display device. At this time, it is laminated on the liquid crystal cell on the polarizing layer side of the reflective polarizing plate. That is, as shown in FIG. 3, a polarizing plate of the type shown in FIG. 1 is laminated on the liquid crystal cell 9 on the polarizing layer 5 side. In addition, in the case of a polarizing plate of the type shown in FIG. 2, as shown in FIG. 4, the light diffusion layer 7 provided on the polarizing layer 5 is laminated on the liquid crystal cell 9. Note that a retardation plate may be provided between the liquid crystal cell 9 and the polarizing layer 5 or the light diffusion layer 7 of the reflective polarizing plate, if necessary. Further, another polarizing plate (not shown) is usually arranged on the front side of the liquid crystal cell 9 (the side opposite to the surface on which the reflective polarizing plate is arranged). As the front-side polarizing plate, a polarizing plate containing a normal polyvinyl alcohol-based polarizer can be used. Further, if a polarizing plate having a coating type dye-based polarizing layer with a thickness of 20 to 1,500 nm provided on a transparent substrate according to the present invention is used as the front-side polarizing plate, the thickness can be further reduced. Becomes In this case, usually, the polarizing layer is arranged so as to be the outermost surface. In addition, a retardation plate can be arranged on the front side of the liquid crystal cell as needed.

[0020]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1 A substrate having a thickness of about 30 nm and silver deposited on the upper surface of a polyethylene terephthalate film having a thickness of about 50 μm was used.
An aqueous solution containing a dye having a flat plate structure (“LCP N015” obtained from Optiva) was applied to the upper surface thereof using a Meyer bar No. 5 bar coater at an application speed of 100 mm / sec. (21 ° C.) for 1 day and dried. The thickness of the polarizing layer after drying was about 1,000 nm.

Example 2 A diffusion adhesive was applied to the polarizing layer side surface of the reflective polarizing plate obtained in Example 1, and then bonded to the lower surface of a TN type liquid crystal cell via the adhesive. On the upper surface of the TN type liquid crystal cell, a polyvinyl alcohol / iodine type polarizing plate “SQ1852A” obtained from Sumitomo Chemical Co., Ltd. was bonded via an adhesive to form a TN type liquid crystal display device. . The obtained TN liquid crystal display device has a small parallax and is easy to see.

Comparative Example 1 A polarizing plate bonded to the lower surface of a TN type liquid crystal cell was a polyvinyl alcohol / iodine polarizing plate, "SQ12852A" (about 180 μm thick) obtained from Sumitomo Chemical Co., Ltd.
A TN type liquid crystal display device was assembled in the same manner as in Example 2 except that the product was changed to a bonded product of a silver reflector and a silver reflector. The obtained TN liquid crystal display device had a large parallax and was hard to see.

[0024]

The reflection type polarizing plate of the present invention is very thin,
Further, since the distance between the polarizing layer and the reflective layer is 10 μm or less, there is almost no parallax. Therefore, this reflective polarizing plate is a portable electronic device, for example, a mobile phone, a personal digital assistant,
It can be suitably used for liquid crystal display devices such as smart cards and IC cards.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing an example of a layer configuration of a polarizing plate according to the present invention.

FIG. 2 is a schematic cross-sectional view showing another example of a layer configuration of the polarizing plate according to the present invention.

FIG. 3 is a schematic cross-sectional view showing an example in which the polarizing plate of FIG. 1 is laminated on a liquid crystal cell.

FIG. 4 is a schematic sectional view showing an example in which the polarizing plate of FIG. 2 is laminated on a liquid crystal cell.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Base material, 3 ... Reflective layer, 5 ... Polarizing layer, 7 ... Light diffusion layer, 9 ... Liquid crystal cell.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H042 BA02 BA12 BA14 BA20 DA02 DA04 DA11 DA21 DB01 DE00 2H049 BA02 BA27 BA37 BB03 BB44 BB62 BB63 BC22 2H091 FA08X FA08Z FA14Z LA30

Claims (5)

[Claims] (1) a thickness of 20 to 20 on a surface having a reflection characteristic;
A polarizing plate comprising a 1,500 nm polarizing layer. 2. The polarizing plate according to claim 1, wherein the polarizing layer is composed of a plate-like dye. 3. The polarizing plate according to claim 1, wherein the surface having reflection characteristics is roughened. 4. The polarizing plate according to claim 1, wherein a light diffusion layer is formed on the polarizing layer. 5. A liquid crystal display device comprising the polarizing plate according to claim 1 laminated on a liquid crystal cell on the polarizing layer side.