Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-09-28
2004-09-14
Dudek, James A. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06791649
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an anti-reflection film, a polarizing plate having the same, and an image display device utilizing the anti-reflection film or the polarizing plate.
Particularly, the present invention relates to an anti-reflection film that comprises a low-refractive-index layer, and a high-refractive-index layer, which comprises inorganic fine particles having a core composed mainly of titanium dioxide and a shell composed mainly of an inorganic compound other than titanium dioxide, or an anti-reflection film having a low-refractive-index layer in which fine voids exist between inorganic fine particles in a short fiber form.
Further, the present invention relates to a polarizing plate that has optical compensation capacity and anti-reflection ability. The present also relates to a liquid crystal display type, or a color liquid crystal display type, image display device utilizing this polarizing plate.
BACKGROUND OF THE INVENTION
Anti-reflection films are used for various image display devices, such as liquid crystal displays (LCD), plasma display panels (PDP), electro luminecence displays (ELD), and cathode-ray tube displays (CRT). Further, anti-reflection films are also used for lenses of glasses or cameras.
As an anti-reflection film, a multi-layered film, in which transparent metal oxide thin films are laminated, has been ordinarily used. Multiple transparent thin films are used to prevent reflection of lights of various wavelengths. The transparent metal oxide thin film is formed by a chemical vapor deposition (CVD) process or a physical vapor deposition (PVD) process, and particularly by a vacuum vapor deposition process, which is a physical vapor deposition process. The transparent metal oxide thin film has excellent optical characteristics as an anti-reflection film. However, the method of forming a transparent matal oxide thin film by such vapor deposition has insufficient productivity for mass production.
In place of the vapor deposition process, methods have been proposed, in which a coating solution containing inorganic fine particles is applied, to form an anti-reflection film.
JP-B-60-59250 (“JP-B” means an examined Japanese patent publication) discloses an anti-reflection layer comprising micro voids (cavities) and inorganic fine particles. The anti-reflection layer is formed by a coating method. Then, the thus-formed layer is subjected to active gas treatment, whereby the gas escapes from the layer, to form micro voids.
JP-A-59-50401 (“JP-A” means an unexamined published Japanese patent application) discloses an anti-reflection film comprising a support, a high-refractive-index layer, and a low-refractive-index layer, superposed in this order. This publication also discloses an anti-reflection film further comprising a middle-refractive-index layer, superposed between the support and-the high-refractive-index layer. The low-refractive-index layer is formed by coating a polymer or inorganic fine particles.
JP-A-2-245702 discloses an anti-reflection film comprising a mixture of two or more kinds of ultra fine particles (e.g. MgF
2
, SiO
2
), whose mixing ratio is designed to be different in the direction of film thickness. By changing the refractive index due to the different mixing ratio, the film of this publication attained similar optical characteristics to those of the anti-reflection film disclosed in JP-A-59-50401, which film comprises both high- and low-refractive-index layers. The ultra-fine particles are adhered with SiO
2
which is formed by thermal decomposition of ethyl silicate. In the thermal decomposition of ethyl silicate, the ethyl part thereof is burned, to evolve carbon dioxide and water vapor. As illustrated in
FIG. 1
of the publication, the above-mentioned carbon dioxide and water vapor escape from the layer, to form voids among the ultra-fine particles.
JP-A-5-13021 discloses changing the voids among ultra-fine particles existing in the anti-reflection film described in the above JP-A-2-245702, with a binder. JP-A-7-48527 discloses an anti-reflection film containing inorganic fine particles of porous silica, and a binder.
JP-A-8-110401 and JP-A-8-179123 disclose a technique that a high-refractive-index layer, having a refractive index of 1.80 or more, is made by incorporating inorganic fine particles having a high refractive index into a plastic, and then the high-refractive-index layer is applied to an anti-reflection film.
High-refractive-index Layer Formation:
A method for making a high-refractive-index layer by application of inorganic fine particles has high productivity and is suitable for mass production.
A transparent high-refractive-index layer is formed by finely dispersing inorganic fine particles, and then forming a high-refractive-index layer while the finely dispersed state is kept. By incorporating a larger amount of inorganic fine particles having a high refractive index into a high-refractive-index layer, the formed high-refractive-index layer comes to have a higher refractive index.
It is very effective to incorporate fine particles of titanium dioxide, which are colorless and have an especially high refractive index, into a high-refractive-index layer.
Meanwhile, a high-refractive-index layer is arranged on a display face of an image display device or an outside surface of a lens. Therefore, for the high-refractive-index layer, high physical strengths (abrasion resistance and the like), and weathering resistance (light resistance, moisture/heat resistance, and the like) are required. Fine particles of titanium dioxide have a photocatalyst function to decompose organic compounds that contact the particles and deteriorate the physical strengths, transparency, and the like, remarkably. Furthermore, the fine particles cause a drop in the refractive index of any high-refractive-index layer. Such a phenomenon arises remarkably, in particular, in high-refractive-index layers containing fine particles of titanium dioxide that keep finely dispersed state.
Low-refractive-index Layer Formation:
A low-refractive-index layer having a very low refractive index can be obtained by forming micro voids among fine particles contained in the layer. Since the low-refractive-index layer is placed on the display face of an image display device or on the outer surface of a lens, the layer needs to have sufficient mechanical strength. Further, since the low-refractive-index layer is placed as mentioned above, the layer must have very few defects on the surface (e.g. pointing defect on the surface), to prevent the deterioration of visibility.
The low-refractive-index layer described in JP-A-2-245702 had voids among piled fine particles, so that the refractive index of the layer was very low. However, there was a problem that the low-refractive-index layer described in the publication substantially consisted of only an inorganic compound, and therefore it was very fragile.
JP-A-11-006902 describes a low-refractive-index-layer in which at least two inorganic fine particles were piled, to form voids among these fine particles, thereby obtaining a low-refractive-index layer having both a very low refractive index and high mechanical strength.
JP-A-9-288201 discloses an anti-reflection layer having a low-refractive-index layer in which, by piling up two or more layers of fine particles comprising a fluorine-containing polymer, voids were made between the fine particles.
On the other hand, when an anti-reflection film is formed by applying, onto a substrate, a low-refractive-index layer as described, for example, in JP-A-2-245702, a problem arises that surface defects (pointing defects) are apt to occur, and consequently the thus-produced anti-reflection film is unsatisfactory.
The construction of a conventional liquid crystal display type image display device is shown in FIG.
12
. An ordinary liquid crystal display type image display device is composed of a backlight
211
of an edge light type on the furthest back surface and, in the order from the furthest back surface, a light introductive plate
212
for
Amimori Ichiro
Ikeyama Akihiro
Nakamura Ken'ichi
Watanabe Jun
Burns Doane Swecker & Mathis L.L.P.
Dudek James A.
Fuji Photo Film Co. , Ltd.
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