Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-04-06
2002-07-23
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S064000
Reexamination Certificate
active
06424395
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a light scattering film, and a liquid crystal display device having a light scattering film. In the present invention, the terms “scattering” and “diffusion” are used with no distinction as long as they are used in relation to optics.
A light scattering film is used in a liquid crystal display device in order to achieve a wide viewing angle or to achieve display of a uniform brightness over the entire screen. In a reflection type liquid crystal display device, such a light scattering film is pasted to a display surface of a liquid crystal panel.
It was customary in the past to use a light scattering film prepared by roughening the surface of a polymer film. Such a light scattering film is prepared by applying a physical processing such as a sand blasting treatment to the surface of a polymer film or by a chemical treatment using an acidic or basic solution.
The light scattering film permits all the incident light to be diffused without relying on the incident angle, the incident direction or the incidence plane. Therefore, where such a light scattering film is used in a reflection type liquid crystal display device utilizing the solar light or external illumination as a light source, the light scattering takes place both at the time when the light emitted from the light source is incident on the liquid crystal panel and at the time when the light modulated by the liquid crystal layer became reflected and emerges out of the liquid crystal panel. As a result, a double image is observed, or the image is blurred. In other words, the displayed image is made unclear or the contrast is lowered.
Since the light scattering film diffuses the incident light isotropically, a wide viewing angle can be obtained. However, the viewing angle and the brightness of display bears a trade-off relationship. Specifically, it is difficult to achieve a bright display by using the light scattering film.
In general, it suffices for the liquid crystal display device used in a portable telephone or PDA to have a viewing angle permitting a single user to recognize the displayed image. In other words, the viewing angle in a horizontal direction need not be unduly large in the liquid crystal display device used in these instruments. Since these instruments are used at a height of the eye or disposed on the lap, the viewing angle should desirably be large in a vertical direction. By contraries, in a liquid crystal television, etc., the viewing angle of the liquid crystal display device need not be large in a vertical direction and should desirably be large in a horizontal direction.
As describe above, the required direction of a large viewing angle differs depending on the use of the liquid crystal display device. Therefore, a sufficient brightness of display and a large viewing angle can be obtained simultaneously by increasing the viewing angle in a required direction alone. It follows that the light scattering film used in a liquid crystal display device is required to scatter light anisotropically.
It is known to the art that a polymer film having light diffusing fine particles dispersed therein can be used as a light scattering film. In order to realize the above-noted light scattering characteristics in the light scattering film, various efforts are being made in an attempt to control the refractive index, size, shape, etc. of the light diffusing fine particles. However, it is technically difficult to realize the particular light scattering characteristics by the method referred to above. Even if realized, the light scattering characteristics are not satisfactory enough to put the light scattering film to practical use.
For example, Japanese Patent Disclosure (Kokai) No. 8-201802 discloses a light scattering plate which permits transmitting the light incident on one main surface while suppressing the light scattering substantially completely and also permits selectively scattering the light incident on the other main surface. However, this prior art simply teaches that the light scattering plate is obtained by solidifying transparent fine particles with a transparent polymerizable high molecular compound, failing to teach the specific construction of the light scattering plate. It is considered reasonable to understand that the light scattering plate disclosed in JP '802 is equal in construction to the known polymer film having fine light diffusing particles dispersed therein, and therefore, the light scattering characteristics above cannot be obtained.
Japanese Patent Disclosure No. 9-152602 discloses a liquid crystal display device using a hologram. The device disclosed in this prior art is a transmitting type liquid crystal display device having a back light as a light source arranged behind a liquid crystal panel. In this device, a light scattering plate is arranged between the liquid crystal panel and the back light, and a hologram is arranged on the front face of the liquid crystal panel. The hologram thus arranged permits anisotropically diffusing the light. In the case of using a hologram, however, the light is unavoidably dispersed to exhibit the spectral colors, with the result that the color of the displayed image differs depending on the viewing point.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide a light scattering film which permits displaying a clear image when used in a liquid crystal display device and a liquid crystal display device using the particular light scattering film.
Another object is to provide a light scattering film which permits realizing a sufficiently large viewing angle and also permits a bright display when used in a liquid crystal display device and a liquid crystal display device using the particular light scattering film.
Still another object of the present invention is to provide a light scattering film which permits preventing the color of the displayed image from being changed in accordance with movement of the viewing point and a liquid crystal display device using the particular light scattering film.
According to an aspect of the present invention, there is provided a light scattering film, comprising a plurality of first transparent regions each having a fibril-like cross section, and a plurality of second transparent regions differing in refractive index range from the first transparent region, wherein each of the first transparent regions is positioned to permit the long axis of the fibril-like cross section to cross one main surface of the film and to permit each of the fibril-like cross sections of the first transparent regions to be sandwiched between adjacent second transparent regions in a direction of the short axis of the fibril-like cross section.
According to another aspect of the present invention, there is provided a liquid crystal display device, comprising a liquid crystal panel, and a light scattering film mounted on one main surface of the liquid crystal panel, wherein the light scattering film includes a plurality of first transparent regions each having a fibril-like cross section, and a plurality of second transparent regions differing in refractive index range from the first transparent region, and wherein each of the first transparent regions is positioned to permit the long axis of the fibril-like cross section to cross one main surface of the film and to permit each of the fibril-like cross sections of the first transparent regions to be sandwiched between adjacent second transparent regions in a direction of the short axis of the fibril-like cross section.
The light scattering film of the present invention comprises a plurality of first transparent regions each having a fibril-like cross section and a plurality of second transparent regions each interposed between adjacent first transparent regions. The first transparent region and the second transparent region differ from each other in refractive index range. It follows that, where each of the fibril-like cross sections of the first transparent regions has a width narrow enough to dif
Murillo-Mora Luis Manuel
Sato Atsushi
Nguyen Hoan
Sikes William L.
Staas & Halsey , LLP
Toppan Printing Co. Ltd.
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