Optical: systems and elements – Glare or unwanted light reduction
Reexamination Certificate
1999-12-13
2001-04-17
Sikder, Mohammad Y. (Department: 2872)
Optical: systems and elements
Glare or unwanted light reduction
C359S608000, C359S613000, C359S599000
Reexamination Certificate
active
06217176
ABSTRACT:
TECHNICAL FIELD
This invention relates to an antiglare film for provision on the surface of displays for high definition images, such as CRT and liquid crystal panels, used in image display in computers, word processors, televisions and the like, and a polarizing film and a transmission type display device using the antiglare film.
BACKGROUND ART
In the above displays, when light emitted mainly from the interior of the display goes straight without diffusion on the surface of the display, the surface of the display, when viewed with the naked eye, is in the glare of the light. In order to prevent this phenomenon, an antiglare film for diffusing the light emitted from the interior of the display to some extent is provided on the surface of the display.
For example, Japanese Patent Laid-Open Publication Nos. 18706/1994 and 20103/1998 disclose antiglare films formed by coating a resin containing a filler, such as silicon dioxide (silica), onto the surface of a transparent substrate film.
These antiglare films are classified into a type wherein concaves and convexes are formed on the surface of the antiglare layer by coagulation of particles, such as coagulative silica, a type wherein organic fillers having a particle diameter larger than the coating thickness are added to a resin to form concaves and convexes on the surface of the layer, and a type wherein a film having thereon concaves and convexes is laminated on a layer to transfer the concaves and convexes onto the layer.
In all the types of the above conventional antiglare films, light diffusing/antiglare action is created by the surface shape of the antiglare layer, and increasing the size of concaves and convexes is necessary for enhancing antiglare properties. Increasing the size of concaves and convexes, however, increases the haze of the coating and in its turn disadvantageously lowers the transmissive visibility.
A light-diffusive film similar to the above antiglare films is disclosed, for example, for a reflection type liquid crystal display device (Journal of the Illuminating Engineering Institute of Japan MD-96-48, 277-282 (1996)). In this light-diffusive film, fine particles are dispersed within the layer to attain a light diffusion effect.
In order to attain satisfactory light diffusion effect by the contemplated internal scattering effect, the diameter of the fine particles should be increased. This poses a problem in that the sharpness of images is very low although the haze is high.
When a film for attaining light diffusion effect by the internal scattering effect, such as the light-diffusive film, is provided on the surface of a display for antiglare purposes, the reflection of external light on the surface of the display cannot be prevented because the surface of the film is substantially flat. That is, the film does not disadvantageously have the so-called “external light reflection preventive properties.”
In addition, in the conventional antiglare films described above, shining called “scintillation” occurs on the film surface, disadvantageously leading to deteriorated visibility of the display screen.
For the antiglare films, haze is one of the evaluation criteria. Lowering the haze of the surface increases shining called scintillation. When the haze is increased in order to eliminate this problem, the whole image becomes whitish and the black density is lowered. This unfavorably results in lowered contrast. On the other hand, lowering the haze for removing the whitening effect disadvantageously increases the so-called “external light reflection” and “shining.”
With a view to solving the above problems, the present inventors have developed an antiglare film which, without sacrificing the diffusing and antiglare properties, can improve the sharpness of transmitted images, can lower scintillation, and has external light reflection preventive properties. An application relating to this antiglare film has been filed as Japanese Patent Laid-Open No. 126494/1998.
In order to realize the above properties, the haze should be regulated by the internal scattering effect. The internal scattering effect can be regulated by regulating the mixing ratio of the light-transparent fine particles and the light-transparent resin, the difference in refractive index between the light-transparent fine particles and the light-transparent resin, the particle diameter of the light-transparent fine particles, and the thickness on a dry basis of the antiglare layer.
The regulation of the mixing ratio, the particle diameter, and the coating thickness, however, affect the surface shape. Therefore, the haze cannot be solely regulated while maintaining a certain level of sharpness of transmitted images, that is, external light reflection preventive properties.
The internal scattering effect can also be regulated by the refractive index of the light-transparent fine particles. The regulation of the refractive index, however, disadvantageously causes a limitation on the regulation of the haze.
DISCLOSURE OF THE INVENTION
Under the above circumstances, the present invention has been made, and it is an object of the present invention to provide an antiglare film, which has a desired range of haze, does not lower external light reflection preventive properties, can improve sharpness of transmitted images, and can lower scintillation, and to provide a polarizing plate and a transmission type display device using the antiglare film.
According to one aspect of the present invention, there is provided an antiglare film comprising: a transparent substrate film; and an antiglare layer stacked onto the transparent substrate film, the antiglare layer being formed of a light-transparent resin containing two or more types of light-transparent fine particles, the difference in refractive index between the light-transparent fine particles and the light-transparent resin being not less than 0.03 and not more than 0.20, said two or more types of light-transparent fine particles being different from each other in refractive index.
According to a preferred embodiment of the present invention, the difference in refractive index between said two or more types of light-transparent fine particles is not less than 0.02 and not more than 0.10.
The refractive index of the light-transparent resin may be 1.49 to 1.53 with the refractive index of the light-transparent fine particles being 1.53 to 1.57 in one type and 1.58 to 1.62 in another type.
According to a preferred embodiment of the present invention, the antiglare film has a haze of not less than 10%.
The light-transparent resin may be an ionizing radiation-cured resin, the two or more types of light-transparent fine particles may have a particle diameter of 1 to 5 &mgr;m, and the content of the two or more types of light-transparent fine particles in the antiglare layer may be 5 to 30% by weight.
The light-transparent fine particles may be monodisperse organic fine particles, and the light-transparent fine particles may be inorganic fine particles.
The transparent substrate film may be a triacetylcellulose film.
According to another aspect of the present invention, there is provided a polarizing plate comprising: a polarizing element; and the above antiglare film, the antiglare film being stacked onto the surface of the polarizing element so that the transparent substrate film in its surface remote from the antiglare layer faces the polarizing element.
According to a further aspect of the present invention, there is provided a transmission type display device comprising: a flat, light-transparent display; a light source device for backlighting the light-transparent display; and the above antiglare film, the antiglare film being stacked on the surface of the light-transparent display.
REFERENCES:
patent: 5919555 (1999-07-01), Yasuda et al.
patent: 5995288 (1999-11-01), Kashima et al.
patent: 6008940 (1999-12-01), Michihata et al.
patent: 6060183 (2000-05-01), Higashi et al.
patent: 6074741 (2000-06-01), Murata et al.
Dai Nippon Printing Co. Ltd.
Parkhurst & Wendel L.L.P
Sikd-er Mohammad Y.
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