Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-01-14
2004-08-03
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S113000, C349S183000
Reexamination Certificate
active
06771336
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical diffusion element and a display device, and, more particularly, to an optical diffusion element that can diffuse light forward without causing optical scattering and a reflection type liquid crystal display with an optical diffusion film that can provide the liquid crystal display with an effectively decreased loss of light and a widened viewing angle, a reflection type liquid crystal display with an optical diffusion film that prevents depolarization even though it is put inside the polarization film, and a reflection type liquid crystal display with a thin film optical diffusion element that prevents an occurrence of depolarization and turbulent orientation of liquid crystal and even though it is put within a liquid crystal cell and provides a high optical diffusion effect.
2. Description of the Related Art
Optical diffusion materials are commonly used for light modulation materials, optical elements, optical display elements, etc. Recent days, such an optical diffusion material is widely used for a display element of, for example, a liquid crystal display with an aim to enhance a display quality and improve viewing angle characteristics of the liquid crystal display. The optical diffusion element is conventionally provided in the form of an optically transparent plate formed with fine concavities and convexities or fine irregularities in the surface thereof such as a frosted or obscured glass plate or in the form of a resin film with several microns to tens microns of particles dispersed therein. While, on one hand, these optical diffusion elements can cause scattering of light, they are accompanied by enhanced back scattering of light. This results in a decrease in the amount of light transmission and deterioration of a contrast of an image display surface and, in addition, an occurrence of depolarization, so that these optical diffusion elements are hard to be used for liquid crystal displays that are strongly demand recent days. Further, when these optical diffusion materials are used as a display material, they increase a load of a light source due to a low light transmission.
In order to eliminate these drawbacks of the conventional light diffusion elements, it has been proposed to make use of refraction of light by forming a number of concavities and convexities in the form of a lens array. This technique is however quite troublesome in fabrication of fine concavities and convexities and is inferior in productivity. In addition, when the optical diffusion element comprising concavities and convexities that are sensitive to stains and external impact is installed within a liquid crystal cell of a liquid crystal display, the liquid crystal causes turbulent orientation, as a result of which the liquid crystal display encounters significant deterioration of display quality.
It has further been proposed to make use of fine particles. In particular, there has been proposed a light diffusion element using fine particles as an optical diffusion material. Such a fine particle has a uniform distribution of refraction, namely a refractivity varying from the center to the periphery, for the purpose of using not scattering of light but refraction of light. The optical diffusion element has a secured optical diffusibility while providing somewhat less back scattering.
However, in producing the optical diffusion element, the particles are dispersed in a binder and fused together through the binder. As a result, it is difficult to increase an in-plane number of the particles, so that the optical diffusion element is hard to have a sufficient optical diffusion effect and to make a film thinner.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an optical diffusion element that can be made in the form of thin film and has secured optical diffusibility.
It is another object of the present invention to provide an optical display device that has a widened viewing angle without being accompanied by a loss of light and an occurrence of depolarization.
The above objects of the present invention are accomplished by an optical diffusion element comprising a layer of polymer particles self-fused together, each polymer particle having a refractivity varying from the center to the periphery thereof. The polymer particles have a mean particle size between approximately 0.5 &mgr;m and 20 &mgr;m. The polymer particle desirably has an outermost component having a glass transition temperature lower than 100° C.
The optical diffusion element may further comprise a transparent layer, desirably formed in a dry-laminating method, in contact with one of opposite sides of the polymer particle layer.
The optical diffusion element is installed in a reflection type display device such as a liquid crystal display. In particular, the optical diffusion element is put within a liquid crystal cell of the liquid crystal display.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The following description is directed to an optical diffusion element according to a preferred embodiment of the present invention. In order to produce fine polymer particles each of which comprises more than two components and has an ununiform distribution of the components, it is common to form core-shell latex using conventional emulsification polymerization. In this case, the fine polymer particles thus produced have a particle size of approximately 0.1 &mgr;m which is too small to show an optical diffusibility favorable for the light diffusion element of the present invention. It is necessary for fine polymer particles for the optical diffusion element to have particle sizes between approximately 0.5 &mgr;m to approximately 20 &mgr;m.
In order to produce fine polymer particles having particle sizes between approximately 0.5 &mgr;m to approximately 20 &mgr;m, various types of particles and methods of producing the particles are available. For example, fine particles are prepared as seed particles and polymerized with another monomer. Specifically, the seed particles are formed by polymerizing a first monomer using, for example, soap-free emulsification polymerization. The seed particles are added with a second monomer so as to be polymerized as the seed particles absorb the second monomer. In this manner, the seed particle is provided with a distribution of polymer therein. The second monomer may be added all at once, may be partly added separately over several days, or may be added separately but continually. In this event, although it is not always necessary that the polymer made of the first monomer concentrates at the core and the polymer made of the second monomer concentrates at the shell, the seed particle can be controlled to a desirable morphological constitution by adjusting hydrophilic/hydrophobic properties of the first and second monomers and an adding speed of the second monomer as known from, for example, “New Technology And Development Of Use Of Fine Polymer Particles” published by CMC, 1997 and “Polymer Latex” (New Polymer library 26), by Soichi Muroi and Ikuo Morino, published by Polymer Publishing Society, 1988.
The first seed particle may be used after
a growth to a desired particle size by repeating absorption and polymerization of the first monomer. This manner makes it possible to use a combination of a polymer made of the first monomer in this manner and a polymer made of a second monomer that are substantially different in refractivity. In this instance, each of the first and second monomers may consist of a single type of monomer or more that two types of monomers as long as there is a substantial difference in refractivity between a copolymer made of the more than two types of first monomers and a copolymer made of the more than two types of second monomers.
The utilization can be made of a micro-suspension polymerization method. This method is used in conventional suspension polymerization to produce what is called a Grin lens as known from, for example, “Applied Optics” Vo. 33, 1994. Acc
Tatsuta Sumitaka
Wakata Yuichi
Chowdhury Tarifur R.
Fuji Photo Film Co. , Ltd.
Young & Thompson
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