Optical: systems and elements – Lens – Fluid
Reexamination Certificate
1999-05-25
2001-09-25
Schwartz, Jordan M. (Department: 2873)
Optical: systems and elements
Lens
Fluid
C359S228000
Reexamination Certificate
active
06295167
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates an optical material, the light transmittance, the light scattering property and the light absorbance of which can be reversibly controlled by an external stimulus, and an optical device using the same.
BACKGROUND OF THE INVENTION
An optical material has been known, which control the amount of light transmission and a light scattering property by using a polymer gel, whose volume is reversibly changed (swelling and contraction) in response to the change in pH, the change in ion concentration, the adsorption, desorption of a chemical substance, heat, light, electric stimulus, or the like.
For example, JP-A-61-151621, JP-A-62-925 and JP-A-4-134325 disclose a device utilizing a polymer gel whose volume is changed by absorbing or releasing a liquid caused by a temperature change or an electric stimulus, the device displaying or erasing an image by changing the refractive index of the polymer gel by changing its density. JP-A-5-188354 discloses an optical device utilizing polymer gel particles whose volume is changed by absorbing or releasing a liquid caused by a stimulus of an electric field, the optical device becoming white turbid or transparent by making the diameter of the polymer gel particles larger or smaller than the wavelength of light to change the refractive index.
However, in these optical devices disclosed in these publications, because the usable materials of the polymer gels are restricted, the difference in refractive index between the polymer gel and the liquid cannot be made large, and, as a result, a contrast between the background (white turbid part) and the image (transparent part), i.e., the display contrast, is low.
JP-A-61-149926 and JP-A-7-95172 disclose an optical device constituted by a composition comprising a composition containing a polymer gel whose volume is changed by absorbing or releasing a liquid caused by a stimulus of an electric field, and a liquid colored with a coloring matter. In this optical device, the colored liquid moves by the change in shape of the polymer gel, to display or erase an image by the change in light absorption.
However, in these optical devices disclosed in these publications, the colored liquid is mixed in the polymer gel by the repetition of swelling and contraction of the polymer gel, to thereby contaminate the polymer gel, and, as a result, there is a possibility that the display contrast is lowered.
JP-A-61-151625 and JP-A-62-927 disclose a device using a colored polymer gel which swells or contracts by heat. This device utilizes such a mechanism that when the polymer gel swells, i.e., the volume of the polymer gel is increased, the concentration of the coloring matter is decreased to lower the optical density, and when the polymer gel contracts, the concentration of the coloring matter is increased to increase the optical density.
However, in the optical device disclosed in the above publication, because the polymer gel is colored when the volume thereof is small, a sufficient display contrast cannot be obtained.
JP-A-4-274480 discloses an optical device utilizing a polymer gel, to which a dye is connected by a covalent bond, swelling or contracting by an electric field. The optical device utilizes such a mechanism that when the polymer gel swells, i.e., the volume of the polymer gel is increased, the optical density is increased by increasing the area of the polymer gel capable of absorbing light, and when the polymer gel contracts, i.e., the volume of the polymer gel is decreased, the optical density is lowered by decreasing that area.
However, in the optical device proposed in the above publication, a sufficient display contrast cannot be obtained because the concentration of the dye contained in the polymer gel is low.
JP-A-9-160081 discloses an optical device utilizing colored fine particles and a polymer gel adsorbed on the colored fine particles. In this optical device, the polymer gel swells or contracts by the action of an electric field, and the optical density is changed by the change in the ratio of that surface of the colored fine particles which is covered with the polymer gel.
However, in the optical device disclosed in the above publication, when the used amount of the polymer gel is increased with respect to the amount of the colored fine particles, the optical density is not sufficiently increased when the polymer gel contracts, and the display contrast is lowered. When the used amount of the polymer gel is decreased, on the other hand, the optical density is not sufficiently increased when the polymer gel swells, and the display contrast is lowered.
The inventors have proposed a novel optical material in Japanese Patent Application No. 9-345541. The optical material disclosed in the above application comprises a polymer gel which swells or contracts by absorbing or releasing a liquid by providing a stimulus and contains a pigment in a concentration larger than the saturated absorbing concentration. In the optical material, when the polymer gel contracts, the pigment locally agglomerates to lower the light absorption efficiency and the optical density, so as to cause discoloration. When the polymer gel swells, on the other hand, the light absorption efficiency is increased by dispersing the pigment throughout the optical material, and the optical density is increased to cause color generation.
However, in the optical material disclosed in the above application, because the agglomerated pigment contained in the polymer gel in a high concentration absorbs light even when the polymer gel contracts, the optical material cannot be completely discolored.
SUMMARY OF THE INVENTION
The invention has been developed in view of the problems associated with the conventional techniques, and an object of the invention is to provide a novel optical material and a novel optical device that have a high display contrast.
The above and other objects can be attained by the invention described below.
The invention provides an optical material comprising a polymer gel, whose volume is reversibly changed by absorbing or releasing a liquid in response to an external stimulus, and a light scattering member covering at least part of the surface of the polymer gel.
The invention also provides an optical device comprising an optical material, a liquid released from or absorbed by the optical material, and a cell in which a pair of substrates, between which the optical material and the liquid are maintained.
As the light scattering member in the optical material and the optical device, a light scattering material having a refractive index different from a refractive index of the liquid, or a polymer material containing the light scattering material dispersed therein. A second polymer gel that contracts in a condition where the polymer gel swells, and swells in a condition where the polymer gel contracts, containing the light scattering material dispersed therein may also be used. The light scattering member preferably is in a form of particles having an average particle diameter of from 0.01 &mgr;m to 5 mm when the polymer gel contracts. In the case where the light scattering member contains the polymer material, the light scattering member preferably is in the form of particle having an average particle diameter of from 0.01 &mgr;m to 1 mm. The light scattering material preferably is in the form of particle having an average particle diameter of from 0.001 &mgr;m to 10 &mgr;m. The light scattering material may contain a coloring matter. In this case, it is preferred that the concentration of the coloring matter when the polymer gel contracts is the saturated absorption concentration or higher. It is also preferred that the light absorption efficiency of the coloring matter when the polymer gel swells is higher than that when the polymer gel contracts. Furthermore, the coloring matter is contained in the polymer gel in such a manner that when the coloring matter is agglomerated or concentrated on contraction of the polymer gel, a concentration of the coloring matter higher t
Akashi Ryojiro
Komura Akinori
Uematsu Takashi
Fuji 'Xerox Co., Ltd.
Oliff & Berridg,e PLC
Schwartz Jordan M.
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