Etching a substrate: processes – Forming or treating optical article
Reexamination Certificate
1998-09-08
2001-04-24
Alanko, Anita (Department: 1746)
Etching a substrate: processes
Forming or treating optical article
C216S058000, C216S067000, C216S083000, C264S001700, C264S313000, C264S442000, C427S180000
Reexamination Certificate
active
06221267
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for making spinnable balls, a method for making a display medium and a method for making a display device.
2. Description of the Related Art
In recent years, the need for thin display devices with low electricity consumption has been increasing with the development of information devices, encouraging intensive research and development of display devices to satisfy this need. In particular, there has been intensive development of liquid crystal devices which satisfy this need, since electrical control of the arrangement of liquid crystal molecules causes a change in optical characteristics. In current liquid crystal devices, however, character visibility on a display deteriorates when the angle of vision or reflected light is inadequate. Further, flicker or low luminescence of the light source strains the eye. Energetic study of novel display devices which reduce eyestrain is now in progress.
N. K. Sheridon et al. disclosed a new type of display device that uses the twisting of fine balls driven by an electric field (“A Twisting Ball Display”, Proc. of the SID, Vol. 18, No. 3/4, p. 289, 1977; U.S. Pat. Nos. 4,126,854, 4,143,103 and 5,389,945; and Japanese Patent Laid-Open No. 64-42683). The display device uses fine balls each consisting of a white hemisphere and a black hemisphere. The fine balls are placed in cavities formed on a carrier. The cavities are filled with a highly resistant liquid so that balls can rotate without restriction. Charging states of the black and white hemispheres differ from each other in a certain type of liquid, and application of an external electric field can control the spinning of the fine ball such that a white or black hemisphere faces the observation side. Display of an image is achieved in such a manner. Such a mechanical type of display system is extremely stable against temperature change and noises from electrical disturbance. Since the display can be memorized, the unchanged display does not consume electricity. Further, the display using reflection and scattering of natural light on the ball surfaces is an ideal display that can reduce eyestrain caused by flicker of the light source which is inevitable in CRT displays.
Known methods for making dichroic balls used in such a display device include a method for joining and solidifying two melted droplets having different colors in a host liquid, and a method for joining and solidifying two melted droplets having different colors by centrifugal force (Japanese Patent Publication No. 7-67754 and Japanese Patent Laid-Open No. 5-279486). The former method forms dichroic balls by solidification of a melted material in the host liquid, whereas the latter method forms dichroic balls by centrifugal solidification of a melted material.
These conventional methods, however, have the following problems. Since these balls are generally made of organic thermoplastic resins, selection of usable materials is limited. Also, selection of a usable liquid is limited, since some types of liquid will swell rotating organic colored balls.
M. Saitoh et al. disclosed another method for making colored balls used in the above-described display device in Proc. of the SID, Vol. 23/4, pp. 249-252, 1982. According to this method, fine white balls are embedded onto an adhesive layer provided on a substrate, and a black layer is formed on the exposed hemisphere of each white ball by a vacuum deposition process. M. Saitoh et al. does not mention the problem that the particle sizes of the produced balls are not equalized. Further, the black layers formed on the white hemispheres of the fine balls are not equalized.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a method for making spinnable balls, on which can be formed a uniform layer on the hemispheres of the fine balls, the layer having different optical characteristics from those of fine balls, even if these fine balls have different particle sizes.
Accordingly, it is an object of the present invention to provide a method for easily mass-producing colored balls composed of an inorganic material, e.g. glass or ceramic, a thermosetting resin, or a low-temperature softening resin having high chemical resistance.
It is another object of the present invention to provide a display device having improved contrast by using balls having a distinct border between a hemisphere with a layer and another hemisphere without a layer.
In accordance with the present invention, a method for making spinnable balls each consisting of two surfaces having different optical characteristics, includes the steps of: forming a plurality of balls having the same specific gravity on a thermoplastic film; softening the thermoplastic film by controlling the heating temperature of the thermoplastic film in response to the specific gravity of the balls so that the hemispheres of the balls are embedded into the thermoplastic film by their own weight; forming a layer on the exposed surface of each ball, in which the layer has different optical characteristics from these of the ball; and detaching the balls provided with the layers from the thermoplastic film.
The particle sizes of the balls may be different. The lower hemispheres of the balls are satisfactorily embedded into the thermoplastic film by their own weight regardless of uneven particle size. Since the layer is formed on the upper exposed hemisphere, a distinct boundary can be formed between the upper hemisphere provided with the layer and the lower hemisphere, resulting in a high contrast in a display device using these balls.
The step of removing the thermoplastic film by dissolution may be performed while applying ultrasonic vibration to the thermoplastic film. The ultrasonic vibration can increase the dissolution rate of the thermoplastic film, and can readily remove flashes of the deposited films adhering to the spinnable balls.
Preferably, after detaching the balls from the thermoplastic film, the balls are exposed to plasma containing ozone or oxygen to completely remove any organic material remaining on the ball surfaces. Such a cleaning process satisfactorily maintains different discharging states on the upper hemisphere and the lower hemisphere.
The method may further include a step of controlling the heating temperature of the balls in response to the specific gravity of the balls to soften the thermoplastic film. This step can suppress fluctuation of embedding time of the balls caused by a difference in heat capacity of balls having different sizes.
The step of detaching the balls from the thermoplastic film may include removing the thermoplastic film by etching in a vapor phase. A material which is not resistant to solvents or water can be used for the formation of the layer.
Another aspect of the present invention is a method for making a display medium performing display by spinning spinnable balls, each comprising two surfaces having different optical characteristics, including the above-mentioned steps for making the spinnable balls, and a step of dispersing the balls provided with the layers into a medium.
A further aspect of the present invention is a method for making a display device performing display by spinning spinnable balls each comprising two surfaces having different optical characteristics, including the above-mentioned steps for making the spinnable balls, and steps of dispersing the balls provided with the layers into a medium, and forming an electrode on the surface of the medium.
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patent: 3222204 (1965-12-01), Weber et al.
patent: 4126854 (1978-11-01), Sheridon
patent: 4143103 (1979-03-01), Sheridon
patent: 4438160 (1984-03-01), Ishikawa et al.
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patent: 4678695 (1987-07-01), Tung et al.
patent: 4725494 (1988-02-01), Belisle et al.
patent: 4898633 (1990-02-01), Doree et al.
patent: 5059262 (1991-10-01), Calhoun et al.
patent: 5389945 (1995-02-01), Sheridon
patent: 5777782 (1998-07-01), Sheridon
patent: 5828431 (1998-10-01),
Ikeda Tsutomu
Kishi Etsuro
Yagi Takayuki
Alanko Anita
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
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