Image formation and erasure on and from scattering-mode light-modulation device

Abstract: An image formation apparatus using a recording medium including a scattering-mode light-modulation member which takes an opaque state in response to a heat and takes a transparent state in response to an electric field. The apparatus comprises a heater and an electrode device which are disposed in opposed relation to the recording medium. The heater preheats the recording medium in accordance with a control signal from an external device and the electrode device applies an electric field to the recording medium after the heating, thereby completely erasing an image previously recorded in the recording medium. After the erasure, the recording medium is heated by a thermal head in accordance with an information signal from an external device so as to form a new image in the recording medium.

Description: The present invention relates to an image formation apparatus using a scattering-mode light-modulation device as a recording medium and a method of erasing an image formed on the scattering-mode light-modulation device. Various recording mediums and methods of image formation have been known previously. US-A-4675699 discloses an image recording medium comprising a pair of substrates and a thermo-optical liquid crystal provided therebetween. The medium is prepared for recording by heating the liquid crystal and then cooling it under the influence of an electric field such that it is held in a transparent state. Recording of an image may be achieved by selectively heating the liquid crystal without an electric field such that the selected areas become opaque. Erasure of the medium is achieved by heating the entire medium and once again cooling it under the influence of an electric field. Recently, as an information writable and erasable type apparatus there is known an image formation apparatus equipped with, as a recording medium, a scattering-mode light-modulation device comprising a scattering-mode light-modulation plate and an electrode plate which are overlaid with each other on a base plate. The scattering-mode light-modulation device allows the recording and erasure of an electromagnetic-wave information such as an image through heating and application of an electric field, for example. Although such an image formation apparatus can form an extremely fine image, there is a problem, however, in that difficulty is encountered to completely erase the recorded image from the scattering-mode light-modulation device whereby an afterimage occurs and the contrast deteriorates due to the affection of the electric charge left irrespective of the erasing electrification. It is therefore an object of the present invention to provide an image formation apparatus and image-erasing method which is capable of completely erasing the recorded image so as not to generate the afterimage and not to deteriorate the contrast of a newly written image. According to the present invention, there is provided an image formation apparatus comprising: a recording medium including a scattering-mode light-modulation member which takes an opaque state in response to heat and takes a transparent state in response to only an electric field; erasure-auxiliary means for heating said recording medium in accordance with a control signal from an external device; erasure means for applying an electric field to said recording medium after the heating due to said erasure-auxiliary means; and image-writing means for heating said recording medium in accordance with an information signal from an external device after the application of the electric field to said recording medium due to said erasure means. Preferably, the erasure-auxiliary means and the image-writing means is constructed with one thermal head comprising a plurality of heating elements each generating a heat in response to the control signal and the information signal. In addition, according to this invention there is provided a method of forming an image in a recording medium including a scattering-mode light-modulation member which takes an opaque state in response to heat and takes a transparent state in response to only an electric field, said method comprising the steps of: heating said recording medium; applying an electric field to said recording medium after the heating so as to erase an image previously recorded in said recording medium; and selectively heating parts of said recording medium after the application of said electric field thereto so as to write a new image in said recording medium. The object and features of the present invention will become more readily apparent from the following detailed description of the preferred embodiments taken in conjunction with the accompanying drawings in which: Fig. 1 is a cross-sectional view showing an arrangement of an image formation apparatus according to an embodiment of the present invention; Fig. 2 is a partial broken view showing an arrangement of a recording medium to be used in the image formation apparatus according to this invention; Figs. 3A and 3B are illustrations for describing the relation between a recording medium and an electrode device in an image-erasure process; Fig. 4A is an illustration for describing the relation between a thermal head and a recording medium in an image-writing process; Fig. 4B is a perspective view showing an arrangement of a reproducing system for reproducing an image recorded in a recording medium; and Figs. 5A to 5C are illustrations for describing the erasure-auxiliary process, erasure process and image-writing process to be effected by the image formation apparatus according to said embodiment of this invention. DETAILED DESCRIPTION OF THE INVENTION Referring now to Figs. 1 and 2 there is illustrated an arrangement of an image formation apparatus according to a first embodiment of the present invention. In Figs. 1 and 2, designated at numeral 16 is a metal-made drum having a cylindrical configuration and having on its circumferential surface a recording medium 2. The recording medium 2 is integrally constructed with the drum 16 or individually constructed and attached to the surface of the drum 16. The drum 16 is arranged to be rotatable about a shaft 16a in a direction indicated by an arrow A in Fig. 1. The shaft 16a is coupled through a well-known transmission mechanism to a drive motor, not shown, so as to be rotatable in response to the rotational control of the drive motor. Further, designated at numeral 11 is a thermal head which is provided in opposed relation to the recording medium 2 and which is composed of a plurality of heating elements successively arranged in the primary scanning directions (the directions along the shaft 16a of the drum 16). The heating elements are arranged to have a resolution of about 8 dot/mm to 16 dot/mm and to generate heats corresponding to information signals inputted. Also, in opposed relation to the recording medium 2 and at the upstream side of the thermal head 11 there is provided an electric-field erasing device such as an electrode device 8 coupled through a switch 18 to a power source 9. The recording medium 2, as illustrated in Fig. 2, comprises a base 3, an electrode 4, a color-stripe filter 5 and a scattering-mode light-modulation member 6 which respectively have plate-like configurations and which are arranged to be overlaid with each other so as to take an integrally laminated structure in accordance with a well-known technique. More specifically, as illustrated in Fig. 3A, on the base plate 3 made of a transparent PET (polyethylene terephthalate) material there is provided the electrode plate 4 made from a transparent ITO (indium-tin oxide) film. Further, on the electrode plate 4 there is placed the color-stripe filter 5 comprising a plurality of sets of stripes each linearly extending in directions (transverse directions) indicated by arrows W in Fig. 2. Each set of stripes has a plurality of different colors, for example, red (R), green (G) and blue (B), corresponding to color-signal components of an electromagnetic-wave information signal to be supplied to the thermal head 11. The R, G and B filter stripes are successively and repeatedly arranged in order in directions (longitudinal directions) indicated by arrows L which is coincident with the primary scanning directions. Further, each of the R, G and B filter stripes has a width substantially equal to the dimension of each of the heating elements of the thermal head 11. In addition, on the color-stripe filter 5 there is provided the scattering-mode light-modulation member 6 constructed with a material including a liquid crystal film such as a polymer dispersed liquid crystal film and a ferroelectric liquid crystal film or constructed with a ceramics such as PLZT. The scattering-mode light-modulation member 6 has an optical characteristic to scatter light when heated and keep the light-scattering state even after cooled, and further has an optical characteristic to take a transparent state in response to application of an electric field thereto and keep the transparent state by removal of the electric field. That is, the scattering-mode light-modulation member 6 can take two states (an opaque state and a transparent state) in accordance with heat and electric field. For example, in the case of using the polymer dispersed liquid crystal film for the scattering-mode light-modulation member 6, the polymer-liquid crystal film 6 is made of any one of methacrylic resin, polyester resin, polycarbonate resin, vinyl chloride resin, polyamide resin, polyethylene resin, polypropylene resin, polystyrene resin, silicon resin and others, and constructed as a porous polmeric film randomly having a number of microscopic holes so as to have a volume resistivity of above 10 14 Ωcm, the number of microscopic holes whose diameters are below 0.5 microns (for example) being filled with a nematic liquid crystal. It is also appropriate that the polmer-liquid crystal film 6 is constructed with a smectic liquid crystal being randomly mixed with acrylate resin. Here, the laminating order is not limited to that shown in Fig. 2. For instance, it is appropriate that the scattering-mode light-modulation member 6 is directly placed on the electrode plate 4 and the color-stripe filter 5 is piled up on the scattering-mode light-modulation member 6. Moreover, it is also appropriate that as illustrated in Fig. 3B the electrode plate 4 is not provided integrally with the other plates 3, 5 and 6 but an electrode plate 10 is individually disposed in opposed relation to a recording medium 2A comprising the plates 3, 5 and 6 as illustrated in Fig. 3B. In this case, it is possible to use the drum 16 as the electrode plate 10. Secondly, a description will be made hereinbelow in terms of the basic operation principle of the erasure, recording and reproduction of an image in the recording medium 2. As shown in Fig. 3A, the electrode device 8 coupled to one terminal of the power source 9 is disposed in opposed relation to the scattering-mode light-modulation member 6 of the recording medium 2, the other terminal of the power source 9 being coupled to the electrode plate 4 interposed between the base plate 3 and the color-stripe filter 5, so that an electric field can be applied to the recording medium 2. It is also appropriate that the recording medium 2A is provided between the electrode plate 10 and the electrode device 8 as illustrated in Fig. 3B. When applying an electric field to the recording medium 2 (2A), the scattering-mode light-modulation member 6 constructed with a polymer dispersed liquid crystal film takes a transparent state because the liquid crystal is oriented in the direction of the electric field. The erasing operation of the image formed is effected in accordance with the principle that the scattering-mode light-modulation member 6 enters into the transparent state. Here, it is also appropriate that in place of the electrode device 8 a corona electrifier is provided to face the scattering-mode light-modulation member 6 so that the corona electrifier scans and charges the recording medium 2. In addition, as shown in Fig. 4A, the thermal head 11 acting as a heating device is disposed to face the scattering-mode light-modulation member 6 so as to heat the recording medium 2. In response to the heating due to the thermal head 11, the scattering-mode light-modulation member 6 takes an opaque state because the liquid crystal first enters into an isotropic-phase state when heated and then becomes an irregularly arranged state when cooled. This principle that the scattering-mode light-modulation member 6 takes the opaque state is used for recording operation and easure-auxiliary operation (full-writing operation) which will be described hereinafter. Fig. 4B shows a system for reproducing the image recorded in the recording medium 2 through the heating. In Fig. 4B, a light beam emitted from a light source 13 is incident through a reflection plate 12 on the recording medium 2 from the base plate 3 side. A light beam passing through the recording medium is incident on a lens 14 so as to be diverged and projected onto a screen 15. That is, this system is arranged as a transmission type projector. In the case that the base plate 3 is made of an opaque material, the system is constructed as a reflection type projector. A description will hereinbelow be made in detail with reference to Figs. 5A to 5C in terms of an image erasure of the image formation apparatus according to this embodiment, Fig. 5A showing an erasure-auxiliary process to be effected prior to the erasure and Fig. 5B showing an erasure process to be effected after the erasure-auxiliary process. In Fig. 5A, the recording medium 2 is first heated from the scattering-mode light-modulation member 6 side by means of a heater 20 which is positioned at an upstream side with respect to the electrode device 8 in the drum 16 rotating direction A and disposed to face the scattering-mode light-modulation member 6 of the recording medium 2. This heating due to the heater 20 causes the recording medium 2 to uniformly take an opaque state (i.e., full-written state). After the erasure-auxiliary process, an electric field is applied to the recording medium 2 through the electrode device which acts as the electric-field erasing device, as illustrated in Fig. 5B. This application of the electric field to the recording medium 2 allows the recording medium 2 to take a transparent state because the liquid crystal of the scattering-mode light-modulation member 6 is oriented in the electric-field direction. In other words, the image previously recorded can be erased from the recording medium 2. In the control operation for the easure-auxiliary process and the erasure process, when the drum 16 is rotating in the direction A, the heater 20 is turned ON to start the heating and then the switch 16 is closed to generate the electric field with respect to the recording medium 2. Here, although in the above-described embodiment the heater 20 and the thermal head 11 are individually provided, it is appropriate to arrange the thermal head 11 so as to act as both the erasure-auxiliary means and writing means. According to this arrangement, since the the electrode device 8 applies an electric field to the recording medium 2 to previously make clear the scattering-mode light-modulation member 6 after the heater heats the recording medium 2 so that the recording medium 2 becomes a uniformly opaque state, the image previously recorded can be erased completely. After the erasure, the thermal head 11 positioned at the downstream side with respect to the electrode device 8 newly writes an image in the recording medium as illustrated in Fig. 5C. In Fig. 1, numeral 19 designates a cooling device for removing the heat applied in the erasure-auxiliary process. The cooling device 19 can be provided if required.

Claims: An image formation apparatus comprising: a recording medium (2) including a scattering-mode light-modulation member (6) which takes an opaque state in response to heat and takes a transparent state in response to only an electric field; erasure-auxiliary means (11,20) for heating said recording medium (2) in accordance with a control signal from an external device; erasure means (8) for applying an electric field to said recording medium (2) after the heating due to said erasure-auxiliary means (11,10); and image-writing means (11) for heating said recording medium (2) in accordance with an information signal from an external device after the application of the electric field to said recording medium (2) due to said erasure means (8). An image formation apparatus as claimed in claim 1, wherein said erasure-auxiliary means (11) and said image-writing means (11) is constructed with one thermal head (11) comprising a plurality of heating elements each for generating heat in response to said control signal and said information signal. A method of forming an image in a recording medium (2) including a scattering-mode light-modulation member (6) which takes an opaque state in response to heat and takes a transparent state in response to only an electric field, said method comprising the steps of: heating said recording medium (2); applying an electric field to said recording medium (2) after the heating so as to erase an image previously recorded in said recording medium (2); and selectively heating parts of said recording medium (2) after the application of said electric field thereto so as to write a new image in said recording medium (2).

Inventors: ASAKURA TSUTOU, BONDE HIROYUKI, KOYAMA YOSHIHISA, NAKAGAKI SHINTARO, TAKANASHI ITSUO, ASAKURA, TSUTOU, BONDE, HIROYUKI, KOYAMA, YOSHIHISA, NAKAGAKI, SHINTARO, TAKANASHI, ITSUO
Applicants: VICTOR COMPANY OF JAPAN, VICTOR COMPANY OF JAPAN, LIMITED
Application year: 1992
Main classification: G09G3
IPC codes: G02F1, B41M5, G09G3