Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Reexamination Certificate
1991-01-18
2001-04-17
Nguyen, Hoa T. (Department: 2651)
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
Reexamination Certificate
active
06219329
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical disk made of a plastic material and having pits on one surface thereof for storing data therein, which data can be regenerated by a light beam such as a laser beam.
2. Description of the Related Art
Recent remarkable developments of optical disks have caused these optical disks to supplant conventional recordable disks in the field of sound recording, and further in the field of electronic computers when used as CD-ROMs.
The conventional recordable disk is provided with a continuous spiral groove for storing data as sound or in the form of analogue signals, but an optical disk is provided with discontinuous pits (recesses) on one surface of the plastic body of the disk, to store data, such as sound, in the form of digital signals. To this end, the pits are formed in a predetermined pattern on one surface of the plastic optical disk, and a reflecting layer is formed by an aluminum evaporation process over the surface of the disk having the pits.
In addition, a protecting layer is formed over this reflecting layer. In the use of the optical disk, a laser beam is applied to the exposed surface of the plastic disk, opposite to the surface thereof containing the pits, so that the laser beam is transmitted through the plastic disk from the exposed surface to the surface having pits, and is reflected at the reflecting layer. The reflected beam is again transmitted through the plastic disk and is emitted from the exposed surface, and the output light is delivered to the regenerating device for reading the data stored in the optical disk, based on the intensity of the output light.
There are many severe requirements for a material for constituting an optical disk. For example, such a material must have such properties as a high transparency, to allow a light to be transmitted therethrough with a low loss, a low birefringence, a low hygroscopicity, to prevent a warping of the optical disk, a high resistance to heat, a high fluidity during a molding process, a good demolding property upon completion of a molding process, and a low contamination by foreign substances and impurities. To satisfy these requirements, an acrylic resin such as polymethyl methacrylate resin was developed as a material for the optical disk, and recently, a polycarbonate resin has been developed for an optical disk intended for use in a hot environment; for example, in an audio system in an automobile.
A problem arises if the plastic optical disk contains a large amount of foreign substances and impurities in that, when the laser beam is transmitted through the plastic disk, and the reflected light again transmitted through the plastic disk, the laser beam is absorbed by the foreign substances and impurities and the intensity of the output light becomes weak, and thus the signal to noise (S/N) ratio is lowered. Therefore, the development of optical disks has been concentrated on determining how to obtain a plastic material having a high transparency. It is, therefore, a conventionally immutable concept that a colorless transparent plastic material is used for the optical disk, and efforts have been made to establish a manufacturing process which precludes the entry of foreign substances and impurities into the optical disk material.
As the popularity of optical disks becomes greater, a demand has arisen for a colored optical disk, for example, a red or yellow disk, but a plastic material inherently having a good transparency and a desired color is not known, and to obtain an optical disk having a desired color, it is necessary to mix a coloring material into a transparent plastic material.
Nevertheless, a coloring material or a pigment for coloring is deemed to be an impurity, in view of the transmission of the laser beam, which coloring material absorbs the light to some extent, and accordingly, under the conventional concept of completely precluding foreign substances and impurities, it is not conceivable to use a coloring material at a region through which the laser beam is transmitted, and thus it is commonly considered that it is impossible to obtain a colored optical disk.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an optical disk having a particular color and providing less absorption of a laser beam, to thereby enable more sensitive data regeneration.
According to the present invention, there is provided an optical disk comprising a plastic disk body having opposing first and second surfaces, with pits provided on the first surface, a reflecting layer formed on the pitted first surface of the plastic disk body, and a protecting layer covering the reflecting layer, the second surface being adapted to be subjected to a light, characterized in that the plastic disk body has a fluorescent coloring material dispersed in the plastic disk body.
With this arrangement, an external light will be incident on the optical disk regardless of whether or not it is used, and a component of the external light having a wavelength shorter than the wavelength of the fluorescent coloring material at which a fluorescent radiation is emitted is once absorbed in the fluorescent coloring material. The absorbed light energy is then converted into a fluorescent radiation which presents a particular color. In this way, the fluorescent radiation is induced by the external light having a wavelength in the visible range, so that, in usual circumstances where the optical disk can be seen, the fluorescent radiation is normally emitted and the optical disk appears to be colored. Also, in the use of the optical disk, a laser beam is applied to the optical disk for regenerating the stored data therein. The typical laser beam has a wavelength of 780 nm, which is close to the boundary, of the visible range of wave lengths, on the infrared side. In contrast, the fluorescent radiation of a particular color has a wavelength within the visible range, and is shorter than 780 nm at the boundary of the wave length of the visible range on the infrared side. Therefore, the fluorescent coloring material absorbs a light component having a wave length shorter than the wavelength of a particular color within the visible range, but does not absorb the laser beam having a wavelength longer than the wavelength of a particular color. Accordingly, the laser beam is not substantially absorbed in the fluorescent coloring material when the laser beam is incident on the fluorescent coloring material and can be transmitted through the plastic disk without a reduction of the intensity of the light, to thereby enable a more sensitive regeneration of the data.
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Compact Disc Catalogue '88, 1988, p. 1065.
Japanese Food Research Laboratories, Test Report, Feb. 22, 1996.
Kojima Yuji
Sawada Hisashi
Tanaka Akira
Fujitsu Limited
Nguyen Hoa T.
Staas & Halsey , LLP
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