AU718994C - Single surfaced super-density optical discs - Google Patents

Description

SINGLE SϋRFaCED STTPgR-DFNSTTV OPTICAL DISCS Field of Inv nt nn This invention relates to the shaping of plastic compact discs (CD's) by injection molding for storing data in an optical medium. In particular it relates to the provision of super-density compact discs where only one surface is required for the storage of information.

Background Qf The Inven ion

Plastic discs having a pit optical track structure are well known as compact discs. Double sided discs in which information is recorded on two sides of such a structure formed by binding two compact discs and apparatus for playing such discs is also well known, as in U.S. patents 4,903,140; 4,939,011/ 5,097,465; 4,811,324.

The term compact disc as used in thiβ application includes any disc shaped recorded medium having pits and lands forming an optical track structure on a data information recording planar surface. Thus it includes such discs where the information stored as pits and lands is digital information or analog information.

Digital information may be encoded into the pits and lands as pits of quantized lengths interpretable as a stream of digital data, wherein the length of each pit or land segment may be, for example, related to the number of l's or O's in a data stream. An example of such a system is the compact disc ("CD"} audio or video disc. Analog information may be encoded into the pits and lands as pit lengths that may vary over a continuum of values, wherein the length of each pit or land segment may be, for example, related to a voltage level in a desired output. An example of such a system is the laser disc video recording system.

Brief Description Of The Invention The present invention is a novel compact disc. Such discs are known to be plastic discs having pits and lands representing optically recorded data on an internal surface in which the internal surface carries a light reflective film and is overcoated by a transparent layer, that exposes a flat surface. In very high density applications two such discs are bonded to each other back to back. Where there is only the need for one surface to carry data the second disc is blank. Thus a technology for providing large data storage is employed even where it is not necessary. The present invention provides a way to economize on the steps required for the manufacture of such discs .

In the present invention, the d sc has two thickness regions. The first thickness region is a central cylindrical region. The second thickness region is the remaining annular region of the disc and has only a fraction of the thickness of said first region, said fraction being less than 3/4 and more than 1/4. The second annular region is overcoated with materials of different composition.

Brief Description Of The Drawings Figure 1 depicts a prior art system employing a thin compact disc bonded to a blank compact disc to result in a disc that is usable in a double sided system even though all the data is present on only one side thereof.

Figure 2 depicts a preferred embodiment of the present invention using a compact disc the plastic portion of which has substantial variations in thickness.

Detailed Description Of A Preferred Embodiment Of The Invention The invention comprises a plastic disc having pits and lands representing optically recorded data on an internal surface thereof, the internal surface having a light reflective film thereon, and the surface being overcoated by a transparent layer exposing a flat surface. The disc has first and second thickness regions. The first thickness region is a central cylindrical region of a first predetermined thickness. The second thickness region comprises the remaining annular region of the disc and has a fraction of the thickness of said first region, the fraction being less than 3/4 and more than 1/4. The annular region is then overcoated with materials of different composition. While there have been shown and described and pointed out the fundamental novel features of the invention as applied to preferred embodiments thereof, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention, which is specified in the following claims.

Claims (2)

I claim:

1. A plastic disc having pits and lands representing optically recorded data on an internal surface thereof, the internal surface having a light reflective film thereon, and the surface being overcoated by a transparent layer exposing a flat surface, said disc comprising first and second thickness regions, said first thickness region comprising a central cylindrical region of a first pre- determined thickness, said second thickness region comprising a remaining annular region of the disc having a fraction of the thickness of said first region, said fraction being less than 3/4 and more than 1/4.

2. The plastic disc of claim 1 wherein remaining annular region is overcoated with materials of different composition from the composition of said disc.