Glass manufacturing – Processes – Utilizing parting or lubricating layer
Patent
1990-06-01
1992-02-25
Fisher, Richard V.
Glass manufacturing
Processes
Utilizing parting or lubricating layer
65 601, 65 605, 65106, 3692754, C03B 3500
Patent
active
050909827
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method of producing a surface microstructure on glass, particularly to a method of producing tracking grooves on the glass substrate for an optical memory element. The invention also relates to glass articles produced by the method according to the invention, particularly optical memory disk substrates and optical memory disks having tracking grooves.
Optical memory systems have been developed which store information in high density. The high density is achievable by using a beam diameter of approximately 1 micron. However, the beam position needs to be accurately controlled so that information is recorded at a pre-determined position and the information is read out from a pre-selected position. Certain types of optical memory devices require the use of guide signals or guide addresses to control the optical beam position. Typically these take the form of microscopic grooves, which in conjunction with a sensing mechanism and a servo system operating upon the optical beam, serve to guide the beam in the correct direction during recording and reading operations. Various methods for forming the grooves on the optical memory element have been proposed. In one such known method a nickel stamper having a corresponding pattern of grooves formed upon its surface is used to shape a photopolymer which is interposed between the stamper and a substrate made of glass or acrylic. A UV curable acrylic resin is often used as the photopolymer and is cured by exposure to light through the glass or acrylic substrate. Removal of the stamper then leaves a substrate having a thin acrylic layer fixed to it in which there is a micro structure. In a more simplified version of this procedure the stamper is used to form a surface having a microstructure by injection moulding acrylic or polycarbonate resin into a mould of which the stamper forms part. Both methods employ a resin layer in the optical memory element which introduces a possibility of oxygen and moisture permeation into the recording medium via the resin layer. Such permeation is thought to deteriorate modern recording materials and it is therefore considered desirable to form the tracking grooves directly on a glass substrate.
U.S. Pat. No. 4,544,443 assigned to Sharp KK describes a proposed method for forming the tracking grooves directly on a glass substrate. It is suggested that an optical memory element may be manufactured by depositing a resist film on the glass substrate and forming a groove pattern in the resist film. Reactive ion etching is conducted through the groove pattern formed in the resist film so as to form the tracking grooves in the glass substrate. After removing the resist film from the glass substrate, a magneto-optical recording layer is formed on the glass substrate in a conventional manner. In a preferred embodiment of the invention a layer of silica is deposited on the glass substrate and the grooves are actually formed in the silica layer. This preferred embodiment reveals the practical difficulties in forming grooves in glass by means of an etching process, irrespective of the cost penalties of using such a process. The stated disadvantages of glass etching are groove depth control and slow processing. Using a silica layer is expensive and probably not much faster.
Throughout this specification references to tracking grooves should be understood to include header data and other information permanently recorded in the microstructure. Furthermore, tracking grooves may be continuous or discontinuous, spiral or circular or any other configuration or combination desired.
The standards for optical disks are laid down in draft ISO 9171. This standard includes a specification for the various limits allowed for tracking groove geometry.
The present invention seeks to provide a method for forming the tracking grooves directly in the glass surface without the need to use an etching process and in an economical manner which uses a minimum of process steps. In addition to forming tracking grooves on the surface of an optical di
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Bradshaw John M.
Gelder Richard
Bruckner John J.
Fisher Richard V.
Pilkington plc
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