Stock material or miscellaneous articles – Circular sheet or circular blank
Reexamination Certificate
1998-06-09
2001-02-20
Evans, Elizabeth (Department: 1774)
Stock material or miscellaneous articles
Circular sheet or circular blank
C428S064200, C428S064400, C428S913000, C430S270110, C430S321000, C430S328000, C430S945000, C369S275100
Reexamination Certificate
active
06190748
ABSTRACT:
The present invention relates to a method of manufacturing optical discs. By “optical disc” is meant a disc in which the required information is recorded on, and played back from, the disc by optical means.
In a conventional method of manufacturing an optical disc the upper surface of a glass master plate is prepared using a suitable adhesion promoter. This prepared surface is then coated with a thin layer of a photoresist. The intensity of a laser beam is modulated in accordance with the information to be recorded on the disc, and the laser beam is focused on the photoresist layer. The master is rotated and the laser beam commences the recording session at the centre of the disc and moves radially outwardly to produce a spiral pattern of exposed photoresist in the photoresist layer. The depth of the exposed pattern will be proportional to the intensity of the focused laser beam. Because the laser beam is modulated digitally this means that the spiral pattern will either have a depth of 0 or 1, where 0 corresponds to the upper surface of the photoresist layer and 1 corresponds to the lower surface of the photoresist layer.
On developing the photoresist layer the exposed parts of the photoresist dissolve, and these dissolved parts of the photoresist layer are washed away to leave pits which provide in digital form information corresponding to the information source used to modulate the laser beam.
A layer of sputtered nickel or evaporated silver is formed on the surface of the developed master containing the pits, a nickel father is formed from the master, a mother is formed from the father, and a stamper is formed from the mother, in accordance with conventional known methods of manufacturing optical discs.
A plastic polycarbonate optical disc is injection moulded from the stamper, a reflective metallic layer is placed on the surface of the disc containing the pits, and a layer of curable lacquer is placed on the aluminium layer. A label providing the desired information on the contents of the disc is then imprinted on the now cured surface of the lacquer layer.
It is an aim of the invention to provide a distinguishing mark beneath a surface of the optical disc.
In this specification the term “distinguishing mark” covers a mark of any desired visual content such as for example an illustration, a logo, written matter or any combination of these.
According to the present invention there is provided a method of manufacturing an optical disc master comprising the preparation of the surface of a glass master plate to receive a layer of photoresist, applying the said layer of photoresist, subjecting the photoresist layer to a first exposure of a modulated laser beam to produce an exposed first pattern corresponding to the information used to modulate the laser beam, locating a distinguishing mark in the path of light from a second light source directed onto the previously exposed surface of the photoresist layer to locate thereon an exposed second pattern corresponding to said distinguishing mark.
In the subsequent development stage of manufacturing the optical disc master, the distinguishing mark is developed to the same parameter as is required to develop the laser exposed first pattern. As the distinguishing mark is now contained within the glass master, during the known production sequence of a glass master through to a production stamper and onto subsequent disc replication, the distinguishing mark is transferred onto the polycarbonate replica along with the laser exposed first pattern. Both images are subsequently coated with a metallic layer and then a protective lacquer layer. Thus resulting in a mark that cannot be readily erased or removed from the disc.
The distinguishing mark may be contained in a transparent sheet which may be placed in contact with the surface of the photoresist receiving the said light.
In one embodiment of the invention the photoresist layer is exposed twice to the source light. The light source may be passed across the photoresist layer at a constant speed of 0.5 meters per second, the light is then extinguished and returned to the starting point. The light source is then passed across the photoresist layer a second time, and the light is then extinguished and returned to the start point. This sweeping action ensures that the distinguishing mark is evenly exposed to an equal amount of source light each time the source light passes across the photoresist layer.
Preferably, the light source is approximately 300 watts and at least 200 mm in length to ensure that it fully covers the photoresist area to be exposed; the optical disc being 120 mm in diameter in this embodiment of the invention.
The invention is not restricted to the photoresist layer being exposed only twice. The number of exposure sweeps would depend upon the type of photoresist being used in the process because each type of photoresist is designed to be used with, i.e. exposed by, a light source of a particular wavelength.
When the transparent sheet is placed in contact with the photoresist layer, great care has to be taken in handling the transparent sheet in order to avoid the introduction of contaminants to the photoresist layer thereby causing physical disturbance to the photoresist layer during the development step.
REFERENCES:
patent: 5607188 (1997-03-01), Bahn
patent: 5608718 (1997-03-01), Schiewe
patent: 5645978 (1997-07-01), Inui et al.
patent: 5766495 (1998-06-01), Parette
patent: 5843626 (1998-12-01), Ohta et al.
Goldman Martin John
Xavier Miguel Nunes
Disctronics Manufacturing
Evans Elizabeth
Lyon & Lyon LLP
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