A PROCESS FOR MANUFACTURING OPTICAL DISCS HAVING IMPROVED BLOCK ERROR RATE(BLER) AND AN APPARATUS THEREFOR.
FIELD OF THE INVENTION
The present invention in general, relates to a process for manufacturing optical
discs with improved block error rate(BLER) and an apparatus therefore and in
particular to a process for optimization of moisture content in TFP (2,2,3,3
Tetrafluoropropanol),applied as a dying solvent, during the dying process of
optical discs.
BACKGROUND OF THE INVENTION
The moisture absorbing problem in the dye manufacturing process and storage is
the subject of much research in the industry.
The rate of moisture diffusion in and out of the polycarbonate substrate is very different at its two surfaces. Water diffusion through the metal coated side is essentially nil; water diffusion through the free polycarbonate surface, though slow but it is appreciable.
Traditionally, during the manufacturing process of optical discs, the dying process is carried out by applying TFP (2,2,3,3 Tetrafluoropropanol) as a dying solvent having approximately 750ppm moisture content. It is a colorless transparent liquid with density of 1.48gm/c.c at ambient temperature, with mild alcohol smell, flammability, low toxicity and strong water absorption characteristics. TFP is mainly used as a solvent for dyes in the optical disc manufacturing process. However, due to its strong hygroscopic nature, it absorbs moisture, as a result the product quality deteriorates in terms of BLER value when a high moisture content TFP is used in the process. It is known to persons skilled in the art that BLER means block error rate. The term describes the error rate of a finished disc before error correction will activate. According to standard, a CD must not exceed 220 BLERs per second within a measurement period of 10 seconds. If the count exceeds this value, it can be assumed that erroneous

data cannot be corrected. Therefore, a BLER is then and erroneous block per
second that contains detectable errors at the input of the CI decoder.
It has been observed over the years, that application of TFP (2,2,3,3 Tetrafluoropropanol) as a dying solvent, in the dying process, during the manufacturing of optical discs, results in optical discs having BLER values not within the acceptable limits. This has been primarily due to the approximately 750ppm moisture content in said TFP and this has been a matter of great concern, in the Industry.
Hence, there was a long felt need to optimize the moisture content in said TFP, or in other words to reduce the hygroscopic nature of TFP so that the BLER value is kept within acceptable limits and simultaneously, the effectiveness of the dying process is ensured.
OBJECTS OF THE INVENTION
It is a prime object of the present invention to provide a process for manufacturing optical discs having improved BLER value.
It is a further object of the present invention to provide an apparatus for manufacturing optical discs having improved BLER value.
It is another object of the present invention to reduce the hygroscopic nature of the dye used in the disc manufacturing process.
It is a further object of the present invention to provide an optical disc having improved BLER value .
The foregoing objects and other aspects of the present invention will be clear from the following description, which is purely for the sake of understanding and not by way of any limitation
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a process for manufacturing optical discs including forming at least a reflective layer on said discs, followed by

forming of at least a coating of organic dye thereon, wherein the dying process is carried out by applying TFP (2,2,3,3 Tetrafluoropropanol) as a dying solvent, having a moisture level of less than 200ppm dye, the moisture diffusion rate on the polycarbonate substrate of said optical discs being nil on the metal coating side and on the other side being appreciable, whereby, optical discs having block error rate(BLER) within acceptable limits, is obtained, resulting in enhancement of quality of the optical discs manufactured.
In accordance with preferred embodiments of the process for manufacturing optical discs of the instant invention:
-the BLER value is less than 220 per second within a measurement of 10 seconds.
-the moisture level of said TFP is optimized to 175ppm, based on experimentation and requirement.
The present invention also provides an apparatus for manufacturing optical discs, said apparatus including means adapted to form at least a reflective layer on said discs as well as dispensing means, adapted to initiate dispensing dye for forming at least an organic dye coating on said discs, wherein said apparatus is adapted to carry out the dying process by applying TFP (2,2,3,3 Tetrafluoropropanol) as a dying solvent, having a moisture level of less than 200ppm dye, the moisture diffusion rate on the polycarbonate substrate of said optical discs being nil on the metal coating side and on the other side being appreciable, whereby,optical discs having block error rate(BLER) within acceptable limits, is obtained, resulting in enhancement of quality of the optical discs manufactured.
In accordance with preferred embodiment of the apparatus of the invention: -said dispensing means comprises nozzle(s).
The present invention also provides an optical disc manufactured by the process as described hereinbefore.

DETAILED DESCRIPTION OF THE INVENTION
As stated hereinbefore traditionally, during the manufacturing process of optical discs, the dying process is carried out by applying TFP (2,2,3,3 Tetrafluoropropanoi) as a dying solvent having approximately 750ppm moisture
content. It is a colourless transparent liquid with density of 1.48gm/c.c at ambient temperature, with mild alcohol smell, flammability, low toxicity and strong water absorption characteristics. However, due to its strong hygroscopic nature, it absorbs moisture, as a result the product quality deteriorates in terms of BLER value when a high moisture content TFP is used in the process. The meaning and implication of BLER value, is known to persons skilled in the art and furthermore, such meaning and implications have been explained hereinbefore.
It has been observed over the years, that application of TFP (2,2,3,3 Tetrafluoropropanoi) as a dying solvent, in the dying process, during the manufacturing of optical discs, results in optical discs having BLER values not within the acceptable limits. This has been primarily due to the approximately 750ppm moisture content in said TFP and this has been a matter of great concern, in the Industry.
Hence extensive experimentation was on over the years to optimize the moisture content of TFP as a dying solvent to ensure effectiveness of the dying process and also to simultaneously ensure manufacturing of optical discs , having acceptable BLER value. To overcome the problems associated with the existing manufacturing process, after extensive experimentation, a relatively simpler solution has been deciphered and accomplished by the present invention. It has been found that if the moisture content of the TFP solvent used can be reduced, a vast improvement can be achieved.
As conventionally known, the normal TFP extensively applied for the

manufacturing process contains 750 ppm of moisture. It has been found that use of TFP with moisture level less than 200 ppm vastly improves the product quality in terms of better BLER value as well as line yield. This hitherto unknown, optimization of the moisture level has been achieved after several experimentation This technical advancement was hitherto not known or conceived by persons skilled in the art.
The present invention has been described with the help of some preferred embodiments, solely for the sake of understanding, but in no way is limited to such embodiments and so, the present invention includes all legitimate developments within the ambit of what has been described hereinbefore and claimed in the claims hereinafter.

WE CLAIM
1.A process for manufacturing optical discs including forming at least a
reflective layer on said discs, followed by forming of at least a coating of organic dye thereon, wherein the dying process is carried out by applying TFP (2,2,3,3 Tetrafluoropropanol) as a dying solvent, having a moisture level of less than 200ppm dye, the moisture diffusion rate on the polycarbonate substrate of said optical discs being nil on the metal coating side and on the other side being appreciable, whereby,optical discs having block error rate(BLER) within acceptable limits, is obtained, resulting in enhancement of quality of the optical discs manufactured.
2.The process as claimed in claim 1 wherein the BLER value is less than 220 per second within a measurement of 10 seconds.
3.The process as claimed in any preceding claim wherein the moisture level of said TFP is optimized to 175ppm, based on experimentation and requirement.
4.An apparatus for manufacturing optical discs, said apparatus including means adapted to form at least a reflective layer on said discs as well as dispensing means, adapted to initiate dispensing dye for forming at least an organic dye coating on said discs, wherein said apparatus is adapted to carry out the dying process by applying TFP (2,2,3,3 Tetrafluoropropanol) as a dying solvent, having a moisture level of less than 200ppm dye, the moisture diffusion rate on the polycarbonate substrate of said optical discs being nil on the metal coating side and on the other side being appreciable, whereby.optical discs having block error rate(BLER) within acceptable limits, is obtained, resulting in enhancement of quality of the optical discs manufactured.

5. An apparatus as claimed in claim 4 wherein said dispensing means comprises
nozzle(s).
6. An optical disc manufactured by the process as claimed in claims 1 to 3.