Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-09-07
2004-06-08
Toomer, Cephia D. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C428S064400, C428S412000
Reexamination Certificate
active
06747080
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polycarbonate resin composition for the production of a substrate for an optical information medium. More particularly, the present invention is concerned with a polycarbonate resin composition for the production of a substrate for an optical information medium, which comprises 100 parts by weight of a polycarbonate resin and 0.0005 to 1.0 part by weight of a mold release agent, wherein the polycarbonate resin composition exhibits a specific relative viscosity (&eegr;
r
), and wherein the relative viscosity (&eegr;
r
) and a melt index (MI) of the polycarbonate resin composition satisfy specific relationships. The polycarbonate resin composition of the present invention is advantageous not only in that the polycarbonate resin composition exhibits an excellent moldability even when molded at low temperatures, but also in that the polycarbonate resin composition can be molded with a short cycle time (that is, the polycarbonate resin composition enables the so-called “high cycle moldings”). Further, the polycarbonate resin composition exhibits excellent thermal stability during the molding thereof, and is capable of suppressing the occurrence of mold deposit (MD) during the molding thereof. Moreover, when the polycarbonate resin composition is molded to obtain a substrate for an optical information medium, such as an optical disc (e.g., a CD or a DVD), the substrate exhibits a satisfactorily high mechanical strength.
2. Prior Art
Polycarbonates have been widely used in various fields as engineering plastics having excellent heat resistance, impact resistance and transparency. Especially, due to the recent expansion of information society, there has been a growing demand for polycarbonates for producing storage media for music and image, and storage media for digital information (such as a storage medium for a personal computer). Nowadays, polycarbonates have become indispensable resins for producing optical discs and optical cards, such as a CD, a CD-ROM, a CD-R, a DVD-ROM and a DVD-R.
In the production of a substrate for an optical information medium, such as an optical disc, formation of precise microgrooves and micropits on the substrate is necessary. Polycarbonates for use in the production of such a substrate need to have high transferability and excellent optical properties, such as low birefringence. Therefore, low molecular weight polycarbonates having a weight average molecular weight of about 15,500 and having a high melt fluidity have hitherto been used in the production of the substrates for the optical information media. In recent years, with respect to the storage media, conventional CD's have been being replaced by DVD's which have recording densities much higher than those of the CD's. For producing substrates used in such optical information media having a high recording density, it is necessary to form very precise microgrooves and micropits on the substrates. Accordingly, as a resin for use in the production of a substrate for the optical information medium, it is demanded to develop a polycarbonate exhibiting a transferability higher than those of the conventional polycarbonates. In addition, due to the fact that the thickness of a substrate for a DVD (DVD substrate) is only about 0.6 mm which is very small as compared to the thickness (about 1.2 mm) of a substrate for a CD (CD substrate), there is also a growing demand for the development of a polycarbonate which has a melt fluidity higher than those of the conventional polycarbonates and, hence, can be used for the production of a substrate having such a small thickness. When a DVD substrate is produced from a conventional polycarbonate, which has a weight average molecular weight of about 15,500 and which has hitherto been used for producing the CD substrates, at a molding temperature employed in the conventional production of the CD substrates (i.e., about 300 to 320° C.), the substrate produced does not have a satisfactorily-low birefringence or a satisfactorily high transferability because the melt fluidity of the polycarbonate is unsatisfactory. Therefore, in order to alleviate this problem, the DVD substrates are produced at a molding temperature as high as 380 to 390° C. so as to lower the melt viscosity of the polycarbonate. Such a molding temperature is too high and, hence, is not generally employed for molding polycarbonates (the molding temperature in the production of molded articles other than optical information media is generally from 270 to 300° C., and the molding temperature in the production of the CD substrates is about 320° C.). The employment of such a high molding temperature causes problems, such as heat deterioration of the polycarbonate, and large warpage of the produced substrate. Further, since the time needed for cooling the substrate becomes long, molding cycle necessarily becomes long, thereby leading to a lowering of the productivity and marked occurrence of mold deposit. The marked occurrence of mold deposit not only causes a lowering of the quality of the substrate, but also necessitates frequent dismantling and cleaning of the mold employed for molding the polycarbonate. Therefore, it has been desired to solve the problems accompanying the above-mentioned high temperature molding.
It is well known that a low molecular weight polycarbonate has an improved melt fluidity. However, it has been impossible to solve the problems accompanying the above-mentioned high temperature molding simply by using a low molecular weight polycarbonate for producing DVD substrates. Therefore, several attempts have been made to solve the problems by methods other than the method which simply uses a low molecular weight polycarbonate. For example, in an attempt to shorten the time needed for cooling a shaped article by using, in a high temperature molding, a polycarbonate composition having improved mold release characteristics, Unexamined Japanese Patent Application Laid-Open Specification No. 10-60105 proposes a polycarbonate composition containing 3.5 to 8% by weight of polycarbonate oligomers which have a polymerization degree of not more than 4. Although this polycarbonate composition has improved mold release characteristics, the molding of the polycarbonate composition needs to be conducted at high temperatures. Therefore, the polycarbonate composition is disadvantageous in that, when the molding of the polycarbonate composition is conducted at high temperatures for a long time, the polycarbonate oligomers are likely to adhere to the mold used, thereby causing the mold deposit.
Unexamined Japanese Patent Application Laid-Open Specification No. 9-320110 (corresponding to EP 794 209 and U.S. Pat. No. 5,783,653) proposes a method for solving a problem accompanying the use of a low molecular weight polycarbonate which is used for achieving a low melt viscosity of a polycarbonate, i.e., a problem that, due to the low molecular weight of the polycarbonate, the mechanical strength of the polycarbonate is lowered to cause a cracking in the resultant molded article. Specifically, this patent document proposes the use of a polycarbonate having a specific terminal group. However, by this method, the processability of the polycarbonate cannot be satisfactorily improved. Further, since this method uses a specific molecular weight modifier, the content of polycarbonate oligomers in the polycarbonate increases, so that mold deposit markedly occurs.
Unexamined Japanese Patent Application Laid-Open Specification No. 8-293128 (corresponding to EP 691 361 and U.S. Pat. No. 5,633,060) proposes a polycarbonate resin obtained by copolymerizing specific dihydroxy compounds, which has excellent optical properties and an excellent moldability which enables the production of an optical information medium capable of high density recording and storage of information. However, the polycarbonate resin exhibits a poor melt fluidity during the molding thereof, so that the polycarbonate resin is not suitable for the hig
Hachiya Hiroshi
Namba Nobutsugu
Asahi Kasei Kabushiki Kaisha
Birch & Stewart Kolasch & Birch, LLP
Toomer Cephia D.
LandOfFree
Polycarbonate resin composition for the production of a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Polycarbonate resin composition for the production of a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Polycarbonate resin composition for the production of a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3293675