Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
2000-04-27
2003-01-14
Boykin, Terressa M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
C428S064200, C428S412000, C528S198000
Reexamination Certificate
active
06506870
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polycarbonate resin for use in the production of a substrate for an optical information medium. More particularly, the present invention is concerned with-a substantially chlorine-free polycarbonate resin which is produced by subjecting an aromatic dihydroxy compound and a carbonic diester to a transesterification reaction and which comprises a plurality of aromatic polycarbonate main chains which collectively contain specific heterounits (A) and (B), wherein the weight average molecular weight of the polycarbonate resin is from 13,000 to 18,000. The polycarbonate resin of the present invention exhibits a high melt fluidity during the injection molding thereof. By virtue of this property, the polycarbonate resin of the present invention can be advantageously used for producing an excellent substrate for an optical information medium, wherein the substrate has not only excellent optical properties, such as a low birefringence, but also a high precision transferability of information (that is, information of a stamper (a mold for forming microgrooves and micropits on a substrate) can be transferred to the substrate with high precision) (such a property is referred to as “high precision transferability”). Such a substrate can be advantageously used as a substrate for an optical information medium having a high recording density, such as a DVD. The present invention is also concerned with a polycarbonate resin composition comprising the above-mentioned polycarbonate resin-and an acidic compound, and a substrate for an optical information medium, which is produced by molding the above-mentioned polycarbonate resin or the above-mentioned polycarbonate resin composition.
2. Prior Art
Polycarbonates have been widely used in various fields as engineering plastics having excellent heat resistance, impact resistance and transparency. Due to the recent expansion of information society, there has been a growing demand for polycarbonates to be used 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 disks and optical cards, such as a CD, a CD-ROM, CD-R, a DVD-ROM, a DVD-R, an MO and an MD.
In the production of a substrate for optical information medium, such as an optical disk, precise formation of microgrooves and micropits on the substrate is necessary. Polycarbonates for use in the production of such a substrate need to have a high transferability and excellent optical properties, such as a low birefringence. Therefore, low molecular weight polycarbonates having a weight average molecular weight of about 15,500 and having a high melt fluidity are used in the production of the substrates for the optical information media. In recent years, with respect to the storage media, conventional CD's are being replaced by DVD's which have a recording density much higher than 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 substrate. Accordingly, as a resin for use in the production of a substrate for the optical information medium, the development of a polycarbonate which has a transferability higher than that of the conventional polycarbonates is demanded. 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 having a melt fluidity higher than that of the conventional polycarbonates. When a DVD substrate is produced from a polycarbonate, which has conventionally 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 melt fluidity of the polycarbonate is insufficient to obtain a satisfactory level of transferability. Therefore, in order to solve 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 used 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 use of such a high molding temperature causes problems, such as heat deterioration of a polycarbonate, long molding cycle, and large warpage of the produced substrate.
Further, with respect to the optical information media, there is especially a large demand for a storage medium capable of retaining the stored information for a prolonged period of time. Stability under conditions wherein both temperature and humidity are high is required for a storage medium to be able to retain the stored information for a prolonged period of time.
In the production of the substrates for the optical information media, polycarbonates produced by the phosgene process have conventionally been used. However, the use of the polycarbonates produced by the phosgene process in the production of the substrates for the optical information media is accompanied by the following problems: (1) phosgene used in this process is difficult to handle; (2) methylene chloride used as a solvent in this process causes polycarbonates to contain impurities (chlorine ions and residual methylene chloride) which not only adversely affects the thermal stability of the polycarbonates, but also causes corrosion of a mold used for the molding of the polycarbonates; and (3) the quality of the produced substrate for the optical information medium is poor.
In order to alleviate these problems accompanying the phosgene process polycarbonates, various proposals for polycarbonate compositions containing decreased amounts of the above-mentioned impurities and methods for decreasing the amounts of the impurities contained in the polycarbonates have been made in a number of documents, including Unexamined Japanese Patent Application Laid-Open Specification No. 63-316313 (corresponding to US Patent No. 4,880,896), Unexamined Japanese Patent Application Laid-Open Specification No. 4-146922, and Unexamined Japanese Patent Application Laid-Open Specification No. 63-97627 (corresponding to U.S. Pat. No. 4,798,767). However, when the molding of polycarbonates is conducted-at a high temperature, methylene chloride remaining in a small amount in the polycarbonates is easily converted into hydrochloric acid. The removal of impurities by the conventional methods is unsatisfactory and, hence, it has been desired to develop a method for almost completely removing the impurities from polycarbonates.
On the other hand, since the complete removal of impurities from polycarbonates requires a great deal of labor, polycarbonates produced by the transesterification process, which uses no phosgene or methylene chloride, have recently been drawing attention.
However, the transesterification polycarbonates have the following problem. The transesterification polycarbonates contain a large amount of hydroxyl terminals as compared to the phosgene process polycarbonates (see “Kobunshi Bunseki Handbook (Handbook for Polymer Analysis)”, page 345, published in 1985 by Asakura Shoten, Japan). Such polycarbonates suffer severe heat deterioration during the high temperature molding and, hence, cannot be used for producing a substrate for the optical information medium.
At the present, there is no transesterification polycarbonate which can be used for producing a substrate for the optical information medium, especially a high recording density medium, such-as DVD, the production of which requires a molding at a high temperature. Therefore, the deve
Hachiya Hiroshi
Kawasoe Shinya
Asaki Kasei Kabushiki Kaisha
Boykin Terressa M.
LandOfFree
Polycarbonate resin for use in the production of a substrate... 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 for use in the production of a substrate..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Polycarbonate resin for use in the production of a substrate... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3072627