Stock material or miscellaneous articles – Circular sheet or circular blank
Reexamination Certificate
2000-07-17
2002-09-10
Evans, Elizabeth (Department: 1774)
Stock material or miscellaneous articles
Circular sheet or circular blank
C428S064400, C430S270110, C269S133000
Reexamination Certificate
active
06447868
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical molding material, and an optical disk substrate and a production method thereof, and more particularly to an optical molding material which is high in transfer accuracy and toughness, small in birefringence, particularly, birefringence occurred in a thicknesswise direction, good in optical disk properties and free of occurrence of silver streak, or to an optical molding material which is small in the variation range of retardation depending on light wavelength and good in optical properties when it is molded into an optical disk substrate by injection molding in particular, and also to an optical disk substrate making use of such a molding material, and further to a production method of an optical disk substrate which is free of occurrence of silver streak upon its production, high in transfer accuracy and toughness, small in warpage, narrow in scatter of birefringence properties, particularly, concyclic birefringence, and good in optical disk properties.
2. Description of the Background Art
In recent years, amorphous plastics including polycarbonate and polymethyl methacrylate have been utilized and applied in a field of optical disks such as compact disk (CD), CD-ROM, DVD and MO and optical materials for optical lenses, optical fibers, light guide plates, etc., and their various new uses have been investigated.
However, polycarbonate and the like is high in dependence of retardation (birefringence) on wavelength, and their molded products have small retardation at a specific wavelength, but become great in retardation in the case where light having any other wavelength is used. Therefore, such properties have been unsatisfactory as product characteristics required.
More specifically, optical instruments have currently taken striking strides. For example, drives capable of conducting recording and reproduction on plural optical disks (for example, 780 nm in the CD system and 650 nm in DVD system) different in wavelength of light used are going to come on the market. Further, in the next generation drives, the development of those capable of coping with blue laser of short wavelength (about 400 nm) are being advanced. Therefore, there is a demand in the market for development of optical molding materials stable in optical properties (retardation) over a wide wavelength range.
In the case of optical disks that information is read and written by using a fine laser beam, their product characteristics are greatly affected by differences in their optical properties. Therefore, when a great change is caused in retardation depending on wavelength used, production conditions corresponding to individual media must be newly preset. Accordingly, if a material exhibiting comparatively fixed retardation over a wide wavelength range is provided, great merits such as improvement in production efficiency would be obtained. Therefore, there is an increasing demand for development of such a material. In addition, an optical disk capable of reading and writing by a plurality of laser beams can also be developed, if retardation from a low wavelength to a high wavelength becomes stable. Therefore, they may become a material and optical disk for developing new technical fields.
On the other hand, cyclic polyolefin resins have such features that they have a high glass transition temperature owing to the stiffness of their main chain structure, are amorphous and high in light transmittance because a bulk group is present in the main chain structure, and exhibit low birefringence properties because they are small in anisotropy of polarizability, and attract attention as transparent thermoplastic resins excellent in heat resistance, transparency and optical properties.
Such cyclic polyolefin resins are disclosed in, for example, Japanese Patent Application Laid-Open Nos. 132625/1989, 132626/1989, 218726/1988, 133413/1990, 120816/1986 and 115912/1986.
In recent years, the cyclic polyolefin resins have been investigated in application thereof to fields such as various kinds of optical materials, and sealing materials such as sealants for optical semiconductors.
However, the cyclic polyolefin resins are comparatively low in toughness due to their bulky structure and hence cause burr by gate cutting and circumferential burr by handling and the like upon production of products such as optical disks and optical lenses, so that yield of such products may be lowered, or secondary processability thereof may be markedly inhibited.
On the other hand, in order to improve the toughness, it is considered to increase the molecular weight of a cyclic polyolefin resin. According to such a method, the toughness is improved, but the birefringence of molded products obtained from such a resin may become great to the contrary, so that the optical properties may be deteriorated to a marked extent.
It is generally conducted to control the molecular weight distribution for the purpose of balancing the toughness with the birefringence. In such a case, however, it has been relatively difficult to balance the toughness with the birefringence, and particularly, it has been difficult to obtain those small in birefringence in a thicknesswise direction or narrow in scatter of birefringence at concyclic positions (on a circumference of the same radius position), and further it has been considerably difficult to obtain a molded product having good optical disk properties with high yield because silver streak occurs on the surface of the molded product upon its production by injection molding or the like. In particular, a thin-wall molded product having a great surface area such as an optical disk is easy to cause silver streak, and it is difficult to reduce birefringence occurred upon the molding. In addition, since burr is easy to be formed upon gate cutting or handling, subsequent secondary processing for forming a metal film, organic film and/or the like involves a problem that the yield of the product is lowered.
In such an application field of optical disks, recording density of information has become high with the change of times, and so more improved optical properties have been required. Among these, there is great nee d to enlarge the numerical aperture of an objective lens due to the reduced diameter of a laser light spot used in reading and writing of information to an optical disk, and so great importance is attached to the influence of birefringence properties, particularly, birefringence in a thicknesswise direction or scatter of birefringence at concyclic positions on optical disks.
SUMMARY OF THE INVENTION
The present invention has been made on the basis of the foregoing circumstances.
It is the first object of the present invention to provide a molding material suitable for optical uses, or an optical molding material which is high in transfer accuracy and toughness, small in birefringence, particularly, birefringence occurred in a thicknesswise direction, good in optical disk properties and free of occurrence of silver streak when it is molded into an optical disk substrate by injection molding in particular, and an optical disk substrate made of the molding material.
The second object of the present invention is to provide a molding material suitable for optical uses, or an optical molding material which is high in transfer accuracy, narrow in concyclic scatter of retardation, small in the variation range of retardation in a wavelength range of from 400 nm to 830 nm in particular and good in optical properties in the above-described wide wavelength range when it is molded into an optical disk substrate by injection molding in particular, and an optical disk substrate made of the molding material.
The third object of the present invention is to provide a production method of an optical recording medium which is free of occurrence of silver streak upon its production, high in transfer accuracy and toughness, small in warpage, narrow in scatter of birefringence properties, particularly, concyclic birefringence, and good i
Hirono Tatsuya
Ishigaki Takatoshi
Ohtsuki Toshihiro
Sekiguchi Masayuki
Evans Elizabeth
JSR Corporation
LandOfFree
Optical molding material, and optical disk substrate and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical molding material, and optical disk substrate and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical molding material, and optical disk substrate and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2845752