Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1986-07-02
1988-11-15
Pertilla, Theodore E.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
525100, 525103, 525165, 525175, 525182, 525189, 525217, 525308, 525468, 525474, 525479, 526262, C08L 6900
Patent
active
047850531
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an optical resin material with good birefringence. More particularly, it relates to a resin material suitable as a material of an optical recording substrate for optically recording and reproducing video information and the like.
PRIOR ARTS
Recently, a system for reproducing images and sounds by detecting informations recorded in the form of minute irregularities formed on a disc substrate by means of laser beam spot and a system for high density recording and reproducing of informations through change of optical properties of a recording film applied on a surface of a substrate attract attention has been developed.
The disc substrate used in such recording and reproducing systems is required to have not only transparency but also such properties as dimensional stability, optical homogeneity and a small birefringence. Although plenty of duplicated disc substrates can be economically produced by using the resin material as a material of the disc substrate, it is widely recognized that the resin flows during molding of the disc substrate and molecules are oriented during cooling so that birefringence is induced. Optical anisotropy caused by birefringence is a fatal defect for the optical disc substrate.
The molecular orientation caused during molding is inevitable particularly in injection molding. From these points of view, a polymer comprising methyl methacrylate is the only resin material with little optical anisotropy.
When the hiterto known polymer comprising methyl methacrylate is used as the substrate material, it lacks dimensional stability due to its large hygroscopicity so that it has the drawback in that it wraps and twists in a humid atmosphere. Such a drawback is described in detail in Nikkei Elctronics, page 133 (published on June 7, 1982). Therefore, as a material for an acoustic compact disc, used is an aromatic polycarbonate resin with low hygroscopicity.
Since the aromatic polycarbonate resin contains atomatic rings with large anisotropy in its backbone chain, it is difficult to reduce birefringence of the molded substrate. To solve such problems, molding conditions including decreases in molecular weight are being investigated. However, since birefringence of the substrate originates from the material itself, it is impossible to constantly produce substrates with small birefrigence and it is very difficult to produce a substrate with small birefringence, having a diameter larger than that of the acoustic compact disc, by injection molding.
To improve dimensional stability, which is a drawback of the polymer comprising methyl methacrylate, copolymers comprising methyl methacrylate and aromatic vinyl monomer are proposed in Japanese Patent Kokai Publication (unexamined) Nos. 33446/1982, 162135/1982 and 88843/1983. The copolymer comprising methyl methacrylate and an aromatic vinyl monomer tends to induce birefringence and cannot be practically used.
Further, Japanese Patent Kokai Publication (unexamined) Nos. 5318/1983 and 127754/1983 propose copolymers of methyl methacrylate and cyclohexyl methacrylate for reducing hygroscopicity without deteriorating the birefringence. Since cyclohexyl methacrylate should be copolymerized in an amount larger than the aromatic vinyl monomer to decrease the hygroscopicity of the copolymer, the copolymer suffers from deterioration of heat resistance and strength.
For the disc substrate which is used not only for reproducing but also recording of informations, a material is required to have better birefringence and dimensional stability. However, any known resin material does not satisfy these requirements.
DETAILED DESCRIPTION OF THE INVENTION
One object of the present invention is, in view of the above circumstances, to provide an optical resin material the birefringence of which is kept at an acceptable level after injection or compression molding and which has such good dimensional stability that it does not warp or twist.
Further, the present invention intends to produce an ideal material as an
REFERENCES:
patent: 4196276 (1980-04-01), Schreckenberg et al.
patent: 4319003 (1982-03-01), Gardlund
patent: 4373065 (1983-02-01), Prest, Jr.
patent: 4495345 (1985-01-01), Kawakami et al.
Patent Abstracts of Japan, vol. 10, No. 38 (P-428) [2095], Feb. 14, 1986, Matsushita Denko K.K.
Imai Shozaburo
Isobe Michihisa
Ito Iko
Pertilla Theodore E.
Sumitomo Chemical Company Limited
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