Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-09-04
2002-08-13
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
57, 57, 57
Reexamination Certificate
active
06433102
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a hydrogenated polymer (may also be referred to as “a hydrogenated product of an aromatic vinyl polymer”) obtained by hydrogenating an aromatic vinyl polymer, a resin composition comprising the hydrogenated polymer and a production process of a substrate for information recording media, and more particularly to a substrate for information recording media, which is excellent in mechanical strength, a resin composition excellent in moisture resistance and molding and processing ability, and a hydrogenated product of an aromatic vinyl polymer suitable for use in providing such substrate and resin composition. The present invention also relates to a high-quality hydrogenated product of an aromatic vinyl polymer containing little foreign matter.
BACKGROUND ART
Hydrogenated polymers obtained by hydrogenating aromatic rings in aromatic vinyl polymers such as polystyrene have heretofore been known to be molding materials suitable for use in substrates for information recording media, which are small in birefringence. For example, Japanese Patent Application Laid-Open No. 43910/1988 proposes the use of polymers containing at least 30% by weight of a vinylcyclohexane polymer component in its molecular chain for molding materials for optical disk substrates. The publication specifically discloses examples where a hydrogenated product of an aromatic vinyl polymer having a hydrogenation rate of 97% at the aromatic ring portion thereof, a weight average. molecular weight (Mw) of 92,000 and a molecular weight distribution (Mw/Mn) of 1.84, or a hydrogenated product of an aromatic vinyl polymer having a hydrogenation rate of 85% at the aromatic ring portion thereof, a weight average molecular weight (Mw) of 150,000 and a molecular weight distribution (Mw/Mn) of 1.87 was used to mold an optical disk substrate.
However, these optical disk substrates are recognized to be high in light transmittance, small in water absorptivity and relatively small in birefringence, but they have such problems that their mechanical strength is insufficient, the value of birefringence does not reach a sufficiently satisfactory level, and reliability such as long-term heat resistance is insufficient.
Japanese Patent Application Laid-Open No. 318015/1989 proposes optical disk substrates formed of a polyvinylcyclohexane resin having a number average molecular weight (Mn) of at least 50,000 and a softening point of at least 150° C. The publication specifically discloses an example where polyvinylcyclohexane having a hydrogenation rate of 99% at the aromatic ring portion thereof and a weight average molecular weight (Mw) of at least 160,000 was used to mold an optical disk substrate. However, the birefringence of this optical disk was not reduced to a satisfactory level.
For reasons of the above-described facts, there is a strong demand for development of a molding material for providing a substrate which has a sufficiently small birefringence value, is excellent in mechanical strength and is balanced among various properties required of the substrate at a high level.
Further, it has been proven that in the hydrogenated products of the aromatic vinyl polymers, impurities such as finely particulate matter and fibrous matter are mixed in various processes such as their polymerization processes, hydrogenation processes and post-treatment processes, polymerization catalysts and hydrogenation catalysts remain, or gel-like matter is formed, and so they contain an extremely great number of foreign matter when they are minutely inspected. When the hydrogenated products of an aromatic vinyl polymers containing these foreign matter in plenty are molded into moldings such as optical parts such as optical lenses, and substrates for information recording media such as optical disk substrates and magnetic disk substrates, the performance and functions of the resulting moldings are seriously and adversely affected, since these fine foreign matter is not compatible with the hydrogenated products of an aromatic vinyl polymers.
In the case of, for example, an optical lens, a haze value becomes great when the fine foreign matter is contained in plenty, and so the lens tends to become a state that an opaque haze hangs on the surface or in the interior of the lens. When the fine foreign matter is present in plenty in the case of the optical disk, it forms the case of noise and signal error upon reproduction of a signal. A high-capacity optical information recording medium such as DVD (digital video disk) is extremely greater in recording density than the conventional CD (compact disk) and LD (laser disk), and the spot diameter of a laser beam used in recording and reading of information is also extremely small. Accordingly, even the fine foreign matter in the optical disk substrate tends to cause an error, and a bit error rate tends to become great. When the fine foreign matter is present in plenty in the case of a magnetic disk substrate, these foreign matter appears as a great number of projections on the surface of the substrate. A tracking error is easily caused by the surface projections. When a molding formed of a hydrogenated product of an aromatic vinyl polymer containing these foreign matter in plenty is used as a semiconductor related parts such as a carrier (plastic case) of a silicon wafer, the fine foreign matter occurs out of the molding to easily contaminate the silicon wafer.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a molding material capable of providing a substrate for information recording medium having a sufficiently small birefringence value and excellent mechanical strength in combination.
Another object of the present invention is to provide a hydrogenated polymer and a hydrogenated polymer resin composition as molding materials which can provide a substrate having a sufficiently small birefringence value and excellent mechanical strength and moisture resistance, and are also excellent in molding and processing ability, and a substrate for information recording media obtained by molding such a resin material.
A further object of the present invention is to provide a high-quality hydrogenated product of an aromatic vinyl polymer, which is extremely little in the content of fine foreign matter having no compatibility with the polymer.
The present inventors have carried out an extensive investigation with a view toward achieving the above objects. As a result, it has been found that substrates for information recording media molded from a specific hydrogenated polymer having a molecular weight within a specific range and a narrow molecular weight distribution and highly hydrogenated at its aromatic ring portion not only have a sufficiently small birefringence, but also are excellent in mechanical strength. It has further been. found that the above-described hydrogenated polymer the content of a component having a molecular weight (M) of at most 10,000 in which is not higher than a certain level, or a resin composition containing the hydrogenated polymer and a specific compounding additive can be molded into moldings excellent in moisture resistance such as anti-whitening property under high-temperature and high-humidity environment and surface smoothness in addition to the above-described properties.
In addition, it has been found that when the content of foreign matter having a particle diameter of at least 0.5 &mgr;m contained in a hydrogenated product of an aromatic vinyl polymer is reduced to 3.0×10
4
particles/g or lower, a molding material suitable for use in optical parts excellent in transparency, heat resistance and low moisture absorption property, small in birefringence and markedly improved in haze value can be provided.
The resin materials containing the hydrogenated product according to the present invention is most suitable for use as a material for optical parts, in particular, a material for substrates for information recording media. The present inventors have been led to completion of the present invention o
Kohara Teiji
Murakami Toshihide
Nagamune Tsutomu
Suzuki Teruhiko
Takahashi Haruhiko
Armstrong Westerman & Hattori, LLP
Lipman Bernard
Nippon Zeon Co. Ltd.
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