Nippon Zeon Company, Ltd.

Sony Corporation

Masayoshi Oshima

Teiji Kohara

Tadao Natsuume

Yoshikatsu Nishi

Hiroshi Takino

Toshihide Murakami

Miyuki Kuromiya

Takeshi Sasa

Tohru Hosaka

Eiki Oyanagi

Yasuyuki Imai

Disc medium substrate and disc device

Using a thermoplastic norbornene type plastic as a material for the magnetic disc substrate, a magnetic disc substrate having a small deformation and a high modulus of elasticity is prepared. By optimizing the thickness of the substrate, the resonance frequency of the magnetic disc can be elevated to a level higher than the servo band. As a result, a magnetic disc substrate can form a servo mark having a high positional precision, and can carry out tracking with high precision.

Magnetic disc substrate and a magnetic disc using the same

Ring-opening hydrogenated copolymer and process for producing the same

A molding material suitable as an optical material and an optical recording medium formed of the molding material are disclosed. The molding material comprises a hydrogenated product of a polymer formed by ring-opening polymerization of a norbornene-type monomer, the hydrogenated product having a number average molecular weight (Mn) of 20,000 to 50,000, a weight average molecular weight (Mw) of 40,000 to 80,000 and a molecular distribution (Mw/Mn) of not more than 2.5 and having a volatile content of not more than 0.3% by weight.

Molding material

There is disclosed an optical disk having an optical reflectivity of 70% or above which comprises a substrate made of a thermoplastic saturated norbornene type polymer having a glass transition temperature of 100.degree. C. or above and a light reflecting layer formed by laminating, on said substrate, a multi-layer film constituted of at least one compound selected from the group consisting of metallic oxides and metallic fluorides.

Optical disk

(1) A solvent-soluble ring-opened polymer constituted of 100-50% by weight of a norbornene derivative of monomer (A) represented by the formula ##STR1## wherein, R.sub.1 and R.sub.2 are the same or different and each denote hydrogen or alkyl and m denotes an interger of 0 to 2, and 0-50% by weight of another norbornene derivative of monomer (B) capable of undergoing ring-opening copolymerization with the preceding monomer (A), the polymer having a number average molecular weight of 10,000 to 50,000, a weight average molecular weight-to-number average molecular weight ratio (Mw/Mn) of up to 3, and a glass transition temperature of at least 80.degree. C., and (2) a process for producing such ring-opened polymers as stated above.

Ring-opened polymer from norbornene type of polycyclic monomer and

There is disclosed an optical material comprising a cyclization product of a conjugated diene polymer having a cyclization ratio of not less than 80% or a hydrogenated product thereof.

Novel optical material

A process for producing a polymer by ring-opening polymerization of a norbornene-type monomer, which comprises starting the ring-opening polymerization in the presence of a Ziegler-type catalyst consisting essentially of an organometallic compound of a metal belonging to the groups I to III of the periodic table and titanium tetrahalide, carrying out the ring-opening polymerization until the norbornene-type monomer shows a conversion ratio of not less than 60%, and then adding a tungsten and/or molybdenum-based metathesis catalyst to the polymerization reaction system to continue the ring-opening polymerization.

Growing community of inventors

Niiza, Japan

Masayoshi Oshima