Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
1999-04-22
2001-10-30
McPherson, John A. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S270110, C428S064400
Reexamination Certificate
active
06309794
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to resin films for use in optical disks or magnetooptical disks, and particularly resin compositions for resin films serving as a protective layer or adhesive layer in direct contact with a metal film.
PRIOR ART
Optical disks and magnetooptical disks have been used as media taking advantage of light to read or read/write memory data.
For example, optical disks used as compact disks are made by forming a metal film having pits on a transparent resin disk to archive some data by pit sequences, then forming a protective layer on the surface of the metal film, and are irradiated with laser beams from the side of the transparent resin disk in the direction of the metal film to read the reflected beams.
In such optical disks, characteristics of the protective layer significantly influence the lives of the optical disks because they end their lives when atmospheric moisture penetrating the resin film corrodes the metal film to hinder reading of data, therefore various materials have been studied.
For example, JPA No. 206926/88 discloses an optical disk of a structure comprising a metal film sandwiched between two transparent disks wherein a high-hardness resin is used for a protective layer or adhesive layer to obtain a protective layer with low moisture permeability and high moisture resistance.
JPA No. 287847/89 discloses a protective layer having a given tensile stress in view of stress corrosion of the metal film and describes that a medium with high weathering resistance is obtained.
Thus, many studies have been devoted to characteristics, materials or the like of the protective layer to prevent corrosion of the metal film. However, high-hardness resins lower moisture permeability, but increase cure shrinkage to strain the optical disk as a whole leading to stress corrosion. On the contrary, resins based on tensile stress are thermosetting type which is more likely to cause thermal stress than UV-curable resins.
JPA No. 101656/90 discloses a protective layer with cure shrinkage, moisture permeability, water absorption and moisture absorption within a given range to prevent oxidation of the metal film and provide a highly reliable medium. However, it is difficult to control all these conditions in terms of manufacturing processes.
In order to solve the problems of the prior art described above, the present invention aims to provide a resin suitable for use as a protective layer or adhesive layer formed on the surface of a metal film.
SUMMARY OF THE INVENTION
In the course of studies of the relation between corrosion of the metal thin film of optical recording media and the material of the resin film used for a protective layer or adhesive layer, we found that the specific gravity of liquid oligomers which give corrosion-inhibitive resin films is lower than the specific gravity of conventional liquid oligomers.
Resin films which expose metal films to less corrosion are generally believed to have low water permeability. However, high-specific gravity liquid oligomers which have many bulky substituents are believed to prevent penetration of moisture by the bulky substituents to provide a resin film with low water permeability when they are polymerized.
Corrosion tests on resin films prepared from resin compositions using liquid oligomers with various specific gravities revealed that high-specific gravity liquid oligomers having an average specific gravity of 1.10 or more provide corrosion-inhibitive resin films.
The present invention is based on the above findings. According to an aspect of the present invention, a resin composition containing a photocurable resin involved in photopolymerization reaction wherein the photocurable resin comprises a liquid oligomer having a specific gravity of 1.10 or more.
Here the liquid oligomer may be an epoxy acrylate.
Further the liquid oligomer may be contained in the photocurable resin within the range from 35% by weight to 78% by weight both inclusive based on 100 parts by weight of the photocurable resin.
Here the liquid oligomer may be an epoxy acrylate.
The resin compositions can be photopolymerized to form resin films serving as a protective layer or adhesive layer.
According to another aspect of the present invention, the invention relates to an optical recording medium comprising a substrate and a metal film formed on the substrate wherein data are readably recorded in the metal film and a resin film is formed on the metal film by applying a resin composition and curing it by photopolymerization, characterized in that the photocurable resin in the resin composition contains a liquid oligomer having a specific gravity of 1.10 or more.
Here the liquid oligomer may be an epoxy acrylate.
Further the liquid oligomer may be contained in the photocurable resin within the range from 35% by weight to 78% by weight both inclusive based on 100 parts by weight of photocurable resin.
Here the liquid oligomer may be an epoxy acrylate.
The resin compositions of the present invention can be used to form a resin film on a metal film. The resin film can serve as a protective layer or adhesive layer for the metal film to form an optical recording medium. Optical recording media of the present invention include those read with laser beams such as compact disks as well as magnetooptical disks using a combination of laser means and magnetic means.
REFERENCES:
patent: 5609990 (1997-03-01), Ha et al.
patent: A-63-206926 (1988-08-01), None
patent: A-1-287847 (1989-11-01), None
patent: A-2-101656 (1990-04-01), None
Hayashi Kozaburo
Kominami Hiraku
Konishi Misao
Tanaka Mieko
McPherson John A.
Oliff & Berridg,e PLC
Sony Chemicals Corporation
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