SANS 10108: The Classification Of Hazardous Locations And The ....pdf
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SANS® 10108: 2004
10108
Category:Safety codes1. Field of the Invention
The present invention relates to an optical information recording medium, and more particularly, it relates to an optical information recording medium having a track guiding groove.
2. Related Background Art
Various optical information recording mediums have been conventionally proposed and commercialized. In particular, optical information recording mediums having a recording layer on a substrate are expected to be practically used because of advantages in size, mass productivity, and cost.
Such an optical information recording medium usually has a substrate formed of a transparent material and a recording layer formed on the substrate by a vacuum film formation method. In general, there is provided a track guiding groove which is formed on the substrate along an information track in order to separate the information track from other information tracks so that the information track can be separated from each other. In the information track, an information pit is formed in order to record information. When the substrate is formed of a transparent material, the information pit can be observed through the substrate.
In general, the substrate is formed of a polycarbonate resin having a thickness of 1 mm to 1.5 mm. The substrate is formed by injection molding or extrusion molding. It is necessary to perform finishing such as plane finishing of the surface of the substrate and/or surface roughness finishing for suppressing a surface state of the substrate and protecting the surface of the substrate from being damaged by foreign matter.
However, in the method of injection molding, a thick-walled portion is formed in a core formed of a resin material, which results in difficulty in removing the thick-walled portion. Therefore, a blank for injection molding is formed of a resin material having a small Young's modulus such as a nylon material or a polystyrene material, which is inferior in flatness. The blank is formed into a substrate for molding by an injection molding method, whereby the surface of the substrate is finished.
In the case where the substrate is formed of a transparent material, the surface roughness finishing is performed by lapping in order to suppress the surface state of the substrate. In this case, the surface of the substrate is finished by lapping. Therefore, the surface of the substrate cannot be flattened sufficiently by lapping. If the surface of the substrate is not flattened sufficiently, the surface state of the substrate is maintained in the next process such as coating. In this case, a surface
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