Coated disk substrate having a small thickness region
AssigneeMitsubishi Chemical Corporation
InventorShoji Yokota
Life of this patent
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Abstract
A disk substrate for use in manufacturing a recording disk therefrom has an outer non-recording area, recording area, inner non-recording area and a central opening. The inner non-recording area includes a small thickness region having a thickness 70 to 90% of the thickness of the recording area and occupying an area 3 to 30% of the entire disk area including the central opening. The outer non-recording area has a large thickness region having a thickness larger than the thickness of the recording area. The disk substrate is free from warp and improves optical characteristics of the resultant disk.
Claims7
A molded disk substrate for use in manufacturing a recording disk comprising an outer non-recording area, an optical recording area, an inner non-recording area and a central opening area consecutively arranged from an outer periphery to a center of said disk substrate, said disk substrate having a first thickness in said recording area, a second thickness equal to 70 to 96% of said first thickness in a part of said inner non-recording area which part occupies 3 to 30% of an entire surface area of one side of said disk substrate including said central opening area, and a third thickness larger than said first thickness in a part of said outer non-recording area in the vicinity of said outer periphery whereby bith warping of the recording disk and the birefringence are reduced.
Dependencies are inferred from the claim text.