| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an optical disk having high transparency, heat resistance, flaw resistance and excellent low birefringence. <P>SOLUTION: The protective layer is composed of a copolymer having (i) an unsaturated alkyl carboxylate unit, (ii) a glutaric acid anhydride unit of formula (1) (wherein R<SP>1</SP>and R<SP>2</SP>may be the same or different and are each a hydrogen atom or a 1-5C alkyl group), or a copolymer having (iii) an unsaturated carboxylic acid unit besides the units (i) and (ii), or copolymer having (iv) other vinyl type monomer unit. The optical disk has a protective layer having 0.01 to 0.6 mm thickness which composed of an absolute value of birefringence of 1.0×10<SP>-4</SP>or lower and reads information record out by laser beam through the protective layer. <P>COPYRIGHT: (C)2008,JPO&INPIT |
