Magnetic disc substrate for external computer data storage units has a specified linear expansion coefficient in both thickness and radial directions

摘要

The disc substrate is molded in a thermoplastic resin whose linear expansion coefficient is 2.0/*10<->5 to 8.0/*10<->5cm/cm per deg C at 25-120 deg C in the thickness direction or a similar figure in the radial direction at 25-150 deg C or a similar figure in both radial and thickness directions at the stated temperature ranges for these directions. Independent claims are made for: a) a process for manufacturing the magnetic disc substrate in which the injection molded thermoplastic resin has a glass transition temperature of 135-165 deg C and moisture absorption of 0.001-0.01% at 60 deg C and 80% relative humidity. Molding parameters include a resin temperature of 250-400 deg C, injection rate of 50-300mm/s, tool clamping pressure of 30-150kg/sq cm and tool temperature of 100-160 deg C; b) a magnetic recording medium using the claimed substrate.