| 摘要 |
<p>1. Smooth, thin, circular, rigid substrate made of polymeric material, for a magnetic recording disc, characterized by the following points : the said polymer is a thermotropic polymer chosen from wholly aromatic polyesters, alkylaromatic polyesters, wholly aromatic poly(esteramides), alkylaromatic poly(esteramides), aromatic polyazomethines, aromatic carbonate polyesters and mixtures of these polymers, the said polymer having a flow temperature which lies in the range from 200 degrees C to 350 degrees C and an inherent viscosity of at least 1 dlg**-1 ; during its preparation, the said substrate is subjected to a very high molecular orientation, the said preparation consisting in performing an injection-moulding operation on the thermotropic polymer in a suitable mould fitted with a central injection system for the polymeric material, the temperature of the walls of the said mould lying in the range from 100 degrees C to 200 degrees C, the temperature of the injected molten polymer lying in the range from 280 degrees C to 350 degrees C, the injection time lying in the range from 2 to 10 seconds, the injection pressure lying in the range from 80 to 160 MPa and the holding pressure after injection lying in the range from 40 to 120 MPa ; the said moulded substrate has a relative density of less than 1.8, a modulus of elasticity in the radial direction ranging from 9,000 MPa to 18,000 MPa, a coefficient of thermal expansion in the radial direction which lies between 10 and 20 mu m/m/degrees C and a deformation temperature under load of at least 150 degrees C.</p> |
