Highly oriented thermotropic optical disc member

A dimensionally stable, circular, rigid and planar substrate, adapted for use as a support substrate for a radiation sensitive layer for an optical disc, said substrate having an external diameter of from 60 mm to 360 mm, a thickness of from 0.5 mm to 4 mm, a relative density of less than 1.8, a modulus of elasticity in the radial direction of from 9000 MPa to 18000 MPa, a coefficient of heat expansion in the radial injection which is less than 30 m/m/.degree.C., a deformation temperature under load of at least 150.degree. C., and, on part or all of at least one of its faces, an etching made at the time of the injection molding operation consisting of a groove in the form of a spiral or of concentric tracks, with a pitch of between 0.4 and 1 .mu.m;

• said substrate being formed by injection molding a thermotropic aromatic polyester polymer having a flow temperature ranging from 200.degree. to 350.degree. C. and an inherent viscosity of at least 1 dl/g in a mold fitted with a central injection system under the following conditions:
• (1) temperature of the molten polymer of from 280.degree. to 350.degree. C.;
• (2) injection pressure of from 80 MPa to 160 MPa;
• (3) a temperature of the mold walls which ranges from 100.degree. to 200.degree. C.;
• (4) an injection time which ranges from 2 to 10 seconds and (5) a holding pressure after injection which ranges from 40 MPa to 120 MPa, whereby said substrate is substantially perfectly smooth on the non-etched parts of its faces as reflected in a surface roughness of less than 0.05 m and is substantially perfectly planar as reflected in a warp angle of less than 1.times.10.sup.-5 radian.