Pilkington Plc

John M Bradshaw

Richard Gelder

Ashley Carl Torr

Stanley Lythgoe

Ian Heaton Smith

A glass composition capable of being chemically strengthened by ion-exchange within 100 hours to provide a glass with a surface compressive stress of greater then 400 MPa and an ion-exchange depth greater then 200 microns comprising: SiO 58% to 70% (by weight), Al O 5% to 15%, Na O 12% to 18%, K O 0.1% to 5%, MgO 4% to 10%, CaO 0% to 1% with the provisos that the total of the Al O and MgO is in excess of 13%, the total of the amounts of Al O plus MgO divided by the amount of K O is at least 3 and that the sum of the amounts of Na O, K O and MgO is at least 22%.

Chemically toughened glasses

The present invention provides a process for producing a metal substrate for a thin film magnetic data storage disc, the process including the steps of: (a) providing a metal substrate; (b) printing a masking pattern onto at least a portion of the surface of the substrate; and (c) etching the unmasked surface of the substrate thereby to texture the substrate surface. The present invention also provides a metal substrate for a thin film magnetic data storage disc, the substrate having a roughened surface produced by preferential area etching, the roughened surface being composed of a regular pattern of peaks separated by valleys.

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Chorley, United Kingdom

John M Bradshaw