Roll finishing process

Claim 1

In the process for the preparation of die rolls used in the manufacture of plastic sheet for laminated safety glass which process comprises: A. selecting a metal roll which is free of pits, holes or scratches or other defects and which has a surface roughness of 32 RMS or smoother; B. blasting the roll with abrasive grit to obtain a saturated surface on the roll; C. plating the roll with a suitable metal; and then D. roughening the plated surface by blasting with fine grit; the improvement which comprises blasting the roll with glass beads after the grit blasting step and before the chrome plating step wherein the glass beads have a particle size larger than the base diameters of the prominent peaks on the surface of the roll whereby the size and number of peaks on the roll is reduced such that the sheet material cast on the roll has a sheet surface which is characterized by having: (1) an arithmetic average roughness in the range of from 12 to 18 × 10 - 5 inches (3.1 to 4.6 microns) as calculated around a roughness mean centerline drawn through the peaks and valleys on the surface of the sheet; and (2) a roughness height in the range of from 48 to 10 - 5 to 72 × 10 - 5 inches (12.2 to 18.3 microns) wherein at a distance of 0.4 mil (10.2 microns) or less from the mean centerline going in the direction to the center of the sheet there are substantially no valleys on the surface of the sheet.