Method of forming stretched acrylic sheets
AssigneePPG Industries, Inc.
InventorRobert B. Rau
Life of this patent
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Abstract
A stretched acrylic sheet which is to be formed into a vision panel at an elevated temperature has its major surfaces reheated to an elevated temperature to intentionally generate a class of surface formations thereon for subsequent removal by polishing prior to the formation of the final vision panel. Such surface deformations are otherwise undesirably generated during vision panel formation and detract from the optical quality of the final product.
Claims8
In a method of producing a vision panel having a stretched acrylic sheet as a portion thereof, comprising the steps of applying stretching forces at a first elevated temperature to a blank of acrylic material to provide a sheet of a desired physical configuration, cooling said sheet to a second temperature below the softening temperature of said acrylic material, initially polishing the major surfaces of said sheet to remove surface deformations therefrom, and heating said sheet to a third elevated temperature to form said vision panel, whereby said heating step generates additional surface deformations upon said major surfaces of said sheet, the improvement comprising the steps of:
- after practicing said cooling step and before practicing said heating step, increasing the temperature of at least the major surfaces of said sheet to a fourth elevated temperature sufficient to initiate the generation of said additional surface deformations without substantially altering the desired physical configuration of said sheet;
- recooling said sheet to a temperature below the softening temperature of said acrylic material;
- and
- secondly polishing the major surfaces of said sheet to remove said additional surface deformations.
Dependencies are inferred from the claim text.