Abstract Pressure polished polycarbonate or polysulfone sheet substantially free of ripples, wiggles, extrusion die lines, and stresses and having a light transmittance greater than, a percentage haze lower than and a distortion lower than the as extruded sheet so that the polished sheet can be mechanically or thermo-formed into such articles as airplane windshields, canopies, protective headgears and see-through enclosures requiring minimal wall thickness, and a method of polishing the sheet between mirror finish plates using a combination of preheating to the heat distortion temperature at zero or minimal pressure, heating to higher temperatures while rapidly increasing the pressure so as to transfer the mirror finish from the plates to the sheet surfaces, and cooling the sheet while decreasing the pressure to fix the mirror finish in the sheet surfaces as the sheet contracts and solidifies.
The method of claim 1 wherein the sheet is polycarbonate and the heat distortion temperature in the pre-heat stage is about 270* F.
Claim 2
Dependent Claim
23 words
The method of claim 1 wherein the sheet is polysulfone and the heat distortion temperature in the pre-heat stage is about 320* F.
Claim 3
Dependent Claim
30 words
The method of claim 1 wherein the mirror polished plates are made of spring hard brass having a clean alpha crystal structure polished so that no polishing lines are visible.
Claim 4
Dependent Claim
16 words
The method of Claim 4 wherein the mirror polished brass plates are nickel or nickel-chrome plated.
Claim 5
Dependent Claim
30 words
The method of claim 1 wherein the sheet is at least three-eighths inch thick and the step of confining the sheet laterally throughout the entire process to restrain lateral flow.
Claim 6
Independent Claim
162 words
A method of pressure polishing an extruded transparent unfilled sheet of polycarbonate or polysulfone resin having ripples, wiggles, extrusion die lines and stresses comprising first pre-heating the sheet between a pair of mirror polished plates at a pressure of zero to a maximum of 50 psi to the heat distortion temperature of the sheet to expel air entrapped between the sheet and the plates, then increasing the pressure to about 300 to 500 psi while allowing the temperature to rise to about 310*-330* F to transfer the mirror finish of the plates to the sheet surfaces and substantially eliminating the ripples, wiggles, extrusion die lines and stresses, then reducing the pressure to about 100 to 150 psi while elevating the temperature to a maximum of 360* F to destroy the molecular memory of the material, then cooling the sheet while reducing the pressure to fix the mirror finish in the sheet surfaces as the sheet contracts and solidifies and thermoforming said sheet.
Claim 7
Dependent Claim
27 words
The method of claim 7 wherein the pressure in the cooling stage is decreased to about 100 to 150 psi and the temperature to about 150* F.
Claim 8
Dependent Claim
47 words
The method of claim 8 wherein the temperature in the pre-heat stage is slowly raised to the heat distortion temperature, then the pressure is rapidly increased to about 300 to 500 psi in the next heating stage and the sheet is slowly cooled in the cooling stage.