Method of avoiding distortion in synthetic resin sheet manufacture

Claim 1

IN A PROCESS FOR THE PREPARATION OF METHYL METHACRYLATE POLYMER SHEETING WHEREIN A LAYER OF MONOMERIC AND POLYMERIC METHYL METHACRYLATE SYRUP IS POURED ON A MOVING SUBSTANTIALLY HORIZONTAL SURFACE OF AN AQUEOUS LIQUID SATURATED WITH A SALT, THE ESTER BEING POLYMERIZED THEREON TO FORM A SHEET, THE LAYER OF ESTER AND THE SALT SOLUTION MOVING CO-DIRECTIONALLY THROUGH AN ENCLOSED CHAMBER, THE STEPS WHICH COMPRISE INTRODUCING AN INERT GAS INTO THE ENCLOSED CHAMBER AT A POSITION REMOVED FROM THE PLACE AT WHICH THE MONOMERIC AND POLYMERIC METHYL METHACRYLATE SYRUP IS POURED ON THE MOVING SURFACE OF THE SATURATED SALT SOLUTION AND BEYOND THE DIVISION BETWEEN THE POLYMERIZING MASS OF SYRUP AND THE SUBSTANTIALLY SOLID POLYMERIZED SHEET, MAINTAINING A STAGNANT VAPOR IN THE SPACE ABOVE THE SYRUP AND A FLOW OF THE INERT GAS IN THE SPACE ABOVE THE SOLID POLYMERIZED SHEET, WHEREBY OPTICAL DISTORTION OF THE POLYMERIC METHYL METHACRYLATE SHEET IS INHIBITED.