Process for the manufacture of hollowware articles composed of thermoplastic material

Claim 1

IN A PROCESS FOR THE MANUFACTURE OF TRANSPARENT, THERMOPLASTIC, HOLLOW-WARE ARTICLES OF IMPROVED TOUGHNESS AND STRENGTH CONSISTING OF HEATING A SHEET OF THERMOPLASTIC MATERIAL SELECTED FROM THE GROUP CONSISTING OF POLYSTYRENE AND ACRYLONITRILE STYRENE COPOLYMER, STRETCHING SAID HEATED SHEET BEFORE IT HAS COOLED FROM SAID INITIAL HEAT-TREATMENT, AND MOLDING SAID STRETCHED SHEET INTO THE SHAPE OF A HOLLOW-WARE ARTICLE, THAT IMPROVEMENT CONSISTING OF THE STEPS OF STRETCHING SAID SHEET LONGITUDINALLY AND LATERALLY WHILE CLAMPING OPPOSED EDGES WITH CO-ACTING, ARTIFICIALLY-COOLED CLAMPS GRIPPING SAID EDGES AND DRIVEN APART TO PROVIDE LATERAL STRETCHING AND SIMULTANEOUSLY CONTACTING SAID SHEET WITH SETS OF ROLLERS DRIVEN AT DIFFERENT SPEEDS BETWEEN SAID OPPOSED COOLED CLAMPS TO LONGITUDINALLY STRETCH SAID SHEET BEFORE COOLING TO INCREASE ITS AREA, THEREAFTER VACUUM MOLDING SAID STRETCHED SHEET AS SOON AS IT HAS BEEN STRETCHED BY CLAMPING TO THE TOP SURFACE OF A MOLD IN THE SHAPE OF A HOLLOW-WARE ARTICLE, SAID STRETCH SHEET BEING CLAMPED WHILE SIMULTANEOUSLY APPLYING VACUUM AT THE BASE AND SIDES OF THE MOLD TO THEREBY VACUUM FORM THE STRETCHED SHEET, CUTTING THE NON-VACUUM-FORMED PROJECTING EDGES OF THE SHEET AND REMOVING THE SHAPED ARTICLE FROM THE MOLD.