SOLID-PHASE PRESSURE FORMING FOR PROFIT.

This paper describes the solid-phase pressure forming (SPPF) technique which has been developed for mass production of containers for food and beverage. Unlike melt-phase thermoforming, SPPF forms solid plastic sheet at a temperature below the polymer's melting point. Whereas melt-phase forming of polypropylene takes place at temperatures ranging from 165 to 175 degree C, SPPF is performed at temperatures of 150 to 160 degree C (usually around the middle section to high end of the range, which is below its crystalline melting point of 166 degree C). Because solid plastic sheet is transformed into biaxially stressed containers or other hollow shapes by the application of a rapidly descending shaped plug, followed immediately by high-pressure air (100 psi for polypropylene), the containers are stiffer, have greater impact, tensile, and yield strength, develop transparency and gloss, as well as gas and water-vapor barrier properties, and are more uniform from piece to piece. Economic advantages of the new system are outlined.