Process for preparing biaxially oriented hollow shaped articles from thermoplastic materials

A process for preparing transparent biaxially oriented hollow shaped articles from polyethylene glycol terephthalate by biaxial draw- and blow-molding which comprises the steps of:

• (a) introducing a thermoplastic material comprising polyethylene glycol terephthalate which is in the shape of a hollow preform into the mold cavity of a mold adapted for blow-molding in the heat;
• (b) bringing the thermoplastic material to about its temperature of biaxial orientation;
• (c) bringing the thermoplastic materials into close contact with the walls of the mold by applying an internal pressure to the interior of the hollow preform within the mold cavity by means of a pressure transfer fluid, at least a portion of the material being stretched sufficiently to avoid spherullitic crystallization upon heat treatment;
• (d) maintaining the thermoplastic material in close contact with the walls of the mold, including those portions of the material which have been stretched sufficiently to avoid spherullitic crystallization upon heat treatment, at a temperature which is suitable for molding and which is in the range from about the minimum effective temperature for biaxial orientation of the thermoplastic material to about 40.degree. C. above the minimum effective temperature for biaxial orientation of the thermoplastic material for a period between about 1 and about 25 seconds to form a partially thermo-stabilized hollow shaped article within the mold, the mold being maintained at a temperature below 130.degree. C., whereby an average temperature of the material of between about 80.degree.-120.degree. C. is reached during the period during which the internal pressure is maintained;
• (e) allowing the hollow shaped article to cool;
• and
• (f) removing the hollow shaped article from the mold.