Abstract: A method is disclosed for blow molding poly(ethylene terephthalate) preforms, such as injection molded parison, to achieve exterior surface embossed designs on blown containers without using profiled blow mold cavity walls. In the method, a raised profile is molded or otherwise formed on the exterior wall of the preform, defining a preform wall portion having embossed areas. Then the entire preform is heated to blowing temperature and it is also disclosed that when the raised portion is at the same time raised to a higher temperature the embossed design of the preform is opacified by crystallization without crystallizing the balance of the preform. Thereafter, the preform is blow molded under conditions such that the poly(ethylene terephthalate) material strain hardens in order to cause the different wall thicknesses to expand and stretch essentially proportionately.

Abstract: A method is disclosed for blow molding polyethylene terephthalate preforms, such as injection molded parisons, to achieve exterior surface indentations on blown containers without using profiled mold cavity walls. In the method, a profile is molded or otherwise formed in the exterior wall of the preform, defining a preform wall portion having sections of different thicknesses. Then, the preform is blow molded under conditions so that the polyethylene terephthalate material strain hardens in order to cause the different wall thicknesses to expand and stretch proportionately. As a result, the blown containers formed by this method include a surface contour which is essentially proportionately shaped to the surface profile formed on the pre-existing preforms.

Abstract: A method is disclosed for enhancing the yield strength and density of polyethylene terephthalate and other similar thermoplastic materials which are susceptible to strain hardening. In the method, the plastic material is thermally conditioned to a temperature within a range conducive to molecular orientation, and then is mechanically conditioned by stretching in a first direction to a length at least about 2.6 to 2.75 times the original length. Thereafter, the plastic material is stretched in a second direction, with strain hardening and strain-induced crystallization increasing drastically substantially immediately upon the initiation of the second stretching operation due to the mechanical conditioning by elongation during the first stretch.