Experimental study of preform reheat temperature in two-stage injection stretch blow molding

Plastic bottles used for carbonated soft drink (CSD) packages are most commonly made from poly(ethylene terephthalate) (PET) by injection stretch blow molding (ISBM). The required bottle performance criteria vary with its application but typically include top-load strength, burst strength, optical clarity, thermal stability, and barrier properties. An experimental study of the preform reheat temperature was carried out for a 1.5-l PET bottle produced by a two-stage ISBM machine. The overall temperature of the preform was changed by controlling the reheat temperature of the preform; all the other process variables and preform dimensions were kept constant. Performance of the PET bottles for differing preform reheat temperatures was measured experimentally in terms of top-load strength, burst pressure resistance, environmental stress cracking resistance (ESCR), and thermal stability. It was observed that the ESCR values and the burst strength decreased with the increasing reheat temperature, whereas the top-load strength increased. Thermal stability tests confirmed that high-preform reheat temperatures had a detrimental effect on the self-standing feature of the bottles. Decreasing the reheat temperature as low as possible, while maintaining a certain preform temperature profile, ensured high ESCR and burst strength values and prevented the concaveness at the bottom of the bottle.