| 摘要 |
A method is disclosed for conditioning strain hardenable thermoplastic materials, such as polyethylene terephthalate, so that a highly developed strain crystallized morphology may be established during a blow molding operation. In the method, a thermoplastic parison is heated to a temperature in a range conducive to molecular orientation and then initially stretched at that temperature. Next, the stretched parison is cooled to a temperature slightly below glass transition temperature and stretched further at the reduced temperature. The combined stretching in these two separate phases is chosen to condition the material so that it is either on the verge of being strained hardened or has actually started strain hardening. Thereafter, the parison may be again heated to a temperature conducive to molecular orientation and blown; to a final article, with the resulting expansion of the material during the blowing operation achieving the desired strain crystallized morphology and strain hardening.
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