PRODUCTION OF POLYESTER HOLLOW MOLDED ARTICLE

摘要

This new method for producing polyester hollow-moulded articles comprises the following processes. (i) A preform of a thermoplastic polyester (comprising mainly ethylene terephthalate) is fitted into a hollow-moulding die which is kept at a temp. as high as possible within a range such that a final moulded article can be released without any deformation under non-cooling conditions. (ii) Blowing hot air, having a higher temp. (10 deg.C) than the preforming temp. continuously during process (iii). (iii) Expansion-stretching the preform in the two axial directions at a stretching speed of at least 2.5 times/sec. in the axial direction and at least 4.5 times/sec. in the circumferential direction. The preforming temp., T, is determined by the following equation. T0k(100.IV-8.DEG+42) where IV is the specific viscosity of the thermoplastic polyester (dl/g); DEG is the wt.% of diethyleneglycol contd. in the thermoplastic polyester; k is a number between 0.95 and 1.05. Typical conditions are as follows. The hollow-moulding die can be kept at a temp. of 100 deg.C -120 deg.C, IV=0.67 dl/g, DEG=2.0 wt.%. The blown hot air is 10 deg.C higher than the preforming temp. (T). The hollow moulded article has a deg. of crystallinity of at least 28%, at the centre of the shoulder of a container, and a refractive index in the direction of thickness on the outer surface side of the shoulder centre, which is greater than the refractive index in the direction of the thickness on the inner surface side of the shoulder centre, and has a distribution of mol. orientation of 0.95 or below.