HOLLOW PET VESSEL AND ITS MANUFACTURE

PURPOSE:To improve shock resistance without spoiling pressure resistance and heat resistance, by a method wherein thermo-crystallinity of a circumferential part and the center part of the thermo-crystallized central part of the bottom of a hollow PET vessel are made respectively high and low. CONSTITUTION:Molten resin is cast into a molding tool through an injection nozzle, a molded parison 11 is taken out by breaking the tool after cure through cooling and a neck part 3 and the central part 15 of the center of the bottom are heat-treated. A circumferential part 17 is thermo-crystallized at thermo- crystallinity of about 25-50%, the crystallinity is lowered toward the central part 16 of the bottom and that of the central part 16 is made 20% or less. In this instance, the outside diameter D1 of the circumferential part 17 which is to be crystallized is made into 15-95% of the outside diameter D2 (= the outside diameter of a belly part 12) of the bottom of the parison. Then a vessel main body is molded of the parison 11 with blow molding. In addition, the circumference of a circumferential part 17 of a thermo-crystallized sphere of the thermo-crystallized central part 15 of the bottom of the parison becomes a state of a circular or polygonal ring in succession.