MOUTH CYLINDRICAL PART OF SYNTHETIC RESIN BOTTLE BODY

摘要

This invention is aimed at equalizing as much as possible the effect of thread-formed portions on the crystallization of a molten resin material along the circumferential direction of the neck, and thereby, obtaining a resource-saving neck having high resistance to pressure and heat and a high, stable sealing property. The means of achieving these objects comprises (1) forming screw threads of a multi-threaded screw structure on the outer surface of the round neck wall, each screw thread comprising a main thread, a starting extension and an ending extension extending from the main thread, with width and height thereof being reduced gradually from the dimensions of the main thread measured at the main thread start point (a) and the main thread end point (b); (2) disposing the starting extension of a screw thread vertically above the ending extension of another thread; and (3) whitening the entire neck by thermal crystallization. Even if the neck 1 has a wide diameter or if the upper temperature limit is raised, the sinks are prevented from occurring in the top end face of the round neck wall 2, and the neck height can be restricted in spite of an increase in the diameter of the neck 1.