Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Including application of internal fluid pressure to hollow...
Patent
1998-05-04
2000-05-30
Timm, Catherine
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
Including application of internal fluid pressure to hollow...
425525, 425533, B29C 4906
Patent
active
060688114
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method for forming an inner thread at the neck portion of a preform that is used for molding a packaging container such as a PET bottle having a thin body portion by stretch blow molding.
BACKGROUND ART
Most plastic bottle used for a packaging container has an outer thread at the neck portion and a cap is screwed on the thread to seal the opening portion. This outer thread can be formed by using a split mold, so there is no technical hardness in the injection molding. However, in the case of an inner thread, it is transferred from an outer thread pattern formed on the outer surface of a core mold. Therefore, the core should be pulled out rotating it after molding.
This pulling-out of the core is performed not only by rotating the core but also by moving the core in the axial direction. Therefore, the rotation and the axial moving should be synchronized. However, the synchronizing action mechanically limits the number of products per one molding. Thus, it is difficult to mold many products at one time like a preform molding because of a mechanical restriction. For this reason, even if a screw-plug is suitable for sealing the opening portion of a certain packaging container, a screw cap sealing with an outer thread is used to avoid difficulty of forming an inner thread.
The object of the present invention is to provide a novel method for forming an inner thread at the neck portion of the preform, the method enabling an injection core whose base portion forms an inner thread being pulled out after molding by enlarging the neck portion by blowing air, which has been desired in the molding of the preform for a packaging container such as a bottle having an inner thread at the neck portion thereof.
DISCLOSURE OF THE INVENTION
The present invention for achieving the above-mentioned object is a method for forming an inner thread in a preform, the method comprising the steps of forming a neck portion having a transferred inner thread using a neck mold having a mold surface of a barrel spacer inserted removably from the side of an injection mold for molding a body portion of the preform, and an injection core that is inserted into the injection mold through the neck mold, the outer surface of the base portion of the injection core being provided with a thread pattern; forming an expansion space within the neck mold by removing the spacer; and expanding the neck portion fully in the expansion space by blowing air between the injection core and the neck portion while a temperature of the neck portion is high enough for deforming, so that a gap for removing the core is formed between the inner surface of the neck portion and the outer surface of the base portion of the injection core.
Furthermore, the present invention provides another method for forming an inner thread in a preform, in which a double-wall neck portion is formed having an outer wall and an inner wall with the transferred inner thread by defining outer and inner portions of the neck cavity in the neck mold by the spacer, and while a temperature of the inner wall is high enough for deforming, the expansion space is formed between the inner wall and the outer wall by removing the spacer, and the inner wall is expanded by the blown air until the inner wall contacts the outer wall, so that the gap is formed for removing the core between the inner surface of the inner wall and the outer wall of the base portion of the injection core.
Furthermore, the present invention provides another method for forming an inner thread in a preform, in which the base portion of the injection core is tapered off toward the core end and the inner surface of the spacer facing the thread pattern of the base portion has substantially the same angle with the base portion so that neck portion or the inner wall is formed in the tapered angle with the thread formed by transferring onto the tapered inner surface, and then the neck portion or the inner wall is expanded fully in the expansion space by the blown air so as t
REFERENCES:
patent: 3029468 (1962-04-01), Valyi
patent: 3733309 (1973-05-01), Wyeth et al.
patent: 3969060 (1976-07-01), Rosenkranz et al.
patent: 4131665 (1978-12-01), Bodson et al.
A.K. Technical Laboratory Inc.
Timm Catherine
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