Method for hot crystallization of neck portion in preform of biaxial stretch blow molded bottle and jig for use in the method

Abstract

A method for thermally crystallizing a neck of a primary molded product for forming a bottle-shaped container made of polyethylene terephthalate as principal ingredient, said neck having a functional part and a neck ring at a lower end thereof, said functional part being formed with screw threads at an upper portion thereof and a bead ring below the screw threads, said method comprising: heating the neck, and then squeezing the bead ring heated to the heat-deformable temperature, from outside so as to form an outer diameter of the bead ring within a dimensional tolerance for deformation with regard to sealing effect. Preferably, the primary molded product includes at least one resin layer(s) made of polyethylene terephthalate as principal ingredient and at least one gas barrier material layer(s), and has a multilayer structure. Also, preferably, the bead ring is squeezed by 0.1 mm to 0.4 mm in terms of an outer diameter of the bead ring immediately after a completion of heating. Also, a jig for the above method is provided.

Description

BACKGROUND OF THE INVENTION [0001] This invention relates to a thermal crystallization method of a neck of a primary molded product of a bottle-shaped container having a single layer or a multilayer including a gas barrier material. The present invention also relates to a jig to be used for the thermal crystallization method of the neck. [0002] Bottles formed by biaxially oriented blow-molding of polyethylene terephthalate resin (to be referred to as PET resin hereinafter) have been made to show a small wall thickness in recent years for the purpose of cost reduction. Bottles having a thin wall are then required to show an effective gas barrier property in order to prolong the shelf life of the beverage contained in the bottle. [0003] This requirement is currently met by using a primary molded product (to be referred to as “preform” hereinafter) having a multilayer structure of PET resin / gas barrier material / PET resin for molding a bottle, or by forming a primary molded product by i...

AI Technical Summary

Benefits of technology

The invention provides a method for thermally crystallizing the neck of a primary molded product made of polyethylene terephthalate to form a bottle-shaped container. The method involves heating the neck and then squeezing the bead ring to form an outer diameter within a tolerance for sealing effect. The method prevents problems such as poor screwing performance and poor sealing effect by preventing deformation of the bead ring. The primary molded product may include a gas barrier material layer and a resin layer made of polyethylene terephthalate. The method can be carried out using a jig that engages the neck to prevent the primary molded product from being pulled up. The invention also provides a multilayer structure including a gas barrier material layer in a resin layer made of polyethylene terephthalate as principal ingredient.

Problems solved by technology

Even if the temperature of the injection machine is defined rigorously, it is difficult to accurately control the temperatures of the resin and the gas barrier material in the injection machine.

Thus, when molding the perform, part of the leading edge of the flowing gas barrier material is displaced toward the free end of the neck from the defined position on the circular periphery of the neck, while the remaining leading edge is displaced toward the body, because of a delicate change in the fluidity that is caused by fluctuations of various parameters including the injection pressure, the injection rate and temperature.

However, as pointed out above, it is difficult to accurately control the position of the leading edge of the gas barrier material layer at the time of injection molding.

Thus, there arises a problem that the neck is formed to show a diameter greater than the defined value.

As described above, the leading edge of the gas barrier material layer cannot be rigorously controlled for its position.

Particularly, if the functional part of the neck is not molded to the defined dimensions, problems such as a poor sealing effect and a poor screwing performance of the cap can arise.

Additionally, even in the case of a bottle having a single layer of polyethylene terephthalate, there can arise an occasion where the neck does not show its proper profile due to the fluidity of resin during the injection molding process.

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