JPH0430888B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for injection molding a low-density parison used for manufacturing containers such as multilayer bottles made of synthetic resin.

[Conventional technology]

In this method, a thermoplastic resin is injected into a mold to form a parison with a thickness of 100 to 300 mm, and the parison is stretched in the axial direction in a blowing mold and air is sucked in to form a container such as a bottle. When making the body multilayered, it is necessary to make the parison multilayered.

Various methods have been considered for making the parison multilayered, but most of them involve press-fitting a thermoplastic resin with excellent barrier properties and heat resistance into the thermoplastic resin forming the parison.

In general, thermoplastic resins such as polyethylene terephthalate, polypropylene, and polyvinyl chloride are used as synthetic resins for containers such as bottles, and as intermediate layers, saponified ethylene vinyl alcohol copolymers, acrylonitrile, Thermoplastic resins such as polyvinylidene chloride, polyamide, polyamide copolymerized polyethylene terephthalate, polyethylene isophthalate, acrylic styrene, polystyrene, polycarbonate, polyethylene-2,6-naphthalate, and polyarylate are used.

[Problem that the invention seeks to solve]

The problem when injection molding the above multilayer parison is that the temperature of the two types of thermoplastic resins (hereinafter referred to as resins) released into the cavity is 200℃.
Based on the above, when a multilayer parison with three or more layers is injection molded using a double nozzle, an intermediate layer 2 is formed up to the open end surface of the parison 1, as shown in FIG. It is formed separately from the outer layer 1b. Although the intermediate layer 2 and the inner and outer layers 1a and 1b are formed during melting, they are not bonded together after cooling.
It is in a state where it is easy to peel off due to external pressure.

For this reason, even after the multilayer parison is formed into a bottle by stretch blow molding, the open end remains as the open end of the bottle, and when the bottle is used as a container for carbonated drinks, the open end surface becomes a cap liner, Even if the bottle is covered with a packing material, internal pressure will cause gas to enter between the two layers, causing peeling and damaging the impression of the bottle as a packaging bottle.

In addition, when hot filling is required, even if the intermediate layer is made of heat-resistant resin, the inner layer may peel off from the intermediate layer due to differences in heat shrinkage and deformation temperature, and the outer layer may also peel off, causing the intermediate layer to peel off due to differences in heat shrinkage and deformation temperature. Even though the layer provides heat resistance, thermal deformation occurs in the layer, making it impossible to seal the cap.

As a means to eliminate such drawbacks, some of the resin for bottle body molding is first injected, and then the intermediate layer molding resin and the container molding resin are injected. Since both resins are in a molten state, the position of the tip of the intermediate layer 2 cannot be determined, and due to the slight temperature difference in the cavity, setting the tip of the intermediate layer 2 close to the open end requires advanced molding technology. It is said that it requires

[Means for solving problems]

This invention was devised to solve the above-mentioned problems with the multi-layered parison, and its purpose is to allow the tip of the intermediate layer to always be located close to the open end. To provide a method for injection molding a multi-layered low-profile parison, thereby producing containers such as bottles with excellent barrier properties and heat resistance by forming multiple layers from the bottom of the low-profile parison to near the open end.

The feature of the present invention for the above-mentioned purpose is that in injecting the thermoplastic resin that forms the inner and outer layers of the parison and the thermoplastic resin that forms the intermediate layer into the cavity to inject a multi-layered parison with three or more layers, The width of the cavity end forming the opening end of the parison is formed to be smaller than the width of the neck molding cavity, and the inner and outer layer molding resin injected into the cavity prior to the cavity end is partially press-fitted to form the parison. The purpose is to form the open end.

This invention will be explained in detail below using examples shown in FIGS. 1 to 4.

〔Example〕

In the figure, 11 is an injection mold with a gate at the bottom;
2 is a neck mold consisting of a pair of split molds; 13 is a core mold that penetrates through the neck mold 12 and is located inside the injection mold; around this core mold 13, the injection mold 11 and the neck mold 12 A cavity 15 of a parison 14 is formed.

The body and bottom of the parison 14 are formed by a cavity 15a on the injection mold side, and the neck is formed by a cavity 15b on the neck mold side. The upper end of the cavity of the neck mold 12, that is, the portion 17 forming the open end 16 of the parison 14 is
The width is smaller than the width of the neck molding cavity 15b.

As shown in FIG. 2, the width t of the open end molded portion 17
is formed in a range of 0.5 mm to 2.5 mm, depending on a comparison with the width T of the neck molding cavity 15b, and the height H is preferably up to 2.5 mm. If these values are exceeded, it becomes difficult to partially press fit the resin into the open end molded portion 17, and it becomes difficult to cool the open end 16 faster than other parts.

Therefore, the width t is wider than the neck molding cavity 15b.
In the open end molded part 17 formed small, even if it is cooled like the neck molded cavity 15b,
The open end 16 of the parison 14 formed therein is thin and is more easily cooled than other parts.

Therefore, first, the inner layer 14a and the outer layer 1 of the parison 14 are
4b and the required amount of resin to form the cavity 15.
When the resin forming the intermediate layer 18 is injected into the cavity 15 alone or together with the inner and outer layer molding resin, a part of the previously injected inner and outer layer molding resin is press-fitted into the open end molding part 17 to form the parison. 14 open ends 16 are formed. In addition, since the open end 16 cools and solidifies almost simultaneously with press-fitting, even if the secondarily injected intermediate layer molding resin reaches the open end 16, the open end 16 has already solidified and presents resistance. In this case, the intermediate layer resin cannot enter the open end 16, and its tip is located below the open end 16.
That is, it stops at the upper end of the parison neck.

As a result, the parison 14 injection molded therein
In this case, the intermediate layer 18 exists close to the opening end, and the opening end surface is formed by the inner layer 14a and the outer layer 1.
4b, and completely covers the tip of the intermediate layer 18.

〔Effect of the invention〕

As described above, the width of the cavity end forming the parison opening end is formed smaller than the width of the neck molding cavity, and the resin press-fitted into the cavity end is affected by heat more than other parts. The intermediate layer molding resin injected later is prevented from entering by cooling and solidifying, and an open end is formed there with one resin, and the tip of the intermediate layer molding resin is brought close to the open end. Since the intermediate layer is positioned, there is no possibility that the intermediate layer will be able to penetrate the open end of the resin forming the parison and be exposed at the open end surface. This prevents the inner and outer layers from peeling off from the intermediate layer at the open end, making it possible to stretch-blow mold containers such as multilayer bottles with excellent barrier properties or improved heat resistance due to the intermediate layer. The parison can be shaped.

In addition, when molding, there is no need for any other special means, just by narrowing the width of the open end molding part, and the molding can be done using the conventional multilayer injection molding method as is. have

[Brief explanation of drawings]

Fig. 1 is a longitudinal sectional front view of the mold device showing the state before and after molding, Fig. 2 is a longitudinal sectional view of the parison neck forming section, Fig. 3 is a longitudinal sectional view of the parison neck, and Fig. 4 is a conventional FIG. 3 is a vertical cross-sectional view of the neck of the multilayer parison. 11... Injection mold, 12... Network mold, 13...
... core type, 14 ... parison, 14a ... inner layer,
14b... Outer layer, 15... Cavity, 16...
Open end, 17... Open end molding part, 18... Intermediate layer.

Claims (1)

[Claims] 1 When injection molding a multi-layered parison with three or more layers by injecting thermoplastic resin that forms the inner and outer layers of the parison and a thermoplastic resin that forms the intermediate layer into the cavity, the cavity that forms the open end of the parison is The width of the end portion is formed to be smaller than the width of the neck molding cavity, and the molding resin for the inner and outer layers injected into the cavity is partially press-fitted into the cavity in advance of the end portion of the cavity to mold the opening end of the balisong. Characteristic injection molding method for multi-layered low parison.