JP7639560B2 - Preform and method for manufacturing synthetic resin container - Google Patents

Description

The present invention relates to a preform for producing relatively small-volume synthetic resin containers by blow molding, and to a method for producing such synthetic resin containers.

Conventionally, synthetic resin containers are made by producing a bottomed cylindrical preform using a thermoplastic resin such as polyethylene terephthalate, and then molding this preform into a bottle shape using biaxial stretch blow molding or other methods. These containers are used in a wide range of fields as containers for various beverages, seasonings, etc.

This type of synthetic resin container has become increasingly common in recent years, and the products using such containers have become more diverse. In this situation, containers of various volumes have been proposed depending on the product contents, ranging from large volumes exceeding 2000 mL to small volumes of around 100 mL (see, for example, Patent Document 1).

JP 2017-210266 A

However, according to the inventors' research, it was found that when blow molding a preform made for a relatively small-capacity container, for example 120 mL or less, there is a tendency for whitening to occur at the bottom of the molded container due to overstretching. As a countermeasure, it was also found that if the heating temperature is increased when heating and softening the preform prior to blow molding, there is a risk of core misalignment occurring, in which the stretching direction deviates from the axial direction when the preform is stretched in the axial direction.

Based on this knowledge, the inventors conducted extensive research to provide a preform suitable for producing relatively small-volume synthetic resin containers by blow molding, and as a result, they completed the present invention.

The preform according to the present invention is a preform for manufacturing a synthetic resin container by blow molding, and is formed in a bottomed tubular shape including a mouth portion that is open at the upper end and a body portion that is closed at the lower end, the mass of the portion below the neck ring provided at the mouth portion is 6 g or less, the outer diameter of the neck portion formed directly below the neck ring is 23.4 to 24.0 mm, the outer diameter of the body portion is reduced to 60 to 80% of the outer diameter of the neck portion via a reduced diameter portion, and the minimum thickness of the neck portion is 41 to 71% of the maximum thickness of the body portion.

The method for producing a synthetic resin container according to the present invention is a method for producing a synthetic resin container by blow molding the preform, in which the longitudinal stretch ratio of the preform is 2.6 times or less.

According to the present invention, it is possible to manufacture synthetic resin containers of relatively small capacity by blow molding without causing whitening or core misalignment due to overstretching.

FIG. 2 is a partial cross-sectional view showing an outline of a preform according to an embodiment of the present invention. FIG. 2 is a perspective view showing an outline of a synthetic resin container produced by blow molding the preform shown in FIG. 1 .

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a partial cross-sectional view showing an example of a preform according to the present embodiment, and shows a longitudinal section on the right side of a central axis C shown by a dashed line in the drawing.
FIG. 2 is a perspective view of a round bottle-shaped container with a capacity of 65 mL, which is shown as an example of a synthetic resin container produced by blow molding the preform 1 shown in FIG.

First, in this embodiment, an example of a synthetic resin container to be manufactured will be described. The container 10 shown in FIG. 2 has a mouth 20 that serves as an inlet/outlet for pouring the contents, and a storage section 30 in which the contents are stored. The storage section 30 can be molded to include a body 40 whose upper end portion tapers toward the mouth 20 and is connected to the lower end of the mouth 20, and a bottom 50 that closes the lower end side in the height direction of the body 40. In the example shown, the container 10 is molded to have a generally cylindrical container shape, but the shape of the container 10 is not limited to this.

In the example shown in Fig. 2, the peripheral surface of the cylindrically formed mouth 20 is provided with a screw thread 2a for attaching a lid (not shown) that seals the container 10, but the sealing means for the container 10 is not limited to this. The lid may be attached by plugging, or a film-like lid having a heat seal layer may be heat sealed to the opening edge of the mouth 20.
Further, an annular neck ring 2b is provided on the lower end side of the mouth portion 20 so as to protrude outward in the circumferential direction.

The preform 1 shown in FIG. 1, which is suitable for manufacturing such a container 10 by blow molding, is formed in a bottomed tubular shape including a mouth portion 2 that is open at the top end and a body portion 3 that is closed at the bottom end. The mouth portion 2 of the preform 1 is not stretched by blow molding, and is the portion that will become the mouth portion 20 of the container 10 while generally maintaining its appearance. The mouth portion 2 of the preform 1 is provided with a screw thread 2a and a neck ring 2b, which are indicated by the same reference numerals as those given to the container 10.

Here, the top, bottom, left, right and length and width directions of the preform 1 are defined as shown in Figure 1 with the mouth part 2 facing up.

The preform 1 can be formed by injection molding, compression molding, or the like using any thermoplastic resin capable of being blow molded. Specifically, thermoplastic polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, amorphous polyarylate, polylactic acid, polyethylene furanoate, or copolymers thereof are used, and in particular, ethylene terephthalate-based thermoplastic polyesters such as polyethylene terephthalate are preferably used. Two or more of these resins may be mixed, or other resins may be blended. Polycarbonate, acrylonitrile resin, polypropylene, propylene-ethylene copolymer, polyethylene, or the like may also be used. The preform 1 formed using such a thermoplastic resin is not limited to being formed in a single layer, but can also be formed in a multilayer including a gas barrier layer, etc., depending on the characteristics required for the container 10.
In addition, various environmentally friendly materials have been developed for the above-mentioned materials. For example, mechanically recycled materials, chemically recycled materials, flake materials obtained by crushing used products, and plant-derived bioplastic materials may be used alone or blended with other materials.

Such a preform 1 is softened by heating to a state where it can be blow molded, and then set in a blow mold (not shown). If necessary, it is stretched in the axial direction (vertical direction) by a stretching rod, and is stretched in the axial and circumferential directions (horizontal direction) by blown air blown into the preform 1. At this time, the body 3 is stretched starting from below the neck ring 2b provided at the mouth 2, and the cavity shape of the blow mold is transferred, so that the stretched body 3 is molded to become the storage section 30 of the container 10.

The mouth 2 of the preform 1 is the portion that will become the mouth 20 of the container 10. For example, when a lid body that meets standards for this type of container, commonly referred to as a PET bottle, is attached to the mouth 20 to seal the container 10, the dimensions and shape of the mouth 2 must be designed according to the lid body. Also, when a film-like lid body having a heat seal layer is heat sealed to seal the container 10, it must be designed to be suitable as an injection outlet (or drinking spout) for the contents, so there is a limit to the degree of freedom in design. For this reason, in this embodiment, the portion below the neck ring 2b provided on the mouth 2 is designed as follows to achieve the intended purpose.

In other words, this embodiment is based on the idea of setting an upper limit on the amount of resin that forms the preform 1 for manufacturing a container 10 with a relatively small capacity (preferably 50 to 120 mL, more preferably 60 to 90 mL) so that the mass of the portion below the neck ring 2b provided on the mouth 2 is 6 g or less, and ensuring the wall thickness (amount of resin) of the body 3 by effectively distributing this limited amount of resin and preventing whitening due to overstretching.

More specifically, the neck portion 2c formed directly below the neck ring 2b of the preform 1 is usually formed so that its inner surface is flush with the inner surface of the mouth portion 2, but in this case, the thickness of the neck portion 2c is made as thin as possible, and the outer diameter D2c of the neck portion 2c is set to 23.4 to 24.0 mm so that the corresponding amount of resin is distributed to the body portion 3. The outer diameter D3 of the body portion 3 is reduced to 60 to 80% of the outer diameter D2c of the neck portion 2c via the reduced diameter portion 3a, so that the thickness of the body portion 3 increases by the amount of the reduced outer diameter, and as a result, the minimum thickness t2c of the neck portion 2c is designed to be relatively thin, at 41 to 71% of the maximum thickness t3 of the body portion 3.

The preform 1 can be molded by, for example, injection molding or compression molding, and the molding method is not particularly limited. However, when molding the preform 1 by injection molding, it is preferable to set the outer diameter D2c of the neck portion 2c in the above range and the minimum wall thickness t2c of the neck portion 2c to 0.76 to 1.41 mm in order to avoid short shots.

According to this embodiment, by designing the preform 1 as described above and effectively distributing a limited amount of resin to ensure the thickness of the body portion 3, it is possible to suppress overstretching during blow molding of the preform 1 and prevent whitening due to overstretching. From the viewpoint of more effectively suppressing overstretching, the maximum thickness t3 of the body portion 3 is preferably 1.6 to 3.4 mm.
In addition, as a measure to suppress overstretching when blow molding the preform 1, it is possible to increase the heating temperature of the preform 1 to soften the preform 1 and make it easier to stretch, but in this case, there is a risk of core misalignment occurring, in which the stretching direction deviates from the axial direction, when the preform 1 is stretched in the axial direction. According to this embodiment, by heating the preform 1 to an extent that does not cause such a problem and subjecting it to blow molding, it is possible to effectively suppress whitening due to overstretching while avoiding core misalignment.

In this embodiment, in order to more effectively achieve such an effect, it is preferable that the reduced diameter portion 3a of the body portion 3 is reduced in diameter while curving so as to be convex radially inward along the axial direction. In this way, it becomes easy to design the body portion 3 so that it is naturally stretched during blow molding and the wall thickness of the body portion 3 is increased by reducing the diameter. When the outer diameter D2c of the neck portion 2c is reduced to the outer diameter D3 of the body portion 3 through the reduced diameter portion 3a, the range in which the reduced diameter portion 3a is formed can be appropriately designed based on the balance between the reduction rate of the body portion 3 relative to the neck portion 2c and the maximum wall thickness t3 of the body portion 3. For example, it is preferable that the length _L0 along the axial direction from the base end of the neck ring 2b to the lower end of the reduced diameter portion 3a is 32 to 51% of the length L along the axial direction of the portion below the neck ring 2b.

In order to effectively prevent whitening due to overstretching, it is preferable to set the longitudinal stretch ratio to 2.6 times or less when blow molding the preform 1. In addition, it is preferable to design the preform 1 so that the length L along the axial direction of the portion of the preform 1 below the neck ring 2b is as long as possible, and it is preferable to set this length L to 25 to 35 mm, and it is particularly preferable to set this length L to 27.6 to 31.5 mm.

The present invention will be explained in more detail below with specific examples.

[Examples 1-5, Comparative Examples 1-3]
The preform shown in Fig. 1 was injection molded using polyethylene terephthalate. The mass below the neck ring, the outer diameter D2c of the neck portion, the diameter reduction rate D3/D2c of the outer diameter D3 of the body portion relative to the outer diameter D2c of the neck portion, the minimum wall thickness t2c of the neck portion, the ratio t2c/t3 of the minimum wall thickness t2c of the neck portion relative to the maximum wall thickness t3 of the body portion, and the ratio _L0 / _L of the length L to the lower end of the diameter reduction portion relative to the length below the neck ring were as shown in Table 1.

The containers obtained by blow molding the preforms in each of the Examples and Comparative Examples were evaluated by the following evaluation methods. The evaluation results are shown in Table 1.
Table 1 also shows the longitudinal stretching ratio during blow molding and the volume of the blow molded container.

<Evaluation method>
(Moldability)
When the preforms were injection molded, those which could be molded without the occurrence of short shots were marked with "◯", and those in which short shots occurred were marked with "X".
(Misalignment)
The bottom of the blow molded container was visually observed, and those in which the gate center was within 2 mm in diameter from the center of the bottom were marked "O", and those that were not were marked "X".
(Bleaching)
The bottom of the blow molded container was visually observed, and those in which no whitening was observed were marked with "◯", and those in which whitening was observed were marked with "X".

In Examples 1-5, the preforms could be injection molded without any short shots. Furthermore, the evaluation of the blow molded containers showed good results in all respects.
In contrast, in Comparative Example 1, t2c/t3 was small, and the resin flow path was narrow, resulting in a short shot. In Comparative Examples 2 and 3, t2c/t3 was large, and although there was no problem with moldability, misalignment and whitening were observed in the blow-molded container.

[Comparative Example 4]
The same preform as in Example 3 was used, and blow molding was carried out by changing the longitudinal stretching ratio to 2.81 times.

[Comparative Example 5]
The same preform as in Example 5 was used, and blow molding was carried out at a longitudinal stretching ratio of 2.9 times.

The results of Comparative Examples 4 and 5 confirmed that when the longitudinal stretch ratio exceeds 2.6 times, core misalignment and whitening occur in the blow-molded container.

The present invention has been described above by showing preferred embodiments, but it goes without saying that the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the present invention.

REFERENCE SIGNS LIST 1 Preform 2 Mouth portion 2b Neck ring 2c Neck portion 3 Body portion 3a Reduced diameter portion 10 Container

Claims (7)

A preform for producing a synthetic resin container by blow molding,
The container is formed in a cylindrical shape with a bottom, including a mouth portion that is open at the upper end and a body portion that is closed at the lower end,
The mass of the part below the neck ring provided on the mouth portion is 6 g or less,
The outer diameter of the neck portion formed directly below the neck ring is 23.4 to 24.0 mm;
The outer diameter of the body portion is reduced to 60 to 80% of the outer diameter of the neck portion via a reduced diameter portion,
A preform characterized in that the minimum thickness of the neck portion is 41 to 71% of the maximum thickness of the body portion. The preform according to claim 1, in which the reduced diameter portion reduces in diameter while curving in a radially inward convex manner along the axial direction. The preform according to claim 1 or 2, wherein the length along the axial direction from the base end of the neck ring to the lower end of the reduced diameter portion is 32 to 51% of the length along the axial direction of the portion below the neck ring. A preform according to any one of claims 1 to 3, in which the length along the axial direction of the portion below the neck ring is 25 to 35 mm. A preform according to any one of claims 1 to 4, in which the maximum wall thickness of the body is 1.6 to 3.4 mm. A preform according to any one of claims 1 to 5, in which the minimum wall thickness of the neck portion is 0.76 to 1.41 mm. A method for producing a synthetic resin container by blow molding the preform according to any one of claims 1 to 6,
A method for producing a synthetic resin container, characterized in that the longitudinal stretching ratio of the preform is set to 2.6 times or less.

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