Preform and method for manufacturing synthetic resin container

Abstract

To provide a preform suitable for manufacturing a synthetic resin container of a relatively small volume by blow molding.SOLUTION: A preform 1 is formed in a bottomed cylindrical shape including a mouth part 2 opening on an upper end side and a body part 3 occluded on a lower end side, where a mass of a part lower than a neck ring 2b disposed in the mouth part 2 is 6 g or less; an outer diameter D2c of a neck lower part 2c formed immediately below the neck ring 2b is 23.4-24.0 mm; an outer diameter D3 of the body part 3 is reduced in diameter to 60-80% of the outer diameter D2c of the neck lower part 2c via a diameter reduced part 3a; and a minimum thickness t2c of the neck lower part 2c is 41-71% of a maximum thickness t3 of the body part 3.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a preform for producing a relatively small-volume synthetic resin container by blow molding, and to a method for producing such a synthetic resin container. [Background technology]

[0002] Conventionally, synthetic resin containers have been used in a wide range of fields as containers for various beverages, seasonings, and the like, by producing a bottomed cylindrical preform from a thermoplastic resin such as polyethylene terephthalate and molding this preform into a bottle shape by biaxial stretch blow molding or the like.

[0003] In recent years, this type of synthetic resin container has become more and more familiar, and the products using such containers have become more diverse. In this situation, containers of various volumes have been proposed according to the contents of the products, from large volumes exceeding 2000 mL to small volumes of about 100 mL (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-210266 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, according to the study by the present inventors, it was found that when blow molding a preform made for a container with a relatively small capacity of, for example, 120 mL or less, whitening due to overstretching tends to occur at the bottom of the molded container. As a countermeasure, it was also found that if the heating temperature when heating and softening the preform prior to blow molding is increased, there is a risk of core misalignment occurring, in which the stretching direction is deviated from the axial direction when the preform is stretched in the axial direction.

[0006] Based on these findings, the present inventors have conducted extensive research to provide a preform suitable for producing synthetic resin containers of relatively small capacity by blow molding, and as a result have completed the present invention. [Means for solving the problem]

[0007] The preform according to the present invention is a preform for producing a synthetic resin container by blow molding, and is formed in a bottomed cylindrical 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 a neck ring provided at the mouth portion is 6 g or less, the outer diameter of a 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.

[0008] In addition, 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 above-mentioned preform, in which the longitudinal stretching ratio of the preform is 2.6 times or less. Effect of the Invention

[0009] According to the present invention, it is possible to produce synthetic resin containers of relatively small capacity by blow molding without causing whitening or core misalignment due to over-stretching. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is a partial cross-sectional view showing an outline of a preform according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a perspective view showing an outline of a synthetic resin container produced by blow molding the preform shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] 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 this 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.

[0012] First, in this embodiment, an example of a synthetic resin container to be manufactured will be described. A container 10 shown in Fig. 2 has a mouth 20 which 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 is tapered toward the mouth 20 and connected to the lower end of the mouth 20, and a bottom 50 which 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 thereto.

[0013] 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, on the lower end side of the mouth portion 20, an annular neck ring 2b is provided which protrudes outward in the circumferential direction.

[0014] 1, which is suitable for producing such a container 10 by blow molding, is formed in a bottomed tubular shape including a mouth 2 that is open at the top end and a body 3 that is closed at the bottom end. The mouth 2 of the preform 1 is a portion that is not stretched by blow molding and that will become the mouth 20 of the container 10 while generally maintaining its appearance. The mouth 2 of the preform 1 is provided with a screw thread 2a and a neck ring 2b, which are indicated by the same reference characters as those attached to the container 10.

[0015] Here, the up-down, left-right and length-width directions of the preform 1 are defined as being in the state shown in FIG. 1 with the mouth portion 2 side facing up.

[0016] The preform 1 can be formed by injection molding, compression molding, or the like using any thermoplastic resin that can be 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, and 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.

[0017] 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), and while being stretched in the axial direction (longitudinal direction) by a stretching rod as necessary, it is stretched in the axial and circumferential directions (lateral directions) by blow air blown into the preform 1. At this time, the body 3 is stretched starting from below the neck ring 2b provided in the mouth 2, and the cavity shape of the blow mold is transferred to the body 3, so that the stretched body 3 is molded to become the container portion 30 of the container 10.

[0018] Since the mouth 2 of the preform 1 is the portion that becomes the mouth 20 of the container 10, for example, when a lid body that is regulated for this type of container generally called a PET bottle is attached to the mouth 20 to seal the container 10, the dimensions, shape, etc. of the mouth 2 must be designed according to the lid body, and even 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 that the degree of freedom in design is limited. 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.

[0019] In other words, this embodiment is based on the idea of ​​setting an upper limit on the amount of resin forming a preform 1 for manufacturing a container 10 of a relatively small volume (preferably 50 to 120 mL, more preferably 60 to 90 mL) so that the mass of the portion below the neck ring 2b provided at the mouth 2 is 6 g or less, and ensuring the thickness (amount of resin) of the body 3 by effectively distributing this limited amount of resin and preventing whitening due to over-stretching.

[0020] 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, and in this case, the outer diameter D2c of the neck portion 2c is set to 23.4 to 24.0 mm so that the thickness of the neck portion 2c is as thin as possible and 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 thinned to 41 to 71% of the maximum thickness t3 of the body portion 3.

[0021] Here, the preform 1 can be molded, for example, by injection molding or compression molding, and the molding method is not particularly limited. However, when molding the preform 1 by injection molding, in order to avoid short shots, it is preferable that the outer diameter D2c of the neck portion 2c is in the above range and the minimum thickness t2c of the neck portion 2c is 0.76 to 1.41 mm.

[0022] 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. As a measure to prevent 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 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 prevent whitening due to overstretching while avoiding misalignment.

[0023] In this embodiment, in order to more effectively achieve such an effect, it is preferable that the diameter-reduced portion 3a of the body portion 3 is reduced while being curved 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 of the body portion 3. When the outer diameter D2c of the neck portion 2c is reduced to the outer diameter D3 of the body portion 3 through the diameter-reduced portion 3a, the range in which the diameter-reduced portion 3a is formed can be appropriately designed based on the balance between the diameter-reducing 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 diameter-reduced portion 3a is 32 to 51% of the length L along the axial direction of the portion below the neck ring 2b.

[0024] In order to effectively suppress whitening due to overstretching, the longitudinal stretching ratio is preferably set 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 the length L is preferably set to 25 to 35 mm, and particularly preferably 27.6 to 31.5 mm. EXAMPLES

[0025] The present invention will now be described in more detail with reference to specific examples.

[0026] [Examples 1-5, Comparative Examples 1-3] Using polyethylene terephthalate, the preform shown in Figure 1 was injection molded. The mass below the neck ring, the outer diameter of the neck part D2c, the reduction ratio D3 / D2c of the outer diameter D3 of the body part to the outer diameter D2c of the neck part, the minimum thickness of the neck part t2c, the ratio t2c / t3 of the minimum thickness of the neck part t2c to the maximum thickness of the body part t3, and the ratio L0 / L of the length to the bottom end of the reduced diameter part L0 to the length below the neck ring L were as shown in Table 1.

[0027] 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.

[0028] <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 inspected, and those in which the gate center was within 2 mm of the center of the bottom were marked "O", and those that were not were marked "X". (whitening) 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".

[0029] [Table 1]

[0030] In Examples 1-5, when the preforms were injection molded, molding was possible without the occurrence of short shots. Furthermore, the evaluation of the blow molded containers also 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 containers.

[0031] [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.

[0032] [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.

[0033] [Table 2]

[0034] From the results of Comparative Examples 4 and 5, it was confirmed that when the longitudinal stretching ratio exceeded 2.6 times, the core shift and whitening occurred in the blow-molded container.

[0035] Although the present invention has been described above by showing preferred embodiments, it goes without saying that the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the present invention. [Explanation of symbols]

[0036] 1 Preform 2 Mouth 2b ネックリング 2c Lower bow 3 trunk 3a Reduced diameter 10 Container

Claims

1. 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 portion 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.

2. 2. The preform according to claim 1, wherein the reduced diameter portion reduces in diameter while curving in a radially inward convex manner along the axial direction.

3. 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.

4. The preform according to any one of claims 1 to 3, wherein the length along the axial direction of the portion below the neck ring is 25 to 35 mm.

5. The preform according to any one of claims 1 to 4, wherein the maximum thickness of the body portion is 1.6 to 3.4 mm.

6. The preform according to any one of claims 1 to 5, wherein the minimum wall thickness of the neck portion is 0.76 to 1.41 mm.

7. 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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