JPH0560407B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a preform for stretch blow molding.

(Prior Art) Stretch-blow-molded plastic bottles, especially polyester bottles, have excellent transparency and suitable gas barrier properties, so they are used not only as containers for liquids such as liquid detergents, shampoos, cosmetics, soy sauce, and sauces, but also for beer, beer, etc. It is widely used in containers for carbonated drinks such as cola and cider, as well as beverages such as fruit juice and mineral water.

This type of plastic bottle is produced by stretching a bottomed tubular body, generally in the shape of a test tube and much smaller in size than the final container, in the axial direction in a blow mold within the stretching temperature range of the plastic material, and in the circumferential direction. It is manufactured by blow stretching.

The method for manufacturing the preform used in this method for manufacturing plastic bottles includes:
A pipe manufactured by extruding plastic material is cut to a predetermined length, one end of which is heat-sealed to form a closed end, and the other end is formed with a neck corresponding to the mouth and neck of the final container. and preform it. The so-called pipe method is known.

(Problems with the Prior Art) However, the axial and circumferential dimensions of the preform must be determined in relation to the axial and circumferential stretching ratios of the final container.

When manufacturing a preform using the above-mentioned pipe method, the axial dimension of the preform can be set arbitrarily according to the stretching ratio, but the circumferential dimension (diameter) is determined by the pipe diameter, so the circumferential stretching ratio It is difficult to set it arbitrarily depending on the situation.

For example, if the pipe diameter is close to the body diameter of the final container, it will be difficult to provide effective circumferential molecular orientation to the final container body. If this is not applied, the barrel wall will expand in the circumferential direction due to the internal pressure caused by the carbon dioxide gas filled as the contents, and this expansion will cause problems such as the labels attached to the barrel wall coming off. .

(Object of the Invention) Therefore, the object of the present invention is to provide a method for manufacturing a preform that can arbitrarily set the stretching ratio according to the final container shape and that can impart sufficient molecular orientation to the container body. be.

Another object of the present invention is to provide a method in which the stretching ratio can be changed without changing the pipe diameter in manufacturing a preform by the pipe method.

(Structure of the Invention) According to the present invention, a closed bottom is formed by heat-sealing one end of a tubular body obtained by cutting a pipe formed by extrusion molding into a predetermined length, and this plastic A method for manufacturing a preform for stretch blow molding is provided, which comprises drawing the body of a bottomed tubular body so that the diameter of the body is smaller than the diameter of the neck of the tubular body.

(Description of preferred embodiments of the invention) The present invention will be described below based on specific examples shown in the accompanying drawings.

In FIG. 1 showing each step in the preform manufacturing method of the present invention, a pipe obtained by extrusion molding of plastic, which is a container material, is cut into a predetermined length to manufacture a tubular body 1 (step (A)).

In the present invention, plastics for the container material include plastics known as container materials, such as isotactic polypropylene, crystalline propylene-ethylene copolymer, crystalline propylene-butene-1 copolymer, and crystalline propylene-butene-1 copolymer. -1-Olefin diameter resins such as ethylene copolymer, ethylene-vinyl alcohol copolymer, etc.; Polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene terephthalate/isophthalate; nylon 6, nylon 6,6, nylon 6,10 Polyamides such as polystyrene, styrene-butadiene block copolymers, styrene-acrylonitrile copolymers, styrene-butadiene-acrylonitrile copolymers (ABS resins), and other styrenic copolymers; polyvinyl chloride, vinyl chloride-vinyl acetate Vinyl chloride copolymers such as copolymers; acrylic copolymers such as polymethyl methacrylate and methyl methacrylate/ethyl acrylate copolymers; polycarbonates, etc. are used. These thermoplastic resins may be used alone or in the form of a blend of two or more.

Further, the pipe may have a single layer structure, or may have a laminated structure of two or more layers, for example, by simultaneous melt extrusion.

In the present invention, a closed bottom portion 2 is formed on one end surface of a tubular body 1 obtained by cutting a pipe to form a bottomed tubular body 3 (step (B)).

The bottom is formed by heating one end of the pipe to an appropriate temperature, placing it in a mold, and blowing high-pressure air into it.

According to the present invention, the bottomed tubular body 3 thus obtained is subjected to drawing processing, and the diameter l of the body 4 is adjusted to the neck 5.
(step (C)).

By performing such a drawing process, it is possible to make the body diameter smaller than the original pipe diameter while increasing the body wall thickness without reducing the body wall thickness, and thus the final container. This makes it possible to provide sufficient molecular orientation depending on the diameter of the body. In this case, the aperture ratio l/m may be determined as appropriate depending on the diameter of the body of the final container.

This drawing process can be performed by a method known per se, for example, as shown in FIG.
The entire bottomed tubular body 3 is heated to an appropriate temperature, and held in a mold 10 having a cavity space that conforms to the desired shape, and an extrusion punch (not shown) is inserted if necessary. This can be done by

The drawing process is performed to reduce the diameter of the body, and the bottomed tubular body 6 is formed with a threaded portion 7 corresponding to the neck of the container at the neck 5, thereby forming a bottomed preform 8 (step (D)). .

The threaded portion 7 is easily formed by heating the neck portion 5 to an appropriate temperature, placing it between screw molds, and blowing high-pressure air into the neck portion 5. Of course, such a threaded portion 7 can also be formed by injection molding separately from the preform body, and by fusing and integrating the preform body and the threaded portion within or outside the injection mold. can be done.

Incidentally, such a threaded portion 7 may be formed at a stage before the drawing process, or may be formed at a stage after the drawing process as described above.

Further, in the present invention, during the drawing process described above, the connecting portion 20 between the neck portion 5 and the body portion 4 is formed in the mold 1 so as to form a constant slope as shown in the figure.
It is preferable to define a shape such as 0.

This connecting portion 20 usually corresponds to the shoulder of the final container, so if the connecting portion 20 forms a horizontal surface, that is, the transition from the neck 5 to the body 4 is step-like. In some cases, the connecting portion 20 is stretched irregularly, and a portion of the formed bottle from the neck to the body has irregularly varying thickness, resulting in a lens effect due to the variation in thickness. Therefore, when the container is observed, the inside of the container appears to be significantly distorted, resulting in a poor appearance of the container itself, which tends to reduce its commercial value.

As described above, when the connecting portion 20 forms an inclined slope, the above-mentioned disadvantages can be effectively prevented.

Furthermore, during the drawing process described above, by blowing air simultaneously with the drawing process, it is also possible to form the bottom part into an arbitrary shape.

In the above-mentioned method of the present invention, when applying the so-called one-stage method in which the manufactured preform is stretch-blow-molded as it is without cooling, the temperature of the preform is adjusted using the mold used during drawing. is possible.

The preform thus obtained is subjected to stretch blow molding, which is known per se, to form the final container.

First, in stretch blow molding, a preform is preheated to a temperature suitable for stretching by means of hot air, an infrared heater, high frequency dielectric heating, or the like. The temperature range is preferably between 85 and 120°C, particularly between 95 and 110°C.

This preform is fed into a stretch blow molding machine known per se, set in a mold, and stretched in the axial direction by pushing a stretch rod.
Blow stretching in the circumferential direction by blowing fluid. At this time, the stretching ratio in the circumferential direction is larger than the stretching ratio in the axial direction, so that the molecular orientation in the circumferential direction is performed to a higher degree than the molecular orientation in the axial direction. The fact that the molecular orientation in the circumferential direction occurs more highly than the molecular orientation in the axial direction can be confirmed by subjecting the polyester wall of the bottle body to an in-plane orientation measurement method using fluorescence polarization method. Confirmed by comparing with the coefficient.

(Effects of the Invention) According to the present invention, it is possible to vary the diameter of the body portion of the preform without reducing its wall thickness.

Therefore, especially when manufacturing a preform from a pipe, it is possible to manufacture a preform that imparts a high degree of molecular orientation to the final container shape without being limited by the pipe diameter. That is, the remarkable advantage that the stretching ratio can be adjusted appropriately and a container having sufficient strength can be obtained is achieved.

[Brief explanation of the drawing]

FIG. 1 is a process diagram showing an example of the manufacturing method of the present invention. 3... Bottomed tubular body, 4... Torso, 5... Neck,
7...Threaded part, 10...Mold, 20...Connection part.

Claims (1)

[Claims] 1. One end of a tubular body obtained by cutting a pipe formed by extrusion molding into a predetermined length is heat-sealed to form a closed bottom, and this plastic tubular body with a bottom is 1. A method for manufacturing a preform for stretch blow molding, comprising drawing a trunk portion of the body so that the diameter of the trunk portion is smaller than the diameter of the neck portion of the tubular body. 2. The manufacturing method according to claim 1, wherein a portion corresponding to the container neck is formed in the neck of the bottomed tubular body before or after the drawing process.