JPS62187012A - Manufacture of hollow container - Google Patents

Abstract

PURPOSE:To manufacture a container with pressure-resistant bottom easily by pinching the bottom of a container from inside and outside with a stretching rod and a bottom mold and blowing in pressurizing fluid to swell and stretch. CONSTITUTION:During stretching, the bottom of parison is pinched with a stretching rod and a bottom mold. The mold face 11 at the end of the stretching rod 10 corresponds with the inner face of bottom of a container, while a mold face 13 at the upper end of a bottom mold 12 corresponds with the outer face of bottom of the container. As shown in the drawing of stretch blowing mold, the container is swollen and stretched by a pressurizing fluid blown in from a slit 14, and during stretching, a stretching rod 10 and a bottom mold 12 move downward pinching the bottom of parison 1. Pinching pressure by the stretching rod 10 and the bottom old 12 and the like are selected according to the thickness of container and kind of plastic to prepare a container having uniform and specified thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) This invention relates to a method for manufacturing a blow-molded container, and more particularly, a hollow container having a desired thickness and shape of the bottom wall is manufactured by stretch-blow molding. This article relates to a method for making eel.

(Prior art and its problems) In stretch blow molding, a vibrator-shaped or test tube-shaped parison is formed by extrusion molding or injection molding, and after adjusting the parison to the stretching temperature, pressurized gas is placed inside the parison. Stretch molding is performed by blowing into the material. In this molding process, the parison molding and stretching processes are independent, so each process is controlled under optimal conditions.Also, since the stretching temperature is low, molecular orientation is utilized to improve strength, shelf life, and aesthetics. It is possible to manufacture hollow containers that are not suitable.

Hollow containers obtained by stretch blow molding, for example biaxial stretch blow molding, have a sufficiently strong II! (
However, the degree of stretching varies greatly depending on the position around the bottom of the container, resulting in uneven wall thickness. When such a container is used to store contents that have a self-generating pressure, such as carbonated drinks, beer, aerosols, etc., the bottom wall portion is relatively easily deformed by internal pressure and has an uneven wall thickness. Deformation in which the bottom wall of the container protrudes outward due to internal pressure, ie, buckling, occurs.

In order to solve these problems, various molding methods have been proposed. For example, the bottom wall of a hemispherical container may be provided with legs that protrude outward in the shape of petals (Special Publication No. 48-5
No. 708), the bottom wall of the container includes an outer truncated conical portion that is smoothly connected to the body wall and extends inwardly and downwardly, and a truncated outer conical portion extending inwardly and upwardly from the lower end of the outer truncated conical portion. It has already been proposed (Japanese Unexamined Patent Publication No. 163137/1983) to provide the inner circumferential frustum portion extending in a predetermined angular and dimensional relationship. However, despite such proposals, it is difficult to form a bottom wall portion that has sufficient strength and has the intended shape and dimensions.

The present invention has been made against the background of the above-mentioned circumstances, and its purpose is to provide a method for manufacturing a hollow container having a desired wall thickness and shape of the bottom wall, particularly a container bottom suitable for a pressure-resistant container. It is to provide.

(Means for Solving the Problems) The present inventor has proposed a method of forming a parison (preform) having a shape and a bottom wall substantially matching the bottom wall of a container;
Furthermore, it has been found that it is effective to achieve the object of the present invention by holding the bottom of the parison between inside and outside molds during stretching of the parison to form a container bottom having a desired thickness and shape. This invention was completed.

That is, the method for manufacturing a hollow container of the present invention uses a parison whose temperature is adjusted to the stretching temperature, and simultaneously or simultaneously performs stretching in the axial direction of the parison and expansion and stretching in the circumferential direction of the parison in the cavity of a mold. A method for manufacturing a blow-molded container by sequentially performing the steps, the parison comprising: a core mold having a mold surface corresponding to the inner surface of the container bottom wall; and a cavity having a mold surface corresponding to the outer surface of the container bottom wall. The container is characterized in that it has a bottom wall that substantially matches the bottom wall of a container that is molded using a mold.

Hereinafter, the present invention will be explained in more detail with reference to the accompanying drawings.

The method of this invention is a method of manufacturing a plastic container, and examples of plastics that can be used in this invention include polyethylene, polypropylene, styrene resin, polyvinyl chloride, polyvinylidene chloride, polyamide resin,
Examples include polycarbonate resin and polyester resin.

When utilizing molecular orientation during molding, polyethylene terephthalate, polypropylene, etc. are preferred. It is also possible to blend various additives such as golent with other polymers, ultraviolet absorbers, colorants, etc. according to conventional techniques.

As shown in FIG. 1, the parison in this invention may be a bottomed parison having a bottom wall that is approximately the same as the bottom wall of a container manufactured by plastic injection molding, or a pipe obtained by extrusion molding. A parison with a bottom can be used, which is obtained by cutting the material into a size, fusing one end thereof, and molding the material into a shape substantially the same as the bottom wall of the container. FIG. 1 shows a bottomed parison 1 molded by injection molding. The parison 1 in this example has an injection nozzle 5 to a gate 6 in a space formed by cavity molds 2 and 2', a neck mold 3, and a core mold 4.
Molded by molten plastic injected through.

In this invention, the parison is temperature conditioned to the stretching temperature prior to blow molding. It is desirable to change the stretching humidity as appropriate depending on the type of plastic used. For example, when using polyester, 80 to 130°C,
In particular, the temperature is between 90 and 110°C.

Blow molding of the parison heated to the stretching temperature can be carried out by means known per se, such as sequential stretch blow molding or simultaneous stretch blow molding.

For example, in the case of Moe, the parison is mechanically stretched in the axial direction using a stretching rod under the blowing of fluid at a relatively low pressure, and then the parison is expanded in the circumferential direction by blowing fluid under a relatively high pressure. Stretch. In the latter case, fluid is blown in from the beginning under high pressure to simultaneously perform stretching in the circumferential direction and in the axial direction.

In a preferred embodiment of the invention, during stretching, the bottom of the parison is held between the stretching rod and the bottom die from the inner and outer surfaces. This will be explained with reference to FIGS. 2 and 3. Sandwich the neck of parison 1 between neck mold 3 and mandrel 8, and blow mold 1.
Load it inside 6.

In this case, prior to stretching, the bottom of the parison is clamped from its inner surface by a stretching rod 10 and from its outer surface by a bottom mold 12. The mold surface 11 at the tip of the stretching rod 10 corresponds to the inner surface of the bottom wall of the container, while the mold surface 13 at the upper end of the bottom mold 12 corresponds to the outer surface of the bottom wall of the container. As shown in FIG. 3 during stretch blow molding, the material is expanded and stretched by pressurized fluid blown through the slit 14. During this stretching, the stretching rod 10 and the bottom mold 12 move downward while holding the bottom of the parison 1 (container 15). The clamping pressure between the drawing rod 10 and the bottom mold 12 and the distance between the drawing rod 10 and the bottom mold 12 are as follows.
It can be changed as appropriate depending on the desired wall thickness of the container, the type of plastic, etc.

The bottom wall of a container obtained by the method of the invention is schematically shown in FIG. Further, a bottom wall portion of a container formed by conventional biaxial stretch blow molding is schematically shown in FIG.

As can be seen from the comparison between these two drawings, while the method according to the present invention provides a wall thickness sufficient to withstand the internal pressure at the lower convex portions 17 and 17' of the bottom of the container,
In conventional containers, the walls of the container become thin due to this protrusion.

Also, whereas the method according to the invention provides a wall thickness and a uniform wall thickness distribution at the central bottom portions 18 and 18', an excessive wall thickness and an uneven wall thickness distribution are achieved with the conventional method. become.

(Example) This invention will be specifically explained by the following examples.

Polyethylene terephthalate with an intrinsic viscosity of 1.0 is molded in an injection molding machine into a parison having a bottom approximately the same shape as the final container, and then the parison is reheated to a stretching temperature of 100°C, and then Stretch blow molding was performed using a blow mold as shown in FIG. 3 to obtain a blow molded container.

The thickness of the convex portion 17 at the bottom of the container is 1.0 mm,
The wall thickness of the central bottom is substantially uniform at 1,2111 mm,
The impact resistance and other strengths of the bottom part were excellent.

On the other hand, the wall thickness of the convex portion 17' at the bottom of the container formed by the conventional molding method is 0.5rnjR, the wall thickness of the center bottom is 2.5#IIm, and the impact resistance is It was considerably inferior to the resulting container.

(Operation and Effects of the Invention) In conventional stretch blow molding, the wall thickness of the bottom wall of the container is a3 J
: It was difficult to control the shape. This is because when the parison is stretched and expanded into the container, the degree of stretching and expansion differs depending on the location of the parison.

In this invention, during stretching, the bottom of the container is held between the molds from the inside and the outside. Therefore, this clamped mold can be desired to serve as a reference for drawing the parison.

In the case of plus deck containers for carbonated beverages, approximately 1 g/ai (
It is required to withstand high pressure (gauge pressure). By the manufacturing method of the present invention, it is possible to easily produce a container that can withstand sufficient internal pressure, especially a container that has a bottom wall.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of the injection mold used for molding the parison, Figure 2 is an explanatory diagram showing the state of the parison before stretching, and Figure 3
FIG. 4 is a sectional view of the bottom of the container according to the present invention, and FIG. 5 is a sectional view of the bottom of the container according to the conventional method. DESCRIPTION OF SYMBOLS 1... Parison, 2... Cavity type, 3... Neck type, 4... Core type, 5... Nozzle, 6... Game 1-18... Mandrel, 10... Stretching rod, 11
... Mold surface, 12... Bottom mold, 13... View surface, 14.
...Slit, 15...Container, 16...Blow mold,
17...Convex part, 18...Central bottom part. Applicant's agent Mr. Sato Figure 1

Claims (1)

[Claims] 1. Using a parison whose temperature is adjusted to the stretching temperature, stretching in the axial direction of the parison and expansion and stretching in the circumferential direction of the parison are performed simultaneously or in this order in the cavity of a mold to create a hollow A method for manufacturing a molded container, the parison being molded using a core mold having a mold surface corresponding to the inner surface of the container bottom wall and a cavity mold having a mold surface corresponding to the outer surface of the container bottom wall. 1. A method for manufacturing a hollow container, characterized in that the container has a bottom wall that substantially corresponds to a bottom wall of the container. 2. The manufacturing method according to claim 1, wherein the thickness and shape of the container bottom wall are controlled by stretching and forming the parison bottom wall while being held from the inner and outer surfaces thereof.