JPH051730B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for manufacturing a blow molded container, and more specifically, a method for manufacturing a hollow container having a desired bottom wall thickness and shape by stretch blow molding. The present invention relates to a method of manufacturing the same.

(Prior art and its problems) Stretch blow molding involves forming a pipe-shaped or test tube-shaped parison by extrusion molding or injection molding, adjusting the temperature to the stretching temperature, and then blowing pressurized gas into the inside of the parison. Stretch molding is carried out using . 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. hollow containers can be manufactured.

Hollow containers obtained by stretch blow molding, such as biaxial stretch blow molding, have sufficient strength (pressure resistance, rigidity, flexibility, However, the degree of stretching varies greatly depending on the position around the bottom of the container, resulting in uneven thickness of the container wall. 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, that is, buckling occurs.

In order to solve these problems, conventionally,
Various moldings have been proposed. For example, the bottom wall of a hemispherical container may be provided with legs that protrude outward like petals (Japanese Patent Publication No. 48-5708), and the bottom wall of the container may be smoothly connected to the body wall. The outer frustum portion extending inwardly and downwardly and the inner frustum portion extending inwardly and upwardly from the lower end of the outer frustum portion are provided in a predetermined angular and dimensional relationship (particularly 163137) has already been proposed. 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 developed a method of forming a parison (preform) having a bottom wall portion substantially matching the bottom wall portion of a desired blow-molded container, and stretching the parison. It was discovered that it is effective to achieve the object of the present invention by holding the bottom of the middle parison with molds from the inside and outside, and forming the bottom of the container with the desired thickness and shape, and completed the present invention. It came to this.

That is, the method for manufacturing a hollow container of this invention is as follows:
A method for producing a blow-molded container by using a parison whose temperature is adjusted to the stretching temperature, and performing stretching in the axial direction of the parison and expanding and stretching in the circumferential direction of the parison simultaneously or in this order in the cavity of a mold. A desired blow-molded container in which this parison is 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. The device is characterized in that it has a bottom wall portion that substantially corresponds to the bottom wall portion of the device.

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, polycarbonate resin, and polyester resin. be. When utilizing molecular orientation during molding, polyethylene terephthalate, polypropylene, etc. are preferred. Further, blends with other polymers, and various additives such as ultraviolet absorbers and colorants can also be incorporated 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 injection molding of plastic, or a pipe obtained by extrusion molding to a predetermined size. A parison with a bottom can be used, which is obtained by cutting the material into pieces, 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 formed by injection molding. Parison 1 in this example has cavity types 2 and 2', a neck type 3,
An injection nozzle 5 is inserted into the space formed by the core mold 4.
It is molded from molten plastic injected through gate 6.

In this invention, the parison is temperature conditioned to the stretching temperature prior to blow molding. It is desirable to change this stretching temperature as appropriate depending on the type of plastic used. For example, when using polyester, the temperature is from 80 to 130°C, especially from 90°C to 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 former case, the parison is mechanically stretched in the axial direction using a stretching rod while fluid is injected under a relatively small pressure, and then fluid is blown in at a relatively high pressure to expand and stretch the parison in the circumferential direction. do. 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. The neck of the parison 1 is sandwiched between the neck mold 3 and the mandrel 8, and the parison 1 is loaded into the blow mold 16. 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 stretch blow molding in FIG. 3, the material is expanded and stretched by pressurized fluid blown from the slit 14. During this stretching,
The stretching rod 10 and the bottom mold 12 are used for the parison 1 (container 1
5) Move downward while holding the bottom part. The clamping pressure between the drawing rod 10 and the bottom mold 12, the distance between the drawing rod 10 and the bottom mold 12, etc. 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. In addition, the bottom wall of the container obtained by conventional biaxial stretch blow molding was
Shown schematically in Figure. As can be seen from the comparison between these two drawings, the lower protrusions 17 and 17' on the bottom of the container
The method according to the present invention provides a wall thickness sufficient to withstand the internal pressure at the container, whereas the container wall formed by the conventional method becomes thin due to the convex portion. Also, a wall thickness and a uniform thickness distribution in the central bottom portions 18 and 18' are obtained with the method according to the invention, whereas a container according to the conventional method results in an excessive wall thickness and an uneven thickness distribution.

(Example) The present invention will be specifically explained using the following example.

EXAMPLE Polyethylene terephthalate with an intrinsic viscosity of 1.0 is formed in an injection molding machine into a parison having a bottom approximately identical to the bottom shape of the final container, the parison is then reheated to a stretching temperature of 100°C, and then Stretch blow molding was performed using a blow mold as shown in the figure to obtain a blow molded container. The thickness of the protrusion 17 on the bottom of the container was 1.0 mm, and the thickness of the central bottom was 1.2 mm, which was substantially uniform, and the bottom had excellent strength such as impact resistance.

On the other hand, the wall thickness of the convex part 17' at the bottom of the container obtained by the conventional molding method is 0.5 mm, and the wall thickness of the center bottom is 2.5 mm. It was quite inferior in comparison.

(Operation and Effects of the Invention) In conventional stretch blow molding, it is difficult to control the thickness and shape of the bottom wall of the container. 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 clamped by molds from the inside and outside, respectively. Therefore, this clamped mold may be desired to serve as a reference for drawing the parison.

In the case of plastic containers for carbonated beverages, approximately 10
It is required to withstand high pressure of Kg/cm ² (gauge pressure). By the manufacturing method of the present invention, a container that can withstand sufficient internal pressure, especially a container having a bottom wall portion, can be easily manufactured.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of the injection mold used to mold the parison, Figure 2 is an explanatory diagram showing the state of the parison before stretching, Figure 3 is an explanatory diagram showing the state of the parison after stretching, and Figure 4 5 is a sectional view of the bottom of a container according to the present invention, and FIG. 5 is a sectional view of the bottom of a container according to the conventional method. 1...Parison, 2...Cavity type, 3...
Net type, 4... Core type, 5... Nozzle, 6...
Gate, 8...Mandrel, 10...Stretching rod, 1
1... Mold surface, 12... Bottom mold, 13... Mold surface, 14
... Slit, 15 ... Container, 16 ... Blow mold, 17 ... Convex portion, 18 ... Center bottom.

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 shape. 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 producing a hollow container, characterized in that the container has a bottom wall that substantially corresponds to the bottom wall of a desired blow-molded 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.