JPS625048B2 - - Google Patents

Description

Detailed Description of the Invention The present invention relates to a plastic hollow body such as a bottle, tank, case, etc., in which the corner portions of the hollow body are reinforced by making the wall thickness uniform, or more specifically, thick. This invention relates to a blow molding method.

Generally, the blow molding method for hollow bodies is as shown in Figs. 1 and 2, in which a plasticized parison 11 is placed in a mold
After extrusion into the parison 11, the mold is closed and pressurized fluid is blown into the parison 11 to blow the parison, so the corners 13 with a high blow ratio tend to be thinned. The hollow bodies thus obtained have the disadvantage of poor chemical and physical properties.

The present invention relates to a method of blow molding a plastic hollow body, which eliminates the above-mentioned drawbacks and makes the wall thickness of the corner portions of the hollow body uniform and, preferably, thick.

The present invention will be explained below based on the drawings. As shown in FIG. 3, 1 is a mold consisting of a pair of divided half molds 2, 2 facing each other and a lower mold 3 located at the bottom, and 4 is a hollow body-shaped outer shape on the inner surface of the mold 1. It is a cavity with a shaped shape. 5 is a parison, 6 is an extrusion head for extruding the parison 5,
A parison cutter 7 is installed below the extrusion head 6 for closing and cutting the lower end of the extruded parison 5. Further, reference numeral 8 denotes a cavity gap formed on the outside of the corner portion of the hollow body obtained by the cavity 4, and the cavity gap 8 is formed at the boundary between the half mold cavity and the lower mold cavity. , the cavity gap 8 can be changed by moving the lower mold 3 up and down. In addition, 9 is a blowing nozzle.

Next, to explain the method of blow molding a plastic hollow body, thermoplastic plastics such as polyethylene, polypropylene, vinyl chloride, polyamide, etc. are melt-kneaded in an extruder (not shown) and plasticized by an extrusion head 6. Extruded as Next, the lower end of the parison 5 is closed and cut using a parison cutter 7. Then, as the parison 5 is further extruded, pressurized fluid is blown into the bottomed parison 5 from the blowing nozzle 9 to perform pre-blowing.The mold 1 is closed and the pre-blown parison 5 is inserted into the half molds 2, 2. The upper part of the bottomed parison 5 is held. Then, pressurized fluid is blown into the parison 5 to blow the parison 5 into pressure contact with the cavity 4 and the cavity gap 8. Then the fourth
While maintaining the air flow inside the parison 5 as shown in the figure,
By raising the lower die 3, the cavity gap 8 is reduced, the cavity gap 8 is filled with the parison 5', and the crushed parison 5' is heaped up inside the cavity 4. In this way, the parison 5' is raised inside the cavity 4, and the corners of the hollow body are made to have a uniform wall thickness, and preferably a thick wall. Thereafter, the parison 5 is cooled, the hollow body is taken out from the mold 1, and the cast flash located in the cavity gap 8 is removed, thereby obtaining a plastic hollow body. As shown in FIG. 5, at the same time as the parison 5' within the cavity gap 8 is crushed and raised inward of the cavity 4, the parison 5' still located within the cavity gap 8 is cut by the edge 10 in the mold. , the parison 5' still located within the cavity gap 8 and the parison on the cavity 4 side may be connected by a thin portion and then removed later.

The plastic hollow body obtained by the present invention is
A general term for products manufactured by blow molding, such as bottles, tanks, cases, housing members, and dish-shaped members.

With the structure described above, the method of blow molding a plastic hollow body according to the present invention does not pinch off the lower part of the hollow body, so the parison on the lower mold side does not become flat, and the parison expands tightly while maintaining its external shape. When this is done, the amount of parison disposed in the cavity gap can be made uniform throughout, and variations in the thickness of the corner portion in the circumferential direction (lateral direction) can be prevented and made uniform.

Furthermore, by crushing the parison in the cavity gap, the parison is raised inward to the cavity, and the wall thickness at the desired location is made uniform (uniform wall thickness in the vertical direction), and even more aggressively, it is reinforced by making it thicker. be able to.

[Brief explanation of the drawing]

Fig. 1 is a schematic cross-sectional view of a mold showing the conventional blow molding method, Fig. 2 is a perspective view of a hollow body obtained by the conventional blow molding method, and Fig. 3 is a mold showing the blow molding method of the present invention. 4A and 4B are schematic cross-sectional views of the main part of the mold showing the molding process of the present invention, and FIG. 5 is a schematic cross-sectional view of the main part of the mold showing another example corresponding to FIG. 4B. 1...Mold, 2...Half mold, 3...Lower mold, 5...
Parison, 8... Cavity gap.

Claims (1)

[Scope of Claims] 1. A method for blow molding a hollow body using a three-part mold having a cavity shaped to correspond to the external shape of the hollow body, consisting of a pair of half molds and a lower mold, comprising: 3 The split-type mold is opened, a bottomed parison with a closed bottom end is placed in the mold, and then the pair of half molds and the lower mold are closed. While holding the upper part of the bottom parison, the parison is sealed with a mold while maintaining a cavity gap at the boundary between the half mold cavity corresponding to the corner of the hollow body and the lower mold cavity, and then inside the parison. By injecting pressurized fluid into the mold, the mold is expanded and brought into close contact with the walls of the cavity and the cavity gap, thereby forming a lower surface with no pinch-off portion between the main body and the lower mold, which is then moved in the direction of the half mold so as to narrow the cavity gap. A blow molding method for a plastic hollow body, characterized in that the parison in the cavity gap is crushed, the parison is heaped up inside the cavity, and the corners of the hollow body are thickly reinforced.