JPS6378706A - Manufacture of biaxially stretched bottle - Google Patents

Abstract

PURPOSE:To easily obtain a lightweight bottle with the thin-walled bottom part by a method wherein the bottom part of a bottomed parison is formed into a spherical shape in such a manner that the curvature radius at the inner side of the bottom part is made smaller than that at its outer side and the wall thickness at the central part of the bottom part is made thinner. CONSTITUTION:A bottomed parison 3 is formed by injection-molding thermoplastic resin in an injection mold 1 so as to form the bottom part of the bottomed parison 3 into a spherical shape in such a manner that the curvature radius R1 at the inner side of the bottom part is made smaller than the curvature radius R3 at its outer side and the wall thickness at its central part is made thinner. The curvature radius R2 at the port of transition from the tip to the cylinder is made smaller than R3 and at the same time larger than R1 so as to make the transition from the curved part to the straight part smoother. At the same time, when the runner part solidifies itself so as to be able to remove from a mold, the solidified part of the injection-molded bottomed parison is only the central part 31 of the bottom part. The part 32, which is a little apart from the central part keeps on being thermoplastic or easily restores to be thermoplastic by controlling temperature. Accordingly, the remaining part excluding the central part 31 of the bottom part are fully stretched by blow molding so as to obtain a bottle the wall thickness at the bottom part of which is thin is obtained.

Description

[Detailed description of the invention]

Eifuku Toyodangu

[Industrial application field]

The present invention relates to an improvement in a method for manufacturing a two-wheeled stretched bottle.

[Conventional technology]

In the production of plastic bottles by blow molding,
Biaxial stretching blowing, which provides products with high strength despite being thin, has been widely used in recent years. The typical technique is the hot parison method, in which a bottomed parison is prepared by injection molding, reheated to the necessary extent to a temperature suitable for blow molding, and then transferred to a blow mold for blowing. It's a method. This technique includes, for example, 1. l! Polyester is used in the production of four oil bottles. However, bottles obtained by currently practiced manufacturing methods have too thick bottoms because the bottom material is difficult to stretch during blow molding. Since the bottom part is not very important for the strength of the bottle, we want to make it as thin as possible without causing any problems, thereby reducing the weight and cost of the bottle. In order to make the bottom of the bottle thinner, it is sufficient to make the bottom of the bottomed parison thinner, but in order to ensure that the molten plastic flows well in the mold during injection molding and produces a good-quality bottomed parison, It is necessary that the bottom of the bottomed parison has a certain degree of thickness. In the injection mold of the biaxial stretching blow machine currently in use, the bottom of the parison is flat and thinner than the wall. This is to allow the bottom part to solidify first so that a portion of the runner can be quickly assimilated, making it easier to remove it from the mold. This part does not substantially extend during the blow molding stage. As described above, there is a limit to making the bottom of the parison thinner in order to make the bottom of the bottle thinner. [Problem to be Solved by the Invention 1] The purpose of the present invention is to overcome the current state of the art as described above and provide a method for manufacturing a biaxially stretched bottle that can easily produce a lightweight bottle with a thin bottom wall. be. Structure of the Invention [Means for Solving Problems] As shown in FIG. 1, the method for packaging a biaxially stretched bottle of the present invention involves injection molding a thermoplastic resin in an injection mold 1. In the method for producing a biaxially stretched bottle, which consists of forming a bottomed parison 3, performing necessary temperature adjustment on the bottomed parison 3, and then blow molding, the entire structure is shown in FIG. 1 and shown in FIG. As shown in detail, the bottom of the bottomed parison 3 is spherical, and the inner radius of curvature R1 is smaller than the outer radius of curvature R3, so that the bottom central portion 31 is formed thin. In the present invention, the term "spherical shape" is not limited to the shape of a spherical surface, but also includes a three-dimensional shape that occurs when a parabola or hyperbola is rotated about an axis, which can be substantially identical to the spherical shape. In the example shown in FIG. 2, the outside of the bottom of the bottomed parison has a hemispherical shape with a radius of curvature R3, but the inside tip has a radius of curvature R3.
1. The transition part from the tip to the body is smaller than R3 and R1
It is formed with a larger radius of curvature R2 to smooth the transition from the curved part to the straight part. [Function 1 According to the present invention, a bottomed parison with a spherical bottom and different radii of curvature on the inside and outside is prepared, and only the central part is made thin, and the parts farther from the center are made thicker. Form. In this way, in the injection-molded bottomed parison, when a portion of the runner is solidified and can be removed from the mold, only the bottom central portion 31 is solidified, as shown in FIG. , the portion 32 further from the center retains its thermoplasticity or easily regains its thermoplasticity upon temperature adjustment. Therefore, the parts other than the bottom central part 31 are well centrifuged by blow molding, and in this way, the bottle 5 shown in FIG. 4 with a thin bottom part 55 is obtained. On the other hand, in the conventional manufacturing method, as shown in FIG. 5, it is not possible to obtain a bottle 6 with a bottom 65 of 19 mm. [Example] A bottomed parison having the shape shown in FIG. 1 was injection molded using polyethylene terephthalate. The bottomed parison has an overall length of about 120mm and an outer diameter of about 3mm.
01M1, the wall thickness is about 3 m, and the spherical bottom has a radius of curvature Ri = 8.5 cocoon, R2 = 12° 5 #, R3 as shown in Figure 2.
=13#. This bottomed parison is taken out from the injection mold, and after adjusting the temperature, it is transferred into a blow molding metal mold and blow molded to have an inner volume of approximately 1. l! I bought 1q of bottles. The ff1ffi of the obtained bottle is 31.09,
Bottle mold set 33゜5g molded using conventional manufacturing method
It was 2.59 ('7.4%) lighter than the previous model. This is because the ff1fi at the bottom of the bottle was reduced by half. Of course, the strength of the entire bottle did not change. Effects of the Invention According to the method for manufacturing a biaxially stretched bottle of the present invention, a lightweight bottle with a thin bottom can be easily obtained.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the step of forming a bottomed parison in the method for manufacturing a biaxially stretched bottle of the present invention. Figures 2 and 3 are enlarged sectional views of the bottom of the bottomed parison shown in Figure 1, where 2- indicates the radius of curvature of each part, and Figure 3 shows the solidified bottom center. shows. Figures 4 and 5 are both cross-sectional views of biaxially stretched bottles, with Figure 4 showing the bottle obtained by the manufacturing method of the present invention, and Figure 5 showing the bottle produced by the conventional manufacturing method. Each bottle is shown below. 1... Injection mold 3... Bottomed parison 31... Bottom center portion 5.
6... Bottle patent applicant Dainippon Printing Co., Ltd. agent Patent attorney Souo Suga w & 4 Figure 5

Claims (1)

[Claims] In a method for producing a biaxially stretched bottle, which involves injection molding a thermoplastic resin to form a bottomed parison, subjecting the bottomed parison to the necessary temperature adjustment, and then performing blow molding, the bottom of the bottomed parison is A method for manufacturing a biaxially stretched bottle, characterized in that the bottle is shaped like a sphere, and the inner radius of curvature is smaller than the outer radius of curvature to form a thinner bottom central portion.