JPH0430901B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for molding a bottomed parison used when manufacturing a hollow molded product such as a bottle made of thermoplastic resin by stretch blow molding. (Prior art) For stretch blow molding of hollow molded products such as bottles made of thermoplastic resin, there is a one-stage or hot parison method in which the parison is injection molded and then the parison is stretch blow molded into a hollow molded product. There is a two-stage or cold parison method in which the injection-molded parison is cooled and stored, then taken out according to the demand for the blow-molded product, reheated, and stretch-blow molded. There is a method. In any of these methods, it is said that the larger the stretching ratio when forming a parison into a blow molded product, the more excellent the strength and barrier properties of the blow molded product can be obtained due to biaxial orientation. The actual strength measurement results for three types of parisons A, B, and C, with the same weight (59g) parisons having different stretching ratios as shown below, are as follows:

As shown in the table, sample B, which had the highest cumulative stretching ratio, had excellent strength. (Problem to be solved by the invention) By the way, in stretch blow molding, the dimensions of the parison are usually determined by the dimensions and weight of the hollow molded product to be molded, and in order to increase the stretch ratio as much as possible, it is necessary to increase the weight. If the parison is made shorter than it would normally be without any change, the wall thickness of the parison increases as the length decreases. Generally, in injection molding, as the wall thickness of the parison increases, the injection time, cooling and holding time, etc. during parison molding also become relatively long. In fact, each sample A, B,
The molding cycle for sample C requires 22 seconds/shot, 30 seconds/shot, and 28 seconds/shot, and the thickest sample B has the longest molding cycle. In addition, if the material used for molding is a crystalline resin, if the wall thickness increases, the parison cannot be rapidly cooled by the injection mold, and crystallization progresses during the cooling process, resulting in loss of transparency. I often get caught. Therefore, in stretch blow molding, due to problems such as molding cycles and crystallization, there is a limit to the parison size determined from the dimensions of the blow molded product.
In order to obtain a hollow molded product with even greater toughness, it is difficult to shorten the molding cycle to mold a parison that exceeds the limits of its dimensions, so it is necessary to create a hollow molded product with a thicker wall than usual. In the case of stretch blow molding, there are problems such as sacrificing the stretch ratio. (Means for Solving the Problems) This invention was devised to solve the above-mentioned problems regarding parison forming during stretch blow molding, and its purpose is to provide blow molded products. The stretching ratio can be increased regardless of the dimensions of the parison, the molding cycle does not become particularly long even if the thickness of the parison is increased compared to the normal case, and the material is crystalline resin. Another object of the present invention is to provide a method for forming a parison without worrying about crystallization. According to the present invention, a parison with a bottom is injection molded using a neck mold and an injection mold, as is generally practiced in injection stretch blow molding. After the parison is cooled to a state where it can be released from the mold, the parison is transferred to a temperature control mold with its neck held between neck molds, and the lower neck of the parison is shortened in this temperature control mold. This shortening is performed by compressing the other part (hereinafter referred to as the lower neck), excluding the neck, in the axial direction using a temperature control mold. Due to this compression, the length under the neck of the parison becomes shorter than that during injection molding, and the wall thickness increases in proportion to the shortening. The dimensions of the above-mentioned parison during injection molding vary depending on the wall thickness of the hollow molded product to be molded. When the wall thickness of a hollow molded product is normal, it is determined from the dimensions of the hollow molded product, but when molding a hollow molded product with a thickness thicker than usual, the length under the neck of the parison when shortened is usually determined. As the length under the neck of the parison,
During injection molding, the lower neck of the parison is made longer.
This longer neck section becomes the normal length by being compressed in the temperature control mold, and becomes thicker by the shortened length. Furthermore, in order to prevent deformation of the parison during compression and to ensure smooth temperature control, a molding core that also serves as temperature control is inserted into the parison through the neck mold.
This molding core is extracted after the temperature control of the parison is completed, and the parison is transferred to the next position together with the neck mold. When stretch blow molding is performed using the hot parison method, the next position to which the parison is transferred is the blow mold position, and the shortened and temperature-controlled parison is immediately stretch blow molded into a hollow molded product.
In the case of the cold parison method, the next location is the cooling device, where the cooled and solidified parison is released from the neck mold and stored. (Example) Fig. 1 (Parison injection molding) The injection mold 1 and the neck mold 3 on the lower surface of the transfer plate 2 are clamped by inserting the core mold 4 into the injection mold 1 from above the neck mold. , a bottomed parison 5 is injection molded. The length, diameter, weight, etc. of this parison 5 are determined from the dimensions of the hollow product to be molded. Fig. 2 (Transferring the parison) When the injection molding of the parison 5 is completed, the parison 5 is released from the mold at as high a temperature as possible, and the neck portion 5 is
While holding a, transfer it to the upper part of the temperature control mold 6. The temperature control mold 6 is provided so as to be movable up and down with respect to the neck mold 3, and the depth of the cavity 7 opened at the upper part is formed to be shallower than the length of the lower neck 5b of the parison 5 by a required dimension. Further, above the temperature control mold 6, a temperature control core 8 that penetrates the neck mold 3 and is inserted into the parison is provided so as to be able to move up and down, and the diameter of the portion 8a of the temperature control core 8 located inside the parison is ,
It is formed smaller than the inner diameter of the parison 5. FIG. 3 (Shortening of parison and temperature control) When the parison 5 stops at the upper part of the temperature control mold 6, first lower the temperature control core 8 and insert it into the inside of the parison 5 from the neck mold 3. do. Next, the temperature control mold 6 is raised, the parison 5 is inserted into the cavity 7, and the mold is closed with the neck mold 3. In the process of closing the mold, due to the difference between the length of the under-neck 5a and the depth of the cavity 7, the under-neck 5a is
b is compressed in the axial direction and shortened, and since there is a gap between the parison 5 and the temperature control core 8, the excess portion generated by compression is pushed into the gap, increasing the wall thickness and forming the mold. When the closing is completed, the length of the lower neck 5b is shorter than when injection molded, and the shortened parison 9 has an increased wall thickness. This mold closing accompanied by shortening of the parison is performed by temperature-controlled mold 6.
The temperature control core 8 is maintained at the required temperature, and the temperature is controlled at the same time as the parison is compressed. As a result, due to changes in wall thickness due to compression and heat from outside the parison, the temperature distribution under the neck 5b becomes uniform in a shorter time than when heat is applied from outside, and also due to the distortion caused during injection molding. etc. will also be removed. Figure 4 (Transferring the shortened parison) Once the shortening of the parison and temperature control are completed, the temperature control mold 6 and the temperature control core 8 are returned to their original positions, the mold is opened, and the shortened parison is transferred together with the neck mold 3. 9 to the next working position. The present invention can be carried out using the injection stretch blow molding machine disclosed in Japanese Patent Publication No. 53-22096. (Effects of the Invention) As described above, the present invention compresses an injection-molded parison in the axial direction in a temperature control mold during temperature control to shorten the length under the neck and mold it thickly. Therefore, it is possible to mold thick parisons using a normal molding cycle, which is difficult in injection molding due to cooling issues. In addition, because the shortening and thickening are performed simultaneously in a temperature-controlled mold, crystallization of the material is less likely to occur, and the stretching ratio is also increased, compared to when molded with a parison of the same size as injection molding. The strength and barrier properties of the blow molded product can be improved. Furthermore, it has the advantage of being able to form thick hollow molded products without sacrificing the stretching ratio.

[Brief explanation of drawings]

1 to 4 are longitudinal sectional front views showing the method for forming a parison for stretch blow molding according to the present invention in the order of steps. DESCRIPTION OF SYMBOLS 1... Injection mold, 3... Net mold, 5... Parison, 5a... Neck, 5b... Under neck, 6... Temperature control mold, 7... Cavity, 8... Temperature control core, 9... …
Shortened parison.

Claims (1)

[Claims] 1 Injection mold a parison of the required dimensions, clamp the neck of the parison with a neck mold, transfer it to a temperature control mold, compress the entire lower neck of the parison in the axial direction in the temperature control mold, and complete the injection molding. A method for forming a parison for stretch blow molding, characterized by shortening the length below the neck and forming it thicker than when used for stretch blow molding.