JPH0463765B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a molding method for thermoplastic resin containers, and particularly to a molding method suitable for deep drawing and molding of inorganic filler-containing sheets. BACKGROUND ART Conventionally, a method of forming various containers by stretching a heated thermoplastic resin sheet using a pressure difference using a vacuum or compressed air to form a female shape is known.
Among these molding methods, a so-called clamp-type plug-assist molding method is employed, particularly for containers that require relatively deep drawing, such as pot-shaped containers. 1 to 4 show a conventional clamp type plug assist molding method.
In these figures, a resin sheet 1 is interposed between a female mold 3 and a clamp plate 4, with both ends thereof being gripped by gripping means 2. Also, the back side of the clamp plate 4 (the opposite side to the resin sheet 1)
A plug 5 is disposed at. In this conventional method, as shown in FIG. 2, the resin sheet 1 is first clamped to the end surface of the female mold 3 by the clamp plate 4. Next, as shown in FIG. 3, the resin sheet 1 is pushed into the female mold 3 by a predetermined depth by the plug 5 to be pre-tensioned, and then,
As shown in FIG. 4, the resin sheet 1 is molded along the female mold shape of the female mold 3 using vacuum or compressed air. However, in such conventional methods,
Since the resin sheet 1 is completely clamped between the female mold 3 and the clamp plate 4 and then pre-tensioned by the plug 5, there are difficulties in the molding operation such as the clamping part being stretched abnormally. Ta. Furthermore, it is necessary to mold products with a high deep drawing ratio (H/D is about 0.8 to 2.0, where H is the product height and D is the product diameter), or products that contain a large amount of polyolefin resin, especially inorganic fillers. When molding the contained polyolefin resin, the moldability was not sufficient, and the wall pressure of the molded resin containers was likely to become uneven. For this reason, the resin sheet 1 is made thicker in advance, and currently it has not been able to replace paper containers in terms of economy and resources. The purpose of the present invention is to provide excellent moldability even when deep drawing or forming inorganic filler-containing sheets, and to equalize the wall pressure of resin containers that are molded products (therefore, improve the strength of the product). It is an object of the present invention to provide a method for molding resin containers that can Therefore, in the present invention, the resin sheet is pushed into the female mold by a predetermined amount using a plug without being clamped onto the female mold end face while holding both ends of the resin sheet and stretched, thereby achieving extremely uniform pre-tensioning. , attempts to achieve the above object by clamping a pre-stretched resin sheet to the end face of a female mold by a clamping means, and then molding the resin sheet along the female mold into a female mold shape using a pressure difference. . Hereinafter, the present invention will be explained based on the drawings. 5 to 8 show an example of a molding apparatus to which the method for molding resin containers according to the present invention is applied. In these figures, a plurality of cavity portions 11A are formed in the female mold 11 to a predetermined depth from the female mold end face 11B, and the female mold 11 is designed for so-called multi-cavity molding. Further, an air flow path 12 is provided at the bottom of each cavity portion 11A. A predetermined amount of the plug 13 can be inserted into each cavity 11A, and the tip end of the plug 13 can be loosely inserted into an insertion hole 14A formed in a clamp plate 14 serving as a clamping means. Further, each plug 13 is also provided with an air flow path 15. A thermoplastic resin sheet 16 heated to molding temperature is interposed between the female mold 11 and the plug 13. The thickness of this resin sheet is usually 0.2 to 3.0 mm, although it depends on the shape and purpose of the resin container that is the molded product.
and preferably about 0.3 to 2.0 mm. Further, the structure of the resin sheet 16 is not particularly limited, but polyolefin resin, especially polyolefin resin, and inorganic filler, such as talc, are added in an amount of 20 to 70% by weight.
In particular, it may be contained in a relatively large amount of 40 to 60%. The resin sheet 16 is gripped on both sides by gripping means 17 and is transported in a direction perpendicular to the plane of the paper. FIG. 5 shows a state in which the resin sheet 16 has not yet been pretensioned. From this state, the female mold 11 and the plug 13 approach each other with the resin sheet 16 in between, as shown in FIG.
The resin sheet 16 is pretensioned by the tip of the plug 13 coming into contact with the resin sheet 16 and pushing it into the cavity 11A by a predetermined amount. At this time, since the clamp plate 14 is not clamping the resin sheet 16, the pre-tensioning of the resin sheet 16 is performed not only on the part of the resin sheet 16 where the female die 11 is located, but also on the resin sheet 16 between both gripping means 17. It is carried out over the entire width of the country. After the plug 13 pushes the sheet 16 into the cavity 11A by a predetermined amount without clamping the resin sheet 16 to the female end face 11B, as shown in FIG. 16 is clamped to the end surface 11B by the clamp plate 14 for the first time. Thereafter, the plug 13 may be further pushed into the cavity 11A to further stretch the sheet 16 within the cavity 11A. Then, the sheet 16 is
A plurality of resin containers are molded by creating a pressure difference on both sides (either vacuum or compressed air) and aligning the resin sheet 16 along the cavity part 11A (female shape). (see figure). Note that the female mold 11 applied to the molding method of the present invention
are plural, and the interval between the openings of each cavity 11A is preferably 10 mm or more, preferably relatively wide, about 1/3 to 1/5 of the opening diameter of the cavity 11A. By increasing the width, various excellent effects such as making the wall thickness of the molded product uniform can be achieved. According to this molding method, the resin sheet 1
6 is a so-called inorganic filler blended sheet that contains a relatively large amount of inorganic filler, and even if it is extremely difficult to deep draw in the past, it can produce molded products with uniform wall thickness and little uneven thickness. It has the effect of being able to obtain Further, since the molded product has a uniform wall thickness, the strength of the molded product is high, and even if the resin sheet 16 is thin, resin containers having enough strength to withstand use can be obtained. Therefore, it is also economically superior. In addition, since both ends of the resin sheet 1 are gripped and the sheet width before and after molding is the same during pre-stretching and subsequent molding, high-speed molding is possible while maintaining molding stability, resulting in product quality. is also stable. Furthermore, it is easy to take out a large number of pieces and the productivity is high. Furthermore, there is little unevenness in elongation at the mouth of the molded resin containers, and the curlability of the beverage cup is also good. Next, the present invention will be explained in more detail using the following examples and comparative examples. Examples 1 and 2 Polypropylene homopolymer (density 0.91g/
^cm3 , MI0.6g/10min), 25% by weight of high-density polyethylene (density 0.964g/ ^cm3 , MI0.4g/10min), and talc (talc) with an average particle size of 15μm, which is an inorganic filler. ) 50% by weight was melt-kneaded using a Banbury mixer to form pellets, and then molded into a resin sheet of a predetermined thickness using an extrusion molding machine. Next, from the resin sheet using a pressure molding machine,
A cup-shaped molded product (height 90 mm, average diameter 60 mm), a female mold with 12 cavities (the spacing between each cavity is 25 mm),
It was molded using a phenol felt-wound plug (80% smaller than the female mold) and a clamp plate. First, the resin sheet is heated to 150°C, the heated resin sheet is introduced between the female mold and the plug (see Figure 5), the plug is pushed into the female mold by a predetermined amount (see Figure 6), and then , clamp the resin sheet with a clamp plate (see Fig. 7), and then,
Further, the plug was advanced to 95% of the depth of the female mold cavity, and then air-pressure forming was performed. The strength, area weight, and wall thickness of the molded resin container thus obtained were measured, and the results are shown in the table below.
Shown in 1. Comparative Examples 1 to 3 Examples 1 and 2 were performed under exactly the same conditions, except that the plug was pressed to 95% of the depth of the female mold cavity with the resin sheet pre-clamped to perform air pressure forming. I did some molding.

[Table] Next, for the containers obtained in Example 2 and Comparative Example 1, the average basis weight (container weight), variation in basis weight, and flange wall thickness accuracy were measured when 12 pieces were taken, and wrinkles at the mouth were observed. The results are shown in Table 2. In addition, as Comparative Example 4, a container obtained by using a resin sheet with a thickness of 1.1 mm, pre-tensioning in the same manner as in Example 2, and then air-forming without clamping with a clamp plate was also prepared. The results of measurements and observations are shown in Table 2.

[Table] From Table 2, it can be seen that both the containers according to Example 2 and Comparative Example 1 were pre-tensioned, then clamped and air-formed, so there were no problems with the average basis weight, variation in basis weight, or accuracy of flange wall thickness. It can be seen that no wrinkles were formed around the mouth area. However, the container according to Comparative Example 1 has a problem in that the average basis weight is smaller than that of Example 2 in which the sheet thickness is the same. On the other hand, in the case of the container according to Comparative Example 4, since it was air-formed without clamping after pre-tensioning, there were problems with variations in basis weight and flange thickness accuracy, and wrinkles were generated at the mouth. From these results, according to the present invention, even if deep drawing is performed using a thin resin sheet containing an inorganic filler, a large number of molded products with uniform wall thickness and excellent strength can be produced. I know that I can take it.

[Brief explanation of drawings]

Figures 1 to 4 are cross-sectional views of mutually different processes showing an example of a molding apparatus to which a conventional molding method is applied, and Figures 5 to 8 are molding to which a molding method for resin containers according to the present invention is applied, respectively. FIG. 3 is a cross-sectional view showing an example of the device in different steps. DESCRIPTION OF SYMBOLS 11... Female mold, 13... Plug, 14... Clamp plate, 16... Resin sheet, 17... Gripping means.

Claims (1)

[Claims] 1. Thermoplastic resin containers in which a plurality of containers are simultaneously molded by stretching a heated thermoplastic resin sheet using a pressure difference using a female mold in which a plurality of cavity parts are formed and a plurality of plugs. In the molding method,
While holding both ends of the resin sheet with the gripping means, without clamping it to the end face of the female mold, push this resin sheet into the female mold by a predetermined amount with a plug and stretch it, and then clamp the resin sheet to the end face of the female mold with the clamping means. and then molding the resin sheet along the female mold into a female mold shape using a pressure difference. 2. The method for molding thermoplastic resin containers according to claim 1, wherein the resin sheet contains 20 to 70% by weight of an inorganic filler. Method.