JPS6034443B2 - Method for manufacturing polyester preform - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a polyester preform, which is an intermediate molded product for a polyester bottle, by stretch-oriented blowing, and more specifically, the present invention relates to a method for manufacturing a polyester preform, which is an intermediate molded product for a polyester bottle, by stretching and oriented blowing. By the tube method, both ends of a tube with open ends are heated to the molding temperature, one end is welded closed in a mold and formed into a bottom, and the other end is formed into the desired neck shape to form a preform. The present invention relates to a method for producing a polyester preform.

Linear polyester in general, and polyester ethylene terephthalate in particular, has attracted attention as a material for plastic bottles due to its excellent mechanical and mechanical properties, and the development of manufacturing technology for it is rapidly progressing.

There are many methods used to manufacture bottles from polyester, such as direct blow and injection flow, but among them, a preform is first manufactured from polyester, and then this preform is reheated and stretched. The so-called cold parison method, which involves oriented blowing, is the best method for producing polyester bottles.

The preform molding method is the injection molding method, in which the resin is directly molded into the preform using an injection molding machine, and the
It is broadly divided into the tube method, which uses a tube with both ends open as a starting material and molds it into a preform, as announced in Japanese Patent No. 7-3907.The latter method in particular is a method that uses a tube with both ends open as a starting material and molds it into a preform. This method allows a homogeneous preform with excellent blow processability to be molded, and the mold cost is lower than that of injection molding.If the neck design is the same, changing the preform size requires changing the metal. This has a great advantage in terms of operation, as it can be implemented by simply changing the tube size.

As shown in Figure 2, preform molding using the tube method involves cutting a continuously extruded pipe into a fixed length, heating one end of the resulting tube with a heater, and then settling the tip in a bottom mold. Then, the pond edge is heated in the same way and the neck is molded in the neck mold to complete the preform.

However, a problem with this forming method is that when the heated tip is welded and closed in a dome shape in the bottom mold and formed into the bottom, random cracks in the form of vertical lines tend to occur on the bottom surface. . Although the cracks are superficial, when this preform is formed into a bottle by stretch-oriented blowing, it becomes a cause of stretching and enlarged appearance defects, and this is explained in Plastics Vol. 129.
, No. Although this has been reported in 5-18, there is still no known method for preventing the occurrence of cracks.

The inventors of the present invention solved the problem of cracks on the bottom surface that occur when manufacturing a polyester preform with one end welded closed and the other end molded into the desired neck shape using the tube method using a polyester tube with both ends open. After conducting extensive research on ways to prevent this, we found that when the tube end heated to the molding temperature is welded closed in a mold and formed into a bottom, the settling closure part of the bottom is closed, as shown in Figures 1 and 2. The present inventors have discovered that the occurrence of cracks is significantly reduced when the outer diameter of the bent tube tip falls within a range that satisfies the following formula.

f/d, ≧0.4 0} (However, in the formula, d, the outer diameter of the tip of the tube bent at the bottom settling closure part, is the outer diameter of the preform body and is equal to the outer diameter of the tube.

) Tubes that may be used in the practice of the present invention are open-ended tubes of defined length and having defined outer and inner diameters manufactured by extrusion from polyester in which the predominant repeating unit is ethylene terephthalate.

Forming from a tube to a hollow molded body was conducted under the Special Publication Act of 1973-390.
The apparatus described in Japanese Patent No. 7 can be used, and the bottom molding die is as illustrated in FIG.

The weld closure of the tube end is achieved by bending the tube end 1 heated to the molding temperature along the mold by the action of the mold 4 and mandrel 5, and cooling and solidifying the softened polymer after filling the weld closure part 3. Although the tube is completed, the outermost and innermost layers of the tube, which have softened during this process, are rapidly cooled by contact with a cold mold, resulting in a decrease in moldability.

For this reason, the weld closure is mainly composed of polymer that has flowed from the middle layer of the tube wall, and the outermost layer of the tube remains as a skin layer, so the outermost layer of the tube forms the border of the weld. In many cases, it can be easily identified as It is assumed that cracks occur as a result when the outer layer with reduced formability is bent too tightly, and in order to prevent the occurrence of cracks, it is necessary to prevent the tip of the tube from becoming too tight. For this purpose, it is an absolutely necessary condition that the outer diameter of the tip 2 of the tube, which has poor formability, satisfies the formula 1 with respect to the outer diameter d of the preform body. As mentioned above, the boundary between the tube tip and the welded closure part can usually be identified with the naked eye, but if the boundary is unclear, it can be determined using a polarizing plate.

Also, it is very convenient to mark the tip of the tube in advance, such as by coloring it, at the stage of considering condition settings. As shown in Fig. 4, the bulging of the tube tip outside at the welded closure part is controlled by the distance h between the head of the mandrel 5 and the tube tip, and by changing h, {1
} The value of 4 can be adjusted so as to satisfy the expression.

If h is too large, the spread will be below the range of equation '1), and cracks will occur, and conversely, if h is too small, the weld closure will be incomplete. The bottom shape when welded and closed can be selected without any particular problem, whether it is a dome shape or a concave shape, but it is best to choose a bottom shape with a flat top as shown in Figure 1, or a bottom shape as shown in Figure 2. The bottom shape of a semi-elongated ellipsoid as shown above is an example of a preferable shape because control is relatively easy. The polyester preform obtained according to the present invention is used as a preform for producing stretch-oriented blow bottles. Next, the present invention will be specifically explained by showing examples and comparative examples.

Examples 1 to 6, Comparative Examples 1 to 4 Both ends of a tube manufactured by extrusion molding from polyethylene terephthalate and having the characteristics shown in Table 1 were heated under the conditions shown in Table 2 using an infrared heater.

This tube was molded into the preform shown in Table 3 using a preform molding tester model VBE-3 (manufactured by Corpoplast) using a mold suitable for bottom molding as illustrated in FIGS. 1 and 2. By changing the distance h between the head of the mandrel and the tip of the tube during molding, the outer diameter 4 of the tip of the tube at the welded closure part was changed, and as the do was larger, a preform with a beautiful appearance without the occurrence of cracks was obtained. I was able to do that. Furthermore, when the preforms obtained in Examples 1 to 6 were molded into bottles of 1,000 mm using an oriented blow molding machine after heating, it was possible to obtain bottles with a beautiful appearance and no cracks on the bottom.

Table 1 (Note) However, the intrinsic viscosity in Table 1 was determined from the value measured at 20 oo in a phenol/tetrachloroethane equivalent mixed solvent.

Table 2 Table 3

[Brief explanation of the drawing]

1 and 2 are bottom sectional views of the polyester preform produced by the method of the present invention, do is the outer diameter of the tube tip bent at the welded closure part of the bottom, and d is the outer diameter of the preform and the same part. 1 indicates the height of the curved portion, and R and R2 each indicate the radius of curvature of the bottom portion. FIG. 3 shows an example of a bottom molding die used in carrying out the present invention, in which 1 shows the tube end, 2 the outer tip of the tube, 3 the welded closure, 4 the mold, and 5 the mandrel. FIG. 4 shows an example of an embodiment of the present invention, and explains the positional relationship h between the mandrel 5 and the tube end 1.
Figure 5 shows the preform molding process using the tube method, in which one end of the tube is heated in the A zone,
The bottom is welded and closed in the B zone, and the other end is further heated in the C zone, and the preform is adjusted to the desired neck shape in the D zone. Tube, E, indicates the tube holder, H indicates the bottom molding outer mold, G indicates the bottom molding inner mold, CH indicates the neck molding inner mold, and Kawama neck molding outer mold. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1. Both ends of a tube molded from polyester whose main repeat unit is ethylene terephthalate and which are open at both ends are heated to a molding temperature, and one end is welded closed in a mold to form a bottom. A polyester preform made by the tube method, characterized in that when the preform is manufactured by molding the other end into a neck shape, the outer diameter of the tip of the tube bent at the welded closure part of the bottom satisfies the following formula: manufacturing method. d_0/d_1≧0.4 (1) (However, in the formula, d_0 is the outer diameter of the tip of the tube bent at the bottom weld closure, and d_1 is the outer diameter of the preform body and is equal to the tube outer diameter.)