JPS6139882B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a preform using a tube-shaped raw material made of thermoplastic plastic with open ends as a starting material, and more specifically, by heating both ends of the tube-shaped raw material and forming one end into a bottom part. The object of this invention is to mold a preform hollow body having a beautiful appearance by preventing the occurrence of cracks that are likely to occur on the bottom surface when the toner is tightly closed in a mold and molded into a preform. Plastic bottles are manufactured from thermoplastic plastics such as polyethylene, vinyl chloride, and polypropylene using direct blow, injection blow, and other molding methods, and are used for foods, cosmetics,
Polyethylene terephthalate resin bottles are widely used in products ranging from detergents to industrial chemical containers, but in recent years bottles made of polyethylene terephthalate resin have been attracting attention due to their hygienic properties, excellent physical properties, transparency, and gas barrier properties. The so-called ``cold parison method'', in which a preform is first manufactured and then reheated and oriented blown, is becoming mainstream for bottle molding methods. The preform is molded using an injection molding method in which resin is directly molded into a preform using an injection molding machine, and the Japanese Patent Publication No. 47-3907
It is broadly divided into the tube method, which uses a tube-shaped raw material as a starting material and molds it into a preform, as announced in the publication, but the latter method in particular uses a homogeneous tube obtained by extrusion molding to improve blow processability. A preform rich in color can be molded, and the mold cost is lower than that of injection molding.If the neck design is the same, the preform size can be changed to the tube size without changing the mold. It has great merits in terms of actual operation, such as being able to be implemented with only changes. However, in this molding method, when both ends of the tube are heated and one end is welded and closed in a dome shape in the bottom mold, vertical streak-like cracks are likely to occur on the bottom surface. Although this crack is superficial and does not affect the physical properties of the final product, the bottle, it may become a problem in applications where the aesthetic appearance of the container is important. The present invention was made for the purpose of preventing the above-mentioned cracks that occur when forming a preform by the tube method. A tube-shaped raw material with both ends open is heated to the preforming temperature, and one end is attached to the bottom. When welding and closing the preform in the mold and molding the other end into the desired neck shape in the neck mold, cracks are likely to occur at the bottom of the preform when using a bottom mold with a patterned inner surface. The purpose is to actively apply patterns to certain areas to hide any cracks that may occur. The clearer and denser the shape and number of patterns, the greater the effect, and preferably a depth of 0.05 mm or more and a density of 30 pieces/cm ² or more. Texturing is generally used to create a pattern on a mold, but any other method may be used. The tube-shaped raw material that can be used in the practice of the present invention is a tube with both ends open and made of thermoplastic plastic of a fixed length and having a fixed outer and inner diameter obtained by extrusion molding or injection molding. The tube made of polyethylene terephthalate resin thus obtained is one of the desirable materials. The drawings illustrate an example of a preferred apparatus, mold, and preform obtained by carrying out the invention. Figures 1 and 2 show an apparatus for forming a tube into a preform. In Figure 1, tube 1, whose both ends are heated to the preforming temperature using a separately prepared heater, is moved vertically by a cylinder 6. It is attached to a mandrel 2 that can be used. After the tube is installed, the mandrel 2 rises to the position of the neck mold 3 as shown in FIG.
At the same time as the tube is closed, the cylinder 5 is actuated to lower the bottom molding die 4, so that the upper end of the tube is tightly closed in a dome shape, and the lower end is molded into the desired neck shape. FIG. 3 is an enlarged view of the bottom molding section, where the heated tube end is tightly closed and patterned in a dome shape between the bottom molding die and the head of the mandrel. FIG. 4 is a cross-sectional view and a plan view of a preform obtained when the present invention is not implemented, and FIG. 5 is a cross-sectional view and a plan view of a preform obtained by implementing the present invention. The apparatus and method described here are basically based on Japanese Patent Publication No. 47-3907. Next, the present invention will be specifically explained by showing examples and comparative examples. Example 1 Both ends of a polyethylene terephthalate tube manufactured by an extrusion molding method having the characteristics shown in Table 1 were heated using an infrared heater under the conditions shown in Table 2. When this heating tube was molded into a preform using the equipment shown in the drawing, a mold with a depth of 0.7 mm and approximately 100 mesh patterns per 1 cm ² was textured on the inner surface was used as the bottom mold. , a beautiful-looking preform with a regular mesh pattern on the bottom instead of cracks was obtained. Subsequently, the body of the obtained preform was preheated to approximately 90℃ using an infrared heater, and 20Kg/cm ² of high-pressure air was blown into it using an oriented blow molding machine to form a 1000ml bottle, which resulted in a regular mesh pattern on the bottom. A bottle with a beautiful appearance and no cracks was obtained.

[Table] Calculated from values measured at °C.

[Table] Comparative Example 1 Both ends of the polyethylene terephthalate tube having the characteristics shown in Table 1 used in Example 1 were
When heating and molding into a preform under the following conditions, a bottom mold with a mirror-finished inner surface was used.
A preform with disfiguring random cracks on the bottom was obtained. Subsequently, when the obtained preform was molded into a bottle in the same manner as in Example 1, the bottom of the bottle mold was embossed with a mesh pattern of about 100 meshes per cm ² to a depth of 0.7 mm. A regular mesh pattern was formed on the bottom of the resulting bottle, but the cracks that had occurred in the preform remained. As is clear from comparing the examples and comparative examples,
The method of the present invention hides cracks that occur when manufacturing a preform from a thermoplastic tube with a pattern added to a preform that is not yet oriented and is highly workable, making it possible to manufacture bottles with excellent aesthetics. It is meant to be.

[Brief explanation of the drawing]

1 and 2 show an apparatus for forming a thermoplastic tube into a preform used in the practice of the present invention, and FIG. 3 is an enlarged view of the bottom forming section. Further, FIG. 4 is a sectional view and a plan view of the preform when the present invention is not implemented, and FIG. 5 is a sectional view and a plan view of the preform when the present invention is implemented. In the figure, 1 is a thermoplastic tube, 2
is a mandrel, 3 is a neck mold, 4 is a bottom mold, and 5 and 6 are air cylinders.

Claims (1)

[Claims] 1. Both ends of a tube-shaped raw material with open ends are heated to a preforming temperature, one end is welded closed in a bottom mold, and the other end is closed as desired in a neck mold. A method for manufacturing a preform, characterized by using a bottom mold with a patterned inner surface when molding it into the shape of a neck. 2. The method for manufacturing a preform according to claim 1, wherein the tube-shaped raw material is made of thermoplastic plastic. 3. The method for manufacturing a preform according to claim 2, wherein the thermoplastic plastic is polyethylene terephthalate.