JPS586677Y2 - Stretch rod in stretch blow molding - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a stretching rod used in stretch blow molding, in which a parison with a bottom is stretched in the axial direction and air is blown into the rod to form a hollow molded product such as a bottle.

In this type of molding method, a heated and softened parison with a bottom is placed in a blowing mold, and after the mold is closed, a stretching rod in the center of the blowing core inserted into the inner bottom surface from the opening of the parison is stretched to stretch the parison in the axial direction. Usually, air is blown into the mold to form a hollow molded product that matches the mold surface of the blow mold.

Various thermoplastic synthetic resins are used as materials for this stretch blow molding, but when a parison molded from a highly viscous thermoplastic resin such as polyester resin is stretched, the inner bottom of the parison is stretched due to the stretching force. However, there were cases in which the end of the rod adhered to the extension, making it impossible to blow mold the bottom of the parison using air pressure.

This invention eliminates the above-mentioned drawbacks and configures the stretching rod so that no matter what kind of resin is used as the molding material, adhesion to the stretching head, which causes defective products, can be prevented.

This invention will be explained in detail below with reference to illustrated embodiments.

1 is a blow mold, 2 is a neck mold, and 3 is a blow core in the center of the neck mold through which a stretching rod 4 is inserted, and an air passage 5 is formed around the rod.

6 is an elongated head at the tip of the rod, and 7 is a parison.

The parison 7 is stretched until the outer bottom surface of the parison comes into contact with the bottom mold 8 by stretching the rod 4 with the stretching head 6 in contact with the inner bottom surface of the parison.

During this stretching, in a parison made of highly viscous resin, there is a strong tendency for the inner bottom surface to adhere around the stretching head 6 due to the stretching force.

This adhesive is forcibly peeled off from above due to the expansion of the parison caused by air blowing, but
Since the peeled part expands immediately, the expansion of the parison becomes uneven, and since the part that came into contact with the mold first is cooled, there is a significant difference between the expanded part and the unexpanded part, as shown in Figure 2. Thin wall part 10 is attached to the hollow molded product 9.
They appear in clusters of 11.

However, when a plurality of vertical grooves 12, 12 for air circulation are formed at required intervals on the circumferential side of the stretching head 6 as shown in FIG. 3, the contact area of the inner bottom of the parison is reduced. This is because the adhesive force with the extension head 6 becomes smaller and the air blown into the parison 7 is guided through the vertical grooves 12, 12, causing the inner bottom of the parison around the stretching rod to separate and expand. Even if adhesion occurs due to stretching force, peeling is extremely easy, and since the peeling action occurs at the same time as the expansion of other parts of the parison 7, uneven expansion due to adhesion is unlikely to occur.

In particular, if the stretching head 6 is made of Teflon, or if the surface of the stretching head is made slippery by applying Teflon or the like, the peeling becomes easier.

As mentioned above, this device is equipped with a stretching head 6 having a smooth surface at the tip of the rod 4, and a plurality of vertical grooves 12, 12 for air circulation are provided on the circumferential side of the stretching head 6. Since the inner bottom of the parison around the drawing head is peeled off by the air pressure inside the parison, poor expansion due to adhesion is unlikely to occur, and a hollow molded product with a uniform thickness distribution at the bottom can be obtained.

Also, since it is only necessary to make vertical grooves on the peripheral side of the stretching head,
It does not need to be communicated with the air passage inside the stretching rod, and has the feature that it can also be applied to those in which the air inlet is located above the rod.

[Brief explanation of the drawing]

Figure 1 is a vertical cross-sectional view of a blow mold equipped with a conventional stretching rod, and Figure 2 is a vertical cross-sectional view of a blow mold when blow molding is performed after stretching using a conventional stretching rod. FIG. 3 is a front view of the tip of the stretching rod according to this invention, and FIG. 4 is a longitudinal sectional view of the stretching head showing the peeling state. 1...Blowing mold, 2...Neck, 3.
... Blowing core, 4 ... Rod, 5 ...
...Air path, 6...Stretching head, 12...
...Vertical grooves for air circulation.

Claims (1)

[Scope of utility model registration request] A stretching rod for stretch blow molding, which is formed by providing a stretching head with a smooth surface at the tip of a rod inserted into a blowing core, and providing a plurality of vertical grooves for air circulation on the circumferential side of the stretching head.