JPH03142222A - Blow molding method - Google Patents

Abstract

PURPOSE:To previously prevent generation of molding defect based on static electricity charged on the surface of a parison by correcting the parison sagged between the split molds to a vertically sagged state with a gripper provided to the lower part of the split molds and closing the split molds and introducing pressurized fluid into the parison. CONSTITUTION:A plurality of grippers 5, 6 are equipped freely movably and regulatively in the position for pinching the lower part of a parison according to the respective cavities 2 in the lower part of the split molds 1. The parisons 4 are extruded from the extrusion heads 3 and sagged between the split molds 1. The lower parts of the sagged parisons 4 are pinched between the grippers 5, 6. Before the split molds 1 are closed, the curves of the parisons 4 are corrected by moving and regulating the grippers 5, 6 and the parisons are rightly regulated to a vertical state. The parisons 4 are held in this state and the split molds 1 are closed. Pressurized fluid such as pressurized air in introduced into the parisons 4 and simultaneously two hollow bodies made of plastic are molded. In such a way, a plurality of pieces of parisons are corrected to the right vertical state and therefore molding defect is not caused even when a plurality of moldings are obtained at once.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a blow molding method for obtaining various hollow plastic bodies.

[Prior Art] Conventionally, blow molding involves dropping a parison of molten thermoplastic plastic from an extrusion head between split molds, then closing the split mold and introducing pressure fluid into the parison to obtain a hollow plastic body. There is also a blow molding method in which a plurality of parisons are simultaneously extruded to obtain a plurality of molded products at once.

[Problem to be solved by the invention] In the plastic blow molding process, the parison is extruded from the extrusion head, and the molten plastic causes friction with each other during the extrusion process, causing rough contact between the extrusion head and the flow path leading to it. As friction occurs between the extrusion heads, the surface of the parison suspended from the extrusion head is charged with a large amount of static electricity.

For this reason, the parison extruded from the extrusion head and suspended between the split molds is often subjected to attractive or repulsive force due to the static electricity charged on its surface, and is often not held in the correct vertical position. When several parisons are extruded and suspended, a strong repulsive action occurs between the bari-men, and the degree of bending increases. This bending phenomenon of the parison occurs to an irregular degree due to the influence of the molding environment, especially humidity, so it is extremely difficult to arrange the mold by considering the degree of bending of the parison in advance. It is.

In view of the above-mentioned circumstances, the present invention corrects the parison hanging from the extrusion head between the split molds to the correct vertical state before closing the split molds even if the parison is bent.
It is an object of the present invention to provide a blow molding method that can prevent molding defects caused by electrostatic charges on the surface of a parison.

[Means for Solving the Problem] The present invention employs the following blow molding method as a technical means to achieve the object.

That is, in the blow molding method according to the present invention, a parison of thermoplastic plastic is suspended between divided molds, and the parison suspended between the divided molds is made to hang vertically by a gripping means provided at the lower part of the divided molds. The method is characterized in that the split mold is then closed and a pressure fluid is introduced into the parison to obtain a plastic hollow body.

[Function] According to the blow molding method of the present invention, the parison extruded from the extrusion head and suspended between the split molds has its lower part corrected to a vertically hanging state by the gripping means, so that the surface of the parison is Even if the parison is charged with static electricity and an attractive or repulsive force is applied to the parison, causing it to bend, the correct vertical hanging condition occurs when the split mold is closed, and molding defects due to the parison's bending do not occur. In particular, when multiple molded products are obtained by extruding and hanging multiple parisons at the same time, a strong repulsive force acts between the multiple parisons, resulting in large bending of the parisons. Since both parisons are adjusted to the correct vertical position, no molding defects occur even when a plurality of molded products are obtained at the same time.

[Example ] Embodiments of the present invention will be described with reference to the drawings.

The drawing shows an example of n* in which two parisons are simultaneously extruded and blow-molded, where 1.1 is a split mold, 2.2 is a cavity thereof, and 3, 3 is an extrusion head. Thermoplastic parison 4, 4 extruded from 3 is an open split mold! .

It hangs down for 1 hour. At the bottom of the split mold 1.1, a plurality of gripping tools 5, 5 and 6, 6 are movably provided at positions sandwiching the cavities 2.2, corresponding to each cavity 2.2.
The lower part of the parison 4, 4 extruded from the extrusion heads 3, 3 and suspended between the split molds 1.1 is held by the gripping tools 5, 5 and 6.
, sandwiched between 6. Therefore, before closing the split mold 1.1, the curvature of the parison 4.4 is corrected by adjusting the movement of the gripping tools 5, 5 and 6, 6 so that it is properly vertical. Then, with the parisons 4, 4 held in this correct vertical state, the split mold 1.1 is closed, and a pressurized fluid such as pressurized air is introduced into the parisons 4, 4 to simultaneously separate the two plastics. Form a hollow body.

Although not shown, a sensor is provided at the bottom of the split mold 1.1 to detect the hanging position of the parison 4.4, and the parison 4.4 is located between the split molds 1.1. When the sensor detects that the parison 4.4 has hung down to a predetermined lower position, the extrusion of the parison 4.4 is stopped and the bending is corrected by the gripping tools 5, 5 and 6.6 as described above.

By the way, the parison 4 extruded from the extrusion heads 3, 3
．． The parisons 4, 4 hanging from the extrusion heads 3, 3 cause friction between the melted plastics during the extrusion process, and friction between the extrusion heads 3, 3 and the flow path leading to them. There is a phenomenon in which the surface is charged with a lot of static electricity.

Then, it is extruded from the extrusion heads 3, 3 and divided mold 1.
The two parisons 4,4 suspended between the two parisons 4,4 are charged with the same charge on their surfaces, so the two parisons 4.4 repel each other, and the two parisons 4.4 are divided molds. 1
．． However, by adjusting the movement of the grippers 5, 5 and 6.6 as described above, the lower parts of the two parisons 4.4 are deformed in a direction that corrects the bending. The parison 4.4 can be hung in the correct vertical position, and the split mold 1.1
When closing the parison 4.4 with the split mold 1.1
tries to be attracted, but since the parison 4.4 is held between the gripping tools 5, 5 and 6, 6, the vertically hanging state can be maintained. Therefore, a plurality of molded products can be obtained simultaneously without causing molding defects.

[Effects of the Invention] According to the blow molding method of the present invention, the parison of thermoplastic plastic is suspended between the split molds, and the parison hanging between the split molds is gripped by a gripping means provided at the lower part of the split mold. The plastic hollow body is obtained through the process of correcting the mold to a vertically hanging state, then closing the split mold and introducing pressure fluid into the parison, so that the parison suspended between the split molds from the extrusion head is not charged with static electricity. Even if the mold is bent, it can be corrected to the correct vertical position before closing the split mold to prevent molding defects caused by static electricity charged on the surface of the parison. In particular, when extruding multiple parisons at the same time to obtain multiple molded products at once, even if a strong repulsive force acts between the parisons, it is possible to keep the multiple parisons in the correct vertical position.
High-quality plastic molded products can be efficiently molded without causing molding defects.

[Brief explanation of the drawing]

The drawings show an embodiment of the blow molding method according to the present invention,
Figure 1 is a front view showing the parison suspended between the split molds with one mold removed; Figure 2 is a front view after the parison has been corrected to the correct vertical position; Figure 3 is the split. FIG. 3 is a perspective view showing the mold in an open state. 1.1...divided mold, 2.2...its cavity,
3, 3... Extrusion head, 4.4... Parison, 5,
5.6.6...Gripper

Claims (1)

[Claims] A parison of thermoplastic plastic is suspended between the split molds, the parison hanging between the split molds is corrected to a vertically hanging state by a gripping means provided at the bottom of the split mold, and then the split molds are closed and the parison is suspended inside the parison. A blow molding method characterized by introducing a pressurized fluid to obtain a hollow plastic body.