JPH0790591B2 - Blow molding method - Google Patents

Description

The present invention relates to a blow molding method for obtaining various hollow plastic bodies.

[Prior Art] Conventionally, a blow molding in which a molten thermoplastic parison is hung from an extrusion head between split molds, then the split molds are closed, and a pressure fluid is introduced into the parison to obtain a hollow plastic body. There is also a method, and as shown in FIG. 5, a blow molding method in which a plurality of parisons are simultaneously extruded to obtain a plurality of molded products at the same time is also used. In the figure,
a, a are split molds, b, b are cavities thereof, c, c are extrusion heads, d, d are parisons.

[Problems to be Solved by the Invention] In a plastic blow molding process, a parison extruded from an extrusion head has a structure in which plastics melted in the extrusion process cause friction with each other, and further, between the extrusion head and a flow path leading to it. Since friction occurs at, the phenomenon that a lot of static electricity is charged on the surface of the Paris hanging from the extrusion head is seen.

For this reason, the parison that is extruded from the extrusion head and hung between the split molds is often not in the correct vertical state due to the attractive force or repulsive force due to the static electricity charged on the surface of the parison. When a book parison is pushed out and drooped, a strong repulsion action occurs between the parisons, and the degree of bending increases. Since the bending phenomenon of the parison occurs irregularly under the influence of the molding environment, particularly humidity, it is extremely difficult to arrange the mold in consideration of the bending degree of the parison in advance. (See FIG. 5).

In view of the conventional situation as described above, the present invention provides static electricity removing means in the air space in contact with the parison extruded from the extrusion head, neutralizes the static electricity charged on the surface of the parison, and electrostatically removes static electricity on the surface of the parison. It is an object of the present invention to provide a blow molding method capable of preventing a bending phenomenon due to being charged, and thus preventing the occurrence of molding defects caused by the static electricity charged on the surface of the parison. is there.

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

That is, the blow molding method according to the present invention is a blow molding method in which a thermoplastic parison is hung between divided dies, and then the divided dies are closed and a pressure fluid is introduced into the parison to obtain a plastic hollow body. In the above, the static electricity removing means is provided in the air space in contact with the extruded parison when the parison is extruded.

Then, one of the static electricity removing means is specifically by ionizing the air contacting the parison by electric discharge.

[Operation] According to the blow molding method of the present invention, the parison extruded from the extrusion head is often charged with static electricity. However, static electricity removing means is provided in the air space in contact with the extruded parison. As a result, the static electricity charged on the surface of the parison is neutralized through the air space in contact with it. Therefore, the surface of the parison is not charged with static electricity,
Since the attractive force or repulsive force due to electrostatic charging does not act, the parison is in the correct vertical hanging state when the split mold is closed, and the molding failure due to the bending of the parison does not occur. In particular, even when multiple parisons are simultaneously extruded and drooped to obtain multiple molded products at once, the repulsive force due to static electricity does not act between the parisons, and the parisons are both held in the correct vertical state. Therefore, in this case also, defective molding does not occur.

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

FIGS. 1 to 3 exemplify a mode in which two parisons are simultaneously extruded and blow-molded. 1, 1 is a split mold, 2, 2 is its cavity, 3 and 3 are extrusion heads, and thermoplastic parisons 4 and 4 extruded from the extrusion heads 3 and 3 are open split molds. It is drooped between 1 and 1. An electrode 5 for corona discharge is arranged between the extrusion heads 3,3 and the split molds 1,1 in the vicinity of the surface of the parison 4,4 extruded from the extrusion heads 3,3. , Extrusion head 3,
Corona discharge is generated in the air space contacting the surfaces of the parisons 4 and 4 extruded from 3, and the air contacting the surfaces of the parisons 4 and 4 is ionized to destroy the insulation. The electrodes 5 are provided in a pair with the extruded parisons 4, 4 interposed therebetween, or the electrodes 5 are one and the extrusion heads 3, 3 are the other electrodes. It is preferable to apply a high frequency voltage capable of causing corona discharge at a relatively low voltage to the electrode 5.

FIG. 4 shows another example in which the electrodes 5 for corona discharge are arranged so as to project from the lower surface of the extrusion head 3. In this example, the parison 4 extruded from the extrusion heads 3, 3 is shown. Corona discharge is generated in the internal space.

By the way, parison 4,4 extruded from the extrusion head 3,3
In the extrusion process, the melted plastics cause friction with each other, and further cause friction between the extrusion heads 3, 3 and the flow path leading to them. For this reason, the surface of the parisons 4,4 extruded from the extrusion heads 3,3 is seen to be charged with a large amount of static electricity.
Corona discharge is generated by the electrode 5 in the air space in contact with the surfaces of 4, 4, and the air in contact with the parisons 4, 4 is ionized to destroy the insulation. The electrostatic charges on the surface of the are immediately discharged and neutralized through the air in contact with them. Therefore, static electricity is not charged on the surface of the parisons 4, 4 extruded from the extrusion heads 3, 3, and the parisons 4, 4 are not charged.
Is hung between the split molds 1 and 1 while maintaining a correct vertical state without being subjected to suction force or repulsive force.

In particular, even in blow molding in which a plurality of parisons 4, 4 are simultaneously extruded from the extrusion heads 3, 3 and hung between the split molds 1, 1, the plurality of parisons 4, 4 do not repel each other, Parison 4,4 can hang in the correct vertical position. Therefore, a plurality of molded products can be obtained at the same time without causing molding defects.

[Effect of the Invention] According to the blow molding method of the present invention, a thermoplastic plastic parison is hung down between divided dies, and then the divided dies are closed and a pressure fluid is introduced into the parison to form a hollow plastic body. In the blow molding method for obtaining the above, since the static electricity removing means is applied to the air space in contact with the extruded parison at the time of extruding the parison, the static electricity charged on the surface of the parison extruded from the extrusion head is immediately transferred through the air in contact therewith. By bending, it is possible to prevent a bending phenomenon due to static electricity being charged on the surface of the parison, and thus to prevent occurrence of defective molding due to static electricity charged on the surface of the parison.

When the method of ionizing air by discharge and destroying its insulation is used as the static electricity removing means, the static electricity charged on the surface of the parison can be efficiently removed by a simple constitutional means, and a better blow molding can be performed. .

[Brief description of drawings]

1 to 4 show an embodiment of a blow molding method according to the present invention, and FIG. 1 is a front view showing a state in which a parison is hung between divided molds, except for one divided mold, FIG. 2 is a side view showing a process of extruding the parison from the extrusion head,
FIG. 3 is a partially cutaway side view showing a state in which the extrusion of the parison is completed, and FIG. 4 is a fragmentary front view showing another embodiment. FIG. 5 is a front view showing a conventional example. 1,1 …… Split mold, 2,2 …… its cavity, 3,3 …… extrusion head, 4,4… Parisson, 5 …… electrode for corona discharge

Claims (2)

[Claims] 1. A blow molding method in which a thermoplastic plastic parson is suspended between divided dies, and then the divided dies are closed to introduce a pressure fluid into the parison to obtain a plastic hollow body. A blow molding method, wherein static electricity removing means is applied to an air space in contact with the extruded parison. 2. The blow molding method according to claim 1, wherein the static electricity removing means is based on ionization of air contacting the parison by electric discharge.