JPH1134158A - Molding method of hollow plastic molded article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent sink marks from developing on the surface of a thin-walled part and make it possible to thin the wall of a molded article by a method wherein the inner surfaces of a parison, which form an attaching-together part, are brought into close contact with each other after the parison is inflated by being blown air therein for shaping at blow molding. SOLUTION: A parison P is extruded between the split molds 11a and 11b of a blow mold 10 and, after that, pinched by the split molds 11a and 11b by closing them. At this time, as for the one split mold 11a, its molding surface at an attaching-together mold part 13 is kept at a retracted state. Next, the parison P is inflated so as to shape the form of a molded article except the molding surface portion of the attaching- together mold part 13. In succession, the attaching-together mold part 13 is advanced so as to bring the inner surfaces of the parison Pa at the location of the attaching- together mold part 13 into close contact with each other. Thus, the parison Pa portions are made into an integrate body of a thin-walled attaching-together part G. In this case, since the formation of the attaching-together part G is carried out after the cooling of the parison P, even through the natural cooling after demolding, the amount of shrinkage of the attaching-together part G becomes small, resulting in preventing sink marks from developing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming a hollow plastic molded product.

[0002]

2. Description of the Related Art There is a blow molding method as a simple method for molding a hollow plastic molded product. In this blow molding method, as shown in FIG. 7, a parison 30 made of plastic in a heat-melted state and extruded into a tube shape is guided into a blow mold 40 made of a split mold.
In this method, the parison 30 is inflated by blowing air into the mold to form a mold surface shape, and then the molded product is taken out from the blow molding die 40.

[0003] Depending on the application and the like, a hollow plastic molded product may have a shape such as a molded product 50 shown in FIG.
In some cases, the thin portion 51 is required. For example,
The surface of the object to which the molded article 50 is attached and the molded article 5
This is for improving the appearance by reducing the level difference from the zero surface. At this time, in order to make it thinner, the gap 55 is eliminated by joining the wall surfaces 53 of the thin part 51 to form a thin part 61 like a molded product 60 shown in FIG. 8B. Is most effective.

In order to obtain a hollow plastic molded product 60 in which the gap in the thin portion 61 is eliminated by a blow molding method, FIG.
As shown in FIG. 3, the inner surface of the predetermined portion 31 of the parison 30 corresponding to the thin portion is brought into close contact with the blow molding die 4.
0 is closed, and in this state, air is blown into the parison 30 to inflate the parison 30 and the close contact portion 31 is integrated to form the joint portion 32, and the joint portion 32 forms the thin portion 61.
Is configured. However, in the hollow plastic molded product obtained in this manner, a sink mark 62 made of a concave portion or wavy appears on the surface of the thin portion 61, and a problem occurs that the appearance of the molded product 60 is impaired. The reason for the occurrence of the sink marks 62 is that the thickness of the joint portion 32 is approximately twice the thickness of the parison 30 and is larger than the thickness of the other non-joined portions. The amount of heat accumulated in the inside becomes extremely larger than the amount of heat of the non-joined portion, and the degree of shrinkage caused by the subsequent cooling becomes remarkable in the joined portion 32, so that a concave portion or waving occurs on the surface of the joined portion 32. Conceivable.

Therefore, in the conventional blow molding method, there is no sink mark unless a gap of at least about 1 mm is provided between the wall surfaces 53 of the thin portion 51 as in a molded product 50 shown in FIG. There was a problem that a good appearance was not obtained and the thickness of the thin portion 51 could not be sufficiently reduced.

[0006]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has been made in consideration of the above-mentioned problems. Therefore, the present invention provides a hollow plastic molded product which can have a sufficiently small thickness without causing sink marks on the surface of the thin portion. A molding method is provided.

[0007]

SUMMARY OF THE INVENTION According to the present invention, air is blown into the parison when blow molding a hollow plastic molded product having a joint portion in which the inner surface of a predetermined portion of the parison is in close contact with the product portion. The present invention relates to a method for molding a hollow plastic molded product, wherein the parison is inflated and shaped, and then the inner surface of a predetermined portion of the parison serving as the joining portion is brought into close contact and joined.

[0008]

FIG. 1 is a cross-sectional view of one example of a blow molding die used in the method of molding a hollow plastic molded article of the present invention, and FIG. 2 is an embodiment of a method of molding a hollow plastic molded article of the present invention. 3 is a cross-sectional view showing a state in which the parison is led between the split dies, FIG. 3 is a cross-sectional view showing a state in which the joining mold part is opened and the other part is closed in the same embodiment, and FIG. FIG. 5 is a cross-sectional view showing a blow-in state, FIG. 5 is a cross-sectional view showing a state in which a joint mold part is closed, and FIG. 6 is a cross-sectional view showing a mold opening.

A blow molding die 10 shown in FIG. 1 is used in the method of molding a hollow plastic molded product of the present invention, and comprises split dies 11a and 11b.
Blow molding is performed between the parisons 11b.

[0010] Mold surfaces 12a, 12b of split molds 11a, 11b
Consists of the outer shape of the desired hollow plastic molding. The hollow plastic molded product formed by the split dies 11a and 11b has a thin portion formed of a parison joint at one end, similarly to the molded product of FIG. 8B described in the description of the prior art. . The split mold 11a includes a joint mold portion 13 for shaping the joint portion of the parison and a main body mold portion 15 for shaping the other portion. In this example, the bonding mold portion 13 is configured to shape the bonded portion of the molded article and the vicinity thereof, but may be configured to shape only the bonded portion. It is appropriately determined according to the shape and the like near the joint portion of the product. The joint type part 13 is provided on the main body type part 15 so as to be able to move forward and backward with a hydraulic cylinder (not shown) or the like.
At the most advanced position, the mold surface 13a of the joint mold portion 13 and the mold surface 15a of the main body mold portion 15 are arranged in series. The joining mold part 13 formed as a series with the mold surface 15a of the main body mold part 15.
When the blow molding die 10 is closed, the space between the mold surface 13a and the joint forming surface 13b of the other split mold 11b is
The narrowest part is set to have a dimension of twice or less the thickness of the parison.

The joint mold 13 may be provided not only on one split mold 11a but also on the other split mold 11b. However, as shown in this example, a molded article which is concealed when the molded article is used. Is provided on the split mold 11a for shaping, so that the dividing line between the mold face 13a of the joining mold part 13 and the mold face 15a of the main body mold part 15 does not appear on the design surface of the molded product. Is preferred.

Next, an example of a method for forming a hollow plastic molded product using the blow molding die 10 will be described. First, as shown in FIG.
Extrusion molding machine (not shown) between split molds 11a and 11b
, A parison P made of a thermoplastic plastic is extruded and arranged in a molten state.

Subsequently, as shown in FIG.
a, 11b are closed and the parison P is sandwiched. At this time, with respect to one split mold 11a, the joint mold portion 13 is retracted, and the mold surface 13a of the joint mold portion 13 is retracted. The receding amount of the joining mold portion 13 may be such that the inner surface of the parison Pa located in the portion of the joining mold portion 13 does not adhere.
When the mold 3 is closed in advance, wrinkles and the like are easily generated in the joint portion of the parison Pa. Normally, the parison Pa is set to have a narrowest inner surface interval at the position of the jointing mold portion 13 so as to be about 1 mm to 10 mm.

Then, as shown in FIG. 4, air A at about room temperature is blown into the parison P through an air blowing pipe (not shown), as in the ordinary blow molding.
Is blown into the shape of the mold surface of the blow molding die 10, and is shaped into a molded product except for the portion of the mold surface 13 a of the joint mold 13. At this time, the parison Pa located at the part of the joint part 13 is in a state in which the mold surface 13a of the joint part 13 is retracted, so that the parison Pa swells more than a desired product shape. A gap S is formed in the gap. Also,
The parison P is cooled from the inside by blowing air into the parison P, and the parison P
The temperature becomes lower than the temperature at the time of arrangement to 0. At this time, the parison Pa located at the jointing portion 13 is efficiently cooled by the blown air because the gap S exists between its inner surfaces.

Subsequently, as shown in FIG. 5, the joining mold portion 13 is advanced, the portion of the joining mold portion 13 is closed, and the inner surface of the parison Pa at the position of the joining mold portion 13 is closed. To adhere. The temperature of the parison P at the time of closing the jointing portion 13 is preferably a temperature at which the weldability of the inner surface of the parison P is not completely lost, and differs depending on the type of the resin constituting the parison P. The parison Pa portion of the joint mold portion 13 that is brought into close contact by closing the mold is integrated into a thin joint portion G, which is shaped into a molded product.

Since the joining portion G is formed after the parison P is cooled by the blowing air, the amount of heat held by the joining portion G at the time of the formation is limited to a high-temperature state immediately after being placed in the blow mold 10. Compared to a case in which air is blown into the parison of the above to form the joint portion and other portions at one time.
As a result, the amount of shrinkage of the joint portion G is reduced even by the subsequent natural cooling after the mold release, the surface shape at the time of forming the joint portion G is maintained, and sink is prevented.

Thereafter, as shown in FIG.
By opening 0 and taking out the molded product 20 and removing the unnecessary portion, a desired hollow plastic molded product can be obtained. The obtained hollow plastic molded product has a thin joint portion G having a good appearance without sink marks on the surface.

[0018]

As shown and described above, in the method of molding a hollow plastic molded article according to the present invention, air is blown into the parison to inflate it into a required shape, and then the inner surface of the parison is brought into close contact with the parison. Then, the joint is formed.
For this reason, the parison is cooled by the blown air at the time of shaping the joint portion, and the parison has a smaller amount of heat than at the time of shaping by air blowing. as a result,
The amount of shrinkage due to a change in the amount of heat between the formation of the joint portion and the subsequent molded product is reduced, and sinks are less likely to occur on the surface of the joint portion. Therefore, according to the present invention, it is possible to easily obtain a hollow plastic molded product having good appearance without sink marks on the surface of the thin wall portion formed by the joint portion of the parison. In addition, since there is no gap in the joint portion, the thickness of the thin portion can be sufficiently reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of one example of a blow molding die used in a method of molding a hollow plastic molded product according to the present invention.

FIG. 2 is a cross-sectional view showing a state in which a parison is led between split molds in one embodiment of the method for molding a hollow plastic molded product of the present invention.

FIG. 3 is a cross-sectional view showing a state in which a joint type part is opened and another part is closed in the embodiment.

FIG. 4 is a sectional view showing a state in which air is blown into a parison in the embodiment.

FIG. 5 is a cross-sectional view showing a state in which the joining mold part is closed in the embodiment.

FIG. 6 is a sectional view showing a mold opening in the embodiment.

FIG. 7 is a sectional view of a blow molding die showing a general blow molding method.

FIG. 8 is a sectional view showing an example of a hollow plastic molded product.

FIG. 9 is a cross-sectional view of a blow molding die when a plastic molded product having a thin portion is molded by a conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Blow molding die 11a, 11b Split mold 13 Joint part 15 Main body part G Joint part P Parison

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Akira Sugiura 8-1, Tocho, Fujii-cho, Anjo-shi, Aichi Prefecture Inoac Corporation Sakurai Office

Claims (1)

[Claims] 1. When blow molding a hollow plastic molded product having a joint portion in which the inner surface of a predetermined portion of a parison is in close contact with a product portion, air is blown into the parison and the parison is inflated and shaped. A method of forming a hollow plastic molded product, wherein the inner surface of a predetermined portion of the parison, which becomes the bonding portion, is brought into close contact and bonded.