JPH07124986A - Preparation of blow molded article - Google Patents

Abstract

PURPOSE:To realize a method for preparing a blow molded article wherein no pinhole is generated and good moldability is provided. CONSTITUTION:A mold 1 is clamped and under a condition wherein the apex part of a core mold 3 is projected into a cavity 2, a molten resin is injected and fed into the cavity 2 through a gate 4 from an injection nozzle 5a of an injection apparatus 5 to form a bottomed cylindrical body 12 consisting of a molten resin so as to envelop the apex part of the core mold 3. Thereafter, feeding of a pressurized fluid under pressure is started under a pressure of at most 10kg/cm<2> into the inside of the bottomed cylindrical body 12 through a path 3a. The bottomed cylindrical body is expanded by starting to feed this pressurized fluid under pressure and at the same time, injection and feeding of the molten resin is continuously performed and it is expanded along the cavity 2 while the molten resin with a volume corresponding to the expansion of the bottomed cylindrical body 12 is fed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hollow molded article having good moldability.

[0002]

2. Description of the Related Art Conventionally, as a method for producing a hollow molded article by so-called injection hollow molding, as shown in FIG.
After the core mold 103 is protruded from one end of the cavity 102 having the shape of an umbrella 01 and clamped, the sprue gate 1
04, the molten resin 106 is injected, and when the molten resin 106 reaches a predetermined amount, the injection is stopped, and the pressurized fluid is blown from the air blowing pipe 105 to form bubbles 107 and expand the shape along the cavity 102. The method is proposed (see Japanese Patent Laid-Open No. 5-84762).

[0003]

SUMMARY OF THE INVENTION In the above conventional technique,
Since the injection of the molten resin is stopped at the time of injecting a predetermined amount of the molten resin into the cavity, the pressurized fluid such as pressurized air or nitrogen gas is blown into the molten resin to expand it.
The pressure of the pressurized fluid must be high, or the temperature of the molten resin must be set to a high temperature to enhance the fluidity.

However, the pressure of the pressurized fluid is high (usually 1
It is set to 00 to 150 kg / cm ² . ) Or when the molten resin temperature is high, when the bubbles expand,
There is a problem that a pinhole is generated at the tip of the molten resin while the molten resin does not reach the entire cavity, and pressurized fluid leaks from the pinhole, resulting in defective molding. The present invention has been made in view of the problems of the above-mentioned conventional techniques, and an object thereof is to realize a method for producing a hollow molded article having good moldability without causing pinholes. is there.

[0005]

In order to achieve the above-mentioned object, a method for manufacturing a hollow molded article according to the present invention is a method of producing a split mold having a cavity for restricting an outer peripheral surface of the hollow molded article. After projecting the tip end of the core mold into the mold, the molten resin is injected and injected into the cavity so as to wrap the tip end of the core mold to form a bottomed tubular body made of the molten resin, Then, the pressurized fluid is forced into the bottomed tubular body through the core mold at a pressure of 10 kg / cm ² or less to expand the fluid, and the injection of the molten resin is continuously performed to cause the bottomed fluid to flow. It is characterized in that the molten resin is replenished in an amount corresponding to the expansion of the tubular body and is molded along the cavity.

Further, it is effective to make the shape of the cavity tubular and to project the tip of the core mold from one end thereof.

[0007]

The molten resin is injected and injected into the cavity to form a bottomed cylindrical body made of molten resin so as to wrap around the tip of the core mold, and then pressurized fluid is applied through the core mold at a pressure of 10 kg / Since the molten resin is continuously injected and injected while being injected into the bottomed tubular body to be expanded at a cm ² or less, an amount of the molten resin commensurate with the expansion of the bottomed tubular body is replenished. The molten resin forming the bottomed cylindrical body is uniformly expanded along the cavity without breaking through the tip of the molten resin and generating a pinhole.

[0008]

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

First, an example of an apparatus for manufacturing a hollow molded article used for carrying out the present invention will be described.

As shown in FIG. 1, the core mold 3 is freely movable toward and away from the mold 1, and the passage 3a of the core mold 3 is connected to one end of the supply / exhaust pipe line 6, and the supply / exhaust pipe line is formed. The other end side of 6 is branched into a first branch pipeline 6a and a second branch pipeline 6b. The first branch conduit 6a is connected to one end of an air supply conduit 10 with a pressure adjusting portion 8 interposed via a first valve 7a. On the other hand, the second branch pipeline 6b is connected to the exhaust pipeline 11 via the second valve 7b, and the other end of the exhaust pipeline 11 is open to the atmosphere or is connected to a recovery tank (not shown). .

The mold 1 is of a split type,
The connecting portion forming portion 2a is provided at one end and the connecting portion forming portion 2 is provided at the other end.
a and a cylindrical cavity 2 having a bent tubular shape having an unnecessary portion forming portion 2b communicating therewith and a core mold 3 protruding at one end of the cavity 2 by injection-injecting a molten resin to form a bottomed tubular shape It comprises a gate 4 for forming the body 12.

Next, an embodiment of the method for producing a hollow molded article of the present invention will be described.

The mold 1 is clamped together with the core mold 3
With the tip of the injection nozzle 5 a protruding into the cavity 2, the injection device 5 is moved forward to bring the tip of the injection nozzle 5 a into contact with the opening of the gate 4.

After the above, the molten resin is injected from the injection nozzle 5a through the gate 4 into the gap between the outer peripheral surface of the core mold 3 and the inner peripheral surface of the cavity 2 by 30% of the total injection amount. Then, the bottomed cylindrical body 12 made of molten resin is formed so as to wrap around the tip of the core die 3.

After the above, open the first valve 7a,
The pressure is increased by the compressor 9, and the pressure is adjusted by the pressure adjusting unit 8.
A pressurized fluid such as air whose pressure is adjusted to a pressure of less than kg / cm ² (for example, 6 kg / cm ² ) is introduced into the bottomed tubular body 12 through the supply / exhaust pipe line 6 and the passage 3a of the core mold 3. Start press fitting.

Although the bottomed tubular body 12 expands as described above, at the same time, 70% of the total injection amount of the molten resin is continuously injected and injected from the injection nozzle 5a, and the bottomed tubular body 12 is injected. The hollow molded product 13 is molded as shown in FIG. 2 by expanding along the cavity 2 while replenishing the molten resin in an amount corresponding to the expansion.

After the above, after the pressure holding step of maintaining the pressure of the pressurized fluid for a while, the first valve 7a is closed and the second valve 7b is opened to remove the pressurized fluid in the hollow molded product 13. The pressure is released by discharging from the exhaust pipe line 11 or by collecting in a recovery tank or the like.

After the above, the hollow molded product 13 is cooled in the mold 1, and then the mold is opened and taken out.
By cutting a at the cutting portion 13b, the tubular body 20 having the connecting portions 20a at both ends as shown in FIG. 3 is obtained.

In this embodiment, the unnecessary portion 13a having a relatively large wall thickness is cut off by the cutting portion 13b, whereby the tubular body 20 having a uniform wall thickness can be obtained.

In the present invention, the respective injection amounts of the injection injection process A of the molten resin for forming the initial bottomed tubular body and the subsequent process B for continuing the injection injection with the pressurization of the pressurized fluid are , Is appropriately adjusted by a control device (not shown). Preferably, when the total injection amount excluding the volume of the gate 4 is 100%, a resin amount of 10 to 50% in step A and 90 to 50% in step B are injected.

According to the experiment of the present inventor, 10% is obtained in the step A.
If the amount of resin is less than that, a good tubular body with a bottom will not be formed, and if it exceeds 50%, the flow of the pressurized fluid will be poor, and it will be difficult to obtain the desired hollow portion.

According to the present invention, the inner surface of a hollow molded product can be regulated by a core mold, a hollow molded product having a three-dimensional axial core and a three-dimensionally bent shape can be easily molded, and a molten resin having an elongated shape can be used. A tubular body such as a duct or pipe that transfers gas or liquid used for automobile parts, etc., because it can be molded even with a hollow molded product that travels a long distance, and the hollow inner surface can be molded smoothly. Is useful as a manufacturing method of.

In the present invention, the pressurized fluid may be air, nitrogen gas, water, a vaporizable liquid, or the like. Especially, the use of air is preferable because the facility is simple, the handling is easy, and the cost is low. Resins are hard resins such as ABS resin, polypropylene, polystyrene, polyethylene, modified polyphenylene oxide, polycarbonate, polyamide, polyethylene terephthalate, polybutylene terephthalate, soft polyvinyl chloride, polyethylene elastomer, polystyrene elastomer, polypropylene elastomer. A thermoplastic synthetic resin material such as a resin having elastomeric properties such as a polyamide elastomer can be used. In addition, known fillers, flame retardants, pigments, foaming agents and the like can be added to the above-mentioned materials as required.

The present invention is not limited to the above-described embodiment, and a tubular body having an outer surface shape conforming to the shape of the cavity is manufactured by using a mold having a cavity which does not form an unnecessary portion, and various shapes such as a panel shape and a container shape. By using a mold having the above cavity, hollow molded articles having various outer surface shapes can be manufactured.

[0025]

Since the present invention is configured as described above, it has the following effects.

When the bottomed cylindrical body made of the molten resin expands in the cavity by the pressure of the pressurized fluid of 10 kg / cm ² or less, the amount of the molten resin corresponding to the expansion is replenished. Even if the molten resin temperature is not set to an excessively high level, its fluidity is maintained well, so there is no possibility of pinholes breaking through the tip wall of the bottomed cylindrical body and good molding. Is possible.

The pressure of the pressurized fluid is 10 kg / cm ²
Because of the following, equipment and maintenance costs of the pressurized fluid generation source and accessories such as pipelines and valves are low,
As a result, the manufacturing cost of the hollow molded product can be reduced, and the safety of the worker can be secured.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of an apparatus for manufacturing a hollow molded product used for carrying out the present invention.

FIG. 2 is a cross-sectional view showing one step of the method for producing a hollow molded article of the present invention, which is cut along a mating surface of a mold.

FIG. 3 is a plan view of a tubular body manufactured by the method for manufacturing a hollow molded article of the present invention.

FIG. 4 is a cross-sectional view of an essential part showing a molding process of a conventional hollow molded product manufacturing method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mold 2 Cavity 2a Connection part forming part 2b Unnecessary part forming part 3 Core type 3a Passage 4 Gate 5 Injection device 5a Injection nozzle 6 Air supply / exhaust pipe line 8 Pressure adjusting part 9 Compressor 10 Air supply pipe line 11 Exhaust pipe line 12 Bottomed Cylindrical body 13 Hollow molded product 13a Unnecessary portion 13b Cutting portion 20 Tubular body 20a Connection portion

Claims (2)

[Claims] 1. A split mold having a cavity for restricting the outer peripheral surface of a hollow molded product is clamped by projecting the tip of a core die into the cavity, and then wrapping the tip of the core die. Thus, the molten resin is injected and injected into the cavity to form a bottomed tubular body made of the molten resin, and then a pressurized fluid is passed through the core mold at 10 kg / cm ²
While press-fitting and expanding the bottomed tubular body at the following pressure, by continuously injecting and injecting the molten resin, the molten resin in an amount commensurate with the expansion of the bottomed tubular body is replenished and A method for producing a hollow molded article, which comprises molding along a cavity. 2. The method for producing a hollow molded article according to claim 1, wherein the shape of the cavity is tubular, and the tip of the core mold is projected to one end of the cavity.