JP3043849B2 - Injection mold manufacturing method - Google Patents

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 thermoplastic resin mold by injection molding.

[0002] In the case of obtaining a molding die of a thermoplastic resin, a method of feeding a gaseous fluid into a flow of a molten resin to obtain a hollow portion is being widely adopted at present. Such a molding method has many advantages such as sink prevention, molding distortion reduction and weight reduction, and is suitable for reinforcing members and structural members. However, FIG.
In many cases, the distribution of the hollow portion 2 due to the gaseous fluid in the resin portion 1 of the molded article does not go as designed or is not constant.

If molding is performed in such a state, the distribution of other types of fluids in the molded product cannot be controlled in an ideal manner in many cases. In the worst case, there is a situation that the resin layer is penetrated, and there is a disadvantage that the product yield is deteriorated.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of manufacturing an injection-molded product which can solve the above-mentioned disadvantages of the prior art and can obtain a fluid distribution as expected.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a method of manufacturing a molding die, in which a molten resin is injected into a mold cavity to perform molding. While injecting the seed fluid, selectively compressing the part of the mold cavity required for optimizing the arrangement of the low-viscosity fluid in the molten resin, while filling the entire mold cavity with the molten resin. The method is characterized by a method of manufacturing an injection-molded die, wherein the low-viscosity fluid is distributed at a desired position.

In the present invention, a desired fluid distribution can be obtained by appropriately adjusting the timing of compressing the whole or a part of the mold cavity.

[0007]

The present invention is based on the fact that when a mixture of a high-viscosity fluid and a low-viscosity fluid is compressed, the low-viscosity fluid is first preferentially removed from the pressurized portion. According to the present invention, a molten resin, which is a high-viscosity fluid, is injected into a mold cavity, and an appropriate amount of a gas, which is a low-viscosity fluid, is injected. At the same time or with appropriate timing delay, control is performed so as to compress the entire or a part of the mold cavity and reduce the volume of the mold cavity.

[0008] The contents of the mold cavity subjected to such compression have low viscosity fluid removed from the pressurized portion. Therefore, if the low-viscosity fluid is converted into a gas such as nitrogen gas or carbon dioxide gas and injected into the molten resin in the mold cavity, a hollow portion can be obtained. However, the hollow portion can be appropriately distributed to a desired position. .

That is, among the constituent parts of the mold, the part to be solid and the part to be hollowed out are clarified, and pressure is applied to the former part so as not to be applied to the latter part so as to reduce the viscosity. The distribution of the gaseous fluid, which is a fluid, can be arbitrarily controlled. Naturally, such compression must be performed before solidification of the molten resin which is a high-viscosity fluid, but many modifications are conceivable. For example, by changing the rate of pressure rise, dividing the time and / or location into a plurality of stages, and further employing means such as performing compression with each adjusted pressure,
A more desirable distribution of hollows and solids can be achieved.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be disclosed below with reference to the accompanying drawings showing embodiments. FIG. 1 is a conceptual diagram showing the principle of a method for manufacturing an injection mold according to the present invention. The left part (I) of the figure shows a state in which the molten resin 11 has been injected into the mold cavity 10. FIG. 2 (II) at the center shows a state in which a gaseous fluid is injected into the molten resin 11 and the hollow portion 12 is formed. Simultaneously or with an appropriate timing delay, pressure is applied to the whole or a part of the mold cavity as indicated by an arrow to compress the contents. As a result, as shown in the right part (III) of the figure, a strong compressive force acts on the horizontal portion of the mold, and the solid portion becomes a reliable solid state. On the other hand, a hollow portion is formed from the base of the vertical portion where compression force is reduced to the vertical portion.

This embodiment shows a state in which the left and right horizontal portions of the molding die are uniformly compressed. However, by appropriately changing the compression force or changing the compression timing, the hollow portion 1 is compressed.
It is also possible to change the position, shape and other conditions of the second.

FIG. 2 shows an example of an apparatus suitable for carrying out the present invention. The positional relationship between the mold 15 and the heating cylinder of the injection molding machine and the injection nozzle 16 is the same as that in the molding machine according to the prior art.

The mold 15 has a sprue 17 and a runner 18 and communicates with the mold cavity 10 via these. Behind the mold cavity 10, the compression bodies 19 and 21
Is provided. These compression bodies 19 and 21
The pressure is increased by a pressure system having a pressure gauge and a variable valve connected via a solenoid valve 23. Although a pressurizing cylinder 20 is provided in the mold for the compression body 19, a fluid cylinder 22 is provided outside as shown in the lower part of the figure, and only the mechanical acting force is transmitted to the compression body 21. It can also be configured as follows.

In practicing the present invention, means for injecting a gaseous fluid as a low-viscosity fluid into the molten resin is required. As such means, the injection nozzle 24 from the injection nozzle 16 can be used. Others
Injection can be performed simultaneously or at different times from one or more locations such as the sprue 17, the runner 18, the mold cavity 10, and the like.

FIG. 3 to FIG. 6 illustrate steps in carrying out the manufacturing method according to the present invention separately. FIG. 3 shows a state in which the molten resin stored at the tip of the heating cylinder 16 of the injection molding machine is injected into the sprue 17 of the mold 15. In this case, the compression bodies 19 and 21 behind the mold cavity 10 are retracted.

FIG. 4 shows that a predetermined amount of molten resin is sprue 17,
FIG. 3 shows a state in which the mold is injected into the mold cavity 10 through the runner 18. Also in this case, the compression bodies 19 and 21 behind the mold cavity 10 remain retracted.

FIG. 5 shows a fluid nozzle 24 provided at the injection nozzle for the molten resin injected into the mold cavity 10.
FIG. 2 shows a state in which a gaseous fluid is injected into the mold cavity 10 while extending into the mold cavity 10 while forming a hollow portion inside the molten resin.

FIG. 6 shows that during or at the same time as the injection of the gaseous fluid or at the end of the injection, the compression bodies 19 and 21 behind the mold cavity 10 are operated to pressurize the whole or a part of the molded article. As a result, the molten resin reaches the end of the mold cavity 10, and the gas body, which is a low-viscosity fluid, is repelled from the pressurized portion to other portions, forming a hollow portion at a predetermined portion. Therefore, the contact surface shapes and arrangements of the compression bodies 19 and 21 and the compression stroke are extremely important for obtaining a desired molded product, and should be appropriately set according to the desired molded product shape.

By controlling the pressure of the gas body, controlling the number of times of pressurizing, and the like, it is possible to obtain a molded article having a good appearance and a distribution of hollow portions optimized for a desired portion.

As the resin suitable for the production method according to the present invention, many plastics can be mentioned. It can be applied to multiple blended resins.

[0021]

According to the method of manufacturing an injection mold according to the present invention, when the mold cavity is compressed, the molten resin, which is a high-viscosity fluid, and the gas, which is a low-viscosity fluid, flow simultaneously. An undesired phenomenon such as penetrating the resin layer is unlikely to occur. Furthermore, if a portion that is to be solid becomes solid to the end and a portion that is to be hollow is not compressed, the hollow state can be almost certainly achieved. As a result, it is possible to obtain a mold having a hollow portion optimized at a desired portion.

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram of a method for producing an injection mold according to the present invention.

FIG. 2 is an explanatory diagram showing a configuration of a main part of an apparatus suitable for carrying out a method of manufacturing an injection mold according to the present invention.

FIG. 3 is an explanatory diagram showing a main step 1 of the method for producing an injection mold according to the present invention.

FIG. 4 is an explanatory view showing a main step 2 of the method for producing an injection mold according to the present invention.

FIG. 5 is an explanatory view showing main step 3 of the method for producing an injection mold according to the present invention.

FIG. 6 is an explanatory view showing main step 4 of the method for producing an injection mold according to the present invention.

FIG. 7 is a cross-sectional view of a structural model of an injection mold according to the related art.

[Explanation of symbols]

 10 mold cavity 11 molten resin 12 hollow part

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hiyoshi Okamoto 3-7-2 Nihonbashi Honcho, Chuo-ku, Tokyo Japan GE Plastics Co., Ltd. (56) References JP-A-4-353408 (JP, A) JP-A-4-182106 (JP, A) JP-A-4-74617 (JP, A) JP-A-3-133618 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 45 / 00-45/84

Claims (1)

(57) [Claims] 1. A method of manufacturing a molding die for injecting a molten resin into a mold cavity to perform molding, wherein a different fluid having a lower viscosity than the molten resin is injected into a flow of the molten resin, and The part of the mold cavity required for optimizing the arrangement of the low viscosity fluid in the molten resin is selectively compressed, and the low viscosity fluid is moved to a desired position while filling the entire mold cavity with the molten resin. And distributing it.