JPH0788845A - Method for molding of hollow resin product and core for molding hollow resin article - Google Patents

Abstract

PURPOSE:To prepare stably a hollow resin product by a lost core method by using a core which is not made of a low m.p. alloy and hardly generates cracks. CONSTITUTION:A core 1 is formed by impregnating a soft porous body 10 with a substance for impregnation liquid at ordinary temp. in a liquid state and solidifying it by cooling and after a molded item with a built-in core 1 is formed by arranging the core in a mold 4, the molded item is heated to ordinary temp. and the impregnating substance is melted to make it flow out from the soft porous body 10 and then, the soft porous body 10 is removed from the molded item. As the stress of expansion when it is frozen is absorbed in the soft porous body, cracks in the impregnating substance in the core 1 can be prevented from developing and the core is prevented from breaking and defects on the surface of the hollow part can be prevented from occurring.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for molding a hollow resin product and a core used during the molding.

[0002]

2. Description of the Related Art The lost core method has been conventionally known as a method for forming a hollow resin product. With this lost core method, a predetermined shape is retained during molding,
This is a method using a core that can be easily removed by means such as melting after molding. As the material of this core,
Low melting point alloys having a melting point lower than that of the resin are generally used. Then, the low melting point alloy is removed from the molded body by heating and melting after resin molding, whereby a hollow resin product can be formed.

However, the low melting point alloy has a large specific gravity because it is a metal even though it has a low melting point, and therefore the weight of the core becomes large, which causes problems in handling workability and transportation equipment. Further, when the core is removed from the molded body, the loss of the expensive low melting point alloy is unavoidable, and there is a problem that the cost of the hollow resin product increases accordingly. From the aspect of casting technology, there is a limit to the hollowness of the core made of low melting point alloy, and there is also a limit to the weight reduction of the core. Furthermore, many low melting point alloys are toxic, which poses a problem in terms of working environment.

Therefore, a core material to replace the low melting point alloy has been studied. For example, Japanese Patent Laid-Open No. 62-135325 discloses that
A molding method utilizing an ice mold formed from ice is disclosed. Further, in Japanese Patent Application Laid-Open No. 1-118337, a bag body filled with a flowable substance such as ice is placed in a molding die for core molding, and the flowable substance is fluidized and removed after core molding. A method of removing the bag and manufacturing a hollow core is disclosed.

[0005]

However, when the core is formed from an ice mold, cracks are generated in the core due to the effects of gases such as oxygen dissolved in water and the effects of volume expansion during freezing. There is a problem that it easily occurs. This crack is likely to occur especially in the case of quick freezing. In addition, since ice has low toughness, even when relatively small cracks are formed, it may progress and be destroyed when an external force is applied. Furthermore, there is also a problem that the dimensional stability of the core is low due to volume expansion during freezing.

The present invention has been made in view of the above circumstances, and it is possible to stably manufacture a hollow resin product by the lost core method using a core which is not made of a low melting point alloy and is less likely to cause cracks. With the goal.

[0007]

According to the method for molding a hollow resin product of the present invention, which solves the above-mentioned problems, a soft porous body is impregnated with a liquid impregnating substance in a liquid state at room temperature and solidified by cooling to form a core. Then, the core is placed in the mold and resin is injected to form a molded body containing the core, and then the molded body is returned to room temperature and the core is impregnated and solidified to melt the impregnated substance. And the soft porous body is removed from the molded body.

The core of the present invention is characterized in that a substance that is liquid at room temperature is impregnated in a liquid state into a soft porous body, and the substance impregnated in the soft porous body is solidified by cooling. Further, the soft porous body is a foam, and it is desirable that some of the cells include closed cells.

Water is a typical impregnating substance that is liquid at room temperature, but a mixture of water and an organic solvent such as alcohol, an aqueous solution in which a salt is dissolved, or the like can also be used. As the soft porous body, a foam such as urethane foam or polyolefin foam, or a fiber structure in which fibers are intertwined can be used. In the case of a foam, it is desirable that about 10% of the cells contain closed cells. As a result, the expansion of the liquid impregnating substance when it solidifies is absorbed by the deformation of the closed cells, so that the dimensional stability of the core is improved.

The size of the pores of the soft porous body is preferably 2 mm or less in order to prevent the development of cracks in the impregnated substance. Furthermore, in order to facilitate the removal of the core from the hollow resin product, the hardness of the soft porous body should be 30 kg / 314c as measured by JIS-K6401.
It is preferably m ² or less. In addition, it is also preferable to form a surface layer made of a material having a small thermal conductivity such as a synthetic resin on the surface of the core that comes into contact with the mold. This prevents the core surface from melting and deforming when it comes into contact with the mold. Further, it is more preferable that this surface layer is made of a material having high flexibility.

[0011]

In the core for molding a hollow resin product of the present invention, a soft porous body is impregnated with a liquid impregnating substance at a normal temperature to form a predetermined shape, and the impregnating substance is solidified by cooling the impregnating substance. The shape is retained. The core whose shape is maintained in this way is placed in a mold, and resin is injected between the core surface and the mold surface by injection molding or the like. When the resin is cooled and solidified, the core gradually becomes room temperature.

By the time the core reaches room temperature, the impregnated substance that has solidified becomes liquid and the soft porous body is easily deformed, so that it can be easily removed from the resin molded body, A hollow portion is formed. Here, the core is composed of a soft porous body and an impregnated substance which is solidified by impregnating its pores. Therefore, even if minute cracks are generated in the impregnated substance solidified by the stress acting during rapid freezing, the progress of the cracks is restricted by the mesh of the porous body and the energy is absorbed by the deformation of the mesh. Are prevented from making further progress.

Further, even when an external force is applied to the core, the development of fine cracks caused by the external force is prevented,
The strength of the core is uniform and damage is prevented.

[0014]

EXAMPLES The present invention will be specifically described below with reference to examples. (Example 1) Foam-molded from a urethane foam resin to have a density of 0.05 g / cm ³ , a 25% hardness defined in JIS-K6401 of 15 kg / 314 cm ² , and about 1 closed cell.
Foam molded article 10 made of urethane foam containing 0%
Was formed. Then, liquid silicone rubber is applied to the side peripheral surface of the foamed molded body 10 and left standing at room temperature to cure, and the skin layer 1
1 was formed. Urethane foam is exposed on both end faces of the foamed molded body 10. The skin layer 11 is not limited to silicone rubber, and a skin layer made of ice frozen after spraying water can be used, for example.

On the other hand, a pair of holding members 20 and 21 were formed from a phenol resin and sandwiched and held from both ends of the foam molding 10. The state is shown in FIG. This was placed in a rubber mold 3 for freeze molding as shown in FIG. 2, and water was supplied from a water injection pipe 30 to the foamed molded product 10 to impregnate it. And -20
It was left to freeze in a freezer at ℃ for about 2 hours to form a core 1 shown in FIG. 3 having an apparent density of about 0.8 g / cm ³ . No large cracks that would adversely affect the quality of the hollow resin product were observed in the core 1.

The core 1 is further immersed in liquid nitrogen and cooled to -196 ° C., then placed in the molding die 4 shown in FIG. 4, and molten polypropylene is injected from the injection molding machine 5 into the cavity 40. Injection molding was performed. After the molded body in the cavity 40 is cooled, the core 1 is taken out from the mold 4 together with the resin product 6 as shown in FIG.
0 and 21 were removed and left naturally. As a result, the ice impregnated and solidified in the foamed molded body 10 was melted and turned into water, which flowed out from the lower end surface of the foamed molded body 10. When the foamed molded body 10 became deformable by melting the ice, the foamed molded body 10 was pulled out from the resin product 6, and the hollow resin product 6 shown in FIG. 6 was obtained.

Since the hollow resin product 6 thus obtained had a smooth inner peripheral surface of the hollow portion, it was judged that the core 1 was not broken during molding. In another experiment, when a foamed molded body was formed from urethane foam having no closed cells and a hollow resin product was molded in the same manner, the shape of the core 1 expanded by about 10%, whereas in this example, Although the water expanded, the shape of the core 1 maintained the predetermined shape, and the post-processing of the hollow resin product was unnecessary. This is due to the presence of approximately 10% closed cells in the foamed molded body 10. (Example 2) Polyester fiber (diameter 40 μm, length 6)
cm) and heat fusion fibers (diameter 40 μm, length 6 cm) were mixed at a weight ratio of 7: 3 and defibrated to form a web. The heat-fusible fiber is a polyester having a melting point of 250 ° C. in the core and a modified polyester having a melting point of 170 ° C. in the sheath.

This was filled in a mold so that the apparent density was 40 kg / m ^3, and heated in a hot air oven at 200 ° C. for 5 minutes. As a result, only the sheath portion of the heat-sealing fiber was melted, functioning as a binder to fuse the surrounding fibers, and thereby a fiber structure having the same shape as the foam-molded body of Example 1 was obtained.
Further, this fiber structure exhibited the same cushioning property as the foamed molded article of Example 1.

This fiber structure was used as the foamed molded article 1 of Example 1.
When a hollow resin product was formed in the same manner as in Example 1 by using instead of 0, a hollow resin product having the same surface condition as in Example 1 was obtained. In order to prevent the core from cracking, the diameter is 100 μm or less and the apparent density is 3 μm.
It is desirable to use 0-100 kg / m ³ of fibers.

[0020]

That is, according to the hollow resin product molding method and the hollow resin product molding core of the present invention, the core can be formed from an inexpensive material having no toxicity. Since it is lighter in weight than the conventional core made of low melting point alloy, it is excellent in handling workability. Since a large crack is prevented from being generated in the core, the core is excellent in strength and surface smoothness, and a hollow resin product excellent in quality can be stably manufactured.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a state in which a foam molding used in an embodiment of the present invention is held by a holding member.

FIG. 2 is a cross-sectional view showing a state in which the foam molded article used in one example of the present invention is placed in a rubber mold and water is injected.

FIG. 3 is a cross-sectional view showing a state where a core used in one embodiment of the present invention is held by a holding member.

FIG. 4 is a cross-sectional view showing a state where a core is placed in a mold and injection-molded in one embodiment of the present invention.

FIG. 5 is a cross-sectional view of a resin product having a core obtained in one example of the present invention.

FIG. 6 is a cross-sectional view of a hollow resin product obtained in one example of the present invention.

[Explanation of symbols]

1: Core 10: Foamed molded product (soft porous material)
11: Skin layer 20, 21: Holding member 3: Rubber mold 30: Water injection pipe 4: Mold
40: Cavity 5: Injection molding machine 6: Hollow resin product

Claims (3)

[Claims] 1. A core is formed by impregnating a soft porous body in a liquid state with an impregnating substance which is liquid at room temperature to solidify by cooling, and the core is placed in a molding die and resin is injected into the core. After forming a molded body containing therein, the molded body is returned to room temperature, the impregnated substance impregnated and solidified in the core is melted and allowed to flow out from the soft porous body, and the soft porous body is removed from the molded body. A method for molding a hollow resin product, which comprises removing the hollow resin product. 2. A core obtained by impregnating a soft porous body in a liquid state with a substance that is liquid at room temperature and solidifying the substance impregnated in the soft porous body by cooling. 3. The core according to claim 2, wherein the soft porous body is a foam and contains closed cells in some of the cells.