JP2579997B2 - Method for manufacturing resin molded products - Google Patents

Description

The present invention relates to a method for producing a resin molded article having a hollow portion by using a hollow core that is melted by heating.

<< Prior Art >> A method using a core is generally used for manufacturing a resin molded product having a hollow portion. In order to easily remove the core from the molded article, a method is known in which the core is formed from a low melting point alloy, and the core is eluted from the molded article by heating after the injection molded article. When the core is made of an alloy as described above, the specific gravity of the alloy is large, so that the core becomes heavy and handling becomes difficult.

Therefore, by reducing the core made of such a low melting point alloy into a hollow shape, the weight of the core is reduced.

However, when this hollow core is used for manufacturing an injection-molded product, the core whose strength has been reduced by making it hollow may not be able to withstand the pressure during resin injection and may be deformed.

Also, as another problem, when an alloy core is used, if this operation is performed in an oxidizing atmosphere when the core is melted after injection molding, the molten alloy is oxidized and reused. Can not be done.

To solve the above strength problems, for example,
As disclosed in Japanese Patent Application Laid-Open No. 60-14912, it has been proposed to arrange a reinforcing rib on the inner peripheral surface of a hollow core to increase the strength thereof.

A method has also been proposed in which a liquid is sealed in the hollow portion of the hollow core to increase the strength.

<< Problems to be Solved by the Invention >> However, in the former method of forming a reinforcing portion such as a rib on the core, there is a dislike that the production of the core is complicated, and depending on the shape of the core, the rib may There is a case where it is difficult to secure required strength because there is a restriction in a place where the ridge is provided. On the other hand, in the latter method of enclosing the liquid in the hollow portion of the core, the liquid itself has no rigidity, so that the core may still be deformed as a whole.

To solve such a problem, for example, it is conceivable to melt and fill a wax product which becomes solid at room temperature in a hollow core.

However, this method reinforces the strength of the hollow core, but has the following new technical problems. That is, since the low-melting-point alloy and the wax product of the hollow core eluted from the molded article are usually used repeatedly plural times, the elution of the wax product or the hollow core is carried out in a non-oxidizing atmosphere, for example, in oil. However, when the wax product is eluted in such a state, there is a problem that the separation is particularly difficult because the specific gravity of the oil and the wax product is close.

Therefore, an object of the present invention is to provide a hollow core used in the production of a resin molded article in a hollow portion with a strength sufficient to withstand a force applied at the time of resin injection, and at the same time, in a non-oxidizing atmosphere when the core is molten. An object of the present invention is to propose a method of manufacturing a resin molded product that can be molded in a preferable state.

<< Means for Solving the Problems >> In order to solve the above problems, in the method of the present invention, in the method for producing a resin molded article having a hollow portion using a hollow core, the hollow core Then, a wax product having a lower melting point and specific gravity than the material of the core is melted and filled, and the hollow core obtained by solidifying the filled wax product is placed in a mold and subjected to injection molding. The wax product is eluted by heating later, the hollow core is immersed in the eluted molten wax product, and the core material is heated in a state where it is shielded from the atmosphere, so that the core material is melted. A resin molded product was manufactured by a process of elution into the resin.

According to the method of the present invention, injection molding is performed with the solidified wax product filled in the hollow core. Therefore, unlike the conventional case where the liquid is filled, the core is given strength by the wax product itself, so that the core is not deformed by the force applied at the time of injection. Further, since the melting point of the wax product is lower than the melting point of the core, the wax product is eluted from the core in a low heating state.

If the amount of the eluted wax product is sufficient to immerse the core, the wax product blocks the core from the atmosphere, and thus does not oxidize the core in the next step. Can be eluted from the molded article.

Examples of the above-mentioned wax molded product include a hydrocarbon-based product, which has a specific gravity of about 0.9 and a typical value 1 of the specific gravity of the alloy forming the core.
Much smaller than 0.

Therefore, the wax product and the alloy forming the core do not mix with each other in their molten state, and the wax product covers the molten alloy.

<< Example >> Hereinafter, an example to which the method of the present invention is applied will be described with reference to the drawings.

FIG. 1 shows a resin molded product manufactured by the method of this example. As shown in the figure, the molded article 1 has a shape including a hollow spherical portion 11 and a cylindrical portion 12 protruding from the spherical portion.

In order to manufacture the above-mentioned molded article 1, in this example, a hollow core 2 having a size to be accommodated in the hollow portion 13 of the molded article 1 as shown in FIG. 2 is prepared.

The core 2 is made of an alloy containing Sn and Bi at a weight distribution ratio of 42:58, and has a melting point of 137 ° C.

Next, the hollow portion 21 of the hollow core 2 is filled with a hydrocarbon wax 3 (melting point: 100 ° C.) in a molten state, and then the hollow core 2 is cooled to solidify the filled wax 3. Was.

Next, as shown in FIG. 3, the hollow core 2 filled with the solidified wax is placed in a mold 4 for injection molding.
As shown in the figure, resin was injected from the gate opened in the mold 4.

The resin used in this example is nylon-6, which has a melting point of 220 ° C.

After the completion of the injection molding, the molded article 5 is taken out of the mold 4 as shown in FIG. 5, and the same wax as the washer 3 in the core 2 is melted as shown in FIG. Into the collecting tank 6 stored in the above.

Thereafter, the inside of the recovery tank was first heated to a temperature slightly higher than 100 ° C., which is the melting point of the wax 3, whereby the wax 3 in the hollow core 2 was eluted from the core 2.

Next, the inside of the recovery tank 6 is heated to a temperature higher than the melting point of the core 2 to elute the core 2 from the inside of the molded article 5. The specific gravity of the alloy forming the core 2 is about 10 and the specific gravity of the wax is
Since it is much larger than 0.9, the molten alloy 2 ′ accumulates at the bottom of the recovery tank 6, as shown in FIG. 6, and is covered with wax 3, so that the molten alloy does not come into contact with the atmosphere. Absent.

Also, both materials are completely separate, so that they can be reused.

In this example, a certain amount of wax was previously stored in the recovery tank, and the non-oxidizing atmosphere when the core 2 was melted was formed by the wax and the wax eluted from the hollow core 2. However, there is a sufficient amount of wax in the core 2,
When the non-oxidized state of the core 2 at the time of melting can be formed only by the amount of the wax, it is not necessary to store the wax in the recovery tank 6 in advance.

<< Effects of the Invention >> As described above, according to the method of the present invention, since the hollow core is filled with the wax product in a solidified state, the core is deformed by the force acting upon injection of the resin. Can be avoided.

Also, since the wax eluted from the core can be used to form a non-oxidizing atmosphere of the core when the core is melted, there is an advantage that such a non-oxidizing atmosphere can be formed at low cost and easily.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a resin molded product manufactured according to an embodiment to which the present invention is applied, FIG. 2 is a cross-sectional view showing a hollow core filled with wax, and FIG. FIG. 4 is a configuration diagram showing a state after resin injection is performed, FIG. 5 is a cross-sectional view showing a molded product taken out of the molding die, and FIG. 6 is a collection tank. FIG. DESCRIPTION OF SYMBOLS 1 ... Molded product 2 ... Hollow core 2 '... Molted core alloy 3 ... Wax 3' ... Molted wax 4 ... Mold 5 ... Molded product having a core 6 …… Recovery tank

Claims (1)

(57) [Claims] 1. A method for producing a resin molded article having a hollow portion using a hollow core, wherein a wax product having a lower melting point and specific gravity than the material of the core is melted in the hollow core. The hollow core, in which the filled wax product is solidified, is placed in a mold to perform injection molding, and thereafter, the wax product is eluted by heating, and the eluted molten wax is produced. A method for producing a resin molded article, comprising a step of immersing a hollow core in a product and heating the hollow core in a state in which it is shielded from the atmosphere to elute the core material into a molten wax product.