JPH07237242A - Forming of synthetic resin hollow molding - Google Patents

Abstract

PURPOSE:To make it possible to form a hollow molding without using a core by injecting a resin which adheres firmly to a material resin for an inner hollow form and is molded at an adequately higher temperature than the material resin of the inner hollow form, into an injection molding space, and forming an outer peripheral surface layer which covers the outer peripheral surface of the inner hollow form integrally on the outer peripheral surface of the inner hollow form. CONSTITUTION:An inner hollow form 1 molded by assembling split parts is set in the cavity 2 of an injection molding die B for a finished product hollow molding. This cavity 2 has a shape and a size which are equivalent to the outer profile of a hollow molding as a finished product, and is one size large than the inner hollow form 1. Next, an injection-molding material for an outer peripheral layer which firmly adheres to the material resin of the inner hollow form 1 and is molded at an adequately higher resin temperature than that of the material resin of the inner hollow form 1, is injected into an injection molding space 22 formed between the inner hollow form 1 and the inner surface of the cavity 2. Thus a hollow molding can be obtained without using a core by forming the outer surface layer integrally at the outer side of the inner hollow form 1 in such a manner that the outer side is enveloped.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hollow molded article formed by injection molding, for example, a hollow shape such as an S-shaped, U-shaped, or meandering pipe whose inner portion cannot be molded using a slide mold. The present invention relates to a method of injection molding a molded product.

[0002]

2. Description of the Related Art Conventionally, when a hollow molded article to be molded cannot be molded by using a slide mold such as S-shape, U-shape, meandering shape, etc. as described above, the core is made of an injection molding material ( It is made of a low-melting metal (melting point 130 ° C) whose melting point is lower than the injection temperature of 250 ° C, and this core is installed in the mold and injection molding is performed (the amount of heat that the core melts during injection is given by the injection molding material). Since the core is not melted, the molded product is taken out with the core inside, and then the core is melted at a temperature below the melting point of the molded product and above the melting point of the core. The method of letting it out is adopted.

However, according to this method, a core manufacturing process and a core melting and excluding process are required for the pre-process and post-process of injection molding, resulting in uneconomical material cost and complicated molding process. Not only that, a separate facility or the like for carrying in a heavy core is also required, resulting in a sharp rise in the facility cost.

Therefore, in the Japanese Patent Application No. 5-60256 filed earlier by the applicant of the present invention, a method for forming a pipe-shaped hollow molded article such as an S-shape, a U-shape, a meandering shape, etc., which cannot be formed using a slide mold. As a result, by assembling a pair of half-divided parts, for example, an inner hollow body formed in a U shape with an open end, and a virtual longitudinal direction of the inner hollow body as a mold matching surface and forming a cavity therein. An injection molding die to be prepared, and the inner layer hollow body is set in a cavity of the injection molding die with the open end of the end closed to form an injection molding space around the hollow body, We proposed a method to obtain a hollow molded article integrally provided with an inner hollow body by injecting an injection molding material to form an outer surface layer around the inner hollow body. In the above method, the inner layer hollow body and the outer surface layer that is wrapped around the inner layer hollow body and integrally formed by injection molding are made of the same resin, and when the outer surface layer is injection-molded around the inner layer hollow body, it is injected. In order to prevent the inner hollow body from being pushed toward the side opposite to the gate and eccentric due to resin pressure, the outer surface of the hollow preformed product is provided with several protrusions corresponding to the thickness of the outer surface layer. A predetermined injection molding space is secured around the preformed body.

However, in a subsequent study, when the inner hollow body and the outer surface layer were molded with the same resin, the two had insufficient adhesiveness at the interface, and when a liquid or gas was passed through the hollow molded article, the inner hollow There is a risk that liquid or gas may enter the interface between the inner hollow body and the outer layer from the mating surfaces of the half-parts that make up the body, and may leak out of the product through the interface from the protrusions or the end of the product. It turned out to be.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to improve the method of the invention of Japanese Patent Application No. 5-60256 mentioned above without using a core. A hollow molded product can be molded into a hollow molded product, and even if a liquid or gas is passed through the hollow molded product, there is no risk of leakage of the liquid or gas.

[0007]

In order to achieve the above object, in the method for molding a synthetic resin hollow article of the present invention, an inner layer hollow body made of synthetic resin, which is one size smaller than the hollow molded article of the product, is used. The inner layer hollow body formed by dividing and molding into a plurality of parts of a shape that can be molded without using a core, in the cavity of the injection molding die of the product hollow molding product, The injection molding space is set in the surroundings, and a resin having a high adhesiveness with the material resin of the inner hollow body and a molding resin temperature sufficiently higher than that of the material resin of the inner hollow body is set in the injection molding space. By injection, an outer surface layer that covers the inner hollow body is integrally formed on the outer peripheral surface of the inner hollow body.

[0008]

In the method of molding a synthetic resin hollow article having the above-described structure, the inner layer hollow body is formed by assembling a plurality of parts, each of which is divided into a shape that can be molded without using the core. Instead, an outer surface layer is integrally formed on the outer surface by injection molding, and a hollow molded article is formed by the inner layer hollow body and the outer surface layer that wraps the outside thereof. When molding the outer surface layer, the material resin has compatibility with the material resin of the inner hollow body, and the molding resin temperature is sufficiently higher than that of the material resin of the inner hollow body. When the resin on the outer surface of the inner hollow body is melted and cured by the molding resin temperature, at the interface between the inner hollow body and the outer surface layer, the two resins are cured in a mixed state and firmly adhere to each other as a unit.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. 4 and 5 show an automobile air intake manifold as an example of a synthetic resin hollow molded product A molded by the method of the present invention. In the illustrated example, the air intake manifold has an upward U-shape and connection flanges at both ends. a.

To form the hollow molded product A, first, an inner hollow body 1 having a shape similar to that of the product hollow molded product A and slightly smaller than the product hollow molded product A is prepared. The inner hollow body 1
Is molded from a thermoplastic resin having heat resistance, for example, 6 nylon (PA6), by a well-known appropriate method such as injection molding. However, in order to mold without using a core, two half-divided parts are formed in the axial direction. The parts 11 and 11 are divided into parts, and the pair of parts 11 and 11 formed by dividing the parts into half are abutted to each other to be assembled to form the upward U-shaped hollow body shape. To do.

Further, the joint surface of each half-split part 11 has a concave portion 111 and a convex portion which engage with each other in a normally assembled state.
112 is provided, and the protrusions 113 having a height corresponding to the thickness of the outer surface layer, which will be described later, are formed at appropriate positions on the outer surface. By forming the above-mentioned half-divided parts 11 as 180 ° symmetrical parts, a pair of molds to be combined to form the inner layer hollow body 1 can be formed by one molding die.

Next, the inner-layer hollow body 1 formed by assembling the half-split parts 11, 11 is set in the cavity 2 of the injection molding die B for the hollow product. Cavity 2
Has a shape and size corresponding to the outer shape of the hollow molded product A of the product, and is one size larger than the inner hollow body 1. When the inner hollow body 1 is set in the cavity 2, the protrusion 113 protruding to the outer surface of the inner hollow body 1 abuts the inner surface of the cavity 2 and the injection molding space 22 of uniform width is formed around the inner hollow body 1.
It functions as a spacer that constitutes. Then, next, the injection molding material c for the outer surface layer is injected into the injection molding space 22 formed between the inner hollow body 1 and the inner surface of the cavity 2, and is injected outside the inner hollow body 1. The outer surface layer 4 is formed so as to wrap it.

The injection mold B is composed of a mold body 5 and a slide core 6, and the mold body 5 comprises a pair of split molds 51 and 52, and the cavity 2 has both split molds.
It is formed across 51 and 52.

The cavity 2 has a shape corresponding to one obtained by dividing the hollow molded product A of the product into two parts in the axial direction into a mold matching surface 511 of one split mold 51 and a shape corresponding to the other split mold 52 of the other split mold 52.
Each of the mold matching surfaces 521 is provided with a recess, and when the mold is clamped, the shape of the hollow molded product is slightly larger than the inner hollow body 1. Both ends of the cavity 2 corresponding to both ends in the axial direction of the hollow molded product A are provided with slide core guide spaces 53 that are recessed in the outer surface portion of the molding die body 5 so as to straddle the split dies 51 and 52. And communicates with the outside of the mold body 5.

The slide core 6 has a plate-shaped main body portion 61 having an external shape that is in sliding contact with the guide space 53, and the cavity 2.
The inner layer hollow body 1 housed inside has a closing projection 62 that fits into the end of the opening 3 and closes the same, and the main body 61 is outside the mold 5 of the injection molding material c. To prevent the injection molding material c from entering the opening 3 of the inner hollow body 1. Although not shown, the injection mold 5 is provided with a runner through which the injection molding material c is pushed into the mold 5.

At this time, in the present invention, the outer layer injection molding material c is a resin having a high adhesion to the material resin of the inner hollow body 1 and a molding resin temperature sufficiently higher than that of the material resin of the inner hollow body 1. It is characterized by And in this embodiment,
Since the inner-layer hollow body 1 is molded with 6-nylon, the outer-layer injection-molding material c has a high adhesiveness with 6-nylon and a molding resin temperature sufficiently higher than that of 6-nylon. Used as. As a resin having high adhesion to 6-nylon and a molding resin temperature sufficiently higher than that of 6-nylon, 66-nylon (PA66) having compatibility with 6-nylon can be mentioned. Incidentally, the molding resin temperature of 6-nylon is about 220 ° C and the molding resin temperature of 66-nylon is about 260 ° C, which is injected at about 300 ° C.

A required amount of a reinforcing material such as glass fiber is mixed in the injection molding material c in order to secure the strength. It is optional to reinforce the inner layer hollow body 1 by adding a reinforcing material to the material resin, but the hollow molded article A of the product may be a product such as an air intake manifold, through which a gas such as air is passed, or a liquid. For the material to be passed, if a reinforcing material is added to the material resin of the inner hollow body 1, the smoothness of the surface of the inner hollow body 1 decreases microscopically and the fluid resistance increases, so it is not reinforced. Is desirable.

By the injection of the injection molding material c, the resin is melted on the surface of the inner hollow body 1 including the protrusions 113, and the melted resin is mixed with the injection molding material c. As a result, when the injection molding material c for the outer surface layer is cured, both resins are cured in a mixed state at the interface b between the inner hollow body 1 and the outer surface layer 4. Then, after the injection molding material c is cured, the slide core 6 is removed, the molding die main body 51 is opened, and the molding is released to obtain a hollow product A.

The hollow molded article A thus obtained has an outer surface layer 4 integrally formed on the outer side of the inner layer hollow body 1 by injection molding and enclosing the inner layer hollow body 1. At the interface b between the hollow body 1 and the outer surface layer 4, the resins of both 1 and 4 are cured in a mixed state, and both 1 and 4 are firmly adhered and integrated.

In the embodiment described above, the inner layer hollow body 1 is used.
Was formed by combining the two parts 11 and 11,
It goes without saying that it may be necessary to divide the hollow molded article A into two or more parts depending on the shape of the hollow molded article A to be obtained.

Further, each part 11 of the inner layer hollow body 1 may be molded with a material resin other than 6 nylon depending on the use of the hollow molded article A of the product, and the material resin of the outer surface layer 4 is also an inner layer. Depending on the material resin of the hollow body 1, an appropriate resin having high adhesion to the material resin and a molding resin temperature sufficiently higher than that is used. As a combination of resins that have high mutual adhesiveness and one of which has a molding resin temperature sufficiently higher than the other, PC having compatibility with each other
/ ABS, modified PPO / PS, AS / ABS, PS / P
Combinations of MMA, ABS / PET, PA6 / PA66 and the like can be mentioned. Further, although it cannot be said that they have compatibility, the combination of ABS and PBT has a high adhesiveness at the interface between the former and the latter and is sufficiently applicable to the method of the present invention, based on the experimental results. For example, in the case of an air intake manifold for automobiles, a combination of 6 nylon / 66 nylon is preferable due to reasons such as heat resistance and chemical resistance.

[0022]

EFFECTS OF THE INVENTION Since the present invention is constituted as described above, the resin on the surface of the inner hollow body is melted by the injection molding of the outer surface layer,
The resin at the interface between the inner hollow body and the outer surface layer is in a mixed state or in a mutually intertwined state, and a clear interface is not formed between the two, and the inner hollow body and the outer surface layer are firmly adhered to each other. No peeling occurs between them. Therefore, even if a liquid or gas is passed inside the hollow molded article of the product, there is no possibility that the liquid or gas enters the interface between the two parts of the inner layer hollow body and leaks to the outside through the interface. . Therefore, not only the hollow molding product can be injection-molded without using the core, the molding process can be simplified, the maintenance cost can be reduced, and the material cost can be drastically reduced. It is possible to provide a hollow molded article of extremely high practicality, which is free from the possibility that these liquids and gases will leak to the outside even when passing through gas.

[Brief description of drawings]

FIG. 1 is a plan view of a pair of divided and molded parts that form an inner hollow body.

FIG. 2 is a sectional view showing a state in which the inner hollow body is set in an injection molding die.

FIG. 3 is a sectional view taken along the line (3)-(3) of FIG. 2, showing a state where an outer surface layer material resin is injected into an injection mold.

FIG. 4 is a plan view showing a hollow molded product that has been demolded.

5 is a cross-sectional view taken along the line (5)-(5) of FIG.

FIG. 6 is a perspective view of a half mold that constitutes a mold body of the injection mold.

[Explanation of symbols]

A: Hollow molded product B: Injection molding die 1: Inner hollow body 2: Cavity of injection molding die 4: Outer surface layer 11: Inner hollow body part 22: Injection molding space c: Injection molding material for outer surface layer

Claims (1)

[Claims] 1. An inner-layer hollow body made of synthetic resin, which is one size smaller than a hollow-molded product, is divided into a plurality of parts each of which can be molded without using a core, and the plurality of parts are molded. The inner-layer hollow body formed by assembling is set in a cavity of an injection-molding die of a product hollow-molded product such that an injection-molding space exists around the cavity, and the material resin of the inner-layer hollow body is set in the injection-molding space. And a molding resin having a sufficiently higher molding resin temperature than the material resin of the inner hollow body is injected to integrally mold an outer surface layer covering the outer peripheral surface of the inner hollow body. A method for molding a hollow molded article made of synthetic resin.