JPH06293039A - Method of foam injection molding - Google Patents

Abstract

PURPOSE:To carry out a mass production of an excellent foam molded product of high degree of freedom of shape by composing a method of foam injection molding of a semi-fabricated products fitting process in the inside of a cavity which consists of 3 mold elements, a cavity-forming process, a molding material filling process, a cavity scale-up process and a foaming process. CONSTITUTION:An initial cavity 24 is formed with a semi-fabricated product 22 which is fitted into by a semi-fabricated product fitting process, a movable side mold element 23b and a sliding mold element 23c, and the formed cavity 24 is filled with foam molding material. The cavity 24 which is filled with molding material in the filling process is, without relative motion of anyone of the semi-fabricated product 22, a fixed side mold element 23a, and the movable side mold element 23b, but by withdrawing the sliding mold element 23c, scaled-up while being closed. Then, the molding material in the initial cavity which is scaled-up by a cavity scale-up process is foamed and a foam molded product 25 which has the same shape as a final cavity in the final cavity is formed. The molded products that consist of the foam molded product 25 and the semi-fabricated product 22 are, for example, seat arm pads for an automobile.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an injection molding method for foaming in a mold. More specifically, the present invention relates to a multicolor foam injection molding method in which a molded product that has already been molded in a separate step is integrally foam-molded.

[0002]

2. Description of the Related Art Plastic has new properties obtained by foaming, and in particular, various properties such as heat insulation, sound absorption, buoyancy, elasticity and light weight are utilized. Recently, composite molded products, in which a foam molded product is partially incorporated, have been manufactured.

Foam molding is mainly carried out by injection molding and extrusion molding. Of these, foam injection molding is a method in which a relatively small amount of molding material containing a foaming agent is injected into a cavity in a mold at a low pressure, and the cavity is filled by foaming the foaming agent. Although a petroleum-based low boiling point solvent may be used as the foaming agent, an azodicarbonamide-based or oxybissulfonylhydrazide-based one is generally used.

In the foam injection molding method, since the molding material is filled by foaming in a cavity having a fixed volume, it is difficult to control the injection amount of the molding material. Therefore, the molded product is generally a low-foam molded product having a low expansion ratio.

For this reason, as shown in FIG.
Cavity 1 formed by two molds 10a, 10b
1 is rapidly filled with the molding material, and immediately after filling, the movable mold 10
A molding method has been proposed in which b is retracted to increase the cavity volume. According to this molding method, it is possible to increase the expansion ratio, that is, high foam molding. Further, the material at the interface with the cavity wall is cooled immediately after filling, and forms a skin, so that a relatively lightweight molded product having a skin layer can be obtained.

In the conventional method shown in FIG. 7, when the molding material is filled (a), all the cavity wall surfaces that contribute to molding are not exposed. It is a surface where the wall surfaces a and b are not exposed.
As a matter of course, all the cavity wall surfaces are exposed by the time of foam molding (b). That is, not only the cavity volume but also the cavity wall surface that contributes to the molding change between the time of filling the molding material and the time of foam molding. Therefore, the degree of freedom of the shape of the molded product is limited by the change of the cavity wall surface, and for example, a spherical product cannot be molded.

That is, in the conventional foam injection molding method, since foam molding is performed using two molds, for example, an annular molded product having a spherical shape or a circular cross section cannot be molded.

[0008]

The present invention has been made under the technical background described above, and achieves the following objects.

An object of the present invention is to provide a foam injection molding method capable of high-foam molding and adaptable to molded articles of various shapes.

Another object of the present invention is to provide a foam injection molding method which improves the mass productivity of a molded product in which a foam molded article is incorporated.

[0011]

The means for solving the problems of the present invention will now be described, in which the components of the present invention are shown in parentheses in correspondence with one or several embodiments. The reason for adding is to refer to the correspondence relationship between the components of the present invention and the embodiment in an easy-to-understand manner, and not to limit the present invention to the embodiment.

The foam injection molding method of the present invention uses a foam injection using at least three molds (1a, 1b, 2) including a slide mold (2) slidable with respect to another mold (1a, 1b). A molding method comprising: a. Forming a small cavity (4a) having a volume smaller than that of the molded product by introducing the slide mold (2) into the inside of the cavity formed by the three molds; b. Filling the small cavity (4a) with a molding material containing a foaming agent; c. A foam injection molding method comprising a step of retracting the slide mold (2) from the inside of the cavity to form a large cavity (4b) having the same volume as the volume of the molded product and foaming.

One of the molds other than the slide mold (2) is a molded product (3) molded in a separate process.

[0014]

The method of the present invention is the same as the conventional method in that the volume of the cavity changes as the slide die 2 moves into and out of the cavity. However, the cavity wall surfaces a, b, and c that contribute to molding do not change between when the molding material is filled (a) and when foam molding is performed (b). Therefore, the shape of the molded product has a high degree of freedom, and various shapes such as a spherical shape can be molded.

[0015]

EXAMPLES Examples of the present invention will be described below.

(Embodiment 1) FIG. 2 is a sectional view showing Embodiment 1 of the foam injection molding method of the present invention. FIG. 3 is an exploded perspective view showing a part of the mold. Example 1 is a case where a tire of a wheel is molded by foam injection molding and the tire is integrally molded with the wheel body. These figures show a plurality of split molds used to carry out the foam injection molding method of the present invention. The mold 1 which moves in the radial direction is a mold 1a divided into four,
It consists of 1b, 1c and 1d. The mold 2 that moves in the axial direction is composed of slide molds 2a and 2b that are divided into two.

The mold 1 has a partial torus surface, and the wheel body 3 is positioned inside the mold 1. The outer peripheral surface of the wheel body 3 is also formed as a partial torus surface. A pair of ring-shaped slide molds 2 inside the mold 1 and outside the wheel body 3
a and 2b are provided. The slide molds 2 a and 2 b slide with respect to the mold 1 and the wheel body 3. Slide type 2a, 2
The opposing surfaces of b are also formed as partial torus surfaces. The mold 1, the slide molds 2a and 2b, and the wheel main body 3 form one set of molds, and the partial torus surfaces form one torus surface. The wheel body 3 is supported by an injection molding machine (not shown), and the mold 1 and the slide molds 2a and 2b are moved radially and axially by the injection molding machine, respectively. The mold is provided with a gate 5 for injecting the foaming molding material into the cavity.

The operating wheel body 3 of the first embodiment is preformed in a process different from the process described below. Through the gate 5, a cavity formed by the mold 1, the slide molds 2a and 2b, and the wheel body 3 is filled with a foaming molding material. The positional relationship among the mold 1, the slide mold 2, and the wheel body 3 at the time of such injection is shown in FIG.
In this state, the slide molds 2a and 2b have entered the cavity, and the volume of the cavity 4a in this state is smaller than the volume of the molded product. The injection pressure of the molding material is the same as in the case of normal injection molding.

Following the above steps, the slide molds 2a and 2b are axially retracted as shown in FIG. In this process,
The wall surface of the cavity 4b is formed in a torus shape and has an increased volume. The pressure drop due to the increase of the cavity volume promotes the vaporization of the volatile substances constituting the foaming agent, thereby generating high-magnification bubbles in the molding material. The outer peripheral surface of the torus foam is cooled and a skin layer is formed. The torus foam formed in this way is integrated with the wheel body 3,
The wheels shown in Figure 5 are made.

In the above embodiment, various engineering plastics are used for the wheel body 3. As the molding material, a thermoplastic resin or an elastomer is used. These materials are used as a mixture with a known foaming agent that is appropriately vaporized at a predetermined pressure, temperature and time, for example, an azodicarbonamide-based or oxybissulfonylhydrazide-based foaming agent.

(Embodiment 2) FIG. 6 is a sectional view showing Embodiment 2 of the foam injection molding method of the present invention. This Example 2
Is a case of molding an arm pad of a car seat. The arm pad is made as follows.

First, using a first mold 20 composed of a fixed mold 20a and a movable mold 20b, a molding material such as a thermoplastic resin is injected into a cavity 21 formed by both molds 20a and 20b to make a primary molded product. (FIG. 6 (a)).

Next, the primary molded product 22 is placed in the second mold 23 (FIG. 6 (b)). The second mold 23 is a fixed mold 23.
a, a movable die 23b, and a slide die 23c that slides with respect to the movable die 23b. After arranging the primary molded product 22, the foaming molding material is injected into the cavity 24 formed in the second mold. Slide type 2 immediately after injection
3c is retracted to increase the cavity volume and foam. As a result, the partially foamed secondary molded product arm pad 25 is molded (FIG. 6C).

(Other Embodiments) The present invention is not limited to the above embodiments, and design changes are made within the scope of the gist of the present invention.

For example, in the above embodiment, the description has been made by taking the case of forming the wheel and the arm pad of the seat of the automobile as an example.
In addition to these, the present invention is applied to various cushion portions, and conversely, molding of a portion requiring hardness, particularly so-called multicolor molding. Further, the foam of the molded product and the portion other than the foam can be fused and integrated at the time of molding.

[0026]

According to the present invention, the following effects are exhibited.

Since the cavity volume is increased during foaming, high foaming molding is possible. In addition, in combination with multicolor molding, mass production of a molded product having a foamed molded product as a part can be enabled. Furthermore, the flexibility of the shape of the molded product is high,
Various molded articles can be manufactured.

[Brief description of drawings]

FIG. 1 is a diagram showing the principle of a molding method of the present invention.

FIG. 2 is a first embodiment of the foam injection molding method of the present invention.
FIG.

FIG. 3 is a first example of the foam injection molding method of the present invention.
FIG.

FIG. 4 is a cross-sectional view showing when the cavity volume is increased.

FIG. 5 is a perspective view showing a molded product molded by the foam injection molding method of the present invention.

FIG. 6 is a second embodiment of the foam injection molding method of the present invention.
FIG.

FIG. 7 is a diagram showing a conventional method.

[Explanation of symbols]

 1, 1a, 1b, 1c, 1d ... Mold 2a, 2b ... Slide mold 3 ... Wheel body 4a ... Small cavity 4b ... Large cavity

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[Procedure amendment]

[Submission date] June 29, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction content]

[Document name] Statement

Title: Foam injection molding method

[Claims]

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foam injection molding method for high foaming in a mold. More particularly, it relates to a foam injection molding method for high foaming in a mold by moving the mold element and enlarging the cavity while it is closed.

[0002]

2. Description of the Related Art Plastics can be given various new properties by foaming them.
In particular, various properties such as heat insulation, sound absorption, vibration control, buoyancy, elasticity, light weight, liquid induction, dustproof (filter), friction, and slip resistance can be imparted. It is a recent trend to make extensive use of foamed molded products by utilizing such properties. In the future, it is expected that the demand for composite molded products that incorporate foamed molded products in one part and utilize each property will increase.

Foam molding is currently mainly performed by injection molding and extrusion molding. Among these, injection molding, which has excellent moldability, is a method of injecting a relatively small amount of molding material containing a foaming agent into a cavity in a mold at low pressure and filling the cavity by foaming the foaming agent. Although a petroleum-based low boiling point solvent may be used as the foaming agent, an azodicarbonamide-based or oxybissulfonylhydrazide-based one is generally used. In such a foam injection molding method, since the molding material is filled by foaming in a cavity having a fixed volume, it is difficult to control the injection amount of the molding material. Therefore, the foamed molded product is generally a low foamed molded product having a low expansion ratio, and is not a high foamed molded product having a high expansion ratio.

FIG. 6 shows a known high-foam injection molding method. As shown in FIG. 6, the conventionally known injection molding method uses an injection molding die including two die elements, a fixed side die element 10a and a movable side die element 10b. Both mold elements 1
0a and 10b, the initial cavity 11 shown in FIG. 6 (a) is rapidly filled with a molding material containing a foaming agent, and immediately after filling, the movable side mold element 10b is retracted with respect to the fixed side mold element to form a cavity. The volume is expanded to form the final cavity 11 shown in FIG. 6 (b). The previously filled molding material is foamed in the expanded cavity 11 thus formed. Such a foam injection molding method can increase the foaming ratio. That is, such a foam injection molding method enables high foam molding.

When the molding die is cooled immediately after filling the molding material, the material at the interface between the cavity and the inner surface of the die is cooled immediately after filling. In this way, the foam-molded product in which the material of the interface portion is rapidly cooled to form the skin can be obtained as a relatively lightweight molded product having a skin layer. Such a foam-molded article can be utilized as a product or material having various properties with the inside protected by a skin layer.

[0006]

According to the conventional method in which two mold elements are moved relative to each other to expand the cavity and highly foam, a cavity expansion portion, that is, a cavity expansion portion added to the initial cavity is formed. 6 (b) is the final cavity except the initial cavity shown in FIG. 6 (a).
The line of intersection of the cavity forming surface of a and the cavity forming surface of the movable side mold element 10b having a sliding surface that slides on this surface is limited to the surface that is moved and scanned. The freedom of morphology is significantly limited.

More generally, two cavities are kept from the initial cavity to the final cavity with the cavity closed.
The interface of the cavity formed by moving the two mold elements must be two parallel sliding surfaces formed by scanning when the two molds slide relative to each other or a collection surface of parallel lines must be the element surface. As a result, the molded product is restricted to have an interface of the same shape on such two parallel sliding surfaces.

Due to such restrictions, a three-dimensional object having parallel line gathering surfaces, such as a cylinder, can be molded by the high-foam injection molding method, but the two parallel sliding surfaces also have parallel line gathering surfaces. Three-dimensional molded product with an interface that does not have, for example, a spherical product with a spherical interface, a toroidal product with a torus surface, or a regular tetrahedron in which none of the two interfaces is parallel. It is not possible to mold a complex three-dimensional product such as a tetrahedron, which is a tetrahedron, a conical surface or a combination of a plurality of conical surfaces, by a high foaming injection molding method.

Although a skin layer for protecting the inside can be formed to some extent by cooling the molding die immediately after filling with the molding material, insufficient skin can be formed by giving priority to molding conditions that fully utilize the properties to be utilized by foaming. You get only layers.

The present invention was invented under the technical background described above, and achieves the following objects. An object of the present invention is to provide a foam injection molding method capable of molding composite high foam molded articles of various shapes.

[0011]

The means for solving the problems of the present invention will now be described, in which the components of the present invention are shown in parentheses in correspondence with one or several embodiments. The reason for adding is to refer to the correspondence relationship between the components of the present invention and the embodiment in an easy-to-understand manner, and not to limit the present invention to the embodiment.

The method of foam injection molding according to the present invention comprises at least three mold elements (23a, 23a) which are relatively movable with respect to each other.
b, 23c) a semi-finished product mounting step of mounting a semi-finished product 22 made in a separate process in a cavity formed by using the above step, and the semi-finished products (22) and 3 mounted by the semi-finished product mounting step.
A cavity forming step of forming one closed initial cavity (24) by at least two mold elements (23b, 23c) of the one mold element (23a, 23b, 23c), and forming by the cavity forming step. A filling step of filling the molding material into the initial cavity (24),
2 of the 3 mold elements (23a, 23b, 23c)
The two mold elements (23a, 23b) and the semi-finished product are not moved relative to each other, and the remaining at least one mold element (23c) is moved with respect to the two mold elements (23a, 23b) and the semi-finished product, A cavity enlargement step of forming a final cavity having a volume larger than that of the initial cavity (22) while keeping the cavity formed by the two mold elements (23b, 23c) and the semi-finished product (22) closed; A foam molding step of foaming the filled molding material in the final cavity expanded by the cavity expanding step to form a foam molded article having the same shape as the final cavity in the final cavity. It has a feature.

[0013]

The name of the present invention is expanded by the movement of one mold element while the cavity formed by the two mold elements and the semi-finished product is closed. No movement of one other mold and semi-finished product element is required during this expansion process. The final expanding cavity, which is not parallel to any part of the interface, can be formed by moving one mold. The molding material is highly foamed in the cavity thus obtained, and a composite highly foamed molded article having a high degree of freedom in shape is manufactured by the injection molding method.

[0014]

EXAMPLES Examples of the present invention will be described below. (Embodiment 1) Injection Molding FIGS. 1 (a), 1 (b) and 1 (c) are sectional views showing an injection molding die used in Embodiment 1 of the foam injection molding method of the present invention. Injection mold 23 used in the foam injection molding method of the present invention
Is basically composed of three elements, as shown in FIG. The basic three elements are composed of a mold element 23a, a mold element 23b, and a mold element 23c. The mold element 23a and the mold element 23b are relatively movable. The mold element 23c is slidable and relatively movable with respect to the mold element 23b. For convenience of description of this embodiment, the mold element 23a is referred to as a fixed-side mold element, and the mold element 23b is referred to as a movable-side mold element. The mold element 23c is referred to as a sliding type element.

Foam Injection Molding Method Next, a first embodiment of the foam injection molding method of the present invention will be described. FIG. 1A shows a step of molding the semi-finished product 22 by injection molding. This process includes
This is a step of forming a cavity 21 with an injection molding die 20 composed of the movable side die element 20b, filling the cavity 21 with a molding material, and molding a primary molded product 22. The material of the primary molded product 22 is a thermoplastic resin, an elastomer, or the like.

Next, as shown in FIG. 1B, a cavity for forming the primary molded product 22 molded in the previous step by the fixed side mold element 23a, the movable side mold element 23b and the sliding mold element 23c. Install inside. The semi-finished product (22) mounted in the semi-finished product mounting step and at least two mold elements of the three mold elements 23a, 23b, 23c, that is, the movable mold element 23b.
And the sliding element 23c form an initial cavity 24. The initial cavity 24 formed by such a cavity forming step is filled with the foaming molding material. As the foaming molding material, a thermoplastic resin or an elastomer is used. These molding materials are used as a mixture with a known foaming agent capable of being appropriately vaporized at a predetermined pressure, temperature and time, for example, an azodicarbonamide type or oxybissulfonylhydrazide type.

The cavity 24 filled with the molding material in the filling step retracts the sliding mold element 23c without relatively moving any of the semi-finished product 22, the fixed mold element 23a and the movable mold element 23b. By doing so, it expands while being closed. FIG. 1C shows a state in which a final cavity having a volume larger than that of the initial cavity 24 is formed. The molding material foams in the final cavity expanded by the cavity expansion process, and a foamed molded product 25 having the same shape as the final cavity is formed in the final cavity. The molded product including the foamed molded product 25 and the semi-finished product 22 is, for example, an arm pad for a seat of an automobile.

(Embodiment 2) FIG. 2 is a sectional view showing an injection mold used in Embodiment 2 of the foam injection molding method of the present invention. FIG. 3 is an oblique-axis projection view showing a part of the mold in an exploded manner. Example 2 is a case where a tire of a wheel is molded by foam injection molding and the tire is integrally molded with the wheel body. 2 and 3 show a plurality of divided mold elements.

The mold element 1 which moves in the radial direction is composed of mold elements 1a, 1b, 1c and 1d divided into four parts. The axially movable die element 2 is composed of sliding die elements 2a and 2b divided into two parts.
The mold element 1 has a partial torus surface and the wheel body 3 is located inside the mold element 1. The outer peripheral surface of the wheel body 3 is also formed as a partial torus surface.

A pair of annular sliding mold elements 2a, 2b are provided inside the mold element 1 and outside the wheel body 3. The sliding mold elements 2 a, 2 b slide with respect to the mold element 1 and the wheel body 3. Opposing surfaces of the sliding elements 2a and 2b are also each formed as a partial torus surface. The mold element 1, the sliding mold elements 2a and 2b, and the wheel main body 3 form one set of mold elements, and those partial torus surfaces form one torus surface.

The wheel body 3 is supported by an injection molding machine (not shown), and the mold element 1 and the sliding mold elements 2a and 2b are moved by the injection molding machine in a radial direction and an axial direction, respectively. The mold element is provided with a gate 5 for injecting the foaming molding material into the cavity.

The operating wheel body 3 of the second embodiment is preformed in a step different from the step described below. The wheel body 3 is attached to the mold. Gate 5
Through, the initial cavity 4a formed by the mold element 1, the sliding mold elements 2a and 2b, and the wheel body 3 is filled with the foaming molding material. Mold element 1, sliding mold element 2 during such injection,
The positional relationship of the wheel body 3 is shown in FIG. The cavity 4a in this state is the inner surface of the mold element 1, the wheel body 3
In addition to the outer surface, the annular surface opposed to the axial direction of the sliding die elements 2a and 2b, the sliding surface that slides on the wheel body 3 and the die element 1 is formed.

Following the filling step, the sliding elements 2a, 2b are axially retracted as shown in FIG. In this process,
The wall surface of the cavity 4b is formed in a torus shape and has an increased volume. The pressure drop due to the increase of the cavity volume promotes the vaporization of the volatile substances constituting the foaming agent, thereby generating high-magnification bubbles in the molding material. The outer peripheral surface of the torus foam is cooled and a skin layer is formed. The torus foam formed in this way is integrated with the wheel body 3,
The wheels shown in Figure 5 are made.

Various engineering plastics are used for the wheel body 3. As the molding material, a thermoplastic resin or an elastomer is used. These materials are used as a mixture with a known foaming agent that is appropriately vaporized at a predetermined pressure, temperature and time, for example, an azodicarbonamide-based or oxybissulfonylhydrazide-based foaming agent.

(Other Embodiments) The present invention is not limited to the above embodiments, and design changes are made within the scope of the gist of the present invention. For example, in the above embodiment, the sphere was selected to explain the principle of high foam injection molding, but various forms of high foam injection molding are possible.

[0026]

According to the present invention, the following effects are exhibited.
It is possible to mass-produce high-foam molded products with a high degree of freedom in shape.

[Brief description of drawings]

FIG. 1 (a), (b), (c) is a cross-sectional view showing an injection mold used in Example 1 of the foam injection molding method of the present invention.

FIG. 2 is a second embodiment of the foam injection molding method of the present invention.
FIG. 3 is a cross-sectional view showing an injection molding die used in.

FIG. 3 is an oblique-axis projection view showing a part of the mold shown in FIG. 2 in a disassembled state.

FIG. 4 is a cross-sectional view showing a step different from the step shown in FIG.

FIG. 5 is a perspective view showing a foam injection-molded article.

6 (a) and 6 (b) are cross-sectional views showing a mold used in a conventional foam injection molding method.

[Explanation of reference numerals] 3,22 ... Semi-finished products 1a, 1b, 1c, 1d ... Mold elements 2a, 2b ... Mold elements 23a, 23b, 23c ... Mold elements 4a, 24 ... Initial cavity 4b ... Final cavity

[Procedure 3]

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[Correction target item name] All drawings

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[Figure 1]

[Fig. 2]

[Figure 3]

[Figure 4]

[Figure 5]

[Figure 6]

Claims (2)

[Claims] 1. At least three molds (1a, 1) including a slide mold (2) slidable with respect to another mold (1a, 1b).
A foam injection molding method using b, 2), comprising: a. Forming a small cavity (4a) having a volume smaller than that of the molded product by introducing the slide mold (2) into the inside of the cavity formed by the three molds; b. Filling the small cavity (4a) with a molding material containing a foaming agent; c. A foam injection molding method comprising a step of retracting the slide mold (2) from the inside of the cavity to form a large cavity (4b) having the same volume as the volume of the molded product and foaming. 2. The foam injection molding method according to claim 1, wherein one of the molds other than the slide mold (2) is a molded product (3) molded in a separate step.