JPH04279311A - Manufacture of foamed synthetic resin hollow article - Google Patents

Abstract

PURPOSE:To smoothly extrude a synthetic resin extruded article consisting of a substantially non-foamed rigid outer skin in its inner surface and outer surface and having a hollow foamed cross section. CONSTITUTION:A narrow part 6 is provided on the connection part between the mandrel 4 of an extrusion mold 2 and the inner mold 5 of a forming die 3, and onto the enlargement of a flow conduit resulted therefrom, foamable resin is allowed to foam in order to relax the foaming strength, thereby rendering the fluidity of the resin smooth, and further by the reduction of heat transfer through the reduction of the cross-sectional area in the connection part, the effective cooling in the inner mold of the forming die is carried out, whereby a non-foamed rigid skin layer is formed even in the inner surface of an article.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a foamed synthetic resin product having a hollow cross-section, the inner and outer surfaces of which are comprised of substantially unfoamed outer skins.

0002

BACKGROUND OF THE INVENTION As a method for producing an extruded product of foamed synthetic resin having a hard shell with a substantially unfoamed surface, the method described in Japanese Patent Publication No. 45-29919 is well known.

This publication discloses that a hollow foam extrusion product is manufactured using an extrusion die 2 and a forming die 3 as shown in FIG. The AA cross section of this extrusion die 2 is shown in FIG. 5, the BB cross section of the forming die 3 is shown in FIG. 6, and the annular gap formed by the mandrel 4 in FIG. It is said that the resin is filled with foam and that the area sandwiched between the forming die 3 and the inner mold 5 in FIG. 6 is finally obtained with a hard outer skin on the inner and outer surfaces.

[0004] At first glance, it appears that by such a method it is possible to produce a foamed synthetic resin extrusion product having a hollow cross section and a hard outer skin on its inner and outer surfaces. However, with this method, the annular void (channel) often gets clogged with resin due to the large foaming force and the presence of a hard outer skin created by cooling, making continuous molding difficult. Also,
Extrusion molds like the one shown in Figure 4 are complex and require considerable difficulty in manufacturing. Therefore, in order to have molds for different types of products, a very large investment is required. It wasn't realistic.

Therefore, as one development of the above-mentioned technology, a method using a mold 2 and a forming die 3 as shown in FIG. 7 has been proposed as a method for manufacturing a foamed synthetic resin hollow extrusion product with a hard outer skin. According to this manufacturing method, foamable resin melted and kneaded by a screw extruder (not shown) flows into a forming die 3 through an extrusion die 2 . Since the cross-sectional area of the inner die 5 of the forming die 3 is made smaller than that of the mandrel 4 of the extrusion die 2, the foamable resin is foamed inward and pressed against the inner die 5. On the other hand, since the forming die 3 and the inner mold 5 are cooled, the resin in the surface layer does not foam, and it is said that a hard outer skin is formed. Furthermore, it is said that this method has a simpler mold structure than the case of the above-mentioned Japanese Patent Publication No. 45-29919, and therefore costs can be reduced.

[0006]

[Problems to be Solved by the Invention] However, in reality, even when trying to obtain a foam with a hard outer skin by the above method, a very large foaming force is generated, so that the resin cannot be extruded. Problems often occur such as leakage from a small gap at the joint between the mold 2 and the forming die 3, or resin clogging inside the forming die 3 and preventing it from flowing.

Furthermore, in this method, since the mandrel 4 of the extrusion die 2 and the inner die 5 of the forming die 3 are in direct contact with each other, heat conduction from the mandrel is large, and therefore the inner layer of the hollow product is not foamed. In order to obtain a hard outer skin, it is difficult to control the temperature of the inner mold 5 of the forming die to a low temperature.

[0008] In view of the above points, the present invention
To produce a foamed synthetic resin hollow product with smooth inner and outer surfaces and an outer skin by smoothly extruding foaming without resin clogging in a mixing die.

[0009]

[Means for Solving the Problems] The present invention provides an extruder with a mold having a mandrel and a forming die having an inner mold having a smaller cross section than the mandrel in this order. In the method of foaming the foamable resin raw material in the forming die section through the mold, an enlarged resin flow path is formed by providing a constriction in the part connected to the mandrel of the inner mold, and the mold is connected to the mandrel of the mold. A constriction is provided between the mold and the inner mold of the molding die, and the resin raw material is foamed in the enlarged part of the resulting flow path to alleviate the foaming force, thereby smoothing the flow of the resin, and further improving extrusion by reducing the cross-sectional area. Four from mold mandrel
By reducing heat transfer to the inner mold of the forming die, the inner mold of the forming die is effectively cooled, thereby solving the above-mentioned problem.

0010

[Operation] By providing a constriction between the mandrel and the inner mold of the forming die connected to the mandrel, the flow path in that part is expanded, and the foaming force of the foamable resin raw material is relaxed there. This allows the resin to flow smoothly.

Furthermore, since the cross-sectional area of the constriction is reduced and heat transfer from the mandrel to the mold within the forming die is reduced, the mold within the forming die is effectively cooled.

0012

EXAMPLES The present invention will be explained in more detail below with reference to Examples. First, the apparatus used in the examples will be explained.

FIG. 1 is a sectional view showing an example of an apparatus used in the method of the present invention. 1 is the tip of the extruder, and a mold 2 and a forming die 3 are attached thereto in this order. The mold 2 has a mandrel 4 for extruding a hollow product. Note that 8 is a bridge for supporting the mandrel 4. The forming die 3 has an inner surface having the same shape as the outer surface of the molten resin extruded from the mold 2,
It consists of an outer mold equipped with a cooling jacket (not shown) for cooling its inner surface, and an inner mold 5 smaller than the mandrel 4. This inner mold 5 is attached to the mandrel 4 via a constriction 6. Note that the inner mold 5 has a cooling passage 7.
The inner mold 5 is cooled by a cooling fluid such as water flowing through the bridge 8 and the mandrel 4.

FIG. 3 shows another example in which the inner mold and constriction of the device are different. The inner mold 5a is connected in a dumpling shape to reduce frictional resistance with the foamed resin, and the constriction 6a is shaped like a thin rod.

In this embodiment, the inner mold 5a is cooled by
This is done by using cooling air passing through the cooling path 7a, and the cooling fluid is not circulated as shown in FIG. 1, but is blown out at the tip.

Next, embodiments of the present invention using each of the illustrated devices will be described. Example 1 Using the extrusion mold and forming die shown in Fig. 1,
A foamed hollow extruded product as shown in Figure 1 was molded. A PVC formulation was used as the resin, and 6% by weight of sodium bicarbonate was added as the blowing agent. Extrusion temperature is 170℃
It was set to In addition, the inner die of the forming die has a bridge 8 that supports the mandrel 4 of the extrusion die 2, as shown in FIG.
Water cooling was performed through. By such a method, the specific gravity is 0.
．． It was possible to continuously and smoothly extrude 55 foamed products with a hard outer skin.

Example 2 A foamed hollow extruded product with an outer skin was manufactured using a forming die 3a as shown in FIG. The material used was a system in which 3 parts by weight of sodium bicarbonate was added to 100 parts by weight of polystyrene beads. Extrusion temperature is 150℃
The mold temperature was set at 130°C. In this way, smooth extrusion could be continued, and a smooth, substantially unfoamed foamed product with a hard shell having a specific gravity of 0.49 could be obtained.

[0018]

Effects of the Invention In the present invention, two effects can be obtained by providing a constriction at the connection between the mandrel of the extrusion mold and the inner mold of the forming die. One is that the flow path in this area expands and the resin foams in that area, which alleviates the excessive foaming force and prevents resin leakage and resin clogging of the flow path due to this. That's what happened.

[0019] The second effect is that the constricted part reduces heat transfer through this part, and as a result, it becomes possible to freely control the cooling of the inner mold of the forming die following this part. It is. This makes it possible to freely form the inner wall surface of the hollow product into a hard, unfoamed outer skin.

[0020] In this way, it has become possible to smoothly and continuously extrude a foamed hollow synthetic resin product having an unfoamed, smooth and hard outer skin on both the inner and outer surfaces. Although the obtained product is a foamed product, it has a smooth and hard outer skin on the inner and outer surfaces, giving it a luxurious feel and high strength.

As a result of these inventions, the applications of synthetic resin hollow foam products have expanded significantly in the fields of building materials and industrial materials. As described above, the industrial significance of the present invention is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an extrusion mold and a forming die for molding a hollow foamed product with a skin according to the present invention.

FIG. 2 is a perspective view of an example of a hollow foam product with skin obtained according to the present invention.

FIG. 3 is a cross-sectional view of another form of a forming die for forming hollow foam products with skins according to the invention;

FIG. 4 is a sectional view showing an extrusion mold and a forming die for forming a hollow foam product with skin according to the prior art.

FIG. 5 is a sectional view taken along line AA in FIG. 4;

FIG. 6 is a sectional view taken along line BB in FIG. 4;

FIG. 7 is a sectional view of an extrusion die and a forming die for forming a hollow foam product with skin according to another conventional technique.

[Explanation of symbols]

1 Extruder 2 Mold 3 Forming die 4 Mandrel 5, 5a Inner die of forming die 6, 6a Constriction provided at the connection between the mandrel and the inner die of forming die 7 Cooling water 8 Bridge

Claims (1)

[Claims] Claim 1: A mold having a mandrel and a forming die having an inner mold having a smaller cross section than the mandrel are attached in this order to an extruder, and the foamable resin raw material sent from the extruder is passed through the mold. The method of foaming in a forming die section is characterized in that an enlarged resin flow path is formed by providing a constriction in a portion of the inner mold that connects to the mandrel, and the foamable resin raw material is foamed in the resin flow path. A method for producing a foamed synthetic resin hollow product.