JPH0148855B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a cylindrical foam body of irregular cross-section made of a thermoplastic resin and useful as a lightweight packaging material, a cushioning packaging material, or a heat insulating material.

BACKGROUND ART Conventionally, cylindrical foamed thermoplastic resins such as polyolefin resins have often been used as packaging materials for protection, cushioning, or heat retention of articles.

As a method for continuously producing such a cylindrical foam, a method of extrusion molding a foamable thermoplastic resin composition is widely used. As applications expand, foams with irregular cross-sections are often required, and in order to manufacture cylindrical or rod-shaped foams with such irregular cross-sections, foamable thermoplastic resin compositions have traditionally been used. The conventional method is to extrude and foam the material through a specially shaped molding die, or to extrude it into a perfect circular cross section using a normal extruder, and then shape it into an irregular cross section through a sizing device.

However, in the former method, there is a problem that it is difficult to manufacture a long product with a uniform cross-sectional shape, and the cross-sectional shape tends to vary widely in the length direction.

In addition, even if it is not a long one, the foaming ratio is 15 to 40.
In the case of foams with a high magnification of about 2.5 times, it is extremely difficult to control the flow and foaming direction of the thermoplastic resin by changing the cross-sectional shape of the die. Or just a foam with a cylindrical cross section. The latter method using a sizing device has the problem of requiring a large and complicated device.

In particular, in the case of manufacturing high-magnification foams, great efforts are required such as pouring lubricant and creating a pressurized air layer to ensure slipperiness on the inside of the sizing device, which results in even larger products. This requires complicated equipment.

The present invention was made to solve these problems, and provides a method for continuously manufacturing high-magnification foams with irregular cross-sections without requiring the above-mentioned complicated equipment or highly difficult techniques. The purpose is to

That is, the method for producing a foam with an irregular cross-section of the present invention involves continuously extruding and foaming a thermoplastic resin composition containing a predetermined amount of a blowing agent into a cylindrical or rod shape using an extruder. It is characterized by locally rapidly cooling the molded product immediately after extrusion molding in the vicinity of the molding die to suppress foaming.

The details of the present invention will be explained below with reference to the drawings showing one embodiment thereof.

As shown in FIG. 1, reference numeral 1 denotes an extruder, which is adjacent to the discharge hole 3 of the molding die 2 having a cylindrical cross section, and has a cooling hole that opens in a direction perpendicular to the direction in which the resin is extruded. A tube 4 is attached. Thermoplastic resin 5 extruded into a cylindrical shape by an extruder 1
starts foaming immediately after being discharged, but only the portion 6 that is rapidly cooled by the cooling medium discharged from the cooling pipe 4 is suppressed from foaming, and as a result, has a cross section as shown in FIG. A continuous foam is obtained.

Methods for locally quenching the discharged molded product include spraying compressed air depending on the degree of quenching and the area of the surface to be quenched, a water coating method, a method using alcohol such as ethylene glycol, etc.
Any rapid cooling method is not particularly limited as long as it is effective in suppressing foaming. Furthermore, by increasing the number of cooling points or cooling areas, it is possible to produce foams with various cross-sectional shapes.

Example 1 A composition consisting of MFR5 low-density polyethylene mixed with 30 parts by weight of dichlorodifluoromethane as a blowing agent was supplied to an extruder with an outer diameter of 50 mm as shown in Fig. 1, and a cylindrical outer mold was formed. The foaming agent-containing polyethylene composition was passed through the molding die 2, which had a structure in which a substantially cylindrical inner mold was separated by a fixed bridge in the center, and was passed through the perfectly circular forming die 2 from within the molding die, to a total weight of 15.0 kg. The foam was expanded approximately 30 times while extrusion molding was carried out at a speed of /Hr, and at the same time, cooling water was jetted from the cooling pipe 4 from the front upper surface of the die.

In this way, a semicircular polyolefin-based resin foam cylinder was obtained, as shown in FIG. 2, in which foaming was suppressed on the upper surface and the internal voids were also of substantially the same shape.

Example 2 The same composition as in Example 1 was extruded under the same conditions, and compressed air was blown out from three directions in front of the extrusion die to foam at a magnification of about 30 times, forming the triangle shown in Figure 3. A cylindrical body was obtained.

Example 3 The same composition as in Example 1 was extruded under the same conditions, and compressed air was blown out from four directions in front of the extrusion die to obtain a polyolefin resin foam cylinder having a square cross section as shown in FIG. It was done.

As is clear from the above examples, according to the present invention, foams with various irregular cross sections can be stably and continuously produced without the need for complicated equipment or advanced operating techniques. .

[Brief explanation of drawings]

Fig. 1 is a perspective view for explaining the production of the present invention, Fig. 2 is a cross-sectional view of the foam produced by the extruder shown in Fig. 1, and Fig. 3 is a cross-section of the foam obtained by cooling at three locations. FIG. 4 is a sectional view of a foam obtained by cooling at four locations. 1... Extruder, 2... Molding die, 3... Discharge hole, 4... Cooling pipe, 5... Thermoplastic resin, 6...
The part that is rapidly cooled.

Claims (1)

[Claims] 1. When foaming a foamable thermoplastic resin composition while continuously extruding it into a cylindrical or rod shape using an extruder, the molded product immediately after extrusion is locally quenched near the molding die of the extruder to prevent foaming. A method for producing a foam with an irregular cross-section, characterized by suppressing the shape of the foam.