JPS635849Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an apparatus for coating a core material with a thermoplastic resin foam. More specifically, the present invention suppresses rapid diameter expansion of the foam by creating a unique shape at the tip of the inner mold of the coating mold and the vicinity thereof, thereby improving adhesion to the core material and at the same time making it smooth and smooth. The present invention relates to an apparatus capable of forming a perfectly circular coating layer.

Prior Art A resin foam coated on electric wires and the like functions as both an insulating material and a heat insulating material. The resin foam therefore needs to be highly foamed. Tokko Akira
The method of covering a power cable with a foam disclosed in Japanese Patent No. 43-8900 involves directly connecting an extrusion head to a vacuum container and creating a vacuum between the guide of the crosshead and the core wire when extruding the insulating layer. According to this method, when attempting to obtain a coating layer of a thermoplastic resin foam with a high expansion ratio, the foam rapidly expands in diameter at the exit of the mold, resulting in wave-like wrinkles in the coating layer. As a result, a smooth and perfectly round coating layer cannot be obtained. Moreover, since the diameter is large, the coating layer cannot be brought into close contact with the core wire even after vacuuming. Japanese Unexamined Patent Publication 1973-
Publication No. 128367 also discloses a method of coating a metal pipe with foamed resin. In this method, a pressure fluid chamber is adjacent to the die for passing the foamable resin coating from the die, and the fluid pressure in this fluid chamber is increased.
The degree of foaming of the coating layer is adjusted by adjusting the temperature. In this method, pressure is applied from the outside during resin foaming at the exit of the mold, so foaming is suppressed. As a result, a coating layer with a high expansion ratio cannot be obtained.

Purpose of the invention The purpose of the invention is to facilitate foaming in the direction of the core material to be covered, suppress rapid expansion of the diameter of the foam, improve adhesion to the core material, and create a smooth and perfectly circular foam coating layer. The purpose of the present invention is to provide a device for forming. Another object of the present invention is to provide an apparatus that forms a smooth and perfectly circular covering layer that adheres closely to a core material using a thermoplastic resin foam with a high expansion ratio of 10 times or more.

Summary of the invention The apparatus for covering a core material with a thermoplastic resin foam according to the invention is such that the outer surface of the inner mold of the covering mold has a plurality of grooves in the axial direction at least at its tip and in the vicinity thereof. The above objective is achieved.

Example The present invention will be described below with reference to embodiments.

As shown in FIG. 1, the device of the present invention has an outer mold 1
This is a covering mold including an inner mold 2 housed therein. The inner mold 2 has a rear part 1 of the outer mold 1 compared to the outer mold 1.
1, the resin passage 3 is connected by screw means 12 or the like.
It is fixed across. One end of this resin passage 3 is connected to a supply port 31 for the foamable thermoplastic resin, and the other end is connected to an extrusion port 32 at the tip of the mold. This extrusion port 32 is formed by the inner mold 2 and the nozzle 4 at the tip of the outer mold 1. A through hole 100 is provided in the center of the inner mold 2, and the core material 10 to be coated is inserted through this hole into the roll 5.
The core material is moved from the rear of the mold to the front by a core material transfer means such as the following. Behind this through hole 100 is a packing 6 provided between the inner mold inner surface 20 and the core material 10.
It is hermetically sealed. In the front, a gap 21 between the inner surface of the tip of the inner mold 2 and the core material 10 is formed.
The space 70 between the resin foam 7 and the core material 10 is
It is familiar to This through hole 100 is evacuated through the suction port 8 by a vacuum pump (not shown) and maintained in a reduced pressure state.

The inner mold 2 has an inner surface 20 as shown in FIG.
has a gap between it and the core material 10 that moves there, at least at the tip and in the vicinity thereof. The outer surface has a plurality of grooves 22 in the axial direction at least at the tip and in the vicinity. The grooves 22 are preferably arranged at equal intervals on the outer surface of the inner mold so that the foamed resin can evenly adhere around the core material 10 from the extrusion port 32 toward the core material 10. Although there is no particular restriction on the shape, it is preferable that the bottom of the groove has an appropriate curvature in order for the foamed resin to flow smoothly along the groove 22.

Using the apparatus of the present invention, the core material 10 is coated with the resin foam 7, for example, in the following manner.

The core material 10 is supplied to the through hole 100 of the inner mold 2 and is moved at a constant speed by the rolls 5 from the rear of the inner mold to the front. On the other hand, a foamable thermoplastic resin obtained by dispersing and mixing a foaming agent into a heated and melted resin in an extruder (not shown) is supplied into the mold from a supply port 31. This resin flows uniformly through the passage 3 and flows out from the extrusion port 32 into the atmospheric pressure zone. The resin that flows out immediately foams and solidifies. Resin foam 7 near the extrusion port 32
In the space 70 between the core material 10 and the gas generated during extrusion and air leaking from the packing 6, gas is exhausted through the suction port 8 by a vacuum pump (not shown). Therefore, this space 70 is always
It is in a depressurized state. Therefore, rapid diameter expansion of the foam is suppressed, and the grooves 22 on the outer surface of the inner mold
The presence of the foamable resin facilitates foaming in the direction of the core material 10 when the foamable resin flows out of the system from the extrusion port 32. As a result, as shown in FIG. 3, the inner periphery 77 of the formed pipe-shaped foam 7 comes into close contact with the outer periphery of the core material 10. Moreover, this pipe-shaped foam 7
has a perfect circular cross section, and its outer surface is smooth and wrinkle-free.

The core material 10 is made of metal such as steel, copper, aluminum, etc.
It is a long body made of synthetic resin, glass, wood, woven thread, rubber, etc., and its shape is a solid round bar, wire, hollow tube, square tube, oval tube, etc. Note that the core material may be co-extruded from synthetic resin or the like. The thermoplastic resin for covering the core material 10 is a resin that can be foamed by mixing a foaming agent therein. Examples include polystyrene, polyethylene, polypropylene, polyvinyl chloride, polymethyl methacrylate, polyvinylidene chloride, ethylene-vinyl acetate copolymer, and ethylene-propylene copolymer. As the blowing agent, a volatile blowing agent or a blowing agent that decomposes upon heating is used. Examples include propane, butane,
Low-boiling aliphatic hydrocarbons such as pentane and hexane; low-boiling organic compounds such as alcohols, ketones, and esters; halogenated hydrocarbons such as monochlorodifluoromethane, dichlorodifluoromethane, and dichlorotetrafluoroethane Volatile blowing agents such as; thermally decomposable blowing agents such as azo compounds, sulfohydrazide compounds, azide compounds, ammonium carbonate, and soda bicarbonate. The blowing agent mixed into the thermoplastic resin can be mixed into the resin in advance, but in the case of a volatile blowing agent, the blowing agent is directly injected into the extruder cylinder and kneaded into the heated and melted resin. I can do it.

A specific example of coating a core material with a foam will be described below as an experimental example.

Experimental Example 1 The nozzle inner diameter of the extrusion opening of the coating mold was 16 mm, and the outer diameter of the extrusion tip of the inner mold was 14.8 mm. Twelve semicircular grooves with a cross section of 1 mm radius are provided at equal intervals on the outer surface of the inner mold. The inner diameter of the inner mold is 10.5mm
It is. A copper tube with an outer diameter of 10 mm was used as the core material.

The foamable thermoplastic resin was prepared using polyethylene (density 0.92 g/cm ³ , melt index 2.0) 100
Mix 0.8 parts by weight of fine talc powder to parts by weight,
This mixture is put into an extruder, and Freon is press-mixed into it at a ratio of 20 parts by weight per 100 parts by weight of polyethylene through a blowing agent injection port near the center of the extruder cylinder. The temperature of the extruder cylinder was 120°C at the bottom, 130°C at the center and 110°C at the top. The foamable polyethylene resin was supplied to the coating mold from the tip of this cylinder. This mold was held at 100°C. The feed rate of this foamable polyethylene resin to the mold was 4 kg/hr. The resin extruded from the extrusion port of the mold immediately foams and adheres concentrically to the outer circumference of the core copper tube, which moves in the extrusion direction at a speed of 150 cm/min from inside the inner mold, forming a 10 mm thick coating layer. did. The outer surface was smooth and no wrinkles were observed. Its cross section was also perfectly circular. The foaming ratio was 30 times. The pressure inside the inner mold was reduced to 600 mmHg.

As a comparative example, a coating mold was used in which the extrusion port had a nozzle inner diameter of 15 mm and the extrusion tip of the inner mold had an outer diameter of 13 mm. No grooves are provided on the outer surface of the inner diameter. The diameter of the inner surface of the inner mold is 10.5 mm. All other details were the same as in Experimental Example 1 above. The obtained foam coating layer had wrinkles on its outer surface and could not form a smooth, perfectly round tubular body.

Experimental Example 2 As the expandable thermoplastic resin, 0.2 parts by weight of sodium bicarbonate was mixed with 100 parts by weight of expandable polystyrene particles in which polystyrene was impregnated with 6% by weight of propane as a blowing agent. This was put into an extruder. The extruder cylinder temperature is 100℃ at the bottom of the hopper, 130℃ at the center, and 130℃ at the tip.
It was 110℃. The coating mold was the same as in Experimental Example 1 and was maintained at 105°C. The feed rate of the expandable polystyrene resin was 4.5 Kg/hr. The pressure inside the inner mold was reduced to 600 mmHg. All other details were the same as in Experimental Example 1. The obtained foam coating layer adhered concentrically to the outer periphery of the core copper tube and had a wall thickness of 9 mm. This coating layer had no wrinkles on the outer surface and formed a smooth, perfectly round tubular body. The foaming ratio was 28 times.

Effects of the Invention In this way, the device of the present invention has such a structure that the inner surface of the inner mold has a gap with the core material at least at its tip and the vicinity thereof, and the groove is provided in the axial direction at the tip of the inner diameter outer surface. Therefore, when the foamable resin is extruded from the mold, rapid expansion of the diameter of the foam in the direction of the core material is suppressed. As a result, the foam adheres closely to the core material, forming a wrinkle-free, smooth, perfectly circular covering layer on the outer surface.

[Brief explanation of the drawing]

Fig. 1 is a side sectional view showing an example of the device of the present invention, Fig. 2 is a front sectional view of the inner mold taken along line XX in Fig. 1, and Fig. 3 is a front view showing the covering state of the foam coating layer. It is a diagram. 1...Outer mold, 2...Inner mold, 3...Resin passage, 4
...Nozzle, 5...Roll, 6...Putkin, 7
... Resin foam, 10 ... Core material, 20 ... Inner mold inner surface, 21 ... Gap between inner mold inner surface and core material, 22 ...
Groove, 32... Extrusion port, 70... Space, 100...
...Through hole.

Claims (1)

[Claims for Utility Model Registration] 1. Supplying a foamable thermoplastic resin to a resin passage between the inner and outer molds of a covering mold consisting of an inner and outer mold, extruding the resin from an extrusion port at the end of the passage, and foaming the resin at the same time. In an apparatus for supplying a core material into an inner mold and moving it in the extrusion direction of the resin to cover the entire surface of the core material with the resin, the inner mold has a plurality of core materials in the axial direction at least at the tip and the vicinity thereof. A device for covering a core material with a thermoplastic resin foam having grooves. 2. The device according to claim 1, wherein the grooves on the outer surface of the inner mold are provided at equal intervals.