JPS5933707A - Method of producing foaming fluorine resin insulating coated wire - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field The present invention relates to an improved method of manufacturing an electric wire coated with foamed fluororesin.

(B) Background Art As an insulating material with excellent flame retardancy and low smoke properties, there is an increasing demand for coaxial cables and the like whose insulating coating is made of foamed fluororesin. In these foam insulation extrusions, the fluororesin has low viscoelasticity when melted, so when it is extruded from the die opening and the pressure is released, the blowing agent gas dissolved in the molten resin expands rapidly. The bubbles reach the outer surface and cause surface roughness, and in severe cases bubbles may cause wrinkles in the epidermal layer. Therefore, the obtained cable not only has non-uniform outer diameter but also has poor voltage resistance due to pinholes and the like.

(C) Disclosure of the Invention In order to overcome these drawbacks, the inventors of the present invention have made extensive research and have obtained the following knowledge, and based on this knowledge they have arrived at the present invention.

That is, the molten resin comes out of the die opening and starts foaming, and before the bubbles start growing on the surface layer, the outer peripheral surface layer is rapidly cooled and solidified, a hard shell of a non-foamed layer is generated on the surface, and a certain amount of foam is formed inside. By foaming under pressure, it is possible to obtain a uniform foamed insulating layer with small cell diameters and to maintain a smooth surface. In this case, the extrusion temperature of the fluororesin is approximately 250°C to Since the temperature is as high as 400℃, when it is cooled with a normal cooling medium such as water, the surface hardens rapidly, and the inside is soft enough to be a trench, so the result is a shape in which air bubbles flow in the longitudinal direction of the wire, and in extreme cases bubble breakage occurs in the longitudinal direction. Therefore, it was found that by cooling under as gentle a temperature as possible, at a temperature lower than the melting point of the extruded melt, bubbles running in the longitudinal direction can be prevented and bubbles with a uniform diameter and shape can be obtained. Ta. The temperature conditions differ depending on the type of fluororesin, but
As a result of various studies, if the temperature is about 100℃ or higher,
It was found that bubble running can be prevented. The upper limit temperature is below the melting point of the resin, which is 50° C., and if it exceeds this temperature, the cooling capacity will decrease.

Any cooling means may be used as long as it can cool at 100°C or higher, but after exiting die A of the extruder, as a cooling medium inside the sizing die B (cylindrical) as shown in Fig. 1. It is preferable to keep silicone oil C or the like at a constant temperature of 100°C or higher and circulate it.After leaving the sizing die, the foamed insulating layer has already solidified, but in order to cool it to room temperature, it must be placed in a water cooling bath or It is sufficiently cooled through an air-cooled tank.

The fluororesin used in the present invention is a fluoroethylene-hexafluoroprohylene copolymer (FF
! P), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), chlorotrifluoroethylene-ethylene copolymer (ECTFE),
Ethylene-tetrafluoroethylene copolymer (FiTT
PE L HoI+ 7 Hinylide 7(T)VdF)
The foaming agent is freon-12, -
Gaseous Freon such as 22, Chakutake Freon-113,-
In addition to liquid Freon such as 114, chemical blowing agents can also be used.

FIG. 2 shows cross-sectional views (A horizontal cross-sectional view, 1 longitudinal cross-sectional view) of a foam insulation-coated electric wire obtained by the method of the present invention, and it shows that a uniform foam insulation coating 2 with fine foam cells can be obtained on the outer periphery of the conductor 1. Moreover, since the outer surface is a solid non-foamed skin layer 3, a smooth surface and stable outer diameter with little variation can be obtained, and the two layers of the surface skin layer and the inner foamed layer can be obtained. Because it is insulated, it has excellent mechanical strength and electrical properties such as withstand voltage.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view showing the state of cooling using a sizing die according to the present invention, and FIG. 2 is a cross-sectional view of a foam-coated insulated wire obtained by the method of the present invention. is a cross-sectional view, and (b) is a vertical cross-sectional view. Agents 1) Akira's agent Ryo Hagiwara - Figure 1

Claims (1)

[Claims] In a method of manufacturing an electric wire in which a heat-melted extrudable fluororesin is foamed around a conductor to form an insulating coating, the foamable heat-molten fluororesin exits from a die opening of an extruder and the bubbles reach a final foamed diameter. A method for manufacturing a foamed fluororesin insulated electric wire, which comprises: first forcibly cooling the outer circumferential surface at a temperature of 100° C. or higher.