JPS58214296A - Electric wire for skin current heating tube - 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 The present invention relates to an electric wire for a skin current heating tube, and particularly to an electric wire for a skin current heating tube that can be used under high temperature, humidity, and heat conditions.

The conventional 5ECT (epidermal heating) method has been put into practical use for heating liquid transport pipes or other heating applications, and this method has a small size (25A
degree) Insert the coated electric wire 2 into the steel pipe 1, connect one end of the electric wire 2 to one end of the steel pipe 1, connect the other end to the other end of the steel pipe 1 via the energizing device S, and connect the electric wire 2 to the other end of the steel pipe 1. A current closed circuit is formed by the flowing current (see arrow) flowing through the steel pipe 1 as a return path.

and! 4. The current flowing through the tube 1 becomes a so-called skin current flowing in the inner surface skin, causing the steel tube 1 to generate heat. (Of course, the electric wire 2 itself also generates heat.) Such a 5-
According to the E-CT theory, the purpose is achieved by attaching the steel pipe 1 to be heated to the object 4 to be heated.

In the case of the figure, the object 4 is a pipeline for transporting a high viscosity fluid, and in this case, a small-sized steel pipe is integrally welded to the main pipe in the longitudinal direction and heated indirectly.

This type of wire is required to have a practical lifespan of 20 years.
Since it is used in a sealed steel pipe, heat aging resistance in the sealed pipe is important.

Conventionally, heat-resistant soaked silicone rubber has been used as the material for the covering layer around the conductor of this type of electric wire, but when this rubber is exposed to high temperatures in a sealed area isolated from the outside air, the rubber compound It deteriorates severely due to trace amounts of moisture or acid contained within the pipe, or moisture that seeps into the steel pipe during installation. Therefore, silicone rubber, which can be used at temperatures of 180'C or higher in a normal atmosphere, has a limit of 30'C at most when used in this type of electric wire.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the prior art described above and to provide a wire for a skin current heating tube that can be used at a temperature of 160'C or higher.

That is, the gist of the present invention is to use a crosslinked product of a composition mainly composed of a tetrafluoroethylene-propylene copolymer as a material for a coating layer on the circumference of a conductor in an electric wire for a skin current heating tube. There is a particular thing.

Examples of rubber materials having better heat resistance than silicone rubber include fluorine-containing epilastomers.

However, conventional fluorine-containing elastomers, typified by hexafluoropropylene-vinylidene fluoride copolymers,
Although it has sufficient heat resistance, it has poor resistance to moisture and is also a poor electrical insulator, so it cannot be used for the purposes intended in the present invention.

Although the tetrafluoroethylene-propylene copolymer used in the present invention has been recently developed, it has excellent properties in terms of heat resistance, heat and humidity resistance, and electrical insulation properties, and is at least 30°C higher than silicone rubber. It can be used at temperatures above 160°C.

Here, the tetrafluoroethylene-propylene copolymer includes, in addition to the main components tetrafluoroethylene and propylene, components copolymerizable with these, such as ethylene, isobutylene, acrylic acid and its alkyl esters, methacrylic acid, and The alkyl ester thereof, vinyl fluoride, nylidene fluoride, hexafluoropropene, chloroethyl vinyl ether, chlorotrifluoroethylene, perfluoroalkyl vinyl ether, etc. may be appropriately contained therein.

In such a copolymer, the molar ratio of tetrafluoroethylene/propylene is 9515 to 30/70,
In particular, it is preferable to select from the range of 90/10 to 45/'55 from the viewpoint of heat resistance, moldability, etc., and the content of components other than the main component that may be added as appropriate is usually 50/10 to 45/'55.
It is preferable to select from a range of mol % or less, particularly 30 mol % or less.

Crosslinking can be carried out by the action of a chemical crosslinking agent or ionizing radiation, but from the viewpoint of ease of operation, chemical crosslinking agents, especially dicumyl peroxide, 2゜5-dimethyl-2,5
-Di(benzoylperoxy)-hexane and the like are suitable organic peroxides.

An embodiment of the present invention will be described.

Tetrafluoroethylene-propylene copolymer with a number average molecular weight of 50,000 (molar ratio of C2F4/C3Hs of 54
．． , /46) 100 parts by weight, 2,5-lame blue 2,
5-di(benzoylperoxy)-hexane (crosslinking agent)
1 part by weight, triallyl isocyanurate (crosslinking aid), 5 parts by weight, mono-lium stearate (lubricant), 1 part by weight, magnesium silicate (filler > 20 parts by weight), 50 parts by weight.
The mixture is uniformly dispersed and mixed by kneading for 15 minutes using rolls heated to ~60°C. Next, add this mixture to the head: 8
0゛C, cylinder 1:80'C, cylinder 2:60
90m, -'m extrusion 1fi (L,,/D
= 22), and after coating a copper conductor with an outer diameter of 3 mrt+ with an insulation thickness of 2 mm, steam at 13 atm (approximately 190°C) was
The mixture was allowed to crosslink for 1 minute.

Next, as shown in FIG.
The mixture was wrapped around a mtn glass rod R, sealed in a sealed tube S, and incubated in a constant temperature bath at 200'C for 2 years.

However, since no cracks appeared in the coating layer of the electric wire C, a life of at least 20 years at 160° C. can be guaranteed.

On the other hand, when a silicone rubber insulated electric wire having a structure similar to that of the above-mentioned example was tested under the same conditions, "cracking" occurred after two months.

The crosslinked composition of the present invention can be used not only as an insulating coating layer as in the above embodiments, but also as a protective coating layer formed on an insulated wire core.

[Brief explanation of drawings]

Figure 1 shows an example of the skin current heating tube heating method (A).
(B) is an explanatory diagram showing the heated object (main pipe) and the heating tube installation situation, and (B) is a principle explanatory diagram showing the connection relationship between the heating tube and the insulated wire. FIG. 2 is an explanatory diagram showing the test situation of the electric wire of the present invention.

Claims (1)

[Claims] This is an electric wire for a skin current heating tube that is used in a high temperature and steam atmosphere with a humidity of 150°C or higher, and is characterized in that its coating layer is composed of a crosslinked product of a composition mainly consisting of a tetrafluoroethylene-propylene copolymer. Electric wire for skin current heating tubes.