JPS6362043B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improvement in a method for manufacturing an electric cable having a conductive coating on the circumferential surface of an anti-corrosion layer made of polyethylene, polyvinyl chloride, etc. applied on a metal sheath made of lead, aluminum, etc. of the cable. Such a cable corrosion protection layer is generally insulative and serves not only to mechanically protect the metal sheath, but also to protect it from electrical or chemical corrosion. However, if a defect occurs in this anti-corrosion layer for some reason, the metal sheath will corrode due to water entering through it, and if the reaction progresses further, water will also seep into the metal sheath, reducing the insulation performance of the cable. There is a risk. Therefore, it is desirable to inspect the integrity of the corrosion protection layer from time to time after the cable is put into use. As one means for facilitating this health inspection, a cable is used in which a conductive coating is provided on the outer peripheral surface of an insulating anti-corrosion layer. With this conductive coating, the corrosion protection layer over the entire length of the cable can be easily inspected by applying a current between the metal sheath and the conductive coating, ie, ground. The typical conventional method for forming a conductive film on the outer circumferential surface of the anticorrosion layer is to dissolve conductive powder, which is a mixture of carbon powder and polyvinyl chloride powder, in a solvent such as methyl ethyl ketone to make a conductive paint, and then pour this into a paint tank. and passing the anti-corrosion cable through the paint bath to adhere the conductive paint to the outer peripheral surface of the anti-corrosion layer,
A conductive film was formed by evaporating the solvent in air. However, with this method, there is a risk that the conductivity of the coating may be uneven, the coating may peel off, or cracks may occur in the anticorrosive layer itself, and it cannot be applied to polyethylene anticorrosive layers. There was a problem. Furthermore, the vaporized solvent may have an odor.
Management of the working environment at the cable manufacturing site was also an important issue, as the solvent itself was dangerous. As a method for solving these problems, a film forming method that does not use a solvent has already been proposed.
That is, an anti-corrosion cable is passed through a frozen and pulverized composite powder, such as conductive powder and plastic powder kneaded in a Banbury mixer or the like, to form a conductive film on the surface. However, since the conductive composite powder obtained by this method is coated with plastic powder around the conductive powder, the electrical resistance of the coating varies greatly.
It also has the disadvantage of peeling off due to oil. The present invention provides a method for forming a conductive coating on the circumferential surface of a cable anti-corrosion layer of a corrosion-proof cable having a conductive coating that eliminates the drawbacks of the conductive coating formed without using a solvent, as shown in the drawings below. The invention will be explained in detail with reference to examples. The drawing is a cross-sectional view of an embodiment of an electric cable according to the present invention, in which 1 is a cable core, 2 is a metal sheath made of lead, aluminum, etc., 3 is a corrosion protection layer made of polyethylene, vinyl chloride, etc., and 4 is the above-mentioned corrosion protection layer 3. It is a conductive coating applied to the outer peripheral surface of the This conductive coating 4 is made by applying a composite powder in which conductive powder is coated around resin powder to the outer peripheral surface of the cable anticorrosion layer 3, and then heating it to melt and integrate the resin powder. The resin powder is a material that has excellent adhesion to the anticorrosion layer, and is a resin that does not easily peel off even if it comes into contact with insulating oil of an OF cable or the like after adhesion. One or more selected from polyethylene, ethylene/vinyl acetate copolymer, polystyrene, polyvinyl butyral, polyvinyl chloride, and polyvinyl acetal is used, and the average particle size thereof is 10 to 300 μm. If the average particle size is 10 μm or less, it is difficult to manufacture and increases the cost, making it impractical. If it is 300 μm or more, the paintability is poor, so the average particle size is set to 10 to 300 μm. Carbon, graphite, or metal powder is used as the conductive powder, and its average particle size is 1 to 150 μm. If the average particle size is less than 1μm, the electrical resistance will be high and the cost will be high.
If the particle size is 150 μm or more, the paintability is poor, so the average particle size was set to 1 to 150 μm. The ratio of resin powder and conductive powder as a composite powder is 30% by weight.
-95, conductive powder 5-70 is desirable. resin powder
This is because if the amount of the conductive powder is less than 30% by weight, the adhesiveness will be poor, if it is more than 95% by weight, the electrical resistance will be large, if the amount of the conductive powder is less than 5% by weight, the electrical resistance will be large, and if it is more than 70% by weight, the adhesiveness will be poor. Note that preferably resin powder
60 to 80% by weight and 40 to 20% by weight of conductive powder are good from both electrical resistance and adhesive properties. There are various methods for coating conductive powder around resin powder. For example, there is a method in which hot air is sent to a place where resin and graphite are placed in a container and flowed, or a method in which the container is heated to heat the atmosphere and resin is coated. There is a method of melting the surface and attaching graphite powder. The table below shows a comparison table when the composite powder according to the present invention, the composite powder according to the conventional method, and the solvent-type conductive paint are applied to the surface of the anticorrosion layer.

[Table] As is clear from the table above, when the composite powder according to the present invention is applied to a cable anti-corrosion layer, it is superior in all aspects to the conventional powder.

[Brief explanation of drawings]

The drawing is a cross-sectional view of an embodiment of an electrical cable according to the invention. 1 cable core, 2 cable metal sheath, 3 anti-corrosion layer, 4 conductive coating.

Claims (1)

[Claims] 1. Around one or more resin powders selected from polyethylene, ethylene/vinyl acetate copolymer, polystyrene, polyvinyl butyral, polyvinyl chloride, and polyvinyl acetal with an average particle size of 10 to 300 μm, a powder with an average particle size of 1 A method for forming a conductive coating on the circumferential surface of a cable anti-corrosion layer, which comprises applying a composite powder coated with conductive powder of ~150 μm to the circumferential surface of a plastic anti-corrosion layer of a cable and melting and integrating it.