DE3024070A1 - ELECTRIC CABLE WITH AN OUTER ELECTRICALLY CONDUCTIVE COATING FILM - Google Patents

Description

Patent attorneys Dipl.-Ing. Curt Wallach Dipl.-Ing. Günther Koch Dipl.-Phys. Dr Tino Haibach Dipl.-Ing. Rainer Feldkamp

D-8000 Munich 2 ■ Kaufingerstraße 8 · Telephone (0 89) 24 02 75 · Telex 5 29 513 wakai d

Date: June 2, 1980

Our reference: 16 W "H / Nu

Toagosei Chemical Industry Co., Ltd., Tokyo, Japan

Sumitomo Electric Industries, Ltd., Osaka, Japan

Cable with electrically conductive outer coating film

The invention relates to an electrical cable with is coated with an electrically conductive PiIm.

Among the various types of cables, there are those in which one on the outer surface surrounds the cable Polyethylene layer an electrically conductive layer must be created. Such an electric one A conductive layer is therefore applied to prevent the cable from being laid directly underground without a protective tube or the like to be able to check the occurrence of breaks in the outer layer of the cable by checking after completion of the cable laying work a high voltage between the mentioned outer electrically conductive layer

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and the inner, electrically conductive metal part ■ and then determines whether an electrical power line or arcing occurs between the outer layer and the electrically conductive layer. For the production of such an outer electrically conductive layer have hitherto been organic-based coating materials Solvent made by dissolving or dispersing a binder and electrically conductive Carbon in the organic solvent were produced, or aqueous coating materials used that by dissolving or dispersing a binder and electrically conductive carbon in water (in some Cases with a smaller proportion of a water-soluble organic solvent) were used.

The coating materials based on organic solvents, however, have disadvantages with regard to environmental _{protection problems 9} danger of explosion and fire, toxicity, saving of raw materials, saving of energy; the aqueous coating materials. are disadvantageous in, for example, defects * that may be caused by water repellency in the coating film, various problems resulting from a large amount of latent heat of evaporation, and the need for countermeasures for waste water treatment.

Based on these circumstances and considerations and the extensive investigations caused by them, the It is an object of the invention to produce an electrically conductive coating film on the outer surface

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a polyethylene layer surrounding the cable in a cost-saving, reliable and with regard to raw material and to enable energy saving more expedient way.

According to the gist of the invention, this object of efficiently producing such a conductor film can be achieved on the outer surface of the polyethylene layer by means of dissolve a powdery coating material, which is a special polyethylene or modified polyolefin and Contains electrically conductive carbon.

Specifically, according to the invention, for producing an electrically conductive coating film on a cable, the outer surface of a polyethylene layer surrounding the cable is coated with an electrically conductive powdery coating material having an average particle size of 200 µm or less and containing 100 parts by weight of a polyethylene or modified Polyolefin powder with a melt index (MI) at 190 ⁰ C of not more than 200 g / 10 minutes and a Vicat softening point of 50 ⁰ C to 120 ⁰ C, and 30 to 130 parts by weight of electrically conductive carbon powder, and that then the coating material melts together.

The polyethylene material suitable for the purposes of the invention is both lower polyethylene and polyethylene high density, the polyethylene according to the high pressure, the low pressure or the medium pressure process can be made. Such polyethylenes are available under a variety of trade names Companies in trade; according to the letterpress process

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manufactured low density polyethylenes are among others for example Arason (trade name of E. I. du Pont), Hubolen (trade name of the company BASF), Sumikasen (trade name of Sumitomo Chemical Co., Ltd.), Mirason (trade name of Mitsui Polychemical Industries, Ltd.), ÜBE Polyäthylen (trade name of Übe Industries, Ltd.) etc .; suitable high density polyethylenes produced by the medium pressure process include for example Sholex (trade name of Showa Yuka Co., Ltd.), Sutaflen (trade name of the company Furukawa Chemical Co., Ltd.), etc .; High density polyethylenes produced by the low pressure process are under others, for example, Hizex (Mitsui Petrochemical Industries, Ltd.), Hostalen (Hoechst) etc. Examples of Modified polyolefins used for the purposes of the invention include ethylene / vinyl acetate copolymers such as Evaflex (Mitsui Polychemical Industries, Ltd.) and the like; certain by Introduction of a special functional group in a polyethylene or a polypropylene obtained polyolefins such as Admer (Mitsui Petrochemical Industries, Ltd.), etc .; reactive polyolefins such as Bondfast (Sumitomo Chemical Co., Ltd.) and the like; Ionomers such as Surlyn (Mitsui Polychemical Industries, Ltd.) etc.

Among the named polyethylenes and modified polyolefins (these are referred to briefly as polyolefins below) are suitable for the purposes of the invention which have a melt index (MI) of not more than 200 g / 10 minutes ^{at 190 ° C., in particular in the range}

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from 0.1 to 200 g / 10 minutes, preferably in the range from 10 to 200 g / 10 minutes and particularly preferably in the range from 50 to 150 g / 10 minutes, and a Vicat softening point of 50 ⁰ to 120 ⁰ C, preferably have from 60 ⁰ C to 110 ⁰ C. The melt index at 190 ⁰ C is measured according to JIS D 6760 to 1977 and the Vicat softening point according to ASTM D 1525-70.

If the melt index of the polyolefin at 190 ^° C. exceeds a value of 200 g / 10 minutes, the film obtained has poor toughness and flexibility. On the other hand, if the melt index is too low, the flowability of the polyolefin upon heating and melting and the wetting of the substrate by the coating material are insufficient, so that the film produced has insufficient surface properties and surface adhesion. Therefore, the melt index should preferably be 0.1 g / 10 minutes or more. If the softening point of the polyolefin is below 50 ⁰ C ₉ so, the film has low heat resistance, and it can inconveniences result from the fact that the coated cable stick to each other due to the tackiness of the film at high temperatures and high humidities under pressure. At a softening point above 100 ^° G, however, the flowability of the coating material and the substrate wetting by the coating material are insufficient due to the heat restriction on the polyethylene layer to be coated, so that the film does not look good and does not adhere well.

Examples of electrically conductive carbon powder suitable for the purposes of the invention include

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natural or artificial graphite, electrically conductive furnace black, acetylene black, etc., each in mixed components_ of the carbon powder from 30 to 130 parts by weight, preferably 45 to 100 parts by weight per 100 parts by weight of the polyethylene or modified polyolefin. With a carbon powder content below 30 parts by weight the required electrical conductivity of the film is not guaranteed, with carbon parts above 130 Parts by weight are given to that produced from the coating material Film has poor adhesive properties and poor mechanical strength.

In the context of the invention, the powder properties and fluidity properties upon heating and melting of the powdery electroconductive coating material as well as the electrical conductivity, flexibility and other physical properties of the improve the film obtained on the coating material by dipping into the powdery electroconductive coating material in addition to the polyolefin. · and the electrically conductive carbon powder, if necessary incorporates one or more of the following additives: a gown to control flowability such as Benzoin, dimethyl terephthalate, Modaflow (trade name from Monsanto), Aeronal (BASF) or the like; a plasticizer such as dioctyl phthalate, p-hydroxybenzoic acid or the like; a phosphorus compound such as triphenyl phosphate or similar; a stabilizer such as a hindered *) phenol or the like; a filler such as calcium carbonate, zinc oxide, titanium oxide, talc, glass fiber, Aerosil or the like; from

*) ("hindered" ₃ blocked)

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Polyolefins various resins such as "for example thermoplastic polyester., nylon, .epoxy resin, petroleum resin or similar.

The following, for example, are suitable as a preferred method for producing an electrically conductive powdery coating material from the various starting materials mentioned and, if necessary, additives: was ground, optionally additives with particle sizes of 200 η or below, and from an electrically conductive carbon powder is heated to a temperature above the softening point but below the melting point of the polyolefin, while stirring the mixture by means of a mixing device, which is equipped with a heat control device such as For example, a heating jacket is provided, for example a Henschel Mdscher, a super mixer or the like, the rotor blades of the mixer rotating at high speed, for example at 500 to 1000 rpm, in order to achieve an intimate A to ensure adhesion of the electrically conductive carbon powder particles to the surface of the polyolefin powder particles; or (B) a melt blending method in which a polyolefin and optional additives are melted and mixed together with an electrically conductive carbon powder by means of a kneader equipped with a heater, a screw extruder or the like, the mixture thus obtained is cooled, frozen and pulverized and then the powder thus obtained for adjustment to one

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^ mean particle density classified as 200 yu or less will"

Coating a cable enclosed with polyethylene with the electroconductive powdery coating material having an average particle size of 200 η or less, preferably 100 ai or less, can be carried out by a conventional method such as immersion in a fluidized bed, an electrostatic coating method or the like; if the mean particle size of the powdery coating material exceeds 200 / u, it shows a poor coating efficiency and also poor throwing power with an uneven surface of the polyethylene layer, and the film obtained after heating has an unsatisfactory appearance; therefore the mean particle size should not be more than 200 / U, preferably not more than 100 η .

The electroconductive film is formed by heating and melting the powdery coating material after it has been applied in the above-mentioned manner by a conventional method and, if necessary, after performing a polishing treatment with a cloth or the like. The particular heating method and the heating conditions are appropriately selected depending on the softening point, melting point and melt viscosity of the polyolefin, the mixing ratio of the electroconductive carbon powder, the additive effects of the various optional additives and the like; The surface of the coating is preferably ^{heated to 100 to 200 °} C. for 0.05 to 20 minutes, specifically by means of a cylindrical

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Far infrared radiation heater.

In this way, according to the invention, a with an electrical Conductive coated cable is obtained in which the coated film is firmly attached to the outer surface the polyethylene layer surrounding the cable adheres and has excellent oil resistance and excellent properties tes appearance *

The invention is explained in more detail below with the aid of specific examples, which, however, do not restrict them in any way of importance.

example 1

A low density polyethylene having a melt index of 75 "and a softening point of 76 ⁰ C was frozen, pulverized, and then to obtain a polyethylene powder having a particle size of 200 or less yu classified. 2.1 kg of this polyethylene powder were 0.9 kg of natural graphite (sold under the trade name cp by Japan Graphite Co., Ltd.), the mixture thus obtained is introduced into a 20-1 Henschel mixer and the internal temperature is increased to a value of 85 ⁰ O by appropriate control of a heating jacket, with simultaneous rotation of the stirrer blades at 2000 rpm This mixing process was continued for 5 minutes at the specified temperature to obtain a powdery coating material

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80 mm in diameter was coated with the powdery coating material; the surface of the thus obtained coating was rubbed by means of a rotary grinder using a cloth to make the surface even; then the coating was heated and melted (heating time 0.5 minutes, highest temperature reached 200 ^° C.) by means of a cylinder furnace with radiation in the far infrared. In this way, an electroconductive coating film of about 10 yrs was formed on the cable . Good quality thickness achieved. The properties of the film are listed in Table 1 *

Example 2

A powdery coating material was produced by exactly the same procedure as in Example 1, except that instead of the polyethylene powder, a polyolefin material Admer NS-100 (trade name of Mitsui Petrochemical Industries, Ltd. for a special polyolefin with a melt index of 10 g / 10 minutes and a softening point of 98 ⁰ C) was used and the internal temperature was set to 105 ⁰ O; under the otherwise identical conditions as in example 1, a cable with an electrically conductive coating film of about 10 m thickness of good quality was again obtained, the properties of which can also be seen from table 1 .

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Example 3

The procedure was the same as in Example 1, with the difference that in the preparation of the powdery Coating material instead of 0.9 kg 0.63 kg natural graphite (cp) was used. The powdery coating material thus obtained was used in the same Way and under the same conditions as in Example 1 and on the cable an electrically conductive one Coating film of good quality with a thickness of about 10 / U was obtained, the properties of which are shown in Table 1 can be seen.

Example 4

The procedure was as in Example 1, with the difference that the powdery coating material was produced instead of 0.9 kg, an amount of 2.73 kg natural graphite (cp) was used, the one obtained in this way Powdered coating material was prepared under the same conditions as in Example 1 to produce an electric Good quality coating film with a thickness of about 10 η processed on the cable; the properties of the coating film are shown in Table 1.

example 5

The procedure was again as in Example 1, with the only difference that instead of the natural

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Graphite an amount of 0.9 kg of a carbon black powder (Corax L from DEGGUSSA) was used to produce the powdery coating material; with this powdery coating material was among the under the same conditions as in Example 1, an electroconductive coating film of good quality was applied to the cable a thickness of about 10 ". obtained, the properties of which can be seen from Table 1.

Table 1

Example Ur. after one-time
Rub in
after five times
Rub in
after ten times
Rub in KXl10-cm 1 5 2 3 4th 5 Surface resistance of
electrically conductive film
(at the beginning) * 1 I!
!!
Il 20th
50
150 5 10 3 10 Oil
constant
dig-
ability
test
* 2 28
100
200 50
100
200 30th
80
150 30th
120
200

* 1: The probes of a tester were placed with any two at a distance of 10 cm from each other Points on the surface of the electrically conductive film brought into contact and the surface resistance was measured.

* 2: Surface resistance after rubbing the coating surface with one impregnated with an insulating oil Cloth.

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Example 6

A low density polyethylene having a melt index of 4 g / 10 minutes and a softening point of 100 ⁰ C was frozen, pulverized, and then to obtain a polyethylene powder of particle size 200 η or less classified. 2.1 kg of this polyethylene powder were mixed with 0.9 kg of natural graphite (cp), the mixture thus obtained was introduced into a 20-1 Henschel mixer and its internal temperature was increased to 108 ⁰ O by regulating the temperature of a heating jacket accordingly simultaneous rotation of the agitator blades at a speed of 2000 rpm. The stirring was continued for 5 minutes at the specified temperature, thus obtaining a powdery coating material. A cable with a diameter of 80 mm enclosed with a polyethylene layer was coated with the powdery coating material; the surface of the obtained coating was rubbed by a rotary grinder using a cloth for leveling; Thereafter, the coating was heated by means of an operating with far-infrared radiation cylinder furnace and brought to melting (heating time 0.5 minute, the highest temperature region of 200 ⁰ C); In this way, a good quality electroconductive coating film of about 10 η thick having the properties shown in Table 2 was obtained on the cable.

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Example 7

A powdery coating material was produced in exactly the same way as in Example 6, with the difference that instead of the polyethylene powder from Example 6, Evaflex 360 (trade name of! "Irma Mitsui Polychemical Industries, Ltd. for an ethylene / Vinyl acetate copolymer with a melt index of 2 g / 10 minutes and a softening point of 54- ° 0) was used, which was then classified to a particle size of 200 yu or less, and with the further difference that the internal temperature of the furnace 60 ⁰ O, using this powdery coating material under the same conditions as in Example 6, a good quality electroconductive coating film of about 10 µm in thickness having the properties shown in Table 2 was applied to the cable.

Table 2

Example no. after rubbing in once
after being rubbed in five times
after rubbing in ten times KHIO-cm 6th 5 7th 5 Surface resistance of the electrical
conductive film (at the beginning) * 1 Il
Il
It 25th
60
180 25th
40
130 oil-resistant
dignity
test
* 2

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ή-f.

* 1 tind * 2 have the same meaning as in the footnotes to table .1.

Summary

The invention relates to a cable with an electrically conductive coating film; the coating is produced in such a way that the outer surface of a polyethylene layer surrounding the cable is coated with an electrically conductive powdery coating material with an average particle size of 200 η or less, the 100 parts by weight of a polyethylene or modified polyolefin powder with a melt index (MI) at 190 ⁰ G of not more than 200 g / 10 minutes and a Vicat softening point of 50 ⁰ G to 120 ⁰ G, and 30 to 130 parts by weight of an electrically conductive carbon powder, with subsequent melting together of the coating material. The adhesion of the polyethylene or modified polyolefin to the polyethylene layer of the cable is excellent, and the cable thus coated has a high oil resistance and an excellent appearance.

Patent claims:

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Claims (6)

2 a JUN11980 claims Applied [1! Electrical cable with one on the outer surface s v- a cable enclosing polyethylene layer outer electrically conductive coating film, characterized in that, to prepare the coating film on the outer surface of the cable enclosing polyethylene layer, an electrically conductive powdery coating material of a mean particle size of 20OyU or less, the 100 parts by weight of a polyethylene or modified polyolefin powder with a melt index (MI) at 190 ⁰ C of not more than 200 g / 10 minutes and a Vicat softening point of 50 ⁰ C to 120 ⁰ G, and 30 contains up to 130 parts by weight of an electrically conductive carbon powder, and that the coating material is fused together. 2. Cable with an electrically conductive coating film according to claim 1, characterized in that that the polyethylene or modified polyolefin powder has a melt index of 10 to 200 g / 10 minutes owns. 3. Cable with electrically conductive coating film according to claim 1 or 2, characterized et that the polyethylene or modified polyolefin from the group of low-density polyethylene, high-density polyethylene, ethylene / vinyl acetate 030064/0815 ο? Copolymers, reactive polyolefins and ionomers are selected is. 4-. Cable with an electrically conductive coating film according to one or more of the preceding claims, characterized in that the polyethylene or modified polyolefin has a Vicat softening point of 60 ⁰ C to 110 ⁰ C. 5. Cable with an electrically conductive coating film according to one or more of the preceding claims, characterized in that the electrically conductive carbon powder more powdery natural or artificial graphite, electrically conductive powdery furnace black or acetylene black powder is. 6. Cable with an electrically conductive coating film according to one or more of the preceding claims, characterized in that the electrically conductive powdery coating material in addition a flow agent, a plasticizer, a phosphorus compound, a stabilizer ! Fillers as well as other than polyolefin resins, in addition to the polyethylene or modified polyolefin powder and the electrically conductive carbon powder. G3O064 / O815