CA1281832C - Insulation composition for cables - Google Patents
Insulation composition for cablesInfo
- Publication number
- CA1281832C CA1281832C CA 484950 CA484950A CA1281832C CA 1281832 C CA1281832 C CA 1281832C CA 484950 CA484950 CA 484950 CA 484950 A CA484950 A CA 484950A CA 1281832 C CA1281832 C CA 1281832C
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- ethylene
- acrylate
- cross
- copolymer
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Abstract
Abstract Insulation composition for cables comprising a homo-polymer of ethylene or a copolymer of ethylene and an alpha--olefin and an ethylene-acrylate copolymer. The compositions have very good thermal and electrical stability properties.
They are preferably used for medium and high voltage cable.
The insulation composition is preferably cross-linked.
They are preferably used for medium and high voltage cable.
The insulation composition is preferably cross-linked.
Description
~2~3~
Insulation composition for cables The present invention reLates to an insulation com-position particuLarly suitable for medium and high vol-tage cables. The composition, which is cross-linkable or 5- cross-linked, consists essentially of a combination of a homopolyrner of ethylene, or a copolymer of ethylene and an alpha-olefin, and an ethylene-alkyl acrylate or ethylene-alkyl methacrylate copolymer. The compositions of the in-vention have very good thermal and electrical stability 10. propertieS~
The development ;n the field of power cables goestowards higher and higher service temperatures and higher demands are thus made on the ability of the insulation material to withstand these and to withstand increased, 15- very high, temperatures due to overload and short-circuit currents. It is further extremely important that the mat-erial can withs-tand formation of so-called water trees, which are initiated, among other things, from sites with specially high electrical stress, but will grow at a lower 20- stress, and which gradually can lead to breakdown and con-siderably reduce the service life of the wire or cable.
Polyethylene is widely used as a cable insulating material. On the other hand, copolymers of ethylene and polar materials such as vinyl acetate and ethylene acrylate Z5 are essentially used only as jacketing material and only to an insignificant extent as insulation material, and then only for low voltage purposes. The thermomechanical stability is generally improved by cross-linking and cross-linked materials are thus predominan-tly usecl. Copolymers of ethylene and alpha-olefins, linear ethylene polymers, have, as such, better thermomechanical properties than conventional branched homopolymers of corresponding density.
Several additives have been suggested in order to solve the problems of water treeing, eg different silanes. It 35- has also been suggested to add an ethylene-vinyl acetate copolymer as a water treeing inhibitor to polyethylene.
According to the present invention it has been found that compositions of ethylene polymers and ethylene-alkyl acrylate or ethylene-alkyl methacrylate copolymers ~ave v,~
12~3~L83~
very good thermal properties and that they are particularly suitable as insulation material for high voltage wire and cable, conferr;ng resistance to water tree formation.
The compositions of the invention are utilized cross-5. linked on the cables. They can be cross-linked by radiation or by chemical cross-linking without risk o-f degrada-tion.
A particular advantaye is that they can stand the very high cross-linking temperatures which are utilized in the more recent cross-linking processes such as in dry cross-10. linking e.g. in n;trogen atmosphere, without being degradedand giving rise to corrosive degradation products.
The present invention thus relates to a cross-linkable or cross-l;nked cable insulation composition, for medium and high voltage cable, which consists essentially of an 15. ethylene polymer, said ethylene polymer being a homopolymer of ethylene or a copolymer of ethylene and an alpha-olefin, and an ethylene-alkyl acrylate or an ethylene-alkyl meth-acrylate copolymer in an amount of 10 to 40 per cent by weight based on the combination of ethylene polymer and 20. acrylate poLymer. The invention relates particularly to a composition as stated above which contains a cross-linking agent.
The base polymer in the present compositions is a homopolymer of ethylene or a linear copolymer of ethylene 25~ and one or several alpha-olefins. The latter ethylene poly-mers are essentially linear and are produced by copolymer-ization of ethylene and alpha-olefins having 3 to 14 carbon atoms. Generally 1 to 20 per cent by weight of the copolymer is used. The ethylene polymer in the present compositions 30. suitably has a dens;ty which does not exceed 940 kg/m3, as non-cross-linked material, and the density is suitably within the range of from 915 to 935 kg/m3. The melt index for the ethylene base polymer, MI2, (measured according to IS0 1133, 2.16 kg weight at 190C) should preferably 35. be within the range of 0.1 to 20 g/10 min., and most prefer-ably wi-thin the range of from 0.5 to 10. The base polymer in the compositions is preferably a hornopolymer of ethylene, and preferably high pressure polyethylene.
The acrylate copolymers in the compositions are co-~L28~83~
polymers of ethylene and alkyl acrylate or alkyl methacryl-ate where-in the alkyl groups usually have 1 to 8 carbon atoms, eg methyl acryLate, e-thyl acrylate, propyi acrylate, n-butyl acrylate, i-butyl acrylate, methyl methacrylate, ethyl methacrylate. Copolymers of two or more of the men-tioned acrylates or methacrylates may of course also be used. The copolymers can be present in amounts of 10 to 50 per cent by weight and suitably in an amount of 25 to per cent based on the combination with the ethylene 10. base polymer. Ethylene-alkyl acrylate copolymers are prefer-red and especially copolymers of ethylene and n-butyl acryl-ate which have especially satisfactory therrno-oxidative stability in contact with copper. The acrylate copolymer suitably has a melt index of 2 to 60 9/10 min. (MI2 measured 15. as stated earlier). The content of acrylate in the copolymer should suitably be within the range of from 9 to 50 per cent by weight. ~igher acrylate contents in the copolymers seem to lead to shorter trees and lower tree densi-ty, and thus a copolymer with an acrylate content of 15 to 35 per 20. cent by weight is preferably used, and most preferably a copolymer with an acrylate content within the range of from 18 to 30 per cent by weight. In the present composi-tions the acrylate copolymer is present in an amount of to 40 per cent by weight and preferably in an amount 25. of 10 to 35 per cent by weight. The mentioned values are per cent of the acrylate copolymer based on the combination of this and the ethylene polymer.
The insulation composition is particularly suitable for medium and high voltage cable and hereby is meant wire and cable for an electr;cal field strength above 1 kV/mm and particularly above 1.8 kV/mm.
The cornpositions according to the invention are used in a cross-linked stage on the cables and they can be cross--linked in a known manner by rad;at;on cross-l;nk;ng or 35. using chemical cross-link;ng agents. Chem;cal cross-linking agents are convent;onal such agents such as organ;c per-oxides and a~o compounds and also silanes. Chemical cross-l;nking agents can be present in the compositions of the invention or be added afterwards, at the cable production.
"
~.2~3~L83~
Preferred compositions contain an effective amount of a cross-linking agent selected from organic peroxides, azo compounds ancl silanes. Organic perox;des are preferred and as examples of such can be mentioned dicumyl peroxide 5. and di-tert. butyl peroxide. The required amoun-t of cross-linking agent depends among other things on the desired degree of cross-linking, the type of cross-linking agent and the type of ethylene base polymer. When the base mater-ial is polyethylene the amount of cross-linking agent is 10. suitably within the range of from 0.5 to 6 per cent by weight, based on the combination of ethylene base polymer and acrylate copolymer. For linear ethylene polymers smaller amounts of cross-linking agent can be used to ob-tain the same degree of cross-linking and the amount is here suitably 15. within the range of from 0.2 to 5 per cent by weight.
Particularly preferred compositions according to the present invention comprise polyethylene as base poly-mer, an ethylene-alkyl acrylate copolymer and a cross-link-ing agent, preferably an organic peroxide.
20. For high voltage cables an outer bonded semicon-ducting layer of an ethylene-alkylacrylate copolymer is often used. The present compositions give the highest com-patibility with such layers and thus the highest adhesion.
Medium and high voltage cables with a bonded outer semicon-25- ducting layer of an ethylene-acrylate copolymer and an insulation of the present composition will thus have the best possible total electrical properties.
If an ethylene-vinyl acetate copolymer, or a non--acrylate copolymer, is used in the outer semiconducting 30- layer for strippable such layers, which are sometimes de-sired, the strippability will presùmably be improved in combination with the present insulation composition~
The present insulation compositions consist essential-ly of the ethylene polymer and the ethylene-acrylate co-35- polyrner as previously defined. Even if other polymeric materials may be included the compositions do preferably not contain any other polymeric materials, and at least not more than 10 per cent by weight of such materials.
The compositions can of course contain additives which 83~
are conventional for this type of materials such as anti-oxidants, cross~linking accelerators and cross-linking retardants, other additives to inhibit water treeing, pro-rads, field strength regulators etc, which are used in 5. minor amounts with regard to the base composition. Inorganic materials, for example fillers such as aluminium hydroxides, kaolin and antimony oxides, should preferably not be present in the compositions, and at least not in higher amounts than 2 per cent by weight as most such materials have a 10. negative effect on dielectric losses in higher amounts.
The composit;ons can be prepared in a conventional manner by mixing in conventional, batch or continuous, mixing equipment. The added ethylene-acrylate copolymer can suitably be used as a carrier for other additives such 15. as cross-linking agents, antioxidants etc.
The compositions are applied to a metal conductor, over the on this usually present semi-conducting layer, as insulation. One embodiment of the present invention also relates to an insulated cable comprising a metal con-20. ductor, a semi-conducting layer and an insulation of the present composition and an outer semiconducting layer ex-truded over this and then cross-linked. The compositions can be cross-linked and at this the recently developed and increasingly utilized high temperature cross-linking 25- processes, dry curing processes where the temperatures are at about 250C or h;gher, can be used. In contrast to other types of copolymers, such as ethylene-vinyl acetate copolymers, the present compositions with acrylate copoly-mers can be treated at these high temperatures without 30- any substantial degradation and w;thout release of corrosive degradation products. This rneans that insulation according to the invention has an extremely good resistance to -thermal degradation and thus an increased service life. [nsulation according to the invention also has a very good electrical 35- stability and reduced or inhibited water tree formation.
The inven-tion is further illustrated in the following examples, which, however, are not intended to limit the same~ Parts and per cent relate to parts by weight and per cent by weight, respectively, unless o-therwise stated.
~X~3~83~
Example The ability of compositions according to the invention to withstand formation of water trees was examined by test-ing on Rogowsky objects. The presence of so-called bow tie trees and so-called vented trees were examined and also the average size of the longest trees. Bow tie trees grow from irregularities inside the insulation while vented trees grow frorn the interface between insulation and semi-conductor. Royowsky objects g;ve a homogeneous electrical 10. field as in a cable in service. The objects look like small containers and from the earth s;de there is an alum;n;um sheet serving as a water diffus;on barr;er and earth elec-trode. Next to this sheet there is a semiconductor and the two sheets are moulded together. Next to the semicon-ductor is the insulation, prepressed from extruded tape.Upon the insulation a water container is placed and the water is connected with a high voltage generator~ The con-tainer, insulation and semiconductor with the aluminium sheet are assembled in a mould and pressed and the insula-20. tion is cross-linked. The samples are conditioned three days at 90C in an oven with air circulation. The objects are then subjected to an electrical stress of 6kV/mm at 90C for 3 weeks. Slices are then microtomed from the ob-jects, dyed and examined in a microscope.
25. The following composi-tions were examined as described above (In all compositions the base polymer was a poly-ethylene with a density of 922 kg/m3 and a MI2 of 2):
a) 70 % polyethylene and 30 % of an ethylene-n-butylacrylate copolymer (MI2 = 4) with an acrylate content of 27 %.
30. b) 81.5 % of polyethylene and 18.5 % of ethylene-n-bu-tyl-acrylate copolymer according to a) c) 70 % of polyethyLene and 30 % of an ethylene-n-butyl-acrylate copolymer (MI2 = 4) with an acrylate content of 17 %~
35. d) 75 % of polyethylene and 25 % of ethylene-n-butylacrylate copolyrner according to a) Comparison was made with the polyethylene base polymer (e) ref.) and also with an ethylene-ethylacrylate copolymer containing 1.8 % of ethylacrylate (f) ref.). All samples 83~
were cross-linked with peroxide and tested in the cross-linked stage.
The results are shown in the following table. The tree density has been classified according to a scale where 5. 0 = 0 trees per cm3, 1 = up to 300 trees, 2 = 301 to 800 trees, 3 =801 to 1500 trees, 4 = 1501 to 2000 trees and 5 = more than 2000 trees.
Composition Bow tie trees Vented trees density size)um density sizeJum 10. a~ 0~1 ~10 0 0 b) 0-1 35 0 0 c) 1 25 0 0 d) 0-1 15 0 0 e~ref. 3 90 2 180 15. f)ref. 1-2 27 1-2 35 It should be noted that all compositions according to the invention were completely free from vented trees while both the reference compositions showed high amounts of such trees and also higher amounts of bow tie trees.
20. It should also be mentioned that most commercial cross-link-ed polyethylene cable insulations at these test show a bow tie tree density according to the above scale of 3 to 5.
Insulation composition for cables The present invention reLates to an insulation com-position particuLarly suitable for medium and high vol-tage cables. The composition, which is cross-linkable or 5- cross-linked, consists essentially of a combination of a homopolyrner of ethylene, or a copolymer of ethylene and an alpha-olefin, and an ethylene-alkyl acrylate or ethylene-alkyl methacrylate copolymer. The compositions of the in-vention have very good thermal and electrical stability 10. propertieS~
The development ;n the field of power cables goestowards higher and higher service temperatures and higher demands are thus made on the ability of the insulation material to withstand these and to withstand increased, 15- very high, temperatures due to overload and short-circuit currents. It is further extremely important that the mat-erial can withs-tand formation of so-called water trees, which are initiated, among other things, from sites with specially high electrical stress, but will grow at a lower 20- stress, and which gradually can lead to breakdown and con-siderably reduce the service life of the wire or cable.
Polyethylene is widely used as a cable insulating material. On the other hand, copolymers of ethylene and polar materials such as vinyl acetate and ethylene acrylate Z5 are essentially used only as jacketing material and only to an insignificant extent as insulation material, and then only for low voltage purposes. The thermomechanical stability is generally improved by cross-linking and cross-linked materials are thus predominan-tly usecl. Copolymers of ethylene and alpha-olefins, linear ethylene polymers, have, as such, better thermomechanical properties than conventional branched homopolymers of corresponding density.
Several additives have been suggested in order to solve the problems of water treeing, eg different silanes. It 35- has also been suggested to add an ethylene-vinyl acetate copolymer as a water treeing inhibitor to polyethylene.
According to the present invention it has been found that compositions of ethylene polymers and ethylene-alkyl acrylate or ethylene-alkyl methacrylate copolymers ~ave v,~
12~3~L83~
very good thermal properties and that they are particularly suitable as insulation material for high voltage wire and cable, conferr;ng resistance to water tree formation.
The compositions of the invention are utilized cross-5. linked on the cables. They can be cross-linked by radiation or by chemical cross-linking without risk o-f degrada-tion.
A particular advantaye is that they can stand the very high cross-linking temperatures which are utilized in the more recent cross-linking processes such as in dry cross-10. linking e.g. in n;trogen atmosphere, without being degradedand giving rise to corrosive degradation products.
The present invention thus relates to a cross-linkable or cross-l;nked cable insulation composition, for medium and high voltage cable, which consists essentially of an 15. ethylene polymer, said ethylene polymer being a homopolymer of ethylene or a copolymer of ethylene and an alpha-olefin, and an ethylene-alkyl acrylate or an ethylene-alkyl meth-acrylate copolymer in an amount of 10 to 40 per cent by weight based on the combination of ethylene polymer and 20. acrylate poLymer. The invention relates particularly to a composition as stated above which contains a cross-linking agent.
The base polymer in the present compositions is a homopolymer of ethylene or a linear copolymer of ethylene 25~ and one or several alpha-olefins. The latter ethylene poly-mers are essentially linear and are produced by copolymer-ization of ethylene and alpha-olefins having 3 to 14 carbon atoms. Generally 1 to 20 per cent by weight of the copolymer is used. The ethylene polymer in the present compositions 30. suitably has a dens;ty which does not exceed 940 kg/m3, as non-cross-linked material, and the density is suitably within the range of from 915 to 935 kg/m3. The melt index for the ethylene base polymer, MI2, (measured according to IS0 1133, 2.16 kg weight at 190C) should preferably 35. be within the range of 0.1 to 20 g/10 min., and most prefer-ably wi-thin the range of from 0.5 to 10. The base polymer in the compositions is preferably a hornopolymer of ethylene, and preferably high pressure polyethylene.
The acrylate copolymers in the compositions are co-~L28~83~
polymers of ethylene and alkyl acrylate or alkyl methacryl-ate where-in the alkyl groups usually have 1 to 8 carbon atoms, eg methyl acryLate, e-thyl acrylate, propyi acrylate, n-butyl acrylate, i-butyl acrylate, methyl methacrylate, ethyl methacrylate. Copolymers of two or more of the men-tioned acrylates or methacrylates may of course also be used. The copolymers can be present in amounts of 10 to 50 per cent by weight and suitably in an amount of 25 to per cent based on the combination with the ethylene 10. base polymer. Ethylene-alkyl acrylate copolymers are prefer-red and especially copolymers of ethylene and n-butyl acryl-ate which have especially satisfactory therrno-oxidative stability in contact with copper. The acrylate copolymer suitably has a melt index of 2 to 60 9/10 min. (MI2 measured 15. as stated earlier). The content of acrylate in the copolymer should suitably be within the range of from 9 to 50 per cent by weight. ~igher acrylate contents in the copolymers seem to lead to shorter trees and lower tree densi-ty, and thus a copolymer with an acrylate content of 15 to 35 per 20. cent by weight is preferably used, and most preferably a copolymer with an acrylate content within the range of from 18 to 30 per cent by weight. In the present composi-tions the acrylate copolymer is present in an amount of to 40 per cent by weight and preferably in an amount 25. of 10 to 35 per cent by weight. The mentioned values are per cent of the acrylate copolymer based on the combination of this and the ethylene polymer.
The insulation composition is particularly suitable for medium and high voltage cable and hereby is meant wire and cable for an electr;cal field strength above 1 kV/mm and particularly above 1.8 kV/mm.
The cornpositions according to the invention are used in a cross-linked stage on the cables and they can be cross--linked in a known manner by rad;at;on cross-l;nk;ng or 35. using chemical cross-link;ng agents. Chem;cal cross-linking agents are convent;onal such agents such as organ;c per-oxides and a~o compounds and also silanes. Chemical cross-l;nking agents can be present in the compositions of the invention or be added afterwards, at the cable production.
"
~.2~3~L83~
Preferred compositions contain an effective amount of a cross-linking agent selected from organic peroxides, azo compounds ancl silanes. Organic perox;des are preferred and as examples of such can be mentioned dicumyl peroxide 5. and di-tert. butyl peroxide. The required amoun-t of cross-linking agent depends among other things on the desired degree of cross-linking, the type of cross-linking agent and the type of ethylene base polymer. When the base mater-ial is polyethylene the amount of cross-linking agent is 10. suitably within the range of from 0.5 to 6 per cent by weight, based on the combination of ethylene base polymer and acrylate copolymer. For linear ethylene polymers smaller amounts of cross-linking agent can be used to ob-tain the same degree of cross-linking and the amount is here suitably 15. within the range of from 0.2 to 5 per cent by weight.
Particularly preferred compositions according to the present invention comprise polyethylene as base poly-mer, an ethylene-alkyl acrylate copolymer and a cross-link-ing agent, preferably an organic peroxide.
20. For high voltage cables an outer bonded semicon-ducting layer of an ethylene-alkylacrylate copolymer is often used. The present compositions give the highest com-patibility with such layers and thus the highest adhesion.
Medium and high voltage cables with a bonded outer semicon-25- ducting layer of an ethylene-acrylate copolymer and an insulation of the present composition will thus have the best possible total electrical properties.
If an ethylene-vinyl acetate copolymer, or a non--acrylate copolymer, is used in the outer semiconducting 30- layer for strippable such layers, which are sometimes de-sired, the strippability will presùmably be improved in combination with the present insulation composition~
The present insulation compositions consist essential-ly of the ethylene polymer and the ethylene-acrylate co-35- polyrner as previously defined. Even if other polymeric materials may be included the compositions do preferably not contain any other polymeric materials, and at least not more than 10 per cent by weight of such materials.
The compositions can of course contain additives which 83~
are conventional for this type of materials such as anti-oxidants, cross~linking accelerators and cross-linking retardants, other additives to inhibit water treeing, pro-rads, field strength regulators etc, which are used in 5. minor amounts with regard to the base composition. Inorganic materials, for example fillers such as aluminium hydroxides, kaolin and antimony oxides, should preferably not be present in the compositions, and at least not in higher amounts than 2 per cent by weight as most such materials have a 10. negative effect on dielectric losses in higher amounts.
The composit;ons can be prepared in a conventional manner by mixing in conventional, batch or continuous, mixing equipment. The added ethylene-acrylate copolymer can suitably be used as a carrier for other additives such 15. as cross-linking agents, antioxidants etc.
The compositions are applied to a metal conductor, over the on this usually present semi-conducting layer, as insulation. One embodiment of the present invention also relates to an insulated cable comprising a metal con-20. ductor, a semi-conducting layer and an insulation of the present composition and an outer semiconducting layer ex-truded over this and then cross-linked. The compositions can be cross-linked and at this the recently developed and increasingly utilized high temperature cross-linking 25- processes, dry curing processes where the temperatures are at about 250C or h;gher, can be used. In contrast to other types of copolymers, such as ethylene-vinyl acetate copolymers, the present compositions with acrylate copoly-mers can be treated at these high temperatures without 30- any substantial degradation and w;thout release of corrosive degradation products. This rneans that insulation according to the invention has an extremely good resistance to -thermal degradation and thus an increased service life. [nsulation according to the invention also has a very good electrical 35- stability and reduced or inhibited water tree formation.
The inven-tion is further illustrated in the following examples, which, however, are not intended to limit the same~ Parts and per cent relate to parts by weight and per cent by weight, respectively, unless o-therwise stated.
~X~3~83~
Example The ability of compositions according to the invention to withstand formation of water trees was examined by test-ing on Rogowsky objects. The presence of so-called bow tie trees and so-called vented trees were examined and also the average size of the longest trees. Bow tie trees grow from irregularities inside the insulation while vented trees grow frorn the interface between insulation and semi-conductor. Royowsky objects g;ve a homogeneous electrical 10. field as in a cable in service. The objects look like small containers and from the earth s;de there is an alum;n;um sheet serving as a water diffus;on barr;er and earth elec-trode. Next to this sheet there is a semiconductor and the two sheets are moulded together. Next to the semicon-ductor is the insulation, prepressed from extruded tape.Upon the insulation a water container is placed and the water is connected with a high voltage generator~ The con-tainer, insulation and semiconductor with the aluminium sheet are assembled in a mould and pressed and the insula-20. tion is cross-linked. The samples are conditioned three days at 90C in an oven with air circulation. The objects are then subjected to an electrical stress of 6kV/mm at 90C for 3 weeks. Slices are then microtomed from the ob-jects, dyed and examined in a microscope.
25. The following composi-tions were examined as described above (In all compositions the base polymer was a poly-ethylene with a density of 922 kg/m3 and a MI2 of 2):
a) 70 % polyethylene and 30 % of an ethylene-n-butylacrylate copolymer (MI2 = 4) with an acrylate content of 27 %.
30. b) 81.5 % of polyethylene and 18.5 % of ethylene-n-bu-tyl-acrylate copolymer according to a) c) 70 % of polyethyLene and 30 % of an ethylene-n-butyl-acrylate copolymer (MI2 = 4) with an acrylate content of 17 %~
35. d) 75 % of polyethylene and 25 % of ethylene-n-butylacrylate copolyrner according to a) Comparison was made with the polyethylene base polymer (e) ref.) and also with an ethylene-ethylacrylate copolymer containing 1.8 % of ethylacrylate (f) ref.). All samples 83~
were cross-linked with peroxide and tested in the cross-linked stage.
The results are shown in the following table. The tree density has been classified according to a scale where 5. 0 = 0 trees per cm3, 1 = up to 300 trees, 2 = 301 to 800 trees, 3 =801 to 1500 trees, 4 = 1501 to 2000 trees and 5 = more than 2000 trees.
Composition Bow tie trees Vented trees density size)um density sizeJum 10. a~ 0~1 ~10 0 0 b) 0-1 35 0 0 c) 1 25 0 0 d) 0-1 15 0 0 e~ref. 3 90 2 180 15. f)ref. 1-2 27 1-2 35 It should be noted that all compositions according to the invention were completely free from vented trees while both the reference compositions showed high amounts of such trees and also higher amounts of bow tie trees.
20. It should also be mentioned that most commercial cross-link-ed polyethylene cable insulations at these test show a bow tie tree density according to the above scale of 3 to 5.
Claims (13)
1. Cross-linkable or cross-linked cable insulation composition for medium and high voltage cables characterized in that it consists essentially of an ethylene polymer, which is a homopolymer of ethylene or a copolymer of ethylene and an alpha-olefin, and an ethylene-alkyl acrylate or ethylene-alkyl methacrylate copolymer in an amount of 10 to 40 per cent by weight, based on the combination of ethylene polymer and acrylate copolymer.
2. A composition according to claim 1, characterized in that it contains a crosslinking agent.
3. A composition according to claim 2, characterized in that the cross-linking agent is an organic peroxide.
4. A composition according to claim 1, characterized in that it contains 10 to 35 per cent by weight of acrylate or methacrylate copolymer, based on the combination of ethylene polymer and acrylate or methacrylate copolymer.
5. A composition according to claim 1, characterized in that the acrylate or methacrylate copolymer is ethylene-n-butyl acrylate copolymer.
6. A composition according to claim 1, characterized in that the acrylate or methacrylate content in the acrylate or methacrylate copolymer is within the range of from 9 to 50 per cent by weight.
7. A composition according to claim 1 characterized in that it is free of inorganic material or contains not more than 2% by weight of inorganic material.
8. A composition according to claim 1 characterized in that it contains an organic peroxide as cross-linking agent, that it contains 10 to 35 per cent by weight of acrylate or methacrylate copolymer and that the acrylate or methacrylate content in the acrylate or methacrylate copolymer is within the range of from 9 to 50 per cent by weight.
9. A composition according to claim 8 characterized in that the acrylate or methacrylate copolymer is an ethylene-n-butyl acrylate copolymer.
10. An insulated cable comprising a metal conductor, a semiconducting layer and an insulation comprising a composition according to any one of claims 1 to 9 and an outer semi-conducting layer.
11. An insulated cable according to claim 10 characterized in that it is capable of use at an electrical field strength above 1 kV/mm.
12. An insulated cable according to claim 10 characterized in that it 15 capable of use at an electrical field strength above 1.8 kV/mm.
13. A process for preparing an insulated cable according to claim 11 or 12 characterized in that a metal conductor is covered with a semiconducting layer the semiconducting layer is covered with a composition according to any one of claims 1 to 9, an outer semiconducting layer is extruded over the composition and the composition is then cross-linked.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 484950 CA1281832C (en) | 1985-06-24 | 1985-06-24 | Insulation composition for cables |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 484950 CA1281832C (en) | 1985-06-24 | 1985-06-24 | Insulation composition for cables |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1281832C true CA1281832C (en) | 1991-03-19 |
Family
ID=4130807
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 484950 Expired - Fee Related CA1281832C (en) | 1985-06-24 | 1985-06-24 | Insulation composition for cables |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1281832C (en) |
-
1985
- 1985-06-24 CA CA 484950 patent/CA1281832C/en not_active Expired - Fee Related
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