Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
  • H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
  • H01B3/30—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes
  • H01B3/44—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
  • H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
  • H01B3/30—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes
  • H01B3/44—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins
  • H01B3/441—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins from alkenes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B7/00—Insulated conductors or cables characterised by their form
  • H01B7/17—Protection against damage caused by external factors, e.g. sheaths or armouring
  • H01B7/28—Protection against damage caused by moisture, corrosion, chemical attack or weather
  • H01B7/2813—Protection against damage caused by electrical, chemical or water tree deterioration

Definitions

• the present invention relates to a composition for electric cables. More specifically, the invention relates to a (meth) acrylate-ester-containing ethylene polymer which is usable in compositions for electric cables, more particularly in compositions for inner and outer semiconducting layers as well as insulating layers for electric cables .
• Electric cables and particularly electric power cables for medium and high voltages are composed of a plurality of polymer layers extruded round the electric conductor.
• the electric conductor is usually coated first with an inner semiconductor layer followed by an insulating layer, then an outer semiconductor layer followed by water barrier layers, if any, and on the outside a sheath layer.
• the insulating layer and the semiconductor layers normally consist of cross-linked ethylene homo- and/or copolymers.
• LDPE low density polyethylene, i.e. polyethylene prepared by radical polymerisation at a high pressure
• peroxide for instance dicumyl peroxide
• a limitation of conventional LDPE is its tendency to be exposed, in the presence of water and under the action of strong electric fields, to the formation of dendritically branched defects, so-called water trees, which can lead to breakdown and possible electric failure. This tendency is strongly affected by the presence of inhomogeneities, microcavities and impurities in the material.
• EP-A-0 057 604 it is known to inhibit water treeing by adding to a semiconducting composition, which mainly consists of a poly- olefin and 5-50% by weight carbon black based on the weight of the total composition, a polyethylene glycol having a molecular weight of about 1000-20000 in an amount of 0.1-20% by weight.
• This composition is intended for semiconducting layers of electric cables and by adding polyethylene glycol, it is said to be possible to eliminate water trees which grow into the insulating layer from the interface between the insulating layer and the semiconducting layer.
• US Patent Specification US-A-4 , 812, 505 discloses a composition, which is usable as insulating layer in electric cables and which is resistant to water treeing.
• the composition comprises a copolymer of ethylene and at least one alpha-olefin having 4-8 carbon atoms, such as 1-butene, 1-hexane or 1-octene, and besides comprises a polyethylene glycol having a molecular weight in the range of about 1000-20000 in an amount of 0.1-20% by weight.
• European Patent Specification EP-A-0 538 033 dis- closes an extrudable ethylene hydroxy acrylate co- or terpolymer, which, in addition to ethylene, comprises 7-30% by weight hydroxy acrylate, and 0-40% by weight of a third monomer selected among vinyl esters, allyl esters, and acrylic or methacrylic esters which do not contain hydroxyl groups.
• the hydroxy acrylate may consist of any ester of glycol or polyglycol and acrylic acid or methacrylic acid, but preferably is hydroxyethyl meth- acrylate, hydroxymethyl methacrylate, hydroxypropyl acrylate or hydroxypropyl methacrylate.
• hydroxy acrylate is previously known in connection with hot melts, and the extruded product according to the patent specification, e.g. a film, is hydrophilic and absorbs and transmits moisture, the ethylene hydroxy acrylate copolymer improving the adhe- sion to, for instance, polar plastics and other materials and improves the strength properties because of the hydrogen bonds.
• the patent specification does not indicate the use of the polymer in compositions for electric cables . From Derwent ' s Abstract No.
• an ethylene copolymer which comprises 25-99.9% by weight ethylene, 75-0.1% by weight polyalkylene glycol monoacrylate, and 0-65% by weight of other ethylenically unsaturated mono- mers.
• This polymer is said to be usable for paints, inks etc, as coating agents for metal, paper, wool etc, as adhesives etc.
• the use of the polymer in compositions for electric cables is not disclosed.
• composition for elect- ric cables thus is provided, characterised in it comprises an ethylene copolymer which includes as a comonomer a (poly) alkylene glycol mono (meth) acrylate having the formula I
• H 2 C C-C-0-(CH 2 CHO) n -H (I)
• Ri H or CH 3
• R 2 H or CH 3
• n 1-20.
• ethylene copolymer here used is meant an ethylene-based polymer, which is obtained by polymerisation of ethylene and one or more other monomers, one of these other monomers consisting of (poly) - alkylene glycol mono (meth) acrylate having the formula I.
• the ethylene copolymer consists of a polymer of ethylene and the monomer of formula I, or of ethylene, the monomer of formula I and a further monomer, i.e. in the latter case a so-called terpolymer.
• (meth) acrylic acid and " (meth) acrylate” here used are meant acrylic acid and acrylate as well as methacrylic acid and methacrylate.
• Ri in formula I is CH 3 , i.e. the esterifying acid is methacrylic acid, and R 2 in formula I is H, i.e. the esterifying (poly) alkylene glycol is a (poly) ethylene glycol.
• HEMA hydroxyethyl methacrylate
• the amount of the comonomer of formula I in the ethylene copolymer may vary within wide limits, but preferably constitutes about 0.1-15% by weight, more preferred about 2-14% by weight of the copolymer.
• the ethylene copolymer may op- tionally comprise further comonomers in addition to the comonomer of formula I, and it is preferred that the comonomer contains such a further monomer, i.e. that the copolymer is a terpolymer.
• This further comonomer can be selected among monomers, which are copolymerisable with ethylene and (poly) alkylene glycol mono (meth) acrylate of formula I.
• Such monomers are well known to those skilled in the art and no extensive enumeration will be required, but as examples, mention can be made of vinylically unsa- turated monomers, such as C 3 -C 8 alpha olefins, for in- stance propene, butene etc.; vinylically unsaturated monomers containing functional groups, such as hydroxyl groups, alkoxy groups, carbonyl groups, carboxyl groups and ester groups.
• Such monomers may consist of, for instance, (meth) acrylic acid and alkyl esters thereof, such as methyl-, ethyl- and butyl (meth) acrylate; vinylically unsaturated, hydrolysable silane monomers, such as vinyl trimethoxysilane; vinyl acetate etc.
• the amount of further comonomer (s) in addition to (poly) alkylene glycol mono (meth) acrylate of formula I is from 0 to about 40% by weight, preferably about 1-30% by weight of the ethylene copolymer.
• the sum of all the monomer contents is 100% by weight.
• the inventive ethylene copolymer can be prepared by graft copolymerisation or by free-radical-initiated high- pressure polymerisation.
• Graft copolymerisation is a per se well-known polymerisation process in the art and therefore, no detailed description will be needed.
• graft co- polymerisation is carried out by copolymerisation of a vinylically unsaturated monomer with an ethylene polymer, such as an ethylene homopolymer or an ethylene copolymer, under the influence of a free radical initiator, such as a peroxide, for instance dicumyl peroxide (DCP) .
• DCP dicumyl peroxide
• the tem- perature in the graft copolymerisation should be sufficient for decomposition of the free radical initiator with formation of free radicals, which, by using dicumyl peroxide as initiator, means about 150-200 °C, and the polymerisation can be practically effected, for instance, by mixing the components in an extruder.
• Free-radical-initiated high-pressure polymerisation which is also well known in the art, is generally carried out by reacting, in a reactor, such as an autoclave or tube reactor, at a high pressure of about 100-300 MPa and an elevated temperature of about 80-300°C, the monomers under the influence of a radical initiator, such as a peroxide, hydroperoxide, oxygen or azo compound.
• a radical initiator such as a peroxide, hydroperoxide, oxygen or azo compound.
• the inventive ethylene copolymer also leads to other favourable and desirable properties when using it as material in electric cables.
• the ethylene copolymer according to the invention permits an improved dielectric strength, which is of value both to the insulating layer and the semiconducting layers of an electric cable.
• the inventive ethylene copolymer has a good environmental stress cracking resistance (ESCR) , which is of value for semiconducting layers of electric cables .
• ESCR environmental stress cracking resistance
• the water tree resistance (WTR) was determined for three polymer compositions, Polymer 1, Polymer 2 and Polymer 3, by so-called Ashcraft testing.
• Ashcraft testing which is a testing method for determining the WTR properties of polymers, has been described by Ashcraft, A. C, "Water Treeing in Polymeric Dielectrics", World Electrotechnical Congress in Moscow, USSR, 22 June 1977.
• Ashcraft testing well characterised effects are provided, viz. sharp, water-filled indentations, by means of a needle in compression-moulded cups.
• a voltage of 5 kV/6 kHZ is applied across the water, whereas the bottom of the cup is connected to earth.
• the temperature is constantly kept at 65 °C.
• the average length of the water trees after 72 h ageing is considered as a measure of the growth rate of the water trees in the specific insulating material.
• Polymer 1 consisted of a low-density polyethylene (LDPE) hav- ing a melt flow rate (MFR) of 2 g/10 min, which was used as reference
• Polymer 2 consisted of 99.1 parts by weight of the same type of LDPE, to which 0.56 parts by weight of polyethylene glycol (PEG) having a molecular weight of about 20000 had been added as a conventional agent inhibiting water treeing
• the polymer compositions also contained about 2 parts by weight of di
• Example 2 the water tree resistance of two compositions according to the invention was compared by Ashcraft testing.
• One composition contained 6.5% by weight of the water-tree-inhibiting polymer, whereas the other composition contained 14% by weight thereof.
• the dielectric strength of three semiconducting polymer compositions was measured, viz. Polymer A, B and C, which constituted the inner semiconductor of an electric cable.
• the first composition (Polymer A) consisted of an ethylene vinyl acetate copolymer (EVA) having 18% by weight vinylacetate, the composition containing about 40% by weight carbon black in order to make the composition semiconducting. This composition was used as reference.
• the second composition (Polymer B) consisted of the same EVA polymer as in the first composition, with the difference that 0.6% by weight polyethylene glycol (PEG) having a molecular weight of about 20000 had been added. Besides, the composition contained about 40% by weight carbon black.
• EVA ethylene vinyl acetate copolymer
• PEG polyethylene glycol
• the third composition (Polymer C) consisted of a terpolymer of ethylene, 18% by weight vinyl acetate and 3% by weight of a monomer of formula I.
• the composition contained about 40% by weight carbon black. This composition was a composition according to the invention.
• Each of the three compositions above was incorporated as inner semiconducting layers in electric cables, which, seen from inside and outwards, consisted of a 1.4 mm copper conductor, an inner semiconducting layer having an outer diameter of 2.8 mm, an insulating layer having an outer diameter of 5.8 mm and an outer semicon- ducting layer having an outer diameter of 6.1 mm.
• the insulating layer consisted of low-density polyethylene having an MFR of 2 g/10 min
• the outer semiconducting layer consisted of an ethylene butyl acrylate copolymer with an addition of about 40% by weight carbon black.
• the testing of the dielectric strength was carried out on these test cables in accordance with a method developed by Alcatel AG & Co, Hannover, Germany, and described in an article by Land H.G., Schadlich Hans, "Model Cable Test for Evaluating the Ageing Behaviour under Water Influence of Compounds for Medium Voltage Cables", Conference Proceedings of Jlcable 91, 24-28 June 1991, Versaille, France.
• As a value of the dielectric strength is stated 63% of E max from Weibull diagram in kV/mm.
• the dielectric strength was measured on the one hand A) after ageing for 16 h at 90°C in air and, on the other hand, B) after ageing for 1000 h at 9 kV/mm in 85/70°C water. The results of the testing are stated in the Table below.
• Polymer B (prior art) 95.6 40.6
• the composition according to the invention showed good properties as inner semiconducting layers and, in particular, had an excellent electric dielectric strength after ageing for 1000 h at 9 kV/mm in 85/70°C water.
• Example 4 In this Example, the dielectric strength was tested in a similar fashion as in Example 3 on an electric cable, which had as inner semiconducting layer a co posi- tion consisting of a terpolymer of ethylene, about 15% by weight methylacrylate and about 2% by weight hexaethylene glycol monomethacrylate, i.e. the same monomer of formula I as in Example 3, and about 40% by weight carbon black.
• a dielectric strength (63% of E max ) of 59.4 kV/mm was obtained after ageing for 1000 h at 9 kV/mm in 85/70°C water.
• Example 5 the environmental stress cracking resistance (ESCR) was tested, a property that is important, particularly to the outer semiconducting layer of an electric cable.
• the testing was carried out according to ASTM D 1693, on the one hand with 10% Igepal at 50°C and, on the other hand, in air at 50°C.
• the result of the testing of ESCR is shown in the Table below and is stated as the number of test pieces of a total of 10 test pieces that were broken in the testing after a certain time, measured in hours.
• Composition ESCR air 50°C ESCR, 10% Igepal
• the composition according to the invention had a considerably improved ESCR and is consequently well suited as material for outer semiconducting layers of electric cables.

Landscapes

• Physics & Mathematics (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Organic Insulating Materials (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)

Priority Applications (5)

Applications Claiming Priority (2)

Related Child Applications (1)

Publications (1)

Family

ID=20405662

Family Applications (1)

Country Status (7)

Cited By (3)

Families Citing this family (4)

Citations (3)

• 1997
  • 1997-02-04 SE SE9700374A patent/SE508564C2/sv not_active IP Right Cessation
• 1998
  • 1998-01-09 WO PCT/SE1998/000013 patent/WO1998034236A1/en active IP Right Grant
  • 1998-01-09 AU AU60082/98A patent/AU6008298A/en not_active Abandoned
  • 1998-01-09 JP JP53277298A patent/JP2001509946A/ja active Pending
  • 1998-01-09 KR KR10-1999-7007023A patent/KR100537287B1/ko not_active IP Right Cessation
  • 1998-01-09 CN CN98802918A patent/CN1099681C/zh not_active Expired - Fee Related
  • 1998-01-09 EP EP98903313A patent/EP0962021A1/en not_active Withdrawn

Patent Citations (3)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events