Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
2001-10-09
2003-12-23
Jackson, Monique R. (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S375000, C428S379000, C428S391000, C428S457000, C428S447000, C428S450000, C428S461000, C428S463000, C174S068100, C174S1100SR
Reexamination Certificate
active
06667098
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an electrical cable, and more particularly to an electrical rubber cable.
TECHNICAL BACKGROUND
Electrical rubber cables, are flexible electrical cables with a conductor surrounded by an insulating layer and an outer jacketing layer. Several insulated conductors may be enclosed by one jacket. Such rubber cables are usually low or medium voltage cables, i.e. they are intended for voltages up to about 10 kV. The insulating and/or jacketing layers are conventionally made of natural rubber (NR) or ethylene-propylene rubber (EPR), e.g. EPDM or EPM.
There are several disadvantages associated with rubber cables. Thus, the fact that they comprise rubbery components means that they are made according to conventional rubber processing procedures. This includes handling of powdery raw materials, processing of the powdery raw materials in special rubber compounding equipment, and curing of the cables by curing procedures involving sulphur or peroxide curing agents. Further, the ageing resistance of rubber cables often leaves something to be desired as does the resistance against solvents such as gasoline or oils.
It would therefore be an important progress in the art if a rubber cable could be obtained that is made of ordinary ethylene polymer material and that is produced with ordinary polymer processing equipment.
SUMMARY OF THE INVENTION
It is an object of the present invention to ameliorate or eliminate the drawbacks of the prior art and provide an electrical cable of the rubber cable type where the insulation and/or jacketing is made of a crosslinked rubbery ethylene polymer composition.
It is a further object of the invention to provide an electrical cable of the rubber cable type where the insulating and/or jacketing layer(s) are made of pelleted raw materials that are easy to handle.
It is a still further object of the invention to provide an electrical cable of the rubber cable type where the insulating and/or jacketing layer(s) are obtained by extruding the materials (s).
It is another object of the invention to provide an electrical cable of the rubber cable type which is cross linkable by so-called moisture curing.
It is still another preferred object of the invention to provide an electrical cable of the rubber cable type with good ageing and solvent resistance.
Thus, according to the present invention there is provided a cable comprising an electrical conductor with insulating and protecting layers surrounding the conductor, characterised in that at least one layer selected from said insulating and protecting layers consists of a crosslinked ethylene-alkyl (meth)acrylate-unsaturated silane terpolymer composition wherein the alkyl (meth)-acrylate comonomer comprises more than 5 mole % and the terpolymer composition has a tensile modulus, determined according to ISO 527-2 (1 mm/min) of less than 100 MPa.
These and other advantages and characterising features of the present invention will appear from the following specification and the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
Generally, and in connection with the present invention the expression “alkyl (meth)acrylate” includes alkyl acrylates as well as alkyl methacrylates. The alkyl moiety preferably is an alkyl group having 1-4 carbon atoms, such as methyl, ethyl, propyl, and butyl, preferably methyl or butyl.
Conventional ethylene-alkyl (meth)acrylate polymers generally comprise the alkyl (meth)acrylate comonomer in a low amount of up to about 10% by weight. The present invention differs from such conventional ethylene-alkyl (meth)acrylate copolymers in that it is not a copolymer, but a terpolymer containing an unsaturated silane compound as a termonomer, and also in that it contains the alkyl (meth)acrylate comonomer in a high amount of at least 5 mole %, preferably 5-25 mole %. More preferably the alkyl (meth)acrylate comonomer comprises about 9-20 mole % of the polymer. The high alkyl (meth)acrylate comonomer content at the present invention is necessary in order to make the polymer composition sufficiently soft and flexible.
The terpolymer according to the present invention should have a melt flow rate (MFR
2
), determined according to ISO 1133, Condition D, of 0.1-40 g/10 min.
In this connection, it is a general requirement for rubber cables to have a Shore A hardness of less than 85. This requirement thus also applies to the the insulating and jacketing layers of the cable according to the present invention. The Shore A hardness is determined according to ISO 868.
Further, the terpolymer composition according to the present invention should have a tensile modulus, determined according to ISO 527-2 (1 mm/min) of less than 100 MPa, preferably less than 60 MPa, and most preferably less than 30 MPa.
As mentioned above, the ethylene-alkyl (meth)acrylate polymer composition of the insulating or jacketing layer of the inventive cable is crosslinkable.
The crosslinking at the present invention is by way of hydrolysable silane groups which are incorporated in the ethylene-alkyl (meth)acrylate polymer composition constituting the insulation and/or jacketing layer of the cable according to the invention.
The crosslinking of polymers with hydrolysable silane groups is carried out by so-called moisture curing. In a first step, the silane groups are hydrolysed under the influence of water or steam, resulting in the splitting-off of alcohol and the formation of silanol groups. In a second step, the silanol groups are cross linked by a condensation reaction splitting off water. In both steps, a so-called silanol condensation catalyst is used as a catalyst.
Silanol condensation catalysts include carboxylates of metals, such as tin, zinc, iron, lead and cobalt; organic bases; inorganic acids; and organic acids. In practice dibutyl tin dilaurate (DBTL) is generally used as the silanol condensation catalyst.
At the present invention it is preferred, however, to use a specific silanol condensation catalyst of formula I
ArSO
3
H (I)
or a precursor thereof, Ar being a benzene ring substituted with at least one hydrocarbyl radical such that the total number of carbon atoms of the hydrocarbyl radical(s) is 8-20, or a naphthalene ring substituted with at least one hydrocarbyl radical such that the total number of carbon atoms of the hydrocarbyl radical(s) is 4-18, and the catalyst of formula I containing 14-28 carbon atoms in total. This catalyst, as opposed to conventional silanol condensation catalysts such as e.g. DBTL allows crosslinking at ambient temperature such as room temperature.
A silanol condensation catalyst of the above defined type is disclosed in WO 95/17463 for the crosslinking of polymers with hydrolysable silane groups.
With regard to the silanol condensation catalyst of formula I it is preferred that the hydrocarbyl radical in formula I is an alkyl substituent with 10-18 carbon atoms.
The currently most preferred compounds of formula I are dodecyl benzene sulphonic acid and tetrapropyl benzene sulphonic acid.
It is further preferred that the polymer composition includes 0.0001-3% by weight of silanol condensation catalyst.
In the following the crosslinkable hydrolysable silane group containing polymer used for the insulating and/or jacketing layer composition according to the present invention will described.
The crosslinkable base resin generally is an ethylene copolymer or graft polymer which contains hydrolysable silane groups and which is crosslinked under the influence of water and at least one silanol condensation catalyst. Specifically, the crosslinkable polymer is an ethylene-alkyl (meth)acrylate polymer containing crosslinkable silane groups introduced either by copolymerisation or graft polymerisation.
Preferably, the silane-containing polymer has been obtained by copolymerisation of ethylene, an alkyl (meth)acrylate comonomer and an unsaturated silane termonomer compound represented by the formula II
RSiR′
n
Y
3−n
(II)
wherein
R is an ethylenically unsaturated hydrocarbyl, hydrocarbyloxy or (meth)acryloxy hydrocarbyl
Eklind Hans
Fagrell Ola
Gustafsson Bill
Borealis Technology Oy
Jackson Monique R.
Merchant & Gould P.C.
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