Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
2002-02-26
2004-05-25
Jackson, Monique R. (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S379000, C428S380000, C428S458000, C428S461000, C428S463000
Reexamination Certificate
active
06740396
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cable with coating of a composite material.
More particularly, the present invention relates to a cable, in particular for the transmission or distribution of low-voltage or medium-voltage power, which has a coating layer consisting of a composite material that possesses high mechanical, thermal, electrical and barrier properties (very low permeability to water, to solvents and to gases) and fire resistance.
Said cable permits, in particular, the use of high operating temperatures.
2. Description of the Related Art
It is now a requirement in the power and telecommunication cables sector, to find materials that can be used for making coatings that surround the conductor that are able to improve the properties enumerated above.
For this purpose, for example, the addition of mineral fillers to the polymer matrix constituting the coatings that surround the conductor is known, said fillers imparting semiconducting properties to said coatings, for example carbon black and the like; or various types of mineral fillers that are able to impart fireproofing properties to said coatings, for example calcined kaolin, calcium carbonate, magnesium hydroxide, aluminium hydroxide and the like.
Patent application GB 2,113,453 describes an electric cable comprising one or more conductors, a semiconducting screen, a semiconducting layer, an insulating layer, a metallic screen and a sheath. A material that is able to absorb water and so to reduce “water-treeing”, comprising an uncoated montmorillonite, is interposed between the semiconducting layer and the sheath. Instead of the montmorillonite it is possible to use molecular sieves as such or mixed with said montmorillonite. Preferably, said material that is able to absorb water is mixed with an organic carrier so as to form an extrudable mixture or a paste. The carrier can be a viscous organic fluid or a semisolid rubber, for example unvulcanized or depolymerized butyl rubber or polyisobutylene.
Patent application EP 1,033,724 describes an electric cable having at least one coating consisting of a material comprising an organic compound, in particular a polymer, and an inorganic material with lamellar structure. The polymer can be selected from: polyolefins (for example, polyethylene or polypropylene), polybutylene terephthalate, vinyl polymers, elastomers, which may be halogenated, thermoplastic elastomers, silicones, copolymers of ethylene, or their mixtures. Among the copolymers of ethylene, the following can be used: ethylene/vinyl acetate copolymer, ethylene/propylene copolymer, ethylene/ethyl acrylate copolymer, ethylene/methyl acrylate copolymer, ethylene/acrylic acid copolymer, terpolymers of ethylene, polymers of ethylene functionalized with groups such as, for example, acids, epoxides, etc. In some cases it is also possible to use epoxy resins, polyesters, polyamides, polyurethanes, silicones, or their mixtures. A graphite or an inorganic oxide can be used as the inorganic material with lamellar structure. Preferably, the organic oxide is a silicate, in particular an aluminosilicate, for example a natural or artificial clay. Among the clays, it is possible to use, for example, kaolin, smectite, montmorillonite, bentonite, and the like. Said inorganic compound with lamellar structure is treated with a compatibilizing agent, which can be a quaternary ammonium salt, a polyethylene oxide, a phosphorus derivative, etc.
SUMMARY OF THE INVENTION
The Applicant has found, however, that the use of the aforesaid material comprising a polymer and an inorganic material with lamellar structure does not always endow the cable with improved properties. In particular, the Applicant has found that, for the purpose of obtaining a cable that possesses improved properties, the polymer and the inorganic material with lamellar structure must be combined in a suitable manner.
The Applicant has now found that it is possible to improve said properties by making a cable that is provided with at least one coating of composite material, said composite material being obtained by intercalation of a polymer containing a predetermined quantity of polar groups, in an inorganic material with lamellar structure surface-treated with a predetermined quantity of a compatibilizer. The Applicant has found that said intercalation only occurs when using a polymer and an inorganic material with lamellar structure that are mutually compatible. More particularly, achievement of a sufficient degree of intercalation depends essentially on the correct combination of the quantity of polar groups present in the polymer and the quantity of compatibilizer present in the inorganic material with lamellar structure. Once intercalation of the polymer has occurred, with consequent exfoliation of the inorganic material with lamellar structure, a composite material is obtained in which said inorganic material is distributed homogeneously in the polymer and has a particle size of the order of a nanometre. On the other hand, if a polymer and an inorganic material with lamellar structure are selected that are not compatible, the aforesaid intercalation/exfoliation does not occur, and a simple mixture between the two components (polymer/inorganic material with lamellar structure) is thus obtained, in which mixture the particles of said inorganic material still have their initial dimensions (of the order of microns). For equal final performance of the cable, when intercalation occurs it is possible to use a smaller quantity of inorganic material with lamellar structure, with respect to the quantity used in the case when intercalation does not occur.
In a first aspect, the present invention therefore relates to a cable comprising at least one conductor and at least one coating layer consisting of a composite material comprising:
at least one polymer containing a predetermined quantity of polar groups; and
at least one inorganic material with lamellar structure, surface-treated with a predetermined quantity of a compatibilizer;
in which said predetermined quantity of polar groups and said predetermined quantity of compatibilizer are such that said inorganic material exhibits, in the composite material, a d-spacing value in X-ray diffraction analysis at least 20% higher, preferably at least 30% higher, with respect to the d-spacing value of the inorganic material as such.
In the present description and in the subsequent claims, the term “conductor” means a conducting element as such, of elongated shape and preferably of a metallic material, or a conducting element coated with a semiconducting layer.
In a second aspect the present invention relates to a composite material comprising:
at least one polymer containing a predetermined quantity of polar groups; and
at least one inorganic material with lamellar structure, surface-treated with a predetermined quantity of a compatibilizer;
in which said predetermined quantity of polar groups and said predetermined quantity of compatibilizer are such that said inorganic material exhibits, in the composite material, a d-spacing value in X-ray diffraction analysis at least 20% higher, preferably at least 30% higher, with respect to the d-spacing value of the inorganic material as such.
In a further aspect, the present invention relates to the use of a composite material as defined above as a base material for the preparation of a coating layer with properties of electrical insulation, or for the preparation of a coating layer with semiconducting properties, or for the preparation of a coating layer with the function of external protective sheath.
The polymer containing polar groups is generally selected from polymers functionalized with polar groups selected from: hydroxyl groups, carboxyl groups, epoxide groups, anhydride groups, silane groups.
Said polar groups can be introduced into the polymer during the production of the polymer itself, by copolymerization with corresponding functionalized monomers containing at least one ethylenic unsaturation; or by subsequent modifica
Carrus Antonio
Zaopo Antonio
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Jackson Monique R.
Pirelli Cavi e Sistemi S.p.A.
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