Patent EA-001727-B1 (EA)
Title: Cable with impact-resistant coating
Inventor: BELLI SERGIO
IPC: H01B7/00
Filed: 1998-05-08
Abstract: 1. A cable comprising an inner structure and a coating placed around said inner structure in which said coating is made of expanded polymer material, wherein the degree of expansion of said polymer material is from about 20% to about 3000% and has a flexural modulus at room temperature, measured according to ASTM standard D790, of at least 200 MPa. 2. The cable as claimed in claim 1, wherein the cable is a power cable, and the inner structure, comprising a conductor and at least one layer of compact insulating coating placed around the said conductor. 3. The cable as claimed in claim 1, wherein said flexural modulus is between 400 MPa and 1800 MPa. 4. The cable as claimed in claim 1, wherein said flexural modulus is between 600 MPa and 1500 MPa. 5. The cable as claimed in claim 1, wherein the degree of expansion of said polymer material is from about 30% to about 500%. 6. The cable as claimed in claim 1, wherein the degree of expansion of said polymer material is from about 50% to about 200%. 7. The cable as claimed in any one of the preceding claims 1 to 6, wherein said coating of expanded polymer material has a thickness of 0.5 mm. 8. The cable as claimed in any one of the preceding claims 1 to 6, wherein said coating of expanded polymer material has a thickness of between 1 and 6 mm. 9. The cable as claimed in any one of the preceding claims 1 to 6, wherein said coating of expanded polymer material has a thickness of between 2 and 4 mm. 10. The cable as claimed in claim 1, wherein said expanded polymer material is chosen from polyethylene (PE), low density PE (LDPE), medium density PE (MDPE), high density PE (HDPE) and linear low density PE (LLDPE); polypropylene (PP); ethylene-propylene rubber (EPR), ethylene-propylene copolymer (EPM), ethylenepropylene-diene terpolymer (EPDM); natural rubber; butyl rubber; ethylene/vinyl acetate (EVA) copolymer; polystyrene; ethylene/acrylate copolymer, ethylene/methyl acrylate (EMA) copolymer, ethylene/ethyl acrylate (EEA) copolymer, ethylene/butyl acrylate (EBA) copolymer; ethylene/α-olefin copolymer; acrylonitrile-butadiene-styrene (ABS) resins; halogenated polymer, polyvinyl chloride (PVC); polyurethane (PUR); polyamide; aromatic polyester, polyethylene terephthalate (PET), polybutylene terephthalate (PBT); and copolymers or mechanical mixtures thereof. 11. The cable as claimed in claim 1, wherein said expanded polymer material is a polyolefin polymer or copolymer based on PE and/or PP. 12. The cable as claimed in claim 1, wherein said expanded polymer material is a polyolefin polymer or copolymer based on PE and/or PP modified with ethylenepropylene rubber. 13. The cable as claimed in claim 12, wherein said expanded polymer material is polypropylene modified with ethylene-propylene rubber (EPR), the PP/EPR weight ratio being between 90/10 and 50/50. 14. The cable as claimed in claim 13, wherein said PP/EPR weight ratio is between 85/15 and 60/40. 15. The cable as claimed in claim 13, wherein said PP/EPR weight ratio is about 70/30. 16. The cable as claimed in claim 12, wherein said polyolefin polymer or copolymer based on PE and/or PP also contains a predetermined amount of vulcanized rubber in powder form. 17. The cable as claimed in claim 16, wherein the predetermined amount of vulcanized rubber in powder form is between 10% and 60% of the weight of polymer. 18. The cable as claimed in any one of the preceding claims 1 to 17, wherein said cable comprises an outer polymer sheath. 19. The cable as claimed in claim 18, wherein said sheath is in contact with the said expanded polymer coating. 20. The cable as claimed in claim 18 or 19, wherein said sheath has a thickness of greater than 0.5 mm. 21. The cable as claimed in claim 18 or 19, wherein said sheath has a thickness of between 1 and 5 mm. 22. A method for imparting impact strength to a power transmission cable, which comprises coating the said cable with a coating of expanded polymer material. 23. The method as claimed in claim 22, wherein the degree of expansion of said polymer material is from about 20% to about 3000% and has a flexural modulus at room temperature, measured according to ASTM standard D790, at least 200 MPa. 24. The method as claimed in claim 22, wherein the cable is a power cable. 25. The method as claimed in claim 22, which also comprises coating the said expanded coating with an outer polymer sheath. 26. The method as claimed in claim 22, wherein the inner structure comprises at least two adjoining insulating coatings, having a predetermined average peel strength between them, the flexural modulus and wherein the degree of expansion of said polymer material is such that when subjecting the cable to an impact of about 72 joules, the difference between said average peel strength and the peel strength measured at the point of impact is less than about 25%. 27. Use of an expanded polymer material for imparting impact strength to a power transmission cable. 28. A method for evaluating the impact strength of a cable comprising at least one insulating coating, which consists in a) measuring the average peel strength of the said insulating layer; b) subjecting the cable to an impact of predetermined energy; c) measuring the peel strength of the said insulating layer at the point of impact; d) checking that the difference between the average peel strength and the peel strength measured at the point of impact is less than a predetermined value. 29. The method as claimed in claim 28, in which the peel strength is measured between the layer of insulating coating and the layer of outer semiconductive coating. 30. The method as claimed in claim 27, in which the difference between the average peel strength and that measured t the point of impact is less than 25%.