Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
1999-03-26
2001-09-04
Kelly, Cynthia H. (Department: 1774)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C252S511000, C428S372000, C428S379000, C174S1050SC, C174S1060SC, C174S1100PM, C174S1200SC, C524S495000
Reexamination Certificate
active
06284374
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a strippable semiconductive resin composition suitable for an outer semiconductive layer of a crosslinked polyolefin-insulated wire and cable, particularly to a strippable semiconductive resin composition suitable for a crosslinked polyolefin-insulated wire and cable crosslinked by silane grafting/water crosslinking, and a wire and cable using the same.
BACKGROUND OF THE INVENTION
Silane grafting/water crosslinking can provide crosslinked polyolefin materials at lower cost than chemical crosslinking using an organic peroxide and hence has been widely used for crosslinking of wire and cable materials.
According to this method, a polymer is graft copolymerized with a vinylalkoxysilane in the presence of a minor amount of an organic peroxide as a graft reaction initiator in a molding machine (for example, an extruder) at a high temperature, and the wire and cable is then exposed to a high temperature and high humidity atmosphere (or hot water) to induce hydrolysis and condensation of the alkoxysilane grafted onto the polymer through the action of a silanol condensation catalyst, such as dibutyltin dilaurate, which has been mixed into or has permeated from the surface of the polyolefin molding into the interior of the polyolefin molding, thus causing crosslinking.
The inner and outer semiconductive layers of plastic-insulated power cables, particularly high voltage crosslinked polyethylene insulated power cables, are generally formed by extrusion. These semiconductive layers should be in intimate contact with a crosslinked polyethylene insulator from the viewpoint of avoiding corona discharge. In treating the terminal of the cable, however, the outer semiconductive layer should be easily stripped without damage to the insulator. For this reason, what is required of the outer semiconductive layer is that the layer is usually in intimate contact with the insulator and if necessary can be easily separated. A composition composed mainly of an ethylene/vinyl acetate copolymer has hitherto been extensively used as a strippable semiconductive resin composition for the outer semiconductive layer.
Use of the outer semiconductive layer on the insulator crosslinked by silane grafting/water crosslinking enhances the adhesion between the insulator and the outer semiconductive layer through the action of a functional group, such as silanol, making it difficult to strip the outer semiconductive layer. When the content of vinyl acetate in the ethylene/vinyl acetate copolymer is increased (for example, to not less than 45% by weight) to facilitate the stripping, acetic acid is likely to be eliminated upon heating at the time of molding. This poses a problem of deteriorated heat resistance and, in addition, discoloration of copper tape as a shielding layer and copper wire as a conductor by the eliminated acetic acid.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a strippable semiconductive resin composition useful for an outer semiconductive layer of plastic insulated power cables, particularly a strippable semiconductive resin composition that can form an outer semiconductive layer excellent in both adhesion to an insulator crosslinked by silane grafting/water crosslinking and strippability, and a wire and cable using the same.
According to the first feature of the invention, a strippable semiconductive resin composition adapted for formation of a semiconductive layer having a volume resistivity of not more than 5000 &OHgr;·cm at room temperature comprises: a polymer component (a) with a number average molecular weight of not less than 3×10
4
or a weight average molecular weight of not less than 3×10
5
and a melting point of 60 to 80° C., composed mainly of an ethylene/vinyl acetate copolymer, or a polymer component (b) composed mainly of 99 to 50 parts by weight of the ethylene/vinyl acetate copolymer and 1 to 50 parts by weight of a polyolefin having a melting point of 120° C. or above; and conductive carbon black compounded with the polymer component (a) or (b).
According to the second feature of the invention, a wire and cable comprises: a conductor; an insulator layer for insulating the conductor; and an outer semiconductive layer provided on the periphery of the insulator layer, the outer semiconductive layer comprising a strippable semiconductive resin composition, the strippable semiconductive resin composition comprising a polymer component (a), with a number average molecular weight of not less than 3×10
4
or a weight average molecular weight of not less than 3×10
5
and a melting point of 60 to 80° C., composed mainly of an ethylene/vinyl acetate copolymer, or a polymer component (b) composed mainly of 99 to 50 parts by weight of the ethylene/vinyl acetate copolymer and 1 to 50 parts by weight of a polyolefin having a melting point of 120° C. or above, and
conductive carbon black compounded with the polymer component (a) or (b),
the strippable semiconductive resin composition having a volume resistivity of not more than 5000 &OHgr;·cm at room temperature.
REFERENCES:
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patent: 4451536 (1984-05-01), Barlow et al.
patent: 4493787 (1985-01-01), Taniguchi et al.
patent: 4767894 (1988-08-01), Schombourg
patent: 4909960 (1990-03-01), Watanabe et al.
patent: 4933107 (1990-06-01), Watanabe et al.
patent: 5108657 (1992-04-01), Demay et al.
patent: 5214091 (1993-05-01), Tanaka et al.
patent: 5871706 (1999-02-01), Whitehouse
patent: 5872177 (1999-02-01), Whitehouse
Watanabe Kiyoshi
Yamazaki Takanori
Gray J. M.
Hitachi Cable Ltd.
Kelly Cynthia H.
McDermott & Will & Emery
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