Self-regulating heating cable having radiation grafted jacket

Claim 1

An improved, flexible, self-regulating heating cable of the type having at least one pair of elongate electrical conductors spaced-apart from each other coextensively along the length of the cable and electrically interconnected by means of a crosslinked olefinic semi-conductive composition containing from about 5 parts to about 25 parts by weight to the total weight of the semi-conductive composition of electrically conductive particles uniformly dispersed therein and having sufficient crystallinity to provide the self-regulating characteristics desired with both said conductors and said olefinic composition surrounded by an elastomeric polyurethane shape retaining jacket, wherein the improvement is characterized by said cable having improved mechanical and electrical integrity and handling characteristics as a result of said jacket and said olefinic semi-conductive composition being radiation grafted together by a process which includes the steps of: (a) forming the olefinic semi-conductive composition about the conductors along the length thereof to provide the electrical interconnection therebetween; (b) oxidizing the outer surface of the semi-conductive composition provided by step (a); (c) passing the product provided by step (b) through a die head having an entrance and an exit; (d) rendering the elastomeric polyurethane into a melt flowable state; (e) introducing the polyurethane of step (d) into the die head of step (c); (f) forming the polyurethane of step (d) within the die head of step (c) into a shaped annular layer about the product of step (b) by means of a die supported therewithin; (g) introducing a vacuum between the product of step (b) and the shaped annular polyurethane layer of step (f) sufficient to draw said layer snugly thereagainst within not more than about one and one-half inches from the die exit; (h) annealing the product of step (g) at a temperature and for a period of time sufficient to provide the semi-conductive composition with the ambient electrical resistance desired; and (i) exposing the product of step (g) to an amount of radiation sufficient to crosslink the semi-conductive composition to the degree desired and effect a radiation grafted bond of the elastomeric polyurethane layer thereto sufficient to enable said product to act as a unitary structure to improve the mechanical and electrical integrity and the handling characteristics of the cable.

Claim 8

A method for making a self-regulating heating having improved mechanical and electrical integrity and handling characteristics, said cable of the type having at least one pair of elongate electrical conductors spaced-apart from each other coextensively along the length of the cable that are electrically interconnected by means of a crosslinked olefinic semi-conductive composition with both said composition and said conductors encompassed by an elastomeric polyurethane shape retaining jacket, said composition containing from about 5 parts to about 25 parts by weight to the total weight of the semi-conductive composition of electrically conductive particles uniformly dispersed therein and having sufficient crystallinity to provide the self-regulating characteristics desired, and said method including the steps of: (a) forming the olefinic semi-conductive composition about the conductors along the length thereof to provide the electrical interconnection therebetween; (b) oxidizing the outer surface of the semi-conductive composition provided by step (a); (c) passing the product provided by step (b) through a die head having an entrance and an exit; (d) rendering the elastomeric polyurethane into a melt flowable state; (e) introducing the polyurethane of step (d) into the die head of step (c); (f) forming the polyurethane of step (d) within the die head of step (c) into a shaped annular layer about the product of step (b) by means of a die supported therewithin; (g) introducing a vacuum between the product of step (b) and the shaped annular polyurethane layer of step (f) sufficient to draw said layer snugly thereagainst within not more than about one and one-half inches from the die exit; (h) annealing the product of step (g) at a temperature and for a period of time sufficient to provide the semi-conductive composition with the ambient electrical resistance desired; and (i) exposing the product of step (g) to an amount of radiation sufficient to crosslink the semi-conductive composition to the degree desired and effect a radiation grafted bond of the elastomeric polyurethane layer thereto sufficient to enable said product to act as a unitary structure to improve the mechanical and electrical integrity and the handling characteristics of the cable.

Claim 9

A method for making a self-regulating heating having improved mechanical and electrical integrity and handling characteristics, said cable of the type having at least one pair of elongate electrical conductors spaced-apart from each other coextensively along the length of the cable that are electrically interconnected by means of a crosslinked olefinic semi-conductive composition with both said composition and said conductors encompassed by an elastomeric polyurethane shape retaining jacket, said composition containing from about 5 parts to about 25 parts by weight to the total weight of the semi-conductive composition of electrically conductive particles uniformly dispersed therein and having sufficient crystallinity to provide the self-regulating characteristics desired, and said method including the steps of: (a) forming the olefinic semi-conductive composition about the conductors along the length thereof to provide the electrical interconnection therebetween; (b) oxidizing the outer surface of the semi-conductive composition provided by step (a); (c) passing the product provided by step (b) through a die head having an entrance and an exit; (d) rendering the elastomeric polyurethane into a melt flowable state; (e) introducing the polyurethane of step (d) into the die head of step (c); (f) forming the polyurethane of step (d) within the die head of step (c) into a shaped annular layer about the product of step (b) by means of a die supported therewithin; (g) introducing a vacuum between the product of step (b) and the shaped annular polyurethane layer of step (f) sufficient to draw said layer snugly thereagainst within not more than about one and one-half inches from the die exit; (h) annealing the product of step (g) at a temperature and for a period of time sufficient to provide the semi-conductive composition with the ambient electrical resistance desired; and (i) exposing the product of step (g) to an amount of radiation sufficient to crosslink the semi-conductive composition to the degree desired and effect a radiation grafted bond of the elastomeric polyurethane layer thereto sufficient to enable said product to act as a unitary structure to improve the mechanical and electrical integrity and the handling characteristics of the cable.