PCT heater cable composition and method for making same
First Claim
1. In an electrically conductive, self-regulating heater cable formed with a pair of wires that are connected to each other by an elongate extruded layer of self-regulating semi-conductive composition exhibiting a positive temperature coefficient (PTC) of electrical resistance, wherein carbon black is dispersed in an olefinic polymeric matrix, the improvement wherein said polymeric matrix comprises a low density polyethylene polymeric composition having:
- (1) a crystallinity greater than about 20% as measured by x-ray diffraction;
(2) a number average molecular weight of at least about 30,000; and
(3) less than about 8% by weight of molecules having a molecular weight less than about 23,000, and which is present in said composition in an amount of from about 35 to about 60 percent by weight; and
wherein said carbon black comprises a low structure, low resistivity, non-surface treated, conductive carbon black, in an amount of from about 14 to about 15 percent by weight in said composition;
so as to reduce the time for annealing by reliance upon residual heat within the extruded PTC composition to less than about 20 seconds.
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Abstract
A self-temperature regulating heater cable using a PTC polymeric matrix is described. A commercially available low density polyethylene is combined with a desired carbon black so as to enable a continuous extrusion at an elevated temperature while enabling residual heat in the extruded PTC layer to anneal the layer to a desired low resistivity in a short time period before quenching. The polyethylene is of the DFD-6005 type in which the amount of molecules whose molecular weight does not exceed about 23,000 is less than about eight percent by weight. The carbon black preferably is a low structure, low resistivity, non-surface treated, conductive carbon black.
20 Citations
22 Claims
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1. In an electrically conductive, self-regulating heater cable formed with a pair of wires that are connected to each other by an elongate extruded layer of self-regulating semi-conductive composition exhibiting a positive temperature coefficient (PTC) of electrical resistance, wherein carbon black is dispersed in an olefinic polymeric matrix, the improvement wherein said polymeric matrix comprises a low density polyethylene polymeric composition having:
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(1) a crystallinity greater than about 20% as measured by x-ray diffraction; (2) a number average molecular weight of at least about 30,000; and (3) less than about 8% by weight of molecules having a molecular weight less than about 23,000, and which is present in said composition in an amount of from about 35 to about 60 percent by weight; and
wherein said carbon black comprises a low structure, low resistivity, non-surface treated, conductive carbon black, in an amount of from about 14 to about 15 percent by weight in said composition;
so as to reduce the time for annealing by reliance upon residual heat within the extruded PTC composition to less than about 20 seconds. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. In a method of manufacturing an electrically conductive, self-regulating heater cable formed with a conductors that are connected to each other by an elongate extruded layer of self-regulating semiconductive composition exhibiting a positive temperature coefficient (PTC) of electrical resistance, the improvement comprising the steps of:
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extruding a said layer of semiconductive PTC composition containing a carbon black having a low resistivity, is non-surface treated and has a low surface area A in m2 /gram and a low structure x in cc/100 grams of DBP oil absorption such that 0.6≦
A/x≦
1.75, and further containinga polymeric matrix formed with a low density polyethylene polymer with a crystallinity that is greater than about twenty percent (20%) as determined by x-ray diffraction and which, without an addition of polyethylene having a number-average molecular weight of less than about 30,000, has less than about eight percent (8%) of total polymer weight formed of molecules whose molecular weight does not exceed about 23,000, over an electrical conductor at an elevated extrusion temperature; and exposing the conductor with said extruded layer as they emerge from the extrusion step to a gaseous medium that is at a temperature below the extrusion temperature and for a time selected less than about 20 seconds to enable residual heat within the extruded layer to reduce its resistance per unit length of the extruded layer to a desired value. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. In a method of manufacturing an electrically conductive, self-regulating heater cable formed with a pair of spaced-apart, generally parallel wires that are connected to each other by an elongate extruded layer of self-regulating semiconductive composition exhibiting a positive temperature coefficient (PTC) of electrical resistance, the improvement comprising the steps of:
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extruding, at an extrusion temperature, a said layer of semiconductive PTC composition, having a resistance per unit length, containing a polymeric matrix formed with a low density polyethylene polymer with a crystallinity that is greater than about twenty percent (20%) as determined by x-ray diffraction and which, without an addition of polyethylene having a number-average molecular weight of less than about 30,000, has less than about eight percent (8%) of total polymer weight formed of molecules whose molecular weight does not exceed about 23,000, over said spaced-apart wires at said extrusion temperature; and exposing the wires with said extruded layer of self-regulating semiconductive PTC composition as these emerge from the extrusion step to a gaseous medium that is at a temperature below the extrusion temperature and for a time selected less than about 20 seconds to enable residual heat within the extruded layer to reduce the resistance per unit length of the extruded layer to a desired value.
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20. A method for manufacturing an electrically conductive self-temperature regulating heater cable comprising the steps of:
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extruding around a pair of spaced-apart conductors and at an extrusion temperature a layer of self-temperature regulating semi-conductive positive temperature coefficient of resistance composition containing carbon black that is dispersed in a polymeric matrix; wherein the polymeric matrix includes a low density polyethylene polymer with a crystallinity that is greater than about twenty percent (20%) as determined by x-ray diffraction and is present in an amount from about 35 percent to about 60 percent by weight of the composition; wherein the carbon black comprises a low structure, low resistivity, non-surface treated, conductive carbon black whose nitrogen surface area, A as measured in m2 /gram and whose DBP absorption x in cc/100 grams are such that 0.6≦
A/x≦
1.75 and is present in an amount from about 14 percent to about 25 percent of the composition;passing the conductors with the extruded PTC layer as these emerge from the extrusion step along a path that is exposed to a gas at a lower temperature than the extrusion temperature for a path length and at a speed that is selected to enable residual heat inside the extruded layer to reduce resistivity of the extruded layer to a desired value; passing the conductors with the extruded PTC layer through a medium so as to quench the PTC layer to lower its temperature and physically stabilize dimensions of the extruded layer; radiating the conductors with the extruded PTC layer to cause a cross linking of the PTC layer; and extruding an insulating jacket around the PTC layer.
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21. A method for manufacturing an electrically conductive self-temperature regulating heater cable comprising the steps of:
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extruding around a conductor and at an extrusion temperature a layer of self-temperature regulating semi-conductive positive temperature coefficient of resistance composition containing carbon black that is dispersed in a polymeric matrix; wherein the polymeric matrix includes a low density polyethylene polymer with a crystallinity that is greater than about twenty percent (20%) as determined by x-ray diffraction and is present in an amount from about 35 percent to about 60 percent by weight of the composition; wherein the carbon black comprises a low structure, low resistivity, non-surface treated, conductive carbon black whose nitrogen surface area, A as measured in m2 /gram and whose DBP absorption x in cc/100 grams are such that 0.6≦
A/x ≦
1.75 and is present in an amount from about 14 percent to about 25 percent of the composition;passing the conductor with the extruded PTC layer as these emerge from the extrusion step along a path that is exposed to a gas at a lower temperature than the extrusion temperature for a path length and at a speed that is selected to enable residual heat inside the extruded layer to reduce resistivity of the extruded layer to a desired value; passing the conductor with the extruded PTC layer through a medium so as to quench the PTC layer to lower its temperature and physically stabilize dimensions of the extruded layer; irradiating the conductor with the extruded PTC layer to cause a cross linking of the PTC layer, helically wrapping a second conductor around and in electrical contact with the PTC layer; and extruding an insulating jacket around the second conductor.
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22. An electrically conductive, self-regulating heater cable formed with conductors that are connected to each other by an elongate extruded layer of self-regulating semi-conductive composition exhibiting a positive temperature coefficient of electrical resistance and which contains carbon black dispersed in a polymeric matrix wherein the improvement comprises:
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a polymeric matrix having a principal polymer material relied upon for the positive temperature coefficient is DFD-6005 polyethylene; and wherein the carbon black is a low structure, low resistivity, non-surface treated, conductive carbon black in an amount from about 14 percent to about 25 percent by weight of the composition;
so as to reduce the time for annealing by reliance upon residual heat within the extruded layer to less than about 20 seconds.
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Specification