CA1151413A - Electrical heating strip - Google Patents
Electrical heating stripInfo
- Publication number
- CA1151413A CA1151413A CA000397765A CA397765A CA1151413A CA 1151413 A CA1151413 A CA 1151413A CA 000397765 A CA000397765 A CA 000397765A CA 397765 A CA397765 A CA 397765A CA 1151413 A CA1151413 A CA 1151413A
- Authority
- CA
- Canada
- Prior art keywords
- weight
- carbon black
- heating element
- heating strip
- strip according
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Abstract
S P E C I F I C A T I O N
Electrical Heating Strip ABSTRACT OF THE DISCLOSURE
An electrical heating strip comprises a heating element composed of a carbon black-loaded polymeric composition and a pair of elongate electrodes which are electrically connected by the heating element. The heating element is composed of a polymeric matrix having dispersed therein a first carbon black which is a relatively conductive filler and a second carbon black which is a relatively less conductive filler.
Electrical Heating Strip ABSTRACT OF THE DISCLOSURE
An electrical heating strip comprises a heating element composed of a carbon black-loaded polymeric composition and a pair of elongate electrodes which are electrically connected by the heating element. The heating element is composed of a polymeric matrix having dispersed therein a first carbon black which is a relatively conductive filler and a second carbon black which is a relatively less conductive filler.
Description
-`` 115~413 This invention relates to electrical heaters comprising a heating element which is composed of a polymeric matrix having carbon black dispersed therein.
The electrical heating strips of th~ present invention comprises a heating element composed of a carbon black-loaded polymeric composition and a pair of elongate electro~es which are electrically connected by said heating element, the heating element being composed of a polymeric matrix having dispersed therein (i) a first carbon black which is a relatively conductive filler (as hereinafter defined) and (ii) a second carbon black which is a relatively less conductive filler (as hereinafter defined).
The term "relatively conductive filler" is used herein to denote a filler which, when dispersed in polyethylene having a density of 0.916 g/cm3 and a melt flow index of 2, exhibits a curve of impedance versus loading which falls steeply in the range of specific impedance values from 10 to 10 ohm.cm and reaches a specific impedance of less than 5 x 106 ohm.cm, preferably less than 10 ohm.cm, at a loading of 60 parts by weight per 100 parts by weight of polyethylene, the specific impedances being measured at 50 Hz with a field strength of 4 kV/cm. The term "relatively less conductive ,' , ~
,. ._ .. . . .
filler" is used herein to denote a filler which, when dispersed in polyethylene having a density of 0.916 g/cm and a melt flow index of 2, exhibits a curve of impedance versus loading having a relatively shallow qlope with no steep sections and which has a specific impedance greater than 109 ohm.cm, and preferably less than 101 ohm.cm, at a loading of 60 parts by weight per 100 parts by weight of polyethylene, the specific impedances bein~ measured at 50 Hz with a field strength of 4 kV/cm.
The specific impedances referred to in this specification are measured by the procedure given in Example 9 (i.e. by mixing the ingredients in a Banbury mixer, pres~ing the mixture into a slab, and measuring the impedance of the un-annealed slab at room temperature at 50 Hz and a field strength of 4 kV/cm).
The polymeric matrix in the heating strips of the present invention preferably comprises a thermoplastic resin, especially a polyolefin, e.g. polyethylene or polypropylene~
an olefin copolymer, e.g. an ethylene/ethyl acrylate or ethylene/ethyl methacrylate polymer, a halogen-substituted olefin copolymer, e.g. an ethylene/tetrafluoroethylene ccpolymer or polyvinylidene chloride, or a mixture of two or more of these.
The first carbon black (which is a relatively conductive filler) may have an average particle size of 10 to 100 milli-microns, preferably 20 to 60 millimicrons, and an average specific surface area greater than 30 m /g, preferably greater 1~514~3 than 100 m2/g, as measured by the method of ASTM D3037-76.
Suitable carbon blacks can be chosen from carbon blacks which are commercially available as Types HAF, SRF, EPC, FEF and ECF, e.g. those manufactured by Cabot under the trade names Vulcan XC72, Vulcan P, and Vulcan 3, by Columbian under the trade names Statex 160, Statex 125 and Conductex g~0, by AKZ0 Chemie under the trade name Ketjen Black EC, ar.d by Degussa under the trade names Corax L and Corax P. ["Vulcan", "Statex", "Ketjen" and "Corax" are trade marks~.
me second carbon black ~which is a relatively lesq conductive filler) is preferably one of the so-called low structure carbon blacks. Suitable carbon blacks include commercially availab~e Thermal blacks, e.g. those manufactured by Vanderbilt under the trade names Thermax and P-33, by Sevalco under the trade name Sevacarb MT, and by Columbian under the trade name Statex MT. ~"Thermax" is a trade mark].
The second carbon black may have an average particle size of at least 30 millimicrons and an average specific surface area of less then 20 m2/g.
By use of suitable amounts of the first and second carbon blacks, it is possible to prepare conductive composi-tions having a desired level of specific impedance without undue sensitivity to small changes in the loadings of the carbon blacks. The ratio by weight of the second carbon black to the first carbon black is preferably at least 1:1, e.g., 2:1 to 8:1 or 3:1 to 6:1. The amount of the first d~ r/~
.. .. . ..... . , . . . _ . ~ ..... ~ ... . . . . ..
~31 5~13 carbon black may be at least 90/0, e.g. 10 to 25%, by weight, based on the weight of the polymeric matrix. The amount of the second carbon black may be at least 40% by weight, based on the weight of the pol~neric matrix.
The following Examples, in which parts are by weigh~, illustrate compositions suitable for use in the heating element according to the invention.
Example 1 Three sets of compositions were made by blending 62.5 parts of chlorinated polyethylene (CPE 3614 manufactured by Dow Corning), 37.5 parts of low density polyethylene (DYNE 3 manufactured by BXL Bakelite), various amounts of one or both of Vulcan P (a carbon blac~ manufactured by Cabo~ which is a relatively conductive filler) and Thermax MT (a carbon black manufactured by Vanderbilt which is a relatively less conductive filler), and small amounts of conventional anti-oxidants and stabilizers. The ingredients were comp3unded ina Bridge Banbury internal mixer with a charge weight of 1.2 kg, the mixture was pressed 150C into plaque samples 2 mm. thick and the samples cooled to room temperature. Circular electrodes were painted on both sides of each sample which was placed between brass electrodes conforming to BS 2782(201). The specific impedance of the composition was calculated from measurement of both voltage and current at 50 Hz and the known sample dimensions, using a field strength of 4 kV!cm. In the q~/e,"~r/~ , ~
~51413 first set of compositions, Vulcan P was the sole carbon black, in amount 10, 20, 30, 40, 50 or 60 parts. 'n the second set of compositions, Thermax MT was the sole carbon black, in amount 10, 20, 30, 40, 50, 60, 70, 80, 90, ~0~, 110 or 120 parts. In the third set of compositions, ~7ulcan P
and Thermax MT were used together, the ratio by weight in each composition of Vulcan P to Thermax MT being 1:4 and the total amount of both carbon blacks being 10, 20, 30, ~0, 50, 60, 70, 80 or 90 parts.
/ me results obtained are shown graphically in Figure 1, Curves A, B and C showing the specific impedances of the first, second and third sets of compositions respectively.
Example 2 The procedure described in Example 1 was used to determine the specific impedance of compositions (1) to (8) containing the ingredients and amounts thereof shown in the Table below and in addition (same for each composition) 2.5 parts of a conventional polymer stabiliser (Agerite Resin D), 4.375 parts of dibasic lead phthalate, 1.875 parts of tetra-basic lead fumarate and 1.875 parts of triallyl cyanurate.
The various ingredients listed by their trade names in the Table are identified above or as set out below.
DPD 6169 is an ethylene/ethyl acrylate poly~er ~anu-factured by Union Carbide and having a melt flow index of 6 and a density of 0,931, Royalene 611 is an ethylene/
.
:~ tr~o~<
.. ... . . .. . .. . . . .. . .....
~151413 propylene/non-conjugated diene terpolymer manufactured by Uniroyal. Philips GPF is a furnace black which is a re-latively conductive filler, manufactured by Philips Petroleum Co. ["Philips" is a trade mark.~. The specific impedances of the various compositions are also given in the Table.
Composition ~o. (1) (2) (3) (4) (5) (6) (7) (8) -DYNH 3 37.5 - - 37.537.5 37.5 37.5 37.5 CPE 3614 - 100 - 62.562.5 62.5 62.5 62.5 DPD 6169 ~ - - 100 - - - - -.,~, .
Royalene 611 62.5 Vulcan P 14 14 14 20 16.6 10 Phillips GPF - - - - - - 16 20 -Thermax MT 56 56 56 40 33.3 60 64 80 Specific Impedance 5.6 3.2 1.6 0.38 2.2 7.6 6.3 0.32 (ohm.cm) D
" ' ',:
The electrical heating strips of th~ present invention comprises a heating element composed of a carbon black-loaded polymeric composition and a pair of elongate electro~es which are electrically connected by said heating element, the heating element being composed of a polymeric matrix having dispersed therein (i) a first carbon black which is a relatively conductive filler (as hereinafter defined) and (ii) a second carbon black which is a relatively less conductive filler (as hereinafter defined).
The term "relatively conductive filler" is used herein to denote a filler which, when dispersed in polyethylene having a density of 0.916 g/cm3 and a melt flow index of 2, exhibits a curve of impedance versus loading which falls steeply in the range of specific impedance values from 10 to 10 ohm.cm and reaches a specific impedance of less than 5 x 106 ohm.cm, preferably less than 10 ohm.cm, at a loading of 60 parts by weight per 100 parts by weight of polyethylene, the specific impedances being measured at 50 Hz with a field strength of 4 kV/cm. The term "relatively less conductive ,' , ~
,. ._ .. . . .
filler" is used herein to denote a filler which, when dispersed in polyethylene having a density of 0.916 g/cm and a melt flow index of 2, exhibits a curve of impedance versus loading having a relatively shallow qlope with no steep sections and which has a specific impedance greater than 109 ohm.cm, and preferably less than 101 ohm.cm, at a loading of 60 parts by weight per 100 parts by weight of polyethylene, the specific impedances bein~ measured at 50 Hz with a field strength of 4 kV/cm.
The specific impedances referred to in this specification are measured by the procedure given in Example 9 (i.e. by mixing the ingredients in a Banbury mixer, pres~ing the mixture into a slab, and measuring the impedance of the un-annealed slab at room temperature at 50 Hz and a field strength of 4 kV/cm).
The polymeric matrix in the heating strips of the present invention preferably comprises a thermoplastic resin, especially a polyolefin, e.g. polyethylene or polypropylene~
an olefin copolymer, e.g. an ethylene/ethyl acrylate or ethylene/ethyl methacrylate polymer, a halogen-substituted olefin copolymer, e.g. an ethylene/tetrafluoroethylene ccpolymer or polyvinylidene chloride, or a mixture of two or more of these.
The first carbon black (which is a relatively conductive filler) may have an average particle size of 10 to 100 milli-microns, preferably 20 to 60 millimicrons, and an average specific surface area greater than 30 m /g, preferably greater 1~514~3 than 100 m2/g, as measured by the method of ASTM D3037-76.
Suitable carbon blacks can be chosen from carbon blacks which are commercially available as Types HAF, SRF, EPC, FEF and ECF, e.g. those manufactured by Cabot under the trade names Vulcan XC72, Vulcan P, and Vulcan 3, by Columbian under the trade names Statex 160, Statex 125 and Conductex g~0, by AKZ0 Chemie under the trade name Ketjen Black EC, ar.d by Degussa under the trade names Corax L and Corax P. ["Vulcan", "Statex", "Ketjen" and "Corax" are trade marks~.
me second carbon black ~which is a relatively lesq conductive filler) is preferably one of the so-called low structure carbon blacks. Suitable carbon blacks include commercially availab~e Thermal blacks, e.g. those manufactured by Vanderbilt under the trade names Thermax and P-33, by Sevalco under the trade name Sevacarb MT, and by Columbian under the trade name Statex MT. ~"Thermax" is a trade mark].
The second carbon black may have an average particle size of at least 30 millimicrons and an average specific surface area of less then 20 m2/g.
By use of suitable amounts of the first and second carbon blacks, it is possible to prepare conductive composi-tions having a desired level of specific impedance without undue sensitivity to small changes in the loadings of the carbon blacks. The ratio by weight of the second carbon black to the first carbon black is preferably at least 1:1, e.g., 2:1 to 8:1 or 3:1 to 6:1. The amount of the first d~ r/~
.. .. . ..... . , . . . _ . ~ ..... ~ ... . . . . ..
~31 5~13 carbon black may be at least 90/0, e.g. 10 to 25%, by weight, based on the weight of the polymeric matrix. The amount of the second carbon black may be at least 40% by weight, based on the weight of the pol~neric matrix.
The following Examples, in which parts are by weigh~, illustrate compositions suitable for use in the heating element according to the invention.
Example 1 Three sets of compositions were made by blending 62.5 parts of chlorinated polyethylene (CPE 3614 manufactured by Dow Corning), 37.5 parts of low density polyethylene (DYNE 3 manufactured by BXL Bakelite), various amounts of one or both of Vulcan P (a carbon blac~ manufactured by Cabo~ which is a relatively conductive filler) and Thermax MT (a carbon black manufactured by Vanderbilt which is a relatively less conductive filler), and small amounts of conventional anti-oxidants and stabilizers. The ingredients were comp3unded ina Bridge Banbury internal mixer with a charge weight of 1.2 kg, the mixture was pressed 150C into plaque samples 2 mm. thick and the samples cooled to room temperature. Circular electrodes were painted on both sides of each sample which was placed between brass electrodes conforming to BS 2782(201). The specific impedance of the composition was calculated from measurement of both voltage and current at 50 Hz and the known sample dimensions, using a field strength of 4 kV!cm. In the q~/e,"~r/~ , ~
~51413 first set of compositions, Vulcan P was the sole carbon black, in amount 10, 20, 30, 40, 50 or 60 parts. 'n the second set of compositions, Thermax MT was the sole carbon black, in amount 10, 20, 30, 40, 50, 60, 70, 80, 90, ~0~, 110 or 120 parts. In the third set of compositions, ~7ulcan P
and Thermax MT were used together, the ratio by weight in each composition of Vulcan P to Thermax MT being 1:4 and the total amount of both carbon blacks being 10, 20, 30, ~0, 50, 60, 70, 80 or 90 parts.
/ me results obtained are shown graphically in Figure 1, Curves A, B and C showing the specific impedances of the first, second and third sets of compositions respectively.
Example 2 The procedure described in Example 1 was used to determine the specific impedance of compositions (1) to (8) containing the ingredients and amounts thereof shown in the Table below and in addition (same for each composition) 2.5 parts of a conventional polymer stabiliser (Agerite Resin D), 4.375 parts of dibasic lead phthalate, 1.875 parts of tetra-basic lead fumarate and 1.875 parts of triallyl cyanurate.
The various ingredients listed by their trade names in the Table are identified above or as set out below.
DPD 6169 is an ethylene/ethyl acrylate poly~er ~anu-factured by Union Carbide and having a melt flow index of 6 and a density of 0,931, Royalene 611 is an ethylene/
.
:~ tr~o~<
.. ... . . .. . .. . . . .. . .....
~151413 propylene/non-conjugated diene terpolymer manufactured by Uniroyal. Philips GPF is a furnace black which is a re-latively conductive filler, manufactured by Philips Petroleum Co. ["Philips" is a trade mark.~. The specific impedances of the various compositions are also given in the Table.
Composition ~o. (1) (2) (3) (4) (5) (6) (7) (8) -DYNH 3 37.5 - - 37.537.5 37.5 37.5 37.5 CPE 3614 - 100 - 62.562.5 62.5 62.5 62.5 DPD 6169 ~ - - 100 - - - - -.,~, .
Royalene 611 62.5 Vulcan P 14 14 14 20 16.6 10 Phillips GPF - - - - - - 16 20 -Thermax MT 56 56 56 40 33.3 60 64 80 Specific Impedance 5.6 3.2 1.6 0.38 2.2 7.6 6.3 0.32 (ohm.cm) D
" ' ',:
Claims (8)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An electrical heating strip comprising a heating element composed of a carbon black-loaded polymeric composition and a pair of elongate electrodes which are electrically connected by said heating element, the heating element being composed of a polymeric matrix having dispersed therein (i) a first carbon black which is a relatively conductive filler and (ii) a second carbon black which is a relatively less conductive filler, the relatively conductive filler being a filler which, when dispersed in polyethylene having a density of 0.916 g/cm3 and a melt flow index of 2, exhibits a curve of impedance versus loading which falls steeply in the range of specific impedance values from 109 to 106 ohm.cm and reaches a specific impedance of less than 5 x 106 ohm.cm at a loading of 60 parts by weight per 100 parts by weight of polyethylene, the specific impedances being measured at 50 Hz with a field strength of 4 kV/cm, and the relatively less conductive filler being a filler which, when dispersed in polyethylene having a density of 0.916 g/cm3 and a melt flow index of 2, exhibits a curve of impedance versus loading having a relatively shallow slope with no steep sections and which has a specific impedance greater than 109 ohm.cm at a loading of 60 parts by weight per 100 parts by weight of polyethylene, the specific impedances being measured at 50 Hz with a field strength of 4 kV/cm.
2. A heating strip according to claim 1, wherein the weight of the second carbon black is greater than the weight of the first carbon black.
3. A heating strip according to claim 1, wherein the heating element contains at least 10% by weight, based on the weight of the polymeric matrix, of the first carbon black.
4. A heating strip according to claim 3, wherein the heating element contains 10 to 25% by weight, based on the weight of the polymeric matrix, of the first carbon black.
5. A heating strip according to any one of claims 1 to 3, wherein the heating element contains at least 40% by weight, based on the weight of the polymeric matrix, of the second carbon black.
6. A heating strip according to any one of claims 1 to 3, wherein the ratio by weight of the second carbon black to the first carbon black is from 2:1 to 8:1.
7. A heating strip according to any one of claims 1 to 3, wherein the polymeric matrix comprises a polyolefin, an olefin copolymer or a halogen-substituted olefin copolymer.
8. A heating strip according to any one of claims 1 to 3 claim 7,wherein the polymeric matrix comprises polyethylene or an ethylene/ethyl acrylate copolymer or both.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000397765A CA1151413A (en) | 1977-04-27 | 1982-03-05 | Electrical heating strip |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB1755077 | 1977-04-27 | ||
| GB17550 | 1977-04-27 | ||
| CA302001 | 1978-04-26 | ||
| CA000397765A CA1151413A (en) | 1977-04-27 | 1982-03-05 | Electrical heating strip |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1151413A true CA1151413A (en) | 1983-08-09 |
Family
ID=27165634
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000397765A Expired CA1151413A (en) | 1977-04-27 | 1982-03-05 | Electrical heating strip |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1151413A (en) |
-
1982
- 1982-03-05 CA CA000397765A patent/CA1151413A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |