EP0063440B1 - Radiation cross-linking of ptc conductive polymers - Google Patents
Radiation cross-linking of ptc conductive polymers Download PDFInfo
- Publication number
- EP0063440B1 EP0063440B1 EP82301765A EP82301765A EP0063440B1 EP 0063440 B1 EP0063440 B1 EP 0063440B1 EP 82301765 A EP82301765 A EP 82301765A EP 82301765 A EP82301765 A EP 82301765A EP 0063440 B1 EP0063440 B1 EP 0063440B1
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- electrodes
- ptc element
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- cross
- ptc
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- 229920001940 conductive polymer Polymers 0.000 title claims description 22
- 230000005855 radiation Effects 0.000 title claims description 18
- 238000004132 cross linking Methods 0.000 title claims description 10
- 238000000034 method Methods 0.000 claims description 17
- 229910052751 metal Inorganic materials 0.000 claims description 11
- 239000002184 metal Substances 0.000 claims description 11
- 239000011888 foil Substances 0.000 claims description 9
- 230000001678 irradiating effect Effects 0.000 claims description 4
- 238000002360 preparation method Methods 0.000 claims description 3
- 238000001816 cooling Methods 0.000 claims description 2
- 238000007689 inspection Methods 0.000 claims 2
- 239000000203 mixture Substances 0.000 description 11
- 229920000642 polymer Polymers 0.000 description 5
- 239000006229 carbon black Substances 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- 239000004594 Masterbatch (MB) Substances 0.000 description 2
- MXRIRQGCELJRSN-UHFFFAOYSA-N O.O.O.[Al] Chemical compound O.O.O.[Al] MXRIRQGCELJRSN-UHFFFAOYSA-N 0.000 description 2
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 2
- 239000011231 conductive filler Substances 0.000 description 2
- 229920001577 copolymer Polymers 0.000 description 2
- 238000010894 electron beam technology Methods 0.000 description 2
- 239000004615 ingredient Substances 0.000 description 2
- 238000002156 mixing Methods 0.000 description 2
- 239000000178 monomer Substances 0.000 description 2
- -1 polyethylene Polymers 0.000 description 2
- 238000007493 shaping process Methods 0.000 description 2
- 150000004684 trihydrates Chemical class 0.000 description 2
- NIXOWILDQLNWCW-UHFFFAOYSA-M Acrylate Chemical compound [O-]C(=O)C=C NIXOWILDQLNWCW-UHFFFAOYSA-M 0.000 description 1
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- VGGSQFUCUMXWEO-UHFFFAOYSA-N Ethene Chemical compound C=C VGGSQFUCUMXWEO-UHFFFAOYSA-N 0.000 description 1
- 239000005977 Ethylene Substances 0.000 description 1
- 229920000339 Marlex Polymers 0.000 description 1
- 239000004698 Polyethylene Substances 0.000 description 1
- 239000004743 Polypropylene Substances 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 150000001336 alkenes Chemical class 0.000 description 1
- 230000004075 alteration Effects 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- 239000003963 antioxidant agent Substances 0.000 description 1
- 230000003078 antioxidant effect Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 230000001747 exhibiting effect Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 235000012438 extruded product Nutrition 0.000 description 1
- 238000001125 extrusion Methods 0.000 description 1
- 239000000945 filler Substances 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 229920001903 high density polyethylene Polymers 0.000 description 1
- 239000004700 high-density polyethylene Substances 0.000 description 1
- 238000009413 insulation Methods 0.000 description 1
- 230000001788 irregular Effects 0.000 description 1
- 239000000155 melt Substances 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- JRZJOMJEPLMPRA-UHFFFAOYSA-N olefin Natural products CCCCCCCC=C JRZJOMJEPLMPRA-UHFFFAOYSA-N 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 239000003208 petroleum Substances 0.000 description 1
- 229920000573 polyethylene Polymers 0.000 description 1
- 238000006116 polymerization reaction Methods 0.000 description 1
- 229920000098 polyolefin Polymers 0.000 description 1
- 229920001155 polypropylene Polymers 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 229920001187 thermosetting polymer Polymers 0.000 description 1
- 239000004634 thermosetting polymer Substances 0.000 description 1
- 229920001567 vinyl ester resin Polymers 0.000 description 1
Images
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01C—RESISTORS
- H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
- H01C7/02—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material having positive temperature coefficient
- H01C7/027—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material having positive temperature coefficient consisting of conducting or semi-conducting material dispersed in a non-conductive organic material
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
- H01B1/20—Conductive material dispersed in non-conductive organic material
- H01B1/24—Conductive material dispersed in non-conductive organic material the conductive material comprising carbon-silicon compounds, carbon or silicon
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B3/00—Ohmic-resistance heating
- H05B3/10—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor
- H05B3/12—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material
Definitions
- This invention relates to the radiation cross-linking of PTC conductive polymers.
- US-A-3 351 882 discloses the preparation of electrical devices by embedding electrodes having a considerable area and an irregular surface, e.g. a metal mesh, in a resistor composed of a PTC conductive polymer, followed by cross-linking of the conductive polymer.
- the stated purpose of using electrodes of considerable area is to avoid excessive current concentrations and consequent damage to the conductive polymer.
- the stated purposes of the radiation are (a) to cross-link the conductive polymer adjacent the electrodes, so that the electrodes are firmly gripped, and (b) to cross-link the bulk of the conductive polymer so that it will resist softening.
- the cross-linking can be effected by radiation, and the patent discloses subjecting the entire resistor to a dose of 50 to 100 megarads of radiation of one or two million electron volt electrons. As shown by US-A-3 858 144 and 3 861 029, a dose of 2-15 megarads is sufficient to prevent softening of PTC conductive polymers, and higher doses are regarded as disadvantageous because they reduce crystallinity.
- the invention provides a process for the preparation of an electrical device comprising (1) a cross-linked PTC conductive polymer element and (2) two electrodes which can be connected to a power source to cause current to flow through the PTC element, which process comprises cross-linking the PTC element by radiation, characterized in that the essential parts of the PTC element are irradiated to a dosage of at least 50 Mrads, subject to the proviso that if each of the electrodes has a substantially planar configuration, then one or both of the following conditions is fulfilled:
- the radiation dose is, therefore, preferably at least 60 Mrads, particularly at least 80 Mrads, with yet higher dosages, e.g. at least 120 Mrads or at least 160 Mrads, being preferred when satisfactory PTC characteristics are maintained and the desire for improved performance outweighs the cost of radiation.
- This method involves the use of a scanning electron microscope (SEM) to measure the maximum rate at which the voltage changes in the PTC element when the device is in the tripped state. This maximum rate occurs in the so-called "hot zone" of the PTC element. The lower the maximum rate, the greater the number of trips that the device will withstand.
- SEM scanning electron microscope
- an electrical device which comprises (a) a radiation cross-linked PTC conductive polymer element and (b) two electrodes which can be connected to a power source to cause current to flow through the PTC element, characterized in that if the device, while it is powered by a 200 volts DC power source and is in the tripped condition, is inspected by means of a scanning electron microscope using voltage contrast to determine the way in which the potential of the device changes between the electrodes, the maximum difference in voltage between two points separated by 10 microns is less than 4.2 volts, preferably less than 3 volts, particularly less than 2 volts, especially less than 1 volt, subject to the proviso that if each of the electrodes has a substantially planar configuration, the maximum difference is less than 3 volts.
- SEM scanning is used herein to denote the following procedure.
- the device is inspected to see whether the PTC element has an exposed clean surface which is suitable for scanning in an SEM and which lies between the electrodes. If there is no such surface, then one is created, keeping the alteration of the device to a minimum.
- the device (or a portion of it if the device is too large, e.g. if it is an elongate heater) is then mounted in a scanning electron microscope so that the electron beam can be traversed from one electrode to the other and directed obliquely at the clean exposed surface.
- a slowly increasing current is passed through the device, using a DC power source of 200 volts, until the device has been "tripped" and the whole of the potential dropped across it.
- the electron beam is then traversed across the surface and, using voltage contrast techniques known to those skilled in the art, there is obtained a photomicrograph in which the trace is a measure of the brightness (and hence the potential) of the surface between the electrodes; such a photomicrograph is often known as a line scan.
- a diagrammatic representation of a typical photomicrograph is shown in Figure 1. It will be seen that the trace has numerous small peaks and valleys and it is believed that these are due mainly or exclusively to surface imperfections. A single “best line” is drawn through the trace (the broken line in Figure 1) in order to average out small variations, and from this "best line", the maximum difference in voltage between two points separated by 10 microns is determined.
- an electrode having a substantially planar configuration
- each of the electrodes has a columnar shape.
- Such a device is shown in isometric view in Figure 2, in which wire electrodes 2 are embedded in PTC conductive polymer element 1 having a hole through its centre portion.
- circuit protection devices In a second class of devices, usually circuit protection devices,
- each of the electrodes has a substantially planar configuration.
- Meshed planar electrodes can be used, but metal foil electrodes are preferred. If metal foil electrodes are applied to the PTC element before it is irradiated, there is a danger that gases evolved during irradiation will be trapped. It is preferred, therefore, that metal foil electrodes be applied after the radiation cross-linking step.
- a preferred process comprises the
- PTC conductive polymers suitable for use in this invention are disclosed in the patents and applications referenced above. Their resistivity at 23°C is preferably less than 1250 ohm.cm, e.g. less than 750 ohm.cm, particularly less than 500 ohm.cm, with values less than 50 ohm.cm being preferred for circuit protection devices.
- the polymeric component should be one which is cross-linked and not significantly degraded by radiation.
- the polymeric component is preferably free of thermosetting polymers and often consists essentially of one or more crystalline polymers. Suitable polymers include polyolefins, e.g.
- the conductive filler is preferably carbon black.
- the composition may also contain a non-conductive filler, e.g. alumina trihydrate.
- the composition can, but preferably does not, contain a radiation cross-linking aid. The presence of a cross-linking aid can substantially reduce the radiation dose required to produce a particular degree of cross-linking, but its residue generally has an adverse affect on electrical characteristics.
- Shaping of the conductive polymer will generally be effected by a melt-shaping technique, e.g. by melt-extrusion or molding.
- Statex G available from Columbian Chemicals, has a density of 1.8 g/cc, a surface area (S) of 35 m 2 /g, and an average particle size (D) of 60 millimicrons.
- Marlex 6003 is a high density polyethylene with a melt index of 0.3 which is available from Phillips Petroleum.
- Hydral 705 is alumina trihydrate available from Aluminum Co. of America.
- the antioxidant used was an oligomer of 4,4-thio bis (3-methyl-6-5-butyl phenol) with an average degree of polymerization of 3 ⁇ 4, as described in U.S. Patent Number 3,986,981.
- the ingredients for the masterbatch were dry blended and then mixed for 12 minutes in a Banbury mixer turning at high gear. The mixture was dumped, cooled, and granulated. The final mix was prepared by dry blending 948.3 g of Hydral 705 with 2439.2 g of the masterbatch, and then mixing the dry blend for 7 minutes in a Banbury mixer turning at high gear. The mixture was dumped, cooled, granulated, and then dried at 70°C and 1 torr for 16 hours.
- the granulated final mix was melt extruded as a strip 1 cm wide and 0.25 cm thick, around three wires. Two of the wires were preheated 20 AWG (0.095 cm diameter) 19/32 stranded nickel-plated copper wires whose centers were 0.76 cm apart, and the third wire, a 24 AWG (0.064 cm diameter) solid nickel-plated copper wire, was centered between the other two. Portions 1 cm long were cut from the extruded product and from each portion the polymeric composition was removed from about half the length, and the whole of the center 24 AWG wire was removed, leaving a hole running through the polymeric element.
- the products were heat treated in nitrogen at 150°C for 30 minutes and then in air at 110°C for 60 minutes, and were then irradiated.
- Samples were irradiated to dosages of 20 Mrads, 80 Mrads or 160 Mrads. These samples, when subjected to SEM scanning, were found to have a maximum difference in voltage between two points separated by 10 microns of about 5.2, about 4.0 and about 2.0 respectively. Some of these samples were then sealed inside a metal can, with a polypropylene envelope between the conductive element and the can.
- the resulting circuit protection devices were tested to determine how many test cycles they would withstand when tested in a circuit consisting essentially of a 240 volt AC power supply, a switch, a fixed resistor and the device.
- the devices had a resistance of 20-30 ohms at 23°C and the fixed resistor had a resistance of 33 ohms, so that when the power supply was first switched on, the initial current in the circuit was 4-5 amps.
- Each test cycle consisted of closing the switch, thus tripping the device, and after a period of about 10 seconds, opening the switch and allowing the device to cool for 1 minute before the next test cycle.
- the resistance of the device at 23°C was measured initially and after every fifth cycle.
- the Table below shows the number of cycles needed to increase the resistance to 1-1/2 times its original value.
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- Physics & Mathematics (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Ceramic Engineering (AREA)
- Electromagnetism (AREA)
- Spectroscopy & Molecular Physics (AREA)
- Thermistors And Varistors (AREA)
- Conductive Materials (AREA)
- Processes Of Treating Macromolecular Substances (AREA)
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Description
- This invention relates to the radiation cross-linking of PTC conductive polymers.
- Conductive polymer compositions exhibiting PTC behavior, and electrical devices comprising them, have been described in published documents and in our earlier specifications. Reference may be made, for example, to U.S. Patents Nos. 2,952,761, 2,978,665, 3,243,753, 3,351,882, 3,571,777, 3,757,086, 3,793,716, 3,823,217, 3,858,144, 3,861,029, 4,017,715, 4,072,848, 4,085,286, 4,117,312, 4,177,376, 4,177,446, 4,188,276, 4,237,441, 4,242,573, 4,246,468, 4,250,400, 4,255,698, 4,272,471, 4,276,466 and 4,314,230; J. Applied Polymer Science 19, 813-815 (1975), Klason and Kubat; Polymer Engineering and Science 18, 649-653 (1978), Narkis et al; German OLS 2,634,999, 2,746,602, 2,755,076, 2,755,077, 2,821,799 and 3,030,799; European Published Applications Nos. 0028142, 0030479, 0038713, 0038714, 0038715 and 0038718; pending European Applications No. 81,301,767.0, 81,301,768.8 and 81,302,201.9; and pending U.S. Applications Nos. 176,300, 184,647, 254,352, 272,854 and 300,709. The disclosures of these patents, publications and applications are incorporated herein by reference.
- It is known to cross-link PTC conductive polymers by radiation, and in practice the dosages employed have been relatively low, e.g. 10-20 Mrads. Higher dosages have, however, been proposed for some purposes. Thus OLS 2,634,999 recommends a dose of 20-45 Mrads; U.K. Specification No. 1,071,032 describes irradiated compositions comprising a copolymer of ethylene and a vinyl ester or an acrylate monomer and 50-400% by weight of a filler, e.g. carbon black, the radiation dose being about 2 to about 100 Mrads, preferably about 2 to about 20 Mrads, and the use of such compositions as tapes for grading the insulation on cables; US-A-3 351 882 discloses the preparation of electrical devices by embedding electrodes having a considerable area and an irregular surface, e.g. a metal mesh, in a resistor composed of a PTC conductive polymer, followed by cross-linking of the conductive polymer. The stated purpose of using electrodes of considerable area is to avoid excessive current concentrations and consequent damage to the conductive polymer. The stated purposes of the radiation are (a) to cross-link the conductive polymer adjacent the electrodes, so that the electrodes are firmly gripped, and (b) to cross-link the bulk of the conductive polymer so that it will resist softening. The cross-linking can be effected by radiation, and the patent discloses subjecting the entire resistor to a dose of 50 to 100 megarads of radiation of one or two million electron volt electrons. As shown by US-A-3 858 144 and 3 861 029, a dose of 2-15 megarads is sufficient to prevent softening of PTC conductive polymers, and higher doses are regarded as disadvantageous because they reduce crystallinity.
- The higher the voltage applied to an electrical device comprising a PTC conductive polymer, the more likely it is that intermittent application of the voltage will cause the device to fail. This has been a serious problem, for example, in the use of circuit protection devices where the voltage dropped over the device in the "tripped" (i.e. high resistance) condition is more than about 200 volts. [Voltages given herein are DC values or RMS values for AC power sources]. We have now discovered that the likelihood of such failure can be substantially reduced by irradiating the conductive polymer so that it is very highly cross-linked.
- In its first aspect, the invention provides a process for the preparation of an electrical device comprising (1) a cross-linked PTC conductive polymer element and (2) two electrodes which can be connected to a power source to cause current to flow through the PTC element, which process comprises cross-linking the PTC element by radiation, characterized in that the essential parts of the PTC element are irradiated to a dosage of at least 50 Mrads, subject to the proviso that if each of the electrodes has a substantially planar configuration, then one or both of the following conditions is fulfilled:
- (a) the essential parts of the PTC element are irradiated to a dosage of at least 120 Mrads,
- (b) the PTC element is irradiated in the absence of the electrodes and metal foil electrodes are secured to the PTC element after it has been cross-linked.
- Our experiments indicate that the higher the radiation dose, the greater the number of "trips" (i.e. conversions to the tripped state) a device will withstand without failure. The radiation dose is, therefore, preferably at least 60 Mrads, particularly at least 80 Mrads, with yet higher dosages, e.g. at least 120 Mrads or at least 160 Mrads, being preferred when satisfactory PTC characteristics are maintained and the desire for improved performance outweighs the cost of radiation.
- We have further discovered a method of determining the likelihood that a device will withstand a substantial number of trips at a voltage of 200 volts. This method involves the use of a scanning electron microscope (SEM) to measure the maximum rate at which the voltage changes in the PTC element when the device is in the tripped state. This maximum rate occurs in the so-called "hot zone" of the PTC element. The lower the maximum rate, the greater the number of trips that the device will withstand. Accordingly, the present invention provides, in a second aspect, an electrical device which comprises (a) a radiation cross-linked PTC conductive polymer element and (b) two electrodes which can be connected to a power source to cause current to flow through the PTC element, characterized in that if the device, while it is powered by a 200 volts DC power source and is in the tripped condition, is inspected by means of a scanning electron microscope using voltage contrast to determine the way in which the potential of the device changes between the electrodes, the maximum difference in voltage between two points separated by 10 microns is less than 4.2 volts, preferably less than 3 volts, particularly less than 2 volts, especially less than 1 volt, subject to the proviso that if each of the electrodes has a substantially planar configuration, the maximum difference is less than 3 volts.
- The term "SEM scanning" is used herein to denote the following procedure. The device is inspected to see whether the PTC element has an exposed clean surface which is suitable for scanning in an SEM and which lies between the electrodes. If there is no such surface, then one is created, keeping the alteration of the device to a minimum. The device (or a portion of it if the device is too large, e.g. if it is an elongate heater) is then mounted in a scanning electron microscope so that the electron beam can be traversed from one electrode to the other and directed obliquely at the clean exposed surface. A slowly increasing current is passed through the device, using a DC power source of 200 volts, until the device has been "tripped" and the whole of the potential dropped across it. The electron beam is then traversed across the surface and, using voltage contrast techniques known to those skilled in the art, there is obtained a photomicrograph in which the trace is a measure of the brightness (and hence the potential) of the surface between the electrodes; such a photomicrograph is often known as a line scan. A diagrammatic representation of a typical photomicrograph is shown in Figure 1. It will be seen that the trace has numerous small peaks and valleys and it is believed that these are due mainly or exclusively to surface imperfections. A single "best line" is drawn through the trace (the broken line in Figure 1) in order to average out small variations, and from this "best line", the maximum difference in voltage between two points separated by 10 microns is determined.
- When reference is made herein to an electrode "having a substantially planar configuration", we mean an electrode whose shape and position in the device are such that substantially all the current enters (or leaves) the electrode through a surface which is substantially planar.
- The present invention is particularly useful for circuit protection devices, but is also applicable to heaters, particularly laminar heaters. In one class of devices, each of the electrodes has a columnar shape. Such a device is shown in isometric view in Figure 2, in which
wire electrodes 2 are embedded in PTCconductive polymer element 1 having a hole through its centre portion. - In a second class of devices, usually circuit protection devices,
- (A) the PTC element is in the form of a strip with substantially planar parallel ends, the length of the strip being greater than the largest cross-sectional dimension of the strip; and
- (B) each of the electrodes is in the form of a cap having (i) a substantially planar end which contacts and has substantially the same cross-section as one end of the PTC element and (ii) a side wall which contacts the side of the PTC element. Such a device is shown in cross-section in Figure 3, in which
cap electrodes 2 contact either end of cylindrical PTCconductive polymer element 1 having ahole 11 through its centre portion. - In a third class of devices, usually heaters,
- (A) the PTC element is laminar; and
- (B) the electrodes are displaced from each other so that current flow between them is along one of the large dimensions of the element.
- In a fourth class of devices, each of the electrodes has a substantially planar configuration. Meshed planar electrodes can be used, but metal foil electrodes are preferred. If metal foil electrodes are applied to the PTC element before it is irradiated, there is a danger that gases evolved during irradiation will be trapped. It is preferred, therefore, that metal foil electrodes be applied after the radiation cross-linking step. Thus a preferred process comprises the
- (1) irradiating a laminar PTC conductive polymer element in the absence of electrodes;
- (2) contacting the cross-linked PTC element from step (1) with metal foil electrodes under conditions of heat and pressure, and
- (3) cooling the PTC element and the metal foil electrodes while continuing to press them together.
- PTC conductive polymers suitable for use in this invention are disclosed in the patents and applications referenced above. Their resistivity at 23°C is preferably less than 1250 ohm.cm, e.g. less than 750 ohm.cm, particularly less than 500 ohm.cm, with values less than 50 ohm.cm being preferred for circuit protection devices. The polymeric component should be one which is cross-linked and not significantly degraded by radiation. The polymeric component is preferably free of thermosetting polymers and often consists essentially of one or more crystalline polymers. Suitable polymers include polyolefins, e.g. polyethylene, and copolymers of at least one olefin and at least one olefinically unsaturated monomer containing a polar group. The conductive filler is preferably carbon black. The composition may also contain a non-conductive filler, e.g. alumina trihydrate. The composition can, but preferably does not, contain a radiation cross-linking aid. The presence of a cross-linking aid can substantially reduce the radiation dose required to produce a particular degree of cross-linking, but its residue generally has an adverse affect on electrical characteristics.
- Shaping of the conductive polymer will generally be effected by a melt-shaping technique, e.g. by melt-extrusion or molding.
- The invention is illustrated by the following Example
-
- Statex G, available from Columbian Chemicals, has a density of 1.8 g/cc, a surface area (S) of 35 m2/g, and an average particle size (D) of 60 millimicrons.
- Marlex 6003 is a high density polyethylene with a melt index of 0.3 which is available from Phillips Petroleum.
- Hydral 705 is alumina trihydrate available from Aluminum Co. of America.
- The antioxidant used was an oligomer of 4,4-thio bis (3-methyl-6-5-butyl phenol) with an average degree of polymerization of 3―4, as described in U.S. Patent Number 3,986,981.
- After drying the polymer at 70°C and the carbon black at 150°C for 16 hours in a vacuum oven, the ingredients for the masterbatch were dry blended and then mixed for 12 minutes in a Banbury mixer turning at high gear. The mixture was dumped, cooled, and granulated. The final mix was prepared by dry blending 948.3 g of Hydral 705 with 2439.2 g of the masterbatch, and then mixing the dry blend for 7 minutes in a Banbury mixer turning at high gear. The mixture was dumped, cooled, granulated, and then dried at 70°C and 1 torr for 16 hours.
- Using a cross-head die, the granulated final mix was melt extruded as a
strip 1 cm wide and 0.25 cm thick, around three wires. Two of the wires were preheated 20 AWG (0.095 cm diameter) 19/32 stranded nickel-plated copper wires whose centers were 0.76 cm apart, and the third wire, a 24 AWG (0.064 cm diameter) solid nickel-plated copper wire, was centered between the other two.Portions 1 cm long were cut from the extruded product and from each portion the polymeric composition was removed from about half the length, and the whole of the center 24 AWG wire was removed, leaving a hole running through the polymeric element. The products were heat treated in nitrogen at 150°C for 30 minutes and then in air at 110°C for 60 minutes, and were then irradiated. Samples were irradiated to dosages of 20 Mrads, 80 Mrads or 160 Mrads. These samples, when subjected to SEM scanning, were found to have a maximum difference in voltage between two points separated by 10 microns of about 5.2, about 4.0 and about 2.0 respectively. Some of these samples were then sealed inside a metal can, with a polypropylene envelope between the conductive element and the can. - The resulting circuit protection devices were tested to determine how many test cycles they would withstand when tested in a circuit consisting essentially of a 240 volt AC power supply, a switch, a fixed resistor and the device. The devices had a resistance of 20-30 ohms at 23°C and the fixed resistor had a resistance of 33 ohms, so that when the power supply was first switched on, the initial current in the circuit was 4-5 amps. Each test cycle consisted of closing the switch, thus tripping the device, and after a period of about 10 seconds, opening the switch and allowing the device to cool for 1 minute before the next test cycle. The resistance of the device at 23°C was measured initially and after every fifth cycle. The Table below shows the number of cycles needed to increase the resistance to 1-1/2 times its original value.
Claims (11)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AT82301765T ATE46982T1 (en) | 1981-04-02 | 1982-04-02 | RADIATION CROSSLINKING OF PTC-CONDUCTIVE POLYMERS. |
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US25049181A | 1981-04-02 | 1981-04-02 | |
US250491 | 1981-04-02 | ||
US06/254,352 US4426633A (en) | 1981-04-15 | 1981-04-15 | Devices containing PTC conductive polymer compositions |
US254352 | 1981-04-15 |
Related Child Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP88117360.3 Division-Into | 1988-10-19 |
Publications (3)
Publication Number | Publication Date |
---|---|
EP0063440A2 EP0063440A2 (en) | 1982-10-27 |
EP0063440A3 EP0063440A3 (en) | 1983-04-13 |
EP0063440B1 true EP0063440B1 (en) | 1989-10-04 |
Family
ID=26940917
Family Applications (2)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP88117360A Expired - Lifetime EP0311142B1 (en) | 1981-04-02 | 1982-04-02 | Radiation cross-linking of ptc conductive polymers |
EP82301765A Expired EP0063440B1 (en) | 1981-04-02 | 1982-04-02 | Radiation cross-linking of ptc conductive polymers |
Family Applications Before (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP88117360A Expired - Lifetime EP0311142B1 (en) | 1981-04-02 | 1982-04-02 | Radiation cross-linking of ptc conductive polymers |
Country Status (6)
Country | Link |
---|---|
EP (2) | EP0311142B1 (en) |
JP (1) | JPH053101A (en) |
DE (2) | DE3279970D1 (en) |
GB (1) | GB2096393B (en) |
HK (1) | HK83689A (en) |
SG (1) | SG89388G (en) |
Families Citing this family (23)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4724417A (en) * | 1985-03-14 | 1988-02-09 | Raychem Corporation | Electrical devices comprising cross-linked conductive polymers |
EP0242029B1 (en) | 1986-02-20 | 1991-12-11 | RAYCHEM CORPORATION (a Delaware corporation) | Method and articles employing ion exchange material |
US4907340A (en) * | 1987-09-30 | 1990-03-13 | Raychem Corporation | Electrical device comprising conductive polymers |
US4924074A (en) * | 1987-09-30 | 1990-05-08 | Raychem Corporation | Electrical device comprising conductive polymers |
ATE296478T1 (en) * | 1995-03-22 | 2005-06-15 | Tyco Electronics Corp | ELECTRICAL DEVICE |
TW309619B (en) | 1995-08-15 | 1997-07-01 | Mourns Multifuse Hong Kong Ltd | |
EP0953992A1 (en) | 1995-08-15 | 1999-11-03 | Bourns Multifuse (Hong Kong), Ltd. | Surface mount conductive polymer devices and methods for manufacturing such devices |
DE19548741A1 (en) * | 1995-12-23 | 1997-06-26 | Abb Research Ltd | Process for the production of a material for PTC resistors |
US5814264A (en) * | 1996-04-12 | 1998-09-29 | Littelfuse, Inc. | Continuous manufacturing methods for positive temperature coefficient materials |
TW343423B (en) * | 1996-08-01 | 1998-10-21 | Raychem Corp | Method of making a laminate comprising a conductive polymer composition |
US6020808A (en) | 1997-09-03 | 2000-02-01 | Bourns Multifuse (Hong Kong) Ltd. | Multilayer conductive polymer positive temperature coefficent device |
CN1319235A (en) | 1998-09-25 | 2001-10-24 | 伯恩斯公司 | Two-step method for preparing positive temperature coefficient polymeric material |
DE10310722A1 (en) | 2003-03-10 | 2004-09-23 | Tesa Ag | Electrically heatable adhesive composition, useful for adhesive tape in automotive applications such as electrically heated mirrors, comprises an adhesive component and an electrically conductive filler |
KR20060127854A (en) * | 2003-10-21 | 2006-12-13 | 타이코 일렉트로닉스 레이켐 케이. 케이. | Ptc element and fluorescent lamp starter circuit |
DE102007007617A1 (en) | 2007-02-13 | 2008-08-14 | Tesa Ag | Intrinsically heatable hot melt tacky fabrics |
DE102008034748A1 (en) | 2008-07-24 | 2010-01-28 | Tesa Se | Flexible heated surface element |
DE102008063849A1 (en) | 2008-12-19 | 2010-06-24 | Tesa Se | Heated surface element and method for its attachment |
DE102009010437A1 (en) | 2009-02-26 | 2010-09-02 | Tesa Se | Heated surface element |
CN102412094B (en) * | 2010-09-20 | 2014-12-31 | 胜德国际研发股份有限公司 | Protective circuit |
US10373745B2 (en) | 2014-06-12 | 2019-08-06 | LMS Consulting Group | Electrically conductive PTC ink with double switching temperatures and applications thereof in flexible double-switching heaters |
US11332632B2 (en) | 2016-02-24 | 2022-05-17 | Lms Consulting Group, Llc | Thermal substrate with high-resistance magnification and positive temperature coefficient ink |
WO2020016853A1 (en) | 2018-07-20 | 2020-01-23 | LMS Consulting Group | Thermal substrate with high-resistance magnification and positive temperature coefficient |
US10822513B1 (en) | 2019-04-26 | 2020-11-03 | 1-Material Inc | Electrically conductive PTC screen printable ink composition with low inrush current and high NTC onset temperature |
Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3351882A (en) * | 1964-10-09 | 1967-11-07 | Polyelectric Corp | Plastic resistance elements and methods for making same |
Family Cites Families (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS5123543A (en) * | 1974-08-22 | 1976-02-25 | Dainippon Printing Co Ltd | DODENSEI KOBUNSHIZAIRYO |
FR2321751A1 (en) * | 1975-08-04 | 1977-03-18 | Raychem Corp | MATERIALS OF HIGH ELECTRICAL RESISTANCE AT HIGH TEMPS. - comprise crystalline thermoplastic (co)polymer and conducting filler used for heating elements |
GB1604735A (en) * | 1978-04-14 | 1981-12-16 | Raychem Corp | Ptc compositions and devices comprising them |
BE859776A (en) * | 1976-10-15 | 1978-04-14 | Raychem Corp | COMPOSITIONS WITH A POSITIVE TEMPERATURE COEFFICIENT AND DEVICES INCLUDING |
US4200973A (en) * | 1978-08-10 | 1980-05-06 | Samuel Moore And Company | Method of making self-temperature regulating electrical heating cable |
-
1982
- 1982-04-02 GB GB8209923A patent/GB2096393B/en not_active Expired
- 1982-04-02 DE DE8282301765T patent/DE3279970D1/en not_active Expired
- 1982-04-02 EP EP88117360A patent/EP0311142B1/en not_active Expired - Lifetime
- 1982-04-02 DE DE3280447T patent/DE3280447T2/en not_active Expired - Lifetime
- 1982-04-02 EP EP82301765A patent/EP0063440B1/en not_active Expired
-
1988
- 1988-12-28 SG SG893/88A patent/SG89388G/en unknown
-
1989
- 1989-10-19 HK HK836/89A patent/HK83689A/en not_active IP Right Cessation
-
1991
- 1991-07-16 JP JP3175067A patent/JPH053101A/en active Pending
Patent Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3351882A (en) * | 1964-10-09 | 1967-11-07 | Polyelectric Corp | Plastic resistance elements and methods for making same |
Also Published As
Publication number | Publication date |
---|---|
EP0311142A3 (en) | 1989-04-26 |
GB2096393B (en) | 1986-01-02 |
EP0063440A2 (en) | 1982-10-27 |
JPH053101A (en) | 1993-01-08 |
EP0311142B1 (en) | 1993-12-15 |
SG89388G (en) | 1989-07-14 |
GB2096393A (en) | 1982-10-13 |
EP0311142A2 (en) | 1989-04-12 |
EP0063440A3 (en) | 1983-04-13 |
DE3279970D1 (en) | 1989-11-09 |
HK83689A (en) | 1989-10-27 |
DE3280447D1 (en) | 1994-01-27 |
DE3280447T2 (en) | 1994-07-14 |
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