US4315237A
Expired / Lapsed
US
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PTC Devices comprising oxygen barrier layers
Assignee: Littelfuse Inc
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Filing: 1979-11-30
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Granted: 1982-02-09
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Expires: 1999-11-30
Abstract
Abstract Electrical devices comprising PTC elements have improved electrical stability when they comprise an oxygen barrier which restricts access of air to the element so that the PTC element absorbs oxygen at a rate less than 10 -6 cc/sec/gram. The devices are for example circuit control devices or self-limiting heaters. Preferred PTC elements comprise a polymer having dispersed therein carbon black and an additive which stabilizes the polymer against degradation, especially an organic antioxidant. The oxygen barrier may for example be a layer of a polymeric composition or a self-supporting container principally made of metal and filled with an inert gas.
Inventors
- 👤 Lee M. Middleman
- 👤 Alan J. Gotcher
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 12:33
CPC Classifications
H; H01; H01C; H01C7/00; H01C7/02; H01C7/027
Claims Analysis
Total Claims: 31
Claim 1
Independent Claim
110 words
An electrical device which comprises (1) a PTC element which is composed of a composition which exhibits PTC behavior with a switching temperature T s and which comprises (a) a macromolecular polymer; and (b) conductive particles dispersed in said polymer; (2) at least two electrodes which can be connected to a source of electrical power and which, when so connected, cause current to flow through said PTC element; and (3) an oxygen barrier which, when the device is in air at standard temperature and pressure, restricts access of air to the PTC element so that the rate at which the PTC element absorbs oxygen is less than 10 -6 cc/sec/gram.
Claim 2
Dependent Claim
110 words
An electrical device which comprises (1) a PTC element which is composed of a composition which exhibits PTC behavior with a switching temperature T s and which comprises (a) a macromolecular polymer; and (b) conductive particles dispersed in said polymer; (2) at least two electrodes which can be connected to a source of electrical power and which, when so connected, cause current to flow through said PTC element; and (3) an oxygen barrier which, when the device is in air at standard temperature and pressure, restricts access of air to the PTC element so that the rate at which the PTC element absorbs oxygen is less than 10 -6 cc/sec/gram.
Claim 3
Dependent Claim
73 words
A device according to claim 1 which exhibits a change in resistance, at at least one temperature between (T s -110)°C. and T s , of -50% to +200%, after having been subjected to an aging treatment which comprises passing current through the device for 250 hours, the current being such that I 2 R heating of the device maintains said PTC element at a temperature between T s and (T s +50)°C.
Claim 4
Dependent Claim
22 words
A device according to claim 1 wherein said rate at which the PTC element absorbs oxygen is less than 4×10 -7 cc/sec/gram.
Claim 5
Dependent Claim
15 words
A device according to claim 3 wherein said rate is less than 3×10 -7 cc/sec/gram.
Claim 6
Dependent Claim
15 words
A device according to claim 4 wherein said rate is less than 2×10 -7 cc/sec/gram.
Claim 7
Dependent Claim
37 words
A device according to claim 2 which exhibits a change in resistance, at at least one temperature between (T s -110)°C. and T s , of -50% to +100%, after having been subjected to said aging treatment.
Claim 8
Dependent Claim
37 words
A device according to claim 2 which exhibits a change in resistance, at at least one temperature between (T s -60)°C. and T s , of -50% to +100%, after having been subjected to said aging treatment.
Claim 9
Dependent Claim
73 words
A device according to claim 2 which exhibits a change in resistance, at at least one temperature between (T s -110)°C. and T s , of -50% to +200%, after having been subjected to an aging treatment which comprises passing current through the device for 500 hours, the current being such that I 2 R heating of the device maintains said PTC element at a temperature between T s and (T s +50)°C.
Claim 10
Dependent Claim
27 words
A device according to claim 1 wherein said barrier is composed of a material having an oxygen permeability rate of less than 5×10 -9 cc(STP)/cm 2 /mm/sec/cmHg.
Claim 11
Dependent Claim
19 words
A device according to claim 9 wherein said oxygen permeability rate is less than 10 -9 cc(STP)/cm 2 /mm/sec/cmHg.
Claim 12
Dependent Claim
42 words
A device according to claim 9 wherein said barrier is 0.001 to 0.050 inch thick and comprises at least one layer of an electrically insulating composition which comprises at least one polymer and which has a Young's Modulus greater than 100,000 psi.
Claim 13
Dependent Claim
16 words
A device according to claim 11 wherein said barrier layer is 0.01 to 0.03 inch thick.
Claim 14
Dependent Claim
54 words
A device according to claim 9 wherein said barrier comprises at least one polymer selected from the group consisting of polyvinylidene chloride, polyvinyl fluoride, polyethylene terephthalate, rubber hydrochloride, polychlorotrifluoroethylene, phenol-formaldehyde resins, polyamides, epoxy resins, styrene/acrylonitrile copolymers, cellulose acetate, butadiene/acrylonitrile copolymers, polycarbonates, polystyrene, isobutylene/isoprene copolymers, polyethylene, ethylene/tetrafluoroethylene copolymers, vinylidene fluoride/hexafluoropropylene polymers and fluorinated ethylene/propylene copolymers.
Claim 15
Dependent Claim
45 words
A device according to claim 9 wherein said barrier is such that, when the device is placed in air, the only oxygen which can contact at least 95% of the surface area of the PTC element is oxygen which has passed through the barrier layer.
Claim 16
Independent Claim
17 words
A device according to calim 14 wherein said barrier provides a hermetic seal around said PTC element.
Claim 17
Independent Claim
17 words
A device according to calim 14 wherein said barrier provides a hermetic seal around said PTC element.
Claim 18
Dependent Claim
41 words
A device according to claim 9 which is a circuit control device and wherein the barrier comprises a self-supporting container which is principally made of metal, with the electrodes passing through a wall composed of a ceramic or rigid plastics material.
Claim 19
Dependent Claim
17 words
A device according to claim 16 wherein said container is filled with a gas free from oxygen.
Claim 20
Dependent Claim
18 words
A device according to claim 9 which is free from voids between said PTC element and said barrier.
Claim 21
Dependent Claim
19 words
A device according to claim 1 wherein at least one of said electrodes provides a part of said barrier.
Claim 22
Dependent Claim
30 words
A device according to claim 1 wherein said PTC composition further comprises an additive which stabilises said macromolecular polymer against degradation and which reduces said change in resistance on aging.
Claim 23
Dependent Claim
57 words
A device according to claim 20 wherein each of said electrodes is in contact with a conductive polymer composition which comprises a macromolecular polymer and conductive particles dispersed in said polymer, and at least the outer surface of each of said electrodes is composed of a metal which does not catalyse degradation of said conductive polymer composition.
Claim 24
Dependent Claim
43 words
A device according to claim 20 wherein each of said electrodes is in contact with said PTC element and at least the outer surface of each of said electrodes is composed of a metal which does not catalyse degradation of said PTC element.
Claim 25
Dependent Claim
33 words
A device according to claim 22 wherein at least the outer surface of each of said electrodes is composed of a metal selected from the group consisting of nickel, tin, silver and gold.
Claim 26
Dependent Claim
35 words
A device according to claim 1 wherein said PTC composition comprises an organic polymer having at least 10% crystallinity and having dispersed therein a carbon black having a particle size of 20 to 250 millimicrons.
Claim 27
Dependent Claim
13 words
A device according to claim 24 wherein said organic polymer is a polyolefin.
Claim 28
Dependent Claim
16 words
A device according to claim 24 wherein said PTC composition also comprises a non-conductive inorganic filler.
Claim 29
Dependent Claim
20 words
A device according to claim 9 which is a circuit control device and wherein the barrier comprises a self-supporting container.
Claim 30
Dependent Claim
13 words
A device according to claim 27 wherein the barrier comprises a polymeric material.
Claim 31
Dependent Claim
13 words
A device according to claim 28 wherein the barrier also comprises a metal.
References Cited (Backward Citations)
US2861163A
Cited
US3239785A
Cited
GB988184A
Cited
US3243753A
Cited
GB1167551A
Cited
GB1168162A
Cited
US3619560A
Cited
US3914363A
Cited
US3824328A
Cited
US3858141A
Cited
GB1458720A
Cited
US4151401A
Cited
US4238812A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1985-02-08 | 1985-08-10 | 1986-02-09 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1989-02-08 | 1989-08-10 | 1990-02-09 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1993-02-08 | 1993-08-10 | 1994-02-09 | $7700.00 | Window Closed / Lapsed |