US4534889A
Expired / Lapsed
US
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PTC Compositions and devices comprising them
Assignee: Littelfuse Inc
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Filing: 1983-02-11
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Granted: 1985-08-13
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Expires: 2003-02-11
Abstract
Abstract Novel conductive polymer compositions which exhibit useful PTC behavior are produced by cross-linking processes. By correlating the polymer, the conductive filler dispersed therein, and the cross-linking conditions, PTC compositions having desired resistance/temperature characteristics can be prepared. In particular the cross-linking can be carried out so as to provide compositions having a switching temperature around the cross-linking temperature. The invention is applicable to both elastomeric and thermoplastic polymers, and provides for the first time a method of making PTC compositions exhibiting useful PTC behavior from elastomers.
Inventors
- 👤 Peter H. van Konynenburg
- 👤 Bernard J. Lyons
- 👤 Robert Smith-Johannsen
- 👤 Wendell W. Moyer
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 19:25
CPC Classifications
H; H01; H01B; H01B1/00; H01B1/20; H01B1/24; C; C08; C08K; C08K3/00; C08K3/02; C08K3/04; H01C; H01C7/00; H01C7/02; H01C7/027; H05; H05B; H05B3/00; H05B3/10; H05B3/12; H05B3/14; H05B3/146
Claims Analysis
Total Claims: 49
Claim 1
Independent Claim
130 words
A process for the preparation of a PTC composition which comprises (1) dispersing conductive particles having a size of at least 18 millimicrons in a polymer; (2) cross-linking the dispersion from step (1) at a first temperature (T c1 ) and (3) further cross-linking the cross-linked composition from step (2) at a second temperature (T c2 ) which is substantially different from T c1 the composition obtained in step (3) having a gel fraction of at least 0.6; exhibiting PTC behavior with an R 14 value of at least 2.5 or a R 100 value of at least 10 and at least one T s within the temperature range of -100 to 250° C.; and having a volume resistivity at temperatures below T s of 25 to 10 5 ohm·cm.
Claim 2
Dependent Claim
130 words
A process for the preparation of a PTC composition which comprises (1) dispersing conductive particles having a size of at least 18 millimicrons in a polymer; (2) cross-linking the dispersion from step (1) at a first temperature (T c1 ) and (3) further cross-linking the cross-linked composition from step (2) at a second temperature (T c2 ) which is substantially different from T c1 the composition obtained in step (3) having a gel fraction of at least 0.6; exhibiting PTC behavior with an R 14 value of at least 2.5 or a R 100 value of at least 10 and at least one T s within the temperature range of -100 to 250° C.; and having a volume resistivity at temperatures below T s of 25 to 10 5 ohm·cm.
Claim 3
Dependent Claim
22 words
A process according to claim 1 wherein the polymer is a thermoplastic and T c1 is substantially lower than T c2 .
Claim 4
Dependent Claim
23 words
A process according to claim 1 wherein the cross-linked polymer is an elastomer and T c1 is substantially higher than T c2 .
Claim 5
Dependent Claim
13 words
A process according to claim 1 wherein the polymer is an elastomer gum.
Claim 6
Dependent Claim
12 words
A process according to claim 4 wherein the polymer is a polysiloxane.
Claim 7
Dependent Claim
14 words
A process according to claim 5 wherein the polysiloxane contains silica as a filler.
Claim 8
Dependent Claim
21 words
A process according to claim 1 wherein the polymer has a tensile stress of at least 10 psi at 20% elongation.
Claim 9
Dependent Claim
21 words
A process according to claim 1 wherein the polymer has a tensile stress of less than 10 psi at 20% elongation.
Claim 10
Dependent Claim
18 words
A process according to claim 7 wherein the polymer is annealed at each cross-linking temperature prior to cross-linking.
Claim 11
Dependent Claim
13 words
A process according to claim 1 wherein the polymer is cross-linked by irradiation.
Claim 12
Dependent Claim
19 words
A process according to claim 1 wherein the polymer is cross-linked with the aid of a chemical cross-linking agent.
Claim 13
Dependent Claim
35 words
A process according to claim 1 wherein at least one of the cross-linking temperatures is above 20° C. and the conductive filler is a carbon black having a particle size of at least 20 millimicrons.
Claim 14
Dependent Claim
35 words
A process according to claim 1 wherein at least one of the cross-linking temperatures is above 100° C. and the conductive filler is a carbon black having a particle size of at least 30 millimicrons.
Claim 15
Dependent Claim
35 words
A process according to claim 1 wherein at least one of the cross-linking temperatures is above 150° C. and the conductive filler is a carbon black having a particle size of at least 40 millimicrons.
Claim 16
Dependent Claim
123 words
A process for the preparation of a PTC composition which comprises: (1) dispersing conductive particles having a size of at least 18 millimicrons in a crystalline polymer; and (2) cross-linking the dispersion from step (1) at a temperature above 60° C. by means of radiation to obtain a composition having a gel fraction of at least 0.6; the particles, the polymer and the cross-linking conditions being such that the cross-linked composition exhibits PTC behavior with an R 14 value of at least 2.5 or an R 100 value of at least 10 and at least one T s within the range of -100° C. to +250° C., and has a volume resistivity at temperatures below T s of 25 to 10 5 ohm·cm.
Claim 17
Dependent Claim
123 words
A process for the preparation of a PTC composition which comprises: (1) dispersing conductive particles having a size of at least 18 millimicrons in a crystalline polymer; and (2) cross-linking the dispersion from step (1) at a temperature above 60° C. by means of radiation to obtain a composition having a gel fraction of at least 0.6; the particles, the polymer and the cross-linking conditions being such that the cross-linked composition exhibits PTC behavior with an R 14 value of at least 2.5 or an R 100 value of at least 10 and at least one T s within the range of -100° C. to +250° C., and has a volume resistivity at temperatures below T s of 25 to 10 5 ohm·cm.
Claim 18
Dependent Claim
121 words
A process according to claim 15 wherein the cross-linked composition (a) exhibits PTC behavior with a first T s near the crystalline melting point of the polymer (T s1 ) and a second T s near the temperature of the cross-linking step (2) (T s2 ); (b) has a volume resistivity at temperatures below the lower of T s1 and T s2 between 25 and 10 5 ohm·cm; and (c) has an R 14 value between T s1 and T s2 or above the higher of T s1 and T s2 of at least 2.5 or has an R 100 value between T s1 and T s2 or above the higher of T s1 and T s2 of at least 10.
Claim 19
Dependent Claim
26 words
A process according to claim 15 wherein the temperature of the dispersion in step (2) is above the T s of the composition prior to cross-linking.
Claim 20
Dependent Claim
24 words
A process according to claim 15 wherein the temperature of the dispersion in step (2) is above the crystalline melting point of the polymer.
Claim 21
Dependent Claim
125 words
A PTC composition comprising: (1) a cross-linked crystalline polymer; and (2) conductive particles enclosed within the cross-linked network of said polymer, the particles having a size of at least 18 millimicrons; which composition (a) has a gel fraction of at least 0.6; (b) exhibits PTC behavior in two distinct temperature ranges, each having an R 14 value of at least 2.5 or an R 100 value of at least 10, and a T s which is within the temperature range of -100° to +250° C. and the T s is one of the temperature ranges being above the T s of the composition prior to cross-linking; and (c) has a volume resistivity at a temperature below each T s of 25 to 10 5 ohm·cm.
Claim 22
Dependent Claim
125 words
A PTC composition comprising: (1) a cross-linked crystalline polymer; and (2) conductive particles enclosed within the cross-linked network of said polymer, the particles having a size of at least 18 millimicrons; which composition (a) has a gel fraction of at least 0.6; (b) exhibits PTC behavior in two distinct temperature ranges, each having an R 14 value of at least 2.5 or an R 100 value of at least 10, and a T s which is within the temperature range of -100° to +250° C. and the T s is one of the temperature ranges being above the T s of the composition prior to cross-linking; and (c) has a volume resistivity at a temperature below each T s of 25 to 10 5 ohm·cm.
Claim 23
Dependent Claim
51 words
A PTC composition according to claim 19 whose T s remains substantially unchanged when repeatedly subjected to thermal cycling which comprises heating the composition from a temperature below T s to a temperature above T s but below the peak temperature, followed by cooling to a temperature below T s .
Claim 24
Dependent Claim
23 words
A PTC composition according to claim 19 wherein the conductive particles are carbon black particles having a size of 22 to 80 millimicrons.
Claim 25
Dependent Claim
103 words
A PTC composition comprising: (1) an elastomer obtained by cross-linking a thermoplastic elastomer; and (2) conductive particles enclosed within the cross-linked network of said elastomer, the particles having a size of at least 18 millimicrons; which composition (a) has a gel fraction of at least 0.6; (b) exhibits PTC behavior with an R 14 value of at least 2.5 or an R 100 value of at least 10, and at least one T s which is within the temperature range of -100° to 250° C.; and (c) has a volume resistivity at temperatures below said T s between 25 and 10 5 ohm·cm.
Claim 26
Dependent Claim
103 words
A PTC composition comprising: (1) an elastomer obtained by cross-linking a thermoplastic elastomer; and (2) conductive particles enclosed within the cross-linked network of said elastomer, the particles having a size of at least 18 millimicrons; which composition (a) has a gel fraction of at least 0.6; (b) exhibits PTC behavior with an R 14 value of at least 2.5 or an R 100 value of at least 10, and at least one T s which is within the temperature range of -100° to 250° C.; and (c) has a volume resistivity at temperatures below said T s between 25 and 10 5 ohm·cm.
Claim 27
Dependent Claim
51 words
A PTC composition according to claim 22 whose T s remains substantially unchanged when repeatedly subjected to thermal cycling which comprises heating the composition from a temperature below T s to a temperature above T s but below the peak temperature, followed by cooling to a temperature below T s .
Claim 28
Dependent Claim
23 words
A PTC composition according to claim 22 wherein the conductive particles are carbon black particles having a size of 22 to 80 millimicrons.
Claim 29
Dependent Claim
137 words
A PTC composition comprising: (1) a cross-linked polymer which has been cross-linked by means of radiation; and (2) conductive particles enclosed within the cross-linked network of said polymer, the particles having a size of at least 18 millimicrons; which composition (a) has a gel fraction of at least 0.6; (b) exhibits PTC behavior with an R 14 value of at least 2.5 or an R 100 value of at least 10, and at least one T s which is within the temperature range of -100° to 250° C., subject to the proviso that, in the case of a cross-linked crystalline polymer, the composition has a T s which is above the T s of the composition prior to cross-linking; and (c) has a volume resistivity at temperatures below said T s between 25 and 10 5 ohm·cm.
Claim 30
Dependent Claim
137 words
A PTC composition comprising: (1) a cross-linked polymer which has been cross-linked by means of radiation; and (2) conductive particles enclosed within the cross-linked network of said polymer, the particles having a size of at least 18 millimicrons; which composition (a) has a gel fraction of at least 0.6; (b) exhibits PTC behavior with an R 14 value of at least 2.5 or an R 100 value of at least 10, and at least one T s which is within the temperature range of -100° to 250° C., subject to the proviso that, in the case of a cross-linked crystalline polymer, the composition has a T s which is above the T s of the composition prior to cross-linking; and (c) has a volume resistivity at temperatures below said T s between 25 and 10 5 ohm·cm.
Claim 31
Dependent Claim
15 words
A PTC composition according to claim 25 wherein the said cross-linked polymer is an elastomer.
Claim 32
Dependent Claim
16 words
A PTC composition according to claim 25 which exhibits PTC behavior in two distinct temperature ranges.
Claim 33
Dependent Claim
51 words
A PTC composition according to claim 25 whose T s remains substantially unchanged when repeatedly subjected to thermal cycling which comprises heating the composition from a temperature below T s to a temperature above T s but below the peak temperature, followed by cooling to a temperature below T s .
Claim 34
Dependent Claim
23 words
A PTC composition according to claim 25 wherein the conductive particles are carbon black particles having a size of 22 to 80 millimicrons.
Claim 35
Dependent Claim
29 words
A PTC composition according to claim 29 wherein the cross-linked polymer is an elastomer and the composition further comprises non-conductive particles enclosed with the cross-linked network of the polymer.
Claim 36
Dependent Claim
19 words
A PTC composition according to claim 30 wherein the polymer is a polysiloxane and the non-conductive filler is silica.
Claim 37
Dependent Claim
34 words
A PTC composition according to claim 26 wherein the elastomer is a polysiloxane and the conductive filler is a carbon black selected from the gruop consisting of furnace blacks, thermal blacks and channel blacks.
Claim 38
Dependent Claim
17 words
A PTC composition according to claim 25 wherein the cross-linked polymer contains less than 5% carbon-carbon unsaturation.
Claim 39
Dependent Claim
15 words
A PTC composition according to claim 25 wherein the polymer is a cross-linked thermoplastic elastomer.
Claim 40
Independent Claim
183 words
A method for the preparation of a PTC composition which comprises: (1) dispersing conductive particles having a size of at least 18 millimicrons in a polymer which comprises an amorphous polymer having a tensile stress of at least 10 psi at 20% elongation; (2) heating the dispersion from step (1) to an elevated temperature; (3) maintaining the dispersion at the elevated temperature for a time such that the amorphous polymer molecules assume a substantially unstrained configuration; and (4) cross-linking the equilibrated dispersion from step (3) to obtain a composition which has a gel fraction of at least 0.6 and which comprises the conductive particles enclosed within a cross-linked network of the amorphous polymer; the particles, the polymer, and the cross-linking conditions being such that the cross-linked composition (a) exhibits PTC behavior with an R 14 value of at least 2.5 or an R 100 value of at least 10, and at least one T s within the temperature range of -100° C. to +250° C.; and (b) has a volume resistivity at a temperature below T s of 25 to 10 5 ohm·cm.
Claim 41
Independent Claim
183 words
A method for the preparation of a PTC composition which comprises: (1) dispersing conductive particles having a size of at least 18 millimicrons in a polymer which comprises an amorphous polymer having a tensile stress of at least 10 psi at 20% elongation; (2) heating the dispersion from step (1) to an elevated temperature; (3) maintaining the dispersion at the elevated temperature for a time such that the amorphous polymer molecules assume a substantially unstrained configuration; and (4) cross-linking the equilibrated dispersion from step (3) to obtain a composition which has a gel fraction of at least 0.6 and which comprises the conductive particles enclosed within a cross-linked network of the amorphous polymer; the particles, the polymer, and the cross-linking conditions being such that the cross-linked composition (a) exhibits PTC behavior with an R 14 value of at least 2.5 or an R 100 value of at least 10, and at least one T s within the temperature range of -100° C. to +250° C.; and (b) has a volume resistivity at a temperature below T s of 25 to 10 5 ohm·cm.
Claim 42
Dependent Claim
13 words
A method according to claim 35 wherein the polymer is an elastomer gum.
Claim 43
Dependent Claim
23 words
A method according to claim 35 wherein the polymer is maintained at the elevated temperature for at least 0.5 minute prior to cross-linking.
Claim 44
Dependent Claim
13 words
A method according to claim 35 wherein the polymer is cross-linked by irradiation.
Claim 45
Dependent Claim
19 words
A method according to claim 35 wherein the polymer is cross-linked with the adi of a chemical cross-linking agent.
Claim 46
Dependent Claim
23 words
A method according to claim 35 wherein the conductive filler is a carbon black having a particle size of at least 20 millimicrons.
Claim 47
Dependent Claim
31 words
A method according to claim 35 wherein the elevated temperature is above 100° C. and the conductive filler is a carbon black having a particle size of at least 30 millimicrons.
Claim 48
Dependent Claim
31 words
A method according to claim 35 wherein the elevated temperature is above 150° C. and the conductive filler is a carbon black having a particle size of at least 40 millimicrons.
Claim 49
Dependent Claim
14 words
A method according to claim 35 wherein the conductive filler is a metal powder.
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