PTC Compositions and devices comprising them
First Claim
1. 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 (Tc1) and(3) further cross-linking the cross-linked composition from step (2) at a second temperature (Tc2) which is substantially different from Tc1the composition obtained in step (3) having a gel fraction of at least 0.6;
exhibiting PTC behavior with an R14 value of at least 2.5 or a R100 value of at least 10 and at least one Ts within the temperature range of -100 to 250°
C.; and
having a volume resistivity at temperatures below Ts of 25 to 105 ohm·
cm.
1 Assignment
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Accused Products
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.
104 Citations
43 Claims
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1. 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 (Tc1) and (3) further cross-linking the cross-linked composition from step (2) at a second temperature (Tc2) which is substantially different from Tc1 the composition obtained in step (3) having a gel fraction of at least 0.6;
exhibiting PTC behavior with an R14 value of at least 2.5 or a R100 value of at least 10 and at least one Ts within the temperature range of -100 to 250°
C.; and
having a volume resistivity at temperatures below Ts of 25 to 105 ohm·
cm. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A process for the preparation of a PTC composition which comprises:
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(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 R14 value of at least 2.5 or an R100 value of at least 10 and at least one Ts within the range of -100°
C. to +250°
C., and has a volume resistivity at temperatures below Ts of 25 to 105 ohm·
cm. - View Dependent Claims (16, 17, 18)
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19. A PTC composition comprising:
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(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 R14 value of at least 2.5 or an R100 value of at least 10, and a Ts which is within the temperature range of -100°
to +250°
C. and the Ts is one of the temperature ranges being above the Ts of the composition prior to cross-linking; and(c) has a volume resistivity at a temperature below each Ts of 25 to 105 ohm·
cm. - View Dependent Claims (20, 21)
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22. A PTC composition comprising:
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(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 R14 value of at least 2.5 or an R100 value of at least 10, and at least one Ts which is within the temperature range of -100°
to 250°
C.; and(c) has a volume resistivity at temperatures below said Ts between 25 and 105 ohm·
cm. - View Dependent Claims (23, 24)
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25. A PTC composition comprising:
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(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 R14 value of at least 2.5 or an R100 value of at least 10, and at least one Ts 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 Ts which is above the Ts of the composition prior to cross-linking; and(c) has a volume resistivity at temperatures below said Ts between 25 and 105 ohm·
cm. - View Dependent Claims (26, 27, 28, 29, 30, 31, 32, 33, 34)
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35. A method for the preparation of a PTC composition which comprises:
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(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 R14 value of at least 2.5 or an R100 value of at least 10, and at least one Ts within the temperature range of -100°
C. to +250°
C.; and(b) has a volume resistivity at a temperature below Ts of 25 to 105 ohm·
cm. - View Dependent Claims (36, 37, 38, 39, 40, 41, 42, 43)
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Specification