PTC compositions and devices comprising them
First Claim
1. An electrical device which comprises two or more electrodes and a PTC composition in contact therewith, the PTC composition comprising:
- (1) a cross-linked elastomer prepared by cross-linking an elastomeric gum having a tensile stress of less than 10 psi at 20% elongation; and
(2) conductive particles enclosed with 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 within the temperature range from room temperature to +250°
C.; and
(c) has a volume resistivity at temperatures below said Ts between 25 and 105 ohm.cm.
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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.
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Citations
26 Claims
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1. An electrical device which comprises two or more electrodes and a PTC composition in contact therewith, the PTC composition comprising:
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(1) a cross-linked elastomer prepared by cross-linking an elastomeric gum having a tensile stress of less than 10 psi at 20% elongation; and (2) conductive particles enclosed with 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 within the temperature range from room temperature to +250°
C.; and(c) has a volume resistivity at temperatures below said Ts between 25 and 105 ohm.cm. - View Dependent Claims (2, 3, 4, 5, 6, 7, 11, 12)
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8. A PTC composition comprising:
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(1) a cross-linked elastomer prepared by cross-linking an elastomeric gum having a tensile stress of less than 10 psi at 20% elongation; 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 within the temperature range from room temperature to +250°
C.; and(c) has a volume resistivity at temperatures below said Ts between 25 and 105 ohm.cm. - View Dependent Claims (9, 10, 13, 14, 15, 16)
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17. 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 an elastomeric gum having a tensile stress of less than 10 psi at 20% elongation; and (2) cross-linking the dispersion from step (1) to obtain a composition which has a gel fraction of at least 0.6 and which comprises conductive particles enclosed with the elastomer resulting from said cross-linking; the particles, the elastomeric gum, 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 from room temperature to +250°
C.; and(b) has a volume resistivity at temperatures below Ts between 25 and 105 ohm.cm. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24, 25, 26)
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Specification