Conductive polymer composition
First Claim
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1. An electrical device which comprises(1) a PTC element comprising a conductive polymer composition which exhibits PTC behavior, which has a resistivity Rcp at 20°
- C. and which comprises(a) an organic polymer which has a crystallinity of at least 5% and a melting point Tm, and(b) carbon black which has a pH of less than 4.0; and
(2) two electrodes which can be connected to a source of electrical power to pass current through the PTC element,said electrical device having a resistance Ri at 20°
C. and being such that if the device is maintained at a temperature equal to Tm for a period of 50 hours and is then cooled to 20°
C., its resistance at 20°
C., Rf50, is from 0.25Ri to 1.75Ri.
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Abstract
Electrical devices with improved resistance stability comprise a PTC element comprising a conductive polymer and two electrodes. The conductive polymer composition comprises an organic crystalline polymer and carbon black with a pH of less than 5.0. Particularly preferred conductive polymer compositions comprise carbon blacks which have a pH of less than 5.0, a dry resistivity RCB and a particle size D in nanometers such that RCB /D is at most 0.1. Electrical devices of the invention include heaters and circuit protection devices.
57 Citations
19 Claims
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1. An electrical device which comprises
(1) a PTC element comprising a conductive polymer composition which exhibits PTC behavior, which has a resistivity Rcp at 20° - C. and which comprises
(a) an organic polymer which has a crystallinity of at least 5% and a melting point Tm, and (b) carbon black which has a pH of less than 4.0; and (2) two electrodes which can be connected to a source of electrical power to pass current through the PTC element, said electrical device having a resistance Ri at 20°
C. and being such that if the device is maintained at a temperature equal to Tm for a period of 50 hours and is then cooled to 20°
C., its resistance at 20°
C., Rf50, is from 0.25Ri to 1.75Ri. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
- C. and which comprises
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14. A conductive polymer composition which exhibits PTC behavior and which comprises
(1) an organic polymer which has a crystallinity of at least 5% and a melting point Tm, and (2) carbon black which has a pH of less than 4.0, a particle size of D nanometers and a dry resistivity RCB such that (RCB /D) is less than or equal to 0.1.
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17. An electrical device which comprises
(1) a PTC element comprising a conductive polymer composition which exhibits PTC behavior and which comprises (a) an organic polymer which has crystallinity of at least 5% and a melting point Tm, and (b) carbon black which has a pH of less than 4.0, a particle size of D nanometers and a dry resistivity RCB such that (RCB /D) is less than or equal to 0.1; - and
(2) two electrodes which can be connected to a source of electrical power to pass current through the PTC element. - View Dependent Claims (18, 19)
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Specification
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Current AssigneeLittelfuse Incorporated
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Original AssigneeRaychem Limited (TE Connectivity Limited)
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InventorsTrammell, Bernadette A., McCarty, Gordon, Straley, O. James, Shafe, Jeff, Oswal, Ravinder K.
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Primary Examiner(s)Envall, Jr., Roy N.
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Application NumberUS07/416,748Time in Patent Office448 DaysField of Search219/548, 219/549, 219/541, 219/553, 219/504, 219/505, 338/223, 338/327, 338/22 R, 338/306, 106/472US Class Current219/548CPC Class CodesH01C 7/027 consisting of conducting or...
