Conductive polymer compositions and devices

Claim 2

A conductive polymer composition which exhibits PTC behavior with a switching temperature T s and which comprises: (1) an organic polymeric material which comprises a crystalline, thermoplastic polymer, and (2) dispersed in said polymeric material a filler component which comprises (a) at least about 10% by volume, based on the total volume of the composition of a first conductive particulate filler which has a first particle size D 1 from 0.01 to 200 microns and which consists of a metal having a resistivity at 25° C. of less than 10 -3 ohm. cm; and (b) at least 4% by volume, based on the total volume of the composition, of a second particulate filler which has a second average particle size D 2 from 0.001 to 50 microns and which is composed of non-metallic material; said composition having a resistivity at 25° C., ρ 25 , of less than 10 5 ohm-cm and a resistivity at a temperature in the range T s to (T s +100)°C. which is at least 1000×ρ 25 .

Claim 3

A composition in accordance with claim 1 wherein ρ 25 is less than 10 ohm.cm.

Claim 4

A composition in accordance with claim 1 wherein said composition has a volume resistivity of less than 1 ohm-cm at a temperature in the range of from about -40° C. to T s , where T s is the switching temperature of the composition.

Claim 5

A composition in accordance with claim 1 wherein ρ 25 is less than 0.1 ohm.cm.

Claim 6

A composition in accordance with claim 1 which has a resistivity at a temperature in the range of T s to (T s +100)°C. which is at least 10,000×ρ 25 .

Claim 7

A composition in accordance with claim 1 wherein the first particulate filler is composed of a metal selected from the group consisting of nickel, tungsten, molybdenum, iron, chromium, aluminum, copper, silver, gold, platinum, tantalum, zinc, cobalt, brass, tin, titanium and nichrome.

Claim 8

A composition in accordance with claim 1 wherein the first particulate filler is composed of a metal selected from the group consisting of nickel, tungsten and molybdenum.

Claim 9

A composition in accordance with claim 1 wherein the first particulate filler is composed of nickel.

Claim 10

A composition in accordance with claim 1 wherein D 1 is 0.01 to 25 microns.

Claim 11

A composition in accordance with claim 9 wherein D 1 is 0.02 to 25 microns.

Claim 12

A composition in accordance with claim 10 wherein D 1 is 0.5 to 5 microns.

Claim 13

A composition in accordance with claim 11 wherein D 1 is 0.5 to 2 microns.

Claim 14

A composition in accordance with claim 1 wherein the first particulate filler is present in an amount from 10 to 60 volume %, based on the total volume of the composition.

Claim 15

A composition in accordance with claim 13 wherein the first particulate filler is present in an amount from 30 to 60 volume % based on the total volume of the composition.

Claim 16

A composition in accordance with claim 1 wherein the second particulate filler is composed of a non-metallic conductive material.

Claim 17

A composition in accordance with claim 1 wherein the second particulate filler is a carbon black.

Claim 18

A composition in accordance with claim 1 wherein the second particulate filler is a graphite.

Claim 19

A composition in accordance with claim 1 wherein the second particulate filler is composed of non-conductive particles.

Claim 20

A composition in accordance with claim 1 wherein D 2 is substantially less than D 1 .

Claim 21

A composition in accordance with claim 1 wherein D 2 is substantially less than D 1 .

Claim 22

A composition in accordance with claim 1 wherein D 2 is 0.001 to 50 microns.

Claim 23

A composition in accordance with claim 1 wherein D 2 is 0.01 to 5 microns.

Claim 24

A composition in accordance with claim 1 wherein the second particulate filler is present in an amount from 4 to 50 volume %, based on the total volume of the composition.

Claim 25

A composition in accordance with claim 23 wherein the second particulate filler is present in an amount from 6 to 25 volume %, based on the total volume of the composition.

Claim 26

A composition in accordance with claim 1 wherein said thermoplastic polymer is selected from the group consisting of polyethylene, polypropylene, copolymers of ethylene with ethyl acrylate or acrylic acid, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymers and mixtures thereof.

Claim 27

A composition in accordance with claim 1 wherein said polymeric material is cross-linked.

Claim 28

A composition in accordance with claim 1 wherein said polymeric material comprises elastomeric gum.

Claim 29

A composition in accordance with claim 27 wherein said polymeric material comprises a silicone rubber.

Claim 30

An electrical device which comprises at least one electrode in electrical contact with a conductive polymer composition in accordance with claim 1.

Claim 31

An electrical device in accordance with claim 29 wherein said device is a heater.

Claim 32

A current limiting device which comprises two electrodes in contact with a conductive polymer composition in accordance with claim 1.

Claim 33

An electromagnetic interference shield comprising a conductive polymer composition in accordance with claim 1.

Claim 34

A composition according to claim 19 wherein D 1 is 100 to 1000 times D 2 .

Claim 35

A conductive polymer composition which exhibits PTC behavior with a switching temperature T s and which comprises (1) an organic polymeric material which comprises a crystalline thermoplastic polymer, and (2) dispersed in said polymeric material, a filler component which comprises (a) at least 10% by volume, based on the total volume of the composition, of a first conductive particulate filler which has a first average particle size, D 1 , from 0.01 to 200 microns and which consists of a metal having a resistivity at 25° C. of less than 10 -3 ohm.cm; and (b) at least 4% by volume, based on the total volume of the composition, of a second conductive particulate filler which (i) has a second average particle size D 2 , which is less than 0.5×D 1 and is from 0.001 to 50 microns and (ii) consists of a metal having a resistivity at 25° C. of less than 10 -3 ohm.cm; the composition having a resistivity at 25° C., ρ 25 , of less than 10 5 ohm.cm and a resistivity at a temperature in the range T s to (T s +100)°C. which is at least 1000×ρ 25 .

Claim 36

A conductive polymer composition which exhibits PTC behavior with a switching temperature T s and which comprises (1) an organic polymeric material which comprises a crystalline thermoplastic polymer, and (2) dispersed in said polymeric material, a filler component which comprises (a) at least 10% by volume, based on the total volume of the composition, of a first conductive particulate filler which has a first average particle size, D 1 , from 0.01 to 200 microns and which consists of a metal having a resistivity at 25° C. of less than 10 -3 ohm.cm; and (b) at least 4% by volume, based on the total volume of the composition, of a second conductive particulate filler which (i) has a second average particle size D 2 , which is less than 0.5×D 1 and is from 0.001 to 50 microns and (ii) consists of a metal having a resistivity at 25° C. of less than 10 -3 ohm.cm; the composition having a resistivity at 25° C., ρ 25 , of less than 10 5 ohm.cm and a resistivity at a temperature in the range T s to (T s +100)°C. which is at least 1000×ρ 25 .

Claim 37

A composition according to claim 34 wherein the first and second fillers are composed of different metals.

Claim 38

A composition according to claim 34 wherein D 1 is from 10 to 5,000 times D 2 .

Claim 39

A composition according to claim 36 wherein D 1 is from 100 to 1,000 times D 2 .

Claim 40

A composition according to claim 34 wherein the first and second particulate fillers are composed of a metal selected from the group consisting of nickel, tungsten, molybdenum, iron, chromium, aluminum, copper, silver, gold, platinum, tantalum, zinc, cobalt, brass, tin, titanium and nichrome.

Claim 41

A composition according to claim 38 wherein at least one of the particulate fillers is composed of a metal selected from the group consisting of nickel, tungsten and molybdenum.

Claim 42

A composition according to claim 34 wherein ρ 25 is less than 10 ohm.cm.

Claim 43

A composition according to claim 34 wherein ρ 25 is less than 0.1 ohm.cm.

Claim 44

A composition according to claim 34 which has a resistivity in the temperature range T s to (T s 100)°C. which is at least 10,000 times ρ 25 .

Claim 45

A composition according to claim 34 wherein D 1 is from 0.1 to 25 microns.

Claim 46

A composition according to claim 43 wherein D 1 is from 0.5 to 5 microns.

Claim 47

A composition according to claim 34 which contains 30 to 60% by volume of the first filler and 6 to 25% by volume of the second filler.

Claim 48

A composition in accordance with claim 6 wherein the second particulate filler is selected from the group consisting of carbon black and graphite.

Claim 49

A composition in accordance with claim 6 wherein the second particulate filler is selected from the group consisting of alumina trihydrate, silica, glass beads and zinc sulfide.

Claim 50

A composition according to claim 34 wherein the organic polymeric material also comprises an elastomer.

Claim 51

A composition according to claim 1 wherein the organic polymeric material also comprises an elastomer.