Abstract Conductive polymer having a steeply-sloped positive temperature coefficient (PTC) of resistance with a sharply defined anomaly temperature is provided by selecting a polymer having crystalline structure at room temperature, a glass transition of approximately 13*F. or lower and a narrow molecular weight distribution as measured by a flow ratio of less than 9 or a melting point range of 30* C. or less. The polymer is filled with conductive particles and may include additional additives such as stabilizing agents and flame retardants. The ingredients are mixed, subjected to shearing forces and then formed into the desired configuration. The maximum permissible processing temperature is identified for the specific polymers employed.
The method according to claim 1 in which the temperature of the mix is maintained below the oxygen pick up temperature for the polymer employed.
Claim 2
Dependent Claim
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The method according to claim 1 further including providing a sharp transition between the resistance level at a temperature below the anomaly and the steeply sloped portion of the resistance temperature curve at temperatures above the anomaly by choosing a polymer having a narrow molecular weight distribution.
Claim 3
Dependent Claim
18 words
The method according to claim 3 in which the polymer has a flow ratio of less than 9.
Claim 4
Dependent Claim
19 words
The method according to claim 3 in which the polymer has a melting temperature range within approximately 30* Centigrade.
Claim 5
Dependent Claim
21 words
The method according to claim 1 in which the conductive filler is carbon black from 14 to 20 percent by weight.
Claim 6
Dependent Claim
37 words
The method according to claim 1 in which the polymer is selected from the group consisting of high density polyethylene, low density polyethylene, polypropylene, polyethylene oxide, trans 4 polybutadiene and a mixture of polyethylene and polyethyl acrylate.
Claim 7
Dependent Claim
23 words
The method according to claim 1 in which the conductive particles are selected from the group consisting of carbon, tin, silver and gold.
Claim 8
Dependent Claim
33 words
The method according to claim 7 in which the approximate maximum processing temperatures for the group of polymers are 350* F., 320* F., 420* F., 190* F., 300* F. and 350* F. respectively.