Polymer Thick Film Positive Temperature Coefficient Carbon Resistor Composition
A polymer thick film positive temperature coefficient carbon resistor composition is provided. The composition includes an organic medium including a fluoropolymer resin and an organic solvent The composition includes a conductive carbon powder. The composition exhibits a resistivity of at least 65,000 ohm/sq/25 μm when dried for a time of about 1 minute to about 24 hours at a temperature of about 90° C. to about 210° C. Methods for forming a positive temperature coefficient circuit are also provided.
1 . A polymer thick film positive temperature coefficient carbon resistor composition, comprising:
an organic medium comprising a fluoropolymer resin and an organic solvent; and
conductive carbon powder;
wherein the composition exhibits a resistivity of at least 65,000 ohm/sq/25 μm when dried for a time of about 1 minute to about 24 hours at a temperature of about 90° C. to about 210° C.
2 . The composition of claim 1 , wherein the composition exhibits a resistivity of at least 100,000 ohm/sq/25 μm up to about 1,000,000 ohm/sq/25 μm.
3 . The composition of claim 1 , wherein the composition exhibits a resistivity of at least about 250,000 ohm/sq/25 μm to about 800,000 ohm/sq/25 μm.
4 . The composition of claim 1 , wherein the fluoropolymer resin comprises a copolymer of vinylidene difluoride and hexafluoropropylene.
5 . The composition of claim 1 , wherein the organic solvent comprises one or more trialkyl phosphates, tetraethyl urea, or a combination thereof.
6 . The composition of claim 5 , wherein a ratio of the trialkyl phosphate to the tetraethyl urea is about 5:1 to about 12:1.
7 . The composition of claim 1 , wherein the conductive powder comprises an oxidized carbon black.
8 . The composition of claim 7 , wherein the oxidized carbon black has a total oxygen content of at least about 0.1 wt. % to about 15 wt. % based on the total weight of the oxidized carbon black as determined by inert gas fusion.
9 . The composition of claim 7 , wherein the oxidized carbon black has a BET surface area of about 5 m 2 /g to about 1500 m 2 /g as determined in accordance with ASTM-D6556.
10 . The composition of claim 7 , wherein the oxidized carbon black has an oil absorption number (OAN) ranging from 35 cm 3 /100 g to 500 cm 3 /100 g as determined in accordance with ASTM-D2414.
11 . The composition of claim 7 , wherein the oxidized carbon black has a volatile content ranging from about 0.1 wt. % to about 25 wt. % relative to the total weight of the oxidized carbon black, as determined by weight loss at 950° C.
12 . The composition of claim 1 , wherein the conductive carbon powder is present in an amount of about 2 wt. % to about 20 wt. %.
13 . A positive temperature coefficient circuit comprising the polymer thick film positive temperature coefficient carbon resistor composition of claim 1 , wherein the polymer thick film positive temperature coefficient carbon resistor composition has been dried to remove the organic solvent.
14 . The positive temperature coefficient circuit of claim 13 , wherein the composition exhibits a resistivity of at least 250,000 ohm/sq/25 μm up to about 1,000,000 ohm/sq/25 μm.
15 . The positive temperature coefficient circuit of claim 13 , wherein the composition exhibits a resistivity of at least 500,000 ohm/sq/25 μm up to about 1,000,000 ohm/sq/25 μm.
16 . The positive temperature coefficient circuit of claim 13 , wherein the fluoropolymer resin comprises a copolymer of vinylidene difluoride and hexafluoropropylene.
17 . The positive temperature coefficient circuit of claim 13 , wherein the oxidized carbon powder comprises an oxidized carbon black.
18 . The positive temperature coefficient circuit of claim 17 , wherein the oxidized carbon black has at least one of the following:
(a) a total oxygen content of at least about 0.1 wt. % to about 15 wt. % based on the total weight of the oxidized carbon black as determined by inert gas fusion;
(b) a BET surface area of about 5 m 2 /g to about 1500 m 2 /g as determined in accordance with ASTM-D6556;
(c) an oil absorption number (OAN) ranging from 35 cm 3 /100 g to 500 cm 3 /100 g as determined in accordance with ASTM-D2414; or
(d) has a surface area ranging from about 5 m 2 /g to about 750 m 2 /g.
19 . An article comprising the positive temperature coefficient circuit of claim 13 .
20 . A method for forming a PTC circuit, the method comprising:
depositing a polymer thick film positive temperature coefficient carbon resistor composition on a substrate, the polymer thick film positive temperature coefficient carbon resistor composition comprising an organic medium comprising a fluoropolymer resin and an organic solvent, and an oxidized carbon black, the oxidized carbon black comprising at least one of the following:
(a) a total oxygen content of at least about 0.1 wt. % to about 15 wt. % based on the total weight of the oxidized carbon black as determined by inert gas fusion;
(b) a BET surface area of about 5 m 2 /g to about 1500 m 2 /g as determined in accordance with ASTM-D6556;
(c) an oil absorption number (OAN) ranging from 35 cm 3 /100 g to 500 cm 3 /100 g as determined in accordance with ASTM-D2414; or
(d) has a surface area ranging from about 5 m 2 /g to about 750 m 2 /g; and
drying the positive temperature coefficient composition for a time of about 1 minute to about 60 minutes at a temperature of about 90° C. to about 210° C. to form a positive temperature coefficient circuit on the substrate, wherein the positive temperature coefficient circuit has a resistivity of at least 65,000 ohm/sq/25 μm.