Positive temperature coefficient materials with reduced negative temperature coefficient effect
View Patent ↗Positive temperature coefficient (PTC) compositions having a reduced negative temperature coefficient effect (NTC) are provided that are achieved without crosslinking the thermoplastic base material. The PTC compositions include a thermoplastic base resin, an electrically conductive filler and particles of a polymeric additive dispersed in the PTC composition.
1. A positive temperature coefficient composition comprising:
a) from 20 to 90% by weight of a thermoplastic polymer;
b) from 10 to 60% by weight of at least one conductive filler; and
c) from 0.1 to 20% by weight of a particulate polymer additive having monomer units of <50,000;
wherein the polymer additive has a melting or softening temperature greater than the melting temperature of the thermoplastic polymer;
wherein the particulate polymer additive is dispersed in the positive temperature coefficient composition.
2. The positive temperature coefficient composition of claim 1 wherein the thermoplastic polymer is selected from high-density polyethylene, linear low-density polyethylene, low-density polyethylene, mid-density polyethylene, maleic anhydride functionalized polyethylene, a maleic anhydride functionalized elastomeric ethylene copolymer, an ethylene-butene copolymer, an ethylene-octene copolymer, an ethylene-acrylate copolymer, glycidyl methacrylate modified polyethylene, polypropylene, maleic anhydride functionalized polypropylene, glycidyl methacrylate modified polypropylene, polyvinyl chloride, polyvinyl acetate, polyvinyl acetyl, acrylic resin, syndiotactic polystyrene, polyphenylene-sulfide, polyamideimide, polyimide, polyetheretherketone, polyetherketone, polyethylene vinyl acetate, glycidyl methacrylate modified polyethylene vinyl acetate, polyvinylalcohol, polyisobutylene, poly(vinylidene chloride), poly(vinylidene fluoride), poly(methylacrylate), polyacrylonitrile, polybutadiene, polyesters, polyethylene-terephthalate, polybutylene-terephthalate, poly(8-aminocaprylic acid), poly(vinyl alcohol), polycaprolactone, polyamides or blends or a combination including at least one of the forgoing polymers.
3. The positive temperature coefficient composition of claim 2 , wherein the polyamide is selected from PA11, PA12, PA6, PA6.6, PA 6.10, polyphthalamide, high temperature nylon or blends or a combination including at least one of the forgoing polyamides.
4. The positive temperature coefficient composition of claim 1 wherein the conductive filler is selected from a ceramic filler, a metallic filler, a carbon-containing filler or a combination including at least one of the foregoing fillers.
5. The positive temperature coefficient composition of claim 1 wherein the polymer additive comprises a polyamide polymer.
6. The positive temperature coefficient composition of claim 1 , wherein the thermoplastic polymer comprises a polyolefin, wherein the conductive filler comprises carbon black and wherein the polymer additive comprises a polyamide.
7. An article of manufacture comprising the composition of claim 1 .
8. The positive temperature coefficient composition of claim 1 , wherein the composition has a reduced negative temperature coefficient (NTC) effect as compared to a composition without the polymer additive.
9. The positive temperature coefficient composition of claim 1 , wherein the composition comprises a compatibilizer.
10. A method of making a positive temperature coefficient composition comprising the steps of:
a) mixing from 10 to 60% by weight of at least one conductive filler with from 20 to 90% by weight of a thermoplastic polymer; and
b) dispersing from 0.1 to 20% by weight of a particulate polymer additive having monomer units of <50,000 into the positive temperature coefficient composition;
wherein the polymer additive has a softening or melting temperature greater than the melting temperature of the thermoplastic polymer; and
wherein the dispersed polymer additive is present substantially in particle form in the positive temperature coefficient composition.
11. The method of claim 10 , wherein the thermoplastic polymer comprises a polyolefin, wherein the conductive filler comprises carbon black and wherein the polymer additive comprises a polyamide.
12. The method of claim 10 , wherein the composition is injection moldable.
13. The method of claim 10 , comprising mixing a compatibilizer with the conductive filler and the thermoplastic polymer in step (a).