Conductive polymeric composite material with a resistance which is self-regulated by the temperature

Abstract

The present invention relates to a composite material comprising, by weight, the total being 100% : A) 40 to 90% of PVDF homopolymer or copolymer crystallized essentially in the β form, B) 10 to 60% of a conductive filler, C) 0 to 40% of a crystalline or semi-crystalline polymer, D) 0 to 40% of a filler other than C, such that the crystals in the β form are nucleated on the surface of the particles of the conductive filler. This material is conductive with a resistance which is self-regulated by the temperature. It shows an increase in the resistance as a function of the temperature (PTC or “Positive Temperature Coefficient” effect), so that the intensity stabilizes at an equilibrium temperature.

1 . Composite material comprising, by weight, the total being 100%: 
 A) 40 to 90% of polyvinyl difluoride (PVDF) homopolymer or copolymer crystallized sufficiently in the β form to provide the components with a positive temperature coefficient (PTC) effect,    B) 10 to 60% of a conductive filler,    C) 0 to 40% of a crystalline or semi-crystalline polymer,    D) 0 to 40% of a filler other than (C),    such that the crystals in the β form are nucleated on the surface of the particles of the conductive filler.    
     
     
         2 . Material according to  claim 1 , in which (A) is chosen from copolymers of vinylidene difluoride (VF2) and trifluoroethylene (VF3) having at least 60 mol % of VF2.  
     
     
         3 . Material according to  claim 1 , in which (A) is chosen from copolymers of VF2 tetrafluoroethylene (TFE) and hexafluoropropylene (HFP) having at least 15 mol % of TFE units.  
     
     
         4 . Material according to  claim 3 , in which (A) is chosen from VF2-TFE-HFP copolymers with the respective molar composition 60 to 80/ 15 to 20/0 to 25.  
     
     
         5 . Material according to  claim 1 , comprising (C), in which (C) comprises a PVDF homopolymer which is not in the β form or a VF2-HFP copolymer comprising at least 85% of VF2.  
     
     
         6 . A heating device comprising the composite material according to  claim 1 .  
     
     
         7 . Material according to  claim 1 , comprising (C).  
     
     
         8 . Material according to  claim 1 , wherein the conductive filler (B) comprises a metal powder, carbon black, graphite or a metal oxide.  
     
     
         9 . Material according to  claim 8 , wherein the conductive filler (B) comprises graphite.  
     
     
         10 . Material according to  claim 5 , wherein the conductive filler (B) comprises a metal powder, carbon black, graphite or a metal oxide.  
     
     
         11 . Material according to  claim 2 , comprising (C), in which (C) comprises a PVDF homopolymer which is not in the β form or a VF2-HFP copolymer comprising at least 85% of VF2.  
     
     
         12 . Material according to  claim 3 , comprising (C), in which (C) comprises a PVDF homopolymer which is not in the β form or a VF2-HFP copolymer comprising at least 85% of VF2.  
     
     
         13 . Material according to  claim 1 , wherein (A) comprises at least 60% of the β form.  
     
     
         14 . Material according to  claim 1 , wherein (A) comprises at least 75% of the β form.  
     
     
         15 . Material according to  claim 10 , comprising (D) wherein (D) comprises at least one of silica, polymethyl methacrylate and a UV inhibitor.  
     
     
         16 . An article comprising an insulating surface coated with a coating of the composite material according to  claim 1 .  
     
     
         17 . An article according to  claim 16 , wherein the insulating surface is a ceramic.  
     
     
         18 . A paint comprising a solvent dispersion of the composite material according to  claim 1 .  
     
     
         19 . A process of producing the article according to  claim 16 , comprising applying the coating as a melt of the composite material to the insulating surface.  
     
     
         20 . A process of producing the article according to  claim 16 , comprising applying the coating as a solvent dispersion of the composite material to the insulating surface.