PPTC material with low percolation threshold for conductive filler
A polymeric positive temperature coefficient (PPTC) device including a PPTC body, a first electrode disposed on a first side of the PPTC body, and a second electrode disposed on a second side of the PPTC body, wherein the PPTC body is formed of a PPTC material that includes a polymer matrix and a conductive filler, wherein the conductive filler defines 20%-39% by volume of the PPTC material.
1. A polymeric positive temperature coefficient (PPTC) device, comprising:
a PPTC body;
a first electrode disposed on a first side of the PPTC body; and
a second electrode disposed on a second side of the PPTC body;
wherein the PPTC body is formed of a PPTC material that includes a polymer matrix and a conductive filler comprising tungsten carbide, the conductive filler further comprising a volume fraction parameter and a median diameter of conductive particles parameter such that PPTC material exhibits a resistivity of approximately 0.15 ohm-cm; wherein the volume fraction parameter and median diameter of conductive particles parameter are selected from a group consisting of:
27% volume fraction of conductive particles with a median diameter of 0.55 μm;
37% volume fraction of conductive particles with a median diameter of 1.0 μm;
39% volume fraction of conductive particles with a median diameter of 1.57 μm;
41.2% volume fraction of conductive particles with a median diameter of 2.15 μm;
42.5% volume fraction of conductive particles with a median diameter of 3.21 μm; and
45.5% volume fraction of conductive particles with a median diameter of 4.82 μm.
2. The PPTC device of claim 1 , wherein the PPTC material exhibits a hold current density of between 0.05 to 0.4A/mm 2 .
3. The PPTC device of claim 1 , wherein the polymer matrix includes at least one of a polyvinylidene fluoride (PVDF) polymer, an ethylene vinyl acetate (EVA) polymer, a high-density polyethylene (HDPE) polymer, an ethylene tetrafluoroethylene (ETFE) polymer, and a perfluoroalkoxy (PFA).
4. The PPTC device of claim 1 , wherein at least one of the first electrode and the second electrode is formed of copper foil.
5. The PPTC device of claim 4 , wherein the copper foil is plated with nickel.
6. A polymeric positive temperature coefficient (PPTC) material comprising:
a polymer matrix; and
a conductive filler comprising tungsten carbide, the conductive filler further comprising a volume fraction parameter and a median diameter of conductive particles parameter such that PPTC material exhibits a resistivity of approximately 0.15 ohm-cm; wherein the volume fraction parameter and median diameter of conductive particles parameter are selected from a group consisting of:
27% volume fraction of conductive particles with a median diameter of 0.55 μm;
37% volume fraction of conductive particles with a median diameter of 1.0 μm;
39% volume fraction of conductive particles with a median diameter of 1.57 μm;
41.2% volume fraction of conductive particles with a median diameter of 2.15 μm;
42.5% volume fraction of conductive particles with a median diameter of 3.21 μm; and
45.5% volume fraction of conductive particles with a median diameter of 4.82 μm.
7. The PPTC material of claim 6 , wherein the PPTC material exhibits a hold current density of between 0.05 to 0.4A/mm 2 .
8. The PPTC material of claim 6 , wherein the polymer matrix includes at least one of a polyvinylidene fluoride (PVDF) polymer, an ethylene vinyl acetate (EVA) polymer, a high-density polyethylene (HDPE) polymer, an ethylene tetrafluoroethylene (ETFE) polymer, and a perfluoroalkoxy (PFA).