A flexible sheet of positive temperature coefficient (PTC) material formed of a polymer resin and a conductive filler, the sheet of PTC material having a thickness in a range of 10 μm to 100 μm. A method for forming the flexible sheet of positive temperature coefficient material may include preparing a PTC ink from a polymer resin, a conductive filler, and a solvent, applying the PTC ink to a substrate, pulling a blade over the PTC ink to create a uniformly thick layer of the PTC ink on the substrate, and allowing the PTC ink to dry so that the solvent evaporates and leaves a solid layer of PTC material on the substrate.

A positive temperature coefficient component includes: a substrate (32); a conductive ink (36) disposed over at least a portion of the substrate (32); a positive temperature coefficient layer (38) disposed over at least a portion of the substrate (32) and/or the conductive ink (36); and a topcoat layer (42) formed from a coating composition including a dielectric material disposed over at least a portion of the positive temperature coefficient layer (38) and/or the conductive ink (36).

A radial-leaded over-current protection device comprises a PTC element, a first electrode lead, a second electrode lead and an electrically insulating encapsulation layer. The PTC element comprises a first conductive layer, a second conductive layer and a PTC material layer laminated therebetween. The PTC material layer comprises crystalline polymer and conductive filler dispersed therein. The first electrode lead has an end connecting to the first conductive layer, whereas the second electrode lead has an end connecting to the second conductive layer. The electrically insulating encapsulation layer includes a fluorine-containing polymer, and wraps around an entire outer surface of the PTC element and the ends of the first and second electrodes connecting to the PTC element. The electrically insulating encapsulation layer has a thickness of 10.sup.2˜10.sup.5 nm, and the radial-leaded over-current protection device has an initial resistance R.sub.bf of 0.0017˜0.0027Ω.

A radial-leaded over-current protection device comprises a PTC element, a first electrode lead, a second electrode lead and an electrically insulating encapsulation layer. The PTC element comprises a first conductive layer, a second conductive layer and a PTC material layer laminated therebetween. The PTC material layer comprises crystalline polymer and conductive filler dispersed therein. The first electrode lead has an end connecting to the first conductive layer, whereas the second electrode lead has an end connecting to the second conductive layer. The electrically insulating encapsulation layer includes a fluorine-containing polymer, and wraps around an entire outer surface of the PTC element and the ends of the first and second electrodes connecting to the PTC element. The electrically insulating encapsulation layer has a thickness of 10.sup.2˜10.sup.5 nm, and the radial-leaded over-current protection device has an initial resistance R.sub.bf of 0.0017˜0.0027Ω.

An over-current protection device comprises first and second electrode layers and a PTC material layer laminated therebetween. The PTC material layer comprises a polymer matrix and carbon black. The polymer matrix comprises a fluoropolymer having a melting point higher than 150° C. The carbon black is dispersed in the polymer matrix. A resistance jump R.sub.jump_1000@16V/50A of the over-current protection device at 16V/50 A by 1000 cycles is 0.80-1.20. A resistance jump R.sub.1000@16V/50A of the over-current protection device at 25V/50 A by 1000 cycles is 0.90-1.30.

A surface-mountable over-current protection device comprises at least one PTC material layer, a first conductive layer, a second conductive layer, a first electrode, a second electrode, an insulating layer, and a cover layer. The PTC material layer comprises crystalline polymer and conductive fillers dispersed therein. The first conductive layer and the second conductive layer are disposed on a first surface and a second surface of the PTC material layer, respectively. The first electrode and the second electrode are electrically connected to the first conductive layer and the second conductive layer, respectively. The insulating layer is disposed between the first electrode and the second electrode for insulation. The cover layer includes a fluorine-containing polymer, and wraps around an entire outer surface of the surface-mountable over-current protection device.

An over-current protection device comprises first and second electrode layers and a PTC material layer laminated therebetween. The PTC material layer comprises a polymer matrix, a conductive ceramic filler, a carbon- containing conductive filler, and an inner filler. The polymer matrix comprises a fluoropolymer having a melting point higher than 150° C. The inner filler is selected from one of aluminum nitride, silicon carbide, zirconium oxide, boron nitride, graphene, aluminum oxide, or any mixtures thereof, and comprises 2-10% by volume of the PTC material layer. The over-current protection device is able to mitigate negative temperature coefficient (NTC) behavior after trip of device, and achieves high hold current and high endurable power.

An over-current protection device comprises first and second electrode layers and a PTC material layer laminated therebetween. The PTC material layer comprises a polymer matrix and carbon black. The polymer matrix comprises a fluoropolymer having a melting point higher than 150° C. The carbon black is dispersed in the polymer matrix. A resistance jump R.sub.jump_1000@16V/50A of the over-current protection device at 16V/50 A by 1000 cycles is 0.80-1.20. A resistance jump R.sub.jump_1000@25V/50A of the over-current protection device at 25V/50 A by 1000 cycles is 0.90-1.30.

A composite circuit protection device includes: a first positive temperature coefficient (PTC) component; a first voltage-dependent resistor (VOR); a second VOR; and a plurality of conductive leads that correspondingly connect to the first PTC component, the first VOR and the second VOR. The second VOR and the first PTC component are electrically connected in series, the first VOR and the second VOR are electrically connected in parallel, the first PTC component and the first VOR are electrically connected in parallel, and the first VOR has a varistor voltage greater than that of the second VOR as determined at 1 mA.

A co-continuous mouldable polymeric composite with PTC effect has a matrix that comprises at least two immiscible polymers (HDPE, POM), and an electrically conductive filler (CB) in the matrix. At least one of said immiscible polymers is high-density polyethylene (HDPE), and at least one other of said immiscible polymers is polyoxymethylene (POM).