TWI643215B - Over-current protection device - Google Patents

Abstract

An overcurrent protection component includes a first electrode layer, a second electrode layer, and a layer of PTC material stacked therebetween. The PTC material layer has a volume resistance value of less than 0.05 Ω·cm and comprises a high molecular polymer substrate, a conductive ceramic filler, and a carbon-containing conductive filler. The high molecular polymer substrate comprises a fluorine-containing high molecular polymer having a melting point higher than 150 ° C, and its volume percentage is 50-60%. The conductive ceramic filler is dispersed in the high molecular polymer substrate, and has a volume percentage of 40-45% and a volume resistance value of less than 500 mΩ·cm. The carbon-containing conductive filler is dispersed in the polymer base material and has a volume percentage of 0.5 to 5%. The ratio of the sustain current to the area of the overcurrent protection element at 25 ° C is 0.21 to 0.3 A/mm ² . The ratio of the withstandtable power of the overcurrent protection element to its area at 25 ° C is 4.8 to 7.2 W/mm ² .

Description

Overcurrent protection component

The present invention relates to an overcurrent protection component, and more particularly to an overcurrent protection component having a high hold current characteristic.

Since the resistance of a conductive composite material having a positive temperature coefficient (PTC) characteristic is sensitive to temperature changes, it can be used as a material of a current sensing element, and has been widely used as an overcurrent protection element or circuit. On the component. Since the resistance of the PTC conductive composite at normal temperatures can be maintained at a very low value, the circuit or battery can operate normally. However, when an over-current over-current phenomenon occurs in a circuit or a battery, the resistance value is instantaneously increased to a high-resistance state (at least 10 ⁴ Ω or more), which is called a trip. The excess current is reversed to offset the purpose of protecting the battery or circuit components.

Overcurrent protection components used in high temperature environments usually have to meet the following two characteristics: (1) The time to trip cannot be too fast, for example, greater than 2 seconds for a certain temperature, current and voltage; (2) It must be able to trigger at room temperature of 25 ° C and 12 amps. In general, the overcurrent protection elements are small in size, and conventional PTC elements using carbon black as a conductive filler are not easy to achieve the above requirements. Nickel powder has also been used as a conductive filler for testing. However, when nickel powder is mixed with a fluorine-containing polymer, hydrofluoric acid is easily generated at a high temperature, which is not suitable.

For example, an overcurrent protection component applied to a car is required to have good heat dissipation characteristics because it is often exposed to strong sunlight. Conventionally, a component using carbon black as a conductive filler has a high electrical resistance, a small hold current, and a disadvantage of easily generating heat. U.S. Patent No. 7,286,038 discloses the use of titanium carbide as a conductive filler to achieve a maximum current per unit area of 0.2 A/mm ² and a withstand voltage of about 15 V, but with a greater need to maintain current and withstand voltage.

In summary, it is necessary to increase the sustain current value and the withstand voltage characteristic of the overcurrent protection element, thereby providing a need for application in a high temperature environment.

The invention provides an overcurrent protection component, which can effectively increase the sustain current, heat dissipation efficiency and withstand voltage characteristics of the overcurrent protection component through introduction of the fluorine-containing polymer, the conductive ceramic filler and the carbon-containing conductive filler. The so-called holding current refers to the maximum withstand current that does not occur in the trigger. Thereby, the overcurrent protection element of the present invention can be applied to an environment in which an automobile or the like is liable to be at a high temperature.

In accordance with an embodiment of the invention, an overcurrent protection component includes a first electrode layer, a second electrode layer, and a layer of PTC material stacked therebetween. The PTC material layer has a volume resistance value of less than 0.05 Ω·cm, and the PTC material layer comprises a high molecular polymer substrate, a conductive ceramic filler, and a carbon-containing conductive filler. The polymer base material comprises a fluorine-containing polymer having a melting point higher than 150 ° C, and the volume percentage of the polymer substrate is 50-60%. The conductive ceramic filler is dispersed in the polymer base material, and the conductive ceramic filler has a volume percentage of 40-45% and a volume resistance value of less than 500 mΩ·cm. The carbon-containing conductive filler is dispersed in the polymer base material, and the volume percentage of the carbon-containing conductive filler is 0.5 to 5%. The ratio of the sustain current to the area of the overcurrent protection element at 25 ° C is 0.21 to 0.3 A/mm ² . The ratio of the withstandtable power of the overcurrent protection element to its area at 25 ° C is 4.8 to 7.2 W/mm ² .

In one embodiment, the fluoropolymer comprises polyvinylidene fluoride (PVDF), ethylene-tetra-fluoro-ethylene (ETFE), and polytetrafluoroethylene (polytetrafluoroethylene). (tetrafluoroethylene); PTFE), tetrafluoroethylene-hexafluoro-propylene copolymer (FEP), ethylene-tetrafluoroethylene copolymer (PETFE), perfluorocarbon oxygen modification Perfluoroalkoxy modified tetrafluoroethylenes (PFA), poly(chlorotri-fluorotetrafluoroethylene; PCTFE), vinylidene fluoride-tetrafluoroethylene copolymer; VF-2- TFE), poly(vinylidene fluoride), tetrafluoroethylene-perfluorodioxole copolymer, difluoroethylene-hexafluoropropylene copolymer (vinylidene fluoride- Hexafluoropropylene copolymer), vinylidene fluoride-hexafluoropropylene-tetrafluoroeth At least one of ylene terpolymer).

In one embodiment, the conductive ceramic filler is selected from the group consisting of tungsten carbide, titanium carbide, vanadium carbide, zirconium carbide, tantalum carbide, tantalum carbide, molybdenum carbide, tantalum carbide, titanium boride, vanadium boride, zirconium boride, boride At least one of cerium, molybdenum boride, lanthanum boride or zirconium nitride.

In one embodiment, the carbon-containing conductive filler comprises carbon black.

In one embodiment, the polymeric substrate further comprises high density polyethylene (HDPE).

In one embodiment, the fluoropolymer comprises a mixture of different melting point polymers, and the difference between the highest melting point and the lowest melting point is between 4 and 15 °C.

In one embodiment, the difference between the low melting point and the adjacent melting point of the different melting point polymers is between 3 and 8 °C.

In one embodiment, the different melting point polymer comprises a plurality of mixtures of polytetrafluoroethylene (PVDF).

In one embodiment, the overcurrent protection component can be burned through 100 cycles through a 24V and 50A cycle life test.

In one embodiment, the overcurrent protection component has a Time-to-Trip (TtT) greater than 2 seconds at 85 ° C, 16 V, and 20 A test conditions.

The overcurrent protection device of the present invention uses a fluorine-containing polymer to provide a high temperature environment. By using a specific proportion of polymer substrate, conductive ceramic filler and carbon-containing conductive filler, high holding current, high withstand power and high withstand voltage (≧24V) can be achieved at the same time.

The above and other technical contents, features and advantages of the present invention will become more apparent from the following description.

Table 1 shows the formulation components shown by volume percentage of each of Examples (E1 to E5) and Comparative Examples (C1 to C3), wherein the carbon black as the conductive filler was selected from the model RAVEN 430 manufactured by Columbia Chemical Company. ULTRA products, tungsten carbide ceramic powder as conductive filler is selected from Micron Metals, Inc. product WP-301; high molecular weight polymer substrate, high density polyethylene (HDPE) is selected from Formosa Plastics, Inc. ) The model TAISOX HDPE-8010 is produced. PVDF is selected from the group consisting of kynar 740, kynar 761, kuraha 850, and kuraha 1100 with melting points of 165 ^o C, 168 ^o C, 173 ^o C and 175 ^o C, respectively. Examples E1 and E2 comprise tungsten carbide, carbon black and PVDF of four different melting points. Example E3 contained tungsten carbide and four different melting point PVDFs, but no carbon black. Examples E4 and E5 comprise tungsten carbide, carbon black, PVDF 740, and HDPE. In general, the sustain current decreases as the temperature increases, a so-called thermal derating effect. Since HDPE has a lower melting point of about 130 ° C and PVDF has a higher melting point of about 165 ° C, the use of PVDF can slow the tendency of the holding current to decrease. Comparative Example C1 contained a carbon black conductive filler and PVDF 740, but did not contain tungsten carbide. C2 contains tungsten carbide, carbon black and PVDF 740. C3 contains tungsten carbide, carbon black and PVDF with four different melting points, but the ratio of carbon black is high and the proportion of tungsten carbide is low.

Table 1  <TABLE border="1" borderColor="#000000" width="85%"><TBODY><tr><td> </td><td> Tungsten Carbide</td><td> Carbon Black</td ><td> PVDF 740 </td><td> PVDF 761 </td><td> PVDF 850 </td><td> PVDF 1100 </td><td> HDPE </td></tr>< Tr><td> E1 </td><td> 41% </td><td> 3% </td><td> 17% </td><td> 12% </td><td> 17 % </td><td> 10% </td><td> - </td></tr><tr><td> E2 </td><td> 41% </td><td> 3.5 % </td><td> 11.5% </td><td> 16% </td><td> 16% </td><td> 12% </td><td> - </td>< /tr><tr><td> E3 </td><td> 44% </td><td> 0.5% </td><td> 16.5% </td><td> 13% </td> <td> 13% </td><td> 13% </td><td> - </td></tr><tr><td> E4 </td><td> 40% </td> <td> 5.0% </td><td> 49.0% </td><td> - </td><td> - </td><td> - </td><td> 6% </td ></tr><tr><td> E5 </td><td> 41.7% </td><td> 2.8% </td><td> 6.2% </td><td> - </td ><td> - </td><td> - </td><td> 49.3% </td></tr><tr><td> C1 </td><td> - </td>< Td> 32% </td><td> 68% </td><td> - </td><td> - </td><td> - </td><td> - </td>< /tr><tr><td> C2 </td><td> 41.7% </td><td> 2.8% </td><td> 55.5% </td><td> - </td>< Td> - < /td><td> - </td><td> - </td></tr><tr><td> C3 </td><td> 38.6% </td><td> 6.4% </ Td><td> 11% </td><td> 16% </td><td> 16% </td><td> 12% </td><td> - </td></tr> </TBODY></TABLE>

The materials of the above respective examples and comparative examples were added to a twin-screw kneader manufactured by HAAKE Co., Ltd. for mixing as shown in the volume percentages shown. The temperature of the mixing was set at 215 ° C, the premixing time was 3 minutes, and the mixing time was 15 minutes.

The conductive polymer which was kneaded was pressed into a sheet at 210 ° C and a pressure of 150 kg / cm ² by a hot press. Then, the sheet is cut into a square of about 20 cm × 20 cm, and two nickel-plated copper foils are bonded to both sides of the sheet by a hot press at a temperature of 210 ° C and a pressure of 150 kg / cm ² , and finally a punching machine A PTC wafer as shown in Fig. 1, which is the overcurrent protection element 10 of the present invention, is punched out. The overcurrent protection element 10 includes a PTC material layer 11 composed of the conductive polymer and a first electrode layer 12 and a second electrode layer 13 composed of the nickel-plated copper foil. The thickness of the PTC material layer 11 is 0.28 to 0.77 mm. 2 is a top view of the overcurrent protection component 10 of FIG. 1. The area "A x B" of the overcurrent protection component 10 is equivalent to the area of the PTC material layer 11, and the area is 32.15 to 70 mm ² .

In one embodiment, the outer surfaces of the first and second electrode layers 12, 13 may be coated with solder paste, and two pieces of copper electrodes having a thickness of 0.5 mm are respectively placed on the first and second electrode layers 12, 13 An external-type solder paste is used as an external electrode, and the assembled component is subjected to a 300 ° C reflow process to obtain an axial-type or radial-lead type PTC component. Alternatively, a notch is formed by etching in the first and second electrode layers 12 and 13 by a related process, and then an insulating layer, an outer electrode layer, a vertical via hole, and the like are formed to form an SMD type PTC element.

The above PTC wafers were taken as samples for five samples according to different formulations: (1) initial resistance Ri; (2) 85 ° C, 16 V, 20 A to time-to-trip (TtT); 3) a holding current (I-hold) at 24 ° C, applying a voltage of 24 V; and (4) a cycle life test of 24 V, 50 A over 100 cycles (on: 10 seconds; off: 60 seconds), each A loop represents the process of a trigger and reply. The volume resistance value ρ of the material can be calculated from the thickness of the Ri and PTC material layers. According to the sustain current and the element area, the unit current holding current value (A/mm ² ) and the unit area of the withstand power (W/mm ² ) can be calculated. Tables 2 and 3 show the test results of the respective Examples E1 to E5 and Comparative Examples C1 to C3.

Table 2  <TABLE border="1" borderColor="#000000" width="85%"><TBODY><tr><td> </td><td> Ri (mΩ) </td><td> ρ(Ω -cm) </td><td> thickness (mm) </td><td> area (mm²) </td><td> TtT@85<sup>o</sup >C(16V/20A) (sec) </td></tr><tr><td> E1 </td><td> 2.87 </td><td> 0.0287 </td><td> 0.7 < /td><td> 70 </td><td> 10.6 </td></tr><tr><td> E2 </td><td> 3 </td><td> 0.03 </td> <td> 0.7 </td><td> 70 </td><td> 8.4 </td></tr><tr><td> E3 </td><td> 2.78 </td><td> 0.0306 </td><td> 0.77 </td><td> 70 </td><td> 10.51 </td></tr><tr><td> E4 </td><td> 4.79 </ Td><td> 0.0385 </td><td> 0.35 </td><td> 32.15 </td><td> 0.48 </td></tr><tr><td> E5 </td>< Td> 3.1 </td><td> 0.0249 </td><td> 0.4 </td><td> 32.15 </td><td> 0.88 </td></tr><tr><td> C1 </td><td> 105 </td><td> 0.9145 </td><td> 0.28 </td><td> 32.15 </td><td> 0.015 </td></tr><tr ><td> C2 </td><td> 2.96 </td><td> 0.0326 </td><td> 0.77 </td><td> 70 </td><td> 10.6 </td>< /tr><tr><td> C3 </td><td> 3.57 </td><td> 0.0393 </td><td> 0.77 </td><td> 70 </td><td> 6.77 </td></tr></ TBODY></TABLE>

table 3  <TABLE border="1" borderColor="#000000" width="85%"><TBODY><tr><td> </td><td> I-hold@25^oC (A) </td><td> I-hold@25^oC / area (A/mm²) </td><td> Cycle Life Test@ 24V/50A </td><td> withstand power/area (W/mm²) </td></tr><tr><td> E1 </td><td> 16.4 </td><td> 0.234 </td><td> by</td><td> 5.62 </td></tr><tr><td> E2 </td><td> 15.9 </ Td><td> 0.227 </td><td> by </td><td> 5.45 </td></tr><tr><td> E3 </td><td> 15.2 </td>< Td> 0.217 </td><td> by </td><td> 5.21 </td></tr><tr><td> E4 </td><td> 7.92 </td><td> 0.254 </td><td> by</td><td> 6.10 </td></tr><tr><td> E5 </td><td> 8.6 </td><td> 0.267 </td ><td> By</td><td> 6.41 </td></tr><tr><td> C1 </td><td> 2.6 </td><td> 0.08 </td><td > By</td><td> 1.92 </td></tr><tr><td> C2 </td><td> 14.2 </td><td> 0.203 </td><td> Failed </td><td> 4.87 </td></tr><tr><td> C3 </td><td> 12 </td><td> 0.171 </td><td> by </td ><td></td></tr></TBODY></TABLE>

In Table 2, since C1 does not contain tungsten carbide, its initial volume resistance value Ri is significantly higher than 100 mΩ, and the holding current (I-hold) is too low at 25 ° C, and the holding current per unit area is only 0.08 A/mm ² . C2 uses a lower proportion of carbon black, which burns out during the cycle life test of 100 cycles, showing that its withstand voltage characteristics are not good. However, although the carbon black ratio of E5 is equivalent to that of C2, its high molecular polymer contains PVDF and HDPE, and it can pass the cycle life test of 100 cycles by adjusting the appropriate polymer. C3 has a high carbon black ratio (>5%) and a low tungsten carbide ratio (<40%), resulting in a low holding current at 25 ° C and a holding current per unit area of only 0.171 A/mm ² . E1~E5 can use a high proportion of tungsten carbide and a proper proportion of carbon black to obtain a volume resistance of less than 0.05 Ω·cm and a holding current per unit area of 0.21 A/mm ² at 25 ° C. Withstand voltage cycle life test. The introduction of HDPE into the polymer matrix of E4 may cause micro-phase separation inside the material, resulting in a relatively high volume resistance value.

Embodiments E1 to E3 have a triggering time of about 8 to 11 seconds under the test conditions of the automatic lock rotor of 85 ° C, 16 V, and 20 A, and meet the specifications for the trigger time of more than 2 seconds. Although Comparative Examples C2 and C3 have a TtT time of more than 2 seconds, their withstand voltage and sustain current characteristics are not good. In addition to PVDF, Examples E4 and E5 are additionally added to HDPE. Although their TtT time is short, they can be applied to applications where long TtT is not required. Therefore, the fluoropolymer in the PTC material layer of the present invention may be mixed with other polyethylene (PE), and as long as the PVDF still has a sufficient ratio to dominate the properties of the polymer after mixing, it can still obtain good effects.

In summary, the volume percentage of the polymer of the PTC material layer in the overcurrent protection element of the present invention is 50-60%, or 52%, 55% or 58%, for example; the volume percentage of the conductive ceramic filler is 40-45. %, or for example 41%, 43% or 44%; the volume percentage of the carbon-containing conductive filler is 0.5 to 5%, or for example 1%, 2% or 4%. Thereby, the ratio of the sustain current to the area of the overcurrent protection element of the present invention at 25 ° C is 0.21 to 0.3 A/mm ² , such as 0.23 A/mm ² , 0.25 A/mm ² or 0.27 A/mm ² , It can be tested by 24V and 50A without burning, and achieves excellent electrical characteristics such as high voltage resistance, high unit area holding current and high unit area withstand power. Since the withstand voltage of the component can be increased to 24V, the power that can be withstood under the unit area is also increased to 4.8~7.2W/mm ² , such as 5W/mm ² , 6W/mm ² or 7W/mm ² .

The fluorine-containing polymer of the present invention preferably has a melting point of more than 150 ° C. The fluorine-containing polymer added by the present invention is not limited to the use of PVDF, and other fluorine-containing polymers having similar properties and having a melting point higher than 150 ° C. Polymers are also encompassed by the present invention. For example: polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoro-propylene copolymer (FEP), ethylene-tetrafluoroethylene copolymer (PETFE) , perfluoroalkoxy modified tetrafluoroethylenes (PFA), poly(chlorotri-fluorotetrafluoroethylene) (PCTFE), difluoroethylene-tetrafluoroethylene polymer (vinylidene) Fluoride-tetrafluoroethylene copolymer; VF-2-TFE), poly(vinylidene fluoride), tetrafluoroethylene-perfluorodioxole copolymers, difluoroethylene - a hexafluoropropylene copolymer (vinylidene fluoride-hexafluoropropylene copolymer), and a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer. Preferably, a plurality of fluoropolymers having different melting points are selected, as in Examples E1 to E3. Because of the different melting point characteristics, a smoother resistance-temperature curve (R-T curve) can be obtained, which improves the stability of the cycle life test and better withstand voltage characteristics. The difference between the highest melting point and the lowest melting point of a plurality of fluorine-containing high molecular polymers is 4 to 15 °C. Preferably, the plurality of fluoropolymers have a difference from low to high adjacent melting points of 3 to 8 °C.

The electrically conductive ceramic filler may be selected from metal carbides, metal borides or metal nitrides having a volume resistance value of less than 500 μΩ·cm. For example: strontium carbide (WC), titanium carbide (TiC), vanadium carbide (VC), zirconium carbide (ZrC), niobium carbide (NbC), tantalum carbide (TaC), molybdenum carbide (MoC), niobium carbide (HfC) Titanium boride (TiB ₂ ), vanadium boride (VB ₂ ), zirconium boride (ZrB ₂ ), niobium boride (NbB ₂ ), molybdenum boride (MoB ₂ ), hafnium boride (HfB ₂ ) or nitrogen Zirconium (ZrN).

The overcurrent protection component of the invention simultaneously achieves excellent electrical characteristics of high voltage resistance, high unit area maintaining current and high unit area withstand power, and is resistant to high temperature and harsh environments, and is suitable for high temperature overcurrent protection applications.

The technical contents and technical features of the present invention have been disclosed as above, and those skilled in the art can still make various substitutions and modifications without departing from the spirit and scope of the invention. Therefore, the scope of the present invention should be construed as being limited by the scope of the appended claims

10‧‧‧Overcurrent protection components

11‧‧‧ PTC material layer

12‧‧‧First electrode layer

13‧‧‧Second electrode layer

1 shows an overcurrent protection component in accordance with an embodiment of the present invention; and FIG. 2 shows a top view of the overcurrent protection component of FIG. 1.

Claims (9)

An overcurrent protection component comprising: a first electrode layer; a second electrode layer; and a PTC material layer stacked between the first electrode layer and the second electrode layer, the volume resistance value of which is less than 0.05 Ω. Cm, the PTC material layer comprises: a polymer substrate comprising a fluorine-containing polymer having a melting point higher than 150 ° C, the volume percentage of the polymer substrate is 50-58%; a conductive ceramic filler, Dispersed in the polymer substrate, the conductive ceramic filler has a volume percentage of 40-45%, and its volume resistance value is less than 500μΩ. And a carbon-containing conductive filler dispersed in the polymer base material, the volume percentage of the carbon-containing conductive filler is 0.5 to 5%; wherein the fluorine-containing polymer comprises a mixture of different melting point polymers, and The difference between the highest melting point and the lowest melting point is 4 to 15 ° C; wherein the ratio of the holding current of the overcurrent protection element to the area at 25 ° C is 0.21 to 0.3 A/mm ² ; wherein the overcurrent protection element is at 25 ° C The ratio of the tolerable power to its area is 4.8~7.2W/mm ² . The overcurrent protection element according to claim 1, wherein the fluoropolymer comprises polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, ethylene- Tetrafluoroethylene copolymer, perfluoro-oxygen-modified tetrafluoroethylene, polychlorotrifluoro-tetrafluoroethylene, difluoroethylene -tetrafluoroethylene polymer, polydifluoroethylene, tetrafluoroethylene-perfluorodioxole copolymer, difluoroethylene-hexafluoropropylene copolymer, and difluoroethylene-hexafluoropropylene-tetrafluoroethylene At least one of the trimers. The overcurrent protection component according to claim 1, wherein the conductive ceramic filler is selected from the group consisting of tungsten carbide, titanium carbide, vanadium carbide, zirconium carbide, tantalum carbide, tantalum carbide, molybdenum carbide, tantalum carbide, titanium boride, vanadium boride, At least one of zirconium boride, lanthanum boride, molybdenum boride, lanthanum boride or zirconium nitride. An overcurrent protection element according to claim 1, wherein the carbon-containing conductive filler comprises carbon black. An overcurrent protection element according to claim 1, wherein the high molecular weight polymer substrate further comprises high density polyethylene. The overcurrent protection element according to claim 1, wherein the difference in the low melting point adjacent melting point of the different melting point polymer is between 3 and 8 °C. An overcurrent protection element according to claim 1, wherein the different melting point polymer comprises a mixture of a plurality of polyvinylidene fluorides. The overcurrent protection component of claim 1, wherein the overcurrent protection component is capable of passing 100 cycles through 24V and 50A cycle life tests without burning. The overcurrent protection component of claim 1, wherein the overcurrent protection component has a trigger time of greater than 2 seconds at 85 ° C, 16 V, and 20 A test conditions.