Overcurrent protection element

Abstract

An over-current protection element comprises an electrode layer and a thermistor layer. The thermistor layer has a positive temperature coefficient characteristic and is stacked between the upper metal layer and the lower metal layer in the electrode layer. In addition, the thermistor layer contains a high-molecular polymer base material and a conductive filler. The high-molecular polymer base material comprises a first fluorine-containing polymer and a second fluorine-containing polymer. The first fluorine-containing polymer has a first melting point, the second fluorine-containing polymer has a second melting point less than the first melting point, and the first melting point and the second melting point are reduced by 14 DEG C. The second fluoropolymer has a second melt flow index between 0.4 g / 10 min and 0.7 g / 10 min.

Description

Technical Field

[0001] The present invention relates to an overcurrent protection element, and more specifically, to an overcurrent protection element with high voltage resistance and good resistance stability. Background Art

[0002] The resistance of existing conductive composite materials with positive temperature coefficient (PTC) characteristics is very sensitive to changes in specific temperature. They can be used as materials for current sensing elements and are currently widely used in overcurrent protection elements or circuit elements. Specifically, the resistance of PTC conductive composite materials can be maintained at an extremely low value at normal temperature, allowing the circuit or battery to operate normally. However, when the circuit or battery has an overcurrent (over-current) or overtemperature (over-temperature) phenomenon, its resistance value will instantly increase to a high resistance state (at least 10 4 Ω or more), which is called a trip, and the overcurrent is cut off to protect the battery or circuit components.

[0003] As for the most basic structure of the overcurrent protection element, it is composed of a PTC material layer and metal electrodes attached to both sides thereof. The PTC material layer will at least include a substrate and a conductive filler. The substrate is composed of a high molecular polymer, and the conductive filler is dispersed in the high molecular polymer as a conductive path. For electronic devices with higher protection temperature requirements, the substrate often uses a fluorinated polymer (such as polyvinylidene fluoride) as its main component. Traditionally, in order to facilitate processing, the melting point of the aforementioned fluorinated polymer can be lowered, so that the melting point of the entire substrate can be lowered, and it is easier to melt at high temperatures, which is beneficial to the high-temperature mixing and subsequent pressing of the PTC material layer. However, the overcurrent protection element is in a high temperature state when triggered, and the aforementioned low melting point fluorinated polymer will cause the PTC material layer structure to be unstable and lack support, affecting the integrity of the overall structure of the overcurrent protection element. In addition, after multiple triggering, the resistance value of the traditional overcurrent protection element is not easy to recover to a low resistance state even at room temperature. It should be understood that component miniaturization is a current trend, and the structural stability and the problems derived therefrom are aggravated as the size (especially the thickness) of the overcurrent protection component becomes smaller.

[0004] It can be seen that, conventionally, when the processability of overcurrent protection components is improved, there is still considerable room for improvement in resistance stability and other electrical characteristics. Summary of the invention

[0005] The present invention provides an overcurrent protection element with good resistance stability and high voltage resistance. More specifically, the overcurrent protection element of the present invention has an electrode layer and a thermistor layer, and the thermistor layer includes a polymer matrix and a conductive filler. In order to improve the structural stability of the thermistor layer, the polymer matrix includes a main component composed of at least two fluoropolymers (hereinafter referred to as the first fluoropolymer and the second fluoropolymer). The second fluoropolymer has low fluidity, and its melt flow index is between 0.4g / 10min and 0.7g / 10min, which is beneficial to the material stability of the thermistor layer when it is actuated at high temperature. In addition, the melting point of the second fluoropolymer is lower than the melting point of the first fluoropolymer, which is beneficial to the recrystallization process. The second fluoropolymer can be quickly recrystallized with the first fluoropolymer as the nucleation center, while providing better structural stability. Based on the above, the present invention further found that the overcurrent protection element has significant improvements in electrical properties. The overcurrent protection element can not only withstand high voltage or high power, but also has improved resistance stability, especially the high resistance state after triggering is quite stable.

[0006] According to one embodiment of the present invention, an overcurrent protection element includes an electrode layer and a thermistor layer. The electrode layer has an upper metal layer and a lower metal layer, and the thermistor layer contacts the upper metal layer and the lower metal layer and is stacked therebetween. The thermistor layer has a positive temperature coefficient characteristic and includes a polymer substrate and a conductive filler. The polymer substrate includes a first fluoropolymer and a second fluoropolymer. The first fluoropolymer has a first melting point. The second fluoropolymer has a second melting point that is less than the first melting point, and the first melting point and the second melting point are less than 14°C. The second fluoropolymer has a second melt flow index between 0.4g / 10min and 0.7g / 10min. The conductive filler is dispersed in the polymer substrate to form a conductive path for the thermistor layer.

[0007] According to some embodiments, the difference between the first melting point and the second melting point is 5°C to 14°C.

[0008] According to some embodiments, based on 100% of the volume of the thermistor layer, the first fluorine-containing polymer accounts for 28% to 48% by volume, and the second fluorine-containing polymer accounts for 10% to 30% by volume.

[0009] According to some embodiments, the second fluoropolymer is represented by formula (I):

[0010]

[0011] wherein R1 and R2 are selected from the group consisting of CH2, CF2, CHF, C2HF3, C2H2F2, C2H3F, C2H4 and C2F4, R1 and R2 are different, and n is at least 9000.

[0012] According to some embodiments, the second melting point of the second fluoropolymer is between 168°C and 174°C.

[0013] According to some embodiments, the first fluoropolymer has a first melt flow index between 0.8 g / 10 min and 1.4 g / 10 min.

[0014] According to some embodiments, the second fluoropolymer is polyvinylidene fluoride.

[0015] According to some embodiments, the polymer matrix further comprises a third fluorine-containing polymer selected from the group consisting of polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, perfluorocarbon oxide-modified tetrafluoroethylene, poly(chlorotri-fluorotetrafluoroethylene), difluoroethylene-tetrafluoroethylene polymer, tetrafluoroethylene-perfluorodioxole copolymer, difluoroethylene-hexafluoropropylene copolymer, difluoroethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, and any combination thereof.

[0016] According to some embodiments, the third fluorine-containing polymer is polytetrafluoroethylene, and based on 100% of the volume of the thermistor layer, the volume percentage of the polytetrafluoroethylene is 4% to 6%.

[0017] According to some embodiments, the thermistor layer further comprises a flame retardant selected from the group consisting of zinc oxide, antimony oxide, aluminum oxide, silicon oxide, calcium carbonate, magnesium sulfate or barium sulfate, magnesium hydroxide, aluminum hydroxide, calcium hydroxide, barium hydroxide and any combination thereof.

[0018] According to some embodiments, the conductive filler consists of carbon black.

[0019] According to some embodiments, the overcurrent protection element has a first resistance jump rate between 1.3 and 1.5, wherein the overcurrent protection element has an initial resistance value; the overcurrent protection element has a second resistance value after 16V / 40A is applied for 3 minutes and cooled to room temperature; and the second resistance value divided by the initial resistance value is the first resistance jump rate.

[0020] According to some embodiments, the overcurrent protection element has a second resistance jump rate between 1.5 and 1.8, wherein the overcurrent protection element has an initial resistance value; the overcurrent protection element has a third resistance value after being subjected to a 30V / 40A cycle life test for 2000 cycles and cooled to room temperature; and the third resistance value divided by the initial resistance value is the second resistance jump rate.

[0021] According to some embodiments, a standard deviation of the third resistance value is between 0.0009Ω and 0.0011Ω.

[0022] According to some embodiments, the thermistor layer has a thickness between 0.11 mm and 0.17 mm, and the over-current protection element can withstand a power of 1400W to 1500W.

[0023] According to some embodiments, the overcurrent protection element has a trigger current thermal decay rate between 35% and 42%, wherein the trigger current thermal decay rate is defined as the trigger current required by the overcurrent protection element in an environment of 125°C divided by the trigger current required by the overcurrent protection element in an environment of 25°C, and then converted into a percentage.

[0024] According to some embodiments, the overcurrent protection element has a resistance peak maintenance rate between 0.4 and 1.1, wherein the overcurrent protection element is triggered once at a temperature of 200°C and has a first resistance peak; the overcurrent protection element is triggered three times at a temperature of 200°C and has a second resistance peak; and the second resistance peak divided by the first resistance peak is the resistance peak maintenance rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A cross-sectional view showing an overcurrent protection element according to an embodiment of the present invention; and

[0026] Figure 2 show Figure 1 Top view of the overcurrent protection element.

[0027] The reference numerals are described as follows:

[0028] 10Overcurrent protection element

[0029] 11Thermistor layer

[0030] 12 Upper metal layer

[0031] 13 Lower metal layer

[0032] A Length

[0033] B Width DETAILED DESCRIPTION

[0034] In order to make the above and other technical contents, features and advantages of the present invention more clearly understood, relevant embodiments are given below and described in detail with reference to the accompanying drawings.

[0035] Please refer to Figure 1, showing the basic state of the overcurrent protection element of the present invention. The overcurrent protection element 10 includes a thermistor layer 11 and an electrode layer. The thermistor layer 11 has an upper surface and a lower surface, and the electrode layer has an upper metal layer 12 and a lower metal layer 13 respectively attached to the upper surface and the lower surface of the thermistor layer 11. In this way, the thermistor layer 11 is physically in direct contact with the upper metal layer 12 and the lower metal layer 13, and is stacked between the two. In one embodiment, the upper metal layer 12 and the lower metal layer 13 can be composed of nickel-plated copper foil or other conductive metals. In addition, the thermistor layer 11 includes a polymer substrate and a conductive filler. The polymer substrate is an insulator that is easily expanded by heat, and the conductive filler is a conductor, so that the thermistor layer 11 has a positive temperature coefficient characteristic. When the overcurrent protection element 10 is not triggered, the conductive filler is evenly dispersed in the polymer matrix and connected in series to form a conductive channel; when the overcurrent protection element 10 is affected by high temperature, the polymer matrix will expand rapidly, causing the conductive filler particles to be pulled apart from each other, resulting in the truncation of the conductive channel.

[0036] In the present invention, the main component of the high molecular polymer matrix includes two fluoropolymers with different melting points and different flow properties (hereinafter referred to as the first fluoropolymer and the second fluoropolymer). The first fluoropolymer may be polyvinylidene fluoride with a higher melting point, while the second fluoropolymer is a fluoropolymer having the same or similar skeleton as the first fluoropolymer, but having a lower melting point. More specifically, the first fluoropolymer has a first melting point, and the second fluoropolymer has a second melting point less than the first melting point. Moreover, the difference between the first melting point and the second melting point is less than 14°C. In addition, the second fluoropolymer not only has a lower melting point, but also has lower fluidity than the first fluoropolymer. According to the standard specification of ASTM D1238, at a temperature of 230°C, the first fluoropolymer has a first melt flow index, and the second fluoropolymer has a second melt flow index lower than the first melt flow index. The first melt flow index is between about 0.8 g / 10 min and 1.4 g / 10 min, and the second melt flow index is between about 0.4 g / 10 min and 0.7 g / 10 min. The first fluorinated polymer and the second fluorinated polymer can form an interpenetrating polymer network (IPN) structure, which constitutes the main component of the polymer matrix.

[0037] It should be noted that conventional overcurrent protection elements often use a single type of fluorinated polymer (such as polyvinylidene fluoride) as a high-protection temperature polymer matrix; if two fluorinated polymers with different physical and chemical properties but the same polymerization monomer (such as two polyvinylidene fluorides) are used at the same time, there is often no significant improvement in electrical properties, or the performance is poor. Regarding the latter, the main reason is the complexity of the formulation design. Every time a compound composition is added, the compatibility of the compound composition with the existing polymer matrix, conductive filler and other internal fillers must be considered. Even if the compound composition is compatible with the existing polymer matrix, conductive filler and other internal fillers, it needs to be accurately adjusted to an appropriate ratio to maintain good electrical properties, otherwise there will be the aforementioned problem of no significant improvement or poor performance. However, after the present invention appropriately adjusts the content ratio and physical properties, it is found that the combination of two fluorinated polymers is far superior to a matrix composed of a single fluorinated polymer. More specifically, the introduction of a fluorinated polymer (i.e., a second fluorinated polymer) that is easier to melt but less likely to flow into the polymer matrix not only effectively stabilizes the material structure, but also significantly improves the electrical properties. Since the melting point of the second fluoropolymer is lower than that of the first fluoropolymer, the melting point of the entire substrate can be lowered, and it is easier to melt at high temperatures and is convenient for mixing with other materials. Although the second fluoropolymer is easier to melt, it has a melt flow index (i.e., the second melt flow index) that is much lower than that of the first fluoropolymer. This low flow property helps maintain the integrity of the overall structure of the overcurrent protection element 10 without excessive deformation in the case of repeated high and low temperature alternation (for example, multiple triggering). However, it should be noted that the second melt flow index must be adjusted within an appropriate range. If the second melt flow index is lower than 0.4g / 10min, the adjustment of the content of the second fluoropolymer will be difficult to control. The reason is that if the fluidity of the second fluoropolymer is too low, a slight change in its content will be excessively reflected in the overall fluidity of the substrate, and the same is true for the electrical properties. If the second melt flow index is higher than 0.7g / 10min, the fluidity of the second fluoropolymer is too good and is not much different from that of the first fluoropolymer. Even if its content ratio is adjusted to a higher level, it will not have much improvement on the overall fluidity of the substrate. In one embodiment, the second melt flow index is between about 0.4 g / 10 min and 0.6 g / 10 min, for example, the second melt flow index is 0.4 g / 10 min, 0.45 g / 10 min, 0.5 g / 10 min, 0.55 g / 10 min or 0.6 g / 10 min.

[0038] In addition, as mentioned above, the second melting point of the second fluoropolymer is less than the first melting point of the first fluoropolymer. In addition to the aforementioned advantages of processability, the present invention further considers the problem of polymer recrystallization and adjusts the difference between the first melting point and the second melting point to a specific range. Specifically, the difference between the first melting point and the second melting point is 5°C to 14°C, such as 5°C, 6°C, 7°C, 8°C, 9°C, 10°C, 11°C, 12°C, 13°C or 14°C. When the temperature drops to the first melting point, the first fluoropolymer is substantially solid. In this way, the second fluoropolymer can be recrystallized with the first fluoropolymer as the nucleation center and restore a stable crystalline state. In other words, the presence of the first fluoropolymer can improve the crystallization efficiency of the second fluoropolymer, and the second fluoropolymer can support the structural stability of the thermistor layer 11, and the combination of the two makes the electrical characteristics have better performance. If the aforementioned difference is less than 5°C, the phase change of the two at high temperature is too consistent, so the second fluoropolymer cannot effectively help the first fluoropolymer recrystallize. If the aforementioned difference is greater than 14°C, there will be a problem of phase separation between the first fluoropolymer and the second fluoropolymer. The aforementioned phase separation problem mainly occurs when the temperature gradually decreases, and the difference in the process of recrystallization between the two is too large, so that the efficiency of the first fluoropolymer and the second fluoropolymer being interwoven into an IPN structure is not good. In detail, when the temperature drops from a high temperature to a first melting point, the first fluoropolymer begins to recrystallize and form orderly arranged crystals. As the temperature continues to drop from the first melting point to the second melting point, the crystal arrangement of the first fluoropolymer gradually stabilizes. However, due to the large difference between the first melting point and the second melting point, when the temperature drops to near the second melting point, the structure of the first fluoropolymer has already been finalized, and the second fluoropolymer in a molten state is ready to start recrystallization efficiently. In this way, part of the second fluoropolymer will be independent of the first fluoropolymer and form a phase of its own, rather than being interwoven with the first fluoropolymer into a compatible IPN structure. In the present invention, the second melting point of the second fluoropolymer can be 171°C; however, considering the influence of errors and actual application situations, the second melting point between 168°C and 174°C has the same or similar technical effects. As for the first melting point of the first fluoropolymer, it can be adjusted accordingly according to the aforementioned melting point difference. For example, when the second melting point is 168°C, the first melting point can be 173°C to 182°C; when the second melting point is 171°C, the first melting point can be 176°C to 185°C; or when the second melting point is 174°C, the first melting point can be 179°C to 188°C. When the second melting point is 169°C, 170°C, 172°C or 173°C, the first melting point can be deduced in the aforementioned manner, and no further praise is given here. Based on the above-mentioned physical properties, the present invention further adjusts the content of the first fluoropolymer and the content of the second fluoropolymer to an appropriate ratio.Taking the volume of the thermistor layer as 100%, the volume percentage of the first fluoropolymer is 28% to 48%, and the volume percentage of the second fluoropolymer is 10% to 30%. It should be noted that the upper limit value (30%) of the content of the second fluoropolymer is lower than the upper limit value (48%) of the content of the first fluoropolymer. Because the second fluoropolymer has poor fluidity, if the ratio is too high, the material of the thermistor layer 11 will be difficult to flow during production, which is not conducive to mixing. In the present invention, the content of the first fluoropolymer is greater than the content of the second fluoropolymer, which helps to mix the polymer and the conductive filler, and is conducive to the manufacture of the thermistor layer 11. In a preferred embodiment of the present invention, the volume percentage of the first fluoropolymer is 29% to 46%, and the volume percentage of the second fluoropolymer is 11% to 28%.

[0039] In addition, the present invention further notes that the second fluorine-containing polymer can have similar effects as long as it has the core skeleton of the first fluorine-containing polymer. More specifically, if the first fluorine-containing polymer is polyvinylidene fluoride, the chemical structure of the second fluorine-containing polymer is as shown in formula (I):

[0040]

[0041] In formula (I), the repeating unit of the second fluorine-containing polymer has a core skeleton of -CH2CF2-, which connects two functional groups (i.e., R1 and R2). R1 ​​and R2 are both selected from the group consisting of CH2, CF2, CHF, C2HF3, C2H2F2, C2H3F, C2H4 and C2F4, and R1 and R2 are different. For example, when R1 is CH2, R2 is selected from the group consisting of CF2, CHF, C2HF3, C2H2F2, C2H3F, C2H4 and C2F4. In addition, n is the number of repeating units, which is at least 9000. In one embodiment, the second fluorine-containing polymer can also be polyvinylidene fluoride, so R1 is CF2 and R2 is CH2.

[0042] In addition, the polymer matrix of the present invention may further include a third fluoropolymer. The third fluoropolymer is selected from the group consisting of polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, perfluorocarbon oxide-modified tetrafluoroethylene, poly(chlorotri-fluorotetrafluoroethylene), difluoroethylene-tetrafluoroethylene polymer, tetrafluoroethylene-perfluorodioxole copolymer, difluoroethylene-hexafluoropropylene copolymer, difluoroethylene-hexafluoropropylene-tetrafluoroethylene terpolymer and any combination thereof. The melting point of the third fluoropolymer is much higher than the melting points of the aforementioned first fluoropolymer and the second fluoropolymer. For example, the melting points of the first fluoropolymer and the second fluoropolymer are between 168°C and 188°C, while the melting point of the third fluoropolymer is between 320°C and 335°C. When the ambient temperature is higher than the melting points of the first fluoropolymer and the second fluoropolymer and lower than the melting point of the third fluoropolymer, the first fluoropolymer and the second fluoropolymer will melt while the third fluoropolymer will not. Accordingly, the third fluoropolymer can be present as solid particles uniformly dispersed in the thermistor layer 11 and serve as a nucleation center when the fluoropolymer recrystallizes, which is conducive to the formation of crystals. Alternatively, based on the high melting point characteristics of the third fluoropolymer, the deformation degree of the third fluoropolymer is small at high temperatures, thereby effectively stabilizing the structural form of the thermistor layer 11 without excessive deformation. In one embodiment, the third fluoropolymer is polytetrafluoroethylene, and the volume percentage of polytetrafluoroethylene is 4% to 6% based on the volume of the thermistor layer 11 being 100%.

[0043] In addition to the polymer matrix and the conductive filler, the thermistor layer 11 further includes a flame retardant. The flame retardant is selected from the group consisting of zinc oxide, antimony oxide, aluminum oxide, silicon oxide, calcium carbonate, magnesium sulfate or barium sulfate, magnesium hydroxide, aluminum hydroxide, calcium hydroxide, barium hydroxide and any combination thereof. In one embodiment, the flame retardant is preferably magnesium hydroxide. In addition to effectively reducing the flammability of the thermistor layer 11, magnesium hydroxide can also neutralize the hydrofluoric acid generated by the fluorine-containing polymer at high temperatures.

[0044] In addition to the improved formula, the overcurrent protection element 10 of the present invention can also have different sizes. Figure 2 ,for Figure 1 The overcurrent protection element 10 has a length A and a width B, and the area "A×B" is also equal to the area of ​​the thermistor layer 11. The thermistor layer 11 may have a top view area of ​​4mm depending on the product model. 2 Up to 72mm 2 For example, the area "A x B" can be 2 x 2 mm 2 , 4×4mm 2 , 5×5mm 2 、5.1×6.1mm 2 , 5×7mm2 、7.62×7.62mm 2 、7.8×8.15mm 2 、7.3×9.5mm 2 or 7.62×9.35mm 2 . In addition, the overall thickness of the overcurrent protection element 10 (i.e., the sum of the thicknesses of the upper metal layer 12, the thermistor layer 11, and the lower metal layer 13) is between 0.18 mm and 0.24 mm. Specifically, the thicknesses of the upper metal layer 12 and the lower metal layer 13 are 0.035 mm each, and the thickness of the thermistor layer 11 is 0.11 mm to 0.17 mm, for example, 0.11 mm, 0.12 mm, 0.13 mm, 0.14 mm, 0.15 mm, 0.16 mm, or 0.17 mm. In one embodiment, the top view area of ​​the overcurrent protection element 10 may be 35 mm 2 (ie 5×7mm 2 ), and the thickness is 0.18 mm. In another embodiment, the top view area of ​​the overcurrent protection element 10 may be 63.57 mm 2 (i.e. 7.8×8.15mm 2 ), and the thickness is 0.21mm. It should be understood that the overcurrent protection element 10 of the present invention has the same effect when applied to the above dimensions. In addition, the overcurrent protection element 10 can be processed into a common component type in the industry according to needs, such as a surface-mount device (SMD), an axial-leaded device (ALD), a radial-leaded device (RLD) or other types of components.

[0045] Based on the above formula and size, the overcurrent protection element 10 of the present invention further includes several other electrical characteristics, which are described below using a specific power trigger test (trip jump test), a cycle life test (cycle life test), a thermal derating effect test (thermal derating effect test) and a resistance-temperature test (resistance-temperature test).

[0046] In the specific power triggering test, the overcurrent protection element 10 of the present invention has a first resistance jump rate between 1.3 and 1.5. Specifically, the overcurrent protection element 10 of the present invention has an initial resistance value before any test, and has a second resistance value after 16V / 40A is applied for 3 minutes and cooled to room temperature. The second resistance value divided by the initial resistance value is the first resistance jump rate. The overcurrent protection element 10 of the present invention can be triggered by the continuous application of a specific power (16V / 40A). In this way, the first resistance jump rate can evaluate the resistance recovery ability of the overcurrent protection element 10 of the present invention after at least one triggering. The first resistance jump rate of the overcurrent protection element 10 of the present invention is preferably 1.33 to 1.48. In contrast, the first resistance jump rate of the conventional overcurrent protection element is at least 1.5, which is higher than the upper limit value of the first resistance jump rate of the overcurrent protection element 10 of the present invention (i.e., 1.48), indicating that the resistance recovery ability of the overcurrent protection element 10 of the present invention is better and can be restored to a lower resistance state after being triggered.

[0047] In the cycle life test, the overcurrent protection element 10 of the present invention has a second resistance jump rate between 1.5 and 1.8. Specifically, the overcurrent protection element 10 of the present invention has an initial resistance value before any test, and has a third resistance value after 2000 cycles of the cycle life test and cooling to room temperature. The third resistance value divided by the initial resistance value is the second resistance jump rate. The conditions of the aforementioned cycle life test are that the voltage / current of 30V / 40A is applied for 10 seconds and then closed for 60 seconds as one cycle. In this way, 2000 cycles are repeated. The cycle life test can not only evaluate the durability of the overcurrent protection element 10 of the present invention (i.e., whether it will burn out), but also evaluate its resistance recovery ability after multiple triggering through the second resistance jump rate. After the aforementioned cycle life test, the second resistance jump rate of the traditional overcurrent protection element is at least 1.98, which is much larger than the upper limit value of the second resistance jump rate of the overcurrent protection element 10 of the present invention (i.e., 1.8). It can be seen that the overcurrent protection element 10 of the present invention has better resistance recovery ability and can recover to a lower resistance state after multiple triggering. It is worth noting that the electrical performance of the overcurrent protection element 10 of the present invention also has better reproducibility. In the cycle life test, the standard deviation of the third resistance value of the overcurrent protection element 10 of the present invention is between 0.0009Ω and 0.0011Ω. In comparison, the standard deviation of traditional overcurrent protection elements is greater than 0.0015Ω, which means that the overcurrent protection element 10 of the present invention has good resistance consistency, the electrical characteristics of the element are stable, and there will be no large gap during mass production.

[0048] In order to more accurately evaluate the durability of the overcurrent protection element, the present application further designs three conditions for cycle life tests (hereinafter referred to as the first cycle life test, the second cycle life test and the third cycle life test). The power of the first cycle life test is 24V / 40A, and the number of cycles is 6700. The power of the second cycle life test is 30V / 40A, and the number of cycles is 3000. The power of the third cycle life test is 36V / 40A, and the number of cycles is 1000. It is worth noting that the overcurrent protection element 10 of the present invention can pass the above-mentioned first cycle life test, the second cycle life test and the third cycle life test without burning. That is, when the thickness of the thermistor layer 11 is extremely thin (0.11mm-0.17mm), the overcurrent protection element 10 of the present invention can withstand a high power of 1400W to 1500W without burning. In contrast, when the applied power exceeds 1200W, most traditional overcurrent protection elements will burn and cannot be used.

[0049] In the thermal drop effect test, the overcurrent protection element 10 of the present invention has a trigger current thermal decay rate between 35% and 42%. Specifically, the trigger current thermal decay rate is defined as the trigger current required by the overcurrent protection element in an environment of 125°C divided by the trigger current required by the overcurrent protection element in an environment of 25°C, and then converted into a percentage. The thermal drop effect test is used to compare the difference in the trigger current of the overcurrent protection element 10 of the present invention under different ambient temperatures, thereby evaluating the impact of high temperature on operability. Ideally, it is expected that the trigger current of the overcurrent protection element 10 of the present invention can be maintained at the same value under various temperatures, stabilized at the preset trigger current to play a protective role, and facilitate operation. In contrast, the trigger current thermal decay rate of the conventional overcurrent protection element is lower than 34%, which means it is lower than the lower limit value (35%) of the trigger current thermal decay rate of the overcurrent protection element 10 of the present invention. It can be seen from this that the current required for the overcurrent protection element 10 of the present invention to be triggered is less affected by temperature, and can be stabilized at the preset trigger current to play a protective role, which is convenient for operation.

[0050] In the resistance-temperature test, the overcurrent protection element 10 of the present invention has a resistance peak maintenance rate between 0.4 and 1.1. Specifically, the overcurrent protection element has a first resistance peak when triggered once at a temperature of 200°C, and has a second resistance peak when triggered three times at a temperature of 200°C. The second resistance peak divided by the first resistance peak is the aforementioned resistance peak maintenance rate. The resistance peak maintenance rate can be used to evaluate the stability of the high-resistance state of the overcurrent protection element at high temperatures. In more detail, after the overcurrent protection element 10 of the present invention is triggered multiple times, its resistance peak maintenance rate is not only within the aforementioned range, but can generally be maintained at 1. It can be seen that after the overcurrent protection element 10 of the present invention is actuated multiple times, it can still jump to a high-resistance state and maintain excellent current interruption capability. In contrast, the resistance peak maintenance rates of most traditional overcurrent protection elements are far below 0.3, indicating that the amplitude of the resistance value jump after multiple actuations is low, and the overcurrent protection capability is poor.

[0051] As described above, the present invention can make the overcurrent protection element 10 have good electrical characteristics at high temperatures. The following Tables 1 to 7 are further explained with actual verification data.

[0052] Table 1. Main polymers of polymer matrix

[0053] polymer Melt flow index (g / 10min) Melting point(℃) PVDF-1 1.1 181 PVDF-2 0.55 171 PVDF-3 1.5 170

[0054] Table 2. Ratio of thermistor layer (vol%)

[0055] Group PVDF-1 PVDF-2 PVDF-3 PTFE <![CDATA[Mg(OH)2]]> CB E1 46.1 11 0 4.7 3.2 35 E2 35.1 22 0 4.7 3.2 35 E3 29.1 28 0 4.7 3.2 35 C1 57.1 0 0 4.7 3.2 35 C2 0 0 57.1 4.7 3.2 35 C3 59 0 0 4.2 3.2 33.6

[0056] As shown in Table 1, the main polymers that can be used for the polymer matrix include three types of polyvinylidene difluoride (PVDF), which can also be referred to as the first polyvinylidene fluoride (PVDF-1), the second polyvinylidene fluoride (PVDF-2) and the third polyvinylidene fluoride (PVDF-3). In terms of melting point, the melting points of PVDF-1, PVDF-2 and PVDF-3 are 181°C, 171°C and 170°C respectively. As for the melt flow index, it is measured according to the standard specification of ASTM D1238. Among the three, PVDF-2 has the lowest melt flow index of 0.55g / 10min; while PVDF-1 and PVDF-3 have higher melt flow indexes of 1.1g / 10min and 1.5g / 10min respectively.

[0057] Continuing to refer to Table 2, Table 2 shows the formula ingredients of thermistor layer of each embodiment of the present invention (Group E1 to Group E3) and comparative example (Group C1 to Group C3) in volume percentage. The first column shows each group from top to bottom, namely, embodiment E1 to comparative example C3. The first row shows the various material ingredients in the thermistor layer from left to right, namely polyvinylidene fluoride (PVDF-1, PVDF-2 and PVDF-3), polytetrafluoroethylene (Polytetrafluoroethylene, PTFE), magnesium hydroxide (Magnesium oxide, Mg(OH)2) and carbon black (Carbon black, CB). Magnesium hydroxide can be used as a flame retardant and neutralize the hydrofluoric acid generated by fluorine-containing polymers at high temperatures. In order to improve the voltage resistance characteristics, the conductive filler in this experiment is composed of carbon black.

[0058] In Examples E1 to E3 of the present invention, the main component of the polymer matrix is ​​composed of two PVDFs (PVDF-1 and PVDF-2), and the secondary component is PTFE. Since PTFE has a melting point much higher than that of PVDF (about 330°C), the proportion of PTFE should not be too large to avoid affecting the processability and triggering characteristics of the overcurrent protection element. In other words, the relative proportion of PVDF and PTFE must be appropriately adjusted. However, it should be noted that the main component of the polymer matrix has two PVDFs with different physical and chemical properties, rather than a single type of PVDF, so the complexity of the formula design between PVDF and PTFE is greater. In combination with the types of flame retardants and conductive fillers, the optimal ratio of PVDF:PTFE obtained by the present invention is about 12:1. Therefore, in the formula of Table 2, the total volume percentage of PVDF-1 and PVDF-2 is about 57.1%, and the volume percentage of PTFE is 4.7%. In addition, since PVDF-2 has low fluidity at high temperatures, a high content will be detrimental to mixing, pressing or other similar processing inconveniences and affect electrical properties. Alternatively, if the PVDF-2 content is too high, when a higher light dose is subsequently used to promote polymer cross-linking, the PTC composite material (i.e., thermistor layer 11) is prone to generate bubbles and destroy the structure of the layer. Considering the impact of errors, the PVDF-2 content is roughly less than or equal to PVDF-1, that is, the ratio of PVDF-1:PVDF-2 between 5:1 and 1:1 has the same technical effect.

[0059] In Comparative Examples C1 to C3, the main component of the polymer matrix is ​​a single type of PVDF, and the secondary component is PTFE. In combination with the types of flame retardants and conductive fillers, traditionally, a single PVDF is often used as the main component of the polymer matrix. However, whether PVDF-1 or PVDF-3 is selected, the electrical characteristics of the overcurrent protection element are not good. Subsequent tests will show that Examples E1 to E3 of the present invention are better than Comparative Examples C1 to C3 in performance.

[0060] The manufacturing process of the overcurrent protection element of Examples E1 to E3 of the present invention and Comparative Examples C1 to C3 is described as follows. First, based on the formula presented in Table 1, the materials in the formula are added to a twin-screw mixer produced by HAAKE for mixing. The mixing temperature is set to 215°C, the premixing time is 3 minutes, and the mixing time is 15 minutes. After mixing, a conductive polymer can be obtained and a hot press is used at 210°C and 150kg / cm 2 The sheet was then cut into squares of about 20 cm x 20 cm. Then, the hot press was used again at 210°C and 150 kg / cm 2 The two nickel-plated copper foils are pressed onto the two sides of the conductive polymer sheet with a pressure of 100° to form a three-layer plate. Finally, a punch is used to punch out multiple chips from the plate, which are the overcurrent protection components. The length and width of the overcurrent protection component are 7.8 mm and 8.15 mm respectively (i.e., the top view area is 63.57 mm). 2 ), and the thickness is 0.21 mm. Then, after the wafers prepared in the embodiment and the comparative example were irradiated with a light dose of 200 kGy (the light dose can be adjusted according to the needs and is not a limiting condition of the present invention), 15 wafers were taken as test samples for subsequent tests.

[0061] Tables 3 to 7 respectively show the test data of the specific power trigger test, the cycle life test (I), the cycle life test (II), the heat drop effect test and the resistance-temperature test.

[0062] Table 3. Specific power trigger test

[0063]

[0064] As shown in Table 3, the first column shows the verification items from left to right.

[0065] R i , refers to the initial resistance value of the overcurrent protection element at room temperature.

[0066] R trip , refers to the resistance value of the overcurrent protection element after 16V / 40A is applied for 3 minutes and cooled to room temperature. Based on this, Rtrip / R i , which is the first resistance jump rate mentioned above.

[0067] In addition, according to the volume resistivity formula ρ = R × A / L, R is the resistance value, L is the thickness, and A is the area. Based on this, R i and R trip Substitute into the formula to obtain the volume resistivity ρ i and trip .

[0068] The overcurrent protection element is also known as a resettable fuse, so after the actuation (triggering) is completed, it can be restored to a low resistance state by cooling down. Therefore, the resistance recovery ability after triggering is very important. If the resistance recovery ability is good, the overcurrent protection element can be reused without affecting the normal operation of other elements. It also means that the resistance of the overcurrent protection element is more stable. The first resistance jump rate (R trip / R i ) is the resistance recovery capability after a single trigger. The lower the value, the better the ability of the overcurrent protection element to recover the low resistance state. As shown in Table 3, the first resistance jump rate (R trip / R i ) is 1.333 to 1.484, while the first resistance jump rate (R trip / R i ) is 1.505 to 1.706. It can be noted that the first resistance jump rate (R trip / R i ) is lower than the first resistance jump rate (R trip / R i ), that is, the first resistance jump rate (R trip / R i ) are lower than the first resistance jump rate (R trip / R i ). It can be seen from this that the resistance recovery capability and resistance stability of the overcurrent protection element 10 of the present invention are far superior to those of the traditional overcurrent protection element.

[0069] Table 4. Cycle life test (I)

[0070]

[0071] As shown in Table 4, the first column shows the verification items from left to right.

[0072] R 2000C, refers to the resistance value of the overcurrent protection element after 2000 cycles of cycle life test and cooling to room temperature. The cycle life test conditions are 30V / 40A voltage / current applied for 10 seconds, then turned off for 60 seconds as one cycle. This is repeated 2000 times.

[0073] Unlike the aforementioned specific power trigger test, the cycle life test uses a high power that can cause a trigger event to be applied repeatedly. In this way, the cycle life test can further observe the resistance stability of the overcurrent protection element after multiple triggers. 2000C / R i This is the second resistance jump rate mentioned above, which can be used to evaluate the resistance stability after multiple triggering. The second resistance jump rate (R 2000C / R i ) is 1.583 to 1.78, while the second resistance jump rate (R 2000C / R i ) is 1.989 to 2.364. Similarly, the second resistance jump rate (R 2000C / R i ) are much higher than the second resistance jump rate (R 2000C / R i ), indicating that the resistance recovery capability and resistance stability of the overcurrent protection element 10 of the present invention are far superior to those of the traditional overcurrent protection element.

[0074] In addition, to ensure the consistency of the overcurrent protection element of the present invention during mass production, this experiment further calculates R 2000C Please refer to the following standard deviation formula:

[0075]

[0076] S is the standard deviation. n is the number of samples. As mentioned above, each group takes 15 wafers to be tested for verification, so n is 15. i is the R of each chip 2000C . R for 15 chips 2000C Referring to Table 4, the R 2000C The standard deviation is 0.000934Ω to 0.001098Ω, which is much lower than the R of Comparative Examples C1 to C3. 2000CThe above results show that after the cycle life test, the resistance values ​​of the 15 overcurrent protection elements of each embodiment are less different from each other. In other words, the electrical characteristics of the element are stable, and when the overcurrent protection elements are actually mass-produced, the resistance values ​​of the overcurrent protection elements are more consistent.

[0077] Table 5. Cycle life test (II)

[0078] Group 24V / 40A_6700C 30V / 40A_3000C 36V / 40A_1000C Power handling capacity (W) E1 pass pass pass 1440 E2 pass pass pass 1440 E3 pass pass pass 1440 C1 pass Failed Failed 1200 C2 pass Failed Failed 1200 C3 pass pass pass 1440

[0079] In order to truly evaluate the durability of the overcurrent protection element, this experiment further designs three cycle life test conditions.

[0080] 24V / 40A_6700C refers to the conditions of the first cycle life test, the applied power is 24V / 40A, and the number of cycles is 6700. 30V / 40A_3000C refers to the conditions of the second cycle life test, the applied power is 30V / 40A, and the number of cycles is 3000. 36V / 40A_1000C refers to the conditions of the third cycle life test, the applied power is 36V / 40A, and the number of cycles is 1000.

[0081] As can be seen from Table 5, the embodiments E1 to E3 of the present invention can all pass the first cycle life test, the second cycle life test and the third cycle life test without burning. However, the comparative examples C1 to C2 all burned in the second cycle life test and the third cycle life test, and only the comparative example C3 did not burn. In other words, most of the conventional overcurrent protection elements cannot withstand the repeated application of power higher than 1200W. On the contrary, the overcurrent protection element 10 of the present invention has excellent durability, and can withstand 1000 cycles of testing without burning even when the applied power is as high as 1440W.

[0082] Table 6. Thermal drop effect test

[0083]

[0084] As shown in Table VI, the first column shows the verification items from left to right.

[0085] IT 25℃ and IT 125℃ , respectively, refers to the trigger current of the overcurrent protection element at 25℃ and 125℃. 25℃ / area is the trigger current per unit area at 25°C. In addition, the voltage at the time of triggering in this test is 30V to 36V, which can be further calculated to obtain the power per unit area of ​​the overcurrent protection element at 25°C.

[0086] IT 125℃ / IT 25℃ This is the thermal decay rate of the trigger current defined above. For ease of discussion, IT 125℃ Divide by IT 25℃ The ratio obtained is converted into a percentage. As mentioned above, the current required to trigger the overcurrent protection element will be different at different ambient temperatures. In a low temperature environment, the overcurrent protection element has a lower resistance value, and the current required to trigger will be relatively large. In a high temperature environment, the overcurrent protection element has a higher resistance value, and the current required to trigger will be relatively small. Therefore, the thermal decay rate of the trigger current (IT 125℃ / IT 25℃ ) can be used to evaluate the effect of temperature rise on the operability of the overcurrent protection element. The trigger current thermal decay rate (IT) of the embodiments E1 to E3 of the present invention is 125℃ / IT 25℃ ) is 36.9% to 41.2%, while the trigger current thermal decay rate (IT 125℃ / IT 25℃ ) is 30.5% to 33.6%. Obviously, the trigger current thermal decay rate (IT 125℃ / IT 25℃ ) are much higher, which means that the trigger current is more stable under different ambient temperatures. 125℃ / IT 25℃ ) is as low as 30.5%, indicating that the trigger current is far less than half at 125°C, which is quite unstable. From the above, it can be seen that at the untriggered ambient temperature, the embodiments E1 to E3 of the present invention can play a relatively stable protective role, which is convenient for operation.

[0087] Table VII. Resistance-Temperature Test

[0088] Group <![CDATA[R max1 ]]> <![CDATA[R max3 ]]> <![CDATA[R max3 / R max1 ]]> E1 <![CDATA[2.734×10 5 ]]> <![CDATA[1.339×10 5 ]]> 0.49 E2 <![CDATA[1.784×10 5 ]]> <![CDATA[1.859×10 5 ]]> 1.04 E3 <![CDATA[1.334×10 5 ]]> <![CDATA[1.459×10 5 ]]> 1.09 C1 <![CDATA[2.919×10 5 ]]> <![CDATA[2.561×10 4 ]]> 0.09 C2 <![CDATA[1.278×10 3 ]]> <![CDATA[3.769×10 2 ]]> 0.29 C3 <![CDATA[2.058×10 5 ]]> <![CDATA[1.590×10 4 ]]> 0.08

[0089] This experiment further analyzes the stability of the high resistance state of the overcurrent protection element after it is triggered by the resistance-temperature test. The resistance-temperature test is to place the overcurrent protection element in a heating device and observe the corresponding resistance value of the overcurrent protection element at a specific temperature. The heating device starts from 40℃ and continues to heat up to 230℃ at a rate of 5℃ / min. The overcurrent protection element will be triggered to the highest resistance state at about 200℃, and the corresponding resistance value (i.e. resistance peak) at this temperature point can be measured.

[0090] It should be understood that after the overcurrent protection element is triggered by high temperature multiple times, its resistance jump ability will also decay. Therefore, the above resistance-temperature test can be cycled multiple times, and the change in the resistance value of the overcurrent protection element at 200°C can be observed. The above action of rising from low temperature (40°C) to high temperature (230°C) and then falling back to low temperature (40°C) is a cycle. After the overcurrent protection element is cycled through the resistance-temperature test once, its resistance peak value R at 200°C can be measured. max1 , which is the first resistance peak mentioned above. After the overcurrent protection element is subjected to three cycles of resistance-temperature test, its resistance peak value R at 200°C in the third cycle can be measured. max3 , which is the second resistance peak mentioned above. R max3 With R max1 The ratio (R max3 / R max1 ) can be used to evaluate the stability of the resistance value in the high resistance state, which can also be called the resistance peak maintenance rate. As shown in Table 7, the resistance peak maintenance rate (R max3 / R max1 ) is 0.49 to 1.09, which is much higher than 0.29 (i.e., the resistance peak maintenance rate of the best comparative example C2). It should be particularly noted that the resistance peak maintenance rate (R max3 / R max1 ) is about 1, which means that after three cycles of resistance-temperature testing, the resistance value in the high resistance state can still be maintained at almost the same value. It can be seen that the overcurrent protection element 10 of the present invention can maintain a stable resistance jump capability when triggered, and the resistance stability is excellent.

[0091] The technical content and technical features of the present invention have been disclosed as above, but a person skilled in the art with ordinary knowledge may still make various substitutions and modifications based on the teachings and disclosures of the present invention without departing from the spirit of the present invention. Therefore, the protection scope of the present invention should not be limited to those disclosed in the embodiments, but should include various substitutions and modifications without departing from the present invention, and be covered by the following claims.

Claims

1. An overcurrent protection element, comprising: an electrode layer having an upper metal layer and a lower metal layer; and A thermistor layer contacts the upper metal layer and the lower metal layer and is stacked therebetween, wherein the thermistor layer has a positive temperature coefficient characteristic and comprises: A polymer substrate comprises a first fluorine-containing polymer and a second fluorine-containing polymer, wherein: The first fluorine-containing polymer has a first melting point; The second fluorine-containing polymer has a second melting point less than the first melting point, and the first melting point is less than the second melting point by less than 14° C.; and The second fluorine-containing polymer has a second melt flow index between 0.4 g / 10 min and 0.7 g / 10 min; and A conductive filler is dispersed in the high molecular polymer matrix and is used to form a conductive channel of the thermistor layer. 2 . The overcurrent protection device according to claim 1 , wherein a difference between the first melting point and the second melting point is 5° C. to 14° C. 3 . The overcurrent protection element according to claim 1 , wherein based on 100% of the volume of the thermistor layer, the volume percentage of the first fluorine-containing polymer is 28% to 48%, and the volume percentage of the second fluorine-containing polymer is 10% to 30%.

4. The overcurrent protection element according to claim 1, wherein the second fluorine-containing polymer is represented by the following formula (I): in: R1 and R2 are selected from the group consisting of CH2, CF2, CHF, C2HF3, C2H2F2, C2H3F, C2H4 and C2F4; R1 is different from R2; and n is at least 9000. 5 . The overcurrent protection device as claimed in claim 1 , wherein the second melting point of the second fluorine-containing polymer is between 168° C. and 174° C. 6 . The overcurrent protection device as claimed in claim 1 , wherein the first fluorine-containing polymer has a first melt flow index between 0.8 g / 10 min and 1.4 g / 10 min. The overcurrent protection device as claimed in claim 1 , wherein the second fluorine-containing polymer is polyvinylidene fluoride.

8. The overcurrent protection device according to claim 1, wherein the high molecular polymer substrate further comprises a third fluorine-containing polymer selected from the group consisting of polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, perfluoroalkylene-modified tetrafluoroethylene, poly(chlorotri-fluorotetrafluoroethylene), difluoroethylene-tetrafluoroethylene polymer, tetrafluoroethylene-perfluorodioxole copolymer, difluoroethylene-hexafluoropropylene copolymer, difluoroethylene-hexafluoropropylene-tetrafluoroethylene terpolymer and any combination thereof. 9 . The overcurrent protection device according to claim 8 , wherein the third fluorine-containing polymer is polytetrafluoroethylene, and based on the volume of the thermistor layer being 100%, the volume percentage of polytetrafluoroethylene is 4% to 6%.

10. The overcurrent protection device according to claim 1, wherein the thermistor layer further comprises a flame retardant selected from the group consisting of zinc oxide, antimony oxide, aluminum oxide, silicon oxide, calcium carbonate, magnesium sulfate or barium sulfate, magnesium hydroxide, aluminum hydroxide, calcium hydroxide, barium hydroxide and any combination thereof. The overcurrent protection device according to claim 1 , wherein the conductive filler consists of carbon black.

12. The overcurrent protection device according to claim 1, wherein the overcurrent protection device has a first resistance jump rate between 1.3 and 1.5, wherein: The overcurrent protection element has an initial resistance value; The overcurrent protection element has a second resistance value after being applied with 16V / 40A for 3 minutes and cooled to room temperature; and The second resistance value divided by the initial resistance value is the first resistance jump rate.

13. The overcurrent protection device according to claim 1, wherein the overcurrent protection device has a second resistance jump rate between 1.5 and 1.8, wherein: The overcurrent protection element has an initial resistance value; The over-current protection element has a third resistance value after being subjected to a 30V / 40A cycle life test for 2000 times and cooled to room temperature; and The third resistance value divided by the initial resistance value is the second resistance jump rate. 14 . The over-current protection device as claimed in claim 13 , wherein a standard deviation of the third resistance value is between 0.0009Ω and 0.0011Ω. 15 . The over-current protection device as claimed in claim 1 , wherein the thermistor layer has a thickness between 0.11 mm and 0.17 mm, and the over-current protection device can withstand a power of 1400 W to 1500 W.

16. The overcurrent protection element according to claim 1, wherein the overcurrent protection element has a trigger current thermal decay rate between 35% and 42%, wherein the trigger current thermal decay rate is defined as the trigger current required by the overcurrent protection element in an environment of 125°C divided by the trigger current required by the overcurrent protection element in an environment of 25°C, and then converted into a percentage.

17. The overcurrent protection device according to claim 1, wherein the overcurrent protection device has a resistance peak maintenance ratio between 0.4 and 1.1, wherein: The overcurrent protection element is triggered once at a temperature of 200° C. and has a first resistance peak value; The overcurrent protection element is triggered three times at a temperature of 200° C. and has a second resistance peak value; as well as The second resistance peak divided by the first resistance peak is the resistance peak maintenance rate.

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