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 fluoropolymer has a first volume and a first melt flow index, and the second fluoropolymer has a second volume and a second melt flow index. The second melt flow index is between 0.4 g / 10min and 0.7 g / 10min and is lower than the first melt flow index, and the volume ratio of the first volume divided by the second volume is between 0.4 and 0.6.

Description

Technical Field

[0001] The present invention relates to an overcurrent protection element, and more particularly to an overcurrent protection element with low volume resistivity for high power applications. 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 channel. For electronic devices with higher protection temperature requirements, the substrate often uses a fluorine-containing polymer (such as polyvinylidene fluoride) as its main component. In addition, the composition of the conductive filler can be roughly divided into two types: the first type of conductive filler is composed of carbon black and at least one conductive ceramic powder, metal particles or metal compounds, and the second type of conductive filler is composed of carbon black. The first type of conductive filler mentioned above can be called a low volume resistivity conductive filler, and the overcurrent protection element containing such a conductive filler can be called a low volume resistivity overcurrent protection element. Traditionally, the low volume resistivity overcurrent protection element with polyvinylidene fluoride as the main component of the substrate (hereinafter referred to as "PVDF low volume resistivity overcurrent protection element") has better electrical conduction capability, but has poor voltage resistance characteristics and cannot withstand high power impact. In more detail, the overcurrent protection element is also known as a resettable fuse. After the actuation (triggering) is completed, it can be restored to a low resistance state by cooling down, which means that the fuse can be reused (perform multiple protection actions). However, the power it withstands during the aforementioned actuation (triggering) is not unlimited. If the power is too large, the overcurrent protection element will burn out directly and can no longer be reused. In other words, the power that the overcurrent protection element can withstand (also called the use power) and the number of cycles it can withstand have their limits. It should be understood that the miniaturization of components is the current trend, and the above-mentioned high-power impact problem is aggravated as the size of the overcurrent protection element becomes smaller.

[0004] In summary, the durability of existing low volume resistivity overcurrent protection components still has considerable room for improvement. Summary of the invention

[0005] The present invention provides an overcurrent protection element. 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 durability 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 fluidity of the second fluoropolymer is less than that of the first fluoropolymer, and the melt flow index is between 0.4g / 10min and 0.7g / 10min, which is conducive to supporting the material stability of the thermistor layer when it is actuated at high temperature. In addition, the present invention further adjusts the first fluoropolymer with high fluidity and the second fluoropolymer with low fluidity to a specific volume ratio, and it is observed that the overcurrent protection element can have excellent durability, which means that it can withstand repeated high-power impacts without burning.

[0006] According to one embodiment of the present invention, an overcurrent protection element comprises an electrode layer and a thermistor layer. The electrode layer has an upper metal layer and a lower metal layer. 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 comprises a polymer substrate and a conductive filler. The polymer substrate comprises a first fluoropolymer and a second fluoropolymer. The first fluoropolymer has a first volume and a first melt flow index, and the second fluoropolymer has a second volume and a second melt flow index. The second melt flow index is between 0.4 g / 10 min and 0.7 g / 10 min and is lower than the first melt flow index, and the volume ratio obtained by dividing the second volume by the first volume is between 0.4 and 0.6. The conductive filler is dispersed in the polymer substrate to form a conductive path of the thermistor layer.

[0007] According to some embodiments, based on 100% of the volume of the high molecular polymer matrix, the volume percentage of the second fluorine-containing polymer is 12% to 16%.

[0008] According to some embodiments, based on 100% of the volume of the thermistor layer, the volume percentage of the high molecular polymer matrix is ​​32% to 56%.

[0009] According to some embodiments, based on 100% of the volume of the thermistor layer, the volume percentage of the conductive filler is 40% to 50%.

[0010] According to some embodiments, the conductive filler includes carbon black and metal carbide.

[0011] According to some embodiments, the metal carbide is selected from the group consisting of tungsten carbide, titanium carbide, vanadium carbide, zirconium carbide, niobium carbide, tantalum carbide, molybdenum carbide, and hafnium carbide.

[0012] According to some embodiments, the overcurrent protection element has a top view area of ​​4 mm 2 Up to 12mm 2 .

[0013] According to some embodiments, the overcurrent protection element has a top surface area of ​​5 mm 2 Up to 10mm 2 , and the thickness of the thermistor layer is less than 0.21 mm.

[0014] According to some embodiments, the thickness of the thermistor layer is 0.11 mm to 0.21 mm.

[0015] According to some embodiments, the first fluoropolymer is polyvinylidene fluoride, and the second fluoropolymer is represented by formula (I):

[0016]

[0017] 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.

[0018] According to some embodiments, the overcurrent protection element has a usage power of 900W or less.

[0019] According to some embodiments, the overcurrent protection element has a use power of 600 W to 900 W. The overcurrent protection element can be cycled for 6000 times at a power of 600 W to 800 W without burning out. The overcurrent protection element can be cycled for 500 times at a power of 900 W without burning out.

[0020] According to some embodiments, the resistance value of the over-current protection element after being subjected to 600W cycles for 500 times and then cooled to room temperature is between 0.05Ω and 0.2Ω.

[0021] According to some embodiments, the resistance value of the over-current protection element after being subjected to 800W cycles for 500 times and then cooled to room temperature is between 0.09Ω and 0.7Ω.

[0022] According to some embodiments, the overcurrent protection device has a low temperature trigger current thermal decay ratio between 0.5 and 0.6. The low temperature trigger current thermal decay ratio is defined as the trigger current required by the overcurrent protection device at 85°C divided by the trigger current required by the overcurrent protection device at 23°C.

[0023] According to some embodiments, the overcurrent protection device has a high temperature trigger current thermal decay ratio between 0.2 and 0.3. The high temperature trigger current thermal decay ratio is defined as the trigger current required by the overcurrent protection device at 125°C divided by the trigger current required by the overcurrent protection device at 23°C.

[0024] According to some embodiments, the trigger power of the over-current protection element at 23° C. is between 60W and 93W.

[0025] According to some embodiments, the ratio of the trigger power of the over-current protection element to its area at 23° C. is between 9 W / mm 2 With 12W / mm 2 between. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A cross-sectional view showing an overcurrent protection element according to an embodiment of the present invention; and

[0027] Figure 2 show Figure 1 Top view of the overcurrent protection element.

[0028] The reference numerals are described as follows:

[0029] 10Overcurrent protection element

[0030] 11Thermistor layer

[0031] 12 Upper metal layer

[0032] 13 Lower metal layer

[0033] A Length

[0034] B Width DETAILED DESCRIPTION

[0035] 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.

[0036] 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.

[0037] In the present invention, the main component of the high molecular polymer matrix includes two fluoropolymers with different flow characteristics (hereinafter referred to as the first fluoropolymer and the second fluoropolymer). The first fluoropolymer can be the conventionally selected polyvinylidene fluoride, which has higher fluidity in a high temperature environment, and its melt flow index is between about 0.8g / 10min and 1.4g / 10min, such as 0.8g / 10min, 0.9g / 10min, 1g / 10min, 1.1g / 10min, 1.2g / 10min, 1.3g / 10min or 1.4g / 10min. The second fluoropolymer is a fluoropolymer having the same or similar skeleton as the first fluoropolymer, and has lower fluidity in a high temperature environment, and its melt flow index is between about 0.4g / 10min and 0.7g / 10min, such as 0.4g / 10min, 0.45g / 10min, 0.5g / 10min, 0.55g / 10min or 0.6g / 10min. Furthermore, in order to optimize the durability of the overcurrent protection device 10 , the volume ratio of the first fluorine-containing polymer to the second fluorine-containing polymer is adjusted to a specific range.

[0038] In more detail, conventional overcurrent protection elements often use a single type of fluoropolymer (such as polyvinylidene fluoride) as a high-temperature protection polymer matrix; if two fluoropolymers 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 lies in 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 precisely 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 fluoropolymers is far superior to a matrix composed of a single fluoropolymer. Specifically, the introduction of a fluoropolymer that is not easy to flow (i.e., the second fluoropolymer) into the polymer matrix can effectively stabilize the material structure. Furthermore, the present invention notes that when the content of the second fluoropolymer is less than that of the first fluoropolymer and the contents of both are set to a constant value, the overcurrent protection element 10 can withstand multiple cycles of high power without burning. That is, the first fluoropolymer has a first volume and a first melt flow index, and the second fluoropolymer has a second volume and a second melt flow index. The second melt flow index is between 0.4 g / 10min and 0.7 g / 10min and is lower than the first melt flow index, and the volume ratio obtained by dividing the second volume by the first volume is between about 0.4 and 0.6, for example, 0.4, 0.45, 0.5, 0.55 or 0.6. In a preferred embodiment, the aforementioned volume ratio is 0.45 to 0.55. In a best embodiment, the aforementioned volume ratio is 0.5. It should also be mentioned that if the second melt flow index is lower than 0.4 g / 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 electrical properties (especially in high-power applications). If the second melt flow index is higher than 0.7g / 10min, the fluidity of the second fluoropolymer is too good and not much different from that of the first fluoropolymer. Even if the content ratio is adjusted to a higher level, the overall fluidity of the substrate will not be greatly improved.

[0039] Regarding the specific volume content, based on the volume of the polymer substrate being 100%, the volume percentage of the second fluorinated polymer is 12% to 16%, such as 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, 15.5% or 16%. For example, when the volume ratio mentioned above is 0.4, the volume percentage of the first fluorinated polymer can be 30% to 40%; when the volume ratio is 0.5, the volume percentage of the first fluorinated polymer can be 24% to 32%; and when the volume ratio is 0.6, the volume percentage of the first fluorinated polymer can be 20% to 27%. In a preferred embodiment, the volume percentage of the second fluorinated polymer is 13% to 15%. In a best embodiment, the volume percentage of the second fluorinated polymer is 14%. As described above, the present invention not only utilizes two fluorine-containing compounds with different flow characteristics, but also limits the volume ratio of the two compounds to a small range of 0.4 to 0.6, thereby greatly improving the durability of the overcurrent protection element 10.

[0040] 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):

[0041]

[0042] 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.

[0043] 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 170°C and 186°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 fluorine-containing polymer can be present as solid particles uniformly dispersed in the thermistor layer 11 and serve as a nucleation center when the fluorine-containing copolymer recrystallizes, which is conducive to the formation of crystals. Alternatively, based on the high melting point characteristics of the third fluorine-containing polymer, the deformation degree of the third fluorine-containing polymer is small at high temperatures, thereby effectively stabilizing the structural form of the thermistor layer 11 without excessive deformation.

[0044] As for the conductive filler, in addition to carbon black, it also includes at least one metal compound so that the overcurrent protection element 10 has better electrical conduction characteristics. The metal compound is selected from the group consisting of tungsten carbide, titanium carbide, vanadium carbide, zirconium carbide, niobium carbide, tantalum carbide, molybdenum carbide, hafnium carbide, titanium boride, vanadium boride, zirconium boride, niobium boride, molybdenum boride, hafnium boride and zirconium nitride. Considering the compatibility problem, the aforementioned metal compound is preferably selected from the group consisting of metal carbide. That is to say, in a preferred embodiment, the metal carbide is selected from the group consisting of tungsten carbide, titanium carbide, vanadium carbide, zirconium carbide, niobium carbide, tantalum carbide, molybdenum carbide and hafnium carbide. Taking the volume of the thermistor layer 11 as 100%, the volume percentage of the conductive filler is 40% to 50%.

[0045] In addition to the aforementioned high molecular polymer substrate and conductive filler, the thermistor layer 11 further includes an internal filler. The internal filler is selected from the group consisting of barium titanate, strontium titanate, calcium titanate and any combination thereof. More specifically, the present invention does not include conventionally selected flame retardants (such as boron nitride, aluminum nitride, aluminum oxide or magnesium hydroxide), but selects compounds with a perovskite structure (i.e., the above-mentioned barium titanate, strontium titanate and calcium titanate). These compounds have better dielectric properties, and when combined with the first fluorinated polymer and the second fluorinated polymer, the flame retardant effect is also better than that of conventional flame retardants, which can further enhance the overall voltage resistance characteristics of the overcurrent protection element 10.

[0046] 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 , 2.3×2.3mm 2 , 2.5×3mm 2 , 2.8×3.5mm 2 , 4×4mm 2 , 5×5mm 2 、5.1×6.1mm 2 , 5×7mm 2 、7.62×7.62mm 2 、8.2×7.15mm 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 0.25 mm and 0.35 mm. Specifically, the thicknesses of the upper metal layer 12 and the lower metal layer 13 of the overcurrent protection element 10 of the present invention are 0.07 mm each, and the thickness of the thermistor layer 11 is correspondingly 0.11 mm to 0.21 mm, which may be, for example, 0.11 mm, 0.12 mm, 0.13 mm, 0.14 mm, 0.15 mm, 0.16 mm, 0.17 mm, 0.18 mm, 0.19 mm, 0.2 mm, or 0.21 mm. Due to the improved durability, the overcurrent protection element 10 of the present invention can be made smaller in size and has good reproducibility in resisting high-power shocks. In a preferred embodiment, the overcurrent protection element 10 may have a top viewing area of ​​4 mm 2 Up to 12mm 2 , and the thickness of the thermistor layer 11 can be adjusted to be extremely thin (about 0.15mm to 0.17mm). In a preferred embodiment, the top surface area of ​​the overcurrent protection element 10 is 5mm 2 Up to 10mm 2, and the thickness of the thermistor layer 11 is 0.16mm. The overcurrent protection element 10 under this specification is the most stable during electrical testing. 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 demand, such as a surface-mount device (SMD), an axial-leaded device (ALD), a radial-leaded device (RLD) or other types of components.

[0047] 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 cycle life test and a thermal derating effect test.

[0048] In the cycle life test, the use power of the overcurrent protection element 10 of the present invention can reach 600W to 900W. The aforementioned "use power" refers to the applied power that the overcurrent protection element 10 can withstand a certain number of cycles without burning. The condition of the cycle life test is to apply a specific power for 10 seconds and then turn it off for 60 seconds as one cycle. For example, the overcurrent protection element 10 can be cycled 6000 times with a power of 600W to 800W without burning. Or, the overcurrent protection element 10 can be cycled 500 times with a power of 900W without burning. In summary, the overcurrent protection element 10 of the present invention has been significantly improved in durability after being improved. When the number of cycles is fixed, the overcurrent protection element 10 of the present invention can withstand higher power without burning. Or, when the applied power is fixed, the overcurrent protection element 10 of the present invention can withstand higher number of cycles without burning. Regardless of the above situation, the ability of the overcurrent protection element 10 to withstand energy impact can be greatly improved, that is, the durability is improved.

[0049] In addition, the overcurrent protection element 10 of the present invention can not only withstand several impacts of high power, but also can be restored to a low resistance state. For example, the resistance value of the overcurrent protection element after 600W cycle application 500 times and cooling to room temperature is between about 0.05Ω and 0.2Ω. In one embodiment, the aforementioned resistance value is between 0.05Ω and 0.18Ω. In a preferred embodiment, the aforementioned resistance value is between 0.05Ω and 0.11Ω. When the applied power is increased, the overcurrent protection element 10 of the present invention is also not burned and can be restored to a low resistance state. The resistance value of the overcurrent protection element after 800W cycle application 500 times and cooling to room temperature is between about 0.09Ω and 0.7Ω. In one embodiment, the aforementioned resistance value is between 0.09Ω and 0.66Ω. In a preferred embodiment, the aforementioned resistance value is between 0.09Ω and 0.13Ω.

[0050] In the thermal derating test, the overcurrent protection element 10 of the present invention has two trigger current thermal decay ratios for showing the thermal derating conditions at relatively low temperatures (85°C) and relatively high temperatures (125°C). More specifically, the overcurrent protection element 10 of the present invention has a low temperature trigger current thermal decay ratio between 0.5 and 0.6. The low temperature trigger current thermal decay ratio is defined as the trigger current required by the overcurrent protection element in an environment of 85°C divided by the trigger current required by the overcurrent protection element in an environment of 23°C. Secondly, the overcurrent protection element 10 of the present invention has a high temperature trigger current thermal decay ratio between 0.2 and 0.3. The high temperature trigger current thermal decay ratio 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 23°C. The thermal derating 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 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, and stabilized at the preset trigger current to play a protective role, which is convenient for operation. The overcurrent protection element 10 of the present invention is not only resistant to high voltage and high power, but also has no significant thermal drop, and has good operability.

[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 6 further illustrate the actual verification data.

[0052] Table 1. Main polymers of polymer matrix

[0053] polymer Melt flow index (g / 10min) PVDF-1 1.1 PVDF-2 0.55 PVDF-3 6

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

[0055] Group PVDF-1 PVDF-2 PVDF-3 PTFE <![CDATA[BaTiO3]]> <![CDATA[Mg(OH)2]]> CB WC E1 28 14 0 4 10 0 4 40 E2 28 14 0 4 10 0 4 40 E3 28 14 0 4 10 0 4 40 C1 43 0 0 5 10 0 0 42 C2 0 0 45 0 0 5 0 45

[0056] Table 3. Size of overcurrent protection components and proportion of PVDF-2

[0057]

[0058] As shown in Table 1, the main polymers that can be used for polymer substrates 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). According to the standard specification of ASTM D1238, PVDF-2 has the lowest melt flow index of 0.55g / 10min; while PVDF-1 and PVDF-3 have higher melt flow indexes, which are 1.1g / 10min and 6g / 10min respectively.

[0059] Continuing to refer to Table 2, Table 2 shows the formula components of the thermistor layer of each embodiment of the present invention (Group E1 to Group E3) and the comparative examples (Group C1 and Group C2) in volume percentage. The first column shows the groups from top to bottom, namely, Embodiment E1 to Comparative Example C2. The first row shows the various material components in the thermistor layer from left to right, namely, polyvinylidene fluoride (PVDF-1, PVDF-2 and PVDF-3), polytetrafluoroethylene (Polytetrafluoroethylene, PTFE), barium titanate (Barium titanate, BaTiO3), magnesium hydroxide (Magnesium oxide, Mg(OH)2), carbon black (Carbon black, CB) and tungsten carbide (Tungsten carbide, WC). Groups E1 to C1 all use barium titanate to replace the flame retardant traditionally used in overcurrent protection elements, while Group C2 uses the flame retardant traditionally used in overcurrent protection elements (i.e., magnesium hydroxide). As for the conductive filler, in order to improve the conductivity of the component, tungsten carbide is the main component, and carbon black is the secondary component. The combination of tungsten carbide and carbon black can generally be called a conductive filler of a low volume resistivity system.

[0060] 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 10:1 to 11:1. Therefore, in the formula of Table 2, the total volume percentage of PVDF-1 and PVDF-2 is about 42%, and the volume percentage of PTFE is 4%. In addition, the present invention notes that when the ratio of PVDF-1:PVDF-2 is 2:1, the overcurrent protection element has the best durability, so the PVDF-1 and PVDF-2 of Examples E1 to E3 of the present invention are all fixed values. As for Comparative Examples C1 and C2, 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, a single PVDF is traditionally used as the main component of the polymer matrix. However, regardless of whether PVDF-1 or PVDF-3 is selected, the electrical characteristics of the overcurrent protection element are not good. Subsequent experiments will show that Examples E1 to E3 of the present invention are superior to Comparative Examples C1 and C2 in performance.

[0061] Please continue to refer to Table 3. In order to verify that the overcurrent protection element of the present invention can have the same effect when the size is enlarged or reduced, the top view areas of the embodiments E1 to E3 of the present invention are different. In detail, the overcurrent protection elements of the embodiments E2, comparative examples C1 and C2 of the present invention all have the same top view area (i.e., 7.5 mm 2 ), and corresponds to the same product model (ie, 1210); the size of the overcurrent protection element of embodiment E1 of the present invention is slightly enlarged, with an upper viewing area of ​​9.8mm 2 , and its corresponding model is between 1210 and 1812; and the size of the overcurrent protection element of the third embodiment of the present invention is slightly reduced, with a top view area of ​​5.29mm 2, and its corresponding model is 1206. It should be noted that in the industry, the length of the overcurrent protection element of the aforementioned model 1210 is about 3mm to 3.43mm, and the width is about 2.35mm to 2.8mm; the length of the overcurrent protection element of model 1812 is about 4.37mm to 4.73mm, and the width is about 3.07mm to 3.41mm; and the length of the overcurrent protection element of model 1206 is about 3mm to 3.4mm, and the width is about 1.5mm to 1.8mm. As for thickness, the upper metal layer and the lower metal layer of all groups of overcurrent protection elements are copper foil, and each copper foil has a thickness of 2oz (i.e. 0.07mm). Therefore, the thickness of the thermistor layer of embodiments E1 to E3 of the present invention and comparative example C1 is 0.16mm; and the thickness of the thermistor layer of comparative example C2 is 0.21mm. In addition, as mentioned above, the present invention sets PVDF-1 and PVDF-2 to fixed values ​​in order to optimize durability, so Table 3 also lists the ratio of PVDF-1 to PVDF-2. PVDF-2 / PVDF-1 refers to the ratio of the volume of PVDF-2 divided by the volume of PVDF-1. Considering the influence of errors and the allowable range of variation, the aforementioned ratio (PVDF-2 / PVDF-1) of about 0.4 to 0.6 has the same technical effect, such as 0.4, 0.45, 0.5, 0.55 or 0.6. PVDF-2 / (PVDF-1+PVDF-2) refers to the ratio of PVDF-2 to the main components of the substrate, that is, the volume of PVDF-2 divided by the sum of the volumes of PVDF-1 and PVDF-2. Considering the influence of errors and the allowable variation range, the aforementioned ratio (PVDF-2 / (PVDF-1+PVDF-2)) of about 0.3 to 0.4 has the same technical effect, such as 0.3, 0.35 or 0.4.

[0062] The manufacturing process of the overcurrent protection element of Examples E1 to E3 of the present invention and Comparative Examples C1 to C2 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 at 210°C and 150 kg / cm 2The two nickel-plated copper foils are pressed onto the two sides of the conductive polymer sheet with a pressure of , forming a plate with a three-layer structure. Finally, a punch press is used to punch out a plurality of chips from the plate, and these chips are the overcurrent protection elements. Next, the chips prepared in the embodiment and the comparative example are 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), and 15 of each are taken as test samples for subsequent tests.

[0063] Table 4. Cycle life test

[0064]

[0065] As shown in Table 4, the first column shows the verification items from left to right.

[0066] R 500C @12V / 50A refers to the resistance value of the overcurrent protection element after 500 cycles of cycle life test and cooling to room temperature. The condition of this cycle life test is that the voltage / current of 12V / 50A is applied for 10 seconds and then turned off for 60 seconds as one cycle. This is repeated 500 times.

[0067] R 500C @16V / 50A refers to the resistance value of the overcurrent protection element after 500 cycles of cycle life test and cooling to room temperature. The condition of this cycle life test is that the voltage / current of 16V / 50A is applied for 10 seconds and then turned off for 60 seconds as one cycle. This is repeated 500 times.

[0068] In addition, in order to ensure the durability of the overcurrent protection element, this test also designed three cycle life test conditions. 600W_6000C refers to the cycle life test condition with an applied power of 600 watts (W) (i.e. 12V / 50A) and a cycle number of 6000. 800W_6000C refers to the cycle life test condition with an applied power of 800W (i.e. 16V / 50A) and a cycle number of 6000. 900W_500C refers to the cycle life test condition with an applied power of 900W (i.e. 18V / 50A) and a cycle number of 500.

[0069] As can be seen from Table 4, Examples E1 to E3 of the present invention can all pass the cycle life test of 800W cycles for 6000 times without burning, and Examples E1 to E2 can further pass the cycle life test of 900W cycles for 500 times without burning. It should be mentioned that when the applied power is 900W, if the number of cycles exceeds 500, Examples E1 to E2 will still burn. In any case, the overcurrent protection element composed of this formula can cycle 500 times under ultra-high power, and the performance is quite good. On the contrary, Comparative Examples C1 and C2 will burn in any of the above-mentioned cycle life tests, and cannot even withstand 600W (12V / 50A) cycles for 500 times. In addition, Examples E1 to E3 of the present invention not only have good durability, but can also recover to a low resistance state after the cycle life test, and their R 500C @12V / 50A is between 0.05Ω and 0.18Ω, and R 500C @16V / 50A is between 0.09Ω and 0.7Ω. As for Comparative Examples C1 and C2, since they cannot pass any cycle life test, the R 500C @12V / 50A and R 500C @16V / 50A, no data can be measured.

[0070] Table 5. Thermal drop effect test

[0071]

[0072] As shown in Table 5, the first column shows the verification items from left to right.

[0073] IT 23℃ 、IT 85℃ and IT 125℃ , respectively, refers to the trigger current of the overcurrent protection element at 23℃, 85℃ and 125℃. 25℃ / area、IT 85℃ / area and IT 125℃ / area refers to the trigger current per unit area of ​​the overcurrent protection element under 23°C, 85°C and 125°C environments, respectively. It should be mentioned that the voltage of the embodiments E1 to E3 when triggered is about 16V, while the voltage of the comparative examples C1 and C2 when triggered is about 6V.

[0074] IT 85℃ / IT 23℃ That is, the low temperature trigger current thermal decay ratio defined above, and IT 125℃ / IT 23℃This is the high temperature trigger current thermal decay ratio defined above. 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 trigger current thermal decay ratio can be used to evaluate the impact of temperature rise on the operability of the overcurrent protection element.

[0075] The low temperature trigger current thermal decay ratio (IT) of the embodiments E1 to E3 of the present invention 85℃ / IT 23℃ ) is 0.53 to 0.56, and the high temperature trigger current thermal decay ratio (IT 125℃ / IT 23℃ ) is 0.27 to 0.28. The low temperature trigger current thermal decay ratio (IT) of Comparative Example C1 and Comparative Example C2 85℃ / IT 23℃ ) and high temperature trigger current thermal decay ratio (IT 125℃ / IT 23℃ ) also roughly falls within the aforementioned range. It can be seen that after the improvement of the embodiments E1 to E3 of the present invention, the durability is greatly improved, and there is no significant reduction in operability. In other words, the composition formula of the present invention will not sacrifice the performance of another electrical characteristic (operability) in order to improve a certain electrical characteristic (durability).

[0076] Table 6. Other electrical characteristics

[0077]

[0078] Table 6 also lists other verification data.

[0079] R i , refers to the initial resistance value of the overcurrent protection element at room temperature.

[0080] R1 refers to the resistance value of the wafer to be tested after it has been reflowed once and then cooled to room temperature. The reflow temperature is between 140°C and 300°C, and the processing time is about 5 minutes. 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 R1 are substituted into the formula to obtain the volume resistivity ρ i And ρ1.

[0081] As mentioned above, the voltage of the embodiments E1 to E3 when triggered is about 16V, and the voltage of the comparative examples C1 and C2 when triggered is about 6V. The triggering power and the triggering power per unit area of ​​the overcurrent protection element under a 23° C. environment can be further calculated.

[0082] In the embodiments E1 to E3 of the present invention, the initial resistance value (R i ) is 0.0042Ω to 0.0099Ω, and R1 is 0.0108Ω to 0.0261Ω. The above values ​​are similar to those of R1 of Comparative Examples C1 and C2. i and R1. However, in terms of the power that can be sustained when triggered (trigger power), the overcurrent protection element 10 of the present invention is significantly higher. More specifically, the trigger power of embodiments E1 to E3 of the present invention is 61.76W to 92.12W, which is much higher than the trigger power of comparative examples C1 and C2 (27W to 44.52W). Similarly, the trigger power per unit area of ​​embodiments E1 to E3 of the present invention is 9.4W / mm 2 Up to 11.675W / mm 2 , which is much higher than the trigger power per unit area of ​​Comparative Example C1 and Comparative Example C2 (3.6W / mm 2 Up to 5.936W / mm 2 The overcurrent protection element 10 of the present invention can not only pass various high-power cycle life tests, but also withstand much higher power when triggered.

[0083] 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 fluoropolymer has a first volume and a first melt flow index; and The second fluoropolymer has a second volume and a second melt flow index, wherein the second melt flow index is between 0.4 g / 10 min and 0.7 g / 10 min and lower than the first melt flow index, and a volume ratio obtained by dividing the second volume by the first volume is between 0.4 and 0.6; and A conductive filler is dispersed in the high molecular polymer matrix to form a conductive channel of the thermistor layer. 2 . The overcurrent protection device according to claim 1 , wherein based on the volume of the high molecular polymer substrate being 100%, the volume percentage of the second fluorine-containing polymer is 12% to 16%. 3 . The overcurrent protection device according to claim 1 , wherein based on the volume of the thermistor layer being 100%, the volume percentage of the high molecular polymer matrix is ​​32% to 56%. 4 . The overcurrent protection device according to claim 1 , wherein based on the volume of the thermistor layer being 100%, the volume percentage of the conductive filler is 40% to 50%. The overcurrent protection device as claimed in claim 1 , wherein the conductive filler comprises carbon black and metal carbide. 6 . The overcurrent protection device according to claim 5 , wherein the metal carbide is selected from the group consisting of tungsten carbide, titanium carbide, vanadium carbide, zirconium carbide, niobium carbide, tantalum carbide, molybdenum carbide and hafnium carbide.

7. The overcurrent protection device according to claim 1, wherein the overcurrent protection device has a top surface area of ​​4 mm 2 Up to 12mm 2 .

8. The overcurrent protection device according to claim 7, wherein the overcurrent protection device has a top view area of ​​5 mm 2 Up to 10mm 2 , and the thickness of the thermistor layer is less than 0.21 mm. 9 . The overcurrent protection element according to claim 8 , wherein the thickness of the thermistor layer is 0.11 mm to 0.21 mm.

10. The overcurrent protection device according to claim 1, wherein the first fluorine-containing polymer is polyvinylidene fluoride, and 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. 11 . The over-current protection device as claimed in claim 1 , wherein the over-current protection device has a power usage of less than 900 W.

12. The overcurrent protection device according to claim 11, wherein the overcurrent protection device has a power usage of 600W to 900W, wherein: The overcurrent protection element can be subjected to 6000 cycles of power application of 600W to 800W without burning out; as well as The overcurrent protection element can withstand 900W power cycle application 500 times without burning out. 13 . The over-current protection device according to claim 12 , wherein the resistance value of the over-current protection device after being subjected to 600W cycle application for 500 times and then cooled to room temperature is between 0.05Ω and 0.2Ω. 14 . The over-current protection device according to claim 13 , wherein the resistance value of the over-current protection device after being subjected to 800W cycle application for 500 times and then cooled to room temperature is between 0.09Ω and 0.7Ω.

15. The overcurrent protection element according to claim 1 has a low-temperature trigger current thermal decay ratio between 0.5 and 0.6, wherein the low-temperature trigger current thermal decay ratio is defined as the trigger current required by the overcurrent protection element in an environment of 85°C divided by the trigger current required by the overcurrent protection element in an environment of 23°C.

16. The overcurrent protection element according to claim 1, wherein the overcurrent protection element has a high-temperature trigger current thermal decay ratio between 0.2 and 0.3, wherein the high-temperature trigger current thermal decay ratio 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 23°C. 17 . The over-current protection device as claimed in claim 1 , wherein a trigger power of the over-current protection device at 23° C. is between 60 W and 93 W.

18. The over-current protection device according to claim 17, wherein the ratio of the trigger power to the area of ​​the over-current protection device at 23°C is between 9W / mm 2 With 12W / mm 2 between.

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