Overcurrent protection element

Abstract

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 is disposed therebetween. The thermistor layer has a positive temperature coefficient characteristic and includes a polymer base material and a conductive filler. The conductive filler includes a metal compound dispersed in the polymer base material, thereby forming a conductive path of the thermistor layer. The metal compound is composed of a metal carbide and inevitable impurities. The metal carbide accounts for 90% or more, based on 100% of the metal carbide and the inevitable impurities.

Description

Technical Field

[0001] This invention relates to an overcurrent protection element, and more specifically, to an overcurrent protection element with low volume resistivity and high resistance stability. Background Technology

[0002] Existing conductive composite materials with a positive temperature coefficient (PTC) exhibit highly sensitive resistance changes to specific temperature variations, making them suitable materials for current sensing elements. They are currently widely used in overcurrent protection components and circuit elements. Specifically, PTC conductive composite materials maintain extremely low resistance at normal temperatures, allowing circuits or batteries to operate normally. However, when an overcurrent or overtemperature event occurs in the circuit or battery, its resistance instantaneously increases to a high-resistance state (at least 10 ohms). 4 (Above Ω), which is called a trip, cuts off the overcurrent to protect the battery or circuit components.

[0003] In terms of basic structure, overcurrent protection elements consist of a PTC material layer and metal electrodes attached to both sides of it. The PTC material layer includes at least a matrix and conductive filler. The matrix is ​​composed of a polymer, while the conductive filler is composed of carbon black and / or metallic materials (such as pure metals, alloys, or other conductive metallic materials) and dispersed within the polymer. As mentioned above, the positive temperature coefficient characteristic of overcurrent protection elements mainly comes from the PTC material layer; therefore, various electrical characteristics of overcurrent protection elements can be further adjusted by modifying the PTC material layer.

[0004] To achieve lower volume resistivity, conductive fillers often incorporate a certain proportion of metallic materials. However, in the raw material market, metallic materials generally suffer from insufficient purity, resulting not only in poor conductivity of overcurrent protection components but also in poor resistance stability. For example, titanium carbide is a viable metallic material, but its production process inevitably leaves behind one or more reactants or byproducts. Therefore, commercially available titanium carbide is not actually pure titanium carbide. For instance, in some common processes, titanium tetrachloride (TiCl4) can be reacted with carbon at high temperatures in a hydrogen atmosphere to produce titanium carbide. However, incomplete reactions can occur during high-temperature processing, leaving unreacted titanium tetrachloride residue. It should be understood that titanium tetrachloride hydrolyzes to produce hydrogen chloride, which can easily corrode components in the PTC material layer, harm the environment, or adversely affect electrical properties. Therefore, magnesium hydroxide (Mg(OH)2) is often added to the PTC material layer to neutralize titanium tetrachloride through an acid-base reaction, avoiding the aforementioned problems. In other commonly used processes, titanium dioxide (TiO2) can react with carbon at high temperatures to form titanium carbide. However, this process can also result in incomplete reactions, leaving some titanium dioxide residue. The surface of titanium dioxide easily adsorbs moisture, causing an increase in the material's resistance. The reactants or byproducts remaining in the aforementioned titanium tetrachloride, titanium dioxide, or other processes can be collectively referred to as impurities. In other words, commercially available titanium carbide inevitably contains excessive impurities. These impurities can adversely affect conductivity, resistance stability, and / or other electrical properties.

[0005] It should also be understood that the resistance stability of overcurrent protection components is particularly important for certain protected products. For example, in a laptop, the motherboard has many USB ports that can connect to external USB connectors for data transfer. Overcurrent may occur the instant the USB port connects to the USB connector; therefore, an overcurrent protection component can be installed on the motherboard in series with the USB port to provide protection. However, it should be noted that the connection between the USB port and the USB connector is detachable, meaning the USB connector will be inserted and removed from the USB port multiple times during use. This repeated connection action is particularly frequent, increasing the risk of multiple triggers; therefore, the resistance stability of the overcurrent protection component is especially important.

[0006] In view of this, there is an urgent need to develop a new overcurrent protection element that has low volume resistivity and excellent resistance stability. Summary of the Invention

[0007] 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. The thermistor layer is stacked between the upper metal layer and the lower metal layer. The thermistor layer has a positive temperature coefficient and includes a polymer substrate and a conductive filler. The polymer substrate includes a polyolefin polymer. The conductive filler includes a metal compound dispersed in the polymer substrate, thereby forming a conductive channel in the thermistor layer. The metal compound consists of metal carbides and unavoidable impurities. The metal carbides account for more than 90% of the content of 100% of the content of the metal carbides and unavoidable impurities.

[0008] According to some embodiments, the maximum particle size of the metal compound is less than 20 μm.

[0009] According to some embodiments, the metal carbide is titanium carbide.

[0010] According to some embodiments, unavoidable impurities include titanium oxide and / or titanium tetrachloride.

[0011] According to some embodiments, the metal compound accounts for 50% to 60% of the thermistor layer volume, which is 100%.

[0012] According to some embodiments, the polyolefin polymer accounts for 40% to 50% of the volume of the thermistor layer, which is 100%.

[0013] According to some embodiments, the polyolefin polymers are selected from the group consisting of low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, polypropylene, and polybutene.

[0014] According to some embodiments, the thermistor layer does not contain flame retardants.

[0015] According to some embodiments, the polymer substrate does not contain fluoropolymers. Fluoropolymers are selected from the group consisting of polyvinylidene fluoride, polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, perfluoroalkyl oxygen-modified tetrafluoroethylene, poly(chlorotrifluorotetrafluoroethylene), difluoroethylene-tetrafluoroethylene polymer, tetrafluoroethylene-perfluorodioxane copolymer, difluoroethylene-hexafluoropropylene copolymer, difluoroethylene-hexafluoropropylene-tetrafluoroethylene trimer, and combinations thereof.

[0016] According to some embodiments, the overcurrent protection element has a resistance jump rate between 1.4 and 1.6. The overcurrent protection element has an initial resistance value; the overcurrent protection element has a first resistance value after being triggered once and cooled to room temperature; and the first resistance value divided by the initial resistance value is the aforementioned resistance jump rate.

[0017] According to some embodiments, the overcurrent protection element has a first volume resistivity between 0.006 Ω·cm and 0.018 Ω·cm, wherein the first volume resistivity is defined as the volume resistivity of the overcurrent protection element without any heat treatment.

[0018] According to some embodiments, the overcurrent protection element has a second volume resistivity between 0.008 Ω·cm and 0.03 Ω·cm, wherein the second volume resistivity is defined as the volume resistivity of the overcurrent protection element after a heat treatment.

[0019] According to some embodiments, the overcurrent protection element has a first permissible current value between 0.4 A / mm². 2 With 0.9A / mm 2 Between, where the first permissible current value is the minimum current value required to trigger the overcurrent protection element at 23°C per unit area.

[0020] According to some embodiments, the overcurrent protection element has a second allowable current value between 0.2 A / mm². 2 With 0.5A / mm 2 Between, where the second permissible current value is the minimum current value required to trigger the overcurrent protection element at 85°C per unit area.

[0021] According to some embodiments, at 85°C, the leakage current of the overcurrent protection element is between 0.04A and 0.06A.

[0022] According to some embodiments, the top view area of ​​the overcurrent protection element is 2 mm². 2 Up to 81mm 2 .

[0023] According to some embodiments, the thickness of the thermistor layer is between 0.13 mm and 0.2 mm. Attached Figure Description

[0024] Figure 1 This shows a cross-sectional view of an overcurrent protection element according to an embodiment of the present invention;

[0025] Figure 2 show Figure 1 Top view of the overcurrent protection element;

[0026] Figure 3 The XRD pattern of commercially available titanium carbide without any treatment is displayed; and

[0027] Figure 4 The XRD patterns of commercially available titanium carbide and carbon black after heat treatment are shown.

[0028] The reference numerals in the attached figures are explained as follows:

[0029] 10 Overcurrent Protection Components

[0030] 11 Thermistor Layer

[0031] 12 upper metal layer

[0032] 13 Lower metal layer

[0033] A Length

[0034] B width Detailed Implementation

[0035] To make the above and other technical contents, features and advantages of the present invention more apparent and understandable, relevant embodiments are provided below, and detailed descriptions are given in conjunction with the accompanying drawings.

[0036] Please refer to Figure 1 This illustrates a basic embodiment 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, while the electrode layer has an upper metal layer 12 and a lower metal layer 13 respectively attached to the upper and lower surfaces of the thermistor layer 11. Thus, the thermistor layer 11 contacts the upper metal layer 12 and the lower metal layer 13 and is stacked between them. In one embodiment, the upper metal layer 12 and the lower metal layer 13 may 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 expands easily when heated, while the conductive filler is a conductor, thereby enabling the thermistor layer 11 to have a positive temperature coefficient characteristic. When the overcurrent protection element 10 is not triggered, the conductive filler is uniformly distributed in the polymer substrate and connected in series to form a conductive channel; while when the overcurrent protection element 10 is affected by high temperature, the volume of the polymer substrate expands and the crystalline region transforms into an amorphous region, causing the conductive channel to be interrupted.

[0037] It should be noted that the conductive filler of the present invention contains high-purity metal compounds dispersed in the polymer substrate, which not only optimizes the conductivity of the conductive channels, but also ensures that the overcurrent protection element 10 maintains a relatively low resistance after multiple triggers, i.e., excellent resistance stability. More specifically, the aforementioned metal compound may be composed of metal carbides and unavoidable impurities, and with the content of metal carbides and unavoidable impurities being 100%, the metal carbides account for more than 90%.

[0038] Regarding PTC materials, it is generally believed that a high-temperature sintering process is required to heat-treat the ceramic filler to obtain ideal low volume resistivity and other electrical properties when subsequently manufacturing overcurrent protection components. The aforementioned sintering process requires a temperature of approximately 1400°C, and in some cases, it is even limited to a specific atmosphere (such as hydrogen). However, the heating equipment used in current industry (e.g., sintering furnaces) at excessively high temperatures (e.g., close to or above 1500°C) significantly increases the likelihood of shortened service life or damage. Furthermore, higher-temperature heat treatment also generates a larger carbon footprint, which is inconsistent with the current trend of sustainable development. In contrast, this invention mixes a metal compound and carbon black in a certain proportion and heat-treats the mixture under vacuum at a temperature far below 1500°C (approximately 1000°C) to obtain a metal compound of extremely high purity. For example, the metal compound can be commercially available titanium carbide, and the metal carbide refers to pure titanium carbide. Therefore, it can be understood that commercially available titanium carbide is actually an impurity, composed of titanium carbide and unavoidable impurities (titanium oxide, titanium tetrachloride, and / or other titanium-containing impurities generated during processing). Under the temperature and atmosphere conditions set in this invention, these impurities can react with carbon black to form titanium carbide. X-ray diffractometer (XRD) analysis shows that the purity of the titanium carbide in this invention can reach over 90%. In this way, the impurity content can be greatly reduced or even completely eliminated, thus significantly improving the purity of commercially available titanium carbide. Besides the aforementioned issues with resistance and resistance stability, low-purity titanium carbide can cause other problems. For example, when the purity is below 90% (i.e., the titanium carbide content is below 90%), these impurities can easily cause PTC materials to absorb water and generate harmful gases (such as hydrogen chloride).

[0039] In the heat treatment of this invention, the molar ratio (mol) of commercially available titanium carbide to carbon black is approximately 1:1 to 10:1. Preferably, the ratio of commercially available titanium carbide is higher than that of carbon black, for example, 3:1 to 5:1. The maximum particle size of the carbon black must be less than 10 micrometers (μm) to prevent the carbon black from agglomerating into clumps and coating impurities, resulting in incomplete carbonization of the impurities. To further ensure the purity of the titanium carbide, large particles of impurities and clumps of residual carbon are sieved out using a sorting machine. Thus, the maximum particle size of the metal compound of this invention is less than 20 μm. At the same time, setting the aforementioned particle size to less than 20 μm also avoids the thermistor layer 11 from being too thick. In one embodiment, the maximum particle size of the metal compound is from 14 μm to 20 μm, for example 14 μm, 14.3 μm, 14.8 μm, 15.1 μm, 15.5 μm, 16 μm, 16.6 μm, 17.3 μm, 18 μm, 18.5 μm, 19 μm, 19.6 μm, 19.9 μm or 20 μm.

[0040] Regarding the composition of the PTC material, the polymer substrate of this invention mainly uses polyolefin polymers, while the conductive filler is mainly composed of the aforementioned metal compounds. The polyolefin polymer is selected from the group consisting of low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, polypropylene, and polybutene. Preferably, the polyolefin polymer is low-density polyethylene or high-density polyethylene. In one embodiment, based on the volume of the thermistor layer 11 as 100%, the polyolefin polymer accounts for 40% to 50%, preferably 44% to 48%, for example 44%, 44.5%, 44.7%, 44.9%, 45%, 45.5%, 45.7%, 45.9%, 46%, 46.5%, 46.7%, 46.9%, 47%, 47.5%, 47.9%, or 48%. In one embodiment, the metal compound comprises 50% to 60% of the thermistor layer 11 by volume, preferably 52% to 56%, for example 52%, 52.1%, 52.5%, 53%, 53.1%, 53.3%, 53.5%, 54%, 54.1%, 54.3%, 54.5%, 55%, 55.1%, 55.3%, 55.5%, or 56%.

[0041] It should be noted that the thermistor layer 11 of the present invention does not contain a flame retardant. Flame retardants are selected from the group consisting of zinc oxide, antimony oxide, aluminum oxide, silicon oxide, calcium carbonate, magnesium sulfate, barium sulfate, magnesium hydroxide, aluminum hydroxide, calcium hydroxide, and barium hydroxide. Traditionally, overcurrent protection elements 10 can have their flammability reduced by flame retardants, allowing them to withstand high currents or high power without burning out. Additionally, in some cases, magnesium hydroxide can be used as an internal filler for acid-base neutralization. However, the present invention does not require flame retardants to withstand high currents or high power without burning out, and it also eliminates the need to consider acid-base neutralization. As a result, the composition of the PTC material is simpler; that is, the present invention reduces the complexity of formulation design while maintaining excellent electrical properties. Furthermore, in some embodiments, the polymer substrate of the overcurrent protection element 10 does not use a fluoropolymer. Fluoropolymers are selected from the group consisting of polyvinylidene fluoride, polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, perfluorocarbon-oxygen-modified tetrafluoroethylene, poly(chlorotrifluorotetrafluoroethylene), difluoroethylene-tetrafluoroethylene polymer, tetrafluoroethylene-perfluorodioxane copolymer, difluoroethylene-hexafluoropropylene copolymer, difluoroethylene-hexafluoropropylene-tetrafluoroethylene trimer, and combinations thereof. It should be understood that the aforementioned polyolefin polymers have higher crystallinity, and therefore generally exhibit better resistance reproducibility than fluorinated polymers. Furthermore, polyolefin polymers often have lower melting points than fluorinated polymers, resulting in correspondingly lower protection temperatures (i.e., lower triggering temperatures). Therefore, in some embodiments, the overcurrent protection element 10, specifically designed for low-temperature protection and high resistance stability, does not contain fluorinated polymers.

[0042] By means of the thermistor layer 11 mentioned above, the overcurrent protection element 10 of the present invention can have good electrical characteristics such as resistance stability, low volume resistivity, high electrical conductivity and low leakage current. These are described in detail below.

[0043] In this invention, resistance stability can be determined by the resistance jump rate (i.e., R below). jump The overcurrent protection element 10 is evaluated. The resistance jump rate is between 1.4 and 1.6, significantly lower than the resistance jump rate of conventional overcurrent protection elements (1.7). Specifically, the overcurrent protection element 10 has an initial resistance value at room temperature when not triggered, and a first resistance value after being triggered once (e.g., due to high reflow temperatures) and cooled to room temperature. The first resistance value divided by the initial resistance value is the aforementioned resistance jump rate. A lower resistance jump rate means better resistance recovery capability or resistance reproducibility of the overcurrent protection element 10, and better resistance reproducibility.

[0044] Regarding volume resistivity, the overcurrent protection element 10 of the present invention maintains a low volume resistivity range regardless of whether it undergoes heat treatment. Specifically, the overcurrent protection element 10 has a first volume resistivity between 0.006 Ω·cm and 0.018 Ω·cm, where the first volume resistivity is defined as the volume resistivity of the overcurrent protection element 10 without any heat treatment; the overcurrent protection element 10 has a second volume resistivity between 0.008 Ω·cm and 0.03 Ω·cm, where the second volume resistivity is defined as the volume resistivity of the overcurrent protection element 10 after one heat treatment. The aforementioned heat treatment may be caused by the high temperature of soldering during component assembly (such as reflow soldering).

[0045] Regarding the high electrical conductivity, the overcurrent protection element 10 of the present invention allows for a larger current flow when not activated, therefore, the minimum current value required for triggering is correspondingly higher. Therefore, the aforementioned minimum current value required for triggering is defined herein as the allowable current value, and it tends to be higher at different temperatures. The overcurrent protection element 10 has a first allowable current value between 0.4 A / mm². 2 With 0.9A / mm 2 The first permissible current value is the minimum current value required to trigger the overcurrent protection element 10 at 23°C, per unit area. The overcurrent protection element 10 has a second permissible current value between 0.2 A / mm². 2 With 0.5A / mm 2The second permissible current value is the minimum current required to trigger the overcurrent protection element 10 at 85°C, per unit area. Furthermore, high-temperature environments highlight other advantages of the invention. At 85°C, the leakage current of the overcurrent protection element 10 is between 0.04A and 0.06A, lower than the leakage current of conventional overcurrent protection elements.

[0046] Please continue to refer to Figure 2 ,for Figure 1 The overcurrent protection element 10 is shown in a top view. The overcurrent protection element 10 has a length A and a width B, and its area "A×B" is equal to the area of ​​the thermistor layer 11. Depending on the product model, the thermistor layer 11 may have a top-view area of ​​2 mm². 2 Up to 81mm 2 For example, an area of ​​"A×B" can be 1.5×1.5mm. 2 2×2mm 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 7.62×9.35mm 2 Or 9×9mm 2 Furthermore, 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 0.2 mm and 0.27 mm. For example, the thickness of the upper metal layer 12 and the lower metal layer 13 of the overcurrent protection element 10 of the present invention can each be 0.035 mm, while the thickness of the thermistor layer 11 can be correspondingly 0.13 mm to 0.2 mm, such as 0.13 mm, 0.14 mm, 0.15 mm, 0.16 mm, 0.17 mm, 0.18 mm, 0.19 mm, or 0.2 mm. In a preferred embodiment, the overcurrent protection element 10 has a top viewing area of ​​7.5 mm². 2 Up to 16mm 2The thickness of the upper metal layer 12 and the lower metal layer 13 is 0.035 mm each; while the thickness of the thermistor layer 11 is 0.15 mm. Considering the influence of error and the allowable range of variation, the thickness of the thermistor layer 11 in the aforementioned preferred embodiment can be adjusted to a range of 0.14 mm to 0.16 mm. Of course, in some embodiments, a thicker metal layer can also be used for the pressure plate, and the thickness of the upper metal layer 12 and the lower metal layer 13 can be adjusted to 0.04 mm each. It should also be noted that a single metal layer (i.e., the upper metal layer 12 or the lower metal layer 13) will not exceed 0.05 mm, which would increase the mass production cost to a level that is not commercially viable, and would not help with the protection stability (such as resistance jump rate) claimed by the present invention. It should be understood that the overcurrent protection element 10 of the present invention has the same technical effect when applied to the above-mentioned dimensions. Furthermore, the overcurrent protection element 10 can be manufactured into industrially common element forms as required, such as surface-mount devices (SMD), axial-leaded devices (ALD), radial-leaded devices (RLD), or other forms of elements.

[0047] To illustrate the technical content of the present invention in more detail, Tables 1 to 7 below are further discussed using actual verification data.

[0048] Table 1. Material Composition of Heating Treatment

[0049]

[0050] As shown in Table 1, groups E1 to E4 are Examples E1 to E4 of the present invention, while group C1 is Comparative Example C1. In Table 1, TiC refers to commercially available titanium carbide, and CB refers to carbon black. Commercially available titanium carbide and carbon black are mixed in different proportions for subsequent heat treatment. In Example E1, the molar percentages of titanium carbide and carbon black are 90.91% and 9.09% (approximately 10:1), respectively, and the weight percentages are 98.04% and 1.96%, respectively. In Example E2, the molar percentages of titanium carbide and carbon black are 83.33% and 16.67% (approximately 5:1), respectively, and the weight percentages are 96.15% and 3.85%, respectively. In Example E3, the molar percentages of titanium carbide and carbon black are 75% and 25% (approximately 3:1), respectively, and the weight percentages are 93.74% and 6.26%, respectively. In Example E4, the molar percentages of titanium carbide and carbon black were 50% and 50% (approximately 1:1), respectively, while the weight percentages were 83.31% and 16.69%, respectively. Comparative Example C1 served as a control group, and therefore its titanium carbide was not mixed with carbon black.

[0051] Table 2. Purity of Titanium Carbide at the Same Heat Treatment Temperature

[0052]

[0053] As shown in Table 2, each group was first heat-treated in a vacuum environment at the same temperature (1050℃). Groups E5 to E8 are Examples E5 to E8 of the present invention, and their material sources correspond to Examples E1 to E4. Group C2 is Comparative Example C2, and its material source corresponds to Comparative Example C1. After heat treatment, XRD analysis was performed. Through XRD, the light intensity corresponding to a specific diffraction angle (2θ) of the sample can be obtained, thereby calculating its material composition. It is known that the diffraction angles (2θ) corresponding to titanium carbide are 36.14°, 41.9°, 60.62°, 70.56°, and 76.34°, while the diffraction angles (2θ) corresponding to impurities are 25.56° and 55.16°. Thus, taking the sum of the intensities corresponding to all the aforementioned diffraction angles as 100%, the proportion of the sum of intensities corresponding to 36.14°, 41.9°, 60.62°, 70.56°, and 76.34° can be calculated, which represents the purity of titanium carbide. The sum of the aforementioned proportions of titanium carbide at 36.14°, 41.9°, 60.62°, 70.56°, and 76.34° can also be referred to as the content of titanium carbide (such as the content of metallic carbides mentioned above), while the sum of the proportions of impurities at 25.56° and 55.16° represents the content of impurities (such as the content of unavoidable impurities mentioned above). For example, in Example E5, the strengths corresponding to 36.14°, 41.9°, 60.62°, 70.56°, and 76.34° accounted for 33.5%, 37.6%, 12.5%, 9.8%, and 5.2%, respectively, totaling 98.5%. In other words, the titanium carbide content in Example E5 was 98.5%, i.e., the purity was 98.5%. Similarly, the titanium carbide content in Examples E6 to E8 was all 100%, i.e., the purity was 100%. In contrast, the titanium carbide purity in Comparative Example C2 was only 89%, indicating that commercially available titanium carbide was not heat-treated with carbon black, and its purity was significantly lower.

[0054] To further clarify the XRD analysis results, please refer to [link / reference]. Figure 3 and Figure 4 . Figure 3 The image shows the XRD analysis results for comparative example C2. Figure 4 This is a graph showing the XRD results of Example E6. The horizontal axis represents the diffraction angle (2θ), expressed in degrees (°). The vertical axis represents intensity, expressed in arbitrary units (au). As mentioned above, titanium carbide exhibits peaks at 36.14°, 41.9°, 60.62°, 70.56°, and 76.34°, while impurities exhibit peaks at 25.56° and 55.16°. Figure 3In the figure, the strengths corresponding to 25.56° and 55.16° are 4568 and 2884, respectively, while the strengths corresponding to 36.14°, 41.9°, 60.62°, 70.56°, and 76.34° are 19321, 22221, 10601, 5452, and 2775, respectively. Figure 4 In the figure, the strength corresponding to 25.56° and 55.16° is 0, while the strengths corresponding to 36.14°, 41.9°, 60.62°, 70.56° and 76.34° are 16188, 21089, 6048, 4528 and 2284 respectively. Therefore, it can be seen that the present invention does indeed obtain titanium carbide with extremely high purity.

[0055] Table 3. Particle size and purity of titanium carbide at different heat treatment temperatures

[0056]

[0057] Based on the results obtained above, this experiment further employed different temperatures to heat-treat each group and control their particle size. Groups E9 to E13 are Examples E9 to E13 of this invention. The materials for Examples E9 to E12 were derived from Example E2, while the materials for Example E13 were derived from Example E4. Examples E9 to E13 were heat-treated in a vacuum at a temperature range of 1050°C to 1250°C. It should be noted that commercially available titanium carbide and carbon black, after the aforementioned heat treatment, are further dispersed using a pulverizer and finally passed through a separator (such as a cyclone separator) to control the titanium carbide particles within the ideal particle size range. Particle size was measured using a Malvern Mastersizer 2000 particle size analyzer. D represents particle size distribution, and the number in square brackets after D represents the proportion of the number of particles. For example, 0.1, 0.5, and 0.9 represent 10%, 50%, and 90%, respectively. For example, D(0.1) represents the particle size represented by this value for 10% of the total particles; the same applies to D(0.5) and d(0.9). D(max) refers to the maximum particle size that can be represented among all particles. Additionally, D(0.5) is the median value of the particle size distribution, also known as the median particle size. As shown in Table 3, the titanium carbide in Examples E9 to E13 all have a purity of 100%, and the maximum particle size is less than 20 μm, falling between 14 μm and 20 μm.

[0058] Next, this experiment continued to apply the aforementioned high-purity titanium carbide to PTC materials, as detailed in Tables 4 to 7 below.

[0059] Table 4. Material Composition of the Thermistor Layer (I) and Component Resistance

[0060]

[0061] Table 4 shows the composition of the thermistor layers in groups E14 to E18 (i.e., Examples E14 to E18) by volume percentage. The polymer substrate is high-density polyethylene (HDPE), and the conductive filler is high-purity titanium carbide (TiC) from Examples E9 to E13. This experiment first produced overcurrent protection elements using thermistor layers with fixed composition ratios to preliminarily verify their resistance characteristics. The fabrication process of the overcurrent protection element is described below. Based on the formulations presented in Table 4, the materials in the formulations were added to a twin-screw mixer manufactured by HAAKE for mixing. The mixing temperature was set at 215°C, the premixing time was 3 minutes, and the mixing time was 15 minutes. After mixing, a conductive polymer was obtained and hot-pressed at 210°C and 150 kg / cm². 2 The material is pressed into thin sheets under pressure, and then cut into squares of approximately 20 cm x 20 cm. Next, it is pressed again using a hot press at 210°C and 150 kg / cm². 2 Pressure is applied to press two nickel-plated copper foils onto both sides of a conductive polymer sheet, forming a three-layer structure. Finally, a punch press is used to stamp multiple wafers from this sheet; these wafers are the overcurrent protection elements. The length and width of the overcurrent protection element are 2.8 mm and 3.5 mm respectively (i.e., a top-view area of ​​9.8 mm²). 2 The overall thickness is 0.22 mm, of which the thermistor layer has a thickness of 0.15 mm. Next, the fabricated wafers are irradiated with a light dose of 15 kGy (the light dose can be adjusted as needed and is not a limitation of this invention), and 15 wafers are taken as test samples for subsequent experiments.

[0062] R i This refers to the initial resistance value of the overcurrent protection element at room temperature. Furthermore, according to the formula for volume resistivity ρ=R×A / L, where R is the resistance value, L is the thickness, and A is the area, R can be further... i Substituting into the formula, the volume resistivity (ρ) is obtained. iIt is known that overcurrent protection elements manufactured using carbon black as a conductive filler generally have a volume resistivity that is difficult to lower than 0.2 Ω·cm. As shown in Table 4, the volume resistivity of Examples E14 to E18 falls within the range of 0.005 Ω·cm to 0.02 Ω·cm, far lower than the aforementioned 0.2 Ω·cm, thus exhibiting extremely low volume resistivity. Particularly noteworthy are the lowest volume resistivity in Examples E16 and E17, at 0.005724 Ω·cm and 0.005123 Ω·cm, respectively. The high-purity titanium carbide used in Examples E16 and E17 were derived from Examples E11 and E12, respectively. Subsequent experiments will use these two types of titanium carbide to adjust the composition ratio of the thermistor layer. Please see Tables 5 to 7 below.

[0063] Table 5. Material Composition (II) of Thermistor Layer and Basic Electrical Characteristics of Components

[0064]

[0065] Table 6. Electrical characteristics of overcurrent protection components at 23°C

[0066]

[0067] Table 7. Electrical characteristics of overcurrent protection components at 85°C

[0068]

[0069] Table 5 also shows the composition of the thermistor layer in groups E19 to E23 (i.e., Examples E19 to E23) and group C3 (i.e., Comparative Example C3) as a volume percentage. The polymer substrate in each group is high-density polyethylene, and the conductive filler is titanium carbide treated under different conditions. The titanium carbide in Example E19 is derived from Example E11, while the titanium carbide in Examples E20 to E23 is derived from Example E12. The titanium carbide in Comparative Example C3 is derived from Comparative Example C2, which is commercially available low-purity titanium carbide, i.e., the control group. The overcurrent protection element is manufactured in the same way as described above and will not be repeated here. However, it should be noted that when manufacturing the overcurrent protection element with the material composition of Comparative Example C3, the thickness of the thermistor layer needs to be adjusted to 0.18 mm, thus achieving an overall thickness of 0.25 mm. The reason is that if the thickness of the thermistor layer in Comparative Example C3 is as thin as that in Examples E19 to E23 (i.e., 0.15 mm), it is prone to burnout when subjected to the same trigger voltage, making comparison impossible. Furthermore, as mentioned above, considering the influence of error and the allowable range of variation, the volume percentage of high-density polyethylene can be appropriately adjusted within the range of 40% to 50%, and the volume percentage of titanium carbide can be appropriately adjusted within the range of 50% to 60%. Within the aforementioned ranges, the overcurrent protection element can have the same or similar technical effects. As can be seen from the above, with the same thickness, the present invention has better voltage withstand capability. For example, in this test (i.e., the tests in Tables 6 and 7), the applied voltage is 6 volts (V). The thickness of the thermistor layer in Comparative Example C3 or other conventional overcurrent protection elements must reach 0.18 mm or even 0.2 mm or more to avoid burnout, while the present invention, with a thickness of 0.15 mm, still does not burn out. The same applies when a higher voltage withstand value is required. To enable the component to withstand a 16V voltage without burning out, the thermistor layer thickness of comparative example C3 or other conventional overcurrent protection components must be approximately 0.4mm, while the thermistor layer thickness of the present invention only needs to be 0.33mm. Incidentally, to increase conductivity, conventional overcurrent protection components may adjust the volume percentage of conductive filler to over 62%, or over 89% by weight. This results in the PTC material becoming too hard, making it prone to cracking during pressing. In the embodiments of the present invention, in addition to avoiding the above-mentioned disadvantages, reducing the thickness of the thermistor layer and the content of conductive filler helps to reduce material usage, i.e., reduce production costs.

[0070] R i and ρ iThe definition has been described above and will not be repeated here. R1 refers to the resistance value measured after the overcurrent protection component has undergone one reflow soldering process and cooled to room temperature. The reflow soldering temperature is between 140℃ and 300℃, and the processing time is approximately 5 minutes. Similarly, according to the aforementioned formula for volume resistivity, R1 can be substituted into the formula to obtain the volume resistivity ρ1. ρ i This refers to the first volume resistivity defined above, while ρ1 is the second volume resistivity defined above. In Table 5, it can be observed that embodiments E19 to E23 of the present invention have considerably low resistance, both in the initial state and after reflow. The ρ1 of embodiments E19 to E23... i The value falls within the range of 0.00602 Ω·cm to 0.1718 Ω·cm, which is far lower than the ρ of comparative example C3. i (0.0198 Ω·cm). After reflow, the ρ1 of Examples E19 to E23 falls between 0.00899 Ω·cm and 0.02436 Ω·cm, which is also much lower than the ρ1 of Comparative Example C3 (0.03362 Ω·cm). More importantly, the overcurrent protection elements of Examples E19 to E23 can still be restored to a low resistance after reflow. As shown in Table 5, R jump , is R1 divided by R i The obtained value represents the rate of increase in resistance. R i This refers to the initial resistance value defined above, while R1 is the first resistance value defined above. A lower resistance jump rate means better resistance recovery capability or resistance reproducibility of the overcurrent protection element, and better resistance reproducibility. In embodiments E19 to E23, R... jump The values ​​range from 1.4 to 1.57. As for comparative example C3, its R... jump The value is 1.7. Clearly, the overcurrent protection elements in embodiments E19 to E23 have a better ability to return to their initial state after being triggered.

[0071] Please refer to Tables 6 and 7 to verify the electrical characteristics of the overcurrent protection components at different temperatures.

[0072] I trip1 This refers to the minimum current value required to trigger the first activation of an overcurrent protection element. trip2 This refers to the minimum current value required to trigger the overcurrent protection element a second time. trip3 This refers to the minimum current value required to trigger the overcurrent protection element for the third time. Additionally, during operation, the overcurrent protection element may not be able to completely cut off the current, resulting in leakage current. The leakage current is measured when the overcurrent protection element triggers for the third time. trip1 / Component area refers to I trip1 Divide by the top apparent area of ​​the overcurrent protection element (i.e., 9.8 mm²).2 The values ​​obtained are as follows. Furthermore, with an applied voltage of 6V, the minimum power (W) required for the first trigger per unit area can be calculated, i.e., W. trip1 / Component area.

[0073] Table 6 shows the electrical characteristics of the overcurrent protection element at 23°C. In embodiments E19 to E23 of the present invention, I at 23°C trip1 The range is 4.88A to 8.44A; I at 23°C trip2 The range is from 4.3A to 8.19A; while I trip3 The I value ranged from 3.92 A to 7.85 A. In comparison, the I value of Comparative Example C3 at 23°C was... trip1 I trip2 and I trip3 All are significantly lower than the lower limit of the trigger current in embodiments E19 to E23. It can be understood that, per unit area, the current and power required for triggering the overcurrent protection element are also similar. In embodiments E19 to E23 of the present invention, I at 23°C trip1 The component area is 0.498 A / mm². 2 Up to 0.861A / mm 2 And W trip1 The component area is 2.988W / mm². 2 Up to 5.167W / mm 2 Both were significantly higher than that of comparative example C3. Furthermore, at 23°C, I... trip1 The component area is the aforementioned first allowable current value. The overcurrent protection element of the present invention requires a higher current value to trigger, thus allowing a larger current to flow before triggering, and can also withstand the application of a larger current and power without burning out.

[0074] Table 6 shows the electrical characteristics of the overcurrent protection element at 85°C. In embodiments E19 to E23 of the present invention, I at 85°C trip1 The range is from 2A to 4.25A; I at 23℃ trip2 The range is from 1.82A to 3.98A; while I trip3 The I value ranged from 1.62 A to 3.81 A. In comparison, the I value of Comparative Example C3 at 85 °C was... trip1 I trip2 and I trip3 All are significantly lower than the lower limit of the trigger current in embodiments E19 to E23. Similarly, the current and power required to trigger the overcurrent protection element per unit area are also similar. In embodiments E19 to E23 of the present invention, I at 85°C trip1 The component area is 0.204 A / mm². 2 Up to 0.434A / mm 2 And Wtrip1 The component area is 1.224 W / mm². 2 Up to 2.602W / mm 2 Both were significantly higher than that of comparative example C3. Furthermore, I at 85°C trip1 The component area is the aforementioned second allowable current value. At high temperatures, the overcurrent protection element of this invention requires a higher trigger current, thus allowing a larger current to flow before triggering, and can withstand the application of larger current and power without burning out. It is also noted that the leakage current of embodiments E19 to E23 of this invention remains below 0.057A, far less than the leakage current of comparative example C3 (0.0726A), meaning that the overcurrent protection element of this invention has a better current-intercepting capability. Therefore, the overcurrent protection element of this invention also exhibits its advantages at high temperatures.

[0075] The technical content and features of this invention have been disclosed above. However, those skilled in the art may still make various substitutions and modifications without departing from the concept of this invention based on the teachings and disclosures of this invention. Therefore, the scope of protection of this invention should not be limited to what is disclosed in the embodiments, but should include various substitutions and modifications without departing from this invention, and is 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 is stacked between the upper metal layer and the lower metal layer, wherein the thermistor layer has a positive temperature coefficient and includes: A polymer substrate comprising a polyolefin polymer; and A conductive filler comprising a metal compound dispersed within the polymer substrate, thereby forming a conductive channel in the thermistor layer, wherein: The metal compound consists of a metal carbide and unavoidable impurities; and Assuming the content of the metal carbide and unavoidable impurities is 100%, the metal carbide accounts for more than 90%.

2. The overcurrent protection element according to claim 1, wherein the maximum particle size of the metal compound is less than 20 μm.

3. The overcurrent protection element according to claim 1, wherein the metal carbide is titanium carbide.

4. The overcurrent protection element according to claim 1, wherein the unavoidable impurity comprises titanium oxide and / or titanium tetrachloride.

5. The overcurrent protection element according to claim 1, wherein the metal compound accounts for 50% to 60% of the volume of the thermistor layer, which is 100%.

6. The overcurrent protection element according to claim 5, wherein the polyolefin polymer accounts for 40% to 50% of the volume of the thermistor layer, which is 100%.

7. The overcurrent protection element according to claim 1, wherein the polyolefin polymer is selected from the group consisting of low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, polypropylene and polybutene.

8. The overcurrent protection element according to claim 1, wherein the thermistor layer does not contain a flame retardant.

9. The overcurrent protection element according to claim 1, wherein the polymer substrate does not contain a fluoropolymer, wherein the fluoropolymer is selected from the group consisting of polyvinylidene fluoride, polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, perfluorocarbon oxygen-modified tetrafluoroethylene, poly(chlorotrifluorotetrafluoroethylene), difluoroethylene-tetrafluoroethylene polymer, tetrafluoroethylene-perfluorodioxane copolymer, difluoroethylene-hexafluoropropylene copolymer, difluoroethylene-hexafluoropropylene-tetrafluoroethylene trimer, and combinations thereof.

10. The overcurrent protection element according to claim 1, wherein the overcurrent protection element has a resistance jump rate between 1.4 and 1.6, wherein: The overcurrent protection element has an initial resistance value; The overcurrent protection element has a first resistance value after being triggered once and cooled to room temperature; and The first resistance value divided by the initial resistance value is the resistance jump rate.

11. The overcurrent protection element according to claim 1, wherein the overcurrent protection element has a first volume resistivity between 0.006 Ω·cm and 0.018 Ω·cm, wherein the first volume resistivity is defined as the volume resistivity of the overcurrent protection element without any heat treatment.

12. The overcurrent protection element according to claim 1, wherein the overcurrent protection element has a second volume resistivity between 0.008 Ω·cm and 0.03 Ω·cm, wherein the second volume resistivity is defined as the volume resistivity of the overcurrent protection element after a heat treatment.

13. The overcurrent protection element according to claim 1, wherein the overcurrent protection element has a first allowable current value between 0.4 A / mm². 2 With 0.9A / mm 2 Between, where the first permissible current value is the minimum current value required to trigger the overcurrent protection element at 23°C per unit area.

14. The overcurrent protection element according to claim 1, wherein the overcurrent protection element has a second allowable current value between 0.2 A / mm². 2 With 0.5A / mm 2 Between, where the second permissible current value is the minimum current value required to trigger the overcurrent protection element at 85°C per unit area.

15. The overcurrent protection element according to claim 14, wherein the leakage current of the overcurrent protection element is between 0.04A and 0.06A.

16. The overcurrent protection element according to claim 1, wherein the top view area of ​​the overcurrent protection element is 2 mm². 2 Up to 81mm 2 .

17. The overcurrent protection element according to claim 1, wherein the thickness of the thermistor layer is between 0.13 mm and 0.2 mm.

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