Overcurrent protection element

Abstract

An overcurrent protection device includes an electrode layer and a thermistor layer. The thermistor layer includes a high-molecular polymer substrate and a conductive filler. The high-molecular polymer base material contains a polyolefin polymer and an olefin-acrylate copolymer. The polyolefin polymer is represented by the following formula (I): # imgabs0 #, wherein R1 and R2 are selected from the group consisting of CH3, C2H5 and C3H7. The olefin-acrylate copolymer is represented by the following formula (II): # imgabs 1 # wherein R is selected from the group consisting of COOCH3, COOC2H5, and COOC4H9.

Description

Technical Field

[0001] The present invention relates to an overcurrent protection element, and more particularly to an overcurrent protection element for low temperature protection. 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 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 (matrix) and a conductive filler. The substrate is composed of a high molecular polymer, and the conductive filler is dispersed in the high molecular polymer as a conductive path. As mentioned above, the positive temperature coefficient characteristic of the overcurrent protection element mainly comes from the PTC material layer, so its protection temperature can be further adjusted by improving the PTC material layer. Traditionally, in order to make the overcurrent protection element play a protective role at low temperatures, high-density polyethylene (HDPE) is often used as the main component of the substrate, so that the overcurrent protection element can cut off the current at about 120°C to prevent the protected electronic products from continuing to heat up due to continuous power supply. However, in specific product areas, the protection temperature required for certain types of electronic products will be much lower than the aforementioned 120°C, such as game controllers in the video game industry. More specifically, the protection temperature required for game controllers is below 85°C. If the overcurrent protection element only works at 120°C, the circuit in the game controller will not operate normally or even be damaged. In addition, even if the protection temperature of the existing overcurrent protection element can be improved to below 85°C, there are often problems such as high volume resistivity or unstable resistance.

[0004] In view of this, there is an urgent need to develop a new overcurrent protection element for low temperature protection. Summary of the invention

[0005] The present invention provides an overcurrent protection element, comprising a thermistor layer with a positive temperature coefficient characteristic. The thermistor layer comprises a polymer substrate and a conductive filler. In order to reduce the protection temperature, the present invention introduces a polyolefin polymer and an olefin-acrylate copolymer with a lower protection temperature into the polymer substrate. Through the side chain (acrylate repeating unit) in the olefin-acrylate copolymer, the degree of disturbance between molecules of the polymer substrate can be increased, and the protection temperature of the overcurrent protection element can be further reduced.

[0006] According to one embodiment of the present invention, an overcurrent protection element includes an electrode layer and a thermistor layer. The electrode layer has an upper metal layer and a lower metal layer. The thermistor layer contacts the upper metal layer and the lower metal layer and is stacked therebetween. The thermistor layer has a positive temperature coefficient characteristic and includes a polymer substrate and a conductive filler. The polymer substrate includes a polyolefin polymer and an olefin-acrylate copolymer. Based on 100% of the volume of the thermistor layer, the olefin-acrylate copolymer accounts for less than 12%. The polyolefin polymer is represented by the following formula (I):

[0007]

[0008] wherein R1 and R2 are selected from the group consisting of CH3, C2H5 and C3H7, m is 3000 to 8000, and n is 1000 to 3000. The olefin-acrylate copolymer is represented by the following formula (II):

[0009]

[0010] R is selected from the group consisting of COOCH3, COOC2H5 and COOC4H9, m is 800 to 5000, and n is 500 to 1000. The conductive filler is dispersed in the high molecular polymer matrix to form a conductive channel of the thermistor layer.

[0011] According to some embodiments, based on 100% by volume of the thermistor layer, the polyolefin polymer accounts for 43% to 56%.

[0012] According to some embodiments, based on 100% by volume of the thermistor layer, the polyolefin polymer accounts for 45% to 48% and the olefin-acrylate copolymer accounts for 7% to 12%.

[0013] According to some embodiments, the olefin-acrylate copolymer has an acrylate repeating unit represented by the following formula (III):

[0014]

[0015] The acrylic acid ester repeating unit accounts for less than 20% based on the weight of the high molecular polymer substrate being 100%.

[0016] According to some embodiments, based on 100% by weight of the high molecular weight polymer matrix, the acrylate repeating unit accounts for 15% to 20%.

[0017] According to some embodiments, the thermal cut-out temperature of the overcurrent protection element is between 40°C and 81°C.

[0018] According to some embodiments, the overcurrent protection element has a sustaining current thermal drop ratio less than 0.55, wherein the sustaining current thermal drop ratio is defined as a ratio of a sustaining current of the overcurrent protection element at 60° C. divided by a sustaining current of the overcurrent protection element at 23° C.

[0019] According to some embodiments, the overcurrent protection element has a first high resistance state change value between 0.1 and 2.2. After being heated from 40°C to 160°C once, the overcurrent protection element has a first high resistance corresponding temperature point; after being heated from 40°C to 160°C five times, the overcurrent protection element has a second high resistance corresponding temperature point; and the value obtained by subtracting the second high resistance corresponding temperature point from the first high resistance corresponding temperature point is the aforementioned first high resistance state change value.

[0020] According to some embodiments, the first high-resistance state change value is between 0.1 and 1.

[0021] According to some embodiments, the overcurrent protection element has a second high resistance state change value between 2 and 6.3. After being heated from 40°C to 160°C once, the overcurrent protection element has a first high resistance corresponding temperature point; after being heated from 40°C to 160°C ten times, the overcurrent protection element has a third high resistance corresponding temperature point; and the value obtained by subtracting the third high resistance corresponding temperature point from the first high resistance corresponding temperature point is the aforementioned second high resistance state change value.

[0022] According to some embodiments, the overcurrent protection element has a second high resistance state change value between 2 and 3.

[0023] According to some embodiments, the volume resistivity of the overcurrent protection element is between 0.01 Ω·cm and 0.065 Ω·cm. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0025] Figure 2 show Figure 1 a top view of an overcurrent protection element; and

[0026] Figure 3 Displays the resistance value-temperature curve of the overcurrent protection element.

[0027] The reference numerals are described as follows:

[0028] 10: Overcurrent protection element

[0029] 11: Thermistor layer

[0030] 12: Upper metal layer

[0031] 13: Lower metal layer

[0032] A: Length

[0033] B: Width DETAILED DESCRIPTION

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

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

[0036] In the present invention, in order to effectively reduce the protection temperature (i.e., thermal cut-off temperature) of the overcurrent protection element 10, the polymer matrix includes a polyolefin polymer and an olefin-acrylate copolymer. Taking the volume of the thermistor layer 11 as 100%, the polyolefin polymer accounts for 43% to 56%, and the olefin-acrylate copolymer accounts for less than 12%. More specifically, the polyolefin polymer is represented by the following formula (I):

[0037]

[0038] wherein R1 and R2 are selected from the group consisting of CH3, C2H5 and C3H7, m is 3000 to 8000, and n is 1000 to 3000; and the olefin-acrylate copolymer is represented by the following formula (II):

[0039]

[0040] Wherein R is selected from the group consisting of COOCH3, COOC2H5 and COOC4H9, m is 800 to 5000, and n is 500 to 1000. In the following experiment, m in the aforementioned formula (I) is 7300, and n is 2500; and m in the aforementioned formula (II) is 3000, and n is 740. The polyolefin polymer may be low-density polyethylene (LDPE). Compared with high-density polyethylene (HDPE), the temperature required to trigger low-density polyethylene is lower, and it can be triggered to a high-resistance state and cut off the current when it is below 85°C. R1 and R2 in the aforementioned formula (I) may be the same or different. For example, in one embodiment, R1 and R2 in formula (I) are both C3H7. In another embodiment, R1 in formula (I) is CH3, and R2 is C3H7. In addition, the present invention adds olefin-acrylate copolymer to the polymer matrix because it has a high content of side chains, which can further reduce the temperature required to trigger the polymer matrix, so that the overcurrent protection element 10 has an extremely low protection temperature. The high content of side chains in the aforementioned olefin-acrylate copolymer mainly comes from the acrylate repeating unit (i.e., the repeating unit shown as m in formula (II)), which is represented by the following formula (III):

[0041]

[0042] When R is COOCH3, the acrylate repeating unit is a methyl acrylate repeating unit, and the olefin-acrylate copolymer is an ethylene-methyl acrylate copolymer (Ethylene methyl acrylate, EMA). When R is COOC2H5, the acrylate repeating unit is an ethyl acrylate repeating unit, and the olefin-acrylate copolymer is an ethylene-ethyl acrylate copolymer (Ethylene ethyl acrylate, EEA). When R is COOC4H9, the acrylate repeating unit is a butyl acrylate repeating unit, and the olefin-acrylate copolymer is an ethylene-butyl acrylate copolymer (Ethylene butylacrylate, EBA). In the present invention, the olefin-acrylate copolymer can form an interpenetrating polymer network (IPN) structure with a polyolefin polymer to form the main component of a polymer substrate. Through the acrylate repeating unit, the arrangement of the overall molecular chain in the polymer substrate can be made more irregular. Accordingly, the polymer substrate is less likely to form an orderly arranged crystalline region. In other words, the acrylate repeating unit has the effect of destroying the crystallization of the polymer substrate, so that the melting point of the polymer substrate is reduced, and thus the protection temperature of the overcurrent protection element 10 is lowered. However, it should be noted that the content of the acrylate repeating unit should not be too high, otherwise the protection temperature of the polymer substrate will be too low. For example, when the protection temperature of the overcurrent protection element 10 is lower than the operating temperature of the electronic product to be protected, the electronic product will be cut off from the current at the temperature at which it can operate normally, causing a malfunction. Therefore, based on the weight of the polymer substrate being 100%, the acrylate repeating unit accounts for less than 20%.

[0043] In the present invention, the protection temperature mentioned above can be defined as the thermal cutting-off temperature. The thermal cutting-off temperature generally refers to the temperature point corresponding to when the overcurrent protection element 10 cuts off the current. More specifically, the thermal cutting-off temperature of the overcurrent protection element 10 is between about 40°C and 81°C, such as 40°C, 41°C, 42°C, 46°C, 47°C, 48°C, 49°C, 50°C, 51°C, 54°C, 55°C, 56°C, 60°C, 61°C, 62°C, 63°C, 64°C, 65°C, 74°C, 75°C, 76°C, 79°C, 80°C or 81°C. The thermal cutting-off temperature of the overcurrent protection element 10 of the present invention is much lower than 120°C, so it can be applied to electronic products that require a lower protection temperature, such as game controllers in the video game industry. In order to avoid affecting the normal operation of the circuit in the game controller, the thermal cutting-off temperature can be adjusted to above 50°C. In one embodiment, the thermal cut-off temperature of the overcurrent protection element 10 is between 50°C and 60°C. It should also be noted that the overcurrent protection element 10 of the present invention is also known as a resettable fuse, which can be restored to a low resistance state by cooling down after actuation (triggering), meaning that it is a fuse that can be reused (perform multiple protection actions). Therefore, whether the overcurrent protection element 10 can maintain the same resistance state after repeated use is also one of the considerations. In the present invention, a resistance-temperature test is used to evaluate the stability of the high resistance state of the overcurrent protection element 10. In the resistance-temperature test, the overcurrent protection element 10 is placed in a heating device. The temperature of the heating device can be increased from 40°C to 160°C (i.e., heating treatment), and the resistance of the overcurrent protection element 10 is observed to rise to 10 5Ω corresponds to the temperature point (such as the first high resistance corresponding temperature point, the second high resistance corresponding temperature point and the third high resistance corresponding temperature point below). It should also be noted that in the present invention, after the temperature rises from 40°C to 160°C and then drops back to 40°C from 160°C, it is defined as a temperature rise treatment. The above-mentioned action can be repeated, that is, the temperature rise treatment can be cycled multiple times. After the temperature rise treatment from 40°C to 160°C once, the overcurrent protection element 10 has a first high resistance corresponding temperature point; after the temperature rise treatment from 40°C to 160°C five times, the overcurrent protection element 10 has a second high resistance corresponding temperature point; and after the temperature rise treatment from 40°C to 160°C ten times, the overcurrent protection element 10 has a third high resistance corresponding temperature point. The value obtained by subtracting the second high resistance corresponding temperature point from the first high resistance corresponding temperature point can be defined as the first high resistance state change value, and the value obtained by subtracting the third high resistance corresponding temperature point from the first high resistance corresponding temperature point can be defined as the second high resistance state change value. In one embodiment, the overcurrent protection element 10 has a first high resistance state change value between 0.1 and 2.2. In one embodiment, the overcurrent protection element 10 has a second high resistance state change value between 2 and 6.3. It should be noted that one of the reasons why the overcurrent protection element 10 has good high resistance state stability is the coupling ability of the olefin-acrylate copolymer. The olefin-acrylate copolymer can be used as a coupling agent to enhance the bonding force between the interface of inorganic materials (such as the upper metal layer 12 and the lower metal layer 13) and the organic material (such as thermistor layer 11). The -OR group in the acrylate repeating unit can form a bond with the surface of the inorganic material in a chemical manner. In this way, the thermistor layer 11 can be stably combined with the upper metal layer 12 and the lower metal layer 13, and the overcurrent protection element 10 can maintain good structural integrity. The overcurrent protection element 10 is less likely to cause irreversible deformation due to multiple triggering. If the content of the olefin-acrylate copolymer is appropriately increased, the high resistance state stability of the overcurrent protection element 10 can be effectively increased. For example, in one embodiment, based on the volume of thermistor layer 11 being 100%, the polyolefin polymer accounts for 45% to 48%, and the olefin-acrylate copolymer accounts for 7% to 12%. In one embodiment, based on the weight of the high molecular polymer substrate being 100%, the acrylate repeating unit accounts for 15% to 20%. After the above-mentioned appropriate adjustment, the overcurrent protection element 10 preferably has a first high resistance state change value between 0.1 and 1, and a second high resistance state change value between 2 and 3.

[0044] Since the thermal cut-off temperature of the overcurrent protection element 10 is lower than that of the conventional overcurrent protection element, the holding current of the overcurrent protection element 10 will also be lower than that of the conventional overcurrent protection element at the same specific temperature. The holding current refers to the maximum current that the overcurrent protection element 10 can withstand without being triggered. The overcurrent protection element 10 with a low thermal cut-off temperature has a higher resistance value at low temperatures, so it has a lower holding current accordingly. Generally speaking, the holding current decreases with increasing temperature, i.e., the thermal derating effect. In one embodiment, the overcurrent protection element 10 has a holding current thermal derating ratio less than 0.55, wherein the "holding current thermal derating ratio" is defined as the ratio of the holding current of the overcurrent protection element 10 at 60°C divided by the holding current of the overcurrent protection element 10 at 23°C. In another embodiment, the holding current thermal derating ratio of the overcurrent protection element 10 is between 0.3 and 0.4. In comparison, the current heat drop ratio of the conventional overcurrent protection element is about 0.65, which is much higher than the current heat drop ratio (such as the aforementioned 0.55) of the overcurrent protection element 10. Obviously, as the temperature rises, the overcurrent protection element 10 of the present invention can block the flow of current in advance.

[0045] In addition, the improved polymer matrix of the present invention can be applied to low volume resistivity type overcurrent protection elements. That is, the conductive filler of the present invention can be composed of a metal ceramic material, and the volume resistivity of the overcurrent protection element 10 is between about 0.01Ω·cm and 0.065Ω·cm, such as 0.01Ω·cm, 0.015Ω·cm, 0.02Ω·cm, 0.025Ω·cm, 0.03Ω·cm, 0.035Ω·cm, 0.04Ω·cm, 0.045Ω·cm, 0.05Ω·cm, 0.055Ω·cm, 0.06Ω·cm or 0.065Ω·cm. The aforementioned metal ceramic material 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, zirconium nitride and any combination thereof. It is also worth mentioning that, in addition to the conductive filler, no other functional fillers need to be added to the thermistor layer 11 of the overcurrent protection element 10 of the present invention to maintain good electrical properties, such as thermal cut-off temperature, resistance stability, durability, or other similar or unexpected properties. The aforementioned functional filler can be a conventional common flame retardant 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. The aforementioned functional filler can also be a perovskite compound selected from the group consisting of barium titanate, strontium titanate and calcium titanate. In one embodiment, the thermistor layer 11 of the overcurrent protection element 10 of the present invention does not contain the aforementioned flame retardant and perovskite compound, which can effectively simplify the design of the formulation. In this way, the overcurrent protection element 10 of the present invention can reduce material costs and the complexity of material composition, which is beneficial to the setting of various parameters in the process.

[0046] Please continue to refer to 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. For example, the thicknesses of the upper metal layer 12 and the lower metal layer 13 of the overcurrent protection element 10 of the present invention may be 0.07 mm each, and the thickness of the thermistor layer 11 may be 0.11 mm to 0.21 mm, such as 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. In a preferred embodiment, the overcurrent protection element 10 has a top view area of ​​4 mm 2 Up to 12mm 2 , and the thickness of the thermistor layer 11 is about 0.15mm to 0.17mm. It should be understood that the overcurrent protection element 10 of the present invention has the same effect when applied to the above-mentioned dimensions. In addition, the overcurrent protection element 10 can be processed into a common component type in the industry according to requirements, such as a surface-mount device (SMD), an axial-leaded device (ALD), a radial-leaded device (RLD) or other types of components.

[0047] To more specifically illustrate the technical content of the present invention, the following Tables 1 to 3 are further discussed with actual verification data.

[0048] Table 1. Ratio of thermistor layer (vol%)

[0049] Group HDPE LDPE Copolymer WC E1 0 55 0 45 E2 0 53.35 1.65 45 E3 0 50.05 4.95 45 E4 0 48.40 6.60 45 E5 0 46.75 8.25 45 E6 0 46.20 8.80 45 E7 0 44.00 11.00 45 E8 0 44.00 11.00 45 E9 0 44.00 11.00 45 C1 55 0 0 45

[0050] As shown in Table 1, the composition of the thermistor layer of each embodiment of the present invention (group E1 to group E9) and the comparative example (group C1) is shown in volume percentage. The first row shows the various materials in the thermistor layer from left to right, respectively, high density polyethylene (HDPE), low density polyethylene (LDPE), copolymer and tungsten carbide (WC). The copolymer in Table 1 is the olefin-acrylate copolymer mentioned above. In embodiments E2 to E7, the copolymer used in the thermistor layer is ethylene-butyl acrylate copolymer. Since embodiments E2 to E7 have good improvements in component performance, embodiments E8 and E9 try two other different olefin-acrylate copolymers. In embodiment E8, the copolymer used in the thermistor layer is ethylene-methyl acrylate copolymer. In embodiment E9, the copolymer used in the thermistor layer is ethylene-ethyl acrylate copolymer. Considering the influence of errors and the allowable range of variation, the volume percentage of LDPE can be appropriately adjusted within the range of 43% to 56%, and the volume percentage of Copolymer can be appropriately adjusted within the range of 0% to 12%. Within the aforementioned range, the overcurrent protection element can have the same or similar technical effects. In order to improve the conductivity of the overcurrent protection element and have a larger current flow capacity, the conductive filler does not contain carbon black. In other words, the conductive filler is composed of tungsten carbide. If the conductive filler uses carbon black, the volume resistivity of the overcurrent protection element will generally be greater than 0.1Ω·cm. In addition, this formula does not contain any flame retardants (such as traditional magnesium hydroxide) and other internal fillers, and the required low-temperature protection overcurrent protection element can be produced. It can be noted that in order to simplify the formula design, this formula not only does not contain any flame retardants and other internal fillers, but the conductive filler also uses a single composition (i.e. tungsten carbide).

[0051] The manufacturing process of the overcurrent protection element of Examples E1 to E9 of the present invention and Comparative Example C1 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 100° to form a three-layer plate. Finally, a punch is used to punch out multiple chips from the plate, which are the overcurrent protection components. The length and width of the overcurrent protection component are 2.8 mm and 3.5 mm respectively (i.e., the top surface area is 9.8 mm). 2 ), and the overall thickness is 0.3 mm. Then, the wafers prepared in the embodiment and the comparative example were irradiated with a light dose of 15 kGy (the light dose can be adjusted according to the needs and is not a limiting condition of the present invention), and 15 wafers were taken as test samples for subsequent tests.

[0052] Table 2. Various electrical characteristics

[0053]

[0054] R i , refers to the initial resistance value of the overcurrent protection element at room temperature. 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 Substitute this into the formula to obtain the volume resistivity (ρ).

[0055] TCO refers to the thermal cutting-off temperature, and its measurement method is described below. The overcurrent protection element is placed in an oven and connected to an external power supply (power is 12V / 1.6A). The temperature in the oven gradually rises from room temperature, and the heating rate is 1°C per minute. When the temperature in the oven rises to a certain temperature, the overcurrent protection element will not be able to conduct the external power supply. The aforementioned specific temperature is the thermal cutting-off temperature of the overcurrent protection element.

[0056] IH 23℃ and IH 60℃ , respectively, refers to the magnitude of the holding current of the overcurrent protection element at 23°C and 60°C. The overcurrent protection element is placed directly in a 23°C oven and the maximum current it can withstand is measured without being triggered, and IH is obtained. 23℃ The overcurrent protection element is placed directly in a 60°C oven and the maximum current it can withstand is measured without being triggered, and IH is obtained. 60℃ . IH 60℃ / IH 23℃ This is the “maintaining current thermal drop ratio” defined above.

[0057] As can be seen from Table 2, the volume resistivity of embodiments E1 to E9 of the present invention is maintained in the range of 0.0155Ω·cm to 0.0637Ω·cm. Although the aforementioned range is higher than the volume resistivity of comparative example C1 (i.e., 0.0011Ω·cm), it is much lower than the conventional overcurrent protection element (not shown) that uses carbon black as a conductive filler. In other words, embodiments E1 to E9 of the present invention can be used to produce overcurrent protection elements with low volume resistivity, which meets the power supply requirements of the protected electronic products. As for the thermal cut-off temperature, all embodiments E1 to E9 of the present invention are maintained below 85°C, which meets the application requirements of low-temperature protection in the industry. In comparison, the thermal cut-off temperature of comparative example C1 is as high as 121.5°C, which will cause the overcurrent protection element to cut off the current too late, resulting in damage or burning of the electronic product.

[0058] It should be understood that an overcurrent protection element with a low thermal cutoff temperature (such as embodiments E1 to E9 of the present invention) has a higher resistance value at low temperatures, so it can cut off the flow of current at low temperatures. It is conceivable that at a specific temperature, an overcurrent protection element with a low thermal cutoff temperature will have a lower holding current; and as the temperature rises, it will also have a lower holding current thermal drop ratio. In embodiments E1 to E9, the holding current thermal drop ratio (IH 60℃ / IH 23℃ ) is 0.264 to 0.541. In comparison, the maintenance current heat drop ratio (IH 60℃ / IH 23℃ ) is 0.654, which is much higher than the aforementioned range. It can be seen that the heat drop of the embodiments E1 to E9 of the present invention at low temperatures is more significant, and the flow of current can be blocked in advance.

[0059] Table 3. Resistance-temperature test

[0060]

[0061] It should be mentioned first that since the thermal cut-off temperature of Comparative Example C1 is much higher than the application requirements of low temperature protection, there is no need to further test Comparative Example C1. Therefore, there is no data for Comparative Example C1 in Table 3. The resistance-temperature test is to place the overcurrent protection element in an oven and observe the corresponding resistance value of the overcurrent protection element at a specific temperature. The oven starts at 40°C and continues to heat up to 160°C at a rate of 5°C / min. As mentioned above, the temperature increase process can be cycled multiple times, and the resistance value of the overcurrent protection element is observed to reach 10 5 T1 refers to the temperature change required for the first temperature rise process when the resistance value is 10 5 Ω corresponds to the temperature point (i.e. the temperature point corresponding to the first high resistance). T5 refers to the temperature point at which the resistance value is 10 5The temperature point corresponding to Ω (i.e. the temperature point corresponding to the second highest resistance). 10 , means that in the tenth heating treatment, the resistance value is 10 5 The temperature point corresponding to Ω (i.e. the temperature point corresponding to the third high resistance). The difference between T1 and T5 (T1-T5) is the first high resistance state change value defined above. 10 The difference (T1-T 10 ) is the second high resistance state change value defined above. The smaller the first high resistance state change value or the second high resistance state change value, the more stable the high resistance state. In addition, Table 3 also lists the weight percentage of the acrylate repeating unit in the polymer matrix (i.e., LDPE and Copolymer), i.e., the acrylate content.

[0062] In Examples E2 to E7, the copolymer used in the thermistor layer is ethylene-butyl acrylate copolymer. As the acrylate content increases from 0% to 20%, T1-T5 and T1-T 10 However, in this upward trend, T1-T5 and T1-T 10 It can be seen that when the acrylate content of the ethylene-butyl acrylate copolymer is adjusted to 15%, the overcurrent protection element can have the best high-resistance state stability. Figure 3 As shown, curve 1st, curve 5th and curve 10th respectively show the result curves of the first, fifth and tenth heating treatments of Example E5. In curve 1st, the resistance value is 10 5 The corresponding temperature point is about 87.9℃. In the 5th curve, the resistance value is 10 5 The corresponding temperature point is about 87.1℃. In the 10th curve, the resistance value is 10 5 Ω, the corresponding temperature point is about 85.8°C. In addition, if other different olefin-acrylate copolymers are used, the stability of the high resistance state can also be greatly improved. In Examples E8 and E9, the copolymers used in the thermistor layer are ethylene-methyl acrylate copolymer and ethylene-ethyl acrylate copolymer, respectively. When the acrylate content reaches 20%, T1-T5 of Examples E8 and E9 is 0.2 to 0.9, and T1-T 10 is 2.2 to 2.7, both of which are similar to T1-T5 and T1-T 10 From the above, it can be seen that when the acrylate content is at least 15%, the overcurrent protection element can have the best high-resistance state stability.

[0063] 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 polyolefin polymer and an olefin-acrylate copolymer, wherein the olefin-acrylate copolymer accounts for less than 12% of the volume of the thermistor layer as 100%, and: The polyolefin polymer is represented by the following formula (I): wherein R1 and R2 are selected from the group consisting of CH3, C2H5 and C3H7, m is 3000 to 8000, and n is 1000 to 3000; and The olefin-acrylate copolymer is represented by the following formula (II): wherein R is selected from the group consisting of COOCH3, COOC2H5 and COOC4H9, m is 800 to 5000, and n is 500 to 1000; and A conductive filler is dispersed in the high molecular polymer matrix and is used to form a conductive channel of the thermistor layer. 2 . The overcurrent protection element according to claim 1 , wherein based on 100% by volume of the thermistor layer, the polyolefin polymer accounts for 43% to 56%. 3 . The overcurrent protection element according to claim 2 , wherein based on 100% by volume of the thermistor layer, the polyolefin polymer accounts for 45% to 48%, and the olefin-acrylate copolymer accounts for 7% to 12%.

4. The overcurrent protection device according to claim 1, wherein the olefin-acrylate copolymer has an acrylate repeating unit represented by the following formula (III): The acrylic acid ester repeating unit accounts for less than 20% based on the weight of the high molecular polymer substrate being 100%. 5 . The overcurrent protection device according to claim 4 , wherein based on 100% by weight of the high molecular polymer substrate, the acrylate repeating unit accounts for 15% to 20% by weight. 6 . The over-current protection device as claimed in claim 1 , wherein a thermal cut-off temperature of the over-current protection device is between 40° C. and 81° C.

7. The overcurrent protection element according to claim 1, wherein the overcurrent protection element has a maintaining current thermal drop ratio less than 0.55, wherein the maintaining current thermal drop ratio is defined as the ratio of the maintaining current of the overcurrent protection element at 60°C divided by the maintaining current of the overcurrent protection element at 23°C.

8. The overcurrent protection element according to claim 1, wherein the overcurrent protection element has a first high resistance state change value between 0.1 and 2.2, wherein: After being subjected to a temperature rise treatment from 40° C. to 160° C., the overcurrent protection element has a first high-resistance corresponding temperature point; After being subjected to a temperature rise treatment from 40° C. to 160° C. for five times, the overcurrent protection element has a second high resistance corresponding temperature point; as well as A value obtained by subtracting the second high resistance corresponding temperature point from the first high resistance corresponding temperature point is the first high resistance state change value. 9 . The over-current protection device as claimed in claim 8 , wherein the first high-resistance state change value is between 0.1 and 1.

10. The overcurrent protection device according to claim 1, wherein the overcurrent protection device has a second high resistance state change value between 2 and 6.3, wherein: After being subjected to a temperature rise treatment from 40° C. to 160° C., the overcurrent protection element has a first high-resistance corresponding temperature point; After being subjected to a temperature rise treatment from 40°C to 160°C for ten times, the overcurrent protection element has a third high resistance corresponding temperature point; as well as A value obtained by subtracting the third high resistance corresponding temperature point from the first high resistance corresponding temperature point is the second high resistance state change value. 11 . The over-current protection device as claimed in claim 10 , wherein the second high-resistance state change value of the over-current protection device is between 2 and 3. 12 . The overcurrent protection device as claimed in claim 1 , wherein a volume resistivity of the overcurrent protection device is between 0.01 Ω·cm and 0.065 Ω·cm.

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