Chip type PTC thermistor and method for manufacturing the same

Abstract

The application relates to the field of PTC thermistors, in particular to a sheet type PTC thermistor and a preparation method thereof. The sheet type PTC thermistor comprises a heat-conducting insulating framework and a PTC high polymer matrix, the heat-conducting insulating framework is a face-centered cubic structure PU framework and high-heat-conducting insulating particles coated on the surface of the PU framework; the PTC high polymer matrix is made of the following raw materials in mass percentage: 15-30% of hydrophobic modified conductive composite filler, 0.5-2% of anti-aging auxiliary agent, 0.2-0.8% of zinc stearate, and the rest is a thermoplastic high polymer resin with high linear thermal expansion coefficient. The heat induction sensitivity of the application is relatively excellent, the temperature induction lag time of the thermistor is shorter, the temperature monitoring module applied to a lithium battery cell can timely give an early warning, the safe driving coefficient of a vehicle is improved, and the property loss and the personal injury risk are reduced.

Description

Technical Field

[0001] This invention relates to the field of PTC thermistors, and in particular to a chip PTC thermistor and its preparation method. Background Technology

[0002] PTC thermistors are positive temperature coefficient thermistors, meaning their resistance changes with temperature: the resistance increases as temperature rises. PTC thermistors are divided into linear and nonlinear types. Linear PTC thermistors are made of metals and alloys such as platinum, copper, and nickel, and exhibit the PTC effect, where resistance increases linearly with temperature. Nonlinear PTC thermistors are made of polymers and exhibit a rapid increase in resistance of several to tens of orders of magnitude over a narrow temperature range.

[0003] Currently, temperature monitoring of lithium battery cells in new energy vehicle lithium battery modules is crucial for thermal runaway prevention and battery cycle life. During charging, the battery temperature should remain below 45°C; excessively high temperatures can lead to cell failure. If the operating temperature of the lithium battery cell exceeds 65°C while the vehicle is in motion, an alarm is triggered to alert the driver. The temperature monitoring module for lithium battery cells relies heavily on PTC thermistors.

[0004] Conventional fusible metal fuses cannot meet the temperature monitoring requirements of lithium battery cells. The thermistor element in the temperature monitoring module of lithium battery cells is mainly a self-healing polymer PTC thermistor, which provides overcurrent protection and temperature monitoring for the lithium battery module, thereby improving the thermal runaway protection performance of new energy vehicles.

[0005] Currently available commercial thermistors are mainly made of carbon black-filled high-density polyethylene (HDPE), and they exhibit high performance at a specific temperature T. c At a specific temperature (T), high-density polyethylene undergoes linear expansion due to thermal expansion, causing the conductive network formed by carbon black to break. c At this point, its resistance increases sharply.

[0006] For example, Chinese Patent Publication No. CN1416141A discloses a polymer PTC thermistor consisting of a core material, metal foils attached to both sides of the core material, lead electrodes welded to the outer surface of the metal foils, and an insulating layer covering the outside. The core material is characterized by being formed by mixing and pressing two powdered conductive polymer composite materials. The powdered conductive polymer composite material is composed of a polymer, carbon black, carbon black dispersant, and other processing aids. Its formula by weight percentage is as follows: Powdered conductive polymer composite material 1: 35%–50% polymer, 46%–60% carbon black, 0.1%–10% processing aids; Powdered conductive polymer composite material 2: 55%–70% polymer, 30%–45% carbon black, 0.1%–10% processing aids.

[0007] In the temperature monitoring module of lithium battery cells, higher requirements are placed on the thermal sensitivity of polymer PTC thermistors. Timely warnings can help drivers and the back-end system respond, improving vehicle safety and reducing the risk of property damage and personal injury. Polymer PTC thermistors prepared using traditional carbon black as the conductive and thermally conductive material have low thermal conductivity and poor thermal sensitivity to the external environment. Therefore, this invention provides a chip-type PTC thermistor and its preparation method. Summary of the Invention

[0008] To address the technical problem of thermal sensitivity deviation in existing polymer PTC thermistors, this invention provides a chip PTC thermistor and its preparation method.

[0009] The chip-type PTC thermistor provided by this invention is achieved through the following technical solution:

[0010] A chip-type PTC thermistor includes a thermally conductive insulating skeleton and a PTC polymer matrix. The thermally conductive insulating skeleton is a face-centered cubic PU skeleton and highly thermally conductive insulating particles coated on the surface of the PU skeleton. The PTC polymer matrix is ​​made of the following raw materials in the indicated mass percentages: 15-30% hydrophobic modified conductive composite filler, 0.5-2% anti-aging additives, 0.2-0.8% zinc stearate, and the balance being a thermoplastic polymer resin with a high linear coefficient of thermal expansion.

[0011] In this invention, the thermally conductive and insulating skeleton is a face-centered cubic PU skeleton, which effectively improves the overall thermal conductivity, significantly enhances the thermal sensitivity of the chip PTC thermistor, and effectively shortens the temperature sensing lag time of the thermistor. When applied to the temperature monitoring module of lithium battery cells, it can provide timely warnings, improve the vehicle's safe driving coefficient, and reduce the risk of property damage and personal injury.

[0012] Preferably, the high thermal conductivity insulating particles are any one of aluminum nitride, boron nitride, titanium nitride, and silicon nitride with a particle size ≤200nm.

[0013] High thermal conductivity insulating particles are coated onto the surface of a face-centered cubic (FCC) PU skeleton using self-assembly or chemical bonding techniques. This gives the FCC PU skeleton excellent thermal conductivity and heat dissipation while also providing insulation, effectively improving the thermal sensitivity of chip PTC thermistors and shortening the temperature sensing hysteresis time of the thermistors.

[0014] Preferably, the method for preparing the thermally conductive and insulating skeleton is as follows:

[0015] S1. Perform surface plasma treatment on the PU skeleton with a face-centered cubic structure;

[0016] S2. The PU skeleton with a face-centered cubic structure after surface plasma treatment is sequentially immersed in an aqueous dispersion containing high thermal conductivity insulating particles with surface-grafted aminosilane and an aqueous dispersion containing high thermal conductivity insulating particles with surface-grafted epoxysilane. The high thermal conductivity insulating particles are coated on the surface of the face-centered cubic PU skeleton by self-assembly. After removal, washing and drying, the thermally conductive insulating skeleton is obtained.

[0017] Preferably, the temperature of the aqueous dispersion containing surface-grafted aminosilane high thermal conductivity insulating particles in S2 is 20-60°C, and the content of the surface-grafted aminosilane high thermal conductivity insulating particles is 1-5 wt%; the mass ratio of the surface-grafted aminosilane high thermal conductivity insulating particles to the face-centered cubic PU skeleton is 1:(9-49); and the immersion time of the face-centered cubic PU skeleton in the aqueous dispersion containing surface-grafted aminosilane high thermal conductivity insulating particles is 8-24 h.

[0018] Preferably, the temperature of the aqueous dispersion of surface-grafted epoxy-silane-rich thermally conductive insulating particles in S2 is 20-60°C, and the content of the surface-grafted epoxy-silane-rich thermally conductive insulating particles is 1-5 wt%; the mass ratio of the surface-grafted epoxy-silane-rich thermally conductive insulating particles to the face-centered cubic PU skeleton is 1:(9-49); and the immersion time of the face-centered cubic PU skeleton in the aqueous dispersion of surface-grafted epoxy-silane-rich thermally conductive insulating particles is 8-24 h.

[0019] This invention employs a self-assembly technique to prepare a thermally conductive and insulating framework. High thermal conductivity insulating particles with aminosilane grafted onto their surface are deposited on the PU framework surface through hydrogen bonds and intermolecular forces. High thermal conductivity insulating particles with epoxysilane grafted onto their surface are then further coated with the high thermal conductivity insulating particles with aminosilane grafted onto the PU framework surface through epoxy and amino chemical grafting. This forms a dense and uniformly covered layer of high thermal conductivity insulating particles on the PU framework surface, effectively improving the thermal conductivity of the thermally conductive and insulating framework. Consequently, this effectively enhances the thermal sensitivity of the chip PTC thermistor and effectively shortens the temperature sensing hysteresis time of the thermistor.

[0020] Preferably, the method for preparing the thermally conductive and insulating skeleton is as follows:

[0021] S1. Perform surface plasma treatment on the PU skeleton with a face-centered cubic structure;

[0022] S2. The PU skeleton with a face-centered cubic structure after surface plasma treatment is immersed in a mercaptosilane aqueous solution at a temperature of 40-60℃ and under magnetic stirring at 200-600 rpm for 0.5-2 hours. The skeleton is then removed and dried to obtain a PU skeleton with a face-centered cubic structure grafted with mercaptosilane.

[0023] S3. The face-centered cubic PU skeleton with surface grafted mercaptosilane is immersed in an aqueous dispersion of high thermal conductivity insulating particles modified with methacrylate silane. Under photoinitiator or thermal initiation conditions, the high thermal conductivity insulating particles are coated on the surface of the face-centered cubic PU skeleton. The skeleton is then removed, washed, and dried to obtain the thermally conductive insulating skeleton.

[0024] Preferably, in step S3, the face-centered cubic PU skeleton with surface-grafted mercaptosilane is immersed in an aqueous dispersion containing methacrylic acid silane-modified high thermal conductivity insulating particles. The content of methacrylic acid silane-modified high thermal conductivity insulating particles in the aqueous dispersion is 1-5 wt%, and the mass ratio of the methacrylic acid silane-modified high thermal conductivity insulating particles to the face-centered cubic PU skeleton is 1:(9-49). The temperature of the aqueous dispersion is controlled at 30-80℃, and the reaction is maintained at 30-80℃ for 2-24 hours. After removal, washing, and drying, the thermally conductive insulating skeleton is obtained.

[0025] In this invention, the PU skeleton is first subjected to surface plasma treatment to make its surface contain active groups. The PU skeleton with surface-grafted mercaptosilane is obtained by dehydration condensation with the active groups on its surface to obtain a face-centered cubic structure PU skeleton. The mercapto-SH groups on the surface of the PU skeleton and the methacrylate groups on the surface of the methacrylate-modified high thermal conductivity insulating particles undergo a click chemical reaction under photoinitiator or thermal initiation conditions. The high thermal conductivity insulating particles are coated on the surface of the face-centered cubic structure PU skeleton through chemical bond grafting technology, which gives the face-centered cubic structure PU skeleton good thermal conductivity and heat dissipation performance as well as insulation performance, effectively improving the thermal sensitivity of the chip PTC thermistor and effectively shortening the temperature sensing hysteresis time of the thermistor.

[0026] Compared to the self-assembly technology used to prepare the thermally conductive insulating skeleton, the chemical bond grafting technology produces a thermally conductive insulating skeleton with better surface uniformity and the resulting high thermal conductivity insulating particles are not easily detached, giving the chip PTC thermistor a better heat resistance and service life. After aging at 85℃ / 75%RH for 1000℃, the drift value is ≤0.10%.

[0027] Preferably, the thermoplastic polymer resin with a high linear coefficient of thermal expansion is composed of HDPE, LDPE, and LLDPE in a mass ratio of 100:(5-30):(5-20).

[0028] In this invention, HDPE is used as the rigid skeleton support material, and LDPE and LLDPE with high linear thermal expansion coefficients are used as auxiliary PTC materials. Because LDPE and LLDPE have higher linear thermal expansion coefficients, the switching temperature T can be controlled by controlling LDPE and LLDPE during use. c The resistance increase of the chip PTC thermistor within the operating state temperature window. As the LDPE and LLDPE content increases, the chip PTC thermistor in this invention reaches the switching temperature T. c After that, the resistance increase of the chip PTC thermistor becomes more obvious.

[0029] The anti-aging additive is composed of antioxidant 1010, antioxidant 168, and UV-234 in a mass ratio of 100:(10-15):(50-150).

[0030] The anti-aging additives composed of antioxidant 1010, antioxidant 168, and UV-234 in this invention can improve the overall antioxidant and UV aging resistance of chip PTC thermistors.

[0031] Preferably, the hydrophobically modified conductive composite filler is composed of a main conductive filler, an auxiliary conductive filler, and a modifier in a mass ratio of 100:(20-40); the main conductive filler is any one of nano-sized carbon black, natural graphite, or artificial synthetic graphite; the auxiliary conductive filler is any one of graphene, carbon nanotubes, carbon nanofibers, or MAX phase materials; and the modifier is aminosilane or lauric acid.

[0032] This invention optimizes the dispersibility and compatibility of the conductive composite filler with the matrix resin. Traditionally, the main conductive filler surface is hydrophilic, while the matrix resin is hydrophobic, resulting in the main conductive filler not being uniformly dispersed within the matrix resin, thus affecting the overall thermal and electrical conductivity of the chip PTC thermistor. To address this, the inventors performed a surface hydrophobic modification treatment on the main conductive filler. First, aminosilane was grafted onto the surface of the main conductive filler through a dehydration condensation reaction. Then, lauric acid was used to hydrophobically modify the surface of the main conductive filler. The carboxyl group (-COOH) in the lauric acid and the amino group (-NH2) in the aminosilane undergo dehydration condensation to form an amide bond (-(C=O)-(NH)-). The resulting main conductive filler exhibits good compatibility with the matrix resin and can be uniformly dispersed within the matrix resin, improving the overall thermal and electrical conductivity of the chip PTC thermistor. This enhances the thermal sensitivity of the chip PTC thermistor and shortens the temperature sensing hysteresis time.

[0033] The auxiliary conductive filler can be any one of hydrophilically modified graphene, carbon nanotubes, carbon nanofibers, or MAX phase materials. The main conductive filler and auxiliary conductive filler can be mixed and then subjected to surface hydrophobic modification treatment, which helps to improve overall production efficiency and reduce overall production costs. If any one of the unmodified graphene, carbon nanotubes, carbon nanofibers, or MAX phase materials is used, surface activation treatment (such as calcination at medium to high temperatures to form oxygen-containing residual bonds) or surface plasma treatment is required. This facilitates the grafting of aminosilanes onto the surface of the auxiliary conductive filler through dehydration condensation reaction. The prepared auxiliary conductive filler has good compatibility with the matrix resin and can be uniformly dispersed inside the matrix resin, improving the overall thermal conductivity and electrical conductivity of the chip PTC thermistor, enhancing the thermal sensitivity of the chip PTC thermistor, and shortening the temperature sensing hysteresis time of the thermistor.

[0034] The present invention provides a method for fabricating a chip PTC thermistor, which is achieved through the following technical solution:

[0035] A method for fabricating a chip PTC thermistor includes the following steps:

[0036] Step 1: Preparation of the thermally conductive and insulating framework;

[0037] Simultaneously, the preparation of hydrophobically modified conductive composite filler is as follows: The main conductive filler and auxiliary conductive filler are mixed uniformly according to a specified ratio to obtain a conductive composite filler. Ten parts by weight of the conductive composite filler are added to 100-200 parts by weight of an aminosilane aqueous solution with a concentration of 0.5-3 wt%. The mixture is magnetically stirred at 200-600 rpm for 0.5-2 hours, ultrasonically dispersed for 0.5-1 hours, and filtered under reduced pressure. The resulting filter media is then vacuum dried to obtain an aminosilane-modified conductive composite filler. Subsequently, ten parts by weight of the aminosilane-modified conductive composite filler are added to 500-1000 parts by weight of a lauric acid aqueous solution with a concentration of 0.2-0.4 wt%. The mixture is magnetically stirred at 200-600 rpm for 0.5-2 hours, ultrasonically dispersed for 0.5-1 hours, and filtered under reduced pressure. The resulting filter media is rinsed with deionized water at least three times, and then vacuum dried to obtain the hydrophobically modified conductive composite filler.

[0038] Step 2: Mix the accurately measured hydrophobic modified conductive composite filler, anti-aging additive, zinc stearate, and thermoplastic polymer resin with a high coefficient of thermal linear expansion evenly. Put the resulting mixture into an internal mixer for internal mixing and homogenization treatment. The mixing temperature is 145-150℃ and the mixing time is 4-6 minutes.

[0039] Step 3: The rubber compound obtained in Step 2 is fed into a twin-screw extruder for melt extrusion. The resulting molten extruded material is injected into a molding die with a pre-placed thermally conductive and insulating skeleton. The temperature of the molding die is 130-140℃, and it is maintained at 130-140℃ for 0.5-2 hours. After naturally cooling to room temperature, a sheet-like polymer PTC thermistor is obtained.

[0040] The preparation method provided by this invention is relatively simple and facilitates large-scale production. Large-scale production can reduce the production cost of a single chip PTC thermistor, thereby enhancing its market competitiveness.

[0041] In summary, the present invention has the following advantages:

[0042] 1. This invention effectively improves the overall thermal sensitivity by incorporating a built-in thermally conductive and insulating skeleton, effectively shortening the temperature sensing lag time of the thermistor. When applied to the temperature monitoring module of lithium battery cells, it can provide timely warnings, improve the vehicle's safe driving coefficient, and reduce the risk of property damage and personal injury.

[0043] 2. In this invention, aminosilane is grafted onto the surface of the conductive composite filler through a dehydration condensation reaction. Subsequently, lauric acid is used to hydrophobically modify the surface of the conductive composite filler. The carboxyl group -COOH in the lauric acid and the amino group -NH2 in the aminosilane undergo dehydration condensation to form an amide bond -(C=O)-(NH)-. The conductive composite filler treated with the above hydrophobic modification has good compatibility with the matrix resin and can be uniformly dispersed inside the matrix resin. This can improve the overall thermal conductivity and electrical conductivity of the chip PTC thermistor, enhance the thermal sensitivity of the chip PTC thermistor, and shorten the temperature sensing hysteresis time of the thermistor.

[0044] 3. In this invention, any one of graphene, carbon nanotubes, carbon nanofibers, or MAX phase materials is used as an auxiliary conductive filler. Its excellent thermal conductivity improves the overall thermal and electrical conductivity, thus enhancing the overall thermal and electrical performance of the chip PTC thermistor and increasing its thermal sensitivity, while shortening the temperature sensing hysteresis time. Furthermore, under the premise of the same electrical conductivity for the chip PTC thermistor, using an auxiliary conductive filler effectively reduces the amount of main conductive filler used, thereby reducing the overall filler content of the chip PTC thermistor and improving its overall toughness and impact resistance. This also reduces the overall production cost.

[0045] 4. The preparation method provided by this invention is relatively simple and facilitates large-scale production. Attached Figure Description

[0046] Figure 1 This is a bar graph showing the resistance changes of the chip PTC thermistors at different temperatures in Examples 1, 11-12, and Comparative Example 5. Detailed Implementation

[0047] To further understand the inventiveness and technical advancements of this invention, the preferred embodiments of this invention will be discussed in detail below with reference to examples and comparative examples.

[0048] Example: A chip-type PTC thermistor includes a thermally conductive insulating framework and a PTC polymer matrix. The thermally conductive insulating framework is a face-centered cubic (FCC) PU framework and highly thermally conductive insulating particles coated on the surface of the PU framework. The highly thermally conductive insulating particles are any one of aluminum nitride, boron nitride, titanium nitride, and silicon nitride with a particle size ≤200nm. Preferably, the highly thermally conductive insulating particles are aluminum nitride with a particle size ≤200nm.

[0049] The PU skeleton is a face-centered cubic PU skeleton prepared by 3D printing technology. It is located inside the PTC polymer matrix and can effectively improve the overall thermal conductivity, effectively enhance the thermal sensitivity of the chip PTC thermistor, and effectively shorten the temperature sensing hysteresis time of the thermistor.

[0050] There are two methods for preparing thermally conductive insulating skeletons: the first method uses self-assembly technology, and the second method uses chemical grafting of high thermal conductivity insulating particles.

[0051] The first method for preparing a thermally conductive and insulating skeleton is as follows:

[0052] S1. Perform surface plasma treatment on the PU skeleton with a face-centered cubic structure;

[0053] S2. The PU skeleton with a face-centered cubic structure after surface plasma treatment is sequentially immersed in an aqueous dispersion containing high thermal conductivity insulating particles with surface-grafted aminosilane and an aqueous dispersion containing high thermal conductivity insulating particles with surface-grafted epoxysilane. The high thermal conductivity insulating particles are coated on the surface of the face-centered cubic PU skeleton by self-assembly. The skeleton is then removed, washed, and dried to obtain the thermally conductive insulating skeleton.

[0054] The temperature of the aqueous dispersion containing highly thermally conductive insulating particles with surface-grafted aminosilane in S2 is 20-60℃, and the content of the highly thermally conductive insulating particles with surface-grafted aminosilane is 1-5wt%; the mass ratio of the highly thermally conductive insulating particles with surface-grafted aminosilane to the face-centered cubic PU skeleton is 1:(9-49); the immersion time of the face-centered cubic PU skeleton in the aqueous dispersion containing highly thermally conductive insulating particles with surface-grafted aminosilane is 8-24h.

[0055] The temperature of the aqueous dispersion of S2 containing surface-grafted epoxy-silane high thermal conductivity insulating particles is 20-60℃, and the content of the surface-grafted epoxy-silane high thermal conductivity insulating particles is 1-5wt%; the mass ratio of the surface-grafted epoxy-silane high thermal conductivity insulating particles to the face-centered cubic PU skeleton is 1:(9-49); the immersion time of the face-centered cubic PU skeleton in the aqueous dispersion containing surface-grafted epoxy-silane high thermal conductivity insulating particles is 8-24h.

[0056] The second method for preparing a thermally conductive and insulating skeleton is as follows:

[0057] S1. Perform surface plasma treatment on the PU skeleton with a face-centered cubic structure;

[0058] S2. The PU skeleton with a face-centered cubic structure after surface plasma treatment is immersed in a mercaptosilane aqueous solution at a temperature of 40-60℃ and under magnetic stirring at 200-600 rpm for 0.5-2 hours. The skeleton is then removed and dried to obtain a PU skeleton with a face-centered cubic structure grafted with mercaptosilane.

[0059] S3. The face-centered cubic PU skeleton with surface-grafted mercaptosilane is immersed in an aqueous dispersion containing methacrylic acid silane-modified high thermal conductivity insulating particles. The content of methacrylic acid silane-modified high thermal conductivity insulating particles in the aqueous dispersion is 1-5 wt%, and the mass ratio of the methacrylic acid silane-modified high thermal conductivity insulating particles to the face-centered cubic PU skeleton is 1:(9-49). The temperature of the aqueous dispersion is controlled at 30-80℃, and the reaction is maintained at 30-80℃ for 2-24 hours. After removal, washing, and drying, the thermally conductive insulating skeleton is obtained.

[0060] PTC polymer matrix is ​​made from the following raw materials in the following weight percentages: 15-30% hydrophobic modified conductive composite filler, 0.5-2% anti-aging additives, 0.2-0.8% zinc stearate, and the balance being thermoplastic polymer resin with a high coefficient of thermal linear expansion.

[0061] The thermoplastic polymer with a high coefficient of thermal linear expansion in the PTC polymer matrix formulation is composed of HDPE, LDPE, and LLDPE in a mass ratio of 100:(5-30):(5-20).

[0062] The anti-aging additives in the PTC polymer matrix formulation are composed of antioxidant 1010, antioxidant 168, and UV-234 in a mass ratio of 100:(10-15):(50-150).

[0063] The hydrophobically modified conductive composite filler in the PTC polymer matrix formulation is composed of a main conductive filler, an auxiliary conductive filler, and a modifier in a mass ratio of 100:(20-40). The main conductive filler is any one of nano-sized carbon black, natural graphite, or artificial synthetic graphite. The auxiliary conductive filler is any one of graphene, carbon nanotubes, carbon nanofibers, or MAX phase materials. The modifier is aminosilane or lauric acid.

[0064] The preparation method of hydrophobic modified conductive composite packing is as follows: The main conductive packing and auxiliary conductive packing are mixed evenly according to a specified ratio to obtain the conductive composite packing. 10 parts by weight of the conductive composite packing are added to 100-200 parts by weight of an aminosilane aqueous solution with a concentration of 0.5-3 wt%. The mixture is magnetically stirred at 200-600 rpm for 0.5-2 hours, ultrasonically dispersed for 0.5-1 hours, and filtered under reduced pressure. The resulting filter media is then vacuum dried to obtain the aminosilane modified conductive composite packing. Subsequently, 10 parts by weight of the aminosilane modified conductive composite packing are added to 500-1000 parts by weight of a lauric acid aqueous solution with a concentration of 0.2-0.4 wt%. The mixture is magnetically stirred at 200-600 rpm for 0.5-2 hours, ultrasonically dispersed for 0.5-1 hours, and filtered under reduced pressure. The resulting filter media is rinsed with deionized water at least three times, and then vacuum dried to obtain the hydrophobic modified conductive composite packing.

[0065] The fabrication method of a chip PTC thermistor includes the following steps:

[0066] Step 1: Preparation of thermally conductive and insulating framework; simultaneously, preparation of hydrophobically modified conductive composite filler;

[0067] Step 2: Mix the accurately measured hydrophobic modified conductive composite filler, anti-aging additive, zinc stearate, and thermoplastic polymer resin with a high coefficient of thermal linear expansion evenly. Put the resulting mixture into an internal mixer for internal mixing and homogenization treatment. The mixing temperature is 145-150℃ and the mixing time is 4-6 minutes.

[0068] Step 3: The rubber compound obtained in Step 2 is fed into a twin-screw extruder for melt extrusion. The resulting molten extruded material is injected into a molding die with a pre-placed thermally conductive and insulating skeleton. The temperature of the molding die is 130-140℃, and it is maintained at 130-140℃ for 0.5-2 hours. After naturally cooling to room temperature, a sheet-like polymer PTC thermistor is obtained.

[0069] Example 1: A chip-type PTC thermistor includes a thermally conductive and insulating skeleton and a PTC polymer matrix. The thermally conductive and insulating skeleton is a face-centered cubic (FCC) PU skeleton and highly thermally conductive insulating particles coated on the surface of the PU skeleton. The highly thermally conductive insulating particles are nano-aluminum nitride with an average particle size of 40 nm. The PU skeleton is a face-centered cubic PU skeleton prepared by 3D printing technology - fused deposition modeling (FDM). Specifically, TPU (Wanhua Chemical TPU PU90AN) is heated and melted through the heating nozzle of the 3D printer and precisely extruded from the nozzle. The nozzle diameter of the 3D printer is 0.10 mm. The layers are stacked layer by layer on the printing platform according to the set path of face-centered cubic structure (the side length of a single cube is 1.0 mm). Each layer cools and solidifies rapidly after extrusion and firmly bonds to the layer below, and the layers are stacked to form a face-centered cubic PU skeleton.

[0070] The PTC polymer matrix is ​​made from the following raw materials in the indicated weight percentages: 20% hydrophobically modified conductive composite filler, 0.9% antioxidant 1010, 0.1% antioxidant 168, 1% UV-234, 0.6% zinc stearate, 51.6% HDPE (Formosa Plastics 9001, injection molding grade, melt flow rate 1.14 g / 10 min), 15.48% LDPE (Saudi Arabia SABIC 2602X1, melt flow rate 1.5 g / 10 min), and 10.32% LLDPE (Saudi Arabia SABIC 222WJ, melt flow rate 1.9 g / 10 min). The hydrophobically modified conductive composite filler in the PTC polymer matrix formulation consists of 15.5% hydrophobically modified carbon black, 3% hydrophobically modified graphene, and 1.5% hydrophobically modified carbon nanotubes.

[0071] A method for fabricating a chip PTC thermistor includes the following steps:

[0072] Step one, the preparation method of the thermally conductive and insulating skeleton is as follows:

[0073] First, a PS-HX-53311 plasma surface treatment machine was used to perform surface plasma treatment on a face-centered cubic (FCC) PU skeleton. Compressed air was used as the plasma generator to obtain a FCC PU skeleton with surface plasma treatment. Then, the FCC PU skeleton was sequentially immersed in an aqueous dispersion A containing surface-grafted aminosilane KH550-containing nano-aluminum nitride. (Preparation of surface-grafted aminosilane KH550-containing nano-aluminum nitride: 5 parts by weight of XT-ALN-01 nano-aluminum nitride with an average particle size of 40 nm from Shanghai Xiangtian Nanomaterials Co., Ltd. were added to 100 parts by weight of a 0.5 wt% aminosilane KH550 aqueous solution, and the mixture was heated at room temperature at 200 rpm.) The mixture was magnetically stirred for 2 hours, followed by ultrasonic dispersion for 1 hour at a frequency of 20 kHz and a power of 600 W. After ultrasonic dispersion, it was filtered under reduced pressure, rinsing three times with deionized water. The resulting filter media was then transferred to a vacuum dryer for vacuum drying at 105°C for 2 hours to obtain nano-aluminum nitride with surface-grafted aminosilane KH550. Two parts by weight of the nano-aluminum nitride with surface-grafted aminosilane KH550 and 98 parts by weight of deionized water were mixed evenly to obtain the final aqueous dispersion A. The temperature of aqueous dispersion A was 45°C, and the content of nano-aluminum nitride in aqueous dispersion A was 2.0 wt%. The mass ratio of aluminum to a face-centered cubic (FCC) PU skeleton is 1:19, and the impregnation time is 24 hours. After 24 hours of impregnation, the PU skeleton is removed from the aqueous dispersion A and immersed in deionized water for surface washing. It is then placed in an oven and air-dried at 60°C for 4 hours to obtain a semi-finished thermally conductive and insulating skeleton. Subsequently, the semi-finished thermally conductive and insulating skeleton is impregnated in an aqueous dispersion B containing surface-grafted epoxy silane KH560 nano-aluminum nitride. (The preparation of surface-grafted amino silane KH560 nano-aluminum nitride: 5 parts by weight of XT-ALN-01 nano-aluminum nitride with an average particle size of 40 nm from Shanghai Xiangtian Nanomaterials Co., Ltd. are added to 100 parts by weight of 0.5 wt% epoxy silane KH560.) In a 60% aqueous solution, the mixture was magnetically stirred at 200 rpm for 2 hours at room temperature, followed by ultrasonic dispersion for 1 hour at an ultrasonic frequency of 20 kHz and an ultrasonic power of 600 W. After ultrasonic dispersion, the mixture was filtered under reduced pressure, rinsing three times with deionized water. The resulting filter material was then transferred to a vacuum dryer for vacuum drying at 105°C for 2 hours to obtain nano-aluminum nitride with surface-grafted epoxy silane KH560. Two parts by weight of the nano-aluminum nitride with surface-grafted epoxy silane KH560 and 98 parts by weight of deionized water were mixed evenly to obtain the finished aqueous dispersion B. The temperature of aqueous dispersion B was 40°C, and the content of nano-aluminum nitride in aqueous dispersion B was 2%.The mass ratio of nano-aluminum nitride to face-centered cubic PU skeleton in aqueous dispersion B is 1:19 (5 wt%). The immersion time is 6 hours. After 6 hours of immersion, the PU skeleton is removed from the aqueous dispersion and immersed in deionized water for surface washing. Then, it is placed in an oven and air-dried at 60°C for 4 hours to obtain a semi-finished thermally conductive and insulating skeleton.

[0074] Simultaneously, the preparation method of the hydrophobically modified conductive composite filler is as follows: 15.5 parts by weight of carbon black (Cabot conductive carbon black VULCAN XC72), 3 parts by weight of hydroxylated graphene TF12141 (fineness ~300nm / 0.5-5um) from Suzhou Kaifa New Material Technology Co., Ltd., and 1.5 parts by weight of hydroxyl-functionalized multi-walled carbon nanotubes (inner diameter: 3-5nm, outer diameter: 8-15nm) from Shandong Xiya Chemical Co., Ltd. are placed in a dispersion vessel and dispersed at high speed for 2 hours to obtain a uniformly mixed conductive composite filler; then, 10 parts by weight of the conductive composite filler are weighed and added to 200 parts by weight of a 1.0wt% aminosilane KH550 aqueous solution, and magnetically stirred at 320rpm for 1 hour, followed by 0.5 hours of ultrasonic dispersion treatment at an ultrasonic frequency of 20kHz and an ultrasonic power of 600W. After ultrasonic dispersion treatment, the mixture is filtered under reduced pressure. The filter media was rinsed three times with deionized water during the process. The resulting filter media was then transferred to a vacuum dryer for vacuum drying at 105°C for 2 hours to obtain aminosilane-modified conductive composite filler. Subsequently, 10 parts by weight of the aminosilane-modified conductive composite filler were added to 800 parts by weight of a 0.25wt% lauric acid aqueous solution and magnetically stirred at 24 rpm for 2 hours. Then, ultrasonic dispersion was performed for 1 hour at an ultrasonic frequency of 20 kHz and an ultrasonic power of 600 W. After ultrasonic dispersion, the filter media was subjected to vacuum filtration, during which it was rinsed three times with deionized water. The resulting filter media was then transferred to a vacuum dryer for vacuum drying at 105°C for 2 hours to obtain hydrophobic-modified conductive composite filler.

[0075] Step 2: Accurately measured 15 parts by weight of the hydrophobic modified conductive composite filler prepared in Step 1, 0.9 parts by weight of antioxidant 1010, 0.1 parts by weight of antioxidant 168, 1 part by weight of UV-234, 0.6 parts by weight of zinc stearate, 51.6 parts by weight of HDPE, 15.48 parts by weight of LDPE, and 10.32 parts by weight of LLDPE are placed in a dispersion vessel and mixed and dispersed at 400 rpm for 4 hours to obtain a mixture. The obtained mixture is then fed into an internal mixer for internal mixing and homogenization treatment at a temperature of 150℃ for 5 minutes.

[0076] Step 3: The rubber compound obtained in Step 2 is fed into a twin-screw extruder for melt extrusion. The twin-screw extruder is divided into five heating temperature zones: the first zone is set at 165°C, the second zone at 175°C, the third zone at 185°C, the fourth zone at 190°C, and the fifth zone at 190°C. The screw speed is 42 r / min, and the die temperature is 190.1°C. The molten extruded material is injected into a molding die containing the thermally conductive and insulating skeleton prepared in Step 1 through a resin delivery pump. The temperature of the molding die is 135°C. The material is kept at 135°C for 1 hour for heat conditioning, and then naturally cooled to room temperature to obtain a sheet-like polymer PTC thermistor.

[0077] The difference between Example 2 and Example 1 is that in step one of the preparation method of the chip PTC thermistor, the mass ratio of nano-aluminum nitride to face-centered cubic PU skeleton in aqueous dispersion A is 1:19; the mass ratio of nano-aluminum nitride to face-centered cubic PU skeleton in aqueous dispersion B is 1:9, and the remaining steps remain unchanged.

[0078] The difference between Example 3 and Example 1 is that in step one of the preparation method of the chip PTC thermistor, the mass ratio of nano-aluminum nitride to face-centered cubic PU skeleton in aqueous dispersion A is 1:19; the mass ratio of nano-aluminum nitride to face-centered cubic PU skeleton in aqueous dispersion B is 1:29, and the remaining steps remain unchanged.

[0079] The difference between Example 4 and Example 1 is that in step one of the preparation method of the chip PTC thermistor, the mass ratio of nano-aluminum nitride to face-centered cubic PU skeleton in aqueous dispersion A is 1:19; the mass ratio of nano-aluminum nitride to face-centered cubic PU skeleton in aqueous dispersion B is 1:39, and the remaining steps remain unchanged.

[0080] The difference between Example 5 and Example 1 is that in step one of the preparation method of the chip PTC thermistor, the mass ratio of nano-aluminum nitride to face-centered cubic PU skeleton in aqueous dispersion A is 1:19; the mass ratio of nano-aluminum nitride to face-centered cubic PU skeleton in aqueous dispersion B is 1:49, and the remaining steps remain unchanged.

[0081] The difference between Example 6 and Example 1 is as follows: In step one of the preparation method of the chip PTC thermistor, a face-centered cubic PU skeleton is first subjected to surface plasma treatment using a PS-HX-53311 plasma surface treatment machine. The plasma generator is compressed air, and a face-centered cubic PU skeleton with surface plasma treatment is obtained. The face-centered cubic PU skeleton after low-temperature plasma treatment is then immersed in an aqueous solution of mercaptosilane KH-591. The mass ratio of the face-centered cubic PU skeleton to the mercaptosilane KH-591 aqueous solution is 1:50, and the concentration of mercaptosilane KH-591 in the mercaptosilane KH-591 aqueous solution is 1%. The PU skeleton was immersed in a 0 wt% KH-591 aqueous solution at 60°C with magnetic stirring at 320 rpm for 2 hours. Afterward, the skeleton was removed from the KH-591 aqueous solution and immersed in deionized water for surface washing. It was then air-dried in an oven at 60°C for 4 hours to obtain a face-centered cubic PU skeleton with KH-591 grafted onto its surface. The KH-591-grafted face-centered cubic PU skeleton was then immersed in an aqueous dispersion C containing KH-570-modified nano-aluminum nitride (KH-570-modified nano-aluminum nitride). Preparation of nano-aluminum nitride: 5 parts by weight of XT-ALN-01 nano-aluminum nitride with an average particle size of 40 nm from Shanghai Xiangtian Nanomaterials Co., Ltd. were added to 100 parts by weight of a 0.5 wt% aqueous solution of methacrylate silane KH-570. The mixture was magnetically stirred at 200 rpm for 2 hours at room temperature, followed by ultrasonic dispersion treatment for 1 hour at an ultrasonic frequency of 20 kHz and an ultrasonic power of 600 W. After ultrasonic dispersion treatment, the mixture was filtered under reduced pressure, and rinsed three times with deionized water during the process. The resulting filter material was then transferred to a vacuum dryer for vacuum drying at 105℃ for 2 hours to obtain the final product. Nano-aluminum nitride grafted with methacrylate silane KH-570 is prepared by mixing 2 parts by weight of nano-aluminum nitride grafted with methacrylate silane KH-570 and 98 parts by weight of deionized water to obtain the finished aqueous dispersion C. The mass ratio of nano-aluminum nitride to face-centered cubic PU skeleton in aqueous dispersion C is 1:19. Aqueous dispersion C is heated to 60°C in a water bath and reacted for 12 hours at 60°C. The PU skeleton is then removed from aqueous dispersion C and immersed in deionized water for surface washing. Subsequently, it is placed in an oven and air-dried at 60°C for 4 hours to obtain a thermally insulating skeleton. The remaining steps remain unchanged.

[0082] The difference between Example 7 and Example 6 is that in step one of the preparation method of the chip PTC thermistor, the concentration of mercaptosilane KH-591 in the aqueous solution of mercaptosilane KH-591 is 2.0 wt%, and the mass ratio of nano-aluminum nitride to face-centered cubic PU skeleton in aqueous dispersion C is 1:9.

[0083] The difference between Example 8 and Example 6 is that in step one of the preparation method of the chip PTC thermistor, the concentration of mercaptosilane KH-591 in the aqueous solution of mercaptosilane KH-591 is 0.5wt%, and the mass ratio of nano-aluminum nitride to face-centered cubic PU skeleton in aqueous dispersion C is 1:29.

[0084] The difference between Example 9 and Example 1 is that in step one of the preparation method of the chip PTC thermistor, the concentration of mercaptosilane KH-591 in the aqueous solution of mercaptosilane KH-591 is 0.67wt%, and the mass ratio of nano-aluminum nitride to face-centered cubic PU skeleton in aqueous dispersion C is 1:39.

[0085] The difference between Example 10 and Example 1 is that in step one of the preparation method of the chip PTC thermistor, the concentration of mercaptosilane KH-591 in the aqueous solution of mercaptosilane KH-591 is 0.4wt%, and the mass ratio of nano-aluminum nitride to face-centered cubic PU skeleton in aqueous dispersion C is 1:49.

[0086] The difference between Example 11 and Example 1 is that the PTC polymer matrix is ​​made of 20% hydrophobic modified conductive composite filler, 0.9% antioxidant 1010, 0.1% antioxidant 168, 1% UV-234, 0.6% zinc stearate, 56.4% HDPE, 14% LDPE, and 7% LLDPE.

[0087] The difference between Example 12 and Example 1 is that the PTC polymer matrix is ​​made of 20% hydrophobic modified conductive composite filler, 0.9% antioxidant 1010, 0.1% antioxidant 168, 1% UV-234, 0.6% zinc stearate, 65.4% HDPE, 8% LDPE, and 4% LLDPE.

[0088] The difference between Comparative Example 1 and Example 1 is that: a chip PTC thermistor is made of a PTC polymer matrix, which is made of the following raw materials in the indicated mass percentages: 20% hydrophobically modified conductive composite filler, 0.9% antioxidant 1010, 0.1% antioxidant 168, 1% UV-234, 0.6% zinc stearate, 51.6% HDPE, 15.48% LDPE, and 10.32% LLDPE. The hydrophobically modified conductive composite filler in the PTC polymer matrix formulation consists of 15.5% hydrophobically modified carbon black, 3% hydrophobically modified graphene, and 1.5% hydrophobically modified carbon nanotubes.

[0089] The fabrication method of chip PTC thermistors is as follows:

[0090] Step 1: Preparation of hydrophobically modified conductive composite filler. The specific preparation method is as follows: 15.5 parts by weight of carbon black, 3 parts by weight of hydroxylated graphene, and 1.5 parts by weight of hydroxylated carbon nanotubes are placed in a dispersion vessel and dispersed at high speed for 2 hours to obtain a uniformly mixed conductive composite filler. Then, 10 parts by weight of the conductive composite filler are weighed and added to 200 parts by weight of a 1.0 wt% aminosilane KH550 aqueous solution. The mixture is magnetically stirred at 320 rpm for 1 hour, followed by ultrasonic dispersion treatment for 0.5 hours at an ultrasonic frequency of 20 kHz and an ultrasonic power of 600 W. After ultrasonic dispersion treatment, the mixture is filtered under reduced pressure. During the reduced pressure filtration process, the filter media is rinsed three times with deionized water. The resulting filter media is then transferred to a vacuum chamber. The filter media was vacuum dried at 105°C for 2 hours to obtain aminosilane-modified conductive composite filler. Then, 10 parts by weight of the aminosilane-modified conductive composite filler were added to 800 parts by weight of a 0.25 wt% lauric acid aqueous solution and magnetically stirred at 24 rpm for 2 hours. Following this, ultrasonic dispersion was performed for 1 hour at a frequency of 20 kHz and a power of 600 W. After ultrasonic dispersion, the filter media was filtered under reduced pressure, rinsing three times with deionized water. The resulting filter media was then transferred to a vacuum dryer for further vacuum drying at 105°C for 2 hours to obtain hydrophobic-modified conductive composite filler.

[0091] Step 2: Accurately measured 15 parts by weight of the hydrophobic modified conductive composite filler prepared in Step 1, 0.9 parts by weight of antioxidant 1010, 0.1 parts by weight of antioxidant 168, 1 part by weight of UV-234, 0.6 parts by weight of zinc stearate, 51.6 parts by weight of HDPE, 15.48 parts by weight of LDPE, and 10.32 parts by weight of LLDPE are placed in a dispersion vessel and mixed and dispersed at 400 rpm for 4 hours to obtain a mixture. The obtained mixture is then fed into an internal mixer for internal mixing and homogenization treatment at a temperature of 150℃ for 5 minutes.

[0092] Step 3: The rubber compound obtained in Step 2 is fed into a twin-screw extruder for melt extrusion. The twin-screw extruder is divided into five heating temperature zones: the first zone is set at 165℃, the second zone at 175℃, the third zone at 185℃, the fourth zone at 190℃, and the fifth zone at 190℃. The screw speed is 42 r / min, and the die temperature is 190.1℃. The molten extruded material is injected into the molding die through a resin delivery pump. The temperature of the molding die is 135℃. The material is kept at 135℃ for 1 hour for conditioning and tempering, and then naturally cooled to room temperature to obtain sheet-like polymer PTC thermistors.

[0093] The difference between Comparative Example 2 and Example 1 is that: a chip PTC thermistor includes a PU skeleton and a PTC polymer matrix. The PU skeleton is a face-centered cubic structure PU skeleton prepared by 3D printing technology - fused deposition modeling (FDM). Specifically, TPU (Wanhua Chemical TPU PU90AN) is heated and melted into a 0.8 mm diameter filament through the heating nozzle of the 3D printer, and then precisely extruded by the nozzle. It is stacked layer by layer on the printing platform according to the set face-centered cubic structure (the side length of a single cube is 2.5 mm). Each layer cools and solidifies rapidly after extrusion and is firmly bonded to the lower layer. The layers are stacked to form a face-centered cubic structure PU skeleton.

[0094] The PTC polymer matrix formulation of Comparative Example 2 is the same as that of Example 1.

[0095] The difference between the preparation method of the chip PTC thermistor in Comparative Example 2 and the preparation method of the chip PTC thermistor in Example 1 is as follows:

[0096] Step 1: Preparation of hydrophobically modified conductive composite filler. The specific preparation method is as follows: 15.5 parts by weight of carbon black, 3 parts by weight of hydroxylated graphene, and 1.5 parts by weight of hydroxylated carbon nanotubes are placed in a dispersion vessel and dispersed at high speed for 2 hours to obtain a uniformly mixed conductive composite filler. Then, 10 parts by weight of the conductive composite filler are weighed and added to 200 parts by weight of a 1.0 wt% aminosilane KH550 aqueous solution. The mixture is magnetically stirred at 320 rpm for 1 hour, followed by ultrasonic dispersion treatment for 0.5 hours at an ultrasonic frequency of 20 kHz and an ultrasonic power of 600 W. After ultrasonic dispersion treatment, the mixture is filtered under reduced pressure. During the reduced pressure filtration process, the filter media is rinsed three times with deionized water. The resulting filter media is then transferred to a vacuum chamber. The filter media was vacuum dried at 105°C for 2 hours to obtain aminosilane-modified conductive composite filler. Then, 10 parts by weight of the aminosilane-modified conductive composite filler were added to 800 parts by weight of a 0.25 wt% lauric acid aqueous solution and magnetically stirred at 24 rpm for 2 hours. Following this, ultrasonic dispersion was performed for 1 hour at a frequency of 20 kHz and a power of 600 W. After ultrasonic dispersion, the filter media was filtered under reduced pressure, rinsing three times with deionized water. The resulting filter media was then transferred to a vacuum dryer for further vacuum drying at 105°C for 2 hours to obtain hydrophobic-modified conductive composite filler.

[0097] Step 2: Accurately measured 15 parts by weight of the hydrophobic modified conductive composite filler prepared in Step 1, 0.9 parts by weight of antioxidant 1010, 0.1 parts by weight of antioxidant 168, 1 part by weight of UV-234, 0.6 parts by weight of zinc stearate, 51.6 parts by weight of HDPE, 15.48 parts by weight of LDPE, and 10.32 parts by weight of LLDPE are placed in a dispersion vessel and mixed and dispersed at 400 rpm for 4 hours to obtain a mixture. The obtained mixture is then fed into an internal mixer for internal mixing and homogenization treatment at a temperature of 150℃ for 5 minutes.

[0098] Step 3: The rubber compound obtained in Step 2 is fed into a twin-screw extruder for melt extrusion. The twin-screw extruder is divided into five heating temperature zones: the first zone is set at 165℃, the second zone at 175℃, the third zone at 185℃, the fourth zone at 190℃, and the fifth zone at 190℃. The screw speed is 42 r / min, and the die temperature is 190.1℃. The melt extruded material is injected into a molding die with a face-centered cubic PU skeleton pre-placed through a resin delivery pump. The temperature of the molding die is 135℃. The material is kept at 135℃ for 1 hour for conditioning and tempering, and then naturally cooled to room temperature to obtain a sheet-like polymer PTC thermistor.

[0099] The difference between Comparative Example 3 and Example 1 is that in step one of the preparation method of the chip PTC thermistor, the mass ratio of nano-aluminum nitride to face-centered cubic PU skeleton in aqueous dispersion A is 1:99; the mass ratio of nano-aluminum nitride to face-centered cubic PU skeleton in aqueous dispersion B is 1:99, and the remaining steps remain unchanged.

[0100] The difference between Comparative Example 4 and Example 6 is that in step one of the preparation method of the chip PTC thermistor, the concentration of mercaptosilane KH-591 in the aqueous solution of mercaptosilane KH-591 is 0.2wt%, and the mass ratio of nano-aluminum nitride to face-centered cubic PU skeleton in aqueous dispersion C is 1:99.

[0101] The difference between Comparative Example 5 and Example 1 is that the PTC polymer matrix is ​​composed of 20% hydrophobic modified conductive composite filler, 0.9% antioxidant 1010, 0.1% antioxidant 168, 1% UV-234, 0.6% zinc stearate, and 77.4% HDPE resin.

[0102] Test sample specifications: The chip PTC thermistors in Examples 1-12 and Comparative Examples 1-5 were cut and processed to prepare test sample thermistor sheets with a diameter of 20 mm and a thickness of 2.0 mm.

[0103] Performance testing - Switching temperature T cTest method: Take a chip PTC thermistor and connect it to 10VDC with a copper wire of resistance of 0.1Ω at 25℃. Measure the temperature-time curve of the chip PTC thermistor and find the inflection point of the resistance change in the Rt curve, i.e., T. n Lower resistance value → T n+1 If the resistance change is ≥15%, then the temperature point value T n为 Switching temperature T c .

[0104] Performance Testing - Response Time of Chip PTC Thermistor from Room Temperature to 65℃: A chip PTC thermistor was tested at 25℃ using a copper wire with a resistance of 0.1Ω connected to a Jinke JK2515 thermistor tester to measure its resistance value R at 25℃. 25℃ A single-piece PTC thermistor was placed in a 65℃ oven for 5 minutes. Then, a copper wire with a resistance of 0.1Ω was connected to a Jinke JK2515 thermistor tester to measure its resistance value R at 65℃. 65℃ The resistance value of the surface-mount PTC thermistor connected to the Jinke JK2515 thermistor tester was recorded by transferring it from a 25℃ environment to a 65℃ oven environment and recording the resistance value R. 25℃ →Resistance value R 65℃ Time t, time t is T 25℃ →Tc response time.

[0105] Performance Testing - Aging Resistance: The chip PTC thermistors in Examples 1-12 and Comparative Examples 1-5 were placed in an aging test chamber and aged for 1000 hours at 85℃ / 75%RH in air. Their resistance value and switching temperature T at 25℃ were measured using a Jinke JK2515 thermistor tester. c Calculate the resistance value, drift value at 25℃, and switching temperature T. c The drift value at 25℃ was calculated, and the average of 10 tests was recorded in Table 1. 25℃ = (R1 - R0) * 100 / R0, where R0 is the resistance value at 25℃ before aging, and R1 is the resistance value at 25℃ after aging. Switching temperature T c The drift value △P Tc = (R3 - R2) * 100 / R2, where R2 is the switching temperature T before aging. c The resistance value below, R3 is the switching temperature T after aging. c The resistance value below.

[0106] Table 1: Test parameters of chip PTC thermistors in Examples 1-12 and Comparative Examples 1-5

[0107]

[0108] Combining Examples 1-5 and Comparative Examples 1-2 with Table 1, it can be seen that adding a thermally conductive insulating frame to a chip PTC thermistor can increase the switching temperature T of the chip PTC thermistor. c and T 25℃ →T 65℃ The response time significantly improves the thermal sensitivity of the chip PTC thermistor, effectively shortening the temperature sensing lag time of the thermistor. After aging at 85℃ / 75%RH for 1000℃, the drift value is ≤0.10%. The chip PTC thermistor has good stability in use, meeting the stability requirements of thermistors used in temperature monitoring modules of lithium battery cells.

[0109] Based on Examples 1-5 and Comparative Example 3, and referring to Table 1, it can be seen that the low content of nano-aluminum nitride in aqueous dispersion A and aqueous dispersion B prevents them from effectively coating the surface of the PU skeleton to form a good thermally conductive network structure. This results in low thermal conductivity of the thermally conductive insulating skeleton, leading to a longer response time for the prepared chip PTC thermistor. Therefore, the mass ratio of nano-aluminum nitride in aqueous dispersion A to the face-centered cubic PU skeleton should be 1:(9-49); the mass ratio of nano-aluminum nitride in aqueous dispersion B to the face-centered cubic PU skeleton should also be 1:(9-49). This ensures that the chip PTC thermistor has excellent thermal sensitivity and effectively shortens the temperature sensing hysteresis time of the thermistor.

[0110] Based on Examples 6-10 and Comparative Example 4, and referring to Table 1, it can be seen that the low content of nano-aluminum nitride in the aqueous dispersion C is insufficient to effectively coat the surface of the PU skeleton and form a good thermally conductive network structure. This results in low thermal conductivity of the thermally conductive insulating skeleton, which in turn leads to a longer response time of the prepared chip PTC thermistor. The mass ratio of nano-aluminum nitride in the aqueous dispersion C to the face-centered cubic PU skeleton is 1:(9-49), which can ensure that the chip PTC thermistor has excellent thermal sensitivity and effectively shorten the temperature sensing hysteresis time of the thermistor.

[0111] Table 2: Test parameters of resistance values ​​of chip PTC thermistors at different temperatures in Examples 1, 11-12 and Comparative Example 5

[0112]

[0113] In conjunction with Examples 1, 11-12 and Comparative Example 5, and in conjunction with Tables 1-2 and Figure 1 It can be seen that the addition of LDPE resin and LLDPE resin can improve the switching temperature T of the chip PTC thermistor. cThe resistance increase of the chip PTC thermistor within the operating state temperature window. As the LDPE and LLDPE content increases, the chip PTC thermistor reaches the switching temperature T... c After that, the resistance increase of the chip PTC thermistor becomes more obvious.

[0114] In summary, the thermally conductive and insulating PU skeleton with a face-centered cubic structure effectively improves the overall thermal conductivity, significantly enhances the thermal sensitivity of the chip PTC thermistor, and effectively shortens the temperature sensing lag time of the thermistor. When applied to the temperature monitoring module of lithium battery cells, it can provide timely warnings, improve vehicle driving safety, and reduce the risk of property damage and personal injury.

[0115] It should be noted that this specific embodiment is merely an explanation of the technical solution of the present invention and is not intended to limit the present invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but as long as they are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. A chip-type PTC thermistor, characterized in that: The product comprises a thermally conductive and insulating skeleton and a PTC polymer matrix. The thermally conductive and insulating skeleton is a face-centered cubic PU skeleton and highly thermally conductive insulating particles coated on the surface of the PU skeleton. The PTC polymer matrix is ​​made from the following raw materials in the indicated mass percentages: 15-30% hydrophobic modified conductive composite filler, 0.5-2% anti-aging additives, 0.2-0.8% zinc stearate, and the balance being a thermoplastic polymer resin with a high linear coefficient of thermal expansion. The hydrophobic modified conductive composite filler is composed of a main conductive filler, an auxiliary conductive filler, and a modifier; the main conductive filler is any one of nanoscale carbon black, natural graphite, or artificial synthetic graphite; the auxiliary conductive filler is any one of graphene, carbon nanotubes, carbon nanofibers, or MAX phase materials; and the modifier is aminosilane or lauric acid. The thermoplastic polymer resin with a high linear coefficient of thermal expansion is composed of HDPE, LDPE, and LLDPE in a mass ratio of 100:(5-30):(5-20); the anti-aging additive is composed of antioxidant 1010, antioxidant 168, and UV-234 in a mass ratio of 100:(10-15):(50-150). The high thermal conductivity insulating particles are any one of aluminum nitride, boron nitride, titanium nitride, and silicon nitride with a particle size ≤200nm; The method for preparing the thermally conductive and insulating skeleton is as follows: S1. Perform surface plasma treatment on the PU skeleton with a face-centered cubic structure; S2. The PU skeleton with a face-centered cubic structure after surface plasma treatment is sequentially immersed in an aqueous dispersion containing highly thermally conductive insulating particles with surface-grafted aminosilane and an aqueous dispersion containing highly thermally conductive insulating particles with surface-grafted epoxysilane. The mass ratio of the highly thermally conductive insulating particles with surface-grafted aminosilane to the PU skeleton with a face-centered cubic structure is 1:(9-49); the mass ratio of the highly thermally conductive insulating particles with surface-grafted epoxysilane to the PU skeleton with a face-centered cubic structure is 1:(9-49); the highly thermally conductive insulating particles are coated on the surface of the PU skeleton with a face-centered cubic structure by self-assembly. After removal, washing, and drying, the thermally conductive insulating skeleton is obtained. Alternatively, the preparation method of the thermally conductive and insulating skeleton is as follows: S1. Perform surface plasma treatment on the PU skeleton with a face-centered cubic structure; S2. The PU skeleton with a face-centered cubic structure after surface plasma treatment is immersed in a mercaptosilane aqueous solution at a temperature of 40-60℃ and under magnetic stirring at 200-600 rpm for 0.5-2 hours. The skeleton is then removed and dried to obtain a PU skeleton with a face-centered cubic structure grafted with mercaptosilane. S3. The face-centered cubic PU skeleton with surface-grafted mercaptosilane is immersed in an aqueous dispersion containing methacrylic silane-modified high thermal conductivity insulating particles, wherein the mass ratio of the methacrylic silane-modified high thermal conductivity insulating particles to the face-centered cubic PU skeleton is 1:(9-49). Under photoinitiator or thermal initiation conditions, the high thermal conductivity insulating particles are coated on the surface of the face-centered cubic PU skeleton. After removal, washing, and drying, the thermally conductive insulating skeleton is obtained.

2. The chip PTC thermistor according to claim 1, characterized in that: The temperature of the aqueous dispersion containing highly thermally conductive insulating particles with surface-grafted aminosilane in S2 is 20-60℃, and the content of highly thermally conductive insulating particles with surface-grafted aminosilane in the aqueous dispersion is 1-5wt%; the immersion time of the face-centered cubic PU skeleton in the aqueous dispersion containing highly thermally conductive insulating particles with surface-grafted aminosilane is 8-24h.

3. A chip-type PTC thermistor according to claim 1, characterized in that: The temperature of the aqueous dispersion containing surface-grafted epoxy-based silane-rich, highly thermally conductive insulating particles in S2 is 20-60°C, and the content of surface-grafted epoxy-based silane-rich, highly thermally conductive insulating particles in the aqueous dispersion is 1-5 wt%; the immersion time of the face-centered cubic PU skeleton in the aqueous dispersion containing surface-grafted epoxy-based silane-rich, highly thermally conductive insulating particles is 8-24 h.

4. A chip-type PTC thermistor according to claim 1, characterized in that: In step S3, the face-centered cubic PU skeleton with surface-grafted mercaptosilane is immersed in an aqueous dispersion containing methacrylate-modified high thermal conductivity insulating particles. The content of methacrylate-modified high thermal conductivity insulating particles in the aqueous dispersion is 1-5 wt%. The temperature of the aqueous dispersion is controlled at 30-80℃, and the reaction is maintained at 30-80℃ for 2-24 hours. After removal, washing, and drying, the thermally conductive insulating skeleton is obtained.

5. A method for preparing a chip PTC thermistor according to any one of claims 1-4, characterized in that: Includes the following steps: Step 1: Preparation of the thermally conductive and insulating framework; Simultaneously, the preparation of hydrophobically modified conductive composite filler is as follows: The main conductive filler and auxiliary conductive filler are mixed uniformly according to a specified ratio to obtain a conductive composite filler. Ten parts by weight of the conductive composite filler are added to 100-200 parts by weight of an aminosilane aqueous solution with a concentration of 0.5-3 wt%. The mixture is magnetically stirred at 200-600 rpm for 0.5-2 hours, ultrasonically dispersed for 0.5-1 hours, and filtered under reduced pressure. The resulting filter media is then vacuum dried to obtain an aminosilane-modified conductive composite filler. Subsequently, ten parts by weight of the aminosilane-modified conductive composite filler are added to 500-1000 parts by weight of a lauric acid aqueous solution with a concentration of 0.2-0.4 wt%. The mixture is magnetically stirred at 200-600 rpm for 0.5-2 hours, ultrasonically dispersed for 0.5-1 hours, and filtered under reduced pressure. The resulting filter media is rinsed with deionized water at least three times, and then vacuum dried to obtain the hydrophobically modified conductive composite filler. Step 2: Mix the accurately measured hydrophobic modified conductive composite filler, anti-aging additive, zinc stearate, and thermoplastic polymer resin with a high linear coefficient of thermal expansion evenly. Put the resulting mixture into an internal mixer for internal mixing and homogenization treatment. The mixing temperature is 145-150℃ and the mixing time is 4-6 minutes. Step 3: The rubber compound obtained in Step 2 is fed into a twin-screw extruder for melt extrusion. The resulting molten extruded material is injected into a molding die with a pre-placed thermally conductive and insulating skeleton. The temperature of the molding die is 130-140℃, and it is maintained at 130-140℃ for 0.5-2 hours. After naturally cooling to room temperature, a sheet-like polymer PTC thermistor is obtained.

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