Polymer-based PTC (Positive Temperature Coefficient) composite material with good thermal stability and preparation method thereof

Abstract

The invention relates to a polymer-based PTC (Positive Temperature Coefficient) composite material with good thermal stability and a preparation method thereof. The method comprises the following steps: S1, mixing a carbon-series conductive filler and a first solvent, carrying out a heating reaction, and carrying out centrifugal separation, washing and drying to obtain a pretreated carbon-series conductive filler; s2, dispersing a titanate agent in a first solvent, adding the pretreated carbon-based conductive filler, uniformly dispersing, reacting, adding a silane coupling agent, and reacting to obtain a modified carbon-based conductive filler; s3, mixing a fluororesin monomer, tetrafluoroethylene, an initiator and an emulsifier, carrying out a hydrothermal reaction to obtain a copolymer emulsion, adding a demulsifier, and carrying out a secondary reaction to obtain modified fluororesin; and S4, fully mixing the modified fluororesin, the modified carbon black powder and a heat stabilizer, performing melt blending, and performing extrusion granulation to obtain the polymer-based PTC composite material with improved heat stability. The polymer-based PTC composite material provided by the invention has excellent thermal stability and high temperature resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer thermoelectric composite materials, and in particular relates to a polymer-based PTC composite material with good thermal stability and a preparation method thereof. Background Art

[0002] In frigid regions, electric tracing cables, as a kind of heat preservation and heating equipment widely used in industrial, civil and commercial fields, its core function is to generate heat through the conversion of electrical energy, providing necessary temperature maintenance or thawing ability for various pipelines, storage tanks, etc. The key to this technology lies in its built-in heating materials, which usually have high resistance characteristics and can quickly generate heat after being energized. Its heating materials include metal alloy wires, carbon-based conductive fillers, and polymer composite materials, etc. Their selection and design directly determine the heating efficiency, safety performance and service life of the electric tracing cable.

[0003] However, in practical applications, especially in extremely high-temperature environments, the heating materials of electric tracing cables will face severe challenges. Continuous high-temperature exposure will not only accelerate the internal aging process of the materials, but may also trigger a series of physical and chemical changes. For example, the metal alloy wire may undergo deformation or fracture of the microstructure due to the thermal expansion and contraction effect, and the polymer composite material may generate gas due to thermal decomposition, resulting in damage or performance degradation of the insulation layer.

[0004] Among them, the most common and important ones are its polymer matrix and conductive fillers. The unstable internal structure formed by the two-phase blending will change. These internal structural changes, even if tiny, will have a significant impact on the electrical performance and heating efficiency of the electric tracing cable. Specifically, it is manifested as the erratic resistance value, overloaded or too small output power, uneven heating temperature, reduced energy efficiency and even complete failure. More seriously, if the internal deterioration of the material reaches a certain degree, it may also cause safety hazards such as short circuits and fires.

[0005] Therefore, for electric tracing cables used in high-temperature environments, special attention must be paid to the high-temperature resistance and long-term thermal stability of their heating materials to ensure that they can continuously, safely and efficiently provide the required heating effect. Summary of the Invention

[0006] The purpose of the present invention is to provide a polymer-based PTC composite material with good thermal stability and a preparation method thereof. The polymer-based PTC composite material provided by the present invention has excellent thermal stability and high-temperature resistance.

[0007] To achieve the above purpose, the present invention provides the following technical solutions: The first aspect of the embodiment of the present invention provides a preparation method of a polymer-based PTC composite material with good thermal stability, including the following steps: S1. Mix the carbon-based conductive filler and the first solvent, heat and react. After the reaction ends, centrifuge, separate, wash, and dry to obtain the pretreated carbon-based conductive filler. S2. Disperse the titanate agent in the first solvent, then add the pretreated carbon-based conductive filler, adjust the pH to 8 - 10, stir for the first reaction, then adjust the pH to 4 - 6, add the silane coupling agent, stir for the second reaction. After the reaction ends, centrifuge, wash, and freeze-dry to obtain the modified carbon-based conductive filler. S3. Mix the fluororesin monomer, initiator, and emulsifier and carry out a hydrothermal reaction to obtain a copolymer emulsion. Then add a demulsifier and carry out a second reaction. After the reaction ends, obtain the fluororesin. S4. Thoroughly mix the modified fluororesin, modified carbon black powder, and heat stabilizer, then melt-blend and extrude and pelletize to obtain a polymer-based PTC composite with improved thermal stability.

[0008] In step S1, the carbon-based conductive filler is any one of graphite, carbon nanofibers, carbon nanotubes, carbon fibers, and carbon black.

[0009] Preferably, in step S1, the conditions for the first reaction are: reaction temperature 60 - 100 °C, reaction time 1 - 3 h.

[0010] Preferably, in step S1, the first solvent is nitric acid or sulfuric acid.

[0011] Preferably, in step S1, the dosage ratio of the carbon-based conductive filler to the first solvent is 1 g : (15 - 30 ml).

[0012] Preferably, in step S1, the conditions for the second reaction are: reaction temperature 60 - 100 °C, reaction time 1 - 3 h.

[0013] Preferably, in step S2, the titanate agent is one or more of TC-27, TM-931, TM-P, TMC-105, KT-201, KT-27, LD-122, LD-123.

[0014] Preferably, in step S2, the silane coupling agent is one or more of γ-glycidoxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-β-aminoethyl-γ-aminopropyltrimethoxysilane, vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane.

[0015] Preferably, in step S2, the second solvent is one or more of methanol, ethanol, and water.

[0016] Preferably, in step S2, the dosage ratio of the titanate agent, silane coupling agent, second solvent and pretreated carbon-based conductive filler is (1 - 3 ml):(2 - 5 ml):(1500 ml - 3000 ml):100 g.

[0017] Preferably, in step S2, the conditions for the stirring reaction are: reaction temperature 40 - 80°C, reaction time 1 - 4 h.

[0018] Preferably, in step S3, the fluororesin monomer is one or more of tetrafluoroethylene, chlorotrifluoroethylene, vinyl fluoride, hexafluoropropylene, ethylene, perfluoropropyl vinyl ether.

[0019] Preferably, in step S3, the initiator is potassium persulfate.

[0020] Preferably, in step S3, the emulsifier is ammonium perfluorooctanoate.

[0021] Preferably, in step S3, the demulsifier is magnesium sulfate.

[0022] Preferably, in step S3, the dosage ratio of the fluororesin monomer, tetrafluoroethylene, initiator, emulsifier, demulsifier is 10 g:(0.5 - 2 g):(0.05 - 2 ml):(0.0005 - 0.1 g):(0.01 - 0.1 g).

[0023] Preferably, in step S3, the conditions for the hydrothermal reaction are: reaction temperature 70 - 120°C, reaction pressure 2 - 4 MPa, reaction time 4 - 8 h.

[0024] Preferably, in step S3, the conditions for the secondary reaction are: reaction temperature 40 - 80°C, reaction time 10 - 30 min.

[0025] Preferably, in step S4, the heat stabilizer is a mixture of fluorine-modified nano lanthanum oxide and lead stabilizer with a mass ratio of 1:(0.5 - 2).

[0026] Preferably, the fluorine-modified nano lanthanum oxide includes the following preparation method: Mix nano lanthanum oxide, γ-methacryloxypropyltrimethoxysilane, perfluorooctyltriethoxysilane, ethanol, and carry out ultrasonic reaction. After the reaction ends, centrifuge and dry to obtain fluorine-modified nano lanthanum oxide.

[0027] Preferably, the particle size of the nano lanthanum oxide is 50 - 200 nm.

[0028] Preferably, the dosage ratio of the lanthanum oxide nanoparticles, ethanol, γ-methacryloxypropyltrimethoxysilane, and perfluorooctyltriethoxysilane is 1 g : (20 - 80 ml) : (0.3 - 1 ml) : (0.1 - 0.5 ml).

[0029] Preferably, the ultrasonic reaction conditions are as follows: the reaction temperature is 60 - 80°C, the reaction time is 1 - 3 h, and the ultrasonic power is 200 - 400 W.

[0030] Preferably, the lead stabilizer is one or more of dibasic lead stearate, tribasic lead sulfate trihydrate, dibasic lead phthalate, and dibasic lead phosphite.

[0031] Preferably, in step S4, the mass ratio of the fluororesin, modified carbon black powder, and heat stabilizer is 100 : (5 - 20) : (0.1 - 1).

[0032] In a second aspect, an embodiment of the present invention provides a polymer-based PTC composite material obtained by the preparation method of the polymer-based PTC composite material with good thermal stability as described above.

[0033] Compared with the prior art, the present invention has the following beneficial effects: 1. The composite material obtained in this application has excellent high-temperature resistance. Specifically, the PCTFE-TFE copolymer synthesized in a high-pressure autoclave significantly enhances the thermal stability of the matrix by introducing tetrafluoroethylene monomers. The introduction of tetrafluoroethylene increases the proportion of C-F bonds in the polymer main chain, and the bond energy of C-F bonds is much higher than that of C-Cl bonds and C-H bonds, which directly raises the thermal decomposition temperature of the material. Ammonium perfluorooctanoate, as an emulsifier, not only promotes the dispersion of monomers in the aqueous phase but also forms microphase separation in the copolymer through its long-chain perfluorinated structure, further inhibiting the thermal movement of molecular chains at high temperatures. In addition, the synergistic effect of free radical polymerization initiated by potassium persulfate and ionic crosslinking of MgSO4 forms a dynamic crosslinking network, enabling the material to maintain melt strength during the mixing process and preventing the aggregation of carbon black fillers due to excessive matrix flow. The modified carbon black powder undergoes dual treatment with acid oxidation and titanate / silane coupling agents, generating abundant carboxyl and amino functional groups on the surface. The alkoxy groups of the titanate agent form chemical bonding with the hydroxyl groups on the carbon black surface through esterification reactions, while the silane coupling agent enhances the interfacial compatibility with the fluorocarbon chain of polychlorotrifluoroethylene through hydrogen bonding. This strong interfacial bonding buffers the difference in thermal expansion coefficients between carbon black and the matrix, thereby reducing interfacial peeling caused by thermal stress at high temperatures (such as 250°C).

[0034] 2. The composite material obtained in this application has excellent thermal stability. Through the surface modification of fluorinated nano-lanthanum oxide with KH-570 and perfluorooctylsilane, efficient compatibility with the polychlorotrifluoroethylene matrix is achieved. The methacryloxy group of KH-570 undergoes a grafting reaction with the matrix at high temperature during internal mixing to form a covalent bond; while the perfluorooctyl chain segment is embedded in the fluorocarbon chain of the matrix through fluorine-fluorine interaction, controlling the dispersion size of the nanoparticles within the nanometer range. The high specific surface area and rigid lattice structure of nano-lanthanum oxide form a physical crosslinking network in the matrix, restricting the thermal movement of polymer segments, reducing the coefficient of thermal expansion of the material, and thus reducing the internal stress caused by volume change at high temperature. Dibasic lead phthalate, as a heat stabilizer, inhibits material degradation through a chemical mechanism: its phthalate root can efficiently capture HCl released by polychlorotrifluoroethylene at high temperature, blocking the autocatalytic fracture effect of HCl on the polymer chain; at the same time, the lead ion binds to the oxygen vacancies on the surface of nano-lanthanum oxide to form a La-O-Pb composite structure, which not only stabilizes the lattice of lanthanum oxide but also improves the thermal conductivity of the material, promoting uniform heat diffusion and avoiding local overheating.

[0035] 3. The composite material obtained in this application has excellent resistivity stability. Among them, the surface energy of the modified carbon black powder is significantly reduced under the coating of titanate and silane coupling agents, which improves its dispersion uniformity in the matrix and reduces the percolation threshold. The carbon black particles are anchored in the matrix through the dual actions of chemical bonding and physical adsorption. Even during the internal mixing and hot pressing processes, they still maintain a nanoscale dispersion particle size, forming a continuous three-dimensional conductive network. The addition of fluorinated nano-lanthanum oxide further fills the micropores between the matrix and carbon black, and its high modulus characteristic effectively inhibits the damage of the matrix thermal expansion to the conductive path. In addition, dibasic lead phthalate indirectly protects the conductive network by inhibiting matrix degradation: the captured Cl⁻ ions reduce the oxidative corrosion of the carbon black surface, and the synergistic effect of lead salt and lanthanum oxide reduces the attack of free radicals on the carbon black-matrix interface. In addition, the crosslinking network of PCTFE-TFE copolymer dynamically reorganizes at high temperature, which can wrap the carbon black particles and restrict their migration, enabling the resistivity to quickly reset after multiple PTC effect triggers. Brief Description of the Drawings

[0036] Figure 1 The resistivity change curve and change rate of the material obtained in Example 1 of the present invention and Comparative Example 1; Figure 2 The resistance-temperature curve of Comparative Example 1 of the present invention treated at high temperature for different times; Figure 3 The resistance-temperature curve of the material obtained in Example 1 of the present invention treated at high temperature for different times; Figure 4 The change rate of the PTC strength of the material obtained in Example 1 of the present invention and Comparative Example 1; Figure 5 The resistivity change curves and change rates of the materials obtained in Example 2 of the present invention and Comparative Example 1; Figure 6 The resistance-temperature curves of the materials obtained in Example 2 of the present invention at different high-temperature treatment times; Figure 7 The change rates of the PTC strengths of the materials obtained in Example 2 of the present invention and Comparative Example 1; Figure 8 The resistivity change curves and change rates of the materials obtained in Example 3 of the present invention and Comparative Example 1; Figure 9 The resistance-temperature curves of the materials obtained in Example 3 of the present invention at different high-temperature treatment times; Figure 10 The change rates of the PTC strengths of the materials obtained in Example 3 of the present invention and Comparative Example 1. Detailed implementation manners

[0037] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented on the premise of the technical solution of the present invention, and the detailed implementation manners and specific operation processes are given, but the protection scope of the present invention is not limited to the following embodiments.

[0038] Unless otherwise specified, the reagents and raw materials used in the present invention are all obtained commercially.

[0039] Carbon black, model LX-900, purchased from Longxing Chemical Co., Ltd.; Chlorotrifluoroethylene, model JH-PCTFE-M100, purchased from Zhejiang Juhua Co., Ltd.; Nanometer lanthanum oxide, with an average particle size of 50 nm, purchased from Baotou Research Institute of Rare Earths; Dibasic lead phthalate, model LM-22D, purchased from Jiangsu Alliance Chemical Co., Ltd.; Dibasic lead phosphite, model SY-24P, purchased from Hangzhou Sanye New Materials Co., Ltd.; Polychlorotrifluoroethylene resin, model JH-PCTFE-R200, purchased from Zhejiang Juhua Co., Ltd. Example 1

[0040] This example provides a polymer-based PTC composite material with good thermal stability, and its preparation method is as follows: S1, Take 10 g of untreated carbon black and dissolve it in 200 ml of 3 M nitric acid solution, stir in a water bath at 80 °C for 4 hours, after the reaction is completed, centrifuge and separate, wash with deionized water until neutral, and dry in vacuum at 80 °C to obtain acid-oxidized carbon black; S2. Disperse 0.15 ml of titanate agent TMC-105 in 200 ml of absolute ethanol. Then add 10 g of acid-oxidized carbon black, and ultrasonically disperse it in a water bath at 60 °C with 300 W for 1 hour. Add ammonia water to adjust the pH to 8, stir and react at 60 °C for 2 h. Then use hydrochloric acid to adjust the pH to 5. Then add 0.3 ml of γ-aminopropyltriethoxysilane (KH-550), stir and react at 60 °C for 2 h. After the reaction, centrifuge, wash, and freeze-dry to obtain modified carbon black powder; S3. Add 200 ml of deionized water, 10 ml of ammonium perfluorooctanoate, and 0.1 g of potassium persulfate to a high-pressure reactor. Then add 200 g of chlorotrifluoroethylene and 20 g of tetrafluoroethylene, heat up to 90 °C, maintain the pressure at 3 MPa, and react for 6 hours to produce a PCTFE-TFE copolymer emulsion. Then add 1 g of MgSO4 and react for 20 min. After the reaction, wash with water and dry to obtain modified polychlorotrifluoroethylene; S4. Disperse 5 g of nano-lanthanum oxide in 200 ml of ethanol, add 3 ml of γ-methacryloxypropyltrimethoxysilane (KH-570) and 1 ml of perfluorooctyltriethoxysilane, ultrasonically treat at 70 °C for 2 hours, centrifuge and dry to obtain fluorine-modified nano-lanthanum oxide; Mix 200 g of modified polychlorotrifluoroethylene, 16 g of modified carbon black powder, 0.2 g of fluorine-modified nano-lanthanum oxide, and 0.2 g of dibasic lead phthalate by internal mixing in a torque rheometer. The internal mixing temperature is 250 °C, the rotation speed is 40 rmp, and the internal mixing time is 20 min. Finally, hot press the blended sample into a sheet at 250 °C with a flat vulcanizer to obtain a polymer-based PTC composite material. Example 2

[0041] This example provides a polymer-based PTC composite material with good thermal stability, and its preparation method is as follows: S1. Take 10 g of untreated carbon black and dissolve it in 200 ml of 3M nitric acid solution, stir in a water bath at 80 °C for 4 hours. After the reaction, centrifuge and wash with deionized water until neutral, and vacuum dry at 80 °C to obtain acid-oxidized carbon black; S2. Disperse 0.25 ml of titanate agent TMC-105 in 200 ml of absolute ethanol. Then add 10 g of acid-oxidized carbon black, and ultrasonically disperse it in a water bath at 60 °C with 300 W for 1 hour. Add ammonia water to adjust the pH to 8, stir and react at 60 °C for 2 h. Then use hydrochloric acid to adjust the pH to 5. Then add 0.4 ml of γ-aminopropyltriethoxysilane (KH-550), stir and react at 60 °C for 2 h. After the reaction, centrifuge, wash, and freeze-dry to obtain modified carbon black powder; S3. Add 200 ml of deionized water, 10 ml of ammonium perfluorooctanoate, and 0.1 g of potassium persulfate into a high-pressure reactor. Then add 200 g of chlorotrifluoroethylene and 25 g of tetrafluoroethylene. Heat up to 90 °C and maintain the pressure at 3 MPa. React for 6 hours to form a PCTFE-TFE copolymer emulsion. Then add 1 g of MgSO4 and react for 20 min. After the reaction, wash with water and dry to obtain modified polychlorotrifluoroethylene. S4. Disperse 5 g of nano lanthanum oxide in 200 ml of ethanol. Add 3 ml of γ-methacryloxypropyltrimethoxysilane (KH-570) and 1 ml of perfluorooctyltriethoxysilane. Perform ultrasonic treatment at 70 °C for 2 hours, then centrifuge and dry to obtain fluorine-modified nano lanthanum oxide. Mix 200 g of modified polychlorotrifluoroethylene, 16 g of modified carbon black powder, 0.2 g of fluorine-modified nano lanthanum oxide, and 0.2 g of dibasic lead phthalate through a torque rheometer for intensive mixing. The mixing temperature is 250 °C, the rotation speed is 40 rmp, and the mixing time is 20 min. Finally, hot press the mixed sample into a sheet at 250 °C through a flat vulcanizer to obtain a polymer-based PTC composite material. Example 3

[0042] This example provides a polymer-based PTC composite material with good thermal stability, and its preparation method is as follows: S1. Dissolve 10 g of untreated carbon black in 200 ml of 3M nitric acid solution. Stir in a water bath at 80 °C for 4 hours. After the reaction, perform centrifugal separation and wash with deionized water until neutral. Then dry in vacuum at 80 °C to obtain acid-oxidized carbon black. S2. Disperse 0.15 ml of titanate agent TMC-105 in 200 ml of absolute ethanol. Then add 10 g of acid-oxidized carbon black. Perform ultrasonic dispersion in a water bath at 60 °C with 300 W for 1 hour. Add ammonia water to adjust the pH to 8 and stir and react at 60 °C for 2 h. Then use hydrochloric acid to adjust the pH to 5. Then add 0.3 ml of γ-aminopropyltriethoxysilane (KH-550) and stir and react at 60 °C for 2 h. After the reaction, perform centrifugal washing and freeze-drying to obtain modified carbon black powder. S3. Add 200 ml of deionized water, 10 ml of ammonium perfluorooctanoate, and 0.1 g of potassium persulfate into a high-pressure reactor. Then add 200 g of chlorotrifluoroethylene and 20 g of tetrafluoroethylene. Heat up to 90 °C and maintain the pressure at 3 MPa. React for 6 hours to form a PCTFE-TFE copolymer emulsion. Then add 1 g of MgSO4 and react for 20 min. After the reaction, wash with water and dry to obtain modified polychlorotrifluoroethylene. S4. Disperse 5 g of nanometer lanthanum oxide in 200 ml of ethanol, add 4 ml of γ-methacryloxypropyltrimethoxysilane (KH-570) and 1.5 ml of perfluorooctyltriethoxysilane, ultrasonically treat for 2 hours at 70 °C, centrifuge and dry to obtain fluorine-modified nanometer lanthanum oxide. Mix 200 g of modified polychlorotrifluoroethylene, 16 g of modified carbon black powder, 0.3 g of fluorine-modified nanometer lanthanum oxide, and 0.6 g of dibasic lead phosphite by kneading and blending using a torque rheometer. The blending temperature is 250 °C, the rotation speed is 40 rmp, and the blending time is 20 min. Finally, hot press the blended sample into a sheet at 250 °C using a flat vulcanizer to obtain a polymer-based PTC composite material.

[0043] Comparative Example 1 The difference between this comparative example and Example 1 is that steps S1 and S2 are not carried out, and the modified carbon black powder is changed to untreated carbon black.

[0044] Comparative Example 2 The difference between this comparative example and Example 1 is that the titanate agent TMC-105 is not added in step S2. Comparative Example 3 The difference between this comparative example and Example 1 is that γ-aminopropyltriethoxysilane is not added in step S2.

[0045] Comparative Example 4 The difference between this comparative example and Example 1 is that step S3 is not carried out, and the modified polychlorotrifluoroethylene in step S4 is changed to polychlorotrifluoroethylene resin.

[0046] Comparative Example 5 The difference between this comparative example and Example 1 is that the fluorine-modified nanometer lanthanum oxide in step S4 is changed to nanometer lanthanum oxide.

[0047] Comparative Example 6 The difference between this comparative example and Example 1 is that dibasic lead phthalate is not added in step S4.

[0048] Comparative Example 7 The difference between this comparative example and Example 1 is that step S2 is changed as follows: S2. Disperse 0.3 ml of γ-aminopropyltriethoxysilane (KH-550) and 0.15 ml of titanate agent TMC-105 in 200 ml of absolute ethanol, then add 10 g of acid-oxidized carbon black, ultrasonically disperse in a water bath at 300 W at 60 °C for 1 hour, then add ammonia water to adjust the pH to 8, stir and react at 60 °C for 2 h. After the reaction, centrifuge, wash, and freeze-dry to obtain modified carbon black powder.

[0049] Performance Test The samples obtained in Example 1 were subjected to a thermal stability evaluation test. In a high-temperature atmosphere at 200 °C, the changes in resistance and PTC strength were observed over time to evaluate the thermal stability of the material.

[0050] See Figure 1 , Figure 2 , Figure 3 and Figure 4 , where Figure 1 are the resistivity change curves and change rates of the material obtained in Example 1 and Comparative Example 1, Figure 2 is the resistance-temperature curve of Comparative Example 1 of the present invention at different high-temperature treatment times; Figure 3 is the resistance-temperature curve of the material obtained in Example 1 at different high-temperature treatment times, Figure 4 is the change rate of the PTC strength of the material obtained in Example 1 and Comparative Example 1; it can be seen from Figure 1 that the resistivity change rate of the sample obtained in Example 1 is slightly lower than that of Comparative Example 1. Combining Figure 2 , Figure 3 and Figure 4 , it can be known that after long-term high-temperature heat treatment, the PTC strength of the sample obtained in Example 1 can still maintain a good state, and its change degree is much smaller than that of Comparative Example 1; in summary, the thermal stability of the sample obtained through Example 1 is improved.

[0051] Similarly, referring again to Figure 2 , Figure 5 , Figure 6 and Figure 7 , it can be known that among them, Figure 2 is the resistance-temperature curve of Comparative Example 1 of the present invention at different high-temperature treatment times; Figure 5 is the resistivity change curve and change rate of the material obtained in Example 2 of the present invention and Comparative Example 1; Figure 6 is the resistance-temperature curve of the material obtained in Example 2 of the present invention at different high-temperature treatment times; Figure 7 is the change rate of the PTC strength of the material obtained in Example 2 of the present invention and the comparative example; it can be known that the resistivity change of the sample obtained in Example 2 is significantly lower than that of Comparative Example 1; combining Figure 2 , Figure 6 and Figure 7 , after long-term high-temperature heat treatment, the PTC strength of the sample obtained in Example 2 can also maintain a good state, and its change degree is much smaller than that of Comparative Example 1; in summary, the thermal stability of the sample obtained through Example 2 is also improved.

[0052] Similarly, please refer to Figure 1 , Figure 8 , Figure 9 and Figure 10 , Figure 8The resistivity change curves and change rates of the materials obtained in Example 3 of the present invention and Comparative Example 1; Figure 9 The resistance-temperature curves of the materials obtained in Example 3 of the present invention at different times of high-temperature treatment; Figure 10 The change rates of the PTC strengths of the materials obtained in Example 3 of the present invention and Comparative Example 1. Figure 8 It can be seen that the change in resistivity of the sample obtained in Example 3 is significantly lower than that of Comparative Example 1; Figure 2 , Figure 9 and Figure 10 , after the sample obtained in Example 3 undergoes long-term high-temperature heat treatment, its PTC strength, compared with that of Comparative Example 1, has a smaller degree of change than that of Comparative Example 1, and the sample obtained in Example 3 also improves its thermal stability.

[0053] Calculate the resistance change rates of the products obtained in Example 1 and Comparative Examples 1 to 6, and test their flame retardancy and heat distortion temperature. The flame retardancy test standard is UL94, and the heat distortion temperature test standard is ISO75-2. The results are shown in Table 1.

[0054] Table 1 Performance test results

[0055] From the above performance test results, it can be seen that the products obtained in the embodiments of the present application have good thermal stability and excellent high-temperature resistance performance. This is mainly because of the synergistic effect among the modified carbon black powder, modified polychlorotrifluoroethylene, and fluorine-modified nano-lanthanum oxide in the present application.

[0056] In the comparative examples, because the necessary technical solutions are not adopted, their performance in the corresponding performance tests is significantly worse than that of the examples. This better proves the irreplaceability of the specific technical solutions of the present application for achieving the technical effects and solving the technical problems.

[0057] The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and use the invention. Those skilled in the art can obviously make various modifications to these embodiments easily and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A preparation method of a polymer-based PTC composite material with good thermal stability, characterized in that, The following steps are involved: S1, mixing a carbon-based conductive filler and a first solvent, heating for reaction, and centrifuging, washing, and drying after the reaction to obtain a pretreated carbon-based conductive filler; S2, dispersing the titanate agent in the first solvent, then adding the pretreated carbon-based conductive filler, adjusting the pH to 8-10, stirring for a primary reaction, then adjusting the pH to 4-6, adding the silane coupling agent, stirring for a secondary reaction, and after the reaction, centrifugally washing and freeze-drying to obtain a modified carbon-based conductive filler; S3, mixing fluororesin monomer, initiator, and emulsifier and performing hydrothermal reaction to obtain copolymer emulsion, then adding demulsifier to perform secondary reaction, and obtaining fluororesin after the reaction is completed; S4, fully mixing the fluororesin, modified carbon black powder and thermal stabilizer, melt blending, extruding and granulating, and obtaining a polymer-based PTC composite material with improved thermal stability.

2. The preparation method of the polymer-based PTC composite material with good thermal stability according to claim 1, wherein In step S1, the carbon-based conductive filler is any one of graphite, carbon nanofiber, carbon nanotube, carbon fiber and carbon black; And / or, in step S1, the conditions of the primary reaction are: reaction temperature 60-100° C., reaction time 1-3 h; And / or, in step S1, the first solvent is nitric acid or sulfuric acid; And / or, in step S1, the amount ratio of the carbon-based conductive filler to the first solvent is 1g: (15-30ml); And / or, in step S1, the conditions of the secondary reaction are: reaction temperature 60-100° C., reaction time 1-3 h.

3. The preparation method of the polymer-based PTC composite material with good thermal stability according to claim 1, characterized in that, In step S2, the titanate agent is one or more of TC-27, TM-931, TM-P, TMC-105, KT-201, KT-27, LD-122, and LD-123; And / or, in step S2, the silane coupling agent is one or more of γ-glycidyloxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-β-aminoethyl-γ-aminopropyltrimethoxysilane, vinyltriethoxysilane, and γ-methacryloxypropyltrimethoxysilane; And / or, in step S2, the second solvent is one or more of methanol, ethanol, and water; and / or, in step S2, the titanate agent, the silane coupling agent, the second solvent and the pretreated carbon-based conductive filler are used in a ratio of (1-3 ml): (2-5 ml): (1500 ml-3000 ml): 100 g; And / or, in step S2, the stirring reaction conditions are: reaction temperature 40-80° C., reaction time 1-4 h.

4. The preparation method of the polymer-based PTC composite material with good thermal stability according to claim 1, characterized in that, In step S3, the fluororesin monomer is one or more of tetrafluoroethylene, chlorotrifluoroethylene, vinyl fluoride, hexafluoropropylene, ethylene, and perfluoropropyl vinyl ether; And / or, in step S3, the initiator is potassium persulfate; And / or, in step S3, the emulsifier is ammonium perfluorooctanoate; And / or, in step S3, the demulsifier is magnesium sulfate; and / or, in step S3, the usage ratio of the fluororesin monomer, tetrafluoroethylene, initiator, emulsifier and demulsifier is 10g: (0.5-2g): (0.05-2ml): (0.0005-0.1g): (0.01-0.1g); And / or, in step S3, the conditions of the hydrothermal reaction are as follows: reaction temperature is 70 - 120 °C, reaction pressure is 2 - 4 MPa, and reaction time is 4 - 8 h; And / or, in step S3, the conditions of the secondary reaction are as follows: reaction temperature is 40 - 80 °C, and reaction time is 10 - 30 min.

5. The preparation method of the polymer-based PTC composite material with good thermal stability according to claim 1, characterized in that, In step S4, the heat stabilizer is a mixture of fluorine - modified nano - lanthanum oxide and lead stabilizer with a mass ratio of 1:(0.5 - 2).

6. The preparation method of the polymer-based PTC composite material with good thermal stability according to claim 5, characterized in that, The fluorine - modified nano - lanthanum oxide includes the following preparation method: Mix nano - lanthanum oxide, γ - methacryloxypropyltrimethoxysilane, perfluorooctyltriethoxysilane, and ethanol, and carry out ultrasonic reaction. After the reaction ends, centrifuge and dry to obtain fluorine - modified nano - lanthanum oxide.

7. The preparation method of the polymer-based PTC composite material with good thermal stability according to claim 6, characterized in that, The particle size of the nano - lanthanum oxide is 50 - 200 nm; And / or, the dosage ratio of the nano - lanthanum oxide, ethanol, γ - methacryloxypropyltrimethoxysilane, and perfluorooctyltriethoxysilane is 1 g:(20 - 80 ml):(0.3 - 1 ml):(0.1 - 0.5 ml); And / or, the ultrasonic reaction conditions are as follows: reaction temperature is 60 - 80 °C, reaction time is 1 - 3 h, and ultrasonic power is 200 - 400 W.

8. The preparation method of the polymer-based PTC composite material with good thermal stability according to claim 6, characterized in that, The lead stabilizer is one or more of dibasic lead stearate, tribasic lead sulfate trihydrate, dibasic lead phthalate, and dibasic lead phosphite.

9. The preparation method of the polymer-based PTC composite material with good thermal stability according to claim 1, characterized in that, In step S4, the mass ratio of the fluororesin, modified carbon black powder, and heat stabilizer is 100:(5 - 20):(0.1 - 1).

10. A polymer - based PTC composite material obtained by the preparation method of a polymer - based PTC composite material with good thermal stability according to any one of claims 1 - 9.

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