PTC (Positive Temperature Coefficient) composite material as well as preparation method and application thereof

Abstract

The invention discloses a PTC (Positive Temperature Coefficient) composite material as well as a preparation method and application thereof, and relates to a PTC material technology, barium titanate, lead titanate, niobium oxide, ruthenium oxide and tantalum pentoxide are modified by KH550, then the modified materials, polypyrrole and epoxy resin are added into DMF (Dimethyl Formamide), conductive carbon black and modified carbon fibers are added, ultrasonic dispersion is performed, a solvent is removed by evaporation, and hot press molding is performed to obtain the PTC composite material. The composite material has the characteristics of sensitive temperature response, large resistance switching ratio, good reproducibility and the like, overcomes the defects of large brittleness and difficult processing of the traditional ceramic PTC material, avoids the defects of small temperature coefficient and poor stability of the polymer PTC material, realizes advantage complementation and performance integration of the ceramic PTC material and the polymer PTC material, and has a wide application prospect. The processing formability, the mechanical toughness and the use reliability of the material are remarkably improved while the excellent PTC effect is maintained.

Description

Technical Field

[0001] The present invention relates to the technical field of PTC materials, and in particular to a PTC composite material and a preparation method and application thereof. Background Art

[0002] Positive Temperature Coefficient (PTC) materials are functional materials whose resistance increases significantly with increasing temperature. When a specific temperature is reached, the resistance jumps sharply, offering unique features such as automatic current limiting, overload protection, and constant temperature control. PTC materials are widely used in electronic circuit protection, intelligent heating devices, sensors, switching elements, and other fields, and are essential key functional materials in the modern electronics industry.

[0003] Currently, PTC materials are primarily classified into two categories: ceramic-based and polymer-based. Ceramic-based PTC materials are typically based on barium titanate (BaTiO3) and are prepared by doping with rare earth elements or transition metal oxides. These materials offer advantages such as a significant PTC effect, a large resistance switching ratio, and a wide operating temperature range. However, they also suffer from drawbacks such as brittleness, high density, difficulty in processing and molding, and poor compatibility with the base material, limiting their application in complex-shaped devices and lightweight applications.

[0004] Polymer-based PTC materials, primarily composed of conductive polymers or polymer / conductive filler composites, offer advantages such as light weight, good toughness, easy processing, and low cost. However, they commonly suffer from issues such as a weak PTC effect, a relatively small resistance switching ratio, insufficient long-term stability, and a limited operating temperature range. Polymer-based PTC materials are particularly susceptible to performance degradation and failure in high-temperature or harsh environments.

[0005] In recent years, researchers have attempted to combine ceramic PTC materials with polymer matrices, hoping to develop composite materials that combine the advantages of both, exhibiting both excellent PTC effects and good processing properties. However, existing technologies suffer from poor interfacial compatibility between ceramic fillers and polymer matrices, resulting in suboptimal conductive network formation. The resulting PTC effects are often unstable, and their reproducibility and reliability need to be improved. Furthermore, traditional conductive fillers such as carbon black and carbon fibers tend to aggregate and disperse poorly in composite systems, impacting the overall performance of the material.

[0006] As electronic devices develop towards miniaturization, intelligence, and high reliability, higher requirements are placed on PTC materials. It is necessary to develop new composite materials with significant PTC effects, excellent mechanical properties, good processability, and long service life. Therefore, exploring new composite material system designs, interface modification technologies, and preparation processes is of great significance to promoting the advancement of PTC material technology. Summary of the Invention

[0007] In order to address the deficiencies in the prior art, the present invention aims to provide a PTC composite material, a preparation method thereof, and an application thereof. The composite material has the characteristics of sensitive temperature response, large resistance switching ratio, and good reproducibility. It overcomes the defects of traditional ceramic PTC materials such as high brittleness and difficulty in processing, while avoiding the shortcomings of polymer PTC materials such as small temperature coefficient and poor stability. It achieves the complementary advantages and performance integration of ceramic PTC materials and polymer PTC materials, and significantly improves the material's processability, mechanical toughness, and reliability while maintaining an excellent PTC effect.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A method for preparing a PTC composite material comprises the following steps:

[0010] (1) dispersing barium titanate, lead titanate, niobium oxide, ruthenium oxide, and tantalum pentoxide into an ethanol aqueous solution, then adding KH550, stirring and mixing, filtering, washing, and drying the product to obtain a mixed powder;

[0011] Preferably, in step (1), the amount ratio of barium titanate, lead titanate, niobium oxide, ruthenium oxide, tantalum pentoxide, ethanol aqueous solution, and KH550 is 10-25 g: 2-8 g: 3-6 g: 3-6 g: 4-10 g: 200-300 mL: 3-9 mL; the concentration of the ethanol aqueous solution is 85-95 wt%; and the stirring and mixing conditions are stirring and mixing at 60-75 ° C for 5-8 h.

[0012] (2) Dissolving polypyrrole and epoxy resin in DMF, then adding mixed powder, conductive carbon black, and modified carbon fiber, ultrasonically dispersing, evaporating and removing the solvent, crushing the solid material, and hot-pressing in a mold to obtain the PTC composite material.

[0013] Preferably, in step (2), the amount ratio of polypyrrole, epoxy resin, DMF, mixed powder, conductive carbon black, and modified carbon fiber is 100g: 25-40g: 300-500mL: 15-30g: 10-20g, 20-30g; the ultrasonic dispersion conditions are oscillation at a frequency of 10-20MHz and a temperature of 20-40°C for 60-90min; the solid material is crushed into 0.05-0.5mm; and the hot pressing molding conditions are hot pressing at 140-200°C and 15-24MPa for 10-20min.

[0014] Preferably, in step (2), the modified carbon fiber is prepared by the following method steps:

[0015] a. Immerse the carbon fiber in a sulfuric acid / nitric acid mixture, mechanically stir, filter the product, wash it until neutral, and dry it, add it to dichloromethane, add DMF and oxalyl chloride under a nitrogen atmosphere, stir to react, filter the product, wash it, and dry it to obtain chlorinated carbon fiber;

[0016] Mixed acid oxidation pretreatment and acyl chlorination reaction: Concentrated nitric acid, as a strong oxidant, attacks the carbon atoms on the carbon fiber surface under the catalytic and dehydrating effects of concentrated sulfuric acid, breaking the C-C bonds and introducing a large number of active sites such as carboxyl, hydroxyl, and carbonyl groups on the carbon fiber surface. In the subsequent acyl chlorination reaction, DMF first reacts with oxalyl chloride to form an active Vilsmeier intermediate, which further activates the surface carboxyl and hydroxyl groups to form highly active acyl chloride groups on the carbon fiber surface, providing reaction sites for the next reaction.

[0017] Preferably, in step a, the carbon fiber has a diameter of 2 to 10 μm and a length of 0.05 to 2 mm.

[0018] Preferably, in step a, the sulfuric acid concentration in the sulfuric acid / nitric acid mixture is 95-98wt%, the nitric acid concentration is 65-70wt%, and the volume ratio of sulfuric acid to nitric acid is 3:1; the amount ratio of carbon fiber, sulfuric acid / nitric acid mixture, dichloromethane, DMF, and oxalyl chloride is 10g:200-300mL:150-250mL:0.2-1mL:3-8mL; and the stirring reaction conditions are stirring and reacting at 20-35°C for 4-10h.

[0019] b. Immerse the chlorinated fiber in THF, add triethylamine and thiophene methanol under a nitrogen atmosphere, stir to react, filter, wash, and dry the product to obtain an intermediate carbon fiber;

[0020] Thiophene methanol esterification reaction: First, triethylamine acts as a proton acceptor and combines with the acidic protons in the system to provide an alkaline environment for the reaction. Subsequently, the hydroxyl oxygen atom of thiophene methanol acts as a nucleophile to attack the electron-deficient center of the acyl chloride carbon atom, forming a tetrahedral transition state intermediate, which quickly eliminates the HCl molecule to obtain the final product. The generated HCl is immediately captured by triethylamine to form a triethylamine hydrochloride precipitate, which drives the reaction in the positive direction. This step successfully grafts thiophene groups on the surface of carbon fibers, which are firmly connected through covalent ester bonds, providing nucleation sites for thiophene monomers for subsequent polymerization reactions.

[0021] Preferably, in step b, the usage ratio of chlorinated fiber, THF, triethylamine, and thiophene methanol is 10 g: 100-150 mL: 2.8-10.2 mL: 2.3-9.1 g; and the stirring reaction conditions are 45-60° C. and 2-8 h.

[0022] c. Immerse the intermediate carbon fiber in acetonitrile, add thiophene under a nitrogen atmosphere, stir and disperse, slowly add anhydrous ferric chloride in batches, vigorously stir and react in an ice bath, centrifuge, wash, and dry the product to obtain modified carbon fiber.

[0023] FeCl3 oxidative polymerization reaction: Under the oxidative action of FeCl3, the thiophene monomer loses an electron to form a thiophene cation radical. At the same time, the thiophene group on the carbon fiber surface is also oxidized, followed by a free radical coupling reaction. The two thiophene cation radicals combine to form a bithiophene dication. This intermediate quickly loses two protons to form a stable bithiophene unit. During the polymerization process, the thiophene group on the carbon fiber surface acts as a polymerization starting point and undergoes a chain growth reaction with the free thiophene monomer to form a polythiophene chain covalently linked to the carbon fiber surface. Throughout the process, the polythiophene chain grows in situ on the carbon fiber surface, forming a uniform conductive polymer coating, which significantly improves the surface properties and interfacial compatibility of the carbon fiber.

[0024] Preferably, in step c, the ratio of the intermediate carbon fiber, acetonitrile, thiophene, and anhydrous ferric chloride is 10 g: 150-300 mL: 8-16 mL: 10-20 g; the ice bath is 0-10° C., and the stirring reaction time is 6-24 h.

[0025] The present invention also claims protection for a PTC composite material prepared by the preparation method.

[0026] The present invention also claims protection for the use of the PTC composite material in overcurrent, overvoltage and overheat protection devices.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The present invention provides a PTC composite material, in which barium titanate serves as the primary PTC effect carrier, undergoing a phase transition near the Curie temperature, causing a sharp increase in resistance and providing a basic temperature control function. The addition of lead titanate lowers the Curie temperature and enhances the sensitivity of the PTC effect. Niobium oxide and tantalum pentoxide serve as dopants to improve the semiconductor properties of the ceramic powder, increasing carrier concentration and conductivity. The introduction of ruthenium oxide further optimizes the stability of the conductive network. KH550 silane coupling agent is used to surface-modify the mixed powder, significantly enhancing the interfacial bonding and compatibility between the inorganic filler and the organic matrix. Polypyrrole, as a conductive polymer matrix, provides a continuous conductive path, and its inherent conductivity and temperature sensitivity form a synergistic effect with the ceramic filler. Epoxy resin imparts excellent mechanical strength, thermal stability, and processability to the composite material. Conductive carbon black, at low addition levels, constructs a percolation conductive network, forming a multi-scale conductive structure with other conductive components. Modified carbon fibers, through a surface polythiophene grafted layer, provide a highly efficient conductive path, while also enhancing the mechanical properties and interfacial bonding of the composite material. Modified carbon fibers and conductive carbon black can form a significant synergistic effect. The modified carbon fibers act as a one-dimensional fibrous conductive filler to construct a long-range conductive skeleton, while the conductive carbon black acts as a zero-dimensional granular filler to fill the interfiber gaps and provide short-range connection points. The two work together to construct a multi-scale, multi-layered three-dimensional conductive network, effectively reducing the conductive percolation threshold and significantly improving the conductive efficiency and stability of the composite material. The PTC composite material prepared by this method combines the advantages of ceramic PTC resistors and polymer PTC resistors, namely excellent mechanical strength, resistance stability, processing performance, and reproducibility. This multi-component composite system achieves an optimal balance of conductivity, PTC effect, mechanical properties, and processing performance.

[0029] 2. The present invention provides a modified carbon fiber. A mixed acid oxidation pretreatment introduces a large number of active functional groups, such as carboxyl and hydroxyl groups, onto the carbon fiber surface, providing abundant reaction sites for subsequent chemical modification. An acyl chloride reaction converts the surface functional groups into highly active acyl chloride groups, ensuring efficient grafting of thiophene groups. A thiophene methanol esterification reaction firmly attaches the thiophene groups to the carbon fiber surface via covalent bonds, avoiding the instability of physical adsorption. During the FeCl3 oxidative polymerization process, the thiophene rings on the intermediate carbon fiber polymerize with the thiophene monomer to form polythiophene, which then wraps the carbon fiber to form a conductive polymer modified layer chemically bonded to the carbon fiber. The modified carbon fiber forms a core-shell structure composed of carbon fiber and polythiophene. The carbon fiber, as the conductive core, exhibits excellent electrical conductivity. The polythiophene wrapping significantly improves the dispersion of the carbon fiber, prevents aggregation, and enables uniform dispersion in the matrix, thereby enhancing the conductivity of the matrix. Polythiophene itself is a highly conductive polymer, and wrapping the carbon fiber further enhances its electrical conductivity. This modification strategy significantly improves the surface activity and interfacial compatibility of carbon fibers. The modified carbon fibers construct an efficient and stable three-dimensional conductive network in the PTC composite material, enhancing the controllability and reproducibility of the temperature response. At the same time, it improves the mechanical properties and service life of the composite material, providing key functional fillers for the preparation of high-performance PTC devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only show schematic diagrams of certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0031] Figure 1 These are the resistivity-temperature curves of Example 1, Comparative Example 1, and Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the embodiments. Of course, the specific embodiments described here are only used to explain the present invention and are not used to limit the present invention.

[0033] Unless otherwise specified, the chemical reagents and materials in the present invention are purchased from commercial sources or synthesized from commercially purchased raw materials.

[0034] Epoxy resin was purchased from Nantong Xingchen Synthetic Materials Co., Ltd., brand E51;

[0035] Polypyrrole was purchased from Zhejiang Jinjinle Chemical Co., Ltd.;

[0036] Conductive carbon black was purchased from Tianjin Yiborui Chemical with an average particle size of 3 μm.

[0037] A method for preparing a PTC composite material comprises the following steps:

[0038] (1) 10-25 g of barium titanate, 2-8 g of lead titanate, 3-6 g of niobium oxide, 3-6 g of ruthenium oxide, and 4-10 g of tantalum pentoxide are dispersed in 200-300 mL of 85-95 wt% ethanol aqueous solution, and then 3-9 mL of KH550 are added. The mixture is stirred and mixed at 60-75° C. for 5-8 h. The product is filtered, washed, and dried to obtain a mixed powder;

[0039] (2) Immerse 10 g of carbon fiber in 200-300 mL of sulfuric acid / nitric acid mixed acid (95-98 wt% sulfuric acid, 65-70 wt% nitric acid, volume ratio 3:1), mechanically stir, filter the product, wash it to neutrality, and dry it. Add it to 150-250 mL of dichloromethane, add 0.2-1 mL of DMF and 3-8 mL of oxalyl chloride under a nitrogen atmosphere, stir and react at 20-35 ° C for 4-10 hours, filter, wash, and dry the product to obtain chlorinated carbon fiber;

[0040] (3) Immerse 10 g of chlorinated fiber in 100-150 mL of THF, add 2.8-10.2 mL of triethylamine and 2.3-9.1 g of thiophene methanol under a nitrogen atmosphere, stir and react at 45-60 ° C for 2-8 h, filter, wash, and dry the product to obtain an intermediate carbon fiber;

[0041] (4) Immerse 10 g of the intermediate carbon fiber in 150-300 mL of acetonitrile, add 8-16 mL of thiophene under a nitrogen atmosphere, stir and disperse, slowly add 10-20 g of anhydrous ferric chloride in batches, vigorously stir and react at 0-10 ° C in an ice bath for 6-24 h, centrifuge, wash, and dry the product to obtain modified carbon fiber;

[0042] (5) 100 g of polypyrrole and 25-40 g of epoxy resin are dissolved in 300-500 mL of DMF, and then 15-30 g of mixed powder, 10-20 g of conductive carbon black, and 20-30 g of modified carbon fiber are added. The mixture is ultrasonically vibrated at 10-20 MHz and 20-40° C. for 60-90 min, and the solvent is evaporated to remove the solvent. The solid material is crushed into 0.05-0.5 mm and hot-pressed in a mold at 140-200° C. and 15-24 MPa for 10-20 min to obtain the PTC composite material.

[0043] The present invention will be further described below with reference to specific examples.

[0044] Example 1

[0045] A method for preparing a PTC composite material comprises the following steps:

[0046] (1) 25 g of barium titanate, 8 g of lead titanate, 6 g of niobium oxide, 6 g of ruthenium oxide, and 10 g of tantalum pentoxide were dispersed in 250 mL of 90 wt% ethanol aqueous solution, and then 9 mL of KH550 was added. The mixture was stirred and mixed at 75° C. for 5 h. The product was filtered, washed, and dried to obtain a mixed powder;

[0047] (2) 10 g of carbon fiber was immersed in 250 mL of sulfuric acid / nitric acid mixture (98 wt% sulfuric acid, 65 wt% nitric acid, volume ratio 3:1), mechanically stirred, the product was filtered, washed to neutrality, and dried, and added to 200 mL of dichloromethane. 0.6 mL of DMF and 8 mL of oxalyl chloride were added under a nitrogen atmosphere, and the reaction was stirred at 35 ° C for 4 h. The product was filtered, washed, and dried to obtain chlorinated carbon fiber;

[0048] (3) 10 g of acyl chloride fiber was immersed in 120 mL of THF, and 10.2 mL of triethylamine and 9.1 g of thiophene methanol were added under a nitrogen atmosphere. The reaction was stirred at 60 ° C for 2 h. The product was filtered, washed, and dried to obtain the intermediate carbon fiber;

[0049] (4) Immerse 10 g of the intermediate carbon fiber in 200 mL of acetonitrile, add 16 mL of thiophene under a nitrogen atmosphere, stir and disperse, slowly add 20 g of anhydrous ferric chloride in batches, vigorously stir and react in an ice bath at 3 ° C for 24 h, centrifuge, wash, and dry the product to obtain modified carbon fiber;

[0050] (5) 1000 g of polypyrrole and 400 g of epoxy resin were dissolved in 5000 mL of DMF, and then 300 g of mixed powder, 200 g of conductive carbon black, and 300 g of modified carbon fiber were added. The mixture was ultrasonically shaken at 15 MHz and 30° C. for 75 min, and the solvent was evaporated to remove the solvent. The solid material was crushed into 0.25 mm and hot pressed in a mold at 180° C. and 18 MPa for 15 min to obtain the PTC composite material.

[0051] Example 2

[0052] A method for preparing a PTC composite material comprises the following steps:

[0053] (1) 20 g of barium titanate, 6 g of lead titanate, 5 g of niobium oxide, 5 g of ruthenium oxide, and 8 g of tantalum pentoxide were dispersed in 250 mL of a 90 wt% ethanol aqueous solution, and then 7 mL of KH550 was added. The mixture was stirred and mixed at 70° C. for 6 h. The product was filtered, washed, and dried to obtain a mixed powder.

[0054] (2) 10 g of carbon fiber was immersed in 250 mL of sulfuric acid / nitric acid mixture (98 wt% sulfuric acid, 65 wt% nitric acid, volume ratio 3:1), mechanically stirred, the product was filtered, washed to neutrality, and dried, and added to 200 mL of dichloromethane. 0.6 mL of DMF and 6 mL of oxalyl chloride were added under a nitrogen atmosphere, and the reaction was stirred at 30 ° C for 6 h. The product was filtered, washed, and dried to obtain chlorinated carbon fiber;

[0055] (3) Immerse 10 g of acyl chloride fiber in 120 mL of THF, add 7.7 mL of triethylamine and 6.8 g of thiophene methanol under a nitrogen atmosphere, and stir the reaction at 55 ° C for 4 h. Filter, wash, and dry the product to obtain the intermediate carbon fiber;

[0056] (4) Immerse 10 g of the intermediate carbon fiber in 200 mL of acetonitrile, add 12 mL of thiophene under a nitrogen atmosphere, stir and disperse, slowly add 18 g of anhydrous ferric chloride in batches, vigorously stir and react in an ice bath at 3 ° C for 18 h, centrifuge, wash, and dry the product to obtain modified carbon fiber;

[0057] (5) 1000 g of polypyrrole and 350 g of epoxy resin were dissolved in 4000 mL of DMF, and then 250 g of mixed powder, 170 g of conductive carbon black, and 260 g of modified carbon fiber were added. The mixture was ultrasonically shaken at 15 MHz and 30° C. for 75 min, and the solvent was evaporated to remove the solvent. The solid material was crushed into 0.25 mm pieces and hot pressed in a mold at 180° C. and 18 MPa for 15 min to obtain the PTC composite material.

[0058] Example 3

[0059] A method for preparing a PTC composite material comprises the following steps:

[0060] (1) 15 g of barium titanate, 4 g of lead titanate, 4 g of niobium oxide, 4 g of ruthenium oxide, and 6 g of tantalum pentoxide were dispersed in 250 mL of a 90 wt% aqueous ethanol solution, and then 5 mL of KH550 was added. The mixture was stirred and mixed at 65° C. for 6 h. The product was filtered, washed, and dried to obtain a mixed powder.

[0061] (2) 10 g of carbon fiber was immersed in 250 mL of sulfuric acid / nitric acid mixture (98 wt% sulfuric acid, 65 wt% nitric acid, volume ratio 3:1), mechanically stirred, the product was filtered, washed to neutrality, and dried, and added to 200 mL of dichloromethane. 0.6 mL of DMF and 5 mL of oxalyl chloride were added under a nitrogen atmosphere, and the reaction was stirred at 25 ° C for 6 h. The product was filtered, washed, and dried to obtain chlorinated carbon fiber;

[0062] (3) Immerse 10 g of acyl chloride fiber in 120 mL of THF, add 5.4 mL of triethylamine and 4.7 g of thiophene methanol under a nitrogen atmosphere, and stir at 50 ° C for 4 h. Filter, wash, and dry the product to obtain an intermediate carbon fiber;

[0063] (4) Immerse 10 g of the intermediate carbon fiber in 200 mL of acetonitrile, add 12 mL of thiophene under a nitrogen atmosphere, stir and disperse, slowly add 14 g of anhydrous ferric chloride in batches, vigorously stir and react in an ice bath at 3 ° C for 12 h, centrifuge, wash, and dry the product to obtain modified carbon fiber;

[0064] (5) 1000 g of polypyrrole and 300 g of epoxy resin were dissolved in 4000 mL of DMF, and then 200 g of the mixed powder, 140 g of conductive carbon black, and 240 g of modified carbon fiber were added. The mixture was ultrasonically vibrated at 15 MHz and 30° C. for 75 min, and the solvent was evaporated to remove the solvent. The solid material was crushed into 0.25 mm and hot pressed in a mold at 180° C. and 18 MPa for 15 min to obtain the PTC composite material.

[0065] Example 4

[0066] A method for preparing a PTC composite material comprises the following steps:

[0067] (1) 10 g of barium titanate, 2 g of lead titanate, 3 g of niobium oxide, 3 g of ruthenium oxide, and 4 g of tantalum pentoxide were dispersed in 250 mL of a 90 wt% ethanol aqueous solution, and then 3 mL of KH550 was added. The mixture was stirred and mixed at 60° C. for 8 h. The product was filtered, washed, and dried to obtain a mixed powder.

[0068] (2) 10 g of carbon fiber was immersed in 250 mL of sulfuric acid / nitric acid mixture (98 wt% sulfuric acid, 65 wt% nitric acid, volume ratio 3:1), mechanically stirred, the product was filtered, washed to neutrality, and dried, and added to 200 mL of dichloromethane. 0.6 mL of DMF and 3 mL of oxalyl chloride were added under a nitrogen atmosphere, and the reaction was stirred at 20 ° C for 10 h. The product was filtered, washed, and dried to obtain chlorinated carbon fiber;

[0069] (3) Immerse 10 g of acyl chloride fiber in 120 mL of THF, add 2.8 mL of triethylamine and 2.3 g of thiophene methanol under a nitrogen atmosphere, and stir the reaction at 45 ° C for 8 h. Filter, wash, and dry the product to obtain the intermediate carbon fiber;

[0070] (4) Immerse 10 g of the intermediate carbon fiber in 200 mL of acetonitrile, add 8 mL of thiophene under a nitrogen atmosphere, stir and disperse, slowly add 10 g of anhydrous ferric chloride in batches, vigorously stir and react in an ice bath at 3 ° C for 24 h, centrifuge, wash, and dry the product to obtain modified carbon fiber;

[0071] (5) 1000 g of polypyrrole and 250 g of epoxy resin were dissolved in 3000 mL of DMF, and then 150 g of the mixed powder, 100 g of conductive carbon black, and 200 g of modified carbon fiber were added. The mixture was ultrasonically shaken at 15 MHz and 30° C. for 75 min, and the solvent was evaporated to remove the solvent. The solid material was crushed into 0.25 mm and hot pressed in a mold at 180° C. and 18 MPa for 15 min to obtain the PTC composite material.

[0072] Comparative Example 1

[0073] A method for preparing a PTC composite material comprises the following steps:

[0074] (1) 25 g of barium titanate, 8 g of lead titanate, 6 g of niobium oxide, 6 g of ruthenium oxide, and 10 g of tantalum pentoxide were dispersed in 250 mL of 90 wt% ethanol aqueous solution, and then 9 mL of KH550 was added. The mixture was stirred and mixed at 75° C. for 5 h. The product was filtered, washed, and dried to obtain a mixed powder;

[0075] (2) 10 g of carbon fiber was immersed in 250 mL of sulfuric acid / nitric acid mixture (98 wt% sulfuric acid, 65 wt% nitric acid, volume ratio 3:1), mechanically stirred, and the product was filtered, washed to neutrality, and dried to obtain pretreated carbon fiber;

[0076] (3) Immerse 10 g of pretreated carbon fiber in 200 mL of acetonitrile, add 16 mL of thiophene under a nitrogen atmosphere, stir and disperse, slowly add 20 g of anhydrous ferric chloride in batches, vigorously stir and react in an ice bath at 3 ° C for 24 h, centrifuge, wash, and dry the product to obtain modified carbon fiber;

[0077] (4) 1000 g of polypyrrole and 400 g of epoxy resin were dissolved in 5000 mL of DMF, and then 300 g of mixed powder, 200 g of conductive carbon black, and 300 g of modified carbon fiber were added. The mixture was ultrasonically shaken at 15 MHz and 30° C. for 75 min, and the solvent was evaporated to remove the solvent. The solid material was crushed into 0.25 mm and hot pressed in a mold at 180° C. and 18 MPa for 15 min to obtain the PTC composite material.

[0078] Comparative Example 2

[0079] A method for preparing a PTC composite material comprises the following steps:

[0080] (1) 25 g of barium titanate, 8 g of lead titanate, 6 g of niobium oxide, 6 g of ruthenium oxide, and 10 g of tantalum pentoxide were dispersed in 250 mL of 90 wt% ethanol aqueous solution, and then 9 mL of KH550 was added. The mixture was stirred and mixed at 75° C. for 5 h. The product was filtered, washed, and dried to obtain a mixed powder;

[0081] (2) 10 g of carbon fiber was immersed in 250 mL of sulfuric acid / nitric acid mixture (98 wt% sulfuric acid, 65 wt% nitric acid, volume ratio 3:1), mechanically stirred, and the product was filtered, washed to neutrality, and dried to obtain pretreated carbon fiber;

[0082] (3) 1000 g of polypyrrole and 400 g of epoxy resin were dissolved in 5000 mL of DMF, and then 300 g of mixed powder, 200 g of conductive carbon black, and 300 g of pretreated carbon fiber were added. The mixture was ultrasonically shaken at 15 MHz and 30° C. for 75 min, and the solvent was evaporated to remove the solvent. The solid material was crushed into 0.25 mm and hot pressed in a mold at 180° C. and 18 MPa for 15 min to obtain the PTC composite material.

[0083] Examples 1 to 4 and Comparative Examples 1 to 2 were grouped, and 5 test specimens were taken from each group. The tensile strength and elongation at break of the specimens were tested using a universal testing machine with reference to ASTM D638 "Standard Test Method for Tensile Properties of Plastics" at a tensile speed of 20 mm / min. The results were averaged. Specific data are shown in Table 1.

[0084] Table 1 Mechanical properties test results of PTC composite materials

[0085] Tensile strength (MPa) Elongation at break (%) Example 1 58.4 153 Example 2 57.6 147 Example 3 57.3 145 Example 4 56.1 141 Comparative Example 1 51.4 132 Comparative Example 2 39.8 103

[0086] The composite materials of Examples 1 to 4 and Comparative Examples 1 to 2 were made into thin sheets with a thickness of 1.5 mm, and conductive silver paste was coated on both ends of the thin sheet samples and placed in an oven for polarization to obtain samples. The sample thin sheet was sandwiched between the upper and lower layers of copper electrodes, and the copper electrodes were connected to a digital multimeter through wires. The sample thin sheet was then placed in an oven and subjected to a heating and cooling cycle operation. The sample was heated to 150°C at a rate of 5°C / min, and then air-cooled to 20°C. This cycle was repeated 3 times in total, and the PTC strength (logarithm of the ratio of maximum resistivity to room temperature resistivity) of the sample was tested each time it was cooled to 20°C. The change in PTC strength after high-temperature treatment of the material can reflect the stability of the material. The smaller the change, the higher the stability of the material. See Table 2 for specific data. Figure 1 .

[0087] Table 2 PTC material electrical performance test results

[0088] Initial PTC strength First cycle Second cycle The third cycle Example 1 <![CDATA[1.73×10 5 ]]> <![CDATA[1.69×10 5 ]]> <![CDATA[1.65×10 5 ]]> <![CDATA[1.52×10 5 ]]> Example 2 <![CDATA[8.56×10 4 ]]> <![CDATA[8.50×10 4 ]]> <![CDATA[8.45×10 4 ]]> <![CDATA[8.31×10 4 ]]> Example 3 <![CDATA[7.83×10 4 ]]> <![CDATA[7.75×10 4 ]]> <![CDATA[7.69×10 4 ]]> <![CDATA[7.56×10 4 ]]> Example 4 <![CDATA[4.29×10 4 ]]> <![CDATA[4.22×10 4 ]]> <![CDATA[4.17×10 4 ]]> <![CDATA[4.03×10 4 ]]> Comparative Example 1 <![CDATA[2.35×10 4 ]]> <![CDATA[2.22×10 4 ]]> <![CDATA[2.11×10 4 ]]> <![CDATA[2.93×10 4 ]]> Comparative Example 2 <![CDATA[6.73×10 3 ]]> <![CDATA[6.51×10 3 ]]> <![CDATA[6.33×10 3 ]]> <![CDATA[6.05×10 3 ]]>

[0089] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing a PTC composite material, characterized in that: The steps include: (1) dispersing barium titanate, lead titanate, niobium oxide, ruthenium oxide, and tantalum pentoxide into an ethanol aqueous solution, then adding KH550, stirring and mixing, filtering, washing, and drying the product to obtain a mixed powder; (2) Dissolving polypyrrole and epoxy resin in DMF, then adding mixed powder, conductive carbon black, and modified carbon fiber, ultrasonically dispersing, evaporating and removing the solvent, crushing the solid material, and hot-pressing in a mold to obtain the PTC composite material.

2. The preparation method according to claim 1, characterized in that In step (2), the modified carbon fiber is prepared by the following method steps: a. Immerse the carbon fiber in a sulfuric acid / nitric acid mixture, mechanically stir, filter the product, wash it until neutral, and dry it, add it to dichloromethane, add DMF and oxalyl chloride under a nitrogen atmosphere, stir to react, filter the product, wash it, and dry it to obtain chlorinated carbon fiber; b. Immerse the chlorinated fiber in THF, add triethylamine and thiophene methanol under a nitrogen atmosphere, stir to react, filter, wash, and dry the product to obtain an intermediate carbon fiber; c. Immerse the intermediate carbon fiber in acetonitrile, add thiophene under a nitrogen atmosphere, stir and disperse, slowly add anhydrous ferric chloride in batches, vigorously stir and react in an ice bath, centrifuge, wash, and dry the product to obtain modified carbon fiber.

3. The preparation method according to claim 1, characterized in that In step (1), the ratio of barium titanate, lead titanate, niobium oxide, ruthenium oxide, tantalum pentoxide, ethanol aqueous solution, and KH550 is 10-25 g: 2-8 g: 3-6 g: 3-6 g: 4-10 g: 200-300 mL: 3-9 mL; the concentration of the ethanol aqueous solution is 85-95 wt%; and the stirring and mixing conditions are stirring and mixing at 60-75° C. for 5-8 hours.

4. The preparation method according to claim 1, characterized in that In step (2), the amount ratio of polypyrrole, epoxy resin, DMF, mixed powder, conductive carbon black, and modified carbon fiber is 100g: 25-40g: 300-500mL: 15-30g: 10-20g, 20-30g; the ultrasonic dispersion conditions are oscillation at a frequency of 10-20MHz and a temperature of 20-40°C for 60-90min; the solid material is crushed into 0.05-0.5mm; and the hot pressing molding conditions are hot pressing at 140-200°C and 15-24MPa for 10-20min.

5. The preparation method according to claim 2, characterized in that In step a, the sulfuric acid concentration in the sulfuric acid / nitric acid mixed acid is 95-98wt%, the nitric acid concentration is 65-70wt%, and the volume ratio of sulfuric acid to nitric acid is 3:1; the amount ratio of carbon fiber, sulfuric acid / nitric acid mixed acid, dichloromethane, DMF, and oxalyl chloride is 10g:200-300mL:150-250mL:0.2-1mL:3-8mL; and the stirring reaction conditions are stirring and reacting at 20-35°C for 4-10h.

6. The preparation method according to claim 2, characterized in that In step b, the usage ratio of acyl chloride fiber, THF, triethylamine, and thiophene methanol is 10 g: 100-150 mL: 2.8-10.2 mL: 2.3-9.1 g; and the stirring reaction conditions are 45-60° C. and 2-8 h.

7. The preparation method according to claim 2, characterized in that In step c, the ratio of the intermediate carbon fiber, acetonitrile, thiophene, and anhydrous ferric chloride is 10 g: 150-300 mL: 8-16 mL: 10-20 g; the ice bath is 0-10° C., and the stirring reaction time is 6-24 h.

8. The preparation method according to claim 2, characterized in that In step a, the carbon fiber has a diameter of 2 to 10 μm and a length of 0.05 to 2 mm.

9. A PTC composite material prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the PTC composite material according to claim 9 in overcurrent, overvoltage and overheat protection devices.

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