Epoxy resin-based NTC composite material containing ionic liquid and carbon black as well as preparation method and application of epoxy resin-based NTC composite material

Abstract

The invention discloses an epoxy resin-based NTC (Negative Temperature Coefficient) composite material containing ionic liquid and carbon black as well as a preparation method and application of the epoxy resin-based NTC composite material. The preparation method of the material comprises the following steps: mixing the ionic liquid and the epoxy curing agent, heating on a heating table, stirring and mixing at the same time, then adding the epoxy resin, the carbon black, the surfactant and the solvent, mechanically stirring and uniformly mixing, and heating in a vacuum oven to remove the solvent to obtain the material. And then carrying out hot pressing for a certain time through a press vulcanizer at a certain temperature to obtain the epoxy resin-based NTC composite material containing the ionic liquid and the carbon black. The epoxy resin-based NTC composite material containing the ionic liquid and the carbon black has the advantages of high B value, good mechanical strength, high heat conductivity coefficient, high crosslinking density and the like, and the preparation method is simple to operate, mild in reaction condition, low in raw material cost and suitable for large-scale industrial production and application.

Description

Technical Field

[0001] The present invention relates to the field of NTC thermosensitive materials, and particularly to an epoxy resin-based NTC composite containing ionic liquid and carbon black, and a preparation method and application thereof. Background Art

[0002] Negative temperature coefficient (NTC) materials are a class of functional materials with special resistance-temperature response characteristics. Their resistivity shows an exponential decrease trend with the increase of temperature, and they are widely used in fields such as temperature sensing, temperature control, overload protection, and voltage stabilization and amplitude limiting of electronic circuits. Traditional NTC materials are mostly semiconductor ceramics with transition metal oxides (such as manganese, nickel, cobalt, copper, etc.) as the main components, and are prepared by high-temperature sintering methods. With the development of miniaturization and multifunctionalization of electronic devices, as well as the continuous improvement of material performance requirements, traditional ceramic NTC materials gradually expose disadvantages such as large brittleness, poor toughness, difficult processing, and difficulty in realizing complex-shaped devices, and are difficult to meet the development needs of new-generation electronic components. Therefore, epoxy resin-based NTC composites with good flexibility, easy processability, and high performance are a good alternative.

[0003] The literature (Zhang Bangwen, Li Baowei, NTC effect and its regulation of nano-carbon-coated nickel / epoxy resin composites, Acta Materiae Compositae Sinica. Vol. 25, No. 5, October, 2008) reported that a nano-carbon-coated nickel (Ni-C) / epoxy resin (EP) composite with a negative temperature coefficient (NTC) effect was prepared by a magnetic field-assisted curing process. This process was used to control the arrangement of nanoparticles in the resin matrix. Without magnetic field curing, the nanoparticles were uniformly distributed; after applying a magnetic field, the nanoparticles were linearly arranged along the magnetic field direction, forming a fibrous structure. The greater the magnetic field strength, the thicker the fibrous structure, thereby reducing the resistivity of the composite material. The composite material exhibited a negative temperature coefficient effect (NTC), that is, as the temperature increased, the resistivity of the material decreased. This effect could be controlled by adjusting the filler content and magnetic field strength. However, its disadvantages are as follows: (1) Magnetic field dependence: The arrangement of nanoparticles highly depends on the applied magnetic field strength. Although this method can control the material performance, if large-scale production is required, uniform magnetic field application may become a problem, limiting the application scope of this process. (2) Material uniformity problem: In the absence of a magnetic field, the nanoparticles may agglomerate, affecting the uniformity of the composite material and thus its electrical properties. (3) Process complexity: The magnetic field-assisted curing process complicates the material preparation process, may lead to an increase in production costs, and has higher operation requirements compared with conventional composite material preparation processes.

[0004] In recent years, as a new type of conductive medium, ionic liquids have received extensive attention due to their low vapor pressure, high conductivity, wide temperature adaptability, and excellent thermal stability. The uniqueness of the chemical structure of ionic liquids shows great potential in regulating the electrical conductivity, thermal conductivity, and mechanical properties of composite materials, making them ideal fillers for preparing NTC materials.

[0005] Therefore, it is of great significance to develop an epoxy-based NTC composite material with high B value, high mechanical strength, and good thermal conductivity. Summary of the Invention

[0006] In order to overcome the problems of insufficient electrical conductivity, low thermal conductivity efficiency, and limited mechanical properties of existing NTC composite materials, the purpose of the present invention is to provide an epoxy-based NTC composite material containing ionic liquid and carbon black with excellent electrical conductivity, NTC performance, thermal conductivity, and mechanical properties, as well as its preparation method and application.

[0007] In the present invention, by introducing ionic liquid and surfactant into the epoxy resin matrix, a tight interfacial double electric layer is formed through the π-π interaction between carbon black and ionic liquid, promoting the uniform dispersion of carbon black in the matrix and the formation of a three-dimensional cross-linked network structure, effectively reducing the conductive percolation threshold of the composite material, and improving the interfacial charge migration ability and conductive stability of the material. At the same time, carbon black forms a continuous thermal conduction path through the interfacial effect, significantly enhancing the thermal conductivity of the composite material and reducing the interfacial thermal resistance; in addition, carbon black can also enhance the cross-linking density of the material and the compatibility between the filler and the resin matrix, improving the tensile strength and overall structural stability of the composite material, avoiding the performance degradation caused by the aggregation of high-content carbon black, and further realizing the synergistic improvement of the electrical conductivity, NTC performance, thermal conductivity, mechanical properties, and structural stability of the material.

[0008] The purpose of the present invention is specifically achieved through the following technical solutions.

[0009] A preparation method of an epoxy-based NTC composite material containing ionic liquid and carbon black, comprising the following steps:

[0010] Mix the ionic liquid and the epoxy curing agent, place them on a heating table and heat up while stirring and mixing, then add epoxy resin, carbon black, surfactant, and solvent. After mechanically stirring and mixing evenly, place it in a vacuum oven for heat treatment to remove the solvent, and then hot press it on a flat vulcanizer at a certain temperature for a certain time to obtain an epoxy-based NTC composite material containing ionic liquid and carbon black.

[0011] Preferably, the mass ratio of the epoxy resin to the curing agent is 1:0.5 - 1.50.

[0012] More preferably, the mass ratio of the epoxy resin to the curing agent is 1:1.

[0013] Preferably, the mass ratio of the epoxy resin to the ionic liquid is 1:0.69 - 0.80.

[0014] More preferably, the mass ratio of the epoxy resin to the ionic liquid is 1:0.74.

[0015] Preferably, the mass ratio of the epoxy resin to the carbon black is 1:0.02 - 0.39.

[0016] More preferably, the mass ratio of the epoxy resin to the carbon black is 1:0.18.

[0017] Preferably, the mass ratio of the epoxy resin to the surfactant is 1:0.01 - 0.08.

[0018] More preferably, the mass ratio of the epoxy resin to the surfactant is 1:0.03.

[0019] Preferably, the epoxy resin is at least one of epoxy resin E-51, epoxy resin E-44, bisphenol A diglycidyl ether, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, and tetrabromobisphenol A diglycidyl ether.

[0020] More preferably, the epoxy resin is epoxy resin E-51.

[0021] Preferably, the curing agent is at least one of diethylenetriamine, polyamide curing agent (650), polyamide curing agent (651), phthalic anhydride, 1,2-hexanedithiol, and 2-methylimidazole.

[0022] More preferably, the curing agent is polyamide curing agent (650).

[0023] Preferably, the ionic liquid is at least one of 1-butyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium hexafluorophosphate, and 1-octyl-3-methylimidazolium chloride.

[0024] More preferably, the ionic liquid is 1-butyl-3-methylimidazolium chloride.

[0025] Preferably, the carbon black is at least one of Super-P nano carbon black, N110 nano carbon black, N330 nano carbon black, acetylene carbon black, and Ketjen black.

[0026] More preferably, the carbon black is Super-P nano carbon black.

[0027] Preferably, the surfactant is at least one of sodium nonylphenol polyoxyethylene ether (10) sulfate, polyethylene glycol octyl phenyl ether, polyoxyethylene sorbitan fatty acid ester, and polyoxyethylene polyoxypropylene ether.

[0028] More preferably, the surfactant is sodium nonylphenol polyoxyethylene ether (10) sulfate.

[0029] Preferably, the solvent is at least one of ethanol, diethyl ether, acetone, dichloromethane, n-hexane, and petroleum ether.

[0030] More preferably, the solvent is acetone.

[0031] Preferably, the temperature of the heating stage is 50 - 150 °C.

[0032] More preferably, the temperature of the heating stage is 80 °C.

[0033] Preferably, the temperature for heating in the vacuum oven is 40 - 140 °C, and the heating time is 0.5 - 3 h.

[0034] More preferably, the temperature for heating in the vacuum oven is 60 °C, and the heating time is 1 h.

[0035] Preferably, the temperature for hot pressing by the flat vulcanizer is 65 - 140 °C, and the hot pressing time is 1 - 6 h.

[0036] More preferably, the temperature for hot pressing by the flat vulcanizer is 80 °C, and the hot pressing time is 4 h.

[0037] An epoxy resin-based NTC composite containing ionic liquid and carbon black prepared by the above-described preparation method has a composite structure in which uniformly dispersed fillers are contained in the epoxy matrix.

[0038] The application of the above-described epoxy resin-based NTC composite containing ionic liquid and carbon black. Due to its excellent NTC, thermal conductivity, and tensile properties, this NTC composite has good application prospects in temperature sensors, temperature control circuits, overheat protection devices, electric vehicle battery management systems, smart home temperature control systems, and overload protection of electrical components.

[0039] In the present invention, an ionic liquid containing an imidazole structure is introduced into the epoxy resin-based NTC composite material system, which not only significantly optimizes the conductive network structure but also is expected to effectively improve the dispersion of the second filler, carbon black, thereby improving the NTC performance of the composite material. In addition, the epoxy resin-based NTC composite containing ionic liquid has better flexibility and processability, is easy to realize the manufacture of devices with complex structures, and is expected to overcome the disadvantages of large brittleness and difficult processing of traditional ceramic NTC materials.

[0040] Compared with the prior art, the present invention has the following advantages and technical effects:

[0041] (1) The present invention introduces an ionic liquid into the system. Due to the characteristic that the resistance of the ionic liquid decreases with increasing temperature, the resistivity of the composite material decreases significantly when the temperature rises, showing excellent NTC characteristics.

[0042] (2) The present invention introduces carbon black into the system to form a stable conductive network inside the composite material, and constructs an electric double layer structure through the significant interfacial interaction between the carbon black and the ionic liquid, enhancing the charge migration ability and improving the NTC performance.

[0043] (3) The present invention promotes the uniform dispersion of carbon black inside the material through the ionic liquid and the surfactant, forming a stable, continuous and efficient three-dimensional network structure, improving the crosslinking density, enhancing the tensile strength of the composite material, promoting the rapid and stable conduction and diffusion of heat, increasing the thermal conductivity, and shortening the thermal response time of the material.

[0044] (4) The preparation method of the epoxy resin-based NTC composite material containing ionic liquid and carbon black of the present invention has stable process, and the material formula is easy to obtain, which is suitable for large-scale industrial production and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is the resistivity-temperature and NTC curve graph of the epoxy resin-based NTC composite material containing ionic liquid and carbon black in Example 3.

[0046] Figure 2 It is the tensile strength curve graph of the epoxy resin-based NTC composite material containing ionic liquid and carbon black in Examples 1-6 and the epoxy resin-based NTC composite material containing ionic liquid in the comparative example.

[0047] Figure 3 It is the thermal conductivity curve graph of the epoxy resin-based NTC composite material containing ionic liquid and carbon black in Examples 1-6 and the epoxy resin-based NTC composite material containing ionic liquid in the comparative example.

[0048] Figure 4 It is the storage modulus curve graph of the epoxy resin-based NTC composite material containing ionic liquid and carbon black in Examples 1, 3, 6 and the epoxy resin-based NTC composite material containing ionic liquid in the comparative example.

[0049] Figure 5 It is the scanning electron microscope image of the epoxy resin-based NTC composite material containing ionic liquid and carbon black in Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0050] The following further specifically describes the specific implementation of the present invention in combination with examples and drawings, but the implementation manners of the present invention are not limited thereto. It should be noted that for the processes not specifically described in detail below, those skilled in the art can implement or understand them with reference to the prior art. The reagents or instruments not indicating the manufacturer are regarded as conventional products that can be obtained through commercial purchase.

[0051] Example 1:

[0052] Preparation of an epoxy resin-based NTC composite containing an ionic liquid and carbon black: Mix 12.5 g of 1-butyl-3-methylimidazolium chloride with 18 g of polyamide curing agent (650), place it on an 80°C heating table and heat for 10 min while stirring evenly. Then add 18 g of epoxy resin E-51, 1 g of Super-P nano carbon black, 0.5 g of sodium nonylphenol polyoxyethylene ether (10) sulfate, and 15 mL of acetone, stir evenly. Then transfer the obtained mixture to a PP tray, vacuum process it at 60°C in a vacuum oven for 1 h to remove acetone and pre-polymerize. Then transfer the prepolymer to a standard mold and hot press and cure it at 80°C in a flat vulcanizer for 4 h to obtain an epoxy resin-based NTC composite containing an ionic liquid and carbon black (denoted as CB2).

[0053] Example 2:

[0054] Preparation of an epoxy resin-based NTC composite containing an ionic liquid and carbon black: Mix 12.5 g of 1-butyl-3-methylimidazolium chloride with 17.5 g of polyamide curing agent (650), place it on an 80°C heating table and heat for 10 min while stirring evenly. Then add 17.5 g of epoxy resin E-51, 2 g of Super-P nano carbon black, 0.5 g of sodium nonylphenol polyoxyethylene ether (10) sulfate, and 15 mL of acetone, stir evenly. Then transfer the obtained mixture to a PP tray, vacuum process it at 60°C in a vacuum oven for 1 h to remove acetone and pre-polymerize. Then transfer the prepolymer to a standard mold and hot press and cure it at 80°C in a flat vulcanizer for 4 h to obtain an epoxy resin-based NTC composite containing an ionic liquid and carbon black (denoted as CB4).

[0055] Example 3:

[0056] Preparation of an epoxy-based NTC composite containing ionic liquid and carbon black: 12.5 g of 1-butyl-3-methylimidazolium chloride was mixed with 17 g of polyamide curing agent (650) and placed on an 80 °C heating stage for 10 min while stirring evenly. Then, 17 g of epoxy resin E-51, 3 g of Super-P nano carbon black, 0.5 g of sodium nonylphenol polyoxyethylene ether (10) sulfate, and 15 mL of acetone were added and stirred evenly. Next, the obtained mixture was transferred to a PP tray and vacuum-treated at 60 °C for 1 h in a vacuum oven to remove acetone and pre-polymerize. Then, the prepolymer was transferred to a standard mold and hot-pressed and cured at 80 °C for 4 h in a flat vulcanizer to obtain an epoxy-based NTC composite containing ionic liquid and carbon black (denoted as CB6).

[0057] Example 4:

[0058] Preparation of an epoxy-based NTC composite containing ionic liquid and carbon black: 12.5 g of 1-butyl-3-methylimidazolium chloride was mixed with 16.5 g of polyamide curing agent (650) and placed on an 80 °C heating stage for 10 min while stirring evenly. Then, 16.5 g of epoxy resin E-51, 4 g of Super-P nano carbon black, 0.5 g of sodium nonylphenol polyoxyethylene ether (10) sulfate, and 15 mL of acetone were added and stirred evenly. Next, the obtained mixture was transferred to a PP tray and vacuum-treated at 60 °C for 1 h in a vacuum oven to remove acetone and pre-polymerize. Then, the prepolymer was transferred to a standard mold and hot-pressed and cured at 80 °C for 4 h in a flat vulcanizer to obtain an epoxy-based NTC composite containing ionic liquid and carbon black (denoted as CB8).

[0059] Example 5:

[0060] Preparation of an epoxy-based NTC composite containing ionic liquid and carbon black: 12.5 g of 1-butyl-3-methylimidazolium chloride was mixed with 16 g of polyamide curing agent (650) and placed on an 80 °C heating stage for 10 min while stirring evenly. Then, 16 g of epoxy resin E-51, 5 g of Super-P nano carbon black, 0.5 g of sodium nonylphenol polyoxyethylene ether (10) sulfate, and 15 mL of acetone were added and stirred evenly. Next, the obtained mixture was transferred to a PP tray and vacuum-treated at 60 °C for 1 h in a vacuum oven to remove acetone and pre-polymerize. Then, the prepolymer was transferred to a standard mold and hot-pressed and cured at 80 °C for 4 h in a flat vulcanizer to obtain an epoxy-based NTC composite containing ionic liquid and carbon black (denoted as CB10).

[0061] Example 6:

[0062] Preparation of an epoxy-based NTC composite containing ionic liquid and carbon black: 12.5 g of 1-butyl-3-methylimidazolium chloride was mixed with 15.5 g of polyamide curing agent (650) and placed on an 80 °C heating table for 10 min while stirring evenly. Then, 15.5 g of epoxy resin E-51, 6 g of Super-P nano carbon black, 0.5 g of sodium nonylphenol polyoxyethylene ether (10) sulfate, and 15 mL of acetone were added and stirred evenly. Next, the obtained mixture was transferred to a PP tray and vacuum-treated at 60 °C for 1 h in a vacuum oven to remove acetone and pre-polymerize. Then, the prepolymer was transferred to a standard mold and hot-pressed and cured at 80 °C for 4 h in a flat vulcanizer to obtain an epoxy-based NTC composite containing ionic liquid and carbon black (denoted as CB12).

[0063] Comparative example:

[0064] Preparation of an epoxy-based NTC composite containing ionic liquid: 12.5 g of 1-butyl-3-methylimidazolium chloride was mixed with 18.5 g of polyamide curing agent (650) and placed on an 80 °C heating table for 10 min while stirring evenly. Then, 18.5 g of epoxy resin E-51, 0.5 g of sodium nonylphenol polyoxyethylene ether (10) sulfate, and 15 mL of acetone were added and stirred evenly. Next, the obtained mixture was transferred to a PP tray and vacuum-treated at 60 °C for 1 h in a vacuum oven to remove acetone and pre-polymerize. Then, the prepolymer was transferred to a standard mold and hot-pressed and cured at 80 °C for 4 h in a flat vulcanizer to obtain an epoxy-based NTC composite containing ionic liquid (denoted as CB0).

[0065] Performance test:

[0066] (1) Temperature-volume resistivity tests were carried out on the epoxy-based NTC composite containing ionic liquid and carbon black in Example 3 (test process: The sample was cut into rectangular strips with a length of 80 mm, a width of 1 mm, and a thickness of 2 mm. Copper foil electrodes with a width of 10 mm were wrapped around both ends of the strip to reduce contact impedance. Wires were connected through a U-shaped metal fixture, and the sample was encapsulated with polyimide insulating tape. Then, resistance tests were carried out using a Fluke digital multimeter Fluke 15B+. The test temperature range was 30 - 130 °C, and the temperature interval was 10 °C). Then, the volume resistivity was calculated through the volume resistivity calculation formula, and the B value was calculated through the B value calculation formula. The resistivity-temperature and NTC curves obtained are as Figure 1 shown.

[0067] The volume resistivity calculation formula is as follows: ρ = Rhw / l, where R is the measured resistance value in Ω; h, w, and l are the thickness, width, and effective conductive length of the sample in cm, respectively.

[0068] The calculation formula for the B value is as follows: B = (lnR1 - lnR2) / (1 / T1 - 1 / T2), where T1 and T2 are two different test temperatures in K; R1 and R2 are the zero-power resistance values at the corresponding temperatures in Ω. The B value calculated from the data of two temperature points is usually denoted as B T1 / T2 For example, when calculating the material constant B value by taking 30°C and 130°C, it is denoted as B 30 / 130 .

[0069] It can be seen from Figure 1 that: the resistivity of the epoxy resin-based NTC composite containing ionic liquid and carbon black in Example 3 is 69.5 kΩ·cm at 30°C and 6.0 kΩ·cm at 130°C. The B 30 / 130 value is 5181 K, showing high temperature sensitivity. The reason is that: the imidazole cation in the ionic liquid has conjugated π electrons and can be adsorbed on the surface of the sp 2 C atoms on the surface of carbon black through π-π interaction to form a tight inner-layer adsorption. At the same time, the anions in the ionic liquid form a diffusion layer outside the cation adsorption layer under electrostatic attraction, constituting a double-layer structure, which improves the local capacitance, charge mobility at the interface and the stability of the conductive network, making the epoxy resin-based NTC composite containing ionic liquid and carbon black have a high B 30 / 130 value and stable cycling performance. As can be seen from Figure 1 the temperature sensitivity of CB6 does not show obvious weakening after three cycles.

[0070] (2) Tensile tests were carried out on the epoxy resin-based NTC composites containing ionic liquid and carbon black in Examples 1 to 5 and the epoxy resin-based NTC composites containing ionic liquid in the comparative examples (test process: the NTC composite samples were sheared into rectangular strips with a length of 80 mm, a width of 1 mm and a thickness of 2 mm, and then tensile tests were carried out using a universal material testing machine Z010 at a tensile rate of 500 mm / min), and the obtained tensile strength curves are as Figure 2 shown.

[0071] It can be seen from Figure 2It can be seen that the tensile strength of the epoxy resin-based NTC composites containing ionic liquid and carbon black in Examples 1 to 5 is above 6 MPa, showing a relatively high level of mechanical properties. And as the content of carbon black increases, the tensile strength of the epoxy resin-based NTC composites containing ionic liquid and carbon black first decreases and then increases. The reason is that an appropriate amount of carbon black is uniformly dispersed in the epoxy resin matrix under the synergistic action of the surfactant and the ionic liquid, forming a stable three-dimensional network structure, showing a higher tensile strength than the epoxy resin-based NTC composites containing ionic liquid in the comparative example. However, excessive carbon black is prone to particle agglomeration, forming stress concentration areas, resulting in a decrease in tensile strength. The tensile strength of the epoxy resin-based NTC composites containing ionic liquid and carbon black in Example 5 is the highest, up to 7.41 MPa, which is more than 1.6 times that of the epoxy resin-based NTC composites containing ionic liquid in the comparative example.

[0072] (3) Conduct thermal conductivity tests on the epoxy resin-based NTC composites containing ionic liquid and carbon black in Examples 1 to 5 and the epoxy resin-based NTC composites containing ionic liquid in the comparative example (test process: measure the density of the material with a density balance, measure the thermal diffusivity of the material with a flash method thermal conductivity meter, and measure the specific heat capacity of the material with a differential scanning calorimeter). Then calculate the thermal conductivity through the thermal conductivity calculation formula, and the changes in the thermal conductivity of the obtained samples are as Figure 3 shown.

[0073] Thermal conductivity calculation formula: λ = ρ·α·C p , where ρ is the density, with the unit of g / cm 3 ; α is the thermal diffusivity, with the unit of mm 2 / s; C ρ is the specific heat capacity, with the unit of J / g·K.

[0074] From Figure 3It can be known that the thermal conductivity coefficients of the epoxy resin-based NTC composites containing ionic liquid and carbon black in Examples 1 to 5 are all above 0.18 W / m·K, and with the increase of the carbon black content, the thermal conductivity coefficients of the epoxy resin-based NTC composites containing ionic liquid and carbon black show a gradually increasing trend. The reason is that carbon black itself has high thermal conductivity. As a thermal conductive filler in the epoxy resin matrix, through the synergistic effect with ionic liquid and surfactant, it significantly improves the interfacial compatibility between the filler and the resin matrix, promotes the uniform dispersion of carbon black particles in the matrix, and forms effective local thermal conduction micro-channels, effectively reducing the interfacial thermal resistance. In addition, when the carbon black content reaches a certain level, continuous thermal conduction networks can be formed between the fillers, further enhancing the heat conduction and diffusion capabilities. The epoxy resin-based NTC composite containing ionic liquid and carbon black in Example 6 has the highest thermal conductivity coefficient, up to 0.239 W / m·K, which is more than 1.3 times that of the epoxy resin-based NTC composite containing ionic liquid in the comparative example.

[0075] (4) Dynamic mechanical tests were carried out on the epoxy resin-based NTC composites containing ionic liquid and carbon black in Examples 1, 3, and 6 and the epoxy resin-based NTC composites containing ionic liquid in the comparative example. Using a dynamic thermomechanical analyzer from TA Company in the United States, in the tensile mode, the test was set with a constant frequency of 1 Hz and an oscillation amplitude of 50 μm, and a temperature scan was performed at a heating rate of 5 °C / min in the temperature range of -40 °C to 140 °C. The crosslink density was calculated through the rubber elasticity theory calculation formula, and the storage modulus curve is as Figure 4 shown.

[0076] Crosslink density calculation formula: v e = E r / 3RT, where E r is the storage modulus in the rubber plateau region (glass transition temperature + 50 °C), with the unit of MPa; T is the temperature in the rubber plateau region (glass transition temperature + 50 °C), with the unit of K; R is the universal gas constant, which is 8.314 J / mol·K.

[0077] It can be known from Figure 4 that the crosslink densities of the epoxy resin-based NTC composites containing ionic liquid and carbon black in Examples 1, 3, and 6 are all above 570 mol / m 3 and with the increase of the carbon black content, the crosslink densities of the epoxy resin-based NTC composites containing ionic liquid and carbon black show a gradually increasing trend. The reason is that carbon black particles can effectively fill the free volume and pores in the epoxy resin matrix, and at the same time enhance the physical crosslinking effect between molecular chains and the intermolecular interaction, thus making the crosslinking structure more dense. The epoxy resin-based NTC composite containing ionic liquid and carbon black in Example 6 has the highest crosslink density, reaching 1083 mol / m3 , more than 1.8 times that of the epoxy resin-based NTC composite containing ionic liquid in the comparative example.

[0078] (5) The epoxy resin-based NTC composite containing ionic liquid and carbon black in Example 3 was subjected to scanning electron microscopy test. The cross-section of the composite was characterized by a Quanta 200 environmental scanning electron microscope. The specimen was brittle fractured after being soaked in liquid nitrogen at low temperature for 30 s and placed under a low vacuum mode for observation. The cross-section morphology characteristics and filler dispersion state were analyzed. The obtained scanning electron microscope images are as Figure 5 shown.

[0079] It can be seen from Figure 5 that: the cross-section of the epoxy resin-based NTC composite containing ionic liquid and carbon black in Example 3 is smooth and void-free. The reason is that: carbon black fills the defects and pores inside the matrix, adsorbs ionic liquid through π-π interaction, and jointly promotes the uniform distribution of ionic liquid with the surfactant, inhibits the formation of pores caused by phase separation, and improves the performance of the epoxy resin-based NTC composite containing ionic liquid and carbon black. Generally speaking, the epoxy resin-based NTC composite obtained with a carbon black content of 6 wt% (Example 3) shows the best performance: the resistivity at 30 °C is 69.5 kΩ·cm, the resistivity at 130 °C is 6.0 kΩ·cm, B 30 / 130 is 5181 K, the tensile strength is 8.56 MPa, the thermal conductivity is 0.200 W / m·K, and the crosslinking density is 884.6 mol / m 3 .

[0080] The above embodiments are only the preferred embodiments of the present invention, which are only used to explain the present invention, rather than limiting the present invention. Any changes, substitutions, modifications, etc. made by those skilled in the art without departing from the spirit and essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A preparation method of an epoxy resin-based NTC composite containing ionic liquid and carbon black, characterized in that It includes the following steps: Mix the ionic liquid with the epoxy curing agent, place it on a heating table to heat up and stir simultaneously, then add epoxy resin, carbon black, surfactant and solvent. After mechanically stirring and mixing evenly, place it in a vacuum oven for heat treatment to remove the solvent, and then hot press it with a flat vulcanizer to obtain an epoxy resin-based NTC composite containing ionic liquid and carbon black.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the epoxy resin to the curing agent is 1:0.5 - 1.50; the mass ratio of the epoxy resin to the ionic liquid is 1:0.69 - 0.80; the mass ratio of the epoxy resin to the carbon black is 1:0.02 - 0.39; the mass ratio of the epoxy resin to the surfactant is 1:0.01 - 0.

08.

3. The preparation method according to claim 1, characterized in that, The epoxy resin is at least one of epoxy resin E-51, epoxy resin E-44, bisphenol A diglycidyl ether, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, and tetrabromobisphenol A diglycidyl ether.

4. The preparation method according to claim 1, wherein The curing agent is at least one of diethylenetriamine, polyamide curing agent 650, polyamide curing agent 651, phthalic anhydride, 1,2-hexanedithiol, and 2-methylimidazole.

5. The preparation method according to claim 1, characterized in that, The carbon black is at least one of Super-P nano carbon black, N110 nano carbon black, N330 nano carbon black, acetylene carbon black, and Ketjen black.

6. The preparation method according to claim 1, characterized in that, The ionic liquid is at least one of 1-butyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium hexafluorophosphate, and 1-octyl-3-methylimidazolium chloride.

7. The preparation method according to claim 1, characterized in that, The surfactant is at least one of sodium nonylphenol polyoxyethylene ether (10), polyethylene glycol octyl phenyl ether, polyoxyethylene sorbitan fatty acid ester, and polyoxyethylene polyoxypropylene ether; the solvent is at least one of ethanol, diethyl ether, acetone, dichloromethane, n-hexane, and petroleum ether.

8. The preparation method according to claim 1, characterized in that, The temperature of the heating table is 50 - 150 °C; the temperature of the vacuum oven heating is 40 - 140 °C, and the heating time is 0.5 - 3 h; the temperature of the flat vulcanizer hot press is 65 - 140 °C, and the hot press time is 1 - 6 h.

9. An epoxy resin-based NTC composite containing ionic liquid and carbon black prepared by the preparation method according to any one of claims 1 - 8.

10. Application of the epoxy resin-based NTC composite containing ionic liquid and carbon black according to claim 9 in temperature sensors, temperature control circuits, overheat protection devices, electric vehicle battery management systems, smart home temperature control systems, and overload protection of electrical components.

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