Electric heating carbon nanotube composite coating and preparation method thereof

Abstract

The invention relates to the technical field of coatings, in particular to an electric heating carbon nanotube composite coating and a preparation method thereof. The coating is composed of a water-based acrylic resin emulsion, propylene glycol monomethyl ether, modified carbon nanotubes and an auxiliary agent. The modified carbon nano tube is obtained by firstly aminating a carbon nano tube, then sequentially grafting 2, 3-epoxypropyl trimethyl ammonium chloride and 3-thiophenecarboxylic acid, and further carrying out in-situ polymerization with 3-hexylthiophene and 3-diether thiophene. The obtained composite coating is stable in network structure, high in electron conduction and electro-thermal conversion efficiency, fast in heating response and uniform in temperature distribution, and has excellent adhesive force and cold and heat cycle resistance. According to the invention, the problems of poor dispersibility and conductive stability of the existing conductive coating are effectively overcome, and the electric heating performance and comprehensive application value are remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of coatings, and in particular to an electrically heated carbon nanotube composite coating and a preparation method thereof. Background Art

[0002] Carbon nanotubes, as one-dimensional nanomaterials, possess excellent electrical and thermal conductivity and mechanical strength, showing great potential for application in electric heating coatings. Traditional electric heating coatings primarily utilize metal heating wires, carbon fibers, or conductive carbon black as heating materials, but these materials suffer from uneven heating, high energy consumption, and poor thermal stability. Carbon nanotubes, with their high electrical conductivity, low density, large surface area, and excellent thermal stability, can form a uniformly distributed conductive network, enabling efficient and uniform electrical-to-heat conversion. They are expected to become the core material for a new generation of high-performance electric heating coatings.

[0003] The technical challenges faced by carbon nanotubes in practical applications are particularly prominent in the field of electric heating coatings. The first is the problem of dispersion. Due to the lack of active groups on the surface and the strong van der Waals force, carbon nanotubes are very easy to agglomerate in the polymer matrix, resulting in a discontinuous conductive network. In electric heating applications, uneven dispersion can lead to local resistivity differences, resulting in uneven heating, affecting the heating effect and may cause local overheating or even burning. Secondly, the problem of weak interfacial bonding between carbon nanotubes and the polymer matrix is ​​more prominent under the action of external forces and thermal stress. During repeated thermal expansion and contraction, the tube-substrate interface is prone to peeling, causing damage to the conductive network and performance degradation. Thirdly, the problem of conductive stability is more obvious in a dynamic temperature environment. Carbon nanotubes are prone to rearrangement during the heating process, resulting in resistance drift, which in turn affects the power output and the accuracy of temperature control.

[0004] Furthermore, while traditional carbon nanotube surface modification methods (such as strong acid oxidation) can improve dispersibility, they severely damage the conjugated structure of the carbon nanotubes, leading to a decrease in intrinsic electrical and thermal conductivity. This loss of conductivity significantly reduces energy conversion efficiency in electric heating applications. The key technical challenge in developing high-performance carbon nanotube composite coatings for electric heating is achieving effective surface functionalization while maintaining the excellent intrinsic properties of the carbon nanotubes and constructing a durable and stable conductive network structure.

[0005] Therefore, developing a new technical solution that can simultaneously solve the problems of poor dispersion of carbon nanotubes in electric heating coatings, weak interface bonding, and insufficient conductive stability, and achieve efficient, uniform, and stable heating at low addition amounts has become a technical bottleneck that the industry urgently needs to break through. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide an electrically heated carbon nanotube composite coating and a preparation method thereof, so as to solve the problems of poor dispersion of conductive fillers, weak interface bonding and insufficient conductive stability in existing carbon nanotube conductive coatings.

[0007] Based on the above objectives, the present invention provides an electrically heated carbon nanotube composite coating, which is prepared from the following raw materials, by weight: 60-100 parts of water-based acrylic resin emulsion, 10-30 parts of propylene glycol methyl ether, 6-10 parts of modified carbon nanotubes, 0.5-1 part of leveling agent, 0.3-0.8 part of dispersant and 0.05-0.2 part of defoaming agent.

[0008] Preferably, the aqueous acrylic resin emulsion is obtained by semi-continuous emulsion polymerization using methyl methacrylate, acrylic acid, butyl methacrylate, butyl acrylate and styrene as polymerization monomers; the weight ratio of methyl methacrylate, acrylic acid, butyl methacrylate, butyl acrylate and styrene is 5:15:35:10:35.

[0009] Preferably, the leveling agent is BYK-333.

[0010] Preferably, the dispersant is BYK-190.

[0011] Preferably, the defoaming agent is BYK-024.

[0012] Preferably, the preparation method of the aqueous acrylic resin emulsion is as follows: methyl methacrylate, acrylic acid, butyl methacrylate, butyl acrylate and styrene are mixed to obtain a monomer solution; ammonium persulfate is dissolved in deionized water to obtain an initiator solution; sodium lauryl sulfate is dissolved in deionized water, the monomer solution is added, the temperature is raised to 40-50°C, and the mixture is stirred for 25-35 minutes, the initiator solution is added, the temperature is raised to 85-90°C, and the mixture is stirred for 25-35 minutes, the monomer solution and the initiator solution are added dropwise, and the addition is completed within 0.8-1.2 hours, the reaction is continued with stirring for 3.5-4.5 hours, the temperature is lowered to room temperature, and aqueous ammonia is added dropwise to adjust the pH to 8.2-8.6 to obtain an aqueous acrylic resin emulsion.

[0013] Preferably, the modified carbon nanotubes are obtained by first grafting 2,3-epoxypropyltrimethylammonium chloride onto amination carbon nanotubes and then grafting 3-thiophenecarboxylic acid to obtain thiophene-containing quaternized carbon nanotubes, and then polymerizing 3-hexylthiophene and 3-dietherthiophene with the thiophene groups on the surface of the thiophene-containing quaternized carbon nanotubes; the 2,3-epoxypropyltrimethylammonium chloride and 3-thiophenecarboxylic acid react with the amino groups on the amination carbon nanotubes through the epoxy group and carboxyl group, respectively.

[0014] Preferably, the amino content of the amino-modified carbon nanotubes is greater than 0.4 wt%.

[0015] Preferably, the weight ratio of the amino-modified carbon nanotubes to 2,3-epoxypropyltrimethylammonium chloride is 5-15:0.04-0.2.

[0016] Preferably, the weight ratio of the amino-modified carbon nanotubes to 3-thiophenecarboxylic acid is 5-15:0.4-1.2.

[0017] Preferably, the weight ratio of the thiophene-containing quaternized carbon nanotubes, 3-hexylthiophene and 3-dietherthiophene is 5-15:8-20:2-4.

[0018] Preferably, the preparation method of 3-dietherthiophene is as follows: under a nitrogen atmosphere, 3-thiopheneethanol, 2-chloroethyl methyl ether, potassium hydroxide and methyltri-n-octylammonium chloride are mixed, the temperature is raised to 180° C., the reaction is stirred for 48 hours, and purification is performed to obtain 3-dietherthiophene.

[0019] Preferably, the specific preparation steps of the modified carbon nanotubes are as follows:

[0020] (1) adding the aminated carbon nanotubes to deionized water, sonicating for 20-40 min, then adding 2,3-epoxypropyltrimethylammonium chloride, heating to 75-85° C., stirring for 3-5 h, centrifuging, washing with ethanol, and vacuum drying to obtain quaternized carbon nanotubes;

[0021] (2) adding quaternized carbon nanotubes to N,N-dimethylformamide, ultrasonicating for 20-40 min, then adding N,N'-dicyclohexylcarbodiimide and 3-thiophenecarboxylic acid, heating to 115-125 ° C, stirring and reacting for 10-15 h, centrifuging, washing with ethanol, and vacuum drying to obtain quaternized carbon nanotubes containing thiophene;

[0022] (3) Under a nitrogen atmosphere, quaternized carbon nanotubes containing thiophene and ferric chloride are added to chloroform and ultrasonicated for 20-40 minutes to obtain a quaternized carbon nanotube dispersion containing thiophene. 3-Hexylthiophene and 3-dietherthiophene are then added to the chloroform and stirred for 20-40 minutes to obtain a thiophene monomer solution. The thiophene monomer solution is added dropwise to the quaternized carbon nanotube dispersion containing thiophene, and the reaction is stirred for 24-36 hours. The mixture is centrifuged, washed with methanol, and vacuum dried to obtain modified carbon nanotubes.

[0023] Furthermore, the present invention also provides a method for preparing an electrically heated carbon nanotube composite coating, comprising the following steps: mixing an aqueous acrylic resin emulsion and propylene glycol methyl ether, heating the mixture to 38-42° C., stirring the mixture for 20-40 minutes, adding modified carbon nanotubes, stirring the mixture at a speed of 5000-10000 rpm for 40-50 minutes, adding a leveling agent BYK-333, a dispersant BYK-190, and a defoaming agent BYK-024, stirring the mixture at a speed of 400-600 rpm for 8-12 minutes, and obtaining the electrically heated carbon nanotube composite coating.

[0024] Beneficial effects of the present invention:

[0025] The electrically heated carbon nanotube composite coating provided by this invention exhibits numerous significant benefits. First, through the synergistic chemical modification of carbon nanotubes with quaternization and thiophene groups, a variety of functional groups are introduced onto the nanotube surface, significantly enhancing their dispersion stability and interfacial bonding within the polymer matrix. This grafting method promotes the construction of a continuous and stable conductive network within the composite system, achieving more efficient electron conduction channels and significantly optimizing the material's overall electrical conductivity and electrothermal response efficiency.

[0026] Secondly, the unique molecular design effectively promotes the synergistic effect between the polymer chain and the nanofiller. Multiple thiophene monomers form a regular composite conductive layer on the surface of the carbon nanotubes through in-situ chemical polymerization. This not only improves carrier mobility and enhances the current uniformity and thermal conductivity of the composite system, but also ensures faster heating and more uniform temperature distribution of the final coating, contributing to the safety and reliability of practical applications.

[0027] Furthermore, surface functionalization and in-situ polymerization impart stronger mechanical anchoring capabilities to the carbon nanotubes, effectively improving the adhesion between the coating and the substrate. Even under harsh conditions such as multiple thermal cycles, the coating's structural integrity and bonding properties are well maintained, ensuring its long-term stability and durability.

[0028] In summary, the composite coating of the present invention has achieved significant comprehensive technological progress in conductivity, adhesion, thermal stability, and electrothermal conversion, providing a new solution for the development and industrialization of high-performance electric heating coating materials. DETAILED DESCRIPTION

[0029] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to specific embodiments.

[0030] In a specific embodiment of the present invention, the amino-modified carbon nanotubes were purchased from Delta Biotechnology, and the amino content was 0.45 wt%.

[0031] Preparation Example 1:

[0032] Mix 5g of methyl methacrylate, 15g of acrylic acid, 35g of butyl methacrylate, 10g of butyl acrylate and 35g of styrene to obtain a monomer solution; dissolve 0.5g of ammonium persulfate in 20g of deionized water to obtain an initiator solution; dissolve 0.5g of sodium lauryl sulfate in 120g of deionized water, add 20g of the monomer solution, heat to 45°C, stir for 30min, add 2g of the initiator solution, heat to 88°C, stir for 30min, add 80g of the monomer solution and 18.5g of the initiator solution dropwise within 1h, continue stirring and react for 4h, cool to room temperature, add aqueous ammonia to adjust the pH to 8.4, and obtain a water-based acrylic resin emulsion.

[0033] Preparation Example 2:

[0034] Under a nitrogen atmosphere, 1.28 g of 3-thiopheneethanol, 1.71 g of 2-chloroethyl methyl ether, 1.22 g of potassium hydroxide, and 0.08 g of methyltri-n-octylammonium chloride were mixed, heated to 180°C, and stirred for 48 hours. After the reaction, 10 g of deionized water was added to dilute the mixture, followed by extraction with ether, concentration under reduced pressure, and purification by column chromatography (n-hexane / ethyl acetate = 75 / 25) to obtain 3-dietherthiophene.

[0035] Example 1:

[0036] (1) 5 g of amino-modified carbon nanotubes were added to 30 g of deionized water, ultrasonicated for 20 min, and then 0.04 g of 2,3-epoxypropyltrimethylammonium chloride was added. The temperature was raised to 75 ° C. and stirred for 3 h. The reaction was centrifuged, washed with ethanol, and vacuum dried to obtain quaternized carbon nanotubes.

[0037] (2) 5 g of quaternized carbon nanotubes were added to 30 g of N, N-dimethylformamide, ultrasonicated for 20 min, and then 0.4 g of N, N'-dicyclohexylcarbodiimide and 0.2 g of 3-thiophenecarboxylic acid were added. The temperature was raised to 115 ° C. and stirred for 10 h. The mixture was centrifuged, washed with ethanol, and vacuum dried to obtain quaternized carbon nanotubes containing thiophene.

[0038] (3) Under a nitrogen atmosphere, 5 g of quaternized carbon nanotubes containing thiophene and 16 g of ferric chloride were added to 150 g of chloroform and ultrasonicated for 20 min to obtain a quaternized carbon nanotube dispersion containing thiophene. 8 g of 3-hexylthiophene and 2 g of 3-dietherthiophene were added to 50 g of chloroform and stirred for 20 min to obtain a thiophene monomer solution. The thiophene monomer solution was added dropwise to the quaternized carbon nanotube dispersion containing thiophene, stirred for 24 h, centrifuged, washed with methanol, and vacuum dried to obtain modified carbon nanotubes.

[0039] (4) 60 g of aqueous acrylic resin emulsion and 10 g of propylene glycol methyl ether were mixed, heated to 38 ° C, stirred for 20 min, and then 6 g of modified carbon nanotubes were added. The mixture was stirred at a speed of 5000 rpm for 40 min. Then, 0.5 g of leveling agent BYK-333, 0.3 g of dispersant BYK-190 and 0.05 g of defoaming agent BYK-024 were added. The mixture was stirred at a speed of 400 rpm for 8 min to obtain an electrically heated carbon nanotube composite coating.

[0040] Example 2:

[0041] (1) 10 g of amino-modified carbon nanotubes were added to 50 g of deionized water, ultrasonicated for 30 min, and then 0.1 g of 2,3-epoxypropyltrimethylammonium chloride was added. The temperature was raised to 80 ° C. and stirred for 4 h. The reaction was centrifuged, washed with ethanol, and vacuum dried to obtain quaternized carbon nanotubes.

[0042] (2) 10 g of quaternized carbon nanotubes were added to 50 g of N, N-dimethylformamide, ultrasonicated for 30 min, and then 0.8 g of N, N'-dicyclohexylcarbodiimide and 0.4 g of 3-thiophenecarboxylic acid were added. The temperature was raised to 120 ° C, stirred for 12 h, centrifuged, washed with ethanol, and vacuum dried to obtain quaternized carbon nanotubes containing thiophene;

[0043] (3) Under a nitrogen atmosphere, 10 g of quaternized carbon nanotubes containing thiophene and 27 g of ferric chloride were added to 200 g of chloroform and ultrasonicated for 30 min to obtain a quaternized carbon nanotube dispersion containing thiophene. 14 g of 3-hexylthiophene and 3 g of 3-dietherthiophene were added to 100 g of chloroform and stirred for 30 min to obtain a thiophene monomer solution. The thiophene monomer solution was added dropwise to the quaternized carbon nanotube dispersion containing thiophene, stirred for 30 h, centrifuged, washed with methanol, and vacuum dried to obtain modified carbon nanotubes.

[0044] (4) 80 g of aqueous acrylic resin emulsion and 20 g of propylene glycol methyl ether were mixed, heated to 40 ° C, and stirred for 30 min. Then, 8 g of modified carbon nanotubes were added and stirred at a speed of 8000 rpm for 45 min. Then, 0.8 g of leveling agent BYK-333, 0.5 g of dispersant BYK-190 and 0.1 g of defoaming agent BYK-024 were added and stirred at a speed of 500 rpm for 10 min to obtain an electrically heated carbon nanotube composite coating.

[0045] Example 3:

[0046] (1) 15 g of amino-modified carbon nanotubes were added to 80 g of deionized water, ultrasonicated for 40 min, and then 0.2 g of 2,3-epoxypropyltrimethylammonium chloride was added. The temperature was raised to 85 ° C. and stirred for 5 h. The reaction was centrifuged, washed with ethanol, and vacuum dried to obtain quaternized carbon nanotubes.

[0047] (2) 15 g of quaternized carbon nanotubes were added to 50 g of N, N-dimethylformamide, ultrasonicated for 40 min, and then 1.2 g of N, N'-dicyclohexylcarbodiimide and 0.6 g of 3-thiophenecarboxylic acid were added. The temperature was raised to 125 ° C. and stirred for 15 h. The mixture was centrifuged, washed with ethanol, and vacuum dried to obtain quaternized carbon nanotubes containing thiophene.

[0048] (3) Under a nitrogen atmosphere, 15 g of quaternized carbon nanotubes containing thiophene and 40 g of ferric chloride were added to 250 g of chloroform, and ultrasonicated for 40 min to obtain a quaternized carbon nanotube dispersion containing thiophene. 20 g of 3-hexylthiophene and 4 g of 3-dietherthiophene were added to 150 g of chloroform and stirred for 40 min to obtain a thiophene monomer solution. The thiophene monomer solution was added dropwise to the quaternized carbon nanotube dispersion containing thiophene, stirred for 36 h, centrifuged, washed with methanol, and vacuum dried to obtain modified carbon nanotubes.

[0049] (4) 100 g of aqueous acrylic resin emulsion and 30 g of propylene glycol methyl ether were mixed, heated to 42 ° C, stirred for 40 min, and then 10 g of modified carbon nanotubes were added. The mixture was stirred at a speed of 10,000 rpm for 50 min. Then, 1 g of leveling agent BYK-333, 0.8 g of dispersant BYK-190 and 0.2 g of defoaming agent BYK-024 were added. The mixture was stirred at a speed of 600 rpm for 12 min to obtain an electrically heated carbon nanotube composite coating.

[0050] Comparative Example 1:

[0051] The difference between Comparative Example 1 and Example 2 is that the quaternized carbon nanotubes in step (2) are replaced by amino carbon nanotubes;

[0052] The specific steps are as follows:

[0053] (1) Add 10 g of amino-modified carbon nanotubes to 50 g of N,N-dimethylformamide, sonicate for 30 min, then add 0.8 g of N,N'-dicyclohexylcarbodiimide and 0.4 g of 3-thiophenecarboxylic acid, heat to 120 °C, stir and react for 12 h, centrifuge, wash with ethanol, and vacuum dry to obtain carbon nanotubes containing thiophene;

[0054] (2) Under a nitrogen atmosphere, 10 g of thiophene-containing carbon nanotubes and 27 g of ferric chloride were added to 200 g of chloroform and ultrasonicated for 30 min to obtain a thiophene-containing carbon nanotube dispersion. 14 g of 3-hexylthiophene and 3 g of 3-dietherthiophene were then added to 100 g of chloroform and stirred for 30 min to obtain a thiophene monomer solution. The thiophene monomer solution was added dropwise to the thiophene-containing carbon nanotube dispersion, stirred for 30 h, centrifuged, washed with methanol, and vacuum dried to obtain modified carbon nanotubes.

[0055] (3) 80 g of aqueous acrylic resin emulsion and 20 g of propylene glycol methyl ether were mixed, heated to 40° C., and stirred for 30 min. 8 g of modified carbon nanotubes were added, and stirred at 8000 rpm for 45 min. 0.8 g of leveling agent BYK-333, 0.5 g of dispersant BYK-190, and 0.1 g of defoaming agent BYK-024 were added, and stirred at 500 rpm for 10 min to obtain a coating.

[0056] Comparative Example 2:

[0057] The difference between Comparative Example 2 and Example 2 is that the 3-dietherthiophene in step (3) is replaced by 3-hexylthiophene;

[0058] The specific steps are as follows:

[0059] (1) 10 g of amino-modified carbon nanotubes were added to 50 g of deionized water, ultrasonicated for 30 min, and then 0.1 g of 2,3-epoxypropyltrimethylammonium chloride was added. The temperature was raised to 80 ° C. and stirred for 4 h. The reaction was centrifuged, washed with ethanol, and vacuum dried to obtain quaternized carbon nanotubes.

[0060] (2) 10 g of quaternized carbon nanotubes were added to 50 g of N, N-dimethylformamide, ultrasonicated for 30 min, and then 0.8 g of N, N'-dicyclohexylcarbodiimide and 0.4 g of 3-thiophenecarboxylic acid were added. The temperature was raised to 120 ° C, stirred for 12 h, centrifuged, washed with ethanol, and vacuum dried to obtain quaternized carbon nanotubes containing thiophene;

[0061] (3) Under a nitrogen atmosphere, 10 g of quaternized carbon nanotubes containing thiophene and 27 g of ferric chloride were added to 200 g of chloroform, and ultrasonicated for 30 min to obtain a quaternized carbon nanotube dispersion containing thiophene. 17 g of 3-hexylthiophene was then added to 100 g of chloroform and stirred for 30 min to obtain a thiophene monomer solution. The thiophene monomer solution was added dropwise to the quaternized carbon nanotube dispersion containing thiophene, stirred for 30 h, centrifuged, washed with methanol, and vacuum dried to obtain modified carbon nanotubes.

[0062] (4) 80 g of aqueous acrylic resin emulsion and 20 g of propylene glycol methyl ether were mixed, heated to 40° C., and stirred for 30 min. 8 g of modified carbon nanotubes were added, and stirred at 8000 rpm for 45 min. 0.8 g of leveling agent BYK-333, 0.5 g of dispersant BYK-190, and 0.1 g of defoaming agent BYK-024 were added, and stirred at 500 rpm for 10 min to obtain a coating.

[0063] Comparative Example 3:

[0064] The difference between Comparative Example 3 and Example 2 is that 3-hexylthiophene in step (3) is replaced by 3-dietherthiophene;

[0065] The specific steps are as follows:

[0066] (1) 10 g of amino-modified carbon nanotubes were added to 50 g of deionized water, ultrasonicated for 30 min, and then 0.1 g of 2,3-epoxypropyltrimethylammonium chloride was added. The temperature was raised to 80 ° C. and stirred for 4 h. The reaction was centrifuged, washed with ethanol, and vacuum dried to obtain quaternized carbon nanotubes.

[0067] (2) 10 g of quaternized carbon nanotubes were added to 50 g of N, N-dimethylformamide, ultrasonicated for 30 min, and then 0.8 g of N, N'-dicyclohexylcarbodiimide and 0.4 g of 3-thiophenecarboxylic acid were added. The temperature was raised to 120 ° C, stirred for 12 h, centrifuged, washed with ethanol, and vacuum dried to obtain quaternized carbon nanotubes containing thiophene;

[0068] (3) Under a nitrogen atmosphere, 10 g of quaternized carbon nanotubes containing thiophene and 27 g of ferric chloride were added to 200 g of chloroform, and ultrasonicated for 30 min to obtain a quaternized carbon nanotube dispersion containing thiophene. 17 g of 3-dietherthiophene was then added to 100 g of chloroform and stirred for 30 min to obtain a thiophene monomer solution. The thiophene monomer solution was added dropwise to the quaternized carbon nanotube dispersion containing thiophene, stirred for 30 h, centrifuged, washed with methanol, and vacuum dried to obtain modified carbon nanotubes.

[0069] (4) 80 g of aqueous acrylic resin emulsion and 20 g of propylene glycol methyl ether were mixed, heated to 40° C., and stirred for 30 min. 8 g of modified carbon nanotubes were added, and stirred at 8000 rpm for 45 min. 0.8 g of leveling agent BYK-333, 0.5 g of dispersant BYK-190, and 0.1 g of defoaming agent BYK-024 were added, and stirred at 500 rpm for 10 min to obtain a coating.

[0070] Comparative Example 4:

[0071] The difference between Comparative Example 4 and Example 2 is that the modified carbon nanotubes in step (4) are replaced by a mixture of 3.2 g of quaternized carbon nanotubes and 4.8 g of a polythiophene derivative; the polythiophene derivative is obtained by polymerizing 14 g of 3-hexylthiophene and 3 g of 3-dietherthiophene;

[0072] The specific steps are as follows:

[0073] (1) 10 g of amino-modified carbon nanotubes were added to 50 g of deionized water, ultrasonicated for 30 min, and then 0.1 g of 2,3-epoxypropyltrimethylammonium chloride was added. The temperature was raised to 80 ° C. and stirred for 4 h. The reaction was centrifuged, washed with ethanol, and vacuum dried to obtain quaternized carbon nanotubes.

[0074] (2) Under a nitrogen atmosphere, 27 g of ferric chloride was added to 200 g of chloroform and ultrasonicated for 30 min to obtain a dispersion. Then, 14 g of 3-hexylthiophene and 3 g of 3-dietherthiophene were added to 100 g of chloroform and stirred for 30 min to obtain a thiophene monomer solution. The thiophene monomer solution was added dropwise to the dispersion, stirred for 30 h, and purified to obtain a polythiophene derivative.

[0075] (3) 80 g of aqueous acrylic resin emulsion and 20 g of propylene glycol methyl ether were mixed, heated to 40° C., and stirred for 30 min. 3.2 g of quaternized carbon nanotubes and 4.8 g of polythiophene derivatives were added, and stirred at a speed of 8000 rpm for 45 min. 0.8 g of leveling agent BYK-333, 0.5 g of dispersant BYK-190, and 0.1 g of defoaming agent BYK-024 were added, and stirred at a speed of 500 rpm for 10 min to obtain a coating.

[0076] Performance testing:

[0077] Sample preparation: A Q235 steel plate with a size of 150 mm × 70 mm × 1 mm was selected, and it was polished with 400-grit sandpaper, ultrasonically cleaned with acetone for 15 minutes, rinsed with deionized water, and then dried with nitrogen for later use. The coating prepared in each embodiment and comparative example was evenly sprayed on the surface of the steel plate, and the wet film thickness was controlled to be 120 ± 5 μm. The steel plate was cured at 80°C for 1 hour, then cured at 120°C for 2 hours, and naturally cooled to obtain a coating sample.

[0078] Surface resistivity test: A four-probe resistance tester (model RTS-9) was used to apply a constant current of 1 mA to the sample surface to test the surface resistivity. The results are shown in Table 1.

[0079] Long-term stability test: Hot and cold cycle, -40℃ (2h) to room temperature (1h) to 85℃ (2h) as one cycle, performed continuously 50 times, the surface resistivity after 50 cycles, and the resistivity change rate were calculated. The results are shown in Table 1.

[0080] Electric heating performance test: After the sample was placed in a -20°C cryostat for 2 hours, a 12V DC voltage was applied. The heating curve was recorded using an infrared thermal imager (FLIR T540). Nine equidistant temperature measurement points were set on the sample surface, and the steady-state temperature and temperature uniformity (the temperature difference between the highest and lowest points) were recorded. The results are shown in Table 1.

[0081] Adhesion test: Referring to GB / T 9286-1998, a 6×6 grid was formed on the coating surface using a crosshatch with a blade spacing of 2 mm. 3M 610 tape was applied vertically and then peeled off at a speed of 0.8 m / s. The number of detached grids was observed under a microscope and evaluated on a scale of 0-5. The results are shown in Table 1.

[0082] Table 1 Performance test results

[0083]

[0084]

[0085] Data Analysis:

[0086] According to the experimental data of Example 2, the composite coating prepared by the present invention exhibits excellent comprehensive performance characteristics. Resistivity tests show that the material system can form a continuous and stable conductive network structure, which may benefit from the synergistic mechanism between the quaternized carbon nanotubes and the thiophene groups. Through the chemical grafting modification of the carbon nanotube surface, it is speculated that the effective load of the thiophene group forms a multidimensional channel for electron transmission, and the presence of quaternary ammonium ions may enhance the dispersion uniformity of the nanomaterial in the polymer matrix. In terms of thermal stability, the resistivity change rate after cycling is low, reflecting the integrity retention ability of the material structure under temperature stress, which may be related to the chemical bonding effect formed at the quaternary ammonium-thiophene composite interface. The advantages of steady-state temperature and temperature uniformity in the electric heating performance data show that the composite material has efficient electric heat conversion efficiency and a three-dimensional heat-conducting network structure. The excellent adhesion grade suggests that effective interface compatibility has been established between the specifically modified carbon nanotubes and the acrylic resin matrix, which may be closely related to the directional modification of the surface functional groups and the in-situ polymerization process.

[0087] The performance difference analysis of Example 2 and Comparative Example 1 shows that quaternization treatment has a significant impact on material properties. It is speculated that after the amino carbon nanotubes are modified by epoxypropyl quaternization, the surface charge state and steric hindrance change, which may enhance the covalent binding ability with the thiophene group. This molecular-level interaction is conducive to building a more complete conductive path network, and the cationic properties of the quaternary ammonium group may promote the dispersion stability of carbon nanotubes in an aqueous system. In comparison, Comparative Example 1 without quaternary ammonium modification may cause a decrease in the uniformity of nanomaterial dispersion and a decrease in interfacial bonding strength due to insufficient functional group reactivity, thereby affecting the integrity and mechanical anchoring effect of the conductive network.

[0088] Analysis of the performance differences between Example 2 and Comparative Example 2 reveals that the structural differences incorporating 3-dietherthiophene significantly impact material properties. It is speculated that the ether bond in this substituent may improve the solubility of the monomer in the reaction system, favoring the orderly growth of the molecular chain during polymerization. Furthermore, the steric hindrance of the ether group may regulate the conformational arrangement of the polymer, forming a regular molecular structure that is conducive to charge transport. This structural advantage may manifest as more efficient carrier mobility and more uniform current distribution, resulting in a significant improvement in electrothermal performance.

[0089] Analysis of the performance differences between Example 2 and Comparative Example 3 revealed a synergistic effect between the two thiophene monomers. It is speculated that the long-chain alkyl group of 3-hexylthiophene may enhance the flexibility of the molecular chain, while the polar group of 3-dietherthiophene may strengthen interfacial interactions. Copolymerization of the two monomers may form a conductive polymer layer with a gradient electronic structure. This dual composite modification can more effectively suppress carrier scattering than single-structure monomers, improving the material's conductive stability and thermal conductivity.

[0090] The performance difference analysis of Example 2 and Comparative Example 4 shows that the in-situ polymerization process shows significant advantages. The data show that graft polymerization directly on the surface of carbon nanotubes can form a more stable core-shell structure. It is speculated that this process allows the conductive polymer molecular chains to tightly coat the surface of the nanotubes through chemical bonding, forming a continuous three-dimensional conductive network. Compared with the comparison scheme of physical mixing, this in-situ formed interface layer may have stronger mechanical bonding and electronic coupling effects. At the same time, the structured growth of polymer chains may effectively inhibit the agglomeration of nanotubes and improve the stress transfer efficiency between the filler and the matrix, which may be an important reason for the better adhesion and thermal stability of Example 2.

[0091] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention is limited to these examples. Within the scope of the present invention, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.

Claims

1. An electrically heated carbon nanotube composite coating, characterized in that: The invention is prepared from the following raw materials in parts by weight: 60-100 parts of aqueous acrylic resin emulsion, 10-30 parts of propylene glycol methyl ether, 6-10 parts of modified carbon nanotubes, 0.5-1 parts of leveling agent, 0.3-0.8 parts of dispersant and 0.05-0.2 parts of defoaming agent; The modified carbon nanotubes are prepared by first grafting 2,3-epoxypropyltrimethylammonium chloride onto ammoniated carbon nanotubes and then grafting 3-thiophenecarboxylic acid to obtain thiophene-containing quaternized carbon nanotubes, and then polymerizing 3-hexylthiophene and 3-dietherthiophene with the thiophene groups on the surface of the quaternized carbon nanotubes containing thiophene.

2. The electrically heated carbon nanotube composite coating according to claim 1, characterized in that: The weight ratio of the amino-modified carbon nanotubes to 2,3-epoxypropyltrimethylammonium chloride is 5-15:0.04-0.

2.

3. The electrically heated carbon nanotube composite coating according to claim 1, characterized in that: The weight ratio of the amino-modified carbon nanotubes to 3-thiophenecarboxylic acid is 5-15:0.4-1.

2.

4. The electrically heated carbon nanotube composite coating according to claim 1, characterized in that: The weight ratio of the thiophene-containing quaternized carbon nanotubes, 3-hexylthiophene and 3-dietherthiophene is 5-15:8-20:2-4.

5. The electrically heated carbon nanotube composite coating according to claim 1, characterized in that: The water-based acrylic resin emulsion is obtained by semi-continuous emulsion polymerization using methyl methacrylate, acrylic acid, butyl methacrylate, butyl acrylate and styrene as polymerization monomers; the weight ratio of the methyl methacrylate, acrylic acid, butyl methacrylate, butyl acrylate and styrene is 5:15:35:10:

35.

6. The electrically heated carbon nanotube composite coating according to claim 1, characterized in that: The amino content of the amino-treated carbon nanotubes is greater than 0.4 wt %.

7. The electrically heated carbon nanotube composite coating according to claim 1, characterized in that: The preparation method of 3-diether thiophene is as follows: under a nitrogen atmosphere, 3-thiophene ethanol, 2-chloroethyl methyl ether, potassium hydroxide and methyl tri-n-octylammonium chloride are mixed, the temperature is raised to 180° C., the mixture is stirred for reaction for 48 hours, and the mixture is purified to obtain 3-diether thiophene.

8. The electrically heated carbon nanotube composite coating according to claim 1, characterized in that: The specific preparation steps of the modified carbon nanotubes are as follows: (1) adding the aminated carbon nanotubes to deionized water, sonicating for 20-40 min, then adding 2,3-epoxypropyltrimethylammonium chloride, heating to 75-85° C., stirring for 3-5 h, centrifuging, washing with ethanol, and vacuum drying to obtain quaternized carbon nanotubes; (2) adding quaternized carbon nanotubes to N,N-dimethylformamide, ultrasonicating for 20-40 min, then adding N,N'-dicyclohexylcarbodiimide and 3-thiophenecarboxylic acid, heating to 115-125 ° C, stirring and reacting for 10-15 h, centrifuging, washing with ethanol, and vacuum drying to obtain quaternized carbon nanotubes containing thiophene; (3) Under a nitrogen atmosphere, quaternized carbon nanotubes containing thiophene and ferric chloride are added to chloroform and ultrasonicated for 20-40 minutes to obtain a quaternized carbon nanotube dispersion containing thiophene. 3-Hexylthiophene and 3-dietherthiophene are then added to the chloroform and stirred for 20-40 minutes to obtain a thiophene monomer solution. The thiophene monomer solution is added dropwise to the quaternized carbon nanotube dispersion containing thiophene, and the reaction is stirred for 24-36 hours. The mixture is centrifuged, washed with methanol, and vacuum dried to obtain modified carbon nanotubes.

9. The electrically heated carbon nanotube composite coating according to claim 1, characterized in that: The leveling agent is BYK-333; the dispersant is BYK-190; and the defoaming agent is BYK-024.

10. A method for preparing the electrically heated carbon nanotube composite coating according to any one of claims 1 to 9, characterized in that: The following steps are involved: The aqueous acrylic resin emulsion and propylene glycol methyl ether were mixed, heated to 38-42° C., stirred for 20-40 minutes, and then the modified carbon nanotubes were added. The mixture was stirred at a speed of 5000-10000 rpm for 40-50 minutes. Then, the leveling agent BYK-333, the dispersant BYK-190 and the defoaming agent BYK-024 were added. The mixture was stirred at a speed of 400-600 rpm for 8-12 minutes to obtain an electrically heated carbon nanotube composite coating.

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