An electric heating carbon nanotube composite coating and a preparation method thereof

Abstract

The present application relates to the technical field of paint, in particular to a kind of electric heating carbon nanotube composite coating and preparation method thereof.The coating is composed of water-based acrylic resin emulsion, propylene glycol methyl ether, modified carbon nanotube and auxiliary agent.The modified carbon nanotube is first aminated by carbon nanotube, then grafted with 2,3-epoxypropyltrimethylammonium chloride and 3-thiophene carboxylic acid in turn, and further in-situ polymerized with 3-hexylthiophene and 3-dioxane thiophene.The obtained composite coating has stable network structure, high electron conduction and electric heating conversion efficiency, fast heating response and uniform temperature distribution, and has excellent adhesion and cold-heat cycle resistance.The present application effectively overcomes the problems of poor dispersibility and conductivity stability of existing conductive coatings, significantly improves the electric heating performance and comprehensive application value.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of paint, in particular to an electric heating carbon nanotube composite paint and a preparation method thereof. BACKGROUND

[0002] As a one-dimensional nanomaterial, carbon nanotubes have excellent electrical conductivity, thermal conductivity and mechanical strength, and show great application potential in the field of electric heating paint. Traditional electric heating paint mainly uses metal heating wire, carbon fiber or conductive carbon black as heating material, but these materials have the disadvantages of uneven heating, high energy consumption and poor thermal stability. Carbon nanotubes, with their high electrical conductivity, low density, large specific surface area and good thermal stability, can form a uniform conductive network, achieving efficient and uniform electric heating conversion, and are expected to become the core material of the new generation of high-performance electric heating paint.

[0003] The technical challenges faced by carbon nanotubes in practical applications are particularly prominent in the field of electric heating paint. First, the dispersion problem. Carbon nanotubes are prone to agglomeration in polymer matrix due to the lack of active groups on their surface and strong van der Waals forces, resulting in discontinuous conductive network. In electric heating applications, uneven dispersion will lead to local resistivity difference, causing uneven heating, affecting heating effect and possibly causing local overheating and even burning. Second, the weak interfacial bonding problem between carbon nanotubes and polymer matrix is more prominent under external force and thermal stress. During repeated thermal expansion and cold shrinkage, the tube-matrix interface is prone to peeling, causing damage to the conductive network and performance degradation. Third, the problem of conductive stability is more obvious in dynamic temperature environment. Carbon nanotubes are prone to rearrangement during heating, leading to resistance drift, and thus affecting the accuracy of power output and temperature control.

[0004] In addition, traditional surface modification methods of carbon nanotubes (such as strong acid oxidation) can improve dispersion, but will severely damage the conjugated structure of carbon nanotubes, resulting in a decrease in intrinsic electrical conductivity and thermal conductivity. This loss of electrical conductivity will significantly reduce the energy conversion efficiency in electric heating applications. How to achieve effective surface functionalization while maintaining the excellent intrinsic properties of carbon nanotubes and building a persistent and stable conductive network structure is a key technical problem in developing high-performance electric heating carbon nanotube composite paint.

[0005] Therefore, it is urgent to develop a new technical solution that can simultaneously solve the problems of poor dispersion, weak interfacial bonding and insufficient conductive stability of carbon nanotubes in electric heating paint, and achieve efficient, uniform and stable heating with low addition amount, which has become a technical bottleneck that the industry urgently needs to break through. SUMMARY

[0006] Therefore, the present application aims to provide an electric heating carbon nanotube composite coating and a preparation method thereof, so as to solve the problems of poor dispersibility of conductive fillers, weak interface combination and insufficient conductive stability of existing carbon nanotube conductive coatings.

[0007] Based on the above purpose, the present application provides an electric heating carbon nanotube composite coating, which is prepared from the following raw materials in parts 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 water-based acrylic resin emulsion is obtained by semi-continuous emulsion polymerization with methyl methacrylate, acrylic acid, butyl methacrylate, butyl acrylate and styrene as polymerized monomers; and the weight ratio of the 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 water-based acrylic resin emulsion is as follows: mixing methyl methacrylate, acrylic acid, butyl methacrylate, butyl acrylate and styrene to obtain a monomer solution; dissolving ammonium persulfate in deionized water to obtain an initiator solution; dissolving sodium dodecyl sulfate in deionized water, then adding the monomer solution, heating to 40-50℃, stirring for 25-35min, then adding the initiator solution, heating to 85-90℃, stirring for 25-35min, dropping the monomer solution and the initiator solution, dropping them completely within 0.8-1.2h, continuing to stir for 3.5-4.5h, cooling to room temperature, dropping ammonia water to adjust the pH to 8.2-8.6, and obtaining the water-based acrylic resin emulsion.

[0013] Preferably, the modified carbon nanotube is obtained by grafting 2,3-epoxypropyl trimethyl ammonium chloride on amino-functionalized carbon nanotubes, then grafting 3-thiophene carboxylic acid to obtain quaternary ammonium carbon nanotubes containing thiophene, and then polymerizing 3-hexyl thiophene and 3-dioxane thiophene with the thiophene groups on the surface of the quaternary ammonium carbon nanotubes containing thiophene; the 2,3-epoxypropyl trimethyl ammonium chloride and the 3-thiophene carboxylic acid react with the amino groups on the amino-functionalized carbon nanotubes through the epoxy and carboxyl groups, respectively.

[0014] Preferably, the amino content of the amino-functionalized carbon nanotubes is >0.4wt%.

[0015] Preferably, the weight ratio of the aminated carbon nanotube and 2,3-epoxypropyl trimethyl ammonium chloride is 5-15:0.04-0.2.

[0016] Preferably, the weight ratio of the aminated carbon nanotube and 3-thiophene carboxylic acid is 5-15:0.4-1.2.

[0017] Preferably, the weight ratio of the aminated carbon nanotube and 3-thiophene carboxylic acid is 5-15:0.4-1.2.

[0018] Preferably, the preparation method of the 3-dioxo thiophene is as follows: 3-thiophene ethanol, 2-chloroethyl methyl ether, potassium hydroxide and methyl tri-n-octyl ammonium chloride are mixed under a nitrogen atmosphere, heated to 180℃, stirred for 48h, purified to obtain 3-dioxo thiophene.

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

[0020] (1) The aminated carbon nanotube is added to deionized water, ultrasonic for 20-40min, then 2,3-epoxypropyl trimethyl ammonium chloride is added, heated to 75-85℃, stirred for 3-5h, centrifuged, washed with ethanol, vacuum dried to obtain the quaternary ammonium carbon nanotube;

[0021] (2) The quaternary ammonium carbon nanotube is added to N,N-dimethylformamide, ultrasonic for 20-40min, then N,N'-dicyclohexyl carbodiimide and 3-thiophene carboxylic acid are added, heated to 115-125℃, stirred for 10-15h, centrifuged, washed with ethanol, vacuum dried to obtain the quaternary ammonium carbon nanotube containing thiophene;

[0022] (3) Under a nitrogen atmosphere, the quaternary ammonium carbon nanotube containing thiophene and ferric chloride are added to chloroform, ultrasonic for 20-40min to obtain a quaternary ammonium carbon nanotube containing thiophene dispersion, then 3-hexyl thiophene and 3-dioxo thiophene are added to chloroform, stirred for 20-40min to obtain a thiophene monomer solution, the thiophene monomer solution is added dropwise to the quaternary ammonium carbon nanotube containing thiophene dispersion, stirred for 24-36h, centrifuged, washed with methanol, vacuum dried to obtain the modified carbon nanotube.

[0023] Further, the application also provides a preparation method of the electric heating carbon nanotube composite coating, comprising the following steps: mixing water-based acrylic resin emulsion and propylene glycol methyl ether, heating to 38-42℃, stirring for 20-40min, then adding modified carbon nanotubes, stirring at a speed of 5000-10000rpm for 40-50min, then adding leveling agent BYK-333, dispersing agent BYK-190 and defoaming agent BYK-024, stirring at a speed of 400-600rpm for 8-12min, to obtain the electric heating carbon nanotube composite coating.

[0024] The application has the following beneficial effects:

[0025] The electric heating carbon nanotube composite coating provided by the application has the following advantages. First, the surface of the carbon nanotube is introduced with various functional groups through the synergistic chemical modification of quaternary ammonium and thiophene groups, which greatly improves the dispersion stability and interfacial bonding force of the nanotube in the polymer matrix. This grafting method promotes the construction of a continuous and stable conductive network structure in the composite system, realizes a more efficient electron conduction channel, and significantly optimizes the overall electrical conductivity and electrothermal response efficiency of the material.

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

[0027] In addition, the surface functionalization and in-situ polymerization process give the carbon nanotube stronger mechanical anchoring ability, effectively improving the adhesion of the coating to the substrate. Even under harsh conditions such as multiple cold and hot cycles, the structural integrity and adhesion performance of the coating can still be well maintained, ensuring its long-term stability and durability.

[0028] In summary, the composite coating of the application has made significant comprehensive technical progress in terms of electrical conductivity, adhesion, thermal stability, electro-thermal conversion, etc., providing a new solution for the development and industrialization of high-performance electrothermal coating materials. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical scheme and advantages of the application clearer, the application is further described in detail below with specific examples.

[0030] The amino-functionalized carbon nanotubes in the specific embodiment of the application are purchased from Delta Bio, and the amino content is 0.45wt%.

[0031] Preparation Example 1:

[0032] Mixing 5 g of methyl methacrylate, 15 g of acrylic acid, 35 g of butyl methacrylate, 10 g of butyl acrylate and 35 g of styrene to obtain a monomer solution; dissolving 0.5 g of ammonium persulfate in 20 g of deionized water to obtain an initiator solution; dissolving 0.5 g of sodium dodecyl sulfate in 120 g of deionized water, then adding 20 g of the monomer solution, heating to 45°C, stirring for 30 min, then adding 2 g of the initiator solution, heating to 88°C, stirring for 30 min, dropping 80 g of the monomer solution and 18.5 g of the initiator solution, dropping for 1 h, continuing to stir for 4 h, cooling to room temperature, dropping ammonia water to adjust the pH to 8.4, to obtain an aqueous acrylic resin emulsion.

[0033] Preparation Example 2:

[0034] Mixing 1.28 g of 3-thiophene ethanol, 1.71 g of 2-chloroethyl methyl ether, 1.22 g of potassium hydroxide and 0.08 g of methyl tri-n-octyl ammonium chloride under a nitrogen atmosphere, heating to 180°C, stirring for 48 h, after the reaction is completed, diluting with 10 g of deionized water, then extracting with diethyl ether, concentrating under reduced pressure, purifying by column chromatography (n-hexane / ethyl acetate = 75 / 25) to obtain 3-dioxolane thiophene;

[0035] Example 1:

[0036] (1) Adding 5 g of amino carbon nanotubes to 30 g of deionized water, ultrasonicating for 20 min, then adding 0.04 g of 2,3-epoxypropyl trimethyl ammonium chloride, heating to 75°C, stirring for 3 h, centrifuging, washing with ethanol, and vacuum drying to obtain quaternary ammonium carbon nanotubes;

[0037] (2) Adding 5 g of quaternary ammonium carbon nanotubes to 30 g of N,N-dimethylformamide, ultrasonicating for 20 min, then adding 0.4 g of N,N'-dicyclohexyl carbodiimide and 0.2 g of 3-thiophene carboxylic acid, heating to 115°C, stirring for 10 h, centrifuging, washing with ethanol, and vacuum drying to obtain thiophene-containing quaternary ammonium carbon nanotubes;

[0038] (3) Under a nitrogen atmosphere, adding 5 g of thiophene-containing quaternary ammonium carbon nanotubes and 16 g of iron chloride to 150 g of chloroform, ultrasonicating for 20 min to obtain a thiophene-containing quaternary ammonium carbon nanotube dispersion, then adding 8 g of 3-hexyl thiophene and 2 g of 3-dioxolane thiophene to 50 g of chloroform, stirring for 20 min to obtain a thiophene monomer solution, dropping the thiophene monomer solution into the thiophene-containing quaternary ammonium carbon nanotube dispersion, stirring for 24 h, centrifuging, washing with methanol, and vacuum drying to obtain modified carbon nanotubes;

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

[0040] Example 2:

[0041] (1) 10 g of aminated carbon nanotubes were added to 50 g of deionized water, ultrasonically treated for 30 min, 0.1 g of 2,3-epoxypropyltrimethylammonium chloride was added, warmed to 80°C, stirred for 4 h, centrifuged, washed with ethanol, and vacuum dried to obtain quaternary ammonium carbon nanotubes;

[0042] (2) 10 g of the quaternary ammonium carbon nanotubes were added to 50 g of N,N-dimethylformamide, ultrasonically treated for 30 min, 0.8 g of N,N'-dicyclohexyl carbodiimide and 0.4 g of 3-thiophene carboxylic acid were added, warmed to 120°C, stirred for 12 h, centrifuged, washed with ethanol, and vacuum dried to obtain thiophene-containing quaternary ammonium carbon nanotubes;

[0043] (3) 10 g of the thiophene-containing quaternary ammonium carbon nanotubes and 27 g of iron chloride were added to 200 g of chloroform under a nitrogen atmosphere, ultrasonically treated for 30 min to obtain a thiophene-containing quaternary ammonium carbon nanotube dispersion, 14 g of 3-hexyl thiophene and 3 g of 3-dioxane thiophene were added to 100 g of chloroform, stirred for 30 min to obtain a thiophene monomer solution, the thiophene monomer solution was added dropwise to the thiophene-containing quaternary ammonium carbon nanotube dispersion, stirred for 30 h, centrifuged, washed with methanol, and vacuum dried to obtain modified carbon nanotubes;

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

[0045] Example 3:

[0046] (1) 15 g of aminated carbon nanotubes were added to 80 g of deionized water, ultrasonically treated for 40 min, 0.2 g of 2,3-epoxypropyltrimethylammonium chloride was added, warmed to 85°C, stirred for 5 h, centrifuged, washed with ethanol, and vacuum dried to obtain quaternary ammonium carbon nanotubes;

[0047] (2) 15 g of the quaternary ammonium carbon nanotubes were added into 50 g of N,N-dimethylformamide, and ultrasonic treatment was performed for 40 min. Then, 1.2 g of N,N'-dicyclohexyl carbodiimide and 0.6 g of 3-thiophene carboxylic acid were added, and the temperature was raised to 125°C. Stirring was performed for 15 h, centrifugation was performed, ethanol was used for washing, and vacuum drying was performed to obtain the quaternary ammonium carbon nanotubes containing thiophene;

[0048] (3) Under a nitrogen atmosphere, 15 g of the quaternary ammonium carbon nanotubes containing thiophene and 40 g of iron chloride were added into 250 g of chloroform, and ultrasonic treatment was performed for 40 min to obtain a dispersion solution of the quaternary ammonium carbon nanotubes containing thiophene. Then, 20 g of 3-hexyl thiophene and 4 g of 3-dioxane thiophene were added into 150 g of chloroform, and stirring was performed for 40 min to obtain a thiophene monomer solution. The thiophene monomer solution was added dropwise into the dispersion solution of the quaternary ammonium carbon nanotubes containing thiophene, and stirring was performed for 36 h. Centrifugation was performed, ethanol was used for washing, and vacuum drying was performed to obtain the modified carbon nanotubes;

[0049] (4) 100 g of an aqueous acrylic resin emulsion and 30 g of propylene glycol methyl ether were mixed, and the temperature was raised to 42°C. Stirring was performed for 40 min. Then, 10 g of the modified carbon nanotubes were added, and stirring was performed at a speed of 10,000 rpm for 50 min. Then, 1 g of a leveling agent BYK-333, 0.8 g of a dispersant BYK-190, and 0.2 g of an antifoaming agent BYK-024 were added, and stirring was performed at a speed of 600 rpm for 12 min to obtain the electric heating carbon nanotube composite coating.

[0050] Comparative Example 1

[0051] The difference between Comparative Example 1 and Example 2 is that the quaternary ammonium carbon nanotubes in step (2) are replaced by aminated carbon nanotubes.

[0052] The specific steps are as follows:

[0053] (1) 10 g of aminated carbon nanotubes were added into 50 g of N,N-dimethylformamide, and ultrasonic treatment was performed for 30 min. Then, 0.8 g of N,N'-dicyclohexyl carbodiimide and 0.4 g of 3-thiophene carboxylic acid were added, and the temperature was raised to 120°C. Stirring was performed for 12 h, centrifugation was performed, ethanol was used for washing, and vacuum drying was performed to obtain the carbon nanotubes containing thiophene;

[0054] (2) Under a nitrogen atmosphere, 10 g of the carbon nanotubes containing thiophene and 27 g of iron chloride were added into 200 g of chloroform, and ultrasonic treatment was performed for 30 min to obtain a dispersion solution of the carbon nanotubes containing thiophene. Then, 14 g of 3-hexyl thiophene and 3 g of 3-dioxane thiophene were added into 100 g of chloroform, and stirring was performed for 30 min to obtain a thiophene monomer solution. The thiophene monomer solution was added dropwise into the dispersion solution of the carbon nanotubes containing thiophene, and stirring was performed for 30 h. Centrifugation was performed, ethanol was used for washing, and vacuum drying was performed to obtain the modified carbon nanotubes;

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

[0056] Comparative Example 2:

[0057] Comparative Example 2 differs from Example 2 in that 3-hexylthiophene in step (3) is replaced by 3-dioxetane thiophene;

[0058] The specific steps are as follows:

[0059] (1) 10 g of aminated carbon nanotubes were added to 50 g of deionized water, ultrasonicated for 30 min, 0.1 g of 2,3-epoxypropyltrimethylammonium chloride was added, warmed to 80°C, stirred for 4 h, centrifuged, washed with ethanol, and vacuum dried to obtain quaternary ammonium carbon nanotubes;

[0060] (2) 10 g of the quaternary ammonium carbon nanotubes were added to 50 g of N,N-dimethylformamide, ultrasonicated for 30 min, 0.8 g of N,N'-dicyclohexyl carbodiimide and 0.4 g of 3-thiophene carboxylic acid were added, warmed to 120°C, stirred for 12 h, centrifuged, washed with ethanol, and vacuum dried to obtain thiophene-containing quaternary ammonium carbon nanotubes;

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

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

[0063] Comparative Example 3:

[0064] Comparative Example 3 differs from Example 2 in that 3-hexylthiophene in step (3) is replaced by 3-dioxetane thiophene;

[0065] The specific steps are as follows:

[0066] (1) 10 g of aminated carbon nanotubes were added to 50 g of deionized water, ultrasonicated for 30 min, 0.1 g of 2,3-epoxypropyltrimethylammonium chloride was added, heated to 80°C, stirred for 4 h, centrifuged, washed with ethanol, and vacuum dried to obtain quaternary ammonium carbon nanotubes;

[0067] (2) 10 g of quaternary ammonium carbon nanotubes were added to 50 g of N,N-dimethylformamide, ultrasonicated for 30 min, 0.8 g of N,N'-dicyclohexyl carbodiimide and 0.4 g of 3-thiophene carboxylic acid were added, heated to 120°C, stirred for 12 h, centrifuged, washed with ethanol, and vacuum dried to obtain thiophene-containing quaternary ammonium carbon nanotubes;

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

[0069] (4) 80 g of an aqueous acrylic resin emulsion and 20 g of propylene glycol methyl ether were mixed, heated to 40°C, stirred for 30 min, 8 g of modified carbon nanotubes were added, stirred at a speed of 8000 rpm for 45 min, 0.8 g of a leveling agent BYK-333, 0.5 g of a dispersant BYK-190, and 0.1 g of an antifoaming agent BYK-024 were added, stirred at a speed of 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 quaternary ammonium carbon nanotubes and 4.8 g of a polythiophene derivative; the polythiophene derivative is obtained by polymerization of 14 g of 3-hexylthiophene and 3 g of 3-dioxolane thiophene;

[0072] The specific steps are as follows:

[0073] (1) 10 g of aminated carbon nanotubes were added to 50 g of deionized water, ultrasonicated for 30 min, 0.1 g of 2,3-epoxypropyltrimethylammonium chloride was added, heated to 80°C, stirred for 4 h, centrifuged, washed with ethanol, and vacuum dried to obtain quaternary ammonium carbon nanotubes;

[0074] (2) 27 g of iron chloride was added into 200 g of chloroform under a nitrogen atmosphere, and ultrasonic treatment was performed for 30 min to obtain a dispersion liquid. Then, 14 g of 3-hexylthiophene and 3 g of 3-dioxolane thiophene were added into 100 g of chloroform, and stirring was performed for 30 min to obtain a thiophene monomer solution. The thiophene monomer solution was added dropwise into the dispersion liquid, and stirring reaction was performed for 30 h. After purification, a polythiophene derivative was obtained;

[0075] (3) 80 g of an aqueous acrylic resin emulsion and 20 g of propylene glycol methyl ether were mixed, and the temperature was raised to 40°C. Stirring was performed for 30 min, and then 3.2 g of a quaternary ammonium carbon nanotube and 4.8 g of a polythiophene derivative were added. Stirring was performed at a speed of 8000 rpm for 45 min. Then, 0.8 g of a leveling agent BYK-333, 0.5 g of a dispersant BYK-190, and 0.1 g of an antifoaming agent BYK-024 were added. Stirring was performed at a speed of 500 rpm for 10 min to obtain a coating.

[0076] Performance test:

[0077] Sample preparation: Q235 steel plates with a size of 150 mm x 70 mm x 1 mm were selected, and 400-mesh sandpaper was used for polishing, ultrasonic cleaning with acetone for 15 min, deionized water washing, and nitrogen blowing for drying. The coating prepared in each example and the comparative example was uniformly sprayed on the surface of the steel plate, and the wet film thickness was controlled to be 120 ± 5 μm. Curing was performed at 80°C for 1 h, and then curing was performed at 120°C for 2 h. After natural cooling, a coating sample was obtained.

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

[0079] Long-term stability test: Cold and hot cycles were performed for 50 times, with one cycle being -40°C (2 h) to room temperature (1 h) to 85°C (2 h). After 50 times of testing, the surface resistivity was tested, and the resistivity change rate was calculated. The results are shown in Table 1.

[0080] Electric heating performance test: After the sample was placed in a -20°C low-temperature box for 2 h, a 12V direct current voltage was applied. An infrared thermal imager (FLIR T540) was used to record the temperature rising curve. Nine equidistant temperature measurement points were set on the surface of the sample, 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: According to GB / T 9286-1998, a grating device with a knife gap of 2 mm was used to form a 6 x 6 grid on the surface of the coating. After vertical pasting with 3M 610 adhesive tape, peeling was performed at a speed of 0.8 m / s. The number of fallen grids was observed under a microscope, and the results were evaluated according to the 0-5 level standard. 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 application exhibits excellent comprehensive performance characteristics. The resistivity test shows that the material system can form a continuous and stable conductive network structure, which may be due to the synergistic mechanism between the quaternary ammonium carbon nanotubes and the thiophene groups. Through the chemical grafting modification of the surface of the carbon nanotubes, it is speculated that the effective loading of the thiophene groups forms a multi-dimensional channel for electron transport, and the presence of quaternary ammonium ions may enhance the uniformity of the dispersion of the nanomaterials in the polymer matrix. In terms of thermal stability, the resistivity change rate after cycling is low, reflecting the ability of the material structure to maintain integrity under temperature stress, which may be related to the chemical bonding effect of the quaternary ammonium-thiophene composite interface. The advantages of steady-state temperature and temperature uniformity in the electrical heating performance data show that the composite material has high electrical-to-thermal conversion efficiency and a three-dimensional heat conduction network structure. The excellent adhesion grade suggests that the carbon nanotubes modified in a specific way and the acrylic resin matrix establish effective interfacial compatibility, which may be closely related to the directional modification of the surface functional groups and the in-situ polymerization process.

[0087] According to the performance difference analysis of Example 2 and Comparative Example 1, quaternary ammonium treatment has a significant impact on material performance. It is speculated that after the amination of carbon nanotubes is modified by epoxy propyl quaternary ammonium, the surface charge state and steric hindrance change, which may enhance the covalent binding ability with thiophene groups. This molecular-level interaction is conducive to building a more perfect conductive path network, and the cationic nature of the quaternary ammonium group may promote the dispersion stability of carbon nanotubes in the aqueous system. In comparison, Comparative Example 1, which has not been modified by quaternary ammonium, may have insufficient functional group reactivity, resulting in reduced dispersion uniformity of nanomaterials and decreased interfacial bonding strength, which in turn affects the integrity of the conductive network and the mechanical anchoring effect.

[0088] According to the performance difference analysis of Example 2 and Comparative Example 2, the structural difference of introducing 3-dioxyl thiophene has a significant impact on the performance of the material. It is speculated that the ether bond in this substituent may improve the solubility of the monomer in the reaction system, which is conducive to the ordered growth of the molecular chain during polymerization. At the same time, the steric hindrance effect 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 higher carrier mobility and more uniform current distribution, resulting in a significant improvement in electrical heating performance.

[0089] For the performance difference analysis between Example 2 and Comparative Example 3, it is found that the combination of the two thiophene monomers has a synergistic effect. It is speculated that the long-chain alkyl group of 3-hexylthiophene may enhance the flexibility of the molecular chain, and the polar group of 3-dioxane thiophene may strengthen the interfacial interaction. The copolymerization of the two may form a conductive polymer layer with a gradient electronic structure. This dual composite modification can more effectively suppress carrier scattering than a single structure monomer, improving the conductive stability and heat conduction efficiency of the material.

[0090] For the performance difference analysis between Example 2 and Comparative Example 4, the in-situ polymerization process shows significant advantages. The data shows that grafting polymerization directly on the surface of carbon nanotubes can form a more stable core-shell structure. It is speculated that this process makes the conductive polymer molecular chain tightly cover the surface of the nanotube through chemical bonding, forming a continuous three-dimensional conductive network. Compared with the physical mixing of the comparative scheme, this in-situ formed interface layer may have stronger mechanical bonding and electronic coupling effect. At the same time, the structured growth of the polymer chain may effectively inhibit the agglomeration phenomenon of the nanotubes, improving 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] It should be understood by those of ordinary skill in the art that the above discussion of any of the embodiments is merely exemplary and is not intended to suggest that the scope of the present application is limited to these examples; under the idea of the present application, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other changes of different aspects of the present application as described above. In order to be brief, they are not provided in detail.

Claims

1. An electrically heatable carbon nanotube composite coating, characterized in that Prepared by the following raw materials in parts by weight: water-based acrylic resin emulsion 60-100 parts, propylene glycol methyl ether 10-30 parts, modified carbon nanotube 6-10 parts, leveling agent 0.5-1 part, dispersing agent 0.3-0.8 part and defoaming agent 0.05-0.2 part; The modified carbon nanotube is obtained by grafting 2,3-epoxypropyltrimethylammonium chloride on the amino-functionalized carbon nanotube, and then grafting 3-thiophene carboxylic acid to obtain a thiophene-containing quaternary ammonium-functionalized carbon nanotube, and then polymerizing 3-hexylthiophene and 3-dioxolane thiophene with the thiophene groups on the surface of the thiophene-containing quaternary ammonium-functionalized carbon nanotube; The preparation method of the 3-dioxolane thiophene is as follows: under a nitrogen atmosphere, 3-thiophene ethanol, 2-chloroethyl methyl ether, potassium hydroxide and methyl tri-n-octyl ammonium chloride are mixed, heated to 180°C, stirred for 48 hours, and then purified to obtain 3-dioxolane thiophene.

2. The electrically heating carbon nanotube composite coating according to claim 1, wherein, The weight ratio of the amino-functionalized carbon nanotube and 2,3-epoxypropyltrimethylammonium chloride is 5-15:0.04-0.

2.

3. The electrically heating carbon nanotube composite coating according to claim 1, wherein, The weight ratio of the amino-functionalized carbon nanotube and 3-thiophene carboxylic acid is 5-15:0.4-1.

2.

4. The electrically heating carbon nanotube composite coating according to claim 1, wherein, The weight ratio of the thiophene-containing quaternary ammonium-functionalized carbon nanotube, 3-hexylthiophene and 3-dioxolane thiophene is 5-15:8-20:2-4.

5. The electrically heating carbon nanotube composite coating according to claim 1, wherein, 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 heating carbon nanotube composite coating of claim 1, wherein, The amino content of the amino-functionalized carbon nanotube is >0.4wt%.

7. The electrically heating carbon nanotube composite coating according to claim 1, wherein, The specific preparation steps of the modified carbon nanotube are as follows: (1) The amino-functionalized carbon nanotube is added to deionized water and ultrasonicated for 20-40 minutes, then 2,3-epoxypropyltrimethylammonium chloride is added, heated to 75-85°C, stirred for 3-5 hours, centrifuged, washed with ethanol, and vacuum dried to obtain a quaternary ammonium-functionalized carbon nanotube; (2) The quaternary ammonium-functionalized carbon nanotube is added to N,N-dimethylformamide and ultrasonicated for 20-40 minutes, then N,N'-dicyclohexyl carbodiimide and 3-thiophene carboxylic acid are added, heated to 115-125°C, stirred for 10-15 hours, centrifuged, washed with ethanol, and vacuum dried to obtain a thiophene-containing quaternary ammonium-functionalized carbon nanotube; (3) Under a nitrogen atmosphere, the thiophene-containing quaternary ammonium-functionalized carbon nanotube and ferric chloride are added to chloroform, ultrasonicated for 20-40 minutes to obtain a thiophene-containing quaternary ammonium-functionalized carbon nanotube dispersion, then 3-hexylthiophene and 3-dioxolane thiophene are added to chloroform, stirred for 20-40 minutes to obtain a thiophene monomer solution, the thiophene monomer solution is added dropwise to the thiophene-containing quaternary ammonium-functionalized carbon nanotube dispersion, stirred for 24-36 hours, centrifuged, washed with methanol, and vacuum dried to obtain a modified carbon nanotube.

8. The electrically heating carbon nanotube composite coating of claim 1, wherein, The leveling agent is BYK-333; the dispersing agent is BYK-190; and the defoaming agent is BYK-024.

9. A method of preparing an electrically heatable carbon nanotube composite coating according to any one of claims 1 to 8, characterized in that The method comprises the following steps: The water-based acrylic resin emulsion and propylene glycol methyl ether are mixed, heated to 38-42℃, stirred for 20-40 min, then the modified carbon nanotubes are added, stirred at a speed of 5000-10000 rpm for 40-50 min, then the leveling agent BYK-333, the dispersing agent BYK-190 and the defoaming agent BYK-024 are added, stirred at a speed of 400-600 rpm for 8-12 min, to obtain the electric heating carbon nanotube composite coating.

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