Environment-friendly ultra-light electromagnetic wave absorbing coating and preparation method thereof

Abstract

The application provides an environment-friendly ultralight electromagnetic wave absorbing coating, which comprises the following components in percentage by weight: carbon nanotubes 3-10%, hollow microbeads 1-5%, film-forming resin and curing agent 50-70%, active diluent 15-25%, coupling agent 0.5-2% and dispersant 5-15%. The carbon nanotubes are a mixture of single-walled carbon nanotubes and multi-walled carbon nanotubes, and the active diluent is a compound participating in addition curing reaction in the film-forming resin. The electromagnetic wave absorbing coating of the application is compounded by using different proportions of single-walled and multi-walled carbon nanotubes, and the electromagnetic parameters are adjusted to adjust the best absorption wave band of the wave absorbing coating, and the electromagnetic wave absorbing performance is excellent. Meanwhile, the carbon nanotubes are uniformly distributed in the coating by dispersing the carbon nanotubes by high-speed mechanical stirring and ultrasonic wave at the same time, and the wave absorbing performance of the coating is ensured.

Description

Technical Field

[0001] This invention relates to the field of radar stealth materials technology, and more specifically to an environmentally friendly ultralight electromagnetic wave absorbing coating and its preparation method. Background Technology

[0002] With the advancement of radar technology, more and more equipment needs to possess radar stealth capabilities, and one of the main technical means is to coat the surface of the equipment with electromagnetic wave absorbing coatings, simply called radar-absorbing coatings. Radar-absorbing coatings can convert the energy of incident electromagnetic waves into heat energy for dissipation, or effectively reduce the energy of reflected electromagnetic waves through the cancellation of resonance effects.

[0003] Microwave-absorbing coatings are made by uniformly dispersing absorbers with specific electromagnetic parameters in a matrix primarily composed of film-forming resin. Many types of absorbers are used, with common types including those with electrical and magnetic losses. Magnetic loss absorbers, which are commonly used, are related to the material's complex permeability μ = μ' - iμ” and also have complex permittivity losses. Therefore, they offer more ways to control electromagnetic parameters and can overcome some of the drawbacks of electrical losses, making them the mainstream absorbers. However, these absorbers have a high specific gravity, requiring a large amount of filler; after coating production, their bulk density is typically greater than 3000 kg / m³. 3 However, when the coating on mobile equipment is thick, especially when the coating adhesive on aircraft is thick, there are many limitations. Therefore, there is a need to develop a lightweight radar-absorbing coating.

[0004] Carbon nanotubes are one-dimensional carbon nanomaterials with unique hollow tubular structures, high aspect ratios, low density, excellent electrical and mechanical properties, and special dielectric losses, making them promising candidates for electromagnetic wave absorption. Therefore, using carbon nanotubes as absorbers can address the aforementioned issues, but it only reduces the weight of coatings to a certain extent. Furthermore, current technologies often use single carbon nanotubes, making it difficult to adjust suitable electromagnetic parameters, resulting in an effective absorption frequency band that is too high. Additionally, all these methods require complex pretreatment of the carbon nanotubes, leading to complex processes, low production efficiency, high costs, and failure to meet environmental protection requirements.

[0005] On the other hand, film-forming resins are generally based on polymer resins, supplemented with curing agents, solvents, and other auxiliary materials. This allows the absorbent to adhere to the substrate, providing certain mechanical properties and environmental resistance, and meeting the needs of processes such as spraying and brushing. These auxiliary materials generate TVOCs. As national environmental protection requirements become increasingly stringent, the TVOC of microwave absorbing coatings must be as low as possible. Environmental labeling certification standards require a TVOC content of ≤80 g / L, and developed countries have even stricter requirements. Therefore, the development of low-TVOC environmentally friendly microwave absorbing coatings is urgently needed.

[0006] Existing technical documents:

[0007] Chinese Patent: CN110423535

[0008] Chinese Patent: CN109880591

[0009] Chinese Patent: CN107032325 Summary of the Invention

[0010] The purpose of this invention is to address the shortcomings of existing technologies by providing an environmentally friendly, ultra-light electromagnetic wave absorbing coating and its preparation method, which has advantages such as good wave absorption effect, low density, good environmental performance, and simple preparation.

[0011] According to a first aspect of the present invention, an environmentally friendly ultralight electromagnetic wave absorbing coating is provided, comprising the following components by weight percentage: 3% to 10% carbon nanotubes, 1% to 5% hollow microspheres, 50% to 70% film-forming resin and curing agent, 15% to 25% reactive diluent, 0.5% to 2% coupling agent, and 5% to 15% dispersant;

[0012] The carbon nanotubes are a mixture of single-walled and multi-walled carbon nanotubes, and the reactive diluent is a compound that participates in the addition curing reaction in the film-forming resin.

[0013] As an optional implementation, the mixing ratio of single-walled carbon nanotubes and multi-walled carbon nanotubes by weight is (1:3) to (1:10).

[0014] As an optional implementation, the single-walled carbon nanotubes have a diameter of 1–3 nm and a length of 8–15 μm.

[0015] As an optional implementation, the multi-walled carbon nanotubes have a diameter of 15–50 nm and a length of 30–50 μm.

[0016] As an optional implementation, the diameter of the hollow microspheres is 5 to 30 μm.

[0017] As an optional implementation, the film-forming resin includes epoxy resin, polyurethane, phenolic resin, or acrylic resin.

[0018] As an optional implementation, the reactive diluent is selected according to the type of film-forming resin, including low-molecular-weight compounds containing epoxy groups, low-molecular-weight polyols, or monofunctional acrylates.

[0019] According to a second aspect of the present invention, a method for preparing the aforementioned environmentally friendly ultralight electromagnetic wave absorbing coating is provided, comprising the following steps:

[0020] S1. Add carbon nanotubes, reactive diluent, coupling agent, and dispersant to a mechanical disperser according to their weight percentages, and stir until homogeneous to obtain the first solution;

[0021] S2. The film-forming resin weighed according to the weight percentage is added to the first solution, heated to the required temperature and kept at that temperature, and then dispersed by mechanical and ultrasonic co-dispersion methods to obtain the second solution.

[0022] S3. Add the hollow microspheres weighed according to the weight percentage to the second solution, and disperse them evenly in a mechanical disperser to obtain the third solution;

[0023] S4. When using, add the curing agent weighed according to the weight percentage to the third solution, stir and disperse evenly to obtain the desired electromagnetic wave absorbing coating.

[0024] As an optional implementation, the required temperature in step S2 is 60°C.

[0025] As an optional implementation, in step S2, an immersion ultrasonic generator with an ultrasonic frequency of 20-40 kHz is placed in the mechanically dispersed barrel, and ultrasonic power of 600 W / kg is input at 3-minute intervals with a duty cycle of 50%, and ultrasonic dispersion is performed synchronously with mechanical dispersion at a speed of 1500-2500 r / min for 60-90 minutes.

[0026] As can be seen from the above technical solutions of the present invention, the environmentally friendly ultralight electromagnetic wave absorbing coating proposed in this invention uses single-walled carbon nanotubes and multi-walled carbon nanotubes in a proportionally adjusted compound to obtain suitable electromagnetic parameters, thereby adjusting the absorbing coating to the optimal absorption band and exhibiting excellent electromagnetic wave absorption performance. At the same time, the present invention combines high-speed mechanical stirring and ultrasonic waves to disperse the carbon nanotubes simultaneously, ensuring that the carbon nanotubes are evenly distributed in the coating and guaranteeing the coating's wave absorption performance.

[0027] The composite carbon nanotubes used in this invention have a low percolation threshold and low filling amount. Combined with the use of hollow microspheres, this results in a very low bulk density, with the prepared microwave absorbing coating dry film having a density of 600 kg / m³. 3 ~900kg / m 3 It is more suitable for use in weight-sensitive equipment such as aircraft; in addition, it can retain the relevant properties of film-forming resin, has good physical and mechanical properties, and reduces the selectivity of film-forming resin; moreover, by selecting different film-forming resin substrates, it can be applied to most indoor and outdoor environments, as well as various equipment surfaces.

[0028] This invention uses an active diluent that participates in the addition curing reaction in the film-forming resin, so that there is virtually no release of volatile organic compounds during the spraying and curing process, thereby reducing the TVOC of the coating and improving its environmental performance.

[0029] The production process of the product of this invention is simple, does not require complex modification of carbon nanotubes, reduces the use of strong acids, strong alkalis and other chemicals, can directly use commercially available products, has high production efficiency, low cost and is green and environmentally friendly. Attached Figure Description

[0030] Figure 1 This is a planar vertical reflectivity diagram of the electromagnetic wave of the coating in Embodiment 1 of the present invention.

[0031] Figure 2 This is a planar vertical reflectivity diagram of the electromagnetic wave of the coating in Embodiment 2 of the present invention.

[0032] Figure 3 This is a planar vertical reflectivity diagram of the electromagnetic wave of the coating in Embodiment 3 of the present invention. Detailed Implementation

[0033] To better understand the technical content of the present invention, specific embodiments are described below in conjunction with the accompanying drawings.

[0034] Various aspects of the invention are described in this disclosure with reference to the accompanying drawings, in which numerous illustrative embodiments are shown. The embodiments of this disclosure are not necessarily intended to encompass all aspects of the invention. It should be understood that the various concepts and embodiments described above, as well as those described below in more detail, can be implemented in any of a number of ways.

[0035] In an exemplary embodiment of the present invention, an environmentally friendly ultralight electromagnetic wave absorbing coating is provided, comprising the following components by weight percentage: 3% to 10% carbon nanotubes, 1% to 5% hollow microspheres, 50% to 70% film-forming resin and curing agent, 15% to 25% reactive diluent, 0.5% to 2% coupling agent, and 5% to 15% dispersant.

[0036] The carbon nanotubes are a mixture of single-walled and multi-walled carbon nanotubes, and the reactive diluent is a compound that participates in the addition curing reaction in the film-forming resin.

[0037] To reduce the weight of the microwave absorbing coating, this invention uses a lightweight carbon nanotube-based electrical loss absorber, employing a blend of single-walled and multi-walled carbon nanotubes. The high conductivity of single-walled carbon nanotubes improves the electrical loss of the coating, while the lower conductivity of multi-walled carbon nanotubes increases the real part of the dielectric constant without excessively increasing conductivity. By simultaneously using carbon nanotubes of different diameters, particularly different lengths, the size differences create anisotropic electromagnetic parameters, effectively broadening the absorption bandwidth and adjusting the electromagnetic parameters of the coating.

[0038] As an optional implementation, the mixing ratio of single-walled carbon nanotubes and multi-walled carbon nanotubes can be adjusted according to the center frequency of the absorption band. The mixing ratio of the two by weight is (1:3) to (1:10), which can achieve good absorption performance in the microwave band (2GHz to 40GHz).

[0039] As an optional implementation, the single-walled carbon nanotubes have a diameter of 1–3 nm and a length of 8–15 μm.

[0040] As an optional implementation, the multi-walled carbon nanotubes have a diameter of 15–50 nm and a length of 30–50 μm.

[0041] To reduce the weight of the microwave absorbing coating and facilitate the adjustment of electromagnetic parameters, hollow microspheres are added to the coating material. The amount of hollow microspheres added is adjusted according to the filling amount of multi-walled carbon nanotubes to achieve the desired dielectric parameters. The hollow microspheres not only reduce the material's specific gravity but also create cavity resonance, further improving the electromagnetic wave loss performance of the microwave absorbing coating.

[0042] As an optional implementation, the hollow microspheres have a diameter of 5–30 μm and can be made of glass, silica, or polymer resins such as phenolic resin and polystyrene. The amount added is 20–50% of the volume ratio of the absorbing coating. The resulting absorbing coating has a low density and good absorption performance, approximately 20% of the density of magnetic absorbing coatings.

[0043] This invention uses polymeric resins as film-forming base materials, such as epoxy resin, polyurethane, phenolic resin, or acrylic resin, and employs environmentally friendly flexible curing agents, such as polyetheramine curing agents for epoxy resins and end-capping isocyanate curing agents for polyurethane resins, to provide the basic mechanical properties of the microwave absorbing coating, such as adhesion, flexibility, and impact strength.

[0044] It is understandable that the curing agent and film-forming resin are complementary products, and their ratio can be set according to existing technology.

[0045] This invention employs a reactive diluent, selected based on the type of film-forming resin, to reduce the resin's viscosity. This diluent can be a compound that participates in the resin's curing and film-forming reaction, permanently residing in the coating film. Examples include low-molecular-weight compounds containing epoxy groups, low-molecular-weight polyols, or monofunctional acrylates. Utilizing its solubility, the microwave-absorbing coating is diluted to a lower viscosity, providing conditions for the spraying process. Because it participates in the addition curing reaction within the film-forming resin, virtually no volatile organic compounds are released during spraying and curing, reducing the coating's TVOC and improving its environmental performance.

[0046] Understandably, coupling agents and dispersants can be substances commonly used in existing technologies, which will not be elaborated here.

[0047] Because carbon nanotubes are difficult to disperse evenly, and the filling amount of this invention is large, their extremely large aspect ratio makes them prone to entanglement and the formation of carbon nanotube agglomerates, which will have a serious impact on the microwave absorption performance.

[0048] Therefore, this invention employs high-speed mechanical stirring and ultrasonic waves simultaneously to disperse carbon nanotubes. The cavitation effect of ultrasound generates localized high temperature and pressure, producing tremendous impact force and microjets, thereby achieving dispersion. However, carbon nanotubes, reaching lengths of tens of micrometers, tend to entangle and form clusters, exceeding the optimal distance for ultrasonic cavitation, thus reducing the dispersion effect. Therefore, high-speed mechanical stirring is simultaneously used to loosen the carbon nanotubes from the ultrasonic cavitation effect, moving them away from the clusters. The high-viscosity resin creates spatial resistance sites, ensuring uniform distribution of the nanotubes within the coating.

[0049] In an exemplary embodiment of the present invention, a method for preparing the aforementioned environmentally friendly ultralight electromagnetic wave absorbing coating is provided, comprising the following steps:

[0050] S1. Add carbon nanotubes, reactive diluent, coupling agent, and dispersant to a mechanical disperser according to their weight percentages. Stir and mix at a speed of 500-1000 r / min for 15-30 min to adsorb the coupling agent and dispersant onto the surface of the carbon nanotubes, thus obtaining the first solution.

[0051] S2. The film-forming resin weighed according to the weight percentage is added to the first solution, heated to 60℃ and maintained, and mechanical dispersion and ultrasonic dispersion are carried out simultaneously for 60-90 minutes; the mechanical dispersion is carried out using a high-speed disperser at a speed of 1500-2500 r / min, and at the same time, an immersion ultrasonic generator with an ultrasonic frequency of 20-40KHz is placed in the same barrel, and ultrasonic dispersion is carried out at a frequency of 600W per kilogram of coating material, with a 3-minute interval and a duty cycle of 50%, to obtain the second solution;

[0052] Excessive ultrasonic dispersion power will shorten carbon nanotubes, which is detrimental to their microwave absorption performance. Insufficient power will not disperse the carbon nanotubes well. Therefore, the ultrasonic dispersion of this invention adopts an intermittent working mode, controlling the input power at 600W / kg and the duty cycle at 50%.

[0053] S3. Add the hollow microspheres weighed according to the weight percentage to the second solution, and disperse them in a mechanical disperser at a speed of 100-300 r / min for 15-30 min to obtain the third solution.

[0054] S4. When using, add the matching curing agent weighed according to the weight percentage to the third solution, and disperse it for about 5 minutes using a mechanical disperser at a speed of 100-300 r / min to obtain an electromagnetic wave absorbing coating for spraying process.

[0055] The electromagnetic wave absorbing coating prepared by this invention has a dry film density between 600 kg / m3 and 900 kg / m3. It can achieve excellent absorption performance in the microwave frequency band (2 GHz to 40 GHz), exhibiting superior absorption performance. Furthermore, it is a high-solids-content product with extremely low TVOC, demonstrating excellent environmental performance.

[0056] To facilitate better understanding, the present invention will be further illustrated below with several specific examples, but the preparation process is not limited to these examples, and the content of the present invention is not limited to these examples.

[0057] Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0058] Example 1

[0059] (1) 13g of carbon nanotubes, 25g of epoxy reactive diluent H62, 1g of epoxy silane coupling agent KH560, and 15g of polyvinylpyrrolidone (PVP) dispersant, which are compounded in a mass ratio of single-walled to multi-walled nanotubes of 1:3, are added to a mechanical disperser and mixed at a speed of 1000r / min for 30min. Then, 50g of epoxy resin E51 is added, and the temperature is raised to 60℃ and maintained. Mechanical dispersion and ultrasonic dispersion are carried out simultaneously for 90min. The mechanical dispersion is carried out using a high-speed disperser at a speed of 2500r / min. At the same time, an immersion ultrasonic generator with an ultrasonic frequency of 40KHz is placed in the same barrel and ultrasonic dispersion is carried out at a speed of 600W per kilogram of coating, with a 3min interval and a duty cycle of 50%. Finally, 5g of hollow glass microspheres are added and dispersed in a mechanical disperser at a speed of 300r / min for 30min to obtain component A of the microwave absorbing coating.

[0060] (2) When using, add 20g of D230 polyetheramine curing agent (component B) that is compatible with epoxy resin to component A, and disperse it for 5 minutes using a high-speed disperser at a speed of 300r / min to prepare a microwave absorbing coating for spraying process.

[0061] (3) Apply the above coating to the aluminum substrate using a standard airless spray gun, spraying in 10 coats to a thickness of 2.5 mm, combining... Figure 1 As shown, the electromagnetic wave absorption rate is over 90% in the 4-8 GHz frequency band, and the dry film density of the absorbing coating is 900 kg / m³. 3 Its TVOC content is ≤10 g / L.

[0062] Example 2

[0063] 1) Add 10g of carbon nanotubes, 20g of epoxy reactive diluent H62, 1g of epoxy silane coupling agent KH560, and 10g of polyvinylpyrrolidone (PVP) dispersant, which are compounded in a single-walled:multi-walled ratio of 1:5 by mass, to a mechanical disperser and mix at a speed of 1000 r / min for 30 min. Then add 50g of epoxy resin E51, heat to 60℃ and maintain it, and disperse simultaneously using mechanical dispersion and ultrasonic dispersion for 90 min. The mechanical dispersion is carried out using a high-speed disperser at a speed of 2500 r / min. At the same time, an immersion ultrasonic generator with an ultrasonic frequency of 40 kHz is placed in the same barrel and ultrasonic dispersion is carried out at a speed of 600W per kilogram of coating, with a 3-min interval and a duty cycle of 50%. Finally, add 3g of hollow glass microspheres and disperse in the mechanical disperser at a speed of 300 r / min for 30 min to obtain component A of the microwave absorbing coating.

[0064] (2) When using, add 17g of polyetheramine curing agent (component B) that is compatible with epoxy resin to component A, and disperse it for 5 minutes using a high-speed disperser at a speed of 300r / min to prepare a microwave absorbing coating for spraying process.

[0065] (3) Apply the above coating to the aluminum substrate using a standard airless spray gun, spraying in 6 coats to a thickness of 1.5 mm, combining... Figure 2 As shown, the electromagnetic wave absorption rate is over 90% in the 8-12 GHz frequency band, and the dry film density of the absorbing coating is 800 kg / m³. 3 Its TVOC content is ≤10 g / L.

[0066] Example 3

[0067] (1) 6g of carbon nanotubes, 15g of butanediol BDO, 1g of aminosilane coupling agent KH550, and 10g of polymeric dispersant DY-9006, which are compounded in a mass ratio of single-walled to multi-walled at 1:10, are added to a mechanical disperser and mixed at a speed of 1000r / min for 30min. Then, 40g of polyether polyurethane polyol PTMG is added, heated to 60℃ and maintained, and mechanical dispersion and ultrasonic dispersion are carried out simultaneously for 90min. The mechanical dispersion is carried out using a high-speed disperser at a speed of 2500r / min. At the same time, an immersion ultrasonic generator with an ultrasonic frequency of 40KHz is placed in the same barrel and ultrasonic dispersion is carried out at a speed of 600W per kilogram of coating, with a 3min interval and a duty cycle of 50%. Finally, 3g of hollow phenolic microspheres are added and dispersed in a mechanical disperser at a speed of 300r / min for 30min to obtain component A of the microwave absorbing coating.

[0068] (2) When using, add 30g of the end-sealed isocyanate MDI curing agent (component B) that is compatible with polyurethane resin to component A, and disperse it for 5 minutes using a high-speed disperser at a speed of 300r / min to prepare a microwave absorbing coating for spraying process.

[0069] (3) Apply the above coating onto the aluminum plate using a regular air spray gun, spraying in four coats to a thickness of 1 mm, combining... Figure 3 As shown, within the 12-18GHz frequency band, the electromagnetic wave absorption rate is above 90%, and the dry film density of the absorbing coating is 600 kg / m³. Its TVOC content is ≤5 g / L.

[0070] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. An environmentally friendly, ultralight electromagnetic wave absorbing coating, characterized in that, The components, by weight percentage, are as follows: carbon nanotubes 3%~10%, hollow microspheres 1%~5%, film-forming resin and curing agent 50%~70%, reactive diluent 15%~25%, coupling agent 0.5%~2%, and dispersant 5%~15%; Wherein, the carbon nanotubes are a mixture of single-walled carbon nanotubes and multi-walled carbon nanotubes, and the reactive diluent is a compound that participates in the addition curing reaction in the film-forming resin; The mixing ratio of single-walled carbon nanotubes and multi-walled carbon nanotubes by weight is (1:3) to (1:10), and the diameter of the hollow microspheres is 5 to 30 μm. The single-walled carbon nanotubes have a diameter of 1-3 nm and a length of 8-15 μm; the multi-walled carbon nanotubes have a diameter of 15-50 nm and a length of 30-50 μm.

2. The environmentally friendly ultralight electromagnetic wave absorbing coating according to claim 1, characterized in that, The film-forming resin includes epoxy resin.

3. The environmentally friendly ultralight electromagnetic wave absorbing coating according to claim 1, characterized in that, The active diluent is selected according to the type of film-forming resin, including low molecular weight compounds containing epoxy groups.

4. A method for preparing the environmentally friendly ultralight electromagnetic wave absorbing coating according to any one of claims 1-3, characterized in that, Includes the following steps: S1. Add carbon nanotubes, reactive diluent, coupling agent, and dispersant to a mechanical disperser according to their weight percentages, and stir until homogeneous to obtain the first solution; S2. The film-forming resin weighed according to the weight percentage is added to the first solution, heated to the required temperature and kept at that temperature, and then dispersed by mechanical and ultrasonic co-dispersion methods to obtain the second solution. S3. Add the hollow microspheres weighed according to the weight percentage to the second solution, and disperse them evenly in a mechanical disperser to obtain the third solution; S4. When using, add the curing agent weighed according to the weight percentage to the third solution, stir and disperse evenly to obtain the desired electromagnetic wave absorbing coating.

5. The preparation method according to claim 4, characterized in that, In step S2, the required temperature is 60°C.

6. The preparation method according to claim 4, characterized in that, In step S2, an immersion ultrasonic generator with an ultrasonic frequency of 20-40KHz is placed in the mechanically dispersed barrel. The ultrasonic power is 600W / kg, and ultrasonic dispersion is performed synchronously with mechanical dispersion at a speed of 1500-2500r / min for 60-90min at 3min intervals and a duty cycle of 50%.

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