An interface modification method for enhancing mechanical properties of wave-absorbing coating and an absorbing agent and wave-absorbing coating

Abstract

The application discloses an interface modification method for enhancing mechanical properties of a wave-absorbing coating, an absorbent and a wave-absorbing coating, and belongs to the technical field of electromagnetic wave absorbing materials. The method is characterized in that: the surface of flaky magnetic metal micropowder is activated to improve the reaction activity of the surface of the absorbent; the flaky absorbent after activation is modified on the surface by fluorosilane; the grafting amount of fluorosilane is controlled, so that the surface of the flaky magnetic metal micropowder absorbent is grafted with appropriate fluorosilane, and part of active hydroxyl sites are reserved, thereby forming semi-fluorine modified absorbent in a semi-fluorine and activated state; and the semi-fluorine modified absorbent is used as an electromagnetic wave absorbing material for the wave-absorbing coating, so that the mechanical properties of the wave-absorbing coating can be enhanced. The semi-fluorine modified absorbent prepared by the application has good filling rate, mechanical properties and electromagnetic properties, effectively solves the problem that the existing wave-absorbing coating is difficult to consider mechanical properties and wave-absorbing properties at the same time, and has important uses in the fields of electronics, airplanes, satellites, radars, communication and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic wave absorbing materials, and in particular to an interface modification method for enhancing the mechanical properties of an absorbing coating, an absorbent, and an absorbing coating. Background Art

[0002] Absorbent coatings are a key functional material for both military and civilian use. As described in the background of Chinese patent CN101699564A, high-performance absorbing coating materials must achieve the comprehensive goals of "thin thickness, light weight, wide bandwidth, and strong absorption." According to the theory of the bandwidth-to-thickness ratio limit of absorbing materials in the literature (Rozanov, K. N. IEEE Transactions on Antennas and Propagation, 2000, 48(8):1230-1234), the broadband, thin-layer, strong absorption performance of absorbing materials primarily depends on high magnetic permeability and magnetic loss. Magnetic metal micropowders with flaky micromorphology have surpassed the Snoek limit and can exponentially increase magnetic permeability, making them the preferred thin-layer, broadband absorbing materials. Furthermore, a high absorbent filling ratio is one of the basic conditions for ensuring good absorption performance of absorbing coatings. To ensure its absorbing performance, a large proportion of absorbent is usually required. Generally speaking, the mass filling rate of the absorber needs to reach more than 50%, but this will cause the mechanical properties of the coating to deteriorate rapidly. Modern instruments and military equipment work in a complex environment full of vibration and impact. This requires the absorbing coating to have higher mechanical strength such as flexibility, tensile strength and adhesion while meeting excellent absorbing performance.

[0003] A coupling agent is an organic compound that enhances the interaction between inorganic fillers and polymers. Common coupling agents include silanes, titanates, aluminates, chloroacetates, organic complexes, and fatty acids. By introducing additional coupling agents to optimize the filler-matrix interface, the mechanical properties of composite materials can be significantly improved. For example, Chinese patent CN116769382A discloses a method for modifying Fe3O4-MoS2 hybrid nanoparticles using a silane coupling agent. The modified Fe3O4-MoS2 nanohybrid is added to epoxy resin to improve the mechanical properties of epoxy resin-based composite coatings. Similarly, Chinese patent CN 113861723 A discloses a method for modifying Fe3O4 particles using a silane coupling agent. The modified Fe3O4 particles exhibit good compatibility with epoxy resin, significantly inhibiting crack propagation and improving the mechanical properties of epoxy coatings in low-temperature environments. However, in such composite coating materials, the filler filling fraction is relatively low (the filling mass fraction is less than 50%), while the mass filling rate of the thin-layer broadband absorbing coating absorber usually needs to reach more than 50%. The above conventional modification methods can only improve one aspect of the mechanical properties, such as adhesion or flexibility, and cannot take into account both.

[0004] literature( J. Magn. Magn. Mate r 2011, Vol. 323, 1643-1651) used A151 silane coupling agent to modify the surface of Sr-ferrite. The prepared polyurethane composite coating material (Sr-ferrite absorber filling mass fraction 81.8%) had improved tensile strength and significantly reduced elongation at break. Similarly, the literature ( Polym. Compos .2014, Vol. 35, 1318-24) used KH550 silane coupling agent to modify carbonyl iron powder. The prepared epoxy composite coating material (carbonyl iron powder filling mass fraction 83.3%) had improved tensile strength, but the elongation at break, that is, the flexibility, decreased.

[0005] In addition, existing literature and technologies on the surface modification of absorbers, including the surface modification of sheet absorbers, are not uncommon. The modification methods include the application of inorganic oxides such as silica, alumina, titanium oxide, etc., as well as the use of organic substances such as epoxy resins and silane coupling agents. However, these methods of surface modification of absorbers are all focused on preventing the absorbers from overlapping each other to form a conductive network and reducing the dielectric constant of the absorbing material. For example, in the typical methods and results reported in the literature (Functional Materials 2014, (10) 10058-10062), the dielectric constant of the absorbing material was significantly reduced, while the magnetic permeability did not change significantly. There is no report showing that the comprehensive mechanical properties of the absorbing coating material obtained by modifying the absorber with this type of silane coupling agent are improved.

[0006] Publication number CN113652199A Chinese invention patent provides a preparation method of a one-step forming absorbing material, utilizes curing agent to react with the polymer of different structures, makes bridge between molecular chains, forms three-dimensional network structure, and by directly solidifying in the casting process, reduces a hot pressing process, reduces production cost, improves production efficiency, realizes the continuous production of flat absorbing materials with controllable thickness and excellent performance. However, its magnetic powder activation degree is low, prone to agglomeration, and the use of filtering to remove undissolved binder and agglomerated magnetic powder will also cause waste of raw materials. Publication number CN118240428A Chinese invention patent then discloses a corrosion-resistant super-hydrophobic absorbing coating and its preparation method, by the synergistic effect of epoxy absorbing bottom layer and fluorocarbon super-hydrophobic surface layer, shows excellent super-hydrophobic performance, and excellent super-hydrophobic performance makes the absorbing coating have excellent corrosion resistance and self-cleaning performance. And fluorine-containing group modification performance reduces material surface energy, reduces the occurrence of agglomeration in practical applications. However, when fluorine-containing groups are introduced through fluorine modification, a large amount of active groups on the surface of the material will be consumed, which will reduce the active sites for cross-linking between the material and the resin, making it difficult to effectively form a strong cross-linking structure, resulting in a decrease in coating adhesion and an inability to achieve a balance between absorption and mechanical properties.

[0007] In summary, an interface modification method for enhancing the mechanical properties of the absorbing coating is provided. While improving the flexibility of the absorbing coating, it ensures the adhesion of the coating and the stability of the absorbing performance, providing a solution to the difficult problem of balancing the mechanical properties and absorbing performance of the absorbing coating, which is of great significance for expanding the application of electromagnetic wave absorbing materials. Summary of the Invention

[0008] In view of the above-mentioned deficiencies in the prior art, in a first aspect of the present invention, a method for interfacial modification of an absorbing coating is provided, which can significantly improve the dispersibility of powders in resins, avoid the formation of large cluster structures, and balance the flexibility, adhesion, and stable absorbing performance of the coating to enhance the mechanical properties of the absorbing coating. A semi-fluorinated modified absorbent is used as the absorbing functional component of the absorbing coating. The preparation method of the semi-fluorinated modified absorbent comprises the following steps:

[0009] (1) Mixing 2-5 parts of sodium hydroxide, 1-3 parts of ammonium persulfate and 70-100 parts of water in parts by weight to form an activation treatment solution; adding 3-8 parts of flaky magnetic metal micropowder to the activation treatment solution for surface treatment, and recovering the product after completion to obtain a flaky magnetic metal micropowder absorbent;

[0010] (2) Adding 0.1-0.5 parts of fluorosilane coupling agent to a mixed solvent formed by 60-90 parts of water and 20-30 parts of ethanol to obtain a modified treatment liquid; adding 4-8 parts of flaky magnetic metal micropowder absorbent to the modified treatment liquid for treatment, and recovering the product after completion to obtain a semi-fluorinated modified absorbent.

[0011] Preferably, in (1), the component types of the flaky magnetic metal powder include at least one of carbonyl iron powder, sendust powder, sendust chromium powder and sendust chromium powder.

[0012] Further preferably, the diameter of the flaky magnetic metal powder is in the range of 10-120 μm, and the ratio of the flake thickness to the flake diameter is in the range of 1:5-60.

[0013] Materials such as carbonyl iron powder, sendust powder, sendust chromium powder, and sendust chromium powder possess unique microwave absorption advantages and are suitable for use in different frequency bands and specific environments. Powders with these composition and flake diameter parameters exhibit high magnetic permeability and excellent microwave absorption, making them preferred raw materials for this invention.

[0014] Preferably, in (1), the surface treatment method is as follows: treatment at room temperature for 10-30 min under stirring conditions.

[0015] Preferably, in (1), the method of recovering the product includes filtering and collecting the filter cake, and drying; the drying temperature is 45-60 ° C, and the drying time is 1-2 h.

[0016] Preferably, in (2), the fluorosilane coupling agent includes at least one of tridecafluorooctyltriethoxysilane, trifluoropropyltriethoxysilane, dodecafluoroheptylpropyltrimethoxysilane, and heptadecafluorodecyltriethoxysilane.

[0017] Preferably, in said (2), the treatment method is as follows: treatment at room temperature for 150-200 min under stirring conditions.

[0018] Preferably, in (2), the method of recovering the product includes filtering and collecting the filter cake, and drying; the drying temperature is 45-60 ° C, and the drying time is 1-2 h.

[0019] Preferably, in (2), the contact angle parameters of the semi-fluorinated modified absorbent and the liquid are as follows: when the liquid is water, the contact angle of water and the semi-fluorinated modified absorbent is 60°-90°; when the liquid is diiodomethane, the contact angle of diiodomethane and the semi-fluorinated modified absorbent is 20°-40°.

[0020] In the second aspect of the present invention, a semi-fluorinated modified absorbent is provided which is precisely modified and takes into account both powder fluidity and active state. The absorbent is prepared by the method of the first aspect of the present invention.

[0021] In the third aspect of the present invention, a microwave-absorbing coating having excellent flexibility, coating adhesion and microwave-absorbing performance stability is provided, wherein the semi-fluorinated modified absorbent according to the second aspect of the present invention is used as the microwave-absorbing functional component of the microwave-absorbing coating.

[0022] Preferably, the preparation method of the radar absorbing coating comprises the following steps:

[0023] S1. Mix 15-25 parts of epoxy resin with 60-80 parts of solvent by weight to form a coating;

[0024] S2. Mix the semi-fluorinated modified absorbent and the coating according to a certain proportion, and then add 8-10 parts of a curing agent to obtain an absorbing coating.

[0025] Further preferably, the mass ratio of the semi-fluorinated modified absorbent to the coating is 0.75-1.5:1.25-2.5.

[0026] Radar-absorbing coatings are easy to apply and well-suited for a variety of working conditions. A skilled artisan can prepare a coating with a total thickness of 0.3-1.5 mm by spraying it in successive layers. After each layer is applied, the coating is allowed to dry at room temperature before spraying the next layer. Once the desired total thickness is reached, the coating is then baked at an appropriate temperature (e.g., 60°C) until fully cured.

[0027] Epoxy resin has good mechanical properties and weather resistance and is widely used in the field of coatings. In the present invention, the type of epoxy resin is diverse, and those skilled in the art can select the appropriate type of epoxy resin according to actual conditions and needs. For example, in the present invention, the optional types of epoxy resin include bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin, bisphenol H epoxy resin, novolac epoxy resin, multifunctional glycidyl ether epoxy resin, multifunctional glycidyl amine epoxy resin, and one or more halogenated epoxy resins.

[0028] The solvent ratio determines the drying speed of the coating and affects its appearance, mechanical properties, and other aspects. Therefore, the solvent ratio in the present invention is an optimized ratio determined through research. Accordingly, based on the properties of the specific epoxy resin, those skilled in the art can select an appropriate coating organic solvent, such as one or more of n-butanol, toluene, xylene, acetone, and the like.

[0029] Similar to conventional epoxy resin coating formulations in the art, the type of curing agent can be selected as needed. According to the above scheme, the curing agent can be selected from one or more of aliphatic amine / modified aliphatic amine curing agents, alicyclic amine / modified alicyclic amine curing agents, low molecular weight polyamide curing agents, aromatic amine / modified aromatic amine curing agents, phenalkamine curing agents, acid anhydride curing agents, imidazole curing agents, and thiol curing agents to achieve the desired curing effect.

[0030] Based on the above technical solutions, the design concept and principle of the present invention are as follows:

[0031] The interface modification method of the present invention first uses a strong oxidant to activate the surface of the flaky magnetic metal powder. Sodium hydroxide and ammonium persulfate are dissolved in water and ionized to produce hydroxide ions (OH - ) and persulfate ions (S2O8 2- ) etc. Persulfate ions are highly oxidizing and can oxidize some of the metal atoms on the surface of the flaky magnetic metal micropowder, forming metal oxides or hydroxides. This increases the number of surface active sites, such as hydroxyl groups (-OH). This provides a reaction base for the subsequent grafting of the fluorosilane coupling agent. Because hydroxyl groups can participate in chemical reactions with fluorosilanes, forming chemical bonds and other interactions, fluorosilanes can be more effectively grafted onto the absorbent surface. Adjusting various parameters in this activation step plays a significant role in enhancing the semi-fluorinated modification. These factors are primarily the ratio of sodium hydroxide and ammonium persulfate used, and the activation reaction time. If the sodium hydroxide and ammonium persulfate used are too low or the reaction time is too short, the surface of the flaky magnetic metal micropowder may not be fully oxidized, resulting in insufficient surface active sites, impairing the grafting effect of the fluorosilane, and preventing the absorbent from achieving the ideal semi-fluorinated and activated state. On the contrary, if the dosage is too high or the reaction time is too long, the flaky magnetic metal powder may be over-oxidized, which means that the magnetic powder is over-oxidized and the magnetic properties are reduced, which will affect the overall absorption performance of the absorbing coating. Only by setting appropriate activation parameters can the appropriate activation effect be achieved for the subsequent semi-fluorination modification.

[0032] During the modification step, the activated flaky magnetic metal micropowder absorbent undergoes a semi-fluorination treatment. Semi-fluorination refers to the process of grafting a moderate amount of fluorosilane onto the surface of the flaky magnetic metal micropowder absorbent through a specific process, creating a unique surface state. Physically, the water droplet contact angle is within a certain range (e.g., 60°-90°), indicating a certain degree of hydrophobicity, but not complete hydrophobicity. This is because the introduction of some fluorine atoms changes the surface energy, lowering the powder's surface energy, improving powder fluidity, and reducing clustering in the resin. Chemically, the absorbent retains some active hydroxyl sites on its surface, a key difference from fluorine-free and traditional perfluorinated modifications.

[0033] Taking into account the application scenarios of the absorbent of the present invention, the advantages of semi-fluorine modification are mainly reflected in the following aspects. Compared with fluorine-free modification, the absorbent surface lacks fluorine atom modification during fluorine-free modification, the surface energy is higher, and it is easy to agglomerate in the resin, resulting in poor flexibility of the coating. Semi-fluorine modification reduces the surface energy and improves the dispersibility of the powder. At the same time, the retained hydroxyl groups can be cross-linked with the resin, thereby enhancing the flexibility of the coating, and the adhesion does not show a significant decrease. Compared with perfluorinated modification, perfluorinated modification consumes a large amount of surface hydroxyl groups. Although it can greatly reduce the surface energy, it lacks active sites for cross-linking with the resin and cannot effectively form a strong cross-linked structure, which reduces the adhesion of the coating and cannot achieve a balance between absorbing performance and mechanical properties. Ultimately, semi-fluorine modification achieves a balance between reducing surface energy and retaining active sites by precisely controlling the amount of fluorosilane grafting on the surface of the activated magnetic powder. Based on this, when preparing the absorbing coating, the flaky absorber can be evenly dispersed and arranged flat in the resin, reducing agglomeration, thereby improving the flexibility of the coating while ensuring the stability of adhesion and absorbing performance.

[0034] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0035] The present invention provides an interface modification method for enhancing the mechanical properties of absorbing coatings. The method has the advantage of simple process. The method can greatly improve the dispersibility of powder in resin, realize the flat arrangement of flaky absorbers during use, avoid the formation of large cluster structures of flaky absorbers, and take into account the flexibility, adhesion and stable absorbing performance of the coating.

[0036] The present invention provides a semi-fluorinated modified absorbent, which is precisely modified and takes both powder fluidity and activity state into consideration.

[0037] The present invention provides a radar-absorbing coating with excellent flexibility, strong coating adhesion, stable radar-absorbing performance and good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Infrared spectra (IR) of the semi-fluorinated modified absorbent or flaky magnetic metal powder absorbent prepared in Example 1 and Comparative Examples 1-3;

[0039] Figure 2 The contact angles (a) and surface energy calculation results (b) of the semi-fluorinated modified absorbent or flaky magnetic metal powder absorbent prepared in Example 1 and Comparative Examples 1-3 with water and diiodomethane;

[0040] Figure 3 This is a scanning electron microscope (SEM) image of the cross section of the radar absorbing coating prepared in Example 1. DETAILED DESCRIPTION

[0041] The present invention is further illustrated by way of examples below, but the present invention is not limited to the scope of the examples. Experimental methods in the following examples where specific conditions are not specified were performed according to conventional methods and conditions, or selected according to the product specifications.

[0042] Example 1

[0043] In this embodiment, the preparation method of the semi-fluorinated modified absorbent is as follows:

[0044] (1) By weight, 3 parts of sodium hydroxide and 2 parts of ammonium persulfate were added to 80 parts of deionized water and stirred for 10 minutes to form an activation treatment solution; then 4 parts of flaky iron, silicon, aluminum and chromium powder were added to the activation treatment solution and mechanically stirred for 10 minutes for surface treatment; after filtration, the mixture was dried in an oven at 60°C for 120 minutes to obtain a flaky magnetic metal micropowder absorbent;

[0045] (2) 70 parts of deionized water and 0.2 parts of tridecafluorooctyl triethoxysilane were added to 25 parts of anhydrous ethanol and stirred for 30 minutes to obtain a modified treatment liquid; then 6 parts of flaky magnetic metal micropowder absorbent was added to the modified treatment liquid, mechanically stirred for 180 minutes, filtered, and dried in an oven at 60 °C for 120 minutes to obtain a semi-fluorinated modified absorbent.

[0046] The preparation and construction of the coating were completed using a semi-fluorinated modified absorbent as the electromagnetic wave adsorption material in the coating. The corresponding steps are as follows:

[0047] S1. Add 15 parts of epoxy resin to 60 parts of solvent by weight, and stir and disperse at a speed of 1000 r / min for 45 minutes to form a coating;

[0048] S2. The semi-fluorinated modified absorbent and the coating are uniformly mixed in a mass ratio of 2:1, and 8 parts of a curing agent (composed of 15 wt.% of a flexible curing agent polyetheramine and 85 wt.% of a polyether-type polythiol) are added and stirred to obtain an absorbing coating;

[0049] The absorbing coating is prepared by spraying in batches with a total thickness of 0.3-1.5 mm. After each spraying, the surface is dried at room temperature for 30 minutes, and then the next layer is sprayed. After reaching the required total thickness, it is baked at 60°C for 10-24 hours until the coating is completely cured to obtain the absorbing coating.

[0050] Example 2

[0051] In this embodiment, the preparation method of the semi-fluorinated modified absorbent is as follows:

[0052] (1) By weight, 2 parts of sodium hydroxide and 1 part of ammonium persulfate were added to 80 parts of deionized water and stirred for 10 minutes to form an activation treatment solution; then 4 parts of flaky iron, silicon, aluminum and chromium powder were added to the activation treatment solution and mechanically stirred for 20 minutes for surface treatment; after filtration, the mixture was dried in an oven at 60°C for 120 minutes to obtain a flaky magnetic metal micropowder absorbent;

[0053] (2) 70 parts of deionized water and 0.4 parts of tridecafluorooctyl triethoxysilane were added to 25 parts of anhydrous ethanol and stirred for 30 minutes to obtain a modified treatment liquid; then 6 parts of flaky magnetic metal micropowder absorbent was added to the modified treatment liquid, mechanically stirred for 160 minutes, filtered, and dried in an oven at 60 °C for 120 minutes to obtain a semi-fluorinated modified absorbent.

[0054] The semi-fluorinated modified absorbent was used as the microwave absorbing component in the coating to complete the preparation and construction of the coating. The corresponding steps are as follows:

[0055] S1. Add 15 parts of epoxy resin to 60 parts of solvent by weight, and stir and disperse at a speed of 1000 r / min for 45 minutes to form a coating;

[0056] S2. The semi-fluorinated modified absorbent and the coating are uniformly mixed in a mass ratio of 2:1, and 8 parts of a curing agent (composed of 15 wt.% of a flexible curing agent polyetheramine and 85 wt.% of a polyether-type polythiol) are added and stirred to obtain an absorbing coating;

[0057] The absorbing coating is prepared by spraying in batches with a total thickness of 0.3-1.5 mm. After each spraying, the surface is dried at room temperature for 30 minutes, and then the next layer is sprayed. After reaching the required total thickness, it is baked at 60°C for 10-24 hours until the coating is completely cured to obtain the absorbing coating.

[0058] Example 3

[0059] In this embodiment, the preparation method of the semi-fluorinated modified absorbent is as follows:

[0060] (1) By weight, 3 parts of sodium hydroxide and 2 parts of ammonium persulfate were added to 80 parts of deionized water and stirred for 10 minutes to form an activation treatment solution; then 4 parts of flaky iron, silicon, aluminum and chromium powder were added to the activation treatment solution and mechanically stirred for 20 minutes for surface treatment; after filtration, the mixture was dried in an oven at 60°C for 120 minutes to obtain a flaky magnetic metal micropowder absorbent;

[0061] (2) 70 parts of deionized water and 0.1 parts of tridecafluorooctyl triethoxysilane were added to 25 parts of anhydrous ethanol and stirred for 30 minutes to obtain a modified treatment liquid; then 6 parts of flaky magnetic metal micropowder absorbent was added to the modified treatment liquid, mechanically stirred for 200 minutes, filtered, and dried in an oven at 60 °C for 120 minutes to obtain a semi-fluorinated modified absorbent.

[0062] The semi-fluorinated modified absorbent was used as the microwave absorbing component in the coating to complete the preparation and construction of the coating. The corresponding steps are as follows:

[0063] S1. Add 15 parts of epoxy resin to 60 parts of solvent by weight, and stir and disperse at a speed of 1000 r / min for 45 minutes to form a coating;

[0064] S2. The semi-fluorinated modified absorbent and the coating are uniformly mixed in a mass ratio of 2:1, and 8 parts of a curing agent (composed of 15 wt.% of a flexible curing agent polyetheramine and 85 wt.% of a polyether-type polythiol) are added and stirred to obtain an absorbing coating;

[0065] The absorbing coating is prepared by spraying in batches with a total thickness of 0.3-1.5 mm. After each spraying, the surface is dried at room temperature for 30 minutes, and then the next layer is sprayed. After reaching the required total thickness, it is baked at 60°C for 10-24 hours until the coating is completely cured to obtain the absorbing coating.

[0066] Comparative Example 1

[0067] This comparative example 1 is basically the same as Example 1, except that only the surface of the absorbent is activated. The specific preparation method is as follows:

[0068] 3 parts by weight of sodium hydroxide and 2 parts of ammonium persulfate were added to 80 parts of deionized water and stirred for 10 minutes to form an activation treatment solution. 4 parts of flaky sendusticaluminum chromium powder was then added to the activation treatment solution and mechanically stirred for 10 minutes for surface treatment. After filtration, the mixture was dried in a 60°C oven for 120 minutes to obtain a flaky magnetic metal micropowder absorbent.

[0069] The flaky magnetic metal powder absorbent of this comparative example is used as the wave absorbing component in the coating. The preparation and construction of the coating are the same as those in Example 1. The steps are as follows:

[0070] S1. Add 15 parts of epoxy resin to 60 parts of solvent by weight, and stir and disperse at a speed of 1000 r / min for 45 minutes to form a coating;

[0071] S2. The flaky magnetic metal powder absorber and the coating are uniformly mixed in a mass ratio of 2:1, and 8 parts of a curing agent (composed of 15 wt.% of a flexible curing agent polyetheramine and 85 wt.% of a polyether-type polythiol) are added and stirred to obtain an absorbing coating;

[0072] The absorbing coating is prepared by spraying in batches with a total thickness of 0.3-1.5 mm. After each spraying, the surface is dried at room temperature for 30 minutes, and then the next layer is sprayed. After reaching the required total thickness, it is baked at 60°C for 10-24 hours until the coating is completely cured to obtain the absorbing coating.

[0073] Comparative Example 2

[0074] This comparative example 1 is basically the same as Example 1, except that the surface of the absorbent is grafted with fluorosilane without activation. The specific preparation method is as follows:

[0075] 70 parts of deionized water and 0.2 parts of tridecafluorooctyltriethoxysilane were added to 25 parts of anhydrous ethanol and stirred for 30 minutes to obtain a modified treatment liquid. Then, 6 parts of flaky iron silicon aluminum chromium powder were added to the modified treatment liquid, mechanically stirred for 180 minutes, filtered, and dried in a 60°C oven for 120 minutes to obtain a semi-fluorinated modified absorbent.

[0076] The semi-fluorinated modified absorbent of this comparative example is used as the wave absorbing component in the coating. The preparation and construction of the coating are the same as those in Example 1. The steps are as follows:

[0077] S1. Add 15 parts of epoxy resin to 60 parts of solvent by weight, and stir and disperse at a speed of 1000 r / min for 45 minutes to form a coating;

[0078] S2. The flaky magnetic metal powder absorber and the coating are uniformly mixed in a mass ratio of 2:1, and 8 parts of a curing agent (composed of 15 wt.% of a flexible curing agent polyetheramine and 85 wt.% of a polyether-type polythiol) are added and stirred to obtain an absorbing coating;

[0079] The absorbing coating is prepared by spraying in batches with a total thickness of 0.3-1.5 mm. After each spraying, the surface is dried at room temperature for 30 minutes, and then the next layer is sprayed. After reaching the required total thickness, it is baked at 60°C for 10-24 hours until the coating is completely cured to obtain the absorbing coating.

[0080] Comparative Example 3

[0081] This comparative example 1 is basically the same as Example 1, except that the surface of the absorbent is treated with excessive fluorosilane. The specific preparation method is as follows:

[0082] (1) By weight, 3 parts of sodium hydroxide and 2 parts of ammonium persulfate were added to 80 parts of deionized water and stirred for 10 minutes to form an activation treatment solution; then 4 parts of flaky iron, silicon, aluminum and chromium powder were added to the activation treatment solution and mechanically stirred for 10 minutes for surface treatment; after filtration, the mixture was dried in an oven at 60°C for 120 minutes to obtain a flaky magnetic metal micropowder absorbent;

[0083] (2) 70 parts of deionized water and 0.6 parts of tridecafluorooctyl triethoxysilane were added to 25 parts of anhydrous ethanol and stirred for 30 minutes to obtain a modified treatment liquid; then 6 parts of flaky magnetic metal micropowder absorbent was added to the modified treatment liquid, mechanically stirred for 180 minutes, filtered and dried in an oven at 60 °C for 120 minutes to obtain a semi-fluorinated modified absorbent.

[0084] The semi-fluorinated modified absorbent of this comparative example is used as the wave absorbing component in the coating. The preparation and construction of the coating are the same as those in Example 1. The steps are as follows:

[0085] S1. Add 15 parts of epoxy resin to 60 parts of solvent by weight, and stir and disperse at a speed of 1000 r / min for 45 minutes to form a coating;

[0086] S2. The semi-fluorinated modified absorbent and the coating are uniformly mixed in a mass ratio of 2:1, and 8 parts of a curing agent (composed of 15 wt.% of a flexible curing agent polyetheramine and 85 wt.% of a polyether-type polythiol) are added and stirred to obtain an absorbing coating;

[0087] The absorbing coating is prepared by spraying in batches with a total thickness of 0.3-1.5 mm. After each spraying, the surface is dried at room temperature for 30 minutes, and then the next layer is sprayed. After reaching the required total thickness, it is baked at 60°C for 10-24 hours until the coating is completely cured to obtain the absorbing coating.

[0088] Test Example 1

[0089] In this test example, IR was used to characterize the semi-fluorinated modified absorbent or flaky magnetic metal powder absorbent prepared in Example 1 and Comparative Examples 1-3. The results are as follows: Figure 1 shown.

[0090] Depend on Figure 1 It can be seen that the activated absorbent powder is at 3426 cm -1 The results show a strong hydroxyl resonance peak, while no obvious CF absorption peak is observed when the surface of the flake absorber is directly modified with fluorosilane, indicating that the activation step plays an important role in controlling the degree of fluorination of the powder (Comparative Example 2). However, after excessive fluorination, the intensity of the hydroxyl peak of the flake absorber gradually weakens, while the CF peak gradually strengthens, which is not conducive to improving the material performance.

[0091] Test Example 2

[0092] This test example tests the contact angles of the semi-fluorinated modified absorbent or the flaky magnetic metal powder absorbent prepared in Example 1 and Comparative Examples 1-3 with water and diiodomethane, and calculates the corresponding surface energies; the results are as follows: Figure 2 As shown in (a) and (b).

[0093] Figure 2 (a) and (b) show the contact angle and surface energy changes of the aforementioned powders. It can be seen that when the powder is unactivated, the fluorosilane cannot be effectively grafted onto the surface of the flake absorbent, resulting in a small contact angle with water and a minimal reduction in surface energy. However, excessive fluorination significantly consumes surface hydroxyl groups, lowering the surface energy. Therefore, it is impossible to obtain a semi-fluorinated, activated modified absorbent powder.

[0094] Test Example 3

[0095] In this test example, SEM was used to observe the microstructure of the absorbing coating prepared in Example 1. The results are as follows: Figure 3 shown.

[0096] Figure 3 A microscopic cross-sectional scan of the coating in Example 1 shows the uniform dispersion and flat orientation of the absorber within the coating, without the formation of large powder clusters. The present invention aims to improve the mechanical and absorbing properties of the absorbing coating. The uniform dispersion of the absorber helps reduce stress concentration points, thereby enhancing the coating's mechanical properties, such as flexibility and adhesion. Furthermore, a well-dispersed state also helps the absorber fully exert its absorbing properties, ensuring stable absorbing performance.

[0097] Test Example 4

[0098] This example tested the performance parameters of the absorbing coatings prepared in Example 1 and Comparative Examples 1-3, including mass, density, coating thickness, elongation at break, flexibility, adhesion, and absorbing performance. Mass was measured using a balance, with the result rounded to one decimal place; density was tested using the displacement method; coating thickness was tested according to the method specified in GB / T 13452.2-2008; elongation at break was tested according to the method specified in GB / T 528-2009; flexibility was measured using the method specified in GB / T 1731-2020; adhesion was tested using the method specified in GB / T 5210-2006; and absorbing performance was tested according to the procedures specified in SJ20512-1995. Coaxial method was used to measure and calculate the coating's electromagnetic parameters. The specific performance parameters tested are shown in Table 1.

[0099] Table 1: Test results of performance parameters of absorbing coating

[0100]

[0101] Based on the test results in Table 1, it can be seen that under the same conditions, the absorbing coating material prepared in Example 1 by using a semi-fluorinated and activated modified flaky absorber has significantly higher flexibility than that of the other comparative examples, and its adhesion and absorbing properties can be maintained stable. The absorbing coating material prepared using this method has both excellent mechanical properties and absorbing properties, and is suitable for large-scale promotion and application.

[0102] In summary, the present invention realizes precise modification of the absorbent surface by using a strong oxidant to activate the hydroxyl groups on the surface of the magnetic metal micropowder and effectively grafting a fluorosilane coupling agent. By regulating the grafting amount of fluorosilane, the degree of fluorination of the absorbent powder can be accurately controlled so that its surface reaches semi-fluorinated and remains in an activated state. This modification strategy not only significantly reduces the surface energy of the powder, improves the fluidity of the powder, and effectively reduces the clustering phenomenon of the powder in the resin matrix, but also retains the hydroxyl groups on the surface of the absorbent as active sites to form a strong cross-linked structure with the resin. Therefore, the present invention greatly improves the flexibility of the absorbing coating while ensuring the basic stability of the adhesion of the coating and the absorbing performance, providing an innovative solution to the current problem of balancing the mechanical properties and absorbing performance of the absorbing coating, showing great application potential and value.

[0103] The above describes in detail the preferred embodiments of the present invention. It should be understood that those skilled in the art can make numerous modifications and variations based on the concepts of the present invention without inventive effort. Therefore, any technical solutions that can be derived by those skilled in the art through logical analysis, reasoning, or limited experimentation based on the concepts of the present invention and the prior art should be within the scope of protection defined by the claims.

Claims

1. An interface modification method for enhancing the mechanical properties of an absorbing coating, characterized in that: A semi-fluorinated modified absorbent is used as the absorbing functional component of the absorbing coating; and the preparation method of the semi-fluorinated modified absorbent comprises the following steps: (1) Mixing 2-5 parts of sodium hydroxide, 1-3 parts of ammonium persulfate and 70-100 parts of water in parts by weight to form an activation treatment solution; adding 3-8 parts of flaky magnetic metal micropowder to the activation treatment solution for surface treatment, and recovering the product after completion to obtain a flaky magnetic metal micropowder absorbent; (2) Adding 0.1-0.5 parts of fluorosilane coupling agent to a mixed solvent formed by 60-90 parts of water and 20-30 parts of ethanol to obtain a modified treatment liquid; adding 4-8 parts of flaky magnetic metal micropowder absorbent to the modified treatment liquid for treatment, and recovering the product after completion to obtain a semi-fluorinated modified absorbent.

2. The interface modification method for enhancing the mechanical properties of an absorbing coating according to claim 1, wherein: In (1), the component types of the flaky magnetic metal powder include at least one of carbonyl iron powder, sendust powder, sendust chromium powder, and sendust chromium powder; the flake diameter of the flaky magnetic metal powder is in the range of 10-120 μm, and the ratio of flake thickness to flake diameter is in the range of 1:5-60.

3. The interface modification method for enhancing the mechanical properties of an absorbing coating according to claim 1, wherein: In the above (1), the surface treatment method is as follows: treatment at room temperature for 10-30 min under stirring conditions.

4. The interface modification method for enhancing the mechanical properties of an absorbing coating according to claim 1, characterized in that: In (2), the fluorosilane coupling agent includes at least one of tridecafluorooctyltriethoxysilane, trifluoropropyltriethoxysilane, dodecafluoroheptylpropyltrimethoxysilane, and heptadecafluorodecyltriethoxysilane.

5. The interface modification method for enhancing the mechanical properties of an absorbing coating according to claim 1, wherein: In the above (2), the treatment method is as follows: treatment at room temperature for 150-200 min under stirring conditions.

6. The interface modification method for enhancing the mechanical properties of an absorbing coating according to claim 1, wherein: In (1) or (2), the method for recovering the product includes filtering and collecting the filter cake, and drying; the drying temperature is 45-60°C and the drying time is 1-2 hours.

7. The interface modification method for enhancing the mechanical properties of an absorbing coating according to claim 1, characterized in that: In (2), the contact angle parameters of the semi-fluorinated modified absorbent and the liquid are as follows: when the liquid is water, the contact angle of water and the semi-fluorinated modified absorbent is 60°-90°; when the liquid is diiodomethane, the contact angle of diiodomethane and the semi-fluorinated modified absorbent is 20°-40°.

8. A semi-fluorinated modified absorbent, characterized in that: The method according to any one of claims 1 to 7 is used for the preparation.

9. A radar absorbing coating, characterized in that: The semi-fluorinated modified absorbent as claimed in claim 8 is used as the absorbing functional component of the absorbing coating.

10. The radar absorbing coating according to claim 9, characterized in that: The preparation method of the radar absorbing coating comprises the following steps: S1. Mix 15-25 parts of epoxy resin with 60-80 parts of solvent by weight to form a coating; S2. Mix the semi-fluorinated modified absorbent and the coating in a mass ratio of 0.75-1.5:1.25-2.5, and then add 8-10 parts of a curing agent to obtain an absorbing coating.

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