A stealth wave-absorbing coating for marine engineering and its preparation method

Abstract

This invention discloses a stealthy microwave absorbing coating for marine engineering and its preparation method, belonging to the field of microwave absorbing coating technology. By weight, it comprises 40-60 parts of polysiloxane resin, 15-30 parts of conductive acrylic resin, 0.2-0.4 parts of benzoin, 30-45 parts of microwave absorbing filler, 1-1.5 parts of leveling agent, 0.5-1 part of dispersant, 45-65 parts of solvent, and 15-40 parts of aliphatic diisocyanate curing agent. The microwave absorbing filler has a wider effective absorption bandwidth and better absorption effect in the 2-18GHz range. The needle-shaped nano-zinc oxide, as a matrix, not only enhances the absorption effect of the microwave absorbing filler but also provides support, preventing the collapse of the filler particles. When applied to coatings, its slip properties can disperse coating stress, improve the coating's impact resistance, reduce crack formation, and help extend the coating's lifespan.

Description

Technical Field

[0001] This invention belongs to the field of wave-absorbing coating technology, specifically relating to a stealth wave-absorbing coating for marine engineering and its preparation method. Background Technology

[0002] Radar is a system that uses radio waves to detect and determine the distance, angle, and radial velocity of objects. It is a commonly used device in fields such as air and ground traffic control, autonomous driving, weather warning, and geological exploration. With technological advancements, human exploration of the ocean has deepened, and marine engineering has expanded towards marine resource utilization, deep-sea resource development, and marine ecological protection. Some equipment in marine engineering can interfere with radar operation. For example, the towers of offshore wind turbines can interfere with the transmission and reception directions of sea-skimming radar, preventing the radar from fully detecting targets and affecting the detection and tracking of marine targets.

[0003] Offshore facilities typically require anti-corrosion coatings. To reduce electromagnetic interference, radar-absorbing materials are usually added to the coatings to improve the facility's stealth and radar absorption performance. Radar-absorbing materials are classified according to their absorption mechanism into dielectric loss type, magnetic loss type, and composite type. Dielectric loss type materials include carbon nanotubes, carbon fibers, zinc oxide, and graphene, while magnetic loss type materials include ferrites and magnetic metal powders. In practical applications, composite radar-absorbing materials are generally used to leverage the synergistic effect of multiple materials in terms of loss.

[0004] To achieve better wave absorption, the amount of wave-absorbing material added to the coating can be as high as 50%, but this can also lead to excessively high coating hardness. This means that the coating becomes more brittle and less tough, making it more prone to cracking and peeling. This problem is especially prominent in high-temperature and high-humidity marine environments, increasing facility maintenance costs. Summary of the Invention

[0005] One objective of this invention is to provide a stealth wave-absorbing coating for marine engineering, which avoids excessive coating hardness through improved wave-absorbing filler; another objective is to provide a method for preparing the stealth wave-absorbing coating for marine engineering.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A stealth wave-absorbing coating for marine engineering, comprising the following raw materials by weight:

[0008] 40-60 parts polysiloxane resin, 15-30 parts conductive acrylic resin, 0.2-0.4 parts benzoin, 30-45 parts microwave absorbing filler, 1-1.5 parts leveling agent, 0.5-1 part dispersant, 45-65 parts solvent, and 15-40 parts aliphatic diisocyanate curing agent.

[0009] Furthermore, the solvent is one or more of toluene, xylene, and dichloromethane mixed in any proportion.

[0010] Furthermore, the conductive acrylic resin is prepared through the following steps:

[0011] Graphene and xylene are added to the reactor and stirred and dispersed at 300-500 r / min for 5-10 min. Then, acrylate monomer and 2,2′-azobisisobutyronitrile as an initiator are added to the reactor at a uniform rate over 2-3 h. The mixture is refluxed for 2-3 h, xylene is removed by vacuum distillation, and the mixture is cooled to obtain conductive acrylic resin.

[0012] Furthermore, the mass ratio of graphene, xylene, acrylate monomer, and 2,2′-azobisisobutyronitrile is 5:10-12:10:0.2-0.3.

[0013] Furthermore, the acrylate monomers are at least two of methyl acrylate, ethyl acrylate, propyl acrylate, methyl methacrylate, ethyl methacrylate and propyl methacrylate mixed in any proportion.

[0014] Furthermore, the microwave absorbing filler is prepared through the following steps:

[0015] Step 1: Add four needle-shaped nano zinc oxide and deionized water to the reaction vessel and sonicate for 10-15 min. Adjust the pH value to 8.5 with Tris buffer solution with a molar concentration of 10 mmol / L. Then add cobalt chloride, nickel chloride and dopamine hydrochloride to the reaction vessel. Stir and react for 24 h under the conditions of oxygen introduction and 20-25℃. Filter and wash the filter cake 3-5 times with anhydrous ethanol. Vacuum dry at 60-80℃ to obtain polymer-coated zinc oxide particles.

[0016] Step 2: Dissolve γ-benzyl-L-glutamic acid-N-carboxylic anhydride in dimethyl sulfoxide and transfer it to a reaction vessel. Under nitrogen protection at 20-25℃, add polymer-coated zinc oxide particles and ammonium persulfate to the reaction vessel and stir at 200-300 r / min for 45-50 h. Mix the reaction product with 5 times the volume of 17.5% sodium hydroxide solution for 20-30 min, filter, wash the filter cake with deionized water 3-5 times, vacuum dry to obtain a powdered composite precursor, and transfer it to a tube furnace. Under nitrogen protection, heat the furnace to 900℃ at a rate of 5℃ / min and hold for pyrolysis for 2.5 h to obtain the microwave absorbing filler.

[0017] Furthermore, the dosage of the four needle-shaped nano zinc oxide, deionized water, cobalt chloride, nickel chloride and dopamine hydrochloride is 1.5g: 100-120mL: 1.36g: 1.36g: 2g.

[0018] Furthermore, the ratio of γ-benzyl-L-glutamic acid-N-carboxylic anhydride, dimethyl sulfoxide, polymer-coated zinc oxide particles, and ammonium persulfate is 10g:200-220mL:2.5g:0.05-0.1g.

[0019] Furthermore, γ-benzyl-L-glutamic acid-N-carboxylic anhydride is prepared by the following steps:

[0020] L-glutamic acid-α-benzyl ester and tetrahydrofuran were added to a reaction vessel and stirred for 5-10 min at 200-300 r / min under nitrogen protection. Then, di(trichloromethyl) carbonate was added to the reaction vessel, the temperature was raised to 55-60℃ and stirring was continued for 3.5-4 h. After natural cooling, the mixture was distilled under reduced pressure. The remaining reaction solution was mixed with 10 times its volume of n-hexane and stirred for 10-15 min. After the precipitate was formed, it was filtered. The filter cake was dried under vacuum at 40-60℃ to obtain γ-benzyl-L-glutamic acid-N-carboxylic anhydride.

[0021] Furthermore, the ratio of L-glutamic acid-α-benzyl ester, tetrahydrofuran, and di(trichloromethyl) carbonate is 10-12.5g: 80-100mL: 6.5-8.2g.

[0022] A method for preparing a stealthy radar-absorbing coating for marine engineering includes the following steps:

[0023] Polysiloxane resin, conductive acrylate resin and solvent are mixed evenly to obtain a resin solution; the resin solution, benzoin, microwave absorbing filler, leveling agent and dispersant are added to a coating dispersion tank, stirred at 250-300 r / min for 5-10 min, stirred at 400-500 r / min for 10-15 min, stirred at 800-900 r / min for 10-20 min, and then aliphatic diisocyanate curing agent is added and stirred for 4-6 min to obtain a stealthy microwave absorbing coating for marine engineering.

[0024] The beneficial effects of this invention are:

[0025] (1) The raw materials of the stealth wave-absorbing coating for marine engineering of the present invention contain polysiloxane resin and conductive acrylic resin. The two resins can be cured to form an interpenetrating network after being combined, which helps to improve the water resistance, corrosion resistance and weather resistance of the coating and meet the requirements of marine environment.

[0026] (2) Conductive acrylic resin is polymerized by acrylate monomers. Graphene is added when the viscosity of the system is low before the reaction, which helps to disperse the graphene evenly and improve the electromagnetic shielding performance of the coating. Graphene helps to improve the thermal conductivity of the coating, prevent stress caused by temperature changes, and improve the weather resistance of the coating.

[0027] (3) The microwave absorbing filler of this invention uses tetraneedle-shaped nano-zinc oxide as a group. Under alkaline conditions, it generates viscous polydopamine through dopamine polymerization. The polydopamine coats the tetraneedle-shaped nano-zinc oxide to form polymer-coated zinc oxide particles. After ring opening, γ-benzyl-L-glutamic acid-N-carboxylic anhydride reacts with polydopamine to form a polymer with a fluffy surface. The polar amino or hydroxyl groups contained in this polymer adsorb nickel and cobalt ions. After carbonization, it forms a microwave absorbing filler with a large specific surface area and loaded with nickel and cobalt bimetals. This microwave absorbing filler has a larger effective absorption bandwidth and better absorption effect in the 2-18GHz range. The tetraneedle-shaped nano-zinc oxide, as a matrix, can not only improve the absorption effect of the microwave absorbing filler, but also play a supporting role to prevent the collapse of the microwave absorbing filler particles. When applied to coatings, its slip properties can be used to disperse coating stress, improve the impact resistance of the coating, reduce crack generation, help improve the coating life, and reduce facility maintenance costs. Detailed Implementation

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1: This example provides a stealthy wave-absorbing coating for marine engineering, prepared by the following method:

[0030] Step 1: Add 10 kg of L-glutamic acid-α-benzyl ester and 80 L of tetrahydrofuran to the reactor, stir for 5 min at 200 r / min under nitrogen protection, then add 6.5 kg of di(trichloromethyl) carbonate to the reactor, heat to 55 °C and continue stirring for 3.5 h, cool naturally, distill under reduced pressure, mix the remaining reaction solution with 10 times the volume of n-hexane and stir for 10 min, filter after precipitation, and dry the filter cake under vacuum at 40 °C to obtain γ-benzyl-L-glutamic acid-N-carboxylic anhydride.

[0031] Step 2: Add 15 kg of four-needle-shaped nano zinc oxide and 1000 L of deionized water to the reaction vessel and sonicate for 10 min. Adjust the pH value to 8.5 with Tris buffer solution with a molar concentration of 10 mmol / L. Then add 13.6 kg of cobalt chloride, 13.6 kg of nickel chloride and 20 kg of dopamine hydrochloride to the reaction vessel. Stir and react for 24 h under the conditions of oxygen introduction and 20 °C. Filter and wash the filter cake three times with anhydrous ethanol. Dry it under vacuum at 60 °C to obtain polymer-coated zinc oxide particles.

[0032] Step 3: Dissolve 4 kg of γ-benzyl-L-glutamic acid-N-carboxylic anhydride prepared in Step 1 in 80 L of dimethyl sulfoxide and transfer it to a reaction vessel. Under nitrogen protection at 20 °C, add 1 kg of polymer-coated zinc oxide particles and 20 g of ammonium persulfate to the reaction vessel. Stir at 200 r / min for 45 h. Mix the reaction product with 5 times the volume of 17.5% sodium hydroxide solution for 20 min. Filter the mixture, wash the filter cake three times with deionized water, and vacuum dry it to obtain a powdered composite precursor. Transfer the precursor to a tube furnace and heat it to 900 °C at a rate of 5 °C / min under nitrogen protection. Hold the temperature for 2.5 h to obtain the microwave absorbing filler.

[0033] Step 4: Mix methyl acrylate and ethyl acrylate at a mass ratio of 1:2 to obtain acrylate monomers. Add 5 kg of graphene and 10 kg of xylene to the reactor and stir and disperse at 300 r / min for 5 min. Then, add 10 kg of acrylate monomers and 0.2 kg of 2,2′-azobisisobutyronitrile as an initiator to the reactor at a uniform rate over 2 h. Reflux for 2 h, remove xylene by vacuum distillation, and cool to obtain conductive acrylic resin.

[0034] Step 5: Mix 400g of polysiloxane resin, 150g of conductive acrylate resin and 450g of toluene evenly to obtain a resin solution. Then add 2g of benzoin, 300g of microwave absorbing filler, 10g of leveling agent and 5g of dispersant into a coating dispersion tank. Stir at 250r / min for 5min, 400r / min for 10min and 800r / min for 10min. Then add 150g of aliphatic diisocyanate curing agent and continue stirring for 4min to obtain a stealth microwave absorbing coating for marine engineering.

[0035] Example 2: This example provides a stealth wave-absorbing coating for marine engineering, prepared by the following method:

[0036] Step 1: Add 10.8 kg of L-glutamic acid-α-benzyl ester and 90 L of tetrahydrofuran to the reactor and stir for 8 min at 250 r / min under nitrogen protection. Then add 7.3 kg of di(trichloromethyl) carbonate to the reactor, heat to 55-60℃ and continue stirring for 3.8 h. After natural cooling, distill under reduced pressure. Mix the remaining reaction solution with 10 times the volume of n-hexane and stir for 12 min. After the precipitate is formed, filter it and dry the filter cake under vacuum at 50℃ to obtain γ-benzyl-L-glutamic acid-N-carboxylic anhydride.

[0037] Step 2: Add 15 kg of four-needle-shaped nano zinc oxide and 1100 L of deionized water to the reaction vessel and sonicate for 12 min. Adjust the pH value to 8.5 with Tris buffer solution with a molar concentration of 10 mmol / L. Then add 13.6 kg of cobalt chloride, 13.6 kg of nickel chloride and 20 kg of dopamine hydrochloride to the reaction vessel. Stir and react for 24 h under the conditions of oxygen introduction and 22 °C. Filter and wash the filter cake three times with anhydrous ethanol. Dry it under vacuum at 70 °C to obtain polymer-coated zinc oxide particles.

[0038] Step 3: Dissolve 4 kg of γ-benzyl-L-glutamic acid-N-carboxylic anhydride prepared in Step 1 in 82 L of dimethyl sulfoxide and transfer it to a reaction vessel. Under nitrogen protection at 22 °C, add 1 kg of polymer-coated zinc oxide particles and 25 g of ammonium persulfate to the reaction vessel. Stir at 250 r / min for 48 h. Mix the reaction product with 5 times the volume of 17.5% sodium hydroxide solution for 25 min. Filter the mixture, wash the filter cake three times with deionized water, and vacuum dry it to obtain a powdered composite precursor. Transfer the precursor to a tube furnace and heat it to 900 °C at a rate of 5 °C / min under nitrogen protection. Hold the temperature for 2.5 h to obtain the microwave absorbing filler.

[0039] Step 4: Methyl acrylate, propyl acrylate, and methyl methacrylate are mixed in a mass ratio of 1:1:2 to obtain acrylate monomers. 5 kg of graphene and 11 kg of xylene are added to the reactor and stirred and dispersed at 350 r / min for 8 min. Then, 10 kg of acrylate monomers and 0.25 kg of 2,2′-azobisisobutyronitrile as an initiator are added to the reactor at a uniform rate over 2.5 h. The mixture is refluxed for 2.5 h, xylene is removed by vacuum distillation, and the mixture is cooled to obtain conductive acrylic resin.

[0040] Step 5: Mix 450g of polysiloxane resin, 200g of conductive acrylate resin and 500g of xylene evenly to obtain a resin solution. Then add 2.5g of benzoin, 340g of microwave absorbing filler, 12g of leveling agent and 6.5g of dispersant into a coating dispersion tank. Stir at 250r / min for 6min, 400r / min for 12min and 800r / min for 15min. Then add 200g of aliphatic diisocyanate curing agent and continue stirring for 5min to obtain a stealth microwave absorbing coating for marine engineering.

[0041] Example 3: This example provides a stealth radar-absorbing coating for marine engineering, prepared by the following method:

[0042] Step 1: Add 11.5 kg of L-glutamic acid-α-benzyl ester and 90 L of tetrahydrofuran to the reactor and stir for 5-10 min at 250 r / min under nitrogen protection. Then add 7.4 kg of di(trichloromethyl) carbonate to the reactor, heat to 55-60℃ and continue stirring for 3.8 h. After natural cooling, distill under reduced pressure. Mix the remaining reaction solution with 10 times the volume of n-hexane and stir for 13 min. After the precipitate is formed, filter it and dry the filter cake under vacuum at 50℃ to obtain γ-benzyl-L-glutamic acid-N-carboxylic anhydride.

[0043] Step 2: Add 15 kg of four-needle-shaped nano zinc oxide and 1100 L of deionized water to the reaction vessel and sonicate for 13 min. Adjust the pH value to 8.5 with Tris buffer solution with a molar concentration of 10 mmol / L. Then add 13.6 kg of cobalt chloride, 13.6 kg of nickel chloride and 20 kg of dopamine hydrochloride to the reaction vessel. Stir and react for 24 h under the conditions of oxygen introduction and 23 °C. Filter and wash the filter cake 4 times with anhydrous ethanol. Dry under vacuum at 70 °C to obtain polymer-coated zinc oxide particles.

[0044] Step 3: Dissolve 4 kg of γ-benzyl-L-glutamic acid-N-carboxylic anhydride prepared in Step 1 in 84 L of dimethyl sulfoxide and transfer it to a reaction vessel. Under nitrogen protection at 23 °C, add 1 kg of polymer-coated zinc oxide particles and 30 g of ammonium persulfate to the reaction vessel. Stir at 250 r / min for 48 h. Mix the reaction product with 5 times the volume of 17.5% sodium hydroxide solution for 25 min. Filter the mixture and wash the filter cake 4 times with deionized water. Vacuum dry the mixture to obtain a powdered composite precursor, which is then transferred to a tube furnace. Under nitrogen protection, heat the furnace to 900 °C at a rate of 5 °C / min and hold for 2.5 h to obtain the microwave absorbing filler.

[0045] Step 4: Methyl acrylate, methyl methacrylate, and ethyl methacrylate are mixed in a mass ratio of 1:1:1 to obtain acrylate monomers. 5 kg of graphene and 11 kg of xylene are added to the reactor and stirred and dispersed at 400 r / min for 8 min. Then, 10 kg of acrylate monomers and 0.25 kg of 2,2′-azobisisobutyronitrile (2,2′-Azobisisobutyronitrile) are added to the reactor at a uniform rate over 2.5 h. The mixture is refluxed for 2.5 h, xylene is removed by vacuum distillation, and the mixture is cooled to obtain conductive acrylic resin.

[0046] Step 5: Mix 500g of polysiloxane resin, 250g of conductive acrylate resin and 550g of dichloromethane evenly to obtain a resin solution. Then add 3g of benzoin, 400g of microwave absorbing filler, 14g of leveling agent and 8g of dispersant into a coating dispersion tank. Stir at 280r / min for 8min, 450r / min for 13min and 850r / min for 15min. Then add 300g of aliphatic diisocyanate curing agent and continue stirring for 5min to obtain a stealth microwave absorbing coating for marine engineering.

[0047] Example 4: This example provides a stealth radar-absorbing coating for marine engineering, prepared by the following method:

[0048] Step 1: Add 12.5 kg of L-glutamic acid-α-benzyl ester and 100 L of tetrahydrofuran to the reactor, stir for 10 min at 300 r / min under nitrogen protection, then add 8.2 kg of di(trichloromethyl) carbonate to the reactor, heat to 60 °C and continue stirring for 4 h, cool naturally, distill under reduced pressure, mix the remaining reaction solution with 10 times the volume of n-hexane for 15 min, filter after precipitation, and dry the filter cake under vacuum at 60 °C to obtain γ-benzyl-L-glutamic acid-N-carboxylic anhydride.

[0049] Step 2: Add 15 kg of four-needle-shaped nano zinc oxide and 1200 L of deionized water to the reaction vessel and sonicate for 15 min. Adjust the pH value to 8.5 with Tris buffer solution with a molar concentration of 10 mmol / L. Then add 13.6 kg of cobalt chloride, 13.6 kg of nickel chloride and 20 kg of dopamine hydrochloride to the reaction vessel. Stir and react for 24 h under the conditions of oxygen introduction and 25 °C. Filter and wash the filter cake 5 times with anhydrous ethanol. Dry under vacuum at 80 °C to obtain polymer-coated zinc oxide particles.

[0050] Step 3: Dissolve 4 kg of γ-benzyl-L-glutamic acid-N-carboxylic anhydride prepared in Step 1 in 88 L of dimethyl sulfoxide and transfer it to a reaction vessel. Under nitrogen protection at 25 °C, add 1 kg of polymer-coated zinc oxide particles and 40 g of ammonium persulfate to the reaction vessel. Stir at 300 r / min for 50 h. Mix the reaction product with 5 times the volume of 17.5% sodium hydroxide solution for 30 min. Filter the mixture and wash the filter cake 5 times with deionized water. Vacuum dry the mixture to obtain a powdered composite precursor, which is then transferred to a tube furnace. Under nitrogen protection, heat the furnace to 900 °C at a rate of 5 °C / min and hold for pyrolysis for 2.5 h to obtain the microwave absorbing filler.

[0051] Step 4: Ethyl acrylate, ethyl methacrylate, and propyl methacrylate are mixed in a mass ratio of 2:1:1 to obtain acrylate monomers. 5 kg of graphene and 12 kg of xylene are added to the reactor and stirred and dispersed at 500 r / min for 10 min. Then, 10 kg of acrylate monomers and 0.3 kg of 2,2′-azobisisobutyronitrile as an initiator are added to the reactor at a uniform rate over 3 h. The mixture is refluxed for 3 h, xylene is removed by vacuum distillation, and the mixture is cooled to obtain conductive acrylic resin.

[0052] Step 5: Prepare a solvent by mixing toluene, xylene, and dichloromethane in a mass ratio of 2:2:1. Mix 600g of polysiloxane resin, 300g of conductive acrylate resin, and 650g of solvent evenly to obtain a resin solution. Then, add 4g of benzoin, 450g of microwave absorbing filler, 15g of leveling agent, and 10g of dispersant to a coating dispersion tank. Stir at 300r / min for 10min, 500r / min for 15min, and 900r / min for 20min. Then, add 400g of aliphatic diisocyanate curing agent and continue stirring for 6min to obtain a stealth microwave absorbing coating for marine engineering.

[0053] Comparative Example 1: Based on Example 4, the wave-absorbing filler was replaced with the same mass of four-needle nano zinc oxide, while the other steps remained unchanged, to prepare a stealth wave-absorbing coating for marine engineering.

[0054] Comparative Example 2: Based on Example 4, without undergoing the γ-benzyl-L-glutamic acid-N-carboxylic anhydride reaction treatment, the polymer-coated zinc oxide particles were directly transferred to a tube furnace. Under nitrogen protection, the temperature was increased to 900°C at a rate of 5°C / min and held for pyrolysis for 2.5 hours to obtain microwave absorbing powder. This microwave absorbing powder was used to replace the microwave absorbing filler, while the other steps remained unchanged, to prepare a stealth microwave absorbing coating for marine engineering.

[0055] Comparative Example 3: Based on Example 4, step 2 was performed without adding tetra-needle-shaped nano-zinc oxide, while the remaining steps remained unchanged, to prepare a stealth wave-absorbing coating for marine engineering.

[0056] The polysiloxane resin used in the examples and comparative examples was SH-1069 phenylmethyl silicone resin purchased from Hubei Longsheng Sihai New Material Co., Ltd.; benzoin was a commercially available industrial product; the leveling agent was BYK-306; the dispersant was BYK-163; and the aliphatic diisocyanate curing agent was purchased from Shanghai Kaiyin Chemical Co., Ltd.

[0057] Performance tests were conducted on Examples 1-4 and Comparative Examples 1-3. Different microwave absorbing coatings were applied according to different test standards to prepare corresponding samples.

[0058] Different microwave absorbing coatings were sprayed onto polyimide films and dried and cured to form a 2mm thick coating. Different annular samples with an inner diameter of 3mm and an outer diameter of 7mm were prepared using the coaxial method. The effective absorption bandwidth (reflection loss <10dB) of different annular samples in the 2-18GHz range was tested using a vector network analyzer. The adhesion of the coatings on different samples was tested according to GB / T 9286-2021, with grade 0 being the best. The impact resistance of the coatings on different samples was tested according to GB / T 1732-2020. An aging test was conducted using a Q-sunXe-1-BC xenon lamp accelerated aging test chamber according to GB / T1865-2009, consisting of 4 hours of 50℃ light irradiation and 4 hours of 40℃ water vapor circulation test, for a total test duration of 1500 hours. The appearance of the coating was observed to determine if it was intact or showed signs of cracking.

[0059] The results are shown in Table 1:

[0060] Table 1

[0061]

[0062] As shown in Table 1, compared with Comparative Example 1, the stealth absorbing coatings prepared in Examples 1-4 have a larger effective absorption bandwidth and better absorption effect in the 2-18 GHz range. In terms of mechanical properties, the coatings prepared with the stealth absorbing coatings in Examples 1-4 have better adhesion and impact resistance, no cracks appeared after aging tests, and the coating life is longer. In Comparative Example 1, the direct use of tetra-needle-shaped nano-zinc oxide reduced the toughness of the coating, making it prone to stress concentration and causing cracks. After treatment with γ-benzyl-L-glutamic acid-N-carboxylic anhydride, the composite precursor formed a fluffy surface, which, after carbonization, had a higher specific surface area and slip properties. Comparative Example 2 shows that this surface structure can increase the absorption performance of the absorbing filler and disperse stress, improving the mechanical properties of the coating. In Comparative Example 3, the absorbing filler did not contain tetra-needle-shaped nano-zinc oxide, resulting in decreased absorption performance and loss of support for the absorbing filler particles. The carbonized material collapsed, which was detrimental to improving the impact resistance of the coating.

[0063] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0064] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A stealthy wave-absorbing coating for marine engineering, characterized in that, By weight, it includes the following raw materials: 40-60 parts polysiloxane resin, 15-30 parts conductive acrylic resin, 0.2-0.4 parts benzoin, 30-45 parts microwave absorbing filler, 1-1.5 parts leveling agent, 0.5-1 part dispersant, 45-65 parts solvent, and 15-40 parts aliphatic diisocyanate curing agent; The microwave absorbing filler is prepared by the following steps: γ-Benzyl-L-glutamic acid-N-carboxylic anhydride was dissolved in dimethyl sulfoxide and transferred to a reaction vessel. Under nitrogen protection at 20-25°C, polymer-coated zinc oxide particles and ammonium persulfate were added, and the mixture was stirred at 200-300 r / min for 45-50 h. The reaction product was then mixed with 5 times its volume of 17.5 wt% sodium hydroxide solution for 20-30 min, filtered, washed, and vacuum dried to obtain a composite precursor, which was then transferred to a tube furnace. Under nitrogen protection, the temperature was increased to 900°C at 5°C / min and pyrolyzed for 2.5 h to obtain the microwave absorbing filler. The ratio of γ-benzyl-L-glutamic acid-N-carboxylic anhydride, dimethyl sulfoxide, polymer-coated zinc oxide particles, and ammonium persulfate is 10g:200-220mL:2.5g:0.05-0.1g; The γ-benzyl-L-glutamic acid-N-carboxylic anhydride is prepared by the following steps: L-glutamic acid-α-benzyl ester and tetrahydrofuran were added to a reaction vessel and stirred at 200-300 r / min under nitrogen protection for 5-10 min. Then, di(trichloromethyl) carbonate was added and stirred at 55-60℃ for 3.5-4 h. After natural cooling, the mixture was distilled under reduced pressure. The remaining reaction solution was mixed with 10 times its volume of n-hexane and stirred for 10-15 min. The mixture was then filtered and the filter cake was dried under vacuum to obtain γ-benzyl-L-glutamic acid-N-carboxylic anhydride.

2. The stealth wave-absorbing coating for marine engineering according to claim 1, characterized in that, The solvent is one or more of toluene, xylene, and dichloromethane mixed in any proportion.

3. The stealth wave-absorbing coating for marine engineering according to claim 1, characterized in that, The conductive acrylic resin is prepared by the following steps: Graphene and xylene are added to the reactor and stirred at 300-500 r / min for 5-10 min. Then, acrylate monomer and 2,2′-azobisisobutyronitrile are added to the reactor at a uniform rate over 2-3 h. The mixture is refluxed for 2-3 h. Xylene is removed by vacuum distillation and the mixture is cooled to obtain conductive acrylic resin.

4. The stealth wave-absorbing coating for marine engineering according to claim 3, characterized in that, The mass ratio of graphene, xylene, acrylate monomer and 2,2′-azobisisobutyronitrile is 5:10-12:10:0.2-0.

3.

5. The stealth wave-absorbing coating for marine engineering according to claim 3, characterized in that, The acrylate monomer is at least two of the following: methyl acrylate, ethyl acrylate, propyl acrylate, methyl methacrylate, ethyl methacrylate, and propyl methacrylate, mixed in any proportion.

6. The stealth wave-absorbing coating for marine engineering according to claim 1, characterized in that, The polymer-coated zinc oxide particles are prepared through the following steps: Four needle-shaped nano-zinc oxide and deionized water were added to a reaction vessel and ultrasonically dispersed for 10-15 min. The pH was adjusted to 8.5 with 10 mmol / L Tris buffer. Then, cobalt chloride, nickel chloride and dopamine hydrochloride were added, oxygen was introduced, and the mixture was stirred at 20-25℃ for 24 h. The mixture was then filtered, and the filter cake was washed 3-5 times with anhydrous ethanol and vacuum dried to obtain polymer-coated zinc oxide particles.

7. The stealth wave-absorbing coating for marine engineering according to claim 6, characterized in that, The dosage of the four needle-shaped nano zinc oxide, deionized water, cobalt chloride, nickel chloride and dopamine hydrochloride is 1.5g: 100-120mL: 1.36g: 1.36g: 2g.

8. The stealth wave-absorbing coating for marine engineering according to claim 7, characterized in that, The ratio of L-glutamic acid-α-benzyl ester, tetrahydrofuran and di(trichloromethyl) carbonate is 10-12.5g: 80-100mL: 6.5-8.2g.

9. The method for preparing a stealthy wave-absorbing coating for marine engineering according to claim 1, characterized in that, The steps include: Polysiloxane resin, conductive acrylate resin and solvent are mixed evenly to obtain a resin solution; the resin solution, benzoin, microwave absorbing filler, leveling agent and dispersant are added to a coating dispersion tank, stirred at 250-300 r / min for 5-10 min, stirred at 400-500 r / min for 10-15 min, stirred at 800-900 r / min for 10-20 min, and then aliphatic diisocyanate curing agent is added and stirred for 4-6 min to obtain a stealthy microwave absorbing coating for marine engineering.

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