X-band stealthy skin and method of making, use

Abstract

The application belongs to the technical field of skin materials, and particularly relates to an X-waveband stealth skin, a preparation method and application thereof. The preparation method of the X-waveband stealth skin comprises the following steps: (1) preparing a modified epoxy resin system; (2) laying a carbon fiber mixture to obtain a carbon fiber mixture film layer; (3) laying a conductive mixture on the surface of the carbon fiber mixture film layer to obtain a conductive mixture film layer; (4) laying a wave-absorbing mixture on the surface of the conductive mixture film layer to obtain a wave-absorbing mixture film layer; (5) laying a wave-transmitting mixture on the surface of the wave-absorbing mixture film layer to obtain a skin material; and (6) vacuumizing and heating and curing the skin material to obtain an X-waveband stealth lightning-proof skin. The X-waveband stealth skin has excellent stealth performance and lightning-proof capability, and has a higher mechanical performance retention rate in an ultralow-temperature environment.

Description

Technical Field

[0001] This invention belongs to the field of skin material technology, specifically relating to an X-band stealth skin, its preparation method, and its application. Background Technology

[0002] The X-band, as the primary operating frequency band for fire control radar and seekers, is the core frequency band for achieving radar stealth in aircraft. Existing aircraft skin technologies typically pursue multi-functional integration, that is, integrating multiple functions such as stealth, lightning protection, and weather resistance while ensuring structural load-bearing capacity.

[0003] For example, Chinese invention patent CN115431605A discloses an "X-band stealth / lightning protection skin and its preparation method." This technology aims to solve problems such as poor adhesion and easy detachment caused by the mismatch of physical and chemical properties between the conductive layer and the stealth coating by setting specific conductive and stealth layers. This patent represents a current direction of technological development, namely, improving the functionality and reliability of the skin by optimizing the interlayer structure and interface treatment.

[0004] However, most existing stealth skin solutions still suffer from a significant and under-emphasized technical deficiency: insufficient consideration of the mechanical performance of aircraft in extreme climatic environments, especially under ultra-low temperature conditions. Specifically, modern aircraft have an increasingly expanded mission range, requiring frequent traversal or prolonged stays in high-latitude, high-altitude, and other extreme low-temperature airspaces. In such environments, temperatures can drop to -50°C or even lower. When existing stealth skins undergo drastic temperature cycling, especially the abrupt change from room temperature to ultra-low temperatures, some resin matrices become brittle at ultra-low temperatures, resulting in decreased toughness. This causes a significant deterioration in key mechanical properties such as tensile strength and impact resistance when the skin is subjected to aerodynamic loads or vibrations, making it unable to meet the requirements for use in extreme environments.

[0005] Therefore, there is an urgent need to develop a new type of X-band stealth skin that not only has excellent stealth performance and lightning protection capabilities, but more importantly, it is necessary to solve the problem of maintaining its mechanical properties in ultra-low temperature environments. Summary of the Invention

[0006] The purpose of this invention is to provide an X-band stealth skin, its preparation method, and its application.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for preparing an X-band stealth skin includes the following steps:

[0009] (1) Tungsten zirconate powder was modified with polyvinylpyrrolidone and then mixed with epoxy resin, curing agent and accelerator to obtain a modified epoxy resin system.

[0010] (2) Mix carbon fiber and the modified epoxy resin system of step (1) to obtain carbon fiber mixture, lay carbon fiber mixture to obtain carbon fiber mixture film layer;

[0011] (3) Mix silver powder, the modified epoxy resin system of step (1) and carbon fiber to obtain a conductive mixture; lay the conductive mixture on the surface of the carbon fiber mixture film to obtain a conductive mixture film.

[0012] (4) A microwave absorbing mixture is laid on the surface of the conductive mixture film to obtain a microwave absorbing mixture film;

[0013] (5) A wave-transmitting mixture is laid on the surface of the wave-absorbing mixture film to obtain the skin material;

[0014] (6) The skin material is vacuumed and heated to solidify, thereby obtaining an X-band stealth skin.

[0015] Preferably, the preparation method of the modified epoxy resin system includes the following steps:

[0016] S1: Add tungsten zirconate powder to an ethanol aqueous solution, add polyvinylpyrrolidone, heat to 50-55℃, react for 4-6 hours, centrifuge, dry, and pulverize to obtain modified tungsten zirconate powder.

[0017] S2: Mix modified tungsten zirconate powder, epoxy resin, curing agent, and accelerator, and stir to obtain a modified epoxy resin system.

[0018] Tungsten zirconate is a material with negative thermal expansion. Through the negative thermal expansion effect, it can effectively suppress the shrinkage stress of the matrix at low temperatures. This invention modifies tungsten zirconate with polyvinylpyrrolidone and then adds it to a compounded epoxy resin. The two have a synergistic effect, which can improve the room temperature and low temperature tensile properties of the skin. At the same time, the uniformly dispersed powder after modification constructs a more optimized electromagnetic wave loss structure, which simultaneously enhances the stealth performance of the skin in the X-band. The two work together to achieve the best results. When polyvinylpyrrolidone (PVP) is added to an ethanol-water solution containing tungsten zirconate powder, PPVP molecules adhere firmly to the particle surface by forming hydrogen bonds or coordination bonds with metal ions or surface hydroxyl groups on the surface of the tungsten zirconate particles through their polar groups (carbonyl oxygen). After adsorption onto the particle surface, the long chain structure of PPVP molecules extends into the surrounding solution, forming an organic polymer coating layer on the outside of the particles. The long molecular chains of PPVP fully extend in the solvent, preventing direct contact and proximity between particles, thus effectively preventing particle aggregation in a wet state. This transforms the originally hydrophilic inorganic powder surface into a surface with better compatibility with organic systems.

[0019] In this invention, the conductive layer functions to protect against lightning strikes and discharge the instantaneous large current of lightning. Its high silver content enables low contact resistance and the formation of a continuous conductive path. The key to lightning protection is to discharge current quickly, which requires the conductive layer to have high conductivity. The high amount of silver powder added meets this core requirement.

[0020] The carbon black in the microwave absorbing mixture of this invention is uniformly dispersed in a modified epoxy resin system. The matrix system consists of a blend of three epoxy resins and modified tungsten zirconate powder. The blended epoxy resins optimize the rheological properties, and the organic coating layer on the surface of the modified tungsten zirconate has excellent compatibility with the epoxy resin. Together, they synergistically prevent carbon black agglomeration, significantly improving electrical loss efficiency compared to traditional dispersion systems. Under the influence of X-band electromagnetic waves, carbon black exhibits strong conductivity and polarization losses. The superposition of these two losses efficiently dissipates electromagnetic wave energy, eliminating the need for additional magnetic loss materials.

[0021] Preferably, the epoxy resin comprises epoxy resin A, epoxy resin B and epoxy resin C in a mass ratio of (1.3-1.5):(0.4-0.6):1.

[0022] Preferably, epoxy resin A has an epoxy equivalent of 205-225 g / eq and a viscosity of 19000-24000 cps.

[0023] Preferably, epoxy resin B has an epoxy equivalent of 184-190 g / eq and a viscosity of 12000-15000 cps.

[0024] Preferably, the epoxy resin C has an epoxy equivalent of 176-184 g / eq and a viscosity of 8000-11000 cps.

[0025] This invention employs a compound of three specific types of epoxy resins, utilizing their differences in epoxy equivalent and viscosity to construct a matrix system that combines high strength with excellent processability. This compound system not only directly enhances the tensile strength of the skin by forming a denser cross-linked network, but its optimized rheological properties also facilitate the highly uniform dispersion of functional fillers such as modified tungsten zirconate. This homogeneous and stable microstructure ensures that the skin possesses consistent and excellent electromagnetic properties, thereby significantly improving its stealth performance.

[0026] Preferably, modified tungsten zirconate powder and epoxy resin are mixed in a mass ratio of (3-4):100.

[0027] Preferably, the weight-average molecular weight of polyvinylpyrrolidone is 3500-5500.

[0028] The second aspect of the present invention provides an X-band stealth skin prepared by the above-described preparation method.

[0029] The third aspect of this invention provides the application of an X-band stealth skin prepared by the above-described method in the manufacture of aircraft.

[0030] Preferably, the aircraft is an airplane.

[0031] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0032] 1. This invention improves the low-temperature resistance of the skin by adding modified tungsten zirconate to epoxy resin. The modification of tungsten zirconate with polyvinylpyrrolidone not only enhances the low-temperature performance of the skin but also results in more uniform dispersion within the system and superior stealth properties.

[0033] 2. By using three types of compounded epoxy resin, the present invention improves the tensile strength of the skin and also helps the dispersion of other components in the system, thereby improving the stealth performance of the skin.

[0034] 3. This invention refers to GJB2038A-2011 "Test Method for Reflectivity of Radar Absorbing Materials". This method can be used to measure the reflection loss of materials in the microwave band, which is one of the core standards for evaluating the performance of stealth materials. The more negative the RL value, the stronger the radar absorption performance. In engineering, it is generally believed that in the X-band, RL≤-10dB means that the material has effective radar stealth capability; RL≤-15dB indicates excellent performance. Through testing, the skin of this invention has excellent stealth capability. Detailed Implementation

[0035] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] All raw materials used in the following embodiments of the present invention are commercially available products:

[0037] Polyvinylpyrrolidone, weight average molecular weight 3500, model PVPK12, manufactured by Gongbike New Material Technology (Shanghai) Co., Ltd.

[0038] ZrW2O8, tungsten zirconate powder, CAS: 16853-74-0, item number T836246, Shanghai Maclean Biochemical Technology Co., Ltd.

[0039] The curing agent is a latent curing agent, dicyandiamide, CAS Registry No. 461-58-5.

[0040] Carbon fiber, Resoo Trading (Shanghai) Co., Ltd., 6MM carbon fiber short chopped C6-4.0 / 240-T190.

[0041] Glass fiber, 9-13μm, Shandong Tonghui Glass Fiber Co., Ltd.

[0042] Carbon black, fumed silica A200, Jinan Zhongbei Fine Chemical Co., Ltd.

[0043] Quartz fiber, Henan Shenjiu Tianhang New Material Co., Ltd., Shenjiu quartz fiber short chopped filament SJ104, diameter 1μm, length 1mm.

[0044] Example 1

[0045] This embodiment provides a method for preparing an X-band stealth skin, including the following steps:

[0046] (1) Preparation of modified epoxy resin system; the preparation method includes the following steps:

[0047] S1: Add 5 times the mass of 70wt% ethanol aqueous solution to tungsten zirconate powder, add 4% of the mass of tungsten zirconate powder in polyvinylpyrrolidone, stir and heat to 52℃, continue stirring and react for 5h, centrifuge, dry the centrifuged precipitate at 85℃ for 4h, and pulverize to less than 325 mesh to obtain modified tungsten zirconate powder.

[0048] S2: Mix modified tungsten zirconate powder and epoxy resin at a mass ratio of 3.5:100. Then add 6% of the latent curing agent dicyandiamide and 0.7% of the accelerator 2-methylimidazole by mass of epoxy resin. Stir and mix to obtain the modified epoxy resin system.

[0049] The epoxy resin comprises epoxy resin A, epoxy resin B, and epoxy resin C in a mass ratio of 1.4:0.5:1. Epoxy resin A has an epoxy equivalent of 205-225 g / eq and a viscosity of 19000-24000 cps / 25℃, and is model NPEL-128S; epoxy resin B has an epoxy equivalent of 184-190 g / eq and a viscosity of 12000-15000 cps / 25℃, and is model NPEL-128; epoxy resin C has an epoxy equivalent of 176-184 g / eq and a viscosity of 8000-11000 cps / 25℃, and is model NPEL-127; all sourced from Shanghai Qunsheng Chemical Co., Ltd.

[0050] (2) Mix carbon fiber and modified epoxy resin system from step (1) at a mass ratio of 1:5 to obtain carbon fiber mixture. Lay a carbon fiber mixture with a thickness of 1.8 mm to obtain a carbon fiber mixture film layer.

[0051] (3) Mix silver powder, modified epoxy resin system from step (1), and carbon fiber in a mass ratio of 4:5:1 to obtain a conductive mixture; lay a conductive mixture with a thickness of 0.12 mm on the surface of the carbon fiber mixture film to obtain a conductive mixture film.

[0052] (4) Mix glass fiber, carbon black and modified epoxy resin system of step (1) in a mass ratio of 4:1:5 to obtain microwave absorbing mixture; lay microwave absorbing mixture with a thickness of 0.88 mm on the surface of conductive mixture film to obtain microwave absorbing mixture film.

[0053] (5) Mix the quartz fiber and the modified epoxy resin system of step (1) at a mass ratio of 2.5:5 to obtain a microwave-transparent mixture; lay 0.12 mm of microwave-transparent mixture on the surface of the microwave-absorbing mixture film to obtain a skin material;

[0054] (6) The skin material is bagged and vacuumed, and cured at 130°C for 6 hours to obtain X-band stealth / lightning protection skin.

[0055] Example 2

[0056] This embodiment provides a method for preparing an X-band stealth skin, including the following steps:

[0057] (1) Preparation of a modified epoxy resin system; the preparation method of the modified epoxy resin system includes the following steps:

[0058] S1: Add 5 times the mass of 70wt% ethanol aqueous solution to tungsten zirconate powder, add 5% of the mass of tungsten zirconate powder in polyvinylpyrrolidone, stir and heat to 50℃, continue to react for 6h, centrifuge, dry at 85℃ for 4h, and pulverize to less than 325 mesh to obtain modified tungsten zirconate powder.

[0059] S2: Mix modified tungsten zirconate powder and epoxy resin at a mass ratio of 3:100, then add 7% of the latent curing agent dicyandiamide and 0.5% of the accelerator 2-methylimidazole by mass of epoxy resin, and stir to obtain the modified epoxy resin system.

[0060] The epoxy resin comprises epoxy resin A, epoxy resin B, and epoxy resin C in a mass ratio of 1.5:0.4:1. Epoxy resin A has an epoxy equivalent of 205-225 g / eq and a viscosity of 19000-24000 cps / 25℃, and is designated NPEL-128S; epoxy resin B has an epoxy equivalent of 184-190 g / eq and a viscosity of 12000-15000 cps / 25℃, and is designated NPEL-128; epoxy resin C has an epoxy equivalent of 176-184 g / eq and a viscosity of 8000-11000 cps / 25℃, and is designated NPEL-127. (Source: Shanghai Qunsheng Chemical Co., Ltd.)

[0061] (2) Mix carbon fiber and modified epoxy resin system from step (1) at a mass ratio of 1:5 to obtain carbon fiber mixture, lay 1.8 mm of carbon fiber mixture to obtain carbon fiber mixture film layer.

[0062] (3) Mix silver powder, modified epoxy resin system from step (1), and carbon fiber in a mass ratio of 4:5:1 to obtain a conductive mixture; lay a conductive mixture with a thickness of 0.12 mm on the surface of the carbon fiber mixture film to obtain a conductive mixture film.

[0063] (4) Mix glass fiber, carbon black and modified epoxy resin system of step (1) in a mass ratio of 4:1:5 to obtain microwave absorbing mixture; lay microwave absorbing mixture with a thickness of 0.88 mm on the surface of conductive mixture film to obtain microwave absorbing mixture film.

[0064] (5) The quartz fiber and the modified epoxy resin system of step (1) are mixed at a mass ratio of 2.5:5 to obtain a microwave-transparent mixture; 0.12 mm of microwave-transparent mixture is laid on the surface of the microwave-absorbing mixture film to obtain the skin material;

[0065] (6) The skin material is bagged and vacuumed, and cured at 130°C for 6 hours to obtain X-band stealth / lightning protection skin.

[0066] Comparative Example 1

[0067] The difference between this comparative example and Example 1 is as follows: Tungsten zirconate powder was added to 5 times its mass of 70wt% ethanol aqueous solution, and 2.5% by mass of silane coupling agent KH560 was added. The mixture was stirred and heated to 50°C, and the reaction was continued for 6 hours. After centrifugation, the mixture was dried at 85°C for 4 hours and pulverized to less than 325 mesh to obtain modified tungsten zirconate powder.

[0068] Comparative Example 2

[0069] The difference between this comparative example and Example 1 is that the mass ratio of modified tungsten zirconate powder to epoxy resin is 5:100.

[0070] Comparative Example 3

[0071] The difference between this comparative example and Example 1 is that the mass ratio of modified tungsten zirconate powder to epoxy resin is 2:100.

[0072] Comparative Example 4

[0073] The difference between this comparative example and Example 1 is that the epoxy resin is epoxy resin B, with an epoxy equivalent of 184-190 g / eq, a viscosity of 12000-15000 cps / 25℃, and the model is NPEL-128.

[0074] Comparative Example 5

[0075] The difference between this comparative example and Example 1 is that the epoxy resin comprises epoxy resin A and epoxy resin C in a mass ratio of 1.5:1. Epoxy resin A has an epoxy equivalent of 205-225 g / eq, a viscosity of 19000-24000 cps / 25℃, and is model NPEL-128S; epoxy resin C has an epoxy equivalent of 176-184 g / eq, a viscosity of 8000-11000 cps / 25℃, and is model NPEL-127. Sourced from Shanghai Qunsheng Chemical Co., Ltd.

[0076] Comparative Example 6

[0077] The difference between this comparative example and Example 1 is that the epoxy resin comprises epoxy resin A, epoxy resin B, and epoxy resin C in a mass ratio of 1:1:1. Epoxy resin A has an epoxy equivalent of 205-225 g / eq, a viscosity of 19000-24000 cps / 25℃, and is model NPEL-128S; epoxy resin B has an epoxy equivalent of 184-190 g / eq, a viscosity of 12000-15000 cps / 25℃, and is model NPEL-128; epoxy resin C has an epoxy equivalent of 176-184 g / eq, a viscosity of 8000-11000 cps / 25℃, and is model NPEL-127. Source: Shanghai Qunsheng Chemical Co., Ltd.

[0078] Performance testing

[0079] 1. Samples were prepared according to the preparation methods of Examples 1-2 and Comparative Examples 1-6. Tensile tests were conducted according to ASTM D3039 / D3039M-2017, "Tensive Properties of Polymer Matrix Composites". The sample was placed in a fixture, and the tensile speed was set to 2 mm / min. The load was continuously applied until the sample failed and the loading was stopped. The test was then completed, and the tensile strength at room temperature was obtained. The sample was then placed at -50℃ for 100 h and allowed to recover to room temperature. The retention rate of the low-temperature tensile strength was determined as follows: (Tensile strength after low-temperature placement ÷ Tensile strength at room temperature) × 100%.

[0080] 2. Referring to GJB2038A-2011 "Test Method for Reflectivity of Radar Absorbing Materials", the bow-shaped method was used to determine the reflection loss of the skin material in the X-band, RL(dB)=10log 10 (Pr / Pi), where Pr is the reflected power and Pi is the incident power.

[0081] The test results are shown in Table 1.

[0082] Table 1 Performance Test Results

[0083] room temperature tensile strength (MPa) Low temperature tensile strength retention rate % RL(dB) Example 1 457 93.0 -15.7 Example 2 433 91.7 -15.2 Comparative Example 1 325 86.5 -14.7 Comparative Example 2 389 88.2 -14.5 Comparative Example 3 476 78.9 -12.9 Comparative Example 4 358 76.1 -12.6 Comparative Example 5 405 80.4 -13.8 Comparative Example 6 411 85.6 -14.0

[0084] As shown in Table 1, the skin materials of Examples 1-2 not only have excellent stealth performance and lightning protection, but also have good tensile properties at room temperature and higher mechanical property retention rate in ultra-low temperature environments.

[0085] Comparative Example 1 demonstrates that using polyvinylpyrrolidone as a dispersant, through steric hindrance, prevents powder particle agglomeration, which is more effective than using silane coupling agents and imparts better performance to the material.

[0086] Comparative Examples 2 and 3 show that if the amount of tungsten zirconate is too low, the low-temperature resistance of the material decreases; if the amount is too high, the tensile properties of the material deteriorate.

[0087] Comparative Examples 4-6 demonstrate that the multiphase synergistic cross-linking network formed by the three types of epoxy resins can more effectively terminate and disperse microcracks, especially at low temperatures, resulting in better toughness of the skin material. It also facilitates powder dispersion and improves the overall performance of the skin material.

[0088] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing an X-band stealth skin, characterized in that, Includes the following steps: (1) Tungsten zirconate powder was modified with polyvinylpyrrolidone and then mixed with epoxy resin, curing agent and accelerator to obtain a modified epoxy resin system. (2) Mix carbon fiber and the modified epoxy resin system of step (1) to obtain carbon fiber mixture, lay carbon fiber mixture to obtain carbon fiber mixture film layer; (3) Mix silver powder, the modified epoxy resin system of step (1) and carbon fiber to obtain a conductive mixture; lay the conductive mixture on the surface of the carbon fiber mixture film to obtain a conductive mixture film. (4) Mix glass fiber, carbon black and modified epoxy resin system from step (1) in a mass ratio of 4:1:5 to obtain microwave absorbing mixture; spread microwave absorbing mixture on the surface of conductive mixture film to obtain microwave absorbing mixture film. (5) A wave-transmitting mixture is laid on the surface of the wave-absorbing mixture film to obtain the skin material; (6) The skin material is vacuumed and heated to cure, thereby obtaining an X-band stealth skin; Epoxy resins include epoxy resin A, epoxy resin B, and epoxy resin C in a mass ratio of (1.3-1.5):(0.4-0.6):1; epoxy resin A has an epoxy equivalent of 205-225 g / eq and a viscosity of 19000-24000 cps; epoxy resin B has an epoxy equivalent of 184-190 g / eq and a viscosity of 12000-15000 cps; epoxy resin C has an epoxy equivalent of 176-184 g / eq and a viscosity of 8000-11000 cps. The mass ratio of modified tungsten zirconate powder to epoxy resin is (3-4):

100.

2. The method for preparing the X-band stealth skin according to claim 1, characterized in that, The preparation method of the modified epoxy resin system includes the following steps: S1: Add tungsten zirconate powder to an ethanol aqueous solution, add polyvinylpyrrolidone, heat to 50-55℃, react for 4-6 hours, centrifuge, dry, and pulverize to obtain modified tungsten zirconate powder. S2: Mix modified tungsten zirconate powder, epoxy resin, curing agent, and accelerator, and stir to obtain a modified epoxy resin system.

3. The method for preparing the X-band stealth skin according to claim 1, characterized in that, The weight-average molecular weight of polyvinylpyrrolidone is 3500-5500.

4. An X-band stealth skin prepared by the preparation method according to any one of claims 1-3.

5. The application of an X-band stealth skin prepared by the preparation method according to any one of claims 1-3 in the preparation of an aircraft.