An infrared camouflage composite coating with micro-nano structure and its preparation method

Abstract

The present invention discloses an infrared camouflage composite coating with a micro-nano structure, comprising an infrared camouflage layer sprayed onto a target substrate and a micro-nano structured layer sprayed onto the infrared camouflage layer. The infrared camouflage layer is an Al@PU infrared camouflage layer, and the micro-nano structured layer is constructed from silica particles with both micron and nanometer sizes. The present invention also discloses a method for preparing the infrared camouflage composite coating. The infrared camouflage composite coating with a micro-nano structure of the present invention combines excellent infrared camouflage, super-hydrophobic properties at room temperature, and anti-icing properties at low temperatures.

Description

Technical Field

[0001] The present invention relates to an infrared camouflage composite coating with a micro-nano structure and also relates to a preparation method of the composite coating. Background Art

[0002] In recent years, with the rapid development of various advanced infrared detection and thermal imaging technologies, the use of low-infrared emissivity materials to reduce the infrared radiation intensity of various aircraft is an effective means, especially the use of low-infrared emissivity coatings constructed from various organic resin matrices and flaky metal powders to reduce the infrared radiation intensity of targets. This can not only significantly improve the infrared stealth effectiveness of various targets, but also has the advantages of low cost, ease of use, and little impact on the aerodynamic performance of aircraft. It is very suitable for large-scale use on various aircraft.

[0003] However, the coating is easily contaminated by dust and stains during long-term use. After long-term use, the surface of the low-infrared emissivity coating is seriously contaminated, and the infrared emissivity is significantly increased, which greatly weakens the infrared stealth performance of the target; at the same time, the low-infrared emissivity coating will quickly freeze within half a minute at minus 20 degrees Celsius. In many industrial fields, such as aerospace, wind turbines, power lines, etc., ice accumulation on the surface of outdoor equipment will cause serious safety hazards and energy loss. Summary of the Invention

[0004] Purpose of the invention: The purpose of the present invention is to provide an infrared camouflage composite coating with a micro-nano structure, which can enable the coating to have self-cleaning ability at room temperature and delayed freezing performance at low temperatures without affecting the infrared camouflage performance; another purpose of the present invention is to provide a preparation method of the above-mentioned infrared camouflage composite coating.

[0005] Technical solution: The infrared camouflage composite coating with a micro-nano structure described in the present invention includes an infrared camouflage layer sprayed on a target substrate and a micro-nano structure layer sprayed on the infrared camouflage layer; wherein, the infrared camouflage layer is an Al@PU infrared camouflage layer; the micro-nano structure layer is constructed of silica particles with both micron and nanometer sizes.

[0006] Wherein, the thickness of the infrared camouflage layer is 70 to 80 μm; the thickness of the micro-nano structure layer is 20 to 21.5 μm.

[0007] Among them, multiple silica nanospheres are arranged in order on the silica microspheres to form silica particles with both micron and nanometer sizes.

[0008] Among them, in the micro-nano structure layer, the mass ratio of silica nanospheres to silica microspheres is 3 to 7:1.

[0009] The particle size of the silicon dioxide nanospheres is 25 to 30 nm; the particle size of the silicon dioxide microspheres is 8 to 10 μm.

[0010] The method for preparing the above-mentioned infrared camouflage composite coating comprises the following steps:

[0011] (1) adding polyurethane resin (PU) to butyl acetate, ultrasonically stirring at room temperature, and then adding aluminum silver paste thereto; stirring thoroughly until flaky aluminum powder floats in the solution; adding a curing agent thereto, dispersing uniformly, and then adding an organic solvent to adjust the viscosity of the coating; spraying the coating onto a target substrate using a compressed air spray method to obtain an infrared camouflage layer;

[0012] (2) adding hydrophobically modified silica microspheres to butyl acetate, adding hydrophobically modified silica nanospheres after ultrasonic stirring, adding silane coupling agent KH-550 after ultrasonic stirring, and continuing ultrasonic stirring to obtain HNMSiO2 dispersion;

[0013] (3) HNMSiO2 dispersion, polyurethane resin and butyl acetate are mixed and stirred evenly, and then a curing agent is added thereto. After uniform dispersion, an organic solvent is added to adjust the viscosity of the coating; the coating is sprayed onto the infrared camouflage layer using a compressed air spray method to obtain a composite coating consisting of an infrared camouflage layer and a micro-nano structure layer.

[0014] Wherein, in step (1), aluminum-silver paste is added at a mass ratio of polyurethane resin to aluminum powder of 1.2125 to 1.22:1.

[0015] Wherein, in step (1) and step (3), the curing agent is a polyurethane enamel curing agent.

[0016] Wherein, in step (1) and step (3), during the spraying process, the pressure of the spray gun is 0.4 MPa; the spraying angle is 90°; and the spraying speed is 0.15 m / s.

[0017] Wherein, in step (2), the hydrophobic modification method of silica microspheres or silica nanospheres is specifically as follows:

[0018] (2.1) Adding silica microspheres or silica nanospheres to an ammonia solution and magnetically stirring to obtain a SiO2 suspension;

[0019] (2.2) Hexadecyltrimethoxysilane (HDTMS) was added to anhydrous ethanol and stirred magnetically to obtain a silane solution;

[0020] (2.3) Add the SiO2 suspension dropwise to the silane solution, stir the mixed solution at 40-50°C for at least 24 hours to allow the hydrolysis and condensation reaction to proceed completely, and cool to room temperature after the reaction;

[0021] (2.4) The suspension after the reaction is centrifuged, and the solid product after centrifugation is washed and dried to obtain hydrophobically modified SiO2 particles.

[0022] Beneficial effects: Compared with the existing technology, the present invention has the following significant advantages: the infrared camouflage composite coating with a micro-nano structure of the present invention can have excellent infrared camouflage, super-hydrophobicity at room temperature and anti-icing performance at low temperature; it can remain ice-free for more than 10 minutes at -20°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The SEM images of the composite coating surfaces of Examples 1, 3, and 5 are shown;

[0024] Figure 2 SEM images of the cross sections of the composite coatings of Examples 1, 3, and 5;

[0025] Figure 3 is the infrared emissivity value of the composite coatings of Examples 1, 2, 3, 4, and 5 in the 8-14 μm band;

[0026] Figure 4 Infrared thermal images of the composite coatings of Examples 1, 3, and 5 taken with a human hand as the background;

[0027] Figure 5 The water contact angle and sliding angle of the composite coatings of Examples 1, 2, 3, 4, and 5;

[0028] Figure 6 This is the delayed freezing condition of the composite coatings of Examples 1, 3, and 5 at -20°C. DETAILED DESCRIPTION

[0029] Example 1

[0030] The method for preparing the infrared camouflage composite coating of the present invention comprises the following steps:

[0031] (1) Weigh 4.85g of polyurethane resin and add it to 10mL of butyl acetate. After ultrasonic stirring at room temperature for 5min, add aluminum silver paste, wherein the mass ratio of polyurethane resin to aluminum powder is 1.2125:1. Then add 7mL of butyl acetate to disperse and dissolve, stir it evenly with a glass rod, and then stir it ultrasonically for 5min. Then add 4g of polyurethane enamel curing agent and continue ultrasonic stirring for 10min. After uniform dispersion, add appropriate amount of butyl acetate to adjust the viscosity of the coating (by naked eye observation, 2 to 3 drops of liquid on the glass rod within 1s are sufficient). Spray the coating onto the treated substrate using compressed air spraying at a thickness of 80μm. The pressure of the spray gun is 0.4MPa, the spraying angle is 90°, and the spraying speed is 0.15m / s. After spraying, dry the substrate surface at room temperature for 30min.

[0032] (2) Weigh 0.15 g of hydrophobically modified silica microspheres (HMSiO2) and add them to 3 mL of butyl acetate. Ultrasonic stirring is performed at 40 °C for 5 min. Then, 0.45 g of hydrophobically modified silica nanospheres (HNSiO2) are added thereto. Then, 5 mL of ethyl acetate is added. Ultrasonic stirring is performed at 40 °C for 20 min. Finally, 1 g of KH-550 is added. Ultrasonic stirring is performed for 20 min to obtain a HNMSiO2 dispersion, which is recorded as 3HNMSiO2.

[0033] (3) The HNMSiO2 dispersion of step (2), 0.48g of polyurethane resin and 5mL of butyl acetate were mixed (in the mixed solution, the mass of the silica particles was the same as that of the polyurethane resin), and after preliminary stirring with a glass rod, ultrasonic stirring was continued for 5 minutes. Then, 0.4g of polyurethane enamel curing agent was added thereto, and ultrasonic stirring was continued for 10 minutes. After uniform dispersion, an appropriate amount of butyl acetate solvent was added to adjust the viscosity of the coating (by naked eye observation, 2 to 3 drops of liquid on the glass rod were dripped within 1 second); the coating was sprayed onto the infrared camouflage layer by compressed air spraying at a thickness of 20μm, with a spray gun pressure of 0.4MPa, a spray angle of 90°, and a spray speed of 0.15m / s; after spraying, the substrate was surface dried at room temperature and then placed in a 60℃ oven for curing for 6h to obtain a composite coating 3HNMSiO2-Al@PU.

[0034] The hydrophobic modification method of silica microspheres or silica nanospheres is specifically as follows:

[0035] (2.1) Add 15 g of silica microspheres or silica nanospheres to 100 mL of aqueous ammonia solution and stir magnetically at 40°C for 30 min to obtain a SiO2 suspension; the aqueous ammonia solution is prepared from 30 mL of aqueous ammonia and 70 mL of deionized water.

[0036] (2.2) Add 5 mL of hexadecyltrimethoxysilane to 500 mL of anhydrous ethanol and stir magnetically at 40°C for 90 min to obtain a silane solution.

[0037] (2.3) Add the SiO2 suspension from step (2.1) dropwise to the silane solution from step (2.2). Stir the mixed solution at 40°C for 24 hours to complete the hydrolysis and condensation reaction.

[0038] (2.4) After the reaction, the suspension was cooled to room temperature and centrifuged at 5000 rpm for 10 min. The solid matter after centrifugation was washed with anhydrous ethanol and centrifuged twice. The centrifuged product was then placed in a vacuum drying oven at 60°C and dried for 24 h to obtain hydrophobic SiO2 particles.

[0039] Example 2

[0040] The method for preparing the infrared camouflage composite coating in Example 2 is basically the same as that in Example 1, with the only difference being that in step (2), 0.12 g of hydrophobically modified silica microspheres were weighed and added to 3 mL of butyl acetate, and then 0.48 g of hydrophobically modified silica nanospheres were added thereto after ultrasonic stirring at 40°C for 5 min, to finally obtain the infrared camouflage composite coating 4HNMSiO2-Al@PU.

[0041] Example 3

[0042] The method for preparing the infrared camouflage composite coating in Example 3 is basically the same as that in Example 1, with the only difference being that in step (2), 0.10 g of hydrophobically modified silica microspheres are weighed and added to 3 mL of butyl acetate, and then 0.50 g of hydrophobically modified silica nanospheres are added thereto after ultrasonic stirring at 40°C for 5 min, to finally obtain the infrared camouflage composite coating 5HNMSiO2-Al@PU.

[0043] Example 4

[0044] The method for preparing the infrared camouflage composite coating in Example 4 is basically the same as that in Example 1, with the only difference being that in step (2), 0.085 g of hydrophobically modified silica microspheres are weighed and added to 3 mL of butyl acetate, and then 0.515 g of hydrophobically modified silica nanospheres are added thereto after ultrasonic stirring at 40°C for 5 min, to finally obtain the infrared camouflage composite coating 6HNMSiO2-Al@PU.

[0045] Example 5

[0046] The method for preparing the infrared camouflage composite coating in Example 5 is basically the same as that in Example 1, with the only difference being that in step (2), 0.075 g of hydrophobically modified silica microspheres are weighed and added to 3 mL of butyl acetate, and then 0.525 g of hydrophobically modified silica nanospheres are added thereto after ultrasonic stirring at 40°C for 5 min, to finally obtain the infrared camouflage composite coating 7HNMSiO2-Al@PU.

[0047] The infrared emissivity and super-hydrophobicity at room temperature of the infrared camouflage composite coatings prepared in Examples 1, 2, 3, 4, and 5 were tested, specifically:

[0048] (1) Infrared camouflage test:

[0049] The emissivity was tested using the IR-2 dual-band, and the infrared camouflage situation was recorded using an infrared thermal imager.

[0050] (2) Superhydrophobicity test:

[0051] The water contact angle of the coating was measured using a CA measurement system (JC2000D2). The test results are shown in Figure 2. Figure 5 As shown, through Figure 5 It can be seen that the composite coatings of Examples 1 to 5 all achieved superhydrophobicity, with water contact angles all being above 150° and sliding angles all being below 10°.

[0052] Figure 1 The following are SEM images of the composite coating surfaces of Examples 1, 3, and 5. All three images show that HMSiO2 particles (approximately 10 μm) are surrounded by numerous HNSiO2 particles (approximately 30 nm), forming a relatively complete structure resembling a strawberry or raspberry, forming micron-nanoscale secondary strawberry silica particles. The size difference between the micron- and nanoparticles increases the specific surface area of ​​the secondary strawberry silica particles and improves their surface roughness.

[0053] Figure 2 The SEM images of the cross sections of the composite coatings of Examples 1, 3, and 5, specifically the SEM images of the cross sections of the 3HNMSiO2-Al@PU, 5HNMSiO2-Al@PU, and 7HNMSiO2-Al@PU grafted substrates, are shown in FIG. Figure 2 It can be clearly seen that in the two-layer structure of the 5HNMSiO2-Al@PU composite coating, the thickness of the infrared camouflage layer Ag@PU is controlled at about 80μm, and the thickness of the micro-nanostructure layer HNMSiO2@PU is controlled at about 20μm.

[0054] Figure 3The infrared emissivity values ​​for the composite coatings of Examples 1, 2, 3, 4, and 5 in the 8-14 μm band are shown. As the mass ratio of nanoparticles to micronized particles increases from 3:1 to 7:1, the infrared emissivity of the composite coatings increases from 0.235 to 0.438. When the mass ratio increases from 3:1 to 5:1, the increase in infrared emissivity is slow. When the mass ratio increases from 5:1 to 7:1, the infrared emissivity of the composite coatings increases rapidly, from 0.297 to 0.438.

[0055] Figure 4 For the composite coatings of Examples 1, 3, and 5, infrared thermal images of the samples were taken with a human hand as the background. When photographing HNMSiO2-Al@PU, Al@PU was placed together as a control to simulate the infrared thermal stealth performance of HNMSiO2-Al@PU applied to wearable equipment. The color of the thermal image shows the infrared radiation intensity of the material. For the Al@PU material, the color is dark blue, which can be well integrated with the background. The reason is that the infrared emissivity of Al@PU is low, resulting in its infrared radiation being low and close to the background infrared radiation. Compared with Al@PU, the color of the infrared thermal image of 3HNMSiO2-Al@PU is still blue and can be well integrated with the room temperature environment, indicating that the effect of adding the micro-nano structure layer on the infrared emissivity is negligible, and the infrared camouflage performance is guaranteed. Compared with Al@PU, the infrared emissivity of 5HNMSiO2-Al@PU is slightly increased, and it appears light blue in the infrared thermal image, which has good infrared stealth performance. Compared with Al@PU, the difference is very small, and it can still blend well into the room temperature environment, and the infrared camouflage performance is still maintained. The difference between 7HNMSiO2-Al@PU and Al@PU is larger because its infrared emissivity is increased, resulting in a yellow-blue color in its infrared thermal image, and its infrared stealth performance is reduced.

[0056] Figure 5The water contact angle and sliding angle of the composite coating of Examples 1, 2, 3, 4, and 5. When the mass fraction of micro-nano fillers is controlled at 50% (the mass of silica particles is the same as that of polyurethane resin), the water contact angle of the 3HNMSiO2-Al@PU infrared camouflage composite coating is 158.79°±0.6°, and the rolling angle is 3.9°±0.4°; as the mass ratio of nano-sized particles to micro-sized particles continues to increase, the water contact angle also gradually increases, and the rolling angle gradually decreases, but the increase tends to be stable, which are 160.90°±0.8° for water contact angle and 3.10°±0.3° for rolling angle (mass ratio 4:1) and 162.97°±0.5° for water contact angle and 2.2°±0.3° for rolling angle (mass ratio 5:1). However, when the mass ratio continues to increase, the water contact angle decreases instead of increases, and an inflection point appears at 5HNMSiO2-Al@PU, but the downward trend is gentle, indicating that micron-nanoscale second-order strawberry silica particles can significantly improve the superhydrophobic properties of the coating.

[0057] Figure 6 The results show that the composite coatings of Examples 1, 3, and 5 delayed freezing at -20°C. When the HNSiO2:HMSiO2 mass ratio was 3:1, the droplets began to freeze on the coating surface after 292.98 seconds and were completely frozen after 31.25 seconds. Finally, the super-hydrophobic coating achieved a delayed freezing time of 324.23 seconds at -20°C. When the HNSiO2:HMSiO2 mass ratio was 5:1, the surface of the 5HNMS-Al@PU coating remained liquid until 763.34 seconds, and after 31.82 seconds, the droplets completely froze and protruded. Finally, the super-hydrophobic coating achieved a delayed freezing time of 795.16 seconds at -20°C. When the HNSiO2 in the filler continued to increase, the freezing delay time of the coating at -20℃ began to show a decreasing trend. When the HNSiO2 filler continued to be increased to a HNSiO2:HMSiO2 mass ratio of 7:1, freezing began at 664.14s, and the total freezing delay time was 695.56s.

Claims

1. An infrared camouflage composite coating with a micro-nano structure, characterized by: The invention comprises an infrared camouflage layer sprayed on a target substrate and a micro-nano structure layer sprayed on the infrared camouflage layer; wherein the infrared camouflage layer is an Al@PU layer; and the micro-nano structure layer is constructed of silicon dioxide particles having both micron and nanometer sizes; Multiple silica nanospheres are arranged in an orderly manner on the silica microspheres to form silica particles with both micron and nanometer sizes; in the micro-nano structure layer, the mass ratio of the silica nanospheres to the silica microspheres is 3 to 6:1; when the mass ratio of the silica nanospheres to the silica microspheres is 3:1, the infrared emissivity of the composite coating is 0.235; when the mass ratio of the silica nanospheres to the silica microspheres is 4:1, the infrared emissivity of the composite coating is 0.272; when the mass ratio of the silica nanospheres to the silica microspheres is 5:1, the infrared emissivity of the composite coating is 0.297; when the mass ratio of the silica nanospheres to the silica microspheres is 6:1, the infrared emissivity of the composite coating is 0.333; the water contact angle of the composite coating is greater than 150 degrees, and the rolling angle is less than 10 degrees; the composite coating can remain ice-free for more than 10 minutes at -20 degrees Celsius; The method for preparing the above-mentioned infrared camouflage composite coating comprises the following steps: (1) Adding polyurethane resin to butyl acetate, adding aluminum silver paste after ultrasonic stirring, adding curing agent after thorough stirring, adding organic solvent to adjust the viscosity of the coating after uniform dispersion; spraying the coating onto the target substrate by compressed air spraying to obtain an infrared camouflage layer; (2) adding hydrophobically modified silica microspheres to butyl acetate, adding hydrophobically modified silica nanospheres after ultrasonic stirring, adding silane coupling agent KH-550 after ultrasonic stirring, and continuing ultrasonic stirring to obtain HNMSiO2 dispersion; (3) HNMSiO2 dispersion, polyurethane resin and butyl acetate are mixed and stirred evenly, and then a curing agent is added thereto. After uniform dispersion, an organic solvent is added to adjust the viscosity of the coating; the coating is sprayed onto the infrared camouflage layer using a compressed air spray method to obtain a composite coating consisting of an infrared camouflage layer and a micro-nano structure layer.

2. The infrared camouflage composite coating according to claim 1, characterized in that: The thickness of the infrared camouflage layer is 70-80 μm; the thickness of the micro-nano structure layer is 20-21.5 μm.

3. The infrared camouflage composite coating according to claim 1, characterized in that: The particle size of the silicon dioxide nanospheres is 25-30 nm; the particle size of the silicon dioxide microspheres is 8-10 μm.

4. The infrared camouflage composite coating according to claim 1, characterized in that: In step (1), aluminum-silver paste is added at a mass ratio of polyurethane resin to aluminum powder of 1.2125-1.22:

1.

5. The infrared camouflage composite coating according to claim 1, characterized in that: In step (1) and step (3), the curing agent is a polyurethane enamel curing agent.

6. The infrared camouflage composite coating according to claim 1, characterized in that: In step (1) and step (3), during the spraying process, the pressure of the spray gun is 0.4-0.5 MPa; the spraying angle is 90°; and the spraying speed is 0.15-0.2 m / s.

7. The infrared camouflage composite coating according to claim 1, characterized in that: In step (2), the hydrophobic modification method of silica microspheres or silica nanospheres is specifically as follows: (2.1) Adding silica microspheres or silica nanospheres to an aqueous ammonia solution and magnetically stirring to obtain a SiO2 suspension; (2.2) Hexadecyltrimethoxysilane was added to anhydrous ethanol and stirred magnetically to obtain a silane solution. (2.3) Add the SiO2 suspension dropwise to the silane solution, and conduct a hydrolysis-condensation reaction of the mixed solution at 40-50°C. After the reaction, cool to room temperature. (2.4) The suspension after the reaction is centrifuged, and the solid product after centrifugation is washed and dried to obtain hydrophobically modified SiO2 particles.

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