Special coating system suitable for inner cavity of aircraft antenna housing and spraying process

Abstract

The invention belongs to the technical field of coatings for aircrafts, and particularly relates to a special coating system suitable for an inner cavity of an aircraft antenna housing and a spraying process. The special coating system comprises a primer and a finish, wherein the primer comprises resin color paste A1, a curing agent B1 and a diluent C1; the resin color paste A1 is prepared from 80 to 120 parts of organic silicon modified epoxy resin, 20 to 30 parts of surface modified hollow glass beads, 10 to 15 parts of modified flake mica and 6 to 10 parts of zinc phosphate; the diluent C1 accounts for 20-30% of the resin color paste A1; the finish paint is prepared from hydroxy acrylic resin color paste A2, an organic silicon modified polyisocyanate water-based curing agent B2 and a diluent C2; the hydroxy acrylic resin color paste A2 comprises 35-45 parts of hydroxy acrylic resin, 8-12 parts of silicon dioxide, 12-18 parts of graphite, 1-3 parts of carbon black and 3-8 parts of iron oxide; and the diluent C2 accounts for 20-30% of the hydroxyl acrylic resin color paste A2.

Description

Technical Field

[0001] This invention belongs to the field of coating technology for aircraft, specifically relating to a special coating system and spraying process suitable for the inner cavity of an aircraft radome. Background Technology

[0002] As a crucial component of radio equipment such as radar, communication, and navigation systems, the radome's primary function is to protect the antenna from environmental factors (such as wind, rain, snow, ultraviolet radiation, and dust) and interference, while ensuring the accurate capture of infrared signatures. When aircraft fly at high speeds through the atmosphere, they detect, track, and guide targets by absorbing their infrared radiation energy. They also need to transmit or receive electromagnetic waves (such as radar waves and lasers), utilizing the reflection, scattering, or transmission characteristics of these waves to detect targets. Because the infrared radiation and electromagnetic waves of targets are absorbed, scattered, and refracted in the atmosphere, and are also affected by atmospheric conditions such as clouds, rain, and fog, the identification and tracking capabilities are significantly reduced. Therefore, using a special coating to protect the radome is an economical, effective, and reliable method. As a key surface treatment technology, radome protective coatings play a vital role in eliminating stray light reflection and reducing diffuse reflection from internal optical system components.

[0003] Existing protective coatings mostly employ an epoxy / silicone primer + matte resin topcoat system. The primer focuses on adhesion, corrosion resistance, and rapid curing, while the topcoat focuses on providing a uniform matte appearance, weather resistance, and a certain degree of abrasion resistance, thus achieving physical protection for aircraft radomes. However, traditional coatings have a relatively high dielectric constant in their initial state. When moisture or electrolytes penetrate into the coating through microscopic defects or resin free volume, the high dielectric constant of water causes a sharp increase in the local dielectric constant of the coating, thereby enhancing the electric field strength within the coating, accelerating the directional migration of ions, reducing the activation energy of corrosion reactions on the metal surface, and ultimately leading to premature coating failure.

[0004] Moreover, traditional methods for applying paint to the interior cavity of a housing are mostly brush-applied, where paint is applied to the surface of the cavity using a brush. This method is simple and flexible, but it has low construction efficiency, unstable coating quality, and requires high technical skills from the workers. The thickness of the paint applied by brushing is uneven, resulting in inconsistent coating quality. Spraying, on the other hand, uses a spray gun to spray paint into the surface of the interior cavity in a mist form. For complex shapes of the interior cavity, spraying can quickly cover a large area, improving construction efficiency. Spraying can form a more uniform coating, and the coating thickness can be controlled, which helps to ensure coating quality.

[0005] When spraying special coatings in confined spaces, conventional spraying methods often result in numerous coating defects, such as uneven coating thickness, sagging, pinholes, and missed areas due to small spray width. Inconsistencies in the diluent ratio, spray gun selection, nozzle diameter selection, spray gun width adjustment, and spraying speed can all prevent the coating from properly atomizing and forming a film, making it difficult to meet batch production requirements in terms of quality consistency and production schedule. Summary of the Invention

[0006] In view of the defects and problems existing in the current protective coating system, the present invention provides a special coating system and spraying process suitable for the inner cavity of aircraft radome.

[0007] The present invention provides a special coating system suitable for the inner cavity of an aircraft radome, comprising a primer and a topcoat; the primer comprises resin pigment A1, curing agent B1, and diluent C1; the ratio of resin pigment A1 to curing agent B1 is 6:1; the resin pigment A1 comprises 80-120 parts of silicone-modified epoxy resin, 20-30 parts of surface-modified hollow glass microspheres, 10-15 parts of modified flake mica, and 6-10 parts of zinc phosphate; the diluent C1 accounts for 20-30% of the resin pigment A1; The topcoat comprises hydroxyl acrylic resin color paste A2, silicone-modified polyisocyanate waterborne curing agent B2, and diluent C2; the ratio of hydroxyl acrylic resin color paste A2 to silicone-modified polyisocyanate waterborne curing agent B2 is 4:1; the hydroxyl acrylic resin color paste A2 comprises 35-45 parts hydroxyl acrylic resin, 8-12 parts silica, 12-18 parts graphite, 1-3 parts carbon black, and 3-8 parts ferrite compound; the diluent C2 accounts for 20-30% of the hydroxyl acrylic resin color paste A2.

[0008] The aforementioned special coating system suitable for the inner cavity of aircraft radomes, wherein the surface-modified hollow glass microspheres are epoxy-silane coupling agent-modified hollow glass microspheres, and their D... 50 It is 5 μm.

[0009] In the aforementioned special coating system suitable for the inner cavity of an aircraft radome, the epoxy silane coupling agent is 0.5-1.0% of the mass of the hollow glass microspheres.

[0010] The aforementioned special coating system suitable for the inner cavity of aircraft radomes, wherein the modified flake mica is flake mica treated with a silane coupling agent, and its D... 50 It is 15 μm.

[0011] In the aforementioned special coating system suitable for the inner cavity of aircraft radomes, diluent C1 accounts for 25% of resin pigment A1.

[0012] In the aforementioned special coating system suitable for the inner cavity of aircraft radomes, diluent C2 accounts for 25% of resin pigment A2.

[0013] The aforementioned special coating system for the inner cavity of an aircraft radome, wherein the hydroxyl acrylic resin color paste A2 comprises 40 parts hydroxyl acrylic resin, 10 parts silica, 15 parts graphite, 2 parts carbon black, and 5 parts ferrite compound.

[0014] This invention also provides a spraying process for a special coating system suitable for the inner cavity of an aircraft radome, comprising the following steps: (1) Substrate cleaning and pretreatment: Clean the spray gun and the containers and instruments used, and clean the inner surface of the radome; (2) Primer preparation and spraying: Weigh components A1 and B1 according to the ratio, mix the two components and stir evenly, add thinner C1 to adjust the viscosity of the paint to 15-18s and stir evenly, then let it mature for 10-20 minutes; after filtering, use an air suction spray gun to spray the mixed primer onto the surface to be coated, spray pressure 0.20-0.40MPa, speed 120 rpm, distance between the spray gun nozzle and the surface to be coated 100-150mm, the thickness of each spray is 10-12 μm, after each spray, let it dry for 5-10 minutes before the next spray, spray a total of 2-3 times; (3) Primer layer treatment: After the primer is sprayed, let it air dry at room temperature for 30 to 45 minutes, and then heat it at 55 to 65℃ for 5 to 6 hours to complete the curing; after curing, lightly sand the surface of the primer coating until it is smooth and glossy, and then wipe it clean with thinner. (4) Preparation and spraying of topcoat: Weigh components A2 and B2 according to the ratio, mix the two components and stir evenly, add thinner to adjust the viscosity to 15-18s, stir evenly again, and let it mature for 10-30 minutes; after filtering, use an air suction spray gun to spray the mixed topcoat onto the surface to be coated, with a spraying pressure of 0.20-0.40MPa, a rotation speed of 120 rpm, a distance of 100-150mm between the spray gun nozzle and the surface to be coated, and a thickness of 10-15μm for each coat. After each coat, let it dry for 5-10 minutes before applying the next coat. A total of 2-3 coats are applied. (5) Curing: After the topcoat is sprayed, let it air dry at room temperature for 30 to 45 minutes, and then heat it at 55 to 65℃ for 4 to 5 hours to complete the curing.

[0015] In the above-mentioned special coating system for the inner cavity of aircraft radome, the spraying pressure of the first coat of primer in step (2) is 0.20 MPa; the spraying pressure of the second and third coats is 0.25 MPa.

[0016] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention utilizes a carefully selected primer filler system, leveraging the low water absorption and spherical structure of surface-modified hollow glass microspheres, and the dense physical barrier effect of modified sheet-like mica, to synergistically construct a highly efficient composite physical barrier, significantly extending the penetration paths of water, oxygen, and corrosive ions. On this basis, zinc phosphate provides active chemical corrosion inhibition protection. This composite system effectively blocks media penetration while also optimizing the dielectric properties of the coating: low-dielectric hollow glass microspheres help reduce the overall dielectric loss and ion migration tendency of the coating, while high-dielectric, sheet-like mica powder, in addition to physical barrier properties, also contributes to homogenizing the local electric field distribution through its interface effect. These three elements work synergistically from the perspectives of physical barrier, chemical corrosion inhibition, and dielectric property optimization, jointly constructing a comprehensive protection mechanism for the inner cavity of the aircraft radome. Attached Figure Description

[0017] Figure 1 Images of the coating in Embodiment 1 of the present invention; Figure 2 This is a coating image of Comparative Example 1 of the present invention; Figure 3 This is a coating image for Comparative Example 2 of the present invention; Figure 4 This is a coating image of Comparative Example 3 of the present invention; Figure 5 This is a picture of the coating in Comparative Example 4 of the present invention. Detailed Implementation

[0018] To address the shortcomings and problems of current protective coating systems, this invention provides a special coating system and spraying process suitable for the inner cavity of aircraft radomes. The invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0019] Example 1: The special coating system for the inner cavity of an aircraft radome provided in this example includes a primer and a matte topcoat; wherein: the primer includes resin color paste A1, curing agent B1 and ethyl acetate; the ratio of resin color paste A1 to curing agent B1 is 6:1; the resin color paste A1 includes 80-120 parts of silicone-modified epoxy resin, 20-30 parts of surface-modified hollow glass microspheres, 10-15 parts of modified flaky mica and 6-10 parts of zinc phosphate; the ethyl acetate accounts for 20-30% of the resin color paste A1.

[0020] The matte topcoat comprises hydroxyl acrylic resin color paste A2, silicone-modified polyisocyanate waterborne curing agent B2, and ethyl acetate; the ratio of hydroxyl acrylic resin color paste A2 to silicone-modified polyisocyanate waterborne curing agent B2 is 4:1; the hydroxyl acrylic resin color paste A2 comprises 40 parts hydroxyl acrylic resin, 10 parts silica, 15 parts graphite, 2 parts carbon black, and 5 parts ferrite compound; the ethyl acetate accounts for 20-30% of the hydroxyl acrylic resin color paste A2.

[0021] Common nozzle diameters range from 0.5 to 5.0 mm. Generally, 0.5 mm to 0.7 mm nozzles are used for easily atomized coatings such as colorants; 1.0 mm to 1.8 mm nozzles are used for synthetic resin coatings; 2.0 mm to 2.5 mm nozzles are used for higher viscosity coatings such as orange peel paint; and 3.0 mm to 5.0 mm nozzles are used for viscous coatings such as quick-setting adhesives and anti-stone chip coatings. Therefore, experiments were conducted using different nozzle diameters on suction spray guns. Smaller diameter nozzles can produce highly atomized coatings, allowing for more even coating coverage during spraying. While small-diameter nozzles limit paint flow and reduce spraying efficiency, medium-diameter nozzles achieve a good balance between paint flow and atomization, ensuring both sufficient spraying efficiency and uniform paint coverage. Large-diameter nozzles, due to their high flow rate, can hold more paint, making them suitable for large-area spraying and thicker coatings, but they reduce paint atomization, resulting in uneven paint coverage on the object's surface. To meet the spraying requirements of the confined space within the radome, a custom-designed 1.5mm nozzle diameter suction spray gun was selected for spraying paint into the radome's interior.

[0022] To ensure coating uniformity, the aforementioned coating system was used. Both the primer and topcoat were applied in three coats, with the spray gun nozzle 120mm from the surface. Each coat was allowed to dry at room temperature for 10 minutes before the next coat. The pressure for the first coat was 0.2MPa, and the pressure for the second and third coats was 0.25MPa. Several different spray angles were also tested. a) The first coat is sprayed at an angle of 90°, the second coat at an angle of 45-60°, and the third coat at an angle of 90°. b) The first coat is sprayed at an angle of 45-60°, the second coat at an angle of 90°, and the third coat at an angle of 45-60°. c) The first coat is sprayed at an angle of 45-60°, the second coat at an angle of 45-60°, and the third coat at an angle of 90°. d) The first coat is sprayed at an angle of 45°, the second coat at an angle of 90°, and the third coat at an angle of 90°. e) The first coat is sprayed at an angle of 45°, the second coat at an angle of 90°, and the third coat at an angle of 60°; f) The first coat is sprayed at an angle of 45°, the second coat at an angle of 60°, and the third coat at an angle of 90°; g) The first coat is sprayed at an angle of 90°, the second coat at an angle of 90°, and the third coat at an angle of 45°; h) The first coat is sprayed at an angle of 90°, the second coat at an angle of 60°, and the third coat at an angle of 45°; After multiple rounds of testing and verification, methods c, f, and h showed the best results. The sloped and reflective surfaces were found to be uniform, with no gaps or drips. Ultimately, the f method was selected for spraying angle in subsequent tests.

[0023] To verify the effect of rotational speed and spraying time per pass on the coating, the following five rotational speeds and spraying times were tested respectively. a) At a speed of 60 rpm, the spraying time for each coat is 1 second, 1 second, and 1 second; b) At a rotation speed of 80 rpm, the spraying time is 1.5 seconds, 1.5 seconds, and 1.5 seconds; c) At a rotation speed of 100 rpm, the spraying time is 2 seconds, 2 seconds, and 2 seconds; d) At a rotation speed of 120 rpm, the spraying time is 2.5 seconds, 2.5 seconds, and 2.5 seconds respectively; e) At a rotation speed of 140 rpm, the spraying time is 3 seconds, 3 seconds, and 3 seconds; After multiple rounds of testing, methods c and d showed the best results, producing a uniform and delicate paint surface in the wet film state. The thickness of the beveled and reflective surfaces was uniform within the ideal range, with no missed spots or runs. Method e had reached its maximum paint film thickness, and some paint films showed a tendency towards an orange peel texture. Therefore, the appropriate spraying time for each coat was controlled at 2–2.5 seconds, and the rotation speed of the rotary table during spraying was 100–120 rpm. Ultimately, the rotation speed and spraying time of scheme d were selected for subsequent tests.

[0024] Based on industry experience, a temperature of 15-25℃ is suitable for spraying operations. Taking into account the characteristics of this functional paint, a humidification device was added to the semi-enclosed operating space that controls air flow and air filtration to test the paint film formation under different humidity conditions.

[0025] When the humidity is 15-25%, there are tiny particles on the surface of the paint film, with a probability of about 30%, and the surface drying time is about 1 hour. When the humidity is 25-35%, there is only one small particle on the paint film surface, with a probability of about 10%, and the surface drying time is about 1 hour. When the humidity is 35-45%, the paint film surface is smooth and the surface drying time is about 2 hours. When the humidity is 45-55%, the paint film surface is smooth and the surface drying time is about 2.5 hours. When the humidity is 65-75%, it is difficult to achieve a high humidity in a non-completely enclosed space because the season is relatively dry during the test period. Therefore, this condition will not be verified.

[0026] It is evident that the optimal spraying conditions are within the range of 15–25℃ and 35–55% humidity; ultimately, a humidity of 35–45% was selected as the optimal spraying and drying conditions.

[0027] Based on the above parameter optimization results, the spraying process of the special coating system suitable for the inner cavity of the aircraft radome adopted in this embodiment specifically includes the following steps: (1) Substrate cleaning and pretreatment: Clean the spray gun and the containers and instruments used with ethyl acetate, and clean and dry blow sandblast the inner surface of the radome. After sandblasting, use compressed air to remove the dust, debris and abrasive remaining on the surface. Then use a silk cloth dipped in ethyl acetate to wipe the surface to be coated. After wiping, remove dirt from the cloth surface. (2) Primer preparation and spraying: Weigh components A1 and B1 according to the ratio, mix the two components and stir evenly, add ethyl acetate to adjust the viscosity of the paint to 15-18s and stir evenly, then let it mature for 10-20 min; after filtering, use an air suction spray gun to spray the mixed primer onto the surface to be coated, spray pressure 0.20MPa, distance between the spray gun nozzle and the surface to be coated 120mm, speed 120 rpm, spray for 2.5s; the thickness of each spray is 10-12 μm, after each spray, let it dry for 10min before the next spray, spray a total of 3 coats; (3) Primer layer treatment: After the primer is sprayed, let it air dry at room temperature for 30 to 45 minutes, and then heat it at 55 to 65℃ for 5 hours to complete the curing. After curing, gently sand the surface of the primer coating until it is smooth and glossy, and then wipe it clean with thinner. (4) Preparation and spraying of topcoat: Weigh components A2 and B2 according to the ratio, mix the two components and stir evenly, add thinner to adjust the viscosity to 15-18s, stir evenly again, and mature for 10-30min; after filtering, use an air suction spray gun to spray the mixed topcoat onto the surface to be coated, spray pressure 0.20MPa, speed 120 rpm, spray for 2.5s, distance between the spray gun nozzle and the surface to be coated 120mm, each spray thickness 10-15μm, after each spray, let it dry for 5-10min before the next spray, spray a total of 3 coats; (5) Curing: After the topcoat is sprayed, allow it to air dry at room temperature for 30-45 minutes, then heat it at 55-65℃ for 4 hours to complete the curing. The coating is as follows: Figure 1 As shown, the coating surface is smooth and uniform, with no defects.

[0028] The results of tests on the flexibility, adhesion and impact resistance of the coating are shown in Table 1 below.

[0029]

[0030] Comparative Example 1: The similarities between this comparative example and the embodiments will not be repeated, except that the addition ratio of thinner in the primer and topcoat is 15% of the resin material; the resulting coating is as follows. Figure 2 As shown in the figure, when the diluent addition ratio is reduced, defects such as pinholes and uneven paint film appear in the coating after spraying. The test results of the coating's flexibility, adhesion, and impact resistance are shown in Table 2 below.

[0031]

[0032] Comparative Example 2: The similarities between this comparative example and Example 1 will not be repeated here. The difference lies in that the diluent added to the primer and topcoat is 40% of the resin material; the resulting coating is as follows... Figure 3 As shown, when the diluent content is high, defects such as sagging and edge buildup appear in the coating after spraying. The test results of the coating's flexibility, adhesion, and impact resistance are shown in Table 3 below.

[0033]

[0034] Comparative Example 3: The similarities between this comparative example and Example 1 will not be repeated here. The difference is that a gravity spray gun was used for spraying; the resulting coating is as follows. Figure 4 As shown, the coating applied using a gravity spray gun exhibits defects such as snowflake-like patterns and uneven paint film. The test results for the coating's flexibility, adhesion, and impact resistance are shown in Table 4 below.

[0035]

[0036] Comparative Example 4: The similarities between this comparative example and Example 1 will not be repeated here. The difference is that a special spray gun with a long nozzle was used for spraying; the resulting coating is as follows. Figure 5 As shown, using a special spray gun with a long nozzle resulted in defects such as undercoat defects and uneven paint film. The test results for the coating's flexibility, adhesion, and impact resistance are shown in Table 5 below.

[0037]

[0038] The above description is only a preferred embodiment of the present invention and does not limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A special coating system suitable for the inner cavity of an aircraft radome, characterized in that: Includes primer and topcoat; The primer comprises resin color paste A1, curing agent B1, and diluent C1; the ratio of resin color paste A1 to curing agent B1 is 6:1; resin color paste A1 comprises 80-120 parts of silicone-modified epoxy resin, 20-30 parts of surface-modified hollow glass microspheres, 10-15 parts of modified flaky mica, and 6-10 parts of zinc phosphate; the diluent C1 accounts for 20-30% of resin color paste A1. The topcoat comprises hydroxyl acrylic resin color paste A2, silicone-modified polyisocyanate waterborne curing agent B2, and diluent C2; the ratio of hydroxyl acrylic resin color paste A2 to silicone-modified polyisocyanate waterborne curing agent B2 is 4:1; the hydroxyl acrylic resin color paste A2 comprises 35-45 parts hydroxyl acrylic resin, 8-12 parts silica, 12-18 parts graphite, 1-3 parts carbon black, and 3-8 parts ferrite compound; the diluent C2 accounts for 20-30% of the hydroxyl acrylic resin color paste A2.

2. The special coating system for the inner cavity of an aircraft radome according to claim 1, characterized in that: The surface-modified hollow glass microspheres are epoxy-silane coupling agent-modified hollow glass microspheres, and their D... 50 It is 5 μm.

3. The special coating system for the inner cavity of an aircraft radome according to claim 2, characterized in that: The epoxy silane coupling agent is 0.5-1.0% of the mass of the hollow glass microspheres.

4. The special coating system for the inner cavity of an aircraft radome according to claim 1, characterized in that: The modified flaky mica is flaky mica treated with a silane coupling agent, and its D... 50 It is 15 μm.

5. The special coating system for the inner cavity of an aircraft radome according to claim 1, characterized in that: The diluent C1 is ethyl acetate, which accounts for 25% of the resin color paste A1.

6. The special coating system for the inner cavity of an aircraft radome according to claim 1, characterized in that: The diluent C2 is ethyl acetate, which accounts for 25% of the resin color paste A2.

7. The special coating system for the inner cavity of an aircraft radome according to claim 1, characterized in that: The hydroxyl acrylic resin color paste A2 comprises 40 parts hydroxyl acrylic resin, 10 parts silica, 15 parts graphite, 2 parts carbon black, and 5 parts iron oxide compound.

8. A spraying process for a special coating system suitable for the inner cavity of an aircraft radome, characterized in that: Includes the following steps: (1) Substrate cleaning and pretreatment: Clean the spray gun and the containers and instruments used, and clean the inner surface of the radome; (2) Primer preparation and spraying: Weigh components A1 and B1 according to the ratio, mix the two components and stir evenly, add thinner C1 to adjust the viscosity of the paint to 15-18s and stir evenly, then let it mature for 10-20 minutes; after filtering, use an air suction spray gun to spray the mixed primer onto the surface to be coated, spray pressure 0.20-0.40MPa, speed 120 rpm, distance between the spray gun nozzle and the surface to be coated 100-150mm, the thickness of each spray is 10-12 μm, after each spray, let it dry for 5-10 minutes before the next spray, spray a total of 2-3 times; (3) Primer layer treatment: After the primer is sprayed, let it air dry at room temperature for 30 to 45 minutes, and then heat it at 55 to 65℃ for 5 to 6 hours to complete the curing; after curing, lightly sand the surface of the primer coating until it is smooth and glossy, and then wipe it clean with thinner. (4) Preparation and spraying of topcoat: Weigh components A2 and B2 according to the ratio, mix the two components and stir evenly, add thinner to adjust the viscosity to 15-18s, stir evenly again, and let it mature for 10-30 minutes; after filtering, use an air suction spray gun to spray the mixed topcoat onto the surface to be coated, with a spraying pressure of 0.20-0.40MPa, a rotation speed of 120 rpm, a distance of 100-150mm between the spray gun nozzle and the surface to be coated, and a thickness of 10-15μm for each coat. After each coat, let it dry for 5-10 minutes before applying the next coat. A total of 2-3 coats are applied. (5) Curing: After the topcoat is sprayed, let it air dry at room temperature for 30 to 45 minutes, and then heat it at 55 to 65℃ for 4 to 5 hours to complete the curing.

9. The spraying process for the special coating system suitable for the inner cavity of an aircraft radome according to claim 8, characterized in that: In step (2), the pressure for the first coat of primer is 0.20 MPa; the pressure for the second and third coats is 0.25 MPa.

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