An electromagnetic shielding coating material for a foam frangible cap and a method of preparing the same

Abstract

This invention provides an electromagnetic protective coating material for a fragile foam cover and its preparation method. The material is polyurethane foam, and a six-layer coating structure is applied to the concave and convex surfaces of the polyurethane foam fragile cover. The concave surface of the fragile cover contains five coating layers, and the convex surface contains one coating layer. Heat treatment and post-curing treatment of the polyurethane foam fragile cover substrate effectively improve the polymerization degree of polyurethane, remove adsorbed moisture from the substrate, and avoid blistering and bulging problems during coating curing and high-temperature testing. This invention employs a multi-layer coating system, namely, by applying a microwave-absorbing putty in two coats, preparing a sealing clear coat layer and a primer layer, etc., to improve the airtightness of the porous foam fragile cover, providing an effective sealed environment for the inert gas filled inside the missile cartridge, preventing corrosion of precision components in the missile, and has significant potential for widespread application.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic shielding materials, and in particular to an electromagnetic shielding coating material for fragile foam covers and its preparation method. Background Technology

[0002] There are three types of opening methods for missile storage and launch containers: mechanical opening, explosive opening, and fragile opening. The fragile opening type uses uncontrolled opening technology. Due to its advantages such as light weight, high reliability, superior safety, and ease of use, the fragile end cap type has received widespread attention and is developing rapidly. Currently, resin-based composite materials or foam substrates are mainly used as the main materials for fragile missile launch container covers in China. Polyurethane foam fragile covers have become one of the more widely used materials due to their light weight, low cost, and controllable manufacturing process.

[0003] However, in actual use, it was found that polyurethane foam is extremely hygroscopic, causing the coatings sprayed on the inner and outer surfaces of the polyurethane foam fragile cover, such as the primer and topcoat, to blister during the curing process. This is particularly noticeable when the fragile cover is subjected to high-temperature environmental performance tests, resulting in large-scale bulging and leading to substandard product quality and a significant drop in yield. Furthermore, because the polyurethane foam fragile cover is a wave-transparent material, it lacks electromagnetic shielding capabilities and cannot protect the delicate electronic components inside the missile launch tube from being ablated by external high-energy electromagnetic waves, making it unsuitable for the protection requirements of current electromagnetic warfare.

[0004] Chinese patent document CN116200103A discloses a corrosion-resistant electromagnetic shielding coating, its preparation method, application, and wind power generation equipment. The method involves uniformly mixing nitrides, oxides, resins, and organic solvents, followed by dispersion treatment. By adjusting the ratio of nitrides to oxides, different electromagnetic interference resistance properties are obtained. A self-cleaning coating is prepared based on this electromagnetic shielding coating. During coating spraying, the corrosion-resistant shielding coating possesses the dual advantages of corrosion resistance and electromagnetic interference resistance. However, while this corrosion-resistant electromagnetic shielding coating meets the requirements for seawater corrosion resistance, it is not suitable for use in high-temperature environments. Furthermore, this shielding coating requires the dispersion treatment of multiple components to form the first component of nitrides and oxides. High-speed mixers are used for filler processing, dispersion filtration, and grinding. Subsequent batching and pre-firing are also required, making the process complex, demanding high-end equipment, and limiting its application. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an electromagnetic protection coating material for foam fragile covers and its preparation method, thereby solving the problems that existing polyurethane foam fragile covers do not have electromagnetic protection function, and that fragile covers blister and bubble due to the material's easy absorption of moisture.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: an electromagnetic protective coating material for a foam fragile cover and its preparation method, comprising a fragile cover, the fragile cover material being polyurethane foam, and a six-layer coating structure being coated on the concave and convex surfaces of the polyurethane foam fragile cover, wherein the concave surface of the fragile cover contains five layers of coating structure and the convex surface of the fragile cover contains one layer of coating structure.

[0007] In the preferred embodiment, the five-layer coating structure of the concave surface of the fragile cover, from the closest to the substrate, consists of: a microwave-absorbing putty layer; a sealing varnish layer; a primer layer; an electromagnetic shielding layer; and a topcoat layer.

[0008] The convex surface of the fragile cap is the second coat of paint.

[0009] In the preferred embodiment, the resin used in the microwave-absorbing putty layer is one or more of epoxy resin, polyurethane resin, polyurea resin, fluorocarbon resin, and polyacrylamide resin.

[0010] The absorbents used in the microwave-absorbing putty layer include one or more of the following: magnetic absorbents, dielectric absorbents, and semiconductor absorbents.

[0011] In the preferred embodiment, the sealing varnish layer is one or more of nitrocellulose varnish, acrylic varnish, epoxy resin varnish, polyurethane varnish, fluorocarbon varnish, and epoxy polyamide varnish.

[0012] In the preferred embodiment, the primer layer is one or more of the following: epoxy zinc-rich primer, iron oxide alkyd primer, inorganic zinc silicate primer, epoxy zinc phosphate primer, and zinc yellow polyurethane primer.

[0013] In the preferred embodiment, the resin used for the electromagnetic shielding layer is one or more of epoxy resin, polyurethane resin, polyurea resin, fluorocarbon resin, and polyacrylamide resin.

[0014] The conductive powder used in the electromagnetic shielding layer includes one or more of the following: copper powder, silver powder, silver-coated copper powder, nickel-plated carbon nanotubes, and three-dimensional graphite.

[0015] In the preferred embodiment, the thickness of the electromagnetic shielding layer is 60μm~180μm, and the thickness of the electromagnetic shielding layer is controlled by the amount of material applied during spraying.

[0016] In the preferred embodiment, the topcoat layer and the second topcoat layer are one or more of the following: chlorofluoroethylene anticorrosive topcoat, acrylic polyurethane topcoat, nitrocellulose matte topcoat, polyvinyl chloride fluorinated topcoat, epoxy phenolic resin topcoat, and fluorocarbon semi-gloss topcoat.

[0017] An electromagnetic protection coating material for a fragile foam cover and its preparation method, the method being: S1, substrate grinding: grinding the concave and convex surfaces of the fragile polyurethane foam cover, removing the release agent on the two outer surfaces, puncturing the release agent film outside the pores, and grinding the inner surface of the pores to roughness.

[0018] S2. Heat treatment: Place the polished polyurethane foam fragile cover at 60℃ and dry for 12 hours;

[0019] S3. Let stand: Place the heat-treated polyurethane foam fragile cover in a spray booth at room temperature and humidity not exceeding 65%RH for 1 to 2 hours.

[0020] S4. Apply microwave-absorbing putty: Mix microwave-absorbing putty of appropriate viscosity and apply it to the concave surface of the fragile polyurethane foam cover.

[0021] S5. Putty curing and sanding: Place the polyurethane foam fragile cover after applying the microwave-absorbing putty at 60℃ and bake until fully cured; use sandpaper with a grit of not less than 120 to sand the microwave-absorbing putty layer until the surface is smooth.

[0022] S6. Preparation of sealing varnish layer: Spray the sealing varnish onto the microwave-absorbing putty layer and bake it at 60°C until it is fully cured. After curing, lightly sand the varnish layer with sandpaper of not less than 240 grit until the surface is rough.

[0023] S7. Preparation of primer layer: Spray the primer onto the sealing clear coat and bake at 60°C until fully cured. After curing, lightly sand the primer layer with sandpaper of not less than 240 grit until the surface is rough.

[0024] S8. Preparation of electromagnetic shielding layer: Spray electromagnetic shielding paint onto the primer layer and bake at 60°C until fully cured. Generally, the electromagnetic shielding layer is not polished.

[0025] S9. Preparation of topcoat layer: Spray the topcoat onto the electromagnetic shielding layer and bake it at 60°C until fully cured. Then, follow the same procedure to prepare the second topcoat layer on the convex surface of the polyurethane foam fragile cover.

[0026] In the preferred embodiment, in step S4, the microwave-absorbing putty layer needs to be applied in two coats: the first coat fills the holes in the concave surface of the foam substrate, and the second coat further fills the holes based on the first coat and fills the pores that were formed after the first coat of putty. The second coat can only be applied after the microwave-absorbing putty after the first coat has dried to the touch.

[0027] This invention provides an electromagnetic protective coating material for fragile foam covers and its preparation method. The invention involves heat treatment and post-curing treatment of the polyurethane foam fragile cover substrate, which effectively improves the degree of polymerization of polyurethane, removes the moisture adsorbed in the substrate, and avoids problems such as blistering and bulging during coating curing and high-temperature testing.

[0028] This invention employs a multi-layer coating system, namely, by applying two coats of microwave-absorbing putty, preparing a sealing varnish layer, and a primer layer, which improves the airtightness of the porous foam fragile cover. This provides an effective sealed environment for the inert gas filling the missile tube, preventing corrosion of the precision components inside the missile. Simultaneously, the smooth, dense, and continuous surface enables high and stable electromagnetic shielding effectiveness when coated with a thin electromagnetic shielding layer.

[0029] The dual protection method of electromagnetic wave absorption by the electromagnetic wave absorption property of the absorbing putty and electromagnetic wave shielding property of the electromagnetic shielding layer can effectively improve the electromagnetic shielding performance of the fragile foam cover, protecting the precision electronic components inside the missile tube and missile warhead from being burned by high-energy electromagnetic waves, making it suitable for widespread use. Attached Figure Description

[0030] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0031] Figure 1 This is a schematic diagram of the fragile cover substrate and its coating system on its uneven surfaces according to the present invention;

[0032] In the diagram: Wave-absorbing putty layer 1; Sealing varnish layer 2; Primer layer 3; Electromagnetic shielding layer 4; Topcoat layer 5; Second topcoat layer 6; Fragile cap 7. Detailed Implementation

[0033] Example 1:

[0034] like Figure 1 This invention discloses an electromagnetic protection coating material for a fragile foam cover and its preparation method. The material of the fragile foam cover 7 is polyurethane foam. A six-layer coating structure is applied to the concave and convex surfaces of the polyurethane foam fragile cover 7. The concave surface of the fragile cover 7 contains five coating layers, and the convex surface contains one coating layer. With this structure, the present invention effectively improves the degree of polymerization of polyurethane by performing heat treatment and post-curing treatment on the polyurethane foam fragile cover substrate, removes adsorbed moisture from the substrate, and avoids problems such as blistering and bulging during coating curing and high-temperature testing.

[0035] 2. This invention employs a multi-layer coating system, namely, by applying microwave-absorbing putty in two coats, preparing a sealing varnish layer and a primer layer, etc., to improve the airtightness of the porous foam fragile cover, providing an effective sealed environment for the inert gas filled inside the missile tube and preventing corrosion of the precision components in the missile. At the same time, the smooth, dense and continuous surface enables high and stable electromagnetic shielding performance when a thin electromagnetic shielding layer is applied.

[0036] 3. The dual protection method of electromagnetic wave absorption by the electromagnetic wave absorption property of the electromagnetic shielding layer and electromagnetic wave shielding property of the electromagnetic wave absorption putty can effectively improve the electromagnetic shielding performance of the fragile foam cover and protect the precision electronic components inside the missile tube and the missile warhead from being burned by high-energy electromagnetic waves.

[0037] In the preparation method of the electromagnetic protective coating material for the fragile foam cover, the heat treatment involves two aspects. First, it removes moisture from the hygroscopic polyurethane foam substrate to prevent bubbling during coating preparation. Second, it performs a post-curing treatment on the polyurethane foam to further improve the degree of polymerization of the material, remove residual small molecules, and prevent bulging of the fragile polyurethane foam cover 7 during high-temperature testing.

[0038] By performing a curing treatment on the fragile cover 7, the degree of polymerization of polyurethane is further improved, preventing the bubbling of the substrate caused by the evaporation of incompletely polymerized small molecules in the polyurethane foam during high-temperature environmental testing. Secondly, by heat-treating the polyurethane foam fragile cover 7, the moisture absorbed by the substrate is removed, and then the pores are filled with putty in a dry environment. Combined with the use of a sealing varnish layer 2, a dense and continuous sealing film is formed on the concave surface of the fragile cover 7. This effectively prevents the foam fragile cover 7 from absorbing moisture again and from bubbling. It can provide an effective sealed environment for the inert gas filled in the cartridge; thirdly, the surface of the porous foam substrate is coated with a three-layer structure, namely, filling with microwave-absorbing putty layer 1, sealing varnish layer 2 and primer layer 3, to form a smooth, dense and continuous surface, and then an electromagnetic shielding layer 4 is sprayed on it, which can achieve high electromagnetic shielding efficiency and performance stability under relatively thin conditions; fourthly, the dual protection method of electromagnetic wave absorption of microwave-absorbing putty and electromagnetic wave shielding of electromagnetic shielding layer 4 can effectively improve the electromagnetic shielding efficiency of the fragile foam cover 7.

[0039] In the preferred embodiment, the five-layer coating structure contained in the concave surface of the fragile cover 7, from the closest to the substrate, is as follows: microwave absorbing putty layer 1; sealing clear varnish layer 2; primer layer 3; electromagnetic shielding layer 4; topcoat layer 5;

[0040] The convex surface of the fragile cap 7 is the second paint layer 6.

[0041] In the preferred embodiment, the resin used in the microwave absorbing putty layer 1 is one or more of epoxy resin, polyurethane resin, polyurea resin, fluorocarbon resin, and polyacrylamide resin.

[0042] The absorbent used in the microwave absorbing putty layer 1 includes one or more of magnetic absorbents, dielectric absorbents, and semiconductor absorbents. Magnetic absorbents, by definition, are adsorbents or separators that can adsorb or separate substances through magnetic action. Magnetic adsorbents can be applied in various fields such as water treatment, environmental cleaning, food processing, and pharmaceuticals. Their main characteristics are high efficiency, convenience, environmental friendliness, and the ability to be easily recycled and reused using an external magnetic field. Magnetic absorbents include magnetic nanoparticles, magnetic activated carbon, magnetic ion exchange resins, or magnetic porous materials. Dielectric absorbents are absorbing materials that can absorb electromagnetic waves through their dielectric properties. Dielectric absorbents are generally composite materials, whose basic components are materials with high dielectric constants and high dielectric loss factors. Dielectric absorbents include polymer composite materials: such as polymer resins and rubber; and metal oxides: such as ferrites and strontium titanate. Semiconductor absorbents are electromagnetic wave absorbing materials prepared using semiconductor materials. Common semiconductor absorbers include carbon-based materials: graphene, carbon nanotubes; silicon carbide; silicon nitride; zinc oxide.

[0043] In the preferred embodiment, the sealing varnish layer 2 is one or more of nitrocellulose varnish, acrylic varnish, epoxy resin varnish, polyurethane varnish, fluorocarbon varnish, and epoxy polyamide varnish.

[0044] In the preferred embodiment, the primer layer 3 is one or more of the following: epoxy zinc-rich primer, iron oxide alkyd primer, inorganic zinc silicate primer, epoxy zinc phosphate primer, and zinc yellow polyurethane primer.

[0045] In the preferred embodiment, the resin used for the electromagnetic shielding layer 4 is one or more of epoxy resin, polyurethane resin, polyurea resin, fluorocarbon resin, and polyacrylamide resin.

[0046] The conductive powder used in the electromagnetic shielding layer 4 includes one or more of the following: copper powder, silver powder, silver-coated copper powder, nickel-plated carbon nanotubes, and three-dimensional graphite.

[0047] In the preferred embodiment, the thickness of the electromagnetic shielding layer 4 is 60μm~180μm, and the thickness of the electromagnetic shielding layer 4 is controlled by the amount of material applied during spraying.

[0048] In the preferred embodiment, the topcoat layer 5 and the second topcoat layer 6 are one or more of the following: chlorofluoroethylene anticorrosive topcoat, acrylic polyurethane topcoat, nitrocellulose matte topcoat, polyvinyl chloride fluorinated topcoat, epoxy phenolic resin topcoat, and fluorocarbon semi-gloss topcoat.

[0049] Example 2:

[0050] Further explanation based on Example 1: An electromagnetic protective coating material for a foam fragile cover and its preparation method, including the following steps: An electromagnetic protective coating material for a foam fragile cover and its preparation method, the method is: S1, substrate grinding: Grinding the concave and convex surfaces of the polyurethane foam fragile cover 7, removing the release agent on the two outer surfaces, puncturing the release agent film outside the pores, and grinding the inner surface of the pores to roughness;

[0051] S2. Heat treatment: Place the polished polyurethane foam fragile cover 7 at 60℃ and dry for 12 hours.

[0052] S3. Let stand: Place the heat-treated polyurethane foam fragile cover 7 in a spray booth at room temperature and humidity not exceeding 65%RH for 1 to 2 hours.

[0053] S4. Apply microwave-absorbing putty: Mix microwave-absorbing putty of appropriate viscosity and apply it to the concave surface of the fragile polyurethane foam cover 7.

[0054] S5. Putty curing and sanding: Place the polyurethane foam fragile cover 7 after applying the microwave-absorbing putty at 60℃ and bake until fully cured; use sandpaper with a grit of not less than 120 to sand the microwave-absorbing putty layer 1 until the surface is smooth.

[0055] S6. Preparation of sealing varnish layer 2: Spray the sealing varnish onto the microwave absorbing putty layer 1, bake it at 60°C until it is completely cured, and lightly sand the cured varnish layer with sandpaper of not less than 240 grit until the surface is rough.

[0056] S7. Preparation of primer layer 3: Spray the primer onto the sealing clear coat layer 2, bake at 60°C until fully cured, and lightly sand the cured primer layer with sandpaper of not less than 240 grit until the surface is rough.

[0057] S8. Preparation of electromagnetic shielding layer 4: Spray electromagnetic shielding paint onto primer layer 3 and bake at 60°C until fully cured. Generally, electromagnetic shielding layer 4 is not polished.

[0058] S9. Preparation of topcoat layer 5: Spray the topcoat onto the electromagnetic shielding layer 4 and bake it at 60°C until fully cured. Then, follow the same procedure to prepare the second topcoat layer 6 on the convex surface of the polyurethane foam fragile cover 7.

[0059] In the preparation method of the electromagnetic protective coating material for the fragile foam cover, the heat treatment involves two aspects. First, it removes moisture from the hygroscopic polyurethane foam substrate to prevent bubbling during coating preparation. Second, it performs a post-curing treatment on the polyurethane foam to further improve the degree of polymerization of the material, remove residual small molecules, and prevent bulging of the fragile polyurethane foam cover 7 during high-temperature testing.

[0060] In the preferred embodiment, in step S4, the application of the microwave-absorbing putty layer 1 requires a two-coat application method: the first coat fills the holes in the concave surface of the foam substrate, and the second coat further fills the holes based on the first coat and fills the pores generated after the first coat of putty. The second coat can only be applied after the microwave-absorbing putty after the first coat has dried to the touch. The use of a sealing varnish layer 2 forms a dense and continuous sealing film on the concave surface of the fragile cover 7. This effectively prevents the foam fragile cover 7 from absorbing moisture and bubbling again, and provides an effective sealed environment for the inert gas filled in the cartridge. Thirdly, the porous foam substrate surface is coated with a three-layer structure, namely, a microwave-absorbing putty layer 1, a sealing varnish layer 2, and a primer layer 3, to form a smooth, dense, and continuous surface. Then, an electromagnetic shielding layer 4 is sprayed on it, which can achieve high electromagnetic shielding efficiency and performance stability under relatively thin conditions. Fourthly, the dual protection method of electromagnetic wave absorption by the microwave-absorbing putty and electromagnetic wave shielding by the electromagnetic shielding layer 4 can effectively improve the electromagnetic shielding efficiency of the foam fragile cover 7.

[0061] Example 3:

[0062] Further explanation based on Examples 1-2: An electromagnetic shielding coating material for fragile foam covers and its preparation method are used. In this example, the resin used in the microwave absorbing putty layer 1 is epoxy resin, and the added absorbent is a magnetic absorbent; the sealing varnish layer 2 is epoxy resin varnish; the primer layer 3 is epoxy zinc-rich primer; the resin used in the electromagnetic shielding layer 4 is epoxy resin, and the added conductive powder is silver-coated copper powder; the thickness of the electromagnetic shielding layer 4 is 100μm; the topcoat layer 5 and the second topcoat layer 6 are acrylic polyurethane topcoats.

[0063] Example 4:

[0064] Further explanation based on Examples 1-2: An electromagnetic shielding coating material for fragile foam covers and its preparation method are used. In this example, the resin used in the microwave absorbing putty layer 1 is epoxy resin, and the added absorbent is a magnetic absorbent; the sealing varnish layer 2 is epoxy resin varnish; the primer layer 3 is epoxy zinc-rich primer; the resin used in the electromagnetic shielding layer 4 is epoxy resin, and the added conductive powder is silver-coated copper powder; the thickness of the electromagnetic shielding layer 4 is 150μm; the topcoat layer 5 and the second topcoat layer 6 are acrylic polyurethane topcoats.

[0065] Example 5:

[0066] Further explanation based on Examples 1-2: An electromagnetic shielding coating material for fragile foam covers and its preparation method are used. In this example, the resin used in the microwave absorbing putty layer 1 is epoxy resin, and the added absorbent is a magnetic absorbent; the sealing varnish layer 2 is epoxy resin varnish; the primer layer 3 is epoxy zinc-rich primer; the resin used in the electromagnetic shielding layer 4 is epoxy resin, and the added conductive powder is silver-coated copper powder; the thickness of the electromagnetic shielding layer 4 is 60μm; the topcoat layer 5 and the second topcoat layer 6 are acrylic polyurethane topcoats.

[0067] Example 6:

[0068] Further explanation based on Examples 1-2: An electromagnetic shielding coating material for fragile foam covers and its preparation method are used. In this example, the resin used in the microwave absorbing putty layer 1 is epoxy resin, and the added absorbent is a magnetic absorbent; the sealing varnish layer 2 is epoxy resin varnish; the primer layer 3 is epoxy zinc-rich primer; the resin used in the electromagnetic shielding layer 4 is epoxy resin, and the added conductive powder is silver-coated copper powder; the thickness of the electromagnetic shielding layer 4 is 100 μm; the topcoat layer 5 and the second topcoat layer 6 are acrylic polyurethane topcoats.

[0069] The heat treatment in step S2 and the static setting operation in step S3 of Example 2 were removed during the preparation process.

[0070] Example 7:

[0071] Further explanation based on Examples 1-2: An electromagnetic shielding coating material for a fragile foam cover and its preparation method are used. In this example, the concave surface of the fragile cover 7 contains a four-layer coating structure. Starting from the layer closest to the substrate, the first layer is a sealing clear varnish layer 2, a primer layer 3, an electromagnetic shielding layer 4, and a topcoat layer 5. The convex surface of the fragile foam cover contains a second topcoat layer 6.

[0072] The sealing clear coat 2 is a fluorocarbon clear coat; the primer 3 is an iron oxide alkyd primer; the electromagnetic shielding layer 4 uses fluorocarbon resin and silver powder as the added conductive powder, and the thickness of the electromagnetic shielding layer 4 is 150μm; the topcoat layer 5 and the second topcoat layer 6 are fluorocarbon semi-gloss topcoats.

[0073] The process involves removing the application of microwave-absorbing putty in step S4 and the putty curing and sanding operations in step S5 of Example 2.

[0074] Example 8:

[0075] Further explanation based on Examples 1-2: An electromagnetic shielding coating material for a fragile foam cover and its preparation method are used. In this example, the concave surface of the fragile cover 7 contains a four-layer coating structure. Starting from the layer closest to the substrate, the first layer is an absorbing putty layer 1, a primer layer 3, an electromagnetic shielding layer 4, and a topcoat layer 5. The convex surface of the fragile foam cover contains a second topcoat layer 6.

[0076] The resin used in the microwave absorbing putty layer 1 is epoxy resin, and the added absorbent is a magnetic absorbent; the primer layer 3 is iron oxide alkyd primer; the resin used in the electromagnetic shielding layer 4 is fluorocarbon resin, and the added conductive powder is silver powder, with a thickness of 100μm; the topcoat layer 5 is fluorocarbon semi-gloss topcoat.

[0077] The preparation process involves removing the varnish layer from step S6 of Example 2.

[0078] Example 9:

[0079] Further explanation based on Examples 1-2: An electromagnetic shielding coating material for a fragile foam cover and its preparation method are used. In this example, the concave surface of the fragile cover 7 includes a three-layer coating structure, starting from the layer closest to the substrate: a first primer layer 3, an electromagnetic shielding layer 4, and a topcoat layer 5. The convex surface of the fragile foam cover includes a second topcoat layer 6.

[0080] In this embodiment, the primer layer 3 is iron oxide alkyd primer; the resin used in the electromagnetic shielding layer 4 is fluorocarbon resin, the added conductive powder is silver powder, and the thickness of the electromagnetic shielding layer 4 is 100μm; the topcoat layer 5 is nitrocellulose matte topcoat.

[0081] The process involves removing the microwave-absorbing putty in step S4, the putty curing and sanding in step S5, and the preparation of the varnish layer in step S6 of Example 2.

[0082] Example 10:

[0083] Further explanation based on Examples 1-2: An electromagnetic shielding coating material for a fragile foam cover and its preparation method are used. In this example, the concave surface of the fragile cover 7 comprises a five-layer coating structure, starting from the layer closest to the substrate: an absorbing putty layer 1, a sealing varnish layer 2, a primer layer 3, an electromagnetic shielding layer 4, and a topcoat layer 5. The convex surface of the fragile foam cover comprises a two-layer coating structure, with an additional absorbing putty layer added between the layer closest to the substrate and the second topcoat layer 6.

[0084] The resin used in the microwave absorbing putty layer 1 is epoxy resin, and the added absorbent is a magnetic absorbent; the sealing varnish layer 2 is epoxy resin varnish; the primer layer 3 is epoxy zinc-rich primer; the resin used in the electromagnetic shielding layer 4 is epoxy resin, and the added conductive powder is silver-coated copper powder, and the thickness of the electromagnetic shielding layer 4 is 100μm; the topcoat layer 5 and the second topcoat layer 6 are acrylic polyurethane topcoats.

[0085] In Example 2, steps S10 and S11 are added after the steps. Step S10: Prepare the microwave absorbing putty layer: Prepare the microwave absorbing putty layer on the convex surface according to the same process as the concave surface of the polyurethane foam fragile cover.

[0086] Step S11: Prepare the topcoat layer: Prepare the topcoat layer on the convex microwave-absorbing putty layer using the same procedure as the concave surface of the polyurethane foam fragile cover.

[0087] Example 11:

[0088] Further explanation based on Example 10: A schematic diagram of the coating system for the fragile cover substrate and its uneven surfaces is shown below. Figure 1 As shown in Table 1, the overall shielding effectiveness, high-temperature resistance, and burst value of the foam fragile caps with coating systems prepared in Examples 3-10 were tested respectively. The test methods involved are as follows:

[0089] 1. Shielding effectiveness test method:

[0090] The shielding effectiveness of the prepared coated foam fragile cover was tested using an NA7500 vector network analyzer, in accordance with the ASTM D4935-10 test standard.

[0091] 2. Temperature resistance test method:

[0092] The temperature resistance of the prepared coated foam fragile cover was tested using a KCW-408-2TS high and low temperature test chamber, in accordance with the GJB150.3A-2009 test standard.

[0093] 3. Burst pressure test method:

[0094] The WDW-E200D microcomputer-controlled electronic universal testing machine was used to load the fragile cover fixed on the fixture, and the installation and testing were carried out according to the tooling.

[0095]

[0096] Table 1: Summary of performance results of the foam fragile caps prepared in the examples

[0097] Example 12: In this invention, heat treatment and post-curing treatment of the moisture-absorbing polyurethane foam fragile cover are used to improve the degree of polymerization of polyurethane, remove the moisture adsorbed in the substrate, and avoid problems such as blistering and bulging during coating curing and high-temperature testing. As can be seen from Examples 3 and 6, under basically the same test conditions, the fragile cover prepared in Example 6 without heat treatment showed blistering after high-temperature testing.

[0098] In this invention, the fragility cover possesses excellent electromagnetic protection capabilities through the dual protection of the electromagnetic wave absorption properties of the absorbing putty layer 1 and the electromagnetic wave shielding properties of the electromagnetic shielding layer 4. Simultaneously, to ensure that the designed burst pressure of the fragility cover meets the technical specifications, this invention also verifies the effects of different thicknesses of the electromagnetic shielding layer 4 and the addition of the absorbing putty layer 1 to the convex surface of the fragility cover 7 on the burst pressure. As can be seen from Examples 3-5 and Example 10, the shielding effectiveness of the electromagnetic shielding layer 4 tends to increase with increasing thickness, but the increase is not significant after the thickness exceeds 100 μm; instead, it leads to an increase in burst pressure, causing it to fail to meet the design requirements. While adding the absorbing putty layer to the convex surface can further improve the overall shielding effectiveness and sealing of the fragility cover, the increased cohesion due to the increased total coating thickness significantly increases the burst pressure of the fragility cover, causing it to fail to meet the design requirements.

[0099] In this invention, the airtightness of the porous foam fragile cover is improved by applying a two-coat method of microwave-absorbing putty, preparing a sealing varnish layer 2, and a primer layer 3. This provides an effective sealed environment for the inert gas filling the missile cartridge, preventing corrosion of precision components. Furthermore, it effectively avoids secondary moisture absorption by the fragile cover and blistering and bulging during coating curing and high-temperature testing. Examples 3 and 5-7 show that reducing either the microwave-absorbing putty layer 1 or the sealing varnish layer 2 negatively impacts the temperature resistance of the fragile cover. Simultaneously, the multi-coat system manufacturing process makes the originally uneven concave surface of the fragile cover 7 smoother. The dense and continuous surface improves the continuity of the electromagnetic shielding layer 4, allowing it to achieve optimal electrical continuity with a thinner coating thickness, resulting in greater electromagnetic shielding performance. The above examples also demonstrate that the presence or absence of the microwave-absorbing putty layer 1 and the sealing varnish layer 2 significantly affects the overall electromagnetic shielding effectiveness of the fragile cover.

[0100] In summary, this invention solves the problem of coating blistering or substrate bulging caused by moisture absorption in polyurethane foam fragile covers, and enables the traditional foam fragile cover 7 to have excellent electromagnetic shielding performance of more than 60dB, protecting the internal components of the cartridge from damage by external high-energy electromagnetic waves.

[0101] The above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The embodiments and features described in these embodiments can be arbitrarily combined without conflict. The scope of protection of the present invention should be limited to the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A method for preparing an electromagnetic protection coating material for a fragile foam cover, the method comprising: Including S1, substrate grinding: Grind the concave and convex surfaces of the polyurethane foam fragile cover (7), remove the release agent on the two outer surfaces, puncture the release agent film outside the pores, and grind the inner surface of the pores to roughness. S2, Heat treatment: Place the polished polyurethane foam fragile cover (7) at 60℃ and dry for 12 hours; S3, stand: Place the heat-treated polyurethane foam fragile cover (7) in a spray booth at room temperature and humidity not exceeding 65%RH for 1 to 2 hours. S4. Apply absorbent putty: Prepare absorbent putty of appropriate viscosity and apply it to the concave surface of the polyurethane foam fragile cover (7); S5. Putty curing and sanding: Place the polyurethane foam fragile cover (7) after applying the microwave absorber putty at 60°C until it is fully cured; use sandpaper with a grit of not less than 120 to sand the microwave absorber putty layer (1) until the surface is smooth. S6. Preparation of sealing varnish layer (2): Spray the sealing varnish onto the microwave absorbing putty layer (1), bake it at 60°C until it is completely cured, and lightly sand the cured varnish layer with sandpaper of not less than 240 grit until the surface is rough. S7. Preparation of primer layer (3): Spray the primer onto the sealing clear coat layer (2), bake at 60°C until fully cured, and lightly sand the cured primer layer with sandpaper of not less than 240 grit until the surface is rough. S8. Preparation of electromagnetic shielding layer (4): Spray electromagnetic shielding paint onto primer layer (3) and bake at 60°C until fully cured. Do not polish electromagnetic shielding layer (4). S9. Preparation of topcoat layer (5): Spray the topcoat onto the electromagnetic shielding layer (4), bake it at 60°C until fully cured, and then prepare the second topcoat layer (6) on the convex surface of the polyurethane foam fragile cover (7) according to the same procedure. The preparation method uses an electromagnetic shielding coating material for a foam fragile cover. The electromagnetic shielding coating material for a foam fragile cover includes: a fragile cover (7), the material of the fragile cover (7) is polyurethane foam, and a six-layer coating structure is applied to the concave and convex surfaces of the polyurethane foam fragile cover (7). The concave surface of the fragile cover (7) contains five layers of coating structure, and the convex surface of the fragile cover (7) contains one layer of coating structure. The five-layer coating structure of the concave surface of the fragile cap (7) is as follows, starting from the closest to the substrate: microwave absorbing putty layer (1); sealing clear varnish layer (2); primer layer (3); electromagnetic shielding layer (4); topcoat layer (5); The convex surface of the fragile cap (7) is the second paint layer (6); The resin used in the microwave absorbing putty layer (1) is one or more of epoxy resin, polyurethane resin, polyurea resin, fluorocarbon resin, and polyacrylamide resin; The absorbent used in the microwave absorbing putty layer (1) includes one or more of magnetic absorbents, dielectric absorbents, and semiconductor absorbents; The type of resin used in the electromagnetic shielding layer (4) is one or more of epoxy resin, polyurethane resin, polyurea resin, fluorocarbon resin, and polyacrylamide resin; The conductive powder used in the electromagnetic shielding layer (4) includes one or more of copper powder, silver powder, silver-coated copper powder, nickel-plated carbon nanotubes, and three-dimensional graphite; The thickness of the electromagnetic shielding layer (4) is 60μm~100μm, and the thickness of the electromagnetic shielding layer (4) is controlled by the amount of material applied during spraying.

2. The method for preparing an electromagnetic protective coating material for a fragile foam cover according to claim 1, characterized in that: The sealing varnish layer (2) is one or more of nitrocellulose varnish, acrylic varnish, epoxy resin varnish, polyurethane varnish, fluorocarbon varnish, and epoxy polyamide varnish.

3. The method for preparing an electromagnetic protective coating material for a fragile foam cover according to claim 1, characterized in that: The primer layer (3) is one or more of the following: epoxy zinc-rich primer, iron oxide alkyd primer, inorganic zinc silicate primer, epoxy zinc phosphate primer, and zinc yellow polyurethane primer.

4. The method for preparing an electromagnetic protective coating material for a fragile foam cover according to claim 1, characterized in that: The topcoat layer (5) and the second topcoat layer (6) are one or more of the following: chlorofluoroethylene anticorrosive topcoat, acrylic polyurethane topcoat, nitrocellulose matte topcoat, polyvinyl chloride fluorinated topcoat, epoxy phenolic resin topcoat, and fluorocarbon semi-gloss topcoat.

5. The method for preparing an electromagnetic protective coating material for a fragile foam cover according to claim 1, characterized in that: Step S4 In the process of applying the microwave-absorbing putty layer (1), two coats of putty are required: the first coat is to fill the holes in the concave surface of the foam substrate, and the second coat is to fill the holes further on the basis of the first coat and fill the shrinkage pores generated after the first coat of putty. Before applying the second coat, it is necessary to wait until the surface of the microwave-absorbing putty after the first coat is dry.

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