A multilayer gradient wave-absorbing film for metal surface and a preparation method thereof

Abstract

The application discloses a multilayer gradient wave-absorbing film for a metal surface, which is arranged on the metal surface and sequentially comprises, from bottom to top, a primer layer, an absorber layer A, a transition layer, an absorber layer B and a flame-retardant layer; the primer layer is a resin layer; the transition layer is made of a flexible resin, and a reinforcing body is obtained by alternately stacking a wave-transparent material A and a wave-absorbing material B; the flame-retardant layer is made of a vinyl resin, and a reinforcing body is obtained by alternately stacking a wave-transparent material C and a wave-absorbing material D; and the multilayer gradient wave-absorbing film is provided with square resistance values that increase from top to bottom. The multilayer gradient wave-absorbing film is easy to bond with the metal surface, has high bonding strength, is provided with a multilayer structure, and can improve the overall environmental high-low temperature performance of the wave-absorbing film. The application can directly prepare a wave-absorbing layer on the metal surface of a weapon device or a carrier, and can make the weapon device or the carrier have a stealth performance without changing the original metal structure and appearance.

Description

A multilayer gradient absorbing film for metal surfaces and its preparation method Technical Field

[0001] This invention belongs to the field of microwave absorbing materials technology, specifically relating to a multilayer gradient microwave absorbing film for metal surfaces, its preparation method, and its application. Background Technology

[0002] With the rapid advancements in modern detection equipment and weaponry, the demand for stealth materials is constantly evolving to enhance the survivability and combat effectiveness of these systems. Requirements now extend beyond stealth performance to include flame retardancy, room temperature operability, and resistance to extreme temperatures. Upgrading the stealth capabilities of existing weapons and equipment typically involves directly applying stealth coatings or attaching radar-absorbing patches to the metal casing. The former method has high maintenance costs, while the latter, primarily using rubber-based radar-absorbing patches, often encounters problems like bulging and detachment during the bonding process, especially on large, curved surfaces. These issues not only affect the appearance but also negatively impact the overall stealth performance. Summary of the Invention

[0003] To enhance the stealth and flame-retardant properties of metal casings for weapons, equipment, or carriers, this invention provides a multilayer gradient absorbing film for metal surfaces without altering the original structural shape. This film achieves good adhesion to metal equipment and provides excellent stealth and flame-retardant properties without changing the structural shape of the weapon or carrier.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] This invention discloses a multilayer gradient absorbing film for use on a metal surface. The multilayer gradient absorbing film is disposed on the metal surface and, from bottom to top, consists of a base coating layer, absorber layer A, a transition layer, absorber layer B, and a flame-retardant layer.

[0006] The base coating is a resin layer;

[0007] The matrix of the transition layer is a flexible resin, and the reinforcement is obtained by alternating layers of wave-transparent material A and wave-absorbing material B.

[0008] The flame-retardant layer is based on vinyl resin, and the reinforcement is obtained by alternating layers of wave-transparent material C and wave-absorbing material D.

[0009] The sheet resistance of the multilayer gradient absorbing film increases sequentially from top to bottom.

[0010] The multilayer gradient absorbing film for metal surfaces provided by this invention features a base layer that enhances the adhesion between the absorbing film and the metal surface. Simultaneously, the multilayer gradient absorbing film forms a thermal insulation layer on the metal surface, improving the overall high and low temperature resistance of the metal device or equipment. Furthermore, the base layer, transition layer, and flame-retardant layer all possess wave-absorbing capabilities, and the sheet resistance of the absorbing film increases sequentially from top to bottom, achieving a gradual increase in wave absorption performance and thus broadband wave absorption. Moreover, the transition layer and flame-retardant layer of the multilayer gradient absorbing film for metal surfaces provided by this invention employ alternating layers of wave-transmitting and wave-absorbing materials, which improves both wave absorption and transmission efficiency, thereby enhancing the wave absorption effect of the multilayer gradient absorbing film.

[0011] In a preferred embodiment, the base coating is formed by curing one of an elastomer-modified vinyl resin and a bisphenol A epoxy vinyl ester resin at room temperature.

[0012] In this invention, the resin used for the base coating is a high-toughness resin, which gives it excellent adhesion to metal. The adhesion strength of this invention to stainless steel is ≥6MPa.

[0013] In a preferred embodiment, the flexible resin in the transition layer has a tensile elongation at break of ≥8%.

[0014] In a preferred embodiment, the flexible resin in the transition layer is formed by curing one of an elastomer-modified vinyl resin or a bisphenol A epoxy vinyl ester resin at room temperature.

[0015] In a preferred embodiment, the wave-transparent material A in the transition layer is selected from one of glass fiber mat, glass fiber cloth, and quartz fiber cloth.

[0016] In a preferred embodiment, the microwave absorbing material B in the transition layer is selected from at least one of silicon carbide modified fiber felt and carbon fiber modified fiber felt.

[0017] In a preferred embodiment, the flame-retardant layer contains a vinyl resin with an oxygen index ≥ 25.

[0018] The flame-retardant layer is made of vinyl ester resin, and the transition layer is made of flexible resin. This ensures that the multi-layered gradient absorbing film maintains its microwave absorption performance while achieving both flame-retardant and low-temperature resistance. If the absorbing film uses ordinary resin, it will lack flame-retardant properties. If a flexible resin is not used and the film is directly applied to the metal casing, it is prone to cracking and delamination at low temperatures.

[0019] In a preferred embodiment, the wave-transparent material C in the flame-retardant layer is selected from at least one of glass fiber mat, glass fiber cloth, and quartz fiber cloth.

[0020] In a preferred embodiment, the microwave absorbing material D in the flame retardant layer is selected from one of silicon carbide modified fiber felt and carbon fiber modified fiber felt.

[0021] In this invention, the wave-transmitting material A and the wave-transmitting material C can be the same or different materials, and the wave-absorbing material B and the wave-absorbing material D can be the same or different materials.

[0022] In this invention, silicon carbide modified fiber mat refers to silicon carbide modified fiber mat obtained by incorporating silicon carbide fibers during the preparation of glass fiber mat. The dielectric constant of the resulting fiber mat can be adjusted by modifying the fiber mat.

[0023] In a preferred embodiment, the flame retardant layer is a flame retardant layer laid on a substrate, and the flame retardant is composed of one or more of brominated bisphenol A type flame retardants and epoxy vinyl flame retardants.

[0024] In a preferred embodiment, the reflectivity of absorber layer A is less than that of absorber layer B.

[0025] In this invention, the absorber layer has progressively increasing wave absorption performance from top to bottom, which can further enhance the wave absorption performance and thus achieve the absorption of different electromagnetic wave wavelengths.

[0026] In a preferred embodiment, both absorbent layer A and absorbent layer B are composed of an absorbent and an adhesive, wherein the absorbent is an electromagnetic wave absorber with an electromagnetic wave absorption frequency of 0.5 to 40 GHz.

[0027] In a preferred embodiment, the total thickness of the multilayer gradient absorbing film is ≤3.5mm.

[0028] This invention discloses a method for preparing a multilayer gradient absorbing film for metal surfaces. First, a resin raw material for a base coating is applied to the metal surface to obtain a base coating blank. Then, wave-transparent material A and wave-absorbing material B are alternately layered, and during the alternating layering process, a flexible resin is applied to form a transition layer blank. Next, wave-transparent material C and wave-absorbing material D are alternately layered, and during the alternating layering process, a vinyl ester resin is applied to obtain a flame-retardant layer blank. Finally, the entire film is cured at room temperature for 12-24 hours to obtain the final product. An absorber layer is laid between any two layers of the multilayer gradient absorbing film.

[0029] In a preferred embodiment, the absorbent layer is a layered structure consisting of a uniform mixture of carbon fiber or magnetized carbon fiber and Cu / Co / C absorbent.

[0030] A further preferred embodiment is that the Cu / Co / C absorbent is composed of Co 2+ The mixture was prepared by mixing Cu3(BTC)2 particles at a mass ratio of 50:50 to 100.

[0031] Beneficial effects of this invention:

[0032] The multilayer gradient absorbing film of this invention adheres easily and with high bonding strength to metal surfaces. Its multilayer structure enhances the overall high and low temperature resistance of the absorbing film. This invention allows for the direct fabrication of absorbing layers on the metal surfaces of weapons, equipment, or carriers, enabling stealth capabilities without altering the original metal structure's shape. Compared to absorbing patches and stealth coatings, the multilayer gradient absorbing film provided by this invention is easier to apply, adaptable to various complex curved surfaces, and exhibits high bonding strength to metal surfaces after curing. It is also resistant to high and low temperatures, possesses flame-retardant properties, and facilitates subsequent maintenance and repair. Figure description:

[0033] Figure 1. Schematic diagram of multilayer gradient absorbing film combined with metal surface.

[0034] In the attached diagram: 1. Metal surface; 2. Primer coating; 3. Transition layer; 4. Flame retardant layer; 5. Wave-absorbing material; 6. Wave-transmitting material. Detailed implementation method:

[0035] To further illustrate the present invention, the following description is provided in conjunction with the accompanying drawings and embodiments, but this does not limit the present invention to the scope of the described embodiments.

[0036] Example 1:

[0037] 1) Prepare a stainless steel plate of 300mm x 300mm and clean the surface with alcohol;

[0038] 2) Use 150-grit sandpaper to roughen the surface of the stainless steel plate;

[0039] 3) Cut the wave-transmitting layer material glass fiber mat and the wave-absorbing material layer silicon carbide modified fiber mat, and lay the silicon carbide modified fiber mat and glass fiber mat alternately.

[0040] 4) First, apply a primer resin to the surface of the stainless steel plate, then lay the transition layer of silicon carbide modified fiber felt and glass fiber felt, and finally lay the flame retardant layer of silicon carbide modified fiber felt and glass fiber felt. After each layer of felt is laid, apply resin and then use a bristle roller to roll back and forth to remove air bubbles and compact it.

[0041] 5) Place the laid stainless steel sheet—multi-layer gradient absorbing film—at room temperature for 12-24 hours to cure. After curing, cut it into appropriate sizes as required and test the reflectivity. The adhesion performance to the stainless steel sheet is tested using the GBT33334-2016 test method for the tensile shear strength of adhesives with single lap joints.

[0042] The multilayer gradient absorbing film prepared in this embodiment has a reflectivity of less than -2dB in the 4-8GHz range, an average reflectivity of less than -10dB in the 8-12GHz and 12-18GHz ranges, and a radar reflectivity of less than -20dB in the 26.5-40GHz range, exhibiting excellent wave absorption performance. After bonding with a stainless steel plate, the tensile shear strength is 9MPa, and it does not delaminate after being kept at -55℃ for 72 hours. The multilayer gradient absorbing film provided by this invention has excellent wave absorption performance, high bonding strength with metal surfaces, and low-temperature resistance.

[0043] Example 2:

[0044] 1) Prepare an aluminum alloy plate of 300mm×300mm and clean the surface with alcohol;

[0045] 2) Use 240-grit sandpaper to roughen the aluminum alloy plate;

[0046] 3) Cut the wave-transmitting layer material glass fiber mat and the wave-absorbing material layer carbon fiber modified fiber mat, and lay the carbon fiber modified fiber mat and glass fiber mat alternately.

[0047] 4) First, apply a primer resin to the surface of the aluminum alloy plate, then lay the carbon fiber modified fiber felt and glass fiber felt for the transition layer, and then lay the carbon fiber modified fiber felt and glass fiber felt for the flame retardant layer. After each layer of felt is laid, apply resin and then use a bristle roller to roll back and forth to remove air bubbles and compact it.

[0048] 5) Place the laid aluminum alloy plate—multi-layer gradient absorbing film—vertically at room temperature for 12-24 hours to cure. After curing, cut it into appropriate sizes as required and test the reflectivity.

[0049] The multilayer gradient absorbing film prepared in this embodiment has a reflectivity of less than -3dB in the 4-8GHz range, an average reflectivity of less than -10dB in the 8-12GHz and 12-18GHz ranges, and a radar reflectivity of less than -15dB in the 26.5-40GHz range, exhibiting excellent wave absorption performance. After bonding with an aluminum alloy plate, the tensile shear strength is 7MPa, and it does not delaminate after being kept at -55℃ for 72 hours. The multilayer gradient absorbing film provided by this invention has excellent wave absorption performance, high bonding strength with metal surfaces, and low-temperature resistance.

[0050] Example 3:

[0051] When the absorbing layer on the carrier surface is damaged or detached, a multi-layer gradient absorbing film can be used for repair, restoring the carrier to excellent absorbing performance.

[0052] In this embodiment, the carrier is a stainless steel-based microwave absorbing material. First, the microwave absorbing film is cut off at the damaged and detached areas using an angle grinder, and then the surface is polished with 150-grit sandpaper and wiped clean with alcohol. Then, a base coating resin, a flexible resin transition layer, a microwave-transparent layer, and a microwave-absorbing material layer are sequentially applied to the damaged areas, followed by a flame-retardant resin layer and a microwave-transparent layer. Each layer needs to be rolled back and forth with a bristle roller to remove bubbles. Finally, vacuum bag pressing is performed to cure and shape the material, thus completing the repair work of the microwave absorbing material on the carrier surface.

[0053] The multilayer gradient absorbing film prepared in this embodiment has a reflectivity of less than -2dB in the 4-8GHz range, an average reflectivity of less than -10dB in the 8-12GHz and 12-18GHz ranges, and a radar reflectivity of less than -15dB in the 26.5-40GHz range, exhibiting excellent wave absorption performance. After bonding with a stainless steel plate, the tensile shear strength is 9MPa, and it does not delaminate after being kept at -55℃ for 72 hours. The multilayer gradient absorbing film provided by this invention has excellent wave absorption performance, high bonding strength with metal surfaces, and low-temperature resistance.

[0054] Comparative Example 1

[0055] All other conditions were the same as in Example 1, except that a primer resin was not used. After curing in the comparative example, the fiberglass and stainless steel plates delaminated after being kept at -55°C for 1 hour, and the fiberglass completely lost its effectiveness.

[0056] Comparative Example 2

[0057] All other conditions were the same as in Example 1, except that the modified silicon carbide fiber felt was replaced with ordinary glass fiber felt. After comparative curing and molding, the radar reflectivity was less than -1dB in the 4-8 GHz range, and less than -5dB in the 8-12 GHz, 12-18 GHz and 26.5-40 GHz ranges.

[0058] Finally, it should be noted that the above case descriptions are merely preferred embodiments of the present invention. Those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A multilayer gradient absorbing film for a metal surface, wherein the multilayer gradient absorbing film is disposed on the metal surface, characterized in that, The multilayer gradient absorbing film is divided into, from bottom to top, a base layer, absorber layer A, a transition layer, absorber layer B, and a flame retardant layer. The base layer is a resin layer. The matrix of the transition layer is flexible resin, and the reinforcement is obtained by alternating layers of wave-transparent material A and wave-absorbing material B. The matrix of the flame retardant layer is vinyl resin, and the reinforcement is obtained by alternating layers of wave-transparent material C and wave-absorbing material D. The sheet resistance of the multilayer gradient absorbing film increases sequentially from top to bottom.

2. The multilayer gradient absorbing film for metal surfaces according to claim 1, characterized in that, The base coating is formed by curing one of the following at room temperature: an elastomer-modified vinyl resin or a bisphenol A epoxy vinyl ester resin.

3. The multilayer gradient absorbing film for metal surfaces according to claim 1, characterized in that, The flexible resin is formed by curing one of the following at room temperature: elastomer-modified vinyl resin or bisphenol A epoxy vinyl ester resin.

4. The multilayer gradient absorbing film for metal surfaces according to claim 1, characterized in that, The wave-transparent material A used in the transition layer is selected from one of glass fiber mat, glass fiber cloth, and quartz fiber cloth; the wave-absorbing material B used in the transition layer is selected from at least one of silicon carbide modified fiber mat and carbon fiber modified fiber mat.

5. A multilayer gradient absorbing film for a metal surface according to claim 1, characterized in that, The wave-transparent material C used in the flame-retardant layer is selected from at least one of glass fiber mat, glass fiber cloth, and quartz fiber cloth; the wave-absorbing material D used in the flame-retardant layer is selected from one of silicon carbide modified fiber mat and carbon fiber modified fiber mat.

6. A multilayer gradient absorbing film for a metal surface according to claim 1, characterized in that, The flame retardant layer is a flame retardant layer laid on the substrate, and the flame retardant is composed of one or more of brominated bisphenol A type flame retardant and epoxy vinyl flame retardant.

7. A multilayer gradient absorbing film for a metal surface according to claim 1, characterized in that, The reflectivity of absorber layer A is less than that of absorber layer B.

8. The method for preparing a multilayer gradient absorbing film for a metal surface as described in claim 1, characterized in that, First, a base coating material is obtained by applying a base coating resin to the metal surface. Then, wave-transmitting material A and wave-absorbing material B are alternately layered. During the alternating layering process, a flexible resin is applied to form a transition layer blank. Next, wave-transmitting material C and wave-absorbing material D are alternately layered. During the alternating layering process, a vinyl resin is applied to obtain a flame-retardant layer blank. Finally, the entire layer is cured at room temperature for 12-24 hours to form the final product. An absorber layer is laid between any two layers of the multilayer gradient wave-absorbing film.

9. A method for preparing a multilayer gradient absorbing film for a metal surface according to claim 8, characterized in that, The absorbent layer is a layered structure consisting of a uniform mixture of carbon fiber or magnetized carbon fiber and Cu / Co / C absorbent.

10. A method for preparing a multilayer gradient absorbing film for a metal surface according to claim 9, characterized in that, The Cu / Co / C absorbent is composed of Co 2+ The mixture was prepared by mixing Cu3(BTC)2 particles at a mass ratio of 50:50 to 100.

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