Lightweight broadband polyurethane foam wave-absorbing material and preparation method thereof

Abstract

The invention discloses a lightweight broadband polyurethane foam wave-absorbing material and a preparation method thereof, and belongs to the technical field of electromagnetic wave-absorbing materials. The light broadband polyurethane foam wave-absorbing material is composed of the polyurethane pyramid wave-absorbing structure, the polyurethane foam and the reflecting layer, electromagnetic waves are reflected and refracted for multiple times between the pyramids through the pyramid structure, and then the electromagnetic waves are fully absorbed; meanwhile, carbon fiber chopped strands and crushed carbon fibers are added into a polyurethane pyramid wave-absorbing structure to serve as a composite absorbent, the wave-absorbing performance of the material is further improved by means of the wave-absorbing performance of the carbon fibers, and finally the light broadband polyurethane foam wave-absorbing material which shows excellent wave-absorbing performance at typical frequency points of 2 GHz, 10 GHz, 18 GHz and 35 GHz is obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of electromagnetic absorbing materials, and in particular relates to a lightweight broadband polyurethane foam absorbing material and a preparation method thereof. Background Art

[0002] The continuous development of radio information technology has led to the emergence of radar detection technology, and with it comes "wave-absorbing materials". As modern detection technology leaps forward in the direction of higher accuracy and sensitivity, the possibility of targets being detected, tracked, and attacked is increasing. Therefore, conducting research on radar absorbing materials and their preparation methods is one of the important means to counter radar detection.

[0003] At present, there are two main types of absorbing materials: structural materials and coating materials. Coating materials mainly soak the base material in a coating with absorbing properties to form an absorbing layer on the surface of the base material. However, since the immersion time is difficult to control, the resulting absorbing material has the problem of being heavy. In addition, the absorbing coating will be worn out during long-term use and requires regular maintenance or even re-brushing, which undoubtedly increases the production cost. Structural absorbing materials include laminate type, honeycomb sandwich type, foam sandwich type and other forms. Among them, foam sandwich type materials have a special and important position due to their light weight, simple preparation process and excellent processing performance. Foam sandwich structure absorbing materials are improved absorbing layers in laminate structures, and a variety of absorbing mechanisms and other physical and mechanical properties are introduced through foaming structures. By designing the foaming structure, electromagnetic waves can be reflected more inside the material, increase the propagation path of electromagnetic waves inside the material, and minimize the loss of incident electromagnetic waves. However, the existing foam sandwich structure absorbing materials still have the problem of poor absorbing performance in the high-frequency terahertz stage. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a lightweight broadband polyurethane foam absorbing material and a preparation method thereof. The lightweight broadband polyurethane foam absorbing material provided by the present invention exhibits excellent absorbing performance at typical frequencies of 2 GHz, 10 GHz, 18 GHz and 35 GHz.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention provides a lightweight broadband polyurethane foam absorbing material, which comprises a polyurethane pyramid absorbing structure composed of a plurality of pyramid structures, polyurethane foam filled between the pyramid structures, and a reflective layer adhered to one side of the polyurethane foam;

[0007] The raw materials for preparing the polyurethane pyramid absorbing structure include, by weight: 120-200 parts of polyurethane white material, 120-200 parts of polyurethane black material, 12-15 parts of carbon fiber chopped strands and 10-15 parts of crushed carbon fiber.

[0008] Technical principle:

[0009] The present invention adopts a polyurethane pyramid absorbing structure, polyurethane foam and a reflective layer to form a lightweight broadband polyurethane foam absorbing material, and utilizes the pyramid structure to make electromagnetic waves reflect and refract multiple times between the cones, thereby fully absorbing the electromagnetic waves; at the same time, by adding carbon fiber chopped strands and crushed carbon fiber as a composite absorber in the polyurethane pyramid absorbing structure, the absorbing performance of the carbon fiber is utilized to further improve the absorbing performance of the material, and finally a lightweight broadband polyurethane foam absorbing material with excellent absorbing performance at typical frequencies of 2 GHz, 10 GHz, 18 GHz and 35 GHz is obtained.

[0010] Furthermore, the length of the carbon fiber chopped strands is 1 to 2 mm.

[0011] Furthermore, the particle size of the crushed carbon fiber is 200 to 500 μm.

[0012] Furthermore, the pyramid structure is composed of a rectangular frustum and a square pyramid; the size of the rectangular frustum is (6-8) mm×(6-8) mm×(5-10) mm, and the height of the square pyramid is 9-15 mm.

[0013] Furthermore, the reflective layer is composed of an epoxy resin panel and aluminum foil.

[0014] Furthermore, the lightweight broadband polyurethane foam absorbing material has a thickness of 15 to 20 mm and a surface density of 4.0 to 5.0 kg / m 2 .

[0015] The present invention also provides a method for preparing the lightweight broadband polyurethane foam absorbing material described in the above technical solution, comprising the following steps:

[0016] (1) adding crushed carbon fiber and chopped carbon fiber to polyurethane white material and polyurethane black material respectively, stirring evenly, then mixing the polyurethane white material and polyurethane black material, and continuing to stir to obtain a mixture; curing, cutting and pyramid processing the mixture to obtain a polyurethane pyramid wave absorbing structure;

[0017] (2) mixing the polyurethane white material and the polyurethane black material and pouring them into a mold, and then placing the polyurethane pyramid absorbing structure obtained in step (1) into the mold with the pyramid facing downward, and curing and molding to obtain a sandwich structure absorbing material;

[0018] (3) Pasting an epoxy resin panel with aluminum foil on one side of the surface of the sandwich structure absorbing material obtained in step (2) to obtain the lightweight broadband polyurethane foam absorbing material.

[0019] Furthermore, in step (1), the stirring time is 20 to 30 seconds; and / or,

[0020] The cutting thickness is 15-20 mm and the size is 300 mm×300 mm.

[0021] Furthermore, in step (2), the mass ratio of the polyurethane white material to the polyurethane black material is 1:1.

[0022] Furthermore, in step (3), the thickness of the epoxy resin panel is 0.3-0.5 mm, and the thickness of the aluminum foil is 0.06-0.1 mm.

[0023] Compared with the prior art, the present invention has the following advantages and technical effects:

[0024] (1) The lightweight broadband polyurethane foam absorbing material provided by the present invention is made of polyurethane foam and is compounded with different resistive carbon fiber absorbers, that is, short-cut carbon fiber and crushed carbon fiber are used as composite absorbers. The obtained lightweight broadband polyurethane foam absorbing material has the characteristics of good absorbing performance, safety, environmental protection, good compatibility and light weight.

[0025] (2) The preparation method of the lightweight broadband polyurethane foam absorbing material provided by the present invention can not only realize the cutting of the absorbing structure by controlling the process parameters of the wire cutting machine and reduce the loss of the polyurethane absorbing foam, but also flexibly design the absorbing structure, thereby optimizing the broadband absorbing performance of the polyurethane foam. The polyurethane absorbing structure, polyurethane foam and reflective layer are integrated into a two-step foaming process, and finally a thickness of 15 to 20 mm and a density of 4.0 to 5.0 kg / m 2 , a lightweight broadband polyurethane foam absorbing material with excellent absorbing performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0027] Figure 1 This is a process flow chart of the method for preparing the lightweight broadband polyurethane foam absorbing material in Examples 1-3 of the present invention;

[0028] Figure 2 is a front view of the pyramid structure of the present invention;

[0029] Figure 3The radar reflectivity curve of the lightweight broadband polyurethane foam absorbing material in Example 1 at 2 to 18 GHz;

[0030] Figure 4 The radar reflectivity curve of the lightweight broadband polyurethane foam absorbing material in Example 1 at 26.5-40 GHz;

[0031] Figure 5 The radar reflectivity curve of the lightweight broadband polyurethane foam absorbing material in Example 2 at 2 to 18 GHz;

[0032] Figure 6 The radar reflectivity curve of the lightweight broadband polyurethane foam absorbing material in Example 2 at 26.5-40 GHz;

[0033] Figure 7 The radar reflectivity curve of the lightweight broadband polyurethane foam absorbing material in Example 3 at 2 to 18 GHz;

[0034] Figure 8 This is a radar reflectivity curve of the lightweight broadband polyurethane foam absorbing material in Example 3 at 26.5-40 GHz. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] The embodiment of the present invention provides a lightweight broadband polyurethane foam absorbing material, which includes a polyurethane pyramid absorbing structure composed of a plurality of pyramid structures, a polyurethane foam filled between the pyramid structures, and a reflective layer attached to one side of the polyurethane foam. The present invention uses polyurethane foam to prepare the absorbing material. Polyurethane foam (PUR) is a type of material with a main chain having a carbamate polymer prepared by the reaction of a polyhydroxy compound and a polyisocyanate group. It has the characteristics of low density, excellent mechanical properties, thermal conductivity and heat resistance. At the same time, the electrical properties of the absorbing material are regulated by combining the pyramid structure, and the absorbing effect of the absorbing material is further improved by combining the reflective layer, and finally a lightweight, broadband, and highly efficient absorbing polyurethane foam absorbing material is obtained.

[0038] In a preferred embodiment, the raw materials for preparing the polyurethane pyramidal absorbing structure include, by weight: 120-200 parts of polyurethane white material, 120-200 parts of polyurethane black material, 12-15 parts of carbon fiber chopped strands, and 10-15 parts of crushed carbon fiber. The present invention adopts a high-content composite absorber polyurethane pyramidal absorbing structure formula, which can effectively regulate the electrical properties of the absorbing material, and is conducive to obtaining a polyurethane foam absorbing material with high efficiency. The conductivity of carbon fiber is between that of metal and non-metal, and its electrical properties are similar to those of metal. It mainly relies on the ions therein to conduct electricity, generate eddy current losses, and has certain absorbing properties. The present invention uses both chopped carbon fiber and crushed carbon fiber as composite absorbers, and the crushed carbon fiber can be filled in the gaps of the chopped carbon fiber, thereby increasing the content of the composite absorber in the absorbing material and enhancing the absorbing effect.

[0039] In a preferred embodiment, the length of the carbon fiber chopped strands is 1 to 2 mm. The present invention uses carbon fiber chopped strands with a length within the above range, which has the advantages of increasing the content of the composite absorber in the absorbing material and enhancing the absorbing effect. If the length of the carbon fiber chopped strands is too long, it will cause a bridging effect between the fibers, forming a conductive channel, enhancing the material's reflection performance for electromagnetic waves, which is not conducive to absorbing waves. If the length of the carbon fiber chopped strands is too short, the carbon fiber chopped strands will agglomerate and be difficult to disperse in the resin matrix, thereby affecting the absorbing effect.

[0040] In a preferred embodiment, the particle size of the pulverized carbon fiber is 200 to 500 μm. The present invention uses pulverized carbon fiber with a particle size within the above range, which has the advantages of filling gaps, reducing local bridging of carbon fiber chopped strands, and making carbon fiber chopped strands easy to disperse. If the particle size of the pulverized carbon fiber is too small, the powder will agglomerate and it will be difficult to disperse in the resin matrix, thereby affecting the wave absorbing effect.

[0041] In a preferred embodiment, the pyramid structure is composed of a rectangular cone and a square pyramid; the size of the rectangular cone is (6-8) mm×(6-8) mm×(5-10) mm, and the cone height of the square pyramid is 9-15 mm; the cone height refers to the distance from the upper surface of the rectangular cone to the top of the square pyramid. The present invention can effectively regulate the electrical properties of the absorbing material by controlling the cone size and cone height of the pyramid structure. When the cone height of the cone remains unchanged, as the size of the rectangular cone increases, the electrical properties of the absorbing material move to low frequencies. When the size of the rectangular cone remains unchanged, as the cone height increases, the electrical properties of the absorbing material move to high frequencies. However, if the size of the rectangular cone and the cone height are too small, the electrical properties of the absorbing material will be adversely affected.

[0042] In a preferred embodiment, the front view of the pyramid structure is shown in Figure 2It can be seen that the pyramid structure is composed of a rectangular cone and a square pyramid, and the cone is a rectangular parallelepiped with a square bottom. Front view and side view of the pyramid structure Figure 1 The top view is square.

[0043] In a preferred embodiment, the polyurethane foam is prepared by foaming polyurethane white material and polyurethane black material.

[0044] In a preferred embodiment, the reflective layer is composed of an epoxy resin panel and an aluminum foil; the epoxy resin panel is preferably an epoxy resin fiberglass panel. The epoxy resin panel in the present invention is used to connect the aluminum foil and the polyurethane foam, and the aluminum foil plays a reflective role.

[0045] In a preferred embodiment, the lightweight broadband polyurethane foam absorbing material has a thickness of 15 to 20 mm and a surface density of 4.0 to 5.0 kg / m 2 .

[0046] The present invention also provides a method for preparing the lightweight broadband polyurethane foam absorbing material described in the above technical solution, comprising the following steps:

[0047] (1) adding crushed carbon fiber and chopped carbon fiber to polyurethane white material and polyurethane black material respectively, stirring evenly, then mixing the polyurethane white material and polyurethane black material, and continuing to stir to obtain a mixture; curing, cutting and pyramid processing the mixture to obtain a polyurethane pyramid wave absorbing structure;

[0048] (2) mixing the polyurethane white material and the polyurethane black material and pouring them into a mold, and then placing the polyurethane pyramid absorbing structure obtained in step (1) into the mold with the pyramid facing downward, and curing and molding to obtain a sandwich structure absorbing material;

[0049] (3) Pasting an epoxy resin panel with aluminum foil on one side of the surface of the sandwich structure absorbing material obtained in step (2) to obtain the lightweight broadband polyurethane foam absorbing material.

[0050] In a preferred embodiment, in step (1), the stirring time is 20 to 30 seconds.

[0051] In a preferred embodiment, in step (1), the cutting thickness is 15-20 mm, and the size is 300 mm×300 mm; the equipment used for cutting is a vertical band saw.

[0052] In a preferred embodiment, in step (1), the size of the pyramid structure obtained by the pyramid processing is (6-10) mm×(6-10) mm×(5-10) mm, and the pyramid height is 9-15 mm.

[0053] In a preferred embodiment, in step (2), the mass ratio of the polyurethane white material to the polyurethane black material is 1:1.

[0054] In a preferred embodiment, in step (3), the thickness of the epoxy resin panel is 0.3-0.5 mm, and the thickness of the aluminum foil is 0.06-0.1 mm; the epoxy resin panel is preferably an epoxy resin fiberglass panel.

[0055] In a preferred embodiment, in step (3), one side of the surface of the sandwich structure absorbing material is away from the pyramid structure.

[0056] Unless otherwise specified, the raw materials in the examples of the present invention were purchased from commercial sources.

[0057] Polyurethane white material is a combination of polyether and polyurethane rigid foam, while polyurethane black material is polymerized MDI.

[0058] Example 1

[0059] A lightweight broadband polyurethane foam absorbing material comprises a polyurethane pyramid absorbing structure composed of a plurality of adjacent and repeatedly arranged pyramid structures, polyurethane foam filled between the pyramid structures, and a reflecting layer adhered to the bottom of the polyurethane foam; the pyramid structure is composed of a rectangular frustum and a square pyramid, the size of the rectangular frustum of each pyramid structure is 8mm×8mm×5mm, and the cone height of the square pyramid is 13mm; the lightweight broadband polyurethane foam absorbing material has a thickness of 19.5mm and a surface density of 4.0kg / m 2 ;

[0060] The raw materials for preparing the polyurethane pyramid absorbing structure are composed of the following components by weight: 150 parts of polyurethane white material, 150 parts of polyurethane black material, 12 parts of crushed carbon fiber with a particle size of 400 μm, and 12 parts of carbon fiber chopped strands with a length of 2 mm;

[0061] The reflective layer is composed of an epoxy resin fiberglass panel and an aluminum foil. The thickness of the epoxy resin fiberglass panel is 0.3 mm, and the thickness of the aluminum foil is 0.08 mm.

[0062] Preparation method of lightweight broadband polyurethane foam absorbing material, the process flow is shown in Figure 1 , the specific steps are as follows:

[0063] (1) Add crushed carbon fiber and carbon fiber chopped strands to polyurethane white material and polyurethane black material respectively, stir evenly with a pneumatic stirring rod, then mix the polyurethane black material and polyurethane white material, and continue stirring with a pneumatic stirring rod for 22 seconds to obtain a mixture. Pour the obtained mixture into a mold, let it stand for 1 hour, wait for the polyurethane black material and polyurethane white material to react completely, and after curing and forming, obtain a polyurethane foam absorbing material, the mass content of the absorbent in the polyurethane foam absorbing material is 7.4%;

[0064] (2) The polyurethane foam absorbing material obtained in step (1) is cut into a thickness of 19.5 mm and a size of 300 mm×300 mm, and then processed into a pyramid structure using a wire saw to obtain a polyurethane pyramid absorbing structure; wherein the polyurethane pyramid absorbing structure is composed of a plurality of adjacent and repeatedly arranged pyramid structures, the pyramid structure is composed of a rectangular cone and a square pyramid, and the rectangular cone size of each pyramid structure is 8 mm×8 mm×5 mm, and the cone height of the square pyramid is 13 mm.

[0065] (3) The polyurethane white material and the polyurethane black material are mixed in a mass ratio of 1:1 and evenly spread on the surface of the epoxy resin glass fiber reinforced plastic panel with a thickness of 0.1 mm at the bottom of the foaming mold (lower mold), and then the polyurethane corner pyramid absorbing structure obtained in step (2) is placed upside down in the mold (that is, the corner pyramid is placed in the mold with the corner pyramid facing downward), and the upper and lower molds are closed (the upper mold also has an epoxy resin glass fiber reinforced plastic panel), so that the polyurethane white material and the polyurethane black material are fully reacted between the epoxy resin glass fiber reinforced plastic panels of the upper and lower molds and then cured to obtain a sandwich structure absorbing material, that is, the epoxy resin glass fiber reinforced plastic panels of the upper and lower molds are the upper and lower sandwich panels of the sandwich structure absorbing material.

[0066] (4) Paste an epoxy resin fiberglass panel with aluminum foil on the side of the sandwich structure absorbing material obtained in step (3) away from the pyramid structure to form a reflective layer, and demold the panel to obtain a lightweight broadband polyurethane foam absorbing material.

[0067] Example 2

[0068] A lightweight broadband polyurethane foam absorbing material comprises a polyurethane pyramid absorbing structure composed of a plurality of adjacent and repeatedly arranged pyramid structures, polyurethane foam filled between the pyramid structures, and a reflecting layer adhered to the bottom of the polyurethane foam; the pyramid structure is composed of a rectangular frustum and a square pyramid, the size of the rectangular frustum of each pyramid structure is 8mm×8mm×5mm, and the cone height of the square pyramid is 9mm; the lightweight broadband polyurethane foam absorbing material has a thickness of 15mm and a surface density of 4.4kg / m 2 ;

[0069] The raw materials for preparing the polyurethane pyramid absorbing structure are composed of the following components by weight: 120 parts of polyurethane white material, 120 parts of polyurethane black material, 10 parts of crushed carbon fiber with a particle size of 400 μm, and 12 parts of carbon fiber chopped strands with a length of 2 mm;

[0070] The reflective layer is composed of an epoxy resin fiberglass panel and an aluminum foil. The thickness of the epoxy resin fiberglass panel is 0.5 mm, and the thickness of the aluminum foil is 0.06 mm.

[0071] Preparation method of lightweight broadband polyurethane foam absorbing material, the process flow is shown in Figure 1 , the specific steps are as follows:

[0072] (1) Add crushed carbon fiber and carbon fiber chopped strands to polyurethane white material and polyurethane black material respectively, stir them evenly with a pneumatic stirring rod, then mix the polyurethane black material and the polyurethane white material, and continue stirring with a pneumatic stirring rod for 20 seconds to obtain a mixture. Pour the obtained mixture into a mold, let it stand for 1 hour, wait for the polyurethane black material and the polyurethane white material to react completely, and then solidify and form a polyurethane foam absorbing material, wherein the mass content of the absorbent in the polyurethane foam absorbing material is 8.4%.

[0073] (2) The polyurethane foam absorbing material obtained in step (1) is cut into a thickness of 15 mm and a size of 300 mm×300 mm, and then processed into a pyramid structure using a wire saw to obtain a polyurethane pyramid absorbing structure; wherein the polyurethane pyramid absorbing structure is composed of a plurality of adjacent and repeatedly arranged pyramid structures, the pyramid structure is composed of a rectangular cone and a square pyramid, and the rectangular cone size of each pyramid structure is 8 mm×8 mm×5 mm, and the cone height of the square pyramid is 9 mm.

[0074] (3) The polyurethane white material and the polyurethane black material are mixed in a mass ratio of 1:1 and evenly spread on the surface of the epoxy resin glass fiber reinforced plastic panel with a thickness of 0.1 mm at the bottom of the foaming mold (lower mold), and then the polyurethane corner pyramid absorbing structure obtained in step (2) is placed upside down in the mold (that is, the corner pyramid is placed in the mold with the corner pyramid facing downward), and the upper and lower molds are closed (the upper mold also has an epoxy resin glass fiber reinforced plastic panel), so that the polyurethane white material and the polyurethane black material are fully reacted between the epoxy resin glass fiber reinforced plastic panels of the upper and lower molds and then cured to obtain a sandwich structure absorbing material, that is, the epoxy resin glass fiber reinforced plastic panels of the upper and lower molds are the upper and lower sandwich panels of the sandwich structure absorbing material.

[0075] (4) Paste an epoxy resin fiberglass panel with aluminum foil on the side of the sandwich structure absorbing material obtained in step (3) away from the pyramid structure to form a reflective layer, and demold the panel to obtain a lightweight broadband polyurethane foam absorbing material.

[0076] Example 3

[0077] A lightweight broadband polyurethane foam absorbing material comprises a polyurethane pyramid absorbing structure composed of a plurality of adjacent and repeatedly arranged pyramid structures and a reflecting layer adhered to the bottom of the polyurethane pyramid absorbing structure; the pyramid structure is composed of a rectangular frustum and a square pyramid, the size of the rectangular frustum of each pyramid structure is 8mm×8mm×10mm, and the cone height of the square pyramid is 10mm; the lightweight broadband polyurethane foam absorbing material has a thickness of 20mm and a surface density of 5.0kg / m 2 ;

[0078] The raw materials for preparing the polyurethane pyramid absorbing structure are composed of the following components by weight: 200 parts of polyurethane white material, 200 parts of polyurethane black material, 15 parts of crushed carbon fiber with a particle size of 400 μm and 15 parts of carbon fiber chopped strands with a length of 2 mm;

[0079] The reflective layer is composed of an epoxy resin fiberglass panel and an aluminum foil. The thickness of the epoxy resin fiberglass panel is 0.5 mm, and the thickness of the aluminum foil is 0.08 mm.

[0080] Preparation method of lightweight broadband polyurethane foam absorbing material, the process flow is shown in Figure 1 , the specific steps are as follows:

[0081] (1) Add crushed carbon fiber and carbon fiber chopped strands to polyurethane white material and polyurethane black material respectively, stir them evenly with a pneumatic stirring rod, then mix the polyurethane black material and the polyurethane white material, and continue stirring with the pneumatic stirring rod for 30 seconds to obtain a mixture. Pour the obtained mixture into a mold, let it stand for 1 hour, wait for the polyurethane black material and the polyurethane white material to react completely, and then solidify and form a polyurethane foam absorbing material, wherein the mass content of the absorbent in the polyurethane foam absorbing material is 7.0%.

[0082] (2) The polyurethane foam absorbing material obtained in step (1) is cut into a thickness of 20 mm and a size of 300 mm×300 mm, and then processed into a pyramid structure using a wire saw device to obtain a polyurethane pyramid absorbing structure; wherein the polyurethane pyramid absorbing structure is composed of a plurality of adjacent and repeatedly arranged pyramid structures, the pyramid structure is composed of a rectangular cone and a square pyramid, and the rectangular cone size of each pyramid structure is 8 mm×8 mm×10 mm, and the cone height of the square pyramid is 10 mm.

[0083] (3) The polyurethane white material and the polyurethane black material are mixed in a mass ratio of 1:1 and evenly spread on the surface of the epoxy resin glass fiber reinforced plastic panel with a thickness of 0.1 mm at the bottom of the foaming mold (lower mold), and then the polyurethane corner pyramid absorbing structure obtained in step (2) is placed upside down in the mold (that is, the corner pyramid is placed in the mold with the corner pyramid facing downward), and the upper and lower molds are closed (the upper mold also has an epoxy resin glass fiber reinforced plastic panel), so that the polyurethane white material and the polyurethane black material are fully reacted between the epoxy resin glass fiber reinforced plastic panels of the upper and lower molds and then cured to obtain a sandwich structure absorbing material, that is, the epoxy resin glass fiber reinforced plastic panels of the upper and lower molds are the upper and lower sandwich panels of the sandwich structure absorbing material.

[0084] (4) Paste an epoxy resin fiberglass panel with aluminum foil on the side of the polyurethane corner pyramid absorbing structure obtained in step (3) away from the corner pyramid structure to form a reflective layer, and demold the panel to obtain a lightweight broadband polyurethane foam absorbing material.

[0085] Figure 3 The radar reflectivity curve of the lightweight broadband polyurethane foam absorbing material in Example 1 at 2 to 18 GHz. Figure 3 It can be seen that at 2-18 GHz, the lightweight broadband polyurethane foam absorbing material in Example 1 has excellent absorbing performance, especially at 18 GHz, the reflectivity can reach -40.7 dB.

[0086] Figure 4 The radar reflectivity curve of the lightweight broadband polyurethane foam absorbing material in Example 1 at 26.5-40 GHz. Figure 4 It can be seen that at 26.5-40 GHz, the lightweight broadband polyurethane foam absorbing material in Example 1 has excellent absorbing performance, especially at 30 GHz, the reflectivity can reach -22.5 dB.

[0087] Figure 5 The radar reflectivity curve of the lightweight broadband polyurethane foam absorbing material in Example 2 at 2 to 18 GHz. Figure 5 It can be seen that at 2 to 18 GHz, the lightweight broadband polyurethane foam absorbing material in Example 1 has excellent absorbing performance, especially at 18 GHz, the reflectivity can reach -32.5 dB.

[0088] Figure 6 The radar reflectivity curve of the lightweight broadband polyurethane foam absorbing material in Example 2 at 26.5-40 GHz. Figure 6 It can be seen that at 26.5-40 GHz, the lightweight broadband polyurethane foam absorbing material in Example 1 has excellent absorbing performance, especially at 40 GHz, the reflectivity can reach -17.5 dB.

[0089] Figure 7 The radar reflectivity curve of the lightweight broadband polyurethane foam absorbing material in Example 3 at 2 to 18 GHz. Figure 7 It can be seen that at 2 to 18 GHz, the lightweight broadband polyurethane foam absorbing material in Example 1 has excellent absorbing performance, especially at 18 GHz, the reflectivity can reach -35.5 dB.

[0090] Figure 8 The radar reflectivity curve of the lightweight broadband polyurethane foam absorbing material in Example 3 at 26.5-40 GHz. Figure 8 It can be seen that at 26.5-40 GHz, the lightweight broadband polyurethane foam absorbing material in Example 1 has excellent absorbing performance, especially at 33 GHz, the reflectivity can reach -30 dB.

[0091] Comparative Example 1

[0092] The difference from Example 3 is that the size of the rectangular cone of each pyramid structure is 10mm×10mm×10mm, and the cone height of the square cone is 10mm; the thickness of the lightweight broadband polyurethane foam absorbing material is 20mm, and the surface density is 4.9kg / m 2 , the rest is the same as Example 3.

[0093] Comparative Example 2

[0094] The difference from Example 1 is that, measured by weight, the raw materials for preparing the polyurethane pyramid absorbing structure consist of the following components: 180 parts of polyurethane white material, 180 parts of polyurethane black material, 10 parts of crushed carbon fiber with a particle size of 400 μm and 10 parts of carbon fiber chopped strands with a length of 2 mm, that is, the mass content of the absorber in the polyurethane foam absorbing material is 5.3%, and the rest is the same as Example 1.

[0095] Comparative Example 3

[0096] The difference from Example 1 is that, by weight, the raw materials for preparing the polyurethane pyramid absorbing structure consist of the following components: 150 parts of polyurethane white material, 150 parts of polyurethane black material and 24 parts of crushed carbon fiber with a particle size of 400 μm, and the rest are the same as Example 1.

[0097] Comparative Example 4

[0098] The difference from Example 1 is that, in parts by weight, the raw materials for preparing the polyurethane pyramidal absorbing structure consist of the following components: 150 parts of polyurethane white material, 150 parts of polyurethane black material, 10 parts of crushed carbon fiber with a particle size of 600 μm and 10 parts of carbon fiber chopped strands with a length of 2 mm, and the rest are the same as Example 1.

[0099] Comparative Example 5

[0100] The difference from Example 1 is that, measured by weight, the raw materials for preparing the polyurethane pyramidal absorbing structure consist of the following components: 150 parts of polyurethane white material, 150 parts of polyurethane black material, 10 parts of crushed carbon fiber with a particle size of 400 μm and 10 parts of carbon fiber chopped strands with a length of 4 mm, and the rest are the same as Example 1.

[0101] Comparative Example 6

[0102] The difference from Example 3 is that the size of the rectangular cone of each pyramid structure is 4mm×4mm×5mm, the cone height of the square pyramid is 10mm, and the rest is the same as Example 3.

[0103] At specific electromagnetic wave frequencies of 2 GHz, 10 GHz, 18 GHz and 35 GHz, the vertical incidence maximum reflectivity of the polyurethane foam absorbing materials prepared in Examples 1 to 3 and Comparative Examples 1 to 6 was measured, and the results are shown in Table 1. Table 1 Vertical incidence maximum reflectivity of the polyurethane foam absorbing materials prepared in Examples 1 to 3 and Comparative Examples 1 to 6

[0104]

[0105] As can be seen from Table 1, the polyurethane foam absorbing material prepared in Example 1 exhibits excellent electrical properties at typical frequencies of 2 GHz, 10 GHz, 18 GHz and 35 GHz. Compared with Example 3, Comparative Example 1 changes the cone size and cone height of the pyramid structure, and the vertical incidence maximum reflectivity of the obtained polyurethane foam absorbing material decreases, especially at frequencies of 18 GHz and 35 GHz, indicating that pyramid structures of different heights and sizes will affect the electrical properties of the polyurethane foam absorbing structure. Compared with Example 1, Comparative Example 2 changes the mass content of the absorbent in the polyurethane foam absorbing material, and the vertical incidence maximum reflectivity of the obtained polyurethane foam absorbing material also decreases, especially at a frequency of 18 GHz, indicating that the content of the absorbent will also affect the electrical properties of the polyurethane foam absorbing material. Compared with Example 1, Comparative Example 3 omits carbon fiber chopped strands, and the vertical incidence maximum reflectivity of the obtained polyurethane foam absorbing material decreases significantly, especially at a frequency of 18 GHz, indicating that a single absorbent cannot achieve excellent absorbing effects. Compared with Example 1, Comparative Example 4 changes the particle size of the crushed carbon fiber, and Comparative Example 5 changes the length of the carbon fiber chopped filaments, and the vertical incidence maximum reflectivity of the obtained polyurethane foam absorbing material decreases, especially at a frequency of 18 GHz, indicating that the particle size of the crushed carbon fiber and the length of the carbon fiber chopped filaments will affect the electrical properties of the polyurethane foam absorbing material. Compared with Example 3, Comparative Example 6 changes the size of the frustum of the pyramid structure, and the vertical incidence maximum reflectivity of the obtained polyurethane foam absorbing material decreases, especially at a frequency of 18 GHz, indicating that pyramid structures of different sizes will affect the electrical properties of the polyurethane foam absorbing structure.

[0106] The above are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A lightweight broadband polyurethane foam absorbing material, characterized in that: The lightweight broadband polyurethane foam absorbing material comprises a polyurethane pyramid absorbing structure composed of a plurality of pyramid structures, polyurethane foam filled between the pyramid structures, and a reflective layer adhered to one side of the polyurethane foam; The raw materials for preparing the polyurethane pyramid absorbing structure include, by weight: 120-200 parts of polyurethane white material, 120-200 parts of polyurethane black material, 12-15 parts of carbon fiber chopped strands and 10-15 parts of crushed carbon fiber.

2. The lightweight broadband polyurethane foam absorbing material according to claim 1, characterized in that: The length of the carbon fiber chopped strands is 1 to 2 mm.

3. The lightweight broadband polyurethane foam absorbing material according to claim 1, characterized in that: The particle size of the pulverized carbon fiber is 200 to 500 μm.

4. The lightweight broadband polyurethane foam absorbing material according to claim 1, characterized in that: The pyramid structure is composed of a rectangular frustum and a square pyramid; the size of the rectangular frustum is (6-8) mm×(6-8) mm×(5-10) mm, and the cone height of the square pyramid is 9-15 mm.

5. The lightweight broadband polyurethane foam absorbing material according to claim 1, characterized in that: The reflective layer is composed of an epoxy resin panel and an aluminum foil.

6. The lightweight broadband polyurethane foam absorbing material according to claim 1, characterized in that: The lightweight broadband polyurethane foam absorbing material has a thickness of 15 to 20 mm and a surface density of 4.0 to 5.0 kg / m 2 .

7. A method for preparing the lightweight broadband polyurethane foam absorbing material according to any one of claims 1 to 6, characterized in that: The following steps are involved: (1) adding crushed carbon fiber and chopped carbon fiber to polyurethane white material and polyurethane black material respectively, stirring evenly, then mixing the polyurethane white material and polyurethane black material, and continuing to stir to obtain a mixture; curing, cutting and pyramid processing the mixture to obtain a polyurethane pyramid wave absorbing structure; (2) mixing the polyurethane white material and the polyurethane black material and pouring them into a mold, and then placing the polyurethane pyramid absorbing structure obtained in step (1) into the mold with the pyramid facing downward, and curing and molding to obtain a sandwich structure absorbing material; (3) Pasting an epoxy resin panel with aluminum foil on one side of the surface of the sandwich structure absorbing material obtained in step (2) to obtain the lightweight broadband polyurethane foam absorbing material.

8. The method for preparing a lightweight broadband polyurethane foam absorbing material according to claim 7, characterized in that: In step (1), the stirring time is 20 to 30 seconds; and / or, The cutting thickness is 15-20 mm and the size is 300 mm×300 mm.

9. The method for preparing a lightweight broadband polyurethane foam absorbing material according to claim 7, characterized in that: In step (2), the mass ratio of the polyurethane white material to the polyurethane black material is 1:

1.

10. The method for preparing a lightweight broadband polyurethane foam absorbing material according to claim 7, characterized in that: In step (3), the thickness of the epoxy resin panel is 0.3-0.5 mm, and the thickness of the aluminum foil is 0.06-0.1 mm.

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