Lightweight broadband polyurethane foam wave-absorbing material and preparation method thereof
By designing a polyurethane pyramidal absorbing structure and a carbon fiber composite absorber, the problem of poor high-frequency absorbing performance of foam sandwich structures was solved, achieving excellent absorbing effect of lightweight broadband polyurethane foam absorbing material.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NANJING UNIV
- Filing Date
- 2025-02-25
- Publication Date
- 2026-07-24
AI Technical Summary
Existing foam sandwich structure microwave absorbing materials have poor absorption performance in the high-frequency terahertz stage, and coating materials have problems such as heavy weight and easy wear.
A lightweight broadband polyurethane foam absorbing material is composed of a polyurethane pyramidal absorbing structure, polyurethane foam, and a reflective layer. The pyramidal structure reflects and refracts electromagnetic waves, and short-cut carbon fiber and crushed carbon fiber are added as composite absorbers to improve the absorbing performance.
It exhibits excellent absorption performance at typical frequencies of 2GHz, 10GHz, 18GHz and 35GHz. The material is lightweight and has good absorption performance, good compatibility, and flexible fabrication methods for designing absorption structures.
Smart Images
Figure CN119898087B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of electromagnetic wave absorbing materials technology, and particularly relates to a lightweight broadband polyurethane foam wave absorbing material and its preparation method. Background Technology
[0002] The continuous development of radio information technology has led to the emergence of radar detection technology, along with "radar absorbing materials." As modern detection technology advances towards higher accuracy and sensitivity, the possibility of targets being detected, tracked, and attacked is increasing. Therefore, research on radar absorbing materials and their preparation methods is one of the important means of countering radar detection.
[0003] Currently, there are two main types of microwave absorbing materials: structural materials and coating materials. Coating materials are mainly made by immersing a substrate material in a coating with microwave-absorbing properties to form an absorbing layer on the substrate surface. However, due to the difficulty in controlling the immersion time, the resulting absorbing materials are relatively heavy. In addition, the absorbing coating will wear down during long-term use, requiring regular maintenance or even repainting, which undoubtedly increases production costs. Structural microwave absorbing materials include various forms such as laminated, honeycomb sandwich, and foam sandwich types. Among them, foam sandwich materials hold a special and important position due to their light weight, simple manufacturing process, and excellent processing performance. Foam sandwich structural microwave absorbing materials improve upon the microwave-absorbing layer in laminated structures by introducing various absorption mechanisms and other physical and mechanical properties through the foaming structure. By designing the foaming structure, electromagnetic waves can be reflected more within the material, increasing the propagation path of electromagnetic waves within the material and minimizing the loss of incident electromagnetic waves. However, existing foam sandwich structural microwave absorbing materials still suffer from poor absorption performance in the high-frequency terahertz stage. Summary of the Invention
[0004] To address the aforementioned technical problems, this invention proposes a lightweight broadband polyurethane foam absorbing material and its preparation method. The lightweight broadband polyurethane foam absorbing material provided by this invention exhibits excellent microwave absorption performance at typical frequencies of 2GHz, 10GHz, 18GHz, and 35GHz.
[0005] To achieve the above objectives, the present invention provides the following technical solution:
[0006] This invention provides a lightweight broadband polyurethane foam absorbing material, which includes a polyurethane pyramidal absorbing structure composed of multiple pyramidal structures, a polyurethane foam filling the spaces between the pyramidal structures, and a reflective layer adhered to one side of the polyurethane foam.
[0007] The raw materials for preparing the polyurethane pyramidal microwave absorbing structure, by weight, include: 120-200 parts of white polyurethane, 120-200 parts of black polyurethane, 12-15 parts of chopped carbon fiber, and 10-15 parts of crushed carbon fiber.
[0008] Technical principle:
[0009] This invention employs a polyurethane pyramidal absorbing structure, polyurethane foam, and a reflective layer to form a lightweight broadband polyurethane foam absorbing material. The pyramidal structure allows electromagnetic waves to undergo multiple reflections and refractions between the cones, thereby fully absorbing electromagnetic waves. Simultaneously, by adding short-cut carbon fiber filaments and crushed carbon fiber as composite absorbers to the polyurethane pyramidal absorbing structure, the absorbing properties of carbon fiber are utilized to further improve the material's absorbing performance. Ultimately, a lightweight broadband polyurethane foam absorbing material exhibiting excellent absorbing performance at typical frequencies of 2GHz, 10GHz, 18GHz, and 35GHz is obtained.
[0010] Furthermore, the length of the chopped carbon fiber filaments is 1–2 mm.
[0011] Furthermore, the particle size of the pulverized carbon fiber is 200–500 μm.
[0012] Furthermore, the pyramidal structure is composed of a cuboid frustum and a square pyramid; the dimensions of the cuboid frustum are (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 an aluminum foil.
[0014] Furthermore, the lightweight broadband polyurethane foam absorbing material has a thickness of 15–20 mm and an areal density of 4.0–5.0 kg / m³. 2 .
[0015] This invention also provides a method for preparing the lightweight broadband polyurethane foam microwave absorbing material described in the above technical solution, comprising the following steps:
[0016] (1) Add crushed carbon fiber and short carbon fiber filaments to polyurethane white material and polyurethane black material respectively, stir evenly, then mix polyurethane white material and polyurethane black material, continue stirring to obtain a mixture; the mixture is cured, cut and processed into a pyramid to obtain a polyurethane pyramidal microwave absorbing structure.
[0017] (2) Mix the polyurethane white material and polyurethane black material and pour them into the mold. Then, place the polyurethane pyramidal microwave absorbing structure obtained in step (1) into the mold with the pyramid facing down. After curing, the sandwich structure microwave absorbing material is obtained.
[0018] (3) The epoxy resin panel with aluminum foil is pasted onto 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] Further, in step (1), the continued stirring time is 20–30 s; and / or,
[0020] The thickness of the cut is 15-20mm, and the size is 300mm×300mm.
[0021] In further step (2), the mass ratio of the polyurethane white material to the polyurethane black material is 1:1.
[0022] Further, in step (3), the thickness of the epoxy resin panel is 0.3 to 0.5 mm, and the thickness of the aluminum foil is 0.06 to 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 resulting lightweight broadband polyurethane foam absorbing material has the characteristics of good wave absorption performance, safety, environmental protection, good compatibility and light weight.
[0025] (2) The method for preparing lightweight broadband polyurethane foam absorbing material provided by this invention not only allows for the control of wire cutting machine process parameters to achieve nesting of the absorbing structure and reduce the loss of polyurethane absorbing foam, but also allows for flexible design of the absorbing structure, thereby optimizing the broadband absorbing performance of the polyurethane foam. A two-step foaming process is used to integrate the polyurethane absorbing structure, polyurethane foam, and reflective layer into a single unit, ultimately producing a material with a thickness of 15–20 mm and a density of 4.0–5.0 kg / m³. 2 A lightweight, broadband polyurethane foam absorbing material with excellent wave absorption properties. Attached Figure Description
[0026] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:
[0027] Figure 1 The process flow diagram is shown for the preparation method of the lightweight broadband polyurethane foam microwave absorbing material in Examples 1-3 of the present invention;
[0028] Figure 2 This is a front view of the pyramidal structure in this invention;
[0029] Figure 3This is a radar reflectivity curve of the lightweight broadband polyurethane foam absorbing material in Example 1 at 2–18 GHz.
[0030] Figure 4 The radar reflectivity curve of the lightweight broadband polyurethane foam absorbing material in Example 1 at 26.5–40 GHz is shown.
[0031] Figure 5 This is a radar reflectivity curve of the lightweight broadband polyurethane foam absorbing material in Example 2 at 2–18 GHz.
[0032] Figure 6 The radar reflectivity curve of the lightweight broadband polyurethane foam absorbing material in Example 2 is shown in the range of 26.5–40 GHz.
[0033] Figure 7 This is a radar reflectivity curve of the lightweight broadband polyurethane foam absorbing material in Example 3 at 2–18 GHz.
[0034] Figure 8 The image shows the radar reflectivity curves of the lightweight broadband polyurethane foam absorbing material in Example 3 at 26.5–40 GHz. Detailed Implementation
[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0036] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.
[0037] This invention provides a lightweight broadband polyurethane foam microwave absorbing material. The material comprises a polyurethane pyramidal absorbing structure composed of multiple pyramidal structures, polyurethane foam filling the spaces between the pyramidal structures, and a reflective layer adhered to one side of the polyurethane foam. This invention uses polyurethane foam to prepare the absorbing material. Polyurethane foam (PUR) is a type of material with a urethane polymer backbone prepared by reacting polyhydroxy compounds with polyisocyanate groups. It possesses characteristics such as low density, excellent mechanical properties, thermal conductivity, and heat resistance. Furthermore, the pyramidal structure is used to regulate the electrical properties of the absorbing material, and the reflective layer further enhances the microwave absorption effect, ultimately resulting in a lightweight, broadband, and highly efficient polyurethane foam microwave absorbing material.
[0038] In a preferred embodiment, the raw materials for preparing the polyurethane pyramidal absorbing structure, by weight, include: 120-200 parts of white polyurethane, 120-200 parts of black polyurethane, 12-15 parts of chopped carbon fiber filaments, and 10-15 parts of crushed carbon fiber. This invention employs a high-content composite absorber polyurethane pyramidal absorbing structure formulation, which can effectively control the electrical properties of the absorbing material, thus facilitating the production of highly efficient polyurethane foam absorbing materials. Carbon fiber has conductivity between that of metals and non-metals, and its electrical properties are similar to those of metals. It primarily relies on ionic conductivity to generate eddy current losses, thus possessing certain absorbing properties. This invention, by simultaneously using chopped carbon fiber filaments and crushed carbon fiber as composite absorbers, allows the crushed carbon fiber to fill the gaps in the chopped carbon fiber filaments, thereby increasing the composite absorber content in the absorbing material and enhancing the absorbing effect.
[0039] In a preferred embodiment, the length of the chopped carbon fiber filaments is 1-2 mm. This invention uses chopped carbon fiber filaments within this length range, which has the advantages of increasing the content of the composite absorber in the absorbing material and enhancing the absorption effect. If the chopped carbon fiber filaments are too long, they will cause bridging between fibers, forming conductive channels and enhancing the material's reflection performance of electromagnetic waves, which is detrimental to absorption. Conversely, if the chopped carbon fiber filaments are too short, they will cause agglomeration and be difficult to disperse in the resin matrix, thus affecting the absorption effect.
[0040] In a preferred embodiment, the particle size of the pulverized carbon fiber is 200–500 μm. This invention uses pulverized carbon fiber with a particle size within the above range, which has the advantages of filling gaps, reducing local bridging of chopped carbon fiber filaments, and making the chopped carbon fiber filaments easier to disperse. If the particle size of the pulverized carbon fiber is too small, it will cause powder agglomeration, making it difficult to disperse in the resin matrix, thus affecting the microwave absorption effect.
[0041] In a preferred embodiment, the pyramidal structure is composed of a cuboid frustum and a square pyramid; the dimensions of the cuboid frustum are (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 cuboid frustum to the top of the square pyramid. This invention can effectively regulate the electrical properties of the absorbing material by controlling the dimensions of the frustum and the cone height of the pyramidal structure. When the cone height remains constant, as the dimensions of the cuboid frustum increase, the electrical properties of the absorbing material shift towards lower frequencies; conversely, when the dimensions of the cuboid frustum remain constant, as the cone height increases, the electrical properties of the absorbing material shift towards higher frequencies. However, excessively small dimensions of the cuboid frustum and cone height can also adversely affect the electrical properties of the absorbing material.
[0042] In a preferred embodiment, the front view of the pyramidal structure is shown below. Figure 2As can be seen, the pyramidal structure consists of a cuboid frustum and a square pyramid, with the frustum being a cuboid and its base being a square. (Front view and side view of the pyramidal structure are shown.) Figure 1 The top view is a square.
[0043] In a preferred embodiment, the polyurethane foam is obtained 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. In this invention, the epoxy resin panel connects the aluminum foil and the polyurethane foam, with the aluminum foil providing the reflective function.
[0045] In a preferred embodiment, the lightweight broadband polyurethane foam absorbing material has a thickness of 15–20 mm and a surface density of 4.0–5.0 kg / m³. 2 .
[0046] This invention also provides a method for preparing the lightweight broadband polyurethane foam microwave absorbing material described in the above technical solution, comprising the following steps:
[0047] (1) Add crushed carbon fiber and short carbon fiber filaments to polyurethane white material and polyurethane black material respectively, stir evenly, then mix polyurethane white material and polyurethane black material, continue stirring to obtain a mixture; the mixture is cured, cut and processed into a pyramid to obtain a polyurethane pyramidal microwave absorbing structure.
[0048] (2) Mix the polyurethane white material and polyurethane black material and pour them into the mold. Then, place the polyurethane pyramidal microwave absorbing structure obtained in step (1) into the mold with the pyramid facing down. After curing, the sandwich structure microwave absorbing material is obtained.
[0049] (3) The epoxy resin panel with aluminum foil is pasted onto 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 thickness of the cut is 15-20 mm and the size is 300 mm × 300 mm; the equipment used for the cut is a vertical band saw.
[0052] In a preferred embodiment, in step (1), the dimensions of the pyramid structure obtained by processing the pyramid are (6~10)mm×(6~10)mm×(5~10)mm, and the cone height is 9~15mm.
[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 opposite to the side of the pyramidal structure.
[0056] Unless otherwise specified, all raw materials used in the embodiments of this invention were purchased through commercial channels.
[0057] The white polyurethane component is a polyurethane rigid foam composite polyether, while the black polyurethane component is polymeric MDI.
[0058] Example 1
[0059] A lightweight broadband polyurethane foam absorbing material includes a polyurethane pyramidal absorbing structure composed of multiple adjacent and repeating pyramidal structures, polyurethane foam filling the spaces between the pyramidal structures, and a reflective layer adhered to the bottom of the polyurethane foam. The pyramidal structure is composed of a cuboid frustum and a square pyramid, each cuboid frustum measuring 8mm × 8mm × 5mm, and each square pyramid having a height of 13mm. The lightweight broadband polyurethane foam absorbing material has a thickness of 19.5mm and a surface density of 4.0kg / m³. 2 ;
[0060] The raw materials for preparing the polyurethane pyramidal microwave 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 400μm and 12 parts of carbon fiber short shreds with a length of 2mm.
[0061] The reflective layer consists of an epoxy resin fiberglass panel and an aluminum foil. The epoxy resin fiberglass panel is 0.3 mm thick, and the aluminum foil is 0.08 mm thick.
[0062] The preparation method and process flow of lightweight broadband polyurethane foam microwave absorbing material are as follows: Figure 1 The specific steps are as follows:
[0063] (1) Add crushed carbon fiber and short carbon fiber filaments to polyurethane white material and polyurethane black material respectively, and 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, and wait for the polyurethane black material and polyurethane white material to react completely. After curing and molding, polyurethane foam microwave absorbing material is obtained. The mass content of absorber in polyurethane foam microwave absorbing material is 7.4%.
[0064] (2) Cut the polyurethane foam absorbing material obtained in step (1) into a thickness of 19.5 mm and a size of 300 mm × 300 mm. Then, use a wire saw to process it into a pyramidal structure to obtain a polyurethane pyramidal absorbing structure. The polyurethane pyramidal absorbing structure is composed of multiple adjacent and repeated pyramidal structures. The pyramidal structure is composed of a cuboid frustum and a square pyramid. The cuboid frustum of each pyramidal structure is 8 mm × 8 mm × 5 mm in size, and the pyramidal height of each square pyramidal structure is 13 mm.
[0065] (3) Mix polyurethane white material and polyurethane black material in a mass ratio of 1:1 and spread them evenly on the surface of the epoxy resin fiberglass panel with a thickness of 0.1mm at the bottom of the foaming mold (lower mold). Then, the polyurethane pyramidal microwave absorbing structure obtained in step (2) is inverted into the mold (i.e., placed into the mold with the pyramid facing down). The upper and lower molds are closed (the upper mold also contains epoxy resin fiberglass panels). The polyurethane white material and polyurethane black material are fully reacted between the epoxy resin fiberglass panels of the upper and lower molds and then cured to form a sandwich structure microwave absorbing material. That is, the epoxy resin fiberglass panels of the upper and lower molds are the upper and lower sandwich panels of the sandwich structure microwave absorbing material.
[0066] (4) The epoxy resin fiberglass panel with aluminum foil is pasted onto the side of the sandwich structure absorbing material obtained in step (3) away from the pyramid structure to form a reflective layer. The lightweight broadband polyurethane foam absorbing material is obtained by demolding.
[0067] Example 2
[0068] A lightweight broadband polyurethane foam absorbing material includes a polyurethane pyramidal absorbing structure composed of multiple adjacent and repeating pyramidal structures, polyurethane foam filling the spaces between the pyramidal structures, and a reflective layer adhered to the bottom of the polyurethane foam. The pyramidal structure consists of a cuboid frustum and a square pyramid, with each cuboid frustum measuring 8mm × 8mm × 5mm and each square pyramid having a height of 9mm. The lightweight broadband polyurethane foam absorbing material has a thickness of 15mm and a surface density of 4.4kg / m³. 2 ;
[0069] The raw materials for preparing the polyurethane pyramidal microwave 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 400μm and 12 parts of carbon fiber short shreds with a length of 2mm.
[0070] The reflective layer consists of an epoxy resin fiberglass panel and an aluminum foil. The epoxy resin fiberglass panel is 0.5 mm thick, and the aluminum foil is 0.06 mm thick.
[0071] The preparation method and process flow of lightweight broadband polyurethane foam microwave absorbing material are as follows: Figure 1 The specific steps are as follows:
[0072] (1) Crushed carbon fiber and chopped carbon fiber filaments were added to polyurethane white and polyurethane black components respectively, and stirred evenly with a pneumatic stirring rod. Then, the polyurethane black and polyurethane white components were mixed and stirred for another 20 seconds with a pneumatic stirring rod to obtain a mixture. The resulting mixture was poured into a mold and allowed to stand for 1 hour until the polyurethane black and polyurethane white components had completely reacted and solidified to obtain a polyurethane foam microwave absorbing material. The mass content of the absorbent in the polyurethane foam microwave absorbing material was 8.4%.
[0073] (2) Cut the polyurethane foam absorbing material obtained in step (1) into a thickness of 15mm and a size of 300mm×300mm, and then process it into a pyramidal structure using a wire saw to obtain a polyurethane pyramidal absorbing structure; wherein, the polyurethane pyramidal absorbing structure is composed of multiple adjacent and repeated pyramidal structures, the pyramidal structure is composed of a cuboid frustum and a square pyramid, and the cuboid frustum of each pyramidal structure is 8mm×8mm×5mm in size, and the pyramidal height of each square pyramidal structure is 9mm.
[0074] (3) Mix polyurethane white material and polyurethane black material in a mass ratio of 1:1 and spread them evenly on the surface of the epoxy resin fiberglass panel with a thickness of 0.1mm at the bottom of the foaming mold (lower mold). Then, the polyurethane pyramidal microwave absorbing structure obtained in step (2) is inverted into the mold (i.e., placed into the mold with the pyramid facing down). The upper and lower molds are closed (the upper mold also contains epoxy resin fiberglass panels). The polyurethane white material and polyurethane black material are fully reacted between the epoxy resin fiberglass panels of the upper and lower molds and then cured to form a sandwich structure microwave absorbing material. That is, the epoxy resin fiberglass panels of the upper and lower molds are the upper and lower sandwich panels of the sandwich structure microwave absorbing material.
[0075] (4) The epoxy resin fiberglass panel with aluminum foil is pasted onto the side of the sandwich structure absorbing material obtained in step (3) away from the pyramid structure to form a reflective layer. The lightweight broadband polyurethane foam absorbing material is obtained by demolding.
[0076] Example 3
[0077] A lightweight broadband polyurethane foam absorbing material includes a polyurethane pyramidal absorbing structure composed of multiple adjacent and repeating pyramidal structures, and a reflective layer adhered to the bottom of the polyurethane pyramidal absorbing structure. The pyramidal structure is composed of a cuboid frustum and a square pyramid, each cuboid frustum having dimensions of 8mm × 8mm × 10mm, and each square pyramid having a height of 10mm. The lightweight broadband polyurethane foam absorbing material has a thickness of 20mm and a surface density of 5.0kg / m³. 2 ;
[0078] The raw materials for preparing the polyurethane pyramidal microwave 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 400μm and 15 parts of carbon fiber short chopped filaments with a length of 2mm.
[0079] The reflective layer consists of an epoxy resin fiberglass panel and an aluminum foil. The epoxy resin fiberglass panel is 0.5 mm thick, and the aluminum foil is 0.08 mm thick.
[0080] The preparation method and process flow of lightweight broadband polyurethane foam microwave absorbing material are as follows: Figure 1 The specific steps are as follows:
[0081] (1) Crushed carbon fiber and chopped carbon fiber were added to polyurethane white and polyurethane black components respectively, and stirred evenly with a pneumatic stirring rod. Then, the polyurethane black and polyurethane white components were mixed and stirred for another 30 seconds with a pneumatic stirring rod to obtain a mixture. The resulting mixture was poured into a mold and left to stand for 1 hour until the polyurethane black and polyurethane white components had completely reacted and solidified to obtain a polyurethane foam microwave absorbing material. The mass content of the absorbent in the polyurethane foam microwave absorbing material was 7.0%.
[0082] (2) Cut the polyurethane foam absorbing material obtained in step (1) into a thickness of 20mm and a size of 300mm×300mm, and then process it into a pyramidal structure using a wire saw to obtain a polyurethane pyramidal absorbing structure; wherein, the polyurethane pyramidal absorbing structure is composed of multiple adjacent and repeated pyramidal structures, the pyramidal structure is composed of a cuboid frustum and a square pyramid, and the cuboid frustum of each pyramidal structure is 8mm×8mm×10mm in size, and the cone height of the square pyramid is 10mm.
[0083] (3) Mix polyurethane white material and polyurethane black material in a mass ratio of 1:1 and spread them evenly on the surface of the epoxy resin fiberglass panel with a thickness of 0.1mm at the bottom of the foaming mold (lower mold). Then, the polyurethane pyramidal microwave absorbing structure obtained in step (2) is inverted into the mold (i.e., placed into the mold with the pyramid facing down). The upper and lower molds are closed (the upper mold also contains epoxy resin fiberglass panels). The polyurethane white material and polyurethane black material are fully reacted between the epoxy resin fiberglass panels of the upper and lower molds and then cured to form a sandwich structure microwave absorbing material. That is, the epoxy resin fiberglass panels of the upper and lower molds are the upper and lower sandwich panels of the sandwich structure microwave absorbing material.
[0084] (4) The epoxy resin fiberglass panel with aluminum foil is pasted onto the side of the polyurethane pyramidal microwave absorbing structure obtained in step (3) to form a reflective layer. The lightweight broadband polyurethane foam microwave absorbing material is obtained by demolding.
[0085] Figure 3 This is a radar reflectivity curve of the lightweight broadband polyurethane foam absorbing material in Example 1 at 2–18 GHz. Figure 3 It can be seen that the lightweight broadband polyurethane foam absorbing material in Example 1 has excellent wave absorption performance in the range of 2 to 18 GHz, especially at 18 GHz, the reflectivity can reach -40.7 dB.
[0086] Figure 4 This is a radar reflectivity curve of the lightweight broadband polyurethane foam absorbing material in Example 1 at 26.5–40 GHz. From... Figure 4 It can be seen that the lightweight broadband polyurethane foam absorbing material in Example 1 has excellent wave absorption performance in the range of 26.5 to 40 GHz, especially at 30 GHz, the reflectivity can reach -22.5 dB.
[0087] Figure 5 This is a radar reflectivity curve of the lightweight broadband polyurethane foam absorbing material in Example 2 at 2–18 GHz. From... Figure 5 It can be seen that the lightweight broadband polyurethane foam absorbing material in Example 1 has excellent wave absorption performance in the range of 2 to 18 GHz, especially at 18 GHz, the reflectivity can reach -32.5 dB.
[0088] Figure 6 This is a radar reflectivity curve of the lightweight broadband polyurethane foam absorbing material in Example 2 at 26.5–40 GHz. From... Figure 6 It can be seen that the lightweight broadband polyurethane foam absorbing material in Example 1 has excellent wave absorption performance in the range of 26.5 to 40 GHz, especially at 40 GHz, the reflectivity can reach -17.5 dB.
[0089] Figure 7 This is a radar reflectivity curve of the lightweight broadband polyurethane foam absorbing material in Example 3 at 2–18 GHz. Figure 7 It can be seen that the lightweight broadband polyurethane foam absorbing material in Example 1 has excellent wave absorption performance in the range of 2 to 18 GHz, especially at 18 GHz, the reflectivity can reach -35.5 dB.
[0090] Figure 8 This is a radar reflectivity curve of the lightweight broadband polyurethane foam absorbing material in Example 3 at 26.5–40 GHz. From... Figure 8 It can be seen that the lightweight broadband polyurethane foam absorbing material in Example 1 has excellent wave absorption performance in the range of 26.5 to 40 GHz, especially at 33 GHz, the reflectivity can reach -30 dB.
[0091] Comparative Example 1
[0092] The difference from Example 3 is that the cuboid frustum of each pyramidal structure has dimensions of 10mm × 10mm × 10mm, and the cone height of each square pyramid is 10mm; the thickness of the lightweight broadband polyurethane foam absorbing material is 20mm, and the areal density is 4.9kg / m³. 2 The rest is the same as in Example 3.
[0093] Comparative Example 2
[0094] The difference from Example 1 is that, by weight, the raw materials for preparing the polyurethane pyramidal microwave absorbing structure consist of the following components: 180 parts of white polyurethane, 180 parts of black polyurethane, 10 parts of pulverized carbon fiber with a particle size of 400 μm, and 10 parts of short carbon fiber filaments with a length of 2 mm. That is, the mass content of absorber in the polyurethane foam microwave absorbing material is 5.3%, and the rest is the same as in Example 1.
[0095] Comparative Example 3
[0096] The difference from Example 1 is that, by weight, the raw materials for preparing the polyurethane pyramidal microwave absorbing structure consist of the following components: 150 parts of white polyurethane, 150 parts of black polyurethane, and 24 parts of pulverized carbon fiber with a particle size of 400 μm, with the other components being the same as in Example 1.
[0097] Comparative Example 4
[0098] The difference from Example 1 is that, by weight, the raw materials for preparing the polyurethane pyramidal microwave absorbing structure consist of the following components: 150 parts of white polyurethane, 150 parts of black polyurethane, 10 parts of pulverized carbon fiber with a particle size of 600 μm, and 10 parts of short carbon fiber filaments with a length of 2 mm. The rest is the same as in Example 1.
[0099] Comparative Example 5
[0100] The difference from Example 1 is that, by weight, the raw materials for preparing the polyurethane pyramidal microwave absorbing structure consist of the following components: 150 parts of white polyurethane, 150 parts of black polyurethane, 10 parts of pulverized carbon fiber with a particle size of 400 μm, and 10 parts of short carbon fiber filaments with a length of 4 mm. The rest is the same as in Example 1.
[0101] Comparative Example 6
[0102] The difference from Example 3 is that the dimensions of the cuboid frustum of each pyramid structure are 4mm×4mm×5mm, and the cone height of the square pyramid is 10mm. The rest is the same as in Example 3.
[0103] The maximum vertical incident reflectivity of the polyurethane foam absorbing materials prepared in Examples 1-3 and Comparative Examples 1-6 was measured at specific electromagnetic wave frequencies of 2 GHz, 10 GHz, 18 GHz, and 35 GHz. The results are shown in Table 1. Table 1: Maximum Vertical Incident Reflectivity of the Polyurethane Foam Absorbing Materials Prepared in Examples 1-3 and Comparative Examples 1-6
[0104]
[0105] As shown in 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 to Example 3, Comparative Example 1 changed the frustum size and cone height of the pyramidal structure, resulting in a decrease in the maximum vertical incident reflectivity of the obtained polyurethane foam absorbing material, especially at frequencies of 18 GHz and 35 GHz, indicating that different heights and sizes of pyramidal structures affect the electrical properties of the polyurethane foam absorbing structure. Compared to Example 1, Comparative Example 2 changed the mass content of the absorber in the polyurethane foam absorbing material, also resulting in a decrease in the maximum vertical incident reflectivity of the obtained polyurethane foam absorbing material, especially at frequency of 18 GHz, indicating that the absorber content also affects the electrical properties of the polyurethane foam absorbing material. Compared to Example 1, Comparative Example 3 omitted the short carbon fiber filaments, resulting in a significant decrease in the maximum vertical incident reflectivity of the obtained polyurethane foam absorbing material, especially at frequency of 18 GHz, indicating that a single absorber cannot achieve excellent absorption effects. Compared to Example 1, Comparative Example 4 changed the particle size of the shredded carbon fiber, and Comparative Example 5 changed the length of the chopped carbon fiber filaments. The maximum vertical incident reflectivity of the resulting polyurethane foam absorbing material decreased, especially at the 18 GHz frequency, indicating that both the particle size of the shredded carbon fiber and the length of the chopped carbon fiber filaments affect the electrical properties of the polyurethane foam absorbing material. Compared to Example 3, Comparative Example 6 changed the frustum size of the pyramidal structure, resulting in a decrease in the maximum vertical incident reflectivity of the resulting polyurethane foam absorbing material, especially at the 18 GHz frequency, indicating that different sizes of pyramidal structures affect the electrical properties of the polyurethane foam absorbing structure.
[0106] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.
Claims
1. A method for preparing a lightweight broadband polyurethane foam microwave absorbing material, characterized in that, Includes the following steps: (1) Add crushed carbon fiber and short carbon fiber filaments to polyurethane white material and polyurethane black material respectively, stir evenly, then mix polyurethane white material and polyurethane black material, continue stirring to obtain a mixture; the mixture is cured, cut and processed into a pyramid to obtain a polyurethane pyramidal microwave absorbing structure. Of these, by weight, the polyurethane white component is 120-200 parts, the polyurethane black component is 120-200 parts, the carbon fiber short filaments are 12-15 parts, and the crushed carbon fiber is 10-15 parts. The pyramidal structure is composed of a cuboid frustum and a square pyramid; the cuboid frustum has dimensions of (6~8)mm×(6~8)mm×(5~10)mm, and the square pyramid has a height of 9~15mm. The length of the chopped carbon fiber filaments is 1~2mm; The particle size of the pulverized carbon fiber is 200~500µm; (2) After mixing polyurethane white material and polyurethane black material, pour them into the mold, and then place the polyurethane pyramidal microwave absorbing structure obtained in step (1) into the mold with the pyramid facing downwards. After curing, the sandwich structure microwave absorbing material is obtained. The mass ratio of the polyurethane white component to the polyurethane black component is 1:
1. (3) The epoxy resin panel with aluminum foil attached is attached to one side of the surface of the sandwich structure microwave absorbing material obtained in step (2) to obtain the lightweight broadband polyurethane foam microwave absorbing material. In steps (1) and (2), the polyurethane white material is a polyurethane rigid foam polyether, and the polyurethane black material is polymeric MDI.
2. The method for preparing the lightweight broadband polyurethane foam microwave absorbing material according to claim 1, characterized in that, In step (1), the stirring time is 20~30s; and / or the cutting thickness is 15~20mm and the size is 300mm×300mm.
3. The method for preparing the lightweight broadband polyurethane foam microwave absorbing material according to claim 1, characterized in that, In step (3), the thickness of the epoxy resin panel is 0.3~0.5mm and the thickness of the aluminum foil is 0.06~0.1mm.
4. A lightweight broadband polyurethane foam microwave absorbing material prepared by the preparation method according to any one of claims 1 to 3, characterized in that, The lightweight broadband polyurethane foam absorbing material includes a polyurethane pyramidal absorbing structure composed of multiple pyramidal structures, polyurethane foam filling the spaces between the pyramidal structures, and a reflective layer adhered to one side of the polyurethane foam.
5. The lightweight broadband polyurethane foam microwave absorbing material according to claim 4, characterized in that, The reflective layer consists of an epoxy resin panel and an aluminum foil.
6. The lightweight broadband polyurethane foam microwave absorbing material according to claim 4, characterized in that, The lightweight broadband polyurethane foam absorbing material has a thickness of 15-20 mm and a surface density of 4.0-5.0 kg / m³. 2 .