Hot-melt wave-absorbing resin, low-frequency wave-absorbing prepreg and application of hot-melt wave-absorbing resin and low-frequency wave-absorbing prepreg in low-broadband magnetic wave-absorbing composite material

Abstract

The invention provides hot-melt wave-absorbing resin, a low-frequency wave-absorbing prepreg and application of the hot-melt wave-absorbing resin and the low-frequency wave-absorbing prepreg in a low-broadband magnetic wave-absorbing composite material. The hot-melt wave-absorbing resin is prepared from the following raw materials: hot-melt resin and a composite absorbent, the composition comprises a combination of a coupling agent modified conductive absorbent and a magnetic absorbent. The raw materials of the low-frequency wave-absorbing prepreg comprise the hot-melt wave-absorbing resin and reinforced fibers with low dielectric constant and low gram weight. The hot-melt wave-absorbing resin provided by the invention realizes the low-frequency wave-absorbing performance covering 1GHz. Through the synergistic effect of the conductive absorbent and the magnetic absorbent, the broadband wave-absorbing prepreg covering low frequency is prepared by using a hot melting method, the dielectric loss of the wave-absorbing prepreg is improved, and the low-frequency wave-absorbing performance is enhanced. And the formula can be changed according to frequency band requirements to meet the wave absorbing requirements of different frequency bands (from 0.3 GHz to 18GHz). According to the low-broadband magnetic wave-absorbing composite material with the wave-absorbing honeycomb provided by the invention, the wave-absorbing bandwidth coverage is expanded by 1-18 GHz.

Description

Technical Field

[0001] This invention relates to the field of microwave absorbing materials technology, and in particular to a hot-melt microwave absorbing resin, a low-frequency microwave absorbing prepreg, and their application in low-bandwidth magnetic microwave absorbing composite materials. Background Technology

[0002] Radar-absorbing materials are electromagnetic functional materials, also known as microwave absorbing materials or radar wave absorbing materials, and are widely used in the military field. They can be used to reduce the visibility of targets detected by radar, thus achieving military objectives more covertly. Stealth technology has been listed as a fundamental element of "competitive strategy" and is considered a top priority in the military field.

[0003] Existing microwave absorbing adhesives, after adding magnetic particles to the resin matrix, have high viscosity, making film formation difficult. When preparing composite materials, high-temperature curing is required, and the magnetic particles may demagnetize at high temperatures, reducing absorption efficiency. Furthermore, traditional microwave absorbing honeycomb structures are almost ineffective in the P and L bands, and their absorption performance significantly decreases in the S band. Existing microwave absorbing coatings have poor processability, high cost, and use environmentally unfriendly solvents, resulting in poor environmental resistance and requiring repeated maintenance. Microwave absorbing patches are only suitable for flat panels and are difficult to process into curved surfaces or other irregular structures, making them unsuitable for the needs of stealth technology development.

[0004] Therefore, in order to address the above problems, the present invention urgently needs to provide a low-bandwidth magnetic absorbing composite material, its preparation method, and a low-bandwidth magnetic absorbing composite material with absorbing honeycomb.

[0005] Patent CN 118744542 A discloses a method for preparing low-frequency absorbing prepreg for P and L bands. The method includes preparing a slurry, preparing a film, and preparing the prepreg. It utilizes a thermosetting resin and FeSiAl, FeSiCr, or FeSiNi alloys, and achieves the preparation of the low-frequency absorbing prepreg through a drum vulcanizing process and strict control of parameters at each step. This patent, with a limited amount of low-frequency absorber added, orients the sheet-like low-frequency absorber in the prepreg, significantly increasing the magnetic parameters and solving the problem of low permeability caused by low addition of sheet-like low-frequency absorbers, which affects low-frequency absorption performance. However, the resulting magnetic absorbing material has low dielectric loss and a low imaginary part of the dielectric constant, especially as it extends to higher frequency bands, where the imaginary part of the dielectric constant attenuates significantly. This means that the magnetic absorbing material will have low absorption efficiency during use and hinders its application across a wider frequency range. Summary of the Invention

[0006] This invention provides a hot-melt absorbing resin, a low-frequency absorbing prepreg, and their application in low-bandwidth magnetic absorbing composite materials. It addresses the technical problems in existing technologies where the addition of magnetic particles to the absorbing adhesive in the resin matrix results in high viscosity, making film formation difficult; high-temperature curing is required when preparing composite materials; magnetic particles may demagnetize at high temperatures, reducing absorption efficiency; and traditional absorbing honeycomb structures are almost ineffective in the P and L bands, with a significant decrease in absorption performance in the S band.

[0007] The hot-melt absorbing resin comprises hot-melt resin and composite absorber; the ratio of hot-melt resin to composite absorber is (5-3):(5-7). The hot melt resin comprises epoxy resin, cyanate ester, fluorocarbon resin and ammonia curing agent; The composite absorbent comprises a combination of a conductive absorbent modified with a coupling agent and a magnetic absorbent.

[0008] The ratio of the conductive absorbent to the magnetic absorbent is (1~3):(99~97).

[0009] The particle size of the composite absorbent is 1-100 μm.

[0010] The conductive absorber is selected from one or more of the following: flake graphite, carbon black, carbon nanotubes, graphene powder, and Mxene-based compounds.

[0011] The magnetic absorber is selected from one or more of ferrite, carbonyl iron, or iron-silicon-aluminum.

[0012] The coupling agent modification method involves refluxing the absorbent and coupling agent at 70-90℃ for 12-15 hours, drying them at 70-90℃ after treatment, and then pulverizing them by stirring with a high-speed stirrer for 5-10 minutes to obtain a modified absorbent powder that is easy to disperse; the coupling agent includes one or more of KH550, KH560, KH570 and A151.

[0013] The mass ratio of epoxy resin, cyanate ester, ammonia curing agent, siloxane compound and fluorocarbon resin in hot melt resin is (50-80): (20-50): (8-10): (2-3): (2-5).

[0014] The melting temperature of the hot-melt absorbing resin is between 70℃ and 90℃, and its melt viscosity is ≤12000mps.

[0015] The method for preparing the hot-melt microwave absorbing resin involves stirring the absorber and hot-melt resin in a high-speed mixer for more than 3 minutes, and then calendering them in a calender for 3-6 cycles to obtain the hot-melt microwave absorbing resin.

[0016] Low-frequency absorbing prepreg can be obtained using the aforementioned hot-melt absorbing resin; the composition of the low-frequency absorbing prepreg includes the hot-melt absorbing resin composite with low-weight reinforcing fibers; and the mass ratio of the hot-melt absorbing resin accounts for 40%-90% of the total weight; The mechanical properties of the low-weight reinforced fiber are as follows: fiber fabric breaking strength ≥200 N / 25 mm; The low-basis-weight reinforced fiber has a dielectric constant ≤4.5 and a dielectric loss ≤0.018. The fabric surface density of the low-weight reinforcing fiber is 10-40 g / m². 2 ; The low-weight reinforcing fiber is any one of unidirectional fiber, woven fabric, stitch-knitted fabric, or fiber felt; Preferably, the low-weight reinforcing fiber is selected from low-dielectric fiber fabrics such as glass fiber cloth, quartz fiber cloth, polyester fiber felt, aramid fiber fabric, polyethylene or polypropylene.

[0017] The preparation method of the low-frequency absorbing prepreg involves heating and melting a hot-melt absorbing resin to form an adhesive film, which is then compounded with low-basis-weight reinforcing fibers or low-basis-weight reinforcing fiber cloth to obtain the low-frequency absorbing magnetic prepreg. The thickness of a single-layer adhesive film is <0.1 mm.

[0018] After the low-frequency absorbing prepreg is heated and cured, a low-bandwidth magnetic absorbing composite material is obtained.

[0019] The curing temperature of the low-frequency absorbing magnetic prepreg is ≤130℃.

[0020] The present invention also provides a low-bandwidth magnetic absorbing composite structure material, which is obtained by laying and curing absorbing prepreg with honeycomb, skin and other structures according to electromagnetic structure design.

[0021] The present invention also provides a low-bandwidth magnetic absorbing composite material, which comprises a wave-transparent outer skin and a carbon fiber / metal film reflective layer, wherein at least one set of absorbing layers is sandwiched between the wave-transparent outer skin and the carbon fiber / metal film reflective layer, and the absorbing layer comprises a wave-absorbing honeycomb and the low-bandwidth magnetic absorbing composite material.

[0022] Preferably, the thickness of the wave-transmitting outer skin of the low-bandwidth magnetic wave-absorbing composite material is 0.05mm-2mm; the thickness of the low-bandwidth magnetic wave-absorbing composite material is 1mm-10mm; and the thickness of the wave-absorbing honeycomb is 2.8mm-30mm.

[0023] The hot-melt absorbing resin of this invention reduces the overall viscosity of the resin base and improves the dispersion effect of the absorber by adding siloxane compounds and fluorocarbon resins. The viscosity of the resin base can be controlled, and the viscosity of the resin base is less than or equal to 12000 mps at 60℃-90℃. Furthermore, by adding ammonia curing agents, medium and low temperature curing can be achieved, avoiding the absorber material from losing its absorbing properties due to demagnetization at high temperature curing.

[0024] The hot-melt absorbing resin provided by the present invention first uses a coupling agent to treat the surface of the absorber, thereby improving the dispersibility of the absorber in the resin matrix and achieving a high proportion of absorber addition, thus achieving low-frequency absorbing performance covering 1GHz.

[0025] This invention utilizes the synergistic effect of conductive and magnetic absorbers to prepare a broadband absorbing prepreg covering low frequencies, thereby improving the dielectric loss of the prepreg and enhancing its low-frequency absorption performance. The formulation can be modified to meet absorption requirements in different frequency bands (from 0.3 GHz to 18 GHz) according to frequency band requirements.

[0026] The low-bandwidth magnetic absorbing composite material with absorbing honeycomb provided by the present invention extends the absorbing bandwidth to cover 1-18GHz. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the low-frequency absorbing structure described in Embodiment 1 of the present invention.

[0028] Figure 2 This is a schematic diagram of the mid-frequency absorbing structure described in Embodiment 2 of the present invention.

[0029] Figure 3 This is a schematic diagram of the low-bandwidth absorbing structure described in Embodiment 3 of the present invention.

[0030] Figure 4 This is a schematic diagram of the low-bandwidth absorbing structure described in Embodiment 4 of the present invention.

[0031] Figure 5 This is a schematic diagram of the low-bandwidth absorbing structure described in Embodiment 5 of the present invention.

[0032] The attached figures are labeled as follows: 1. Wave-transparent outer skin; 2. Low-frequency absorbing composite material; 3. Carbon fiber / metal film reflective layer; 4. Mid-frequency absorbing composite material; 5. Absorbing honeycomb. Detailed Implementation Example 1

[0033] The method for preparing low-frequency (0.3GHz~1GHz) magnetic microwave absorbing composite material provided in this embodiment includes the following steps:

[0034] 101) The absorbent is treated with a coupling agent to obtain a modified absorbent; The absorbent consists of 1.5% flake graphite, 1.5% carbon nanotubes, and 97% iron, silicon, and aluminum. The particle size of the absorbent is 1-100 μm; the thickness of a single-layer film is <0.1 mm.

[0035] The modified absorbent preparation process is as follows: the absorbent and coupling agent are refluxed at 70°C for 15 hours, dried at 70°C after treatment, and then stirred with a high-speed stirrer for 10 minutes to obtain a modified absorbent powder that is easy to disperse; the coupling agent is KH570.

[0036] 102) Epoxy resin, cyanate ester, ammonia curing agent, siloxane compound and fluorocarbon resin are mixed to obtain hot melt resin. The viscosity of the hot melt resin at 60℃-90℃ is ≤12000mps. The mass ratio of epoxy resin, cyanate ester, ammonia curing agent, siloxane compound and fluorocarbon resin is 80:50:10:3:5. 103) The modified absorbent and hot melt resin are mixed in a mass ratio of 7:3 to obtain the hot melt absorbing resin.

[0037] The hot-melt resin obtained from 1-A is melted at 90°C to prepare a film. The film is then combined with fiber cloth to obtain a low-frequency absorbing magnetic prepreg.

[0038] The fiber cloth is a low-dielectric material fiber fabric—quartz fiber cloth—with a fiber cloth surface density of 40 g / m³. 2 Tensile strength (N / 25mm): 272.4 in the warp direction and 313.1 in the weft direction; dielectric constant 3.7, dielectric loss 0.005.

[0039] The content of hot-melt absorbing resin in the medium-frequency absorbing magnetic prepreg is 90%.

[0040] Low-frequency absorbing magnetic prepreg is cured by heating at 120℃ to obtain a low-bandwidth magnetic absorbing composite material.

[0041] A 3 mm long low-bandwidth magnetic absorbing composite material was prepared using the low-bandwidth magnetic absorbing composite material obtained from 1-C. The electromagnetic parameters were measured, and the electromagnetic parameters of the low-bandwidth magnetic absorbing composite material in the range of 0.2 GHz to 18.0 GHz are shown in Table 1.

[0042] Table 1 Electromagnetic parameters of the low-bandwidth magnetic absorbing composite material in Example 1

[0043] A 6mm low-bandwidth magnetic absorbing composite material was prepared using the low-bandwidth magnetic absorbing composite material obtained from 1-C. A 0.05mm transparent outer skin and a 0.05mm metallic copper film reflective layer were added. The absorption performance of the resulting structural composite material is shown in Table 2.

[0044] Table 2. Absorption performance of the low-bandwidth magnetic absorbing composite material obtained in Example 1

[0045] A 3mm low-bandwidth magnetic absorbing composite material was prepared using the low-bandwidth magnetic absorbing composite material obtained from 1-C. A 0.05mm transparent outer skin and a 0.05mm metallic copper film reflective layer were added. The absorption performance of the resulting structural composite material is shown in Table 3. Table 3. Absorption performance of the low-bandwidth magnetic absorbing composite material obtained in Example 1 Example 2

[0046] The method for preparing low-to-medium frequency (1GHz~14GHz) magnetic absorbing composite material provided in this embodiment includes the following steps: A. Preparation of hot-melt microwave absorbing resin A modified absorbent is obtained by treating the absorbent with a coupling agent; The absorbent consists of 0.5% flake graphite, 0.5% carbon nanotubes, and 99% iron, silicon, and aluminum.

[0047] The absorbent has a particle size of 1-100μm; the thickness of a single-layer film is <0.1mm.

[0048] The modified absorbent preparation process is as follows: the absorbent and coupling agent are refluxed at 90℃ for 12h, dried at 90℃ after treatment, and then stirred with a high-speed stirrer for 5min to obtain a modified absorbent powder that is easy to disperse; the coupling agent is KH550.

[0049] 202) Epoxy resin, cyanate ester, ammonia curing agent, siloxane compound and fluorocarbon resin are mixed to obtain a hot melt resin. The viscosity of the hot melt resin is ≤12000mps at 60℃-90℃. The mass ratio of epoxy resin, cyanate ester, ammonia curing agent, siloxane compound and fluorocarbon resin is 50:20:8:2:2. 203) The modified absorbent and the hot-melt resin are mixed, with the mass ratio of the modified absorbent to the resin base being 5:5, to obtain the hot-melt microwave absorbing resin.

[0050] The hot-melt absorbing resin is melted at 70°C to prepare a film. The film is then combined with fiber cloth to obtain a mid-frequency absorbing magnetic prepreg. The fiber cloth is a low-dielectric material fiber fabric—quartz fiber cloth—with a fiber cloth surface density of 40 g / m³. 2 Tensile strength (N / 25mm): 272.4 in the warp direction and 313.1 in the weft direction; dielectric constant 3.7, dielectric loss 0.005.

[0051] The content of hot-melt absorbing resin in the medium-frequency absorbing magnetic prepreg is 40%.

[0052] The mid-frequency magnetic absorbing prepreg obtained in 2-B was heated and cured at 120℃ to obtain a mid-frequency magnetic absorbing composite material.

[0053] The mid-frequency magnetic absorbing composite material obtained from 2-C was used to prepare mid-low frequency magnetic absorbing composite materials of 3 mm and 6 mm. The absorption performance was measured. The electromagnetic parameters of the mid-low frequency magnetic absorbing composite material in the range of 0.2 GHz to 18.0 GHz are shown in Table 4.

[0054] Table 4 Electromagnetic parameters of the low-frequency magnetic absorbing composite material in Example 2

[0055] The absorption performance of the 6mm mid-frequency magnetic absorbing composite material prepared from the 2-C mid-frequency magnetic absorbing composite material, with the addition of a 0.05mm wave-transparent outer skin and a 0.05mm metallic copper film reflective layer, is shown in Table 5.

[0056] Table 5. Absorption performance of the low-frequency magnetic absorbing composite material obtained in Example 2 Comparative Example 1

[0057] The absorbent used in this comparative example is a magnetic absorbent, which does not contain a conductive absorbent. The rest of the steps are the same as in Example 1, including the following: 301) The absorbent is treated with a coupling agent to obtain a modified absorbent; The absorbent composition is 0.5% flake graphite, 0.5% carbon nanotubes, and 99% iron, silicon, and aluminum.

[0058] The absorbent has a particle size of 1-100μm; the thickness of a single-layer film is <0.1mm.

[0059] The modified absorbent preparation process is as follows: the absorbent and coupling agent are refluxed at 70-90℃ for 12-15h, dried at 70-90℃ after treatment, and then stirred with a high-speed stirrer for 5-10min to obtain a modified absorbent powder that is easy to disperse; the coupling agent is KH570.

[0060] 302) Epoxy resin, cyanate ester, ammonia curing agent, siloxane compound and fluorocarbon resin are mixed to obtain hot melt resin. The viscosity of the hot melt resin is ≤12000mps at 60℃-90℃. The mass ratio of epoxy resin, cyanate ester, ammonia curing agent, siloxane compound and fluorocarbon resin is 80:50:10:3:5.

[0061] 303) The modified absorbent and hot melt resin are mixed in a mass ratio of 7:3 to obtain the hot melt absorbing resin.

[0062] The hot-melt resin obtained from 3-A is melted at 90°C to prepare a film. The film is then combined with fiber cloth to obtain a low-frequency absorbing magnetic prepreg.

[0063] The fiber cloth is a low-dielectric material fiber fabric—quartz fiber cloth—with a fiber cloth surface density of 40 g / m³. 2 Tensile strength (N / 25mm): 272.4 in the warp direction and 313.1 in the weft direction; dielectric constant 3.7, dielectric loss 0.005.

[0064] The content of hot-melt absorbing resin in the medium-frequency absorbing magnetic prepreg is 40%.

[0065] Low-frequency absorbing magnetic prepreg is cured by heating at 120℃ to obtain a low-bandwidth magnetic absorbing composite material.

[0066] A 3 mm long low-bandwidth magnetic absorbing composite material was prepared using the 3-C low-bandwidth magnetic absorbing composite material. The electromagnetic parameters of the 3 mm long low-bandwidth magnetic absorbing composite material in the range of 0.2 GHz to 18.0 GHz are shown in Table 7.

[0067] Table 7 Electromagnetic parameters of the 3mm low-bandwidth magnetic absorbing composite material (Comparative Example 1)

[0068] A 6mm low-bandwidth magnetic absorbing composite material was prepared using the low-bandwidth magnetic absorbing composite material obtained from 3-C. A 0.05mm transparent outer skin and a 0.05mm metallic copper film reflective layer were added. The absorption performance of the resulting structural composite material is shown in Table 8.

[0069] Table 8 shows the microwave absorption performance of the 6mm low-bandwidth magnetic absorbing composite material obtained in Comparative Example 1.

[0070] A 3mm low-bandwidth magnetic absorbing composite material was prepared using the low-bandwidth magnetic absorbing composite material obtained from 3-C. A 0.05mm transparent outer skin and a 0.05mm metallic copper film reflective layer were added. The absorption performance of the resulting structural composite material is shown in Table 9.

[0071] Table 9 shows the microwave absorption performance of the 3mm low-bandwidth magnetic absorbing composite material obtained in Comparative Example 1. Comparative Example 2

[0072] The absorbent used in this comparative example was not modified with a coupling agent, and was otherwise the same as in Example 1, including the following steps: 401) The absorbent is directly mixed without using a coupling agent to treat it, thus obtaining a composite absorbent; The absorbent composition is 1.5% flake graphite, 1.5% carbon nanotubes, and 97% iron, silicon, and aluminum.

[0073] The absorbent has a particle size of 1-100μm; the thickness of a single-layer film is <0.1mm.

[0074] 402) Epoxy resin, cyanate ester, ammonia curing agent, siloxane compound and fluorocarbon resin are mixed to obtain hot melt resin. The viscosity of the hot melt resin is ≤12000mps at 60℃-90℃. The mass ratio of epoxy resin, cyanate ester, ammonia curing agent, siloxane compound and fluorocarbon resin is 80:50:10:3:5.

[0075] 403) The absorbent and hot melt resin are mixed in a mass ratio of 7:3 to obtain the hot melt absorbing resin.

[0076] The hot-melt resin obtained from 4-A is melted at 90°C to prepare a film. The film is then combined with fiber cloth to obtain a low-frequency absorbing magnetic prepreg.

[0077] The fiber cloth is a low-dielectric material fiber fabric—quartz fiber cloth—with a fiber cloth surface density of 40 g / m³. 2 Tensile strength (N / 25mm): 272.4 in the warp direction and 313.1 in the weft direction. Dielectric constant: 3.7, dielectric loss: 0.005.

[0078] The content of hot-melt absorbing resin in the medium-frequency absorbing magnetic prepreg is 40%.

[0079] Low-frequency absorbing magnetic prepreg is cured by heating at 120℃ to obtain a low-bandwidth magnetic absorbing composite material.

[0080] The electromagnetic parameters of the low-bandwidth magnetic absorbing composite material prepared from the 4-C low-bandwidth magnetic absorbing composite material were measured. The electromagnetic parameters of the low-bandwidth magnetic absorbing composite material in the range of 0.2 GHz to 18.0 GHz are shown in Table 10.

[0081] Table 10 Electromagnetic parameters of the low-bandwidth magnetic absorbing composite material in Comparative Example 2

[0082] A 6mm low-bandwidth magnetic absorbing composite material was prepared using the low-bandwidth magnetic absorbing composite material obtained from 4-C. A 0.05mm transparent outer skin and a 0.05mm metallic copper film reflective layer were added. The absorption performance of the resulting structural composite material is shown in Table 11.

[0083] Table 11 shows the microwave absorption performance of the low-bandwidth magnetic absorbing composite material obtained in Comparative Example 2.

[0084] A 3mm low-bandwidth magnetic absorbing composite material was prepared using the low-bandwidth magnetic absorbing composite material obtained from 4-C. A 0.05mm transparent outer skin and a 0.05mm metallic copper film reflective layer were added. The absorption performance of the resulting structural composite material is shown in Table 12.

[0085] Table 12 shows the microwave absorption performance of the low-bandwidth magnetic absorbing composite material obtained in Comparative Example 2. Example 3

[0086] This embodiment provides a low-bandwidth magnetic absorbing composite material with absorbing honeycomb, including a wave-transparent outer skin and a carbon fiber reflective layer. Two absorbing layers are sandwiched between the wave-transparent outer skin and the carbon fiber reflective layer. The absorbing layers include absorbing honeycomb and the low-frequency absorbing composite material described in Embodiment 1.

[0087] The laying sequence in this embodiment is: wave-transparent outer skin, low-frequency wave-absorbing composite material, wave-absorbing honeycomb, and carbon fiber reflective layer.

[0088] The transparent outer skin of this embodiment has a thickness of 1.0 mm; The thickness of the low-frequency absorbing composite material in this embodiment is 3mm.

[0089] The thickness of the absorbing honeycomb in this embodiment is 15mm.

[0090] The carbon fiber reflective layer used in this embodiment has a thickness of 1 mm.

[0091] The absorption performance of the low-bandwidth magnetic absorbing composite material with absorbing honeycomb obtained in this embodiment at 0.3GHz~18.0GHz is shown in Table 13.

[0092] Table 13. Absorption performance of the low-bandwidth magnetic absorbing composite material with absorbing honeycomb in Example 3.

[0093] Example 4 This embodiment provides a mid-bandwidth magnetic absorbing composite material with absorbing honeycomb, including a wave-transparent outer skin and a carbon fiber reflective layer. Two types of absorbing layers are sandwiched between the wave-transparent outer skin and the carbon fiber reflective layer. The absorbing layers include absorbing honeycomb and the mid-frequency absorbing composite material described in Embodiment 2.

[0094] The laying sequence in this embodiment is: wave-transparent outer skin, mid-to-low frequency wave-absorbing composite material, wave-absorbing honeycomb, and carbon fiber reflective layer.

[0095] The transparent outer skin of this embodiment has a thickness of 1.0 mm; The thickness of the mid-frequency absorbing composite material in this embodiment is 3 mm.

[0096] The thickness of the absorbing honeycomb in this embodiment is 15mm.

[0097] The carbon fiber reflective layer used in this embodiment has a thickness of 1 mm.

[0098] The absorption performance of the low-bandwidth magnetic absorbing composite material with absorbing honeycomb obtained in this embodiment at 0.84GHz~18.0GHz is shown in Table 14.

[0099] Table 14. Absorption performance of mid-frequency magnetic absorbing composite material with absorbing honeycomb in Example 4

[0100] This embodiment provides a low-bandwidth magnetic absorbing composite material with a wave-absorbing honeycomb, including a wave-transparent outer skin and a carbon fiber reflective layer. Three types of wave-absorbing layers are sandwiched between the wave-transparent outer skin and the carbon fiber reflective layer. The wave-absorbing layers include the wave-absorbing honeycomb and the low-bandwidth magnetic absorbing composite material described in Embodiment 1 and Embodiment 2.

[0101] The laying sequence in this embodiment is: wave-transparent outer skin, mid-frequency absorbing composite material as described in Embodiment 2, mid-frequency absorbing composite material as described in Embodiment 1, absorbing honeycomb, and carbon fiber reflective layer.

[0102] The transparent outer skin of this embodiment has a thickness of 1.0 mm; The thickness of the low-frequency absorbing composite material in this embodiment is 3mm; The thickness of the mid-frequency absorbing composite material in this embodiment is 3 mm.

[0103] The thickness of the absorbing honeycomb in this embodiment is 15mm.

[0104] The carbon fiber reflective layer used in this embodiment has a thickness of 1 mm.

[0105] The absorption performance of the mid-frequency magnetic absorbing composite material with absorbing honeycomb obtained in this embodiment at 0.3 GHz and ~18 GHz is shown in Table 15.

[0106] Table 15. Absorption performance of mid-frequency magnetic absorbing composite material with absorbing honeycomb in Example 5

Claims

1. A hot-melt microwave absorbing resin, characterized in that, Its raw material composition includes hot melt resin and composite absorbent; the ratio of hot melt resin to composite absorbent is (5-3):(5-7); The hot melt resin comprises epoxy resin, cyanate ester, fluorocarbon resin and ammonia curing agent; The composite absorbent comprises a combination of a conductive absorbent modified with a coupling agent and a magnetic absorbent. The ratio of the conductive absorbent to the magnetic absorbent is (1~3):(99~97).

2. The hot-melt absorbing resin according to claim 1, characterized in that, The particle size of the composite absorbent is 1-100 μm.

3. The hot-melt absorbing resin according to claim 1, characterized in that, The conductive absorber is selected from one or more of the following: flake graphite, carbon black, carbon nanotubes, graphene powder, and Mxene-based compounds.

4. The hot-melt absorbing resin according to claim 1, characterized in that, The magnetic absorber is selected from one or more of ferrite, carbonyl iron, or iron-silicon-aluminum.

5. The hot-melt absorbing resin according to claim 1, characterized in that, The method for modifying the coupling agent involves refluxing the absorbent and the coupling agent at 70-90°C for 12-15 hours, drying them at 70-90°C after treatment, and then pulverizing them to obtain modified absorbent powder. Preferably, the coupling agent is selected from one or more of KH550, KH560, KH570, and A151.

6. The hot-melt absorbing resin according to claim 1, characterized in that, The mass ratio of epoxy resin, cyanate ester, ammonia curing agent, siloxane compound and fluorocarbon resin is (50-80): (20-50): (8-10): (2-3): (2-5).

7. The hot-melt absorbing resin according to claim 1, characterized in that, The melting temperature of the hot-melt absorbing resin is between 70℃ and 90℃, and its melt viscosity is ≤12000mps.

8. A method for preparing the hot-melt absorbing resin according to any one of claims 1-6, characterized in that, The absorbent and hot-melt resin are stirred in a high-speed mixer for more than 3 minutes, and then calendered in a calender for 3-6 cycles to obtain the hot-melt microwave absorbing resin.

9. A low-frequency microwave absorbing prepreg, characterized in that, The hot-melt absorbing resin of claim 1 is used; its raw material composition includes the hot-melt absorbing resin and low dielectric constant, low basis weight reinforcing fibers; and the mass ratio of the hot-melt absorbing resin accounts for 40%-90% of the total weight. The mechanical properties of the low-weight reinforced fiber are as follows: fiber fabric breaking strength ≥200N / 25mm; The dielectric constant of the low-basis-weight reinforcing fiber is ≤4.5, and the dielectric loss is ≤0.

018. The fabric surface density of the low-weight reinforcing fiber is 10-40 g / m². 2 ; The low-weight reinforcing fiber is any one of unidirectional fiber, woven fabric, stitch-knitted fabric, or fiber felt; Preferably, the low-weight reinforcing fiber is selected from low-dielectric fiber fabrics such as glass fiber cloth, quartz fiber cloth, polyester fiber felt, aramid fiber fabric, polyethylene or polypropylene.

10. The low-frequency absorbing prepreg according to claim 9, characterized in that, The curing temperature of the low-frequency absorbing magnetic prepreg is ≤130℃.

11. The method for preparing the low-frequency absorbing prepreg according to claim 9, characterized in that, The hot-melt absorbing resin is heated and melted to form a film, which is then compounded with low dielectric constant and low basis weight reinforcing fibers to obtain the low-frequency absorbing magnetic prepreg.

12. The method for preparing the low-frequency absorbing prepreg according to claim 11, characterized in that, The thickness of a single layer of adhesive film is <0.1mm.

13. A low-bandwidth magnetic wave-absorbing composite material, characterized in that, After the low-frequency absorbing prepreg is heated and cured, a low-bandwidth magnetic absorbing composite material is obtained.

14. A low-bandwidth magnetic wave-absorbing composite material, characterized in that, It includes a wave-transparent outer skin and a carbon fiber / metal film reflective layer, with at least one set of wave-absorbing layers sandwiched between the wave-transparent outer skin and the carbon fiber / metal film reflective layer, the wave-absorbing layer including the low-bandwidth magnetic wave-absorbing composite material.

15. The low-bandwidth magnetic wave-absorbing composite material according to claim 14, characterized in that, The absorbing layer includes the absorbing honeycomb and low-bandwidth magnetic absorbing composite material.

16. The low-bandwidth magnetic wave-absorbing composite material according to claim 16, characterized in that, The thickness of the wave-transparent outer skin is 0.05mm-2mm; the thickness of the low-bandwidth magnetic wave-absorbing composite material is 1mm-10mm; and the thickness of the wave-absorbing honeycomb is 2.8mm-30mm.

Images