Aramid fiber wave-absorbing honeycomb with microscopic sandwich hole wall structure and in-situ manufacturing method of aramid fiber wave-absorbing honeycomb

Abstract

The invention relates to the technical field of honeycomb composite materials, in particular to an aramid wave-absorbing honeycomb with a microcosmic sandwich hole wall structure and an in-situ manufacturing method of the aramid wave-absorbing honeycomb, and the in-situ manufacturing method comprises the steps of 1, aramid honeycomb protoblank preparation, 2, first-stage impregnation, 3, second-stage impregnation, 4, third-stage impregnation and 5, stepped high-temperature post-curing and cross-layer co-curing. And finally, a micro sandwich hole wall structure consisting of a pure resin substrate layer, a wave-absorbing functional layer and a pure resin cover layer which are sequentially distributed along the thickness direction of the honeycomb hole wall is formed. Through three-order alternate impregnation, a micro sandwich structure composed of the pure resin substrate layer, the wave-absorbing functional layer and the pure resin envelope layer is constructed in the honeycomb hole wall, and the mechanical enhancement of the hole wall, the introduction of the wave-absorbing function and the packaging stability of the wave-absorbing particles are favorably considered.

Description

Technical Field

[0001] This invention relates to the field of honeycomb composite material technology, and in particular to an aramid absorbing honeycomb with a microscopic sandwich pore wall structure and its in-situ manufacturing method. Background Technology

[0002] Aramid paper honeycomb possesses advantages such as light weight, high specific strength, high specific stiffness, good heat resistance, and ease of sandwich composite application, making it widely used in lightweight sandwich structures in aerospace, rail transportation, radomes, and drones. With the increasing demands for lightweight, load-bearing capacity, and electromagnetic stealth performance in structural components, structurally functional aramid honeycomb materials that combine mechanical support and electromagnetic absorption functions are attracting growing attention.

[0003] Existing microwave-absorbing aramid honeycomb structures typically employ post-treatment methods such as spraying, impregnation, or brushing to adhere the microwave-absorbing slurry to the surface of the formed honeycomb cell walls. While these methods are relatively simple, the microwave-absorbing layer relies heavily on surface adhesion, resulting in limited interlayer bonding stability. Subsequent slicing, processing, assembly, and service operations can lead to localized detachment, particle exposure, and surface damage. Furthermore, the microwave-absorbing components exposed on the cell wall surface are susceptible to moisture, heat, oxidation, friction, and environmental erosion, resulting in poor long-term stability. If a single impregnation method is used to directly introduce highly filled microwave-absorbing agents into the honeycomb cell walls, problems such as poor slurry flowability, pore blockage, localized glue buildup, uncontrolled weight gain, and uneven distribution of microwave-absorbing components can easily arise, especially when using heavy magnetic absorbers such as carbonyl iron powder and iron-silicon-aluminum powder. Therefore, existing processes struggle to simultaneously achieve cell wall reinforcement, microwave absorption, and maintenance of pore structure integrity.

[0004] Therefore, in order to solve the above-mentioned technical problems, this application needs to propose an aramid absorbing honeycomb with a microscopic sandwich pore wall structure and its in-situ manufacturing method. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing an aramid absorbing honeycomb with a microscopic sandwich pore wall structure and its in-situ manufacturing method, which enables the absorbing functional components to be integrated in-situ into the pore wall during the honeycomb manufacturing process, thereby improving the integration level of structure and function and service stability.

[0006] To achieve the above objectives, the present invention employs the following technical solution: an in-situ manufacturing method for an aramid absorbing honeycomb with a microscopic sandwich pore wall structure, comprising the following steps:

[0007] Step 1: Preparation of aramid honeycomb preforms

[0008] A aramid paper is coated with node adhesive according to a predetermined stripe width. After being stacked and cured by hot pressing, it is stretched and shaped along the direction perpendicular to the node adhesive stripes to obtain an aramid honeycomb preform that has not yet been impregnated with structural resin.

[0009] Step 2, First stage of impregnation

[0010] The aramid honeycomb preform obtained in step 1 is immersed in the first resin solution for 1 to 3 minutes. After being removed, excess resin in the pores is blown away with compressed air at 0.1 to 0.2 MPa. Then, the preform is subjected to a first heat treatment at 70 to 90°C to make the resin reach a shallow gel state (Soft B-stage) and form a pure resin base layer in situ on the surface of the aramid fiber.

[0011] Step 3, Second stage impregnation

[0012] The aramid honeycomb preform treated in step 2 is immersed in a resin functional slurry containing microwave absorbing agent for 3 to 5 minutes. After being removed, it is blown through with compressed air pulse at 0.3 to 0.5 MPa. Then, a secondary heat treatment is carried out using a stepped heating program to make it reach a deep semi-cured state, forming a microwave absorbing functional layer in situ on the outside of the pure resin base layer.

[0013] Step 4, Third-stage impregnation

[0014] The aramid honeycomb preform treated in step 3 is immersed again in the third resin solution for 1 to 2 minutes. After being removed, the pores are purged with low-pressure compressed air of 0.1 to 0.2 MPa to remove excess droplets, and a pure resin sealing layer is formed in situ on the outside of the microwave absorbing functional layer.

[0015] Step 5: Stepped high-temperature post-curing and cross-layer co-curing

[0016] The aramid honeycomb preform processed in step 4 is sent to a programmed temperature curing oven for high-temperature overall curing, so that the resin matrix in the first impregnation layer, the second impregnation layer and the third impregnation layer undergo cross-layer synergistic curing, and finally form a microscopic sandwich pore wall structure consisting of a pure resin base layer, a microwave absorbing functional layer and a pure resin capping layer distributed sequentially along the thickness direction of the honeycomb pore wall.

[0017] Preferably, in step 2, the first resin liquid is a highly permeable pure structural resin without solid fillers, and the highly permeable pure structural resin is selected from one of low molecular weight linear phenolic resin, bisphenol A type epoxy prepolymer or cyanate ester resin.

[0018] Preferably, in step 2, the impregnation viscosity of the first resin solution is 10–50 mPa·s, and the thickness of the pure resin substrate layer formed is 10–20 μm.

[0019] By adopting the above technical solution: due to the extremely low viscosity of the first resin liquid, it can penetrate deeply into the interior of the dense aramid fiber bundles by capillary action; and after low-temperature short-time heat treatment, the resin macromolecular chains only undergo slight branching, and after the solvent evaporates, the surface exhibits a highly viscoelastic "tacky" state, providing a strong physical anchoring and chemical gripping foundation for the subsequent heavy microwave absorbing slurry.

[0020] Preferably, in step 3, the functional resin slurry is composed of a structural resin matrix, a toughening modifier, and a radar wave absorber uniformly dispersed therein; the absorber is selected from one or a combination of carbonyl iron powder, iron-silicon-aluminum powder, carbon nanotubes, or graphene; when the absorber is a magnetic powder, its mass fraction in the solid content of the slurry is 40% to 75%, more preferably 60% to 70%.

[0021] Preferably, in step 3, the impregnation viscosity of the resin functional slurry is 300-800 mPa·s; the step heating program is as follows: first, keep at 50-60℃ for 30-45 minutes, then raise the temperature to 110-130℃ and keep at 110-130℃ for 20-30 minutes.

[0022] By adopting the above technical solution: since the resin base layer obtained by the first impregnation is in a viscous semi-cured state, the second high-viscosity functional slurry can form a good interface with it; the use of low temperature slow exhaust at 50-60℃ avoids the boiling and foaming of solvent in the thick slurry; the subsequent heat treatment at 110-130℃ makes the microwave absorbing layer resin lose its fluidity and set, successfully "freezing" the heavy metal micro powder in the middle area of ​​the hole wall, effectively preventing scouring and bottoming during subsequent impregnation.

[0023] Preferably, in step 4, the third resin liquid is a low-viscosity pure resin system rich in crosslinking agents, with an impregnation viscosity of 10–30 mPa·s; its function is to provide a corrosion barrier with high crosslinking density without significantly increasing the thickness of the honeycomb pore wall.

[0024] Preferably, when using an epoxy system, the resin matrix of the third resin liquid is bisphenol F type epoxy resin or alicyclic epoxy resin (such as ERL-4221), and the crosslinking agent is an aromatic diamine crosslinking agent (such as DDS) or liquid methylhexahydrophthalic anhydride (MHHPA).

[0025] Preferably, when a phenolic system is used, the resin matrix of the third resin liquid is a low molecular weight thermosetting phenolic resin, and the crosslinking agent is melamine resin (melamine-formaldehyde resin) or hydrogen-containing silicone oil (methylhydrosiloxane) to greatly improve surface hardness and hydrophobic corrosion resistance.

[0026] By adopting the above technical solution: due to the extremely low viscosity of the third resin liquid, it can fill the gaps of exposed metal powder on the surface of the second-stage absorbing layer as a "microscopic varnish". This not only avoids clogging the honeycomb channels, but also forms a dense and non-porous physical barrier, completely encapsulating the easily rusting absorbing agent inside the pore wall, and thoroughly isolating the intrusion of water vapor and salt spray in the marine environment.

[0027] Preferably, in step 5, the high-temperature total curing includes the following procedure: first, holding at 80-100°C for 0.5-1 hour to remove residual solvent; then, raising the temperature to 120-140°C and holding for 1-2 hours to promote the continued reaction of each resin layer and interlayer bonding; finally, raising the temperature to 150-180°C and holding for 2-4 hours to achieve overall thermo-curing.

[0028] By adopting the above technical solution, during the co-curing process, the resin matrix in the B-stage state in the first, second, and third-stage impregnation layers undergoes cross-layer synergistic curing, thereby forming a stable integrated pore wall composite structure.

[0029] The present invention also provides an aramid absorbing honeycomb structure, which is prepared by the above method;

[0030] The honeycomb pore wall comprises, along its thickness direction, a pure resin base layer located near the aramid fiber, a wave-absorbing functional layer in the middle, and a pure resin sealing layer on the outside, thereby forming a microscopic sandwich pore wall structure; wherein, the layers are bonded to each other by co-curing with the resin matrix.

[0031] The absorbing particles in the absorbing functional layer are encapsulated inside the honeycomb pore wall.

[0032] The pure resin base layer, the microwave absorbing functional layer, and the pure resin cover layer are co-cured with the resin matrix to form an integrated pore wall composite structure.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1. This invention achieves in-situ integration of the microwave absorbing components during the impregnation and curing process of the honeycomb preform, which is more conducive to forming a honeycomb pore wall composite structure with integrated structure and function.

[0035] 2. This invention constructs a micro-sandwich structure consisting of a pure resin base layer, a microwave absorption functional layer, and a pure resin encapsulation layer in the honeycomb pore wall through three-stage alternating impregnation, which is beneficial to balance the mechanical enhancement of the pore wall, the introduction of microwave absorption function, and the encapsulation stability of microwave absorption particles.

[0036] 3. This invention achieves a stable interlayer bonding structure by using a phased semi-curing process followed by a step-by-step co-curing process. This improves the bonding strength of the microwave absorbing functional layer in the honeycomb pore wall and enhances the structural stability during subsequent slicing, processing, and service. Attached Figure Description

[0037] Figure 1 This is a process flow diagram of the preparation of the present invention. Detailed Implementation

[0038] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings, so that those skilled in the art can better understand the advantages and features of the present invention, thereby making a clearer definition of the scope of protection of the present invention. The embodiments described in this invention are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0039] Example 1: Phenolic resin + carbonyl iron powder system (best preferred option)

[0040] Step 1: Select an aramid honeycomb preform with a side length of 3.2mm (not yet impregnated with structural resin).

[0041] Step 2: Immerse the preform in the first resin solution (low molecular weight linear phenolic pure resin, no filler, immersion viscosity 20 mPa·s) for 2 minutes, remove it and blow off the excess resin with 0.15 MPa compressed air, and heat treat it at 80℃ for 15 minutes to form a pure resin base layer with a slightly tack surface.

[0042] Step 3: Immerse the preform in a resin functional slurry containing microwave absorbing agent (phenolic resin matrix + 65wt% carbonyl iron powder, impregnation viscosity 500 mPa·s) for 4 minutes, remove it and blow holes with 0.4 MPa pulsed air; perform stepped heat treatment: hold at 55℃ for 40 minutes, then raise the temperature to 120℃ and hold for 25 minutes to form a microwave absorbing functional layer in situ.

[0043] Step 4: Immerse again in the third resin solution (low molecular weight thermosetting phenolic resin + melamine resin crosslinking agent, immersion viscosity 15 mPa·s) for 1.5 minutes, and purge with low-pressure air at 0.15 MPa to form a hydrophobic pure resin encapsulation layer in situ.

[0044] Step 5: Place the product into a curing oven and perform cross-layer co-curing at 90℃×1h → 130℃×1.5h → 160℃×3h.

[0045] Example 2: Lightweight carbon-based microwave absorption system

[0046] The process parameters for steps 1, 2, 4, and 5 are the same as in Example 1.

[0047] The difference lies in step 3: the microwave absorber in the resin functional slurry is a composite powder of carbon nanotubes and graphene (non-magnetic), and its mass fraction in the slurry solid content is reduced to 8%, and the slurry impregnation viscosity is adjusted to 400 mPa·s.

[0048] Comparative Example 1: Traditional one-step impregnation method (proving the necessity of microscopic three-layer separation)

[0049] Mix all materials together, and directly mix low molecular weight phenolic resin, melamine crosslinking agent and 65wt% carbonyl iron powder into a single uniform slurry (adjust the viscosity to 500 mPa·s).

[0050] The aramid honeycomb preform was directly immersed in the mixed slurry for 4 minutes, blown through holes at 0.4 MPa, and then directly subjected to the high-temperature total curing in step 5 of Example 1. No staged impregnation was performed.

[0051] Comparative Example 2: The "first-stage pure resin base layer" is missing (proving the necessity of bottom anchoring).

[0052] Skip step 2 in Example 1. Immerse the aramid honeycomb preform directly into the functional slurry containing carbonyl iron powder in step 3, process it according to step 3, then process it according to step 4 (pure resin sealing layer), and finally cure it according to step 5.

[0053] Comparative Example 3: The "third-stage pure resin sealing layer" is missing (proving the necessity of external sealing).

[0054] Skip step 4 in Example 1.

[0055] After being processed in step 2 (pure resin base layer) and step 3 (functional layer containing carbonyl iron powder), the aramid honeycomb preform directly enters step 5 for high-temperature total curing. There is no pure varnish layer for sealing on the outside.

[0056] To verify the technical effects of the present invention, the aramid absorbing cell fabrics prepared in all embodiments and comparative examples were subjected to the following macroscopic performance tests:

[0057] Interface anchoring force test (vibration dust loss rate): Place a honeycomb sample of a specific size on a standard vibration table and vibrate continuously for 2 hours at a specific frequency and amplitude. Weigh the mass difference before and after vibration and calculate the dust loss rate.

[0058] Absorption performance test (waveguide method or bow method): Measure the lowest reflection loss (RL_min) in the range of 8~18 GHz (X, Ku band).

[0059] Process assessment: Macroscopic visual inspection of the honeycomb pores to check for pore blockage or flow problems. See Table 1 for details.

[0060] Table 1

[0061]

[0062] In summary, by using three-stage alternating impregnation, a microscopic sandwich structure consisting of a pure resin substrate layer, a microwave absorbing functional layer, and a pure resin encapsulation layer is constructed in the honeycomb pore wall, which is beneficial for balancing the mechanical enhancement of the pore wall, the introduction of microwave absorbing function, and the encapsulation stability of the microwave absorbing particles.

[0063] The descriptions and practices disclosed in this invention are readily apparent and understandable to those skilled in the art, and various modifications and refinements can be made without departing from the principles of this invention. Therefore, any modifications or improvements made without departing from the spirit of this invention should also be considered within the scope of protection of this invention.

Claims

1. An in-situ manufacturing method for an aramid absorbing honeycomb with a microscopic sandwich-shaped pore wall structure, characterized in that, Includes the following steps: Step 1: Preparation of aramid honeycomb preforms A aramid paper is coated with node adhesive according to a predetermined stripe width. After being stacked and cured by hot pressing, it is stretched and shaped along the direction perpendicular to the node adhesive stripes to obtain an aramid honeycomb preform that has not yet been impregnated with structural resin. Step 2, First stage of impregnation The aramid honeycomb preform obtained in step 1 is immersed in the first resin solution for 1 to 3 minutes. After being removed, excess resin in the pores is blown away with compressed air at 0.1 to 0.2 MPa. Then, a primary heat treatment is performed at 70 to 90°C to make the resin reach a shallow gel state and form a pure resin base layer in situ on the surface of the aramid fiber. Step 3, Second stage impregnation The aramid honeycomb preform treated in step 2 is immersed in a resin functional slurry containing microwave absorbing agent for 3 to 5 minutes. After being removed, it is blown through with compressed air pulse at 0.3 to 0.5 MPa. Then, a secondary heat treatment is carried out using a stepped heating program to make it reach a deep semi-cured state, forming a microwave absorbing functional layer in situ on the outside of the pure resin base layer. Step 4, Third-stage impregnation The aramid honeycomb preform treated in step 3 is immersed again in the third resin solution for 1 to 2 minutes. After being removed, the pores are purged with low-pressure compressed air of 0.1 to 0.2 MPa to remove excess droplets, and a pure resin sealing layer is formed in situ on the outside of the microwave absorbing functional layer. Step 5: Stepped high-temperature post-curing and cross-layer co-curing The aramid honeycomb preform processed in step 4 is sent to a programmed temperature curing oven for high-temperature overall curing, so that the resin matrix in the first impregnation layer, the second impregnation layer and the third impregnation layer undergo cross-layer synergistic curing, and finally form a microscopic sandwich pore wall structure consisting of a pure resin base layer, a microwave absorbing functional layer and a pure resin capping layer distributed sequentially along the thickness direction of the honeycomb pore wall.

2. The in-situ manufacturing method of an aramid absorbing honeycomb with a microscopic sandwich pore wall structure according to claim 1, characterized in that, In step 2, the first resin solution is a highly permeable pure structural resin without solid fillers. The highly permeable pure structural resin is selected from one of the following: low molecular weight linear phenolic resin, bisphenol A type epoxy prepolymer, or cyanate ester resin.

3. The in-situ manufacturing method of an aramid absorbing honeycomb with a microscopic sandwich pore wall structure according to claim 2, characterized in that, In step 2, the impregnation viscosity of the first resin solution is 10–50 mPa·s, and the thickness of the pure resin substrate layer formed is 10–20 μm.

4. The in-situ manufacturing method of an aramid absorbing honeycomb with a microscopic sandwich-shaped pore wall structure according to claim 1, characterized in that, In step 3, the functional resin slurry is composed of a structural resin matrix, a toughening modifier, and a radar wave absorber uniformly dispersed therein; the absorber is selected from one or a combination of carbonyl iron powder, iron-silicon-aluminum powder, carbon nanotubes, or graphene; when the absorber is a magnetic powder, its mass fraction in the solid content of the slurry is 40% to 75%.

5. The in-situ manufacturing method of an aramid absorbing honeycomb with a microscopic sandwich pore wall structure according to claim 4, characterized in that, In step 3, the impregnation viscosity of the resin functional slurry is 300-800 mPa·s; the step heating program is as follows: first, hold at 50-60℃ for 30-45 minutes, then raise the temperature to 110-130℃ and hold for 20-30 minutes.

6. The in-situ manufacturing method of an aramid absorbing honeycomb with a microscopic sandwich pore wall structure according to claim 1, characterized in that, In step 4, the third resin solution is a low-viscosity pure resin system rich in crosslinking agents, with an impregnation viscosity of 10–30 mPa·s.

7. The in-situ manufacturing method of an aramid absorbing honeycomb with a microscopic sandwich pore wall structure according to claim 6, characterized in that, When using an epoxy system, the resin matrix of the third resin liquid is bisphenol F type epoxy resin or alicyclic epoxy resin, and the crosslinking agent is an aromatic diamine crosslinking agent or liquid methylhexahydrophthalic anhydride.

8. The in-situ manufacturing method of an aramid absorbing honeycomb with a microscopic sandwich pore wall structure according to claim 6, characterized in that, When using a phenolic system, the resin matrix of the third resin liquid is a low molecular weight thermosetting phenolic resin, and the crosslinking agent is melamine resin or hydrogen-containing silicone oil.

9. The in-situ manufacturing method of an aramid absorbing honeycomb with a microscopic sandwich pore wall structure according to claim 1, characterized in that, In step 5, the high-temperature overall curing includes the following procedures: first, maintain the temperature at 80-100℃ for 0.5-1 hour to remove residual solvent; then, raise the temperature to 120-140℃ and maintain it for 1-2 hours to promote the continued reaction of each resin layer and interlayer bonding; finally, raise the temperature to 150-180℃ and maintain it for 2-4 hours to achieve overall thermo-curing.

10. An aramid-based microwave-absorbing honeycomb structure, characterized in that, Prepared by the method according to any one of claims 1 to 9; The honeycomb pore wall comprises, along its thickness direction, a pure resin base layer located near the aramid fiber, a wave-absorbing functional layer in the middle, and a pure resin sealing layer on the outside, thereby forming a microscopic sandwich pore wall structure; wherein, the layers are bonded to each other by co-curing with the resin matrix. The absorbing particles in the absorbing functional layer are encapsulated inside the honeycomb pore wall. The pure resin base layer, the microwave absorbing functional layer, and the pure resin cover layer are co-cured with the resin matrix to form an integrated pore wall composite structure.

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