CN115821643A - Wave-absorbing honeycomb with absorbent distributed in gradient manner and preparation method thereof - Google Patents
Wave-absorbing honeycomb with absorbent distributed in gradient manner and preparation method thereof Download PDFInfo
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Abstract
The invention provides a wave-absorbing honeycomb with gradient distribution of an absorbent and a preparation method thereof. Mixing different contents of absorbents into aramid fiber paper to obtain the serialized wave-absorbing aramid fiber paper; and then according to the electrical property design, arranging different aramid fiber absorbing papers in sequence to prepare the wave-absorbing honeycomb, forming a structure with gradually changed impedance gradient in the direction vertical to the cells, and obtaining the wave-absorbing honeycomb with excellent performance in the direction vertical to the cells. According to the invention, the absorbent is doped into the aramid paper, the addition amount can be accurately controlled, the process is stable, the obtained wave-absorbing honeycomb has excellent environment resistance, and the defects that the performance of the existing impregnated wave-absorbing honeycomb is difficult to stably control and is easy to fall off are overcome.
Description
Technical Field
The invention relates to a wave-absorbing honeycomb with an absorbent distributed in a gradient manner and a preparation method thereof, belonging to the technical field of wave-absorbing material preparation.
Background
The aramid paper honeycomb has low density and stronger compression strength along the honeycomb cell direction, and is widely applied to aircrafts. With the development of detection technology, stealth requirements are put forward on an aircraft. The traditional method is that a layer of absorbent can be deposited in the walls of the honeycomb holes by an absorbent impregnation method so as to obtain the wave absorbing performance. Or through a gradient impregnation mode, the absorbent is distributed in a gradient manner along the direction of the honeycomb cells to obtain an impedance matching structure, and better wave-absorbing performance is obtained along the direction of the cells. However, for some special applications, the gradient impregnation method cannot achieve good effect. A honeycomb sandwich structure is adopted in the airfoil structure, the direction of honeycomb holes is vertical to the course, and the mechanical bearing capacity of the honeycomb sandwich structure is exerted; however, the detection direction of the electromagnetic waves is mainly the course, and the wave-absorbing structure design needs to be carried out in the direction perpendicular to the honeycomb holes. In a design and preparation method (CN 114228266A) of a honeycomb wave-absorbing material for an airfoil structure, a multi-layer structure design with gradient perpendicular to a cell direction is designed, and an integral white honeycomb is impregnated in layers according to design requirements by an impregnation method. However, the wave-absorbing honeycomb obtained by the impregnation method has the defects that the absorbent is attached to the pore wall and is easy to fall off, the environment resistance is poor, the impregnation process is difficult to control, and the process stability is poor.
In order to avoid the defects of the dipping wave-absorbing honeycomb, in a patent of dielectric loss aramid paper, a wave-absorbing honeycomb and a preparation method (CN 112553942A), a method for adding a carbon fiber absorbent into aramid paper is provided, the wave-absorbing aramid paper is obtained, and the wave-absorbing honeycomb is prepared by using a traditional honeycomb preparation method. The method has the advantages that the absorbent is in the aramid fiber paper, the environment resistance is good, the addition amount of the absorbent can be accurately controlled, and the process is stable. The other method is that absorbent is coated on aramid paper to obtain wave-absorbing aramid paper, and then a traditional honeycomb preparation method is used to obtain wave-absorbing honeycombs, such as patent wave-absorbing honeycombs and preparation methods thereof (CN 109796624A, CN 114214871A). The two methods can obtain the wave-absorbing honeycomb with stable performance and excellent environment resistance, but the content of the absorbent in the honeycomb is fixed, the wave-absorbing structure design is not carried out, the wave-absorbing honeycomb integrally presents single electromagnetic property, the impedance matching design is not carried out, and the excellent wave-absorbing performance is difficult to obtain.
In the patent wave-absorbing paper and the preparation method and application thereof (CN 104404814A), wave-absorbing paper with different absorbent contents is prepared first, and wave-absorbing sandwich is prepared; and combining the wave-absorbing sandwich by using the wave-transmitting layer, and curing the impregnating resin to obtain the wave-absorbing material. In a paper-based material with transverse gradient distribution of electromagnetic properties and a manufacturing method and application thereof (CN 114606794A), wave-absorbing aramid paper with gradient distribution of an absorbent in the transverse width direction is prepared first, and then wave-absorbing honeycombs are prepared, so that the obtained wave-absorbing honeycombs have gradient distribution of electromagnetic properties in the thickness direction. The two wave-absorbing honeycomb structural designs are both characterized in that the absorbents are distributed in a gradient manner along the direction (thickness) of honeycomb holes so as to carry out impedance matching design and obtain better wave-absorbing performance.
However, in the application occasions such as airfoil, the wave-absorbing honeycomb has structural bearing capacity, and the threat direction of electromagnetic waves is inconsistent with the bearing direction. Therefore, in the wave-absorbing honeycomb sandwich structure, the direction of the honeycomb holes is perpendicular to the course, and the wave-absorbing structure needs to be designed according to the course. I.e., impedance matching design is performed in the honeycomb length or width direction, rather than in the thickness direction (along the honeycomb cell). The wave-absorbing honeycomb is prepared by using wave-absorbing aramid paper laminated layers with different absorbent contents, and the wave-absorbing honeycomb with gradient gradually changed in the direction vertical to the cells can be obtained. The traditional honeycomb preparation method has higher requirements on aramid paper and has the same tension; when the aramid fiber paper is stretched after being laminated, the uniformity of the cells is ensured at a constant speed. And the aramid paper is doped with absorbents with different contents, so that the aramid paper in different areas has different forces, partial area cells are fully pulled in the stretching process, and the cells in other areas are not pulled, so that the uniformity of the whole cells of the honeycomb is seriously influenced, and the honeycomb preparation fails. A method for preparing a polyimide film honeycomb (CN 112223772A) discloses a method for preparing a honeycomb by using a template, which comprises the steps of carrying out compression molding on a thermoplasticity polyurethane composite film to obtain units with a corrugated structure, and superposing and heating a plurality of units to obtain a polyimide film honeycomb product. The method provides another idea for honeycomb preparation, but the aramid paper does not have thermoplasticity capability per se, and the method cannot be directly utilized for honeycomb preparation.
Disclosure of Invention
The invention aims to overcome the difference of the prior art and provides a wave-absorbing honeycomb with an absorbent in gradient distribution and a preparation method thereof.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a wave-absorbing honeycomb with an absorbent distributed in a gradient manner comprises a plurality of wave-absorbing aramid fiber papers and cured resin soaked on the wave-absorbing aramid fiber papers; the wave-absorbing aramid paper is prepared by mixing aramid chopped fibers, aramid pulp, water, a dispersant and an absorbent, papermaking and hot pressing; the content of the absorbent in the wave-absorbing aramid paper is in gradient difference; each wave-absorbing aramid paper contains a plurality of pieces, and each piece of wave-absorbing aramid paper is in a uniform half-hole lattice shape; the wave-absorbing aramid fiber papers are pasted together according to the same kind of wave-absorbing aramid fiber paper to form a gradient layer, the aramid fiber papers of different kinds are pasted together in a gradient manner according to the content of the absorbent, and the half-cell shapes of two adjacent wave-absorbing aramid fiber papers are aligned when the two adjacent wave-absorbing aramid fiber papers are pasted to form a complete cell shape; the absorbent content gradient of the wave-absorbing honeycomb is perpendicular to the direction of the cells from low to high and is the same as the incident direction of the electromagnetic waves.
A preparation method of a wave-absorbing honeycomb with an absorbent distributed in a gradient manner comprises the following steps:
1) And (3) honeycomb structure design: determining the type of the absorbent according to the wave-absorbing frequency band, calculating an optimal wave-absorbing structure with gradient electromagnetic characteristics by using electromagnetic simulation software, determining the electromagnetic characteristics of each gradient layer and the size of each gradient layer along the incident direction of electromagnetic waves, further determining the number of wave-absorbing aramid paper of each gradient layer, the content and the size of the absorbent and the size of a honeycomb cell, and then performing subsequent steps based on the calculation result.
2) Preparing wave-absorbing aramid paper: mixing aramid chopped fibers, aramid pulp, water, a dispersing agent and different amounts of absorbents, and then carrying out papermaking and hot pressing to prepare various wave-absorbing aramid papers with different absorbent contents;
3) Wave-absorbing aramid paper impregnating resin: completely soaking the wave-absorbing aramid paper in resin, taking out the wave-absorbing aramid paper, vertically placing the wave-absorbing aramid paper, removing redundant resin by vibration, and then performing semi-curing treatment;
4) Preparing a corrugated structure unit: pressing the semi-cured wave-absorbing aramid paper by using a pre-designed pressing die to obtain wave-absorbing aramid paper with a half-cell shape, namely a corrugated structure unit, and coating core strip glue on convex edges among the half cells;
5) And (3) superposing the corrugated units: aligning each corrugated structure unit according to the connection of the same kind of wave-absorbing aramid paper and the connection of different kinds of wave-absorbing aramid paper according to the gradient height, and adhering the corrugated structure units through the core strips to obtain a wave-absorbing honeycomb semi-finished product;
6) Heating treatment: and putting the wave-absorbing honeycomb semi-finished product into a die, inserting bars with the same shape into the honeycomb cell holes, applying certain pressure to the honeycomb hole walls to ensure the bonding strength of the core bar glue, and then heating and curing to obtain the wave-absorbing honeycomb with the absorbent distributed in a gradient manner in the direction perpendicular to the honeycomb cell direction.
Further, the content of the absorbent is 0.1-90 wt%.
Furthermore, the absorbent is fibrous and has electromagnetic loss capacity, at least one of carbon fiber, organic conductive fiber, iron-nickel fiber and iron-silicon-aluminum fiber is selected according to the wave-absorbing frequency band, the diameter is 0.01-1 mm, and the length is 1-20 mm.
Further, for the absorbed electromagnetic wave frequency band lower than 8GHz, the absorbent is selected from a magnetic fiber absorbent, namely at least one of iron fiber, iron-nickel fiber and iron-silicon-aluminum fiber; for the absorbed electromagnetic wave frequency band higher than 8GHz, the absorbent is dielectric fiber absorbent, namely at least one of carbon fiber and organic conductive fiber; for ultra-wide or full-band absorption of electromagnetic waves, the absorbent is selected from at least one of the magnetic absorbent and at least one of the dielectric absorbent.
Further, the resin is selected from one of phenolic resin and polyimide resin, and is preferably phenolic resin.
Further, the wave-absorbing aramid fiber paper is soaked for 5-30 min; after the excess resin is removed by vibration, the weight gain ratio is 50-300%.
Further, the conditions of the semi-curing treatment are as follows: the semi-curing temperature is 120-400 ℃, and the semi-curing time is 0.5-3 h.
Further, the conditions of the heating curing are as follows: the heating temperature is 180-450 ℃, and the curing time is 3-10 h.
Further, the shape of the honeycomb cells is one of hexagonal shape, rectangular shape, circular shape and irregular shape, and is preferably hexagonal shape.
Compared with the prior art, the invention has the beneficial effects that:
(1) According to the invention, the absorbent is doped into the aramid paper, the addition amount can be accurately controlled, the process is stable, the obtained wave-absorbing honeycomb has excellent environment resistance, and the defects that the performance of the existing impregnated wave-absorbing honeycomb is difficult to stably control and is easy to fall off are overcome.
(2) The traditional honeycomb preparation technology is suitable for the condition that the characteristics of aramid paper are consistent by stretching after lamination, and can ensure that cells are pulled apart at the same time and the shape is uniform. According to the invention, by utilizing a plurality of aramid paper with different characteristics (different absorbent contents), when a traditional lamination stretching process is adopted, the honeycomb cells of different aramid paper can not be pulled open at the same time due to different characteristics such as different aramid paper tension, so that the conditions of uneven cell shape or stretching failure are easily caused. According to the invention, the wave-absorbing honeycomb is prepared by a template method, the uniformity of the sizes of the cells can be ensured, and the problem that the cells are not uniformly spread when the aramid paper laminated plate containing different types is stretched in the existing preparation process is solved.
(3) The absorbent content in the wave-absorbing honeycomb is distributed in a gradient manner in the direction vertical to the honeycomb holes, so that the wave-absorbing structure can be finely regulated, excellent wave-absorbing performance is obtained, the wave-absorbing honeycomb has wide application prospect in an airfoil sandwich structure, and the structure/function integration of the wave-absorbing honeycomb can be fully exerted.
Drawings
FIG. 1 is a schematic diagram of a preparation process of a wave-absorbing honeycomb with an absorbent distributed in a gradient manner according to the invention;
FIG. 2 is a flow chart of the preparation of the wave-absorbing honeycomb with the absorbent distributed in a gradient manner.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, the present invention shall be described in further detail with reference to the following detailed description and accompanying drawings.
The invention provides a wave-absorbing honeycomb with an absorbent in gradient distribution, which comprises a plurality of wave-absorbing aramid fiber papers and cured resin soaked on the wave-absorbing aramid fiber papers; the wave-absorbing aramid paper is prepared by mixing aramid chopped fibers, aramid pulp, water, a dispersant and an absorbent, papermaking and hot pressing; the content of the absorbent in the wave-absorbing aramid paper is in gradient difference (for example, the content is in a sequence from low to high or in a sequence from high to low); each wave-absorbing aramid paper contains a plurality of pieces, and each piece of wave-absorbing aramid paper is in a uniform half-hole lattice shape; the wave-absorbing aramid paper is characterized in that the wave-absorbing aramid paper of the same kind is pasted together to form a gradient layer, the aramid paper of different kinds is pasted together in a gradient manner according to the content of the absorbent (for example, the content is sorted from low to high or from high to low), and when two adjacent wave-absorbing aramid papers are pasted, the half-cell shapes are aligned to form a complete cell shape; the absorbent content gradient of the wave-absorbing honeycomb is vertical to the direction of the cells from low to high and is the same as the incident direction of the electromagnetic waves.
The invention also provides a preparation method of the wave-absorbing honeycomb with the absorbent distributed in a gradient manner, the preparation process is shown in the figures 1 and 2, and the preparation method is realized by the following steps:
1) And (3) honeycomb structure design:
determining the type of an absorbent according to a wave-absorbing frequency band, calculating and optimizing by utilizing electromagnetic simulation software to obtain an optimal gradient-gradual-change wave-absorbing structure, and determining the electromagnetic property of each gradient layer and the size of each gradient layer along the incident direction of electromagnetic waves; thereby determining the content and the size of the absorbent in each gradient layer, the dosage of the wave-absorbing aramid paper and the size of the honeycomb cells.
2) Preparing wave-absorbing aramid paper:
the wave-absorbing aramid fiber paper in the step is composed of aramid fiber pulp, aramid fiber chopped fibers and an absorbent, wherein the content of the absorbent is 0.1-90 wt%.
The absorbent is fibrous, has electromagnetic loss capability, and is one or more of carbon fiber, organic conductive fiber, iron-nickel fiber, iron-silicon-aluminum fiber, and the like. And determining the type of the absorbent in the wave-absorbing aramid paper according to the wave-absorbing frequency band requirement. The fibrous absorbent has a diameter of 0.01 to 1mm and a length of 1 to 20mm.
Adding An absorbent into paper pulp, wherein the wave-absorbing paper pulp comprises the absorbent, aramid chopped fibers, aramid pulp, water and a dispersing agent, and obtaining the wave-absorbing aramid paper A1, A2, A3. An with different absorbent contents after papermaking. The preparation process of the aramid paper is a known technology in the field, and specific process parameters are determined according to actual production requirements.
The wave-absorbing aramid fiber paper has different absorbent contents, and the obtained various wave-absorbing aramid fiber papers have gradient electromagnetic characteristics so as to meet the design of a wave-absorbing structure in the direction vertical to the honeycomb cell.
3) Wave-absorbing aramid paper impregnating resin:
the resin in this step is one of phenolic resin and polyimide resin, preferably phenolic resin. The resin impregnation time is 5-30 min, and the resin impregnation time is determined according to the state of the wave-absorbing aramid paper, so that the wave-absorbing aramid paper can be completely soaked. And vertically placing the soaked aramid paper, and vibrating to remove redundant resin, so as to ensure the weight gain of the resin and control the density of the final wave-absorbing honeycomb. The weight gain proportion is 50-300%, and the specific weight gain is determined according to the density of the wave-absorbing honeycomb.
And then purifying the wave-absorbing aramid paper soaked with the resin, removing the solvent, and performing semi-curing treatment to enable the wave-absorbing aramid paper to obtain the thermoplasticity capability. The semi-curing temperature is 120-400 ℃, the semi-curing time is 0.5-3 h, and the specific technological parameters are selected according to the resin system.
4) Preparing a corrugated structure unit:
the structural parameters of the corrugated structure unit are determined according to the honeycomb cell shape. The honeycomb cell shape is determined according to actual requirements, and is generally one of a hexagon, a rectangle, a circle and an irregular shape, and is preferably a hexagon.
Preparing a corrugated structure unit, designing the shape of a pressing mould according to the determined honeycomb cell shape, continuously pressing the semi-cured wave-absorbing aramid fiber paper through the mould, and smearing core strip glue on the straight edge or the edge of the corrugated unit in the pressing process.
The corrugated structure unit determines the shape of the final honeycomb cell; the corrugated structure units with different shapes are prepared through the die, and finally the honeycomb cell shape can be hexagonal, circular, square, irregular and the like.
5) And (3) superposing the corrugated units:
the superposition sequence of the corrugated units is determined according to the electrical property design, and the corrugated units prepared by different wave-absorbing aramid papers are superposed according to the designed sequence of the number of layers and the gradient of the impedance of the wave-absorbing aramid papers A1, A2 and A3. When the corrugated units are overlapped, the two corrugated units are aligned and glued through the core strip glue to form a complete honeycomb cell which is arranged periodically.
6) Heating treatment:
the corrugated units after being bonded and arranged are placed in a die, bars with the same shape as the honeycomb holes are inserted into the honeycomb holes, and meanwhile, certain pressure can be applied to the walls of the honeycomb holes to ensure the bonding strength of the core bar glue. Heating at 180-450 deg.c for 3-10 hr, and determining the parameters based on the core strip glue and resin. On one hand, the core strip glue is ensured to be completely bonded, on the other hand, the impregnated resin is ensured to be completely cured, and the wave-absorbing honeycomb (shown in figure 1) with the absorbent distributed in a gradient manner and perpendicular to the honeycomb hole direction is obtained, and the wave-absorbing honeycomb can obtain excellent wave-absorbing effect in the ultra-wide frequency range in the gradient change direction.
The invention provides a wave-absorbing honeycomb design and a preparation method with absorbent distributed in a gradient manner by combining the characteristics of absorbent-doped aramid fiber paper wave-absorbing honeycomb, and the wave-absorbing honeycomb design and the preparation method are characterized in that absorbents with different contents are doped into aramid fiber paper to obtain serialized wave-absorbing aramid fiber paper; according to electrical property design, different aramid fiber absorbing papers are sequentially arranged to prepare the wave absorbing honeycomb, and a structure with gradually changed impedance gradient in the direction perpendicular to the cells is formed, so that the wave absorbing honeycomb with excellent performance in the direction perpendicular to the cells is obtained, and the requirement of structure/stealth integration in sandwich structures such as wing surfaces is met. The invention has the innovation points that aramid paper with different electromagnetic properties (different absorbent contents) is laminated, impedance matching design is carried out, and the wave-absorbing honeycomb is obtained, has a gradient structure vertical to the direction of the cells, and meets ultra-wide frequency stealth requirements. The method is not realized by a post-impregnation method, but is obtained by honeycomb integrated preparation. After the wave-absorbing aramid paper with different electromagnetic properties is laminated, if a traditional stretching process is utilized, the honeycomb cells are not uniformly stretched and deformed, so that the finally formed honeycomb cells are not uniform, and therefore, the wave-absorbing honeycomb with the gradient gradual change structure is prepared by adopting a template method.
The present invention is described in detail below with reference to the attached drawings and specific examples.
Example 1
According to the requirement, the electromagnetic wave frequency band of the wave-absorbing honeycomb is mainly determined to be 8-40 GHz, and the wave-absorbing honeycomb has excellent wave-absorbing performance in the frequency band perpendicular to the honeycomb cell direction. According to the wave-absorbing frequency band, the carbon fiber is determined as the absorbent in the wave-absorbing aramid paper.
According to the electrical property design, an optimal gradient-gradual-change wave-absorbing structure is obtained through calculation and optimization by utilizing electromagnetic simulation software, and the length of a carbon fiber absorbent in wave-absorbing aramid paper is determined to be 1mm, and the diameter of the carbon fiber absorbent is determined to be 0.01mm; the content of carbon fiber in the wave-absorbing aramid paper is 0.5%,1%,2%,4% and 10% of the total mass ratio of the aramid paper. Respectively adding carbon fibers, aramid chopped fibers and aramid pulp into water containing a dispersing agent, defibering, dispersing and mixing, and preparing wave-absorbing aramid paper with different electromagnetic properties by papermaking and hot pressing processes, wherein the wave-absorbing aramid paper is A1, A2, A3, A4 and A5.
Respectively impregnating wave-absorbing aramid fiber papers of different specifications with phenolic resin for 10min; and after resin impregnation, vertically airing for 15min, removing redundant resin by vibration, and increasing the weight by 50%. And then placing the wave-absorbing aramid fiber paper in a purification room, keeping blowing and exhausting for 2 hours, and completely removing the solvent in the resin. And heating the wave-absorbing aramid paper to 120 ℃, and preserving the heat for 30min to obtain the wave-absorbing aramid paper in a semi-cured state, thereby obtaining the thermoplasticity capability.
A corrugated structural unit is prepared. According to the wave-absorbing structure designed according to the electrical property of the wave-absorbing honeycomb, the final honeycomb cell shape is determined to be hexagonal, and the side length is 2.77mm. The corrugated units are half of hexagonal cells and are periodically distributed, and the wave-absorbing aramid paper is continuously pressed by using a mould to obtain a corrugated structure unit; and meanwhile, core bar glue is smeared outside the straight edges of the hexagonal corrugated structure units.
The corrugated units are superposed. According to the wave-absorbing structure design of the wave-absorbing honeycomb impedance matching, the layer sequence and the layer number of the wave-absorbing aramid fiber paper with different electromagnetic properties are determined. Wherein the number of the wave-absorbing aramid paper layers of A1, A2, A3, A4 and A5 is 30. When the corrugated units are overlapped, the two corrugated units are aligned and glued through the core strip glue at the straight edges to form a complete hexagonal honeycomb cell which is arranged periodically.
And (4) heating treatment. The corrugated units after being bonded and arranged are placed in a die, hexagonal metal bars are inserted into the honeycomb holes, and meanwhile certain pressure can be applied to the walls of the honeycomb holes to ensure the bonding strength of the core bar glue. And (4) heating, raising the temperature to 180 ℃, and preserving the heat for 3 hours to ensure that the core bar adhesive and the phenolic resin can be completely cured. And cooling to below 60 ℃, taking out the metal bar and obtaining the wave-absorbing honeycomb with the absorbent distributed in a gradient manner in the direction vertical to the honeycomb holes.
The wave-absorbing honeycomb has hexagonal cells which are uniformly distributed, the phenomenon that the cells are not opened is avoided, and the side length size tolerance of the cells is controlled within the range of +/-0.15 mm; along the direction of the cells, the compression strength of the wave-absorbing honeycomb is 3.5MPa; the reflectivity is tested in the direction vertical to the cells, the reflectivity is less than or equal to-4 dB at 1-2 GHz, less than or equal to-10 dB at 2-8 GHz, less than or equal to-25dB at 8-18 GHz and less than or equal to-30 dB at 18-40 GHz. The wave-absorbing honeycomb has excellent wave-absorbing effect in a required electromagnetic wave frequency band (8-40 GHz).
Example 2
According to the requirement, the electromagnetic wave frequency band of the wave-absorbing honeycomb is determined to be mainly 1-8 GHz, and the wave-absorbing honeycomb has excellent wave-absorbing performance in the frequency band perpendicular to the honeycomb cell direction. According to the wave-absorbing frequency band, the absorbent in the wave-absorbing aramid paper is determined to be iron fiber. And (3) performing electrical property design, calculating and optimizing by using electromagnetic simulation software to obtain an optimal gradient-gradual-change wave-absorbing structure, and determining that the length of the iron fiber absorbent is 6mm and the diameter is 0.2mm. The iron fiber content in the wave-absorbing aramid paper accounts for 5%,10%,20%,40%,60% and 90% of the total mass ratio of the aramid paper, and the number of layers is 30, 25, 20, 15 and 10. The shape of the cells is rectangular, the long side is 4mm, and the short side is 2mm. In the preparation process, the soaking time of the wave-absorbing aramid paper is 5min; after the excess resin is removed by vibration, the weight gain ratio is 100 percent; the semi-curing temperature is 200 ℃, and the semi-curing time is 3 hours; the heating temperature is 200 ℃, and the curing time is 10 hours; the rest is the same as the embodiment 1, and the wave-absorbing honeycomb with the absorbent distributed in the gradient direction vertical to the honeycomb holes is obtained.
The wave-absorbing honeycomb has rectangular cells which are uniformly distributed, the phenomenon that the cells are not opened is avoided, and the side length size tolerance of the cells is controlled within the range of +/-0.15 mm; along the direction of the cells, the compression strength of the wave-absorbing honeycomb is 3.2MPa; the reflectivity is tested in the direction vertical to the cells, the reflectivity is less than or equal to-20dB at 1-2 GHz, the reflectivity is less than or equal to-25dB at 2-8 GHz, the reflectivity is less than or equal to-12dB at 8-18 GHz, and the reflectivity is less than or equal to-10 dB at 18-40 GHz. The wave-absorbing honeycomb has excellent wave-absorbing effect in a required electromagnetic wave frequency band (1-8 GHz).
Example 3
According to the requirement, the electromagnetic wave frequency band of the wave-absorbing honeycomb is determined to be mainly 0.5-40 GHz, and the wave-absorbing honeycomb has excellent wave-absorbing performance in the frequency band perpendicular to the honeycomb cell direction. According to the wave-absorbing frequency band, the absorbent in the wave-absorbing aramid paper is determined to be carbon fiber and iron-silicon-aluminum fiber absorbent. Performing electrical property design, calculating and optimizing by using electromagnetic simulation software to obtain an optimal gradient-gradual-change wave-absorbing structure, and determining that the length of the carbon fiber absorbent is 20mm and the diameter is 1mm; the length of the Fe-Si-Al fiber absorbent is 4mm, and the diameter of the Fe-Si-Al fiber absorbent is 0.3mm. The content of carbon fiber in the wave-absorbing aramid paper accounts for 1%,2%,4%,8% and 16% of the total mass ratio of the aramid paper respectively. The wave-absorbing aramid paper with the carbon fiber content of 4%,8% and 16% is added with iron-silicon-aluminum magnetic fibers, and the mass fractions of the iron-silicon-aluminum magnetic fibers are 20%,40% and 80% respectively. In the preparation process, the soaking time of the wave-absorbing aramid paper is 30min; after the excess resin is removed by vibration, the weight gain ratio is 300 percent; the semi-curing temperature is 400 ℃, and the semi-curing time is 2 hours; the heating temperature is 450 ℃, and the curing time is 5h; the rest is the same as the embodiment 1, and the wave-absorbing honeycomb with the absorbent distributed in the gradient direction vertical to the honeycomb holes is obtained.
The wave-absorbing honeycomb has hexagonal cells which are uniformly distributed, the phenomenon that the cells are not opened is avoided, and the side length size tolerance of the cells is controlled within the range of +/-0.15 mm; along the direction of the cells, the compression strength of the wave-absorbing honeycomb is 3.4MPa; the reflectivity is tested in the direction vertical to the cells, the reflectivity is less than or equal to-6 dB at 0.5-1 GHz, less than or equal to-15dB at 1-2 GHz, less than or equal to-20dB at 2-8 GHz, less than or equal to-25dB at 8-18 GHz, and less than or equal to-30 dB at 18-40 GHz. The wave-absorbing honeycomb has excellent wave-absorbing effect in a required electromagnetic wave frequency band (0.5-40 GHz).
Comparative example 1: the carbon fibers in the aramid paper were all 0, and the honeycomb was obtained as in example 1. The honeycomb cells are hexagonal, the cells are uniformly distributed, the phenomenon that the cells are not opened is avoided, and the side length size tolerance of the cells is controlled within the range of +/-0.15 mm; along the direction of the cells, the compression strength of the wave-absorbing honeycomb is 3.6MPa; testing reflectivity in the direction perpendicular to the cells without absorbing wave
Comparative example 2: the wave-absorbing honeycomb prepared by the traditional preparation method is obtained by the processes of core strip gluing, laminating, hot pressing, stretching, gum dipping, drying and curing of wave-absorbing aramid paper and the rest of the wave-absorbing honeycomb is the same as the wave-absorbing honeycomb prepared in the embodiment 1. The wave-absorbing honeycomb has hexagonal cells, but the cells are not uniformly distributed, the phenomenon that the cells are not opened exists, the side length size fluctuation of the cells is large, and the tolerance is within the range of +/-2.0 mm; along the direction of the cells, the compression strength of the wave-absorbing honeycomb is 2.5MPa; the reflectivity is tested in the direction vertical to the cells, the reflectivity is less than or equal to-3 dB at 1-2 GHz, less than or equal to-5 dB at 2-8 GHz, less than or equal to-12dB at 8-18 GHz and less than or equal to-15 dB at 18-40 GHz. The wave absorption performance of the wave absorption honeycomb in a required electromagnetic wave frequency band (8-40 GHz) is not outstanding.
The invention has not been described in detail and is in part known to those of skill in the art.
The foregoing disclosure of the specific embodiments of the present invention and the accompanying drawings is directed to an understanding of the present invention and its implementation, and it will be appreciated by those skilled in the art that various alternatives, modifications, and variations may be made without departing from the spirit and scope of the invention. The present invention should not be limited to the disclosure of the embodiments and drawings in the specification, and the scope of the present invention is defined by the scope of the claims.
Claims (10)
1. The wave-absorbing honeycomb with the absorbent distributed in a gradient manner is characterized by comprising a plurality of wave-absorbing aramid paper and cured resin soaked on the wave-absorbing aramid paper; the wave-absorbing aramid paper is prepared by mixing aramid chopped fibers, aramid pulp, water, a dispersant and an absorbent, papermaking and hot pressing; the content of the absorbent in the wave-absorbing aramid fiber paper is in gradient difference; each wave-absorbing aramid paper contains a plurality of pieces, and each piece of wave-absorbing aramid paper is in a uniform half-hole lattice shape; the wave-absorbing aramid fiber papers are pasted together according to the same kind of wave-absorbing aramid fiber paper to form a gradient layer, the aramid fiber papers of different kinds are pasted together in a gradient manner according to the content of the absorbent, and the half-cell shapes of two adjacent wave-absorbing aramid fiber papers are aligned when the two adjacent wave-absorbing aramid fiber papers are pasted to form a complete cell shape; the absorbent content gradient of the wave-absorbing honeycomb is perpendicular to the direction of the cells from low to high and is the same as the incident direction of the electromagnetic waves.
2. The wave absorbing honeycomb of claim 1, wherein the absorber is present in an amount of 0.1 to 90wt%.
3. The wave absorbing honeycomb of claim 1, wherein the absorbent is fibrous and has electromagnetic loss capability, and at least one of carbon fiber, organic conductive fiber, iron-nickel fiber and iron-silicon-aluminum fiber is selected, the diameter is 0.01-1 mm, and the length is 1-20 mm.
4. A preparation method of a wave-absorbing honeycomb with an absorbent distributed in a gradient manner is characterized by comprising the following steps:
1) And (3) honeycomb structure design: determining the type of the absorbent according to the wave-absorbing frequency band, calculating an optimal wave-absorbing structure with gradient electromagnetic characteristics by using electromagnetic simulation software, determining the electromagnetic characteristics of each gradient layer and the size of each gradient layer along the incident direction of electromagnetic waves, further determining the number of wave-absorbing aramid paper of each gradient layer, the content and the size of the absorbent and the size of a honeycomb cell, and then performing subsequent steps based on the calculation result.
2) Preparing wave-absorbing aramid paper: mixing aramid chopped fibers, aramid pulp, water, a dispersing agent and different amounts of absorbents, and then carrying out papermaking and hot pressing to prepare various wave-absorbing aramid papers with different absorbent contents;
3) Wave-absorbing aramid paper impregnating resin: completely soaking the wave-absorbing aramid paper in resin, taking out the wave-absorbing aramid paper, vertically placing the wave-absorbing aramid paper, removing redundant resin by vibration, and then performing semi-curing treatment;
4) Preparing a corrugated structure unit: pressing the semi-cured wave-absorbing aramid paper by using a pre-designed pressing die to obtain wave-absorbing aramid paper with a half-cell shape, namely a corrugated structure unit, and coating core strip glue on convex edges among the half cells;
5) And (3) superposing the corrugated units: aligning each corrugated structure unit according to the connection of the same kind of wave-absorbing aramid paper and the connection of different kinds of wave-absorbing aramid paper according to the gradient height, and adhering the corrugated structure units through the core strips to obtain a wave-absorbing honeycomb semi-finished product;
6) Heating treatment: and putting the wave-absorbing honeycomb semi-finished product into a die, inserting bars with the same shape into the honeycomb cell holes, applying certain pressure to the honeycomb hole walls to ensure the bonding strength of the core bar glue, and then heating and curing to obtain the wave-absorbing honeycomb with the absorbent distributed in a gradient manner in the direction perpendicular to the honeycomb cell direction.
5. The method according to claim 4, wherein the absorbent is contained in an amount of 0.1 to 90wt%.
6. The method according to claim 4, wherein the absorbent is fibrous and has an electromagnetic loss capability, and at least one of carbon fiber, organic conductive fiber, iron-nickel fiber, and iron-silicon-aluminum fiber is selected, and has a diameter of 0.01 to 1mm and a length of 1 to 20mm.
7. The preparation method of claim 4, wherein for the absorbed electromagnetic wave frequency band below 8GHz, the absorbent is selected from at least one of magnetic fiber absorbent, namely iron fiber, iron-nickel fiber and iron-silicon-aluminum fiber; for the absorbed electromagnetic wave frequency band higher than 8GHz, the absorbent is dielectric fiber absorbent, namely at least one of carbon fiber and organic conductive fiber; for ultra-wide or full-band absorption of electromagnetic waves, the absorbent is selected from at least one of the magnetic absorbent and at least one of the dielectric absorbent.
8. The method according to claim 4, wherein the resin is selected from one of a phenol resin and a polyimide resin.
9. The preparation method of claim 4, wherein the wave-absorbing aramid paper is soaked for 5-30 min; after the excess resin is removed by vibration, the weight gain ratio is 50-300%.
10. The method according to claim 4, wherein the semi-curing treatment is performed under the following conditions: the semi-curing temperature is 120-400 ℃, and the semi-curing time is 0.5-3 h; the conditions for heating and curing are as follows: the heating temperature is 180-450 ℃, and the curing time is 3-10 h.
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