CN112898893A - Waterborne polyurethane emulsion, waterborne polyurethane wave-absorbing coating, preparation method of waterborne polyurethane wave-absorbing coating and wave-absorbing honeycomb - Google Patents
Waterborne polyurethane emulsion, waterborne polyurethane wave-absorbing coating, preparation method of waterborne polyurethane wave-absorbing coating and wave-absorbing honeycomb Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
- C09D175/00—Coating compositions based on polyureas or polyurethanes; Coating compositions based on derivatives of such polymers
- C09D175/04—Polyurethanes
- C09D175/14—Polyurethanes having carbon-to-carbon unsaturated bonds
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G18/00—Polymeric products of isocyanates or isothiocyanates
- C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
- C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
- C08G18/67—Unsaturated compounds having active hydrogen
- C08G18/671—Unsaturated compounds having only one group containing active hydrogen
- C08G18/672—Esters of acrylic or alkyl acrylic acid having only one group containing active hydrogen
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
- C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
- C09D5/32—Radiation-absorbing paints
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Wood Science & Technology (AREA)
- Health & Medical Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Paints Or Removers (AREA)
Abstract
The invention relates to an aqueous polyurethane emulsion, an aqueous polyurethane wave-absorbing coating, a preparation method thereof and a wave-absorbing honeycomb. The waterborne polyurethane emulsion is prepared from the following raw material components in parts by weight: 60-70 parts of polyurethane prepolymer, 2-4 parts of cross-linking agent, 0.1-5 parts of active assistant and 14-34 parts of water; wherein the cross-linking agent is selected from at least one of maleic acid derivatives, polyethylene polyamines and hydroxyl-containing acrylate compounds; the chemical formula of the active assistant comprises at least one active group of double bond, hydroxyl, amido, carboxyl and epoxy. The waterborne polyurethane emulsion has good system stability, and the waterborne polyurethane wave-absorbing coating for the wave-absorbing honeycomb prepared by taking the waterborne polyurethane emulsion as the basic emulsion has strong adhesive force with a composite material honeycomb core material, effectively improves the wave-absorbing performance of the waterborne polyurethane wave-absorbing coating, and is green and environment-friendly.
Description
Technical Field
The invention relates to a wave-absorbing coating, in particular to an aqueous polyurethane emulsion, an aqueous polyurethane wave-absorbing coating, a preparation method thereof and a wave-absorbing honeycomb.
Background
Absorbing coating (also called microwave absorbing coating or radar wave absorbing coating) is a functional material which is covered on a target in a coating form to realize radar stealth. Wave-absorbing coatingThe energy of incident radar waves can be converted into heat energy to be dissipated or eliminated or weakened through a resonance effect, and the purposes of effective absorption and attenuation are achieved. The wave-absorbing coating mainly comprises a film-forming substance and an absorber, wherein the film-forming substance is an organic polymer or an inorganic adhesive, and the absorber is powder, short fiber or chiral substance which has a loss function on electromagnetic waves. The main performance characterization parameters of the wave-absorbing coating comprise reflectivity (-dB), absorption frequency bandwidth (delta f) and surface density (kg/m)2) And the like. Generally, a lower reflectance over a wider frequency band is required under the condition that the density and thickness of the coating are strictly controlled. The wave-absorbing coating can be used for reducing the radar scattering cross section (RCS) of a target, so that military targets such as aircrafts, naval vessels and the like have stealth performance, and can also be used for eliminating the electromagnetic wave interference of a radar system and the electromagnetic wave shielding of microwave equipment. The wave-absorbing coating is comprehensively applied with stealth technologies such as structural design, electronic countermeasure and the like, and can realize qualitative leap of self-protection and attack capability of weaponry such as airplanes and the like.
The wave-absorbing coating for the wave-absorbing honeycomb, namely a specific coating used in a honeycomb core material. The honeycomb structure has the characteristics of high compressive strength, high specific stiffness and the like, and is an excellent light-weight high-strength structural material. The wave-absorbing material with the honeycomb structure has excellent mechanical property and wave-absorbing property. The excellence in the adhesion of the resin to the inner wall of the honeycomb is a major cause of the influence on the compression performance of the honeycomb. Under the same sizing process condition, different formulas directly influence the honeycomb compression performance; under the condition of the same resin proportion, different sizing processes directly influence the honeycomb compression performance.
Most of the existing wave-absorbing coatings for wave-absorbing honeycombs are oil-soluble or solvent-based coatings, and the oil-soluble or solvent-based coatings contain a large amount of Volatile Organic Compounds (VOC) and pollute the environment, and when the oil-soluble or solvent-based coatings are applied to composite honeycomb core materials, residual solvents can cause the difficulty that a large amount of volatile gas is filled in the composite honeycomb core materials, and the volatile gas cannot be volatilized or discharged, so that the problems of bulging, drying cracking, stripping and the like often occur in the coatings in the application process, and the use and the stability of the wave-absorbing performance are directly influenced. With the increasing attention of people to the problem of environmental pollution, the waterborne polyurethane is gradually becoming a new favorite in the modern industry. The waterborne polyurethane is a novel polyurethane system which uses water as a medium to replace an organic solvent, and has the advantages of nonflammability, small smell, no environmental pollution, large molecular weight, relatively low viscosity, energy conservation, easy processing, high wear resistance, luster and the like. However, when the waterborne polyurethane is applied to the honeycomb core material, the adhesive force on the honeycomb core material is poor, and meanwhile, the stability of the system of the waterborne polyurethane is poor, so that the wave-absorbing performance of the waterborne polyurethane is unstable and/or the mechanical property of the waterborne polyurethane is poor.
Disclosure of Invention
Based on this, there is a need for an aqueous polyurethane emulsion. The waterborne polyurethane emulsion has good system stability, and the waterborne polyurethane wave-absorbing coating for the wave-absorbing honeycomb prepared by taking the waterborne polyurethane emulsion as the basic emulsion has strong adhesive force with a honeycomb core material, effectively improves the wave-absorbing performance of the waterborne polyurethane wave-absorbing coating, and is green and environment-friendly.
The waterborne polyurethane emulsion is prepared from the following raw material components in parts by weight:
wherein the cross-linking agent is selected from at least one of maleic acid derivatives, polyethylene polyamines and hydroxyl-containing acrylate compounds;
the chemical formula of the active assistant comprises at least one active group of double bond, hydroxyl, amido, carboxyl and epoxy.
In one embodiment, the coagent is selected from at least one of Tego 760W (sourced from or an agent of Degaco, Germany, chemical composition: polymer containing high pigment affinity groups), Tego 740W (sourced from or an agent of Degaco, Germany, chemical composition: non-ionically modified fatty acid derivative without aromatic), 2-amino-2-methyl-1-propanol, ammonia, and triethylamine.
The invention also provides a preparation method of the waterborne polyurethane emulsion, which comprises the following steps:
mixing the polyurethane prepolymer and a cross-linking agent to carry out a cross-linking reaction; and then adding the active assistant and water for continuous reaction, and adjusting the pH value of the system to 8-10.
The invention also provides a water-based polyurethane wave-absorbing coating which is prepared from the following raw material components in parts by weight:
in one embodiment, the wave-absorbing material is selected from at least one of carbon black, graphite, carbon fiber, carbon nanotube, football graphene and graphene.
In one embodiment, the dispersant is at least one selected from the group consisting of a hydrophobically modified ammonium acrylate copolymer dispersant, a pigment-philic group-containing copolymer dispersant, a polycaprolactone polyol-polyethyleneimine block copolymer dispersant, an acrylate polymer dispersant, a polyurethane polymer dispersant and a polyester polymer dispersant.
In one embodiment, the pH adjusting agent is selected from at least one of 2-amino-2-methyl-1-propanol, ammonia water, and triethylamine; and/or
The defoaming agent is selected from at least one of a mixture of organic silicon and mineral oil, fatty acid salt, polyether siloxane copolymer and organic silicon derivative; and/or
The curing agent is selected from polyisocyanates.
The invention also provides a preparation method of the waterborne polyurethane wave-absorbing coating, which comprises the following steps:
mixing a proper amount of water, the dispersing agent, the defoaming agent and the wave-absorbing material, and stirring and dispersing; then adding the pH regulator to regulate the pH of the system to 8-10, adding the basic emulsion and the rest water, and stirring and dispersing; then adding the curing agent, and stirring and dispersing; the mixture obtained is ground.
The invention also provides a wave-absorbing honeycomb which comprises a honeycomb core material and the water-based polyurethane wave-absorbing coating attached to the honeycomb core material.
Compared with the prior art, the invention has the following beneficial effects:
the waterborne polyurethane emulsion has better stability of a waterborne polyurethane emulsion system by matching the polyurethane prepolymer with a proper cross-linking agent and an active assistant, and the waterborne polyurethane wave-absorbing coating for the wave-absorbing honeycomb prepared by taking the waterborne polyurethane prepolymer as a basic emulsion has strong adhesive force with a honeycomb core material, so that the wave-absorbing performance of the waterborne polyurethane wave-absorbing coating is effectively improved, and meanwhile, the thickness of the waterborne polyurethane wave-absorbing coating can be regulated and controlled by adjusting the using amounts of the cross-linking agent and the active assistant. In addition, the waterborne polyurethane emulsion does not use an organic solvent, does not generate Volatile Organic Compounds (VOC), pollutes the environment, and does not influence the stability of the wave-absorbing coating.
The waterborne polyurethane wave-absorbing coating prepared from the waterborne polyurethane emulsion can be stably attached to a honeycomb core material, exerts an excellent and stable wave-absorbing effect, has a large molecular weight and relatively low viscosity, is highly wear-resistant, glossy and non-flammable, can be cured at a lower temperature, has appropriate construction performance, is simple in construction method, and is beneficial to production and application.
The wave-absorbing honeycomb prepared from the waterborne polyurethane wave-absorbing coating has the advantages of thin thickness, light weight, wide frequency band and strong absorption.
Drawings
Fig. 1 is a flow chart of a wave-absorbing honeycomb preparation process according to an embodiment of the invention.
Detailed Description
The aqueous polyurethane emulsion, the aqueous polyurethane wave-absorbing coating, the preparation method thereof and the wave-absorbing honeycomb of the invention are further described in detail with reference to specific embodiments.
The water used in the embodiment of the invention is deionized water, which is the deionized water from which impurities in the form of ions are removed and mainly serves as a solvent.
The embodiment of the invention provides a waterborne polyurethane emulsion which is prepared from the following raw material components in parts by weight:
wherein the cross-linking agent is selected from at least one of maleic acid derivatives, polyethylene polyamines and hydroxyl-containing acrylate compounds;
the active assistant is at least one selected from Tego 760W, Tego 740W, 2-amino-2-methyl-1-propanol, ammonia water and triethylamine.
The honeycomb core material is usually phenolic resin, the inner wall of the honeycomb core material contains reactive groups such as hydroxyl (-OH which is a common polar group), hydroxymethyl and the like, and theoretically, the reactive groups can react with reactive-NCO groups in polyurethane emulsion, so that sizing of polyurethane is realized. However, when the solvent of the polyurethane prepolymer is water, that is, the solvent is an aqueous polyurethane emulsion, in order to maintain the stability of the system, the conventional aqueous polyurethane emulsion usually does not contain a reactive-NCO group, or the content of the reactive-NCO group is very low, which is not enough to form a stable adhesion relationship with the honeycomb core material through crosslinking, and the curing effect is poor, so that the stability of the wave-absorbing coating is poor. Based on the above, the invention introduces proper cross-linking agent and active auxiliary agent into polyurethane prepolymer, introduces reactive functional group on polyurethane Prepolymer (PU) main chain or latex particle by self-crosslinking method, forms water-based PU emulsion capable of self-crosslinking at ambient temperature or water-based PU emulsion capable of further crosslinking by heat treatment, the aqueous PU emulsion can be cured by utilizing the cohesion and adhesion generated by polar groups in molecules, meanwhile, active groups (mainly comprising at least one of double-bond unsaturated groups, hydroxyl, amino, carboxyl, epoxy and other active functional groups) capable of reacting with the phenolic resin are added, the system stability of the aqueous polyurethane emulsion is enhanced, therefore, the stability and the adhesive force of the wave-absorbing coating formed after the aqueous polyurethane emulsion system is cured on the honeycomb core material are improved, and the wave-absorbing performance is enhanced. In addition, the adhesive amount of the wave-absorbing coating on the inner wall of the honeycomb core material can be regulated and controlled by controlling the using amounts of the cross-linking agent and the active assistant, so that the thickness of the wave-absorbing coating can be regulated and controlled.
In one specific embodiment, the maleic acid derivative in the crosslinking agent can be glycolic acid, the polyethylene polyamine can be diethylenetriamine, and the hydroxyl-containing acrylate compound can be hydroxypropyl acrylate. Preferably, the crosslinking agent is a hydroxyl-containing acrylate compound (such as HPA (full name: hydroxypropyl acrylate) available from Shandongtai and Water treatment science and technology Co., Ltd.), which is miscible with water in any ratio and also dissolves most of the organic solvents, which contributes to the improvement of the stability of the aqueous PU emulsion, and also is easy to polymerize and can rapidly introduce a reactive functional group.
In one particular embodiment, the co-agent is selected from at least one of Tego 760W, Tego 740W, 2-amino-2-methyl-1-propanol (AMP-95), aqueous ammonia, and triethylamine. Wherein, the AMP-95 contains relatively more active groups and types, and can further increase the reaction activity of the PU emulsion.
Preferably, the coagents are Tego 760W, Tego 740W and 2-amino-2-methyl-1-propanol. The three components are compounded for use, so that the reaction activity can be further enhanced through mutual cooperation, and the stability and the adhesive force of the wave-absorbing coating formed after the aqueous polyurethane emulsion system is cured on the honeycomb core material are improved.
In one specific embodiment, the aqueous polyurethane emulsion is prepared from the following raw materials in parts by weight:
preferably, the aqueous polyurethane emulsion is prepared from the following raw material components in parts by weight:
the raw material components in the aqueous polyurethane emulsion are reasonably compatible according to the parts by weight, so that the cohesive force and the adhesive force of a system can be enhanced, the reaction activity is ensured, and the adhesive force of a wave-absorbing coating formed by subsequent curing on a honeycomb core material is further improved.
The embodiment of the invention provides a preparation method of the waterborne polyurethane emulsion, which comprises the following steps:
mixing the polyurethane prepolymer and a cross-linking agent to carry out a cross-linking reaction; and then adding the active assistant and water for continuous reaction, and adjusting the pH value of the system to 8-10.
Specifically, the finally obtained aqueous polyurethane emulsion is translucent. According to the requirement, a pH regulator can be adopted to regulate the pH value of the system to be 8-10, and the pH regulator can be at least one selected from 2-amino-2-methyl-1-propanol, ammonia water and triethylamine, and is mainly used for regulating the pH value of the coating system and stabilizing the activity of the emulsion. Preferably, the pH adjusting agent is AMP-95.
In one specific embodiment, the temperature of the crosslinking reaction is 75-85 ℃ and the time is 0.8-1.2 h.
In one specific embodiment, the step of adding the coagent to continue the reaction comprises: adding Tego 760W and Tego 740W, and reacting for 2.5-3.5 h at the temperature of 75-85 ℃; and then, when the temperature is reduced to 35-45 ℃, adding the 2-amino-2-methyl-1-propanol.
In one specific embodiment, after the pH of the system is adjusted to 8-10, the system is further dispersed, and the method comprises the following steps: dispersing for 30min-60min under the action of high-speed (1000rpm) shearing force.
The embodiment of the invention also provides the water-based polyurethane wave-absorbing coating, which adopts the water-based polyurethane emulsion as the basic emulsion.
In one specific embodiment, the water-based polyurethane wave-absorbing coating is prepared from the following raw materials in parts by weight:
specifically, the wave-absorbing material may be a wave-absorbing material existing in the field, and is not particularly limited. However, the traditional wave-absorbing materials (such as ferrite, ceramics and the like) have the defects of high density and narrow absorption frequency, and cannot meet the following requirements: thin, light, wide and strong. In comparison, the carbon material absorbent has more excellent electromagnetic shielding and absorption characteristics, is light in weight, high in strength and hardness, low in resistivity and good in thermal conductivity, and is better in compatibility in the water-based polyurethane wave-absorbing coating system of the invention, and the curing of the coating is not influenced, so that the carbon material absorbent is preferably adopted as the wave-absorbing material and mainly comprises at least one of carbon black, graphite, carbon fibers, carbon nanotubes, football graphene and graphene (including Graphene Oxide (GO) and the like).
More preferably, the wave-absorbing material is Graphene Oxide (GO). Besides good mechanical property, mechanical property and thermal stability, the graphene oxide can also improve the ageing resistance of the coating, and can generate strong interface interaction with the aqueous polyurethane emulsion, so that the mobility of polymer molecular chains is poor, the cohesive strength and the creep resistance of the coating are enhanced, and the surface of a core material has no obvious powder removal or chapping phenomenon. In addition, graphene oxide is an amphiphilic substance, and the main reason is that the graphene sheet exhibits a property distribution from hydrophilic to hydrophobic from the edge to the center, which can exist at the interface as a surfactant and reduce the energy between the interfaces, and the graphene oxide has a large number of oxygen-containing groups on the surface and the edge, and can stably exist in an aqueous solution and a polar solvent.
In one specific embodiment, the dispersant is selected from at least one of a water-resistant polymeric dispersant (e.g., hydrophobically modified ammonium acrylate copolymer dispersant (e.g., model: H5028, Shanghai Kangji chemical Co., Ltd.) or a copolymer containing a pigment-philic group (e.g., model: BOK-3864, Guangzhou Xin Ying trade Co., Ltd.), a polycaprolactone polyol-polyethyleneimine block copolymer dispersant (e.g., propylene glycol methyl ether acetate, Qingdao Minfar New Material Co., Ltd.), an acrylate polymeric dispersant (e.g., Tego 745W, Germany Digao, or an agent thereof), a polyurethane polymeric dispersant (e.g., BYK-163, Bikk chemical), and a polyester polymeric dispersant (e.g., 1100W, Taiwan Houtch Co., Ltd.). By adopting the dispersant, the interfacial energy of a system when water is used as a solvent can be improved, the dispersion stability effect of a water-based system is greatly improved, the raw material components are stably suspended and dispersed in water, the prepared coating has moderate viscosity and good physical properties such as coating sizing rate, adhesive force and the like, and the system stability of the water-based polyurethane coating can be improved. Preferably, the dispersant is a hydrophobically modified acrylate ammonium salt copolymer dispersant, such as SN-2725, available from Shanghai deep bamboo chemical technology, Inc.
In one particular embodiment, the defoamer is selected from at least one of a mixture of silicone and mineral oil, a fatty acid salt, a polyether siloxane copolymer, and a derivative of silicone. The defoaming agent is mainly used for removing harmful foams generated in the production process of the coating. Preferably, the defoamer is a polyether siloxane copolymer (e.g., Tego 810, digao, germany, or an agent thereof).
In one specific embodiment, the curing agent is selected from polyisocyanates, which are important basic raw materials of polyurethane, and have the characteristics of easy drying, wear resistance, high hardness, good fullness, good flexibility, easy polishing, strong compatibility with solvents and stable performance. Preferably, the curing agent is Toluene Diisocyanate (TDI), which is typically a mixture of two isomers of 2,4-TDI and 2,6-TDI, which has excellent weather and temperature resistance properties, and may include 3 designations: TDI-80/20, TDI-100 and TDI-65/35. The preceding numbers indicate the content of 2,4-TDI in the composition. For example, 80 in TDI-80/20 means that the composition is 80% 2,4-TDI and 20% 2, 6-TDI. More preferably, the curing agent is TDI-80/20, has good solubility in various solvents and good compatibility with a coating system, and is beneficial to ensuring the stability of the coating system.
The preparation method of the waterborne polyurethane wave-absorbing coating comprises the following steps:
mixing a proper amount of water, the dispersing agent, the defoaming agent and the wave-absorbing material, and stirring and dispersing; then adding the pH regulator to regulate the pH of the system to 8-10, adding the basic emulsion and the rest water, and stirring and dispersing; then adding the curing agent, and stirring and dispersing; the mixture obtained is ground. The proper amount of water can be adjusted according to the dispersing effect, for example, 10-20 parts of water is added firstly.
In a specific embodiment, the grinding refers to grinding the mixture to the fineness of 1-5 microns.
The embodiment of the invention also provides a wave-absorbing honeycomb which comprises a honeycomb core material and the waterborne polyurethane wave-absorbing coating attached to the honeycomb core material.
The preparation method of the wave-absorbing honeycomb comprises the following steps:
and sizing the honeycomb core material by using the water-based polyurethane wave-absorbing coating, and then drying and curing.
In one specific embodiment, the sizing method is dipping, curtain coating or spraying.
In one specific embodiment, the drying method is air blast drying, the drying temperature is 75-85 ℃, and the drying time is 15-25 min.
In one specific embodiment, the curing temperature is 30-80 ℃ and the curing time is 3-24 hours. For example, 3 hours at 80 ℃, 10 hours at 50 ℃ and 24 hours at 30 ℃.
In the following, specific examples are shown, and all the raw materials used are commercially available ones unless otherwise specified.
In the following specific examples, in order to illustrate the performance of the aqueous polyurethane emulsion of the present invention, the aqueous polyurethane emulsion of each example is applied to the aqueous polyurethane wave-absorbing coating with the same weight part, but the application cannot be taken as a limitation of the formulation of the aqueous polyurethane wave-absorbing coating of the present invention, and the formulation of the aqueous polyurethane wave-absorbing coating of the present invention is subject to the above-mentioned content.
The performance test method of each example is as follows:
(1) flat panel reflectance test
And the transmitting antenna and the receiving antenna are symmetrically arranged on the circular arc, and the plane of the circular arc is vertical to the plane of the wave-absorbing material. The transmitting antenna generates an excitation signal to the wave-absorbing material, and the signal of the mirror reflection part is acquired by the receiving antenna. Then, an ideal conductive metal plate is used for replacing the wave-absorbing material to measure the reflected signal; finally, the reflected signals under the front and the back conditions are compared to obtain the reflectivity of the material. Test size 300mm by 300mm, test band: 2GHz-18 GHz; the microwave flat plate reflectivity test is carried out according to GJB 2038A-2011 radar absorbing material reflectivity test method, and the result is expressed by absorption intensity and-4 dB bandwidth.
The testing steps are as follows:
1) starting up the instrument for preheating, and simultaneously building a test platform;
2) the metal standard plate is placed on a test board, a time domain door range is set by utilizing the time domain function of a vector network analyzer, antenna coupling is isolated, a main reflection peak is selected, and the test dynamic range is improved.
3) After the time domain is set, setting a test plan (an example is a 10-degree semi-automatic sampling test) by using test software, and starting the test (sequentially testing the metal standard plate and the wave-absorbing material sample); after the test is finished, the absorption intensity and the-4 dB bandwidth can be obtained by processing and analyzing the test data.
(2) Plane compressive Strength test
Taking GB/T1453-2005 test method as an example:
A. preparing a sample: cutting into sample honeycomb of 60mm 5mm and 60mm 40 mm;
B. testing equipment: a universal material testing machine;
C. compressing the clamp: a fixed flat press plate and a press plate with a spherical seat (self-centering) should be used to introduce force into the test piece, the press plate is well centered and no eccentric load is applied, and the press plate surface should exceed the test piece profile. If the platens have insufficient hardness or to protect the platen surfaces, a relatively hard flat plate (parallel to the surface) may be inserted between the clamp and each end face of the respective platen.
The test method comprises the following steps: when the flat compression strength is tested, the spherical support is adjusted to enable the upper cushion block to be parallel to the lower pressing sheet of the testing machine, then the upper cushion block and the lower pressing sheet are uniformly and continuously loaded until the upper cushion block is damaged, the damage load is read, and the damage form is recorded. The recommended loading speed is 0.5 mm/min.
E. Destruction form: uniform destruction of the sample honeycomb is the only acceptable form of destruction, and compressive destruction limited to one corner or edge is ineffective.
F. Data processing: the 3 th position after the decimal point is retained, ultimate strength, P ═ F/a. Wherein P is not flat compressive strength, MPa; f is the ultimate load before failure, N; a is the cross-sectional area of the specimen, mm2。
Example 1
The embodiment is a wave-absorbing honeycomb, and the preparation method thereof is as follows (see the process flow chart in fig. 1):
preparation of water-based polyurethane wave-absorbing coating
1.1, preparing PU emulsion: putting 65 parts of PU into a reaction container, adding 4 parts of HPA in the process of continuously stirring at normal temperature, gradually heating to 80 ℃, reacting for 1h, properly cooling, adding 1.6 parts of Tego 760W and 1.2 parts of Tego 740W, continuing to react for 3h at 80 ℃, cooling to 40 ℃, adding 1.6 parts of AMP-95 and 25 parts of deionized water under high-speed stirring, adjusting the pH value of the dispersion to 8-10 by using 0.1 part of AMP-95, dispersing for 30-60 min under the action of high-speed shearing force, cooling and sealing for later use, thus obtaining the semitransparent aqueous PU emulsion.
1.2, preparing wave-absorbing slurry: weighing a proper amount of deionized water (20 parts) at room temperature, putting 0.6 part of SN-2725, 0.2 part of Tego 810 and 0.8 part of GO into a container in sequence, stirring at 500rpm until the GO is uniformly dispersed, adding 0.4 part of AMP-95, adjusting the pH value of the dispersion to 8-10, adding 60 parts of PU emulsion and a proper amount of deionized water (10 parts), stirring at 2000rpm vigorously for 30 minutes until the emulsion is uniform, and finally adding 8 parts of TDI-80/20 and continuously stirring at 1000rpm for 20 minutes for later use;
1.3, grinding:
grinding the mixture for later use by a horizontal sand mill (2000rpm/30min) to obtain the PU wave-absorbing coating with the fineness of about 1-5 microns;
(II) preparation of wave-absorbing honeycomb
2.1 sizing
And uniformly distributing the PU wave-absorbing coating on the honeycomb core material through curtain coating.
2.2 drying and curing
And drying and curing the sized honeycomb core material to obtain the wave-absorbing honeycomb material. The drying adopts forced air drying, the zone temperature is 80 ℃, and the drying time is 20 min; the curing temperature was 80 ℃ and the time was 3 hours.
(III) test
And cutting the prepared wave-absorbing honeycomb into samples of 300mm by 15mm for microwave flat reflectivity test.
And (3) testing results: the absorption intensity in the range of 2GHz-18GHz is-17 dB and-4 dB, and the bandwidth is 9 GHz.
The sample with the tested electromagnetic parameter flat plate reflectivity is cut into sample honeycombs with the thickness of 60mm x 15mm to be subjected to flat pressing test, and the strength is 5.9 MPa.
Example 2
The embodiment is a wave-absorbing honeycomb, and the preparation method comprises the following steps:
preparation of water-based polyurethane wave-absorbing coating
1.1, preparing PU emulsion: putting 60 parts of PU into a reaction container, adding 3 parts of HPA in the process of continuously stirring at normal temperature, gradually heating to 80 ℃, reacting for 1h, properly cooling, adding 0.1 part of Tego 760W and 0.05 part of Tego 740W, continuing to react for 3h at 80 ℃, cooling to 40 ℃, adding 0.1 part of AMP-95 and 15 parts of deionized water under high-speed stirring, adjusting the pH value of the dispersion to 8-10 by using 0.1 part of AMP-95, dispersing for 30-60 min under the action of high-speed shearing force, cooling and sealing for later use, thus obtaining the semitransparent aqueous PU emulsion.
1.2, preparing wave-absorbing slurry: weighing a proper amount of deionized water (20 parts) at room temperature, putting 0.6 part of SN-2725, 0.2 part of Tego 810 and 0.8 part of GO into a container in sequence, stirring at 500rpm until the GO is uniformly dispersed, adding 0.4 part of AMP-95, adjusting the pH value of the dispersion to 8-10, adding 60 parts of PU emulsion and a proper amount of deionized water (10 parts), stirring at 2000rpm vigorously for 30 minutes until the emulsion is uniform, and finally adding 8 parts of TDI-80/20 and continuously stirring at 1000rpm for 20 minutes for later use;
1.3, grinding:
grinding the mixture for later use by a horizontal sand mill (2000rpm/30min) to obtain the PU wave-absorbing coating with the fineness of about 1-5 microns;
(II) preparation of wave-absorbing honeycomb
2.1 sizing
And uniformly distributing the PU wave-absorbing coating on the honeycomb core material through curtain coating.
2.2 drying and curing
And drying and curing the sized honeycomb core material to obtain the wave-absorbing honeycomb material. The drying adopts forced air drying, the zone temperature is 80 ℃, and the drying time is 20 min; the curing temperature was 50 ℃ and the time was 10 hours.
(III) test
And cutting the prepared wave-absorbing honeycomb into samples of 300mm by 5mm for microwave flat reflectivity test.
And (3) testing results: the absorption intensity in the range of 2GHz-18GHz is-15 dB and-4 dB, and the bandwidth is 8 GHz.
The sample with the tested electromagnetic parameter flat plate reflectivity is cut into sample honeycombs with the thickness of 60mm x 5mm to be subjected to flat pressing test, and the strength is 4.6 MPa.
Example 3
The embodiment is a wave-absorbing honeycomb, and the preparation method comprises the following steps:
preparation of water-based polyurethane wave-absorbing coating
1.1, preparing PU emulsion: putting 70 parts of PU into a reaction container, adding 2 parts of HPA in the process of continuously stirring at normal temperature, gradually heating to 80 ℃, reacting for 1h, properly cooling, adding 0.8 part of Tego 760W and 0.5 part of Tego 740W, continuing to react for 3h at 80 ℃, cooling to 40 ℃, adding 0.3 part of AMP-95 and 32 parts of deionized water under high-speed stirring, adjusting the pH value of the dispersion to 8-10 by using 0.4 part of AMP-95, dispersing for 30-60 min under the action of high-speed shearing force, cooling and sealing for later use, thus obtaining the semitransparent aqueous PU emulsion.
1.2, preparing wave-absorbing slurry: weighing a proper amount of deionized water (20 parts) at room temperature, putting 0.6 part of SN-2725, 0.2 part of Tego 810 and 0.8 part of GO into a container in sequence, stirring at 500rpm until the GO is uniformly dispersed, adding 0.4 part of AMP-95, adjusting the pH value of the dispersion to 8-10, adding 60 parts of PU emulsion and a proper amount of deionized water (10 parts), stirring at 2000rpm vigorously for 30 minutes until the emulsion is uniform, and finally adding 8 parts of TDI-80/20 and continuously stirring at 1000rpm for 20 minutes for later use;
1.3, grinding:
grinding the mixture for later use by a horizontal sand mill (2000rpm/30min) to obtain the PU wave-absorbing coating with the fineness of about 1-5 microns;
(II) preparation of wave-absorbing honeycomb
2.1 sizing
And uniformly distributing the PU wave-absorbing coating on the honeycomb core material through curtain coating.
2.2 drying and curing
And D, drying and curing the wave-absorbing honeycomb prepared in the step C to obtain the wave-absorbing honeycomb material. Drying temperature and time: the temperature of the forced air drying area is 80 ℃, and the drying time is 20 min; the curing temperature was 30 ℃ and the time was 24 hours.
(III) test
And cutting the prepared wave-absorbing honeycomb into samples of 300mm by 40mm for microwave flat plate reflectivity test.
And (3) testing results: the absorption intensity in the range of 2GHz-18GHz is-16 dB and-4 dB, and the bandwidth is 7 GHz.
The sample with the tested electromagnetic parameter flat plate reflectivity is cut into sample honeycombs with the thickness of 60mm x 40mm to be subjected to flat pressing test, and the strength is 4.8 MPa.
Example 4
The embodiment is a wave-absorbing honeycomb, and the preparation method comprises the following steps:
preparation of water-based polyurethane wave-absorbing coating
1.1, preparing PU emulsion: putting 65 parts of PU into a reaction container, adding 4 parts of diethylenetriamine in the process of continuously stirring at normal temperature, gradually heating to 80 ℃, reacting for 1h, properly cooling, adding 1.6 parts of Tego 760W and 1.2 parts of Tego 740W, continuing to react for 3h at 80 ℃, cooling to 40 ℃, adding 1.6 parts of AMP-95 and 25 parts of deionized water under high-speed stirring, adjusting the pH value of the dispersion to 8-10 by using 0.1 part of AMP-95, dispersing for 30-60 min under the action of high-speed shearing force, cooling and sealing for later use, thus obtaining the semitransparent aqueous PU emulsion.
1.2, preparing wave-absorbing slurry: weighing a proper amount of deionized water (20 parts) at room temperature, putting 0.6 part of SN-2725, 0.2 part of Tego 810 and 0.8 part of GO into a container in sequence, stirring at 500rpm until the GO is uniformly dispersed, adding 0.4 part of AMP-95, adjusting the pH value of the dispersion to 8-10, adding 60 parts of PU emulsion and a proper amount of deionized water (10 parts), stirring at 2000rpm vigorously for 30 minutes until the emulsion is uniform, and finally adding 8 parts of TDI-80/20 and continuously stirring at 1000rpm for 20 minutes for later use;
1.3, grinding:
grinding the mixture for later use by a horizontal sand mill (2000rpm/30min) to obtain the PU wave-absorbing coating with the fineness of about 1-5 microns;
(II) preparation of wave-absorbing honeycomb
2.1 sizing
And uniformly distributing the PU wave-absorbing coating on the honeycomb core material through curtain coating.
2.2 drying and curing
And drying and curing the sized honeycomb core material to obtain the wave-absorbing honeycomb material. The drying adopts forced air drying, the zone temperature is 80 ℃, and the drying time is 20 min; the curing temperature was 80 ℃ and the time was 3 hours.
(III) test
And cutting the prepared wave-absorbing honeycomb into samples of 300mm by 15mm for microwave flat reflectivity test.
And (3) testing results: the absorption intensity in the range of 2GHz-18GHz is-16 dB and-4 dB, and the bandwidth is 7 GHz.
The sample with the tested electromagnetic parameter flat plate reflectivity is cut into sample honeycombs with the thickness of 60mm x 15mm to be subjected to flat pressing test, and the strength is 4.8 MPa.
Example 5
The embodiment is a wave-absorbing honeycomb, and the preparation method comprises the following steps:
preparation of water-based polyurethane wave-absorbing coating
1.1, preparing PU emulsion: putting 65 parts of PU into a reaction container, adding 4 parts of HPA in the process of continuously stirring at normal temperature, gradually heating to 80 ℃, reacting for 1h, properly cooling, adding 1.6 parts of triethylamine and 1.2 parts of Tego 740W, continuing to react for 3h at 80 ℃, cooling to 40 ℃, adding 1.6 parts of AMP-95 and 25 parts of deionized water under high-speed stirring, adjusting the pH value of the dispersion to 8-10 by using 0.1 part of AMP-95, dispersing for 30-60 min under the action of high-speed shearing force, cooling and sealing for later use, thus obtaining the semitransparent water-based PU emulsion.
1.2, preparing wave-absorbing slurry: weighing a proper amount of deionized water (20 parts) at room temperature, putting 0.6 part of SN-2725, 0.2 part of Tego 810 and 0.8 part of GO into a container in sequence, stirring at 500rpm until the GO is uniformly dispersed, adding 0.4 part of AMP-95, adjusting the pH value of the dispersion to 8-10, adding 60 parts of PU emulsion and a proper amount of deionized water (10 parts), stirring at 2000rpm vigorously for 30 minutes until the emulsion is uniform, and finally adding 8 parts of TDI-80/20 and continuously stirring at 1000rpm for 20 minutes for later use;
1.3, grinding:
grinding the mixture for later use by a horizontal sand mill (2000rpm/30min) to obtain the PU wave-absorbing coating with the fineness of about 1-5 microns;
(II) preparation of wave-absorbing honeycomb
2.1 sizing
And uniformly distributing the PU wave-absorbing coating on the honeycomb core material through impregnation.
2.2 drying and curing
And drying and curing the sized honeycomb core material to obtain the wave-absorbing honeycomb material. The drying adopts forced air drying, the zone temperature is 80 ℃, and the drying time is 20 min; the curing temperature was 80 ℃ and the time was 3 hours.
(III) test
And cutting the prepared wave-absorbing honeycomb into samples of 300mm by 15mm for microwave flat reflectivity test.
And (3) testing results: the absorption intensity in the range of 2GHz-18GHz is-16 dB and-4 dB, and the bandwidth is 6.5 GHz.
The sample with the tested electromagnetic parameter flat plate reflectivity is cut into sample honeycombs with the thickness of 60mm x 15mm to be subjected to flat pressing test, and the strength is 4.4 MPa.
Example 6
The embodiment is a wave-absorbing honeycomb, and the preparation method comprises the following steps:
preparation of water-based polyurethane wave-absorbing coating
1.1, preparing PU emulsion: putting 65 parts of PU into a reaction container, adding 4 parts of HPA in the process of continuously stirring at normal temperature, gradually heating to 80 ℃, reacting for 1h, properly cooling, adding 1.6 parts of Tego 760W and 1.2 parts of Tego 740W, continuing to react for 3h at 80 ℃, cooling to 40 ℃, adding 1.6 parts of AMP-95 and 25 parts of deionized water under high-speed stirring, adjusting the pH value of the dispersion to 8-10 by using 0.1 part of AMP-95, dispersing for 30-60 min under the action of high-speed shearing force, cooling and sealing for later use, thus obtaining the semitransparent aqueous PU emulsion.
1.2, preparing wave-absorbing slurry: weighing a proper amount of deionized water (20 parts) at room temperature, putting 0.6 part of Tego 745W, 0.2 part of Tego 810 and 0.8 part of GO into a container in sequence, stirring at 500rpm until the GO is uniformly dispersed, adding 0.4 part of AMP-95, adjusting the pH value of the dispersion to 8-10, adding 60 parts of PU emulsion and a proper amount of deionized water (10 parts), stirring at 2000rpm vigorously for 30 minutes until the emulsion is uniform, and finally adding 8 parts of TDI-80/20 and continuously stirring at 1000rpm for 20 minutes for later use;
1.3, grinding:
grinding the mixture for later use by a horizontal sand mill (2000rpm/30min) to obtain the PU wave-absorbing coating with the fineness of about 1-5 microns;
(II) preparation of wave-absorbing honeycomb
2.1 sizing
And uniformly distributing the PU wave-absorbing coating on the honeycomb core material through curtain coating.
2.2 drying and curing
And drying and curing the sized honeycomb core material to obtain the wave-absorbing honeycomb material. The drying adopts forced air drying, the zone temperature is 80 ℃, and the drying time is 20 min; the curing temperature was 80 ℃ and the time was 3 hours.
(III) test
And cutting the prepared wave-absorbing honeycomb into samples of 300mm by 15mm for microwave flat reflectivity test.
And (3) testing results: the absorption intensity in the range of 2GHz-18GHz is-15 dB and-4 dB, and the bandwidth is 6 GHz.
The sample with the tested electromagnetic parameter flat plate reflectivity is cut into sample honeycombs with the thickness of 60mm x 15mm to be subjected to flat pressing test, and the strength is 4.9 MPa.
Example 7
The embodiment is a wave-absorbing honeycomb, and the preparation method comprises the following steps:
preparation of water-based polyurethane wave-absorbing coating
1.1, preparing PU emulsion: putting 65 parts of PU into a reaction container, adding 4 parts of HPA in the process of continuously stirring at normal temperature, gradually heating to 80 ℃, reacting for 1h, properly cooling, adding 2.8 parts of Tego 740W, continuously reacting for 3h at 80 ℃, cooling to 40 ℃, adding 1.6 parts of AMP-95 and 25 parts of deionized water under high-speed stirring, adjusting the pH value of the dispersion to 8-10 by using 0.1 part of AMP-95, dispersing for 30-60 min under the action of high-speed shearing force, cooling and sealing for later use, thus obtaining the semitransparent water-based PU emulsion.
1.2, preparing wave-absorbing slurry: weighing a proper amount of deionized water (20 parts) at room temperature, putting 0.6 part of SN-2725, 0.2 part of Tego 810 and 0.8 part of GO into a container in sequence, stirring at 500rpm until the GO is uniformly dispersed, adding 0.4 part of AMP-95, adjusting the pH value of the dispersion to 8-10, adding 60 parts of PU emulsion and a proper amount of deionized water (10 parts), stirring at 2000rpm vigorously for 30 minutes until the emulsion is uniform, and finally adding 8 parts of TDI-80/20 and continuously stirring at 1000rpm for 20 minutes for later use;
1.3, grinding:
grinding the mixture for later use by a horizontal sand mill (2000rpm/30min) to obtain the PU wave-absorbing coating with the fineness of about 1-5 microns;
(II) preparation of wave-absorbing honeycomb
2.1 sizing
And uniformly distributing the PU wave-absorbing coating on the honeycomb core material through curtain coating.
2.2 drying and curing
And drying and curing the sized honeycomb core material to obtain the wave-absorbing honeycomb material. The drying adopts forced air drying, the zone temperature is 80 ℃, and the drying time is 20 min; the curing temperature was 80 ℃ and the time was 3 hours.
(III) test
And cutting the prepared wave-absorbing honeycomb into samples of 300mm by 15mm for microwave flat reflectivity test.
And (3) testing results: the absorption intensity in the range of 2GHz-18GHz is-17 dB and-4 dB, and the bandwidth is 8.5 GHz.
The sample with the tested electromagnetic parameter flat plate reflectivity is cut into sample honeycombs with the thickness of 60mm x 15mm to be subjected to flat pressing test, and the strength is 4.8 MPa.
Comparative example 1
The comparative example is a wave-absorbing honeycomb, and the preparation method comprises the following steps:
preparation of water-based polyurethane wave-absorbing coating
1.1, preparing wave-absorbing slurry: weighing a proper amount of deionized water (20 parts) at room temperature, putting 0.6 part of SN-2725, 0.2 part of Tego 810 and 0.8 part of GO into a container in sequence, stirring at 500rpm until the GO is uniformly dispersed, adding 0.4 part of AMP-95, adjusting the pH value of the dispersion to 8-10, adding 60 parts of aqueous PU emulsion (model: FT-6001, manufacturer: Nanjing Feiteng chemical Co., Ltd.) and a proper amount of deionized water (10 parts), stirring vigorously at 2000rpm for 30 minutes until the emulsion is uniform, finally adding 8 parts of TDI-80/20, continuously stirring at 1000rpm for 20 minutes for later use;
1.2, grinding:
grinding the mixture for later use by a horizontal sand mill (2000rpm/30min) to obtain the PU wave-absorbing coating with the fineness of about 1-5 microns;
(II) preparation of wave-absorbing honeycomb
2.1 sizing
And uniformly distributing the PU wave-absorbing coating on the honeycomb core material through curtain coating.
2.2 drying and curing
And drying and curing the sized honeycomb core material to obtain the wave-absorbing honeycomb material. The drying adopts forced air drying, the zone temperature is 80 ℃, and the drying time is 20 min; the curing temperature was 80 ℃ and the time was 3 hours.
(III) test
And cutting the prepared wave-absorbing honeycomb into samples of 300mm by 15mm for microwave flat reflectivity test.
And (3) testing results: the absorption intensity in the range of 2GHz-18GHz is-17 dB and-4 dB, and the bandwidth is 6 GHz.
The sample with the tested electromagnetic parameter flat plate reflectivity is cut into sample honeycombs with the thickness of 60mm x 15mm to be subjected to flat pressing test, and the strength is 2.8 MPa.
The PU emulsion adopted by the wave-absorbing honeycombs in the embodiments 1 to 6 and the comparative example 1 and the performance test results are respectively shown in the following tables 1 to 2:
TABLE 1 PU emulsion formulation tables described in examples 1 to 6 and comparative example 1 (parts by weight)
Table 2 results of performance test of the wave-absorbing honeycomb described in examples 1 to 6 and comparative example 1
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (10)
1. The waterborne polyurethane emulsion is characterized by being prepared from the following raw material components in parts by weight:
wherein the cross-linking agent is at least one selected from maleic acid derivatives, polyethylene polyamine compounds and hydroxyl-containing acrylate compounds;
the chemical formula of the active assistant comprises at least one active group of double bond, hydroxyl, amido, carboxyl and epoxy.
2. The aqueous polyurethane emulsion of claim 1, wherein the coagent is selected from at least one of Tego 760W, Tego 740W, 2-amino-2-methyl-1-propanol, ammonia, and triethylamine.
3. The aqueous polyurethane emulsion of claim 2, wherein the coagents are Tego 760W, Tego 740W and 2-amino-2-methyl-1-propanol.
4. A method for producing the aqueous polyurethane emulsion according to any one of claims 1 to 3, characterized by comprising the steps of:
mixing the polyurethane prepolymer and a cross-linking agent to carry out a cross-linking reaction; and then adding the active assistant and water for continuous reaction, and adjusting the pH value of the system to 8-10.
5. The water-based polyurethane wave-absorbing coating is characterized by being prepared from the following raw material components in parts by weight:
6. the waterborne polyurethane wave-absorbing coating of claim 5, wherein the wave-absorbing material is selected from at least one of carbon black, graphite, carbon fiber, carbon nanotube, football alkene and graphene.
7. The waterborne polyurethane wave-absorbing coating of claim 5, wherein the dispersant is at least one selected from the group consisting of a hydrophobically modified ammonium acrylate copolymer dispersant, a pigment-philic group-containing copolymer dispersant, a polycaprolactone polyol-polyethyleneimine block copolymer dispersant, an acrylate polymer dispersant, a polyurethane polymer dispersant and a polyester polymer dispersant.
8. The waterborne polyurethane wave-absorbing coating of any one of claims 5 to 7, wherein the pH regulator is at least one selected from the group consisting of 2-amino-2-methyl-1-propanol, ammonia water and triethylamine; and/or
The defoaming agent is selected from at least one of a mixture of organic silicon and mineral oil, fatty acid salt, polyether siloxane copolymer and organic silicon derivative; and/or
The curing agent is selected from polyisocyanates.
9. The preparation method of the waterborne polyurethane wave-absorbing coating of any one of claims 5 to 8, which is characterized by comprising the following steps:
mixing a proper amount of water, the dispersing agent, the defoaming agent and the wave-absorbing material, and stirring and dispersing; then adding the pH regulator to regulate the pH of the system to 8-10, adding the basic emulsion and the rest water, and stirring and dispersing; then adding the curing agent, and stirring and dispersing; the mixture obtained is ground.
10. A wave-absorbing honeycomb, which is characterized by comprising a honeycomb core material and the waterborne polyurethane wave-absorbing coating of any one of claims 5 to 8 attached on the honeycomb core material.
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| CN114591645A (en) * | 2022-03-04 | 2022-06-07 | 中国人民解放军火箭军工程大学 | Carbon-based wave-absorbing coating, preparation method thereof and honeycomb sandwich structure composite wave-absorbing material |
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