Preparation method and application of multi-layer light skin

Abstract

The invention relates to the technical field of wave-absorbing skins, and discloses a preparation method and application of a multi-layer light skin, the multi-layer light skin comprises a wave-absorbing coating, a transition layer, a reflecting layer and a heat insulation substrate layer; the wave-absorbing coating comprises 100 parts by weight of a polyurethane emulsion, 16-30 parts by weight of a polypyrrole coated ferroferric oxide wave-absorbing agent and the like; the light aerogel reinforced ceramic fiber felt is used as a heat insulation substrate layer, the metal grid and the like are used as a reflecting layer, the light silicon dioxide aerogel, glass bead and epoxy resin compound is used as a transition layer and used as a base material of the skin, and the polyurethane wave-absorbing coating is used as a wave-absorbing coating of the skin. The obtained multi-layer skin material has the advantages of light weight, wide absorption frequency band and high wave absorption performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wave-absorbing skin, in particular to a preparation method and application of a multi-layer light skin. BACKGROUND

[0002] Wave-absorbing materials can convert electromagnetic waves into heat energy through dielectric loss, magnetic loss, etc. for dissipation, and have important applications in electromagnetic shielding, stealth materials, national defense and military industry, etc. Wave-absorbing materials mainly include wave-absorbing coating, wave-absorbing skin, wave-absorbing rubber, etc., and mainly add wave-absorbing media such as magnetic loss media such as ferroferric oxide, dielectric loss media such as polypyrrole, and resistance type loss media such as graphene into the materials.

[0003] Coating a resin coating on the surface of the skin material can give the skin good waterproof, corrosion-resistant, wave-absorbing, etc. properties, and the polyurethane coating has good toughness and excellent weather resistance, and is widely used. Adding wave-absorbing materials such as polypyrrole and ferroferric oxide to the coating layer can give the coating good wave-absorbing performance, and the patent application file with publication number CN119265941A discloses a self-cleaning sensing type composite coating for fabric and a preparation method thereof, which forms a composite coating of polypyrrole, ferroferric oxide and polyurea, etc., and has good sensing and wave-absorbing performance. However, nano-ferroferric oxide is prone to agglomeration, and the compatibility of polypyrrole and polyurethane is poor, and adding both to the polyurethane coating will affect the wave-absorbing and mechanical properties of the coating. SUMMARY

[0004] (I) The technical problem solved: In view of the deficiencies of the prior art, the present application provides a preparation method and application of a multi-layer light skin, which solves the problem of poor wave-absorbing performance of the skin coating material.

[0005] (II) Technical solution: A multi-layer light skin is composed of a wave-absorbing coating, a transition layer, a reflective layer and a heat-insulating base layer.

[0006] The preparation method of the multi-layer light skin is as follows:

[0007] (1) Sodium hydroxyethyl sulfonate is added to acetone, stirred, and then chloroethyl isocyanate and triethylamine are added, stirred and reacted, and then the product is washed with petroleum ether after reduced pressure distillation, and then purified by recrystallization in water to obtain sodium chloroethyl amine ester base ethanesulfonate. The reaction formula is as follows:

[0008] .

[0009] (2) Polyvinyl alcohol is added to water, heated and stirred to dissolve, then cooled to the reaction temperature, sodium hydroxide is added as a catalyst, stirred, and then sodium chloroethyl amine ester base ethanesulfonate is added, stirred to perform etherification reaction, and then ethanol is added, stirred, filtered, the filter cake is washed with ethanol, and dried to obtain sodium sulfonate base polyvinyl alcohol.

[0010] .

[0011] (3) Add nano-Fe3O4, sodium sulfonate-based polyvinyl alcohol into water, stir and mix, cool in ice bath, add pyrrole, stir, then drop water solution of ferric chloride, stir and react, filter, wash the filter cake with water and ethanol, dry, to obtain poly-pyrrole coated Fe3O4 wave-absorbing agent.

[0012] (4) Add poly-pyrrole coated Fe3O4 wave-absorbing agent, defoaming agent, and leveling agent into polyurethane emulsion, stir and disperse, to obtain wave-absorbing coating.

[0013] (5) Add epoxy resin, glass microbeads, and aerogel powder into ethyl acetate, stir and disperse, then add curing agent, stir, to obtain transition layer slurry.

[0014] (6) Lay the reflective layer on the heat insulation base layer, heat press in a hot press, then coat the transition layer slurry on the surface of the reflective layer, bake and cure, then spray the wave-absorbing coating, bake and cure, to obtain the multi-layer lightweight skin.

[0015] Preferably, the reflective layer is metal mesh or metal film.

[0016] Preferably, the heat insulation base layer is aerogel reinforced ceramic fiber felt.

[0017] Preferably, in (1), the amount of sodium hydroxyethyl sulfonate is 100 parts by weight, the amount of chloroethyl isocyanate is 71-78 parts by weight, and the amount of triethylamine is 56-68 parts by weight.

[0018] Preferably, in (1), the reaction temperature is 50-55℃, and the reaction time is 2-3h.

[0019] Preferably, in (2), the amount of polyvinyl alcohol is 100 parts by weight, the amount of sodium hydroxide is 12-50 parts by weight, and the amount of chloroethyl amine ester-based sodium ethanesulfonate is 20-60 parts by weight.

[0020] Preferably, in (2), the reaction temperature is 50-80℃, and the stirring reaction time is 3-6h.

[0021] Preferably, in (3), the amount of nano-Fe3O4 is 100 parts by weight, the amount of sodium sulfonate-based polyvinyl alcohol is 3-8 parts by weight, the amount of pyrrole is 30-50 parts by weight, and the amount of ferric chloride is 75-140 parts by weight.

[0022] Preferably, in (3), the temperature during stirring and mixing is 25-60℃, and the mixing time is 2-4h.

[0023] Preferably, in (3), the stirring reaction time is 10-16h.

[0024] Preferably, in (4), the amount of polyurethane emulsion is 100 parts by weight, the amount of polypyrrole-coated iron oxide microwave absorber is 16-30 parts by weight, the amount of defoamer is 0.2-0.5 parts by weight, and the amount of leveling agent is 0.1-0.3 parts by weight.

[0025] Preferably, in (6), the coating of the transition layer slurry is cured by first curing at 80-100℃ for 20-30 min, then at 120-140℃ for 2-3 h, and finally at 150-160℃ for 1-1.5 h.

[0026] Preferably, in (6), the microwave absorbing coating is sprayed and baked to cure at 90-100℃ for 3-5 hours.

[0027] Preferably, multi-layered lightweight skin is used in microwave absorbing materials.

[0028] (III) Beneficial technical effects: The sodium sulfonate-based polyvinyl alcohol of the present invention contains a large number of active groups such as hydroxyl groups, which can interact with the surface of nano-Fe3O4 to achieve the dispersion of Fe3O4, which is beneficial to improve the agglomeration of Fe3O4. At the same time, the sulfonate anions introduced by polyvinyl alcohol form doping and electrostatic effects with the imino group of polypyrrole, thereby improving the interfacial performance between Fe3O4 and polypyrrole. Through in-situ polymerization reaction, the coating effect of polypyrrole on Fe3O4 is effectively realized, which is beneficial to improve the impedance matching between the two and improve the microwave absorption performance.

[0029] The sodium sulfonate-based polyvinyl alcohol of the present invention contains a large number of urethane groups that are the same as those in polyurethane, which makes the polypyrrole-coated iron oxide microwave absorber more compatible with polyurethane. It can be uniformly dispersed in the coating to form a continuous microwave absorption network with dielectric and magnetic losses, while reducing the impact on the mechanical properties of the coating, and exhibiting better microwave absorption performance, adhesion and impact resistance.

[0030] This invention uses lightweight aerogel-reinforced ceramic fiber felt as the heat insulation base layer, metal mesh as the reflective layer, and lightweight silica aerogel, glass microspheres and epoxy resin compound as the transition layer to form a skin substrate. Polyurethane microwave absorbing coating is used as the microwave absorbing coating of the skin. The resulting multi-layer skin material has the advantages of being lightweight, having a wide absorption frequency band and strong microwave absorption performance. Attached Figure Description

[0031] Figure 1 This is a structural diagram of a multi-layered lightweight skin.

[0032] Figure 2 It is the infrared spectrum of sodium sulfonate-based polyvinyl alcohol. Detailed Implementation

[0033] The polyurethane emulsion type PU572 with solid content of 40% was from Sanhechuanshun (Suzhou) Technology Co., Ltd. The polyvinyl alcohol type 1788 was from Shandong Yanfa Chemical Co., Ltd. The curing agent type 100S was from Alzchem Group, Germany. The aerogel reinforced ceramic fiber felt was ceramic fiber aerogel from Qingdao Jiujiang Thermal Insulation Energy-saving Materials Co., Ltd. The aerogel powder was silica aerogel powder. The nano-magnetite had an average particle size of 200 nm and was from Qinghe County Ruijiang Metal Material Co., Ltd.

[0034] Example 1:

[0035] (1) 2 g of sodium hydroxyethyl sulfonate was added to 20 mL of acetone, and after stirring, 1.42 g of chloroethyl isocyanate and 1.36 g of triethylamine were added. The mixture was heated to 55°C and stirred and condensed to reflux for 2 h. After distillation under reduced pressure, the product was washed with petroleum ether and then purified by recrystallization in water to obtain sodium chloroethyl amine sulfonate.

[0036] (2) 4 g of polyvinyl alcohol was added to 30 mL of water, heated to 95°C and stirred to dissolve, then cooled to 70°C, 2 g of sodium hydroxide was added, stirred for 20 min, 2.4 g of sodium chloroethyl amine sulfonate was added, stirred for 4 h, and then ethanol was added. After stirring, the mixture was filtered, the filter cake was washed with ethanol and dried to obtain sodium sulfonate-based polyvinyl alcohol. Figure 2 In the infrared spectrum of the sodium sulfonate-based polyvinyl alcohol, the peak at 3403 cm -1 is the stretching vibration peak of -OH in polyvinyl alcohol, the peak at 1721 cm -1 is the stretching vibration peak of C=O in ester group, and the peak at 1278 cm -1 is the stretching vibration peak of sulfonic acid -S=O-.

[0037] (3) 100 g of nano-magnetite and 3 g of sodium sulfonate-based polyvinyl alcohol were added to 8 L of water, stirred and mixed at 40°C for 2 h, cooled in an ice bath, 30 g of pyrrole was added, and then 500 mL of an aqueous solution containing 75 g of ferric chloride was added dropwise after stirring. The mixture was stirred for 12 h, filtered, the filter cake was washed with water and ethanol, and dried to obtain a poly-pyrrole coated four-iron oxide wave-absorbing agent.

[0038] (4) 160 g of poly-pyrrole coated four-iron oxide wave-absorbing agent, 3 g of defoaming agent BYK-024, and 1 g of leveling agent Dow Corning DC67 were added to 1 kg of polyurethane emulsion, and stirred and dispersed for 1 h to obtain a wave-absorbing coating.

[0039] (5) 470 g of epoxy resin E44, 650 g of glass microbeads, and 480 g of aerogel powder were added to 300 mL of ethyl acetate, stirred and dispersed, and then 48 g of curing agent was added. After stirring, a transition layer slurry was obtained.

[0040] (6) The aluminum mesh (opening rate of 50%, line width of 20 μm) is laid as a reflective layer on the aerogel reinforced ceramic fiber felt thermal insulation base layer, and is placed in a hot press for hot pressing, with a temperature of 160°C and a pressure of 2 MPa. Then, a transition layer slurry is coated on the surface of the reflective layer, which is first baked and solidified at 80°C for 30 min, then solidified at 120°C for 3 h, and finally solidified at 160°C for 1 h. Then, the wave-absorbing coating is sprayed, and baked and solidified at 100°C for 3 h, to obtain a multi-layer lightweight skin.

[0041] Example 2:

[0042] (1) 2 g of sodium hydroxyethyl sulfonate is added to 30 mL of acetone, stirred, and then 1.56 g of chloroethyl isocyanate and 1.12 g of triethylamine are added. The mixture is heated to 50°C and stirred and condensed to reflux for 3 h. After distillation under reduced pressure, the product is washed with petroleum ether, and then purified by recrystallization in water to obtain sodium chloroethyl amine ester sulfonate.

[0043] (2) 4 g of polyvinyl alcohol is added to 30 mL of water, heated to 95°C, and stirred to dissolve. Then, the mixture is cooled to 80°C, 0.48 g of sodium hydroxide is added, stirred for 20 min, and then 0.8 g of sodium chloroethyl amine ester sulfonate is added. The mixture is stirred and reacted for 3 h, and then ethanol is added. After stirring, the mixture is filtered, the filter cake is washed with ethanol, and dried to obtain sodium sulfonate-based polyvinyl alcohol.

[0044] (3) 100 g of nano-magnetic iron oxide and 5 g of sodium sulfonate-based polyvinyl alcohol are added to 8 L of water, stirred and mixed at 25°C for 4 h, cooled in an ice bath, and then 40 g of pyrrole is added. After stirring, 650 mL of an aqueous solution containing 110 g of ferric chloride is added dropwise, and the mixture is stirred and reacted for 16 h. After filtration, the filter cake is washed with water and ethanol, and dried to obtain poly-pyrrole coated magnetic iron oxide wave-absorbing agent.

[0045] (4) 240 g of poly-pyrrole coated magnetic iron oxide wave-absorbing agent, 2 g of defoaming agent BYK-024, and 3 g of leveling agent Dow Corning DC67 are added to 1 kg of polyurethane emulsion, and stirred and dispersed for 2 h to obtain a wave-absorbing coating.

[0046] (5) 420 g of epoxy resin E44, 600 g of glass microbeads, and 540 g of aerogel powder are added to 300 mL of ethyl acetate, stirred and dispersed, and then 44 g of a curing agent is added. After stirring, a transition layer slurry is obtained.

[0047] (6) A copper film (thickness of 0.02 mm) is laid as a reflective layer on the aerogel reinforced ceramic fiber felt thermal insulation base layer, and is placed in a hot press for hot pressing, with a temperature of 160°C and a pressure of 2 MPa. Then, a transition layer slurry is coated on the surface of the reflective layer, which is first baked and solidified at 100°C for 20 min, then solidified at 140°C for 2 h, and finally solidified at 150°C for 1.5 h. Then, the wave-absorbing coating is sprayed, and baked and solidified at 90°C for 5 h, to obtain a multi-layer lightweight skin.

[0048] Example 3:

[0049] (1) 4 g of polyvinyl alcohol was added to 40 mL of water, heated to 95°C, stirred and dissolved, then cooled to 50°C, 1.3 g of sodium hydroxide was added, stirred for 20 min, 1.5 g of chloroethyl carbamate sodium sulfonate (prepared according to the method of Example 1) was added, stirred and reacted for 6 h, ethanol was added, stirred and filtered, the filter cake was washed with ethanol and dried to obtain sodium sulfonate-based polyvinyl alcohol.

[0050] (2) 100 g of nanometer-sized magnetite was added to 8 L of water, 8 g of sodium sulfonate-based polyvinyl alcohol was added, stirred and mixed at 60°C for 2 h, cooled in an ice bath, 50 g of pyrrole was added, stirred and 800 mL of an aqueous solution containing 140 g of ferric chloride was added dropwise, stirred and reacted for 16 h, filtered and the filter cake was washed with water and ethanol and dried to obtain a polypyrrole-coated magnetite wave-absorbing agent.

[0051] (3) 300 g of polypyrrole-coated magnetite wave-absorbing agent, 5 g of defoaming agent BYK-024, and 1 g of leveling agent Dow Corning DC67 were added to 1 kg of polyurethane emulsion, stirred and dispersed for 2 h to obtain a wave-absorbing coating.

[0052] (4) 360 g of epoxy resin E44, 520 g of glass microbeads, and 560 g of aerogel powder were added to 300 mL of ethyl acetate, stirred and dispersed, then 38 g of a curing agent was added, stirred and a transition layer slurry was obtained.

[0053] (5) An aluminum mesh (opening rate of 50%, line width of 20 μm) was laid on the aerogel-reinforced ceramic fiber felt heat insulation base layer as a reflective layer, placed in a hot press for hot pressing at a temperature of 170°C and a pressure of 1 MPa, then the transition layer slurry was coated on the surface of the reflective layer, first baked and cured at 80°C for 30 min, then cured at 130°C for 3 h, and finally cured at 160°C for 1 h, then the wave-absorbing coating was sprayed, baked and cured at 90°C for 5 h to obtain a multi-layer lightweight skin.

[0054] Comparative Example 1, the difference between this comparative example and Example 1 is that sodium sulfonate-based polyvinyl alcohol is not added.

[0055] (1) 100 g of nanometer-sized magnetite was added to 8 L of water, stirred at 40°C for 2 h, cooled in an ice bath, 30 g of pyrrole was added, stirred and 500 mL of an aqueous solution containing 75 g of ferric chloride was added dropwise, stirred and reacted for 12 h, filtered and the filter cake was washed with water and ethanol and dried to obtain a polypyrrole-magnetite wave-absorbing agent.

[0056] (2) Add 160 g of polypyrrole-ferroferric oxide wave-absorbing agent, 3 g of defoaming agent BYK-024, and 1 g of leveling agent Dow Corning DC67 to 1 kg of polyurethane emulsion, and stir and disperse for 1 h to obtain a wave-absorbing coating.

[0057] (3) The aluminum grid (opening rate 50%, line width 20 μm) is laid on the aerogel-reinforced ceramic fiber felt heat insulation base layer as a reflective layer, and is placed in a hot press for hot pressing at a temperature of 160°C and a pressure of 2 MPa. Then, the transition layer slurry is coated on the surface of the reflective layer, and is first baked and cured at 80°C for 30 min, then cured at 120°C for 3 h, and finally cured at 160°C for 1 h. Then, the wave-absorbing coating is sprayed, and baked and cured at 100°C for 3 h to obtain a multi-layer lightweight skin.

[0058] Comparative Example 2, the difference between this comparative example and Example 1 is that polyvinyl alcohol is used instead of sodium sulfonate-based polyvinyl alcohol.

[0059] (1) Add 100 g of nano-ferroferric oxide, 3 g of polyvinyl alcohol, and 40°C stirring and mixing for 2 h, and then cool in an ice bath. Add 30 g of pyrrole, stir, and then add 500 mL of an aqueous solution containing 75 g of ferric chloride dropwise. Stir for 12 h, filter, wash the filter cake with water and ethanol, and dry to obtain a polypyrrole-ferroferric oxide wave-absorbing agent.

[0060] (2) Add 160 g of polypyrrole-ferroferric oxide wave-absorbing agent, 3 g of defoaming agent BYK-024, and 1 g of leveling agent Dow Corning DC67 to 1 kg of polyurethane emulsion, and stir and disperse for 1 h to obtain a wave-absorbing coating.

[0061] (3) The aluminum grid (opening rate 50%, line width 20 μm) is laid on the aerogel-reinforced ceramic fiber felt heat insulation base layer as a reflective layer, and is placed in a hot press for hot pressing at a temperature of 160°C and a pressure of 2 MPa. Then, the transition layer slurry is coated on the surface of the reflective layer, and is first baked and cured at 80°C for 30 min, then cured at 120°C for 3 h, and finally cured at 160°C for 1 h. Then, the wave-absorbing coating is sprayed, and baked and cured at 100°C for 3 h to obtain a multi-layer lightweight skin.

[0062] Comparative Example 3, the difference between this comparative example and Example 1 is that sodium dodecyl benzene sulfonate is used instead of sodium sulfonate-based polyvinyl alcohol.

[0063] (1) Add 100 g of nano-ferroferric oxide, 3 g of polyvinyl alcohol, and 40°C stirring and mixing for 2 h, and then cool in an ice bath. Add 30 g of pyrrole, stir, and then add 500 mL of an aqueous solution containing 75 g of ferric chloride dropwise. Stir for 12 h, filter, wash the filter cake with water and ethanol, and dry to obtain a polypyrrole-ferroferric oxide wave-absorbing agent.

[0064] (2) 160 g of the polypyrrole-ferroferric oxide wave-absorbing agent, 3 g of the defoaming agent BYK-024, and 1 g of the leveling agent Dow Corning DC67 were added into 1 kg of the polyurethane emulsion, and stirred and dispersed for 1 h to obtain the wave-absorbing coating.

[0065] (3) The aluminum grid (with an opening rate of 50% and a line width of 20 pm) was laid on the aerogel-reinforced ceramic fiber felt heat insulation base layer as a reflective layer, and was placed in a hot press for hot pressing at a temperature of 160 °C and a pressure of 2 MPa. Then, the transition layer slurry was coated on the surface of the reflective layer, and was baked and cured at 80 °C for 30 min, at 120 °C for 3 h, and at 160 °C for 1 h. Then, the wave-absorbing coating was sprayed, and was baked and cured at 100 °C for 3 h to obtain the multilayer lightweight skin.

[0066] Comparative Example 4, the difference between this comparative example and Example 1 is that sodium hydroxyethyl sulfonate is used instead of sodium sulfonate-based polyvinyl alcohol.

[0067] (1) 100 g of nano-ferroferric oxide, 3 g of sodium hydroxyethyl sulfonate, 40 °C stirring mixed 2 h, cooling in ice bath, 30 g of pyrrole was added, stirred and then 500 mL of aqueous solution containing 75 g of ferric chloride was added dropwise, and stirred for 12 h. After filtration, the filter cake was washed with water and ethanol, and dried to obtain the polypyrrole-ferroferric oxide wave-absorbing agent.

[0068] (2) 160 g of the polypyrrole-ferroferric oxide wave-absorbing agent, 3 g of the defoaming agent BYK-024, and 1 g of the leveling agent Dow Corning DC67 were added into 1 kg of the polyurethane emulsion, and stirred and dispersed for 1 h to obtain the wave-absorbing coating.

[0069] (3) The aluminum grid (with an opening rate of 50% and a line width of 20 pm) was laid on the aerogel-reinforced ceramic fiber felt heat insulation base layer as a reflective layer, and was placed in a hot press for hot pressing at a temperature of 160 °C and a pressure of 2 MPa. Then, the transition layer slurry was coated on the surface of the reflective layer, and was baked and cured at 80 °C for 30 min, at 120 °C for 3 h, and at 160 °C for 1 h. Then, the wave-absorbing coating was sprayed, and was baked and cured at 100 °C for 3 h to obtain the multilayer lightweight skin.

[0070] Comparative Example 5, the difference between this comparative example and Example 1 is that 2-chloroethyl sodium sulfonate (CAS No. 15484-44-3) is used instead of chloroethyl urethane-based ethanesulfonic acid sodium.

[0071] (1) 4 g of polyvinyl alcohol was added into 30 mL of water, heated to 95 °C, and stirred and dissolved. Then, the temperature was cooled to 70 °C, 2 g of sodium hydroxide was added, stirred for 20 min, 2.4 g of 2-chloroethyl sulfonate was added, and stirred for 4 h. Ethanol was added, stirred, filtered, the filter cake was washed with ethanol, and dried to obtain the sodium sulfonate-based polyvinyl alcohol.

[0072] (2) Add 100 g of nanometer-sized magnetite, 3 g of sodium sulfonate-based polyvinyl alcohol to 8 L of water, stir and mix at 40°C for 2 h, cool in an ice bath, add 30 g of pyrrole, stir, and then add 500 mL of an aqueous solution containing 75 g of ferric chloride dropwise, stir for 12 h, filter the cake, wash with water and ethanol, and dry to obtain a polypyrrole-coated magnetite wave-absorbing agent.

[0073] (3) Add 160 g of polypyrrole-coated magnetite wave-absorbing agent, 3 g of defoamer BYK-024, and 1 g of leveling agent Dow Corning DC67 to 1 kg of polyurethane emulsion, stir and disperse for 1 h to obtain a wave-absorbing coating.

[0074] (4) Place an aluminum mesh (opening rate of 50%, line width of 20 μm) as a reflective layer on an aerogel-reinforced ceramic fiber felt thermal insulation base layer, place it in a hot press, heat at a temperature of 160°C and a pressure of 2 MPa, then coat a transition layer slurry on the surface of the reflective layer, first bake and cure at 80°C for 30 min, then cure at 120°C for 3 h, and finally cure at 160°C for 1 h, then spray the wave-absorbing coating, and bake and cure at 100°C for 3 h to obtain a multi-layer lightweight skin.

[0075] The wave-absorbing performance of the multi-layer lightweight skin was tested according to the GJB 2038A-2011 standard. The grid test and adhesion of the polyurethane wave-absorbing coating were tested according to the GB / T 9286-2021 standard, and the impact resistance was tested according to the GB / T 1732-2020 standard.

[0076] Table 1 Performance test

[0077] Reflectance (26.5-40 GHz average, dB) Reflectance (26.5-40 GHz average, dB) Crosshatch test rating (scale) Impact resistance (kg-cm) Example 1 -18.7 -9.5 1 45 Example 2 -31.6 -13.2 2 45 Example 3 -34.4 -14.9 2 35 Comparative Example 1 -14.8 -7.4 3 30 Comparative Example 2 -16.3 -8.1 2 40 Comparative Example 3 -15.8 -7.9 2 35 Comparative Example 4 -15.5 -7.8 3 35 Comparative Example 5 -17.0 -8.6 2 40

[0078] The multi-layer lightweight skin of Comparative Example 1 has a minimum reflectivity of only -14.8 db and -7.4 dB in the frequency bands of 2-18 GHz and 26.5-40 GHz, mainly because the interface performance and impedance matching between polypyrrole and nanometer-sized magnetite are poor, which affects wave absorption. In addition, the nanometer-sized magnetite has poor dispersibility and poor compatibility with polyurethane, and tends to agglomerate in the polyurethane coating, which seriously reduces the wave-absorbing performance and mechanical properties of the coating. The grid test grade is only 3, and the impact resistance is only 30 kg·cm, indicating that the adhesion and impact resistance of the coating are poor.

[0079] Embodiments 1-3 add sodium sulfonate-based polyvinyl alcohol, which contains a large number of active groups such as hydroxyl groups, can form interaction with the surface of nanometer ferroferric oxide, realize the dispersion of ferroferric oxide, and is conducive to improving the agglomeration of ferroferric oxide. At the same time, the sulfonate negative ions introduced by polyvinyl alcohol form doping, electrostatic and other effects with the imino groups of polypyrrole, thereby improving the interface performance between ferroferric oxide and polypyrrole, effectively realizing the coating effect of polypyrrole on ferroferric oxide, and being conducive to improving the impedance matching of the two, improving the wave absorption performance, and sodium sulfonate-based polyvinyl alcohol contains a large number of urethane groups which are the same as polyurethane. ), so that the polypyrrole-coated ferroferric oxide wave-absorbing agent has better compatibility with polyurethane, can be uniformly dispersed in the coating to form a continuous wave-absorbing network, while reducing the influence on the mechanical properties of the coating, and exhibits better wave-absorbing performance, adhesion and impact resistance.

[0080] Comparative Example 2 adds polyvinyl alcohol as a dispersant, which does not contain sulfonic acid groups and urethane groups, Comparative Example 3 uses sodium dodecyl benzene sulfonate as a dispersant, Comparative Example 4 uses sodium hydroxyethyl sulfonate, and Comparative Example 5 uses sodium sulfonate-based polyvinyl alcohol which does not contain urethane groups. The wave-absorbing coatings prepared by the four have poor adhesion and impact resistance, and poor wave-absorbing performance.

Claims

1. A multi-layer lightweight skin, characterized in that, The multi-layer lightweight skin includes a microwave absorbing coating, a transition layer, a reflective layer, and a heat-insulating base layer; The microwave absorbing coating comprises 100 parts by weight of polyurethane emulsion, 16-30 parts by weight of polypyrrole-coated iron oxide microwave absorbing agent, 0.2-0.5 parts by weight of defoamer, and 0.1-0.3 parts by weight of leveling agent; The polypyrrole-coated ferric oxide microwave absorber is prepared by the following method: (1) Add polyvinyl alcohol to water, heat and stir to dissolve, then cool to the reaction temperature, add sodium hydroxide, stir and then add sodium chloroethyl amino ethanesulfonate, stir to react, add ethanol, stir and then filter, wash the filter cake, dry to obtain sodium sulfonate polyvinyl alcohol; (2) Add nano-iron oxide and sodium sulfonate polyvinyl alcohol to water, stir and mix, cool in an ice bath, add pyrrole, stir and then add ferric chloride aqueous solution dropwise, stir to react, filter, wash filter cake, dry, and obtain polypyrrole-coated iron oxide microwave absorber.

2. The multi-layer lightweight skin according to claim 1, characterized in that, The transition layer is composed of glass microspheres, aerogel, epoxy resin, and curing agent; the reflective layer is a metal mesh or a metal film; and the heat insulation base layer is an aerogel-reinforced ceramic fiber felt.

3. The multi-layer lightweight skin according to claim 1, characterized in that, In (1), the amount of polyvinyl alcohol used is 100 parts by weight, the amount of sodium hydroxide used is 12-50 parts by weight, and the amount of sodium chloroethyl urethanesulfonate used is 20-60 parts by weight.

4. The multi-layer lightweight skin according to claim 1, characterized in that, The reaction temperature in (1) is 50-80℃, and the stirring reaction time is 3-6h.

5. The multi-layer lightweight skin according to claim 1, characterized in that, In (2), the amount of nano-ferric oxide is 100 parts by weight, the amount of sodium sulfonate-based polyvinyl alcohol is 3-8 parts by weight, the amount of pyrrole is 30-50 parts by weight, and the amount of ferric chloride is 75-140 parts by weight.

6. The multi-layer lightweight skin according to claim 1, characterized in that, The temperature during stirring and mixing in (2) is 25-60℃, and the mixing time is 2-4h.

7. The multi-layer lightweight skin according to claim 1, characterized in that, The stirring reaction time in (2) is 10-16 h.

8. The multi-layer lightweight skin according to claim 1, characterized in that, The sodium chloroethylamino ethanesulfonate is prepared by the following method: 100 parts by weight of sodium hydroxyethyl sulfonate are added to acetone, and after stirring, 71-78 parts by weight of chloroethyl isocyanate and 56-68 parts by weight of triethylamine are added. The mixture is heated to 50-55°C, stirred, refluxed, and reacted for 2-3 hours. The product is washed with petroleum ether after vacuum distillation, and then purified by recrystallization in water to obtain sodium chloroethylamino ethanesulfonate.

9. A method for preparing a multi-layer lightweight skin as described in any one of claims 1-8, characterized in that, The preparation method is as follows: (1) Add polypyrrole-coated iron oxide microwave absorber, defoamer and leveling agent to polyurethane emulsion, stir and disperse to obtain microwave absorbing coating; (2) Add epoxy resin, glass microspheres and aerogel powder to ethyl acetate, stir and disperse, then add curing agent, stir and obtain transition layer slurry; (3) The reflective layer is laid flat on the heat insulation base layer and placed in a hot press for hot pressing. Then, a transition layer slurry is coated on the surface of the reflective layer, baked and cured, and then a microwave absorbing coating is sprayed and baked and cured to obtain a multi-layer lightweight skin.

10. The application of a multilayer lightweight skin obtained by the preparation method as described in claim 9 in microwave absorbing materials.

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