Method for manufacturing a multilayer lightweight skin and use thereof

Abstract

This invention relates to the field of microwave absorbing skin technology, and discloses a method for preparing and applying a multi-layer lightweight skin. The multi-layer lightweight skin of this invention includes a microwave absorbing coating, a transition layer, a reflective layer, and a heat-insulating base layer. The microwave absorbing coating includes 100 parts by weight of polyurethane emulsion and 16-30 parts by weight of polypyrrole-coated iron oxide microwave absorbing agent, etc. In this invention, a lightweight aerogel-reinforced ceramic fiber felt is used as the heat-insulating base layer, a metal mesh is used as the reflective layer, and a lightweight silica aerogel, glass microspheres, and epoxy resin composite are used as the transition layer. As the substrate of the skin, the 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.

Description

Technical Field

[0001] This invention relates to the field of microwave absorbing skin technology, specifically to a method for preparing and applying a multi-layer lightweight skin. Background Technology

[0002] Microwave-absorbing materials can dissipate electromagnetic waves by converting them into heat energy through dielectric loss and magnetic loss, and have important applications in electromagnetic shielding, stealth materials, and national defense. Microwave-absorbing materials mainly include microwave-absorbing coatings, microwave-absorbing skins, and microwave-absorbing rubbers. They are mainly made by adding microwave-absorbing media to the materials, such as magnetic loss media such as iron(III) oxide, dielectric loss media such as polypyrrole, and resistive loss media such as graphene.

[0003] Coating the surface of skin materials with resin coatings can impart excellent waterproof, corrosion-resistant, and wave-absorbing properties. Among these, polyurethane coatings are widely used due to their good toughness and excellent weather resistance. Adding wave-absorbing materials such as polypyrrole and iron oxide to the coating can also give it good wave-absorbing properties. Patent application CN119265941A discloses a self-cleaning sensing composite coating for fabrics and its preparation method, which uses polypyrrole, iron oxide, and polyurea to form a composite coating with good sensing and wave-absorbing properties. However, nano-iron oxide is prone to agglomeration, and polypyrrole has poor compatibility with polyurethane. Adding these two materials to the polyurethane coating will affect the coating's wave-absorbing and mechanical properties. Summary of the Invention

[0004] (I) Technical problem to be solved: In view of the shortcomings of the existing technology, the present invention provides a method for preparing and applying a multi-layer lightweight skin, which solves the problem of poor wave absorption performance of the skin coating material.

[0005] (II) Technical solution: A multi-layer lightweight skin, consisting of a microwave absorbing coating, a transition layer, a reflective layer and a heat insulation base layer.

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

[0007] (1) Sodium hydroxyethyl sulfonate was added to acetone, stirred, and then chloroethyl isocyanate and triethylamine were added. The mixture was stirred and reacted. The product was washed with petroleum ether after vacuum distillation, and then purified by recrystallization in water to obtain sodium chloroethyl amino ethanesulfonate. The reaction formula is as follows:

[0008] .

[0009] (2) Add polyvinyl alcohol to water, heat and stir to dissolve, then cool to the reaction temperature, add sodium hydroxide catalyst, stir and then add sodium chloroethyl amino ethanesulfonate, stir to carry out etherification reaction, add ethanol, stir and filter, wash the filter cake with ethanol, dry to obtain sodium sulfonate polyvinyl alcohol.

[0010] .

[0011] (3) 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 and wash the filter cake with water and ethanol, dry to obtain polypyrrole-coated iron oxide microwave absorber.

[0012] (4) Add polypyrrole-coated iron oxide microwave absorber, defoamer and leveling agent to polyurethane emulsion, stir and disperse to obtain microwave absorbing coating.

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

[0014] (6) 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 the microwave absorbing coating is sprayed and baked and cured to obtain a multi-layer lightweight skin.

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

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

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

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

[0019] Preferably, in (2), the amount of polyvinyl alcohol is 100 parts by weight, sodium hydroxide is 12-50 parts by weight, and sodium chloroethyl urethanesulfonate 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-ferric oxide is 100 parts by weight, sodium sulfonate polyvinyl alcohol is 3-8 parts by weight, pyrrole is 30-50 parts by weight, and ferric chloride is 75-140 parts by weight.

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

[0023] Preferably, the stirring reaction time in (3) 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 cured by baking 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, model PU572, with a solid content of 40%, is sourced from Sanheshun (Suzhou) Technology Co., Ltd. The polyvinyl alcohol, model 1788, is sourced from Shandong Yanfa Chemical Co., Ltd. The curing agent, model DYHARD® 100S, is sourced from Alzchem Group, Germany. The aerogel-reinforced ceramic fiber felt is ceramic fiber aerogel, sourced from Qingdao Jiuqiang Thermal Insulation and Energy Saving Materials Co., Ltd. The aerogel powder is silica aerogel powder. The nano-ferric oxide, with an average particle size of 200nm, is sourced from Qinghe County Ruijiang Metal Materials Co., Ltd.

[0034] Example 1:

[0035] (1) Add 2g of sodium hydroxyethyl sulfonate to 20mL of acetone, stir, add 1.42g of chloroethyl isocyanate and 1.36g of triethylamine, heat to 55℃, stir and reflux for 2h, wash the product with petroleum ether after vacuum distillation, and then recrystallize and purify in water to obtain sodium chloroethyl amino ethanesulfonate.

[0036] (2) Add 4g of polyvinyl alcohol to 30mL of water, heat to 95℃, stir to dissolve, then cool to 70℃, add 2g of sodium hydroxide, stir for 20min, add 2.4g of sodium chloroethyl amino ester ethanesulfonate, stir to react for 4h, add ethanol, stir and filter, wash the filter cake with ethanol, dry, and obtain sodium sulfonate polyvinyl alcohol. Figure 2 In the infrared spectrum, 3403 cm⁻¹ -1 The stretching vibration peak of -OH in polyvinyl alcohol, 1721 cm⁻¹ -1 It is the stretching vibration peak of C=O in the ester group, 1278 cm⁻¹ -1 It is the stretching vibration peak of sulfonic acid -S=O-.

[0037] (3) Add 100g of nano-iron oxide and 3g of sodium sulfonate polyvinyl alcohol to 8L of water, stir and mix at 40℃ for 2h, cool in an ice bath, add 30g of pyrrole, stir and add 500mL of aqueous solution containing 75g of ferric chloride, stir and react for 12h, filter and wash the filter cake with water and ethanol, dry to obtain polypyrrole-coated iron oxide microwave absorber.

[0038] (4) Add 160g of polypyrrole-coated iron oxide microwave absorber, 3g of defoamer BYK-024 and 1g of leveling agent Dow Corning DC67 to 1kg of polyurethane emulsion, stir and disperse for 1h to obtain microwave absorbing coating.

[0039] (5) Add 470g of epoxy resin E44, 650g of glass microspheres and 480g of aerogel powder to 300mL of ethyl acetate, stir and disperse, then add 48g of curing agent and stir to obtain a transition layer slurry.

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

[0041] Example 2:

[0042] (1) Add 2g of sodium hydroxyethyl sulfonate to 30mL of acetone, stir, add 1.56g of chloroethyl isocyanate and 1.12g of triethylamine, heat to 50℃, stir and reflux for 3h, wash the product with petroleum ether after vacuum distillation, and then recrystallize and purify in water to obtain sodium chloroethyl amino ethanesulfonate.

[0043] (2) Add 4g of polyvinyl alcohol to 30mL of water, heat to 95℃, stir to dissolve, then cool to 80℃, add 0.48g of sodium hydroxide, stir for 20min, add 0.8g of sodium chloroethyl amino ester ethanesulfonate, stir to react for 3h, add ethanol, stir and filter, wash the filter cake with ethanol, dry to obtain sodium sulfonate polyvinyl alcohol.

[0044] (3) Add 100g of nano-iron oxide and 5g of sodium sulfonate polyvinyl alcohol to 8L of water, stir and mix at 25℃ for 4h, cool in an ice bath, add 40g of pyrrole, stir and add 650mL of aqueous solution containing 110g of ferric chloride, stir and react for 16h, filter and wash the filter cake with water and ethanol, dry to obtain polypyrrole-coated iron oxide microwave absorber.

[0045] (4) Add 240g of polypyrrole-coated iron oxide microwave absorber, 2g of defoamer BYK-024 and 3g of leveling agent Dow Corning DC67 to 1kg of polyurethane emulsion, stir and disperse for 2h to obtain microwave absorbing coating.

[0046] (5) Add 420g of epoxy resin E44, 600g of glass microspheres and 540g of aerogel powder to 300mL of ethyl acetate, stir and disperse, then add 44g of curing agent and stir to obtain a transition layer slurry.

[0047] (6) A copper film (thickness of 0.02 mm) is laid flat on the aerogel-reinforced ceramic fiber felt heat insulation substrate as a reflective layer and placed in a hot press for hot pressing at 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, and it is first baked and cured at 100°C for 20 min, then cured at 140°C for 2 h, and finally cured at 150°C for 1.5 h. Then, a microwave absorbing coating is sprayed and baked and cured at 90°C for 5 h to obtain a multi-layer lightweight skin.

[0048] Example 3:

[0049] (1) Add 4g of polyvinyl alcohol to 40mL of water, heat to 95℃, stir to dissolve, then cool to 50℃, add 1.3g of sodium hydroxide, stir for 20min, add 1.5g of sodium chloroethyl amino ester ethanesulfonate (prepared according to the method of Example 1), stir to react for 6h, add ethanol, stir and filter, wash the filter cake with ethanol, dry to obtain sodium sulfonate polyvinyl alcohol.

[0050] (2) Add 100g of nano-iron oxide and 8g of sodium sulfonate polyvinyl alcohol to 8L of water, stir and mix at 60℃ for 2h, cool in an ice bath, add 50g of pyrrole, stir and add 800mL of aqueous solution containing 140g of ferric chloride, stir and react for 16h, filter and wash the filter cake with water and ethanol, dry to obtain polypyrrole-coated iron oxide microwave absorber.

[0051] (3) Add 300g of polypyrrole-coated iron oxide microwave absorber, 5g of defoamer BYK-024 and 1g of leveling agent Dow Corning DC67 to 1kg of polyurethane emulsion, stir and disperse for 2h to obtain microwave absorbing coating.

[0052] (4) Add 360g of epoxy resin E44, 520g of glass microspheres and 560g of aerogel powder to 300mL of ethyl acetate, stir and disperse, then add 38g of curing agent, and stir to obtain a transition layer slurry.

[0053] (5) The aluminum mesh (with an opening ratio of 50% and a line width of 20μm) is laid flat on the aerogel-reinforced ceramic fiber felt heat insulation substrate as a reflective layer and placed in a hot press for hot pressing at a temperature of 170℃ and a pressure of 1MPa. Then, a transition layer slurry is coated on the surface of the reflective layer, and it is first baked and cured at 80℃ for 30min, then cured at 130℃ for 3h, and finally cured at 160℃ for 1h. Then, the microwave absorbing coating is sprayed and baked and cured at 90℃ for 5h to obtain a multi-layer lightweight skin.

[0054] Comparative Example 1 differs from Example 1 in that sodium sulfonate-based polyvinyl alcohol is not added.

[0055] (1) Add 100g of nano-iron oxide to 8L of water, stir at 40℃ for 2h, cool in an ice bath, add 30g of pyrrole, stir, add 500mL of aqueous solution containing 75g of ferric chloride, stir and react for 12h, filter, wash the filter cake with water and ethanol, dry, and obtain polypyrrole-iron oxide microwave absorber.

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

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

[0058] Comparative Example 2 differs from Example 1 in that it uses polyvinyl alcohol instead of sodium sulfonate-based polyvinyl alcohol.

[0059] (1) Add 100g of nano-iron oxide and 3g of polyvinyl alcohol to 8L of water, stir and mix at 40℃ for 2h, cool in an ice bath, add 30g of pyrrole, stir and add 500mL of aqueous solution containing 75g of ferric chloride, stir and react for 12h, filter and wash the filter cake with water and ethanol, dry to obtain polypyrrole-iron oxide microwave absorber.

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

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

[0062] Comparative Example 3 differs from Example 1 in that sodium dodecylbenzene sulfonate is used instead of sodium sulfonate-based polyvinyl alcohol.

[0063] (1) Add 100g of nano-Fe3O4 and 3g of sodium dodecylbenzenesulfonate to 8L of water, stir and mix at 40℃ for 2h, cool in an ice bath, add 30g of pyrrole, stir and add 500mL of aqueous solution containing 75g of ferric chloride, stir and react for 12h, filter and wash the filter cake with water and ethanol, dry to obtain polypyrrole-Fe3O4 microwave absorber.

[0064] (2) Add 160g of polypyrrole-ferric oxide microwave absorber, 3g of defoamer BYK-024 and 1g of leveling agent Dow Corning DC67 to 1kg of polyurethane emulsion, stir and disperse for 1h to obtain microwave absorbing coating.

[0065] (3) The aluminum mesh (with an opening ratio of 50% and a line width of 20μm) is laid flat on the aerogel-reinforced ceramic fiber felt heat insulation substrate as a reflective layer and placed in a hot press for hot pressing at a temperature of 160℃ and a pressure of 2MPa. Then, a transition layer slurry is coated on the surface of the reflective layer, and it is first baked and cured at 80℃ for 30min, then cured at 120℃ for 3h, and finally cured at 160℃ for 1h. Then, the microwave absorbing coating is sprayed and baked and cured at 100℃ for 3h to obtain a multi-layer lightweight skin.

[0066] Comparative Example 4 differs from Example 1 in that sodium hydroxyethyl sulfonate is used instead of sodium sulfonate-based polyvinyl alcohol.

[0067] (1) Add 100g of nano-Fe3O4 and 3g of sodium hydroxyethyl sulfonate to 8L of water, stir and mix at 40℃ for 2h, cool in an ice bath, add 30g of pyrrole, stir and then add 500mL of aqueous solution containing 75g of ferric chloride, stir and react for 12h, filter and wash the filter cake with water and ethanol, dry to obtain polypyrrole-Fe3O4 microwave absorber.

[0068] (2) Add 160g of polypyrrole-ferric oxide microwave absorber, 3g of defoamer BYK-024 and 1g of leveling agent Dow Corning DC67 to 1kg of polyurethane emulsion, stir and disperse for 1h to obtain microwave absorbing coating.

[0069] (3) The aluminum mesh (with an opening ratio of 50% and a line width of 20μm) is laid flat on the aerogel-reinforced ceramic fiber felt heat insulation substrate as a reflective layer and placed in a hot press for hot pressing at a temperature of 160℃ and a pressure of 2MPa. Then, a transition layer slurry is coated on the surface of the reflective layer, and it is first baked and cured at 80℃ for 30min, then cured at 120℃ for 3h, and finally cured at 160℃ for 1h. Then, the microwave absorbing coating is sprayed and baked and cured at 100℃ for 3h to obtain a multi-layer lightweight skin.

[0070] Comparative Example 5 differs from Example 1 in that sodium 2-chloroethyl sulfonate (CAS No. 15484-44-3) is used instead of sodium chloroethyl amino ethanesulfonate.

[0071] (1) Add 4g of polyvinyl alcohol to 30mL of water, heat to 95℃, stir to dissolve, then cool to 70℃, add 2g of sodium hydroxide, stir for 20min, add 2.4g of sodium 2-chloroethyl sulfonate, stir to react for 4h, add ethanol, stir and filter, wash the filter cake with ethanol, dry to obtain sodium sulfonate-based polyvinyl alcohol.

[0072] (2) Add 100g of nano-iron oxide and 3g of sodium sulfonate polyvinyl alcohol to 8L of water, stir and mix at 40℃ for 2h, cool in an ice bath, add 30g of pyrrole, stir and add 500mL of aqueous solution containing 75g of ferric chloride, stir and react for 12h, filter and wash the filter cake with water and ethanol, dry to obtain polypyrrole-coated iron oxide microwave absorber.

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

[0074] (4) The aluminum mesh (with an opening ratio of 50% and a line width of 20μm) is laid flat on the aerogel-reinforced ceramic fiber felt heat insulation substrate as a reflective layer and placed in a hot press for hot pressing at a temperature of 160℃ and a pressure of 2MPa. Then, a transition layer slurry is coated on the surface of the reflective layer, and it is first baked and cured at 80℃ for 30min, then cured at 120℃ for 3h, and finally cured at 160℃ for 1h. Then, the microwave absorbing coating is sprayed and baked and cured at 100℃ for 3h to obtain a multi-layer lightweight skin.

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

[0076] Table 1 Performance Tests

[0077] Reflectivity (minimum value from 2-18 GHz, dB) Reflectivity (average, dB, 26.5–40 GHz) Cross-cut test grade (level) 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 lowest reflectivity of the multilayer lightweight skin in Comparative Example 1 was only -14.8dB and -7.4dB in the 2-18GHz and 26.5-40GHz frequency bands, respectively. This was mainly due to the poor interfacial performance and impedance matching between polypyrrole and nano-ferric oxide, which affected the wave absorption. At the same time, the nano-ferric oxide had poor dispersion and poor compatibility with polyurethane, and was prone to agglomeration in the polyurethane coating, which seriously reduced the wave absorption performance and mechanical properties of the coating. The cross-cut test level was only 3, and the impact resistance was only 30 kg·cm, indicating poor adhesion and impact resistance of the coating.

[0079] Examples 1-3 incorporated sodium sulfonate-based polyvinyl alcohol, which contains numerous active groups such as hydroxyl groups. These groups interact with the surface of nano-ferric oxide (Fe3O4), dispersing the Fe3O4 and improving its agglomeration. Simultaneously, the sulfonate anions introduced by polyvinyl alcohol form doping and electrostatic interactions with the imino groups of polypyrrole, thereby enhancing the interfacial properties between Fe3O4 and polypyrrole. This effectively achieves the coating effect of polypyrrole on Fe3O4, improving impedance matching and microwave absorption performance. Sodium sulfonate-based polyvinyl alcohol contains a large number of urethane groups, similar to those in polyurethane. This process improves the compatibility between polypyrrole-coated iron oxide microwave absorber and polyurethane, allowing it to be uniformly dispersed in the coating to form a continuous microwave absorbing network. It also reduces the impact on the mechanical properties of the coating, resulting in better microwave absorption performance, adhesion, and impact resistance.

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

Claims

1. A multi-layered 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-Fe3O4 and sodium sulfonate-based 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 Fe3O4 microwave absorber. 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.

2. The multi-layer lightweight skin of claim 1, wherein, 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. A method for preparing a multi-layer lightweight skin as described in any one of claims 1-7, 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.

9. The application of a multilayer lightweight skin obtained by the preparation method as described in claim 8 in microwave absorbing materials.

Images