Low-defect wave-absorbing foam material and preparation method thereof

Abstract

The invention relates to the technical field of foam materials, and particularly discloses a low-defect wave-absorbing foam material and a preparation method thereof. The low-defect wave-absorbing foam material is prepared from the following raw materials in parts by mass: 400 to 600 parts of PVC (Polyvinyl Chloride) resin, 350 to 550 parts of isocyanate, 20 to 40 parts of curing agent, 40 to 80 parts of foaming agent, 6 to 10 parts of cross-linking agent, 10 to 30 parts of plasticizer, 2 to 8 parts of stabilizer and 40 to 70 parts of wave-absorbing material, the wave-absorbing material has a core-shell structure with a carboxylated carbon nanotube as a core and modified ferrite as a shell, the modified ferrite is ferrite containing a component A and a component B; the general formula of the ferrite is AxB (1-x) Fe2O4, the component A comprises at least two variable valence metals; and the component B comprises at least two non-variable valence metals. The low-defect wave-absorbing foam material prepared by the preparation method disclosed by the invention realizes broadband multi-absorption valley and high mechanical property.

Description

Technical Field

[0001] This application relates to the technical field of foam materials, and more specifically, to a low-defect microwave absorbing foam material and its preparation method. Background Technology

[0002] Microwave-absorbing materials are materials that can absorb or significantly reduce the electromagnetic wave energy received on their surface, and have very low reflection, refraction, and scattering, thereby reducing electromagnetic interference. With the rapid development of industries such as 5G communication, new energy vehicles, intelligent transportation, and defense equipment, the complexity of the electromagnetic environment has increased significantly, making the demand for "broadband, high-performance, and lightweight" microwave-absorbing materials increasingly urgent. In 5G base station scenarios, microwave-absorbing materials need to balance lightweight support and multi-band electromagnetic interference suppression; in the field of new energy vehicle battery packs, microwave-absorbing foams need to meet both electromagnetic compatibility and lightweight requirements.

[0003] In the current field of microwave absorbing materials, polyvinyl chloride (PVC) foam has become one of the mainstream matrices for microwave absorbing composite materials due to its advantages such as lightweight and adjustable mechanical properties. Existing technologies typically achieve electromagnetic loss by composite carbon-based and magnetic microwave absorbing agents into the PVC matrix, but its performance still has significant shortcomings due to limitations in formulation design and preparation processes. For example, patent application CN119613892A discloses a microwave absorbing PVC structured foam, comprising the following raw material components by weight: 400-600 parts of PVC resin, 300-550 parts of isocyanate, 10-50 parts of curing agent, 30-80 parts of foaming agent, 0.1-10 parts of crosslinking agent, 5-30 parts of plasticizer, and 30-90 parts of electromagnetic wave absorber; the curing agent is an acid anhydride compound; the electromagnetic wave absorber is conductive carbon black and modified carbon nanotubes, wherein the modified carbon nanotubes are carboxyl functional group modified carbon nanotubes or hydroxyl modified carbon nanotubes.

[0004] In this technical solution, the microwave absorbing filler uses two types of carbon-based materials: conductive carbon black and carboxyl / hydroxyl-modified carbon nanotubes. Both are typical electrically depleting microwave absorbing agents, capable of dissipating electromagnetic waves solely through dielectric loss, thus constructing a single dielectric loss absorption mechanism. Due to the overlapping loss principles of the two microwave absorbing agents, the loss effect in the mid-to-low frequency band (2~8GHz) mainly exhibits a single absorption trough; the absorption performance curve only covers a limited frequency band of 2~12GHz. Summary of the Invention

[0005] To address the problems in the prior art, this application provides a low-defect microwave absorbing foam material and its preparation method.

[0006] In a first aspect, this application provides a low-defect microwave absorbing foam material, employing the following technical solution: A low-defect microwave absorbing foam material, comprising the following raw materials in parts by weight: 400-600 parts of PVC resin, 350-550 parts of isocyanate, 20-40 parts of curing agent, 40-80 parts of foaming agent, 6-10 parts of crosslinking agent, 10-30 parts of plasticizer, 2-8 parts of stabilizer and 40-70 parts of microwave absorbing material; The microwave absorbing material has a core-shell structure with carboxylated carbon nanotubes as the core and modified ferrite as the shell. The modified ferrite is a ferrite comprising component A and component B; the general formula of the ferrite is A. x B 1-x Fe2O4; Component A comprises at least two variable-valence metals; component B comprises at least two non-variable-valence metals.

[0007] In this technical solution, carboxylated carbon nanotubes easily overlap to form a conductive network in the foam matrix, mainly contributing to conductive losses. The carboxyl functional groups on their surface not only improve dispersibility but also serve as active sites for bonding with subsequent components. Using a multi-component doped ferrite as the shell, the introduction of variable-valence metal components can create controllable defects in the lattice, enhancing interfacial polarization losses. The synergistic doping of at least two non-variable-valence metal components can effectively control the complex permeability of the ferrite, providing significant magnetic losses. This core-shell structure tightly integrates dielectric and magnetic losses at the nanoscale, achieving synergistic control of electromagnetic parameters and providing an intrinsic basis for efficient electromagnetic wave absorption across a wide frequency range. Simultaneously, the strong chemical bonding between the core and shell avoids phase separation of the filler during processing, facilitating uniform dispersion in the composite material.

[0008] Preferably, the method for preparing the microwave absorbing material includes the following steps: Variable valence metal salt, non-variable valence metal salt and iron salt are dissolved in an ethanol aqueous solution, a complexing agent is added and mixed evenly, carboxylated carbon nanotubes are added and mixed evenly, the pH is adjusted to 8-9, mixed for 2-3 hours, dried, placed in a sintering device under an inert atmosphere, heated to 800-900℃, held for 2-4 hours, and cooled to obtain the microwave absorbing material.

[0009] In this technical solution, the dissolved metal salt precursor is adsorbed on the surface of carboxylated carbon nanotubes, and through the complexation effect of the complexing agent, a uniformly wrapped ferrite precursor layer is generated in situ on the surface of the carbon nanotubes under alkaline conditions. Subsequently, the precursor layer is crystallized into a complete ferrite crystalline shell in an inert atmosphere. During this process, the variable valence metal undergoes a valence state change, and the resulting lattice defects synergistically with the permeability regulation of the non-variable valence metal of component B, enabling the absorbing material to form multiple absorption troughs in the 2~18GHz frequency band, ultimately achieving broadband strong absorption.

[0010] Preferably, the complexing agent is citric acid.

[0011] Preferably, the molar ratio of the variable valence metal salt, non-variable valence metal salt, iron salt and complexing agent is (0.2~0.4):(0.6~0.8):2:(6~9).

[0012] Preferably, the ratio of the iron salt to the carboxylated carbon nanotubes is 1 mol: (10~20) g.

[0013] Preferably, the variable valence metal salt is selected from at least two of variable valence rare earth metal salts and variable valence transition metal salts.

[0014] Preferably, the variable-valence rare earth metal salt is a cerium salt or a praseodymium salt.

[0015] Preferably, the variable valence transition metal salt is a manganese salt or a cobalt salt.

[0016] Preferably, the non-variable valence metal salt is selected from at least two of nickel salts, aluminum salts, and zinc salts.

[0017] Preferably, the method for preparing the microwave absorbing material further includes a step of mixing with phosphate after the drying step and before the sintering step.

[0018] Preferably, the molar ratio of the phosphate to the iron salt is (0.03~0.05):1.

[0019] In this technical solution, phosphates (such as sodium phosphite) can form a thin glassy phase during sintering, filling the tiny defects in the ferrite shell and improving the stability of magnetic permeability.

[0020] Preferably, the isocyanate is diphenylmethane diisocyanate or hexamethylene diisocyanate.

[0021] More preferably, the isocyanate is diphenylmethane diisocyanate.

[0022] In this technical solution, isocyanate can react with components such as curing agents in the system to form a stable chemical cross-linking network, which enhances the strength of the matrix structure; this network also helps to anchor and stabilize the microwave absorbing material and reduce interface defects.

[0023] Preferably, the curing agent includes anhydride compounds and dicyandiamide.

[0024] Preferably, the mass ratio of the acid anhydride to dicyandiamide is (3~5):1.

[0025] Preferably, the acid anhydride compound is phthalic anhydride or pyromellitic dianhydride.

[0026] More preferably, the acid anhydride compound is pyromellitic dianhydride.

[0027] In this technical solution, acid anhydride compounds and dicyandiamide form a synergistic curing system, which improves the curing reaction efficiency and ensures that the crosslinking reaction is fully carried out. The crosslinking network formed by the compound system is more uniform and dense, which can significantly improve the material's resistance to deformation and structural stability, while enhancing the matrix's ability to bear and disperse the microwave absorbing material.

[0028] Preferably, the foaming agent is mainly a foaming agent and an activator.

[0029] Preferably, the main foaming agent is azodicarbonamide.

[0030] Preferably, the activator is zinc stearate.

[0031] Preferably, the mass ratio of the main foaming agent to the activator is (5~10):1.

[0032] Preferably, the crosslinking agent is trimethylolpropane triacrylate or divinylbenzene.

[0033] More preferably, the crosslinking agent is trimethylolpropane triacrylate.

[0034] In this technical solution, trimethylolpropane triacrylate can rapidly improve the melt strength of PVC resin, effectively inhibit cell merging and collapse during foaming, and ensure the integrity and uniformity of the cell structure; at the same time, the network formed by its cross-linking can strengthen the mechanical strength of the matrix.

[0035] Preferably, the plasticizer is a citrate ester or epoxidized soybean oil.

[0036] Preferably, the citrate ester is tributyl citrate or trioctyl citrate.

[0037] Preferably, the citrate ester is tributyl citrate.

[0038] Preferably, the stabilizer is a calcium-zinc stabilizer.

[0039] Preferably, the PVC resin is a suspension PVC resin powder with a degree of polymerization of 1000~1500.

[0040] In this technical solution, calcium-zinc stabilizers can effectively inhibit the degradation reaction of PVC resin at high processing temperatures, avoiding structural defects caused by small molecule impurities or degradation products; suspension PVC resin has suitable melt strength, which not only ensures the stable growth of cells during foaming, but also takes into account the requirements of material lightweighting and mechanical support.

[0041] Preferably, the low-defect absorbing foam material further includes 2-3 parts by weight of lubricant.

[0042] Preferably, the lubricant is calcium stearate.

[0043] Preferably, the low-defect microwave absorbing foam material further includes 30-50 parts by weight of a rubber toughening component and 2-4 parts by weight of a compatibilizer.

[0044] Preferably, the rubber toughening component is nitrile rubber powder.

[0045] Preferably, the compatibilizer is chlorinated polyethylene.

[0046] In this technical solution, nitrile rubber powder can significantly improve the flexibility and impact resistance of the material, reducing the risk of breakage due to stress during processing or use; the compatibilizer can form a continuous transition layer at the interface between the rubber and the matrix, eliminating phase separation defects between the two and ensuring that the nitrile rubber is uniformly dispersed in the matrix.

[0047] Secondly, this application provides a method for preparing a low-defect microwave absorbing foam material, comprising the following steps: PVC resin, plasticizer, and stabilizer are placed in a mixer and mixed at 80-100°C for 5-10 minutes. Microwave-absorbing material is added, and mixing continues for 10-20 minutes. The temperature is then lowered to 40-50°C, and isocyanate, curing agent, foaming agent, and crosslinking agent are added. The mixture is mixed for 5-15 minutes, molded, and foamed. After cooling and demolding, the material is finished in saturated steam to obtain a low-defect microwave-absorbing foam material.

[0048] Preferably, the specific conditions for the molding foaming are: pressure 10~14MPa, temperature 160~180℃, and time 20~25min.

[0049] Preferably, the specific steps for post-treatment in the saturated steam are as follows: first, treat in saturated steam at 90~100℃ and 100% humidity for 6~8 hours, and then treat in saturated steam at 60~70℃ and 100% humidity for 5~7 days.

[0050] In this technical solution, PVC resin is first premixed with plasticizer and stabilizer at a suitable temperature to ensure uniform fusion of matrix components, providing a stable foundation for the subsequent dispersion of microwave absorbing materials. Continuous mixing after adding the microwave absorbing material ensures its uniform dispersion. Adding reactive components after cooling avoids premature reaction and the generation of impurities and defects. Molding foaming is used to ensure that foaming and curing occur simultaneously, ensuring uniform and complete cell structure. Saturated steam finishing can effectively eliminate internal stress in the material, further improving structural stability and performance consistency, ultimately obtaining a low-defect, stable microwave absorbing foam material.

[0051] Preferably, after adding the microwave absorbing material, the step of adding a lubricant is also included.

[0052] Preferably, after adding the stabilizer, the method further includes the steps of adding a rubber toughening component and a compatibilizer.

[0053] In summary, this application has the following beneficial effects: This application, firstly, employs a core-shell structure with carboxylated carbon nanotubes as the core and multi-doped ferrite as the shell as the microwave absorbing material, achieving synergy between dielectric loss and magnetic loss at the nanoscale, thus enabling the material to exhibit multi-band absorption characteristics over a wide frequency range. Secondly, by optimizing the foaming and cross-linking system of the PVC matrix and matching it with a corresponding molding foaming process, the uniformity and stability of the microwave absorption performance are ensured. Optionally, the flexibility of the material can be further improved by introducing toughening components. Attached Figure Description

[0054] Figure 1 : A physical image of the low-defect absorbing foam material in Embodiment 1 of this application; Figure 2 The reflectivity test curve of the low-defect absorbing foam material in Example 1 of this application in the 2~18GHz frequency band; Figure 3 The reflectivity test curve of the low-defect absorbing foam material in the 2~18GHz frequency band in Example 3 of this application; Figure 4 The reflectivity test curve of the low-defect absorbing foam material in the 2~18GHz frequency band in Example 5 of this application; Figure 5 The reflectivity test curve of the low-defect absorbing foam material in the 1~18GHz frequency band in Example 7 of this application; Figure 6 The reflectivity test curves of the low-defect absorbing foam material in Comparative Example 1 of this application in the 2~18GHz frequency band. Detailed Implementation

[0055] The present application will be further described in detail below with reference to the embodiments.

[0056] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this application are all commercially available.

[0057] The carboxylated carbon nanotubes are carboxylated multi-walled carbon nanotubes with a diameter of 5~50nm and a length of 0.5~30µm, and more preferably, a length of 1~20µm; the content of carboxyl functional groups is not less than 0.7wt%, and the purity is not less than 95%.

[0058] Preparation of microwave absorbing materials in Examples 1-7 Preparation Example 1 The preparation method of the microwave absorbing material in this example includes the following steps: 0.05 mol of cobalt nitrate hexahydrate, 0.05 mol of manganese nitrate hexahydrate, 0.2 mol of nickel nitrate hexahydrate, 0.2 mol of zinc nitrate hexahydrate, and 1 mol of iron nitrate nonahydrate were added to 2 L of a 1:1 volume ratio ethanol-water mixture. The mixture was stirred in a water bath at 55 °C for 30 min at a stirring speed of 200 rpm. Then, 3 mol of citric acid was added, and the mixture was stirred for another 60 min. Next, a pre-dispersion of carboxylated carbon nanotubes (10 g of carboxylated carbon nanotubes and 200 mL of a 1:1 volume ratio ethanol-water mixture, ultrasonically dispersed at 300 W for 30 min) was added. The pH was then adjusted to 8.0 with 8% ammonia solution, and the mixture was stirred for 2 h. The mixture was dried at 100 °C to constant weight, ground, and then heated to 800 °C at a rate of 3 °C / min under a nitrogen atmosphere. The temperature was maintained for 4 h, and the mixture was allowed to cool naturally to room temperature. The mixture was then ground and dispersed, and passed through a 200-mesh standard sieve to obtain the microwave absorbing material.

[0059] Preparation Example 2 The preparation method of the microwave absorbing material in this example includes the following steps: 0.075 mol of cerium nitrate hexahydrate, 0.075 mol of manganese nitrate hexahydrate, 0.15 mol of nickel nitrate hexahydrate, 0.05 mol of aluminum nitrate nonahydrate, 0.15 mol of zinc nitrate hexahydrate, and 1 mol of ferric nitrate nonahydrate were added to 2 L of a 1:1 volume ratio ethanol-water mixture. The mixture was stirred in a 55°C water bath for 30 min at 200 rpm. Then, 3.5 mol of citric acid was added, and the mixture was stirred for another 60 min. Finally, carboxyl groups were added. The pre-dispersion solution of carboxylated carbon nanotubes (10g of carboxylated carbon nanotubes and 200mL of ethanol-water mixture with a volume ratio of 1:1, ultrasonically dispersed evenly with an ultrasonic power of 300W and an ultrasonic time of 30min) was then adjusted to pH 8.0 with 8% ammonia water by mass, stirred and mixed for 3h, dried at 100℃ to constant weight, ground, heated to 800℃ at 3℃ / min under a nitrogen atmosphere, held at that temperature for 4h, naturally cooled to room temperature, ground and dispersed, and passed through a 200-mesh standard sieve to obtain the microwave absorbing material.

[0060] Preparation Example 3 The preparation method of the microwave absorbing material in this example includes the following steps: 0.075 mol of cerium nitrate hexahydrate, 0.075 mol of praseodymium nitrate hexahydrate, 0.15 mol of nickel nitrate hexahydrate, 0.05 mol of aluminum nitrate nonahydrate, 0.15 mol of zinc nitrate hexahydrate, and 1 mol of ferric nitrate nonahydrate were added to 2 L of a 1:1 volume ratio ethanol-water mixture. The mixture was stirred in a 55°C water bath for 30 min at 200 rpm. Then, 3.5 mol of citric acid was added, and the mixture was stirred for another 60 min. Finally, carboxyl groups were added. A pre-dispersion of carboxylated carbon nanotubes (15g of carboxylated carbon nanotubes and 400mL of a 1:1 volume ratio ethanol-water mixture, ultrasonically dispersed uniformly at 300W for 30min) was prepared. The pH was then adjusted to 8.0 with 8% ammonia, stirred for 2h, dried at 100℃ to constant weight, ground, heated to 800℃ at 3℃ / min under a nitrogen atmosphere, held for 4h, naturally cooled to room temperature, ground and dispersed, and passed through a 200-mesh standard sieve to obtain the microwave absorbing material.

[0061] Preparation Example 4 The preparation method of the microwave absorbing material in this example includes the following steps: 0.1 mol of cerium nitrate hexahydrate, 0.1 mol of cobalt nitrate hexahydrate, 0.125 mol of nickel nitrate hexahydrate, 0.05 mol of aluminum nitrate nonahydrate, 0.125 mol of zinc nitrate hexahydrate, and 1 mol of ferric nitrate nonahydrate were added to 2 L of a 1:1 volume ratio ethanol-water mixture. The mixture was stirred in a 55°C water bath for 30 min at 200 rpm. Then, 3.5 mol of citric acid was added, and the mixture was stirred for another 60 min. Finally, carboxylation was added. The pre-dispersion solution of carbon nanotubes (20g of carboxylated carbon nanotubes and 400mL of ethanol-water mixture with a volume ratio of 1:1, ultrasonically dispersed evenly with an ultrasonic power of 300W and an ultrasonic time of 30min) was then adjusted to pH 9.0 with 8% ammonia water by mass, stirred and mixed for 3h, dried at 100℃ to constant weight, ground, heated to 900℃ at 3℃ / min under a nitrogen atmosphere, held at that temperature for 2h, naturally cooled to room temperature, ground and dispersed, and passed through a 200-mesh standard sieve to obtain the microwave absorbing material.

[0062] Preparation Example 5 The preparation method of the microwave absorbing material in this example includes the following steps: 0.1 mol of cerium nitrate hexahydrate, 0.1 mol of praseodymium nitrate hexahydrate, 0.125 mol of nickel nitrate hexahydrate, 0.05 mol of aluminum nitrate nonahydrate, 0.125 mol of zinc nitrate hexahydrate, and 1 mol of ferric nitrate nonahydrate were added to 2 L of a 1:1 volume ratio ethanol-water mixture. The mixture was stirred in a 55°C water bath for 30 min at 200 rpm. Then, 4.5 mol of citric acid was added, and the mixture was stirred for another 60 min. Finally, carboxylation was added. The pre-dispersion solution of carbon nanotubes (20g of carboxylated carbon nanotubes and 400mL of ethanol-water mixture with a volume ratio of 1:1, ultrasonically dispersed evenly with an ultrasonic power of 300W and an ultrasonic time of 30min) was then adjusted to pH 9.0 with 8% ammonia water by mass, stirred and mixed for 3h, dried at 100℃ to constant weight, ground, heated to 900℃ at 3℃ / min under a nitrogen atmosphere, held at that temperature for 3h, naturally cooled to room temperature, ground and dispersed, and passed through a 200-mesh standard sieve to obtain the microwave absorbing material.

[0063] Preparation Example 6 The preparation method of the microwave absorbing material in this example includes the following steps: 0.1 mol of cerium nitrate hexahydrate, 0.05 mol of manganese nitrate hexahydrate, 0.05 mol of praseodymium nitrate hexahydrate, 0.05 mol of aluminum nitrate nonahydrate, 0.25 mol of zinc nitrate hexahydrate, and 1 mol of ferric nitrate nonahydrate were added to 2 L of a 1:1 volume ratio ethanol-water mixture. The mixture was stirred in a 55°C water bath for 30 min at 200 rpm. Then, 4.5 mol of citric acid was added, and the mixture was stirred for another 60 min. Finally, pre-dispersed carboxylated carbon nanotubes were added. The mixture (20g of carboxylated carbon nanotubes and 400mL of a 1:1 ethanol-water mixture was ultrasonically dispersed until uniform, with an ultrasonic power of 300W and an ultrasonic time of 30min). The pH was then adjusted to 9.0 with 8% ammonia water, stirred and mixed for 2h, dried at 100℃ to constant weight, mixed and ground with 0.03mol sodium phosphite, heated to 900℃ at 3℃ / min under a nitrogen atmosphere, held for 2h, naturally cooled to room temperature, ground and dispersed, and passed through a 200-mesh standard sieve to obtain the microwave absorbing material.

[0064] Preparation Example 7 The preparation method of the microwave absorbing material in this example includes the following steps: Take 0.1 mol of cerium nitrate hexahydrate, 0.05 mol of manganese nitrate hexahydrate, 0.05 mol of praseodymium nitrate hexahydrate, 0.125 mol of nickel nitrate hexahydrate, 0.05 mol of aluminum nitrate nonahydrate, 0.125 mol of zinc nitrate hexahydrate, and 1 mol of ferric nitrate nonahydrate and add them to 2 L of a 1:1 volume ratio ethanol-water mixture. Stir in a 55°C water bath for 30 min at 200 rpm. Then add 4.5 mol of citric acid and continue stirring for 60 min. Finally, add the carboxyl group. A pre-dispersion of carboxylated carbon nanotubes (20g of carboxylated carbon nanotubes and 400mL of a 1:1 ethanol-water mixture, ultrasonically dispersed uniformly at 300W for 30min) was prepared. The pH was then adjusted to 9.0 with 8% ammonia, stirred for 2h, dried at 100℃ to constant weight, mixed and ground with 0.05mol sodium phosphite, heated to 900℃ at 3℃ / min under a nitrogen atmosphere, held for 2h, naturally cooled to room temperature, ground and dispersed, and passed through a 200-mesh standard sieve to obtain the microwave absorbing material.

[0065] Example 1 The method for preparing the low-defect microwave absorbing foam material in this embodiment includes the following steps: 400g of PVC resin, 10g of epoxidized soybean oil, and 2g of calcium-zinc stabilizer were placed in a high-speed mixer and mixed at 80°C for 5 minutes. Then, 40g of the microwave absorbing material from Preparation Example 1 was added, and the mixture was mixed for another 10 minutes. The mixture was then cooled to 40°C, and 350g of hexamethylene diisocyanate, 15g of phthalic anhydride, 5g of dicyandiamide, 33g of azodicarbonamide, 7g of zinc stearate, and 6g of divinylbenzene were added. The mixture was mixed for 5 minutes, poured into a mold, placed in a hot press, pressurized to 10MPa, and kept at 160°C for 20 minutes. After depressurization and cooling, the mixture was demolded and placed in saturated steam at 90°C and 100% humidity for 6 hours. Then, it was placed in saturated steam at 60°C and 100% humidity for 5 days to obtain a low-defect microwave absorbing foam material.

[0066] Example 2 The method for preparing the low-defect microwave absorbing foam material in this embodiment includes the following steps: 600g of PVC resin, 30g of trioctyl citrate, and 8g of calcium-zinc stabilizer were placed in a high-speed mixer and mixed at 100°C for 10 minutes. Then, 70g of the microwave absorbing material from Preparation Example 2 and 3g of calcium stearate were added, and the mixture was continued for 20 minutes. The temperature was lowered to 50°C, and then 550g of diphenylmethane diisocyanate, 33g of pyromellitic dianhydride, 7g of dicyandiamide, 73g of azodicarbonamide, 7g of zinc stearate, and 10g of trimethylolpropane triacrylate were added. The mixture was mixed for 15 minutes, poured into a mold, placed in a hot press, pressurized to 14MPa, and kept at 180°C for 20 minutes. After depressurization and cooling, the material was demolded and placed in saturated steam at 100°C and 100% humidity for 8 hours. Then, it was placed in saturated steam at 70°C and 100% humidity for 7 days to obtain a low-defect microwave absorbing foam material.

[0067] Example 3 The method for preparing the low-defect microwave absorbing foam material in this embodiment includes the following steps: 500g of PVC resin, 20g of tributyl citrate, and 6g of calcium-zinc stabilizer were placed in a high-speed mixer and mixed at 100°C for 10 minutes. Then, 45g of the microwave absorbing material and 2g of calcium stearate from Preparation Example 3 were added, and the mixture was continued to mix for 20 minutes. The temperature was then lowered to 50°C, and 460g of diphenylmethane diisocyanate, 28g of pyromellitic dianhydride, 7g of dicyandiamide, 56g of azodicarbonamide, 7g of zinc stearate, and 8g of trimethylolpropane triacrylate were added. The mixture was mixed for 15 minutes, poured into a mold, placed in a hot press, pressurized to 13MPa, and kept at 170°C for 25 minutes. After depressurization and cooling, the material was demolded and placed in saturated steam at 100°C and 100% humidity for 8 hours. Then, it was placed in saturated steam at 70°C and 100% humidity for 7 days to obtain a low-defect microwave absorbing foam material.

[0068] Example 4 The difference between this embodiment and embodiment 3 is as follows: The microwave absorbing material was prepared in Example 4; Everything else is the same as in Example 3.

[0069] Example 5 The difference between this embodiment and embodiment 3 is as follows: The microwave absorbing material was prepared in Example 5; Everything else is the same as in Example 3.

[0070] Example 6 The difference between this embodiment and embodiment 3 is as follows: The microwave absorbing material was prepared in Example 6; Everything else is the same as in Example 3.

[0071] Example 7 The difference between this embodiment and embodiment 3 is as follows: The microwave absorbing material was prepared in Example 7; Everything else is the same as in Example 3.

[0072] Example 8 The method for preparing the low-defect microwave absorbing foam material in this embodiment includes the following steps: 500g of PVC resin, 20g of tributyl citrate, 6g of calcium-zinc stabilizer, 30g of nitrile rubber powder, and 2g of chlorinated polyethylene were placed in a high-speed mixer and mixed at 100°C for 10 minutes. Then, 45g of the microwave absorbing material from Preparation Example 3 and 2g of calcium stearate were added, and the mixture was continued for 20 minutes. The temperature was lowered to 50°C, and then 460g of diphenylmethane diisocyanate, 28g of pyromellitic dianhydride, 7g of dicyandiamide, 56g of azodicarbonamide, 7g of zinc stearate, and 8g of trimethylolpropane triacrylate were added. The mixture was mixed for 15 minutes, poured into a mold, placed in a hot press, pressurized to 13MPa, and kept at 170°C for 25 minutes. After depressurization and cooling, the material was demolded and placed in saturated steam at 100°C and 100% humidity for 8 hours. Then, it was placed in saturated steam at 70°C and 100% humidity for 7 days to obtain a low-defect microwave absorbing foam material.

[0073] Example 9 The method for preparing the low-defect microwave absorbing foam material in this embodiment includes the following steps: 500g of PVC resin, 20g of tributyl citrate, 6g of calcium-zinc stabilizer, 50g of nitrile rubber powder, and 4g of chlorinated polyethylene were placed in a high-speed mixer and mixed at 100°C for 10 minutes. Then, 45g of the microwave absorbing material from Preparation Example 3 and 3g of calcium stearate were added, and the mixture was continued to mix for 20 minutes. The mixture was then cooled to 50°C, and 460g of diphenylmethane diisocyanate, 28g of pyromellitic dianhydride, 7g of dicyandiamide, 56g of azodicarbonamide, 7g of zinc stearate, and 8g of trimethylolpropane triacrylate were added. The mixture was mixed for 15 minutes, poured into a mold, placed in a hot press, pressurized to 13MPa, and kept at 170°C for 25 minutes. After depressurization and cooling, the mixture was demolded and placed in saturated steam at 100°C and 100% humidity for 8 hours. Then, it was placed in saturated steam at 70°C and 100% humidity for 7 days to obtain a low-defect microwave absorbing foam material.

[0074] Comparative Example 1 The difference between this comparative example and Example 1 is as follows: The preparation method of the microwave absorbing material in this comparative example includes the following steps: 0.05 mol of cobalt nitrate hexahydrate, 0.05 mol of manganese nitrate hexahydrate, 0.2 mol of nickel nitrate hexahydrate, 0.2 mol of zinc nitrate hexahydrate, and 1 mol of iron nitrate nonahydrate were added to 2 L of a 1:1 volume ratio ethanol-water mixture. The mixture was stirred in a water bath at 55 °C for 30 min at a stirring speed of 200 rpm. Then, 3 mol of citric acid was added, and the mixture was stirred for another 60 min. The pH was then adjusted to 8.0 using 8% ammonia solution, and the mixture was stirred for 2 h. The mixture was dried at 100 °C to constant weight. After mixing and grinding with 10 g of carboxylated carbon nanotubes, the mixture was heated to 800 °C at a rate of 3 °C / min under a nitrogen atmosphere and held at that temperature for 4 h. After naturally cooling to room temperature, the mixture was ground and dispersed, and then passed through a 200-mesh standard sieve to obtain the microwave absorbing material.

[0075] Everything else is the same as in Example 1.

[0076] Performance testing The low-defect absorbing foam materials prepared in Examples 1-9 and Comparative Example 1 were sampled and their performance was tested, as shown in Table 1.

[0077] Table 1 Performance test data of Examples 1-9 and Comparative Example 1

[0078] Combination Figures 1-6 As shown in Table 1, and from Examples 1-7 and Comparative Example 1, the core-shell structure absorbing material constructed in situ achieves a synergistic improvement in both absorption and mechanical properties compared to physically mixed materials of the same composition. The reflectivity and compressive strength of all examples are significantly better than those of the comparative example. Figure 6 The reflectance curve of the middle (Comparative Example 1) shows a single absorption trough, and the reflectance rebounds significantly after 10 GHz; Figure 2 The reflectivity curve of (Example 1) shows a double absorption trough, and the reflectivity tends to stabilize after 10 GHz, indicating that the basic core-shell structure has strong absorption characteristics. Figure 3 The multi-absorption trough curves in Example 3 show that increasing the doping amount of rare earth variable valence metals and carboxylated carbon nanotubes can effectively broaden the effective absorption band of the material. Figure 4 The multi-absorption valley distribution in Example 5 demonstrates the effect of increasing rare earth doping on the regulation of magnetic loss frequency band. Figure 5 The curve in (Example 7) is flatter and wider, which is a comprehensive reflection of the material's ability to achieve stable and efficient absorption over a wider frequency range.

[0079] As can be seen from Examples 8-9, the mechanical properties of the material were further optimized by introducing rubber toughening components, while maintaining excellent wave absorption performance, thus expanding its application potential in scenarios requiring high impact resistance.

[0080] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A low-defect microwave absorbing foam material, characterized in that, Raw materials including the following parts by weight: 400-600 parts of PVC resin, 350-550 parts of isocyanate, 20-40 parts of curing agent, 40-80 parts of foaming agent, 6-10 parts of crosslinking agent, 10-30 parts of plasticizer, 2-8 parts of stabilizer and 40-70 parts of microwave absorbing material; The microwave absorbing material has a core-shell structure with carboxylated carbon nanotubes as the core and modified ferrite as the shell. The modified ferrite is a ferrite containing component A and component B; The general formula of the ferrite is A x B 1-x Fe2O4; Component A comprises at least two variable-valence metals; component B comprises at least two non-variable-valence metals.

2. The low-defect absorbing foam material according to claim 1, characterized in that, The method for preparing the microwave absorbing material includes the following steps: Variable valence metal salt, non-variable valence metal salt and iron salt are dissolved in an ethanol aqueous solution, a complexing agent is added and mixed evenly, carboxylated carbon nanotubes are added and mixed evenly, the pH is adjusted to 8-9, mixed for 2-3 hours, dried, placed in a sintering device under an inert atmosphere, heated to 800-900℃, held for 2-4 hours, and cooled to obtain the microwave absorbing material.

3. The low-defect absorbing foam material according to claim 2, characterized in that, The molar ratio of the variable valence metal salt, non-variable valence metal salt, iron salt and complexing agent is (0.2~0.4):(0.6~0.8):2:(6~9).

4. The low-defect absorbing foam material according to claim 2, characterized in that, The ratio of the iron salt to the carboxylated carbon nanotubes is 1 mol: (10~20) g.

5. The low-defect absorbing foam material according to claim 2, characterized in that, The variable valence metal salt is selected from at least two of the variable valence rare earth metal salts and variable valence transition metal salts.

6. The low-defect absorbing foam material according to claim 2, characterized in that, The non-variable valence metal salt is selected from at least two of nickel salts, aluminum salts, and zinc salts.

7. The low-defect absorbing foam material according to claim 2, characterized in that, The method for preparing the microwave absorbing material includes a step of mixing with phosphate after the drying step and before the sintering step.

8. The low-defect absorbing foam material according to claim 7, characterized in that, The molar ratio of the phosphate to the iron salt is (0.03~0.05):

1.

9. The low-defect absorbing foam material according to claim 1, characterized in that, The isocyanate is diphenylmethane diisocyanate or hexamethylene diisocyanate.

10. A method for preparing a low-defect microwave absorbing foam material as described in claim 1, characterized in that, Includes the following steps: PVC resin, plasticizer, and stabilizer are placed in a mixer and mixed at 80-100°C for 5-10 minutes. Microwave-absorbing material is added, and mixing continues for 10-20 minutes. The temperature is then lowered to 40-50°C, and isocyanate, curing agent, foaming agent, and crosslinking agent are added. The mixture is mixed for 5-15 minutes, molded, and foamed. After cooling and demolding, the material is finished in saturated steam to obtain a low-defect microwave-absorbing foam material.

Images