Organic modified expanded graphite composite polymer wave-absorbing material and preparation method therefor

Abstract

The present invention belongs to the technical field of wave-absorbing materials, and provides an organic modified expanded graphite composite polymer wave-absorbing material and a preparation method therefor. The wave-absorbing material comprises conductive polymer foam particles and modified expanded graphite attached to the surface of the conductive polymer foam particles. 0.5-20 kg of modified expanded graphite is attached to the surface per cubic meter of the conductive polymer foam particles. The absorption principle of the organic modified expanded graphite composite polymer wave-absorbing material of the present invention lies in that electromagnetic waves are converted into heat to be dissipated, and when the conductive polymer foam particles are of a ring structure, due to large surface area of the particles, more organic modified expanded graphite can be adhered without affecting particle compression molding, which not only significantly increases the oxygen index, but also, thanks to the ring structure, enhances the tolerance power of the ring polymer wave-absorbing material to exceed 2500 W during high-power testing, and the heat dissipation effect thereof is superior to that of a wave-absorbing material pressed from solid foam particles.

Description

An organically modified expanded graphite composite polymer microwave absorbing material and its preparation method Technical Field

[0001] This invention relates to the field of microwave absorbing materials, and in particular to an organically modified expanded graphite composite polymer microwave absorbing material and its preparation method. Background Technology

[0002] In applications such as microwave anechoic chambers, military vehicles, and aircraft camouflage, microwave absorbing materials for anechoic chambers have extremely high requirements for flame retardancy and power handling, while those for military vehicles and aircraft camouflage have high requirements for flame retardancy and even higher requirements for mechanical properties. Currently, microwave absorbing materials for military vehicles and aircraft camouflage are mainly made of thermosetting polyurethane, thermosetting adhesives, and wood chips pressed into sheets. However, due to their relatively brittle mechanical properties, the vibrations from high-speed aircraft flight, vehicle movement, and door opening and closing often cause the absorbing materials to break and fall off.

[0003] When high-power testing is required in a microwave anechoic chamber, the continuous wave power radiation density that ordinary sponge absorbing material can withstand is about 1200W. Due to the high water absorption rate of sponge, the electromagnetic parameters of sponge change significantly when the air moisture content is high on rainy days, which has a significant impact on the performance of the anechoic chamber.

[0004] Traditional polystyrene foam microwave absorbing materials have a continuous wave power radiation density of about 800W. Due to the good adhesion of the adhesive, polystyrene foam is generally made by mixing thermoplastic adhesives with absorbers and flame retardants to coat the surface of the foam particles and then pressing them into microwave absorbing materials. However, because polystyrene foam itself has poor mechanical strength and poor temperature resistance, the material will deform and shrink when the temperature exceeds 80℃.

[0005] Conventional polypropylene or polyethylene foam microwave absorbing materials with poor flame retardancy have a continuous wave power radiation density tolerance of approximately 1200W. Exceeding this tolerance density, the insufficiently mechanically strong absorbing material will deform, detach, and ignite if its flame retardancy is poor. To improve flame retardancy, if thermoplastic adhesives are used to coat the surface of polypropylene and polyethylene foam particles with absorbents and flame retardants before pressing them into microwave absorbing materials, the poor adhesion of the adhesive to the polypropylene or polyethylene foam surface, resulting in a layer of adhesive between the foam particles, will significantly reduce the mechanical strength of the finished material. When the material is broken, the fracture surface shows a tear between the foam particles. Generally, the temperature resistance of thermoplastic adhesives is lower than that of the polypropylene and polyethylene foam themselves. Therefore, if the microwave absorbing material is bonded by thermoplastic adhesives, its continuous wave power radiation density tolerance will be less than 1200W.

[0006] Currently manufactured polypropylene or polyethylene microwave absorbing materials have different oil absorption values, iodine absorption values, and specific surface areas due to variations in carbon black, graphite, and conductive agents of different specifications. Even when the same type of conductive agent powder is added in the same proportion, different extrusion processes can lead to different dispersion effects, resulting in significant differences in resistance. Consequently, the electromagnetic parameters of the final microwave absorbing materials will vary considerably.

[0007] Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of existing technologies and provide an organically modified expanded graphite composite polymer microwave absorbing material and its preparation method. Due to the unique and reliable flame-retardant mechanism of expanded graphite, a low-softening-point organic material is used to coat the surface of the expanded graphite. A certain proportion of modified expanded graphite is then adhered to the surface of conductive polymer foam particles using a hot-melt method. While ensuring the flame-retardant performance of the microwave absorbing material, regardless of the density of the polymer foam particles, an adhesion rate of 0.5-20 kg / m³ is achieved on the surface of each cubic meter of conductive polymer foam particles. 3 Expanded graphite, along with the flame retardant inside the conductive polymer foam particles and the modified expanded graphite on the surface, works synergistically to not only solve the problem of high oxygen index in conductive polymer foam microwave absorbing materials, but also greatly improve the mechanical strength and continuous wave power tolerance performance of polymer foam microwave absorbing materials.

[0009] The technical solution adopted in this invention is as follows:

[0010] An organic modified expanded graphite composite polymer microwave absorbing material, comprising conductive polymer foam particles and modified expanded graphite attached to the surface of the conductive polymer foam particles, wherein 0.5-20 kg of modified expanded graphite is attached to the surface of each cubic meter of conductive polymer foam particles.

[0011] Preferably, the organic modified expanded graphite composite polymer microwave absorbing material comprises, by weight, 60-93 parts of expanded graphite, 2-40 parts of low softening point organic material, 0.1-20 parts of plasticizer, 0.1-25 parts of conductive agent, and 0.1-5 parts of coupling agent.

[0012] Preferably, the organic modified expanded graphite composite polymer microwave absorbing material is wherein: the low softening point organic material is selected from one or more of polyvinyl butyral, polyvinyl acetate, acrylic resin, modified acrylic resin, maleic anhydride-grafted ethylene-acrylic acid copolymer, ethylene-acrylic acid copolymer, phenolic resin, aromatic hydrocarbon-modified terpene resin, dammar resin, aldehyde-ketone resin, chlorinated polypropylene, chloroacetic acid resin, and soluble polyurethane.

[0013] Preferably, in the organic modified expanded graphite composite polymer microwave absorbing material: the conductive polymer foam particles are selected from conductive polypropylene foam particles and conductive polyethylene foam particles; the shape of the conductive polymer foam particles is selected from columnar, annular, and spherical; the resistance of the conductive polymer foam particles is 300 ohms-200 MΩ; the particle size is 1-6 mm, including both diameter and length; and both the diameter and length of the conductive polymer foam particles are within the range of 1-6 mm.

[0014] Preferably, the organic modified expanded graphite composite polymer microwave absorbing material comprises, by weight, 5-70 parts of polypropylene or polyethylene resin with a melting point greater than 120°C, 30-90 parts of conductive masterbatch, 2-30 parts of flame retardant masterbatch, 0.1-2 parts of nucleating agent masterbatch, and 0.3-1 parts of antioxidant masterbatch.

[0015] Preferably, in the organic modified expanded graphite composite polymer microwave absorbing material, the resistance of the conductive masterbatch is 10 ohms to 200K ohms.

[0016] Preferably, in the organic modified expanded graphite composite polymer microwave absorbing material, the flame retardant masterbatch comprises, by mass percentage, 40-60% polypropylene or polyethylene resin and 40-60% flame retardant, wherein the flame retardant is selected from one or more of aluminum phosphate, zinc phosphate, aluminum tripolyphosphate, hydroxyethylidene diphosphonic acid, aluminum dihydrogen phosphate, ammonium polyphosphate, pentaerythritol aluminum phosphate, coated red phosphorus, decabromodiphenyl ethane, and brominated polystyrene.

[0017] This invention also provides a method for preparing an organically modified expanded graphite composite polymer microwave absorbing material, comprising the following steps:

[0018] Step S1. By weight, add 60-93 parts of expanded graphite to a mixer, control the temperature of the mixer to 80-100℃, then dilute 0.1-5 parts of coupling agent with solvent and spray it onto the surface of expanded graphite and dry it. Then, dissolve 2-40 parts of low softening point organic material with solvent, and add 0.1-20 parts of plasticizer and 0.1-25 parts of conductive agent to obtain a mixture. Finally, use a timed automatic sprayer to spray the mixture onto the surface of the expanded graphite during stirring, and dry it to obtain modified expanded graphite.

[0019] Step S2. Mix 5-70 parts of polypropylene or polyethylene resin, 30-90 parts of conductive masterbatch, 2-30 parts of flame retardant masterbatch, 0.1-2 parts of nucleating agent masterbatch, and 0.3-1 parts of antioxidant masterbatch and extrude the mixture through a twin-screw extruder to obtain polymer microparticles.

[0020] Step S3. The polymer microparticles obtained in step S2 are put into the reactor, water and dispersant are added, then heated and carbon dioxide is introduced to reach the target temperature and pressure for foaming, then the material is released and washed, and finally dried to obtain conductive polymer foam particles.

[0021] Step S4. Add the conductive polymer foam particles obtained in step S3 to a mixer, control the temperature of the mixer to 100-120℃, then add modified expanded graphite and stir, and then cool to obtain the composite material.

[0022] Step S5. The composite material obtained in step S4 is molded into a microwave absorbing material using a foam molding machine.

[0023] Preferably, in the preparation method of the organic modified expanded graphite composite polymer microwave absorbing material, the solvent in step S1 is one or more of water, ethanol, n-butanol, ethyl acetate, acetone, toluene, xylene, butyl acetate, cyclohexanone, isoamyl acetate, ethylene glycol ethyl ether acetate, and ammonia.

[0024] Preferably, in the preparation method of the organic modified expanded graphite composite polymer microwave absorbing material, the polymer microparticles in step S2 are one of columnar microparticles, ring-shaped microparticles, and spherical microparticles. When the polymer microparticles are columnar microparticles, the resistivity of the polymer microparticles is 50 ohms-200K ohms, the particle length is 0.5-5mm, and the diameter is 0.5-2mm; when the polymer microparticles are ring-shaped microparticles, the resistivity of the polymer microparticles is 50 ohms-200K ohms, the inner diameter is 0.1-0.5mm, the outer diameter is 0.6-2mm, and the length is 1-5mm; when the polymer microparticles are spherical microparticles, the resistivity of the polymer microparticles is 50 ohms-200K ohms, and the diameter is 0.5-1.8mm.

[0025] The advantages of this invention are:

[0026] (1) In the organic modified expanded graphite composite polymer microwave absorbing material and its preparation method described in this invention, the flame retardant masterbatch inside the conductive polymer foam particles and the modified expanded graphite on the surface work together to not only solve the problem of high oxygen index in the microwave absorbing material manufactured by molding conductive polymer foam particles, but also because the modified expanded graphite is uniformly and discontinuously distributed on the surface of the foam particles, and no organic adhesive completely covers the surface of the foam particles, the foam particles are not affected by the weldability and conductivity continuity when they are steam heated and extruded inside the mold of the foam molding machine. At the same time, the organic material on the surface of the organic modified expanded graphite is also melted together with the surface of the foam particles, which greatly improves the mechanical strength and power resistance performance of the microwave absorbing material manufactured by molding composite material.

[0027] (2) The absorption principle of the microwave absorbing material is to convert electromagnetic waves into heat and dissipate them. In the organic modified expanded graphite composite polymer microwave absorbing material and its preparation method described in this invention, when the conductive polymer foam particles are in a ring structure, the surface area of ​​the particles is large. Without affecting the particle molding, more modified expanded graphite can be adhered, which can not only greatly improve the oxygen index, but also the heat dissipation effect of the ring particle microwave absorbing material is far better than that of the microwave absorbing material pressed by solid foam particles. In high power tests, the ring structure can increase the power tolerance of the ring polymer microwave absorbing material to more than 2500W. Attached Figure Description

[0028] Figure 1 is a SEM image of the composite material prepared in Example 1.

[0029] Figure 2 is a SEM image of the composite material prepared in Example 2.

[0030] Figure 3 is a SEM image of the composite material prepared in Example 2 after it has been cut open.

[0031] Figure 4 is a schematic diagram of the plate-type microwave absorbing material with grooved surface prepared in Examples 1-2.

[0032] Figure 5 is a magnified view of the part indicated by circle A in Figure 4. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Unless otherwise stated, the terminology used herein should be understood in accordance with the conventional usage of those skilled in the art.

[0034] As used herein, the low softening point organic material is an organic material with a glass transition temperature below 100°C. The low softening point organic material has good flexibility and will not melt when hot-melt attached to polymer foam particles, and the adhesion is good. Preferred low softening point organic materials in this application are one or more of the following: polyvinyl butyral, polyvinyl acetate, acrylic resin, modified acrylic resin, maleic anhydride-grafted ethylene-acrylic acid copolymer, ethylene-acrylic acid copolymer, phenolic resin, aromatic modified terpene resin, dammar resin, aldehyde-ketone resin, chlorinated polypropylene, chloroacetic acid resin, and soluble polyurethane.

[0035] Preferably, the polymer microparticle low softening point organic material of the present invention is one or more of acrylic resin, modified acrylic resin, maleic anhydride-grafted ethylene-acrylic acid copolymer, aromatic hydrocarbon-modified terpene resin, ethylene-acrylic acid copolymer, and chlorinated polypropylene.

[0036] As used in this article, the continuous wave power withstand performance refers to microwave signals with continuous waveforms, typically between 1 GHz and 100 GHz. When continuously emitting electromagnetic waves, the material has high requirements for temperature resistance and flame retardancy. When continuously emitting electromagnetic waves, the material will continuously heat up without cooling down. The absorbing material can convert most of the incident electromagnetic waves into heat energy and dissipate it. A small portion will be transmitted. The continuous accumulation of heat can melt or burn the absorbing material.

[0037] As used herein, the polymer microparticles are microparticles obtained by mixing polypropylene or polyethylene resin with a melting point greater than 120°C, conductive masterbatch, flame retardant masterbatch, nucleating agent masterbatch, and antioxidant masterbatch, and extruding them through a twin-screw extruder. Melting point is the critical temperature at which a solid substance transforms into a liquid; it is the specific temperature at which a crystalline substance transforms from a solid to a liquid state. The polymer microparticles are one of columnar microparticles, cyclic microparticles, or spherical microparticles. When the polymer microparticles are columnar, their resistance is 50 ohms-200K ohms, with a particle length of 0.5-5mm and a diameter of 0.5-2mm; when the polymer microparticles are ring-shaped, their resistance is 50 ohms-200K ohms, with an inner diameter of 0.1-0.5mm, an outer diameter of 0.6-2mm, and a length of 1-5mm; when the polymer microparticles are spherical, their resistance is 50 ohms-200K ohms and their diameter is 0.5-1.8mm. By extruding the polymer microparticles into a ring structure, the power tolerance performance of the microwave absorbing material can be improved.

[0038] Preferably, when the polymer microparticles of the present invention are columnar microparticles, the particle length is 1-4 mm and the diameter is 0.8-1 mm; when the polymer microparticles are ring-shaped microparticles, the inner diameter is 0.2-0.4 mm, the outer diameter is 0.8-1.5 mm, and the length is 2-4 mm; when the polymer microparticles are spherical microparticles, the diameter is 0.8-1 mm.

[0039] Preferably, the conductive polymer foam particles of the present invention have a resistance of 300 ohms-200 MΩ and a particle size of 1-6 mm. The particle size includes both diameter and length. The diameter and length of the conductive polymer foam particles are both within the range of 1-6 mm, preferably 1.5-2 mm in diameter and 2-3 mm in length. Smaller particle sizes can increase the total number of foam particles and the total surface area per cubic meter. The more foam particles there are, the larger the total surface area. The more dispersed the fixed-mass organically modified expanded graphite is on the surface of the foam particles, the less impact the organically modified expanded graphite has on foam molding.

[0040] The modified expanded graphite of this invention comprises 60-93 parts expanded graphite, 2-40 parts low-softening-point organic material, 0.1-20 parts plasticizer, 0.1-25 parts conductive agent, and 0.1-5 parts coupling agent. Since the expanded graphite cannot adhere to the surface of polypropylene and polyethylene resin foam particles without modification, it needs to be modified first to allow an organic material with good adhesion to polypropylene and polyethylene foam to adhere to its surface. This allows the expanded graphite to adhere to the surface of the polypropylene and polyethylene foam particles. The preferred low-softening-point organic material of this invention is selected from one or more of the following: polyvinyl butyral, polyvinyl acetate, acrylic resin, modified acrylic resin, maleic anhydride-grafted ethylene-acrylic acid copolymer, ethylene-acrylic acid copolymer, phenolic resin, aromatic hydrocarbon-modified terpene resin, dammar resin, aldehyde-ketone resin, chlorinated polypropylene, chloroacetic acid resin, and soluble polyurethane.

[0041] The modified expanded graphite of this invention adheres to the surface of conductive polymer foam particles and is cooled to obtain a composite material. The surface morphology of the composite material can be observed and the quality of the obtained composite material can be detected by cutting the composite material and performing SEM testing.

[0042] Example 1

[0043] A method for preparing an organically modified expanded graphite composite polymer microwave absorbing material includes the following steps:

[0044] Step S1. Add 85 kg of expanded graphite to a ribbon mixer and control the temperature of the mixer to 100°C. Then dilute 5 kg of KH-550 coupling agent with 5 kg of ethanol. Spray the diluted solution onto the surface of the expanded graphite and dry it. Dissolve 20 kg of acrylic resin in 200 kg of ammonia water, add 5 kg of diethyl phthalate, 2 kg of carbon black, and 0.2 kg of Dow Corning defoamer AFE3168. Mix to obtain a mixture. The pH value of the ammonia water is greater than 12. Slowly spray the mixture onto the surface of the expanded graphite while it is being stirred using a timed automatic sprayer. Dry to obtain modified expanded graphite.

[0045] Step S2. Mix 8 kg of polypropylene resin with a melting point greater than 130℃, 85 kg of polypropylene conductive masterbatch with a resistance of 80 ohms, 15 kg of polypropylene flame retardant masterbatch, 1 kg of zinc borate nucleating agent masterbatch, and 1 kg of aromatic amine antioxidant masterbatch and extrude them through a twin-screw extruder to obtain polymer microparticles with a resistance of 160 ohms, a particle length of 3 mm, and a diameter of 1 mm.

[0046] By weight percentage, the polypropylene conductive masterbatch comprises 60% polypropylene, 32% conductive carbon black, and 8% PE wax; the polypropylene flame retardant masterbatch comprises 60% polypropylene and 40% coated red phosphorus; the zinc borate nucleating agent masterbatch comprises 85% polypropylene, 10% zinc borate, and 5% PE wax; and the aromatic amine antioxidant masterbatch comprises 10% 1010 antioxidant, 85% polypropylene, and 5% PE wax.

[0047] Step S3. Add polymer microparticles to the reactor, along with water (70% of the total reactor volume) and sodium dodecylbenzenesulfonate (3% of the total polymer microparticle mass). Heat to the polymer's melting point, and slowly introduce carbon dioxide multiple times until foaming occurs at a pressure of 4 MPa. Then, discharge the material, wash, and dry to obtain a material with a resistivity of 1800 ohms, a diameter of 2.5 mm, a length of 4 mm, and a density of 45 kg / m³. 3 Conductive polymer foam particles;

[0048] Step S4. Add 45kg of conductive polymer foam particles to the mixer and control the temperature of the mixer to 120℃. When the material temperature is reached, add 10kg of modified expanded graphite and continue stirring at a speed of 35r / min for 5min. The modified expanded graphite will adhere to the surface of the conductive polymer foam particles. After cooling, the composite material is obtained.

[0049] Step S5. The composite material is molded using a foam molding machine to obtain a flat plate-type microwave absorbing material with a thickness of 25mm and grooves on the surface.

[0050] Example 2

[0051] A method for preparing an organically modified expanded graphite composite polymer microwave absorbing material includes the following steps:

[0052] Step S1. Add 85 kg of expanded graphite to a ribbon mixer and control the temperature of the mixer to 100°C. Then, dilute 5 kg of KH-550 coupling agent with 5 kg of ethanol and spray it onto the surface of the expanded graphite. After drying, dissolve 20 kg of acrylic resin in 200 kg of ammonia water, add 5 kg of diethyl phthalate, 2 kg of carbon black, and 0.2 kg of Dow Corning defoamer AFE3168, and mix to obtain a mixture. The pH value of the ammonia water is greater than 12. Use a timed automatic sprayer to slowly spray the mixture onto the surface of the expanded graphite while it is being stirred, and dry to obtain modified expanded graphite.

[0053] Step S2. Mix 8 kg of polypropylene resin with a melting point greater than 130℃, 85 kg of polypropylene conductive masterbatch with a resistance of 80 ohms, 15 kg of polypropylene flame retardant masterbatch, 1 kg of zinc borate nucleating agent masterbatch, and 1 kg of aromatic amine antioxidant masterbatch and extrude them through a twin-screw extruder to obtain polymer microparticles with a resistance of 160 ohms, a particle length of 3 mm, an inner diameter of 0.3 mm, and an outer diameter of 1 mm. The polymer microparticles are in the shape of ring-shaped microparticles.

[0054] By weight percentage, the polypropylene conductive masterbatch comprises 60% polypropylene, 32% conductive carbon black, and 8% PE wax; the polypropylene flame retardant masterbatch comprises 60% polypropylene and 40% coated red phosphorus; the zinc borate nucleating agent masterbatch comprises 85% polypropylene, 10% zinc borate, and 5% PE wax; and the aromatic amine antioxidant masterbatch comprises 10% 1010 antioxidant, 85% polypropylene, and 5% PE wax.

[0055] Step S3. Add polymer microparticles to the reactor, along with water (70% of the total reactor volume) and sodium dodecylbenzenesulfonate (3% of the total polymer microparticle mass). Heat to the polymer's melting point and introduce carbon dioxide to a pressure of 4 MPa for foaming. Discharge the material, wash, and dry to obtain a material with a resistivity of 1800 ohms, an outer diameter of 3.5 mm, an inner diameter of 1.6 mm, a length of 4 mm, and a density of 35 kg / m³. 3 Circular conductive polypropylene foam particles;

[0056] Step S4. Add 35 kg of conductive polymer foam particles to the mixer and control the temperature of the mixer to 120°C. Then add 10 kg of modified expanded graphite and continue stirring at a speed of 35 r / min for 5 min. The modified expanded graphite adheres to the surface of the conductive polymer foam particles. After cooling, the composite material is obtained.

[0057] Step S5. The composite material is molded using a foam molding machine to obtain a flat plate-type microwave absorbing material with a thickness of 25mm and grooves on the surface.

[0058] Comparative Example 1

[0059] A method for preparing an organically modified expanded graphite composite polymer microwave absorbing material includes the following steps:

[0060] Step S1. Mix 8 kg of polypropylene resin with a melting point greater than 130℃, 85 kg of polypropylene conductive masterbatch with a resistance of 80 ohms, 15 kg of polypropylene flame retardant masterbatch, 1 kg of zinc borate nucleating agent masterbatch, and 1 kg of aromatic amine antioxidant masterbatch and extrude them through a twin-screw extruder to obtain polymer microparticles with a resistance of 160 ohms, a particle length of 3 mm, and a diameter of 1 mm.

[0061] By weight percentage, the polypropylene conductive masterbatch comprises 60% polypropylene, 32% conductive carbon black, and 8% PE wax; the polypropylene flame retardant masterbatch comprises 60% polypropylene and 40% coated red phosphorus; the zinc borate nucleating agent masterbatch comprises 85% polypropylene, 10% zinc borate, and 5% PE wax; and the aromatic amine antioxidant masterbatch comprises 10% 1010 antioxidant, 85% polypropylene, and 5% PE wax.

[0062] Step S2. Add polymer microparticles to the reactor, along with water (70% of the total reactor volume) and sodium dodecylbenzenesulfonate (3% of the total polymer microparticle mass). Heat to the polymer melting point, then purge with carbon dioxide to a pressure of 4 MPa. Discharge the material, wash, and dry to obtain a material with a resistivity of 1800 ohms, a diameter of approximately 2.5 mm, a length of approximately 4 mm, and a density of 45 kg / m³. 3 Conductive polymer foam particles;

[0063] Step S3. The conductive polymer foam particles are molded by a foam molding machine to obtain a flat plate-shaped microwave absorbing material with a thickness of 25mm and grooves on the surface.

[0064] Comparative Example 2

[0065] A method for preparing an organically modified expanded graphite composite polymer microwave absorbing material includes the following steps:

[0066] Step S1. Add 85 kg of expanded graphite to a ribbon mixer and control the temperature of the mixer to 100°C. Then dilute 5 kg of KH-550 coupling agent with 5 kg of ethanol. Spray the diluted solution onto the surface of the expanded graphite and dry it. Dissolve 20 kg of acrylic resin in 200 kg of ammonia water, add 5 kg of diethyl phthalate, 2 kg of carbon black, and 0.2 kg of Dow Corning defoamer AFE3168. Mix to obtain a mixture. The pH value of the ammonia water is greater than 12. Slowly spray the mixture onto the surface of the expanded graphite while it is being stirred using a timed automatic sprayer. Dry to obtain modified expanded graphite.

[0067] Step S2. Mix 8 kg of polypropylene resin with a melting point greater than 130℃, 85 kg of polypropylene conductive masterbatch with a resistance of 80 ohms, 15 kg of polypropylene flame retardant masterbatch, 1 kg of zinc borate nucleating agent masterbatch, and 1 kg of aromatic amine antioxidant masterbatch and extrude them through a twin-screw extruder to obtain polymer microparticles with a resistance of 160 ohms, a particle length of 3 mm, and a diameter of 1 mm.

[0068] By weight percentage, the polypropylene conductive masterbatch comprises 60% polypropylene, 32% conductive carbon black, and 8% PE wax; the polypropylene flame retardant masterbatch comprises 60% polypropylene and 40% coated red phosphorus; the zinc borate nucleating agent masterbatch comprises 85% polypropylene, 10% zinc borate, and 5% PE wax; and the aromatic amine antioxidant masterbatch comprises 10% 1010 antioxidant, 85% polypropylene, and 5% PE wax.

[0069] Step S3. Add polymer microparticles to the reactor, along with water (70% of the total reactor volume) and sodium dodecylbenzenesulfonate (3% of the total polymer microparticle mass). Heat to the polymer melting point and slowly purge with carbon dioxide multiple times until the pressure reaches 4 MPa. Discharge the material, wash, and dry to obtain a material with a resistivity of 1800 ohms, a diameter of approximately 2.5 mm, a length of approximately 4 mm, and a density of 45 kg / m³. 3 Conductive polymer foam particles;

[0070] Step S4. Add 45 kg of conductive polymer foam particles to the mixer and control the temperature of the mixer to 120°C. Then add 25 kg of modified expanded graphite and continue stirring at a speed of 35 r / min for 5 min. The modified expanded graphite adheres to the surface of the conductive polymer foam particles. After cooling, the composite material is obtained.

[0071] Step S5. The composite material is molded using a foam molding machine to obtain a flat plate-type microwave absorbing material with a thickness of 25mm and grooves on the surface.

[0072] The absorbing materials of Examples 1 and 2 and Comparative Examples 1 and 2 were tested, and the test results are shown in Table 1 below.

[0073] Table 1

[0074] As can be seen from Table 1 above, in Example 1, modified expanded graphite was added according to the method of the present invention. The mechanical properties remained unchanged, but the flame retardant properties were greatly improved.

[0075] Comparative Example 1 shows that the flame retardant performance of the sample directly ignited due to its poor withstand power.

[0076] Comparative Example 2 used a lot of expanded graphite to coat the surface of the foam particles. The excessive presence of modified expanded graphite on the surface of the foam particles caused the modified expanded graphite to fall off significantly. The foam particles could not be fused together by their own material, but were fused together by the low softening point organic material on the surface. Therefore, during high-power testing, when the temperature reached the glass transition temperature of the low softening point organic material, the foam began to deform and collapse.

[0077] Example 2 is a microwave absorbing material made of cyclic polymer foam particles. Organic modified expanded graphite is added and prepared according to the method described in this invention, without affecting the welding performance of the material itself. Due to the 2.5 cm thick plate and cyclic foam particle structure, the overall air permeability and heat dissipation performance of the foam is good, so the power tolerance can be increased to more than 2500W.

[0078] Furthermore, as shown in Figure 1, the SEM image of the composite material prepared in Example 1 shows that the modified expanded graphite adheres to the surface of the solid conductive polymer foam particles. In the areas where the modified expanded graphite does not adhere, there is no low softening point organic material attached, which does not affect the steam molding of the foam particles. The particle surface has a certain roughness, which can improve the adhesion of the modified expanded graphite to the surface of the conductive polymer foam particles.

[0079] Furthermore, based on the SEM images of the composite material prepared in Example 2 shown in Figure 2 and the SEM images of the composite material prepared in Example 2 after being cut open shown in Figure 3, it can be seen that modified expanded graphite is attached to the inner ring and surface of the annular conductive polymer foam particles. There is no low softening point organic material attached to the areas where modified expanded graphite is not attached, which does not affect the steam molding of the conductive polymer foam particles. After the annular foam particles are cut open, the pores are evenly distributed along the arc, the annular structure has good heat dissipation effect, and the organic modified expanded graphite is attached to the surface of the annular particles. It works synergistically with the internally added flame retardant, which greatly improves the flame retardant and power resistance performance of the microwave absorbing material.

[0080] Figures 4 and 5 are schematic diagrams of the plate-shaped absorbing materials with grooved surfaces prepared in Examples 1-2, illustrating that the surface of the absorbing material is designed with a frequency-selective surface structure. The regularly designed grooved grid on the surface enables the plate-shaped absorbing material to have a good absorption rate over a wide frequency range.

[0081] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the claims of the present invention.

Claims

1. An organic modified expanded graphite composite polymer wave-absorbing material, characterized in that: The modified expanded graphite is attached to the surface of the conductive polymer foam particles, and 0.5-20 kg of the modified expanded graphite is attached to the surface of the conductive polymer foam particles per cubic meter. 2.The organic modified expanded graphite composite polymer wave-absorbing material according to claim 1, characterized in that: The modified expanded graphite comprises expanded graphite 60-93 parts by weight, low softening point organic material 2-40 parts by weight, plasticizer 0.1-20 parts by weight, conductive agent 0.1-25 parts by weight, and coupling agent 0.1-5 parts by weight. 3.The organic modified expanded graphite composite polymer wave-absorbing material according to claim 2, characterized in that: The low softening point organic material is selected from one or more of polyvinyl butyral ester, polyvinyl acetate, acrylic resin, modified acrylic resin, maleic anhydride grafted ethylene acrylic acid copolymer, ethylene acrylic acid copolymer, phenolic resin, aromatic hydrocarbon modified terpene resin, dammar resin, aldehyde ketone resin, chlorinated polypropylene, chlorinated acetate resin, and soluble polyurethane. 4.The organic modified expanded graphite composite polymer wave-absorbing material according to claim 1, characterized in that: The conductive polymer foam particles are selected from one of conductive polypropylene foam particles and conductive polyethylene foam particles, the shape of the conductive polymer foam particles is selected from one of columnar, ring-shaped, and spherical, the resistance of the conductive polymer foam particles is 300 ohms-200 M ohms, and the particle size is 1-6 mm. 5.The organic modified expanded graphite composite polymer wave-absorbing material according to claim 4, characterized in that: The conductive polymer foam particles comprise polypropylene or polyethylene resin with a melting point greater than 120℃ 5-70 parts by weight, conductive master batch 30-90 parts by weight, flame retardant master batch 2-30 parts by weight, nucleating agent master batch 0.1-2 parts by weight, and antioxidant master batch 0.3-1 part by weight. 6.The organic modified expanded graphite composite polymer wave-absorbing material according to claim 5, characterized in that: The resistance of the conductive master batch is 10 ohms-200 K ohms. 7.The organic modified expanded graphite composite polymer wave-absorbing material according to claim 5, characterized in that: The flame retardant master batch comprises polypropylene or polyethylene resin 40-60% by mass and flame retardant 40-60% by mass, and the flame retardant is selected from one or more of aluminum phosphate, zinc phosphate, aluminum tripolyphosphate, hydroxyethylidene diphosphonic acid, aluminum dihydrogen phosphate, ammonium polyphosphate, aluminum pentaerythritol phosphate, coated red phosphorus, decabromodiphenyl ethane, and brominated polystyrene.

8. The method for preparing the organic modified expanded graphite composite polymer wave-absorbing material according to any one of claims 1-7, characterized in that, The method comprises the following steps: Step S1. 60-93 parts by weight of expanded graphite is added into a mixing machine, the temperature of the mixing machine is controlled to be 80-100℃, then 0.1-5 parts by weight of coupling agent is diluted with a solvent and sprayed onto the surface of the expanded graphite and dried, then 2-40 parts by weight of low softening point organic material is dissolved with a solvent, and 0.1-20 parts by weight of plasticizer and 0.1-25 parts by weight of conductive agent are added to obtain a mixed solution, finally the mixed solution is sprayed onto the surface of the expanded graphite in the mixing machine by an automatic spraying machine, and the modified expanded graphite is obtained after drying; Step S2. Polypropylene or polyethylene resin 5-70 parts by weight, conductive master batch 30-90 parts by weight, flame retardant master batch 2-30 parts by weight, nucleating agent master batch 0.1-2 parts by weight, and antioxidant master batch 0.3-1 part by weight are mixed and extruded by a double screw extruder to obtain polymer micro-particles; Step S3. The polymer micro-particles obtained in step S2 are put into a reaction kettle, water and a dispersing agent are added, then heated and carbon dioxide is introduced until the target temperature and gas pressure are reached to foam, then the material is discharged and washed, and finally dried to obtain conductive polymer foam particles; Step S4. The conductive polymer foam particles obtained in step S3 are added into a mixing machine, the temperature of the mixing machine is controlled to be 100-120℃, then the modified expanded graphite is added and stirred, and then cooled to obtain a composite material; Step S5. The composite material prepared in step S4 is shaped into a wave-absorbing material by a foam forming machine.

9. The method for preparing the organically modified expanded graphite composite polymer microwave absorbing material according to claim 8, characterized in that: The solvent in step S1 is one or more of water, ethanol, n-butanol, ethyl acetate, acetone, toluene, xylene, butyl acetate, cyclohexanone, isoamyl acetate, ethylene glycol ethyl ether acetate, and ammonia.

10. The method for preparing the organically modified expanded graphite composite polymer microwave absorbing material according to claim 8, characterized in that: The polymer microparticles prepared in step S2 are one of columnar microparticles, ring-shaped microparticles, and spherical microparticles. When the polymer microparticles are columnar microparticles, the polymer microparticles have a resistance of 50 ohms-200K ohms, a length of 0.5-5 mm, and a diameter of 0.5-2 mm. When the polymer microparticles are ring-shaped microparticles, the polymer microparticles have a resistance of 50 ohms-200K ohms, an inner diameter of 0.1-0.5 mm, an outer diameter of 0.6-2 mm, and a length of 1-5 mm. When the polymer microparticles are spherical microparticles, the polymer microparticles have a resistance of 50 ohms-200K ohms and a diameter of 0.5-1.8 mm.

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