Wave-absorbing foam material doped with flame-retardant polymer sheet and preparation method therefor

Abstract

Provided are a wave-absorbing foam material doped with a flame-retardant polymer sheet and a preparation method therefor. In parts by weight, each cubic meter of the polymeric wave-absorbing foam material comprises 3-58 parts of a flame-retardant polymer sheet and 30-97 parts of a polymeric wave-absorbing foam particle. A flame retardant and a polymer are mixed to prepare a small particle sheet with a thickness of 0.01-0.5 mm, the small particle sheet is then mixed with a polymeric wave-absorbing particle and the mixture is molded into a wave-absorbing material by means of a machine. Thus, the flame retardance, environmental friendliness, and mechanical properties of the polymeric wave-absorbing foam material are improved, and the present invention has good application prospects.

Description

A foam microwave absorbing material doped with flame-retardant polymer sheets and its preparation method Technical Field

[0001] This invention relates to the field of microwave absorbing materials technology, specifically to a foam microwave absorbing material doped with flame-retardant polymer sheets and its preparation method. Background Technology

[0002] In the application of microwave absorbing materials, they are mainly divided into polyurethane foam, polystyrene foam, and polypropylene foam. Polyurethane open-cell foam is a microwave absorbing material made by impregnating absorbents; polystyrene foam is a microwave absorbing material made by coating polystyrene particles with an adhesive and flame retardant; polypropylene or polyethylene foam is a microwave absorbing material made by mixing absorbents and flame retardants with polypropylene resin, extruding the mixture, and then foaming it using supercritical carbon dioxide. This method prioritizes electromagnetic wave absorption performance, often resulting in insufficient flame retardancy. According to the "Technical Specification for Electromagnetic Anechoic Chamber Engineering GB50826-2012," the oxygen index of microwave absorbing materials used in anechoic chambers must be greater than 28, and many large microwave anechoic chamber customers even require an oxygen index greater than 32. Furthermore, many anechoic chambers require testing according to the "Indoor Air Quality Standard GB / T18883-2002" after construction to ensure that the indoor air quality meets relevant national standards.

[0003] Currently, to achieve an oxygen index greater than 28 in the flame retardant performance of polypropylene or polyethylene foam microwave absorbing materials, one solution is to coat the surface of the foam particles with a mixture of adhesive and flame retardant absorbent. However, general adhesives have relatively poor adhesion to polypropylene or polyethylene, and the use of adhesives requires solvents. The use of general solvents poses significant safety hazards and is not environmentally friendly, negatively impacting the health and well-being of workers. Furthermore, although the solvent has evaporated by the time the material leaves the factory, incomplete evaporation can negatively affect air quality inside a darkroom as the solvent takes time to fully evaporate. To achieve an oxygen index greater than 28 in the flame retardant performance of polypropylene or polyethylene foam microwave absorbing materials, expanded graphite can be added. Expanded graphite is a relatively good flame retardant. However, because it is flake graphite with a large particle size, it cannot be blended with polymers and then foamed like powdered flame retardants. If expanded flake graphite is blended with polymers and then foamed, a small amount will not have a flame retardant effect, while an excessive amount will result in very large pores in the polymer resin. When the extruder expels the supercooled water, the polymer resin will absorb a lot of water. When it is put into the reactor for foaming, the presence of large-particle expanded graphite will prevent the polymer resin from encapsulating the gas, resulting in a very high pore rate in the foam particles. This will prevent the prepared polymer microwave absorbing particles from being steam molded.

[0004] Summary of the Invention

[0005] To address the aforementioned shortcomings of existing technologies, the inventors, through continuous exploration and research, discovered that before molding polymer microwave absorbing particles such as polypropylene or polyethylene, it is necessary to extract the foam particles into a pressure vessel, inject air into the pressure vessel, and maintain pressure for a certain period of time to allow the air to permeate into the microwave absorbing particles. The air acts as a foaming agent. During steam molding, the microwave absorbing particles expand within the mold. When the microwave absorbing particles are extracted into the pressure vessel, if there is a significant difference in density, when the foam particles fall freely inside the pressure vessel, particles with a higher density and the same surface area will preferentially fall to the bottom of the pressure vessel, resulting in density stratification, which greatly affects the performance of the manufactured microwave absorbing material. In this case, if the particles extracted into the pressure vessel have similar or consistent free-fall velocities, density stratification will not occur.

[0006] Therefore, the inventors have developed a foam microwave absorbing material doped with flame-retardant polymer sheets and its preparation method. By preparing sheet-like flame-retardant polymer and mixing it with polymer microwave absorbing particles, since the surface area ratio of a single flame-retardant polymer sheet is close to that of a single or multiple foam particles, and their mass ratio is also close, the falling speed remains consistent when the material is freely dropped into a pressure vessel. This results in a foam microwave absorbing material that not only improves flame-retardant performance, but also ensures that the thermoplastic polymer sheet and the polymer microwave absorbing particle substrate are consistent, thus not affecting the weldability of the microwave absorbing particles during vapor molding. Furthermore, the use of solvents is avoided in this preparation process. Therefore, the air quality of a microwave anechoic chamber built with the foam microwave absorbing material doped with flame-retardant polymer sheets described in this invention is far superior to that of a microwave anechoic chamber built with a microwave absorbing material prepared using solvents.

[0007] Specifically, the technical solution adopted in this invention is as follows:

[0008] This invention provides a foam absorbing material doped with flame-retardant polymer sheets, characterized in that: by weight, each cubic meter of polymer foam absorbing material includes 3-58 parts of flame-retardant polymer sheets and 30-97 parts of polymer absorbing foam particles; preferably, it includes 5-35 parts of flame-retardant polymer sheets and 30-95 parts of polymer absorbing particles.

[0009] Furthermore, in the foam absorbing material of the flame-retardant polymer sheet described in this invention, the flame-retardant polymer sheet comprises, by weight: 18-80 parts of polymer resin, 5-70 parts of flame retardant A, 0-30 parts of conductive masterbatch, and 0-30 parts of plasticizer; preferably, the conductive masterbatch comprises 0.1-30 parts and the plasticizer comprises 0.1-30 parts.

[0010] Furthermore, in the foam microwave absorbing material of the flame-retardant polymer sheet described in this invention, the flame retardant A is selected from one or more of the following: pentaerythritol phosphate, melamine, melamine polyphosphate, tetrabromobisphenol A, p-isopropylbenzene polymer, expanded graphite, red phosphorus, coated red phosphorus, ammonium polyphosphate, chlorinated paraffin, decabromodiphenyl ethane, brominated polystyrene, aluminum phosphate, zinc phosphate, aluminum tripolyphosphate, hydroxyethylidene diphosphonic acid, aluminum dihydrogen phosphate, aluminum hydroxide, and magnesium hydroxide.

[0011] In the foam absorbing material of the flame-retardant polymer sheet described in this invention, the conductive masterbatch includes polypropylene or polyethylene resin and a conductive agent, wherein the conductive agent is selected from one or more of carbon black, graphite, carbon nanotubes, carbon fibers, and graphene.

[0012] Furthermore, in the foam absorbing material of the present invention, the flame-retardant polymer sheet is a granular sheet with a thickness of 0.01-0.5 mm and a weight of 0.01-60 mg; preferably with a thickness of 0.03-0.3 mm; more preferably with a thickness of 0.05-0.25 mm and a weight of 0.3-5 mg.

[0013] In the foam absorbing material of the flame-retardant polymer sheet described in this invention, the polymer absorbing foam particles include: polypropylene absorbing foam particles or polyethylene absorbing foam particles.

[0014] Furthermore, in the foam absorbing material of the present invention, the polypropylene absorbing foam particles, by weight, comprise: 5-80 parts of polypropylene resin, 20-90 parts of conductive masterbatch, 2-30 parts of flame retardant masterbatch, and 0.2-2 parts of foaming agent masterbatch.

[0015] In the foam microwave absorbing material of the flame-retardant polymer sheet described in this invention, the polyethylene microwave absorbing foam particles, by weight, comprise: 5-80 parts of polyethylene resin, 20-90 parts of conductive masterbatch, 2-30 parts of flame retardant masterbatch, and 0.2-2 parts of foaming agent masterbatch.

[0016] Preferably, the conductive masterbatch for preparing polypropylene microwave absorbing foam particles is a polypropylene-based conductive masterbatch, and the conductive masterbatch for preparing polyethylene microwave absorbing foam particles is a polyethylene-based conductive masterbatch.

[0017] Furthermore, in the foam absorbing material of the flame-retardant polymer sheet described in this invention, the polymer absorbing foam particles are solid foam particles or ring-shaped foam particles.

[0018] In the foam microwave absorbing material of the flame-retardant polymer sheet described in this invention: the flame retardant masterbatch includes flame retardant B, which is selected from one or more of the following: red phosphorus, coated red phosphorus, ammonium polyphosphate, melamine, melamine polyphosphate, tetrabromobisphenol A, p-isopropylbenzene polymer, aluminum dihydrogen phosphate, pentaerythritol phosphate, aluminum tripolyphosphate, chlorinated paraffin, decabromodiphenyl ethane, and brominated polystyrene.

[0019] In the foam microwave absorbing material doped with flame-retardant polymer sheets described in this invention, the flame-retardant polymer sheets comprise polymer sheets extruded, calendered, or cast from an extruder and / or a rubber mixing mill; the polymer sheets are selected from: polypropylene, polyethylene, polystyrene, polyvinyl chloride, cellulose acetate, polybutene, polycarbonate, acrylonitrile-styrene-butadiene copolymer, polyvinyl acetate, acrylic resin, epoxy resin, modified epoxy resin, ethylene-vinyl acetate copolymer, modified acrylic resin, maleic anhydride-grafted polypropylene, maleic anhydride-grafted polyethylene, ethylene-acrylic acid copolymer, phenolic resin, aromatic hydrocarbon-modified terpene resin, dammar resin, ethylene-ethyl acrylate copolymer, and polyethylene terephthalate. One or more of the following: ethylene glycol ester, acrylonitrile-styrene copolymer, acrylonitrile-styrene-acrylate copolymer, aldehyde-ketone resin, chlorinated polypropylene, chlorinated polyethylene, chloroacetic acid resin, thermoplastic elastomer, polyethylene octene co-elastomer, and polyurethane; preferably, one or more of the following: polypropylene, polyethylene, polyvinyl acetate, acrylic resin, epoxy resin, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, acrylonitrile-styrene-acrylate copolymer, modified acrylic resin, maleic anhydride-grafted polypropylene, maleic anhydride-grafted polyethylene, ethylene-acrylic acid copolymer, chlorinated polypropylene, chlorinated polyethylene, thermoplastic elastomer, and polyethylene octene co-elastomer.

[0020] In the foam absorbing material of the present invention, which is doped with flame-retardant polymer sheet: the foam absorbing material is obtained by mixing the flame-retardant polymer sheet and polymer absorbing foam particles and then molding it with a foam molding machine; preferably, the flame-retardant polymer sheet and polymer absorbing foam particles are mixed in a mixer, the mixture is pumped into a pressure vessel, air is injected into the pressure vessel, a certain pressure and a certain time are maintained, and then the foam absorbing material is obtained by molding it with a foam molding machine.

[0021] Another aspect of the present invention is to provide a method for preparing a foam absorbing material doped with flame-retardant polymer sheets, comprising the following steps:

[0022] Step S1: By weight, mix 18-80 parts of polymer resin, 5-70 parts of flame retardant A, 0.1-30 parts of conductive masterbatch, and 0.1-30 parts of plasticizer, and extrude the mixture using an extruder and / or a rubber mixing mill. The granules are then passed through a calender and / or a casting machine and / or a slitting machine and / or a pelletizer and / or a stamping machine to obtain granules with a thickness of 0.01-0.5 mm and a weight of 0.01-60 mg; preferably, the thickness is about 0.03-0.3 mm and the weight is about 0.1-5 mg.

[0023] Step S2: By weight, mix 5-80 parts of polypropylene resin or polyethylene resin, 20-90 parts of conductive masterbatch, 2-30 parts of flame retardant masterbatch, and 0.2-2 parts of foaming agent masterbatch, and then extrude the mixture through a twin-screw extruder to obtain polypropylene or polyethylene resin microwave absorbing particles with a diameter of approximately 0.5-1.5 mm, a length of approximately 1-6 mm, and a weight of approximately 0.1-3.5 mg.

[0024] Step S3: Add at least one polypropylene or polyethylene resin microwave absorbing particles obtained in step S2 into the reactor, and add water and dispersant to the reactor at the same time. Then start stirring, heat and introduce carbon dioxide. Heat in stages until the melting point of polypropylene resin or polyethylene resin is reached. When the carbon dioxide pressure reaches the set pressure, release the material to obtain polypropylene microwave absorbing foam particles or polyethylene microwave absorbing foam particles.

[0025] Step S4: By weight, 3-58 parts of the flame-retardant polymer sheet obtained in step S1 and 30-97 parts of the polymer microwave absorbing particles obtained in step S3 are mixed in a mixer. The mixture is then pumped into a pressure vessel, air is injected into the pressure vessel, and after maintaining a certain pressure and a certain time, it is molded into the foam microwave absorbing material using a foam molding machine.

[0026] Furthermore, in the preparation method of the foam microwave absorbing material doped with flame-retardant polymer sheets according to the present invention: the temperature of the reactor in step S3 is set to 148 or 118 degrees Celsius, which is the melting point of polypropylene or polyethylene resin microwave absorbing particles, and the pressure is 2.0-4.5 MPa; in step S4, after the mixture is pumped into the pressure vessel, the pressure is increased from 0 to 0.5 MPa for 1-2 hours, then maintained at 0.5 MPa for 5-6 hours, and then reduced to 0.2-0.4 MPa, preferably 0.3 MPa, and then maintained at 0.3 MPa for molding.

[0027] The advantages and beneficial effects of this invention are as follows:

[0028] (1) In the foam microwave absorbing material with flame-retardant polymer sheet of the present invention, the flame retardant such as expanded graphite added to the flame-retardant polymer sheet works synergistically with the phosphorus flame retardant added inside the microwave absorbing particles, and the oxygen index can reach more than 32, which meets the highest level UL94-V0 flame retardant standard, greatly improving the flame retardant performance of the foam microwave absorbing material.

[0029] (2) In the foam absorbing material of the flame-retardant polymer sheet described in this invention, the polymer substrate is of the same type. When the absorbing particles are steam molded, the welding performance of the absorbing particles is not affected, and the mechanical properties of the absorbing material are completely unaffected.

[0030] (3) In the preparation method of the foam microwave absorbing material doped with flame-retardant polymer sheets described in this invention, flame retardants such as expanded graphite, polymer resins, and conductive agents are mixed and then extruded, calendered, and cast into polymer sheets using an extruder and / or a rubber mixing mill. The resulting sheets are then granulated into thin sheets of a certain thickness and length. Since it is an extrusion process, the use of solvents is avoided. The air quality of the microwave anechoic chamber built with the polymer foam microwave absorbing material is far superior to that of the microwave anechoic chamber built with the microwave absorbing material prepared using solvents in the prior art. While improving the flame-retardant performance of the polymer foam microwave absorbing material, its preparation process and the resulting product are relatively more environmentally friendly.

[0031] (4) In the foam absorbing material of the present invention, the polymer substrate is the same type of substrate and there is no adhesive attached to the absorbing material. After the waste material and the old darkroom are demolished, the absorbing material can be melted and recycled, which can save costs and increase economic benefits on the one hand, and is also relatively more environmentally friendly on the other hand. Attached Figure Description

[0032] Figure 1 is a physical image of the foam absorbing material monomer prepared in Example 1.

[0033] Figure 2 is a schematic diagram of the overall structure of the foam absorbing materials prepared in Examples 1 to 4.

[0034] Figure 3 is a scanning electron microscope (SEM) image of the surface of the flame-retardant polymer sheet prepared in Example 1. Detailed Implementation

[0035] The present invention will be further described below with reference to the accompanying drawings and preferred embodiments. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention. The raw materials, masterbatches, reagents, etc. used in the following embodiments are all commercially available or conventionally obtainable.

[0036] As described in this invention, the flame retardant A in the flame retardant polymer sheet of this invention includes, but is not limited to: pentaerythritol phosphate, melamine, melamine polyphosphate, tetrabromobisphenol A, p-isopropylbenzene polymer, expanded graphite, red phosphorus, coated red phosphorus, ammonium polyphosphate, chlorinated paraffin, decabromodiphenyl ethane, brominated polystyrene, aluminum phosphate, zinc phosphate, aluminum tripolyphosphate, hydroxyethylidene diphosphonic acid, aluminum dihydrogen phosphate, aluminum hydroxide, magnesium hydroxide, etc.

[0037] As described in this invention, the plasticizer in the flame-retardant polymer sheet of this invention includes, but is not limited to, triphenyl phosphate.

[0038] As described in this invention, the conductive masterbatch comprises a polymer substrate and a conductive agent. The polymer substrate comprises polypropylene or polyethylene resin, and the conductive agent comprises, but is not limited to, carbon black, graphite, carbon nanotubes, carbon fibers, graphene, etc.

[0039] As described in this invention, the flame retardant masterbatch in the polymer microwave absorbing foam particles of this invention includes a polymer substrate and a flame retardant B, wherein the flame retardant B includes, but is not limited to: red phosphorus, coated red phosphorus, ammonium polyphosphate, melamine, melamine polyphosphate, tetrabromobisphenol A, p-isopropylbenzene polymer, aluminum dihydrogen phosphate, pentaerythritol phosphate, aluminum tripolyphosphate, chlorinated paraffin, decabromodiphenyl ethane, brominated polystyrene, etc.

[0040] As described in this invention, the foaming agent masterbatch used in the method described in this invention is a foaming agent material commonly used in the field of microwave absorbing materials.

[0041] Example 1:

[0042] A foam microwave absorbing material doped with flame-retardant polymer sheets, the preparation method of which includes the following steps:

[0043] Step S1: By weight, mix 48 parts of polypropylene resin, 50 parts of expanded graphite flame retardant, 1 part of conductive masterbatch, and 1 part of triphenyl phosphate, and extrude the mixture using an extruder. Then, pass the mixture through a calender and pelletizer to obtain a polypropylene-based flame retardant polymer sheet with a thickness of 0.1-0.3 mm, a length of 5-15 mm, a width of approximately 2-5 mm, and a weight of approximately 0.3-10 mg.

[0044] Step S2: By weight, 21 parts of polypropylene resin, 68 parts of conductive masterbatch, 1 part of foaming agent masterbatch, and 10 parts of red phosphorus flame retardant masterbatch are mixed and extruded through a twin-screw extruder to obtain polypropylene resin microwave absorbing particles with a diameter of about 1 mm, a length of about 1.8 mm, and a weight of about 0.18 mg.

[0045] Step S3: Add the polypropylene resin microwave-absorbing particles obtained in Step S2 to the reactor, along with water and the dispersant fatty alcohol polyoxyethylene ether. Then, start stirring, heat, and introduce carbon dioxide. Heat in stages to 148 degrees Celsius. When the carbon dioxide pressure reaches 3.0 MPa, release the material for washing, yielding a particle with a diameter of approximately 2 mm, a length of approximately 3 mm, and a density of 45 kg / m³. 3 Polypropylene microwave absorbing foam particles;

[0046] Step S4: By weight, mix 30 kg of the polypropylene substrate flame retardant polymer sheet obtained in step S1 and 70 kg of the polypropylene microwave absorbing particles obtained in step S3 using a mixer. Then, pump the mixture into a pressure vessel, inject air into the pressure vessel, and after 8 hours, maintain a pressure of 0.3 MPa. Use a foam molding machine to mold the mixture into a pyramidal microwave absorbing material with a vertical height of 500 mm.

[0047] Example 2

[0048] A foam microwave absorbing material doped with flame-retardant polymer sheets, the preparation method of which includes the following steps:

[0049] Step S1: By weight, mix 48 parts of polypropylene resin, 50 parts of expanded graphite flame retardant, 1 part of conductive masterbatch, and 1 part of triphenyl phosphate, and extrude the mixture using an extruder. Then, pass the mixture through a calender and pelletizer to obtain a polypropylene-based flame retardant polymer sheet with a thickness of 0.1-0.3 mm, a length of 5-15 mm, a width of approximately 2-5 mm, and a weight of approximately 0.3-10 mg.

[0050] Step S2: By weight, 19 parts of polypropylene resin, 68 parts of conductive masterbatch, 1 part of foaming agent masterbatch, and 12 parts of red phosphorus flame retardant masterbatch are mixed and extruded through a twin-screw extruder to obtain polypropylene resin microwave absorbing particles with a diameter of about 1 mm and a length of about 1.8 mm.

[0051] Step S3: Add the polypropylene resin microwave-absorbing particles obtained in Step S2 to the reactor, along with water and the dispersant fatty alcohol polyoxyethylene ether. Then, start stirring, heat, and introduce carbon dioxide. Heat in stages to 148 degrees Celsius. When the carbon dioxide pressure reaches 3.0 MPa, release the material and wash it to obtain a particle with a diameter of approximately 2 mm, a length of approximately 3 mm, and a density of 45 kg / m³. 3 Polypropylene absorbing foam particles;

[0052] Step S4: By weight, mix 30 kg of the polypropylene substrate flame retardant polymer sheet obtained in step S1 and 70 kg of the polypropylene microwave absorbing particles obtained in step S3 using a mixer. Then, pump the mixture into a pressure vessel, inject air into the pressure vessel, and after 8 hours, maintain a pressure of 0.3 MPa. Use a foam molding machine to mold the mixture into a pyramidal microwave absorbing material with a vertical height of 500 mm.

[0053] Example 3

[0054] A foam microwave absorbing material doped with flame-retardant polymer sheets, the preparation method of which includes the following steps:

[0055] Step S1: By weight, mix 48 parts of polypropylene resin, 50 parts of expanded graphite flame retardant, 1 part of conductive masterbatch, and 1 part of triphenyl phosphate, and extrude the mixture using an extruder. Then, pass the mixture through a calender and pelletizer to obtain a polypropylene-based flame retardant polymer sheet with a thickness of 0.1-0.3 mm, a length of 5-15 mm, a width of approximately 2-5 mm, and a weight of approximately 0.3-10 mg.

[0056] Step S2: By weight, 21 parts of polypropylene resin, 68 parts of conductive masterbatch, 1 part of foaming agent masterbatch, and 10 parts of red phosphorus flame retardant masterbatch are mixed and extruded through a twin-screw extruder to obtain cyclic polypropylene resin microwave absorbing particles with an inner diameter of about 0.5 mm, an outer diameter of about 1.2 mm, and a length of about 5 mm.

[0057] Step S3: Add the polypropylene resin microwave-absorbing particles obtained in Step S2 to the reactor, along with water and the dispersant fatty alcohol polyoxyethylene ether. Then, start stirring, heat, and introduce carbon dioxide. Heat in stages to 148 degrees Celsius. When the carbon dioxide pressure reaches 2.0 MPa, release the material and wash it to obtain particles with an inner diameter of approximately 1 mm, an outer diameter of approximately 2.5 mm, a length of 3 mm, and a density of 45 kg / m³. 3 Circular polypropylene microwave absorbing foam particles;

[0058] Step S4: By weight, 30 kg of the polypropylene substrate flame-retardant polymer sheet obtained in step S1 and 70 kg of the polypropylene microwave absorbing particles obtained in step S3 are mixed in a mixer. The mixture is then pumped into a pressure vessel, air is injected into the pressure vessel, and after 8 hours, the pressure is maintained at 0.3 MPa. The mixture is then molded into a pyramidal microwave absorbing material with a vertical height of 500 mm using a foam molding machine.

[0059] In this embodiment 3, cyclic polypropylene absorbing particles were used to make the absorbing material. The absorbing material prepared from these cyclic foam particles is lighter in density than that made from solid foam particles. This reduces the material cost and improves the heat dissipation of the absorbing material during testing, thereby improving the power resistance of the absorbing material.

[0060] Example 4

[0061] A foam microwave absorbing material doped with flame-retardant polymer sheets, the preparation method of which includes the following steps:

[0062] Step S1: By weight, mix 48 parts of polyethylene resin, 50 parts of expanded graphite flame retardant, 1 part of conductive masterbatch, and 1 part of triphenyl phosphate, and extrude the mixture using an extruder. Then, pass the mixture through a calender and pelletizer to obtain a polyethylene-based flame-retardant polymer sheet with a thickness of 0.1-0.3 mm, a length of 5-15 mm, a width of approximately 2-5 mm, and a weight of approximately 0.3-10 mg.

[0063] Step S2: By weight, 21 parts of polyethylene resin, 68 parts of conductive masterbatch, 1 part of foaming agent masterbatch, and 10 parts of red phosphorus flame retardant masterbatch are mixed and extruded through a twin-screw extruder to obtain polyethylene resin microwave absorbing particles with a diameter of about 1 mm and a length of about 1.8 mm.

[0064] Step S3: Add the polyethylene resin microwave-absorbing particles obtained in Step S2 to the reactor, along with water and the dispersant fatty alcohol polyoxyethylene ether. Then, start stirring, heat, and introduce carbon dioxide. Heat in stages to 118 degrees Celsius. When the carbon dioxide pressure reaches 3.5 MPa, release the material and wash it to obtain particles with a diameter of approximately 2 mm, a length of approximately 3 mm, and a density of 45 kg / m³. 3 Polyethylene absorbing foam particles;

[0065] Step S4: By weight, mix 30 kg of the polyethylene-based flame-retardant polymer sheet obtained in step S1 and 70 kg of the polyethylene microwave absorbing particles obtained in step S3 using a mixer. Then, pump the mixture into a pressure vessel, inject air into the pressure vessel, and after 8 hours, maintain a pressure of 0.3 MPa. Use a foam molding machine to mold the mixture into a pyramidal microwave absorbing material with a vertical height of 500 mm.

[0066] In Example 4, a polyethylene substrate was used to make the microwave absorbing material. Due to the use of linear low-density polyethylene substrate, the prepared polymer foam microwave absorbing material has very good toughness and has greater market application prospects.

[0067] Comparative Example 1

[0068] The preparation method of the foam absorbing material doped with flame-retardant polymer sheets includes the following steps:

[0069] Step S1: By weight, mix 48 parts of polypropylene resin, 50 parts of expanded graphite flame retardant, 1 part of conductive masterbatch, and 1 part of triphenyl phosphate, and extrude the mixture using an extruder. Then, pass the mixture through a calender and pelletizer to obtain a polypropylene-based flame retardant polymer sheet with a thickness of 0.1-0.3 mm, a length of 5-15 mm, a width of approximately 2-5 mm, and a weight of approximately 0.3-10 mg.

[0070] Step S2: By weight, 19 parts of polypropylene resin, 68 parts of conductive masterbatch, 1 part of foaming agent masterbatch, and 12 parts of red phosphorus flame retardant masterbatch are mixed and extruded through a twin-screw extruder to obtain polypropylene resin microwave absorbing particles with a diameter of about 1 mm and a length of about 1.8 mm.

[0071] Step S3: Add the polypropylene resin microwave-absorbing particles obtained in Step S2 to the reactor, along with water and the dispersant fatty alcohol polyoxyethylene ether. Then, start stirring, heat, and introduce carbon dioxide. Heat in stages to 148 degrees Celsius. When the carbon dioxide pressure reaches 3.0 MPa, release the material and wash it to obtain a particle with a diameter of approximately 2 mm, a length of approximately 3 mm, and a density of 45 kg / m³. 3 Polypropylene absorbing foam particles;

[0072] Step S4: By weight, mix 2 kg of the polypropylene substrate flame retardant polymer sheet obtained in step S1 and 98 kg of the polypropylene microwave absorbing particles obtained in step S3 using a mixer. Then, pump the mixture into a pressure vessel, inject air into the pressure vessel, and after 8 hours, maintain a pressure of 0.3 MPa. Use a foam molding machine to mold the mixture into a pyramidal microwave absorbing material with a vertical height of 500 mm.

[0073] Comparative Example 2

[0074] The preparation method of the foam absorbing material doped with flame-retardant polymer sheets includes the following steps:

[0075] Step S1: By weight, mix 48 parts of polypropylene resin, 50 parts of expanded graphite flame retardant, 1 part of conductive masterbatch, and 1 part of triphenyl phosphate, and extrude the mixture using an extruder. Then, pass the mixture through a calender and pelletizer to obtain a polypropylene-based flame retardant polymer sheet with a thickness of 0.1-0.3 mm, a length of 5-15 mm, a width of approximately 2-5 mm, and a weight of approximately 0.3-10 mg.

[0076] Step S2: By weight, 19 parts of polypropylene resin, 68 parts of conductive masterbatch, 1 part of foaming agent masterbatch, and 12 parts of red phosphorus flame retardant masterbatch are mixed and extruded through a twin-screw extruder to obtain polypropylene resin microwave absorbing particles with a diameter of about 1 mm and a length of about 1.8 mm.

[0077] Step S3: Add the polypropylene resin microwave-absorbing particles obtained in Step S2 to the reactor, along with water and the dispersant fatty alcohol polyoxyethylene ether. Then, start stirring, heat, and introduce carbon dioxide. Heat in stages to 148 degrees Celsius. When the carbon dioxide pressure reaches 3.0 MPa, release the material and wash it to obtain a particle with a diameter of approximately 2 mm, a length of approximately 3 mm, and a density of 45 kg / m³. 3 Polypropylene absorbing foam particles;

[0078] Step S4: By weight, 60 kg of the polypropylene substrate flame retardant polymer sheet obtained in step S1 and 40 kg of the polypropylene microwave absorbing particles obtained in step S3 are mixed in a mixer. The mixture is then pumped into a pressure vessel, air is injected into the pressure vessel, and after 8 hours, the pressure is maintained at 0.3 MPa. The mixture is then molded into a pyramidal microwave absorbing material with a vertical height of 500 mm using a foam molding machine.

[0079] Comparative Example 3

[0080] The preparation method of the foam absorbing material doped with flame-retardant polymer sheets includes the following steps:

[0081] Step S1: By weight, mix 48 parts of polypropylene resin, 50 parts of expanded graphite flame retardant, 1 part of conductive masterbatch, and 1 part of triphenyl phosphate, and extrude the mixture using an extruder. Then, pass the mixture through a calender and pelletizer to obtain a polypropylene-based flame retardant polymer sheet with a thickness of 0.1-0.3 mm, a length of 5-15 mm, a width of approximately 2-5 mm, and a weight of approximately 0.3-10 mg.

[0082] Step S2: By weight, 68 parts of polypropylene conductive masterbatch, 1 part of foaming agent masterbatch, and 31 parts of red phosphorus flame retardant masterbatch are mixed and extruded through a twin-screw extruder to obtain polypropylene resin microwave absorbing particles with a diameter of about 1 mm and a length of about 1.8 mm.

[0083] Step S3: Add the polypropylene resin microwave-absorbing particles obtained in Step S2 to the reactor, along with water and the dispersant fatty alcohol polyoxyethylene ether. Then, start stirring, heat, and introduce carbon dioxide. Heat in stages to 148 degrees Celsius. When the carbon dioxide pressure reaches 3.0 MPa, release the material and wash it to obtain a particle with a diameter of approximately 2 mm, a length of approximately 3 mm, and a density of 65 kg / m³. 3 Polypropylene absorbing foam particles;

[0084] Step S4: By weight, mix 30 kg of the polypropylene substrate flame retardant polymer sheet obtained in step S1 and 70 kg of the polypropylene microwave absorbing particles obtained in step S3 using a mixer. Then, pump the mixture into a pressure vessel, inject air into the pressure vessel, and after 8 hours, maintain a pressure of 0.3 MPa. Use a foam molding machine to mold the mixture into a pyramidal microwave absorbing material with a vertical height of 500 mm.

[0085] Comparative Example 4

[0086] The preparation method of the foam absorbing material doped with flame-retardant polymer sheets includes the following steps:

[0087] Step S1: By weight, mix 48 parts of polypropylene resin, 50 parts of expanded graphite flame retardant, 1 part of conductive masterbatch, and 1 part of triphenyl phosphate, and extrude the mixture using an extruder. Then, pass the mixture through a calender and pelletizer to obtain a polypropylene-based flame retardant polymer sheet with a thickness of 0.1-0.3 mm, a length of 5-15 mm, a width of approximately 2-5 mm, and a weight of approximately 0.3-10 mg.

[0088] Step S2: By weight, mix 30 parts of polypropylene resin, 68 parts of conductive masterbatch, 1 part of foaming agent masterbatch, and 1 part of red phosphorus flame retardant masterbatch, and then extrude the mixture through a twin-screw extruder to obtain polypropylene resin microwave absorbing particles with a diameter of about 1 mm and a length of about 1.8 mm.

[0089] Step S3: Add the polypropylene resin microwave-absorbing particles obtained in Step S2 to the reactor, along with water and the dispersant fatty alcohol polyoxyethylene ether. Then, start stirring, heat, and introduce carbon dioxide. Heat in stages to 148 degrees Celsius. When the carbon dioxide pressure reaches 3.0 MPa, release the material for washing, yielding a particle with a diameter of approximately 2 mm, a length of approximately 3 mm, and a density of 45 kg / m³. 3 Polypropylene absorbing foam particles;

[0090] Step S4: By weight, mix 30 kg of the polypropylene substrate flame retardant polymer sheet obtained in step S1 and 70 kg of the polypropylene microwave absorbing particles obtained in step S3 using a mixer. Then, pump the mixture into a pressure vessel, inject air into the pressure vessel, and after 8 hours, maintain a pressure of 0.3 MPa. Use a foam molding machine to mold the mixture into a pyramidal microwave absorbing material with a vertical height of 500 mm.

[0091] According to market application specifications and requirements, the microwave absorbing materials prepared in Examples 1 to 4 and Comparative Examples 1 to 4 were tested for oxygen index, resistivity, and environmental performance. The testing standard, "Indoor Air Quality Standard GB / T18883-2002," requires testing to be conducted in a closed room. Therefore, the inventors filled a room with 20 square meters of the sample to be tested in a room with dimensions of 5 meters long, 4 meters wide, and 3 meters high, and conducted the tests according to standard GB / T18883-2002. The test results are shown in Table 1 below.

[0092] Table 1

[0093] in conclusion:

[0094] Figure 1 is a physical image of the foam absorbing material monomer obtained in Example 1, wherein the expanded graphite is gray, and the gray stripes on the surface of the pyramid are the doped flame-retardant polymer sheets. Because the expanded graphite is conductive, the prepared flame-retardant polymer sheets also have conductive properties. Figure 2 is a schematic diagram of the overall structure of the foam absorbing materials obtained in Examples 1 to 4.

[0095] As can be seen from the above figures and Table 1, the foam microwave absorbing materials with flame-retardant polymer sheets prepared in Examples 1 to 4 all have an oxygen index of 32 or higher, meeting the highest level UL94-V0 flame retardant standard. Furthermore, the preparation method of the foam microwave absorbing material with flame-retardant polymer sheets described in this invention does not require the use of solvents, so that the air quality of the microwave anechoic chamber built with the prepared polymer foam microwave absorbing material fully complies with the GB / T18883-2002 standard. Its preparation process and the product obtained are more environmentally friendly than the microwave absorbing materials prepared using solvents in the prior art.

[0096] On the other hand, in the microwave absorbing material prepared in Comparative Example 1, the proportion of flame-retardant polymer sheets was too low compared to the polymer absorbing particles, with a measured oxygen index of only 27%, failing to meet the standard of an oxygen index greater than 28%. In the microwave absorbing material prepared in Comparative Example 4, the amount of flame retardant added to the polypropylene absorbing particles was too low, with a measured oxygen index of only 26.5%, also failing to meet the standard of an oxygen index greater than 28%; and the flame retardant ratings of both were also low. This indicates that in the foam microwave absorbing materials with flame-retardant polymer sheets prepared in Examples 1 to 4, the expanded graphite flame retardant and the phosphorus-based flame retardant added inside the absorbing particles have a synergistic effect, greatly improving the flame retardant performance of the foam microwave absorbing materials.

[0097] Furthermore, the microwave absorbing material prepared in Comparative Example 2 contained excessive flame-retardant polymer sheets. Although it achieved an oxygen index and flame retardant rating comparable to Examples 1 to 4, the finished microwave absorbing foam exhibited numerous flame-retardant polymer sheets, affecting its appearance and smoothness. In the microwave absorbing material prepared in Comparative Example 3, the polypropylene microwave absorbing particles contained excessive flame-retardant masterbatch. Although it also achieved an oxygen index and flame retardant rating comparable to Examples 1 to 4, its density was difficult to reduce during foaming, increasing the difficulty of the preparation process and affecting the volume resistivity of the material.

[0098] In the foam absorbing material of the present invention, the polymer substrate is of the same type, and no adhesive is attached to the absorbing material. After the waste material and old anechoic chamber are demolished, the absorbing material can be melted and recycled, which can save costs, increase economic benefits, and is also relatively more environmentally friendly. The above embodiments and figures all demonstrate that the present invention has achieved good technical effects.

[0099] 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 or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A foam absorbing material doped with flame-retardant polymer sheets, characterized in that: By weight, each cubic meter of polymer foam absorbing material includes 3-58 parts of flame-retardant polymer sheets and 30-97 parts of polymer absorbing foam particles.

2. The foam absorbing material with doped flame-retardant polymer sheet according to claim 1, characterized in that: By weight, the flame-retardant polymer sheet comprises: 18-80 parts polymer resin, 5-70 parts flame retardant A, 0-30 parts conductive masterbatch, and 0-30 parts plasticizer.

3. The foam absorbing material with doped flame-retardant polymer sheet according to claim 2, characterized in that: The flame retardant A is selected from one or more of the following: pentaerythritol phosphate, melamine, melamine polyphosphate, tetrabromobisphenol A, p-cumene polymer, expanded graphite, red phosphorus, coated red phosphorus, ammonium polyphosphate, chlorinated paraffin, decabromodiphenyl ethane, brominated polystyrene, aluminum phosphate, zinc phosphate, aluminum tripolyphosphate, hydroxyethylidene diphosphonic acid, aluminum dihydrogen phosphate, aluminum hydroxide, and magnesium hydroxide; the conductive masterbatch includes polypropylene or polyethylene resin and a conductive agent, wherein the conductive agent is selected from one or more of the following: carbon black, graphite, carbon nanotubes, carbon fibers, and graphene.

4. The foam absorbing material with doped flame-retardant polymer sheet according to any one of claims 1 to 3, characterized in that: The flame-retardant polymer sheet is a granular sheet with a thickness of 0.01-0.5 mm and a weight of 0.01-60 mg.

5. The foam absorbing material with doped flame-retardant polymer sheet according to claim 1, characterized in that: The polymer absorbing foam particles include: polypropylene absorbing foam particles or polyethylene absorbing foam particles; wherein, by weight, The polypropylene microwave absorbing foam particles comprise: 5-80 parts polypropylene resin, 20-90 parts conductive masterbatch, 2-30 parts flame retardant masterbatch, and 0.2-2 parts foaming agent masterbatch; the polyethylene microwave absorbing foam particles comprise: 5-80 parts polyethylene resin, 20-90 parts conductive masterbatch, 2-30 parts flame retardant masterbatch, and 0.2-2 parts foaming agent masterbatch; wherein the polymer microwave absorbing foam particles are solid foam particles or ring-shaped foam particles.

6. The foam absorbing material with doped flame-retardant polymer sheet according to claim 5, characterized in that: The flame retardant masterbatch includes flame retardant B, which is selected from one or more of the following: red phosphorus, coated red phosphorus, ammonium polyphosphate, melamine, melamine polyphosphate, tetrabromobisphenol A, p-isopropylbenzene polymer, aluminum dihydrogen phosphate, pentaerythritol phosphate, aluminum tripolyphosphate, chlorinated paraffin, decabromodiphenyl ethane, and brominated polystyrene.

7. The foam absorbing material with doped flame-retardant polymer sheet according to claim 1, characterized in that: The flame-retardant polymer sheet comprises polymer sheets extruded, calendered, or cast from an extruder and / or a rubber mixing mill; the polymer sheet is selected from: polypropylene, polyethylene, polystyrene, polyvinyl chloride, cellulose acetate, polybutene, polycarbonate, acrylonitrile-styrene-butadiene copolymer, polyvinyl acetate, acrylic resin, epoxy resin, modified epoxy resin, ethylene-vinyl acetate copolymer, modified acrylic resin, maleic anhydride-grafted polypropylene, maleic anhydride-grafted polyethylene, ethylene-acrylic acid copolymer, phenolic resin, aromatic hydrocarbon-modified terpene resin, dammar resin, ethylene-ethyl acrylate copolymer, polyethylene terephthalate, acrylonitrile-styrene... One or more of the following: ethylene copolymer, acrylonitrile-styrene-acrylate copolymer, aldehyde-ketone resin, chlorinated polypropylene, chlorinated polyethylene, chloroacetic acid resin, thermoplastic elastomer, polyethylene octene co-elastomer, and polyurethane; preferably, one or more of the following: polypropylene, polyethylene, polyvinyl acetate, acrylic resin, epoxy resin, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, acrylonitrile-styrene-acrylate copolymer, modified acrylic resin, maleic anhydride-grafted polypropylene, maleic anhydride-grafted polyethylene, ethylene-acrylic acid copolymer, chlorinated polypropylene, chlorinated polyethylene, thermoplastic elastomer, and polyethylene octene co-elastomer.

8. A method for preparing a foam absorbing material doped with flame-retardant polymer sheets, characterized in that: Includes the following steps: Step S1: By weight, mix 18-80 parts of polymer resin, 5-70 parts of flame retardant A, 0.1-30 parts of conductive masterbatch, and 0.1-30 parts of plasticizer, and extrude the mixture using an extruder and / or a rubber mixing mill. The granules are then obtained by passing the mixture through a calender and / or a casting machine and / or a slitting machine and / or a pelletizer and / or a stamping machine. The granules have a thickness of 0.01-0.5 mm and a weight of approximately 0.01-60 mg. Step S2: By weight, mix 5-80 parts of polypropylene resin or polyethylene resin, 20-90 parts of conductive masterbatch, 2-30 parts of flame retardant masterbatch, and 0.2-2 parts of foaming agent masterbatch, and then extrude the mixture through a twin-screw extruder to obtain polypropylene or polyethylene resin microwave absorbing particles with a diameter of approximately 0.5-1.5 mm, a length of approximately 1-6 mm, and a weight of approximately 0.1-3.5 mg. Step S3: Add at least one polypropylene or polyethylene resin microwave absorbing particles obtained in step S2 into the reactor, and add water and dispersant to the reactor at the same time. Then start stirring, heat and introduce carbon dioxide. Heat in stages until the melting point of polypropylene resin or polyethylene resin is reached. When the carbon dioxide pressure reaches the set pressure, release the material to obtain polypropylene microwave absorbing foam particles or polyethylene microwave absorbing foam particles. Step S4: By weight, 3-58 parts of the flame-retardant polymer sheet obtained in step S1 and 30-97 parts of the polymer microwave absorbing particles obtained in step S3 are mixed in a mixer. The mixture is then pumped into a pressure vessel, air is injected into the pressure vessel, and after maintaining a certain pressure and a certain time, it is molded into the foam microwave absorbing material using a foam molding machine.

9. The method for preparing the foam microwave absorbing material of the doped flame-retardant polymer sheet according to claim 8, characterized in that: In step S3, the reactor temperature is set to 148 or 118 degrees Celsius, which is the melting point of polypropylene or polyethylene resin microwave absorbing particles, and the pressure is 2.0-4.5 MPa. In step S4, after the mixture is pumped into the pressure vessel, the pressure is increased from 0 to 0.5 MPa over 1-2 hours, then maintained at 0.5 MPa for 5-6 hours, and then reduced to 0.2-0.4 MPa. After that, the pressure is maintained at 0.2-0.4 MPa for molding.

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