Millimeter wave radar wave-absorbing polypropylene composite material and preparation method and application thereof

Abstract

The application relates to the technical field of high polymer materials, and particularly discloses a millimeter wave radar wave-absorbing polypropylene composite material, a preparation method and application thereof. The millimeter wave radar wave-absorbing polypropylene composite material comprises the following raw material components in parts by mass: 40-70 parts of polypropylene resin, 4-8 parts of carboxylated multi-walled carbon nanotubes, 10-20 parts of wave-absorbing master batches and 10-20 parts of inorganic fillers. The wave-absorbing master batch comprises the following raw material components in percentage by mass: 70%-85% of polyolefin elastomer resin, 10%-20% of ceramic-based dielectric loss materials and 3%-10% of compatilizers. The polypropylene resin, the carboxylated multi-walled carbon nanotubes, the wave-absorbing master batches and the inorganic fillers are synergistically compounded, so that the millimeter wave radar wave-absorbing polypropylene composite material has excellent wave-absorbing effect and mechanical properties; the reflection loss value can be stably lower than -16 dB; and the Izod notched impact strength can be higher than 30 kJ / m2.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a millimeter-wave radar absorbing polypropylene composite material, its preparation method, and its application. Background Technology

[0002] Millimeter-wave radar operates in the millimeter-wave band. Millimeter-wave radar technology is characterized by high precision, high speed, and strong penetration. It can monitor the vehicle's surrounding environment in real time, including other vehicles, pedestrians, and obstacles, providing accurate and real-time data support for integrated driver assistance systems and preventing collisions. In certain scenarios, such as in severe weather conditions like fog or sandstorms, millimeter waves have better penetration than visible and infrared light, giving them a unique advantage in outdoor applications such as transportation. Furthermore, millimeter-wave radar can be used as a human presence sensor, automatically activating lights, air conditioning, and other devices upon detecting human movement, improving comfort and convenience. It can also be used to monitor breathing, heart rate, sleep, and falls. Therefore, millimeter-wave radar technology, with its ultra-high frequency and extremely short wavelength, has been widely applied in fields such as automotive and intelligent transportation, smart homes, meteorological and environmental monitoring, security inspection, and healthcare.

[0003] Currently, millimeter-wave radar technology for automobiles is undergoing rapid iteration from 24GHz to higher frequency bands (77GHz and 79GHz). High-frequency radar offers higher detection accuracy, wider bandwidth, and smaller antenna size, better meeting the demands of Advanced Driver Assistance Systems (ADAS) for long-range detection (LRR) and high-resolution imaging. However, high-frequency electromagnetic waves are also more susceptible to interference from the surrounding environment. Metal brackets, bumper inner surfaces, and vehicle logos near the radar installation location can generate strong reflected signals, creating clutter that severely affects the radar system's signal-to-noise ratio and target recognition accuracy.

[0004] Existing microwave absorbing materials mainly include magnetic loss materials such as ferrite and carbonyl iron powder, and dielectric loss materials such as carbon fiber and graphene. Magnetic loss materials have high density, high cost, and their absorption performance degrades at high frequencies (such as millimeter waves). As for traditional dielectric loss materials, when the amount of dielectric loss material added to the polypropylene matrix is ​​high, it can easily lead to a significant deterioration in the material's mechanical properties, making it difficult to meet the stringent requirements for material toughness and reliability in specific scenarios such as automotive parts, robots, radomes, and wind turbine blades.

[0005] Therefore, developing a composite material that can efficiently absorb waves at high frequencies while maintaining the excellent mechanical properties of polypropylene has become a key step in improving millimeter-wave radar technology. Summary of the Invention

[0006] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. Therefore, the first objective of the present invention is to provide a millimeter-wave radar absorbing polypropylene composite material. The second objective of the present invention is to provide a method for preparing this millimeter-wave radar absorbing polypropylene composite material. The third objective of the present invention is to provide applications of this millimeter-wave radar absorbing polypropylene composite material.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a millimeter-wave radar absorbing polypropylene composite material, comprising the following raw material components in parts by weight: 40-70 parts of polypropylene resin, 4-8 parts of carboxylated multi-walled carbon nanotubes, 10-20 parts of absorbing masterbatch, and 10-20 parts of inorganic filler; wherein the absorbing masterbatch is composed of the following raw material components in weight percentage: 70%-85% of polyolefin elastomer (POE) resin, 10%-20% of ceramic-based dielectric loss material, and 3%-10% of compatibilizer.

[0008] This invention relates to a millimeter-wave radar absorbing polypropylene composite material comprising polypropylene resin, carboxylated multi-walled carbon nanotubes (MWCNTs), absorbing masterbatch, and inorganic fillers. The carboxylated MWCNTs are synergistically compounded with a ceramic-based dielectric loss material in the absorbing masterbatch to enhance the radar absorption performance of the polypropylene composite. The carboxylated MWCNTs serve as the primary absorbing agent, exhibiting extremely high aspect ratio, excellent conductivity, and lightweight properties. The ceramic-based dielectric loss material acts as an auxiliary absorbing agent, possessing excellent dielectric properties and high thermal stability. Under a high-frequency electric field, interfacial polarization and dipole reversal polarization occur within the ceramic-based dielectric loss material. The relaxation effects of these polarization processes cause energy loss, which is compensated for by the dielectric loss mechanism of the MWCNTs to compensate for the resistive loss of the multi-walled carbon nanotubes. This invention combines two absorbing materials with different mechanisms, enabling the composite material to achieve efficient radar absorption over a wider frequency range. Furthermore, the introduction of high-toughness polyolefin elastomer resin into the absorbing masterbatch and the use of compatibilizers to improve interfacial compatibility enable the millimeter-wave radar absorbing polypropylene composite material of the present invention to achieve efficient radar absorption while maintaining excellent impact toughness.

[0009] Preferably, the polypropylene resin has a mass fraction of 45-70 parts; more preferably, the polypropylene resin has a mass fraction of 50-70 parts; even more preferably, the polypropylene resin has a mass fraction of 55-69 parts; and even more preferably, the polypropylene resin has a mass fraction of 58-68 parts.

[0010] Preferably, the carboxylated multi-walled carbon nanotubes are present in a mass fraction of 5 to 8 parts; more preferably, the carboxylated multi-walled carbon nanotubes are present in a mass fraction of 6 to 8 parts.

[0011] Preferably, the microwave absorbing masterbatch has a mass fraction of 12-18 parts; more preferably, the microwave absorbing masterbatch has a mass fraction of 14-16 parts.

[0012] Preferably, the inorganic filler has a mass fraction of 12-20 parts; more preferably, the inorganic filler has a mass fraction of 15-20 parts.

[0013] Preferably, the mass percentage of polyolefin elastomer resin in the microwave absorbing masterbatch is 70%~85%; more preferably, the mass percentage of polyolefin elastomer resin is 72%~82%; and even more preferably, the mass percentage of polyolefin elastomer resin is 75%~80%.

[0014] Preferably, the ceramic-based dielectric loss material in the microwave absorbing masterbatch has a mass percentage content of 12% to 20%; more preferably, the ceramic-based dielectric loss material has a mass percentage content of 15% to 20%.

[0015] Preferably, the compatibilizer in the microwave absorbing masterbatch has a mass percentage content of 3% to 8%; more preferably, the compatibilizer has a mass percentage content of 3% to 6%; and even more preferably, the compatibilizer has a mass percentage content of 4.5% to 5.5%.

[0016] Preferably, the polypropylene resin includes one or a combination of two of copolymer polypropylene and homopolymer polypropylene; more preferably, the polypropylene resin is copolymer polypropylene.

[0017] Preferably, the melt flow rate of the polypropylene resin is 30 g / 10 min to 50 g / 10 min; more preferably, the melt flow rate of the polypropylene resin is 35 g / 10 min to 45 g / 10 min; even more preferably, the melt flow rate of the polypropylene resin is 37 g / 10 min to 42 g / 10 min. The melt flow rate of the polypropylene resin was measured under test conditions of 230°C and a load of 2.16 kg.

[0018] Preferably, the notched strength of the polypropylene resin in the cantilever beam is 9 kJ / m. 2 ~11 kJ / m 2 The notch strength of the cantilever beam was tested according to ISO 180:2023.

[0019] Preferably, the purity of the carboxylated multi-walled carbon nanotubes is ≥95%; more preferably, the purity of the carboxylated multi-walled carbon nanotubes is ≥99.9%.

[0020] Preferably, the carboxyl group content in the carboxylated multi-walled carbon nanotubes is 1.1 mmol / g to 1.4 mmol / g; more preferably, the carboxyl group content in the carboxylated multi-walled carbon nanotubes is 1.2 mmol / g to 1.4 mmol / g; and even more preferably, the carboxyl group content in the carboxylated multi-walled carbon nanotubes is 1.3 mmol / g to 1.4 mmol / g.

[0021] Preferably, the inner diameter of the carboxylated multi-walled carbon nanotube is 3 nm to 5 nm; more preferably, the inner diameter of the carboxylated multi-walled carbon nanotube is 4 nm to 5 nm.

[0022] Preferably, the outer diameter of the carboxylated multi-walled carbon nanotube is 8 nm to 15 nm; more preferably, the outer diameter of the carboxylated multi-walled carbon nanotube is 10 nm to 15 nm; and even more preferably, the outer diameter of the carboxylated multi-walled carbon nanotube is 11 nm to 13 nm.

[0023] Preferably, the length of the carboxylated multi-walled carbon nanotube is 10 μm-30 μm; more preferably, the length of the carboxylated multi-walled carbon nanotube is 15 μm-25 μm; and even more preferably, the length of the carboxylated multi-walled carbon nanotube is 18 μm-22 μm.

[0024] Preferably, the specific surface area of ​​the carboxylated multi-walled carbon nanotubes is ≥200 m². 2 / g; More preferably, the specific surface area of ​​the carboxylated multi-walled carbon nanotubes is ≥250m². 2 / g; More preferably, the specific surface area of ​​the carboxylated multi-walled carbon nanotubes is 400m². 2 / g~2000m 2 / g.

[0025] Preferably, the polyolefin elastomer resin includes ethylene-butene copolymer, ethylene-hexene copolymer, and ethylene-octene copolymer; more preferably, the polyolefin elastomer resin is ethylene-butene copolymer.

[0026] Preferably, the melt flow rate of the polyolefin elastomer resin is 4 g / 10 min to 7 g / 10 min; the melt flow rate of the polyolefin elastomer resin is 5 g / 10 min to 7 g / 10 min; the melt flow rate of the polyolefin elastomer resin is 6 g / 10 min to 7 g / 10 min. The melt flow rate of the polyolefin elastomer resin was measured under test conditions of 230°C and a load of 2.16 kg.

[0027] Preferably, the ceramic-based dielectric loss material includes at least one of silicon carbide, silicon nitride, titanium carbide, zirconium carbide, and titanium nitride; more preferably, the ceramic-based dielectric loss material is silicon carbide; even more preferably, the ceramic-based dielectric loss material is nano-silicon carbide.

[0028] Preferably, the purity of the nano-silicon carbide is ≥99.9%; more preferably, the purity of the nano-silicon carbide is ≥99.99%; even more preferably, the purity of the nano-silicon carbide is ≥99.999%.

[0029] Preferably, the particle size of the nano-silicon carbide is 30nm~40nm; more preferably, the particle size of the nano-silicon carbide is 32nm~38nm; and even more preferably, the particle size of the nano-silicon carbide is 34nm~36nm.

[0030] Preferably, the specific surface area of ​​the nano-silicon carbide is 30 m². 2 / g ~60m 2 / g; More preferably, the specific surface area of ​​nano-silicon carbide is 35m². 2 / g ~55m 2 / g; More preferably, the specific surface area of ​​nano-silicon carbide is 40m². 2 / g ~50m 2 / g.

[0031] Preferably, the compatibilizer comprises a maleic anhydride-grafted compatibilizer; more preferably, the maleic anhydride-grafted compatibilizer comprises at least one of maleic anhydride-grafted polypropylene, maleic anhydride-grafted polyethylene, maleic anhydride-grafted polyolefin elastomer, maleic anhydride-grafted polystyrene, maleic anhydride-grafted ABS resin (ABS-g-MAH), and maleic anhydride-grafted SEBS (SEBS-g-MAH).

[0032] In the millimeter-wave radar absorbing polypropylene composite material of the present invention, the -COOH groups in the carboxylated multi-walled carbon nanotubes will covalently bond with the compatibilizer (maleic anhydride), which is beneficial to the better dispersion of multi-walled carbon nanotubes in the polypropylene matrix, forming a three-dimensional conductive network. The incident electromagnetic wave induces a current in the conductive network, and the current generates Joule heating due to resistance during migration, thereby dissipating the electromagnetic energy.

[0033] Preferably, the grafting rate of maleic anhydride in the maleic anhydride graft compatibilizer is 1.5% to 1.8%; more preferably, the grafting rate of maleic anhydride is 1.5% to 1.7%; and even more preferably, the grafting rate of maleic anhydride is 1.6% to 1.7%.

[0034] Preferably, the inorganic filler includes at least one of hollow glass microspheres, talc, and calcium carbonate; more preferably, the inorganic filler is hollow glass microspheres.

[0035] In the millimeter-wave radar absorbing polypropylene composite material of this invention, hollow glass microspheres are used as inorganic fillers to improve impedance matching. Introducing hollow glass microspheres can effectively reduce the overall dielectric constant of the composite material, making it closer to the dielectric constant of free space (air). This helps reduce the direct reflection of electromagnetic waves on the material surface, allowing more energy to enter the material and be absorbed.

[0036] Preferably, the hollow glass microspheres have a particle size of 70μm to 80μm; more preferably, the hollow glass microspheres have a particle size of 72μm to 78μm; and even more preferably, the hollow glass microspheres have a particle size of 74μm to 76μm.

[0037] Preferably, the wall thickness of the hollow glass microspheres is 1.5μm to 2.5μm; more preferably, the wall thickness of the hollow glass microspheres is 1.8μm to 2.3μm; and even more preferably, the wall thickness of the hollow glass microspheres is 1.9μm to 2.1μm.

[0038] Preferably, the millimeter-wave radar absorbing polypropylene composite material further includes 0.5 to 2 parts by weight of an additive; more preferably, the additive is 0.8 to 1.8 parts by weight; and even more preferably, the additive is 1 to 1.5 parts by weight.

[0039] Preferably, the additives include one or a combination of antioxidants and lubricants; more preferably, the additives include antioxidants and lubricants; even more preferably, the mass ratio of antioxidants to lubricants is (1~3):2.

[0040] Preferably, the antioxidant includes one or a combination of two of antioxidant 1010 and antioxidant 168; more preferably, the antioxidant includes antioxidant 1010 and antioxidant 168; even more preferably, the mass ratio of antioxidant 1010 to antioxidant 168 is (1~3):2; even more preferably, the mass ratio of antioxidant 1010 to antioxidant 168 is 1:2.

[0041] Preferably, the lubricant comprises one or more of polypropylene wax, polyethylene wax, polytetrafluoroethylene wax, oxidized polyethylene wax, calcium stearate, and zinc stearate.

[0042] Preferably, the millimeter-wave radar absorbing polypropylene composite material comprises the following components in parts by weight: 40-70 parts polypropylene resin, 4-8 parts carboxylated multi-walled carbon nanotubes, 10-20 parts absorbing masterbatch, 10-20 parts inorganic filler, and 0.5-2 parts additives; the absorbing masterbatch is composed of the following components in weight percentage: 70%-85% polyolefin elastomer resin, 10%-20% ceramic-based dielectric loss material, and 3%-10% compatibilizer.

[0043] More preferably, the millimeter-wave radar absorbing polypropylene composite material is composed of the following components in parts by weight: 40-70 parts polypropylene resin, 4-8 parts carboxylated multi-walled carbon nanotubes, 10-20 parts absorbing masterbatch, 10-20 parts inorganic filler, and 0.5-2 parts additives; the absorbing masterbatch comprises the following components in weight percentage: 70%-85% polyolefin elastomer resin, 10%-20% ceramic-based dielectric loss material, and 3%-10% compatibilizer.

[0044] More preferably, the millimeter-wave radar absorbing polypropylene composite material is composed of the following components in parts by weight: 40-70 parts polypropylene resin, 4-8 parts carboxylated multi-walled carbon nanotubes, 10-20 parts absorbing masterbatch, 10-20 parts inorganic filler, and 0.5-2 parts additives; the absorbing masterbatch is composed of the following components in weight percentage: 70%-85% polyolefin elastomer resin, 10%-20% nano-silicon carbide, and 3%-10% compatibilizer.

[0045] In a second aspect, the present invention provides a method for preparing the millimeter-wave radar absorbing polypropylene composite material described in the first aspect of the present invention: after the raw material components are mixed evenly, they are melt-blended and extruded and granulated to obtain the millimeter-wave radar absorbing polypropylene composite material.

[0046] Preferably, the extrusion is performed using a twin-screw extruder.

[0047] Preferably, the mixing method is mixing in a mixing machine.

[0048] Preferably, the mixing order of the raw material components is as follows: first, the polyolefin elastomer resin, ceramic-based dielectric loss material, and compatibilizer are mixed to obtain microwave absorbing masterbatch, and then the microwave absorbing masterbatch is mixed evenly with other raw material components; more preferably, the mixing order of the raw material components is as follows: first, the polyolefin elastomer resin, ceramic-based dielectric loss material, and compatibilizer are mixed to obtain microwave absorbing masterbatch, and then the microwave absorbing masterbatch is mixed evenly with polypropylene resin, carboxylated multi-walled carbon nanotubes, and additives, and the inorganic filler is added during the extrusion process; even more preferably, the inorganic filler is added to the twin-screw extruder at 7 / 12 of the total melt extrusion process (i.e., the 7th side feed port).

[0049] Preferably, the temperature of each zone of the twin-screw extruder is 180°C to 220°C; more preferably, the temperature of each zone of the twin-screw extruder is 190°C to 210°C; and even more preferably, the temperature of each zone of the twin-screw extruder is 195°C to 205°C.

[0050] Preferably, the screw speed of the twin-screw extruder is 350~450 rpm; more preferably, the screw speed of the twin-screw extruder is 370~430 rpm; even more preferably, the screw speed of the twin-screw extruder is 390~410 rpm.

[0051] Thirdly, the present invention provides an application of the millimeter-wave radar absorbing polypropylene composite material described in the first aspect of the present invention in the fields of automobiles and intelligent transportation, smart homes, meteorological and environmental monitoring, security inspection equipment, and medical devices.

[0052] Preferably, the automotive and intelligent transportation field includes one of radar absorbers, radar brackets, or sign covers.

[0053] Preferably, the smart home includes one of a smart speaker, a smart air conditioner, a smart TV, or a sensor-activated light.

[0054] Preferably, the meteorological and environmental monitoring includes one of a meteorological radar, a radar radome, or a wind turbine blade.

[0055] Preferably, the medical device includes one of a medical robot, a non-contact detection device, and a health monitoring device.

[0056] The beneficial effects of this invention are: (1) The millimeter-wave radar absorbing polypropylene composite material of the present invention comprises polypropylene resin, carboxylated multi-walled carbon nanotubes, absorbing masterbatch, and inorganic filler. The carboxylated multi-walled carbon nanotubes are synergistically compounded with the ceramic-based dielectric loss material in the absorbing masterbatch to construct a highly efficient conductive network to achieve resistive loss. The resistive loss of the multi-walled carbon nanotubes is supplemented through the dielectric loss mechanism, enabling the polypropylene composite material to achieve efficient radar absorption over a wider frequency range. A high-toughness polyolefin elastomer resin is introduced into the absorbing masterbatch, and a compatibilizer is used to improve interfacial compatibility, so that the millimeter-wave radar absorbing polypropylene composite material of the present invention maintains excellent impact toughness while achieving efficient radar absorption.

[0057] (2) This invention uses hollow glass microspheres as inorganic fillers to improve impedance matching. Introducing hollow glass microspheres can effectively reduce the overall dielectric constant of the composite material, making it closer to the dielectric constant of free space. This helps to reduce the direct reflection of electromagnetic waves on the material surface, allowing more energy to enter the material and be absorbed. This invention uses carboxylated multi-walled carbon nanotubes. During melt extrusion processing, the -COOH groups in the carboxylated multi-walled carbon nanotubes will covalently bond with maleic anhydride in the compatibilizer, which is conducive to the formation of an effective conductive path, improving wave absorption, and avoiding the problem that multi-walled carbon nanotubes are prone to agglomeration in the polypropylene matrix and are not easy to form a three-dimensional conductive network.

[0058] (3) The present invention adopts conventional extrusion process, such as twin-screw extrusion. Its preparation method is simple, easy to operate, and the raw materials used are cheap and readily available. It has low requirements for equipment and is suitable for conventional equipment, reducing the dependence on special equipment and making it suitable for large-scale industrial production.

[0059] (4) The millimeter-wave radar absorbing polypropylene composite material of the present invention possesses both excellent absorption effect and mechanical properties. It exhibits excellent absorption performance in high-frequency bands (such as the critical 77GHz band for automotive radar), with a reflection loss (RL) value consistently below -16dB, effectively suppressing clutter interference and significantly improving the detection performance of the radar system. The notched impact strength of the millimeter-wave radar absorbing polypropylene composite material can reach over 30kJ / m², fully meeting the stringent safety standards for automotive components, especially radar bracket structures. It can be well applied in fields such as automobiles and intelligent transportation, smart homes, meteorological and environmental monitoring, security inspection, and healthcare. Detailed Implementation

[0060] To enable those skilled in the art to better understand this application, the present invention will be further described in detail below with reference to embodiments. However, it should be understood that the following embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims.

[0061] In the description of this invention, it should be noted that unless specific conditions are specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0062] Furthermore, to better illustrate the present invention, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that the present invention can be practiced without certain specific details. In some embodiments, materials, methods, and means well-known to those skilled in the art are not described in detail in order to highlight the spirit of the invention.

[0063] In this invention, the test conditions for melt flow rate are all 230℃ and 2.16kg load.

[0064] The sources of the raw materials and reagents used in the embodiments and comparative examples of this invention are as follows: Polypropylene resin: Copolymer polypropylene: Grade: EP548R (melt flow rate 30g / 10min, cantilever beam notched strength 9kJ / m) 2 Brand: CNOOC Shell; Polyolefin elastomer resin: Model: 9371; Brand: ExxonMobil; Nano-silicon carbide: Grade: YT-SiC-Y30, particle size: 30~40nm, specific surface area: 30~60m² 2 / g, purchased from Suzhou Yuante New Materials; Carbon black: Type: N330; Particle size: 2000~2500 mesh; Purchased from Huifeng Chemical. Carboxylated multi-walled carbon nanotubes: carboxyl content 1.1~1.4 mmol / g, inner diameter 3~5 nm, outer diameter 8~15 nm, length 10~30 μm, specific surface area ≥250 m² / g. 2 / g; Purchased from Jiacai Technology; Multi-walled carbon nanotubes: JCCF-95, inner diameter 3~5nm, outer diameter 8~15nm, length 10~30μm, specific surface area ≥250m² 2 / g: Purchased from JiaCai Technology; Hollow glass microspheres: Grade: BR60; Particle size: 70~80μm; Wall thickness: 1.5~2.5μm; Brand: Hengyuan New Materials; Talc: Brand: ty90-7-C; Powder fineness: 2500 mesh; Purchased from Sanzhi. Compatibilizer: Maleic anhydride-grafted polyolefin elastomer, with a maleic anhydride grafting rate of 1.6%; purchased from Dongguan Yitian New Materials. Antioxidants: Antioxidant 1010 and Antioxidant 168; Brand: BASF; Lubricant: Polyethylene wax (BN500); purchased from Bonnie Chemical.

[0065] Example 1 A millimeter-wave radar absorbing polypropylene composite material comprises the following raw material components in parts by weight: 63 parts polypropylene resin, 6 parts carboxylated multi-walled carbon nanotubes, 15 parts absorbing masterbatch, 15 parts inorganic filler, and 1 part additive; the absorbing masterbatch comprises the following raw material components in weight percentage: 80% polyolefin elastomer resin, 15% ceramic-based dielectric loss material, and 5% compatibilizer. The inorganic filler is hollow glass microspheres; the additive is antioxidant 1010 and antioxidant 168 in a mass ratio of 1:2; the ceramic-based dielectric loss material is nano-silicon carbide; and the compatibilizer is maleic anhydride-grafted polyolefin elastomer.

[0066] The above-mentioned millimeter-wave radar absorbing polypropylene composite material was prepared using the following method: S1: Polyolefin elastomer resin, ceramic-based dielectric loss material and compatibilizer are mixed in a mixer to obtain microwave absorbing masterbatch; S2: Mix the microwave absorbing masterbatch, polypropylene resin, carboxylated multi-walled carbon nanotubes, and additives evenly to obtain a mixture; S3: Add the mixture to the main feed port of the twin-screw extruder. Add the inorganic filler to the twin-screw extruder at 7 / 12 of the total melt extrusion process (i.e., the 7th side feed port). Control the temperature of each zone of the twin-screw extruder to 180℃~220℃ and the screw speed to 350~450 rpm. Perform melt blending, extrusion, cooling, and pelletizing to obtain the millimeter-wave radar absorbing polypropylene composite material.

[0067] Example 2 The difference between this embodiment and Embodiment 1 is that in this embodiment, the mass fraction of polypropylene resin is 68 parts and the mass fraction of microwave absorbing masterbatch is 10 parts, while the rest are the same as in Embodiment 1.

[0068] Example 3 The difference between this embodiment and Embodiment 1 is that the mass fraction of polypropylene resin in this embodiment is 58 parts and the mass fraction of microwave absorbing masterbatch is 20 parts, while the rest are the same as in Embodiment 1.

[0069] Example 4 The difference between this embodiment and Embodiment 1 is that the mass fraction of polypropylene resin in this embodiment is 61 parts, the mass fraction of carboxylated multi-walled carbon nanotubes is 8 parts, and the rest are the same as in Embodiment 1.

[0070] Example 5 The difference between this embodiment and Embodiment 1 is that in this embodiment, the mass fraction of polypropylene resin is 58 parts and the mass fraction of inorganic filler is 20 parts, while the rest are the same as in Embodiment 1.

[0071] Example 6 The difference between this embodiment and Embodiment 1 is that the microwave absorbing masterbatch in this embodiment includes the following raw material components by mass percentage: 75% polyolefin elastomer resin, 20% ceramic-based dielectric loss material, and 5% compatibilizer. All other components are the same as in Embodiment 1.

[0072] Example 7 In this embodiment, the raw material composition of the millimeter-wave radar absorbing polypropylene composite material is the same as that in Example 1. The difference between this comparative example and Example 1 is that in preparation method S3, the inorganic filler is added together with the mixture in S2 into the main feed port of the twin-screw extruder. All other aspects are the same as in Example 1.

[0073] Comparative Example 1 The difference between this comparative example and Example 1 is that the microwave absorbing masterbatch in this comparative example does not contain ceramic-based dielectric loss material. The raw material components of the microwave absorbing masterbatch in this comparative example include 95% polyolefin elastomer resin by mass and 5% compatibilizer by mass, and the rest are the same as in Example 1.

[0074] Comparative Example 2 The difference between this comparative example and Example 1 is that the mass fraction of polypropylene resin in this comparative example is 69 parts, and it does not contain carboxylated multi-walled carbon nanotubes. All other aspects are the same as in Example 1.

[0075] Comparative Example 3 The difference between this comparative example and Example 1 is that this comparative example does not contain carboxylated multi-walled carbon nanotubes, but rather 6 parts by mass of multi-walled carbon nanotubes; in the preparation method S2, multi-walled carbon nanotubes are added instead of carboxylated multi-walled carbon nanotubes; all other aspects are the same as in Example 1.

[0076] Comparative Example 4 The difference between this comparative example and Example 1 is that the mass fraction of polypropylene resin in this comparative example is 78 parts, and it does not contain inorganic fillers. All other aspects are the same as in Example 1.

[0077] Comparative Example 5 The difference between this comparative example and Example 1 is that the inorganic filler in this comparative example is talc powder, instead of the hollow glass microspheres in Example 1. Everything else is the same as in Example 1.

[0078] Comparative Example 6 The difference between this comparative example and Example 1 is that the raw material components of the absorber masterbatch in this comparative example do not contain ceramic-based dielectric loss materials, but rather carbon black. That is, the absorber masterbatch in this comparative example includes the following raw material components by mass percentage: 80% polyolefin elastomer resin, 15% carbon black, and 5% compatibilizer. All other components are the same as in Example 1.

[0079] Performance testing 1. Tensile strength: Tested according to ISO 527-1:2019 standard; 2. Flexural modulus: Tested according to ISO 178:2019 standard; 3. Notched impact strength of cantilever beam at room temperature: tested according to ISO 180:2023 standard; 4. Reflection Loss (RL): Tested using the bow-shaped support method according to standard GB2038A-2011. A 200mm×200mm×2mm sample of millimeter-wave radar absorbing polypropylene composite material was prepared and tested in a microwave anechoic chamber using a vector network analyzer at a frequency of 77GHz. The more negative the RL value, the better the absorption performance. For example, when RL ≤ -10 dB, it indicates that the material absorbs more than 90% of the electromagnetic wave energy.

[0080] The millimeter-wave radar absorbing polypropylene composite materials prepared in Examples 1-7 and Comparative Examples 1-6 were subjected to the above performance tests, and the test results are shown in Table 1.

[0081]

[0082] The test results in Table 1 show that: The millimeter-wave radar absorbing polypropylene composite materials of Examples 1-7 of this invention synergistically combine a resistive loss absorbing material (carboxylated multi-walled carbon nanotubes) with a dielectric loss absorbing material (ceramic-based dielectric loss material). The carboxylated multi-walled carbon nanotubes are the primary absorbing agent, and the ceramic-based dielectric loss material is the secondary absorbing agent, thus improving the absorption performance of the polypropylene composite material. The reflection loss (RL) values ​​of the millimeter-wave radar absorbing polypropylene composite materials of Examples 1-7 are all below -16dB, meeting the requirements for high-efficiency radar absorption. Simultaneously, the notched impact strength of the cantilever beam is above 30 kJ / m², far exceeding that of general radar-absorbing modified plastics, demonstrating excellent toughness. The millimeter-wave radar absorbing polypropylene composite material of this invention achieves a balance between radar absorption performance and mechanical properties. In Example 4, due to the high content of carboxylated multi-walled carbon nanotubes, this content allows for good dispersion within the polypropylene resin matrix, further improving the radar absorption performance, with an RL value reaching -20.5dB.

[0083] A comparison of Examples 1 and 7 shows that when the hollow glass microspheres in Example 7 are added from the main feed inlet, the RL value of the millimeter-wave radar absorbing polypropylene composite material in Example 7 is -17.4 dB, slightly lower than -18.6 dB in Example 1, indicating a decrease in absorption performance. This is because when added from the main feed inlet, the hollow glass microspheres are excessively sheared, causing them to break and affecting the absorption performance.

[0084] Comparing Example 1, Comparative Example 1, and Comparative Example 2, it can be seen that Comparative Example 1, which does not contain ceramic-based dielectric loss material in its absorbing masterbatch, has an RL value of -10.2 dB for its millimeter-wave radar absorbing polypropylene composite material. Comparative Example 2, which does not contain carboxylated multi-walled carbon nanotubes in its raw material components, has an RL value of only -8.7 dB for its millimeter-wave radar absorbing polypropylene composite material. Comparative Example 1, which only contains carboxylated multi-walled carbon nanotubes, is slightly better than Comparative Example 2, which only contains ceramic-based dielectric loss material. This indicates that carboxylated multi-walled carbon nanotubes are key to achieving efficient radar absorption, but adding carboxylated multi-walled carbon nanotubes alone cannot achieve the best results. Example 1 uses a synergistic composite of carboxylated multi-walled carbon nanotubes and ceramic-based dielectric loss materials. The combination of the two has a synergistic effect, constructing an efficient conductive network to achieve resistive loss. At the same time, the resistive loss of multi-walled carbon nanotubes is supplemented through the dielectric loss mechanism, so that the polypropylene composite material can achieve efficient wave absorption in a wider frequency range. The RL value of the millimeter-wave radar absorbing polypropylene composite material of Example 1 can reach -18.6dB.

[0085] A comparison of Example 1 and Comparative Example 3 shows that Comparative Example 3 added multi-walled carbon nanotubes. The RL value of the millimeter-wave radar absorbing polypropylene composite material prepared in Comparative Example 3 was -15.4 dB, which is greater than -18.6 dB in Example 1, indicating a decrease in absorption capacity. This is because Example 1 added carboxylated multi-walled carbon nanotubes. Carboxylation introduces -COOH groups into the multi-walled carbon nanotubes. During melt extrusion, the -COOH groups covalently bond with maleic anhydride in the compatibilizer, which is beneficial for better dispersion of multi-walled carbon nanotubes in PP, thereby improving the absorption capacity of the millimeter-wave radar absorbing polypropylene composite material.

[0086] A comparison of Example 1 and Comparative Example 4 shows that Comparative Example 4 did not add inorganic fillers, i.e., it did not add the hollow glass microspheres found in Example 1. The RL value of the millimeter-wave radar absorbing polypropylene composite material in Comparative Example 4 is -14.5 dB, which is greater than -18.6 dB in Example 1, indicating a decrease in absorption capacity. This is because the introduction of hollow glass microspheres effectively reduces the overall dielectric constant of the polypropylene composite material, making it closer to the dielectric constant of free space. This helps reduce the direct reflection of electromagnetic waves on the material surface, allowing more energy to enter the material and be absorbed.

[0087] A comparison of Example 1 and Comparative Example 5 shows that Comparative Example 5 uses talc as the inorganic filler, and its millimeter-wave radar absorbing polypropylene composite material has an RL value of -14.8 dB, which is greater than the -18.6 dB in Example 1, indicating a decrease in absorption capacity. Furthermore, the notched impact strength of the cantilever beam is 28 kJ / m². 2 Lower than 34 kJ / m in Example 1 2This indicates that, compared to talc, hollow glass microspheres can not only improve the wave absorption capacity of polypropylene composites, but also enhance their toughness.

[0088] A comparison of Example 1 and Comparative Example 6 reveals that the absorbing masterbatch in Comparative Example 6 is composed of carbon black, not a ceramic-based dielectric loss material. The RL value of the millimeter-wave radar absorbing polypropylene composite material in Comparative Example 6 is -15.0 dB, which is greater than the -18.6 dB in Example 1, indicating a decrease in absorption capacity. This is because carbon black is a resistive loss absorbing material, and its functionality overlaps with that of multi-walled carbon nanotubes. In contrast, the ceramic-based dielectric loss material used in Example 1 is a dielectric loss absorbing material, which can synergistically complement the absorption properties of multi-walled carbon nanotubes, thus better improving the absorption performance of the millimeter-wave radar absorbing polypropylene composite material.

[0089] In summary, the millimeter-wave radar absorbing polypropylene composite material of this invention possesses both excellent absorption performance and superior mechanical properties. It exhibits outstanding absorption performance in high-frequency bands (such as the critical 77GHz band for automotive radar), with a reflection loss (RL) value consistently below -16dB, effectively suppressing clutter interference and significantly improving the detection performance of radar systems. The notched impact strength of the millimeter-wave radar absorbing polypropylene composite material can reach over 30kJ / m², fully meeting the stringent safety standards for automotive components, especially radar bracket structures. It can be well applied in fields such as automotive and intelligent transportation, smart homes, meteorological and environmental monitoring, security inspection, and healthcare.

[0090] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A millimeter wave radar absorbing polypropylene composite material, characterized by, The raw material components include the following parts by weight: 40-70 parts of polypropylene resin, 4-8 parts of carboxylated multi-walled carbon nanotubes, 10-20 parts of microwave absorbing masterbatch, and 10-20 parts of inorganic filler; the microwave absorbing masterbatch includes the following raw material components by weight percentage: 70%-85% of polyolefin elastomer resin, 10%-20% of ceramic-based dielectric loss material, and 3%-10% of compatibilizer.

2. The millimeter wave radar absorbing polypropylene composite material according to claim 1, characterized in that, The polypropylene resin includes one or a combination of two of copolymer polypropylene and homopolymer polypropylene.

3. The millimeter wave radar absorbing polypropylene composite material according to claim 1, characterized in that, The carboxyl group content in the carboxylated multi-walled carbon nanotubes is 1.1 mmol / g to 1.4 mmol / g.

4. The millimeter-wave radar absorbing polypropylene composite material according to claim 1, characterized in that, The ceramic-based dielectric loss material includes at least one of silicon carbide, silicon nitride, titanium carbide, zirconium carbide, and titanium nitride.

5. The millimeter-wave radar absorbing polypropylene composite material according to claim 1, characterized in that, The compatibilizer includes a maleic anhydride grafted compatibilizer.

6. The millimeter-wave radar absorbing polypropylene composite material according to claim 1, characterized in that, The inorganic filler includes at least one of hollow glass microspheres, talc, and calcium carbonate.

7. The millimeter-wave radar absorbing polypropylene composite material according to any one of claims 1 to 6, characterized in that, The microwave-absorbing polypropylene composite material also includes 0.5 to 2 parts by weight of additives.

8. The millimeter-wave radar absorbing polypropylene composite material according to claim 7, characterized in that, The additives include one or a combination of two of antioxidants and lubricants.

9. The method for preparing the millimeter-wave radar absorbing polypropylene composite material according to any one of claims 1 to 8, characterized in that, The process includes the following steps: after mixing the raw material components evenly, performing melt blending and extrusion granulation to obtain the microwave-absorbing polypropylene composite material.

10. The application of the millimeter-wave radar absorbing polypropylene composite material according to any one of claims 1 to 8 in automobiles and intelligent transportation, smart homes, meteorological and environmental monitoring, security inspection equipment, and medical devices.

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