A fiber-based air filter with an electret meltblown core / shell rough structure and its preparation method

Abstract

This invention provides an electret meltblown core / shell rough-structure fiber-based air filter and its preparation method, including an electret meltblown core / shell wrinkled fiber-based air filter and an electret meltblown core / shell nano-protrusion structure fiber-based air filter. It belongs to the field of meltblown nonwoven technology. During the water electret process, due to the wrinkled and nano-protrusion structures of the fibers in the fiber web, its roughness is higher than that of smooth fibers, thereby increasing the contact area with water and causing the fiber web to generate a higher density of surface charge. Because the fiber core layer can be doped with more nucleating agents and electret additives, it promotes high crystallinity, thus allowing more charge to be trapped in deep pits during the heat drying process, resulting in the fiber web storing more charge. Furthermore, the corona electret and water electret processes imparting a rough structure to the fiber web help prevent surface charge dissipation.

Description

Technical Field

[0001] This invention relates to an electret meltblown core / shell rough structure fiber-based air filter and its preparation method, belonging to the field of meltblown nonwoven technology. Background Technology

[0002] With urbanization and industrialization, air pollution has become one of the world's three major environmental pollution problems, alongside noise and water pollution. Aerosols, as a major component of air pollution and a carrier of bacteria and viruses, can cause respiratory infections, pneumonia, and cancer with long-term inhalation, seriously threatening human health and even leading to death. Air filter materials are an important means of reducing the harm caused by air pollution, facilitating airflow while effectively capturing aerosol particles. However, the smooth surface of air filter materials prepared using meltblown technology results in low surface charge after corona electret or water electret treatment; simultaneously, the low crystallinity of meltblown fibers leads to low charge storage. These issues, such as easy electret failure and short service life, prevent air filter materials from meeting the requirements of practical filtration applications.

[0003] Therefore, there is an urgent need in this field for a high-efficiency, low-resistance, long-lasting and stable air filter material to solve the problems of low filtration efficiency, large pressure drop, and short service life of air filter materials prepared by existing meltblown technology. Summary of the Invention

[0004] The purpose of this invention is to solve the problems of low filtration efficiency, large pressure drop, and short service life of air filter materials prepared by meltblown technology in the prior art.

[0005] To address the aforementioned problems, the present invention provides an electret meltblown core-shell coarse-structured fiber-based air filter and its preparation method.

[0006] In a first aspect, the present invention provides an electret meltblown core / shell rough structure fiber-based air filter, including an electret meltblown core / shell pleated structure fiber-based air filter and an electret meltblown core / shell nano-protrusion structure fiber-based air filter.

[0007] Preferably, the electret meltblown core / shell pleated fiber-based air filter comprises the following components:

[0008] 50–90 parts of rigid polymer in the core layer; 40–90 parts of rigid polymer for the shell layer; 10-60 parts of shell-flexible polymer; Nucleating agent and electret additive 10-50 parts; The core and shell rigid polymers are polyolefin or polyester polymers; the shell flexible polymers include polycaprolactone, polybutylene succinate, polyurethane or polybutylene adipate / terephthalate, with each part calculated by mass.

[0009] Preferably, the polyolefin polymer is polypropylene or polyethylene, and the polyester polymer is polyoxymethylene, polychlorotrifluoroethylene, polylactic acid, polyhydroxyalkanoates or polymethyl methacrylate.

[0010] Preferably, the electret meltblown core / shell nano-protrusion structure fiber-based air filter comprises the following components: 50–90 parts of rigid polymer in the core layer; 10-50 parts of nucleating agent and electret additive; 50-90 parts of rigid polymer for the shell layer; 10-50 parts of shell-inorganic nucleating agent and electret additive; The core and shell rigid polymers are polyolefin or polyester polymers.

[0011] Preferably, the polyolefin polymer is polypropylene or polyethylene, and the polyester polymer is polyoxymethylene, polychlorotrifluoroethylene, polylactic acid, polyhydroxyalkanoates or polymethyl methacrylate.

[0012] In a second aspect, the present invention provides a method for preparing the above-mentioned electret meltblown core / shell rough structure fiber-based air filter, including a method for preparing an electret meltblown core / shell pleated structure fiber-based air filter and a method for preparing an electret meltblown core / shell nano-protrusion structure fiber-based air filter. The preparation method of the electret meltblown core / shell pleated structure fiber-based air filter includes the following steps: Step 1: Place the core rigid polymer, shell rigid polymer, shell flexible polymer, nucleating agent and electret additive in a forced-air drying oven and dry at 80℃ for 6-10 hours. Step 2: The dried core rigid polymer, nucleating agent and electret additive are put into a granulator, mixed evenly, heated and extruded into shape; the shell rigid and flexible polymers are put into a granulator, mixed evenly, heated and extruded into shape. Step 3: The core and shell mixed melt obtained in Step 2 is cooled and then pelletized by a pelletizer to obtain core and shell meltblown masterbatch respectively. Step 4: The meltblown masterbatch obtained in Step 3 is added to a two-component meltblown equipment for meltblown spinning. Under the action of hot air, high speed, and high pressure, the rigid polymer melt in the shell layer thickens, while the flexible polymer melt thins, forming a pleated fiber structure with vertical axial shear texture. The fibers are further stacked to finally obtain a pleated fiber matrix. The meltblown temperature is controlled at 180~290℃, with the temperature of zones one to five of the core layer meltblown system being 10℃ lower than that of zones one to five of the shell layer meltblown system. The core layer melt is doped with nucleating agents and electret additives to promote rapid crystallization and solidification of the core layer, thus supporting the shell layer melt and making it easier for the airflow to stretch and shear, forming pleats. Step 5: Perform corona electret or water electret on the meltblown pleated fiber mesh obtained in Step 4 to obtain an electret meltblown core / shell pleated fiber-based air filter. Preferably, in step 1, the ratio of the rigid shell polymer to the flexible shell polymer is (0.1~4):1.

[0013] Preferably, in step 4, during the meltblowing process, the metering pump frequency is 5-30Hz, the conveyor screen frequency is 1-10Hz, the hot air temperature is 220-290℃, the hot air pressure is 0.20-0.28MPa, the receiving distance is 15-30cm, and the resulting pleated fiber structure has a pleated wavelength of 130-960nm and an amplitude of 20-80nm.

[0014] Preferably, in step 5, the electret process is as follows: under the action of high voltage electrostatic force of 25-40KV, the air is partially broken down, and the neutral molecules are ionized to generate a large number of positive ions that accumulate on the meltblown core / shell rough structure fiber matrix under the action of the electric field, thus obtaining a corona electret meltblown core / shell pleated structure fiber matrix filter. The water electret treatment process is as follows: purified pure water with a resistivity of 18.2MΩ·cm is sprayed out from a fan-shaped nozzle under the action of a high-pressure water pump. The meltblown core / shell rough structure fiber matrix passes through the fan-shaped high-pressure water mist with a pressure of 2-4MPa on both sides under the drive of the conveyor curtain with a frequency of 1-3Hz for electret treatment. Then, it is dried in a hot air drying system with a temperature of 45-55℃ to obtain a water electret meltblown core / shell pleated structure fiber matrix filter.

[0015] The preparation method of the electret meltblown core / shell nano-protrusion structure fiber-based air filter includes the following steps: Step a: Place the rigid polymer and organic or inorganic nucleating agent in a forced-air drying oven and dry at 80°C for 6-10 hours; Step b: The dried core rigid polymer, inorganic or organic nucleating agent and electret additive are put into a granulator, mixed evenly, heated and extruded into shape; the shell rigid polymer, inorganic nucleating agent and electret additive are put into a granulator, mixed evenly, heated and extruded into shape, to obtain core and shell mixed melts respectively. Step c: The core and shell mixed melt obtained in step b is cooled and then pelletized by a pelletizer to obtain core and shell meltblown masterbatch respectively.

[0016] Step d: The meltblown masterbatch obtained in step c is added to a two-component meltblown equipment for meltblown spinning. Under the action of hot air, high speed, and high pressure, the thickness of the rigid shell melt becomes thinner and the viscosity concentration decreases. This allows the inorganic nucleating agent or electret additive to diffuse perpendicularly to the interface of the thinner shell melt with lower viscosity concentration, causing the surface of the shell melt to bulge, thus obtaining nano-protruding fiber structure. The fibers are further stacked to finally obtain a meltblown nano-protruding fiber web. The meltblown temperature is controlled at 180~290℃, and the melting temperature of the core meltblown masterbatch is 10℃ lower than that of the shell meltblown masterbatch. Step e: Subject the meltblown nano-protrusion structure fiber mesh obtained in step d to corona electret or water electret to obtain an electret meltblown core / shell nano-protrusion structure fiber-based air filter.

[0017] Preferably, in step c, the molecular weight of the shell-mixed melt is 30 to 350.

[0018] Preferably, in step d, the hot air temperature is 220–290°C, the hot air pressure is 0.20–0.28 MPa, the receiving distance during meltblowing is 15–30 cm, and the transmission screen frequency is 1–12 Hz.

[0019] Preferably, in step e, the electret process is as follows: under the action of high voltage electrostatic force of 25-40KV, the air is partially broken down, and neutral molecules are ionized to generate a large number of positive ions that accumulate on the meltblown core / shell rough structure fiber matrix under the action of electric field, thus obtaining a corona electret meltblown core / shell nano-protrusion structure fiber matrix filter. The water electret treatment process is as follows: purified pure water with a resistivity of 18.2MΩ·cm is sprayed out from a fan-shaped nozzle under the action of a high-pressure water pump. The meltblown core / shell rough structure fiber matrix passes through a fan-shaped high-pressure water mist with a pressure of 2-4MPa on both sides under the drive of a conveyor curtain with a frequency of 1-3Hz for electret treatment. Then, it is dried in a hot air drying system with a temperature of 45-55℃ to obtain a water electret meltblown core / shell nano-protrusion structure fiber matrix filter.

[0020] In a third aspect, the present invention provides an electret meltblown core / shell rough structure fiber-based air filter prepared by the above method, including a corona electret and water electret meltblown core / shell pleated structure fiber-based air filter and a corona electret and water electret meltblown core / shell nano-protrusion structure fiber-based air filter.

[0021] The technical principle of the preparation method is as follows: During the formation of the meltblown core / shell rough structure fiber matrix, the core / shell structure of the fiber is formed. High-temperature and high-speed airflow causes mass transfer and heat transfer between the mixed melt and the airflow. The heat from the airflow ensures the differentiation of the two layers, such as molecular weight, dynamic viscosity, and crystallization behavior. The shell melt covers the core melt. According to Fick's diffusion law, the core melt diffuses a unit cross-sectional area of ​​mass per unit time through the diffusion direction perpendicular to the shell melt. Subsequently, the core melt diffuses into the inner interface of the shell melt, and thermal adhesion occurs at the interface between the two layers, thereby obtaining a stable core / shell structure. However, the formation mechanisms of the meltblown wrinkles and protrusions in the meltblown core / shell rough structure fiber matrix are different.

[0022] In the formation of the folded structure, due to the differential characteristics of the two melt layers in the core-shell structure formation, the core melt crystallizes and solidifies before the shell melt, and plays a supporting and fixing role. First, under the action of high-speed and high-pressure airflow, the thickness of the shell-shell mixed melt interface changes (the rigid polymer melt becomes thicker, and the flexible polymer melt becomes thinner), further forming folds in situ. The airflow generates strong shear on the mixed melt. In the shell-shell mixed melt, the outer interface of the melt is vertically stretched by the airflow, forming tension cracks with vertical textures. The inner side of the tension cracks is compressed, forming axial shear textures. Finally, as the core / shell mixed melt descends vertically (approaching the meltblown receiving field), the heat of the meltblown jet flow field gradually decreases, and the airflow causes the shell-shell mixed melt to transform from a liquid phase to a solid phase. The folded structure of the shell melt interface is fixed, forming a folded structure.

[0023] To better facilitate the formation of nanoprotrusion structures, the relative molecular weight and viscosity of the shell-shell melt mixture must be reduced. In the formation of the nanoprotrusion structure, firstly, under the action of high-speed, high-pressure gas flow, the shell-shell melt mixture undergoes deformation and unstable fluctuations, resulting in a thinner shell-shell melt mixture and a decrease in interfacial viscosity and concentration. Subsequently, high-concentration solid inorganic nuclei diffuse perpendicularly to the low-concentration shell-shell melt interface, causing the shell-shell melt interface to protrude. Finally, as the core / shell melt mixture descends vertically (approaching the meltblown receiving field), the heat of the meltblown gas flow field gradually decreases, and the gas flow causes the shell-shell melt mixture to transform from a liquid phase to a solid phase, fixing the protrusion structure at the shell-shell melt interface and forming the nanoprotrusion structure.

[0024] Compared with the prior art, the present invention has the following beneficial effects: (1) During the water electret friction process, the core / shell rough structure fiber network has a folded structure and a nano-rough structure. The roughness of the fiber base network is higher than that of the smooth surface fiber base network, which is conducive to generating a higher density of surface charge. The fiber core layer can be doped with more nucleating and electret additives, so that the fiber core layer obtains high crystallinity. Therefore, during the hot drying process, more charges are trapped in the deep trap, so that the fiber base network stores more charges. In addition, after the fiber network with rough structure is subjected to corona electret and water electret, it is beneficial to prevent the surface charge from dissipating.

[0025] (2) Compared with the existing rough structure produced by stretching the fiber matrix through heat treatment, the fiber rough structure prepared by the present invention is more controllable, and the process is simpler, faster and more energy-saving. Attached Figure Description

[0026] Figure 1 The core / shell folded fiber matrix prepared by this invention Figure 2 The core / shell nanoprotrusion structure fiber matrix prepared by this invention Detailed Implementation To make the present invention more apparent and understandable, preferred embodiments are described in detail below with reference to the accompanying drawings: like Figure 1-2 As shown, the present invention provides an electret meltblown core / shell rough structure fiber-based air filter.

[0027] Example 1 (1) Shell polyurethane and shell polypropylene are mixed evenly at a mass ratio of 3:2 and then melt-extruded through a granulator to obtain shell flexible / rigid meltblown masterbatch; core polyethylene and nucleating agent and electret additive are mixed evenly at a mass ratio of 4:1 and then melt-extruded through a granulator to obtain core rigid / electret meltblown masterbatch. The meltblown machine process parameters are as follows: the meltblown temperature is controlled at 180~220℃, wherein the temperature of the first to fifth zones of the core meltblown system is 10℃ lower than that of the first to fifth zones of the shell meltblown system; the core and shell metering pump frequencies are 15 and 6Hz, respectively; the hot air temperature is 230℃; the hot air pressure is 0.3MPa; the receiving distance is 20cm; and the conveyor curtain frequency is 4Hz. Core / shell pleated fiber matrix is ​​prepared by meltblown process.

[0028] (2) Corona electret treatment: under the action of high voltage electrostatics of 38KV, a corona electret core / shell pleated fiber-based air filter is obtained.

[0029] At a flow rate of 32 L / min, the electret core / shell pleated fiber-based air filter achieved a filtration efficiency of 99.53% for sodium chloride aerosol particles with an average diameter of 0.3 μm, which was 11.36% higher than the control sample. The pressure drop was 27 Pa, 11 Pa lower than the control sample. After 6 months of storage, the filtration efficiency decreased to 96.64%, still 44.18% higher than the control sample. At a flow rate of 85 L / min, the electret core / shell pleated fiber-based air filter achieved a filtration efficiency of 98.74% for sodium chloride aerosol particles with an average diameter of 0.3 μm, which was 16.38% higher than the control sample. The pressure drop was 53 Pa, 26 Pa lower than the control sample. After 6 months of storage, the filtration efficiency decreased to 94.27%, still 60.52% higher than the control sample. The control sample was prepared by corona electret treatment of pure polylactic acid meltblown fiber-based mesh.

[0030] Example 2 (1) Shell polycaprolactone and shell polyoxymethylene were mixed evenly at a mass ratio of 5:2 and then melt-extruded through a granulator to obtain shell flexible / rigid meltblown masterbatch; core polyoxymethylene, nucleating agent and electret additive were mixed evenly at a mass ratio of 4:1 and then melt-extruded through a granulator to obtain core rigid / electret meltblown masterbatch. The meltblown machine process parameters were as follows: the meltblown temperature was controlled at 200~240℃, of which the temperature of the first to fifth zones of the core meltblown system was 10℃ lower than that of the first to fifth zones of the shell meltblown system; the core and shell metering pump frequencies were 17 and 5Hz, respectively; the hot air temperature was 250℃; the hot air pressure was 0.23MPa; the receiving distance was 26cm; and the conveyor curtain frequency was 6Hz. Core / shell pleated fiber matrix was prepared by meltblown process.

[0031] (2) Pure water with a resistivity of 18.2 MΩ·cm after purification is sprayed out from the fan-shaped nozzle under the action of a high-pressure water pump. The fiber web containing the meltblown core / shell rough structure is driven by the conveyor curtain with a frequency of 3.2 Hz and passes through the fan-shaped high-pressure water mist with a pressure of 4 MPa on both sides for electret. At the same time, the negative pressure suction system below the conveyor curtain removes the water in the meltblown cloth. The hot air drying system with a temperature of 45℃ dries the fiber web containing the meltblown core / shell rough structure to obtain the water electret meltblown core / shell rough structure fiber-based filter screen.

[0032] At a flow rate of 32 L / min, the water-electret core / shell pleated fiber-based air filter achieved a filtration efficiency of 99.97% for sodium chloride aerosol particles with an average diameter of 0.3 μm, which was 11.8% higher than the control sample. The pressure drop was 24 Pa, 14 Pa lower than the control sample. After 6 months of storage, the filtration efficiency decreased to 98.75%, still 46.29% higher than the control sample. At a flow rate of 85 L / min, the water-electret core / shell pleated fiber-based air filter achieved a filtration efficiency of 99.32% for sodium chloride aerosol particles with an average diameter of 0.3 μm, which was 16.96% higher than the control sample. The pressure drop was 46 Pa, 33 Pa lower than the control sample. After 6 months of storage, the filtration efficiency decreased to 97.91%, still 64.16% higher than the control sample. The control sample was prepared by corona electret treatment of pure polylactic acid meltblown fiber-based mesh.

[0033] Example 3 (1) Shell polypropylene and nucleating agent and electret additive are mixed evenly at a mass ratio of 3:1 and then melt-extruded through a granulator to obtain shell rigid electret meltblown masterbatch; core polymethyl acrylate and nucleating agent and electret additive are mixed evenly at a mass ratio of 4:3 and then melt-extruded through a granulator to obtain core rigid / electret meltblown masterbatch. The meltblown machine process parameters are as follows: the meltblown temperature is controlled at 200~240℃, wherein the temperature of the core meltblown system zones 1 to 5 is 10℃ lower than that of the shell meltblown system zones 1 to 5; the core and shell metering pump frequencies are 14 and 4Hz, respectively; the hot air temperature is 240℃; the hot air pressure is 0.20MPa; the receiving distance is 28cm; and the conveyor screen frequency is 5Hz. Core / shell nano-protrusion structure fiber matrix is ​​prepared by meltblown process.

[0034] (2) Corona electret treatment: under the action of high voltage electrostatics of 35KV, a corona electret core / shell nano-protrusion structure fiber-based air filter is obtained.

[0035] At a flow rate of 32 L / min, the electret core / shell pleated fiber-based air filter achieved a filtration efficiency of 99.15% for sodium chloride aerosol particles with an average diameter of 0.3 μm, which was 10.98% higher than the control sample. The pressure drop was 29 Pa, 9 Pa lower than the control sample. After 6 months of storage, the filtration efficiency decreased to 96.87%, still 44.41% higher than the control sample. At a flow rate of 85 L / min, the electret core / shell pleated fiber-based air filter achieved a filtration efficiency of 98.42% for sodium chloride aerosol particles with an average diameter of 0.3 μm, which was 16.06% higher than the control sample. The pressure drop was 57 Pa, 22 Pa lower than the control sample. After 6 months of storage, the filtration efficiency decreased to 93.84%, still 60.09% higher than the control sample. The control sample was prepared by corona electret treatment of pure polylactic acid meltblown fiber-based mesh.

[0036] Example 4 (1) Shell polylactic acid and nucleating agent and electret additive are mixed evenly at a mass ratio of 5:4 and then melt-extruded through a granulator to obtain shell rigid electret meltblown masterbatch; core polyethylene and nucleating agent and electret additive are mixed evenly at a mass ratio of 3:2 and then melt-extruded through a granulator to obtain core rigid / electret meltblown masterbatch. The meltblown machine process parameters are as follows: the meltblown temperature is controlled at 210~250℃, wherein the temperature of the core meltblown system zones one to five is 10℃ lower than that of the shell meltblown system zones one to five; the core and shell metering pump frequencies are 16 and 7Hz, respectively; the hot air temperature is 260℃; the hot air pressure is 0.26MPa; the receiving distance is 30cm; and the conveyor screen frequency is 7Hz. Core / shell nano-protrusion structure fiber matrix is ​​prepared by meltblown process.

[0037] (2) Pure water with a resistivity of 18.2 MΩ·cm after purification is sprayed out from a fan-shaped nozzle under the action of a high-pressure water pump. The fiber web containing the meltblown core / shell rough structure is driven by a conveyor curtain with a frequency of 2.8 Hz and passes through the fan-shaped high-pressure water mist with a pressure of 3.5 MPa on both sides for electret. At the same time, the negative pressure suction system below the conveyor curtain removes the water in the meltblown cloth. The hot air drying system with a temperature of 50℃ dries the fiber web containing the meltblown core / shell rough structure to obtain a water electret meltblown core / shell rough structure fiber-based filter screen.

[0038] At a flow rate of 32 L / min, the water-electret core / shell pleated fiber-based air filter achieved a filtration efficiency of 99.98% for sodium chloride aerosol particles with an average diameter of 0.3 μm, which was 11.81% higher than the control sample. The pressure drop was 25 Pa, 13 Pa lower than the control sample. After 6 months of storage, the filtration efficiency decreased to 98.91%, still 46.45% higher than the control sample. At a flow rate of 85 L / min, the water-electret core / shell pleated fiber-based air filter achieved a filtration efficiency of 99.54% for sodium chloride aerosol particles with an average diameter of 0.3 μm, which was 17.18% higher than the control sample. The pressure drop was 49 Pa, 30 Pa lower than the control sample. After 6 months of storage, the filtration efficiency decreased to 97.69%, still 63.94% higher than the control sample. The control sample was prepared by corona electret treatment of pure polylactic acid meltblown fiber-based mesh.

[0039] Comparative Example (1) Polylactic acid meltblown masterbatch was added to the feed port of the meltblown machine. The meltblown process parameters were as follows: the temperature of the first to fifth zones of the meltblown machine was controlled at 180~220℃, the metering pump frequency was 10Hz, the hot air temperature was 230℃, the hot air pressure was 0.25MPa, the receiving distance was 20cm, and the conveyor screen frequency was 3Hz. Meltblown fiber base mesh was prepared by the meltblown process.

[0040] (2) Corona electret treatment: under the action of high voltage electrostatics of 40KV, the electret meltblown fiber base air filter is formed.

[0041] At a flow rate of 32 L / min, the electret meltblown fiber-based air filter achieved a filtration efficiency of 88.17% for sodium chloride aerosol particles with an average diameter of 0.3 μm and a pressure drop of 38 Pa. After 6 months of storage, the filtration efficiency decreased to 52.46%. At a flow rate of 85 L / min, the electret meltblown fiber-based air filter achieved a filtration efficiency of 82.36% for sodium chloride aerosol particles with an average diameter of 0.3 μm and a pressure drop of 79 Pa. After 6 months of storage, the filtration efficiency decreased to 33.75%.

[0042] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any form or substance. It should be noted that those skilled in the art can make various improvements and additions without departing from the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention. Any modifications, alterations, and equivalent changes made by those skilled in the art based on the above-disclosed technical content without departing from the spirit and scope of the present invention are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, and evolutions made to the above embodiments based on the essential technology of the present invention still fall within the scope of the technical solution of the present invention.

[0043] The test method of this invention: Filtration efficiency: Tested using a TSI8130 automatic filter media tester, with the flow rate of sodium chloride aerosol particles with an average diameter of 0.3 μm set at 32 L / min or 85 L / min.

Claims

1. A method for preparing an electret meltblown core / shell rough structure fiber-based air filter, characterized in that, This includes methods for preparing electret meltblown core / shell pleated fiber-based air filters or methods for preparing electret meltblown core / shell nano-protrusion fiber-based air filters: The preparation method of the electret meltblown core / shell pleated structure fiber-based air filter includes the following steps: Step 1: Place the core rigid polymer, shell rigid polymer, shell flexible polymer, nucleating agent and electret additive in a forced-air drying oven and dry at 80℃ for 6-10 hours. Step 2: The dried core rigid polymer, nucleating agent and electret additive are put into a granulator, mixed evenly, heated and extruded into shape; the shell rigid and flexible polymers are put into a granulator, mixed evenly, heated and extruded into shape. Step 3: The core and shell mixed melt obtained in Step 2 is cooled and then pelletized by a pelletizer to obtain core and shell meltblown masterbatch respectively. Step 4: The meltblown masterbatch obtained in Step 3 is added to a two-component meltblown equipment for meltblown spinning. Under the action of hot air, high speed and high pressure, the rigid polymer melt in the shell layer becomes thicker and the flexible polymer melt becomes thinner, forming a pleated fiber structure with vertical axial shear texture. The fibers are further stacked to finally obtain a pleated fiber matrix. The meltblown temperature is controlled at 180~290℃. The temperature of the core layer meltblown system in zones one to five is 10℃ lower than that of the shell layer meltblown system in zones one to five. The core layer melt is doped with nucleating agent and electret additive to promote rapid crystallization and solidification of the core layer, thereby supporting the shell layer melt and making the shell layer melt easy to be stretched and sheared by airflow to form pleats. Step 5: Perform corona electret or water electret on the meltblown pleated fiber mesh obtained in Step 4 to obtain an electret meltblown core / shell pleated fiber-based air filter. The preparation method of the electret meltblown core / shell nano-protrusion structure fiber-based air filter includes the following steps: Step a: Place the rigid polymer and organic or inorganic nucleating agent in a forced-air drying oven and dry at 80°C for 6-10 hours; Step b: The dried core rigid polymer, inorganic or organic nucleating agent and electret additive are put into a granulator, mixed evenly, heated and extruded into shape; the shell rigid polymer, inorganic nucleating agent and electret additive are put into a granulator, mixed evenly, heated and extruded into shape, to obtain core and shell mixed melts respectively. Step c: The core and shell mixed melt obtained in step b is cooled and then pelletized by a pelletizer to obtain core and shell meltblown masterbatch respectively. Step d: The meltblown masterbatch obtained in step c is added to a two-component meltblown equipment for meltblown spinning. Under the action of hot air, high speed and high pressure, the thickness of the rigid shell melt becomes thinner and the viscosity concentration becomes less, so that the inorganic nucleating agent or electret additive diffuses perpendicular to the interface of the thinner shell melt with low viscosity concentration, causing the surface of the shell melt to bulge, and obtaining nano-bulged structured fibers. The fibers are further stacked to finally obtain a meltblown nano-bulged structured fiber web. The meltblown temperature is controlled at 180~290℃, and the melting temperature of the core meltblown masterbatch is 10℃ lower than that of the shell meltblown masterbatch. Step e: Subject the meltblown nano-protrusion structure fiber mesh obtained in step d to corona electret or water electret to obtain an electret meltblown core / shell nano-protrusion structure fiber-based air filter.

2. The method for preparing the electret meltblown core / shell rough structure fiber-based air filter as described in claim 1, characterized in that, The electret meltblown core / shell pleated fiber-based air filter comprises the following components: 50–90 parts of rigid polymer in the core layer; 40–90 parts of rigid polymer for the shell layer; 10-60 parts of shell-flexible polymer; Nucleating agent and electret additive 10-50 parts; The core and shell rigid polymers are polyolefin polymers or polyester polymers; the shell flexible polymers include polycaprolactone, polybutylene succinate, polyurethane or polybutylene adipate / terephthalate, and each part is calculated by mass.

3. The method for preparing the electret meltblown core / shell rough structure fiber-based air filter as described in claim 2, characterized in that, The polyolefin polymers are polypropylene and polyethylene, and the polyester polymers are polyoxymethylene, polychlorotrifluoroethylene, polylactic acid, polyhydroxyalkanoates or polymethyl methacrylate.

4. The method for preparing the electret meltblown core / shell rough structure fiber-based air filter as described in claim 1, characterized in that, The electret meltblown core / shell nano-protrusion structure fiber-based air filter comprises the following components: 50–90 parts of rigid polymer in the core layer; 10-50 parts of nucleating agent and electret additive; 50-90 parts of rigid polymer for the shell layer; 10-50 parts of shell-inorganic nucleating agent and electret additive; Among them, the rigid polymer of the shell layer and the rigid polymer of the core layer are polyolefin polymers or polyester polymers.

5. The electret meltblown core / shell rough structure fiber-based air filter as described in claim 4, characterized in that, The polyolefin polymers are polypropylene and polyethylene, and the polyester polymers are polyoxymethylene, polychlorotrifluoroethylene, polylactic acid, polyhydroxyalkanoates or polymethyl methacrylate.

6. The method for preparing the electret meltblown core / shell rough structure fiber-based air filter as described in claim 1, characterized in that, In step 1, the ratio of the rigid shell polymer to the flexible shell polymer is (0.1~4):

1.

7. The method for preparing the electret meltblown core / shell rough structure fiber-based air filter as described in claim 1, characterized in that, In step 4, during the meltblown process, the metering pump frequency is 5-30Hz, the conveyor curtain frequency is 1-10Hz, the hot air temperature is 220-290℃, the hot air pressure is 0.20-0.28MPa, and the receiving distance is 15-30cm, forming a pleated fiber structure with a pleated wavelength of 130-960nm and an amplitude of 20-80nm.

8. The method for preparing the electret meltblown core / shell rough structure fiber-based air filter as described in claim 1, characterized in that, In step c, the relative molecular weight of the shell-mixed melt is 30-350; in step d, the hot air temperature is 220-290℃, the hot air pressure is 0.20-0.28MPa, the receiving distance during meltblowing is 15-30cm, and the conveyor screen frequency is 1-12Hz.

9. An electret meltblown core / shell rough-structure fiber-based air filter prepared by any one of the methods of claims 1 to 8, characterized in that, Including corona electret and water electret meltblown core / shell pleated fiber-based air filters, and corona electret and water electret meltblown core / shell nano-protrusion fiber-based air filters.

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