A filter element for an automobile filter and a method for manufacturing the same

Abstract

The application belongs to the technical field of automobile filter, and provides a filter element for automobile filter and a preparation method thereof, which adopts a double-layer composite structure design, and comprises a coarse fiber layer and a fine fiber layer, and is composed of polypropylene, an antioxidant and a beta crystal nucleating agent; the fiber surface has a nano-pore structure; the mass fraction of the beta crystal nucleating agent on the fine fiber layer side is higher than that on the coarse fiber layer side, and the mass fraction difference is 0.06-0.10 wt%; the surface potential difference between the two layers is 80-200 V; the supercritical CO2 assisted melt-blowing forming and layered reverse corona electrostatic preparation process are adopted, so that the filtering efficiency is greatly improved while the airflow resistance is significantly reduced; the beta phase thickness gradient construction and the layered electrostatic technology effectively enhance the fiber surface charge density; the CO2 recovery rate is more than 95%, and the technical problem that high efficiency and low resistance cannot be considered together is solved, so that the application has wide industrial application value.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of automobile filter, and relates to a filter element for automobile filter and a preparation method thereof. BACKGROUND

[0002] With the rapid development of automobile industry and the increasingly stringent environmental regulations, the performance requirements of automobile air filter as a key component of engine intake system are continuously improved. Modern automobile engines have extremely high requirements for air quality. Not only does the filter need to efficiently filter harmful substances such as particulate matter, dust and pollen in the air to ensure the cleanliness of the engine and prolong the service life, but also needs to have extremely low airflow resistance to ensure the power performance and fuel economy of the engine. In the environment of frequent urban smog and intensified industrial dust pollution, the filtration efficiency of the filter is directly related to the reliability of the engine and the emission level of the vehicle, while excessive airflow resistance will lead to a decrease in engine power and an increase in fuel consumption, affecting the overall performance of the vehicle. Therefore, developing a filter element material for automobile filter with high filtration efficiency and low airflow resistance has important strategic significance for improving the competitiveness of automobile products, meeting stringent environmental standards and promoting the sustainable development of automobile industry, and has become an important research direction in the fields of material science and automobile engineering.

[0003] At present, there are still significant technical bottlenecks in balancing high efficiency and low resistance of filter elements for automobile filter, mainly due to the inherent limitations of traditional filter element material structure design and preparation process. For example, a filter element for automobile air filter is disclosed in Chinese Patent No. CN204041300U, but there is a problem that the filtration efficiency and airflow resistance are difficult to coordinate. Traditional single-layer or simple multi-layer filter element structure often uses uniform fiber distribution and pore size design, which leads to an increase in material density and thickness when pursuing high filtration efficiency, thereby significantly increasing airflow resistance, and reducing resistance will sacrifice filtration performance, forming a contradictory relationship between performance indicators. In addition, the existing preparation process lacks precise control ability of fiber microstructure, and cannot realize directional design of fiber surface properties at the molecular level, which leads to insufficient electrostatic adsorption capacity and further limits the improvement of filtration efficiency. At the same time, the traditional electret process has problems of uneven charge distribution and poor stability, which makes the performance of the filter element decay significantly during long-term use, and cannot maintain the excellent performance in the initial stage, which seriously restricts the further breakthrough of the overall performance of automobile filter and the improvement of the industry technology level. SUMMARY

[0004] (1) Technical problems solved

[0005] The purpose of the present application is to provide a filter element for automobile filter and a preparation method thereof, which solves the problem that the current filter element for automobile filter cannot balance high efficiency and low resistance.

[0006] (2) Technical solutions

[0007] To achieve the above object, the present application provides the following technical solutions:

[0008] A filter element for an automobile filter, comprising a double-layer composite structure of a coarse fiber layer and a fine fiber layer arranged in sequence in the direction of air flow,

[0009] The coarse fiber layer and the fine fiber layer are both composed of polypropylene, an antioxidant and a beta crystal nucleating agent.

[0010] The fiber surface of the coarse fiber layer and the fine fiber layer both has a nano-pore structure,

[0011] The mass fraction of the beta crystal nucleating agent on the fine fiber layer side is higher than that on the coarse fiber layer side, the mass fraction difference is 0.06-0.10 wt%, and there is a surface potential difference of 80-200 V between the coarse fiber layer side and the fine fiber layer side, wherein the coarse fiber layer side is a positive potential and the fine fiber layer side is a negative potential.

[0012] Further, the thickness of the coarse fiber layer is 50-150 μm, and the thickness of the fine fiber layer is 20-80 μm.

[0013] The average fiber diameter of the coarse fiber layer is 8-12 μm, and the average fiber diameter of the fine fiber layer is 2-5 μm.

[0014] Further, the mass fraction of the antioxidant in the coarse fiber layer and the fine fiber layer is both 0.1-0.3 wt%, and the antioxidant is one or more of 2,6-di-tert-butyl-4-methylphenol, tetra[methylene-3-(3',5'-di-tert-butyl-4'-hydroxyphenyl) propionate] methane, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl) benzene.

[0015] Further, the beta crystal nucleating agent is selected from one or more of N,N'-dicyclohexyl naphthalene-2,6-dicarboxamide, phenylacetone carbazate, N,N'-diphenyl adipamide.

[0016] The mass fraction of the beta crystal nucleating agent in the fine fiber layer is 0.11-0.22 wt%.

[0017] The application adopts a double-layer composite structure design mainly for enhancing the filtering performance and low resistance performance of the filter element of the automobile filter. By sequentially arranging the coarse fiber layer and the fine fiber layer in the airflow direction, the technical strategy of staged filtration is realized, wherein the coarse fiber layer undertakes the pre-filtering function, the fine fiber layer is responsible for fine filtering, and the synergistic effect of the two layers significantly improves the overall filtering efficiency. The use of polypropylene matrix material and antioxidants effectively guarantees the long-term stability of the filter element, and the introduction of antioxidants such as 2,6-di-tert-butyl-4-methylphenol, tetra[methylene-3-(3',5'-di-tert-butyl-4'-hydroxyphenyl) propionate] methane, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl) benzene, etc. can prevent the oxidative degradation of the material during use. The differential distribution design of the beta crystal nucleating agent such as N,N'-dicyclohexyl naphthalene-2,6-dicarboxamide, phenylacetone carbamido urea, and N,N'-diphenyl adipamide is the core innovation point of the application. The higher mass fraction of the beta crystal nucleating agent on the fine fiber layer side promotes the formation of a specific crystal form, improves the microstructure and surface properties of the fiber. The construction of the nanopore structure increases the specific surface area of the fiber, improves the particle capture efficiency, and the surface potential difference formed by the positive potential of the coarse fiber layer and the negative potential of the fine fiber layer further enhances the electrostatic adsorption capacity. The gradient design of different fiber diameters realizes the optimization balance of resistance and efficiency, and the synergistic effect between the components realizes the unity of high-efficiency filtering and low resistance.

[0018] The application also discloses a preparation method of the filter element for the automobile filter, which comprises supercritical CO2 assisted melt blowing forming and layered reverse corona electrification, and specifically comprises the following steps:

[0019] S1: formula pretreatment and supercritical injection preparation: dry mixing and drying polypropylene, antioxidants and beta crystal nucleating agent, and delivering carbon dioxide to the post-extruder mixing zone to make the mass fraction of the melt be 0.5-2.0 wt%;

[0020] S2: double-layer melt blowing deposition and beta phase thickness gradient construction: adopting a double-extrusion double-metering mode to construct a thickness formula difference, so that the mass fraction of the beta crystal nucleating agent on the fine fiber layer side is higher than that on the coarse fiber layer side, and the mass fraction difference is 0.06-0.10 wt%;

[0021] S3: layered reverse corona electrification: applying a positive voltage of +25 to +45 kV to the coarse fiber layer side and a negative voltage of -25 to -45 kV to the fine fiber layer side to obtain a thickness surface potential difference of 80-200 V.

[0022] Further, the step S1 heats the cylinder and the die head to 230-255 DEG C, controls the die head pressure to 0.8-1.2 MPa through a back pressure valve, dry mixes for 10-20 min in a closed mixer, transports the carbon dioxide under the conditions of 31-50 DEG C and 7.5-12 MPa, and controls the CO2 residence time in the melt to 20-60 s.

[0023] Further, the step S2 deposits the coarse fiber layer first and then the fine fiber layer, sets the hot air temperature to 220-260 DEG C, the air speed to 150-220 m / s -1 , the distance from the spinning nozzle to the collection net to 0.20-0.35 m, and the collection line speed to 0.5-1.5 m / min -1 .

[0024] Further, the coarse fiber layer has a unit area mass of 10-15 g / m -2 , the fine fiber layer has a unit area mass of 6-10 g / m -2 , the process parameters are fine tuned through online mass and air permeability closed loop control, and the recovery rate is ≥95% through CO2 condensation and compression recovery.

[0025] Further, the step S3 has an electrode-material distance of 50-80 mm, adopts a straight or serpentine scanning track, a duty cycle of 40-80%, and a scanning speed of 0.1-0.5 m / s -1 , and then is heat treated at 50-70 DEG C for 10-20 min, and further is post-processed and formed: the material is shaped and then is hot-pressed with a polypropylene spun-bond base cloth, and is formed into a pleat with a pleat height of 20-30 mm and a pitch of 2.0-3.0 mm.

[0026] The application adopts a supercritical CO2 assisted melt-blowing forming and layered reverse corona electret preparation method, mainly used for enhancing the filtering efficiency and low resistance performance of the filter element of the automobile filter. The supercritical CO2 is introduced into the polypropylene melt as a physical foaming agent, and the melt flowability and fiber forming quality are improved through its unique thermodynamic properties. Meanwhile, the rapid phase change process of the supercritical CO2 helps to form a more fine fiber structure and increase the specific surface area. The uniform dry mixing of polypropylene, antioxidant and beta crystal nucleating agent in the formula pretreatment link lays a foundation for the subsequent forming. The construction of the beta phase thickness gradient realized by the double-extrusion double-metering method is the core innovation of the preparation process. By accurately controlling the mass fraction difference of the beta crystal nucleating agent between the fine fiber layer side and the coarse fiber layer side, the differential development of the crystal structure between different layers is promoted, and then the microstructure and performance of the fiber are affected. The layered reverse corona electret technology applies a positive voltage to the coarse fiber layer and a negative voltage to the fine fiber layer for differential treatment, and a stable electric field gradient is established in the material, which significantly enhances the electrostatic adsorption capacity of the fiber. The accurate control of process parameters such as barrel die temperature, die pressure, hot air parameters and electrode spacing, combined with the CO2 condensation compression recovery system, not only ensures the stability of product quality, but also realizes the green and environmentally friendly production process. The synergistic optimization between the process links finally realizes the efficient preparation of high-performance filter elements.

[0027] The application of a filter element to an automobile air filter.

[0028] (3) Beneficial technical effects

[0029] 1. Significantly improve the filtering efficiency and reduce the air flow resistance: through the double-layer composite structure design, the coarse fiber layer undertakes the pre-filtering function, and the fine fiber layer is responsible for fine filtering, realizing the staged filtering strategy. The nano-pore structure increases the specific surface area of the fiber, improves the particulate matter capture efficiency, and the fiber diameter gradient design between the coarse fiber layer and the fine fiber layer effectively balances the filtering efficiency and air flow resistance, solving the technical problem that the traditional filter element is difficult to balance high efficiency and low resistance.

[0030] 2. Effectively enhance the electrostatic adsorption capacity: through the layered reverse corona electret technology, the surface potential difference of the coarse fiber layer positive potential and the fine fiber layer negative potential is established, a stable electric field gradient is formed in the material, and the electrostatic adsorption capacity of the fiber is significantly enhanced. Meanwhile, the differential distribution of the beta crystal nucleating agent such as N,N'-dicyclohexyl naphthalene-2,6-dicarboxamide, phenyl ketone semicarbazide and N,N'-diphenyl adipamide promotes the formation of specific crystal forms, improves the fiber microstructure and surface properties, and further improves the electrostatic capture effect.

[0031] 3. Significantly improve the long-term stability of the material: by introducing 2,6-di-tert-butyl-4-methylphenol, tetra[methylene-3-(3',5'-di-tert-butyl-4'-hydroxyphenyl) propionate] methane, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl) benzene and other antioxidants, effectively prevent the oxidative degradation of the polypropylene matrix material during use, ensure the stability of the long-term use performance of the filter element, and prolong the service life of the product.

[0032] 4. Realize the green and environmentally friendly production process: adopt supercritical CO2 assisted melt blowing forming technology, supercritical CO2 as a clean physical foaming agent to improve the melt flowability and fiber forming quality, and at the same time implement CO2 condensation compression recovery system, the recovery rate can reach more than 95%, reduce environmental pollution, realize green and sustainable production process, meet the modern industrial environmental protection requirements.

[0033] 5. Improve the precise control ability of the preparation process: by means of double extrusion and double metering, the beta phase thickness gradient is constructed, the mass fraction difference of beta crystal nucleating agent of fine fiber layer and coarse fiber layer is precisely controlled, the process parameters are fine tuned by combining online grammage and air permeability closed loop control system, the precise control of product quality and stable production are realized, and the controllability and reproducibility of the preparation process are improved. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 The fine fiber layer morphology diagram prepared for example 2 of the present application.

[0035] Figure 2 The coarse fiber layer morphology diagram prepared for example 2 of the present application.

[0036] Figure 3 The XRD phase analysis diagram of the fine fiber layer and the coarse fiber layer prepared for example 2 of the present application.

[0037] Figure 4 The fine fiber layer morphology diagram of comparative example 5 of the present application.

[0038] Figure 5 The influence of the mass fraction difference of beta crystal nucleating agent on the filtration efficiency and initial resistance.

[0039] Figure 6 The influence of the surface potential difference on the filtration efficiency and initial resistance.

[0040] Figure 7 The influence of the heating temperature of the machine cylinder and the die on the filtration efficiency and initial resistance.

[0041] Figure 8 The influence of the CO2 mass fraction on the filtration efficiency and initial resistance.

[0042] Figure 9This invention relates to the effect of hot air temperature on filtration efficiency and initial resistance. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Example 1

[0044] A filter element for an automotive air filter includes a double-layer composite structure consisting of a coarse fiber layer and a fine fiber layer arranged sequentially in the airflow direction. In this embodiment, both the coarse and fine fiber layers are composed of polypropylene, an antioxidant, and a β-crystal nucleating agent. The fiber surfaces of both the coarse and fine fiber layers have a nanoporous structure. The mass fraction of the β-crystal nucleating agent on the fine fiber layer side is higher than that on the coarse fiber layer side, with a mass fraction difference of 0.08 wt%. There is a surface potential difference of 130 V between the coarse and fine fiber layers, with the coarse fiber layer side having a positive potential and the fine fiber layer side having a negative potential. The thickness of the coarse fiber layer in this embodiment is 90 μm, and the thickness of the fine fiber layer is 50 μm. The average fiber diameter of the coarse fiber layer is 10 μm, and the average fiber diameter of the fine fiber layer is 3.5 μm. The antioxidant in this embodiment has a mass fraction of 0.2 wt% in both the coarse and fine fiber layers, and the antioxidant in this embodiment is 2,6-di-tert-butyl-4-methylphenol. In this embodiment, the β-crystal nucleating agent is selected from N,N'-dicyclohexylnaphthalene-2,6-dicarboxamide; wherein, the mass fraction of the β-crystal nucleating agent in the fine fiber layer is 0.16 wt%. The preparation method includes supercritical CO2-assisted melt-blown molding and layered reverse corona electret, specifically including the following steps: S1 Formulation pretreatment and supercritical injection preparation: Polypropylene, antioxidant and β-crystal nucleating agent are dry-mixed and dried, and carbon dioxide is transported to the mixing zone of the extruder to make the mass fraction relative to the melt 1.2 wt%; S2 Bilayer melt-blown deposition and β-phase thickness gradient construction: A thickness gradient is constructed by using a dual extrusion dual metering method so that the mass fraction of the β-crystal nucleating agent on the fine fiber layer side is higher than that on the coarse fiber layer side and the mass fraction difference is 0.08 wt%; S3 Layered reverse corona electret: A positive voltage of +35 kV is applied to the coarse fiber layer side and a negative voltage of -35 kV is applied to the fine fiber layer side to obtain a thickness surface potential difference of 130 V. In step S1 of this embodiment, the barrel and die head are heated to 240°C, and the die pressure is controlled to 1.0 MPa by a back pressure valve. Dry mixing is performed for 15 minutes in a closed mixer. Carbon dioxide is supplied at 40°C and 10 MPa, and the CO2 residence time in the melt is controlled to be 40 seconds. In step S2 of this embodiment, a coarse fiber layer is deposited first, followed by a fine fiber layer. The hot air temperature is set to 240°C, and the air velocity is 180 m / s. -1 The distance from the spinneret to the collecting net is 0.28 m, and the collecting linear velocity is 1.0 m·min. -1 The mass per unit area of ​​the coarse fiber layer is 12 g·m³.-2 , the fine fiber layer unit area mass is 8 g·m -2 , the process parameters are fine-tuned through online closed-loop control of the grammage and the air permeability, CO2 condensation compression recovery is implemented to make the recovery rate 95%. In step S3 of the embodiment, the electrode and the material are spaced apart by 65 mm, a linear scanning trajectory is adopted, the duty cycle is 60%, and the scanning speed is 0.3 m·s -1 , then heat-treated at 60℃ for 15 min, further post-processing forming: the material is shaped and then hot-pressed with a polypropylene spun-bond base cloth to form a pleat, the pleat height is 25 mm, and the pitch is 2.5 mm.

[0045] The embodiment adopts moderately conservative parameter configurations, has the characteristics of good process stability and controllable product quality, and is suitable for batch production application scenarios of standard passenger vehicle air filters. Example 2

[0046] The application discloses a filter element for an automobile filter, which comprises a double-layer composite structure of a coarse fiber layer and a fine fiber layer arranged in sequence in the direction of air flow; the coarse fiber layer and the fine fiber layer are both composed of polypropylene, an antioxidant and a beta crystal nucleating agent; the fiber surfaces of the coarse fiber layer and the fine fiber layer both have nano-pore structures; the mass fraction of the beta crystal nucleating agent on the fine fiber layer side is higher than that on the coarse fiber layer side, the mass fraction difference is 0.06 wt%, and the surface potential difference between the coarse fiber layer side and the fine fiber layer side is 80 V, wherein the coarse fiber layer side is a positive potential, and the fine fiber layer side is a negative potential; the thickness of the coarse fiber layer is 50 microns, and the thickness of the fine fiber layer is 20 microns; the average fiber diameter of the coarse fiber layer is 8 microns, and the average fiber diameter of the fine fiber layer is 2 microns; the mass fraction of the antioxidant in the coarse fiber layer and the fine fiber layer is both 0.1 wt%, and the antioxidant is tetra[methylene-3-(3',5'-di-tert-butyl-4'-hydroxyphenyl) propionate] methane; the beta crystal nucleating agent is selected from acetophenone semicarbazone; the mass fraction of the beta crystal nucleating agent in the fine fiber layer is 0.11 wt%. The preparation method comprises supercritical CO2 assisted melt-blowing forming and layered reverse corona charging, and specifically comprises the following steps: S1, formula pretreatment and supercritical injection preparation: dry mixing and drying polypropylene, an antioxidant and a beta crystal nucleating agent, and conveying carbon dioxide to the rear mixing zone of an extruder to make the mass fraction of the carbon dioxide in the melt be 0.5 wt%; S2, double-layer melt-blowing deposition and beta phase thickness gradient construction: adopting a double-extrusion double-metering mode to construct a thickness formula difference to make the mass fraction of the beta crystal nucleating agent on the fine fiber layer side be higher than that on the coarse fiber layer side, and the mass fraction difference be 0.06 wt%; S3, layered reverse corona charging: applying a positive voltage of +25 kV to the coarse fiber layer side and a negative voltage of -25 kV to the fine fiber layer side to obtain a thickness surface potential difference of 80 V. In the step S1, the cylinder and the die head are heated to 230 DEG C, the die head pressure is controlled to be 0.8 MPa through a back pressure valve, dry mixing is performed in a closed mixer for 10 minutes, the carbon dioxide is conveyed under the condition of 31 DEG C and 7.5 MPa, and the CO2 residence time in the melt is controlled to be 20 seconds. In the step S2, the coarse fiber layer is deposited first and then the fine fiber layer is deposited, the hot air temperature is set to be 220 DEG C, the air speed is 150 m / s -1 , the distance from the spinning port to the collection net is 0.20 m, and the collection line speed is 0.5 m / min -1 . The unit area mass of the coarse fiber layer is 10 g / m -2 , the unit area mass of the fine fiber layer is 6 g / m -2 , the process parameters are finely adjusted through online weight and air permeability closed loop control, CO2 condensation compression recovery is implemented to make the recovery rate be 96%. In the step S3, the electrode and the material spacing is 50 mm, a snake-shaped scanning track is adopted, the duty cycle is 40%, and the scanning speed is 0.1 m / s -1, followed by heat treatment at 50℃ for 10 min, further post-processing forming: after shaping the material, hot-press composite with polypropylene spun-bond base cloth, fold forming to make the fold height 20 mm, pitch 2.0 mm.

[0047] The embodiment adopts low-resistance optimized parameter configuration, has the characteristics of small air flow resistance and good air permeability, and is suitable for high-power engines or sports vehicles with high requirements for low resistance in application scenarios. Embodiment 3

[0048] A filter element for an automobile filter includes a double-layer composite structure composed of a coarse fiber layer and a fine fiber layer arranged in sequence in the direction of air flow. The coarse fiber layer and the fine fiber layer of the embodiment are composed of polypropylene, an antioxidant, and a beta crystal nucleating agent. The fiber surfaces of the coarse fiber layer and the fine fiber layer of the embodiment have nano-pore structures. The mass fraction of the beta crystal nucleating agent on the fine fiber layer side is higher than that on the coarse fiber layer side, and the mass fraction difference is 0.10 wt%. There is a surface potential difference of 200 V between the coarse fiber layer side and the fine fiber layer side, wherein the coarse fiber layer side is a positive potential, and the fine fiber layer side is a negative potential. The thickness of the coarse fiber layer of the embodiment is 150 μm, and the thickness of the fine fiber layer is 80 μm. The average fiber diameter of the coarse fiber layer of the embodiment is 12 μm, and the average fiber diameter of the fine fiber layer is 5 μm. The mass fraction of the antioxidant in the coarse fiber layer and the fine fiber layer of the embodiment is 0.3 wt%. The antioxidant of the embodiment is a mixture of 2,6-di-tert-butyl-4-methylphenol and tetra[methylene-3-(3',5'-di-tert-butyl-4'-hydroxyphenyl) propionate] methane, with a mass ratio of 1:1. The beta crystal nucleating agent of the embodiment is selected from N,N'-diphenyl adipamide. The mass fraction of the beta crystal nucleating agent in the fine fiber layer is 0.22 wt%. The preparation method includes supercritical CO2 assisted melt blowing and layered reverse corona electrification, and specifically includes the following steps: S1. Formula pretreatment and supercritical injection preparation: dry mixing and drying polypropylene, an antioxidant, and a beta crystal nucleating agent, and delivering carbon dioxide to the extruder rear section mixing zone to make the mass fraction relative to the melt 2.0 wt%; S2. Double-layer melt blowing deposition and beta phase thickness gradient construction: using a double-extrusion double-metering method to construct a thickness formula difference to make the mass fraction of the beta crystal nucleating agent on the fine fiber layer side higher than that on the coarse fiber layer side, and the mass fraction difference is 0.10 wt%; S3. Layered reverse corona electrification: applying a positive voltage of +45 kV to the coarse fiber layer side and a negative voltage of -45 kV to the fine fiber layer side to obtain a thickness surface potential difference of 200 V. In step S1 of the embodiment, the barrel and die are heated to 255℃, the die pressure is controlled to 1.2 MPa by a back pressure valve, dry mixing is performed in a closed mixer for 20 min, carbon dioxide is delivered at 50℃ and 12 MPa, and the CO2 residence time in the melt is controlled to 60 s. In step S2 of the embodiment, the coarse fiber layer is deposited first and then the fine fiber layer is deposited. The hot air temperature is set to 260℃, and the air speed is 220 m·s-1 The distance from the spinneret to the collection net is 0.35 m, and the collection line speed is 1.5 m·min -1 The mass per unit area of the coarse fiber layer is 15 g·m -2 The mass per unit area of the fine fiber layer is 10 g·m -2 The process parameters are fine-tuned through online weight and air permeability closed-loop control, CO2 condensation compression recovery is implemented to make the recovery rate 95%. In step S3 of this embodiment, the electrode and material spacing is 80 mm, a straight scanning trajectory is adopted, the duty cycle is 80%, and the scanning speed is 0.5 m·s -1 Then, heat treatment is performed at 70℃ for 20 min, further post-processing is performed: the material is shaped and then hot-pressed with a polypropylene spun-bond base cloth, and pleat forming is performed to make the pleat height 30 mm and the pitch 3.0 mm.

[0049] This embodiment has the characteristics of high filtering efficiency and strong electrostatic adsorption capacity, and is suitable for heavy vehicles and special working condition application scenarios in severe sand and dust environment or with extremely high requirements for air quality. Example 4

[0050] The application discloses a filter element for an automobile filter, which comprises a double-layer composite structure of a coarse fiber layer and a fine fiber layer arranged in sequence in the direction of air flow; the coarse fiber layer and the fine fiber layer are both composed of polypropylene, an antioxidant and a beta crystal nucleating agent; the fiber surfaces of the coarse fiber layer and the fine fiber layer both have nano-pore structures; the mass fraction of the beta crystal nucleating agent on the fine fiber layer side is higher than that on the coarse fiber layer side, the mass fraction difference is 0.09 wt%, and the surface potential difference between the coarse fiber layer side and the fine fiber layer side is 170 V, wherein the coarse fiber layer side is a positive potential, and the fine fiber layer side is a negative potential; the thickness of the coarse fiber layer is 120 mu m, and the thickness of the fine fiber layer is 65 mu m; the average fiber diameter of the coarse fiber layer is 9 mu m, and the average fiber diameter of the fine fiber layer is 4 mu m; the mass fraction of the antioxidant in the coarse fiber layer and the fine fiber layer is both 0.25 wt%; the antioxidant is a mixture of 2,6-di-tert-butyl-4-methylphenol, tetra[methylene-3-(3',5'-di-tert-butyl-4'-hydroxyphenyl) propionate] methane and 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl) benzene, and the mass ratio is 2:1:1; the beta crystal nucleating agent is selected from a mixture of N,N'-dicyclohexyl naphthalene-2,6-dicarboxamide and phenylacetone amino urea, and the mass ratio is 3:1; the mass fraction of the beta crystal nucleating agent in the fine fiber layer is 0.19 wt%; and the preparation method comprises supercritical CO2 assisted melt-blowing and layered reverse corona charging, and specifically comprises the following steps: S1, formula pretreatment and supercritical injection preparation: dry mixing and drying polypropylene, an antioxidant and a beta crystal nucleating agent, and delivering carbon dioxide to the melt mixing zone of the rear section of an extruder to make the mass fraction of the carbon dioxide in the melt be 1.7 wt%; S2, double-layer melt-blowing deposition and beta phase thickness gradient construction: adopting a double-extrusion double-metering mode to construct a thickness formula difference to make the mass fraction of the beta crystal nucleating agent on the fine fiber layer side be higher than that on the coarse fiber layer side, and the mass fraction difference be 0.09 wt%; S3, layered reverse corona charging: applying a positive voltage of +42 kV to the coarse fiber layer side and a negative voltage of -42 kV to the fine fiber layer side to obtain a thickness surface potential difference of 170 V. -1 , wherein the barrel and the die head are heated to 248 DEG C in the step S1, the die head pressure is controlled to be 1.1 MPa through a back pressure valve, the dry mixing is performed in a closed mixer for 18 min, the carbon dioxide is delivered under the conditions of 45 DEG C and 11 MPa, and the CO2 residence time in the melt is controlled to be 50 s; the coarse fiber layer is deposited first and then the fine fiber layer is deposited in the step S2, the hot air temperature is set to be 250 DEG C, the air speed is 200 m / s -1 , the distance from the spinning port to the collection net is 0.32 m, and the collection line speed is 1.2 m / min -2 ; the unit area mass of the coarse fiber layer is 13 g / m -2, the process parameters are fine-tuned through online basis weight and air permeability closed-loop control, CO2 condensation compression recovery is implemented to achieve a recovery rate of 97%. In step S3 of the embodiment, the electrode and material spacing is 70 mm, a serpentine scanning trajectory is used, the duty cycle is 65%, and the scanning speed is 0.4 m·s -1 , and then heat-treated at 65°C for 18 min, further post-processing forming: after shaping, the material is hot-pressed with a polypropylene spun-bond base cloth, and pleat forming is performed to make the pleat height 28 mm and the pitch 2.8 mm.

[0051] The embodiment adopts balanced and optimized parameter configurations, has excellent comprehensive performance and long service life, and is suitable for high-end passenger vehicles and commercial vehicles that require both filtration efficiency and low resistance in all operating conditions.

[0052] Comparative Example 1: substantially the same as Example 1, except that the mass fraction difference of the beta crystal nucleating agent between the coarse fiber layer side and the fine fiber layer side is 0.03 wt%.

[0053] Comparative Example 2: substantially the same as Example 1, except that the surface potential difference between the coarse fiber layer side and the fine fiber layer side is 40 V.

[0054] Comparative Example 3: substantially the same as Example 1, except that a single-layer structure is used, only containing a fine fiber layer, and the setting of a coarse fiber layer is removed.

[0055] Comparative Example 4: substantially the same as Example 1, except that no beta crystal nucleating agent is added in the coarse fiber layer and the fine fiber layer, and only polypropylene and an antioxidant are used.

[0056] Comparative Example 5: substantially the same as Example 1, except that the fiber surface does not have a nanopore structure, and a conventional melt-blown process is used to prepare smooth-surface fibers.

[0057] Comparative Example 6: substantially the same as Example 1, except that the barrel and die are heated to 200°C in step S1.

[0058] Comparative Example 7: substantially the same as Example 1, except that no supercritical CO2 is added in step S1, and only a conventional melt-blown forming process is used.

[0059] Comparative Example 8: substantially the same as Example 1, except that a positive voltage of +35 kV is applied to both the coarse fiber layer side and the fine fiber layer side in step S3, and no layered reverse corona and electret treatment is used.

[0060] Comparative Example 9: substantially the same as Example 1, except that the average fiber diameter of the fine fiber layer is 8 μm, which is the same as the average fiber diameter of the coarse fiber layer, and no fiber diameter gradient is formed.

[0061] Comparative Example 10: Essentially the same as Example 1, except that the hot air temperature in Step S2 was set to 180°C.

[0062] Comparative Example 11: Essentially the same as Example 1, except that the mass fraction of antioxidant was 0.05 wt%.

[0063] Comparative Example 12: Essentially the same as Example 1, except that the CO2 residence time in the melt was controlled to 5 s in Step S1.

[0064] Comparative Example 13: Essentially the same as Example 1, except that the fine fiber layer thickness was 100 pm and the coarse fiber layer thickness was 50 pm, so that the fine fiber layer thickness was greater than the coarse fiber layer thickness.

[0065] Comparative Example 14: Essentially the same as Example 1, except that the electrode-to-material distance was 30 mm in Step S3.

[0066] Comparative Example 15: Essentially the same as Example 1, except that sodium benzoate was used as the beta crystal nucleating agent.

[0067] Performance Test:

[0068] Filter Efficiency Test: Test Object: Double-layer composite structure material for filter cartridges for automotive air filters. Test Purpose: To evaluate the filter efficiency of the filter cartridge for different particle sizes and to verify its core performance in automotive air filtration applications. Test Principle: Measure the upstream and downstream particle concentrations by passing standard test dust through the filter cartridge at a specified flow rate, and calculate the filtration efficiency. Experimental Method: Install the filter cartridge sample on a standard test bench, use ISO 12103-1 A2 fine test dust as the challenge particles, test at a flow rate of 1000 L / min, and use a laser particle size analyzer to monitor the upstream and downstream particle concentration distributions simultaneously. Standard Basis: Test according to ISO 5011:2020 “Test Method for Air Filters for Road Vehicles”. Key Parameters: Test temperature is 23±2°C, relative humidity is 45-75%, test dust concentration is 200±10 mg / m³, and test time continues until the dust capacity reaches the design value. Data Processing: The filtration efficiency η is calculated by the formula η=(Cup-Cdown) / Cup×100%, where Cup is the upstream concentration and Cdown is the downstream concentration. The statistical efficiency value is required in the range of 0.3-10 pm particle size.

[0069] Initial Resistance Test: Test object: Double-layer composite structure material for filter element of automotive air cleaner. Test purpose: Measure the air flow resistance of the filter element in a clean state and evaluate its impact on the engine intake system. Test principle: Under standard flow conditions, measure the pressure difference before and after the air passes through the filter element to reflect the degree of air flow obstruction. Experimental method: Install the clean filter element in a sealed test chamber, use a standard fan to provide a constant air flow, and measure the pressure difference upstream and downstream of the filter element through a high-precision differential pressure sensor, while monitoring the flow stability. Standard basis: Perform according to the resistance test method in ISO 5011:2020 standard. Key parameters: Standard test flow is 1000 L / min, test environment temperature is 23±2℃, relative humidity is 45-75%, pressure difference measurement accuracy is not less than ±1 Pa. Data processing: Initial resistance Δp is recorded in Pa, requires continuous measurement for 5 times to take average value, test result should meet the technical requirements of automobile manufacturers, generally not more than 250 Pa.

[0070] Dust Holding Capacity Test: Test object: Double-layer composite structure material for filter element of automotive air cleaner. Test purpose: Evaluate the dust holding capacity and service life of the filter element during use and determine its replacement cycle under actual working conditions. Test principle: Continuously supply standard test dust to the filter element and monitor the resistance growth process, stop testing when the resistance reaches the set endpoint value and weigh the dust holding capacity. Experimental method: Continuously supply ISO 12103-1 A2 test dust under constant flow, monitor the resistance change of the filter element in real time, stop testing when the resistance reaches 5 times the initial resistance or the absolute value reaches 2500 Pa, take out the filter element and weigh the total dust holding capacity. Standard basis: Strictly follow the dust holding capacity test procedure in ISO 5011:2020 standard. Key parameters: Test flow is 1000 L / min, dust concentration is 200±10 mg / m³, test temperature is 23±2℃, relative humidity is 45-75%, weighing accuracy is 0.1g. Data processing: Dust holding capacity is calculated in g / m², resistance growth curve is recorded at the same time, dust holding characteristics and service performance of the filter element are evaluated, dust holding capacity should not be less than the average level of similar products in the industry.

[0071] Surface potential distribution test experiment: The surface of the coarse fiber layer and the fine fiber layer of the double-layer composite structure of the filter element for automobile filter is tested. Test purpose: Measure the surface potential distribution of the filter element after electrostatic treatment, and verify the effect of the layered reverse corona electrostatic process. Test principle: The non-contact surface potential meter is used to measure the static potential of the material surface, and the distribution and stability of the electrostatic charge are evaluated. Experimental method: The surface potential meter is used to measure the surface potential of the filter element in a grid scan, with a measurement point spacing of 5 mm. The surface potential of the coarse fiber layer side and the fine fiber layer side is measured respectively, and the potential distribution graph and statistical data are recorded. Key parameters: Test environment temperature 23±2℃, relative humidity 45-55%, probe to sample distance 2 mm, measurement accuracy ±5 V, scanning speed 10 mm / s. Data processing: Calculate the average surface potential difference between the coarse fiber layer and the fine fiber layer, which should be within the range of 80-200 V. At the same time, evaluate the uniformity of the potential distribution, and the standard deviation should be less than 15% of the average value.

[0072] Thermal stability test experiment: The double-layer composite structure material of the filter element for automobile filter is tested. Test purpose: Evaluate the thermal stability of the filter element material in high temperature environment to ensure its reliability in the application of automobile engine compartment. Test principle: The mass change of the material during programmed temperature rise is monitored by thermal gravimetric analysis to analyze the thermal decomposition behavior and thermal stability temperature. Experimental method: Take 10 mg of sample and place it in the thermal gravimetric analyzer. Heat from room temperature to 600℃ at a rate of 10℃ / min under nitrogen protection, and record the mass change and temperature. Analyze the thermal decomposition temperature and weight loss behavior. Standard basis: Test according to ASTM E1131-08 (2014) "Thermal Gravimetric Analysis Implementation Procedure". Key parameters: Sample mass 8-12 mg, nitrogen flow rate 50 mL / min, heating rate 10℃ / min, temperature accuracy ±1℃, balance accuracy 0.1 μg. Data processing: Determine the 5% mass loss temperature T5% and the maximum decomposition rate temperature Tmax, draw the TGA and DTG curves, and require that T5% be not less than 280℃. Evaluate the long-term stability of the material in the engine compartment environment temperature.

[0073] Dust holding capacity test: The test object is a double-layer composite structure material for filter cartridges of automotive filters. The test purpose is to evaluate the dust holding capacity and service life of the filter cartridge during use and determine its replacement cycle under actual working conditions. The test principle is to continuously supply standard test dust to the filter cartridge and monitor the resistance growth process. When the resistance reaches the set endpoint value, the test is stopped and the dust holding capacity is weighed. Experimental method: Continuously supply ISO 12103-1 A2 test dust at a constant flow rate, monitor the resistance change of the filter cartridge in real time, stop the test when the resistance reaches 5 times the initial resistance or the absolute value reaches 2500 Pa, remove the filter cartridge and weigh the total dust holding capacity. Key parameters: test flow rate 1000 L / min, dust concentration 200±10 mg / m³, test temperature 23±2℃, relative humidity 45-75%, weighing accuracy 0.1 g. Data processing: The dust holding capacity is calculated in g / m², the resistance growth curve is recorded, the dust holding characteristics and use performance of the filter cartridge are evaluated, and the dust holding capacity is required to be not less than the average level of similar products in the industry.

[0074] Surface potential distribution test: The test object is the surface of the coarse fiber layer and the fine fiber layer of the double-layer composite structure of the filter cartridge for automotive filters. The test purpose is to measure the potential distribution on the surface of the filter cartridge after the electret treatment and verify the effect of the layered reverse corona electret process. The test principle is to measure the static potential on the surface of the material using a non-contact surface potential meter to evaluate the distribution and stability of the electret charge. Experimental method: Use the surface potential meter to perform grid scanning measurement on the surface of the filter cartridge, the measurement point spacing is 5 mm, and the surface potential of the coarse fiber layer side and the fine fiber layer side is measured respectively, and the potential distribution graph and statistical data are recorded. Key parameters: test environment temperature 23±2℃, relative humidity 45-55%, probe to sample distance 2 mm, measurement accuracy ±5 V, scanning speed 10 mm / s. Data processing: Calculate the average surface potential difference between the coarse fiber layer and the fine fiber layer, which should be in the range of 80-200 V, and evaluate the uniformity of the potential distribution, the standard deviation should be less than 15% of the average value.

[0075] The performance of the examples and comparative examples is summarized in Table 1. The performance of each comparative example is mainly due to the lack of key technical elements or the imbalance of structure-performance relationship caused by deviating from the optimal parameter range. In Comparative Example 1, the insufficient gradient difference of the β-crystal nucleating agent leads to insufficient β-phase crystal transformation, reducing the surface active site density of the fiber, and reducing the filtration efficiency and dust holding capacity. The surface potential difference of Comparative Example 2 is too low, which directly weakens the electrostatic adsorption capacity, and the filtration efficiency is significantly reduced but the resistance changes little. The single-layer structure of Comparative Example 3 destroys the hierarchical filtration mechanism, loses the pre-filtration function of the coarse fiber layer, and significantly reduces the filtration efficiency and dust holding capacity, while the resistance decreases but the overall performance is severely damaged. The lack of β-crystal nucleating agent in Comparative Example 4 causes the microstructure of the fiber to lose control, and the filtration performance and thermal stability are deteriorated. The smooth fiber surface of Comparative Example 5 reduces the specific surface area and surface roughness, reducing the mechanical interception and inertial collision effect, and affecting the filtration efficiency and dust holding capacity. The low-temperature heating of Comparative Example 6 leads to insufficient melt flowability of the polymer, and the fiber forming quality is reduced, which also affects the β-phase crystallization, and the filtration performance and thermal stability are both damaged. The lack of supercritical CO2 assistance in Comparative Example 7 leads to a decrease in fiber microstructure roughness and specific surface area, and a decrease in filtration efficiency and dust holding capacity. The same polarity electrostatic treatment of Comparative Example 8 cannot establish an effective electric field gradient, and the electrostatic adsorption capacity is almost lost, and the filtration efficiency is significantly reduced. The same fiber diameter of Comparative Example 9 destroys the gradient filtration structure, and the synergistic effect of coarse and fine fibers disappears, and the filtration efficiency and dust holding capacity are significantly reduced, but the resistance increases. The low-temperature hot air of Comparative Example 10 affects the final forming quality and surface structure of the fiber, and the filtration performance is reduced and the thermal stability is deteriorated. The low antioxidant content of Comparative Example 11 mainly affects the long-term stability, and the short-term filtration performance changes little but the thermal stability is significantly reduced. The insufficient CO2 residence time of Comparative Example 12 leads to insufficient foaming effect, and the fiber structure density increases, and the filtration efficiency and dust holding capacity decrease. The wrong layer thickness configuration of Comparative Example 13 violates the principle of hierarchical filtration, and the fine fiber layer is too thick, which leads to a sharp increase in resistance, and the coarse fiber layer is too thin, which makes the pre-filtration effect insufficient, and the overall performance is severely deteriorated. The small electrode spacing of Comparative Example 14 leads to uneven distribution of the electrostatic field, and the surface potential difference decreases, and the electrostatic adsorption effect is weakened. The improper β-crystal nucleating agent used in Comparative Example 15 cannot effectively promote the formation of the target crystal form, and the microstructure of the fiber is not controlled, and the filtration performance and thermal stability are affected. The deviation of these technical elements reflects the importance of the synergy of each component of the technical solution and the scientificity of the optimal parameter range.

[0076]

[0077] From Figure 1 and Figure 2The morphology analysis of the fine fiber layer prepared in Example 2 can be clearly observed, the fiber diameter of the fine fiber layer is about 2 μm, and the surface has obvious nanopore structure, this unique surface morphology significantly increases the specific surface area and surface roughness of the fiber, providing more active sites for mechanical interception and electrostatic adsorption of particulate matter, while the coarse fiber layer has a fiber diameter of about 8 μm, also has a nanopore structure but the density is relatively low, forming a reasonable hierarchical filtration gradient. Figure 3 The XRD phase analysis results show that by precisely controlling the thickness gradient distribution of the β crystal nucleating agent, the differential regulation of the β phase crystal form is successfully realized, the β phase crystallinity in the fine fiber layer is significantly higher than that in the coarse fiber layer, and this gradient distribution of crystal phase structure not only optimizes the micro morphology of the fiber, but also enhances the mechanical strength and thermal stability of the material, providing a solid material basis for high-efficiency filtration performance. Figure 4 The morphology of the fine fiber layer of Comparative Example 5 can be clearly seen, the smooth fiber surface lacks nanopore structure, this difference in surface morphology directly leads to a decrease in filtration efficiency from 94.2% in Example 2 to 91.8% in Comparative Example 5, fully verifying the key role of nanopore structure in improving filtration performance. Through single-factor experiment verification of five key parameters, the theoretical optimum point of each parameter is located within the patent range of 72-75%, maintaining a sufficient safety distance from the boundary value, this internal optimal distribution mode not only proves the scientificity and forwardness of the patent parameter range setting, but more importantly ensures the stability and reproducibility of the technical solution in actual application.

[0078] Based on the single-factor variable experiment results of the five key parameters shown in Figures 5-9 The rationality, reliability and effectiveness of the technical solution of the present application have been systematically scientifically verified. Figure 5 The significant influence of the mass fraction difference of the β crystal nucleating agent in the range of 0.06-0.10 wt% on the filtration performance is clearly shown, when the mass fraction difference increases from 0.03 wt% to the theoretical optimum point of 0.087 wt%, the filtration efficiency increases steadily from 93.5% to 97.5%, while the initial resistance presents a reasonable change trend of first decreasing and then increasing, reaching the lowest resistance of 155 Pa at 0.06 wt%, and then moderately increasing with the increase of the β phase nucleation density, this change rule completely conforms to the material science mechanism of β phase crystal form regulation of fiber microstructure, verifying the scientific basis of the parameter optimization interval setting. Figure 6The surface potential difference influence law shows that in the technical interval of 80-200 V, the filtration efficiency increases obviously with the increase of surface potential difference, and reaches the peak value of 97.6% near the theoretical optimum point of 170 V, while the change trend of initial resistance is highly consistent with the theory of electrostatic field strength distribution, and the insufficient electrostatic adsorption force cannot be provided by the low surface potential difference, and the uneven distribution of electric field between fibers increases the airflow resistance caused by the high field strength, and the balance point is just located in the middle and upper position of the technical interval, which fully proves the rationality of the parameter optimization of the layered reverse corona process. Figure 7 The exhibited barrel and die heating temperature influence curve shows the typical polymer melt processing characteristics, in the technical interval of 230-255℃, the filtration efficiency continuously improves with the increase of temperature and reaches the optimal value of 97.8% near 248℃, the initial resistance is the lowest at 230℃, and then increases moderately with the improvement of melt flowability and the improvement of fiber forming quality, and the change law is completely consistent with the rheological properties and beta phase crystallization behavior of polypropylene, which verifies the process rationality of the temperature control strategy. Figure 8 The reflected CO2 mass fraction influence mechanism shows that the regulation effect of supercritical CO2 on the microstructure of the fiber presents obvious stage characteristics in the technical interval of 0.5-2.0 wt%, the filtration efficiency reaches the peak value of 97.8% near the theoretical optimum point of 1.6 wt%, and the change curve of initial resistance clearly reflects the physical and chemical processes of bubble nucleation, growth and stabilization in the supercritical foaming process, and the over-low CO2 concentration cannot form sufficient microporous structure, and the over-high concentration leads to the collapse of pore structure and increases the resistance, and the distribution of the optimal point located at 73% of the technical interval is completely consistent with the expectation of the supercritical fluid theory. Figure 9 The exhibited hot air temperature effect further confirms the key role of temperature control in the final forming stage of the fiber, in the technical interval of 220-260℃, the filtration efficiency reaches the highest value of 98.0% near 250℃ with the increase of hot air temperature, and the change of initial resistance reflects the dynamic balance process of fiber surface structure optimization and airflow channel evolution, and the temperature dependence is highly consistent with the thermal forming mechanism of polymer fibers.

[0079] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit it, although the present application has been described in detail with reference to the above examples, those skilled in the art should understand that any equivalent structural transformation made under the concept of the present application, using the contents of the present application specification and drawings, should be covered within the protection scope of the claims of the present application.

Claims

1. A filter element for an automotive filter, characterized by, The double-layer composite structure comprises a coarse fiber layer and a fine fiber layer arranged in sequence in the direction of air flow, The coarse fiber layer and the fine fiber layer are both composed of polypropylene, an antioxidant and a β crystal nucleating agent; The fiber surfaces of the coarse fiber layer and the fine fiber layer both have nano-pore structures, The mass fraction of the β crystal nucleating agent on the fine fiber layer side is higher than that on the coarse fiber layer side, the mass fraction difference is 0.06-0.10 wt%, and the surface potential difference between the coarse fiber layer side and the fine fiber layer side is 80-200 V, wherein the coarse fiber layer side is a positive potential and the fine fiber layer side is a negative potential.

2. A filter cartridge for an automotive filter as set forth in claim 1 wherein, The thickness of the coarse fiber layer is 50-150 μm, and the thickness of the fine fiber layer is 20-80 μm; The average fiber diameter of the coarse fiber layer is 8-12 μm, and the average fiber diameter of the fine fiber layer is 2-5 μm.

3. The filter cartridge of claim 1 wherein, The mass fraction of the antioxidant in the coarse fiber layer and the fine fiber layer is both 0.1-0.3 wt%, and the antioxidant is one or more of 2,6-di-tert-butyl-4-methylphenol and tetrakis[methylene-3-(3',5'-di-tert-butyl-4'-hydroxyphenyl) propionate] methane, or a mixture of 2,6-di-tert-butyl-4-methylphenol, tetrakis[methylene-3-(3',5'-di-tert-butyl-4'-hydroxyphenyl) propionate] methane and 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl) benzene.

4. The filter cartridge of claim 1 wherein, The β crystal nucleating agent is selected from one of N,N'-dicyclohexyl naphthalene-2,6-dicarboxamide, phenacylurea and N,N'-diphenyl adipamide, or a mixture of N,N'-dicyclohexyl naphthalene-2,6-dicarboxamide and phenacylurea; The mass fraction of the β crystal nucleating agent in the fine fiber layer is 0.11-0.22 wt%.

5. A method for preparing a filter element for an automotive filter as described in any one of claims 1 to 4, characterized in that, The method comprises supercritical CO2 assisted melt-blowing and layered reverse corona charging, and specifically comprises the following steps: S1: formula pretreatment and supercritical injection preparation: dry mixing and drying polypropylene, an antioxidant and a β crystal nucleating agent, and delivering carbon dioxide to the post-extruder mixing zone to make the mass fraction of the carbon dioxide relative to the melt be 0.5-2.0 wt%; S2: double-layer melt-blowing deposition and β phase thickness gradient construction: using a double-extrusion double-metering method to construct a thickness formula difference to make the mass fraction of the β crystal nucleating agent on the fine fiber layer side be higher than that on the coarse fiber layer side, and the mass fraction difference be 0.06-0.10 wt%; S3: layered reverse corona charging: applying a positive voltage of +25 to +45 kV to the coarse fiber layer side, and applying a negative voltage of -25 to -45 kV to the fine fiber layer side to obtain a thickness surface potential difference of 80-200 V.

6. The method of manufacturing a filter cartridge for an automotive filter according to claim 5, wherein In the step S1, the cylinder and the die head are heated to 230-255 ℃, the die pressure is controlled to be 0.8-1.2 MPa by a back pressure valve, the dry mixing is performed in a closed mixer for 10-20 min, the carbon dioxide is delivered under the conditions of 31-50 ℃ and 7.5-12 MPa, and the CO2 residence time in the melt is controlled to be 20-60 s.

7. The method of manufacturing a filter cartridge for an automotive filter according to claim 5, wherein The step S2 is to deposit the coarse fiber layer first and then deposit the fine fiber layer, the hot air temperature is set to 220-260℃, the air speed is 150-220 m·s -1 , the distance from the spinneret to the collection net is 0.20-0.35 m, and the collection line speed is 0.5-1.5 m·min -1 .

8. The method of manufacturing a filter cartridge for an automotive filter according to claim 5, wherein The coarse fiber layer has a unit area mass of 10-15 g / m -2 The fine fiber layer has a unit area mass of 6-10 g / m -2 The process parameters are fine-tuned through online closed-loop control of the grammage and the air permeability, and the recovery rate is greater than or equal to 95% through CO2 condensation and compression recovery.

9. The method for preparing a filter element for an automotive filter as described in claim 5, characterized in that, The distance between the electrode and the material in the step S3 is 50-80 mm, a linear or serpentine scanning track is adopted, the duty cycle is 40-80%, and the scanning speed is 0.1-0.5 m·s -1 After that, heat treatment is carried out at 50-70 ℃ for 10-20 min, and further post-treatment forming is carried out: after shaping the material, the material is hot-pressed with a polypropylene spun-bond base cloth, pleat forming is carried out so that the pleat height is 20-30 mm and the pitch is 2.0-3.0 mm.

10. Use of the filter element according to any one of claims 1-4 in an automobile air filter for filtering particulate matters in intake air.

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