Air filtering membrane, preparation method thereof and filter element

Abstract

The invention relates to the technical field of membrane materials, and provides an air filtering membrane, a preparation method thereof and a filter element. The air filtering membrane comprises a substrate layer and an electrostatic spinning layer, wherein the substrate layer is bent to form convex structures and concave structures which are arranged in a staggered manner; the average height of the protruding structures ranges from 0.1 mm to 0.6 mm. The electrostatic spinning layer is arranged on the surface of one side of the protruding structure of the base layer and comprises a plurality of electrostatic spinning fibers, and the average diameter of the electrostatic spinning fibers ranges from 50 nm to 1500 nm. According to the air filtering membrane provided by the invention, the diameters of the electrostatic spinning fibers and the heights of the bulge structures are controlled to be within a certain range, so that the electrostatic spinning layer can give consideration to better filtering effect and durability.

Description

Technical Field

[0001] This application belongs to the field of membrane material technology, and in particular relates to an air filter membrane, its preparation method and filter element. Background Technology

[0002] The production process of lithium batteries requires extremely high levels of cleanliness and precise control of temperature and humidity. Excessive dust particles in the environment can cause internal short circuits and accelerate capacity decay. Therefore, air purification equipment is typically installed in large-scale lithium battery production processes to reduce the impact of airborne dust and other substances on the batteries.

[0003] The core structure of air purification equipment, the filter membrane, mainly consists of an electrospun layer and a substrate. In practical applications, dust particles in the air, such as cathode material powder, are highly adhesive and easily clump together inside the filter membrane. These clumps clog the membrane pores, necessitating increased backflushing force to eliminate the clumps and restore the membrane's flow capacity. However, excessive backflushing force exacerbates the risk of peeling between the electrospun layer and the substrate, ultimately leading to a significant reduction in the filter membrane's durability.

[0004] To alleviate the aforementioned contradictions, current attempts are being made to add crosslinking agents to the spinning solution, aiming to improve the bonding strength between the electrospun layer and the substrate. However, existing crosslinking agents focus more on enhancing the connectivity between electrospun fibers in the electrospun layer, contributing little to the bonding at the fiber-substrate interface; moreover, the addition of crosslinking agents increases the overall hardness and brittleness of the fibers, which weakens the structural damage resistance of the filter membrane under backflushing conditions, ultimately negatively impacting the durability of the filter membrane. Summary of the Invention

[0005] The purpose of this application is to provide an air filter membrane, a method for preparing the same, and a filter element thereof, with the aim of improving the durability of the air filter membrane.

[0006] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows:

[0007] A first aspect of this application provides an air filter membrane, comprising a base layer and an electrospun layer, wherein...

[0008] The base layer is bent to form an alternating pattern of protrusions and depressions, with the average height of the protrusions being 0.1mm-0.6mm.

[0009] The electrospinning layer is disposed on one side of the raised structure of the substrate layer, and the electrospinning layer includes a number of electrospinning fibers with an average diameter of 50nm-1500nm.

[0010] The air filter membrane provided in the first aspect of this application includes a base layer and an electrospun layer. By bending the base layer to create an alternating pattern of raised and recessed structures, and further adjusting the matching relationship between the height of the raised structures and the diameter of the electrospun fibers in the electrospun layer, the two work together to effectively improve the durability of the air filter membrane. Specifically:

[0011] On the one hand, by setting protruding and recessed structures in the base layer, the recessed structures provide filling space for the electrospun layer, making it easier for the electrospun layer to embed. Meanwhile, the electrospun layer embedded in the recessed area easily interlocks with the surrounding protruding structures, forming a mechanical lock, thus increasing the bonding force between the electrospun layer and the base layer. Moreover, this structural design gives the base layer a larger specific surface area, resulting in a larger bonding area with the electrospun layer and a stronger bond. Furthermore, the bonding surface between the electrospun layer and the base layer is no longer completely perpendicular to the direction of the back-blowing airflow, but rather inclined to a certain extent. While ensuring the dust removal effect of the back-blowing airflow, the impact force of the back-blowing airflow on the bonding surface is weakened, making it less likely for the electrospun layer and the base layer to peel off. Furthermore, for air filter membranes, since the electrospun layer primarily functions to intercept particles, its stability directly affects the durability of the air filter membrane. Therefore, in addition to the necessary fiber-forming polymer, a certain amount of crosslinking agent is generally added to the spinning solution to crosslink the fiber-forming polymers with each other and with the substrate (receiving substrate), thereby improving the durability of the final electrospun layer and the air filter membrane. This application incorporates a raised structure on the substrate layer. Due to the enhanced "tip effect" of the raised structure compared to the recessed structure, the raised structure has a relatively larger electric field strength and stronger attraction, resulting in a relatively larger deposition of fiber-forming polymers and crosslinking agents on the surface of the raised structure on the substrate layer. Moreover, from a molecular behavior perspective, during electrospinning, the overall distribution of the fiber-forming polymers and crosslinking agents is relatively uniform. However, near the substrate surface, the stronger electric field strength of the raised structure may lead to a stronger attraction to crosslinking agents with smaller molecular weights, thereby inducing crosslinking... The crosslinking agent preferentially reaches the surface of the raised structure at a relatively faster speed during the instant of electrospun fiber deposition, or migrates to the surface of the raised structure relatively quickly after electrospun fiber deposition. (It should be noted that this effect of stronger attraction of small molecules of crosslinking agent under the action of enhanced electric field, leading to deposition / migration of crosslinking agent to the substrate layer, is only effective for electrospun fibers that have just come into contact with the substrate layer in the initial stage of electrospunting. When the electrospun fibers continue to deposit, it is actually a stacking of electrospun fibers, and enhanced electric field will not continue to induce the above-mentioned deposition behavior of crosslinking agent on the substrate layer surface.) At the same time, due to the larger area and higher curvature of the raised structure, the solvent evaporates relatively faster at the raised structure. Due to capillary effect, the solvent in the recessed structure and inside the electrospun layer (when not fully cured) will be transported to the raised structure. The flow of solvent will carry some small molecule crosslinking agent and migrate to the raised structure together, ultimately resulting in a relatively higher crosslinking agent content at the raised structure. The combined effect of these factors causes the crosslinking agents to form multiple dispersed interlayer "chemical bonding sites" on the substrate during the subsequent curing reaction, resulting in stronger adhesion between the electrospun layer and the substrate, thereby further enhancing the adhesion performance between the electrospun layer and the substrate.The significantly improved bonding between the electrospun layer and the substrate layer substantially reduces the risk of delamination, ultimately enhancing the durability of the air filter membrane. It should be noted that the aforementioned "sharp tip effect" is not primarily generated by the protruding structure. Rather, it arises from the substrate layer's inherent roughness, resulting in small protrusions and depressions on its surface microstructure. These tiny protrusions with smaller radii of curvature generate a weak "sharp tip effect" during electrostatic processing. This application, by further incorporating protruding and recessed structures, strengthens the "sharp tip effect" of the tiny protrusions, ultimately leading to greater deposition of the crosslinking agent. Of course, the tiny protrusions on the substrate layer also create a certain mechanical interlocking effect with the electrospun layer, ensuring a solid interlayer bond.

[0012] On the other hand, this application further controls the diameter of the electrospun fibers and the height of the protrusion structure within a certain range, so that the electrospun layer can achieve both better filtration effect and durability.

[0013] First, the diameter of the electrospun fibers affects the pore size of the filter membrane. If the electrospun fiber diameter is too large, the resulting pore size will also be large, reducing the particle interception effect. Conversely, if the electrospun fiber diameter is too small, the resulting pore size will be too small, affecting air permeability. Furthermore, the strength of the electrospun fibers will be lower, resulting in a lower overall strength of the electrospun layer. This can lead to deformation of the electrospun fiber structure during forward and reverse blowing, further impacting filtration.

[0014] Secondly, the size of the protrusions in the substrate layer also affects the deposition of electrospun fibers during electrospinning, thus influencing the structure of the electrospun layer and the performance of the air filter membrane. When the height of the protrusions is too large, the "tip effect" of the top surface of the protrusion relative to the recessed structure is too strong, and the electric field strength at the protrusions is too high. This leads to more crosslinking agents and fiber-forming polymers being concentrated and deposited on the protrusions of the substrate layer during electrospinning. On the one hand, this causes uneven distribution of electrospun fibers on the substrate layer, thus affecting the overall interception effect of the filter membrane; on the other hand, excessive distribution of crosslinking agents on the protrusions leads to insufficient crosslinking between electrospun fibers, resulting in poor overall integrity of the electrospun layer and also affecting its filtration effect. Furthermore, when the protrusions are too high, the electrospun fibers are more likely to "overlap" between the protrusions in the substrate layer and cannot be well deposited on the surface of the recessed structure. In this case, the area of ​​the electrospun layer, i.e. the filtration area, will not increase, and cavities are easily formed between the electrospun layer and the substrate layer in the recessed structure. The electrospun layer cannot be well embedded between the protrusions, resulting in a weakened mechanical interlocking effect, which will weaken the bonding force between the electrospun layer and the substrate layer. Moreover, at this time, the electrospun fiber layer will be more subjected to the direct vertical impact of the back-blowing air, which will reduce the durability of the filter membrane. When the height of the protrusion is too small, the mechanical interlocking effect between the electrospun layer and the substrate layer is weak, which will also affect the bonding force between the two. Furthermore, when the protrusion is too low, its enhancement of the "tip effect" relative to the concave structure may not be significant, which will still affect the distribution of the crosslinking agent on the surface of the substrate layer during electrospinning, and thus affect the "chemical bonding" effect of the crosslinking agent on the substrate layer and the electrospun layer. At the same time, when the height of the protrusion is too low, the weakening effect on the impact force of the back-blowing on the bonding surface is not significant, resulting in the electrospun layer being subjected to greater impact from the back-blowing, and thus being more prone to peeling.

[0015] It should be noted that when the base layer is bent, regardless of the bending shape, both protruding and recessed structures will exist simultaneously; in other words, the interval between adjacent protruding structures is the recessed structure. In this application, the average height of the protruding structure is the average vertical distance between the highest and lowest points of the protruding structure on the base layer surface. Since the staggered protruding and recessed structures on the base layer are macroscopic structures as a whole, the average height of the protruding structure can be tested using a distance-measuring optical microscope or similar device. Because the protruding and recessed structures on the base layer are formed after the base layer is bent, their distribution and structure are relatively uniform. Therefore, in actual measurement, a certain cross-sectional length range can be selected, such as 2cm or 5cm, the specific length depending on the actual situation. Then, the height of all protruding structures within this cross-sectional length range can be measured (the number of protruding structures counted should not be less than 10), and then the average height of the protruding structure in this area can be calculated as the average height of the protruding structure on the base layer. To eliminate the influence of substrate thickness, the vertical distance between the highest and lowest points of the raised structure on the same surface of the substrate layer is used as the height of the raised structure. Furthermore, due to the good adhesion of the electrospun layer to the substrate layer, the electrospun layer exhibits a wavy pattern of alternating raised and recessed areas. Since the electrospun layer is relatively thin and evenly distributed on the substrate layer, the height of the raised structure on one side of the electrospun layer can be directly measured as the height of the raised structure on the substrate layer. Alternatively, since the raised structure exists on the surface of the substrate layer near the electrospun layer, the raised structure actually appears as a recess on the surface of the substrate layer away from the electrospun layer. Therefore, the depth of the corresponding recess on the surface of the substrate layer away from the electrospun layer can also be measured as the height of the raised structure on the substrate layer, using the same testing method. Of course, those skilled in the art can obtain the above parameters through other measurement methods; the above measurement methods are for reference only.

[0016] Similarly, it is understandable that the measurement of various surface morphology parameters of the membrane (such as thickness, fiber diameter, etc.) can be performed by characterizing the membrane structure using a scanning electron microscope, followed by measurement using computer software (such as Matlab, NIS-Elements, ImageJ, Nano Measure, etc.) or manually, and then performing corresponding calculations. In actual measurement, for example, when measuring fiber diameter, the membrane surface (or cross-section) can be characterized using an electron microscope to obtain the corresponding SEM image. A certain area can be selected, such as 10μm×10μm or 100μm×100μm, the specific area size depending on the actual situation. Then, the diameter of all fibers in that area can be measured using appropriate computer software or manually (the number of fibers counted should be no less than 20), and then the average fiber diameter of that area can be calculated. Of course, those skilled in the art can also obtain the above parameters through other measurement methods; the above measurement methods are for reference only.

[0017] It is understood that this application does not specifically limit the shape of the protrusion, which may include, but is not limited to, wavy, sawtooth, rectangular, etc. The average height of the protrusion refers to the vertical distance between the highest and lowest points of the protrusion. See also Figure 1 The raised structure is a wavy structure, composed of smooth curves without obvious sharp edges, and the raised areas exhibit continuous arc-shaped undulations. See also Figure 2 The raised structure is a rectangular raised structure, formed by alternating horizontal and vertical line segments, creating a continuous "rectangular step-like" raised structure. The top and bottom of the raised structure are horizontal straight lines, with right-angle transitions at the edges. See also Figure 3 The raised structure is an intermittent sawtooth-shaped structure, composed of alternating triangular protrusions and horizontal line segments. Each triangular protrusion has a pointed tip, and the protrusions are connected by horizontal line segments, creating an overall alternating "sawtooth-flat segment" shape. See also... Figure 4 The raised structure is a continuous sawtooth-shaped raised structure: it is composed of continuous triangular raised structures, with the apex of adjacent triangles directly connected to the bottom edge, without horizontal intervals, and the whole structure presents a dense "sawtooth" continuous undulation.

[0018] For any of the protruding structures in this application, its height parameter can be found in [reference needed]. Figures 1-4 The dimension H in the figure, its width parameter can be found in [reference]. Figures 1-4 The dimension W1 in the middle.

[0019] In some examples, the average height of the protrusion can be any one of 0.1mm, 0.2mm, 0.3mm, 0.4mm, 0.5mm, 0.6mm, or within any combination of both.

[0020] In some examples, the average diameter of the electrospun fibers can be any of 50nm, 100nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, 1500nm, etc., or fall within any range of two.

[0021] In some embodiments, the width of the protrusion gradually increases from the top to the bottom, and the average width of the protrusion is 0.8mm-6mm; for example, any one of 0.8mm, 1.5mm, 2mm, 3mm, 4mm, 5mm, 6mm, etc., or within any two of them.

[0022] In some embodiments, the top of the protruding structure and the connection between the protruding structure and the recessed structure are smooth transitions.

[0023] In this application, more preferably, the width of the protruding structure gradually increases from the top to the bottom, meaning that the protruding structure itself has a "sharp" structure, which is more conducive to providing an enhanced "sharp effect". It should be noted that the "sharp" structure here does not mean that the protruding structure necessarily has very sharp edges. On the contrary, more preferably, the top of the protruding structure and the connection between the protruding structure and the recessed structure in this application are smooth transitions. At this time, the protruding structure and the recessed structure on the substrate surface form a smooth wavy surface. This can ensure the "sharp" advantage of the protruding structure, thereby obtaining a better interlayer bonding effect, while also avoiding membrane damage caused by sharp edges and improving the stability of the membrane structure.

[0024] Setting the average width of the protrusions within the aforementioned range can more effectively promote the uniform distribution of the electrospun layer on the substrate surface, while significantly enhancing the interlayer bonding strength, thereby improving the structural stability and long-term durability of the air filter membrane, as detailed below:

[0025] By controlling the width of the protruding structure, the degree of "sharp tip effect" and "mechanical interlocking effect" can be further modulated. Under the combined effect of a stable interlocking structure and sufficient chemical bonding sites, the electrospun layer is less prone to structural deformation or interlayer delamination during repeated backflushing, thus improving the durability of the air filter membrane. Specifically, when the height of the protruding structure is constant, its width can be further controlled to better control the sharpness of the protruding structure on the substrate layer. This helps to control the enhancement of the "sharp tip effect" of the protruding structure relative to the recessed structure on the micro-protrusions, so as to more accurately control the preferential deposition / migration of the crosslinking agent and guide the electrospun fibers to more uniformly cover the protruding and recessed areas. If the width of the protrusion is too large, despite its height, the surface of the substrate layer will still become relatively flat. This will weaken the "tip effect" and "mechanical interlocking effect" to some extent, making the preferential deposition / migration of the crosslinking agent on the substrate layer surface less obvious or insufficient. In this case, the crosslinking agent is still mainly used to strengthen the crosslinking between electrospun fibers to improve the durability of the electrospun layer, rather than enhancing the bonding between the substrate layer and the electrospun layer. Furthermore, when the surface of the substrate layer is relatively flat, the interface between the electrospun layer and the substrate layer is still close to perpendicular to the direction of the back-blowing air. The vertical impact of the back-blowing air is strong, making the electrospun layer prone to peeling. If the width of the protrusion is too small, the "tip effect" on the top surface of the protrusion will be too strong, making the electrospun fibers more likely to deposit at the top of the protrusion. This will damage the uniformity and integrity of the filter membrane, affecting the filtration effect and membrane life.

[0026] It should be noted that the average width of the protruding structure is the average of its maximum width (i.e., the bottom width, or the distance between the connection points of the protruding structure and the recessed structures on both sides). The average width of the protruding structure can be tested using an optical microscope with a ranging function, and the test procedure can be performed in accordance with the aforementioned test method for the average height of the protruding structure.

[0027] In some embodiments, the angle of the protrusion structure is 70°-175°, such as any one of 70°, 90°, 100°, 100°, 120°, 140°, 150°, 175°, or within any combination of both.

[0028] Setting the angle of the protruding structure within the aforementioned range results in a superior overall "sharpness." On one hand, this maintains the "sharpness effect" of the protruding structure surface within an optimal range, prompting the crosslinking agent to form uniformly dispersed strong bonding sites on the preferential protruding structure surface. This ensures a strong interlayer bond between the substrate layer and the electrospun layer, making the electrospun layer less prone to interlayer peeling during back-blowing. On the other hand, within this angle range, the inclination of the bonding surface is also more appropriate, enabling sufficient bonding area between the electrospun fibers and the substrate layer on the bonding surface. Simultaneously, it also provides a better weakening effect against the impact of back-blowing, improving the durability of the air filter membrane.

[0029] It should be noted that the angle of the protruding structure refers to the apex angle formed by the convergence of its two side surfaces towards the top surface (or the center line of the top surface). This angle affects the sharpness of the top of the protruding structure and the tilt shape of its sides. During testing, lines are drawn from the apex (or center point of the top surface) of the protruding structure to the connection points between the protruding structure and the two recessed structures on both sides. The included angle formed by these lines is taken as the apex angle of the protruding structure, and the angle of this apex angle is taken as the angle of the protruding structure. The specific testing process can be carried out using an optical microscope with ranging capabilities, and the testing procedure can be performed in accordance with the aforementioned testing method for the average height of the protruding structure.

[0030] In some embodiments, the ratio of the average width of the recessed structure to the average width of the protruding structure is (1-3):1, for example, it can be any one of 1:1, 2:1, 1.5:1, 2.5:1, 3:1, etc., or within any range of two.

[0031] By controlling the width ratio of the recessed and raised structures within the aforementioned range, on the one hand, suitable lateral space can be formed in the recessed areas between the raised structures, promoting full filling of the electrospun layer and tight interlocking with the raised structures, thereby increasing the bonding force between the electrospun layer and the substrate layer. On the other hand, since the preferential deposition / migration of the crosslinking agent depends on the raised structures, this portion of the crosslinking agent is mainly deposited on the surface of the raised structures. Therefore, by controlling the width ratio of the raised and recessed structures, the density of the raised structures on the substrate layer can be controlled, thereby regulating the distribution density and dispersion of the crosslinking agent on the substrate layer. This ensures sufficient interlayer bonding while avoiding pore blockage caused by excessive local crosslinking. When the average width ratio is too large, the recessed structures are too wide, which weakens the interlocking and anchoring effect between the electrospun layer and the substrate layer. At the same time, the density of the raised structures is also low, which leads to insufficient preferential deposition / migration of the crosslinking agent, resulting in weak interlayer bonding.

[0032] It should be noted that the average width of the recessed structure is the average distance between the vertices (or center points of the top surfaces) of two adjacent protruding structures. The ratio of the average width of the protruding structure to the average width of the recessed structure can be calculated by first measuring the average width of each structure using an optical microscope with ranging capabilities, and then dividing by the average width of each structure. The testing procedure can be performed in accordance with the aforementioned testing method for the average height of the protruding structure. For any recessed structure, its width parameter can be found in [reference needed]. Figures 1-4 The size W2 in the middle.

[0033] In some embodiments, when the angle of the protruding structure is 70°-120°, the ratio of the average width of the recessed structure to the average width of the protruding structure is (1.5-3):1. For example, it can be any one of 1.5:1, 2:1, 2.5:1, 3:1, or within any range of two.

[0034] Within the aforementioned angular range of the protruding structures, the angles are relatively small, resulting in a significant tip effect. Controlling the average width of the recessed structures and the average width of the protruding structures within this range allows for a slightly larger interval between the protruding structures, preventing excessive deposition of electrospun fibers in the recessed structures. Therefore, combining these two approaches not only fully leverages the tip effect of the protruding structures, promoting preferential deposition / migration of the crosslinking agent and effectively enhancing the bonding between the electrospun layer and the substrate layer, but also suppresses excessive deposition of electrospun fibers, reducing the risk of insufficient overall interception efficiency due to uneven distribution of electrospun fibers.

[0035] In some embodiments, when the angle of the protruding structure is 120°-175°, the ratio of the average width of the recessed structure to the average width of the protruding structure is (1-2):1. For example, it can be any one of 1:1, 1.1:1, 1.2:1, 1.3:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, or within any range of two.

[0036] Within the aforementioned angular range of the protruding structure, the angle of the protruding structure is relatively large. For protruding structures with larger angles, the lateral space occupied by a single protrusion is relatively larger. At this time, the ratio of the average width of the recessed structure to the average width of the protruding structure is within the aforementioned range, which makes the density of the protruding structure within a suitable range, providing sufficient pathways for the migration of the crosslinking agent. This allows the crosslinking agent to be evenly distributed throughout the entire structure, fully exerting the crosslinking effect. This ensures sufficient interlayer bonding connections while avoiding the problem of pore blockage caused by excessive local crosslinking.

[0037] In some embodiments, the electrospun layer contains a plurality of bonding points, and the density of bonding points is greater than 10 per 360 μm based on the total area of ​​the electrospun layer. 2 .

[0038] Because the substrate layer has alternating raised and recessed structures, during electrospinning, some crosslinking agents preferentially deposit or migrate to the surface of the raised structures to form interlayer chemical bonding sites between the substrate layer and the electrospun layer. Most of the crosslinking agent is still used for crosslinking between fiber-forming polymers to form stronger electrospun fibers, or further for crosslinking between electrospun fibers to form a more durable electrospun layer. The crosslinking between electrospun fibers manifests as overlapping and bonding between multiple electrospun fibers, forming a blocky structure on the electrospun layer that differs from the electrospun fibers themselves. In this application, blocky regions with a length and width of not less than twice the diameter of the electrospun fibers on the surface of the electrospun layer are used as bonding points. The density of bonding points can be obtained by characterizing the surface morphology of one side of the air filter membrane electrospun layer and then measuring the number of bonding points within a 60μm × 60μm area using computer software or manually.

[0039] Controlling the density of bonding points within the aforementioned range helps increase the bonding ability between electrospun fibers and improves the overall strength of the electrospun layer. If the density of bonding points is too low, the bonding effect between electrospun fibers is insufficient, and the electrospun layer is prone to cracking and detachment, thus affecting the integrity of the air filter membrane. In addition, the crosslinking agent also plays a role in shaping the electrospun fibers. Too low a density of bonding points will lead to insufficient fixation of the electrospun fibers. During use and backflushing, the electrospun fibers may become misaligned, which will also affect the filtration accuracy of the air filter membrane. If the density of bonding points is too high, since the bonding points are solid block structures, a high density of bonding points means that more pores in the electrospun layer are blocked, resulting in a decrease in air permeability. Furthermore, the bonding points usually have a stronger adsorption effect on particles. When the density of bonding points is too high, it means that more particles adhere to the surface of the electrospun layer with a stronger force, which will greatly increase the difficulty of backflushing and regenerating the air filter membrane.

[0040] In some embodiments, the base layer includes a plurality of base fibers with an average diameter of 10 μm-50 μm; for example, it can be any one of 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, etc., or within any range of two.

[0041] By controlling the diameter of the base fibers within the aforementioned range, sufficient rigidity can be achieved, resulting in a high-strength base layer. This not only stably supports the electrospun layer but also resists structural fatigue caused by long-term backflushing, thus improving the durability of the air filter membrane. Simultaneously, the base fibers within this range form a base layer with appropriately sized pores, allowing airflow to pass smoothly through it. Therefore, the base layer combines high structural support with excellent air permeability.

[0042] In some embodiments, the diameter ratio of the base fiber to the electrospun fiber is 100-500; for example, it can be any one of 100, 200, 300, 400, 500, etc., or within any range of two.

[0043] In this application, controlling the ratio of the base fiber diameter to the electrospun fiber diameter within the aforementioned relatively small range not only balances interception efficiency, air permeability, and compressive strength, but also achieves superior anti-peeling performance. Specifically:

[0044] The diameter of electrospun fibers affects the permeability and interception efficiency of air filter membranes, with a clear upper limit constraint. Specifically, as the diameter of electrospun fibers increases, the cross-sectional area of ​​the pore channels formed between the fibers increases, the gas flow resistance decreases, and the permeability of the filter membrane is significantly improved. However, along with the increase in the diameter of electrospun fibers, the average pore size also increases, and the interception ability of fine particles will decrease significantly, leading to a decline in filtration efficiency. Under the premise that the diameter of electrospun fibers does not exceed the maximum critical value (i.e., to ensure interception efficiency), by reasonably reducing the diameter of the base fiber, the air filter membrane can balance permeability and interception efficiency. After slightly reducing the diameter of the base fiber, the pores between its fibers are finer, and the flow resistance of gas passing through the base layer will increase moderately, reducing the pressure difference of the backflushing airflow across the base layer (i.e., the airflow impact energy is partially buffered by the base layer). The buffered airflow significantly reduces the direct impact force on the electrospun layer attached to the surface of the base layer, further enhancing the adhesion stability of the electrospun layer during the backflushing process and extending the service life of the filter membrane. However, the diameter of the base fiber cannot be too low, otherwise it will lead to a decrease in its own porosity, affecting the overall permeability of the filter membrane.

[0045] The peeling of the electrospun layer during the back-blowing process is due to two main reasons: insufficient bonding between the electrospun layer and the substrate layer, and significant structural differences between the two layers. When the back-blowing air crosses the substrate layer and blows towards the electrospun layer, a high interlayer pressure difference exists, causing the electrospun layer to experience greater back-blowing pressure and thus making it more prone to peeling. Therefore, this application further controls the ratio of the substrate fiber diameter to the electrospun fiber diameter to be relatively small. This reduces the structural difference between the two layers, weakens the interlayer pressure difference, and improves the peeling resistance of the electrospun layer. Furthermore, a smaller ratio of the two fiber diameters actually means a relatively smaller substrate fiber diameter and increased substrate fiber density. During the back-blowing process, more pressure will be borne and dissipated by the substrate fiber, thus reducing the pressure on the electrospun layer. Alternatively, if the electrospun fibers are relatively large and close to the aforementioned critical value, they can also withstand higher pressure, resulting in stronger compressive strength and better peeling resistance.

[0046] Furthermore, due to the larger diameter of the base fiber, the surface of the base layer will have a relatively large micro-roughness (caused by the base fiber rather than the protruding and recessed structures). Therefore, the electrospun layer can also form a micro-interlocking with the base layer, thereby improving the bonding force between the two layers. However, since the diameter of the base fiber is much larger than that of the electrospun fiber, the excessive size difference will actually weaken the micro-interlocking effect. Therefore, by controlling the ratio of the diameters of the two fiber layers to be relatively small, a better micro-interlocking effect can be obtained. Moreover, when the micro-roughness of the base layer is relatively large, the "tip effect" at the micro-protrusions is stronger, which is more conducive to the deposition of crosslinking agents, so as to further enhance the bonding between the electrospun layer and the base layer.

[0047] In some embodiments, the mass percentage of the electrospun layer is 0.01%-0.5% based on the total mass of the air filter membrane. For example, it can be any one of 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, or within any range of both.

[0048] The materials of the electrospun layer fibers and the base layer fibers are usually different. The mass percentage of the electrospun layer can be determined by a dissolution method. During the preparation process, the mass of the base layer can be tested first, and then the mass of the air filter membrane formed after the base layer receives the electrospun fibers can be tested. The increase in mass and the mass of the electrospun layer are combined, and the ratio of the mass of the electrospun layer to the mass of the air filter membrane is the mass percentage of the electrospun layer.

[0049] The mass ratio of the electrospun layer affects the pore structure and flow resistance of the air filter membrane. If the electrospun layer proportion is too low, the coverage density of the electrospun fibers on the substrate surface is insufficient, allowing small particles to easily pass through the gaps not covered by the electrospun fibers, resulting in a significant decrease in interception efficiency. Simultaneously, a sparse electrospun layer is difficult to form a continuous interception network, resulting in weak broad-spectrum interception capability for particles of different sizes. Conversely, if the electrospun layer proportion is too high, the electrospun fibers tend to accumulate on the substrate surface, forming an excessively dense electrospun layer and filter layer. This leads to a surge in gas flow resistance, reducing the air permeability of the filter membrane. Therefore, within the aforementioned range, the electrospun layer forms a "dense yet non-clogging" pore structure, achieving efficient filtration through the physical interception of the electrospun fibers while providing a smooth flow path for airflow.

[0050] In some embodiments, the thickness of the substrate layer is 100μm-1000μm, for example, it can be any one of 100μm, 200μm, 300μm, 400μm, 500μm, 600μm, 700μm, 800μm, 900μm, 1000μm, etc., or within any range of two.

[0051] Setting the thickness of the base layer within the aforementioned range ensures the air filter membrane possesses high mechanical strength, while also maintaining its air permeability and improving its durability. If the base layer thickness is too small, its mechanical strength is insufficient, making it prone to tensile fracture, wrinkling, or permanent deformation during air filtration and backflushing. This causes the electrospun layer to lose its supporting structure. Furthermore, an insufficiently thin base layer results in inadequate dissipation of backflushing pressure, leading to excessive pressure on the electrospun layer and potential peeling. In such cases, increasing the interlacing density of the base fibers is necessary to improve strength, which reduces the porosity of the base layer and reduces the overall air permeability of the air filter membrane. Conversely, an excessively thick base layer requires airflow to traverse longer fiber network channels, increasing air resistance and hindering the improvement of the air filter membrane's permeability.

[0052] In some embodiments, the thickness of the electrospun layer is no greater than 2 μm. For example, it can be any of 100 nm, 300 nm, 500 nm, 700 nm, 1000 nm, 1200 nm, 1400 nm, 1600 nm, 1800 nm, 2000 nm, etc., or within any range of two.

[0053] Setting the thickness of the electrospun layer within the aforementioned range not only yields superior filtration efficiency and air permeability but also enhances its bonding with the substrate layer, thereby improving the durability of the air filter membrane. Specifically, controlling the thickness of the electrospun layer to be smaller allows for better microscopic interlocking and macroscopic bonding with the substrate layer, and also facilitates the crosslinking agent in bonding the electrospun layer to the substrate layer as a whole.

[0054] In some embodiments, the base fiber includes at least one of cellulose fiber, polyester fiber, polypropylene fiber, polyethylene fiber, polytetrafluoroethylene fiber, polyamide fiber, and glass fiber.

[0055] In some embodiments, the electrospun fibers include at least one of polyester fibers, polypropylene fibers, polyethylene fibers, polytetrafluoroethylene fibers, and polyamide fibers.

[0056] In some embodiments, under a filtration flow rate of 32 L / min, the air filter membrane has an interception efficiency of over 65% and a resistance of less than 130 Pa; after 16 rubs, the interception efficiency decreases by no more than 18%.

[0057] In the air filter membrane preparation stage, the air filter membrane's peel resistance can be characterized by the percentage decrease in its interception efficiency through friction testing. A smaller percentage decrease indicates better efficiency maintenance, better integrity of the electrospun layer, and better adhesion to the substrate layer, resulting in better peel resistance. In this application, by bending the substrate layer and controlling the formed protrusion structure and the size of the electrospun fibers, the obtained air filter membrane can meet the interception requirements of different precision levels while achieving better peel resistance and superior long-term durability.

[0058] The second aspect of this application provides a method for preparing an air filter membrane, comprising the following steps:

[0059] Step S10: Provide a base layer, which is bent to form an alternating protrusion and depression structure, with the average height of the protrusion structure being 0.1mm-0.6mm;

[0060] Step S20: Provide a spinning solution including a fiber-forming polymer, a crosslinking agent, a catalyst, and a solvent; wherein, based on the total mass of the spinning solution, the mass content of the fiber-forming polymer is 3%-15%, the mass ratio of the fiber-forming polymer to the crosslinking agent is 1:(0.05-0.13), and the mass ratio of the fiber-forming polymer to the catalyst is 1:(0.005-0.05);

[0061] Step S30: The spinning solution is electrospun to form an electrospun layer on one side of the raised structure of the substrate layer, and then cured to obtain an air filter membrane; wherein the average diameter of the electrospun fibers contained in the electrospun layer is 50nm-1500nm.

[0062] The method for preparing the air filter membrane provided in the second aspect of this application selects a substrate layer with staggered raised and recessed structures, and sets the average height of the raised structures as shown above. During electrospinning in the spinning solution, the raised structures have a stronger "tip effect" and a relatively stronger electric field, making it easier for fiber-forming polymers and crosslinking agents to deposit more on the surface of the raised structures. It may also induce small molecule crosslinking agents to deposit more preferentially or migrate to the surface of the raised structures more quickly. Due to the greater curvature of the raised structures, the residual solvent in the initially deposited electrospun fibers evaporates faster on the surface of the raised structures. This may cause other parts of the solvent to be transported to the raised structures due to capillary action. When the solvent is transported, it is easy to carry a small portion of the small molecule crosslinking agent along with it, resulting in a relatively high crosslinking agent content at the raised structures. This forms multiple dispersed "chemical bonding sites" between the electrospun layer and the substrate layer, enabling the electrospun fibers to be quickly and firmly anchored to the surface of the substrate layer, greatly improving the interfacial adhesion between the electrospun layer and the substrate layer, and avoiding fiber shedding or interlayer migration problems in the electrospun layer. In addition, the alternating raised and recessed structures on the base layer can provide a certain mechanical interlocking effect to enhance the bonding between the electrospun layer and the base layer. On the other hand, it also makes the surface of the electrospun layer tilted to a certain extent and no longer completely perpendicular to the direction of the back-blowing, which is also conducive to weakening the impact of the back-blowing and improving the durability of the air filter membrane.

[0063] In addition to controlling the morphology of the substrate layer, it is also necessary to further control the composition of the spinning solution. This application controls the crosslinking agent content in the spinning solution to be low. Generally speaking, in order to ensure the strength of the electrospun fibers and the bonding strength between electrospun fibers and between the electrospun fibers and the substrate layer, a high crosslinking agent content is usually required. However, when the crosslinking agent content is high, it is easy for the electrospun fibers to aggregate and block the gaps between the fibers, affecting the air permeability; or it can cause the electrospun fibers to become brittle, affecting their compressive strength; moreover, a large amount of crosslinking agent can also cause the particles intercepted after filtration to adhere too strongly on the electrospun layer, affecting the back-blowing effect, or require a greater back-blowing pressure, which may cause the electrospun layer to still be prone to peeling. In this application, the spinning solution has a relatively low crosslinking agent content, achieving a balance between interception efficiency, air permeability, and peel resistance. This is because the "tip effect" of the protruding structure on the substrate layer can induce the crosslinking agent to be deposited preferentially and more extensively on the substrate layer surface. Furthermore, by controlling the height of the protruding structure, the degree of enhancement of the "tip effect" can be controlled, thereby enabling more precise control over the deposition amount and distribution of the crosslinking agent to be at the optimal level. At this point, a smaller amount of crosslinking agent can form sufficient interlayer bonding sites, and the electrospun fibers in the electrospun layer can also achieve sufficient crosslinking and bonding, avoiding the problem of excessive crosslinking agent causing fiber agglomeration and embrittlement, affecting air permeability and strength, as well as excessive particle adhesion affecting backflush.

[0064] In some embodiments, the selection of the base layer in step S10, such as the screening of the base fiber diameter of the base fiber component, has been described in detail above and will not be repeated here.

[0065] In some embodiments, in step S20, the crosslinking agent includes at least one of melamine-formaldehyde resin, urea-formaldehyde resin, and isocyanate.

[0066] As mentioned above, the crosslinking agent has a smaller molecular weight than the fiber-forming polymer. Therefore, although the overall distribution of both is relatively uniform during electrospinning, in the early stages of spinning, the crosslinking agent with a smaller molecular weight will deposit / migrate to the surface of the raised structure relatively faster due to the "tip effect" enhanced by the raised structure. Based on this, this application further selects a crosslinking agent with relatively high polarity. While achieving the crosslinking function, this type of crosslinking agent, due to its higher polarity, is more easily polarized by the electric field during electrospinning, thus carrying more charge than the fiber-forming polymer. Combined with its smaller molecular weight, this further accelerates the preferential deposition / migration of the crosslinking agent on the surface of the raised structure in the early stages of electrospinning, thereby achieving a better interlayer bonding effect.

[0067] In some embodiments, in step S20, the fiber-forming polymer includes at least one of polyamide, polyester, polypropylene, polyethylene, and polytetrafluoroethylene resin.

[0068] In some embodiments, in step S20, the solvent includes an alcohol solvent.

[0069] This application uses an alcohol system as a solvent to achieve a faster evaporation rate. Generally, the electrospinning process usually requires controlling the solvent evaporation rate to be relatively slow so that the crosslinking agent has enough time to migrate to the surface of the substrate layer, thereby providing interlayer bonding between the electrospinned layer and the substrate layer. However, a slow evaporation rate may lead to excessive fusion, adhesion, or even deformation of the electrospinned fibers, thereby affecting the pore structure of the electrospinned layer and ultimately degrading the filtration performance of the air filter membrane. In this application, by bending the substrate layer to form a protruding structure, the "tip effect" can be used to achieve preferential deposition / migration of the crosslinking agent to ensure interlayer bonding. Therefore, the evaporation rate can be controlled to be faster, thereby avoiding the problem of electrospinned fiber deformation affecting the pore structure of the electrospinned layer.

[0070] In some embodiments, the parameters of electrospinning in step S30 include: spinning voltage of 30kV-80kV, receiving distance of 10cm-50cm, feeding speed of 0.001g / min.hole-0.1g / min.hole, and spinning temperature of 20℃-30℃.

[0071] During electrospinning, by adjusting the parameters of spinning voltage, receiving distance, feed rate, and spinning temperature within the above range, the synergistic control of spinning solution stretching, solvent evaporation, fiber deposition, and film formation processes can be achieved. This ultimately results in electrospinned fibers with uniform morphology, a uniformly distributed pore structure, and a firmly bonded electrospinned layer, thereby improving the filtration efficiency and long-term durability of the air filter membrane.

[0072] In some embodiments, the curing temperature in step S30 is 120°C-150°C. For example, any one of 120°C, 130°C, 140°C, 150°C, etc., or within a range of any two.

[0073] Curing at the above temperature allows the crosslinking agent to more fully crosslink the electrospun fibers and the electrospun layer and the base layer through a crosslinking reaction, thereby improving the peel resistance of the air filter membrane. On the other hand, it also helps to release the internal stress of the fibers during the electrospun process, prevent the electrospun fibers from becoming brittle and maintain their toughness, thereby improving the durability of the air filter membrane.

[0074] The third aspect of this application provides an air filter element, including the air filter membrane provided in the first aspect or the air filter membrane prepared by the preparation method provided in the second aspect.

[0075] This application can bring the following beneficial effects:

[0076] The air filter membrane provided in this application has superior overall performance compared to existing air filter membranes: it can meet the interception requirements of different precision levels, achieve better anti-peeling effect, extend its service life, and endow it with better durability. The preparation method provided by this invention can conveniently, quickly, and effectively prepare the above-mentioned air filter membrane. Attached Figure Description

[0077] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0078] Figure 1 This is an example of a cross-section of a protruding structure in the base layer provided in some embodiments of this application;

[0079] Figure 2 This is an example of a cross-section of a protruding structure in the base layer provided in some embodiments of this application;

[0080] Figure 3This is an example of a cross-section of a protruding structure in the base layer provided in some embodiments of this application;

[0081] Figure 4 This is an example of a cross-section of a protruding structure in the base layer provided in some embodiments of this application;

[0082] Figure 5 This is a scanning electron microscope (SEM) schematic diagram of the surface of the electrospun layer of the air filter membrane provided in some embodiments of this application, with a magnification of 500×.

[0083] Figure 6 This is a scanning electron microscope (SEM) schematic diagram of the cross-section of an air filter membrane provided in some embodiments of this application, with a magnification of 500×.

[0084] Figure 7 This is a scanning electron microscope (SEM) schematic diagram of the surface of the base layer of an air filter membrane provided in some embodiments of this application, with a magnification of 100×. Detailed Implementation

[0085] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0086] Example 1

[0087] This embodiment provides an air filter membrane and its preparation method.

[0088] An air filter membrane includes a base layer and an electrospun layer. The base layer is bent to form an alternating protrusion and depression structure. The electrospun layer is disposed on one side of the protrusion structure of the base layer and includes a plurality of electrospun fibers. The base layer includes a plurality of base fibers.

[0089] The specific parameters of the basal layer are as follows:

[0090] See Appendix for the cross-sectional shape of the protruding structure. Figure 1 The width of the raised structure gradually increases from top to bottom; the top of the raised structure and the connection between the raised and recessed structures are smooth transitions; the average height of the raised structure is 0.26 mm, the average width is 4.4 mm, and the angle is 166°; the ratio of the average width of the recessed structure to the average width of the raised structure is 1:1; the diameter of the base fiber is 27 μm, and the thickness of the base layer is 330 μm.

[0091] The specific parameters of the electrospun layer are as follows:

[0092] The average diameter of the electrospun fibers is 140 nm; the electrospun layer contains several bonding points, and based on the total area of ​​the electrospun layer, the density of bonding points is greater than 10 per 360 μm. 2 Based on the total mass of the air filter membrane, the mass percentage of the electrospun layer is 0.04%; the thickness of the electrospun layer is less than 2 μm.

[0093] The diameter ratio of the base fiber to the electrospun fiber is 193.

[0094] For detailed parameters of the air filter membrane, please refer to Table 1-5.

[0095] The method for preparing the above-mentioned air filter membrane includes the following steps:

[0096] Step S10: Provide a base layer, which is bent to form an alternating arrangement of protruding and recessed structures. The cross-sectional shape of the protruding structures is shown in the appendix. Figure 1 The average height of the raised structure is 0.26 mm, and the base layer contains polypropylene fibers.

[0097] Step S20: Add the fiber-forming polymer (polyamide resin, i.e., nylon resin), crosslinking agent (melamine-formaldehyde resin), and catalyst (phenoxyacetic acid) to the solvent (ethanol) and mix them evenly to form a spinning solution; wherein, based on the total mass of the spinning solution, the mass content of the fiber-forming polymer is 7%, the mass ratio of the fiber-forming polymer to the crosslinking agent is 1:0.08, and the mass ratio of the fiber-forming polymer to the catalyst is 1:0.03;

[0098] Step S30: The above spinning solution is electrospun to form an electrospun layer on one side of the raised structure of the substrate layer, and then cured at 130°C to obtain an air filter membrane. The electrospun parameters include: spinning voltage of 50kV, receiving distance of 30cm, feed rate of 0.05g / min, and spinning temperature of 25°C. The average diameter of the electrospun fibers contained in the electrospun layer is 140nm.

[0099] For details of the specific process parameters in the above preparation process, please refer to the process parameter section of Table 1-5. For product parameters involved in the process, such as the shape and size of the protrusion structure, please refer directly to the product parameter section of Table 1-5. The process parameter section of Table 1-5 will not be repeated here.

[0100] Examples 2-18 and Comparative Examples 1-4

[0101] Based on Example 1, the air filter membranes of Examples 2-18 and Comparative Examples 1-4 differ in at least one of the following: the average height, average width, angle, base fiber diameter, shape of the protrusions in the substrate layer, the ratio of the average width of the recessed structure to the average width of the protrusions, the thickness of the substrate layer, and the diameter of the electrospun fibers, the ratio of the diameter of the base fibers to the diameter of the electrospun fibers, and the mass percentage of the electrospun layer in the electrospun layer. In terms of the manufacturing process, this is manifested in adjustments to the shape and size of the protrusions in the substrate layer, the composition of the spinning solution, and the spinning parameters. See Tables 1-5 for details.

[0102] According to Examples 1-18 and Comparative Examples 1-4, corresponding control samples 1a-18a and 1b-4b were prepared respectively. The difference between the control samples 1a-18a and 1b-4b and Examples 1-18 and Comparative Examples 1-4 is that the substrate layer does not have a protruding or recessed structure. Other parameters are basically the same. They are used to investigate the changes in the performance of the air filter membrane before and after the substrate layer has a protruding structure.

[0103] Table 1

[0104]

[0105]

[0106] Table 2

[0107]

[0108]

[0109] Table 3

[0110]

[0111]

[0112] Table 4

[0113]

[0114]

[0115] Table 5

[0116]

[0117]

[0118] The air filter membranes provided in the above embodiments and comparative examples were tested, and the results are shown in Table 6 below.

[0119] Morphological parameter testing: The morphology of the air filter membrane is characterized using a scanning electron microscope or an optical microscope, and then measured by computer software or manually.

[0120] Interception efficiency and resistance tests: Using an efficiency test bench, particles of different sizes were intercepted at a flow rate of 32 L / min, with a test area of ​​100 cm². 2 The particles were 0.3μm oily particles (DEHS), and the interception efficiency and corresponding resistance were tested.

[0121] Friction test: A Martindale tribometer (model YG401E) was used to conduct a friction test on one side of the electrospun layer of the filter membrane. The friction area was 100 cm². 2 The friction rate was 47 RPM, and the number of friction cycles was 16. After friction, the interception efficiency was tested again, and the percentage decrease in interception efficiency of the air filter membrane after friction was calculated compared to before friction. The percentage decrease in interception efficiency of Examples 1-18 and Comparative Examples 1-4 was subtracted from the percentage decrease in interception efficiency of Control Samples 1a-18a and Comparative Examples 1b-4b, and the resulting difference was used to reflect the anti-peeling effect of the air filter membrane. The larger the difference, the better the friction resistance of the air filter membrane, which indirectly reflects the better the anti-peeling performance of the air filter membrane.

[0122] Table 6

[0123]

[0124] As shown in Tables 1-6, compared to conventional air filter membranes without a bending structure in the base layer, the base layer with a bending structure used in Examples 1-18, and the size of the protrusions formed by bending the base layer and the electrospun fibers are controlled, so that the obtained air filter membrane can not only meet the interception requirements of different precisions, but also further improve the friction resistance, obtain better anti-peeling effect, and have better long-term durability.

[0125] A comparison of Example 1 and Comparative Examples 1-2 shows that the height of the protrusion structure affects the performance of the air filter membrane. Compared to Example 1, the height of the protrusion structure in the substrate layer of Comparative Example 1 is too high, resulting in an excessively strong tip effect. This can easily lead to uneven distribution of electrospun fibers, resulting in a decrease in interception efficiency. Furthermore, the abrasion resistance of the air filter membrane decreases, which negatively impacts its anti-peeling effect. In contrast, the height of the protrusion structure in the substrate layer of Comparative Example 2 is too low, resulting in an insignificant tip effect and limited improvement in the anti-peeling effect of the air filter membrane.

[0126] Comparative Examples 3-4 show that the fiber diameter of the electrospun layer also affects the performance of the air filter membrane. In Comparative Example 3, the electrospun fiber diameter is too small, and the fiber distribution is too dense. Although the air filter membrane has a high interception efficiency, the filtration resistance is significantly increased. Moreover, the excessively fine electrospun fibers themselves have poor strength, and whether or not the protrusion structure is added has little impact on the peel resistance of the filter membrane. In Comparative Example 4, the electrospun fiber diameter is too large, resulting in excessively large pores in the electrospun layer, which leads to a low interception efficiency of the air filter membrane.

[0127] A comparison of Examples 1 and 6 and 8 shows that the shape parameters of the protrusion structure also affect the performance of the air filter membrane. When the width of the protrusion structure gradually increases from the top to the bottom, and the top of the protrusion structure and the connection between the protrusion structure and the recessed structure are smooth transitions, it is more conducive to providing an enhanced "tip effect" and can improve the stability of the membrane structure. In this case, the increase of the protrusion structure has a more significant effect on the peel resistance of the air filter membrane.

[0128] Comparing Examples 3 and 11, and Examples 4 and 12, it can be seen that the width and angle of the protrusion structure affect the performance of the air filter membrane. In Example 11, the width and angle of the protrusion structure are too wide, the protrusion structure is not obvious, the surface of the base layer is still relatively flat, and the "tip effect" and "mechanical interlocking effect" are weak, resulting in a small improvement in the peel resistance of the air filter membrane. In Example 12, the width and angle of the protrusion structure are too small, which makes the "tip effect" on the top surface of the protrusion structure strong. This leads to a relatively uneven distribution of electrospun fibers and crosslinking agents, resulting in a relatively poor interception efficiency of the air filter membrane, and the protrusion structure has a limited effect on improving the peel resistance of the membrane.

[0129] By comparing Examples 1 and 7, 9, and Examples 10 and 13-16, it can be seen that the overall effect is better when the width ratio of the raised and recessed structures is matched with the angle of the raised structure to meet the following relationship: when the angle of the raised structure is small, its tip effect is obvious, and the width ratio should be slightly larger; while when the angle of the raised structure is large, the lateral space occupied by a single raised structure is relatively larger, and the width ratio should be slightly smaller. Under the above matching relationship, the bonding force between the electrospun layer and the substrate layer can be improved, and the interception performance of the air filter membrane can be guaranteed, thus achieving a better effect in improving the peel resistance of the air filter membrane. In Example 7, both the angle and width ratio of the raised structure are large; in Example 15, both the angle and width ratio of the raised structure are small; and in Example 16, the width ratio is too large. All three have a small improvement in the peel resistance of the air filter membrane.

[0130] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. An air filter membrane, comprising a base layer and an electrospun layer, characterized in that, The base layer is bent to form an alternating pattern of protrusions and depressions, and the average height of the protrusions is 0.1mm-0.6mm. The electrospinning layer is disposed on one side of the raised structure of the substrate layer, and the electrospinning layer includes a plurality of electrospinning fibers with an average diameter of 50nm-1500nm.

2. The air filter membrane according to claim 1, characterized in that, The width of the protruding structure gradually increases from the top to the bottom, and the average width of the protruding structure is 0.8mm-6mm; the top of the protruding structure and the connection between the protruding structure and the recessed structure are smooth transitions.

3. The air filter membrane according to claim 2, characterized in that, The angle of the protruding structure is 70°-175°.

4. The air filter membrane according to claim 2, characterized in that, The ratio of the average width of the recessed structure to the average width of the protruding structure is (1-3):

1.

5. The air filter membrane according to claim 3, characterized in that, When the angle of the protruding structure is 70°-120°, the ratio of the average width of the recessed structure to the average width of the protruding structure is (1.5-3):1; and / or, When the angle of the protruding structure is 120°-175°, the ratio of the average width of the recessed structure to the average width of the protruding structure is (1-2):

1.

6. The air filter membrane according to claim 1, characterized in that, The electrospun layer contains a number of bonding points, and based on the total area of ​​the electrospun layer, the density of the bonding points is greater than 10 per 360 μm. 2 .

7. The air filter membrane according to claim 1, characterized in that, The base layer includes a plurality of base fibers, the average diameter of which is 10μm-50μm; and / or the diameter ratio of the base fibers to the electrospun fibers is 100-500.

8. The air filter membrane according to any one of claims 1 to 7, characterized in that, Based on the total mass of the air filter membrane, the mass percentage of the electrospun layer is 0.01%-0.5%.

9. The air filter membrane according to any one of claims 1 to 7, characterized in that, The thickness of the substrate layer is 100μm-1000μm; and / or the thickness of the electrospun layer is not greater than 2μm.

10. The air filter membrane according to claim 7, characterized in that, The base fiber includes at least one selected from cellulose fiber, polyester fiber, polypropylene fiber, polyethylene fiber, polytetrafluoroethylene fiber, polyamide fiber, and glass fiber; and / or, The electrospun fibers include at least one of polyester fiber, polypropylene fiber, polyethylene fiber, polytetrafluoroethylene fiber, and polyamide fiber.

11. The air filter membrane according to claim 1, characterized in that, Under the condition of a filtration flow rate of 32L / min, the air filter membrane has an interception efficiency of over 65% and a resistance of less than 130Pa; after 16 rubs, the interception efficiency decreases by no more than 18%.

12. The method for preparing the air filter membrane according to any one of claims 1-11, characterized in that, Includes the following steps: Step S10: Provide a base layer, which is bent to form an alternating protrusion structure and a recess structure, wherein the average height of the protrusion structure is 0.1mm-0.6mm; Step S20: Provide a spinning solution comprising a fiber-forming polymer, a crosslinking agent, a catalyst, and a solvent; wherein, based on the total mass of the spinning solution, the mass content of the fiber-forming polymer is 3%-15%, the mass ratio of the fiber-forming polymer to the crosslinking agent is 1:(0.05-0.13), and the mass ratio of the fiber-forming polymer to the catalyst is 1:(0.005-0.05); Step S30: The spinning solution is electrospun to form an electrospun layer on one side of the raised structure of the substrate layer, and then cured to obtain an air filter membrane; wherein the average diameter of the electrospun fibers contained in the electrospun layer is 50nm-1500nm.

13. The method for preparing an air filter membrane according to claim 12, wherein the crosslinking agent comprises at least one selected from melamine-formaldehyde resin, urea-formaldehyde resin, and isocyanate; and / or, The fiber-forming polymer includes at least one of polyamide, polyester, polypropylene, polyethylene, and polytetrafluoroethylene resin; and / or, The catalyst comprises at least one of p-toluenesulfonic acid, phenoxyacetic acid, and dodecylbenzenesulfonic acid; and / or, The solvent includes alcohol solvents.

14. The method for preparing an air filter membrane according to claim 12 or 13, characterized in that, The electrospinning parameters include: spinning voltage of 30kV-80kV, receiving distance of 10cm-50cm, feed rate of 0.001g / min.hole-0.1g / min.hole, and spinning temperature of 20℃-30℃; and / or, The curing temperature is 120℃-150℃.

15. An air filter element, characterized in that, Includes the air filter membrane according to any one of claims 1-11 or the air filter membrane prepared by the preparation method according to any one of claims 12-14.

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