An electret enhanced composite filter and a preparation method thereof

Abstract

The application belongs to the technical field of filter materials, and particularly relates to a kind of electret enhanced composite filter material and its preparation method, and the electret enhanced composite filter material includes PET fiber layer, aramid nanofiber layer and alkali-free glass fiber layer from top to bottom, and the mass ratio of PET fiber layer, aramid nanofiber layer and alkali-free glass fiber layer is (30-60):(5-20):(20-50). The application uses PET fiber layer as support base material to provide good mechanical strength and structural stability for the composite filter material, and provides preliminary filtering function; the aramid nanofiber layer is set to significantly improve the filtering precision and efficiency of the composite filter material; the alkali-free glass fiber layer is set to further enhance the filtering performance and thermal stability of the composite filter material; the synergistic effect of the three-layer structure realizes a filtering precision of up to 0.1 μm, while taking into account the mechanical strength and economy of the filter material, and has excellent comprehensive performance.

Description

Technical Field

[0001] This invention belongs to the field of filter material technology, specifically relating to an electret-reinforced composite filter material and its preparation method. Background Technology

[0002] In the field of filtration and separation, filter media is a core component, and its performance directly affects the filtration effect and application range. Fiberglass filter media, as a common filtration material, is characterized by its low cost due to its wide availability of raw materials and relatively simple production process, and has been widely used in many fields such as industrial dust removal and air purification.

[0003] However, fiberglass filter media also has significant limitations. Its relatively coarse fiber diameter and large pores between fibers result in lower filtration accuracy. In applications requiring high-precision filtration, such as electronics manufacturing and biopharmaceuticals—industries with extremely high environmental cleanliness requirements—fiberglass filter media often falls short, failing to effectively intercept fine particles and impurities, thus impacting product quality and production process stability.

[0004] To improve the filtration accuracy of glass fiber filter media, researchers have experimented with adding aramid fibers. Aramid fibers possess excellent high-temperature resistance and chemical corrosion resistance, and their finer diameter can improve the filtration performance of the media to some extent. However, aramid fibers also have some inherent limitations. Firstly, the production cost of aramid fibers is high, and adding them significantly increases the overall cost of the filter media, limiting its large-scale application. Secondly, aramid fibers have weak electrostatic adsorption capabilities, creating a bottleneck in improving filtration accuracy and typically failing to meet filtration requirements down to 0.1 μm.

[0005] Therefore, how to develop a new type of filter material that combines high filtration accuracy with good economic efficiency has become an important issue that urgently needs to be addressed in the current research field of filter materials. Summary of the Invention

[0006] The purpose of this invention is to provide an electret-reinforced composite filter material and its preparation method. This composite filter material uses a PET fiber layer as a supporting substrate, providing good mechanical strength, structural stability, and preliminary filtration function. An aramid nanofiber layer is added, significantly improving the filtration accuracy and efficiency of the composite filter material. An alkali-free glass fiber layer is added, further enhancing the filtration performance and thermal stability of the composite filter material. The three-layer structure works synergistically to achieve a filtration accuracy of up to 0.1 μm while also considering the mechanical strength and economy of the filter material, exhibiting excellent comprehensive performance.

[0007] Technical solution to achieve the purpose of this invention:

[0008] An electret-reinforced composite filter material includes, from top to bottom, a PET fiber layer, an aramid nanofiber layer, and an alkali-free glass fiber layer, wherein the mass ratio of the PET fiber layer, the aramid nanofiber layer, and the alkali-free glass fiber layer is (30~60):(5~20):(20~50).

[0009] Furthermore, the aramid nanofiber layer comprises aramid nanofibers, an electret agent, and an organic solvent; the mass percentages of the aramid nanofibers, electret agent, and organic solvent are: 5-10 wt% electret agent, 10-15 wt% aramid nanofibers, and the remainder being organic solvent.

[0010] Furthermore, the electret is selected from one or any combination of titanium dioxide, zinc oxide, silicon dioxide, polytetrafluoroethylene, polymethyl methacrylate, polyacrylonitrile, polystyrene, organosilicon modified resin, fluorosilicone copolymer, and ionic liquid, or a combination of polyethyleneimine and polyvinylidene fluoride; the organic solvent is selected from one or any combination of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, cyclohexanone, trifluoroethanol, and hexafluoroisopropanol.

[0011] Furthermore, the alkali-free glass fiber layer comprises alkali-free glass fiber, fluorinated polyvinyl alcohol, and deionized water, with the following mass percentages: alkali-free glass fiber 5-10 wt%, fluorinated polyvinyl alcohol 1-3 wt%, and the remainder being deionized water.

[0012] A method for preparing an electret-reinforced composite filter material, comprising:

[0013] S1: Add aramid nanofibers and electret to an organic solvent, mix thoroughly and sieve to obtain an electrospinning solution; load the electrospinning solution into a syringe and connect it to a spinning needle, output it to the PET fiber layer of the receiving device through electrospinning, deposit an aramid nanofiber layer on the PET fiber layer, and obtain a PET-aramid composite substrate after drying.

[0014] S2: Add alkali-free glass fiber and fluorinated polyvinyl alcohol to deionized water and mix thoroughly to obtain glass fiber slurry; use a spraying process to uniformly spray the glass fiber slurry onto the aramid nanofiber layer in the PET-aramid composite substrate, and after drying, obtain the PET-aramid-glass fiber composite substrate.

[0015] S3: The PET-aramid-glass fiber composite substrate is subjected to gradient pressure reduction hot pressing to obtain electret-reinforced composite filter material.

[0016] Further, in step S1, the mixing method is magnetic stirring or high-speed shear stirring, and the mixing and sieving parameters are as follows: stirring speed 300~600 rpm, stirring and mixing time 30~60 min, and filtration through a 200~400 mesh stainless steel screen; the electrospinning parameters are as follows: spinning voltage 15~25 kV, spinning distance 15~20 cm, syringe flow rate 0.3~0.8 mL / h, and receiving device rotation speed 1000~2000 rpm; the drying parameters after electrospinning are as follows: drying temperature 80~100℃, drying time 30~60 min.

[0017] Furthermore, in step S1, after obtaining the PET-aramid composite substrate, it is necessary to place it under a DC voltage of 10~20 kV for 10~30s for high-voltage polarization discharge treatment.

[0018] Further, in step S2, the mixing method is high-speed shear stirring, and the mixing parameters are as follows: stirring speed is 500~800 rpm, stirring time is 20~40 min; before spraying, the glass fiber slurry is heated to 60~80℃ to make its viscosity reach 150~250 mPa·s; the spraying rate is 1 m / s; the drying temperature is 100~110℃, and the drying time is 5~10 min.

[0019] Furthermore, in step S2, after high-speed shearing and stirring, ultrasonic dispersion is used for further mixing to obtain glass fiber slurry; the parameters of ultrasonic dispersion are as follows: frequency is 20~40 kHz, and time is 10~20 min.

[0020] Further, in step S3, the gradient pressure reduction hot pressing molding process is as follows: first, the PET-aramid-glass fiber composite substrate is hot-pressed at 12~15 MPa and 105~110℃ for 3~5 minutes; then, it is hot-pressed at 8~10 MPa and 105~110℃ for 2~3 minutes; finally, it is hot-pressed at 3~6 MPa and 20~40℃ for 1~2 minutes to obtain the electret-reinforced composite filter material.

[0021] The beneficial technical effects of this invention are as follows:

[0022] 1. In this invention, the PET fiber layer serves as the supporting substrate, providing excellent mechanical strength and structural stability for the entire composite filter material. It also provides preliminary filtration, intercepting larger particles and protecting the subsequent fine filtration layer. The aramid nanofiber layer, as the core fine filtration layer, has a fiber diameter as small as 50-200 nm. By adding an electret agent, it can efficiently intercept particles with a precision greater than 0.1 μm, significantly improving overall filtration accuracy and efficiency. The alkali-free glass fiber layer further enhances the filtration performance and thermal stability of the filter material, ensuring stable operation under high temperatures or complex environments. Simultaneously, a reasonable ratio effectively reduces overall costs. This three-layer structure works synergistically to achieve a filtration precision as high as 0.1 μm while maintaining the mechanical strength and economy of the filter material, exhibiting excellent comprehensive performance.

[0023] 2. In this invention, polyvinylidene fluoride (PVDF) is selected as one of the electret agents, possessing excellent electret capability and good thermal stability. During long-term use, it effectively maintains charge stability, avoiding charge decay caused by environmental changes. By combining it with polyethyleneimine, the charge capture and storage capacity is further enhanced, extending the electret life and enabling the filter media to maintain high filtration efficiency under complex operating conditions, significantly outperforming single electret agent systems.

[0024] 3. This invention employs a gradient pressure-reducing hot-pressing process, strictly controlling the hot-pressing temperature within the range of 105~110℃, effectively avoiding charge dissipation of the electret agent caused by high temperatures. Simultaneously, through a three-stage pressure reduction method, the internal stress of the material is gradually released, reducing the risk of structural deformation and promoting tight bonding and interfacial adhesion between layers, ultimately resulting in a dense and stable composite filter material.

[0025] 4. In this invention, fluorinated polyvinyl alcohol is selected as a bonding agent in glass fiber slurry. It can not only enhance the bonding strength between glass fiber and substrate and improve the overall structural stability, but also the fluorinated groups in its molecular chain have the function of stabilizing charge.

[0026] 5. After electrospinning, the aramid nanofiber layer is subjected to a 10-20 kV DC high-voltage polarization discharge treatment for 10-30 seconds. This treatment can significantly increase the charge density on the fiber surface in a short time, enhance its adsorption capacity for fine particles, and thus further improve the initial filtration efficiency and electret durability of the filter material. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of an electret-reinforced composite filter material structure provided in Embodiment 1 of the present invention.

[0028] In the diagram: 1-PET fiber layer; 2-aramid nanofiber layer; 3-alkali-free glass fiber layer. Detailed Implementation

[0029] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0030] This invention provides an electret-reinforced composite filter material, comprising a three-layer composite structure from top to bottom, namely a PET fiber layer, an aramid nanofiber layer, and an alkali-free glass fiber layer, wherein the mass ratio of the PET fiber layer, the aramid nanofiber layer, and the alkali-free glass fiber layer is (30~60):(5~20):(20~50).

[0031] The aramid nanofiber layer comprises aramid nanofibers, electret agent, and organic solvent; the mass percentages of aramid nanofibers, electret agent, and organic solvent are: electret agent 5~10 wt%, aramid nanofibers 10~15 wt%, and the remainder is organic solvent.

[0032] The electret is selected from one or any combination of titanium dioxide, zinc oxide, silicon dioxide, polytetrafluoroethylene, polymethyl methacrylate, polyacrylonitrile, polystyrene, organosilicon modified resin, fluorosilicone copolymer, and ionic liquid, or a combination of polyethyleneimine and polyvinylidene fluoride. When the electret is a combination of polyethyleneimine and polyvinylidene fluoride, the mass ratio of polyethyleneimine to polyvinylidene fluoride is (2~4):1.

[0033] The organic solvent is selected from one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, cyclohexanone, trifluoroethanol, hexafluoroisopropanol, or any combination thereof.

[0034] The alkali-free glass fiber layer comprises alkali-free glass fiber, fluorinated polyvinyl alcohol, and deionized water. The mass percentages of alkali-free glass fiber, fluorinated polyvinyl alcohol, and deionized water are: 5-10 wt% alkali-free glass fiber, 1-3 wt% fluorinated polyvinyl alcohol, and the remainder is deionized water.

[0035] The PET fiber layer has a fiber diameter of 1-10 μm, preferably 4-6 μm, and a thickness of 0.13-0.54 mm; the aramid nanofiber layer has a fiber diameter of 50-200 nm, preferably 100-150 nm, and a thickness of 0.03-0.13 mm; the alkali-free glass fiber layer has a fiber diameter of 0.3-0.8 μm, preferably 0.4-0.6 μm, and the fineness of the alkali-free glass fiber is ≥80°, with a thickness of 0.1-0.4 mm; after hot pressing, the total thickness of the electret-reinforced composite filter material is 0.2-1 mm; the areal density of the PET fiber layer, aramid nanofiber layer, and alkali-free glass fiber layer is 10-40 g / m³. 2 .

[0036] The electret-reinforced composite filter media has a filtration accuracy of ≥0.1μm and a filtration efficiency of ≥99.99% for 0.1μm particles.

[0037] This invention provides a method for preparing electret-reinforced composite filter material, specifically including the following steps:

[0038] S1: Add aramid nanofibers and electret to an organic solvent, mix thoroughly and sieve to obtain an electrospinning solution; then load the electrospinning solution into a syringe and connect it to a spinning needle, output it to the PET fiber layer of the receiving device through electrospinning, deposit an aramid nanofiber layer on the PET fiber layer, and obtain a PET-aramid composite substrate after drying.

[0039] In step S1, the electret agent accounts for 5-10 wt% of the electrospinning solution, the aramid nanofibers account for 10-15 wt% of the electrospinning solution, and the remainder is an organic solvent.

[0040] The electret is selected from one or any combination of titanium dioxide, zinc oxide, silicon dioxide, polytetrafluoroethylene, polymethyl methacrylate, polyacrylonitrile, polystyrene, organosilicon modified resin, fluorosilicone copolymer, and ionic liquid, or a combination of polyethyleneimine and polyvinylidene fluoride. When the electret is a combination of polyethyleneimine and polyvinylidene fluoride, the mass ratio of polyethyleneimine to polyvinylidene fluoride is (2~4):1.

[0041] The organic solvent is selected from one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, cyclohexanone, trifluoroethanol, hexafluoroisopropanol, or any combination thereof.

[0042] In step S1, the mixing method is magnetic stirring or high-speed shear stirring. The specific parameters for mixing and sieving are as follows: stirring speed 300~600 rpm, mixing time 30~60 min, and filtration through a 200~400 mesh stainless steel screen.

[0043] In step S1, the electrospinning parameters are as follows: the spinning voltage is 15~25 kV, the spinning distance is 15~20 cm, the syringe flow rate is 0.3~0.8 mL / h, and the receiving device rotation speed is 1000~2000 rmp.

[0044] In step S1, the drying parameters after electrospinning are as follows: drying temperature 80~100℃, drying time 30~60 min; preferably, drying temperature 90℃, drying time 45 min.

[0045] In step S1, after obtaining the PET-aramid composite substrate, it is necessary to place it under a DC voltage of 10~20 kV for 10~30s for high-voltage polarization discharge treatment.

[0046] S2: Add alkali-free glass fiber and fluorinated polyvinyl alcohol to deionized water and mix thoroughly to obtain glass fiber slurry; then use a spraying process to uniformly spray the glass fiber slurry onto the aramid nanofiber layer in the PET-aramid composite substrate, and after drying, obtain the PET-aramid-glass fiber composite substrate. The mass ratio of PET fiber layer, aramid nanofiber layer and alkali-free glass fiber layer in the PET-aramid-glass fiber composite substrate is (30~60):(5~20):(20~50).

[0047] In step S2, the mass percentage of alkali-free glass fiber in the glass fiber slurry is 5-10 wt%, the mass percentage of fluorinated polyvinyl alcohol in the glass fiber slurry is 1-3 wt%, and the remainder is deionized water.

[0048] In step S2, the mixing method is high-speed shear stirring, and the mixing parameters are as follows: stirring speed is 500~800 rpm, and stirring time is 20~40 min.

[0049] In step S2, after high-speed shearing and mixing, ultrasonic dispersion can be used for further mixing to obtain glass fiber slurry. The parameters for ultrasonic dispersion are as follows: frequency 20~40 kHz, time 10~20 min.

[0050] In step S2, the glass fiber slurry is heated to 60~80℃ before spraying, so that its viscosity reaches 150~250 mPa·s; the spraying rate is 1 m / s; the drying temperature is 100~110℃, and the drying time is 5~10 min.

[0051] S3: The PET-aramid-glass fiber composite substrate from step S2 is subjected to gradient pressure reduction hot pressing to finally obtain electret-reinforced composite filter material.

[0052] In step S3, the gradient pressure reduction hot pressing process is as follows: First, the PET-aramid-glass fiber composite substrate is hot-pressed at 12~15 MPa and 105~110℃ for 3~5 minutes; then it is hot-pressed at 8~10 MPa and 105~110℃ for 2~3 minutes; finally, it is hot-pressed at 3~6 MPa and 20~40℃ for 1~2 minutes to obtain the electret-reinforced composite filter material.

[0053] Example 1

[0054] like Figure 1 As shown, the electret-reinforced composite filter material provided in this embodiment includes a three-layer composite structure from top to bottom, namely a PET fiber layer 1, an aramid nanofiber layer 2, and an alkali-free glass fiber layer 3, wherein the mass ratio of the PET fiber layer 1, the aramid nanofiber layer 2, and the alkali-free glass fiber layer 3 is 40:15:45.

[0055] The aramid nanofiber layer comprises aramid nanofibers, electret agent, and organic solvent; the mass percentages of aramid nanofibers, electret agent, and organic solvent are: electret agent 7 wt%, aramid nanofibers 12 wt%, and the remainder is organic solvent.

[0056] The electret contains polyethyleneimine and polyvinylidene fluoride, with a mass ratio of polyethyleneimine to polyvinylidene fluoride of 3:1; the organic solvent is N-methylpyrrolidone.

[0057] The alkali-free glass fiber layer comprises alkali-free glass fiber, fluorinated polyvinyl alcohol, and deionized water. The mass percentages of alkali-free glass fiber, fluorinated polyvinyl alcohol, and deionized water are as follows: 8 wt% alkali-free glass fiber, 1.5 wt% fluorinated polyvinyl alcohol, and the remainder is deionized water.

[0058] The average fiber diameter in PET fiber layer 1 is 5 μm, the thickness of PET fiber layer 1 is 0.34 mm, and the areal density is 25 g / m³. 2 The average fiber diameter in aramid nanofiber layer 2 is 120 nm, the thickness of aramid nanofiber layer 2 is 0.08 mm, and the areal density is 10 g / m³. 2 The alkali-free glass fiber layer 3 is made of alkali-free glass fiber with a fiber diameter of 0.5 μm, a fiber fineness ≥80°, a thickness of 0.2 mm, and an areal density of 25 g / m³. 2 After hot pressing, the total thickness of the electret-reinforced composite filter material is 0.55 mm.

[0059] The preparation method of the electret-reinforced composite filter material provided in this embodiment specifically includes the following steps:

[0060] S1: Aramid nanofibers and electret agents are added to N-methylpyrrolidone and stirred magnetically or by high-speed shear stirring at 400 rpm for 40 min. After thorough mixing, the mixture is passed through a 200-mesh sieve to obtain the electrospinning solution. The electret agent accounts for 7 wt% of the electrospinning solution, the aramid nanofibers account for 12 wt%, and the remainder is N-methylpyrrolidone. The electret agent includes polyethyleneimine and polyvinylidene fluoride, with a mass ratio of polyethyleneimine to polyvinylidene fluoride of 3:1.

[0061] The electrospinning solution was then loaded into a syringe and connected to a spinning needle. The solution was electrospinned onto the PET fiber layer of the receiving device, where an aramid nanofiber layer was deposited. The electrospinning parameters were as follows: spinning voltage of 20 kV, spinning distance of 15 cm, syringe flow rate of 0.5 mL / h, receiving device rotation speed of 1200 rpm, and spinning time of 30 min. After drying at 90℃ for 45 min, a PET-aramid composite substrate was obtained. This substrate was then subjected to a 30-second high-voltage polarization discharge treatment at 15 kV DC to further increase the surface electret charge density.

[0062] S2: Add alkali-free glass fiber and fluorinated polyvinyl alcohol to deionized water, and use high-speed shear stirring at 600 rpm for 30 min to mix thoroughly to obtain glass fiber slurry. The mass percentage of alkali-free glass fiber in the glass fiber slurry is 8 wt%, the mass percentage of fluorinated polyvinyl alcohol in the glass fiber slurry is 1.5 wt%, and the remainder is deionized water.

[0063] The glass fiber slurry was then heated to 70°C to achieve a viscosity of 200 mPa·s. A spraying process was then used to uniformly spray the glass fiber slurry onto the aramid nanofiber layer in the PET-aramid composite substrate at a spraying rate of 1 m / s. After spraying, the substrate was dried at 110°C for 10 min to obtain the PET-aramid-glass fiber composite substrate. The mass ratio of the PET fiber layer, aramid nanofiber layer, and alkali-free glass fiber layer in the PET-aramid-glass fiber composite substrate was 40:15:45.

[0064] S3: The PET-aramid-glass fiber composite substrate from step S2 is subjected to gradient pressure reduction hot pressing. The gradient pressure reduction hot pressing process is as follows: First, the PET-aramid-glass fiber composite substrate is hot-pressed at 12 MPa and 110℃ for 3 minutes. Then, it is hot-pressed at 8 MPa and 110℃ for 2 minutes. Finally, it is hot-pressed at 5 MPa and 25℃ for 1 minute to obtain the electret-reinforced composite filter material.

[0065] Using 0.1 μm NaCl particles as the test medium, the filtration efficiency of the electret-reinforced composite filter material prepared in this embodiment was determined under standard experimental conditions according to relevant ASTM standard test methods. The test results show that the filter material achieves a filtration efficiency of 99.99%, demonstrating excellent high-precision filtration capabilities.

[0066] According to the EN 1822-3 standard test method, under constant airflow conditions with a wind speed of 5.3 cm / s, the initial pressure drop of the electret-reinforced composite filter material prepared in this embodiment was measured. The test results showed that its initial resistance was ≤60 Pa, indicating that the material has low airflow resistance, which is beneficial to reducing energy consumption and improving efficiency.

[0067] To verify the performance retention capability of the electret-reinforced composite filter material prepared in this embodiment under high-temperature conditions, a hot air aging test was conducted. The sample was placed in a 120°C oven and heated for 2 hours, after which its filtration efficiency and pressure drop were tested again using the method described above. The test results show that the filtration efficiency and resistance of the filter material did not change significantly after the heat aging treatment, and the electret charge retention rate was ≥98%, demonstrating good thermal stability and long-term reliability.

[0068] The air permeability of the electret-reinforced composite filter material prepared in this embodiment was tested using the Gurley method. During the test, the time required for a certain volume of air (100 mL) to pass through a unit area of ​​filter material under a specified pressure was recorded, expressed as s / 100 mL. The test results show that the air permeability of this composite filter material is approximately 140 s / 100 mL, exhibiting good air permeability and contributing to improving the overall ventilation efficiency of the filtration system.

[0069] The areal density of the electret-reinforced composite filter material prepared in this embodiment was determined using a gravimetric method. Several groups of samples with a specified area were selected, accurately weighed, and the mass per unit area was calculated. The test results showed that the average areal density of the electret-reinforced composite filter material was 56.2 g / m², ensuring the material's lightweight nature and structural stability.

[0070] Example 2

[0071] In this embodiment, except for the parameters and preparation methods of the composite filter material which differ from those in Example 1, the other parameters and preparation methods are the same as in Example 1.

[0072] In the electret-reinforced composite filter material provided in this embodiment, the mass ratio of PET fiber layer 1, aramid nanofiber layer 2, and alkali-free glass fiber layer 3 is 30:20:50.

[0073] The PET fiber layer 1 has a thickness of 0.22 mm and an areal density of 20 g / m².

[0074] The thickness of the aramid nanofiber layer 2 is 0.05 mm, and the areal density is 12 g / m².

[0075] The alkali-free glass fiber layer 3 has a thickness of 0.18 mm and a surface density of 22 g / m³. 2 ;

[0076] After hot pressing, the total thickness of the electret-reinforced composite filter material is 0.38 mm.

[0077] In the preparation method of the electret-reinforced composite filter material provided in this embodiment,

[0078] In step S1:

[0079] The electret agent accounts for 5 wt% of the electrospinning solution, the aramid nanofiber accounts for 10 wt% of the spinning solution, and the remainder is N-methylpyrrolidone; the electret agent includes polyethyleneimine and polyvinylidene fluoride, wherein the mass ratio of polyethyleneimine to polyvinylidene fluoride is 2:1.

[0080] The specific parameters for mixing and sieving are as follows: stirring speed 300 rpm, mixing time 30 min, and filtration through a 200-mesh stainless steel sieve.

[0081] The electrospinning parameters are as follows: spinning voltage is 15 kV, spinning distance is 15 cm, syringe flow rate is 0.3 mL / h, and receiving device rotation speed is 1000 rmp.

[0082] The drying parameters after electrospinning are as follows: drying temperature 90℃, drying time 45 min;

[0083] Polarization discharge: High-voltage polarization discharge treatment for 10 seconds under 10 kV DC voltage.

[0084] In step S2:

[0085] The mass percentage of alkali-free glass fiber in the glass fiber slurry is 5 wt%, the mass percentage of fluorinated polyvinyl alcohol in the glass fiber slurry is 1 wt%, and the remainder is deionized water.

[0086] The glass fiber slurry was preheated to 60°C to achieve a viscosity of 150 mPa·s. The spraying rate was 1 m / s. After spraying, the slurry was dried at 100°C for 5 minutes.

[0087] In step S3:

[0088] The gradient pressure reduction hot pressing process is as follows: First, the PET-aramid-glass fiber composite substrate is hot-pressed at 12 MPa and 105℃ for 3 minutes; then it is hot-pressed at 8 MPa and 105℃ for 2 minutes; finally, it is hot-pressed at 3 MPa and 20℃ for 1 minute to obtain the electret reinforced composite filter material.

[0089] The electret-reinforced composite filter material prepared in this embodiment has a filtration efficiency of 99.98%, an initial pressure drop of 58 Pa, and no significant change in efficiency / resistance after thermal aging (120℃×2 h), with a charge retention rate ≥97%. The air permeability of the composite filter material is approximately 150 s / 100 mL.

[0090] Example 3

[0091] In this embodiment, except for the parameters and preparation methods of the composite filter material which differ from those in Example 1, the other parameters and preparation methods are the same as in Example 1.

[0092] In the electret-reinforced composite filter material provided in this embodiment, the mass ratio of PET fiber layer 1, aramid nanofiber layer 2, and alkali-free glass fiber layer 3 is 45:12:43.

[0093] The PET fiber layer 1 has a thickness of 0.30 mm and an areal density of 25 g / m².

[0094] The thickness of the aramid nanofiber layer 2 is 0.08 mm, and the areal density is 14 g / m².

[0095] The alkali-free glass fiber layer 3 has a thickness of 0.20 mm and a surface density of 22 g / m³. 2 ;

[0096] After hot pressing, the total thickness of the electret-reinforced composite filter material is 0.55 mm.

[0097] In the preparation method of the electret-reinforced composite filter material provided in this embodiment,

[0098] In step S1:

[0099] The electret agent accounts for 7.5 wt% of the electrospinning solution, the aramid nanofiber accounts for 12.5 wt% of the electrospinning solution, and the remainder is N-methylpyrrolidone; the electret agent includes polyethyleneimine and polyvinylidene fluoride, wherein the mass ratio of polyethyleneimine to polyvinylidene fluoride is 3:1.

[0100] The specific parameters for mixing and sieving are as follows: stirring speed 500 rpm, mixing time 45 min, and filtration through a 200-mesh stainless steel sieve.

[0101] The electrospinning parameters are as follows: spinning voltage is 20 kV, spinning distance is 17.5 cm, syringe flow rate is 0.55 mL / h, and receiving device rotation speed is 1500 rmp.

[0102] The drying parameters after electrospinning are as follows: drying temperature 90℃, drying time 45 min;

[0103] Polarization discharge: High-voltage polarization discharge treatment for 20s under 15 kV DC voltage.

[0104] In step S2:

[0105] The mass percentage of alkali-free glass fiber in the glass fiber slurry is 7.5 wt%, the mass percentage of fluorinated polyvinyl alcohol in the glass fiber slurry is 2 wt%, and the remainder is deionized water;

[0106] The glass fiber slurry was preheated to 70°C to achieve a viscosity of 200 mPa·s. The spraying rate was 1 m / s. After spraying, the slurry was dried at 105°C for 7.5 min.

[0107] In step S3:

[0108] The gradient pressure reduction hot pressing process is as follows: First, the PET-aramid-glass fiber composite substrate is hot-pressed at 13.5 MPa and 107℃ for 4 minutes; then it is hot-pressed at 9 MPa and 107℃ for 2.5 minutes; finally, it is hot-pressed at 4.5 MPa and 30℃ for 1.5 minutes to obtain the electret-reinforced composite filter material.

[0109] The electret-reinforced composite filter material prepared in this embodiment has a filtration efficiency of 99.99%, an initial pressure drop of 55 Pa, and no significant change in efficiency / resistance after thermal aging (120℃×2 h), with a charge retention rate ≥98%. The air permeability of the composite filter material is approximately 145 s / 100 mL.

[0110] Example 4

[0111] In this embodiment, except for the parameters and preparation methods of the composite filter material which differ from those in Example 1, the other parameters and preparation methods are the same as in Example 1.

[0112] In the electret-reinforced composite filter material provided in this embodiment, the mass ratio of PET fiber layer 1, aramid nanofiber layer 2, and alkali-free glass fiber layer 3 is 60:5:35.

[0113] The PET fiber layer 1 has a thickness of 0.40 mm and a surface density of 30 g / m².

[0114] The thickness of the aramid nanofiber layer 2 is 0.04 mm, and the areal density is 10 g / m².

[0115] The alkali-free glass fiber layer 3 has a thickness of 0.16 mm and a surface density of 18 g / m³. 2 ;

[0116] After hot pressing, the total thickness of the electret-reinforced composite filter material is 0.48 mm.

[0117] In the preparation method of the electret-reinforced composite filter material provided in this embodiment,

[0118] In step S1:

[0119] The electret agent accounts for 10 wt% of the electrospinning solution, the aramid nanofiber accounts for 15 wt% of the spinning solution, and the remainder is N-methylpyrrolidone; the electret agent includes polyethyleneimine and polyvinylidene fluoride, wherein the mass ratio of polyethyleneimine to polyvinylidene fluoride is 4:1.

[0120] The specific parameters for mixing and sieving are as follows: stirring speed 600 rpm, mixing time 60 min, and filtration through a 300-mesh stainless steel sieve.

[0121] The electrospinning parameters are as follows: spinning voltage is 25 kV, spinning distance is 20 cm, syringe flow rate is 0.8 mL / h, and receiving device rotation speed is 2000 rmp.

[0122] The parameters for drying after electrospinning are as follows: drying temperature 100℃, drying time 60 min;

[0123] Polarization discharge: High-voltage polarization discharge treatment for 30 seconds under 20 kV DC voltage.

[0124] In step S2:

[0125] The mass percentage of alkali-free glass fiber in the glass fiber slurry is 10 wt%, the mass percentage of fluorinated polyvinyl alcohol in the glass fiber slurry is 3 wt%, and the remainder is deionized water.

[0126] The glass fiber slurry was preheated to 80°C to achieve a viscosity of 250 mPa·s. The spraying rate was 1 m / s. After spraying, the slurry was dried at 110°C for 10 min.

[0127] In step S3:

[0128] The gradient pressure reduction hot pressing process is as follows: First, the PET-aramid-glass fiber composite substrate is hot-pressed at 15 MPa and 110℃ for 5 minutes; then it is hot-pressed at 10 MPa and 110℃ for 3 minutes; finally, it is hot-pressed at 6 MPa and 40℃ for 2 minutes to obtain the electret reinforced composite filter material.

[0129] The electret-reinforced composite filter material prepared in this embodiment has a filtration efficiency of 99.99%, an initial pressure drop of 60 Pa, and no significant change in efficiency / resistance after thermal aging (120℃×2 h), with a charge retention rate ≥99%. The air permeability of the composite filter material is approximately 140 s / 100 mL.

[0130] Example 5

[0131] In this embodiment, except for the parameters and preparation methods of the composite filter material which differ from those in Example 1, the other parameters and preparation methods are the same as in Example 1.

[0132] In the electret-reinforced composite filter material provided in this embodiment, the mass ratio of PET fiber layer 1, aramid nanofiber layer 2, and alkali-free glass fiber layer 3 is 35:18:47.

[0133] The PET fiber layer 1 has a thickness of 0.24 mm and an areal density of 22 g / m².

[0134] The thickness of the aramid nanofiber layer 2 is 0.10 mm, and the areal density is 16 g / m².

[0135] The alkali-free glass fiber layer 3 has a thickness of 0.22 mm and a surface density of 24 g / m³. 2 ;

[0136] After hot pressing, the total thickness of the electret-reinforced composite filter material is 0.52 mm.

[0137] In the preparation method of the electret-reinforced composite filter material provided in this embodiment,

[0138] In step S1:

[0139] The electret agent accounts for 9 wt% of the electrospinning solution, the aramid nanofiber accounts for 14 wt% of the spinning solution, and the remainder is N-methylpyrrolidone; the electret agent includes polyethyleneimine and polyvinylidene fluoride, wherein the mass ratio of polyethyleneimine to polyvinylidene fluoride is 3:1.

[0140] The specific parameters for mixing and sieving are as follows: stirring speed 500 rpm, mixing time 45 min, and filtration through a 200-mesh stainless steel sieve.

[0141] The electrospinning parameters are as follows: spinning voltage is 22 kV, spinning distance is 18 cm, syringe flow rate is 0.6 mL / h, and receiving device rotation speed is 1600 rmp.

[0142] The drying parameters after electrospinning are as follows: drying temperature 90℃, drying time 45 min;

[0143] Polarization discharge: High-voltage polarization discharge treatment for 25 seconds under 18 kV DC voltage.

[0144] In step S2:

[0145] The mass percentage of alkali-free glass fiber in the glass fiber slurry is 9 wt%, the mass percentage of fluorinated polyvinyl alcohol in the glass fiber slurry is 2.5 wt%, and the remainder is deionized water.

[0146] The glass fiber slurry was preheated to 75°C to achieve a viscosity of 220 mPa·s. The spraying rate was 1 m / s. After spraying, the slurry was dried at 108°C for 9 minutes.

[0147] In step S3:

[0148] The gradient pressure reduction hot pressing process is as follows: First, the PET-aramid-glass fiber composite substrate is hot-pressed at 14 MPa and 109℃ for 4.5 min; then it is hot-pressed at 9 MPa and 109℃ for 2.5 min; finally, it is hot-pressed at 5 MPa and 35℃ for 1.5 min to obtain electret-reinforced composite filter material.

[0149] The electret-reinforced composite filter material prepared in this embodiment has a filtration efficiency of 99.993%, an initial pressure drop of 57 Pa, and no significant change in efficiency / resistance after thermal aging (120℃×2 h), with a charge retention rate ≥98%. The air permeability of the composite filter material is approximately 148 s / 100 mL.

[0150] Compare with Example 1

[0151] To verify the unique features of the aramid nanofiber layer and its formulation in this invention, the following comparative experiments were also conducted:

[0152] The composite filter material in the control test consists of two composite layers: a PET fiber layer and an alkali-free glass fiber layer, with a mass ratio of 40:60 between the PET fiber layer and the alkali-free glass fiber layer.

[0153] The alkali-free glass fiber layer comprises alkali-free glass fiber, fluorinated polyvinyl alcohol, and deionized water. The mass percentages of alkali-free glass fiber, fluorinated polyvinyl alcohol, and deionized water are as follows: 8 wt% alkali-free glass fiber, 1.5 wt% fluorinated polyvinyl alcohol, and the remainder is deionized water.

[0154] The average fiber diameter in the PET fiber layer is 5 μm, the thickness of the PET fiber layer is 0.34 mm, and the areal density is 25 g / m³. 2 The alkali-free glass fiber layer is made of alkali-free glass fiber with a fiber diameter of 0.5 μm, a fiber fineness ≥80°, a thickness of 0.28 mm, and an areal density of 25 g / m³. 2 .

[0155] The preparation method of the composite filter material in this comparative example specifically includes the following steps:

[0156] S1: Alkali-free glass fiber and fluorinated polyvinyl alcohol are added to deionized water and mixed thoroughly to obtain glass fiber slurry. The mass percentage of alkali-free glass fiber in the glass fiber slurry is 8 wt%, the mass percentage of fluorinated polyvinyl alcohol in the glass fiber slurry is 1.5 wt%, and the remainder is deionized water.

[0157] The glass fiber slurry was then heated to 70°C to achieve a viscosity of 200 mPa·s. Subsequently, the glass fiber slurry was uniformly sprayed onto the PET fiber layer using a spraying process at a rate of 1 m / s. After spraying, the slurry was dried at 110°C for 10 min to obtain the PET-glass fiber composite substrate. The mass ratio of the PET fiber layer to the alkali-free glass fiber layer in the PET-glass fiber composite substrate was 40:60.

[0158] S2: The PET-glass fiber composite substrate from step S1 is subjected to gradient pressure reduction hot pressing. The gradient pressure reduction hot pressing process is as follows: First, the PET-glass fiber composite substrate is hot-pressed at 12 MPa and 110℃ for 3 minutes. Then, it is hot-pressed at 8 MPa and 110℃ for 2 minutes. Finally, it is hot-pressed at 5 MPa and 25℃ for 1 minute to obtain the composite filter material.

[0159] Using 2 μm NaCl particles as the test medium, the filtration efficiency of the composite filter material in this control example was determined under standard experimental conditions according to the relevant ASTM standard test methods. The test results showed that the filtration efficiency of this filter material reached 99.94%. Using 0.1 μm NaCl particles as the test medium, the filtration efficiency of the control filter material was 92.3% under standard experimental conditions. Therefore, without the addition of aramid nanofibers, the filtration precision of the composite filter material in this control example can only reach 2 μm, which is insufficient to achieve the filtration efficiency ≥99.99% for 0.1 μm particles, and thus cannot achieve the 0.1 μm filtration precision described in Example 1.

[0160] According to the EN 1822-3 standard test method, under constant airflow conditions with a wind speed of 5.3 cm / s, the initial pressure drop of the composite filter material in this comparative example was measured. The test results showed that its initial resistance was 72 Pa, which was higher than that of Example 1, indicating that the material exhibits relatively high flow resistance when airflow passes through it.

[0161] To verify the performance retention capability of the composite filter material in this comparative example under high-temperature conditions, a hot air aging test was conducted. The sample was placed in a 120℃ oven and heated for 2 hours, after which its filtration efficiency and pressure drop were tested again using the method described above. The test results show that the filtration efficiency and resistance of the filter material did not change significantly after the heat aging treatment, demonstrating good thermal stability and long-term reliability.

[0162] The air permeability of the composite filter material in this comparative example was tested using the Gurley method. During the test, the time required for a certain volume of air (100 mL) to pass through a unit area of ​​filter material under a specified pressure was recorded, expressed in seconds per 100 mL. The test results showed that the air permeability of this composite filter material reached 165 s / 100 mL, which is slightly worse than that of Example 1.

[0163] The areal density of the composite filter material in this comparative example was determined using a gravimetric method. Several groups of samples with a specified area were selected, accurately weighed, and the mass per unit area was calculated. The test results showed that the average areal density of the composite filter material was 52.5 g / m², which was lower than that of Example 1.

[0164] The present invention has been described in detail above with reference to the accompanying drawings and embodiments. However, the present invention is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention. All contents not described in detail in the present invention can be derived from existing technologies.

Claims

1. An electret-enhanced composite filter material, characterized by, The composite filter material comprises a PET fiber layer, an aramid nanofiber layer and an alkali-free glass fiber layer from top to bottom, and the mass ratio of the PET fiber layer, the aramid nanofiber layer and the alkali-free glass fiber layer is (30-60):(5-20):(20-50); the aramid nanofiber layer comprises aramid nanofibers, an electret and an organic solvent; and the mass percentage of the aramid nanofibers, the electret and the organic solvent is: 5-10wt% of the electret, 10-15wt% of the aramid nanofibers and the rest of the organic solvent.

2. The electret enhanced composite filter media of claim 1, wherein, The electret is selected from one or any combination of titanium dioxide, zinc oxide, silicon dioxide, polytetrafluoroethylene, polymethyl methacrylate, polyacrylonitrile, polystyrene, silicone modified resin, fluorosilicone copolymer and ionic liquid, or a combination of polyethyleneimine and polyvinylidene fluoride; and the organic solvent is selected from one or any combination of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, cyclohexanone, trifluoroethanol and hexafluoroisopropanol.

3. The electret enhanced composite filter media of claim 1, wherein, The alkali-free glass fiber layer comprises alkali-free glass fibers, fluorinated polyvinyl alcohol and deionized water, and the mass percentage of the alkali-free glass fibers, the fluorinated polyvinyl alcohol and the deionized water is: 5-10wt% of the alkali-free glass fibers, 1-3wt% of the fluorinated polyvinyl alcohol and the rest of the deionized water.

4. A method for preparing an electret-enhanced composite filter material, for preparing an electret-enhanced composite filter material according to any one of claims 1 to 3, characterized in that The composite filter material comprises: Step S1: aramid nanofibers and an electret are added to an organic solvent, uniformly mixed and sieved to obtain an electrostatic spinning solution; The electrostatic spinning solution is loaded into a needle tube syringe and connected to a spinning needle, output to the PET fiber layer of a receiving device through electrostatic spinning to deposit an aramid nanofiber layer on the PET fiber layer, and the PET-aramid composite substrate is obtained after drying; Step S2: alkali-free glass fibers and fluorinated polyvinyl alcohol are added to deionized water, uniformly mixed to obtain a glass fiber slurry; the glass fiber slurry is uniformly sprayed on the aramid nanofiber layer in the PET-aramid composite substrate by a spraying process, and the PET-aramid-glass fiber composite substrate is obtained after drying; Step S3: the PET-aramid-glass fiber composite substrate is subjected to gradient pressure reduction hot pressing to obtain a composite filter material with an electret enhancement.

5. The method for preparing an electret-reinforced composite filter material according to claim 4, characterized in that, In the step S1, the uniform mixing method is magnetic stirring or high-speed shearing stirring, and the uniform mixing and sieving parameters are as follows: stirring speed 300-600rpm, stirring and mixing time 30-60min, and filtering through a 200-400mesh stainless steel sieve; the electrostatic spinning parameters are as follows: spinning voltage 15-25kV, spinning distance 15-20cm, syringe flow rate 0.3-0.8mL / h, and receiving device rotating speed 1000-2000rpm; and the drying parameters after electrostatic spinning are as follows: drying temperature 80-100℃ and drying time 30-60min.

6. The method for preparing an electret-reinforced composite filter material according to claim 4, characterized in that, In the step S1, after obtaining the PET-aramid composite substrate, it needs to be subjected to high-voltage polarization discharge treatment under a direct current voltage of 10-20kV for 10-30s.

7. The method for preparing an electret-reinforced composite filter material according to claim 4, characterized in that, In the step S2, the mixing method is high-speed shearing stirring, and the mixing parameters are as follows: the stirring speed is 500-800 rpm, the stirring time is 20-40 min; the glass fiber slurry is heated to 60-80℃ before spraying, so that the viscosity reaches 150-250 mPa·s; the spraying speed is 1 m / s; the drying temperature is 100-110℃, and the drying time is 5-10 min.

8. The method for preparing an electret-reinforced composite filter material according to claim 7, characterized in that, In the step S2, after high-speed shearing stirring, ultrasonic dispersion is used for further mixing to obtain the glass fiber slurry; the ultrasonic dispersion parameters are as follows: the frequency is 20-40 kHz, and the time is 10-20 min.

9. The method for preparing an electret-reinforced composite filter material according to claim 4, characterized in that, In the step S3, the gradient pressure reduction hot-pressing forming process is as follows: the PET-aramid-glass fiber composite substrate is first hot-pressed at 12-15 MPa and 105-110℃ for 3-5 min; then it is hot-pressed at 8-10 MPa and 105-110℃ for 2-3 min; finally, it is hot-pressed at 3-6 MPa and 20-40℃ for 1-2 min, to obtain the electret enhanced composite filter material.

Images