Hyperfine electret filter material and preparation method thereof

Abstract

The invention discloses a hyperfine electret filter material and a preparation method thereof. The filter material is formed by mixing polyimide fibers and polytetrafluoroethylene fibers. And in the dust facing surface, the proportion of the polyimide superfine fibers is 25-50%, the proportion of the polyimide fibers with common fineness is 0-25%, and the proportion of the tetrafluoroethylene fibers is 25-75%. Polar silicon salt particles are attached to the surface layer of the dust facing face, the attached particles are evenly distributed in a scattered mode, the average particle diameter of the particles ranges from 1 micrometer to 10 micrometers, and the diameter of at least 80% of the particles ranges from 1.5 micrometers to 9.5 micrometers. The filter material effectively solves the problems that the dust removal efficiency of electrostatic adsorption is not high in the dust removal theory and a common filter bag cannot efficiently filter over-fine dust in the smoke dust of the sintering machine head, and is not only suitable for the smoke dust of the sintering machine head, but also suitable for other working conditions containing the ultra-fine dust. In the using process, the efficient filtering effect can be kept, compared with a common PTFE film covering filtering material, the air permeability is larger, the pressure loss is smaller, and the obvious effect on energy consumption reduction is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of filter media preparation, and particularly relates to an ultra-fine electret filter material and a preparation method thereof. Background Art

[0002] A sintering machine is an important metallurgical equipment used to sinter powdered materials through a sintering process at high temperature, enabling the particles to bond with each other to form hard lumps. The filter material of the dust removal head is a key component in the dust removal equipment. Its performance directly affects the efficiency and service life of the dust collector. It can effectively filter dust and particulate matter in the air, improve air quality, minimize resistance and energy consumption while ensuring the filtration efficiency, adapt to harsh working environments, extend the service life, and the surface of the filter material is not prone to dust accumulation, making it easy for dust cleaning operations to ensure the continuous and efficient operation of the dust collector.

[0003] Currently, the dust removal of the sintering machine head mainly uses an electrostatic precipitator to capture dust in the flue gas by static electricity. However, the electrostatic precipitator has low efficiency and cannot meet the ultra-low emission requirements; it consumes a large amount of energy and needs to increase the voltage to improve the filtration performance; the maintenance of the electrode plates is difficult. Long-term dust accumulation on the electrode plates will cause the voltage to decrease and the filtration effect to deteriorate, and the electrode plates need to be cleaned regularly. When cleaning, personnel need to enter the dust collector to knock on the electrode plates. Before this, due to the problem of overly fine dust particles, bag filters are difficult to be used in this working condition. Therefore, it is necessary to propose a new filter bag to solve the above problems.

[0004] For example, the utility model CN216654936U discloses an efficient electrostatic precipitator for a sintering machine, which can effectively remove part of the sintering machine flue dust. However, as is well known, electrostatic dust removal, even if efficient, is difficult to exceed 95%, and the power consumption is huge.

[0005] The present invention effectively solves the problems of low dust removal efficiency of electrostatic adsorption in the dust removal theory and the inability of ordinary filter bags to efficiently filter overly ultra-fine dust in the sintering machine head flue dust. It is not only applicable to the sintering machine head flue dust, but also applicable to other working conditions that generate ultra-fine dust. During use, it can not only maintain the effect of efficient filtration, but also has a greater air permeability and a smaller pressure loss compared with general PTFE membrane filter materials, and has a significant effect on energy consumption savings. Summary of the Invention

[0006] An ultra-fine electret filter material and a preparation method thereof, wherein the filter material is a mixture of polyimide fiber and polytetrafluoroethylene fiber. Polyimide has the characteristics of high temperature resistance and good acid and alkali resistance, and polytetrafluoroethylene has the characteristics of high temperature resistance and acid and alkali resistance. When only polytetrafluoroethylene is used, the filtration performance is extremely poor due to the uneven fiber shape and uneven thickness; polyimide has a stable cross-sectional shape, and after being combined with polytetrafluoroethylene fiber, it can not only meet the requirements of long-term use in a high temperature and high acid and alkali environment, but also improve the filtration performance.

[0007] The proportion of polyimide ultrafine fibers on the dust-facing surface is 25-50%, the proportion of polyimide ordinary fineness fibers is 0-25%, and the proportion of tetrafluoroethylene fibers is 25-75%. The addition of ultrafine polyimide can more effectively improve the filtering performance of the filter material. However, when the proportion of ultrafine fibers is higher than 50%, the cost will increase and the initial filtering pressure will increase. Therefore, this case requires not more than 50%, and the percentages in this case are all weight percentages.

[0008] Polar silicon salt particles are attached to the surface of the dust-facing surface. The attached particles are evenly scattered, with an average particle diameter of 1-10 μm, and at least 80% of the particles are between 1.5-9.5 μm in diameter. There are many complex working conditions in the field of industrial dust removal, and sintering machine head dust removal is one of them. The dust generated is ultrafine dust. Even if ultrafine fibers are used, it is difficult to control the emission to 5 mg / Nm 3 In order to achieve the effect of ultra-low emission within 100%, the commonly used countermeasure for ultra-fine dust is to use PTFE coating technology, but this technology has defects such as high initial pressure loss, easy breakage, and poor effect after a certain period of use. The polar silicon salt particles in this case have excellent adsorption effect on dust, especially ultra-fine dust, and can effectively adsorb ultra-fine dust on the surface of the filter material, and the effect will not decrease after long-term use. The average particle diameter of the polar silicon salt particles is preferably 3-6μm. This particle diameter will not cause the polar silicon salt particles to fall off and fail during use due to the particles being too large, and large particles will sometimes block the pores between fibers and cause high pressure during use. It will not be too small, resulting in low polarity effect and inability to effectively adsorb ultra-fine dust.

[0009] The average fineness of the polyimide ultrafine fiber on the dust-facing side is 0.8-1.2 denier, and the average fineness of the polyimide ordinary fineness fiber is 1.4-2.3 denier. If the ultrafine warp is too thin, the manufacturing cost will be greatly increased, and combing will also be difficult. The fiber denier within the specified range of this case is the most reasonable, which can not only improve the filtering performance, but also make combing relatively easy, and the combed cotton net is also more uniform, and the cost will not be too high. The polyimide fiber has a circular cross-section, or a Y-shaped cross-section, or a mixture of a circular and a Y-shaped cross-section.

[0010] The PTFE fibers are flattened PTFE fibers produced by the fibrillation method. There are also circular PTFE fibers on the market. Although circular PTFE fibers can further improve the filtration performance, their price is too high. The PTFE fibrillation fibers with obvious price advantages are preferred.

[0011] The polar silicate is preferably a polar silicate formed by metal calcium or metal iron. Polar silicates have formations of various metals, such as aluminum, iron, potassium, calcium, etc. Among them, the polar silicate formed by metal calcium or metal iron has the best adsorption effect on ultrafine dust. The distribution of the polar silicate on the fiber is in a particulate state, and the average interval between particles is 5-20 μm. The particles are concentrated and dispersed on the fibers with a thickness of 0-50 μm in the uppermost layer of the dust-facing surface. The particles dispersed on the fiber surface below a thickness of 50 μm are less than 20% of the fibers with a thickness of 0-50 μm. The uniform dispersion and surface concentration of the particles are also one of the factors enabling this filter material to filter ultrafine dust more effectively. The polar silicate particles concentrated on the surface layer can effectively block the ultrafine dust on the surface layer of the filter material to form an ultrafine dust cake layer.

[0012] The surface of the non-dust-facing side is also attached with polar silicate particles, and the attached particles are distributed in a uniform scattered dot pattern. The average particle diameter of the particles is 1-10 μm, and at least 90% of the particle diameters are between 3-6 μm. The non-dust-facing side is made of a mixture of polyimide fibers and polytetrafluoroethylene fibers. The polar silicate particles on the non-dust-facing side are not necessarily present, and the processing method determines their presence. When processed by the impregnation method, not only the dust-facing side but also the non-dust-facing side will be attached with polar silicate particles. If it is the spraying method, only the dust-facing side needs to be sprayed.

[0013] The surface of this filter material also contains modified high silicate resin, PTFE, a water repellent with a valence of 6 or 8, and a surfactant. Among them, the nano-modified high silicate resin can effectively make the polar silicate particles adhere more firmly to the fiber surface; PTFE is formed after adding and drying PTFE emulsion, which can make the filter material not easily affected by acid condensation and slightly increase the chemical resistance of the filter material; the water repellent with a valence of 6 or 8 can more effectively improve the waterproof and oil-proof properties; the surfactant can more effectively disperse the polar silicate particles, making the particles more evenly dispersed in the emulsion, and the surface attachment of the processed filter material is also more uniform and effective. The surfactant is preferably any one of methyl pentanol and polyacrylamide. The dispersion effect of these two surfactants on the polar silicate particles is better than that of other varieties of surfactants.

[0014] In this case, the grammage of the filter material is specified to be 500-900 g / m 2 , and the base fabric is a fabric made of polyimide fibers or polytetrafluoroethylene fibers, and the grammage of the base fabric is 90-150 g / m 2However, the gram weight range can be further expanded according to special circumstances or customer requirements.

[0015] Preparation method of superfine electret filter material: Step 1: Card and lay the mixed raw materials of polyimide fiber and polytetrafluoroethylene fiber, adjust the laying amount of the bottom layer and the surface layer, and the proportion of the surface layer is 40%-60%; Step 2: Add the base fabric and needled the laid web, and the needling density is 1000-1600 needles / cm 2 to form a semi-finished filter material; Step 3: Feed the filter material obtained in Step 2 into a singeing machine to singe and press the surface of the filter material; this is a common production method for filter materials; Step 4: Attach the mixed solution to the surface of the filter material. The mixed solution includes the following components by weight percentage: polar silicate 10%-20%, modified high-silicate resin finishing agent 2%-6%, PTFE emulsion 5%-15%, water repellent 2%-4%, surfactant 2%-8%, and the rest is water. Specifying the addition ratio of polar silicate and adjusting the ratio to 10%-20% can better achieve the dust removal effect and will not cause the adverse results of fiber pore blockage and pressure increase due to excessive addition. The ratios of other reagents have also been adjusted to the optimal ratio through experiments. Especially for the ratio of surfactant 2%-8%, preferably 3%-6%. If too little is added, the polar silicate cannot be evenly dispersed. If too much is added, the polar silicate will penetrate into the interior of the filter material and cannot form a dense powder cake layer on the surface of the filter material.

[0016] When attaching the mixture to the surface of the filter material, it is preferred to pass the filter material through the mixed solution tank to make the mixed solution evenly adhere to the surface of the filter material, and then extrude the excess mixed solution through a pressure roller; then enter a dedicated drying equipment for primary drying, and wind up after discharging. The primary drying uses a relatively low temperature, and the purpose is only to remove moisture.

[0017] Feed the wound filter material into the dedicated drying equipment again for secondary drying and shaping, and this process is without liquid. The secondary drying is not only for shaping. Drying in two steps can more effectively make the polar silicate firmly adhere to the fiber surface and will not fall off during long-term use.

[0018] The temperature of the above primary drying is 170°C - 230°C, the time is 2 min - 6 min, the temperature of the secondary drying is 260°C - 320°C, and the time is 2 min - 6 min.

[0019] The gram weight increases by 5 - 40 g / m 2 If the increase in gram weight is too small, the polar silicate cannot effectively play the role of adsorbing ultrafine dust. If the increase in gram weight is too large, it will greatly affect the original filtration effect and increase the pressure.

[0020] The filter bag made of this filter material can be used in the fields of sintering machine head dust removal, iron and steel metallurgy, etc. Its filtering effect on ultra-fine dust is better than that of general ultra-fine fiber filter materials. Specific embodiments

[0021] The structure and performance of the present invention can be verified through tests. Examples of some test methods are given below.

[0022] For the average particle diameter of particles, the average fineness of fibers, particle dispersion, and PTFE fibers, an electron microscope or magnification of 500 - 3000 times can be used to photograph and observe the structure, and the magnification can also be enlarged or reduced according to the actual situation.

[0023] The fiber type can be tested by infrared testing, and the particle type can be tested by microscopic infrared testing. The filtering performance is tested by a VDI device.

[0024] The filtering performance and the advantages and disadvantages of pressure loss can also be confirmed through on-site project installation experiments.

[0025] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The following detailed descriptions are all illustrative and are intended to provide further explanations for this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs.

[0026] The embodiment of the present invention provides a preparation method for a filter material for a sintering flue gas bag type dust removal machine head, including: Step 1: Card and lay the mixed polyimide fiber and polytetrafluoroethylene fiber raw materials, adjust the laying amount of the bottom layer and the surface layer, and the proportion of the surface layer is 40 - 60%; Step 2: Add a base cloth, and needle the laid wool web, with a needling density of 1000 - 1600 needles / cm 2 , to form a semi-finished filter material; Step 3: Feed the filter material obtained in Step 2 into a singeing machine to singe and press the surface of the filter material; Step 4: Attach the mixture to the surface of the filter material. The mixture includes the following components in weight percentages: polar silicate 10% - 20%, nano-modified high silicate resin finishing agent 2% - 6%, PTFE emulsion 5% - 15%, water repellent 2% - 4%, surfactant 2% - 8%, and the balance is water.

[0027] Different fibers show different spinnability characteristics in each production link such as carding, laying, and needling. Here, a large number of experiments are required to obtain the optimal ratio and optimal gram weight.

[0028] The carding process parameters are shown in the following table, but are not limited to the process conditions in Table 1 below and can be adjusted according to the actual situation: Table 1 Carding process parameters: Chest cylinder Large cylinder Work roll Upper doffer Upper condenser Upper stripper Upper conveyor Lower doffer Lower condenser Lower stripper Lower conveyor Face 350 900 40 24.44 35.53 0.00 26.66 28 21.13 22.64 29 Bottom 350 900 40 24.44 35.53 0.00 26.66 28 21.13 22.64 29 The needling process parameters are shown in the following table, but are not limited to the process conditions in Table 2 below and can be adjusted according to the actual situation: Table 2 Needling process parameters: Face Bottom 2 3 4 5 6 7 Needle density 46 46 150 150 0 0 240 / 240 260 / 260 Needle depth 15.8 19.6 17.1 16.0 0 0 12.0 / 11.9 5.3 / 4.4

[0029] Example 1: Mix in the ratio of 30% of polyimide superfine 1.0 denier fiber, 20% of polyimide ordinary fineness 2.0 denier fiber, and 50% of polytetrafluoroethylene fiber as the surface layer. Card and lay the web with the thoroughly mixed polyimide fiber and polytetrafluoroethylene fiber raw materials. The non-dust-facing side is evenly mixed by 2.0 denier polyimide ordinary fineness fiber and polytetrafluoroethylene fiber in a ratio of 50:50. Adjust the web laying amount of the bottom layer and the surface layer, and the proportion of the surface layer is 50%. The above polyimide all has a circular cross-section.

[0030] Add the base fabric, and needle the laid wool web with a needling density of 1300 needles / cm 2 , to form a semi-finished filter material; then send the semi-finished filter material into a singeing machine to singe and press the surface of the filter material; Attach the mixed liquid to the surface of the filter material. The mixed liquid includes the following components by weight percentage: polar silicate 12%, nano-modified high silicate resin finishing agent 3%, PTFE emulsion 10%, hexavalent water repellent 3%, methyl pentanol surfactant 4%, and the rest is water. The average particle diameter of the above polar silicate is 5μm, and 98% of the particle diameters are concentrated in the range of 3 - 6μm.

[0031] Attach the above mixed liquid to the surface of the filter material: Process by the dipping method, then extrude the excess mixed liquid through a pressure roller, and then enter a special drying equipment for primary drying. After discharging, wind it up; send the wound filter material into the special drying equipment again for secondary drying and shaping, and this process is without liquid. The temperature of the primary drying is 190°C, the time is 3min, the temperature of the secondary drying is 290°C, and the time is 3min. The gram weight increases by 20g / m after drying 2 .

[0032] The surface layer of the prepared filter material is attached with polar silicate particles, and the attached particles show a uniform scattered dot distribution. The average interval between particles is 8μm. The particles are concentrated and dispersed on the fibers with a thickness of 0 - 50μm in the outermost layer of the dust-facing side. The number of particles dispersed on the fiber surface below 50μm thickness is only 4% of that on the fibers with a thickness of 0 - 50μm.

[0033] When using this filter material for VDI testing, the filtration efficiency reaches 99.9997%. The static filtration effect for 0.3 - 0.5μm reaches 99.95%. When used for treating the sintering machine head soot, the measured on-site emission concentration is 1.2mg / Nm 3 after one week of use, and the measured on-site emission concentration is 1.1mg / Nm 3 after one year of use, and the measured on-site emission concentration is 1.4mg / Nm 3 ; With regular jet blowing, on the premise of the same jet blowing interval, the pressure loss is reduced by more than 25% compared with the PTFE membrane filter material.

[0034] Example 2, Example 3: Details of the fiber ratio and emulsion ratio are shown in Table 3. When the fiber ratio is changed and the emulsion ratio remains unchanged, the particle attachment on the surface of the filter material is the same as that in Example 1.

[0035] In Example 2, due to the increase in the proportion of ultra-fine polyimide fibers, the measured filtration efficiency is slightly better than that in Example 1. The static filtration effect for 0.3 - 0.5μm reaches 99.98%, and the pressure loss is about 15% higher than that in Example 1.

[0036] In Example 3, due to the decrease in the proportion of ultra-fine polyimide fibers, the measured filtration efficiency is slightly lower than that in Example 1. The static filtration effect for 0.3 - 0.5μm reaches 99.9%, and the pressure loss is approximately equal to that in Example 1. It can also meet the emission requirement of 5mg / Nm 3 at the sintering machine head soot treatment site.

[0037] Example 4, Example 5, Example 6: Examples of adjusting the particle diameter and proportion of polar silicate are shown in Table 3, and other conditions are the same as those in Example 1.

[0038] In Example 4, due to the increase in the average particle diameter of polar silicate and the increase in the particle diameter distribution, the measured filtration efficiency is slightly worse than that in Example 1. The static filtration effect for 0.3 - 0.5μm is 99.93%, but due to the blockage by large particles, the pressure loss is about 25% higher than that in Example 1.

[0039] In Example 5, due to the decrease in the average particle diameter of polar silicate and the increase in the particle diameter distribution, resulting in a decrease in polarity, the measured filtration efficiency is worse than that in Example 1. The static filtration effect for 0.3 - 0.5μm is 99.87%, and when dealing with small particles, the pressure loss is about 7% lower than that in Example 1.

[0040] In Example 6, due to the increase in the proportion of polar silicate, the measured filtration efficiency is slightly better than that in Example 1. The static filtration effect for 0.3 - 0.5μm is 99.991%, but due to the large number of particles causing blockage of the fiber pores, the pressure loss is about 20% higher than that in Example 1.

[0041] Examples 7 and 8: The effect of the amount of dispersant on the dispersion of polar silicate was studied.

[0042] In Example 7, due to the addition of a small amount of dispersant, polar silicate particles adhered to the surface layer of the filter material prepared. The adhered particles showed a slightly worse uniformity of scatter point distribution than that in Example 1. 83% of the particle diameters were concentrated in the range of 3 - 6 μm. The average interval between particles was 8 μm. The particles were concentrated and dispersed on the fibers with a thickness of 0 - 50 μm in the outermost layer facing the dust. The number of particles dispersed on the fiber surface below 50 μm thickness was only 2% of that on the fibers with a thickness of 0 - 50 μm. The measured filtration efficiency was slightly worse than that in Example 1. The static filtration effect on particles with a size of 0.3 - 0.5 μm was 99.91%, and the pressure loss was slightly higher than that in Example 1 by about 10%.

[0043] In Example 8, due to the addition of a large amount of dispersant, polar silicate particles adhered to the surface layer of the filter material prepared. The adhered particles in Example 1 penetrated more to the fiber surface below 50 μm thickness. 99% of the particle diameters were concentrated in the range of 3 - 6 μm. The average interval between particles was 8 μm. The number of particles dispersed on the fiber surface below 50 μm thickness was 19% of that on the fibers with a thickness of 0 - 50 μm. The measured filtration efficiency was equal to that in Example 1. The static filtration effect on particles with a size of 0.3 - 0.5 μm was 99.95%, and the pressure loss was higher than that in Example 1 by about 20%.

[0044] Example 9: Just by changing the gram weight and the proportion of the surface layer, its filtration performance is better. Affected by polar silicate particles to a greater extent, so the filtration efficiency is similar to that in Example 1. Due to the increase in gram weight resulting in a decrease in air permeability, the pressure loss is slightly higher than that in Example 1 by 10%.

[0045] Comparative Example 1: No polar silicate particles were added, and the other conditions were the same as in Example 1.

[0046] When using this filter material for VDI test, the filtration efficiency was 99.9952%. The static filtration effect on particles with a size of 0.3 - 0.5 μm reached 71%. When used for sintering machine head flue gas treatment, the on-site measured emission concentration after one week of use was 19 mg / Nm 3 , and the on-site measured emission concentration after one year of use was 12 mg / Nm 3 , and the on-site measured emission concentration after three years of use was 12 mg / Nm 3 ; With regular jetting and the same jetting interval, the pressure loss was reduced by 20% compared with the PTFE membrane filter material.

[0047] Table 3 Examples: Dust-facing surface PTFE fiber Dust-facing surface polyimide fiber Polar silicate / particle diameter / emulsion proportion Modified high silicic acid / PTFE emulsion / water repellent / surfactant Filter material structure Example 1 50% Ultra-fine 1.0 denier 30% / 2.0 denier 20% Average particle diameter 5.0μm / 98% of the particle diameter in the range of 3.0 - 6.0μm / emulsion proportion 12% Modified high silicic acid 3% / PTFE emulsion 10% / water repellent 3% / surfactant 4% Filter felt grammage 650g / ㎡ / PTFE base fabric 110g / ㎡ / Dust-facing surface : non-dust-facing surface = 50 : 50 / Emulsion weight gain after drying 20 g / ㎡ Example 2 25% Ultra-fine 1.0 denier 50% / 2.0 denier 25% Average particle diameter 5.0μm / 98% of the particle diameter in the range of 3.0 - 6.0μm / emulsion proportion 12% Modified high silicic acid 3% / PTFE emulsion 10% / water repellent 3% / surfactant 4% Filter felt grammage 650g / ㎡ / PTFE base fabric 110g / ㎡ / Dust-facing surface : non-dust-facing surface = 50 : 50 / Emulsion weight gain after drying 20 g / ㎡ Example 3 75% Ultra-fine 1.0 denier 15% / 2.0 denier 10% Average particle diameter 5.0μm / 98% of the particle diameter in the range of 3.0 - 6.0μm / emulsion proportion 12% Modified high silicic acid 3% / PTFE emulsion 10% / water repellent 3% / surfactant 4% Filter felt grammage 650g / ㎡ / PTFE base fabric 110g / ㎡ / Dust-facing surface : non-dust-facing surface = 50 : 50 / Emulsion weight gain after drying 20 g / ㎡ Example 4 50% Ultra-fine 1.0 denier 30% / 2.0 denier 20% Average particle diameter 9.0μm / 81% of the particle diameter in the range of 2.0 - 9.0μm / emulsion proportion 12% Modified high silicic acid 3% / PTFE emulsion 10% / water repellent 3% / surfactant 4% Filter felt grammage 650g / ㎡ / PTFE base fabric 110g / ㎡ / Dust-facing surface : non-dust-facing surface = 50 : 50 / Emulsion weight gain after drying 20 g / ㎡ Example 5 50% Ultra-fine 1.0 denier 30% / 2.0 denier 20% Average particle diameter 2.0μm / 81% of the particle diameter in the range of 1.5 - 9.5μm / emulsion proportion 12% Modified high silicic acid 3% / PTFE emulsion 10% / water repellent 3% / surfactant 4% Filter felt grammage 650g / ㎡ / PTFE base fabric 110g / ㎡ / Dust-facing surface : non-dust-facing surface = 50 : 50 / Emulsion weight gain after drying 20 g / ㎡ Example 6 50% Ultra-fine 1.0 denier 30% / 2.0 denier 20% Average particle diameter 5.0μm / 98% of the particle diameter in the range of 3.0 - 6.0μm / emulsion proportion 20% Modified high silicic acid 3% / PTFE emulsion 10% / water repellent 3% / surfactant 4% Filter felt grammage 650g / ㎡ / PTFE base fabric 110g / ㎡ / Dust-facing surface : non-dust-facing surface = 50 : 50 / Emulsion weight gain after drying 20 g / ㎡ Example 7 50% Ultra-fine 1.0 denier 30% / 2.0 denier 20% Average particle diameter 5.0 μm, 98% of the particle diameters are in the range of 3.0 - 6.0 μm, accounting for 12% in the emulsion Modified metasilicic acid 3%, PTFE emulsion 10%, water repellent 3%, surfactant 2% Filter felt grammage 650 g / ㎡, PTFE base fabric 110 g / ㎡, dust-facing side : non-dust-facing side = 50 : 50, weight gain after emulsion drying 20 g / ㎡ Example 8 50% Ultra-fine 1.0 denier 30%, 2.0 denier 20% Average particle diameter 5.0 μm, 98% of the particle diameters are in the range of 3.0 - 6.0 μm, accounting for 12% in the emulsion Modified metasilicic acid 3%, PTFE emulsion 10%, water repellent 3%, surfactant 8% Filter felt grammage 650 g / ㎡, PTFE base fabric 110 g / ㎡, dust-facing side : non-dust-facing side = 50 : 50, weight gain after emulsion drying 20 g / ㎡ Example 9 50% Ultra-fine 1.0 denier 30%, 2.0 denier 20% Average particle diameter 5.0 μm, 98% of the particle diameters are in the range of 3.0 - 6.0 μm, accounting for 12% in the emulsion Modified metasilicic acid 3%, PTFE emulsion 10%, water repellent 3%, surfactant 8% Filter felt grammage 800 g / ㎡, PTFE base fabric 110 g / ㎡, dust-facing side : non-dust-facing side = 60 : 40, weight gain after emulsion drying 40 g / ㎡ Comparative Example 1 50% Ultra-fine 1.0 denier 30%, 2.0 denier 20% None Modified metasilicic acid 3%, PTFE emulsion 10%, water repellent 3%, surfactant 4% Filter felt grammage 650 g / ㎡, PTFE base fabric 110 g / ㎡, dust-facing side : non-dust-facing side = 50 : 50, weight gain after emulsion drying 20 g / ㎡

Claims

1. A superfine electret filtration material, characterized in that The filter material is made of a mixture of polyimide fibers and polytetrafluoroethylene fibers. In the dust-facing surface, the proportion of polyimide ultrafine fibers is 25-50%, the proportion of polyimide ordinary fineness fibers is 0-25%, and the proportion of polytetrafluoroethylene fibers is 25-75%. Polar silicate particles are attached to the surface layer of the dust-facing surface, and the attached particles show a uniform scattered dot distribution. The average particle diameter of the particles is 1-10 μm, and at least 80% of the particle diameters are between 1.5-9.5 μm.

2. The superfine electret filtration material according to claim 1, characterized in that The average fineness of the polyimide ultrafine fibers in the dust-facing surface is 0.8-1.2 denier, the average fineness of the polyimide ordinary fineness fibers is 1.4-2.3 denier, the PTFE fibers are flat PTFE fibers made by the film splitting method, and the polyimide fibers are of circular cross-section, or Y-shaped cross-section, or a mixture of circular and Y-shaped cross-sections.

3. The superfine electret filtration material according to claim 1, characterized in that The polar silicate, the polar silicate formed by metallic calcium or metallic iron, the distribution of the polar silicate on the fibers shows a granular state, and the average interval between the particles is 5-20 μm. The particles are concentrated and dispersed on the fibers with a thickness of 0-50 μm in the uppermost layer of the dust-facing surface, and the particles dispersed on the fiber surface below 50 μm thickness are less than 20% of the fibers with a thickness of 0-50 μm.

4. The superfine electret filtration material according to claim 1, characterized in that Polar silicate particles are also attached to the surface of the non-dust-facing surface, and the attached particles show a uniform scattered dot distribution. The average particle diameter of the particles is 1-10 μm, and at least 90% of the particle diameters are between 3-6 μm. The non-dust-facing surface is made of a mixture of polyimide fibers and polytetrafluoroethylene fibers.

5. The superfine electret filtration material according to claim 1, characterized in that The surface of the filter material also contains modified high silicate resin, PTFE, a water repellent with a valence of 6 or 8, and a surfactant.

6. The superfine electret filtration material according to claim 5, characterized in that Any one of the surfactants methyl pentanol and polyacrylamide.

7. The superfine electret filtration material according to claim 1, characterized in that, The grammage of the filter material is 500 - 900 g / m 2 , and the reinforcing base fabric is a fabric made of polyimide fiber or polytetrafluoroethylene fiber, with a grammage of 90 - 150 g / m 2 .

8. A preparation method of the superfine electret filtration material according to claim 1 and claim 5, characterized in that: Step 1: Card and lay the mixed raw materials of polyimide fibers and polytetrafluoroethylene fibers, and adjust the laying amount of the bottom layer and the surface layer. The proportion of the surface layer is 40-60%. Step 2: Add the base fabric and needlepunch the laid web with a needling density of 1000 - 1600 needles / cm 2 to form a semi-finished filter material; Step 3: Feed the filter material obtained in Step 2 into a singeing machine to singe and press the surface of the filter material. Step 4: Attach the mixed liquid to the surface of the filter material. The mixed liquid includes the following components in weight percentages: polar silicate 10%-20%, nano-modified high silicate resin finishing agent 2-6%, PTFE emulsion 5-15%, water repellent 2%-4%, surfactant 2-8%, and the balance is water.

9. The preparation method of the superfine electret filtration material according to claim 8, characterized in that, Attach the mixture to the surface of the filter medium: Pass the filter medium through the mixture tank to evenly attach the mixture to the surface of the filter medium, and then extrude the excess mixture through a pressure roller; then enter the drying equipment for primary drying, and wind up after discharging; Feed the wound filter medium into the drying equipment again for secondary drying and shaping. This process is liquid-free. The temperature of the primary drying is 170°C - 230°C, the time is 2 min - 6 min, the temperature of the secondary drying is 260°C - 320°C, the time is 2 min - 6 min, and the grammage increases by 5 - 40 g / m after drying 2 .

10. The superfine electret filtration material according to claim 1, characterized in that The filter bag made of this filter material can be used in fields such as sintering machine head dust removal and iron and steel metallurgy.