PTFE (polytetrafluoroethylene) porous membrane filter felt with 3D (three-dimensional) structure and filter bag made of filter felt

Abstract

The invention discloses a 3D structured PTFE porous membrane filter felt and a filter bag made of the filter felt, and is characterized in that the PTFE membrane filter felt is composed of a PTFE porous membrane layer and a support layer, the PTFE membrane is composed of a PTFE skeleton and ultrafine PTFE fibers, the skeleton is strip-shaped, the average width of the skeleton is 3-12 microns, the average length of the skeleton is more than 20 times of the width of the skeleton, and the ultrafine PTFE fibers are uniformly distributed in the skeleton. The average distance between the two parallel frameworks is 30-80 micrometers, the PTFE superfine fibers are arranged and distributed in the direction perpendicular to the frameworks, the two parallel frameworks are connected with each other, the average width of the superfine fibers is 200-1000 nanometers, and the average distance between the superfine fibers is 1-7 micrometers. The method can be applied to the fields of industrial dust removal, waste incineration, solid waste disposal and the like. Compared with a traditional PTFE membrane filter material, the filter material has the advantages that the service life is longer, the filter material can be used at a higher filtering air speed, the pressure difference is lower than that of a traditional membrane product, the filtering effect is higher, and the discharge requirement within 5mg / Nm < 3 > can be completely met.

Description

Technical Field

[0002] The invention relates to a 3D-structured PTFE porous membrane filter felt and a filter bag made from the filter felt, which is suitable for the fields of industrial dust removal, garbage incineration, solid waste disposal, etc. Background Art

[0003] With the acceleration of urbanization, the increase in urban population, the continuous expansion of industrial systems, and the continuous increase in the amount of garbage generated, PTFE coated filter bags are often used in these fields. Not only can they be used in more complex working conditions, but they can also effectively remove dust, especially ultra-fine dust.

[0004] However, PTFE filter membranes also have some technical bottlenecks. For example, they have certain limitations in use in projects with high wind speeds. Another example is that they are not wear-resistant. After a period of use, the filtration effect is reduced due to friction. Another example is that in order to improve wear resistance, increasing the thickness actually reduces the air permeability, resulting in high initial pressure loss during use.

[0005] CN108261838A discloses a special filter material for garbage incineration and its preparation method and application, including a coating layer, a surface layer, a base fabric layer and a bottom layer arranged in sequence from the outside to the inside, the coating layer is made of a PTFE membrane, and the specification also describes that the pore size of the PTFE membrane is 0.3-2µm, but the specific structure of the PTFE membrane is not described in detail, and it can be regarded as a general multi-node radial PTFE porous membrane. This coating filter material has the characteristics of high capture efficiency and is suitable for garbage incinerators, steel and chemical industries. However, this technology cannot provide a lower running resistance at the beginning of operation, and the membrane is more easily damaged after a long period of operation. Dust invades the inside of the filter material to cause blockage, and the dust cannot be effectively removed, and the running resistance increases. After exceeding the running resistance limit, it can only be replaced, and the service life cannot be guaranteed.

[0006] In addition, CN112218696B discloses a filter material and a filter unit having the filter material. The specification states that the material is composed of micron-scale fibers and nano-scale fibers, and the nano-scale fibers and micron-scale fibers are interwoven to form nodes. The size of the nodes is also defined and rich in pictures. This is a multi-node radial PTFE porous membrane in the general sense. A small thickness can achieve a low resistance effect, but the life span is obviously insufficient. If the thickness is greatly increased, the life span and filtration accuracy can be increased, but it will lead to high initial pressure loss.

[0007] In view of the shortcomings of the current PTFE membrane filter material, the present invention provides a 3D structure PTFE porous membrane filter felt. The PTFE membrane is composed of a PTFE skeleton and ultrafine PTFE fibers between the skeletons. The skeleton plays a supporting role. Compared with the node membrane, it can significantly improve the use fastness and extend the service life. The ultrafine PTFE fibers can give full play to the filtering effect. And the PTFE porous membrane is composed of 3 to 8 layers of the same structure stacked. This 3D structure can achieve excellent dust removal effect while improving air permeability and reducing pressure loss. Summary of the invention

[0008] The purpose of the invention is to provide a 3D structured PTFE porous membrane filter felt and a filter bag made from the filter felt. The specific embodiments of the invention are as follows: The invention discloses a special PTFE porous membrane, which is composed of a PTFE skeleton and ultra-fine PTFE fibers. The skeleton is actually a relatively thick PTFE fiber, and the skeleton is a long strip. The average width of the skeleton is 1-12 microns, and the average length of the skeleton is more than 20 times the width of the skeleton. The existence of the skeleton is different from the star-shaped distribution of nodes of a general PTFE porous membrane. The thicker skeleton plays a role in supporting the overall membrane surface, and will not be damaged during long-term use, even at a higher wind speed, it will not be damaged and fail. The average width of the skeleton is in a suitable interval, which can not only ensure high fastness, but also ensure high filtering effect and pressure difference within a reasonable range. If the skeleton is too short, it will not play a supporting role similar to the star-shaped distribution of nodes of a general PTFE porous membrane. It is preferred that the average length of the skeleton is more than 60 times the width of the skeleton. The formation of the skeleton is inseparable from a special PTFE membrane processing method. Unlike other membrane making methods, this case has its own unique steps and conditions when the membrane is stretched and formed.

[0009] The description of width in the above paragraph is because the skeleton and fibers in the PTFE membrane are flat, and its thickness is preferably less than 50% of the width.

[0010] The average distance between the upper and lower parallel skeletons is 30-80 microns. The distance between the skeletons should not be too large or too short. If it is too large, the structure will be loose and the life will be short. If it is too short, the air permeability will be reduced and the pressure difference will be high during use. The upper and lower skeletons are basically parallel, which can also ensure that the PTFE ultrafine fibers are evenly arranged and the filtering performance is stable and uniform.

[0011] PTFE ultrafine fibers are arranged perpendicular to the skeleton direction, connecting the upper and lower skeletons. The average width of the ultrafine fibers is 200-1000 nanometers, and the average distance between the ultrafine fibers is 1-7 microns. The thickness and distance of the fibers determine the quality of the filtration performance. Only the average fiber width within the specified range can achieve the ideal filtration performance. When the fiber width is too thick and the distance is too large, the filtration effect is insufficient. When the fiber width is too thin and the distance is too short, the durability differential pressure difference is high.

[0012] The PTFE porous membrane is composed of 3 to 8 layers of the above structure. A single layer of PTFE membrane is not durable enough for long-term use, nor is it sufficient to provide sufficient filtering performance. Too many layers will seriously affect the pressure difference, and the initial pressure difference will be extremely high during use, increasing the energy consumption of the induced draft fan.

[0013] There are also branched PTFE fibers on the PTFE ultrafine fibers, and the average width of the branched PTFE fibers does not exceed 50% of the PTFE ultrafine fibers. The average length of the branched PTFE fibers is 5-100 times the average width of the branched PTFE fibers. The branched PTFE fibers are thinner than the ultrafine PTFE fibers and are used to fill the gaps between the ultrafine PTFE fibers, truly achieving zero emissions.

[0014] 0.5%-3.0% of vinyl acetate resin is evenly dispersed in the PTFE that constitutes the PTFE porous membrane. Vinyl acetate resin mixed into PTFE can improve the toughness of PTFE fibers. After PTFE is formed into fibers, its stability can be improved, and its service life and wind speed can be further increased. It can even be used at a filtering wind speed of 1.2m / min. Vinyl acetate resin is also one of the aspects that distinguish this case from other known examples. In the process of studying PTFE porous membranes, the inventors found that trace addition of vinyl acetate resin can effectively increase fiber toughness.

[0015] The PTFE porous membrane is formed by stacking at least three layers of the same structure, preferably a four- to five-layer stacked structure. The micropores of the first layer do not overlap with the micropores of the second layer, and present a staggered arrangement of at least 20%. The micropores of the third layer do not overlap with the first and second layers, and present a staggered arrangement of at least 20% with the micropores of the second layer, and so on. A staggered arrangement of more than 20% can better block the passage of dust, especially ultrafine dust. A 3D filtering structure is formed in which dust cannot pass and air can pass freely.

[0016] The air permeability of the filter material is 2.5-6.0cc / cm2*s@125Pa, and its static filtration effect is greater than or equal to 99.9% for the removal of 0.3-0.5 micron dust, and greater than 99.99% for the removal of 0.5-1.0 micron dust. The support layer of the filter felt is composed of PTFE fibers, the total weight of the filter felt is 600-900g / ㎡, and the thickness is 1.1-1.7mm.

[0017] The supporting layer is composed of PTFE, and the proportion of PTFE is greater than 50 weight percent, and the remaining fibers are one or more of PPS, aramid, and polyester.

[0018] The filter material can be used in industrial dust removal, waste incineration, solid waste disposal and other fields.

[0019] The PTFE porous membrane used in this filter material has extremely high control requirements for the stretching process during the production process. The total ratio of unidirectional stretching must be greater than or equal to 4 times the total ratio of stretching in the other direction, preferably 6 times to 12 times. And in the direction with a large unidirectional stretching ratio, stretching needs to be divided into stretching, the first stretching is 1.5-1.8 times, the second stretching is 2.0-3.0 times, and the remaining stretching ratio is implemented in the third stretching. The total unidirectional stretching ratio must be 4 times that of the other direction, and it must be stretched in batches, so that the unique PTFE skeleton structure of this case can be better formed.

[0020] The various performance structures described in the present invention can be verified by testing. The following are examples of some testing methods.

[0021] The structure of the PTFE membrane, the average diameter of the fibers, the number of layers, etc., can be observed by photographing the surface of the PTFE using a scanning electron microscope, a transmission electron microscope, or a microscope that can clearly magnify more than 1000 times. The magnification of the photograph is 1000-4000 times, which can be adjusted up or down according to the actual situation.

[0022] Air permeability: GB / T5453-1997 standard is used to test the air permeability of the material. Except for static filtration, the filtration performance (including dust removal efficiency and pressure difference) is tested based on the VDI3926 standard.

[0023] Example 1: A layer of 3D structured PTFE porous membrane disclosed in the present invention is covered on the PTFE filter felt. Through microscopic observation, the average width of the skeleton of the porous membrane is 8.5 microns, the average length of the skeleton is 0.56 mm, the average distance between two parallel skeletons is 55 microns, the average width of the PTFE ultrafine fiber is 450 nanometers, the interval between the ultrafine fibers is 2.2 microns, and the 3D structured PTFE porous membrane is composed of four layers of orderly staggered stacking. There are branched PTFE fibers on the PTFE fibers, which are thinner than the ultrafine PTFE fibers, and the average width is only 200 nanometers.

[0024] 1.0 weight percent of vinyl acetate resin is uniformly added to the PTFE resin forming the PTFE membrane. The vinyl acetate resin is added before the membrane is stretched and molded.

[0025] The performance of PTFE filter felt after laminating with 3D structure PTFE porous membrane is excellent. According to VDI test, the dust removal efficiency of the filter felt with a gram weight of 750g / ㎡ after lamination reached 100%, and no dust penetration occurred. After aging 10,000 times, the pressure difference of the last 30 times was only 260Pa, and the cycle interval reached 10,800 seconds. After being made into filter bags, they were tried in the on-site garbage incineration conditions. The outlet concentration was less than 2mg / Nm3. When sprayed regularly, the pressure difference was more than 30% lower than that of general PTFE coated products. After one year of use, the outlet concentration of the project with a wind speed of 1. lm / min did not change, and the pressure difference hardly increased. After one year of use, a filter bag was pulled out for disassembly analysis, and it was found that the dust did not penetrate, concentrated on the upper layer of the PTFE membrane on the surface, and the membrane was not damaged.

[0026] Example 2: A layer of 3D structured PTFE porous membrane disclosed in the present invention is covered on the PTFE filter felt. Through microscopic observation, the average width of the skeleton of the porous membrane is 8.5 microns, the average length of the skeleton is 0.56 mm, the average distance between two parallel skeletons is 55 microns, the average width of the PTFE ultrafine fiber is 1000 nanometers, the interval between the ultrafine fibers is 7 micrometers, and the 3D structured PTFE porous membrane is composed of three layers of orderly staggered stacking. There are branched PTFE fibers on the PTFE fibers, which are thinner than the ultrafine PTFE fibers and have a width of 500 nanometers.

[0027] 1.0 weight percent of vinyl acetate resin is uniformly added to the PTFE resin forming the PTFE membrane. The vinyl acetate resin is added before the membrane is stretched and formed.

[0028] The performance of the PTFE filter felt after laminating the 3D structure PTFE porous membrane is excellent. According to the VDI test, the dust removal efficiency of the filter felt with a gram weight of 750g / ㎡ after lamination is 99.9980%. After aging for 10,000 times, although the initial pressure difference is 20% lower than that of Example 1, the pressure difference of the last 30 times is 320Pa, which is higher than that of Example 1, and the cycle interval is 8010 seconds, which is shorter than that of Example 1.

[0029] Compared with Example 1, the PTFE ultrafine fibers of Example 2 are thicker, resulting in larger intervals between the fibers, and the filtration performance is also worse than that of Example 1, but the filtration performance is still higher than that of ordinary PTFE membranes.

[0030] Embodiment 3: The PTFE filter felt is covered with a layer of the 3D structure PTFE porous membrane disclosed in the present invention. Through microscopic observation, the average width of the skeleton of the porous membrane is 8.5 microns, the average length of the skeleton is 0.56 mm, the average distance between the two parallel skeletons is 55 microns, the average width of the PTFE ultrafine fibers is 200 nanometers, the interval between the ultrafine fibers is 1 micron, and the 3D structure PTFE porous membrane is formed by six layers of orderly staggered stacking. There are branched PTFE fibers on the PTFE fibers, and the branched PTFE fibers are thinner than the ultrafine PTFE fibers and have a width of 90 nanometers.

[0031] 1.0 weight percent of vinyl acetate resin is uniformly added to the PTFE resin forming the PTFE membrane. The vinyl acetate resin is added before the membrane is stretched and formed.

[0032] The performance of the PTFE filter felt after laminating the 3D structure PTFE porous membrane is excellent. The filter felt with a gram weight of 750g / ㎡ after lamination has a dust removal efficiency of 100% according to the VDI test. After aging for 10,000 times, the initial pressure difference is 40% higher than that of Example 1. The pressure difference of the last 30 times is 290Pa, slightly higher than that of Example 1. The cycle interval is 9900 seconds, slightly shorter than that of Example 1.

[0033] Compared with Example 1, the PTFE ultrafine fibers of Example 3 are thinner and have more layers. Although dust intrusion is prevented and the filtration performance is the same as that of Example 1, the initial air permeability is slightly worse and the pressure loss is slightly higher than that of Example 1.

[0034] Embodiment 4: A PTFE filter felt is covered with a layer of 3D structure PTFE porous membrane disclosed in the present invention. Through microscopic observation, the average width of the skeleton of the porous membrane is 3 microns, the average length of the skeleton is 0.22 mm, the average distance between two parallel skeletons is 55 microns, the average width of the PTFE ultrafine fibers is 450 nanometers, the interval between the ultrafine fibers is 2.2 microns, and the 3D structure PTFE porous membrane is formed by four layers of orderly staggered stacking. There are branched PTFE fibers on the PTFE fibers, and the branched PTFE fibers are thinner than the ultrafine PTFE fibers, and the average width is only 200 nanometers.

[0035] 1.0 weight percent of vinyl acetate resin is uniformly added to the PTFE resin forming the PTFE membrane. The vinyl acetate resin is added before the membrane is stretched and molded.

[0036] The performance of PTFE filter felt after laminating with 3D structure PTFE porous membrane is excellent. According to VDI test, the dust removal efficiency of the composite filter felt with a gram weight of 750g / ㎡ reached 99.9990%. After aging for 10,000 times, the pressure difference of the last 30 times was 290Pa, and the cycle interval was 8700 seconds. Through the microscope, it was found that the skeleton was thin, and there was a very small amount of membrane tissue damage after a period of use. This damage phenomenon is not as serious as the traditional multi-node radial PTFE porous membrane.

[0037] Embodiment 5: The PTFE filter felt is covered with a layer of 3D structure PTFE porous membrane disclosed in the present invention. Through microscopic observation, the average width of the skeleton of the porous membrane is 12 microns, the average length of the skeleton is 0.60 mm, the average distance between the two parallel skeletons is 55 microns, the average width of the PTFE ultrafine fibers is 450 nanometers, the interval between the ultrafine fibers is 2.2 microns, and the 3D structure PTFE porous membrane is formed by four layers of orderly staggered stacking. There are branched PTFE fibers on the PTFE fibers, and the branched PTFE fibers are thinner than the ultrafine PTFE fibers, and the average width is only 200 nanometers.

[0038] 1.0 weight percent of vinyl acetate resin is uniformly added to the PTFE resin forming the PTFE membrane. The vinyl acetate resin is added before the membrane is stretched and formed.

[0039] The performance of PTFE filter felt after laminating with 3D structure PTFE porous membrane is excellent. According to VDI test, the dust removal efficiency of the composite filter felt with a gram weight of 750g / ㎡ reached 100%, and no dust penetration occurred. After aging for 10,000 times, the pressure difference of the last 30 times was 297Pa, and the cycle interval was 8400 seconds. Although the thick skeleton did not break, it slightly blocked the air circulation, resulting in slightly higher pressure loss and slightly longer cycle time.

[0040] Example 6: Other conditions are exactly the same as those in Example 1.

[0041] 0.5 weight percent of vinyl acetate resin is uniformly added to the PTFE resin forming the PTFE membrane. The vinyl acetate resin is added before the membrane is stretched and formed.

[0042] The performance of PTFE filter felt after laminating with 3D structure PTFE porous membrane is excellent. According to VDI test, the dust removal efficiency of the composite filter felt with a gram weight of 750g / ㎡ reached 99.9996%, with slight dust penetration. After aging for 10,000 times, the pressure difference of the last 30 times was only 277Pa, and the cycle interval reached 9200 seconds. Reducing the proportion of vinyl acetate resin will slightly reduce the capriciousness of the membrane, but it is still within a good range.

[0043] Comparative Example 1: A traditional multi-node radial PTFE porous membrane and PTFE filter felt are used in combination, with a total weight of 800 g / m2.

[0044] According to the VDI test, the dust removal efficiency is 99.9980%, and slight dust penetration occurs. After aging for 10,000 times, the pressure difference of the last 30 times reached 380Pa, and the cycle interval reached 7,800 seconds. After being made into filter bags, it is used in on-site waste incineration conditions. The outlet concentration is less than 5mg / Nm3. When sprayed regularly, the pressure difference is more than 30% higher than that of the PTFE3D membrane in this case. And it cannot be used in projects with wind speeds above 0.8m / min.

[0045] Comparative Example 2: PTFE filter felt without film coating, with a total weight of 800 g / ㎡.

[0046] According to the VDI test, the dust removal efficiency is 99.9705%, and severe dust penetration occurs. After aging for 10,000 times, the pressure difference in the last 30 times is 640Pa, and the cycle interval is shortened to 1,200 seconds. This filter bag is not suitable for on-site use.

[0047] The above embodiments of the present invention are merely examples to clearly illustrate the present invention, but are not intended to limit the protection scope of the present invention. All equivalent technical solutions also belong to the scope of the present invention. The patent protection scope of the present invention should be defined by the claims.

Claims

1. The present invention discloses a 3D structured PTFE porous membrane filter felt and a filter bag made from the filter felt, characterized in that The PTFE coated filter felt is composed of a PTFE porous membrane layer and a support layer, the PTFE membrane is composed of a PTFE skeleton and ultrafine PTFE fibers, the PTFE skeleton is long strip-shaped, the average width of the skeleton is 1-12 microns, the average length of the skeleton is more than 20 times the width of the skeleton, the average distance between two parallel skeletons is 30-80 microns, the PTFE ultrafine fibers are arranged and distributed perpendicular to the skeleton direction, connecting the two parallel skeletons to each other, the average width of the ultrafine fibers is 200-1000 nanometers, and the average distance between the ultrafine fibers is 1-7 microns. And the PTFE porous membrane is stacked by the same 3-8 layers of the above structure.

2. A 3D structured PTFE porous membrane filter felt and a filter bag made of the filter felt as claimed in claim 1, characterized in that There are also branched PTFE fibers on the PTFE ultrafine fibers, and the average width of the branched PTFE fibers does not exceed 50% of the PTFE ultrafine fibers. The average length of the branched PTFE fibers is 5-100 times the average width of the branched PTFE fibers. 0.5%-3.0% of vinyl acetate resin is evenly dispersed in the PTFE that makes up the PTFE porous membrane.

3. A 3D structured PTFE porous membrane filter felt and a filter bag made of the filter felt as claimed in claim 1, characterized in that The PTFE porous membrane is formed by stacking at least three layers of the same structure, preferably a four- to five-layer stacking structure. The micropores of the first layer do not overlap with the micropores of the second layer, and present a staggered arrangement of at least 20%. The micropores of the third layer do not overlap with the first and second layers, and present a staggered arrangement of at least 20% of the micropores of the second layer, and so on.

4. A 3D structured PTFE porous membrane filter felt as described in claim 1, having an air permeability of 2.5-6.0 cc / cm2*s@125Pa.

5. A 3D structured PTFE porous membrane filter felt as described in claim 1, wherein the support layer of the filter felt is composed of PTFE fibers, the total weight of the filter felt is 600-900 g / m2, and the thickness is 1.1-1.7 mm.

6. A 3D structured PTFE porous membrane filter felt as claimed in claim 5, wherein the support layer is composed of PTFE, and the proportion of PTFE is greater than or equal to 50 weight percent, and the remaining fibers are one or more of PPS, aramid, and polyester.

7. A 3D structured PTFE porous membrane filter felt and a filter bag made of the filter felt as described in claim 1, which can be used in the fields of industrial dust removal, waste incineration, solid waste disposal, etc.