3D structured PTFE porous membrane filter felt and filter bag prepared from the filter felt

Abstract

The application discloses a 3D structure PTFE porous film filter felt and a filter bag prepared from the filter felt, and is characterized in that the PTFE film filter felt is composed of a PTFE porous film layer and a supporting layer; the PTFE film is composed of a PTFE skeleton and superfine PTFE fibers; the skeleton is in a strip shape; 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; the average distance between two parallel skeletons is 30-80 microns; the superfine PTFE fibers are arranged and distributed perpendicularly to the direction of the skeleton; the two parallel skeletons are connected to each other; the average width of the superfine fibers is 200-1000 nanometers; and the average distance between the superfine fibers is 1-7 microns. The application can be applied to the fields of industrial dust removal, garbage incineration, solid waste disposal and the like. Compared with traditional PTFE film filter materials, the application has a longer service life, can be used at a higher filtering air speed, has a lower pressure difference compared with traditional film products, has a higher filtering effect and can completely meet the emission requirement of less than 5 mg / Nm3.

Description

TECHNICAL FIELD

[0001] The present application relates to a 3D structured PTFE porous membrane filter felt and a filter bag made of the filter felt, which is suitable for industrial dust removal, waste incineration, solid waste disposal and other fields. BACKGROUND

[0002] With the acceleration of urbanization, the number of urban population increases, and the industrial system expands, the amount of garbage is also increasing. PTFE membrane filter bags are often used in these fields. Not only can it be applied to more complex working conditions, but also can effectively remove dust, especially ultrafine dust.

[0003] However, PTFE filter membrane also has some technical bottlenecks, for example, it has certain use limitations on projects with high wind speed, and it is not resistant to friction, which leads to reduced filtering effect after a period of use. In order to improve wear resistance, increasing the thickness will actually reduce the air permeability, resulting in high initial pressure loss during use.

[0004] CN108261838A discloses a special filter material for waste incineration and its preparation method and application, which comprises a coating layer, a surface layer, a base cloth layer and a bottom layer arranged from the outside to the inside. The coating layer is made of PTFE membrane. 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, which can be considered as a general multi-node radial PTFE porous membrane. This kind of coated filter material has high trapping efficiency and is suitable for waste incinerator, steel and chemical industry. However, this technology cannot provide a relatively low running resistance at the beginning of operation, and the membrane is easily damaged after a long time of operation. Dust enters the inside of the filter material, causing blockage, and cannot effectively remove dust, resulting in increased running resistance. When the running resistance exceeds the limit, it can only be replaced, and the service life cannot be guaranteed.

[0005] In addition, CN112218696B discloses a filter material and a filter unit with the filter material. The specification states that the material is composed of micron-level fibers and nanometer-level fibers, and the nanometer-level fibers are interwoven with the micron-level fibers to form nodes. The size of the nodes is also defined, and there are pictures. This is a general multi-node radial PTFE porous membrane. The thickness is small, which can achieve low resistance effect, but the service life is obviously insufficient. If the thickness is greatly increased, the service life and filtering precision can be improved, but the initial pressure loss will be high.

[0006] In view of the shortcomings of the current PTFE coated filter material, the application provides a 3D structured PTFE porous coated filter felt, the PTFE film is composed of PTFE skeleton and superfine PTFE fibers between the skeletons, the skeleton plays a supporting role, and can significantly improve the service life compared with the node film, the superfine PTFE fibers can fully play the filtering effect. And the PTFE porous film is stacked by the same 3-8 layers of the above structure. The 3D structure can improve the air permeability and reduce the pressure loss while achieving excellent dust removal effect. SUMMARY

[0007] The purpose of the application is to provide a 3D structured PTFE porous coated filter felt and a filter bag made of the filter felt, and the specific embodiments of the application are as follows:

[0008] The application discloses a special PTFE porous film, which is composed of PTFE skeleton and superfine PTFE fibers, the skeleton is actually relatively thick PTFE fibers, the skeleton is in a strip shape, 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 skeleton is different from the node star-shaped distribution of the general PTFE porous film, and the relatively thick skeleton plays a supporting role for the whole film surface, and will not be damaged in long-term use, and will not be damaged and fail even at a high wind speed. The average width of the skeleton is in a proper range, which can ensure high firmness, high filtering effect and reasonable pressure difference. If the skeleton is too short, the node star-shaped distribution of the general PTFE porous film cannot play a supporting role. Preferably, the average length of the skeleton is more than 60 times the width of the skeleton. The formation of the skeleton cannot be separated from the special PTFE film processing method, and the application has its own unique steps and conditions when the film is stretched and formed.

[0009] In the above article, the width is described because the skeleton and the fibers in the PTFE film are in a flat state, and the thickness is preferably less than 50% of the width.

[0010] The average distance between the upper and lower two parallel skeletons is 30-80 microns, and the distance between the skeletons cannot be too large or too short, too large structure is loose, and the service life is short. Too short will reduce the air permeability and increase the pressure difference during use. The upper and lower two skeletons are basically parallel, which can ensure uniform arrangement of the PTFE superfine fibers and stable and uniform filtering performance.

[0011] The PTFE ultra-fine fibers are arranged vertically to the skeleton direction, and the upper and lower skeletons are connected to each other. The average width of the ultra-fine fibers is 200-1000 nanometers, and the average distance between the ultra-fine fibers is 1-7 micrometers. The thickness and distance of the fibers determine the filtering performance. Only the average fiber width within the specified range can achieve ideal filtering performance. When the thickness and distance are too large, the filtering effect is insufficient, and when the thickness and distance are too small, the durability is poor and the pressure difference is high.

[0012] The PTFE porous membrane is formed by stacking the same three layers of the above structure. A single layer of PTFE membrane is insufficient to support long-term use durability and 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 air blower.

[0013] The PTFE ultra-fine fibers also have branch PTFE fibers, and the average width of the branch PTFE fibers is not more than 50% of the PTFE ultra-fine fibers. The average length of the branch PTFE fibers is 5-100 times the average width of the branch PTFE fibers. The branch PTFE fibers are finer than the ultra-fine PTFE fibers and are used to fill the pores between the ultra-fine PTFE fibers, achieving true zero emission.

[0014] The PTFE in the PTFE porous membrane uniformly disperses 0.5%-3.0% of vinyl acetate resin. The mixing of vinyl acetate resin into PTFE can improve the toughness of PTFE fibers. After the formation of PTFE fibers, the stability can be improved, and the service life and use wind speed can be further increased. Even at a filtering wind speed of 1.2 m / min. Vinyl acetate resin is one of the differences between the present case and other known examples. During the study of PTFE porous membrane, the inventor found that the addition of a small amount of vinyl acetate resin can effectively increase the toughness of the fibers.

[0015] The PTFE porous membrane is formed by stacking at least three layers of the same structure, preferably four to five layers of the stacking structure. The micropores of the first layer and the micropores of the second layer do not coincide and are arranged with a misalignment of at least 20%. The micropores of the third layer do not coincide with the first and second layers, and the micropores of the second layer are arranged with a misalignment of at least 20%, and so on. A misalignment of more than 20% can block dust from passing through, especially ultra-fine dust. A 3D filtering structure is formed, which prevents dust from passing through and allows air to pass freely.

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

[0017] The support layer is composed of PTFE, and the proportion of PTFE is greater than or equal to 50% by weight, and the remaining fibers are one or several of PPS, aramid and polyester.

[0018] The filter material can be applied in the fields of industrial dust removal, waste incineration, solid waste disposal and the like.

[0019] The PTFE porous membrane used in the filter material has very high control requirements for the stretching process in the production process. The total stretching ratio in one direction must be greater than or equal to 4 times, preferably 6-12 times, the total stretching ratio in another direction. And the direction with large one-way stretching ratio needs to be stretched in several times, the first time 1.5-1.8 times, the second time 2.0-3.0 times, and the remaining stretching ratio is implemented in the third time. The total stretching ratio in one direction must be 4 times that in another direction, and it needs to be stretched in several times, which can better form the unique PTFE skeleton structure of the case.

[0020] The various performance configurations described in the application can be verified by tests, and the following are examples of some test methods.

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

[0022] Air permeability, using GB / T5453-1997 standard to test the air permeability of the material, in addition to the static filtering performance (including dust removal efficiency, pressure difference), based on the standard test of VDI3926.

[0023] Example 1: PTFE filter felt is coated with a layer of 3D structured PTFE porous membrane disclosed in the present application. Microscopic observation shows that the average width of the skeleton of the porous membrane is 8.5 microns, the average length of the skeleton is 0.56 millimeters, the average distance between two parallel skeletons is 55 microns, the average width of the PTFE ultrafine fibers is 450 nanometers, the spacing between the ultrafine fibers is 2.2 microns, and the 3D structured PTFE porous membrane is formed by four layers of ordered staggered lamination. There are branch PTFE fibers on the PTFE fibers, and the branch PTFE fibers are thinner than the ultrafine PTFE fibers, with an average width of only 200 nanometers.

[0024] 1.0% by weight of vinyl acetate resin is uniformly added to the PTFE resin for forming the PTFE membrane, and the vinyl acetate resin is added before the membrane is stretched and formed.

[0025] The performance of the PTFE filter felt coated with the 3D structured PTFE porous membrane is excellent. According to the VDI test, the dust removal efficiency of the filter felt with a grammage of 750 g / m2 after compounding reaches 100%, and no dust penetration occurs. After 10,000 cycles of aging, the pressure difference of the last 30 cycles is only 260 Pa, and the cycle interval is 10,800 seconds. After being made into a filter bag and used in the field of garbage incineration, the outlet concentration is less than 2 mg / Nm3, and the pressure difference is more than 30% lower than that of general PTFE coated membranes when blowing at regular intervals. After one year of use at a wind speed of 1. lm / min, the outlet concentration does not change, and the pressure difference hardly increases. After one year of use, a filter bag is pulled out for disassembly analysis, and it is found that there is no dust penetration, and the dust is concentrated on the upper layer of the PTFE membrane, and the membrane is not damaged.

[0026] Example 2: PTFE filter felt is coated with a layer of 3D structured PTFE porous membrane disclosed in the present application. Microscopic observation shows that the average width of the skeleton of the porous membrane is 8.5 microns, the average length of the skeleton is 0.56 millimeters, the average distance between two parallel skeletons is 55 microns, the average width of the PTFE ultrafine fibers is 1000 nanometers, the spacing between the ultrafine fibers is 7 microns, and the 3D structured PTFE porous membrane is formed by three layers of ordered staggered lamination. There are branch PTFE fibers on the PTFE fibers, and the branch PTFE fibers are thinner than the ultrafine PTFE fibers, with a width of 500 nanometers.

[0027] 1.0% by weight of vinyl acetate resin is uniformly added to the PTFE resin for forming the PTFE membrane, and the vinyl acetate resin is added before the membrane is stretched and formed.

[0028] The PTFE filter felt coated with the 3D structured PTFE porous membrane has excellent performance. According to the VDI test, the dust removal efficiency of the filter felt with a grammage of 750 g / m2 after compounding is 99.9980%, and after aging for 10,000 times, although the initial pressure difference is 20% lower than that of Example 1, the pressure difference in the last 30 times is 320 Pa, which is higher than that of Example 1, and the cycle interval is 8,010 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 spacing between the fibers, and the filtration performance is slightly worse than that of Example 1, but the filtration performance is still higher than that of ordinary PTFE coated membranes.

[0030] Example 3: The PTFE filter felt is coated with a layer of the 3D structured PTFE porous membrane disclosed in the present application. 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 millimeters, the average distance between two parallel skeletons is 55 microns, the average width of the PTFE ultrafine fibers is 200 nanometers, the spacing between the ultrafine fibers is 1 micron, and the 3D structured PTFE porous membrane is composed of six ordered and staggered layers. There are branch PTFE fibers on the PTFE fibers, and the branch PTFE fibers are thinner than the ultrafine PTFE fibers, with a width of 90 nanometers.

[0031] The PTFE resin used to form the PTFE membrane is uniformly added with 1.0% by weight of vinyl acetate resin, which is added before the membrane is stretched and formed.

[0032] The PTFE filter felt coated with the 3D structured PTFE porous membrane has excellent performance. According to the VDI test, the dust removal efficiency of the filter felt with a grammage of 750 g / m2 after compounding is 100%, and after aging for 10,000 times, the initial pressure difference is 40% higher than that of Example 1, the pressure difference in the last 30 times is 290 Pa, which is slightly higher than that of Example 1, and the cycle interval is 9,900 seconds, which is slightly shorter than that of Example 1.

[0033] Compared with Example 1, the PTFE ultrafine fibers of Example 3 are thinner, and the number of layers is larger, which prevents dust from entering and has the same filtration performance as Example 1, but the initial air permeability is slightly lower, and the pressure loss is slightly higher than that of Example 1.

[0034] Example 4: PTFE filter fabric coated with a layer of 3D structured PTFE porous membrane according to the present disclosure, observed under microscope, the average width of the skeleton of the porous membrane is 3 microns, the average length of the skeleton is 0.22 millimeters, 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 structured PTFE porous membrane is four layers of ordered staggered layers. There are branch PTFE fibers on the PTFE fibers, and the branch PTFE fibers are thinner than the ultrafine PTFE fibers, with an average width of only 200 nanometers.

[0035] The PTFE resin forming the PTFE membrane is uniformly added with 1.0% by weight of vinyl acetate resin, and the vinyl acetate resin is added before the membrane is stretched and formed.

[0036] The performance of the PTFE filter fabric coated with a 3D structured PTFE porous membrane is excellent. According to the VDI test, the dust removal efficiency of the filter fabric with a grammage of 750 g / m2 after compounding reaches 99.9990%, and after 10,000 cycles of aging, the pressure difference of the last 30 cycles is 290 Pa, and the cycle interval is 8,700 seconds. Microscopy shows that the skeleton is thin, and after being used for a period of time, there is a small amount of membrane tissue damage phenomenon, which is not as serious as the traditional multi-node radial PTFE porous membrane.

[0037] Example 5: PTFE filter fabric coated with a layer of 3D structured PTFE porous membrane according to the present disclosure, observed under microscope, the average width of the skeleton of the porous membrane is 12 microns, the average length of the skeleton is 0.60 millimeters, 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 structured PTFE porous membrane is four layers of ordered staggered layers. There are branch PTFE fibers on the PTFE fibers, and the branch PTFE fibers are thinner than the ultrafine PTFE fibers, with an average width of only 200 nanometers.

[0038] The PTFE resin forming the PTFE membrane is uniformly added with 1.0% by weight of vinyl acetate resin, and the vinyl acetate resin is added before the membrane is stretched and formed.

[0039] The performance of the PTFE filter fabric coated with a 3D structured PTFE porous membrane is excellent. According to the VDI test, the dust removal efficiency of the filter fabric with a grammage of 750 g / m2 after compounding reaches 100%, and no dust penetration occurs, and after 10,000 cycles of aging, the pressure difference of the last 30 cycles is 297 Pa, and the cycle interval is 8,400 seconds. Although no damage occurs due to the thicker skeleton, it slightly hinders air flow, resulting in slightly higher pressure loss and slightly longer cycle time.

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

[0041] The PTFE resin forming the PTFE film is uniformly added with 0.5% by weight of vinyl acetate resin, which is added before the film is stretched and formed.

[0042] The PTFE filter felt is coated with a 3D structured PTFE porous film, and the performance is excellent. According to the VDI test, the filter felt with a total grammage of 750 g / m2 has a dust removal efficiency of 99.9996%, a slight dust breakthrough occurs, and after 10,000 cycles of aging, the pressure difference of the last 30 cycles is only 277 Pa, and the cycle interval is 9,200 seconds. Reducing the proportion of vinyl acetate resin will slightly reduce the flexibility of the film, but it is still within a good range.

[0043] Comparative Example 1: The traditional multi-node radial PTFE porous film is coated with a PTFE filter felt, and the total grammage is 800 g / m2.

[0044] According to the VDI test, the dust removal efficiency is 99.9980%, a slight dust breakthrough occurs, and after 10,000 cycles of aging, the pressure difference of the last 30 cycles reaches 380 Pa, and the cycle interval is 7,800 seconds. After being made into a filter bag, it is used in the field of garbage incineration, and the outlet concentration is less than 5 mg / Nm3. When the pressure difference is higher than 30% of the PTFE 3D film, the cycle interval is shortened to 1,200 seconds. And it cannot be used in projects with a wind speed of 0.8 m / min or more.

[0045] Comparative Example 2: PTFE filter felt without coating, total grammage 800 g / m2.

[0046] According to the VDI test, the dust removal efficiency is 99.9705%, a serious dust breakthrough occurs, and after 10,000 cycles of aging, the pressure difference of the last 30 cycles is 640 Pa, and the cycle interval is shortened to 1,200 seconds. Such a filter bag is not suitable for use in the field.

[0047] The above examples of the present application are only used to illustrate the examples made by the present application, but not to limit the protection scope of the present application. All equivalent technical solutions also belong to the scope of the present application, and the patent protection scope of the present application should be defined by the claims.

Claims

1. A 3D structured PTFE porous membrane filter blanket, characterized by The PTFE coated filter felt is composed of PTFE porous membrane and support layer, the PTFE porous membrane is composed of PTFE skeleton and ultrafine PTFE fiber, the PTFE skeleton is long strip type, the average width of the skeleton is 1-12 microns, the average length of the skeleton is more than 20 times of the width of the skeleton, the average distance between two parallel skeletons is 30-80 microns, the PTFE ultrafine fiber is arranged and distributed perpendicular to the skeleton direction, the two parallel skeletons are connected to each other, the average width of the ultrafine fiber is 200-1000 nanometers, the average distance between the ultrafine fibers is 1-7 microns, and the PTFE porous membrane is composed of the same 3-8 layers of the above structure, the PTFE ultrafine fiber has branch PTFE fiber, the average width of the branch PTFE fiber is not more than 50% of the PTFE ultrafine fiber, the average length of the branch PTFE fiber is 5-100 times of the average width of the branch PTFE fiber, and the PTFE in the PTFE porous membrane is uniformly dispersed with 0.5%-3.0% of vinyl acetate resin.

2. The 3D structured PTFE porous membrane filter mat of claim 1, wherein The PTFE porous membrane is at least composed of the same three layers of the above structure, the micropores of the first layer and the micropores of the second layer do not coincide, and present at least 20% or more misalignment arrangement, the micropores of the third layer and the micropores of the first and second layers do not coincide, and the micropores of the second layer present at least 20% misalignment arrangement.

3. The 3D structured PTFE porous membrane filter mat of claim 2, wherein The PTFE porous membrane is at least composed of the same four or five layers of the above structure.

4. The 3D structure PTFE porous coated membrane filter felt of claim 1 has a gas permeability of 2.5-6.0 cc / cm²*s@125Pa.

5. The 3D structure PTFE porous coated membrane filter felt of claim 1, the support layer of the filter felt is composed of PTFE fiber and the proportion of PTFE is greater than or equal to 50% by weight, the rest of the fiber is one or several of PPS, aramid fiber and polyester fiber, the total grammage of the filter felt is 600-900 g / m², and the thickness is 1.1-1.7 mm.