A polytetrafluoroethylene filter material

Abstract

The application discloses a polytetrafluoroethylene filter material and relates to the technical field of filter materials. 2 The polytetrafluoroethylene filter material has a grammage of 650-950 g / m 3 , the average fineness of polytetrafluoroethylene fibers of a dust-approaching layer is 2D-4D, the average fineness of polytetrafluoroethylene fibers of a non-dust-approaching layer is 4D-6D, the porosity of the uppermost one fifth to one third thickness of fibers from the surface of the dust-approaching layer to the base cloth direction is 15-30%, the porosity of the remaining four fifths to two thirds thickness is 40-60%, and the porosity of the non-dust-approaching layer is 50%-70%. The polytetrafluoroethylene filter material can meet the effects of ultra-low emission (5 mg / N 3 ) and low resistance, can be used on site for more than three years at least even at a filter wind speed of greater than or equal to 1.0 m / min, the filtering effect does not decrease, the cost does not increase compared with a PTFE film product, and the polytetrafluoroethylene filter material is suitable for fields such as waste incineration, industrial dust removal, solid waste disposal and steel smelting.

Description

Technical Field

[0001] This invention relates to the field of filter material technology, and in particular to a polytetrafluoroethylene (PTFE) filter material, which is suitable for applications such as waste incineration, industrial dust removal, solid waste disposal, and iron and steel metallurgy. Background Technology

[0002] In recent years, filter bags have been widely used to meet ultra-low emission requirements. Microfiber filter bags coated with polytetrafluoroethylene (PTFE) have been proven to be effective in meeting these requirements.

[0003] In the field of waste incineration, PTFE membrane filter bags are the most widely used. These are PTFE filter materials, also known as PTFE filter felts, with a PTFE porous membrane laminated to their surface. Due to their high-temperature resistance and chemical corrosion resistance, PTFE fibers are often used in harsh environments.

[0004] Currently, to achieve ultra-low emissions, most PTFE filter felts used to compose PTFE filter bags employ PTFE membranes to filter dust through porous PTFE membranes. However, PTFE membranes are unsuitable for certain operating conditions, including filtration velocities exceeding 1.0 m / min, high pressure differential requirements, low-pressure operation, and projects prone to condensation. Therefore, ensuring the filtration efficiency of PTFE filter bags while meeting the demands of high velocities, low pressure loss, and condensation has become a pressing problem. This invention utilizes a non-membrane-coated PTFE filter felt, overcoming the common drawback of poor filtration performance compared to previous non-membrane-coated PTFE filter felts. Furthermore, this invention eliminates the need for round PTFE fibers, requiring only relatively inexpensive white PTFE fibers produced via membrane splitting, resulting in a significant cost advantage.

[0005] Chinese utility model patent CN200720069361.7 discloses a PTFE fiber high-temperature resistant needle-punched filter felt, which consists of symmetrically bonded fiber layers on the upper and lower surfaces of a base fabric. The base fabric is a PTFE woven fabric, and the fiber layers are PTFE short fiber layers. The advantages disclosed in this patent include superior temperature resistance (withstanding temperatures up to 240℃), strong acid and alkali resistance, good oxidation resistance, smooth surface for easy cleaning, low operating resistance, good low-friction properties, flame retardancy, insulation, and heat insulation; high filtration efficiency, and long service life. However, because it does not involve PTFE membrane coating or any special processing technology, it cannot achieve the high filtration performance and low pressure drop required by this patent, thus failing to meet the requirements of high-velocity projects.

[0006] Chinese utility model patent CN201620867307.6 discloses a flexible hydroentangled filter felt, which reinforces the filter mesh through airflow forming and the addition of metal fibers to the base fabric, making the filter felt less prone to deformation and pore enlargement during use. This application achieves the same filtration performance of PTFE non-membrane filter felt after long-term use through other methods. The method is fundamentally different from that of patent CN201620867307.6, is simpler to implement, lower in cost, and more effective.

[0007] To address the shortcomings of current non-membrane-coated PTFE filter mats, this invention provides a method that can still meet ultra-low emissions of 5 mg / Nm³ even without a PTFE membrane. 3 Furthermore, the low resistance of PTFE filter felt products ensures that they can be used on-site for at least 3 years without loss of filtration efficiency, even at filtration velocities of 1.0 m / min or higher. Compared to PTFE membrane products, the cost of PTFE filter felt products is not increased. Summary of the Invention

[0008] The purpose of this invention is to provide a polytetrafluoroethylene (PTFE) filter material that can achieve high filtration performance, low resistance, and no reduction in filtration performance after long-term use, even without a PTFE membrane.

[0009] The technical solution of the present invention is as follows: a polytetrafluoroethylene (PTFE) filter material, wherein the PTFE filter material has a basis weight of 650-950 g / m³. 2 The average fineness of the polytetrafluoroethylene (PTFE) fibers in the dust-receiving layer is 2D-4D, and the average fineness of the PTFE fibers in the non-dust-receiving layer is 4D-6D. From the surface of the dust-receiving layer towards the base fabric, the porosity of the fibers in the top one-fifth to one-third thickness is 15-30%, the porosity of the remaining four-fifths to two-thirds thickness is 40-60%, and the porosity of the non-dust-receiving layer is 50%-70%.

[0010] From the surface of the dust-attracting layer toward the base fabric, the top layer, which is one-fifth to one-third thick, contains 10%-20% by mass of polyvinylidene fluoride (PVDF) fibers, which are uniformly mixed between the fibers. The average fineness of the PVDF fibers is 2D-4D.

[0011] The surface of the dust-attracting layer has 5-15 g / m 2 The foaming agent is a mixture of aluminum stearate or potassium stearate, wherein the main component of the foaming agent is a fluorocarbon compound. The addition ratio of foaming agent to aluminum stearate is 5:1 to 10:1 by mass, and the addition ratio of foaming agent to potassium stearate is 8:1 to 12:1 by mass.

[0012] The thickness of this PTFE filter material is 1.1~1.6mm, the base fabric is made of PTFE, and the basis weight of the base fabric is 100~200g / m². 2 The mass ratio of the dust-attracting layer to the non-dust-attracting layer is 4:6 to 6:4.

[0013] The polytetrafluoroethylene (PTFE) fibers used are 48-75 mm in length, with 10-16 crimps per 25 mm and a crimp degree of 8-12%. The average curvature of the PTFE fibers in the filter material is 0.005-0.05 µm. -1 .

[0014] Filter bags made from this polytetrafluoroethylene (PTFE) filter material can be used in fields with high temperatures and harsh working environments, such as waste incineration, solid waste disposal, and industrial dust removal.

[0015] The beneficial effects of this invention are: it can meet the ultra-low emission standard of 5mg / Nm³. 3 Furthermore, its low resistance means it can be used on-site for at least 3 years even at filtration velocities of 1.0 m / min or higher, without any reduction in filtration efficiency. Compared to PTFE membrane products, its cost is not increased. Detailed Implementation

[0016] This invention discloses a polytetrafluoroethylene (PTFE) filter material, wherein the basis weight of the PTFE filter material is 650-950 g / m³. 2 The PTFE filter material here is a non-woven filter material made of PTFE short fiber needle-punched or spunlace and needle-punched combination. It has a three-layer structure consisting of a dust-receiving layer, a middle base fabric layer, and a non-dust-receiving layer. The surface does not contain a PTFE porous membrane. The average fineness of the PTFE fibers in the dust-receiving layer is 2D-4D. Using finer PTFE fibers in the dust-receiving layer can effectively improve the filtration accuracy. When the average fiber fineness of the PTFE fibers is less than 2D, the fibers are too fine and have poor combing properties. The cotton web combed out of the carding machine is full of knots, and its filtration performance will decrease, failing to meet the ultra-low emission requirements.

[0017] The average fineness of the PTFE fibers in the non-dust-attracting layer is 4D-6D. Using coarser PTFE short fibers in this layer will reduce the overall air permeability of the filter felt and result in high resistance during actual use. When the fineness is greater than 6D, the fibers are too coarse, increasing the porosity between fibers and failing to provide support for the dust-attracting layer, leading to low overall weft strength.

[0018] From the surface of the dust-attracting layer towards the base fabric, the porosity of the fibers in the top fifth to third thickness is 15-30%, the porosity of the remaining thickness is 40-60%, and the porosity of the non-dust-attracting layer is 50%-70%. The pores in the top fifth to third thickness are the smallest, gradually increasing in size to achieve surface filtration, increasing filtration efficiency while reducing resistance. When the portion with a porosity of 15-30% is larger than the top third, the resistance is high, failing to meet the low-resistance requirement of this design. When the porosity is less than 15%, the pores are too small, resulting in high initial pressure loss and resistance. When the thickness is less than one-fifth or the porosity is greater than 30%, the filtration effect will be poor. The remaining part of the dust-attracting layer uses 2D-4D PTFE fibers with a finer average fineness, while the non-dust-attracting layer uses 4D-6D PTFE fibers with a coarser average fineness. Under the same needle-punching process, the finer fibers are more densely packed, resulting in naturally lower porosity.

[0019] In addition, when the present invention is used in the field, in a long-term blowing environment, even after 20,000 blows at a blowing pressure of 5 kg, the porosity of the top one-fifth to one-third thickness of the fiber can still be maintained at over 95%.

[0020] From the surface of the dust-collecting layer towards the base fabric, the top one-fifth to one-third thickness of PTFE fibers is uniformly mixed with 10%-20% by mass of polyvinylidene fluoride (PVDF) fibers. The inclusion of a small amount of PVDF fibers reduces porosity and eliminates macropores. During heat setting and field use, when the temperature exceeds 180°C, the PVDF fibers begin to melt and shrink, bringing the top one-fifth to one-third thickness of PTFE fibers closer together and fixing the distance between them, thus reducing their porosity compared to the lower layers. Furthermore, because PVDF is a fluorinated resin, it remains stable at temperatures above 180°C after melt curing. It continues to stabilize the top layer in long-term blow-drying environments; however, excessive addition can decrease the overall heat resistance of the filter bag.

[0021] Setting the average fineness of polyvinylidene fluoride fiber to 2D-4D allows it to be mixed evenly with PTFE fiber. Only under the premise of uniform mixing can uniform shrinkage and fixation be achieved, enabling the filter felt to achieve excellent filtration performance and long-term stability.

[0022] The surface of the dust-attracting layer has 5-15 g / m 2The foaming agent is a mixture of foaming agent and aluminum stearate or foaming agent and potassium stearate, wherein the main component of the foaming agent is a fluorocarbon compound. The addition ratio of foaming agent to aluminum stearate is 5:1 to 10:1 by mass, and the addition ratio of foaming agent to potassium stearate is 8:1 to 12:1 by mass. The foaming agent can increase the microporosity, and aluminum stearate and potassium stearate can fix the foaming agent and PTFE fibers, with an adhesion amount greater than 15 g / m². 2 This can easily cause micropore blockage, leading to increased resistance; the adhesion amount is less than 15g / m 2 If the number of micropores is insufficient, the filtration performance will decrease. If the proportion of aluminum stearate and potassium stearate is too small, they will not play a fixing role; if the proportion is too high, the pore-forming effect of the foaming agent will be weakened, thus reducing the filtration performance.

[0023] The thickness of the PTFE filter material is 1.1~1.6mm, and the base fabric is made of PTFE with a basis weight of 100~200g / m². 2 The mass ratio of the dust-attracting layer to the non-dust-attracting layer is 4:6 to 6:4, which are all standard specifications.

[0024] The PTFE fibers used are 48-75mm in length, with 10-16 crimps per 25mm and a crimp degree of 8-12%. The average curvature of the PTFE fibers in the filter felt is 0.005-0.05 (1 / µm). Curvature refers to the degree of bending of the PTFE fibers in the filter felt; the higher the value, the more curved the fibers. When the average curvature is less than 0.005 (1 / µm), the fibers are too straight, and after continuous blowing, the pores are more likely to enlarge, resulting in a lower porosity retention rate, which is not conducive to long-term stable use. After a period of use, the filtration performance decreases. Conversely, when the average curvature is greater than 0.005 (1 / µm), the fibers are too curved and cannot be fully combed, leading to more knots in the combed web and a higher product outlet concentration.

[0025] The PTFE fibers here are short PTFE fibers for the dust-receiving layer. The number of curls and the degree of curl both affect the average curvature of the PTFE fibers in the filter felt. When the number of curls is 10-16 / 25mm and the degree of curl is 8-12%, the curvature is most likely to reach the required range of 0.005~0.05 (1 / µm).

[0026] The processing method also affects the curvature. Compared with simple needle punching or simple hydroentangling, it is easier to achieve the required range of 0.005~0.05 (1 / µm) by implementing the production steps of pre-needling, hydroentangling, and needle punch finishing.

[0027] Filter bags made from this uncoated PTFE filter material can be used in fields with high temperatures and harsh working environments, such as waste incineration, solid waste disposal, and industrial dust removal.

[0028] The performance structures described in this invention can all be verified through testing. The following are some examples of testing methods.

[0029] Porosity: The mass and thickness of the PTFE filter felt were measured using mass and density calculation methods to confirm the true density of the PTFE material (density without voids), and the porosity was calculated. An area of ​​1 cm² was taken. 2 The PTFE sample was cut and weighed using a blade, denoted as Mg. The sample thickness was measured using a TECLOCK thickness gauge (SM-114, measuring tube diameter 10mm), denoted as D cm. The actual density ρ of the PTFE material was then calculated (e.g., PE = 0.95 g / cm³). 3 PTFE = 2.20 g / cm³ 3 To calculate porosity, the formula for porosity is as follows: Porosity = (1-M / ρD) ×100%.

[0030] Weight: Based on the provisions of GB / T 4669-2008 "Determination of unit length mass and unit area mass of textile woven fabrics", the filter material is cut into 200×200 mm squares, and the weight of the filter material is calculated from the weight.

[0031] Weight = Filter cloth weight / (length × width), n = 5, and the average value is taken.

[0032] Filtration efficiency, outlet concentration, pressure drop, and circulation time: The performance of filter materials was determined based on the standard test method for evaluating cleanable filter media (VDI 3926). The experimental sample size was 150 mm in diameter. The feed dust concentration was 5.0 ± 0.5 g / m³. 3 The filtration velocity is 2 m / min (air volume 2.0 m³ / min). 3 The experimental sequence was: initial 30 cycles + forced aging 5000 cycles + final 30 cycles. The initial and final 30 cycles were performed as follows: as the operating time increased, the pressure difference across the filter material gradually increased. When the pressure difference reached 1000 Pa, pulsed air was used to clean the dust from the filter material surface, and then the next process was repeated 30 times. During the experiment, the experimental time (t / s) and pressure changes were recorded, and the weight M (g) of dust passing through the filter material was measured. The forced aging process involved cleaning the filter material at 5-second intervals during operation, with a cleaning pressure of 5 bar, for a total of 5000 cleaning cycles.

[0033] The final results of the tests were statistically analyzed based on the results of the last 30 rounds: The outlet dust concentration C = weight of dust passing through the filter material M / (2.0 × time t / 3600), and the unit of outlet dust concentration C is g / m³. 3 .

[0034] Filtration efficiency = (1 - outlet dust concentration C / 5) × 100%.

[0035] Pressure loss is the pressure loss automatically recorded by the equipment after the last injection in the last 30 cycles.

[0036] The loop time is the total time spent on the last 30 iterations.

[0037] The export concentration exceeds 0.30 mg / Nm³. 3 If the pressure drop exceeds 300Pa or the cycle time is less than 6000s, it is considered that the requirements are not met.

[0038] Durability (resistance to spraying): Following the forced aging process outlined in VDI 3926, "Standard Test Methods for Evaluating Cleanable Filter Media," 20,000 cycles of powder-free blowing were performed at a blowing pressure of 5 kg. The change in surface porosity was then tested. The durability evaluation method is as follows: ◎ indicates that after 20,000 cycles, the porosity retention rate is greater than or equal to 99%. △ indicates a porosity retention rate greater than or equal to 97%, △ indicates a porosity retention rate greater than or equal to 95% after injection, and ╳ indicates less than 95%.

[0039] Example 1: The top layer of the dust-facing surface: the ratio of PTFE fiber and polyvinylidene fluoride fiber is 85:15. The average fineness of the two fibers is 2.4D, the average length is 60mm, the average crimp is 10%, the average number of crimps is 12 / 25mm, and the average curvature is 0.02 (1 / micrometer).

[0040] The bottom layer of the dust-facing surface is a PTFE fiber layer, followed by a PTFE base fabric layer with a weight of 130 grams. Next is the non-dust-facing layer, which is made of PTFE fiber with an average fineness of 5D.

[0041] The top layer of PTFE and polyvinylidene fluoride fibers, after being uniformly mixed, undergoes pre-needling and hydroentangling steps after being carded. Hydroentangling can be performed directly if conditions permit. The lower layer, basic layer, and non-dust-facing layer of the dust-facing surface are made using ordinary carding and needle punching methods. These three layers are combined together using a needle punching machine, and then the hydroentangled top layer of the dust-facing surface is stacked on top and needle punched. The needles used are 42# or finer than 42#, with a needle density of 200-400 needles / cm². 2 PTFE needle-punched felt was produced.

[0042] The above-mentioned filter felt was surface-treated with an emulsion of foaming agent: aluminum stearate = 8:1 by spraying or scraping, followed by heat setting and drying. The heat setting and drying temperature was 260℃ for 4 minutes. After surface treatment and drying, the basis weight increased by 10g / m³. 2 The top layer of the filter material occupies one-third of the thickness of the dust-facing surface and has a porosity of 20%. The lower layer of the dust-facing surface has a porosity of 50%, and the non-dust-facing surface has a porosity of 65%. The final basis weight is 800 g / m³. 2 .

[0043] The filter material was tested for its filtration performance using a VDI filter material performance testing device according to the VDI 3926 test method. The VDI performance of the last 30 tests is shown in the Performance column of Example 1 in Table 1. The outlet concentration exceeded 0.30 mg / Nm³. 3 If the pressure drop exceeds 300 Pa or the cycle time is less than 6000 s, the requirements are considered not met. In Example 1, all three data points meet the requirements.

[0044] The durability of the filter material was tested by VDI. After 20,000 powderless blows at a blowing pressure of 5 kg, the change in surface porosity was tested, and the retention rate reached 99.4%, which was rated as ◎ (excellent).

[0045] Example 2: The remaining conditions are completely the same as in Example 1. The average fineness of the uppermost fiber is 2.0D. Since the fineness is reduced compared to Example 1, even if the method is completely the same, the porosity of the uppermost layer is changed from 20% in Example 1 to 17%.

[0046] The filter material was tested for its filtration performance using VDI. The VDI performance of the last 30 cycles is shown in the Performance column of Example 2 in Table 1. All three data points in Example 2 met the requirements. Compared with Example 1, the outlet concentration was lower, but the pressure drop was slightly higher and the cycle time was slightly lower.

[0047] The durability of the filter material was tested by VDI. After 20,000 powderless blows at a blowing pressure of 5 kg, the change in surface porosity was tested, and the retention rate reached 99.5%, which was rated as ◎ (excellent).

[0048] Example 3: The remaining conditions are exactly the same as in Example 1. The average fineness of the uppermost fiber is 4.0D. Since the fineness is increased compared to Example 1, even if the method is exactly the same, the porosity of the uppermost layer is changed from 20% in Example 1 to 27%.

[0049] The filter material was tested for its filtration performance using VDI. The VDI performance of the last 30 cycles is shown in the Performance column of Example 3 in Table 1. All three data points in Example 3 met the requirements. Compared with Example 1, the outlet concentration increased, the pressure drop decreased, and the circulation time was slightly longer.

[0050] The durability of the filter material was tested by VDI. After 20,000 powderless blows at a blowing pressure of 5 kg, the change in surface porosity was tested, and the retention rate reached 99.1%, which was rated as ◎ (excellent).

[0051] Example 4: All other conditions are exactly the same as in Example 1, with the thickness of the top layer being one-quarter of the dust-receiving layer.

[0052] The filter material was tested for its filtration performance using VDI. The VDI performance of the last 30 cycles is shown in the Performance column of Example 4 in Table 1. All three data points of Example 4 met the requirements. Compared with Example 1, the outlet concentration increased slightly, the pressure drop decreased, and the cycle time increased.

[0053] The durability of the filter material was tested by VDI. After 20,000 powderless blows at a blowing pressure of 5 kg, the change in surface porosity was tested, and the retention rate reached 99.0%, which was rated as ◎ (excellent).

[0054] Example 5: The remaining conditions are exactly the same as in Example 1, with the thickness of the top layer being one-fifth of that of the dust-receiving layer.

[0055] The filter material was tested for its filtration performance using VDI. The VDI performance of the last 30 cycles is shown in the Performance column of Example 5 in Table 2. All three data points of Example 5 met the requirements. Compared with Example 1, the outlet concentration increased significantly, the pressure drop decreased, and the circulation time was reduced.

[0056] The durability of the filter material was tested by VDI. Due to the thinness of the top layer, it could not fully maintain its original shape after 20,000 powderless blows at a blowing pressure of 5 kg. The change in surface porosity was tested, and the retention rate reached 96.5%, which was rated as △ (average).

[0057] Example 6: The remaining conditions are exactly the same as in Example 1, but the porosity of the uppermost layer is changed from 20% in Example 1 to 15% by strengthening the hydroentanglement method.

[0058] The filter material was tested for its filtration performance using VDI. The VDI performance of the last 30 cycles is shown in the Performance column of Example 6 in Table 2. All three data points for Example 6 met the requirements. Compared with Example 1, the outlet concentration decreased due to the smaller porosity, but the pressure drop increased and the circulation time decreased.

[0059] The durability of the filter material was tested using VDI. After 20,000 powderless blows at a blowing pressure of 5 kg, the change in surface porosity was tested, and the retention rate reached 99.7%, which was rated as ◎ (excellent).

[0060] Example 7: The remaining conditions are exactly the same as in Example 1, except that the porosity of the uppermost layer is changed from 20% in Example 1 to 30% by weakening the hydroentanglement method.

[0061] The filter material was tested for its filtration performance using VDI. The VDI performance of the last 30 cycles is shown in the Performance column of Example 7 in Table 2. All three data points in Example 7 met the requirements. Compared with Example 1, the outlet concentration increased due to the larger porosity. Moreover, the larger porosity allowed dust to penetrate into the filter material, resulting in no reduction in pressure loss and no increase in cycle time.

[0062] The manufactured filter material was tested for durability using VDI. After 20,000 powder-free blow cycles at a blowing pressure of 5 kg, the change in surface porosity was measured, and the retention rate reached 98.2%, which was rated as excellent. (good).

[0063] Example 8: The remaining conditions are exactly the same as in Example 1, except that the porosity of the remaining part of the dust-collecting layer is reduced to 40% by enhancing the needle punching method.

[0064] The filter material was tested for its filtration performance using VDI. The VDI performance of the last 30 cycles is shown in the Performance column of Example 8 in Table 2. All three data points in Example 8 met the requirements. Compared with Example 1, due to the reduced porosity of the remaining part of the dust-collecting layer, the outlet concentration remained unchanged due to the influence of the uppermost layer. Moreover, the reduced porosity of the lower layer led to poorer air permeability, resulting in increased pressure loss and reduced circulation time.

[0065] The durability of the filter material was tested by VDI. After 20,000 powderless blows at a blowing pressure of 5 kg, the change in surface porosity was tested, and the retention rate reached 99.5%, which was rated as ◎ (excellent).

[0066] Example 9: The remaining conditions are exactly the same as in Example 1, except that the porosity of the remaining part of the dust-collecting layer is increased to 60% by weakening the needle punching method.

[0067] The filter material was tested for its filtration performance using VDI. The VDI performance of the last 30 cycles is shown in the Performance column of Example 9 in Table 3. All three data points of Example 9 met the requirements. Compared with Example 1, due to the increased porosity of the remaining part of the dust-collecting layer, the outlet concentration remained unchanged due to the influence of the uppermost layer. Moreover, the increased porosity of the lower layer increased the air permeability, reduced the pressure drop, and slightly prolonged the circulation time.

[0068] The durability of the filter material was tested by VDI. After 20,000 powderless blows at a blowing pressure of 5 kg, the change in surface porosity was tested, and the retention rate reached 99.3%, which was rated as ◎ (excellent).

[0069] Example 10: The remaining conditions are exactly the same as in Example 1, except that the proportion of polyvinylidene fluoride fiber in the top layer is reduced to 10%, and the porosity of the top layer after processing is 27%.

[0070] The filter material was tested for its filtration performance using VDI. The VDI performance of the last 30 tests is shown in the Performance column of Example 10 in Table 3. All three data points of Example 10 met the requirements. Compared with Example 1, the porosity increased and the outlet concentration increased due to the reduced proportion of polyvinylidene fluoride fiber in the top layer, resulting in insufficient shrinkage during heat setting.

[0071] The manufactured filter material was tested for durability using VDI. After 20,000 powder-free blow cycles at a blowing pressure of 5 kg, the change in surface porosity was tested, and the retention rate reached 98.1%, which was rated as excellent. (Good), due to the lack of stretching and fixing of polyvinylidene fluoride fibers, the retention rate is lower than that of Example 1.

[0072] Example 11: The remaining conditions are exactly the same as in Example 1, except that the proportion of polyvinylidene fluoride fiber in the top layer is increased to 20%, and the porosity of the top layer after processing is 16%.

[0073] The filter material was tested for its filtration performance using VDI. The VDI performance of the last 30 cycles is shown in the Performance column of Example 11 in Table 3. All three data points of Example 11 met the requirements. Compared with Example 1, due to the increased proportion of polyvinylidene fluoride fiber in the top layer, the shrinkage during heat setting increased, the porosity was lower than that of Example 1, the outlet concentration increased, but the pressure drop also increased, and the circulation time decreased.

[0074] The durability of the filter material was tested by VDI. After 20,000 powderless blows at a blowing pressure of 5 kg, the change in surface porosity was tested, and the retention rate reached 99.6%, which was rated as ◎ (excellent).

[0075] Example 12: All other conditions are exactly the same as in Example 1, except that a foaming agent is used and aluminum stearate is not used.

[0076] The filter material was tested for its filtration performance using VDI. The VDI performance of the last 30 cycles is shown in the Performance column of Example 12 in Table 3. All three data points for Example 12 met the requirements. Compared with Example 1, the filter material's durability was slightly reduced by VDI testing due to the absence of aluminum stearate. After 20,000 cycles of powder-free blowing at a blowing pressure of 5 kg, the change in surface porosity was tested, and the retention rate reached 98.1%, which was evaluated as... (good).

[0077] Example 13: The remaining conditions are exactly the same as in Example 1, except that the surface treatment mixture is replaced with a foaming agent: potassium stearate, with an addition ratio of 8:1 (mass ratio).

[0078] The filter material was tested for its filtration performance using VDI. The VDI performance after the last 30 cycles is shown in the Performance column of Example 13 in Table 4. All three data points in Example 13 met the requirements. Regarding durability, after 20,000 cycles of powder-free blowing at a blowing pressure of 5 kg, the change in surface porosity was tested, and the retention rate was 98.5%, which was rated as [performance rating missing]. (good).

[0079] Example 14: The remaining conditions are exactly the same as in Example 1, except that the mixture used for surface treatment is replaced with a foaming agent: potassium stearate, with an addition ratio of 12:1 (mass ratio).

[0080] The filter material was tested for its filtration performance using VDI. The VDI performance of the last 30 cycles is shown in the Performance column of Example 14 in Table 4. All three data points in Example 14 met the requirements. Regarding durability, after 20,000 cycles of powder-free blowing at a blowing pressure of 5 kg, the change in surface porosity was tested, and the retention rate was 98.8%, which was rated as [performance rating missing]. (good).

[0081] Comparative Example 1: The top layer of the dust-facing surface: the ratio of PTFE fiber to polyvinylidene fluoride fiber is 85:15. The average fineness of the two fibers is 1.8D, the average length is 60mm, the average crimp is 10%, the average number of crimps is 12 / 25mm, and the average curvature is 0.02 (1 / micrometer).

[0082] The bottom layer of the dust-facing surface is a PTFE fiber layer, followed by a PTFE base fabric layer with a weight of 130 grams. Next is the non-dust-facing layer, which is made of PTFE fiber with an average fineness of 5D.

[0083] The top layer of PTFE and polyvinylidene fluoride fibers, after being uniformly mixed, undergoes pre-needling and hydroentangling steps after being carded. Hydroentangling can be performed directly if conditions permit. The lower layer, basic layer, and non-dust-facing layer of the dust-facing surface are made using ordinary carding and needle punching methods. These three layers are combined together using a needle punching machine, and then the top layer of the hydroentangled dust-facing surface is stacked on top and needle punched. The needles used are 42# or finer than 42#, with a needle density of 200-400 needles / cm². 2 PTFE needle-punched felt was produced.

[0084] The above-mentioned filter felt was surface-treated with an emulsion of foaming agent: aluminum stearate = 8:1 by spraying or scraping, followed by heat setting and drying. The heat setting and drying temperature was 260℃ for 4 minutes. After surface treatment and drying, the basis weight increased by 10g / m³. 2 Due to the excessively fine fibers, compared to Example 1, the top layer of the filter material occupies one-third of the thickness of the dust-facing surface, and its porosity is reduced to 14%. The porosity of the lower layer on the dust-facing surface is 50%, and the porosity of the non-dust-facing surface is 65%, resulting in a final basis weight of 800 g / m³. 2 .

[0085] The filter material was tested for its filtration performance using VDI. The VDI performance of the last 30 tests is shown in Table 5, Comparative Example 1, Performance Column. The outlet concentration exceeded 0.30 mg / Nm³. 3 If the pressure drop exceeds 300 Pa or the cycle time is less than 6000 s, it is considered that the requirements are not met. Comparative Example 1: Pressure drop does not meet the requirements.

[0086] The durability of the filter material was tested by VDI. After 20,000 powderless blows at a blowing pressure of 5 kg, the change in surface porosity was tested, and the retention rate reached 99.3%, which was rated as ◎ (excellent).

[0087] Comparative Example 2: All other conditions were exactly the same as in Example 1. The average fineness of the two fibers was 4.5D. Due to the excessively coarse fibers, the porosity of the upper layer increased to 33%.

[0088] The filter material was tested for its filtration performance using VDI. The performance of the last 30 VDI tests is shown in the performance column of Comparative Example 2 in Table 5. The outlet concentration exceeded 0.30 mg / Nm³. 3 If the pressure drop exceeds 300 Pa or the circulation time is less than 6000 s, it is considered that the requirements are not met. Comparative Example 2 shows that the outlet concentration does not meet the requirements.

[0089] The durability of the filter material was tested by VDI. After 20,000 powderless blows at a blowing pressure of 5 kg, the change in surface porosity was tested, and the retention rate reached 99.3%, which was rated as ◎ (excellent).

[0090] Comparative Example 3: All other conditions are exactly the same as in Example 1, except that the thickness of the top layer is half.

[0091] The filter material was tested for its filtration performance using VDI. The performance of the last 30 VDI tests is shown in the performance column of Comparative Example 3 in Table 5. The outlet concentration exceeded 0.30 mg / Nm³. 3 If the pressure drop exceeds 300 Pa or the cycle time is less than 6000 s, it is considered that the requirements are not met. Comparative Example 3 shows that the pressure drop does not meet the requirements.

[0092] The durability of the filter material was tested by VDI. After 20,000 powderless blows at a blowing pressure of 5 kg, the change in surface porosity was tested, and the retention rate reached 99.9%, which was rated as ◎ (excellent).

[0093] Comparative Example 4: All other conditions are exactly the same as in Example 1, except that the thickness of the top layer is one-sixth.

[0094] The filter material was tested for its filtration performance using VDI. The performance of the last 30 VDI tests is shown in the Performance column of Comparative Example 4 in Table 5. The outlet concentration exceeded 0.30 mg / Nm³. 3 If the pressure drop exceeds 300 Pa or the circulation time is less than 6000 s, it is considered that the requirements are not met. Comparative Example 4 shows that the outlet concentration does not meet the requirements.

[0095] The durability of the filter material was tested by VDI. After 20,000 powderless blows at a blowing pressure of 5 kg, the change in surface porosity was tested, and the retention rate reached 96.9%, which was rated as △ (average).

[0096] Table 1. VDI Performance of Filter Materials in Examples 1-4

[0097] Table 2 VDI Performance of Filter Materials in Examples 5-8

[0098] Table 3. VDI Performance of Filter Materials in Examples 9-12

[0099] Table 4. VDI Performance of Filter Materials in Examples 13-14

[0100] Table 5. VDI Performance of Filter Materials in Comparative Examples 1-4

[0101] The above embodiments of the present invention are merely examples to clearly illustrate the present invention, and are not intended to limit the scope of protection of the present invention. All equivalent technical solutions also fall within the scope of the present invention, and the patent protection scope of the present invention should be defined by the claims.

Claims

1. A polytetrafluoroethylene filter material, characterized in that: The polytetrafluoroethylene filter material has a basis weight of 650-950 g / m³. 2 The average fineness of the PTFE fibers in the dust-receiving layer is 2D-4D, and the average fineness of the PTFE fibers in the non-dust-receiving layer is 4D-6D. From the surface of the dust-receiving layer towards the base fabric, the porosity of the fibers in the top one-fifth to one-third thickness is 15-30%, the porosity of the remaining four-fifths to two-thirds thickness is 40-60%, and the porosity of the non-dust-receiving layer is 50%-70%. From the surface of the dust-receiving layer towards the base fabric, the top one-fifth to one-third thickness of PTFE fibers is uniformly mixed with 10%-20% by mass of polyvinylidene fluoride fibers, and the average fineness of the polyvinylidene fluoride fibers is 2D-4D.

2. The polytetrafluoroethylene filter material according to claim 1, characterized in that: The surface of the dust-attracting layer has 5-15 g / m 2 The foaming agent is a mixture of aluminum stearate or potassium stearate, wherein the main component of the foaming agent is a fluorocarbon compound.

3. The polytetrafluoroethylene filter material according to claim 2, characterized in that: The foaming agent and aluminum stearate are added in a mass ratio of 5:1 to 10:1, and the foaming agent and potassium stearate are added in a mass ratio of 8:1 to 12:

1.

4. The polytetrafluoroethylene filter material according to claim 1, characterized in that: The thickness of the polytetrafluoroethylene (PTFE) filter material is 1.1~1.6mm, and the base fabric is made of PTFE with a basis weight of 100~200g / m². 2 The mass ratio of the dust-attracting layer to the non-dust-attracting layer is 4:6 to 6:

4.

5. The polytetrafluoroethylene filter material according to claim 1, characterized in that: The polytetrafluoroethylene fibers used are 48-75mm in length, with 10-16 crimps per 25mm and a crimp degree of 8-12%.

6. The polytetrafluoroethylene filter material according to claim 1, characterized in that: The average curvature of polytetrafluoroethylene (PTFE) fibers in filter materials is 0.005–0.05 µm. -1 .

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