A thermoplastic fiber filter material

Abstract

The present invention discloses a thermoplastic fiber filter material, which relates to the field of filter material technology. The material comprises a filter layer, a non-filter layer, and an intermediate fabric reinforcement layer. The surface of the filter layer contains nodes formed by melting thermoplastic fibers. The average node area is less than or equal to 0.02 square millimeters, the CV% of the node area is less than or equal to 40%, and the number of nodes distributed within any 1 square millimeter area is 5 to 20. Compared with traditional filter materials, the present invention has better filtering performance, lower manufacturing costs, and longer service life. It can achieve low-cost and low-emission effects and is suitable for various fields such as industrial dust removal and air filtration, with a broad prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of filter materials, in particular to a thermoplastic fiber filter material. Background Art

[0002] Over the past decade, countries around the world have become increasingly determined to combat air pollution, with increasingly stringent emission requirements for industrial enterprises. Dust and particulate matter pollution is a significant component of air pollution, and dust emissions directly contribute to elevated PM2.5 levels, posing a serious threat to the health and safety of residents. Using dust removal equipment to remove dust from industrial emissions is an effective method of dust control. The quality of filter materials determines whether dust emissions meet environmental requirements and also impacts operating and material costs. With increasingly stringent environmental regulations and intensified price competition, achieving both low-cost and high-efficiency dust removal has become a fundamental requirement for filter material manufacturers.

[0003] Previous patents have also addressed surface-treated filter materials. For example, Chinese patent publication number CN103816717B discloses a high-temperature filter material that calenders and shapes filter needle fabric, singes the dust-facing surface of the calendered filter fabric to facilitate cleaning, and impregnates the treated filter fabric with polytetrafluoroethylene emulsion. The material exhibits excellent filtering performance, improves dust removal during cleaning, and prevents dust from penetrating the filter cloth, reducing filtration resistance. However, this improvement is achieved by implanting polyimide fibers into the filter material surface (dust-facing side) through a composite method to improve the filter material's filtration performance. While polyimide fibers have a special (leaf-shaped) cross-sectional structure, resulting in a large filtration surface area, this approach is extremely costly, and the effect of post-processing surface morphology on filtration performance is not discussed.

[0004] Chinese patent publication number CN105597425A discloses a process for processing washable filter materials, including singeing, calendering, and waterproofing steps. This invention, produced through a singeing-then-calendering process, allows for the removal of surface deposits, ensuring continued use. The material also exhibits excellent hydrolysis resistance and can be washed multiple times for reuse. The application does not specify the density, size, or uniformity of the nodes after singeing, merely requiring ease of scouring, which has limited impact on improving filtration performance. Summary of the Invention

[0005] The purpose of the present invention is to solve the above technical problems and provide a thermoplastic fiber filter material.

[0006] In order to achieve the above technical objectives and meet the above technical requirements, the technical solution adopted by the present invention is: a thermoplastic fiber filter material, including a filter layer, a non-filter layer, and an intermediate fabric reinforcement layer, the surface of the filter layer contains nodes produced by melting thermoplastic fibers, the average area of the nodes is less than or equal to 0.02 square millimeters, the CV% of the node area is less than or equal to 40%, and the number of nodes distributed in any 1 square millimeter area is 5 to 20.

[0007] Preferably: not less than 80% of the nodes are spherical or elliptical in shape, and the shapes of the other nodes are irregular, including but not limited to long strips and radial shapes. The fibers of the filter material are treated with a flame retardant, the flame retardant contains more than 50% ammonium polyphosphate, and the proportion of the flame retardant content in the filter material is 0.05-0.16wt%.

[0008] Preferably, the number of hairs with a surface height higher than 0.5 mm on the filter material is less than 4 per square centimeter.

[0009] Preferably, the fiber surfaces of the filter layer are attached with a coating, the coating is evenly applied to the surface of each fiber, and the fibers adhered to each other by the coating do not exceed 10% of the total number of fibers.

[0010] Preferably, the weight percentage of thermoplastic fibers in the filter layer is greater than or equal to 50%, the melting point of the thermoplastic fibers is 170°C to 300°C, the surface of the thermoplastic fibers contains 0.05 to 0.5 weight percent of an oil, of which the sizing agent accounts for 5% to 15% and the emulsifier accounts for 10 to 40%.

[0011] Preferably, the sizing agent is a mixture of higher fatty acid diethanolamine salt and alkyl alcohol phthalamide, and the proportion of one of them is not less than 25%, and the emulsifier is a non-ionic emulsifier.

[0012] Preferably, the filter material has a gram weight of 300-900 g / m 2 , the air permeability of the filter material is 8-15cm 3 / cm 2 / s.

[0013] Preferably, the filter material has a singeing step during the processing, the flame height is controlled at 3-8 cm, and the distance between the filter material and the burner is 60-90% of the flame height. A filter bag can be made from this filter material, which is used in asphalt, cement kilns, waste incineration, thermal power generation, steel and other fields.

[0014] Compared with traditional structures, the beneficial effects of the present invention are as follows: the present application provides a porous filter material, the pore structure of which is formed by cross-arranged fibers, and has the characteristics of uniform pore size distribution and a strong and durable surface fiber mesh cross structure. Under the premise of the same fiber diameter, the filter material prepared according to this case has better filtering performance and can be applied to multiple fields such as industrial dust removal and air filtration. Not only can it meet the demand for ultra-low emissions, compared with previous high-efficiency dust removal products, through a special surface singeing treatment different from traditional methods, it does not require PTFE membrane coating, and even ultrafine fibers can be used less or not at all. Its manufacturing cost is lower and its service life is longer, which can achieve the effect of low cost and low emissions. Its service life is also longer than that of general filter materials on the market, and it has a broader application prospect. DETAILED DESCRIPTION

[0015] The present invention will be further described below.

[0016] A thermoplastic fiber filter material comprises a filter layer, a non-filter layer, and an intermediate fabric reinforcement layer. The surface of the filter layer contains nodes formed by melting the thermoplastic fibers. These nodes are created by singeing. The average node area is less than or equal to 0.02 square millimeters, the CV% value of the node area is less than or equal to 40%, and the number of nodes distributed within any 1 square millimeter area is 5 to 20. The uniform distribution of the melted nodes on the filter material surface effectively reduces the size of large pores on the filter material surface and provides excellent resistance to long-term spraying, preventing the pores from deforming or enlarging after spraying. The above description of the area and distribution of nodes is to express the characteristics that nodes need to be small and evenly distributed. When the average node area is greater than 0.02 square millimeters and the node CV% is greater than 40%, it means that there are too large fused nodes, which will block gas circulation and affect the overall air permeability of the filter material, resulting in low air permeability, high pressure loss in actual use, and failure to meet low pressure requirements; the number of fused nodes distributed in any 1 square millimeter area is to illustrate the distribution uniformity. When the number of fused nodes in a certain 1 square millimeter area is less than 5, and the number in another area is more than 20, it means that the node distribution is very uneven. After long-term spraying of the filter material during filtration, the holes in areas with fewer nodes become larger, resulting in powder permeability. Areas with more fused nodes have poor air permeability, uneven filtration effect, poor pressure loss, and failure to meet filtration requirements.

[0017] This thermoplastic fiber filter material has no fewer than 80% of its nodes in a spherical or elliptical shape, while the remaining nodes are irregular shapes, such as elongated strips and radials. The fibers of the filter material are treated with a flame retardant containing at least 50% ammonium polyphosphate, with the flame retardant content ranging from 0.05 to 0.16% by weight of the filter material. The addition of the flame retardant helps form uniform, small-area fusion nodes. When the flame retardant content is less than 0.05% by weight, the effect is less pronounced, resulting in larger and uneven fusion nodes. When the flame retardant content exceeds 0.16% by weight, the number of fusion nodes formed is too small. The flame retardant can be applied to the filter material via surface treatment or mixed with thermoplastic particles during the melt spinning stage. The flame retardant addition ratio is closely related to the flame retardant properties of the thermoplastic fiber itself. When using non-flame-retardant thermoplastic fibers such as polyester and nylon, a flame retardant content of 0.05-0.16wt% is optimal; when using flame-retardant fibers such as PPS, a flame retardant content of 0.05-0.10wt% is optimal. Compared to other flame retardants, ammonium polyphosphate is more effective at organizing thermoplastic fiber droplets, thereby maintaining small and uniform melt nodes in the filter material after singeing.

[0018] After uniform singeing, the number of hairs taller than 0.5 mm on the filter felt surface should ideally be less than 4 per square centimeter. The fibers in the filter layer are coated evenly, with no more than 10% of the fibers adhering to each other. PTFE emulsion is preferably used for impregnation or spraying to optimize surface dust removal. However, the ratio must be controlled; excessive amounts can cause fibers to stick together, resulting in reduced filtration performance.

[0019] The filter layer of this filter material comprises thermoplastic fibers comprising greater than or equal to 50% by weight. The thermoplastic fibers have a melting point of 170°C to 300°C. The surface of the thermoplastic fibers contains 0.05% to 0.5% by weight of an oil, of which 5% to 15% is a sizing agent, and 10% to 40% is an emulsifier. The sizing agent is a mixture of higher fatty acid diethanolamine salts and alkyl alcohol phthalamides, with one of the two agents comprising at least 25%. The emulsifier is a nonionic emulsifier. Both the sizing agent and the emulsifier optimize the CV% and distribution of the melting node area. The melting node distribution is preferably such that the number of melting nodes per square millimeter is 7 to 14. Adding the sizing agent in this ratio helps reduce the CV% of the node area and achieves more uniform node size. Adding the emulsifier in this ratio facilitates achieving the optimal range for node distribution. Higher fatty acid diethanolamine salts and alkyl alcohol phthalamides are the most effective sizing agents, while nonionic emulsifiers are also the most effective.

[0020] The weight of the filter material is 300-900g / m 2, the air permeability of the filter material is 8-15cm 3 / cm 2 / s.

[0021] During the processing of the filter material, a singeing step is performed. The flame height is controlled at 3-8 cm, more preferably 4-6 cm. The distance between the filter material and the burner is 60-90% of the flame height. In other words, when the flame height is 5 cm from the burner, the distance between the surface of the filter material and the burner is 3.0-4.5 cm. The flame height and the distance from the burner to the filter material also affect the size and uniformity of the fusion node distribution. The above range can better control the node distribution on the surface of the filter material. A filter bag can be made from this filter material, which is used in asphalt, cement kilns, waste incineration, thermal power generation, steel and other fields.

[0022] This case has low manufacturing cost and longer service life. After more than 3 years of long-term use, the filtration performance can still be maintained at more than 95% of the new product, which can achieve the effect of low cost and low emission. The service life is also longer than that of general filter materials on the market.

[0023] The present invention is described in more detail by the following examples and comparative examples. The physical properties of the examples are tested by the following methods, and may also be tested by other methods.

[0024] [Size and distribution of fusion nodes]

[0025] The surface of the sample was photographed using a scanning electron microscope, and 10 points were extracted from the surface of the filter material for sample preparation and testing. The test magnification of each point was 200 times. The number of nodes in each sample was counted, the size of each node was measured, and the average area of the node, the CV% of the node area, and the number of nodes distributed in any 1 square millimeter area were calculated.

[0026]

Average pore size

[0027] Cut the filter material into a circular shape with a diameter of 1.5 cm. After soaking it in a surfactant, place the sample with the filter surface (singeing surface) facing upward into the test slot of the capillary flow porosity tester. After tightening the slot, perform the test. The test results are directly converted into the distribution of the proportion (%) of each pore size (µm) of the filter material to the entire material (including the average pore size, maximum pore size µm, minimum pore size µm, etc.). The final result is the average of these 5 measurements.

[0028] The average pore size of the filter material is obtained by the following formula:

[0029] ,

[0030] Where, d: fiber diameter (denier),

[0031] ρW: Density of filter material (g / cm 3 ),

[0032] ρp: Fiber density (g / cm 3 ).

[0033]

Weight

[0034] The filter material was cut into 10 cm × 10 cm square blocks, and the grammage per unit area of the filter material was calculated from the weight. The average measurement was performed 5 times, and the final result was the average of the 5 times.

[0035] [VDI collection efficiency, outlet concentration, pressure loss, and cycle time]

[0036] The performance of the filter material was determined based on the VDI3926 "Standard Test Method for Evaluating Cleanable Filter Media". The size of the test sample was 15 cm in diameter. The dust concentration fed was 5.0 ± 5 g / m 3 , the filtration wind speed is 2m / min (air volume 1.85m 3 / h). The experimental sequence was an initial 30 cycles, followed by 10,000 forced aging pulse jets, and a final 30 cycles. The initial and final 30 cycles were performed as follows: as the operating time increased, the pressure differential across the filter material gradually increased. When the pressure differential reached 1000 Pa, pulse air was used to clean dust from the filter material surface, and then the next cycle was repeated 30 times. During the experiment, the experimental time (t / s) and pressure changes were recorded, and the weight (M) of dust passing through the filter material was measured. The forced aging pulse jet process involved removing dust from the filter material at 5-second intervals during operation, at a cleaning pressure of 5 bar, for 10,000 cycles.

[0037] The outlet dust concentration C = the weight of dust passing through the filter material M / (1.85×time t / 3600). The unit of outlet dust concentration C is mg / Nm 3 , outlet concentration is less than or equal to 0.40mg / Nm 3 The outlet concentration is less than or equal to 0.25 mg / Nm 3 Excellent judgment.

[0038] The pressure loss is the pressure loss automatically recorded by the equipment after the last injection of the last 30 times. A pressure loss of 350 Pa or less meets the requirements of this case, and a pressure loss of 300 Pa or less is considered excellent.

[0039] The cycle time is the total time spent on the last 30 cycles.

[0040] Durability (blow-off resistance)

[0041] The evaluation method for durability (blow-resistant) is as follows: 5 bar pressure, powder-free blowing, the blowing direction is from the non-dust-facing surface to the dust-facing surface, with an interval of 5 seconds. The best ★★ indicates that the average pore size retention rate is above 98% after 50,000 sprays, excellent ★ indicates that the average pore size retention rate is above 95% after 50,000 sprays, qualified ▲ indicates that the average pore size retention rate is above 95% after 30,000 sprays, and unqualified × indicates that the average pore size retention rate is below 95% after 30,000 sprays.

[0042] Calculation method of porosity retention rate:

[0043] .

[0044] Example 1: A polyester filter felt made of 2.0D polyester fiber has a three-layer structure consisting of a dust-facing surface layer, an intermediate base fabric reinforcement layer, and a non-dust-facing layer. The dust-facing surface fibers contain 0.3% oil, of which 8% is a sizing agent and 25% is an emulsifier. The sizing agent is a 50:50 mixture of a higher fatty acid diethanolamine salt and an alkyl alcohol phthalamide. The emulsifier is a nonionic emulsifier. The dust-facing surface is also impregnated with a flame retardant at a weight ratio of 0.14%, with ammonium polyphosphate comprising 75% of the flame retardant.

[0045] The filter felt was used to singe the dust-facing surface. The flame height was adjusted to 6 cm, the distance between the dust-facing surface and the burner was adjusted to 4.5 cm, and the singeing speed was 18 m / min. The obtained filter felt was tested for the melting point under a microscope. The average area was found to be 0.005 mm. 2 , the CV% of the node area is 18%, 1mm 2 The average number of nodes within the area is 13.

[0046] The singed filter felt was subjected to VDI test and VDI durability test, and the VDI outlet concentration in the last 30 times was 0.22 mg / Nm 3 In the VDI durability test, after 50,000 sprays, the average pore size retention rate was 99%, with almost no decrease.

[0047] Example 2: A polyester filter felt made of 2.0D polyester fiber has a three-layer structure consisting of a dust-facing surface layer, an intermediate base fabric reinforcement layer, and a non-dust-facing layer. The dust-facing surface fibers contain 0.3% oil, of which 8% is a sizing agent and 25% is an emulsifier. The sizing agent is a 50:50 mixture of a higher fatty acid diethanolamine salt and an alkyl alcohol phthalamide, and the emulsifier is a nonionic emulsifier. The dust-facing surface is also impregnated with a flame retardant at a weight ratio of 0.10%, with ammonium polyphosphate comprising 60%. For singeing method, knot state, and VDI performance, refer to Example 2 in Table 1.

[0048] Example 3: A polyester filter felt made of 2.0D polyester fiber has a three-layer structure consisting of a dust-facing surface layer, an intermediate base fabric reinforcement layer, and a non-dust-facing layer. The dust-facing layer fibers contain 0.2% oil, of which 5% is a sizing agent and 25% is an emulsifier. The sizing agent is a 50:50 mixture of a higher fatty acid diethanolamine salt and an alkyl alcohol phthalamide, and the emulsifier is a nonionic emulsifier. The dust-facing surface layer is also impregnated with a flame retardant at a weight ratio of 0.14%, with ammonium polyphosphate comprising 75% of the flame retardant. For singeing method, knot state, and VDI performance, refer to Example 3 in Table 1.

[0049] Examples 4 and 5: The emulsifier content in the oil was varied; in Example 4, the emulsifier content was 15%, and in Example 5, the emulsifier content was 35%. Other conditions were the same as in Example 1. This demonstrates the effect of varying emulsifier content on the number of melt nodes per unit area: less emulsifier content results in fewer nodes, while more emulsifier content results in more nodes. The singeing method was the same as in Example 1. For the node state and VDI performance, refer to Table 1 for Examples 4 and 5.

[0050] Examples 6 and 7: Other conditions were the same as in Example 1. In Example 6, the flame height was adjusted to 8 cm during singeing, the distance between the dust-facing surface of the filter felt and the burner was adjusted to 6 cm, and the singeing speed was 18 m / min. In Example 7, the flame height was adjusted to 3 cm, the distance between the dust-facing surface of the filter felt and the burner was adjusted to 2.3 cm, and the singeing speed was 18 m / min. The effect of singeing conditions on the average node area was verified: higher flame heights resulted in larger node areas, while lower flame heights resulted in smaller nodes. For node status and VDI performance, refer to Table 1 for Example 6 and Table 2 for Example 7.

[0051] Example 8 and Example 9: Other conditions were the same as in Example 1. In Example 8, the flame height was adjusted to 6 cm during singeing, the distance between the dust-facing surface of the filter felt and the burner was adjusted to 5.4 cm, and the singeing speed was 18 m / min. In Example 9, the flame height was adjusted to 6 cm during singeing, the distance between the dust-facing surface of the filter felt and the burner was adjusted to 3.6 cm, and the singeing speed was 18 m / min. The effect of singeing conditions on the number of nodes per unit area was verified: a larger distance between the dust-facing surface and the burner resulted in a greater number of nodes per unit area. For the node status and VDI performance, refer to Examples 8 and 9 in Table 2.

[0052] Example 10: Other conditions were the same as in Example 1. The dust-facing side of the filter felt in Example 10 consisted of 60% polyester fiber, with the remainder made of thermosetting acrylic fiber. Because acrylic doesn't melt, the number of nodes per unit area is reduced. For node structure and VDI performance, refer to Table 2 for Example 10.

[0053] Example 11: A PPS filter felt made from 2.0DPPS fibers has a three-layer structure consisting of a dust-facing surface layer, an intermediate base fabric reinforcement layer, and a non-dust-facing layer. The dust-facing surface fibers contain 0.3% oil, of which 8% is a sizing agent and 25% is an emulsifier. The sizing agent is a 50:50 mixture of a higher fatty acid diethanolamine salt and alkyl alcohol phthalamide, and the emulsifier is a nonionic emulsifier. The dust-facing surface is also impregnated with a flame retardant at a weight ratio of 0.07%, with ammonium polyphosphate comprising 60%. Because flame-retardant PPS fibers are used, the effects of Example 1 can be achieved even with a reduced amount of flame retardant compared to Example 1. For singeing method, node state, and VDI performance, refer to Example 11 in Table 2.

[0054] Example 12: Other conditions were the same as in Example 10. The polyester fiber used on the dust-facing side of Example 12 had a fineness of 1.0D. Due to the VDI performance improvement caused by singeing, the VDI performance of Example 12 did not increase significantly compared to Example 10. For details on the node state and VDI performance, refer to Table 2 for Example 12.

[0055] Example 13: A polyester filter felt made of 2.0D polyester fiber has a three-layer structure consisting of a dust-facing surface layer, an intermediate base fabric reinforcement layer, and a non-dust-facing layer. The dust-facing surface layer fibers contain 0.3% oil, of which 8% is a sizing agent and 25% is an emulsifier. The sizing agent is a 50:50 mixture of a higher fatty acid diethanolamine salt and an alkyl alcohol phthalamide. The emulsifier is a nonionic emulsifier. The dust-facing surface layer is also impregnated with a flame retardant at a weight ratio of 0.14% and 35% ammonium polyphosphate. For singeing method, knot state, and VDI performance, refer to Example 13 in Table 3.

[0056] Example 14: A polyester filter felt made of 2.0D polyester fiber has a three-layer structure consisting of a dust-facing surface layer, an intermediate base fabric reinforcement layer, and a non-dust-facing layer. The dust-facing surface fiber is oil-free. A flame retardant is added during the spinning process, with a gram-to-weight ratio of 0.14% and ammonium polyphosphate comprising 75% of the flame retardant. For singeing method, knot state, and VDI performance, refer to Example 14 in Table 3.

[0057] Example 15: A PPS filter felt made from 2.0 DPPS fibers has a three-layer structure consisting of a dust-facing surface layer, an intermediate base fabric reinforcement layer, and a non-dust-facing layer. The dust-facing surface fibers contain 0.3% oil, of which 8% is a sizing agent and 25% is an emulsifier. The sizing agent is a 50:50 mixture of a higher fatty acid diethanolamine salt and alkyl alcohol phthalamide, and the emulsifier is a nonionic emulsifier. The dust-facing surface is also impregnated with a flame retardant at a weight ratio of 0.02%, with ammonium polyphosphate comprising 25% of the flame retardant. For singeing method, node state, and VDI performance, refer to Example 15 in Table 3.

[0058] Comparative Example 1: A polyester filter felt made of 2.0D polyester fiber has a three-layer structure consisting of a dust-facing surface layer, an intermediate base fabric reinforcement layer, and a non-dust-facing layer. The dust-facing surface fiber contains 0.3% oil, of which 8% is a sizing agent and 25% is an emulsifier. The sizing agent is a 50:50 mixture of higher fatty acid diethanolamine salt and alkyl alcohol phthalamide, and the emulsifier is a non-ionic emulsifier. The dust-facing surface is also impregnated with a flame retardant, with a weight ratio of 0.14%, of which ammonium polyphosphate accounts for 75%.

[0059] Different from Example 1, Comparative Example 1 was not singed and had no nodes.

[0060] The filter felt was subjected to VDI test and VDI durability test, and the outlet concentration of VDI in the last 30 times was 0.51 mg / Nm 3 In the VDI durability test, after 30,000 sprays, the average pore size retention rate was 89%.

[0061] Comparative Example 2: PPS filter felt made of 2.0DPPS fiber, without oil agent and flame retardant, without singeing, the tested VDI performance and durability are similar to those of Comparative Example 1, see Table 4 Comparative Example 2 for details.

[0062] Comparative Example 3: A polyester filter felt made of 2.0D polyester fiber has a three-layer structure consisting of a dust-facing surface layer, an intermediate base fabric reinforcement layer, and a non-dust-facing layer. The dust-facing surface fibers contain 0.3% oil, of which 8% is a sizing agent and 25% is an emulsifier. The sizing agent is a 50:50 mixture of higher fatty acid diethanolamine salt and alkyl alcohol phthalamide, and the emulsifier is a non-ionic emulsifier. The dust-facing surface layer is also impregnated with a flame retardant at a weight ratio of 0.14% and 75% ammonium polyphosphate. During singeing, the flame height was adjusted to 10 cm, the distance between the dust-facing surface layer and the burner was adjusted to 10 cm, and the singeing speed was 18 m / min. The resulting filter felt surface node area is excessively large. For node status and VDI performance, refer to Comparative Example 3 in Table 4.

[0063] Comparative Example 4: The polyester filter felt made of 2.0D polyester fiber is divided into a three-layer structure of a dust-facing surface layer, an intermediate base fabric reinforcement layer, and a non-dust-facing layer. The dust-facing surface layer fiber contains 0.2% oil agent, and the oil agent does not contain a sizing agent. The emulsifier accounts for 25%, and the emulsifier is a non-ionic emulsifier. The dust-facing surface layer is also impregnated with a flame retardant, with a gram-to-weight ratio of 0.14%, and the proportion of ammonium polyphosphate in the flame retardant is 75%. When singeing, the flame height is adjusted to 6 cm, the distance between the dust-facing surface layer of the filter felt and the burner is adjusted to 6 cm, and the singeing speed is 18 m / min. It can be seen that the CV% of the node area on the surface of the obtained filter felt is too large. For the node state and VDI performance, please refer to Comparative Example 4 in Table 4.

[0064] Comparative Example 5: A polyester filter felt made of 2.0D polyester fiber has a three-layer structure consisting of a dust-facing surface layer, an intermediate base fabric reinforcement layer, and a non-dust-facing layer. The dust-facing layer fibers contain 0.3% oil, of which a sizing agent accounts for 8%. The sizing agent is a 50:50 mixture of higher fatty acid diethanolamine salt and alkyl alcohol phthalamide, with no emulsifier. The dust-facing surface layer is also impregnated with a flame retardant at a weight ratio of 0.14%, with ammonium polyphosphate accounting for 75%. During singeing, the flame height was adjusted to 3 cm, the distance between the dust-facing surface layer and the burner was adjusted to 2 cm, and the singeing speed was 18 m / min. The resulting filter felt has a very low number of nodes per unit area. For node status and VDI performance, refer to Comparative Example 5 in Table 4.

[0065] Comparative Example 6: A polyester filter felt made of 2.0D polyester fiber has a three-layer structure consisting of a dust-facing surface layer, an intermediate base fabric reinforcement layer, and a non-dust-facing layer. The dust-facing layer fibers contain 0.3% oil, of which 8% is a sizing agent and 60% is an emulsifier. The sizing agent is a 50:50 mixture of higher fatty acid diethanolamine salt and alkyl alcohol phthalamide, and the emulsifier is a cationic emulsifier. The dust-facing surface layer is also impregnated with a flame retardant at a weight ratio of 0.14% and 75% ammonium polyphosphate. During singeing, the flame height was adjusted to 10 cm, the distance between the dust-facing surface layer and the burner was adjusted to 5.5 cm, and the singeing speed was 18 m / min. The resulting filter felt exhibits an excessive number of nodes per unit area. For node status and VDI performance, refer to Comparative Example 6 in Table 4.

[0066]

[0067]

[0068]

[0069]

[0070] The above embodiments of the present invention are merely examples to clearly illustrate the present invention, but 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. The scope of patent protection of the present invention should be defined by the claims.

Claims

1. A thermoplastic fiber filter material comprising a filter layer, a non-filter layer, and an intermediate fabric reinforcement layer, characterized in that: The surface of the filter layer contains nodes generated by melting thermoplastic fibers. The average area of the nodes is less than or equal to 0.02 square millimeters, the CV% of the node area is less than or equal to 40%, and the number of nodes distributed in any 1 square millimeter area is 5 to 20. The gram weight of the filter material is 300-900g / m 2 , the air permeability of the filter material is 8-15cm 3 / cm 2 / s, and the fiber fineness of the filter material is 1.0D-2.0D.

2. The thermoplastic fiber filter material according to claim 1, characterized in that: No less than 80% of the nodes are spherical or elliptical in shape, and the shapes of the other nodes are irregular, including but not limited to long strips and radial shapes. The fibers of the filter material are treated with a flame retardant, the flame retardant contains more than 50% ammonium polyphosphate, and the proportion of the flame retardant content in the filter material is 0.05-0.16wt%.

3. The thermoplastic fiber filter material according to claim 1, characterized in that: The number of hairs on the surface of the filter material with a height higher than 0.5 mm is less than 4 per square centimeter.

4. The thermoplastic fiber filter material according to claim 1, characterized in that: The fiber surface of the filter layer is attached with a coating, which is evenly applied on the surface of a single fiber. The fibers adhered to each other by the coating do not exceed 10% of the total number of fibers. The coating is PTFE emulsion.

5. The thermoplastic fiber filter material according to claim 1, characterized in that: The weight percentage of the thermoplastic fiber in the filter layer is greater than or equal to 50%, the melting point of the thermoplastic fiber is 170℃~300℃, the surface of the thermoplastic fiber contains 0.05~0.5 weight percentage of oil, in which the sizing agent accounts for 5%-15% and the emulsifier accounts for 10-40%.

6. The thermoplastic fiber filter material according to claim 5, characterized in that: The sizing agent is a mixture of higher fatty acid diethanolamine salt and alkyl alcohol phthalamide, and the proportion of one of them is not less than 25%. The emulsifier is a non-ionic emulsifier.

7. The thermoplastic fiber filter material according to claim 1, characterized in that: During the processing of the filter material, a singeing step is performed, the flame height is controlled at 3-8 cm, and the distance between the filter material and the burner is 60-90% of the flame height. A filter bag can be made from the filter material.

Images