Hard cloth needled felt filter material for industrial filtration and its processing method

Abstract

This invention discloses a rigid needle-punched felt filter media for industrial filtration and its processing method. The method includes: sequentially layering surface-activated dust-facing fiber material, a base fabric, and dust-backing fiber material; performing a progressive needle-punching process involving pre-needling, main needle-punching, and finishing needle-punching to form a three-dimensional interlocking asymmetric substrate with a dense dust-facing surface and a loose dust-backing surface; then performing heat setting and calendering to obtain the rigid fabric substrate; finally, attaching a PTFE membrane under longitudinal tension using medium-pressure hot-melt bonding. This invention achieves an asymmetric structure in the substrate through progressive needle-punching, combined with a high-temperature longitudinal tension medium-pressure membrane coating process, significantly improving air permeability, reducing operating resistance, and extending the cleaning cycle while ensuring filtration accuracy.

Description

Technical Field

[0001] This invention relates to the field of industrial filtration, and more particularly to a rigid needle-punched felt filter media for industrial filtration and its processing method. Background Technology

[0002] Industrial filter membrane media are typically prepared by hot-melt bonding a polytetrafluoroethylene (PTFE) membrane to the dust-facing side of a needle-punched felt substrate. Dust-laden airflow passes through the PTFE membrane surface and is then discharged as clean gas from the substrate.

[0003] Existing membrane filter media substrates mostly use symmetrical needle-punched felt with identical structures on both the dust-facing and dust-repelling sides, making it difficult to balance filtration accuracy and operating resistance: if the pores on the dust-facing side are too small, the resistance increases; if the pores are too large, the filtration accuracy is insufficient. Furthermore, traditional high-temperature, high-pressure coating processes easily cause the micropores of the PTFE membrane to collapse, resulting in a filter media permeability generally below 45 L / dm²·min, presenting technical challenges such as low flux, high operating resistance, and short cleaning cycles. In addition, conventional needle-punched felt lacks stiffness and is prone to pleat collapse after folding, affecting the structural stability of the filter unit. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the defects of the existing technology. The present invention proposes a rigid needle-punched felt filter material for industrial filtration and its processing method.

[0005] The "hard cloth" mentioned in this invention refers to needle-punched felt filter material with high stiffness and structural stability after heat setting and calendering hardening treatment. It can maintain the pleated shape for a long time after being folded and formed, and will not deform or collapse under pulse cleaning impact.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: In a first aspect, the present invention provides a method for processing rigid needle-punched felt filter media for industrial filtration, comprising: Step 1, Web Laying: The dust-facing fiber material, the base fabric, and the dust-backing fiber material are laid in sequence with the dust-facing fiber material on top, the base fabric in the middle, and the dust-backing fiber material at the bottom to obtain a three-layer composite fiber web structure; wherein, the dust-facing fiber material is polyphenylene sulfide fiber, aramid fiber, or polyester fiber that has undergone surface activation treatment, and the dust-backing fiber material is polyphenylene sulfide fiber; Step 2, progressive needle punching: The three-layer composite fiber web structure is sequentially subjected to pre-needling, main needle punching, and finishing needle punching, so that the fibers of the dust-facing fiber material and the dust-removing fiber material pass through the base fabric and interlock with each other, forming a three-dimensional interlocking asymmetric substrate with a dense dust-facing surface and a fluffy dust-removing surface; wherein, the needle punching density of the pre-needling, the main needle punching, and the finishing needle punching increases sequentially, the needle punching depth decreases sequentially, and the needle punching depth of the pre-needling is greater than the total thickness of the three-layer composite fiber web structure; Step 3, hardening and shaping: The three-dimensional interlocking asymmetric substrate is subjected to heat setting and calendering treatment in sequence to obtain a hardened filter material substrate; Step 4, High-temperature longitudinal stretching and medium-pressure coating: After preheating the dust-facing surface of the hardened filter material substrate, the polytetrafluoroethylene membrane is applied to the dust-facing surface of the hardened filter material substrate under longitudinal stretching along the running direction of the hardened filter material substrate with medium-pressure coating heat fusion. After cooling, the industrial filtration hard cloth needle-punched felt filter material is obtained. The progressive needle punching process makes the areal density of the dust-facing fiber material greater than that of the dust-repelling fiber material, and the fiber density of the dust-facing surface is higher than that of the dust-repelling surface, forming an asymmetric structure with a dense dust-facing surface and a fluffy dust-repelling surface.

[0007] Preferably, in step 1, the areal density of the dust-facing fiber material is 80-100 g / m², the areal density of the base fabric is 80-100 g / m², and the areal density of the dust-repelling fiber material is 120-150 g / m².

[0008] Preferably, in step 2, the pre-needling density is 60-80 needles / cm² and the needle depth is 8-10mm; the main needleling density is 150-200 needles / cm² and the needle depth is 6-8mm; and the finishing needleling density is 250-300 needles / cm² and the needle depth is 3-5mm.

[0009] Preferably, in step 3, the heat setting temperature is 190–200°C and the time is 60–90 s; the roll temperature for the calendering process is 180–190°C and the roll linear pressure is 40–60 N / mm.

[0010] Preferably, in step 4, the preheating temperature is 120-140°C, the longitudinal stretching rate is 5%-12% relative to the original length of the polytetrafluoroethylene film, the hot melt bonding pressure is 0.3-0.5 MPa, and the bonding temperature is 200-220°C.

[0011] Preferably, the preparation method of the dust-receiving fiber material is as follows: according to the bath ratio of fiber to silane coupling agent aqueous solution of 1:15, polyphenylene sulfide fiber, aramid fiber or polyester fiber is added to a 3% (w / w) silane coupling agent aqueous solution, immersed at 40°C for 30 min, taken out and dried at 110°C to constant weight, and then opened and combed to obtain the dust-receiving fiber material; wherein, the fineness of the polyphenylene sulfide fiber, the aramid fiber or the polyester fiber is 1.5 to 2.0 denier and the length is 51 to 64 mm.

[0012] Preferably, the polytetrafluoroethylene membrane is a biaxially stretched microporous membrane, wherein the average pore size of the polytetrafluoroethylene membrane is 0.2 to 0.8 μm, the areal density is 3 to 7 g / m², and the thickness is 15 to 35 μm.

[0013] Preferably, the base fabric is prepared by weaving polyester filaments into a plain weave fabric with a warp density of 10-12 threads / cm and a weft density of 8-10 threads / cm, thereby obtaining the base fabric, which does not require surface activation treatment.

[0014] Preferably, the preparation method of the dust-backing fiber material is as follows: the polyphenylene sulfide fiber is opened and combed to obtain the dust-backing fiber material, and the dust-backing fiber material does not require surface activation treatment; wherein, the fineness of the polyphenylene sulfide fiber is 2.5 to 3.0 denier and the length is 51 to 64 mm.

[0015] Preferably, the stiffness of the hardened filter material substrate is increased by more than 30% compared with that before hardening and shaping, and the stiffness is determined according to the cantilever method specified in GB / T18318.1-2009.

[0016] Secondly, the present invention provides a rigid needle-punched felt filter media for industrial filtration, which is prepared by the processing method of the aforementioned rigid needle-punched felt filter media for industrial filtration.

[0017] Compared with the prior art, the beneficial effects of the present invention include: First, through a progressive needle punching process in which the needle density increases sequentially and the needle depth decreases sequentially in the stages of pre-needling, main needle punching, and finishing needle punching, a three-dimensional interlocking asymmetric substrate with a dense dust-facing surface and a fluffy dust-repelling surface is formed. This reduces airflow resistance while ensuring filtration accuracy, and solves the defects of traditional substrates with symmetrical structures and difficulty in differentiating the dust-facing and dust-repelling surfaces.

[0018] Secondly, the "hard cloth" characteristics are obtained through heat setting and calendering, which gives the filter material high stiffness and dimensional stability, providing a high-quality base material for subsequent high-precision pleating and setting, and ensuring that the pleats do not deform or collapse under long-term pulse cleaning impact.

[0019] Third, by applying medium pressure to the membrane under longitudinal tension, the interfacial effect between the PTFE membrane and the hard cloth substrate is eliminated, micropore crushing is avoided, and the air permeability of the filter material breaks through the industry bottleneck of 45L / dm²·min, significantly reducing operating resistance and extending the cleaning cycle.

[0020] Fourth, the use of medium-temperature and medium-pressure lamination instead of traditional high-temperature and high-pressure lamination avoids the problem of PTFE film sticking to the lamination roller after softening, thus improving continuous production efficiency. Detailed Implementation

[0021] To facilitate understanding of the present invention, a more complete description is provided below. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0023] In this invention, the "dust-facing side" refers to the side of the filter material that directly contacts the dust-laden airflow during use, while the "dust-removing side" refers to the side of the filter material from which the purified gas is discharged. "Progressive needle punching" refers to a multi-stage needle punching process where the needle punching density increases sequentially and the needle punching depth decreases sequentially. "Hard cloth" refers to needle-punched felt filter material whose stiffness is increased by more than 30% after hardening and shaping compared to before shaping. The stiffness is measured using the cantilever method specified in GB / T18318.1-2009.

[0024] Preparation Example 1 A dust-facing fiber material, prepared by the following method: The polyphenylene sulfide fiber and the silane coupling agent aqueous solution were mixed at a bath ratio of 1:15 (i.e., 15L of silane coupling agent aqueous solution was used for every 1kg of polyphenylene sulfide fiber). The polyphenylene sulfide fiber was added to a 3% silane coupling agent aqueous solution and immersed at 40℃ for 30min. After being removed, it was dried at 110℃ to constant weight, and then opened and combed to obtain the dust-facing fiber material. The fineness of the polyphenylene sulfide fiber was 1.5-2.0 denier, the length was 51-64mm, and the areal density of the dust-facing fiber material was 80-100g / m².

[0025] The polyphenylene sulfide fiber was purchased from Jiangsu Ruitai Technology Co., Ltd.

[0026] The silane coupling agent was purchased from Nanjing Shuguang Chemical Group Co., Ltd., model: KH-550.

[0027] Preparation Example 2 A dust-facing fiber material, which differs from Preparation Example 1, replaces polyphenylene sulfide fiber with aramid fiber, wherein the aramid fiber has a fineness of 1.5 to 2.0 denier and a length of 51 to 64 mm.

[0028] Among them, the aramid fiber was purchased from Taihe New Materials Group Co., Ltd.

[0029] Preparation Example 3 A dust-facing fiber material, which differs from Preparation Example 1 in that the polyphenylene sulfide fiber is replaced with polyester fiber, the polyester fiber having a fineness of 1.5 to 2.0 denier and a length of 51 to 64 mm.

[0030] The polyester fiber was purchased from Jiangsu Zhonglu Technology Development Co., Ltd.

[0031] Preparation Example 4 A base fabric, prepared by the following method: Polyester filaments are woven into plain weave fabric with a warp density of 10-12 threads / cm and a weft density of 8-10 threads / cm. The base fabric does not require surface activation treatment and has an areal density of 80-100 g / m².

[0032] The polyester filament was purchased from Jiangsu Zhonglu Technology Development Co., Ltd.

[0033] Preparation Example 5 A dust-backing fiber material is prepared as follows: Polyphenylene sulfide (PPS) fibers are opened and combed to obtain a dust-backed fiber material that can be directly used for web laying. The dust-backed fiber material does not require surface activation treatment. The fineness of the PPS fibers is 2.5–3.0 denier, the length is 51–64 mm, and the areal density of the dust-backed fiber material is 120–150 g / m².

[0034] The polyphenylene sulfide fiber was purchased from Jiangsu Ruitai Technology Co., Ltd.

[0035] Preparation Example 6 A polytetrafluoroethylene (PTFE) membrane, wherein the PTFE membrane is a biaxially stretched microporous membrane, the average pore size of the PTFE membrane is 0.2-0.5 μm, the areal density is 3-5 g / m², and the thickness is 15-25 μm.

[0036] The polytetrafluoroethylene (PTFE) membrane was purchased from Zhejiang Gertes Environmental Protection Special Materials Technology Co., Ltd.

[0037] Preparation Example 7 A polytetrafluoroethylene (PTFE) membrane, which differs from Preparation Example 6, has an average pore size of 0.5–0.8 μm, an areal density of 5–7 g / m², and a thickness of 25–35 μm.

[0038] Example 1 An industrial filtration rigid cloth needle-punched felt filter media includes the following processing steps: Step 1, Web Laying: The dust-facing fiber material, the base fabric, and the dust-backing fiber material are laid in sequence with the dust-facing fiber material on top, the base fabric in the middle, and the dust-backing fiber material at the bottom to obtain a three-layer composite fiber web structure; wherein, the dust-facing fiber material is prepared according to Preparation Example 1 and has an areal density of 90 g / m², the base fabric is prepared according to Preparation Example 4 and has an areal density of 90 g / m², and the dust-backing fiber material is prepared according to Preparation Example 5 and has an areal density of 135 g / m².

[0039] Step 2, progressive needle punching: The three-layer composite fiber web structure is sequentially subjected to pre-needling, main needle punching, and finishing needle punching, allowing the fibers of the dust-facing and dust-repelling fiber materials to penetrate the base fabric and interlock with each other, forming a three-dimensional interlocking asymmetric substrate with a dense dust-facing surface and a fluffy dust-repelling surface. Specifically, the needle punching density of pre-needling is 60-80 needles / cm², and the needle punching depth is 8-10mm; the needle punching density of main needle punching is 150-200 needles / cm², and the needle punching depth is 6-8mm; the needle punching density of finishing needle punching is 250-300 needles / cm², and the needle punching depth is 3-5mm. The needle punching density of pre-needling, main needle punching, and finishing needle punching increases sequentially, and the needle punching depth decreases sequentially. The needle punching depth of pre-needling is greater than the total thickness of the three-layer composite fiber web structure, so that the fibers can fully penetrate the base fabric to form interlayer interlocking.

[0040] In the above technical solution, this application increases the needle density and decreases the needle depth of pre-needling, main needleling, and finishing needleling in sequence. In the early stage of processing, the pre-needling with a large depth and low density allows the fibers of the dust-facing and dust-receiving surfaces to pass through the base fabric and complete the initial interlayer connection. In the middle stage of processing, the main needleling with a medium depth and medium density strengthens the interlayer bond. In the later stage of processing, the finishing needleling with a small depth and high density makes the fibers of the dust-facing surface highly dense. This forms a three-dimensional interlocking asymmetric substrate with a dense dust-facing surface to ensure filtration accuracy and a fluffy dust-receiving surface to reduce airflow resistance. This overcomes the defects of traditional coated substrates with symmetrical structures and difficulty in differentiating the dust-facing and dust-receiving surfaces.

[0041] Step 3, hardening and shaping: The three-dimensional interlocking asymmetric substrate is subjected to heat setting and calendering treatment in sequence to obtain the hardened filter material substrate; wherein, the heat setting temperature is 190~200℃ and the time is 60~90s; the calendering roll temperature is 180~190℃ and the roll linear pressure is 40~60N / mm.

[0042] In the above technical solution, this application eliminates the internal stress generated during the needle punching process of the three-dimensional interlocking asymmetric substrate by heat setting to improve its dimensional stability, and makes the dust-facing surface of the hardened filter material substrate flat and dense by calendering, providing a flat bonding base for subsequent film coating, and avoiding poor adhesion or local gaps in the polytetrafluoroethylene film due to unevenness of the base surface.

[0043] Step 4, High-temperature longitudinal stretching and medium-pressure coating: Preheat the dust-facing surface of the hardened filter material substrate to 120-140°C. Apply a longitudinal stretch of 5%-8% relative to the original length of the polytetrafluoroethylene membrane to the dust-facing surface of the hardened filter material substrate along the running direction of the hardened filter material substrate. Apply a coating pressure of 0.3-0.5 MPa and a coating temperature of 200-220°C to the coating surface. After cooling, a hard cloth needle-punched felt filter material for industrial filtration is obtained. The polytetrafluoroethylene membrane is prepared according to Preparation Example 6.

[0044] In the above-mentioned technical solution, this application applies moderate longitudinal stretching to the polytetrafluoroethylene (PTFE) membrane during lamination and uses medium-pressure lamination, so that the PTFE membrane adheres to the hardened filter material substrate in a taut and flat state. This avoids the high lamination pressure from crushing the micropores of the PTFE membrane, which would cause a sharp drop in air permeability, and also eliminates the interface gap between the PTFE membrane and the hardened filter material substrate. Thus, while ensuring adhesion, the air permeability of the filter material is significantly improved. Furthermore, by using medium lamination temperature and medium-pressure lamination, the problem of the PTFE membrane softening and sticking to the lamination roller in the traditional high-temperature and high-pressure lamination process is effectively avoided, thus improving production efficiency.

[0045] Example 2 An industrial filtration rigid cloth needle-punched felt filter material, which differs from Example 1 in that the dust-facing fiber material is prepared according to Example 2.

[0046] Example 3 An industrial filtration rigid cloth needle-punched felt filter material, which differs from Example 1 in that the dust-facing fiber material is prepared according to Example 3.

[0047] Example 4 An industrial filtration rigid cloth needle-punched felt filter material differs from Example 1 in that the needle density of pre-needling, main needle-punching, and finishing needle-punching in step 2 is the same, all being 200 needles / cm², and the needle depth is the same, all being 6mm.

[0048] Example 5 An industrial filtration rigid cloth needle-punched felt filter material, which differs from Example 1 in that the polytetrafluoroethylene membrane in step 4 is prepared according to Example 7.

[0049] Example 6 An industrial filtration rigid cloth needle-punched felt filter material, which differs from Example 1 in that the longitudinal stretching in step 4 is 8% to 12% of the original length of the polytetrafluoroethylene membrane.

[0050] Comparative Example 1 A type of rigid needle-punched felt filter media for industrial filtration differs from Example 1 in that step 2 does not involve progressive needle punching, but rather single-pass needle punching with a needle density of 200 needles / cm² and a needle depth of 6mm.

[0051] Comparative Example 2 A type of rigid needle-punched felt filter media for industrial filtration differs from Example 1 in that, in step 4, no longitudinal stretching is applied, and the polytetrafluoroethylene membrane is directly heat-fused and attached to the dust-facing surface of the hardened filter media substrate at a coating pressure of 0.3–0.5 MPa and a coating temperature of 200–220°C.

[0052] Comparative Example 3 An industrial filtration rigid cloth needle-punched felt filter material differs from Example 1 in that step 4 is replaced by a conventional high-temperature and high-pressure coating process, in which a polytetrafluoroethylene membrane is hot-melted and attached to the dust-facing surface of the hardened filter material substrate at a coating pressure of 1.5 to 2.0 MPa and a coating temperature of 240 to 260°C.

[0053] Comparative Example 4 A type of rigid needle-punched felt filter material for industrial filtration differs from Example 1 in that no base fabric is set in step 1; instead, the fiber material on the dust-facing side and the fiber material on the dust-removing side are simply overlapped and laid out as a mesh.

[0054] Comparative Example 5 A type of rigid needle-punched felt filter media for industrial filtration, which differs from Example 1 in that step 3, hardening and shaping, is omitted.

[0055] Experimental Example 1 The air permeability of the filter media was tested using a fully automatic air permeability meter under a pressure difference of 200 Pa, in accordance with the provisions of GB / T 5453. The test results are shown in Table 1.

[0056] Experiment Example 2 Filtration accuracy of the filter media: In accordance with the provisions of GB / T 6719, a filter media performance test bench was used to test the filtration efficiency of the filter media prepared in the above embodiments and comparative examples with dust with a mass median diameter of 1 μm. The filtration efficiency of the filter media for dust of 0.3 to 0.5 μm was recorded. The test results are shown in Table 1.

[0057] Experimental Example 3 Testing the operating resistance and cleaning cycle of the filter media: The filter media prepared in the above embodiments and comparative examples were installed on a pulse bag filter test bench and continuously operated under the conditions of a filtration velocity of 1.0 m / min and an inlet dust concentration of 5 g / m³. The stable value of the operating resistance when the filter media reached a resistance of 1500 Pa and the time interval between two adjacent pulse cleanings, i.e., the cleaning cycle, were recorded. The test results are shown in Table 2.

[0058] Table 1: The air permeability of Examples 1–6 is all higher than 230 L / dm²·min, which is significantly better than that of Comparative Examples 1–5 (41.2–215.3 L / dm²·min), and the filtration efficiency is all higher than 99.9%, indicating that the method of the present invention significantly improves air permeability while maintaining high filtration accuracy.

[0059] Table 2: The stable operating resistance values ​​of Examples 1–6 were all below 900 Pa, and the cleaning cycle was all greater than 60 min, which showed significant advantages over Comparative Examples 1–5 (operating resistance 1098–1512 Pa, cleaning cycle 27.9–41.2 min), verifying the technical effect of the synergistic effect of progressive needle punching and high-temperature longitudinal tension medium-pressure coating.

[0060] Based on Examples 1-6, Comparative Examples 1-5, and Tables 1 and 2, it can be found that the filter media of Examples 1-6 have high air permeability, high filtration accuracy, low operating resistance, and long cleaning cycle. The air permeability of Examples 1-6 is higher than that of conventional membrane filter media to a certain extent, and the filtration efficiency for 0.3-0.5μm dust is higher than 99.8%.

[0061] Specifically, based on the analysis of Example 1 and Comparative Example 1, the difference between Comparative Example 1 and Example 1 is that step 2 of Comparative Example 1 does not use progressive needle punching but uses single needle punching. The air permeability and filtration efficiency of Comparative Example 1 are lower than those of Example 1 to a certain extent, the operating resistance is higher than that of Example 1, and the dust cleaning cycle is shorter than that of Example 1. From this analysis, it can be concluded that this application uses a progressive needle punching process in which the needle punching density increases sequentially and the needle punching depth decreases sequentially in the order of pre-needling, main needle punching, and finishing needle punching. This process enables the dust-facing fiber material, the base fabric, and the dust-backing fiber material to form a three-dimensional interlocking asymmetric substrate with a dense dust-facing surface and a fluffy dust-backing surface. This reduces the operating resistance while ensuring filtration accuracy and overcomes the structural defects of traditional coated substrates.

[0062] Specifically, based on the analysis of Example 1 and Comparative Examples 2-3, Comparative Example 2 did not apply longitudinal stretching during membrane coating, while Comparative Example 3 adopted a conventional high-temperature and high-pressure membrane coating process. The air permeability of Comparative Examples 2-3 was lower than that of Example 1 to a certain extent, and the operating resistance was higher and the cleaning cycle was shorter than that of Example 1. From this analysis, it can be concluded that this application, through a high-temperature longitudinal stretching and medium-pressure membrane coating process, applies medium-pressure membrane coating while applying longitudinal stretching to the polytetrafluoroethylene membrane, effectively eliminates the interface effect between the polytetrafluoroethylene membrane and the hardened filter material substrate, preventing the micropores of the polytetrafluoroethylene membrane from being crushed during the membrane coating process, thereby increasing the air permeability of the filter material, reducing the operating resistance, and extending the cleaning cycle.

[0063] Specifically, based on the analysis of Example 1 and Comparative Example 4, Comparative Example 4 did not have a base fabric. The filtration efficiency and cleaning cycle of Comparative Example 4 were lower than those of Example 1 to a certain extent, while the operating resistance was higher than that of Example 1. From this analysis, it can be concluded that this application improves the dimensional stability and deformation resistance of the filter material by setting a base fabric between the dust-facing fiber material and the dust-receiving fiber material and forming a three-dimensional interlocking structure through progressive needle punching. This reduces the decrease in filtration accuracy caused by the loose structure of the filter material during long-term high-pressure pulse cleaning.

[0064] Specifically, based on the analysis of Example 1 and Comparative Example 5, Comparative Example 5 omits the hardening and shaping step 3. The operating resistance of Comparative Example 5 is higher than that of Example 1, and the filtration efficiency and cleaning cycle are lower than those of Example 1. From this analysis, it can be concluded that this application hardens and shapes the substrate through heat setting and calendering, making the filter material surface flat and dense, providing a flat adhesion base for subsequent membrane coating, and further improving the overall filtration performance of the filter material.

[0065] Specifically, combining the analysis of Examples 1 and 4, step 2 of Example 4 uses non-progressive needle punching with the same needle density and needle depth. The air permeability and dust removal cycle of Example 4 are lower than those of Example 1 to a certain extent, while the operating resistance is higher than that of Example 1. Further analysis shows that only when the needle density of pre-needling, main needle punching, and finishing needle punching increases sequentially and the needle depth decreases sequentially can a three-dimensional interlocking asymmetric substrate with a dense dust-facing surface and a fluffy dust-removing surface be formed, thereby achieving better air permeability and lower operating resistance while ensuring filtration accuracy.

[0066] Specifically, based on the analysis of Examples 1 and 5-6, the polytetrafluoroethylene membrane in Example 5 was prepared using a larger pore size and thickness, the longitudinal tensile strength of Example 6 was greater than that of Example 1, and the air permeability of Examples 5-6 was higher than that of Example 1 to a certain extent. From this analysis, it can be concluded that the pore size and longitudinal tensile strength of the polytetrafluoroethylene membrane can adjust the air permeability of the filter material within the range defined by the examples. Those skilled in the art can select appropriate parameters within the range according to the actual filtration accuracy and air permeability requirements.

[0067] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0068] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for processing rigid needle-punched felt filter media for industrial filtration, characterized in that, include: Step 1, Web Laying: The dust-facing fiber material, the base fabric, and the dust-backing fiber material are laid in sequence with the dust-facing fiber material on top, the base fabric in the middle, and the dust-backing fiber material at the bottom to obtain a three-layer composite fiber web structure; wherein, the dust-facing fiber material is polyphenylene sulfide fiber, aramid fiber, or polyester fiber that has undergone surface activation treatment, and the dust-backing fiber material is polyphenylene sulfide fiber; Step 2, progressive needle punching: The three-layer composite fiber web structure is sequentially subjected to pre-needling, main needle punching, and finishing needle punching, so that the fibers of the dust-facing fiber material and the dust-removing fiber material pass through the base fabric and interlock with each other, forming a three-dimensional interlocking asymmetric substrate with a dense dust-facing surface and a fluffy dust-removing surface; wherein, the needle punching density of the pre-needling, the main needle punching, and the finishing needle punching increases sequentially, the needle punching depth decreases sequentially, and the needle punching depth of the pre-needling is greater than the total thickness of the three-layer composite fiber web structure; Step 3, hardening and shaping: The three-dimensional interlocking asymmetric substrate is subjected to heat setting and calendering treatment in sequence to obtain a hardened filter material substrate; Step 4, High-temperature longitudinal stretching and medium-pressure coating: After preheating the dust-facing surface of the hardened filter material substrate, the polytetrafluoroethylene membrane is applied to the dust-facing surface of the hardened filter material substrate under longitudinal stretching along the running direction of the hardened filter material substrate with medium-pressure coating heat fusion. After cooling, the industrial filtration hard cloth needle-punched felt filter material is obtained. The progressive needle punching process makes the areal density of the dust-facing fiber material greater than that of the dust-repelling fiber material, and the fiber density of the dust-facing surface is higher than that of the dust-repelling surface, forming an asymmetric structure with a dense dust-facing surface and a fluffy dust-repelling surface.

2. The method for processing rigid needle-punched felt filter media for industrial filtration according to claim 1, characterized in that, In step 1, the areal density of the dust-facing fiber material is 80-100 g / m², the areal density of the base fabric is 80-100 g / m², and the areal density of the dust-repelling fiber material is 120-150 g / m².

3. The processing method of a rigid needle-punched felt filter media for industrial filtration according to claim 1, characterized in that, In step 2, the pre-needling density is 60-80 needles / cm² and the needle depth is 8-10mm; the main needleling density is 150-200 needles / cm² and the needle depth is 6-8mm; the finishing needleling density is 250-300 needles / cm² and the needle depth is 3-5mm.

4. The processing method of a rigid needle-punched felt filter media for industrial filtration according to claim 1, characterized in that, In step 3, the heat setting temperature is 190-200℃ and the time is 60-90s; the roll temperature for the calendering process is 180-190℃ and the roll linear pressure is 40-60N / mm.

5. The method for processing rigid needle-punched felt filter media for industrial filtration according to claim 1, characterized in that, In step 4, the preheating temperature is 120-140°C, the longitudinal stretching rate is 5%-12% of the original length of the polytetrafluoroethylene film, the hot melt bonding pressure is 0.3-0.5 MPa, and the bonding temperature is 200-220°C.

6. The processing method of a rigid needle-punched felt filter media for industrial filtration according to claim 1, characterized in that, The preparation method of the dust-receiving fiber material is as follows: according to the bath ratio of fiber to silane coupling agent aqueous solution of 1:15, polyphenylene sulfide fiber, aramid fiber or polyester fiber is added to silane coupling agent aqueous solution with a mass concentration of 3%, and impregnated at 40°C for 30 min. After being taken out, it is dried at 110°C to constant weight, and then opened and combed to obtain the dust-receiving fiber material; wherein, the fineness of the polyphenylene sulfide fiber, the aramid fiber or the polyester fiber is 1.5 to 2.0 denier and the length is 51 to 64 mm.

7. The method for processing rigid needle-punched felt filter media for industrial filtration according to claim 1, characterized in that, The polytetrafluoroethylene (PTFE) membrane is a biaxially stretched microporous membrane with an average pore size of 0.2–0.8 μm, an areal density of 3–7 g / m², and a thickness of 15–35 μm.

8. The method for processing rigid needle-punched felt filter media for industrial filtration according to claim 1, characterized in that, The base fabric is prepared by weaving polyester filaments into a plain weave fabric with a warp density of 10-12 threads / cm and a weft density of 8-10 threads / cm. The base fabric does not require surface activation treatment.

9. A method for processing rigid needle-punched felt filter media for industrial filtration according to claim 1, characterized in that, The preparation method of the dust-backing fiber material is as follows: the polyphenylene sulfide fiber is opened and combed to obtain the dust-backing fiber material, and the dust-backing fiber material does not require surface activation treatment; wherein, the fineness of the polyphenylene sulfide fiber is 2.5 to 3.0 denier and the length is 51 to 64 mm.

10. A type of rigid needle-punched felt filter media for industrial filtration, characterized in that, It is prepared by the processing method of the industrial filtration rigid cloth needle-punched felt filter material as described in any one of claims 1 to 9.

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