Preparation method of composite filter material based on hot-pressing reinforced PTFE (Polytetrafluoroethylene) foaming coating

Abstract

The invention discloses a PPS / PTFE composite filter material based on hot-pressing reinforcement and a preparation method thereof, and belongs to the technical field of industrial flue gas purification. The material is prepared by taking a PPS needled felt as a base material, coating the surface of the PPS needled felt with a PTFE (Polytetrafluoroethylene) foam coating containing nano silicon dioxide and carrying out hot-pressing treatment at 200 DEG C. According to the method, by optimizing the hot pressing process, the bonding strength of the PTFE coating and the PPS base material is remarkably enhanced, and the pore structure of the material is effectively improved. The filtering efficiency of the obtained filter material on particles with the particle size larger than or equal to 1.0 micrometer reaches 92.6% or above, the abrasion resistance is greatly improved, the abrasion loss of a coating is only 0.0325-0.0337 g after 300 times of abrasion, the filtering resistance is kept between 136 Pa and 160 Pa, and meanwhile the filter material has good temperature resistance and corrosion resistance and is suitable for efficient purification of high-temperature and high-corrosion industrial flue gas.

Description

Technical Field

[0001] This invention belongs to the field of industrial flue gas purification, specifically relating to a method for preparing a composite filter material based on hot-pressed reinforced PTFE foam coating. Background Technology

[0002] In industrial flue gas purification, the performance of the filter material directly determines the pollutant removal efficiency and equipment lifespan. Currently, polyphenylene sulfide (PPS) needle-punched felt, widely used in the market, has become the mainstream substrate for high-temperature flue gas filtration due to its excellent high-temperature resistance and acid and alkali corrosion resistance. However, pure PPS needle-punched felt has two major drawbacks: first, the pore structure between the fibers is relatively loose, making it prone to dust penetration under the impact of high-velocity flue gas, resulting in filtration efficiency that fails to meet increasingly stringent environmental standards; second, its surface abrasion resistance is poor, and the fibers are prone to wear and shedding during long-term use, which not only shortens the material's service life but may also generate secondary dust pollution.

[0003] To address these issues, the industry commonly modifies PPS needle-punched felt by coating it with polytetrafluoroethylene (PTFE). PTFE possesses extremely low surface energy, excellent resistance to high and low temperatures, and abrasion resistance, forming a protective layer on the PPS substrate surface and reducing dust adhesion and fiber wear. However, existing coating processes often employ room temperature or low-temperature curing, resulting in low bonding strength between the PTFE coating and the PPS substrate, leading to cracking and peeling. Furthermore, the coating can easily form closed pores, increasing filtration resistance and impacting equipment energy consumption.

[0004] Therefore, how to improve the filtration efficiency and abrasion resistance of PPS needle-punched felt and PTFE-coated composite materials while ensuring low filtration resistance has become a pressing technical challenge for the industry. For example, existing technologies such as CN202410680730A improve the temperature resistance and filtration efficiency of materials by using composite high-temperature resistant base fabric and PTFE / PVDF mixed foam coating, but do not involve hot-pressing reinforcement processes, making the coating prone to peeling under high-temperature and high-impact conditions; CN202410835194A optimizes the pore size distribution and improves filtration accuracy by using a layered, gradient foam layer structure, but multi-layer coating may introduce additional resistance and is not optimized for the hot-pressing mechanism of PPS substrates; CN201910979064A uses PTFE foam coating finishing liquid to post-finish aramid needle-punched felt, improving filtration performance and corrosion resistance, but this technology is mainly for aramid materials and has limited applicability to PPS substrates, and it does not solve the problem of coating stability at high temperatures. Therefore, while existing technologies optimize filter material performance from single dimensions such as substrate composites, coating structures, or material compatibility, none of them address the specific thermoplasticity (e.g., softening characteristics at approximately 200°C), porous structure (loose pores allowing easy penetration), and insufficient surface abrasion resistance of PPS substrates through precise hot-pressing processes to achieve a synergistic improvement in filtration efficiency and low resistance. Some technologies, lacking a hot-pressing reinforcement step, are ill-suited to the high-temperature, high-impact conditions of industrial flue gas; others, while optimizing pore size or filtration precision, fail to address the increased resistance caused by multi-layer coatings; still others focus on coating modifications of other substrates (such as aramid), failing to directly adapt to the thermal and mechanical properties of PPS substrates, resulting in performance shortcomings or process compatibility issues when applied to PPS-based composite filter materials. These technological deficiencies make it difficult for existing products to simultaneously meet the comprehensive requirements of industrial flue gas purification for high-efficiency filtration, long-term durability, and low-energy operation. Therefore, a preparation method that specifically addresses these problems is urgently needed. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing PPS needle-punched felt and PTFE coated composite materials, and to provide a method for preparing composite filter materials through hot pressing. By precisely controlling the hot pressing temperature and process parameters, a synergistic improvement in filtration efficiency and wear resistance is achieved, while filtration resistance is stabilized within a reasonable range for low-energy operation of the equipment, meeting the stringent requirements of industrial flue gas purification for the comprehensive performance of materials. The specific preparation method includes the following steps:

[0006] (1) Substrate pretreatment: The PPS needle-punched felt substrate is pre-dried to remove moisture and oil before use.

[0007] (2) Preparation of PTFE foam coating: PTFE emulsion, nano silica particles and deionized water are mixed in a mass ratio of 10:1:3. After stirring evenly, 0.5-1% foaming agent is added and stirred at 50-55℃ for 15-20 min to obtain PTFE foam coating slurry.

[0008] (3) Coating process: The PTFE foam coating slurry is uniformly coated on the pretreated PPS needle-punched felt surface by scraping. The coating thickness is controlled to be 500-600μm. Then, it is pre-cured at 80-100℃ for 20-25min to allow the coating to be initially set.

[0009] (4) Hot pressing treatment: The pre-cured composite material is placed in a hot press molding machine, and the hot pressing temperature is set to 180-220℃, the hot pressing pressure is 0.8-1.0MPa, and the hot pressing time is 5-10min. During this process, the PPS fibers will undergo slight softening, and the contact points between the fibers will form a molten bond, reducing the large pores inside the substrate; at the same time, the microporous structure in the PTFE foam coating is further optimized, and the coating and the PPS fibers on the substrate surface form a physical intercalation and chemical adsorption bond, which significantly improves the coating bonding strength.

[0010] (5) Post-processing: After hot pressing, the composite material is naturally cooled to room temperature, and then cut and rolled to obtain the finished filter material.

[0011] Preferably, in step (2), the solid content of the PTFE emulsion is 60-65%, and the particle size of the nano-silica particles is 50-80nm.

[0012] Preferably, the hot-pressing temperature selected in step (4) is controlled within the range of 180-220℃, which is determined based on the softening characteristics of PPS fibers and the thermal stability of the PTFE coating. Hot-pressing within this temperature range allows the PPS fibers to reach a suitable softening state, which is beneficial for the formation of bonds between fibers and the optimization of substrate pores; at the same time, the PTFE coating structure remains stable and does not undergo significant thermal decomposition. If the temperature is below 180℃, the PPS fibers are insufficiently softened, resulting in limited improvement in pore optimization and bonding strength; if the temperature is above 220℃, the PPS fibers are prone to over-melting, leading to substrate pore blockage, a significant increase in filtration resistance, and potentially affecting the long-term temperature resistance of the PTFE coating.

[0013] Preferably, the reason for selecting a hot pressing pressure of 0.8-1.2 MPa in step (4) is that if the pressure is too low, the effective bonding of PPS fibers and the optimization of coating micropores cannot be achieved; if the pressure is too high, it will damage the microporous structure of the PTFE foam coating, resulting in a decrease in filtration efficiency.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] Significantly improved filtration efficiency: Through hot pressing, the PPS substrate fibers undergo slight softening and fusion bonding at the contact points, effectively reducing large pores within the substrate and preventing dust penetration under high-velocity flue gas impact. Simultaneously, the microporous structure of the PTFE foam coating is optimized, forming a denser and more permeable filter layer. Testing shows a filtration efficiency of over 92.6% for particles ≥1.0μm in diameter, representing an improvement of over 50% compared to untreated materials (filtration efficiency of only 59.9%), meeting stringent environmental standards.

[0016] Significantly enhanced wear resistance and coating bonding stability: During hot pressing, the PTFE coating and the PPS fibers on the substrate surface form a dual bond of physical intercalation and chemical adsorption, solving the problems of low coating bonding strength and easy cracking and peeling in traditional room temperature curing processes. Wear resistance tests show that after 300 wear cycles, the coating wear amount is only 0.0325-0.0337g, far lower than the 0.0867g of the un-hot-pressed material; and compared to the material treated with low-temperature hot pressing at 180℃ (0.0421g after 300 wear cycles), the wear resistance is further improved, significantly extending the material's service life and avoiding secondary dust pollution caused by fiber shedding.

[0017] Precise control of filtration resistance: By optimizing hot-pressing temperature and pressure parameters, the softening degree of PPS fibers and the microporous structure of the coating are precisely controlled. The finished material prepared under these conditions has a stable filtration resistance within a reasonable range of 136-160 Pa. This avoids the high penetration risk caused by insufficient pore optimization and also prevents high resistance problems caused by excessive melting or coating densification, ensuring stable operation of the equipment with low energy consumption. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the filter media structure.

[0019] Figure 2 This is a process flow diagram for filter media.

[0020] Figure 3 PM of filter media before and after hot pressing 1.0 Filtration efficiency graph.

[0021] Figure 4 This is a diagram showing the pressure drop of the filter media before and after hot pressing.

[0022] Figure 5 This is a quality factor diagram of the filter media before and after hot pressing. Detailed Implementation

[0023] To enable those skilled in the art to better understand the technical solutions of this invention, the specific implementation of this invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but the implementation of this invention is not limited thereto.

[0024] Example 1 (Hot pressing temperature 200℃)

[0025] The specific preparation method includes the following steps:

[0026] (1) Substrate pretreatment: PPS needle-punched felt with a surface density of 550 g / m² was selected as the substrate and placed in a hot air drying oven and dried at 120°C for 60 min to remove residual moisture and oil stains inside the substrate and avoid the generation of bubbles during subsequent coating.

[0027] (2) Preparation of PTFE foam coating: PTFE emulsion, nano silica particles and deionized water are mixed in a mass ratio of 10:1:3. After stirring evenly, 0.5% foaming agent is added and stirred at 50°C for 20 min to obtain PTFE foam coating slurry.

[0028] (3) Coating process: The PTFE foam coating slurry is uniformly coated on the pretreated PPS needle-punched felt surface by scraper coating method. The coating thickness is controlled to be 500μm. Then, it is pre-cured at 80℃ for 30min to allow the coating to be initially set.

[0029] (4) Hot pressing at 200℃: The pre-cured composite material is placed in a hot press molding machine, and the hot pressing temperature is set to 200℃, the hot pressing pressure is 1.2MPa, and the hot pressing time is 10min. During this process, the PPS fibers will undergo slight softening, and the contact points between the fibers will form a molten bond, reducing the large pores inside the substrate; at the same time, the microporous structure in the PTFE foam coating is further optimized, and the coating and the PPS fibers on the substrate surface form a physical intercalation and chemical adsorption bond, which significantly improves the coating bonding strength.

[0030] (5) Post-processing: After hot pressing, the composite material is naturally cooled to room temperature, and then cut and rolled to obtain the finished filter material.

[0031] Preferably, in step (2), the solid content of the PTFE emulsion is 60%, and the particle size of the nano-silica particles is 50 nm.

[0032] The filter media was tested and found to have a filtration efficiency of 93.2% for particles with a diameter ≥1.0μm. After 100 abrasion tests, the coating wear was 0.0228g; after 200 abrasion tests, the coating wear was 0.0245g; and after 300 abrasion tests, the coating wear was 0.0325g. The filtration resistance was 136Pa, and the quality factor was 0.0198Pa. -1 .

[0033] Example 2 (Hot pressing temperature 200℃)

[0034] The specific preparation method includes the following steps:

[0035] (1) Substrate pretreatment: PPS needle-punched felt with a surface density of 650 g / m² was selected as the substrate and placed in a hot air drying oven and dried at 130°C for 30 min to remove residual moisture and oil stains inside the substrate and avoid the generation of bubbles during subsequent coating.

[0036] (2) Preparation of PTFE foam coating: PTFE emulsion, nano silica particles and deionized water are mixed in a mass ratio of 10:1:3. After stirring evenly, 1% foaming agent is added and stirred at 55℃ for 15 min to obtain PTFE foam coating slurry.

[0037] (3) Coating process: The PTFE foam coating slurry is uniformly coated on the pretreated PPS needle-punched felt surface by scraper coating method. The coating thickness is controlled to be 600μm. Then, it is pre-cured at 100℃ for 20min to allow the coating to be initially set.

[0038] (4) Hot pressing at 200℃: The pre-cured composite material is placed in a hot press molding machine, and the hot pressing temperature is set to 200℃, the hot pressing pressure is 1.0MPa, and the hot pressing time is 5min. During this process, the PPS fibers will undergo slight softening, and the contact points between the fibers will form a molten bond, reducing the large pores inside the substrate; at the same time, the microporous structure in the PTFE foam coating is further optimized, and the coating and the PPS fibers on the substrate surface form a physical intercalation and chemical adsorption bond, which significantly improves the coating bonding strength.

[0039] (5) Post-processing: After hot pressing, the composite material is naturally cooled to room temperature, and then cut and rolled to obtain the finished filter material.

[0040] Preferably, in step (2), the solid content of the PTFE emulsion is 65%, and the particle size of the nano-silica particles is 80 nm.

[0041] Tests showed that the filter media had a filtration efficiency of 92.6% for particles with a diameter ≥1.0μm. After 100 abrasion tests, the coating wear amount was 0.0232g, after 200 abrasion tests, the coating wear amount was 0.0248g, and after 300 abrasion tests, the coating wear amount was 0.0337g. The filtration resistance was 160Pa.

[0042] Comparative Example 1 (without hot pressing)

[0043] (1) Substrate pretreatment: PPS needle-punched felt with a surface density of 550 g / m² was selected as the substrate and placed in a hot air drying oven and dried at 120°C for 60 min to remove residual moisture and oil stains inside the substrate and avoid the generation of bubbles during subsequent coating.

[0044] (2) Preparation of PTFE foam coating: PTFE emulsion, nano silica particles and deionized water are mixed in a mass ratio of 10:1:3. After stirring evenly, 0.5% foaming agent is added and stirred at 50°C for 15 min to obtain PTFE foam coating slurry.

[0045] (3) Coating process: The PTFE foam coating slurry is uniformly coated on the pretreated PPS needle-punched felt surface by scraper coating method. The coating thickness is controlled to be 500μm. Then, it is pre-cured at 80℃ for 30min to set the coating.

[0046] (4) Post-processing: After the coating process is completed, the composite material is naturally cooled to room temperature, and then cut and rolled to obtain the finished filter material.

[0047] Preferably, in step (2), the solid content of the PTFE emulsion is 60%, and the particle size of the nano-silica particles is 50 nm.

[0048] The filter media was tested and found to have a filtration efficiency of 59.9% for particles with a diameter ≥1.0μm. After 100 abrasion tests, the coating wear was 0.058g; after 200 abrasion tests, the coating wear was 0.0695g; and after 300 abrasion tests, the coating wear was 0.0867g. The filtration resistance was 49Pa, and the quality factor was 0.0186Pa. -1 .

[0049] Comparative Example 2 (Hot-pressing temperature 180℃)

[0050] (1) Substrate pretreatment: PPS needle-punched felt with a surface density of 550 g / m² was selected as the substrate and placed in a hot air drying oven and dried at 120°C for 60 min to remove residual moisture and oil stains inside the substrate and avoid the generation of bubbles during subsequent coating.

[0051] (2) Preparation of PTFE foam coating: PTFE emulsion, nano silica particles and deionized water are mixed in a mass ratio of 10:1:3. After stirring evenly, 0.5% foaming agent is added and stirred at 50°C for 20 min to obtain PTFE foam coating slurry.

[0052] (3) Coating process: The PTFE foam coating slurry is uniformly coated on the pretreated PPS needle-punched felt surface by scraper coating method. The coating thickness is controlled to be 500μm. Then, it is pre-cured at 80℃ for 30min to allow the coating to be initially set.

[0053] (4) Hot pressing at 180℃: The pre-cured composite material is placed in a hot press molding machine, and the hot pressing temperature is set to 180℃, the hot pressing pressure is 1.2MPa, and the hot pressing time is 10min. During this process, the PPS fibers will undergo slight softening, and the contact points between the fibers will form a molten bond, reducing the large pores inside the substrate; at the same time, the microporous structure in the PTFE foam coating is further optimized, and the coating and the PPS fibers on the substrate surface form a physical intercalation and chemical adsorption bond, which significantly improves the coating bonding strength.

[0054] (5) Post-processing: After hot pressing, the composite material is naturally cooled to room temperature, and then cut and rolled to obtain the finished filter material.

[0055] Preferably, in step (2), the solid content of the PTFE emulsion is 60%, and the particle size of the nano-silica particles is 50 nm.

[0056] Tests showed that the filter media had a filtration efficiency of 91.4% for particles with a diameter ≥1.0μm. After 100 abrasion tests, the coating wear amount was 0.0268g, after 200 abrasion tests, the coating wear amount was 0.0359g, and after 300 abrasion tests, the coating wear amount was 0.0421g. The filtration resistance was 159Pa.

[0057] Comparative Example 3 (Hot-pressing temperature 220℃)

[0058] (1) Substrate pretreatment: PPS needle-punched felt with a surface density of 550 g / m² was selected as the substrate and placed in a hot air drying oven and dried at 120°C for 60 min to remove residual moisture and oil stains inside the substrate and avoid the generation of bubbles during subsequent coating.

[0059] (2) Preparation of PTFE foam coating: PTFE emulsion, nano silica particles and deionized water are mixed in a mass ratio of 10:1:3. After stirring evenly, 0.5% foaming agent is added and stirred at 50°C for 20 min to obtain PTFE foam coating slurry.

[0060] (3) Coating process: The PTFE foam coating slurry is uniformly coated on the pretreated PPS needle-punched felt surface by scraper coating method. The coating thickness is controlled to be 500μm. Then, it is pre-cured at 80℃ for 30min to allow the coating to be initially set.

[0061] (4) Hot pressing at 220℃: The pre-cured composite material is placed in a hot press molding machine, and the hot pressing temperature is set to 220℃, the hot pressing pressure is 1.2MPa, and the hot pressing time is 10min. During this process, the PPS fibers will undergo slight softening, and the contact points between the fibers will form a molten bond, reducing the large pores inside the substrate; at the same time, the microporous structure in the PTFE foam coating is further optimized, and the coating and the PPS fibers on the substrate surface form a physical interlocking and chemical adsorption bond, which significantly improves the coating bonding strength.

[0062] (5) Post-processing: After hot pressing, the composite material is naturally cooled to room temperature, and then cut and rolled to obtain the finished filter material.

[0063] Preferably, in step (2), the solid content of the PTFE emulsion is 60%, and the particle size of the nano-silica particles is 50 nm.

[0064] The filter media was tested and found to have a filtration efficiency of 75.3% for particles with a diameter of ≥1.0μm. After 100 abrasion tests, the coating wear amount was 0.0229g, after 200 abrasion tests, the coating wear amount was 0.0244g, and after 300 abrasion tests, the coating wear amount was 0.0313g. The filtration resistance was 98Pa.

[0065] According to the appendix Figure 3 , 4As shown in Sections 5 and the test data in the specific embodiments, the present invention significantly improves the overall performance of the composite filter material through hot-pressing at 200℃. Regarding filtration efficiency, Examples 1 and 2 (hot-pressing temperature 200℃) achieved filtration efficiencies of 93.2% and 92.6% for particles with a diameter ≥1.0μm, respectively, far exceeding the 59.9% of Comparative Example 1 (without hot pressing), representing an improvement of over 50%. Compared to 91.4% of Comparative Example 2 (hot-pressing temperature 180℃) and 75.3% of Comparative Example 3 (hot-pressing temperature 220℃), it also exhibits superior and more stable filtration effects. In terms of abrasion resistance, after 300 abrasion cycles, the coating wear amounts of Examples 1 and 2 were 0.0325g and 0.0337g, respectively, significantly lower than the 0.0867g of Comparative Example 1 and better than the 0.0421g of Comparative Example 2, demonstrating excellent coating bonding stability. Regarding filtration resistance, the filtration resistances of Examples 1 and 2 were 136 Pa and 160 Pa, respectively. Although slightly higher than the 49 Pa of Comparative Example 1, they were significantly lower than the high resistance caused by pore blockage due to high-temperature hot pressing, and were within a reasonable range acceptable for equipment operation. Furthermore, the quality factor of Example 1 was 0.0198 Pa⁻¹, higher than the 0.0186 Pa⁻¹ of Comparative Example 1, indicating a better balance between filtration efficiency and resistance. In summary, under 200℃ hot pressing conditions, this invention effectively achieves synergistic optimization of filtration efficiency, wear resistance, and filtration resistance, overcoming the technical contradictions of insufficient bonding strength under low-temperature hot pressing and pore blockage under high-temperature hot pressing, and possesses outstanding comprehensive performance and industrial applicability.

[0066] Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Those skilled in the art can make various specific changes according to different practical needs without departing from the scope and spirit of the present invention, but such changes still fall within the scope of protection of this application.

Claims

1. A method for preparing a composite filter material based on a hot-pressed reinforced PTFE foam coating, characterized in that, Includes the following steps: S1. Substrate pretreatment: Pre-dry the PPS needle-punched felt substrate to remove moisture and oil before use. S2. Preparation of PTFE foam coating: Mix PTFE emulsion, nano silica particles and deionized water at a mass ratio of 10:1:3, stir evenly and then add 0.5-1% foaming agent. Stir and foam at 50-55℃ for 15-20 minutes to obtain PTFE foam coating slurry. S3. Coating process: The PTFE foam coating slurry is uniformly coated on the pretreated PPS needle-punched felt surface using a scraper coating method. The coating thickness is controlled to be 500-600μm. Then, it is pre-cured at 80-100℃ for 20-25min to allow the coating to initially set. S4. Hot Pressing Treatment: Place the pre-cured composite material into a hot press molding machine, set the hot pressing temperature to 180-220℃, the hot pressing pressure to 0.8-1.0MPa, and the hot pressing time to 5-10min. During this process, the PPS fibers will undergo slight softening, and the contact points between the fibers will form a molten bond, reducing large pores inside the substrate; at the same time, the microporous structure in the PTFE foam coating is further optimized, and the coating and the PPS fibers on the substrate surface form a physical intercalation and chemical adsorption bond, significantly improving the coating bonding strength; S5. Post-processing: After hot pressing, the composite material is naturally cooled to room temperature, and then cut and rolled to obtain the finished filter material.

2. The method for preparing a composite filter material based on a hot-pressed reinforced PTFE foam coating according to claim 1, characterized in that, The solid content of the PTFE emulsion in S2 is 60-65%, and the particle size of the nano-silica particles is 50-80nm.

3. The method for preparing a composite filter material based on a hot-pressed reinforced PTFE foam coating according to claim 1, characterized in that, The hot-pressing temperature in S4 is controlled within the range of 180-220℃, which is determined based on the softening characteristics of PPS fibers and the thermal stability of the PTFE coating. If the temperature is below 180℃, the softening degree of PPS fibers is insufficient, the optimization effect of substrate pores is poor, and the improvement of the bonding strength between the PTFE coating and the substrate is limited. If the temperature is above 220℃, PPS fibers are prone to over-melting, which leads to blockage of substrate pores, a sharp increase in filtration resistance, and the PTFE coating may undergo thermal decomposition, affecting the temperature resistance of the material.

4. The method for preparing a composite filter material based on a hot-pressed reinforced PTFE foam coating according to claim 1, characterized in that, The reason for the hot pressing pressure of 0.8-1.2MPa in S4 is that if the pressure is too low, the effective bonding of PPS fibers and the optimization of coating micropores cannot be achieved; if the pressure is too high, it will damage the microporous structure of the PTFE foam coating, resulting in a decrease in filtration efficiency.

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