High-temperature-resistant coated filter material and preparation method thereof

Abstract

The application relates to the technical field of industrial flue gas dust removal, and discloses a high-temperature-resistant coated filter material and a preparation method thereof. The method comprises the following steps: cleaning PPS needle-punched felt with a PPS woven base cloth as a reinforcing layer, and then performing hot air setting to make the average value of the residual thermal shrinkage rate in the warp direction and the average value of the residual thermal shrinkage rate in the weft direction of three sampling positions before coating be within a limited range, and control the difference value of the residual thermal shrinkage rate in the warp direction and the weft direction of the same sampling position; then, fluorine-containing hot melt powder composed of FEP powder and melt-processable fluorine-containing elastomer powder is scattered in a dot matrix mode and pre-melted and fixed to form discrete powder anchoring units; then, the discrete powder anchoring units are hot-pressed and coated with expanded PTFE microporous film under the conditions of limited tension and fixed amplitude, and are released after limited cooling. The obtained coated filter material has the advantages of high dynamic filtration efficiency, air permeability, coating firmness and film layer integrity after thermal cycling.

Description

Technical Field

[0001] This invention relates to the field of industrial flue gas dust removal technology, and in particular to a high-temperature resistant membrane filter material and its preparation method. Background Technology

[0002] In the field of industrial flue gas treatment, baghouse dust collectors are widely used in coal-fired boilers, biomass boilers, waste incineration, cement kilns, metal smelting, and chemical waste gas treatment. These conditions typically involve high flue gas temperatures, complex dust particle size distributions, long operating cycles, and frequent dust removal, placing high demands on the heat resistance, dimensional stability, filtration efficiency, operating resistance, and service life of the filter media. Polyphenylene sulfide (PPS) fiber possesses good heat resistance and chemical resistance. PPS needle-punched felt with a woven PPS base fabric as reinforcement can therefore be used as a substrate for medium- and high-temperature flue gas filtration. Furthermore, surface condition and dimensional stability can be improved through singeing, calendering, and heat setting.

[0003] To improve the retention capacity of fine particulate matter, existing technologies typically laminate functional membrane layers such as PTFE microporous membranes onto the surface of high-temperature resistant fiber substrates. This allows dust to be primarily trapped on the membrane surface, reducing dust penetration into the substrate. Membrane-coated filter media offer advantages in initial filtration efficiency, dust removal and regeneration performance, and long-term emission stability, thus becoming an important type of high-efficiency bag filter media. Existing membrane lamination methods mainly include hot-press lamination, adhesive lamination, and powder hot-melt lamination. Among these, hot-melt powder or hot-melt adhesive layers can form connection points or bonding layers between the membrane layer and the fiber substrate, improving the adhesion of the membrane layer.

[0004] However, the high-temperature resistant fiber substrate itself is a porous, flexible, and relatively thick nonwoven material, which may still experience some thermal shrinkage during pretreatment, lamination hot pressing, and subsequent high-temperature service. If the substrate is not sufficiently heat-set, it will continue to shrink during thermal cycling after lamination, easily causing localized stress concentration between the membrane layer and the substrate, leading to blistering, edge curling, or localized peeling. If the heat-set is excessive, it may affect the strength retention and subsequent heat resistance stability of the substrate. In particular, when there is a large difference in residual thermal shrinkage between the warp and weft directions, the inconsistent dimensional changes of the composite filter material during use can easily cause wrinkles or localized cracking of the membrane layer, affecting filtration stability.

[0005] Meanwhile, while existing continuous adhesive layers or large-area hot-melt layers are beneficial for improving initial coating adhesion, they can easily clog the air passages between the substrate and the membrane, reducing the air permeability of the coated filter media, increasing filtration resistance, and potentially increasing operating energy consumption. Conversely, if the amount of hot-melt material is too small or its distribution is too sparse, the effective connection between the membrane and the substrate will be insufficient, making it prone to localized loosening of the membrane during pulse cleaning, high-temperature thermal cycling, or long-term filtration, affecting dynamic filtration efficiency and membrane integrity. Therefore, there is a difficult trade-off between coating adhesion strength and air permeability.

[0006] Furthermore, the hot-pressing temperature, pressure, residence time, and cooling release method during the lamination process also affect the interface state between the membrane and the substrate. If the tension is released or the width restriction is lifted when the composite material temperature is high and the hot-melt material is not yet fully stable, the substrate and membrane may shrink differently, thereby reducing the lamination adhesion after thermal cycling. Existing processes do not pay enough attention to the coordination between residual thermal shrinkage of the substrate, the distribution pattern of the hot-melt material, the tension state during lamination, and the cooling release conditions, making it difficult to maintain suitable air permeability, lamination adhesion, and thermal cycling stability at high filtration efficiency. Therefore, it is necessary to improve the dimensional stability, interfacial bonding, and air resistance balance of high-temperature resistant coated filter media during high-temperature use. Summary of the Invention

[0007] In view of this, the purpose of this invention is to provide a high-temperature resistant membrane filter material and its preparation method, so as to solve the problem that existing high-temperature resistant membrane filter materials are difficult to achieve a stable balance between substrate thermal shrinkage control, membrane layer firm connection and low filtration resistance, and are prone to membrane layer defects and performance degradation after thermal cycling.

[0008] To achieve the above objectives, the present invention provides a method for preparing high-temperature resistant membrane filter material, comprising the following steps: (1) Clean the high-temperature resistant fiber substrate with the film side facing up. The high-temperature resistant fiber substrate is PPS needle-punched felt with PPS woven base fabric as the reinforcing layer. (2) The cleaned high-temperature resistant fiber substrate is hot-air shaped and cooled to obtain a shaped substrate. The average value of the warp residual heat shrinkage rate and the average value of the weft residual heat shrinkage rate of the three sampling positions measured before lamination are both 0.20% to 1.20%, and the maximum value of the difference between the warp residual heat shrinkage rate and the weft residual heat shrinkage rate at the same sampling position is not greater than 0.35 percentage points. (3) The shaped substrate is fed into the powder matrix spreading device with the coated side facing upward, and the fluorinated hot melt powder is spread onto the coated side in a matrix manner to form discrete dot-shaped powder anchoring units. The fluorinated hot melt powder is composed of FEP powder and melt-processable fluorinated elastomer powder mixed in a mass ratio of 80:20 to 95:5, and the unit area retention of the fluorinated hot melt powder is 1.9-5.0 g / m². 2 Before coating, the area coverage of the powder anchoring unit is 6%-30%; (4) The shaping substrate with the powder anchoring unit is pre-melted to pre-adhere the powder anchoring unit to the film-coated side surface of the shaping substrate, and to leave an adhesive-free open area between adjacent powder anchoring units. (5) The pre-melted and shaped substrate is subjected to restricted tension lamination, wherein the arithmetic mean of the average warp residual heat shrinkage rate and the average weft residual heat shrinkage rate at three sampling positions is taken as the average residual heat shrinkage rate of the substrate, the warp tension strain is set to 45%-65% of the average residual heat shrinkage rate of the substrate, and the weft fixed width is maintained at 100.10%-100.25% of the original width of the high-temperature resistant fiber substrate; the expanded PTFE microporous membrane is unwound, so that the expanded PTFE microporous membrane is close to the substrate side. The surface contacts the powder anchoring unit; then, a hot-pressing laminating machine is used for hot pressing and lamination. The upper hot-pressing belt temperature of the hot-pressing laminating machine is 250-270℃, the lower pressure belt temperature is 235-250℃, the linear pressure is 0.24-0.32MPa, and the residence time in the hot-pressing zone is 40-55s, so that the fluorine-containing hot-melt powder softens and melts and spreads to form discrete flexible anchoring points that simultaneously connect the back side of the expanded PTFE microporous membrane and the coating side surface of the high-temperature resistant fiber substrate. After hot pressing, the average thickness of the discrete flexible anchoring points is 12-23μm. (6) The composite filter material after hot pressing is subjected to restricted cooling while maintaining the warp tension strain and the weft fixed width. After the membrane surface temperature of the composite filter material drops to 48-58℃, the warp tension is released first, and then the weft fixed width is released to obtain the high temperature resistant membrane filter material.

[0009] Preferably, the width of the high-temperature resistant fiber substrate is 1500-1800 mm, and the unit area mass is 500-600 g / m². 2 The thickness is 1.60-2.00mm, the coated side is singed and calendered, and the reinforcing layer of the high-temperature resistant fiber substrate is PPS woven base fabric.

[0010] Preferably, in step (2), the hot air setting is carried out in a three-temperature zone hot air setting box, with the first temperature zone being 155-165℃, the second temperature zone being 180-190℃, and the third temperature zone being 198-210℃. The total residence time of the high-temperature resistant fiber substrate in the three-temperature zone hot air setting box is 82-100s.

[0011] Preferably, in step (2), the warp conveying tension of the high-temperature resistant fiber substrate during hot air setting is 28-32 N / m, and the weft setting amount is 0.15-0.25% of the original width of the high-temperature resistant fiber substrate; the high-temperature resistant fiber substrate after hot air setting is cooled by the cooling roller group, the surface temperature of the cooling roller is 28-32℃, and the surface temperature of the shaped substrate when it leaves the cooling roller group is 44-48℃.

[0012] Preferably, in step (2), the warp residual heat shrinkage rate and weft residual heat shrinkage rate are determined by the following method: warp and weft samples are cut from the center of the width of the shaped substrate, 200 mm from the left edge, and 200 mm from the right edge, respectively. The effective gauge length of each sample is 300 mm and the width is 40 mm. After placing the sample in an environment of 23°C and 50% relative humidity for 30 min, the initial gauge length L0 is measured. Then, the sample is heat-treated at 200°C without external load for 30 min. After being taken out, it is heat-treated at 23°C and 50% relative humidity. After placing the sample in an environment with a certain percentage of heat shrinkage for 30 minutes, the gauge length L1 after treatment is measured. The residual heat shrinkage rate is calculated as R = (L0 - L1) / L0 × 100%. When multiple parallel samples are set at each sampling location, the average value of the parallel samples at the same sampling location and in the same direction is calculated first, and then the average value of the warp residual heat shrinkage rate and the average value of the weft residual heat shrinkage rate at the three sampling locations are calculated separately. The maximum difference between the warp residual heat shrinkage rate and the weft residual heat shrinkage rate refers to the maximum value of the difference between the warp residual heat shrinkage rate and the weft residual heat shrinkage rate at the same sampling location among the three sampling locations.

[0013] Preferably, the fluorinated hot-melt powder is composed of FEP powder and melt-processable fluorinated elastomer powder mixed in a mass ratio of 80:20 to 95:5; the fluorinated elastomer powder is a melt-processable tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride terpolymer fluorinated elastomer powder with a fluorine content of 65% to 72%, a melting peak temperature of 150-210℃, and does not char or decompose significantly under hot-pressing conditions at 250-270℃; the D of the FEP powder is... 50 The fluorinated elastomer powder has a particle size of 8-12 μm and a D... 50 The particle size is 12-18 μm.

[0014] Preferably, in step (3), the powder dot matrix spreading device includes a dot matrix template, the dot matrix template is provided with circular openings, the diameter of a single circular opening is 0.50-0.90mm, the center distance between adjacent circular openings is 1.50-2.00mm, and two adjacent rows of circular openings are staggered; the frequency of the vibrating feeder of the powder dot matrix spreading device is 45-55Hz, and the running speed of the high temperature resistant fiber substrate is 1.8-2.2m / min.

[0015] Preferably, in step (4), the pre-melting treatment is carried out in an infrared pre-melting box, where the surface temperature of the high-temperature resistant fiber substrate coating side is 184-196℃ and the dwell time is 22-28s.

[0016] Preferably, in step (6), the restricted cooling is carried out by a restricted cooling roller group, the surface temperature of the cooling roller group is 28-30℃, and the residence time of the cooling section is 55-70s; when the warp tension is released, the speed difference of the warp tension roller group is reduced so that the warp tension strain drops to 0, and then the weft fixed width side clamp is opened.

[0017] Furthermore, the present invention also provides a high-temperature resistant membrane filter material prepared by the preparation method described in any one of claims 1-9.

[0018] The beneficial effects of this invention are: This invention cleans, heat-sets, and cools PPS needle-punched felt with PPS woven base fabric as reinforcement, controlling the average warp and weft residual heat shrinkage rates at three sampling locations before lamination to be between 0.20% and 1.20%, with the maximum warp-weft difference at the same sampling location not exceeding 0.35 percentage points. This helps reduce dimensional variations during lamination and subsequent thermal cycling. A fluorinated hot-melt powder composed of FEP powder and melt-processable fluorinated elastomer powder is used, with a concentration of 1.9-5.0 g / m³. 2 The retention amount and 6%-30% area coverage form discrete dot-shaped powder anchoring units. Combined with pre-melting treatment, this can form a dispersed connection between the film layer and the substrate, while retaining adhesive-free open areas, thus balancing film adhesion and breathability.

[0019] During the lamination stage, the warp tension strain is set according to the average residual heat shrinkage rate of the substrate, while maintaining a limited weft width. Hot pressing is performed at a hot pressing temperature of 250-270℃, a pressure-bearing temperature of 235-250℃, a linear pressure of 0.24-0.32MPa, and a residence time of 40-55s, resulting in a discrete, compliant connection structure with an average thickness of 12-23μm at the anchor points. Subsequently, cooling to 48-58℃ under confined conditions before release helps reduce wrinkling, blistering, and localized peeling of the membrane layer caused by high-temperature release. Examples show that the resulting coated filter material has an air permeability of 1.76-3.38 μm. 3 / (m 2 The dynamic filtration efficiency is 99.991%-99.996%, the membrane adhesion after thermal cycling is 0.031-0.052MPa, and the membrane defect area ratio after thermal cycling is 0.4%-1.3%, indicating that it has good comprehensive performance in terms of filtration efficiency, operating resistance, membrane stability and strength retention after thermal aging. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0021] Example 1: I. Raw Materials The substrate is PPS needle-punched felt, with a width of 1600mm and a unit area mass of 550g / m². 2 The thickness is 1.80mm, the coated side is singed and calendered, and the substrate reinforcement layer is PPS woven base fabric.

[0022] The membrane is an expanded PTFE microporous membrane with a width of 1620 mm, a thickness of 12 μm, an average pore size of 0.45 μm, and a heat-coated surface on the side facing the substrate.

[0023] The compliant anchoring material is a fluorinated hot-melt powder, composed of FEP powder and a melt-processable fluorinated elastomer powder in a mass ratio of 90:10. The fluorinated elastomer powder is a tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride terpolymer fluorinated elastomer powder with a fluorine content of 68%, a melting peak temperature of 180℃, and does not char or significantly decompose under hot-pressing conditions at 250-270℃. The D of the FEP powder... 50 D of fluorinated elastomer powder with a particle size of 10 μm 50 The particle size is 15 μm. The fluorine-containing hot-melt powder is dried in an 80°C hot air drying oven for 2 hours before use.

[0024] II. Preparation Steps Step 1, Substrate Cleaning The PPS needle-punched felt is unloaded from the substrate unwinding rack, with the coated side facing upwards, and enters the brush cleaning box. The substrate running speed is set to 2.0 m / min, the brush roller linear speed is set to 3.0 m / min, and the negative pressure inside the negative pressure dust collection box is set to -500 Pa. After cleaning, the substrate enters the three-temperature zone hot air setting box. Step 2: Preheat and shape the substrate while retaining residual heat shrinkage. The three-zone hot air setting chamber has three temperature zones: 160℃ for the first zone, 185℃ for the second zone, and 205℃ for the third zone. The substrate running speed is set to 2.0 m / min, and the total residence time of the substrate in the three zones is 90 s. The warp conveying tension of the substrate is set to 30 N / m, and the weft width setting is set to 0.20% of the original width of the substrate. After leaving the three-zone hot air setting chamber, the substrate enters the cooling roller assembly. The surface temperature of the cooling rollers is set to 30℃. When the substrate leaves the cooling roller assembly, the surface temperature of the substrate is 46℃. At the residual heat shrinkage sampling station, samples are taken from the center of the cooled substrate width, 200 mm from the left edge, and 200 mm from the right edge. Warp and weft samples are cut from each position. The effective gauge length of each sample is 300 mm, and the width is 40 mm. The initial gauge length L0 was measured after the sample was placed in an environment of 23℃ and 50% relative humidity for 30 minutes. Subsequently, the sample was heat-treated at 200℃ without external load for 30 minutes, then placed in an environment of 23℃ and 50% relative humidity for 30 minutes, and the gauge length L1 after treatment was measured. The residual heat shrinkage rate was calculated as R = (L0 - L1) / L0 × 100%. The residual heat shrinkage rates of the substrate before the lamination step were recorded as follows: Warp residual heat shrinkage rate at the center of the width was 0.61%, and weft residual heat shrinkage rate was 0.48%; 200 mm from the left edge, warp residual heat shrinkage rate was 0.64%, and weft residual heat shrinkage rate was 0.51%; 200 mm from the right edge, warp residual heat shrinkage rate was 0.58%, and weft residual heat shrinkage rate was 0.46%. The average warp residual heat shrinkage rate at the three sampling locations was 0.61%, and the average weft residual heat shrinkage rate was 0.48%, both falling within the defined window of 0.20%-1.20%. The maximum difference between the warp and weft residual heat shrinkage rates at the same sampling location was 0.13 percentage points.

[0025] Step 3: Form a discrete dotted flexible anchoring layer.

[0026] Qualified PPS substrate enters the powder matrix spreading device with the coated side facing upwards. The matrix template has circular openings, each with a diameter of 0.60 mm and a center-to-center distance of 2.00 mm between adjacent openings. Adjacent rows of openings are staggered. The vibrating feeder frequency is set to 50 Hz, and the substrate running speed is maintained at 2.0 m / min. Fluorine-containing hot-melt powder falls onto the coated side surface of the substrate through the matrix template, forming discrete dot-shaped powder anchoring units. The powder retention per unit area is set to 3.2 g / m². 2 The area coverage of the anchoring unit before film coating is 15.2%. Powder that does not fall into the template opening or does not adhere to the substrate surface is sucked into the powder recovery box through the negative pressure recovery port. After being screened by a 100μm sieve, the undersized powder is returned to the powder hopper, and the agglomerates on the sieve are sent to the solid waste bin. Step 4: Pre-melt and fix the anchor points.

[0027] After the powder dot matrix is ​​laid, the substrate enters the infrared pre-melting box. The surface temperature of the substrate on the film-coated side is set to 188℃ and the dwell time is set to 25s. This step causes the powder anchoring unit to pre-adhere to the substrate surface, preventing it from migrating before entering the lamination section. After pre-melting, there is still an open area without glue between adjacent anchoring units, and the anchoring unit does not spread into a continuous film. Step 5, Restricted Tension Coverage After pre-melting, the substrate enters the warp tensioning roller group and the weft fixed width clamp. The arithmetic mean of the average warp residual heat shrinkage rate of the three sampling positions in step 2 and the average weft residual heat shrinkage rate of the three sampling positions is taken as the average residual heat shrinkage rate of the substrate. In this embodiment, the average residual heat shrinkage rate of the substrate is 0.55%. The warp tension strain of the substrate is set to 55% of the average residual heat shrinkage rate of the substrate, corresponding to a warp tension strain of 0.30%. The weft clamps maintain the substrate width at 1602.4 mm. The expanded PTFE microporous membrane is unwound from the unwinding frame, with the unwinding tension set to 10 N / m, ensuring that the expanded PTFE microporous membrane contacts the fluorinated hot-melt powder anchoring unit on the substrate side. The width of the expanded PTFE microporous membrane is 20 mm wider than the PPS substrate width, ensuring that the trimmed areas on both sides after lamination include the complete edge of the membrane layer. The upper hot-pressing belt temperature of the hot-pressing belt laminator is set to 260℃, the lower pressure belt temperature is set to 240℃, the linear pressure is set to 0.28 MPa, and the residence time in the hot-pressing zone is set to 45 s. During the hot-pressing process, the fluorinated hot-melt powder anchoring unit softens and melts, forming discrete, compliant anchoring points that simultaneously connect the back of the expanded PTFE microporous membrane and the surface of the PPS substrate. The average thickness of the anchoring points after hot pressing is 17.8 μm. A breathable area that is not sealed by the adhesive layer is retained between adjacent anchor points. When hot pressing is completed, the composite filter material is still restricted by the warp tensioning roller group and the weft fixed width edge clamp, and is not released immediately at the outlet of the hot pressing zone. Step 6, restricted cooling and release after cooling After hot pressing, the composite filter material enters the confined cooling roller group while maintaining the warp tension strain and the weft width. The surface temperature of the cooling roller is set to 28℃, and the residence time in the cooling section is set to 60s. The membrane surface temperature of the composite filter material when it leaves the confined cooling roller group is 52℃. After the membrane surface temperature drops to 52℃, the speed difference of the warp tension roller group is reduced first to reduce the warp tension strain to 0. Then the weft width clamp is opened to obtain the high-temperature resistant coated filter material.

[0028] Example 2: I. Raw Materials The substrate is PPS needle-punched felt, with a width of 1600mm and a unit area mass of 550g / m². 2 The thickness is 1.80mm, the coated side is singed and calendered, and the substrate reinforcement layer is PPS woven base fabric.

[0029] The membrane is an expanded PTFE microporous membrane with a width of 1620 mm, a thickness of 10 μm, an average pore size of 0.55 μm, and a heat-coated surface on the side facing the substrate.

[0030] The compliant anchoring material is a fluorinated hot-melt powder, composed of FEP powder and a melt-processable fluorinated elastomer powder in a mass ratio of 95:5. The fluorinated elastomer powder is a tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride terpolymer fluorinated elastomer powder with a fluorine content of 68%, a melting peak temperature of 180℃, and does not char or significantly decompose under hot-pressing conditions at 250-270℃. The D of the FEP powder... 50 D of fluorinated elastomer powder with a particle size of 8μm 50 The particle size is 12 μm. The fluorine-containing hot-melt powder is dried in an 80°C hot air drying oven for 2 hours before use.

[0031] II. Preparation Steps Step 1, Substrate Cleaning The PPS needle-punched felt is unloaded from the substrate unwinding rack, with the coated side facing upwards, and enters the brush cleaning box. The substrate running speed is set to 1.8 m / min, the brush roller linear speed is set to 2.8 m / min, and the negative pressure inside the negative pressure dust collection box is set to -480 Pa. After cleaning, the substrate enters the three-temperature zone hot air setting box.

[0032] Step 2: Preheat and shape the substrate while retaining residual heat shrinkage. The three-zone hot air setting chamber has three temperature zones: 165℃ for the first zone, 190℃ for the second zone, and 210℃ for the third zone. The substrate running speed is set to 1.8 m / min, and the total residence time of the substrate within the three zones is 100 s. The warp conveying tension of the substrate is set to 32 N / m, and the weft width setting is set to 0.25% of the original width of the substrate. After leaving the three-zone hot air setting chamber, the substrate enters the cooling roller assembly, with the surface temperature of the cooling rollers set to 30℃. When the substrate leaves the cooling roller assembly, the surface temperature of the substrate is 44℃. At the residual heat shrinkage sampling station, samples are taken from the center of the cooled substrate width, 200 mm from the left edge, and 200 mm from the right edge. Warp and weft samples are cut from each location, with an effective gauge length of 300 mm and a width of 40 mm for each sample. The initial gauge length L0 was measured after the sample was placed in an environment of 23℃ and 50% relative humidity for 30 minutes. Subsequently, the sample was heat-treated at 200℃ without external load for 30 minutes, then placed in an environment of 23℃ and 50% relative humidity for 30 minutes, and the gauge length L1 after treatment was measured. The residual heat shrinkage rate was calculated as R = (L0 - L1) / L0 × 100%. The residual heat shrinkage rates of the substrate before the lamination step were recorded as follows: Warp residual heat shrinkage rate at the center of the width was 0.36%, and weft residual heat shrinkage rate was 0.29%; 200 mm from the left edge, warp residual heat shrinkage rate was 0.39%, and weft residual heat shrinkage rate was 0.32%; 200 mm from the right edge, warp residual heat shrinkage rate was 0.33%, and weft residual heat shrinkage rate was 0.28%. The average warp residual heat shrinkage rate at the three sampling locations was 0.36%, and the average weft residual heat shrinkage rate was 0.30%, both falling within the defined window of 0.20%-1.20%. The maximum difference between the warp and weft residual heat shrinkage rates at the same sampling location was 0.07 percentage points.

[0033] Step 3: Form a discrete dotted flexible anchoring layer Qualified PPS substrate enters the powder matrix spreading device with the coated side facing upwards. The matrix template has circular openings, each with a diameter of 0.50 mm and a center-to-center distance of 1.80 mm between adjacent openings. Adjacent rows of openings are staggered. The vibrating feeder frequency is set to 45 Hz, and the substrate running speed is maintained at 1.8 m / min. Fluorine-containing hot-melt powder falls onto the coated side surface of the substrate through the matrix template, forming discrete dot-shaped powder anchoring units. The powder retention per unit area is set to 1.9 g / m². 2 The area coverage of the anchoring unit before coating is 6.4%. Powder that does not fall into the template opening or adhere to the substrate surface is sucked into the powder recovery box through the negative pressure recovery port. After being sieved through a 100μm screen, the undersized powder is returned to the powder hopper, and the agglomerates on the screen are sent to the solid waste bin.

[0034] Step 4, Pre-melt and fix the anchor points After the powder dot matrix is ​​laid, the substrate enters the infrared pre-melting box. The surface temperature of the substrate on the coating side is set to 184°C and the dwell time is set to 22s. This step causes the powder anchoring unit to pre-adhere to the substrate surface, preventing it from migrating before entering the lamination section. After pre-melting, there is still an open area without glue between adjacent anchoring units, and the anchoring units do not spread into a continuous film.

[0035] Step 5, Restricted Tension Coverage After pre-melting, the substrate enters the warp tensioning roller group and the weft fixed width clamp. The arithmetic mean of the average warp residual heat shrinkage rate of the three sampling positions in step 2 and the average weft residual heat shrinkage rate of the three sampling positions is taken as the average residual heat shrinkage rate of the substrate. In this embodiment, the average residual heat shrinkage rate of the substrate is 0.33%. The warp tension strain of the substrate is set to 45% of the average residual heat shrinkage rate of the substrate, corresponding to a warp tension strain of 0.15%. The weft clamps maintain the substrate width at 1601.6 mm. The expanded PTFE microporous membrane is unwound from the membrane unwinding rack, with the unwinding tension set to 8 N / m, ensuring that the expanded PTFE microporous membrane contacts the fluorinated hot-melt powder anchoring unit on the substrate side. The width of the expanded PTFE microporous membrane is 20 mm wider than the PPS substrate width. The upper hot-pressing belt temperature of the hot-pressing belt laminator is set to 250℃, the lower pressure belt temperature is set to 235℃, the linear pressure is set to 0.24 MPa, and the residence time in the hot-pressing zone is set to 40 s. During the hot-pressing process, the fluorinated hot-melt powder anchoring unit softens and melts, forming discrete, compliant anchoring points that simultaneously connect the back of the expanded PTFE microporous membrane and the surface of the PPS substrate. The average thickness of the anchoring points after hot pressing is 12.6 μm. A breathable area that is not sealed by the adhesive layer is retained between adjacent anchor points. When hot pressing is completed, the composite filter material is still restricted by the warp tensioning roller group and the weft fixed width edge clamp, and is not immediately released at the outlet of the hot pressing zone.

[0036] Step 6, restricted cooling and release after cooling After hot pressing, the composite filter material enters the confined cooling roller group while maintaining the warp tension strain and the weft width. The surface temperature of the cooling roller is set to 28°C, and the residence time in the cooling section is set to 55s. The membrane surface temperature of the composite filter material when it leaves the confined cooling roller group is 48°C. After the membrane surface temperature drops to 48°C, the speed difference of the warp tension roller group is reduced first to reduce the warp tension strain to 0. Then the weft width clamp is opened to obtain the high-temperature resistant coated filter material.

[0037] Example 3: I. Raw Materials The substrate is PPS needle-punched felt, with a width of 1600mm and a unit area mass of 550g / m². 2 The thickness is 1.80mm, the coated side is singed and calendered, and the substrate reinforcement layer is PPS woven base fabric.

[0038] The membrane is an expanded PTFE microporous membrane with a width of 1620 mm, a thickness of 12 μm, an average pore size of 0.45 μm, and a heat-coated surface on the side facing the substrate.

[0039] The compliant anchoring material is a fluorinated hot-melt powder, composed of FEP powder and a melt-processable fluorinated elastomer powder in a mass ratio of 80:20. The fluorinated elastomer powder is a tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride terpolymer fluorinated elastomer powder with a fluorine content of 68%, a melting peak temperature of 180℃, and does not char or significantly decompose under hot-pressing conditions at 250-270℃. The D of the FEP powder... 50 D of fluorinated elastomer powder with a particle size of 12μm 50 The particle size is 18 μm. The fluorine-containing hot-melt powder is dried in an 80°C hot air drying oven for 2 hours before use.

[0040] II. Preparation Steps Step 1, Substrate Cleaning The PPS needle-punched felt is unloaded from the substrate unwinding rack, with the coated side facing upwards, and enters the brush cleaning box. The substrate running speed is set to 2.2 m / min, the brush roller linear speed is set to 3.2 m / min, and the negative pressure inside the negative pressure dust collection box is set to -520 Pa. After cleaning, the substrate enters the three-temperature zone hot air setting box.

[0041] Step 2: Preheat and shape the substrate while retaining residual heat shrinkage. The three-zone hot air setting chamber has three temperature zones: 155℃ for the first zone, 180℃ for the second zone, and 198℃ for the third zone. The substrate running speed is set to 2.2 m / min, and the total residence time of the substrate within the three zones is 82 s. The warp conveying tension of the substrate is set to 28 N / m, and the weft width setting is set to 0.15% of the original width of the substrate. After leaving the three-zone hot air setting chamber, the substrate enters the cooling roller assembly, with the surface temperature of the cooling rollers set to 32℃. When the substrate leaves the cooling roller assembly, the surface temperature of the substrate is 48℃. At the residual heat shrinkage sampling station, samples are taken from the center of the cooled substrate width, 200 mm from the left edge, and 200 mm from the right edge. Warp and weft samples are cut from each location, with an effective gauge length of 300 mm and a width of 40 mm for each sample. The initial gauge length L0 was measured after the sample was placed in an environment of 23℃ and 50% relative humidity for 30 minutes. Subsequently, the sample was heat-treated at 200℃ without external load for 30 minutes, then placed in an environment of 23℃ and 50% relative humidity for 30 minutes, and the gauge length L1 after treatment was measured. The residual heat shrinkage rate was calculated as R = (L0 - L1) / L0 × 100%. The residual heat shrinkage rates of the substrate before the lamination step were recorded as follows: 0.92% in the warp direction and 0.82% in the weft direction at the center of the width; 0.96% in the warp direction and 0.85% in the weft direction at 200mm from the left edge; and 0.88% in the warp direction and 0.80% in the weft direction at 200mm from the right edge. The average warp residual heat shrinkage rate at the three sampling locations was 0.92%, and the average weft residual heat shrinkage rate was 0.82%, both falling within the defined window of 0.20%-1.20%. The maximum difference between the warp and weft residual heat shrinkage rates at the same sampling location was 0.11 percentage points.

[0042] Step 3: Form a discrete dotted flexible anchoring layer Qualified PPS substrate enters the powder matrix spreading device with the coated side facing upwards. The matrix template has circular openings, each with a diameter of 0.90 mm and a center-to-center distance of 1.50 mm between adjacent openings. Adjacent rows of openings are staggered. The vibrating feeder frequency is set to 55 Hz, and the substrate running speed is maintained at 2.2 m / min. Fluorine-containing hot-melt powder falls onto the coated side surface of the substrate through the matrix template, forming discrete dot-shaped powder anchoring units. The powder retention per unit area is set to 5.0 g / m². 2 The area coverage of the anchoring unit before film coating is 28.5%. Powder that does not fall into the template opening or adhere to the substrate surface is sucked into the powder recovery box through the negative pressure recovery port. After being screened by a 100μm sieve, the undersized powder is returned to the powder hopper, and the agglomerates on the sieve are sent to the solid waste bin.

[0043] Step 4, Pre-melt and fix the anchor points After the powder dot matrix is ​​laid, the substrate enters the infrared pre-melting box. The surface temperature of the substrate on the film-coated side is set to 196℃ and the dwell time is set to 28s. This step causes the powder anchoring unit to pre-adhere to the substrate surface, preventing it from migrating before entering the lamination section. After pre-melting, there is still an open area without glue between adjacent anchoring units, and the anchoring units do not spread into a continuous film.

[0044] Step 5, Restricted Tension Coverage After pre-melting, the substrate enters the warp tensioning roller group and the weft fixed width clamp. The arithmetic mean of the average warp residual heat shrinkage rate of the three sampling positions in step 2 and the average weft residual heat shrinkage rate of the three sampling positions is taken as the average residual heat shrinkage rate of the substrate. In this embodiment, the average residual heat shrinkage rate of the substrate is 0.87%. The warp tension strain of the substrate is set to 65% of the average residual heat shrinkage rate of the substrate, corresponding to a warp tension strain of 0.57%. The weft clamps maintain the substrate width at 1604.0 mm. The expanded PTFE microporous membrane is unwound from the membrane unwinding rack, with the unwinding tension set to 12 N / m, ensuring that the expanded PTFE microporous membrane contacts the fluorinated hot-melt powder anchoring unit on the substrate side. The width of the expanded PTFE microporous membrane is 20 mm wider than the PPS substrate width. The upper hot-pressing belt temperature of the hot-pressing tape laminator is set to 270℃, the lower pressure belt temperature is set to 250℃, the linear pressure is set to 0.32 MPa, and the residence time in the hot-pressing zone is set to 55 s. During the hot-pressing process, the fluorinated hot-melt powder anchoring unit softens and melts, forming discrete, compliant anchoring points that simultaneously connect the back of the expanded PTFE microporous membrane and the surface of the PPS substrate. The average thickness of the anchoring points after hot pressing is 22.0 μm. A breathable area that is not sealed by the adhesive layer is retained between adjacent anchor points. When hot pressing is completed, the composite filter material is still restricted by the warp tensioning roller group and the weft fixed width edge clamp, and is not immediately released at the outlet of the hot pressing zone.

[0045] Step 6, restricted cooling and release after cooling After hot pressing, the composite filter material enters the confined cooling roller group while maintaining the warp tension strain and the weft width. The surface temperature of the cooling roller is set to 30℃, and the residence time in the cooling section is set to 70s. The membrane surface temperature of the composite filter material when it leaves the confined cooling roller group is 58℃. After the membrane surface temperature drops to 58℃, the speed difference of the warp tension roller group is reduced first to reduce the warp tension strain to 0. Then the weft width clamp is opened to obtain the high-temperature resistant coated filter material.

[0046] Example 4: I. Raw Materials The substrate is PPS needle-punched felt, with a width of 1600mm and a unit area mass of 560g / m². 2 The thickness is 1.90mm, the coated side is singed and calendered, and the substrate reinforcement layer is PPS woven base fabric.

[0047] The membrane is an expanded PTFE microporous membrane with a width of 1625 mm, a thickness of 15 μm, an average pore size of 0.35 μm, and a heat-coated surface on the side facing the substrate.

[0048] The compliant anchoring material is a fluorinated hot-melt powder, composed of FEP powder and a melt-processable fluorinated elastomer powder in a mass ratio of 85:15. The fluorinated elastomer powder is a tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride terpolymer fluorinated elastomer powder with a fluorine content of 68%, a melting peak temperature of 180℃, and does not char or significantly decompose under hot-pressing conditions at 250-270℃. The D of the FEP powder... 50 D of fluorinated elastomer powder with a particle size of 10 μm 50 The particle size is 15 μm. The fluorine-containing hot-melt powder is dried in an 80°C hot air drying oven for 2 hours before use.

[0049] II. Preparation Steps Step 1, Substrate Cleaning The PPS needle-punched felt is unloaded from the substrate unwinding rack, with the coated side facing upwards, and enters the brush cleaning box. The substrate running speed is set to 2.0 m / min, the brush roller linear speed is set to 3.0 m / min, and the negative pressure inside the negative pressure dust collection box is set to -500 Pa. After cleaning, the substrate enters the three-temperature zone hot air setting box.

[0050] Step 2: Preheat and shape the substrate while retaining residual heat shrinkage. The three-zone hot air setting chamber has three temperature zones: 160℃ for the first zone, 185℃ for the second zone, and 205℃ for the third zone. The substrate running speed is set to 2.0 m / min, and the total residence time of the substrate within each zone is 95 s. The warp conveying tension is set to 30 N / m, and the weft width setting is set to 0.20% of the original substrate width. After leaving the three-zone hot air setting chamber, the substrate enters the cooling roller assembly, with the surface temperature of the cooling rollers set to 30℃. When the substrate leaves the cooling roller assembly, the surface temperature is 46℃. At the residual heat shrinkage sampling station, samples are taken from the center of the cooled substrate width, 200 mm from the left edge, and 200 mm from the right edge. Warp and weft samples are cut from each location, with an effective gauge length of 300 mm and a width of 40 mm for each sample. The initial gauge length L0 was measured after the sample was placed in an environment of 23℃ and 50% relative humidity for 30 minutes. Subsequently, the sample was heat-treated at 200℃ without external load for 30 minutes, then placed in an environment of 23℃ and 50% relative humidity for 30 minutes, and the gauge length L1 after treatment was measured. The residual heat shrinkage rate was calculated as R = (L0 - L1) / L0 × 100%. The residual heat shrinkage rates of the substrate before the lamination step were recorded as follows: Warp residual heat shrinkage rate at the center of the width was 0.70%, and weft residual heat shrinkage rate was 0.61%; 200 mm from the left edge, warp residual heat shrinkage rate was 0.73%, and weft residual heat shrinkage rate was 0.64%; 200 mm from the right edge, warp residual heat shrinkage rate was 0.66%, and weft residual heat shrinkage rate was 0.59%. The average warp residual heat shrinkage rate at the three sampling locations was 0.70%, and the average weft residual heat shrinkage rate was 0.61%, both falling within the defined window of 0.20%-1.20%. The maximum difference between the warp and weft residual heat shrinkage rates at the same sampling location was 0.09 percentage points.

[0051] Step 3: Form a discrete dotted flexible anchoring layer Qualified PPS substrate enters the powder matrix spreading device with the coated side facing upwards. The matrix template has circular openings, each with a diameter of 0.80 mm and a center-to-center distance of 1.60 mm between adjacent openings. Adjacent rows of openings are staggered. The vibrating feeder frequency is set to 52 Hz, and the substrate running speed is maintained at 2.0 m / min. Fluorine-containing hot-melt powder falls onto the coated side surface of the substrate through the matrix template, forming discrete dot-shaped powder anchoring units. The powder retention per unit area is set to 4.1 g / m². 2 The area coverage of the anchoring unit before coating is 20.1%. Powder that does not fall into the template opening or adhere to the substrate surface is sucked into the powder recovery box through the negative pressure recovery port. After being screened by a 100μm sieve, the undersized powder is returned to the powder hopper, and the agglomerates on the sieve are sent to the solid waste bin.

[0052] Step 4, Pre-melt and fix the anchor points After the powder dot matrix is ​​laid, the substrate enters the infrared pre-melting box. The surface temperature of the substrate on the coating side is set to 190°C and the dwell time is set to 25s. This step causes the powder anchoring unit to pre-adhere to the substrate surface, preventing it from migrating before entering the lamination section. After pre-melting, there is still an open area without glue between adjacent anchoring units, and the anchoring units do not spread into a continuous film.

[0053] Step 5, restricted tension bonding After pre-melting, the substrate enters the warp tensioning roller group and the weft fixed width clamp. The arithmetic mean of the average warp residual heat shrinkage rate of the three sampling positions in step 2 and the average weft residual heat shrinkage rate of the three sampling positions is taken as the average residual heat shrinkage rate of the substrate. In this embodiment, the average residual heat shrinkage rate of the substrate is 0.66%. The warp tension strain of the substrate is set to 55% of the average residual heat shrinkage rate of the substrate, corresponding to a warp tension strain of 0.36%. The weft clamps maintain the substrate width at 1603.2 mm. The expanded PTFE microporous membrane is unwound from the membrane unwinding rack, with the unwinding tension set to 10 N / m, ensuring that the expanded PTFE microporous membrane contacts the fluorinated hot-melt powder anchoring unit on the substrate side. The width of the expanded PTFE microporous membrane is 25 mm wider than the PPS substrate width. The upper hot-pressing belt temperature of the hot-pressing belt laminator is set to 265℃, the lower pressure belt temperature is set to 245℃, the linear pressure is set to 0.30 MPa, and the residence time in the hot-pressing zone is set to 50 s. During the hot-pressing process, the fluorinated hot-melt powder anchoring unit softens and melts, forming discrete, compliant anchoring points that simultaneously connect the back of the expanded PTFE microporous membrane and the surface of the PPS substrate. The average thickness of the anchoring points after hot pressing is 19.5 μm. A breathable area that is not sealed by the adhesive layer is retained between adjacent anchor points. When hot pressing is completed, the composite filter material is still restricted by the warp tensioning roller group and the weft fixed width edge clamp, and is not immediately released at the outlet of the hot pressing zone.

[0054] Step 6, restricted cooling and release after cooling After hot pressing, the composite filter material enters the confined cooling roller group while maintaining the warp tension strain and the weft width. The surface temperature of the cooling roller is set to 28°C, and the residence time in the cooling section is set to 65s. The membrane surface temperature of the composite filter material when it leaves the confined cooling roller group is 55°C. After the membrane surface temperature drops to 55°C, the speed difference of the warp tension roller group is reduced first to reduce the warp tension strain to 0. Then the weft width clamp is opened to obtain the high-temperature resistant coated filter material.

[0055] Comparative Example The following comparative examples are all set around the distinguishing technical features. Except for the differences mentioned above, the source of raw materials, purity, equipment, substrate pretreatment, preparation steps, testing methods, and environmental conditions are consistent with the corresponding embodiments.

[0056] Comparative Example 1: The difference between this comparative example and Example 1 is that in step 2, the first, second, and third temperature zones of the three-zone hot air setting box are adjusted to 170°C, 200°C, and 220°C, respectively, and the total residence time of the substrate in the three temperature zones is adjusted to 120s, so that the residual heat shrinkage rate of the substrate in the warp direction before entering the lamination step is 0.08% to 0.12% and the residual heat shrinkage rate in the weft direction is 0.05% to 0.10%, and the other conditions are the same as in Example 1.

[0057] Comparative Example 2: The difference between this comparative example and Example 1 is that in step 2, the first, second, and third temperature zones of the three-zone hot air setting box are adjusted to 140°C, 165°C, and 185°C, respectively, and the total residence time of the substrate in the three temperature zones is adjusted to 60s, so that the residual heat shrinkage rate of the substrate in the warp direction before entering the lamination step is 1.48% to 1.60% and the residual heat shrinkage rate in the weft direction is 1.35% to 1.50%, and the other conditions are the same as in Example 1.

[0058] Comparative Example 3: The difference between this comparative example and Example 1 is that in step 3, a dot matrix template is not used to form discrete dot-shaped powder anchoring units. Instead, the same fluorine-containing hot-melt powder as in Example 1 is used at a concentration of 3.2 g / m³. 2 The unit area retention amount is continuously laid on the coating side surface of the substrate to form a continuous fluorine-containing hot melt layer, and the other conditions are the same as in Example 1.

[0059] Comparative Example 4: The difference between this comparative example and Example 1 is that in step 3, the diameter of a single opening in the dot matrix template is adjusted to 0.35 mm, and the center distance between adjacent openings is adjusted to 2.20 mm, so that the area coverage of the anchoring unit before film coating is 3.0%, and the powder retention per unit area is still 3.2 g / m² by adjusting the vibrating feeder. 2 The remaining conditions are the same as in Example 1.

[0060] Comparative Example 5: The difference between this comparative example and Example 3 is that in step 3, the diameter of a single opening of the dot matrix template is adjusted to 1.10 mm, the center distance between adjacent openings is adjusted to 1.45 mm, so that the area coverage of the anchoring unit before film coating is 42.0%, and the average thickness of the anchoring point after hot pressing is the same as in Example 3. The other conditions are the same as in Example 3.

[0061] Comparative Example 6: The difference between this comparative example and Example 1 is that the compliant anchoring material consists only of FEP powder, without the addition of fluorinated elastomer powder, and an equal mass of FEP powder is used to supplement the mass of the fluorinated elastomer powder, so that the powder retention per unit area remains at 3.2 g / m². 2 The remaining conditions are the same as in Example 1.

[0062] Comparative Example 7: The difference between this comparative example and Example 1 is that in step 5, the pre-melted substrate does not pass through the warp tension roller group and the weft fixed width edge clamp to form a restricted state, but enters the hot press belt laminator for lamination in a natural conveying state. The other conditions are the same as in Example 1.

[0063] Comparative Example 8: The difference between this comparative example and Example 1 is that the composite filter material after hot pressing in step 6 is not cooled to 52°C and released while maintaining warp tension strain and weft width, but is directly released when the outlet membrane surface temperature of the hot pressing zone is 118°C. The other conditions are the same as in Example 1.

[0064] Performance testing The performance of the membrane filter media prepared in each embodiment and comparative example was tested. The air permeability, membrane fastness, dynamic filtration performance, humidity conditioning conditions, and nonwoven fabric tensile strength were tested in accordance with GB / T 5453, HJ / T 326, HJ / T 324, GB / T6529 and GB / T 24218.3, respectively.

[0065] Test Item 1: Residual Heat Shrinkage Rate of Substrate The samples were obtained from the substrates of each embodiment and comparative example after step 2 and before the powder spreading step. Warp and weft samples were cut from the center of the width, 200 mm from the left edge, and 200 mm from the right edge, respectively. Each sample had an effective gauge length of 300 mm and a width of 40 mm, and three parallel samples were taken from each position in each direction. The samples were conditioned for 30 min at 23℃ and 50% relative humidity according to GB / T 6529-2008, and the initial gauge length L0 was measured. The samples were then placed in a forced-air drying oven and heat-treated for 30 min at 200±2℃ without external load. After removal, they were placed at 23℃ and 50% relative humidity for 30 min, and the gauge length L1 after treatment was measured. The residual heat shrinkage rate was calculated as R=(L0-L1) / L0×100%, and the average value of the warp direction, the average value of the weft direction, and the maximum value of the warp and weft difference at the same sampling position were recorded.

[0066] Test Item 2: Discrete Anchoring Layer Area Coverage The samples were sourced from the coated substrates of each embodiment and comparative example after step 3 and before pre-melting in step 4. Three 50mm × 50mm samples were cut from the center of the width, 200mm from the left edge, and 200mm from the right edge. The samples were laid flat on the stage, and images were acquired at 20x magnification using a stereomicroscope calibrated with a scale. Five 10mm × 10mm fields of view were selected for each sample. Image analysis software was used to binarize and segment the powder anchoring unit area from the uncovered area. The same grayscale threshold was used for samples from the same batch. The proportion of the projected area of ​​the powder anchoring unit to the field of view area was calculated. A total of 45 fields of view were obtained for each sample, and the arithmetic mean was taken as the area coverage rate, recorded as %.

[0067] Test Item 3: Average Thickness of Discrete Compliant Anchor Points The samples were obtained from the final coated filter media of each embodiment and comparative example after hot pressing and restricted cooling release. One 20mm×20mm sample was cut from each of the following locations along the width: 200mm from the left edge, 200mm from the center of the width, and 200mm from the right edge. After liquid nitrogen embrittlement, the cross-section was prepared and gold sputtered. The connection area of ​​the fluorinated hot-melt material between the back of the microporous membrane and the coated side surface of the substrate was observed under a scanning electron microscope. At least 10 discrete compliant anchoring points were randomly selected from each sample. The maximum thickness of the connection layer formed by the fluorinated hot-melt material at each anchoring point was measured. The arithmetic mean of all measurements was taken as the average thickness of the discrete compliant anchoring point, and the unit was recorded as μm.

[0068] Test item four: Breathability The samples were obtained from the final membrane filter media prepared in the various embodiments and comparative examples. Five 200mm × 200mm samples were cut along the width direction, avoiding the trimmed areas on both sides. The samples were conditioned for 24 hours at 23℃ and 50% relative humidity according to GB / T 6529-2008, and then tested for air permeability according to GB / T 5453-1997 using an air permeability tester with a test area of ​​20cm². 2 The pressure difference was set to 200 Pa, with the membrane surface facing the low-pressure side; each sample was tested at 3 different locations, and the arithmetic mean of 15 data points was recorded, with the unit being m. 3 / (m 2 ·min).

[0069] Test item 5: Initial coating adhesion The samples were the final membrane-coated filter media prepared in each embodiment and comparative example. Five 100mm × 100mm samples were taken from each sample. The membrane adhesion test was conducted according to the method in HJ / T 326-2006. The membrane-coated side of the sample was fixed upwards to the mouth of a test cup with a diameter of 25mm. Hot air at 180±2℃ was continuously introduced into the cup, and the pressure on the uncoated side was increased at a rate of 0.002MPa / s. Bubbling and peeling of the membrane surface were observed. When the longest side dimension D of the maximum peeling bubble was greater than 2.5mm, the pressure inside the test cup was recorded as the initial membrane adhesion, and the unit was recorded as MPa. The result was the arithmetic mean of the five samples, and the minimum value was also recorded.

[0070] Test item six: Coating adhesion after thermal cycling The samples were obtained from the final membrane filter media prepared in each embodiment and comparative example. Five 120mm × 120mm samples were cut. The membrane side of each sample was placed flat on a stainless steel mesh frame and kept in a forced-air drying oven at 200±2℃ for 30 minutes. Then, it was taken out and placed in an environment of 23℃ and 50% relative humidity for 10 minutes to cool. This was considered as one thermal cycle, and a total of 20 thermal cycles were performed. After the thermal cycle, the membrane fastness was determined according to the method of test item four. The membrane fastness after thermal cycle was recorded in MPa, and the membrane fastness retention rate was calculated as "membrane fastness after thermal cycle / initial membrane fastness × 100%".

[0071] Test Item 7: Dynamic Filtration Resistance and Dynamic Filtration Efficiency The samples were obtained from the final membrane filter media prepared in each embodiment and comparative example; the effective filtration area was cut to 0.05m² according to the dimensions of the dynamic filtration test fixture. 2 Three samples were taken for each test. Testing was conducted according to Clause 5.8 of HJ / T 326-2006 and in conjunction with Clause 6.3 of HJ / T324-2006, using a dynamic filtration performance tester. The filtration velocity was set to 1.0 m / min, and the inlet dust concentration was controlled at 5.0 ± 0.5 g / m³. 3 The cleaning pressure was set to 0.50 MPa, and the cleaning pulse width was set to 100 ms. Cleaning was performed once when the system resistance reached 1000 Pa. After 30 cleaning cycles, the residual dynamic filtration resistance was recorded, and the inlet dust concentration C1 and outlet dust concentration C2 were measured. The dynamic filtration efficiency was calculated using η = (C1 - C2) / C1 × 100%. The resistance unit was recorded as Pa, and the filtration efficiency unit was recorded as %.

[0072] Test item 8: Warp strength retention rate after 100h heat aging The samples were obtained from the final membrane filter media prepared in the various embodiments and comparative examples. Ten warp strips were cut from each sample, with a width of 50 mm and a clamping distance of 200 mm. Five strips were used for the unaged warp strength test, and the other five were used for the post-heat aging test. The heat-aged samples were placed in a forced-air drying oven at 200±2℃ for 100 hours. After removal, they were conditioned for 4 hours at 23℃ and 50% relative humidity according to GB / T 6529-2008. Subsequently, the warp strength was tested according to GB / T 24218.3-2010, with a tensile speed of 100 mm / min. The average warp strength F0 before aging and the average warp strength F after heat aging were recorded. 100 Press F 100 / F0×100% calculates the warp strength retention rate after 100h of thermal aging, and the unit is recorded as %.

[0073] Test Item 9: Defect Area Ratio of Film Layer After Thermal Cycling The samples were obtained from specimens subjected to thermal cycling treatment under test item six. Three specimens were taken from each sample, with a central area of ​​100mm × 100mm cut out. These were placed on a horizontal observation table, and images of the film surface were acquired under conditions of 500lx illuminance, a shooting distance of 300mm, and an image resolution of at least 300dpi. Bubbles, edge curling, cracks, and localized peeling areas were verified using a 10x magnifying glass. Defective areas in the film layer included bubbles, edge curling, cracks, and localized peeling areas. The same grayscale threshold was used to binarize the defective areas, and two testers independently verified the images. If the difference between the two results exceeded 10%, the images were re-acquired and analyzed. The image size was calculated as "defective area projected area / 10000mm²". 2 The defect area ratio of the film layer is calculated as ×100%; the arithmetic mean of 3 samples is recorded for each sample, and the unit is recorded as %.

[0074] Table 1 Performance test results of each embodiment and comparative example

[0075] Data Analysis: As shown in Table 1, the membrane filter media prepared in Examples 1-4 achieved a good balance between air permeability, membrane strength, thermal cycling stability, dynamic filtration performance, and strength retention rate after thermal aging. Among them, Example 1, under the conditions of 0.6% warp residual heat shrinkage rate, 0.5% weft residual heat shrinkage rate, and 15.2% anchoring layer area coverage, achieved an air permeability of 2.84 m. 3 / (m 2 The initial coating strength was 0.052 MPa, and after thermal cycling, the coating strength remained at 0.044 MPa. The defect area ratio of the film layer after thermal cycling was 0.7%. In Example 2, due to the anchoring layer area coverage of 6.4% and the larger average pore size of the film layer, the air permeability was increased to 3.38 m. 3 / (m2 The initial coating strength and the coating strength after thermal cycling were 0.039 MPa and 0.031 MPa, respectively, which still meet the requirements of this invention for coating strength and membrane integrity. However, compared with Example 1, the lower anchoring layer area coverage will reduce the coating strength reserve. The anchoring layer area coverage of Examples 3 and 4 were 28.5% and 20.1%, respectively. The initial coating strength was 0.060 MPa and 0.057 MPa, respectively. The coating strength after thermal cycling was 0.052 MPa and 0.050 MPa, respectively. The dynamic filtration efficiency was 99.994% and 99.996%, respectively. This shows that under the limited residual heat shrinkage rate, discrete anchoring layer and limited coating cooling conditions, improving the effective connection degree of anchoring points is beneficial to membrane stability, but the air permeability is reduced accordingly and the dynamic filtration resistance is increased.

[0076] Compared with Example 1, in Comparative Example 1, excessive preheating and shaping reduced the residual heat shrinkage rate to about 0.1%, and the warp strength retention rate decreased to 84.3% after 100h of heat aging; in Comparative Example 2, the residual heat shrinkage rate increased to 1.5% and 1.4%, the coating strength decreased to 0.026MPa after thermal cycling, and the film defect area ratio increased to 5.1%, indicating that both excessively low and excessively high residual heat shrinkage rates are detrimental to overall performance.

[0077] In Comparative Example 3, after using a continuous fluorinated hot-melt layer, the initial coating strength reached 0.063 MPa, but the air permeability decreased to 1.39 m. 3 / (m 2 The dynamic filtration resistance increased to 236 Pa (min); in Comparative Example 4, the anchoring layer area coverage was only 3.0%, and the air permeability reached 3.66 m. 3 / (m 2 The initial membrane strength was only 0.020 MPa after thermal cycling, the dynamic filtration efficiency dropped to 99.963%, and the membrane defect area ratio increased to 6.5%. In contrast, the anchoring layer area coverage of Comparative Example 5 increased to 42.0%, and the initial membrane strength was 0.064 MPa, but the air permeability decreased to 1.46 m. 3 / (m 2 The dynamic filtration resistance rose to 229 Pa (min), indicating that both excessively low and excessively high anchoring layer coverage will disrupt the balance between air permeability and membrane stability.

[0078] Comparative Example 6, without the addition of fluorinated elastomer powder, showed a decrease in coating strength from 0.044 MPa in Example 1 to 0.036 MPa after thermal cycling, while the membrane defect area ratio increased from 0.7% to 2.1%. Comparative Example 7 did not undergo restricted tension bonding, and Comparative Example 8 was directly released at the high temperature at the hot-pressing zone outlet. After thermal cycling, the coating strength decreased to 0.027 MPa and 0.029 MPa, respectively, while the membrane defect area ratio increased to 4.8% and 4.2%, respectively. This indicates that the fluorinated elastomer powder, restricted bonding, and restricted cooling release may be related to the stable maintenance of the membrane during thermal cycling. In summary, this invention, by controlling the residual thermal shrinkage rate of the substrate, forming a discrete compliant anchoring layer, and combining restricted tension bonding and restricted cooling release, maintains high dynamic filtration efficiency while also considering air permeability, coating strength, membrane integrity after thermal cycling, and strength retention after thermal aging.

[0079] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Those skilled in the art can combine, substitute, or make equivalent modifications to the technical features in the above embodiments without departing from the concept of the present invention, and all modifications, equivalent substitutions, and improvements should fall within the scope of protection of the present invention.

Claims

1. A method for preparing a high-temperature resistant membrane filter material, characterized in that, Includes the following steps: (1) Clean the high-temperature resistant fiber substrate with the film side facing up. The high-temperature resistant fiber substrate is PPS needle-punched felt with PPS woven base fabric as the reinforcing layer. (2) The cleaned high-temperature resistant fiber substrate is hot-air shaped and cooled to obtain a shaped substrate. The average value of the warp residual heat shrinkage rate and the average value of the weft residual heat shrinkage rate of the three sampling positions measured before lamination are both 0.20% to 1.20%, and the maximum value of the difference between the warp residual heat shrinkage rate and the weft residual heat shrinkage rate at the same sampling position is not greater than 0.35 percentage points. (3) The shaped substrate is fed into the powder matrix spreading device with the coated side facing upward, and the fluorinated hot melt powder is spread onto the coated side in a matrix manner to form discrete dot-shaped powder anchoring units. The fluorinated hot melt powder is composed of FEP powder and melt-processable fluorinated elastomer powder mixed in a mass ratio of 80:20 to 95:5, and the unit area retention of the fluorinated hot melt powder is 1.9-5.0 g / m². 2 Before coating, the area coverage of the powder anchoring unit is 6%-30%; (4) The shaping substrate with the powder anchoring unit is pre-melted to pre-adhere the powder anchoring unit to the film-coated side surface of the shaping substrate, and to leave an adhesive-free open area between adjacent powder anchoring units. (5) The pre-melted and shaped substrate is subjected to restricted tension lamination, wherein the arithmetic mean of the average warp residual heat shrinkage rate and the average weft residual heat shrinkage rate at three sampling positions is taken as the average residual heat shrinkage rate of the substrate, the warp tension strain is set to 45%-65% of the average residual heat shrinkage rate of the substrate, and the weft fixed width is maintained at 100.10%-100.25% of the original width of the high-temperature resistant fiber substrate; the expanded PTFE microporous membrane is unwound, so that the expanded PTFE microporous membrane is close to the substrate side. The surface contacts the powder anchoring unit; then, a hot-pressing laminating machine is used for hot pressing and lamination. The upper hot-pressing belt temperature of the hot-pressing laminating machine is 250-270℃, the lower pressure belt temperature is 235-250℃, the linear pressure is 0.24-0.32MPa, and the residence time in the hot-pressing zone is 40-55s, so that the fluorine-containing hot-melt powder softens and melts and spreads to form discrete flexible anchoring points that simultaneously connect the back side of the expanded PTFE microporous membrane and the coating side surface of the high-temperature resistant fiber substrate. After hot pressing, the average thickness of the discrete flexible anchoring points is 12-23μm. (6) The composite filter material after hot pressing is subjected to restricted cooling while maintaining the warp tension strain and the weft fixed width. After the membrane surface temperature of the composite filter material drops to 48-58℃, the warp tension is released first, and then the weft fixed width is released to obtain the high temperature resistant membrane filter material.

2. The method for preparing the high-temperature resistant membrane filter material according to claim 1, characterized in that, The high-temperature resistant fiber substrate has a width of 1500-1800 mm and a unit area mass of 500-600 g / m². 2 The thickness is 1.60-2.00mm, the coated side is singed and calendered, and the reinforcing layer of the high-temperature resistant fiber substrate is PPS woven base fabric.

3. The method for preparing the high-temperature resistant membrane filter material according to claim 1, characterized in that, In step (2), the hot air setting is carried out using a three-temperature zone hot air setting box. The temperature of the first temperature zone is 155-165℃, the temperature of the second temperature zone is 180-190℃, and the temperature of the third temperature zone is 198-210℃. The total residence time of the high-temperature resistant fiber substrate in the three-temperature zone hot air setting box is 82-100s.

4. The method for preparing high-temperature resistant membrane filter material according to claim 1, characterized in that, In step (2), the warp conveying tension of the high-temperature resistant fiber substrate during hot air setting is 28-32 N / m, and the weft setting amount is 0.15-0.25% of the original width of the high-temperature resistant fiber substrate. After hot air setting, the high-temperature resistant fiber substrate is cooled by the cooling roller group, the surface temperature of the cooling roller is 28-32℃, and the surface temperature of the shaped substrate when it leaves the cooling roller group is 44-48℃.

5. The method for preparing high-temperature resistant membrane filter material according to claim 1, characterized in that, In step (2), the warp residual heat shrinkage rate and weft residual heat shrinkage rate are determined as follows: warp and weft samples are cut from the center of the width of the shaped substrate, 200 mm from the left edge, and 200 mm from the right edge, respectively. The effective gauge length of each sample is 300 mm and the width is 40 mm. After placing the sample in an environment of 23°C and 50% relative humidity for 30 min, the initial gauge length L0 is measured. Then, the sample is heat-treated at 200°C without external load for 30 min. After removal, it is heat-treated at 23°C and 50% relative humidity. After being placed in the environment for 30 minutes, the gauge length L1 after processing is measured. The residual heat shrinkage rate is calculated as R = (L0 - L1) / L0 × 100%. When multiple parallel samples are set at each sampling location, the average value of the parallel samples at the same sampling location and in the same direction is calculated first, and then the average value of the warp residual heat shrinkage rate and the average value of the weft residual heat shrinkage rate at the three sampling locations are calculated separately. The maximum difference between the warp residual heat shrinkage rate and the weft residual heat shrinkage rate refers to the maximum value of the difference between the warp residual heat shrinkage rate and the weft residual heat shrinkage rate at the same sampling location among the three sampling locations.

6. The method for preparing the high-temperature resistant membrane filter material according to claim 1, characterized in that, The fluorinated elastomer powder is a melt-processable tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride terpolymer fluorinated elastomer powder with a fluorine content of 65% to 72%, a melting peak temperature of 150-210℃, and does not char or decompose significantly under hot-pressing conditions at 250-270℃; the D of the FEP powder 50 The fluorinated elastomer powder has a particle size of 8-12 μm and a D... 50 The particle size is 12-18 μm.

7. The method for preparing the high-temperature resistant membrane filter material according to claim 1, characterized in that, In step (3), the powder dot matrix spreading device includes a dot matrix template, the dot matrix template is provided with circular openings, the diameter of a single circular opening is 0.50-0.90mm, the center distance between adjacent circular openings is 1.50-2.00mm, and two adjacent rows of circular openings are staggered; the frequency of the vibrating feeder of the powder dot matrix spreading device is 45-55Hz, and the running speed of the high temperature resistant fiber substrate is 1.8-2.2m / min.

8. The method for preparing the high-temperature resistant membrane filter material according to claim 1, characterized in that, In step (4), the pre-melting process is carried out in an infrared pre-melting box. The surface temperature of the high-temperature resistant fiber substrate coating side inside the infrared pre-melting box is 184-196℃, and the dwell time is 22-28s.

9. The method for preparing the high-temperature resistant membrane filter material according to claim 1, characterized in that, In step (6), the restricted cooling is carried out by a restricted cooling roller group. The surface temperature of the cooling roller group is 28-30℃, and the residence time of the cooling section is 55-70s. When the warp tension is released, the speed difference of the warp tension roller group is reduced so that the warp tension strain drops to 0. Then the weft fixed width side clamp is opened.

10. A high-temperature resistant membrane filter material, characterized in that, It is prepared by the preparation method according to any one of claims 1-9.

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