Special heat-resistant filter cotton for high-temperature oven and preparation process thereof

Abstract

The present application relates to filter cotton technical field, specifically, it is a kind of high-temperature oven special heat-resistant filter cotton and its preparation process.It includes the following raw materials: polytetrafluoroethylene fiber, fluoroethylene carbonate, silicone resin, 2,2-dimethylol propionic acid, oil agent, pore-forming agent, adhesive and silicon carbide fiber.In the present application, under high-temperature oven working condition, polytetrafluoroethylene fiber melts and flows to wrap silicon carbide fiber to form "sheath-core" sealing structure, which can block the penetration of corrosive medium;fluoroethylene carbonate decomposition product reacts with the surface of silicon carbide fiber to form nanocomposite layer, its micro-nano level rough interface can induce airflow turbulence, and micropore can prolong airflow path, further improve the diffusion capture efficiency of submicron particles, so that filter cotton can still maintain high interlaminar peeling strength after thermal cycling under high-temperature oven working condition, thereby ensuring the premise of filtration performance to improve the high-temperature resistance of filter cotton.

Description

Technical Field

[0001] This invention relates to the field of filter cotton technology, and more specifically, to a heat-resistant filter cotton for high-temperature ovens and its preparation process. Background Technology

[0002] Textile filter cotton, often simply called filter cotton, is a filtration tool specifically designed to separate, capture, and retain solid particles or other contaminants from fluids. Filter cotton is generally made of fibers formed into a three-dimensional mesh structure with a certain thickness and bulkiness through nonwoven or woven processes.

[0003] For example, CN105113128A discloses a high flame-retardant filter cotton, which comprises the following components by weight percentage: 10-40% 2-5D flame-retardant fiber, 20-35% 7D flame-retardant fiber, 25-40% 12D flame-retardant fiber, and 5-25% 18-20D flame-retardant fiber. The flame-retardant fiber is formed by adding a flame retardant agent before fiber forming and then drawing it into filaments. This invention also discloses a method for preparing the flame-retardant filter cotton, which includes: preparing the flame-retardant fiber; blending the cotton; opening; carding; web laying; and hot air setting.

[0004] While the flame-retardant filter cotton formulation and preparation process disclosed in the aforementioned patent documents exhibit good flame-retardant properties under normal conditions, their application in high-temperature ovens has the following key drawbacks:

[0005] First, the flame-retardant fibers used in the above-mentioned formulations are mostly polyester, with a glass transition temperature of approximately 70-80℃ and a long-term operating temperature typically not exceeding 150℃. However, typical operating temperatures in high-temperature ovens need to reach 220-250℃, and even withstand short-term impacts of 300℃. At these temperatures, polyester fibers easily soften and melt, leading to the collapse and failure of the filter structure.

[0006] Second, high-temperature drying ovens often contain organic solvents, acidic fumes, or oily particles. When polyester fiber is used as a flame-retardant fiber raw material, it has the disadvantages of weak chemical resistance and easy corrosion, which leads to a decrease in fiber strength. Summary of the Invention

[0007] The purpose of this invention is to provide a filter cotton that can be used in high-temperature oven working environments and can avoid filter structure failure caused by fiber softening and corrosion.

[0008] The purpose of this invention is to provide a heat-resistant filter cotton for high-temperature ovens and its preparation process. By using polytetrafluoroethylene fiber and silicon carbide fiber as the heat-resistant skeleton and combining them with components such as fluoroethylene carbonate, a heat-resistant filter cotton that can avoid fiber softening and corrosion can be prepared.

[0009] To achieve the above objectives, one of the objectives of this invention is to provide a heat-resistant filter cotton for high-temperature ovens, comprising the following raw materials in the indicated mass percentages.

[0010] The composition consists of 20-25% polytetrafluoroethylene fiber, 3-5% fluoroethylene carbonate, 8-10% silicone resin, 2-3% 2,2-dimethylolpropionic acid, 1-2% oil, 4-6% pore-forming agent, 5-8% adhesive, and the balance being silicon carbide fiber.

[0011] As a further improvement to this technical solution, the silicon carbide fiber is a continuous fiber formed by coating silicon carbide onto a carbon fiber core filament.

[0012] As a further improvement to this technical solution, the oil is phenyl-modified silicone oil, the pore-forming agent is ammonium bicarbonate, and the adhesive is a polyimide precursor.

[0013] In summary, the formulation of this invention includes silicon carbide fiber, polytetrafluoroethylene fiber, fluoroethylene carbonate, organosilicon resin, 2,2-dimethylolpropionic acid, oil, pore-forming agent, and adhesive; wherein:

[0014] The silicon carbide fiber serves as the core of the heat-resistant skeleton. Its surface is wetted with oil and subjected to high-temperature fluorination treatment with fluoroethylene carbonate to form a Si-F bond ceramic passivation layer, which blocks oxygen diffusion channels and inhibits high-temperature oxidation and acid etching.

[0015] The polytetrafluoroethylene fiber melt-wrapped silicon carbide fiber forms a "sheath-core sealed structure" to prevent the penetration of corrosive media.

[0016] The fluoroethylene carbonate is used to release fluorine free radicals to react with silicon carbide fibers to generate a Si-FOC composite layer, which synergistically enhances the creep resistance of polytetrafluoroethylene fibers.

[0017] The organosilicon resin undergoes dehydration condensation under the catalysis of 2,2-dimethylolpropionic acid to form a three-dimensional cross-linked network, thereby endowing the interlayer with dynamic repair capabilities.

[0018] The pore-forming agent is used to generate through-holes, extend the airflow path, and increase dust holding capacity; the adhesive is used to melt and temporarily fix the fiber nodes, and forms a heat-resistant permanent bonding phase through closed-ring imidization.

[0019] The second objective of this invention is to provide a preparation process for the aforementioned heat-resistant filter cotton for high-temperature ovens, comprising the following steps:

[0020] Step S1: Weigh the raw materials according to the mass ratio;

[0021] Pretreatment was performed on silicon carbide fibers, polytetrafluoroethylene fibers, and pore-forming agents, and fluoroethylene carbonate was formulated into a treatment solution.

[0022] Step S2: The silicon carbide fiber, polytetrafluoroethylene fiber, and pore-forming agent mentioned above are put into a mixer for dry mixing, and then transferred to a twin-screw mixer and sprayed with silicone resin, 2,2-dimethylolpropionic acid, and adhesive for wet mixing.

[0023] The treatment liquid is then atomized and sprayed into a twin-screw mixer. After mixing for another 5 minutes, the mixture is extruded and pelletized to obtain composite pellets.

[0024] Step S3: The composite granules are fed into a twin-screw extruder, melted and plasticized, and then extruded through a spinneret to obtain nascent fibers. The nascent fibers are then rapidly cooled and solidified by a side-blowing system and then wound to output composite fibers.

[0025] The composite fibers are opened by a sawtooth roller and then deposited on the cotton condensation curtain. With the help of negative pressure adsorption under the web, the fibers are vertically oriented. After 6-10 layers of cross-laying, a fluffy fiber web is formed. Then, a pre-needle punching treatment is performed to form a solidified structure.

[0026] Step S4: The fiber web enters the double-belt hot press, is heated to 80°C and pressure is applied at 0.1MPa until the pore-forming agent is decomposed by heat. Then the temperature is stepped up to 150°C and the pressure is increased to 0.3MPa to make the adhesive melt and flow.

[0027] The temperature is then raised to 280℃ and simultaneously pressurized to 0.6MPa for hot pressing. After the hot pressing is terminated, the temperature is rapidly cooled to 100℃ to release the pressure. Finally, the filter cotton is obtained by hot air shaping, winding and cutting.

[0028] As a further improvement to this technical solution, in step S1, the pretreatment involves immersing silicon carbide fibers in an oil and then drying them at 50-70°C for 30 minutes.

[0029] After the polytetrafluoroethylene fiber is opened, it is then subjected to plasma treatment.

[0030] Grind the pore-forming agent to a particle size ≤10μm;

[0031] Fluoroethylene carbonate is prepared into a treatment solution. The silicon carbide fibers that have been treated above are then immersed in the treatment solution for 20-40 seconds and then removed. Next, they are pre-dried at 70-90℃ for 5 minutes and then treated at 260℃ for 10-30 minutes under nitrogen protection.

[0032] The treatment solution is prepared by mixing fluoroethylene carbonate and anhydrous ethanol, with a volume ratio of fluoroethylene carbonate to anhydrous ethanol of 1:20.

[0033] As a further improvement to this technical solution, in step S2, during the dry mixing process, the speed of the mixer is 150-250 rpm and the mixing time is 8-12 min.

[0034] During wet mixing, the twin-screw mixer rotates at 110-180 rpm and the mixing time is 10-20 min.

[0035] As a further improvement to this technical solution, in step S2, composite particles are obtained by extrusion pelletizing using a twin-screw extruder, and the diameter of the composite particles is 1.3-1.7 mm.

[0036] As a further improvement to this technical solution, in step S3, after the composite particles are dried and pretreated, they are fed into a twin-screw extruder, melted and plasticized at 250-300℃ in the feeding zone, and then conveyed to the spinning box for fluidization. Subsequently, they are extruded through a spinneret to obtain nascent fibers.

[0037] The drying pretreatment involves hot air drying the composite particles at a temperature of 70-90℃ for 1-3 hours.

[0038] The spinneret has an aspect ratio of 5:1 and an aperture of 0.10-0.25mm.

[0039] As a further improvement to this technical solution, in step S3, the pre-needling treatment is to use hook-tooth needles to pre-needle the fiber web, and use an ion air bar to eliminate static electricity, so that the fibers entangle to form a solidified structure.

[0040] The needle surface is coated with a molybdenum disulfide lubricating layer during pre-needle insertion, and punctures are performed at a depth of 3.5-4.5 mm with a frequency of 300-500 punctures / cm².

[0041] As a further improvement to this technical solution, in step S4, the cooling rate after hot pressing is 10-20℃ / s.

[0042] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0043] In this high-temperature oven-specific heat-resistant filter cotton and its preparation process, silicon carbide fiber is first used as the core of the high-temperature skeleton. Its surface is modified by fluoroethylene carbonate at high temperature under nitrogen protection to generate a Si-F bond ceramic passivation layer with super oxidation resistance. Then, it is combined with plasma-activated polytetrafluoroethylene fiber to construct a chemical barrier resistant to acids / alkalis / solvents. At the same time, the organosilicon resin is dehydrated and crosslinked by 2,2-dimethylolpropionic acid to form a three-dimensional heat-resistant network skeleton. Secondly, ammonium bicarbonate pore-forming agent is introduced and decomposed during the hot pressing stage to generate through-pores. Combined with phenyl-modified silicone oil to lubricate the fiber and reduce processing damage, the fiber nodes are temporarily fixed by the melting of the adhesive.

[0044] It is worth noting that under high-temperature oven conditions, the molten flow of polytetrafluoroethylene fibers encapsulates silicon carbide fibers to form a "sheath-core" sealed structure, which can block the penetration of corrosive media. The decomposition products of fluoroethylene carbonate react with the surface of silicon carbide fibers to generate a nanocomposite layer. Its micro-nano rough interface can induce airflow turbulence, and the micropores can extend the airflow path, further improving the diffusion and capture efficiency of submicron particles. In addition, surface turbulence can enhance the inertial collision of particles and form local vortices in the channels, significantly increasing the dust holding capacity. Furthermore, the cross-linked network of organosilicon and 2,2-dimethylolpropionic acid continues to condense at 280°C, dynamically repairing cracks caused by thermal stress. This allows the filter cotton to maintain high interlayer peel strength after thermal cycling under high-temperature oven conditions, thereby improving the high-temperature resistance of the filter cotton while ensuring filtration performance. Attached Figure Description

[0045] Figure 1 This is a flowchart of the present invention;

[0046] Figure 2 A schematic diagram showing the dust holding capacity per unit area of ​​filter cotton when the mass percentage of fluoroethylene carbonate is different.

[0047] Figure 3 This diagram illustrates the strength retention rate of filter cotton when the mass percentage of fluoroethylene carbonate is different. Detailed Implementation

[0048] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] One of the objectives of this invention is to provide a heat-resistant filter cotton for high-temperature ovens, comprising the following raw materials in the indicated mass percentages.

[0050] The composition consists of 20-25% polytetrafluoroethylene fiber, 3-5% fluoroethylene carbonate, 8-10% silicone resin, 2-3% 2,2-dimethylolpropionic acid, 1-2% oil, 4-6% pore-forming agent, 5-8% adhesive, and the balance being silicon carbide fiber.

[0051] Furthermore, silicon carbide fiber is a continuous fiber formed by coating silicon carbide onto carbon fiber core filaments. It acts as a heat-resistant skeleton in filter cotton, providing mechanical strength and dimensional stability.

[0052] Furthermore, the oil is phenyl-modified silicone oil, which is used to lubricate the fibers during the preparation process, reduce spinning breakage, and prevent damage to the silicon carbide fibers during processing. The pore-forming agent is ammonium bicarbonate, which is used for thermal decomposition to create pores, improve air permeability and dust holding capacity. The adhesive is a polyimide precursor, which is used to fix the fiber position in the short term during the preparation process and is converted into high-temperature resistant polyimide during hot pressing.

[0053] In summary, the formulation of this invention includes silicon carbide fiber, polytetrafluoroethylene fiber, fluoroethylene carbonate, organosilicon resin, 2,2-dimethylolpropionic acid, oil, pore-forming agent, and adhesive; wherein:

[0054] Silicon carbide fiber serves as the core of the heat-resistant skeleton. Its surface is impregnated with oil and subjected to high-temperature fluorination treatment with fluoroethylene carbonate to form a Si-F bond ceramic passivation layer, which blocks oxygen diffusion channels and inhibits high-temperature oxidation and acid etching.

[0055] Polytetrafluoroethylene fiber is melt-wrapped with silicon carbide fiber to form a "sheath-core sealed structure" that prevents corrosive media from penetrating.

[0056] Fluorinated ethylene carbonate is used to release fluorine free radicals and react with silicon carbide fibers to generate a Si-FOC composite layer, which synergistically enhances the creep resistance of polytetrafluoroethylene fibers.

[0057] Organosilicon resin undergoes dehydration condensation under the catalysis of 2,2-dimethylolpropionic acid to form a three-dimensional cross-linked network, which endows the interlayer with dynamic repair capabilities.

[0058] Pore-forming agents are used to create through-holes, extend the airflow path, and increase dust holding capacity; adhesives are used to melt and temporarily fix fiber nodes, and form a heat-resistant permanent bonding phase through closed-ring imidization.

[0059] The second objective of this invention is to provide a preparation process for the aforementioned heat-resistant filter cotton for high-temperature ovens, comprising the following steps:

[0060] Step S1: Weigh the raw materials according to the mass ratio.

[0061] Silicon carbide fibers are impregnated in an oil and then dried at 50-70°C for 30 minutes to reduce the coefficient of friction in subsequent processes and prevent brittle fracture.

[0062] After the polytetrafluoroethylene fibers are opened, they are then subjected to plasma treatment (200W power, argon environment) to increase surface activity and improve adhesion.

[0063] Grind the pore-forming agent to a particle size ≤10μm to ensure uniform decomposition.

[0064] Fluorinated ethylene carbonate is prepared into a treatment solution. The pre-treated silicon carbide fibers are then immersed in the treatment solution for 20-40 seconds and removed. Next, they are pre-dried at 70-90°C for 5 minutes, followed by treatment at 260°C for 10-30 minutes under nitrogen protection to form a fluorinated silicon carbide protective layer on the surface of the silicon carbide fibers. The treatment solution is prepared by mixing fluorinated ethylene carbonate and anhydrous ethanol, with a volume ratio of fluorinated ethylene carbonate to anhydrous ethanol of 1:20.

[0065] Step S2: The silicon carbide fiber, polytetrafluoroethylene fiber, and pore-forming agent are put into a high-speed mixer for dry mixing. During dry mixing, the speed of the high-speed mixer is 150-250 rpm and the mixing time is 8-12 min. Then, the mixture is transferred to a twin-screw mixer and sprayed with silicone resin, 2,2-dimethylolpropionic acid, and adhesive for wet mixing. During wet mixing, the speed of the twin-screw mixer is 110-180 rpm and the mixing time is 10-20 min.

[0066] The treatment liquid is then atomized and sprayed into the twin-screw mixer (temperature controlled ≤50℃). After mixing for 5 minutes, the mixture is extruded and pelletized through a twin-screw extruder to obtain composite pellets with a diameter of 1.3-1.7 mm.

[0067] Step S3: After drying and pre-treating the composite granules, the composite granules are fed into a twin-screw extruder. The polytetrafluoroethylene fiber component is melted and plasticized at 250-300℃ in the feeding zone, and then conveyed to a 300℃ spinning box for complete fluidization. Subsequently, the nascent fibers are obtained by extrusion through a spinneret. The high shear force makes the PTFE melt uniformly coat the silicon carbide fiber core filament.

[0068] The drying pretreatment involves hot air drying the composite particles in a circulating oven at 70-90℃ for 1-3 hours to prevent air bubbles from bursting during the spinning process.

[0069] The spinneret has an aspect ratio of 5:1 and an aperture of 0.10-0.25mm. The high shear force ensures uniform coating of polytetrafluoroethylene and prevents silicon carbide fibers from being exposed.

[0070] The nascent fibers are then rapidly cooled and solidified by a side-blowing system (20℃ / (0.5m / s)). The fiber diameter is controlled at a winding speed of 800m / min to 15±2μm, and the composite fibers are then wound out.

[0071] The composite fibers are opened by a sawtooth roller (1500 rpm / 0.3 mm spacing) to achieve single fiberization, and then deposited on the condensing curtain at a speed of 2.0 m / min. With the help of -500 Pa negative pressure adsorption under the web, the fibers are vertically oriented. After 6-10 layers of cross-laying, a fluffy fiber web is formed. Then, the fiber web is pre-needled with hook-tooth needles, and static electricity is eliminated with the help of ion air bars to make the fibers entangled and form a solidified structure. The surface of the needles during pre-needling is coated with a molybdenum disulfide lubricating layer. The puncture is performed at a frequency of 800 times / min and a puncture depth of 3.5-4.5 mm, with 300-500 punctures / cm².

[0072] Step S4: The fiber web enters a dual-belt hot press, where it is heated to 80°C at a rate of ≤2°C / min and a pressure of 0.1MPa is applied until the pore-forming agent, ammonium bicarbonate, decomposes due to heat, and the gas diffuses to form 30-100μm through-holes. Then, the temperature is stepped up to 150°C and the pressure is increased to 0.3MPa, causing the polyimide precursor adhesive to melt and flow, wetting the fiber intersections to form localized bonding zones.

[0073] The temperature is then rapidly increased to 280℃ (at a rate of 10℃ / s), and simultaneously pressurized to 0.6MPa for hot pressing, triggering a triple reaction during this stage:

[0074] 1. 2,2-Dimethylolpropionic acid catalyzes the dehydration of silanol groups, forming a three-dimensional network structure;

[0075] 2. Polytetrafluoroethylene fibers melt and flow at temperatures above 327°C, and achieve continuous phase encapsulation through molecular chain reconstruction (crystallinity ≥ 60%).

[0076] 3. The precursor undergoes closed-loop dehydration to generate heat-resistant polyimide.

[0077] After hot pressing is terminated, the temperature is rapidly cooled to 100°C at a cooling rate of 10-20°C / s to release the pressure, suppressing the thermal decomposition of the resin. Finally, the filter cotton is obtained by hot air setting, winding and slitting.

[0078] The following specific embodiments will further illustrate the heat-resistant filter cotton for high-temperature ovens and its preparation process provided by the present invention.

[0079] Example 1

[0080] Step S1: Weigh out 20% polytetrafluoroethylene fiber, 5% fluoroethylene carbonate, 8% silicone resin, 3% 2,2-dimethylolpropionic acid, 1% oil, 6% pore-forming agent, 5% adhesive, and the remainder is silicon carbide fiber according to the mass ratio.

[0081] Silicon carbide fibers are impregnated in an oil and then dried at 70°C for 30 minutes.

[0082] After the polytetrafluoroethylene fiber is opened, it is then subjected to plasma treatment (power 200W, argon environment).

[0083] The pore-forming agent is ground to a particle size ≤10μm.

[0084] Fluoroethylene carbonate was prepared into a treatment solution. The silicon carbide fibers treated as described above were then immersed in the treatment solution for 20 seconds and removed. Next, they were pre-dried at 90°C for 5 minutes, followed by treatment at 260°C for 10 minutes under nitrogen protection. The treatment solution was prepared by mixing fluoroethylene carbonate and anhydrous ethanol, with a volume ratio of fluoroethylene carbonate to anhydrous ethanol of 1:20.

[0085] Step S2: The silicon carbide fiber, polytetrafluoroethylene fiber, and pore-forming agent are put into a high-speed mixer for dry mixing. During dry mixing, the speed of the high-speed mixer is 250 rpm and the mixing time is 8 min. Then, the mixture is transferred to a twin-screw mixer and sprayed with silicone resin, 2,2-dimethylolpropionic acid, and adhesive for wet mixing. During wet mixing, the speed of the twin-screw mixer is 180 rpm and the mixing time is 10 min.

[0086] The treatment liquid is then atomized and sprayed into the twin-screw mixer (temperature controlled ≤50℃). After mixing for 5 minutes, the mixture is extruded and pelletized through a twin-screw extruder to obtain composite pellets with a diameter of 1.7 mm.

[0087] Step S3: After drying and pre-treating the composite granules, the composite granules are fed into a twin-screw extruder. The polytetrafluoroethylene fiber component is melt-plasticized at 250°C in the feeding zone, and then conveyed to a spinning box at 300°C for complete fluidization. Subsequently, the nascent fibers are obtained by extrusion through a spinneret.

[0088] The drying pretreatment involved hot air drying the composite particles at 90°C for 1 hour in a circulating oven.

[0089] The spinneret has a length-to-diameter ratio of 5:1 and an aperture of 0.25mm.

[0090] The nascent fibers are then rapidly cooled and solidified by a side-blowing system (20℃ / (0.5m / s)). The fiber diameter is controlled at a winding speed of 800m / min to 15±2μm, and the composite fibers are then wound out.

[0091] The composite fibers are opened by a toothed roller (1500 rpm / 0.3 mm spacing), and then deposited on a condensing curtain at a speed of 2.0 m / min. With the help of -500 Pa negative pressure adsorption under the net, the fibers are vertically oriented. After 6 layers of cross-laying, a fluffy fiber web is formed. Then, the fiber web is pre-needled with hook-tooth needles, and static electricity is eliminated with the help of ion air bars, so that the fibers entangle and form a solidified structure. The surface of the needles during pre-needling is coated with a molybdenum disulfide lubricating layer. The puncture is performed at a frequency of 800 times / min and a puncture depth of 4.5 mm, with 300 punctures / cm².

[0092] Step S4: The fiber web enters a dual-belt hot press, where it is heated to 80°C at a rate of ≤2°C / min and a pressure of 0.1MPa is applied until the pore-forming agent decomposes due to heat, and gas diffusion forms 30-100μm through-holes. Then, the temperature is stepped up to 150°C and the pressure is increased to 0.3MPa, causing the adhesive to melt and flow.

[0093] The temperature is then rapidly increased to 280℃ (at a rate of 10℃ / s), and the pressure is simultaneously increased to 0.6MPa for hot pressing. After the hot pressing is terminated, the temperature is rapidly cooled to 100℃ at a cooling rate of 10℃ / s to release the pressure. Finally, the filter cotton is obtained by hot air shaping, winding and cutting.

[0094] Example 2

[0095] Step S1: Weigh out the following components according to the mass ratio: 23% polytetrafluoroethylene fiber, 4% fluoroethylene carbonate, 9% silicone resin, 2% 2,2-dimethylolpropionic acid, 2% oil, 5% pore-forming agent, 7% adhesive, and the remainder is silicon carbide fiber.

[0096] Silicon carbide fibers are impregnated in an oil and then dried at 60°C for 30 minutes.

[0097] After the polytetrafluoroethylene fiber is opened, it is then subjected to plasma treatment (power 200W, argon environment).

[0098] The pore-forming agent is ground to a particle size ≤10μm.

[0099] Fluoroethylene carbonate was prepared into a treatment solution. The silicon carbide fibers treated as described above were then immersed in the treatment solution for 30 seconds and removed. Next, they were pre-dried at 80°C for 5 minutes, followed by treatment at 260°C for 20 minutes under nitrogen protection. The treatment solution was prepared by mixing fluoroethylene carbonate and anhydrous ethanol, with a volume ratio of fluoroethylene carbonate to anhydrous ethanol of 1:20.

[0100] Step S2: The silicon carbide fiber, polytetrafluoroethylene fiber, and pore-forming agent are put into a high-speed mixer for dry mixing. During dry mixing, the speed of the high-speed mixer is 200 rpm and the mixing time is 10 min. Then, the mixture is transferred to a twin-screw mixer and sprayed with silicone resin, 2,2-dimethylolpropionic acid, and adhesive for wet mixing. During wet mixing, the speed of the twin-screw mixer is 150 rpm and the mixing time is 15 min.

[0101] The treatment liquid is then atomized and sprayed into the twin-screw mixer (temperature controlled ≤50℃). After mixing for 5 minutes, the mixture is extruded and pelletized through a twin-screw extruder to obtain composite pellets with a diameter of 1.5 mm.

[0102] Step S3: After drying and pre-treating the composite granules, the composite granules are fed into a twin-screw extruder. The polytetrafluoroethylene fiber component is melt-plasticized at 280°C in the feeding zone and then conveyed to a spinning box at 300°C for complete fluidization. Subsequently, the nascent fibers are extruded through a spinneret.

[0103] The drying pretreatment involved hot air drying the composite particles at 80°C for 2 hours in a circulating oven.

[0104] The spinneret has a length-to-diameter ratio of 5:1 and an aperture of 0.20 mm.

[0105] The nascent fibers are then rapidly cooled and solidified by a side-blowing system (20℃ / (0.5m / s)). The fiber diameter is controlled at a winding speed of 800m / min to 15±2μm, and the composite fibers are then wound out.

[0106] The composite fibers are opened by a sawtooth roller (1500 rpm / 0.3 mm spacing), and then deposited on a condensing curtain at a speed of 2.0 m / min. With the help of -500 Pa negative pressure adsorption under the web, the fibers are vertically oriented. After 8 layers of cross-laying, a fluffy fiber web is formed. Then, the fiber web is pre-needled with hook-tooth needles, and static electricity is eliminated with the help of ion air bars, so that the fibers entangle and form a solidified structure. The surface of the needles during pre-needling is coated with a molybdenum disulfide lubricating layer. The puncture is performed at a frequency of 800 times / min and a puncture depth of 4.0 mm, with 400 punctures / cm².

[0107] Step S4: The fiber web enters a dual-belt hot press, where it is heated to 80°C at a rate of ≤2°C / min and a pressure of 0.1MPa is applied until the pore-forming agent decomposes due to heat, and gas diffusion forms 30-100μm through-holes. Then, the temperature is stepped up to 150°C and the pressure is increased to 0.3MPa, causing the adhesive to melt and flow.

[0108] The temperature is then rapidly increased to 280℃ (at a rate of 10℃ / s), and the pressure is simultaneously increased to 0.6MPa for hot pressing. After the hot pressing is terminated, the temperature is rapidly cooled to 100℃ at a cooling rate of 15℃ / s to release the pressure. Finally, the filter cotton is obtained by hot air shaping, winding and cutting.

[0109] Example 3

[0110] Step S1: Weigh out 25% polytetrafluoroethylene fiber, 3% fluoroethylene carbonate, 10% silicone resin, 2% 2,2-dimethylolpropionic acid, 2% oil, 4% pore-forming agent, 8% adhesive, and the remainder is silicon carbide fiber according to the mass ratio.

[0111] Silicon carbide fibers are impregnated in an oil and then dried at 50°C for 30 minutes.

[0112] After the polytetrafluoroethylene fiber is opened, it is then subjected to plasma treatment (power 200W, argon environment).

[0113] The pore-forming agent is ground to a particle size ≤10μm.

[0114] Fluoroethylene carbonate was prepared into a treatment solution. The silicon carbide fibers treated as described above were then immersed in the treatment solution for 40 seconds and removed. Next, they were pre-dried at 70°C for 5 minutes, followed by treatment at 260°C for 30 minutes under nitrogen protection. The treatment solution was prepared by mixing fluoroethylene carbonate and anhydrous ethanol, with a volume ratio of fluoroethylene carbonate to anhydrous ethanol of 1:20.

[0115] Step S2: The silicon carbide fiber, polytetrafluoroethylene fiber, and pore-forming agent are put into a high-speed mixer for dry mixing. During dry mixing, the speed of the high-speed mixer is 150 rpm and the mixing time is 12 min. Then, the mixture is transferred to a twin-screw mixer and sprayed with silicone resin, 2,2-dimethylolpropionic acid, and adhesive for wet mixing. During wet mixing, the speed of the twin-screw mixer is 110 rpm and the mixing time is 20 min.

[0116] The treatment liquid is then atomized and sprayed into the twin-screw mixer (temperature controlled ≤50℃). After mixing for 5 minutes, the mixture is extruded and pelletized through a twin-screw extruder to obtain composite pellets with a diameter of 1.3 mm.

[0117] Step S3: After drying and pre-treating the composite granules, the composite granules are fed into a twin-screw extruder. The polytetrafluoroethylene fiber component is melt-plasticized at 300°C in the feeding zone, and then conveyed to a 300°C spinning box for complete fluidization. Subsequently, the nascent fibers are extruded through a spinneret.

[0118] The drying pretreatment involved hot air drying the composite particles at 70°C for 3 hours in a circulating oven.

[0119] The spinneret has a length-to-diameter ratio of 5:1 and an aperture of 0.10 mm.

[0120] The nascent fibers are then rapidly cooled and solidified by a side-blowing system (20℃ / (0.5m / s)). The fiber diameter is controlled at a winding speed of 800m / min to 15±2μm, and the composite fibers are then wound out.

[0121] The composite fibers are opened by a toothed roller (1500 rpm / 0.3 mm spacing), and then deposited on a condensing curtain at a speed of 2.0 m / min. With the help of -500 Pa negative pressure adsorption under the net, the fibers are vertically oriented. After 10 layers of cross-laying, a fluffy fiber web is formed. Then, the fiber web is pre-needled with hook-tooth needles, and static electricity is eliminated with the help of ion air bars, so that the fibers entangle and form a solidified structure. The surface of the needles during pre-needling is coated with a molybdenum disulfide lubricating layer. The puncture is performed at a frequency of 800 times / min and a puncture depth of 3.5 mm, with 500 punctures / cm².

[0122] Step S4: The fiber web enters a dual-belt hot press, where it is heated to 80°C at a rate of ≤2°C / min and a pressure of 0.1MPa is applied until the pore-forming agent decomposes due to heat, and gas diffusion forms 30-100μm through-holes. Then, the temperature is stepped up to 150°C and the pressure is increased to 0.3MPa, causing the adhesive to melt and flow.

[0123] The temperature is then rapidly increased to 280℃ (at a rate of 10℃ / s), and the pressure is simultaneously increased to 0.6MPa for hot pressing. After the hot pressing is terminated, the temperature is rapidly cooled to 100℃ at a cooling rate of 20℃ / s to release the pressure. Finally, the filter cotton is obtained by hot air shaping, winding and cutting.

[0124] After the filter cotton was prepared according to the preparation process of Examples 1-3, the filter cotton was tested for filtration performance and high temperature resistance.

[0125] The filtration performance test method was based on ISO 11057:2011 Air quality—Test methods for filtration properties of washable filter media—using an AFT-1000 dust holding capacity tester, with ISO A2 fine dust (d) as the standard. 50 =8μm) was loaded with dust, maintaining a concentration of 200±20 mg / m³ and a constant airflow of 2.0 m / s. The resistance increase was monitored in real time, and the process was terminated when the pressure difference reached twice the initial value or the 500 Pa threshold. The accumulated dust mass was weighed and the dust holding capacity per unit area (g / m²) was calculated.

[0126] The high-temperature resistance test method is GB / T 3923.1-2013 Textiles - Tensile Properties of Fabrics, using the Instron 6800 high-temperature tensile system. Filter cotton was cut into samples (50×200mm). The breaking strength reference value was first measured at 25℃, followed by a constant temperature of 300℃ in an environmental chamber for 30 minutes. The samples were then stretched at a rate of 100mm / min until fracture, and the high-temperature breaking strength was recorded. The strength retention rate was calculated (strength retention rate = high-temperature breaking strength / breaking strength reference value × 100%). The dust holding capacity per unit area and strength retention rate measured by the above test method are recorded in Table 1.

[0127] Table 1. Dust holding capacity and strength retention rate of the filter cotton prepared in Examples 1-3

[0128]

[0129] As shown in Table 1, the dust holding capacity per unit area of ​​the filter cotton prepared in Examples 1-3 is all higher than 816 g / m², and the strength retention rate is all higher than 87%, indicating that the heat-resistant filter cotton for high-temperature ovens provided by the present invention and the filter cotton produced by its preparation process have good filtration performance and high-temperature resistance.

[0130] In this invention, silicon carbide fiber is first used as the core of a high-temperature skeleton. Its surface is modified by fluoroethylene carbonate at high temperature under nitrogen protection to generate a Si-F bond ceramic passivation layer with super oxidation resistance. Then, it is combined with plasma-activated polytetrafluoroethylene fiber to construct a chemical barrier resistant to acids, alkalis and solvents. At the same time, the organosilicon resin is dehydrated and crosslinked by 2,2-dimethylolpropionic acid to form a three-dimensional heat-resistant network skeleton. Secondly, ammonium bicarbonate pore-forming agent is introduced and decomposed during the hot pressing stage to generate through-pores. Phenyl modified silicone oil is used to lubricate the fiber to reduce processing damage, and the fiber nodes are temporarily fixed by the melting of the adhesive.

[0131] It is worth noting that under high-temperature oven conditions (250-300℃), the molten flow of polytetrafluoroethylene fibers encapsulates silicon carbide fibers to form a "sheath-core" sealed structure, which can block the penetration of corrosive media. The decomposition products of fluoroethylene carbonate react with the surface of silicon carbide fibers to generate a nanocomposite layer. Its micro-nano rough interface can induce airflow turbulence, and the micropores can extend the airflow path, further improving the diffusion and capture efficiency of submicron particles. In addition, surface turbulence can enhance the inertial collision of particles and form local vortices in the channels, significantly increasing the dust holding capacity. Furthermore, the cross-linked network of organosilicon and 2,2-dimethylolpropionic acid continues to condense at 280℃, dynamically repairing cracks caused by thermal stress. This allows the filter cotton to maintain high interlayer peel strength after thermal cycling under high-temperature oven conditions, thereby improving the high-temperature resistance of the filter cotton while ensuring filtration performance.

[0132] Example 4

[0133] In this invention, silicon carbide fiber is used as a heat-resistant skeleton to provide rigid support. During the preparation process, fluoroethylene carbonate is used as a surface passivating agent, which decomposes at 260°C under nitrogen protection to release active fluorine free radicals. The active fluorine free radicals react with the surface of silicon carbide fiber to form a Si-F bonded ceramic layer, ultimately forming a dense Si-FOC composite passivation layer. The specific process is as follows:

[0134]

[0135]

[0136]

[0137]

[0138] In the formula, It is fluoroethylene carbonate. It is an active fluorine radical. It is carbon monoxide. It is ethylene oxide. It is made of silicon carbide fiber. It is silicon tetrafluoride. It is carbon. For water, It is silicon dioxide. It is hydrogen fluoride. The methane is used in the preparation process. Fluoroethylene carbonate is decomposed at high temperature under nitrogen protection to obtain ethylene oxide, carbon monoxide, and active fluorine radicals. The active fluorine radicals combine with the surface of silicon carbide fibers to generate silicon tetrafluoride and carbon. Silicon tetrafluoride then undergoes surface hydrolysis to produce silicon dioxide and hydrogen fluoride. Hydrogen fluoride is then used to combine with the surface of silicon carbide fibers to generate silicon tetrafluoride and methane. Through cyclic strengthening, a dense Si-FOC composite passivation layer is finally formed. The Si-F bond energy is higher than that of the Si-O bond, which can inhibit silicon dioxide growth and reduce the oxidation rate in an oxygen-containing environment at 300℃. Furthermore, the carbonaceous deposits generated by the cracking of fluoroethylene carbonate can fill the defects on the fiber surface and form a "ceramic-carbon" composite barrier with silicon carbide, thereby improving the strength retention rate in corrosive environments.

[0139] First, to prove that silicon carbide fiber is one of the important components of the preparation process provided by this invention that can produce filter cotton with good filtration performance and high temperature resistance, this embodiment is based on the above embodiment 2, except that the silicon carbide fiber is replaced with polyester fiber or polypropylene fiber, and then the filter cotton is prepared. Then, the filtration performance and high temperature resistance of the filter cotton are tested according to the test method provided in the above embodiment, and the test values ​​are recorded in Table 2.

[0140] Table 2 Comparison of filtration performance and high-temperature resistance of filter cotton with different compositions

[0141]

[0142] As shown in Table 2, when silicon carbide fibers in the filter cotton are replaced with polyester fibers or polypropylene fibers, the dust holding capacity per unit area and the strength retention rate of the filter cotton decrease significantly. That is, the filtration performance and high temperature resistance of the filter cotton are reduced. Therefore, it can be shown that silicon carbide fiber is one of the important components that enable the preparation process provided by this invention to produce filter cotton with good filtration performance and high temperature resistance.

[0143] Secondly, to demonstrate that the fluoroethylene carbonate component and its 3-5% mass percentage in the filter cotton are key factors in the preparation process provided by this invention, enabling the production of filter cotton with good filtration performance and high-temperature resistance, this embodiment, based on Example 2 above, sets the mass percentage of fluoroethylene carbonate in the filter cotton to 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, or 8%, and then prepares the filter cotton. The filtration performance and high-temperature resistance of the filter cotton are tested according to the testing methods provided in the above embodiments. The test results are as follows: Figure 2 , Figure 3 As shown.

[0144] according to Figure 2 It can be seen that when the mass percentage of fluoroethylene carbonate in the filter cotton is 0%, 1%, 2%, 6%, 7% or 8%, that is, not 3-5%, the dust holding capacity per unit area of ​​the filter cotton is significantly lower than that when the mass percentage of fluoroethylene carbonate in the filter cotton is 3-5%.

[0145] according to Figure 3 It can be seen that when the mass percentage of fluoroethylene carbonate in the filter cotton is 0%, 1%, 2%, 6%, 7% or 8%, that is, not 3-5%, the strength retention rate of the filter cotton is significantly lower than the strength retention rate when the mass percentage of fluoroethylene carbonate in the filter cotton is 3-5%.

[0146] In summary, it can be seen that the fluoroethylene carbonate component and the 3-5% mass percentage of fluoroethylene carbonate in the filter cotton are important factors in the preparation process provided by this invention, which can produce filter cotton with good filtration performance and high temperature resistance.

[0147] Example 5

[0148] The filter cotton is prepared according to the method provided in the above embodiments, and then tested according to the test methods for filtration performance and high temperature resistance provided in the above embodiments.

[0149] Experiments have shown that, under the conditions of this embodiment, the prepared filter cotton has good filtration performance and high temperature resistance, indicating that the filter cotton provided by this invention can be used in high-temperature oven environments.

[0150] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A process for the preparation of heat resistant filter cotton for high temperature ovens, characterized in that, The method comprises the following steps: Step S1: Take polytetrafluoroethylene fiber 20-25%, fluoroethylene carbonate 3-5%, silicone resin 8-10%, 2,2-dihydroxy methyl propionic acid 2-3%, oil agent 1-2%, pore-forming agent 4-6%, adhesive 5-8%, and the rest is silicon carbide fiber according to mass ratio; Pretreat the silicon carbide fiber, polytetrafluoroethylene fiber and pore-forming agent, and prepare the fluoroethylene carbonate into a treatment solution; Step S2: Put the above-mentioned silicon carbide fiber, polytetrafluoroethylene fiber and pore-forming agent into a mixing machine for dry mixing treatment, then transfer to a double screw mixing machine, and spray silicone resin, 2,2-dihydroxy methyl propionic acid and adhesive for wet mixing treatment; Then spray the treatment solution into the double screw mixing machine, continue to mix for 5 minutes, then extrude and cut to obtain composite particles; Step S3: Feed the composite particles into a double screw extruder, melt and plasticize, then extrude through a spinneret to obtain primary fibers, quench and solidify the primary fibers by a side blowing system, then wind and output the composite fibers; Open the composite fibers by a zigzag roller, then deposit on a cotton coagulation curtain, cooperate with negative pressure adsorption under the net to make the fibers vertically oriented, cross-lay 6-10 layers to form a fluffy fiber web, then form a solid structure by pre-needling treatment; Step S4: Put the fiber web into a double belt hot press, heat to 80℃ and apply a pressure of 0.1 MPa until the pore-forming agent is decomposed by heat, then increase the temperature to 150℃ and the pressure to 0.3 MPa to make the adhesive melt and flow; Then heat to 280℃ and apply a pressure of 0.6 MPa for hot pressing, quench to 100℃ after hot pressing to release the pressure, finally, heat the wind to shape, wind, cut to obtain filter cotton.

2. The process for the preparation of heat resistant filter cotton for high temperature ovens as claimed in claim 1, wherein: In the step S1, the silicon carbide fiber is a continuous fiber formed by coating silicon carbide on a carbon fiber core.

3. The process for the preparation of heat resistant filter cotton for high temperature ovens as claimed in claim 1 wherein: In the step S1, the oil agent is phenyl modified silicone oil, the pore-forming agent is ammonium bicarbonate, and the adhesive is polyimide precursor.

4. The process for the preparation of heat resistant filter cotton for high temperature ovens as claimed in claim 1 wherein: In the step S1, the pretreatment is to immerse the silicon carbide fiber in the oil agent, then dry at 50-70℃ for 30 minutes; The polytetrafluoroethylene fiber is opened and treated by plasma; Grind the pore-forming agent to a particle size of ≤10 μm; Prepare the fluoroethylene carbonate into a treatment solution, immerse the silicon carbide fiber treated above in the treatment solution for 20-40 seconds, then pre-dry at 70-90℃ for 5 minutes, and then treat at 260℃ for 10-30 minutes under nitrogen protection; The treatment solution is prepared by mixing fluoroethylene carbonate and anhydrous ethanol, and the volume ratio of fluoroethylene carbonate to anhydrous ethanol in the treatment solution is 1:

20.

5. The process for the preparation of heat resistant filter cotton for high temperature ovens as claimed in claim 1 wherein: In the step S2, the rotating speed of the mixing machine is 150-250 rpm during dry mixing treatment, and the mixing time is 8-12 minutes; The rotating speed of the double screw mixing machine is 110-180 rpm during wet mixing treatment, and the mixing time is 10-20 minutes.

6. The process for the preparation of heat resistant filter cotton for high temperature ovens as claimed in claim 1 wherein: In the step S2, the composite particles are obtained by extruding and cutting through a double screw extrusion granulator, and the diameter of the composite particles is 1.3-1.7 mm.

7. The process for the preparation of heat resistant filter cotton for high temperature ovens as claimed in claim 1 wherein: In the step S3, the composite particles are dried and pretreated, and then fed into a double-screw extruder, melted and plasticized at 250-300 DEG C in the feeding area, and then transported to the spinneret fluidization, and then extruded through the spinneret to obtain the primary fibers; The drying pretreatment is hot air drying the composite particles at 70-90 DEG C for 1-3 hours; The length-diameter ratio of the spinneret is 5:1, and the pore size is 0.10-0.25 mm.

8. The process for the preparation of heat resistant filter cotton for high temperature ovens as claimed in claim 1 wherein: In the step S3, the pre-needling treatment is pre-needling the fiber web with the hook-tooth needle, and eliminating static electricity with the ion wind stick to make the fibers entangle and form a consolidated structure. The surface of the needle is coated with a molybdenum disulfide lubricating layer during pre-needling, and the needle depth is 3.5-4.5 mm, and the puncture is 300-500 punctures / cm2.

9. The process for the preparation of heat resistant filter cotton for high temperature ovens as claimed in claim 1 wherein: In the step S4, the cooling rate after the hot pressing is terminated is 10-20 DEG C / s.

10. The heat-resistant filter cotton for high-temperature ovens, prepared according to the process of any one of claims 1-9, characterized in that, The following raw materials are included: Silicon carbide fibers, polytetrafluoroethylene fibers, fluoroethylene carbonate, silicone resin, 2,2-dimethylol propionic acid, oil agent, pore-forming agent, adhesive; wherein: The silicon carbide fibers serve as a temperature-resistant framework core, and their surfaces are infiltrated with an oil agent and high-temperature fluorinated with fluoroethylene carbonate to form a Si-F bond ceramic passivation layer, block the oxygen diffusion channel, and inhibit high-temperature oxidation and acid erosion; the polytetrafluoroethylene fibers melt and wrap the silicon carbide fibers to form a "sheath-core sealing structure" to isolate the penetration of corrosive media; the fluoroethylene carbonate is used to release fluorine radicals to react with the silicon carbide fibers to form a Si-F-O-C composite layer, and the polytetrafluoroethylene is used to enhance the anti-creep performance; The silicone resin is dehydrated and condensed under the catalysis of 2,2-dimethylol propionic acid to form a three-dimensional cross-linked network, and the interlayer dynamic repair ability is given; The pore-forming agent is used to generate through channels to extend the airflow path and improve the dust holding capacity; the adhesive is used to melt and temporarily fix the fiber nodes, and form a heat-resistant permanent bonding phase through closed-loop imidization.

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