Efficient polytetrafluoroethylene filter material and preparation method thereof

Abstract

The invention discloses a high-efficiency polytetrafluoroethylene filter material and a preparation method thereof, and relates to the technical field of filter materials, and the preparation method comprises the following steps: taking a polytetrafluoroethylene base band, and carrying out three-direction stretching to obtain an ePTFE layer; and placing the ePTFE layer on the non-woven fabric layer, and carrying out stacking, compounding and heat setting to obtain the filter material. On the basis of transverse and longitudinal two-way stretching, the olive-shaped rollers are adopted to carry out upward or downward arc stretching on the middle part of the polytetrafluoroethylene base band, and opposite stress is applied to two sides, so that the thickness of the middle part of the polytetrafluoroethylene base band is smaller than that of the two sides, and compensation for transverse expanding stretching is formed; the polytetrafluoroethylene base band is fully stretched, generation of nodes is reduced, the fibration degree of the film is improved, the pore shape tends to be complicated, pores in the ePTFE layer generate a more three-dimensional space structure, and the pore performance and strength are optimized, so that the filtering efficiency and mechanical strength of the prepared filtering material are improved.

Description

Technical Field

[0001] The invention relates to the technical field of filter materials, in particular to a high-efficiency polytetrafluoroethylene filter material and a preparation method thereof. Background Art

[0002] Due to the particularity of its molecular structure, polytetrafluoroethylene has excellent chemical stability, resistance to strong acids, strong alkalis and a variety of chemical reagents, and has a wide range of temperature resistance, making the prepared polytetrafluoroethylene stretched film an ideal material for preparing high-performance microporous membranes, and is widely used in air filtration, liquid filtration, textiles and clothing, construction, electronic communications, medical treatment, chemical environmental protection and other fields. With the improvement of scientific and technological levels, people's demand for the filtration efficiency of filter materials is also getting higher and higher. Effective air filtration is the basis for ensuring the removal of air impurities, reducing equipment wear, corrosion, and failure caused by impurities, reducing gas flow resistance, reducing equipment energy consumption, and improving the air environment. The polytetrafluoroethylene membrane material used in general filter materials is a microporous membrane formed by calendering, extrusion, and biaxial stretching. It has evenly distributed tiny pores and provides good porosity and air permeability. In traditional biaxial stretching, the film is affected by tensile stress, process temperature and its distribution during transverse stretching, and there is insufficient stretching and uneven film thickness, which will cause the generation of nodes, which will affect the filtration efficiency of polytetrafluoroethylene filter materials. Therefore, we propose a high-efficiency polytetrafluoroethylene filter material and a preparation method thereof. Summary of the invention

[0003] The object of the present invention is to provide a high-efficiency polytetrafluoroethylene filter material and a preparation method thereof to solve the problems raised in the above background technology.

[0004] In order to solve the above technical problems, the present invention provides the following technical solutions: a high-efficiency polytetrafluoroethylene filter material, comprising a stacked ePTFE layer and a non-woven fabric layer, wherein the ePTFE layer is located in the inner layer of the non-woven fabric layer.

[0005] Furthermore, the non-woven fabric layer is one of a needle-punched non-woven fabric and a melt-blown non-woven fabric; The fiber material is a mixture of one or more of polyphenylene sulfide, polytetrafluoroethylene, glass fiber, polyester and polypropylene.

[0006] Furthermore, the thickness of the ePTFE layer is 10 to 180 μm.

[0007] In the above technical solution, the ePTFE layer has many fine fibrils and a microporous structure formed by nodes connected to each other by the fibrils, forming a porous structure with continuous porosity. While retaining the good high and low temperature resistance, low friction, non-stick properties, mechanical properties and chemical stability of polytetrafluoroethylene, it gives it softness, fluid permeability, fine particle capture, filtration and other characteristics, which can intercept fine particles and deposit them on the surface of the filter material to achieve efficient filtration.

[0008] Furthermore, the ePTFE layer is obtained by triaxially stretching a polytetrafluoroethylene tape.

[0009] Further, the polytetrafluoroethylene-based tape includes components of polytetrafluoroethylene resin and an extrusion aid; The extrusion aid is one of white oil, aviation kerosene, degreased kerosene, synthetic alkane and liquid paraffin, and the added amount is 30% to 40% of the mass of the polytetrafluoroethylene resin.

[0010] A method for preparing a high-efficiency polytetrafluoroethylene filter material comprises the following processes: The ePTFE layer and the non-woven fabric layer are stacked, compounded, and heat-set to obtain a filter material.

[0011] Furthermore, the composite process conditions are: composite temperature 150-230° C., composite pressure 0.5-2.0 MPa, composite roller speed 0.5-5.0 m / min.

[0012] Furthermore, the process conditions of the heat setting are: temperature 50-150° C., roller speed 0.5-2.5 m / min.

[0013] Furthermore, before use, the side of the ePTFE layer in contact with the non-woven fabric layer is preheated and ionized.

[0014] Furthermore, the preheating process conditions are: temperature 85-135° C., time 10-23 min.

[0015] Furthermore, the process conditions of the ionization are: ion air volume 1-10m 3 / min, duration 1 to 15 minutes.

[0016] Further, the ePTFE layer is prepared by the following process: The polytetrafluoroethylene resin and the extrusion aid are mixed, pre-pressed and calendered to obtain a polytetrafluoroethylene tape; and three-axis stretching is performed to obtain an ePTFE layer.

[0017] Furthermore, the process conditions of pre-pressing are: pressure 16-22 MPa, duration 120-150 s; The calendering process conditions are: heating temperature 50-70°C, roller speed 0.05-5m / min, and die diameter 16-22mm.

[0018] Further, the process conditions of triaxial stretching are: Longitudinal stretching: temperature 220-320°C, stretching ratio 5-9; Up and down stretching: temperature 300-400°C, α angle 10-60°; Transverse stretching: temperature 120-260°C, stretching ratio 5-10; After three-way stretching, heat setting is performed at a temperature of 230-320°C to stabilize the structure formed during the stretching process and improve the mechanical properties of the ePTFE layer membrane.

[0019] In the above technical scheme, on the basis of bidirectional stretching in the transverse and longitudinal directions, an olive-shaped roller is used to perform arc stretching on the middle part of the polytetrafluoroethylene-based tape in an upward or downward arc shape, and opposite stresses are applied to the two sides, so that the middle thickness of the polytetrafluoroethylene-based tape is smaller than the thickness on both sides, thereby forming compensation for the transverse expansion stretching. In the subsequent transverse stretching process, it can promote the complete stretching of the polytetrafluoroethylene-based tape, reduce the generation of nodes, improve the fiberization degree of the film, and make the pore shape more complicated. The pores in the ePTFE layer produce a more three-dimensional spatial structure, and the pore performance and strength are optimized, thereby improving the filtration efficiency and mechanical strength of the prepared filter material.

[0020] Furthermore, the polytetrafluoroethylene-based tape is surface treated before the triaxial stretching, and the specific process is as follows: The polyurethane and polyethersulfone are mixed in a solvent, and an additive is added to obtain a membrane-making solution; The film-forming liquid is applied to the surface of the polytetrafluoroethylene-based tape and cured to form a modified layer, thereby obtaining a composite base tape.

[0021] Further, the additives are polyethylene glycol, fluorine-containing monomers and photoinitiators; The polyethylene glycol is one of PEG600 and PEG700 or a mixture of the two; The fluorinated monomer is a perfluoroacrylate compound, specifically a mixture of one or more of perfluorohexylethyl methacrylate (CAS: 2144-53-8), perfluorooctylethyl methacrylate (CAS: 1996-88-9), 2-(N-ethylperfluorooctanesulfonamide)ethyl acrylate (CAS: 423-82-5), 2-acrylic acid-2-[butyl[(heptadecafluorooctyl)-sulfonyl]-amino]-ethyl ester (CAS: 383-07-3), and 1,6-di(acryloyloxy)-2,2,3,3,4,4,5,5-octafluorohexane (CAS: 2264-01-9); The solvent is N,N-dimethylformamide.

[0022] Further, the film-making solution includes the following components by mass: 1 to 3 parts of polyurethane, 7 to 9 parts of polyethersulfone, 0.2 to 0.6 parts of polyethylene glycol, 6.5 to 8.8 parts of fluorine-containing monomer, 0.2 to 0.5 parts of photoinitiator and 58.2 to 83.3 parts of solvent; The photoinitiator includes a mixture of one or more of the photoinitiator MBF, the photoinitiator 184, and the photoinitiator XBPO.

[0023] Furthermore, the coating thickness is 10 to 100 μm.

[0024] Furthermore, the curing process conditions are: 60 to 180 seconds of anaerobic excimer lamp irradiation and 5 to 15 minutes of ultraviolet irradiation; After curing, soak it in deionized water for 12 hours to remove residual solvent and dry it.

[0025] In the above technical scheme, polyurethane and polyethersulfone are mixed with a film-making liquid, and are arranged on the surface of a polytetrafluoroethylene-based tape. After curing, a composite film layer of polyethersulfone / polyurethane is formed, which is recorded as a modified layer. In the modified layer system, polyurethane and polyethersulfone have phase separation characteristics. Under the irradiation of an anaerobic (nitrogen) excimer lamp, the double bonds in the system undergo polymerization, and the fluorine-containing structure migrates to the surface. Due to the different shrinkage ratios between the materials, uneven shrinkage occurs, and the modified layer produces a stress difference in the thickness direction, forming a thickness gradient and wrinkling. Then, ultraviolet irradiation is performed to cure the film-making liquid as a whole to form a modified layer with wrinkles.

[0026] The modified layer is compounded with the polytetrafluoroethylene-based tape and stretched in three directions together. While the polytetrafluoroethylene-based tape forms a three-dimensional pore structure, the modified layer and the polytetrafluoroethylene-based tape are mechanically interlocked under the influence of the upper and lower stretching processes, and the interface between the two is more tightly bonded; the surface wrinkles of the modified layer and the interlocking structure between the modified layer and the polytetrafluoroethylene-based interface are fibrotic under the influence of the lateral expansion stretching, which further promotes the establishment of a three-dimensional spatial pore structure on the surface of the ePTFE layer (modified layer and its interface), and its surface pore shape is more complex, and the pore performance is further optimized, which can promote the ePTFE layer to effectively block, intercept, capture, and adsorb fine particles, and achieve more efficient filtration. The surface roughness of the ePTFE layer increases, the specific surface area increases, and the probability of fine particles colliding with the ePTFE layer and being captured increases, further improving the filtration efficiency of the filter material; and avoiding the direct impact of fine particles on the ePTFE layer, improving the impact of fine particle scouring on the ePTFE layer, and improving the wear resistance of the ePTFE layer.

[0027] Polyethersulfone has good high temperature stability, chemical resistance and mechanical strength; polyurethane has good elasticity, flexibility and wear resistance. The combination of the two on the surface of polytetrafluoroethylene helps to improve the wear resistance and mechanical properties of the filter material, increase the erosion resistance of fine particles, and improve its wear resistance and durability. The polyethylene glycol in the membrane-making liquid system can play a pore-forming role, forming cavities, which promotes the formation of pores in the modified layer. The fluorine-containing monomer is a perfluoroacrylate compound that can play a surfactant role, significantly reduce its surface tension, and dust is less likely to adhere to its surface, thereby enhancing the dust-proof performance of the filter material; at the same time, it can participate in the polymerization in the membrane-making liquid system, improve the water resistance, heat resistance, chemical stability and mechanical properties of the modified layer, and enhance the interface bonding ability between the modified layer and the polytetrafluoroethylene-based tape.

[0028] The setting of the modified layer and its combination with the polytetrafluoroethylene layer to form a composite base belt, and the microporous layer (the surface layer of the ePTFE layer) prepared after triaxial stretching, can be used as a buffer and dust-holding functional layer. It can intercept, deposit and filter particles in the air, alleviate the intensity of air vortex, and reduce the pressure loss of the ePTFE layer. The mechanical strength, stability, wear resistance and filtration efficiency of the filter material are enhanced, and its durability and service life are improved.

[0029] Furthermore, the polyurethane is an unsaturated polyurethane, which is specifically prepared by the following process: Mix diisocyanate and hexafluorobisphenol A, add a catalyst, and under the protection of a nitrogen atmosphere, heat up to 40-60°C and react for 100-150 minutes; add a polyol, heat up to 60-70°C, and react for 100-150 minutes; add a chain extender, heat up to 80-85°C and react for 100-150 minutes; add an inhibitor and hydroxy acrylate, cool down to 60-65°C, react until the acid value is below 30 mg / KOH, cool down to 40-45°C, add triethylamine, stir and react for 20-30 minutes to obtain an unsaturated polyurethane.

[0030] Furthermore, the unsaturated polyurethane includes the following components by mass: 27 to 44 parts of diisocyanate, 20 to 33 parts of hexafluorobisphenol A, 20 to 30 parts of polyol, 0.05 to 0.5 parts of catalyst, 1.6 to 4.0 parts of chain extender, 0.002 to 0.03 parts of inhibitor, 1.8 to 3.0 parts of hydroxy acrylate, and 1.2 to 4.5 parts of triethylamine.

[0031] Furthermore, the polyol is a mixture of one or more of polyethylene glycol, polytetramethylene glycol, polypropylene glycol, and polypropylene oxide glycol; The diisocyanate is a mixture of one or more of isophorone diisocyanate, toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, 1,4-cyclohexane diisocyanate and dicyclohexylmethane diisocyanate; The chain extender is a mixture of one or more of 2,2-dimethylol propionic acid, hexafluorobisphenol A, resorcinol diglycidyl ether, 1,4-bis(2-hydroxyethoxy)benzene, and 4,4'-diaminobiphenyl sulfone; The hydroxy acrylate is a mixture of one or more of hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, trimethylolpropane diacrylate, trimethylolpropane triacrylate, and pentaerythritol triacrylate; The catalyst is one of dibutyltin dilaurate and dibutyltin dioctoate; The inhibitor is hydroquinone.

[0032] In the above technical solution, the modulus of the unsaturated polyurethane prepared by using bisphenol A is closer to that of polyethersulfone, and the blending dispersion of the two is improved, which improves the uniformity between the materials and helps to improve the stability and durability of the modified layer.

[0033] Furthermore, the polyethersulfone is an unsaturated polyethersulfone, which is specifically prepared by the following process: Chloromethyl polyether sulfone, 2-allyl phenol, potassium carbonate and toluene are mixed in N,N-dimethylformamide, heated to 145-153°C, and refluxed for 4-6 hours; precipitated in deionized water, washed and dried to obtain unsaturated polyether amine.

[0034] Furthermore, the unsaturated polyetheramine is prepared from the following components by mass: 10 parts of chloromethyl polyether sulfone, 0.5-0.6 parts of 2-allyl phenol, 0.38-0.55 parts of potassium carbonate, 5-8 parts of toluene, and 50-100 parts of N,N-dimethylformamide.

[0035] In the above technical scheme, polyethersulfone has a chlorine end group, which can react with the hydroxyl group in 2-allylphenol. Under alkaline solvent conditions, the double bond isomerizes to obtain propylene-terminated polyethersulfone, which is recorded as unsaturated polyethersulfone. The conjugated structure of the double bond and the benzene ring can significantly improve its reaction activity under light irradiation, which helps the unsaturated polyethersulfone to participate in the polymerization and reaction of unsaturated polyurethane and fluorine-containing monomers (perfluoroacrylate compounds) to form an interpenetrating network, which can prolong phase separation and promote the formation of sponge-like structure, avoid the generation of obvious phase interface microporous structure, and the initial shape of the pores is easier to remember. The micropores can return to their initial state, which is beneficial to the comprehensive improvement of the performance of polyurethane, polyethersulfone composite system and ePTFE layer.

[0036] Furthermore, before coating the membrane-making solution, the polytetrafluoroethylene-based tape is subjected to ionization treatment to improve the interface bonding performance between the modified polytetrafluoroethylene-based tape and the polytetrafluoroethylene-based tape. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] In the following specific implementations, The non-woven fabric layer is PET dry-laid non-woven fabric, model 2024, weight 71g / m2, thickness 0.31mm, from Suzhou Youkefa New Material Technology Co., Ltd. Polytetrafluoroethylene resin: F-201, from Daikin Corporation of Japan; Extrusion aid: ExxonMobil ISOPAR H; Polyethylene glycol: PEG600, PEG700, PEG1000, from Shanghai MacLean Biochemical Technology Co., Ltd.; Chloromethyl polyether sulfone: dissolve polyether sulfone in N-methylpyrrolidone (15g / 100mL), add 1,4-dichloromethoxybutane (3 times the mass of polyether amine) and zinc chloride (6.5% of the mass of polyether amine), heat to 90°C, react for 6h; wash and dry to obtain; The photoinitiator is a mixture of photoinitiator MBF, photoinitiator 184, and photoinitiator XBPO, with a mass ratio of 2:2:1; Before using the ePTFE layer, the side in contact with the non-woven fabric layer was preheated and ionized. The preheating process conditions were: temperature 110°C, duration 15 minutes, and the ionization process conditions were: ion air volume 5.0m 3 / min, duration 6min; before coating the film-making solution, the side of the polytetrafluoroethylene-based tape to be coated was ionized, and the ionization process conditions were: ion air volume 8m 3 / min, duration 10min; Polyurethane: 1180, from Tianjin Daqiuzhuang Foam Plastic Co., Ltd.; Polyethersulfone: Mw=58000, from BASF Chemical Company.

[0039] Embodiment 1: A method for preparing a high-efficiency polytetrafluoroethylene filter material, comprising the following process: Step 1: Preparation of membrane solution: 1.1. Mix diisocyanate and hexafluorobisphenol A, add catalyst dibutyltin dilaurate, and heat to 40℃ under nitrogen atmosphere for 150min; add polyol, heat to 60℃, and react for 150min; add chain extender, heat to 80℃ and react for 150min; add inhibitor hydroquinone and hydroxy acrylate, cool to 60℃, react until the acid value is below 30mg / KOH, cool to 40℃, add triethylamine, stir and react. The reaction mixture was stirred for 25 minutes to obtain an unsaturated polyurethane. The unsaturated polyurethane comprises the following components by weight: 27 parts of diisocyanate, 20 parts of hexafluorobisphenol A, 20 parts of polyol, 0.05 parts of catalyst, 1.6 parts of chain extender, 0.002 parts of polymerization inhibitor, 1.8 parts of hydroxy acrylate, and 4.5 parts of triethylamine. The polyol is PEG1000. The diisocyanate is isophorone diisocyanate. The chain extender is 2,2-dihydroxymethyl propionic acid. The hydroxy acrylate is hydroxyethyl acrylate. 1.2. Chloromethyl polyether sulfone, 2-allyl phenol, potassium carbonate and toluene are mixed in N,N-dimethylformamide, heated to 145°C, and refluxed for 6 hours; precipitated in deionized water, washed, and dried to obtain unsaturated polyether amine; the unsaturated polyether amine is prepared from the following components by mass: 10 parts of chloromethyl polyether sulfone, 0.5 parts of 2-allyl phenol, 0.38 parts of potassium carbonate, 5 parts of toluene, and 50 parts of N,N-dimethylformamide; 1.3. Unsaturated polyurethane and unsaturated polyethersulfone are mixed in N,N-dimethylformamide, and polyethylene glycol, fluorine-containing monomer and photoinitiator are added to obtain a film-making solution; the film-making solution includes the following components by mass: 1 part of polyurethane, 9 parts of polyethersulfone, 0.2 parts of polyethylene glycol, 6.5 parts of fluorine-containing monomer, 0.2 parts of photoinitiator and 58.2 parts of N,N-dimethylformamide; polyethylene glycol is PEG600; the fluorine-containing monomer is perfluorohexylethyl methacrylate; Step 2: Preparation of ePTFE layer The polytetrafluoroethylene resin and the extrusion aid are mixed, pre-pressed and calendered. The process conditions of the pre-pressed molding are: pressure 16MPa, duration 150s; the process conditions of calendering are: heating temperature 50°C, roller speed 0.5m / min, die diameter 16mm, to obtain a polytetrafluoroethylene tape; The film-making liquid was coated on the surface of the polytetrafluoroethylene-based tape with a coating thickness of 10 μm, and cured under the following process conditions: irradiation with an oxygen-free excimer lamp for 60 seconds and ultraviolet irradiation for 5 minutes; after curing, the film was immersed in deionized water for 12 hours, residual solvent was removed, and the film was dried to form a modified layer, thereby obtaining a composite base tape; The process conditions of three-axis stretching are as follows: longitudinal stretching: temperature 270°C, stretching ratio 9; vertical stretching: temperature 300°C, α angle 10°; transverse stretching: temperature 150°C, stretching ratio 5; after three-axis stretching, heat setting is performed at 230°C to obtain an ePTFE layer; Step 3: Preparation of filter material: The ePTFE layer and the non-woven fabric layer are stacked and compounded under the following process conditions: compounding temperature of 150°C, compounding pressure of 2.0 MPa, and compounding roller speed of 0.5 m / min; and heat setting under the following process conditions: temperature of 50°C and roller speed of 0.5 m / min, to obtain a filter material.

[0040] Embodiment 2: A method for preparing a high-efficiency polytetrafluoroethylene filter material, comprising the following process: Step 1: Preparation of membrane solution: 1.1. Mix diisocyanate and hexafluorobisphenol A, add catalyst dibutyltin dilaurate, and heat to 50°C under nitrogen atmosphere for 120 min; add polyol, heat to 65°C, and react for 120 min; add chain extender, heat to 82°C, and react for 120 min; add inhibitor hydroquinone and hydroxy acrylate, cool to 62°C, react until the acid value is below 30 mg / KOH, cool to 42°C, add triethylamine, and stir for 20 min to obtain Unsaturated polyurethane; the unsaturated polyurethane comprises the following components by mass: 36 parts of diisocyanate, 27 parts of hexafluorobisphenol A, 25 parts of polyol, 0.3 parts of catalyst, 2.8 parts of chain extender, 0.02 parts of polymerization inhibitor, 2.4 parts of hydroxy acrylate, and 1.2 parts of triethylamine; the polyol is polypropylene oxide diol; the diisocyanate is dicyclohexylmethane diisocyanate; the chain extender is a mixture of 2,2-dihydroxymethylpropionic acid and hexafluorobisphenol A in equal mass; the hydroxy acrylate is trimethylolpropane triacrylate; 1.2. Chloromethyl polyether sulfone, 2-allyl phenol, potassium carbonate and toluene are mixed in N,N-dimethylformamide, heated to 149°C, and refluxed for 5 hours; precipitated in deionized water, washed, and dried to obtain unsaturated polyether amine; the unsaturated polyether amine is prepared from the following components by mass: 10 parts of chloromethyl polyether sulfone, 0.55 parts of 2-allyl phenol, 0.47 parts of potassium carbonate, 7 parts of toluene, and 75 parts of N,N-dimethylformamide; 1.3. Unsaturated polyurethane and unsaturated polyethersulfone are mixed in N,N-dimethylformamide, and polyethylene glycol, fluorine-containing monomer and photoinitiator are added to obtain a film-forming solution; the film-forming solution includes the following components by weight: 2 parts of polyurethane, 8 parts of polyethersulfone, 0.4 parts of polyethylene glycol, 7.7 parts of fluorine-containing monomer, 0.4 parts of photoinitiator and 70.8 parts of N,N-dimethylformamide; the polyethylene glycol is PEG600; the fluorine-containing monomer is a mixture of perfluorohexylethyl methacrylate, perfluorooctylethyl methacrylate and 1,6-di(acryloyloxy)-2,2,3,3,4,4,5,5-octafluorohexane in equal weight; Step 2: Preparation of ePTFE layer The polytetrafluoroethylene resin and the extrusion aid are mixed, pre-pressed and calendered. The process conditions of the pre-pressed molding are: pressure 19 MPa, time 135 s; the process conditions of the calendering are: heating temperature 60°C, roller speed 1.0 m / min, die diameter 20 mm, to obtain a polytetrafluoroethylene tape; The film-making liquid is coated on the surface of the polytetrafluoroethylene-based tape with a coating thickness of 30 μm, and cured under the following process conditions: irradiation with an oxygen-free excimer lamp for 90 seconds and ultraviolet irradiation for 10 minutes; after curing, the film is immersed in deionized water for 12 hours, residual solvent is removed, and the film is dried to form a modified layer, thereby obtaining a composite base tape; Three-axis stretching, the process conditions are: longitudinal stretching: temperature 260°C, stretching ratio 7; up and down stretching: temperature 350°C, α angle 30°; transverse stretching: temperature 180°C, stretching ratio 8; after three-axis stretching, heat setting is performed at a temperature of 250°C to obtain an ePTFE layer; Step 3: Preparation of filter material: The ePTFE layer and the non-woven fabric layer were stacked and compounded under the following process conditions: compounding temperature of 180°C, compounding pressure of 1.0 MPa, and compounding roller speed of 2.0 m / min; and heat setting under the following process conditions: temperature of 100°C, and roller speed of 1.5 m / min, to obtain a filter material.

[0041] Embodiment 3: A method for preparing a high-efficiency polytetrafluoroethylene filter material, comprising the following process: Step 1: Preparation of membrane solution: 1.1. Mix diisocyanate and hexafluorobisphenol A, add catalyst dibutyltin dilaurate, and heat to 60°C under nitrogen atmosphere for 100 min; add polyol, heat to 70°C, and react for 100 min; add chain extender, heat to 85°C, and react for 100 min; add inhibitor hydroquinone and hydroxy acrylate, cool to 65°C, react until the acid value is below 30 mg / KOH, cool to 45°C, add triethylamine, and stir for 30 min to obtain Unsaturated polyurethane; the unsaturated polyurethane comprises the following components by mass: 44 parts of diisocyanate, 33 parts of hexafluorobisphenol A, 30 parts of polyol, 0.5 parts of catalyst, 4.0 parts of chain extender, 0.03 parts of polymerization inhibitor, 3.0 parts of hydroxy acrylate, and 2.5 parts of triethylamine; the polyol is polypropylene oxide diol; the diisocyanate is toluene diisocyanate; the chain extender is a mixture of 2,2-dimethylol propionic acid and resorcinol diglycidyl ether in equal mass; the hydroxy acrylate is pentaerythritol triacrylate; 1.2. Chloromethyl polyether sulfone, 2-allyl phenol, potassium carbonate and toluene are mixed in N,N-dimethylformamide, heated to 153°C, and refluxed for 4 hours; precipitated in deionized water, washed, and dried to obtain unsaturated polyether amine; the unsaturated polyether amine is prepared from the following mass components: 10 parts of chloromethyl polyether sulfone, 0.6 parts of 2-allyl phenol, 0.55 parts of potassium carbonate, 8 parts of toluene, and 100 parts of N,N-dimethylformamide; 1.3. Unsaturated polyurethane and unsaturated polyethersulfone are mixed in N,N-dimethylformamide, and polyethylene glycol, fluorine-containing monomer and photoinitiator are added to obtain a film-making solution; the film-making solution includes the following components by mass: 3 parts of polyurethane, 7 parts of polyethersulfone, 0.6 parts of polyethylene glycol, 8.8 parts of fluorine-containing monomer, 0.5 parts of photoinitiator and 83.3 parts of N,N-dimethylformamide; the polyethylene glycol is PEG700; the fluorine-containing monomer is 1,6-di(acryloyloxy)-2,2,3,3,4,4,5,5-octafluorohexane; Step 2: Preparation of ePTFE layer The polytetrafluoroethylene resin and the extrusion aid are mixed, pre-pressed and calendered. The process conditions of the pre-pressing are: pressure 22MPa, duration 120s; the process conditions of calendering are: heating temperature 70°C, roller speed 5m / min, die diameter 22mm, to obtain a polytetrafluoroethylene tape; The film-making liquid was coated on the surface of the polytetrafluoroethylene-based tape with a coating thickness of 60 μm, and cured under the following process conditions: irradiation with an oxygen-free excimer lamp for 180 seconds and ultraviolet irradiation for 15 minutes; after curing, the film was immersed in deionized water for 12 hours, residual solvent was removed, and the film was dried to form a modified layer, thereby obtaining a composite base tape; The process conditions of three-axis stretching are as follows: longitudinal stretching: temperature 250°C, stretching ratio 5; vertical stretching: temperature 400°C, α angle 60°; transverse stretching: temperature 210°C, stretching ratio 10; after three-axis stretching, heat setting is performed at 260°C to obtain an ePTFE layer; Step 3: Preparation of filter material: The ePTFE layer and the non-woven fabric layer were stacked and compounded under the following process conditions: compounding temperature of 230°C, compounding pressure of 0.5 MPa, and compounding roller speed of 5.0 m / min; and heat setting under the following process conditions: temperature of 150°C and roller speed of 2.5 m / min, to obtain a filter material.

[0042] Comparative Example 1: A method for preparing a high-efficiency polytetrafluoroethylene filter material, comprising the following process: Step 1: Preparation of membrane solution: The polyurethane and polyethersulfone are mixed in N,N-dimethylformamide, and polyethylene glycol, a fluorine-containing monomer and a photoinitiator are added to obtain a film-making solution; the film-making solution includes the following components by weight: 1 part of polyurethane, 9 parts of polyethersulfone, 0.2 parts of polyethylene glycol, 6.5 parts of fluorine-containing monomer, 0.2 parts of photoinitiator and 58.2 parts of N,N-dimethylformamide; the polyethylene glycol is PEG600; the fluorine-containing monomer is perfluorohexylethyl methacrylate; Steps 2 and 3 are the same as those in Example 1 to obtain a filter material.

[0043] Comparative Example 2: A method for preparing a high-efficiency polytetrafluoroethylene filter material, comprising the following process: Step 1: Preparation of membrane solution: The polyurethane and polyethersulfone are mixed in N,N-dimethylformamide, and polyethylene glycol and perfluorohexylethyl methacrylate are added to obtain a film-making solution; the film-making solution includes the following components by weight: 1 part of polyurethane, 9 parts of polyethersulfone, 0.2 parts of perfluorohexylethyl methacrylate, 0.5 parts of fluorine-containing monomer and 37.0 parts of N,N-dimethylformamide; the polyethylene glycol is PEG600; Step 2: Preparation of ePTFE layer The polytetrafluoroethylene resin and the extrusion aid are mixed, pre-pressed and calendered to obtain a polytetrafluoroethylene-based tape; the film-making liquid is coated on the surface of the polytetrafluoroethylene-based tape, and dried at 80° C. for 4 hours to form a modified layer to obtain a composite base tape; and the ePTFE layer is obtained by three-dimensional stretching; The process parameters of step 2 and step 3 are the same as those in Example 1 to obtain a filter material.

[0044] Comparative Example 3: A method for preparing a high-efficiency polytetrafluoroethylene filter material, comprising the following process: Step 1: Preparation of ePTFE layer The polytetrafluoroethylene resin and the extrusion aid are mixed, pre-pressed and calendered to obtain a polytetrafluoroethylene tape; and three-dimensionally stretched to obtain an ePTFE layer; Step 2 is the same as step 3 of Example 1 to obtain a filter material.

[0045] Comparative Example 4: A method for preparing a high-efficiency polytetrafluoroethylene filter material, comprising the following process: Step 1: Preparation of ePTFE layer The polytetrafluoroethylene resin and the extrusion aid are mixed, pre-pressed and calendered to obtain a polytetrafluoroethylene tape; biaxial stretching, the process conditions are: longitudinal stretching: temperature 270°C, stretching ratio 9; transverse stretching: temperature 150°C, stretching ratio 5; after triaxial stretching, heat setting is performed at 230°C to obtain an ePTFE layer; Step 2 is the same as step 3 of Example 1 to obtain a filter material.

[0046] Experiment: Take the filter materials obtained in Examples 1-3 and Comparative Examples 1-4, prepare samples, test their performances respectively and record the test results: Mechanical properties test: Using GB / T 1040 as reference standard, test the mechanical properties of the ePTFE layer specimens; Filtration performance test: Use a filtration efficiency and resistance tester to test the filtration efficiency and filtration resistance of the sample. The median diameter of sodium chloride aerosol particles is 0.3μm, the wind speed is 32L / min, and the detection area is 100cm 2 ; Erosion and wear performance test: The erosion and wear test was carried out on the sample using sandblasting equipment, with an airflow pressure of 0.1 MPa, a sandblasting distance of 2 cm, 1250 mesh talcum powder as the erosion particle, an erosion time of 10 s, and an erosion angle of 90°.

[0047]

[0048] According to the data in the above table, we can clearly draw the following conclusions: The filter materials obtained in Examples 1-3 are compared with the filter materials obtained in Comparative Examples 1-4. The test results show that: Compared with the comparative example, the filter materials obtained in Examples 1-3 have higher porosity, filtration efficiency, mechanical properties, and wear resistance data, and maintain lower filtration resistance, which fully demonstrates that the present invention achieves the improvement of the filtration efficiency, mechanical properties, and wear resistance of the filter material.

[0049] Compared with Example 1, the membrane-making liquid in Comparative Example 1 replaces unsaturated polyurethane and unsaturated polyethersulfone with polyurethane and polyethersulfone; the membrane-making liquid in Comparative Example 2 reduces the amount of fluorine-containing monomer on the basis of Comparative Example 1; no modified layer is set in Comparative Example 3; no modified layer is set in Comparative Example 4, and the stretching process is biaxial stretching. The filter materials obtained in Comparative Examples 1-4 have low porosity, filtration efficiency, and mechanical properties. It can be seen that the setting of the ePTFE layer process and the components used in the present invention can promote the improvement of the filtration efficiency, mechanical properties, and wear resistance of the filter material.

[0050] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

Claims

1. A method for preparing a high-efficiency polytetrafluoroethylene filter material, characterized in that: Including the following processes: Take a polytetrafluoroethylene tape and stretch it in three directions to obtain an ePTFE layer; The ePTFE layer is placed on the non-woven fabric layer, stacked, compounded, and heat-set to obtain a filter material.

2. The method for preparing a high-efficiency polytetrafluoroethylene filter material according to claim 1, characterized in that: The polytetrafluoroethylene-based tape is surface treated before triaxial stretching, and the specific process is as follows: The polyurethane and polyethersulfone are mixed in a solvent, and an additive is added to obtain a membrane-making solution; The film-forming liquid is applied to the surface of the polytetrafluoroethylene-based tape and cured to form a modified layer, thereby obtaining a composite base tape.

3. The method for preparing a high-efficiency polytetrafluoroethylene filter material according to claim 2, characterized in that: The additives are polyethylene glycol, fluorine-containing monomers and photoinitiators; The fluorine-containing monomer is a perfluoroacrylate compound.

4. The method for preparing a high-efficiency polytetrafluoroethylene filter material according to claim 3, characterized in that: The curing process conditions are: irradiation with an oxygen-free excimer lamp for 60 to 180 seconds and ultraviolet irradiation for 5 to 15 minutes.

5. The method for preparing a high-efficiency polytetrafluoroethylene filter material according to claim 3, characterized in that: The polyurethane is an unsaturated polyurethane, which is specifically prepared by the following process: Mix diisocyanate and hexafluorobisphenol A, add a catalyst, and under the protection of a nitrogen atmosphere, heat up to 40-60°C and react for 100-150 minutes; add a polyol, heat up to 60-70°C, and react for 100-150 minutes; add a chain extender, heat up to 80-85°C and react for 100-150 minutes; add an inhibitor and hydroxy acrylate, cool down to 60-65°C, react until the acid value is below 30 mg / KOH, cool down to 40-45°C, add triethylamine, stir and react for 20-30 minutes to obtain an unsaturated polyurethane.

6. The method for preparing a high-efficiency polytetrafluoroethylene filter material according to claim 3, characterized in that: The polyethersulfone is an unsaturated polyethersulfone, which is specifically prepared by the following process: Chloromethyl polyether sulfone, 2-allyl phenol, potassium carbonate and toluene are mixed in N,N-dimethylformamide, heated to 145-153° C., and refluxed for 4-6 hours to obtain unsaturated polyether amine.

7. The method for preparing a high-efficiency polytetrafluoroethylene filter material according to claim 1, characterized in that: The process conditions of the triaxial stretching are: Longitudinal stretching: temperature 220-320°C, stretching ratio 5-9; Up and down stretching: temperature 300-400°C, α angle 10-60°; Transverse stretching: temperature 120-260°C, stretching ratio 5-10; After three-way stretching, heat setting is carried out at a temperature of 230-320°C.

8. The method for preparing a high-efficiency polytetrafluoroethylene filter material according to claim 5, characterized in that: The unsaturated polyurethane comprises the following components by mass: 27 to 44 parts of diisocyanate, 20 to 33 parts of hexafluorobisphenol A, 20 to 30 parts of polyol, 0.05 to 0.5 parts of catalyst, 1.6 to 4.0 parts of chain extender, 0.002 to 0.03 parts of polymerization inhibitor, 1.8 to 3.0 parts of hydroxy acrylate, and 1.2 to 4.5 parts of triethylamine.

9. The method for preparing a high-efficiency polytetrafluoroethylene filter material according to claim 6, characterized in that: The unsaturated polyetheramine is prepared from the following components by mass: 10 parts of chloromethyl polyether sulfone, 0.5-0.6 parts of 2-allyl phenol, 0.38-0.55 parts of potassium carbonate, 5-8 parts of toluene, and 50-100 parts of N,N-dimethylformamide.

10. A high-efficiency polytetrafluoroethylene filter material prepared according to the preparation method according to any one of claims 1 to 9.

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