A high-efficiency polytetrafluoroethylene filter material and a preparation method thereof

Abstract

The application discloses a kind of high-efficiency polytetrafluoroethylene filter material and preparation method thereof, it is related to filter material technical field, including following process: polytetrafluoroethylene base band is stretched in three directions, and ePTFE layer is obtained;ePTFE layer is placed above non-woven fabric layer, laminated, compounded, heat setting, and filter material is obtained.The application is based on horizontal and vertical stretching, and the middle part of polytetrafluoroethylene base band is stretched upward or downward arc by adopting olive-shaped roller, and reaction force is applied to both sides, so that the thickness of the middle of polytetrafluoroethylene base band is less than the thickness of both sides, the compensation of horizontal expansion stretching is formed, the complete stretching of polytetrafluoroethylene base band is promoted, the generation of node is reduced, the degree of fiberization of film is improved, the pore shape tends to be complex, the three-dimensional space structure of pore in ePTFE layer is generated more, and the pore performance and strength are optimized, so as to improve the filtering efficiency and mechanical strength of the prepared filter material.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of filtering materials, and particularly relates to a high-efficiency polytetrafluoroethylene filtering material and a preparation method thereof. BACKGROUND

[0002] Due to the particularity of the molecular structure, the polytetrafluoroethylene has excellent chemical stability, can resist the corrosion of strong acid, strong alkali and various chemical reagents, and has wide temperature resistance, so that the prepared polytetrafluoroethylene stretched film can become an ideal material for preparing high-performance microporous membranes and is widely applied to the fields of air filtration, liquid filtration, textile and garment, building, electronic communication, medical treatment, chemical industry and environmental protection. With the improvement of the technological level, people have higher and higher requirements on the filtering efficiency of filtering materials. Effective air filtration is the basis for ensuring the removal of air impurities, reducing the equipment wear, corrosion and failure caused by impurities, reducing the gas flow resistance, reducing the equipment energy consumption and improving the air environment. The polytetrafluoroethylene film material used in general filtering materials is a microporous membrane formed through calendering, extrusion and bidirectional stretching, has uniformly distributed small pores and provides good porosity and air permeability. However, the traditional bidirectional stretching is influenced by the stretching stress, process temperature and distribution of the film in the transverse stretching, and the stretching is insufficient, the film thickness is uneven and the nodes are caused, which affects the filtering efficiency of the polytetrafluoroethylene filtering material. Therefore, the application provides a high-efficiency polytetrafluoroethylene filtering material and a preparation method thereof. SUMMARY

[0003] The application aims to provide a high-efficiency polytetrafluoroethylene filtering material and a preparation method thereof, so as to solve the problems in the background.

[0004] In order to solve the above technical problems, the application provides the following technical scheme: a high-efficiency polytetrafluoroethylene filtering material, which comprises an ePTFE layer and a non-woven fabric layer arranged in a stack, and the ePTFE layer is located in the inner layer of the non-woven fabric layer.

[0005] Further, the non-woven fabric layer is one of needle-punched non-woven fabric and melt-blown non-woven fabric.

[0006] The fiber material is one or a mixture of multiple kinds of polyphenylene sulfide, polytetrafluoroethylene, glass fiber, polyester and polypropylene.

[0007] Further, the thickness of the ePTFE layer is 10-180 mu m.

[0008] In the above technical solution, the ePTFE layer has a plurality of fibrils and a microporous structure formed by nodes connected by the fibrils, forming a continuous porous structure with air holes, which retains the good high and low temperature resistance, low friction, non-stick, mechanical properties and chemical stability of polytetrafluoroethylene, while imparting softness, fluid permeability, fine particle trapping, filtration and other properties, which can trap fine particles and deposit on the surface of the filter material to achieve high efficiency filtration.

[0009] Further, the ePTFE layer is obtained by three-way stretching of a polytetrafluoroethylene base tape.

[0010] Further, the polytetrafluoroethylene base tape includes a component polytetrafluoroethylene resin and an extrusion aid;

[0011] The extrusion aid is one of white oil, aviation kerosene, degreasing kerosene, synthetic alkane, and liquid paraffin, and the addition amount is 30% to 40% of the mass of the polytetrafluoroethylene resin.

[0012] A preparation method of a high-efficiency polytetrafluoroethylene filter material includes the following processes:

[0013] The ePTFE layer is laminated and compounded with the non-woven fabric layer, and heat set to obtain the filter material.

[0014] Further, the process conditions for compounding are: compounding temperature 150-230℃, compounding pressure 0.5-2.0MPa, and compounding roller speed 0.5-5.0m / min.

[0015] Further, the process conditions for heat setting are: temperature 50-150℃, and roller speed 0.5-2.5m / min.

[0016] Further, before use, the side of the ePTFE layer in contact with the non-woven fabric layer is preheated and ionized.

[0017] Further, the process conditions for preheating are: temperature 85-135℃, and time 10-23min.

[0018] Further, the process conditions for ionization are: ion wind amount 1-10m 3 / min, and time 1-15min.

[0019] Further, the ePTFE layer is obtained by the following process:

[0020] Mixing the polytetrafluoroethylene resin and the extrusion aid, pre-pressing, calendering, to obtain a polytetrafluoroethylene base tape; three-way stretching to obtain the ePTFE layer.

[0021] Further, the process conditions for pre-pressing are: pressure 16-22MPa, and time 120-150s;

[0022] The process conditions of calendering are as follows: heating temperature 50-70℃, roller speed 0.05-5m / min, and die diameter 16-22mm.

[0023] Further, the process conditions of three-way stretching are as follows:

[0024] Longitudinal stretching: temperature 220-320℃, stretching ratio 5-9;

[0025] Up-down stretching: temperature 300-400℃, angle 10-60°;

[0026] Transverse stretching: temperature 120-260℃, stretching ratio 5-10;

[0027] After three-way stretching, heat setting is performed at a temperature of 230-320℃ to stabilize the structure formed in the stretching process and improve the mechanical properties of the ePTFE layer film.

[0028] In the above technical solution, on the basis of longitudinal and transverse stretching, the middle part of the polytetrafluoroethylene base tape is stretched in an arc shape upward or downward by using an olive-shaped roller, and a counterforce is applied to the two sides, so that the thickness of the middle part of the polytetrafluoroethylene base tape is smaller than that of the two sides, forming compensation for transverse expansion stretching, which can promote complete stretching of the polytetrafluoroethylene base tape in the subsequent transverse stretching process, reduce the generation of nodes, improve the degree of fiberization of the film, and make the pore shape more complex, so that the pores in the ePTFE layer form a more three-dimensional spatial structure, the pore performance and strength are optimized, thereby improving the filtering efficiency and mechanical strength of the prepared filtering material.

[0029] Further, the polytetrafluoroethylene base tape is surface treated before three-way stretching, and the specific process is as follows:

[0030] Mixing polyurethane and polyether sulfone in a solvent, adding an additive to obtain a film-forming solution;

[0031] Coating the film-forming solution on the surface of the polytetrafluoroethylene base tape, solidifying to form a modified layer, and obtaining a composite base tape.

[0032] Further, the additive is polyethylene glycol, a fluorine-containing monomer, and a photoinitiator;

[0033] The polyethylene glycol is one or a mixture of two of PEG600 and PEG700;

[0034] The fluorine-containing monomer is one or more of perfluoroacrylate compounds, specifically perfluorohexylethyl methacrylate (CAS: 2144-53-8), perfluorooctylethyl methacrylate (CAS: 1996-88-9), 2-(N-ethyl perfluorooctanesulfonamide) ethyl acrylate (CAS: 423-82-5), 2-acrylic acid-2-[butyl[(heptadecafluorooctyl)-sulfonyl]-amino]-ethyl ester (CAS: 383-07-3), 1,6-bis(acryloyloxy)-2,2,3,3,4,4,5,5-octafluorohexane (CAS: 2264-01-9).

[0035] The solvent is N,N-dimethylformamide.

[0036] Further, the film-forming solution includes the following mass components: 1-3 parts of polyurethane, 7-9 parts of polyether sulfone, 0.2-0.6 parts of polyethylene glycol, 6.5-8.8 parts of fluorine-containing monomer, 0.2-0.5 parts of photoinitiator, and 58.2-83.3 parts of solvent.

[0037] The photoinitiator includes one or more of photoinitiator MBF, photoinitiator 184, and photoinitiator XBPO.

[0038] Further, the coating thickness is 10-100 μm.

[0039] Further, the curing process conditions are: 60-180 s of irradiation by an oxygen-free excimer lamp and 5-15 min of ultraviolet irradiation.

[0040] After curing, the film is immersed in deionized water for 12 h to remove residual solvent and is air-dried.

[0041] In the above technical solution, the polyurethane and polyether sulfone are mixed by the film-forming solution, are arranged on the surface of the polytetrafluoroethylene base tape, and form a polyether sulfone / polyurethane composite film layer after curing, which is referred to as a modified layer. In the modified layer system, the polyurethane and the polyether sulfone have a phase separation characteristic, the double bonds in the system undergo a polymerization reaction under the irradiation of an oxygen-free (nitrogen) excimer lamp, the fluorine-containing structure migrates to the surface, and uneven shrinkage occurs through different shrinkage ratios between materials, resulting in a stress difference in the thickness direction of the modified layer, forming a thickness gradient, and causing a wrinkling phenomenon. Then, ultraviolet irradiation is performed to cure the entire film-forming solution, forming a modified layer with wrinkles.

[0042] The modified layer is compounded with the polytetrafluoroethylene base tape, and the three-dimensional stereoscopic pore structure is formed on the polytetrafluoroethylene base tape through three-way stretching. Meanwhile, the mechanical embedding between the modified layer and the polytetrafluoroethylene base tape is caused due to the influence of the up-down stretching process, and the combination between the two interfaces is more compact. The surface wrinkles of the modified layer and the embedding structure between the interface of the modified layer and the polytetrafluoroethylene base tape are affected by the horizontal expansion stretching and are fiberized, which further promotes the establishment of the three-dimensional space stereoscopic pore structure on the surface of the ePTFE layer (the modified layer and the interface thereof), the surface pore shape is more complex, the pore performance is further optimized, and the effective blocking, interception, capture and adsorption of the ePTFE layer to the fine particles are promoted, so that higher filtration efficiency is achieved. The surface roughness of the ePTFE layer is increased, the specific surface area is improved, the probability of collision and capture of the fine particles with the ePTFE layer is increased, the filtration efficiency of the filtration material is further improved, the direct impact of the fine particles on the ePTFE layer is avoided, the influence of the fine particle scouring on the ePTFE layer is improved, and the wear resistance of the ePTFE layer is improved.

[0043] The polyether sulfone has good high-temperature stability, chemical reagent resistance and mechanical strength; the polyurethane has good elasticity, flexibility and wear resistance. The combination of the two on the surface of the polytetrafluoroethylene helps to improve the wear resistance and mechanical properties of the prepared filtration material, increase the resistance to fine particle scouring, and improve the wear resistance and durability. The polyethylene glycol in the film-forming liquid system can play a pore-forming role to form a cavity and promote the formation of pores in the modified layer. The fluorine-containing monomer is a perfluoroacrylate compound, which can play a surfactant role, significantly reduce the surface tension, and make it more difficult for dust to adhere to the surface, thereby enhancing the dustproof performance of the filtration material; meanwhile, it can participate in the polymerization in the film-forming liquid system to improve the water resistance, heat resistance, chemical stability and mechanical properties of the modified layer, and enhance the interface bonding capacity between the modified layer and the polytetrafluoroethylene base tape.

[0044] The setting of the modified layer and the combination of the modified layer and the polytetrafluoroethylene layer to form a composite base tape, and the microporous layer (the surface layer of the ePTFE layer) prepared after three-way stretching can be applied as a buffer and dust-containing functional layer, intercept, deposit and filter the particles in the air, relieve the strength of the air vortex, reduce the pressure loss of the ePTFE layer, and enhance the mechanical strength, stability, wear resistance and filtration efficiency of the filtration material, thereby improving the durability and service life.

[0045] Further, the polyurethane is an unsaturated polyurethane, which is prepared by the following process:

[0046] The diisocyanate, hexafluorobisphenol A are mixed, a catalyst is added, and the temperature is raised to 40-60℃ under nitrogen atmosphere protection, and the reaction is carried out for 100-150 min; the polyhydric alcohol is added, the temperature is raised to 60-70℃, and the reaction is carried out for 100-150 min; the chain extender is added, the temperature is raised to 80-85℃, and the reaction is carried out for 100-150 min; the polymerization inhibitor, hydroxy acrylate is added, the temperature is reduced to 60-65℃, and the reaction is carried out until the acid value is below 30 mg / KOH, the temperature is reduced to 40-45℃, triethylamine is added, and the reaction is carried out for 20-30 min to obtain the unsaturated polyurethane.

[0047] Further, the unsaturated polyurethane comprises the following mass components: 27-44 parts of diisocyanate, 20-33 parts of hexafluorobisphenol A, 20-30 parts of polyhydric alcohol, 0.05-0.5 parts of catalyst, 1.6-4.0 parts of chain extender, 0.002-0.03 parts of polymerization inhibitor, 1.8-3.0 parts of hydroxy acrylate, and 1.2-4.5 parts of triethylamine.

[0048] Further, the polyhydric alcohol is one or more of polyethylene glycol, polytetrahydrofuran ether glycol, polypropylene glycol, and polypropylene oxide glycol;

[0049] The diisocyanate is one or more of isophorone diisocyanate, toluene diisocyanate, 4,4'-diphenyl methane diisocyanate, and 1,4-cyclohexane diisocyanate;

[0050] The chain extender is one or more of 2,2-dimethylol propionic acid, hexafluorobisphenol A, resorcinol diglycidyl ether, 1,4-bis(2-hydroxyethoxy)benzene, and 4,4'-diaminodiphenyl sulfone;

[0051] The hydroxy acrylate is one or more of hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, trimethylolpropane diacrylate, trimethylolpropane triacrylate, and pentaerythritol triacrylate;

[0052] The catalyst is one of dibutyltin dilaurate and dibutyltin dioctoate;

[0053] The polymerization inhibitor is hydroquinone.

[0054] In the above technical solution, the unsaturated polyurethane prepared from bisphenol A has a modulus closer to that of polyether sulfone, the dispersion degree of the two is improved, the uniformity between the materials is improved, and the stability and durability of the modified layer are improved.

[0055] Further, the polyether sulfone is unsaturated polyether sulfone, which is prepared by the following process:

[0056] Mixing chloromethyl polyether sulfone, 2-allyl phenol, potassium carbonate, toluene in N,N-dimethylformamide, heating to 145-153℃, refluxing for 4-6h; precipitating in deionized water, washing, drying, obtaining unsaturated polyether amine.

[0057] Further, the unsaturated polyether amine is prepared from the following mass components: 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, 50-100 parts of N,N-dimethylformamide.

[0058] In the above technical solution, the polyether sulfone has a chlorine end group, which can react with the hydroxyl group in the 2-allyl phenol, and under alkaline solvent conditions, the double bond isomerizes to obtain a propenyl-terminated polyether sulfone, which is denoted as unsaturated polyether sulfone. The conjugated structure of the double bond and the benzene ring can significantly improve the reactivity under light irradiation, which helps the unsaturated polyether sulfone to participate in the polymerization and reaction of unsaturated polyurethane, fluorine-containing monomer (perfluoroacrylate compound), forming an interpenetrating network, which can prolong the phase separation, promote the formation of a sponge-like structure, avoid the formation of a clear phase interface microporous structure, and the initial shape of the micropore is more easily remembered. The micropore can return to its initial state, which is beneficial to the comprehensive improvement of the performance of the polyurethane, polyether sulfone composite system, and ePTFE layer.

[0059] Further, before coating the film-forming liquid, the polytetrafluoroethylene base tape is subjected to ionization treatment, which improves the interfacial bonding performance between the modified polytetrafluoroethylene base tape. DETAILED DESCRIPTION

[0060] The technical solutions in the embodiments of the present application will be described below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0061] In the following detailed description,

[0062] The non-woven fabric layer is selected from PET dry non-woven fabric, model 2024, with a grammage of 71g / m2 and a thickness of 0.31mm, and is sourced from Suzhou Youkefa New Material Technology Co., Ltd.

[0063] The polytetrafluoroethylene resin is F-201, sourced from Daikin Industries, Ltd., Japan.

[0064] The extrusion aid is Exxon Mobil ISOPAR H.

[0065] The polyethylene glycol is PEG600, PEG700, PEG1000, sourced from Shanghai Maikelin Biochemical Technology Co., Ltd.

[0066] Chloromethyl polyether sulfone: polyether sulfone is dissolved in N-methyl pyrrolidone (15 g / 100 mL), 1,4-dichloromethoxy butane (3 times the mass of polyether amine), zinc chloride (6.5% of the mass of polyether amine) is added, and the temperature is raised to 90°C, and the reaction is carried out for 6h; washing, drying, obtaining;

[0067] The photoinitiator is a mixture of photoinitiator MBF, photoinitiator 184, and photoinitiator XBPO, with a mass ratio of 2:2:1;

[0068] Before use, the ePTFE layer is preheated and ionized on the side in contact with the non-woven fabric layer. The preheating process conditions are: temperature 110°C, time 15min, and ionization process conditions: ionizing air flow 5.0m 3 / min, time 6min; before coating, the polytetrafluoroethylene base to be coated is ionized, and the ionization process conditions are: ionizing air flow 8m 3 / min, time 10min;

[0069] Polyurethane: 1180, from Tianjin Dahuozhu Foam Plastics Co., Ltd.;

[0070] Polyether sulfone: Mw=58000, from BASF Chemical Company.

[0071] Example 1: A method for preparing a high-efficiency polytetrafluoroethylene filter material, comprising the following processes:

[0072] Step 1, preparation of the film-forming solution:

[0073] 1.1. Mix diisocyanate and hexafluorobisphenol A, add catalyst dibutyltin dilaurate, and heat to 40°C under nitrogen atmosphere protection, and react for 150min; add polyol, heat to 60°C, and react for 150min; add chain extender, heat to 80°C, and react for 150min; add polymerization inhibitor hydroquinone and hydroxy acrylate, cool to 60°C, and react until the acid value is below 30mg / KOH, cool to 40°C, add triethylamine, and stir for 25min to obtain unsaturated polyurethane; the unsaturated polyurethane comprises the following mass components: 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-dimethylol propionic acid; and the hydroxy acrylate is hydroxyethyl acrylate;

[0074] 1.2. Mix chloromethyl polyether sulfone, 2-allyl phenol, potassium carbonate, toluene in N,N-dimethylformamide, heat to 145℃, reflux for 6h; precipitate in deionized water, wash, dry, to obtain unsaturated polyether amine; unsaturated polyether amine is prepared from the following mass components: 10 parts of chloromethyl polyether sulfone, 0.5 parts of 2-allyl phenol, 0.38 parts of potassium carbonate, 5 parts of toluene, 50 parts of N,N-dimethylformamide;

[0075] 1.3. Mix unsaturated polyurethane and unsaturated polyether sulfone in N,N-dimethylformamide, add polyethylene glycol, fluorine-containing monomer and photoinitiator to obtain a film-forming solution; the film-forming solution includes the following mass components: 1 part of polyurethane, 9 parts of polyether sulfone, 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 perfluorohexyl ethyl methacrylate;

[0076] Step 2, preparation of ePTFE layer

[0077] Mix polytetrafluoroethylene resin and extrusion aid, pre-press, calender, the process conditions of pre-pressing are: pressure 16 MPa, time length 150 s; the process conditions of calendering are: heating temperature 50℃, roller speed 0.5 m / min, die diameter 16 mm, to obtain a polytetrafluoroethylene base tape;

[0078] Coat the film-forming solution on the surface of the polytetrafluoroethylene base tape, the coating thickness is 10 μm, and cure, the process conditions are: oxygen-free excimer lamp irradiation for 60 s, ultraviolet irradiation for 5 min; after curing, immerse in deionized water for 12 h to remove residual solvents, air dry, form a modified layer, to obtain a composite base tape;

[0079] Three-way stretching, the process conditions are: longitudinal stretching: temperature 270℃, stretching ratio 9; up and down stretching: temperature 300℃, α angle 10°; transverse stretching: temperature 150℃, stretching ratio 5; after three-way stretching, heat setting at a temperature of 230℃, to obtain an ePTFE layer;

[0080] Step 3, preparation of filter material:

[0081] Stack and composite the ePTFE layer and the non-woven fabric layer, the process conditions are: composite temperature 150℃, composite pressure 2.0 MPa, composite roller speed 0.5 m / min; heat setting, the process conditions are: temperature 50℃, roller speed 0.5 m / min, to obtain a filter material.

[0082] Example 2: a preparation method of a high-efficiency polytetrafluoroethylene filter material, including the following processes:

[0083] Step 1, preparation of film-forming solution:

[0084] 1.1. Mix diisocyanate, hexafluorobisphenol A, add catalyst dibutyltin dilaurate, under the protection of nitrogen atmosphere, heat to 50℃, react for 120 min; add polyol, heat to 65℃, react for 120 min; add chain extender, heat to 82℃, react for 120 min; add polymerization inhibitor hydroquinone, hydroxy acrylate, cool to 62℃, react until the acid value is below 30 mg / KOH, cool to 42℃, add triethylamine, stir for 20 min, to obtain unsaturated polyurethane; the unsaturated polyurethane comprises the following mass components: 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, 1.2 parts of triethylamine; the polyol is polypropylene glycol diol; the diisocyanate is dicyclohexylmethane diisocyanate; the chain extender is an equal mass mixture of 2,2-dimethylol propionic acid and hexafluorobisphenol A; the hydroxy acrylate is trimethylolpropane triacrylate;

[0085] 1.2. Mix chloromethyl polyether sulfone, 2-allyl phenol, potassium carbonate, toluene in N,N-dimethylformamide, heat to 149℃, reflux for 5 h; precipitate in deionized water, wash, dry, to obtain unsaturated polyether amine; the unsaturated polyether amine is prepared from the following mass components: 10 parts of chloromethyl polyether sulfone, 0.55 parts of 2-allyl phenol, 0.47 parts of potassium carbonate, 7 parts of toluene, 75 parts of N,N-dimethylformamide;

[0086] 1.3. Mix the unsaturated polyurethane and the unsaturated polyether sulfone in N,N-dimethylformamide, add polyethylene glycol, fluorine-containing monomer and photoinitiator, to obtain a film forming solution; the film forming solution comprises the following mass components: 2 parts of polyurethane, 8 parts of polyether sulfone, 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 an equal mass mixture of perfluorohexylethyl methacrylate, perfluorooctylethyl methacrylate and 1,6-bis(acryloyloxy)-2,2,3,3,4,4,5,5-octafluorohexane;

[0087] Step 2, preparation of the ePTFE layer

[0088] Mix the polytetrafluoroethylene resin and the extrusion aid, pre-press form, calender, the process conditions of pre-press forming are: pressure 19 MPa, time length 135 s; the process conditions of calendering are: heating temperature 60℃, roller speed 1.0 m / min, die diameter 20 mm, to obtain a polytetrafluoroethylene base tape;

[0089] The film-forming liquid is coated on the surface of a polytetrafluoroethylene base tape with a coating thickness of 30 μm, and cured under the following process conditions: 90 s of anoxic excimer lamp irradiation and 10 min of ultraviolet irradiation; after curing, the sample is soaked in deionized water for 12 h to remove residual solvents, and then dried to form a modified layer, thereby obtaining a composite base tape;

[0090] Three-way stretching is performed under the following process conditions: longitudinal stretching at a temperature of 260 ℃ and a stretching ratio of 7; up-and-down stretching at a temperature of 350 ℃ and an α angle of 30°; and transverse stretching at a temperature of 180 ℃ and a stretching ratio of 8; and after three-way stretching, heat setting is performed at a temperature of 250 ℃, thereby obtaining an ePTFE layer.

[0091] Step 3: Preparation of a filter material

[0092] The ePTFE layer and the non-woven fabric layer are laminated and combined under the following process conditions: a combination temperature of 180 ℃, a combination pressure of 1.0 MPa, and a combination roller speed of 2.0 m / min; and heat setting is performed under the following process conditions: a temperature of 100 ℃ and a roller speed of 1.5 m / min, thereby obtaining a filter material.

[0093] Example 3: A method for preparing a high-efficiency polytetrafluoroethylene filter material, which comprises the following processes:

[0094] Step 1: Preparation of a film-forming liquid

[0095] 1.1. The diisocyanate and the hexafluorobisphenol A are mixed, and a catalyst dibutyltin dilaurate is added. Under the protection of a nitrogen atmosphere, the temperature is raised to 60 ℃, and the reaction is performed for 100 min. A polyol is added, the temperature is raised to 70 ℃, and the reaction is performed for 100 min. A chain extender is added, the temperature is raised to 85 ℃, and the reaction is performed for 100 min. A polymerization inhibitor hydroquinone and a hydroxyl acrylate are added, the temperature is lowered to 65 ℃, and the reaction is performed until the acid value is less than 30 mg / KOH. The temperature is lowered to 45 ℃, triethylamine is added, and the reaction is performed for 30 min, thereby obtaining an 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 hydroxyl acrylate, and 2.5 parts of triethylamine. The polyol is polypropylene glycol. The diisocyanate is toluene diisocyanate. The chain extender is an equal-mass mixture of 2,2-dimethylol propionic acid and resorcinol diglycidyl ether. The hydroxyl acrylate is pentaerythritol triacrylate.

[0096] 1.2. The chloromethyl polyether sulfone, 2-allyl phenol, potassium carbonate, and toluene are mixed in N,N-dimethylformamide, heated to 153 ℃, and refluxed for 4 h. The product is precipitated in deionized water, washed, and dried, thereby obtaining an unsaturated polyether amine. The unsaturated polyether amine is prepared from the following components by mass: 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.

[0097] 1.3. The unsaturated polyurethane and the unsaturated polyether sulfone are mixed in N,N-dimethylformamide, polyethylene glycol, fluorine-containing monomer and photoinitiator are added to obtain a film forming solution; the film forming solution includes the following mass components: 3 parts of polyurethane, 7 parts of polyether sulfone, 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-bis(acryloyloxy)-2,2,3,3,4,4,5,5-octafluorohexane;

[0098] Step 2, preparation of the ePTFE layer

[0099] The polytetrafluoroethylene resin and the extrusion aid are mixed, pre-pressed, and calendered; the process conditions for pre-pressing are: pressure 22 MPa, time length 120 s; the process conditions for calendering are: heating temperature 70℃, roller speed 5 m / min, die diameter 22 mm, to obtain a polytetrafluoroethylene base tape;

[0100] The film forming solution is coated on the surface of the polytetrafluoroethylene base tape at a coating thickness of 60 μm, and is cured under the process conditions of: 180 s of irradiation by an oxygen-free excimer lamp and 15 min of ultraviolet irradiation; after curing, it is soaked in deionized water for 12 h to remove residual solvents, and is air-dried to form a modified layer, to obtain a composite base tape;

[0101] Three-way stretching under the process conditions of: longitudinal stretching: temperature 250℃, stretching ratio 5; up-and-down stretching: temperature 400℃, α angle 60°; transverse stretching: temperature 210℃, stretching ratio 10; after three-way stretching, heat setting is performed at a temperature of 260℃ to obtain an ePTFE layer;

[0102] Step 3, preparation of the filter material:

[0103] The ePTFE layer and the non-woven fabric layer are laminated and compounded under the process conditions of: compounding temperature 230℃, compounding pressure 0.5 MPa, compounding roller speed 5.0 m / min; heat setting is performed under the process conditions of: temperature 150℃, roller speed 2.5 m / min, to obtain a filter material.

[0104] Comparative Example 1: a method for preparing a high-efficiency polytetrafluoroethylene filter material, including the following processes:

[0105] Step 1, preparation of the film forming solution:

[0106] The polyurethane and the polyether sulfone are mixed in N,N-dimethylformamide, the polyethylene glycol, the fluorine-containing monomer and the photoinitiator are added to obtain a film forming solution; the film forming solution comprises the following mass components: 1 part of polyurethane, 9 parts of polyether sulfone, 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 perfluorohexyl ethyl methacrylate;

[0107] Steps 2 and 3 are the same as those in Example 1 to obtain the filter material.

[0108] Comparative Example 2: A method for preparing a high-efficiency polytetrafluoroethylene filter material, comprising the following processes:

[0109] Step 1: Preparation of a film forming solution

[0110] The polyurethane and the polyether sulfone are mixed in N,N-dimethylformamide, the polyethylene glycol, the fluorine-containing monomer and the photoinitiator are added to obtain a film forming solution; the film forming solution comprises the following mass components: 1 part of polyurethane, 9 parts of polyether sulfone, 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 perfluorohexyl ethyl methacrylate;

[0111] Step 2: Preparation of an ePTFE layer

[0112] The polytetrafluoroethylene resin and the extrusion aid are mixed, pre-pressed and formed, and calendered to obtain a polytetrafluoroethylene base tape; the film forming solution is coated on the surface of the polytetrafluoroethylene base tape, dried at 80°C for 4h to form a modified layer, and the composite base tape is obtained; three-way stretching is performed to obtain an ePTFE layer.

[0113] The process parameters of Step 2 and Step 3 are the same as those in Example 1 to obtain the filter material.

[0114] Comparative Example 3: A method for preparing a high-efficiency polytetrafluoroethylene filter material, comprising the following processes:

[0115] Step 1: Preparation of an ePTFE layer

[0116] The polytetrafluoroethylene resin and the extrusion aid are mixed, pre-pressed and formed, and calendered to obtain a polytetrafluoroethylene base tape; three-way stretching is performed to obtain an ePTFE layer.

[0117] Step 2 is the same as Step 3 in Example 1 to obtain the filter material.

[0118] Comparative Example 4: A method for preparing a high-efficiency polytetrafluoroethylene filter material, comprising the following processes:

[0119] Step 1: Preparation of an ePTFE layer

[0120] The polytetrafluoroethylene resin and the extrusion aid are mixed, pre-pressed, and calendered to obtain a polytetrafluoroethylene base tape; the base tape is biaxially stretched under the following process conditions: longitudinal stretching: temperature 270℃, stretching ratio 9; transverse stretching: temperature 150℃, stretching ratio 5; after three-way stretching, heat setting is performed at a temperature of 230℃ to obtain an ePTFE layer;

[0121] Step 2 is the same as Step 3 of Example 1 to obtain the filter material.

[0122] Experiment: The filter materials obtained in Examples 1-3 and Comparative Examples 1-4 are used to prepare samples, and the performance of the samples is detected and the detection results are recorded:

[0123] Mechanical property test: The mechanical properties of the ePTFE layer samples are detected according to GB / T 1040 as the reference standard;

[0124] Filtering performance test: A filter efficiency and resistance detector is used to detect the filtering efficiency and filtering resistance of the samples. The median diameter of sodium chloride aerosol particles is 0.3μm, the wind speed is 32L / min, and the detection area is 100cm 2 ;

[0125] Erosion wear performance test: A sandblasting device is used to perform an erosion wear experiment on the samples, the air flow pressure is 0.1MPa, the sandblasting distance is 2cm, 1250-mesh talcum powder is used as the erosion particles, the erosion time is 10s, and the erosion angle is 90°.

[0126]

[0127] According to the data in the above table, the following conclusions can be clearly obtained:

[0128] The filter materials obtained in Examples 1-3 and the filter materials obtained in Comparative Examples 1-4 are compared, and the detection results show that,

[0129] Compared with the comparative examples, the filter materials obtained in Examples 1-3 have higher porosity, filtering efficiency, mechanical properties, and wear resistance data, and maintain a lower filtering resistance. This fully demonstrates that the present application improves the filtering efficiency of the filter material and its mechanical properties and wear resistance.

[0130] Compared with example 1, the film forming solution in comparative example 1 replaces unsaturated polyurethane and unsaturated polyether sulfone with polyurethane and polyether sulfone; the film forming solution 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 two-way stretching. The porosity, filtration efficiency and mechanical property data of the filtration material obtained in comparative examples 1-4 are low. It can be known that the setting of the ePTFE layer process and the components used by the application can promote the improvement of the filtration efficiency, mechanical property and wear resistance of the filtration material.

[0131] It will be obvious to a person skilled in the art that the application is not limited to the details of the above-described exemplary embodiments, but that the application can be implemented in other concrete forms without departing from the spirit or essential characteristics of the application. Therefore, the embodiments should be considered in all respects as illustrative and not restrictive, the scope of the application being defined by the appended claims rather than the above description, and it is therefore intended that all changes that come within the meaning and range of equivalents of the claims are embraced therein.

Claims

1. A method for preparing a high-efficiency polytetrafluoroethylene filter material, characterized in that: Including the following processes: The polytetrafluoroethylene vinyl tape was stretched in three directions to obtain the ePTFE layer; The ePTFE layer is placed on top of the nonwoven fabric layer, and then laminated, composited, and heat-set to obtain the filter material. The polytetrafluoroethylene vinyl tape undergoes surface treatment before triaxial stretching, and the specific process is as follows: Polyurethane and polyethersulfone are mixed in a solvent, and additives are added to obtain a film-forming solution; The film-forming solution is coated onto the surface of the polytetrafluoroethylene tape and cured to form a modified layer, thus obtaining the composite base tape. The additive is polyethylene glycol, a fluorinated monomer, and a photoinitiator; the fluorinated monomer is a perfluorinated acrylate compound. The curing process conditions are: oxygen-free excimer lamp irradiation for 60-180 seconds, and ultraviolet irradiation for 5-15 minutes; The polyurethane is unsaturated polyurethane, and the polyethersulfone is unsaturated polyethersulfone.

2. The method for preparing a high-efficiency polytetrafluoroethylene filter material according to claim 1, characterized in that: The unsaturated polyurethane is prepared by the following process: Diisocyanate and hexafluorobisphenol A are mixed, a catalyst is added, and the mixture is heated to 40–60 °C and reacted for 100–150 min under a nitrogen atmosphere. A polyol is added, and the mixture is heated to 60–70 °C and reacted for 100–150 min. A chain extender is added, and the mixture is heated to 80–85 °C and reacted for 100–150 min. A polymerization inhibitor and hydroxyl acrylate are added, and the mixture is cooled to 60–65 °C and reacted until the acid value is below 30 mg / KOH. The mixture is then cooled to 40–45 °C, triethylamine is added, and the mixture is stirred and reacted for 20–30 min to obtain unsaturated polyurethane.

3. The method for preparing a high-efficiency polytetrafluoroethylene filter material according to claim 1, characterized in that: The unsaturated polyethersulfone is prepared by the following process: Chloromethyl polyethersulfone, 2-allylphenol, potassium carbonate, and toluene were mixed in N,N-dimethylformamide and heated to 145–153 °C. The mixture was then refluxed for 4–6 h to obtain unsaturated polyethersulfone.

4. The method for preparing a high-efficiency polytetrafluoroethylene filter material according to claim 1, characterized in that: The process conditions for the triaxial stretching are as follows: Longitudinal stretching: temperature 220~320℃, stretching ratio 5~9; Vertical stretching: temperature 300~400℃, α angle 10~60°; Transverse stretching: Temperature 120~260℃, stretching ratio 5~10; After triaxial stretching, heat setting is performed at a temperature of 230–320°C.

5. The method for preparing a high-efficiency polytetrafluoroethylene filter material according to claim 2, characterized in that: The unsaturated polyurethane is prepared from the following components by weight: 27-44 parts diisocyanate, 20-33 parts hexafluorobisphenol A, 20-30 parts polyol, 0.05-0.5 parts catalyst, 1.6-4.0 parts chain extender, 0.002-0.03 parts polymerization inhibitor, 1.8-3.0 parts hydroxy acrylate, and 1.2-4.5 parts triethylamine.

6. The method for preparing a high-efficiency polytetrafluoroethylene filter material according to claim 3, characterized in that: The unsaturated polyethersulfone is prepared from the following components by mass: 10 parts chloromethyl polyethersulfone, 0.5 to 0.6 parts 2-allylphenol, 0.38 to 0.55 parts potassium carbonate, 5 to 8 parts toluene, and 50 to 100 parts N,N-dimethylformamide.

7. A high-efficiency polytetrafluoroethylene filter material prepared by the preparation method according to any one of claims 1-6.

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