Oleophobic polytetrafluoroethylene asymmetric nano film and preparation method thereof

Abstract

The invention discloses an oleophobic polytetrafluoroethylene asymmetric nano film and a preparation method thereof, and the oleophobic polytetrafluoroethylene asymmetric nano film comprises the following components in parts by weight: 60-80 parts of polytetrafluoroethylene dispersion resin, 15-25 parts of petroleum lysate, 2-10 parts of a fluorocarbon surfactant, 1-10 parts of perfluoroalkoxy resin, 2-12 parts of a fluorinated propylene copolymer and 2-15 parts of a low-boiling-point solvent. The oleophobic polytetrafluoroethylene asymmetric nano-film prepared by the method has better oleophobic and hydrophobic properties, tensile strength and creep resistance, films with different pore diameters are hot-pressed and compounded to form an asymmetric gradient deep filtering structure, the air permeability and the pollutant holding amount are improved, the filtering resistance is reduced, the efficient filtering interception efficiency is ensured, and the service life of the nano-film is prolonged. The asymmetric structure reduces the flow velocity attenuation, prolongs the service life of the membrane, has the oleophobic characteristic, can reduce the pollution of oil stains, colloids or organic matters, and is more suitable for the filtration, separation and purification of oily compounds, fat substances, colloids, proteins, particulate matters and the like in the fields of water resistance, air permeability, oil resistance, air permeability or gas filtration.

Description

Technical Field

[0001] The invention relates to the technical field of membrane materials, in particular to the field of filtration separation, and more specifically to an oleophobic polytetrafluoroethylene asymmetric nano-membrane. Background Art

[0002] Polytetrafluoroethylene (PTFE) materials have excellent physical and chemical properties, high temperature resistance, corrosion resistance, and aging resistance, and can be used in many harsh working conditions. PTFE materials have natural hydrophobicity, but due to its low surface energy and low surface tension, it has a certain degree of lipophilicity and is not resistant to oil pollution, which limits the application of PTFE filter membranes in the field of filtration and separation, especially in the field of oily aerosols. The oily compounds in the oily aerosols will adhere to the surface of the membrane, thereby reducing the permeability of the membrane, increasing energy consumption, or infiltrating the membrane pores to cause pollution and blockage, reducing the service life of the membrane.

[0003] Polytetrafluoroethylene material has excellent high temperature resistance and chemical stability, but its creep resistance and mechanical stability are poor. During the process of production and application, the stress is too strong, causing the internal fibers of the membrane to break and form defects or holes, which is not conducive to the production and processing of uniform and stable products, and there is a risk of reduced filtration performance or failure.

[0004] Patent CN113230911A discloses a method for preparing a double-phobic polytetrafluoroethylene asymmetric nano-membrane. The double-phobic modified membrane is prepared by spraying chlorosilane and nanoparticles on the surface of the polytetrafluoroethylene asymmetric nano-membrane, so that the membrane has hydrophobic and oleophobic properties, extending its service life in the field of gas-solid separation. However, the mechanical properties of the membrane, such as creep resistance and tensile strength, are not optimized, and the nanoparticles are easily detached to cause secondary pollution.

[0005] Patent CN201911393925.6 discloses a method for preparing a hydrophobic and oleophobic PTFE membrane. The PTFE membrane is made hydrophobic and oleophobic by preparing a silane waterproof and oil-repellent agent, mixing, extrusion, etc. However, due to the poor high temperature resistance of the waterproof agent, the waterproof agent cannot be decomposed and become ineffective due to high temperature, and the membrane cannot be well cured and shaped during the sintering process, and the mechanical properties of the membrane such as creep resistance and tensile strength cannot be optimized. Summary of the invention

[0006] The purpose of the invention is to disclose an oleophobic polytetrafluoroethylene asymmetric nanomembrane and a preparation method thereof, so as to overcome the problems existing in the prior art such as unstable mechanical properties, poor creep resistance, large pore defects, unstable filtration performance, insufficient oleophobicity, poor anti-pollution performance, small pollution holding capacity, and short service life of the PTFE membrane.

[0007] In order to achieve the above-mentioned purpose, the present invention provides an oleophobic polytetrafluoroethylene asymmetric nanomembrane on one hand. The raw materials of the oleophobic polytetrafluoroethylene asymmetric nanomembrane, measured by weight, include 60-80 parts of polytetrafluoroethylene dispersion resin, 15-30 parts of petroleum cracking product, 1-10 parts of fluorocarbon surfactant, 1-10 parts of perfluoroalkoxy resin, 2-12 parts of fluorinated propylene copolymer, and 3-15 parts of low boiling point solvent.

[0008] Further preferably, the raw materials of the oleophobic polytetrafluoroethylene asymmetric nanomembrane include, by weight, 65-75 parts of polytetrafluoroethylene dispersion resin, 17-25 parts of petroleum cracking product, 2-6 parts of fluorocarbon surfactant, 2-7 parts of perfluoroalkoxy resin, 2-8 parts of fluorinated propylene copolymer, and 3-10 parts of low boiling point solvent.

[0009] Preferably, the polytetrafluoroethylene dispersed resin PTFE is selected from at least one of Daikin F106, Daikin F104, Chemours 601, Chemours 605, 3M TF2021, 3M TF2025, Chenguang 216, Dongyue 206, Dongyue 204F, etc.

[0010] Further preferably, the polytetrafluoroethylene dispersion resin is at least one of Daikin F106, Daikin F104, Chemours 601, Chemours 605, Chenguang 216, and Dongyue 206.

[0011] Preferably, the petroleum cracking product includes at least one of aviation kerosene, white oil, dearomatized solvent oil or paraffin oil.

[0012] Further preferably, the petroleum cracking product is white oil.

[0013] Preferably, the fluorinated ethylene propylene copolymer FEP is a polyperfluoroethylene propylene concentrated dispersion or a polyperfluoroethylene propylene powder, and the manufacturer is DS603 or DS605 of Shandong Huaxia Shenzhou New Materials Co., Ltd.

[0014] PTFE dispersed resin powder particles coexist in an amorphous phase and a crystalline phase. When the relative molecular weight is less than 2 million, the crystalline phase decreases and the mechanical properties deteriorate. When the relative molecular weight is greater than 10 million, the crystalline phase of the polytetrafluoroethylene dispersed resin increases, and the particles easily fill the original gaps and micropores between molecules through movement, thereby reducing the porosity and air permeability. The applicant has found that adding 2-8 parts by weight of fluorinated ethylene propylene copolymer (FEP) and 65-75 parts by weight of polytetrafluoroethylene dispersed resin with a relative molecular weight of 2 million to 10 million can improve the filling rate of the gaps and micropores between molecules when the particles move. Further, the polytetrafluoroethylene dispersed resin used in the present invention The glass transition temperature of tetrafluoroethylene dispersion resin is relatively high, the relative molecular weight is 3-8 million, and the average particle size is 400-700μm. The addition of fluorinated ethylene propylene copolymer can reduce the gaps between molecules and the filling rate of micropores during particle movement, making polytetrafluoroethylene have a larger porosity and air permeability, improving the crystal phase of the material, and enhancing the hydrophobicity and oleophobicity. At the same time, FEP is thermoplastic and fusible. After high-temperature sintering, the molecular clusters are melted, bonded and solidified, which can stabilize the PTFE molecular chain structure, improve the dimensional stability and creep resistance of the nanofilm, and can also solidify the fluorinated surfactant molecules, reduce movement and migration, and prevent the attenuation or loss of oleophobic properties.

[0015] Preferably, the low boiling point solvent includes at least one of isopropanol, methanol, ethanol, acetone, butanone, methyl ethyl ketone, ethyl acetate, butyl acetate, cyclohexane, n-octane and n-heptane.

[0016] Further preferably, the low boiling point solvent includes at least one of isopropanol, ethyl acetate, butyl acetate, acetone and cyclohexane.

[0017] Preferably, the fluorocarbon surfactant includes at least one of perfluoroalkyl acrylate, 2-(perfluorohexyl)ethyl methacrylate, perfluoroalkyl ethyl acrylate, and perfluorooctyl acrylate.

[0018] Further preferably, the fluorocarbon surfactant is 2-(perfluorohexyl) ethyl methacrylate and / or perfluoroalkyl acrylate. The selection of the fluorocarbon surfactant not only improves the crystallinity of the material, reduces the surface free energy of the material, but also improves the hydrophobic and oleophobic properties of the material. The perfluorinated side chain of the copolymer affects the crystallinity, and the fluoroalkyl part migrates to the copolymer-air interface. After forming a crystalline structure, the fluoroalkyl component is fixed on the polymer surface, effectively reducing the surface free energy, resulting in more fluorine elements enriched on the surface of the crystalline copolymer, so that the polymer surface has a better hydrophobic and oleophobic effect.

[0019] Selecting a suitable fluorocarbon surfactant can produce a synergistic effect and form crystals on the surface of the copolymer, thereby increasing the hydrophobic and oleophobic properties. The perfluoroalkyl side chains extend into the air and occupy the interface between the polymer and the air, effectively reducing the surface free energy of the polymer. Due to the enrichment of fluorine-containing groups on the polymer surface, the surface energy of the polymer is effectively reduced. In addition, since the side chains of the long fluorocarbon chains are very long and have crystalline properties, the perfluoro groups are perpendicular to the surface, forming a tightly ordered layered structure to avoid molecular segment migration and rearrangement.

[0020] Preferably, the mass ratio of the perfluoroalkoxy resin PFA to the polytetrafluoroethylene dispersion resin is (2-7): (65-75). The molecular chain rigidity of the polytetrafluoroethylene dispersion resin is relatively large, which affects the movement of the chain segments and molecular chains, thereby reducing the creep performance of PTFE. The applicant has found that when the mass ratio of the soluble perfluoroalkoxy resin (powder or emulsion) to the polytetrafluoroethylene dispersion resin is (2-7): (65-75), the migration and connection between the PTFE molecular chains can be promoted, thereby improving the slippage between the PTFE molecular chains and improving the tensile properties. At the same time, the perfluoroalkoxy resin is a thermoplastic material that melts at high temperature. When the molecular chains of PTFE and the PFA molecules form an interpenetrating network, they are solidified by high-temperature sintering and melt bonding, which can greatly enhance the creep resistance and mechanical strength of the PTFE nanomembrane, improve the pore size uniformity and dimensional stability of the nanomembrane, and improve the filtration interception efficiency and safety of the PTFE nanomembrane.

[0021] The perfluoroalkoxy resin is a soluble polytetrafluoroethylene, a tetrafluoroethylene-perfluoroalkoxy ether copolymer water dispersion emulsion or powder, for example: Zhejiang Juhua Co., Ltd., a polytetrafluoroethylene dispersion emulsion with the item number JF-4DCD or Shandong Huaxia Shenzhou New Materials Co., Ltd., a polytetrafluoroethylene dispersion emulsion with the item number DS 705.

[0022] Further preferably, the mass ratio of the soluble polytetrafluoroethylene to the polytetrafluoroethylene dispersion resin is 3-6:65-75.

[0023] Preferably, the relative molecular weight of the polytetrafluoroethylene dispersion resin is 3-8 million, and the average diameter is 400 μm-700 μm.

[0024] Preferably, the oleophobic polytetrafluoroethylene asymmetric nano-membrane (M0) has an average pore size of 5 nm-10 μm and a thickness of 10-160 μm.

[0025] Further preferably, the pre-filtration layer (N1) of the oleophobic polytetrafluoroethylene asymmetric nano-membrane has an average pore size of 10 nm-20 μm and a thickness of 10 μm-100 μm.

[0026] Further preferably, the interception layer membrane (N2) of the oleophobic polytetrafluoroethylene asymmetric nano-membrane has an average pore size of 5 nm-100 nm and a thickness of 2 μm-80 μm.

[0027] The second aspect of the present invention also provides a method for preparing the above-mentioned oleophobic polytetrafluoroethylene asymmetric nanofilm, the steps of which are as follows:

[0028] S1: mixed ripening;

[0029] Mix polytetrafluoroethylene dispersion resin, petroleum cracking product, fluorocarbon surfactant, perfluoroalkoxy resin, fluorinated ethylene propylene copolymer and low boiling point solvent, stir with a mixing mixer for 4-12 hours at a stirring rate of 10-60r / min to make a paste, and let the paste stand at 5-80°C for 6-24 hours to react and mature.

[0030] S2: preforming;

[0031] The mature paste is sieved with a 20-80 mesh screen, put into a blank making machine, and pre-pressed into a cylindrical blank at 5-40°C and 1-2MPa. The diameter of the blank is 150mm-200mm.

[0032] S3: Extrusion;

[0033] The cylindrical billet is fed into an extruder and extruded into round strips with a diameter of 20-30 mm at a speed of 2.0-3.0 m / min.

[0034] S4: calendering;

[0035] The round strip is fed into a calender to be made into a 0.2-0.3 mm thick film at a calendering rate of 5-16 m / min.

[0036] S5: Skim;

[0037] The membrane is sent to a degreasing furnace and heated for 1-4 minutes at 140-220°C to remove grease and solvent.

[0038] S6: stretch;

[0039] (1) The membrane after solvent removal is sent to a longitudinal stretching furnace, and axially stretched by 4-15 times at 180-260° C. to obtain a longitudinally stretched base membrane. Thereafter, the membrane is transversely stretched by 3-14 times at 100-240° C. to obtain a large-pore membrane M1.

[0040] (2) The film after solvent removal is sent to a longitudinal stretching furnace, and axially stretched by 1.5-8 times at 180-260°C to obtain a longitudinally stretched base film. Thereafter, the film is transversely stretched by 1.2-7 times at 100-240°C to obtain a small-pore membrane M2.

[0041] The pore size and porosity of the membrane are regulated by biaxial stretching. The larger the biaxial stretching ratio, the larger the pore size and porosity of the membrane M1 can be obtained. Conversely, the smaller the biaxial stretching ratio, the smaller the pore size and the lower the porosity of the membrane M2 can be obtained.

[0042] S7: Sintering.

[0043] The biaxially stretched PTFE membrane was sintered at 300-400° C. for 1-10 min to obtain oleophobic polytetrafluoroethylene single-layer nano-membranes N1 and N2.

[0044] S8: Hot pressing compounding.

[0045] Two (or more) PTFE nanomembranes N1 and N2 with different pore size structures are stacked and simultaneously fed into a hot pressing laminating machine for hot pressing lamination (nanomembrane N1 with a large pore size is used as a pre-filtration layer in contact with a cold roller, and nanomembrane N2 with a small pore size is used as a retention layer in contact with a hot roller), with a lamination pressure of 0.4-0.8MPa, a temperature of 360-430°C, and a speed of 1-6m / min, to obtain an oleophobic polytetrafluoroethylene asymmetric nanomembrane M0.

[0046] Beneficial effects:

[0047] 1. The oleophobic polytetrafluoroethylene asymmetric nanomembrane of the present invention has a polytetrafluoroethylene dispersed resin with a relatively high glass transition temperature. When combined with a fluorinated ethylene propylene copolymer and a perfluoroalkoxy resin to prepare the oleophobic polytetrafluoroethylene, the oleophobic polytetrafluoroethylene not only has excellent high temperature resistance, but also increases the crystallinity, improves the mechanical strength, dimensional stability and creep resistance of the oleophobic polytetrafluoroethylene asymmetric nanomembrane, expands the application range of the filtration pressure difference of the polytetrafluoroethylene asymmetric nanomembrane, improves the safety of the filtration membrane, and prolongs the service life of the polytetrafluoroethylene asymmetric nanomembrane.

[0048] 2. The polytetrafluoroethylene asymmetric nanomembrane in the present invention has hydrophobic and oleophobic properties, which further expands the application range of the polytetrafluoroethylene asymmetric nanomembrane and can be used for the separation of oily compounds or particulate matter, or the waterproof and breathable properties of low surface tension liquids. At the same time, it also improves the anti-pollution performance and service life of the polytetrafluoroethylene asymmetric nanomembrane.

[0049] 3. The polytetrafluoroethylene asymmetric nano-membrane in the present invention has an asymmetric structure, and adopts a membrane N1 with a large pore size and a high porosity as a pre-filtration layer, which intercepts large particles, colloids and other pollutants as the upstream surface, thereby increasing the pollutant holding capacity; a membrane N2 with a small pore size and a high interception efficiency is adopted as the interception layer to provide a more efficient interception efficiency; an integrated deep gradient filtration structure is formed by hot pressing and compounding, thereby improving the overall air flux, pollutant holding capacity and interception efficiency of the nano-membrane, and greatly extending the service life of the membrane.

[0050] 4. The polytetrafluoroethylene asymmetric nano-membrane in the present invention has an average pore size of 5nm-10μm and a thickness of 20-240μm under the synergistic effect of polytetrafluoroethylene dispersed resin with a relative molecular weight of 2-10 million, fluorinated ethylene propylene copolymer and perfluoroalkoxy resin. The fusible resin is melt-bonded and solidified at high temperature, which not only improves the pore size uniformity, porosity and air permeability of the polytetrafluoroethylene asymmetric nano-membrane, but also improves the dimensional stability and modulus of the membrane, increases the membrane safety and reduces the filtration energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 This is a scanning electron microscope image of the polytetrafluoroethylene asymmetric nano-membrane pre-filtration layer N1 prepared according to Example 1 at a magnification of 8000.

[0052] Figure 2 This is a scanning electron microscope image of the polytetrafluoroethylene asymmetric nanomembrane retention layer N2 prepared according to Example 1 at a magnification of 8000.

[0053] Figure 3 This is a scanning electron microscope image of a cross section of a polytetrafluoroethylene asymmetric nanomembrane prepared according to Example 1 at a magnification of 1000.

[0054] Figure 4 This is a test diagram of the water contact angle of the polytetrafluoroethylene asymmetric nanofilm prepared in Example 1.

[0055] Figure 5 This is a water contact angle test diagram of the polytetrafluoroethylene asymmetric nanofilm prepared in Example 2.

[0056] Figure 6 This is a water contact angle test diagram of the polytetrafluoroethylene asymmetric nanofilm prepared in Example 3.

[0057] Figure 7 This is a water contact angle test diagram of the polytetrafluoroethylene asymmetric nanofilm prepared in Comparative Example 1.

[0058] Figure 8 This is a water contact angle test diagram of the polytetrafluoroethylene asymmetric nanomembrane prepared in Comparative Example 2.

[0059] Fig. 9 This is a water contact angle test diagram of the polytetrafluoroethylene asymmetric nanomembrane prepared in Comparative Example 3.

[0060] Fig.10 These are the data obtained by measuring the polytetrafluoroethylene dispersion resin of Example 1 using a DSC-500T differential scanning calorimeter. DETAILED DESCRIPTION

[0061] Example

[0062] The technical solution of the present invention is described in detail below by way of examples, but the protection scope of the present invention is not limited to the examples. Unless otherwise specified, the raw materials in the present invention are all commercially available.

[0063] Example 1

[0064] Example 1 provides an oleophobic polytetrafluoroethylene asymmetric nanomembrane, the raw materials of the oleophobic polytetrafluoroethylene asymmetric nanomembrane, in parts by weight, include 72 parts of polytetrafluoroethylene dispersion resin, 18 parts of petroleum cracking product, 3 parts of fluorocarbon surfactant, 3 parts of perfluoroalkyl resin, 7 parts of fluorinated ethylene propylene copolymer, and 10 parts of low boiling point solvent.

[0065] The polytetrafluoroethylene dispersion resin has a relative molecular weight of 4.5-5.5 million, an average particle size of 500 μm, a standard relative density of 2.17 (test method ASTM D4895), a melting point of 327° C., a product number of F104, and is purchased from Daikin, Japan.

[0066] The low boiling point solvent is acetone.

[0067] The petroleum cracking product is white oil.

[0068] The fluorocarbon surfactant is 2-(perfluorohexyl)ethyl methacrylate (CAS: 2144-53-8) purchased from Hubei Xinkang Pharmaceutical Chemical Co., Ltd.

[0069] The perfluoroalkyl resin is soluble polytetrafluoroethylene (article number: DS 705) from Shandong Huaxia Shenzhou New Materials Co., Ltd.

[0070] The fluorinated ethylene propylene copolymer is a fluorinated ethylene fluorinated propylene copolymer (article number: DS603), Shandong Huaxia Shenzhou New Materials Co., Ltd.

[0071] This embodiment also provides a method for preparing the above-mentioned oleophobic polytetrafluoroethylene asymmetric nanofilm, comprising the following steps:

[0072] S1: mixed ripening;

[0073] Add polytetrafluoroethylene dispersion resin, petroleum cracking product, fluorocarbon surfactant, perfluoroalkyl resin, fluorinated propylene copolymer and low boiling point solvent into a mixing mixer according to weight portions at a stirring speed of 15 r / min. After stirring for 12 hours, a paste is made. The paste is left to stand and mature at 45°C for 12 hours.

[0074] S2: preforming;

[0075] The mature paste was sieved with a 28-mesh sieve, placed in a pellet making machine at 60°C and 2MPa, and pre-pressed into 150mm cylindrical pellets.

[0076] S3: Extrusion;

[0077] The 150 mm column blank was fed into the extruder and extruded at a speed of 2.7 m / min to become a round bar with a diameter of 25 mm.

[0078] S4: calendering;

[0079] The round strips were fed into a calender to form a 0.2 mm thick film at a calendering rate of 10 m / min.

[0080] S5: Skim;

[0081] The membrane was placed in a degreasing furnace and heated for 2 minutes at 220°C to remove grease and solvent.

[0082] S6: stretching;

[0083] (1) The membrane after solvent removal was sent to a longitudinal stretching furnace, and axially stretched 9 times at 180°C to obtain a longitudinally stretched base membrane. Thereafter, the membrane was transversely stretched 7 times at 200°C to obtain a large-pore membrane M1.

[0084] (2) The membrane after solvent removal was sent to a longitudinal stretching furnace, and axially stretched 3 times at 215°C to obtain a longitudinally stretched base membrane. Thereafter, the membrane was transversely stretched 1.8 times at 230°C to obtain a small-pore membrane M2.

[0085] S7: Sintering.

[0086] (1) The biaxially stretched PTFE membrane M1 was sintered at 340° C. for 3 min to obtain an oleophobic polytetrafluoroethylene nano-membrane N1 (as a pre-filtration layer) with an average pore size of 100 nm.

[0087] (2) The biaxially stretched PTFE membrane M2 was sintered at 380° C. for 4 min to obtain an oleophobic polytetrafluoroethylene nano-membrane N2 (as a cutoff layer) with an average pore size of 20 nm.

[0088] S8: Hot pressing compounding.

[0089] A PTFE nanomembrane N1 with an average pore size of 100 nm (isopropyl alcohol IPA bubble point value of 0.18 MPa) is used as a pre-filtration layer, and a PTFE nanomembrane N2 with an average pore size of 20 nm (isopropyl alcohol IPA bubble point value of 0.50 MPa) is used as a retention layer. The pre-filtration layer N1 and the retention layer N2 are superimposed and simultaneously fed into a hot pressing laminating machine. By hot pressing lamination (the pre-filtration layer is in contact with a cold roller, and the retention layer is in contact with a hot roller), the lamination pressure is 0.8 MPa, the temperature is 420°C, and the vehicle speed is 3 m / min, to obtain an oleophobic polytetrafluoroethylene asymmetric nanomembrane M0.

[0090] Example 2

[0091] Example 2 provides an oleophobic polytetrafluoroethylene asymmetric nanomembrane, the raw materials of the oleophobic polytetrafluoroethylene asymmetric nanomembrane, in parts by weight, include 68 parts of polytetrafluoroethylene dispersion resin, 20 parts of petroleum cracking product, 5 parts of fluorocarbon surfactant, 5 parts of perfluoroalkyl resin, 6 parts of fluorinated propylene copolymer, and 8 parts of low boiling point solvent.

[0092] The polytetrafluoroethylene dispersion resin has a relative molecular weight of 4.5-5.5 million, an average diameter of 550 μm, a standard relative density of 2.16 (test method ASTM D4895), a melting point of 327° C., a product number of F106, and is purchased from Daikin, Japan.

[0093] The low boiling point solvent is isopropanol (CAS: 67-63-0) purchased from Longxi Science Co., Ltd.

[0094] The petroleum cracking product is aviation kerosene (CAS: 8008-20-6), which is purchased from Jinan Hexin Chemical Co., Ltd.

[0095] The fluorocarbon surfactant was perfluoroalkyl acrylate (CAS: 961-29-5) purchased from Hubei Jusheng Technology Co., Ltd.

[0096] The perfluoroalkyl resin is soluble polytetrafluoroethylene (article number: D210C) purchased from Daikin, Japan.

[0097] The fluorinated propylene copolymer is fluorinated ethylene fluorinated propylene copolymer (article number DS603), purchased from Shandong Huaxia Shenzhou New Materials Co., Ltd.

[0098] This embodiment also provides a method for preparing the above-mentioned polytetrafluoroethylene asymmetric nanofilm, comprising the following steps:

[0099] S1: mixed ripening;

[0100] Add polytetrafluoroethylene dispersion resin, petroleum cracking product, fluorocarbon surfactant, perfluoroalkyl resin, fluorinated propylene copolymer and low boiling point solvent into a mixing mixer according to weight portions, stir for 6 hours at a stirring speed of 20 r / min to make a paste, and let the paste stand and mature at 38°C for 12 hours.

[0101] S2: preforming;

[0102] The mature paste was sieved with a 20-mesh sieve, placed in a pellet making machine at 60°C and 2MPa, and pre-pressed into 150mm cylindrical pellets.

[0103] S3: Extrusion;

[0104] The 150 mm column blank was fed into the extruder and extruded at a speed of 2.5 m / min to become a 20 mm round bar.

[0105] S4: calendering;

[0106] The round strips were fed into a calender to form a 0.2 mm thick film at a calendering rate of 16 m / min.

[0107] S5: Skim;

[0108] The membrane was placed in a degreasing furnace and heated for 2 minutes at 220°C to remove grease and solvent.

[0109] S6: stretching;

[0110] (1) The membrane after solvent removal was sent to a longitudinal stretching furnace, and axially stretched 9 times at 180°C to obtain a longitudinally stretched base membrane. Thereafter, the membrane was transversely stretched 8 times at 190°C to obtain a large-pore membrane M1.

[0111] (2) The membrane after solvent removal was sent to a longitudinal stretching furnace, and axially stretched 3.5 times at 225°C to obtain a longitudinally stretched base membrane. Thereafter, the membrane was transversely stretched 3 times at 210°C to obtain a small-pore membrane M2.

[0112] S7: Sintering.

[0113] (1) The biaxially stretched PTFE membrane M1 was sintered at 320°C for 3 min to obtain an oleophobic polytetrafluoroethylene nanomembrane N1 with an average pore size of 450 nm.

[0114] (2) The biaxially stretched PTFE membrane M2 was sintered at 370°C for 4 min to obtain an oleophobic polytetrafluoroethylene nanomembrane N2 with an average pore size of 30 nm.

[0115] S8: Hot pressing compounding.

[0116] A PTFE nanomembrane N1 with an average pore size of 450 nm (isopropyl alcohol IPA bubble point value of 0.08 MPa) is used as a pre-filtration layer, and a PTFE nanomembrane N2 with an average pore size of 30 nm (isopropyl alcohol IPA bubble point value of 0.37 MPa) is used as a retention layer. The pre-filtration layer N1 and the retention layer N2 are superimposed and simultaneously fed into a hot pressing laminating machine. By hot pressing lamination (the pre-filtration layer is in contact with a cold roller, and the retention layer is in contact with a hot roller), the lamination pressure is 0.8 MPa, the temperature is 420°C, and the vehicle speed is 3 m / min, to obtain an oleophobic polytetrafluoroethylene asymmetric nanomembrane M0.

[0117] Example 3

[0118] Example 3 provides an oleophobic polytetrafluoroethylene asymmetric nanomembrane, the raw materials of the oleophobic polytetrafluoroethylene asymmetric nanomembrane, in parts by weight, include 65 parts of polytetrafluoroethylene dispersion resin, 22 parts of petroleum cracking products, 7 parts of fluorocarbon surfactants, 6 parts of perfluoroalkyl resins, 8 parts of fluorinated propylene copolymers, and 9 parts of low-boiling point solvents.

[0119] The polytetrafluoroethylene dispersion resin has a relative molecular weight of 4-7 million, an average diameter of 450-650 μm, a product number of F104, and is purchased from Daikin, Japan.

[0120] The low boiling point solvent is acetone (CAS: 67-64-1) purchased from Shandong Fengcang Chemical Co., Ltd.

[0121] The petroleum cracking product is aviation kerosene (CAS: 8008-20-6), which is purchased from Jinan Hexin Chemical Co., Ltd.

[0122] The fluorocarbon surfactant is 2-(perfluorohexyl)ethyl methacrylate (CAS: 2144-53-8) purchased from Hubei Xinkang Pharmaceutical Chemical Co., Ltd.

[0123] The perfluoroalkyl resin is a soluble polytetrafluoroethylene (Teflon TM PFAD 335D) was purchased from DuPont.

[0124] The mass ratio of the soluble polytetrafluoroethylene to the polytetrafluoroethylene dispersed resin is 6:65.

[0125] The fluorinated propylene copolymer is fluorinated ethylene fluorinated propylene copolymer (NEOFLON NC1500), purchased from Daikin, Japan.

[0126] This embodiment also provides a method for preparing the oleophobic polytetrafluoroethylene asymmetric nanofilm as described above, and the specific steps are the same as those in Example 1.

[0127] Comparative Example 1

[0128] An oleophobic polytetrafluoroethylene asymmetric nanomembrane, no fluorocarbon surfactant is added, the low boiling point solvent is butanone, and the rest is the same as in Example 1.

[0129] Comparative Example 2

[0130] An oleophobic polytetrafluoroethylene asymmetric nanomembrane, the mass ratio of soluble polytetrafluoroethylene to polytetrafluoroethylene dispersion resin is changed to 12:70 (wherein the soluble polytetrafluoroethylene is 12 parts), the standing aging time in step S1 is changed to 24 hours, and the rest is the same as in Example 1.

[0131] Comparative Example 3

[0132] An oleophobic polytetrafluoroethylene asymmetric nanomembrane, wherein the relative molecular weight of the polytetrafluoroethylene dispersion resin is changed to 200,000-1,000,000, the average diameter is 5-15 μm, the low boiling point solvent is methyl ethyl ketone, and the rest is the same as in Example 1.

[0133] Performance Testing Methods

[0134] 1. Air permeability test: Examples 1-3 and Comparative Examples 1-3 were subjected to air permeability tests. The test method was in accordance with GB1037-1988. The specific values ​​are shown in Table 1.

[0135] 2. Bubble point value test: The bubble point value test was performed on Examples 1-3 and Comparative Examples 1-3. The test method was based on the separation membrane pore size test method of GBT32361-2015. The specific values ​​are shown in Table 1.

[0136] 3. Contact angle test: The contact angle tester of DropMeter A-100P was used to test the embodiments 1-3 and comparative examples 1-3. The specific values ​​are shown in Table 1.

[0137] 4. Tensile strength test: The tensile strength test was performed on Examples 1-3 and Comparative Examples 1-3. The test method was in accordance with GB / T1040-92. The specific values ​​are shown in Table 1.

[0138] 5. Surface morphology test: The structure diagram of Example 1 at magnifications of 8000 and 1000 was analyzed by scanning electron microscopy. Figure 1 , 2 and 3.

[0139] Performance test data

[0140] Table 1

[0141]

Claims

1. An oleophobic polytetrafluoroethylene asymmetric nanofilm, characterized in that: The raw materials of the oleophobic polytetrafluoroethylene asymmetric nanomembrane include, by weight, 60-85 parts of polytetrafluoroethylene dispersion resin, 15-30 parts of petroleum cracking product, 1-10 parts of fluorocarbon surfactant, 1-10 parts of perfluoroalkoxy resin, 1-12 parts of fluorinated ethylene propylene copolymer, and 2-15 parts of low boiling point solvent. The mass ratio of the perfluoroalkoxy resin to the polytetrafluoroethylene dispersion resin is (2-7): (65-75).

2. The oleophobic polytetrafluoroethylene asymmetric nanofilm according to claim 1, characterized in that: The weight proportion of the polytetrafluoroethylene dispersion resin is 65-80 parts, the petroleum cracking product is 17-23 parts, the fluorocarbon surfactant is 2-8 parts, the perfluoroalkoxy resin is 2-7 parts, the fluorinated ethylene propylene copolymer is 3-10 parts, and the low boiling point solvent is 3-12 parts.

3. The oleophobic polytetrafluoroethylene asymmetric nanofilm according to claim 1, characterized in that: The petroleum cracking product includes at least one of aviation kerosene, white oil, paraffin oil or dearomatized solvent oil.

4. The oleophobic polytetrafluoroethylene asymmetric nanofilm according to claim 1, characterized in that: The fluorinated ethylene propylene copolymer is FEP concentrated emulsion or FEP resin powder.

5. The oleophobic polytetrafluoroethylene asymmetric nanofilm according to claim 2, characterized in that: The low boiling point solvent includes one or more of isopropanol, methanol, ethanol, acetone, ethyl acetate, butyl acetate, cyclohexane, n-octane, and n-heptane.

6. An oleophobic polytetrafluoroethylene asymmetric nanofilm according to claim 2 or 3, characterized in that: The fluorocarbon surfactant includes at least one of perfluoroalkyl acrylate, 2-(perfluorohexyl)ethyl methacrylate, and perfluoroalkyl ethyl acrylate.

7. The oleophobic polytetrafluoroethylene asymmetric nanofilm according to claim 6, characterized in that: The relative molecular weight of the polytetrafluoroethylene dispersion resin is 3-8 million, the average particle size is 400-700 μm, the standard relative density is 2.1-2.2, and the melting point temperature is 325-329° C.

8. The oleophobic polytetrafluoroethylene asymmetric nanofilm according to claim 1, characterized in that: The oleophobic polytetrafluoroethylene asymmetric nano-membrane is divided into a pre-filtration layer and a retention layer. The pre-filtration layer has an average pore size of 10nm-20μm and a thickness of 10μm-150μm. The retention layer has an average pore size of 5nm-200nm and a thickness of 2μm-80μm.

9. The oleophobic polytetrafluoroethylene asymmetric nanofilm according to claim 1, characterized in that: The asymmetric structure is an integrated composite asymmetric gradient filtration structure formed by hot-pressing and composite two or more layers of PTFE membrane materials with different pore sizes.

10. A method for preparing an oleophobic polytetrafluoroethylene asymmetric nanofilm according to any one of claims 1 to 9, comprising the following steps: S1: Mixing and ripening reaction; S2: preform blank; S3: Extrusion; S4: calendering; S5: Skim; S6: stretching to form a hole; S7: sintering and shaping; S8: Multi-layer composite.

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