A hydrophilic polytetrafluoroethylene film, its preparation method and application

Abstract

This invention provides a hydrophilic polytetrafluoroethylene (PTFE) film, its preparation method, and its application, belonging to the field of film processing technology. The surface of the hydrophilic PTFE film contains polar groups; hydrophilic particles are uniformly distributed within the film; and the hydrophilic particles account for 0.1–0.7% of the mass of the hydrophilic PTFE film. The hydrophilic PTFE film provided by this invention has high quality, uniform color, and good hydrophilicity.

Description

Technical Field

[0001] This invention relates to the field of thin film processing technology, and in particular to a hydrophilic polytetrafluoroethylene film, its preparation method, and its applications. Background Technology

[0002] Polytetrafluoroethylene (PTFE) has excellent mechanical properties, corrosion resistance, and temperature resistance, and its products are widely used in industrial manufacturing and electronic and electrical fields.

[0003] PTFE materials are extremely hydrophobic, and require hydrophilic treatment before application in electronics, energy, and other fields. Common methods for hydrophilic treatment of PTFE films include plasma surface treatment and surface coating with hydrophilic agents. Among these, plasma surface treatment not only acts on the surface of the film but may also penetrate into the material's interior, affecting its performance, and the equipment cost is relatively high. PTFE films prepared by surface coating with hydrophilic agents have drawbacks such as short-lasting hydrophilic effect and poor water resistance.

[0004] Therefore, there is an urgent need to provide a hydrophilic polytetrafluoroethylene film with excellent hydrophilic properties and low cost. Summary of the Invention

[0005] To address one or more technical problems existing in the prior art, the present invention provides a hydrophilic polytetrafluoroethylene film, its preparation method, and its application. The preparation method provided by the present invention is simple to operate and low in cost, and can meet the needs of mass production of hydrophilic ultrathin biaxially oriented polytetrafluoroethylene films. The hydrophilic polytetrafluoroethylene film obtained is of high quality, uniform color, and good hydrophilicity.

[0006] In a first aspect, the present invention provides a hydrophilic polytetrafluoroethylene (PTFE) film, wherein the surface of the hydrophilic PTFE film contains polar groups; hydrophilic particles are uniformly distributed in the hydrophilic PTFE film; and the hydrophilic particles account for 0.1 to 0.7% of the mass of the hydrophilic PTFE film.

[0007] Preferably, the hydrophilic particles are hydrophilic metal oxides, and more preferably hydrophilic zinc oxide;

[0008] The polar group is at least one of hydroxyl and carboxyl groups;

[0009] Preferably, the thickness of the hydrophilic polytetrafluoroethylene film is 5–15 μm;

[0010] The tensile strength of the hydrophilic polytetrafluoroethylene film is 8–14 MPa.

[0011] The contact angle of the hydrophilic polytetrafluoroethylene film is 45–55°; and / or

[0012] The porosity of the hydrophilic polytetrafluoroethylene film is 80-95%.

[0013] The present invention provides a second aspect a method for preparing the hydrophilic polytetrafluoroethylene film described in the first aspect, the method comprising:

[0014] A metal salt solution and an extrusion aid are mixed to obtain a composite extrusion aid, and the composite extrusion aid is mixed with polytetrafluoroethylene to obtain a mixture.

[0015] The mixture is subjected to blanking, extrusion, calendering, degreasing, and longitudinal stretching to obtain a longitudinally stretched strip;

[0016] The longitudinal stretching strip is subjected to hydrophilic treatment, transverse stretching, high-temperature sintering, and cooling to obtain the hydrophilic polytetrafluoroethylene film.

[0017] Preferably, the metal salt accounts for 1-3% of the mass of the composite extrusion aid; and / or

[0018] The metal salt accounts for 0.2% to 1% of the mass of the mixture.

[0019] Preferably, the extrusion aid is any one or a combination of naphtha, gasoline, aviation kerosene, and petroleum ether.

[0020] Preferably, the extrusion compression ratio of the pushing is 10 to 100;

[0021] The thickness of the calendering is 100–200 μm; and / or

[0022] The degreasing temperature is 120–340°C.

[0023] Preferably, the longitudinal stretching temperature is 160–350°C; and / or

[0024] The longitudinal stretching ratio is 3 to 20 times.

[0025] Preferably, the hydrophilic treatment involves immersing the longitudinally stretched strip in a sodium naphthalene solution under a protective atmosphere to perform a double-sided hydrophilic treatment;

[0026] Preferably, the hydrophilic treatment time is 10 to 300 seconds; more preferably, the concentration of the sodium naphthalene solution is 0.5 to 5 mol / L.

[0027] Preferably, the stretching temperature for the transverse stretching is 150–350°C;

[0028] The stretching ratio of the lateral stretching is 3 to 15 times;

[0029] The high-temperature sintering temperature is 327–410°C; and / or

[0030] The cooling rate of the cooling process is 2 to 60°C / min.

[0031] In a third aspect, the present invention provides the application of the hydrophilic polytetrafluoroethylene film described in the first aspect in the fields of batteries and filtration.

[0032] Compared with the prior art, the present invention has at least the following beneficial effects:

[0033] The hydrophilic polytetrafluoroethylene film provided by this invention has hydrophilic particles uniformly distributed inside, which can improve the wettability of the film. The surface of the hydrophilic polytetrafluoroethylene film contains polar groups, which can increase the surface free energy of the film, further improving wettability and enhancing the hydrophilicity of the film. The hydrophilic polytetrafluoroethylene film provided by this invention has high quality, uniform color, and good hydrophilicity.

[0034] This invention involves uniformly introducing a metal salt into a mixture containing an extrusion aid and polytetrafluoroethylene (PTFE), followed by processes such as compaction, extrusion, calendering, degreasing, and longitudinal stretching. The metal salt undergoes dissolution, drying, precipitation, and baking to obtain a longitudinally stretched strip with uniformly distributed recrystallized metal salt particles on its interior and surface. The strip is then subjected to hydrophilic treatment to introduce polar groups such as hydroxyl and carboxyl groups onto the film surface, which increases the film's surface free energy, improves wettability, and enhances its hydrophilicity. Simultaneously, the OH groups in the alkaline solution during the hydrophilic treatment process... — Ions can react with metal ions in the internal and surface metal salts to generate alkali. Finally, the hydrophilically treated longitudinally stretched tape is laterally stretched. Because the biaxially stretched PTFE is extremely thin (approximately 5-15 μm) and soft, hydrophilic treatment before lateral stretching effectively avoids damage and handling difficulties during the hydrophilic treatment process. The film is shaped by high-temperature sintering, which decomposes the alkali evenly distributed inside and on the surface of the film into hydrophilic metal oxides, further improving the film's wettability and hydrophilicity without affecting its strength. Furthermore, the in-situ generation of hydrophilic metal oxides overcomes the problems of easy agglomeration and uneven dispersion that occur when metal oxide powder is directly added to the mixture, affecting film uniformity and leading to defects and reduced strength. The preparation method of the hydrophilic PTFE film of this invention is simple to operate and low in cost, meeting the needs of mass production of ultra-thin biaxially stretched hydrophilic PTFE films. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a contact angle diagram of the hydrophilic polytetrafluoroethylene film provided in Embodiment 3 of the present invention;

[0037] Figure 2 This is a contact angle diagram of the untreated polytetrafluoroethylene film provided in Comparative Example 6 of the present invention. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0039] The present invention provides a hydrophilic polytetrafluoroethylene (PTFE) film in a first aspect, wherein the surface of the hydrophilic PTFE film comprises polar groups; hydrophilic particles are uniformly distributed in the hydrophilic PTFE film; and the hydrophilic particles account for 0.1 to 0.7% of the mass of the hydrophilic PTFE film (for example, it can be 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, or 0.7%).

[0040] The hydrophilic polytetrafluoroethylene (PTFE) film provided by this invention has hydrophilic particles uniformly distributed inside, which can improve the wettability of the film. The surface of the hydrophilic PTFE film contains polar groups, which can increase the surface free energy of the film, further improving wettability and enhancing the hydrophilicity of the film. The hydrophilic PTFE film provided by this invention has high quality, uniform color, and good hydrophilicity.

[0041] According to some preferred embodiments, the hydrophilic particles are hydrophilic metal oxides, preferably hydrophilic zinc oxide;

[0042] The polar group is at least one of hydroxyl and carboxyl groups;

[0043] According to some preferred embodiments, the thickness of the hydrophilic polytetrafluoroethylene film is 5 to 15 μm (for example, it can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm).

[0044] The hydrophilic polytetrafluoroethylene film has a tensile strength of 8–14 MPa (for example, it can be 8 MPa, 8.5 MPa, 8.6 MPa, 8.8 MPa, 9 MPa, 9.2 MPa, 9.5 MPa, 10 MPa, 10.5 MPa, 11 MPa, 11.5 MPa, 12 MPa, 12.5 MPa, 12.7 MPa, 13 MPa, 13.5 MPa or 14 MPa).

[0045] The contact angle of the hydrophilic polytetrafluoroethylene film is 45–55°; and / or

[0046] The porosity of the hydrophilic polytetrafluoroethylene film is 80-95% (for example, it can be 80%, 82%, 83.5%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 93.6%, 94%, 94.5% or 95%).

[0047] The hydrophilic polytetrafluoroethylene film provided by this invention has a porosity of 80-95% and a higher specific surface area. When used as a fuel cell membrane skeleton material, it can greatly increase the proportion of the membrane body material and improve the ion exchange efficiency.

[0048] The present invention provides a second aspect a method for preparing the hydrophilic polytetrafluoroethylene film described in the first aspect, the method comprising:

[0049] A metal salt solution and an extrusion aid are mixed to obtain a composite extrusion aid, and the composite extrusion aid is mixed with polytetrafluoroethylene to obtain a mixture.

[0050] The mixture is subjected to blanking, extrusion, calendering, degreasing, and longitudinal stretching to obtain a longitudinally stretched strip;

[0051] The longitudinal stretching strip is subjected to hydrophilic treatment, transverse stretching, high-temperature sintering, and cooling to obtain the hydrophilic polytetrafluoroethylene film.

[0052] It should be noted that the solvent in the metal salt solution of the present invention is preferably at least one of petroleum ether, diethyl ether, tetrahydrofuran, and acetone, but is not limited to the above solvents and can be adjusted according to the type of metal salt. After hydrophilic treatment and before transverse stretching, the longitudinal stretching strip after hydrophilic treatment is further included in the steps of cleaning and drying; the cleaning is first done with an organic solvent and then with water; the organic solvent is preferably one or more of acetone and ethanol; the drying temperature is 80-150°C and the drying time is 20-200s.

[0053] This invention involves uniformly introducing a metal salt into a mixture containing an extrusion aid and polytetrafluoroethylene (PTFE), followed by processes such as compaction, extrusion, calendering, degreasing, and longitudinal stretching. The metal salt undergoes dissolution, drying, precipitation, and baking to obtain a longitudinally stretched strip with uniformly distributed recrystallized metal salt particles on its interior and surface. The strip is then subjected to hydrophilic treatment to introduce polar groups such as hydroxyl and carboxyl groups onto the film surface, which increases the film's surface free energy, improves wettability, and enhances its hydrophilicity. Simultaneously, the OH groups in the alkaline solution during the hydrophilic treatment process... — Ions can react with metal ions in the internal and surface metal salts to generate alkali. Then, the hydrophilically treated longitudinally stretched tape is stretched laterally. Because the biaxially stretched PTFE is extremely thin (approximately 5-15 μm) and soft, hydrophilic treatment before lateral stretching effectively avoids damage and handling difficulties during the hydrophilic treatment process. The film is shaped by high-temperature sintering, which decomposes the alkali evenly distributed inside and on the surface of the film into hydrophilic metal oxides, further improving the film's wettability and hydrophilicity without affecting its strength. Furthermore, the in-situ generation of hydrophilic metal oxides overcomes the problems of easy agglomeration and uneven dispersion that occur when metal oxide powder is directly added to the mixture, affecting film uniformity and leading to defects and reduced strength. The preparation method of the hydrophilic PTFE film of this invention is simple to operate and low in cost, meeting the needs of mass production of ultra-thin biaxially stretched hydrophilic PTFE films.

[0054] According to some preferred embodiments, the metal salt accounts for 1-3% of the mass of the composite extrusion aid (e.g., 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, or 3%); and / or

[0055] The metal salt accounts for 0.2% to 1% of the mass of the mixture (for example, it can be 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, or 1%).

[0056] By controlling the amount of metal salt within the above-mentioned range, this invention ensures that the content of hydrophilic particles (hydrophilic metal oxides) in the film is controlled at 0.1-0.7%, thereby improving the hydrophilicity of the film while guaranteeing its uniformity and strength. If the content of metal salt is too small, the improvement in hydrophilicity will not be significant; if the content of metal salt is too large, it will affect the uniformity and strength of the film.

[0057] According to some preferred embodiments, the extrusion aid is any one or a combination of naphtha, gasoline, aviation kerosene, and petroleum ether.

[0058] According to some preferred embodiments, the extrusion compression ratio of the push is 10 to 100 (for example, it can be 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100).

[0059] The thickness of the calendering is 100–200 μm (e.g., it can be 100 μm, 5–15 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm or 200 μm); and / or

[0060] The degreasing temperature is 120–340°C (for example, it can be 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, or 340°C).

[0061] According to some preferred embodiments, the longitudinal stretching temperature is 160–350°C (e.g., it can be 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, or 350°C); and / or

[0062] The longitudinal stretching ratio is 3 to 20 times (for example, it can be 3 times, 4 times, 5 times, 6 times, 7 times, 8 times, 9 times, 10 times, 11 times, 12 times, 13 times, 14 times, 15 times, 16 times, 17 times, 18 times, 19 times or 20 times).

[0063] According to some preferred embodiments, the hydrophilic treatment involves immersing the longitudinally stretched strip in a sodium naphthalene solution under a protective atmosphere for double-sided hydrophilic treatment. This invention uses a sodium naphthalene solution to hydrophilically treat the longitudinally stretched strip, introducing polar groups such as hydroxyl and carboxyl groups onto the surface of the strip, which can increase the surface free energy of the film, improve wettability, and enhance the hydrophilicity of the film.

[0064] Preferably, the hydrophilic treatment time is 10–300 s (e.g., 10 s, 20 s, 30 s, 40 s, 50 s, 60 s, 70 s, 80 s, 90 s, 100 s, 110 s, 120 s, 130 s, 140 s, 150 s, 160 s, 170 s, 180 s, 190 s, 200 s, 210 s, 220 s, 230 s, 240 s, 250 s, 260 s, 270 s, 280 s, 290 s, or 300 s). The hydrophilic treatment time of the present invention can be adjusted according to the concentration of sodium naphthalene solution; the time can be appropriately shortened when the sodium naphthalene concentration is high, and appropriately extended when the sodium naphthalene concentration is low.

[0065] More preferably, the concentration of the sodium naphthalene solution is 0.5 to 5 mol / L (for example, it can be 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L or 5 mol / L).

[0066] By controlling the concentration of the sodium naphthalene solution within the aforementioned range, this invention ensures that polar groups such as hydroxyl and carboxyl groups are introduced onto the surface of the longitudinally stretched tape without reducing the film's performance. If the concentration is too low, the hydrophilic treatment effect is not significant, and the improvement in the film's hydrophilicity is minimal; if the concentration is too high, it will reduce the film's mechanical properties.

[0067] According to some preferred embodiments, the stretching temperature for the transverse stretching is 150-350°C (for example, it can be 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C or 350°C).

[0068] The stretching ratio of the lateral stretching is 3 to 15 times (for example, it can be 3 times, 4 times, 5 times, 6 times, 7 times, 8 times, 9 times, 10 times, 11 times, 12 times, 13 times, 14 times or 15 times).

[0069] The high-temperature sintering temperature is 327–410℃ (for example, it can be 327℃, 330℃, 335℃, 340℃, 345℃, 350℃, 355℃, 360℃, 365℃, 370℃, 375℃, 380℃, 385℃, 390℃, 395℃, 400℃, 405℃, or 410℃). In this invention, after transverse stretching, high-temperature sintering is performed to shape the film and simultaneously decompose the alkali uniformly distributed in the film to generate metal oxides, ultimately obtaining a polytetrafluoroethylene film with hydrophilic metal oxides uniformly dispersed internally and on the surface, and / or...

[0070] The cooling rate of the cooling process is 2 to 60°C / min (for example, it can be 2°C / min, 5°C / min, 10°C / min, 15°C / min, 20°C / min, 25°C / min, 30°C / min, 35°C / min, 40°C / min, 45°C / min, 50°C / min, 55°C / min or 60°C / min).

[0071] In a third aspect, the present invention provides the application of the hydrophilic polytetrafluoroethylene film described in the first aspect in the fields of batteries and filtration.

[0072] The hydrophilic polytetrafluoroethylene (PTFE) membrane provided by this invention has excellent hydrophilicity, tensile properties, and a high specific surface area. When used as a fuel cell membrane skeleton material, it can greatly increase the proportion of the membrane body material and improve ion exchange efficiency. In the field of water filtration, the PTFE membrane provided by this invention benefits from its excellent hydrophilicity and, compared with traditional hydrophobic PTFE filter membranes, has the advantages of large water flux, less susceptibility to contamination, and thus improved membrane lifespan.

[0073] To more clearly illustrate the technical solution and advantages of the present invention, the present invention will be further described below in conjunction with embodiments.

[0074] Contact angle testing standard: GB / T 30693-2014

[0075] Tensile strength test standard: GB / T 1040.3-2006 Plastics - Determination of tensile properties - Part 3: Test conditions for films and sheets (ISO 527-3:1995, IDT)

[0076] Porosity testing standard: GB / T 40260-2021

[0077] Example 1

[0078] ZnCl2 powder was dissolved in diethyl ether to obtain a ZnCl2 solution with a ZnCl2 content of 10 wt%. The obtained ZnCl2 solution was mixed with petroleum ether at a mass ratio of 10:90 to obtain a composite extrusion aid. Then, polytetrafluoroethylene and the composite extrusion aid were thoroughly mixed in a mixer at a mass ratio of 80:20 to obtain a mixture.

[0079] After the mixture is pressed into a blank, it is pushed into a bar with a compression ratio of 25. Then, it is calendered into a sheet with a thickness of 200μm using two pressure rollers, and degreased at 200℃. Then, it is stretched longitudinally by 8 times at a stretching temperature of 240℃ to obtain a longitudinal stretch strip.

[0080] Under a dry nitrogen protective atmosphere, the longitudinal stretching strip was immersed in a 1 mol / L sodium naphthalene solution for 240 s, then removed and washed with ethanol and distilled water respectively, and dried at 120℃ for 60 s to obtain a surface-treated longitudinal stretching strip. The surface-treated longitudinal stretching strip was first stretched 8 times laterally at 260℃, then sintered at 350℃, and finally cooled at a cooling rate of 20℃ / min to obtain a hydrophilic polytetrafluoroethylene film.

[0081] The observed hydrophilic polytetrafluoroethylene film was uniform in color and without patterns. Samples were taken from the four corners and center of a 200cm × 200cm sample, and the water contact angle was measured to be 53.2°. The tensile strength of the film was measured to be 8.47 MPa, and the porosity was 83.47%.

[0082] Example 2

[0083] ZnCl2 powder was dissolved in tetrahydrofuran to obtain a ZnCl2 solution with a ZnCl2 content of 20 wt%. The obtained ZnCl2 solution was mixed with aviation kerosene at a mass ratio of 15:85 to obtain a composite extrusion aid. Then, polytetrafluoroethylene and the composite extrusion aid were thoroughly mixed in a mixer at a mass ratio of 75:25 to obtain a mixture. The mixture was pressed into a blank and then extruded into a bar at a compression ratio of 50. The bar was then calendered into a sheet with a thickness of 150 μm using two pressure rollers and degreased at 200°C. Finally, it was stretched longitudinally by 9 times at a stretching temperature of 240°C to obtain a longitudinally stretched strip.

[0084] Under a dry nitrogen protective atmosphere, the longitudinal stretching strip was immersed in a 1 mol / L sodium naphthalene solution for 240 s, then removed and washed with ethanol and distilled water respectively, and dried at 120℃ for 60 s to obtain a surface-treated longitudinal stretching strip. The surface-treated longitudinal stretching strip was first stretched 8 times laterally at 260℃, then sintered at 350℃, and finally cooled at a cooling rate of 20℃ / min to obtain a hydrophilic polytetrafluoroethylene film.

[0085] The observed hydrophilic polytetrafluoroethylene film was uniform in color and without patterns. Samples were taken from the four corners and the center of a 200cm×200cm sample, and the water contact angle was tested to be 54.3°. The tensile strength of the film was measured to be 9.24MPa, and the porosity was 85.91%.

[0086] Example 3

[0087] ZnCl2 powder was dissolved in acetone to obtain a ZnCl2 solution with a ZnCl2 content of 15 wt%. The ZnCl2 solution was then mixed with gasoline at a mass ratio of 15:85 to obtain a composite extrusion aid. Polytetrafluoroethylene and the composite extrusion aid were then thoroughly mixed in a mixer at a mass ratio of 80:20 to obtain a mixture. The mixture was pressed into a blank and then extruded into a bar at a compression ratio of 70. The bar was then calendered into a sheet with a thickness of 140 μm using two pressure rollers and degreased at 200°C. Finally, the sheet was stretched longitudinally by 13 times at a stretching temperature of 240°C to obtain a longitudinally stretched strip.

[0088] Under a dry nitrogen protective atmosphere, the longitudinal stretching strip was immersed in a 3 mol / L sodium naphthalene solution for 80 seconds, then removed and washed with ethanol and distilled water respectively, and dried at 120℃ for 60 seconds to obtain a surface-treated longitudinal stretching strip. The surface-treated longitudinal stretching strip was first stretched 10 times laterally at 190℃, then sintered at 350℃, and finally cooled at a cooling rate of 30℃ / min to obtain a hydrophilic polytetrafluoroethylene film.

[0089] The observed hydrophilic polytetrafluoroethylene film was uniform in color and without patterns. Samples were taken from the four corners and center of a 200cm × 200cm sample, and the water contact angle was measured to be 51.6°. Figure 1 The tensile strength of the film was measured to be 12.71 MPa, and the porosity was 94.21%.

[0090] Example 4

[0091] ZnCl2 powder was dissolved in tetrahydrofuran to obtain a ZnCl2 solution with a ZnCl2 content of 10 wt%. The obtained ZnCl2 solution was mixed with aviation kerosene at a mass ratio of 15:85 to obtain a composite extrusion aid. Then, polytetrafluoroethylene and the composite extrusion aid were thoroughly mixed in a mixer at a mass ratio of 75:25 to obtain a mixture. The mixture was pressed into a blank and extruded into a bar at a compression ratio of 70. Then, it was calendered into a sheet with a thickness of 200 μm using two pressure rollers and degreased at 150°C. Then, it was stretched longitudinally by 6 times at a stretching temperature of 260°C to obtain a longitudinally stretched strip.

[0092] Under a dry nitrogen protective atmosphere, the longitudinal stretching strip was immersed in a 4 mol / L sodium naphthalene solution for 20 seconds, then removed and washed with ethanol and distilled water respectively, and dried at 120℃ for 60 seconds to obtain a surface-treated longitudinal stretching strip. The surface-treated longitudinal stretching strip was first stretched 14 times laterally at 190℃, then sintered at 350℃, and finally cooled at a cooling rate of 40℃ / min to obtain a hydrophilic polytetrafluoroethylene film.

[0093] The observed hydrophilic polytetrafluoroethylene film was uniform in color and without patterns. Samples were taken from the four corners and center of a 200cm × 200cm sample, and the water contact angle was measured to be 48.7°. The tensile strength of the film was measured to be 12.52 MPa, and the porosity was 93.67%.

[0094] Comparative Example 1

[0095] Polytetrafluoroethylene and petroleum ether are thoroughly mixed in a mixer at a mass ratio of 80:20 to obtain a mixture. The mixture is pressed into a blank and then extruded into a bar at a compression ratio of 25. It is then calendered into a sheet with a thickness of 200μm using two pressure rollers, degreased at 200℃, and then stretched longitudinally by 8 times at a stretching temperature of 240℃ to obtain a longitudinal stretch strip.

[0096] Under a dry nitrogen protective atmosphere, the longitudinal stretching strip was immersed in a 1 mol / L sodium naphthalene solution for 240 s, then removed and washed with ethanol and distilled water respectively, and dried at 120℃ for 60 s to obtain a surface-treated longitudinal stretching strip. The surface-treated longitudinal stretching strip was first stretched 8 times laterally at 260℃, then sintered at 350℃, and finally cooled at a cooling rate of 20℃ / min to obtain a polytetrafluoroethylene film.

[0097] The observed polytetrafluoroethylene (PTFE) film was uniform in color and without patterns. Samples were taken from the four corners and center of a 200cm × 200cm sample, and the water contact angle was measured to be 89.6°. The tensile strength of the film was measured to be 9.26 MPa, and the porosity was 81.73%.

[0098] Comparative Example 2

[0099] ZnCl2 powder was dissolved in acetone to obtain a ZnCl2 solution with a ZnCl2 content of 50 wt%. The ZnCl2 solution was then mixed with gasoline at a mass ratio of 15:85 to obtain a composite extrusion aid. Polytetrafluoroethylene and the composite extrusion aid were then thoroughly mixed in a mixer at a mass ratio of 80:20 to obtain a mixture. The mixture was pressed into a blank and then extruded into a bar at a compression ratio of 70. The bar was then calendered into a sheet with a thickness of 140 μm using two pressure rollers and degreased at 200°C. Finally, the sheet was stretched longitudinally by 13 times at a stretching temperature of 240°C to obtain a longitudinally stretched strip.

[0100] Under a dry nitrogen protective atmosphere, the longitudinal stretching strip was immersed in a 3 mol / L sodium naphthalene solution for 80 seconds, then removed and washed with ethanol and distilled water respectively, and dried at 120℃ for 60 seconds to obtain a surface-treated longitudinal stretching strip. The surface-treated longitudinal stretching strip was first stretched 10 times laterally at 190℃, then sintered at 350℃, and finally cooled at a cooling rate of 30℃ / min to obtain a hydrophilic polytetrafluoroethylene film.

[0101] The observed polytetrafluoroethylene (PTFE) film exhibited numerous light-colored patterns and even holes on its surface. Samples were taken from the four corners and center of a 200cm × 200cm sample, and the water contact angle was measured to be 42.73°. The tensile strength of the film was measured to be 7.14 MPa, and the porosity was 94.68%.

[0102] Comparative Example 3

[0103] ZnCl2 powder was dissolved in tetrahydrofuran to obtain a ZnCl2 solution with a ZnCl2 content of 20 wt%. The obtained ZnCl2 solution was mixed with aviation kerosene at a mass ratio of 15:85 to obtain a composite extrusion aid. Then, polytetrafluoroethylene and the composite extrusion aid were thoroughly mixed in a mixer at a mass ratio of 75:25 to obtain a mixture. The mixture was pressed into a blank and then extruded into a bar at a compression ratio of 50. The bar was then calendered into a sheet with a thickness of 150 μm using two pressure rollers and degreased at 200°C. Finally, it was stretched longitudinally by 9 times at a stretching temperature of 240°C to obtain a longitudinally stretched strip.

[0104] Under a dry nitrogen protective atmosphere, the longitudinal stretching strip was immersed in a 0.1 mol / L sodium naphthalene solution for 240 s, then removed and washed with ethanol and distilled water respectively, and dried at 120℃ for 60 s to obtain a surface-treated longitudinal stretching strip. The surface-treated longitudinal stretching strip was first stretched 8 times laterally at 260℃, then sintered at 350℃, and finally cooled at a cooling rate of 20℃ / min to obtain a polytetrafluoroethylene film.

[0105] The observed hydrophilic polytetrafluoroethylene film was uniform in color and without patterns. Samples were taken from the four corners and center of a 200cm × 200cm sample, and the water contact angle was measured to be 92.2°. The tensile strength of the film was measured to be 10.97 MPa, and the porosity was 83.81%.

[0106] Comparative Example 4

[0107] ZnCl2 powder was dissolved in tetrahydrofuran to obtain a ZnCl2 solution with a ZnCl2 content of 20 wt%. The obtained ZnCl2 solution was mixed with aviation kerosene at a mass ratio of 15:85 to obtain a composite extrusion aid. Then, polytetrafluoroethylene and the composite extrusion aid were thoroughly mixed in a mixer at a mass ratio of 75:25 to obtain a mixture. The mixture was pressed into a blank and then extruded into a bar at a compression ratio of 50. The bar was then calendered into a sheet with a thickness of 150 μm using two pressure rollers and degreased at 200°C. Finally, it was stretched longitudinally by 9 times at a stretching temperature of 240°C to obtain a longitudinally stretched strip.

[0108] Under a dry nitrogen protective atmosphere, the longitudinal stretching strip was immersed in a 6 mol / L sodium naphthalene solution for 240 s, then removed and washed with ethanol and distilled water respectively, and dried at 120℃ for 60 s to obtain a surface-treated longitudinal stretching strip. The surface-treated longitudinal stretching strip was first stretched 8 times laterally at 260℃, then sintered at 350℃, and finally cooled at a cooling rate of 20℃ / min to obtain a polytetrafluoroethylene film.

[0109] The obtained polytetrafluoroethylene film exhibited a uniform color. Samples were taken from the four corners and center of a 200cm × 200cm sample, and the water contact angle was measured to be 42.73°. The tensile strength of the film was measured to be 6.77 MPa, and the porosity was 84.92%.

[0110] Comparative Example 5

[0111] Polytetrafluoroethylene and petroleum ether are thoroughly mixed in a mixer at a mass ratio of 80:20 to obtain a mixture. The mixture is pressed into a blank and then extruded into a bar at a compression ratio of 25. It is then calendered into a sheet with a thickness of 200μm using two pressure rollers, degreased at 200℃, and then stretched longitudinally by 8 times at a stretching temperature of 240℃ to obtain a longitudinal stretch strip.

[0112] The longitudinally stretched strip is first stretched 8 times laterally at 260℃, then sintered at 350℃, and finally cooled at a cooling rate of 20℃ / min to obtain a biaxially stretched polytetrafluoroethylene film.

[0113] Under a dry nitrogen protective atmosphere, a biaxially oriented polytetrafluoroethylene (PTFE) film was immersed in a 1 mol / L sodium naphthalene solution for 150 s, then removed and washed with ethanol and distilled water respectively, and dried at 120 °C for 60 s to obtain a surface-treated PTFE film.

[0114] The surface of the polytetrafluoroethylene film after surface treatment was observed to be uneven. There were multiple damages of different sizes on a randomly sampled 200cm×200cm sample, accounting for 16.7% of the sample area. Samples were taken from the four corners and the center, and the water contact angle was tested to be 56°. The tensile strength of the film was measured to be 4.53MPa and the porosity was 83.81%.

[0115] Comparative Example 6

[0116] Polytetrafluoroethylene and gasoline are thoroughly mixed in a mixer at a mass ratio of 80:20 to obtain a mixture. The mixture is pressed into a blank and then extruded into a bar at a compression ratio of 70. It is then calendered into a sheet with a thickness of 140μm using two pressure rollers, degreased at 200℃, and then stretched longitudinally by 13 times at a stretching temperature of 240℃ to obtain a longitudinal stretch strip.

[0117] The longitudinally stretched strip is first stretched 10 times laterally at 190°C, then sintered at 350°C, and finally cooled at a cooling rate of 30°C / min to obtain a hydrophilic polytetrafluoroethylene film.

[0118] The observed hydrophilic polytetrafluoroethylene film was uniform in color and without patterns. Samples were taken from the four corners and center of a 200cm × 200cm sample, and the water contact angle was measured to be 112.3°. Figure 2 The tensile strength of the film was measured to be 12.97 MPa, and the porosity was 92.55%.

[0119] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a hydrophilic polytetrafluoroethylene film, characterized in that, The preparation method includes: A metal salt solution and an extrusion aid are mixed to obtain a composite extrusion aid, and the composite extrusion aid is then mixed with polytetrafluoroethylene to obtain a mixture; the metal salt accounts for 1-3% of the mass of the composite extrusion aid; The metal salt accounts for 0.2% to 1% of the mass of the mixture; The mixture is subjected to blanking, extrusion, calendering, degreasing, and longitudinal stretching to obtain a longitudinally stretched strip; The longitudinally stretched strip is subjected to hydrophilic treatment, transverse stretching, high-temperature sintering, and cooling to obtain the hydrophilic polytetrafluoroethylene film; the hydrophilic treatment is performed by immersing the longitudinally stretched strip in a sodium naphthalene solution under a protective atmosphere for double-sided hydrophilic treatment; the concentration of the sodium naphthalene solution is 0.5~5 mol / L; The surface of the hydrophilic polytetrafluoroethylene film contains polar groups; hydrophilic particles are uniformly distributed in the hydrophilic polytetrafluoroethylene film; the hydrophilic particles account for 0.1~0.7% of the mass of the hydrophilic polytetrafluoroethylene film.

2. The preparation method according to claim 1, characterized in that, The hydrophilic particles are hydrophilic metal oxides; and / or The polar group is at least one of hydroxyl and carboxyl groups.

3. The preparation method according to claim 2, characterized in that, The hydrophilic particles are hydrophilic zinc oxide.

4. The preparation method according to claim 1, characterized in that, The thickness of the hydrophilic polytetrafluoroethylene film is 5~15μm; The tensile strength of the hydrophilic polytetrafluoroethylene film is 8~14 MPa; The contact angle of the hydrophilic polytetrafluoroethylene film is 45~55°; and / or The porosity of the hydrophilic polytetrafluoroethylene film is 80-95%.

5. The preparation method according to claim 1, characterized in that, The extrusion aid is any one or a combination of naphtha, gasoline, aviation kerosene, and petroleum ether.

6. The preparation method according to claim 1, characterized in that, The extrusion compression ratio of the push is 10~100; The thickness of the calendering is 100~200μm; and / or The degreasing temperature is 120~340℃.

7. The preparation method according to claim 1, characterized in that, The longitudinal stretching temperature is 160~350℃; and / or The longitudinal stretching ratio is 3 to 20 times.

8. The preparation method according to claim 1, characterized in that, The hydrophilic treatment time is 10~300s.

9. The preparation method according to claim 1, characterized in that, The stretching temperature for the transverse stretching is 150~350℃; The stretching ratio of the lateral stretching is 3 to 15 times; The high-temperature sintering temperature is 327~410℃; and / or The cooling rate of the cooling process is 2~60℃ / min.

10. The application of a hydrophilic polytetrafluoroethylene film prepared by any one of claims 1-9 in the fields of batteries and filtration.

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