Manufacturing method and uses of stretched polytetrafluoroethylene film

Abstract

The present invention provides a method for producing a modified polytetrafluoroethylene stretched film and its use. The method for producing the modified polytetrafluoroethylene stretched film includes the steps of: (1) uniformly mixing a modified polytetrafluoroethylene emulsion with a lubricant, extruding and rolling the mixture; (2) stretching the mixture in the longitudinal direction at high temperature, then stretching the mixture in the transverse direction, and sintering and solidifying the mixture at high temperature for 5-15 minutes after stretching, so that the product is a modified polytetrafluoroethylene stretched film. In this method, the modified polytetrafluoroethylene stretched film produced by adding a polymeric AOI modified monomer is softer, has good stretching performance, has small pore size, high porosity, and uniform pore size distribution; and uses an ammonium salt polymer dispersant as a production raw material, so that the product is clean and clean, does not cause environmental pollution, and is not involved in the metabolism of the human body. Compared with the currently widely used perfluoroacid and its salt as a production auxiliary, the present invention is a very environmentally friendly and healthy technical solution, and has good future application prospects.

Description

[Technical field]

[0001] The present invention relates to the field of filter material technology, and in particular to a method for producing and using a modified polytetrafluoroethylene stretched film. [Background technology]

[0002] Polytetrafluoroethylene (Teflon or PTFE) is commonly called the "king of plastics" and is a polymer compound made by polymerizing tetrafluoroethylene. Its special molecular structure gives it excellent chemical stability, and it has a very wide temperature resistance, allowing it to be used for a long time within a temperature range of -180℃ to 260℃, which is difficult to achieve with other polymer materials. It also has excellent corrosion resistance and sealing properties, high lubricity, high viscosity resistance, high electrical insulation, and good aging resistance, which is why it is called the "king of plastics" in the industry. Since Dr. Planket invented polytetrafluoroethylene in 1938, it has brought revolutionary changes to the plastics industry.

[0003] Film technology has made remarkable developments in the past 50-60 years and is widely used in people's lives, industrial fields and scientific research fields. Microporous films made of various organic polymer materials, mainly cellulose acetate, polyamide, polysulfone, nylon 66, polyethersulfone, polyvinylidene fluoride, polyethylene and polypropylene, have been developed. Except for polyethylene and polypropylene, which are produced by the stretching method to produce microporous films, most of the others are obtained by the phase inversion method to produce cellulose esters, which are made of polymer materials, certain solvents and additives. The common disadvantages of these polymer materials are that the use temperature is limited and they are not resistant to acids, alkalis and chemicals.

[0004] The expanded polytetrafluoroethylene microporous film (called expanded polytetrafluoroethylene, ePTFE outside China) developed in the 1970s has overcome the shortcomings of the above-mentioned traditional film materials, and has become an ideal method for producing high-performance microporous films, which are widely used in various harsh environments. The expanded PTFE microporous film was first independently developed by the US company Gore, which uses mechanical stretching such as extrusion rolling stretching of PTFE fine powder to turn the crystals from powder particles into fibers and interweave them into a mesh structure. The film has 9 billion micropores per square centimeter, small pore size, uniform pore size distribution, low relative density, high film strength, and smooth surface.

[0005] Polytetrafluoroethylene microporous film is produced by mechanical stretching of polytetrafluoroethylene under special conditions without adding anything, and the original properties are not changed at all, so polytetrafluoroethylene microporous film still has a wide range of use temperature, chemical resistance, small film material coefficient, biocompatibility and hydrophobicity, etc., and is widely used in the fields of dust removal, sterilization, product purification and material recovery in air, waterproof and moisture permeable textiles, water treatment, food health, biomedicine and filtration separation in the pharmaceutical industry, and especially, its advantages as a filter material are irreplaceable. Accordingly, the research on the base and application of polytetrafluoroethylene microporous film is also relatively common, and the selection of different filling materials and suitable modification methods to obtain new materials of polytetrafluoroethylene porous film with high comprehensive performance and multifunctionality has become the research focus of a wide range of scientific researchers.

[0006] Patent CN112108008A provides a polytetrafluoroethylene biaxially stretched film and its manufacturing method and use, and the PTFE stretched film produced by co-extrusion and stretching at least two layers of film substrate, followed by solidification and molding at high temperature, has a small pore size and high porosity, but the problem of environmental pollution is not solved. Patent CN104448637B provides a manufacturing method for polytetrafluoroethylene film for air filtration, and the produced polytetrafluoroethylene film has a high pore rate, a uniform pore size distribution, and a thin thickness, but its stretching performance needs to be further improved. It is difficult for conventional polytetrafluoroethylene films to simultaneously meet the demands of small pore size, uniform distribution, and high mechanical strength.

[0007] Therefore, in order to better meet the needs of real life, it is necessary to provide a modified polytetrafluoroethylene stretched film that has a small pore size, a high porosity, a uniform pore size distribution, is clean, environmentally friendly, safe, and has excellent stretching performance. Summary of the Invention [Problem to be solved by the invention]

[0008] In view of the problems existing in the prior art, the object of the present invention is to provide a modified polytetrafluoroethylene stretched film having a small pore size, high porosity, uniform pore size distribution, which is clean, environmentally friendly, safe and has excellent stretching performance to meet the needs of actual production and applications.

[0009] To achieve this objective, the technical solution of the present invention is as follows: [Means for solving the problem]

[0010] The present invention provides a method for producing a modified polytetrafluoroethylene stretched film, the method for producing the modified polytetrafluoroethylene film comprising the steps of: (1) uniformly mixing the modified polytetrafluoroethylene emulsion and the lubricant, and extruding and rolling the mixture; and (2) stretching the film in the machine direction at high temperature, then stretching it in the transverse direction, and sintering the film at high temperature for 5-15 minutes after stretching, so that the product is a modified polytetrafluoroethylene stretched film.

[0011] In the method for producing a modified polytetrafluoroethylene stretched film of the present invention, the lubricant described in step (1) is selected from Kryptox EG2000 or Kryptox EG3000.

[0012] In the method for producing a modified polytetrafluoroethylene stretched film of the present invention, the amount of lubricant used in step (1) is 10-15% of the mass of the modified polytetrafluoroethylene emulsion (e.g., 10%, 10.1%, 10.2%, 10.3%, 10.4%, 10.5%, 10.6%, 10.7%, 10.8%, 10.9%, 11%, 11.1%, 11.2%, 11.3%, 11.4%, 11.5%, 11.6%, 11.7%, 11.8%, 11.9%, 12.0%, 12.1%, 12.2%, 12.3%, 12.4%, 12.5%, 12.6%, 12.7%, 12.8%, 12.9%, 13.0%, 13.1%, 13.2%, 13.3%, 13.4%, 13.5%, 13.6%, 13.7%, 13.8%, 13.9%, 14.0%, 14.1%, 14.2%, 14.3%, 14.4%, 14.5%, 14.6%, 14.7%, 14.8%, 14.9%, 15.0%, 15.1%. (The value may be 9%, 12%, 12.1%, 12.2%, 12.3%, 12.4%, 12.5%, 12.6%, 12.7%, 12.8%, 12.9%, 13%, 13.1%, 13.2%, 13.3%, 13.4%, 13.5%, 13.6%, 13.7%, 13.8%, 13.9%, 14%, 14.1%, 14.2%, 14.3%, 14.4%, 14.5%, 14.6%, 14.7%, 14.8%, 14.9%, 15% or any value therein).

[0013] In the method for producing a stretched modified polytetrafluoroethylene film of the present invention, the stretching temperature described in step (2) is 210-230°C (e.g., 210°C, 211°C, 212°C, 213°C, 214°C, 215°C, 216°C, 217°C, 218°C, 219°C, 220°C, 221°C, 222°C, 223°C, 224°C, 225°C, 226°C, 227°C, 228°C, 229°C, 230°C, or thereabouts). and the sintering temperature is 350-370°C (e.g., 350°C, 351°C, 352°C, 353°C, 354°C, 355°C, 356°C, 357°C, 358°C, 359°C, 360°C, 361°C, 362°C, 363°C, 364°C, 365°C, 366°C, 367°C, 368°C, 369°C, 370°C, or any of the temperature values ​​therein).

[0014] In some embodiments of the present invention, the modified polytetrafluoroethylene emulsion comprises 0.5-2 parts of an ammonium salt polymeric dispersant, 0.2-1 parts of an emulsifier, 1-1.5 parts of an AOI modified monomer (AOI is an abbreviation for ethyl isocyanate acrylate), 0.5-3 parts of an initiator, 40-60 parts of a tetrafluoroethylene monomer, and 30-60 parts of water.

[0015] In some embodiments of the present invention, the structure of the ammonium salt polymeric dispersant is shown below: [ka] where x is an integer from 2 to 5, y is an integer from 5 to 8, and * is the attachment site of a chemical bond.

[0016] In some embodiments of the present invention, the method for preparing the ammonium salt polymeric dispersant comprises: Step (1) of adding a solvent to a reactor, heating to increase the temperature, and then dropping perfluorohexanol acrylate, acrylic acid and an initiator into the reactor and keeping the temperature for 2-4 hours to react; and (2) adding diethanolamine to the product obtained in step (1) to react with it, and after completion of the reaction, removing the solvent, so that the product obtained is an ammonium salt polymer dispersant.

[0017] In the method for producing an ammonium salt polymer dispersant of the present invention, the molar ratio of the perfluorohexanol acrylate, acrylic acid, and diethanolamine is 1-4:1:1 (for example, it may be 1:1:1, 2:1:1, 3:1:1, 4:1:1, or any value therein).

[0018] In the method for producing an ammonium salt polymer dispersant in the present invention, the reaction temperature described in step (1) is 60-70°C (for example, 60°C, 61°C, 62°C, 63°C, 64°C, 65°C, 66°C, 67°C, 68°C, 69°C, 70°C, or any of the temperature values ​​therein), the solvent is one or a combination selected from perfluorohexane, perfluoroheptane, perfluorooctane, and monobromododecafluorohexane, the initiator is one or a combination selected from perfluorobutyryl peroxide and perfluorohexanoyl peroxide, and the amount of initiator used is 1%-2% of the total mass of perfluorohexanol acrylate and acrylic acid (for example, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, or any of the values ​​therein).

[0019] In some embodiments of the invention, the emulsifier is one or a combination of more selected from Kryptox EG2000, Kryptox EG3000, Kryptox 143, and Kryptox 280.

[0020] In some embodiments of the invention, the initiator is one or a combination of perfluorobutyryl peroxide and perfluorohexanoyl peroxide.

[0021] In some embodiments of the present invention, the structure of the AOI modified monomer is shown below: [ka] where m is an integer from 1 to 2, n is an integer from 10 to 20, and * is a bonding site for a chemical bond.

[0022] In some embodiments of the present invention, the method for producing the AOI modified monomer includes: Step (1) of adding a solvent to a reactor, heating to increase the temperature, and then dropping perfluorohexanol acrylate, hydroxyethyl acrylate and an initiator into the reactor, and keeping the temperature for 2-4 hours after the dropwise addition is completed; The method includes a step (2) of adding AOI to the product obtained in the step (1) to react with it, and after the reaction is completed, removing the solvent, so that the obtained product is an AOI-modified monomer.

[0023] In the method for producing the AOI-modified monomer of the present invention, the molar ratio of the perfluorohexanol acrylate, hydroxyethyl acrylate, and AOI is 10-20:1:1 (for example, it may be 10:1:1, 11:1:1, 12:1:1, 13:1:1, 14:1:1, 15:1:1, 16:1:1, 17:1:1, 18:1:1, 19:1:1, 20:1:1, or any value therein).

[0024] In the method for producing the AOI modified monomer of the present invention, the reaction temperature described in step (1) is 60-70°C (for example, 60°C, 61°C, 62°C, 63°C, 64°C, 65°C, 66°C, 67°C, 68°C, 69°C, 70°C, or any of the temperature values ​​therein), the solvent is one or a combination selected from perfluorohexane, perfluoroheptane, perfluorooctane, and monobromododecafluorohexane, the initiator is one or a combination selected from perfluorobutyryl peroxide and perfluorohexanoyl peroxide, and the amount of the initiator used is 1%-2% of the total mass of perfluorohexanol acrylate and acrylic acid (for example, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, or any of the values ​​therein).

[0025] In some embodiments of the present invention, the method for producing the modified polytetrafluoroethylene emulsion includes the steps of: (1) adding dispersant, emulsifier and deionized water to a high-pressure emulsification reactor with stirring, and then increasing the temperature to 40-60°C and the pressure of the system to 3-4 MPa; and step (2) adding the tetrafluoroethylene monomer, the AOI modified monomer and the initiator into a high-pressure emulsification reactor, respectively, and reacting for 2-4 hours at elevated temperature. After the reaction is completed, the product is a modified polytetrafluoroethylene emulsion. Effect of the Invention

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) In the modified polytetrafluoroethylene stretched film of the present invention, the addition of an AOI modified monomer affects the overall structure of the modified polytetrafluoroethylene stretched film and reduces the crystallinity of the system, so that the modified polytetrafluoroethylene stretched film produced is softer and has good stretching performance, as well as a relatively small pore size, a relatively high porosity, and a uniform pore size distribution.

[0028] (2) The method for producing modified polytetrafluoroethylene stretched film according to the present invention uses an ammonium salt polymer dispersant as a production raw material, which gives the product good stability. The product is clean and does not cause environmental pollution or affect the human metabolism. Compared with the methods currently available on the market that use perfluoroacids and their salts as production assistants, the present invention is a very environmentally friendly and healthy technical solution. [Brief description of the drawings]

[0029] [Figure 1] FIG. 2 is a schematic diagram showing the structure of the modified polytetrafluoroethylene stretched film produced in Example 1. [Diagram 2] FIG. 1 is a schematic diagram of the structure of a conventional modified polytetrafluoroethylene stretched film. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] The present invention will be described below with reference to specific examples. Note that the following examples are examples of the present invention and are used only to explain the present invention, and do not limit the present invention. Other combinations and various modifications are possible within the scope of the concept of the present invention without departing from the spirit or scope of the present invention.

[0031] All compounds and related reagents used in the following examples are commercially available, and AOI is purchased from Showa Denko KK of Japan.

[0032] (Preparation of Ammonium Salt Polymer Dispersant I) The manufacturing method is as follows. (1) 100 g of perfluoroheptane is added to a reactor, the temperature is raised to 70°C, 1 mol of perfluorohexanol acrylate, 1 mol of acrylic acid, and 1 g of perfluorobutyryl peroxide are added dropwise to the reactor at a constant rate using a peristaltic pump, and after the addition is completed, the mixture is kept at the same temperature for 4 hours to react. (2) 1 mol of diethanolamine is added to the reactor, and the reaction is carried out while maintaining the temperature at 70° C. After the reaction is completed, the perfluoroheptane is removed, and the product is ammonium salt polymer dispersant I.

[0033] (Preparation of Ammonium Salt Polymer Dispersant II) The manufacturing method is as follows. (1) 100 g of perfluoroheptane is added to a reactor, the temperature is raised to 70°C, 4 mol of perfluorohexanol acrylate, 1 mol of acrylic acid, and 1 g of perfluorobutyryl peroxide are added dropwise to the reactor at a constant rate using a peristaltic pump, and after the addition is completed, the reaction is allowed to proceed by keeping the temperature at 4 hours. (2) 1 mol of diethanolamine is added to the reactor, and the reaction is carried out while maintaining the temperature at 70° C. After the reaction is completed, the perfluoroheptane is removed, and the product is ammonium salt polymer dispersant I.

[0034] (Production of AOI Modified Monomer I) The manufacturing method is as follows. (1) 100 g of perfluoroheptane is added to a reactor, the temperature is raised to 70°C, 1 mol of perfluorohexanol acrylate, 0.1 mol of hydroxyethyl acrylate, and 1 g of perfluorobutyryl peroxide are added dropwise to the reactor at a constant rate using a peristaltic pump, and after the completion of the addition, the mixture is kept at the same temperature for 4 hours to react. (2) 0.1 mol of AOI is added to the product obtained in step (1) and reacted. After completion of the reaction, perfluoroheptane is removed, and the resulting product is AOI-modified monomer I.

[0035] (Production of AOI Modified Monomer II) The manufacturing method is as follows. (1) 100 g of perfluoroheptane is added to a reactor, the temperature is raised to 70°C, 2 mol of perfluorohexanol acrylate, 0.1 mol of hydroxyethyl acrylate, and 1 g of perfluorobutyryl peroxide are added dropwise to the reactor at a constant rate using a peristaltic pump, and after the addition is completed, the reaction is allowed to proceed by keeping the temperature at 4 hours. (2) 0.1 mol of AOI is added to the product obtained in step (1) and reacted. After completion of the reaction, perfluoroheptane is removed, and the resulting product is the AOI-modified monomer II.

[0036] (Modified polytetrafluoroethylene emulsion I) A modified polytetrafluoroethylene emulsion comprising 2 parts by weight of ammonium salt polymeric dispersant II, 1 part by weight of Kryptox EG2000, 1.5 parts by weight of AOI modified monomer II, 3 parts by weight of perfluorobutyryl peroxide, 60 parts by weight of tetrafluoroethylene monomer, and 30 parts by weight of deionized water. The manufacturing method is as follows. (1) Add ammonium salt polymer dispersant II, Kryptox EG2000 and deionized water to a high-pressure emulsification reactor with stirring, and then increase the temperature to 60°C by introducing nitrogen gas to increase the system pressure to 4MPa; (2) Tetrafluoroethylene monomer, AOI modified monomer II and perfluorobutyryl peroxide are added to a high-pressure emulsification reactor, and the temperature is raised to react for 3 hours. After the reaction is completed, the product is modified polytetrafluoroethylene emulsion I.

[0037] (Modified polytetrafluoroethylene emulsion II) A modified polytetrafluoroethylene emulsion comprising 0.5 parts by weight of ammonium salt polymeric dispersant II, 1 part by weight of Kryptox EG2000, 1.5 parts by weight of AOI modified monomer II, 3 parts by weight of perfluorobutyryl peroxide, 60 parts by weight of tetrafluoroethylene monomer, and 30 parts by weight of deionized water. The preparation method is the same as that of modified polytetrafluoroethylene emulsion I.

[0038] (Modified polytetrafluoroethylene emulsion III) A modified polytetrafluoroethylene emulsion comprising 0.5 parts by weight of ammonium salt polymeric dispersant II, 1 part by weight of Kryptox EG2000, 1 part by weight of AOI modified monomer II, 3 parts by weight of perfluorobutyryl peroxide, 60 parts by weight of tetrafluoroethylene monomer, and 30 parts by weight of deionized water. The preparation method is the same as that of modified polytetrafluoroethylene emulsion I.

[0039] (Modified polytetrafluoroethylene emulsion IV) A modified polytetrafluoroethylene emulsion comprising 0.5 parts by weight of ammonium salt polymeric dispersant I, 1 part by weight of Kryptox EG2000, 1 part by weight of AOI modified monomer II, 3 parts by weight of perfluorobutyryl peroxide, 60 parts by weight of tetrafluoroethylene monomer, and 30 parts by weight of deionized water. The preparation method is the same as that of modified polytetrafluoroethylene emulsion I.

[0040] (Modified Polytetrafluoroethylene Emulsion V) A modified polytetrafluoroethylene emulsion comprising 0.5 parts by weight of ammonium salt polymeric dispersant I, 1 part by weight of Kryptox EG2000, 1 part by weight of AOI modified monomer I, 3 parts by weight of perfluorobutyryl peroxide, 60 parts by weight of tetrafluoroethylene monomer, and 30 parts by weight of deionized water. The preparation method is the same as that of modified polytetrafluoroethylene emulsion I.

[0041] (Modified polytetrafluoroethylene emulsion VI) A modified polytetrafluoroethylene emulsion comprising 0.5 parts by weight of ammonium salt polymeric dispersant I, 1 part by weight of Kryptox EG2000, 1 part by weight of AOI modified monomer I, 3 parts by weight of perfluorobutyryl peroxide, 40 parts by weight of tetrafluoroethylene monomer, and 30 parts by weight of deionized water. The preparation method is the same as that of modified polytetrafluoroethylene emulsion I.

[0042] (Modified Polytetrafluoroethylene Latex VII) A modified polytetrafluoroethylene emulsion comprising 0.5 parts by weight of ammonium salt polymeric dispersant I, 0.2 parts by weight of Kryptox EG2000, 1 part by weight of AOI modified monomer I, 3 parts by weight of perfluorobutyryl peroxide, 40 parts by weight of tetrafluoroethylene monomer, and 30 parts by weight of deionized water. The preparation method includes the modified polytetrafluoroethylene emulsion I as well.

[0043] (Modified Polytetrafluoroethylene Emulsion VIII) A modified polytetrafluoroethylene emulsion comprising 0.5 parts by weight of ammonium salt polymeric dispersant I, 0.2 parts by weight of Kryptox EG2000, 1 part by weight of AOI modified monomer I, 1 part by weight of perfluorobutyryl peroxide, 40 parts by weight of tetrafluoroethylene monomer, and 30 parts by weight of deionized water. The preparation method is the same as that of modified polytetrafluoroethylene emulsion I.

[0044] (Modified polytetrafluoroethylene emulsion IX) A modified polytetrafluoroethylene emulsion comprising 0.5 parts by weight of ammonium salt polymeric dispersant I, 0.2 parts by weight of Kryptox EG2000, 1 part by weight of AOI modified monomer I, 1 part by weight of perfluorobutyryl peroxide, 40 parts by weight of tetrafluoroethylene monomer, and 60 parts by weight of deionized water. The preparation method is the same as that of modified polytetrafluoroethylene emulsion I. EXAMPLES

[0045] A modified polytetrafluoroethylene stretched film, the modified polytetrafluoroethylene stretched film being produced by the following method: (1) 100 g of modified polytetrafluoroethylene emulsion I and 15 g of Kryptox EG2000 were uniformly mixed and extruded. (2) The film is stretched in the longitudinal direction at 220°C, then stretched in the transverse direction, and after stretching, is sintered and solidified at 360°C for 10 minutes. The product is a modified polytetrafluoroethylene stretched film. The schematic diagram of the structure is shown in FIG. EXAMPLES

[0046] A modified polytetrafluoroethylene stretched film, the modified polytetrafluoroethylene stretched film being produced by the following method: (1) 100 g of modified polytetrafluoroethylene emulsion II and 15 g of Kryptox EG2000 were uniformly mixed and extruded. (2) The film was stretched in the longitudinal direction at 220°C, then stretched in the transverse direction, and after stretching, was sintered and consolidated at 360°C for 10 minutes. The product was a modified polytetrafluoroethylene stretched film. EXAMPLES

[0047] A modified polytetrafluoroethylene stretched film, the modified polytetrafluoroethylene stretched film being produced by the following method: (1) 100 g of modified polytetrafluoroethylene emulsion III and 15 g of Kryptox EG2000 were uniformly mixed and extruded. (2) The film was stretched in the longitudinal direction at 220°C, then stretched in the transverse direction, and after stretching, was sintered and consolidated at 360°C for 10 minutes. The product was a modified polytetrafluoroethylene stretched film. EXAMPLES

[0048] A modified polytetrafluoroethylene stretched film, the modified polytetrafluoroethylene stretched film being produced by the following method: (1) 100 g of modified polytetrafluoroethylene emulsion IV and 15 g of Kryptox EG2000 were uniformly mixed and extruded. (2) The film was stretched in the longitudinal direction at 220°C, then stretched in the transverse direction, and after stretching, was sintered and consolidated at 360°C for 10 minutes. The product was a modified polytetrafluoroethylene stretched film. EXAMPLES

[0049] A modified polytetrafluoroethylene stretched film, the modified polytetrafluoroethylene stretched film being produced by the following method: (1) 100 g of modified polytetrafluoroethylene emulsion V and 15 g of Kryptox EG2000 were uniformly mixed and extruded. (2) The film was stretched in the longitudinal direction at 220°C, then stretched in the transverse direction, and after stretching, was sintered and consolidated at 360°C for 10 minutes. The product was a modified polytetrafluoroethylene stretched film. EXAMPLES

[0050] A modified polytetrafluoroethylene stretched film, the modified polytetrafluoroethylene stretched film being produced by the following method: (1) 100 g of modified polytetrafluoroethylene emulsion VI and 15 g of Kryptox EG2000 were uniformly mixed and extruded. (2) The film was stretched in the longitudinal direction at 220°C, then stretched in the transverse direction, and after stretching, was sintered and consolidated at 360°C for 10 minutes. The product was a modified polytetrafluoroethylene stretched film. EXAMPLES

[0051] A modified polytetrafluoroethylene stretched film, the modified polytetrafluoroethylene stretched film being produced by the following method: (1) 100 g of modified polytetrafluoroethylene emulsion VII and 15 g of Kryptox EG2000 were uniformly mixed and extruded. (2) The film was stretched in the longitudinal direction at 220°C, then stretched in the transverse direction, and after stretching, was sintered and consolidated at 360°C for 10 minutes. The product was a modified polytetrafluoroethylene stretched film. EXAMPLES

[0052] A modified polytetrafluoroethylene stretched film, the modified polytetrafluoroethylene stretched film being produced by the following method: (1) 100 g of modified polytetrafluoroethylene emulsion VIII and 15 g of Kryptox EG2000 were uniformly mixed and extruded. (2) The film was stretched in the longitudinal direction at 220°C, then stretched in the transverse direction, and after stretching, was sintered and consolidated at 360°C for 10 minutes. The product was a modified polytetrafluoroethylene stretched film. EXAMPLES

[0053] A modified polytetrafluoroethylene stretched film, the modified polytetrafluoroethylene stretched film being produced by the following method: (1) 100 g of modified polytetrafluoroethylene emulsion IX and 15 g of Kryptox EG2000 were uniformly mixed and extruded. (2) The film was stretched in the longitudinal direction at 220°C, then stretched in the transverse direction, and after stretching, was sintered and consolidated at 360°C for 10 minutes. The product was a modified polytetrafluoroethylene stretched film. EXAMPLES

[0054] A modified polytetrafluoroethylene stretched film, the modified polytetrafluoroethylene stretched film being produced by the following method: (1) 100 g of modified polytetrafluoroethylene emulsion IX and 10 g of Kryptox EG2000 were uniformly mixed and extruded. (2) The film was stretched in the longitudinal direction at 220°C, then stretched in the transverse direction, and after stretching, was sintered and consolidated at 360°C for 10 minutes. The product was a modified polytetrafluoroethylene stretched film.

[0055] Comparative Example 1 The difference from Example 1 was that the modified polytetrafluoroethylene emulsion raw material used in the production of the modified polytetrafluoroethylene stretched film did not contain the AOI modified monomer.

[0056] Comparative Example 2 The difference from Example 1 was that the amount of lubricant Kryptox EG2000 used in producing the modified polytetrafluoroethylene stretched film was 3 g.

[0057] The performance tests were carried out on the modified polytetrafluoroethylene stretched films produced in the above examples and comparative examples. The tensile strength and elongation at break tests were carried out in accordance with the requirements of GB / T1040.3-2006 standard, the porosity was measured by a porosity tester, and the pore size and pore size distribution were measured by a SEM scanning electron microscope. The measurement results are shown in Table 1.

[0058] [Table 1]

[0059] It can be seen from the comparison of the test results of Comparative Example 1 and Example 1 that the modified polytetrafluoroethylene stretched film produced in Example 1 effectively improves its tensile strength and breaking elongation by adding the high molecular weight AOI modified monomer, and the modified polytetrafluoroethylene stretched film has good stretching performance, and has a relatively small pore size, a relatively high porosity, and a uniform pore size distribution. It can be seen from the comparison of Comparative Example 2 and Example 1 that the modified polytetrafluoroethylene stretched film produced in Example 1 can improve the stretching performance by adding an appropriate amount of lubricant when used as a filter cotton for a moisture-proof mask. It can be seen from the overall comparison of Comparative Example and Example that the modified polytetrafluoroethylene stretched film according to the present invention affects the overall structure of the modified polytetrafluoroethylene stretched film by adding the high molecular weight AOI modified monomer, and reduces the crystallinity of the system, and the modified polytetrafluoroethylene stretched film produced is softer, has good stretching performance, has a relatively small pore size, a relatively high porosity, and a uniform pore size distribution. In addition, the ammonium salt polymer dispersant is used as the raw material, and the product is clean and pure, does not cause environmental pollution, and does not affect the human body's metabolism. Therefore, the manufacturing method of the present invention is a very environmentally friendly and healthy technical solution compared with the method currently available on the market that uses perfluoroacid and its salt as a production auxiliary.

[0060] The above embodiments are merely intended to explain the technical concepts and features of the present invention, and the purpose is to enable those familiar with this technology to understand and practice the contents of the present invention, and are not intended to limit the protection scope of the present invention. All equivalent changes or modifications made substantially based on the spirit of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for producing a modified polytetrafluoroethylene stretched film, comprising the steps of: (1) a step of uniformly mixing a modified polytetrafluoroethylene emulsion and a lubricant, and extruding and rolling the mixture; and (2) stretching the film in the longitudinal direction at a high temperature, then stretching the film in the transverse direction, and sintering the film at a high temperature for 5 to 15 minutes to consolidate the film after stretching, thereby producing a modified polytetrafluoroethylene stretched film.

2. The method for producing a modified polytetrafluoroethylene stretched film according to claim 1, characterized in that the lubricant in step (1) is selected from Kryptox EG2000 or Kryptox EG3000, the amount of lubricant used is 10-15% of the mass of the modified polytetrafluoroethylene emulsion, the stretching temperature in step (2) is 210-230°C, and the sintering solidification temperature is 350-370°C.

3. The modified polytetrafluoroethylene emulsion contains 0.5-2 parts by weight of an ammonium salt polymer dispersant, 0.2-1 parts by weight of an emulsifier, 1-1.5 parts by weight of an AOI modified monomer, 0.5-3 parts by weight of an initiator, 40-60 parts by weight of a tetrafluoroethylene monomer, and 30-60 parts by weight of water, and the method for producing the modified polytetrafluoroethylene emulsion includes: Step (1): adding dispersant, emulsifier and deionized water to a high pressure emulsification reactor with stirring, stirring and raising the temperature to 40-60°C and the pressure of the system to 3-4 MPa; The method for producing a modified polytetrafluoroethylene stretched film according to claim 1, further comprising: adding the tetrafluoroethylene monomer, the AOI-modified monomer and the initiator into a high-pressure emulsification reactor, respectively, and reacting the monomer at elevated temperature for 2-4 hours; and after the reaction is completed, the product is a modified polytetrafluoroethylene emulsion.

4. The structure of the ammonium salt polymeric dispersant is shown below: 【Chemistry 1】 where x is an integer between 2 and 5, y is an integer between 5 and 8, * is a bonding site for a chemical bond, The method for producing the ammonium salt polymer dispersant includes the steps of: Step (1) of adding a solvent to a reactor, heating to increase the temperature, and then dropping perfluorohexanol acrylate, acrylic acid and an initiator into the reactor and keeping the temperature for 2-4 hours to react; The method for producing a modified polytetrafluoroethylene stretched film according to claim 3, further comprising: adding diethanolamine to the product obtained in step (1) to react with the product; and removing the solvent after the reaction is completed, so that the product obtained is an ammonium salt polymer dispersant.

5. The method for producing a modified polytetrafluoroethylene stretched film according to claim 4, characterized in that the molar ratio of the perfluorohexanol acrylate, acrylic acid, and diethanolamine is 1-4:1:1, the reaction temperature described in step (1) is 60-70°C, the solvent is one or a combination selected from perfluorohexane, perfluoroheptane, perfluorooctane, and monobromododecafluorohexane, the initiator is one or a combination selected from perfluorobutyryl peroxide and perfluorohexanoyl peroxide, and the amount of the initiator used is 1%-2% of the total mass of perfluorohexanol acrylate and acrylic acid.

6. The method for producing a modified polytetrafluoroethylene stretched film according to claim 3, characterized in that the emulsifier is one or a combination selected from Kryptox EG2000, Kryptox EG3000, Kryptox 143 and Kryptox 280, and the initiator is one or a combination of perfluorobutyryl peroxide and perfluorohexanoyl peroxide.

7. The structure of the AOI-modified monomer is shown below: 【Chemistry 2】 where m is an integer between 1 and 2, n is an integer between 10 and 20, * is a bonding site for a chemical bond, The method for producing the AOI-modified monomer includes the steps of: Step (1) of adding a solvent to a reactor, heating to raise the temperature, and then dropping perfluorohexanol acrylate, hydroxyethyl acrylate and an initiator into the reactor, and keeping the temperature for 2-4 hours after dropping is completed; The method for producing a modified stretched polytetrafluoroethylene film according to claim 3, further comprising the step of adding AOI to the product obtained in step (1) to react with the product, and removing the solvent after the reaction is completed, thereby obtaining an AOI-modified monomer.

8. The method for producing a modified polytetrafluoroethylene stretched film according to claim 7, characterized in that the molar ratio of the perfluorohexanol acrylate, hydroxyethyl acrylate, and AOI is 10-20:1:1, the reaction temperature described in step (1) is 60-70°C, the solvent is one or a combination selected from perfluorohexane, perfluoroheptane, perfluorooctane, and monobromododecafluorohexane, the initiator is one or a combination selected from perfluorobutyryl peroxide and perfluorohexanoyl peroxide, and the amount of the initiator used is 1%-2% of the total mass of perfluorohexanol acrylate and acrylic acid.

9. A modified polytetrafluoroethylene stretched film produced by the method for producing a modified polytetrafluoroethylene stretched film according to any one of claims 1 to 8.

10. Use of the modified polytetrafluoroethylene stretched film according to claim 9 in the field of filter material production.

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