Air-permeable stretched polytetrafluoroethylene film and method for producing same

Abstract

The present invention discloses a breathable stretched polytetrafluoroethylene film and a method for producing the same. The breathable stretched polytetrafluoroethylene film is produced by mixing and stretching a modified polytetrafluoroethylene resin powder and a modified fluoropolymer powder, and the modified polytetrafluoroethylene resin is produced by mixing and copolymerizing a tetrafluoroethylene monomer and a modified monomer. The modified monomer is produced by reacting hydroxyethyl acrylate, perfluoroalkylethyl acrylate, and 2-isocyanatoethyl acrylate. The modified polytetrafluoroethylene polymer has a multi-branched structure that significantly reduces the crystallinity in the system, and the tensile strength is significantly improved by adding the modified fluoropolymer powder, so that the polytetrafluoroethylene stretched film according to the present invention has strong breathability and waterproofness, and therefore is highly safe and can be used to protect precision instruments such as electronic devices.

Description

[Technical field]

[0001] The present invention relates to the technical field of polymeric film materials, and in particular to a breathable stretched polytetrafluoroethylene film and a method for producing the same. [Background technology]

[0002] Stretched film is a thermoplastic plastic film that is stretched in the longitudinal and transverse directions during production and shrinks when heated during use. Currently, commonly used stretched films are divided into PVC film, polyethylene film, polyester film, polystyrene film, polypropylene film, nylon film, etc. according to the material. Stretched films are used for packaging various products and are used in different fields according to the material, and are widely used in food and beverages, automotive supplies, daily necessities, stationery, medical care and other fields.

[0003] With the increasing consumer demand for health, environmental protection and cleanliness, oriented films are developed in the direction of being non-toxic, degradable, easy to collect and have a high recycling rate. Polyethylene film is one of the substrates commonly used as heat shrinkable film. It has excellent flexibility, strong impact resistance and tear strength, is not easily damaged, has moisture resistance and a large shrinkage rate, so it is widely used in the integrated packaging of products such as wine, pull-top cans, mineral water, various beverages and cloth. PVC film has the characteristics of high transparency, good gloss and high shrinkage rate, and is also rainproof, fireproof, antistatic and easy to mold, and is widely used in the building materials industry and packaging industry.

[0004] Polytetrafluoroethylene oriented film has appeared on the market for use in protecting precision equipment such as circuits and conductors. Polytetrafluoroethylene oriented film, also known as Teflon film (Teflon is a registered trademark), is produced by compression molding suspended polytetrafluoroethylene resin, sintering, cooling to form a blank, and then lathing and rolling. Its most notable advantage is its withstand voltage strength and breakdown voltage, and it is used in capacitor dielectrics, conductor insulation, electrical equipment insulation, sealing gaskets, etc.

[0005] Polytetrafluoroethylene film is produced by biaxial stretching, and it is observed by scanning electron microscope that the film is connected by fiber filaments crossing vertically and horizontally, and the gaps between the fiber filaments form the pores of the film. There are many pores on the surface of the film, about 9 billion pores per square inch, and the diameter distribution of the pores is mainly concentrated in 0.8 to 1 μm. However, since polytetrafluoroethylene has high crystallinity, the size and shape of the pores generated during stretching are not uniform, and large pores are generated. In addition, a larger stretching ratio cannot be used due to the limitation of tensile strength, and there are few pores after final stretching, which affects the air permeability and waterproofness of the polytetrafluoroethylene stretched film, and it cannot be used to protect precision equipment such as electronic products. Summary of the Invention [Problem to be solved by the invention]

[0006] Objective of the Invention: In response to the deficiencies of the prior art, the objective of the present invention is to provide a polytetrafluoroethylene stretched film having high air permeability and waterproofness, and a manufacturing method thereof, in order to improve the safety of the polytetrafluoroethylene stretched film and make it applicable to the protection field of electronic products, etc. [Means for solving the problem]

[0007] Technical proposal: A breathable stretched polytetrafluoroethylene film, which is produced by mixing modified polytetrafluoroethylene resin powder and modified fluoropolymer powder and stretching the mixture, The modified polytetrafluoroethylene resin is produced by mixing and copolymerizing a tetrafluoroethylene monomer and a modified monomer, The modified monomer structure is a compound of formula I: [ka] m:n=1-2:20, and x represents 4, 6, 8, or 10.

[0008] The modified polytetrafluoroethylene polymer has a multi-branched structure, which significantly reduces the crystallinity in the system.

[0009] Furthermore, the modified fluoropolymer powder is a copolymer of propylene and tetrafluoroethylene, and may be Asahi Glass AFLAS100 or Asahi Glass AFLAS150. The addition of the modified fluoropolymer powder can improve the tensile strength of the polytetrafluoroethylene stretched film, and therefore increase the final stretch ratio of the stretched film.

[0010] Furthermore, the method for producing the modified monomer includes the steps of: (1) adding 30-50 parts of perfluoroheptane as a solvent to a reactor, heating to 60-70°C, and then adding 50-70 parts of a mixture of hydroxyethyl acrylate and perfluoroalkylethyl acrylate and 0.5-1 part of an initiator to the reactor at a constant rate after uniformly mixing the mixture, and keeping the mixture warm for 2-4 hours after the completion of the dropping; (2) adding 6-12 parts of 2-isocyanatoethyl acrylate to the reactor, raising the temperature to 70-75°C, and continuing stirring until the -NCO group content of the system is less than 0.05%; and step (3) of cooling the reaction system and removing the perfluoroheptane solvent to obtain the modified monomer.

[0011] The reaction equation for producing the modified monomer is as follows: [ka]

[0012] Further, the initiator in step (1) is selected from one of azobisisobutyronitrile or benzoyl peroxide.

[0013] The perfluoroalkyl ethyl acrylate in step (1) is selected from one of perfluorobutyl ethyl acrylate, perfluorohexyl ethyl acrylate, perfluorooctyl ethyl acrylate, and perfluorodecyl ethyl acrylate.

[0014] Furthermore, the method for producing the modified polytetrafluoroethylene resin powder further comprises the steps of: Step (1) of adding a dispersant, an emulsifier and deionized water into a high-pressure emulsification reactor and uniformly emulsifying the mixture at a stirring speed of 1000-2000 r / min, where the faster the stirring speed and the longer the stirring time, the better the emulsification and the smaller the final particle size; Step (2) of decreasing the stirring speed to 200-400 r / min and increasing the reactor temperature to 40-60° C. and the pressure to 3-4 MPa, where the higher the reactor temperature, the higher the pressure required; and step (3) of simultaneously injecting the mixture of tetrafluoroethylene monomer, modified monomer and initiator into a high-pressure emulsification reactor using a high-pressure pump, raising the temperature of the reactor to 60-80°C, and aging for 2-4 hours to obtain a modified polytetrafluoroethylene resin.

[0015] Furthermore, the mass percentage of each raw material for producing the modified polytetrafluoroethylene resin powder is as follows, with the total amount of the raw materials being 100%, Dispersant 0.1-1% Emulsifier 0.2-1% Tetrafluoroethylene monomer 40-60% Modified monomer 1-1.5% Initiator 0.5-3% The remainder is water.

[0016] Furthermore, in the step (1), the dispersant is ammonium pentadecafluorooctanoate, and the emulsifier is perfluoropolyether.

[0017] Furthermore, in the step (3), the initiator is one of perfluorobutyryl peroxide or perfluorohexanoyl peroxide.

[0018] Furthermore, the method for producing the gas-permeable stretched polytetrafluoroethylene film includes the steps of: (1) homogeneously mixing the modified fluoropolymer powder and the polytetrafluoroethylene resin powder, pressing into a round bar at 50-55°C, and rolling at 60-65°C to form a base film with a thickness of less than 100 mm; Step (2) of degreasing the base film of step (1) at 250-260°C, stretching the base film after the degreasing treatment by 6-8 times in the machine direction and by 3-5 times in the transverse direction; and step (3) sintering the film after stretching in step (2) at 340-360°C for 1-2 minutes.

[0019] Furthermore, the mass ratio of the modified fluoropolymer powder to the modified polytetrafluoroethylene resin is 1-3:10. Effect of the Invention

[0020] Beneficial Effects: (1) The modified polytetrafluoroethylene polymer of the present invention has a hyperbranched structure, which greatly reduces the crystallinity in the system. Therefore, when stretched, it forms very uniform pores, which gives it better breathability. In addition, since the pores are uniform and there are no large pores, the waterproof effect is improved.

[0021] (2) By mixing modified polytetrafluoroethylene with modified fluoropolymer powder in the present invention, the tensile strength can be significantly improved, and therefore the final stretch ratio of the stretched film can be increased, resulting in more pores per unit mass and improved air permeability. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The present invention will be described below with reference to specific embodiments. Note that the following examples are examples of the present invention and are used only to explain the present invention and are not intended to limit the present invention. Other combinations and various improvements are possible within the scope of the concept of the present invention without departing from the spirit or scope of the present invention.

[0023] The perfluoroalkylethyl acrylate in the present invention is purchased from Jinan Guochen Taifu Chemical Co., Ltd., the modified fluoropolymer powder is Asahi Glass AFLAS100 and Asahi Glass AFLAS150 of Asahi Glass Co., Ltd., the polytetrafluoroethylene film and F46 film are purchased from Taizhou Tongjida New Material Co., Ltd. Other reagents and instruments are conventional reagents and instruments in this technical field.

[0024] (Production of Modified Monomer-1) (1) In weight parts, 30 parts of perfluoroheptane is added to a reactor as a solvent, heated to 65°C, and a mixture of 60 parts of hydroxyethyl acrylate, 5 parts of perfluorobutyl ethyl acrylate, and 0.5 parts of azobisisobutyronitrile is mixed uniformly and then dropped into the reactor at a constant speed, and the mixture is kept warm for 3 hours after the dropwise addition is completed; (2) 5 parts of 2-isocyanatoethyl acrylate is added to the reactor, the temperature is raised to 70°C, and stirring is continued until the -NCO content of the system is less than 0.05%; (3) The reaction system is cooled and the perfluoroheptane solvent is removed to obtain modified monomer-1.

[0025] (Production of Modified Monomer-2) The preparation of the modified monomer-1 was basically the same as that of the modified monomer-1, except that perfluorobutyl ethyl acrylate was replaced with perfluorohexyl ethyl acrylate.

[0026] (Production of Modified Monomer-3) The preparation of the modified monomer-1 was basically the same as that of the modified monomer-1, except that perfluorobutylethyl acrylate was changed to perfluorooctylethyl acrylate.

[0027] (Production of Modified Monomer-4) The preparation of modified monomer-1 was basically the same as that of modified monomer-1, except that perfluorobutyl ethyl acrylate was changed to perfluorodecyl ethyl acrylate.

[0028] (Manufacture of modified polytetrafluoroethylene resin-1 powder) (Manufacture of modified polytetrafluoroethylene resin-1 powder) (1) Ammonium pentadecafluorooctanoate, perfluoropolyether, and deionized water are added to a high-pressure emulsification reactor while stirring, and uniformly emulsified at a stirring speed of 1500 r / min; (2) The stirring speed is reduced to 300 r / min, and the temperature of the system is increased to 50°C and the pressure is increased to 3.5 MPa. (3) Two high-pressure pumps inject tetrafluoroethylene monomer, modified monomer-1, and perfluorobutyryl peroxide into the high-pressure emulsification reactor, one high-pressure pump injects tetrafluoroethylene monomer, and one high-pressure pump injects modified monomer and initiator. After all the raw materials are injected, the temperature of the reactor is raised to 70°C, and after aging for 3 hours, modified polytetrafluoroethylene resin powder is obtained.

[0029] The mass percentage of each ingredient is as follows, with the total amount of ingredients being 100%: Ammonium pentadecafluorooctanoate 0.5% Perfluoropolyether 0.5% Tetrafluoroethylene monomer 50% Modified Monomer-1 1% Perfluorobutyryl peroxide 2% The remainder is water.

[0030] (Manufacture of modified polytetrafluoroethylene resin-2 powder) The production process is basically the same as that of the modified polytetrafluoroethylene resin-1 powder, except that modified monomer-1 is replaced with modified monomer-2.

[0031] (Manufacture of modified polytetrafluoroethylene resin-3 powder) The production of the modified polytetrafluoroethylene resin-1 powder was basically the same as that of the modified polytetrafluoroethylene resin-1 powder, except that the modified monomer-1 was replaced with the modified monomer-3.

[0032] (Manufacture of modified polytetrafluoroethylene resin-4 powder) The production process is basically the same as that of the modified polytetrafluoroethylene resin-1 powder, except that modified monomer-1 is replaced with modified monomer-4. EXAMPLES

[0033] (1) 10 parts of Asahi Glass AFLAS100 and 100 parts of modified polytetrafluoroethylene resin-1 powder were uniformly mixed, pressed into a round bar shape using a press at 50°C, and rolled at 60°C to form a base film with a thickness of 90 mm. (2) The base film of step (1) was degreased at 250° C., and after the degreasing treatment, the base film was stretched 7 times in the longitudinal direction and 4 times in the transverse direction. (3) The film stretched in step (2) was sintered at 350° C. for 1 minute to obtain a gas-permeable stretched polytetrafluoroethylene film. EXAMPLES

[0034] The procedure was basically the same as in Example 1, except that in step (1) 10 parts of Asahi Glass AFLAS100 was changed to 20 parts of Asahi Glass AFLAS100, and the modified polytetrafluoroethylene resin-1 powder was changed to modified polytetrafluoroethylene resin-2 powder. EXAMPLES

[0035] The procedure was basically the same as in Example 1, except that in step (1) 10 parts of Asahi Glass AFLAS100 was changed to 30 parts of Asahi Glass AFLAS100, and modified polytetrafluoroethylene resin-1 powder was changed to modified polytetrafluoroethylene resin-3 powder. EXAMPLES

[0036] The procedure was basically the same as in Example 1, except that in step (1), Asahi Glass AFLAS100 was changed to Asahi Glass AFLAS150, and the modified polytetrafluoroethylene resin-1 powder was changed to modified polytetrafluoroethylene resin-4 powder.

[0037] Comparative Example 1 The procedure was basically the same as in Example 1, except that the modified fluoropolymer powder in step (1) was replaced with the same amount of modified polytetrafluoroethylene resin-1 powder, and the base film broke during the stretching process in step (2).

[0038] Comparative Example 2 A commercially available polytetrafluoroethylene film was used.

[0039] Comparative Example 3 Commercially available F46 film was used.

[0040] (Performance test) The pore size of the products of Examples 1-4 and Comparative Examples 2 and 3 was tested according to the following method, and then the air permeability and waterproofness were tested. The test results are shown in Table 1.

[0041] Air permeability: The test method is GBT36138-2018 sterilization polytetrafluoroethylene flat plate microfiltration membrane.

[0042] Waterproof: The test method is GB / T 4745-2012 Water stain test for waterproof performance of textile products.

[0043] Pore ​​size: The test method is according to HYT 039-1995 Pore performance measurement method for pore filtration membrane.

[0044] [Table 1]

[0045] As can be seen by comparing Examples 1-4 with Comparative Examples 2 and 3, the breathable stretched polytetrafluoroethylene film according to the present invention has smaller and more uniform pores, better breathability and stronger waterproof ability.

[0046] In Comparative Example 1, the film breaks during the stretching process, and the modified fluoropolymer powder added in the present invention significantly improves its tensile strength, which explains why the final stretch ratio of the stretched film can be made larger.

[0047] The above embodiments are merely intended to explain the technical ideas and features of the present invention, and are intended to enable those skilled in the art to understand and practice the contents of the present invention, and do not limit the scope of protection of the present invention. Any equivalent changes or modifications made substantially based on the spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A breathable stretched polytetrafluoroethylene film, which is produced by mixing modified polytetrafluoroethylene resin powder and modified fluoropolymer powder and stretching the mixture; The modified polytetrafluoroethylene resin is produced by mixing and copolymerizing a tetrafluoroethylene monomer and a modified monomer, The modified monomer structure is a compound of formula I: 【Chemistry 1】 A breathable stretched polytetrafluoroethylene film, characterized in that m:n=1-2:20, and x represents 4, 6, 8, or 10.

2. 2. The breathable stretched polytetrafluoroethylene film according to claim 1, wherein the modified fluoropolymer powder is a copolymer of propylene and tetrafluoroethylene.

3. The method for producing the modified monomer includes the steps of: Step (1) of adding 30-50 parts of perfluoroheptane as a solvent to a reactor by weight, heating to 60-70°C, and then adding 50-70 parts of a mixture of hydroxyethyl acrylate and perfluoroalkylethyl acrylate and 0.5-1 part of an initiator to the reactor at a constant rate after uniformly mixing the mixture, and keeping the mixture warm for 2-4 hours after the completion of the dropping; (2) adding 6-12 parts of 2-isocyanatoethyl acrylate to the reactor, raising the temperature to 70-75° C., and continuing stirring until the —NCO group content of the system is less than 0.05%; The breathable stretched polytetrafluoroethylene film according to claim 1, further comprising a step (3) of cooling the reaction system and removing the perfluoroheptane solvent to obtain the modified monomer.

4. 4. The breathable polytetrafluoroethylene stretched film according to claim 3, wherein the initiator in step (1) is selected from one of azobisisobutyronitrile and benzoyl peroxide.

5. The method for producing the modified polytetrafluoroethylene resin powder includes the steps of: Step (1) of adding a dispersant, an emulsifier and deionized water into a high-pressure emulsification reactor and emulsifying the mixture uniformly at a stirring speed of 1000-2000 r / min; (2) reducing the stirring speed to 200-400 r / min and increasing the reactor temperature to 40-60° C. and pressure to 3-4 MPa; and (3) simultaneously injecting the mixture of tetrafluoroethylene monomer, modified monomer and initiator into a high-pressure emulsification reactor by a high-pressure pump, raising the temperature of the reactor to 60-80°C, and aging for 2-4 hours to obtain a modified polytetrafluoroethylene resin.

6. The mass percentage of each raw material is as follows, with the total amount of raw materials being 100%: Dispersant 0.1-1% Emulsifier 0.2-1% Tetrafluoroethylene monomer 40-60% Modified monomer 1-1.5% Initiator 0.5-3% 6. The breathable stretched polytetrafluoroethylene film according to claim 5, wherein the remainder is water.

7. 6. The gas-permeable stretched polytetrafluoroethylene film according to claim 5, wherein in the step (1), the dispersing agent is ammonium pentadecafluorooctanoate and the emulsifying agent is perfluoropolyether.

8. The breathable stretched polytetrafluoroethylene film according to claim 4, characterized in that in step (3), the initiator is selected from one of perfluorobutyryl peroxide and perfluorohexanoyl peroxide.

9. (1) uniformly mixing the modified fluoropolymer powder and the modified polytetrafluoroethylene resin powder, pressing into a round bar at 50-55°C, and rolling at 60-65°C to form a base film with a thickness of less than 100 mm; Step (2) of degreasing the base film of step (1) at 250-260°C, stretching the base film after the degreasing treatment by 6-8 times in the machine direction and by 3-5 times in the transverse direction; and (3) sintering the film stretched in step (2) at 340-360 ° C for 1-2 minutes to obtain a gas-permeable stretched polytetrafluoroethylene film. The method for producing a gas-permeable stretched polytetrafluoroethylene film according to any one of claims 1 to 8.

10. 10. The method for producing a gas-permeable stretched polytetrafluoroethylene film according to claim 9, wherein the mass ratio of the modified fluoropolymer powder to the modified polytetrafluoroethylene resin is 1-3:10.

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