A highly permeable polytetrafluoroethylene resin and a method for producing the same

Abstract

This invention discloses a highly permeation-resistant polytetrafluoroethylene (PTFE) resin and its preparation method, belonging to the field of polymer material modification technology. The process of this invention first introduces PTFE monomer and a first modified monomer for polymerization. The reaction is stopped and recovered by controlling the amount of PTFE monomer introduced. Then, a second modified monomer is added, and PTFE monomer polymerization continues. Once a certain amount is reached, a chain transfer agent is added to continue the reaction. Finally, the reaction ends to obtain the PTFE resin product. This preparation method can effectively reduce the melt viscosity of PTFE, regulate its crystallinity, crystal structure and distribution, improve product density, and simultaneously improve the stability of resin end groups. It significantly reduces the phenomenon of decomposition and formation of micropores during high-temperature sintering, significantly improves the permeation resistance of the product, and expands the application fields of PTFE.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high polymer material modification, and particularly relates to a high-penetration-resistance polytetrafluoroethylene resin and a preparation method thereof. BACKGROUND

[0002] Polytetrafluoroethylene (PTFE) is commonly known as plastic king, which has excellent chemical resistance, heat resistance, weather resistance, non-stickiness, low friction coefficient and electrical insulation, and plays an important role in modern industry. At present, polytetrafluoroethylene is mainly prepared by emulsion polymerization and suspension polymerization, and the suspension polymerization is the main method for synthesizing polytetrafluoroethylene in industry, which does not need to use emulsifiers and stabilizers, has low cost and relatively mature process, and is easy to mass production. However, the conventional homopolymerization suspension polytetrafluoroethylene has extremely high melt viscosity, large micro voids, low density and poor penetration resistance, and can only be used for conventional purposes, and cannot be applied to fields with high penetration resistance requirements, such as semiconductor field. Wet electronic chemical equipment lining must have good penetration resistance to prevent high-purity wet electronic chemicals from penetrating the lining and contacting the outer metal to be contaminated. Generally, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) is used to make high-purity wet electronic chemical equipment lining at home and abroad, but PFA is expensive, and the quality of domestic products is unstable, which still has a large gap with foreign super-pure PFA.

[0003] Therefore, how to chemically modify polytetrafluoroethylene to reduce its melt viscosity, improve the density of the product, and make the product have good penetration resistance is of great significance for low-cost substitution of PFA for wet electronic chemical equipment lining. SUMMARY

[0004] In view of the problems in the background art, the purpose of the present application is to provide a high-penetration-resistance polytetrafluoroethylene resin and a preparation method thereof. The present application controls the reaction parameters accurately to control the polymerization degree, and then prepares polytetrafluoroethylene by using two kinds of modified monomers in combination with a special chain transfer agent, so that polytetrafluoroethylene with high strength, good stability and excellent penetration resistance is finally prepared by reaction, which can meet the performance requirements of high-purity wet electronic chemical equipment lining materials, and realize the purpose of low-cost substitution of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer.

[0005] The present application specifically adopts the following technical solutions:

[0006] The present application provides a preparation method of a high-penetration-resistance polytetrafluoroethylene resin, comprising the following steps:

[0007] Step one: water and the first modified monomer are sequentially added to a closed container, then tetrafluoroethylene monomer is introduced and heated, and the first initiator is added for polymerization, when the amount of tetrafluoroethylene monomer reaches a certain amount, the reaction is stopped, and the tetrafluoroethylene monomer is recovered; wherein the first modified monomer is composed of perfluoroalkyl ethylene and perfluoroalkyl vinyl ether;

[0008] Step two: the second modified monomer and tetrafluoroethylene monomer are sequentially introduced into the system after step one until a constant pressure is reached, and the second initiator is added for polymerization, when the amount of tetrafluoroethylene monomer reaches a certain amount, a chain transfer agent is added for further reaction, and the reaction is stopped when the amount reaches the target amount, and the polymer in the kettle is washed, dried, and crushed to obtain a polytetrafluoroethylene resin product.

[0009] Further, the water in step one is high-purity deionized water; after adding water, the container needs to be vacuumed, filled with nitrogen to replace oxygen, and then the first modified monomer is added.

[0010] Further, the first modified monomer in step one is perfluoro-n-propyl vinyl ether and perfluoro-hexyl ethylene, and the mass ratio of the two is (1-5):1, and the total amount is 0.01%-0.2% of the mass of water.

[0011] Further, the conditions of the polymerization reaction in step one are: the tetrafluoroethylene monomer is introduced until the pressure in the container is 0.6-1.2 MPa, and the temperature is raised to 25-50°C and kept constant; the first initiator is an inorganic redox system initiator, the oxidant is at least one of ammonium persulfate, sodium persulfate, potassium persulfate, potassium permanganate, and potassium bromate, and the amount added is 0.0001%-0.003% of the mass of water, the reducing agent is at least one of sodium sulfite, sodium bisulfite, potassium sulfite, ferrous sulfate, and oxalic acid, and the amount added is 0.0003%-0.005% of the mass of water; tetrafluoroethylene monomer is continuously introduced during the polymerization process to maintain the reaction pressure, and the polymerization is stopped when the amount of tetrafluoroethylene monomer introduced reaches 15%-25% of the mass of water.

[0012] Further, the second modified monomer in step two is trifluorochloroethylene, and the amount added is 0.004%-0.08% of the mass of water.

[0013] Further, the conditions of the polymerization reaction in step two are: the tetrafluoroethylene monomer is introduced until the pressure in the container is 1.5-1.8 MPa, and the temperature is raised to 45-65°C and kept constant; the second initiator is peroxide succinic acid, and the amount added is 0.005%-0.05% of the mass of water.

[0014] Further, in step two, the amount of tetrafluoroethylene monomer introduced is 5-15% of the mass of water, and tetrafluoroethylene monomer is continuously introduced during the polymerization reaction to maintain the reaction pressure, and when the amount of tetrafluoroethylene monomer introduced reaches 50-90% of the target amount, a chain transfer agent is added to continue the reaction.

[0015] Further, the chain transfer agent in step two is at least one of 2,2,2-trifluoroethanol, 2,2,3,3,3-pentafluoropropanol, 1,1,1,3,3,3-hexafluoroisopropanol, and 2,2,3,4,4,4-hexafluorobutanol, and the amount of the chain transfer agent added is 0.003-0.1% of the mass of water.

[0016] Compared with the prior art, the beneficial effects of the present application are:

[0017] The process of the present application first uses a first modified monomer to chemically modify polytetrafluoroethylene, introducing side groups on the main chain, not only destroying the rigid structure of the original molecular chain of polytetrafluoroethylene, but also effectively reducing the melt viscosity thereof, in addition, by precisely controlling the pressure and the degree of polymerization reaction, the crystallinity, crystal structure and distribution of polytetrafluoroethylene are effectively controlled, providing a reaction basis for subsequent second monomer modification. The present application further uses a second modified monomer to re-modify polytetrafluoroethylene after the first chemical modification, and the selected second modified monomer copolymerization modification combined with the addition of an organic initiator can reduce the molecular weight of polytetrafluoroethylene, increase the content of amorphous phase, make the product have lower melt viscosity, significantly reduce the inter-particle pores in the processing process, and greatly improve the permeation resistance thereof. At the same time, when the second modified monomer polymerization reaction reaches a certain degree, a fluorine-containing alcohol chain transfer agent is added, and the fluorine-containing alcohol with a high fluorine-hydrogen ratio is used as the chain transfer agent, which can form end groups with high fluorine content on the polymer, so that the resin end group stability is higher, the micro pores formed by the decomposition of the end groups of the resin in the high-temperature sintering process can be greatly reduced, the product density is further improved, and the final product has good permeation resistance. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the present application will be described clearly and completely below in combination with examples. If the specific conditions are not specified in the examples, the conventional conditions or the conditions recommended by the manufacturer are used. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased on the market.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the present application is only for the purpose of describing specific embodiments and is not intended to limit the present application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0020] Example 1

[0021] A method for preparing a high-penetration-resistant polytetrafluoroethylene resin, comprising the following steps:

[0022] 1. 100 parts by weight of high-purity deionized water are injected into a closed polymerization kettle, and then the polymerization kettle is vacuumed, filled with nitrogen to replace oxygen, until the oxygen content is not more than 10 ppm, and then vacuumed to -0.01 MPa. Subsequently, 0.12 parts of perfluoro-n-propyl vinyl ether and 0.03 parts of perfluoro-hexyl ethylene are introduced, and gas-phase tetrafluoroethylene monomer is continuously introduced until the pressure in the kettle is 0.9 MPa. At the same time, the kettle is heated to 35°C and kept at a constant temperature. 0.0012 parts of ammonium persulfate and 0.0024 parts of sodium bisulfite are added to start the polymerization reaction. Gas-phase tetrafluoroethylene monomer is continuously introduced during the reaction to maintain the pressure in the kettle at 0.9 MPa. When the total amount of gas-phase tetrafluoroethylene monomer introduced before and after the reaction reaches 20 parts, the polymerization reaction is stopped, and the gas-phase tetrafluoroethylene monomer is recovered to a pressure of 0.01 MPa in the kettle.

[0023] 2. 0.045 parts of trifluorochloroethylene are continuously introduced into the polymerization kettle after the reaction, and then gas-phase tetrafluoroethylene monomer is introduced until the pressure in the kettle is 1.6 MPa. At the same time, the kettle is heated to 60°C and kept at a constant temperature. 0.028 parts of peroxydicarboxylic acid are added to start the polymerization reaction. Gas-phase tetrafluoroethylene monomer is continuously introduced during the reaction to maintain the pressure in the kettle at 1.6 MPa. When the amount of gas-phase tetrafluoroethylene monomer introduced reaches 9 parts, 0.04 parts of 2,2,3,3,3-pentafluoropropanol is added to continue the reaction. When the amount of gas-phase tetrafluoroethylene monomer introduced reaches the target amount of 12 parts, the polymerization reaction is stopped, and the residual gas-phase tetrafluoroethylene monomer in the kettle is recovered and replaced. The polymer in the kettle is sent to a post-treatment system for washing, drying, and crushing to obtain a polytetrafluoroethylene resin product.

[0024] Example 2

[0025] A method for preparing a high-penetration-resistant polytetrafluoroethylene resin, comprising the following steps:

[0026] 1. 100 parts by weight of high-purity deionized water are injected into a closed polymerization kettle, and then the polymerization kettle is vacuumed, filled with nitrogen to replace oxygen, until the oxygen content is not more than 10 ppm, and then vacuumed to -0.01 MPa. Subsequently, 0.15 parts of perfluoro-n-propyl vinyl ether and 0.05 parts of perfluoro-hexyl ethylene are introduced, and gas-phase tetrafluoroethylene monomer is continuously introduced until the pressure in the kettle is 1.2 MPa. At the same time, the kettle is heated to 30°C and kept at a constant temperature. 0.002 parts of potassium persulfate and 0.003 parts of ferrous sulfate are added to start the polymerization reaction. Gas-phase tetrafluoroethylene monomer is continuously introduced during the reaction to maintain the pressure in the kettle at 1.2 MPa. When the total amount of gas-phase tetrafluoroethylene monomer introduced before and after the reaction reaches 20 parts, the polymerization reaction is stopped, and the gas-phase tetrafluoroethylene monomer is recovered to a pressure of 0.01 MPa in the kettle.

[0027] 2. Continue to introduce 0.025 parts of trifluorochloroethylene into the polymerization reactor after the reaction, and then introduce gaseous tetrafluoroethylene monomer until the pressure inside the reactor reaches 1.5 MPa. At the same time, the temperature inside the reactor is raised to 50°C and maintained at a constant temperature. Add 0.016 parts of succinic acid peroxide to start the polymerization reaction. During the reaction, gaseous tetrafluoroethylene monomer is continuously introduced to maintain the pressure inside the reactor at 1.5 MPa. When the amount of gaseous tetrafluoroethylene monomer introduced reaches 6 parts, add 0.02 parts of 2,2,2-trifluoroethanol to continue the reaction. Stop the polymerization reaction when the amount of gaseous tetrafluoroethylene monomer introduced reaches the target amount of 9 parts. Recover the residual gaseous tetrafluoroethylene monomer in the reactor and replace it. The polymer in the reactor is sent to the post-processing system for washing, drying and pulverizing to obtain polytetrafluoroethylene resin product.

[0028] Example 3

[0029] A method for preparing a highly impermeable polytetrafluoroethylene resin, comprising the following steps:

[0030] 1. Inject 100 parts by weight of high-purity deionized water into a sealed polymerization reactor. Then, evacuate the reactor and purge it with nitrogen to remove oxygen until the oxygen content does not exceed 10 ppm. After evacuating to -0.01 MPa, introduce 0.05 parts of perfluoropropyl vinyl ether and 0.05 parts of perfluorohexyl ethylene. Continue to introduce gaseous tetrafluoroethylene monomer until the pressure inside the reactor reaches 0.6 MPa. Simultaneously, raise the temperature inside the reactor to 40°C and maintain a constant temperature. Add 0.001 parts of potassium permanganate and 0.0018 parts of oxalic acid to start the polymerization reaction. During the reaction, continue to introduce gaseous tetrafluoroethylene monomer to maintain the pressure inside the reactor at 0.6 MPa. When the total amount of gaseous tetrafluoroethylene monomer introduced before and after the reaction reaches 18 parts, stop the polymerization reaction and recover the gaseous tetrafluoroethylene monomer until the pressure inside the reactor is 0.01 MPa.

[0031] 2. Continue to introduce 0.075 parts of trifluorochloroethylene into the polymerization reactor after the reaction, and then introduce gaseous tetrafluoroethylene monomer until the pressure inside the reactor reaches 1.8 MPa. At the same time, the temperature inside the reactor is raised to 50°C and maintained at a constant temperature. Add 0.042 parts of succinic acid peroxide to start the polymerization reaction. During the reaction, gaseous tetrafluoroethylene monomer is continuously introduced to maintain the pressure inside the reactor at 1.8 MPa. When the amount of gaseous tetrafluoroethylene monomer introduced reaches 13.5 parts, add 0.07 parts of 1,1,1,3,3,3-hexafluoroisopropanol to continue the reaction. Stop the polymerization reaction when the amount of gaseous tetrafluoroethylene monomer introduced reaches the target amount of 15 parts. Recover the residual gaseous tetrafluoroethylene monomer in the reactor and replace it. The polymer in the reactor is sent to the post-processing system for washing, drying and pulverizing to obtain polytetrafluoroethylene resin product.

[0032] Comparative Example 1

[0033] Referring to the steps and parameters of Example 1, the difference is that in the second polymerization reaction in step 2, no chain transfer agent is added, and the polymerization reaction is stopped directly when the amount of gaseous tetrafluoroethylene monomer introduced reaches the target amount.

[0034] Comparative Example 2

[0035] Referring to the steps and parameters of Example 1, the difference is that propanol is used instead of 2,2,3,3,3-pentafluoropropanol in step 2.

[0036] Comparative Example 3

[0037] Referring to the steps and parameters of Example 1, the difference is that in step 1, 0.15 parts of perfluoropropyl vinyl ether are used as the first modified monomer.

[0038] Comparative Example 4

[0039] Referring to the steps and parameters of Example 1, the difference is that in step 1, 0.12 parts of perfluoropropyl vinyl ether and 0.03 parts of vinylidene fluoride are used as the first modified monomer.

[0040] Comparative Example 5

[0041] Referring to the steps and parameters of Example 1, the difference is that in step 1, trifluorochloroethylene of equal mass is used instead of the first modified monomer, and in step 2, perfluoropropyl vinyl ether and perfluorohexylethylene of equal mass and proportion are used instead of the second modified monomer.

[0042] Comparative Example 6

[0043] The steps and parameters are the same as in Example 1, except that no modified monomers are added throughout the process.

[0044] Comparative Example 7

[0045] Referring to the steps and parameters of Example 1, the difference is that step 1 reacts to the total target amount (30 parts), and step 2, the second modification, is not performed.

[0046] Test case

[0047] The polytetrafluoroethylene resin samples prepared in the above examples and comparative examples were subjected to performance testing and comparative analysis.

[0048] Standard relative density, tensile strength, elongation at break, and thermal instability index were determined according to the method described in HG / T2902-1997.

[0049] Permeability determination method: A 0.5 mm thick machined film of polytetrafluoroethylene resin was sandwiched between two hemispherical glass containers, one filled with 31% hydrochloric acid and the other with high-purity water. After the test apparatus was placed in a constant temperature chamber at 25°C for 90 days, a water sample was taken from the high-purity water side, and the chloride ion concentration of the water sample was determined by ion chromatography.

[0050] Chloride ion permeability coefficient

[0051] in: P Chloride ion permeability coefficient (unit: g·cm·cm) -2 ·s -1 ), c Chloride ion concentration (unit: mg / L) V Volume of high-purity water injected (unit: L). L The thickness is the membrane thickness (in mm). A The area of ​​the membrane in contact with high-purity water (unit: cm²) 2 ), t The settling time of the test apparatus (in seconds).

[0052] The test results are shown in Table 1.

[0053] Table 1

[0054]

[0055] In summary, the polytetrafluoroethylene products prepared by the method of this invention have improved tensile strength, elongation at break, and thermal stability to varying degrees. In particular, the permeability resistance (chloride ion permeability coefficient) is significantly improved, which can meet the performance requirements of lining materials for high-purity wet electronic chemical equipment in the semiconductor field. At the same time, the raw material and process costs are low, and it can well replace the expensive tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, thus having good market competitiveness.

[0056] The embodiments described above are merely preferred embodiments of the present invention, and while the descriptions are specific and detailed, they are not intended to limit the present invention. It should be noted that various changes and modifications can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the concept and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a highly permeation-resistant polytetrafluoroethylene resin, characterized in that, Includes the following steps: Step 1: Add water and the first modified monomer to a closed container in sequence, then introduce tetrafluoroethylene monomer and heat up, add the first initiator to carry out the polymerization reaction, stop the reaction when the amount of tetrafluoroethylene monomer introduced reaches a certain amount, and recover the tetrafluoroethylene monomer. The first modified monomer is composed of perfluoropropyl vinyl ether and perfluorohexylethylene in a mass ratio of (1-5):1, and the total amount of both added is 0.01%-0.2% of the water mass. The polymerization reaction conditions are as follows: tetrafluoroethylene monomer is introduced until the pressure inside the container is 0.6MPa-1.2MPa, the temperature is raised to 25℃-50℃ and kept constant, tetrafluoroethylene monomer is continuously introduced during the polymerization reaction to maintain the reaction pressure, and polymerization is stopped when the amount of tetrafluoroethylene monomer introduced reaches 15%-25% of the water mass. Step 2: The second modified monomer and tetrafluoroethylene monomer are sequentially introduced into the system after the reaction in Step 1 to a constant pressure. The second initiator is added to carry out the polymerization reaction. When the amount of tetrafluoroethylene monomer introduced reaches a certain amount, the chain transfer agent is added to continue the reaction. The reaction is stopped when the amount introduced reaches the target amount. The polymer in the reactor is washed, dried and crushed to obtain the polytetrafluoroethylene resin product. The second modified monomer is trifluorochloroethylene, and its addition amount is 0.004%-0.08% of the water mass. The polymerization reaction conditions are as follows: tetrafluoroethylene monomer is introduced until the pressure in the container is 1.5MPa-1.8MPa, the temperature is raised to 45℃-65℃ and maintained at a constant temperature, the target amount of tetrafluoroethylene monomer introduced is 5%-15% of the water mass, tetrafluoroethylene monomer is continuously introduced during the polymerization reaction to maintain the reaction pressure, and when the amount of tetrafluoroethylene monomer introduced reaches 50%-90% of the target amount, a chain transfer agent is added to continue the reaction. The chain transfer agent is at least one of 2,2,2-trifluoroethanol, 2,2,3,3,3-pentafluoropropanol, 1,1,1,3,3,3-hexafluoroisopropanol, and 2,2,3,4,4,4-hexafluorobutanol, and its addition amount is 0.003%-0.1% of the water mass.

2. The method for preparing the high-permeability polytetrafluoroethylene resin according to claim 1, characterized in that, The water mentioned in step one is high-purity deionized water; after adding water, the container needs to be evacuated, purged with nitrogen to remove oxygen, and then the first modified monomer is added.

3. The method for preparing the high-permeability polytetrafluoroethylene resin according to claim 1, characterized in that, Step 1: The first initiator is an inorganic redox system initiator. The oxidant is at least one of ammonium persulfate, sodium persulfate, potassium persulfate, potassium permanganate, and potassium bromate, and its addition amount is 0.0001%-0.003% of the water mass. The reducing agent is at least one of sodium sulfite, sodium bisulfite, potassium sulfite, ferrous sulfate, and oxalic acid, and its addition amount is 0.0003%-0.005% of the water mass.

4. The method for preparing the high-permeability polytetrafluoroethylene resin according to claim 1, characterized in that, Step 2: The second initiator is succinic acid peroxide, and its addition amount is 0.005%-0.05% of the water mass.

5. The highly permeability-resistant polytetrafluoroethylene resin obtained by the preparation method according to any one of claims 1-4.

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