High-permeability-resistance polytetrafluoroethylene resin and preparation method thereof

Abstract

The invention discloses high-permeability-resistance polytetrafluoroethylene resin and a preparation method thereof, and belongs to the technical field of high polymer material modification. The process comprises the following steps: firstly introducing a tetrafluoroethylene monomer and a first modified monomer for polymerization, controlling the introduction amount of the tetrafluoroethylene monomer, stopping the reaction, recovering, then adding a second modified monomer, continuing introducing the tetrafluoroethylene monomer for polymerization, adding a chain transfer agent for continuous reaction when a certain amount of the tetrafluoroethylene monomer is reached, and finally obtaining a polytetrafluoroethylene resin product after the reaction is finished. The preparation method provided by the invention can effectively reduce the melt viscosity of polytetrafluoroethylene, regulate and control the crystallinity, crystal structure and distribution of polytetrafluoroethylene, improve the compactness of the product, enable the stability of a resin end group to be better, greatly reduce the phenomenon that tiny pores are formed by decomposition in high-temperature sintering processing, remarkably improve the permeability resistance of the product, and improve the service life of the product. And the application field of polytetrafluoroethylene is expanded.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer material modification, and in particular relates to a high permeability-resistant polytetrafluoroethylene resin and a preparation method thereof. Background Art

[0002] Polytetrafluoroethylene (PTFE), commonly known as the king of plastics, 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. Among them, suspension polymerization is the main method for synthesizing polytetrafluoroethylene in industry. It does not require the use of emulsifiers and stabilizers, etc., has low cost and relatively mature technology, and is easy to mass produce. However, conventional homopolymer suspension polytetrafluoroethylene can only be used for conventional purposes due to its extremely high melt viscosity, large microscopic voids in the product, low density, and poor permeability resistance. It cannot be used in fields with high permeability requirements, such as the semiconductor field. The wet electronic chemical equipment lining must have good permeability resistance to prevent high-purity wet electronic chemicals from penetrating the lining and contacting the outer metal and being contaminated. Tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) is generally used at home and abroad to make high-purity wet electronic chemical equipment linings, but PFA is expensive, and the quality of domestic products is unstable, and there is still a large gap with foreign ultra-pure PFA.

[0003] In view of this, how to chemically modify polytetrafluoroethylene can reduce its melt viscosity, increase the density of the product, and make the product have good permeability resistance, which is of great significance for low-cost replacement of PFA for wet electronic chemical equipment linings. Summary of the invention

[0004] In view of the problems raised by the background technology, the purpose of the present invention is to provide a high permeability-resistant polytetrafluoroethylene resin and a preparation method thereof. The present invention precisely controls the reaction parameters and then regulates the degree of polymerization reaction. On this basis, two modified monomers are successively selected to cooperate with a special chain transfer agent to prepare polytetrafluoroethylene, and finally the reaction is performed to prepare polytetrafluoroethylene with high strength, good stability and excellent permeability resistance, which can meet the performance requirements of high-purity wet electronic chemical equipment lining materials and achieve the purpose of replacing tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer at low cost.

[0005] The present invention specifically adopts the following technical solutions: The present invention provides a method for preparing a polytetrafluoroethylene resin with high permeability resistance, comprising the following steps: Step 1: adding water and a first modified monomer to a closed container in sequence, then introducing tetrafluoroethylene monomer and heating, adding a first initiator to carry out polymerization reaction, stopping the reaction when the amount of tetrafluoroethylene monomer introduced reaches a certain amount, and recovering the tetrafluoroethylene monomer; wherein the first modified monomer is composed of perfluoroalkyl ethylene and perfluoroalkyl vinyl ether; Step 2: sequentially introduce the second modified monomer and tetrafluoroethylene monomer into the system after the reaction in step 1 until the pressure is constant, add the second initiator to carry out polymerization reaction, add the chain transfer agent to continue the reaction when the amount of tetrafluoroethylene monomer introduced reaches a certain amount, stop the reaction when the amount introduced reaches the target amount, wash, dry and crush the polymer in the kettle to obtain the polytetrafluoroethylene resin product.

[0006] Furthermore, the water in step 1 is high-purity deionized water; after adding the water, the container needs to be evacuated, filled with nitrogen to displace and deoxygenate, and then the first modified monomer is added.

[0007] Furthermore, in step 1, the first modified monomer is perfluoro-n-propyl vinyl ether and perfluorohexylethylene, the mass ratio of the two is (1-5):1, and the total amount added is 0.01%-0.2% of the mass of water.

[0008] Furthermore, the conditions of the polymerization reaction in step 1 are: tetrafluoroethylene monomer is introduced until the pressure in the container is 0.6MPa-1.2MPa, the temperature is raised to 25°C-50°C and the temperature is maintained 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 addition amount thereof is 0.0001%-0.003% of the water mass, and the reducing agent is at least one of sodium sulfite, sodium bisulfite, potassium sulfite, ferrous sulfate, and oxalic acid, and the addition amount thereof is 0.0003%-0.005% of the water mass; tetrafluoroethylene monomer is continuously introduced during the polymerization reaction to maintain the reaction pressure, and the polymerization is stopped when the amount of tetrafluoroethylene monomer introduced reaches 15%-25% of the water mass.

[0009] Furthermore, in step 2, the second modified monomer is chlorotrifluoroethylene, and its added amount is 0.004%-0.08% of the mass of water.

[0010] Furthermore, the conditions of the polymerization reaction in step 2 are: introducing tetrafluoroethylene monomer until the pressure in the container is 1.5MPa-1.8MPa, heating to 45°C-65°C and maintaining a constant temperature; the second initiator is peroxysuccinic acid, and the amount added is 0.005%-0.05% of the mass of water.

[0011] Furthermore, in step 2, the target 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. When the amount of tetrafluoroethylene monomer introduced reaches 50%-90% of the target amount, a chain transfer agent is added to continue the reaction.

[0012] Furthermore, the chain transfer agent in step 2 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 added amount is 0.003%-0.1% of the mass of water.

[0013] Compared with the prior art, the present invention has the following beneficial effects: The process of the present invention first uses a first modified monomer to chemically modify polytetrafluoroethylene, and introduces a side group on the main chain, which not only destroys the rigid structure of the original molecular chain of polytetrafluoroethylene and effectively reduces its melt viscosity, but also effectively regulates the crystallinity, crystal structure and distribution of polytetrafluoroethylene by accurately controlling the pressure and degree of polymerization reaction, providing a reaction basis for the subsequent second monomer modification. After the first chemical modification, the present invention also uses a second modified monomer to re-modify polytetrafluoroethylene. The copolymerization modification of the selected second modified monomer combined with the addition of an organic initiator can reduce the molecular weight of polytetrafluoroethylene and increase the content of the amorphous phase, so that the product has a lower melt viscosity, significantly reduces the pores between particles during the processing, and greatly improves its permeability resistance. At the same time, the present invention adds a fluorine-containing alcohol chain transfer agent when the polymerization reaction of the second modified monomer proceeds to a certain extent. By using a fluorine-containing alcohol with a high fluorine-hydrogen ratio as a chain transfer agent, a high-fluorine-content end group can be formed on the polymer, so that the resin end group has higher stability, and can greatly reduce the tiny pores formed by the decomposition of the end group of the resin during the high-temperature sintering process, further improve the product density, and make the final product have good permeability resistance. DETAILED DESCRIPTION

[0014] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the embodiments. If the specific conditions are not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0015] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0016] Example 1 A method for preparing a polytetrafluoroethylene resin with high permeability resistance, comprising the following steps: 1. 100 parts by weight of high-purity deionized water is injected into a closed polymerization kettle, and then the polymerization kettle is evacuated and filled with nitrogen for displacement and deoxygenation until the oxygen content does not exceed 10ppm, and then evacuated to -0.01MPa, and then 0.12 parts of perfluoro-n-propyl vinyl ether and 0.03 parts of perfluorohexylethylene are introduced, and gaseous tetrafluoroethylene monomer is continuously introduced until the pressure in the kettle is 0.9MPa, and at the same time, the temperature in the kettle is raised to 35°C and kept constant, and 0.0012 parts of ammonium persulfate and 0.0024 parts of sodium bisulfite are added to start polymerization reaction, and gaseous tetrafluoroethylene monomer is continuously introduced during the reaction to maintain the pressure in the kettle at 0.9MPa, and the polymerization reaction is stopped when the total amount of gaseous tetrafluoroethylene monomer introduced before and after the reaction reaches 20 parts, and the gaseous tetrafluoroethylene monomer is recovered until the pressure in the kettle is 0.01MPa.

[0017] 2. Continue to introduce 0.045 parts of chlorotrifluoroethylene into the polymerization kettle after the reaction, then introduce gaseous tetrafluoroethylene monomer until the pressure in the kettle reaches 1.6 MPa, and at the same time, raise the temperature in the kettle to 60° C. and maintain a constant temperature, add 0.028 parts of peroxysuccinic acid to start the polymerization reaction, and continue to introduce gaseous tetrafluoroethylene monomer during the reaction to maintain the pressure in the kettle at 1.6 MPa. When the amount of gaseous tetrafluoroethylene monomer introduced reaches 9 parts, add 0.04 parts of 2,2,3,3,3-pentafluoropropanol to continue the reaction, and stop the polymerization reaction when the amount of gaseous tetrafluoroethylene monomer introduced reaches the target amount of 12 parts, recover the residual gaseous tetrafluoroethylene monomer in the kettle and replace it, and send the polymer in the kettle to a post-processing system for washing, drying and crushing to obtain a polytetrafluoroethylene resin product.

[0018] Example 2 A method for preparing a polytetrafluoroethylene resin with high permeability resistance, comprising the following steps: 1. 100 parts by weight of high-purity deionized water are injected into a closed polymerization kettle, and then the polymerization kettle is evacuated and filled with nitrogen for displacement and deoxygenation until the oxygen content does not exceed 10ppm, and then evacuated to -0.01MPa, and then 0.15 parts of perfluoro-n-propyl vinyl ether and 0.05 parts of perfluorohexylethylene are introduced, and gaseous tetrafluoroethylene monomer is continuously introduced until the pressure in the kettle is 1.2MPa, and the temperature in the kettle is raised to 30°C and kept constant, and 0.002 parts of potassium persulfate and 0.003 parts of ferrous sulfate are added to start polymerization reaction, and gaseous tetrafluoroethylene monomer is continuously introduced during the reaction to maintain the pressure in the kettle at 1.2MPa, and the polymerization reaction is stopped when the total amount of gaseous tetrafluoroethylene monomer introduced before and after the reaction reaches 20 parts, and the gaseous tetrafluoroethylene monomer is recovered until the pressure in the kettle is 0.01MPa.

[0019] 2. Continue to introduce 0.025 parts of chlorotrifluoroethylene into the polymerization kettle after the reaction, and then introduce gaseous tetrafluoroethylene monomer until the pressure in the kettle reaches 1.5 MPa. At the same time, the temperature in the kettle is raised to 50° C. and maintained at a constant temperature. 0.016 parts of peroxysuccinic acid are added to start the polymerization reaction. During the reaction, gaseous tetrafluoroethylene monomer is continuously introduced to maintain the pressure in the kettle at 1.5 MPa. When the amount of gaseous tetrafluoroethylene monomer introduced reaches 6 parts, 0.02 parts of 2,2,2-trifluoroethanol are added to continue the reaction. When the amount of gaseous tetrafluoroethylene monomer introduced reaches the target amount of 9 parts, the polymerization reaction is stopped, the residual gaseous tetrafluoroethylene monomer in the kettle is recovered and replaced, and the polymer in the kettle is sent to a post-processing system for washing, drying and crushing to obtain a polytetrafluoroethylene resin product.

[0020] Example 3 A method for preparing a polytetrafluoroethylene resin with high permeability resistance, comprising the following steps: 1. 100 parts by weight of high-purity deionized water are injected into a closed polymerization kettle, and then the polymerization kettle is evacuated and filled with nitrogen for displacement and deoxygenation until the oxygen content does not exceed 10ppm, and then evacuated to -0.01MPa, and then 0.05 parts of perfluoro-n-propyl vinyl ether and 0.05 parts of perfluorohexylethylene are introduced, and gaseous tetrafluoroethylene monomer is continuously introduced until the pressure in the kettle is 0.6MPa, and the temperature in the kettle is raised to 40°C and kept constant, and 0.001 parts of potassium permanganate and 0.0018 parts of oxalic acid are added to start polymerization reaction, and gaseous tetrafluoroethylene monomer is continuously introduced during the reaction to maintain the pressure in the kettle at 0.6MPa, and the polymerization reaction is stopped when the total amount of gaseous tetrafluoroethylene monomer introduced before and after the reaction reaches 18 parts, and the gaseous tetrafluoroethylene monomer is recovered until the pressure in the kettle is 0.01MPa.

[0021] 2. Continue to introduce 0.075 parts of chlorotrifluoroethylene into the polymerization kettle after the reaction, and then introduce gaseous tetrafluoroethylene monomer until the pressure in the kettle reaches 1.8 MPa. At the same time, the temperature in the kettle is raised to 50° C. and maintained at a constant temperature. 0.042 parts of peroxysuccinic acid are added to start the polymerization reaction. During the reaction, gaseous tetrafluoroethylene monomer is continuously introduced to maintain the pressure in the kettle at 1.8 MPa. When the amount of gaseous tetrafluoroethylene monomer introduced reaches 13.5 parts, 0.07 parts of 1,1,1,3,3,3-hexafluoroisopropanol are added to continue the reaction. When the amount of gaseous tetrafluoroethylene monomer introduced reaches the target amount of 15 parts, the polymerization reaction is stopped, the residual gaseous tetrafluoroethylene monomer in the kettle is recovered and replaced, and the polymer in the kettle is sent to a post-processing system for washing, drying and crushing to obtain a polytetrafluoroethylene resin product.

[0022] Comparative Example 1 The step parameters are as in Example 1, except that during the second polymerization reaction in step 2, no chain transfer agent is added, and the polymerization reaction is stopped directly when the amount of gas-phase tetrafluoroethylene monomer introduced reaches the target amount.

[0023] Comparative Example 2 The step parameters are as in Example 1, except that propanol is used in step 2 instead of 2,2,3,3,3-pentafluoropropanol.

[0024] Comparative Example 3 Refer to the step parameters of Example 1, except that in step 1, 0.15 parts of perfluoro-n-propyl vinyl ether is used as the first modifying monomer.

[0025] Comparative Example 4 The step parameters are as shown in Example 1, except that in step 1, 0.12 parts of perfluoro-n-propyl vinyl ether and 0.03 parts of vinylidene fluoride are used as the first modifying monomer.

[0026] Comparative Example 5 The step parameters are as shown in Example 1, except that in step 1, chlorotrifluoroethylene is used in place of the first modifying monomer with the same mass, and in step 2, perfluoro-n-propyl vinyl ether and perfluorohexylethylene are used in place of the second modifying monomer with the same mass and proportion.

[0027] Comparative Example 6 The step parameters are as in Example 1, except that no modified monomer is added during the whole process.

[0028] Comparative Example 7 The step parameters are as in Example 1, except that step 1 is reacted to the total target amount (30 parts), and the second modification in step 2 is not performed.

[0029] Test example The performance of the polytetrafluoroethylene resin samples prepared in the above embodiments and comparative examples was tested and compared.

[0030] Standard relative density, tensile strength, elongation at break, thermal instability index: measured according to the method described in HG / T2902-1997.

[0031] Permeability determination method: Process polytetrafluoroethylene resin into 0.5mm thick turning film, sandwiched between two hemispherical glass containers, the two glass containers are filled with 31% mass concentration of hydrochloric acid and high-purity water respectively. After the test device is placed in a constant temperature room at 25℃ for 90 days, take a water sample from the high-purity water side, and use ion chromatography to detect the chloride ion concentration of the water sample.

[0032] Chloride ion permeability

[0033] in: P is the chloride ion permeability coefficient (unit: g·cm·cm -2 ·s -1 ), c is the chloride ion concentration (in mg / L), V The injection volume of high-purity water (unit: L),L is the film thickness (in mm), A is the area of ​​contact between the membrane and high-purity water (in cm 2 ), t is the static time of the test device (unit: s) The test results are shown in Table 1.

[0034] Table 1

[0035] In summary, the tensile strength, elongation at break and thermal stability of the polytetrafluoroethylene product prepared by the method of the present invention are improved to varying degrees, especially the permeability resistance (chloride ion permeability coefficient) is greatly improved, which can meet the performance requirements of lining materials of high-purity wet electronic chemical equipment in the semiconductor field. At the same time, the raw material process cost is low, and it can well replace the expensive tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, and has good market competitiveness.

[0036] The embodiments described above only express several preferred embodiments of the present invention, and the descriptions thereof are relatively specific and detailed, but are not intended to limit the present invention. It should be noted that for those skilled in the art, the present invention may also have various changes and modifications, and any modifications, equivalent substitutions, improvements, etc. made within the concept and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a polytetrafluoroethylene resin with high permeability resistance, characterized in that: The steps include: Step 1: adding water and a first modified monomer to a closed container in sequence, then introducing tetrafluoroethylene monomer and heating, adding a first initiator to carry out polymerization reaction, stopping the reaction when the amount of tetrafluoroethylene monomer introduced reaches a certain amount, and recovering the tetrafluoroethylene monomer; wherein the first modified monomer is composed of perfluoroalkyl ethylene and perfluoroalkyl vinyl ether; Step 2: sequentially introduce the second modified monomer and tetrafluoroethylene monomer into the system after the reaction in step 1 until the pressure is constant, add the second initiator to carry out polymerization reaction, add the chain transfer agent to continue the reaction when the amount of tetrafluoroethylene monomer introduced reaches a certain amount, stop the reaction when the amount introduced reaches the target amount, wash, dry and crush the polymer in the kettle to obtain the polytetrafluoroethylene resin product.

2. The method for preparing a polytetrafluoroethylene resin with high permeability resistance according to claim 1, characterized in that: The water in step 1 is high-purity deionized water; after adding the water, the container needs to be evacuated, filled with nitrogen to displace and deoxygenate, and then the first modified monomer is added.

3. The method for preparing a polytetrafluoroethylene resin with high permeability resistance according to claim 1, characterized in that: Step 1: The first modified monomer is perfluoro-n-propyl vinyl ether and perfluorohexylethylene, the mass ratio of the two is (1-5):1, and the total amount added is 0.01%-0.2% of the mass of water.

4. The method for preparing a polytetrafluoroethylene resin with high permeability resistance according to claim 1, characterized in that: The conditions of the polymerization reaction in step 1 are as follows: tetrafluoroethylene monomer is introduced until the pressure in the container is 0.6MPa-1.2MPa, the temperature is raised to 25°C-50°C and the temperature is maintained 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 water mass, and 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 water mass; tetrafluoroethylene monomer is continuously introduced during the polymerization reaction to maintain the reaction pressure, and the polymerization is stopped when the amount of tetrafluoroethylene monomer introduced reaches 15%-25% of the water mass.

5. The method for preparing a polytetrafluoroethylene resin with high permeability resistance according to claim 1, characterized in that: Step 2: The second modified monomer is chlorotrifluoroethylene, and the amount added is 0.004%-0.08% of the mass of water.

6. The method for preparing a polytetrafluoroethylene resin with high permeability resistance according to claim 1, characterized in that: The conditions of the polymerization reaction in step 2 are: introducing tetrafluoroethylene monomer until the pressure in the container is 1.5MPa-1.8MPa, heating to 45°C-65°C and maintaining a constant temperature; the second initiator is peroxysuccinic acid, and the addition amount thereof is 0.005%-0.05% of the mass of water.

7. The method for preparing a polytetrafluoroethylene resin with high permeability resistance according to claim 1, characterized in that: In step 2, the target amount of tetrafluoroethylene monomer introduced is 5%-15% of the mass of water. During the polymerization reaction, tetrafluoroethylene monomer is continuously introduced to maintain the reaction pressure. When the amount of tetrafluoroethylene monomer introduced reaches 50%-90% of the target amount, a chain transfer agent is added to continue the reaction.

8. The method for preparing a polytetrafluoroethylene resin with high permeability resistance according to claim 1, characterized in that: The chain transfer agent in step 2 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 mass of water.

9. The high permeability-resistant polytetrafluoroethylene resin obtained by the preparation method according to any one of claims 1 to 8.

Images