Preparation method of high-purity fluorine-containing polymer

Abstract

The invention discloses a preparation method of a high-purity fluorine-containing polymer. The preparation method comprises the following steps: S1, washing the fluorine-containing polymer with pure water until the conductivity of washing water is lower than 3 [mu] s / cm; s2, the fluorine-containing polymer is washed with a mixed solvent, the mixed solvent comprises a first organic solvent and a second organic solvent, the solubility parameter delta1 of the first organic solvent is larger than 11 (cal.cm <-3 >) 1 / 2, the solubility parameter delta2 of the second organic solvent is smaller than 8 (cal.cm <-3 >) 1 / 2 and meets the condition that 9 (cal.cm <-3 >) 1 / 2 < alpha 1 * delta1 + alpha 2 * delta2 < 14 (cal.cm <-3 >) 1 / 2, alpha1 is the molar fraction of the first organic solvent in the total amount of the organic solvent, and alpha2 is the molar fraction of the second organic solvent in the total amount of the organic solvent. According to the method, residual emulsifier / dispersant, paraffin and other impurities in the fluorine-containing polymer can be effectively removed, meanwhile, the drying difficulty and energy consumption can be reduced, and the prepared fluorine-containing polymer has extremely low additive residue and yellow index.

Description

Technical Field

[0001] The present invention relates to the technical field of polymers, and particularly relates to a method for preparing a high-purity fluoropolymer. Background Art

[0002] In industrial production, various additives such as emulsifiers (dispersants), paraffin wax, initiators, and telomers are often added during the process of polymerizing fluoroolefins to obtain fluoropolymers. After polymerization, most impurities need to be removed through post-treatment before the resin can be used normally. Otherwise, it will affect the properties of the resin such as thermal stability and purity.

[0003] As is well known, due to the excellent heat resistance, oxidation resistance, corrosion resistance, low friction, low surface energy, high purity, easy processing and shaping and other characteristics of fluoropolymers, they are widely used in the semiconductor industry, such as wafer carriers, pipeline pumps and valves, sealing rings, etc. Since the manufacturing process of chips has very high requirements for the content of pollutants and does not want to generate new pollution due to the use of fluoropolymers, high-purity fluoropolymers are required.

[0004] To purify fluoropolymers, Arkema patent TW202214715A washes polyvinylidene fluoride with supercritical carbon dioxide fluid, and finally removes the residual supercritical fluid in the resin to obtain purified polyvinylidene fluoride resin. Asahi Glass patent JP2005089524A removes impurities in the crystalline fluororesin through supercritical washing. The impurities are fluorine-containing oligomers with a molecular weight lower than 50,000, emulsifiers, initiators, etc., to obtain purified fluororesin. However, the pressure of the supercritical fluid is too high and the equipment investment is large.

[0005] Daikin patent JP5286737B2 disperses a devolatilization aid in a melt-processable fluororesin, and removes impurities (volatile substances such as unreacted monomers, low-molecular-weight polymers, and polymerization solvents) in the heated and molten state. This method brings a new problem that the devolatilization aid is not easy to be completely removed and is not suitable for preparing high-purity fluoropolymers.

[0006] Ausimont patent US6072020A dissolves an amorphous fluoropolymer in a fluorine-containing solvent, and obtains a purified solution through filtration by semipermeable membranes, ultrafiltration membranes, nanofiltration membranes, etc. This method uses a large amount of expensive fluorine-containing solvents and a filtration membrane system, with many operating steps and high equipment and material costs.

[0007] 3F patent CN102977236A adds C 6 ~C 10The aliphatic alcohol is directly pumped into a cross-flow microfiltration membrane separation system without coagulation to concentrate the fluoropolymer aqueous dispersion, supplemented with high-purity washing water at 0-100 °C, and dried to obtain the fluoropolymer. 3M Patent US6933357B2 removes anions and cations (NH 4 - , H - , OH - ) in the fluororesin emulsion through an ion exchange resin, and no other impurities are introduced during the coagulation process. The common problems of the above technical solutions are the disadvantages of complex operation and high maintenance cost of the filtration system.

[0008] Sinochem Lantian Patent CN114437255A removes the residual emulsifier in the particle gaps by the method of alternating atmospheric stirring and vacuum stirring washing, but cannot remove the impurities inside the particles and the fat-soluble impurities.

[0009] In addition, during the subsequent high-temperature drying process, due to the interaction between impurities such as emulsifiers (dispersants) and paraffin in the polymer and the resin backbone, the aging and yellowing of the polymer will occur, and new impurities will be generated, affecting the quality of the resin.

[0010] Therefore, there is an urgent need to develop a simple and efficient method for removing residual impurities in fluoropolymers to obtain high-purity fluoropolymers. Summary of the Invention

[0011] In order to solve the above problems, the inventors of the present invention found that washing the crude fluoropolymer with at least two organic solvents can effectively remove impurities such as residual emulsifiers / dispersants and paraffin in the resin, and at the same time can reduce the drying difficulty and energy consumption. The prepared fluoropolymer has extremely low additive residues and yellow index.

[0012] The mixed solvent of the present invention utilizes the principle of similar solubility of different types of organic solvents and impurities to remove various oil-soluble and water-soluble impurities. At the same time, the organic solvent can cause the fluoropolymer to swell slightly, which is conducive to the precipitation of impurities inside the fluoropolymer resin particles.

[0013] The object of the present invention is achieved by the following technical solutions:

[0014] The present invention provides a method for preparing a high-purity fluoropolymer, and the preparation method includes the following steps:

[0015] S1: Wash the fluoropolymer with pure water until the conductivity of the washing water is lower than 3 μs / cm,

[0016] S2: Wash the fluoropolymer with a mixed solvent, and the mixed solvent includes a first organic solvent and a second organic solvent,

[0017] The solubility parameter δ of the first organic solvent 1>11 (cal·cm -3 ) 1 / 2 , having good solubility in the water-soluble impurities in the resin. The solubility parameter δ of the second organic solvent 2 <8 (cal·cm -3 ) 1 / 2 , having good solubility in the oil-soluble impurities in the resin, and satisfying 9 (cal·cm -3 ) 1 / 2 <α 1 ×δ 1 +α 2 ×δ 2 <14 (cal·cm -3 ) 1 / 2 , where α 1 is the mole fraction of the first organic solvent in the total amount of organic solvents, and α 2 is the mole fraction of the second organic solvent in the total amount of organic solvents.

[0018] The pure water washing in step S1 can be carried out by the conventional water washing method, or by the alternating method of atmospheric stirring and vacuum stirring washing, aiming to remove the free impurities and the water-soluble impurities between resin particles, reduce the usage amount of the solvent, and save costs.

[0019] The pure water in step S1 is the commonly used pure water in the art. Preferably, the conductivity of the pure water is lower than 2 μs / cm; more preferably, the conductivity of the pure water is lower than 1.5 μs / cm; even more preferably, the conductivity of the pure water is lower than 1 μs / cm.

[0020] The mixed solvent of the present invention only needs to meet the above conditions. For example, the first organic solvent is a water-soluble organic solvent, selected from at least one of methanol, ethanol, and isopropanol. The second organic solvent is a water-insoluble organic solvent, selected from at least one of n-hexane, cyclohexane, n-heptane, and n-octane.

[0021] The volatility R of the mixed solvent of the present invention satisfies 1.4 < R < 8. If the volatility is too large, the mixed solvent volatilizes quickly during the washing process, resulting in large solvent loss and environmental pollution; if the volatility is too small, it is not easy to remove during the drying process after washing.

[0022] The purity standards of the first organic solvent and the second organic solvent of the present invention are independently selected from chemically pure, analytically pure, or guaranteed reagent grade; preferably, they are independently selected from analytically pure or guaranteed reagent grade; more preferably, they are independently selected from guaranteed reagent grade.

[0023] In step S1, the fluoropolymer is washed with pure water until the conductivity of the washing water is lower than 3 μs / cm; preferably, in S1, the fluoropolymer is washed with pure water until the conductivity of the washing water is lower than 2 μs / cm; more preferably, lower than 1 μs / cm. The lower the conductivity of the washing water, the less mixed solvent is used in S2.

[0024] The pure water is the commonly used pure water in the art. Preferably, the conductivity of the pure water is lower than 2 μs / cm; more preferably, the conductivity of the pure water is lower than 1.5 μs / cm; even more preferably, the conductivity of the pure water is lower than 1 μs / cm.

[0025] Furthermore, the mixed solvent further comprises pure water. Based on 100 parts by mass of the mixed solvent, the content of pure water is 0 - 90 parts; preferably, 40 - 80 parts. The higher the content of the organic solvent in the mixed solvent, the better the swelling effect of the fluoropolymer resin. However, a large amount of organic solvent has a high cost, and too little organic solvent cannot achieve the effect of swelling the fluoropolymer to precipitate impurities.

[0026] As an implementation manner, the mixed solvent further comprises pure water. In the drying stage after washing, the organic solvent can form an azeotrope with water, making the water easy to volatilize, which can reduce the drying temperature, shorten the drying time, is beneficial to reducing energy consumption, is also beneficial to the volatilization of residual impurities, and can minimize the yellowing of the fluoropolymer.

[0027] The fluoropolymer described in the present invention is a polyvinylidene fluoride homopolymer or a polyvinylidene fluoride copolymer. The solubility parameter δ of the PVDF resin is 11.34 (cal·cm -3 ) 1 / 2 , and the solubility parameter of the mixed solvent satisfies 9 (cal·cm -3 ) 1 / 2 <α 1 ×δ 1 +α 2 ×δ 2 <14 (cal·cm -3 ) 1 / 2 In this case, it has a certain swelling effect on the PVDF resin, which is beneficial to the precipitation of impurities.

[0028] In step S2, the amount of the mixed solvent used is sufficient to wash the fluoropolymer. Preferably, the volume ratio of the mixed solvent to the fluoropolymer is 2 - 0.5:1; preferably 1.5 - 0.8:1. Too much mixed solvent brings pressure to the subsequent separation work, and too little mixed solvent cannot fully wet the fluoropolymer.

[0029] The polyvinylidene fluoride copolymer is a copolymer of polyvinylidene fluoride and other monomers, and the other monomers are selected from at least one of vinyl fluoride, hexafluoropropylene, trifluoroethylene, chlorotrifluoroethylene, and ethylene.

[0030] The fluoropolymer described in the present invention is prepared by an emulsion method or a suspension method. If the emulsion method is used, the resin obtained after demulsification of the resulting fluoropolymer emulsion is the object to be washed in the present invention. If the suspension method is used, there is no need for demulsification, and the crude suspension resin product is directly used as the object to be washed in the present invention.

[0031] The pure water washing and mixed solvent washing of the fluoropolymer described in the present invention are carried out in a washing container, which is equipped with a stirring device and further equipped with a heating device. The inner material of the washing container is glass or metal material, preferably 304 stainless steel, 316L stainless steel, or Hastelloy.

[0032] The temperature of the pure water washing in step S1 is from room temperature to 75 °C, preferably 40 - 70 °C. Appropriately increasing the washing temperature helps to promote the precipitation of impurities, but if the temperature is too high, it will cause excessive energy consumption.

[0033] The temperature of the mixed solvent washing in step S2 is from room temperature to 75 °C, preferably 30 - 50 °C. Appropriately increasing the washing temperature helps to promote the precipitation of impurities, but if the temperature is too high, it will cause excessive energy consumption and volatilization of organic solvents.

[0034] The pure water washing in step S1 and the mixed solvent washing in step S2 are preferably carried out under stirring. The stirring time is determined according to the impurity content, the amount of washing solvent used, the mass of the fluoropolymer, etc., preferably 10 - 60 minutes; more preferably 10 - 30 minutes. If the time is too short, impurities are not easily precipitated, and if the time is too long, the working efficiency is too low.

[0035] In the washing process of the present invention, the method for solid-liquid separation can be carried out by a filter press or by vacuum filtration. The separated mixed liquid can be reused or can be recovered by distillation.

[0036] After the fluoropolymer is washed with the mixed solvent in step S2 of the present invention, the fluoropolymer is dried. The drying method can be vacuum heating drying or ordinary heating drying, preferably vacuum heating drying. The drying temperature is preferably 60 - 100 °C, and the drying time is preferably 12 - 48 hours. Increasing the drying temperature and prolonging the drying time can effectively remove impurities and moisture, but it will cause the problem of poor resin whiteness and increase energy consumption at the same time. More preferably, the drying temperature is 65 - 80 °C, and the drying time is 20 - 36 hours.

[0037] The emulsifier / dispersant residue of the high-purity fluoropolymer described in the present invention is ≤20 ppm, the paraffin residue is ≤20 ppm, the moisture content is ≤1000 ppm, and the yellowness index after treatment at 250 °C for half an hour is ≤1.5. Preferably, the emulsifier / dispersant residue is ≤10 ppm, the paraffin residue is ≤10 ppm, the moisture content is ≤600 ppm, and the yellowness index after treatment at 250 °C for half an hour is ≤1.0.

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention adopts the method of washing with water and then washing with a mixed solvent, which can comprehensively and effectively remove the residual impurities in the fluoropolymer particles, and the prepared fluoropolymer has an extremely low impurity residue. Detailed implementation manners

[0039] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to these specific implementation manners. Those skilled in the art should recognize that the present invention covers all alternative solutions, improvement solutions, and equivalent solutions that may be included within the scope of the claims.

[0040] The crude PVDF products used in the examples and comparative examples are PVDF resins obtained by demulsifying the PVDF emulsion obtained by emulsion polymerization or by suspension polymerization. Paraffin and emulsifier are not used in suspension polymerization, and dispersant is used; dispersant is not used in emulsion polymerization, and emulsifier and paraffin are used.

[0041] Example 1

[0042] The PVDF crude product obtained by demulsifying the PVDF emulsion obtained by emulsion polymerization is first washed by a conventional water washing method until the conductivity of the washing water is reduced to 2.5 μs / cm. After draining the washing water, a mixed solvent with a volume ratio of 1.5 to the PVDF crude product is added, and the mixture is stirred at 30 °C for 40 minutes. The PVDF resin is obtained by suction filtration, and the PVDF finished resin is obtained by drying in a vacuum oven at 60 °C for 24 hours.

[0043] The mixed solvent is a mixture of methanol and n-hexane, with a molar ratio of methanol accounting for 70% and a molar ratio of n-hexane accounting for 30%.

[0044] Example 2

[0045] The PVDF crude product obtained by suspension polymerization is first washed by a conventional water washing method until the conductivity of the washing water is reduced to 1.8 μs / cm. After draining the washing water, a mixed solvent with a volume ratio of 0.8 to the PVDF crude product is added, and the mixture is stirred at 40 °C for 20 minutes. The PVDF resin is obtained by suction filtration, and the PVDF finished resin is obtained by drying in a vacuum oven at 80 °C for 20 hours.

[0046] The mixed solvent is a mixture of ethanol and cyclohexane, with the ethanol molar ratio accounting for 80% and the cyclohexane molar ratio accounting for 20%.

[0047] Example 3

[0048] The PVDF emulsion obtained by emulsion polymerization is demulsified to obtain a crude PVDF product. First, it is washed by a conventional water washing method until the conductivity of the washing water is reduced to 2.3 μs / cm. After draining the washing water, water and a mixed solvent with a volume ratio of 1.5 to the crude PVDF product are added, where the mixed solvent accounts for 60%. It is stirred at 30 °C for 60 minutes, and the PVDF resin is obtained by suction filtration. The PVDF finished resin is obtained by drying in a vacuum oven at 60 °C for 24 hours.

[0049] The mixed solvent is a mixture of methanol and n-hexane, with the methanol molar ratio accounting for 70% and the n-hexane molar ratio accounting for 30%.

[0050] Example 4

[0051] The crude PVDF product obtained by suspension polymerization is first washed by a conventional water washing method until the conductivity of the washing water is reduced to 1.8 μs / cm. After draining the washing water, water and a mixed solvent with a volume ratio of 0.8 to the crude PVDF product are added, where the mixed solvent accounts for 40%. It is stirred at 40 °C for 30 minutes, and the PVDF resin is obtained by suction filtration. The PVDF finished resin is obtained by drying in a vacuum oven at 80 °C for 20 hours.

[0052] The mixed solvent is a mixture of ethanol and cyclohexane, with the ethanol molar ratio accounting for 80% and the cyclohexane molar ratio accounting for 20%.

[0053] Example 5

[0054] The PVDF emulsion obtained by emulsion polymerization is demulsified to obtain a crude PVDF product. First, it is washed by a conventional water washing method until the conductivity of the washing water is reduced to 1.8 μs / cm. After draining the washing water, a mixed solvent with the same volume as the crude PVDF product is added. It is stirred at 50 °C for 10 minutes, and the PVDF resin is obtained by suction filtration. The PVDF finished resin is obtained by drying in a vacuum oven at 80 °C for 24 hours.

[0055] The mixed solvent is a mixture of isopropanol and n-octane, with the isopropanol molar ratio accounting for 50% and the n-octane molar ratio accounting for 50%.

[0056] Example 6

[0057] The crude PVDF product obtained by suspension polymerization is first washed by conventional water washing until the conductivity of the washing water is reduced to 1.8 μs / cm. After draining the washing water, water and a mixed solvent with the same volume as the crude PVDF product are added, where the mixed solvent accounts for 50%. Stir for 20 minutes at 50 °C, and PVDF resin is obtained by suction filtration. The PVDF finished resin is obtained by drying in a vacuum oven at 80 °C for 24 hours.

[0058] The mixed solvent is a mixture of isopropanol and n-heptane, with the molar ratio of isopropanol accounting for 50% and the molar ratio of n-heptane accounting for 50%.

[0059] Comparative Example 1

[0060] The PVDF emulsion obtained by emulsion polymerization is demulsified to obtain a crude PVDF product, which is washed by conventional water washing until the conductivity of the washing water is reduced to 1.8 μs / cm. After suction filtration, it is dried in a vacuum oven at 60 °C for 24 hours to obtain the PVDF finished resin.

[0061] Comparative Example 2

[0062] The crude PVDF product obtained after demulsification of the PVDF emulsion by emulsion polymerization is washed by conventional water washing until the conductivity of the washing water is reduced to 6.0 μs / cm. The same amount of mixed solvent as in Example 1 is added, and it is stirred at 30 °C for 40 minutes. After suction filtration, it is continuously washed by conventional water washing until the conductivity reaches 1.7 μs / cm. After suction filtration, it is dried in a vacuum oven at 60 °C for 24 hours to obtain the PVDF finished resin.

[0063] Comparative Example 3

[0064] The PVDF emulsion obtained by emulsion polymerization is demulsified to obtain a crude PVDF product. First, it is washed by conventional water washing until the conductivity of the washing water is reduced to 2.5 μs / cm. After draining the washing water, a water and methanol mixed solvent with a volume ratio of 1.5 to the crude PVDF product is added, where methanol accounts for 60%. Stir at 30 °C for 60 minutes, and PVDF resin is obtained by suction filtration. The PVDF finished resin is obtained by drying in a vacuum oven at 60 °C for 24 hours.

[0065] Comparative Example 4

[0066] The PVDF emulsion obtained by emulsion polymerization is demulsified to obtain a crude PVDF product. First, it is washed by conventional water washing until the conductivity of the washing water is reduced to 2.5 μs / cm. After draining the washing water, a water and n-hexane mixed solvent with a volume ratio of 1.5 to the crude PVDF product is added, where n-hexane accounts for 60%. Stir at 30 °C for 60 minutes, and PVDF resin is obtained by suction filtration. The PVDF finished resin is obtained by drying in a vacuum oven at 60 °C for 24 hours.

[0067] For the PVDF finished resins obtained in the examples and comparative examples, the emulsifier / dispersant and paraffin residues were tested, the yellowness index after the static thermal stability test was tested, the moisture content was tested. After the resin was made into pipe fittings, the TOC value in the immersion liquid was tested in the immersion experiment. The test results are shown in Table 1.

[0068] The test methods are as follows:

[0069] Conductivity test: Measure 100 mL of the test solution. After the temperature stabilizes at 25 °C, use a DDS-307 conductivity meter from Shanghai Jingke Instrument Co., Ltd. for testing.

[0070] Emulsifier / dispersant residue test: Take 2 g of the test PVDF resin powder, add 10 ml of methanol and ultrasonicate for 30 min. After the supernatant is filtered, use a liquid chromatography-mass spectrometer (LC-MS) and the external standard method to measure the emulsifier / dispersant residue.

[0071] Paraffin residue test: Take 5 g of the test PVDF resin powder, add 25 ml of n-hexane, stir with a magnetic stirrer for 3 hours, centrifuge for 5 min. After the supernatant is filtered, use a gas chromatograph and the external standard method to measure the paraffin residue.

[0072] Moisture content test: Take 1 g of the test PVDF resin powder and place it in the heating furnace of a Coulometric Karl Fischer moisture meter. After heating at 180 °C for 10 minutes, transfer the moisture to the titration cup through a stable stream of dry air to measure the moisture content.

[0073] Yellowness index test: Take 10 g of the test PVDF resin powder in aluminum foil, place it in an oven at 250 °C for half an hour and take it out. Use a HunterLab ColorFlex EZ colorimeter to measure the yellowness index.

[0074] TOC test: The obtained resin is processed into pipes and tested using the semiconductor standard SEMI-F057.

[0075] Table 1 Performance data of the resins prepared in the examples and comparative examples

[0076]

[0077]

[0078] As can be seen from the data in Table 1, different from conventional water washing, after most of the free water-soluble impurities are removed by conventional water washing, adding a certain amount of mixed solvent can greatly reduce the residues of emulsifier / dispersant and paraffin. The obtained resin has better whiteness and the lowest TOC value in the semiconductor immersion evaluation experiment.

[0079] Comparative Example 1 did not add organic solvents. The residual amounts of emulsifier and paraffin in the resin were higher than those in Examples 1, 3, and 5, and the yellowness index was higher. Under the same drying conditions, the water content of the resin in Comparative Example 1 was higher than that of the resins in Examples 1 and 3. The TOC value obtained for the pipe fittings made of the resin in the semiconductor evaluation experiment was high.

[0080] Comparative Examples 3 and 4 added one organic solvent, and the effect was not good, but still better than Comparative Example 1 without adding organic solvents.

[0081] In Comparative Example 2, the mixed solvent was added earlier. Since there were more residual additives in the resin at this time, the effect was not as good as the washing method of first removing most of the water-soluble impurities by conventional water washing and then adding the mixed solvent.

[0082] Under the same temperature and drying for the same time, the moisture content of the resins in Examples 1 and 3 was significantly lower than that in Comparative Example 1, indicating that adding organic solvents during the post-treatment process was beneficial to the volatilization of water, helped to reduce the drying temperature and time, reduced energy consumption, and reduced the interaction between the residual additives and the resin under heating, thereby reducing yellowing.

Claims

1. A preparation method of high-purity fluoropolymer, Characterized in that: The preparation method includes the following steps: S1: Washing the fluoropolymer with pure water until the conductivity of the washing water is lower than 3 μs / cm, S2: Wash the fluoropolymer with a mixed solvent, the mixed solvent comprising a first organic solvent and a second organic solvent, the solubility parameter δ of the first organic solvent 1 > 11 (cal·cm -3 ) 1 / 2 , the solubility parameter δ of the second organic solvent 2 < 8 (cal·cm -3 ) 1 / 2 , and satisfying 9 (cal·cm -3 ) 1 / 2 < α 1 ×δ 1 + α 2 ×δ 2 < 14 (cal·cm -3 ) 1 / 2 , where α 1 is the mole fraction of the first organic solvent in the total amount of organic solvents, and α 2 is the mole fraction of the second organic solvent in the total amount of organic solvents.

2. The preparation method of high-purity fluoropolymer according to claim 1, Characterized in that: The first organic solvent is a water-soluble organic solvent, selected from at least one of methanol, ethanol, and isopropanol; the second organic solvent is a water-insoluble organic solvent, selected from at least one of n-hexane, cyclohexane, n-heptane, and n-octane.

3. The preparation method of high-purity fluoropolymer according to claim 1, Characterized in that: The volatility R of the mixed solvent satisfies 1.4 < R < 8.

4. The preparation method of high-purity fluoropolymer according to claim 1, Characterized in that: Washing the fluoropolymer with pure water until the conductivity of the washing water is lower than 2 μs / cm.

5. The preparation method of high-purity fluoropolymer according to claim 5, Characterized in that: The conductivity of the pure water is lower than 2 μs / cm.

6. The preparation method of high-purity fluoropolymer according to claim 1, Characterized in that: The mixed solvent further contains pure water. Based on 100 parts by mass of the mixed solvent, the content of pure water accounts for 0 to 90 parts.

7. The preparation method of high-purity fluoropolymer according to claim 1, Characterized in that: The fluoropolymer is vinylidene fluoride homopolymer or vinylidene fluoride copolymer.

8. The preparation method of high-purity fluoropolymer according to claim 7, Characterized in that: The volume ratio of the amount of the mixed solvent to the fluoropolymer is 2 to 0.5:

1.

9. The preparation method of high-purity fluoropolymer according to claim 1, Characterized in that: After step S2, solid-liquid separation and drying are carried out to obtain a high-purity fluoropolymer product. The drying temperature is 60 to 100 °C, and the drying time is 12 to 48 hours.

10. The preparation method of high-purity fluoropolymer according to claim 9, Characterized in that: The residual emulsifier / dispersant of the high-purity fluoropolymer product is ≤20 ppm, the residual paraffin is ≤20 ppm, the water content is ≤1000 ppm, and the yellowness index after being treated at 250 °C for half an hour is ≤1.5.

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