Method for stabilizing end groups of meltable fluororesin pfa

Abstract

A method for stabilizing the end groups of meltable fluororesin PFA, which relates to the technical field of fluororesin preparation. The PFA resin is heat-treated in a water vapor atmosphere, and unstable end groups are further eliminated by means of heat treatment with fluorine gas. Not only can the end group -COF, which is difficult to treat by direct fluorination, be removed, but the number of unstable end groups can also be more thoroughly reduced, to achieve a high-purity PFA product having less than 20 unstable end groups / 106 C atoms. The present method can greatly reduce the unstable end groups present in conventional PFA polymers, to improve quality and meet the high purity requirements for applications in high-end fields.

Description

A method for stabilizing the end groups of meltable fluororesin PFA

[0001] Cross-references

[0002] This application claims priority to Chinese Patent Application No. 202311215957.3, filed on September 20, 2023, entitled “A Method for Stabilizing the End Groups of Meltable Fluororesin PFA,” the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] The present invention relates to the technical field of fluororesin preparation, in particular to a method for stabilizing the end groups of meltable fluororesin PFA. Background Art

[0004] Fluororesin PFA, a copolymer of tetrafluoroethylene (TFE) and perfluoropropyl vinyl ether (PPVE), is a modified form of polytetrafluoroethylene (PTFE), reducing PTFE's high crystallinity. The melt exhibits excellent fluidity, enabling the use of low-cost melt-processing techniques for product fabrication. While maintaining the same excellent chemical resistance, non-stick properties, and low friction as PTFE, PFA also maintains the same long-term operating temperature as PTFE (260°C). Consequently, PFA is used in a wide range of fields, particularly high-end applications such as the semiconductor industry.

[0005] Currently, the industrial production of PFA primarily utilizes emulsion polymerization. This method produces a standard-grade PFA suitable for conventional applications, but is difficult to apply to high-end industries such as semiconductors. This is because the emulsion polymerization process generates a large number of unstable end groups due to the hydrolysis and end-capping of the persulfate initiator. These unstable end groups can produce small molecular compounds and carbon deposition during subsequent high-temperature processing, which not only corrodes equipment but also affects the product's color and performance, limiting its application in high-end applications. Therefore, appropriate technologies are needed to stabilize the end groups of conventional PFA to produce high-purity PFA products that meet the application requirements of the semiconductor industry.

[0006] U.S. Patent No. 5,076,659A discloses a method for end-group stabilization of PFA membranes using ethylenediamine and butanol aqueous solutions, respectively. Experimental results show that both methods can achieve good end-group stabilization effects. However, this method introduces small molecules, and to ensure that the volatile matter of the product is qualified, a process for completely removing the small molecules must be set up. There are also environmental issues, which is not conducive to industrial production.

[0007] U.S. Patent No. 4,743,658A discloses a method for direct fluorination of melt-processable PFA pellets using F₂ diluted with N₂ to stabilize end groups. The method involves adding an appropriate amount of PFA pellets with an average particle size of approximately 3 mm to a fluorination reactor. The reactor is then evacuated with nitrogen and 25 mol% F₂ / N₂ is added to a reactor pressure of 0.1 MPa. The fluorination reaction is then carried out at 200°C for 8 hours. While the fluorinated sample eliminates most of the unstable end groups, a certain number of unstable end groups, such as -COF, still remain. Further treatment is required to reduce these unstable end groups and achieve high purity.

[0008] U.S. Patent No. 5,115,038A discloses a step-by-step end group stabilization technology involving fluorination followed by amination. First, the PFA polymer undergoes preliminary fluorination with fluorine gas. This stabilizes all unstable end groups, except for the acyl fluoride end groups -COF and a small amount of carboxyl -COOH. The PFA is then aminated again with ammonia gas or an ammonia-generating substance, ultimately converting the unreacted -COF and a small amount of carboxyl -COOH from the previous step into -CONH2. This method has the advantage of completely eliminating the -COF end groups, which are not easily reactive with F2. However, the introduction of ammonia as a chemical substance for the amination reaction results in the presence of -CONH2 in the PFA polymer, making it difficult to produce high-purity PFA.

[0009] Therefore, it is necessary to provide an improved method for stabilizing the terminal groups of meltable fluororesin PFA to solve the above problems.

[0010] Summary of the Invention

[0011] The purpose of the present invention is to provide a method for stabilizing the end groups of a meltable fluororesin PFA, which uses water vapor as a high-temperature, wet-heat stabilization raw material, significantly reduces the number of unstable end groups, and is easier to separate from the PFA material. At the same time, it also reduces the use of chemical substances such as ammonium salts, making it more environmentally friendly.

[0012] To achieve the above objectives, the present invention provides a method for stabilizing the end groups of a meltable fluororesin (PFA), comprising: heat-treating the PFA resin in a water vapor atmosphere. The water vapor, as a high-temperature, wet-heat stabilization agent, effectively reduces the amount of -COF and -COOH, while also removing a small amount of -CF2=CF2.

[0013] Furthermore, the PFA resin is heat-treated in water vapor and fluorine atmospheres, respectively. The present invention preferably employs water vapor and fluorine gas for step-by-step treatment of the PFA polymer to stabilize its end groups, thereby producing high-purity PFA polymer. The combination of water vapor and fluorine gas can more thoroughly reduce the number of unstable end groups, resulting in a more pronounced end-group stabilization effect on the PFA polymer.

[0014] Furthermore, the PFA resin is first heat-treated in a water vapor atmosphere, and then heat-treated in a fluorine gas atmosphere.

[0015] The present invention combines water vapor and fluorine gas to treat PFA polymer in steps. First, the PFA polymer is treated with water vapor at high temperature to stabilize some unstable end groups and convert end groups (-COF) that are difficult to stabilize into end groups that are easy to fluorinate. Then, the PFA polymer is treated again with F2 diluted with N2 at high temperature. This step-by-step treatment method can not only remove the end groups -COF that are difficult to treat by direct fluorination, but also more thoroughly reduce the number of unstable end groups, resulting in an unstable end group number of less than 20 / 10 6 High-purity PFA product containing only C atoms.

[0016] Furthermore, the heat treatment temperature is 180-230° C. The reaction pressure is normal pressure.

[0017] Furthermore, the heat treatment time of the water vapor is 2 to 20 hours, preferably 2 to 8 hours.

[0018] Furthermore, the heat treatment time of the fluorine gas is 2 to 20 hours, preferably 2 to 8 hours.

[0019] Furthermore, the flow rate of the water vapor is 0.1 to 2 L / min.

[0020] Furthermore, the flow rate of the fluorine gas is 0.1 to 2 L / min; the fluorine gas is preferably fluorine gas diluted with nitrogen, and the fluorine gas concentration is 10 to 30 mol%.

[0021] Furthermore, the PFA resin is placed in a reactor and the reactor is replaced with nitrogen; then, it is heated to 180-230°C and water vapor is introduced to react for 2-20 hours; after the reaction is completed, the reaction system is replaced with N2, and F2 diluted with N2 is introduced again to react for 2-20 hours; after the reaction is completed, the reaction system is replaced with N2, and the material is cooled to room temperature to obtain a PFA resin with stabilized end groups.

[0022] Furthermore, the PFA resin is a PFA resin powder or granules produced by emulsion polymerization; the particle size of the PFA resin powder is 5 to 30 μm; the particle size of the granules is

[0023] In some specific embodiments, the present invention discloses a novel method for stabilizing the end groups of a meltable fluororesin (PFA), comprising the following steps: adding an appropriate amount of PFA polymer produced by emulsion polymerization to a reactor, displacing the reactor with nitrogen, and continuously adding water vapor to react with the PFA polymer at the reaction temperature; after the reaction is complete, displacing the system with nitrogen, and then continuously introducing nitrogen-diluted F2 into the reactor at the reaction temperature to react with the PFA polymer for fluorination. After the reaction is complete, displacing the reaction system with nitrogen, and cooling the product to room temperature to obtain end-group-stabilized fluororesin (PFA). This method can significantly reduce the unstable end groups present in conventional PFA polymers, thereby improving their quality and meeting the high purity requirements for applications in high-end fields.

[0024] An appropriate amount of the resulting high-purity PFA polymer can be taken out and the number of end groups and fluoride ions can be determined using infrared spectroscopy and solvent extraction, respectively. Furthermore, the waste gas and waste liquid generated during the entire reaction process must be rendered harmless before discharge.

[0025] The present invention also provides a fluororesin PFA, which is obtained by using any of the above methods.

[0026] Furthermore, the number of unstable end groups of the fluororesin PFA is less than 20 / 10 6 C atoms.

[0027] Furthermore, the unstable end groups include -COF, -COOH and -CF2=CF2.

[0028] Preferably, the number of -COF is less than 5 / 10 6 C atoms; the number of -COOH is less than 10 / 10 6 C atoms; -CF2=CF2 number is less than 10 / 10 6 C atoms.

[0029] The beneficial effects of the present invention are as follows:

[0030] 1. The method for stabilizing the end groups of the meltable fluororesin PFA provided by the present invention uses water vapor as a high-temperature, wet-heat stabilization raw material, which can effectively reduce the number of unstable end groups of the PFA resin and make it easier to separate from the PFA material. At the same time, it also reduces the use of chemical substances such as ammonium salts, which is more environmentally friendly.

[0031] 2. It is preferred to use water vapor and fluorine gas to stabilize the end groups of PFA polymer in steps, which can achieve the synergistic effect of high temperature and wet heat stabilization and direct fluorination stabilization, achieve better end group stabilization efficiency, and obtain the number of unstable end groups less than 20 / 10 6 High-purity PFA polymerization product with low C atoms. DETAILED DESCRIPTION

[0032] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention are described clearly and completely below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0033] Example 1

[0034] 500 g of PFA pellets were added to a 1 L stainless steel tubular reactor, and the reaction system was replaced with nitrogen. The reactor was heated to 200° C., and then water vapor was introduced at a flow rate of 1 L / min. The reaction was carried out at a constant temperature for 2 h. After the reaction was completed, the reaction system was replaced with N2, and the material was cooled to room temperature to obtain Sample 1.

[0035] Example 2

[0036] 500 g of PFA pellets were added to a 1 L stainless steel tubular reactor, the reaction system was replaced with nitrogen, the reactor was heated to 200 ° C, and then water vapor was introduced at a flow rate of 1 L / min. The reaction was carried out at a constant temperature for 5 h. After the reaction was completed, the reaction system was replaced with N2, and the material was cooled to room temperature to obtain sample 2.

[0037] Example 3

[0038] 500 g of PFA pellets were added to a 1 L stainless steel tubular reactor, the reaction system was replaced with nitrogen, the reactor was heated to 230°C, and then water vapor was introduced at a flow rate of 1 L / min. The reaction was carried out at a constant temperature for 5 h. After the reaction was completed, the reaction system was replaced with N2, and the material was cooled to room temperature to obtain Sample 3.

[0039] Example 4

[0040] 500 g of PFA pellets were added to a 1 L stainless steel tubular reactor, the reaction system was replaced with nitrogen, the reactor was heated to 230°C, and then water vapor was introduced at a flow rate of 1 L / min, and the reaction was carried out at a constant temperature for 5 hours. The reaction system was then replaced with N2, and F2 diluted with N2 was introduced again at a flow rate of 1 L / min, and the reaction was maintained at 230°C for 3 hours. After the reaction was completed, the reaction system was replaced with N2, and the material was cooled to room temperature to obtain Sample 4.

[0041] Example 5

[0042] 500 g of PFA pellets were added to a 1 L stainless steel tubular reactor, the reaction system was replaced with nitrogen, the reactor was heated to 230°C, and then water vapor was introduced at a flow rate of 1 L / min, and the reaction was carried out at a constant temperature for 5 h. The reaction system was then replaced with N2, and F2 diluted with N2 was introduced again at a flow rate of 1 L / min, and the reaction was maintained at 230°C for 7 h. After the reaction was completed, the reaction system was replaced with N2, and the material was cooled to room temperature to obtain Sample 5.

[0043] Example 6

[0044] 500 g of PFA pellets were added to a 1 L stainless steel tubular reactor, the reaction system was replaced with nitrogen, the reactor was heated to 230 ° C, and then F2 diluted with N2 was introduced at a flow rate of 1 L / min. The reaction temperature was maintained at 230 ° C for 7 h. After the reaction was completed, the reaction system was replaced with N2, and the material was cooled to room temperature to obtain sample 6.

[0045] Example 7

[0046] 500 g of PFA pellets were added to a 1 L stainless steel tubular reactor, the reaction system was replaced with nitrogen, the reactor was heated to 230° C., and then water vapor was introduced at a flow rate of 0.5 L / min, and the reaction was carried out at a constant temperature for 5 h. The reaction system was then replaced with N2, and F2 diluted with N2 was introduced again at a flow rate of 1 L / min, and the reaction was maintained at 230° C. for 3 h. After the reaction was completed, the reaction system was replaced with N2, and the material was cooled to room temperature to obtain Sample 7.

[0047] Example 8

[0048] 500 g of PFA pellets were added to a 1 L stainless steel tubular reactor, the reaction system was replaced with nitrogen, the reactor was heated to 230°C, and then water vapor was introduced at a flow rate of 0.2 L / min, and the reaction was carried out at a constant temperature for 5 h. The reaction system was then replaced with N2, and F2 diluted with N2 was introduced again at a flow rate of 1 L / min, and the reaction was maintained at 230°C for 3 h. After the reaction was completed, the reaction system was replaced with N2, and the material was cooled to room temperature to obtain Sample 8.

[0049] Example 9

[0050] 500 g of PFA pellets were added to a 1 L stainless steel tubular reactor, the reaction system was replaced with nitrogen, the reactor was heated to 230 ° C, and then F2 diluted with N2 was introduced at a flow rate of 1 L / min, and the reaction was maintained at 230 ° C for 3 hours. The reaction system was then replaced with N2, and water vapor was introduced again at a flow rate of 1 L / min, and the reaction was carried out at a constant temperature for 5 hours. After the reaction was completed, the reaction system was replaced with N2, and the material was cooled to room temperature to obtain Sample 9.

[0051] The samples obtained after the above treatment were tested for melting point, melt index, number of unstable end groups, number of fluoride ions, appearance, etc.

[0052] Table 1 Number of unstable end groups in Examples 1-9

[0053] As can be seen from Table 1, the first step of steam treatment of PFA pellets can convert difficult-to-convert unstable end groups such as -COF and -COOH into relatively stable end groups such as -CF2H. Combined with the second step of fluorination, the number of unstable end groups and the concentration of fluoride ion precipitation can be significantly reduced. If fluorine treatment is used first and then steam treatment, the -COOH content is higher, so using steam first and then fluorine treatment is more effective.

[0054] Table 2 Melting point, melt index, fluoride ion number and appearance of Examples 1-9

[0055] As can be seen from Table 2, the main properties of fluororesin PFA (melting point, melt index, etc.) did not change significantly before and after the step-by-step treatment. Therefore, this new combined treatment method can greatly improve the purity and quality of fluororesin PFA and other fluoropolymers, and can be used in the semi-isotropic industry with high requirements.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention. Industrial Applicability

[0057] The present invention provides a method for stabilizing the end groups of meltable fluororesin PFA. The PFA resin is heat treated in a water vapor atmosphere and further eliminated by heat treatment with fluorine gas. Not only can the end groups -COF, which are difficult to be removed by direct fluorination, be removed, but the number of unstable end groups can also be reduced more thoroughly, reaching a number of unstable end groups less than 20 / 10 6 The invention can significantly reduce the unstable end groups in conventional PFA polymers to improve their quality and meet the high purity requirements for applications in high-end fields, thus having good economic value and application prospects.

Claims

1. A method for stabilizing the end groups of meltable fluororesin PFA, characterized in that: include: The PFA resin is heat-treated in a water vapor atmosphere.

2. The method for stabilizing the end groups of meltable fluororesin PFA according to claim 1, characterized in that: include: The PFA resin is heat treated in a water vapor atmosphere and a fluorine gas atmosphere respectively; Preferably, the PFA resin is first heat-treated in a water vapor atmosphere, and then heat-treated in a fluorine gas atmosphere.

3. The method for stabilizing the end groups of meltable fluororesin PFA according to claim 1 or 2, characterized in that: The temperature of the heat treatment is 180-230°C.

4. The method for stabilizing the end groups of meltable fluororesin PFA according to claim 2, characterized in that: The heat treatment time of the water vapor is 2 to 20 hours, preferably 2 to 8 hours; And / or, the heat treatment time of the fluorine gas is 2 to 20 hours, preferably 2 to 8 hours.

5. The method for stabilizing the end groups of meltable fluororesin PFA according to any one of claims 1 to 4, characterized in that: The flow rate of the water vapor is 0.1 to 2 L / min.

6. The method for stabilizing the end groups of meltable fluororesin PFA according to any one of claims 2 to 4, characterized in that: The flow rate of the fluorine gas is 0.1-2 L / min; the fluorine gas is preferably fluorine gas diluted with nitrogen, and the fluorine gas concentration is 10-30 mol%.

7. The method for stabilizing the end groups of meltable fluororesin PFA according to any one of claims 1 to 6, characterized in that: The PFA resin is placed in a reactor and the reactor is replaced with nitrogen; then it is heated to 180-230°C and water vapor is introduced to react for 2-20 hours; after the reaction is completed, the reaction system is replaced with N2, and F2 diluted with N2 is introduced again to react for 2-20 hours; after the reaction is completed, the reaction system is replaced with N2, and the material is cooled to room temperature to obtain a PFA resin with stabilized end groups.

8. The method for stabilizing the end groups of meltable fluororesin PFA according to claim 1, characterized in that: The PFA resin is a PFA resin powder or a granular material; the particle size of the PFA resin powder is 5 to 30 μm; the particle size of the granular material is 9. A fluororesin PFA, characterized in that The method according to any one of claims 1 to 8 is used to obtain the 10. The fluororesin PFA according to claim 9, characterized in that The number of unstable terminal groups of the fluororesin PFA is less than 20 / 10 6 C atoms; The unstable end groups include -COF, -COOH and -CF2=CF2. Preferably, the number of -COF is less than 5 / 10 6 C atoms; the number of -COOH is less than 10 / 10 6 C atoms; -CF2 = the number of CF2 is less than 10 / 10 6 C atoms.

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