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CN-122011260-A - Fusible polytetrafluoroethylene and preparation method thereof

CN122011260ACN 122011260 ACN122011260 ACN 122011260ACN-122011260-A

Abstract

The invention relates to a fusible polytetrafluoroethylene and a preparation method thereof. The preparation method comprises the steps of firstly carrying out tetrafluoroethylene homopolymerization reaction in a polymerization kettle with strictly controlled oxygen content, temperature and pressure to form a regular molecular chain skeleton, then introducing perfluoroalkyl vinyl ether to carry out copolymerization reaction, continuously and stably adding monomers and an initiator to form a tightly entangled structure among molecular chains so as to reduce free volume, and carrying out fluorination treatment on granules after condensing, washing, drying and melting granulation on the obtained emulsion. Compared with the prior art, the invention optimizes the material performance from the molecular structure level through two-step polymerization, obviously improves the permeability resistance and mechanical strength of the product, solves the problem that the traditional blending modification is easy to generate crystal points and white points, and is particularly suitable for the severe requirements of the semiconductor industry on the material performance.

Inventors

  • CHENG JINGDONG
  • KONG XIANDA
  • WU TONG

Assignees

  • 上海华谊三爱富新材料有限公司
  • 常熟三爱富振氟新材料有限公司
  • 福建华谊三爱富氟佑新材料有限公司

Dates

Publication Date
20260512
Application Date
20260205

Claims (10)

  1. 1. A method for preparing fusible polytetrafluoroethylene, which is characterized by comprising the following steps: S1, adding water into a polymerization kettle, evacuating and replacing until the oxygen content is lower than 30ppm, then heating to a set temperature, adding tetrafluoroethylene monomer into the kettle to raise the pressure to the set value, rapidly adding an initiator, controlling the temperature to be constant, continuously adding tetrafluoroethylene to maintain the pressure to be constant, and reacting for a certain time to form a regular molecular chain skeleton; s2, rapidly adding perfluoroalkyl vinyl ether into a polymerization kettle, increasing the pressure to a set value by adding tetrafluoroethylene, keeping the temperature and the pressure constant, continuously and stably adding an initiator and the perfluoroalkyl vinyl ether to carry out copolymerization, so that a tightly entangled structure is formed among molecular chains, the free volume of the molecular chains is reduced, stopping adding after a certain time, slowly discharging a gas phase monomer, and cooling to obtain a fusible polytetrafluoroethylene emulsion; S3, condensing, washing, drying, melting and granulating the fusible polytetrafluoroethylene emulsion; S4, carrying out fluorination treatment on the granules obtained by granulation to obtain the fusible polytetrafluoroethylene with penetration resistance.
  2. 2. The method for preparing the fusible polytetrafluoroethylene according to claim 1, wherein in S1, the setting temperature of a polymerization kettle is 60-90 ℃, so that tetrafluoroethylene monomers are orderly polymerized to form regular chain segments; The set value of the pressure is 0.8-3.5MPa; In S1, after adding tetrafluoroethylene, the reaction is carried out for 10 to 40 minutes to form a regular molecular chain skeleton.
  3. 3. The method for preparing the fusible polytetrafluoroethylene according to claim 1, wherein in the step S1, the initiator is ammonium persulfate, potassium persulfate or a mixture of the ammonium persulfate and the potassium persulfate, and the polymerization reaction of the tetrafluoroethylene is smoothly carried out by controlling the concentration and the feeding rate of the initiator, so that an active growth chain is provided for the copolymerization reaction in the step S2.
  4. 4. The method for preparing the fusible polytetrafluoroethylene according to claim 1, wherein in the step S2, the perfluoroalkyl vinyl ether is added in a manner of firstly adding an initial amount rapidly and then continuously and stably supplementing, the comonomer is uniformly embedded into a molecular chain by controlling the feeding rate to be 3-4g/min, the set value of the pressure is 1.5-4.5MPa, the set temperature of a polymerization kettle is 60-90 ℃, so that the monomer fully permeates to the tail end of a growing chain to form a compact molecular chain entanglement structure; S2, the initiator is ammonium persulfate, potassium persulfate or a mixture of the ammonium persulfate and the potassium persulfate; And S2, stopping adding after lasting for 100-120 minutes, slowly discharging the gaseous monomer and cooling.
  5. 5. The method for producing a fusible polytetrafluoroethylene according to claim 1, wherein in S2, said perfluoroalkyl vinyl ether is any one or a mixture of a plurality of perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, perfluoro-n-propyl vinyl ether.
  6. 6. The method for producing a fusible polytetrafluoroethylene according to claim 1, wherein in S3, a twin-screw extruder is used for the melt granulation treatment, and the twin-screw has an aspect ratio of 35:1 to 64:1.
  7. 7. The method for producing a fusible polytetrafluoroethylene according to claim 1, wherein in S3, the drying treatment temperature is 100 to 300 ℃.
  8. 8. The method for preparing a fusible polytetrafluoroethylene according to claim 1, wherein in S4, fluorine and nitrogen mixed gas is used for the fluorination treatment, and the unstable group at the end of the molecular chain is eliminated by controlling the concentration of fluorine gas to 5 to 30wt% and treating at a temperature of 100 to 300 ℃ and a pressure of 0.05 to 1.0MPa for 1 to 24 hours.
  9. 9. The method for producing a fusible polytetrafluoroethylene according to claim 8, wherein in S4, said fluorination treatment is carried out at a temperature of 150 to 220 ℃ and a pressure of 0.1 to 0.6MPa for 6 to 12 hours.
  10. 10. A fusible polytetrafluoroethylene obtainable by the process of any one of claims 1 to 9.

Description

Fusible polytetrafluoroethylene and preparation method thereof Technical Field The invention relates to the technical field of fluorine chemical industry, in particular to fusible polytetrafluoroethylene and a preparation method thereof. Background The meltable polytetrafluoroethylene (abbreviated as PFA), which is a copolymer of Tetrafluoroethylene (TFE) and a small amount of perfluoroalkyl vinyl ether (PAVE), is an important one of fluoropolymers. The PFA maintains all excellent performances of polytetrafluoroethylene (PTFE for short), and has excellent chemical stability, physical and mechanical properties, electrical insulation properties, lubricity, non-tackiness, ageing resistance, incombustibility and thermal stability, and as the PFA fluorocarbon main chain is introduced with a perfluoroalkoxy side group, the flexibility of a high molecular chain is obviously improved, the crystallinity of the PFA is reduced, the PFA has good thermoplasticity, and the defect that the polytetrafluoroethylene is difficult to process is overcome, so that the polytetrafluoroethylene can be subjected to melt processing at a lower temperature, and the melting point is 300-315 ℃, and can be processed by the molding processing technology of general thermoplastics such as extrusion molding, blow molding, injection molding and the like. PFA is widely used in the semiconductor industry for its excellent physicochemical properties. With the development of the semiconductor industry, higher requirements are put on the performance of PFA, such as pipelines and liners commonly used in the semiconductor industry, and higher requirements are put on the permeability resistance of PFA. Hua Fu in patent CN103122114A, a low molecular weight polytetrafluoroethylene (number average molecular weight less than 5000000 is added to PFA, improving the permeation resistance, stain resistance, abrasion resistance, gloss, etc. of the composition, dupont patent US20120031607A1, US20120034406A1 and US20120035326A1 propose improvements to existing PFA by adding a melt flowable polytetrafluoroethylene to the original PFA polymer and heat treating at least 280 ℃, three-well dupont patent CN101437892A proposes melt kneading PFA with a low molecular weight PTFE powder, the composition achieving flex life exceeding 20000 or even higher, golden plaque and company patent CN110229449a, high strength PFA resins are obtained by blending PTFE with PFA having a synthetic molecular weight of not less than 100 ten thousand. In the above prior art, the PFA with improved mechanical properties such as permeation resistance and high strength is obtained by adding a medium and low molecular weight PTFE emulsion or powder to PFA. The method has the defects that PTFE with various matched molecular weights is synthesized in advance and then is subjected to aftertreatment to obtain PTFE emulsion or powder, meanwhile, PTFE and PFA are blended and subjected to aftertreatment to obtain modified PFA powder or particles, and then the modified PFA powder or particles are subjected to extrusion, injection molding and other aftertreatment to obtain workpieces such as pipelines, films, liners, cables and the like. The production process is complex, PTFE and PFA blend materials are mixed uniformly in a macroscopic manner, but PTFE molecular chain spherulites are difficult to open on a molecular chain layer surface and form effective fusion entanglement with PFA molecular chains, so that defects such as crystal points, pimples and white spots are easy to generate when the obtained modified PFA is processed at the downstream, and further the problems that the product is easy to crack, has silver lines, has mechanical properties, has permeability and the like and cannot achieve ideal effects are caused. Disclosure of Invention The invention aims to overcome the defects of the prior art and provide the fusible polytetrafluoroethylene and the preparation method thereof, the material performance is optimized from the molecular structure level through two-step polymerization, the permeability resistance and the mechanical strength of the product are obviously improved, the problem that the traditional blending modification is easy to generate crystal points and white points is solved, and the fusible polytetrafluoroethylene is particularly suitable for the severe requirements of the semiconductor industry on the material performance. The aim of the invention can be achieved by the following technical scheme: the first aspect of the present invention provides a method for preparing a fusible polytetrafluoroethylene, referring to fig. 1, specifically comprising the following steps: S1, adding water into a polymerization kettle, evacuating and replacing until the oxygen content is lower than 30ppm, then heating to a set temperature, adding tetrafluoroethylene monomer into the kettle to raise the pressure to the set value, rapidly adding an initiator, controlling the temperature to be constan