Preparation process for ultra-clean polyfluoroalkoxy joint

Abstract

The present disclosure belongs to the technical field of ultra-clean plastic joints, and relates to a preparation process for an ultra-clean polyfluoroalkoxy (PFA) joint. The preparation process mainly comprises the following steps: S1, pretreating a PFA material; S2, performing a mold surface treatment; S3, performing extrusion; S4, performing injection molding, and by means of a high-temperature and high-pressure steam treatment, achieving rapid and uniform heating and rapid curing; S5, maintaining the pressure; S6, performing demolding; S7, performing a heat treatment to eliminate internal stress caused during the forming process of a PFA joint and improve the mechanical properties of the PFA joint; and S8, performing a post-treatment. The preparation process of the present disclosure is simple. The prepared polyfluoroalkoxy joint has good cleanliness, a low metal ion precipitation rate, and a low microparticle precipitation rate, and the joint has good hardness, dimensional precision and permeability resistance.

Description

A preparation process for an ultra-clean fusible polytetrafluoroethylene joint

[0001] Cross-references to related applications

[0002] This disclosure claims priority to Chinese Patent Application No. 202411034971.8, filed on July 31, 2024, entitled "Preparation Process of an Ultra-Clean Fusible Polytetrafluoroethylene Joint", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure belongs to the field of ultra-clean plastic joint technology, and relates to a preparation process of an ultra-clean fusible polytetrafluoroethylene joint. Background Technology

[0004] PFA (fusible polytetrafluoroethylene), also known as perfluoroalkoxy resin, is a special plastic with excellent chemical stability, corrosion resistance, and high and low temperature resistance. Ultra-clean PFA connectors fully utilize these properties of PFA in their design and manufacturing process, incorporating special sealing and connection methods to achieve the transmission of ultra-clean fluids. Ultra-clean PFA connectors are important components with wide applications in specific scenarios, such as those requiring the transmission of high-purity fluids.

[0005] The ultra-clean PFA connector employs advanced sealing technology to ensure a tight connection between pipes, effectively preventing the leakage of ultrapure chemicals. This sealing technology not only guarantees stable system operation but also avoids fluid contamination due to leaks, ensuring the purity of the transmitted fluid. Secondly, during the manufacturing process, precise processing and quality control ensure a smooth, impurity-free interior for the ultra-clean PFA connector. This further ensures that the fluid remains uncontaminated during transmission, meeting the requirements of cleanroom applications.

[0006] In addition, the ultra-clean PFA connector has excellent corrosion resistance and can resist the erosion of most chemicals, which enables it to operate stably for a long time in various harsh environments, reducing the frequency of failures and maintenance.

[0007] In summary, ultra-clean PFA connectors, by leveraging the excellent properties of PFA material and combining advanced sealing technology with precise manufacturing processes, provide a reliable and efficient solution for applications requiring high-purity fluid transmission. These connectors are widely used in industries such as semiconductors, pharmaceuticals, electronics, medical and biotechnology, and food processing, providing crucial technical support to these sectors. Summary of the Invention

[0008] The purpose of this disclosure is to provide a preparation process for an ultra-clean fusible polytetrafluoroethylene (PTFE) connector, which has the advantages of simple preparation process, good cleanliness of the prepared fusible PTFE connector, low metal ion migration rate in the material, and good hardness.

[0009] The objective of this disclosure can be achieved through the following technical solutions:

[0010] A process for preparing an ultra-clean fusible polytetrafluoroethylene (PTFE) joint, comprising the following steps:

[0011] S1. PFA particle pretreatment: In a Class 100 clean production workshop, PFA particles are dried at 60°C for 30 minutes using laser drying method, where the laser power is 250W.

[0012] S2. Mold Surface Treatment: PFA resin is ground in a ball mill at 400 r / min for 4–5 hours, and then passed through a 200-mesh sieve to obtain PFA powder. The mold surface is then sandblasted with quartz sand, followed by electrostatic spraying to evenly coat the PFA powder onto the mold surface for the first coating. A step-by-step high-temperature baking process is then performed: first at 270–280℃ for 0.5 hours, then at 320–340℃ for 1–2 hours, and finally at 260–280℃ for 0.5 hours. After baking, the surface is cooled to room temperature at a rate of 5–8℃ / min. Finally, the surface is slowly cooled to room temperature to obtain the second coating. A first coating is formed by ultrasonically dispersing PFA powder evenly in deionized water, followed by a second coating by ultrasonic spraying. The coating is then dried and cured with a 250W laser for 30 minutes. The mold is placed in a magnetron sputtering coating equipment, and chromium and nickel powder are used as sputtering targets and placed on the target holder. A vacuum is drawn, and argon and nitrogen are introduced. The chromium target power supply and the nickel target power supply are alternately turned on to deposit a composite coating on the mold surface. The sputtering power of the chromium target is 250-280W, and the sputtering power of the nickel target is 300-340W. The interval between alternating on the chromium target power supply and the nickel target power supply is 5 minutes. The power supply is turned off after the last nickel target sputtering is completed.

[0013] S3. Extrusion: The pretreated PFA granules are fed into a high-temperature fluoroplastic extruder at a feed temperature of 80-100°C. The high-temperature fluoroplastic extruder is temperature-controlled in stages to ensure that the PFA granules are completely melted and extruded. The high-temperature fluoroplastic extruder is divided into five stages for temperature control: the rear temperature is 350-360°C, the middle temperature is 360-370°C, the front temperature is 370-380°C, the die temperature is 380-390°C, and the nozzle temperature is 390-400°C.

[0014] S4. Injection molding: After the fully molten PFA granules are extruded through the nozzle of a high-temperature fluoroplastic extruder and injected into the mold, the temperature of the mold is kept constant by high-temperature and high-pressure steam. The temperature of the high-temperature and high-pressure steam is 150-200°C and the pressure is 0.4-0.8 MPa. After injection molding is completed, the supply of high-temperature and high-pressure steam is stopped after 5-8 minutes. After the steam is vented, cooling water is introduced to rapidly reduce the temperature of the mold and allow it to cool, solidify, and form.

[0015] S5. Pressure holding: After the mold has completely cooled, apply pressure for 100-150 seconds. After the pressure holding is completed, release the pressure completely to normal pressure.

[0016] S6. Demolding: Remove the formed PFA connector from the mold for demolding;

[0017] S7. Heat treatment: After cooling and curing, place the PFA connector in a tube furnace under a nitrogen atmosphere, raise the temperature to 260-290°C at a rate of 3°C / min, and hold for 4 hours, then anneal naturally to room temperature.

[0018] S8. Post-processing: The heat-treated PFA joint is placed into a freeze trimming machine for edge trimming.

[0019] As a preferred technical solution of this disclosure, in step S2, the parameters of ultrasonic spraying are: ultrasonic power of 40-60W, ultrasonic frequency of 100-200kHz, and spraying distance of 30-60mm.

[0020] As a preferred technical solution of this disclosure, in step S2, the thickness of the first coating layer is 0.5-1 mm, the thickness of the second coating layer is 0.5-1 mm, and the thickness of the PFA coating layer is 1-2 mm.

[0021] As a preferred technical solution of this disclosure, in step S3, the nozzle surface of the high-temperature fluoroplastic extruder is provided with a nickel plating layer.

[0022] As a preferred embodiment of this disclosure, in step S4, the cooling and solidification time is 140–200 s, and the flow rate of the cooling water is 10–20 m³ / s. 3 / h.

[0023] As a preferred technical solution of this disclosure, in step S5, the pressure during pressure holding is 0.6 to 0.7 MPa, and the pressure release rate is 0.1 MPa / min.

[0024] The beneficial effects of this disclosure are:

[0025] This disclosure describes a method for coating a mold surface with a PFA layer. First, the PFA powder is sprayed onto the mold surface using an electrostatic spray gun, increasing the adhesion between the coating and the mold after surface sandblasting. Then, a step-by-step baking process is employed: first, the PFA powder adhering to the mold surface is heat-treated at 270–280°C to remove volatile substances; then, it is baked at 320–340°C for 1–2 hours to completely melt the PFA powder; finally, it is baked at 260–280°C for 0.5 hours and then cooled to room temperature to solidify. A second ultrasonic spraying process is then performed to ensure a more uniform coating thickness distribution. This effectively prevents corrosion of the mold material or migration of metal ions to the PFA joint due to excessively high temperatures during mold forming. The surface PFA layer enhances surface smoothness and increases mold peelability, while also preventing metal ions from migrating into the joint and affecting cleanliness. The PFA coating first makes the mold surface smoother, preventing uneven metal film or peeling during subsequent metal plating due to uneven mold substrate. PFA also helps the metal film adhere more tightly to the mold, improving the overall coating stability. Using nickel and chromium as targets and applying a high-power magnetron sputtering technique, a uniformly thick metal film can be formed on the surface. This ensures coating density, improves the hardness and wear resistance of the mold surface coating, and increases preparation efficiency. The resulting composite coating gives the mold higher wear resistance, effectively preventing coating peeling during frequent injection molding and demolding processes.

[0026] Similarly, the nozzle surface of the high-temperature fluoroplastic extruder is nickel-plated to prevent some of the metal components from seeping into the PFA material at high temperatures when in contact with molten PFA, thus avoiding excessive metal ion content and affecting the performance of the finished product.

[0027] During the injection molding process, molten PFA material is poured into the mold. During molding, high-temperature, high-pressure steam treatment at 150–200°C and 0.4–0.8 MPa promotes rapid and uniform solidification of the PFA joint. Cooling water is then used to ensure the PFA joint reaches sufficient strength and hardness before demolding. This process makes mold release easier and prevents deformation or damage to the PFA joint during demolding.

[0028] The purpose of heat treatment after cooling and solidification of PFA adapters is primarily to improve their material properties. After heat treatment, the grain size and number of grain boundaries in the PFA adapter product are reduced, and the surface internal stress is eliminated, thereby improving the product's resistance to penetration. Controlling the heating rate at 3℃ / min and the heat treatment temperature at 260~290℃ allows elements such as carbon and nitrogen to dissolve into the matrix, forming a solid solution, thus increasing the material's hardness and strength. Furthermore, it allows elements such as carbon and nitrogen to precipitate onto the grain boundaries, forming fine and uniformly distributed particles, thereby improving the toughness of the PFA material. Heat treatment can enhance the material's hardness and wear resistance. By altering the internal crystal structure of the material, reducing the grain size and number of grain boundaries, it improves the material's dimensional stability. Internal stress may be generated during cooling and solidification; heat treatment can eliminate these internal stresses, improving the mechanical properties and dimensional stability of the PFA material.

[0029] The heat-treated finished product, along with the burrs, is deburred under freezing conditions. Liquid nitrogen is used to make the burrs brittle at low temperatures, and specific freezing particles are used to strike the burrs to quickly remove them. This also reduces the powder and debris generated during burr removal. Finally, the surface of the PFA connector is cleaned and dried to remove impurities, thereby improving the cleanliness of the PFA connector. Detailed Implementation

[0030] To further illustrate the technical means and effects adopted by this disclosure in order to achieve the intended purpose of the invention, the following detailed description of the specific implementation methods, structures, features and effects based on this disclosure is provided in conjunction with the embodiments.

[0031] The inner surface of the feed tube and the outer surface of the screw assembly and nozzle of the screw injection molding machine are plated with nickel.

[0032] In the following examples and comparative examples:

[0033] The mold used is manufactured by Dalian Economic and Technological Development Zone Xinghai Mold Co., Ltd., product number / trademark number: XH2317, the specific material is S136 mold steel, the dimensions (length x width x height) are 350 x 350 x 268 mm, and the shape is a square two-plate mold.

[0034] PFA used in PFA granules and PFA coating on mold surfaces: all purchased from Daikin Fluorochemicals (China) Co., Ltd., grade AP-231SH; Quartz sand: purchased from (Kramar) Shanghai Ziming Reagent Factory, item number: 13081076711-25kg.

[0035] Chromium powder: purchased from Hubei Yongkuo Technology Co., Ltd., purity: 99%;

[0036] Nickel powder: purchased from Hubei Yongkuo Technology Co., Ltd., effective substance content: 99%.

[0037] Example 1

[0038] S1. Pretreatment of PFA (fusible polytetrafluoroethylene) particles: In a Class 100 clean production workshop, PFA particles are dried at 60°C for 30 minutes using laser drying method, where the laser power is 250W.

[0039] S2. Mold Surface Treatment: PFA resin is ground in a ball mill at 400 rpm for 4 hours, and then passed through a 200-mesh sieve to obtain PFA powder. The mold surface is then sandblasted with quartz sand, followed by electrostatic spraying to evenly coat the PFA powder onto the mold surface for the first coating. The mold is then baked at 270℃ for 0.5 hours, then at 320℃ for 1-2 hours, and finally at 260℃ for 0.5 hours. After baking, the temperature is lowered to room temperature at a rate of 5℃ / min. The first coating layer is then slowly cooled to room temperature. The PFA powder is then evenly dispersed in deionized water using ultrasonic treatment, followed by a second coating layer using ultrasonic spraying. Finally, the mold is dried with a 250W laser for 30 minutes. n, thereby forming a PFA coating on the mold surface. The ultrasonic power is 40W, the ultrasonic frequency is 100kHz, and the spraying distance is 30mm. The thickness of the first coating layer is 0.5mm, the thickness of the second coating layer is 0.5mm, and the thickness of the PFA coating layer is 1mm. The mold is placed in a magnetron sputtering coating equipment. Chromium powder and nickel powder are used as sputtering targets and loaded onto the target holder. The vacuum is drawn, and argon and nitrogen are introduced. The chromium target power supply and the nickel target power supply are turned on alternately to deposit a composite coating on the mold surface. The sputtering power of the chromium target is 250W, the sputtering power of the nickel target is 300W, and the interval between turning on the chromium target power supply and the nickel target power supply is 5min. After the last nickel target sputtering is completed, the power supply is turned off.

[0040] S3. Extrusion: The pretreated PFA granules are fed into a high-temperature fluoroplastic extruder at a feed temperature of 80°C. The high-temperature fluoroplastic extruder is temperature-controlled in stages to ensure that the PFA granules are completely melted and extruded. The high-temperature fluoroplastic extruder is divided into five stages for temperature control: the rear temperature is 350°C, the middle temperature is 360°C, the front temperature is 370°C, the die temperature is 380°C, and the nozzle temperature is 390°C.

[0041] S4. Injection Molding: After the fully molten PFA granules are extruded through the nozzle of a high-temperature fluoroplastic extruder and injected into the mold, the mold temperature is maintained constant by high-temperature, high-pressure steam. The temperature of the high-temperature, high-pressure steam is 150°C and the pressure is 0.4 MPa. After injection molding is completed, the high-temperature, high-pressure steam supply is stopped after 5 minutes. The steam is then vented, and a flow rate of 10 m³ / min is introduced again. 3 The cooling water is supplied at a rate of / h for 140s, causing the mold temperature to drop rapidly and allowing for cooling, solidification, and molding.

[0042] S5. Pressure holding: After complete cooling, the mold is pressure held at 0.6MPa for 100s. After the pressure holding is completed, the pressure is completely released to atmospheric pressure at a rate of 0.1MPa / min.

[0043] S6. Demolding: Remove the formed PFA connector from the mold for demolding;

[0044] S7. Heat treatment: After cooling and curing, place the PFA connector in a tube furnace under a nitrogen atmosphere, raise the temperature to 260°C at a rate of 3°C / min, and hold for 4 hours, then anneal naturally to room temperature.

[0045] S8. Post-processing: The heat-treated PFA joint is placed into a freeze trimming machine for edge trimming.

[0046] Example 2

[0047] S1. PFA particle pretreatment: In a Class 100 clean production workshop, PFA particles are dried at 60°C for 30 minutes using laser drying method, where the laser power is 250W.

[0048] S2. Mold Surface Treatment: PFA resin is ground in a ball mill at 400 rpm for 4.5 hours, and then passed through a 200-mesh sieve to obtain PFA powder. The mold surface is then sandblasted with quartz sand, followed by electrostatic spraying to evenly coat the PFA powder onto the mold surface for the first coating. The mold is first baked at 275℃ for 0.5 hours, then at 330℃ for 1-2 hours, and finally at 270℃ for 0.5 hours. After baking, the temperature is lowered to room temperature at a rate of 7℃ / min. The first coating layer is then slowly cooled to room temperature. The PFA powder is then evenly dispersed in deionized water using ultrasonic treatment, followed by a second coating layer using ultrasonic spraying. Finally, the mold is dried with a 250W laser for 30 minutes. n, thereby forming a PFA coating on the mold surface. The ultrasonic power is 50W, the ultrasonic frequency is 150kHz, and the spraying distance is 40mm. The thickness of the first coating layer is 0.8mm, the thickness of the second coating layer is 0.7mm, and the thickness of the PFA coating layer is 1.5mm. The mold is placed in a magnetron sputtering coating equipment. Chromium powder and nickel powder are used as sputtering targets and placed on the target holder. The vacuum is drawn, and argon and nitrogen are introduced. The chromium target power supply and the nickel target power supply are turned on alternately to deposit a composite coating on the mold surface. The sputtering power of the chromium target is 260W, and the sputtering power of the nickel target is 320W. The interval between turning on the chromium target power supply and the nickel target power supply alternately is 5min. After the last nickel target sputtering is completed, the power supply is turned off.

[0049] S3. Extrusion: The pretreated PFA granules are fed into a high-temperature fluoroplastic extruder at a feed temperature of 90°C. The high-temperature fluoroplastic extruder is temperature-controlled in stages to ensure that the PFA granules are completely melted and extruded. The high-temperature fluoroplastic extruder is divided into five temperature control sections: the rear section temperature is 355°C, the middle section temperature is 365°C, the front section temperature is 375°C, the die head temperature is 385°C, and the nozzle temperature is 395°C.

[0050] S4. Injection Molding: After the fully molten PFA granules are extruded through the nozzle of a high-temperature fluoroplastic extruder and injected into the mold, the mold temperature is maintained constant by high-temperature, high-pressure steam. The temperature of the high-temperature, high-pressure steam is 160°C and the pressure is 0.6 MPa. After injection molding is completed, the high-temperature, high-pressure steam supply is stopped after 6 minutes. The steam is then vented, and then a flow rate of 15 m³ / min is introduced. 3 The cooling water is supplied at a rate of / h for 180s, which rapidly reduces the mold temperature and allows for cooling, solidification, and molding.

[0051] S5. Pressure holding: After complete cooling, the mold is pressure held at 0.6MPa for 140s. After the pressure holding is completed, the pressure is completely released to atmospheric pressure at a rate of 0.1MPa / min.

[0052] S6. Demolding: Remove the formed PFA connector from the mold for demolding;

[0053] S7. Heat treatment: After cooling and curing, place the PFA connector in a tube furnace under a nitrogen atmosphere, raise the temperature to 280°C at a rate of 3°C / min, and hold for 4 hours, then anneal naturally to room temperature.

[0054] S8. Post-processing: The heat-treated PFA joint is placed into a freeze trimming machine for edge trimming.

[0055] Example 3

[0056] S1. PFA particle pretreatment: In a Class 100 clean production workshop, PFA particles are dried at 60°C for 30 minutes using laser drying method, where the laser power is 250W.

[0057] S2. Mold Surface Treatment: PFA resin is ground in a ball mill at 400 rpm for 5 hours, and PFA powder is obtained by passing through a 200-mesh sieve. The mold surface is then sandblasted with quartz sand, followed by electrostatic spraying to evenly coat the PFA powder onto the mold surface for the first coating. The mold is then baked at 280℃ for 0.5 hours, then at 340℃ for 2 hours, and finally at 280℃ for 0.5 hours. After baking, the temperature is lowered to room temperature at a rate of 8℃ / min. The first coating layer is then slowly cooled to room temperature. The PFA powder is then evenly dispersed in deionized water using ultrasonic treatment, followed by a second coating layer using ultrasonic spraying. Finally, the mold is dried using a 250W laser for 30 minutes. In this process, a PFA coating is formed on the mold surface. The ultrasonic power is 60W, the ultrasonic frequency is 200kHz, and the spraying distance is 60mm. The thickness of the first coating layer is 1mm, the thickness of the second coating layer is 1mm, and the thickness of the PFA coating layer is 2mm. The mold is placed in a magnetron sputtering coating equipment. Chromium powder and nickel powder are used as sputtering targets and placed on the target holder. The vacuum is drawn, and argon and nitrogen are introduced. The chromium target power supply and the nickel target power supply are turned on alternately to deposit a composite coating on the mold surface. The sputtering power of the chromium target is 260W, and the sputtering power of the nickel target is 320W. The interval between turning on the chromium target power supply and the nickel target power supply alternately is 5min. After the last nickel target sputtering is completed, the power supply is turned off.

[0058] S3. Extrusion: The pretreated PFA granules are fed into a high-temperature fluoroplastic extruder at a feed temperature of 100°C. The high-temperature fluoroplastic extruder is temperature-controlled in stages to ensure that the PFA granules are completely melted and extruded. The high-temperature fluoroplastic extruder is divided into five temperature control sections: the rear section temperature is 360°C, the middle section temperature is 370°C, the front section temperature is 380°C, the die head temperature is 390°C, and the nozzle temperature is 400°C.

[0059] S4. Injection Molding: After the fully molten PFA granules are extruded through the nozzle of a high-temperature fluoroplastic extruder and injected into the mold, the mold temperature is maintained constant by high-temperature, high-pressure steam. The temperature of the high-temperature, high-pressure steam is 200°C and the pressure is 0.8 MPa. After injection molding is completed, the high-temperature, high-pressure steam supply is stopped after 8 minutes, the steam is vented, and then a flow rate of 20 m³ / min is introduced. 3 The cooling water is supplied at a rate of / h for 200s, causing the mold temperature to drop rapidly and allowing for cooling, solidification, and molding.

[0060] S5. Pressure holding: After complete cooling, the mold is pressure held at 0.7MPa for 150s. After the pressure holding is completed, the pressure is completely released to atmospheric pressure at a rate of 0.1MPa / min.

[0061] S6. Demolding: Remove the formed PFA connector from the mold for demolding;

[0062] S7. Heat treatment: After cooling and curing, place the PFA connector in a tube furnace under a nitrogen atmosphere, raise the temperature to 290°C at a rate of 3°C / min, and hold for 4 hours, then anneal naturally to room temperature.

[0063] S8. Post-processing: The heat-treated PFA joint is placed into a freeze trimming machine for edge trimming.

[0064] Comparative Example 1

[0065] The difference between Comparative Example 1 and Example 1 is that step S2 was not treated with PFA coating, while the rest of the operations were the same.

[0066] Comparative Example 2

[0067] The difference between Comparative Example 2 and Example 1 is that step S2 does not involve forming a metal film using a magnetron sputtering coating device; all other operations are the same.

[0068] Comparative Example 3

[0069] The difference between Comparative Example 3 and Example 1 lies in step S4: S4, cooling water is introduced to rapidly lower the mold temperature, allowing it to cool and solidify. The cooling time is 200 seconds, and the flow rate of the cooling water is 20 m³ / s. 3 / h; all other operations are the same.

[0070] Comparative Example 4

[0071] The difference between Comparative Example 4 and Example 1 is that the S7 step was not performed; all other operations are the same.

[0072] 1. Hardness: GB / T 2411-2008;

[0073] 2. Pressure resistance test: GB / T 15560-1995.

[0074] Table 1

[0075] 3. The PFA connectors prepared in each embodiment and comparative example were rinsed 10 times with ultrapure water, then injected with 5% nitric acid. The opening of the PFA connector was plugged with an ultrapure PFA plug. After soaking at room temperature for 24 hours, the plug was opened, and samples were taken for testing. The metal ion content was tested using acid extraction combined with ICP-MS and the testing standard: SEMI F57. The method detection limit (MDL) was 0.01, and the unit was ug / m³. 2 ND indicates not detected, meaning the result is below the detection limit. The results are shown in Table 2.

[0076] Table 2

[0077] The performance test data above show that the PFA connector prepared by this disclosure has high hardness and good pressure resistance. At the same time, the metal ion content measured in the examples is lower, indicating that the PFA connector prepared by this disclosure has good cleanliness.

[0078] The above description is merely a preferred embodiment of this disclosure and is not intended to limit this disclosure in any way. Although this disclosure has been disclosed above with reference to preferred embodiments, it is not intended to limit this disclosure. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the technical solution of this disclosure. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of this disclosure without departing from the content of the technical solution of this disclosure shall still fall within the scope of the technical solution of this disclosure. Industrial applicability

[0079] The preparation process disclosed herein is simple, and the prepared fusible polytetrafluoroethylene joint has good cleanliness, low metal ion precipitation rate, low microparticle precipitation rate, and good hardness, dimensional precision, and impermeability.

Claims

1. A process for the preparation of ultra-clean, fusible polytetrafluoroethylene joints, characterized in that: The preparation of the super-clean meltable polytetrafluoroethylene joint comprises the following steps: S1, pretreatment of meltable polytetrafluoroethylene PFA particles: drying the PFA particles at 60 DEG C for 30 min in a clean production workshop by a laser drying method, wherein the power of the laser is 250 W; S2, mold surface treatment: grinding the PFA resin by a ball mill at a rotating speed of 400 r / min for 4-5 h, obtaining PFA powder by passing through a 200-mesh screen, performing sand blasting treatment on the mold surface by using quartz sand as a blasting material, uniformly spraying the PFA powder on the mold surface by an electrostatic spray gun, performing first coating, and then performing step-by-step high-temperature baking, first baking at 270-280 DEG C for 0.5 h, then baking at 320-340 DEG C for 1-2 h, and finally baking at 260-280 DEG C for 0.5 h, and then reducing the temperature to room temperature at a speed of 5-8 DEG C / min; then slowly reducing the temperature to room temperature to obtain a first coating layer, uniformly dispersing the PFA powder in deionized water by ultrasonic treatment, and then performing second coating by ultrasonic spraying, and drying and curing the PFA powder by a 250-W laser for 30 min; placing the mold into a magnetron sputtering film coating device, loading chromium powder and nickel powder as sputtering targets into a target holder, vacuumizing, introducing argon and nitrogen, alternately opening a chromium target power supply and a nickel target power supply, and depositing a composite coating layer on the mold surface, wherein the power of the chromium target sputtering is 250-280 W, the power of the nickel target sputtering is 300-340 W, and the interval time of alternately opening the chromium target power supply and the nickel target power supply is 5 min, and the nickel target power supply is closed after the last sputtering; S3, extrusion: introducing the pretreated PFA particles into a high-temperature fluoroplastic extruder, controlling the temperature in sections in the high-temperature fluoroplastic extruder, and completely melting and extruding the PFA particles, wherein the high-temperature fluoroplastic extruder is divided into five sections for temperature control, the rear temperature is 350-360 DEG C, the middle temperature is 360-370 DEG C, and the front temperature is 370-380 DEG C, the temperature of a die head is 380-390 DEG C, and the temperature of a nozzle is 390-400 DEG C; S4, injection molding: after the completely melted PFA particles are extruded through the nozzle of the high-temperature fluoroplastic extruder, injecting the PFA particles into a mold, and then keeping the temperature of the mold unchanged by high-temperature and high-pressure steam, wherein the temperature of the high-temperature and high-pressure steam is 150-200 DEG C, and the pressure is 0.4-0.8 MPa; after the injection molding is completed, stopping the supply of the high-temperature and high-pressure steam after keeping for 5-8 min, and then introducing cooling water to rapidly reduce the temperature of the mold for cooling and solidification; S5, pressure maintaining: after complete cooling, performing pressure maintaining treatment on the mold for 100-150 s, and then completely releasing the pressure to normal pressure after the pressure maintaining is completed; S6, demolding: taking the formed PFA joint out of the mold for demolding; S7, heat treatment: after the cooling and solidification, placing the PFA joint into a tubular furnace in a nitrogen atmosphere, increasing the temperature to 260-290 DEG C at a speed of 3 DEG C / min, and keeping for 4 h, and then naturally annealing to room temperature. S8, post-processing: the heat-treated PFA joint is put into a freezing edge trimmer for edge trimming.

2. The process for the preparation of ultra-clean, fusible polytetrafluoroethylene joints according to claim 1, characterized in that: In step S2, the parameters of the ultrasonic spraying are as follows: ultrasonic power is 40-60 W, ultrasonic frequency is 100-200 kHz, and spraying distance is 30-60 mm.

3. The process for the preparation of ultra-clean fusible polytetrafluoroethylene joints according to claim 1 or 2, characterized in that: In step S2, the thickness of the first layer of coating is 0.5-1 mm, the thickness of the second layer of coating is 0.5-1 mm, and the thickness of the PFA coating is 1-2 mm.

4. The process for producing an ultra-clean, fusible polytetrafluoroethylene joint according to any one of claims 1 to 3, characterized in that: In step S3, the nozzle surface of the high-temperature fluoroplastic extruder is provided with a nickel plating layer.

5. The process for producing an ultra-clean, fusible polytetrafluoroethylene joint according to any one of claims 1 to 4, characterized in that: The time for cooling and solidifying the formed product in step S4 is 140 to 200 seconds, and the flow rate of the cooling water is 10 to 20 m 3 / h.

6. The process for producing an ultra-clean, fusible polytetrafluoroethylene joint according to any one of claims 1 to 5, characterized in that, In step S5, the pressure during the pressure maintaining is 0.6-0.7 MPa, and the rate of releasing the pressure is 0.1 MPa / min.

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