PTFE diaphragm with long fatigue life for diaphragm valve as well as preparation method and application of PTFE diaphragm

Abstract

The invention discloses a long-fatigue-life PTFE diaphragm for a diaphragm valve as well as a preparation method and application thereof, and relates to the technical field of manufacturing of key parts for semiconductor manufacturing. Aiming at the anti-fatigue requirement of an ultra-clean flow control system for semiconductor manufacturing on a diaphragm under a reciprocating load, PTFE (Polytetrafluoroethylene) suspension resin powder with the number-average molecular weight of 1.4 * 10 < 5 >-1.6 * 10 < 5 > g / mol is selected; through the precisely-locked sintering temperature of 380 DEG C, a thick, strong and flatly-arranged band-shaped crystal network is induced to be generated in a matrix, and plasticity accumulation caused by the ratchet effect is effectively inhibited; a magneto-rheological polishing technology is introduced, fine trimming is conducted on the diaphragm under the magnetic field intensity of 200 mT to 500 mT, and the surface roughness is eliminated till the surface roughness reaches Ralt; and when the thickness is 0.1 mu m, craze generation points are eradicated. Through the synergistic effect of the strategies, the average fatigue life of a finished product can reach 110 hours (about 2 million cycles), and the reliability of a semiconductor flow control system is remarkably enhanced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of key components manufacturing for semiconductor manufacturing, in particular to a high fatigue life PTFE diaphragm for diaphragm valves and a preparation method thereof. BACKGROUND

[0002] In the advanced process flow of semiconductor manufacturing, the super-clean flow control system is the core support for ensuring the precise transportation and cleanliness control of high-purity chemical reagents and ultra-pure water, and its performance directly determines the finished product yield and production efficiency of integrated circuit chips. In the super-clean flow control system, the diaphragm valve is a core component for controlling the flow of highly corrosive and ultra-pure media. The diaphragm valve in the super-clean flow control system mostly uses polytetrafluoroethylene (PTFE) as the diaphragm material. Since the PTFE diaphragm in the diaphragm valve needs to withstand high-frequency cyclic tensile and compressive stresses during frequent valve opening and closing, it is prone to ratchet effect, leading to continuous accumulation of plastic deformation. Therefore, high requirements are placed on the fatigue resistance of the PTFE diaphragm.

[0003] The melt viscosity of PTFE material is extremely high (1010-1011 Pa·s), and traditional processing mostly uses mold pressing and sintering. However, existing general PTFE modification techniques often focus on static sealing or cold and hot impact, and fail to optimize the dynamic fatigue failure mechanism under semiconductor working conditions. The traditional process has the following bottlenecks: 1. Microstructure thermal damage: excessive sintering temperature (such as exceeding 390℃) will cause severe thermal decomposition, producing brittle globular crystals, and changing the material from ductile fracture to brittle fracture.

[0004] 2. Stress concentration on complex curved surface: the PTFE diaphragm in the diaphragm valve has a complex flexible folding deformation zone. Traditional mechanical polishing mostly targets rigid rods, and it is difficult to process such asymmetric flexible curved surfaces, and mechanical stress damage is easily introduced, inducing the generation of silver wire microfibers.

[0005] 3. Performance unevenness: the heat dissipation lag of large-size blanks leads to uneven crystallinity inside and outside, affecting the mechanical stability of the membrane surface. SUMMARY

[0006] The purpose of the present application is to provide a high fatigue life PTFE diaphragm for diaphragm valves and a preparation method and application thereof, to solve the problems existing in the prior art.

[0007] To achieve the above purpose, the present application provides the following solutions: One of the technical solutions of the present application: a preparation method of a high fatigue life PTFE diaphragm for diaphragm valves, comprising the following steps: The PTFE suspension resin powder is subjected to compression molding to obtain a blank; the blank is subjected to step sintering, and the blank after step sintering is machined to obtain a PTFE diaphragm, and the PTFE diaphragm is subjected to magnetorheological polishing to obtain the high fatigue life PTFE diaphragm for the diaphragm valve; The number average molecular weight of the PTFE suspension resin powder is 1.4*10 5 -1.6*10 5 g / mol. The step sintering comprises: first, heating to 300 DEG C and keeping for 100-150 min (which can be regarded as a pre-sintering stage), and then heating to 380 DEG C and keeping for 200-250 min (which can be regarded as a sintering stage).

[0008] The present application is aimed at the ratcheting effect and the silver line evolution characteristics of the PTFE diaphragm used in the ultra-clean flow control system in semiconductor manufacturing under high-frequency reciprocating load, the sintering temperature is accurately controlled to 380 DEG C, which is a performance watershed for inhibiting "over-sintering" and inducing the generation of strip-shaped crystals, and a non-contact flexible ultra-precision modification process of magnetorheological polishing (MRF) is introduced, so that the micro stress concentration points are eliminated, and the fatigue life of the diaphragm is greatly improved. Specifically: the PTFE suspension resin powder with a number average molecular weight of 1.4*10 5 -1.6*10 5 g / mol can effectively disperse alternating stress by using the entanglement density of long-chain molecules, and the yield strength and toughness of the matrix are improved; the sintering temperature is set to 380 DEG C, 380 DEG C is the critical threshold point for the transition of PTFE from ductile fracture to brittle fracture, which can ensure that the molecular chain is fully melted and diffused to form an ideal strip-shaped crystal network structure which is thick, arranged flat and tightly combined, and at the same time prevent brittle spherical crystals from being generated due to "over-sintering", and the crystallinity is controlled between 25-29 %, which is beneficial to improve the mechanical properties and fatigue life of the diaphragm; the magnetorheological polishing can use the controlled flexible grinding head formed by the magnetorheological fluid to conform to the complex shape of the diaphragm for non-contact micro-removal, and eliminate the micro-peak stress concentration points formed by machining to eliminate the fatigue crack initiation point from the physical level.

[0009] Further, the compression molding pressure is 35 MPa.

[0010] The mold pressing pressure is set to 35 MPa, which is the saturation critical point of the particle density growth of the PTFE suspension resin powder, which aims to eliminate the internal air retention and reduce the internal and external density gradient to provide a dense and uniform surface substrate for subsequent flexible curved surface magnetorheological polishing. Setting the mold pressing pressure to 35 MPa can ensure that the powder particles are fully rearranged and the internal air retention is eliminated, so that the density of the blank reaches a saturated and uniform state (about 2.15~2.18 g / cm 3 ).

[0011] Furthermore, the crystallinity of the blank after step-sintering is 25-29%.

[0012] Furthermore, the magnetorheological polishing specifically refers to polishing until the surface roughness Ra < 0.1 μm.

[0013] The magnetorheological polishing in this invention utilizes a controlled flexible grinding head formed by magnetorheological fluid to conform to the complex shape of the diaphragm, especially the complex curved surface, for non-contact micro-shearing. This is more conducive to removing micro-tool marks and subsurface damage in the diaphragm folding deformation zone (i.e., the flexible folded corrugated zone, which is the key stress area), resulting in a surface roughness Ra < 0.1 μm. By eliminating the micro-peak stress concentration points left by machining, the generation of silver streaks under cyclic loading is suppressed, thus eradicating the fatigue crack initiation point from a physical level.

[0014] Furthermore, the parameters of the magnetorheological polishing (MRF) include: the magnetic field strength of the magnetorheological polishing region is 200-500 mT (so that the magnetorheological polishing fluid forms a flexible polishing head with a certain shear yield stress on the diaphragm surface), and the polishing head rotation speed is 100-500 rpm.

[0015] Furthermore, the magnetorheological polishing slurry used in the magnetorheological polishing process is a water-based magnetorheological polishing slurry. By volume percentage, the water-based magnetorheological polishing slurry consists of: 30-40% magnetic particles, 1-5% abrasive particles, 0.5-2% dispersant and stabilizer, and the balance being water.

[0016] Furthermore, the magnetic particles include carbonyl iron powder; the abrasive particles include nano-diamond or nano-cerium oxide; the dispersing stabilizer includes a thickener and a surfactant, wherein the thickener includes at least one of xanthan gum, bentonite and polyvinyl alcohol, and the surfactant includes at least one of sodium dodecylbenzenesulfonate, glycerol and polyethylene glycol.

[0017] Furthermore, the particle size of the abrasive particles is 50-500 nm.

[0018] Furthermore, the heating rate during the stepped sintering process is 65-95 ℃ / h.

[0019] Furthermore, after heating to 380 ℃ and holding at that temperature for 200-250 min, a furnace cooling step is also included, with a cooling rate of 40 ℃ / h. This ensures that the crystal structure changes from an amorphous state to an ordered arrangement of dense banded crystals.

[0020] The second technical solution of the present invention: a high fatigue life PTFE diaphragm for diaphragm valves prepared by the above-described method.

[0021] The third technical solution of the present invention: the application of the above-mentioned high fatigue life PTFE diaphragm for diaphragm valves in an ultra-clean flow control system for semiconductor manufacturing.

[0022] The present invention discloses the following technical effects: (1) Precisely lock the watershed of micro morphology: The present invention does not blindly set the sintering range, but determines 380 ℃ as the precise threshold for suppressing the formation of brittle spherical crystals and obtaining ideal ribbon crystals, thereby ensuring that the matrix has extremely high yield strength (≥13.0 MPa) and fatigue toughness.

[0023] (2) Targeted solution to damage to flexible complex curved surfaces: This invention introduces magnetorheological polishing (MRF) to achieve flexible polishing of flexible surfaces, which solves the problem that the morphology of the diaphragm folded area is difficult to refine through rigid grinding, and eliminates subsurface damage.

[0024] (3) Fatigue life exceeds expectations: By combining microstructure optimization and surface morphology fine polishing modification, the average fatigue life of the diaphragm at a reciprocating frequency of 5Hz is increased to 110 h (about 2 million cycles), and the stability is significantly enhanced, fully meeting the requirements for long-term stable operation of semiconductor production lines.

[0025] (4) Ultra-cleanliness and reliability assurance: The optimized molding process reduces the internal porosity, and combined with the nanoscale surface smoothness, it greatly reduces the risk of adsorption of semiconductor media and particle retention. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the PTFE membrane structure.

[0028] Figure 2 This is a schematic diagram illustrating the principle of magnetorheological polishing to remove tool marks on the surface of a PTFE membrane.

[0029] Figure 3 The images are TEM images of cylindrical blanks after stepped sintering in Example 1 and Comparative Examples 1-2, where (a) is Comparative Example 1, (b) is Comparative Example 2, and (c) is Example 1.

[0030] Figure 4 The stress-strain curves are those of the cylindrical blanks after stepped sintering in Example 1 and Comparative Example 9.

[0031] Figure 5 This is a schematic diagram of the fatigue testing system used in the fatigue life test of this invention.

[0032] Figure 6 This is a physical diagram of the fatigue testing system used in the fatigue life test of this invention.

[0033] Figure 7 The graph shows the statistical line graphs of fatigue fracture time for the PTFE membranes prepared in Example 1 and Comparative Example 9. Detailed Implementation

[0034] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0035] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0036] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0037] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0038] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0039] This invention provides a method for preparing a high fatigue life PTFE diaphragm for diaphragm valves. The core logic lies in addressing the mechanism of ratcheting effect and silver crazing evolution of the diaphragm in the ultra-clean fluid control system of semiconductor manufacturing process during high-frequency reciprocating motion. By precisely controlling the microstructure during the forming stage, the necessary matrix prerequisite is provided for the subsequent magnetorheological polishing modification of complex curved surface diaphragms, thereby fundamentally solving the problem of early fatigue damage of PTFE diaphragms.

[0040] In practical implementation, the first step is to screen raw materials to address the dual requirements of membrane flexibility and high fatigue strength in the ultra-clean fluid control system of semiconductor manufacturing processes. Since the microstructure of PTFE determines its macroscopic mechanical properties, a larger molecular chain length and entanglement density can enhance the material's tensile strength and elongation at break, thus contributing to improved fatigue life. Therefore, a number-average molecular weight of 1.4 × 10⁻⁶ PTFE is preferred. 5 -1.6×10 5 g / mol of PTFE suspension resin powder (such as Daikin M112 grade from Japan). This high molecular weight raw material can form a more robust entangled network after thermal activation, with stronger interaction forces and relative slip resistance between molecular chains, which can effectively disperse alternating stress under high-frequency cyclic loading and slow down the formation of silver streaks.

[0041] In the compaction molding stage of the blank (i.e., the preform), pre-selected PTFE suspension resin powder is placed in a precision mold. The powder undergoes a cold molding process in the mold, and the pressure directly affects the interaction between powder particles and the porosity of the blank. In a specific embodiment, the molding pressure is set to 35 MPa. Under this pressure, the powder inside the mold undergoes sufficient rearrangement, which can effectively eliminate trapped air and overcome the frictional resistance between particles, so that the density of the blank reaches a saturated and uniform state (approximately 2.15-2.18 g / cm³). 3 This reduces microscopic defects formed during the extrusion process.

[0042] The molded blank is then subjected to step-by-step sintering to achieve melt recrystallization. The heating procedure is as follows: heating from room temperature to 300 °C and holding for 100-150 min, followed by further heating to the core sintering temperature of 380 °C and holding for 200-250 min. Sintering temperature is crucial for controlling the crystallinity and morphology of PTFE. In this specific implementation, the sintering temperature is strictly locked at 380 °C to ensure sufficient melting and diffusion of molecular chains and the formation of a robust, flat banded crystal structure. If the sintering temperature exceeds 380 °C, the material will experience significant overheating, leading to intensified thermal decomposition of molecular chains and the formation of brittle spherical crystals, thereby deteriorating mechanical properties. After sintering, the blank is slowly cooled in the furnace at a rate of 40 °C / h to ensure uniform crystal distribution inside and outside the blank and maintain isotropic residual stress, preventing geometric instability due to stress release during magnetorheological polishing of diaphragms with complex curved surfaces.

[0043] After machining, magnetorheological polishing (MRF) is used to refine and modify the diaphragm. The flexible polishing head formed by the MRF polishing slurry under the influence of a magnetic field closely adheres to the diaphragm surface, especially to flexible folded surfaces. This non-contact, micro-shearing action eliminates microscopic peaks left from machining. Unlike conventional mechanical polishing for rigid rods, this invention utilizes the "flexible tool" characteristic of MRF to completely eliminate microscopic tool marks and subsurface damage without altering the macroscopic geometric accuracy of the diaphragm. This step physically eliminates stress concentration points that induce creasing and inhibits microfiber breakage under cyclic loading. After polishing, ultrapure water (UPW) ultrasonic cleaning is performed to ensure semiconductor-grade cleanliness requirements are met.

[0044] Finally, the finished product was comprehensively verified through microscopic characterization and physical experiments. Specifically, differential scanning calorimetry (DSC) was used to monitor the microscopic properties of the material.

[0045] Through the above-mentioned regulation, the crystallinity of the diaphragm is stabilized within the range of 25-29%. The diaphragm manufactured using the method of this invention exhibits a yield strength as high as 13.0 MPa, an elongation at break as high as 515%, and a significantly increased average fatigue life of 110 hours (approximately 2 million cycles), meeting the requirements of semiconductor-grade ultra-clean valves in terms of both performance stability and service life. In the surface fine polishing modification stage, the selection of magnetorheological polishing parameters is highly coupled with the physical properties of the PTFE matrix. Due to the low hardness and significant viscoelasticity of PTFE material, conventional mechanical polishing easily leads to abrasive grain embedding into the matrix or thermal damage. This invention preferably uses a magnetic field strength of 200-500 mT, aiming to control the dynamic yield stress of the magnetorheological flexible grinding head within a specific range—this strength ensures sufficient shear removal force for microscopic peaks (machining marks) without damaging the PTFE ribbon crystal network due to excessive grinding head stiffness. In addition, by using nanodiamond or nanocerium oxide with a particle size of 50-500 nm as abrasive and a controlled rotation speed of 100-500 rpm, it is possible to achieve full coverage and fine finishing of the diaphragm surface, especially the complex folded surface, thereby completely eliminating stress concentration points at the level of Ra > 0.1 μm. This plays an irreplaceable role in suppressing the formation of silver lines driven by the ratchet effect.

[0046] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0047] In the following embodiments, comparative examples and test examples of the present invention, if room temperature is involved, it specifically refers to 20-30 ℃.

[0048] All raw materials used in the following embodiments, comparative examples and test examples of this invention are commercially available products.

[0049] Example 1 A high fatigue life PTFE diaphragm for diaphragm valves is prepared by the following steps: PTFE suspension resin powder of Daikin M112 grade from Japan was selected, placed into a mold, and pressed at room temperature (i.e., cold molding) under a pressure of 35 MPa to form a cylindrical blank with a diameter of 60 mm and a height of 55 mm (density of 2.16 g / cm³). 3 The cylindrical blank was subjected to stepped sintering, specifically as follows: the temperature was increased from room temperature to 300℃ at a rate of 65℃ / h and held for 120 min; then increased to 380℃ at a rate of 95℃ / h and held for 200 min; finally, it was cooled in the furnace at a rate of 40℃ / h. The cylindrical blank after stepped sintering was then machined to obtain a PTFE membrane with folded deformation zones (structural schematic shown in Figure 1). Figure 1(As shown). Magnetorheological polishing equipment was used to perform magnetorheological polishing on the PTFE membrane (the principle of magnetorheological polishing to eliminate tool marks on the PTFE membrane surface is as follows). Figure 2 As shown in the figure, the surface roughness Ra was reduced to 0.08 μm, followed by ultra-clean cleaning to obtain a high fatigue life PTFE diaphragm for diaphragm valves. The magnetorheological polishing slurry used in the process was water-based, and its composition by volume percentage was: 35% carbonyl iron powder, 2% nanodiamond (average particle size 200 nm), 1% dispersant stabilizer (a mixture of xanthan gum and sodium dodecylbenzenesulfonate in a 1:1 mass ratio), and the balance being water. The magnetorheological polishing parameters included: a magnetic field strength of 400 mT in the polishing region and a polishing head rotation speed of 300 rpm.

[0050] Comparative Example 1 Same as Example 1, except that the Daikin M112 grade PTFE suspension resin powder is replaced with Daikin M111.

[0051] Comparative Example 2 Same as Example 1, except that the Daikin M112 grade PTFE suspension resin powder is replaced with Daikin M18.

[0052] Comparative Example 3 Same as Example 1, except that the specific process of stepped sintering is as follows: the temperature is raised from room temperature to 300°C at a heating rate of 65°C / h and held for 120 min, then raised to 365°C at a heating rate of 95°C / h and held for 200 min, and then cooled with the furnace at a cooling rate of 40°C / h.

[0053] Comparative Example 4 Same as Example 1, except that the specific process of stepped sintering is as follows: the temperature is raised from room temperature to 300°C at a heating rate of 65°C / h and held for 120 min, then raised to 375°C at a heating rate of 95°C / h and held for 200 min, and then cooled with the furnace at a cooling rate of 40°C / h.

[0054] Comparative Example 5 Same as Example 1, except that the specific process of stepped sintering is as follows: the temperature is raised from room temperature to 300°C at a heating rate of 65°C / h and held for 120 min, then raised to 385°C at a heating rate of 95°C / h and held for 200 min, and then cooled with the furnace at a cooling rate of 40°C / h.

[0055] Comparative Example 6 Same as Example 1, except that the specific process of stepped sintering is as follows: the temperature is raised from room temperature to 300°C at a heating rate of 65°C / h and held for 120 min, then raised to 390°C at a heating rate of 95°C / h and held for 200 min, and then cooled with the furnace at a cooling rate of 40°C / h.

[0056] Comparative Example 7 Same as Example 1, except that the specific process of stepped sintering is as follows: the temperature is raised from room temperature to 300°C at a heating rate of 65°C / h and held for 120 min, then raised to 405°C at a heating rate of 95°C / h and held for 200 min, and then cooled with the furnace at a cooling rate of 40°C / h.

[0057] Comparative Example 8 Same as Example 1, except that magnetorheological polishing is replaced with mechanical polishing. The surface roughness Ra is still polished to 0.08 μm. Specifically, water polishing is performed step by step using 800-2500 grit SiC sandpaper, followed by fine polishing with 0.5 μm Al2O3 polishing liquid at 250 rpm and 0.05 MPa pressure until the surface roughness Ra reaches 0.08 μm.

[0058] Comparative Example 9 PTFE suspension resin powder of Daikin M111 grade from Japan was selected, placed into a mold, and pressed at room temperature under a pressure of 30 MPa (i.e., cold molding) to form a cylindrical blank with a diameter of 60 mm and a height of 55 mm (density of 2.13 g / cm³). 3 The cylindrical blank was subjected to stepped sintering, specifically as follows: the temperature was increased from room temperature to 300℃ at a rate of 65℃ / h and held for 120 min; then increased to 395℃ at a rate of 95℃ / h and held for 200 min; finally, it was cooled in the furnace at a rate of 40℃ / h. The cylindrical blank after stepped sintering was then machined to obtain a PTFE membrane with folded deformation zones.

[0059] Test Example 1 (1) Molecular weight and crystallinity test Number-average molecular weight was determined by differential scanning calorimetry (DSC). M n ) and crystallinity ( X c The formula for calculating crystallinity is shown in equation (1): (1); In equation (1), Δ H fThe enthalpy of PTFE melting (J / g) measured by DSC; Δ H f0 The reference value for the melting enthalpy of PTFE with 100% crystallinity is 80 J / g.

[0060] The formula for calculating the number-average molecular weight is shown in equation (2): (2); In equation (2), ΔHc is the enthalpy of PTFE crystallization (J / g) measured by DSC.

[0061] The number-average molecular weight and crystallinity of the cylindrical blanks before and after stepped sintering in Example 1 and Comparative Examples 1-2 are shown in Table 1 (the data before sintering represent the number-average molecular weight and crystallinity of the raw material PTFE suspension resin powder, and the data after sintering represent the number-average molecular weight and crystallinity of the final product PTFE).

[0062] Table 1 The number-average molecular weight and crystallinity of the cylindrical blanks sintered at different sintering temperatures in Examples 1, Comparative Examples 3-7, and Comparative Example 9 are shown in Table 2.

[0063] Table 2 (2) Microscopic characterization Figure 3 The images are TEM images of cylindrical blanks after stepped sintering in Example 1 and Comparative Examples 1-2, where (a) is Comparative Example 1, (b) is Comparative Example 2, and (c) is Example 1.

[0064] TEM images revealed that the cylindrical blanks of the three grades of PTFE after sintering all exhibited randomly distributed ribbon-like crystals formed by molecular chain stacking. Specific differences are as follows: Comparative Example 1 (M111): The ribbon-like crystals exhibited a slender, spindle-shaped characteristic, with a relatively loose crystal arrangement and obvious micropores inside. This indicates that the low molecular weight raw materials have a low molecular chain entanglement density during sintering, making it difficult to form a continuous and dense support network. Comparative Example 2 (M18): The crystal thickness increased, and the internal porosity decreased compared to Comparative Example 1, indicating an intermediate transitional state. Example 1 (M112): The ribbon-like crystals were the thickest and most evenly arranged, with extremely tight bonding between crystals and almost no visible pores inside. Conclusion: The above differences in microstructure fully demonstrate the regulatory effect of the number-average molecular weight of the raw materials on crystal morphology. High molecular weight (M112) raw materials, combined with a precise sintering process at 380 ℃, can induce the formation of a high-density "long-chain entanglement-ribbon-like crystal" network. This dense microstructure significantly reduces stress concentration sources and enhances the material's resistance to the accumulation of plastic strain, thereby achieving a leapfrog improvement in the fatigue life of the diaphragm on a macroscopic level.

[0065] Test Example 2 Mechanical property testing The central region of the cylindrical blanks after stepped sintering in each embodiment and comparative example was cut and processed into 1BA type I-beam standard specimens conforming to GB / T 1040.2-2022 for uniaxial tensile testing. The results are as follows: Figure 4 As shown in Table 3.

[0066] Figure 4 The stress-strain curves are those of the cylindrical blanks after stepped sintering in Example 1 and Comparative Example 9.

[0067] Table 3 Test Example 3 Fatigue life test Utilize Figure 5 The fatigue testing system shown was used to perform fatigue life tests on the PTFE diaphragms finally obtained in each embodiment and comparative example (20 samples per group). The fatigue testing system (i.e., fatigue test bench, physical image shown) Figure 6 (As shown) includes: Drive module: A synchronous belt linear slide driven by a stepper motor is used to provide high-precision axial reciprocating linear power to the diaphragm valve core; Clamping module: includes a transparent base and a pressure cap, used to fix the edge of the diaphragm and restrict its degrees of freedom except for axial movement, and the adjustment drive shaft is coaxial with the central axis of the diaphragm through the lifting platform; Control module: A PLC controller is used, with a reciprocating stroke set to 3.5 mm and a reciprocating frequency of 5 Hz, to adjust and ensure the repeatability and positioning accuracy of the diaphragm reciprocating motion.

[0068] Test results are as follows Figure 7 As shown in Table 4.

[0069] Figure 7 The statistical line graphs showing the fatigue fracture times of the PTFE membranes prepared in Example 1 and Comparative Example 9 reveal that the PTFE membrane prepared in Example 1 has an average fatigue life of 110 h (approximately 2 million cycles), while the PTFE membrane prepared in Comparative Example 9 has an average fatigue life of only 67 h (approximately 1.2 million cycles) and a standard deviation as high as 18.2 h, exhibiting high failure variability. The comparison demonstrates that the present invention, through synergistic control of process parameters and surface finishing, improves the fatigue life of the PTFE membrane by approximately 64.2%.

[0070] Table 4 The above test results show that the present invention effectively controls the microstructure and macroscopic mechanical properties of PTFE membranes by reconstructing the process path and utilizing the synergistic effect of molding parameter optimization and magnetorheological polishing surface modification, providing data support and manufacturing solutions for the ultra-long service life of components in ultra-clean fluid control systems for semiconductor manufacturing processes.

[0071] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a high fatigue life PTFE diaphragm for a diaphragm valve, characterized in that, Includes the following steps: PTFE suspension resin powder is pressed into a blank; the blank is sintered in a stepwise manner; the sintered blank is machined into a shape; the PTFE diaphragm obtained by the machined shape is magnetorheologically polished to obtain the high fatigue life PTFE diaphragm for the diaphragm valve. The number average molecular weight of the PTFE suspension resin powder is 1.4 × 10⁻⁶. 5 -1.6×10 5 g / mol; The stepped sintering process includes: first heating to 300 ℃ and holding for 100-150 min, then heating to 380 ℃ and holding for 200-250 min.

2. The method for preparing a high fatigue life PTFE diaphragm as described in claim 1, characterized in that, The pressure for the compression molding is 35 MPa.

3. The method for preparing a high fatigue life PTFE diaphragm for a diaphragm valve as described in claim 1, characterized in that, The crystallinity of the blank after step-sintering is 25-29%.

4. The method for preparing a high fatigue life PTFE diaphragm for a diaphragm valve as described in claim 1, characterized in that, The magnetorheological polishing specifically refers to polishing until the surface roughness Ra < 0.1 μm.

5. The method for preparing a high fatigue life PTFE diaphragm for a diaphragm valve as described in claim 4, characterized in that, The parameters of the magnetorheological polishing include: the magnetic field strength of the magnetorheological polishing region is 200-500 mT, and the polishing head rotation speed is 100-500 rpm.

6. The method for preparing a high fatigue life PTFE diaphragm for a diaphragm valve as described in claim 1, characterized in that, The heating rate during the stepped sintering process is 65-95 ℃ / h.

7. The method for preparing a high fatigue life PTFE diaphragm for a diaphragm valve as described in claim 1, characterized in that, After heating to 380 ℃ and holding for 200-250 min, the process also includes a step of cooling the furnace at a rate of 40 ℃ / h.

8. A high fatigue life PTFE diaphragm for a diaphragm valve prepared by a method according to any one of claims 1-7.

9. The application of a high fatigue life PTFE diaphragm for a diaphragm valve as described in claim 8 in an ultra-clean flow control system for semiconductor manufacturing.

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