Highly clean etching-resistant semiconductor-grade fluororubber sealing ring and preparation process thereof

Abstract

The application relates to the technical field of high polymer materials, and discloses a high-cleanliness etching-resistant semiconductor-grade fluororubber sealing ring and a preparation process thereof, wherein the preparation process comprises the following steps: preparing an emulsion polymerization system and performing oxygen removal pretreatment; starting an emulsion copolymerization reaction and supplementing monomers; in-situ adding PTFE aqueous dispersion liquid when the cumulative yield of polymerization reaches 25% to 67% of the target yield; polymerization termination and raw rubber post-treatment; pretreatment of components; preparation of a mixed rubber; mold pressing; two-stage post-vulcanization; plasma cleaning and ultrapure water washing, and finally, a semiconductor-grade fluororubber sealing ring finished product is obtained.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and more specifically, to a high-purity, etch-resistant semiconductor-grade fluororubber sealing ring and its preparation process. Background Technology

[0002] In the semiconductor integrated circuit manufacturing process, the plasma etching cavity is in an extreme environment of alternating high vacuum and strong corrosive plasma atmosphere containing fluorine and oxygen for a long time. The cavity seals are subjected to the combined effects of high-energy particle bombardment, chemical erosion and high-temperature compressive stress, which puts forward stringent requirements on the cleanliness, corrosion resistance and compression set of the sealing ring material.

[0003] Existing technologies typically involve physically blending polytetrafluoroethylene (PTFE) powder directly into the fluororubber matrix during the mixing stage to improve its resistance to plasma etching.

[0004] However, due to the extremely low surface energy of PTFE and the lack of chemical affinity between it and the fluororubber matrix, the interfacial bonding between the two phases is weak. PTFE particles gradually migrate and accumulate on the surface of the product during vulcanization and subsequent use, leading to particle precipitation and contamination of the chamber. While increasing the PTFE filler content improves etching resistance, the increase in filler content under traditional physical blending methods simultaneously exacerbates the risk of surface precipitation, making it impossible to simultaneously achieve both etching resistance and low precipitation levels. Furthermore, excessive PTFE results in a large amount of free thermoplastic phase in the fluororubber vulcanization network, causing significant creep under high temperature and pressure conditions, deteriorating compression set performance, and leading to a decrease in the long-term reliability of the sealing ring. Summary of the Invention

[0005] This invention provides a high-cleanliness, etch-resistant semiconductor-grade fluororubber sealing ring and its preparation process, solving the technical problems in related technologies such as insufficient cleanliness of fluororubber sealing rings in semiconductor process environments, poor resistance to plasma etching, and poor compatibility between PTFE and fluororubber matrix leading to decreased mechanical properties.

[0006] This invention discloses a process for preparing a high-purity, etch-resistant semiconductor-grade fluororubber sealing ring, comprising the following steps:

[0007] In the emulsion polymerization reaction system, tetrafluoroethylene and perfluoromethyl vinyl ether are copolymerized. When the cumulative polymerization yield reaches 25% to 67% of the target yield, the aqueous dispersion of PTFE is added to the reactor to continue polymerization until the target yield is reached. After coagulation, washing and drying, PTFE in-situ composite fluororubber raw rubber is obtained.

[0008] Based on 100 parts by weight of the PTFE in-situ composite fluororubber raw rubber, PTFE micro powder, crosslinking agent, crosslinking aid and perfluoropolyether lubricant are added during the mixing stage, and the compound is obtained by mixing.

[0009] The compounded rubber was subjected to compression molding vulcanization, two-stage post-vulcanization, plasma cleaning, and ultrapure water washing to obtain a high-cleanliness, etching-resistant semiconductor-grade fluororubber sealing ring.

[0010] Furthermore, the emulsion polymerization reaction system includes deionized water, perfluoropolyether ammonium carboxylate as an emulsifier, diammonium hydrogen phosphate as a pH adjuster, and ammonium persulfate as an initiator; the amount of perfluoropolyether ammonium carboxylate is 3000 to 5000 ppm, the amount of ammonium persulfate is 500 to 2000 ppm, and the pH of the system is 6.5 to 7.5; before the copolymerization reaction, the reactor is subjected to vacuuming and nitrogen purging for deoxygenation treatment, so that the residual oxygen content in the reactor is less than 10 ppm.

[0011] Further, the initial molar ratio of tetrafluoroethylene to perfluoromethyl vinyl ether is 55:45 to 65:35; perfluoro-2-bromoethyl vinyl ether, a monomer with a bromine sulfide point, is added to the copolymerization reaction in an amount of 0.1% to 0.5% of the total molar amount of tetrafluoroethylene and perfluoromethyl vinyl ether; the pressure inside the reactor is 0.5 to 0.8 MPa, and the reaction temperature is 20 to 80 °C.

[0012] Furthermore, the solid content of the PTFE aqueous dispersion is 40% to 60%, wherein the average particle size of the PTFE particles is 1 to 5 μm, and the number-average molecular weight of the PTFE is 1 × 10⁻⁶. 6 Up to 1×10 7 , of which 1×10 6 and 1×10 7 The unit is g / mol; the amount of PTFE solid content added is 2% to 14% of the target mass of fluororubber raw rubber; the addition method is continuous dripping or batch addition, and the continuous dripping time is 0.5 to 3 hours.

[0013] Furthermore, based on 100 parts by weight of fluororubber raw rubber, the total amount of PTFE is 5 to 20 parts by weight, of which the in-situ composite portion accounts for 40% to 70% of the total PTFE, and the supplementary portion in the mixing stage accounts for 30% to 60%; the crosslinking agent is bis(2,4-dichlorobenzoyl) peroxide, and the amount used is 0.5 to 3 parts by weight; the crosslinking aid is triallyl isocyanurate, and the amount used is 1 to 5 parts by weight; the mass ratio of bis(2,4-dichlorobenzoyl) peroxide to triallyl isocyanurate is 1:1.5 to 1:2.5; and the amount of perfluoropolyether lubricant is 0.1 to 2 parts by weight.

[0014] Furthermore, the mixing is carried out on an open mill in a clean room, with the front roll temperature at 40 to 60°C and the rear roll temperature at 35 to 55°C, and the roll temperature not exceeding 60°C throughout the process; after the mixed rubber sheet is left in a clean environment at 23±2°C and relative humidity not exceeding 55% for 8 to 24 hours, the Mooney viscosity is 30 to 80 MU.

[0015] Furthermore, the molding vulcanization temperature is 160 to 180°C, the vulcanization pressure is 10 to 15 MPa, and the vulcanization time is 3 to 10 minutes; the second-stage post-vulcanization is carried out at 200 to 250°C for 4 to 8 hours, and the compression set of the product after post-vulcanization is not higher than 15%, and the mass loss rate below 350°C is less than 0.5%.

[0016] Furthermore, in the copolymerization reaction, tetrafluoroethylene, perfluoromethyl vinyl ether, and perfluoropropyl vinyl ether are ternarily copolymerized in a molar ratio of 45:35:20 to 55:30:15; perfluorohexylethyl triiodide is added as an iodine-containing vulcanizing point monomer, at a dosage of 0.3% to 1.2% of the total molar amount of the three comonomers; the glass transition temperature of the resulting ternary copolymer fluororubber raw rubber is below -40°C; the PTFE aqueous dispersion is replaced with a core-shell structured PTFE microparticle aqueous dispersion, with a core layer of PTFE and a shell layer of perfluoropropylene oxide oligomer grafted layer, the shell layer thickness being 30 to 100 nm.

[0017] Furthermore, the crosslinking agent in the mixing stage is replaced with perfluorocyclobutane tetravinyl crosslinking unit, with an amount of 2 to 5 parts by weight, and the crosslinking aid triallyl isocyanurate is used in an amount of 2 to 5 parts by weight; 3 to 8 parts by weight of perfluoropolyether dual-terminated vinyl oligomer is also added as a compatibilizer, and 1 to 3 parts by weight of perfluoropolyether ether ketone block copolymer is added as a toughening agent; the molding vulcanization temperature is adjusted to 170 to 190°C, and the post-secondary vulcanization temperature is 210 to 260°C.

[0018] This invention discloses a high-purity, etch-resistant semiconductor-grade fluororubber sealing ring prepared by the above-mentioned preparation process. The sealing ring introduces PTFE through a combination of in-situ PTFE composite and supplementary composite during the mixing stage, and is obtained after compression molding vulcanization, two-stage post-vulcanization, plasma cleaning, and ultrapure water washing.

[0019] The beneficial effects of this invention are as follows:

[0020] This invention introduces an aqueous dispersion of polytetrafluoroethylene (PTFE) in situ during a specific window period when the cumulative polymerization yield reaches 25% to 67% of the target yield in the emulsion polymerization process. This allows newly generated fluororubber segments to continuously grow and extend on the surface of PTFE particles, forming a physically entangled coating structure. This solves the technical problems of weak interfacial bonding between PTFE particles and the fluororubber matrix and easy migration and precipitation of particles to the surface of the product in traditional physical blending methods. The invention achieves the technical effects of enhanced anchoring force of PTFE particles in the matrix and controlled particle precipitation.

[0021] The formulation system of this invention consists entirely of organic fluorine-containing compounds, without any fillers or additives containing metal ions. Combined with plasma cleaning and ultrasonic washing with ultrapure water post-treatment processes, it achieves the technical effect of reducing trace organic residues and metal ion precipitation on the product surface. The two-stage post-vulcanization process allows residual low-molecular-weight volatiles to continuously escape and further improves the cross-linking network, achieving the technical effect of suppressing permanent compression deformation of the sealing ring in the high-temperature process environment. Attached Figure Description

[0022] Figure 1 This is a process flow diagram of the preparation process of the high-purity, etch-resistant semiconductor-grade fluororubber sealing ring provided in the embodiments of the present invention;

[0023] Figure 2 This is a schematic diagram showing the comparison of particle precipitation amounts (particle size ≥ 0.2 μm) for various samples provided in the embodiments of the present invention;

[0024] Figure 3 This is a schematic diagram showing a comprehensive comparison between compression set and low-temperature elastic resilience provided in an embodiment of the present invention.

[0025] Figure 4 This is a schematic diagram illustrating the relationship between the timing of in-situ PTFE addition and the amount of particles precipitated, provided in an embodiment of the present invention.

[0026] Figure 5 This is a schematic diagram comparing the low-temperature rebound rates of the routes in Embodiment 1 and Embodiment 2 provided in this invention.

[0027] Figure 6 This is a schematic diagram of the SEM morphology of PTFE in-situ composite fluororubber raw rubber provided in an embodiment of the present invention;

[0028] Figure 7 This is a schematic diagram of a cross-sectional TEM image of a high-cleanliness, etch-resistant semiconductor-grade fluororubber sealing ring provided in an embodiment of the present invention;

[0029] Figure 8 This is a schematic diagram of the FTIR spectrum of the fluororubber sealing ring provided in an embodiment of the present invention. Detailed Implementation

[0030] The subject matter described herein will now be discussed with reference to exemplary embodiments. It should be understood that these embodiments are discussed only to enable those skilled in the art to better understand and implement the subject matter described herein, and changes may be made to the function and arrangement of the elements discussed without departing from the scope of this specification. Various processes or components may be omitted, substituted, or added as needed in the examples. Furthermore, some features described in the examples may be combined in other examples.

[0031] Example 1

[0032] This embodiment discloses a fabrication process for a high-purity, etch-resistant semiconductor-grade fluororubber sealing ring, see [link to documentation]. Figure 1 ,include:

[0033] Step 1: Preparation and deoxygenation pretreatment of the emulsion polymerization reaction system.

[0034] Add 30L of deionized water (conductivity not higher than 1μS / cm) to a 50L stainless steel high-pressure reactor. Then add the emulsifier perfluoropolyether carboxylate ammonium salt, the pH adjuster diammonium hydrogen phosphate, and the initiator ammonium persulfate in sequence. Start stirring to ensure that all components are fully dissolved and homogeneous. The stirring speed is 200 to 400 rpm.

[0035] The dosage of perfluoropolyether ammonium carboxylate is 3000 to 5000 ppm (based on the mass of deionized water), preferably 4000 ppm. The number-average molecular weight of the perfluoropolyether ammonium carboxylate is 500 to 2000, the acid value is 25 to 60 mg KOH / g, and the critical micelle concentration in deionized water at 25°C is 800 to 1500 ppm. The perfluoropolyether ammonium carboxylate does not contain traditional fluorinated surfactants such as perfluorooctanoic acid (PFOA), thus avoiding the introduction of persistent organic pollutants at the source. The amount of diammonium hydrogen phosphate added is sufficient to adjust the pH of the system to 6.5 to 7.5. The dosage of ammonium persulfate is 500 to 2000 ppm (based on the mass of deionized water), preferably 1000 to 1500 ppm.

[0036] After all components have dissolved uniformly, the reactor is deoxygenated: the absolute pressure inside the reactor is reduced to no more than 500 Pa using a vacuum pump and maintained for 5 minutes, then high-purity nitrogen (purity not less than 99.999%) is introduced until atmospheric pressure is reached. This vacuuming and nitrogen purging process is repeated three times to ensure that the residual oxygen content inside the reactor is below 10 ppm. The presence of residual oxygen can inhibit the free radical polymerization reaction; therefore, strict deoxygenation is a prerequisite for ensuring the smooth start-up and uniform progress of the subsequent polymerization reaction.

[0037] Furthermore, ammonium persulfate decomposes at a moderate rate under alkaline to neutral conditions (pH 6.5 to 7.5), maintaining a stable free radical initiation rate. Below pH 6, ammonium persulfate decomposes rapidly, resulting in an excessively fast initiation rate, leading to a wider chain length distribution and lower Mooney viscosity. Above pH 8, ammonium persulfate decomposes too slowly, reducing initiation efficiency and causing unstable polymerization rates. Therefore, adjusting the pH of the diammonium hydrogen phosphate system to 6.5 to 7.5 must be completed before the initiator is added to ensure the initiation rate remains within a controlled range.

[0038] Furthermore, ammonium persulfate is a strong oxidizing solid. When weighing and dissolving it, operators must wear protective gloves and goggles to avoid direct contact with skin and eyes. Ammonium persulfate must be stored in a cool, dry place, away from flammable materials and reducing substances.

[0039] Step 2: Initiation of emulsion copolymerization and monomer replenishment.

[0040] After deoxygenation pretreatment, tetrafluoroethylene (TFE) and perfluoromethyl vinyl ether (PMVE) are introduced into the reactor via a gas mass flow meter. The initial molar ratio of TFE to PMVE is controlled within the range of 55:45 to 65:35, preferably 60:40. Simultaneously, perfluoro-2-bromoethyl vinyl ether, a monomer containing bromine sulfidation points, is injected via a metering pump. The amount of perfluoro-2-bromoethyl vinyl ether is 0.1% to 0.5% of the total molar amount of TFE and PMVE, preferably 0.2% to 0.3%. Perfluoro-2-bromoethyl vinyl ether provides active sites for the raw rubber molecular chains to be used for subsequent peroxide vulcanization crosslinking. The initial pressure inside the reactor is increased to 0.5 to 0.8 MPa, and the temperature inside the reactor is raised to 20 to 80°C using a constant temperature water bath to initiate the emulsion polymerization reaction.

[0041] It should be noted that the molar ratio of TFE to PMVE, ranging from 55:45 to 65:35, was determined based on a comprehensive consideration of the glass transition temperature, elastic recovery properties, and processing fluidity of the resulting perfluoroether rubber raw material. When the TFE ratio is below 55 mol%, the raw rubber has insufficient crystallinity and low tensile strength; when the TFE ratio is above 65 mol%, the glass transition temperature of the raw rubber increases, and its low-temperature elasticity decreases.

[0042] It should be noted that the amount of perfluoro-2-bromoethyl vinyl ether used is 0.1% to 0.5% of the total molar amount of TFE and PMVE. This range of usage ensures that the bromine content in the raw rubber is between 0.3% and 1.5 wt%, providing sufficient density of vulcanization active sites for subsequent peroxide crosslinking.

[0043] During the reaction, the pressure inside the reactor and the monomer consumption are monitored in real time by pressure sensors and flow meters. The mixed monomers of TFE and PMVE are continuously replenished to maintain a constant pressure inside the reactor. At the same time, the monomer replenishment flow rate is integrated to obtain the cumulative polymerization yield, which serves as a quantitative basis for determining the timing of adding PTFE aqueous dispersion.

[0044] Furthermore, in step 2, the polymerization reaction is carried out under a high-purity nitrogen protective atmosphere. A nitrogen micro-positive pressure maintenance device is installed at the top of the reactor to ensure that the nitrogen partial pressure in the gas phase space inside the reactor is not lower than 0.01 MPa, preventing external air from seeping in and causing polymerization inhibition.

[0045] Furthermore, TFE is a flammable and explosive gas. During the monomer filling and replenishment process, it is necessary to ensure that the reactor and pipeline system are well sealed, and the exhaust port is connected to a dedicated waste gas treatment device. An explosive gas detector and alarm must be installed outside the reactor, the operating area must be fully ventilated, and open flames and static electricity are strictly prohibited.

[0046] Step 3: In-situ addition of PTFE aqueous dispersion.

[0047] When the cumulative polymerization yield reaches 25% to 67% of the final target yield, the aqueous PTFE dispersion is added to the reactor through an independent feed line. The solid content of the aqueous PTFE dispersion is 40% to 60%, wherein the average particle size of the PTFE particles is 1 to 5 μm, preferably 2 to 3 μm, the particle size distribution index (PDI) is not greater than 0.3, and the number average molecular weight of PTFE is 1 × 10⁻⁶. 6 Up to 1×10 7 .

[0048] The timing of PTFE addition has a decisive impact on the interphase structure. When the cumulative yield is below 25%, the fluororubber molecular chains in the system are still short, the chain entanglement network has not been formed, and the PTFE particles cannot be effectively coated and anchored, leading to macroscopic phase separation during subsequent molding. When the cumulative yield exceeds 67%, the latex particle concentration is high, the system viscosity increases significantly, and newly added PTFE particles cannot penetrate uniformly into the gaps between latex particles. Within the addition window of 25% to 67%, the system already contains fluororubber molecular chains of sufficient length. As the polymerization reaction continues, the newly generated fluororubber chain segments continue to grow and extend on and around the PTFE particle surface, forming a physical entanglement and coating of the PTFE particles with fluororubber molecular chains, thereby uniformly embedding the PTFE particles into the continuous fluororubber phase.

[0049] It should be noted that, within the cumulative production range of 25% to 67%, the preferred addition window is when the cumulative production reaches 35% to 50% of the target production. Within this window, the fluororubber molecular chains in the system have sufficient chain length and entanglement density, while the gaps between latex particles still have enough space to accommodate the uniform penetration of PTFE particles, resulting in the best entanglement and coating effect at the two-phase interface.

[0050] The PTFE aqueous dispersion is added either continuously dripping or in batches. When adding continuously, it is added to the reactor at a uniform rate using a peristaltic pump, with the addition time controlled between 0.5 and 3 hours, while maintaining a constant stirring speed. When adding in batches, the total amount is divided into 3 to 5 batches, with an interval of 15 to 30 minutes between each batch. After each batch is added, the mixture is stirred for 10 minutes before adding the next batch. The PTFE solid content added is 2% to 14% of the target mass of the fluororubber raw rubber, preferably 4% to 10%.

[0051] Furthermore, when the PTFE aqueous dispersion is introduced through an independent feed line, the feed line is purged and replaced with high-purity nitrogen at least three times before being connected to the reactor to ensure that no air is introduced during the feeding process; the dropping operation is carried out under nitrogen micro-positive pressure protection throughout the process.

[0052] Furthermore, PTFE aqueous dispersions typically contain small amounts of surfactant stabilizers, which, upon addition to the system, may compete with existing perfluoropolyether ammonium carboxylate salts for adsorption, affecting the stability of latex particles. Before using PTFE aqueous dispersions, it is essential to confirm that the emulsifier system is compatible with the perfluoropolyether ammonium carboxylate salt (both are nonionic or of the same ionic type) to avoid introducing cationic surfactants that could lead to latex particle flocculation and demulsification. The PTFE aqueous dispersion must be thoroughly shaken before addition, and only after confirming the absence of sedimentation and stratification can it be transported.

[0053] Step 4: Termination of polymerization reaction and post-treatment of raw rubber.

[0054] Once the cumulative polymerization yield reaches the target yield, monomer replenishment is stopped and the temperature is lowered to room temperature to allow the polymerization reaction to terminate naturally. Unreacted gaseous monomers are recovered to a storage tank, and the reactor is opened after the pressure inside the reactor is reduced to atmospheric pressure. The resulting composite latex is transferred to a coagulation tank, and a 3% to 5% (mass fraction) magnesium sulfate aqueous solution is added as a coagulant at a volume ratio of 5% to 10% of the latex volume. The mixture is stirred and coagulated at 60 to 70°C for 30 to 60 minutes to break down and flocculate the latex particles.

[0055] After coagulation, the rubber particles are collected by filtration and washed repeatedly 5 to 8 times with deionized water (resistivity not less than 18.2 MΩ·cm), with each wash using 10 times the mass of the raw rubber, until the fluoride and sulfate ion content in the washing waste liquid is less than 5 ppm, at which point the washing is considered qualified. The qualified rubber particles are placed in a vacuum oven and dried for 12 to 24 hours at 60 to 80°C and an absolute pressure not exceeding 5 kPa, until the moisture content is less than 0.1%, yielding PTFE in-situ composite fluororubber raw rubber.

[0056] It should be noted that the Mooney viscosity ML(1+4) of the obtained PTFE in-situ composite fluororubber raw rubber is... 100℃ (where ML represents Mooney viscosity, (1+4) means 4 minutes of rotation after 1 minute of preheating, and the subscript 100℃ indicates the measurement temperature) is 40 to 90 MU, the fluorine content is not less than 65 wt% (determined by elemental analysis), and the glass transition temperature is -20 to -10℃ (determined by differential scanning calorimetry, with a heating rate of 10℃ / min).

[0057] Furthermore, the magnesium sulfate aqueous solution used for coagulation must be added under the condition that the pH of the system is not lower than 6 to prevent the system from being too acidic, which would cause the residual ammonium persulfate to decompose and produce excessive sulfuric acid, affecting the cleanliness of the product. The coagulation waste liquid contains free perfluoropolyether carboxylate ammonium salt and coagulant, and must be discharged after wastewater treatment. It must not be directly discharged into the sewer.

[0058] Furthermore, the washing wastewater contains trace amounts of fluoride and sulfate ions. When the cumulative amount is large, it must be collected and handed over to a professional wastewater treatment facility for treatment. It must not be discharged directly without treatment.

[0059] Step 5: Pretreatment of PTFE micro powder and cross-linking system components.

[0060] PTFE micro powder (average particle size 1 to 5 μm, semiconductor grade, number average molecular weight 1 × 10⁻⁶) was used. 6 Up to 1×10 7 (The total metal ion content should not exceed 10 ppb) is placed in a clean glass tray and dried in a forced-air drying oven at 80 to 90°C for 2 to 3 hours to fully remove the moisture adsorbed inside and on the surface of the powder particles. After drying, it is cooled to room temperature in a desiccator and then sealed for later use. The residual moisture content in the PTFE micro powder should be less than 500 ppm, as determined by the Karl Fischer method.

[0061] Meanwhile, the crosslinking agent bis(2,4-dichlorobenzoyl) peroxide (with an effective peroxide content of not less than 40% and a 10-hour half-life temperature of 117 to 119°C) and the crosslinking aid triallyl isocyanurate (TAIC, with a purity of not less than 98% and a functionality of 3) are accurately weighed according to the formula ratio. The mass ratio of bis(2,4-dichlorobenzoyl) peroxide to triallyl isocyanurate is 1:1.5 to 1:2.5. They are premixed evenly under light-protected conditions, placed in a clean container, sealed, and stored for later use. The operating temperature throughout the process does not exceed 30°C to prevent premature decomposition and failure of the peroxide.

[0062] Furthermore, the premixing of bis(2,4-dichlorobenzoyl)peroxide and triallyl isocyanurate must be carried out in an environment where the temperature does not exceed 30°C. The bis(2,4-dichlorobenzoyl)peroxide should be slowly added to the triallyl isocyanurate and stirred evenly, rather than adding the triallyl isocyanurate to the bis(2,4-dichlorobenzoyl)peroxide, in order to reduce the risk of premature decomposition caused by excessively high local peroxide concentration. After premixing, the mixture should be immediately sealed in a light-proof container and stored at 4 to 10°C for later use. Before use, the mixture should be brought to room temperature.

[0063] Furthermore, bis(2,4-dichlorobenzoyl) peroxide releases heat upon decomposition, posing a risk of heat accumulation in closed containers or under high-concentration storage conditions. Premixing and weighing operations must be performed in a fume hood. Before use, ensure the container is properly sealed, and provide dedicated fire extinguishers for organic peroxides in the operating area. The storage quantity of bis(2,4-dichlorobenzoyl) peroxide must comply with relevant regulations for the safety management of hazardous chemicals and must not be exceeded.

[0064] Furthermore, triallyl isocyanurate is a flammable organic liquid with slight irritant properties. Weighing and premixing operations must be carried out in a fume hood, and operators must wear protective gloves and goggles to avoid inhaling its vapors or direct skin contact.

[0065] Step 6, preparation of compound rubber.

[0066] The mixing operation is carried out in an ISO Class 6 clean room. The gap between the open mill rolls is adjusted to 0.5 to 2 mm, the temperature of the front roll is controlled at 40 to 60°C, and the temperature of the rear roll is controlled at 35 to 55°C. The temperature deviation throughout the process does not exceed ±3°C to prevent the premature decomposition of bis(2,4-dichlorobenzoyl) peroxide due to excessively high roll temperature.

[0067] 100 parts by weight of the PTFE in-situ composite fluororubber raw material obtained in step 4 are fed into a two-roll mill and subjected to a thin-pass roll wrapping operation 2 to 3 times to form a smooth, continuous, and pore-free uniform roll wrapping layer on the roll surface. After the roll wrapping of the rubber compound is stable, the PTFE micro powder pretreated in step 5 is added in small batches of 3 to 5 times. After each addition, the rubber is cut and turned 3 to 5 times along the left and right sides of the roll axis. The next batch is added only after the powder is completely wrapped into the rubber layer.

[0068] It should be noted that the PTFE micro powder added during the mixing stage, together with the PTFE introduced in the in-situ compounding stage of step 3, constitutes the total PTFE content. Based on 100 parts by weight of fluororubber raw rubber, the total PTFE content (including the in-situ compounding portion and the portion added during the mixing stage) is controlled between 5 and 20 parts by weight, preferably 10 to 15 parts by weight. The in-situ compounding portion accounts for 40% to 70% (mass fraction) of the total PTFE content, and the portion added during the mixing stage accounts for 30% to 60% (mass fraction), with the corresponding addition amount during the mixing stage being 2 to 12 parts by weight.

[0069] After the PTFE micro powder is evenly mixed, the mixture of bis(2,4-dichlorobenzoyl) peroxide and triallyl isocyanurate pre-mixed in step 5 is added in batches. The amount of bis(2,4-dichlorobenzoyl) peroxide is 0.5 to 3 parts by weight, preferably 1 to 2 parts by weight; the amount of triallyl isocyanurate is 1 to 5 parts by weight, preferably 2 to 3 parts by weight. The mass ratio of bis(2,4-dichlorobenzoyl) peroxide to triallyl isocyanurate is 1:1.5 to 1:2.5. This ratio range allows the free radicals generated by the decomposition of the peroxide to fully react with the three allyl sites of triallyl isocyanurate, forming a uniform and dense cross-linked network. After each batch is added, the rubber is tapped and re-rolled 3 to 5 times, with the roller temperature not exceeding 60°C throughout the process. After the crosslinking system is completed, add 0.1 to 2 parts by weight of perfluoropolyether lubricant (viscosity of 50 to 200 cSt (25°C), number average molecular weight of 1000 to 4000, perfluoromethyl-terminated) and mix evenly.

[0070] After all components have been added, the roller gap is narrowed to 0.5 to 1 mm, and the compound is subjected to 5 to 8 thin passes for homogenization. After each thin pass, the rubber sheet is folded 90° and passed through the rollers again to eliminate local concentration gradients among the components. Then, the roller gap is increased to 2 to 4 mm to produce the compounded rubber sheet.

[0071] The compounded rubber sheets were left to stand in a clean environment at 23±2℃ and relative humidity not exceeding 55% for 8 to 24 hours to allow bis(2,4-dichlorobenzoyl) peroxide and triallyl isocyanurate to fully diffuse and homogenize into the rubber compound, while simultaneously relaxing the internal stress generated during the mixing process. After standing, samples were taken to test the Mooney viscosity ML(1+4) of the compounded rubber. 100℃The acceptable range is 30 to 80 MU, and the Mooney viscosity is determined according to the ASTM D1646 standard method.

[0072] Furthermore, the amounts of each component in this embodiment, by weight, are summarized as follows: 100 parts by weight of PTFE in-situ composite fluororubber raw rubber; 2 to 12 parts by weight of PTFE micro powder (added during the mixing stage); 0.5 to 3 parts by weight of bis(2,4-dichlorobenzoyl) peroxide; 1 to 5 parts by weight of triallyl isocyanurate; and 0.1 to 2 parts by weight of perfluoropolyether lubricant. The total amount of PTFE (the sum of the in-situ composite portion and the portion added during the mixing stage) is 5 to 20 parts by weight.

[0073] Furthermore, the roller temperature during the mixing stage must be strictly controlled below 60℃. The 10-hour half-life temperature of bis(2,4-dichlorobenzoyl) peroxide is 117 to 119℃, but under conditions of uneven local heating or residual initiator catalysis, there is a possibility of premature, trace decomposition at low temperatures. When the roller temperature exceeds 60℃, the free radicals generated by the premature decomposition of bis(2,4-dichlorobenzoyl) peroxide will trigger local pre-crosslinking, leading to granular agglomeration of the rubber compound (i.e., "scorching"), decreased uniformity of the compound, and subsequent vulcanization products exhibiting bubbles or uneven mechanical properties.

[0074] Furthermore, since PTFE powder is a fine powder, its addition may generate dust. Operators must wear dust masks and operate the equipment under normal ventilation conditions in the clean room.

[0075] Step 7, molding.

[0076] The qualified compounded rubber sheets are cut into cylindrical preform blanks at 105% to 110% of the theoretical mass of the sealing ring. Clean ceramic cutters are used to cut the blanks to avoid metal contamination. The blanks are placed in the center of the mold cavity, which has been ultrasonically cleaned with ultrapure water and coated with a perfluoropolyether release agent. After the mold is closed, the blanks are pushed into the flat vulcanizing machine.

[0077] The vulcanization temperature is set to 160 to 180℃, preferably 170℃; the vulcanization pressure is 10 to 15 MPa, preferably 12 MPa; the vulcanization time is 3 to 10 minutes, the heating rate is controlled at 5 to 10℃ / min, and the pressure fluctuation does not exceed ±0.5 MPa. After vulcanization, the mold is quickly opened and the vulcanized product is removed. The flash is peeled off, and the appearance is checked for defects such as bubbles, missing material, and cracks. The product is then allowed to cool naturally to room temperature. The cross-sectional dimensional tolerance of the product should meet the requirement of ±0.05 mm. The cross-sectional dimensions are measured using a contact profilometer or an optical projector.

[0078] It should be noted that the vulcanization time of 3 to 10 minutes is related to the diameter of the sealing ring cross-section. For every 1 mm increase in cross-section diameter, the vulcanization time is extended by about 1 minute.

[0079] Furthermore, during the compression molding and vulcanization process, bis(2,4-dichlorobenzoyl) peroxide decomposes at a high temperature of 160 to 180°C, which may release trace amounts of chlorinated volatile organic compounds. The vulcanizing machine operating area must be well ventilated, and operators must wear protective gloves to avoid contact with high-temperature molds and products that have just been demolded.

[0080] Step 8, second-stage post-vulcanization.

[0081] The primary vulcanized products are neatly arranged on a clean ceramic tray, with a spacing of no less than 5 mm between products, and placed in a clean circulating hot air oven purified by a HEPA filter for post-vulcanization. Post-vulcanization is carried out in three stages: In the first stage, the temperature is increased from room temperature to the post-vulcanization holding temperature at a rate of 2 to 3 °C / min; in the second stage, the temperature is held at 200 to 250 °C for 4 to 8 hours, preferably at 230 °C for 6 hours, to allow the residual decomposition products of bis(2,4-dichlorobenzoyl) peroxide and low-molecular-weight volatiles to continuously escape, and the cross-linking network is further improved; in the third stage, the oven is turned off and allowed to cool naturally to below 50 °C before the products are removed.

[0082] The post-sulfurization stage allows residual low-molecular-weight volatiles to continuously escape, reducing the possibility of them precipitating and contaminating the cavity in the semiconductor process atmosphere.

[0083] After the two-stage vulcanization is completed, batch samples are extracted and subjected to compression set tests (200℃×70h) according to ASTM D395 B method. The acceptance criterion is that the compression set value is not higher than 15%. At the same time, thermogravimetric analysis (nitrogen atmosphere, heating rate 10℃ / min) is performed to confirm that the mass loss rate below 350℃ is less than 0.5%. The mass loss rate is calculated as the ratio of the mass change in the corresponding temperature range in the thermogravimetric curve to the initial sample mass.

[0084] Furthermore, the oven in the post-vulcanization stage must maintain good ventilation to ensure that the escaping low-molecular-weight volatiles are discharged in a timely manner. The post-vulcanization exhaust gas may contain trace amounts of fluorine-containing volatile organic compounds, which must be treated by a dedicated exhaust gas treatment device (such as activated carbon adsorption or thermal oxidation device) before being discharged to avoid direct discharge into the atmosphere.

[0085] Step 9: Plasma cleaning and ultrapure water washing.

[0086] The two-stage vulcanized sealing rings were placed in a single layer on the sample stage of the plasma cleaner. After the sealed chamber was evacuated to an absolute pressure not exceeding 10 Pa, a mixture of argon and oxygen was introduced at a volume ratio of Ar:O2 of 3:1, with a total gas flow rate of 50 to 100 sccm. The chamber pressure was maintained within the range of 5 to 30 Pa. The radio frequency power supply (frequency 13.56 MHz, power 200 W) was turned on, and plasma cleaning was performed for 5 minutes. The active oxygen atoms in the plasma oxidized and decomposed organic residues into CO2 and H2O, which were then discharged with the evacuated gas. At the same time, argon ions physically bombarded and cleaned the surface.

[0087] After plasma cleaning, the sealing ring is ultrasonically assisted in cleaning with ultrapure water (resistivity not less than 18.2 MΩ·cm, TOC not higher than 5 ppb). The ultrasonic frequency is 40 kHz, the power is 100 W / L, and the water temperature is 23±2℃. The cleaning is performed three times, each time for 10 minutes, with fresh ultrapure water used each time. The waste liquid from the last cleaning is then analyzed by inductively coupled plasma mass spectrometry (ICP-MS) to determine the content of each metal ion (Na, K, Ca, Mg, Fe, Ni, Cr, Cu, Al, etc.). The concentration of each metal ion should be less than 0.1 ppb.

[0088] Furthermore, the surface condition of the product after plasma cleaning directly affects the effect of subsequent ultrasonic cleaning. The combination of 200W plasma cleaning power and 5 minutes of processing time requires a balance between effectively removing organic residues from the fluororubber surface and preventing significant degradation of the surface fluororubber matrix. At this frequency, an ultrasonic cleaning power of 100W / L effectively removes particulate residues through cavitation on the sealing ring surface without damaging the cross-linked network of the vulcanized fluororubber, ensuring compatibility between separation effectiveness and product integrity.

[0089] Furthermore, the plasma cleaning exhaust gas contains CO2, H2O and possible fluorine-containing fragments, and the exhaust port of the plasma cleaner must be connected to a dedicated exhaust gas treatment device; the ultrasonic washing waste liquid contains trace amounts of organic residues and must be treated before being discharged.

[0090] After passing the cleanliness test, the sealing rings are dried in a clean, circulating hot air environment at 40-50℃ for 30-60 minutes until no visible water marks remain on the surface. In an ISO Class 5 or higher cleanroom, each product is individually packaged into a verified, clean, sealed polyethylene bag and heat-sealed. An anti-static bag is then placed over the bag to obtain the finished semiconductor-grade fluororubber sealing rings. Finally, batch samples of the products are subjected to Fourier transform infrared spectroscopy (FTIR) and elemental analysis to confirm that the product structure and composition meet the requirements.

[0091] Furthermore, the emulsifier used throughout the entire process of this invention is perfluoropolyether carboxylate ammonium salt, which does not contain persistent organic pollutants such as perfluorooctanoate ammonium; coagulation waste liquid, washing waste liquid and post-sulfurization waste gas are all discharged after corresponding wastewater treatment or waste gas treatment; all solid waste (such as waste PTFE micro powder packaging bags, filter residue, etc.) are collected and disposed of according to the general industrial solid waste classification, which reflects the environmental protection advantages of combining source pollution reduction and process control.

[0092] Example 2

[0093] In advanced semiconductor etching processes, fluororubber seals must withstand the strong corrosive erosion of fluorine-based plasma for a long time. They also face extreme conditions with frequent alternation between low-temperature etching (deep cryogenic etching at -60 to -40°C) and high-temperature in-situ cleaning in the chamber (150 to 200°C), with a temperature difference exceeding 200°C and a daily cycle frequency of dozens of times.

[0094] The TFE-PMVE binary copolymer fluororubber raw material system used in Example 1 has a glass transition temperature of approximately -20 to -10°C. Under cryogenic etching conditions at -60°C, the material enters a deep glassy state, resulting in a sharp increase in elastic modulus and a drastic decrease in the compression and rebound capacity of the sealing ring. Simultaneously, the active bromine sites provided by perfluoro-2-bromoethyl vinyl ether in Example 1 become the preferred targets of fluorine-containing free radicals during the plasma cleaning stage. Furthermore, the oxygen-containing decomposition residues generated during the vulcanization process of the bis(2,4-dichlorobenzoyl) peroxide crosslinking system used in Example 1 are accelerated to degrade on the surface under plasma conditions. This embodiment, based on the in-situ emulsion polymerization composite process framework of Example 1, specifically addresses the above problems by introducing a low glass transition temperature ternary copolymer fluororubber raw material system, core-shell structured PTFE microparticles, perfluorinated compatibilizer components, and an oxygen-free byproduct-free crosslinking system.

[0095] Step 1: Preparation and deoxygenation pretreatment of the emulsion polymerization reaction system.

[0096] Following the same procedure as in Step 1 of Example 1, add 30L of deionized water (conductivity not exceeding 1μS / cm) to a 50L stainless steel high-pressure reactor. Then, sequentially add 3000-5000ppm (based on the mass of deionized water) of perfluoropolyether carboxylate emulsifier, diammonium hydrogen phosphate pH adjuster (to adjust the system pH to 6.5-7.5), and 500-2000ppm (based on the mass of deionized water) of ammonium persulfate initiator. Start stirring (200-400 rpm) to ensure all components are fully dissolved and homogeneous. After homogeneous dissolution, repeat the vacuuming and nitrogen purging cycle three times to ensure the residual oxygen content in the reactor is below 10ppm. The vacuuming and nitrogen purging parameters are the same as in Step 1 of Example 1.

[0097] Furthermore, the safety requirements for handling ammonium persulfate are the same as in step 1 of Example 1.

[0098] Step 2: Initiation of the low glass transition temperature ternary copolymerization reaction and monomer replenishment.

[0099] In Example 1, step 2, perfluoro-2-bromoethyl vinyl ether was replaced with perfluorohexylethyl triiodide, a monomer with an iodine sulfide point. At the same time, perfluoropropyl vinyl ether (PPVE) was added as a third comonomer to the TFE and PMVE monomer system to construct a ternary copolymer system.

[0100] TFE, PMVE, and PPVE are introduced into the reactor via a gas mass flow meter. The molar ratio of the three monomers is controlled to be THE:PMVE:PPVE = 45:35:20 to 55:30:15, preferably 50:32:18. By increasing the proportion of PPVE as the third monomer, the glass transition temperature of the resulting low-glass transition temperature ternary copolymer fluororubber raw rubber is reduced to below -40°C (determined by differential scanning calorimetry, heating rate 10°C / min). Simultaneously, perfluorohexylethyl triiodide is injected via a metering pump. The amount of perfluorohexylethyl triiodide is 0.3% to 1.2% of the total molar amount of TFE, PMVE, and PPVE, preferably 0.5% to 0.8%, acting as a chain transfer agent to participate in iodine transfer polymerization, thereby imparting an iodine vulcanization point to the low-glass transition temperature ternary copolymer fluororubber raw rubber.

[0101] It should be noted that the molar ratio of PPVE is 15 to 20 mol%. Its introduction forms additional perfluoroether side groups on the fluororubber backbone, increases the molecular chain spacing and reduces the intermolecular forces, thereby reducing the glass transition temperature of the low glass transition temperature ternary copolymer fluororubber raw rubber from -20 to -10°C in Example 1 to below -40°C, and it can still maintain its elastic resilience under deep cryogenic etching conditions at -60°C.

[0102] It should be noted that perfluorohexylethyl triiodide (molecular weight 550 to 650, iodine content not less than 55 wt%, purity not less than 97%) acts as a chain transfer agent in iodine transfer polymerization, introducing iodine atoms to the ends of the ternary copolymer fluororubber molecular chains at low glass transition temperatures. The iodine curing point has a lower carbon-halogen bond dissociation energy compared to the bromine curing point in Example 1, with the C1 bond dissociation energy being approximately 209 KJ / mol and the C-Br bond dissociation energy approximately 276 KJ / mol. These bond energies are all homolytic cleavage bond dissociation energies under standard conditions. During subsequent curing, iodine atoms are more easily removed and participate in crosslinking reactions, resulting in a lower density of residual active end groups after curing, reducing the probability of preferential attack of active end groups by fluorine-containing free radicals under plasma conditions.

[0103] The initial pressure inside the reactor is increased to 0.5 to 0.8 MPa, and the temperature inside the reactor is raised to 20 to 80°C using a constant-temperature water bath to initiate the emulsion polymerization reaction. Pressure monitoring and monomer replenishment during the reaction process are the same as in step 2 of Example 1.

[0104] Furthermore, in step 2, the polymerization reaction is carried out under a high-purity nitrogen protective atmosphere, and the gas phase space inside the reactor is maintained at a slightly positive nitrogen pressure of not less than 0.01 MPa to prevent external air from seeping in and causing polymerization inhibition; PPVE must be treated with an activated alumina drying column before being added to remove trace amounts of moisture and avoid introducing polymerization inhibitory impurities.

[0105] Furthermore, the polymerization rate of PPVE in the ternary copolymer system differs from that of TFE and PMVE. During the reaction, the replenishment flow rates of the three monomers must be independently adjusted using a gas mass flow meter. The replenishment ratio of each monomer must be adjusted in a timely manner based on real-time data of the pressure inside the reactor and the monomer consumption rate to ensure that the copolymer segment composition remains uniform throughout the reaction process and to avoid compositional drift that leads to a wider distribution of the glass transition temperature.

[0106] Furthermore, TFE is a flammable and explosive gas, and PPVE is a flammable fluorinated organic compound. During the monomer filling and replenishment process, it is necessary to ensure that the reactor and pipeline system are well sealed, and the exhaust port is connected to a dedicated waste gas treatment device. The operating area should be kept well ventilated, equipped with an explosive gas detection alarm, and open flames and static electricity are strictly prohibited. The safety operation requirements are the same as step 2 of Example 1.

[0107] Furthermore, perfluorohexyl ethyl triiodide contains a high concentration of iodine, which is irritating. Weighing and injection operations must be carried out in a fume hood, and operators must wear protective gloves and goggles to avoid skin contact and inhalation of vapors. Waste perfluorohexyl ethyl triiodide packaging and residues must be collected and disposed of as iodine-containing organic waste.

[0108] Step 3: In-situ addition of the aqueous dispersion of core-shell structured PTFE microparticles.

[0109] The aqueous PTFE dispersion used in step 3 of Example 1 was replaced with an aqueous dispersion of core-shell structured PTFE microparticles. The structural parameters of the core-shell structured PTFE microparticles are: core layer is PTFE, particle size is 2 to 5 μm, and PTFE number-average molecular weight is 1 × 10⁻⁶. 6 Up to 1×10 7 The shell is a perfluoropropylene oxide oligomer graft layer with a thickness of 30 to 100 nm, a number-average molecular weight of 2000 to 8000, and a glass transition temperature below -60°C (determined by differential scanning calorimetry). The shell end groups are perfluoromethyl-terminated. The aqueous dispersion of core-shell structured PTFE microparticles has a liquid solid content of 40% to 60%.

[0110] It should be noted that the perfluoropropylene oxide oligomer grafted shell of the core-shell structured PTFE microparticles serves two purposes: First, the flexible perfluoroether segments with a glass transition temperature below -60℃ form a flexible interface transition layer on the PTFE core surface. The thermodynamic compatibility between this layer and the low-glass transition temperature ternary copolymer fluororubber raw rubber matrix is ​​superior to that of bare PTFE particles without shell coating, which is beneficial for the entanglement and coating of PTFE particles by newly generated fluororubber segments during in-situ composite emulsion polymerization. Second, the perfluoropropylene oxide oligomer grafted shell end groups are perfluoromethyl-terminated and do not contain active end groups such as hydroxyl or carboxyl groups, thus avoiding preferential attack of end groups in a plasma environment, which would lead to degradation and detachment of the perfluoropropylene oxide oligomer grafted shell.

[0111] The timing and method of in-situ addition are the same as step 3 in Example 1, that is, when the cumulative polymerization yield reaches 25% to 67% of the final target yield, the aqueous dispersion of core-shell structured PTFE microparticles is added to the reactor through an independent feed line. Continuous dripping (using a peristaltic pump for uniform dripping at a rate of 0.5 to 3 hours, with the stirring speed maintained constant) or batch addition (3 to 5 batches, with an interval of 15 to 30 minutes between each batch, and stirring for 10 minutes after each batch) is used. The solid content of the PTFE core layer in the core-shell structured PTFE microparticles is 5% to 15% of the target mass of the fluororubber raw rubber, preferably 8% to 12%.

[0112] Furthermore, the aqueous dispersion of core-shell structured PTFE particles must be thoroughly shaken before addition, and it can only be transported by a peristaltic pump after confirming that there is no sedimentation or stratification of the aqueous dispersion of core-shell structured PTFE particles; the feed line is purged with high-purity nitrogen at least 3 times before being connected to the reactor, and nitrogen micro-positive pressure protection is maintained throughout the dripping process.

[0113] Step 4: Termination of polymerization reaction and post-treatment of raw rubber.

[0114] Once the cumulative polymerization yield reaches the target yield, monomer replenishment is stopped and the temperature is lowered to room temperature to allow the polymerization reaction to terminate naturally, and the gaseous monomer is recovered. The composite latex is transferred to a coagulation tank, and a 3% to 5% (mass fraction) magnesium sulfate aqueous solution (added at 5% to 10% of the latex volume, by volume ratio) is used as a coagulant. The mixture is stirred and coagulated at 60 to 70°C for 30 to 60 minutes to break down and flocculate the latex particles. The rubber particles are collected by filtration and washed repeatedly 5 to 8 times with deionized water (resistivity not less than 18.2 MΩ·cm), with each wash using 10 times the mass of the raw rubber, until the fluoride and sulfate ion content in the washing waste liquid is less than 5 ppm. The washed rubber particles are placed in a vacuum oven and dried at 60 to 80°C and an absolute pressure not exceeding 5 kPa for 12 to 24 hours until the moisture content is less than 0.1%, yielding a core-shell structured PTFE in-situ composite low glass transition temperature ternary copolymer fluororubber raw material.

[0115] It should be noted that the Mooney viscosity ML(1+4) of the obtained low glass transition temperature ternary copolymer fluororubber raw material is... 100℃ The content is 35 to 85 MU, the fluorine content is not less than 64 wt% (determined by elemental analysis), and the glass transition temperature is less than -40℃ (determined by differential scanning calorimetry, heating rate 10℃ / min).

[0116] Furthermore, this coagulation operation must be carried out under the condition that the pH of the system is not lower than 6. The coagulated waste liquid is discharged after wastewater treatment, and the operation procedure is the same as step 4 of Example 1.

[0117] Furthermore, the washing wastewater contains trace amounts of fluoride and sulfate ions, which must be collected and treated by a professional wastewater treatment facility. It must not be discharged directly without treatment. The operating procedure is the same as step 4 in Example 1.

[0118] Step 5: Pretreatment of core-shell structured PTFE microparticle solid powder and various functional components.

[0119] Core-shell structured PTFE microparticle solid powder (average particle size 2 to 5 μm, semiconductor grade, total metal ion content not exceeding 10 ppb) was placed in a clean glass tray and dried in a forced-air drying oven at 80 to 90°C for 2 to 3 hours. After drying, it was cooled to room temperature in a desiccator and then sealed for later use. The residual moisture content of the core-shell structured PTFE microparticle solid powder should be less than 500 ppm, as determined by the Karl Fischer method.

[0120] Meanwhile, accurately weigh the following three types of crosslinking and functional components according to the formulation ratio and premix them separately under light-protected conditions, with the operating temperature not exceeding 30℃ throughout the process:

[0121] Step 5.1: Accurately weigh the main crosslinking agent perfluorocyclobutane tetravinyl crosslinking unit (molecular weight 400 to 700, functionality 4, purity not less than 95%, hereinafter referred to as crosslinking unit F) and the co-crosslinking agent triallyl isocyanurate (TAIC, purity not less than 98%, functionality 3) in a mass ratio of crosslinking unit F to triallyl isocyanurate ranging from 1:0.8 to 1:1.5, mix them evenly in advance, and put them into a clean container and seal them for later use.

[0122] It should be noted that crosslinking unit F is a perfluorinated tetrafunctional crosslinking monomer. During vulcanization, its four vinyl end groups form crosslinking bonds with the iodine active sites on the ternary copolymer fluororubber raw material molecular chain at low glass transition temperature through free radical addition reactions. Since both the main chain and the end group connecting chains of crosslinking unit F are perfluorinated carbon bonds, no oxygen-containing byproducts (such as ketones, alcohols, etc.) are generated during the crosslinking reaction, thus avoiding the problem of oxygen-containing residues generated by the decomposition of bis(2,4-dichlorobenzoyl) peroxide in Example 1.

[0123] Step 5.2: Weigh the perfluoropolyether double-ended vinyl oligomer (number average molecular weight 800 to 2000, short-chain branched structure, pour point below -70°C, viscosity 20 to 80 cSt (25°C), main chain containing only perfluorocarbon bonds and perfluoroether bonds, end groups are vinyl groups, hereinafter referred to as compatibilizer G) separately and put it into a clean container for sealing and use.

[0124] It should be noted that the flexible perfluoroether backbone of compatibilizer G exhibits good thermodynamic compatibility with the low glass transition temperature ternary copolymer fluororubber raw material matrix. The vinyl groups at both ends of compatibilizer G participate in the crosslinking reaction during vulcanization, covalently embedding compatibilizer G into the crosslinking network. Compatibilizer G forms a chemical bridge between the perfluoropropylene oxide oligomer grafted shell layer of the core-shell structured PTFE microparticles and the continuous fluororubber phase, further enhancing the bonding strength at the interface between the two phases. The pour point of compatibilizer G is below -70°C, ensuring that it remains flexible even under cryogenic etching conditions.

[0125] Step 5.3: Weigh the perfluoropolyether ether ketone block copolymer (with alternating rigid ether ketone segments and flexible perfluoroether segments, number average molecular weight of 3000 to 8000, and glass transition temperature of 80 to 120°C, hereinafter referred to as toughening agent H) separately and put it into a clean container for sealing and use.

[0126] It should be noted that the rigid ether-ketone segments in toughening agent H provide rigid skeletal support under high-temperature conditions (150 to 200°C), inhibiting the thermal creep of the cross-linked network; the flexible perfluoroether segments are compatible with the fluororubber matrix, allowing toughening agent H to be uniformly dispersed in the cross-linked network. The introduction of toughening agent H improves the material's creep resistance at high temperatures without significantly reducing low-temperature elasticity, and enhances the compression set performance of the sealing ring under frequent thermal cycling conditions over a wide temperature range.

[0127] Furthermore, the four vinyl end groups of crosslinking unit F may undergo self-polymerization during mixing and storage. Premixing and weighing operations must be carried out below 30°C. The premixed crosslinking unit F and triallyl isocyanate mixture must be stored in the dark at 4 to 10°C and brought to room temperature before use to inhibit premature self-polymerization of the vinyl end groups.

[0128] Furthermore, both crosslinking unit F and triallyl isocyanurate are flammable organic materials, and weighing and premixing operations must be carried out in a fume hood, with operators wearing protective gloves and goggles; compatibilizer G is a low-viscosity fluorinated organic liquid, and spillage must be avoided during handling, with the operating area kept ventilated.

[0129] Step 6, preparation of compound rubber.

[0130] The mixing operation is carried out in an ISO Class 6 clean room. The gap between the open mill rolls is adjusted to 0.5 to 2 mm, the temperature of the front roll is controlled at 40 to 60°C, and the temperature of the rear roll is controlled at 35 to 55°C. The temperature deviation throughout the process does not exceed ±3°C.

[0131] 100 parts by weight of the low glass transition temperature ternary copolymer fluorinated rubber obtained in step 4, which is a core-shell structured PTFE in situ composite, are fed into a two-roll mill and subjected to a thin-pass roll wrapping operation 2 to 3 times to form a smooth, continuous, and pore-free uniform roll-wrapping rubber layer. After the rubber compound has stabilized on the rolls, 5 to 15 parts by weight of the core-shell structured PTFE microparticle solid powder pretreated in step 5 are added in 3 to 5 small batches. After each addition, the rubber is cut and turned 3 to 5 times along the left and right sides of the roll axis. The next batch is added only after the powder is completely wrapped into the rubber layer.

[0132] After the core-shell structured PTFE microparticle solid powder is uniformly mixed, the following functional components are added sequentially:

[0133] Step 6.1: Add the pre-mixed crosslinking unit F (2 to 5 parts by weight) and triallyl isocyanurate (2 to 5 parts by weight) from Step 5.1 in batches. After each batch is added, tap and re-roll the rubber 3 to 5 times, with the roller temperature not exceeding 60°C throughout the process. The mass ratio of crosslinking unit F to triallyl isocyanurate is 1:0.8 to 1:1.5.

[0134] Step 6.2: Add the compatibilizer G obtained in step 5.2 (3 to 8 parts by weight) in 2 to 3 batches, and tap and re-roll the rubber 3 to 5 times after each batch.

[0135] Step 6.3: Add toughening agent H obtained in step 5.3 (1 to 3 parts by weight) in 2 batches, and tap and refinish the rubber 3 to 5 times after each batch.

[0136] Step 6.4: Add 0.1 to 0.8 parts by weight of perfluoropolyether lubricant (perfluoromethyl end capped, viscosity 50 to 200 cSt (25°C), number average molecular weight 1000 to 4000), and mix evenly.

[0137] After all components have been added, the roller gap is narrowed to 0.5 to 1 mm and the compound is subjected to 5 to 8 thin passes for homogenization. After each thin pass, the rubber sheet is folded 90° and passed through the rollers again. Then the roller gap is increased to 2 to 4 mm to produce the compounded rubber sheet.

[0138] The compounded rubber sheets were left to stand in a clean environment at 23±2℃ and relative humidity not exceeding 55% for 8 to 24 hours to allow the functional components to fully diffuse and homogenize into the rubber compound, and to fully relax the internal stress generated during the mixing process. After standing, samples were taken to test the Mooney viscosity ML(1+4) of the compounded rubber. 100℃The acceptable range is 30 to 80 MU, and the Mooney viscosity is determined according to the ASTM D1646 standard method.

[0139] It should be noted that the total weight of each component in this embodiment is as follows: 100 parts by weight of core-shell structured PTFE in-situ composite low glass transition temperature ternary copolymer fluororubber raw material; 5 to 15 parts by weight of core-shell structured PTFE microparticle solid powder (added during the mixing stage); 2 to 5 parts by weight of crosslinking unit F; 2 to 5 parts by weight of triallyl isocyanurate; 3 to 8 parts by weight of compatibilizer G; 1 to 3 parts by weight of toughening agent H; and 0.1 to 0.8 parts by weight of perfluoropolyether lubricant. No fillers or additives containing metal components are introduced into the system, and all components are organic fluorinated compounds. The mass ratio of crosslinking unit F to triallyl isocyanurate is 1:0.8 to 1:1.5, and the mass ratio of compatibilizer G to toughening agent H is 3:1 to 8:3 (within the application range).

[0140] Furthermore, if the local temperature exceeds 60°C during the mixing process, there is a risk of copolymerization side reactions occurring between the dual-end vinyl groups of compatibilizer G and the vinyl end groups of crosslinking unit F, leading to local pre-crosslinking of the rubber compound. It is essential to strictly control the roller temperature to not exceed 60°C and add each component sequentially according to the order specified in steps 6.1 to 6.4 to avoid premature crosslinking caused by localized heating of crosslinking unit F and compatibilizer G under high concentration coexistence conditions.

[0141] Furthermore, the addition of core-shell structured PTFE microparticle solid powder may generate dust, and operators must wear dust masks and operate under normal ventilation conditions in the clean room.

[0142] Step 7, molding.

[0143] Based on step 7 of Example 1, the vulcanization temperature is adjusted to 170 to 190°C, the vulcanization pressure to 10 to 15 MPa, and the vulcanization time to 4 to 12 minutes (the vulcanization time is extended by approximately 1 minute for every 1 mm increase in cross-sectional diameter). The heating rate is controlled at 5 to 10°C / min, and the pressure fluctuation does not exceed ±0.5 MPa. The blank cutting ratio is 105% to 110%, the cutting is performed with clean ceramic cutting tools, the mold is cleaned and the release agent is applied, the flash is peeled off after mold opening and the appearance is inspected, and the product cross-sectional dimensional tolerance is ±0.05 mm. The cross-sectional dimensions are measured using a contact profilometer or an optical projector.

[0144] It should be noted that the vulcanization temperature in this embodiment is adjusted from 160 to 180°C in Example 1 to 170 to 190°C because the activation energy required for the free radical addition reaction of the four vinyl groups of crosslinking unit F with the iodine vulcanization point is slightly higher than that required for the crosslinking reaction initiated by bis(2,4-dichlorobenzoyl) peroxide at the bromine vulcanization point. Appropriately increasing the vulcanization temperature is beneficial for the full progress of the crosslinking reaction.

[0145] Furthermore, the vulcanizing machine operating area must be well ventilated, and operators must wear protective gloves to avoid contact with high-temperature molds and products that have just been demolded. The safety operation requirements are the same as step 7 of Example 1.

[0146] Step 8, second-stage post-vulcanization.

[0147] Arrange the primary vulcanized products obtained in step 7 neatly on a clean ceramic tray, with a product spacing of not less than 5 mm, and place them in a clean circulating hot air oven purified by a HEPA filter for post-vulcanization. Post-vulcanization is carried out in three stages: the first stage involves raising the temperature from room temperature to the post-vulcanization holding temperature at a rate of 2 to 3 °C / min; the second stage involves holding the temperature at 210 to 260 °C for 4 to 8 hours, preferably at 240 °C, and preferably for 6 hours; the third stage involves turning off the heating and allowing the oven to cool naturally to below 50 °C before removing the products.

[0148] It should be noted that the upper limit of the post-curing temperature was increased from 250°C in Example 1 to 260°C because the thermal stability of the cross-linking bonds in the iodine sulfide point cross-linking system is slightly lower than that in the bromine sulfide point cross-linking system. Increasing the post-curing temperature is beneficial to allow the residual iodine active sites to further participate in the cross-linking reaction and reduce the density of residual active end groups after post-curing.

[0149] After the two-stage vulcanization is completed, batch samples are extracted and subjected to compression set tests (200℃×70h) according to ASTM D395 B method. The acceptance criterion is that the compression set value is not higher than 12%. At the same time, thermogravimetric analysis (nitrogen atmosphere, heating rate 10℃ / min) is performed to confirm that the mass loss rate below 350℃ is less than 0.5%. The mass loss rate is calculated as the ratio of the mass change in the corresponding temperature range in the thermogravimetric curve to the initial sample mass.

[0150] Furthermore, the post-vulcanization oven must be well ventilated, and the post-vulcanization waste gas should be connected to a dedicated waste gas treatment device for treatment before being discharged. The operating procedure is the same as step 8 in Example 1.

[0151] Step 9: Plasma cleaning and ultrapure water washing.

[0152] The two-stage vulcanized product obtained in step 8 is placed in a single layer on the sample stage of the plasma cleaner. After the sealed chamber is evacuated to an absolute pressure not exceeding 10 Pa, a mixed gas with an Ar:O2 volume ratio of 3:1 (total gas flow rate of 50 to 100 sccm) is introduced to maintain the chamber pressure in the range of 5 to 30 Pa. The radio frequency power supply (frequency 13.56 MHz, power 200 W) is turned on to perform plasma cleaning for 5 minutes.

[0153] After plasma cleaning, ultrasonic-assisted washing was performed using ultrapure water (resistivity not less than 18.2 MΩ·cm, TOC not higher than 5 ppb) (ultrasonic frequency 40 kHz, power 100 W / L, water temperature 23±2℃). The washing was repeated three times, each time for 10 minutes, with fresh ultrapure water used each time. The waste liquid from the last wash was collected and analyzed by inductively coupled plasma mass spectrometry (ICP-MS) to determine the content of each metal ion. The concentration of each metal ion should be less than 0.1 ppb.

[0154] Furthermore, the surface condition of the product after plasma cleaning directly affects the subsequent ultrasonic cleaning effect. The combination of plasma cleaning power (200W) and processing time (5 minutes) requires a balance between effectively removing organic residues from the perfluoropropylene oxide oligomer-grafted shell layer of the core-shell PTFE microparticles and preventing significant degradation of this layer. Ultrasonic cleaning power of 100W / L at this frequency effectively removes microparticle residues through cavitation on the sealing ring surface without damaging the vulcanized crosslinked network or the interfacial bridging structure of the compatibilizer G, ensuring compatibility between separation effectiveness and product integrity.

[0155] Furthermore, the plasma cleaning exhaust gas contains CO2, H2O and possible fluorine-containing fragments, and the exhaust port of the plasma cleaner must be connected to a dedicated exhaust gas treatment device; the ultrasonic washing waste liquid contains trace amounts of organic residues and must be discharged after wastewater treatment, with the operating procedures being the same as step 9 in Example 1.

[0156] After passing the cleanliness test, the sealing rings are dried in a clean, circulating hot air environment at 40-50℃ for 30-60 minutes until no visible water marks remain on the surface. In an ISO Class 5 or higher cleanroom, each product is individually packaged into a verified, clean, sealed polyethylene bag and heat-sealed. An anti-static bag is then placed over the bag to obtain the finished semiconductor-grade fluororubber sealing rings. Finally, batch samples of the products are subjected to Fourier transform infrared spectroscopy (FTIR) and elemental analysis to confirm that the product structure and composition meet the requirements.

[0157] This invention introduces an aqueous PTFE dispersion during the emulsion polymerization process, at a specific window period when the cumulative polymerization yield reaches 25% to 67% of the target yield. This allows newly generated fluororubber segments to continuously grow and extend on and around the PTFE particles as the polymerization reaction continues, forming a physical entanglement structure of fluororubber molecular chains around the PTFE particles. This alters the interfacial state between the PTFE particles and the fluororubber matrix. The PTFE particles are uniformly embedded in the continuous fluororubber phase, with interpenetrating molecular chain entanglement layers at the interface. Compared to traditional physical blending methods, the anchoring force of the PTFE particles in the fluororubber matrix is ​​enhanced. Under plasma etching conditions, the PTFE particles, coated with fluororubber segments, are difficult to detach from the matrix, thus suppressing the "surface whitening" phenomenon caused by the migration and enrichment of PTFE particles to the product surface in traditional physical blending methods, and controlling the amount of particle precipitation.

[0158] The composition system of this invention consists entirely of organic fluorine compounds and contains no fillers or additives with metal ions, thus reducing the possibility of metal ion precipitation from the source of the formulation. The post-treatment process, combining plasma cleaning with ultrasonic washing with ultrapure water, further removes trace organic residues and particulate contamination from the product surface.

[0159] In Example 2, by introducing a low glass transition temperature ternary copolymer fluororubber raw material system, the glass transition temperature is lowered to below -40°C, allowing the sealing ring to maintain its elastic resilience even under cryogenic etching conditions at -60°C. Perfluorohexylethyl triiodide is used instead of perfluoro-2-bromoethyl vinyl ether. Since the CI bond dissociation energy is lower than the C-Br bond dissociation energy, the density of residual active end groups after vulcanization is lower, reducing the probability of preferential attack on active end groups under plasma conditions. The perfluorocarbon bond structure of the crosslinking unit F prevents the generation of oxygen-containing byproducts during the crosslinking reaction, avoiding the problem of accelerated surface degradation of oxygen-containing sites under plasma conditions. The perfluoropropylene oxide oligomer grafted shell layer of the core-shell structured PTFE microparticles forms a flexible interface transition layer between the PTFE core layer and the fluororubber matrix. The dual-terminal vinyl groups of the compatibilizer G covalently embed into the crosslinking network during vulcanization, forming a chemical bridge. The synergistic effect of these two components further enhances the interfacial bonding strength between the two phases. The rigid ether ketone segments in toughening agent H provide rigid skeletal support under high-temperature conditions, inhibiting the thermal creep of the cross-linked network and improving the compression set performance of the sealing ring under frequent thermal cycling conditions over a wide temperature range.

[0160] The two-stage post-vulcanization process of this invention allows residual low-molecular-weight volatiles to continuously escape, further improving the cross-linking network. This suppresses the permanent compression deformation of the sealing ring in the high-temperature process environment, thus contributing to the long-term stability of the sealing performance. The entire preparation process, from emulsion polymerization, mixing, compression molding vulcanization to clean post-treatment, has clearly defined parameters and can be implemented on existing industrial equipment.

[0161] Implementation Example 1

[0162] Step 1: Add 30 L of deionized water (conductivity not higher than 1 μS / cm) to a 50 L stainless steel high-pressure reactor. Then add 3000 ppm of perfluoropolyether carboxylate ammonium salt (number average molecular weight 500, acid value 25 mgKOH / g, critical micelle concentration 800 ppm), diammonium hydrogen phosphate (to adjust the pH of the system to 6.5), and 500 ppm of ammonium persulfate in sequence. Stir at 200 rpm. After all components are dissolved evenly, repeat the vacuuming and nitrogen purging cycle 3 times to make the residual oxygen content in the reactor lower than 10 ppm.

[0163] Step 2: TFE and PMVE are introduced into the reactor via a gas mass flow meter, with an initial molar ratio of TFE:PMVE = 55:45. Simultaneously, 0.1 mol% of perfluoro-2-bromoethyl vinyl ether (based on the total molar amount of TFE and PMVE) is injected via a metering pump. The initial pressure inside the reactor is raised to 0.5 MPa, and the temperature inside the reactor is raised to 20 °C using a constant-temperature water bath to start the emulsion polymerization reaction. The monomer consumption is monitored in real time using a pressure sensor and a flow meter, and the mixed monomer of TFE and PMVE is continuously replenished to maintain a constant pressure.

[0164] Step 3: When the cumulative polymerization yield reaches 25% of the final target yield, feed the PTFE aqueous dispersion (40% solids content, PTFE particle average size 1 μm, PDI not greater than 0.3, PTFE number average molecular weight 1×10⁻⁶) through an independent feed line. 6 The PTFE was continuously added to the reactor using a peristaltic pump over a period of 0.5 hours, while maintaining a constant stirring speed. The added PTFE solid content was 2% of the target mass of the fluororubber raw material.

[0165] Step 4: After the cumulative polymerization yield reaches the target yield, monomer replenishment is stopped and the mixture is cooled to room temperature. Gaseous monomers are recovered, and the composite latex is transferred to a coagulation tank. A 3% (mass fraction) magnesium sulfate aqueous solution (added at 5% of the latex volume, volume ratio) is added and stirred at 60 °C for 30 min to coagulate the latex particles through demulsification and flocculation. The rubber particles are collected by filtration and washed five times with deionized water (resistivity not less than 18.2 MΩ·cm), with each wash using 10 times the mass of the raw rubber, until the fluoride and sulfate ion content in the washing waste liquid is less than 5 ppm. The washed rubber particles are placed in a vacuum oven and dried at 60 °C and an absolute pressure not exceeding 5 kPa for 12 h until the moisture content is less than 0.1%, yielding PTFE in-situ composite fluororubber raw rubber. The Mooney viscosity of the obtained raw rubber is ML(1+4). 100℃ It has a strength of 40 MU and a glass transition temperature of -20 ℃.

[0166] Step 5: Mix PTFE micro powder (average particle size 1 μm, semiconductor grade, number average molecular weight 1×10⁻⁶) with PTFE micro powder.6 The total metal ion content (not exceeding 10 ppb) was dried in an 80 ℃ forced-air drying oven for 2 h, cooled to room temperature, and sealed for later use. The residual moisture content was less than 500 ppm. Bis(2,4-dichlorobenzoyl) peroxide and triallyl isocyanurate (TAIC) were weighed at a mass ratio of 1:2, premixed evenly in the dark below 30 ℃, placed in a clean container, sealed, and refrigerated at 4 to 10 ℃ for later use.

[0167] Step 6: The mixing operation is carried out in an ISO Class 6 clean room. The roll gap of the open mill is adjusted to 0.5 mm, the front roll temperature is 40 ℃, and the rear roll temperature is 35 ℃, with a temperature deviation not exceeding ±3 ℃. 100 parts by weight of the PTFE in-situ composite fluororubber raw rubber obtained in Step 4 is added to the open mill and thinly wrapped around the rolls twice to form a uniform roll-wrapped rubber layer. 2 parts by weight of the PTFE micro powder pretreated in Step 5 is added in 3 batches. After each addition, the rubber is cut and folded 3 times along the left and right sides of the roll axis. The next batch is added only after the powder is completely wrapped into the rubber layer. At this point, the total PTFE content is 4 parts by weight (2 parts by weight of the in-situ composite part, accounting for 50% of the total PTFE; 2 parts by weight are added during the mixing stage, accounting for 50%). Subsequently, the mixture of 0.5 parts by weight of the premixed bis(2,4-dichlorobenzoyl) peroxide and 1 part by weight of TAIC from Step 5 is added in batches. After each batch is added, the rubber is cut and folded 3 times, with the roll temperature not exceeding 60 ℃ throughout the process. Continue adding 0.1 parts by weight of perfluoropolyether lubricant (viscosity 50 cSt (25 ℃), number average molecular weight 1000, perfluoromethyl-terminated) and mix thoroughly. After all components have been added, narrow the roller gap to 0.5 mm and perform 5 thin passes for homogenization. After each thin pass, fold the film 90° and pass it through the rollers again. Then, increase the roller gap to 2 mm and exit the sheet to obtain the compounded rubber sheet. The compounded rubber sheet is then left to stand in a clean environment at 23±2 ℃ and relative humidity not exceeding 55% for 8 hours. After standing, the Mooney viscosity of the compounded rubber is ML(1+4). 100℃ It is 30 MU.

[0168] Step 7: Cut cylindrical preform blanks to 105% of the theoretical mass of the sealing ring using clean ceramic cutters. Place the blank in the center of a mold cavity that has been ultrasonically cleaned with ultrapure water and coated with a perfluoropolyether release agent. After closing the mold, push it into a flat vulcanizing machine. Vulcanization temperature: 160 ℃; vulcanization pressure: 10 MPa; vulcanization time: 3 min; heating rate: 5 ℃ / min; pressure fluctuation: no more than ±0.5 MPa. After demolding, remove the flash, inspect the appearance, and ensure the cross-sectional dimensional tolerance meets the requirement of ±0.05 mm. Allow to cool naturally to room temperature.

[0169] Step 8: Arrange the vulcanized products on a clean ceramic tray (with a spacing of no less than 5 mm between products), and place them in a clean circulating hot air oven purified by a HEPA filter for vulcanization. Heat to 200 ℃ at a rate of 2 ℃ / min, hold for 4 hours, turn off the heating and allow to cool naturally to below 50 ℃ before removing.

[0170] Step 9: Lay the two-stage vulcanized sealing ring in a single layer on the sample stage of the plasma cleaner. After evacuating the sealing chamber to an absolute pressure not exceeding 10 Pa, introduce an Ar:O2 = 3:1 (volume ratio) mixed gas at a total flow rate of 50 sccm, maintaining a chamber pressure of 5 Pa. Turn on the RF power supply (13.56 MHz, 200 W) and clean for 5 min. After cleaning, use ultrapure water (resistivity not less than 18.2 MΩ·cm, TOC not more than 5 ppb) for ultrasonic-assisted washing three times (40 kHz, 100 W / L, 23±2 ℃, 10 min each time, replacing with fresh ultrapure water each time). ICP-MS analysis shows that the concentration of each metal ion in the waste liquid from the last washing is less than 0.1 ppb. After passing the cleanliness test, dry in a clean circulating hot air environment at 40 ℃ for 30 min, and then heat-seal and package each piece in an ISO Class 5 clean room to obtain the finished semiconductor-grade fluororubber sealing ring.

[0171] Implementation Example 2

[0172] Step 1: Stir at 400 rpm, add 5000 ppm of perfluoropolyether ammonium carboxylate (number average molecular weight 2000, acid value 60 mg KOH / g, critical micelle concentration 1500 ppm), adjust the pH of the system to 7.5, add 2000 ppm of ammonium persulfate, and perform the remaining operations as in Step 1 of Example 1.

[0173] Step 2: Initial molar ratio of TFE to PMVE = 65:35, 0.5 mol% of perfluoro-2-bromoethyl vinyl ether (based on the total molar amount of TFE and PMVE), initial pressure in the reactor 0.8 MPa, polymerization temperature 80 ℃, and other operations are the same as in Step 2 of Example 1.

[0174] Step 3: When the cumulative polymerization yield reaches 67% of the final target yield, add the PTFE aqueous dispersion (60% solid content, PTFE particle average size 5 μm, PDI not greater than 0.3, PTFE number average molecular weight 1×10⁻⁶). 7 The PTFE was added to the reactor in 5 batches, with a 30-minute interval between each batch, and stirred for 10 minutes after each batch was added. The PTFE solid content added was 14% of the target mass of the fluororubber raw rubber.

[0175] Step 4: A 5% (mass fraction) magnesium sulfate aqueous solution (added at 10% of the latex volume, volume ratio) was stirred and coagulated at 70 °C for 60 min. The rubber particles were collected by filtration, washed 8 times, and dried at 80 °C and an absolute pressure not exceeding 5 kPa for 24 h to obtain PTFE in-situ composite fluororubber raw rubber. The Mooney viscosity (ML(1+4)) of the obtained raw rubber was... 100℃ It has a strength of 90 MU and a glass transition temperature of -10 ℃.

[0176] Step 5: PTFE micro powder (average particle size 5 μm, number average molecular weight 1×10⁻⁶) 7 Dry at 90 °C for 3 h; premix bis(2,4-dichlorobenzoyl) peroxide and TAIC at a mass ratio of 1:2.5 for later use, and perform the remaining operations as in step 5 of Example 1.

[0177] Step 6: Adjust the open mill roll gap to 2 mm, front roll temperature to 60 ℃, and rear roll temperature to 55 ℃. Add 100 parts by weight of the raw rubber obtained in Step 4 to the open mill, and pass it through the rolls 3 times. Add 12 parts by weight of PTFE micro powder in 5 batches, cutting and refining the rubber 5 times on each side after each addition. At this point, the total PTFE content is 20 parts by weight (8 parts by weight of the in-situ composite portion, accounting for 40% of the total PTFE; 12 parts by weight are added during the mixing stage, accounting for 60%). Then add 3 parts by weight of bis(2,4-dichlorobenzoyl) peroxide and 5 parts by weight of TAIC premix, cutting and refining the rubber 5 times after each batch. Add 2 parts by weight of perfluoropolyether lubricant (viscosity 200 cSt (25 ℃), number average molecular weight 4000), and mix thoroughly. Narrow the roll gap to 1 mm and pass it through the rolls 8 times for homogenization, then increase the roll gap to 4 mm for sheeting. After the compounded rubber sheets were left to stand for 24 hours, the Mooney viscosity of the compounded rubber was measured in ML(1+4). 100℃ It is 80 MU.

[0178] Step 7: Cut the blank to 110% of the theoretical mass of the sealing ring, vulcanize at 180 ℃, vulcanize at 15 MPa, vulcanize for 10 min, and at a heating rate of 10 ℃ / min. The remaining operations are the same as in Step 7 of Example 1.

[0179] Step 8: Increase the temperature to 250 ℃ at a rate of 3 ℃ / min, hold for 8 h, and allow to cool naturally to below 50 ℃ before removing. The remaining operations are the same as in Step 8 of Example 1.

[0180] Step 9: The total gas flow rate for plasma cleaning is 100 sccm, the chamber pressure is 30 Pa, and the other parameters are the same as in Step 9 of Example 1. After cleaning, the product is washed with ultrapure water, and after passing the cleanliness test, it is dried at 50 ℃ for 60 min, packaged, and the semiconductor-grade fluororubber sealing ring is obtained.

[0181] Implementation Example 3

[0182] Step 1: Stir at 300 rpm, add 4000 ppm of perfluoropolyether ammonium carboxylate (number average molecular weight 1250, acid value 40 mg KOH / g, critical micelle concentration 1150 ppm), adjust the pH of the system to 7.0, add 1000 ppm of ammonium persulfate, and perform the remaining operations as in Step 1 of Example 1.

[0183] Step 2: Initial molar ratio of TFE to PMVE = 60:40, 0.3 mol% of perfluoro-2-bromoethyl vinyl ether (based on the total molar amount of TFE and PMVE), initial pressure in the reactor 0.65 MPa, polymerization temperature 50 ℃, and other operations are the same as in Step 2 of Example 1.

[0184] Step 3: When the cumulative polymerization yield reaches 46% of the final target yield, add the PTFE aqueous dispersion (50% solid content, PTFE particle average size 3 μm, PDI not greater than 0.3, PTFE number average molecular weight 5 × 10⁻⁶). 6 The PTFE is introduced via continuous dripping using a peristaltic pump over a period of 1.5 hours. The added PTFE solid content is 8% of the target mass of the fluororubber raw rubber.

[0185] Step 4: The rubber particles were coagulated by stirring at 65°C for 45 min with a 4% (mass fraction) magnesium sulfate aqueous solution (added at 7.5% of the latex volume, volume ratio). The rubber particles were collected by filtration, washed 6 times, and dried at 70°C and an absolute pressure not exceeding 5 kPa for 18 h to obtain PTFE in-situ composite fluororubber raw rubber. The Mooney viscosity (ML(1+4)) of the obtained raw rubber was... 100℃ It has a strength of 65 MU and a glass transition temperature of -15 ℃.

[0186] Step 5: PTFE micro powder (average particle size 3 μm, number average molecular weight 5 × 10⁻⁶) 6 Dry at 85 °C for 2.5 h; premix bis(2,4-dichlorobenzoyl) peroxide with TAIC at a mass ratio of 1:2.0 for later use, and perform the remaining operations as in step 5 of Example 1.

[0187] Step 6: Adjust the roll gap of the open mill to 1 mm, with the front roll temperature at 50 ℃ and the rear roll temperature at 45 ℃. Add 100 parts by weight of the raw rubber obtained in Step 4 to the open mill, and pass it through the rolls twice. Add 5 parts by weight of PTFE micro powder in 4 batches, cutting and refining the rubber 4 times on each side after each addition. At this point, the total PTFE content is 13 parts by weight (8 parts by weight of the in-situ composite portion, accounting for 62% of the total PTFE; 5 parts by weight were added during the mixing stage, accounting for 38%). Then add 1 part by weight of bis(2,4-dichlorobenzoyl) peroxide and 2 parts by weight of TAIC premix, cutting and refining the rubber 4 times after each batch. Add 1 part by weight of perfluoropolyether lubricant (viscosity 100 cSt (25 ℃), number average molecular weight 2000), and mix thoroughly. Narrow the roll gap to 0.5 mm and perform 6 thin passes for homogenization, then increase the roll gap to 3 mm for sheeting. After the compounded rubber sheets were left to stand for 16 hours, the Mooney viscosity of the compounded rubber was measured in ML(1+4). 100℃ It is 55 MU.

[0188] Step 7: Cut the blank to 107% of the theoretical mass of the sealing ring, vulcanize at 170 ℃, vulcanize at 12 MPa, vulcanize for 6 min, and at a heating rate of 7 ℃ / min. The remaining operations are the same as in Step 7 of Example 1.

[0189] Step 8: Increase the temperature to 230 ℃ at a rate of 2 ℃ / min, hold for 6 h, and allow to cool naturally to below 50 ℃ before removing. The remaining operations are the same as in Step 8 of Example 1.

[0190] Step 9: The total gas flow rate for plasma cleaning is 75 sccm, the chamber pressure is 17 Pa, and the other parameters are the same as in Step 9 of Example 1. After cleaning, the product is washed with ultrapure water, and after passing the cleanliness test, it is dried at 45 ℃ for 45 min, packaged, and the semiconductor-grade fluororubber sealing ring is obtained.

[0191] Implementation Example 4

[0192] Step 1: The operation is the same as in Step 1 of Example 1, with a stirring speed of 200 rpm, 3000 ppm of perfluoropolyether carboxylate ammonium salt (number average molecular weight 500, acid value 25 mgKOH / g, critical micelle concentration 800 ppm), the pH of the system is adjusted to 6.5, and 500 ppm of ammonium persulfate.

[0193] Step 2: TFE, PMVE, and PPVE are introduced into the reactor via a gas mass flow meter. The molar ratio of the three monomers is TFE:PMVE:PPVE = 45:35:20. Simultaneously, 0.3 mol% of perfluorohexylethyl triiodide (based on the total molar amount of TFE, PMVE, and PPVE) is injected via a metering pump. The initial pressure inside the reactor is 0.5 MPa, and the polymerization temperature is 20 °C. During the reaction, the replenishment flow rate of each monomer is independently adjusted via three mass flow meters to maintain a constant pressure.

[0194] Step 3: When the cumulative polymerization yield reaches 25% of the final target yield, the aqueous dispersion of core-shell structured PTFE microparticles (40% solid content, average core particle size of 2 μm, shell thickness of 30 nm, and shell number-average molecular weight of 2000) is continuously added via a peristaltic pump through an independent feed line over a period of 0.5 h. The amount of PTFE core solid content added to the core-shell structured PTFE microparticles is 5% of the target mass of the fluororubber raw rubber.

[0195] Step 4: The procedure is the same as in Step 4 of Example 1. A 3% (mass fraction) magnesium sulfate aqueous solution (added at 5% of the latex volume, volume ratio) is stirred and coagulated at 60 °C for 30 min. The mixture is washed 5 times and dried at 60 °C for 12 h to obtain a core-shell structured PTFE in-situ composite ternary copolymer fluororubber with a low glass transition temperature. The Mooney viscosity of the obtained raw rubber is ML(1+4). 100℃ It has a strength of 35 MU and a glass transition temperature below -40 °C.

[0196] Step 5: Dry the core-shell structured PTFE microparticle solid powder (average particle size 2 μm, semiconductor grade, total metal ion content not exceeding 10 ppb) in an 80 ℃ forced-air drying oven for 2 h, cool to room temperature, and seal for later use. The residual moisture content should be less than 500 ppm. Weigh the main crosslinking agent crosslinking unit F (number average molecular weight 400, functionality 4, purity not less than 95%) and TAIC at a mass ratio of 1:1, premix them evenly in the dark below 30 ℃, and store them in a clean container at 4 to 10 ℃ for later use (Step 5.1). Weigh the compatibilizer G (number average molecular weight 800, viscosity 20 cSt (25 ℃), pour point below -70 ℃, double-ended vinyl end capping) separately and store it in a clean container for later use (Step 5.2). Weigh the toughening agent H (number average molecular weight 3000, glass transition temperature 80 ℃) separately and store it in a clean container for later use (Step 5.3).

[0197] Step 6: The mixing operation is carried out in an ISO Class 6 clean room. The roll gap of the open mill is adjusted to 0.5 mm, the front roll temperature is 40 ℃, and the rear roll temperature is 35 ℃, with a temperature deviation not exceeding ±3 ℃. 100 parts by weight of the low glass transition temperature ternary copolymer fluororubber raw material obtained in Step 4 is added to the open mill and thinly rolled twice until a uniform roll-wrapping rubber layer is formed. 5 parts by weight of the pretreated core-shell structure PTFE microparticle solid powder from Step 5 is added in 3 portions, and after each addition, the rubber is cut and refracted 3 times on each side. Add the following ingredients sequentially according to steps 6.1 to 6.4: 2 parts by weight of the premix of crosslinking unit F and 2 parts by weight of TAIC (step 6.1); 3 parts by weight of compatibilizer G, added in two batches (step 6.2); 1 part by weight of toughening agent H, added in two batches (step 6.3); and 0.1 parts by weight of perfluoropolyether lubricant (viscosity 50 cSt (25 ℃), number average molecular weight 1000) (step 6.4). After each batch is added, cut and re-mix the rubber three times, ensuring the roller temperature does not exceed 60 ℃ throughout the process. Narrow the roller gap to 0.5 mm and perform five thin pass homogenizations, then increase the roller gap to 2 mm before sheeting. Let the mixed rubber sheet rest for 8 hours. After resting, the Mooney viscosity ML(1+4) of the mixed rubber is... 100℃ It is 32 MU.

[0198] Step 7: Cut the blank to 105% of the theoretical mass of the sealing ring, vulcanize at 170 ℃, vulcanize at 10 MPa, vulcanize for 4 min, and at a heating rate of 5 ℃ / min. The remaining operations are the same as in Step 7 of Example 1.

[0199] Step 8: Increase the temperature to 210 ℃ at a rate of 2 ℃ / min, hold for 4 h, and allow to cool naturally to below 50 ℃ before removing. The remaining operations are the same as in Step 8 of Example 1.

[0200] Step 9: The total gas flow rate for plasma cleaning is 50 sccm, the chamber pressure is 5 Pa, and the other parameters are the same as in Step 9 of Example 1. After cleaning, the product is washed with ultrapure water, and after passing the cleanliness test, it is dried at 40 ℃ for 30 min, packaged, and the semiconductor-grade fluororubber sealing ring is obtained.

[0201] Implementation Example 5

[0202] Step 1: The operation is the same as Step 1 in Example 2. The stirring speed is 400 rpm, the perfluoropolyether carboxylate ammonium salt is 5000 ppm (number average molecular weight 2000, acid value 60 mgKOH / g, critical micelle concentration 1500 ppm), the pH of the system is adjusted to 7.5, and the ammonium persulfate is 2000 ppm.

[0203] Step 2: The molar ratio of the three monomers TFE:PMVE:PPVE = 55:30:15, the perfluorohexyl ethyl triiodide is 1.2 mol%, the initial pressure in the reactor is 0.8 MPa, the polymerization temperature is 80 ℃, and the rest of the operation is the same as Step 2 of Example 4.

[0204] Step 3: When the cumulative polymerization yield reaches 67% of the final target yield, add the aqueous dispersion of core-shell structured PTFE microparticles (60% solid content, average core particle size of 5 μm, shell thickness of 100 nm, and shell number-average molecular weight of 8000) to the reactor in 5 batches, with an interval of 30 min between each batch, and stirring for 10 min after each batch addition. The amount of PTFE core layer solid content added to the core-shell structured PTFE microparticles is 15% of the target mass of the fluororubber raw rubber.

[0205] Step 4: A 5% (mass fraction) magnesium sulfate aqueous solution (added at 10% of the latex volume, volume ratio) was stirred and coagulated at 70 °C for 60 min. The mixture was washed 8 times and dried at 80 °C for 24 h to obtain a core-shell structured PTFE in-situ composite ternary copolymer fluororubber with a low glass transition temperature. The Mooney viscosity of the obtained raw rubber was ML(1+4). 100℃ It has a strength of 85 MU and a glass transition temperature below -40 °C.

[0206] Step 5: Dry the core-shell structured PTFE microparticle solid powder (average particle size 5 μm) at 90 ℃ for 3 h; premix the crosslinking unit F (number average molecular weight 700) with TAIC at a mass ratio of 1:1.5; weigh the compatibilizer G (number average molecular weight 2000, viscosity 80 cSt (25℃)) and toughening agent H (number average molecular weight 8000, glass transition temperature 120 ℃) ​​separately and seal them for later use. The remaining operations are the same as step 5 of Example 4.

[0207] Step 6: Adjust the open mill roll gap to 2 mm, front roll temperature 60 ℃, rear roll temperature 55 ℃. Add 100 parts by weight of the raw rubber obtained in Step 4 to the open mill, and perform a thin pass through the rolls 3 times. Add 15 parts by weight of core-shell structured PTFE microparticle solid powder in 5 batches, and after each addition, cut and re-roll the rubber 5 times on each side. Add the following in the order of Steps 6.1 to 6.4: a premix of 5 parts by weight of crosslinking unit F and 5 parts by weight of TAIC, 8 parts by weight of compatibilizer G in 3 batches, 3 parts by weight of toughening agent H in 2 batches, and 0.8 parts by weight of perfluoropolyether lubricant (viscosity 200 cSt (25 ℃), number average molecular weight 4000), cutting and re-rolling the rubber 5 times after each batch, ensuring the roll temperature does not exceed 60 ℃ throughout the process. Narrow the roll gap to 1 mm and perform 8 thin pass homogenization cycles, then increase the roll gap to 4 mm for sheet production. After the compounded rubber sheets were left to stand for 24 hours, the Mooney viscosity of the compounded rubber was measured in ML(1+4). 100℃ It is 78 MU.

[0208] Step 7: Cut the blank to 110% of the theoretical mass of the sealing ring, vulcanize at 190 ℃, vulcanize at 15 MPa, vulcanize for 12 min, and at a heating rate of 10 ℃ / min. The remaining operations are the same as in Step 7 of Example 1.

[0209] Step 8: Increase the temperature to 260 ℃ at a rate of 3 ℃ / min, hold for 8 h, and allow to cool naturally to below 50 ℃ before removing. The remaining operations are the same as in Step 8 of Example 1.

[0210] Step 9: The total gas flow rate for plasma cleaning is 100 sccm, the chamber pressure is 30 Pa, and the other parameters are the same as in Step 9 of Example 1. After cleaning, the product is washed with ultrapure water, and after passing the cleanliness test, it is dried at 50 ℃ for 60 min, packaged, and the semiconductor-grade fluororubber sealing ring is obtained.

[0211] Implementation Example 6

[0212] Step 1: Stir at 300 rpm, add 4000 ppm of perfluoropolyether ammonium carboxylate (number average molecular weight 1250, acid value 40 mg KOH / g, critical micelle concentration 1150 ppm), adjust the pH of the system to 7.0, add 1500 ppm of ammonium persulfate, and perform the remaining operations as in Step 1 of Example 4.

[0213] Step 2: The molar ratio of the three monomers TFE:PMVE:PPVE = 50:32:18, the perfluorohexyl ethyl triiodide is 0.5 mol%, the initial pressure in the reactor is 0.65 MPa, the polymerization temperature is 50 ℃, and the remaining operations are the same as in Step 2 of Example 4.

[0214] Step 3: When the cumulative polymerization yield reaches 50% of the final target yield, introduce the aqueous dispersion of core-shell structured PTFE microparticles (50% solid content, average core particle size 3.5 μm, shell thickness 65 nm, shell number-average molecular weight 5000) continuously by peristaltic pump over a period of 1.5 h. The amount of PTFE core layer solids added to the core-shell structured PTFE microparticles is 10% of the target mass of the fluororubber raw rubber.

[0215] Step 4: A 4% (mass fraction) magnesium sulfate aqueous solution (added at 7.5% of the latex volume, volume ratio) was stirred and coagulated at 65℃ for 45 min. The mixture was washed 6 times and dried at 70℃ for 18 h to obtain a core-shell structured PTFE in-situ composite ternary copolymer fluororubber with a low glass transition temperature. The Mooney viscosity of the obtained raw rubber was ML(1+4). 100℃ It has a strength of 60 MU and a glass transition temperature below -40 °C.

[0216] Step 5: Dry the core-shell structured PTFE microparticle solid powder (average particle size 3.5 μm) at 85 °C for 2.5 h; premix the crosslinking unit F (number average molecular weight 550) with TAIC at a mass ratio of 1:1.15; weigh the compatibilizer G (number average molecular weight 1400, viscosity 50 cSt (25 °C)) and toughening agent H (number average molecular weight 5500, glass transition temperature 100 °C) separately and seal them for later use. The remaining operations are the same as step 5 of Example 4.

[0217] Step 6: Adjust the roll gap of the open mill to 1 mm, with the front roll temperature at 50 ℃ and the rear roll temperature at 45 ℃. Add 100 parts by weight of the raw rubber obtained in Step 4 to the open mill, performing a thin pass through the rolls 3 times. Add 10 parts by weight of core-shell structured PTFE microparticle solid powder in 4 batches, cutting and refining the rubber 4 times on each side after each addition. Add the following in the order of Steps 6.1 to 6.4: a premix of 3.5 parts by weight of crosslinking unit F and 3.5 parts by weight of TAIC, 5.5 parts by weight of compatibilizer G in 3 batches, 2 parts by weight of toughening agent H in 2 batches, and 0.45 parts by weight of perfluoropolyether lubricant (viscosity 100 cSt (25 ℃), number average molecular weight 2000), cutting and refining the rubber 4 times after each batch, ensuring the roll temperature does not exceed 60 ℃ throughout the process. Narrow the roll gap to 1 mm and perform 6 thin passes for homogenization, then increase the roll gap to 3 mm for sheet production. After the compounded rubber sheets were left to stand for 16 hours, the Mooney viscosity of the compounded rubber was measured in ML(1+4). 100℃ It is 58 MU.

[0218] Step 7: Cut the blank to 107% of the theoretical mass of the sealing ring, vulcanize at 180 ℃, vulcanize at 12 MPa, vulcanize for 8 min, and at a heating rate of 7 ℃ / min. The remaining operations are the same as in Step 7 of Example 1.

[0219] Step 8: Heat to 240 ℃ at a rate of 2.5 ℃ / min, hold for 6 h, and allow to cool naturally to below 50 ℃ before removing. The remaining operations are the same as in Step 8 of Example 1.

[0220] Step 9: The total gas flow rate for plasma cleaning is 75 sccm, the chamber pressure is 17 Pa, and the other parameters are the same as in Step 9 of Example 1. After cleaning, the product is washed with ultrapure water, and after passing the cleanliness test, it is dried at 45 ℃ for 45 min, packaged, and the semiconductor-grade fluororubber sealing ring is obtained.

[0221] Comparative Example 1

[0222] The operating parameters for steps 1 to 9 are exactly the same as in Implementation Example 3, except that the timing of the in-situ addition of the PTFE aqueous dispersion in step 3 is advanced from 46% of the cumulative polymerization yield to 15%. That is, when the cumulative polymerization yield reaches only 15%, the PTFE aqueous dispersion (50% solid content, PTFE particle average size 3 μm, PDI not greater than 0.3, PTFE number average molecular weight 5 × 10⁻⁶) is added through an independent feed line. 6 The PTFE was introduced via continuous dripping using a peristaltic pump over a period of 1.5 hours. The added PTFE solid content was 8% of the target mass of the fluororubber raw rubber, and the remaining parameters were consistent with those in Example 3. At this point, the fluororubber molecular chains in the system were still short, and the chain entanglement network had not yet formed. The physical coating degree of the PTFE particles was significantly lower than that when added within the window period.

[0223] Comparative Example 2

[0224] The operating parameters for steps 1, 2, 4 (coagulation, washing, and drying operations) and steps 5 through 9 are exactly the same as in Example 3, except that the in-situ addition of the PTFE aqueous dispersion in step 3 is omitted (no PTFE aqueous dispersion is introduced into the polymerization reaction system). The resulting fluororubber raw rubber after polymerization does not contain in-situ composite PTFE. In step 6, during the mixing stage, all PTFE (total amount 13 parts by weight, the same as the total amount of PTFE in Example 3, all semiconductor-grade PTFE micropowder, average particle size 3 μm, number average molecular weight 5 × 10⁻⁶) is added. 6 The fluororubber raw material was physically blended in a single step, with all other steps and parameters remaining consistent with Example 3. This comparative example represents a conventional physical blending process and is used to compare it with the in-situ compounding process of Example 3.

[0225] Comparative Example 3

[0226] The operating parameters for steps 1 to 9 are exactly the same as in Implementation Example 3, except that the timing of the in-situ addition of the PTFE aqueous dispersion in step 3 is delayed from 46% to 75% of the cumulative polymerization yield reaching the final target yield. That is, when the cumulative polymerization yield has reached 75%, the PTFE aqueous dispersion (50% solid content, PTFE particle average particle size 3 μm, PDI not greater than 0.3, PTFE number average molecular weight 5 × 10⁻⁶) is added through an independent feed line. 6 The PTFE was introduced via continuous dripping using a peristaltic pump over a period of 1.5 hours. The added PTFE solids content was 8% of the target mass of the fluororubber raw rubber, and the remaining parameters were consistent with those in Example 3. At this point, the solids content of the system was already high, the latex particle concentration was large, and the system viscosity increased significantly. The newly added PTFE particles were difficult to penetrate evenly into the gaps between the latex particles, and the degree of physical entanglement was significantly lower than that when added within the window period.

[0227] experiment:

[0228] Experiment 1 (Control Experiment): By comparing Comparative Example 1 and Implementation Example 3, the necessity of the in-situ addition timing of the PTFE aqueous dispersion (the window period when the cumulative polymerization yield reaches the final target yield of 25% to 67%) for the formation of the PTFE particle interface entanglement structure was verified. The effects of adding too early (cumulative yield of 15%) on the PTFE particle interface anchoring force and the increase in particle precipitation were characterized. By comparing Comparative Example 3 and Implementation Example 3, the effects of adding too late (cumulative yield of 75%, exceeding the upper limit of 67%) on the system viscosity significantly increased, the PTFE particle penetration was hindered, resulting in a decrease in the degree of interface coating and an increase in particle precipitation were characterized. The technical significance of the 25% to 67% window was verified from both the upper and lower boundaries.

[0229] Experiment 2 (Control Experiment): By comparing Comparative Example 2 with Implementation Example 3, the improvement effect of the in-situ composite process of emulsion polymerization on PTFE particle interface anchoring, inhibition of surface migration and enrichment, and low particle precipitation compared with the traditional physical blending method is verified. The problem of particle precipitation and deterioration of compression set performance caused by the migration and enrichment of PTFE particles to the surface under the traditional physical blending method is characterized.

[0230] Experiment 3 (Comparative Experiment): Comparing Examples 1 to 3 with Examples 4 to 6, the comprehensive differences in low-temperature elastic resilience, plasma etching resistance weight loss rate, and compression set performance between the route of Example 1 (TFE-PMVE binary copolymer + ordinary PTFE + bis(2,4-dichlorobenzoyl) peroxide crosslinking system) and the route of Example 2 (TFE-PMVE-PPVE ternary copolymer + core-shell PTFE microparticles + crosslinking unit F system) are characterized.

[0231] Experimental sample preparation:

[0232] Semiconductor-grade fluororubber sealing rings with a cross-sectional diameter of 5.33 mm, conforming to AS568-214 standard specifications, were prepared according to the formulations and processes described in Examples 1 to 6 and Comparative Examples 1, 2, and 3. At least 30 rings were prepared for performance testing in each example or comparative example, and these were labeled as Sample 1 to Sample 8, corresponding sequentially to Examples 1 to 6 and Comparative Examples 1, 2, and 3. Before testing, all samples were equilibrated for 24 hours in a clean room at 23±2 ℃ and 50±5% relative humidity.

[0233] Experimental conditions:

[0234] Particle precipitation test: Following the SEMI standard (F57), the extract was extracted by soaking in ultrapure water and the particles in the extract were counted. The particle size threshold was 0.2 μm, the extraction temperature was 80 ℃, the extraction time was 1 h, and the volume of the extract was a fixed proportion corresponding to the sample surface area.

[0235] Compression set test: according to ASTM D395 B method, compression amount 25%, test conditions 200 ℃×70 h, the specimen is a cylindrical specimen with a diameter of 29.0 mm×thickness of 12.5 mm, and the average value of 3 specimens in each group is taken.

[0236] Plasma etching weight loss test: The sealing ring sample was placed in an industrial-grade ICP etching simulation device (CF4 / O2 = 4:1, volume ratio, RF power 800 W, chamber pressure 10 Pa, bias voltage 200 V) and continuously exposed for 6 h. The mass of the sample before and after etching was measured using a precision balance (accuracy 0.01 mg), and the mass loss rate was calculated using the formula: ,in For quality loss rate, This represents the mass of the sample before etching. This represents the mass of the sample after etching.

[0237] Low-temperature elastic rebound performance test (-60 ℃): The sealing ring sample is placed in a low-temperature test chamber and cooled to -60 ℃ for 30 min. Immediately afterwards, a 25% compression deformation is applied and held for 5 min. After unloading, the instantaneous rebound height of the sample at -60 ℃ is measured immediately and expressed as the rebound rate, using the formula: ,in For rebound rate, This represents the height of the sample before compression. To determine the immediate rebound height after unloading, synchronous tests were conducted on implementation examples 1 to 3 as a reference.

[0238] Metal ion precipitation test: Take the last ultrapure water washing waste liquid from step 9 and detect the concentration of each metal ion, Na, K, Ca, Mg, Fe, Ni, Cr, Cu and Al, according to the ICP-MS method. The sum of the concentrations of each ion is taken as the total value of metal ion precipitation.

[0239] Experimental steps:

[0240] Step 1: Prepare each batch of samples according to the preparation process of Examples 1 to 6 and Comparative Examples 1 and 2, label Sample 1 to Sample 9, and store them in a clean room for equilibration for 24 hours for later use.

[0241] Step 2: Test the amount of metal ion precipitation for all 9 groups of samples. Take the waste liquid from the last washing in step 9 and send it to ICP-MS for analysis. Record the concentration of each metal ion and the total value.

[0242] Step 3: Test the particle precipitation amount of all 9 groups of samples. Soak and extract with ultrapure water at 80 ℃ for 1 h, take the extract and count the particles in the liquid, and record the number of particles with a particle size of not less than 0.2 μm (particles / mL).

[0243] Step 4: Perform plasma etching resistance weight loss rate tests on all 9 groups of samples, record the sample mass before and after etching, and calculate the mass loss rate η.

[0244] Step 5: Perform compression set tests on all 9 groups of samples according to ASTM D395 B method (200 ℃ × 70 h) and record the compression set values.

[0245] Step 6: Perform an additional -60 ℃ low-temperature elastic rebound rate test on all 9 groups of samples (samples 1 to 9). Samples 1 to 3 (implementation example 1 route) and samples 4 to 6 (implementation example 2 route) are tested simultaneously to compare the differences in low-temperature elasticity between the two technical routes; samples 7 and 8 (comparative examples 1, 2, and 3) are tested simultaneously as controls.

[0246] Step 7: Summarize all test data, calculate the performance improvement ratio of each implementation example relative to the comparison example, and complete the data statistics.

[0247] See experimental or test results Figures 2-8 And as shown in the table below:

[0248] Table 1 Summary of compound formulations for each implementation example and comparative example

[0249]

[0250] As shown in Table 1, the total amount of PTFE in Sample 3 (Example 3), Sample 7 (Comparative Example 1), Sample 8 (Comparative Example 2), and Sample 9 (Comparative Example 3) was 13 parts by weight. The amount of crosslinking agent and TAIC was the same. The only difference was the method of PTFE introduction (in-situ addition timing or whether in-situ compounding was used). This satisfies the single variable principle of the control experiment and can be used to accurately evaluate the independent effects of in-situ addition timing and in-situ compounding process on various performance indicators.

[0251] Table 2 Key process parameters and raw rubber characterization data for each implementation example and comparative example

[0252]

[0253] Table 2 shows that the glass transition temperatures of the raw rubber in Examples 1 to 3 (samples 1 to 3) are in the range of -20 to -10 ℃, while those in Examples 4 to 6 (samples 4 to 6) are all below -40 ℃. There is a significant difference in the glass transition temperatures of the raw rubber between the two technical routes, which directly reflects the improvement in low-temperature elasticity by introducing the third PPVE monomer. The Mooney viscosities of the raw rubber and compound rubber of Comparative Examples 1 (sample 7), 2 (sample 8), and 3 (sample 9) are close to those of Example 3 (sample 3), indicating that the basic processing properties of the samples in the two sets of control experiments are similar, thus eliminating the interference of compound rubber viscosity differences on performance testing.

[0254] Table 3. Test results of particle precipitation, metal ion precipitation, and plasma etching resistance weight loss.

[0255]

[0256] As shown in Table 3, the metal ion precipitation amounts in Examples 1 to 6 (samples 1 to 6) were all below 0.1 ppb, meeting the cleanliness requirements of the semiconductor cavity. This indicates that the combination of the all-organic fluorine-containing formulation system with plasma cleaning and ultrapure water washing processes effectively controlled the metal contamination source. Regarding particle precipitation, Example 3 (sample 3) showed a particle precipitation amount of 9 particles per mL. -1 Comparative Example 1 (Sample 7, PTFE added at 15% of cumulative yield, below the lower limit of 25%) had a particle precipitation of 34 particles / mL. -1 The amount of particles precipitated was approximately 278% higher than that of Sample 3; the amount of particles precipitated in Comparative Example 3 (Sample 9, where the PTFE addition was delayed until the cumulative yield reached 75%, exceeding the upper limit of 67%) was 28 particles per mL. -1 The particle precipitation was approximately 211% higher than that of Sample 3; the particle precipitation in Comparative Example 2 (Sample 8, conventional physical blend) was 52 particles per mL. -1 The increase was approximately 478% compared to sample 3. These data, from both the lower limit (Comparative Example 1, 15%) and upper limit (Comparative Example 3, 75%) of the window period, demonstrate that deviations from the addition timing by 25% to 67% of the window period lead to a significant increase in particle precipitation: adding too early results in short fluororubber molecular chains and incomplete chain entanglement networks, leading to insufficient PTFE particle coating; adding too late results in significantly increased system viscosity and hindered PTFE particle penetration, again preventing the formation of an effective physical entanglement coating structure. In-situ addition within the window period allows newly generated fluororubber chain segments to continuously grow and extend on the PTFE particle surface, significantly inhibiting PTFE particle migration to the product surface. Traditional physical blending completely lacks this interfacial coating mechanism, resulting in the highest particle precipitation. Regarding the weight loss rate during plasma etching, the weight loss rates of Examples 1 to 3 ranged from 0.41% to 0.58%. Comparative Example 2, due to the weak interfacial bonding of PTFE particles and the preferential detachment of particles during etching, had a weight loss rate of 0.52%, slightly higher than the 0.47% of Example 3, an increase of approximately 10.6%. The weight loss rates of Comparative Examples 1 and 3 were basically equivalent to those of Example 3, indicating that the degree of interfacial coating has little effect on the weight loss rate during etching, and the amount of particle precipitation is a more sensitive indicator of the difference in interfacial coating effect.

[0257] Table 4. Results of Compression Permanent Deformation and Low-Temperature Elastic Resilience Tests

[0258]

[0259] As shown in Table 4, the compression set values ​​of Examples 1 to 3 (samples 1 to 3) are all no higher than 15%, meeting the qualification standard. Comparative Example 2 (sample 8, conventional physical blend) has a compression set value as high as 16.9%, exceeding the qualification standard (15%) and deteriorating by approximately 34.1% compared to Example 3 (sample 3), confirming the problem that the large amount of free PTFE thermoplastic phase in conventional physical blending leads to a decrease in the creep resistance of the vulcanized network. Comparative Example 1 (sample 7, added early) has a compression set value of 13.1%, slightly higher than Example 3's 12.6%, an increase of approximately 4.0%. Comparative Example 3 (sample 9, added later to 75%) has a compression set value of 13.4%, deteriorating by approximately 6.3% compared to Example 3. Both indicate that when the addition time deviates from the window period, the degree of PTFE particle interface coating decreases, and the uniformity of the crosslinked network decreases, resulting in varying degrees of higher compression set values, but still better than the conventional physical blending method (16.9%). Regarding the low-temperature elastic rebound rate, Examples 1 to 3 (samples 1 to 3, TFE-PMVE binary copolymer system) showed a rebound rate between 30.1% and 32.6% at -60 ℃. The low-temperature rebound rates of Comparative Examples 1 and 3 (29.8% and 30.2%) were similar to those of Examples 1 to 3, indicating that the timing of addition mainly affects the low-temperature elasticity through the interfacial coating structure rather than the intrinsic elasticity of the raw rubber. In contrast, Examples 4 to 6 (samples 4 to 6, TFE-PMVE-PPVE ternary copolymer + core-shell PTFE + crosslinking unit F system) showed a rebound rate of 68.7% to 73.8% at -60 ℃, which was an average increase of about 119% to 135% compared to Samples 1 to 3. This indicates that after introducing the PPVE third monomer to lower the glass transition temperature of the raw rubber to below -40 ℃, the elastic rebound ability of the material under cryogenic conditions was significantly improved, which can meet the sealing rebound requirements of cryogenic etching conditions at -60 ℃.

[0260] Based on the above experimental results, by introducing an aqueous PTFE dispersion in situ during the emulsion polymerization reaction within the window period when the cumulative polymerization yield reaches 25% to 67% of the final target yield, the newly formed fluororubber segments form a physical entanglement and coating structure on the PTFE particles, controlling the particle precipitation (particle size not less than 0.2 μm) at a low level. Compared with the traditional physical blending comparative example (Comparative Example 2), it is reduced by about 83%, compared with the comparative example where the addition time is below the lower limit (Comparative Example 1, cumulative yield 15%), it is reduced by about 74%, and compared with the comparative example where the addition time is above the upper limit (Comparative Example 3, cumulative yield 75%), it is reduced by about 68%. The all-organic fluorinated formulation system combined with plasma cleaning and ultrapure water ultrasonic washing post-treatment process ensures that the total metal ion precipitation of each batch of products is less than 0.1 ppb. The two-stage post-vulcanization process ensures that the compression set value of each example meets the qualified standard of not exceeding 15%, while the compression set value of the traditional physical blending comparative example exceeds the standard (16.9%). In Example 2, the TFE-PMVE-PPVE ternary copolymer system lowers the glass transition temperature to below -40 °C, increasing the low-temperature elastic resilience of the sealing ring under cryogenic conditions at -60 °C by approximately 119% to 135% compared to Example 1. The synergistic effect of the core-shell structured PTFE microparticles and compatibilizer G further enhances the interfacial bonding between the two phases. Combined with the perfluorocarbon crosslinking system of crosslinking unit F, which has no oxygen-containing byproducts, the compression set value is further reduced to 10.2% to 11.3%, resulting in superior sealing performance over a wide temperature range.

[0261] The embodiments of the present invention have been described above. However, the embodiments are not limited to the specific implementation methods described above. The specific implementation methods described above are merely illustrative and not restrictive. Those skilled in the art can make more equivalent embodiments under the guidance of the present embodiments, and all of them are within the protection scope of the present embodiments.

Claims

1. A manufacturing process for a high-purity, etch-resistant semiconductor-grade fluororubber sealing ring, characterized in that, Includes the following steps: In the emulsion polymerization reaction system, tetrafluoroethylene and perfluoromethyl vinyl ether are copolymerized. When the cumulative polymerization yield reaches 25% to 67% of the target yield, the aqueous dispersion of PTFE is added to the reactor to continue polymerization until the target yield is reached. After coagulation, washing and drying, PTFE in-situ composite fluororubber raw rubber is obtained. Based on 100 parts by weight of the PTFE in-situ composite fluororubber raw rubber, PTFE micro powder, crosslinking agent, crosslinking aid and perfluoropolyether lubricant are added during the mixing stage, and the compound is obtained by mixing. The compounded rubber was subjected to compression molding vulcanization, two-stage post-vulcanization, plasma cleaning, and ultrapure water washing to obtain a high-cleanliness, etching-resistant semiconductor-grade fluororubber sealing ring.

2. The preparation process according to claim 1, characterized in that, The emulsion polymerization reaction system includes deionized water, perfluoropolyether ammonium carboxylate as an emulsifier, diammonium hydrogen phosphate as a pH adjuster, and ammonium persulfate as an initiator; the amount of perfluoropolyether ammonium carboxylate is 3000 to 5000 ppm, the amount of ammonium persulfate is 500 to 2000 ppm, and the pH of the system is 6.5 to 7.5; before the copolymerization reaction, the reactor is subjected to vacuuming and nitrogen purging for deoxygenation treatment, so that the residual oxygen content in the reactor is less than 10 ppm.

3. The preparation process according to claim 1, characterized in that, The initial molar ratio of tetrafluoroethylene to perfluoromethyl vinyl ether is 55:45 to 65:35; perfluoro-2-bromoethyl vinyl ether, a monomer with a bromine sulfide point, is added to the copolymerization reaction in an amount of 0.1% to 0.5% of the total molar amount of tetrafluoroethylene and perfluoromethyl vinyl ether; the pressure inside the reactor is 0.5 to 0.8 MPa, and the reaction temperature is 20 to 80 °C.

4. The preparation process according to claim 1, characterized in that, The solid content of the PTFE aqueous dispersion is 40% to 60%, wherein the average particle size of the PTFE particles is 1 to 5 μm, and the number average molecular weight of the PTFE is 1 × 10⁻⁶. 6 Up to 1×10 7 The PTFE solid content added is 2% to 14% of the target mass of the fluororubber raw rubber; the addition method is continuous dripping or batch addition, and the continuous dripping time is 0.5 to 3 hours.

5. The preparation process according to claim 1, characterized in that, Based on 100 parts by weight of fluororubber raw rubber, the total amount of PTFE is 5 to 20 parts by weight, of which the in-situ composite portion accounts for 40% to 70% of the total PTFE, and the supplementary portion in the mixing stage accounts for 30% to 60%; the crosslinking agent is bis(2,4-dichlorobenzoyl) peroxide, and the amount used is 0.5 to 3 parts by weight; the crosslinking aid is triallyl isocyanurate, and the amount used is 1 to 5 parts by weight; the mass ratio of bis(2,4-dichlorobenzoyl) peroxide to triallyl isocyanurate is 1:1.5 to 1:2.5; and the amount of perfluoropolyether lubricant is 0.1 to 2 parts by weight.

6. The preparation process according to claim 1, characterized in that, The mixing is carried out on an open mill in a clean room, with the front roll temperature at 40 to 60°C and the rear roll temperature at 35 to 55°C, and the roll temperature not exceeding 60°C throughout the process; after the mixed rubber sheet is left in a clean environment at 23±2°C and relative humidity not exceeding 55% for 8 to 24 hours, the Mooney viscosity is 30 to 80 MU.

7. The preparation process according to claim 1, characterized in that, The molding vulcanization temperature is 160 to 180°C, the vulcanization pressure is 10 to 15 MPa, and the vulcanization time is 3 to 10 minutes; the second-stage post-vulcanization is carried out at 200 to 250°C for 4 to 8 hours, and the compression set of the product after post-vulcanization is not higher than 15%, and the mass loss rate is less than 0.5% below 350°C.

8. The preparation process according to claim 1, characterized in that, In the copolymerization reaction, tetrafluoroethylene, perfluoromethyl vinyl ether, and perfluoropropyl vinyl ether are ternarily copolymerized in a molar ratio of 45:35:20 to 55:30:15; perfluorohexylethyl triiodide is added as an iodine-containing vulcanizing point monomer, at a dosage of 0.3% to 1.2% of the total molar amount of the three comonomers; the glass transition temperature of the resulting ternary copolymer fluororubber raw rubber is below -40°C; the PTFE aqueous dispersion is replaced with a core-shell structured PTFE microparticle aqueous dispersion, with a core layer of PTFE and a shell layer of perfluoropropylene oxide oligomer grafted layer, the shell layer thickness being 30 to 100 nm.

9. The preparation process according to claim 8, characterized in that, In the mixing stage, the crosslinking agent is replaced with perfluorocyclobutane tetravinyl crosslinking unit, with an amount of 2 to 5 parts by weight, and the crosslinking aid triallyl isocyanurate is used in an amount of 2 to 5 parts by weight; 3 to 8 parts by weight of perfluoropolyether dual-terminated vinyl oligomer is also added as a compatibilizer, and 1 to 3 parts by weight of perfluoropolyether ether ketone block copolymer is added as a toughening agent; the molding vulcanization temperature is adjusted to 170 to 190°C, and the post-secondary vulcanization temperature is 210 to 260°C.

10. A high-purity, etch-resistant semiconductor-grade fluororubber sealing ring prepared by the preparation process described in any one of claims 1 to 9.

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