A bidirectional piston seal ring and a preparation method thereof

Abstract

The application provides a bidirectional piston sealing ring and a preparation method thereof, and belongs to the technical field of sealing ring preparation, and comprises the following steps: step S1, preparing a pre-reaction solution; step S2, adding pretreated polytetrafluoroethylene, triethylamine, 3-aminopropyl triethoxysilane solution and perfluorooctyl triethoxysilane into the pre-reaction solution, performing ultrasonic treatment, vacuum degassing, performing a thermal imine reaction, filtering, washing, and drying to obtain modified polytetrafluoroethylene; step S3, uniformly mixing the modified polytetrafluoroethylene powder and polytetrafluoroethylene powder, vacuum drying, performing hot-pressing forming, performing pressure relief demolding, then annealing, and then cooling to room temperature to obtain the bidirectional piston sealing ring. The bidirectional piston sealing ring has the advantages of high wear resistance and good anti-creep capacity.

Description

Technical Field

[0001] The present invention relates to the technical field of sealing component preparation, and in particular to a bidirectional piston sealing ring and a preparation method thereof. Background Art

[0002] Currently, polytetrafluoroethylene (PTFE) is widely used as a sealing material in aerospace, petrochemical, mechanical equipment, hydraulic systems, and other fields due to its excellent high-temperature resistance, corrosion resistance, self-lubrication, low friction coefficient, and good chemical stability. While traditional PTFE piston seals possess certain sealing and self-lubricating properties, they also suffer from significant drawbacks: low strength, especially insufficient wear resistance. While the wear rate of PTFE on metal piston rods is low during long-term reciprocating motion, its own wear resistance is poor, and material peeling is prone to occur under high-speed conditions. The weak intermolecular forces between PTFE molecular chains result in severe cold flow, making it prone to creep deformation under long-term loads, causing permanent deformation and failure of the seal. Furthermore, poor interfacial bonding with other materials makes it difficult to form a stable composite structure with resins or additives.

[0003] The patent application document with publication number CN103571114A discloses a polytetrafluoroethylene piston seal ring and its preparation method. The polytetrafluoroethylene piston seal ring is composed of the following components by weight: 100 parts of polytetrafluoroethylene, 30-40 parts of methylphenyl vinyl silicone rubber, 3-5 parts of diisopropyl peroxide, 1-3 parts of trioctanoyl titanate, 18-28 parts of glass fiber, 10-18 parts of molybdenum disulfide, 6-12 parts of bronze powder, and 2-4 parts of graphite. The specific preparation steps are: (1) stirring and mixing the raw materials, placing them into a mold and pressurizing them at a pressure of 10-15 MPa; (2) sintering at a sintering temperature of 380-390°C; then maintaining the temperature at a constant temperature for 2-4 hours; (3) secondary pressurization treatment at a pressure of 8-15 MPa; and (4) natural cooling and shaping. The polytetrafluoroethylene sealing ring prepared by this invention retains the good thermal stability of polytetrafluoroethylene, but fails to improve the problem of polytetrafluoroethylene's easy cold flow creep.

[0004] Therefore, it is necessary to provide a bidirectional piston sealing ring and a preparation method thereof to solve the problems existing in the above-mentioned prior art. Summary of the Invention

[0005] In view of this, the present invention provides a bidirectional piston sealing ring and a preparation method thereof, which can achieve the purpose of the bidirectional piston sealing ring having strong wear resistance and good creep resistance.

[0006] To achieve the above object, the present invention provides a method for preparing a bidirectional piston sealing ring, comprising the following steps:

[0007] Step S1: add 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl to a reaction kettle containing N-methylpyrrolidone, stir until completely dissolved, slowly add 4,4'-(hexafluoroisopropylene) diphthalic anhydride, stir and react to obtain a pre-reaction solution;

[0008] Step S2, adding pretreated polytetrafluoroethylene, triethylamine, 3-aminopropyltriethoxysilane solution and perfluorooctyltriethoxysilane to the pre-reaction liquid, ultrasonically treating, vacuum degassing, performing thermal imidization reaction, filtering, washing and drying to obtain modified polytetrafluoroethylene;

[0009] Step S3: uniformly mix the modified polytetrafluoroethylene powder and the polytetrafluoroethylene powder, vacuum dry, perform hot pressing, anneal after pressure relief and demoulding, and then cool to room temperature to obtain a bidirectional piston sealing ring.

[0010] This solution uses polytetrafluoroethylene (PTFE) as the base material for the bidirectional piston seal. PTFE has excellent temperature resistance, can be used within a temperature range of -190°C to 260°C, and can withstand cyclic heating and cooling operations. PTFE can also maintain a certain degree of flexibility at ultra-low temperatures and good mechanical properties at high temperatures. Its temperature resistance enables the seal to maintain its performance over a wide temperature range. PTFE also has an extremely low coefficient of friction and excellent self-lubricity, ensuring minimal friction during the reciprocating motion of the piston rod, reducing wear and lowering energy consumption.

[0011] Polytetrafluoroethylene is modified using a pre-reaction liquid, in which 4,4'-(hexafluoroisopropylene) diphthalic anhydride is used as a dianhydride monomer and 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl is used as a diamine monomer. The two can synthesize functional polyimide to form a modified polytetrafluoroethylene.

[0012] 4,4'-(Hexafluoroisopropyl)diphthalic anhydride contains a hexafluoroisopropyl group. The introduction of fluorine atoms can significantly improve the chemical stability, thermal stability and hydrophobicity of polyimide, and is similarly compatible with polytetrafluoroethylene. This helps the final polyimide to better wet and coat the polytetrafluoroethylene particles, reduce phase separation, and form a tighter structure, thereby improving the mechanical properties of the modified polytetrafluoroethylene and promoting the improvement of the creep resistance of the sealing ring. 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl also has a fluorine-containing group that can improve compatibility. At the same time, its rigid biphenyl structure can further improve the heat resistance of the polyimide, matching the application temperature range of polytetrafluoroethylene.

[0013] The fluorinated polyimide formed by imidization of 4,4'-(hexafluoroisopropylene) diphthalic anhydride and 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl has high heat resistance, high stability and low hygroscopicity. It can be modified by modifying polytetrafluoroethylene particles, and the plasticity of polytetrafluoroethylene can be used to offset the brittleness of polyimide, achieving a combination of rigidity and plasticity. In combination with 3-aminopropyltriethoxysilane and perfluorooctyltriethoxysilane, a three-dimensional cross-linked network is further formed, which can limit the free slip of polytetrafluoroethylene chain segments, allowing polytetrafluoroethylene to maintain structural stability under high temperature and high pressure working conditions, avoiding material cold flow, improving creep resistance, and ensuring that the sealing ring has good shape retention and dimensional stability under high-pressure reciprocating motion. In addition, the interfacial adhesion and rigidity between the modified polytetrafluoroethylene particles are enhanced, making it less likely to fall off and fail, thereby achieving improved wear resistance.

[0014] Preferably, in step S1, the step of preparing the 3-aminopropyltriethoxysilane solution includes: uniformly mixing 3-aminopropyltriethoxysilane and deionized water in a mass volume ratio of 1:(25-30) to obtain a 3-aminopropyltriethoxysilane solution.

[0015] 3-Aminopropyltriethoxysilane has a siloxane group at one end and an amino group at the other end, which can modify the surface of polytetrafluoroethylene, promote better dispersion of polytetrafluoroethylene in polar solvents, and reduce agglomeration.

[0016] Preferably, in step S1, the stirring reaction temperature is 20-30° C. and the time is 12-16 hours.

[0017] Preferably, the pretreatment process of the pretreated polytetrafluoroethylene is as follows: polytetrafluoroethylene powder is spread flat in a plasma reactor, a mixed gas of nitrogen and oxygen is filled in a ratio of 95:5, and plasma treatment is performed for surface activation to obtain pretreated polytetrafluoroethylene.

[0018] Plasma treatment is used to bombard the surface of polytetrafluoroethylene, breaking its inert CF bonds and introducing oxygen-containing polar groups on the surface, which can significantly improve the chemical activity and reactivity of the polytetrafluoroethylene surface and provide a reliable anchor point for subsequent reactions.

[0019] Preferably, in step S2, modified nano-zirconium phosphate is added at the same time as the pretreated polytetrafluoroethylene; the modified nano-zirconium phosphate is prepared by the following steps:

[0020] The nano zirconium phosphate was added into anhydrous ethanol, and then 3,3,3-trifluoropropyltriethoxysilane and 3-aminopropyltriethoxysilane were added, and the mixture was stirred evenly. The mixture was heated for reaction under nitrogen protection, cooled, centrifuged, washed, and dried to obtain the modified nano zirconium phosphate.

[0021] Nano-zirconium phosphate has strong rigidity. After modification, the nano-zirconium phosphate is improved in its compatibility and can be embedded in the polytetrafluoroethylene matrix without agglomeration, so that it can play a supporting role. During use, the nano-zirconium phosphate can hinder the slippage of the polytetrafluoroethylene chain segments, inhibit stress concentration and cold flow, and the modified nano-zirconium phosphate can also form a cross-linked network with polyimide, further limiting the deformation of the sealing ring.

[0022] Preferably, in step S2, the power of ultrasonic treatment is 300W, the frequency is 20kHz, and the time is 5-7min; the time of vacuum degassing is 10-20min.

[0023] Ultrasonic treatment is used to promote the dispersion of polytetrafluoroethylene particles and avoid agglomeration.

[0024] Preferably, in step S2, the thermal imidization reaction comprises the following steps: heating the reactor to 80-100° C., reacting for 20-40 minutes, then heating to 150-180° C., reacting for 1-2 hours, and finally heating to 220-250° C., reacting for 1-2 hours.

[0025] Preferably, in step S3, the hot pressing molding includes the following steps: the initial temperature is 200°C, the initial pressure is 5 MPa, then the temperature is increased from 250°C to 360°C at a rate of 10°C / min, the pressure is increased from 5 MPa to 20 MPa, the pressure increase rate is 1 MPa / min, and the pressure is maintained at 20 MPa and slowly cooled to 200°C to complete the hot pressing molding.

[0026] To achieve the above object, the present invention further provides a bidirectional piston sealing ring prepared by the above method for preparing a bidirectional piston sealing ring, comprising the following components in parts by weight:

[0027] 10-15 parts of modified polytetrafluoroethylene and 1-1.5 parts of polytetrafluoroethylene.

[0028] The bidirectional piston sealing ring prepared by this scheme can achieve good wear resistance, is not prone to creep, and has a long service life.

[0029] Preferably, the modified polytetrafluoroethylene comprises the following raw materials in parts by weight: 0.5-1 part of modified nano zirconium phosphate, 10-12 parts of pretreated polytetrafluoroethylene, 0.15-0.18 parts of triethylamine, 6-7.2 parts of 3-aminopropyltriethoxysilane solution and 0.05-0.06 parts of perfluorooctyltriethoxysilane.

[0030] The use of raw materials in this weight ratio can enable the bidirectional piston sealing ring to achieve better mechanical properties.

[0031] The above technical solution of the present invention includes at least the following beneficial effects:

[0032] 1. Polytetrafluoroethylene has an extremely low friction coefficient, excellent self-lubrication, a wide operating temperature range, and it also has excellent chemical stability and good resistance to strong acids and alkalis. In addition, polytetrafluoroethylene also has hydrophobic and oleophobic properties. These properties can give the sealing ring better durability and a longer service life under working conditions.

[0033] 2. The fluorinated polyimide formed by 4,4'-(hexafluoroisopropylene) diphthalic anhydride and 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl has high heat resistance, high stability and low hygroscopicity. The polytetrafluoroethylene particles are modified, and the plasticity of polytetrafluoroethylene is used to offset the brittleness of the polyimide, achieving a combination of rigidity and plasticity, and promoting the improvement of the wear resistance and creep resistance of the sealing ring.

[0034] 3. Modified polytetrafluoroethylene is combined with silane coupling agent to form a three-dimensional network structure, which can limit the free slip of polytetrafluoroethylene chain segments, so that polytetrafluoroethylene can maintain structural stability under high temperature and high pressure working conditions, avoid material cold flow, improve creep resistance, and ensure that the sealing ring has good shape retention and dimensional stability under high-pressure reciprocating motion. DETAILED DESCRIPTION

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. The described embodiments are only part of the embodiments of the present invention. All other embodiments obtained by ordinary technicians in this field based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0036] Example 1

[0037] 15g of polytetrafluoroethylene powder was spread flat in a plasma reactor and filled with a mixture of nitrogen and oxygen at a ratio of 95:5. Plasma treatment was performed for surface activation at a power of 100W for 9 minutes to obtain pretreated polytetrafluoroethylene. 1g of 3-aminopropyltriethoxysilane was mixed with 25mL of deionized water to obtain a 3-aminopropyltriethoxysilane solution.

[0038] Under nitrogen protection, 4 g of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl was added to a reaction kettle containing 90 mL of N-methylpyrrolidone and stirred until completely dissolved. 4.4 g of 4,4'-(hexafluoroisopropylene)diphthalic anhydride was slowly added and stirred continuously. The temperature was controlled at 25°C and the reaction was carried out for 14 h to obtain a pre-reaction solution.

[0039] 2 g of nano-zirconium phosphate was added to a beaker containing 200 mL of anhydrous ethanol, and then 0.55 g of 3,3,3-trifluoropropyltriethoxysilane and 0.25 g of 3-aminopropyltriethoxysilane were added to the beaker, stirred evenly, heated to 65 ° C under nitrogen protection, and reacted for 4 h. After the reaction was completed, it was cooled and centrifuged, washed twice with ethanol, and vacuum dried for 12 h to obtain modified nano-zirconium phosphate.

[0040] To the pre-reaction liquid, 10 g of pretreated polytetrafluoroethylene powder, 0.7 g of modified nano-zirconium phosphate, 0.15 g of triethylamine, 6 g of 3-aminopropyltriethoxysilane solution and 0.05 g of perfluorooctyltriethoxysilane were added, and ultrasonic treatment was performed with a power of 300 W, a frequency of 20 kHz, and a time of 6 min. Vacuum degassing was performed for 20 min, and the reactor was heated to 100 ° C. and reacted for 20 min. The temperature was then raised to 170 ° C. and reacted for 1.5 h. Finally, the reaction was heated to 235 ° C. and reacted for 2 h. The modified polytetrafluoroethylene was obtained after filtration, washing, and drying.

[0041] 15g of modified polytetrafluoroethylene powder and 1.5g of polytetrafluoroethylene powder were mixed evenly, vacuum dried, and hot-pressed at an initial temperature of 200°C and an initial pressure of 5MPa. The temperature was then increased from 250°C to 360°C at a rate of 10°C / min, and the pressure was increased from 5MPa to 20MPa at a pressure increase rate of 1MPa / min. The pressure was maintained at 20MPa and slowly cooled to 200°C. The pressure was released and demolded, annealed at 200°C for 30min, and naturally cooled to room temperature to obtain a bidirectional piston sealing ring.

[0042] Example 2

[0043] 15g of polytetrafluoroethylene powder was spread flat in a plasma reactor and filled with a mixture of nitrogen and oxygen at a ratio of 95:5. Plasma treatment was performed for surface activation at a power of 100W for 8 minutes to obtain pretreated polytetrafluoroethylene. 0.5g of 3-aminopropyltriethoxysilane was mixed with 15mL of deionized water to obtain a 3-aminopropyltriethoxysilane solution.

[0044] Under nitrogen protection, 4 g of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl was added to a reaction kettle containing 90 mL of N-methylpyrrolidone and stirred until completely dissolved. 4.4 g of 4,4'-(hexafluoroisopropylene)diphthalic anhydride was slowly added and stirred continuously. The temperature was controlled at 30°C and the reaction was carried out for 12 h to obtain a pre-reaction solution.

[0045] 2 g of nano-zirconium phosphate was added to a beaker containing 200 mL of anhydrous ethanol, and then 0.55 g of 3,3,3-trifluoropropyltriethoxysilane and 0.25 g of 3-aminopropyltriethoxysilane were added to the beaker, stirred evenly, heated to 65 ° C under nitrogen protection, and reacted for 4 h. After the reaction was completed, it was cooled and centrifuged, washed twice with ethanol, and vacuum dried for 12 h to obtain modified nano-zirconium phosphate.

[0046] To the pre-reaction liquid, 12 g of pretreated polytetrafluoroethylene powder, 0.5 g of modified nano-zirconium phosphate, 0.18 g of triethylamine, 7.2 g of 3-aminopropyltriethoxysilane solution and 0.06 g of perfluorooctyltriethoxysilane were added, and ultrasonic treatment was performed with a power of 300 W, a frequency of 20 kHz, and a time of 5 min. Vacuum degassing was performed for 20 min, and the reactor was heated to 90° C. and reacted for 30 min. The temperature was then raised to 150° C. and reacted for 2 h. Finally, the reaction mixture was heated to 250° C. and reacted for 1 h. The modified polytetrafluoroethylene was obtained after filtration, washing, and drying.

[0047] 10g of modified polytetrafluoroethylene powder and 1g of polytetrafluoroethylene powder were mixed evenly, vacuum dried, and hot-pressed at an initial temperature of 200°C and an initial pressure of 5MPa. The temperature was then increased from 250°C to 360°C at a rate of 10°C / min, and the pressure was increased from 5MPa to 20MPa at a pressure increase rate of 1MPa / min. The pressure was maintained at 20MPa and slowly cooled to 200°C. The pressure was released and demolded, annealed at 200°C for 30min, and naturally cooled to room temperature to obtain a bidirectional piston sealing ring.

[0048] Example 3

[0049] 15g of polytetrafluoroethylene powder was spread flat in a plasma reactor and filled with a mixture of nitrogen and oxygen at a ratio of 95:5. Plasma treatment was performed for surface activation at a power of 100W for 10 minutes to obtain pretreated polytetrafluoroethylene. 0.5g of 3-aminopropyltriethoxysilane was mixed with 12.5mL of deionized water to obtain a 3-aminopropyltriethoxysilane solution.

[0050] Under nitrogen protection, 4 g of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl was added to a reaction kettle containing 90 mL of N-methylpyrrolidone and stirred until completely dissolved. 4.4 g of 4,4'-(hexafluoroisopropylene)diphthalic anhydride was slowly added and stirred continuously. The temperature was controlled at 20°C and the reaction was carried out for 16 h to obtain a pre-reaction solution.

[0051] 2 g of nano-zirconium phosphate was added to a beaker containing 200 mL of anhydrous ethanol, and then 0.55 g of 3,3,3-trifluoropropyltriethoxysilane and 0.25 g of 3-aminopropyltriethoxysilane were added to the beaker, stirred evenly, heated to 65 ° C under nitrogen protection, and reacted for 4 h. After the reaction was completed, it was cooled and centrifuged, washed twice with ethanol, and vacuum dried for 12 h to obtain modified nano-zirconium phosphate.

[0052] To the pre-reaction liquid, 10 g of pretreated polytetrafluoroethylene powder, 1 g of modified nano-zirconium phosphate, 0.15 g of triethylamine, 6 g of 3-aminopropyltriethoxysilane solution and 0.05 g of perfluorooctyltriethoxysilane were added, and ultrasonic treatment was performed at a power of 300 W, a frequency of 20 kHz, and a time of 5 min. Vacuum degassing was performed for 10 min, and the reactor was heated to 80° C. and reacted for 40 min. The temperature was then raised to 180° C. and reacted for 1 h. Finally, the reaction mixture was heated to 220° C. and reacted for 2 h. The modified polytetrafluoroethylene was obtained after filtration, washing, and drying.

[0053] 12g of modified polytetrafluoroethylene powder and 1.2g of polytetrafluoroethylene powder were mixed evenly, vacuum dried, and hot-pressed at an initial temperature of 200°C and an initial pressure of 5MPa. The temperature was then increased from 250°C to 360°C at a rate of 10°C / min, and the pressure was increased from 5MPa to 20MPa at a pressure increase rate of 1MPa / min. The pressure was maintained at 20MPa and slowly cooled to 200°C. The pressure was released and demolded, annealed at 200°C for 30min, and naturally cooled to room temperature to obtain a bidirectional piston sealing ring.

[0054] Example 4

[0055] 15g of polytetrafluoroethylene powder was spread flat in a plasma reactor and filled with a mixture of nitrogen and oxygen at a ratio of 95:5. Plasma treatment was performed for surface activation at a power of 100W for 8 minutes to obtain pretreated polytetrafluoroethylene. 1g of 3-aminopropyltriethoxysilane was mixed with 30mL of deionized water to obtain a 3-aminopropyltriethoxysilane solution.

[0056] Under nitrogen protection, 4 g of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl was added to a reaction kettle containing 90 mL of N-methylpyrrolidone and stirred until completely dissolved. 4.4 g of 4,4'-(hexafluoroisopropylene)diphthalic anhydride was slowly added and stirred continuously. The temperature was controlled at 20°C and the reaction was carried out for 15 h to obtain a pre-reaction solution.

[0057] 2 g of nano-zirconium phosphate was added to a beaker containing 200 mL of anhydrous ethanol, and then 0.55 g of 3,3,3-trifluoropropyltriethoxysilane and 0.25 g of 3-aminopropyltriethoxysilane were added to the beaker, stirred evenly, heated to 65 ° C under nitrogen protection, and reacted for 4 h. After the reaction was completed, it was cooled and centrifuged, washed twice with ethanol, and vacuum dried for 12 h to obtain modified nano-zirconium phosphate.

[0058] To the pre-reaction liquid, 10 g of pretreated polytetrafluoroethylene powder, 0.6 g of modified nano-zirconium phosphate, 0.15 g of triethylamine, 6 g of 3-aminopropyltriethoxysilane solution and 0.05 g of perfluorooctyltriethoxysilane were added, and ultrasonic treatment was performed with a power of 300 W, a frequency of 20 kHz, and a time of 7 min. Vacuum degassing was performed for 15 min, and the reactor was heated to 100 ° C. and reacted for 20 min. The temperature was then raised to 180 ° C. and reacted for 1.5 h. Finally, the reaction mixture was heated to 250 ° C. and reacted for 1 h. The modified polytetrafluoroethylene was obtained after filtration, washing, and drying.

[0059] 14 g of modified polytetrafluoroethylene powder and 1.4 g of polytetrafluoroethylene powder were mixed evenly, vacuum dried, and hot-pressed at an initial temperature of 200 ° C and an initial pressure of 5 MPa. Then, the temperature was increased from 250 ° C to 360 ° C at a rate of 10 ° C / min, and the pressure was increased from 5 MPa to 20 MPa at a pressure increase rate of 1 MPa / min. The pressure was maintained at 20 MPa and slowly cooled to 200 ° C. The pressure was released and demolded, annealed at 200 ° C for 30 min, and naturally cooled to room temperature to obtain a bidirectional piston sealing ring.

[0060] Example 5

[0061] 15g of polytetrafluoroethylene powder was spread flat in a plasma reactor and filled with a mixture of nitrogen and oxygen at a ratio of 95:5. Plasma treatment was performed for surface activation at a power of 100W for 10 minutes to obtain pretreated polytetrafluoroethylene. 1g of 3-aminopropyltriethoxysilane was mixed with 25mL of deionized water to obtain a 3-aminopropyltriethoxysilane solution.

[0062] Under nitrogen protection, 4 g of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl was added to a reaction kettle containing 90 mL of N-methylpyrrolidone and stirred until completely dissolved. 4.4 g of 4,4'-(hexafluoroisopropylene)diphthalic anhydride was slowly added and stirred continuously. The temperature was controlled at 30°C and the reaction was carried out for 12 h to obtain a pre-reaction solution.

[0063] 2 g of nano-zirconium phosphate was added to a beaker containing 200 mL of anhydrous ethanol, and then 0.55 g of 3,3,3-trifluoropropyltriethoxysilane and 0.25 g of 3-aminopropyltriethoxysilane were added to the beaker, stirred evenly, heated to 65 ° C under nitrogen protection, and reacted for 4 h. After the reaction was completed, it was cooled and centrifuged, washed twice with ethanol, and vacuum dried for 12 h to obtain modified nano-zirconium phosphate.

[0064] To the pre-reaction liquid, 11 g of pretreated polytetrafluoroethylene powder, 0.7 g of modified nano-zirconium phosphate, 0.15 g of triethylamine, 7 g of 3-aminopropyltriethoxysilane solution and 0.05 g of perfluorooctyltriethoxysilane were added, and ultrasonic treatment was performed with a power of 300 W, a frequency of 20 kHz, and a time of 7 min. Vacuum degassing was performed for 20 min, and the reactor was heated to 85 ° C. and reacted for 25 min. The temperature was then raised to 160 ° C. and reacted for 2 h. Finally, the reaction mixture was heated to 230 ° C. and reacted for 1.5 h. The modified polytetrafluoroethylene was obtained after filtration, washing, and drying.

[0065] 11g of modified polytetrafluoroethylene powder and 1.1g of polytetrafluoroethylene powder were mixed evenly, vacuum dried, and hot-pressed at an initial temperature of 200°C and an initial pressure of 5MPa. The temperature was then increased from 250°C to 360°C at a rate of 10°C / min, and the pressure was increased from 5MPa to 20MPa at a pressure increase rate of 1MPa / min. The pressure was maintained at 20MPa and slowly cooled to 200°C. The pressure was released and demolded, annealed at 200°C for 30min, and naturally cooled to room temperature to obtain a bidirectional piston sealing ring.

[0066] Example 6

[0067] 15g of polytetrafluoroethylene powder was spread flat in a plasma reactor and filled with a mixture of nitrogen and oxygen at a ratio of 95:5. Plasma treatment was performed for surface activation at a power of 100W for 9 minutes to obtain pretreated polytetrafluoroethylene. 0.5g of 3-aminopropyltriethoxysilane was mixed with 15mL of deionized water to obtain a 3-aminopropyltriethoxysilane solution.

[0068] Under nitrogen protection, 4 g of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl was added to a reaction kettle containing 90 mL of N-methylpyrrolidone and stirred until completely dissolved. 4.4 g of 4,4'-(hexafluoroisopropylene)diphthalic anhydride was slowly added and stirred continuously. The temperature was controlled at 30°C and the reaction was carried out for 13 h to obtain a pre-reaction solution.

[0069] 2 g of nano-zirconium phosphate was added to a beaker containing 200 mL of anhydrous ethanol, and then 0.55 g of 3,3,3-trifluoropropyltriethoxysilane and 0.25 g of 3-aminopropyltriethoxysilane were added to the beaker, stirred evenly, heated to 65 ° C under nitrogen protection, and reacted for 4 h. After the reaction was completed, it was cooled and centrifuged, washed twice with ethanol, and vacuum dried for 12 h to obtain modified nano-zirconium phosphate.

[0070] To the pre-reaction liquid, 10 g of pretreated polytetrafluoroethylene powder, 1 g of modified nano-zirconium phosphate, 0.18 g of triethylamine, 6 g of 3-aminopropyltriethoxysilane solution and 0.06 g of perfluorooctyltriethoxysilane were added, and ultrasonic treatment was performed with a power of 300 W, a frequency of 20 kHz, and a time of 6 min. Vacuum degassing was performed for 15 min, and the reactor was heated to 90°C and reacted for 40 min. The temperature was then raised to 150°C and reacted for 2 h. Finally, the reaction was heated to 240°C and reacted for 1 h. The modified polytetrafluoroethylene was obtained after filtration, washing, and drying.

[0071] 15g of modified polytetrafluoroethylene powder and 1.5g of polytetrafluoroethylene powder were mixed evenly, vacuum dried, and hot-pressed at an initial temperature of 200°C and an initial pressure of 5MPa. The temperature was then increased from 250°C to 360°C at a rate of 10°C / min, and the pressure was increased from 5MPa to 20MPa at a pressure increase rate of 1MPa / min. The pressure was maintained at 20MPa and slowly cooled to 200°C. The pressure was released and demolded, annealed at 200°C for 30min, and naturally cooled to room temperature to obtain a bidirectional piston sealing ring.

[0072] Example 7

[0073] 15g of polytetrafluoroethylene powder was spread flat in a plasma reactor and filled with a mixture of nitrogen and oxygen at a ratio of 95:5. Plasma treatment was performed for surface activation at a power of 100W for 8 minutes to obtain pretreated polytetrafluoroethylene. 0.5g of 3-aminopropyltriethoxysilane was mixed with 12.5mL of deionized water to obtain a 3-aminopropyltriethoxysilane solution.

[0074] Under nitrogen protection, 4 g of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl was added to a reaction kettle containing 90 mL of N-methylpyrrolidone and stirred until completely dissolved. 4.4 g of 4,4'-(hexafluoroisopropylene)diphthalic anhydride was slowly added and stirred continuously. The temperature was controlled at 25°C and the reaction was carried out for 15 h to obtain a pre-reaction solution.

[0075] 2 g of nano-zirconium phosphate was added to a beaker containing 200 mL of anhydrous ethanol, and then 0.55 g of 3,3,3-trifluoropropyltriethoxysilane and 0.25 g of 3-aminopropyltriethoxysilane were added to the beaker, stirred evenly, heated to 65 ° C under nitrogen protection, and reacted for 4 h. After the reaction was completed, it was cooled and centrifuged, washed twice with ethanol, and vacuum dried for 12 h to obtain modified nano-zirconium phosphate.

[0076] To the pre-reaction liquid, 10 g of pretreated polytetrafluoroethylene powder, 1 g of modified nano-zirconium phosphate, 0.15 g of triethylamine, 6 g of 3-aminopropyltriethoxysilane solution and 0.05 g of perfluorooctyltriethoxysilane were added, and ultrasonic treatment was performed with a power of 300 W, a frequency of 20 kHz, and a time of 5 min. Vacuum degassing was performed for 15 min, and the reactor was heated to 100 ° C. and reacted for 20 min. The temperature was then raised to 180 ° C. and reacted for 1 h. Finally, the reaction mixture was heated to 235 ° C. and reacted for 1.5 h. The modified polytetrafluoroethylene was obtained after filtration, washing, and drying.

[0077] 10g of modified polytetrafluoroethylene powder and 1g of polytetrafluoroethylene powder were mixed evenly, vacuum dried, and hot-pressed at an initial temperature of 200°C and an initial pressure of 5MPa. The temperature was then increased from 250°C to 360°C at a rate of 10°C / min, and the pressure was increased from 5MPa to 20MPa at a pressure increase rate of 1MPa / min. The pressure was maintained at 20MPa and slowly cooled to 200°C. The pressure was released and demolded, annealed at 200°C for 30min, and naturally cooled to room temperature to obtain a bidirectional piston sealing ring.

[0078] Example 8

[0079] 15g of polytetrafluoroethylene powder was spread flat in a plasma reactor and filled with a mixture of nitrogen and oxygen at a ratio of 95:5. Plasma treatment was performed for surface activation at a power of 100W for 8 minutes to obtain pretreated polytetrafluoroethylene. 0.5g of 3-aminopropyltriethoxysilane was mixed with 12.5mL of deionized water to obtain a 3-aminopropyltriethoxysilane solution.

[0080] Under nitrogen protection, 4 g of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl was added to a reaction kettle containing 90 mL of N-methylpyrrolidone and stirred until completely dissolved. 4.4 g of 4,4'-(hexafluoroisopropylene)diphthalic anhydride was slowly added and stirred continuously. The temperature was controlled at 25°C and the reaction was carried out for 15 h to obtain a pre-reaction solution.

[0081] 2 g of nano-zirconium phosphate was added to a beaker containing 200 mL of anhydrous ethanol, and then 0.55 g of 3,3,3-trifluoropropyltriethoxysilane and 0.25 g of 3-aminopropyltriethoxysilane were added to the beaker, stirred evenly, heated to 65 ° C under nitrogen protection, and reacted for 4 h. After the reaction was completed, it was cooled and centrifuged, washed twice with ethanol, and vacuum dried for 12 h to obtain modified nano-zirconium phosphate.

[0082] To the pre-reaction liquid, 10 g of pretreated polytetrafluoroethylene powder, 0.15 g of triethylamine, 6 g of 3-aminopropyltriethoxysilane solution and 0.05 g of perfluorooctyltriethoxysilane were added, and ultrasonic treatment was performed at a power of 300 W, a frequency of 20 kHz, and a time of 5 min. Vacuum degassing was performed for 15 min, and the reactor was heated to 100 ° C. and reacted for 20 min. The temperature was then raised to 180 ° C. and reacted for 1 h. Finally, the mixture was heated to 235 ° C. and reacted for 1.5 h. The modified polytetrafluoroethylene was obtained after filtration, washing, and drying.

[0083] 10g of modified polytetrafluoroethylene powder and 1g of polytetrafluoroethylene powder were mixed evenly, vacuum dried, and hot-pressed at an initial temperature of 200°C and an initial pressure of 5MPa. The temperature was then increased from 250°C to 360°C at a rate of 10°C / min, and the pressure was increased from 5MPa to 20MPa at a pressure increase rate of 1MPa / min. The pressure was maintained at 20MPa and slowly cooled to 200°C. The pressure was released and demolded, annealed at 200°C for 30min, and naturally cooled to room temperature to obtain a bidirectional piston sealing ring.

[0084] The present invention also carried out comparative examples and related tests.

[0085] Comparative Example 1

[0086] The only difference between Comparative Example 1 and Example 1 is that modified polytetrafluoroethylene is not prepared in Comparative Example 1, but 16.5g polytetrafluoroethylene is used to prepare the sealing ring. The other compositions and preparation methods are the same as those in Example 1, and a bidirectional piston sealing ring is prepared.

[0087] Comparative Example 2

[0088] The difference between Comparative Example 2 and Example 1 is that 3-aminopropyltriethoxysilane solution is not used in the preparation of modified polytetrafluoroethylene in Comparative Example 2, and other compositions and preparation methods are the same as those in Example 1, and a bidirectional piston sealing ring is prepared.

[0089] Performance testing

[0090] The creep resistance of the bidirectional piston sealing rings prepared in Examples 1-8 and Comparative Examples 1-3 was tested according to the ASTM D621 standard, and the compression creep rate was used as the result. The dynamic friction coefficient of the bidirectional piston sealing rings prepared in Examples 1-8 and Comparative Examples 1-3 was tested according to the GB / T 3960-2016 standard, and the test conditions were 196V, 0.42m / s×60min. According to the GB / T 2411-2008 standard, the hardness of the bidirectional piston sealing rings prepared in Examples 1-8 and Comparative Examples 1-3 was tested using an OU2700 Shore hardness tester, and the Shore hardness was used as the test result. The tensile strength of the bidirectional piston sealing rings prepared in Examples 1-8 and Comparative Examples 1-3 was tested according to the ASTM D638 standard. The above test results are summarized in Table 1 below.

[0091] Table 1

[0092]

[0093] It can be seen from the test results in Table 1 above that compared with Example 1, the compression creep rate of the bidirectional piston sealing ring prepared in Comparative Example 1 is significantly increased, the cold flow phenomenon is obvious, and the tensile strength is also greatly reduced, indicating that the modification of polytetrafluoroethylene can effectively limit the segment slippage of polytetrafluoroethylene, improve its creep resistance, and promote the improvement of overall tensile performance; the compression creep rate of the bidirectional piston sealing ring prepared in Comparative Example 2 is also reduced to a certain extent compared with Example 1, indicating that 3-aminopropyltriethoxysilane can promote the formation of a cross-linked network of modified polytetrafluoroethylene and greatly improve the interfacial bonding strength of polytetrafluoroethylene.

[0094] Compared with Example 7, Example 8 does not add modified nano-zirconium phosphate when preparing modified polytetrafluoroethylene. The results show that the sealing ring prepared in Example 8 has a higher compression creep rate, indicating that the modified nano-zirconium phosphate can hinder the slippage of polytetrafluoroethylene chain segments during the use of the sealing ring, inhibit the cold flow phenomenon, and improve the creep resistance of the sealing ring.

[0095] The above is a preferred embodiment of the present invention. Those skilled in the art may make several improvements and modifications without departing from the principles of the present invention. These improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a bidirectional piston sealing ring, characterized in that: The following steps are involved: Step S1: add 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl to a reaction kettle containing N-methylpyrrolidone, stir until completely dissolved, slowly add 4,4'-(hexafluoroisopropylene) diphthalic anhydride, stir and react to obtain a pre-reaction solution; Step S2, adding pretreated polytetrafluoroethylene, triethylamine, 3-aminopropyltriethoxysilane solution and perfluorooctyltriethoxysilane to the pre-reaction liquid, ultrasonically treating, vacuum degassing, performing thermal imidization reaction, filtering, washing and drying to obtain modified polytetrafluoroethylene; Step S3, uniformly mixing the modified polytetrafluoroethylene powder and the polytetrafluoroethylene powder, vacuum drying, hot pressing, annealing after pressure relief and demoulding, and then cooling to room temperature to obtain a bidirectional piston sealing ring; The pre-treated polytetrafluoroethylene is processed by plasma.

2. The method for preparing a bidirectional piston sealing ring according to claim 1, characterized in that: In step S1, the preparation step of the 3-aminopropyltriethoxysilane solution includes: uniformly mixing 3-aminopropyltriethoxysilane and deionized water in a mass volume ratio of 1:(25-30) to obtain the 3-aminopropyltriethoxysilane solution.

3. The method for preparing a bidirectional piston sealing ring according to claim 1, characterized in that: In step S1, the stirring reaction temperature is 20-30° C. and the time is 12-16 hours.

4. The method for preparing a bidirectional piston sealing ring according to claim 1, characterized in that: The preparation of the pretreated polytetrafluoroethylene comprises the following steps: Polytetrafluoroethylene powder is spread flat in a plasma reactor, and a mixed gas of nitrogen and oxygen is filled in a ratio of 95:5 to perform plasma treatment for surface activation to obtain pretreated polytetrafluoroethylene.

5. The method for preparing a bidirectional piston seal ring according to claim 1, characterized in that: In step S2, modified nano-zirconium phosphate is added at the same time as the pretreated polytetrafluoroethylene; the modified nano-zirconium phosphate is prepared by the following steps: The nano zirconium phosphate was added into anhydrous ethanol, and then 3,3,3-trifluoropropyltriethoxysilane and 3-aminopropyltriethoxysilane were added, and the mixture was stirred evenly. The mixture was heated for reaction under nitrogen protection, cooled, centrifuged, washed, and dried to obtain the modified nano zirconium phosphate.

6. The method for preparing a bidirectional piston seal ring according to claim 1, characterized in that: In step S2, the ultrasonic treatment power is 300 W, the frequency is 20 kHz, and the time is 5-7 min; the vacuum degassing time is 10-20 min.

7. The method for preparing a bidirectional piston seal ring according to claim 1, characterized in that: In step S2, the thermal imidization reaction comprises the following steps: heating the reactor to 80-100° C., reacting for 20-40 minutes, then heating to 150-180° C., reacting for 1-2 hours, and finally heating to 220-250° C., reacting for 1-2 hours.

8. The method for preparing a bidirectional piston seal ring according to claim 1, characterized in that: In step S3, the hot pressing molding includes the following steps: the initial temperature is 200°C, the initial pressure is 5 MPa, then the temperature is increased from 250°C to 360°C at a rate of 10°C / min, the pressure is increased from 5 MPa to 20 MPa, the pressure increase rate is 1 MPa / min, and the pressure is maintained at 20 MPa and slowly cooled to 200°C to complete the hot pressing molding.

9. A bidirectional piston seal ring, characterized in that: The bidirectional piston seal ring is prepared by the preparation method of any one of claims 1 to 8, and comprises the following components in parts by weight: 10-15 parts of modified polytetrafluoroethylene and 1-1.5 parts of polytetrafluoroethylene.

10. A bidirectional piston seal according to claim 9, characterized in that: The modified polytetrafluoroethylene comprises the following raw materials in parts by weight: 0.5-1 part of modified nano zirconium phosphate, 10-12 parts of pretreated polytetrafluoroethylene, 0.15-0.18 parts of triethylamine, 6-7.2 parts of 3-aminopropyltriethoxysilane solution and 0.05-0.06 parts of perfluorooctyltriethoxysilane.

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