High wear resistance and creep resistance modified polytetrafluoroethylene composite material and its application in precision shaft sleeve

Abstract

The application relates to the technical field of modified polytetrafluoroethylene composite materials, and discloses a high-wear-resistance and creep-resistance modified polytetrafluoroethylene composite material and application of the material in a precision shaft sleeve. In the material, nano zirconium oxide is fixed on the surface of chopped carbon fibers and near the lap joint nodes together with polyamide acid, preferably, octaaminophenyl cage polysilsesquioxane is further introduced to form a POSS hybrid polyimide interface layer, and then the material is mixed with polytetrafluoroethylene and flaky graphite, cold-pressed and sintered. The obtained multi-scale bearing structure can reduce particle agglomeration and falling, limit the interface and fiber node slip, and improve the wear resistance, compression creep resistance of the material and the long-term dimensional stability of the precision shaft sleeve.

Description

Technical Field

[0001] This invention relates to the field of modified polytetrafluoroethylene (PTFE) composite materials, and more particularly to a high wear-resistant and creep-resistant modified PTFE composite material and its application in precision bushings. Background Technology

[0002] Polytetrafluoroethylene (PTFE) possesses advantages such as low coefficient of friction, chemical corrosion resistance, high and low temperature resistance, and self-lubrication, making it widely used in sliding bearings, guide sleeves, and precision bushings. However, the intermolecular forces of PTFE are relatively weak, making it prone to cold flow and compression creep under sustained loads. Pure PTFE also exhibits poor wear resistance, easily leading to increased bushing inner diameter, clearance drift, and decreased positioning accuracy after long-term operation. Existing technologies typically improve its load-bearing and wear resistance by incorporating carbon fibers, inorganic particles, graphite, or high-temperature resistant polymers. However, even with simple dispersion of the reinforcing phases, problems such as interfacial debonding, particle agglomeration, and discontinuous load transfer still easily arise.

[0003] Chinese patent application CN120923949A discloses a low-creep polytetrafluoroethylene (PTFE) composite material, using PTFE and perfluoroalkoxy resin as the composite matrix. A nickel-aluminum layered bimetallic hydroxide, a silane layer, and a fluorinated organic layer are sequentially constructed on the surface of carbon fibers. Molten perfluoroalkoxy resin is used to impregnate and modify the fibers and fill the matrix pores to improve interfacial bonding and creep resistance. This approach involves numerous surface treatment steps and requires a high proportion of perfluoroalkoxy resin, resulting in complex material composition and hot-pressing processes. Furthermore, it primarily focuses on improving overall density and creep resistance, without specifically addressing the issues of agglomeration and detachment of hard nanoparticles during friction, or the synergistic effect of wear resistance and dimensional stability.

[0004] Chinese patent application CN105295373A discloses a method for preparing carbon fiber reinforced polyimide composite material. The method involves first etching short-cut carbon fibers with concentrated nitric acid, then coating and thermally imidizing them with polyamic acid to form polyimide-coated carbon fibers, thereby improving the interfacial bonding between the carbon fibers and the polyimide matrix. However, this method uses polyimide as the continuous matrix, does not involve a low-friction sliding system based on polytetrafluoroethylene (PTFE), and does not include nano-rigid particles to reinforce the fiber overlap areas. Therefore, it is difficult to directly solve the problem of simultaneous wear and creep of PTFE bushings under long-term sliding and radial loads.

[0005] Therefore, it is still necessary to provide a modified polytetrafluoroethylene composite material with a relatively simplified structure and controllable nanoparticle distribution. By constructing a fiber-scale load-bearing structure and a nanoscale interface reinforcement structure, the wear resistance, compression creep resistance and long-term dimensional stability of the material can be improved while maintaining low friction performance. Summary of the Invention

[0006] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is: to provide a high wear-resistant and creep-resistant modified polytetrafluoroethylene composite material and its application in precision bushings, addressing the problems of easy agglomeration and detachment of nano-hard particles, weak interfacial bonding between carbon fiber and polytetrafluoroethylene, and unstable load transfer between reinforcing phases in existing filled modified polytetrafluoroethylene materials.

[0007] This invention enables nano-zirconia to adhere to the surface of chopped carbon fibers along with polyamic acid, and then forms a zirconia-polyimide composite interface layer through thermal imidization. This pre-fixes the nano-zirconia onto the surface of the chopped carbon fibers and near the fiber overlap nodes. The resulting composite reinforcement is then mixed with polytetrafluoroethylene and flake graphite, pressed, and sintered to reduce the free agglomeration and frictional shedding of the nano-zirconia, thereby improving the load transfer stability between the reinforcing phases.

[0008] Furthermore, an octaaminophenyl cage-type polysilsesquioxane is introduced into the nano-zirconia-polyamic acid system to participate in the formation of the POSS hybrid polyimide interface layer, thereby improving the rigidity, cohesive stability and fixation ability of the coating layer for nano-zirconia, and restricting the relative slippage of fiber overlap nodes under continuous load.

[0009] To achieve the above objectives, the present invention provides a method for preparing a high wear-resistant and creep-resistant modified polytetrafluoroethylene composite material, comprising the following steps:

[0010] 1) 10-14 parts of pulpless chopped carbon fibers were subjected to oxygen plasma treatment to obtain surface-activated chopped carbon fibers;

[0011] 2) Add 1.5-2.5 parts of nano-zirconia to 12-30 parts of N-methylpyrrolidone, and perform ultrasonic treatment and dispersion to obtain a nano-zirconia pre-dispersion; add 25-35 parts of PMDA-ODA type polyamic acid solution to the nano-zirconia pre-dispersion and stir to obtain a dispersion;

[0012] 3) Add the surface-activated chopped carbon fibers obtained in step 1) to the dispersion obtained in step 2), stir and mix to allow the dispersion to adhere to the surface of the chopped carbon fibers; then remove N-methylpyrrolidone and dry, and then perform thermal imidization under a protective atmosphere to convert polyamic acid into polyimide; granulate the obtained material using a oscillating granulator, and then screen out particles with a particle size of 150-425μm to obtain zirconia-polyimide composite coated carbon fiber reinforcement;

[0013] 4) Mix 75-85 parts of polytetrafluoroethylene molding polymer powder and 2-4 parts of flake graphite, then add the zirconia-polyimide composite coated carbon fiber reinforcement obtained in step 3) and mix to obtain a composite mixture;

[0014] 5) The composite mixture is filled into the mold, and vibration degassing, graded cold pressing and slow depressurization are performed in sequence to obtain the modified polytetrafluoroethylene compact;

[0015] 6) The modified polytetrafluoroethylene compact is sintered and cooled under a protective atmosphere to melt the polytetrafluoroethylene particles and obtain a sintered compact.

[0016] 7) The sintered green body is subjected to thermal dimensional stabilization treatment and left to stand at room temperature to obtain a high wear-resistant and creep-resistant modified polytetrafluoroethylene composite material.

[0017] All parts mentioned in the above steps refer to parts by mass.

[0018] Preferably, step 2) can also be: adding 1.5-2.5 parts of nano-zirconia and 0.05-0.20 parts of octaaminophenyl cage-type polysilsesquioxane to 12-30 parts of N-methylpyrrolidone, subjecting them to ultrasonic treatment and dispersion to obtain a zirconia-POSS pre-dispersion; adding 25-35 parts of PMDA-ODA type polyamic acid solution to the zirconia-POSS pre-dispersion and stirring to obtain a zirconia-POSS-polyamic acid dispersion; wherein the octaaminophenyl cage-type polysilsesquioxane has Si8O 12 It has a cage-like core and eight peripheral amino groups, and participates in the formation of a POSS hybrid polyimide interface layer during subsequent thermal imidization.

[0019] Preferably, the effective content of the PMDA-ODA type polyamic acid solution is 10 wt%.

[0020] The PMDA-ODA type polyamic acid solution is prepared by polycondensation of pyromellitic dianhydride and 4,4′-diaminodiphenyl ether in N-methylpyrrolidone, with a molar ratio of pyromellitic dianhydride to 4,4′-diaminodiphenyl ether of 1:1.

[0021] The effective content of the polyamic acid solution refers to the percentage of the mass of the obtained polyimide after the polyamic acid solution has been solvent-removed and fully thermally imidized to constant weight, relative to the mass of the original polyamic acid solution.

[0022] Preferably, in step 1), the oxygen pressure of the oxygen plasma treatment is 20-30 Pa, the treatment power is 80-120 W, and the treatment time is 4-8 min.

[0023] Preferably, in step 2), the ultrasonic treatment power is 400-600W and the time is 15-30min; the dispersion speed is 2500-3500r / min and the time is 8-15min; the stirring speed after adding PMDA-ODA type polyamic acid solution is 600-1000r / min and the stirring time is 15-30min.

[0024] Preferably, in step 3), the surface-activated short-cut carbon fibers are stirred with nano-zirconia-polyamic acid dispersion or zirconia-POSS-polyamic acid dispersion at 60-100 r / min for 15-30 min; N-methylpyrrolidone is gradually removed under conditions of 60-80℃ and absolute pressure not exceeding 20 kPa, and then vacuum dried at 90-110℃ for 3-6 h.

[0025] Preferably, the thermal imidization includes: heating to 140-160°C at 1-3°C / min and holding at that temperature for 45-90 min; heating to 210-230°C at 0.5-1.5°C / min and holding at that temperature for 45-90 min; heating to 290-310°C at 0.5-1.5°C / min and holding at that temperature for 45-90 min; and then cooling to room temperature; the degree of imidization of the polyimide obtained by thermal imidization is not less than 95%.

[0026] Preferably, in step 5), the pressure is first pre-pressurized at 8-12MPa for 1-3 minutes, then depressurized and allowed to stand for 0.5-2 minutes; then pressure is maintained at 18-25MPa for 2-5 minutes, and then the pressure is increased to 30-40MPa and maintained for 8-15 minutes, with the depressurization rate not exceeding 0.5MPa / s.

[0027] Preferably, the sintering process in step 6) includes: heating to 290-310℃ at 0.8-1.2℃ / min and holding for 45-90min; heating to 360-370℃ at 0.3-0.7℃ / min and holding for 90-150min; cooling to 315-335℃ at 0.2-0.5℃ / min and holding for 45-90min; cooling to 180-220℃ at 0.3-0.8℃ / min; and then cooling to below 100℃ at an average cooling rate not exceeding 1.0℃ / min.

[0028] Preferably, in step 7), the sintered green body is held at 230-270℃ for 90-150 min, cooled to below 100℃ at 0.3-0.8℃ / min, and then left to stand for 20-30 h at 20-28℃ and 40-60% relative humidity.

[0029] The present invention also provides a high wear-resistant and creep-resistant modified polytetrafluoroethylene composite material prepared by the above method.

[0030] This invention also provides the application of the above-mentioned high wear-resistant and creep-resistant modified polytetrafluoroethylene composite material in the manufacture of precision bushings. The precision bushing is manufactured from the above-mentioned high wear-resistant and creep-resistant modified polytetrafluoroethylene composite material.

[0031] Preferably, the surface roughness Ra of the inner hole of the precision bushing is not greater than 0.8 μm.

[0032] The precision bushing is suitable for low-speed precision rotating mechanisms, reciprocating guide mechanisms, valve actuators, or instrument rotating support mechanisms.

[0033] Beneficial effects of the present invention

[0034] This invention fixes nano-zirconia onto the surface of chopped carbon fibers and near fiber overlap nodes using polyimide, reducing the free aggregation and frictional shedding of nano-zirconia in polytetrafluoroethylene, and improving the local rigidity and load transfer stability of fiber overlap nodes.

[0035] Further introduction of octaaminophenyl cage-type polysilsesquioxane to form a POSS hybrid polyimide interface layer can improve the rigidity and cohesive stability of the coating layer, and restrict the movement of interface chain segments and fiber node slippage.

[0036] The combination of short-cut carbon fiber load-bearing structure, nano-zirconia node reinforcement structure and POSS hybrid polyimide interface layer can further improve the wear resistance, compressive creep resistance and long-term dimensional stability of the composite material and the precision bushing. Detailed Implementation

[0037] The present invention will be further described below with reference to specific embodiments. These embodiments are used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Unless otherwise stated, all the following quantities are parts by weight.

[0038] The parameters and sources of some raw materials are as follows:

[0039] Polytetrafluoroethylene (PTFE) molding polymer powder, with an average particle size of 350-500 μm and a loose packing density of 0.75-0.90 g / cm³. 3 .

[0040] Pulpless short-cut carbon fibers have an average length of 150-250μm and an average diameter of 6-8μm.

[0041] Nano-zirconia with an average particle size of 30-60 nm.

[0042] Flake graphite with an average particle size of 5-10 μm.

[0043] Octaaminophenyl cage-type polysilsesquioxane, abbreviated as octaaminophenyl POSS, has Si8O 12 Cage-like core and 8 peripheral amino groups, CAS No.: 518359-82-5.

[0044] The preparation method of PMDA-ODA type polyamic acid solution is as follows:

[0045] Pyromellitic dianhydride and 4,4′-diaminodiphenyl ether were dried in a vacuum drying oven, with the pyromellitic dianhydride being dried at 120℃ for 4 hours and the 4,4′-diaminodiphenyl ether being dried at 80℃ for 4 hours. N-methylpyrrolidone with a moisture content of no more than 500 ppm was used as the reaction solvent.

[0046] Under dry nitrogen protection, 700.00 g of N-methylpyrrolidone and 52.38 g of 4,4′-diaminodiphenyl ether were added to the reactor, and stirred at 300 r / min until the 4,4′-diaminodiphenyl ether was completely dissolved. The system was cooled to 5°C, and 57.05 g of pyromellitic dianhydride was added in 6 portions over 60 min, with the system temperature controlled not to exceed 10°C during the addition process. After the addition was completed, 190.57 g of N-methylpyrrolidone was added, and stirring was continued at 5°C for 2 h. The temperature was then raised to 25°C and stirred for 12 h to obtain a polyamic acid solution.

[0047] The obtained polyamic acid solution was filtered through a filter medium with a pore size of 100 μm and degassed for 30 min at 25 °C and an absolute pressure not exceeding 20 kPa to obtain a PMDA-ODA type polyamic acid solution.

[0048] Example 1

[0049] A method for preparing a high wear-resistant and creep-resistant modified polytetrafluoroethylene composite material includes the following steps:

[0050] 1) Place 12 parts by weight of pulpless chopped carbon fiber in an oxygen plasma treatment device and treat for 6 minutes under the conditions of oxygen pressure of 30 Pa and treatment power of 100 W to obtain surface activated chopped carbon fiber; after surface activation treatment, seal and store the chopped carbon fiber and use it for subsequent treatment within 2 hours.

[0051] 2) Add 2 parts by mass of nano-zirconia to 20 parts by mass of N-methylpyrrolidone, treat with ultrasonic power of 500W for 20 min, and then disperse at high speed of 3000 r / min for 10 min to obtain nano-zirconia pre-dispersion; add 30 parts by mass of PMDA-ODA type polyamic acid solution to the nano-zirconia pre-dispersion, and stir at 800 r / min for 20 min to obtain nano-zirconia-polyamic acid dispersion;

[0052] 3) Add the surface-activated chopped carbon fibers obtained in step 1) to the nano-zirconia-polyamic acid dispersion obtained in step 2), and stir at 80 r / min for 20 min to ensure uniform mixing, allowing the nano-zirconia-polyamic acid dispersion to adhere to the surface of the chopped carbon fibers; under stirring, gradually remove N-methylpyrrolidone at 70℃ and an absolute pressure not exceeding 20 kPa until the resulting material is a loose wet powder; dry the resulting material under vacuum at 100℃ for 4 h, and then transfer it to a nitrogen-protected furnace for thermal imidization according to the following procedure: increase the temperature to 150℃ at 2℃ / min and hold for 60 min; increase the temperature to 220℃ at 1℃ / min and hold for 60 min. The material is heated to 300℃ at a rate of 1℃ / min and held for 60min. It is then cooled to room temperature in the furnace. The thermally imidized material is fed into a oscillating granulator equipped with a 1.0mm mesh screen and granulated twice at a oscillation frequency of 60 times / min, each time for 30s. Subsequently, it is sieved using 40-mesh and 100-mesh standard sieves, collecting particles that pass through the 40-mesh sieve but not the 100-mesh sieve, resulting in zirconia-polyimide composite coated carbon fiber reinforcement with a particle size of 150-425μm. The granulation process is used to break down loose agglomerates formed during drying and thermal imidization, avoiding significant breakage of short-cut carbon fibers caused by high-speed impact crushing.

[0053] Infrared spectroscopy analysis showed that the degree of imidization of the obtained polyimide was not less than 95%.

[0054] 4) Add 80 parts by weight of polytetrafluoroethylene molding polymer powder and 3 parts by weight of flake graphite to a three-dimensional mixer and mix at 20 r / min for 5 min to disperse the flake graphite between the polytetrafluoroethylene particles; add the zirconia-polyimide composite coated carbon fiber reinforcement obtained in step 3) and continue mixing at 15 r / min for 8 min to obtain a composite mixture; after adding the zirconia-polyimide composite coated carbon fiber reinforcement, use low-speed mixing to reduce carbon fiber breakage and prevent the polyimide coating layer from peeling off from the carbon fiber surface;

[0055] 5) Fill the composite mixture obtained in step 4) into a tubular mold and apply vibration at a frequency of 10 Hz and an amplitude of 0.2 mm for 30 s to eliminate obvious bridging and large-sized voids; first, pre-press at 10 MPa for 2 min, then release the pressure and let stand for 1 min to expel air from the gaps between the powders; then maintain pressure at 20 MPa for 3 min, then increase the pressure to 35 MPa and maintain the pressure for 10 min; slowly release the pressure at a rate not exceeding 0.5 MPa / s, and after demolding, obtain a modified polytetrafluoroethylene tubular preform; the inner diameter of the tubular preform is 18 mm, the outer diameter is 34 mm, and the length is 24 mm;

[0056] 6) Place the tubular compact obtained in step 5) in a nitrogen-protected sintering furnace, and purge the air in the furnace with nitrogen to ensure that the oxygen volume fraction in the furnace does not exceed 1% during the sintering process; sinter according to the following procedure: heat from room temperature to 300℃ at 1.0℃ / min and hold for 60 min; heat to 365℃ at 0.5℃ / min and hold for 120 min; cool to 325℃ at 0.3℃ / min and hold for 60 min; cool to 200℃ at 0.5℃ / min; then cool to below 100℃ at an average cooling rate not exceeding 1.0℃ / min, and then cool to room temperature with the furnace;

[0057] During the pressing and sintering process, the polyimide-coated chopped carbon fibers overlap each other to form a micron-scale load-bearing support structure; nano-zirconia distributed on the surface of the carbon fibers is used to improve the rigidity of the fiber overlap area and limit the relative slippage between adjacent carbon fibers; the polyimide layer is used to buffer the local stress concentration between the carbon fibers and nano-zirconia and polytetrafluoroethylene body.

[0058] 7) The sintered tubular preform was kept at 250℃ for 120 min and cooled to 100℃ at a rate of 0.5℃ / min, and then cooled to room temperature in the furnace. The resulting tubular preform was placed in an environment with a temperature of 23±2℃ and a relative humidity of 50±10% and left to stand for 24 h to obtain the tubular preform, which is a dimensionally stable high wear-resistant and creep-resistant modified polytetrafluoroethylene composite material.

[0059] Applications in precision bushings

[0060] The inner hole, outer circumferential surface, and end face of the tubular blank obtained in step 7) are precision turned using diamond tools, followed by precision honing of the inner hole. After machining, a precision bushing with an inner diameter of 20.020-20.030 mm, an outer diameter of 30.025-30.035 mm, and a length of 20.00±0.02 mm is obtained. The surface roughness Ra of the inner hole is not greater than 0.8 μm. The precision bushing is press-fitted into a bearing seat hole with an inner diameter of 30.000-30.010 mm, forming an outer diameter interference fit of 0.015-0.035 mm. The diameter of the shaft mating with the precision bushing is 19.997-20.000 mm, the surface hardness of the shaft is not less than 55 HRC, and the surface roughness Ra is not greater than 0.2 μm. The initial diameter clearance between the precision bushing and the shaft is 0.020-0.033 mm.

[0061] The precision bushing is used in low-speed precision rotating mechanisms, reciprocating guide mechanisms, valve actuators, or instrument rotating support mechanisms. During use, the overlapping short-cut carbon fibers bear and transmit radial loads, the nano-zirconia-reinforced fiber overlaps inhibit slippage of the support structure, the polyimide interface layer reduces local stress concentration, and polytetrafluoroethylene and flake graphite maintain the low friction performance of the sliding surface.

[0062] Example 2

[0063] A method for preparing a high wear-resistant and creep-resistant modified polytetrafluoroethylene composite material includes the following steps:

[0064] 1) Place 12 parts by weight of pulpless chopped carbon fiber in an oxygen plasma treatment device and treat for 6 minutes under the conditions of oxygen pressure of 30 Pa and treatment power of 100 W to obtain surface activated chopped carbon fiber; after surface activation treatment, seal and store the chopped carbon fiber and use it for subsequent treatment within 2 hours.

[0065] 2) Add 2 parts by weight of nano-zirconia and 0.10 parts by weight of octaaminophenyl POSS to 20 parts by weight of N-methylpyrrolidone, treat with ultrasonic power of 500W for 20min, and then disperse at high speed of 3000r / min for 10min to obtain zirconia-POSS pre-dispersion.

[0066] Add 30 parts by mass of PMDA-ODA type polyamic acid solution to the zirconium oxide-POSS predispersant and stir at 800 r / min for 20 min at 20°C to obtain zirconium oxide-POSS-polyamic acid dispersion.

[0067] The amino groups surrounding the octaaminophenyl POSS interact with the carboxyl groups, ammonium acid groups, and end groups in the polyamic acid chain segment, and participate in the formation of branched or slightly cross-linked POSS hybrid polyimide structures during subsequent thermal imidization.

[0068] 3) Add the surface-activated short carbon fibers obtained in step 1) to the zirconium oxide-POSS-polyamic acid dispersion obtained in step 2), and stir and mix evenly at 80 r / min for 20 min to allow the zirconium oxide-POSS-polyamic acid dispersion to adhere to the surface of the short carbon fibers.

[0069] Under stirring, N-methylpyrrolidone was gradually removed at 70°C and an absolute pressure not exceeding 20 kPa until the resulting material was a loose, wet powder. The resulting material was dried under vacuum at 100°C for 4 hours, and then transferred to a nitrogen-protected furnace for thermal imidization according to the following procedure: heating to 150°C at 2°C / min and holding for 60 min; heating to 220°C at 1°C / min and holding for 60 min; heating to 300°C at 1°C / min and holding for 60 min; and then cooling to room temperature in the furnace.

[0070] During the thermal imidization process, polyamic acid is converted into polyimide, and octaaminophenyl POSS participates in the formation of a branched or slightly cross-linked POSS hybrid polyimide interface layer, and fixes nano-zirconia onto the surface of short-cut carbon fibers.

[0071] The thermally imidized material was fed into a oscillating granulator equipped with a 1.0 mm sieve and granulated twice for 30 seconds each time at an oscillation frequency of 60 times / min. Subsequently, it was sieved using 40 mesh and 100 mesh standard sieves in sequence. Particles that could pass through the 40 mesh standard sieve but could not pass through the 100 mesh standard sieve were collected to obtain zirconium oxide-POSS hybrid polyimide composite coated carbon fiber reinforced material with a particle size of 150-425 μm.

[0072] Infrared spectroscopy analysis showed that the degree of imidization of the obtained polyimide was not less than 95%.

[0073] 4) Add 79.90 parts by weight of polytetrafluoroethylene molding polymer powder and 3 parts by weight of flake graphite to a three-dimensional mixer and mix at 20 r / min for 5 min to disperse the flake graphite between the polytetrafluoroethylene particles; add the zirconia-POSS hybrid polyimide composite coated carbon fiber reinforcement obtained in step 3) and continue mixing at 15 r / min for 8 min to obtain the composite mixture;

[0074] After adding the zirconium oxide-POSS hybrid polyimide composite coated carbon fiber reinforcement, low-speed mixing is used to reduce carbon fiber breakage and prevent the POSS hybrid polyimide coating layer from peeling off the carbon fiber surface.

[0075] 5) Fill the composite mixture obtained in step 4) into a tubular mold and apply vibration at a frequency of 10 Hz and an amplitude of 0.2 mm for 30 s to eliminate obvious bridging and large-sized voids; first, pre-press at 10 MPa for 2 min, then release the pressure and let stand for 1 min to expel air from the gaps between the powders; then maintain pressure at 20 MPa for 3 min, then increase the pressure to 35 MPa and maintain the pressure for 10 min; slowly release the pressure at a rate not exceeding 0.5 MPa / s, and after demolding, obtain a modified polytetrafluoroethylene tubular preform; the inner diameter of the tubular preform is 18 mm, the outer diameter is 34 mm, and the length is 24 mm;

[0076] 6) Place the tubular compact obtained in step 5) in a nitrogen-protected sintering furnace, and purge the air in the furnace with nitrogen to ensure that the oxygen volume fraction in the furnace does not exceed 1% during the sintering process; sinter according to the following procedure: heat from room temperature to 300℃ at 1.0℃ / min and hold for 60 min; heat to 365℃ at 0.5℃ / min and hold for 120 min; cool to 325℃ at 0.3℃ / min and hold for 60 min; cool to 200℃ at 0.5℃ / min; then cool to below 100℃ at an average cooling rate not exceeding 1.0℃ / min, and then cool to room temperature with the furnace;

[0077] During pressing and sintering, the short-cut carbon fibers coated with POSS hybrid polyimide overlap each other to form a micron-scale load-bearing support structure. The nano-zirconia distributed on the surface of the carbon fibers is used to improve the rigidity of the fiber overlap area and limit the relative slippage between adjacent carbon fibers. The Si-O-Si cage structure of POSS is used to improve the rigidity and cohesive stability of the polyimide interface layer and limit the segment slippage of the interface layer under continuous load. The POSS hybrid polyimide layer is also used to buffer the local stress concentration between the carbon fibers, nano-zirconia and polytetrafluoroethylene body.

[0078] 7) The sintered tubular preform was kept at 250℃ for 120 min and cooled to 100℃ at a rate of 0.5℃ / min, and then cooled to room temperature in the furnace. The resulting tubular preform was placed in an environment with a temperature of 23±2℃ and a relative humidity of 50±10% and left to stand for 24 h to obtain the tubular preform, which is a dimensionally stable high wear-resistant and creep-resistant modified polytetrafluoroethylene composite material.

[0079] Applications in precision bushings

[0080] The inner hole, outer circumferential surface, and end face of the tubular blank obtained in step 7) are precision turned using diamond tools, and then the inner hole is precision honed. After machining, a precision bushing with an inner diameter of 20.020-20.030 mm, an outer diameter of 30.025-30.035 mm, and a length of 20.00±0.02 mm is obtained, and the surface roughness Ra of the inner hole is not greater than 0.8 μm. The precision bushing is press-fitted into a bearing seat hole with an inner diameter of 30.000-30.010 mm to form an outer diameter interference of 0.015-0.035 mm.

[0081] The diameter of the shaft that mates with the precision bushing is 19.997-20.000 mm, the surface hardness of the shaft is not less than 55 HRC, and the surface roughness Ra is not greater than 0.2 μm. The initial diameter clearance between the precision bushing and the shaft is 0.020-0.033 mm.

[0082] The precision bushing is used in low-speed precision rotating mechanisms, reciprocating guide mechanisms, valve actuators, or instrument rotating support mechanisms. During use, the overlapping short-cut carbon fibers bear and transmit radial loads, the nano-zirconia-reinforced fiber overlaps inhibit slippage of the support structure, the POSS hybrid polyimide interface layer improves the rigidity, cohesive strength, and long-term stability of the coating layer, and polytetrafluoroethylene and flake graphite maintain the low friction performance of the sliding surface.

[0083] Comparative Example 1

[0084] The comparative example has the same raw material composition as Example 1, except that short-cut carbon fibers, nano-zirconia and polyimide are added separately, and zirconia-polyimide composite coated carbon fiber reinforcement is not prepared in advance.

[0085] A method for preparing a modified polytetrafluoroethylene composite material includes the following steps:

[0086] 1) Place 12 parts by weight of pulpless chopped carbon fiber in an oxygen plasma treatment device and treat for 6 minutes under the conditions of oxygen pressure of 30 Pa and treatment power of 100 W to obtain surface activated chopped carbon fiber; after surface activation treatment, seal and store the chopped carbon fiber and use it for subsequent treatment within 2 hours.

[0087] 2) Place 30 parts by mass of PMDA-ODA type polyamic acid solution at 70℃ and an absolute pressure not exceeding 20 kPa to remove N-methylpyrrolidone, and then dry it under vacuum at 100℃ for 4 hours; transfer the resulting solid to a nitrogen-protected furnace, heat it to 150℃ at 2℃ / min and hold it for 60 min, heat it to 220℃ at 1℃ / min and hold it for 60 min, and then heat it to 300℃ at 1℃ / min and hold it for 60 min. The polyimide solid obtained by thermal imidization is then cooled to room temperature in the furnace. The solid is cut or pre-crushed into pieces with a maximum size of no more than 5 mm, and then fed into a high-speed universal pulverizer. The pulverizer is pulverized at 6000 r / min for 30 s, then stopped and cooled for 60 s. The pulverization is repeated 3 times. Then, the powder is sieved through 100 mesh and 200 mesh standard sieves in sequence. The powder that can pass through the 100 mesh standard sieve but cannot pass through the 200 mesh standard sieve is collected to obtain polyimide powder with a particle size of 75-150 μm.

[0088] 3) Add 80 parts by weight of polytetrafluoroethylene molding polymer powder, 3 parts by weight of flake graphite, 3 parts by weight of polyimide powder and 2 parts by weight of nano-zirconia into a three-dimensional mixer and mix at 20 r / min for 5 min; add 12 parts by weight of surface-activated short-cut carbon fiber obtained in step 1) and continue mixing at 15 r / min for 8 min to obtain a composite mixture.

[0089] 4) Following the steps 5)-7) of Example 1, cold pressing, nitrogen-protected sintering, dimensional stabilization treatment and precision machining were performed sequentially to obtain the modified polytetrafluoroethylene composite material and precision bushing of Comparative Example 1.

[0090] Comparative Example 2

[0091] The comparative example has the same raw material composition as Example 1, except that polyimide is coated on the surface of chopped carbon fibers, while nano-zirconia is pre-dispersed in polytetrafluoroethylene powder and is not co-loaded with polyimide on the surface of chopped carbon fibers.

[0092] A method for preparing a modified polytetrafluoroethylene composite material includes the following steps:

[0093] 1) Place 12 parts by weight of pulpless chopped carbon fiber in an oxygen plasma treatment device and treat for 6 minutes under the conditions of oxygen pressure of 30 Pa and treatment power of 100 W to obtain surface activated chopped carbon fiber; after surface activation treatment, seal and store the chopped carbon fiber and use it for subsequent treatment within 2 hours.

[0094] 2) Add the surface-activated chopped carbon fibers obtained in step 1) to 30 parts by mass of PMDA-ODA type polyamic acid solution and stir at 80 r / min for 20 min. Under stirring, gradually remove N-methylpyrrolidone at 70℃ and absolute pressure not exceeding 20 kPa until the material is a loose wet powder. Dry the obtained material under vacuum at 100℃ for 4 h, then transfer it to a nitrogen-protected furnace, heat it to 150℃ at 2℃ / min and hold for 60 min, heat it to 220℃ at 1℃ / min and hold for 60 min, then heat it to 300℃ at 1℃ / min and hold for 60 min, and then cool it to room temperature with the furnace. Particles with a particle size of 150-425 μm are sieved to obtain polyimide-coated carbon fiber reinforcement.

[0095] 3) Add 2 parts by weight of nano-zirconia to 20 parts by weight of N-methylpyrrolidone, sonicate at 500W for 20 min, and then disperse at 3000 r / min for 10 min; add 18 parts by weight of polytetrafluoroethylene molding polymer powder, stir at 800 r / min for 15 min, and then stir at 300 r / min for 30 min; remove N-methylpyrrolidone under conditions not exceeding 45℃ and absolute pressure not exceeding 20 kPa, and then dry under vacuum at 80℃ for 8 h; put the dried material into a oscillating granulator equipped with a 1.0 mm sieve, and granulate twice at an oscillation frequency of 60 times / min, 30 s each time; then sieve using 40 mesh and 100 mesh standard sieves in sequence, collect particles that can pass through the 40 mesh standard sieve but cannot pass through the 100 mesh standard sieve, and obtain zirconia pre-dispersion with a particle size of 150-425 μm;

[0096] 4) Add the zirconia pre-dispersed material obtained in step 3), 62 parts by weight of polytetrafluoroethylene molding polymer powder and 3 parts by weight of flake graphite into a three-dimensional mixer and mix at 20 r / min for 5 min; add the polyimide-coated carbon fiber reinforcement obtained in step 2) and continue mixing at 15 r / min for 8 min to obtain a composite mixture.

[0097] 5) Following the steps 5)-7) of Example 1, cold pressing, nitrogen-protected sintering, dimensional stabilization treatment and precision machining were performed sequentially to obtain the modified polytetrafluoroethylene composite material and precision bushing of Comparative Example 2.

[0098] Test Example 1

[0099] Micromorphology testing of composite reinforced structures

[0100] The composite materials obtained in Examples 1-2 and Comparative Examples 1-2 were subjected to brittle fracture in liquid nitrogen, and the cross-section perpendicular to the pressing direction was selected as the observation surface.

[0101] The cross-sectional morphology was observed using field emission scanning electron microscopy, and the surface scans of carbon, fluorine, oxygen, zirconium, and silicon were performed using energy-dispersive X-ray spectroscopy. Five samples were randomly selected from each group, and ten fields of view were selected from each sample for statistical analysis.

[0102] The region where two or more short-cut carbon fibers are close to each other and the distance between their fiber surfaces is no more than 5 μm is defined as a fiber overlap node; the zirconium enrichment region where the center distance from the fiber overlap node is no more than 3 μm is defined as a node-associated zirconium oxide region.

[0103] The node association rate is calculated using the following formula:

[0104] Node association rate = Number of zirconia regions associated with a node ÷ Total number of observed zirconia enrichment regions × 100%.

[0105] At the same time, the number of zirconia aggregates with an equivalent diameter greater than 5 μm and the proportion of carbon fibers with obvious interfacial gaps with a width greater than 1 μm to the total number of carbon fibers observed were also counted.

[0106] For Example 2, the silicon element interface correlation rate was also calculated. The silicon element signal region within 1 μm of the carbon fiber surface was defined as the interface-correlated silicon element region, and the silicon element interface correlation rate was calculated using the following formula:

[0107] Silicon element interface correlation rate = area of ​​silicon element signal associated with interface ÷ total area of ​​observed silicon element signal × 100%.

[0108] The field emission scanning electron microscope (FESEM) used in the tests was a Regulus 8100 (Hitachi High Technology Co., Ltd.); the energy dispersive X-ray spectrometer (EDXPS) was an Ultim Max 65 silicon drift detector (Oxford Instruments NanoAnalysis). For FESEM morphology observation, the accelerating voltage was 3-5 kV and the working distance was 8-10 mm; for EXPS surface scanning, the accelerating voltage was 15 kV and the working distance was 10 mm, with a surface scan acquisition time of 120 s per field of view. The cross-sectional morphology of the samples was observed using FESEM, and surface scan analysis of carbon, fluorine, oxygen, zirconium, and silicon was performed using EXPS.

[0109] Table 1. Microstructure test results of composite materials

[0110] Example 1 73.8±4.2 2.7±0.6 6.5±1.2 Not detected Example 2 82.4±3.6 1.9±0.5 4.2±0.9 88.6±3.1 Comparative Example 1 21.6±3.1 24.3±2.5 28.4±3.0 Not detected Comparative Example 2 15.2±2.7 4.0±1.0 8.1±1.4 Not detected

[0111] As shown in Table 1, in Comparative Example 1, the nano-zirconia agglomerates significantly and there are many gaps at the carbon fiber interface; although Comparative Example 2 improves the dispersion of zirconia and the carbon fiber interface, the correlation between zirconia and the fiber overlap node is low.

[0112] Example 1 uses polyimide to fix nano-zirconia onto the surface of carbon fibers and near the lap joints, improving the zirconia node correlation rate. Example 2 further introduces octaaminophenyl POSS, whose silicon element is mainly distributed in the carbon fiber interface region. Simultaneously, the zirconia node correlation rate increases to 82.4%, and the interface porosity decreases to 4.2%. This indicates that the POSS-hybridized polyimide layer improves the bonding stability between zirconia and carbon fibers, forming a multi-scale composite structure with carbon fiber support, zirconia node reinforcement, and POSS-hybridized polyimide interface strengthening.

[0113] Test Example 2

[0114] Sliding friction and wear performance test

[0115] The sliding friction and wear test was conducted in accordance with GB / T 3960-2016 "Test Method for Sliding Friction and Wear of Plastics".

[0116] Standard samples were processed using the same batch of composite materials from Examples 1-2 and Comparative Examples 1-2, respectively. The mating ring was made of No. 45 steel with a surface hardness of 55-60 HRC and an initial surface roughness Ra of 0.10-0.15 μm.

[0117] Test conditions: test load is 200N, sliding speed is 0.42m / s, test time is 120min, test ambient temperature is 23±2℃, relative humidity is 50±10%, no lubricant is added.

[0118] Record the average friction coefficient during the stable operation phase of the test (30-120 min). Weigh the sample before and after the test, and calculate the wear volume and specific wear rate based on the sample density. Five parallel samples were tested in each group, and the average value was taken. After the test, the surface roughness of the wear-scarred area of ​​the paired steel ring was measured using a surface roughness meter. The test samples were the composite materials obtained in Examples 1-2 and Comparative Examples 1-2; the paired ring was a No. 45 steel ring.

[0119] Table 2. Sliding friction and wear properties of composite materials

[0120] Example 1 0.165±0.006 1.7±0.2 0.16±0.02 Example 2 0.156±0.005 1.2±0.2 0.14±0.02 Comparative Example 1 0.193±0.009 5.2±0.5 0.31±0.04 Comparative Example 2 0.178±0.007 3.0±0.3 0.22±0.03

[0121] As shown in Table 2, Comparative Example 1 has a higher wear rate and surface roughness of the paired steel ring due to zirconia agglomeration and interface defects; Comparative Example 2 improves zirconia dispersion and carbon fiber interface, resulting in improved wear resistance.

[0122] Example 1 reduced particle shedding and abrasive wear by fixing nano-zirconia to the surface of carbon fibers and near the overlap nodes. Example 2 showed a specific wear rate that was approximately 29.4% lower than that of Example 1, indicating that the POSS hybrid polyimide layer can improve the cohesive strength and structural stability of the coating layer, reduce zirconia shedding and interfacial fatigue failure, thereby further improving the wear resistance of the material.

[0123] Test Example 3

[0124] Compression performance testing was conducted according to GB / T 1041-2008 "Determination of Compression Properties of Plastics". Compression specimens were prepared using the same batch of composite mixtures from Examples 1-2 and Comparative Examples 1-2, under the same pressing, sintering, and dimensional stabilization conditions. The specimen dimensions were 10 mm × 10 mm × 4 mm, with the loading direction aligned with the radial direction of the tubular preform. The test environment temperature was 23 ± 2℃, and the test speed was 1 mm / min. The compression modulus was measured. Five parallel specimens were tested in each group, and the average value was taken.

[0125] The constant-load compression creep test was conducted using the isothermal-constant-load compression creep method. A 10mm × 10mm × 4mm specimen was placed between parallel pressure plates and preheated at 80±1℃ for 60 min. A preload of 0.1 MPa was applied and held for 5 min; the specimen thickness at this point was taken as the initial thickness. Subsequently, a constant compressive stress of 8 MPa was applied, and the compressive creep strain was measured at 1 h, 24 h, and 168 h. After 168 h of loading, the load was removed, and the specimen was allowed to recover at 23±2℃ for 24 h; the residual compressive strain was then measured.

[0126] For the precision bushing inner diameter drift test, the precision bushings obtained in Examples 1-2 and Comparative Examples 1-2 were press-fitted into the same steel bearing seat holes and then left to stand at 23±2℃ for 24 hours. A steel mandrel with a diameter of 20.000 mm and a surface hardness of 58-62 HRC was installed inside the bushing, and a constant radial load equivalent to 8 MPa of the bushing's projected bearing area was applied to the mandrel at 80±1℃ and maintained for 168 hours. After unloading, the bushing was left to stand at 23±2℃ for 24 hours, and the inner diameter in two mutually perpendicular directions at the mid-section of the bushing was measured using a pneumatic gauge. The increase in the average inner diameter measurement value relative to the average inner diameter before loading was taken as the permanent inner diameter drift. The test samples were the composite materials and precision bushings obtained in Examples 1-2 and Comparative Examples 1-2.

[0127] Table 3 Compressive and creep properties of composite materials

[0128] Example 1 936±34 2.05±0.12 2.84±0.17 0.82±0.08 8.5±1.2 Example 2 1015±36 1.72±0.11 2.31±0.15 0.61±0.07 6.1±1.0 Comparative Example 1 712±29 3.72±0.21 5.96±0.31 2.20±0.16 25.6±2.8 Comparative Example 2 821±31 2.81±0.18 4.18±0.24 1.43±0.11 16.4±1.9

[0129] As shown in Table 3, in Comparative Example 1, each reinforcing component is independently dispersed, resulting in unstable load transfer, low compressive modulus, and significant long-term creep and bushing inner diameter drift. Comparative Example 2 improved the carbon fiber interface, but zirconia could not effectively strengthen the fiber overlap joints.

[0130] Example 1 improved the load-bearing and creep resistance of the material by reinforcing the carbon fiber overlap joints with zirconia. Example 2 showed an approximately 8.4% increase in compressive modulus compared to Example 1, a approximately 18.7% reduction in 168-hour compressive creep strain, and a approximately 28.2% reduction in permanent bushing inner diameter drift. This indicates that the POSS hybrid polyimide layer can restrict interfacial chain segment movement and fiber node slippage, further improving the composite material's compressive creep resistance and the long-term dimensional stability of the bushing.

[0131] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for preparing a high wear-resistant and creep-resistant modified polytetrafluoroethylene composite material, comprising the following steps: 1) 10-14 parts of pulpless chopped carbon fibers were subjected to oxygen plasma treatment to obtain surface-activated chopped carbon fibers; 2) Add 1.5-2.5 parts of nano-zirconia to 12-30 parts of N-methylpyrrolidone, and perform ultrasonic treatment and dispersion to obtain a nano-zirconia pre-dispersion; add 25-35 parts of PMDA-ODA type polyamic acid solution to the nano-zirconia pre-dispersion and stir to obtain a dispersion; 3) Add the surface-activated chopped carbon fibers obtained in step 1) to the dispersion obtained in step 2), stir and mix to allow the dispersion to adhere to the surface of the chopped carbon fibers; then remove N-methylpyrrolidone and dry, and then perform thermal imidization under a protective atmosphere to convert polyamic acid into polyimide; granulate the obtained material using a oscillating granulator, and then screen out particles with a particle size of 150-425μm to obtain zirconia-polyimide composite coated carbon fiber reinforcement; 4) Mix 75-85 parts of polytetrafluoroethylene molding polymer powder and 2-4 parts of flake graphite, then add the zirconia-polyimide composite coated carbon fiber reinforcement obtained in step 3) and mix to obtain a composite mixture; 5) The composite mixture is filled into the mold, and vibration degassing, graded cold pressing and slow depressurization are performed in sequence to obtain the modified polytetrafluoroethylene compact; 6) The modified polytetrafluoroethylene compact is sintered and cooled under a protective atmosphere to melt the polytetrafluoroethylene particles and obtain a sintered compact. 7) The sintered green body is subjected to thermal dimensional stabilization treatment and left to stand at room temperature to obtain a high wear-resistant and creep-resistant modified polytetrafluoroethylene composite material. All parts mentioned in the above steps refer to parts by mass.

2. The preparation method of the high wear-resistant and creep-resistant modified polytetrafluoroethylene composite material as described in claim 1, characterized in that, Step 2) can also be: adding 1.5-2.5 parts of nano-zirconia and 0.05-0.20 parts of octaaminophenyl cage-type polysilsesquioxane to 12-30 parts of N-methylpyrrolidone, and performing ultrasonic treatment and dispersion to obtain a zirconia-POSS pre-dispersion; adding 25-35 parts of PMDA-ODA type polyamic acid solution to the zirconia-POSS pre-dispersion and stirring to obtain a zirconia-POSS-polyamic acid dispersion.

3. The method for preparing the high wear-resistant and creep-resistant modified polytetrafluoroethylene composite material as described in claim 1, characterized in that, The effective content of the PMDA-ODA type polyamic acid solution is 10wt%; the PMDA-ODA type polyamic acid solution is prepared by polycondensation of pyromellitic dianhydride and 4,4′-diaminodiphenyl ether in N-methylpyrrolidone, with the molar ratio of pyromellitic dianhydride to 4,4′-diaminodiphenyl ether being 1:

1.

4. The method for preparing the high wear-resistant and creep-resistant modified polytetrafluoroethylene composite material as described in claim 1, characterized in that: In step 1), the oxygen pressure of the oxygen plasma treatment is 20-30 Pa, the treatment power is 80-120 W, and the treatment time is 4-8 min.

5. The method for preparing the high wear-resistant and creep-resistant modified polytetrafluoroethylene composite material as described in claim 1, characterized in that: In step 2), the ultrasonic treatment power is 400-600W and the time is 15-30min; the dispersion speed is 2500-3500r / min and the time is 8-15min; the stirring speed after adding PMDA-ODA type polyamic acid solution is 600-1000r / min and the stirring time is 15-30min.

6. The method for preparing the high wear-resistant and creep-resistant modified polytetrafluoroethylene composite material as described in claim 1 or 2, characterized in that: In step 3), the surface-activated short-cut carbon fibers are stirred with nano-zirconia-polyamic acid dispersion or zirconia-POSS-polyamic acid dispersion at 60-100 r / min for 15-30 min; N-methylpyrrolidone is gradually removed under the conditions of 60-80℃ and absolute pressure not exceeding 20 kPa, and then vacuum dried at 90-110℃ for 3-6 h. The thermal imidization includes: heating to 140-160°C at a rate of 1-3°C / min and holding at that temperature for 45-90min; Heat to 210-230℃ at 0.5-1.5℃ / min and hold for 45-90 min; heat to 290-310℃ at 0.5-1.5℃ / min and hold for 45-90 min; then cool to room temperature; the degree of imidization of the polyimide obtained by thermal imidization shall not be less than 95%.

7. The method for preparing the high wear-resistant and creep-resistant modified polytetrafluoroethylene composite material as described in claim 1, characterized in that: In step 5), first pre-pressurize at 8-12MPa for 1-3 minutes, depressurize and let stand for 0.5-2 minutes; then maintain pressure at 18-25MPa for 2-5 minutes, then increase the pressure to 30-40MPa and maintain pressure for 8-15 minutes, with the depressurization rate not exceeding 0.5MPa / s.

8. The method for preparing the high wear-resistant and creep-resistant modified polytetrafluoroethylene composite material as described in claim 1, characterized in that: The sintering process in step 6) includes: heating to 290-310℃ at 0.8-1.2℃ / min and holding for 45-90min; heating to 360-370℃ at 0.3-0.7℃ / min and holding for 90-150min; cooling to 315-335℃ at 0.2-0.5℃ / min and holding for 45-90min; cooling to 180-220℃ at 0.3-0.8℃ / min; and then cooling to below 100℃ at an average cooling rate not exceeding 1.0℃ / min.

9. A high-wear-resistant and creep-resistant modified polytetrafluoroethylene composite material, characterized in that, Prepared by the method described in any one of claims 1-8.

10. The application of the high wear-resistant and creep-resistant modified polytetrafluoroethylene composite material as described in claim 9 in the preparation of precision bushings, characterized in that: The inner surface roughness Ra of the precision bushing is not greater than 0.8μm; the precision bushing is suitable for low-speed precision rotating mechanisms, reciprocating guide mechanisms, valve actuators or instrument rotating support mechanisms.