Corrosion-resistant PTFE sealing ring and production process thereof

Abstract

The application discloses a kind of corrosion-resistant PTFE sealing ring and its production process, the raw material includes polytetrafluoroethylene, modified polytetrafluoroethylene and modified filling material;The production process includes: the modification of filling material, the modification of polytetrafluoroethylene and the preparation of sealing ring;First, the application utilizes perfluorooctyl triethoxysilane and gamma-glycidyl ether oxygen propyl trimethoxysilane modified nano h-boron nitride and silicon carbide powder, prepares filling material, under the effect of not affecting the nature of polytetrafluoroethylene itself, realize the significant improvement of wear resistance, thermal conductivity and anti creep performance of sealing ring;The application introduces ether chain by copolymerizing silane modified polytetrafluoroethylene and perfluoropropyl vinyl ether under ammonium persulfate initiation, finally introduces amino group by gamma-aminopropyl triethoxysilane, realizes the close combination with filling material, binder, to improve the connectivity with material, enhance sealing capacity.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sealing elements, in particular to a corrosion-resistant PTFE sealing ring and a production process thereof. BACKGROUND

[0002] Polytetrafluoroethylene (PTFE) has excellent chemical inertness, a wide temperature resistance range of -200 DEG C to 260 DEG C and a low friction coefficient. A sealing element is a key element in a hydraulic device, and the core requirement is to realize low friction and close to zero leakage in the whole service life of the device. Therefore, polytetrafluoroethylene becomes a core base material of a sealing element in the fields of chemical industry, nuclear power and medicine, and is widely used for preparing static sealing rings and dynamic sealing assemblies. However, although the single PTFE material has very strong corrosion resistance, the traditional polytetrafluoroethylene sealing ring has the following defects:

[0003] Firstly, the cold flow property is obvious, and irreversible plastic deformation is prone to occur under the action of continuous load, so that the fitting degree of the sealing surface is reduced; secondly, the wear resistance is poor, and the pure PTFE is not easy to bond, the volume wear rate of the pure PTFE is higher than the industry standard under the dynamic sealing working condition, the sealing element needs to be frequently replaced, and the bonding property of the pure PTFE with steel parts is poor, so that the sealing performance is affected. Therefore, a production process of a polytetrafluoroethylene sealing ring suitable for severe corrosion working conditions needs to be developed. SUMMARY

[0004] The application aims at solving the defects in the prior art and provides a corrosion-resistant PTFE sealing ring and a production process thereof.

[0005] In order to achieve the above-mentioned purpose, the application adopts the following technical scheme:

[0006] The application first provides a corrosion-resistant PTFE sealing ring, which comprises the following raw materials:

[0007] 100 parts of polytetrafluoroethylene: low molecular weight polytetrafluoroethylene powder provided by the American DuPont Company;

[0008] 30-50 parts of modified polytetrafluoroethylene: perfluoropropyl vinyl ether modified polytetrafluoroethylene powder;

[0009] 20-30 parts of modified filling material: modified nano-h-boron nitride and silicon carbide mixed powder.

[0010] Preferably, the raw materials for preparing the sealing ring not only comprise the modified polytetrafluoroethylene, but also the unmodified polytetrafluoroethylene is a key substance that must be added. Although the modified polytetrafluoroethylene powder has high surface activity and good adhesion, the side chain may affect the crystallinity and mechanical strength of the polytetrafluoroethylene itself, so it is still necessary to be mixed with a large amount of unmodified low molecular weight PTFE powder to maintain high corrosion resistance and low friction coefficient.

[0011] The application further provides a production process of the corrosion-resistant PTFE sealing ring.

[0012] S1, modification of the filling material

[0013] The nano h-boron nitride powder and the silicon carbide powder are mixed uniformly at a mass ratio of 1:1, placed in a muffle furnace, calcined at 400 DEG C in an air atmosphere for 2h, taken out, soaked in nitric acid, ultrasonically treated for 30 min, centrifuged, washed with deionized water, and then full-fluorooctyl triethoxysilane and gamma-glycidyl ether oxypropyl trimethoxysilane are dissolved in an ethanol / water mixture, the mass fraction of each is 1-3%, acetic acid is used to adjust pH to 4.5, stirring is carried out at room temperature for 30 min, 5-8% of the full-fluorooctyl triethoxysilane and gamma-glycidyl ether oxypropyl trimethoxysilane mixed solution is added to the washed mixed powder, 50 DEG C constant-temperature water bath stirring is carried out for 3h, acetone centrifugal washing is carried out for 3 times, and 105 DEG C drying is carried out for 6h, so that the modified filling material is obtained.

[0014] The nano h-boron nitride has a hexagonal crystal structure, and the layers are combined by weak van der waals force, so that the layers are easy to slide, and the nano h-boron nitride has good heat conductivity, corrosion resistance and lubricity. After the nano h-boron nitride is calcined in air, the B-N bond in the surface part of the nano h-boron nitride is broken to form a boron-hydroxyl bond, and then the acidification treatment is carried out by using nitric acid, so that more hydroxyl groups are exposed. The silicon carbide powder contains silicon elements, and after the calcination and the acid treatment, the surface hydroxyl groups are increased.

[0015] ;

[0016] ;

[0017] ;

[0018] ;

[0019] In order to enhance the compatibility of nano h-boron nitride, silicon carbide and polytetrafluoroethylene matrix, perfluorooctyl triethoxysilane and γ-glycidyl ether propyl trimethoxysilane are used for treatment, perfluorooctyl triethoxysilane and γ-glycidyl ether propyl trimethoxysilane are dissolved in aqueous ethanol solution, under acidic conditions, ethoxy is hydrolyzed to hydroxyl, which can condense with the hydroxyl on the surface of nano h-boron nitride and silicon carbide, thereby grafted to its surface, due to the existence of fluorine chain in perfluorooctyl triethoxysilane, the thermal conductivity and wear resistance of the composite material can be improved without damaging the high corrosion resistance of polytetrafluoroethylene itself, at the same time, the existence of fluorine chain ensures that nano h-boron nitride and silicon carbide are uniformly mixed with polytetrafluoroethylene and will not agglomerate in polytetrafluoroethylene; and γ-glycidyl ether propyl trimethoxysilane contains epoxy, which can be covalently connected with the subsequent modified polytetrafluoroethylene, thereby tightly combining nano h-boron nitride and silicon carbide on the surface of modified polyurethane;

[0020]

[0021] S2, modification of polytetrafluoroethylene

[0022] S201, the pretreated low molecular weight polytetrafluoroethylene powder is treated by water vapor plasma for 60-120s, swells in a mixed solvent of perfluorohexane and anhydrous ethanol with a volume ratio of 7:3, stirs for 20-30min, the solid-liquid ratio is 1:10, vinyl trimethoxysilane is dissolved in aqueous ethanol solution, acetic acid is added to adjust the pH, 10-12% of the total amount of the system of vinyl trimethoxysilane solution is added to the polytetrafluoroethylene mixed solution, mechanical stirring is carried out in a 60℃ constant temperature water bath for 2h, centrifugation, ethanol washing and drying are carried out to obtain silane modified polytetrafluoroethylene powder;

[0023] After the low molecular weight polytetrafluoroethylene powder is pretreated by ethanol to remove surface impurities, it is treated by plasma method, first, the surface C-F bond of the low molecular weight polytetrafluoroethylene powder is broken under the bombardment of high energy plasma, surface free radicals (-CF2·, -CF·) are generated, these free radicals react with active -OH・ in water vapor plasma, finally hydroxyl groups are introduced, the introduction rate of hydroxyl groups is about 7%, the low molecular weight polytetrafluoroethylene powder is slightly swelled in a mixed solvent of perfluorohexane and anhydrous ethanol, so that the silane molecules are more easily diffused to the surface and shallow layer of polytetrafluoroethylene, the grafting rate is improved, the silicon hydroxyl groups are generated under acidic hydrolysis conditions of vinyl trimethoxysilane, and the silicon hydroxyl groups condense with the hydroxyl groups on the surface of the low molecular weight polytetrafluoroethylene powder, thereby introducing double bonds into the side chain of polytetrafluoroethylene;

[0024]

[0025] S202. Silane-modified polytetrafluoroethylene powder was placed in a 5wt% aqueous solution of perfluorooctanoic acid (PFOA), ultrasonically dispersed, vacuumed, and protected with nitrogen. Perfluoropropyl vinyl ether was added, stirred and dissolved, and the temperature was raised to 70℃. 1% of 0.1wt% ammonium persulfate was slowly added, and the pressure inside the reactor was adjusted to 1.5MPa. The reaction was carried out for 3 hours. Three times the volume of anhydrous ethanol was added, and the mixture was centrifuged and extracted using a Soxhlet extract. The mixture was then placed in a 2wt% γ-aminopropyltriethoxysilane ethanol hydrolysis solution, heated to 50-60℃, stirred and reacted for 1 hour, washed with ethanol, and centrifuged and dried to obtain perfluoropropyl vinyl ether-modified polytetrafluoroethylene powder.

[0026] Silane-modified polytetrafluoroethylene (PTFE) powder was dispersed in an aqueous solution of perfluorooctanoic acid (PFOA). PFOA significantly reduced the surface tension of water, better wetting the highly hydrophobic PTFE powder and preventing its aggregation, thus forming a stable dispersion system in water. Upon addition of ammonium persulfate, it decomposed to generate two sulfate radicals (SO42-). - The double bonds in silane-modified polytetrafluoroethylene (PTFE) lack electron-withdrawing groups and exhibit high reactivity. Sulfate radicals preferentially undergo radical addition reactions with PTFE. Slow addition is used to regulate the amount of radicals generated, ensuring the grafting rate. The addition product radicals continue to attack the double bonds of perfluoropropyl vinyl ether (PFME) to carry out chain growth. In the later stages of growth, the radical addition terminates. The product is washed with ethanol, and the sulfate ions in the side chains enter the aqueous phase as water-soluble salts. Finally, perfluorohexane is used as a solvent for Soxhlet extraction of the centrifuged product. The solvent has good compatibility with PPVE and is insoluble in PTFE, further removing residual perfluoropropyl vinyl ether impurities.

[0027] Although copolymerization with perfluoropropyl vinyl ether introduces silicon-oxygen bonds and carbon-oxygen bonds, the surface energy of the product remains low. When using adhesives to bond the sealing ring to the steel components, the bond is not tight and leakage is likely to occur. Therefore, the residual hydroxyl groups on the surface of polytetrafluoroethylene powder modified by perfluoropropyl vinyl ether are condensed with the hydrolysis products of γ-aminopropyltriethoxysilane to introduce amino groups. On the one hand, the amino groups are hydrophilic, which enhances the binding. On the other hand, they can bind tightly with the epoxy groups in the adhesive, thereby achieving a tight bond with the components.

[0028]

[0029]

[0030]

[0031] S3. Preparation of the sealing ring

[0032] The low molecular weight polytetrafluoroethylene powder, the perfluoropropyl vinyl ether modified polytetrafluoroethylene powder and the modified filler material are dried respectively, mixed gradually for 40 min by using a planetary mixer, a fluorine-containing release agent is applied in a mold, the mixed powder is filled into a mold, and the pressure is kept for 10-20 min under a pressure of 15-25 MPa; the pre-formed sealing ring is taken out of the mold, the temperature is raised to 300 DEG C at a temperature rising speed of 80 DEG C / h, then the temperature is raised to 340-350 DEG C at a temperature rising speed of 50 DEG C / h, and the temperature is kept for 3 h; the temperature is lowered to 300 DEG C at a temperature lowering speed of 20 DEG C / h, and then the temperature is lowered to 200 DEG C at a temperature lowering speed of 30 DEG C / h; then the temperature is lowered to room temperature naturally; the sintered blank is placed in a 110 DEG C air oven and kept for 5 h, and then the blank is cooled to room temperature in a furnace; the diamond is polished to obtain a finished sealing ring;

[0033] The raw material powder is dried first to remove water molecules in the raw material, so that water molecules are prevented from expanding to form bubbles in the blank when being heated in the subsequent mold pressing; in the mixing stage, the epoxy groups on the surface of the modified filler material slowly combine with the amino groups on the surface of the perfluoropropyl vinyl ether modified polytetrafluoroethylene powder to form weak covalent bonds; in the pre-forming stage, the raw material powders slide and rearrange under the action of pressure, and gradually change from loose powders to closely packed structures;

[0034] After the ether chain is introduced, the melting temperature of the modified polytetrafluoroethylene is lowered; in the sintering stage, the polytetrafluoroethylene is in a transition state from triclinic crystal system to hexagonal crystal system, the molecular chain movement is intensified, but the whole still maintains a crystalline state; above 300 DEG C, the polytetrafluoroethylene crystal completely melts into an amorphous state, the molecular chain becomes disordered, can freely move and highly elastically deform, and the raw material forms a dense whole; the temperature is kept at 345 DEG C for 3 h to ensure that all the polytetrafluoroethylene powder completely melts, the molecules have enough time to diffuse into adjacent powders, completely eliminate the powder boundaries, realize complete sintering, and the gradient slow cooling ensures that the molten state can be highly crystallized.

[0035] Preferably, after the sintering is completed, the sealing ring still needs to be kept at 110 DEG C for 5 h, at which temperature the polytetrafluoroethylene molecular chain can slowly move to release the residual stress accumulated in the mold pressing and sintering process, and cracking caused by stress release in subsequent processing or use is avoided.

[0036] Compared with the prior art, the present application has the following beneficial effects:

[0037] 1、The application selects nano h-boron nitride and silicon carbide as basic filling materials, which have the advantages of single material and synergistic effect. Nano h-boron nitride has excellent lubricity, high temperature stability and corrosion resistance due to its hexagonal layered structure, and can inhibit the sliding of polytetrafluoroethylene molecular chain; silicon carbide has high hardness, high strength and good thermal conductivity as the core advantage, which can enhance the material's wear resistance and deformation resistance. When the two are mixed in a mass ratio of 1:1, a lubricating and reinforcing synergistic system is formed, nano h-boron nitride solves the cold flow problem of polytetrafluoroethylene, silicon carbide improves the wear resistance of the sealing ring, and both maintain excellent weather resistance. With the modification of perfluorooctyltriethoxysilane and gamma-glycidyl ether oxypropyltrimethoxysilane, the interfacial bonding strength with polytetrafluoroethylene is improved, and finally the finished sealing ring has low friction, cold flow resistance, high wear resistance and strong corrosion resistance, which is suitable for harsh sealing scenes such as high temperature and high pressure.

[0038] 2、The application significantly breaks through the performance bottleneck of traditional polytetrafluoroethylene sealing materials through multi-step modification of polytetrafluoroethylene. First, the double bond active site is introduced into polytetrafluoroethylene by vinyltrimethoxysilane modification, and then copolymerization is carried out with perfluoropropyl vinyl ether under the initiation of ammonium persulfate to introduce ether chains, which reduces the crystallinity of polytetrafluoroethylene, effectively inhibits the cold flow problem of polytetrafluoroethylene caused by high crystallinity, reduces the creep, and ensures that the sealing surface is not invalid for a long time. Again, gamma-aminopropyltriethoxysilane is introduced to introduce amino groups, which can form stable covalent bonds with the epoxy groups on the surface of the modified filling material to enhance the interfacial bonding strength and prevent the loss of filling material, and can also react efficiently with the active groups of the adhesive (such as epoxy groups, isocyanate groups, etc.), solving the poor adhesion of traditional polytetrafluoroethylene and the pain points of the material, reducing the sealing leakage rate, and achieving the synergistic improvement of cold flow resistance, strong bonding and high sealing. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 The nuclear magnetic resonance spectrum of perfluoropropyl vinyl ether modified polytetrafluoroethylene powder prepared by the application;

[0040] Figure 2 The process flow chart for producing the sealing ring of the application. DETAILED DESCRIPTION

[0041] The technical solutions in the embodiments of the application will be described in detail below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, not all.

[0042] Example 1:

[0043] S1, modification of filling material

[0044] The nano-h-boron nitride powder and silicon carbide powder are mixed uniformly at a mass ratio of 1:1, placed in a muffle furnace, calcined at 400°C in an air atmosphere for 2h, taken out, soaked in nitric acid for 30min, centrifuged, washed with deionized water, and then full-fluorooctyl triethoxysilane and γ-glycidyl ether oxypropyl trimethoxysilane are dissolved in an ethanol / water mixture, the pH is adjusted to 4.5 with acetic acid, and the mixture is stirred at room temperature for 30min. Then, 6% of the full-fluorooctyl triethoxysilane and γ-glycidyl ether oxypropyl trimethoxysilane mixed solution is added to the washed mixed powder, and the mixture is stirred in a 50°C constant temperature water bath for 3h. The mixture is centrifuged with acetone for 3 times, and then dried at 105°C for 6h to obtain the modified filler material.

[0045] S2, modification of polytetrafluoroethylene

[0046] S201, the pretreated low molecular weight polytetrafluoroethylene powder is treated with water vapor plasma for 90s, swelled in a mixed solvent of full-fluorohexane and anhydrous ethanol at a volume ratio of 7:3, stirred for 30min, and then the solid-liquid ratio is 1:10. Vinyltrimethoxysilane is dissolved in an ethanol aqueous solution, and the pH is adjusted by adding acetic acid. Then, 10% of the vinyltrimethoxysilane solution is added to the polytetrafluoroethylene mixture, and the mixture is mechanically stirred in a 60°C constant temperature water bath for 2h. The mixture is centrifuged, washed with ethanol, and dried to obtain silane modified polytetrafluoroethylene powder.

[0047] S202, the silane modified polytetrafluoroethylene powder is placed in a 5wt% perfluorooctanoic acid aqueous solution, ultrasonically dispersed, vacuumed, and protected by nitrogen. Then, perfluoropropyl vinyl ether is added and stirred to dissolve. The temperature is increased to 70°C, 1% of 0.1wt% ammonium persulfate is slowly added, the pressure in the kettle is adjusted to 1.5MPa, and the reaction is carried out for 3h. Then, three times the volume of anhydrous ethanol is added, the mixture is centrifuged and Soxhlet extracted. The mixture is placed in a 2wt% γ-aminopropyl triethoxysilane ethanol hydrolysis solution, the temperature is increased to 55°C, and the mixture is stirred for 1h. The mixture is washed with ethanol, centrifuged and dried to obtain perfluoropropyl vinyl ether modified polytetrafluoroethylene powder.

[0048] S3, preparation of a sealing ring

[0049] 100 parts of low molecular weight polytetrafluoroethylene powder, 30 parts of perfluoropropyl vinyl ether modified polytetrafluoroethylene powder, 25 parts of modified filler material are dried respectively, mixed step by step for 40 min by using a planetary mixer, a fluorine-containing release agent is applied in the mold, the mixed powder is filled into the mold, and the pressure is kept at 20 MPa for 15 min. The pre-formed sealing ring is taken out of the mold, the temperature is raised to 300℃ at a rate of 80℃ / h, then raised to 345℃ at a rate of 50℃ / h, and kept for 3h, then reduced to 300℃ at a rate of 20℃ / h, and then reduced to 200℃ at a rate of 30℃ / h, and then naturally cooled. The sintered blank is placed in a 110℃ air oven for 5h, and then cooled to room temperature in the furnace. After diamond polishing, the finished sealing ring is obtained.

[0050] Example 2:

[0051] S1, modification of filler material

[0052] The nano-h-boron nitride powder and the silicon carbide powder are mixed uniformly in a mass ratio of 1:1, placed in a muffle furnace, calcined at 400℃ in an air atmosphere for 2h, taken out, soaked in nitric acid for 30min, centrifuged, washed with deionized water, and then dissolved in an ethanol / water mixture. The pH is adjusted to 4.5 with acetic acid, and stirred at room temperature for 30min. 6% of the total system of perfluorooctyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane mixed solution is added to the washed mixed powder, and stirred in a 50℃ constant temperature water bath for 3h. Centrifugal washing with acetone is performed 3 times, and drying is performed at 105℃ for 6h to obtain the modified filler material.

[0053] S2, modification of polytetrafluoroethylene

[0054] S201, the pretreated low molecular weight polytetrafluoroethylene powder is treated with water vapor plasma for 90s, swelled with a mixed solvent of perfluorohexane and anhydrous ethanol in a volume ratio of 7:3, stirred for 30min, and the solid-liquid ratio is 1:10. Vinyltrimethoxysilane is dissolved in an ethanol aqueous solution, and the pH is adjusted by adding acetic acid. 10% of the total system of vinyltrimethoxysilane solution is added to the polytetrafluoroethylene mixture, mechanically stirred in a 60℃ constant temperature water bath for 2h, centrifuged, washed with ethanol, and dried to obtain silane modified polytetrafluoroethylene powder.

[0055] S202, the silane modified polytetrafluoroethylene powder is placed in a 5wt% perfluorooctanoic acid aqueous solution, ultrasonic dispersion, vacuum, nitrogen protection, addition of perfluoropropyl vinyl ether, stirring and dissolving, heating to 70℃, slowly adding 1% of 0.1wt% ammonium persulfate in the total system, adjusting the pressure in the kettle to 1.5MPa, reacting for 3h, adding three times the volume of anhydrous ethanol in the system, centrifuging, Soxhlet extraction, placing it in a 2wt% γ-aminopropyl triethoxysilane ethanol hydrolysis solution, heating to 55℃, stirring for 1h, ethanol washing, centrifuging and drying to obtain perfluoropropyl vinyl ether modified polytetrafluoroethylene powder;

[0056] S3, preparation of the sealing ring

[0057] 100 parts of low molecular weight polytetrafluoroethylene powder, 50 parts of perfluoropropyl vinyl ether modified polytetrafluoroethylene powder, and 25 parts of modified filler material are dried respectively, mixed gradually for 40min using a planetary mixer, a fluorine-containing release agent is applied in the mold, the mixed powder is filled into the mold, and the pressure is maintained at 20MPa for 15min. The pre-formed sealing ring is taken out of the mold, heated to 300℃ at a rate of 80℃ / h, then heated to 345℃ at a rate of 50℃ / h, and kept for 3h, then cooled to 300℃ at a rate of 20℃ / h, and then cooled to 200℃ at a rate of 30℃ / h, and then naturally cooled. The sintered blank is placed in a 110℃ air oven for 5h, cooled to room temperature in the furnace, polished with diamond, and the finished sealing ring is obtained.

[0058] Example 3:

[0059] S1, modification of the filler material

[0060] The nano h-boron nitride powder and silicon carbide powder are mixed uniformly in a mass ratio of 1:1, placed in a muffle furnace, calcined at 400℃ in air for 2h, taken out, soaked in nitric acid for 30min, centrifuged, washed with deionized water, and then dissolved in an ethanol / water mixture. The pH is adjusted to 4.5 with acetic acid, and stirred at room temperature for 30min. 6% of the total system of perfluorooctyl triethoxysilane and γ-glycidyl ether oxypropyl trimethoxysilane mixed solution is added to the washed mixed powder, and stirred in a 50℃ constant temperature water bath for 3h. Centrifugal washing with acetone for 3 times, and drying at 105℃ for 6h to obtain the modified filler material.

[0061] S2, modification of polytetrafluoroethylene

[0062] S201, the pretreated low molecular weight polytetrafluoroethylene powder is treated with water vapor plasma for 90s, swells in a mixed solvent of perfluorohexane and anhydrous ethanol at a volume ratio of 7:3, stirs for 30min, the solid-liquid ratio is 1:10, the vinyltrimethoxysilane is dissolved in an ethanol aqueous solution, acetic acid is added to adjust the pH, 10% of the total amount of the system is added to the polytetrafluoroethylene mixed solution, mechanical stirring is carried out in a 60℃ constant temperature water bath for 2h, centrifugation, ethanol washing, and drying to obtain silane modified polytetrafluoroethylene powder;

[0063] S202, the silane modified polytetrafluoroethylene powder is placed in a 5wt% perfluorooctanoic acid aqueous solution, ultrasonic dispersion, vacuum extraction, nitrogen protection, perfluoropropyl vinyl ether is added, stirred and dissolved, heated to 70℃, 1% of the total amount of the system is slowly added 0.1wt% ammonium persulfate, the pressure in the kettle is adjusted to 1.5MPa, and the reaction is carried out for 3h, three times the volume of anhydrous ethanol is added, centrifuged, and Soxhlet extracted, and then placed in a 2wt% γ-aminopropyl triethoxysilane ethanol hydrolysis solution, heated to 55℃, stirred and reacted for 1h, washed with ethanol, centrifuged and dried to obtain perfluoropropyl vinyl ether modified polytetrafluoroethylene powder;

[0064] S3, preparation of the sealing ring

[0065] 100 parts of low molecular weight polytetrafluoroethylene powder, 40 parts of perfluoropropyl vinyl ether modified polytetrafluoroethylene powder, and 20 parts of modified filler are dried respectively, gradually mixed for 40min by using a planetary mixer, a fluorine-containing release agent is applied in a mold, the mixed powder is filled into a mold, and the pressure is maintained at 20MPa for 15min, the preformed sealing ring is taken out of the mold, the temperature is increased to 300℃ at a rate of 80℃ / h, then increased to 345℃ at a rate of 50℃ / h, and maintained for 3h, then decreased to 300℃ at a rate of 20℃ / h, and then decreased to 200℃ at a rate of 30℃ / h, and then naturally cooled, the sintered blank is placed in a 110℃ air oven for 5h, cooled in the furnace to room temperature, polished by diamond grinding, and the finished sealing ring is obtained.

[0066] Example 4:

[0067] S1, modification of the filler

[0068] The nano-h-boron nitride powder and silicon carbide powder are mixed uniformly at a mass ratio of 1:1, placed in a muffle furnace, calcined at 400°C in an air atmosphere for 2h, taken out, soaked in nitric acid for 30min, centrifuged, washed with deionized water, and then full-fluorooctyl triethoxysilane and γ-glycidyl ether oxypropyl trimethoxysilane are dissolved in an ethanol / water mixture, the pH is adjusted to 4.5 with acetic acid, and the mixture is stirred at room temperature for 30min. Then, 6% of the full-fluorooctyl triethoxysilane and γ-glycidyl ether oxypropyl trimethoxysilane mixed solution is added to the washed mixed powder, and the mixture is stirred in a 50°C constant temperature water bath for 3h. The mixture is centrifuged with acetone for 3 times, and then dried at 105°C for 6h to obtain the modified filler material.

[0069] S2, modification of polytetrafluoroethylene

[0070] S201, the pretreated low molecular weight polytetrafluoroethylene powder is treated with water vapor plasma for 90s, swelled in a mixed solvent of full-fluorohexane and anhydrous ethanol at a volume ratio of 7:3, stirred for 30min, and then the solid-liquid ratio is 1:10. Vinyltrimethoxysilane is dissolved in an ethanol aqueous solution, and the pH is adjusted by adding acetic acid. Then, 10% of the vinyltrimethoxysilane solution is added to the polytetrafluoroethylene mixture, and the mixture is mechanically stirred in a 60°C constant temperature water bath for 2h. The mixture is centrifuged, washed with ethanol, and dried to obtain silane modified polytetrafluoroethylene powder.

[0071] S202, the silane modified polytetrafluoroethylene powder is placed in a 5wt% perfluorooctanoic acid aqueous solution, ultrasonically dispersed, vacuumed, and protected by nitrogen. Then, perfluoropropyl vinyl ether is added and stirred to dissolve. The temperature is increased to 70°C, 1% of 0.1wt% ammonium persulfate is slowly added, the pressure in the kettle is adjusted to 1.5MPa, and the reaction is carried out for 3h. Then, three times the volume of anhydrous ethanol is added, the mixture is centrifuged and Soxhlet extracted. The mixture is placed in a 2wt% γ-aminopropyl triethoxysilane ethanol hydrolysis solution, the temperature is increased to 55°C, and the mixture is stirred for 1h. The mixture is washed with ethanol, centrifuged and dried to obtain perfluoropropyl vinyl ether modified polytetrafluoroethylene powder.

[0072] S3, preparation of a sealing ring

[0073] 100 parts of low molecular weight polytetrafluoroethylene powder, 40 parts of perfluoropropyl vinyl ether modified polytetrafluoroethylene powder, 30 parts of modified filler material are dried respectively, mixed step by step for 40 min by using a planetary mixer, a fluorine-containing release agent is applied in the mold, the mixed powder is filled into the mold, and the pressure is kept at 20 MPa for 15 min. The pre-formed sealing ring is taken out of the mold, the temperature is raised to 300℃ at a rate of 80℃ / h, then raised to 345℃ at a rate of 50℃ / h, and kept for 3h, then reduced to 300℃ at a rate of 20℃ / h, and then reduced to 200℃ at a rate of 30℃ / h, and then naturally cooled. The sintered blank is placed in a 110℃ air oven for 5h, and then cooled to room temperature in the furnace. After diamond polishing, the finished sealing ring is obtained.

[0074] Example 5:

[0075] S1, modification of filler material

[0076] The nano-h-boron nitride powder and the silicon carbide powder are mixed uniformly in a mass ratio of 1:1, placed in a muffle furnace, calcined at 400℃ in an air atmosphere for 2h, taken out, soaked in nitric acid for 30min, centrifuged, washed with deionized water, and then dissolved in an ethanol / water mixture. The pH is adjusted to 4.5 with acetic acid, and stirred at room temperature for 30min. 6% of the total system of perfluorooctyl triethoxysilane and γ-glycidyl ether propyl trimethoxysilane mixed solution is added to the washed mixed powder, and stirred in a 50℃ constant temperature water bath for 3h. Centrifugal washing with acetone is performed 3 times, and drying is performed at 105℃ for 6h to obtain the modified filler material.

[0077] S2, modification of polytetrafluoroethylene

[0078] S201, the pretreated low molecular weight polytetrafluoroethylene powder is treated with water vapor plasma for 90s, swelled in a mixed solvent of perfluorohexane and anhydrous ethanol in a volume ratio of 7:3, stirred for 30min, and the solid-liquid ratio is 1:10. Vinyltrimethoxysilane is dissolved in an ethanol aqueous solution, and the pH is adjusted by adding acetic acid. 10% of the total system of vinyltrimethoxysilane solution is added to the polytetrafluoroethylene mixture, mechanically stirred in a 60℃ constant temperature water bath for 2h, centrifuged, washed with ethanol, and dried to obtain silane modified polytetrafluoroethylene powder.

[0079] S202, the silane modified polytetrafluoroethylene powder is placed in a 5wt% perfluorooctanoic acid aqueous solution, ultrasonic dispersion, vacuum, nitrogen protection, addition of perfluoropropyl vinyl ether, stirring and dissolving, heating to 70℃, slowly adding 1% of the total system 0.1wt% ammonium persulfate, adjusting the pressure in the kettle to 1.5MPa, reacting for 3h, adding three times the volume of anhydrous ethanol to the system, centrifuging, Soxhlet extraction, and placing it in a 2wt% γ-aminopropyl triethoxysilane ethanol hydrolysis solution, heating to 55℃, stirring for 1h, ethanol washing, centrifuging and drying to obtain perfluoropropyl vinyl ether modified polytetrafluoroethylene powder;

[0080] S3, preparation of the sealing ring

[0081] 100 parts of low molecular weight polytetrafluoroethylene powder, 40 parts of perfluoropropyl vinyl ether modified polytetrafluoroethylene powder, and 25 parts of modified filler material are dried separately, mixed gradually for 40min using a planetary mixer, a fluorine-containing release agent is applied in the mold, the mixed powder is loaded into the mold, and the pressure is maintained at 20MPa for 15min. The pre-formed sealing ring is removed from the mold, heated to 300℃ at a rate of 80℃ / h, then heated to 345℃ at a rate of 50℃ / h, maintained for 3h, then cooled to 300℃ at a rate of 20℃ / h, and then cooled to 200℃ at a rate of 30℃ / h, and then naturally cooled. The sintered blank is placed in a 110℃ air oven for 5h, cooled to room temperature in the furnace, polished with diamond, and the finished sealing ring is obtained.

[0082] Comparative Example 1:

[0083] Compared with Example 5, the number of parts of perfluoropropyl vinyl ether modified polytetrafluoroethylene powder added in S3 is 60 parts.

[0084] Comparative Example 2:

[0085] Compared with Example 5, the number of parts of modified filler material added in S3 is 40 parts.

[0086] Comparative Example 3:

[0087] Compared with Example 5, only modified nano-h-boron nitride is used as the filler material.

[0088] Comparative Example 4:

[0089] Compared with Example 5, only modified silicon carbide is used as the filler material.

[0090] Comparative Example 5:

[0091] Compared with Example 5, in S1, only perfluorooctyl triethoxysilane is used to modify the filler material.

[0092] Comparative Example 6:

[0093] Compared with Example 5, in S1, only γ-glycidoxypropyltrimethoxysilane was used to modify the filler material.

[0094] Comparative Example 7:

[0095] Compared with Example 5, in S201, the mixed solvent swelling of perfluorohexane and anhydrous ethanol was not performed.

[0096] Comparative Example 8:

[0097] Compared with Example 5, in S201, after modification with perfluoropropyl vinyl ether, γ-aminopropyl triethoxysilane was not used for treatment.

[0098] Performance test:

[0099] According to the standards and test methods of GB / T1040.1-2018 "Determination of tensile properties of plastics", GB / T2411-2008 "Determination of indentation hardness of plastics and hard rubber using a durometer", GB / T13404-2008 "Non-metallic polytetrafluoroethylene gasket for pipe flange", GB / T3960-2016 "Plastic sliding friction and wear test method", GB / T7759-2015 "Vulcanized rubber or thermoplastic rubber-Compression permanent deformation determination", GB / T11547-2008 "Determination of liquid chemical resistance of plastics", GB / T42919-2023 "Determination of thermal conductivity and thermal diffusivity of plastics", the tensile, hardness, sealing, wear, resilience and thermal conductivity of the sealing ring prepared in all examples and comparative examples of the application were tested.

[0100] Table 1 Performance test data of sealing rings prepared in each group

[0101]

[0102] Data analysis:

[0103] Comparative Example 3 only uses modified nano h-boron nitride as a filler material. Compared with Example 5, the tensile strength decreases, the hardness decreases, the thermal conductivity decreases from 3.26 W / (m·K) to 3.01 W / (m·K), the wear rate increases, and the leakage, compression permanent deformation rate and corrosion rate remain basically unchanged. The core reason is the lack of high hardness enhancement and wear resistance of silicon carbide. The hardness of silicon carbide is much higher than that of h-boron nitride, and its removal leads to a decrease in the carrying capacity of the material, a decrease in tensile strength and hardness, and a disappearance of wear resistance barrier, an increase in wear rate. While the flaky structure of h-boron nitride can still maintain the sealing barrier and part of the thermal conductivity network, the flexible flaky characteristics also slightly improve the tensile rate, so the compression deformation and corrosion rate do not fluctuate significantly.

[0104] Comparative Example 4 uses only modified silicon carbide as a filler material, and the performance is worse than Example 5, with the differences mainly in sealing, thermal conductivity, toughness, and deformation resistance. Compared with Example 5, the leakage amount increased significantly, the thermal conductivity decreased to 1.52 W / (m·K), the tensile rate decreased, and the compression permanent deformation rate increased from 3.82% to 6.72%. Only the tensile strength and wear rate were close. This can be explained as follows: compared with Example 5, Comparative Example 4 lacks the sealing and efficient thermal conduction network function of h-boron nitride sheets. The h-boron nitride sheet structure can block the leakage path, and after its removal, the gap between the silicon carbide particles forms a leakage path, and the leakage amount increases. h-Boron nitride is easy to build a continuous thermal conduction network, while the granular thermal conduction path of silicon carbide is easy to break, and the thermal conductivity decreases sharply. At the same time, the flexibility of h-boron nitride can balance the rigidity of silicon carbide, and its absence increases the brittleness of the material and the presence of rigid particles hinders elastic recovery. Only the enhancement and wear resistance of silicon carbide are retained.

[0105] Comparative Example 5 uses only perfluorooctyltriethoxysilane to modify the filler material, and the performance is overall lower than Example 5: the tensile strength decreases from 25.7 MPa to 24.5 MPa, the tensile rate decreases from 312% to 265%, the leakage amount increases from 4.27 x 10 -6 mbar·L / s to 6.22 x 10 -6 mbar·L / s, the wear rate increases from 4.88 x 10 -6 mm 3 / (N·m) to 6.84 x 10 -6 mm 3 / (N·m), the compression permanent deformation rate increases from 3.82% to 5.52%, the thermal conductivity decreases from 3.26 W / (m·K) to 1.77 W / (m·K), and only the hardness and corrosion rate fluctuate slightly. The reason is the lack of chemical bonding effect of γ-glycidyl ether propyl trimethoxysilane, and perfluorooctyltriethoxysilane can only improve physical compatibility through hydrophobicity, while γ-glycidyl ether propyl trimethoxysilane can form covalent bonds with the matrix amino group, and the interface bonding changes from chemical + physical bonding to pure physical bonding. The sealing ring will have problems such as an increase in interface microcracks, easy falling of the filler, blocked stress transmission, and interrupted thermal conduction path.

[0106] Comparative Example 6 only uses γ-glycidoxypropyltrimethoxysilane to modify the filler material, and the performance is lower than that of Example 5, especially the corrosion performance, the corrosion rate increases from 0.45% to 1.33%, and the thermal conductivity decreases from 3.26 W / (m·K) to 1.69 W / (m·K). The core problem is the lack of hydrophobic compatibility of perfluorooctyltriethoxysilane, although γ-glycidoxypropyltrimethoxysilane can form chemical bonds, it has poor compatibility with the hydrophobic PTFE matrix, and a large number of voids are generated at the interface, so the leakage rate increases, at the same time, the voids provide a penetration channel for the corrosion medium, and the filler and the matrix cannot deform together, the filler is easy to fall off, only the chemical bond maintains part of the interface strength, so the performance is worse than that of Example 5.

[0107] Comparative Example 7 does not use the mixed solvent of perfluorohexane and anhydrous ethanol for swelling, compared with Example 5, the tensile strength, tensile rate, thermal conductivity, leakage amount, wear rate, compression permanent set, hardness and corrosion rate are basically unchanged, which is due to the swelling of the polytetrafluoroethylene chain segment, which can improve the silane grafting rate, and the polytetrafluoroethylene powder treated by plasma is placed in it, which can also expose more hydroxyl sites, after the swelling step is removed, part of the silane cannot effectively penetrate to the surface of the matrix, the interface bonding is weakened, but the double silane modification still retains part of the effect, so the performance decreases less than Comparative Examples 5-6.

[0108] Figure 1 The nuclear magnetic resonance spectrum of the polytetrafluoroethylene modified by vinyltrimethoxysilane and γ-aminopropyltriethoxysilane and copolymerized with perfluoropropyl vinyl ether in Example 5, the strong peaks near 1-2 ppm and 2.5-3 ppm in the spectrum correspond to the hydrogen atoms in the vinyltrimethoxysilane and γ-aminopropyltriethoxysilane groups, which proves that the two silanes have been grafted into the polytetrafluoroethylene system, and the hydrogen-containing copolymer unit is introduced into the polytetrafluoroethylene chain. The peak near 5.5 ppm matches the chemical environment of the characteristic hydrogen in perfluoropropyl vinyl ether, indicating that the copolymer unit is introduced into the polytetrafluoroethylene chain. Comparative Example 8 is modified by perfluoropropyl vinyl ether without γ-aminopropyltriethoxysilane treatment, compared with Example 5, the tensile strength decreases from 25.7 MPa to 22.3 MPa, the tensile rate and the thermal conductivity decrease, the leakage amount, the corrosion rate and the compression permanent set increase. The fundamental reason is the lack of molecular bridging of γ-aminopropyltriethoxysilane, which introduces amino groups into the matrix and forms covalent bonds with the surface epoxy groups of the filler. If it is removed, there is no chemical bonding between the polytetrafluoroethylene matrix and the filler, the interface completely relies on physical action, which will cause interface separation, complete blockage of stress transmission, large penetration of corrosion medium, complete interruption of heat conduction path, easy falling off of the filler, and serious interface slip.

[0109] Figure 2The production process of the sealing ring produced by the application, and the examples 3-8 also prove that the addition of the modified polytetrafluoroethylene and the modified filler material has great benefits on the wear, creep resistance, interface bonding and other properties of the finished sealing ring.

[0110] In the modified polytetrafluoroethylene of the examples 1, 2, 5 and the comparative example 1, the number of parts gradually increases, and the properties in table 1 show a certain change rule. The tensile strength, tensile rate and hardness generally show an upward trend, because after the modified polytetrafluoroethylene is modified by perfluoropropyl vinyl ether, the interaction between the molecular chains is enhanced, which can better transmit stress to increase the tensile strength, the flexibility and the tensibility of the modified polytetrafluoroethylene are increased, and the rigidity of the modified polytetrafluoroethylene is also increased due to the change of the structure. The leakage amount decreases with the increase of the number of parts, which is due to the fact that the modified polytetrafluoroethylene can improve the material density, reduce the internal pores and enhance the barrier ability to gas or liquid.

[0111] In the examples 3, 4, 5 and the comparative example 2, the number of parts of the modified filler material gradually increases while the number of parts of the modified polytetrafluoroethylene and the unmodified polytetrafluoroethylene remains unchanged, and the properties of the finished sealing ring also change regularly. The tensile strength first increases and then stabilizes, because the modified filler material can enhance the stress transmission at the beginning, but too much of the modified filler material may lead to agglomeration and weaken the interface effect. The tensile rate continues to decrease because the rigidity of the filler material limits the molecular chain slip. The hardness obviously increases, and the support density of the rigid particles is increased to improve the anti-deformation ability. The leakage amount and the wear rate first decrease and then increase, because the filler material can fill the pores and enhance the wear resistance and friction reduction at the beginning, but too much of the filler material will have adverse effects due to agglomeration. The compression permanent set first decreases and then stabilizes, because the filler material disperses stress in the early stage, and too much of the filler material limits the elastic deformation in the later stage. The corrosion rate is basically stable, and the corrosion resistance and good interface bonding of the filler material do not have obvious fluctuations due to the change of the number of parts. The thermal conductivity coefficient significantly increases, and the increase of the number of parts makes the heat conduction path more dense, which improves the overall heat conduction ability.

[0112] The above is only the preferred specific embodiment of the application, but the protection scope of the application is not limited thereto, and any person skilled in the art can make equivalent replacement or change according to the technical solution and the inventive concept of the application within the technical range disclosed by the application, which should be covered within the protection scope of the application.

Claims

1. A corrosion-resistant PTFE sealing ring, characterized in that, Including the following parts by weight of raw materials: 100 parts polytetrafluoroethylene: low molecular weight polytetrafluoroethylene powder supplied by DuPont, USA; 30-50 parts of perfluoropropyl vinyl ether modified polytetrafluoroethylene were prepared by the following steps: S1. The pretreated low molecular weight polytetrafluoroethylene powder is treated with steam plasma for 60-120s, swollen by a mixed solvent of perfluorohexane and anhydrous ethanol at a volume ratio of 7:3, stirred for 20-30min, with a solid-liquid ratio of 1:10, and vinyltrimethoxysilane is dissolved in an ethanol-water solution. Acetic acid is added to adjust the pH, and 10-12% of the vinyltrimethoxysilane solution is added to the polytetrafluoroethylene mixture. The mixture is mechanically stirred in a constant temperature water bath at 60℃ for 2h, centrifuged, washed with ethanol, and dried to obtain silane-modified polytetrafluoroethylene powder. S2. Place the silane-modified polytetrafluoroethylene powder in a 5wt% aqueous solution of perfluorooctanoic acid, disperse it ultrasonically, evacuate it under vacuum and nitrogen protection, add perfluoropropyl vinyl ether, stir to dissolve, heat to 70℃, slowly add 0.1wt% ammonium persulfate (1% of the total system volume), adjust the pressure inside the vessel to 1.5MPa, react for 3h, add three times the volume of anhydrous ethanol, centrifuge and Soxhlet extract, place it in a 2wt% γ-aminopropyltriethoxysilane ethanol hydrolysis solution, heat to 50-60℃, stir to react for 1h, wash with ethanol, centrifuge and dry to obtain perfluoropropyl vinyl ether-modified polytetrafluoroethylene powder; 20-30 parts of modified filler material, which is a mixed powder of modified nano-h-boron nitride and silicon carbide, are prepared by the following steps: Nano-h-boron nitride powder and silicon carbide powder were mixed uniformly at a mass ratio of 1:1 and placed in a muffle furnace. The mixture was calcined at 400℃ in air for 2 hours. After removal, the mixture was soaked in 5 mol / L nitric acid, sonicated for 30 minutes, centrifuged, and washed with deionized water. Perfluorooctyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane were dissolved in an ethanol / water mixture with a mass fraction of 1-3% for both. The volume ratio of anhydrous ethanol to water in the ethanol / water solution was 9:

1. The pH was adjusted to 4.0-5.0 with acetic acid and stirred at room temperature for 30 minutes. 5-8% of the total volume of the perfluorooctyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane mixture was added to the washed powder mixture. The mixture was stirred in a constant temperature water bath at 50℃ for 3 hours, washed three times by centrifugation with acetone, and dried at 105℃ for 6 hours to obtain the modified filler material.

2. The corrosion-resistant PTFE sealing ring according to claim 1, characterized in that, The molecular weight of low molecular weight polytetrafluoroethylene powder is between 20,000 and 30,000, and the average particle size is 3-6 μm.

3. The corrosion-resistant PTFE sealing ring according to claim 1, characterized in that, In S1, the pretreatment method is as follows: the low molecular weight polytetrafluoroethylene powder is thoroughly washed 2-3 times with anhydrous ethanol, centrifuged, then washed 2-3 times with deionized water, centrifuged, and placed in a vacuum drying oven to dry at 80°C.

4. The corrosion-resistant PTFE sealing ring according to claim 1, characterized in that, In S1, the detailed parameters for water vapor plasma treatment of low molecular weight polytetrafluoroethylene powder are as follows: the volume ratio of water vapor to argon is 10:1, the total gas flow rate is 20-30 sccm, the plasma power is 100-150W, the mass fraction of vinyltrimethoxysilane solution is 2-5%, and the pH is adjusted to 4.0-5.0 with acetic acid.

5. The corrosion-resistant PTFE sealing ring according to claim 1, characterized in that, In S2, the mass ratio of low molecular weight polytetrafluoroethylene powder, vinyltrimethoxysilane, and perfluoropropyl vinyl ether is 100:3-6:10-12, the solvent for Soxhlet extraction is perfluorohexane, and the extraction time is 24 hours.

6. The manufacturing process of a corrosion-resistant PTFE sealing ring according to any one of claims 1-5, characterized in that, Includes the following steps: Low molecular weight polytetrafluoroethylene powder, perfluoropropyl vinyl ether modified polytetrafluoroethylene powder, and modified filler material are dried separately and gradually mixed in a planetary mixer for 40 minutes. A fluorinated release agent is applied to the mold, and the mixed powder is filled into the mold. The mold is held under pressure of 15-25 MPa for 10-20 minutes. The pre-formed sealing ring is removed from the mold and heated to 300°C at a rate of 80°C / h, then to 340-350°C at a rate of 50°C / h, and held for 3 hours. The temperature is then reduced to 300°C at a rate of 20°C / h, then to 200°C at a rate of 30°C / h, and then allowed to cool naturally. The sintered blank is placed in a 110°C forced-air oven and kept at that temperature for 5 hours. It is then cooled to room temperature with the furnace and polished with diamond to obtain the finished sealing ring.

7. The manufacturing process of a corrosion-resistant PTFE sealing ring according to claim 6, characterized in that, The operating parameters of the planetary mixer are 300-400 rpm. First, the low molecular weight polytetrafluoroethylene powder and the perfluoropropyl vinyl ether modified polytetrafluoroethylene powder are mixed evenly, and then the modified filler material is added in three batches for mixing.

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