A low-friction low-temperature-rise fluoroelastomer and a method for producing the same

Abstract

The application relates to the field of rubber for oil seals, and discloses a fluororubber with low friction and low temperature rise and a preparation method thereof, the fluororubber is made of the following raw materials in parts by weight: modified FKM 100 parts; nickel-coated graphite 0.5-5 parts; flaky graphite 0.5-5 parts; modified PTFE micro powder 1-10 parts; high-activity magnesium oxide 1-10 parts; calcium hydroxide 0-6 parts; WS2800 2 parts; Brazil palm wax 0-2 parts; glass fiber 0-5 parts; modified calcium silicate 0-50 parts; BPP 0.2-1 part; bisphenol AF 0.5-2 parts. The flaky graphite and the modified PTFE micro powder form a lubricating film at the interface to reduce friction, and the nickel-coated graphite is used to build a heat conduction channel to conduct heat out, so that the friction coefficient is reduced and the temperature rise is controlled. In combination with the modified matrix and the reinforcing filler, the stability of the crosslinking network is improved, the material has excellent high-temperature anti-aging performance and rigidity, and the service life of the oil seal is prolonged.

Description

Technical Field

[0001] This invention relates to the field of rubber technology for oil seals, specifically to a low-friction, low-temperature-rise fluororubber and its preparation method. Background Technology

[0002] Rotary oil seals are sealing components used in mechanical transmission equipment to isolate internal lubricating media and prevent the intrusion of external impurities. Fluororubber, due to its oil resistance, high temperature resistance, and chemical stability, is often used as the base material for manufacturing precision transmission rotary oil seals.

[0003] In industrial robots and precision transmission equipment, harmonic reducers impose strict standards on the operating conditions of rotary oil seals. In practical applications, the rotary oil seals of reducers operate in a high-speed and high-frequency start-stop environment for extended periods. The rubber lip of the oil seal needs to maintain a tight fit with the metal rotating shaft to ensure the normal operation of the mechanical equipment.

[0004] Existing fluororubber materials face the technical challenge of generating significant frictional heat and hindering its dissipation under high-speed rotation conditions. Conventional fluororubber materials exhibit a high coefficient of friction when rubbing against a rotating shaft at high speeds, generating substantial frictional heat. Simultaneously, traditional filler systems struggle to balance self-lubrication and high thermal conductivity, preventing rapid heat transfer to the interior and causing localized heat accumulation at the oil seal lip, leading to excessive temperature rise. This localized high temperature accelerates the thermal aging and hardening of the rubber matrix, reduces the material's mechanical properties, and ultimately results in seal failure. Summary of the Invention

[0005] The technical problem solved by this invention is to provide a low-friction, low-temperature-rise fluororubber and its preparation method. Addressing the shortcomings of conventional fluororubber in high-speed rotation of rotary oil seals for robot harmonic reducers—namely, high friction coefficient, large dynamic interface shear heat generation, high lip temperature rise, and heat accumulation leading to rubber aging and failure—this invention modifies the fluororubber matrix and combines it with a solid lubrication system and a heat-conducting system to reduce the friction coefficient, control the temperature rise, and extend the service life of the oil seal.

[0006] To address the above problems, the present invention provides the following technical solution:

[0007] In a first aspect, the present invention provides a low-friction, low-temperature-rise fluororubber, employing the following technical solution: A low-friction, low-temperature-rise fluororubber, made from raw materials comprising the following parts by weight: 100 parts modified FKM; 0.5-5 parts nickel-coated graphite; 0.5-5 parts flake graphite; 1-10 parts modified PTFE micro powder; 1-10 parts highly active magnesium oxide; 0-6 parts calcium hydroxide; 2 parts WS2800; 0-2 parts carnauba wax; 0-5 parts glass fiber; 0-50 parts modified calcium silicate; 0.2-1 parts BPP; 0.5-2 parts bisphenol AF.

[0008] By adopting the above technical solution, this invention introduces a composite lubrication and thermal conductivity system into a fluororubber matrix, with the following innovative mechanism:

[0009] Function of modified FKM matrix: Maleic anhydride grafted modified fluororubber introduces polar groups into the molecular chain, which enhances the interfacial adhesion between the rubber matrix and inorganic fillers and fiber-based reinforcing materials, thereby improving the overall mechanical strength and heat resistance of the material.

[0010] The ternary synergistic lubrication and cooling mechanism is as follows: First, during dynamic friction, flake graphite and modified PTFE micropowder migrate between the rotating oil seal lip and the shaft surface to form a solid lubrication transfer film, reducing the shear stress between the friction pairs. Second, the nickel metal layer in the nickel-coated graphite forms a heat-conducting channel on the graphite particle surface, transferring the heat generated at the friction interface to the interior of the rubber body. Third, the high thermal conductivity of metallic nickel combined with the low friction characteristics of graphite reduces the local accumulation of heat at the lip and suppresses temperature rise.

[0011] Reinforcement and creep resistance: Needle-shaped modified calcium silicate and glass fiber form a skeleton structure in the matrix, which improves the deformation resistance of fluororubber under rotation and prevents lip wear.

[0012] Preferably, the modified FKM is prepared by mixing and reacting raw materials comprising the following parts by weight: 100 parts of vinylidene fluoride-hexafluoropropylene copolymer fluororubber with a Mooney viscosity ML(1+10) of 45 at 121°C; 1-3 parts of maleic anhydride; and 0.1-0.3 parts of dicumyl peroxide. By employing the above technical solution, dicumyl peroxide initiates a free radical grafting reaction of maleic anhydride onto the fluororubber segments. The reaction process consists of: initiator decomposition to generate primary free radicals; primary free radicals abstracting active hydrogen from the fluororubber segments to form macromolecular free radicals; and macromolecular free radicals adding to the maleic anhydride double bonds to complete the grafting. The above reaction process enhances the polarity of the rubber compound and its coating properties for fillers.

[0013] Secondly, this invention provides a method for preparing low-friction, low-temperature-rise fluororubber, employing the following technical solution: A method for preparing low-friction, low-temperature-rise fluororubber includes the following steps: S1, adding modified FKM to a two-roll mill for roll plasticizing, controlling the roll temperature to 50-70℃; S2, sequentially adding highly active magnesium oxide, nickel-coated graphite, flake graphite, modified PTFE micro powder, and the calcium hydroxide, WS280, carnauba wax, glass fiber, and modified calcium silicate contained in the formulation, forming a triangular bundle for uniform mixing; S3, after the materials are uniformly mixed, adding BPP and bisphenol AF, continuing to mix for 5-10 minutes, and then sheeting out to obtain the compound rubber; S4. Let the compounded rubber stand at room temperature for 24 hours, then put it into a flat vulcanizing machine for molding. Perform a first-stage vulcanization at 160-180℃ and 15 MPa for 10-20 minutes. Then demold it and put it into a drying oven for a second-stage vulcanization at 220-240℃ for 12-20 hours. Cool it to room temperature to obtain the final product.

[0014] By adopting the above technical solution, this preparation process ensures the uniform dispersion of multi-component fillers and the stability of cross-linked networks:

[0015] Optimization of the mixing sequence: Add the acid absorber and lubricating filler first, and add BPP and bisphenol AF last. The above order of addition prevents the crosslinking agent from undergoing local vulcanization under the heat of mixing, avoids scorching of the rubber compound, and ensures processing safety.

[0016] Two-stage vulcanization mechanism: First, primary vulcanization achieves initial cross-linking and shaping of the rubber molecular chains, giving the product its geometric dimensions. Second, secondary vulcanization is carried out at a higher temperature, which aims to perfect the cross-linking network, increase the cross-linking density, and promote the removal of vulcanization byproducts. Through 12-20 hours of high-temperature treatment, residual stress within the material is eliminated, compression set is reduced, and fluororubber maintains stable physical properties under aging conditions above 230℃.

[0017] Thirdly, the present invention relates to the preparation of custom modified raw materials, and adopts the following technical solution: Modified PTFE micro powder is obtained by irradiating polytetrafluoroethylene micro powder with cobalt-60 gamma rays, setting the irradiation dose to 50-150 kGrey, and performing heat treatment at 180-220℃.

[0018] By adopting the above technical solution, the modification mechanism is as follows:

[0019] Irradiation degradation effect: Under radiation, PTFE molecular chains break down, producing low-molecular-weight microparticles. The degraded microparticles are fluid within the fluororubber matrix and spread at the friction interface.

[0020] Enhanced surface activity: Irradiation introduces oxygen-containing functional groups at the ends of the molecular chains, improving the compatibility of PTFE with the fluororubber matrix and solving the problems of uneven dispersion and detachment of conventional PTFE from the rubber surface.

[0021] Modified calcium silicate is prepared by surface modification of needle-shaped calcium silicate using the silane coupling agent KH-550 in an ethanol solution system. Through this technique, the hydrolysis products of KH-550 molecules undergo chemical condensation with the hydroxyl groups on the calcium silicate surface, forming chemical bonds. During rubber compounding, the other end of the silane coupling agent interacts with the graft groups of modified FKM, forming interfacial chemical bonds and improving the tensile strength of the material.

[0022] This invention provides a low-friction, low-temperature-rise fluororubber and its preparation method. It has the following beneficial effects:

[0023] 1. This invention achieves a synergistic effect of low friction coefficient and low temperature rise. By compounding nickel-coated graphite, flake graphite, and modified PTFE micropowder into a modified fluororubber matrix, the flake graphite and modified PTFE micropowder form a solid lubricating film at the dynamic friction interface to reduce frictional shear stress. The nickel-coated graphite utilizes its surface nickel metal layer to construct heat-conducting channels, dissipating the heat generated by friction to the interior of the rubber. The synergistic effect of the components reduces local heat accumulation during rotation and controls the temperature rise of the oil seal lip.

[0024] 2. This invention possesses excellent high-temperature aging resistance. The formulation uses maleic anhydride-grafted modified fluororubber as the matrix, combined with a composite acid scavenger composed of highly active magnesium oxide and calcium hydroxide, and a vulcanization system composed of bisphenol AF and BPP. The composite acid scavenger neutralizes the hydrogen fluoride released by the defluorination of fluororubber at high temperatures, preventing acidic byproducts from damaging the cross-linked network. The modified matrix and filler interface are tightly bonded, resulting in a low rate of mechanical property degradation at 230℃, thus extending the service life.

[0025] 3. This invention improves the structural rigidity and deformation resistance of the material. The formulation incorporates needle-shaped modified calcium silicate treated with a silane coupling agent and glass fibers. The functional groups on the surface of the modified calcium silicate undergo interfacial chemical bonding with the fluororubber matrix and, together with the glass fibers, construct an interwoven physical framework structure within the rubber. This structure restricts the slippage of polymer molecular chains under stress, improves the dimensional stability of fluororubber under high-speed rotation conditions, and slows down the fatigue and creep wear process of the oil seal. Attached Figure Description

[0026] Figure 1 This is a flowchart of the method of the present invention;

[0027] Figure 2 This is a flow chart of the preparation process of the modified raw materials of the present invention. Detailed Implementation

[0028] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0029] Modified FKM is prepared by grafting maleic anhydride onto vinylidene fluoride-hexafluoropropylene copolymer. The specific preparation process is as follows: 100 parts by mass of vinylidene fluoride-hexafluoropropylene copolymer fluorinated rubber with a Mooney viscosity of ML (1+10) 121℃ of 45, 2 parts by mass of maleic anhydride and 0.2 parts by mass of dicumyl peroxide are added to a mixer and mixed at 160℃ for 15 minutes. The mixture is then discharged and cooled to room temperature to obtain modified FKM.

[0030] The modified PTFE micro powder uses self-made irradiated degradable polytetrafluoroethylene micro powder. The specific preparation process is as follows: polytetrafluoroethylene micro powder with an average particle size of 5 micrometers is placed under a radiation source and subjected to cobalt-60 gamma ray irradiation treatment in an air atmosphere. The irradiation dose is set to 100 kGrey. After irradiation, it is heat-treated in an oven at 200°C for 2 hours, then cooled and pulverized and ground to an average particle size of 3 micrometers to obtain modified PTFE micro powder.

[0031] Modified calcium silicate is prepared by surface treatment of calcium silicate with a self-made silane coupling agent. The specific preparation process is as follows: 100 parts by mass of needle-shaped calcium silicate are added to a high-speed mixer, the mixer is turned on at 100°C, and a mixed solution prepared by 3 parts by mass of silane coupling agent KH-550 and 10 parts by mass of anhydrous ethanol is evenly sprayed into it. Then, the mixture is dispersed and mixed at high speed at 110°C for 30 minutes. After the mixing is completed, the material is transferred to a vacuum drying oven at 120°C and dried for 2 hours to completely remove the ethanol solvent, and finally modified calcium silicate is obtained.

[0032] Nickel-coated graphite is graphite powder with a surface chemically plated nickel layer, wherein the mass fraction of nickel is 60%, the mass fraction of graphite is 40%, and the average particle size is 50 micrometers.

[0033] The glass fiber is alkali-free chopped glass fiber filaments, with a single fiber diameter of 10 to 13 micrometers and a cut length of 3 to 6 millimeters.

[0034] WS280 is a special processing aid for fluororubber whose main chemical components are a mixture of organosilicon derivatives and fatty acid esters.

[0035] Flake graphite is a natural crystalline graphite with an average particle size of 150 micrometers, and its CAS number is 7782-42-5.

[0036] The active iodine value of highly active magnesium oxide is greater than 120 mg / g, and its CAS number is 1309-48-4.

[0037] The saponification value of carnauba wax is 78 to 95 mg potassium hydroxide / g, and the CAS number is 8015-86-9.

[0038] The chemical name of BPP is benzyltriphenylphosphonium chloride, and its CAS number is 1100-88-5.

[0039] The chemical name of bisphenol AF is 2,2-bis(4-hydroxyphenyl)hexafluoropropane, and the CAS number is 1478-61-1.

[0040] The CAS number for calcium hydroxide is 1305-62-0.

[0041] Preparation Example 1:

[0042] This preparation example provides a modified FKM, including the following steps:

[0043] 100 parts by mass of vinylidene fluoride-hexafluoropropylene copolyfluororubber with a Mooney viscosity ML (1+10) of 45 at 121°C, 1 part by mass of maleic anhydride, and 0.1 parts by mass of dicumyl peroxide were added to an internal mixer and mixed at 155°C for 10 minutes. The mixture was then discharged and cooled to room temperature to obtain modified FKM.

[0044] Preparation Example 2:

[0045] This preparation example provides a modified FKM, including the following steps:

[0046] 100 parts by mass of vinylidene fluoride-hexafluoropropylene copolyfluororubber with a Mooney viscosity ML (1+10) of 45 at 121°C, 2 parts by mass of maleic anhydride, and 0.2 parts by mass of dicumyl peroxide were added to an internal mixer and mixed at 160°C for 15 minutes. The mixture was then discharged and cooled to room temperature to obtain modified FKM.

[0047] Preparation Example 3:

[0048] This preparation example provides a modified FKM, including the following steps:

[0049] 100 parts by mass of vinylidene fluoride-hexafluoropropylene copolyfluororubber with a Mooney viscosity ML (1+10) of 45 at 121°C, 3 parts by mass of maleic anhydride, and 0.3 parts by mass of dicumyl peroxide were added to an internal mixer and mixed at 165°C for 20 minutes. The mixture was then discharged and cooled to room temperature to obtain modified FKM.

[0050] Preparation Example 4:

[0051] This preparation example provides a modified PTFE micro powder, including the following steps:

[0052] Polytetrafluoroethylene (PTFE) micropowder with an average particle size of 5 micrometers was placed under a radiation source and subjected to cobalt-60 gamma irradiation in an air atmosphere. The irradiation dose was set to 50 kGrey. After irradiation, the powder was heat-treated in an oven at 180°C for 1.5 hours, then cooled and pulverized to an average particle size of 3 micrometers to obtain modified PTFE micropowder.

[0053] Preparation Example 5:

[0054] This preparation example provides a modified PTFE micro powder, including the following steps:

[0055] Polytetrafluoroethylene (PTFE) micropowder with an average particle size of 5 micrometers was placed under a radiation source and subjected to cobalt-60 gamma irradiation in an air atmosphere. The irradiation dose was set to 100 kGrey. After irradiation, the powder was heat-treated in an oven at 200°C for 2 hours, then cooled and pulverized to an average particle size of 3 micrometers to obtain modified PTFE micropowder.

[0056] Preparation Example 6:

[0057] This preparation example provides a modified PTFE micro powder, including the following steps:

[0058] Polytetrafluoroethylene (PTFE) micropowder with an average particle size of 5 micrometers was placed under a radiation source and subjected to cobalt-60 gamma irradiation in an air atmosphere. The irradiation dose was set to 150 kGrey. After irradiation, the powder was heat-treated in an oven at 220°C for 2.5 hours. Subsequently, it was cooled and pulverized to an average particle size of 3 micrometers to obtain modified PTFE micropowder.

[0059] Preparation Example 7:

[0060] This preparation example provides a modified calcium silicate, comprising the following steps:

[0061] 100 parts by weight of needle-shaped calcium silicate were added to a high-speed mixer. The mixer was started at 90°C, and a mixed solution prepared by 1 part by weight of silane coupling agent KH-550 and 5 parts by weight of 95% ethanol solution was evenly sprayed into it. Then, the mixture was dispersed and mixed at high speed at 100°C for 20 minutes. After the mixing was completed, the material was transferred to a vacuum drying oven at 110°C and dried for 1.5 hours to finally obtain modified calcium silicate.

[0062] Preparation Example 8:

[0063] This preparation example provides a modified calcium silicate, comprising the following steps:

[0064] 100 parts by weight of needle-shaped calcium silicate were added to a high-speed mixer. The mixer was turned on at 100°C and a mixed solution prepared by 3 parts by weight of silane coupling agent KH-550 and 10 parts by weight of 95% ethanol solution was sprayed evenly into it. Then, the mixture was dispersed and mixed at high speed at 110°C for 30 minutes. After the mixing was completed, the material was transferred to a vacuum drying oven at 120°C and dried for 2 hours to finally obtain modified calcium silicate.

[0065] Preparation Example 9:

[0066] This preparation example provides a modified calcium silicate, comprising the following steps:

[0067] 100 parts by weight of needle-shaped calcium silicate were added to a high-speed mixer. The mixer was started at 110°C, and a mixed solution prepared by 5 parts by weight of silane coupling agent KH-550 and 15 parts by weight of 95% ethanol solution was evenly sprayed into it. Then, the mixture was dispersed and mixed at high speed at 120°C for 40 minutes. After the mixing was completed, the material was transferred to a vacuum drying oven at 130°C and dried for 2.5 hours to finally obtain modified calcium silicate.

[0068] Example 1:

[0069] This embodiment provides a low-friction, low-temperature-rise fluororubber and its preparation method, including the following steps:

[0070] According to the weight parts, accurately weigh 100 parts of modified FKM obtained in Preparation Example 2, 2.5 parts of nickel-coated graphite, 2.5 parts of flake graphite, 5 parts of modified PTFE micro powder obtained in Preparation Example 5, 5 parts of highly active magnesium oxide, 3 parts of calcium hydroxide, 1 part of WS280, 1 part of carnauba wax, 2.5 parts of glass fiber, 25 parts of modified calcium silicate obtained in Preparation Example 8, 0.5 parts of BPP, and 1 part of bisphenol AF;

[0071] The modified FKM was added to a two-roll mill for roll plasticizing, with the roll temperature controlled at 60°C. Then, high-activity magnesium oxide, calcium hydroxide, WS280, carnauba wax, nickel-coated graphite, flake graphite, modified PTFE micro powder, glass fiber, and modified calcium silicate were added in sequence. The mixture was then formed into triangular bags and mixed evenly. After the materials were evenly mixed, BPP and bisphenol AF were added, and the mixture was continued to be mixed for 5 minutes before being sheeted out to obtain the compound.

[0072] The obtained rubber compound was left to stand at room temperature for 24 hours, then placed in a flat vulcanizing machine for molding. It was vulcanized for 15 minutes at 170°C and 15 MPa, then demolded and placed in a forced-air drying oven for a second vulcanization at 230°C for 16 hours. After cooling to room temperature, low-friction, low-temperature-rise fluororubber was obtained.

[0073] Example 2:

[0074] This embodiment provides a low-friction, low-temperature-rise fluororubber and its preparation method, including the following steps:

[0075] According to the weight parts, accurately weigh 100 parts of modified FKM obtained in Preparation Example 3, 5 parts of nickel-coated graphite, 5 parts of flake graphite, 10 parts of modified PTFE micro powder obtained in Preparation Example 6, 10 parts of highly active magnesium oxide, 6 parts of calcium hydroxide, 2 parts of WS280, 2 parts of carnauba wax, 5 parts of glass fiber, 50 parts of modified calcium silicate obtained in Preparation Example 9, 1 part of BPP, and 2 parts of bisphenol AF.

[0076] The modified FKM was added to a two-roll mill for roll plasticizing, with the roll temperature controlled at 70°C. Then, high-activity magnesium oxide, calcium hydroxide, WS280, carnauba wax, nickel-coated graphite, flake graphite, modified PTFE micro powder, glass fiber, and modified calcium silicate were added in sequence. The mixture was then formed into triangular bags and mixed evenly. After the materials were mixed evenly, BPP and bisphenol AF were added, and the mixture was continued to be mixed for 10 minutes before being sheeted out to obtain the compound.

[0077] The obtained compound was left to stand at room temperature for 24 hours, then placed in a flat vulcanizing machine for molding. It was vulcanized for 10 minutes at 180°C and 15 MPa, then demolded and placed in a forced-air drying oven for a second vulcanization at 240°C for 12 hours. After cooling to room temperature, low-friction, low-temperature-rise fluororubber was obtained.

[0078] Example 3:

[0079] This embodiment provides a low-friction, low-temperature-rise fluororubber and its preparation method, including the following steps:

[0080] According to the weight parts, accurately weigh 100 parts of modified FKM obtained in Preparation Example 1, 0.5 parts of nickel-coated graphite, 0.5 parts of flake graphite, 1 part of modified PTFE micro powder obtained in Preparation Example 4, 1 part of highly active magnesium oxide, 1 part of calcium hydroxide, 0.5 parts of WS280, 0.5 parts of carnauba wax, 1 part of glass fiber, 5 parts of modified calcium silicate obtained in Preparation Example 7, 0.2 parts of BPP, and 0.5 parts of bisphenol AF;

[0081] The modified FKM was added to a two-roll mill for roll plasticizing, with the roll temperature controlled at 50°C. Then, high-activity magnesium oxide, calcium hydroxide, WS280, carnauba wax, nickel-coated graphite, flake graphite, modified PTFE micro powder, glass fiber, and modified calcium silicate were added in sequence. The mixture was then formed into triangular bags and mixed evenly. After the materials were mixed evenly, BPP and bisphenol AF were added, and the mixture was continued to be mixed for 5 minutes before being sheeted out to obtain the compound.

[0082] The obtained rubber compound was left to stand at room temperature for 24 hours, then placed in a flat vulcanizing machine for molding. It was vulcanized for 20 minutes at 160°C and 15 MPa, then demolded and placed in a forced-air drying oven for a second vulcanization at 220°C for 20 hours. After cooling to room temperature, low-friction, low-temperature-rise fluororubber was obtained.

[0083] Example 4:

[0084] This embodiment provides a low-friction, low-temperature-rise fluororubber and its preparation method, including the following steps:

[0085] According to the weight parts, accurately weigh 100 parts of modified FKM obtained in Preparation Example 2, 2 parts of nickel-coated graphite, 2 parts of flake graphite, 3 parts of modified PTFE micro powder obtained in Preparation Example 5, 5 parts of highly active magnesium oxide, 0 parts of calcium hydroxide, 0 parts of WS280, 0 parts of carnauba wax, 0 parts of glass fiber, 0 parts of modified calcium silicate, 0.5 parts of BPP, and 1 part of bisphenol AF;

[0086] The modified FKM was added to a two-roll mill for roll plasticizing, and the roll temperature was controlled at 60°C. Then, high-activity magnesium oxide, nickel-coated graphite, flake graphite and modified PTFE micro powder were added in sequence, and the mixture was uniformly mixed in a triangular bag. After the materials were uniformly mixed, BPP and bisphenol AF were added, and the mixture was continued to be mixed for 5 minutes before being sheeted out to obtain the compound.

[0087] The obtained rubber compound was left to stand at room temperature for 24 hours, then placed in a flat vulcanizing machine for molding. It was vulcanized for 15 minutes at 170°C and 15 MPa, then demolded and placed in a forced-air drying oven for a second vulcanization at 230°C for 16 hours. After cooling to room temperature, low-friction, low-temperature-rise fluororubber was obtained.

[0088] Comparative Example 1:

[0089] The difference from Example 1 is that no nickel-coated graphite was added; otherwise, they are the same.

[0090] Comparative Example 2:

[0091] The difference from Example 1 is that no modified PTFE micro powder was added; otherwise, they are the same.

[0092] Comparative Example 3:

[0093] Compared with Example 1, the difference is that the modified PTFE micro powder is replaced with an equal amount of unmodified ordinary polytetrafluoroethylene micro powder, and the modified calcium silicate is replaced with an equal amount of unmodified ordinary needle-shaped calcium silicate; all other aspects are the same.

[0094] Comparative Example 4:

[0095] The difference from Example 1 is that no flake graphite was added; otherwise, they are the same.

[0096] Comparative Example 5:

[0097] Compared with Example 1, the difference is that nickel-coated graphite and flake graphite were not added, but were replaced with conventional semi-reinforcing carbon black in equal amounts; otherwise, they are the same.

[0098] Test Example 1: Physical Properties and Heat Aging Resistance Test

[0099] According to GB / T 528 national standard, the vulcanized rubber sheets prepared in the examples and comparative examples were cut into dumbbell-shaped specimens. The initial tensile strength and elongation at break of the specimens were tested using a tensile testing machine at a tensile speed of 500 mm / min. The initial hardness of the specimens was tested using a Shore A hardness tester according to GB / T 531.1 national standard. The ambient temperature was 23℃ and the relative humidity was 50%. A hot air aging test was conducted according to GB / T 3512 national standard. The specimens were suspended in a hot air aging chamber, ensuring no contact between specimens or between the specimens and the chamber walls. The aging temperature was set to 230℃, and the aging time was 70 hours. After aging, the specimens were removed from the aging chamber and left at ambient temperature for at least 16 hours. Subsequently, the hardness, tensile strength, and elongation at break of the specimens were retested using the same equipment and parameters as the initial performance test. Based on the initial values ​​and the measured values ​​after aging, the changes in hardness, tensile strength, and elongation at break before and after aging were calculated.

[0100] Table 1. Test results of physical properties and heat aging resistance of the examples and comparative examples.

[0101] Example 1 75.3 14.28 213.6 +4.0 -2.1 -5.0 Example 2 81.8 13.45 176.2 +4.5 -3.6 -6.4 Example 3 68.4 12.06 248.1 +3.5 -2.8 -4.7 Example 4 70.9 11.73 224.5 +5.5 -5.4 -8.2 Comparative Example 1 74.6 14.52 208.4 +4.5 -4.6 -7.1 Comparative Example 2 76.1 14.86 196.7 +4.0 -3.8 -6.6 Comparative Example 3 77.5 9.42 141.3 +8.5 -12.7 -19.4 Comparative Example 4 73.8 14.11 215.8 +5.0 -3.5 -6.2 Comparative Example 5 78.2 15.64 188.5 +7.0 -8.9 -13.6

[0102] After aging at 230℃ for 70 hours in Examples 1 to 4, the hardness of Example 1 changed by +4 degrees, the tensile strength changed by -2.1%, and the elongation at break changed by -5.0%. The test results indicate that the composite formulation system has high-temperature structural stability.

[0103] Comparing the data of Example 1 and Comparative Example 3, Comparative Example 3 used unmodified polytetrafluoroethylene (PTFE) micropowder and unmodified needle-shaped calcium silicate. The inorganic filler and the fluororubber matrix had different polarities, causing the filler to agglomerate within the matrix, resulting in an initial tensile strength of 9.42 MPa. During aging, the agglomerates and interfacial defects formed stress concentration points, inducing matrix crack propagation, with a tensile strength change rate of -12.7%. This invention improves the dispersion of the filler in the fluororubber matrix by silane coupling treatment of calcium silicate and irradiation degradation modification of PTFE, increasing interfacial bonding and restricting the movement of polymer chains at high temperatures.

[0104] Comparative Example 5 uses semi-reinforcing carbon black to replace nickel-coated graphite and flake graphite. The carbon black particles have a large specific surface area and numerous surface-active groups, which exacerbates the shrinkage and side reactions of the cross-linked network at 230℃, increasing the hardness by 7 degrees. This invention employs a composite carbon material system, with layered or granular structures blocking the thermal oxidative free radical transport pathway within the rubber matrix. A compound acid scavenger composed of highly active magnesium oxide and calcium hydroxide neutralizes the hydrogen fluoride released during the defluorination reaction of fluororubber, preventing the acidic byproducts from breaking down the cross-linked bonds and maintaining the integrity of the cross-linked network. The combined physical dispersion and chemical interaction between the components enhances the heat aging resistance of the material system.

[0105] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A low-friction, low-temperature-rise fluororubber, characterized in that, It is made from the following raw materials in parts by weight: 100 parts modified FKM; 0.5-5 parts nickel-coated graphite; 0.5-5 parts flake graphite; 1-10 parts modified PTFE micro powder; 1-10 parts highly active magnesium oxide; 0-6 parts calcium hydroxide; 0-2 parts WS280; 0-2 parts of carnauba wax; Glass fiber 0-5 parts; modified calcium silicate 0-50 parts; BPP 0.2-1 part; Bisphenol AF 0.5-2 parts.

2. The low-friction, low-temperature-rise fluororubber according to claim 1, characterized in that, The raw materials are as follows by weight: 100 parts modified FKM; 2-2.5 parts nickel-coated graphite; 2-2.5 parts flake graphite; 3-5 parts modified PTFE micro powder; 5 parts highly active magnesium oxide; 0-3 parts calcium hydroxide; 0-1 parts WS280; 0-1 part of carnauba wax; Glass fiber 0-2.5 parts; modified calcium silicate 0-25 parts; BPP 0.5 parts; Bisphenol AF 1 part.

3. The low-friction, low-temperature-rise fluororubber according to claim 1, characterized in that, The modified FKM is a maleic anhydride-grafted modified vinylidene fluoride-hexafluoropropylene copolymer; the modified FKM is made by mixing and reacting the following raw materials in parts by weight: 100 parts of vinylidene fluoride-hexafluoropropylene copolyrubber with a Mooney viscosity ML (1+10) of 45 at 121°C; 1-3 parts of maleic anhydride; and 0.1-0.3 parts of dicumyl peroxide.

4. The low-friction, low-temperature-rise fluororubber according to claim 1, characterized in that, The modified PTFE micro powder is an irradiation-degradable polytetrafluoroethylene micro powder; the preparation method of the modified PTFE micro powder includes: placing polytetrafluoroethylene micro powder with an average particle size of 5 micrometers in an air atmosphere for cobalt-60 gamma irradiation treatment, setting the irradiation dose to 50-150 kGrey, and after irradiation, heat-treating it in an oven at 180-220℃ for 1.5-2.5 hours, and then grinding it to an average particle size of 3 micrometers.

5. The low-friction, low-temperature-rise fluororubber according to claim 1, characterized in that, The modified calcium silicate is a silane coupling agent surface-treated calcium silicate; the modified calcium silicate is made from raw materials containing the following parts by weight: 100 parts of needle-shaped calcium silicate; 1-5 parts of silane coupling agent KH-550; and 5-15 parts of ethanol solution with a volume fraction of 95%.

6. The low-friction, low-temperature-rise fluororubber according to claim 1, characterized in that, The nickel-coated graphite has a nickel content of 60% and a graphite content of 40%, with an average particle size of 50 micrometers; the flake graphite has an average particle size of 150 micrometers; the highly active magnesium oxide has an active iodine value greater than 120 mg / g; and the glass fiber is a chopped alkali-free glass fiber with a single fiber diameter of 10-13 micrometers and a cut length of 3-6 millimeters.

7. The method for preparing low-friction, low-temperature-rise fluororubber according to any one of claims 1-6, characterized in that, Includes the following steps: S1. Add the modified FKM to a two-roll mill for roll plasticizing; S2. Add high-activity magnesium oxide, nickel-coated graphite, flake graphite, modified PTFE micro powder, as well as calcium hydroxide, WS280, carnauba wax, glass fiber and modified calcium silicate contained in the formula in sequence, and mix them evenly in triangular bags. S3. After the materials are mixed evenly, add BPP and bisphenol AF, continue to mix and then pass through a thin sheet to obtain the compound. S4. After the compounded rubber is left to stand, it is placed in a flat vulcanizing machine for molding and first-stage vulcanization. Then it is demolded, taken out and placed in a drying oven for second-stage vulcanization. After cooling to room temperature, it is ready.

8. The method for preparing low-friction, low-temperature-rise fluororubber according to claim 7, characterized in that, In step S1, the roller temperature is controlled at 50-70℃; in step S3, the mixing time continues for 5-10 minutes.

9. The method for preparing low-friction, low-temperature-rise fluororubber according to claim 7, characterized in that, The specific implementation method of step S4 is as follows: let the rubber compound stand at room temperature for 24 hours; the conditions for the first stage of vulcanization are: 10-20 minutes at 160-180℃ and 15 MPa; the conditions for the second stage of vulcanization are: 12-20 hours at 220-240℃.

10. The method for preparing low-friction, low-temperature-rise fluororubber according to claim 7, characterized in that, Before step S1, the needle-shaped calcium silicate is modified by stirring it at 90-110°C and spraying it evenly into a mixed solution prepared by silane coupling agent KH-550 and ethanol solution. Then, it is dispersed and mixed at 100-120°C for 20-40 minutes, and then transferred to a vacuum drying oven at 110-130°C for drying for 1.5-2.5 hours to obtain modified calcium silicate.

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