An extreme pressure lubricating oil composition and its preparation method

Abstract

This invention relates to the field of lubricating oil technology, specifically disclosing an extreme pressure lubricating oil composition and its preparation method. The composition includes a base oil, extreme pressure additives, anti-wear agents, antioxidants, nano-solid lubricants, friction modifiers, and oiliness agents. The nano-lubricants undergo surface coating treatment and achieve stable distribution through ultrasonic dispersion and shear mixing. The preparation method employs multi-stage control, including premixing, isothermal shearing, nano-dropleting, online monitoring, and high-frequency shear stabilization. This invention achieves a synergistic improvement in lubricating film stability and extreme pressure anti-wear performance under high load, high temperature, and high shear conditions, exhibiting excellent thermal oxidation stability and industrial applicability.

Description

Technical Field

[0001] This invention relates to the field of lubricating oil technology, and more specifically to an extreme pressure lubricating oil composition and its preparation method. Background Technology

[0002] As a key medium in mechanical systems for reducing friction, lowering wear, and extending equipment life, lubricating oil's performance is particularly important under extreme operating conditions. With the increasing speed and heavy load of industrial equipment, traditional lubricating oil compositions are gradually revealing performance bottlenecks in terms of extreme pressure performance, anti-wear ability, and thermal stability, making it difficult to meet the demands of modern industry for high-reliability lubrication protection.

[0003] In existing technologies, functional additives such as extreme pressure agents, anti-wear agents, and friction modifiers are often added to improve the extreme pressure and anti-wear properties of lubricating oils. However, these additives may decompose, oxidize, or migrate under high temperature and high shear conditions, leading to a decline in lubrication performance. Meanwhile, nanomaterials, as a modification method that has emerged in recent years, possess excellent physical lubrication properties, but their dispersion stability in base oil systems is poor, making them prone to agglomeration and sedimentation, affecting their synergistic lubrication effect and potentially causing risks such as system blockage.

[0004] Furthermore, under boundary lubrication conditions, traditional lubricants struggle to sustain the formation of a friction interface film, leading to frequent metal-to-metal contact at micro-contact surfaces, resulting in adhesive wear and exacerbating energy consumption and component wear. Therefore, there is an urgent need for a lubricant composition with structural synergy, performance stability, and a complex action mechanism in its formulation design to address the insufficient overall performance of existing lubrication systems under high loads and complex operating conditions. Summary of the Invention

[0005] To overcome the shortcomings of existing lubricants in terms of extreme pressure performance, anti-wear ability, nanoparticle dispersion stability, and boundary lubrication stability, this invention provides an extreme pressure lubricant composition and its preparation method. Through base oil optimization, multifunctional additive ratio design, and preparation process control, excellent lubrication performance under high load, high temperature, and high shear conditions is achieved.

[0006] To achieve the above objectives, the present invention proposes the following technical solution:

[0007] An extreme pressure lubricating oil composition comprises the following components in weight percentages: 85%–93% base oil, 3%–8% extreme pressure additives, 1%–3% anti-wear agent, 0.5%–2% antioxidant, 0.1%–1% nano-solid lubricant, and 0.2%–1% friction modifier;

[0008] The base oil is selected from Group II or Group III hydrocracked mineral oil, polyα-olefin, polyether ester, or any two of them mixed in a volume ratio of 1:1 to 3:1, and has a kinematic viscosity of 40 to 150 mm² / s.

[0009] The extreme pressure additive is selected from one or more of zinc dialkyl dithiophosphate, triaryl phosphate, and alkyl phosphate.

[0010] The nano-solid lubricant is molybdenum disulfide, graphene, or hexagonal boron nitride with an average particle size of 20-80 nm, and is coated with chitosan quaternary ammonium salt, phosphate ester, or silane coupling agent, with the coating layer accounting for 5%-25% of the total particle mass.

[0011] The friction modifier is an imidazoline salt, an alcohol ether amine, or an N-alkylpyridine surfactant.

[0012] Furthermore, the composition further includes 0.1% to 1.5% of an oiliness agent or adhesion enhancer, wherein the oiliness agent is a hydroxyl fatty acid ester or a polyether-modified silicone oil, and its hydroxyl value is controlled at 30 to 60 mg KOH / g.

[0013] Furthermore, the mass ratio of phosphate ester to zinc dialkyl dithiophosphate in the extreme pressure additive is 1:1 to 2:1, and the phosphate ester includes tricresyl phosphate, triisooctyl phosphate, or triaryl phosphate.

[0014] Furthermore, the anti-wear agent is selected from polyetheramine derivatives, long-chain monoesters or polybutene succinates, wherein the acid value is controlled at 2-5 mg KOH / g and the viscosity index is greater than 140.

[0015] Furthermore, the nano-solid lubricant is a single-layer or few-layer graphene with an interlayer spacing of less than 0.35 nm, and the coating treatment induces a stable dispersion in an organic solvent through cationic charge induction.

[0016] Furthermore, the friction modifier and the extreme pressure additive have an oleophilic chain segment structure, which forms an intermolecular synergistic effect in the lubricating oil, improving the uniformity of the lubricating film and the stability of boundary lubrication.

[0017] The present invention also provides a method for preparing the above-mentioned lubricating oil composition, comprising the following steps:

[0018] S1. Place the base oil in a reaction vessel and stir at 30-40°C. Add antioxidant, friction modifier and oiliness agent in sequence for premixing and stir for 10-20 minutes.

[0019] S2. Add the extreme pressure additive and anti-wear agent at a constant temperature of 60-70°C and continue to shear and stir for 20-30 minutes.

[0020] S3. The coated and ultrasonically pre-dispersed nano-solid lubricant is slowly added dropwise to the mixture at a rate of 0.5-2 ml / min, and sheared at 60-70°C for 20 minutes.

[0021] S4. After cooling to room temperature, the mixture is filtered through a precision filter membrane with a pore size of less than 5μm to obtain a stable lubricating oil composition.

[0022] Furthermore, the pretreatment step of the nano solid lubricant includes sonicating in base oil for 20 minutes at a frequency of 40-60 kHz, and using an ionic oleophilic surface modifier to form a positively charged dispersion system.

[0023] Furthermore, an online particle size laser analyzer and infrared spectrometer linkage detection system is installed before and after the addition of nano solid lubricant to monitor particle size stability and chemical bond changes in real time.

[0024] Furthermore, after step S3 is completed, the semi-finished product is subjected to a short-term high-frequency shearing treatment at a shearing rate of 10,000 to 15,000 rpm for 3 to 5 minutes to enhance the uniformity and storage stability of the lubricating oil nanoparticles.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The above technical solution uses extreme pressure additives such as phosphate esters and zinc dialkyl dithiophosphate (ZDDP) to form a dense chemical adsorption film on the friction surface, which significantly improves the extreme pressure protection capability of the metal contact interface and significantly improves the ultimate load.

[0027] (2) Both friction modifiers and extreme pressure additives contain oleophilic segments in their molecules, which can form a dense interfacial film structure in the lubricating oil through intermolecular synergistic adsorption, thereby achieving rapid film formation and high stability under boundary lubrication conditions. The lubricating film has strong film-forming ability and high stability.

[0028] (3) The synergistic effect of nano lubricants is significant and the dispersion performance is excellent. Specifically, it uses chitosan quaternary ammonium salt, phosphate ester or silane coupling agent to coat the surface of nano solid lubricants such as graphene, molybdenum disulfide or hexagonal boron nitride, and combines ultrasonic dispersion pretreatment and shear injection steps to make the nano particles form a stable positive charge dispersion system in the oil, and the long-term suspension and synergistic lubrication ability are significantly improved.

[0029] (4) The base oil is a compound of Group II or Group III hydrocracked mineral oil with poly-α-olefin and polyether ester, with a wide viscosity range, taking into account both high temperature viscosity maintenance and low temperature fluidity, and is used in combination with antioxidants to form a lubrication system with strong thermal stability and long oxidation induction period.

[0030] (5) The preparation method provided by the present invention introduces a three-stage synergistic control mechanism, namely, the combination of "ultrasonic pre-dispersion → shear drop addition → high-frequency shear stabilization", which are used for nanoparticle deagglomeration, slow-release injection and uniform dispersion, respectively, to ensure the particle size concentration and spatial distribution stability; the particle size laser analyzer and infrared spectrometer linkage system are activated in real time to monitor the particle size distribution and functional group state synchronously; this mechanism can identify dispersion failure or chemical structure change problems in a timely manner, prevent quality fluctuations, and finally achieve the technical effect of ensuring nanoscale uniformity and improving controllability through linkage monitoring. Attached Figure Description

[0031] Figure 1 This is a flowchart of the preparation method of the present invention;

[0032] Figure 2 This is a bar chart comparing the ultimate load of embodiments of the present invention;

[0033] Figure 3 This is a bar chart comparing the wear scar diameters of embodiments of the present invention;

[0034] Figure 4 This is a graph showing the relationship between particle size and sedimentation ratio in an embodiment of the present invention.

[0035] Figure 5 This is a graph showing the change of the friction coefficient over time in an embodiment of the present invention. Detailed Implementation

[0036] To more clearly illustrate the technical solution of the present invention, the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are only used to illustrate the present invention and are not intended to limit the scope of protection of the present invention.

[0037] Example 1

[0038] This embodiment provides an extreme pressure lubricating oil composition, the composition of which is as follows by weight percentage: base oil: 90.0%, extreme pressure additive: 4.5%, anti-wear agent: 2.0%, antioxidant: 1.0%, nano solid lubricant: 0.6%, friction modifier: 0.9%, and oiliness agent: 1.0%;

[0039] The base oil is a composite oil made of Group III hydrocracked mineral oil and polyα-olefin at a volume ratio of 2:1, with a kinematic viscosity of 120 mm² / s.

[0040] The extreme pressure additive is a compound of zinc dialkyl dithiophosphate and triaryl phosphate in a mass ratio of 1:1.2.

[0041] The anti-wear agent is a polybutene succinate with an acid value of 3.8 mgKOH / g and a viscosity index of 150.

[0042] The antioxidant is a compound system of di-tert-butyl-p-cresol and phosphite;

[0043] The nano-solid lubricant is a single layer of graphene with an average particle size of 50 nm and an interlayer spacing of less than 0.35 nm, coated with chitosan quaternary ammonium salt, with the coating layer accounting for 15% of the total mass.

[0044] The friction modifier is an imidazoline salt type surfactant;

[0045] The oiling agent is hydroxylinoleic acid ester with a hydroxyl value of 45 mgKOH / g.

[0046] The preparation steps are as follows:

[0047] S1. Basic premix: Add 90.0% of the base oil to the reactor and stir at 35°C; add antioxidant, friction modifier and oiliness agent in sequence, stir evenly, and premix for 15 minutes to form a basic mixture;

[0048] S2. Addition of functional agents: Heat the mixture to 65℃ and keep it at a constant temperature. Add extreme pressure additives and anti-wear agents. Shear and stir for 25 minutes at a stirring speed of 1000 rpm to promote uniform reaction and synergistic distribution.

[0049] S3. Pretreatment and addition of nano-lubricant: Graphene nano solid lubricant and chitosan quaternary ammonium salt are mixed in base oil and treated with an ultrasonic device (frequency 50kHz) for 20 minutes to form a positively charged dispersion system; then the dispersion is added dropwise to the reaction system at a rate of 0.6 ml / min using a constant flow pump, while shearing and stirring at 65℃ for 20 minutes to ensure uniform dispersion of nanoparticles.

[0050] S4. Real-time linkage detection and monitoring: During the S3 dropping and shearing process, the system connects to the online particle size laser analyzer and infrared spectrometer linkage module to monitor the particle size distribution and chemical bond changes of nanoparticles in real time, ensuring that their dispersion state is stable and that no agglomeration or chemical degradation occurs; the monitoring frequency is set to sample once every 3 minutes, and the curve is saved for subsequent analysis;

[0051] S5. Shear stabilization treatment: After S3, the mixture is subjected to short-term high-frequency shear treatment at a shear rate of 12,000 rpm for 4 minutes to enhance the uniformity of nanoparticle distribution and the storage stability of the composition.

[0052] S6. Final Cooling and Filtration: Allow the system to cool naturally to room temperature, then filter using a precision filter membrane with a pore size of less than 5μm to remove micro-agglomerates and obtain the finished extreme pressure lubricating oil composition.

[0053] Example 2

[0054] This embodiment provides an extreme pressure lubricating oil composition, the composition having the following mass percentage composition: base oil: 92.0%; extreme pressure additive: 2.8%; anti-wear agent: 1.0%; antioxidant: 0.5%; nano solid lubricant: 0.2%; friction modifier: 0.3%; oiliness agent: 0.5%.

[0055] The base oil is a composite oil made by mixing Group II hydrocracking mineral oil and polyα-olefin in a volume ratio of 1:1, with a kinematic viscosity of 45 mm² / s.

[0056] The extreme pressure additive is a composite system of triaryl phosphate and zinc dialkyl dithiophosphate in a mass ratio of 1:1.

[0057] The anti-wear agent is a polyetheramine derivative with an acid value of 2.0 mg KOH / g and a viscosity index of 142.

[0058] The antioxidant is di-tert-butyl-p-cresol (BHT).

[0059] The nano-solid lubricant is hexagonal boron nitride with an average particle size of 80 nm, which is coated with a phosphate ester coupling agent, and the coating layer accounts for 5% of the total mass. The hexagonal boron nitride has a single-layer structure with an interlayer spacing controlled at 0.32 nm, uniform particle size distribution, and good dispersion stability.

[0060] The friction modifier is an alcohol ether amine surfactant;

[0061] The oiliness agent is polyether-modified silicone oil with a hydroxyl value of 30 mg KOH / g.

[0062] The preparation steps are as follows:

[0063] S1. Basic premix: Add 92.0% base oil to the reactor and stir at 30-40°C; add antioxidant, friction modifier and oiliness agent in sequence, stir evenly, and premix for 15 minutes to form basic mixture.

[0064] S2. Addition of functional agents: Heat the mixture to 65°C and add extreme pressure additives and anti-wear agents. Shear and stir for 25 minutes at a stirring speed of 1000 rpm to promote uniform mixing and synergistic distribution.

[0065] S3. Pretreatment and addition of nano-lubricant: Hexagonal boron nitride nano solid lubricant is blended with phosphate coupling agent and treated in base oil using an ultrasonic device (frequency 50kHz) for 20 minutes to form a positively charged dispersion system; then the dispersion is added dropwise to the reaction system at a rate of 0.5ml / min using a constant flow pump, while shearing and stirring at 60-70℃ for 20 minutes to ensure uniform dispersion of nanoparticles.

[0066] S4. Real-time linkage detection and monitoring: During the S3 dropping and shearing process, the system connects to the online particle size laser analyzer and infrared spectrometer linkage module to monitor the particle size distribution and chemical bond changes of nanoparticles in real time, ensuring that their dispersion state is stable and that no agglomeration or chemical degradation occurs.

[0067] S5. Shear stabilization treatment: After S3, the mixture is subjected to short-term high-frequency shear treatment at a shear rate of 10,000 rpm for 3 minutes to enhance the uniformity of nanoparticle distribution and the storage stability of the composition.

[0068] S6. Final Cooling and Filtration: Cool the system naturally to room temperature and filter it using a precision filter membrane with a pore size of no more than 5μm to remove micro-agglomerates and obtain the finished extreme pressure lubricating oil composition.

[0069] Example 3

[0070] This embodiment provides an extreme pressure lubricating oil composition, the composition having the following mass percentage composition: base oil: 85.0%; extreme pressure additive: 7.5%; anti-wear agent: 2.5%; antioxidant: 1.5%; nano solid lubricant: 1.0%; friction modifier: 1.0%; oiliness agent: 1.5%.

[0071] The base oil is a composite oil made by mixing Group III hydrocracked mineral oil and polyether ester at a volume ratio of 3:1, with a kinematic viscosity of 150 mm² / s.

[0072] The extreme pressure additive is a composite system of zinc dialkyl dithiophosphate and alkyl phosphate ester, with a mass ratio of 1:2.

[0073] The anti-wear agent is a polybutene succinate-based anti-wear agent with an acid value of 5.0 mg KOH / g and a viscosity index of 155.

[0074] The antioxidant is a composite system of di-tert-butyl-p-cresol and phosphite;

[0075] The nano solid lubricant is molybdenum disulfide with an average particle size of 20 nm, which is coated with a silane coupling agent, and the coating layer accounts for 25% of the total mass. The molybdenum disulfide has a particle size of 20 nm and an interlayer spacing of about 0.29 nm, forming a monolayer structure. After being dispersed by a cationic coupling agent, it forms a stable suspension.

[0076] The friction modifier is an N-alkylpyridine surfactant;

[0077] The oiling agent is a hydroxy fatty acid ester with a hydroxyl value of 60 mg KOH / g.

[0078] The preparation steps are as follows:

[0079] S1. Basic premix: Add 85.0% of the base oil to the reactor and stir at 35°C; add antioxidant, friction modifier and oiliness agent in sequence, stir evenly, and premix for 20 minutes to form a basic mixture.

[0080] S2. Addition of functional agents: Heat the mixture to 65°C and add extreme pressure additives and anti-wear agents. Shear and stir for 30 minutes at a stirring speed of 1000 rpm to ensure that the functional components are fully and evenly mixed.

[0081] S3. Pretreatment and addition of nano lubricant: Molybdenum disulfide nano solid lubricant and silane coupling agent are mixed in base oil and treated with an ultrasonic device (frequency 50kHz) for 20 minutes to form a positively charged dispersion system. Then, the dispersion is added dropwise to the reaction system at a rate of 1.5ml / min using a constant flow pump, and shearing and stirring are continued at 60-70℃ for 20 minutes to ensure uniform dispersion of nanoparticles.

[0082] S4. Real-time linkage detection and monitoring: During the S3 dropping and shearing process, the linkage laser particle size analyzer and infrared spectrometer module monitor the particle size distribution and chemical bond changes of nanoparticles in real time to confirm the dispersion stability.

[0083] S5. Shear stabilization treatment: After S3, the mixture is subjected to short-term high-frequency shear treatment at a shear rate of 15,000 rpm for 5 minutes to further improve the uniformity of nanoparticles and enhance the storage stability of the finished product.

[0084] S6. Final Cooling and Filtration: The system is naturally cooled to room temperature and filtered using a precision filter membrane with a pore size of no more than 5 μm to obtain a stable and uniform extreme pressure lubricating oil composition.

[0085] Comparative Example 1

[0086] This comparative example provides an extreme pressure lubricating oil composition with the following mass percentage composition: base oil: 90.0%, extreme pressure additive: 4.5%, anti-wear agent: 2.0%, antioxidant: 1.0%, nano solid lubricant: 0%, friction modifier: 0.9%, and oiliness agent: 1.6%.

[0087] The types of components are the same as in Example 1, except that no nano solid lubricant was added, and the proportion of oiliness agent was increased in an attempt to compensate for the lubrication performance.

[0088] The preparation steps are the same as in Example 1.

[0089] Comparative Example 2

[0090] This comparative example provides an extreme pressure lubricating oil composition with the following mass percentage composition: base oil: 90.0%, extreme pressure additive: 6.5%, anti-wear agent: 1.5%, antioxidant: 0.5%, nano solid lubricant: 0.5%, friction modifier: 0.5%, and oiliness agent: 0.5%.

[0091] Among them, the proportion of extreme pressure additives is relatively high, while the proportions of antioxidants, friction modifiers, and oiliness agents are relatively low.

[0092] The preparation steps are the same as in Example 1.

[0093] Comparative Example 3

[0094] This comparative example provides an extreme pressure lubricating oil composition with the following mass percentage composition: base oil: 90.0%, extreme pressure additive: 4.5%, anti-wear agent: 0.5%, antioxidant: 1.0%, nano solid lubricant: 0.6%, friction modifier: 0.9%, and oiliness agent: 2.5%.

[0095] Among them, anti-wear agents were significantly reduced, while oiling agents were increased.

[0096] The preparation steps are the same as in Example 1.

[0097] Comparative Example 4

[0098] This comparative example provides an extreme pressure lubricating oil composition with the following mass percentage composition: base oil: 88.0%, extreme pressure additive: 4.5%, anti-wear agent: 2.0%, antioxidant: 1.0%, nano solid lubricant: 1.6%, friction modifier: 0.9%, and oiliness agent: 2.0%.

[0099] Among them, the proportion of nano-lubricants is relatively high.

[0100] The preparation steps are the same as in Example 1.

[0101] Comparative Example 5

[0102] The comparative example adopts the same component ratio as Example 1, but omits steps S4 and S5, i.e., online monitoring and high-frequency shear stabilization treatment are not performed, and the mixture is only allowed to stand and mix after S3.

[0103] Comparative Example 6

[0104] This comparative example also uses the same component ratio as in Example 1, and performs steps S1, S2, and S3. However, in S3, the ultrasonic dispersion treatment was omitted, and the graphene dispersion was added to the reaction vessel only by conventional stirring.

[0105] To verify the lubrication performance, anti-wear performance, extreme pressure carrying capacity, and thermal oxidation stability of the extreme pressure lubricating oil composition of the present invention, the following examples and comparative examples were designed for comparative experiments. The experiments included tribological performance testing and thermal oxidation stability testing to evaluate the impact of the distribution ratio and key steps of each group on the final performance.

[0106] This experiment included three sets of example samples and six sets of comparative samples, aiming to comprehensively evaluate the impact of different component ratios and key process parameters on lubricant performance. All experimental samples used the compounded base oil system described in this invention as the main oil phase. The base oil was composed of Group II or Group III hydrocracked mineral oil mixed with polyalphaolefin (PAO) or polyether ester in different proportions. Each sample contained functional components such as nano-solid lubricants, extreme pressure additives, anti-wear agents, antioxidants, friction modifiers, and oiliness agents. Specific formulations and preparation processes are detailed in the corresponding examples or comparative samples.

[0107] All experimental samples were prepared independently according to the corresponding process flow, with each sample preparation volume being 100 mL. The finished products were sealed and stored in a constant temperature environment of 25℃ for 7 days before sampling and testing to simulate actual storage stability. To ensure the accuracy and statistical reliability of the test data, each test item of each sample was measured repeatedly 5 times, and the mean and standard deviation were calculated and compared.

[0108] The testing methods and conditions include:

[0109] Extreme pressure performance test: The sintering point (PB value) and ultimate load (PD value) were determined using the four-ball tester method.

[0110] Wear resistance test: The average wear scar diameter was measured after 60 minutes of testing using a four-ball friction tester with a load of 392N, 75℃, and 1200rpm.

[0111] Thermal oxidation stability test: Oxidation induction time (OIT) was determined using a DSC thermal analyzer according to ASTM D6186.

[0112] Dispersion stability test: The D90 particle size of the nano lubricant was determined using a laser particle size analyzer, and the sedimentation ratio of the sample after standing for 24 hours was recorded.

[0113] Friction coefficient test: The SRV friction and wear tester was used, with a load of 200N and a frequency of 50Hz for 10 minutes, and the dynamic friction coefficient curve was recorded.

[0114] Observation of wear track morphology: The microstructure of the wear track surface was observed using a scanning electron microscope.

[0115] For detailed experimental results, please refer to Figures 2-5 and Tables 1 to 3:

[0116] Table 1. Test results of extreme pressure and anti-wear performance of the four-ball machine (n=5)

[0117] Group PB value (N) PD value (N) Average wear scar diameter (mm) Example 1 2400±45 3800±60 0.32±0.01 Example 2 2200±52 3400±50 0.38±0.02 Example 3 2600±40 4000±55 0.30±0.01 Comparative Example 1 1900±35 3000±45 0.45±0.03 Comparative Example 2 2100±42 3100±51 0.48±0.04 Comparative Example 3 2000±40 2900±38 0.51±0.02 Comparative Example 4 2150±50 3200±43 0.42±0.03 Comparative Example 5 2250±46 3300±48 0.39±0.02 Comparative Example 6 2050±37 3100±40 0.46±0.02

[0118] Table 2. Thermal oxidation stability and particle size distribution data (n=5)

[0119] Group Oxidation induction period (OIT) (min) Nanoparticle size D90 (nm) 24-hour settlement ratio (%) Example 1 73.2±2.4 62±4 2.0±0.3 Example 2 68.6±2.7 78±5 3.2±0.4 Example 3 76.5±2.2 54±3 1.8±0.2 Comparative Example 1 45.1±3.1 — — Comparative Example 2 55.3±2.5 84±6 5.0±0.5 Comparative Example 3 52.7±3.0 81±5 6.2±0.7 Comparative Example 4 58.4±2.8 120±8 15.0±1.2 Comparative Example 5 65.0±2.1 92±6 7.1±0.6 Comparative Example 6 57.2±3.2 110±9 12.3±1.0

[0120] Table 3. Variation of SRV dynamic friction coefficient (n=5)

[0121] Group initial μ steady state μ High load μ variation amplitude Example 1 0.110±0.004 0.081±0.003 0.029 Example 2 0.118±0.005 0.089±0.004 0.041 Example 3 0.102±0.003 0.072±0.002 0.03 Comparative Example 1 0.145±0.006 0.121±0.005 0.065 Comparative Example 2 0.139±0.005 0.113±0.004 0.058 Comparative Example 3 0.152±0.007 0.128±0.006 0.069 Comparative Example 4 0.129±0.005 0.101±0.004 0.048 Comparative Example 5 0.124±0.004 0.099±0.003 0.05 Comparative Example 6 0.132±0.006 0.110±0.005 0.057

[0122] To evaluate the synergistic effect of the compounded base oil, extreme pressure additives, and nano-solid lubricants, the data from some samples in the existing examples and comparative examples were combined and analyzed as follows:

[0123] G1: Base oil + extreme pressure additives (Comparative Example 1).

[0124] G2: Base oil + nano solid lubricant (Comparative Example 4);

[0125] G3: Base oil + extreme pressure additives + nano solid lubricant (ultrasonic dispersion process omitted) (Comparative Example 6);

[0126] G4: Example 1 of the present invention (base oil + extreme pressure additive + nano solid lubricant, according to the process of the present invention).

[0127] Table 4. Results of the comparative experiment on synergistic effects

[0128] Group PB value (N) PD value (N) Average wear scar diameter (mm) Stable friction coefficient μ G1 1900 3000 0.45 0.121 G2 2150 3200 0.42 0.101 G3 2050 3100 0.46 0.110 G4 2400 3800 0.32 0.081

[0129] As shown in Table 4, Example 1 significantly outperforms any single-factor combination and the combination lacking a key dispersion step in terms of PD value, wear scar diameter, and stable friction coefficient. Taking PD value as an example, G4 improves by approximately 26% and 19% compared to G1 and G2, respectively, while WSD decreases by approximately 29% and 24% compared to G1 and G2, respectively. This magnitude exceeds the simple summation of the effects of each component, indicating a significant synergistic effect in the formulation of this invention.

[0130] Based on the above data and experimental observations, it can be concluded that the technical solution provided by this invention has the following superior effects:

[0131] (1) Significantly enhanced extreme pressure bearing capacity: The ultimate load (PD value) of Example 1 is 3800N, which is better than that of Example 2 and all comparative examples, and close to 4000N of Example 3, but has more balanced other performance indicators, indicating that its extreme pressure additive ratio (ZDDP to triaryl ester mass ratio 1:1.2) has good system stability while ensuring extreme pressure performance;

[0132] (2) Stable formation of lubricating film: The average wear scar diameter of Example 1 is 0.32 mm, which is slightly higher than that of Example 3 and better than Example 2 and all comparative examples. Under the same friction load and temperature, Example 1 can form a dense lubricating film on the metal surface to slow down wear.

[0133] (3) Excellent nanoparticle dispersibility: The nano lubricant in Example 1 has a particle size D90 of 62nm and a sedimentation ratio of only 2.0% after 24 hours, which shows excellent nanoparticle stability. Compared with the phenomenon in the comparative example where the particle size is greater than 90nm and the sedimentation ratio is as high as 15%, it effectively avoids the problem of film discontinuity caused by nano-agglomeration.

[0134] (4) Enhanced thermal oxidation stability: Under the synergistic effect of antioxidants, the oxidation induction period of the compound base oil system (PAO + Group III mineral oil, PAO + polyether ester) is generally extended to more than 70 min, which is significantly better than the comparative sample and more suitable for high temperature working scenarios;

[0135] (5) Enhanced frictional stability: The initial friction coefficient of Example 1 was 0.110, and the steady state coefficient dropped to 0.081, a decrease of 0.029. Compared with the steady state values ​​of the comparative examples, which were generally higher than 0.099, and Examples 2 and 3, it has better overall temperature stability and fluctuation control while ensuring low friction.

[0136] Figure 4 The correlation between the particle size D90 value of the nano-lubricants and their 24-hour sedimentation ratio in the examples and comparative examples is shown. The figures reveal that the nano-lubricants in Examples 1-3 have particle sizes controlled below 80 nm, with sedimentation ratios below 3%, exhibiting good dispersion stability. In Comparative Examples 4-6, the particle sizes are generally higher than 90 nm, reaching a maximum of 120 nm, and the sedimentation ratios significantly increase to over 15%, with some samples showing obvious agglomeration and sedimentation. The data show a clear positive correlation trend: as the particle size increases, the sedimentation ratio rises rapidly, especially when exceeding 90 nm, the sedimentation stability decreases sharply. This invention, by controlling the particle size of the nano-solid lubricant and employing surface coating and ultrasonic dispersion treatment, can significantly inhibit its agglomeration behavior, improve its distribution stability in the lubricating oil system, and ensure its long-term synergistic lubrication capability.

[0137] Figure 5This reflects the dynamic change of the friction coefficient of Example 1 and Comparative Examples 1 and 6 under SRV test conditions. The curves show that Example 1 exhibits a rapid decrease in friction coefficient at the beginning of the test, reaches a steady state within about 3 minutes, and remains around 0.081 throughout the test with minimal fluctuation. In contrast, the friction coefficients of Comparative Examples C1 and C6 show an irregular increase in the later stages, with steady-state values ​​maintained between 0.110 and 0.121, indicating that their lubricating film is unstable and exhibits periodic rupture or accelerated wear. This verifies that the lubrication system in Example 1 can rapidly form a boundary lubricating film under shear stress and continuously maintain the integrity of the film layer, thereby maintaining a low-friction operating state.

[0138] In this invention, friction modifiers and extreme pressure additives exhibit synergistic lubrication behavior in lubricating oil systems through the molecular structure design of lipophilic segments. The selected friction modifiers (such as imidazoline salts and N-alkylpyridines) contain lipophilic long chains and polar groups in their molecular structure, which can form van der Waals forces, hydrogen bonds, or electrostatic interactions with extreme pressure additives (such as zinc dialkyl dithiophosphate and phosphate esters), forming a synergistic adsorption layer at the lubrication interface. This helps to quickly establish a lubricating film, improves the film density and boundary stability, and enhances the continuity of the film in the boundary lubrication region.

[0139] To further verify the dispersion stability of the nano-solid lubricant in this invention, a 30-day isothermal static observation test was conducted on the lubricating oil composition prepared in Example 1. The samples were sealed and stored at 25°C, and their appearance was observed every 7 days, recording whether significant sedimentation, flocculation, or stratification occurred. The results showed that the samples remained transparent and homogeneous throughout, with no visible phase separation, demonstrating good long-term dispersion stability. This stability is mainly attributed to the synergistic modification strategy employed in this invention: the nano-solid lubricant is coated with chitosan quaternary ammonium salt, phosphate ester, or silane coupling agent to form a positively charged dispersion, which forms a stable suspension under shear, ultrasonic, and high-frequency treatment; the synergistic adsorption of friction modifiers and extreme pressure additives in the system also plays an auxiliary role in the formation of the particle interface film, effectively inhibiting aggregation and sedimentation.

[0140] Furthermore, to further evaluate the long-term performance of the lubricating oil composition under high-temperature conditions, the applicant, referring to the ASTM D6186 standard, simulated the thermal stability under accelerated aging conditions at 120°C, based on the original OIT test. Specifically, the product from Example 1 was placed in a high-temperature chamber and left to stand for 72 hours, after which its color, fluidity, and oxidation induction time changes were observed. The test results showed that the sample did not exhibit significant color darkening or oil phase stratification, and the OIT value decreased by less than 10%, demonstrating good oxidation resistance.

[0141] In summary, Example 1, as the recommended optimal formulation proposed in this invention, achieves optimized matching in multiple aspects such as base oil structure, synergistic effect of functional additives, nano-lubricant coating modification, and process path control.

[0142] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. An extreme pressure lubricating oil composition, characterized in that, It comprises the following components by weight percentage: base oil 85%–93%, extreme pressure additives 3%–8%, anti-wear agent 1%–3%, antioxidant 0.5%–2%, nano solid lubricant 0.1%–1%, friction modifier 0.2%–1%, and oiliness agent 0.1%–1.5%; The base oil is a composite oil made by mixing Group II or Group III hydrocracked mineral oil with poly-α-olefin or polyether ester in a volume ratio of 1:1 to 3:1, with a kinematic viscosity of 40 to 150 mm² / s. The extreme pressure additive is a compound of zinc dialkyl dithiophosphate and phosphate ester; The anti-wear agent is selected from polyetheramine derivatives, long-chain monoesters or polybutene succinates, wherein the acid value is controlled at 2-5 mgKOH / g and the viscosity index is greater than 140. The nano solid lubricant is a single-layer or few-layer graphene with an average particle size of 20-80 nm and an interlayer spacing of less than 0.35 nm, and is coated with chitosan quaternary ammonium salt. The mass ratio of the coating layer is 5%-25% of the total particle mass, and the coating treatment includes the formation of a dispersion in an organic solvent by cationic charge induction. The friction modifier is an imidazoline salt, an alcohol ether amine, or an N-alkylpyridine surfactant. The oiling agent is a hydroxyl fatty acid ester or a polyether-modified silicone oil with a hydroxyl value of 30-60 mgKOH / g. The extreme pressure lubricating oil composition is prepared according to the following steps: S1. Place the base oil in a reaction vessel and stir at 30-40°C. Add antioxidant, friction modifier and oiliness agent in sequence for premixing and stir for 10-20 minutes. S2. Add the extreme pressure additive and anti-wear agent at a constant temperature of 60-70°C and continue to shear and stir for 20-30 minutes. S3. The coated and ultrasonically pre-dispersed nano-solid lubricant is slowly added dropwise to the mixture at a rate of 0.5-2 ml / min, and sheared at 60-70°C for 20 minutes, wherein the dropwise addition is performed by a constant flow pump; S4. After step S3 is completed, perform a short-term high-frequency shearing process on the semi-finished product. S5. After cooling to room temperature, the mixture is filtered through a precision filter membrane with a pore size of less than 5μm to obtain a stable lubricating oil composition. An online particle size laser analyzer and infrared spectrometer are linked before and after the addition of nano solid lubricant to monitor particle size stability and chemical bond changes in real time.

2. The extreme pressure lubricating oil composition according to claim 1, characterized in that, The oiling agent is hydroxylinoleic acid ester with a hydroxyl value of 45 mg KOH / g.

3. The extreme pressure lubricating oil composition according to claim 1, characterized in that, The extreme pressure additive contains a phosphate ester to zinc dialkyl dithiophosphate in a mass ratio of 1:1 to 2:1, and the phosphate ester includes triisooctyl phosphate or triaryl phosphate.

4. The extreme pressure lubricating oil composition according to claim 1, characterized in that, The antioxidants include di-tert-butyl-p-cresol and phosphite.

5. The extreme pressure lubricating oil composition according to claim 1, characterized in that, The graphene has an average particle size of 50 nm, and the coating layer accounts for 15% of the total mass.

6. The extreme pressure lubricating oil composition according to claim 1, characterized in that, The friction modifier is an imidazoline salt, and the imidazoline salt and the extreme pressure additive each have an oleophilic segment structure.

7. A method for preparing the extreme pressure lubricating oil composition according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Place the base oil in a reaction vessel and stir at 30-40°C. Add antioxidant, friction modifier and oiliness agent in sequence for premixing and stir for 10-20 minutes. S2. Add the extreme pressure additive and anti-wear agent at a constant temperature of 60-70°C and continue to shear and stir for 20-30 minutes. S3. The coated and ultrasonically pre-dispersed nano-solid lubricant is slowly added dropwise to the mixture at a rate of 0.5-2 ml / min, and sheared at 60-70°C for 20 minutes, wherein the dropwise addition is performed by a constant flow pump; S4. After step S3 is completed, perform a short-term high-frequency shearing process on the semi-finished product. S5. After cooling to room temperature, the mixture is filtered through a precision filter membrane with a pore size of less than 5μm to obtain a stable lubricating oil composition. An online particle size laser analyzer and infrared spectrometer are linked before and after the addition of nano solid lubricant to monitor particle size stability and chemical bond changes in real time.

8. The method according to claim 7, characterized in that, The pretreatment steps of the nano-solid lubricant include sonication in base oil for 20 minutes at a frequency of 40–60 kHz, and the use of an ionic oleophilic surface modifier to form a positively charged dispersion system.

9. The method according to claim 7, characterized in that, The high-frequency shearing process in step S4 has a shearing rate of 10,000 to 15,000 rpm and a duration of 3 to 5 minutes.

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