Urea-based lubricating grease and preparation method thereof

Abstract

The invention discloses urea-based lubricating grease and a preparation method thereof, and belongs to the technical field of lubricating grease. The urea-based lubricant comprises composite base oil, a thickening agent and an additive, the composite base oil is selected from at least two of II type base oil, III type base oil, ester oil, polyether oil, poly-alpha-olefin synthetic base oil, mineral oil and alkyl naphthalene oil; the thickening agent is selected from a mixture of a diurea thickening agent and a tetraurea thickening agent; the additive is selected from a mixture of an antioxidant and an antirust agent. According to the urea-based lubricating grease, the vibration value and the vibration speed of the urea-based lubricating grease are remarkably reduced by optimizing the composition of the base oil and the thickening agent and particularly selecting the diurea thickening agent raw material and the tetraurea thickening agent raw material of specific types and proportions.

Description

Technical Field

[0001] The present invention relates to the technical field of lubricating grease, and in particular to a urea-based lubricating grease and a preparation method thereof. Background Art

[0002] Bearings are basic components in machines and are widely used in mechanical products in various industries. They are known as the "joints" of machines. With the continuous development of my country's machinery industry, the bearing industry is constantly developing towards high precision, long life, low noise and low torque. Bearing grease is the fifth core "component" of bearings, and about 80% of rolling bearings are lubricated with grease. The high-quality development of the bearing industry has put forward higher requirements for bearing grease, especially with the development trend of miniaturization of mechanical equipment, people's demand for low-noise grease has increased significantly.

[0003] Apart from the bearing itself, the main cause of bearing noise is the agglomerated thickener particles in the grease. The aggregation of these particles in the bearing raceway causes radial displacement, which in turn causes vibration. To improve low noise performance, the grease must have high purity, uniform thickener particle size, appropriate oil film thickness, and good channeling properties.

[0004] Early low-noise bearing grease formulations were mainly lithium soap grease. The reason is that lithium soap grease involves melting and recrystallization of the thickener during its preparation. By controlling the recrystallization process parameters, the size of the lithium soap thickener can be reduced, its uniformity improved, and the thickener agglomeration phenomenon improved. However, the low dropping point of lithium-based grease (about 200°C) limits its use in high-temperature conditions. In addition, the metal atoms contained in its system will accelerate the oxidation of the oil and shorten the service life of the bearing.

[0005] Polyurea grease uses molecules containing urea groups as thickeners. Compared with lithium-based grease, it has a higher dropping point (greater than 260°C) and can be used in high-temperature conditions. In addition, its system does not contain metal atoms, so the bearing life is much longer than that of lithium-based grease. In addition, its raw material cost is also lower than that of lithium-based grease. However, due to the hydrogen bond interaction between its urea groups, the thickener particles are easy to agglomerate in the base oil and the particle size controllability is poor. Therefore, it is naturally inferior to lithium-based grease in terms of low noise performance, which seriously limits the application of polyurea grease in industry.

[0006] Therefore, it is of great significance to research and develop a new type of low-noise polyurea grease so that it can be widely used in industry. Summary of the invention

[0007] In view of this, the technical problem to be solved by the present invention is to provide a urea-based lubricating grease and a preparation method thereof. The vibration value and vibration speed of the urea-based lubricating grease are significantly reduced.

[0008] In order to achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0009] The present invention provides a urea-based lubricating grease, comprising a composite base oil, a thickener and an additive;

[0010] The composite base oil is selected from at least two of group II base oil, group III base oil, ester oil, polyether oil, poly-α-olefin synthetic base oil, mineral oil, and alkyl naphthalene oil;

[0011] The thickener is selected from a mixture of a diurea thickener and a tetraurea thickener;

[0012] The additive is selected from a mixture of antioxidants and rust inhibitors.

[0013] Preferably, the diurea thickener is prepared by reacting diphenylmethane diisocyanate and its isomers with an organic amine;

[0014] The diphenylmethane diisocyanate and its isomers (MDI) include but are not limited to 4,4'-methylenebis(phenyl isocyanate), 2,4'-methylenebis(phenyl isocyanate), 2,2'-methylenebis(phenyl isocyanate) and the like.

[0015] In some specific embodiments of the present invention, the MDI is an industrial product, and its component is a mixture of 2,4'-methylenebis(phenyl isocyanate) and 4,4'-methylenebis(phenyl isocyanate) (and 4,4'-methylenebis(phenyl isocyanate)>97%).

[0016] Preferably, the organic amine is selected from at least three of aniline, cyclohexylamine, octadecylamine and octylamine; more preferably, it is a mixture of cyclohexylamine, octadecylamine and octylamine, or a mixture of aniline, cyclohexylamine and octadecylamine, or a mixture of aniline, octadecylamine and octylamine.

[0017] Preferably, the tetraurea thickener is prepared by reacting toluene diisocyanate and its isomers with monoamine and diamine;

[0018] The toluene diisocyanate and its isomers (TDI) include but are not limited to toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, toluene-2,3-diisocyanate, toluene-2,5-diisocyanate, toluene-3,4-diisocyanate, toluene-3,5-diisocyanate and the like.

[0019] In some specific embodiments of the present invention, the TDI is an industrial product, and its composition is a mixture of toluene-2,4-diisocyanate (80%) and toluene-2,6-diisocyanate (20%).

[0020] Preferably, the monoamine is selected from at least two of aniline, cyclohexylamine, octadecylamine and octylamine, more preferably octadecylamine and octylamine, or cyclohexylamine and octadecylamine.

[0021] Preferably, the diamine is selected from ethylenediamine or hexamethylenediamine.

[0022] Further preferably, the monoamine is selected from octadecylamine and octylamine and the diamine is selected from ethylenediamine, or the monoamine is selected from octadecylamine and cyclohexylamine and the diamine is selected from ethylenediamine.

[0023] Preferably, the composite base oil is a mixture of Group II base oil and polyether oil, or a mixture of ester oil and poly-α-olefin synthetic base oil, or a mixture of Group II base oil, Group III base oil and alkyl naphthalene oil.

[0024] Preferably, the polyether oil is selected from polyglycol ether base oil;

[0025] Preferably, the ester oil is selected from one or more of dioctyl sebacate base oil, trimethylolpropane ester base oil, trimellitate base oil, and pentaerythritol ester base oil;

[0026] Preferably, the alkyl naphthalene oil is selected from one or more of AN5, AN15, and AN23.

[0027] Preferably, the organic amine is selected from cyclohexylamine, octadecylamine and octylamine;

[0028] Preferably, the monoamine is selected from octadecylamine and octylamine, and the diamine is selected from ethylenediamine.

[0029] Preferably, the molar ratio of cyclohexylamine, octadecylamine and octylamine is (0.7-0.8): (0.2-0.3): (0.5-0.6);

[0030] Preferably, the molar ratio of octadecylamine to octylamine is (0.05-0.07): (0.10-0.18). Preferably, the antioxidant is selected from dialkyl diphenylamine, dioctyl diphenylamine, 3-5-di-tert-butyl-4-hydroxyphenyl methyl acrylate or 2,6-di-tert-butylphenol;

[0031] Preferably, the rust inhibitor is selected from barium dinonylnaphthalenesulfonate, pentaerythritol monooleate or N,N-bis(phenylpropanetriazole methylene) laurylamine.

[0032] The present invention also provides a method for preparing the above-mentioned urea-based grease, comprising the following steps:

[0033] (1) Prepare composite base oil;

[0034] (2) mixing an organic amine and a composite base oil uniformly to obtain an amine solution 1; mixing diphenylmethane diisocyanate and its isomers uniformly with a base oil, and then mixing with the amine solution 1 and heating to 85° C.-100° C. to obtain a mixture 1 containing a diurea thickener and a base oil;

[0035] (3) uniformly mixing the monoamine and the diamine with the base oil to obtain an amine solution 2; uniformly mixing toluene diisocyanate and its isomers with the base oil and then mixing with the amine solution 2 and heating to 85° C.-100° C. to obtain a mixture 2 containing a tetraurea thickener and the base oil;

[0036] (4) The mixture 1 and the mixture 2 are fully mixed, the temperature is raised to 140°C-180°C, the temperature is lowered to 80°C, a mixture of an antioxidant and a rust inhibitor is added, and the urea-based grease is obtained by high-pressure homogenization and degassing.

[0037] Preferably, in the step (2), the temperature at which the organic amine and the composite base oil are mixed is 70° C.-80° C.;

[0038] Preferably, in step (2), the temperature at which diphenylmethane diisocyanate and its isomers are mixed with the composite base oil is 60° C.-70° C.;

[0039] Preferably, the reaction time in step (2) is 40-80 min; more preferably 50-70 min.

[0040] Preferably, in the step (3), the temperature at which the monoamine and diamine are mixed with the composite base oil is 70° C.-80° C.;

[0041] Preferably, the temperature at which toluene diisocyanate and its isomers are mixed with the composite base oil in step (3) is 60° C.-70° C.;

[0042] Preferably, the reaction time in step (3) is 40-80 min; more preferably 50-65 min.

[0043] Compared with the prior art, the urea-based lubricant provided by the present invention includes a composite base oil, a thickener and an additive; the composite base oil is selected from at least two of Class II base oil, Class III base oil, ester oil, polyether oil, poly-α-olefin synthetic base oil, mineral oil, and alkyl naphthalene oil; the thickener is selected from a mixture of a diurea thickener and a tetraurea thickener; the additive is selected from a mixture of an antioxidant and a rust inhibitor. The urea-based grease significantly reduces the vibration value and vibration speed of the urea-based grease by optimizing the composition of the base oil and the thickener, especially selecting a specific type and ratio of diurea thickener raw materials and tetraurea thickener raw materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1The vibration value of the urea-based grease prepared in Example 1 and Comparative Examples 1-8 varies with time;

[0045] Figure 2 The graph is a graph showing the vibration velocity of the urea-based grease prepared in Example 1 and Comparative Examples 1-8 changing with time. DETAILED DESCRIPTION

[0046] In order to further illustrate the present invention, the urea-based grease and the preparation method thereof provided by the present invention are described in detail below with reference to the embodiments.

[0047] The following chemical reagents are all commercially available products unless otherwise specified. The following contents are by mass unless otherwise specified. The following reactions are all carried out at room temperature unless otherwise specified.

[0048] Terminology Note:

[0049] Class II oil: refers to base oil produced by hydrogenation process, such as 350N, 500N, 150BS, etc.

[0050] Class III oil: refers to base oil produced by deep hydrocracking / hydroisomerization, such as 100N, 150N, 250N, etc.

[0051] Ester oil: base oil containing ester functional groups in the molecule, such as dioctyl sebacate, trimethylolpropane ester, trimellitic acid ester, pentaerythritol ester base oil, etc.

[0052] Polyether oil: refers to polyglycol ether base oil.

[0053] PAO: refers to poly alpha-olefin synthetic base oil, including PAO4, PAO6, PAO8, PAO10, etc.

[0054] Mineral oil: including 500SN, 350SN, 200SN, 150SN, etc.

[0055] Alkyl naphthalene oil: including AN5, AN15, AN23, etc.

[0056] MDI: diphenylmethane diisocyanate and its isomers.

[0057] TDI: Toluene diisocyanate and its isomers.

[0058] The MDI used in the following examples is an industrial product purchased from Wanhua Chemical Group Co., Ltd., with a brand name of MDI-100. TDI is purchased from Wanhua Chemical Group Co., Ltd., with a brand name of TDI-80. Dialkyldiphenylamine is purchased from BASF Chemical Co., Ltd., with a model name of L57.

[0059] Example 1

[0060] (1) 2112 g of 150BS and 1408 g of polyglycol ether base oil were thoroughly mixed to prepare a mixed base oil.

[0061] (2) 0.77 mol of cyclohexylamine, 0.23 mol of octadecylamine and 0.54 mol of octylamine were dissolved in a 2 / 5 mixed base oil at a dissolution temperature of 70-80°C. After the raw materials were completely dissolved, amine solution 1 was obtained. 0.77 g of MDI (MDI-100, whose components are a mixture of 2,4'-methylenebis(phenyl isocyanate) and 4,4'-methylenebis(phenyl isocyanate) (and 4,4'-methylenebis(phenyl isocyanate)>97%) was dissolved in a 1 / 5 mixed base oil at a dissolution temperature of 60-70°C. After the raw materials were completely dissolved, MDI solution was obtained. Then, amine solution 1 and MDI solution were mixed at high speed, then heated to 85-100°C, and reacted for 60 minutes to obtain a mixture of diurea thickener and base oil.

[0062] (3) 0.06 mol of octadecylamine, 0.14 mol of octylamine and 0.09 mol of ethylenediamine were dissolved in a 1 / 5 mixed base oil at a dissolution temperature of 70-80°C. After the raw materials were completely dissolved, amine solution 2 was obtained. 0.21 mol of TDI was dissolved in a 1 / 5 mixed base oil at a dissolution temperature of 60-70°C. After the raw materials were completely dissolved, TDI (TDI-80, which is a mixture of toluene-2,4-diisocyanate (80%) and toluene-2,6-diisocyanate (20%)) solution was obtained. Then, amine solution 2 and TDI solution were mixed at high speed, then heated to 85-100°C, and reacted for 60 minutes to obtain a mixture of tetraurea thickener and base oil.

[0063] (4) The mixtures obtained in the above steps (2) and (3) are fully mixed, and the temperature is raised to 140-180° C. The temperature is lowered to 80° C. and additives (40 g of dialkyl diphenylamine and 40 g of barium dinonylnaphthalene sulfonate) are added. After high-pressure homogenization and degassing, the finished urea-based grease is obtained.

[0064] Example 2

[0065] (1) 1760 g of 500N base oil, 1056 g of 250N and 800 g of AN5 base oil were thoroughly mixed to prepare a mixed base oil.

[0066] (2) 0.40 mol of cyclohexylamine, 0.55 mol of octadecylamine and 0.05 mol of aniline were dissolved in a 2 / 5 mixed base oil at a dissolution temperature of 70-80°C. After the raw materials were completely dissolved, amine solution 1 was obtained. 0.50 mol of MDI was dissolved in a 1 / 5 mixed base oil at a dissolution temperature of 60-70°C. After the raw materials were completely dissolved, MDI solution was obtained. Then, the amine solution and the MDI solution were mixed at a high speed, and then the temperature was raised to 85-100°C and reacted for 60 minutes to obtain a mixture of diurea thickener and base oil.

[0067] (3) 0.22 mol of octadecylamine, 0.015 mol of cyclohexylamine and 0.18 mol of ethylenediamine were dissolved in a 1 / 5 mixed base oil at a dissolution temperature of 70-80°C. After the raw materials were completely dissolved, amine solution 2 was obtained. 0.37 mol of TDI was dissolved in a 1 / 5 mixed base oil at a dissolution temperature of 60-70°C. After the raw materials were completely dissolved, TDI solution was obtained. Then, amine solution 2 and TDI solution were mixed at high speed, then heated to 85-100°C, and reacted for 60 minutes to obtain a mixture of tetraurea thickener and base oil.

[0068] (4) The mixtures obtained in the above steps (2) and (3) are fully mixed and heated to 140-180° C. The mixture is cooled to 80° C. and additives (40 g of 3-5-di-tert-butyl-4-hydroxyphenyl methyl acrylate and 40 g of barium dinonylnaphthalene sulfonate) are added. The finished urea-based grease is obtained after high-pressure homogenization and degassing.

[0069] Example 3

[0070] (1) 1660 g of dioctyl sebacate base oil and 1660 g of PAO8 were thoroughly mixed to prepare a mixed base oil.

[0071] (2) 0.58 mol of octylamine, 1 mol of octadecylamine and 0.08 mol of aniline were dissolved in a 2 / 5 mixed base oil at a dissolution temperature of 70-80°C. After the raw materials were completely dissolved, amine solution 1 was obtained. 0.83 mol of MDI was dissolved in a 1 / 5 mixed base oil at a dissolution temperature of 60-70°C. After the raw materials were completely dissolved, MDI solution was obtained. Then, amine solution 1 and MDI solution were mixed at high speed, then heated to 85-100°C, and reacted for 60 minutes to obtain a mixture of diurea thickener and base oil.

[0072] (3) 0.14 mol of octadecylamine, 0.14 mol of octadecylamine and 0.14 mol of ethylenediamine were dissolved in a 1 / 5 mixed base oil at a dissolution temperature of 70-80°C. After the raw materials were completely dissolved, amine solution 2 was obtained. 0.28 mol of TDI was dissolved in a 1 / 5 mixed base oil at a dissolution temperature of 60-70°C. After the raw materials were completely dissolved, TDI solution was obtained. Then, amine solution 2 and TDI solution were mixed at high speed, then heated to 85-100°C, and reacted for 60 minutes to obtain a mixture of tetraurea thickener and base oil.

[0073] (4) The mixtures obtained in the above steps (2) and (3) are fully mixed, and the temperature is raised to 140-180° C. The temperature is lowered to 80° C. and additives (40 g of dioctyl diphenylamine and 40 g of pentaerythritol monooleate) are added. After high-pressure homogenization and degassing, the finished urea-based grease is obtained.

[0074] Example 4

[0075] (1) 2380 g of trimellitate base oil and 1020 g of PAO6 were thoroughly mixed to prepare a mixed base oil.

[0076] (2) 0.15 mol of octylamine, 0.07 mol of octadecylamine and 0.2 mol of cyclohexylamine were dissolved in a 2 / 5 mixed base oil at a dissolution temperature of 70-80°C. After the raw materials were completely dissolved, amine solution 1 was obtained. 0.77 mol of MDI was dissolved in a 1 / 5 mixed base oil at a dissolution temperature of 60-70°C. After the raw materials were completely dissolved, MDI solution was obtained. Then, amine solution 1 and MDI solution were mixed at high speed, then heated to 85-100°C, and reacted for 60 minutes to obtain a mixture of diurea thickener and base oil.

[0077] (3) 0.12 mol of octadecylamine, 0.05 mol of octylamine and 0.09 mol of ethylenediamine were dissolved in a 1 / 5 mixed base oil at a dissolution temperature of 70-80°C. After the raw materials were completely dissolved, amine solution 2 was obtained. 0.17 mol of TDI was dissolved in a 1 / 5 mixed base oil at a dissolution temperature of 60-70°C. After the raw materials were completely dissolved, TDI solution was obtained. Then, amine solution 2 and TDI solution were mixed at high speed, then heated to 85-100°C, and reacted for 60 minutes to obtain a mixture of tetraurea thickener and base oil.

[0078] (4) The mixtures obtained in the above steps (2) and (3) are fully mixed and heated to 140-180° C. The mixture is cooled to 80° C. and additives (40 g of 2,6-di-tert-butylphenol and 40 g of N,N-bis(phenylpropionyltriazole methylene) laurylamine) are added. The finished urea-based grease is obtained after high-pressure homogenization and degassing.

[0079] Comparative Example 1

[0080] The difference from Example 1 is that in step (2), 0.44 mol of cyclohexylamine, 0.88 mol of octadecylamine and 0.22 mol of octylamine are used, and the rest are the same.

[0081] Comparative Example 2

[0082] The difference from Example 1 is that in step (2), 0.44 mol of cyclohexylamine, 0.22 mol of octadecylamine and 0.88 mol of octylamine are used, and the rest are the same.

[0083] Comparative Example 3

[0084] The difference from Example 1 is that in step (3), 0.14 mol of octadecylamine and 0.06 mol of octylamine are used, and the rest are the same.

[0085] Comparative Example 4

[0086] The difference from Example 1 is that in step (3), 0.16 mol of octadecylamine and 0.04 mol of octylamine are used, and the rest are the same.

[0087] Comparative Example 5

[0088] The difference from Example 1 is that in step (2), 0.46 mol of octadecylamine and 1.08 mol of octylamine are used, and the rest are the same.

[0089] Comparative Example 6

[0090] The difference from Example 1 is that in step (3), 0.2 mol of octadecylamine is used, and the rest is the same.

[0091] Comparative Example 7

[0092] The difference from Example 1 is that in step (2), octylamine and octadecylamine are replaced by cyclohexylamine in the same molar amount, step (3) is removed, and the rest are the same.

[0093] Comparative Example 8

[0094] The difference from Example 1 is:

[0095] Step (2) was removed, and in step (3), octylamine was replaced by the same molar amount of octadecylamine, and the rest were the same.

[0096] Results Test

[0097] Bearing vibration value test: The test uses 6308 bearings, with a grease injection amount of 9g, a bearing speed of 1800rpm, and an axial load of 110N. A vibration acceleration sensor is used to record the changes in vibration values ​​within 1 hour of operation.

[0098] Bearing vibration speed test: The test uses 6308 bearings, with a grease injection amount of 9g, a bearing speed of 1800rpm, and an axial load of 110N. A vibration speed sensor is used to record the changes in the vibration speed within a frequency range of 1800-10000Hz within 1 hour of operation.

[0099] The test results are as attached Figure 1-2 And as shown in Table 1-2.

[0100] Table 1 Vibration value and vibration velocity results of urea-based grease prepared in Examples 1-4

[0101]

[0102]

[0103] Table 2 Vibration value and vibration velocity results of urea-based grease prepared in Comparative Examples 1-8

[0104]

[0105] From the comparison results, the low-noise urea-based grease of the present invention has a lower bearing vibration value and a lower vibration speed than the urea-based grease of the comparative example, and the numerical curve is more stable during operation with less fluctuation.

[0106] The above embodiments are only used to help understand the method and core idea of ​​the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A urea-based grease, characterized in that: Includes composite base oil, thickener and additives; The composite base oil is selected from at least two of group II base oil, group III base oil, ester oil, polyether oil, poly-α-olefin synthetic base oil, mineral oil, and alkyl naphthalene oil; The thickener is selected from a mixture of a diurea thickener and a tetraurea thickener; The additive is selected from a mixture of antioxidants and rust inhibitors.

2. The urea-based grease according to claim 1, characterized in that: The diurea thickener is prepared by reacting diphenylmethane diisocyanate and its isomers with an organic amine; The organic amines are selected from at least three of aniline, cyclohexylamine, octadecylamine and octylamine; The tetraurea thickener is prepared by reacting toluene diisocyanate and its isomers with monoamine and diamine; The monoamine is selected from at least two of aniline, cyclohexylamine, octadecylamine and octylamine, and the diamine is selected from ethylenediamine or hexamethylenediamine.

3. The urea-based grease according to claim 1, characterized in that: The composite base oil is selected from a mixture of group II base oil and polyether oil, or a mixture of ester oil and poly-α-olefin synthetic base oil, or a mixture of group II base oil, group III base oil and alkyl naphthalene oil.

4. The urea-based grease according to claim 1 or 3, characterized in that: The polyether oil is selected from polyglycol ether base oil; The ester oil is selected from one or more of dioctyl sebacate base oil, trimethylolpropane ester base oil, trimellitate base oil, and pentaerythritol ester base oil; The alkyl naphthalene oil is selected from one or more of AN5, AN15 and AN23.

5. The urea-based grease according to claim 2, characterized in that: The organic amine is selected from cyclohexylamine, octadecylamine and octylamine; The monoamine is selected from octadecylamine and octylamine, and the diamine is selected from ethylenediamine.

6. The urea-based grease according to claim 5, characterized in that: The molar ratio of cyclohexylamine, octadecylamine and octylamine is (0.7-0.8): (0.2-0.3): (0.5-0.6); The molar ratio of octadecylamine to octylamine is (0.05-0.07):(0.10-0.18).

7. The urea-based grease according to claim 1, characterized in that: The antioxidant is selected from dialkyl diphenylamine, dioctyl diphenylamine, 3-5-di-tert-butyl-4-hydroxyphenyl methyl acrylate or 2,6-di-tert-butylphenol; The rust inhibitor is selected from barium dinonylnaphthalenesulfonate, pentaerythritol monooleate or N,N-bis(phenylpropanetriazole methylene) laurylamine.

8. The method for preparing the urea-based grease according to any one of claims 1 to 7, characterized in that: The following steps are involved: (1) Prepare composite base oil; (2) mixing an organic amine and a composite base oil uniformly to obtain an amine solution 1; mixing diphenylmethane diisocyanate and its isomers uniformly with a base oil, and then mixing with the amine solution 1 and heating to 85° C.-100° C. to obtain a mixture 1 containing a diurea thickener and a base oil; (3) uniformly mixing the monoamine and the diamine with the base oil to obtain an amine solution 2; uniformly mixing toluene diisocyanate and its isomers with the base oil and then mixing with the amine solution 2 and heating to 85° C.-100° C. to obtain a mixture 2 containing a tetraurea thickener and the base oil; (4) The mixture 1 and the mixture 2 are fully mixed, the temperature is raised to 140°C-180°C, the temperature is lowered to 80°C, a mixture of an antioxidant and a rust inhibitor is added, and the urea-based grease is obtained by high-pressure homogenization and degassing.

9. The preparation method according to claim 8, characterized in that: The temperature of mixing the organic amine and the composite base oil in step (2) is 70° C.-80° C.; In the step (2), the temperature at which diphenylmethane diisocyanate and its isomers are mixed with the composite base oil is 60° C.-70° C.; The reaction time in step (2) is 40-80 min.

10. The preparation method according to claim 8, characterized in that: The temperature of mixing the monoamine and diamine with the composite base oil in step (3) is 70° C.-80° C.; In the step (3), the temperature at which toluene diisocyanate and its isomers are mixed with the composite base oil is 60° C.-70° C.; The reaction time in step (3) is 40-80 min.

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