Lubricating oil additive suitable for oil-lacking working condition as well as preparation method and application of lubricating oil additive

Abstract

The invention discloses a lubricating oil additive suitable for an oil-lacking working condition, which comprises the following components in parts by weight: 90-99 parts of boric acid ester, 1-10 parts of modified nano boron nitride and 1-10 parts of modified nano silicon dioxide. The invention further provides a preparation method of the lubricating oil additive applicable to the oil-lacking working condition, the modified nano silicon dioxide with excellent dispersion stability in an organic medium is adopted, and the modified nano boron nitride is anchored on the surface of the modified silicon dioxide; the dispersion effect of nano boron nitride in an inorganic system is effectively improved; the modified nano silicon dioxide anchored with the nano boron nitride is bonded on the surface of the boric acid ester, so that the dispersion stability of the lubricating oil additive in the lubricating oil is synergistically improved; when the additive is added into the lubricating oil, the additive is easy to disperse, and the lubricating oil has good stability and wear resistance.

Description

Technical Field

[0001] The invention belongs to the technical field of lubricating oils, and in particular relates to a lubricating oil additive suitable for oil-deficient working conditions, and a preparation method and application thereof. Background Art

[0002] As the most common lubricant, lubricating oil is widely used in various mechanical equipment to reduce friction, wear and extend the service life of equipment. As the working conditions faced by equipment become more and more demanding, the working ability of equipment under extraordinary conditions such as insufficient oil, lack of oil, or even oil outage and no oil has become the focus of attention. Especially in the field of national defense, aircraft often face harsh lubrication conditions such as lack of oil and no oil. At this time, the performance of the lubrication system directly affects the maneuverability and service life of the aircraft. Therefore, lubricating oil is required not only to be able to continuously and effectively lubricate under conventional conditions, but also to be able to stably serve and reduce friction and wear under oil-deficient conditions.

[0003] Lubricating oil mainly consists of two parts: base oil and additives. Additives are chemical substances added to improve the performance of base oil, so that lubricating oil has better anti-wear, anti-oxidation, lubrication and other effects. Therefore, in order to enable lubricating oil to cope with oil-starved conditions, the use of additives is crucial. At present, the commonly used lubricating oil additives under oil-starved conditions are mainly friction modifiers, which can form a lubricating protective film on the metal surface to avoid direct contact between metal peaks, thereby reducing friction resistance and wear.

[0004] However, existing friction modifiers have a single component, a large friction coefficient, poor dispersion with the base oil, and easy stratification during storage. When used in oil-deficient conditions, they cannot effectively maintain stable operation between friction pairs. Summary of the invention

[0005] The present invention aims to solve one of the technical problems in the related art to at least a certain extent. To this end, the main purpose of the present invention is to provide a lubricating oil additive suitable for oil-deficient working conditions and a preparation method thereof. The lubricating oil additive prepared by compounding boric acid ester, modified nano-silicon dioxide and modified nano-boron nitride components can be stably dispersed with the base oil for a long time. The boron nitride in the additive can undergo tribochemical reaction with the metal matrix under oil-deficient working conditions to generate boron oxide, thereby forming a firm and stable protective film on the contact surface of the friction pair, effectively reducing the direct contact of the friction pair, thereby reducing friction and wear. The present invention also discloses the application of the lubricating fluid additive under oil-deficient working conditions.

[0006] The present invention is achieved through the following technical solutions:

[0007] A lubricating oil additive suitable for oil-deficient working conditions, characterized in that, in parts by weight, it comprises 90 to 99 parts of boric acid ester, 1 to 10 parts of modified nano boron nitride and 1 to 10 parts of modified nano silicon dioxide.

[0008] In some specific embodiments, the modification method of modified nano boron nitride comprises the following steps:

[0009] A1) dissolving the nano boron nitride, adding a dispersant, and performing ultrasonic dispersion for 1-2 hours to obtain a dispersion 1;

[0010] A2) adding the silane coupling agent hydrolyzate to the dispersion 1, stirring thoroughly, adjusting the pH value to 10±0.5, and reacting at 50-70° C. for 30-40 min to obtain a reaction solution 1;

[0011] A3) The reaction solution 1 is centrifuged, and the precipitate is collected and dried to obtain modified nano boron nitride.

[0012] In some specific embodiments, the method for preparing the modified nano-silica comprises the following steps:

[0013] B1) Weighing 5-20 parts of nano-silicon dioxide particles by weight and dispersing them into 60-80 parts of aqueous solution, adding 0.5-2.5 parts of initiator, activating, and obtaining pretreated nano-silicon dioxide;

[0014] B2) adding 5-15 parts by weight of acrylic acid and 5-15 parts by weight of acrylamide monomers to the pretreated nano-silica, reacting for 4-12 hours, cooling and filtering, and drying in a vacuum drying oven to obtain polymer-modified silica core-shell particles, i.e., modified nano-silica.

[0015] In some specific embodiments, the dispersant is one of Span 80, sodium polycarboxylate, and sodium dodecylbenzene sulfonate.

[0016] Further, the dispersant is Siban 80;

[0017] In some specific embodiments, the silane coupling agent includes KH-550.

[0018] In some specific embodiments, the particle size of the nano boron nitride is 30-45 nm.

[0019] In some specific embodiments, the weight ratio of the nano boron nitride to the silane coupling agent is (3-6):1.

[0020] The present invention also provides a method for preparing the aforementioned lubricating oil additive, comprising fully mixing modified nano boron nitride, modified nano silicon dioxide and boric acid ester to obtain a target product.

[0021] The present invention also provides the use of the above lubricating oil additive in lubricating oil under oil-starved working conditions.

[0022] Furthermore, the lubricating oil additive is widely applicable to various frictional moving pairs of engines lubricated by lubricating oil.

[0023] Compared with the prior art, the present invention has at least the following advantages:

[0024] 1) The lubricating oil additive provided by the present invention, firstly, by using a dispersant for pre-dispersion, not only can a steric hindrance be generated, but also can be dissociated and charged, adsorbed on the particle surface to increase the particle surface potential, and produce an electrostatic stabilization effect, so that the difficult-to-disperse nano-boron nitride can be well dispersed in water, and the uniformity and stability of the silane coupling agent for modifying the nano-boron nitride can be effectively improved; secondly, by modifying the nano-silicon dioxide particles, on the one hand, the nano-silicon dioxide particles are coated by copolymerization of acrylic acid and acrylamide to form a polymer core-shell particle structure, which can be uniformly dispersed in the lubricating oil with good uniformity; on the other hand, the polymer contains a large number of functional groups such as carboxyl and amino groups, so that the surface of the modified nano-boron nitride The amino group forms a bond with the carboxyl group, amino group, etc. on the surface of the modified nano-silica, so that the easily aggregated modified nano-boron nitride is anchored on the surface of the modified nano-silica, which greatly improves the stability of the nano-boron nitride in the lubricating oil; furthermore, the borate ester is a bis(catechol) diborate ester, which not only has a benzene ring and a carbonyl active group, but also bonds the modified nano-silica with boron nitride anchored on the surface to the borate ester surface, further improving the uniform dispersibility and stability of the lubricating oil additive in the lubricating oil; in addition, the nitrogen atom contains a lone pair of electrons and has a certain reducing property, thereby improving the antioxidant property of the lubricating oil; the additive is easily dispersed when added to the lubricating oil, and makes the lubricating oil have good stability and anti-wear properties.

[0025] 2) The lubricating oil additive provided by the present invention has significant friction reduction and wear resistance effects under both conventional working conditions and oil-deficient working conditions. In the laboratory material-level evaluation experiment, after the friction coefficient is stabilized by adding the additive, the friction coefficient under both conventional and oil-deficient working conditions can be reduced by more than 50%, and the oil-deficient experiment is carried out immediately after the conventional working condition experiment, and the friction coefficient will quickly enter a stable stage, and the stability is significantly improved. That is, the lubricating oil additive can significantly improve the friction reduction and wear resistance of the base oil under oil-deficient working conditions, and extend the stable service time of the lubricating oil under harsh oil-deficient working conditions.

[0026] 3) The preparation method of the present invention has a simple production process, no waste gas or waste liquid is generated during the production process, and the production cost is low. The prepared lubricant additive does not contain harmful substances such as phosphorus and sulfur, and has no harm to the atmosphere and the environment. After being added to the base oil, it can be stably dispersed for a long time without stratification and precipitation, and can be used for a long time; it can be widely used in friction moving pairs lubricated by synthetic lubricating oil, gear oil, and hydraulic oil. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the specific embodiments of the present invention, the drawings required for use in the specific embodiments or the description of the prior art will be briefly introduced below.

[0028] Figure 1 The dispersion stability of the lubricating oil additive in Example 2 of the present invention when used in lubricating oil. DETAILED DESCRIPTION

[0029] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. The following embodiments are only illustrative and not restrictive, and the protection scope of the present invention cannot be limited thereto.

[0030] When a certain amount, concentration or other value or parameter is expressed in the form of a range, a preferred range, or a preferred upper and lower numerical limit, it should be understood that it is equivalent to specifically revealing any range by combining any pair of upper range limits or preferred numerical values ​​with any lower range limit or preferred numerical value, regardless of whether the range is specifically disclosed. Unless otherwise indicated, the numerical range values ​​listed herein include the endpoints of the range, and all integers and fractions within the range.

[0031] Unless otherwise indicated, all percentages, parts, ratios, etc. herein are by weight.

[0032] The materials, methods, and examples herein are illustrative and are not to be construed as limiting unless specifically stated.

[0033] In the following examples, the particle size of the nano boron nitride used is 30 nm; the silane coupling agent used is KH-550; the particle size of the nano silicon dioxide used is 50-100 nm; the dispersant used is Span 80; and the borate used is bis(catechol) diborate.

[0034] Example 1

[0035] The preparation method of the lubricating oil additive suitable for oil-starved working conditions provided in this embodiment comprises the following steps:

[0036] (1) Boron nitride modification:

[0037] Nano boron nitride was dissolved in deionized water to obtain a nano boron nitride aqueous solution, a surfactant was added, and ultrasonic dispersion was performed for 1 hour to obtain a dispersion 1; a silane coupling agent hydrolyzate was added to the dispersion 1 (wherein the mass ratio of nano boron nitride to silane coupling agent was 4:1), and the mixture was fully stirred for 40 minutes. After the stirring was completed, a sodium hydroxide solution was dripped into the dispersion to adjust the pH value to 10, and the mixture was stirred in a water bath at 60° C. and reacted for 30 minutes to obtain a reaction solution 1; the reaction solution 1 was placed in a centrifuge tube, and centrifuged at 5000 rpm for 10 minutes. The precipitate was placed in a vacuum drying oven and vacuum dried at 100° C. for 4 hours to obtain a modified nano boron nitride;

[0038] (2) Silica modification:

[0039] 21) Weigh 5 g of nano-silicon dioxide and disperse it in 80 g of aqueous solution, add 1.5 g of potassium persulfate, heat to 86° C., and stir to activate for 5 min to obtain pretreated nano-silicon dioxide;

[0040] 22) adding 8.5 g of acrylic acid and 5 g of acrylamide monomer to the pretreated nano-silica, reacting for 6 h, cooling and filtering, and drying in a vacuum drying oven at 60° C. for 8 h to obtain polymer-modified silica core-shell particles, i.e., modified nano-silica;

[0041] (3) Additive mixing:

[0042] 90 parts of boric acid ester, 6 parts of modified nano boron nitride and 4 parts of modified nano silicon dioxide were mixed and mechanically stirred for 10 minutes to obtain a lubricating oil additive.

[0043] Example 2

[0044] The preparation method of the lubricating oil additive suitable for oil-starved working conditions provided in this embodiment comprises the following steps:

[0045] (1) Boron nitride modification:

[0046] Nano boron nitride was dissolved in deionized water to obtain a nano boron nitride aqueous solution, a surfactant was added, and ultrasonic dispersion was performed for 1.5 hours to obtain a dispersion 1; a silane coupling agent hydrolyzate was added to the dispersion 1 (wherein the mass ratio of nano boron nitride to silane coupling agent was 4:1), and the mixture was fully stirred for 40 minutes. After the stirring was completed, a sodium hydroxide solution was added dropwise to adjust the pH value to 10, and the mixture was stirred in a water bath at 60° C. and reacted for 35 minutes to obtain a reaction solution 1; the reaction solution 1 was placed in a centrifuge tube, and centrifuged at 5000 rpm for 10 minutes. The precipitate was placed in a vacuum drying oven and vacuum dried at 100° C. for 4 hours to obtain a modified nano boron nitride;

[0047] (2) Silica modification:

[0048] 21) Weigh 5 g of nano-silicon dioxide and disperse it in 80 g of aqueous solution, add 1.5 g of potassium persulfate, heat to 86° C., and stir to activate for 5 min to obtain pretreated nano-silicon dioxide;

[0049] 22) adding 8.5 g of acrylic acid and 5 g of acrylamide monomer to the pretreated nano-silica, reacting for 6 h, cooling and filtering, and drying in a vacuum drying oven at 60° C. for 8 h to obtain polymer-modified silica core-shell particles, i.e., modified nano-silica;

[0050] (3) Additive mixing:

[0051] 92 parts of boric acid ester, 4 parts of modified nano boron nitride and 4 parts of modified nano silicon dioxide were mixed and mechanically stirred for 10 minutes to obtain a lubricating oil additive.

[0052] Example 3

[0053] The preparation method of the lubricating oil additive suitable for oil-starved working conditions provided in this embodiment comprises the following steps:

[0054] (1) Boron nitride modification:

[0055] Nano boron nitride was dissolved in deionized water to obtain a nano boron nitride aqueous solution, a surfactant was added, and ultrasonic dispersion was performed for 2 hours to obtain a dispersion 1; a silane coupling agent hydrolyzate was added to the dispersion 1 (wherein the mass ratio of nano boron nitride to silane coupling agent was 4:1), and the mixture was fully stirred for 40 minutes. After the stirring was completed, a sodium hydroxide solution was added dropwise to adjust the pH value to 10, and the mixture was stirred in a water bath at 60° C. and reacted for 40 minutes to obtain a reaction solution 1; the reaction solution 1 was placed in a centrifuge tube, and centrifuged at 5000 rpm for 10 minutes. The precipitate was placed in a vacuum drying oven and vacuum dried at 100° C. for 4 hours to obtain a modified nano boron nitride;

[0056] (2) Silica modification:

[0057] 21) Weigh 5 g of nano-silicon dioxide and disperse it in 80 g of aqueous solution, add 1.5 g of potassium persulfate, heat to 86° C., and stir to activate for 5 min to obtain pretreated nano-silicon dioxide;

[0058] 22) adding 8.5 g of acrylic acid and 5 g of acrylamide monomer to the pretreated nano-silica, reacting for 6 h, cooling and filtering, and drying in a vacuum drying oven at 60° C. for 8 h to obtain polymer-modified silica core-shell particles, i.e., modified nano-silica;

[0059] (3) Additive mixing:

[0060] 95 parts of boric acid ester, 2 parts of modified nano boron nitride and 3 parts of modified nano silicon dioxide were mixed and mechanically stirred for 10 minutes to obtain a lubricating oil additive.

[0061] Comparative Example 1

[0062] This comparative example provides a method for preparing a lubricating oil additive suitable for oil-starved working conditions, which is basically the same as Example 2, except that the lubricating oil additive contains only borate ester.

[0063] Comparative Example 2

[0064] This comparative example provides a method for preparing a lubricating oil additive suitable for oil-starved working conditions, which is basically the same as Example 2, except that the lubricating oil additive contains only borate and modified nano-silica.

[0065] Comparative Example 3

[0066] This comparative example provides a method for preparing a lubricating oil additive suitable for oil-starved working conditions, which is basically the same as Example 2, except that the lubricating oil additive only contains boric acid ester and modified nano boron nitride.

[0067] Comparative Example 4

[0068] This comparative example provides a method for preparing a lubricating oil additive suitable for oil-starved working conditions, which is basically the same as Example 2, except that nano-silicon dioxide is directly added to the lubricating oil additive, that is, the surface of the nano-silicon dioxide is not modified.

[0069] Comparative Example 5

[0070] This comparative example provides a method for preparing a lubricating oil additive suitable for oil-starved working conditions, which is basically the same as Example 2, except that the lubricating oil additive is directly added with nano boron nitride, that is, the surface of the nano boron nitride is not modified.

[0071] Comparative Example 6

[0072] This comparative example provides a method for preparing a lubricant additive suitable for oil-starved conditions, which is basically the same as Example 2, except that the lubricant additive only contains borate, nano-boron nitride and nano-silicon dioxide (i.e., the nano-boron nitride and nano-silicon dioxide are not surface modified).

[0073] Performance Testing:

[0074] The present invention takes Example 2 as an example, and performs performance tests on the lubricating oil additives prepared in Examples 1-6, specifically:

[0075] 1. Friction and wear performance test

[0076] Under laboratory conditions, a high-temperature end face friction and wear testing machine was used, with load, speed, temperature and other operating parameters of a diesel vehicle engine being used as experimental operating conditions. Friction dual test pieces were prepared using engine piston ring materials and cylinder block materials as test pieces. The existing engine lubricating oil (15W-40 diesel engine oil) and the lubricating oil containing the lubricating oil additive prepared in the present application were used as lubricating media to carry out friction and wear tests, and the friction coefficients of the test pieces detected by the test equipment during the friction and wear tests were compared.

[0077] Test device: MDW-5G screen display high temperature end face friction and wear tester;

[0078] (1) The testing machine parameters were set as follows: temperature 30°C; load 290N; spindle speed 1000rpm;

[0079] (2) Ambient temperature: room temperature;

[0080] (3) Friction specimen material: 65Mn spring steel (the same as the engine piston ring material);

[0081] (4) Material of the specimen under friction: RuT350 vermicular graphite cast iron (the same as the material of the engine cylinder block);

[0082] The lubricating oil used in the experiment was 15W-40 diesel engine oil (CF-4 grade);

[0083] Test method: Weigh 3 ml of lubricant additive and add it to 100 ml of 15W-40 diesel engine oil, mix it with a mechanical stirrer for 30-60 seconds, and successfully prepare engine oil containing 3% of the lubricant additive of the present application. Before the experiment, immerse the friction specimen in anhydrous ethanol and ultrasonically clean it for 30 minutes to remove surface impurities;

[0084] Under normal working conditions, the friction coefficient test results of the products of various embodiments and test examples are shown in Table 1:

[0085] Table 1 Friction coefficient of lubricating oil additives in various embodiments and comparative examples

[0086]

[0087]

[0088] From the data in the table, it can be seen that the lubricating oil additive provided by the present invention has an excellent friction coefficient after being added to the base oil. Compared with similar products on the market (HKS brand ADDII lubricating oil additive (HKS Co., Ltd.), German Liqui Magic 3721 engine oil additive), it has better anti-wear performance under oil-deficient conditions; By comparing the data of Example 2 with Comparative Examples 1-6, it can be seen that when boric acid is used alone as the additive base of the lubricating oil, it can reduce the friction coefficient of the base oil, but the effect of reducing the friction coefficient is limited;

[0089] Comparison of Example 2 and Comparative Examples 2 and 3 shows that the lubricating oil additive prepared by adding modified nano-silicon dioxide or modified nano-boron nitride to the boric acid ester can further reduce the friction coefficient of the base oil;

[0090] By comparing Example 2 with Comparative Examples 4 and 5, it can be seen that, on the basis of borate ester, modified nano-silica is added in combination with unmodified boron nitride; or modified nano-boron nitride is added in combination with unmodified nano-silica. Since the unmodified inorganic nanoparticles cannot form a stable dispersion system with the modified inorganic nanoparticles, nor can they form a stable dispersion system with the borate ester, the friction coefficient performance of the prepared lubricating oil additive for the base oil increases instead of decreases, and the friction coefficient cannot be improved.

[0091] By comparing Example 2 and Comparative Example 6, it can be seen that the addition of unmodified nano-boron nitride and nano-silicon dioxide on the basis of borate not only fails to effectively reduce the friction coefficient of the lubricant additive to the base oil, but because the lubricant additive cannot be well dispersed in the base oil, its friction coefficient performance increases instead of decreases, and it cannot play the role of modifying the friction coefficient.

[0092] The present application also takes Example 2 as an example, and at the same time introduces a base oil (blank control group) to which the lubricant additive of the present application is not added for the stable working time determination. The friction coefficient and stability test under the oil-deficient working condition are as follows: after the tribological experiment of the lubricant oil (not added) containing additives under conventional working conditions is completed, the lubricant oil in the oil pool is drained and the floating oil on the surface of the sample is adsorbed with dust-free paper soaked with anhydrous ethanol for 10 minutes, and then 1 ml of lubricant oil is dripped on the surface of the lower sample to spread and cover the surface of the lower sample, and the tribological experiment of the lubricant oil containing additives under the oil-deficient working condition is carried out. Once the friction coefficient fluctuates greatly, the experiment should be stopped in time and the time node when the friction coefficient jumps should be recorded. The stable working time is shown in Table 2:

[0093] Table 2: Friction coefficient and stable working time of Example 2 and blank control group

[0094] Contains lubricant additives Contains no lubricant additives Friction coefficient under oil-starved conditions 0.07 0.22 Stable working time under oil-deficient conditions 15 hours 5 minutes

[0095] It can be seen from the data in Table 2 that after the lubricating oil additive in the present application is added to the base oil, not only the friction coefficient is greatly reduced, but also the stable working time under the oil-deficient condition is greatly prolonged.

[0096] 2. Stability test

[0097] This application takes Example 2 as an example, and at the same time, the stability test of the lubricating oil additives prepared in Comparative Examples 1-6 is carried out, specifically:

[0098] The lubricating oil additives prepared in Example 2 and Comparative Examples 1-6 were added to the lubricating oil at a mass ratio of 3%, and the stability was tested at room temperature under the same conditions:

[0099] Stability evaluation standard: when placed at room temperature, the lubricant containing lubricant additives remains uniform and transparent, and there is no precipitation of the lubricant;

[0100] Table 1 Friction coefficient of lubricating oil additives in various embodiments and comparative examples

[0101] Project Number stability Example 2 Half a year Comparative Example 1 3 days Comparative Example 2 1 month Comparative Example 3 10 days Comparative Example 4 15 days Comparative Example 5 20 days Comparative Example 6 1.5 days

[0102] It can be seen from the table that the lubricating oil additive prepared in the present application can be well dispersed in the lubricating oil and has excellent dispersion stability. After being placed at room temperature for half a year, the lubricating oil containing the lubricating oil additive in the present application remains in a uniform and transparent state, and the lubricating oil has no precipitation. The results of the stability test of the lubricating oil additive in Example 2 are as follows: Figure 1 As shown in the figure, it can be seen that the lubricating oils containing the lubricating oil additive remain in a uniform and transparent state, and there is no precipitation in the lubricating oil, indicating that the lubricating oil additive has excellent dispersibility when used in the lubricating oil.

[0103] By comparing the stability performance of Example 2 and Comparative Examples 1-6, it can be seen that the lubricating oil additive in the present application adopts modified nano-silica with excellent dispersion stability in an organic medium, and then anchors the modified nano-boron nitride on the surface of the modified silica, thereby effectively improving the dispersion effect of the nano-boron nitride in an inorganic system; and then bonding the modified nano-silica anchored with nano-boron nitride to the surface of the borate ester, synergistically improving the dispersion stability of the lubricating oil additive in the lubricating oil; the additive is added to the lubricating oil, is easily dispersed, and makes the lubricating oil have good stability and anti-wear performance.

[0104] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and specification of the present invention.

Claims

1. A lubricating oil additive suitable for oil-starved working conditions, characterized in that: The invention comprises, by weight, 90 to 99 parts of borate, 1 to 10 parts of modified nano boron nitride and 1 to 10 parts of modified nano silicon dioxide.

2. The lubricating oil additive suitable for oil-starved working conditions according to claim 1, characterized in that: The modification method of modified nano boron nitride comprises the following steps: A1) dissolving the nano boron nitride, adding a dispersant, and ultrasonically dispersing for 1-2 hours to obtain a dispersion 1; A2) adding the silane coupling agent hydrolyzate to the dispersion 1, stirring thoroughly, adjusting the pH value to 10±0.5, and reacting at 50-70° C. for 30-40 min to obtain a reaction solution 1; A3) The reaction solution 1 is centrifuged, and the precipitate is collected and dried to obtain modified nano boron nitride.

3. The lubricating oil additive suitable for oil-starved working conditions according to claim 2, characterized in that: The preparation method of the modified nano-silicon dioxide comprises the following steps: B1) Weighing 5-20 parts of nano-silicon dioxide particles by weight and dispersing them into 60-80 parts of aqueous solution, adding 0.5-2.5 parts of initiator, activating, and obtaining pretreated nano-silicon dioxide; B2) adding 5-15 parts by weight of acrylic acid and 5-15 parts by weight of acrylamide monomers to the pretreated nano-silica, reacting for 4-12 hours, cooling and filtering, and drying in a vacuum drying oven to obtain polymer-modified silica core-shell particles, i.e., modified nano-silica.

4. The lubricating oil additive suitable for oil-starved working conditions according to claim 1, characterized in that: The dispersant is one of Span 80, sodium polycarboxylate, and sodium dodecylbenzene sulfonate.

5. The lubricating oil additive suitable for oil-starved working conditions according to claim 4, characterized in that: The silane coupling agent includes KH-550.

6. The lubricating oil additive suitable for oil-starved working conditions according to claim 3, characterized in that: The particle size of the nano boron nitride is 30-45 nm, and the particle size of the nano silicon dioxide is 50-100 nm.

7. The lubricating oil additive suitable for oil-starved working conditions according to claim 1, characterized in that: The weight ratio of the nano boron nitride to the silane coupling agent is (3-6):

1.

8. A method for preparing a lubricating oil additive according to any one of claims 1 to 7, characterized in that: The method comprises fully mixing modified nano boron nitride, modified nano silicon dioxide and borate to obtain a target product.

9. Use of the lubricating oil additive according to claims 1 to 7 in lubricating oil under oil-starved conditions.

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