Environment-friendly cutting lubricating oil and preparation method thereof

Abstract

The invention relates to the field of lubricating oil, in particular to environment-friendly cutting lubricating oil and a preparation method thereof.The environment-friendly cutting lubricating oil is prepared from, by mass, 50-100 parts of base oil, 1-10 parts of phosphate ammonium salt, 6-22 parts of chalcogenide extreme pressure anti-wear agent and 1-5 parts of nitrogen-doped carbon-coated lanthanum borate. The cutting lubricating oil disclosed by the invention is good in lubricating property, wear resistance and safety performance, environment-friendly, capable of self-repairing micro cracks generated during cutting of a matrix and good in component compatibility.

Description

Technical Field

[0001] The present invention relates to the field of lubricating oil, and in particular to an environmentally friendly cutting lubricating oil and a preparation method thereof. Background Art

[0002] Early researchers conducted follow-up investigations into the health effects of various mechanical process fluids on operators, and published numerous detailed reports on the effects of various additives on human and animal physiology, as well as on the ecological environment. They concluded that aromatic hydrocarbons, nitrites, and phenols are severe skin irritants and can induce cancer; some additives are difficult to biodegrade and can cause severe water and air pollution. Clearly toxic and harmful additives have been completely banned from mechanical process fluids, and additives or surfactants that pose potential ecological risks have been gradually restricted or eliminated. This has led to the emergence of highly efficient and environmentally friendly green mechanical process fluids.

[0003] Cutting oil, as a fluid used in mechanical processes, not only lubricates and cools workpieces and cutting tools, but also lubricates the workpiece support base. This places new demands on the lubricity and viscosity of cutting oils. Cutting fluids used in machining centers must not only lubricate and prevent rust on workpieces and cutting tools, but also on equipment and tool storage.

[0004] Patent application number CN102876435A discloses a "semi-synthetic metal cutting fluid based on trimethylolpropane oleate and its preparation method." This cutting fluid, composed of trimethylolpropane oleate, a nonionic surfactant, an anionic surfactant, a rust inhibitor, a cosolvent, an extreme pressure agent, a defoamer, a fungicide, and water, exhibits excellent lubricity and biodegradability, while being minimally harmful to humans and the environment. However, the large amount of surfactant used in this cutting fluid contributes to its high cost and environmental toxicity. Furthermore, the sodium benzoate used in this component is also toxic to water.

[0005] Another example is patent application CN112662458A, which discloses a "high-temperature alloy cutting oil and its preparation method." This cutting fluid is made from base oils (including 150N and 60N base oils), an oiliness agent, a lubricating extreme pressure agent (a mixture of sulfurized fatty acid esters and sulfurized olefins), a rust inhibitor, and a stabilizer. It exhibits excellent lubrication, extreme pressure, rust prevention, cooling, and stability. However, most of the raw materials used in this cutting oil have poor biodegradability, posing a significant environmental burden upon discharge.

[0006] Therefore, it is urgent to develop a cutting lubricant with good lubrication performance, wear resistance and safety performance and is environmentally friendly. Summary of the Invention

[0007] The main purpose of the present invention is to provide an environmentally friendly cutting lubricant and a preparation method thereof. The cutting lubricant has good lubrication performance, wear resistance and safety performance, is environmentally friendly, can self-repair tiny cracks generated during substrate cutting, and the various components of the cutting lubricant have good compatibility.

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

[0009] On the one hand, the present invention provides an environmentally friendly cutting lubricant, comprising the following components by weight: 50 to 100 parts of base oil, 1 to 10 parts of ammonium phosphate, 6 to 22 parts of sulfur-based extreme pressure anti-wear agent, and 1 to 5 parts of nitrogen-doped carbon-coated lanthanum borate.

[0010] In some embodiments, the base oil is one or more of trimethylolpropane oleate, pentaerythritol oleate, dipentaerythritol oleate, isooctyl oleate, isooctyl stearate, neopentyl glycol oleate, and diisooctyl adipate.

[0011] In some embodiments, the sulfur-based extreme pressure and anti-wear agent includes sulfurized lard and sulfurized fatty acid ester in a mass ratio of 1: (1 to 1.2).

[0012] In some embodiments, the method for preparing the nitrogen-doped carbon-coated lanthanum borate comprises the following steps:

[0013] S1. Mix cardanol glycidyl ether and an auxiliary carbon source, add the mixture to an ethanol solution, add citric acid, heat the mixture to 70-80°C, stir the mixture at a constant temperature for 3-5 hours, concentrate under reduced pressure, and freeze-dry to obtain an activated carbon source;

[0014] S2. Mix lanthanum nitrate and boric acid, add polyethylene glycol, and heat to 170-190° C., stirring constantly for 11-13 hours, centrifuge, and wash to obtain lanthanum borate particles;

[0015] S3, soaking the lanthanum borate particles in step S2 in a sodium hydroxide solution, heating to 55-65° C. and ultrasonically treating for 20-40 minutes, then filtering and drying to obtain activated lanthanum borate particles;

[0016] S4, mixing the activated lanthanum borate particles in step S3 with the activated carbon source in step S1, adding ethanol and ball milling at a speed of 250-350 rpm for 4-7 hours, then taking out and heating to 150-250° C. at a heating rate of 2-5° C. / min and keeping warm for 0.5-1.5 hours, then filling with inert protective gas, heating to 250-350° C., and keeping warm for 1-4 hours to obtain pretreated carbon-coated lanthanum borate;

[0017] S5. Under an inert protective gas atmosphere, the pretreated carbon-coated lanthanum borate in step S4 is heated to 300-350° C. and kept warm for 20-40 min, then heated to 450-550° C. under an ammonia and inert protective gas atmosphere and kept warm for 20-30 min, and then heated to 500-700° C. and kept warm for 10-30 min to obtain nitrogen-doped carbon-coated lanthanum borate.

[0018] The applicant's research has found that borates have excellent extreme pressure and anti-wear properties and are biodegradable. The addition of lanthanum can improve the viscosity and stability of lubricants, enhance oil film strength, and help reduce friction and wear. Lanthanum compounds can enhance the extreme pressure performance of lubricants, enabling them to maintain good lubrication under high load conditions and reducing direct contact between metal surfaces. However, despite these advantages, lanthanum borate has poor dispersion in this system, seriously affecting the normal use of cutting lubricants.

[0019] The present application makes a nitrogen-doped carbon-coated lanthanum borate, which can not only solve the above-mentioned dispersibility problem, but also the modified lanthanum borate still has good biodegradability. At the same time, the nitrogen-doped carbon-coated lanthanum borate can also play a role in repairing microcracks in the substrate, improving the lubrication performance of the cutting lubricant and reducing the friction coefficient. The reasons may be: First, the nitrogen-doped carbon-coated lanthanum borate will form pyridine nitrogen-graphite nitrogen and part of the CN bond during the preparation process, which changes the electron distribution of the nitrogen-doped carbon-coated lanthanum borate, forming an electron-rich region on its surface, reducing the exposure of polar groups (such as -OH, -COOH), thereby improving the dispersion performance of the nitrogen-doped carbon-coated lanthanum borate; second, the pyridine nitrogen-graphite nitrogen active sites formed in the nitrogen-doped carbon layer can release nitrogen-containing small molecules under the triggering of friction heat, and react with lanthanum borate to form an in-situ boron nitride lubricating film and boron nitride, which can repair microcracks on the surface of the substrate and reduce substrate wear; third, the outer coating material of the nitrogen-doped carbon-coated lanthanum borate uses more environmentally friendly cardanol glycidyl ether and auxiliary carbon The source of biodegradable natural ingredients is more environmentally friendly; fourthly, the structure of cashew phenol glycidyl ether contains a large number of epoxy groups. First, during the carbonization process, a part of the epoxy groups can be cross-linked to form a three-dimensional network structure, and the remaining epoxy groups are wrapped in a rigid structural skeleton to prevent decomposition; second, the epoxy groups in the carbonized cashew phenol glycidyl ether will be adsorbed on the metal surface, while the non-polar region on the outside and the long alkyl chain of the base oil are vertically arranged through van der Waals force to form a molecular brush structure, which further significantly reduces the contact area between the two friction surfaces. In addition, during the shear process, the flexibility of the molecular brush can cause the top to bend elastically, and the molecular brush layer slides preferentially, further dissipating the mechanical properties and reducing the friction coefficient.

[0020] In some embodiments, the auxiliary carbon source is chitosan or catechin.

[0021] In some embodiments, in step S1, the mass ratio of the cardanol glycidyl ether to the auxiliary carbon source is 1:(0.1-0.5).

[0022] Preferably, in step S1, the mass ratio of the cardanol glycidyl ether to the auxiliary carbon source is 1:0.3.

[0023] The present application can prevent the excessive cross-linking density between cardanol glycidyl ether and the auxiliary carbon source, which leads to thick accumulation of the carbon layer, by regulating the mass ratio of cardanol glycidyl ether and the auxiliary carbon source. This increases the particle size of the nitrogen-doped carbon-coated lanthanum borate, reduces the specific surface area, and prevents the cutting lubricant from being uniformly adsorbed on the surface of the tool and the workpiece, forming a discontinuous lubricating film that reduces the lubrication performance. At the same time, it can also avoid the risk of matrix wear.

[0024] In some embodiments, in step S1, the amount of citric acid used is 0.2-0.8% of the total mass of cardanol glycidyl ether and the auxiliary carbon source.

[0025] In some embodiments, in step S2, the mass ratio of the lanthanum nitrate to boric acid is 1:(0.2-0.4).

[0026] In some embodiments, in step S2, the mass of the polyethylene glycol is 1.2-1.8% of the total mass of lanthanum nitrate and boric acid.

[0027] In some embodiments, in step S4, the mass ratio of the activated lanthanum borate particles to the activated carbon source is 1:(1.5-2.5).

[0028] In some embodiments, in step S5, the volume ratio of the ammonia gas to the inert protective gas is 1:(8-13).

[0029] Another aspect of the present invention provides a method for preparing an environmentally friendly cutting lubricant, comprising the following steps: mixing a base oil, ammonium phosphate, a sulfur-based extreme pressure anti-wear agent, and nitrogen-doped carbon-coated lanthanum borate, heating the mixture to 70-90° C., and stirring the mixture at a constant temperature for 35-50 minutes to obtain the environmentally friendly cutting lubricant.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The cutting lubricant of the present invention is prepared using base oil, ammonium phosphate, sulfur-based extreme pressure anti-wear agent and nitrogen-doped carbon-coated lanthanum borate as main raw materials. The cutting lubricant has good lubrication performance, wear resistance and safety performance, is environmentally friendly, can self-repair tiny cracks generated during substrate cutting, and the various components of the cutting lubricant have good compatibility.

[0032] (2) The nitrogen-doped carbon-coated lanthanum borate of the present invention is suitable for the cutting fluid system of the present invention and has good dispersibility in the system. At the same time, the nitrogen-doped carbon-coated lanthanum borate can also play a role in repairing microcracks in the matrix, thereby improving the lubricating performance of the cutting lubricant and reducing the friction coefficient. DETAILED DESCRIPTION

[0033] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0034] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0035] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may be used in the practice or testing of the present invention. Various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention, as will be apparent to those skilled in the art. Other embodiments obtained from the present invention description will be apparent to those skilled in the art. This application description and examples are exemplary only.

[0036] In the following preparation examples, embodiments and comparative examples, polyethylene glycol, CAS No. 25322-68-3, was purchased from Jinan Daorong Chemical Co., Ltd.; ammonium phosphate was purchased from Luoyang Pacific United Petrochemical Co., Ltd.

[0037] Preparation Example 1

[0038] The preparation method of nitrogen-doped carbon-coated lanthanum borate comprises the following steps:

[0039] S1. Mix 30 g of cardanol glycidyl ether and 9 g of catechin, add to 500 mL of 50 wt% ethanol solution, add 0.23 g of citric acid, heat to 75 ° C and stir at constant temperature for 4 h, concentrate under reduced pressure, and freeze-dry to obtain an activated carbon source;

[0040] S2. Mix 20 g of lanthanum nitrate and 6 g of boric acid, add 0.4 g of polyethylene glycol, heat to 180° C., stir constantly for 12 h, centrifuge, and wash to obtain lanthanum borate particles;

[0041] S3, soaking 20 g of the lanthanum borate particles prepared in step S2 in 300 mL of a 5 wt% sodium hydroxide solution, heating to 60° C. and ultrasonically treating for 30 min, then filtering and drying to obtain activated lanthanum borate particles;

[0042] S4, 20g of the activated lanthanum borate particles in step S3 were mixed with 40g of the activated carbon source in step S1, 60mL of ethanol was added and ball-milled at a speed of 300rpm for 5h, then taken out and heated to 200℃ at a heating rate of 3℃ / min and kept warm for 1h, then filled with argon, heated to 300℃, and kept warm for 2h to obtain pretreated carbon-coated lanthanum borate;

[0043] S5. Under an argon atmosphere, the pretreated carbon-coated lanthanum borate in step S4 was heated to 320° C. and kept warm for 30 min, then heated to 500° C. under an ammonia and argon atmosphere and kept warm for 25 min, and then heated to 600° C. and kept warm for 20 min to obtain nitrogen-doped carbon-coated lanthanum borate.

[0044] Preparation Example 2

[0045] The preparation method of nitrogen-doped carbon-coated lanthanum borate is the same as that of Preparation Example 1, except that the mass of catechin used is 17 g.

[0046] Preparation Example 3

[0047] The preparation method of nitrogen-doped carbon-coated lanthanum borate is the same as that of Preparation Example 1, except that catechin is not added.

[0048] Preparation Example 4

[0049] The preparation method of nitrogen-doped carbon-coated lanthanum borate is the same as that of Preparation Example 1, except that in step S4, the mass of the activated carbon source used is 55 g.

[0050] Preparation Example 5

[0051] The preparation method of nitrogen-doped carbon-coated lanthanum borate is the same as that of Preparation Example 1, except that in step S4, the mass of the activated carbon source used is 25 g.

[0052] Example 1

[0053] An environmentally friendly cutting lubricant comprises the following components in parts by weight: 80 parts of isooctyl stearate, 5 parts of ammonium phosphate, 14 parts of a sulfur-based extreme pressure anti-wear agent, and 3 parts of nitrogen-doped carbon-coated lanthanum borate.

[0054] The sulfur-based extreme pressure and anti-wear agent includes sulfurized lard and sulfurized fatty acid ester in a mass ratio of 1:1.1; the nitrogen-doped carbon-coated lanthanum borate is prepared according to Preparation Example 1.

[0055] The preparation method of environmentally friendly cutting lubricant comprises the following steps: mixing isooctyl stearate, ammonium phosphate, a sulfur-based extreme pressure anti-wear agent and nitrogen-doped carbon-coated lanthanum borate, heating to 80° C., and stirring at constant temperature for 43 minutes to obtain the environmentally friendly cutting lubricant.

[0056] Example 2

[0057] An environmentally friendly cutting lubricant comprises the following components in parts by weight: 50 parts of isooctyl stearate, 1 part of ammonium phosphate, 6 parts of sulfur-based extreme pressure anti-wear agent, and 1 part of nitrogen-doped carbon-coated lanthanum borate.

[0058] The sulfur-based extreme pressure and anti-wear agent includes sulfurized lard and sulfurized fatty acid ester in a mass ratio of 1:1; the nitrogen-doped carbon-coated lanthanum borate is prepared according to Preparation Example 1.

[0059] The preparation method of environmentally friendly cutting lubricant comprises the following steps: mixing isooctyl stearate, ammonium phosphate, a sulfur-based extreme pressure anti-wear agent and nitrogen-doped carbon-coated lanthanum borate, heating to 70° C., and stirring at constant temperature for 35 minutes to obtain the environmentally friendly cutting lubricant.

[0060] Example 3

[0061] An environmentally friendly cutting lubricant comprises the following components in parts by weight: 100 parts of isooctyl stearate, 10 parts of ammonium phosphate, 22 parts of a sulfur-based extreme pressure anti-wear agent, and 5 parts of nitrogen-doped carbon-coated lanthanum borate.

[0062] The sulfur-based extreme pressure and anti-wear agent includes sulfurized lard and sulfurized fatty acid ester in a mass ratio of 1:1.2; the nitrogen-doped carbon-coated lanthanum borate is prepared according to Preparation Example 1.

[0063] The preparation method of environmentally friendly cutting lubricant comprises the following steps: mixing isooctyl stearate, ammonium phosphate, a sulfur-based extreme pressure anti-wear agent and nitrogen-doped carbon-coated lanthanum borate, heating to 90° C., and stirring at the constant temperature for 50 minutes to obtain the environmentally friendly cutting lubricant.

[0064] Example 4

[0065] An environmentally friendly cutting lubricant and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that the nitrogen-doped carbon-coated lanthanum borate is prepared by Preparation Example 2.

[0066] Example 5

[0067] An environmentally friendly cutting lubricant and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that the nitrogen-doped carbon-coated lanthanum borate is prepared by Preparation Example 3.

[0068] Example 6

[0069] An environmentally friendly cutting lubricant and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that the nitrogen-doped carbon-coated lanthanum borate is prepared by Preparation Example 4.

[0070] Example 7

[0071] An environmentally friendly cutting lubricant and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that the nitrogen-doped carbon-coated lanthanum borate is prepared by Preparation Example 5.

[0072] Comparative Example 1

[0073] An environmentally friendly cutting lubricant and a preparation method thereof, the specific implementation method is the same as Example 1, except that an equal mass of lanthanum borate particles is used instead of nitrogen-doped carbon-coated lanthanum borate. The lanthanum borate particles are prepared by step S2 of Preparation Example 1.

[0074] Performance testing:

[0075] (1) Storage stability test: 50 mL of cutting lubricant was placed in a 100 mL stoppered graduated cylinder and placed at 70°C for 5 h, then at room temperature for 3 h, and then at -12°C for 24 h. Finally, the oil was naturally returned to room temperature and observed for any signs of stratification, precipitation, or turbidity.

[0076] (2)P d Value, P b Determination of wear spot diameter and load-carrying capacity: refer to GBT3142-82 "Determination of lubricant load-carrying capacity (four-ball method)" standard for testing;

[0077] (3) Safety test: 24 male guinea pigs were divided into 8 groups according to their weight, with 3 guinea pigs in each group. The average weight of the guinea pigs in each group was ensured to be similar. The hair on both sides of the spine of the guinea pigs' backs was shaved with a razor, with an area of ​​3 cm × 3 cm. The guinea pigs in the experimental group were smeared with vegetable oil on the left back and 2 ml of the cutting sample on the right back every day. The skin on the back of the guinea pigs was observed for redness, swelling, edema, etc. within 1 to 14 days.

[0078] The cutting lubricants of the embodiments and comparative examples were tested according to the above method. The results are shown in Table 1.

[0079] Table 1 Test results of lubricating performance and safety of cutting lubricants in various embodiments and comparative examples

[0080] Storage stability <![CDATA[P d (N)]]> <![CDATA[P b (N)]]> Wear spot diameter (588N / 20min) Security Example 1 No change 8756 784 0.357mm Normal skin Example 2 No change 8746 784 0.373mm Normal skin Example 3 No change 8748 834 0.393mm Normal skin Example 4 No change 8733 1020 0.443mm Normal skin Example 5 No change 8529 1069 0.473mm Normal skin Example 6 trace precipitates 8721 1118 0.473mm Normal skin Example 7 Slightly turbid 8727 1069 0.473mm Normal skin Comparative Example 1 A small amount of sediment 8612 981 0.837mm Redness of the skin

[0081] According to the experimental data in Table 1, the components of the cutting lubricants prepared in Examples 1 to 3 have good compatibility, are stable for long-term placement, and have good anti-wear and safety performance. In Example 4, due to the change in the mass ratio of phenol glycidyl ether and catechin, the crosslinking density of the two is increased, resulting in an increase in the particle size of nitrogen-doped carbon-coated lanthanum borate, which affects the Pb value and wear spot diameter. In Example 5, due to the lack of catechin as an auxiliary carbon source, the crosslinking density of cardanol glycidyl ether is reduced when used alone, and the steric hindrance formed after carbonization is reduced, resulting in a decrease in the dispersibility of nitrogen-doped carbon-coated lanthanum borate. In addition, the reduction in the hydroxyl content cannot effectively weaken the CN bond energy, resulting in the difficulty of nitrogen element insertion into the carbon skeleton hybridization site, which affects the Pb value and wear spot diameter. Influence; In Example 6, due to the change in the mass ratio of activated lanthanum borate particles and activated carbon source, the increase or decrease in activated carbon source leads to an increase in the thickness of the carbon layer after carbonization, thereby increasing the particle size of nitrogen-doped carbon-coated lanthanum borate, which is not conducive to dispersion, and thus affects the Pb value and wear spot diameter; In Example 7, due to the change in the mass ratio of activated lanthanum borate particles and activated carbon source, the reduction in activated carbon source leads to partial exposure of lanthanum borate, resulting in a decrease in the generated pyridine nitrogen-graphitic nitrogen active sites, and a decrease in the performance of the boron nitride lubricating film generated during use, which is not conducive to self-repairing ability, and thus affects the Pb value and wear spot diameter; In Comparative Example 1, due to the decrease in dispersibility of lanthanum borate particles instead of nitrogen-doped carbon-coated lanthanum borate, the Pb value and wear spot diameter are affected.

[0082] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. An environmentally friendly cutting lubricant, characterized in that: The invention comprises the following components by weight: 50 to 100 parts of base oil, 1 to 10 parts of ammonium phosphate, 6 to 22 parts of sulfur-based extreme pressure anti-wear agent, and 1 to 5 parts of nitrogen-doped carbon-coated lanthanum borate.

2. The environmentally friendly cutting lubricant according to claim 1, characterized in that The base oil is one or more of trimethylolpropane oleate, pentaerythritol oleate, dipentaerythritol oleate, isooctyl oleate, isooctyl stearate, neopentyl glycol oleate and diisooctyl adipate.

3. The environmentally friendly cutting lubricant according to claim 1, characterized in that The sulfur-based extreme pressure anti-wear agent comprises sulfurized lard and sulfurized fatty acid ester in a mass ratio of 1: (1-1.2).

4. The environmentally friendly cutting lubricant according to claim 1, characterized in that The preparation method of the nitrogen-doped carbon-coated lanthanum borate comprises the following steps: S1. Mix cardanol glycidyl ether and an auxiliary carbon source, add the mixture to an ethanol solution, add citric acid, heat the mixture to 70-80°C, stir the mixture at a constant temperature for 3-5 hours, concentrate under reduced pressure, and freeze-dry to obtain an activated carbon source; S2. Mix lanthanum nitrate and boric acid, add polyethylene glycol, and heat to 170-190° C., stirring constantly for 11-13 hours, centrifuge, and wash to obtain lanthanum borate particles; S3, soaking the lanthanum borate particles in step S2 in a sodium hydroxide solution, heating to 55-65° C. and ultrasonically treating for 20-40 minutes, then filtering and drying to obtain activated lanthanum borate particles; S4, mixing the activated lanthanum borate particles in step S3 with the activated carbon source in step S1, adding ethanol and ball milling at a speed of 250-350 rpm for 4-7 hours, then taking out and heating to 150-250° C. at a heating rate of 2-5° C. / min and keeping warm for 0.5-1.5 hours, then filling with inert protective gas, heating to 250-350° C., and keeping warm for 1-4 hours to obtain pretreated carbon-coated lanthanum borate; S5. Under an inert protective gas atmosphere, the pretreated carbon-coated lanthanum borate in step S4 is heated to 300-350° C. and kept warm for 20-40 min, then heated to 450-550° C. under an ammonia and inert protective gas atmosphere and kept warm for 20-30 min, and then heated to 500-700° C. and kept warm for 10-30 min to obtain nitrogen-doped carbon-coated lanthanum borate.

5. The environmentally friendly cutting lubricant according to claim 4, characterized in that: The auxiliary carbon source is chitosan or catechin.

6. The environmentally friendly cutting lubricant according to claim 4, characterized in that: In step S1, the mass ratio of the cardanol glycidyl ether to the auxiliary carbon source is 1:(0.1-0.5).

7. The environmentally friendly cutting lubricant according to claim 4, characterized in that: In step S1, the amount of citric acid used is 0.2-0.8% of the total mass of cardanol glycidyl ether and the auxiliary carbon source.

8. The environmentally friendly cutting lubricant according to claim 4, characterized in that: In step S4, the mass ratio of the activated lanthanum borate particles to the activated carbon source is 1:(1.5-2.5).

9. The environmentally friendly cutting lubricant according to claim 4, characterized in that: In step S5, the volume ratio of the ammonia gas to the inert protective gas is 1:(8-13).

10. A method for preparing the environmentally friendly cutting lubricant according to any one of claims 1 to 9, characterized in that: The method comprises the following steps: mixing base oil, ammonium phosphate, sulfur-based extreme pressure anti-wear agent and nitrogen-doped carbon-coated lanthanum borate, heating to 70-90° C., and stirring at a constant temperature for 35-50 minutes to obtain environmentally friendly cutting lubricant.