An emulsified cutting fluid and a method for preparing the same

Abstract

The application provides an emulsified cutting fluid, which comprises base oil 30-60 parts, long-chain dibasic acid-amino acid 3-15 parts, long-chain dibasic acid ester 3-20 parts, surfactant 5-20 parts, benzotriazole 0.1-5 parts, bactericide 0-5 parts and water, wherein the long-chain dibasic acid-amino acid is connected with two amino acids at the carboxyl groups at two ends of the long-chain dibasic acid; and the long-chain dibasic acid ester is an alkyd ester compound formed by the reaction of long-chain dibasic acid and long-chain monohydric alcohol. In the cutting fluid, the long-chain dibasic acid-amino acid has high rust resistance and amphiphilicity, and the long-chain dibasic acid ester can improve the stability and rust resistance of the cutting fluid together with the long-chain dibasic acid-amino acid, and the cutting fluid can be widely applied to various metal processing scenes.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of cutting fluid, in particular to an emulsified cutting fluid and a preparation method thereof. BACKGROUND

[0002] Copper and its alloys have good corrosion resistance, high electrical conductivity and thermal conductivity, good machinability and ductility, and are widely used in the fields of wire and cable, heat exchanger, ship, pipeline, etc. During the process of making products, the parent material needs to be cut and processed, shaped and processed. As a lubricating medium in the metal processing process, cutting fluid plays a role in lubrication, cooling, chip removal and rust prevention, so that the product has good surface precision and workpiece quality, and the service life of the machine tool is also prolonged. It is a very important part of the copper processing process.

[0003] Water-soluble cutting fluid can be divided into three types: emulsified, semi-synthetic and fully synthetic. Among them, the emulsified cutting fluid has better lubricity and rust prevention ability than the other two types of water-soluble cutting fluid, and has better cooling and cleaning properties than cutting oil, which is very suitable for the processing of copper materials. However, the existing technology has less research on the field of copper alloy cutting fluid, and the existing cutting fluid has the problem of easy precipitation of copper ions in copper and copper alloy during use, which reduces the performance of the material and is not suitable for the processing of high-precision copper alloy parts. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application provides an emulsified cutting fluid and a preparation method thereof. By modifying long-chain dibasic acid with amino acid and then cooperating with long-chain dibasic acid ester, an emulsified cutting fluid is obtained, which has good copper corrosion inhibition and protection effect.

[0005] The technical purpose of the present application is achieved by the following technical scheme:

[0006] The first aspect of the present application is to provide an emulsified cutting fluid, which comprises the following components by weight fraction:

[0007] Base oil 30-60 parts

[0008] Long-chain dibasic acid-amino acid 3-15 parts

[0009] Long-chain dibasic acid ester 3-20 parts

[0010] Surfactant 5-20 parts

[0011] Benzotriazole 0.1-5 parts

[0012] Bactericide 0-5 parts,

[0013] and water,

[0014] The water is added in an amount such that the sum of the mass percentages of the above components in the aqueous solution is 2-90 wt%;

[0015] Further, the long-chain dibasic acid-amino acid and the long-chain dibasic acid ester have a mass ratio of 1:0.8-1:2, preferably 1:1-1:1.5.

[0016] Further, the long-chain dibasic acid-amino acid and the long-chain dibasic acid ester have a mass ratio of 1:0.8-1:2, preferably 1:1-1:1.5.

[0017] Further, the cutting fluid is generally a concentrated cutting fluid in production, which has a high concentration, and the use concentration is generally 2-20 wt%.

[0018] Further, the base oil is selected by those skilled in the art, and as a specific embodiment, it is selected from at least one of naphthenic mineral oil, paraffin-based mineral oil and hydrogenated refined oil.

[0019] Further, the long-chain dibasic acid-amino acid is two amino acids connected to the carboxyl groups at both ends of the long-chain dibasic acid, wherein the long-chain dibasic acid is selected from at least one of undecanedioic acid, dodecanedioic acid, tridecanedioic acid and tetradecanedioic acid, preferably undecanedioic acid or dodecanedioic acid. The amino acid connected to the long-chain dibasic acid is selected from at least one of proline, phenylalanine, methionine, tryptophan, glutamine, cysteine, tyrosine, lysine, arginine and histidine, preferably at least one of histidine, tryptophan and methionine.

[0020] Further, the long-chain dibasic acid-amino acid is prepared by the following method:

[0021] The long-chain dibasic acid is refluxed with dichlorosulfoxide, the dried solid is dissolved with an NaOH solution, reacted, acid is added, and the long-chain dibasic acid-amino acid is obtained by filtration.

[0022] Further, the long-chain dibasic acid-amino acid and the long-chain dibasic acid ester have a mass ratio of 1:0.8-1:2, preferably 1:1-1:1.5.

[0023] Further, the long-chain dibasic acid ester is an alcohol ester compound formed by esterification of long-chain dibasic acid and long-chain monohydric alcohol, wherein the long-chain dibasic acid is at least one selected from undecanedioic acid, dodecanedioic acid, tridecanedioic acid and tetradecanedioic acid, and the long-chain monohydric alcohol is C7-C10 monohydric alcohol, preferably at least one selected from n-heptyl alcohol, n-octyl alcohol, iso-octyl alcohol and iso-nonyl alcohol.

[0024] Further, the long-chain dibasic acid ester is prepared by the following method:

[0025] The long-chain dibasic acid, long-chain monohydric alcohol and catalyst are mixed, and the reaction is carried out by increasing the temperature, and the acid value is determined, and the reaction is ended when the required acid value is reached, to obtain the long-chain dibasic acid ester.

[0026] Further, the reaction is carried out in a container equipped with a thermometer, a condenser, a stirrer and a water separator, and the reaction is uniformly stirred, and the water produced in the reaction is separated by the water separator, and the acid value is determined by sampling when the amount of water reaches the theoretical amount, and then the reaction is terminated, and after the reaction is completed, the temperature is decreased, activated carbon is added for adsorption and filtration, the filtrate is washed with sodium hydroxide solution until neutral, and after the layers are separated by standing, the water layer is removed, and then the unreacted alcohol is removed by distillation under reduced pressure, to obtain the long-chain dibasic acid ester.

[0027] Further, the molar ratio of the long-chain dibasic acid to the long-chain monohydric alcohol is 1:2-1:3, preferably 1:2.6-1:2.8; the reaction temperature is 220-240℃, the catalyst is a supported heteropoly acid catalyst, specifically a catalyst of phosphotungstic acid supported on silica or molecular sieve, which is prepared by an impregnation method, and its mass percentage in the reaction system is 0.8%-1.2%.

[0028] Further, the surfactant is at least one selected from sodium petroleum sulfonate, isomeric tridecanol polyoxyethylene ether and Span 80.

[0029] Further, the bactericide is a hexahydrotriazine compound or a benzisothiazolinone compound, and as a more specific embodiment, is at least one selected from 1,2-benzisothiazolin-3-one, 2-butyl-1,2-benzisothiazolin-3-one and hexahydro-1,3,5-tris(hydroxyethyl)-s-triazine.

[0030] The technical purpose of the second aspect of the present application is to provide a preparation method of an emulsified cutting fluid, comprising the following steps:

[0031] The long-chain dibasic acid is refluxed with dichlorosulfoxide, the solid after rotary evaporation is dried, and the solid is dissolved with NaOH solution, reacted, acid is added, and the long-chain dibasic acid-amino acid is obtained by filtration.

[0032] Mixing long-chain dibasic acid, long-chain alcohol and catalyst, warming reaction, measuring acid value, ending reaction after reaching requirement, obtaining long-chain dibasic acid ester;

[0033] Adding long-chain dibasic acid-amino acid, bactericide and water into reactor, stirring, adding base oil, long-chain dibasic acid ester, benzotriazole and surfactant in sequence after completely dissolving, stirring until system is homogeneous and transparent, obtaining emulsified cutting fluid.

[0034] Further, the selection of long-chain dibasic acid, amino acid and long-chain alcohol and more detailed reaction conditions are the same as the first aspect of the application, which will not be repeated.

[0035] The technical purpose of the third aspect of the application is to provide the application of the above-mentioned emulsified cutting fluid, which is used in metal processing, especially copper processing.

[0036] Further, when the cutting fluid is concentrated, the cutting fluid is diluted with water when used, and the total mass concentration of base oil, long-chain dibasic acid-amino acid, long-chain dibasic acid ester, surfactant, benzotriazole and bactericide is 0.5-8wt%, preferably 2-5wt%.

[0037] Compared with the prior art, the application has the following advantages:

[0038] (1) Long-chain dibasic acid-amino acid has high rust prevention and amphiphilicity, which can improve the stability and rust prevention performance of the cutting fluid together with long-chain dibasic acid ester, and can be widely used in various metal processing scenes.

[0039] (2) Long-chain dibasic acid ester has high lubricating ability and biodegradability, which can effectively improve the extreme pressure performance of the cutting fluid and reduce the amount of base oil, thereby reducing the adverse effects of the cutting fluid on the environment.

[0040] (3) Long-chain dibasic acid-amino acid and benzotriazole have strong copper corrosion inhibition ability, and their combined use can protect copper alloy during use of the cutting fluid, and is suitable for processing of copper alloy. Embodiment

[0041] The following non-limiting examples can make those skilled in the art more fully understand the application, but do not limit the application in any way. Example 1

[0042] This embodiment discloses an emulsified cutting fluid, the constituent components and the weight percentage of each component are as follows:

[0043] Naphthenic mineral oil: 400g

[0044] Dodecanedioic acid-histidine: 100 g

[0045] Undecanedioic acid dioctyl ester: 150 g

[0046] Sodium petroleum sulfonate: 150 g

[0047] Benzotriazole: 10 g

[0048] Hexahydro-1,3,5-tris(hydroxyethyl)-s-triazine: 10 g

[0049] Deionized water: 180 g

[0050] The cutting fluid is prepared by the following method:

[0051] (1) 230 g of dodecanedioic acid and 469 g of dichloro sulfoxide (molar ratio 1:6) are added to a round-bottom flask and refluxed at 80°C for 12 h. The excess dichloro sulfoxide is removed by rotary evaporation, and the product is dried to obtain a solid. 26.7 g of the above solid and 31 g of histidine (molar ratio of dodecanedioic acid to histidine 1:2) are added to a 1 L 0.2 mol / L NaOH solution and dissolved. After stirring for 1 h, 5 mol / L hydrochloric acid solution is added dropwise until the pH of the solution is 2. Dodecanedioic acid-histidine is obtained by filtration.

[0052] (2) A three-necked flask equipped with a thermometer, a condenser, a stirrer and a water separator is charged with 50 g of undecanedioic acid, 80 g of n-octanol and 1 g of silica-supported phosphotungstic acid catalyst. After uniform stirring, the temperature is raised to 220°C. The water produced in the reaction is separated by the water separator. When the amount of water reaches the theoretical amount, the acid value is determined by sampling. If the required acid value is reached, the reaction is terminated. After the reaction is completed, the temperature is lowered, activated carbon is added for adsorption and filtration. The filtrate is washed with sodium hydroxide solution until it is neutral. After standing and separating the layers, the water layer is removed. Then, the unreacted alcohol is removed by distillation under reduced pressure to obtain undecanedioic acid dioctyl ester.

[0053] (3) The dodecanedioic acid-histidine, hexahydro-1,3,5-tris(hydroxyethyl)-s-triazine and deionized water are added to a reaction kettle in the above-mentioned proportions. After stirring, the cycloalkyl mineral oil, undecanedioic acid dioctyl ester, benzotriazole and sodium petroleum sulfonate are added in sequence. After stirring until the system is uniform and transparent, the emulsified cutting fluid is obtained.

[0054] The rust prevention performance of the cutting fluid is tested according to the method of JB / T 7453-2013. The prepared cutting fluid is diluted to a 5 wt% solution (the mass fraction of other substances except water is the same below) for rust prevention testing. The results of the rust prevention experiment are as follows: single sheet rust prevention time ≥ 24 h, stacked sheet rust prevention time ≥ 8 h, and red copper corrosion test ≥ 8 h.

[0055] Cutting fluid carrying capacity test (test method: GB / T 3142-2019), the prepared cutting fluid was diluted to 10wt% solution with distilled water for determination of maximum non-galling load, and the determination result was that the maximum non-galling load value was 600N. Example 2

[0056] This example discloses an emulsified cutting fluid, the constituent components and the weight percentage of each component are as follows:

[0057] Paraffin-based mineral oil: 450g

[0058] Undecanedioic acid-tryptophan: 80g

[0059] Dodecanedioic acid diisooctyl ester: 100g

[0060] Siben 80: 100g

[0061] Benzotriazole: 20g

[0062] 1,2-benzisothiazolin-3-one: 20g

[0063] Deionized water: 230g

[0064] The cutting fluid is prepared by the following method:

[0065] (1) 216g undecanedioic acid and 469g dichlorosulfide (molar ratio 1:6) were added to a round-bottom flask and refluxed at 80°C for 12h, the excess dichlorosulfide was removed by rotary evaporation, the product was dried to obtain a solid, 25.3g of the above solid and 40.8g of tryptophan (molar ratio of undecanedioic acid to tryptophan 1:2) were added to a 1L 0.2mol / L NaOH solution and dissolved, and stirred for 1h, then 5mol / L hydrochloric acid solution was added dropwise until the pH value of the solution was 2, and undecanedioic acid-tryptophan was obtained by filtration.

[0066] (2) In a three-necked flask equipped with a thermometer, a condenser, a stirrer and a water separator, 50g of dodecanedioic acid, 70g of isooctanol and 1g of molecular sieve supported phosphotungstic acid catalyst were added, and stirred uniformly, and heated to 220 degrees. The water produced in the reaction was separated by the water separator, and when the water reached the theoretical amount, the sample was taken to determine the acid value, and if the requirement was met, the reaction was terminated. After the reaction was completed, activated carbon was added for adsorption and filtration, the filtrate was washed with sodium hydroxide solution until it was neutral, and after standing and separating the layers, the water layer was removed, and then the unreacted alcohol was removed by distillation under reduced pressure to obtain dodecanedioic acid diisooctyl ester.

[0067] (3) The above agreed ratio, dodecanedioic acid-histidine, 1,2-benzisothiazoline-3-ketone and deionized water are added to the reaction kettle, stirring is started, after complete dissolution, paraffin-based mineral oil, dodecanedioic acid diisooctyl ester, benzotriazole and Span 80 are added in turn, stirring until the system is homogeneous and transparent to obtain the emulsified cutting fluid.

[0068] The cutting fluid anti-rust performance test (test method: JB / T 7453-2013) is tested by diluting the prepared cutting fluid to 5wt% solution with distilled water. The anti-rust test result is single piece anti-rust time ≥ 24h, laminated piece anti-rust time ≥ 8h, and red copper corrosion test ≥ 8h.

[0069] The cutting fluid carrying capacity test (test method: GB / T 3142-2019) is measured by diluting the prepared cutting fluid to 10wt% solution with distilled water. The maximum non-galling load value is 530N. Example 3

[0070] This embodiment discloses an emulsified cutting fluid, the constituent components and the weight percentage of each component are as follows:

[0071] Naphthenic mineral oil: 400g

[0072] Dodecanedioic acid-histidine: 100g

[0073] Oleic acid: 100g

[0074] Sodium petroleum sulfonate: 150g

[0075] Benzotriazole: 10g

[0076] Hexahydro-1,3,5-tris(hydroxyethyl)-s-triazine: 10g

[0077] Deionized water: 230g

[0078] The cutting fluid is prepared by the following method:

[0079] (1) 230g dodecanedioic acid and 469g dichlorosulfide (molar ratio 1:6) are added to a round-bottom flask, refluxed at 80℃ for 12h, the excess dichlorosulfide is removed by rotary evaporation, the product is dried to obtain a solid, 26.7g of the above solid and 31g of histidine (molar ratio of dodecanedioic acid to histidine 1:2) are added to 1L of 0.2mol / L NaOH solution, dissolved, stirred for 1h, then 5mol / L hydrochloric acid solution is added dropwise until the solution pH value is 2, filtered to obtain dodecanedioic acid-histidine.

[0080] (2) In the three-necked flask equipped with a thermometer, a condenser, a stirrer and a water separator, 50 g of undecanedioic acid, 80 g of n-octanol and 1 g of silica-supported phosphotungstic acid catalyst were added, uniformly stirred, and heated to 220°C. The water produced in the reaction was separated by the water separator, and when the amount of water reached the theoretical amount, a sample was taken to determine the acid value. If the required acid value was reached, the reaction was terminated. After the reaction was completed, the temperature was lowered, activated carbon was added for adsorption and filtration, sodium hydroxide solution was added to wash to neutral, and after standing and separating the layers, the water layer was removed. Then, the unreacted alcohol was removed by distillation under reduced pressure to obtain undecanedioic acid dioctyl ester.

[0081] (3) The above-mentioned components were mixed in the proportions as agreed, and dodecanedioic acid-histidine, hexahydro-1,3,5-tris(hydroxyethyl)-s-triazine and deionized water were added to the reaction kettle, and stirring was started. After complete dissolution, naphthenic mineral oil, undecanedioic acid dioctyl ester, benzotriazole and petroleum sulfonate sodium were added in sequence, and the system was stirred until it became uniform and transparent to obtain the emulsified cutting fluid.

[0082] The rust prevention performance of the cutting fluid was tested (test method: JB / T 7453-2013). The prepared cutting fluid was diluted to 5wt% (the mass fraction of other substances except water, the same below) solution using distilled water for rust prevention test. The rust prevention test results were single piece rust prevention time ≥ 24h, laminated piece rust prevention time ≥ 8h, and red copper corrosion test ≥ 8h.

[0083] The carrying capacity of the cutting fluid was tested (test method: GB / T 3142-2019). The prepared cutting fluid was diluted to 10wt% solution using distilled water for determination of the maximum non-galling load. The determination result was a maximum non-galling load value of 550N.

[0084] Comparative Example 1

[0085] The components of the cutting fluid and the weight percentage of each component are as follows:

[0086] Naphthenic mineral oil: 400g

[0087] Dodecanedioic acid-histidine: 100g

[0088] Undecanedioic acid: 150g

[0089] Petroleum sulfonate sodium: 150g

[0090] Benzotriazole: 10g

[0091] Hexahydro-1,3,5-tris(hydroxyethyl)-s-triazine: 10g

[0092] Deionized water: 180g

[0093] The dodecanedioic acid-histidine was prepared as in Example 1, and the cutting fluid was prepared as in Example 1, except that dodecanedioic acid-histidine was replaced by dodecanedioic acid.

[0094] The rust-preventive property of the cutting fluid was tested (test method: JB / T 7453-2013), and the prepared cutting fluid was diluted to 5% solution with distilled water for rust-preventive test. The rust-preventive test result was that the single-piece rust-preventive time was ≥24 h, the stacked-piece rust-preventive time was ≥8 h, and the red copper corrosion test was ≥8 h.

[0095] The carrying capacity of the cutting fluid was tested (test method: GB / T 3142-2019), and the prepared cutting fluid was diluted to 10% solution with distilled water for determination of the maximum non-galling load. The determination result was that the maximum non-galling load value was 300 N.

[0096] Comparative Example 2

[0097] The components of the cutting fluid and the weight percentage of each component are as follows:

[0098] Naphthenic mineral oil: 400 g

[0099] Dodecanedioic acid: 100 g

[0100] Dodecanedioic acid: 100 g

[0101] Sodium petroleum sulfonate: 150 g

[0102] Benzotriazole: 10 g

[0103] Hexahydro-1,3,5-tris(hydroxyethyl)-s-triazine: 10 g

[0104] Deionized water: 180 g

[0105] The cutting fluid was prepared as in Example 1, except that dodecanedioic acid-histidine was replaced by dodecanedioic acid.

[0106] The rust-preventive property of the cutting fluid was tested (test method: JB / T 7453-2013), and the prepared cutting fluid was diluted to 5% solution with distilled water for rust-preventive test. The rust-preventive test result was that the single-piece rust-preventive time was ≥18 h, the stacked-piece rust-preventive time was ≥6 h, and the red copper corrosion test was ≥4 h.

[0107] The carrying capacity of the cutting fluid was tested (test method: GB / T 3142-2019), and the prepared cutting fluid was diluted to 10% solution with distilled water for determination of the maximum non-galling load. The determination result was that the maximum non-galling load value was 560 N.

[0108] Comparative Example 3

[0109] The components and weight percentages of each component of the cutting fluid are as follows:

[0110] Naphthenic mineral oil: 400g

[0111] Dodecanedioic acid-histidine: 100g

[0112] Dodecanedioic acid-histidine: 100g

[0113] Dodecanedioic acid-histidine: 100g

[0114] Dodecanedioic acid-histidine: 100g

[0115] Dodecanedioic acid-histidine: 100g

[0116] Dodecanedioic acid-histidine: 100g

[0117] Dodecanedioic acid-histidine: 100g

[0118] The rust prevention performance of the cutting fluid was tested (test method: JB / T 7453-2013). The prepared cutting fluid was diluted to a 5% solution with distilled water for rust prevention testing. The rust prevention test results were single piece rust prevention time ≥ 24h, stacked piece rust prevention time ≥ 8h, and red copper corrosion test ≥ 8h.

[0119] The carrying capacity of the cutting fluid was tested (test method: GB / T 3142-2019). The prepared cutting fluid was diluted to a 10% solution with distilled water for determination of the maximum non-galling load. The determination results were a maximum non-galling load value of 480N.

[0120] Comparative Example 4

[0121] The components and weight percentages of each component of the cutting fluid are as follows:

[0122] Naphthenic mineral oil: 400g

[0123] Dodecanedioic acid-histidine: 100g

[0124] Dodecanedioic acid-histidine: 100g

[0125] Dodecanedioic acid-histidine: 100g

[0126] Dodecanedioic acid-histidine: 100g

[0127] Dodecanedioic acid-histidine: 100g

[0128] The dodecanedioic acid-histidine was prepared as in Example 1, and the cutting fluid was prepared as in Example 1, except that no benzotriazole was added.

[0129] The rust-preventive performance of the cutting fluid was tested (test method: JB / T 7453-2013). The prepared cutting fluid was diluted to a 5wt% solution using distilled water for the rust-preventive test. The rust-preventive test results were: single-piece rust-preventive time ≥ 24 h, stacked-piece rust-preventive time ≥ 8 h, and red copper corrosion test ≥ 6 h.

[0130] The carrying capacity of the cutting fluid was tested (test method: GB / T 3142-2019). The prepared cutting fluid was diluted to a 10wt% solution using distilled water for the determination of the maximum non-galling load. The determination results were: maximum non-galling load value 590 N.

Claims

1. An emulsified cutting fluid, characterized by comprising: consists of the following components by weight parts: Base oil 30-60 parts Long-chain diacid-amino acid 3-15 parts Long-chain diacid ester 3-20 parts Surfactant 5-20 parts Benzotriazole 0.1-5 parts Bactericide 0-5 parts, and water, The amount of water added is such that the sum of the mass percentages of the above components, excluding water, in the aqueous solution is 2-90wt%; Wherein, the long-chain diacid-amino acid is two amino acids connected to the carboxyl groups at both ends of the long-chain diacid, the long-chain diacid is selected from at least one of undecanedioic acid, dodecanedioic acid, tridecanedioic acid and tetradecanedioic acid, the amino acid connected to the long-chain diacid is selected from at least one of proline, phenylalanine, methionine, tryptophan, glutamine, cysteine, tyrosine, lysine, arginine and histidine, the long-chain diacid-amino acid is prepared by the following method: refluxing the long-chain diacid with dichloro sulfoxide, dissolving the dried solid after rotary evaporation with NaOH solution, reacting, adding acid, and filtering to obtain the long-chain diacid-amino acid; The long-chain diacid ester is an alcohol ester compound formed by esterification of long-chain diacid with long-chain monohydric alcohol, the long-chain diacid is selected from at least one of undecanedioic acid, dodecanedioic acid, tridecanedioic acid and tetradecanedioic acid, and the long-chain monohydric alcohol is C7-C10 monohydric alcohol.

2. The emulsified cutting fluid according to claim 1, characterized by The mass ratio of long-chain diacid-amino acid to long-chain diacid ester is 1:0.8-1:

2.

3. The emulsified cutting fluid according to claim 2, characterized by The mass ratio of long-chain diacid-amino acid to long-chain diacid ester is 1:1-1:1.

5.

4. The emulsified cutting fluid according to claim 1, characterized by The molar ratio of long-chain diacid to dichloro sulfoxide is 1:1-1:10, the reflux temperature is 50-120℃, and the reflux time is 2-12h; when the amino acid is added, the molar ratio of long-chain diacid to amino acid is 1:0.5-1:4, and the solid after rotary evaporation is dissolved with NaOH solution and stirred for 0.5-3h after reaction.

5. The emulsified cutting fluid according to claim 1, characterized by The long-chain monohydric alcohol is selected from at least one of n-heptanol, n-octanol, isooctanol and isononyl alcohol.

6. The emulsified cutting fluid according to claim 1, characterized by The long-chain diacid ester is prepared by the following method: Mixing long-chain diacid, long-chain monohydric alcohol and catalyst, warming and reacting, measuring acid value, ending the reaction when the required acid value is reached, and obtaining the long-chain diacid ester.

7. The emulsified cutting fluid according to claim 6, characterized by The reaction for preparing long-chain diacid ester is carried out in a container equipped with a thermometer, a condenser, a stirrer and a water separator, and uniform stirring is carried out during the reaction, water produced in the reaction is separated by the water separator, the reaction is terminated after sampling and measuring the acid value when the amount of water reaches the theoretical amount, the reaction is completed after cooling, activated carbon is added for adsorption and filtration, the filtrate is washed with sodium hydroxide solution until neutral, the water layer is removed after standing and separating the layers, and then unreacted alcohol is removed by vacuum distillation to obtain the long-chain diacid ester.

8. The emulsified cutting fluid according to claim 6, characterized by The molar ratio of long-chain diacid to long-chain monohydric alcohol is 1:2-1:3, the reaction temperature is 220-240℃, and the catalyst is a supported heteropoly acid catalyst, the mass percentage of which in the reaction system is 0.8%-1.2%.

9. The emulsified cutting fluid according to claim 1, characterized by, The surfactant is selected from at least one of sodium petroleum sulfonate, isomeric tridecanol polyoxyethylene ether and Span 80.

10. The emulsified cutting fluid according to claim 1, characterized by, The bactericide is a hexahydrotriazine or a benzisothiazolinone compound.

11. The preparation method of the emulsified cutting fluid according to any one of claims 1-10, comprising the following steps: The long-chain dibasic acid is refluxed with dichlorosulfoxide, the dried solid is dissolved with NaOH solution, reacted, acid is added, and the long-chain dibasic acid-amino acid is obtained after filtration; The long-chain dibasic acid, long-chain alcohol and catalyst are mixed, the reaction is carried out at elevated temperature, the acid value is determined, and the reaction is stopped when the required acid value is reached, and the long-chain dibasic acid ester is obtained; The long-chain dibasic acid-amino acid, bactericide and water are added into a reactor, stirred, and after complete dissolution, the base oil, long-chain dibasic acid ester, benzotriazole and surfactant are added in sequence, and the emulsified cutting fluid is obtained after the system is stirred to be uniform and transparent.

12. The use of the emulsified cutting fluid according to claim 1 or the emulsified cutting fluid prepared by the preparation method according to claim 11, wherein the cutting fluid is used in a metal processing process.

13. Use according to claim 12, characterized in that, When the cutting fluid is in a concentrated form, the cutting fluid is diluted with water before use, and the total mass concentration of the base oil, long-chain dibasic acid-amino acid, long-chain dibasic acid ester, surfactant, benzotriazole and bactericide is 0.5-8wt%.