JP7731324B2 - Metalworking oil, metalworking fluid, metal corrosion inhibition method, and metalworking method - Google Patents

Description

The present invention relates to metalworking oils, metalworking fluids, methods for inhibiting metal corrosion, and metalworking methods. More specifically, the present invention relates to metalworking oils, metalworking fluids, methods for inhibiting metal corrosion, and metalworking methods that effectively inhibit corrosion of metals, particularly ferrous metals.

Water-soluble metalworking fluids are used in metalworking processes such as cutting and grinding. Water-soluble metalworking fluids are generally made by blending base oil, surfactants, antioxidants, water, and other ingredients according to the intended purpose, and are often diluted with water before use, for example, as coolant. This presents a problem in that the workpiece is susceptible to corrosion.

Metalworking fluids have traditionally been formulated with corrosion inhibitors to prevent corrosion of the workpiece. Corrosion inhibitors have the effect of preventing the metal in the workpiece from dissolving as ions into the water contained in the metalworking fluid.

Non-Patent Document 1 discloses an adsorption-type corrosion inhibitor containing an alkylamine. The unshared electron pair of the alkylamine is shared with the metal atom, causing the corrosion inhibitor molecules to adsorb to the metal. This forms a film on the metal surface, preventing metal ions from leaching into the metalworking fluid.

Kunitsugu Aramaki, Action of Corrosion Inhibitors (Part 1), Vol. 56, No. 6, Materials and Environment, June 15, 2007, pp. 243-251

When the corrosion inhibitor described in Non-Patent Document 1 is used in metalworking fluids for ferrous metals, the corrosion inhibitor molecules do not adhere strongly to the iron, and the corrosion inhibitor molecules desorb from the iron during use of the metalworking fluid, causing the film to break down, resulting in an insufficient corrosion inhibition effect.

The present invention was made in consideration of the current state of the prior art described above, and its main purpose is to provide a metalworking oil that effectively inhibits metal corrosion.

The inventors conducted extensive research to solve the above-mentioned problems. As a result, they discovered that by including a specific monocarboxylic acid in a metalworking oil, it is possible to suppress the elution of metals into the metalworking oil or into a diluted solution of the metalworking oil. The present invention was completed based on this finding.

In other words, a metalworking oil according to one embodiment of the present invention contains a base oil and at least one monocarboxylic acid having 1 to 9 carbon atoms and/or a salt thereof, and is substantially free of monocarboxylic acids having 10 or more carbon atoms (excluding monocarboxylic acids having an ester bond) and/or salts thereof.

The above-mentioned metalworking oils may contain a monocarboxylic acid having an ester bond.

In the above-mentioned metalworking oil, the monocarboxylic acid having an ester bond may have 50 or more carbon atoms.

In the above-mentioned metalworking oil, the monocarboxylic acid having 1 to 9 carbon atoms may include octanoic acid or nonanoic acid.

In the above-mentioned metalworking oil, the monocarboxylic acid having 1 to 9 carbon atoms may be linear.

A metalworking fluid according to one embodiment of the present invention is prepared by diluting any of the metalworking oils described above with water.

One aspect of the present invention relates to a method for inhibiting metal corrosion, which involves supplying any of the metalworking oils or metalworking fluids described above to a metal surface.

A metalworking method according to one aspect of the present invention processes metal using any of the metalworking oils or metalworking fluids described above.

This disclosure makes it possible to provide a metalworking oil that effectively inhibits metal corrosion.

FIG. 1 shows the structural formula of a tetramer of (9Z,12R)-12-hydroxyoctadec-9-enoic acid. 1 is a graph showing the amount of iron eluted when each monocarboxylic acid is blended. 1 is a graph showing the amount of iron elution in Example 3 and Modifications 1 and 2.

Embodiments of the present invention are described in detail below.

(metalworking oil)
The metalworking oil of the present invention contains a base oil and at least one monocarboxylic acid having 1 to 9 carbon atoms and/or a salt thereof, and is substantially free of a monocarboxylic acid having 10 or more carbon atoms (excluding monocarboxylic acids having an ester bond) and/or a salt thereof.
The composition of the metalworking oil will be specifically described below.

The metalworking oil of this embodiment contains a monocarboxylic acid having 1 to 9 carbon atoms and/or a salt thereof. In this specification, "monocarboxylic acid" refers to a compound having one carboxyl group in the molecule. By including a monocarboxylic acid having a relatively small number of carbon atoms, such as 1 to 9 carbon atoms, the elution of metals (metal ions) into the metalworking oil or a diluted solution of the metalworking oil is effectively suppressed, resulting in excellent metal corrosion inhibition and improved stability of the metalworking oil or a diluted solution of the metalworking oil.

The monocarboxylic acid having 1 to 9 carbon atoms may be either a saturated monocarboxylic acid or an unsaturated monocarboxylic acid, with a saturated monocarboxylic acid being preferred. The monocarboxylic acid having 1 to 9 carbon atoms preferably has a chain structure. If the monocarboxylic acid having 1 to 9 carbon atoms has a chain structure, it may be either linear or branched, with a linear structure being preferred. The monocarboxylic acid having 1 to 9 carbon atoms preferably has a linear or branched alkyl group, with a linear alkyl group being preferred. From the viewpoint of improving corrosion inhibition, the monocarboxylic acid preferably has 8 to 9 carbon atoms, with 9 carbon atoms being more preferred.

Specific examples of monocarboxylic acids having 1 to 9 carbon atoms include nonanoic acid, octanoic acid, heptanoic acid, and hexanoic acid. Among these, nonanoic acid and octanoic acid are preferred, with nonanoic acid being more preferred, from the viewpoint of improving corrosion inhibition. Examples of salts of monocarboxylic acids include alkali metal salts selected from sodium and potassium. Monocarboxylic acids having 1 to 9 carbon atoms may be used alone or in combination of two or more.

The content of monocarboxylic acid having 1 to 9 carbon atoms and/or its salt in the metalworking oil of this embodiment is not limited, but is preferably 1% by mass or more and 4% by mass or less. When two or more types are used in combination, the content refers to the total amount. Within the above range, metal elution can be more effectively suppressed, corrosion inhibition can be excellent, and the stability of the metalworking oil can be improved. The content of monocarboxylic acid having 1 to 9 carbon atoms and/or its salt is more preferably 1.5% by mass or more, even more preferably 2% by mass or more, and more preferably 3.5% by mass or less, even more preferably 3% by mass or less.

The metalworking oil of this embodiment contains a base oil. The base oil may be a natural product or a synthetic product. Examples of base oils include mineral oil and vegetable oil. Of these, mineral oil is preferred, and paraffinic mineral oil is more preferred. The base oil may be used alone or in combination of two or more types.

The content of base oil in a metalworking oil can be set appropriately depending on the type of base oil, the types and content ratios of other blended ingredients, etc. For example, the content of base oil in a metalworking oil according to an embodiment is preferably 5% by mass or more and 50% by mass or less. When two or more types are used in combination, the content refers to the total amount. Within the above range, metal elution can be more effectively suppressed, corrosion inhibition can be excellent, and the stability of the metalworking oil can be improved. The content of base oil is more preferably 7% by mass or more, and more preferably 30% by mass or less, and even more preferably 20% by mass or less.

The ratio of the content of base oil to monocarboxylic acid and/or salt thereof having 1 to 9 carbon atoms is preferably 2.0 to 50 by mass (base oil/monocarboxylic acid and/or salt thereof having 1 to 9 carbon atoms). When the content is within this range, metal elution is more effectively suppressed, corrosion inhibition is excellent, and the stability of the metalworking oil can be improved. The mass ratio is more preferably 2.5 or more, and more preferably 20 or less, and even more preferably 7.5 or less.

The metalworking oil of this embodiment is substantially free of monocarboxylic acids having 10 or more carbon atoms and/or salts thereof, except for monocarboxylic acids having ester bonds. Monocarboxylic acids with a relatively large number of carbon atoms, such as monocarboxylic acids having 10 or more carbon atoms, generally have the effect of enhancing the stability of metalworking oils or their diluted solutions, and are therefore used as stabilizers in many metalworking oils. In contrast, the metalworking oil of this embodiment contains monocarboxylic acids having 1 to 9 carbon atoms and/or salts thereof, and is able to improve the stability of metalworking oils or their diluted solutions and effectively suppress metal elution, even without using monocarboxylic acids having 10 or more carbon atoms (excluding monocarboxylic acids having ester bonds) and/or salts thereof.

As used herein, "monocarboxylic acid having an ester bond" refers to a compound having one carboxyl group and at least one ester bond within the molecule.

As used herein, "substantially free" means that monocarboxylic acids having 10 or more carbon atoms (excluding monocarboxylic acids having ester bonds) and/or salts thereof are not actively added to the metalworking oil of the embodiment, and does not mean that monocarboxylic acids having 10 or more carbon atoms (excluding monocarboxylic acids having ester bonds) and/or salts thereof are not contained at all. Preferably, this means that the content of monocarboxylic acids having 10 or more carbon atoms (excluding monocarboxylic acids having ester bonds) and/or salts thereof in the metalworking oil is 0.1 mass% or less.

The metalworking oil of this embodiment preferably contains a monocarboxylic acid having an ester bond. By using a monocarboxylic acid having an ester bond in combination with a monocarboxylic acid having 1 to 9 carbon atoms and/or a salt thereof, metal elution can be effectively suppressed and the stability of the metalworking oil or its diluted solution can be further improved. The monocarboxylic acid having an ester bond may be used alone or in combination of two or more.

From the viewpoints of improving stability and enhancing synergistic effects with monocarboxylic acids having 1 to 9 carbon atoms and/or salts thereof, the monocarboxylic acid having an ester bond preferably has 50 to 90 carbon atoms, more preferably 70 to 90 carbon atoms, and even more preferably 72 carbon atoms. The monocarboxylic acid having an ester bond is preferably a polymer containing unsaturated fatty acid monomers as polymerization units. These monomers may be used alone or in combination of two or more. A preferred example of such a monocarboxylic acid having an ester bond is a polymer obtained by polymerizing a monomer of (9Z,12R)-12-hydroxyoctadec-9-enoic acid, with the tetramer of (9Z,12R)-12-hydroxyoctadec-9-enoic acid (72 carbon atoms) being particularly preferred. Figure 1 shows the structural formula of a tetramer of (9Z,12R)-12-hydroxyoctadec-9-enoic acid.

The content of monocarboxylic acid having an ester bond in the metalworking oil of this embodiment is not limited, but is preferably 5% by mass or more and 15% by mass or less. When two or more types are used in combination, the content refers to the total amount. Within the above range, metal elution can be more effectively suppressed, corrosion inhibition can be excellent, and the stability of the metalworking oil or its diluted solution can be improved. The content of monocarboxylic acid having an ester bond is more preferably 8% by mass or more, more preferably 12% by mass or less, and even more preferably 10% by mass or less. The content of monocarboxylic acid having an ester bond is most preferably 9% by mass.

The ratio of the content of monocarboxylic acid having an ester bond to monocarboxylic acid having 1 to 9 carbon atoms and/or its salt is preferably 2.5 to 7.5 by mass (monocarboxylic acid having an ester bond/monocarboxylic acid having 1 to 9 carbon atoms and/or its salt). Using a combination of monocarboxylic acid having 1 to 9 carbon atoms and/or its salt with monocarboxylic acid having an ester bond within the above ratio range enhances the synergistic effect, more effectively suppresses metal elution, and improves the stability of the metalworking oil. The mass ratio is more preferably 3.0 or higher, even more preferably 4.0 or higher, and more preferably 7.0 or lower, even more preferably 6.0 or lower.

The metalworking oil of the embodiment preferably contains water. The water used may be tap water, industrial water, ion-exchanged water, distilled water, etc., and may be hard or soft. The water content in the metalworking oil can be set appropriately depending on the type and content of other ingredients. For example, the water content in the metalworking oil of the embodiment is preferably 10% by mass or more and 60% by mass or less, and more preferably 30% by mass or more and 60% by mass or less. Within the above range, excellent corrosion inhibition is achieved, the stability of the metalworking oil is improved, and the preparation of the metalworking oil is facilitated. When the metalworking oil of the embodiment contains water, it preferably also contains an emulsifier. The emulsifiers described below can be suitably used. Note that the water contained in the metalworking oil refers to the water that is a constituent component of the metalworking oil as a stock solution, and differs from the water used as a diluent, which will be described later.

In addition to the components listed above, metalworking oils can contain various additives as needed, provided they do not impair the effects of the present invention. Examples of additives include emulsifiers, rust inhibitors, lubricants, preservatives, and antifoaming agents.

Examples of emulsifiers include surfactants such as nonionic surfactants, anionic surfactants, cationic surfactants, and amphoteric surfactants, and organic amines such as alkanolamines. The emulsifiers may be used alone or in combination of two or more. The content of the emulsifier in the metalworking oil may be, for example, 0.01% by mass or more and 20% by mass or less. Within the above range, the emulsion stability of the metalworking oil can be improved, and corrosion inhibition performance can be effectively exhibited.
As the emulsifier, from the viewpoint of improving the emulsion stability of the monocarboxylic acid having 1 to 9 carbon atoms and/or its salt, nonionic surfactants, alkanolamines, and combinations thereof are preferred, and polyoxyalkylene ethers, N-methylethanolamine, triisopropanolamine, triethanolamine, and combinations thereof are more preferred.

Examples of rust inhibitors include dibasic acids, benzotriazoles, and organic amines. Rust inhibitors may be used singly or in combination of two or more. The content of the rust inhibitor in the metalworking oil may be, for example, 0.001% by mass or more and 6% by mass or less. Within the above range, the rust prevention properties of metals can be improved, and corrosion inhibition performance can be effectively exhibited.
As the rust inhibitor, from the viewpoint of rust prevention, dibasic acids, benzotriazoles, and combinations thereof are preferred, and dodecanedioic acid, dimer acids, benzotriazoles, and combinations thereof are more preferred.

Examples of preservatives include aliphatic amines, triazine compounds, thiazoline compounds, and phenolic compounds. The preservatives may be used singly or in combination of two or more. The content of the preservative in the metalworking oil may be, for example, 0.01% by mass or more and 10% by mass or less. Within the above range, decay of the metalworking oil can be effectively inhibited, and corrosion-inhibiting performance can be effectively exhibited.
As the preservative, from the viewpoint of corrosion inhibition, aliphatic amines, triazine compounds and combinations thereof are preferred, and dicyclohexylamine, hexahydro-1,3,5-tris(2-hydroxyethyl)-1,3,5-triazine and combinations thereof are more preferred.

Antifoaming agents include, for example, silicone-based antifoaming agents such as polyorganosiloxanes having a molecular weight of 100 to 1,000. Antifoaming agents may be used alone or in combination of two or more. The content of antifoaming agent in the metalworking oil may be, for example, 0.001% by mass or more and 1% by mass or less. Within this range, the antifoaming properties of the metalworking oil can be improved, and corrosion inhibition performance can be effectively demonstrated.

The pH of the metalworking oil in this embodiment is preferably 8.5 or higher and 11.0 or lower, more preferably 9.5 or higher and 10.7 or lower, and even more preferably 9.7 or higher and 10.5 or lower. Within this range, the metalworking oil can be effectively prevented from spoiling and exhibits effective corrosion inhibition performance.

The metalworking oil of this embodiment is obtained by mixing and stirring the above components. The metalworking oil of this embodiment is water-soluble and can be used directly for metal processing.

(metal working fluid)
The metalworking fluid of the embodiment is obtained by diluting the metalworking oil of the above embodiment as a stock solution with water. The metalworking fluid (diluted solution) can be used as a coolant for metal processing. The water used may be tap water, industrial water, ion-exchanged water, distilled water, or the like, and the water may be hard water or soft water.

When diluting a metalworking oil with water, the dilution ratio can be adjusted appropriately depending on the composition of the metalworking oil and the performance required during metalworking. There are no limitations on the dilution ratio, but it is generally preferable to dilute the oil at a ratio of 1.5 to 100. From the perspective of further enhancing the effects of the present invention and improving processing characteristics, the dilution ratio is more preferably 5 to 10, even more preferably 10 to 10, and more preferably 50 to 10, even more preferably 30 to 10. When diluting a metalworking oil for use, it is preferable that the undiluted metalworking oil contains an emulsifier. The emulsifiers mentioned above can be suitably used.

The metalworking oils (undiluted solutions) and metalworking fluids (diluted solutions) of the embodiments have excellent corrosion inhibition properties and processability, making them suitable for use in metalworking, such as cutting, grinding, polishing, and cutting. Examples of metals to be processed include iron-based metals and their alloys, and non-ferrous metals such as aluminum, magnesium, and copper and their alloys, with iron-based metals and their alloys being preferred. In particular, when the metalworking oils and metalworking fluids of the embodiments are applied to iron-based metals and their alloys, which are poorly inhibited by conventional corrosion inhibitors, they exhibit an excellent effect of inhibiting metal elution.

(Method for inhibiting metal corrosion)
In the metal corrosion suppression method of the embodiment, a metalworking oil (undiluted solution) or a metalworking fluid (diluted solution) of the embodiment is supplied to a metal surface. In the metal corrosion suppression method of the embodiment, the metalworking oil or metalworking fluid described above is used, and thus metal elution can be effectively suppressed. Examples of the metal to be supplied include the metals described above, with iron-based metals and their alloys being preferred. Supplying to a metal surface may refer to supplying to either a portion or the entire metal surface, with supplying to the entire metal surface being preferred. The method for supplying a metalworking oil or metalworking fluid to a metal surface is not particularly limited, and may include, for example, spraying or applying the metalworking oil or metalworking fluid to the metal surface. Examples of methods for applying a metalworking oil or metalworking fluid to a metal surface include immersion coating, shower coating, spray coating, and jet coating.

(Metal processing method)
In the metalworking method of the embodiment, a metal material is processed using the metalworking oil (undiluted solution) or metalworking fluid (diluted solution) of the embodiment. The metalworking method can be suitably used for various metalworking processes, such as cutting, grinding, polishing, and cutting. When the metalworking oil or metalworking fluid is supplied to the processing point, for example, in liquid or mist form, it can exhibit the effect of suppressing metal elution into the metalworking oil or metalworking fluid. The metalworking oil or metalworking fluid can be supplied to the processing point using, for example, the techniques described above. Examples of the types of metals to be processed include the metals described above, with iron-based metals and their alloys being preferred. In the metalworking method of the embodiment, the metalworking oil described above is used, thereby suppressing metal elution and enabling good processing.

The present invention will be explained in more detail below based on examples and comparative examples, but it is not intended that the present invention be limited to these examples.

1. Preparation of metalworking oil [Example 1]
The following components shown in Table 1 were weighed out to yield the compositions (in mass %) shown in the table: (A) monocarboxylic acid (n-octanoic acid having 8 carbon atoms), (B) base oil, (C) monocarboxylic acid having an ester bond, (D) water, (E) emulsifier, (F) rust inhibitor, (G) preservative, and (H) antifoaming agent. These components were mixed in a mixer until uniform, yielding the metalworking fluid of Example 1. The pH of the resulting metalworking fluid was 10.3 (20°C). pH was measured using a pH meter ("F-52" manufactured by HORIBA, Ltd.). The (C) monocarboxylic acid having an ester bond in Table 1 is the tetramer of the aforementioned (9Z,12R)-12-hydroxyoctadec-9-enoic acid (see FIG. 1), which has 72 carbon atoms. Note that the molar number of the (A) monocarboxylic acid used in each of the examples and comparative examples in Table 1 is the same.

[Example 2]
A metalworking oil of Example 2 was prepared in the same manner as in Example 1, except that n-nonanoic acid having 9 carbon atoms was blended as the (A) monocarboxylic acid and the blending ratio of each component was as shown in Table 1. The pH of the obtained metalworking oil was 10.3 (20°C).

[Comparative Example 1]
A metalworking oil of Comparative Example 1 was prepared in the same manner as in Example 1, except that n-dodecanoic acid having 12 carbon atoms was blended as the (A) monocarboxylic acid and the blending ratio of each component was as shown in Table 1. The pH of the obtained metalworking oil was 10.3 (20°C).

[Comparative Example 2]
A metalworking oil of Comparative Example 2 was prepared in the same manner as in Example 1, except that n-octadecanoic acid having 18 carbon atoms was blended as the (A) monocarboxylic acid and the blending ratio of each component was as shown in Table 1. The pH of the obtained metalworking oil was 10.3 (20°C).

[Comparative Example 3]
A metalworking oil of Comparative Example 3 was prepared in the same manner as in Example 1, except that (9Z)-octadecenoic acid having 18 carbon atoms was blended as the (A) monocarboxylic acid and the blending ratio of each component was as shown in Table 1. The pH of the obtained metalworking oil was 10.3 (20°C).

[Comparative Example 4]
A metalworking oil of Comparative Example 4 was prepared in the same manner as in Example 1, except that (9Z,12R)-12-hydroxyoctadec-9-enoic acid having 18 carbon atoms was blended as (A) monocarboxylic acid, and the blending ratios of the respective components were as shown in Table 1. The pH of the obtained metalworking oil was 10.3 (20°C).

2. Performance evaluation [corrosion inhibition]
The test fluids used were metalworking fluids (diluted solutions) prepared by diluting each metalworking fluid (stock solution) with water to 10%. 10 g of cast iron chips (FC250) were added to 40 g of each diluted solution of the above Examples and Comparative Examples, and the mixture was allowed to stand at 50°C for one week. After standing, the iron concentration in the test solution was measured using an atomic absorption spectrophotometer, and the iron concentration (mg/L) in the test solution was recorded as the amount of iron elution (mg/L). Each test solution was vigorously stirred when adding the cast iron chips and before measurement with the atomic absorption spectrophotometer, and was allowed to stand for the rest of the time. The amount of elution was measured using an atomic absorption spectrophotometer (AA240FS, manufactured by Agilent Technologies) using the atomic absorption method. Corrosion inhibition was judged to be good when the amount of iron elution was less than 30 mg/L. The results for Examples 1 and 2 and Comparative Examples 1 to 4 are shown in Table 2 below.
Figure 2 was created based on Table 2. Figure 2 is a graph showing the amount of iron eluted when each monocarboxylic acid was blended. The vertical axis of Figure 2 represents the amount of iron eluted (unit: mg/L). Each bar graph in Figure 2 represents the amount of iron eluted in Examples 1 and 2 and Comparative Examples 1 to 4, from left to right.

As is clear from Table 2 and Figure 2, the test fluids of Examples 1 and 2, which contained a monocarboxylic acid having 1 to 9 carbon atoms but not a monocarboxylic acid having 10 or more carbon atoms (excluding monocarboxylic acids having an ester bond) and/or a salt thereof, exhibited reduced iron elution into the diluted metalworking oil solution and good corrosion inhibition. In contrast, the test fluids of Comparative Examples 1 to 4, which contained a monocarboxylic acid having 10 or more carbon atoms, did not exhibit sufficient iron elution inhibition and poor corrosion inhibition. The monocarboxylic acid having 1 to 9 carbon atoms is preferably n-octanoic acid or n-nonanoic acid, and more preferably n-nonanoic acid. Each metalworking oil (stock solution) separated without the addition of (A) monocarboxylic acid, but a stable stock solution was obtained when (A) monocarboxylic acid was added, confirming that the addition of (A) monocarboxylic acid improves stability.

Next, the corrosion inhibition effect was investigated when the content of monocarboxylic acid having an ester bond was changed. Note that Modifications 1 and 2 are reference examples.

[Example 3]
A metalworking oil of Example 3 was prepared in the same manner as in Example 1, except that (E) triethanolamine was used instead of triisopropanolamine as the emulsifier, and the blending ratios of each component were as shown in Table 3. The pH of the obtained metalworking oil was 10.3 (20°C).
[Modifications 1 and 2]
Metalworking oils of Modifications 1 and 2 were prepared in the same manner as in Example 3, except that the blending ratio of (C) monocarboxylic acid having an ester bond was as shown in Table 3. The pH of the obtained metalworking oils was 10.4 (20°C) for Modification 1 and 10.1 (20°C) for Modification 2.

The amount of iron eluted (mg/L) was measured for Example 3 and Modifications 1 and 2 using the same method as in the above-mentioned Examples and Comparative Examples. The measurement results are shown in Table 3 below.
Figure 3 was created based on Table 3. Figure 3 is a graph showing the amount of iron elution in Example 3 and Modifications 1 and 2. The vertical axis of Figure 3 represents the amount of iron elution (unit: mg/L). Each bar graph in Figure 3 represents the amount of iron elution in Example 3 and Modifications 1 and 2, from left to right.

As is clear from Table 3 and Figure 3, the amount of iron eluted into the diluted metalworking oil solution in Example 3 was lower than in Modifications 1 and 2, confirming improved corrosion inhibition. The content of monocarboxylic acid having an ester bond in the metalworking oil solution is more preferably 8% by mass or more and 12% by mass or less, even more preferably 8% by mass or more and 10% by mass or less, and most preferably 9% by mass.

From the above, it has been confirmed that the metalworking oil disclosed herein inhibits metal elution and effectively inhibits metal corrosion.

The embodiments disclosed herein are illustrative in all respects and should not be considered limiting. The technical features described in each embodiment can be combined with one another, and the scope of the present invention is intended to include all modifications within the scope of the claims and equivalents to the scope of the claims.

Claims (10)

A metalworking oil containing 1 to 4 mass% of at least one monocarboxylic acid and/or salt thereof having 1 to 9 carbon atoms, 5 to 50 mass% of a base oil, and 8 to 12 mass% of a monocarboxylic acid having an ester bond and having 50 or more carbon atoms , and substantially no monocarboxylic acid having 10 or more carbon atoms (excluding monocarboxylic acids having an ester bond) and/or salts thereof. The monocarboxylic acid having an ester bond has 72 carbon atoms.
The metalworking oil according to claim 1. The ratio of the content of the monocarboxylic acid having an ester bond to the content of the monocarboxylic acid having 1 to 9 carbon atoms and/or a salt thereof is 2.5 to 7.5 by mass.
The metalworking oil according to claim 1 or 2. The metalworking oil according to any one of claims 1 to 3, wherein the monocarboxylic acid having 1 to 9 carbon atoms includes octanoic acid or nonanoic acid. The metalworking oil according to any one of claims 1 to 3, wherein the monocarboxylic acid having 1 to 9 carbon atoms is linear. A metalworking fluid obtained by diluting the metalworking oil agent according to any one of claims 1 to 3 with water. A method for inhibiting corrosion of metals, comprising supplying the metalworking oil according to any one of claims 1 to 3 to a surface of the metal. A method for inhibiting corrosion of metals, comprising supplying the metalworking fluid according to claim 6 to a surface of the metal. A metalworking method comprising processing a metal using the metalworking oil according to any one of claims 1 to 3. A metalworking method comprising processing metal using the metalworking fluid according to claim 6.