JP2022149800A - Lubricating oil composition for machine tool and metallic working - Google Patents

Abstract

To provide a lubricating oil composition for a machine tool and metallic working which has a well balanced high flash point and extreme-pressure performance.SOLUTION: A lubricating oil composition for a machine tool and metallic working comprises: (A) a lubricating oil base oil having a kinematic viscosity at 40°C of 18 mm2/s or more and 40 mm2/s or less; and (B) sulfurized ester. 25 mass% or more of the component (A) is a group III base oil.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a lubricating oil composition for machine tools and metalworking having a high flash point.

Machine tool oils refer to general lubricating oil compositions used for lubricating sliding parts and power transmission parts of machine tools, such as gear oils, bearing oils, sliding surface oils, and hydraulic oils. In addition, metal working oil refers to general lubricating oil compositions used when processing materials such as metals and resins into desired shapes, and specifically includes grinding oil, cutting oil, rolling oil, and forging oil. . Various types are used depending on the lubrication point and processing method, and the required performance varies depending on the type of oil, but high extreme pressure properties are commonly required. In addition, the optimum viscosity is selected according to the purpose, but in recent years, from the viewpoint of energy saving and oil penetration into the processing point, lower viscosity is oriented.

These lubricating oils are required to have various properties other than extreme pressure properties and viscosity. Among them, the flash point is important. The lower the flash point, the higher the risk of fire. Therefore, the handling and storage amount are legally regulated according to the flash point. The increased flash point also increases the safety of fire handling. Therefore, handling such as storage and management becomes easy. In particular, if the flash point of lubricating oil can be raised to 250°C or higher, it will be exempted from dangerous goods under the Fire Service Act of Japan and designated combustibles, so the equipment required for storage and management costs can be reduced. However, lowering the viscosity of the lubricating oil generally lowers the flash point as well.

Lowering the viscosity of the lubricating oil while increasing the flash point requires the use of a higher grade base oil, such as Group III, according to the API standards set by the American Petroleum Institute. However, higher grade base oils often have poor additive solubility. The fact that the additive does not dissolve means that the effect of improving the extreme pressure properties and the like cannot be obtained by the additive. In addition, some additives may lower the flash point, and it has been very difficult to prepare a lubricating oil that satisfies all the required properties such as the desired viscosity, high flash point, and extreme pressure properties.

Japanese Patent Application Laid-Open No. 2016-108492

Patent Document 1 discloses a lubricating oil composition for sliding guide surfaces containing a specific phosphite and fatty acid. However, regarding this composition, a base oil with a high kinematic viscosity at 40° C. has been studied, and a base oil with a lower kinematic viscosity has not been studied. Also, depending on the type of additive, the flash point may be lowered.
Therefore, a base oil having a low kinematic viscosity, specifically a kinematic viscosity at 40° C. of 18 mm ² /s or more and 40 mm ² /s or less, is used for a machine tool having a high flash point and extreme pressure properties in a well-balanced manner. and lubricating oil for metalworking.

The present inventors have extensively studied lubricating oils for machine tools and metalworking that use base oils with low kinematic viscosities, have high flash points, and have extreme pressure properties. Then, (A) a lubricating base oil having a kinematic viscosity at 40° C. of 18 mm ² /s or more and 40 mm ² /s or less and (B) a sulfurized ester are added to the lubricating oil for machine tools and metalworking, and The inventors have completed the invention by making 25% by mass or more of the component (A) Group III base oil.

The present invention has been made based on such findings, and is as follows.
<1>
(A) a lubricating base oil having a kinematic viscosity at 40° C. of 18 mm ² /s or more and 40 mm ² /s or less;
(B) a sulfurized ester, and
25% by mass or more of the component (A) is a Group III base oil,
Lubricating oil compositions for machine tools and metalworking.
<2>
The lubricating oil composition for machine tools and metalworking according to <1>, containing 80% by mass or more and 99% by mass or less of component (A) based on the total amount of the composition.
<3>
(C) The lubricating oil composition for machine tools and metalworking according to <1> or <2>, further comprising an acidic phosphate.
<4>
The lubricating oil composition for machine tools and metalworking according to any one of <1> to <3>, wherein 1% by mass or more and 70% by mass or less of the component (A) is a synthetic base oil.
<5>
The lubricating oil composition for machine tools and metalworking according to any one of <1> to <4>, containing 80% by mass or more and 95% by mass or less of component (A) based on the total amount of the composition.
<6>
The lubricating oil composition for machine tools and metalworking according to any one of <1> to <5>, wherein 50% by mass or more of the component (A) is Group III base oil.
<7>
The lubricating oil composition for machine tools and metalworking according to any one of <1> to <6>, which is used for sliding surfaces.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a lubricating oil composition for machine tools and metalworking that has a high flash point and extreme pressure properties in a base oil with a low kinematic viscosity.

[Component (A): Lubricating base oil]
As the lubricating base oil in the lubricating oil composition for machine tools and metalworking of the present invention (hereinafter sometimes simply referred to as the lubricating oil composition or the lubricating oil composition of the present invention), Group III in the API classification A lubricating base oil, which is a base oil, can be used without particular limitation. API Group III base oils are mineral base oils having a sulfur content of 0.03 wt.% or less, a saturates content of 90 wt.% or more, and a viscosity index of 120 or more. more than one type of Group III base oil may be used, or only one type may be used;

Group III mineral base oils include solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, Mineral base oils such as paraffinic or naphthenic base oils obtained by appropriately combining one or more refining means such as hydrorefining, sulfuric acid washing and clay treatment can be mentioned. API Group III base oils are typically produced via a hydrocracking process.

The lubricating oil composition of the present invention comprises at least 25% by weight, preferably at least 50% by weight, more preferably at least 70% by weight of Group III base oil, based on component (A). The upper limit of the Group III base oil content is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 80% by mass or less, based on component (A). The content of Group III base oil, based on component (A), is preferably 25% by mass or more and 95% by mass or less, more preferably 50% by mass or more and 90% by mass or less, and still more preferably 70% by mass. % or more and 80 mass % or less. When the content of the Group III base oil is equal to or less than the above upper limit value, the solubility of the additive is further improved, and when it is equal to or more than the above lower limit value, the flash point is improved.
The Group III base oil used in the lubricating oil composition of the present invention has a kinematic viscosity at 40° C. of preferably 25 mm ² /s or more and 40 mm ² /s or less, more preferably 28 mm ² /s or more and 40 mm ² /s or less. , more preferably 30 mm ² /s or more and 40 mm ² /s or less, and particularly preferably 32 mm ² /s or more and 38 mm ² /s or less.
The Group III base oil used in the lubricating oil composition of the present invention preferably has a flash point of 234°C or higher, more preferably 238°C or higher, even more preferably 242°C or higher, and particularly preferably 245°C or higher.
The viscosity index and kinematic viscosity at 40°C in this specification mean the viscosity index and the kinematic viscosity at 40°C measured according to JIS K2283:2000, respectively. In addition, the flash point in this specification means the flash point measured according to JIS K 2265-4:2007 (open flash point).

In the lubricating oil composition of the present invention, the component (A) has a kinematic viscosity at 40° C. of 18 mm ² /s or more and 40 mm ² /s or less, preferably 80% by mass or more, based on the total amount of the composition. , more preferably 85% by mass or more, more preferably 90% by mass or more. The upper limit of component (A) is preferably 99% by mass or less, more preferably 97% by mass or less, and even more preferably 95% by mass or less, based on the total amount of the composition. A specific range of the content of component (A) is preferably 80% by mass or more and 99% by mass or less, more preferably 85% by mass or more and 97% by mass or less, and still more preferably 90% by mass or more, based on the total amount of the composition. It is 95% by mass or less. When the content of component (A) is equal to or less than the above upper limit value, the effect of the additive can be easily obtained, and when it is equal to or more than the above lower limit value, it is advantageous in terms of cost.

Component (A) is a synthetic base oil, preferably 1% by mass or more and 75% by mass or less, more preferably 2% by mass or more and 40% by mass or less, still more preferably 2% by mass or more and 30% by mass, based on component (A). % by mass or less, particularly preferably 15 to 30 mass %.

The kinematic viscosity of the synthetic base oil at 40°C is preferably 10 mm ² /s or more and 50 mm ² /s or less, more preferably 15 mm ² /s or more and 48 mm ² /s or less, still more preferably 20 mm ² /s or more and 46 mm ² /s or more. s or less, particularly preferably 25 mm ² /s or more and 44 mm ² /s or less.
The flash point of the synthetic base oil is preferably 230°C or higher, more preferably 240°C or higher, still more preferably 250°C or higher, and particularly preferably 254°C or higher.
Synthetic base oils include, for example, poly-α-olefins (eg, ethylene-propylene copolymer, polybutene, 1-octene oligomer, 1-decene oligomer, etc.) or hydrogenated products thereof; monoesters (eg, butyl stearate, octyl lau rate, etc.); diesters (eg, ditridecyl glutarate, di-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate, di-2-ethylhexyl sepacate, etc.); polyesters (eg, trimellitate esters, etc.); polyol esters (eg, trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol-2-ethylhexanoate, pentaerythritol pelargonate, etc.); aromatic synthetic oils (eg, alkylbenzene, alkylnaphthalene, aromatic esters, etc.); A mixture etc. can be illustrated. When synthetic base oils are included, poly-α-olefins belonging to API Group IV or ester base oils belonging to API Group V such as monoesters, diesters or polyesters are preferred.

(Kinematic viscosity at 40°C)
Component (A) is a lubricating base oil having a kinematic viscosity at 40° C. of 18 mm ² /s or more and 40 mm ² /s or less.
Component (A) may contain a lubricating base oil with a kinematic viscosity at 40° C. outside the above range, but the lubricating base oil as a whole is adjusted to be 18 mm ² /s or more and 40 mm ² /s or less. do. Component (A) can also be free of lubricating base oils whose kinematic viscosities at 40°C are outside the above range.
Component (A) has a kinematic viscosity at 40° C. of preferably 25 mm ² /s or more and 40 mm ² /s or less, more preferably 28 mm ² /s or more and 40 mm ² /s or less, still more preferably 30 mm ² /s or more and 40 mm ² /s or less, particularly preferably 32 mm ² /s or more and 38 mm ² /s or less. When the kinematic viscosity at 40°C is equal to or less than the above upper limit, it is possible to obtain energy saving due to ease of processing or low frictional resistance, and when it is equal to or more than the above lower limit, oil film formation at lubrication points is ensured. Desired extreme pressure properties can be obtained.

[Component (B): sulfurized ester]
As used herein, "sulfurized ester" refers to a compound obtained by sulfurizing an ester compound having an unsaturated bond. Any compound can be used as such a sulfurized ester without any particular limitation. Examples of sulfurized esters that can be used in the lubricating oil composition of the present invention include sulfurized esters of the following general formula (1).

(1)

In general formula (1), R ¹ and R ² each independently represent hydrogen or a hydrocarbyl group having 1 to 24 carbon atoms, preferably 1 to 8 carbon atoms. However, when one of R ¹ and R ² is hydrogen, the other is a hydrocarbyl group having 1 to 24 carbon atoms (preferably 1 to 8 carbon atoms).

Specific examples of hydrocarbyl groups having 1 to 24 carbon atoms include alkyl groups, alkenyl groups, cycloalkyl groups, alkylcycloalkyl groups, aryl groups, alkylaryl groups and arylalkyl groups. Among these, an alkyl group is preferable, and a methyl group and an ethyl group are particularly preferable.

In general formula (1), a1, b1, a2, and b2 are each individually an integer of 3 or more, and the sum of a1 and b1 and the sum of a2 and b2 are each individually 8 to 24, preferably 10 to 20. When the sum of a1 and b1 and the sum of a2 and b2 is equal to or less than the above upper limit value, the processability is further improved, and when the sum is equal to or more than the above lower limit value, the solubility in the base oil is further improved.

Although y in the above formula (1) represents the number of sulfur crosslinks, it represents the average number of sulfur crosslinks in the mixture. A compound obtained by sulfurization is usually a mixture of compounds having different numbers of sulfur bridges. y (average number of sulfur crosslinks) is 1 to 8, preferably 2 to 6. In addition, sulfide esters with y (average number of sulfur crosslinks) of 4 or more are classified as active sulfide esters that are highly likely to cause copper plate corrosion, and sulfide esters with y (average number of sulfur crosslinkages) of 3 or less cause copper plate corrosion. It can be classified as an inert sulfurized ester with a low potential to cause.

The sulfurized ester represented by the above formula (1) is obtained by sulfur-crosslinking an ester of an unsaturated fatty acid having 14 to 20 carbon atoms and having one unsaturated bond in the molecule (for example, oleic acid). The raw unsaturated fatty acid ester is preferably purified, but may be used even if it contains impurities. The content of impurities in the raw material is preferably less than 50% by mass, more preferably 30% by mass or less, and even more preferably 10% by mass or less.
As the unsaturated fatty acid ester, oleic acid esters such as methyl oleate, ethyl oleate, and propyl oleate are preferable, and among these, methyl oleate is more preferable because it exhibits an effective friction reducing effect.

In the lubricating oil composition of the present invention, the sulfurized ester of component (B) is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and still more preferably 1% by mass or more, based on the total amount of the composition. , particularly preferably 2% by mass or more. The upper limit of component (B) is preferably 10% by mass or less, more preferably 8% by mass or less, still more preferably 6% by mass or less, and particularly preferably 5% by mass or less, based on the total amount of the composition. A specific range of the content of component (B) is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.5% by mass or more and 8% by mass or less, still more preferably, based on the total amount of the composition. 1% by mass or more and 6% by mass or less, particularly preferably 2% by mass or more and 5% by mass or less. By setting the amount of the sulfurized ester of component (B) to the above upper limit or less, the flash point can be further increased, and by setting the amount to the above lower limit or more, better extreme pressure properties can be obtained.

In this specification, the term "sulfurized ester" does not include sulfurized fats and oils. However, this does not preclude the combined use of sulfurized fats and oils. Sulfurized fats and oils are obtained by reacting sulfur or sulfur-containing compounds with fats and oils (lard oil, whale oil, vegetable oil, fish oil, etc.), such as sulfurized lard, sulfurized rapeseed oil, sulfurized castor oil, sulfurized soybean oil, and sulfurized rice bran oil. etc. The sulfurized fat may have a crosslinked structure formed by sulfur atoms. The number of sulfur bridges represents the average number of sulfur bridges in the mixture. A compound obtained by sulfurization is usually a mixture of compounds having different numbers of sulfur bridges. Sulfurized oils and fats with an average number of sulfur atoms of 4 or more that form a crosslinked structure are classified as active sulfurized oils and fats that are highly likely to cause copper plate corrosion, and sulfurized oils and fats with an average number of sulfur atoms of 3 or less cause copper plate corrosion. It can be classified as an inert sulfurized fat with a low potential to cause.

[Component (C): Acidic phosphate]
As used herein, "acidic phosphate ester" is represented by the following general formula (2):
(R ³ O) _n P(=O)(OH) _(3-n) (2)
(In formula (2), R ³ represents a hydrocarbyl group having 4 to 30 carbon atoms, n is 1 or 2, and R ³ may be the same or different.)
It is a compound represented by
By including the acidic phosphate of component (C), good positioning accuracy characteristics can be obtained when the lubricating oil composition of the present invention is used as a sliding surface oil.

Specific examples of acidic phosphates of component (C) include monoalkyl acidic phosphates, monoalkenyl acidic phosphates, dialkyl acidic phosphates, dialkenyl acidic phosphates, and mixtures thereof. be done. R ³ of these acidic phosphates may be a linear or branched alkyl or alkenyl group, preferably a linear or branched alkenyl group, more preferably a linear alkenyl group. The number of carbon atoms in R ³ is 4-30, preferably 4-20, more preferably 6-20, still more preferably 8-18. In addition, the number of carbon atoms in two R ³ of the dialkyl acid phosphate and the dialkenyl acid phosphate may be the same or different.

When the number of carbon atoms in the hydrocarbyl group is equal to or less than the above upper limit, the effect of the additive per unit mass increases, and when it is equal to or more than the above lower limit, the solubility in the base oil is further improved.

Acidic phosphates of component (C) include mono-n-oleyl acid phosphate, di-n-oleyl acid phosphate, di-iso-oleyl acid phosphate, mono-n-octyl acid phosphate, di-n-octyl acid phosphate, di-iso- Octyl acid phosphate, mixtures thereof and the like are preferred.

The lubricating oil composition of the present invention preferably contains 0.01% by mass or more, more preferably 0.02% by mass or more, and still more preferably 0.02% by mass or more of the acidic phosphate of component (C), based on the total amount of the composition. 05% by mass or more. The upper limit of component (C) is preferably 4% by mass or less, more preferably 1% by mass or less, and even more preferably 0.4% by mass or less, based on the total amount of the composition. A specific range of the content of component (C) is preferably 0.02% by mass or more and 4% by mass or less, more preferably 0.05% by mass or more and 1% by mass or less, still more preferably, based on the total amount of the composition. It is 0.05 mass % or more and 0.4 mass % or less. When the addition amount of the acidic phosphate of component (C) is equal to or less than the above upper limit value, the flash point can be further increased, and when it is equal to or more than the above lower limit value, better extreme pressure properties can be obtained. Moreover, when used as sliding surface oil, good positioning accuracy characteristics can be obtained.

[Other additives]
The lubricating oil composition of the present invention may optionally contain a phosphate ester. As used herein, the phosphate ester has the following general formula (3):
(R4O) _3P =O( ³ )
[In formula (3), R ⁴ represents a hydrocarbyl group having 1 to 20 carbon atoms, and each R ⁴ may be the same or different. ]
is a compound represented by, preferably an aryl group having 6 to 15 carbon atoms (more preferably an aryl group having 6 to 9 carbon atoms) and an alkyl group having 1 to 20 carbon atoms (which may be linear or branched) , more preferably an alkyl group having 4 to 12 carbon atoms), more preferably an alkyl group having 8 to 12 carbon atoms.

The content of the phosphate ester is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and still more preferably 0.2% by mass or more, based on the total amount of the composition. It is preferably 5% by mass or less, more preferably 3% by mass or less. A specific range of the phosphate ester content is preferably 0.05% by mass or more and 5% by mass or less, more preferably 0.1% by mass or more and 3% by mass or less, based on the total amount of the composition.

In order to further enhance the performance of the lubricating oil composition of the present invention, additives known in the field of lubricating oils can be blended to impart the performance required as a lubricating oil composition.

Such additives include, for example,
Antioxidants such as phenol compounds such as di-tert-butyl-p-cresol and bisphenol A, amine compounds such as phenyl-α-naphthylamine and N,N'-di(2-naphthyl)-p-phenylenediamine ;
oily agents such as carboxylic acids, fatty alcohols, and amines;
metal deactivators such as benzotriazole;
Defoamers such as silicone oil and fluorosilicone oil;
Rust inhibitors such as alkenyl succinic acid, sorbitan monooleate;
Pour point depressants such as polymethacrylates;
Viscosity index improvers such as polybutenes, polyalkylstyrenes, olefin copolymers, styrene-diene copolymers, styrene-maleic anhydride copolymers;
Oil film retention agents for olefinic polymers such as PMA (poly(meth)acrylate), ethylene-propylene copolymers, polybutene and polyisobutylene;
etc.

(Lubricating oil composition)
The lubricating oil composition of the present invention uses a base oil with low kinematic viscosity and has high flash point and extreme pressure properties.
The sulfurized ester of component (B) is highly soluble. Therefore, good extreme pressure properties can be obtained by adding it to the lubricating oil. On the other hand, the addition of sulfurized esters to lubricating oils can lower the flash point.
On the other hand, the use of low viscosity Group III base oils tends to result in poor additive solubility in the base oil. For the lubricating oil composition of the present invention, the optimal combination of base oil and additive was found to solve the problems of the present invention.

(Flash point)
The lubricating oil composition of the present invention preferably has a flash point of 250°C or higher. Some lubricating oil products with a flash point of 250°C or higher are classified as "designated combustible liquids" under the Japanese Fire Service Law, and regulations on storage and management have been greatly relaxed. Therefore, the lubricating oil composition of the present invention can reduce handling costs. The flash point is more preferably 252°C or higher, still more preferably 254°C or higher, and particularly preferably 256°C or higher.

(extreme pressure)
The extreme pressure property can be measured by the method described in Examples below. The lubricating oil composition of the present invention preferably has a weld load (WL) value of 1568 N or more, more preferably 1960 N or more, as measured by the method described in Examples below.
As used herein, extreme pressure properties mean extreme pressure properties measured according to ASTM D2783.

(Kinematic viscosity of lubricating oil composition)
The lubricating oil composition of the present invention has a kinematic viscosity at 40° C. of, for example, 18 mm ² /s or more and 40 mm ² /s or less, preferably 25 mm ² /s or more and 40 mm ² /s or less, more preferably 28 mm ² /s or more and 40 mm ² /s or less, more preferably 30 mm ² /s or more and 40 mm ² /s or less, and particularly preferably 32 mm ² /s or more and 38 mm ² /s or less.

The lubricating oil composition of the present invention can be used for lubrication of sliding parts and power transmission parts of machine tools, and for processing materials such as metals and resins into desired shapes. The lubricating oil compositions of the present invention can be used, for example, as gear oils, bearing oils, sliding surface oils, hydraulic grinding oils, cutting oils, rolling oils, or forging oils.
The lubricating oil composition of the present invention can be suitably used as a lubricating oil composition for sliding surfaces of machine tools. Examples of machine tools in this case include NC machine tools, machining centers, grinding machines, CNCs (Computerized Numerical Control), multitasking machines, and the like. Sliding surfaces include sliding guide surfaces, rolling guide surfaces, and hydrostatic guide surfaces.

Next, the present invention will be described based on examples and comparative examples, but the present invention is not limited by the following examples.

<Combination of lubricating oil>
Lubricating oil compositions for testing were prepared by blending base oils and additives at the blending ratios shown in Tables 1 to 3 for each example and each comparative example. The following evaluations were performed on the obtained lubricating oil composition for test. The evaluation results are shown in Tables 1-3.

(1) Base oil/Base oil 1: Group III base oil Kinematic viscosity 34.0 mm ² /s (40°C), flash point 246°C
・Base oil 2: Group I base oil Kinematic viscosity 31.6 mm ² /s (40°C), flash point 230°C
・Base oil 3: pentaerythritol pelargonate kinematic viscosity 32.2 mm ² /s (40°C), flash point 280°C
・Base oil 4: glycerin tripelargonate kinematic viscosity 15.4 mm ² /s (40°C), flash point 260°C
・Base oil 5: Polyαolefin Kinematic viscosity 42.7 mm ² /s (40°C), flash point 256°C
Base oils were mixed at the mass ratios shown in Tables 1 to 3 to prepare lubricating base oils. In the table, the numerical value of the base oil represents the mass ratio based on the total amount of the base oil.

(2) Additives Additives were added as described in Tables 1-3. The details of the additive are as follows. The amount of base oil (total) and the amount of additives are based on the total amount of the lubricating oil composition.
(B) Sulfurized ester: Sulfurized methyl oleate, average number of sulfur crosslinks 2.4
・(C) Acidic phosphate 1: mixture of mono- and di-n-oleyl acid phosphate ・(C) Acidic phosphate 2: mixture of mono- and di-n-octyl acid phosphate ・Inactive sulfurized oil
・Phosphate ester: Trioctyl phosphate ・Phenolic antioxidant ・Oleylamine
・Metal deactivator: benzotriazole derivative ・Polymer: PMA (weight average molecular weight: 40,000)
・Antifoaming agent: Dimethylpolysiloxane (viscosity 10,000cs)

<Evaluation>
(1) Flash point The flash point of each test lubricating oil composition was measured according to JIS K 2265-4:2007 (open flash point).

(2) Extreme-pressure property In accordance with ASTM D 2783, a high-speed four-ball tester was used to measure the weld load (WL) at 1800 rpm when using each test lubricating oil composition.

(3) Additive solubility 80 mL of each test composition was collected in a transparent glass bottle (capacity: 100 mL), stoppered, and left in a constant temperature bath at 0°C for 30 days in the dark. After that, the appearance was visually confirmed, and those without turbidity or precipitation were regarded as acceptable.

(4) Positioning Accuracy Numerical control is performed to perform fine feed at a fast feed speed (24 m/min) for a total of 20 times, 1 μm in the positive direction every 10 seconds in the Z-axis direction from any coordinate on the NC precision lathe. A command was given, followed by a command to perform a similar minute feed in the negative direction. The actual displacement was measured with a capacitance type displacement meter, and the response accuracy of the guide surface of the lathe to numerical control commands was measured for each lubricating oil.
For the evaluation of the positioning accuracy, the evaluation value was the number of commands required to actually start moving with respect to a command to reverse in the negative direction after sending in the positive direction.
The test was carried out at 25° C., and after sufficient running-in with the test oil, the measurement was repeated three times for each test oil, and the average value was obtained.

The evaluation results of each test lubricating oil composition are shown in Tables 1 to 3 below.

Each of the lubricating oil compositions of Examples 1 to 9 all had a flash point of 250° C. or higher.
Each of the lubricating oil compositions of Examples 1-9 exhibited good extreme pressure properties.
Each of the lubricating oil compositions of Examples 1 to 8 also resulted in good positioning accuracy.

Comparative Example 1, which used a Group I base oil rather than a Group III base oil, resulted in a flash point of 218°C. In Comparative Example 2 in which no sulfurized ester was added, the extreme pressure property was insufficient. In Comparative Example 3, in which only the sulfurized oil was added instead of the sulfurized ester as the sulfur source, the solubility deteriorated, and extreme pressure properties and the like could not be measured. In Comparative Example 4, in which only an acidic phosphoric acid ester was added instead of the sulfurized ester, extreme pressure properties were insufficient.

According to the lubricating oil composition for machine tools and metalworking of the present invention, it is possible to provide a lubricating oil composition for machine tools and metalworking that has a good balance of high flash point and extreme pressure properties.

Claims (7)

(A) a lubricating base oil having a kinematic viscosity at 40° C. of 18 mm ² /s or more and 40 mm ² /s or less;
(B) a sulfurized ester, and
25% by mass or more of the component (A) is a Group III base oil,
Lubricating oil compositions for machine tools and metalworking. The lubricating oil composition for machine tools and metalworking according to claim 1, containing 80% by mass or more and 99% by mass or less of component (A) based on the total amount of the composition. 3. The lubricating oil composition for machine tools and metalworking according to claim 1, further comprising (C) an acidic phosphate ester. The lubricating oil composition for machine tools and metalworking according to any one of claims 1 to 3, wherein 1% by mass or more and 70% by mass or less of the component (A) is a synthetic base oil. The lubricating oil composition for machine tools and metalworking according to any one of claims 1 to 4, containing 80% by mass or more and 95% by mass or less of component (A) based on the total amount of the composition. The lubricating oil composition for machine tools and metalworking according to any one of claims 1 to 5, wherein 50 mass% or more of said component (A) is Group III base oil. The lubricating oil composition for machine tools and metalworking according to any one of claims 1 to 6, which is used for sliding surfaces.