Lubricating oil

Abstract

To provide a lubricating oil that can reduce friction losses in sliding portions of components even when Ca-based detergents are added.SOLUTION: The lubricating oil comprises a base oil, carbon-based nanoparticles, and a neutral Ca-based detergent.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to lubricating oils. [Background technology]

[0002] Conventionally, methods for reducing friction loss in automotive internal combustion engines have been to smooth the sliding parts of components or to apply diamond-like carbon films to those parts. On the other hand, it is also known that the coefficient of friction can be reduced by adding carbon-based nanoparticles to lubricating oil (see, for example, Patent Document 1).

[0003] Patent Document 1 describes a lubricating oil in which fullerenes, which are carbon-based nanoparticles, an oiliness agent, and a Ca-based detergent, which is a metal-based detergent, are added to a polyalphaolefin base oil. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-141049 Summary of the Invention [Problem to be solved by the invention]

[0005] Additives are added to lubricating oils to improve the properties of the base oil or to add new performance to the base oil. Carbon-based nanoparticles are added to reduce friction between sliding parts. Detergents such as Ca-based detergents prevent the formation of sludge and other substances that occur during the use of lubricating oils. Basic detergents capable of neutralizing acids are often used as such detergents. However, adding such basic Ca-based detergents and carbon-based nanoparticles to lubricating oils simultaneously can result in the loss of the friction-reducing effect of the carbon-based nanoparticles.

[0006] The present invention has been made in view of the above problems, and an object of the present invention is to provide a lubricating oil that is capable of reducing friction loss in sliding parts even when a Ca-based detergent is added. [Means for solving the problem]

[0007] The lubricating oil according to the present invention is characterized by comprising a base oil, carbon-based nanoparticles, and a neutral Ca-based detergent.

[0008] According to this configuration, even if a Ca-based detergent is added to a lubricating oil containing carbon-based nanoparticles, a lubricating oil that exhibits a friction-reducing effect can be obtained. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 10 is a diagram showing the results of a friction test according to an example of the present invention. [Figure 2] FIG. 1 is a diagram showing the friction coefficient and the composite surface roughness of a test piece after a friction test according to an example of the present invention. [Figure 3] FIG. 1 is a diagram showing the Ca distribution depth and the friction coefficient according to an example of the present invention. [Figure 4] FIG. 10 is a diagram showing the distribution of Ca after a friction test according to an example of the present invention. [Figure 5] FIG. 10 is a diagram showing the distribution of Ca after a friction test according to an example of the present invention. [Figure 6] FIG. 10 is a diagram showing the distribution of Ca after a friction test according to a comparative example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the lubricating oil according to the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments, and various modifications are possible without departing from the spirit of the present invention.

[0011] The lubricating oil according to the present invention is used, for example, as a lubricating oil for automobiles, ships, and industries, specifically as an engine oil supplied to an automobile internal combustion engine, gear oil, automotive grease, etc.

[0012] The lubricating oil according to the present invention contains a base oil. Examples of base oils include carbonate ester compounds, ester-based synthetic oils such as polyol ester oils, ether-based synthetic oils such as alkyl diphenyl ethers, synthetic hydrocarbon oils such as polyalphaolefins, and mineral oils such as paraffin-based mineral oils, with synthetic hydrocarbon oils being preferred. Synthetic hydrocarbon oils have a molecular structure consisting of carbon and hydrogen, and examples include polyolefins such as polyalphaolefins, polybutene, and polyethylene, and copolymers of alphaolefins and ethylene. These mineral oils and synthetic oils may be used alone, or two or more selected from them may be mixed in any ratio.

[0013] The lubricating oil according to the present invention contains carbon-based nanoparticles. Examples of carbon-based nanoparticles include nanodiamonds, fullerenes, graphene, carbon nanotubes, and carbon nanofibers. The carbon-based nanoparticles may have chemically modified surfaces. Carbon-based nanoparticles have carbon double bonds on their surface, and it is known that friction causes the formation of hydroxyl functional groups on the carbon. Furthermore, carbon-based nanoparticles aggregate to form aggregates in the lubricating oil. Therefore, when carbon-based nanoparticles are added to a base oil, hydrogen bonds are formed between the hydroxyl groups formed on the surface layer of the carbon-based nanoparticle aggregates and polar water or oily agents, generating secondary particles, and forming a low-shear layer on the surface layer of the aggregates. This is thought to reduce friction between sliding surfaces.

[0014] The carbon nanoparticles are preferably fullerenes. There are no particular limitations on the structure or production method of fullerenes, and various types can be used. However, C 60 , C 70 Among fullerenes, C is preferred from the viewpoint of high solubility in lubricating oil. 60 and C 70 is preferred, and C 60 is more preferable. 70Alternatively, a residue obtained after purifying fullerenes may be used as the carbon-based nanoparticles.

[0015] The fullerene content in the lubricating oil is preferably 0.05 to 0.15% by weight, because a fullerene content of 0.05% by weight or more allows a low shear layer to be formed, thereby enabling the lubricating oil to exhibit a friction-reducing effect, and a fullerene content of 0.15% by weight or less prevents fullerenes from excessively agglomerating and precipitating.

[0016] The lubricating oil according to the present invention may contain glycerin monooleate. Glycerin monooleate acts as a dispersant and friction modifier. This allows carbon-based nanoparticles to be uniformly dispersed in the lubricating oil, and hydrogen bonds are formed between the carbon-based nanoparticles and glycerin monooleate, facilitating the formation of a uniform low-shear layer in the lubricating oil. Furthermore, adsorption of glycerin monooleate onto the surfaces of sliding parts of components suppresses contact between the sliding parts at a macro level. Micro-level, a low-shear layer is formed on the surfaces of sliding parts of components due to intermolecular forces between the adsorbed glycerin monooleate on the surface and the base oil, and hydrogen bonds between the glycerin monooleate and the carbon-based nanoparticles. The amount of glycerin monooleate is preferably 5 to 20 times the amount of carbon-based nanoparticles. By including glycerin monooleate in an amount of 5 or more times the amount of carbon-based nanoparticles, a low-shear layer can be efficiently formed. Furthermore, by including glycerin monooleate in an amount of 20 or less times the amount of carbon-based nanoparticles, excessive dispersion of the carbon-based nanoparticles can be suppressed.

[0017] The content of glycerin monooleate in the lubricating oil is preferably 0.5 to 2.0% by weight, and more preferably 0.7 to 1.5% by weight. When the content of glycerin monooleate is 0.5% by weight or more, a low shear layer can be efficiently formed, and when the content is 2.0% by weight or less, aggregation of glycerin monooleate can be suppressed.

[0018] The lubricating oil according to the present invention also contains a neutral Ca (calcium)-based detergent. The neutral Ca-based detergent functions as a detergent and a dispersant. Examples of neutral Ca-based detergents include neutral Ca sulfonates, neutral Ca phenates, and neutral Ca salicylates, with neutral Ca sulfonates being preferred. The neutral Ca sulfonate of the present invention refers to a Ca sulfonate having a total base number (TBN) of 50 KOH / g or less, such as a Ca sulfonate having a total base number of 20 KOH / g. The total base number of the Ca sulfonate of the present invention is a value measured in accordance with JIS K2501.

[0019] Basic Ca-based detergents commonly used as additives in engine oils and other applications are composed of neutral Ca sulfonates, neutral Ca phenates, or neutral Ca salicylates dispersed in oil with alkaline earth metals. These detergents possess high acid-neutralizing properties as overbased detergents. Specifically, basic Ca sulfonates are neutral Ca sulfonates in which alkali is uniformly dispersed as fine particles of calcium hydroxide or calcium carbonate. Adding such basic Ca sulfonates to lubricating oils containing carbon-based nanoparticles can hinder the friction-reducing effects of carbon-based nanoparticles and glycerin monooleate. In particular, when basic Ca sulfonates are added to lubricating oils containing glycerin monooleate, a Ca film is likely to form on the surfaces of sliding parts. This Ca film inhibits the adsorption of glycerin monooleate, making it difficult to form a low-shear layer on the surfaces of the sliding parts. Furthermore, a thick Ca film may inhibit the so-called break-in between two surfaces, making it difficult to flatten the surfaces of the sliding parts. On the other hand, when a neutral Ca-based detergent is added to a lubricating oil containing carbon-based nanoparticles and glycerin monooleate, the friction-reducing effects of the carbon-based nanoparticles and glycerin monooleate are not impaired. This is thought to be because the neutral Ca-based detergent does not easily form a Ca film on the surfaces of the sliding parts of the parts, and does not inhibit the formation of a low-shear layer by fullerenes and glycerin monooleate.

[0020] The neutral Ca-based detergent is preferably contained in an amount 0.5 to 10 times the amount of carbon-based nanoparticles. When the neutral Ca-based detergent is contained in an amount 0.5 times or more the amount of carbon-based nanoparticles, a friction reduction effect and a base oil cleaning effect can be obtained, and when the neutral Ca-based detergent is contained in an amount 10 times or less the amount of carbon-based nanoparticles, the formation of a low shear layer by the carbon-based nanoparticles is not inhibited.

[0021] The content of the neutral Ca-based detergent in the lubricating oil is preferably 0.05 to 1.00% by weight. When the content of the neutral Ca-based detergent is 0.05% by weight or more, the friction reducing effect and the cleaning effect of the base oil can be obtained, and when the content is 1.00% by weight or less, the formation of the low shear layer is not inhibited.

[0022] In addition to the additives described above, the lubricating oil may contain an antioxidant, an anti-wear agent, a viscosity index improver, etc. The balance of these additives is the content of the base oil.

[0023] [Example] Examples of the lubricating oil according to the present invention will be described below, but the present invention is not limited to these examples.

[0024] Example 1 A lubricating oil was prepared by adding powdered fullerenes as carbon nanoparticles and neutral Ca sulfonate as a neutral Ca-based detergent to a polyalphaolefin base oil. The neutral Ca sulfonate in Example 1 had a total base number of 20 KOH / g. The fullerenes were added in an amount of 0.1 wt %, and the neutral Ca sulfonate in an amount of 0.3 wt %. After the additives were added, ultrasonic dispersion was performed four times for 480 seconds using an ultrasonic cleaner.

[0025] Example 2 A lubricating oil was prepared in the same manner as in Example 1, except that 1% by weight of glycerin monooleate was added.

[0026] Example 3 A lubricating oil was prepared in the same manner as in Example 2, except that the amount of neutral Ca sulfonate added was 0.5 wt %.

[0027] (Comparative Example) Comparative Example 1 was prepared as a lubricating oil without adding any additives to polyalphaolefin. Comparative Example 2 was prepared in the same manner as Example 1, except that fullerene was not added. Comparative Example 3 was prepared in the same manner as Example 2, except that a neutral Ca-based detergent was not added. Comparative Example 4 was prepared in the same manner as Example 2, except that 0.1 wt% of a basic Ca sulfonate was added instead of the neutral Ca sulfonate. The basic Ca sulfonate in the comparative example has a total base number of 300 KOH / g. Similarly, Comparative Example 5 was prepared in the same manner as Example 2, except that 0.2 wt% of a basic Ca sulfonate was added instead of the neutral Ca-based detergent. Comparative Example 6 was prepared in the same manner as Example 2, except that 0.3 wt% of a basic Ca sulfonate was added instead of the neutral Ca-based detergent. The amounts of fullerene and other additives added to the polyalphaolefin in the examples and comparative examples are shown in Table 1.

[0028] [Table 1]

[0029] Friction tests were conducted for each of Examples 1 to 3 and Comparative Examples 1 to 6. For Examples 2 to 3 and Comparative Examples 3 to 6, the surface roughness of the test specimens was measured after the wear test. The wear test was conducted using a ring-on-disk method, with SCM440 as the disk test specimen, having a surface roughness of Ra 0.05 and a hardness of HRC 48 to 50. The ring test specimen was a hollow cylinder (Φ20 / Φ30) made of S45C hardened steel, having a surface roughness of Ra 0.3 and a hardness of HRC 45. The test was conducted in lubricating oil at room temperature under a load of 25 kgf and a rotation speed of 60 rpm.

[0030] The surface roughness was measured in accordance with JIS B 0633 using a laser microscope (OLS4000-SAT manufactured by Olympus) to examine the wear tracks on the disk and ring test pieces after the wear test. The measurement direction was perpendicular to the sliding direction of the wear tracks, and the magnification was 50x. The composite surface roughness was then calculated from the arithmetic mean roughness of the disk test piece and the arithmetic mean roughness of the ring test piece.

[0031] FIG. 1 shows the results of friction tests for Examples 1 to 3 and Comparative Examples 1 and 2. Compared with Comparative Examples 1 and 2, the friction coefficient of Example 1 is smaller, demonstrating that adding neutral Ca sulfonate and carbon-based nanoparticles to a lubricating oil can reduce friction. Furthermore, comparing Examples 1 and 2, it is clear that adding glycerin monooleate can reduce the friction coefficient. Since the friction coefficients of Examples 1 and 3 are comparable, it is suggested that even if the amount of neutral Ca sulfonate added is increased, the addition of glycerin monooleate can suppress an increase in the friction coefficient.

[0032] Figure 2 is a graph showing the composite surface roughness after wear testing for Examples 2-3 and Comparative Examples 3-6, plotted on the horizontal axis and the friction coefficient on the vertical axis. Since the friction coefficient of Example 2 was equivalent to that of Comparative Example 3, the addition of neutral Ca sulfonate resulted in a lubricating oil with good friction-reducing effects. On the other hand, the friction coefficients of Comparative Examples 4-6, which contained basic Ca sulfonate, were higher than those of Comparative Example 3, indicating that the addition of basic Ca sulfonate worsened the friction-reducing effect of the lubricating oil. Although the amounts of Ca sulfonate added in Example 2 and Comparative Example 6 were the same, Example 2 exhibited a friction coefficient equivalent to that of Comparative Example 3, suggesting that neutral Ca sulfonate does not inhibit the formation of a low-shear layer due to fullerene or glycerin monooleate. Furthermore, Example 3, which contained a greater amount of neutral Ca sulfonate than Example 2, also exhibited a lower friction coefficient than Comparative Examples 4-6. This indicates that the addition of neutral Ca sulfonate to a lubricating oil containing carbon-based nanoparticles resulted in a lubricating oil that could achieve cleaning effects without impairing the friction-reducing effect.

[0033] Furthermore, in order to evaluate the Ca coating on the surface of the disk test specimens after the friction test for Examples 2 and 3 and Comparative Examples 4 and 6, the Ca distribution depth was examined by Auger spectroscopic depth profile analysis for the disk test specimens after the friction test. The Ca distribution depth was taken as the average value within the measurement field of view. Furthermore, for Examples 2 and 3 and Comparative Example 6, the Ca distribution on the surface of the disk test specimens after the friction test was examined by Auger spectroscopic analysis.

[0034] Figure 3 is a graph with the Ca distribution depth on the horizontal axis and the friction coefficient on the vertical axis. As shown in Figure 3, the Ca distribution depth in Examples 2 and 3 is smaller than that in Comparative Examples 4 and 6. Furthermore, as shown in Examples 2 and 3, the Ca distribution depth was constant for neutral Ca sulfonate regardless of its added amount. On the other hand, as shown in Comparative Examples 4 and 6, it was suggested that the Ca distribution depth increased with increasing added amount of basic Ca sulfonate, and that the friction coefficient increased as the Ca distribution depth increased.

[0035] 4 to 6 show the distribution of Ca on the surfaces of disk test specimens after friction tests according to Examples 2 and 3 and Comparative Example 6. Ca is distributed in the white areas in FIGS. 4 to 6. While Ca is present locally in FIG. 4, it is present throughout the entire surface in FIG. 5, suggesting that a larger amount of neutral Ca sulfonate added facilitates the formation of a uniform Ca film on the surface of the sliding part of the component. Furthermore, as shown in FIG. 6, Ca is also distributed throughout the entire test specimen in Comparative Example 6, suggesting that the greater the amount of Ca added in the lubricating oil, regardless of whether it is neutral or basic, the more uniform the Ca film is formed on the surface of the sliding part of the component. Therefore, it is believed that the greater the Ca content in the lubricating oil, the more likely a Ca film is formed on the entire surface, which inhibits the adsorption of glycerin monooleate to the surface of the sliding part of the component, suppressing the formation of a shear layer and surface flattening, thereby increasing the friction coefficient. From the above, it was found that adding a neutral Ca-based detergent to a lubricating oil can suppress the increase in the thickness of the Ca film on the surface of the sliding parts of parts and allow the Ca to exist locally, making it possible to obtain a lubricating oil that can reduce friction loss in the sliding parts of parts even when a Ca-based detergent is added.

[0036] In the above-described embodiment, the following configurations are envisioned. (1) A lubricating oil comprising a base oil, carbon-based nanoparticles, and a neutral Ca-based detergent.

[0037] According to this configuration, even if a Ca-based detergent is added to a lubricating oil containing carbon-based nanoparticles, a lubricating oil that exhibits a friction-reducing effect can be obtained.

[0038] (2) It is preferable that the lubricating oil of (1) further contains glycerin monooleate.

[0039] According to this configuration, a low shear layer is easily formed between the carbon-based nanoparticles and the glycerin monooleate, making it possible to reduce the friction coefficient of the lubricating oil.

[0040] (3) In the lubricating oil of (1) or (2), it is preferable that the carbon-based nanoparticles are fullerenes and the neutral Ca-based detergent is a neutral Ca sulfonate.

[0041] According to this configuration, by using fullerene as carbon nanoparticles, secondary particles of fullerene and glycerol monooleate are easily formed in the lubricating oil, and the low shear layer can be efficiently formed. In addition, by using neutral Ca sulfonate, which is widely used as a neutral Ca-based detergent, it is possible to impart the cleaning effect of the base oil to the lubricating oil.

[0042] In the lubricating oil of (4)(3), it is preferable that the amount of glycerin monooleate is 5 to 20 times the amount of fullerene, and the amount of neutral Ca sulfonate is 0.5 to 10 times the amount of fullerene.

[0043] According to this configuration, by including 5 to 20 times the amount of glycerin monooleate relative to fullerene, a low shear layer can be efficiently formed. Also, by including 0.5 to 10 times the amount of neutral Ca sulfonate relative to fullerene, it is possible to obtain the cleaning effect of the base oil and reduce friction loss.

[0044] (5) In the lubricating oil of (3) or (4), it is preferable that the fullerene content is 0.05 to 0.15 wt %, the glycerin monooleate content is 0.5 to 2.0 wt %, and the neutral Ca sulfonate content is 0.05 to 1.00 wt %.

[0045] According to this configuration, even if a Ca-based detergent is added, it is possible to form a lubricating oil that can reduce friction loss in the sliding parts. [Industrial Applicability]

[0046] The present invention is applicable to lubricating oils containing carbon-based nanoparticles.

Claims

1. A lubricating oil comprising a base oil, carbon-based nanoparticles, and a neutral Ca-based detergent.

2. 10. The lubricating oil of claim 1, further comprising glycerol monooleate.

3. the carbon-based nanoparticles are fullerenes, 3. The lubricating oil according to claim 2, wherein the neutral Ca-based detergent is a neutral Ca sulfonate.

4. The amount of the glycerin monooleate is 5 to 20 times the amount of the fullerene, 4. The lubricating oil according to claim 3, wherein the neutral Ca sulfonate is contained in an amount of 0.5 to 10 times the amount of the fullerene.

5. the fullerene content is 0.05 to 0.15 wt %, The content of the glycerin monooleate is 0.5 to 2.0% by weight, 5. The lubricating oil according to claim 3, wherein the content of the neutral Ca sulfonate is 0.05 to 1.00% by weight.

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