JP2020158783A - Method for producing lubricating oil composition - Google Patents

Abstract

To provide a method of inspecting a lubricating oil composition, which can stably reproduce wear resistance characteristics, even of a fullerene-contaianing lubricating oil composition, by using a method that is relatively easy to measure, and a method for producing a lubricating oil composition.SOLUTION: There is provided a method of inspecting a lubricating oil composition, in which a dynamic surface tension (Σ) of a lubricating oil composition containing a base oil and fullerene are measured, and a lubricating oil composition is selected on the basis of a predetermined range set by a correlation between measured values of the dynamic surface tensions (Σ) and measured values of wear coefficients of the lubricating oil composition.SELECTED DRAWING: None

Description

The present invention relates to a method for producing a lubricating oil composition.
The present application claims priority based on Japanese Patent Application No. 2018-220721 filed in Japan on November 26, 2018, the contents of which are incorporated herein by reference.

In recent years, with the increase in speed, efficiency, and energy saving, there is a strong demand for improving the performance of lubricating oils used in automobiles, home appliances, industrial machines, and the like. Various additives such as antioxidants, extreme pressure additives, rust preventive additives, and corrosion inhibitors are blended in the lubricating oil composition in order to improve the properties to suit the application.

In order to meet these demands, in order to simultaneously improve multiple performances such as low friction, torque increase, and fuel saving, lubricating base oils such as mineral oil and ester oil, fullerene, which is nanocarbon particles, organic solvent, and viscosity index improvement. An additive composition for an engine lubricating oil containing an agent, an abrasion modifier, and a cleaning dispersant is known (see, for example, Patent Document 1).

Further, fullerenes may be added to the lubricating oil composition used in the refrigerant compressor (see, for example, Patent Document 2).

Generally, an important property of a lubricating oil composition is a wear coefficient or the like, but it is troublesome to measure. Therefore, in the manufacturing process of the lubricating oil composition, the properties of the lubricating oil composition are specified by using the density, kinematic viscosity, viscosity index, pour point, total oxidation, etc., which are easy to measure, as indexes (for example, non-lubricating oil composition). See Patent Document 1).

Japanese Unexamined Patent Publication No. 2008-266501 International Publication No. 2017/141825

Internet <URL: https://www.noe.jxtg-group.co.jp/english/products/lubricants/industrial.html>

However, in the system in which fullerene is added to the lubricating oil composition described in Non-Patent Document 1 and the like, a product that stably reproduces the lubricating characteristics such as the wear coefficient can be obtained even if the product is managed by the above index. I couldn't. That is, even when the characteristics of the product are quantified by the above index and the product within a certain range is accepted, the lubrication characteristics may vary beyond the permissible range.
Further, by measuring the lubrication characteristics of the product of the lubricating oil composition, it is possible to select products having the lubrication characteristics within the allowable range. For that purpose, a wear test such as a ball-on-disk is performed for each product lot. There is a need. In this case, it takes time and effort, and the cost of the test board and the like increases, so that the wear test is not suitable for each production lot.

The present invention has been made in view of the above circumstances, and even a lubricating oil composition containing fullerene can stably reproduce wear resistance characteristics by using a method that is relatively easy to measure. It is an object of the present invention to provide a method for inspecting a lubricating oil composition and a method for producing a lubricating oil composition.

The present invention provides the following means for solving the above problems.
[1] The dynamic surface tension (Σ) of the lubricating oil composition containing the base oil and fullerene is measured, and the measured value of the dynamic surface tension (Σ) and the measured value of the wear coefficient of the lubricating oil composition An inspection step of selecting a lubricating oil composition into a passing lubricating oil composition and a failing lubricating oil composition based on a predetermined range set by the correlation of the above, and a failing product obtained in the inspection step. A method for producing a lubricating oil composition, which comprises a readjustment step of mixing the lubricating oil composition of the above product with the lubricating oil composition of a passing product and performing the inspection step again to obtain a lubricating oil composition of a passing product.
[2] The method for producing a lubricating oil composition according to the above [1], wherein the dynamic surface tension (Σ) is measured by the Wilhelmj plate method.
[3] The method for producing a lubricating oil composition according to the above [2], wherein the dynamic surface tension (Σ) is calculated by any of the following calculation methods (A) and (B).
(A) The magnitude of the force required to pull the substrate out of the liquid of the lubricating oil composition (| LA |) and the magnitude of the force required to submerge the substrate in the liquid of the lubricating oil composition (| LA |). One of | LB |) is defined as the dynamic surface tension (Σ).
(B) Let the difference in magnitude of the force (| LA |-| LB |) be the dynamic surface tension (Σ).
[4] The method for producing a lubricating oil composition according to the above [1], wherein the dynamic surface tension (Σ) is measured by the maximum foam pressure method.
[5] The lubricating oil composition according to the above [4], wherein the dynamic surface tension (Σ) is calculated by any of the following calculation methods (C), (D), (E), and (F). Manufacturing method.
(C) A gas is introduced into a hollow tube arranged in the liquid of the lubricating oil composition, and the gas is introduced.
Bubble lifetime (Tw), which indicates the time from the generation of bubbles at the lower end of the hollow tube to the maximum pressure for introducing gas, and surface tension (σ) (σ = ΔP × γ/2). , ΔP is the difference between the maximum value P _max and the minimum value P _min of the pressure of the gas in the periodic pressure fluctuation, and γ is the cross-sectional area of the hollow portion of the hollow tube).
The surface tension (σ _s ) when the bubble lifetime (Tw) is the minimum value (Tw _min ) is defined as the dynamic surface tension (Σ).
(D) The surface tension when the bubble lifetime (Tw) is the minimum value (Tw _min ) with respect to the surface tension (σ _f ) when the bubble lifetime (Tw) is the maximum value (Tw _max ). The ratio of (σ _s ) (σ _s / σ _f ) is defined as the dynamic surface tension (Σ).
(E) The surface tension (σ) near the minimum value (Tw _min ) of the bubble lifetime (Tw) is linearly approximated, and the obtained linear gradient (S) is referred to as the dynamic surface tension (Σ). To do.
(F) The ratio (S / σ _f ) of the gradient S to the surface tension (σ _f ) is defined as the dynamic surface tension (Σ).
[6] In the inspection step, the dynamic surface tension (Σ) of the lubricating oil composition produced in a plurality of different batches is measured and mixed in the readjustment step. The method for producing a lubricating oil composition according to any one of the above [1] to [5], wherein the acceptable lubricating oil composition includes the lubricating oil compositions produced in the plurality of different batches.

According to the present invention, even in a lubricating oil composition containing fullerene, an inspection method and lubrication of a lubricating oil composition capable of stably reproducing wear resistance characteristics by using a method that is relatively easy to measure. A method for producing an oil composition can be provided.

FIG. 1 is a graph showing the relationship between the bubble lifetime (Tw) and the surface tension (σ) of a lubricating oil composition in which fullerenes are dissolved in mineral oil in the maximum foam pressure method. FIG. 2 shows the surface tension (σ _s ) when the bubble lifetime (Tw) is the minimum value (Tw _min ) and the surface tension (σ _s ) when the bubble lifetime (Tw) is the maximum value (Tw _max ). It is a graph which shows _f )). FIG. 3 is a graph showing the gradient (S) of the approximate straight line of the plot near the minimum bubble lifetime (Tw). FIG. 4 is a graph showing the relationship between the dynamic surface tension (Σ) and the abrasion coefficient measured by the Wilhelmj plate method in the examples. FIG. 5 is a graph showing the relationship between the dynamic surface tension (Σ) and the abrasion coefficient measured by the maximum foam pressure method in the examples. FIG. 6 is a graph showing the relationship between the kinematic viscosity and the abrasion coefficient in the comparative example.

Hereinafter, a method for inspecting the lubricating oil composition and a method for producing the lubricating oil composition according to the embodiment of the present invention will be described. It should be noted that the present embodiment is specifically described in order to better understand the gist of the invention, and is not limited to the present invention unless otherwise specified.

[Inspection method for lubricating oil composition]
In the method for inspecting the lubricating oil composition according to the present embodiment, the dynamic surface tension Σ of the lubricating oil composition containing the base oil and fullerene is measured, the measured value of the dynamic surface tension Σ and the wear of the lubricating oil composition. This is a method of selecting a lubricating oil composition based on a predetermined range set by correlation with a measured value of a coefficient.

(Lubricating oil composition)
The lubricating oil composition inspected by the method for inspecting the lubricating oil composition according to the present embodiment contains a base oil and a fullerene.

(Base oil)
The base oil contained in the lubricating oil composition in the present embodiment is not particularly limited, and usually, mineral oils and synthetic oils widely used as base oils for lubricating oils are preferably used.

Mineral oils used as lubricating oils are generally those in which carbon-carbon double bonds contained therein are saturated by hydrogenation and converted into saturated hydrocarbons. Examples of such mineral oils include paraffin-based base oils and naphthenic base oils.

Examples of synthetic oils include synthetic hydrocarbon oils, ether oils, ester oils and the like. Specifically, polyα-olefin, diester, polyalkylene glycol, polyalphaolefin, polyalkyl vinyl ether, polybutene, isoparaffin, olefin copolymer, alkylbenzene, alkylnaphthalene, diisodecyl adipate, monoester, dibasic acid ester, tribasic acid. Esters, polyol esters (trimethylolpropane caprilate, trimethylolpropane pelargonate, pentaerythritol 2-ethylhexanoate, pentaerythritol pelargonate, etc.), dialkyldiphenyl ether, alkyldiphenyl sulfide, polyphenyl ether, silicone lubricating oil (dimethyl silicone) Etc.), perfluoropolyether and the like are preferably used. Among these, polyα-olefins, diesters, polyol esters, polyalkylene glycols, and polyalkyl vinyl ethers are more preferably used.

One of these mineral oils and synthetic oils may be used alone, or two or more selected from these may be mixed and used at an arbitrary ratio.

(Fullerene)
The fullerene contained in the lubricating oil composition in the present embodiment is not particularly limited in structure and production method, and various fullerenes can be used. Examples of fullerenes include C ₆₀ and C ₇₀ , which are relatively easily available, higher-order fullerenes, and mixtures thereof.
Among fullerenes, C ₆₀ and C ₇₀ are preferable from the viewpoint of high solubility in lubricating oil, and C ₆₀ is more preferable from the viewpoint of less coloring in lubricating oil. In the case of a mixture, it is preferable that C ₆₀ is contained in an amount of 50% by mass or more.

Further, the fullerene may be chemically modified for the purpose of further enhancing the solubility in the base oil. Examples of the chemically modified fullerene include methanofullerene, phenyl C61 butyric acid methyl ester ([60] PCBM), diphenyl C62 dibutyric acid methyl ester (= Bis [60] PCBM), and phenyl C71 butyric acid methyl ester ([70] PCBM). ), Phenyl C85 butyric acid methyl ester ([85] PCBM), phenyl C61 butyric acid butyl ester ([60] PCBB), phenyl C61 butyric acid octyl ester ([60] PCBO), inden adduct of fullerene, fullerene hydroxide, fullerene. Examples thereof include pyrrolidine derivatives.

(Additive)
In addition to the base oil and fullerene, the lubricating oil composition in the present embodiment may contain additives as long as the effects of the present embodiment are not impaired.
The additives to be blended in the lubricating oil composition in the present embodiment are not particularly limited. Examples of the additive include a commercially available antioxidant, a viscosity index improver, an extreme pressure additive, a cleaning dispersant, a pour point lowering agent, a corrosion inhibitor, a solid lubricant, an oiliness improver, a rust preventive additive, and an anti. Examples thereof include emulsifiers, antifoaming agents and hydrolysis inhibitors. One of these additives may be used alone, or two or more of these additives may be used in combination.

As the additive, a compound having an aromatic ring is preferable because fullerene is easily dissolved and the like.
Examples of the antioxidant having an aromatic ring include dibutylhydroxytoluene (BHT), butylhydroxyanisole (BHA), 2,6-di-tert-butyl-p-cresol (DBPC), and 3-arylbenzofuran-2. Examples thereof include −one (intramolecular cyclic ester of hydroxycarboxylic acid), phenyl-α-naphthylamine, dialkyldiphenylamine, and benzotriazole.
Examples of the viscosity index improver having an aromatic ring include polyalkylstyrene, a hydride additive of a styrene-diene copolymer, and the like.
Examples of the extreme pressure additive having an aromatic ring include dibenzyldisulfide, allyl phosphate, allyl subphosphate, allyl phosphate amine salt, allyl thiophosphate, allyl thiophosphate amine salt, and naphthenic acid. Be done.
Examples of the clean dispersant having an aromatic ring include benzylamine succinic acid derivatives, alkylphenol amines and the like.
Examples of the pour point lowering agent having an aromatic ring include a chlorinated paraffin-naphthalene condensate, a chlorinated paraffin-phenol condensate, and a polyalkylstyrene type.
Examples of the anti-emulsifier having an aromatic ring include alkylbenzene sulfonate and the like.
Examples of the corrosion inhibitor having an aromatic ring include dialkylnaphthalene sulfonate and the like.

The lubricating oil composition in the present embodiment is plastically processed such as industrial gear oil, hydraulic hydraulic oil, compressor oil, refrigerating machine oil, cutting oil, rolling oil, pressing oil, forging oil, drawing oil, drawing oil, punching oil and the like. It can be used for various purposes such as metal processing oils such as oils, heat treatment oils and discharge processing oils, slip guide surface oils, bearing oils, rust preventive oils and heat transfer oils.

(Inspection method)
In the method for inspecting the lubricating oil composition of the present embodiment, for example, the dynamic surface tension (Σ) of the lubricating oil composition is measured by the Wilhelmy plate method or the maximum foam pressure method. By adding fullerene to the base oil, the expression or change of dynamic surface tension (Σ) is measured.

(Measurement of dynamic surface tension (Σ) by Wilhelmj plate method)
As the first measuring method, the dynamic surface tension (Σ) of the lubricating oil composition can be measured by the Wilhelmi plate method using a surface tension measuring device. Hereinafter, the downward force is considered as positive.
In the Wilhelmj plate method, the substrate (rectangular parallelepiped plate) is first fixed to the stylus. The downward force observed in this state is the weight of the plate. Here, the downward force (F) acting on the substrate is defined as zero. Next, the substrate is submerged in the liquid of the lubricating oil composition. At this time, the force (F) acting on the substrate is the sum of the upward force (L: L <0 at this time) that pushes the substrate out of the liquid due to surface tension and the upward buoyancy (Shρg) that acts on the substrate. The force (F) is measured with respect to the immersion distance (h) of the substrate. Next, after the substrate reaches a certain depth, the substrate is pulled up. Also at this time, a downward force (L: L> 0 at this time) is generated on the substrate due to surface tension.
The relationship between the force (F) and the immersion distance (h) obtained from the result of this measurement is F = L-Shρg (where L is the force acting on the substrate due to surface tension, and S is the cross-sectional area of the substrate (bottom of the substrate). Area), h is the immersion distance of the substrate, ρ is the density of the lubricating oil composition, and g is the gravitational acceleration). Buoyancy (upward force) is represented by −Shρg. L can be calculated by measuring the force (F) acting on the substrate and the immersion distance (h) using this formula. Normally, the force (L) when sinking the substrate is a negative value (upward force), and the force (L) when pulling out is a positive value.

In the present embodiment, the dynamic surface tension (Σ) can be calculated by any of the following methods (A) and (B) by the Wilhelmj plate method using the above formula.
(A) The magnitude of the force required to pull the substrate out of the liquid of the lubricating oil composition (| LA |) and the magnitude of the force required to submerge the substrate in the liquid of the lubricating oil composition (| LA |). One of | LB |) is defined as the dynamic surface tension (Σ).
(B) Let the difference in magnitude of the force (| LA |-| LB |) be the dynamic surface tension (Σ). At this time, the pulling speed and the pulling speed for measuring | LA | and | LB | are measured at the same speed.

The force (L = LA or LB) is calculated by subtracting the buoyancy acting on the substrate from the force (F) acting on the substrate by the above formula.

The dynamic surface tension (Σ) by the Wilhelmj plate method can be controlled by the pulling speed and pulling speed of the substrate. As the pulling speed and the pulling speed of the substrate are increased, the difference in the magnitude of the above forces (| LA |-| LB |) becomes large, and the difference between the lubricating oil compositions becomes remarkable. Therefore, the dynamic surface tension There is an advantage that the determination of the lubricating oil composition (selection of pass / fail, etc.) by (Σ) becomes easy. On the other hand, since the interval of the immersion distance (h) to be measured becomes wide, the number of measurement points may decrease, and the force (LA) or (LB) may vary, resulting in a decrease in accuracy.
Therefore, there is an optimum range for the pulling speed and the pulling speed of the substrate, and the speed is preferably 0.1 mm / sec or more and 5 mm / sec or less, more preferably 0.2 mm / sec or more and 2 mm / sec or less, and further. It is preferably 0.5 mm / sec or more and 1 mm / sec or less.

The material of the substrate is not particularly limited, but metal, ceramics, glass and the like can be used. Further, the material of the substrate is preferably the same as the material of the mechanical parts to which the lubricating oil composition is applied. For example, when the lubricating oil composition is used in a gas compression device, a liquid compression device, a gas decompression device, an internal combustion engine, or the like, the material of the substrate is preferably iron, aluminum, or stainless steel.
Further, the surface of the substrate is preferably smooth, and more preferably mirror-polished.

(Measurement of dynamic surface tension (Σ) by maximum foam pressure method)
As a second measuring method, the dynamic surface tension (Σ) of the lubricating oil composition can be measured by the maximum foam pressure method.
In the maximum foam pressure method, first, the lower end portion of a hollow tube such as a capillary tube is arranged in the liquid of the lubricating oil composition to be measured.
In this state, when a gas such as air is introduced into the hollow tube from the outside, bubbles are generated from the lower end of the hollow tube, the bubbles become large and detach from the end, and move upward in the liquid. Reach the top surface of the liquid. The series of movements of bubbles from the generation of bubbles at the lower end of the hollow tube to the arrival at the upper surface of the lubricating oil composition is called a bubble life cycle. By continuously introducing gas into the hollow tube, bubbles are repeatedly and continuously generated, and the bubble life cycle is continuously repeated.

At this time, if the pressure applied to the inside of the hollow tube (for example, air pressure when the gas is air) is measured over time, the pressure fluctuates periodically according to the cycle of the bubble life cycle. Based on this periodic pressure fluctuation, if the difference between the maximum value P _max and the minimum value P _min in one cycle is ΔP and the cross section of the hollow part of the hollow tube is γ, the surface tension σ is σ. It is represented by = ΔP × γ / 2.
The bubble lifetime (Tw) refers to the time from the generation of bubbles at the lower end of the hollow tube to the maximum pressure. The bubble lifetime (Tw) can be controlled (changed) by adjusting the introduction speed (flow rate) of the gas introduced into the hollow tube from the outside. While changing the bubble lifetime (Tw), the surface tension (σ) is measured at the same time.

In the graph in which the bubble lifetime (Tw) is plotted on the horizontal axis and the surface tension (σ) is plotted on the vertical axis, in the region where the bubble lifetime (Tw) is small, the surface tension (Tw) is usually increased as the bubble lifetime (Tw) is increased. The value of σ) changes greatly depending on the bubble lifetime (Tw). After that, the change in surface tension (σ) becomes small and takes a substantially constant value with respect to the bubble lifetime (Tw).
For example, in the case of a lubricating oil composition in which fullerenes are dissolved in mineral oil, as shown in FIG. 1, the surface tension (σ) (vertical axis) is relative to the bubble lifetime (Tw) (horizontal axis is the logarithm of Tw). ) Is a downwardly convex downward curve. Therefore, using this graph, the dynamic surface tension (Σ) is quantified by the drawing method.

In the present embodiment, the dynamic surface tension (Σ) can be calculated by any of the following calculation methods (C), (D), (E), and (F) by using the maximum foam pressure method described above. it can.
(C) A gas is introduced into a hollow tube arranged in the liquid of the lubricating oil composition, the bubble lifetime (Tw) and the surface tension (σ) are measured, and the bubble lifetime (Tw) is the minimum. The surface tension (σ _s ) when the value (Tw _min ) is used is defined as the dynamic surface tension (Σ). The minimum value (Tw _min ) of the bubble lifetime (Tw) is set to the smallest value among the bubble lifetimes (Tw) in which the variation in surface tension (σ) is within the allowable range (the same shall apply hereinafter). When the measuring device has a measurable range, it is preferable to set the minimum bubble lifetime (Tw) that can be measured and the variation is within the allowable range to the minimum value (Tw _min ).
(D) The surface tension when the bubble lifetime (Tw) is the minimum value (Tw _min ) with respect to the surface tension (σ _f ) when the bubble lifetime (Tw) is the maximum value (Tw _max ). Let the ratio of (σ _s ) (σ _s / σ _f ) be the dynamic surface tension (Σ). The maximum value (Tw _max ) of the bubble lifetime (Tw) is the bubble lifetime (Tw) in which the standard deviation of the three neighboring points is 1/10 or less of the maximum value (Tw _max ) -minimum value (Tw _min ). Use as a value (the same applies below).
(E) The surface tension (σ) near the minimum value (Tw _min ) of the bubble lifetime (Tw) is linearly approximated, and the gradient (S) of the obtained straight line is defined as the dynamic surface tension (Σ). ..
(F) the ratio of the slope S for the surface tension (sigma _f) the (S / σ _f), the dynamic surface tension (sigma).

In the above (C), which is the first calculation method, as shown in FIG. 2, the minimum value (Tw _min ) of the bubble lifetime (Tw) is defined, and the bubble lifetime (Tw) is the minimum value (Tw). _Find the surface tension (σ _s ) when it is _min ) and define that the surface tension (σ _s ) is equal to the dynamic surface tension (Σ).

In the above (D), which is the second calculation method, as shown in FIG. 2, the maximum value (Tw _max ) and the minimum value (Tw _min ) of the bubble lifetime (Tw) are defined, and the bubble lifetime is defined. The surface tension (σ _s ) when (Tw) is the minimum value (Tw _min ) and the surface tension (σ _f ) when the bubble lifetime (Tw) is the maximum value (Tw _max ) are obtained. We define the ratio (σ _s / σ _f ) to be equal to the dynamic surface tension (Σ).

In the above (E), which is the third calculation method, as shown in FIG. 3, the plot near the minimum bubble lifetime (Tw) is linearly approximated, and the obtained linear gradient (S) is obtained. Find (S = Δσ / Δlog (Tw)) and define that the gradient (S) is equal to the dynamic surface tension (Σ).

In the above (F), which is the fourth calculation method, the ratio (S) is used by using the surface tension (σ _f ) obtained in the above (D) and the linear gradient (S) obtained in the above (E). We define / σ _f ) as equal to dynamic surface tension (Σ).

In the method for inspecting the lubricating oil composition of the present embodiment, the dynamic surface tension (Σ) of the lubricating oil composition is measured by the Wilhelmi plate method or the maximum foam pressure method, and the dynamic surface tension (Σ) is measured. A lubricating oil composition whose measured value is within the predetermined range is rejected, and a lubricating oil composition outside the predetermined range is rejected. Thereby, the lubricating oil composition is selected.
Further, in the above-mentioned predetermined range of the dynamic surface tension (Σ), the wear coefficient is desired from the correlation between the wear coefficient of the lubricating oil composition as shown in Examples described later and the dynamic surface tension (Σ). It is set to be a range.
In the examples described later, the correlation coefficient between the dynamic surface tension (Σ) and the wear coefficient is obtained by, for example, the least squares method, and the correlation exists when the absolute value of the correlation coefficient is 0.8 or more. However, the range of the absolute value of the correlation coefficient for determining the presence or absence of the correlation is not limited to this.

In the inspection method of the lubricating oil composition of the present embodiment, the dynamic surface tension (Σ) of the lubricating oil composition was measured by the Wilhelmi plate method described above or the maximum foam pressure method described above, and the measured values were set. It is preferable to select the lubricating oil composition within the range. By measuring the dynamic surface tension (Σ) in this way and selecting the lubricating oil composition in which the measured value of the dynamic surface tension (Σ) is within the set predetermined range, the accuracy of selection is further improved. Can be improved. As a result, the wear resistance characteristics of the lubricating oil composition can be predicted more stably.

According to the inspection method of the lubricating oil composition of the present embodiment, even if the lubricating oil composition contains fullerenes, the dynamic surface tension (Σ) of the lubricating oil composition by the Wilhelmi plate method or the maximum foam pressure method. The wear resistance characteristics can be stably predicted by using a method called the measurement of, which is relatively easy to measure.

[Manufacturing method of lubricating oil composition]
The method for producing a lubricating oil composition of the present embodiment includes a step of selecting a lubricating oil composition obtained by mixing base oil and fullerene by the inspection method of the lubricating oil composition of the present embodiment.

The method for producing the lubricating oil composition of the present embodiment is, in detail, (1) mixing the base oil and the fullerene, dissolving the dissolved component of the fullerene in the base oil, and filtering, heat-treating, etc., if necessary. The step of obtaining a lubricating oil composition which is a mixture of base oil and fullerene (hereinafter referred to as "dissolving step") and (2) the dynamic surface tension (Σ) of the lubricating oil composition are measured and the same. A step of selecting a lubricating oil composition by passing a lubricant composition within a set range of measured values and rejecting a lubricating oil composition outside the set range of measured values (hereinafter, "inspection step"). ) And, including. In the method for producing a lubricating oil composition of the present embodiment, if necessary, the lubricating oil compositions produced in a plurality of different batches are mixed so that they can be selected as passing in (3) "inspection step". , A step of obtaining a new lubricating oil composition (hereinafter, referred to as “readjustment step”) may be included.
Hereinafter, the method for producing the lubricating oil composition of the present embodiment will be described in detail.

(Dissolution process)
The raw material fullerene is put into the base oil and subjected to a dispersion treatment for 1 hour to 48 hours using a dispersion means such as a stirrer while heating at around room temperature or as necessary.
Examples of the dispersion means for dispersing fullerenes in the base oil include a stirrer, an ultrasonic disperser, a homogenizer, a ball mill, and a bead mill.
In this way, a liquid in which fullerene is dissolved or dispersed in the base oil (sometimes referred to as "fullerene solution") is obtained.

The amount of fullerene added may be any amount as long as the fullerene concentration in the fullerene solution is a desired concentration. Further, when a step of removing the insoluble component described later is provided during the melting step, it is advisable to add a large amount of fullerene in consideration of the amount of fullerene removed by this step. Although it depends on the solvent, in general, the fullerene concentration in the fullerene solution in which fullerene is difficult to precipitate as an insoluble component is preferably in the range of 1 mass ppm to 1 mass%.

Further, a fullerene solution having a desired concentration may be obtained by obtaining a fullerene solution having a higher concentration than desired and diluting with a base oil.

The fullerene solution obtained as described above may be used as it is as a lubricating oil composition.
Further, it is preferable that a step of removing the insoluble component is provided during the dissolution step, and the fullerene solution from which the insoluble component is removed is used as a lubricating oil composition. The step of removing the insoluble component is preferably provided after the dispersion treatment of dispersing the fullerene in the base oil in the dissolution step. Examples of the step of removing the insoluble component include (1) a removal step using a membrane filter, (2) a removal step using a centrifuge, and (3) a removal step using a combination of a membrane filter and a centrifuge. Can be mentioned. Among these removal steps, from the viewpoint of filtration time, (1) a removal step using a membrane filter is preferable when a small amount of lubricating oil composition is obtained, and (2) centrifugation is used when a large amount of lubricating oil composition is obtained. A removal step using a separator is preferred.

In the dissolution step, particularly when the fullerene solution is heated, it is preferable to carry out in a non-oxidizing atmosphere. For example, by substituting the inside of the container containing the fullerene solution with an inert gas such as nitrogen gas or argon gas, or by bubbling the fullerene solution in the container with the inert gas, the fullerene solution becomes an inert gas. It is preferable to achieve an equilibrium state.

(Inspection process)
In the inspection step, the dynamic surface tension (Σ) of the lubricating oil composition obtained in the melting step is measured, and the lubricating oil composition whose measured value of the dynamic surface tension (Σ) is within a predetermined range is passed. This is a step of selecting a lubricating oil composition outside the predetermined range as a failure. As described above, the predetermined range of the dynamic surface tension (Σ) is the dynamic surface tension in which the wear coefficient becomes a desired range from the correlation between the wear coefficient of the lubricating oil composition and the dynamic surface tension (Σ). It can be set by finding (Σ). The dynamic surface tension (Σ) is measured for each lubricating oil composition produced in a plurality of different batches. Thereby, the predetermined range of the dynamic surface tension (Σ) can be determined in consideration of the wear resistance characteristics, and the lubricating oil composition can be classified into a pass product and a reject product.

(Readjustment process)
In the readjustment step, an appropriate amount of the rejected lubricating oil composition is mixed with the accepted lubricating oil composition, so that the newly adjusted lubricating oil composition is again subjected to the dynamic surface tension (in the above inspection step). As a result of the measurement of Σ), the measured value is set within a predetermined range, and a passing lubricating oil composition is obtained. The amount of the rejected lubricating oil composition to be mixed with the accepted product may be determined by measuring the dynamic surface tension (Σ) of the mixed lubricating oil composition.
By classifying the lubricating oil composition, the following effects can be obtained. (1) It is possible to eliminate the lubricating oil composition in which the dynamic surface tension (Σ) fails. (2) By mixing a lubricating oil composition having a dynamic surface tension (Σ) in the range of failing with a passing lubricating oil composition, a lubricating oil composition that can be newly passed can be obtained. ..

As described above, according to the method for producing a lubricating oil composition of the present embodiment, even if the lubricating oil composition contains fullerenes, the dynamic surface of the lubricating oil composition by the Wilhelmi plate method or the maximum foam pressure method. By using a method of measuring tension (Σ), which is relatively easy to measure, wear resistance can be predicted, and the lubricating oil composition can be accurately sorted into acceptable products and unacceptable products.

Although the preferred embodiment of the present invention has been described in detail above, the present invention is not limited to a specific embodiment, and various within the scope of the gist of the present invention described in the claims. Can be transformed / changed.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[Examples 1 to 9]
(Preparation of lubricating oil composition)
1L of mineral oil A (product name: Diana Fresia P-46, manufactured by Idemitsu Kosan Co., Ltd.) and fullerene (manufactured by Frontier Carbon Co., Ltd., nano purple SUT, C ₆₀ ) are mixed and stirred at room temperature for 6 hours using a stirrer. did. Here, 0, 0.005 g and 0.05 g of fullerene were added to the mineral oil to prepare three kinds of solutions A having fullerene concentrations of 0 ppm, 50 ppm and 500 ppm.
After the stirring was completed, these solutions were filtered through a 0.1 μm membrane filter to obtain a lubricating oil composition A.
Further, 100 ml of the lubricating oil composition A is taken out, transferred to 250 ml of a stainless steel pressure resistant container, then the inside is replaced with nitrogen gas and then sealed, and this is not heat-treated or placed in an oil bath at 150 ° C. 2 The heat treatment was carried out by immersing for hours or 15 hours. The obtained lubricating oil compositions a-1 to a-9 are shown in Table 1.

(Measurement of kinematic viscosity)
About 50 mL of the lubricating oil composition a-1 to a-9 was taken out into a glass beaker and immersed in a water bath at 40 ° C. for 30 minutes.
Next, the kinematic viscosity of the lubricating oil composition was measured by a method according to the method for measuring the viscosity of a liquid specified in Japanese Industrial Standards JIS Z8803: 2011 and the method for measuring the viscosity with a thin tube viscometer.

(Measurement of dynamic surface tension (Σ) by Wilhelmj plate method)
The dynamic surface tension (Σ) (mN / m) of the obtained lubricating oil composition was evaluated using a high-performance surface tension meter (manufactured by Kyowa Interface Science Co., Ltd., product name "DyneMaster DY-500").
First, a SUJ2 substrate (15 mm × 15 mm, thickness 2 mm), which is a high carbon chrome bearing steel material whose surface was mirror-polished, was fixed to a stylus. Next, the lubricating oil composition was placed in a 50 ml beaker, and the substrate was immersed therein. From the measurement results of the immersion distance (h) and the force (F), (| LA |) and (| LB |) Was calculated. At this time, the substrate was moved up and down at a speed of 1 mm / sec. Further, this measurement was carried out in an environment where the liquid temperature of the lubricating oil composition was 25 ± 0.1 ° C.
The dynamic surface tension (Σ) of the lubricating oil composition was calculated by the above calculation method (B) (= | LA | − | LB |).

(Measurement of wear coefficient)
The wear resistance characteristics of the obtained lubricating oil composition were evaluated using a friction and wear tester (manufactured by Antonio Par, product name "ball-on-disc tribometer").
The material of the substrate and balls constituting the friction and wear tester was SUJ2, which is a high carbon chrome bearing steel material. The ball had a diameter of 6 mm and the substrate used was a 15 mm square.
First, the lubricating oil composition was applied to one main surface of the substrate.
Next, the balls were slid on one main surface of the substrate through the lubricating oil composition so that the balls would draw concentric orbits. The velocity of the ball on one main surface of the substrate was 10 mm / sec, and the load of the ball on one main surface of the substrate was 25 N. When the sliding distance of the ball on one main surface of the substrate reaches an integrated 15 m, the ball is taken out from the device, the contact surface of the ball with the substrate is observed with an optical microscope, and the wear of the surface is reduced. The maximum diameter of the circle was D (μm). Here, the maximum diameter D is defined as the wear coefficient. That is, the smaller the number of the maximum diameter D, the more the wear is suppressed, which is a preferable state as a characteristic of the lubricating oil composition. It usually wears out in a circular shape, but may be oval. In that case, the portion having the maximum diameter is defined as the maximum diameter D. This measurement was performed in an environment of 25 ± 2 ° C.

Three samples were prepared in each of Examples 1 to 9, and the dynamic surface tension (Σ) and the wear coefficient were measured for a total of 27 samples of the lubricating oil composition, and the dynamic surface tension (Σ) and the wear coefficient were measured. Evaluated the relationship. Table 2 shows the measurement results of the dynamic surface tension (Σ) and the wear coefficient, and FIG. 4 shows the relationship between the dynamic surface tension (Σ) and the wear coefficient.

From the results shown in FIG. 4, the correlation coefficient between the dynamic surface tension (Σ) and the wear coefficient was −0.917, and a correlation was observed between the dynamic surface tension Σ and the wear coefficient. The correlation coefficient was obtained by the least squares method, and when the absolute value of the correlation coefficient was 0.8 or more, it was judged that the correlation existed. Therefore, in Examples 1 to 9, a lubricating oil composition having a dynamic surface tension (Σ) within a specific range is selected, thereby selecting a lubricating oil composition having a wear coefficient within a desired range. I found that I could do it.

For example, in FIG. 4, when the wear coefficient of the lubricating oil composition is B1 (= 175) or less as a acceptable product, the lubricating oil having a dynamic surface tension (Σ) of A1 (= 2.1) or more is accepted. The composition should be selected as a acceptable product. In this case, if a lubricating oil composition having a dynamic surface tension (Σ) of value A1 or more is set as a predetermined range and a lubricating oil composition having a value A1 or more is selected as a acceptable product, the wear coefficient does not exceed the value B1 (= 175). It can be seen that the possibility that acceptable products are included is low. Further, in FIG. 4, when the dynamic surface tension (Σ) of the lubricating oil composition is less than the value A1, the lubricating oil composition having the wear coefficient exceeding the value B1 can be selected as a rejected product. Further, in FIG. 4, if the amount of the rejected lubricating oil composition in the region C1 is small, the dynamic surface tension can be obtained by adding the accepted lubricating oil composition in the region D1 to the small amount. The value (Σ) can be set to A1 or more, and the wear coefficient can be adjusted to a acceptable lubricating oil composition having a value B1 or less.

[Examples 10 to 18]
The dynamic surface tension (Σ) and the wear coefficient were measured in the same manner as in Examples 1 to 9 except that the dynamic surface tension (Σ) of the lubricating oil composition was calculated by the maximum foam pressure method, and the dynamic surface was measured. The relationship between tension (Σ) and wear coefficient was evaluated.

(Measurement of dynamic surface tension (Σ) by maximum foam pressure method)
The dynamic surface tension (Σ) of the obtained lubricating oil compositions a-1 to a-9 was evaluated using a surface tension meter (manufactured by SITA Messtechnik GmbH, product name "SITA science line t100").
First, the lubricating oil compositions a-1 to a-9 were placed in a 50 ml beaker, and the capillary portion (hollow tube) of the surface tension meter was submerged in the liquid of the lubricating oil composition. After leaving it in this state for 30 minutes, the measurement was started by flowing air through the capillary tube. First, bubbles were generated at 15 milliseconds (0.015 seconds), which is the minimum value (Tw _min ) of the bubble lifetime (Tw) (milliseconds) of the device, and the surface tension (σ) was measured. Subsequently, the surface tension (σ) was measured until the bubble lifetime (Tw) reached a maximum of 15 seconds while gradually increasing the bubble generation cycle by reducing the flow rate of the air introduced into the hollow tube. This measurement was performed in an environment of 25 ± 2 ° C.
When plotting with Log (Tw) on the horizontal axis and surface tension σ on the vertical axis, a downwardly convex downward-sloping curve was obtained. Using this graph, the dynamic surface tension (Σ) (mN / m) was calculated using the above calculation method (D).

Table 3 shows the measurement results of the dynamic surface tension (Σ) and the abrasion coefficient, and FIG. 5 shows the relationship between the dynamic surface tension (Σ) and the abrasion coefficient.

From the results shown in FIG. 5, the correlation coefficient between the dynamic surface tension (Σ) and the wear coefficient is -0.953, and the absolute value is 0.8 or more. Therefore, the dynamic surface tension (Σ) A correlation was found in the wear coefficient. Therefore, also in Examples 10 to 18, by selecting a lubricating oil composition having a dynamic surface tension (Σ) within a specific range, a lubricating oil composition having a wear coefficient within a desired range is selected. I found that I could do it.

For example, in FIG. 5, when a lubricating oil composition having a wear coefficient of the lubricating oil composition of a value B2 (= 180) or less is accepted as a passing product, the dynamic surface tension (Σ) is a value A2 (= 13) or more. It is advisable to select the lubricating oil composition of the above as a passing product. In this case, if a lubricating oil composition having a dynamic surface tension (Σ) of a value A2 or more is set as a predetermined range and a lubricating oil composition having a value A2 or more is selected as a acceptable product, a rejected product having a wear coefficient exceeding the value B2 is included. It can be seen that the possibility of being affected is low. Further, in FIG. 5, when the dynamic surface tension (Σ) of the lubricating oil composition is less than the value A2, the lubricating oil composition having the wear coefficient exceeding the value B2 can be selected as a rejected product. Further, in FIG. 5, if the amount of the rejected lubricating oil composition in the region C2 is small, the dynamic surface tension can be obtained by adding the accepted lubricating oil composition in the region D2. Can be set to a value of A2 or more, and can be adjusted to a acceptable lubricating oil composition having a wear coefficient of B2 or less.

[Comparative Examples 1 to 9]
For Comparative Examples 1 to 9, three samples were prepared in the same manner as in Examples 1 to 9, and the kinematic viscosity (mm ² / s) and the wear coefficient were measured for a total of 27 samples of the lubricating oil composition, and the kinematic viscosities were measured. And the relationship between the wear coefficient and the wear coefficient were evaluated. Table 4 shows the measurement results of the kinematic viscosity and the abrasion coefficient, and FIG. 6 shows the relationship between the kinematic viscosity and the abrasion coefficient.

From the results shown in FIG. 6, the correlation coefficient between the kinematic viscosity and the wear coefficient was -0.032, and the absolute value was less than 0.8. Therefore, no correlation was observed between the kinematic viscosity and the wear coefficient. .. Therefore, it was found that the wear coefficient of the lubricating oil composition cannot be specified from the kinematic viscosity of the lubricating oil composition to select the lubricating oil composition.

According to the present invention, wear resistance can be predicted by measuring the dynamic surface tension (Σ) of the lubricating oil composition in the manufacturing process of the lubricating oil composition containing the base oil and fullerene, and the lubricating oil composition can be obtained. It is possible to sort passed products and rejected products with high accuracy. Therefore, the acceptable lubricating oil composition selected in the present invention is effective for suppressing scratches and wear of metal parts in sliding parts of automobiles, home appliances, industrial machines and the like.

Claims (6)

The dynamic surface tension (Σ) of the lubricating oil composition containing the base oil and fullerene is measured, and by the correlation between the measured value of the dynamic surface tension (Σ) and the measured value of the wear coefficient of the lubricating oil composition. An inspection step of sorting a lubricating oil composition into a passing lubricating oil composition and a rejecting lubricating oil composition based on a set predetermined range, and
A readjustment step of mixing the rejected lubricating oil composition obtained in the inspection step with the passing lubricating oil composition and performing the inspection step again to obtain a passing lubricating oil composition.
A method for producing a lubricating oil composition containing. The method for producing a lubricating oil composition according to claim 1, wherein the dynamic surface tension (Σ) is measured by the Wilhelmj plate method. The method for producing a lubricating oil composition according to claim 2, wherein the dynamic surface tension (Σ) is calculated by any of the following calculation methods (A) and (B).
(A) The magnitude of the force required to pull the substrate out of the liquid of the lubricating oil composition (| LA |) and the magnitude of the force required to submerge the substrate in the liquid of the lubricating oil composition (| LA |). One of | LB |) is defined as the dynamic surface tension (Σ).
(B) Let the difference in magnitude of the force (| LA |-| LB |) be the dynamic surface tension (Σ). The method for producing a lubricating oil composition according to claim 1, wherein the dynamic surface tension (Σ) is measured by the maximum foam pressure method. The method for producing a lubricating oil composition according to claim 4, wherein the dynamic surface tension (Σ) is calculated by any of the following calculation methods (C), (D), (E), and (F).
(C) A gas is introduced into a hollow tube arranged in the liquid of the lubricating oil composition, and the gas is introduced.
Bubble lifetime (Tw), which indicates the time from the generation of bubbles at the lower end of the hollow tube to the maximum pressure of gas introduction, and surface tension (σ) (σ = ΔP × γ / 2, ΔP) Is the difference between the maximum value P _max and the minimum value P _min of the pressure of the gas in the periodic pressure fluctuation, and γ is the cross-sectional area of the hollow portion of the hollow tube).
The surface tension (σ _s ) when the bubble lifetime (Tw) is the minimum value (Tw _min ) is defined as the dynamic surface tension (Σ).
(D) The surface tension when the bubble lifetime (Tw) is the minimum value (Tw _min ) with respect to the surface tension (σ _f ) when the bubble lifetime (Tw) is the maximum value (Tw _max ). Let the ratio of (σ _s ) (σ _s / σ _f ) be the dynamic surface tension (Σ).
(E) The surface tension (σ) near the minimum value (Tw _min ) of the bubble lifetime (Tw) is linearly approximated, and the obtained linear gradient (S) is referred to as the dynamic surface tension (Σ). To do.
(F) The ratio (S / σ _f ) of the gradient S to the surface tension (σ _f ) is defined as the dynamic surface tension (Σ). The inspection step measures the dynamic surface tension (Σ) of the lubricating oil composition produced in a plurality of different batches.
Claims 1 to 5 include the lubricating oil composition of the accepted product and the lubricating oil composition of the rejected product, which are mixed in the readjustment step, including the lubricating oil compositions produced in the plurality of different batches. The method for producing a lubricating oil composition according to any one of the above.

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