阅读说明：本技术 润滑油组合物的检查方法及该润滑油组合物的制造方法 (Method for inspecting lubricating oil composition and method for producing lubricating oil composition ) 是由 门田隆二 坂口泰之 金眸 近藤邦夫 于 2020-05-13 设计创作，主要内容包括：本发明提供即使为包含富勒烯的润滑油组合物也可以使用比较容易测定的方法来稳定地再现耐磨损特性的、润滑油组合物的检查方法及润滑油组合物的制造方法。在润滑油组合物的检查方法中,测定存在于包含基油和富勒烯的润滑油组合物中的粒子的粒径(r),根据上述粒子的粒径(r)的测定值与上述润滑油组合物的磨损系数的测定值的相关性来设定粒径(r)的规定范围,基于粒径(r)的规定范围来筛选润滑油组合物。(The invention provides a method for inspecting a lubricating oil composition and a method for producing a lubricating oil composition, by which even a lubricating oil composition containing fullerene can be stably reproduced in wear resistance characteristics by a relatively easy measurement method. In the method for inspecting a lubricating oil composition, the particle diameter (r) of particles present in a lubricating oil composition containing a base oil and fullerene is measured, a predetermined range of the particle diameter (r) is set on the basis of the correlation between the measured value of the particle diameter (r) of the particles and the measured value of the wear coefficient of the lubricating oil composition, and the lubricating oil composition is screened on the basis of the predetermined range of the particle diameter (r).)

1. A method for inspecting a lubricating oil composition, characterized by measuring the particle diameter (r) of particles present in a lubricating oil composition comprising a base oil and fullerene, setting a predetermined range of the particle diameter (r) on the basis of the correlation between the measured value of the particle diameter (r) and the measured value of the wear coefficient of the lubricating oil composition, and screening the lubricating oil composition on the basis of the predetermined range of the particle diameter (r).

2. The method for inspecting a lubricating oil composition according to claim 1, wherein the particle diameter (r) of the particles is measured by a dynamic light scattering method, a laser diffraction method, or an X-ray small angle scattering method (SAXS method).

3. The method for inspecting a lubricating oil composition according to claim 1 or 2, wherein the particle diameter (R) is an average particle diameter (R) of particles present in the lubricating oil composition.

4. The method for inspecting a lubricating oil composition according to claim 3, wherein the average particle diameter (R) of the particles is measured by an X-ray small angle scattering method (SAXS method).

5. The method for inspecting a lubricating oil composition according to claim 4, wherein the average particle diameter (R) of the particles is calculated from the slope of a Ginier plot.

6. The method for inspecting a lubricating oil composition according to claim 4, wherein the average particle diameter (R) of the particles is calculated from a value of a scattering vector at which a scattering intensity ratio of the lubricating oil composition to the base oil is a maximum value with respect to the scattering vector.

7. A method for producing a lubricating oil composition, comprising a step of screening by the method for inspecting a lubricating oil composition according to any one of claims 1 to 6.

Technical Field

The present invention relates to a method for inspecting a lubricating oil composition and a method for producing the lubricating oil composition.

The present application claims priority based on Japanese application laid-open at 5/16/2019, Japanese application No. 2019-092842, the contents of which are incorporated herein by reference.

Background

In recent years, with the increase in speed, efficiency, and energy saving, there has been a strong demand for improving the performance of lubricating oils used in automobiles, home appliances, industrial machines, and the like. In order to improve the properties of the lubricating oil composition so as to be suitable for the use thereof, various additives such as an antioxidant, an extreme pressure additive, an anti-rust additive, and a corrosion inhibitor are blended in the lubricating oil composition.

In response to these demands, a lubricating oil composition is required which simultaneously improves a plurality of performances such as low friction, torque increase, and fuel economy. As such a lubricating oil composition, an additive composition for engine lubricating oils is known, which is obtained by blending a lubricating base oil such as a mineral oil or an ester oil with fullerene as a nano carbon particle, an organic solvent, a viscosity index improver, a wear adjuster, and a detergent dispersant (for example, see patent document 1).

Furthermore, fullerene may be added to a lubricating oil composition used in a refrigerant compressor (see, for example, patent document 2).

In general, important characteristics of a lubricating oil composition include wear coefficient, but measurement is laborious. Therefore, in the production process of a lubricating oil composition, properties of the lubricating oil composition are specified using, as indices, a density, a dynamic viscosity, a viscosity index, a pour point, a total acid value, and the like, which are easy to measure (for example, see non-patent document 1).

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2008-266501

Patent document 2: international publication No. 2017/141825

Non-patent document

Non-patent document 1: network < URL: https: html >/www.noe.jxtg-group.co.jp/english/products/lubricants/industrials

Disclosure of Invention

Problems to be solved by the invention

However, in the system in which fullerene is added to the lubricating oil composition described in non-patent document 1 and the like, even if product management is performed using the above index, a product in which the lubricating properties such as the wear coefficient and the like are stably reproduced cannot be obtained. That is, even when the characteristics of the product are expressed as numerical values by the above-described index and the product falling within a certain range is regarded as acceptable, the lubrication characteristics may fluctuate beyond the allowable range.

Further, by measuring the lubricating properties of the products of the lubricating oil composition, it is possible to screen products having lubricating properties within an acceptable range, but for this purpose, it is necessary to perform wear tests such as a ball-and-disk test for each product lot. In this case, since labor and time are required and the cost of the test substrate or the like is increased, the wear test is not suitable for each manufacturing lot.

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

Means for solving the problems

In order to solve the above problems, the present invention provides the following methods.

[1] A method for inspecting a lubricating oil composition, characterized by measuring the particle diameter (r) of particles present in a lubricating oil composition containing a base oil and fullerene, setting a predetermined range of the particle diameter (r) on the basis of the correlation between the measured value of the particle diameter (r) and the measured value of the wear coefficient of the lubricating oil composition, and screening the lubricating oil composition on the basis of the predetermined range of the particle diameter (r).

[2] The method for inspecting a lubricating oil composition according to [1], wherein the particle diameter (r) of the particles is measured by a dynamic light scattering method, a laser diffraction method, or an X-ray small angle scattering method (SAXS method).

[3] The method for inspecting a lubricating oil composition according to [1] or [2], wherein the particle diameter (R) is an average particle diameter (R) of particles present in the lubricating oil composition.

[4] The method for inspecting a lubricating oil composition according to [3], wherein the average particle diameter (R) of the particles is measured by an X-ray small angle scattering method (SAXS method).

[5] The method for inspecting a lubricating oil composition according to [4], wherein the average particle diameter (R) of the particles is determined by a method of calculating from the slope of a Guinier plot (hereinafter, sometimes referred to as the G method).

[6] The method for inspecting a lubricating oil composition according to [4], wherein the average particle diameter (R) of the particles is determined by a method (hereinafter, sometimes referred to as S method) of calculating a value of a scattering vector when a scattering intensity ratio of the lubricating oil composition to the base oil becomes a maximum value with respect to the scattering vector.

[7] A method for producing a lubricating oil composition, which comprises a step of screening by the method for inspecting a lubricating oil composition according to any one of the above [1] to [6 ].

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, it is possible to provide a method for inspecting a lubricating oil composition and a method for producing the lubricating oil composition, which can stably reproduce wear resistance characteristics even for a lubricating oil composition containing fullerene by a relatively easy measurement method.

Drawings

FIG. 1 is a graph showing the average particle diameter (R) of particles obtained by the G method_G) Graph of wear coefficient.

FIG. 2 is a graph showing the average particle diameter (R) of particles obtained by the S method_S) Graph of wear coefficient.

FIG. 3 is a graph showing the relationship of dynamic viscosity to wear coefficient.

Detailed Description

Hereinafter, a method for inspecting a lubricating oil composition and a method for producing a lubricating oil composition according to an embodiment of the present invention will be described. The present embodiment is specifically described for better understanding of the gist of the present invention, and the present invention is not limited to the embodiments unless otherwise specified.

[ method for inspecting lubricating oil composition ]

The method for inspecting a lubricating oil composition according to the present embodiment is characterized by measuring the particle diameter (r) (hereinafter, sometimes simply referred to as particle diameter (r)) of particles present in a lubricating oil composition containing a base oil and fullerene, and screening the lubricating oil composition based on a predetermined range set based on the correlation between the measured value of the particle diameter (r) and the measured value of the wear coefficient of the lubricating oil composition. That is, the method for inspecting a lubricating oil composition according to the present embodiment includes the following three steps.

The first step is as follows: the particle diameter (r) of particles present in a plurality of lubricating oil compositions and the wear coefficient of the lubricating oil compositions were measured, and the correlation between the particle diameter (r) and the wear coefficient (for example, a straight line fit between the wear coefficient (B) and the particle diameter (r): B ═ kR + c) was calculated.

The second step is as follows: a predetermined range of the particle diameter (r) is set.

The third step: the particle diameter (r) of particles present in the lubricating oil composition to be tested is measured, and if the particle diameter (r) is within a predetermined range, the product is a non-defective product, and if the particle diameter (r) is outside the predetermined range, the product is a defective product.

Preferably, the particle diameter (R) is an average particle diameter (R) of particles present in the lubricating oil composition (hereinafter, may be simply referred to as an average particle diameter (R)).

(lubricating oil composition)

The lubricating oil composition to be inspected by the method for inspecting a lubricating oil composition according to the present embodiment includes a base oil and fullerene.

(base oil)

The base oil included in the lubricating oil composition in the present embodiment is not particularly limited, and mineral oil and synthetic oil that are widely used as base oil of lubricating oil in general are suitably used.

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

Examples of the synthetic oil include synthetic hydrocarbon oil, ether oil, and ester oil. Specific examples of the synthetic oil include polyalphaolefins, diesters, polyalkylene glycols, polyalphaolefins, polyalkylvinyl ethers, polybutenes, isoparaffins, olefin copolymers, alkylbenzenes, alkylnaphthalenes, diisodecyl adipate, monoesters, dibasic esters, tribasic esters, polyol esters (trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol 2-ethylhexanoate, pentaerythritol pelargonate, etc.), dialkyl diphenyl ethers, alkyl diphenyl sulfides, polyphenylene ethers, silicone lubricants (dimethyl silicone, etc.), perfluoropolyethers, and the like. Among these synthetic oils, preferred are polyalphaolefins, diesters, polyol esters, polyalkylene glycols, and polyalkylvinyl ethers.

These mineral oils and synthetic oils may be used alone in 1 kind, or 2 or more kinds selected from them may be used in combination in an arbitrary ratio.

(Fullerene)

The structure and production method of the fullerene included in the lubricating oil composition in the present embodiment are not particularly limited, and various fullerenes can be used. Examples of the fullerene include C which is relatively easily obtainable₆₀、C₇₀Higher order fullerenes, or mixtures thereof. In the fullerene, fromIn view of high solubility in lubricating oil, C is preferred₆₀And C₇₀More preferably C, from the viewpoint of reducing coloring of the lubricating oil₆₀. In the presence of C₆₀In the case of the mixture of (3), it is preferable that C is contained in an amount of 50% by mass or more₆₀。

The fullerene may be chemically modified for the purpose of further improving solubility in the base oil. Examples of the fullerene obtained by chemical modification include phenyl C61 methyl butyrate ([60] PCBM), diphenyl C62 di-methyl butyrate (Bis [60] PCBM), phenyl C71 methyl butyrate ([70] PCBM), phenyl C85 methyl butyrate ([85] PCBM), phenyl C61 butyl butyrate ([60] PCBB), phenyl C61 octyl butyrate ([60] PCBO), an indene adduct of fullerene, and a pyrrolidine derivative of fullerene.

(additives)

The lubricating oil composition in the present embodiment may contain additives in addition to the base oil and the fullerene within a range that does not impair the effects of the present embodiment.

The additive to be blended in the lubricating oil composition in the present embodiment is not particularly limited. Examples of the additives include commercially available antioxidants, viscosity index improvers, extreme pressure additives, detergent dispersants, pour point depressants, corrosion inhibitors, solid lubricants, oil improvers, rust-preventing additives, anti-emulsifiers, defoaming agents, hydrolysis inhibitors, and the like. These additives may be used alone in 1 kind, or may be used in combination in 2 or more kinds.

Examples of the antioxidant include dibutylhydroxytoluene (BHT), Butylhydroxyanisole (BHA), 2, 6-di-tert-butyl-p-cresol (DBPC), 3-arylbenzofuran-2-one (intramolecular cyclic ester of hydroxycarboxylic acid), phenyl- α -naphthylamine, dialkyldiphenylamine, and benzotriazole.

Examples of the viscosity index improver include hydrogenated products of polyalkylstyrenes and styrene-diene copolymers.

Examples of the extreme pressure additive include dibenzyl disulfide (dibenzyl disulfide), allyl phosphate, allyl phosphite, amine salts of allyl phosphate, allyl thiophosphate, amine salts of allyl thiophosphate, naphthenic acid, and the like.

Examples of the detergent dispersant include benzylamine succinic acid derivatives and alkylphenol amines.

Examples of the pour point depressant include a chlorinated paraffin-naphthalene condensate, a chlorinated paraffin-phenol condensate, and a polyalkylstyrene system.

Examples of the anti-emulsifier include alkyl benzene sulfonate and the like.

Examples of the corrosion inhibitor include dialkylnaphthalene sulfonate.

The lubricating oil composition of the present embodiment can be used for various applications as follows: industrial gear oil; hydraulic working oil; compressor oil; a refrigerator oil; cutting oil; plastic processing oil such as rolling oil, pressing oil, forging oil, drawing oil, blanking oil and the like; metal working oils such as heat treatment oil and electric discharge machining oil; sliding guide surface oil; bearing oil; antirust oil; a heat medium oil; and so on.

(measurement of particle diameter (r))

The particles in the lubricating oil composition according to the present embodiment include particles derived from fullerene, such as aggregates of fullerene and base oil molecules. The method of measuring the particle diameter (r) of the particles may be a method capable of measuring the particle diameter of the nano region. Specific examples thereof include a dynamic light scattering method, a laser diffraction method, and an X-ray small angle scattering method. It is assumed that the particle size of the particles present in the lubricating oil composition of the present embodiment is mostly in the range of 1nm to 100nm, and therefore, the X-ray small angle scattering method (hereinafter, sometimes referred to as SAXS method) is preferably used.

Among the above-mentioned measurement methods, when the measured particle diameter (R) is an average particle diameter (R), a strong correlation between the particle diameter (R) and the wear coefficient is easily obtained, which is preferable.

In the small angle scattering method using X-rays, the particle size and distribution of particles in the lubricating oil composition can be determined by analyzing the intensity of scattered X-rays generated by the particles in the lubricating oil composition. For the region where the scattered X-ray is generatedFor example, at a wavelength using a Cu targetThe measurement angle 2 θ is about 0.1 to 10 degrees in the case of the X-ray of (2). For the basic principle of the X-ray small-angle scattering method, reference may be made to the literature "Glatter&Kratky eds(1982)Small Angle X-ray Scattering,Academic Press,London(1982),Pages 17-51.”。

In order to measure the average particle diameter (R) of the particles in the lubricating oil composition, first, an X-ray scattering intensity curve of the particles in the lubricating oil composition was obtained by SAXS method. The longitudinal axis of the X-ray scattering intensity curve of the particles is the X-ray scattering intensity I^SAXS(Q), the horizontal axis represents a scattering vector Q (nm) depending on the measurement angle 2 theta and the wavelength lambda^-1). The magnitude of the scattering vector Q is defined as the following formula (1). Next, the average particle diameter (R) of the particles in the lubricating oil composition was calculated by using the following G method or S method.

[ mathematical formula 1]

[ G method ]

In the lubricating oil composition, assuming that the difference in electron density of the particles with respect to the base oil is constant and the particle diameter (r) is uniform, a Guinier (Guinier) fit can be used in a small angle region where Q < 1/r. Scattering intensity of particles I by Ginier fitting^SAXSThe (Q) can be represented by the following formula (2).

[ mathematical formula 2]

In the formula (2), I^SAXS(Q) is the scattering intensity of the particles,. DELTA.p is the electron density difference between the particles and the base oil, V_pIs the volume of the particle.

Based on measurement by SAXSThe scattering intensity curve of the particles in the lubricating oil composition thus obtained is determined by plotting the LogI on the vertical axis^SAXS(Q), plotting Q on the abscissa²In such a Ginier plot, the average particle diameter (R) of the particles can be determined from the slope of the straight line.

[ S method ]

In the guinier fitting, assumptions such as the shape of the particles may be made, but from the viewpoint that these assumptions are not necessary, it is preferable to analyze the average particle size of the particles by using a simpler S method.

In the S method, the X-ray scattering intensity curve of the particles in the lubricating oil composition and the X-ray scattering intensity curve of the base oil measured by the SAXS method were determined. The ratio of the X-ray scattering intensity of the particles to the X-ray scattering intensity of the base oil with respect to the scattering vector Q is obtained, and the scattering vector Q at which the X-ray scattering intensity ratio is at a maximum is used_maxThe average particle diameter (R) of the particles can be calculated from the following formula (3).

[ mathematical formula 3]

R＝2π/Q_max···(3)

In the method of inspecting the lubricating oil composition of the present embodiment, the average particle diameter (R) of the particles is calculated from the X-ray scattering intensity curve by the SAXS method described above. By screening the lubricating oil compositions whose values calculated by the SAXS method are within the set predetermined ranges, the accuracy of the screening can be further improved. As a result, the wear resistance characteristics of the lubricating oil composition can be predicted more stably.

In the method for inspecting a lubricating oil composition according to the present invention, the average particle diameter (R) of the particles may be calculated by using the G method alone, the S method alone, or both the G method and the S method. When used together, for example, the average particle diameters (R) calculated by 2 methods are each within a predetermined range as a screening criterion. In this case, the accuracy of screening the lubricating oil composition can be improved.

[ method for producing lubricating oil composition ]

The method for producing a lubricating oil composition of the present embodiment includes the steps of: the lubricating oil composition obtained by mixing the base oil and the fullerene is screened by the method for inspecting a lubricating oil composition according to the present embodiment.

Specifically, the method for producing a lubricating oil composition according to the present embodiment preferably includes the following steps.

(1) A step of mixing a base oil with fullerene, dissolving the fullerene dissolved component in the base oil, and optionally subjecting the mixture to filtration, heat treatment, or the like to obtain a lubricating oil composition containing the base oil and the fullerene (hereinafter referred to as "dissolving step").

(2) A step of calculating the average particle diameter (R) of the lubricating oil composition from the X-ray scattering intensity curve by the SAXS method, and selecting the lubricating oil composition by determining that the lubricating oil composition having the value within the set range is acceptable and determining that the lubricating oil composition having the value outside the set range is unacceptable (hereinafter referred to as "inspection step").

The method for producing a lubricating oil composition of the present embodiment may further include the following steps as necessary.

(3) A step (hereinafter, referred to as "reconditioning step") of mixing the lubricating oil compositions produced in a plurality of different batches so as to be able to be screened as acceptable by the "inspection step" to obtain a new lubricating oil composition.

The method for producing the lubricating oil composition of the present embodiment is described in detail below.

(dissolution step)

The fullerene as a raw material is put into the base oil, and the dispersion treatment is performed at about room temperature or, if necessary, while heating, for 1 to 48 hours by using a dispersing means such as a stirrer.

Examples of the dispersing means for dispersing the fullerene in the base oil include a stirrer, an ultrasonic dispersing device, a homogenizer, a ball mill, a bead mill, and the like.

This operation yields a liquid in which fullerene is dissolved or dispersed in the base oil (sometimes referred to as "fullerene solution").

The amount of the fullerene to be charged may be such that the fullerene concentration in the fullerene solution becomes a desired concentration. In the dissolving step, when a step of removing insoluble components, which will be described later, is provided, the fullerene may be introduced in a slightly larger amount in consideration of the amount of fullerene removed in the step. Although the concentration of fullerene in the fullerene solution varies depending on the solvent, the concentration of fullerene in the fullerene solution is preferably in the range of 1 mass ppm to 1 mass% in general, in which fullerene is not easily precipitated as an insoluble component.

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

The fullerene solution obtained as described above can be used as it is as a lubricating oil composition.

Further, it is preferable that a step of removing insoluble components is provided in the dissolving step and the fullerene solution from which the insoluble components have been removed is used as the lubricating oil composition. Preferably, the step of removing the insoluble component is provided after the dispersion treatment of dispersing the fullerene in the base oil in the dissolving 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 centrifugal separator; (3) a removal step of using a membrane filter in combination with a centrifugal separator; and so on. 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 the lubricating oil composition is obtained, and (2) a removal step using a centrifugal separator is preferable when a large amount of the lubricating oil composition is obtained.

In the dissolving step, particularly when the fullerene solution is heated, it is preferable to carry out the dissolving in a non-oxidizing atmosphere. For example, it is preferable that the fullerene solution is brought into an equilibrium state with an inert gas by replacing the interior of a container containing the fullerene solution with an inert gas such as nitrogen or argon, or by further bubbling the fullerene solution in the container with an inert gas.

(inspection step)

The inspection step is a step of calculating the average particle diameter (R) of particles in the lubricating oil composition and screening the lubricating oil composition. The average particle diameter (R) of the particles in the lubricating oil composition obtained in the dissolution step was calculated from the X-ray scattering intensity curve by the SAXS method. The lubricating oil compositions having the average particle diameter (R) within the predetermined range were screened as passing, and the lubricating oil compositions having the average particle diameter (R) outside the predetermined range were screened as failing. The predetermined range of the average particle diameter (R) can be set by obtaining the average particle diameter (R) having a wear coefficient within a desired range from the correlation between the wear coefficient of the lubricating oil composition and the average particle diameter (R) as described above. The determination of the average particle diameter (R) was carried out for each of the lubricating oil compositions prepared by a plurality of different batches. Thus, the predetermined range of the average particle diameter (R) is determined in consideration of the wear resistance characteristics, and the lubricating oil composition can be classified into a non-defective product, a defective product, and the like.

(readjustment step)

The reconditioning step is a step of obtaining a qualified lubricating oil composition by mixing an appropriate amount of a defective lubricating oil composition into a qualified lubricating oil composition. Specifically, the average particle diameter (R) of the particles of the lubricating oil composition after the readjustment is measured again in the above-described inspection step, and the measured values are appropriately mixed so as to fall within a predetermined range, thereby obtaining a non-defective lubricating oil composition. The amount of the lubricating oil composition of the defective product mixed with the non-defective product can be determined by measuring the average particle diameter (R) of the particles in the lubricating oil composition after mixing.

By classifying the lubricating oil compositions, the following effects can be obtained. (1) Lubricating oil compositions in which the average particle diameter (R) of the particles is unacceptable can be excluded. (2) By blending a lubricating oil composition in which the average particle diameter (R) of the particles is within the range of failing to be included into a qualified lubricating oil composition, a lubricating oil composition that can be qualified can be recovered.

As described above, according to the method for producing a lubricating oil composition of the present embodiment, even in the case of a lubricating oil composition containing fullerene, the wear resistance can be predicted by using a method which is relatively easy to measure, and the lubricating oil composition can be accurately screened into non-defective products and defective products. The above method is a method of measuring the average particle diameter (R) of particles in the lubricating oil composition by SAXS method.

While the preferred embodiments of the present invention have been described in detail, the present invention is not limited to the specific embodiments, and various modifications and changes can be made within the scope of the present invention described in the claims.

Examples

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[ preparation of lubricating oil composition ]

2L of mineral oil A (product name: ダイアナフレシア P-46, manufactured by Shikino corporation) and the following predetermined amount of fullerene (manufactured by フロンティアカーボン, Nanom)^TM purple SUT，C₆₀) The mixture was stirred at room temperature for 6 hours using a stirrer. After completion of the stirring, the mixture was filtered through a 0.1 μm membrane filter to obtain a fullerene solution. Here, 0.5mg, 5.0mg and 50.0mg of fullerene were added to mineral oil to prepare 3 kinds of fullerene solutions having fullerene concentrations of 2.5 mass ppm, 25.0 mass ppm and 250.0 mass ppm. The fullerene concentration of the solution was calculated from the amount of fullerene charged.

Further, 100ml of the obtained fullerene solution was taken out, and the fullerene solution was transferred into a 250ml stainless pressure-resistant container. Then, the inside was replaced with nitrogen gas, and the lid was closed without heat treatment. Alternatively, the heat treatment was carried out by immersing the steel sheet in an oil bath at 150 ℃ for 2 hours or 15 hours. 9 kinds of lubricating oil compositions 1 to 9 shown in Table 1 were obtained. Each of the lubricating oil compositions was prepared into 3 samples, that is, 27 samples in total.

[ Table 1]

[ measurement method ]

(X-ray small angle scattering measurement)

For the lubricating oil composition, an X-ray small-angle scattering measurement was performed. Details are as follows.

Measurement System: SAXSpace (manufactured by AntonPaar)

X-ray: wavelength (λ): 0.1524nm

A detector: mythen (one-dimensional counting type detector)

After appropriate exposure conditions (attenuator and exposure time) were selected, two-dimensional scattering patterns of the lubricating oil composition and base oil (background) were recorded. Using image processing software Fit2d (european synchrotron research facility), scattering intensity curves were obtained with the scattering vector on the horizontal axis and the scattering intensity on the vertical axis, respectively. The scattering intensity of the base oil is subtracted from the scattering intensity of the lubricating oil composition, whereby a scattering intensity curve of the particles can be obtained.

(measurement of abrasion coefficient)

The obtained lubricating oil composition was evaluated for wear resistance by using a friction and wear tester (product name "ball-and-disk tribometer" manufactured by Anton Paar).

The substrate and the ball constituting the friction wear tester were made of SUJ2, which is a high carbon chromium bearing steel material. The diameter of the ball was 6mm, and the substrate was used in a 15mm square.

First, a lubricating oil composition is applied to one main surface of a substrate. Next, the balls are made to slide on the one main surface of the substrate through the lubricating oil composition so that the balls draw concentric tracks. The speed of the balls on the one main surface of the substrate was set to 20 mm/sec, and the load on the one main surface of the substrate by the balls was set to 25N. When the sliding distance of the ball on the one main surface of the substrate reached 15m in total, the ball was taken out from the apparatus, the contact surface of the ball with the substrate was observed with an optical microscope, and the maximum diameter of the circle of the wear surface was D (μm) for the wear of the surface. Here, the maximum diameter D is defined as a wear coefficient. That is, the smaller the number of the maximum diameter D, the more the wear is suppressed, and this is a preferable state in terms of the lubricating properties of the lubricating oil composition. Usually wear out into a circular shape but sometimes into an oval shape. In this case, the portion having the largest diameter is defined as the maximum diameter D. The measurement was performed at 25. + -. 2 ℃ environment.

(measurement of dynamic viscosity)

About 50mL of the lubricating oil composition was removed to a glass beaker and immersed in a water bath at 40 ℃ for 30 minutes.

Next, by following JIS Z8803: 2011 the dynamic viscosity of the lubricating oil composition was measured by a viscosity measuring method using a capillary viscometer, which is a method for measuring the viscosity of a liquid defined in the specification.

[ example 1]

The scattering intensity curves of the particles were obtained by performing X-ray small angle scattering measurements on 27 samples of the lubricating oil composition and the base oil (mineral oil a). Using the scattering intensity curve of the obtained particles, the average particle diameter (R) was calculated by the G method_G). Then, the wear coefficient of 27 samples of the lubricating oil composition was measured, and the average particle diameter (R) was determined_G) The relationship with the wear coefficient is shown in fig. 1. Average particle diameter (R)_G) And the values of the wear coefficient are shown in table 2.

[ Table 2]

From the results shown in FIG. 1, the average particle diameter (R)_G) Coefficient of correlation with abrasion coefficient was-0.80 at average particle diameter (R)_G) And the wear coefficient. The correlation coefficient is obtained by the least square method. When the absolute value of the correlation coefficient is 0.70 or more, it is determined that the correlation exists. In example 1 in which correlation exists, the average particle diameter (R) was determined by screening_G) Lubricating oil compositions having a wear coefficient within a desired range can be selected from those having a wear coefficient within a specific range.

For example, in fig. 1, when the wear coefficient of the lubricating oil composition is equal to or less than the value B (═ 200) as a non-defective product, the average particle diameter (R) may be set to be equal to_G) Is a value A₁The lubricating oil composition (1.75) or more was screened as a non-defective product. Therefore, the following steps are carried out: in this case, the average particle diameter (R) is defined as_G) Is a value A₁The average particle diameter (R) is set to the above-mentioned predetermined range_G) Is a value A₁When the lubricating oil composition is screened as a non-defective product, the possibility that a defective product having a wear coefficient exceeding the value B is included is low. Further, in FIG. 1, the average particle diameter (R) of the lubricating oil composition_G) Below the value A₁In the case of (3), the lubricating oil composition having a wear coefficient exceeding the value B can be screened as a defective product. In fig. 1, even in the region C₁The lubricating oil composition of the defective product in the above range can be adjusted to a lubricating oil composition of a non-defective product having a wear coefficient of not more than the value B by the following method, as long as the amount of the lubricating oil composition is small. Can be prepared by adding the lubricant composition in the region D to the defective lubricating oil composition₁The lubricating oil composition of the above (B), thereby reducing the average particle diameter (R)_G) Is a value A₁The above.

[ example 2]

The average particle diameter (R) of the particles was calculated by the above S method using the scattering intensity curve of the particles and the scattering intensity curve of the mineral oil A_S) Except for this, the average particle diameter (R) of the particles was evaluated in the same manner as in example 1_S) The relationship to the wear coefficient.

Average particle diameter (R)_S) And the values of abrasion coefficient are shown in Table 3, and the average particle diameter (R) is_S) The relationship with the wear coefficient is shown in fig. 2.

[ Table 3]

From the results shown in FIG. 2, the average particle diameter (R)_S) The coefficient of correlation with the abrasion coefficient is-0.89, and the absolute value thereof is 0.70 or more, and therefore, the average particle diameter (R) is_S) And the wear coefficient. Therefore, it is understood that the average particle diameter (R) can be selected in example 2_S) Lubricating oil composition in a specific range, thereby screening wear linesAnd a lubricating oil composition in a desired range.

For example, in fig. 2, when the lubricating oil composition having a wear coefficient of not more than the value B (═ 200) is a non-defective product, the average particle diameter (R) may be set to be equal to_S) Is a value A₂The lubricating oil composition (13) or more was screened as a good product. Therefore, the following steps are carried out: in this case, the average particle diameter (R) is defined as_S) Is a value A₂The average particle diameter (R) is set to the above-mentioned predetermined range_S) Is a value A₂When the lubricating oil composition is screened as a non-defective product, the possibility that a defective product having a wear coefficient exceeding the value B is included is low. Further, in FIG. 2, the average particle diameter (R) of the lubricating oil composition_S) Below the value A₂In the case of (3), the lubricating oil composition having a wear coefficient exceeding the value B can be screened as a defective product. In fig. 2, even in the region C₂The lubricating oil composition of the defective product in the above range can be adjusted to a lubricating oil composition of a non-defective product having a wear coefficient of B or less by the following method, as long as the amount thereof is small. Can be prepared by adding the lubricant composition in the region D to the defective lubricating oil composition₂The lubricating oil composition of the above (B), thereby reducing the average particle diameter (R)_S) Is a value A₂The above.

Comparative example 1

Dynamic viscosity (mm) was measured for 27 samples of the above lubricating oil composition²In/s) and wear coefficient, the dynamic viscosity was evaluated in relation to the wear coefficient. The measurement results of the dynamic viscosity and the wear coefficient are shown in table 4, and the relationship between the dynamic viscosity and the wear coefficient is shown in fig. 3.

[ Table 4]

According to the results shown in fig. 3, the correlation coefficient of the dynamic viscosity and the wear coefficient was 0.11, and the absolute value thereof was less than 0.70, and therefore, no correlation was confirmed between the dynamic viscosity and the wear coefficient. Therefore, it is known that the lubricating oil composition cannot be screened by estimating the wear coefficient of the lubricating oil composition from the dynamic viscosity of the lubricating oil composition.

Industrial applicability

The present invention can predict wear resistance by measuring the average particle diameter (R) of particles present in a lubricating oil composition in a process for producing the lubricating oil composition containing a base oil and fullerene, and can accurately screen the lubricating oil composition into a non-defective product and a defective product. Therefore, the lubricant composition of the non-defective product screened out by the present invention is effective for suppressing the occurrence of damage or wear of metal parts in sliding parts of automobiles, household electrical appliances, industrial machines, and the like.