JP7028409B2 - Lubricating oil composition, internal combustion engine, and method of lubricating internal combustion engine - Google Patents

Description

The present invention relates to a lubricating oil composition and a lubrication method for an internal combustion engine and an internal combustion engine using the lubricating oil composition.

In recent years, the number of hybrid vehicles and vehicles equipped with an idling stop mechanism has increased, but in these vehicles, it is difficult for the temperature of the engine oil to rise. Therefore, the engine oil used in these vehicles is particularly required to further improve the low temperature viscosity characteristics such as fuel efficiency at low temperature and low temperature startability of the engine.
Further, the engine oil is required to have not only such low-temperature viscosity characteristics but also good viscosity-temperature characteristics, low evaporability and the like.

As an engine oil with such various characteristics improved in a well-balanced manner, a lubricating oil base oil used as an engine oil that can meet the required performance of such an engine oil is being actively developed.
Patent Documents 1 to 4 disclose lubricating oil base oils in which specific physical property values are adjusted within a predetermined range.

Japanese Unexamined Patent Publication No. 2008-274237 Japanese Unexamined Patent Publication No. 2012-153906 JP-A-2007-016172A Japanese Unexamined Patent Publication No. 2006-241436

By the way, in order to improve the low-temperature viscosity characteristics, it is common to add a polymer component as a pour point lowering agent or a viscosity index improver to the lubricating oil base oil to improve the low-temperature viscosity characteristics of the engine oil. It is done in.
However, the presence of the polymer component blended as a pour point lowering agent or a viscosity index improving agent also causes a factor of lowering the high temperature cleanliness of the piston of the engine oil.
The engine oil using the lubricating oil base oil described in Patent Documents 1 to 4 has a problem in high temperature cleanliness of the piston, and there is room for further improvement in low temperature viscosity characteristics.
Therefore, there is a demand for a lubricating oil composition that can be used as an engine oil having both low-temperature viscosity characteristics and high-temperature cleanliness of a piston improved in a well-balanced manner.

INDUSTRIAL APPLICABILITY The present invention has good low-temperature viscosity characteristics such as low-temperature fuel saving and low-temperature startability of an engine, a lubricating oil composition excellent in high-temperature cleanliness of a piston, and an internal combustion engine using the lubricating oil composition. And to provide a lubrication method for internal combustion engines.

The present inventor has a predetermined kinematic viscosity and viscosity index, and has a mineral oil-based base oil in which the temperature gradient Δ | η * | of the complex viscosity between two points of -10 ° C and -25 ° C is adjusted to a predetermined value or less. , It has been found that a lubricating oil composition containing an olefin-based copolymer can solve the above-mentioned problems.
The present invention has been completed based on this finding.

That is, the present invention provides the following [1] to [3].
[1] A lubricating oil composition containing a mineral oil-based base oil satisfying the following requirements (I) to (III) and an olefin-based copolymer.
-Requirement (I): The kinematic viscosity at 100 ° C. is 2 mm ² / s or more and less than 7 mm ² / s.
-Requirement (II): Viscosity index is 100 or more.
Requirement (III): Complex viscosity between two points of -10 ° C and -25 ° C measured using a rotary rheometer under the conditions of an angular velocity of 6.3 rad / s and a strain of 0.1 to 100%. The temperature gradient Δ | η * | is 60 Pa · s / ° C. or less.
[2] An internal combustion engine having a sliding mechanism including a piston ring and a liner, and comprising the lubricating oil composition according to the above [1].
[3] A method for lubricating an internal combustion engine having a sliding mechanism including a piston ring and a liner, wherein the piston ring and the liner are lubricated by using the lubricating oil composition according to the above [1]. Lubrication method.

The lubricating oil composition of the present invention has good low-temperature viscosity characteristics such as low-temperature fuel efficiency and low-temperature startability of an engine, and is also excellent in high-temperature cleanliness of a piston.

The relationship between the temperature and the complex viscosity η * was shown for the mineral oil-based base oil (2) of Example 2, the mineral oil-based base oil (a) of Comparative Example 1, and the mineral oil-based base oil (b) of Comparative Example 2. It is a graph. It is a schematic diagram which shows the outline of the structure of the sliding mechanism provided with a piston ring and a liner.

In the present specification, the kinematic viscosity and the viscosity index at a predetermined temperature mean the values measured according to JIS K2283: 2000.
In the present specification, the complex viscosity η * at a predetermined temperature is a value measured under the conditions of an angular velocity of 6.3 rad / s and a strain amount of 0.1 to 100% using a rotary rheometer, and is more specific. Means the value measured by the method described in Examples. The above-mentioned "strain amount" is a measurement condition parameter that is appropriately set according to the measurement temperature in the range of 0.1 to 100%.
In the present specification, the mass average molecular weight (Mw) and the number average molecular weight (Mn) of each component are values in terms of standard polystyrene measured by a gel permeation chromatography (GPC) method, and specifically, Examples. Means the value measured by the method described in.
In the present specification, the CCS viscosity (low temperature viscosity) at −35 ° C. means a value measured according to JIS K2010: 1993 (ASTM D 2602).

The lubricating oil composition of the present invention contains a mineral oil-based base oil and an olefin-based copolymer, but is further added for lubricating oils other than synthetic oils and olefin-based copolymers as long as the effects of the present invention are not impaired. It may contain an agent.

However, in the lubricating oil composition of one aspect of the present invention, the total content of the mineral oil-based base oil and the olefin-based copolymer is preferably 60% by mass or more based on the total amount of the lubricating oil composition. It is preferably 65% by mass or more, more preferably 70% by mass or more, and even more preferably 75% by mass or more.
Hereinafter, each component contained in the lubricating oil composition according to one aspect of the present invention will be described.

[Mineral oil-based base oil]
The mineral oil-based base oil contained in the lubricating oil composition of the present invention includes, for example, atmospheric residual oil obtained by atmospheric distillation of crude oil such as paraffin-based mineral oil, intermediate mineral oil, and naphthenic mineral oil; Distillate oil obtained by distillation of oil under reduced pressure; one of the purification treatments such as solvent removal, solvent extraction, hydrofinishing, solvent removal, contact removal, isomerization removal, vacuum distillation, etc. Mineral oil or wax (GTL wax, etc.) that has been subjected to one or more treatments; etc. may be mentioned.
These mineral oil-based base oils may be used alone or in combination of two or more.

The content of the mineral oil-based base oil contained in the lubricating oil composition of one aspect of the present invention is usually 50% by mass or more, preferably 55% by mass or more, based on the total amount (100% by mass) of the lubricating oil composition. , More preferably 60% by mass or more, further preferably 65% by mass or more, still more preferably 70% by mass or more, and preferably 99.9% by mass or less, more preferably 99% by mass or less, still more preferably. It is 95% by mass or less.

The mineral oil-based base oil contained in the lubricating oil composition of the present invention satisfies the following requirements (I) to (III).
-Requirement (I): The kinematic viscosity at 100 ° C. is 2 mm ² / s or more and less than 7 mm ² / s.
-Requirement (II): Viscosity index is 100 or more.
Requirement (III): Complex viscosity between two points of -10 ° C and -25 ° C measured using a rotary rheometer under the conditions of an angular velocity of 6.3 rad / s and a strain of 0.1 to 100%. The temperature gradient Δ | η * | is 60 Pa · s / ° C. or less.
Further, it is preferable that the mineral oil-based base oil used in one aspect of the present invention further satisfies the following requirement (IV).
-Requirement (IV): The complex viscosity η * at −35 ° C. measured at an angular velocity of 6.3 rad / s and a strain amount of 0.1% using a rotary rheometer is 60,000 Pa · s or less. be.
When the mineral oil-based base oil used in one aspect of the present invention is a mixed oil in which two or more kinds of mineral oils are combined, the mixed oil may satisfy the above requirements.
Hereinafter, the above requirements (I) to (IV) will be described.

<Requirement (I)>
Requirement (I) defines the balance between the evaporation loss of mineral oil-based base oil and the effect of improving fuel efficiency.
That is, if the kinematic viscosity of the mineral oil-based base oil of the present invention at 100 ° C. is less than 2 mm ² / s, the evaporation loss becomes large, which is not preferable. On the other hand, when the kinematic viscosity at 100 ° C. is 7 mm ² / s or more, the power loss due to the viscous resistance becomes large, which causes a problem in terms of the fuel efficiency improving effect.
The kinematic viscosity of the mineral oil-based base oil used in one embodiment of the present invention is preferably 2.1 mm ² / s or more, more preferably 2.2 mm ² / s, from the viewpoint of reducing the evaporation loss of the mineral oil-based base oil. It is s or more, more preferably 2.5 mm ² / s or more, preferably 6 mm ² / s or less, more preferably 5.5 mm ² / s or less, and further, from the viewpoint of improving the fuel efficiency improving effect of the mineral oil-based base oil. It is preferably 5 mm ² / s or less, and even more preferably 4.7 mm ² / s or less.

<Requirement (II)>
Requirement (II) is a regulation for making a mineral oil-based base oil with good viscosity-temperature characteristics and fuel efficiency.
That is, when the viscosity index of the mineral oil-based base oil used in the present invention is less than 100, the viscosity-temperature characteristics and the fuel saving property are significantly deteriorated, and the lubricating oil composition using the mineral oil-based base oil has a fuel efficiency. It has a problem in terms of performance.
From this point of view, the viscosity index of the mineral oil-based base oil used in one aspect of the present invention is preferably 105 or more, more preferably 110 or more.

Further, since the mineral oil-based base oil used in the present invention satisfies the requirement (III) described later, even if the viscosity index is not relatively high, the low temperature viscosity such as fuel saving at low temperature and low temperature startability of the engine It is possible to provide a lubricating oil composition having good properties.
Therefore, the viscosity index of the mineral oil-based base oil used in one embodiment of the present invention is preferably 145 or less, more preferably 140 or less, still more preferably 135 or less, still more preferably less than 130.

<Requirement (III)>
The mineral oil-based base oil used in the present invention was measured using a rotary rheometer under the conditions of an angular velocity of 6.3 rad / s and a strain amount of 0.1 to 100%, as specified in Requirement (III), -10. The temperature gradient Δ | η * | of the complex viscosity between the two points of ° C. and -25 ° C. (hereinafter, also simply referred to as "temperature gradient Δ | η * |" of the complex viscosity) is 60 Pa · s / s / Must be below ° C.
The value of the above-mentioned "strain amount" in the requirement (III) is appropriately set in the range of 0.1 to 100% according to the temperature.
In the above "complex viscosity temperature gradient Δ | η * |", the value of the complex viscosity η * at -10 ° C and the value of the complex viscosity η * at -25 ° C are set independently or at -10 ° C, respectively. From -25 ° C or -25 ° C to -10 ° C while continuously changing the temperature, and when the value is placed on the coordinate plane of temperature-complex viscosity, it is between -10 ° C and -25 ° C. It is a value indicating the amount of change (absolute value of slope) per unit of complex viscosity. More specifically, it means a value calculated from the following formula (f1).
-Calculation formula (f1): Temperature gradient of complex viscosity Δ | η * | = | ([complex viscosity η * at -25 ° C]-[complex viscosity η * at -10 ° C]) / (-25- (-10) )) ｜

By giving a specific relationship between the complex viscosity of the mineral oil-based base oil and the temperature, the present inventor can obtain the effects of excellent low-temperature viscosity characteristics such as fuel saving at low temperature and low-temperature startability of the engine, and piston cleanliness. It was also found that the composition, composition, state, production conditions, etc. of the mineral oil-based base oil have a great influence on the relationship between the complex viscosity and the temperature.

FIG. 1 shows the temperature and complex viscosity η * of the mineral oil-based base oil (2) of Example 2 described later, the mineral oil-based base oil (a) of Comparative Example 1, and the mineral oil-based base oil (b) of Comparative Example 2. It is a graph showing the relationship with.
The “complex viscosity temperature gradient Δ | η * |” here is the amount of change in the complex viscosity when the temperature range is −25 ° C. to −10 ° C., that is, the slope of the graph shown in FIG.
Generally, as one of the evaluation indexes of the low temperature viscosity characteristic, the "pour point", which is the temperature immediately before the mineral oil-based base oil solidifies, is used.
The present inventor has found that the temperature at which the complex viscosity increases sharply and the "pour point" are almost the same, and even if the mineral oil has an approximate "pour point" as shown in the graph of FIG. 1, the pour point is further increased. It was found that the increase / decrease in complex viscosity is different in a low temperature environment where the temperature is lowered.
From that point of view, the present inventors have improved the low-temperature viscosity characteristics by considering a specific relationship between the complex viscosity and the temperature of the mineral oil-based base oil in a low-temperature environment in which the temperature is further lowered from the pour point. The present invention was completed on the assumption that a mineral oil-based base oil could be obtained.

In addition, as another method for evaluating low-temperature viscosity characteristics, there are cases where various viscosity values such as CCS viscosity and BF viscosity are used. In these evaluation methods, the mineral oil-based base oil is used in a low-temperature environment. It cannot be said that the low temperature viscosity characteristics in Japan are always accurately specified.
That is, the mineral oil-based base oil contains a wax component, and when this wax component precipitates in a low temperature environment below the pour point, a gel-like structure is formed. This gel-like structure is fragile and its viscosity changes due to mechanical action. Therefore, even in the method for evaluating the low-temperature viscosity characteristic based on the CCS viscosity, it is only the apparent low-temperature viscosity under predetermined conditions, and it is not a physical property that can sufficiently express the viscosity characteristic in a low-temperature environment.
In addition, for example, the mineral oil-based base oil obtained by refining the raw material oil including the bottom oil may have an influence such that the measured value tends to be unstable when measuring the BF viscosity or the like, and the low temperature viscosity. It may not be possible to accurately evaluate the characteristics.

Therefore, as a result of various studies, the present inventors have focused on the above-mentioned “complex viscosity temperature gradient Δ | η * |” in mineral oil-based base oils that cannot be grasped by CCS viscosity, BF viscosity, or the like. The present invention has been completed by finding that a mineral oil-based base oil having improved low-temperature viscosity characteristics can be obtained in consideration of the change in the friction coefficient due to the precipitation of the wax component in consideration of the precipitation rate of the wax component contained in the oil. It is a thing.

According to the study by the present inventors, a mineral oil-based base oil having a temperature gradient Δ | η * | of the above complex viscosity exceeding 60 Pa · s / ° C has a high precipitation rate of wax content, which causes an increase in the coefficient of friction. Cheap. As a result, it was found that the lubricating oil composition using the mineral oil-based base oil is inferior in fuel efficiency in a low temperature environment.

Furthermore, the present inventors have provided a lubricating oil composition (engine oil) in which the high-temperature cleanliness of the piston is further improved by using a mineral oil-based base oil having a small complex viscosity temperature gradient Δ | η * |. It has also been found that it can be prepared.
That is, as shown in Examples described later, a lubricating oil composition using a mineral oil-based base oil having a complex viscosity temperature gradient Δ | η * | of 60 Pa · s / ° C or less has high-temperature cleanliness of a piston. Was found to be good. Further, a lubricating oil composition to which a mineral oil-based base oil having a complex viscosity temperature gradient Δ | η * | of 60 Pa · s / ° C or less and a polymer component such as a pour point lowering agent that can cause deposits is added. Even in the case of, the lubricating oil composition has a small increase in deposit and good piston cleanliness.

From the above viewpoint, in the mineral oil-based base oil used in one aspect of the present invention, the temperature gradient Δ | η * | of the complex viscosity specified in the requirement (III) is preferably 50 Pa · s / ° C or less, more preferably 20 Pa ·. It is s / ° C. or lower, more preferably 15 Pa · s / ° C. or lower, still more preferably 10 Pa · s / ° C. or lower, and particularly preferably 5 Pa · s / ° C. or lower.
Further, in the mineral oil-based base oil used in one aspect of the present invention, the temperature gradient Δ | η * | of the complex viscosity specified in the requirement (III) is not particularly limited as to the lower limit value, but is preferably 0.001 Pa. It is s / ° C. or higher, more preferably 0.01 Pa · s / ° C. or higher, and even more preferably 0.02 Pa · s / ° C. or higher.

<Requirements (IV)>
Requirement (IV) is one of the indicators showing the low temperature viscosity characteristics of mineral oil-based base oil in a low temperature environment, which is independent of Requirement (III).
Mineral oil-based base oils having a low complex viscosity η * at −35 ° C. specified in Requirement (IV) tend to have a low paraffin content. Therefore, by using the mineral oil-based base oil, it is possible to produce a lubricating oil composition having good low-temperature viscosity characteristics such as fuel efficiency at low temperature and low-temperature startability of the engine and improved high-temperature cleanliness of the piston. ..

From the above viewpoint, in the mineral oil-based base oil used in one aspect of the present invention, the complex viscosity η * at −35 ° C. specified in Requirement (IV) is preferably 60,000 Pa · s or less, but more preferably. It is 40,000 Pa · s or less, more preferably 10,000 Pa · s or less, further preferably 6,000 Pa · s or less, still more preferably 2,000 Pa · s or less, and particularly preferably 500 Pa · s or less.
Further, the complex viscosity η * at −35 ° C. specified in the requirement (IV) is not particularly limited in terms of the lower limit value, but is preferably 0.1 Pa · s or more, more preferably 1 Pa · s or more, and further preferably 2 Pa.・ It is s or more.

The naphthenic content (% CN) of the mineral oil _- based base oil used in one embodiment of the present invention is preferably 10 to 30, more preferably 13 to 30, more preferably 15 to 30, still more preferably 16 to 30, and more. More preferably, it is 20 to 30.
In general, it is known that the naphthenic content contained in a mineral oil-based base oil causes a decrease in the viscosity index. Mineral oil-based base oils used in engine oils are required to have good viscosity characteristics over a wide temperature range, and therefore, those having a low naphthenic content are preferably used.
However, since the mineral oil-based base oil used in the present invention particularly satisfies the above requirement (III), it has good low-temperature viscosity characteristics and can sufficiently suppress a decrease in viscosity characteristics due to the naphthenic content.
Furthermore, according to the studies by the present inventors, it was found that the naphthenic acid has an action of dissolving caulking that may occur in a high temperature environment. Therefore, by using a mineral oil-based base oil having a high naphthenic content, it is possible to produce a lubricating oil composition having further improved high-temperature cleanliness of the piston.

Further, the aromatic component (% CA) of the mineral oil _- based base oil used in one aspect of the present invention is preferably a mineral oil-based base oil that can be a lubricating oil composition having excellent high-temperature cleanliness of a piston. It is less than 1.0, more preferably 0.1 or less.

In the present specification, the naphthen content (% CN) and aromatic content (% CA) of the mineral oil _- based base oil are the naphthen content measured by ASTM _D -3238 ring analysis (nd-M method). And the proportion of aromatics (percentage).

The sulfur content of the mineral oil-based base oil used in one embodiment of the present invention is preferably less than 500 mass ppm from the viewpoint of making a mineral oil-based base oil capable of producing a lubricating oil composition having excellent high-temperature cleanliness of a piston. It is preferably less than 100 mass ppm.
In this specification, the sulfur content of the mineral oil-based base oil is a value measured in accordance with JIS K2541-6: 2003 "Crude oil and petroleum products-sulfur content test method".

From the viewpoint of using a mineral oil-based base oil capable of producing a lubricating oil composition having excellent high-temperature cleanliness of a piston, the mineral oil _- based base oil used in one embodiment of the present invention has an aromatic content (% CA) of 0.1. It is preferable that the sulfur content is less than 100 mass ppm and the sulfur content is less than 100 mass ppm.

<Preparation example of mineral oil-based base oil satisfying requirements (I) to (IV)>
Mineral oil-based base oils that satisfy the above requirements (I) to (IV), particularly the above requirements (III) and (IV), can be easily prepared, for example, by appropriately considering the following matters. The following items are examples of the preparation method, and can be prepared by considering other items.

(1) Preparation of mass average molecular weight of mineral oil-based base oil The mass average molecular weight (Mw) of mineral oil-based base oil has the properties specified in the above requirements (I) to (IV) (particularly, the above requirements (III) and (IV). ) Is a physical property that affects the specified properties).
The mass average molecular weight (Mw) of the mineral oil-based base oil used in one embodiment of the present invention is the mineral oil-based base oil satisfying the above requirements (I) to (IV), particularly the requirements (I), (III) and (IV). From the viewpoint of the above, it is preferably 450 or less, and preferably 150 or more.

(2) Selection of Raw Material Oil as a Raw Material for Mineral Oil-based Base Oil The mineral oil-based base oil used in one embodiment of the present invention is preferably obtained by refining the raw material oil.
The raw material oil includes a raw material oil containing a petroleum-derived wax and a petroleum-derived raw material oil from the viewpoint of being a mineral oil-based base oil satisfying the above requirements (I) to (IV), particularly requirements (III) and (IV). It is preferably a raw material oil containing wax and bottom oil. Further, a raw material oil containing a solvent dewaxing oil may be used.

When a raw material oil containing petroleum-derived wax and bottom oil is used, the content ratio [wax / bottom oil] of the wax to the bottom oil in the raw material oil is a mineral oil system that satisfies the requirements (III) and (IV). From the viewpoint of using as a base oil, the mass ratio is preferably 30/70 to 95/5, more preferably 55/45 to 95/5, still more preferably 70/30 to 95/5, and even more preferably 80/20. ~ 95/5.
As the ratio of the bottom oil in the raw material oil increases, the value of the temperature gradient Δ | η * | of the complex viscosity specified in the requirement (III) tends to increase, and it is specified in the requirement (IV). The value of the complex viscosity η * at −35 ° C. also tends to increase.
On the other hand, since the bottom oil contains a large amount of naphthenic acid, a mineral oil _- based base oil having a high naphthenic acid content (% CN) can be prepared by using a raw material oil containing the bottom oil, and the lubricating oil composition can be prepared. Contributes to high temperature cleanliness of the piston.

The bottom oil remains after the oil containing heavy fuel oil obtained from a vacuum distillation apparatus is hydrolyzed and decomposed to separate and remove naphtha and kerosene in a normal fuel oil manufacturing process using crude oil as a raw material. The bottom distillate can be mentioned.

As the wax, in addition to the wax separated by removing the solvent from the bottom distillate, crude oil such as paraffin-based mineral oil, intermediate-based mineral oil, and naphthen-based mineral oil is distilled under atmospheric pressure to separate and remove naphtha and light oil. Wax obtained by removing the solvent from the atmospheric residual oil remaining after the above; Wax obtained by solvent extraction and solvent removal of a hydrofinished product; GTL wax obtained by Fisher Tropush synthesis and the like can be mentioned.

On the other hand, examples of the solvent-dewaxing oil include residual oil after solvent-dewaxing the above-mentioned bottom fraction and the like to separate and remove the above-mentioned wax. Further, the solvent dewaxing oil has been subjected to a refining treatment for solvent dewaxing, and is different from the above-mentioned bottom oil.

As a method for obtaining a wax by solvent dewaxing, for example, a method in which a bottom distillate is obtained by mixing a mixed solvent of methyl ethyl canton and toluene and stirring in a low temperature region to remove the precipitate is preferable.
From the viewpoint of using a mineral oil-based base oil that satisfies the requirements (III) and (IV), the specific temperature in the low temperature environment for solvent dewaxing may be lower than the temperature for general solvent dewaxing. It is preferable, specifically, it is preferably −25 ° C. or lower, and more preferably −30 ° C. or lower.

The oil content of the raw material oil is preferably 5 to 55% by mass, more preferably 7 to 45% by mass, and further preferably 10 to 35% by mass from the viewpoint of making a mineral oil-based base oil satisfying the requirements (III) and (IV). %, More preferably 15 to 32% by mass, and particularly preferably 21 to 30% by mass.

The kinematic viscosity of the raw material oil at 100 ° C. is preferably 2.0 to 7.0 mm ² / s, more preferably 2.3 to 6.5 mm ² from the viewpoint of making the mineral oil-based base oil satisfying the requirement (I). / S, more preferably 2.5 to 6.0 mm ² / s.
The viscosity index of the raw material oil is preferably 100 or more, more preferably 110 or more, still more preferably 120 or more, from the viewpoint of making a mineral oil-based base oil satisfying the requirement (II).

(3) Setting of Refining Conditions for Raw Material Oil It is preferable that the above raw material oil is refined to prepare a mineral oil-based base oil satisfying the above (I) to (IV).
The purification treatment preferably includes at least one of a hydrogenation isomerization dewaxing treatment and a hydrogenation treatment. It is preferable that the type of refining treatment and the refining conditions are appropriately set according to the type of raw material oil used.

More specifically, from the viewpoint of using a mineral oil-based base oil that satisfies the requirements (III) and (IV), it is preferable to select the refining treatment as follows according to the type of raw material oil to be used.
-When using a raw material oil (α) containing petroleum-derived wax and bottom oil in the above-mentioned content ratio, both the hydrogenation isomerization dewaxing treatment and the hydrogenation treatment are performed on the raw material oil (α). It is preferable to carry out a purification treatment including.
When a raw material oil (β) containing a solvent dewaxing oil is used, it is preferable that the raw material oil (β) is subjected to a refining treatment including a hydrogenation treatment without performing a hydrogenation isomerization dewaxing treatment.

Since the above-mentioned raw material oil (α) contains bottom oil, the contents of aromatic, sulfur, and nitrogen tend to be high. The presence of aromatics, sulfurs, and nitrogens causes deposits in the lubricating oil composition and causes a decrease in the high temperature detergency of the piston.
The hydrogenation isomerization dewaxing treatment can remove aromatics, sulfurs, and nitrogens to reduce their contents.
In the hydrogenation isomerization dewaxing treatment, the linear paraffin in the wax is converted into a branched-chain isoparaffin, so that a mineral oil-based base oil satisfying the requirements (III) and (IV) can be obtained.

On the other hand, the above-mentioned raw material oil (β) contains wax, but since linear paraffin is precipitated and separated and removed in a low temperature environment by solvent dewaxing treatment, it is specified in requirements (III) and (IV). The content of linear paraffin that affects the value of complex viscosity is low. Therefore, there is little need to perform "hydrogenation isomerization dewaxing treatment".

(Hydrogenation isomerization dewax treatment)
As described above, the hydrogenation isomerization dewaxing treatment involves isomerization of the linear paraffin contained in the raw material oil into isoparaffin with a branched chain, opening of the aromatic component to convert the paraffin content, and sulfur content and nitrogen content. This is a refining process performed for the purpose of removing impurities such as paraffin. In particular, the presence of linear paraffin is one of the factors that increase the value of the temperature gradient Δ | η * | of the complex viscosity specified in Requirement (III). The value of the temperature gradient Δ | η * | of the complex viscosity is adjusted to be low.

The hydrogenation isomerization dewaxing treatment is preferably carried out in the presence of a hydrogenation isomerization dewaxing catalyst.
Examples of the hydrogenation isomerization dewaxing catalyst include nickel (Ni) / tungsten (W), nickel (Ni) / molybdenum (Mo), and cobalt (Co) on a carrier such as silica aluminophosphate (SAPO) or zeolite. / Examples thereof include catalysts carrying metal oxides such as molybdenum (Mo) and noble metals such as platinum (Pt) and lead (Pd).

The hydrogen partial pressure in the hydrogenation isomerization dewaxing treatment is preferably 2.0 to 220 MPa, more preferably 2.5 to 100 MPa, from the viewpoint of using a mineral oil-based base oil that satisfies the requirements (III) and (IV). It is more preferably 3.0 to 50 MPa, and even more preferably 3.5 to 25 MPa.

The reaction temperature in the hydrogenation isomerization dewax treatment is higher than the reaction temperature in the general hydrogenation isomerization dewax treatment from the viewpoint of using a mineral oil-based base oil that satisfies the requirements (III) and (IV). It is preferably set, specifically, preferably 320 to 480 ° C, more preferably 325 to 420 ° C, still more preferably 330 to 400 ° C, and even more preferably 335 to 370 ° C.
When the reaction temperature is high, the isomerization of the linear paraffin present in the raw material oil to the branched-chain isoparaffin can be promoted, and a mineral oil-based base oil satisfying the requirements (III) and (IV) can be prepared. Becomes easier.

The liquid spatiotemporal velocity (LHSV) in the hydrogenation isomerization dewaxing treatment is preferably 5.0 hr ^-1 or less, more preferably 5.0 hr-1 or less, from the viewpoint of using a mineral oil-based base oil that satisfies the requirements (III) and (IV). Is 2.0 hr ^-1 or less, more preferably 1.0 hr ^-1 or less, still more preferably 0.6 hr ^-1 or less.
Further, from the viewpoint of improving productivity, the LHSV in the hydrogenation isomerization dewaxing treatment is preferably 0.1 hr ^-1 or more, more preferably 0.2 hr ^-1 or more.

The supply ratio of hydrogen gas in the hydrogenation isomerization dewaxing treatment is preferably 100 to 1000 Nm ³ , more preferably 200 to 800 Nm ³ , and further preferably 250 to 650 Nm ³ with respect to 1 kiloliter of the feedstock oil to be supplied. be.
In addition, in order to remove the light fraction, the produced oil subjected to the hydrogenation isomerization dewaxing treatment may be subjected to vacuum distillation.

(Hydrogenation treatment)
The hydrogenation treatment is a refining treatment performed for the purpose of complete saturation of aromatic components contained in raw material oil and removal of impurities such as sulfur and nitrogen.
The hydrogenation treatment is preferably carried out in the presence of a hydrogenation catalyst.
Examples of the hydrogenation catalyst include an amorphous carrier such as silica / alumina and alumina and a crystalline carrier such as zeolite, and nickel (Ni) / tungsten (W), nickel (Ni) / molybdenum (Mo), and cobalt (Co). ) / Catalysts carrying metal oxides such as molybdenum (Mo) and noble metals such as platinum (Pt) and lead (Pd) can be mentioned.

The hydrogen partial pressure in the hydrogenation treatment is preferably set higher than the pressure in the general hydrogenation treatment from the viewpoint of using a mineral oil-based base oil that satisfies the requirements (III) and (IV). It is preferably 16 MPa or more, more preferably 17 MPa or more, still more preferably 20 MPa or more, and preferably 30 MPa or less, more preferably 22 MPa or less.

The reaction temperature in the hydrogenation treatment is preferably 200 to 400 ° C., more preferably 250 to 350 ° C., still more preferably 280 to 330 ° C. from the viewpoint of using a mineral oil-based base oil satisfying the requirements (III) and (IV). Is.

The liquid spatiotemporal velocity (LHSV) in the hydrogenation treatment is preferably 5.0 hr ^-1 or less, more preferably 2.0 hr ^-1 from the viewpoint of using a mineral oil-based base oil that satisfies the requirements (III) and (IV). Below, it is more preferably 1.0 hr ^-1 or less, and from the viewpoint of productivity, it is preferably 0.1 hr ^-1 or more, more preferably 0.2 hr ^-1 or more, still more preferably 0.3 hr ^-1 or more. Is.

The supply ratio of hydrogen gas in the hydrogenation treatment is preferably 100 to 1000 Nm ³ , more preferably 200 to 800 Nm ³ , and even more preferably 250 to 650 Nm ³ with respect to 1 kiloliter of the feed oil to be treated.

In addition, hydrogenated produced oil may be distilled under reduced pressure in order to remove light fractions. The conditions (pressure, temperature, time, etc.) of the vacuum distillation are appropriately adjusted so that the kinematic viscosity of the mineral oil-based base oil at 100 ° C. is within a desired range.

<Various physical properties of mineral oil-based base oil>
The CCS viscosity (low temperature viscosity) of the mineral oil-based base oil used in one embodiment of the present invention at −35 ° C. is preferably 5,000 mPa · s or less, more preferably 4,000 mPa · s or less, still more preferably 3,000 mPa. -S or less, more preferably 2,500 mPa · s or less.

[Synthetic oil]
The lubricating oil composition of one aspect of the present invention may contain synthetic oil together with the above-mentioned mineral oil-based base oil as long as the effects of the present invention are not impaired.
Examples of the synthetic oil include polyα-olefins (PAOs), ester compounds, ether compounds, polyglycols, alkylbenzenes, alkylnaphthalene and the like.
These synthetic oils may be used alone or in combination of two or more.

The content of the synthetic oil in the lubricating oil composition of one aspect of the present invention is preferably 0 to 30 parts by mass with respect to 100 parts by mass of the total amount of the mineral oil-based base oil in the lubricating oil composition. It is preferably 0 to 20 parts by mass, more preferably 0 to 15 parts by mass, still more preferably 0 to 10 parts by mass, and particularly preferably 0 to 5 parts by mass.

[Olefin-based copolymer]
The olefin-based copolymer contained in the lubricating oil composition of the present invention has a function of a viscosity index improver and is added to the lubricating oil composition in order to improve viscosity-temperature characteristics and fuel efficiency.
By the way, polymer components such as an olefin-based copolymer and polymethacrylate added as a viscosity index improver cause caulking that causes a decrease in high-temperature cleanliness of the piston.
Therefore, in order to improve the viscosity-temperature characteristics and fuel efficiency, the lubricating oil composition to which these polymer components are added has a problem that the high temperature cleanliness of the piston is lowered.

On the other hand, in the lubricating oil composition of the present invention, a mineral oil-based base oil satisfying the above requirements (I) to (III) (particularly, requirement (III)) is used, and an olefin-based co-weight is used as a viscosity index improver. By containing the coalescence, the above problem is solved.
That is, in the lubricating oil composition of the present invention, since the mineral oil-based base oil satisfying the above-mentioned requirement (III) is used as the base oil, even if caulking occurs from the viscosity index improver, the high temperature cleanliness of the piston is maintained. Can be kept good.
When the olefin-based copolymer used as the viscosity index improver in the lubricating oil composition of the present invention is used in combination with the above-mentioned mineral oil-based base oil, caulking due to the presence of the olefin-based copolymer is unlikely to precipitate.
Therefore, the lubricating oil composition of the present invention can improve viscosity-temperature characteristics and fuel efficiency, and can have good high-temperature cleanliness of a piston.

The olefin-based polymer used in one embodiment of the present invention is a polymer having a structural unit derived from a monomer having an alkenyl group and has 2 to 20 carbon atoms (preferably 2 to 16, more preferably 2 to 2 to 20). Examples thereof include the α-olefin copolymer of 14), and an ethylene-α-olefin copolymer composed of ethylene and an α-olefin having 3 to 20 carbon atoms is preferable, and an ethylene-propylene copolymer is more preferable.
The number of carbon atoms of the α-olefin constituting the ethylene-α-olefin copolymer is preferably 3 to 20, more preferably 3 to 16, still more preferably 3 to 14, and even more preferably 3 to 6. Is.

The olefin-based copolymer used in one aspect of the present invention may be a non-dispersive olefin-based copolymer or a dispersed olefin-based copolymer.
As the dispersed olefin-based copolymer, a copolymer obtained by graft-polymerizing the above-mentioned ethylene-α-olefin copolymer with maleic acid, N-vinylpyrrolidone, N-vinylimidazole, glycidyl acrylate and the like. Can be mentioned.

Further, the olefin-based copolymer used in one embodiment of the present invention may be a copolymer having only a structural unit derived from an aliphatic hydrocarbon, or a copolymer having only a structural unit derived from an aliphatic hydrocarbon. It may be a copolymer in which an aromatic hydrocarbon group is bonded to the main chain of the polymer.
As a copolymer in which an aromatic hydrocarbon group is bonded to the main chain of a copolymer having only a structural unit derived from an aliphatic hydrocarbon, a styrene-based polymer (for example, a styrene-diene copolymer, styrene-) is used. Isoprene copolymer, etc.).

The mass average molecular weight (Mw) of the olefin-based copolymer used in one embodiment of the present invention is preferably 10,000 to 1,000,000 from the viewpoint of obtaining a lubricating oil composition having improved viscosity-temperature characteristics and fuel efficiency. , More preferably 50,000 to 800,000, still more preferably 100,000 to 700,000, and even more preferably 200,000 to 600,000.

In the lubricating oil composition of one aspect of the present invention, the content of the olefin-based copolymer is preferably 0.01 to 15.0% by mass, based on the total amount (100% by mass) of the lubricating oil composition. It is preferably 0.1 to 10.0% by mass, more preferably 0.5 to 6.0% by mass, and even more preferably 1.0 to 4.0% by mass.
The olefin-based copolymer may be dissolved in a diluted oil and used in the form of a solution, but the above-mentioned "content of the olefin-based copolymer" excludes the mass of the diluted oil. Refers to the solid content of the polymer. The same applies to the “content of polymer component” described later.

[Polymer components other than olefin copolymers]
In the lubricating oil composition of one aspect of the present invention, a polymer component other than the olefin-based copolymer may be contained as long as the effect of the present invention is not impaired.
The above-mentioned "polymer component" is a component that causes caulking, has a mass average molecular weight (Mw) of 1000 or more, and means a compound having at least one repeating unit, and is lubricated. Examples thereof include components added as a viscosity index improver and a pour point lowering agent, which are additives for oil. Therefore, the mineral oil-based base oil and synthetic oil do not fall under the "polymer component" referred to here.

Examples of the polymer component used as the viscosity index improver include polymethacrylate (non-dispersive polymethacrylate, dispersed polymethacrylate) and the like.

Examples of the polymer component used as a pour point lowering agent as an additive for lubricating oil include an ethylene-vinyl acetate copolymer, a condensate of chlorinated paraffin and naphthalene, and a condensate of chlorinated paraffin and phenol. , Polymethacrylate, polyalkylstyrene and the like.

In the lubricating oil composition of one aspect of the present invention, the content of the polymer component other than these olefin-based copolymers is the lubricating oil from the viewpoint of obtaining a lubricating oil composition having good high-temperature cleanliness of the piston. With respect to 100 parts by mass of the total amount of the olefin-based polymer contained in the composition, it is preferably less than 80 parts by mass, more preferably less than 70 parts by mass, still more preferably less than 60 parts by mass, still more preferably 50 parts by mass. Less than a copy.

By the way, polymethacrylate used as a viscosity index improver and a pour point lowering agent tends to cause caulking among polymer components.
In particular, polymethacrylate (α) having a mass average molecular weight of 200,000 or more, which is often used as a viscosity index improver, is generally a component that easily causes caulking, and the smaller the content, the more preferable.

However, since the lubricating oil composition of the present invention uses a mineral oil-based base oil that satisfies the above-mentioned requirement (III), if a small amount of polymethacrylate (α) is used, the occurrence of caulking can be suppressed and the piston can be used. Good high temperature cleanliness can be maintained.
In the lubricating oil composition of one aspect of the present invention, the content of polymethacrylate (α) is preferably 60 with respect to 100 parts by mass of the total amount of the olefin-based copolymer contained in the lubricating oil composition. It is less than parts by mass, more preferably less than 50 parts by mass, still more preferably less than 45 parts by mass.
When the content of polymethacrylate (α) is less than 60 parts by mass, the occurrence of caulking can be suppressed and the high temperature cleanliness of the piston can be kept good.

In addition, the content of polymethacrylate (β), which is often used as a pour point lowering agent and has a mass average molecular weight of less than 200,000, must be adjusted from the viewpoint of maintaining good high-temperature cleanliness of the piston. Is preferable.
In the lubricating oil composition of one aspect of the present invention, the content of polymethacrylate (β) is set from the viewpoint of maintaining good high-temperature cleanliness of the piston with respect to 100 parts by mass of the total amount of the olefin-based copolymer. It is preferably 80 parts by mass or less, more preferably 70 parts by mass or less, further preferably 60 parts by mass or less, still more preferably 50 parts by mass or less, and preferably 0 from the viewpoint of improving low temperature fluidity. It is 5.5 parts by mass or more, more preferably 0.7 parts by mass or more, still more preferably 1.0 part by mass or more.

[Additives for lubricating oil]
Further, the lubricating oil composition of the present invention is added to a lubricating oil other than the above-mentioned viscosity index improver and pour point lowering agent, which are more generally used, if necessary, as long as the effects of the present invention are not impaired. It may contain an agent.
Examples of such additives for lubricating oil include metal detergents, dispersants, abrasion resistant agents, extreme pressure agents, antioxidants, defoaming agents, friction modifiers, rust preventives, and metal inactivating agents. And so on.
As the lubricating oil additive, a commercially available additive package containing a plurality of additives conforming to the API / ILSAC SN / GF-5 standard or the like may be used.
Further, a compound having a plurality of functions as the above-mentioned additive (for example, a compound having a function as an abrasion resistant agent and an extreme pressure agent) may be used.
Further, each lubricating oil additive may be used alone or in combination of two or more.

The content of each of these additives for lubricating oil can be appropriately adjusted within a range that does not impair the effects of the present invention, but is usually 0 based on the total amount (100% by mass) of the lubricating oil composition. It is 001 to 15% by mass, preferably 0.005 to 10% by mass, and more preferably 0.01 to 8% by mass.
In the lubricating oil composition of one aspect of the present invention, the total content of these lubricating oil additives is preferably 0 to 30% by mass based on the total amount (100% by mass) of the lubricating oil composition. It is more preferably 0 to 25% by mass, further preferably 0 to 20% by mass, and even more preferably 0 to 15% by mass.

(Metallic detergent)
Examples of the metal-based cleaning agent include organic acid metal salt compounds containing metal atoms selected from alkali metals and alkaline earth metals, and specifically, metal atoms selected from alkali metals and alkaline earth metals. Examples thereof include metal salicylates, metal phenates, and metal sulfonates containing the above.
In addition, in this specification, "alkali metal" refers to lithium, sodium, potassium, rubidium, cesium, and francium.
The "alkaline earth metal" refers to beryllium, magnesium, calcium, strontium, and barium.
As the metal atom contained in the metal-based cleaning agent, sodium, calcium, magnesium, or barium is preferable, and calcium is more preferable, from the viewpoint of improving the cleanliness at high temperature.

The metal salicylate is preferably a compound represented by the following general formula (1), the metal phenate is preferably a compound represented by the following general formula (2), and the metal sulfonate is preferably the following general formula (3). ) Is preferred.

In the above general formulas (1) to (3), M is a metal atom selected from an alkali metal and an alkaline earth metal, and sodium, calcium, magnesium, or barium is preferable, and calcium is more preferable. Further, M'is an alkaline earth metal, and calcium, magnesium, or barium is preferable, and calcium is more preferable. p is a valence of M, which is 1 or 2. R is a hydrogen atom or a hydrocarbon group having 1 to 18 carbon atoms. q is an integer of 0 or more, preferably an integer of 0 to 3.
Examples of the hydrocarbon group that can be selected as R include an alkyl group having 1 to 18 carbon atoms, an alkenyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 18 ring-forming carbon atoms, and 6 to 18 ring-forming carbon atoms. Examples thereof include an aryl group of, an alkylaryl group having 7 to 18 carbon atoms, an arylalkyl group having 7 to 18 carbon atoms, and the like.

In one aspect of the present invention, these metal-based detergents may be used alone or in combination of two or more.
Among these, at least one selected from calcium salicylate, calcium phenate, and calcium sulfonate is preferable from the viewpoint of improving cleanliness at high temperature and from the viewpoint of solubility in base oil.

In one aspect of the present invention, the metal-based detergent may be any of a neutral salt, a basic salt, a hyperbasic salt, and a mixture thereof.
The total base value of the metal-based detergent is preferably 0 to 600 mgKOH / g.
In one aspect of the present invention, when the metal-based cleaning agent is a basic salt or a hyperbasic salt, the total base value of the metal-based cleaning agent is preferably 10 to 600 mgKOH / g, more preferably. Is 20-500 mgKOH / g.
In the present specification, the "base value" is defined as 7. of JIS K2501 "Petroleum products and lubricating oil-neutralization value test method". It means the base value by the perchloric acid method measured according to.

(Dispersant)
Examples of the dispersant include succinimide, benzylamine, succinic acid ester, and boron-modified products thereof.
Examples of the succinic acid imide include succinic acid having a polyalkenyl group such as a polybutenyl group having a number average molecular weight of 300 to 4,000, and polyethylene such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine and pentaethylenehexamine. Examples thereof include monoimides or bisimides of polyamines, or boron-modified products thereof; Mannig reaction products of phenols having polyalkenyl groups, formaldehyde, and polyethylenepolyamines.

(Abrasion resistant agent)
As the abrasion resistant agent, for example, zinc dialkyldithiophosphate (ZnDTP), zinc phosphate, zinc dithiocarbamate, molybdenum dithiocarbamate, molybdenum dithiophosphate, disulfides, olefins sulfide, oils and fats sulfide, sulfide esters, thiocarbonates, etc. , Sulfur-containing compounds such as thiocarbamates and polysulfides; phosphorus-containing compounds such as phosphite esters, phosphoric acid esters, phosphonic acid esters, and amine salts or metal salts thereof; thio-sulphonic acid esters, Examples thereof include thiophosphate esters, thiophosphonic acid esters, and sulfur- and phosphorus-containing abrasion resistant agents such as amine salts or metal salts thereof.
Among these, zinc dialkyl dithiophosphate (ZnDTP) is preferable, and it is more preferable to use zinc primary alkyl type dialkyl dithiophosphate in combination with zinc secondary alkyl dithiophosphate.

(Extreme pressure agent)
Examples of the extreme pressure agent include sulfur-based extreme pressure agents such as sulfides, sulfoxides, sulfones, and thiophosphinates, halogen-based extreme pressure agents such as chlorinated hydrocarbons, and organic metal-based extreme pressure agents. Be done. Further, among the above-mentioned wear resistant agents, a compound having a function as an extreme pressure agent can also be used.
In one aspect of the present invention, these extreme pressure agents may be used alone or in combination of two or more.

(Antioxidant)
As the antioxidant, any known antioxidant that has been conventionally used as an antioxidant for lubricating oils can be appropriately selected and used. For example, an amine-based antioxidant or a phenol-based antioxidant can be used. Examples thereof include antioxidants, molybdenum-based antioxidants, sulfur-based antioxidants, phosphorus-based antioxidants, and the like.
Examples of the amine-based antioxidant include diphenylamine-based antioxidants such as diphenylamine and alkylated diphenylamine having an alkyl group having 3 to 20 carbon atoms; α-naphthylamine, phenyl-α-naphthylamine, and alkyl having 3 to 20 carbon atoms. Examples include naphthylamine-based antioxidants having a group such as substituted phenyl-α-naphthylamine; and the like.
Examples of the phenolic antioxidant include 2,6-di-tert-butylphenol, 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol, and the like. Monophenolic antioxidants such as isooctyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate and octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate Agents; diphenolic antioxidants such as 4,4'-methylenebis (2,6-di-tert-butylphenol), 2,2'-methylenebis (4-ethyl-6-tert-butylphenol); hinderedphenolic Antioxidants; etc.
Examples of the molybdenum-based antioxidant include a molybdenum amine complex formed by reacting molybdenum trioxide and / or molybdic acid with an amine compound.
Examples of the sulfur-based antioxidant include dilauryl-3,3'-thiodipropionate and the like.
Examples of the phosphorus-based antioxidant include phosphite and the like.
In one aspect of the present invention, these antioxidants may be used alone or in combination of two or more, but it is preferable to use two or more in combination.

(Defoamer)
Examples of the defoaming agent include silicone oil, fluorosilicone oil, fluoroalkyl ether and the like.

(Friction modifier)
Examples of the friction modifier include molybdenum-based friction modifiers such as molybdenum dithiocarbamate (MoDTC), molybdenum dithiophosphate (MoDTP), and amine salts of molybthenoic acid; alkyl groups or alkenyl groups having 6 to 30 carbon atoms are contained in the molecule. Ashless friction modifiers such as aliphatic amines, fatty acid esters, fatty acid amides, fatty acids, aliphatic alcohols, and aliphatic ethers, which have at least one; , Phosphoric acid ester amine salt and the like.

(anti-rust)
Examples of the rust preventive agent include fatty acids, alkenyl succinic acid half esters, fatty acid sucrose, alkyl sulfonates, polyhydric alcohol fatty acid esters, fatty acid amines, oxidized paraffins, alkyl polyoxyethylene ethers and the like.

(Metal inactivating agent)
Examples of the metal inactivating agent include benzotriazole-based compounds, tolyltriazole-based compounds, thiadiazol-based compounds, imidazole-based compounds, pyrimidine-based compounds and the like.
In one aspect of the present invention, these metal inactivating agents may be used alone or in combination of two or more.

<Manufacturing method of lubricating oil composition>
The method for producing the lubricating oil composition of the present invention is not particularly limited, but the method for producing the lubricating oil composition containing various additives containing the above-mentioned olefin-based copolymer includes mineral oil-based base oil. It is preferable to use a method having a step of blending various additives containing an olefin-based copolymer into a base oil containing a synthetic oil as needed.
In the above steps, suitable compounds of various additives to be blended and the contents of each component are as described above.

Then, after blending various additives containing an olefin-based copolymer with the base oil in which synthetic oil is blended with the mineral oil-based base oil as necessary, the mixture is stirred by a known method and contained in the base oil. It is preferable to uniformly disperse various additives including an olefin-based copolymer.
Further, from the viewpoint of uniformly dispersing various additives, after raising the temperature of the base oil containing the mineral oil-based base oil to 40 to 70 ° C., various additives containing the olefin-based copolymer are blended and stirred uniformly. It is more preferable to disperse in.

After adding various additives containing an olefin-based copolymer to the base oil containing the mineral oil-based base oil, the base oil containing the mineral oil-based base oil and some of the various additives containing the olefin-based copolymer are added. Even if the two components are modified or the two components react with each other to form another component, the obtained lubricating oil composition corresponds to the lubricating oil composition obtained by the method for producing the lubricating oil composition of the present invention. It belongs to the technical scope of the invention.

<Various physical characteristics of lubricating oil composition>
The kinematic viscosity of the lubricating oil composition of one aspect of the present invention at 100 ° C. is preferably 4 mm ² / s or more, more preferably 5 mm ² / s or more, still more preferably 6 mm ² / s or more, still more preferably 7 mm. It is ² / s or more, preferably less than 15 mm ² / s, more preferably less than 12.5 mm ² / s, still more preferably less than 11 mm ² / s, still more preferably less than 10 mm ² / s.

The viscosity index of the lubricating oil composition according to one aspect of the present invention is preferably 140 or more, more preferably 150 or more, still more preferably 160 or more, still more preferably 165 or more.

The temperature gradient Δ | η * | of the complex viscosity between the two points of −10 ° C. and −25 ° C., which is defined in the same manner as the above-mentioned requirement (III) of the lubricating oil composition of one aspect of the present invention, is preferable. Is 60 Pa · s / ° C or lower, more preferably 20 Pa · s / ° C or lower, still more preferably 15 Pa · s / ° C or lower, still more preferably 10 Pa · s / ° C or lower, and particularly preferably 5 Pa · s / ° C or lower. ..
Further, in the lubricating oil composition of one aspect of the present invention, the temperature gradient Δ | η * | of the complex viscosity, which is defined in the same manner as the above requirement (III), is not particularly limited in terms of the lower limit value, but is preferable. Is 0.001 Pa · s / ° C or higher, more preferably 0.01 Pa · s / ° C or higher.

The complex viscosity η * at −35 ° C., which is defined in the same manner as the above-mentioned requirement (IV) of the lubricating oil composition of one aspect of the present invention, is preferably 45,000 Pa · s or less, more preferably 35,000 Pa. It is s or less, more preferably 6,000 Pa · s or less, still more preferably 2,000 Pa · s or less, and particularly preferably 500 Pa · s or less.
Further, in the lubricating oil composition of one aspect of the present invention, the complex viscosity η * at −35 ° C., which is defined in the same manner as the above requirement (IV), is not particularly limited in terms of the lower limit value, but is preferably 0. .1 Pa · s or more, more preferably 1 Pa · s or more, still more preferably 2 Pa · s or more.

The CCS viscosity (low temperature viscosity) of the lubricating oil composition according to one aspect of the present invention at −35 ° C. is preferably 9,000 mPa · s or less from the viewpoint of obtaining a lubricating oil composition having good low temperature viscosity characteristics. It is preferably 8,600 mPa · s or less, more preferably 7,500 mPa · s or less, and even more preferably 7,000 mPa · s or less.

The HTHS viscosity (high temperature and high shear viscosity) of the lubricating oil composition according to one aspect of the present invention at 150 ° C. is preferably 1.4 mPa · s or more and less than 3.5 mPa · s, and more preferably 1.6 mPa · s or more 3 It is less than .2 mPa · s, more preferably 1.7 mPa · s or more and less than 3.0 mPa · s, and even more preferably 2.0 mPa · s or more and less than 2.8 mPa · s.
When the HTHS viscosity at 150 ° C. is 1.4 mPa · s or more, a lubricating oil composition having good lubricating performance can be obtained. On the other hand, when the HTHS viscosity at 150 ° C. is less than 3.5 mPa · s, it is possible to suppress a decrease in viscosity characteristics at a low temperature and obtain a lubricating oil composition having good fuel economy performance.
The above-mentioned HTHS viscosity at 150 ° C. can also be assumed as the viscosity in a high temperature region during high-speed operation of the engine. That is, if the HTHS viscosity of the lubricating oil composition at 150 ° C. belongs to the above range, the lubricating oil composition has good properties such as viscosity in a high temperature region assuming high-speed operation of the engine. I can say.
The HTHS viscosity of the above lubricating oil composition at 150 ° C. is a value measured according to ASTM D4741, and more specifically, it means a value measured by the method described in Examples.

In one aspect of the present invention, a lubricating oil composition having a kinematic viscosity at 100 ° C. of less than 12.5 mm ² / s and an HTHS viscosity at 150 ° C. of less than 3.5 mPa · s is preferred.
By satisfying the above requirements, the lubricating oil composition can reduce fluid friction and improve fuel efficiency.

The density of the lubricating oil composition according to one aspect of the present invention at 15 ° C. is preferably 0.80 to 0.90 g / cm ³ , and more preferably 0.82 to 0.87 g / cm ³ .
The density of the above lubricating oil composition at 15 ° C. means a value measured in accordance with JIS K2249: 2011.

In the lubricating oil composition of one aspect of the present invention, the deposit amount measured by the panel caulking test under the conditions described in the examples is preferably less than 100 mg, more preferably less than 90 mg, still more preferably less than 85 mg. Even more preferably less than 80 mg.

<Use of lubricating oil composition>
The lubricating oil composition of the present invention has good low-temperature viscosity characteristics such as low-temperature fuel saving and low-temperature startability of an engine, and is caused by the polymer component even when a polymer component is blended as an additive. Excellent effect of suppressing deterioration of high temperature cleanliness of the piston.
Therefore, examples of the engine filled with the lubricating oil composition of the present invention include engines for vehicles such as automobiles, trains, and aircraft, but automobile engines are preferable, and automobile engines equipped with a hybrid mechanism and an idling stop mechanism. Is more preferable.
The lubricating oil composition according to one aspect of the present invention is preferably used as a lubricating oil composition for an internal combustion engine (engine oil for an internal combustion engine) used for vehicles such as automobiles, trains, and aircraft. It can also be applied to other uses.
Other possible uses for the lubricating oil composition of one aspect of the present invention include, for example, power steering oil, automatic transmission fluid (ATF), stepless transmission oil (CVTF), hydraulic hydraulic oil, turbine oil, compressor oil, and the like. Examples thereof include lubricating oil for machine tools, cutting oil, gear oil, fluid bearing oil, and rolling bearing oil.

The lubricating oil composition of the present invention comprises a piston ring and a sliding mechanism with a liner in a device having a sliding mechanism with a piston ring and a liner, particularly a piston ring and a piston ring in an internal combustion engine (preferably an internal combustion engine of an automobile). It is suitable for lubrication of a sliding mechanism equipped with a liner.
The material for forming the piston ring and the cylinder liner to which the lubricating oil composition of the present invention is applied is not particularly limited. Examples of the material for forming the cylinder liner include aluminum alloys and cast iron alloys.
Examples of the material for forming the piston ring include Si—Cr steel and martensitic stainless steel containing 11 to 17% by mass of chromium. For the piston ring, it is preferable that such a forming material is further subjected to a chrome plating treatment, a chromium nitride treatment or a nitriding treatment, and a base treatment related to a combination thereof.

[Internal combustion engine]
The present invention also provides an internal combustion engine having a sliding mechanism including a piston ring and a liner, and containing the above-mentioned lubricating oil composition of the present invention.
In one aspect of the present invention, an internal combustion engine to which the lubricating oil composition of the present invention is applied to the sliding portion of the sliding mechanism is preferable.
The sliding mechanism provided with the lubricating oil composition, the piston ring, and the liner of the present embodiment is as described above, and the specific configuration of the sliding mechanism includes the one shown in FIG.

The sliding mechanism 1 shown in FIG. 2 includes a block 2 having a piston movement path 2a and a crankshaft accommodating portion 2b, a liner 12 arranged along the inner wall of the piston movement path 2a, and a piston 4 accommodated in the liner 12. It is sandwiched between the piston ring 6 fitted to the piston 4, the crankshaft 10 housed in the crankshaft accommodating portion 2b, the conrod 9 connecting the crankshaft 10 and the piston 4, and the liner 12 and the piston movement path 2a. Has a well-established structure.
The crankshaft 10 is rotationally driven by a motor (not shown), and the piston 4 can be reciprocated via a connecting rod 9.
In the sliding mechanism 1 having such a configuration, the lubricating oil composition 20 of the present invention is above the center of the central axis of the crankshaft 10 and below the uppermost end of the central axis in the crankshaft accommodating portion 2b. It is filled until it reaches the liquid level of. The lubricating oil composition 20 in the crankshaft accommodating portion 2b is a splash type by a rotating crankshaft 10, and is supplied between the liner 12 and the piston ring 6.

[Lubrication method for internal combustion engine]
The present invention is a lubrication method for an internal combustion engine that lubricates a device having a sliding mechanism including a piston ring and a liner, and the piston ring and the liner are lubricated by using the above-mentioned lubricating oil composition of the present invention. Also provides a lubrication method for internal combustion engines.
The lubricating oil composition of the present embodiment and the sliding mechanism provided with the piston ring and the liner are as described above.
In the lubrication method for an internal combustion engine of the present invention, the lubricating oil composition of the present embodiment is used as a lubricating oil in the sliding portion between the piston ring and the cylinder liner, so that both fluid lubrication and mixed lubrication can be performed. The friction can be greatly reduced, which can contribute to the improvement of fuel saving.

Next, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples. The methods for measuring or evaluating various physical properties are as follows.

<Measurement method of various physical properties of mineral oil-based base oil or lubricating oil composition>
(1) Dynamic viscosity at 40 ° C and 100 ° C Measured according to JIS K2283: 2000.
(2) Viscosity index Measured according to JIS K2283: 2000.
(3) CCS viscosity at −35 ° C. Measured according to JIS K2010: 1993 (ASTM D 2602).
(4) Complex viscosity η * at -25 ° C, -10 ° C, and -35 ° C
The measurement was carried out by the following procedure using a rheometer "Physica MCR 301" manufactured by Antonio Par.
First, the mineral oil-based base oil or lubricating oil composition to be measured is inserted into a cone plate (diameter 50 mm, inclination angle 1 °) adjusted to any of -25 ° C, -10 ° C, and -35 ° C. And kept at the same temperature for 10 minutes. At this time, care was taken not to give distortion to the inserted solution.
Then, at a predetermined measurement temperature, the angular velocity is 6.3 rad / s, the strain amount is in the range of 0.1 to 100%, and the values are appropriately set according to the measurement temperature. The complex viscosity η * was measured. In the measurement of the complex viscosity η * at −35 ° C., the strain amount was set to “0.1%”.
Then, from the values of the complex viscosity η * at −25 ° C. and −10 ° C., the “complex viscosity temperature gradient Δ | η * |” was calculated from the above formula (f1).
(5) Mass average molecular weight (Mw), number average molecular weight (Mn)
It was measured under the following conditions using a gel permeation chromatograph device (manufactured by Agilent, "1260 type HPLC"), and the value measured in terms of standard polystyrene was used.
(Measurement condition)
-Column: Two "Shodex LF404" are connected in sequence.
-Column temperature: 35 ° C
・ Developing solvent: Chloroform ・ Flow rate: 0.3 mL / min

<Measurement method of various physical properties of mineral oil-based base oil>
(6) Aromatic content (% _CA ), naphthenic content (% _CN )
It was measured by ASTM D-3238 ring analysis (nd-M method).
(7) Sulfur content Measured according to JIS K2541-6: 2003.
(8) Nitrogen content JIS K2609: 1998 4. Measured according to.

<Measurement method of various physical properties of lubricating oil composition>
(8) HTHS viscosity at 150 ° C (high temperature and high shear viscosity)
According to ASTM D4741, the viscosity of the lubricating oil composition to be measured after shearing was measured at 150 ° C. and a shear rate of ¹⁰⁶ / s.

The manufacturing method of "bottom oil" and "slack wax" used in Examples and Comparative Examples is as follows.

Production Example 1 (Manufacturing of bottom oil)
In the normal fuel oil manufacturing process, the oil containing heavy fuel oil obtained from the vacuum distillation apparatus was hydrolyzed and decomposed, and the bottom fraction remaining after separating and removing naphtha and kerosene was taken out. The bottom fraction was used as "bottom oil" in the following production.
The bottom oil had an oil content of 75% by mass, a sulfur content of 82% by mass, a nitrogen content of 2% by mass, a kinematic viscosity of 4.1 mm ² / s at 100 ° C., and a viscosity index of 134.

Production Example 2 (Manufacture of solvent-dewaxed oil and slack wax)
The bottom oil obtained as described above was solvent-dewaxed in a low temperature region of −35 ° C. to −30 ° C. using a mixed solvent of methyl ethyl ketone and toluene to separate the wax, and “solvent-dewaxed oil” was obtained. .. Then, the separated wax was designated as "slack wax".
The solvent dewaxing oil has an oil content of 100% by mass, a sulfur content of 70% by mass, a nitrogen content of 2% by mass, a kinematic viscosity of 4.1 mm ² / s at 100 ° C., and a viscosity index of 121. rice field.
The slack wax had an oil content of 15% by mass, a sulfur content of 12% by mass, a nitrogen content of less than 1% by mass, a kinematic viscosity at 100 ° C. of 4.2 mm ² / s, and a viscosity index of 169. ..

Example 1 (Manufacturing of mineral oil-based base oil (1))
The solvent dewaxing oil obtained in Production Example 2 was used as the raw material oil (i).
The raw material oil (i) was hydrogenated using a nickel-tungsten catalyst under the conditions of a hydrogen partial pressure of 20 MPa, a reaction temperature of 280 to 320 ° C., and LHSV 1.0 hr ^-1 .
The hydrotreated product oil was distilled under reduced pressure, and a fraction having a kinematic viscosity in the range of 4.2 to 4.4 mm ² / s at 100 ° C. was recovered to obtain a mineral oil-based base oil (1).
For mineral oil _- based base oil (1), aromatic content (% CA) = 0.0, naphthen content (% _CN ) = 26.5, sulfur content = less than 100 mass ppm, mass average molecular weight = 150 to 450. there were.

Example 2 (Manufacturing of mineral oil-based base oil (2))
A mixture of 75 parts by mass of the slack wax obtained in Production Example 2 and 25 parts by mass of the bottom oil obtained in Production Example 1 was used as the raw material oil (ii). The raw material oil (ii) has an oil content of 30% by mass, a sulfur content of 30% by mass, a nitrogen content of less than 1% by mass, a kinematic viscosity of 4.2 mm ² / s at 100 ° C., and a viscosity index of 160. Met.
The raw material oil (ii) was subjected to hydrogenation isomerization dewazing using a hydrogenation isomerization dewazing catalyst under the conditions of a hydrogen partial pressure of 4 MPa, a reaction temperature of 335 ° C., and LHSV 1.0 hr ^-1 .
Next, the hydrogenated isomerized ^delowed product oil was hydrogenated using a nickel tungsten catalyst under the conditions of a hydrogen partial pressure of 20 MPa, a reaction temperature of 280 to 320 ° C., and LHSV 1.0 hr-1.
The hydrotreated product oil was distilled under reduced pressure, and a fraction having a kinematic viscosity in the range of 4.2 to 4.4 mm ² / s at 100 ° C. was recovered to obtain a mineral oil-based base oil (2).
For mineral oil _- based base oil (2), aromatic content (% CA) = 0.0, naphthen content (% _CN ) = 18.3, sulfur content = less than 100 mass ppm, mass average molecular weight = 150 to 450. there were.

Example 3 (Manufacturing of mineral oil-based base oil (3))
A mixture of 90 parts by mass of the slack wax obtained in Production Example 2 and 10 parts by mass of the bottom oil obtained in Production Example 1 was used as the raw material oil (iii). The raw material oil (iii) has an oil content of 21% by mass, a sulfur content of 19% by mass, a nitrogen content of less than 1% by mass, a kinematic viscosity of 4.2 mm ² / s at 100 ° C., and a viscosity index of 166. Met.
The raw material oil (iii) was subjected to hydrogenation isomerization dewazing using a hydrogenation isomerization dewazing catalyst under the conditions of a hydrogen partial pressure of 4 MPa, a reaction temperature of 340 ° C., and LHSV 0.5 hr ^-1 .
Next, the hydrogenated isomerized ^delowed product oil was hydrogenated using a nickel tungsten catalyst under the conditions of a hydrogen partial pressure of 20 MPa, a reaction temperature of 280 to 320 ° C., and LHSV 1.0 hr-1.
The hydrotreated product oil was distilled under reduced pressure, and a fraction having a kinematic viscosity in the range of 4.2 to 4.4 mm ² / s at 100 ° C. was recovered to obtain a mineral oil-based base oil (3).
For mineral oil _- based base oil (3), aromatic content (% CA) = 0.0, naphthen content (% _CN ) = 16.7, sulfur content = less than 100 mass ppm, mass average molecular weight = 150 to 450. there were.

Example 4 (Manufacturing of mineral oil-based base oil (4))
In the production method of Example 2, the hydrotreated product oil was distilled under reduced pressure, and a fraction having a kinematic viscosity in the range of 2.5 to 3.0 mm ² / s at 100 ° C. was recovered. Mineral oil-based base oil (4) was obtained in the same manner as in Example 2.
For mineral oil _- based base oil (4), aromatic content (% CA) = 0.1, naphthen content (% _CN ) = 20.2, sulfur content = less than 100 mass ppm, mass average molecular weight = 150 to 450. there were.

Comparative Example 1 (Manufacturing of mineral oil-based base oil (a))
A heavy fuel oil obtained from a vacuum distillation apparatus in a normal fuel oil manufacturing process was solvent-extracted with a full-fural solvent under a solvent ratio of 1.0 to 2.0 to obtain a raffinate.
Then, the raffinate was subjected to hydrogenation isomerization dewazing using a hydrogenation isomerization dewazing catalyst under the conditions of a hydrogen partial pressure of 4 MPa, a reaction temperature of 260 to 280 ° C., and LHSV 1.0hr ^-1 .
Next, the hydrogenated isomerized ^delowed product oil was hydrogenated using a nickel tungsten catalyst under the conditions of a hydrogen partial pressure of 4 to 5 MPa, a reaction temperature of 280 to 320 ° C., and LHSV 1.0 hr-1. .. The hydrotreated product oil was distilled under reduced pressure, and a fraction having a kinematic viscosity in the range of 4.0 to 4.5 mm ² / s at 100 ° C. was recovered to obtain a mineral oil-based base oil (a).
For the mineral oil _- based base oil (a), the aromatic content (% CA) = 2.8, the naphthen content (% _CN ) = 27.3, the sulfur content = 1000 mass ppm, and the mass average molecular weight = 150 to 450. rice field.

Comparative Example 2 (Manufacturing of mineral oil-based base oil (b))
In the production method of Comparative Example 1, the hydrotreated product oil was distilled under reduced pressure, and a fraction having a kinematic viscosity in the range of 2.0 to 3.0 mm ² / s at 100 ° C. was recovered. Mineral oil-based base oil (b) was obtained by the same method as in Example 1.
For the mineral oil _- based base oil (b), the aromatic content (% CA) = 4.7, the naphthen content (% _CN ) = 28.7, the sulfur content = 2000 mass ppm, and the mass average molecular weight = 150 to 450. rice field.

Comparative Example 3 (Manufacturing of mineral oil-based base oil (c))
A mixture of 20 parts by mass of the slack wax obtained in Production Example 2 and 80 parts by mass of the bottom oil obtained in Production Example 1 was used as the raw material oil (iv). The raw material oil (iv) has an oil content of 62.5% by mass, a sulfur content of 68% by mass, a nitrogen content of 2% by mass, a kinematic viscosity at 100 ° C. of 4.1 mm ² / s, and a viscosity index. It was 141.
Then, in the production method of Example 2, the above-mentioned raw material oil (iv) is used as the raw material oil instead of the raw material oil (ii), and the hydrotreated product oil is distilled under reduced pressure to operate at 100 ° C. A mineral oil-based base oil (c) was obtained by the same method as in Example 2 except that the distillate having a viscosity in the range of 6.0 to 7.0 mm ² / s was recovered.
For the mineral oil _- based base oil (c), the aromatic content (% _CA ) = 0.0, the naphthen content (% CN) = 21.4, the sulfur content = less than 100 mass ppm, and the mass average molecular weight = more than 450. rice field.

Table 1 shows various properties of the mineral oil-based base oils produced in Examples and Comparative Examples. Further, regarding the mineral oil-based base oil (2) of Example 2, the mineral oil-based base oil (a) of Comparative Example 1, and the mineral oil-based base oil (b) of Comparative Example 2, the relationship between the temperature and the complex viscosity η * was determined. The graph shown is shown in FIG.

Examples 5-12, Comparative Examples 4-9
The mineral oil-based base oils (1) to (4) and (a) to (c) produced in the examples and comparative examples of the types shown in Tables 2 and 3 are used and shown in Tables 2 and 3. Lubricating oil compositions (i) to (viii) and (A) to (F) were prepared by blending the types and amounts of the additives for lubricating oil.

The details of the additives for lubricating oil in Tables 2 and 3 are as follows.
OCP (1): An olefin-based copolymer having an Mw of 500,000.
OCP (2): An olefin-based copolymer having an Mw of 300,000 (ethylene-propylene copolymer).
-PMA (1): Polymeta crate with Mw of 400,000.
-PMA (2): Polymeta crate with Mw of 500,000.
-Metallic detergent (1): perbasic calcium salicylate, basic value (perchloric acid method) = 350 mgKOH / g, calcium atom content = 12.1% by mass.
-Metallic detergent (2): perbasic calcium salicylate, base value (perchloric acid method) = 225 mgKOH / g, calcium atom content 7.8% by mass.
Abrasion resistant agent (1): primary alkyl type zinc dialkyldithiophosphate, zinc content = 8.9% by mass, phosphorus atom content = 7.4% by mass.
-Abrasion resistant agent (2): Secondary alkyl type zinc dialkyldithiophosphate, zinc content = 9.0% by mass, phosphorus atom content = 8.2% by mass.
-Antioxidant (1): Amine-based antioxidant.
-Antioxidant (2): Phenolic antioxidant.
Dispersant (1): bisimide polybutenyl succinate, Mn of polybutenyl group = 2000, basic value (perchloric acid method) = 11.9 mgKOH / g, nitrogen atom content = 0.99% by mass.
Dispersant (2): polybutenyl succinate monoimide boronized product, polybutenyl group Mn = 1000, basic value (perchloric acid method) = 25 mgKOH / g, nitrogen atom content = 1.23% by mass, boron atom Content = 1.3% by mass.
-Rust inhibitor, defoamer, pour point lowering agent: Polymethacrylate with Mw of 69,000.

Then, various properties of the prepared lubricating oil compositions (i) to (viii) and (A) to (F) were measured according to the above-mentioned measuring method. In addition, a panel caulking test was carried out based on the method shown below, and the amount of deposit was measured. For the lubricating oil compositions (vi) to (viii) and (E) to (F) containing the pour point lowering agent, the rate of increase in the deposit amount P was also calculated. The results are shown in Tables 2 and 3.

[Panel caulking test]
(1) Measurement of deposit amount 300 mL of the prepared lubricating oil composition was placed in a heating tank and heated to 100 ° C. Then, the operation of splashing the lubricating oil composition heated to 100 ° C. with the blades continuously rotated at a speed of 1000 rpm against the aluminum plate heated to 300 ° C. installed at the upper part of the heating tank is 1 The cycle continued for 3 hours with "rotating the wings for 15 seconds and then stopping for 45 seconds". After 3 hours, the mass (deposit amount) of the deposit adhering to the aluminum plate was measured.
(2) Calculation of increase rate P of deposit amount Based on the deposit amount calculated in (1) above, with respect to the deposit amount (W ₀ ) of the lubricating oil composition (i) of Example 5 containing no pour point lowering agent. The rate of increase P of the deposit amount (W) of the lubricating oil compositions (vi) to (viii) of Examples 10 to 12 containing the pour point lowering agent was calculated based on the following formula (f2).
-Calculation formula (f2): P (unit:%) = (W-W ₀ ) / W ₀ x 100
Similarly, the lubricating oil composition (E) of Comparative Examples 8 to 9 containing the pour point lowering agent with respect to the deposit amount (W ₀ ) of the lubricating oil composition (A) of Comparative Example 4 containing no pour point lowering agent. )-(F), the rate of increase P of the deposit amount (W) was also calculated from the above formula (f2).

From Table 2, the lubricating oil compositions (i) to (viii) of Examples 5 to 11 containing the olefin-based copolymer using the mineral oil-based base oils (1) to (4) obtained in Examples 1 to 4 are used. ) Has good low-temperature viscosity characteristics, and the amount of deposit in the panel caulking test is small, resulting in excellent high-temperature cleanliness of the piston.
On the other hand, from Table 3, the lubricating oil compositions (A) to 9 to 9 of Comparative Examples 4 to 6 and 8 to 9 using any of the mineral oil-based base oils (a) to (c) obtained in Comparative Examples 1 to 3 are used. In (C) and (E) to (F), the low temperature viscosity characteristics were inferior, the deposit amount was large, and there was a problem in the high temperature cleanliness of the piston.
Further, the lubricating oil composition (D) of Comparative Example 7 has a very large deposit amount, and has a problem in high temperature cleanliness of the piston. Therefore, the low temperature viscosity characteristics have not been evaluated.

1: Sliding mechanism 2: Block 2a: Piston movement path 2b: Crankshaft accommodating portion 4: Piston 6, 8: Piston ring 9: Connecting rod 10: Crankshaft 12: Liner 20: Lubricating oil composition

Claims (10)

The following requirements (I) to (III) are satisfied, the naphthen content (% CN ₎ is 15 to 30, the aromatic content (% CA ₎ is 0.1 or less, and the sulfur content is less than 100 mass ppm. The raw material oil having a mass average molecular weight (Mw) of 150 or more and 450 or less and containing petroleum-derived wax and bottom oil is subjected to at least one of hydrogenation isomerization dewaxing treatment and hydrogenation treatment. A lubricating oil composition for an internal combustion engine , which comprises a mineral oil-based base oil obtained by undergoing a refining treatment including the above and an olefin-based copolymer.
-Requirement (I): The kinematic viscosity at 100 ° C. is 2 mm ² / s or more and less than 7 mm ² / s.
-Requirement (II): Viscosity index is 100 or more.
Requirement (III): Complex viscosity between two points of -10 ° C and -25 ° C measured using a rotary rheometer under the conditions of an angular velocity of 6.3 rad / s and a strain of 0.1 to 100%. The temperature gradient Δ | η * | is 0.01 Pa · s / ° C or higher and 50 Pa · s / ° C or lower. The lubricating oil composition for an internal combustion engine according to claim 1, wherein the content of the olefin-based copolymer is 0.01 to 15.0% by mass based on the total amount of the lubricating oil composition. The lubricating oil composition for an internal combustion engine according to claim 1 or 2, wherein the olefin-based copolymer has a mass average molecular weight (Mw) of 10,000 to 1,000,000. One of claims 1 to 3, wherein the content of polymethacrylate (α) having a mass average molecular weight of 200,000 or more is less than 60 parts by mass with respect to 100 parts by mass of the total amount of the olefin-based copolymer. The lubricating oil composition for an internal combustion engine according to. Any of claims 1 to 4, wherein the content of polymethacrylate (β) having a mass average molecular weight of less than 200,000 is 0.5 to 80 parts by mass with respect to 100 parts by mass of the total amount of the olefin-based copolymer. The lubricating oil composition for an internal combustion engine according to item 1. The lubricating oil composition for an internal combustion engine according to any one of claims 1 to 5, wherein the mineral oil-based base oil further satisfies the following requirement (IV).
-Requirement (IV): The complex viscosity η * at −35 ° C. measured at an angular velocity of 6.3 rad / s and a strain amount of 0.1% using a rotary rheometer is 60,000 Pa · s or less. be. The lubricating oil composition for an internal combustion engine according to any one of claims 1 to 6 , wherein the kinematic viscosity at 100 ° C. is 4 mm ² / s or more and less than 15 mm ² / s, and the viscosity index is 140 or more. The kinematic viscosity at 100 ° C. is less than 12.5 mm ² / s, and the high temperature high shear viscosity (HTHS viscosity) at 150 ° C. is less than 3.5 mPa · s, according to any one of claims 1 to 7 . The lubricating oil composition for an internal combustion engine according to the above. An internal combustion engine having a sliding mechanism including a piston ring and a liner, and comprising the lubricating oil composition for an internal combustion engine according to any one of claims 1 to 8 . A method for lubricating an internal combustion engine having a sliding mechanism including a piston ring and a liner, wherein the piston ring and the liner are used with the lubricating oil composition for an internal combustion engine according to any one of claims 1 to 8 . Lubrication method for internal combustion engines.

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