Patent Description:
In recent years, lubricating oil compositions used as driving system oils, such as automatic transmission fluids (ATF), continuously variable transmission fluids (CVTF), and shock absorber fluids (SAF), engine oils, hydraulic fluids, and the like have been required to have various characteristics according to various applications.

Since characteristics of a lubricating oil composition often largely depend on the nature of a base oil used therein, development of such a base oil that can produce a lubricating oil composition capable of exhibiting required characteristics has been actively promoted.

For example, PTL <NUM> discloses a hydrocarbon lubricant base oil having a flash point of <NUM> or higher, a kinematic viscosity at <NUM> of <NUM> to <NUM><NUM>/s, a viscosity index of <NUM> or more, a <NUM> volume percent distillation temperature in a distillation test of <NUM> or higher, a pour point of -<NUM> or lower, and an aromatic content (%CA) of <NUM> or less.

According to the disclosure of PTL <NUM>, the lubricant base oil is suitable for lubricating oil compositions used at high temperature, such as power steering fluids and transmission fluids for automobiles, since the lubricant base oil has a high flash point while maintaining a viscosity a conventional lubricant base oil has.

PTL <NUM> discloses lubricating oil composition comprising (A) a base oil being a hydrocarbon base oil having a ratio (CA/CB) of the proportion of the component of <NUM> or fewer carbon atoms (CA) and the proportion of the component of <NUM> or more carbon atoms (CB) in the carbon number distribution obtained by gas chromatography distillation of <NUM> or higher, the composition having a ratio (Vs/Vk) of the <NUM> high-temperature high-shear (HTHS) viscosity (Vk) and the <NUM> HTHS viscosity (Vs) of <NUM> or higher and a <NUM> kinematic viscosity of <NUM><<NUM>> Is or higher and <NUM><<NUM>> /s or lower.

Meanwhile, lubricating oil compositions used as driving system oils are being required in late years to be improved in fuel-saving performance through further reduction in viscosity while having a high flash point to maintain satisfactory safety.

The lubricant base oil disclosed in PTL <NUM> is a high viscosity base oil having a kinematic viscosity at <NUM> of <NUM><NUM>/s or higher, and thus cannot be considered as a base oil that is suitable for improving fuel-saving performance by reducing the viscosity of a lubricating oil composition.

An object of the present invention is to provide a mineral base oil that can easily produce a lubricating oil composition that has a high flash point while having a further reduced viscosity and thereby having further improved fuel-saving performance; a lubricating oil composition using the mineral base oil; and a method of using a lubricating oil composition.

The present inventors have found that the above problem can be solved by a mineral base oil that has a reduced viscosity due to adjusted kinematic viscosities at <NUM> and <NUM> to prescribed ranges and further has a flash point equal to or higher than a prescribed value, completing the present invention. Specifically, the present invention provides the following [<NUM>] to [<NUM>].

The use of the mineral base oil of the present invention enables easy production of a lubricating oil composition that has a high flash point while having a reduced viscosity and thereby having further improved fuel-saving performance in use as a driving system oil and the like.

The mineral base oil of the present invention satisfies the following Requirements (I) and (II):.

In the Description, the kinematic viscosity at <NUM> or <NUM> means a value measured according to JIS K2283, and the flash point means a value measured by the Cleveland open-cup (COC) method according to JIS K2265-<NUM>.

In the general nature of a mineral base oil, a reduced viscosity tends to lead to a lowered flash point.

In contrast, the mineral base oil of the present invention is a mineral base oil that has a reduced viscosity as defined in Requirement (I) while having a high flash point of <NUM> or higher as defined in Requirement (II).

Thus, the use of the mineral base oil of the present invention enables easy production of a lubricating oil composition that has a high flash point while having a reduced viscosity and thereby having further improved fuel-saving performance in use as a driving system oil and the like.

In addition, the mineral base oil of the present invention has a relatively small difference between the kinematic viscosity at <NUM> and the kinematic viscosity at <NUM> as defined in Requirement (I), and thus the viscosity shows low temperature dependence. For this reason, the use of the mineral base oil of the present invention enables production of a lubricating oil composition that shows small viscosity variation by temperature.

The kinematic viscosity at <NUM> (V<NUM>) of the mineral base oil of the present invention is <NUM><NUM>/s or more, but is preferably <NUM><NUM>/s or more, more preferably <NUM><NUM>/s or more, and further preferably <NUM><NUM>/s or more.

The kinematic viscosity (V<NUM>) is less than <NUM><NUM>/s, but is preferably <NUM><NUM>/s or less, more preferably <NUM><NUM>/s or less, further preferably <NUM><NUM>/s or less.

The kinematic viscosity at <NUM> (V<NUM>) of the mineral base oil of the present invention is <NUM><NUM>/s or more, but is preferably <NUM><NUM>/s or more, more preferably <NUM><NUM>/s or more, further preferably <NUM><NUM>/s or more, and furthermore preferably <NUM><NUM>/s or more.

The kinematic viscosity (V<NUM>) is less than <NUM><NUM>/s, but is preferably <NUM><NUM>/s or less, more preferably <NUM><NUM>/s or less, and further preferably <NUM><NUM>/s or less.

The mineral base oil of the present invention is a mineral oil whose viscosity index measured according to JIS K2283 cannot be calculated.

The flash point of the mineral base oil of the present invention is <NUM> or higher, but is preferably <NUM> or higher, more preferably <NUM> or higher, further preferably <NUM> or higher, further preferably <NUM> or higher, furthermore preferably <NUM> or higher, and particularly preferably <NUM> or higher, and is generally <NUM> or lower.

In a distillation test in accordance with JIS K2254 of the mineral base oil of one embodiment of the present invention, the <NUM> volume percent distillation temperature of the mineral base oil is preferably <NUM> or higher, more preferably <NUM> or higher, further preferably <NUM> or higher, and furthermore preferably <NUM> or higher, and is generally <NUM> or lower.

An aniline point of the mineral base oil of one embodiment of the present invention is preferably <NUM> or higher, more preferably <NUM> or higher, further preferably <NUM> or higher, furthermore preferably <NUM> or higher, and particularly preferably <NUM> or higher, and is generally <NUM> or lower.

A mineral base oil having an aniline point of <NUM> or higher tends to have a high paraffin content and a low aromatic content, likely leading to a high flash point.

The aniline point, as used herein, means a value measured according to JIS K2256 (U-tube method).

A density at <NUM> of the mineral base oil of one embodiment of the present invention is <NUM>/cm<NUM> or less, more preferably <NUM>/cm<NUM> or less, further preferably <NUM>/cm<NUM> or less, furthermore preferably <NUM>/cm<NUM> or less, and particularly preferably <NUM>/cm<NUM> or less, and is generally <NUM>/cm<NUM> or more.

As used herein, the density at <NUM> means a value measured according to JIS K2249.

A paraffin content (%Cp) in the mineral base oil of one embodiment of the present invention is preferably <NUM> to <NUM>, more preferably <NUM> to <NUM>, further preferably <NUM> to <NUM>, and furthermore preferably <NUM> to <NUM>.

A naphthene content (%Cp) in the mineral base oil of one embodiment of the present invention is <NUM> to <NUM>, more preferably <NUM> to <NUM>, further preferably <NUM> to <NUM>, and furthermore preferably <NUM> to <NUM>.

An aromatic content (%CA) in the mineral base oil of one embodiment of the present invention is preferably less than <NUM>, more preferably less than <NUM>, and further preferably less than <NUM>.

As used herein, the paraffin content (%Cp), the naphthene content (%CN), and the aromatic content (%CA) respectively mean proportions (percentages) of a paraffin component, a naphthene component, and an aromatic component measured according to ASTM D-<NUM> ring analysis (n-d-M method).

The mineral base oil of the present invention further satisfies the following Requirement (III):.

In the case where the mineral base oil of one embodiment of the present invention is a mixed oil of two or more mineral oils, it is enough that the mixed oil satisfies the aforementioned Requirement (III).

The "strain amount" described in Requirement (III) is a value that is appropriately set within the range of from <NUM> to <NUM>% according to the temperature.

The aforementioned "temperature gradient Δ|η*| of complex viscosity" is a value indicative of an amount of change (absolute value of a slope) of complex viscosity per unit between two temperature points -<NUM> and -<NUM> as observed when the value of the complex viscosity η* at -<NUM> and the value of the complex viscosity η* at -<NUM> as measured either independently at these temperatures or while continuously varying the temperature from -<NUM> to -<NUM> or from -<NUM> to -<NUM> are placed on a temperature-complex viscosity coordinate plane. More specifically, the temperature gradient Δ|η*| of complex viscosity means a value calculated from the following calculation formula (f1).

That is, the "temperature gradient Δ|η*| of complex viscosity" defined in Requirement (III) represents the temporal change during temperature decrease as the low-temperature characteristics of the mineral oil.

Mineral oil contains a wax component. Thus, when the temperature of a mineral oil is gradually decreased, the wax component in the mineral oil precipitates to form a gel-like structure. Such wax components precipitate at different temperatures depending on the structure of paraffin or the like. The gel-like structure of such a wax component easily breaks, and therefore the viscosity of a mineral oil varies by a mechanical action. Conventionally used parameters of low-temperature viscosity characteristics have been provided without considering such precipitation of wax.

In contrast, the "temperature gradient Δ|η*| of complex viscosity" defined in Requirement (III) is an index that can accurately evaluate the low-temperature viscosity characteristics of a mineral oil by taking into account the precipitation rate of the wax component contained in the mineral oil to consider the variation in the coefficient of friction involved in the precipitation of the wax component.

The mineral base oil that satisfies Requirement (III) has a temperature gradient Δ|η*| of complex viscosity of <NUM> Pa·s/°C or less, and is thus regulated not to have so high precipitation rate of the wax component. Accordingly, since the coefficient of friction is not liable to increase, the mineral oil has lower temperature dependence of viscosity while having a lower viscosity.

Accordingly, the use of the mineral base oil enables production of a lubricating oil composition that is excellent in fuel-saving performance and shows smaller variation in viscosity due to temperature.

The temperature gradient Δ|η*| of complex viscosity defined in Requirement (III) has no particular lower limit, but is preferably <NUM> Pa·s/°C or more, more preferably <NUM> Pa·s/°C or more, further preferably <NUM> Pa·s/°C or more, and furthermore preferably <NUM> Pa·s/°C or more.

The mineral base oil of the present invention that satisfies Requirements (I) to (III) mentioned above can be easily prepared by appropriately considering selection of a feedstock oil as a raw material of the mineral base oil and matters as described below regarding a method of producing the mineral base oil using the feedstock oil. That is, the mineral base oil of the present invention is preferably a mineral oil that is obtained by subjecting a feedstock oil described below to a refining process described below.

The following matters represent one example of the preparation method and such a mineral base oil can be prepared by taking into account other matters.

A raw material for the mineral base oil of the present invention is referred to as a feedstock oil. Examples of the feedstock oil include a topped cruide oil obtained by atmospheric distillation of a crude oil, such as a paraffinic mineral oil, an intermediate mineral oil, or a naphthenic mineral oil; a distillate oil obtained by vacuum distillation of the topped crude oil; and a mineral oil or a wax (e.g., GTL wax) obtained by subjecting the distillate oil to at least one of refining processes, such as solvent deasphalting, solvent extraction, hydrofinishing, solvent dewaxing, catalytic dewaxing, isomerization dewaxing, and vacuum distillation.

These feedstock oils may be used either alone or in combination of two or more thereof.

The feedstock oil preferably contains a gas oil fraction from the viewpoint of preparing a mineral base oil that has a reduced viscosity to the extent defined in Requirement (I) while showing low viscosity dependence on temperature and having a high flash point as defined in Requirement (II), and more preferably contains a gas oil fraction obtained by hydrocracking of a heavy gas oil.

From the above viewpoint, the gas oil fraction preferably has a high paraffin content.

The kinematic viscosity at <NUM> of the feedstock oil is preferably <NUM> to <NUM><NUM>/s, more preferably <NUM> to <NUM><NUM>/s, and further preferably <NUM> to <NUM><NUM>/s.

The flash point of the feedstock oil is generally <NUM> or higher and lower than <NUM>.

The paraffin content (%Cp), the aromatic content (%CA), and the naphthene content (%CN) of the feedstock oil are preferably in the ranges described below as measured according to the ASTM D-<NUM> ring analysis (n-d-M method), from the viewpoint of preparing a mineral base oil that has a reduced viscosity to the extent defined in Requirement (I) while showing low viscosity dependence on temperature.

The proportion of each of the aromatic component, the naphthene component, the n-paraffin component, and the isoparaffin component present in the feedstock oil based on <NUM> % by volume of the total amount of the components is preferably in the range described below as measured according to ASTM D2786 and GC-FID method, from the viewpoint of preparing a mineral base oil that has a reduced viscosity to the extent defined in Requirement (I) while showing low viscosity dependence on temperature.

The <NUM> volume percent distillation temperature of the feedstock oil is preferably <NUM> or higher, more preferably <NUM> or higher, further preferably <NUM> or higher, and furthermore preferably <NUM> or higher, and generally <NUM> or lower as measured by a distillation test in accordance with JIS K2254.

The <NUM> volume percent distillation temperature of the feedstock oil is preferably <NUM> or higher, more preferably <NUM> or higher, further preferably <NUM> or higher, furthermore preferably <NUM> or higher, and particularly preferably <NUM> or higher, and is generally <NUM> or lower as measured by the distillation test.

When the <NUM> volume percent distillation temperature and the <NUM> volume percent distillation temperature fall within the above ranges, a mineral base oil having a high flash point as defined in Requirement (II) can be prepared.

A mass average molecular weight (Mw) of the feedstock oil is preferably <NUM> to <NUM>, more preferably <NUM> to <NUM>, and further preferably <NUM> to <NUM>.

The mass average molecular weight (Mw) of a feedstock oil, as used herein, means a value measured according to ASTM D2502.

A described above, the kinematic viscosities at <NUM> and <NUM> of the feedstock oil to be used in the present invention do not largely differ from the ranges defined in Requirement (I).

However, the flash point of a feedstock oil having a low viscosity as described above is generally lower than <NUM> and does not satisfy Requirement (II). In addition, the feedstock oil also tends to be increased in the temperature gradient Δ|η* | of complex viscosity as defined in Requirement (III), and has a problem in terms of the low-temperature viscosity characteristics.

On the other hand, even though such a feedstock oil is used, the mineral base oil of the present invention has a high flash point and has a low viscosity while having a lowered temperature dependence of the viscosity, that is, having an excellent low-temperature viscosity characteristics, by application of a refining process as described below.

The mineral base oil of one embodiment of the present invention is preferably obtained by subjecting the aforementioned feedstock oil to a refining process. Preferably, the type of the refining process and the refining conditions are appropriately set according to the type of the feedstock oil to be used.

The refining process preferably includes at least a hydrogenation isomerization dewaxing process, and more preferably includes a hydrogenation isomerization dewaxing process and a hydrofinishing process.

That is, the mineral base oil of one embodiment of the present invention is preferably obtained through a hydrogenation isomerization dewaxing process, and more preferably obtained further through a hydrofinishing process after the hydrogenation isomerization dewaxing process.

The "hydrogenation isomerization dewaxing process" and "hydrofinishing process" will be explained below.

Hydrogenation isomerization dewaxing process is a refining process performed for the purpose of isomerization of straight-chain paraffins contained in a feedstock oil to branched-chain isoparaffins as mentioned above.

Hydrogenation isomerization dewaxing process can also achieve ring opening of an aromatic component into a paraffin component, removal of impurities, such as a sulfur component and a nitrogen component, and so on.

The hydrogenation isomerization process leads to increase in the proportion of branched-chain isoparaffin, making it possible to prepare a mineral base oil having low viscosity dependence on temperature and having a high flash point.

The presence of straight-chain paraffin in the feedstock oil is one of the factors of increasing the value of the temperature gradient Δ |η* | of complex viscosity defined in Requirement (III). Thus, in this process, it is preferred that straight-chain paraffins are isomerized to branched-chain isoparaffins to adjust the temperature gradient Δ |η*| of complex viscosity to a low value.

Besides that, this process can also reduce the pour point of the mineral base oil, and therefore a mineral base oil having further improved low-temperature viscosity characteristics can be obtained.

The hydrogenation isomerization dewaxing process is preferably carried out in the presence of a hydrogenation isomerization dewaxing catalyst.

Examples of hydrogenation isomerization dewaxing catalysts include catalysts with metal oxides, such as oxides of nickel (Ni)/tungsten (W), nickel (Ni)/molybdenum (Mo), and cobalt (Co)/molybdenum (Mo), or noble metals, such as platinum (Pt) and lead (Pd), supported on carriers, such as silicoaluminophosphate (SAPO) and zeolite.

From the viewpoint of producing a mineral base oil satisfying Requirements (III) and (IV), the hydrogen partial pressure in the hydrogenation isomerization dewaxing process is preferably <NUM> to <NUM> MPa, more preferably <NUM> to <NUM> MPa, further preferably <NUM> to <NUM> MPa, and furthermore preferably <NUM> to <NUM> MPa.

From the viewpoint of producing a mineral base oil satisfying Requirements (II) and (III), the reaction temperature in the hydrogenation isomerization dewaxing process is preferably set to a temperature higher than the reaction temperature of a common hydrogenation isomerization dewaxing process, and specifically is preferably <NUM> to <NUM>, more preferably <NUM> to <NUM>, further preferably <NUM> to <NUM>, and furthermore preferably <NUM> to <NUM>.

When the reaction temperature is high, the isomerization of straight-chain paraffins into branched-chain isoparaffins can be promoted, whereby it becomes easy to prepare a mineral base oil satisfying Requirements (II) and (III).

From the viewpoint of producing a mineral base oil satisfying Requirements (III) and (IV), the liquid hourly space velocity (LHSV) in the hydrogenation isomerization dewaxing process is preferably <NUM> hr-<NUM> or less, more preferably <NUM> hr-<NUM> or less, further preferably <NUM> hr-<NUM> or less, and furthermore preferably <NUM> hr-<NUM> or less.

From the viewpoint of improving the productivity, the LHSV in the hydrogenation isomerization dewaxing process is preferably <NUM> hr-<NUM> or more, and more preferably <NUM> hr-<NUM> or more.

The supply proportion of the hydrogen gas in the hydrogenation isomerization dewaxing process is preferably <NUM> to <NUM><NUM>, more preferably <NUM> to <NUM><NUM>, and further preferably <NUM> to <NUM><NUM> per kiloliter of the supplied feedstock oil.

The hydrofinishing process is a refining process that is performed for purposes of complete saturation of the aromatic component contained in the feedstock oil, removal of impurities, such as a sulfur component and a nitrogen component, and so on.

The hydrofinishing process is preferably carried out in the presence of a hydrogenation catalyst.

Examples of hydrogenation catalysts include catalysts with metal oxides, such as oxides of nickel (Ni)/tungsten (W), nickel (Ni)/molybdenum (Mo), and cobalt (Co)/molybdenum (Mo), or noble metals, such as platinum (Pt) and lead (Pd), supported on amorphous carriers, such as silica/alumina and alumina, or crystalline carriers, such as zeolite.

From the viewpoint of producing a mineral base oil satisfying Requirements (III), the hydrogen partial pressure in the hydrofinishing process is preferably set to a value higher than a pressure of a common hydrogenation process, and specifically is preferably <NUM> MPa or more, more preferably <NUM> MPa or more, and further preferably <NUM> MPa or more, and is preferably <NUM> MPa or less, and more preferably <NUM> MPa or less.

From the viewpoint of producing a mineral base oil satisfying Requirements (III), the reaction temperature in the hydrofinising process is preferably <NUM> to <NUM>, more preferably <NUM> to <NUM>, and further preferably <NUM> to <NUM>.

From the viewpoint of producing a mineral base oil satisfying Requirements (III), the liquid hourly space velocity (LHSV) in the hydrofinishing process is preferably <NUM> hr-<NUM> or less, more preferably <NUM> hr-<NUM> or less, and further preferably <NUM> hr-<NUM> or less, and from the viewpoint of productivity, it is preferably <NUM> hr-<NUM> or more, more preferably <NUM> hr-<NUM> or more, and further preferably <NUM> hr-<NUM> or more.

The supply proportion of the hydrogen gas in the hydrofinishing process is preferably <NUM> to <NUM>,<NUM><NUM>, more preferably <NUM> to <NUM>,<NUM><NUM>, and further preferably <NUM> to <NUM>,<NUM><NUM> per kiloliter of the supplied oil (the refined oil after the hydrogenation isomerization dewaxing process).

After the completion of the aforementioned refining process, the resulting refined oil is subjected to vacuum distillation to collect a fraction having a kinematic viscosity at <NUM> in the range defined in Requirement (I), whereby the mineral base oil of the present invention can be obtained.

The mineral base oil obtained here has a high flash point while having a lowered viscosity as defined in Requirement (I).

The conditions (pressure, temperature, time, etc.) for the vacuum distillation are appropriately adjusted so that the resulting mineral base oil has kinematic viscosities at <NUM> and <NUM> in the ranges defined in Requirement (I).

The lubricating oil composition of the present invention contains the aforementioned mineral base oil of the present invention. The lubricating oil composition may contain a synthetic oil together with the mineral base oil.

Examples of synthetic oils include poly-α-olefins, such as α-olefin homopolymers and α-olefin copolymers (for example, an α-olefin copolymer having <NUM> to <NUM> carbon atoms, such as an ethylene-α-olefin copolymer); isoparaffins; various esters, such as polyol esters, dibasic acid esters (for example, ditridecyl glutarate), tribasic acid esters (for example, <NUM>-ethylhexyl trimellitate), and phosphoric esters; various ethers, such as polyphenyl ethers; polyalkylene glycols; alkylbenzenes; alkylnaphthalenes; and synthetic oils obtained by isomerizing waxes (GTL waxes) produced by the Fischer-Tropsch process.

The synthetic oils may be used either alone or in combination of two or more thereof.

In the lubricating oil composition in one embodiment of the present invention, the content of the synthetic oil is preferably <NUM> to <NUM> parts by mass, more preferably <NUM> to <NUM> parts by mass, further preferably <NUM> to <NUM> parts by mass, and furthermore preferably <NUM> to <NUM> parts by mass based on <NUM> parts by mass of the whole amount of the mineral base oil of the present invention contained in the lubricating oil composition.

The content of the mineral base oil of the present invention in the lubricating oil composition of one embodiment of the present invention is generally <NUM>% by mass or more, preferably <NUM>% by mass or more, more preferably <NUM>% by mass or more, further preferably <NUM>% by mass or more, and furthermore preferably <NUM>% by mass or more, and is generally <NUM>% by mass or less, more preferably <NUM>% by mass or less, and further preferably <NUM>% by mass or less based on the whole amount (<NUM>% by mass) of the lubricating oil composition.

The lubricating oil composition of the present invention may further contain a commonly-used additive for lubricating oil, as needed, to the extent that does not impair the effect of the present invention.

Examples of such additives for lubricating oil include a pour point depressant, a viscosity index improver, a metal-based detergent, a dispersant, an anti-wear agent, an extreme pressure agent, an antioxidant, an anti-foaming agent, a friction modifier, a rust inhibitor, and a metal deactivator.

As the additive for lubricating oil, a commercially available additive package containing plural additives may be used.

Also, a compound having multiple functions as the aforementioned additives (for example a compound having functions as an anti-wear agent and an extreme pressure agent) may be used.

The additives for a lubricating oil may be used either alone or in combination of two or more thereof.

The content of each of the additives for lubricating oil can be appropriately adjusted according to the type of the additive to the extent that does not impair the effect of the present invention, and is generally <NUM> to <NUM>% by mass, preferably <NUM> to <NUM>% by mass, and more preferably <NUM> to <NUM>% by mass based on the whole amount (<NUM>% by mass) of the lubricating oil composition.

Because of containing the aforementioned mineral base oil of the present invention, the lubricating oil composition of the present invention has a high flash point and is excellent in the fuel-saving performance.

Thus, the lubricating oil composition of the present invention can be suitably used as a driving system oil, such as an automatic transmission fluid (ATF), a continuously variable transmission fluid (CVTF), a shock absorber fluid (SAF), a power steering oil, or an electric motor oil; and engine oil; a hydraulic fluid; a turbine oil; a compressor oil; a machine tool lubricating oil; a cutting machine oil; a gear oil; a fluid bearing oil; a rolling bearing oil; and the like.

In recent years, particularly in electric vehicles and hybrid vehicles, size and weight reduction has been required by packaging a transmission and an electric motor. Thus, there has been a need for a lubricating oil composition having, in addition to the performance required for a transmission oil, the cooling property required for an electric motor oil. The lubricating oil composition of the present invention has a certain cooling performance due to its low viscosity, and therefore is suitable for the use in such electric vehicles and hybrid vehicles.

The lubricating oil composition of the present invention can also be used as a refrigerator oil, a rolling oil, an insulating oil, and an elastomer softening agent.

In other words, the present invention can provide a method of using a lubricating oil composition described in the following (<NUM>) and (<NUM>).

Next, the present invention will be described in more detail below with reference to examples, but the present invention is by no means limited to the examples. The methods of measurement and evaluation of physical properties are as follows.

It was measured using a rheometer "Physica MCR <NUM>" manufactured by Anton Paar according to the following procedure.

First, a mineral base oil to be measured was inserted in a corn plate (diameter: <NUM>, angle of inclination: <NUM>°) adjusted to a measurement temperature of -<NUM> or -<NUM>, and then kept at the same temperature for <NUM> minutes. During the time, care was taken not to give a strain to the inserted solution.

Then, at the measurement temperature of -<NUM> or -<NUM>, the complex viscosity η* at -<NUM> or -<NUM> was measured in a vibration mode under conditions at an angular velocity of <NUM> rad/s and a strain amount appropriately set in the range of <NUM> to <NUM>% according to the measurement temperature.

Then, "temperature gradient Δ |η* | of complex viscosity" was calculated from the value of the complex viscosity η* at -<NUM> or -<NUM> using the aforementioned calculation formula (f1).

The aromatic content, the naphthene content, and the total paraffin content (n-paraffin content + isoparaffin content) were determined according to ASTM D2786. Next, the n-paraffin content was determined according to a GC-FID method, and the isoparaffin content was determined from the difference between the total paraffin content and the n-paraffin content.

Then, the proportion of each of the aromatic component, the naphthene component, the n-paraffin component, and the isoparaffin component based on the <NUM>% by volume of the total amount of the components was calculated.

Table <NUM> shows various properties of feedstock oils (I) to (IV) used in Examples and Comparative Examples.

The feedstock oils (I) and (II) are oils containing a gas oil fraction obtained through hydrocracking of a heavy gas oil with a hydrocracking apparatus.

The feedstock oil (III) is an oil containing a gas oil fraction obtained through hydrocracking of a vacuum heavy oil with a hydrocracking apparatus.

The feedstock oil (IV) is an oil containing a gas oil fraction obtained through deep desulfurization of a straight-run stock gas oil fraction.

The feedstock oil (I) shown in Table <NUM> was subjected to a hydrogenation isomerization dewaxing process using a platinum/zeolite catalyst (a catalyst with platinum supported on zeolite as a carrier) under conditions at a reaction temperature of <NUM>, a hydrogen partial pressure of <NUM> MPa, and a ratio of the supply amount of hydrogen to that of the feed stock oil (I) [hydrogen/feedstock oil (I)] of <NUM><NUM>/kL, and LHSV of <NUM> hr-<NUM>, thereby obtaining a refined oil (i).

Then, the refined oil (i) was subjected to vacuum distillation to collect a fraction having a kinematic viscosity at <NUM> in the range of <NUM> to <NUM><NUM>/s, thereby obtaining a mineral base oil (<NUM>).

The feedstock oil (II) shown in Table <NUM> was subjected to a hydrogenation isomerization dewaxing process using a platinum/zeolite catalyst (a catalyst with platinum supported on zeolite as a carrier) under conditions at a reaction temperature of <NUM>, a hydrogen partial pressure of <NUM> MPa, a ratio of the supply amount of hydrogen to that of the feed stock oil (II) [hydrogen/feedstock oil (II)] of <NUM><NUM>/kL, and LHSV of <NUM> hr-<NUM>, thereby obtaining a refined oil (ii).

Then, the refined oil (ii) was subjected to vacuum distillation to collect a fraction having a kinematic viscosity at <NUM> in the range of <NUM> to <NUM><NUM>/s, thereby obtaining a mineral base oil (<NUM>).

The feedstock oil (I) shown in Table <NUM> was subjected to a hydrogenation isomerization dewaxing process using a platinum/zeolite catalyst (a catalyst with platinum supported on zeolite as a carrier) under conditions at a reaction temperature of <NUM>, a hydrogen partial pressure of <NUM> MPa, a ratio of the supply amount of hydrogen to that of the feed stock oil (I) [hydrogen/feedstock oil (I)] of <NUM><NUM>/kL, and LHSV of <NUM> hr-<NUM>, thereby obtaining a refined oil (iii).

Then, the refined oil (iii) was subjected to a hydrofinishing process using a nickel-tungsten/alumina catalyst (a catalyst with nickel and tungsten supported on alumina as a carrier) under conditions at a reaction temperature of <NUM>, a hydrogen partial pressure of <NUM> MPa, a ratio of the supply amount of hydrogen to that of the feed stock oil (iii) [hydrogen/refined oil (iii)] of <NUM><NUM>/kL, and LHSV of <NUM> hr-<NUM>, thereby obtaining a refined oil (iii-<NUM>).

Then, the refined oil (iii-<NUM>) was subjected to vacuum distillation to collect a fraction having a kinematic viscosity at <NUM> in the range of <NUM><NUM>/s or more and less than <NUM><NUM>/s, thereby obtaining a mineral base oil (<NUM>).

The feedstock oil (II) shown in Table <NUM> was subjected to a hydrogenation isomerization dewaxing process using a platinum/zeolite catalyst (a catalyst with platinum supported on zeolite as a carrier) under conditions at a reaction temperature of <NUM>, a hydrogen partial pressure of <NUM> MPa, a ratio of the supply amount of hydrogen to that of the feed stock oil (II) [hydrogen/feedstock oil (II)] of <NUM><NUM>/kL, and LHSV of <NUM> hr-<NUM>, thereby obtaining a refined oil (iv).

Then, the refined oil (iv) was subjected to a hydrofinishing process using a nickel-tungsten/alumina catalyst (a catalyst with nickel and tungsten supported on alumina as a carrier) under conditions at a reaction temperature of <NUM>, a hydrogen partial pressure of <NUM> MPa, a ratio of the supply amount of hydrogen to that of the feed stock oil (iv) [hydrogen/refined oil (iv)] of <NUM><NUM>/kL, and LHSV of <NUM> hr-<NUM>, thereby obtaining a refined oil (iv-<NUM>).

Then, the refined oil (iv-<NUM>) was subjected to vacuum distillation to collect a fraction having a kinematic viscosity at <NUM> in the range of <NUM><NUM>/s or more and <NUM><NUM>/s or less, thereby obtaining a mineral base oil (<NUM>).

The feedstock oil (III) shown in Table <NUM> was subjected to a hydrogenation isomerization dewaxing process using a platinum/zeolite catalyst (a catalyst with platinum supported on zeolite as a carrier) under conditions at a reaction temperature of <NUM>, a hydrogen partial pressure of <NUM> MPa, a ratio of the supply amount of hydrogen to that of the feed stock oil (III) [hydrogen/feedstock oil (III)] of <NUM><NUM>/kL, and LHSV of <NUM> hr-<NUM>, thereby obtaining a refined oil (v).

Then, the refined oil (v) was subjected to a hydrofinishing process using a nickel-tungsten/alumina catalyst (a catalyst with nickel and tungsten supported on alumina as a carrier) under conditions at a reaction temperature of <NUM>, a hydrogen partial pressure of <NUM> MPa, a ratio of the supply amount of hydrogen to that of the feed stock oil (v) [hydrogen/refined oil (v)] of <NUM><NUM>/kL, and LHSV of <NUM> hr-<NUM>, thereby obtaining a refined oil (v-<NUM>).

Then, the refined oil (v-<NUM>) was subjected to vacuum distillation to collect a fraction having a kinematic viscosity at <NUM> in the range of <NUM> to <NUM><NUM>/s, thereby obtaining a mineral base oil (<NUM>).

The feedstock oil (IV) shown in Table <NUM> was subjected to a hydrogenation isomerization dewaxing process using a platinum/zeolite catalyst (a catalyst with platinum supported on zeolite as a carrier) under conditions at a reaction temperature of <NUM>, a hydrogen partial pressure of <NUM> MPa, a ratio of the supply amount of hydrogen to that of the feed stock oil (IV) [hydrogen/feedstock oil (IV)] of <NUM><NUM>/kL, and LHSV of <NUM> hr-<NUM>, thereby obtaining a refined oil (vi).

Then, the refined oil (vi) was subjected to a hydrofinishing process using a nickel-tungsten/alumina catalyst (a catalyst with nickel and tungsten supported on alumina as a carrier) under conditions at a reaction temperature of <NUM>, a hydrogen partial pressure of <NUM> MPa, a ratio of the supply amount of hydrogen to that of the feed stock oil (vi) [hydrogen/refined oil (vi)] of <NUM><NUM>/kL, and LHSV of <NUM> hr-<NUM>, thereby obtaining a refined oil (vi-<NUM>).

Then, the refined oil (vi-<NUM>) was subjected to vacuum distillation to collect a fraction having a kinematic viscosity at <NUM> in the range of <NUM> to <NUM><NUM>/s, thereby obtaining a mineral base oil (<NUM>).

The feedstock oil (I) shown in Table <NUM> was subjected to a hydrogenation isomerization dewaxing process using a platinum/zeolite catalyst (a catalyst with platinum supported on zeolite as a carrier) under conditions at a reaction temperature of <NUM> to <NUM>, a hydrogen partial pressure of <NUM> MPa, a ratio of the supply amount of hydrogen to that of the feed stock oil (I) [hydrogen/feedstock oil (I)] of <NUM><NUM>/kL, and LHSV of <NUM> hr-<NUM>, thereby obtaining a refined oil (vii).

Then, the refined oil (vii) was subjected to a hydrofinishing process using a nickel-tungsten/alumina catalyst (a catalyst with nickel and tungsten supported on alumina as a carrier) under conditions at a reaction temperature of <NUM>, a hydrogen partial pressure of <NUM> MPa, a ratio of the supply amount of hydrogen to that of the feed stock oil (vii) [hydrogen/refined oil (vii)] of <NUM><NUM>/kL, and LHSV of <NUM> hr-<NUM>, thereby obtaining a refined oil (vii-<NUM>).

Then, the refined oil (vii-<NUM>) was subjected to vacuum distillation to collect a fraction having a kinematic viscosity at <NUM> in the range of <NUM> to <NUM><NUM>/s, thereby obtaining a mineral base oil (<NUM>).

The feedstock oil (II) shown in Table <NUM> was subjected to a hydrogenation isomerization dewaxing process using a platinum/zeolite catalyst (a catalyst with platinum supported on zeolite as a carrier) under conditions at a reaction temperature of <NUM>, a hydrogen partial pressure of <NUM> MPa, a ratio of the supply amount of hydrogen to that of the feed stock oil (II) [hydrogen/feedstock oil (II)] of <NUM><NUM>/kL, and LHSV of <NUM> hr-<NUM>, thereby obtaining a refined oil (viii).

Then, the refined oil (viii) was subjected to a hydrofinishing process using a nickel-tungsten/alumina catalyst (a catalyst with nickel and tungsten supported on alumina as a carrier) under conditions at a reaction temperature of <NUM>, a hydrogen partial pressure of <NUM> MPa, a ratio of the supply amount of hydrogen to that of the feed stock oil (viii) [hydrogen/refined oil (viii)] of <NUM><NUM>/kL, and LHSV of <NUM> hr-<NUM>, thereby obtaining a refined oil (viii-<NUM>).

Then, the refined oil (viii-<NUM>) was subjected to vacuum distillation to collect a fraction having a kinematic viscosity at <NUM> in the range of <NUM> to <NUM><NUM>/s, thereby obtaining a mineral base oil (<NUM>).

The feedstock oil (I) shown in Table <NUM> was subjected to a hydrogenation isomerization dewaxing process and a hydrofinishing process in the same conditions as in Example <NUM>, and the resulting refined oil (iii-<NUM>) was subjected to vacuum distillation to collect a fraction having a kinematic viscosity at <NUM> in the range of <NUM><NUM>/s or more and <NUM><NUM>/s or less, thereby obtaining a mineral base oil (<NUM>).

The feedstock oil (II) shown in Table <NUM> was subjected to a hydrogenation isomerization dewaxing process and a hydrofinishing process in the same conditions as in Example <NUM>, and the resulting refined oil (iv-<NUM>) was subjected to vacuum distillation to collect a fraction having a kinematic viscosity at <NUM> in the range of <NUM><NUM>/s or more and <NUM><NUM>/s or less, thereby obtaining a mineral base oil (<NUM>).

The feedstock oil (III) shown in Table <NUM> was subjected to a hydrofinishing process using a nickel-tungsten/alumina catalyst (a catalyst with nickel and tungsten supported on alumina as a carrier) under conditions at a reaction temperature of <NUM>, a hydrogen partial pressure of <NUM> MPa, a ratio of the supply amount of hydrogen to that of the feed stock oil (III) [hydrogen/feedstock oil (III)] of <NUM><NUM>/kL, and LHSV of <NUM> hr-<NUM>, thereby obtaining a refined oil (iii-<NUM>).

Then, the refined oil (iii-<NUM>) was subjected to vacuum distillation to collect a fraction having a kinematic viscosity at <NUM> in the range of <NUM> to <NUM><NUM>/s, thereby obtaining a mineral base oil (<NUM>).

In Comparative Example <NUM>, the feedstock oil (III) shown in Table <NUM> was used as it was as a mineral base oil (a) to measure the aforementioned properties.

In Comparative Example <NUM>, the feedstock oil (IV) shown in Table <NUM> was used as it was as a mineral base oil (b) to measure the aforementioned properties.

The properties of the mineral base oils (<NUM>) to (<NUM>) and (a) to (b) are shown in Table <NUM> and Table <NUM>.

Examples <NUM> and <NUM> are not according to the invention.

In the results, the mineral base oils (<NUM>) to (<NUM>) produced in Examples <NUM> to <NUM> had a low viscosity while having a high flash point of <NUM> or higher. Accordingly, it is considered that lubricating oil compositions using the mineral base oils would have a high flash point while having a further reduced viscosity and thereby having further improved fuel-saving performance.

Claim 1:
A mineral base oil having:
a kinematic viscosity at <NUM> of <NUM><NUM>/s or more and less than <NUM><NUM>/s,
a kinematic viscosity at <NUM> of <NUM><NUM>/s or more and less than <NUM><NUM>/s,
a flash point of <NUM> or higher, wherein the flash point means a value measured by the Cleveland open-cup method according to JIS K2265-<NUM>;
a density at <NUM> of <NUM>/cm<NUM> or more and <NUM>/cm<NUM> or less measured according to JIS K2249; and
a naphthene content of <NUM> to <NUM> measured according to ASTM D-<NUM> ring analysis
wherein a temperature gradient Δ|η*| of complex viscosity between two temperature points -<NUM> and -<NUM> is <NUM> Pa·s/°C or less as measured with a rotary rheometer under conditions at an angular velocity of <NUM> rad/s and a strain amount of <NUM> to <NUM>%.