阅读说明：本技术 等速万向节用润滑脂组合物 (Grease composition for constant velocity joints ) 是由 古贺麻未 宍仓昭弘 于 2019-09-12 设计创作，主要内容包括：本发明的课题是提供具有优异耐磨损性的等速万向节用润滑脂组合物,得到包含基础油(A)、和下述通式(B1)所示的脲系增稠剂(B)的等速万向节用润滑脂组合物。R～1-NHCONH-R～3-NHCONH-R～2(B1),在上述通式(B1)中,R～1和R～2分别独立地表示碳原子数6～24的1价烃基。R～1和R～2可以相同,也可以彼此不同。R～3表示碳原子数6～18的2价芳族烃基。前述1价烃基包括脂环式烃基和链式烃基,同时也可以包括芳族烃基。在前述通式(B1)中的R～1和R～2中,将前述脂环式烃基的含量设为X摩尔当量、将前述链式烃基的含量设为Y摩尔当量、以及将前述芳族烃基的含量设为Z摩尔当量时,满足下述要件(a)和(b)。要件(a)：｛(X＋Y)/(X＋Y＋Z)｝×100的值为90以上。要件(b)：X/Y比为10/90～75/25。(The invention aims to provide a grease composition for constant velocity universal joints, which has excellent wear resistance and contains a base oil (A),And a urea thickener (B) represented by the general formula (B1). R 1 ‑NHCONH‑R 3 ‑NHCONH‑R 2 (B1) In the above general formula (B1), R 1 And R 2 Each independently represents a C6-24 valent hydrocarbon group. R 1 And R 2 May be the same or different from each other. R 3 Represents a 2-valent aromatic hydrocarbon group having 6 to 18 carbon atoms. The aforementioned 1-valent hydrocarbon group includes alicyclic hydrocarbon groups and chain hydrocarbon groups, and may also include aromatic hydrocarbon groups. R in the aforementioned general formula (B1) 1 And R 2 Wherein the following requirements (a) and (b) are satisfied when the content of the alicyclic hydrocarbon group is X molar equivalents, the content of the chain hydrocarbon group is Y molar equivalents, and the content of the aromatic hydrocarbon group is Z molar equivalents. Requirement (a): the value of { (X + Y)/(X + Y + Z) } × 100 is 90 or more. Requirement (b): the X/Y ratio is 10/90 to 75/25.)

1. A grease composition for use in constant velocity joints, which comprises a base oil (A) and a urea-based thickener (B) represented by the following general formula (B1),

R¹-NHCONH-R³-NHCONH-R²　　　　（B1）

in the above general formula (B1), R¹And R²Each independently represents a C6-24 valent hydrocarbon group, R¹And R²May be the same or different from each other, R³Represents a 2-valent aromatic hydrocarbon group having 6 to 18 carbon atoms,

the aforementioned 1-valent hydrocarbon group includes alicyclic hydrocarbon groups and chain hydrocarbon groups, and may also include aromatic hydrocarbon groups, wherein R in the aforementioned general formula (B1)¹And R²Wherein the following requirements (a) and (b) are satisfied when the content of the alicyclic hydrocarbon group is X molar equivalents, the content of the chain hydrocarbon group is Y molar equivalents, and the content of the aromatic hydrocarbon group is Z molar equivalents,

seed and seed essences (a): the value of { (X + Y)/(X + Y + Z) } × 100 is 90 or more,

seed and seed essences (b): the X/Y ratio is 10/90 to 75/25.

2. The grease composition according to claim 1, wherein the mixing consistency at 25 ℃ is 220 to 385.

3. The grease composition according to claim 1 or 2, wherein a peak having a maximum frequency in a volume-based particle size distribution curve obtained by light scattering particle size measurement of the particles containing the urea-based thickener (B) satisfies the following requirements (I) and (II),

seed and seed essences (I): the particle diameter of the peak at the maximum frequency is 1.0 μm or less,

seed and essence (II): the half width of the peak is 1.0 μm or less.

4. A grease composition according to any one of claims 1 to 3, further comprising an organic molybdenum-based compound (C).

5. A grease composition according to any one of claims 1 to 4, further comprising zinc dithiophosphate (D).

Technical Field

The present invention relates to a grease composition for constant velocity joints.

Background

A constant velocity universal joint is a general term for a joint that is used for transmitting rotational motion, and that can rotate both shafts at a constant velocity and smoothly transmit torque even when an angle is formed between an input shaft and an output shaft.

The applications of the constant velocity joint widely relate to a front wheel drive shaft, a rear wheel drive shaft, a propeller shaft, a steering shaft of an automobile, various general industrial machines, and the like.

However, the constant velocity universal joint receives a complicated rolling sliding action while applying a high surface pressure during rotation. Therefore, a high load is easily applied to the rolling sliding portion of the constant velocity joint, and the rolling sliding portion is easily worn. Therefore, in order to efficiently lubricate the constant velocity joint and to improve the durability of the constant velocity joint, various grease compositions for constant velocity joints having excellent wear resistance have been proposed.

For example, patent document 1 describes a grease composition for constant velocity joints, which contains a base oil, a urea thickener, molybdenum dithiocarbamate, a calcium salt, thiophosphate, and a sulfur-phosphorus extreme pressure agent other than thiophosphate.

Patent document 2 describes a grease composition for constant velocity joints, which contains a base oil, a urea thickener made of a diurea compound, molybdenum dialkyldithiocarbamate sulfide, molybdenum disulfide, a zinc dithiophosphate compound, and a sulfur-based extreme pressure additive containing no phosphorus component.

Documents of the prior art

Patent document

Patent document 1, Japanese patent application laid-open No. 11-172276

Patent document 2, Japanese patent application laid-open No. 10-273691.

Disclosure of Invention

Problems to be solved by the invention

In recent years, demands for a constant velocity joint having a low vibration and a long life have become more severe, focusing on demands for higher performance, quietness, riding comfort, and the like of automobiles, higher performance, quietness, higher accuracy, and the like of general industrial machines.

However, the grease compositions for constant velocity joints described in patent documents 1 and 2 cannot be said to be compositions having sufficient wear resistance.

Accordingly, an object of the present invention is to provide a grease composition for constant velocity joints having excellent wear resistance.

Means for solving the problems

The present inventors have found that the above problems can be solved by using a diurea compound having a specific structure as a urea-based thickener.

Namely, the present invention relates to the following [ 1 ].

[1] A grease composition for use in constant velocity joints, which comprises a base oil (A) and a urea-based thickener (B) represented by the following general formula (B1),

R¹-NHCONH-R³-NHCONH-R²　　　　（B1）

in the above general formula (B1), R¹And R²Each independently represents a C6-24 valent hydrocarbon group. R¹And R²May be the same or different from each other. R³Represents a 2-valent aromatic hydrocarbon group having 6 to 18 carbon atoms.

The aforementioned 1-valent hydrocarbon group includes alicyclic hydrocarbon groups and chain hydrocarbon groups, and may also include aromatic hydrocarbon groups. Wherein R in the above general formula (B1)¹And R²Wherein the following requirements (a) and (b) are satisfied when the content of the alicyclic hydrocarbon group is X molar equivalents, the content of the chain hydrocarbon group is Y molar equivalents, and the content of the aromatic hydrocarbon group is Z molar equivalents.

Seed and seed essences (a): the value of { (X + Y)/(X + Y + Z) } × 100 is 90 or more.

Seed and seed essences (b): the X/Y ratio is 10/90 to 75/25.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, a grease composition for a constant velocity universal joint having excellent wear resistance can be provided.

Brief description of the drawings

Fig. 1 is a schematic cross-sectional view of a grease manufacturing apparatus that can be used in one embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of a stirring section of the grease producing apparatus of FIG. 1 in a horizontal direction.

Fig. 3 is a view showing an example of a volume-based particle size distribution curve obtained by measuring a light scattering particle size of particles containing the urea-based thickener (B) in the grease composition.

Detailed Description

The present invention will be described in detail below.

In the following description, the "grease composition for a constant velocity universal joint" will be referred to simply as "grease composition".

In the following description, "base oil (a)", "urea-based thickener (B)", "organic molybdenum-based compound (C)", and "zinc dithiophosphate (D)" will be referred to simply as "component (a)", "component (B)", "component (C)", and "component (D)".

[ grease composition for constant velocity joints ]

The grease composition for constant velocity joints of the present invention comprises a base oil (a) and a urea thickener (B) represented by the following general formula (B1).

R¹-NHCONH-R³-NHCONH-R²　　　　（B1）

In the above general formula (B1), R¹And R²Each independently represents a C6-24 valent hydrocarbon group. R¹And R²May be the same or different from each other. R³Represents a 2-valent aromatic hydrocarbon group having 6 to 18 carbon atoms.

The aforementioned 1-valent hydrocarbon group includes alicyclic hydrocarbon groups and chain hydrocarbon groups, and may also include aromatic hydrocarbon groups. Wherein R in the above general formula (B1)¹And R²Wherein the following requirements (a) and (b) are satisfied when the content of the alicyclic hydrocarbon group is X molar equivalents, the content of the chain hydrocarbon group is Y molar equivalents, and the content of the aromatic hydrocarbon group is Z molar equivalents.

Seed and seed essences (a): the value of { (X + Y)/(X + Y + Z) } × 100 is 90 or more.

Seed and seed essences (b): the X/Y ratio is 10/90 to 75/25.

The grease composition of the present invention may contain other components than the components (a) and (B) within a range not impairing the effects of the present invention.

In the grease composition according to one embodiment of the present invention, the total content of the component (a) and the component (B) is preferably 70% by mass or more, more preferably 75% by mass or more, even more preferably 80% by mass or more, even more preferably 85% by mass or more, and even more preferably 90% by mass or more, based on the total amount (100% by mass) of the grease composition.

In the grease composition according to one embodiment of the present invention, the upper limit of the total content of the above-mentioned component (a) and component (B) may be 100 mass%, based on the total amount (100 mass%) of the grease composition, but is usually 98 mass% or less, preferably 97 mass% or less, more preferably 96 mass% or less, and still more preferably 95 mass% or less.

Here, the grease composition according to one embodiment of the present invention preferably further contains 1 or more additives selected from the group consisting of the organic molybdenum-based compound (C) and the zinc dithiophosphate (D), in addition to the components (a) and (B). By adding 1 or more additives selected from the group consisting of the organic molybdenum compound (C) and the zinc dithiophosphate (D) to the grease composition, the friction coefficient of the rolling contact portion of the constant velocity joint to which the grease is applied can be further reduced, and a grease composition having further excellent wear resistance can be formed.

In the grease composition according to one embodiment of the present invention, the total content of the component (a), the component (B), and 1 or more additives selected from the component (C) and the component (D) is preferably 75% by mass or more, more preferably 80% by mass or more, still more preferably 85% by mass or more, still more preferably 90% by mass or more, and still more preferably 95% by mass or more, based on the total amount (100% by mass) of the grease composition.

In the grease composition according to one embodiment of the present invention, the upper limit of the total content of the above-mentioned component (a) and component (B) and 1 or more additives selected from the component (C) and component (D) may be 100% by mass based on the total amount (100% by mass) of the grease composition, but is usually 99% by mass or less, and preferably 98% by mass or less.

The grease composition according to one embodiment of the present invention may contain additives for grease other than the components (C) and (D) within a range not impairing the effects of the present invention.

In the following description, the grease additive is also referred to as "other grease additive".

Hereinafter, the base oil (a), the urea-based thickener (B), the organic molybdenum-based compound (C), the zinc dithiophosphate (D), and other additives for grease will be described in detail, and then the method for producing the grease composition, the physical properties of the grease composition, and the method for using the grease composition will be described in detail.

< base oil (A) >)

The grease composition of the present invention contains a base oil (a).

The base oil (a) is not particularly limited, and a general base oil that can be used in a grease composition can be used. For example, 1 or more selected from mineral oils and synthetic oils can be used.

Examples of the mineral oil include distillate oils obtained by atmospheric distillation and/or vacuum distillation of paraffinic crude oils, intermediate base crude oils, or naphthenic crude oils; a purified oil obtained by purifying the distillate oil according to a conventional method; and the like.

Examples of the purification method for obtaining the purified oil include 1 or more selected from hydrogenation modification treatment, solvent extraction treatment, solvent dewaxing treatment, clay treatment, hydroisomerization dewaxing treatment, and hydrorefining treatment. The mineral oil can be used alone 1 kind, or more than 2 kinds can be used together.

Examples of the synthetic oil include hydrocarbon-based oils, aromatic-based oils, ester-based oils, ether-based oils, GTL (gas-liquid) base oils obtained by isomerizing waxes produced from natural gas by the fischer-tropsch process, and the like.

Examples of the hydrocarbon-based oil include poly- α -olefins (PAO) such as n-paraffin, isoparaffin, polybutene, polyisobutylene, 1-decene oligomer, and a copolymer oligomer of 1-decene and ethylene, and hydrogenated products thereof.

Examples of the aromatic oil include alkylbenzenes such as monoalkylbenzenes and dialkylbenzenes; alkylnaphthalenes such as monoalkylnaphthalenes, dialkylnaphthalenes, and polyalkylnaphthalenes.

Examples of the ester-based oil include diester-based oils such as dibutyl sebacate, di (2-ethylhexyl) sebacate, dioctyl adipate, diisodecyl adipate, ditridecyl glutarate, and methyl acetylricinoleate; aromatic ester oils such as trioctyl trimesate, tridecyl trimesate, and tetraoctyl pyromellitate; polyol ester oils such as trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol-2-ethylhexanoate, and pentaerythritol pelargonate; complex ester oils such as oligoesters of polyhydric alcohols with mixed fatty acids of dibasic acids and monobasic acids.

Examples of the ether oil include polyglycols such as polyethylene glycol, polypropylene glycol, polyethylene glycol monoether, and polypropylene glycol monoether; phenyl ether series oils such as monoalkyltriphenyl ether, alkyldiphenyl ether, dialkyldiphenyl ether, pentaphenyl ether, tetraphenyl ether, monoalkyltetraphenyl ether, and dialkyltetraphenyl ether.

The synthetic oil may be used alone in 1 kind, or 2 or more kinds may be used in combination.

The kinematic viscosity at 40 ℃ of the base oil (A) used in one embodiment of the present invention is preferably 30 to 1000mm²(ii) s, more preferably 40 to 700mm²More preferably 50 to 500mm in terms of the mass fraction of the polymer²/s。

By setting the kinematic viscosity to the above range, the oil separation of the grease composition becomes appropriate, and the base oil (a) can be easily supplied to the contact portion between the rolling portion and the sliding portion of the constant velocity joint. Further, the oil film retention between both members by the base oil (a) is also likely to be excellent. Therefore, the grease composition can be easily used for a long period of time.

In addition, the base oil (a) used in one embodiment of the present invention may be a mixed base oil prepared by combining a high viscosity base oil (a 1) and a low viscosity base oil (a 2) and having a kinematic viscosity at 40 ℃ in the above range, in order to further improve the wear resistance of the grease composition.

The viscosity index of the base oil (a) used in one embodiment of the present invention is preferably 60 or more, more preferably 70 or more, further preferably 80 or more, further preferably 90 or more, and still further preferably 100 or more.

Note that, in the present specification, kinematic viscosity and viscosity index refer to a viscosity index according to JIS K2283: 2000 measured and calculated values.

In the grease composition according to one embodiment of the present invention, the content of the base oil (a) is preferably 50% by mass or more, more preferably 60% by mass or more, further preferably 65% by mass or more, and still further preferably 70% by mass or more, based on the total amount (100% by mass) of the grease composition. Further, it is preferably 98% by mass or less, more preferably 97% by mass or less, and still more preferably 96% by mass or less.

< Urea-based thickener (B) >)

The grease composition of the present invention contains a urea thickener (B).

The urea-based thickener (B) used in the grease composition of the present invention is a diurea compound represented by the following general formula (B1).

R¹-NHCONH-R³-NHCONH-R²　　　　（B1）

In the above general formula (B1), R¹And R²Each independently represents a C6-24 valent hydrocarbon group. R¹And R²May be the same or different from each other. R³Represents a 2-valent aromatic hydrocarbon group having 6 to 18 carbon atoms.

The aforementioned 1-valent hydrocarbon group includes alicyclic hydrocarbon groups and chain hydrocarbon groups, and may also include aromatic hydrocarbon groups.

The alicyclic hydrocarbon group and the chain hydrocarbon group may be saturated or unsaturated.

Can be selected as R¹And R²The number of carbon atoms of the 1-valent hydrocarbon group(s) is 6 to 24, and from the viewpoint of forming a grease composition having more excellent wear resistance, the number of carbon atoms is preferably 6 to 20, and more preferably 6 to 18.

As can be selected as R¹And R²The 1-valent saturated chain hydrocarbon group (b) includes a linear or branched alkyl group having 6 to 24 carbon atoms, specifically, a hexyl group, heptyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl groupAlkyl, hexadecyl, heptadecyl, octadecyl (stearyl), nonadecyl, and eicosyl, and the like.

Among them, octadecyl (stearyl) group is preferable.

As can be selected as R¹And R²The 1-valent unsaturated chain hydrocarbon group of (a) may include a linear or branched alkenyl group having 6 to 24 carbon atoms, and specifically may include a hexenyl group, a heptenyl group, an octenyl group, a nonenyl group, a decenyl group, a dodecenyl group, a tridecenyl group, a tetradecenyl group, a pentadecenyl group, a hexadecenyl group, an octadecenyl group, a nonadecenyl group, an eicosenyl group, an oleyl group, a geranyl group, a farnesyl group, and a linoleyl group.

The 1-valent saturated chain hydrocarbon group and the 1-valent unsaturated chain hydrocarbon group may be linear or branched.

As can be selected as R¹And R²Examples of the saturated alicyclic hydrocarbon group having a valence of 1 include cycloalkyl groups such as cyclohexyl, cycloheptyl, cyclooctyl and cyclononyl; and cycloalkyl groups substituted with an alkyl group having 1 to 6 carbon atoms (preferably, cyclohexyl groups substituted with an alkyl group having 1 to 6 carbon atoms), such as methylcyclohexyl groups, dimethylcyclohexyl groups, ethylcyclohexyl groups, diethylcyclohexyl groups, propylcyclohexyl groups, isopropylcyclohexyl groups, 1-methyl-propylcyclohexyl groups, butylcyclohexyl groups, pentylcyclohexyl groups, pentyl-methylcyclohexyl groups, and hexylcyclohexyl groups.

Among them, cyclohexyl is preferable.

As can be selected as R¹And R²Examples of the 1-valent unsaturated alicyclic hydrocarbon group include cycloalkenyl groups such as cyclohexenyl, cycloheptenyl and cyclooctenyl; and cycloalkenyl groups substituted with an alkyl group having 1 to 6 carbon atoms (preferably cyclohexenyl groups substituted with an alkyl group having 1 to 6 carbon atoms), such as methylcyclohexenyl, dimethylcyclohexenyl, ethylcyclohexenyl, diethylcyclohexenyl, and propylcyclohexenyl.

As can be selected as R¹And R²Examples of the 1-valent aromatic hydrocarbon group include a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a diphenylmethyl group, a diphenylethyl group, a diphenylpropyl group, a methylphenyl group, a dimethylphenyl group and an ethyl groupPhenyl, and propylphenyl, and the like.

It should be noted that R in the general formula (B1) can be selected as R³The 2-valent aromatic hydrocarbon group(s) has 6 to 18 carbon atoms, preferably 6 to 15 carbon atoms, and more preferably 6 to 13 carbon atoms.

As can be selected as R³Examples of the 2-valent aromatic hydrocarbon group in (b) include a phenylene group, a diphenylmethylene group, a diphenylethylene group, a diphenylpropylene group, a methylphenylene group, a dimethylphenylene group, an ethylphenylene group and the like.

Among them, a phenylene group, a diphenylmethylene group, a diphenylethylene group, or a diphenylpropylene group is preferable, and a diphenylmethylene group is more preferable.

As described above, the aforementioned 1-valent hydrocarbon group includes alicyclic hydrocarbon groups and chain hydrocarbon groups, and may also include aromatic hydrocarbon groups. Wherein R in the above general formula (B1)¹And R²In the above description, the following requirements (a) and (b) are satisfied when the content of the alicyclic hydrocarbon group is X molar equivalents, the content of the chain hydrocarbon group is Y molar equivalents, and the content of the aromatic hydrocarbon group is Z molar equivalents.

Seed and seed essences (a): the value of { (X + Y)/(X + Y + Z) } × 100 is 90 or more.

Seed and seed essences (b): the X/Y ratio is 10/90 to 75/25.

The alicyclic hydrocarbon group, the chain hydrocarbon group and the aromatic hydrocarbon group are R in the general formula (B1)¹And R²The selected groups, and therefore the sum of the values of X, Y and Z, were 2 molar equivalents relative to 1 mole of the compound represented by the above general formula (B1). The values of the above-mentioned requirements (a) and (B) are average values with respect to the total amount of the compound group represented by the above-mentioned general formula (B1) contained in the grease composition.

By using the compound represented by the general formula (B1) satisfying the requirements (a) and (B), a grease composition having excellent wear resistance can be formed.

When the compound represented by the general formula (B1) which does not satisfy the requirements (a) and (B) is used, the grease composition is not suitable as a grease composition for constant velocity joints because of its poor wear resistance.

The values of X, Y and Z can be calculated from the molar equivalents of the amines used as the raw materials for synthesizing the diurea compound represented by the general formula (B1).

Here, from the viewpoint of forming a grease composition having more excellent wear resistance, the requirement (a) is preferably 95 or more, more preferably 98 or more, and even more preferably 100.

From the same viewpoint, the requirement (b) is preferably 30/70 to 72/28, more preferably 35/65 to 70/30, still more preferably 40/60 to 70/30, and still more preferably 55/45 to 65/35.

(essential elements (I) and (II))

In the grease composition according to one embodiment of the present invention, the peak having the maximum frequency in the volume-based particle size distribution curve obtained by light scattering particle size measurement of the particles containing the urea-based thickener (B) preferably satisfies the following requirements (I) and (II),

seed and seed essences (I): the particle diameter of the peak at the maximum frequency is 1.0 μm or less,

seed and essence (II): the half width of the peak is 1.0 μm or less.

In the present specification, the values specified in the above-mentioned requirements (I) and (II) are values calculated from particle size distribution curves measured by the light scattering particle size measurement in the following examples.

Fig. 3 shows an example of a volume-based particle size distribution curve of particles containing the urea-based thickener (B) measured by light scattering particle size measurement. In the particle size distribution curve shown in FIG. 3, the maximum frequency y is₁Peak P of (1)₁Particle diameter r of₁Is 1.0 μm or less, thereby satisfying the requirement (I). In addition, peak P₁Half peak width x of₁1.0 μm or less, thereby satisfying the requirement (II).

The requirements (I) and (II) are parameters indicating the state of aggregation of the urea-based thickener (B) in the grease composition.

The "particles containing the urea-based thickener (B)" to be measured herein means particles in which the urea-based thickener (B) is aggregated, and also includes particles in which 1 or more additives selected from the component (C), the component (D), and other additives for grease are also aggregated and incorporated together with the urea-based thickener (B).

On the other hand, the aggregate not containing the urea-based thickener (B) but consisting of only 1 or more additives selected from the component (C), the component (D), and other additives for grease is excluded from the above-mentioned "particles containing the urea-based thickener (B)". Here, "excluded" means that the aggregate composed of only 1 or more additives selected from the component (C), the component (D), and other additives for grease is very small compared with the "particle containing the urea-based thickener (B)", and therefore is hardly detected in the light scattering particle size measurement, and is at a negligible level even if detected.

In the requirement (I), the particle size of the peak having the maximum frequency is defined to be 1.0 μm or less. This particle diameter can be said to be an index indicating the degree of aggregation of the urea-based thickener (B).

If the particle diameter is 1.0 μm or less, the coagulation of the urea-based thickener (B) is appropriately suppressed, and a grease composition having excellent frictional properties and further excellent wear resistance is easily formed. In view of forming a grease composition having more excellent friction characteristics and more excellent wear resistance, the particle diameter defined in the requirement (I) and having the maximum frequency of the peak is preferably 0.9 μm or less, more preferably 0.8 μm or less, even more preferably 0.6 μm or less, and usually 0.01 μm or more.

The particle diameter at the maximum frequency of the peak means the value of the particle diameter at the peak of the peak.

On the other hand, in the requirement (II), it is specified that the half-value width of the peak is 1.0 μm or less. This half-value width is an index showing the distribution of particles containing the urea-based thickener (B) larger than the particle diameter defined as the maximum frequency in the requirement (I).

Here, the half-width of the peak defined in the requirement (II) is a developed width of the particle diameter indicating 50% of the maximum frequency of the requirement (I) in a particle diameter distribution curve of the particle on a volume basis obtained by measuring the light scattering particle diameter.

That is, if the half-width is 1.0 μm or less, the proportion of micelle particles of the urea-based thickener (B) having an excessively larger particle diameter than the particle diameter specified in the requirement (I) is suppressed to a small extent, and a grease composition having excellent frictional properties and more excellent wear resistance is easily formed. Here, from the viewpoint of forming a grease composition having more excellent friction characteristics and more excellent wear resistance, the half-width of the peak defined in the requirement (II) is preferably 0.9 μm or less, more preferably 0.8 μm or less, even more preferably 0.6 μm or less, and usually 0.01 μm or more.

The values specified in the requirements (I) and (II) have a large influence on the production conditions of the urea-based thickener (B), the blending conditions of the component (C), the component (D), and other additives for grease.

An example of a specific method for preparing the grease composition so as to obtain the values specified in the requirements (I) and (II) is as described in the section "method for producing a grease composition" below.

In the grease composition according to one embodiment of the present invention, the content of the urea-based thickener (B) can be determined according to the mixing consistency required for the grease composition for constant velocity joints.

Here, in the grease composition according to one embodiment of the present invention, the urea-based thickener (B) is a specific compound represented by the general formula (B1), and thus the amount of the thickener used for adjusting the mixing consistency can be reduced as compared with the case where another urea-based thickener is used. That is, by making the urea-based thickener (B) a specific compound represented by the above general formula (B1), a grease composition having a lower mixing consistency can be formed with a smaller thickener content than in the case of using other urea-based thickeners. Therefore, a grease composition having a lower mixing consistency can be made a grease composition that has the advantage of being easily prepared at a lower cost and that can cope with the problem of cost reduction that has been required for greases for constant velocity joints in recent years.

For example, the content of the urea-based thickener (B) is 3.0 to 7.0% by mass, more preferably 3.5 to 6.5% by mass, and still more preferably 4.0 to 6.0% by mass, from the viewpoint of adjusting the mixing consistency suitable for the grease composition for constant velocity universal joints, for example, preferably 220 to 385, more preferably 250 to 355, and further preferably 220 to 340.

As described above, the grease composition according to one embodiment of the present invention can easily ensure a sufficient mixing consistency required for grease compositions for constant velocity joints even when the amount of the urea-based thickener (B) is small.

< organic molybdenum-based Compound (C) >)

The grease composition according to one embodiment of the present invention preferably contains an organic molybdenum compound (C).

By containing the organic molybdenum compound (C) in the grease composition, the grease composition can be made excellent in frictional properties and can be made more excellent in wear resistance.

The organic molybdenum compound (C) used in one embodiment of the present invention may be any organic compound having a molybdenum atom, but from the viewpoint of further improving the friction characteristics of the grease composition, molybdenum dithiophosphate (MoDTP) and molybdenum dithiocarbamate (MoDTC) are preferable, and molybdenum dithiocarbamate (MoDTC) is more preferable.

The organic molybdenum compound (C) may be used alone or in combination of two or more.

(molybdenum dithiophosphate (MoDTP))

The molybdenum dithiophosphate (MoDTP) is preferably a compound represented by the following general formula (C1-1) or a compound represented by the following general formula (C1-2).

[ solution 1]

In the above general formulae (C1-1) and (C1-2), R¹¹～R¹⁴Each independently represents a hydrocarbon group. R¹¹～R¹⁴May be the same as or different from each other.

X¹～X⁸Each independently represents an oxygen atom or a sulfur atom, and may be the same as or different from each other. Wherein X in the formula (C1-1)¹～X⁸At least two of (a) are sulfur atoms.

In one embodiment of the present invention, X is preferably represented by the general formula (C1-1)¹And X²Is an oxygen atom, X³～X⁸Is a sulfur atom.

In the above general formula (C1-1), X is X from the viewpoint of improving solubility in the base oil (A)¹～X⁸The molar ratio of sulfur atoms to oxygen atoms [ sulfur atoms/oxygen atoms ] in the nitrogen-containing gas is preferably 1/4 to 4/1, more preferably 1/3 to 3/1.

In the general formula (C1-2), X is preferably X¹And X²Is an oxygen atom, X³And X⁴Is a sulfur atom.

In the above general formula (C1-2), X is selected from the same viewpoints as described above¹～X⁴The molar ratio of sulfur atoms to oxygen atoms [ sulfur atoms/oxygen atoms ] in the nitrogen-containing gas is preferably 1/3 to 3/1, more preferably 1.5/2.5 to 2.5/1.5.

Can be selected as R¹¹～R¹⁴The number of carbon atoms of the hydrocarbon group(s) is preferably 1 to 20, more preferably 5 to 18, still more preferably 5 to 16, and still more preferably 5 to 12.

As can be selected as R¹¹～R¹⁴Specific examples of the hydrocarbon group include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, and octadecyl; octenyl, nonenyl, decenyl, undecenyl, dodecenyl, tridecenyl, tetradecenyl, pentadecenylAlkenyl groups such as phenyl; cycloalkyl groups such as cyclohexyl, dimethylcyclohexyl, ethylcyclohexyl, methylcyclohexylmethyl, cyclohexylethyl, propylcyclohexyl, butylcyclohexyl, and heptylcyclohexyl; aryl groups such as phenyl, naphthyl, anthryl, biphenyl, and terphenyl; alkylaryl groups such as tolyl, dimethylphenyl, butylphenyl, nonylphenyl, methylbenzyl, and dimethylnaphthyl; and arylalkyl groups such as phenylmethyl, phenylethyl, and diphenylmethyl.

(molybdenum dithiocarbamate (MoDTC))

As molybdenum dithiocarbamates (MoDTC), dinuclear molybdenum dithiocarbamates containing 2 molybdenum atoms in one molecule and trinuclear molybdenum dithiocarbamates containing 3 molybdenum atoms in one molecule are cited, with dinuclear molybdenum dithiocarbamates being preferred.

The dinuclear molybdenum dithiocarbamate is more preferably a compound represented by the following general formula (C2-1) or a compound represented by the following general formula (C2-2).

[ solution 2]

In the above general formulae (C2-1) and (C2-2), R²¹～R²⁴Each independently represents a hydrocarbon group, and may be the same as or different from each other.

X¹¹～X¹⁸Each independently represents an oxygen atom or a sulfur atom, and may be the same as or different from each other.

Wherein X in the formula (C2-1)¹¹～X¹⁸At least one of (a) and (b) is a sulfur atom.

In one embodiment of the present invention, X in the formula (C2-1) is preferably X¹¹And X¹²Is an oxygen atom, X¹³～X¹⁸Is a sulfur atom.

In the above general formula (C2-1), X is selected from the viewpoint of improving the solubility in the base oil (A)¹¹～X¹⁸Mole of sulfur atom to oxygen atom inThe molar ratio [ sulfur atom/oxygen atom ] is preferably 1/4 to 4/1, more preferably 1/3 to 3/1.

Further, X in the formula (C2-2)¹¹～X¹⁴Preferably an oxygen atom.

In the above general formulae (C2-1) and (C2-2), R can be selected as²¹～R²⁴The number of carbon atoms of the hydrocarbon group(s) is preferably 1 to 20, more preferably 5 to 18, still more preferably 5 to 16, and still more preferably 5 to 13.

As can be selected as R²¹～R²⁴Specific examples of the hydrocarbon group in (1) include those which can be selected as R in the general formulae (C1-1) and (C1-2)¹¹～R¹⁴The hydrocarbon group of (1) is the same group.

< Zinc dithiophosphate (D) >

The grease composition according to one embodiment of the present invention preferably contains zinc dithiophosphate (D).

By containing zinc dithiophosphate (D) in the grease composition, the grease composition is easily made good in frictional properties and excellent in wear resistance.

The zinc dithiophosphate (D) contained in the grease composition according to one embodiment of the present invention is preferably represented by the following general formula (D1).

[ solution 3]

In the above general formula (D1), R³¹～R³⁴Each independently represents a hydrocarbon group. The hydrocarbyl group is not particularly limited as long as it is a 1-valent hydrocarbyl group, but from the viewpoint of further improving the frictional properties of the grease composition, it is preferably an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group, or the like, more preferably an alkyl group, an aryl group, and even more preferably an alkyl group. That is, as the zinc dithiophosphate (D) used in one embodiment of the present invention, zinc dialkyldithiophosphates and zinc diaryldithiophosphates are more preferable, and zinc dialkyldithiophosphates are still more preferable.

R³¹～R³⁴The alkyl group and the alkenyl group in (b) may be either linear or branched, but from the viewpoint of further improving the frictional properties of the grease composition, primary and secondary groups are preferred, and among them, primary alkyl groups and secondary alkyl groups are preferred, and secondary alkyl groups are more preferred. That is, as the zinc dialkyldithiophosphate used in one embodiment of the present invention, zinc diprimyldithiophosphates and zinc diprimyldithiophosphates are preferable, and zinc diprimyldithiophosphates are more preferable.

R³¹～R³⁴The cycloalkyl group and the aryl group in (b) may be, for example, polycyclic groups such as decahydronaphthyl and naphthyl groups.

In addition, can be selected as R³¹～R³⁴The 1-valent hydrocarbon group in (a) may have a substituent containing an oxygen atom and/or a nitrogen atom such as a hydroxyl group, a carboxyl group, an amino group, an amide group, a nitro group, a cyano group, or the like, a part of which may be replaced with a nitrogen atom, an oxygen atom, a halogen atom, or the like, and when the 1-valent hydrocarbon group is a cycloalkyl group or an aryl group, it may further have a substituent such as an alkyl group or an alkenyl group.

R is a number of atoms in the grease composition from the viewpoint of further improving the frictional properties of the grease composition³¹～R³⁴The number of carbon atoms of the hydrocarbon group (b) is preferably 1 or more, more preferably 2 or more, further preferably 3 or more, and as the upper limit, preferably 24 or less, more preferably 18 or less, further preferably 12 or less, when the 1-valent hydrocarbon group is an alkyl group.

When the 1-valent hydrocarbon is an alkenyl group, the upper limit is preferably not less than 2, more preferably not less than 3, and preferably not more than 24, more preferably not more than 18, and further preferably not more than 12.

When the 1-valent hydrocarbon is a cycloalkyl group, the number of carbon atoms is preferably 5 or more, and the upper limit is preferably 20 or less.

When the 1-valent hydrocarbon is an aryl group, the number of carbon atoms is preferably 6 or more, and the upper limit is preferably 20 or less.

< content and content ratio of organic molybdenum-based compound (C) to zinc dithiophosphate (D) >

(content of organic molybdenum-based Compound (C))

In the grease composition according to one embodiment of the present invention, the content of the organic molybdenum compound (C) is preferably 0.01 to 5.0% by mass, more preferably 0.1 to 5.0% by mass, even more preferably 0.2 to 3.0% by mass, and even more preferably 0.5 to 3.0% by mass, based on the total amount (100% by mass) of the grease composition, from the viewpoint of improving the frictional properties of the grease composition.

In the grease composition according to one embodiment of the present invention, the content of the organic molybdenum compound (C) in terms of molybdenum atoms is preferably 0.0005 to 0.2000 mass ppm, more preferably 0.01 to 0.15 mass ppm, and still more preferably 0.02 to 0.15 mass ppm, based on the total amount (100 mass%) of the grease composition.

In the present specification, the content of molybdenum atom is a value measured in accordance with JPI-5S-38-03.

(content of Zinc dithiophosphate (D))

In the grease composition according to one embodiment of the present invention, the content of the zinc dithiophosphate (D) is preferably 0.02 to 6.0 mass%, more preferably 0.2 to 5.0 mass%, even more preferably 0.4 to 4.0 mass%, and even more preferably 0.5 to 3.0 mass% based on the total amount (100 mass%) of the grease composition, from the viewpoint of improving the frictional properties of the grease composition.

In the grease composition according to one embodiment of the present invention, the zinc dithiophosphate (D) is preferably contained in an amount of 0.1 to 3.0 mass ppm, more preferably 0.5 to 2.5 mass ppm, and still more preferably 0.7 to 2.0 mass ppm in terms of zinc atoms based on the total amount (100 mass%) of the grease composition.

In the present specification, the content of zinc atoms is a value measured by JPI-5S-38-03.

(content ratio of organic molybdenum-based Compound (C) to Zinc dithiophosphate (D))

In the grease composition according to one embodiment of the present invention, the content ratio of the organic molybdenum compound (C) to the zinc dithiophosphate (D) [ organic molybdenum compound (C)/zinc dithiophosphate (D) ] is preferably 1/5 to 4, more preferably 1/3 to 2, and still more preferably 1/3 to 1 in terms of a mass ratio.

In addition, in the grease composition according to one embodiment of the present invention, the content ratio [ Mo/Zn ] of the molybdenum atoms (Mo) derived from the organic molybdenum compound (C) to the zinc atoms (Zn) derived from the zinc dithiophosphate (D) is preferably 0.1 to 1.0, more preferably 0.1 to 0.5, and further preferably 0.15 to 0.30 in terms of a mass ratio.

< additives for other greases >

The grease composition according to one embodiment of the present invention may contain additives for grease other than the components (C) and (D), which can be blended in general grease, within a range not to impair the effects of the present invention.

Examples of such additives for greases include antioxidants, rust inhibitors, extreme pressure agents, thickeners, solid lubricants, detergent dispersants, anticorrosive agents, and metal deactivators.

These additives for grease may be used alone or in combination of two or more.

Examples of the antioxidant include a phenol-based antioxidant, an amine-based antioxidant, and a sulfur-based antioxidant.

Examples of the rust inhibitor include carboxylic acid-based rust inhibitors such as alkenyl succinic acid polyol esters, zinc stearate, thiadiazole and derivatives thereof, and benzotriazole and derivatives thereof.

Examples of the extreme pressure agent include ashless thiocarbamates, zinc dithiocarbamates, and other thiocarbamates; sulfur compounds such as sulfurized fats and oils, sulfurized olefins, polysulfides, thiophosphoric acids, thioterpenes, and dialkyl thiodipropionates; phosphoric acid esters of tricresyl phosphate and the like; phosphite esters such as triphenyl phosphite; and the like.

Examples of the thickener include Polymethacrylate (PMA), Olefin Copolymer (OCP), Polyalkylstyrene (PAS), styrene-diene copolymer (SCP), and the like.

Examples of the solid lubricant include polyimide, PTFE, graphite, metal oxide, boron nitride, Melamine Cyanurate (MCA), molybdenum disulfide, and the like.

Examples of the detergent dispersant include ashless dispersants such as non-boronated succinimide and boronated succinimide.

Examples of the anticorrosive agent include benzotriazole compounds and thiazole compounds.

Examples of the metal deactivator include benzotriazole compounds.

In the grease composition according to one embodiment of the present invention, the content of these additives for grease may be appropriately set according to the type of the additive, and each of them is usually 0 to 10 mass%, preferably 0 to 7 mass%, more preferably 0 to 5 mass%, and still more preferably 0 to 2 mass%, based on the total amount (100 mass%) of the grease composition.

[ method for producing grease composition ]

In the following description, a grease composition containing a base oil (a) and a urea-based thickener (B) represented by the above general formula (B1) and before adding 1 or more additives selected from the component (C), the component (D), and other additives for grease is also referred to as "base grease".

The method for producing the grease composition of the present invention is not particularly limited, and examples thereof include a method comprising the following step (1).

Seed planting process (1): and a step of synthesizing a urea thickener (B) by blending a raw material of the urea thickener (B) represented by the general formula (B1) with the base oil (A) to obtain a base grease.

The 1 or more additives selected from the component (C), the component (D), and other additives for grease may be added during the preparation of the base grease in the step (1), or may be added after the preparation of the base grease in the step (1).

The step (1) can be carried out in detail by, for example, the following steps.

< Process (1) >

In the case of using the urea-based thickener (B) represented by the above general formula (B1), a solution β in which a monoamine is dissolved in a base oil (a) is added to a heated solution α in which an isocyanate compound is dissolved in a base oil (a), and the isocyanate compound and the monoamine are reacted with each other, whereby the urea-based thickener (B) represented by the above general formula (B1) can be synthesized, and a base grease can be obtained. In the grease composition in which 1 or more additives selected from the group consisting of the component (C), the component (D), and other grease additives are added to the base grease, it is preferable to perform a milling treatment using a colloid mill, a roll mill, or the like after cooling.

The following method can be mentioned as a method for preparing a grease composition so that the particle size distribution of the particles containing the urea-based thickener (B) satisfies the requirements (I) and (II).

< method for producing grease composition satisfying the above requirements (I) and (II) >

(device)

From the viewpoint of dispersing the urea-based thickener (B) in the grease composition so as to satisfy the requirements (I) and (II), it is preferable to prepare a base grease using a grease manufacturing apparatus as shown in the following [ 1] to manufacture a grease composition.

[1] A grease manufacturing device is provided with:

a container body having an introduction part for introducing a grease raw material and a discharge part for discharging the base grease to the outside, and

a rotor rotatably provided in the container body and having a rotating shaft in an axial direction of an inner periphery of the container body,

the rotor includes a first concave-convex portion

(i) Alternatively providing irregularities along the surface of the rotor, the irregularities being inclined with respect to the rotation axis,

(ii) has a carrying capability from the introduction part toward the discharge part.

The grease manufacturing apparatus described in [ 1] above is described below, but the "preferable" in the following description is a mode in which the urea-based thickener (B) is dispersed in the grease composition so as to satisfy the requirements (I) and (II), unless otherwise specified.

Fig. 1 is a schematic cross-sectional view of the grease manufacturing apparatus according to [ 1] above, which can be used in one embodiment of the present invention.

The grease manufacturing apparatus 1 shown in fig. 1 includes: a container body 2 into which a grease raw material is introduced, and a rotor 3 having a rotary shaft 12 on the central axis of the inner periphery of the container body 2 and rotating about the rotary shaft 12 as the central axis.

The rotor 3 rotates at a high speed about the rotation axis 12 as a center axis, and applies a high shearing force to the grease raw material inside the container body 2. Thus, a base grease containing the urea-based thickener (B) can be produced.

The container body 2 is preferably divided into an introduction portion 4, a retention portion 5, a first inner peripheral surface 6, a second inner peripheral surface 7, and a discharge portion 8 in this order from the upstream side, as shown in fig. 1.

The container body 2 preferably has a truncated cone-shaped inner peripheral surface whose inner diameter gradually increases from the introduction portion 4 to the discharge portion 8, as shown in fig. 1.

The introduction portion 4 formed at one end of the container main body 2 includes a plurality of solution introduction pipes 4A and 4B for introducing the grease raw material from the outside of the container main body 2.

The retention section 5 is a space disposed downstream of the introduction section 4 and configured to temporarily retain the grease raw material introduced from the introduction section 4. When the grease raw material is retained in the retention portion 5 for a long time, the base grease adhering to the inner peripheral surface of the retention portion 5 forms large lumps, and therefore, it is preferable to feed the grease raw material to the first inner peripheral surface 6 on the downstream side in as short a time as possible. Further, it is preferable that the gas is directly sent to the first inner circumferential surface 6 without passing through the retention section 5.

The first inner peripheral surface 6 is disposed in a downstream portion adjacent to the retention portion 5, and the second inner peripheral surface 7 is disposed in a downstream portion adjacent to the first inner peripheral surface 6. As will be described in detail later, it is preferable that the first inner circumferential surface 6 and the second inner circumferential surface 7 function as high shear portions for applying a high shear force to the grease raw material or the base grease by providing the first uneven portion 9 on the first inner circumferential surface 6 and the second uneven portion 10 on the second inner circumferential surface 7.

The discharge portion 8 formed at the other end of the container body 2 is a portion for discharging the base grease stirred by the first inner circumferential surface 6 and the second inner circumferential surface 7, and is provided with a discharge port 11 for discharging the base grease. The discharge port 11 is formed in a direction perpendicular or substantially perpendicular to the rotation shaft 12. Thereby, the base grease is discharged from the discharge port 11 in a direction perpendicular or substantially perpendicular to the rotation shaft 12. However, the discharge port 11 is not necessarily perpendicular to the rotation shaft 12, and may be formed in a direction parallel or substantially parallel to the rotation shaft 12.

The rotor 3 is rotatably provided with a central axis of the truncated cone-shaped inner peripheral surface of the container body 2 as a rotation axis 12, and rotates counterclockwise when the container body 2 is viewed from the upstream portion toward the downstream portion as shown in fig. 1.

The rotor 3 has an enlarged outer peripheral surface in accordance with the enlargement of the inner diameter of the truncated cone of the container body 2, and the outer peripheral surface of the rotor 3 and the inner peripheral surface of the truncated cone of the container body 2 can maintain a constant interval.

On the outer circumferential surface of the rotor 3, a first concave-convex portion 13 of the rotor may be provided in which concave-convex portions are alternately provided along the surface of the rotor 3.

The first uneven portion 13 of the rotor is inclined with respect to the rotation axis 12 of the rotor 3 in the direction from the inlet portion 4 to the outlet portion 8, and has a carrying capability from the inlet portion 4 to the outlet portion 8. That is, the first concave-convex portion 13 of the rotor is inclined in a direction of extruding the solution to the downstream side when the rotor 3 rotates in the direction shown in fig. 1.

The difference in height between the concave portion 13A and the convex portion 13B of the first concave-convex portion 13 of the rotor is preferably 0.3 to 30, more preferably 0.5 to 15, and even more preferably 2 to 7, when the diameter of the concave portion 13A on the outer peripheral surface of the rotor 3 is 100.

The number of the convex portions 13B of the first concave-convex portion 13 of the rotor in the circumferential direction is preferably 2 to 1000, more preferably 6 to 500, and further preferably 12 to 200.

The ratio of the width of the convex portion 13B to the width of the concave portion 13A of the first concave-convex portion 13 of the rotor 3 in the cross section perpendicular to the rotation axis 12 [ width of convex portion/width of concave portion ] is preferably 0.01 to 100, more preferably 0.1 to 10, and further preferably 0.5 to 2.

The inclination angle of the first concave-convex portion 13 of the rotor with respect to the rotation shaft 12 is preferably 2 to 85 degrees, more preferably 3 to 45 degrees, and further preferably 5 to 20 degrees.

The first inner circumferential surface 6 of the container main body 2 preferably includes a first uneven portion 9 having a plurality of irregularities formed along the inner circumferential surface.

It is preferable that the irregularities of the first uneven portion 9 on the container main body side are inclined in the opposite direction to the first uneven portion 13 of the rotor.

That is, the plurality of concavities and convexities of the first concave-convex portion 9 on the container main body side are preferably inclined in a direction in which the solution is pushed out toward the downstream side when the rotation shaft 12 of the rotor 3 rotates in the direction shown in fig. 1. The stirring ability and the discharging ability can be further enhanced by the first uneven portion 9 having a plurality of unevenness provided on the first inner peripheral surface 6 of the container main body 2.

The depth of the concavities and convexities of the first concavities and convexities 9 on the container main body side is preferably 0.2 to 30, more preferably 0.5 to 15, and still more preferably 1 to 5, when the container inner diameter (diameter) is 100.

The number of the first uneven portions 9 on the container main body side is preferably 2 to 1000, more preferably 6 to 500, and still more preferably 12 to 200.

The ratio of the width of the concave portion of the concave-convex portion of the first concave-convex portion 9 on the container main body side to the width of the convex portion between the grooves [ width of concave portion/width of convex portion ] is preferably 0.01 to 100, more preferably 0.1 to 10, and further preferably 0.5 to 2 or less.

The inclination angle of the concavities and convexities of the first concave-convex portion 9 on the container main body side with respect to the rotation axis 12 is preferably 2 to 85 degrees, more preferably 3 to 45 degrees, and further preferably 5 to 20 degrees.

The first uneven portion 9 is provided on the first inner circumferential surface 6 of the container main body, and thus the first uneven portion 9 does not necessarily have to be provided, although the first uneven portion can function as a high shear portion that applies a high shear force to the grease raw material or the base grease on the first inner circumferential surface 6.

It is preferable that a second rotor concave-convex portion 14 in which concave and convex portions are alternately provided along the surface of the rotor 3 is provided on the outer peripheral surface of the downstream portion of the first rotor concave-convex portion 13.

The second uneven portion 14 of the rotor is inclined with respect to the rotation axis 12 of the rotor 3, and has a transport inhibiting ability to push the solution back to the upstream side from the introduction portion 4 toward the discharge portion 8.

The height difference of the second uneven portion 14 of the rotor is preferably 0.3 to 30, more preferably 0.5 to 15, and even more preferably 2 to 7, when the diameter of the concave portion on the outer peripheral surface of the rotor 3 is 100.

The number of projections of the second uneven portion 14 of the rotor in the circumferential direction is preferably 2 to 1000, more preferably 6 to 500, and still more preferably 12 to 200.

The ratio of the width of the convex portion to the width of the concave portion [ width of convex portion/width of concave portion ] of the second concave-convex portion 14 of the rotor 3 in the cross section perpendicular to the rotation axis is preferably 0.01 to 100, more preferably 0.1 to 10, and further preferably 0.5 to 2.

The angle of inclination of the second concave-convex portion 14 of the rotor with respect to the rotation shaft 12 is preferably 2 to 85 degrees, more preferably 3 to 45 degrees, and further preferably 5 to 20 degrees.

The second inner peripheral surface 7 of the container main body 2 is preferably provided with a second uneven portion 10 having a plurality of irregularities formed thereon, adjacent to a downstream portion of the irregularities in the first uneven portion 9 on the container main body side.

It is preferable that a plurality of projections and depressions of the second concave-convex portion 10 on the container main body side are formed on the inner peripheral surface of the container main body 2, and each of the projections and depressions is inclined in a direction opposite to the inclination direction of the second concave-convex portion 14 of the rotor.

That is, the plurality of concavities and convexities of the second concave-convex portion 10 on the container main body side are preferably inclined in a direction of pushing the solution back to the upstream side when the rotation shaft 12 of the rotor 3 rotates in the direction shown in fig. 1. The stirring ability can be further enhanced by the unevenness of the second uneven portion 10 provided on the second inner circumferential surface 7 of the container main body 2. The second inner circumferential surface 7 of the container main body 2 can also function as a high shear portion for applying a high shear force to the grease raw material or the base grease.

The depth of the concave portion of the second uneven portion 10 on the container main body side is preferably 0.2 to 30, more preferably 0.5 to 15, and further preferably 1 to 5, when the container inner diameter (diameter) is 100.

The number of the concave portions of the second uneven portion 10 on the container main body side is preferably 2 to 1000, more preferably 6 to 500, and further preferably 12 to 200.

The ratio of the width of the convex portion to the width of the concave portion [ the width of the convex portion/the width of the concave portion ] of the concave-convex portion of the second concave-convex portion 10 on the container main body side in the cross section perpendicular to the rotation axis 12 of the rotor 3 is preferably 0.01 to 100, more preferably 0.1 to 10, and further preferably 0.5 to 2 or less.

The inclination angle of the second uneven portion 10 on the container main body side with respect to the rotation axis 12 is preferably 2 to 85 degrees, more preferably 3 to 45 degrees, and further preferably 5 to 20 degrees.

The ratio of the length of the first concave-convex section 9 on the container body side to the length of the second concave-convex section 10 on the container body side [ the length of the first concave-convex section/the length of the second concave-convex section ] is preferably 2/1 to 20/1.

Fig. 2 is a horizontal sectional view of the first uneven portion 9 on the container body side of the grease producing apparatus 1.

In the first uneven portion 13 shown in fig. 2, a plurality of scrapers 15 are provided, the tips of which protrude on the inner circumferential surface side of the container main body 2 than the tips of the convex portions 13B of the first uneven portion 13 in the protruding direction. Although not shown in the drawings, the second uneven portion 14 is also provided with a scraper having a plurality of convex portions whose tips protrude on the inner circumferential surface side of the container main body 2, similarly to the first uneven portion 13.

The scraper 15 scrapes the base grease adhering to the inner peripheral surfaces of the first uneven portion 9 on the container body side and the second uneven portion 10 on the container body side.

The ratio [ R2/R1 ] of the projection amount of the tip of the scraper 15 to the projection amount of the convex portion 13B of the first concave-convex portion 13 of the rotor is preferably more than 1.005 and less than 2.0, the ratio being the radius (R2) of the tip of the scraper 15 to the radius (R1) of the tip of the convex portion 13B.

The number of the scrapers 15 is preferably 2 to 500, more preferably 2 to 50, and further preferably 2 to 10.

In the grease manufacturing apparatus 1 shown in fig. 2, the scraper 15 is provided, but may not be provided, or may be provided intermittently.

When the base grease containing the urea-based thickener (B) is produced by the grease producing apparatus 1, the above-described solution α and solution β as grease raw materials are introduced from the solution introduction pipes 4A and 4B of the introduction portion 4 of the container main body 2, respectively, and the rotor 3 is rotated at a high speed, whereby the base grease containing the urea-based thickener (B) can be produced.

Further, even when the grease composition is prepared by blending 1 or more additives selected from the group consisting of the component (C), the component (D), and other grease additives in the obtained base grease, the urea-based thickener (B) may be dispersed in the grease composition so as to satisfy the above requirements (I) and (II).

The shear rate applied to the grease material is preferably 10 as the high-speed rotation condition of the rotor 3²s^-1Above, more preferably 10³s^-1Above, more preferably 10⁴s^-1Above, and usually 10⁷s^-1The following.

The ratio (Max/Min) of the maximum shear rate (Max) to the minimum shear rate (Min) of the shear of the rotor 3 during high-speed rotation is preferably 100 or less, more preferably 50 or less, and still more preferably 10 or less.

By making the shear rate of the mixed liquid as uniform as possible, the state of dispersion of the thickener or the precursor thereof is improved, and a uniform grease structure is formed.

Here, the maximum shear rate (Max) is the maximum shear rate applied to the mixed liquid, and the minimum shear rate (Min) is the minimum shear rate applied to the mixed liquid, and these are defined as follows.

Seeding maximum shear rate (Max) (linear velocity of tip of convex portion 13B of first concave-convex portion 13 of rotor)/(gap a1 between tip of convex portion 13B of first concave-convex portion 13 of rotor and convex portion of first concave-convex portion 9 of first inner peripheral surface portion 6 of container main body)

Seeding minimum shear rate (Min) ((linear velocity of concave portion 13A of first concave-convex portion 13 of rotor)/(gap a2 between concave portion 13A of first concave-convex portion 13 of rotor and concave portion of first concave-convex portion 9 of first inner peripheral surface portion 6 of container main body))

Note that the gap a1 and the gap a2 are shown in fig. 2.

Since the grease producing apparatus 1 is provided with the scraper 15, the base grease adhering to the inner peripheral surface of the container body 2 can be scraped off, and therefore, the generation of lumps during kneading can be prevented, and the base grease in which the urea-based thickener (B) is highly dispersed can be produced continuously and in a short time.

Further, since the scraper 15 can prevent the accumulated base grease from forming resistance to the rotation of the rotor 3 by scraping the adhered base grease, the rotational torque of the rotor 3 can be reduced, the power consumption of the drive source can be reduced, and the base grease can be efficiently continuously produced.

Since the inner peripheral surface of the container body 2 has a truncated cone shape whose inner diameter increases from the inlet portion 4 toward the outlet portion 8, the base grease or the grease material is discharged in the downstream direction by centrifugal force, and the rotational torque of the rotor 3 can be reduced, thereby enabling continuous production of the base grease.

Since the first uneven portion 13 of the rotor is provided on the outer peripheral surface of the rotor 3, the first uneven portion 13 of the rotor is inclined with respect to the rotation axis 12 of the rotor 3 and has a carrying capability from the introduction portion 4 to the discharge portion 8, and the second uneven portion 14 of the rotor is inclined with respect to the rotation axis 12 of the rotor 3 and has a carrying inhibiting capability from the introduction portion 4 to the discharge portion 8, a high shear force can be imparted to the solution, and the urea-based thickener (B) can be dispersed in the grease composition even after the additive is blended, so as to satisfy the above requirements (I) and (II).

Since the first uneven portion 9 is formed on the first inner peripheral surface 6 of the container main body and inclined in the opposite direction to the first uneven portion 13 of the rotor, the base grease or the grease raw material can be sufficiently stirred while being extruded in the downstream direction, and the urea-based thickener (B) can be dispersed in the grease composition so as to satisfy the above requirements (I) and (II) even after the additive is blended, in addition to the effect of the first uneven portion 13 of the rotor.

Further, by providing the second uneven portion 10 on the second inner peripheral surface 7 of the container main body and providing the second uneven portion 14 of the rotor on the outer peripheral surface of the rotor 3, it is possible to prevent the grease raw material more than necessary from flowing out from the first inner peripheral surface 6 of the container main body, and therefore, a high shear force is imparted to the solution to highly disperse the grease raw material, and even after the additive is blended, the urea-based thickener (B) can be dispersed in the grease composition so as to satisfy the above requirements (I) and (II).

[ physical Properties of grease composition ]

< mixed consistency >

The grease composition according to one embodiment of the present invention has a mixing consistency at 25 ℃ of preferably 220 to 385 parts, more preferably 250 to 355 parts, and even more preferably 265 to 340 parts, from the viewpoint of forming a grease composition having excellent wear resistance.

The mixing consistency is defined as a value according to JIS K22207: 2013, value determined at 25 ℃.

< wear scar diameter and coefficient of friction measured by vibration friction wear test (SRV test) >)

The grease composition according to one embodiment of the present invention preferably has a wear scar diameter, as measured by the SRV test, of 0.630mm or less, more preferably 0.625mm or less, still more preferably 0.620mm or less, yet more preferably 0.615mm or less, and yet more preferably 0.610mm or less.

The grease composition according to one embodiment of the present invention has a friction coefficient (load 35N) measured by the SRV test of preferably 0.150 or less, more preferably 0.130 or less, still more preferably 0.100 or less, yet more preferably 0.080 or less, and yet more preferably 0.060 or less.

The grease composition according to one embodiment of the present invention preferably has a friction coefficient (load 200N) of 0.170 or less, more preferably 0.140 or less, even more preferably 0.100 or less, even more preferably 0.080 or less, and even more preferably 0.060 or less, as measured by the SRV test.

The smaller the wear scar diameter and the lower the friction coefficient, the better the friction characteristics, and the grease composition can be said to have excellent wear resistance.

In addition, in the SRV test, the friction coefficient does not vary greatly between a low load condition and a high load condition, and it can be said that the grease composition is extremely suitable for lubricating the rolling sliding portion of a constant velocity joint to which a high load is easily applied.

The SRV test can be performed according to ASTM D5706 by the method described in the examples described later.

[ method of Using grease composition (lubricating method) ]

The grease composition of the present invention is useful for constant velocity joints.

Constant velocity joints are subject to complicated rolling sliding action while exerting high surface pressure during rotation. Therefore, a high load is easily applied to the rolling sliding portion of the constant velocity joint. In recent years, with a view to the demand for higher performance, quietness, riding comfort, and the like of automobiles, and the demand for higher performance, quietness, higher precision, and the like of conventional industrial machines, demands for lower vibration and longer life of constant velocity joints have become more stringent, and wear of constant velocity joints has become more likely to occur.

The grease composition of the present invention has excellent wear resistance, and therefore can efficiently lubricate a joint used under severe conditions, such as a constant velocity joint, to suppress wear and improve the durability of the constant velocity joint.

Accordingly, in one embodiment of the present invention, there is provided a method for using the grease composition of the present invention in a constant velocity joint.

In one embodiment of the present invention, a method for lubricating a constant velocity joint using the grease composition of the present invention is provided.

Constant velocity joint and constant velocity joint structure

The grease composition of the present invention is useful for constant velocity joints.

Therefore, in one embodiment of the present invention, a constant velocity joint filled with the grease composition of the present invention can be provided.

In one embodiment of the present invention, a constant velocity joint structure in which a constant velocity joint is sealed with a boot together with the grease composition of the present invention can be provided.

Examples

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

The following describes the measurement methods of various physical property values in the present example.

[ methods of measuring various physical Property values ]

(1) Kinematic viscosity at 40 ℃, kinematic viscosity at 100 ℃ and viscosity index

According to JIS K2283: 2000 for measurement and calculation.

(2) Mixed consistency

According to JIS K22207: 2013, at 25 ℃.

(3) Particle size distribution of urea-based thickener

The grease composition obtained in the production example described later was degassed in vacuum, then filled into a 1mL syringe, and 0.10 to 0.15mL of the grease composition was extruded from the syringe, and the grease composition was carried on the surface of the plate-like groove of the fixing jig for the paste groove (セル).

Next, another plate-like groove was further superimposed on the grease composition to obtain a measuring groove in which the grease composition was sandwiched by 2 grooves.

Further, as a light scattering particle size measuring apparatus, a laser diffraction type particle size measuring instrument (trade name: LA-920, manufactured by horiba, Ltd.) was used to obtain a particle size distribution curve of the grease composition in the measuring tank based on the volume of the particles containing the urea-based thickener.

In the particle size distribution curve, a peak having the highest frequency is identified, and the value of the particle size having the highest frequency of the peak defined in the above requirement (I) and the half-width of the peak defined in the above requirement (II) are calculated.

[ production example ]

The base greases of example 1 and comparative examples 1 to 3, and the methods for producing the grease compositions of examples 2 to 5 are shown below.

< production example 1 >

As the base oil (A), a mixed base oil obtained by mixing 597.8g of the base oil 1 and 290.0g of the base oil 2 was used.

Seed and base oil 1: paraffinic mineral oil, kinematic viscosity at 40 ℃: 90.51mm²S, kinematic viscosity at 100 ℃: 10.89mm²(s), viscosity index: 107

Seed and base oils 2: paraffinic mineral oil, kinematic viscosity at 40 ℃: 408.80mm²S, kinematic viscosity at 100 ℃: 30.86mm²(s), viscosity index: 105

375.5g of base oil (A) and 24.5g (0.098 mmol) of diphenylmethane-4, 4' -diisocyanate (MDI) were charged into a 1L reactor equipped with a metal container and dissolved by heating to prepare a solution alpha.

Separately, 368.3g of base oil (A), 11.3g (0.114 mmol) of cyclohexylamine (Cy), and 20.4g (0.076 mmol) of stearylamine (C18) were charged into a 1L metal container separately prepared to prepare a solution β.

Then, the solution β was added to the reaction vessel containing the solution α while heating, and stirred to homogenize the solution. Further, 200.0g of the base oil (a) was charged into a metal container containing the solution β, and the mixture was sufficiently stirred, and after the solution β remaining in the metal container was charged into a reaction vessel, the reaction solution in the reaction vessel was stirred.

Then, the reaction solution was heated to 90 ℃ or higher and held for 1 hour, and after the reaction was terminated, the urea-based thickener (B) represented by the above general formula (B1) was synthesized and treated with a three-roll mill to obtain a base grease X1 (example 1).

The urea-based thickener (B) in the base grease X1 corresponds to R in the general formula (B1)¹And R²Selected from the ringHexyl and stearyl radicals, R³A diurea compound that is a diphenylmethylene group.

The value of { (X + Y)/(X + Y + Z) } × 100 defined in the requirement (a) is 100, and the X/Y ratio defined in the requirement (b) is 60/40.

< production example 2 >

As the base oil (A), a mixed base oil obtained by mixing 549.0g of the above base oil 1 and 290.0g of the above base oil 2 was used.

309.0g of base oil (A) and 91g (0.364 mmol) of diphenylmethane-4, 4' -diisocyanate (MDI) were charged into a 1L reactor equipped with a metal container, and dissolved by heating to prepare a solution alpha.

In a separately prepared 1L metal container, 330.0g of base oil (A) and 70.0g (0.706 mmol) of cyclohexylamine (Cy) were charged to prepare a solution β.

Then, the solution β was added to the reaction vessel containing the solution α while heating, and stirred to homogenize the solution. Further, 200.0g of the base oil (a) was charged into a metal container charged with the solution β, and sufficiently stirred, and after the solution β remaining in the metal container was charged into a reaction vessel, the reaction liquid in the reaction vessel was stirred.

Then, a urea thickener (B) was synthesized in the same manner as in production example 1 and treated with a three-roll mill to obtain base grease X2 (comparative example 1).

The urea-based thickener (B) in the base grease X2 corresponds to R in the general formula (B1)¹And R²Is cyclohexyl, R³A diurea compound that is a diphenylmethylene group.

The value of { (X + Y)/(X + Y + Z) } × 100 defined in the requirement (a) is 100, and the X/Y ratio defined in the requirement (b) is 100/0.

< production example 3 >

As the base oil (A), a mixed base oil obtained by mixing 639.8g of the above base oil 1 and 290.0g of the above base oil 2 was used.

365.0g of base oil (A) and 35.0g (0.140 mmol) of diphenylmethane-4, 4' -diisocyanate (MDI) were charged into a 1L reactor equipped with a metal container, and dissolved by heating to prepare a solution alpha.

Separately, 363.9g of base oil (A), 21.5g (0.217 mmol) of cyclohexylamine (Cy), and 14.6g (0.054 mmol) of stearylamine (C18) were charged into a 1L metal vessel separately prepared to prepare a solution β.

Then, the solution β was added to the reaction vessel containing the solution α while heating, and stirred to homogenize the solution. Further, 200.0g of the base oil (a) was charged into a metal container charged with the solution β, and sufficiently stirred, and after the solution β remaining in the metal container was charged into a reaction vessel, the reaction liquid in the reaction vessel was stirred.

Then, a urea thickener (B) was synthesized in the same manner as in production example 1 and treated with a three-roll mill to obtain base grease X3 (comparative example 2).

The urea-based thickener (B) in the base grease X3 corresponds to R in the general formula (B1)¹And R²Selected from cyclohexyl and stearyl, R³A diurea compound that is a diphenylmethylene group.

The value of { (X + Y)/(X + Y + Z) } × 100 defined in the requirement (a) is 100, and the X/Y ratio defined in the requirement (b) is 80/20.

< production example 4 >

As the base oil (A), a mixed base oil obtained by mixing 562.1g of the above base oil 1 and 290.0g of the above base oil 2 was used.

352.1g of base oil (A) and 47.9g (0.191 mmol) of diphenylmethane-4, 4' -diisocyanate (MDI) were charged into a 1L reactor equipped with a metal container, and dissolved by heating to prepare a solution alpha.

Further, 300.0g of base oil (A) and 100.0g (0.371 mmol) of stearylamine (C18) were charged into a separately prepared 1L metal container to prepare a solution β.

Then, the solution β was added to the reaction vessel containing the solution α while heating, and stirred to homogenize the solution. Further, 200.0g of the base oil (a) was charged into a metal container to which the solution β was charged, and sufficiently stirred, and after the solution β remaining in the metal container was charged into a reaction vessel, the reaction solution in the reaction vessel was stirred.

Then, a urea thickener (B) was synthesized in the same manner as in production example 1 and treated with a three-roll mill to obtain base grease X4 (comparative example 4).

The urea-based thickener (B) in the base grease X4 corresponds to R in the general formula (B1)¹And R²Is stearyl, R³A diurea compound that is a diphenylmethylene group.

The value of { (X + Y)/(X + Y + Z) } × 100 defined in the requirement (a) is 100, and the X/Y ratio defined in the requirement (b) is 0/100.

< production example 5 >

Using the solution α and the solution β prepared in production example 1, base grease Y1 and grease composition Y1-1 (example 2) were produced by the following procedure.

First, using the grease manufacturing apparatus 1 shown in fig. 1, a solution α heated to 60 to 80 ℃ is introduced into the container body 2 from the solution introduction pipe 4A at a flow rate of 100 to 200L/h and a solution β heated to 60 to 80 ℃ is introduced into the container body 2 from the solution introduction pipe 4B at a flow rate of 100 to 200L/h, respectively, and the solution α and the solution β are continuously introduced into the container body 2 while the rotor 3 is rotated. The rotational speed of the rotor 3 of the grease producing apparatus 1 used is 7000 to 9000 rpm.

The maximum shear rate (Max) at this time was 10500s^-1The stirring was carried out with the ratio [ Max/Min ] of the maximum shear rate (Max) to the minimum shear rate (Min) set to 3.5.

While stirring the obtained base grease Y1 at 120 ℃, MoDTC (サクラルーブ 525, manufactured by アデカ) as an organic molybdenum compound (C), ZnDTP (HITEC 7169, manufactured by アフトンケミカル) as zinc dithiophosphate (D), and a phenol antioxidant, a vulcanized grease and benzotriazole as other grease additives were added to the base grease so as to have the contents described in example 2 of table 2, and after stirring for 0.5 hour, the mixture was naturally cooled to 25 ℃, and then treated with a triple roll mill to be defoamed, thereby obtaining a grease composition Y1-1.

< production example 6 >

While stirring the base grease Y1 obtained in production example 5 at 120 ℃, a phenolic antioxidant and benzotriazole as other grease additives were added so as to have the contents described in example 3 of table 2, and after stirring for 0.5 hour, the mixture was naturally cooled, cooled to 25 ℃, and then treated with a three-roll mill to be deaerated, thereby obtaining a grease composition Y1-2 (example 3).

< production example 7 >

While the base grease X1 obtained in production example 1 was stirred at 120 ℃, MoDTC as an organic molybdenum compound (C), ZnDTP as zinc dithiophosphate (D), and a phenol antioxidant, a sulfurized grease, and benzotriazole as other grease additives were added so as to be in the contents described in example 4 of table 2, and after stirring for 0.5 hour, the mixture was naturally cooled to 25 ℃, and then treated with a triple roll mill to be deaerated, whereby a grease composition X1-1 (example 4) was obtained.

< production example 8 >

While the base grease X1 obtained in production example 1 was stirred at 120 ℃, a phenolic antioxidant and benzotriazole as other grease additives were added so as to have the contents described in example 5 of table 2, and after stirring for 0.5 hour, the mixture was naturally cooled, cooled to 25 ℃, and then treated with a three-roll mill to be deaerated, thereby obtaining a grease composition X1-2 (example 5).

The base greases produced in production examples 1 to 4 were subjected to the following SRV test 1, and the wear scar diameters were measured. The results are shown in Table 1.

The grease compositions prepared in production examples 5 to 8 were subjected to the following SRV tests 2 and 3, and the friction coefficient at low load and the friction coefficient at high load were measured. The results are shown in Table 2.

In tables 1 and 2, "Cy" means cyclohexylamine, and "C18" means stearylamine.

[ SRV test 1: measurement of wear scar diameter

The ball wear scar diameter (mm) was measured according to ASTM D5706 using an SRV tester (manufactured by Optimol) under the following conditions.

Seed and seed: AISI52100

Planting seeds: AISI52100

Seed and seed frequency: 50Hz

Seed and amplitude: 3.0mm

Seed and seed load: 200N

Seed and seed temperatures: 40 deg.C

Seed dressing and test time: for 30 minutes.

[ SRV test 2: measurement of coefficient of friction (Low load) ]

The friction coefficient of the grease composition was measured according to ASTM D5706 using an SRV tester (manufactured by Optimol corporation) under the following conditions. The average value of the friction coefficient from 20 minutes after the start of the test to 10 minutes after the end of the test was defined as the friction coefficient (low load).

Seed and seed: AISI52100

Planting seeds: AISI52100

Seed and seed frequency: 30Hz

Seed and amplitude: 3.0mm

Seed and seed load: 35N

Seed and seed temperatures: 40 deg.C

Seed dressing and test time: for 30 minutes.

[ SRV test 3: measurement of coefficient of friction (high load) ]

The friction coefficient of the grease composition was measured according to ASTM D5706 using an SRV tester (manufactured by Optimol corporation) under the following conditions. The average value of the friction coefficient from 20 minutes after the start of the test to 10 minutes after the end of the test is defined as the friction coefficient (high load).

Seed and seed: AISI52100

Planting seeds: AISI52100

Seed and seed frequency: 30Hz

Seed and amplitude: 3.0mm

Seed and seed load: 200N

Seed and seed temperatures: 40 deg.C

Seed dressing and test time: for 30 minutes.

[ Table 1]

。

[ Table 2]

。

The following is evident from Table 1.

It is found that the urea-based thickener (B) satisfying the "requirement (B)" specified for the general formula (B1): the X/Y ratio is 10/90 to 75/25. "the base grease X1 of example 1 had a small wear scar diameter and excellent wear resistance, while the base greases X2, X3, and X4 of comparative examples 1 to 3, which included urea-based thickeners that did not satisfy requirement (b), had large wear scar diameters and poor wear resistance.

The following is also clear from table 2.

The grease compositions of examples 2 to 5 had a small friction coefficient in the SRV test at both low and high loads. Therefore, it is found that the friction characteristics are excellent in both the low load and the high load.

In particular, it is found that the friction coefficient in the SRV test is greatly reduced and the friction characteristics are extremely excellent by using MoDTC as the organic molybdenum-based compound (C) and ZnDTP as the zinc dithiophosphate (D) as additives as in the grease compositions Y1-1 and X1-1 of examples 2 and 4.

Further, it was found that the grease compositions obtained by the high dispersion method, as in the grease compositions Y1-1 and Y1-2 of examples 2 and 3, had a lower friction coefficient in the SRV test and more excellent friction characteristics than the grease compositions X1-1 and X1-2 of examples 4 and 5 obtained by the conventional method.

The peak having the maximum frequency in the particle size distribution curve of the grease compositions obtained by the high dispersion method as in the grease compositions Y1-1 and Y1-2 of examples 2 and 3 satisfies the following requirements (I) and (II).

Seed and seed essences (I): the particle diameter of the peak at the maximum frequency is 1.0 μm or less.

Seed and essence (II): the half width of the peak is 1.0 μm or less.

On the other hand, the grease compositions X1-1 and X1-2 of examples 4 and 5 obtained by conventional methods did not satisfy the above requirements (I) and (II).

Thus, it is found that by satisfying the above requirements (I) and (II), a grease composition having a further reduced friction coefficient and more excellent friction characteristics in the SRV test is obtained.