EP4650419A1

EP4650419A1 - Grease composition

Info

Publication number: EP4650419A1
Application number: EP24741546.6A
Authority: EP
Inventors: Go Watanabe
Original assignee: Idemitsu Kosan Co Ltd
Current assignee: Idemitsu Kosan Co Ltd
Priority date: 2023-01-12
Filing date: 2024-01-11
Publication date: 2025-11-19
Also published as: WO2024150774A1; JPWO2024150774A1

Abstract

Provided is a grease composition, which is excellent in extreme pressure property, load-bearing capacity, seizure resistance, and wear resistance under a wide variety of temperature environments, and is also excellent in suppression of its leakage due to a reduction in viscosity of its base oil thereunder. The grease composition includes: a base oil (A); a urea-based thickener (B); a phosphoric acid ester amine salt (C); a sulfur-based extreme pressure agent (D); a zinc dithiophosphate (E); melamine cyanurate (F); and an organic molybdenum compound (G). The base oil (A) is a mixed base oil containing a high-viscosity poly-α-olefin (PAO) (Al) having a 40°C kinematic viscosity of from 288 mm²/s to 506 mm²/s, a low-viscosity poly-α-olefin (PAO) (A2) having a 40°C kinematic viscosity of from 61.2 mm²/s to 74.8 mm²/s, and an ester-based synthetic oil. Particles each containing the urea-based thickener (B) in the grease composition satisfy a requirement (I).

Description

Technical Field

The present invention relates to a grease composition.

Background Art

A grease composition is more easily sealed than a lubricating oil is, and hence the composition enables the downsizing and weight reduction of a machine to which the composition is applied. Accordingly, the composition has heretofore been widely used for the lubrication of the various sliding portions of, for example, an automobile, electrical equipment, industrial machinery, and engineering machinery.
In recent years, from the viewpoints of, for example, an improvement in accuracy, and a weight reduction and compacting, the field of the use of a wave gear device as a speed reducer has been expanding. In addition, various grease compositions to be applied to the sliding surface of the wave gear device have started to be proposed.
In each of, for example, PTL 1 and PTL 2, there is a disclosure of a grease composition to be applied to the sliding surface of a wave gear device.

Citation List

Patent Literature

PTL 1: JP 08-157846 A
PTL 2: JP 03-179094 A

Summary of Invention

Technical Problem

A wave gear device is used under extremely severe conditions in a bearing, in particular, a speed reducer. Accordingly, a grease composition to be applied to the sliding surface of the wave gear device is required to have an extreme pressure property, a load-bearing capacity, seizure resistance, and wear resistance. In addition, in consideration of, for example, an increase in temperature in the wave gear device, the composition is also required to have an extreme pressure property, a load-bearing capacity, seizure resistance, and wear resistance under a wide variety of temperature environments. However, sufficient investigations have not been made on the extreme pressure property, load-bearing capacity, seizure resistance, and wear resistance of the grease composition disclosed in each of PTL 1 and PTL 2 under a wide variety of temperature environments.
In addition, from the viewpoint of the transmission efficiency of the wave gear device, a base oil in the grease composition is required to have a low viscosity. However, when the grease composition is excessively soft, there is a problem in that its leakage from the wave gear device occurs. In addition, in each of PTL 1 and PTL 2, no investigation has been made on the suppression of the leakage of the grease composition due to a reduction in viscosity of its base oil.
In view of the foregoing, an object of the present invention is to provide a grease composition, which is excellent in extreme pressure property, load-bearing capacity, seizure resistance, and wear resistance under a wide variety of temperature environments, and is also excellent in suppression of its leakage due to a reduction in viscosity of its base oil thereunder.

Solution to Problem

The inventor of the present invention has found that a grease composition including a base oil and a urea-based thickener, which includes a phosphoric acid ester amine salt, a sulfur-based extreme pressure agent, a zinc dithiophosphate, melamine cyanurate, and a molybdenum dithiocarbamate, in which the base oil is a specific base oil, and in which particles each containing the urea-based thickener satisfy a specific requirement, can solve the above-mentioned problems. Thus, the inventor has completed the present invention.
That is, the present invention provides the following items [1] and [2].

[1] A grease composition, comprising: a base oil (A); a urea-based thickener (B); a phosphoric acid ester amine salt (C); a sulfur-based extreme pressure agent (D); a zinc dithiophosphate (E); melamine cyanurate (F); and an organic molybdenum compound (G),
- wherein the base oil (A) is a mixed base oil containing a high-viscosity poly-α-olefin (PAO) (A1) having a 40°C kinematic viscosity of from 288 mm²/s to 506 mm²/s, a low-viscosity poly-α-olefin (PAO) (A2) having a 40°C kinematic viscosity of from 61.2 mm²/s to 74.8 mm²/s, and an ester-based synthetic oil, and
- wherein particles each containing the urea-based thickener (B) in the grease composition satisfy the following requirement (I):
  - ·Requirement (I): the particles have an arithmetic average particle diameter on an area basis of 2.0 µm or less, which is measured by a laser diffraction scattering method.
[2] A method of producing a grease composition, comprising the steps of:
1. (1) synthesizing a urea-based thickener (B) in a base oil (A); and
2. (2) blending a phosphoric acid ester amine salt (C), a sulfur-based extreme pressure agent (D), a zinc dithiophosphate (E), melamine cyanurate (F), and an organic molybdenum compound (G) into the synthesized product in the step (1),
- wherein the base oil (A) is a mixed base oil containing a high-viscosity poly-α-olefin (PAO) (A1) having a 40°C kinematic viscosity of from 288 mm²/s to 506 mm²/s, a low-viscosity poly-α-olefin (PAO) (A2) having a 40°C kinematic viscosity of from 61.2 mm²/s to 74.8 mm²/s, and an ester-based synthetic oil, and
- wherein particles each containing the urea-based thickener (B) in the grease composition satisfy the following requirement (I):
  - ·Requirement (I): the particles have an arithmetic average particle diameter on an area basis of 2.0 µm or less, which is measured by a laser diffraction scattering method.

Advantageous Effects of Invention

The present invention can provide the grease composition, which is excellent in extreme pressure property, load-bearing capacity, seizure resistance, and wear resistance under a wide variety of temperature environments, and is also excellent in suppression of its leakage due to a reduction in viscosity of its base oil thereunder.

Brief Description of Drawings

[Fig. 1] Fig. 1 is a schematic sectional view of a grease-producing apparatus to be used in one aspect of the present invention.
[Fig. 2] Fig. 2 is a schematic sectional view of a first irregular portion on the container main body side of the grease-producing apparatus of Fig. 1 in a direction perpendicular to its rotation axis.

Description of Embodiments

The upper limit values and lower limit values of numerical ranges described herein may be arbitrarily combined. For example, when the range of "from A to B" and the range of "from C to D" are described as numerical ranges, the numerical range of "from A to D" and the numerical range of "from C to B" are also included in the scope of the present invention.
In addition, the numerical range of "from a lower limit value to an upper limit value" described herein means that a physical property value is the lower limit value or more and the upper limit value or less unless otherwise stated.
In addition, in this description, the numerical values of Examples are numerical values that may each be used as an upper limit value or a lower limit value.
For example, the term "(meth)acrylate" as used herein is used as a term representing both of an "acrylate" and a "methacrylate", and the same holds true for any other similar term or similar notation.

[Grease Composition]

A grease composition of the present invention is a grease composition including: a base oil (A); a urea-based thickener (B); a phosphoric acid ester amine salt (C); a sulfur-based extreme pressure agent (D); a zinc dithiophosphate (E); melamine cyanurate (F); and an organic molybdenum compound (G),

wherein the base oil (A) is a mixed base oil containing a high-viscosity poly-α-olefin (PAO) (A1) having a 40°C kinematic viscosity of from 288 mm²/s to 506 mm²/s, a low-viscosity poly-α-olefin (PAO) (A2) having a 40°C kinematic viscosity of from 61.2 mm²/s to 74.8 mm²/s, and an ester-based synthetic oil, and
wherein particles each containing the urea-based thickener (B) in the grease composition satisfy the following requirement (I):
- ·Requirement (I): the particles have an arithmetic average particle diameter on an area basis of 2.0 µm or less, which is measured by a laser diffraction scattering method.

To solve the above-mentioned problems, the inventor of the present invention has made extensive investigations, and as a result, has found that when a urea-based grease composition includes the phosphoric acid ester amine salt (C), the sulfur-based extreme pressure agent (D), the zinc dithiophosphate (E), the melamine cyanurate (F), and the organic molybdenum compound (G), the base oil (A) is a mixed base oil containing the high-viscosity poly-α-olefin (PAO) (A1) having a 40°C kinematic viscosity of from 288 mm²/s to 506 mm²/s, the low-viscosity poly-α-olefin (PAO) (A2) having a 40°C kinematic viscosity of from 61.2 mm²/s to 74.8 mm²/s, and the ester-based synthetic oil, and the particles each containing the urea-based thickener satisfy a specific requirement, there is obtained a grease composition, which is excellent in extreme pressure property, load-bearing capacity, seizure resistance, and wear resistance, and can be suppressed from leaking owing to a reduction in viscosity of its base oil under a wide variety of temperature environments.
Specifically, the inventor of the present invention has found the following.
In general, from the viewpoints of improvements in extreme pressure property and load-bearing capacity, a formulation formed mainly of a sulfur-based extreme pressure agent and an organic molybdenum compound is typically used in a frequent manner. Those additives can exhibit a high extreme pressure property and a high load-bearing capacity because when the temperature of a lubrication site is as high as 80°C or more, the additives each react with a sliding surface to form a coat. Meanwhile, when the temperature of the lubrication site is as low as less than 80°C, there is a problem in that the effects of those additives are not sufficiently exhibited.
Herein, the inventor of the present invention has found that when the phosphoric acid ester amine salt (C), the zinc dithiophosphate (E), and the melamine cyanurate (F) are used in combination as additives for a grease composition, the composition can exhibit a high extreme pressure property and a high load-bearing capacity even under a temperature environment as low as less than 80°C. In addition, the inventor of the present invention has found that even when those additives are used in combination with the sulfur-based extreme pressure agent (D) and the organic molybdenum compound (G), a sufficient extreme pressure property and a sufficient load-bearing capacity are exhibited under both temperature environments at 80°C or more and at less than 80°C, that is, under a wide variety of temperature environments without dependence on the temperature of the lubrication site while the performance of each of the additives is not inhibited.
In the present invention, the term "wide variety of temperature environments" means a temperature environment at from 25°C to 100°C.
When a grease composition includes a high-viscosity base oil that has a high oil film-holding property, is excellent in lubricity, and hardly leaks, the transmission efficiency of a wave gear device or the like reduces because the permeability or low-temperature characteristic of the base oil becomes insufficient. Meanwhile, when the grease composition includes a low-viscosity base oil excellent in permeability and low-temperature characteristic, concern is raised in that the grease composition exudes and leaks from the wave gear device or the like.
In view of the foregoing, the inventor of the present invention has found that when the base oil (A) is a mixed base oil containing the high-viscosity poly-α-olefin (PAO) (A1) having a 40°C kinematic viscosity of from 288 mm²/s to 506 mm²/s, the low-viscosity poly-α-olefin (PAO) (A2) having a 40°C kinematic viscosity of from 61.2 mm²/s to 74.8 mm²/s, and the ester-based synthetic oil, and the particles each containing the urea-based thickener (B) in the grease composition satisfy the specific requirement (I), the leakage of the grease composition due to a reduction in viscosity of the base oil can be suppressed without impairment of the transmission efficiency of the wave gear device or the like.
The inventor of the present invention has further made various investigations on the basis of such finding, and has completed the present invention.
In the following description, the "base oil (A)," the "urea-based thickener (B)," the "phosphoric acid ester amine salt (C)," the "sulfur-based extreme pressure agent (D)," the "zinc dithiophosphate (E)," the "melamine cyanurate (F)," and the "organic molybdenum compound (G)" are also referred to as "component (A)," "component (B)," "component (C)," "component (D)," "component (E)," "component (F)," and "component (G)," respectively.
In the grease composition of this embodiment, the total content of the component (A), the component (B), the component (C), the component (D), the component (E), the component (F), and the component (G) is preferably 60 mass% or more, more preferably 70 mass% or more, still more preferably 80 mass% or more, still further more preferably 90 mass% or more with respect to the total amount (100 mass%) of the grease composition. In addition, the total content is typically 100 mass% or less, preferably less than 100 mass%, more preferably 99 mass% or less, still more preferably 98 mass% or less.
The grease composition of one aspect of the present invention may include any other component except the component (A), the component (B), the component (C), the component (D), the component (E), the component (F), and the component (G) to the extent that the effect of the present invention is not impaired.

In the grease composition of one aspect of the present invention, particles each containing the urea-based thickener (B) in the grease composition satisfy the following requirement (I):

·Requirement (I): the particles have an arithmetic average particle diameter on an area basis of 2.0 µm or less, which is measured by a laser diffraction scattering method.

When the above-mentioned requirement (I) is satisfied, there is obtained a grease composition, which can achieve all of an extreme pressure property, a load-bearing capacity, seizure resistance, wear resistance, and the suppression of its leakage due to a reduction in viscosity of its base oil.
It can be said that the above-mentioned requirement (I) is a parameter representing the state of the aggregation of the urea-based thickener (B) in the grease composition.
Herein, the "particles each containing the urea-based thickener (B)" to be subjected to the measurement by the laser diffraction scattering method refer to particles obtained by the aggregation of the urea-based thickener (B) in the grease composition.
Although the grease composition includes an additive except the urea-based thickener (B), the arithmetic average particle diameter specified in the above-mentioned requirement (I) is obtained by subjecting a grease composition, which has been prepared under the same conditions without blending the additive, to the measurement by the laser diffraction scattering method. However, when the additive is liquid at room temperature (25°C), or when the additive is soluble in the base oil (A), a grease composition blended with the additive may be used as a measurement object.
Although the urea-based thickener (B) is typically obtained by causing an isocyanate compound and a monoamine to react with each other, the rate of the reaction is so fast that the urea-based thickener (B) is liable to aggregate to excessively produce a large particle (micelle particle, so-called "lump").
The inventor of the present invention has made extensive investigations, and as a result, has found that when the arithmetic average particle diameter specified in the above-mentioned requirement (I) is more than 2.0 µm, the achievement of all of an extreme pressure property, a load-bearing capacity, seizure resistance, wear resistance, and the suppression of the leakage of the grease composition due to a reduction in viscosity of its base oil cannot be secured under a wide variety of temperature environments. Meanwhile, the inventor has found that when the arithmetic average particle diameter specified in the above-mentioned requirement (I) is miniaturized to 2.0 µm or less, there is obtained a grease composition, which can achieve all of an extreme pressure property, a load-bearing capacity, seizure resistance, wear resistance, and the suppression of its leakage due to a reduction in viscosity of its base oil.
This effect is assumed to be exhibited as follows: when the arithmetic average particle diameter specified in the above-mentioned requirement (I) is miniaturized to 2.0 µm or less, the particles each containing the urea-based thickener (B) easily enter the lubrication site (friction surface) of a wave gear device or the like, and are hardly removed from the lubrication site; and hence the holding force of the grease composition in the lubrication site is improved to exhibit the effect. In addition, when the arithmetic average particle diameter specified in the above-mentioned requirement (I) is miniaturized to 2.0 µm or less, the holding force of the base oil (A) exhibited by the particles is improved. Accordingly, the following action is improved: the base oil (A) is caused to satisfactorily pervade the lubrication site (friction surface) of the wave gear device or the like; and along with the foregoing, the phosphoric acid ester amine salt (C), the sulfur-based extreme pressure agent (D), the zinc dithiophosphate (E), the melamine cyanurate (F), and the organic molybdenum compound (G) are also caused to satisfactorily pervade the lubrication site. Thus, it is assumed that the extreme pressure property, load-bearing capacity, seizure resistance, and wear resistance of the grease composition, and the suppression of the leakage of the grease composition due to a reduction in viscosity of the base oil are further improved.
From the above-mentioned viewpoint, in the grease composition of one aspect of the present invention, the arithmetic average particle diameter specified in the above-mentioned requirement (I) is preferably 1.5 µm or less, more preferably 1.0 µm or less, still more preferably 0.9 µm or less, still further more preferably 0.8 µm or less, yet still further more preferably 0.7 µm or less, even more preferably 0.6 µm or less, still even more preferably 0.5 µm or less, yet still even more preferably 0.4 µm or less. In addition, the arithmetic average particle diameter is typically 0.01 µm or more.

Herein, from the viewpoint of further facilitating an improvement in effect of the present invention, in the grease composition of this embodiment, the particles each containing the urea-based thickener (B) in the grease composition preferably further satisfy the following requirement (II):

·Requirement (II): the particles have a specific surface area of 0.5×10⁵ cm²/cm³ or more, which is measured by the laser diffraction scattering method.

The specific surface area specified in the above-mentioned requirement (II) is a secondary indicator representing the state of the miniaturization of the particles each containing the urea-based thickener (B) in the grease composition and the presence of a large particle (lump). That is, a state in which the above-mentioned requirement (I) is satisfied and the above-mentioned requirement (II) is further satisfied means that the state of the miniaturization of the particles each containing the urea-based thickener (B) in the grease composition is more satisfactory, and hence the presence of a large particle (lump) is further suppressed. Accordingly, there can be obtained a grease composition, which is further excellent in extreme pressure property, load-bearing capacity, seizure resistance, wear resistance, and suppression of its leakage due to a reduction in viscosity of its base oil, and in which effects exhibited by the phosphoric acid ester amine salt (C), the sulfur-based extreme pressure agent (D), the zinc dithiophosphate (E), the melamine cyanurate (F), and the organic molybdenum compound (G) are easily exhibited.
From the above-mentioned viewpoint, the specific surface area specified in the above-mentioned requirement (II) is preferably 0.7×10⁵ cm²/cm³ or more, more preferably 0.8×10⁵ cm²/cm³ or more, still more preferably 1.2×10⁵ cm²/cm³ or more, still further more preferably 1.5×10⁵ cm²/cm³ or more, yet still further more preferably 1.8×10⁵ cm²/cm³ or more, even more preferably 2.0×10⁵ cm²/cm³ or more. The specific surface area is typically 1.0×10⁶ cm²/cm³ or less.
In this description, the values specified in the above-mentioned requirement (I) and the above-mentioned requirement (II) are values measured by methods described in Examples to be described later.
In addition, the values specified in the above-mentioned requirement (I) and the above-mentioned requirement (II) can be adjusted mainly by conditions for the production of the urea-based thickener (B).
Details about the respective components in the grease composition of the present invention are described below while attention is paid to specific means for satisfying the above-mentioned requirement (I) and the above-mentioned requirement (II).

The grease composition of this embodiment includes the base oil (A).
In addition, the base oil (A) is a mixed base oil containing the high-viscosity poly-α-olefin (hereinafter also referred to as "high-viscosity PAO") (A1) having a 40°C kinematic viscosity of from 288 mm²/s to 506 mm²/s, the low-viscosity poly-α-olefin (hereinafter also referred to as "low-viscosity PAO") (A2) having a 40°C kinematic viscosity of from 61.2 mm²/s to 74.8 mm²/s, and the ester-based synthetic oil.
When the base oil (A) contains the high-viscosity PAO (A1), an oil film becomes thicker, and hence the lubricity of the base oil is improved.
When the base oil (A) contains the low-viscosity PAO (A2), the permeability of the base oil is improved, and hence the property by which the base oil is supplied to a lubrication site is improved. In addition, the low-temperature characteristic of the base oil can be made satisfactory.
When the base oil (A) contains the ester-based synthetic oil, the solubility of an additive is improved, and hence the effect of the additive is easily exhibited.
The high-viscosity PAO (A1) is a high-viscosity poly-α-olefin having a 40°C kinematic viscosity of from 288 mm²/s to 506 mm²/s.
Examples of the high-viscosity PAO (A1) include polybutene, polyisobutylene, a 1-decene oligomer, and an ethylene-propylene copolymer, and hydrogenated products thereof.
The high-viscosity PAOs (A1) may be used alone or in combination thereof.
In the grease composition of this embodiment, the 40°C kinematic viscosity of the high-viscosity PAO (A1) is 288 mm²/s or more and 506 mm²/s or less.
When the 40°C kinematic viscosity of the high-viscosity PAO (A1) is 288 mm²/s or more, an oil film thickness can be sufficiently secured. In addition, when the 40°C kinematic viscosity of the high-viscosity PAO (A1) is 506 mm²/s or less, the transmission efficiency of a wave gear device or the like becomes satisfactory.
In the grease composition of this embodiment, the 40°C kinematic viscosity of the high-viscosity PAO (A1) is preferably 300 mm²/s or more and 500 mm²/s or less, more preferably 320 mm²/s or more and 480 mm²/s or less, still more preferably 350 mm²/s or more and 450 mm²/s or less. When the 40°C kinematic viscosity of the high-viscosity PAO (A1) is 300 mm²/s or more and 500 mm²/s or less, the effect of the present invention is more easily improved.
In the grease composition of this embodiment, the 100°C kinematic viscosity of the high-viscosity PAO (A1) is preferably 10 mm²/s or more and 70 mm²/s or less, more preferably 20 mm²/s or more and 60 mm²/s or less. When the 40°C kinematic viscosity of the high-viscosity PAO (A1) is 10 mm²/s or more and 70 mm²/s or less, the effect of the present invention is more easily improved.
In the grease composition of this embodiment, the viscosity index of the high-viscosity PAO (A1) is preferably 100 or more, more preferably 110 or more, still more preferably 120 or more. When the viscosity index of the high-viscosity PAO (A1) is 100 or more, the effect of the present invention is more easily improved.
The low-viscosity PAO (A2) is a low-viscosity poly-α-olefin having a 40°C kinematic viscosity of from 61.2 mm²/s to 74.8 mm²/s.
Examples of the low-viscosity PAO (A2) include polybutene, polyisobutylene, a 1-decene oligomer, and an ethylene-propylene copolymer, and hydrogenated products thereof.
The low-viscosity PAOs (A2) may be used alone or in combination thereof.
In addition, the low-viscosity PAO (A2) may be identical to or different from the high-viscosity PAO (A1) in repeating unit structure.
In the grease composition of this embodiment, the 40°C kinematic viscosity of the low-viscosity PAO (A2) is 61.2 mm²/s or more and 74.8 mm²/s or less.
When the 40°C kinematic viscosity of the low-viscosity PAO (A2) is 61.2 mm²/s or more, the leakage resistance of the grease composition becomes satisfactory. In addition, when the 40°C kinematic viscosity of the low-viscosity PAO (A2) is 74.8 mm²/s or less, the transmission efficiency of a wave gear device or the like becomes satisfactory.
In the grease composition of this embodiment, the 40°C kinematic viscosity of the low-viscosity PAO (A2) is preferably 61.2 mm²/s or more and 74.0 mm²/s or less, more preferably 62.0 mm²/s or more and 72.0 mm²/s or less, still more preferably 62.5 mm²/s or more and 70.0 mm²/s or less. When the 40°C kinematic viscosity of the low-viscosity PAO (A2) is 61.2 mm²/s or more and 74.0 mm²/s or less, the effect of the present invention is more easily improved.
In the grease composition of this embodiment, the 100°C kinematic viscosity of the low-viscosity PAO (A2) is preferably 7.0 mm²/s or more and 13.0 mm²/s or less, more preferably 8.0 mm²/s or more and 12.0 mm²/s or less, still more preferably 9.0 mm²/s or more and 11.0 mm²/s or less. When the 40°C kinematic viscosity of the low-viscosity PAO (A2) is 7.0 mm²/s or more and 13.0 mm²/s or less, the effect of the present invention is more easily improved.
In the grease composition of this embodiment, the viscosity index of the low-viscosity PAO (A2) is preferably 100 or more, more preferably 120 or more, still more preferably 130 or more. When the viscosity index of the low-viscosity PAO (A2) is 100 or more, the effect of the present invention is more easily improved.
Examples of the ester-based synthetic oil include a diester-based oil, an aromatic ester-based oil, a polyol ester-based oil, and a complex ester-based oil.
Those ester-based synthetic oils may be used alone or in combination thereof.
Examples of the diester-based oil include dibutyl sebacate, di(2-ethylhexyl) sebacate, diisodecyl sebacate, ditri(n-decyl) sebacate, diisotridecyl sebacate, dibutyl adipate, di(2-ethylhexyl) adipate, diisodecyl adipate, ditri(n-decyl) adipate, diisotridecyl adipate, ditridecyl glutarate, and methyl acetyl ricinoleate.
Examples of the aromatic ester-based oil include tris(2-ethylhexyl) trimellitate, tri(n-decyl) trimellitate, and tetra(n-octyl) pyromellitate.
Examples of the polyol ester-based oil include trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol-2-ethyl hexanoate, and pentaerythritol pelargonate.
An example of the complex ester-based oil is an oligoester of a polyhydric alcohol, and a mixed fatty acid of a dibasic acid and a monobasic acid.
Those ester-based synthetic oils may be used alone or in combination thereof.
Among them, branched ester-based synthetic oils are preferred, and di(2-ethylhexyl) sebacate, diisodecyl sebacate, diisotridecyl sebacate, di(2-ethylhexyl) adipate, diisodecyl adipate, diisotridecyl adipate, and tris(2-ethylhexyl) trimellitate are more preferred.
In the grease composition of this embodiment, the 40°C kinematic viscosity of the ester-based synthetic oil is preferably 4.0 mm²/s or more and 40 mm²/s or less, more preferably 7.0 mm²/s or more and 30 mm²/s or less, still more preferably 9.0 mm²/s or more and 25 mm²/s or less. When the 40°C kinematic viscosity of the ester-based synthetic oil is 4.0 mm²/s or more and 40 mm²/s or less, the effect of the present invention is more easily improved.
In the grease composition of this embodiment, the 100°C kinematic viscosity of the ester-based synthetic oil is preferably 1.5 mm²/s or more and 6.0 mm²/s or less, more preferably 2.0 mm²/s or more and 5.0 mm²/s or less, still more preferably 2.5 mm²/s or more and 4.0 mm²/s or less. When the 40°C kinematic viscosity of the ester-based synthetic oil is 1.5 mm²/s or more and 6.0 mm²/s or less, the effect of the present invention is more easily improved.
In the grease composition of this embodiment, the viscosity index of the ester-based synthetic oil is preferably 100 or more, more preferably 120 or more, still more preferably 140 or more. When the viscosity index of the ester-based synthetic oil is 100 or more, the effect of the present invention is more easily improved.
The ester-based synthetic oil preferably contains a diester-based oil (A3) and an aromatic ester-based oil (A4). When the ester-based synthetic oil contains the diester-based oil (A3) and the aromatic ester-based oil (A4), an improvement in lubricity of the synthetic oil can be facilitated.
When the ester-based synthetic oil contains the diester-based oil (A3) and the aromatic ester-based oil (A4), from the viewpoint of an improvement in torque transmission efficiency by a reduction in viscosity of the mixed base oil (also simply referred to as "viewpoint of the reduction in viscosity" herein), the content of the diester-based oil (A3) in the ester-based synthetic oil is preferably 60 mass% or more, more preferably 70 mass% or more, still more preferably 80 mass% or more with respect to the total amount of the ester-based synthetic oil, and is preferably 95 mass% or less, more preferably 92 mass% or less, still more preferably 90 mass% or less.
When the ester-based synthetic oil contains the diester-based oil (A3) and the aromatic ester-based oil (A4), from the viewpoint of the reduction in viscosity, the content of the aromatic ester-based oil (A4) in the ester-based synthetic oil is preferably 5 mass% or more, more preferably 8 mass% or more, still more preferably 10 mass% or more with respect to the total amount of the ester-based synthetic oil, and is preferably 30 mass% or less, more preferably 25 mass% or less, still more preferably 20 mass% or less.
When the ester-based synthetic oil contains the diester-based oil (A3) and the aromatic ester-based oil (A4), from the viewpoint of the reduction in viscosity, the content of the diester-based oil (A3) is preferably 15 mass% or more, more preferably 18 mass% or more, still more preferably 20 mass% or more with respect to the total amount of the base oil (A), and is preferably 30 mass% or less, more preferably 28 mass% or less, still more preferably 26 mass% or less.
When the ester-based synthetic oil contains the diester-based oil (A3) and the aromatic ester-based oil (A4), from the viewpoint of the reduction in viscosity, the content of the aromatic ester-based oil (A4) is preferably 2.0 mass% or more, more preferably 3.0 mass% or more, still more preferably 4.0 mass% or more with respect to the total amount of the base oil (A), and is preferably 7.0 mass% or less, more preferably 6.0 mass% or less, still more preferably 5.0 mass% or less.
When the ester-based synthetic oil contains the diester-based oil (A3) and the aromatic ester-based oil (A4), from the viewpoint of the reduction in viscosity, the content of the diester-based oil (A3) is preferably 5 mass% or more, more preferably 10 mass% or more, still more preferably 13 mass% or more with respect to the total amount of the grease composition, and is preferably 30 mass% or less, more preferably 25 mass% or less, still more preferably 22 mass% or less.
When the ester-based synthetic oil contains the diester-based oil (A3) and the aromatic ester-based oil (A4), from the viewpoint of the reduction in viscosity, the content of the aromatic ester-based oil (A4) is preferably 1.0 mass% or more, more preferably 2.0 mass% or more, still more preferably 2.5 mass% or more with respect to the total amount of the grease composition, and is preferably 5.0 mass% or less, more preferably 4.5 mass% or less, still more preferably 4.0 mass% or less.
When the ester-based synthetic oil contains the diester-based oil (A3) and the aromatic ester-based oil (A4), from the viewpoint of the reduction in viscosity, the content ratio [(A3)/(A4)] of the diester-based oil (A3) to the aromatic ester-based oil (A4) is preferably from 1 to 12, more preferably from 2 to 10, still more preferably from 3 to 8 in terms of mass ratio.
In the grease composition of this embodiment, the base oil (A) may contain any other base oil except the high-viscosity PAO (A1), the low-viscosity PAO (A2), and the ester-based synthetic oil.
The other base oil is, for example, one or more kinds selected from a mineral oil, and a synthetic oil except the PAOs and the ester-based synthetic oil.
Examples of the mineral oil include: a normal-pressure residual oil obtained by distilling a crude oil, such as a paraffin base crude oil, an intermediate base crude oil, or a naphthene base crude oil, under normal pressure; a distillate oil obtained by distilling the normal-pressure residual oil under reduced pressure; and a mineral oil obtained by subjecting the distillate oil to one or more of refining treatments, such as solvent deasphalting, solvent extraction, hydrofinishing, hydrocracking, advanced hydrocracking, solvent dewaxing, contact dewaxing, and hydroisomerization dewaxing.
Examples of the synthetic oil except the high-viscosity PAO (A1), the low-viscosity PAO (A2), and the ester-based synthetic oil include: a normal paraffin; an isoparaffin; an aromatic oil; an ether-based oil; and a gas-to-liquid (GTL) base oil obtained by isomerizing a wax (GTL wax) produced by a Fischer-Tropsch process or the like.
Those synthetic oils may be used alone or in combination thereof.
Examples of the aromatic oil include: alkylbenzenes, such as a monoalkylbenzene and a dialkylbenzene; and alkylnaphthalenes, such as a monoalkylnaphthalene, a dialkylnaphthalene, and a polyalkylnaphthalene.
Examples of the ether-based oil include: polyglycols, such as polyethylene glycol, polypropylene glycol, a polyethylene glycol monoether, and a polypropylene glycol monoether; and phenyl ether-based oils, such as a monoalkyl triphenyl ether, an alkyl diphenyl ether, a dialkyl diphenyl ether, pentaphenyl ether, tetraphenyl ether, a monoalkyl tetraphenyl ether, and a dialkyl tetraphenyl ether.
The 40°C kinematic viscosity of the base oil (A) to be used in one aspect of the present invention is preferably 10 mm²/s or more, more preferably 20 mm²/s or more, still more preferably 30 mm²/s or more, still further more preferably 40 mm²/s or more. When the 40°C kinematic viscosity of the base oil (A) is 10 mm²/s or more, the effect of the present invention is easily exhibited.
In addition, the 40°C kinematic viscosity of the base oil (A) of this embodiment is preferably 120 mm²/s or less, more preferably 100 mm²/s or less, still more preferably 90 mm²/s or less, still further more preferably 80 mm²/s or less. When the 40°C kinematic viscosity of the base oil (A) is 120 mm²/s or less, the effect of the present invention is more easily exhibited.
The upper limit values and lower limit values of those numerical ranges may be arbitrarily combined. Specifically, the viscosity is preferably from 10 mm²/s to 120 mm²/s, more preferably from 20 mm²/s to 100 mm²/s, still more preferably from 30 mm²/s to 90 mm²/s, still further more preferably from 40 mm²/s to 80 mm²/s.
The 100°C kinematic viscosity of the base oil (A) to be used in one aspect of the present invention is preferably 2.0 mm²/s or more, more preferably 3.0 mm²/s or more, still more preferably 4.0 mm²/s or more. When the 100°C kinematic viscosity of the base oil (A) is 2.0 mm²/s or more, the effect of the present invention is more easily exhibited.
In addition, the 100°C kinematic viscosity of the base oil (A) of this embodiment is preferably 20 mm²/s or less, more preferably 18 mm²/s or less, still more preferably 16 mm²/s or less. When the 40°C kinematic viscosity of the base oil (A) is 20 mm²/s or less, the effect of the present invention is more easily exhibited.
The upper limit values and lower limit values of those numerical ranges may be arbitrarily combined. Specifically, the viscosity is preferably from 2.0 mm²/s to 20 mm²/s, more preferably from 3.0 mm²/s to 18 mm²/s, still more preferably from 4.0 mm²/s to 16 mm²/s.
A mixed base oil, which is obtained by combining a high-viscosity base oil and a low-viscosity base oil so that its kinematic viscosity may be adjusted within the above-mentioned ranges, may be used as the base oil (A) to be used in one aspect of the present invention.
The viscosity index of the base oil (A) to be used in one aspect of the present invention is preferably 90 or more, more preferably 110 or more, still more preferably 130 or more.
The terms "kinematic viscosity" and "viscosity index" as used herein each mean a value measured or calculated in conformity with JIS K2283:2000.
In the grease composition of one aspect of the present invention, the content of the component (A) is preferably 50 mass% or more, more preferably 55 mass% or more, still more preferably 60 mass% or more, still further more preferably 65 mass% or more with respect to the total amount (100 mass%) of the grease composition, and is preferably 98.5 mass% or less, more preferably 97 mass% or less, still more preferably 95 mass% or less, still further more preferably 93 mass% or less.

<Urea-based Thickener (B)>

The grease composition of one aspect of the present invention includes the urea-based thickener (B).
Although the urea-based thickener (B) in the grease composition of one aspect of the present invention only needs to be a compound having a urea bond, a diurea compound having two urea bonds is preferred, and from the viewpoint of heat resistance, a diurea compound represented by the following general formula (b1) is more preferred.

R¹-NHCONH-R³-NHCONH-R² (b1)
The urea-based thickener (B) to be used in one aspect of the present invention may be formed of one kind, or may be a mixture of two or more kinds.
In the general formula (b1), R¹ and R² each independently represent a monovalent hydrocarbon group having 6 to 24 carbon atoms. R¹ and R² may be identical to or different from each other. R³ represents a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms.
Although the number of the carbon atoms of the monovalent hydrocarbon group that may be selected as each of R¹ and R² in the general formula (b1) is from 6 to 24, the number is preferably from 6 to 20, more preferably from 6 to 18.
In addition, examples of the monovalent hydrocarbon group that may be selected as each of R¹ and R² include a saturated or unsaturated, monovalent chain hydrocarbon group, a saturated or unsaturated, monovalent alicyclic hydrocarbon group, and a monovalent aromatic hydrocarbon group.
Herein, when the content of a chain hydrocarbon group, the content of an alicyclic hydrocarbon group, and the content of an aromatic hydrocarbon group in R¹ and R² in the general formula (b1) are represented by X molar equivalents, Y molar equivalents, and Z molar equivalents, respectively, the following requirements (a) and (b) are preferably satisfied:

·Requirement (a): the value of the ratio "[(X+Y)/(X+Y+Z)]×100" is 90 or more (preferably 95 or more, more preferably 98 or more, still more preferably 100); and
·Requirement (b): the ratio "X/Y" is from 0/100 (X=0, Y=100) to 100/0 (X=100, Y=0) (preferably from 10/90 to 90/10, more preferably from 20/80 to 80/20).

The total sum of the values of X, Y, and Z is 2 molar equivalents with respect to 1 mole of the compound represented by the general formula (b1) because the alicyclic hydrocarbon group, the chain hydrocarbon group, and the aromatic hydrocarbon group are each a group selected as each of R¹ and R² in the general formula (b1). In addition, the values of the above-mentioned requirements (a) and (b) each mean an average with respect to the total amount of a compound group represented by the general formula (b1) in the grease composition.
The use of the compound represented by the general formula (b1), the compound satisfying the above-mentioned requirements (a) and (b), easily provides a grease composition excellent in heat resistance.
The values of X, Y, and Z may be calculated from the molar equivalents of the respective amines to be used as raw materials.
Examples of the monovalent saturated chain hydrocarbon group include linear or branched alkyl groups each having 6 to 24 carbon atoms, and specific examples thereof include a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, an octadecenyl group, a nonadecyl group, and an icosyl group. Among them, an octadecyl group is preferred.
Examples of the monovalent unsaturated chain hydrocarbon group include linear or branched alkenyl groups each having 6 to 24 carbon atoms, and specific examples thereof include a hexenyl group, a heptenyl group, an octenyl group, a nonenyl group, a decenyl group, an undecenyl group, a dodecenyl group, a tridecenyl group, a tetradecenyl group, a pentadecenyl group, a hexadecenyl group, a heptadecenyl group, an octadecenyl group, a nonadecenyl group, an icosenyl group, an oleyl group, a geranyl group, a farnesyl group, and a linoleyl group.
The monovalent saturated chain hydrocarbon groups and the monovalent unsaturated chain hydrocarbon groups may be linear or branched.
Examples of the monovalent saturated alicyclic hydrocarbon group include: cycloalkyl groups, such as a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, and a cyclononyl group; and cycloalkyl groups each substituted with an alkyl group having 1 to 6 carbon atoms (preferably a cyclohexyl group substituted with an alkyl group having 1 to 6 carbon atoms), such as a methylcyclohexyl group, a dimethylcyclohexyl group, an ethylcyclohexyl group, a diethylcyclohexyl group, a propylcyclohexyl group, an isopropylcyclohexyl group, a 1-methyl-propylcyclohexyl group, a butylcyclohexyl group, a pentylcyclohexyl group, a pentyl-methylcyclohexyl group, and a hexylcyclohexyl group. Among them, a cyclohexyl group is preferred.
Examples of the monovalent unsaturated alicyclic hydrocarbon group include: cycloalkenyl groups, such as a cyclohexenyl group, a cycloheptenyl group, and a cyclooctenyl group; and cycloalkenyl groups each substituted with an alkyl group having 1 to 6 carbon atoms (preferably a cyclohexenyl group substituted with an alkyl group having 1 to 6 carbon atoms), such as a methylcyclohexenyl group, a dimethylcyclohexenyl group, an ethylcyclohexenyl group, a diethylcyclohexenyl group, and a propylcyclohexenyl group.
Examples of the monovalent 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, an ethylphenyl group, and a propylphenyl group.
Although the number of the carbon atoms of the divalent aromatic hydrocarbon group that may be selected as R³ in the general formula (b1) is from 6 to 18, the number is preferably from 6 to 15, more preferably from 6 to 13.
Examples of the divalent aromatic hydrocarbon group that may be selected as R³ include a phenylene group, a diphenylmethylene group, a diphenylethylene group, a diphenylpropylene group, a methylphenylene group, a dimethylphenylene group, and an ethylphenylene group.
Among them, a phenylene group, a diphenylmethylene group, a diphenylethylene group, or a diphenylpropylene group is preferred, and a diphenylmethylene group is more preferred.
In the grease composition of one aspect of the present invention, the content of the component (B) is preferably from 1.0 mass% to 20.0 mass%, more preferably from 1.5 mass% to 15.0 mass%, still more preferably from 2.0 mass% to 13.0 mass%, still further more preferably from 4.0 mass% to 12.0 mass%, yet still further more preferably from 5.0 mass% to 11.0 mass% with respect to the total amount (100 mass%) of the grease composition.
When the content of the component (B) is 1.0 mass% or more, the worked penetration of the grease composition to be obtained is easily adjusted within a moderate range.
Meanwhile, when the content of the component (B) is 20.0 mass% or less, the grease composition to be obtained can be adjusted to be soft, and hence the transmission efficiency of a wave gear device or the like is easily improved.

[Method of producing Urea-based Thickener (B)]

The urea-based thickener (B) may be typically obtained by causing an isocyanate compound and a monoamine to react with each other. The reaction is preferably performed by a method including adding, to a heated solution α obtained by dissolving the isocyanate compound in the above-mentioned base oil (A), a solution β obtained by dissolving the monoamine in the base oil (A).
For example, when the compound represented by the general formula (b1) is synthesized, the desired urea-based thickener (B) may be synthesized by the above-mentioned method through use of: a diisocyanate having a group corresponding to the divalent aromatic hydrocarbon group represented by R³ in the general formula (b1) as the isocyanate compound; and an amine having a group corresponding to the monovalent hydrocarbon group represented by each of R¹ and R² as the monoamine.
From the viewpoint of miniaturizing the urea-based thickener (B) in the grease composition so that the above-mentioned requirement (I) and the above-mentioned requirement (II) may be satisfied, a grease composition including the component (A) and the component (B) is preferably produced by using such a grease-producing apparatus as described in the following item [1]:

[1] a grease-producing apparatus, including:
- a container main body having an introducing portion into which grease raw materials are introduced and an ejecting portion that ejects grease to the outside; and
- a rotor, which has a rotation axis in the axial direction of the inner periphery of the container main body and is rotatably arranged in the container main body,
- in which the rotor includes a first irregular portion,
  1. (i) in which irregularities are alternately arranged along the surface of the rotor, and the irregularities are inclined with respect to the rotation axis, and
  2. (ii) which has a delivery ability from the introducing portion toward the ejecting portion.

The grease-producing apparatus described in the above-mentioned item [1] is described below. However, unless otherwise stated, a specification considered to be "preferred" in the following description is an aspect from the viewpoint of miniaturizing the urea-based thickener (B) in the grease composition so that the above-mentioned requirement (I) and the above-mentioned requirement (II) may be satisfied.
Fig. 1 is a schematic sectional view of the grease-producing apparatus of the above-mentioned item [1] that may be used in one aspect of the present invention.
A grease-producing apparatus 1 illustrated in Fig. 1 includes: a container main body 2 into which grease raw materials are introduced; and a rotor 3, which has a rotation axis 12 on the central axis line of the inner periphery of the container main body 2 and rotates about the rotation axis 12.
The rotor 3 rotates about the rotation axis 12 at a high speed, and applies a high shear force to the grease raw materials in the container main body 2. Thus, grease including the urea-based thickener (B) is produced.
As illustrated in Fig. 1, the container main body 2 is preferably divided into an introducing portion 4, a staying portion 5, a first inner peripheral surface 6, a second inner peripheral surface 7, and an ejecting portion 8 in the stated order from its upstream side.
As illustrated in Fig. 1, the container main body 2 preferably has a truncated cone-shaped inner peripheral surface whose inner diameter gradually increases from the introducing portion 4 toward the ejecting portion 8.
The introducing portion 4 serving as one end of the container main body 2 includes a plurality of solution-introducing tubes 4A and 4B through which the grease raw materials are introduced from the outside of the container main body 2.
The staying portion 5 is a space, which is arranged in the downstream portion of the introducing portion 4, and in which the grease raw materials introduced from the introducing portion 4 are caused to temporarily stay. When the grease raw materials stay in the staying portion 5 for a long time period, the grease adhering to the inner peripheral surface of the staying portion 5 forms a large lump. Accordingly, the raw materials are preferably conveyed to the first inner peripheral surface 6 on the downstream side of the container main body in as short a time period as possible. It is more preferred that the raw materials be directly conveyed to the first inner peripheral surface 6 without through the staying portion 5.
The first inner peripheral surface 6 is arranged in a downstream portion adjacent to the staying portion 5, and the second inner peripheral surface 7 is arranged in a downstream portion adjacent to the first inner peripheral surface 6. As described in detail later, it is preferred that a first irregular portion 9 be arranged on the first inner peripheral surface 6, and a second irregular portion 10 be arranged on the second inner peripheral surface 7 in order that the first inner peripheral surface 6 and the second inner peripheral surface 7 may each be caused to function as a high-shear portion that applies a high shear force to the grease raw materials or the grease.
The ejecting portion 8 serving as the other end of the container main body 2 is a portion that ejects the grease stirred on the first inner peripheral surface 6 and the second inner peripheral surface 7, and the portion includes an ejection orifice 11 that ejects the grease. The ejection orifice 11 is formed in a direction perpendicular to the rotation axis 12 or a direction substantially perpendicular thereto. Thus, the grease is ejected from the ejection orifice 11 in the direction perpendicular to the rotation axis 12 or the direction substantially perpendicular thereto. However, the ejection orifice 11 is not necessarily required to be perpendicular to the rotation axis 12, and may be formed in a direction parallel to the rotation axis 12 or a direction substantially parallel thereto.
The rotor 3 is rotatably arranged through use of the central axis line of the truncated cone-shaped inner peripheral surface of the container main body 2 as the rotation axis 12, and rotates counterclockwise when the container main body 2 is viewed from its upstream portion toward its downstream portion as illustrated in Fig. 1.
The rotor 3 has an outer peripheral surface that enlarges with increasing inner diameter of the truncated cone of the container main body 2, and a certain interval is maintained between the outer peripheral surface of the rotor 3 and the truncated cone-shaped inner peripheral surface of the container main body 2.
A rotor first irregular portion 13 in which irregularities are alternately arranged along the surface of the rotor 3 is arranged on the outer peripheral surface of the rotor 3.
The rotor first irregular portion 13 is inclined with respect to the rotation axis 12 of the rotor 3 in a direction from the introducing portion 4 to the ejecting portion 8, and has a delivery ability from the introducing portion 4 toward the ejecting portion 8. That is, the rotor first irregular portion 13 is inclined in a direction in which a solution is pushed out to the downstream side of the container main body when the rotor 3 rotates in a direction illustrated in Fig. 1.
A step between the recess 13A and protrusion 13B of the rotor first irregular portion 13 is preferably from 0.3 to 30, more preferably from 0.5 to 15, still more preferably from 2 to 7 when the diameter of the recess 13A on the outer peripheral surface of the rotor 3 is defined as 100.
The number of the protrusions 13B of the rotor first irregular portion 13 in its circumferential direction is preferably from 2 to 1,000, more preferably from 6 to 500, still more preferably from 12 to 200.
The ratio [width of protrusion/width of recess] of the width of the protrusion 13B of the rotor first irregular portion 13 to the width of the recess 13A thereof in a section perpendicular to the rotation axis 12 of the rotor 3 is preferably from 0.01 to 100, more preferably from 0.1 to 10, still more preferably from 0.5 to 2.
The inclination angle of the rotor first irregular portion 13 with respect to the rotation axis 12 is preferably from 2° to 85°, more preferably from 3° to 45°, still more preferably from 5° to 20°.
The first inner peripheral surface 6 of the container main body 2 preferably includes the first irregular portion 9 in which a plurality of irregularities are formed along the inner peripheral surface.
In addition, the irregularities of the first irregular portion 9 on the container main body 2 side are preferably inclined opposite to the rotor first irregular portion 13.
That is, the plurality of irregularities of the first irregular portion 9 on the container main body 2 side are preferably inclined in the direction in which a solution is pushed out to the downstream side of the container main body when the rotation axis 12 of the rotor 3 rotates in the direction illustrated in Fig. 1. The first irregular portion 9 having a plurality of irregularities, which is arranged on the first inner peripheral surface 6 of the container main body 2, further reinforces a stirring ability and an ejecting ability.
The depth of each of the irregularities of the first irregular portion 9 on the container main body 2 side is preferably from 0.2 to 30, more preferably from 0.5 to 15, still more preferably from 1 to 5 when the inner diameter (diameter) of the container is defined as 100.
The number of the irregularities of the first irregular portion 9 on the container main body 2 side is preferably from 2 to 1,000, more preferably from 6 to 500, still more preferably from 12 to 200.
The ratio [width of recess/width of protrusion] of the width of the recess of the irregularities of the first irregular portion 9 on the container main body 2 side to the width of the protrusion between the grooves thereof is preferably from 0.01 to 100, more preferably from 0.1 to 10, still more preferably from 0.5 to 2 or less.
The inclination angle of each of the irregularities of the first irregular portion 9 on the container main body 2 side with respect to the rotation axis 12 is preferably from 2° to 85°, more preferably from 3° to 45°, still more preferably from 5° to 20°.
When the first irregular portion 9 is arranged on the first inner peripheral surface 6 of the container main body 2, the first inner peripheral surface 6 can be caused to function as a shear portion that applies a high shear force to the grease raw materials or the grease. However, the first irregular portion 9 is not necessarily required to be arranged.
A rotor second irregular portion 14 in which irregularities are alternately arranged along the surface of the rotor 3 is preferably arranged on the outer peripheral surface of the downstream portion of the rotor first irregular portion 13.
The rotor second irregular portion 14 is inclined with respect to the rotation axis 12 of the rotor 3, and has a delivery suppression ability by which a solution is pushed back to the upstream side of the container main body from the introducing portion 4 toward the ejecting portion 8.
The step of the rotor second irregular portion 14 is preferably from 0.3 to 30, more preferably from 0.5 to 15, still more preferably from 2 to 7 when the diameter of the recess on the outer peripheral surface of the rotor 3 is defined as 100.
The number of the protrusions of the rotor second irregular portion 14 in its circumferential direction is preferably from 2 to 1,000, more preferably from 6 to 500, still more preferably from 12 to 200.
The ratio [width of protrusion/width of recess] of the width of the protrusion of the rotor second irregular portion 14 to the width of the recess thereof in a section perpendicular to the rotation axis of the rotor 3 is preferably from 0.01 to 100, more preferably from 0.1 to 10, still more preferably from 0.5 to 2.
The inclination angle of the rotor second irregular portion 14 with respect to the rotation axis 12 is preferably from 2° to 85°, more preferably from 3° to 45°, still more preferably from 5° to 20°.
The second inner peripheral surface 7 of the container main body 2 preferably includes the second irregular portion 10 in which a plurality of irregularities are formed so as to be adjacent to the downstream portions of the irregularities in the first irregular portion 9 on the container main body 2 side.
A plurality of irregularities are formed on the inner peripheral surface of the container main body 2, and the respective irregularities are preferably inclined opposite to the inclination direction of the rotor second irregular portion 14.
That is, the plurality of irregularities of the second irregular portion 10 on the container main body 2 side are preferably inclined in the direction in which a solution is pushed back to the upstream side of the container main body when the rotation axis 12 of the rotor 3 rotates in the direction illustrated in Fig. 1. The irregularities of the second irregular portion 10 arranged on the second inner peripheral portion 7 of the container main body 2 further reinforce the stirring ability. In addition, the second inner peripheral surface 7 of the container main body can be caused to function as a shear portion that applies a high shear force to the grease raw materials or the grease.
The depth of the recess of the second irregular portion 10 on the container main body 2 side is preferably from 0.2 to 30, more preferably from 0.5 to 15, still more preferably from 1 to 5 when the inner diameter (diameter) of the container main body 2 is defined as 100.
The number of the recesses of the second irregular portion 10 on the container main body 2 side is preferably from 2 to 1,000, more preferably from 6 to 500, still more preferably from 12 to 200.
The ratio [width of protrusion/width of recess] of the width of the protrusion of the irregularities of the second irregular portion 10 on the container main body 2 side to the width of the recess thereof in a section perpendicular to the rotation axis 12 of the rotor 3 is preferably from 0.01 to 100, more preferably from 0.1 to 10, still more preferably from 0.5 to 2 or less.
The inclination angle of the second irregular portion 10 on the container main body 2 side with respect to the rotation axis 12 is preferably from 2° to 85°, more preferably from 3° to 45°, still more preferably from 5° to 20°.
The ratio [length of first irregular portion/length of second irregular portion] of the length of the first irregular portion 9 on the container main body 2 side to the length of the second irregular portion 10 on the container main body 2 side is preferably from 2/1 to 20/1.
Fig. 2 is a sectional view of the first irregular portion 9 on the container main body 2 side of the grease-producing apparatus 1 in the direction perpendicular to the rotation axis 12.
A plurality of scrapers 15 whose tips protrude toward the inner peripheral surface of the container main body 2 more than the protruding direction tip of the protrusion 13B of the first irregular portion 13 does are arranged in the rotor first irregular portion 13 illustrated in Fig. 2. In addition, such a plurality of scrapers that the tips of their protrusions protrude toward the inner peripheral surface of the container main body 2 are arranged in the second irregular portion 14 as in the first irregular portion 13, though their illustration is omitted.
The scrapers 15 scrape off the grease adhering to the inner peripheral surfaces of the first irregular portion 9 on the container main body 2 side and the second irregular portion 10 on the container main body 2 side.
With regard to the ratio of the protrusion amount of the tip of each of the scrapers 15 to the protrusion amount of the protrusion 13B of the rotor first irregular portion 13, the ratio [R2/R1] of the radius (R2) of the tip of the scraper 15 to the radius (R1) of the tip of the protrusion 13B is preferably more than 1.005 and less than 2.0.
The number of the scrapers 15 is preferably from 2 to 500, more preferably from 2 to 50, still more preferably from 2 to 10.
Although the scrapers 15 are arranged in the grease-producing apparatus 1 illustrated in Fig. 2, the scrapers 15 may not be arranged, or the scrapers 15 may be intermittently arranged.
When the grease including the urea-based thickener (B) is produced with the grease-producing apparatus 1, a grease base material including the urea-based thickener (B) may be produced by: introducing the solution α and the solution β serving as the above-mentioned grease raw materials from the solution-introducing tubes 4A and 4B of the introducing portion 4 of the container main body 2, respectively; and rotating the rotor 3 at a high speed.
In addition, even when the grease base material thus obtained is blended with the sulfur-phosphorus-based extreme pressure agent (C) and the other additive (D), the urea-based thickener (B) in the grease composition can be miniaturized so that the above-mentioned requirement (I) and the above-mentioned requirement (II) may be satisfied.
With regard to a condition for the high-speed rotation of the rotor 3, a shear rate to be applied to the grease raw materials is preferably 10² s^-1 or more, more preferably 10³ s^-1 or more, still more preferably 10⁴ s^-1 or more, and is typically 10⁷ s^-1 or less.
In addition, the ratio (Max/Min) of the maximum shear rate (Max) to the minimum shear rate (Min) in shearing at the time of the high-speed rotation of the rotor 3 is preferably 100 or less, more preferably 50 or less, still more preferably 10 or less.
When a shear rate to be applied to a mixed liquid is as uniform as possible, the urea-based thickener (B) in the grease composition or a precursor thereof is easily miniaturized, and hence a more uniform grease structure is obtained.
Herein, the maximum shear rate (Max) is the maximum shear rate to be applied to the mixed liquid, and the minimum shear rate (Min) is the minimum shear rate to be applied to the mixed liquid. The shear rates are defined as described below.

·Maximum shear rate (Max)=(linear velocity of tip of protrusion 13B of rotor first irregular portion 13)/(gap A1 between tip of protrusion 13B of rotor first irregular portion 13 and protrusion of first irregular portion 9 of first inner peripheral surface 6 of container main body 2)
·Minimum shear rate (Min)=(linear velocity of recess 13A of rotor first irregular portion 13)/(gap A2 between recess 13A of rotor first irregular portion 13 and recess of first irregular portion 9 of first inner peripheral surface 6 of container main body 2)

The gap A1 and the gap A2 are as illustrated in Fig. 2.
The grease-producing apparatus 1 includes the scrapers 15, and hence the grease adhering to the inner peripheral surface of the container main body 2 can be scraped off. Accordingly, the occurrence of a lump during kneading can be prevented, and hence grease in which the urea-based thickener (B) is miniaturized can be continuously produced in a short time period.
In addition, the scrapers 15 scrape off the adhering grease, and hence the staying grease can be prevented from serving as resistance to the rotation of the rotor 3. Accordingly, the rotation torque of the rotor 3 can be reduced, and hence the power consumption of a driving source therefor can be reduced. Thus, the continuous production of the grease can be efficiently performed.
The inner peripheral surface of the container main body 2 has a truncated cone shape whose inner diameter increases from the introducing portion 4 toward the ejecting portion 8. Accordingly, the inner peripheral surface has such an effect that a centrifugal force discharges the grease or the grease raw materials in a downstream direction, and hence the rotation torque of the rotor 3 can be reduced. Thus, the continuous production of the grease can be performed.
The rotor first irregular portion 13 is arranged on the outer peripheral surface of the rotor 3, and the rotor first irregular portion 13 is inclined with respect to the rotation axis 12 of the rotor 3, and has a delivery ability from the introducing portion 4 toward the ejecting portion 8. Further, the rotor second irregular portion 14 is inclined with respect to the rotation axis 12 of the rotor 3, and has a delivery suppression ability from the introducing portion 4 toward the ejecting portion 8. Accordingly, a high shear force can be applied to a solution, and hence, even after an additive has been blended thereinto, the urea-based thickener (B) in the grease composition can be miniaturized so that the above-mentioned requirement (I) and the above-mentioned requirement (II) may be satisfied.
The first irregular portion 9 is formed on the first inner peripheral surface 6 of the container main body 2, and is inclined opposite to the rotor first irregular portion 13. Accordingly, in addition to the effect of the rotor first irregular portion 13, further, the grease raw materials can be sufficiently stirred while the grease is, or the grease raw materials are, pushed out in the downstream direction. Accordingly, even after an additive has been blended into the stirred product, the urea-based thickener (B) in the grease composition can be miniaturized so that the above-mentioned requirement (I) and the above-mentioned requirement (II) may be satisfied.
In addition, the second irregular portion 10 is arranged on the second inner peripheral surface 7 of the container main body 2, and the rotor second irregular portion 14 is arranged on the outer peripheral surface of the rotor 3. Accordingly, the grease raw materials can be prevented from flowing out of the first inner peripheral surface 6 of the container main body more than necessary, and hence a high shear force can be applied to the solution to highly disperse the grease raw materials. Accordingly, even after an additive has been blended into the dispersion, the urea-based thickener (B) can be miniaturized so that the above-mentioned requirement (I) and the above-mentioned requirement (II) may be satisfied.

The grease composition of this embodiment includes the phosphoric acid ester amine salt (C).
The phosphoric acid ester amine salt (C) is a salt of a phosphoric acid ester and an amine.
When the grease composition of this embodiment includes the phosphoric acid ester amine salt (C), there can be obtained a grease composition, which is excellent in wear resistance even under a temperature environment as low as less than 80°C.
Examples of the phosphoric acid ester of the phosphoric acid ester amine salt (C) include: neutral phosphoric acid esters, such as an aryl phosphate, an alkyl phosphate, an alkenyl phosphate, and an alkylaryl phosphate; acidic phosphoric acid esters, such as a monoaryl acid phosphate, a diaryl acid phosphate, a monoalkyl acid phosphate, a dialkyl acid phosphate, a monoalkenyl acid phosphate, and a dialkenyl acid phosphate; phosphorous acid esters, such as an aryl hydrogen phosphite, an alkyl hydrogen phosphite, an aryl phosphite, an alkyl phosphite, an alkenyl phosphite, an arylalkyl phosphite; and acidic phosphorous acid esters, such as a monoalkyl acid phosphite, a dialkyl acid phosphite, a monoalkenyl acid phosphite, and a dialkenyl acid phosphite. Among them, neutral phosphoric acid esters, such as an aryl phosphate, an alkyl phosphate, an alkenyl phosphate, and an alkylaryl phosphate, and acidic phosphoric acid esters, such as a monoaryl acid phosphate, a diaryl acid phosphate, a monoalkyl acid phosphate, a dialkyl acid phosphate, a monoalkenyl acid phosphate, and a dialkenyl acid phosphate, are preferred, and a monoalkyl acid phosphate and a dialkyl acid phosphate are more preferred from the viewpoint of abrasion resistance.
The number of the carbon atoms of an alkyl group in the phosphoric acid ester of the phosphoric acid ester amine salt (C) is preferably from 1 to 18, more preferably from 1 to 15. The alkyl group is preferably linear or branched, more preferably branched.
Examples of the amine of the phosphoric acid ester amine salt (C) include octylamine, dioctylamine, trioctylamine, dimethyldodecylamine, dibutylethanolamine, and dodecyldiethanolamine. Among them, trioctylamine is preferred from the viewpoint of abrasion resistance.
The number of the carbon atoms of an alkyl group in the amine of the phosphoric acid ester amine salt (C) is preferably from 1 to 15, more preferably from 3 to 12. The alkyl group is preferably linear or branched, more preferably linear.
A monohexyl phosphate amine salt and a dihexyl phosphate amine salt are each preferred as the phosphoric acid ester amine salt.
Those phosphoric acid ester amine salts may be used alone or in combination thereof.
In the grease composition of this embodiment, from the viewpoint of wear resistance, the content of a phosphorus atom derived from the phosphoric acid ester amine salt (C) is preferably from 0.01 mass% to 0.30 mass%, more preferably from 0.03 mass% to 0.20 mass%, still more preferably from 0.05 mass% to 0.15 mass% with respect to the total amount (100 mass%) of the grease composition.
In this description, the content of the phosphorus atom means a value measured in conformity with JPI-5S-38-03.
In the grease composition of this embodiment, from the viewpoint of wear resistance, the content of the phosphoric acid ester amine salt (C) is preferably from 0.5 mass% to 5.0 mass%, more preferably from 0.7 mass% to 4.0 mass%, still more preferably from 1.0 mass% to 3.0 mass% with respect to the total amount (100 mass%) of the grease composition.

<Sulfur-based Extreme Pressure Agent (D)>

The grease composition of this embodiment includes the sulfur-based extreme pressure agent (D).
When the grease composition of this embodiment includes the sulfur-based extreme pressure agent (D), there can be obtained a grease composition, which has a high extreme pressure property even at temperatures as high as 80°C or more.
Examples of the sulfur-based extreme pressure agent (D) include a sulfurized oil and fat, a sulfurized fatty acid, a sulfurized ester, a sulfurized olefin, a monosulfide, a polysulfide, a dihydrocarvyl polysulfide, a thiadiazole compound, an alkylthiocarbamoyl compound, a thiocarbamate compound, a dithiocarbamate compound, a thioterpene compound, and a dialkylthiodipropionate compound. Those sulfur-based extreme pressure agents (D) may be used alone or in combination thereof.
Among them, a sulfurized olefin is preferred from the viewpoint of improving the extreme pressure property of the grease composition.
The sulfurized olefin is preferably a sulfurized product of an olefin having 2 to 10 carbon atoms, more preferably a sulfurized product of a branched olefin having 2 to 10 carbon atoms.
In the grease composition of this embodiment, from the viewpoint of its extreme pressure property, the content of a sulfur atom derived from the sulfur-based extreme pressure agent (D) is preferably from 0.25 mass% to 0.65 mass%, more preferably from 0.30 mass% to 0.60 mass%, still more preferably from 0.35 mass% to 0.55 mass% with respect to the total amount (100 mass%) of the grease composition.
In this description, the content of the sulfur atom means a value measured in conformity with JIS K2541-2:2013.
In the grease composition of this embodiment, from the viewpoint of its extreme pressure property, the content of the sulfur-based extreme pressure agent (D) is preferably from 0.5 mass% to 5.0 mass%, more preferably from 0.7 mass% to 4.0 mass%, still more preferably from 0.9 mass% to 3.0 mass% with respect to the total amount (100 mass%) of the grease composition.

The grease composition of this embodiment includes the zinc dithiophosphate (E).
When the grease composition of this embodiment includes the zinc dithiophosphate (E), there can be obtained a grease composition, which is excellent in wear resistance even under a temperature environment as low as less than 80°C.
The zinc dithiophosphate (E) is preferably, for example, a compound represented by the following general formula (b-1): wherein
in the general formula (b-1), R^b1 to R^b4 each independently represent a monovalent hydrocarbon group. The hydrocarbon group is not particularly limited as long as the group is a monovalent hydrocarbon group, and from the viewpoint of wear resistance, preferred examples thereof include an alkyl group, an alkenyl group, a cycloalkyl group, and an aryl group. Among them, an alkyl group is preferred.
That is, the zinc dithiophosphate (E) to be used in this embodiment is preferably a zinc dialkyldithiophosphate.
The cycloalkyl group and the aryl group that may each be selected as each of R^b1 to R^b4 may be, for example, polycyclic groups, such as a decalyl group and a naphthyl group.
In addition, the monovalent hydrocarbon group that may be selected as each of R^b1 to R^b4 may be a group having a substituent containing an oxygen atom and/or a nitrogen atom, such as a hydroxy group, a carboxy group, an amino group, an amide group, a nitro group, or a cyano group, or may be partially substituted with a nitrogen atom, an oxygen atom, a halogen atom, or the like. When the monovalent hydrocarbon group is a cycloalkyl group or an aryl group, the group may further have a substituent, such as an alkyl group or an alkenyl group.
Although the alkyl group and the alkenyl group that may each be selected as each of R^b1 to R^b4 may be linear or branched, from the viewpoint of wear resistance, each of the groups is preferably a primary or secondary group. Among them, a primary alkyl group or a secondary alkyl group is preferred, and a secondary alkyl group is more preferred.
That is, the zinc dialkyldithiophosphate to be used in this embodiment is preferably a zinc dialkyldithiophosphate having a primary alkyl group or a secondary alkyl group, or a combination thereof, more preferably a primary zinc dialkyldithiophosphate or a secondary zinc dialkyldithiophosphate, or a combination thereof, still more preferably a secondary zinc dialkyldithiophosphate.
From the viewpoint of wear resistance, when the monovalent hydrocarbon group is an alkyl group, the number of the carbon atoms of the hydrocarbon group represented by any one of R^b1 to R^b4 is preferably 1 or more, more preferably 2 or more, still more preferably 3 or more, and the upper limit thereof is preferably 24 or less, more preferably 18 or less, still more preferably 12 or less, still further more preferably 10 or less. When the monovalent hydrocarbon group is an alkenyl group, the number of the carbon atoms thereof is preferably 2 or more, more preferably 3 or more, and the upper limit thereof is preferably 24 or less, more preferably 18 or less, still more preferably 12 or less, still further more preferably 10 or less. In addition, when the monovalent hydrocarbon group is a cycloalkyl group, the number of the carbon atoms thereof is preferably 5 or more, and the upper limit thereof is preferably 20 or less. When the monovalent hydrocarbon group is an aryl group, the number of the carbon atoms thereof is preferably 6 or more, and the upper limit thereof is preferably 20 or less.
The zinc dithiophosphates (E) may be used alone or in combination thereof.
In the grease composition of this embodiment, from the viewpoint of wear resistance, the content of a zinc atom derived from the zinc dithiophosphate (E) is preferably from 0.05 mass% to 0.35 mass%, more preferably from 0.07 mass% to 0.30 mass%, still more preferably from 0.10 mass% to 0.25 mass% with respect to the total amount (100 mass%) of the grease composition.
In this description, the content of the zinc atom means a value measured in conformity with JPI-5S-38-03.
In the grease composition of this embodiment, from the viewpoint of wear resistance, the content of the zinc dithiophosphate (E) is preferably from 0.5 mass% to 5.0 mass%, more preferably from 0.7 mass% to 4.0 mass%, still more preferably from 1.0 mass% to 3.0 mass% with respect to the total amount (100 mass%) of the grease composition.

The grease composition of this embodiment includes the melamine cyanurate (F).
When the grease composition of this embodiment includes the melamine cyanurate (F), there can be obtained a grease composition, which is excellent in wear resistance even under a temperature environment as low as less than 80°C. In addition, when the grease composition of this embodiment includes the melamine cyanurate (F), there can be obtained a grease composition, which is excellent in seizure resistance under a temperature environment as high as 80°C or more.
The melamine cyanurate is an organic salt formed of melamine and cyanuric acid, and has a graphite structure.
The average particle diameter of the melamine cyanurate (F) is preferably 5.0 µm or less, more preferably 4.0 µm or less, still more preferably 3.0 µm or less, still further more preferably 2.5 µm or less, yet still further more preferably 2.0 µm or less. In addition, although the lower limit value of the average particle diameter of the melamine cyanurate (F) is not particularly limited, the lower limit value is typically 0.005 µm or more.
As the average particle diameter of the melamine cyanurate (F) becomes smaller, the grease composition more easily enters a wave gear device or the like, and hence can reduce the wear amount of the wave gear device or the like to a larger extent. Accordingly, the average particle diameter of the melamine cyanurate (F) is preferably as small as possible.
The term "average particle diameter of the melamine cyanurate (F)" as used herein means an average particle diameter measured by the following method. In addition, the particle diameter of the melamine cyanurate (F) alone is maintained at the same particle diameter even in the grease composition (i.e., the average particle diameter of the melamine cyanurate (F) to be incorporated into the grease composition is comparable to the particle diameter of the melamine cyanurate (F) itself).

[Average Particle Diameter of Melamine Cyanurate (F)]

A 50% particle diameter (volume median particle diameter, D₅₀) on a scattering intensity basis calculated from a dispersed particle diameter distribution, which is measured by a dynamic light scattering method (photon correlation method) at 25°C and analyzed by a CONTIN method, may be used as the average particle diameter of the melamine cyanurate (F).
In the grease composition of this embodiment, from the viewpoint of lubricity, the content of the melamine cyanurate (F) is preferably 0.2 mass% or more, more preferably 0.3 mass% or more, still more preferably 0.5 mass% or more with respect to the total amount (100 mass%) of the grease composition. In addition, in the grease composition of the present invention, from the viewpoint of lubricity, the content of the melamine cyanurate (F) is preferably 10.0 mass% or less, more preferably 5.0 mass% or less, still more preferably 3.0 mass% or less, still further more preferably 2.0 mass% or less with respect to the total amount (100 mass%) of the grease composition.

The grease composition of this embodiment includes the organic molybdenum compound (G).
When the grease composition of this embodiment includes the organic molybdenum compound (G), there can be obtained a grease composition, which has a high extreme pressure property and an excellent load-bearing capacity at temperatures as high as 80°C or more because the compound reacts with a sliding surface to form a coat.
Examples of the organic molybdenum compound (G) include a molybdenum dithiophosphate (MoDTP) (G1) and a molybdenum dithiocarbamate (MoDTC) (G2). Those organic molybdenum compounds (G) may be used alone or in combination thereof.
Among them, a molybdenum dithiophosphate (G1) is preferably incorporated into the organic molybdenum compound (G) from the viewpoint that the effect of the present invention is more easily exhibited.

<<Molybdenum Dithiophosphate (G1)>>

The molybdenum dithiophosphate (G1) is, for example, a molybdenum dithiophosphate represented by the following general formula (g1-1) or the following general formula (g1-2), the molybdenum dithiophosphate containing two molybdenum atoms in a molecule thereof.
R⁴¹ to R⁴⁴ in the general formula (g1-1), and R⁵¹ to R⁵⁴ in the general formula (g1-2) each independently represent a hydrocarbon group having 1 to 30 carbon atoms, and these groups may be identical to or different from each other.
X⁴¹ to X⁴¹ in the general formula (g1-1), and X⁵¹ to X⁵⁴ in the general formula (g1-2) each independently represent an oxygen atom or a sulfur atom. Those atoms may be identical to or different from each other, and at least one of each of the pairs of X⁴³ and X⁴⁴, X⁴⁵ and X⁴¹, X⁴¹ and X⁴⁸, and X⁵³ and X⁵⁴ represents a sulfur atom.
Examples of the hydrocarbon group represented by each of R⁴¹ to R⁴⁴ and R⁵¹ to R⁵⁴ include an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group, an alkylaryl group, and an arylalkyl group. Among them, an alkyl group or an alkenyl group is preferred, and an alkyl group is more preferred from the viewpoint of improving the extreme pressure property of the grease composition.
From the same viewpoint as that described above, the number of the carbon atoms of the hydrocarbon group represented by each of R⁴¹ to R⁴⁴ and R⁵¹ to R⁵⁴ is preferably 2 or more, more preferably 4 or more, still more preferably 6 or more, and the upper limit thereof is preferably 24 or less, more preferably 22 or less, still more preferably 20 or less, still further more preferably 18 or less.
As described above, at least two of X⁴¹ to X⁴⁸ in the formula (g1-1) represent sulfur atoms, and it is preferred that X⁴¹ and X⁴² represent oxygen atoms, and X⁴³ to X⁴⁸ represent sulfur atoms.
In addition, X⁵¹ to X⁵⁴ in the formula (g1-2) preferably represent oxygen atoms.
When the organic molybdenum compound (G) contains the molybdenum dithiophosphate (G1), the content of the molybdenum dithiophosphate (G1) is preferably from 50 mass% to 100 mass%, more preferably from 60 mass% to 100 mass%, still more preferably from 70 mass% to 100 mass% with respect to the total amount of the organic molybdenum compound (G).

<<Molybdenum Dithiocarbamate (G2)>>

Examples of the molybdenum dithiocarbamate (G2) include: a binuclear molybdenum dithiocarbamate containing two molybdenum atoms in a molecule thereof; and a trinuclear molybdenum dithiocarbamate containing three molybdenum atoms in a molecule thereof.
Examples of the binuclear molybdenum dithiocarbamate include a compound represented by the following general formula (g2-1) and a compound represented by the following general formula (g2-2): wherein

in the general formulae (g2-1) and (g2-2), R¹¹ to R¹⁴ each independently represent a hydrocarbon group, and these groups may be identical to or different from each other, and
X¹¹ to X¹⁸ each independently represent an oxygen atom or a sulfur atom, and may be identical to or different from each other, provided that at least two of X¹¹ to X¹⁸ in the formula (g2-1) represent sulfur atoms.

The number of the carbon atoms of the hydrocarbon group that may be selected as each of R¹¹ to R¹⁴ is preferably from 6 to 22.
Examples of the hydrocarbon group that may be selected as each of R¹¹ to R¹⁴ in each of the general formulae (g2-1) and (g2-2) include an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group, an alkylaryl group, and an arylalkyl group.
Examples of the alkyl group include a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, and an octadecyl group.
Examples of the alkenyl group include a hexenyl group, a heptenyl group, an octenyl group, a nonenyl group, a decenyl group, an undecenyl group, a dodecenyl group, a tridecenyl group, a tetradecenyl group, and a pentadecenyl group.
Examples of the cycloalkyl group include a cyclohexyl group, a dimethylcyclohexyl group, an ethylcyclohexyl group, a methylcyclohexylmethyl group, a cyclohexylethyl group, a propylcyclohexyl group, a butylcyclohexyl group, and a heptylcyclohexyl group.
Examples of the aryl group include a phenyl group, a naphthyl group, an anthracenyl group, a biphenyl group, and a terphenyl group.
Examples of the alkylaryl group include a tolyl group, a dimethylphenyl group, a butylphenyl group, a nonylphenyl group, and a dimethylnaphthyl group.
Examples of the arylalkyl group include a methylbenzyl group, a phenylmethyl group, a phenylethyl group, and a diphenylmethyl group.
Among them, a molybdenum dialkyldithiocarbamate represented by the following structural formula (g2-3) is preferred: wherein
in the structural formula (g2-3), R¹, R², R³, and R⁴ each independently represent an aliphatic hydrocarbon group having 4 to 22 carbon atoms, X¹ and X² represent sulfur atoms, and X³ and X⁴ represent oxygen atoms.
It is preferred that R¹, R², R³, and R⁴ described above each independently include a short-chain substituent group serving as an aliphatic hydrocarbon group having 4 to 12 carbon atoms or a long-chain substituent group serving as an aliphatic hydrocarbon group having 13 to 22 carbon atoms.
Examples of the aliphatic hydrocarbon group having 4 to 12 carbon atoms that may be selected as the short-chain substituent group include an alkyl group having 4 to 12 carbon atoms and an alkenyl group having 4 to 12 carbon atoms.
Specific examples thereof include a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a butenyl group, a pentenyl group, a hexenyl group, a heptenyl group, an octenyl group, a nonenyl group, a decenyl group, an undecenyl group, and a dodecenyl group. Those aliphatic hydrocarbon groups may be linear or branched. From the viewpoint of further facilitating the exhibition of the effect of the present invention, the number of the carbon atoms of the aliphatic hydrocarbon group that may be selected as the short-chain substituent group is preferably from 5 to 11, more preferably from 6 to 10, still more preferably from 7 to 9.
Examples of the aliphatic hydrocarbon group having 13 to 22 carbon atoms that may be selected as the long-chain substituent group include an alkyl group having 13 to 22 carbon atoms and an alkenyl group having 13 to 22 carbon atoms.
Specific examples thereof include a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group, an icosyl group, a henicosyl group, a docosyl group, a tridecenyl group, a tetradecenyl group, a pentadecenyl group, a hexadecenyl group, a heptadecenyl group, an octadecenyl group, an oleyl group, a nonadecenyl group, an icosenyl group, a henicosenyl group, and a docosenyl group. Those aliphatic hydrocarbon groups may be linear or branched.
From the viewpoint of further facilitating the exhibition of the effect of the present invention, the number of the carbon atoms of the aliphatic hydrocarbon group that may be selected as the long-chain substituent group is preferably from 13 to 20, more preferably from 13 to 16, still more preferably 13 or 14.
A molar ratio (the short-chain substituent group:the long-chain substituent group) between the short-chain substituent group and the long-chain substituent group in all the molecules of the molybdenum dialkyldithiocarbamate represented by the structural formula (1) is preferably from 10:90 to 90:10, more preferably from 30:70 to 70:30, still more preferably from 40:60 to 60:40.
The trinuclear molybdenum dithiocarbamate is, for example, a compound represented by the following general formula (g2-4):

Mo₃S_kE_mL_nA_pQ_z (g2-4)

wherein
in the general formula (g2-4), "k" represents an integer of 1 or more, "m" represents an integer of 0 or more, and k+m is an integer of from 4 to 10, preferably an integer of from 4 to 7, "n" represents an integer of from 1 to 4, "p" represents an integer of 0 or more, and "z" represents an integer of from 0 to 5, and includes a nonstoichiometric value,
Es each independently represent an oxygen atom or a selenium atom, and may each substitute, for example, sulfur in a core to be described later,
Ls each independently represent an anionic ligand having a carbon atom-containing organic group, the total number of the carbon atoms of the organic groups in the respective ligands is 14 or more, and the respective ligands may be identical to or different from each other,
As each independently represent an anion except L, and
Qs each independently represent an electron-donating neutral compound, and are present for filling a vacant coordination on the trinuclear molybdenum compound.
The content of the molybdenum atoms in the trinuclear molybdenum dithiocarbamate is preferably 2.0 mass% or more, more preferably 4.0 mass% or more, still more preferably 5.0 mass% or more with respect to the total amount of the trinuclear molybdenum dithiocarbamate. In addition, the content is preferably 9.0 mass% or less, more preferably 7.0 mass% or less, still more preferably 6.0 mass% or less.
The upper limit values and lower limit values of those numerical ranges may be arbitrarily combined. Specifically, the content is preferably from 2.0 mass% to 9.0 mass%, more preferably from 4.0 mass% to 7.0 mass%, still more preferably from 5.0 mass% to 6.0 mass%.
When the organic molybdenum compound (G) contains the molybdenum dithiocarbamate (G2), the content of the molybdenum dithiocarbamate (G2) is preferably from 50 mass% to 100 mass%, more preferably from 60 mass% to 100 mass%, still more preferably from 70 mass% to 100 mass% with respect to the total amount of the organic molybdenum compound (G).
When the organic molybdenum compound (G) contains the molybdenum dithiophosphate (G1) and the molybdenum dithiocarbamate (G2), the total content of the molybdenum dithiophosphate (G1) and the molybdenum dithiocarbamate (G2) is preferably from 70 mass% to 100 mass%, more preferably from 80 mass% to 100 mass%, still more preferably from 90 mass% to 100 mass% with respect to the total amount of the organic molybdenum compound (G).
In the grease composition of this embodiment, from the viewpoint of its extreme pressure property, the content of a molybdenum atom derived from the organic molybdenum compound (G) is preferably from 0.05 mass% to 0.35 mass%, more preferably from 0.07 mass% to 0.30 mass%, still more preferably from 0.10 mass% to 0.25 mass% with respect to the total amount (100 mass%) of the grease composition.
In this description, the content of the molybdenum atom means a value measured in conformity with JPI-5S-38-03.
In the grease composition of this embodiment, from the viewpoint of its extreme pressure property, the content of the organic molybdenum compound (G) is preferably from 0.5 mass% to 5.0 mass%, more preferably from 0.7 mass% to 4.0 mass%, still more preferably from 0.9 mass% to 3.0 mass% with respect to the total amount (100 mass%) of the grease composition.

The grease composition of one aspect of the present invention may include an additive (H) except the component (B), the component (C), the component (D), the component (E), the component (F), and the component (G) to be blended into general grease to the extent that the effect of the present invention is not impaired.
Examples of the additive (H) include an antioxidant, a viscosity modifier, a rust inhibitor, a solid lubricant, and a detergent dispersant.
The additives (H) may be used alone or in combination thereof.
The composition preferably includes one or more kinds of additives selected from the group consisting of: an antioxidant; a viscosity modifier; and a rust inhibitor among them.
An example of the antioxidant is a phenol-based antioxidant.
Examples of the viscosity modifier include a non-dispersion-type poly(meth)acrylate (PMA), a dispersion-type poly(meth)acrylate, an olefin-based copolymer (olefin copolymer (OCP); e.g., an ethylene-propylene copolymer), a dispersion-type olefin-based copolymer, and a styrene-based copolymer (e.g., a styrene-diene hydrogenated copolymer). Those viscosity modifiers may be used alone or in combination thereof.
The mass-average molecular weight (Mw) of such viscosity modifier is preferably from 5,000 to 50,000, more preferably from 7,000 to 30,000, still more preferably from 10,000 to 20,000 from the following viewpoint: even when high shear is applied to the modifier in a wave gear device or the like, its molecules are hardly cleaved, and hence its mass-average molecular weight is maintained.
In this description, the mass-average molecular weight (Mw) of each component is a value in terms of standard polystyrene measured by a gel permeation chromatography (GPC) method.
Examples of the rust inhibitor include carboxylic acid-based rust inhibitors such as an alkenyl succinic acid polyhydric alcohol ester, zinc stearate, thiadiazole and derivatives thereof, and benzotriazole and derivatives thereof.
Examples of the solid lubricant include polyimide, PTFE, graphite, a metal oxide, boron nitride, and molybdenum disulfide.
Examples of the detergent dispersant include ashless dispersants, such as succinimide and a boron-based succinimide.
In the grease composition of one aspect of the present invention, the contents of those additives (H), which are appropriately set in accordance with the kinds of the additives, are each independently typically from 0.01 mass% to 20 mass%, preferably from 0.01 mass% to 15 mass%, more preferably from 0.01 mass% to 10 mass%, still more preferably from 0.01 mass% to 7 mass% with respect to the total amount (100 mass%) of the grease composition.

A preferred combination of the phosphoric acid ester amine salt (C), the sulfur-based extreme pressure agent (D), the zinc dithiophosphate (E), the melamine cyanurate (F), and the organic molybdenum compound (G) is as follows: the phosphoric acid ester amine salt (C) is an amine salt of a monoalkyl acid phosphate and trioctylamine; the sulfur-based extreme pressure agent (D) is a sulfurized olefin; the zinc dithiophosphate (E) is a zinc dialkyldithiophosphate; the melamine cyanurate (F) is melamine cyanurate having an average particle diameter of 4.0 µm or less; and the organic molybdenum compound (G) is a molybdenum dithiophosphate.
In addition, a more preferred combination of the phosphoric acid ester amine salt (C), the sulfur-based extreme pressure agent (D), the zinc dithiophosphate (E), the melamine cyanurate (F), and the organic molybdenum compound (G) is as follows: the phosphoric acid ester amine salt (C) is an amine salt of isotridecyl acid phosphate and trioctylamine; the sulfur-based extreme pressure agent (D) is a sulfurized product of 6-methyl-1-heptene; the zinc dithiophosphate (E) is a zinc secondary dialkyldithiophosphate; the melamine cyanurate (F) is melamine cyanurate having an average particle diameter of 3.0 µm or less; and the organic molybdenum compound (G) is a (2-ethylhexyl)molybdenum dithiophosphate.

(Unworked Penetration)

The unworked penetration of the grease composition of one aspect of the present invention at 25°C is preferably from 230 to 410, more preferably from 260 to 380, still more preferably from 270 to 360, still further more preferably from 280 to 330 from the viewpoint of its handling at normal temperature.
In this description, the unworked penetration of the grease composition means a value measured at 25°C in conformity with JIS K2220:2013 (Article 7).

(Worked Penetration)

The worked penetration of the grease composition of one aspect of the present invention at 25°C is preferably from 250 to 430, more preferably from 280 to 400, still more preferably from 290 to 380, still further more preferably from 300 to 350 from the viewpoint of achieving both of a reduction in viscosity of its base oil and the suppression of the leakage of the grease composition.
In this description, the worked penetration of the grease composition means a value measured at 25°C in conformity with JIS K2220:2013 (Article 7).

(Difference between Worked Penetration and Unworked Penetration)

A difference obtained by subtracting the numerical value of the unworked penetration of the grease composition of one aspect of the present invention at 25°C from the numerical value of the worked penetration thereof at 25°C is preferably from 0 to 45, more preferably from 1 to 40, still more preferably from 3 to 35, still further more preferably from 5 to 30 from the viewpoint of achieving both of a reduction in viscosity of the base oil and the suppression of the leakage of the grease composition.
A smaller difference obtained by subtracting the numerical value of the unworked penetration from the numerical value of the worked penetration means that the grease composition more hardly leaks because the grease composition more hardly softens even when sheared by working.

[Shell Four-ball Load-bearing Capacity (EP) Test]

When the grease composition of one aspect of the present invention is subjected to a shell four-ball load-bearing capacity (EP) test by a method described in Examples to be described later, its last non-seizure load (LNL) is preferably 618 N or more, more preferably 785 N or more, still more preferably 981 N or more from the viewpoint of its extreme pressure property.
When the grease composition of one aspect of the present invention is subjected to a shell four-ball load-bearing capacity (EP) test by a method described in Examples to be described later, its weld load (WL) is preferably 1,961 N or more, more preferably 2,452 N or more, still more preferably 3,089 N or more from the viewpoint of its extreme pressure property.
When the grease composition of one aspect of the present invention is subjected to a shell four-ball load-bearing capacity (EP) test by a method described in Examples to be described later, its load wear index (LWI) is preferably 300 N or more, more preferably 400 N or more, still more preferably 500 N or more from the viewpoint of its load-bearing capacity.

[Vibration Friction Wear (SRV) Test]

When the grease composition of one aspect of the present invention is subjected to a vibration friction wear (SRV) test by a method described in Examples to be described later, its seizure load is preferably more than 1,500 N, more preferably more than 1,800 N, still more preferably more than 2,000 N from the viewpoint of its seizure resistance.

[Shell Four-ball Wear Test]

When the grease composition of one aspect of the present invention is subjected to a shell four-ball wear test by a method described in Examples to be described later, its wear mark diameter is preferably 0.55 mm or less, more preferably 0.50 mm or less, still more preferably 0.45 mm or less from the viewpoint of its wear resistance.

A method of producing a grease composition of the present invention is a method of producing a grease composition, including the steps of: (1) synthesizing a urea-based thickener (B) in a base oil (A); and (2) blending a phosphoric acid ester amine salt (C), a sulfur-based extreme pressure agent (D), a zinc dithiophosphate (E), melamine cyanurate (F), and an organic molybdenum compound (G) into the synthesized product in the step (1), wherein the base oil (A) is a mixed base oil containing a high-viscosity poly-α-olefin (PAO) (A1) having a 40°C kinematic viscosity of from 288 mm²/s to 506 mm²/s, a low-viscosity poly-α-olefin (PAO) (A2) having a 40°C kinematic viscosity of from 61.2 mm²/s to 74.8 mm²/s, and an ester-based synthetic oil, and wherein particles each containing the urea-based thickener (B) in the grease composition satisfy the following requirement (I):

As one example of the above-mentioned synthesis method, the diurea compound represented by the general formula (b1) may be typically obtained by causing a diisocyanate and a monoamine to react with each other. The reaction is preferably performed by the following method: the diisocyanate is blended into the above-mentioned base oil (A), and is dissolved therein by heating; and while the resultant diisocyanate-containing base oil is heated and stirred, a base oil obtained by dissolving the monoamine in the base oil (A) is added thereto.
For example, when the diurea compound represented by the general formula (b1) is synthesized, the desired diurea compound may be synthesized by the above-mentioned method through use of: a diisocyanate having a group corresponding to the divalent aromatic hydrocarbon group represented by R³ in the general formula (b1) as the diisocyanate; and an amine having a group corresponding to the monovalent hydrocarbon group represented by each of R¹ and R² as the monoamine.
The other additive (H) may be blended in the step (2) as required.
The ester-based synthetic oil is preferably blended in each of the step (1) and the step (2).
It is preferred that the ester-based synthetic oil contain the diester-based oil (A3) and the aromatic ester-based oil (A4), the diester-based oil (A3) be blended in the step (1), and the aromatic ester-based oil (A4) be blended in the step (2).

The grease composition of the present invention is excellent in extreme pressure property, load-bearing capacity, seizure resistance, and wear resistance under a wide variety of temperature environments, and is also excellent in suppression of its leakage due to a reduction in viscosity of its base oil thereunder. Accordingly, the grease composition of one aspect of the present invention may be suitably used in the applications of the lubrication of the sliding portions of various devices.
Examples of a device in which the grease composition of the present invention may be suitably used include: a wave gear device in a speed reducer to be used in the field of an industrial robot or the field of a space probe; and a machine element related to power transmission in the field of a bicycle, the field of an automobile, the field of an office machine, the field of a machine tool, the field of a wind turbine, an architectural field, the field of an agricultural machine, or the field of an industrial robot.
Examples of a lubrication portion in an apparatus in the field of an office machine in which the grease composition of the present invention may be suitably used include: a fixing roll in an apparatus such as a printer; and a bearing and a gear portion in an apparatus such as a polygon motor.
Examples of a lubrication portion in an apparatus in the field of a machine tool in which the grease composition of the present invention may be suitably used include bearing portions in the speed reducers of a spindle, a servomotor, and a machining robot.
In addition, the composition may be suitably used in, for example, a speed reducer included in an industrial robot or the like, or a speed increaser included in a wind power facility.
In addition, examples of the speed reducer and the speed increaser include a speed reducer formed of a gear mechanism and a speed increaser formed of a gear mechanism. However, an object to which the grease composition of one aspect of the present invention is applied is not limited to a speed reducer formed of a gear mechanism and a speed increaser formed of a gear mechanism, and the composition may be applied to, for example. In addition, examples of the speed reducer include a traction drive speed reducer, a harmonic type speed reducer, an RV type speed reducer, and a cyclo type speed reducer, and the composition may be suitably used in any one of the speed reducers. Among them, however, a harmonic type wave gear device is preferred.
In addition, according to one aspect of the present invention, there is provided a device including the grease composition of the present invention in a lubrication site, such as a bearing portion, a sliding portion, a gear portion, or a joining portion, preferably a speed reducer or a speed increaser.

[Method of lubricating Sliding Mechanism]

A method of lubricating a sliding mechanism applicable to the grease composition of the present invention is a method including lubricating the mechanism with the above-mentioned grease composition of the present invention.
According to one aspect of the present invention, there is provided a lubrication method including lubricating the lubrication site (e.g., a bearing portion, a sliding portion, a gear portion, or a joining portion) of a device, such as a speed reducer or a speed increaser, with the grease composition of the present invention.
Examples of the speed reducer and the speed increaser include a speed reducer formed of a gear mechanism and a speed increaser formed of a gear mechanism. However, an object to which the grease composition of one aspect of the present invention is applied is not limited to a speed reducer formed of a gear mechanism and a speed increaser formed of a gear mechanism, and the composition may be applied to, for example. In addition, examples of the speed reducer include a traction drive speed reducer, a harmonic type speed reducer, an RV type speed reducer, and a cyclo type speed reducer, and the composition may be suitably used in any one of the speed reducers. Among them, however, a harmonic type wave gear device is preferred.
According to the method of lubricating a sliding mechanism applicable to the grease composition of the present invention, for example, when the sliding mechanism is a wave gear device or the like, all of an excellent extreme pressure property, an excellent load-bearing capacity, excellent seizure resistance, and excellent wear resistance, and the suppression of the leakage of the grease composition due to a reduction in viscosity of its base oil can be achieved under a wide variety of temperature environments.
According to one aspect of the present invention, there are provided the following items [1] to [12].

[1] A grease composition, including: a base oil (A); a urea-based thickener (B); a phosphoric acid ester amine salt (C); a sulfur-based extreme pressure agent (D); a zinc dithiophosphate (E); melamine cyanurate (F); and an organic molybdenum compound (G),
- wherein the base oil (A) is a mixed base oil containing a high-viscosity poly-α-olefin (PAO) (A1) having a 40°C kinematic viscosity of from 288 mm²/s to 506 mm²/s, a low-viscosity poly-α-olefin (PAO) (A2) having a 40°C kinematic viscosity of from 61.2 mm²/s to 74.8 mm²/s, and an ester-based synthetic oil, and
- wherein particles each containing the urea-based thickener (B) in the grease composition satisfy the following requirement (I):
  - ·Requirement (I): the particles have an arithmetic average particle diameter on an area basis of 2.0 µm or less, which is measured by a laser diffraction scattering method.
[2] The grease composition according to the above-mentioned item [1], wherein the particles each containing the urea-based thickener (B) in the grease composition further satisfy the following requirement (II):
- ·Requirement (II): the particles have a specific surface area of 0.5× 10⁵ cm²/cm³ or more, which is measured by the laser diffraction scattering method.
[3] The grease composition according to the above-mentioned item [1]or [2], wherein the ester-based synthetic oil contains a diester-based oil (A3) and an aromatic ester-based oil (A4).
[4] The grease composition according to the above-mentioned item [3], wherein a content ratio [(A3)/(A4)] of the diester-based oil (A3) to the aromatic ester-based oil (A4) is from 1 to 12 in terms of mass ratio.
[5] The grease composition according to any one of the above-mentioned items [1] to [4], further including one or more kinds of additives selected from the group consisting of: an antioxidant; a viscosity modifier; and a rust inhibitor.
[6] The grease composition according to any one of the above-mentioned items [1] to [5], wherein a content ratio [(C)/(E)] of the phosphoric acid ester amine salt (C) to the zinc dithiophosphate (E) is from 0.5 to 1.5 in terms of mass ratio.
[7] The grease composition according to any one of the above-mentioned items [1] to [6], wherein a content ratio [(F)/(G)] of the melamine cyanurate (F) to the organic molybdenum compound (G) is from 0.1 to 1.0 in terms of mass ratio.
[8] The grease composition according to any one of the above-mentioned items [1] to [7], wherein the grease composition has a worked penetration at 25°C of from 250 to 430.
[9] The grease composition according to any one of the above-mentioned items [1] to [8], wherein the grease composition is used in lubrication of a lubrication site of a speed reducer or a speed increaser.
[10] The grease composition according to the above-mentioned item [9], wherein the speed reducer is a wave gear device.
[11] A lubrication method, including lubricating a lubrication site of a wave gear device with the grease composition of any one of the above-mentioned items [1] to [8].
[12] A method of producing a grease composition, including the steps of:
1. (1) synthesizing a urea-based thickener (B) in a base oil (A); and
2. (2) blending a phosphoric acid ester amine salt (C), a sulfur-based extreme pressure agent (D), a zinc dithiophosphate (E), melamine cyanurate (F), and an organic molybdenum compound (G) into the synthesized product in the step (1),
- wherein the base oil (A) is a mixed base oil containing a high-viscosity poly-α-olefin (PAO) (A1) having a 40°C kinematic viscosity of from 288 mm²/s to 506 mm²/s, a low-viscosity poly-α-olefin (PAO) (A2) having a 40°C kinematic viscosity of from 61.2 mm²/s to 74.8 mm²/s, and an ester-based synthetic oil, and
- wherein particles each containing the urea-based thickener (B) in the grease composition satisfy the following requirement (I):
  - ·Requirement (I): the particles have an arithmetic average particle diameter on an area basis of 2.0 µm or less, which is measured by a laser diffraction scattering method.

Examples

The present invention is specifically described by way of Examples below. However, the present invention is not limited to Examples below.

[Various Physical Property Values]

Methods of measuring various physical property values were as described below.

(1) Average Particle Diameter of Melamine Cyanurate (C)

A 50% particle diameter (volume median particle diameter, D₅₀) on a scattering intensity basis calculated from a dispersed particle diameter distribution, which was measured by a dynamic light scattering method (photon correlation method) at 25°C and analyzed by a CONTIN method, was used.

(2) Unworked Penetration of Grease Composition

The unworked penetration of the grease composition was measured at 25°C in conformity with JIS K2220:2013 (Article 7).

(3) Worked Penetration of Grease Composition

The worked penetration of the grease composition was measured at 25°C in conformity with JIS K2220:2013 (Article 7).

(4) Difference between Worked Penetration and Unworked Penetration of Grease Composition

A difference was calculated by subtracting the numerical value of the unworked penetration in the section (2) from the numerical value of the worked penetration in the section (3).

(5) Contents of Phosphorus Atom, Zinc Atom, and Molybdenum Atom

The contents of a phosphorus atom, a zinc atom, and a molybdenum atom were measured in conformity with JPI-5S-38-03.

(6) Contents of Sulfur Atom

The content of a sulfur atom was measured in conformity with JIS K 2541-2:2013.

[Raw Material]

In each of Examples 1 to 3, and Comparative Examples 1 and 2, the base oil (A), the phosphoric acid ester amine salt (C), the sulfur-based extreme pressure agent (D), the zinc dithiophosphate (E), the melamine cyanurate (F), the organic molybdenum compound (G), and the other additive (H) used as raw materials for preparing a grease composition were as described below.

·Base oil (A1): poly-α-olefin (PAO) (40°C kinematic viscosity: 400 mm²/s, viscosity index: 149)
·Base oil (A2): poly-α-olefin (PAO) (40°C kinematic viscosity: 63 mm²/s, viscosity index: 139)
·Base oil (A3-1): ester-based synthetic oil (di(2-ethylhexyl) sebacate, 40°C kinematic viscosity: 11 mm²/s, viscosity index: 156)
·Base oil (A3-2): ester-based synthetic oil (diisodecyl sebacate, 40°C kinematic viscosity: 20 mm²/s, viscosity index: 164)
·Base oil (A4): ester-based synthetic oil (tris(2-ethylhexyl) trimellitate, 40°C kinematic viscosity: 90 mm²/s, viscosity index: 78)

·Phosphoric acid ester: isotridecyl acid phosphate (content of phosphorus atom: 8.2 mass%)
·Amine: trioctylamine

<Sulfur-based Extreme Pressure Agent (D)>

·Sulfurized product of 6-methyl-1-heptene (content of sulfur atom: 36 mass%)

·Zinc dialkyldithiophosphate (ZnDTP) (secondary) (content of zinc atom: 9.0 mass%, number of carbon atoms of alkyl group: 3 to 6)

·Melamine cyanurate (average particle diameter: about 3.0 µm)

·(2-Ethylhexyl)molybdenum dithiophosphate (MoDTP) (diluted with a mineral oil having a 40°C kinematic viscosity of 60 mm²/s, dilution rate: 50 mass%, content of molybdenum atom: 9.0 mass%)

·Phenol-based antioxidant (6-methylheptyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate)
·Viscosity modifier (ethylene propylene oligomer, Mw: 14,400, Mn: 3,800)
·Rust inhibitor: benzotriazole
·Other components: amide compound, alkylamine, alkyl phosphate, alkyldithiothiazole

(Example 1)

(1) Synthesis of Urea Grease

5.8 Parts by mass of diphenylmethane-4,4'-diisocyanate (MDI) was added to a mixed base oil heated to 70°C, the mixed base oil containing 10 parts by mass of the base oil (A1), 30 parts by mass of the base oil (A2), and 10 parts by mass of the base oil (A3-1), to prepare the solution α.
In addition, 5.6 parts by mass of cyclohexylamine and 3.8 parts by mass of octadecylamine (stearylamine) were added to a separately prepared mixed base oil heated to 70°C, the mixed base oil containing 10 parts by mass of the base oil (A1), 30 parts by mass of the base oil (A2), and 10 parts by mass of the base oil (A3-1), to prepare the solution β.
Then, the grease-producing apparatus 1 illustrated in Fig. 1 was prepared, and the solution α heated to 70°C and the solution β heated to 70°C whose amounts were equal to each other were simultaneously introduced from the solution-introducing tube 4A and the solution-introducing tube 4B into the container main body 2, respectively. The solution α and the solution β were continuously introduced into the container main body 2 under a state in which the rotor 3 was rotated. After that, the temperature of the mixture was increased to 160°C with a stirring device, and the mixture was stirred for 1 hour. Then, the mixture was naturally left standing to cool to 100°C. After that, 5.0 parts by mass of the base oil (A4) and 0.5 part by mass of the amide compound were added to the mixture, and the whole was subjected to roll mill treatment to be uniformized. Thus, urea grease (b1) was synthesized.
The number of revolutions of the rotor 3 of the used grease-producing apparatus 1 was set to 8,000 rpm. In addition, the maximum shear rate (Max) at this time was 10,500 s^-1, and the stirring was performed at a ratio [Max/Min] of the maximum shear rate (Max) to the minimum shear rate (Min) of 3.5.
A urea-based thickener (B1) in the resultant urea grease corresponds to a compound represented by the general formula (b1) in which R¹ and R² each represent a cyclohexyl group or an octadecyl group (stearyl group), and R³ represents a diphenylmethylene group.
In addition, a molar ratio (cyclohexylamine/octadecylamine) between cyclohexylamine and octadecylamine used as raw materials is 80/20.

(2) Preparation of Grease Composition

Next, the respective components ranging from the phosphoric acid ester to the rust inhibitor, and any other component shown in Table 1 were added and mixed in blending amounts shown in Table 1 into the urea grease (b1). After that, the mixture was homogenized with a triple roll to provide a grease composition of Example 1.

(Examples 2 and 3)

The respective grease compositions were each prepared in the same manner as in the grease composition of Example 1 except that the contents of the respective components were changed to those shown in Table 1.

(Comparative Example 1)

A grease composition of Comparative Example 1 was obtained in the same manner as in Example 1 except that in the section "(1) Synthesis of Urea Grease" of Example 1, the contents of the respective components were changed as described below.

·Base oil (A2) heated to 70°C	41 parts by mass
·Diphenylmethane-4,4'-diisocyanate (MDI)	4.6 parts by mass
·Base oil (A2) heated to 70°C that has been separately prepared	41 parts by mass
·Cyclohexylamine	1.5 parts by mass
·Octadecylamine (stearylamine)	6.0 parts by mass
·Base oil (A4)	5.0 parts by mass
·Amide compound	0.5 part by mass

A urea-based thickener (B2) in the resultant urea grease corresponds to a compound represented by the general formula (b1) in which R¹ and R² each represent a cyclohexyl group or an octadecyl group (stearyl group), and R³ represents a diphenylmethylene group.
In addition, a molar ratio (cyclohexylamine/octadecylamine) between cyclohexylamine and octadecylamine used as raw materials is 40/60.

(Comparative Example 2)

A grease composition of Comparative Example 2 was prepared in the same manner as in the grease composition of Comparative Example 1 except that the contents of the respective components were changed to those shown in Table 1.

[Requirement]

The following physical properties of the urea grease synthesized in each of Examples 1 to 3, and Comparative Examples 1 and 2 were calculated.

(1) Calculation of Arithmetic Average Particle Diameter of Particles each containing Urea-based Thickener: Requirement (I)

The arithmetic average particle diameter of particles each containing a urea-based thickener in a grease composition was evaluated. Specifically, the urea grease synthesized in each of Examples 1 to 3, and Comparative Examples 1 and 2 was used as a measurement sample, and the arithmetic average particle diameter of its particles each containing the urea-based thickener (B) was determined by the following procedure.
First, the measurement sample was defoamed in a vacuum, and was then loaded into a 1-milliliter syringe. 0.10 mL to 0.15 mL of the sample was extruded from the syringe, and the extruded sample was mounted on the surface of the plate-like cell of a fixing jig for a paste cell. Next, another plate-like cell was further superimposed on the sample to provide a measurement cell in which the sample was sandwiched between the two cells. Next, the arithmetic average particle diameter of the particles in the sample of the measurement cell on an area basis was measured with a laser diffraction type particle diameter-measuring machine (manufactured by HORIBA, Ltd., product name: LA-920).
The term "arithmetic average particle diameter on an area basis" as used herein means a value obtained by arithmetically averaging a particle diameter distribution on an area basis. The particle diameter distribution on an area basis is obtained by representing the frequency distribution of particle diameters in the entirety of the particles serving as a measurement object on the basis of areas calculated from the particle diameters (more specifically, the sectional areas of particles having the particle diameters). In addition, the value obtained by arithmetically averaging the particle diameter distribution on an area basis may be calculated from the following equation (1):
[Math. 1] $Arithmetic average particle diameter = \sum \{q (J) \times X (J)\} + \sum \{q (J)\}$ wherein
in the equation (1), J means the division number of the particle diameters, q(J) means a frequency distribution value (unit: %), and X(J) represents the representative diameter (unit: µm) of a J-th particle diameter range.

(2) Calculation of Specific Surface Area of Particles each containing Urea-based Thickener: Requirement (II)

A specific surface area was calculated by using the particle diameter distribution of the particles each containing the thickener in the grease composition measured in the above-mentioned section "Requirement (I)." Specifically, the total sum of the surface areas (unit: cm²) of the particles per unit volume (1 cm³) was calculated by using the particle diameter distribution, and the calculated value was used as the specific surface area (unit: cm²/cm³).
Next, Examples 1 to 3, and Comparative Examples 1 and 2 described above are each evaluated for its extreme pressure property, load-bearing capacity, and wear resistance.

[Shell Four-ball Load-bearing Capacity (EP) Test]

The last non-seizure load (LNL) and weld load (WL) of each grease composition were measured by performing a shell four-ball load-bearing capacity (EP) test in conformity with ASTM D2596 under the following test conditions, and the load wear index (LWI) thereof was calculated. As the values of the last non-seizure load (LNL) and the weld load (WL) become larger, the extreme pressure property thereof becomes more satisfactory. When the last non-seizure load (LNL) was 618 N or more, and the weld load (WL) was 1,961 N or more, the extreme pressure property was judged to be satisfactory. In addition, as the value of the load wear index (LWI) becomes larger, the load-bearing capacity thereof becomes more satisfactory. When the load wear index (LWI) was 300 N or more, the load-bearing capacity was judged to be satisfactory.

-Test Conditions-

·Rotational speed: 1,800 revolutions/min
·Sample temperature: room temperature (25±5°C)

[Vibration Friction Wear (SRV) Test]

A vibration friction wear (SRV) test was performed in conformity with ASTM D5706 under the following test conditions. Specifically, a load was increased in increments of 100 N, and then a sliding portion having applied thereto each grease composition was slid for 2 minutes each, followed by the measurement of a load (seizure load) at the time point when seizure occurred to largely increase the friction coefficient of the portion. As the value of the seizure load becomes larger, the seizure resistance of the composition becomes more satisfactory. When the seizure load was more than 1,500 N, the seizure resistance was judged to be satisfactory.

-Test Conditions-

·Ball: SUJ2 (diameter: 10 mm)
·Disc: SUJ2
·Frequency: 50 Hz
·Amplitude: 1.5 mm
·Temperature: 80°C

[Shell Four-ball Wear Test]

A shell four-ball wear test was performed in conformity with ASTM D2266-2001 under the following test conditions, and the wear mark diameter of the point with which a metal ball having applied thereto each grease composition was brought into contact was measured. When the wear mark diameter was 0.55 mm or less, the wear resistance of the grease composition was judged to be satisfactory.

-Test Conditions-

·Test ball: a steel ball having applied thereto the grease composition (diameter: 1/2 inch)
·Rotational speed: 1,200 rpm
·Load: 392 N
·Test time: 60 minutes
·Test temperature: 75°C

The composition, physical property values, and evaluation results of each of the grease compositions of Examples 1 to 3, and Comparative Examples 1 and 2 are shown in Table 1.

[Table 1]

Table 1

				Example			Comparative Example
				1	2	3	1	2
	Base oil (A)	Base oil (A1)	mass%	14.00	14.00	14.00	-	-
		Base oil (A2)	mass%	43.72	43.72	43.72	75.01	80.51
		Base oil (A3-1)	mass%	19.40	-	-	-	-
		Base oil (A3-2)	mass%	-	19.40	17.90	-	-
		Base oil (A4)	mass%	3.50	3.50	3.50	3.50	3.50
	Urea-based thickener (B)	Urea-based thickener (B1)	mass%	8.44	8.44	8.44	-	-
	Urea-based thickener (B)	Urea-based thickener (B2)	mass%	-	-	-	9.79	9.79
	Phosphoric acid ester amine salt (C)	Phosphoric acid ester	mass%	1.00	1.00	1.00	0.50	0.50
Grease composition	Phosphoric acid ester amine salt (C)	Amine salt	mass%	1.50	1.50	1.50	0.75	0.75
	Sulfur-based extreme pressure agent (D)		mass%	1.24	1.24	1.24	0.62	1.24
	Zinc dithiophosphate (E)		mass%	2.00	2.00	2.00	-	-
	Melamine cyanurate (F)		mass%	1.00	1.00	1.00	-	-
	Organic molybdenum compound (G)		mass%	2.00	2.00	2.00	3.00	-
	Other additive (H)	Phenol-based antioxidant	mass%	1.00	1.00	1.00	1.00	1.00
		Viscosity modifier	mass%	-	-	1.50	5.00	1.50
		Rust inhibitor	mass%	0.10	0.10	0.10	0.10	0.10
		Other component	mass%	1.11	1.11	1.11	0.73	1.11
Total			mass%	100.00	100.00	100.00	100.00	100.00
Content ratio [(A3)/(A4)]			-	5.54	5.54	5.11	-	-
Physical property value	Thickener	Arithmetic average particle diameter of particles	µm	0.20	0.25	0.25	0.21	0.22
	Thickener	Specific surface area of particles	cm²/cm³	3.0×10⁵	2.4×10⁵	2.4×10⁵	2.9×10⁵	2.8×10⁵
	Grease composition	Unworked penetration	-	320	309	317	310	286
		Worked penetration	-	328	319	328	327	302
		Difference between worked penetration and unworked penetration	-	8	10	11	17	16
Content of atom in grease composition	Phosphorus atom derived from phosphoric acid ester amine salt (C)		mass%	0.08	0.08	0.08	0.04	0.04
	Sulfur atom derived from sulfur-based extreme pressure agent (D)		mass%	0.45	0.45	0.45	0.23	0.45
	Zinc atom derived from zinc dithiophosphate (E)		mass%	0.18	0.18	0.18	-	-
	Molybdenum atom derived from organic molybdenum compound (G)		mass%	0.18	0.18	0.18	0.27	-
Evaluation result	Shell four-ball load-bearing capacity (EP) test	Last non-seizure load (LNL)	N	1,236	618	785	981	785
		Weld load (WL)	N	2,452	2,452	2,452	2,452	1,961
		Load wear index (LWI)	N	546	364	425	505	359
	Vibration friction wear (SRV) test	Seizure load	N	More than 2,000	More than 2,000	More than 2,000	1,100	700
	Shell four-ball wear test	Wear mark diameter	mm	0.42	0.41	0.44	0.50	0.42

As shown in Table 1, the grease compositions of Examples 1 to 3 each showed a satisfactory result in each of the shell four-ball load-bearing capacity (EP) test at a sample temperature of room temperature (25±5°C), the vibration friction wear (SRV) test at a temperature of 80°C, and the shell four-ball wear test at a test temperature of 75°C. It was found from the foregoing that the grease compositions of Examples 1 to 3 were each able to achieve a sufficient extreme pressure property and a sufficient load-bearing capacity under a wide variety of temperature environments without dependence on the temperature of a lubrication site.
In addition, in each of the grease compositions of Examples 1 to 3, the difference between its worked penetration and unworked penetration was sufficiently as small as from 8 to 11. Accordingly, it was found that the grease composition hardly softened even when sheared by working, and was excellent in suppression of its leakage due to a reduction in viscosity of its base oil.

Reference Signs List

1 grease-producing apparatus
2 container main body
3 rotor
4 introducing portion
4A, 4B solution-introducing tube
5 staying portion
6 first irregular portion
7 second irregular portion
8 ejecting portion
9 first irregular portion on container main body side
10 second irregular portion on container main body side
11 ejection orifice
12 rotation axis
13 rotor first irregular portion
- 13A recess
- 13B protrusion
14 rotor second irregular portion
15 scraper
A1, A2 gap

Claims

A grease composition, comprising:
a base oil (A);

a urea-based thickener (B);

a phosphoric acid ester amine salt (C);

a sulfur-based extreme pressure agent (D);

a zinc dithiophosphate (E);

melamine cyanurate (F); and

an organic molybdenum compound (G),

wherein the base oil (A) is a mixed base oil comprising
a high-viscosity poly-α-olefin (PAO) (A1) having a 40°C kinematic viscosity of from 288 mm²/s to 506 mm²/s,

a low-viscosity poly-α-olefin (PAO) (A2) having a 40°C kinematic viscosity of from 61.2 mm²/s to 74.8 mm²/s, and

an ester-based synthetic oil, and

wherein particles each comprising the urea-based thickener (B) in the grease composition satisfy the following requirement (I):
·Requirement (I): the particles have an arithmetic average particle diameter on an area basis of 2.0 µm or less, which is measured by a laser diffraction scattering method.
The grease composition according to claim 1, wherein the particles each comprising the urea-based thickener (B) in the grease composition further satisfy the following requirement (II):
·Requirement (II): the particles have a specific surface area of 0.5×10⁵ cm²/cm³ or more, which is measured by the laser diffraction scattering method.
The grease composition according to claim 1 or 2, wherein the ester-based synthetic oil comprises a diester-based oil (A3) and an aromatic ester-based oil (A4).
The grease composition according to claim 3, wherein a content ratio [(A3)/(A4)] of the diester-based oil (A3) to the aromatic ester-based oil (A4) is from 1 to 12 in terms of mass ratio.
The grease composition according to any one of claims 1 to 4, further comprising one or more kinds of additives selected from the group consisting of: an antioxidant; a viscosity modifier; and a rust inhibitor.
The grease composition according to any one of claims 1 to 5, wherein a content ratio [(C)/(E)] of the phosphoric acid ester amine salt (C) to the zinc dithiophosphate (E) is from 0.5 to 1.5 in terms of mass ratio.
The grease composition according to any one of claims 1 to 6, wherein a content ratio [(F)/(G)] of the melamine cyanurate (F) to the organic molybdenum compound (G) is from 0.1 to 1.0 in terms of mass ratio.
The grease composition according to any one of claims 1 to 7, wherein the grease composition has a worked penetration at 25°C of from 250 to 430.
The grease composition according to any one of claims 1 to 8, wherein the grease composition is used in lubrication of a lubrication site of a speed reducer or a speed increaser.
The grease composition according to claim 9, wherein the speed reducer is a wave gear device.
A lubrication method, comprising lubricating a lubrication site of a wave gear device with the grease composition of any one of claims 1 to 8.
A method of producing a grease composition, comprising the steps of:
(1) synthesizing a urea-based thickener (B) in a base oil (A); and

(2) blending a phosphoric acid ester amine salt (C), a sulfur-based extreme pressure agent (D), a zinc dithiophosphate (E), melamine cyanurate (F), and an organic molybdenum compound (G) into the synthesized product in the step (1),

wherein the base oil (A) is a mixed base oil comprising
a high-viscosity poly-α-olefin (PAO) (A1) having a 40°C kinematic viscosity of from 288 mm²/s to 506 mm²/s,

a low-viscosity poly-α-olefin (PAO) (A2) having a 40°C kinematic viscosity of from 61.2 mm²/s to 74.8 mm²/s, and

an ester-based synthetic oil, and

wherein particles each comprising the urea-based thickener (B) in the grease composition satisfy the following requirement (I):
·Requirement (I): the particles have an arithmetic average particle diameter on an area basis of 2.0 µm or less, which is measured by a laser diffraction scattering method.